51
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Medeiros PVC, Marks S, Wynn JM, Vasylenko A, Ramasse QM, Quigley D, Sloan J, Morris AJ. Single-Atom Scale Structural Selectivity in Te Nanowires Encapsulated Inside Ultranarrow, Single-Walled Carbon Nanotubes. ACS Nano 2017; 11:6178-6185. [PMID: 28467832 DOI: 10.1021/acsnano.7b02225] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Extreme nanowires (ENs) represent the ultimate class of crystals: They are the smallest possible periodic materials. With atom-wide motifs repeated in one dimension (1D), they offer a privileged perspective into the physics and chemistry of low-dimensional systems. Single-walled carbon nanotubes (SWCNTs) provide ideal environments for the creation of such materials. Here we present a comprehensive study of Te ENs encapsulated inside ultranarrow SWCNTs with diameters between 0.7 nm and 1.1 nm. We combine state-of-the-art imaging techniques and 1D-adapted ab initio structure prediction to treat both confinement and periodicity effects. The studied Te ENs adopt a variety of structures, exhibiting a true 1D realization of a Peierls structural distortion and transition from metallic to insulating behavior as a function of encapsulating diameter. We analyze the mechanical stability of the encapsulated ENs and show that nanoconfinement is not only a useful means to produce ENs but also may actually be necessary, in some cases, to prevent them from disintegrating. The ability to control functional properties of these ENs with confinement has numerous applications in future device technologies, and we anticipate that our study will set the basic paradigm to be adopted in the characterization and understanding of such systems.
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Affiliation(s)
- Paulo V C Medeiros
- Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | | | - Jamie M Wynn
- Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Andrij Vasylenko
- Institute for Condensed Matter Physics, National Academy of Science of Ukraine (NAS Ukraine) , 1 Sventsitskii street, 79011 Lviv, Ukraine
| | - Quentin M Ramasse
- SuperSTEM Laboratory, SciTech Daresbury Campus , Keckwick Lane, Daresbury WA44AD, United Kingdom
| | | | | | - Andrew J Morris
- Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
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52
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Hardcastle TP, Seabourne CR, Kepaptsoglou DM, Susi T, Nicholls RJ, Brydson RMD, Scott AJ, Ramasse QM. Robust theoretical modelling of core ionisation edges for quantitative electron energy loss spectroscopy of B- and N-doped graphene. J Phys Condens Matter 2017; 29:225303. [PMID: 28394256 DOI: 10.1088/1361-648x/aa6c4f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Electron energy loss spectroscopy (EELS) is a powerful tool for understanding the chemical structure of materials down to the atomic level, but challenges remain in accurately and quantitatively modelling the response. We compare comprehensive theoretical density functional theory (DFT) calculations of 1s core-level EEL K-edge spectra of pure, B-doped and N-doped graphene with and without a core-hole to previously published atomic-resolution experimental electron microscopy data. The ground state approximation is found in this specific system to perform consistently better than the frozen core-hole approximation. The impact of including or excluding a core-hole on the resultant theoretical band structures, densities of states, electron densities and EEL spectra were all thoroughly examined and compared. It is concluded that the frozen core-hole approximation exaggerates the effects of the core-hole in graphene and should be discarded in favour of the ground state approximation. These results are interpreted as an indicator of the overriding need for theorists to embrace many-body effects in the pursuit of accuracy in theoretical spectroscopy instead of a system-tailored approach whose approximations are selected empirically.
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Affiliation(s)
- T P Hardcastle
- SuperSTEM Laboratory, STFC Daresbury Campus, Daresbury, WA4 4AD, United Kingdom. School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
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53
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Nedelkoski Z, Kepaptsoglou D, Lari L, Wen T, Booth RA, Oberdick SD, Galindo PL, Ramasse QM, Evans RFL, Majetich S, Lazarov VK. Origin of reduced magnetization and domain formation in small magnetite nanoparticles. Sci Rep 2017; 7:45997. [PMID: 28393876 PMCID: PMC5385549 DOI: 10.1038/srep45997] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 03/07/2017] [Indexed: 11/09/2022] Open
Abstract
The structural, chemical, and magnetic properties of magnetite nanoparticles are compared. Aberration corrected scanning transmission electron microscopy reveals the prevalence of antiphase boundaries in nanoparticles that have significantly reduced magnetization, relative to the bulk. Atomistic magnetic modelling of nanoparticles with and without these defects reveals the origin of the reduced moment. Strong antiferromagnetic interactions across antiphase boundaries support multiple magnetic domains even in particles as small as 12-14 nm.
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Affiliation(s)
- Zlatko Nedelkoski
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | | | - Leonardo Lari
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Tianlong Wen
- Physics Department, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
- State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, China
| | - Ryan A. Booth
- Physics Department, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Samuel D. Oberdick
- Physics Department, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Pedro L. Galindo
- Department of Computer Science and Engineering, Universidad de Cádiz, 11510 Puerto Real, Spain
| | | | | | - Sara Majetich
- Physics Department, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Vlado K. Lazarov
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
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54
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Lord AM, Ramasse QM, Kepaptsoglou DM, Evans JE, Davies PR, Ward MB, Wilks SP. Modifying the Interface Edge to Control the Electrical Transport Properties of Nanocontacts to Nanowires. Nano Lett 2017; 17:687-694. [PMID: 28001420 DOI: 10.1021/acs.nanolett.6b03699] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Selecting the electrical properties of nanomaterials is essential if their potential as manufacturable devices is to be reached. Here, we show that the addition or removal of native semiconductor material at the edge of a nanocontact can be used to determine the electrical transport properties of metal-nanowire interfaces. While the transport properties of as-grown Au nanocatalyst contacts to semiconductor nanowires are well-studied, there are few techniques that have been explored to modify the electrical behavior. In this work, we use an iterative analytical process that directly correlates multiprobe transport measurements with subsequent aberration-corrected scanning transmission electron microscopy to study the effects of chemical processes that create structural changes at the contact interface edge. A strong metal-support interaction that encapsulates the Au nanocontacts over time, adding ZnO material to the edge region, gives rise to ohmic transport behavior due to the enhanced quantum-mechanical tunneling path. Removal of the extraneous material at the Au-nanowire interface eliminates the edge-tunneling path, producing a range of transport behavior that is dependent on the final interface quality. These results demonstrate chemically driven processes that can be factored into nanowire-device design to select the final properties.
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Affiliation(s)
| | - Quentin M Ramasse
- SuperSTEM Laboratory, SFTC Daresbury Campus , Keckwick Lane, Daresbury WA4 4AD, United Kingdom
| | - Despoina M Kepaptsoglou
- SuperSTEM Laboratory, SFTC Daresbury Campus , Keckwick Lane, Daresbury WA4 4AD, United Kingdom
| | | | - Philip R Davies
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University , Park Place, Cardiff CF10 3AT, United Kingdom
| | - Michael B Ward
- Institute for Materials Research, University of Leeds , Leeds, LS2 9JT United Kingdom
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55
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Daniels LM, Kashtiban RJ, Kepaptsoglou D, Ramasse QM, Sloan J, Walton RI. Local A-Site Layering in Rare-Earth Orthochromite Perovskites by Solution Synthesis. Chemistry 2016; 22:18362-18367. [PMID: 27727487 PMCID: PMC5216904 DOI: 10.1002/chem.201604766] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Indexed: 11/08/2022]
Abstract
Cation size effects were examined in the mixed A‐site perovskites La0.5Sm0.5CrO3 and La0.5Tb0.5CrO3 prepared through both hydrothermal and solid‐state methods. Atomically resolved electron energy loss spectroscopy (EELS) in the transmission electron microscope shows that while the La and Sm cations are randomly distributed, increased cation‐radius variance in La0.5Tb0.5CrO3 results in regions of localised La and Tb layers, an atomic arrangement exclusive to the hydrothermally prepared material. Solid‐state preparation gives lower homogeneity resulting in separate nanoscale regions rich in La3+ and Tb3+. The A‐site layering in hydrothermal La0.5Tb0.5CrO3 is randomised upon annealing at high temperature, resulting in magnetic behaviour that is dependent on synthesis route.
