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Ramasse QM. Twenty years after: How “Aberration correction in the STEM” truly placed a “A synchrotron in a Microscope”. Ultramicroscopy 2017; 180:41-51. [DOI: 10.1016/j.ultramic.2017.03.016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 03/06/2017] [Accepted: 03/14/2017] [Indexed: 10/19/2022]
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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] [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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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. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 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] [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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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] [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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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 LETTERS 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] [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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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] [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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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. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 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] [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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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] [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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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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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] [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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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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62
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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63
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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 LETTERS 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] [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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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] [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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65
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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. JOURNAL OF MATERIALS CHEMISTRY. C 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] [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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66
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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] [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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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] [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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68
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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 LETTERS 2015; 15:4248-54. [PMID: 26042356 DOI: 10.1021/nl503743t] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [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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69
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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] [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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70
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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] [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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71
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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. ADVANCED FUNCTIONAL MATERIALS 2014. [PMID: 26213531 PMCID: PMC4511393 DOI: 10.1002/adfm.201401464] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [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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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] [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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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] [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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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] [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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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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