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Affiliation(s)
- Luke M Daniels
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
| | - Reza J Kashtiban
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | | | - Quentin M Ramasse
- SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury, WA4 4AD, UK
| | - Jeremy Sloan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - Richard I Walton
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
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56
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Nedelkoski Z, Kepaptsoglou D, Ghasemi A, Achinuq B, Hasnip PJ, Yamada S, Hamaya K, Ramasse QM, Hirohata A, Lazarov VK. Controlling the half-metallicity of Heusler/Si(1 1 1) interfaces by a monolayer of Si-Co-Si. J Phys Condens Matter 2016; 28:395003. [PMID: 27501822 DOI: 10.1088/0953-8984/28/39/395003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
By using first-principles calculations we show that the spin-polarization reverses its sign at atomically abrupt interfaces between the half-metallic Co2(Fe,Mn)(Al,Si) and Si(1 1 1). This unfavourable spin-electronic configuration at the Fermi-level can be completely removed by introducing a Si-Co-Si monolayer at the interface. In addition, this interfacial monolayer shifts the Fermi-level from the valence band edge close to the conduction band edge of Si. We show that such a layer is energetically favourable to exist at the interface. This was further confirmed by direct observations of CoSi2 nano-islands at the interface, by employing atomic resolution scanning transmission electron microscopy.
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Affiliation(s)
- Zlatko Nedelkoski
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | | | - Arsham Ghasemi
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Barat Achinuq
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Philip J Hasnip
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
| | - Shinya Yamada
- Department of Systems Innovation, Osaka University, Osaka 560-8531, Japan
| | - Kohei Hamaya
- Department of Systems Innovation, Osaka University, Osaka 560-8531, Japan
| | - Quentin M Ramasse
- SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK
| | | | - Vlado K Lazarov
- Department of Physics, University of York, Heslington, York, YO10 5DD, UK
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57
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Harvie AJ, Booth M, Chantry RL, Hondow N, Kepaptsoglou DM, Ramasse QM, Evans SD, Critchley K. Observation of compositional domains within individual copper indium sulfide quantum dots. Nanoscale 2016; 8:16157-16161. [PMID: 27465708 PMCID: PMC5048650 DOI: 10.1039/c6nr03269a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Accepted: 07/18/2016] [Indexed: 06/06/2023]
Abstract
The origin of photoluminescence in copper indium sulfide (CIS) quantum dots (Qdots) has previously been ascribed to a donor-acceptor pair (DAP) recombination, with a crystal lattice defect implicated as the origin of the donor state. In this study, electron energy-loss spectroscopy (EELS) was used to observe defect-rich compositional domains within individual CIS Qdots, supporting a model of defect-state-mediated photoluminescence for these particles, and identifying them as an ideal model system for future study of lattice defects on Qdot properties.
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Affiliation(s)
- Andrew J. Harvie
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , UK .
| | - Matthew Booth
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , UK .
| | - Ruth L. Chantry
- SuperSTEM , STFC Daresbury , Keckwick Lane , Warrington WA4 4AD , UK
| | - Nicole Hondow
- Institute for Materials Research , University of Leeds , Leeds LS2 9JT , UK
| | | | | | - Stephen D. Evans
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , UK .
| | - Kevin Critchley
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , UK .
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58
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Danaie M, Kepaptsoglou D, Ramasse QM, Ophus C, Whittle KR, Lawson SM, Pedrazzini S, Young NP, Bagot PAJ, Edmondson PD. Characterization of Ordering in A-Site Deficient Perovskite Ca1–xLa2x/3TiO3 Using STEM/EELS. Inorg Chem 2016; 55:9937-9948. [DOI: 10.1021/acs.inorgchem.6b02087] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Mohsen Danaie
- University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, U.K
| | - Demie Kepaptsoglou
- SuperSTEM
Laboratory, SciTech Daresbury Campus, Keckwick Ln, Warrington WA4 4AD, U.K
| | - Quentin M. Ramasse
- SuperSTEM
Laboratory, SciTech Daresbury Campus, Keckwick Ln, Warrington WA4 4AD, U.K
| | - Colin Ophus
- National
Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 67 Cyclotron Road, Berkeley, California 94720, United States
| | - Karl R. Whittle
- University of Sheffield, Department of Materials Science & Engineering, Immobilisation Science Laboratory, Mappin Street, Sheffield S1 3JD, U.K
- School
of Engineering, University of Liverpool, Brownlow Hill, Liverpool L69 3GH, U.K
| | - Sebastian M. Lawson
- University of Sheffield, Department of Materials Science & Engineering, Immobilisation Science Laboratory, Mappin Street, Sheffield S1 3JD, U.K
| | - Stella Pedrazzini
- University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, U.K
| | - Neil P. Young
- University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, U.K
| | - Paul A. J. Bagot
- University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, U.K
| | - Philip D. Edmondson
- Materials Science & Technology Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
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59
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Nitiputri K, Ramasse QM, Autefage H, McGilvery CM, Boonrungsiman S, Evans ND, Stevens MM, Porter AE. Nanoanalytical Electron Microscopy Reveals a Sequential Mineralization Process Involving Carbonate-Containing Amorphous Precursors. ACS Nano 2016; 10:6826-35. [PMID: 27383526 PMCID: PMC5404715 DOI: 10.1021/acsnano.6b02443] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A direct observation and an in-depth characterization of the steps by which bone mineral nucleates and grows in the extracellular matrix during the earliest stages of maturation, using relevant biomineralization models as they grow into mature bone mineral, is an important research goal. To better understand the process of bone mineralization in the extracellular matrix, we used nanoanalytical electron microscopy techniques to examine an in vitro model of bone formation. This study demonstrates the presence of three dominant CaP structures in the mineralizing osteoblast cultures: <80 nm dense granules with a low calcium to phosphate ratio (Ca/P) and crystalline domains; calcium phosphate needles emanating from a focus: "needle-like globules" (100-300 nm in diameter) and mature mineral, both with statistically higher Ca/P compared to that of the dense granules. Many of the submicron granules and globules were interspersed around fibrillar structures containing nitrogen, which are most likely the signature of the organic phase. With high spatial resolution electron energy loss spectroscopy (EELS) mapping, spatially resolved maps were acquired showing the distribution of carbonate within each mineral structure. The carbonate was located in the middle of the granules, which suggested the nucleation of the younger mineral starts with a carbonate-containing precursor and that this precursor may act as seed for growth into larger, submicron-sized, needle-like globules of hydroxyapatite with a different stoichiometry. Application of analytical electron microscopy has important implications in deciphering both how normal bone forms and in understanding pathological mineralization.
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Affiliation(s)
- Kharissa Nitiputri
- Department of Materials, Imperial College London, London SW7 2AZ UK
- Department of Bioengineering, Imperial College London, London SW7 2AZ UK
- Institute of Biomedical Engineering, Imperial College London, London SW7 2AZ UK
| | | | - Hélène Autefage
- Department of Materials, Imperial College London, London SW7 2AZ UK
- Department of Bioengineering, Imperial College London, London SW7 2AZ UK
- Institute of Biomedical Engineering, Imperial College London, London SW7 2AZ UK
| | | | - Suwimon Boonrungsiman
- Department of Materials, Imperial College London, London SW7 2AZ UK
- Department of Bioengineering, Imperial College London, London SW7 2AZ UK
- Institute of Biomedical Engineering, Imperial College London, London SW7 2AZ UK
| | - Nicholas D. Evans
- Department of Bioengineering and Institute for Life Sciences, University of Southampton, Southampton, SO17 1BJ
| | - Molly M. Stevens
- Department of Materials, Imperial College London, London SW7 2AZ UK
- Department of Bioengineering, Imperial College London, London SW7 2AZ UK
- Institute of Biomedical Engineering, Imperial College London, London SW7 2AZ UK
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60
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Bulushev DA, Zacharska M, Lisitsyn AS, Podyacheva OY, Hage FS, Ramasse QM, Bangert U, Bulusheva LG. Single Atoms of Pt-Group Metals Stabilized by N-Doped Carbon Nanofibers for Efficient Hydrogen Production from Formic Acid. ACS Catal 2016. [DOI: 10.1021/acscatal.6b00476] [Citation(s) in RCA: 217] [Impact Index Per Article: 27.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Dmitri A. Bulushev
- Boreskov Institute
of Catalysis, SB RAS, 630090 Novosibirsk, Russia
- Novosibirsk State University, 630090 Novosibirsk, Russia
- Nikolaev Institute of
Inorganic Chemistry, SB RAS, 630090 Novosibirsk, Russia
| | - Monika Zacharska
- Chemical & Environmental Sciences Department, University of Limerick, Limerick, Ireland
- Materials & Surface Science Institute, University of Limerick, Limerick, Ireland
| | | | - Olga Yu. Podyacheva
- Boreskov Institute
of Catalysis, SB RAS, 630090 Novosibirsk, Russia
- Novosibirsk State University, 630090 Novosibirsk, Russia
| | - Fredrik S. Hage
- SuperSTEM Laboratory,
SciTech Daresbury Campus, Daresbury WA4 4AD, United Kingdom
| | - Quentin M. Ramasse
- SuperSTEM Laboratory,
SciTech Daresbury Campus, Daresbury WA4 4AD, United Kingdom
| | - Ursel Bangert
- Materials & Surface Science Institute, University of Limerick, Limerick, Ireland
| | - Lyubov G. Bulusheva
- Novosibirsk State University, 630090 Novosibirsk, Russia
- Nikolaev Institute of
Inorganic Chemistry, SB RAS, 630090 Novosibirsk, Russia
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61
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Zhu Y, Ramasse QM, Brorson M, Moses PG, Hansen LP, Topsøe H, Kisielowski CF, Helveg S. Location of Co and Ni promoter atoms in multi-layer MoS2 nanocrystals for hydrotreating catalysis. Catal Today 2016. [DOI: 10.1016/j.cattod.2015.08.053] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Flynn G, Ramasse QM, Ryan KM. Solvent Vapor Growth of Axial Heterostructure Nanowires with Multiple Alternating Segments of Silicon and Germanium. Nano Lett 2016; 16:374-380. [PMID: 26672625 DOI: 10.1021/acs.nanolett.5b03950] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Herein, we report the formation of multisegment Si-Ge axial heterostructure nanowires in a wet chemical synthetic approach. These nanowires are grown by the liquid injection of the respective silicon and germanium precursors into the vapor phase of an organic solvent in which a tin-coated stainless steel substrate is placed. The Si-Ge transition is obtained by sequential injection with the more difficult Ge-Si transition enabled by inclusion of a quench sequence in the reaction. This approach allows for alternating between pure Si and pure Ge segments along the entire nanowire length with good control of the respective segment dimensions. The multisegment heterostructure nanowires presented are Ge-Si, Si-Ge-Si, Ge-Si-Ge, Si-Ge-Si-Ge, and Si-Ge-Si-Ge-Si-Ge. The interfacial abruptness of the Ge to Si interface is also determined through the use of aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy.
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Affiliation(s)
- Grace Flynn
- Materials and Surface Science Institute and Department of Chemical and Environmental Sciences, University of Limerick , Limerick, Ireland
| | - Quentin M Ramasse
- SuperSTEM Laboratory , SciTech Daresbury Campus, Daresbury WA4 4AD, United Kingdom
| | - Kevin M Ryan
- Materials and Surface Science Institute and Department of Chemical and Environmental Sciences, University of Limerick , Limerick, Ireland
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63
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Srivastava D, Norman C, Azough F, Schäfer MC, Guilmeau E, Kepaptsoglou D, Ramasse QM, Nicotra G, Freer R. Tuning the thermoelectric properties of A-site deficient SrTiO3 ceramics by vacancies and carrier concentration. Phys Chem Chem Phys 2016; 18:26475-26486. [PMID: 27711621 DOI: 10.1039/c6cp05523k] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The work demonstrates the relative contributions to enhanced thermoelectric performance in perovskites from (i) vacancies and (ii) charge carriers.
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Affiliation(s)
| | - Colin Norman
- School of Materials
- University of Manchester
- Manchester M13 9PL
- UK
| | - Feridoon Azough
- School of Materials
- University of Manchester
- Manchester M13 9PL
- UK
| | | | | | | | | | | | - Robert Freer
- School of Materials
- University of Manchester
- Manchester M13 9PL
- UK
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64
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Srivastava D, Azough F, Freer R, Combe E, Funahashi R, Kepaptsoglou DM, Ramasse QM, Molinari M, Yeandel SR, Baran JD, Parker SC. Crystal structure and thermoelectric properties of Sr-Mo substituted CaMnO 3: a combined experimental and computational study. J Mater Chem C Mater 2015; 3:12245-12259. [PMID: 28496979 PMCID: PMC5361175 DOI: 10.1039/c5tc02318a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Accepted: 10/30/2015] [Indexed: 06/07/2023]
Abstract
A combination of experimental and computational techniques has been employed to study doping effects in perovskite CaMnO3. High quality Sr-Mo co-substituted CaMnO3 ceramics were prepared by the conventional mixed oxide route. Crystallographic data from X-ray and electron diffraction showed an orthorhombic to tetragonal symmetry change on increasing the Sr content, suggesting that Sr widens the transition temperature in CaMnO3 preventing phase transformation-cracking on cooling after sintering, enabling the fabrication of high density ceramics. Atomically resolved imaging and analysis showed a random distribution of Sr in the A-site of the perovskite structure and revealed a boundary structure of 90° rotational twin boundaries across {101}orthorhombic; the latter are predominant phonon scattering sources to lower the thermal conductivity as suggested by molecular dynamics calculations. The effect of doping on the thermoelectric properties was evaluated. Increasing Sr substitution reduces the Seebeck coefficient but the power factor remains high due to improved densification by Sr substitution. Mo doping generates additional charge carriers due to the presence of Mn3+ in the Mn4+ matrix, reducing electrical resistivity. The major impact of Sr on thermoelectric behaviour is the reduction of the thermal conductivity as shown experimentally and by modelling. Strontium containing ceramics showed thermoelectric figure of merit (ZT) values higher than 0.1 at temperatures above 850 K. Ca0.7Sr0.3Mn0.96Mo0.04O3 ceramics exhibit enhanced properties with S1000K = -180 μV K-1, ρ1000K = 5 × 10-5 Ωm, k1000K = 1.8 W m-1 K-1 and ZT ≈ 0.11 at 1000 K.
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Affiliation(s)
- D Srivastava
- School of Materials , University of Manchester , Manchester , M13 9PL , UK .
| | - F Azough
- School of Materials , University of Manchester , Manchester , M13 9PL , UK .
| | - R Freer
- School of Materials , University of Manchester , Manchester , M13 9PL , UK .
| | - E Combe
- National Institute of Advanced Industrial Science and Technology , Midorigaoka , Ikeda , Osaka 563-8577 , Japan
| | - R Funahashi
- National Institute of Advanced Industrial Science and Technology , Midorigaoka , Ikeda , Osaka 563-8577 , Japan
| | - D M Kepaptsoglou
- SuperSTEM Laboratory , SciTech Daresbury Campus , Daresbury WA4 4AD , UK
| | - Q M Ramasse
- SuperSTEM Laboratory , SciTech Daresbury Campus , Daresbury WA4 4AD , UK
| | - M Molinari
- Department of Chemistry , University of Bath , Claverton Down , Bath BA2 7AY , UK .
| | - S R Yeandel
- Department of Chemistry , University of Bath , Claverton Down , Bath BA2 7AY , UK .
| | - J D Baran
- Department of Chemistry , University of Bath , Claverton Down , Bath BA2 7AY , UK .
| | - S C Parker
- Department of Chemistry , University of Bath , Claverton Down , Bath BA2 7AY , UK .
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65
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Kepaptsoglou D, Hardcastle TP, Seabourne CR, Bangert U, Zan R, Amani JA, Hofsäss H, Nicholls RJ, Brydson RMD, Scott AJ, Ramasse QM. Electronic Structure Modification of Ion Implanted Graphene: The Spectroscopic Signatures of p- and n-Type Doping. ACS Nano 2015; 9:11398-11407. [PMID: 26446310 DOI: 10.1021/acsnano.5b05305] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A combination of scanning transmission electron microscopy, electron energy loss spectroscopy, and ab initio calculations is used to describe the electronic structure modifications incurred by free-standing graphene through two types of single-atom doping. The N K and C K electron energy loss transitions show the presence of π* bonding states, which are highly localized around the N dopant. In contrast, the B K transition of a single B dopant atom shows an unusual broad asymmetric peak which is the result of delocalized π* states away from the B dopant. The asymmetry of the B K toward higher energies is attributed to highly localized σ* antibonding states. These experimental observations are then interpreted as direct fingerprints of the expected p- and n-type behavior of graphene doped in this fashion, through careful comparison with density functional theory calculations.
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Affiliation(s)
- Demie Kepaptsoglou
- SuperSTEM Laboratory , SciTech Daresbury Campus, Daresbury WA4 4AD, United Kingdom
| | - Trevor P Hardcastle
- Institute for Materials Research, SCaPE, University of Leeds , Leeds LS2 9JT, United Kingdom
| | - Che R Seabourne
- Institute for Materials Research, SCaPE, University of Leeds , Leeds LS2 9JT, United Kingdom
| | - Ursel Bangert
- School of Materials, University of Manchester , Manchester M13 9PL, United Kingdom
| | - Recep Zan
- School of Materials, University of Manchester , Manchester M13 9PL, United Kingdom
| | - Julian Alexander Amani
- II. Physikalisches Institut, Georg-August-Universität Göttingen , Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Hans Hofsäss
- II. Physikalisches Institut, Georg-August-Universität Göttingen , Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Rebecca J Nicholls
- Deparment of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Rik M D Brydson
- Institute for Materials Research, SCaPE, University of Leeds , Leeds LS2 9JT, United Kingdom
| | - Andrew J Scott
- Institute for Materials Research, SCaPE, University of Leeds , Leeds LS2 9JT, United Kingdom
| | - Quentin M Ramasse
- SuperSTEM Laboratory , SciTech Daresbury Campus, Daresbury WA4 4AD, United Kingdom
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66
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Zhang H, Reaney IM, Marincel DM, Trolier-McKinstry S, Ramasse QM, MacLaren I, Findlay SD, Fraleigh RD, Ross IM, Hu S, Ren W, Rainforth WM. Stabilisation of Fe2O3-rich Perovskite Nanophase in Epitaxial Rare-earth Doped BiFeO3 Films. Sci Rep 2015; 5:13066. [PMID: 26272264 PMCID: PMC4536528 DOI: 10.1038/srep13066] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2015] [Accepted: 07/14/2015] [Indexed: 11/27/2022] Open
Abstract
Researchers have demonstrated that BiFeO3 exhibits ferroelectric hysteresis but none have shown a strong ferromagnetic response in either bulk or thin film without significant structural or compositional modification. When remanent magnetisations are observed in BiFeO3 based thin films, iron oxide second phases are often detected. Using aberration-corrected scanning transmission electron microscopy, atomic resolution electron energy loss spectrum-mapping and quantitative energy dispersive X-ray spectroscopy analysis, we reveal the existence of a new Fe2O3-rich perovskite nanophase, with an approximate formula (Fe0.6Bi0.25Nd0.15)3+ Fe3+O3, formed within epitaxial Ti and Nd doped BiFeO3 perovskite films grown by pulsed laser deposition. The incorporation of Nd and Bi ions on the A-site and coherent growth with the matrix stabilise the Fe2O3-rich perovskite phase and preliminary density functional theory calculations suggest that it should have a ferrimagnetic response. Perovskite-structured Fe2O3 has been reported previously but never conclusively proven when fabricated at high-pressure high-temperature. This work suggests the incorporation of large A-site species may help stabilise perovskite-structured Fe2O3. This finding is therefore significant not only to the thin film but also to the high-pressure community.
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Affiliation(s)
- Huairuo Zhang
- Department of Materials Science &Engineering, University of Sheffield, Sheffield S1 3JD, UK
| | - Ian M Reaney
- Department of Materials Science &Engineering, University of Sheffield, Sheffield S1 3JD, UK
| | - Daniel M Marincel
- Department of Materials Science and Engineering and Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
| | - Susan Trolier-McKinstry
- Department of Materials Science and Engineering and Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
| | | | - Ian MacLaren
- School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK
| | - Scott D Findlay
- School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia
| | - Robert D Fraleigh
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Ian M Ross
- Kroto Centre for High Resolution Imaging &Analysis, Department of Electronic and Electric Engineering, University of Sheffield, Sheffield S1 3JD, UK
| | - Shunbo Hu
- Department of Physics, International Center for Quantum and Molecular Structures, and Materials Genome Institute, Shanghai University, Shanghai 200444, China
| | - Wei Ren
- Department of Physics, International Center for Quantum and Molecular Structures, and Materials Genome Institute, Shanghai University, Shanghai 200444, China
| | - W Mark Rainforth
- Department of Materials Science &Engineering, University of Sheffield, Sheffield S1 3JD, UK
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67
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Lord AM, Maffeis TG, Kryvchenkova O, Cobley RJ, Kalna K, Kepaptsoglou DM, Ramasse QM, Walton AS, Ward MB, Köble J, Wilks SP. Controlling the Electrical Transport Properties of Nanocontacts to Nanowires. Nano Lett 2015; 15:4248-54. [PMID: 26042356 DOI: 10.1021/nl503743t] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The ability to control the properties of electrical contacts to nanostructures is essential to realize operational nanodevices. Here, we show that the electrical behavior of the nanocontacts between free-standing ZnO nanowires and the catalytic Au particle used for their growth can switch from Schottky to Ohmic depending on the size of the Au particles in relation to the cross-sectional width of the ZnO nanowires. We observe a distinct Schottky to Ohmic transition in transport behavior at an Au to nanowire diameter ratio of 0.6. The current-voltage electrical measurements performed with a multiprobe instrument are explained using 3-D self-consistent electrostatic and transport simulations revealing that tunneling at the contact edge is the dominant carrier transport mechanism for these nanoscale contacts. The results are applicable to other nanowire materials such as Si, GaAs, and InAs when the effects of surface charge and contact size are considered.
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Affiliation(s)
| | | | | | | | | | - Despoina M Kepaptsoglou
- ⊥SuperSTEM Laboratory, SFTC Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, United Kingdom
| | - Quentin M Ramasse
- ⊥SuperSTEM Laboratory, SFTC Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, United Kingdom
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68
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Ilari GM, Hage FS, Zhang Y, Rossell MD, Ramasse QM, Niederberger M, Erni R. Carbon–metal interfaces analyzed by aberration-corrected TEM: How copper and nickel nanoparticles interact with MWCNTs. Micron 2015; 72:52-8. [DOI: 10.1016/j.micron.2015.03.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 03/09/2015] [Accepted: 03/09/2015] [Indexed: 11/17/2022]
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69
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Spurgeon SR, Balachandran PV, Kepaptsoglou DM, Damodaran AR, Karthik J, Nejati S, Jones L, Ambaye H, Lauter V, Ramasse QM, Lau KKS, Martin LW, Rondinelli JM, Taheri ML. Polarization screening-induced magnetic phase gradients at complex oxide interfaces. Nat Commun 2015; 6:6735. [DOI: 10.1038/ncomms7735] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 02/20/2015] [Indexed: 01/07/2023] Open
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70
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Choi EM, Fix T, Kursumovic A, Kinane CJ, Arena D, Sahonta SL, Bi Z, Xiong J, Yan L, Lee JS, Wang H, Langridge S, Kim YM, Borisevich AY, MacLaren I, Ramasse QM, Blamire MG, Jia Q, MacManus-Driscoll JL. Room Temperature Ferrimagnetism and Ferroelectricity in Strained, Thin Films of BiFe 0.5Mn 0.5O 3. Adv Funct Mater 2014. [PMID: 26213531 PMCID: PMC4511393 DOI: 10.1002/adfm.201401464] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ∼ 600K), with a room temperature saturation moment (MS ) of up to 90 emu/cc (∼ 0.58 μB /f.u) on high quality (001) SrTiO3. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above.
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Affiliation(s)
- Eun-Mi Choi
- Department of Materials Science, University of Cambridge 27 Charles Babbage Road, Cambridge, CB3 0FS, UK E-mail:
| | - Thomas Fix
- Department of Materials Science, University of Cambridge 27 Charles Babbage Road, Cambridge, CB3 0FS, UK E-mail:
| | - Ahmed Kursumovic
- Department of Materials Science, University of Cambridge 27 Charles Babbage Road, Cambridge, CB3 0FS, UK E-mail:
| | - Christy J Kinane
- ISIS, Science and Technology Facilities Council, Rutherford Appleton Laboratory Didcot, OX11 0QX, UK
| | - Darío Arena
- National Synchrotron Light Source, Brookhaven National Laboratory Upton, New York, 11973, USA
| | - Suman-Lata Sahonta
- Department of Materials Science, University of Cambridge 27 Charles Babbage Road, Cambridge, CB3 0FS, UK E-mail:
| | - Zhenxing Bi
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory Los Alamos, New Mexico, 87545, USA
| | - Jie Xiong
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory Los Alamos, New Mexico, 87545, USA
| | - Li Yan
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory Los Alamos, New Mexico, 87545, USA
| | - Jun-Sik Lee
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory Menlo Park, California, 94025, USA
| | - Haiyan Wang
- Department of Electrical and Computer Engineering, Texas A&M University College Station, TX, 77843-3128, USA
| | - Sean Langridge
- ISIS, Science and Technology Facilities Council, Rutherford Appleton Laboratory Didcot, OX11 0QX, UK
| | - Young-Min Kim
- Materials Science and Technology Division, Oak Ridge National Laboratory Oak Ridge, Tennessee, 37831, USA ; Division of Electron Microscopic Research, Korea Basic Science Institute Daejeon, 305-806, Republic of Korea
| | - Albina Y Borisevich
- Materials Science and Technology Division, Oak Ridge National Laboratory Oak Ridge, Tennessee, 37831, USA
| | - Ian MacLaren
- SUPA School of Physics and Astronomy, University of Glasgow Glasgow, G12 8QQ, UK
| | | | - Mark G Blamire
- Department of Materials Science, University of Cambridge 27 Charles Babbage Road, Cambridge, CB3 0FS, UK E-mail:
| | - Quanxi Jia
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory Los Alamos, New Mexico, 87545, USA
| | - Judith L MacManus-Driscoll
- Department of Materials Science, University of Cambridge 27 Charles Babbage Road, Cambridge, CB3 0FS, UK E-mail:
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71
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Toth PS, Ramasse QM, Velický M, Dryfe RAW. Functionalization of graphene at the organic/water interface. Chem Sci 2014; 6:1316-1323. [PMID: 29560218 PMCID: PMC5811094 DOI: 10.1039/c4sc03504f] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Accepted: 11/20/2014] [Indexed: 12/05/2022] Open
Abstract
A simple method for the deposition of noble metal (Pd, Au) nanoparticles on a free-standing chemical vapour deposited graphene monolayer is reported. Metal deposition can proceed using either spontaneous or electrochemically-controlled processes. The resultant nanoclusters are characterized using atomic force and electron microscopy techniques, and mapping mode Raman spectroscopy.
A simple method for the deposition of noble metal (Pd, Au) nanoparticles on a free-standing chemical vapour deposited graphene (CVD GR) monolayer is reported. The method consists of assembling the high purity CVD GR, by transfer from poly (methyl methacrylate) (PMMA), at the organic/water interface. Metal deposition can then proceed using either spontaneous or electrochemically-controlled processes. The resultant graphene-based metal nanoclusters are characterized using atomic force and electron microscopy techniques, and the location of the nanostructures underneath the graphene layer is determined from the position and the intensity changes of the Raman bands (D, G, 2D). This novel process for decoration of a single-layer graphene sheet with metal nanoparticles using liquid/liquid interfaces opens an alternative and useful way to prepare low dimensional carbon-based nanocomposites and electrode materials.
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Affiliation(s)
- Peter S Toth
- School of Chemistry , University of Manchester , Oxford Road , Manchester M13 9PL , UK . ; Tel: +44 (0)161-306-4522
| | - Quentin M Ramasse
- SuperSTEM Laboratory , STFC Daresbury Campus , Daresbury WA4 4AD , UK
| | - Matěj Velický
- School of Chemistry , University of Manchester , Oxford Road , Manchester M13 9PL , UK . ; Tel: +44 (0)161-306-4522
| | - Robert A W Dryfe
- School of Chemistry , University of Manchester , Oxford Road , Manchester M13 9PL , UK . ; Tel: +44 (0)161-306-4522
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72
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Harris PJF, Slater TJA, Haigh SJ, Hage FS, Kepaptsoglou DM, Ramasse QM, Brydson R. Bilayer graphene formed by passage of current through graphite: evidence for a three-dimensional structure. Nanotechnology 2014; 25:465601. [PMID: 25354780 DOI: 10.1088/0957-4484/25/46/465601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The passage of an electric current through graphite or few-layer graphene can result in a striking structural transformation, but there is disagreement about the precise nature of this process. Some workers have interpreted the phenomenon in terms of the sublimation and edge reconstruction of essentially flat graphitic structures. An alternative explanation is that the transformation actually involves a change from a flat to a three-dimensional structure. Here we describe detailed studies of carbon produced by the passage of a current through graphite which provide strong evidence that the transformed carbon is indeed three-dimensional. The evidence comes primarily from images obtained in the scanning transmission electron microscope using the technique of high-angle annular dark-field imaging, and from a detailed analysis of electron energy loss spectra. We discuss the possible mechanism of the transformation, and consider potential applications of 'three-dimensional bilayer graphene'.
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Affiliation(s)
- Peter J F Harris
- Electron Microscopy Laboratory, Department of Chemistry, J.J. Thomson Building, University of Reading, Whiteknights, Reading, RG6 6AF, UK
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73
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Pan CT, Hinks JA, Ramasse QM, Greaves G, Bangert U, Donnelly SE, Haigh SJ. In-situ observation and atomic resolution imaging of the ion irradiation induced amorphisation of graphene. Sci Rep 2014; 4:6334. [PMID: 25284688 PMCID: PMC4185388 DOI: 10.1038/srep06334] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 08/20/2014] [Indexed: 12/03/2022] Open
Abstract
Ion irradiation has been observed to induce a macroscopic flattening and in-plane shrinkage of graphene sheets without a complete loss of crystallinity. Electron diffraction studies performed during simultaneous in-situ ion irradiation have allowed identification of the fluence at which the graphene sheet loses long-range order. This approach has facilitated complementary ex-situ investigations, allowing the first atomic resolution scanning transmission electron microscopy images of ion-irradiation induced graphene defect structures together with quantitative analysis of defect densities using Raman spectroscopy.
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Affiliation(s)
- C-T Pan
- 1] School of Materials, University of Manchester, Material Science Centre, Grosvenor Street, Manchester, M13 9PL, United Kingdom [2] School of Physics and Astronomy, University of Manchester, Manchester, Oxford Road, M13 9PL, United Kingdom
| | - J A Hinks
- School of Computing and Engineering, University of Huddersfield, HD1 3DH, United Kingdom
| | - Q M Ramasse
- SuperSTEM Laboratory, STFC Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, United Kingdom
| | - G Greaves
- School of Computing and Engineering, University of Huddersfield, HD1 3DH, United Kingdom
| | - U Bangert
- 1] School of Materials, University of Manchester, Material Science Centre, Grosvenor Street, Manchester, M13 9PL, United Kingdom [2]
| | - S E Donnelly
- School of Computing and Engineering, University of Huddersfield, HD1 3DH, United Kingdom
| | - S J Haigh
- School of Materials, University of Manchester, Material Science Centre, Grosvenor Street, Manchester, M13 9PL, United Kingdom
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74
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Zhu Y, Ramasse QM, Brorson M, Moses PG, Hansen LP, Kisielowski CF, Helveg S. Inside Back Cover: Visualizing the Stoichiometry of Industrial-Style Co-Mo-S Catalysts with Single-Atom Sensitivity (Angew. Chem. Int. Ed. 40/2014). Angew Chem Int Ed Engl 2014. [DOI: 10.1002/anie.201406994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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75
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Zhu Y, Ramasse QM, Brorson M, Moses PG, Hansen LP, Kisielowski CF, Helveg S. Innenrücktitelbild: Visualizing the Stoichiometry of Industrial-Style Co-Mo-S Catalysts with Single-Atom Sensitivity (Angew. Chem. 40/2014). Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201406994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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76
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Zhu Y, Ramasse QM, Brorson M, Moses PG, Hansen LP, Kisielowski CF, Helveg S. Visualizing the stoichiometry of industrial-style Co-Mo-S catalysts with single-atom sensitivity. Angew Chem Int Ed Engl 2014; 53:10723-7. [PMID: 25078562 DOI: 10.1002/anie.201405690] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Indexed: 11/08/2022]
Abstract
The functional properties of transition metal dichalcogenides (TMDs) may be promoted by the inclusion of other elements. Here, we studied the local stoichiometry of single cobalt promoter atoms in an industrial-style MoS2-based hydrotreating catalyst. Aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy show that the Co atoms occupy sites at the (-100) S edge terminations of the graphite-supported MoS2 nanocrystals in the catalyst. Specifically, each Co atom has four neighboring S atoms that are arranged in a reconstructed geometry, which reflects an equilibrium state. The structure agrees with complementary studies of catalysts that were prepared under vastly different conditions and on other supports. In contrast, a small amount of residual Fe in the graphite is found to compete for the S edge sites, so that promotion by Co is strongly sensitive to the purity of the raw materials. The present single-atom-sensitive analytical method therefore offers a guide for advancing preparative methods for promoted TMD nanomaterials.
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Affiliation(s)
- Yuanyuan Zhu
- Haldor Topsøe A/S, Nymøllevej 55, 2800 Kgs. Lyngby (Denmark)
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77
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Zhu Y, Ramasse QM, Brorson M, Moses PG, Hansen LP, Kisielowski CF, Helveg S. Visualizing the Stoichiometry of Industrial-Style Co-Mo-S Catalysts with Single-Atom Sensitivity. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201405690] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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78
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79
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Spurgeon SR, Sloppy JD, Kepaptsoglou DMD, Balachandran PV, Nejati S, Karthik J, Damodaran AR, Johnson CL, Ambaye H, Goyette R, Lauter V, Ramasse QM, Idrobo JC, Lau KKS, Lofland SE, Rondinelli JM, Martin LW, Taheri ML. Thickness-dependent crossover from charge- to strain-mediated magnetoelectric coupling in ferromagnetic/piezoelectric oxide heterostructures. ACS Nano 2014; 8:894-903. [PMID: 24313563 DOI: 10.1021/nn405636c] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Magnetoelectric oxide heterostructures are proposed active layers for spintronic memory and logic devices, where information is conveyed through spin transport in the solid state. Incomplete theories of the coupling between local strain, charge, and magnetic order have limited their deployment into new information and communication technologies. In this study, we report direct, local measurements of strain- and charge-mediated magnetization changes in the La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 system using spatially resolved characterization techniques in both real and reciprocal space. Polarized neutron reflectometry reveals a graded magnetization that results from both local structural distortions and interfacial screening of bound surface charge from the adjacent ferroelectric. Density functional theory calculations support the experimental observation that strain locally suppresses the magnetization through a change in the Mn-eg orbital polarization. We suggest that this local coupling and magnetization suppression may be tuned by controlling the manganite and ferroelectric layer thicknesses, with direct implications for device applications.
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Affiliation(s)
- Steven R Spurgeon
- Department of Materials Science and Engineering, Drexel University , Philadelphia, Pennsylvania, United States
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80
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Hage FS, Kepaptsoglou DM, Seabourne CR, Ramasse QM, Scott AJ, Prytz Ø, Gunnæs AE, Helgesen G. Dielectric response of pentagonal defects in multilayer graphene nano-cones. Nanoscale 2014; 6:1833-1839. [PMID: 24356681 DOI: 10.1039/c3nr05419e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The dielectric response of pentagonal defects in multilayer graphene nano-cones has been studied by electron energy loss spectroscopy and ab initio simulations. At the cone apex, a strong modification of the dielectric response is observed below the energy of the π plasmon resonance. This is attributed to π → π* interband transitions induced by topology-specific resonant π bonding states as well as π*-σ* hybridization. It is concluded that pentagonal defects strongly affect the local electronic structure in such a way that multi-walled graphene nano-cones should show great promise as field emitters.
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Affiliation(s)
- F S Hage
- SuperSTEM Laboratory, SciTech Daresbury, Keckwick Lane, Daresbury, WA4 4AD, UK.
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81
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Zan R, Ramasse QM, Jalil R, Georgiou T, Bangert U, Novoselov KS. Control of radiation damage in MoS(2) by graphene encapsulation. ACS Nano 2013; 7:10167-74. [PMID: 24116975 DOI: 10.1021/nn4044035] [Citation(s) in RCA: 124] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Recent dramatic progress in studying various two-dimensional (2D) atomic crystals and their heterostructures calls for better and more detailed understanding of their crystallography, reconstruction, stacking order, etc. For this, direct imaging and identification of each and every atom is essential. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) are ideal and perhaps the only tools for such studies. However, the electron beam can in some cases induce dramatic structure changes, and radiation damage becomes an obstacle in obtaining the desired information in imaging and chemical analysis in the (S)TEM. This is the case of 2D materials such as molybdenum disulfide MoS2, but also of many biological specimens, molecules, and proteins. Thus, minimizing damage to the specimen is essential for optimum microscopic analysis. In this article we demonstrate, on the example of MoS2, that encapsulation of such crystals between two layers of graphene allows for a dramatic improvement in stability of the studied 2D crystal and permits careful control over the defect nature and formation in it. We present STEM data collected from single-layer MoS2 samples prepared for observation in the microscope through three distinct procedures. The fabricated single-layer MoS2 samples were either left bare (pristine), placed atop a single-layer of graphene, or finally encapsulated between single graphene layers. Their behavior under the electron beam is carefully compared, and we show that the MoS2 sample "sandwiched" between the graphene layers has the highest durability and lowest defect formation rate compared to the other two samples, for very similar experimental conditions.
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Affiliation(s)
- Recep Zan
- School of Physics and Astronomy, University of Manchester , Manchester, M13 9PL, U.K
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82
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Lord AM, Maffeis TG, Walton AS, Kepaptsoglou DM, Ramasse QM, Ward MB, Köble J, Wilks SP. Factors that determine and limit the resistivity of high-quality individual ZnO nanowires. Nanotechnology 2013; 24:435706. [PMID: 24107476 DOI: 10.1088/0957-4484/24/43/435706] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Knowing and controlling the resistivity of an individual nanowire (NW) is crucial for the production of new sensors and devices. For ZnO NWs this is poorly understood; a 10(8) variation in resistivity has previously been reported, making the production of reproducible devices almost impossible. Here, we provide accurate resistivity measurements of individual NWs, using a four-probe scanning tunnelling microscope (STM), revealing a dependence on the NW dimensions. To correctly interpret this behaviour, an atomic level transmission electron microscopy technique was employed to study the structural properties of the NWs in relation to three growth techniques: hydrothermal, catalytic and non-catalytic vapour phase. All NWs were found to be defect free and structurally equivalent; those grown with a metallic catalyst were free from Au contamination. The resistivity measurements showed a distinct increase with decreasing NW diameter, independent of growth technique. The increasing resistivity at small NW diameters was attributed to the dominance of surface states removing electrons from the bulk. However, a fundamental variance in resistivity (10(2)) was observed and attributed to changes in occupied surface state density, an effect which is not seen with other NW materials such as Si. This is examined by a model to predict the effect of surface state occupancy on the measured resistivity and is confirmed with measurements after passivating the ZnO surface. Our results provide an understanding of the primary influence of the reactive nature of the surface and its dramatic effect on the electrical properties of ZnO NWs.
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Affiliation(s)
- Alex M Lord
- Multidisciplinary Nanotechnology Centre, College of Engineering, University of Swansea, Singleton Park, SA2 8PP, UK
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83
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Ramasse QM, Seabourne CR, Kepaptsoglou DM, Zan R, Bangert U, Scott AJ. Probing the bonding and electronic structure of single atom dopants in graphene with electron energy loss spectroscopy. Nano Lett 2013; 13:4989-95. [PMID: 23259533 DOI: 10.1021/nl304187e] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
A combination of scanning transmission electron microscopy, electron energy loss spectroscopy, and ab initio calculations reveal striking electronic structure differences between two distinct single substitutional Si defect geometries in graphene. Optimised acquisition conditions allow for exceptional signal-to-noise levels in the spectroscopic data. The near-edge fine structure can be compared with great accuracy to simulations and reveal either an sp(3)-like configuration for a trivalent Si or a more complicated hybridized structure for a tetravalent Si impurity.
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Affiliation(s)
- Quentin M Ramasse
- SuperSTEM Laboratory, STFC Daresbury Campus , Daresbury WA4 4AD, United Kingdom
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84
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Rossell MD, Abakumov AM, Ramasse QM, Erni R. Direct evidence of stacking disorder in the mixed ionic-electronic conductor Sr4Fe6O12+δ. ACS Nano 2013; 7:3078-3085. [PMID: 23458358 DOI: 10.1021/nn3058449] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Determining the structure-to-property relationship of materials becomes particularly challenging when the material under investigation is dominated by defects and structural disorder. Knowledge on the exact atomic arrangement at the defective structure is required to understand its influence on the functional properties. However, standard diffraction techniques deliver structural information that is averaged over many unit cells. In particular, information about defects and order-disorder phenomena is contained in the coherent diffuse scattering intensity which often is difficult to uniquely interpret. Thus, the examination of the local disorder in materials requires a direct method to study their structure on the atomic level with chemical sensitivity. Using aberration-corrected scanning transmission electron microscopy in combination with atomic-resolution electron energy-loss spectroscopy, we show that the controversial structural arrangement of the Fe2O2+δ layers in the mixed ionic-electronic conducting Sr4Fe6O12+δ perovskite can be unambiguously resolved. Our results provide direct experimental evidence for the presence of a nanomixture of "ordered" and "disordered" domains in an epitaxial Sr4Fe6O12+δ thin film. The most favorable arrangement is the disordered structure and is interpreted as a randomly occurring but well-defined local shift of the Fe-O chains in the Fe2O2+δ layers. By analyzing the electron energy-loss near-edge structure of the different building blocks in the Sr4Fe6O12+δ unit cell we find that the mobile holes in this mixed ionic-electronic conducting oxide are highly localized in the Fe2O2+δ layers, which are responsible for the oxide-ion conductivity. A possible link between disorder and oxygen-ion transport along the Fe2O2+δ layers is proposed by arguing that the disorder can effectively break the oxygen diffusion pathways.
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Affiliation(s)
- Marta D Rossell
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
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85
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Nicotra G, Ramasse QM, Deretzis I, La Magna A, Spinella C, Giannazzo F. Delaminated graphene at silicon carbide facets: atomic scale imaging and spectroscopy. ACS Nano 2013; 7:3045-3052. [PMID: 23530467 DOI: 10.1021/nn305922u] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Atomic-resolution structural and spectroscopic characterization techniques (scanning transmission electron microscopy and electron energy loss spectroscopy) are combined with nanoscale electrical measurements (conductive atomic force microscopy) to study at the atomic scale the properties of graphene grown epitaxially through the controlled graphitization of a hexagonal SiC(0001) substrate by high temperature annealing. This growth technique is known to result in a pronounced electron-doping (∼10(13) cm(-2)) of graphene, which is thought to originate from an interface carbon buffer layer strongly bound to the substrate. The scanning transmission electron microscopy analysis, carried out at an energy below the knock-on threshold for carbon to ensure no damage is imparted to the film by the electron beam, demonstrates that the buffer layer present on the planar SiC(0001) face delaminates from it on the (112n) facets of SiC surface steps. In addition, electron energy loss spectroscopy reveals that the delaminated layer has a similar electronic configuration to purely sp2-hybridized graphene. These observations are used to explain the local increase of the graphene sheet resistance measured around the surface steps by conductive atomic force microscopy, which we suggest is due to significantly lower substrate-induced doping and a resonant scattering mechanism at the step regions. A first-principles-calibrated theoretical model is proposed to explain the structural instability of the buffer layer on the SiC facets and the resulting delamination.
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86
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Geaney H, Mullane E, Ramasse QM, Ryan KM. Atomically abrupt silicon-germanium axial heterostructure nanowires synthesized in a solvent vapor growth system. Nano Lett 2013; 13:1675-1680. [PMID: 23517564 DOI: 10.1021/nl400146u] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The growth of Si/Ge axial heterostructure nanowires in high yield using a versatile wet chemical approach is reported. Heterostructure growth is achieved using the vapor zone of a high boiling point solvent as a reaction medium with an evaporated tin layer as the catalyst. The low solubility of Si and Ge within the Sn catalyst allows the formation of extremely abrupt heterojunctions of the order of just 1-2 atomic planes between the Si and Ge nanowire segments. The compositional abruptness was confirmed using aberration corrected scanning transmission electron microscopy and atomic level electron energy loss spectroscopy. Additional analysis focused on the role of crystallographic defects in determining interfacial abruptness and the preferential incorporation of metal catalyst atoms near twin defects in the nanowires.
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Affiliation(s)
- Hugh Geaney
- Materials and Surface Science Institute and Department of Chemical and Environmental Sciences, University of Limerick, Limerick, Ireland
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87
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Alem N, Ramasse QM, Seabourne CR, Yazyev OV, Erickson K, Sarahan MC, Kisielowski C, Scott AJ, Louie SG, Zettl A. Subangstrom edge relaxations probed by electron microscopy in hexagonal boron nitride. Phys Rev Lett 2012; 109:205502. [PMID: 23215505 DOI: 10.1103/physrevlett.109.205502] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2012] [Indexed: 06/01/2023]
Abstract
Theoretical research on the two-dimensional crystal structure of hexagonal boron nitride (h-BN) has suggested that the physical properties of h-BN can be tailored for a wealth of applications by controlling the atomic structure of the membrane edges. Unexplored for h-BN, however, is the possibility that small additional edge-atom distortions could have electronic structure implications critically important to nanoengineering efforts. Here we demonstrate, using a combination of analytical scanning transmission electron microscopy and density functional theory, that covalent interlayer bonds form spontaneously at the edges of a h-BN bilayer, resulting in subangstrom distortions of the edge atomic structure. Orbital maps calculated in 3D around the closed edge reveal that the out-of-plane bonds retain a strong π(*) character. We show that this closed edge reconstruction, strikingly different from the equivalent case for graphene, helps the material recover its bulklike insulating behavior and thus largely negates the predicted metallic character of open edges.
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Affiliation(s)
- Nasim Alem
- Department of Physics, University of California Berkeley, Berkeley, California 94720, USA
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88
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Aguiar JA, Reed BW, Ramasse QM, Erni R, Browning ND. Quantifying the low-energy limit and spectral resolution in valence electron energy loss spectroscopy. Ultramicroscopy 2012; 124:130-8. [PMID: 23154033 DOI: 10.1016/j.ultramic.2012.08.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 08/15/2012] [Accepted: 08/18/2012] [Indexed: 11/30/2022]
Abstract
While the development of monochromators for scanning transmission electron microscopes (STEM) has improved our ability to resolve spectral features in the 0-5 eV energy range of the electron energy loss spectrum, the overall benefits relative to unfiltered microscopes have been difficult to quantify. Simple curve fitting and reciprocal space models that extrapolate the expected behavior of the zero-loss peak are not enough to fully exploit the optimal spectral limit and can hinder the ease of interpreting the resulting spectra due to processing-induced artifacts. To address this issue, here we present a quantitative comparison of two processing methods for performing ZLP removal and for defining the low-energy spectral limit applied to three microscopes with different intrinsic emission and energy resolutions. Applying the processing techniques to spectroscopic data obtained from each instrument leads in each case to a marked improvement in the spectroscopic limit, regardless of the technique implemented or the microscope setup. The example application chosen to benchmark these processing techniques is the energy limit obtained from a silicon wedge sample as a function of thickness. Based on these results, we conclude on the possibility to resolve statistically significant spectral features to within a hundred meV of the native instrumental energy spread, opening up the future prospect of tracking phonon peaks as new and improved hardware becomes available.
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Affiliation(s)
- Jeffery A Aguiar
- Department of Chemical Engineering and Materials Science, University of California Davis, One Shields Ave, Davis, CA 95618, USA.
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89
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Rossell MD, Ramasse QM, Findlay SD, Rechberger F, Erni R, Niederberger M. Direct imaging of dopant clustering in metal-oxide nanoparticles. ACS Nano 2012; 6:7077-7083. [PMID: 22747340 DOI: 10.1021/nn3021212] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Dopant atoms are used to tailor the properties of materials. However, whether the desired effect is achieved through selective doping depends on the dopant distribution within the host material. The clustering of dopant atoms can have a deleterious effect on the achievable properties because a two-phase material is obtained instead of a homogeneous material. Thus, the examination of dopant fluctuations in nanodevices requires a reliable method to chemically probe individual atoms within the host material. This is particularly challenging in the case of functionalized nanoparticles where the characteristic length scale of the particles demands the use of a high-spatial-resolution and high-sensitivity technique. Here we demonstrate a chemically sensitive atomic resolution imaging technique which delivers direct site-specific information on the dopant distribution in nanoparticles. We employ electron energy-loss spectroscopy imaging in a scanning transmission electron microscope combined with multivariate statistical analysis to map the distribution of Ba dopant atoms in SrTiO(3) nanoparticles. Our results provide direct evidence for clustering of the Ba dopants in the SrTiO(3) nanoparticles outlining a possible explanation for the presence of polar nanoregions in the Ba:SrTiO(3) system. The results we present constitute the first example of site-specific atomic resolution spectroscopy of foreign atoms in doped nanoparticles and suggest a general strategy to ascertain the spatial distribution of impurity atoms in nanocrystals and hence improve the performance of nanoparticle-based devices.
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Affiliation(s)
- Marta D Rossell
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
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90
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Abstract
Nanoholes, etched under an electron beam at room temperature in single-layer graphene sheets as a result of their interaction with metal impurities, are shown to heal spontaneously by filling up with either nonhexagon, graphene-like, or perfect hexagon 2D structures. Scanning transmission electron microscopy was employed to capture the healing process and study atom-by-atom the regrown structure. A combination of these nanoscale etching and reknitting processes could lead to new graphene tailoring approaches.
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Affiliation(s)
- Recep Zan
- School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, United Kingdom
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91
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Aguiar JA, Ramasse QM, Asta M, Browning ND. Investigating the electronic structure of fluorite-structured oxide compounds: comparison of experimental EELS with first principles calculations. J Phys Condens Matter 2012; 24:295503. [PMID: 22739407 DOI: 10.1088/0953-8984/24/29/295503] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Energy loss spectra from fluorite-structured ZrO(2), CeO(2), and UO(2) compounds are compared with theoretical calculations based on density functional theory (DFT) and its extensions, including the use of Hubbard-U corrections (DFT + U) and hybrid functionals. Electron energy loss spectra (EELS) were obtained from each oxide using a scanning transmission electron microscope (STEM). The same spectra were computed within the framework of the full-potential linear augmented plane-wave (FLAPW) method. The theoretical and experimental EEL spectra are compared quantitatively using non-linear least squares peak fitting and a cross-correlation approach, with the best level of agreement between experiment and theory being obtained using the DFT + U and hybrid computational approaches.
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Affiliation(s)
- J A Aguiar
- Department of Chemical Engineering and Materials Science, University of California, Davis, Davis, CA 95616, USA.
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92
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Yu P, Luo W, Yi D, Zhang JX, Rossell MD, Yang CH, You L, Singh-Bhalla G, Yang SY, He Q, Ramasse QM, Erni R, Martin LW, Chu YH, Pantelides ST, Pennycook SJ, Ramesh R. Interface control of bulk ferroelectric polarization. Proc Natl Acad Sci U S A 2012; 109:9710-5. [PMID: 22647612 PMCID: PMC3382509 DOI: 10.1073/pnas.1117990109] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The control of material interfaces at the atomic level has led to novel interfacial properties and functionalities. In particular, the study of polar discontinuities at interfaces between complex oxides lies at the frontier of modern condensed matter research. Here we employ a combination of experimental measurements and theoretical calculations to demonstrate the control of a bulk property, namely ferroelectric polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. More specifically, the control is achieved by exploiting the interfacial valence mismatch to influence the electrostatic potential step across the interface, which manifests itself as the biased-voltage in ferroelectric hysteresis loops and determines the ferroelectric state. A broad study of diverse systems comprising different ferroelectrics and conducting perovskite underlayers extends the generality of this phenomenon.
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Affiliation(s)
- P Yu
- Department of Physics, University of California, Berkeley, CA 94720, USA.
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93
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Ramasse QM, Zan R, Bangert U, Boukhvalov DW, Son YW, Novoselov KS. Direct experimental evidence of metal-mediated etching of suspended graphene. ACS Nano 2012; 6:4063-4071. [PMID: 22533553 DOI: 10.1021/nn300452y] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Atomic resolution high angle annular dark field imaging of suspended, single-layer graphene, onto which the metals Cr, Ti, Pd, Ni, Al, and Au atoms had been deposited, was carried out in an aberration-corrected scanning transmission electron microscope. In combination with electron energy loss spectroscopy, employed to identify individual impurity atoms, it was shown that nanoscale holes were etched into graphene, initiated at sites where single atoms of all the metal species except for gold come into close contact with the graphene. The e-beam scanning process is instrumental in promoting metal atoms from clusters formed during the original metal deposition process onto the clean graphene surface, where they initiate the hole-forming process. Our observations are discussed in the light of calculations in the literature, predicting a much lowered vacancy formation in graphene when metal ad-atoms are present. The requirement and importance of oxygen atoms in this process, although not predicted by such previous calculations, is also discussed, following our observations of hole formation in pristine graphene in the presence of Si-impurity atoms, supported by new calculations which predict a dramatic decrease of the vacancy formation energy, when SiO(x) molecules are present.
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Affiliation(s)
- Quentin M Ramasse
- SuperSTEM Laboratory, STFC Daresbury Campus , Daresbury WA4 4AD, United Kingdom.
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94
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Hansen LP, Ramasse QM, Kisielowski C, Brorson M, Johnson E, Topsøe H, Helveg S. Inside Cover: Atomic-Scale Edge Structures on Industrial-Style MoS2 Nanocatalysts (Angew. Chem. Int. Ed. 43/2011). Angew Chem Int Ed Engl 2011. [DOI: 10.1002/anie.201105816] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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95
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Hansen LP, Ramasse QM, Kisielowski C, Brorson M, Johnson E, Topsøe H, Helveg S. Innentitelbild: Atomic-Scale Edge Structures on Industrial-Style MoS2 Nanocatalysts (Angew. Chem. 43/2011). Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201105816] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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96
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Hansen LP, Ramasse QM, Kisielowski C, Brorson M, Johnson E, Topsøe H, Helveg S. Atomic-Scale Edge Structures on Industrial-Style MoS2 Nanocatalysts. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201103745] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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97
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Hansen LP, Ramasse QM, Kisielowski C, Brorson M, Johnson E, Topsøe H, Helveg S. Atomic-Scale Edge Structures on Industrial-Style MoS2 Nanocatalysts. Angew Chem Int Ed Engl 2011; 50:10153-6. [DOI: 10.1002/anie.201103745] [Citation(s) in RCA: 210] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Indexed: 11/06/2022]
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98
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Arredondo M, Ramasse QM, Bogle K, Nagarajan V. Chemistry of the Fe₂O₃/BiFeO₃ Interface in BiFeO₃ Thin Film Heterostructures. Materials (Basel) 2010; 3:5274-5282. [PMID: 28883382 PMCID: PMC5445815 DOI: 10.3390/ma3125274] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 12/02/2010] [Accepted: 12/13/2010] [Indexed: 11/16/2022]
Abstract
We investigate the interfacial chemistry of secondary Fe₂O₃ phases formed in a BiFeO₃ (BFO) layer in BFO/ La0.67Sr0.33MnO₃ (LSMO)/SrTiO₃ (STO) heterostructures. A combination of high-resolution spherical aberration corrected scanning TEM and spectroscopy results, reveals that specific chemical and crystallographic similarities between Fe₂O₃ and BFO, enable the BFO layer to form a facile host for Fe₂O₃.
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Affiliation(s)
- Miryam Arredondo
- School of Materials Science and Engineering, University of New South Wales, Sydney NSW 2052, Australia.
| | - Quentin M Ramasse
- SuperSTEM Laboratory, STFC Daresbury, Keckwick Lane, Daresbury WA4 4AD, UK.
| | - Kashinath Bogle
- School of Materials Science and Engineering, University of New South Wales, Sydney NSW 2052, Australia.
| | - Valanoor Nagarajan
- School of Materials Science and Engineering, University of New South Wales, Sydney NSW 2052, Australia.
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99
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Yu P, Lee JS, Okamoto S, Rossell MD, Huijben M, Yang CH, He Q, Zhang JX, Yang SY, Lee MJ, Ramasse QM, Erni R, Chu YH, Arena DA, Kao CC, Martin LW, Ramesh R. Interface ferromagnetism and orbital reconstruction in BiFeO3-La(0.7)Sr(0.3)MnO3 heterostructures. Phys Rev Lett 2010; 105:027201. [PMID: 20867733 DOI: 10.1103/physrevlett.105.027201] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Indexed: 05/12/2023]
Abstract
We report the formation of a novel ferromagnetic state in the antiferromagnet BiFeO3 at the interface with ferromagnet La(0.7)Sr(0.3)MnO3. Using x-ray magnetic circular dichroism at Mn and Fe L(2,3) edges, we discovered that the development of this ferromagnetic spin structure is strongly associated with the onset of a significant exchange bias. Our results demonstrate that the magnetic state is directly related to an electronic orbital reconstruction at the interface, which is supported by the linearly polarized x-ray absorption measurement at the oxygen K edge.
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Affiliation(s)
- P Yu
- Department of Physics, University of California, Berkeley, California 94720, USA.
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100
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Arredondo M, Ramasse QM, Weyland M, Mahjoub R, Vrejoiu I, Hesse D, Browning ND, Alexe M, Munroe P, Nagarajan V. Direct evidence for cation non-stoichiometry and cottrell atmospheres around dislocation cores in functional oxide interfaces. Adv Mater 2010; 22:2430-4. [PMID: 20432474 DOI: 10.1002/adma.200903631] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
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