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Procházka P, Čechal J. ProLEED Studio: software for modeling low-energy electron diffraction patterns. J Appl Crystallogr 2024; 57:187-193. [PMID: 38322724 PMCID: PMC10840303 DOI: 10.1107/s1600576723010312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Accepted: 11/29/2023] [Indexed: 02/08/2024] Open
Abstract
Low-energy electron diffraction patterns contain precise information about the structure of the surface studied. However, retrieving the real space lattice periodicity from complex diffraction patterns is challenging, especially when the modeled patterns originate from superlattices with large unit cells composed of several symmetry-equivalent domains without a simple relation to the substrate. This work presents ProLEED Studio software, built to provide simple, intuitive and precise modeling of low-energy electron diffraction patterns. The interactive graphical user interface allows real-time modeling of experimental diffraction patterns, change of depicted diffraction spot intensities, visualization of different diffraction domains, and manipulation of any lattice points or diffraction spots. The visualization of unit cells, lattice vectors, grids and scale bars as well as the possibility of exporting ready-to-publish models in bitmap and vector formats significantly simplifies the modeling process and publishing of results.
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Affiliation(s)
- Pavel Procházka
- CEITEC – Central European Institute of Technology, Brno University of Technology, Brno, Purkyňova 123, 61200, Czechia
| | - Jan Čechal
- CEITEC – Central European Institute of Technology, Brno University of Technology, Brno, Purkyňova 123, 61200, Czechia
- Institute of Physical Engineering, Brno University of Technology, Brno, Technická 2896/2, 61669, Czechia
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Garagnani D, De Padova P, Ottaviani C, Quaresima C, Generosi A, Paci B, Olivieri B, Jałochowski M, Krawiec M. Evidence of sp2-like Hybridization of Silicon Valence Orbitals in Thin and Thick Si Grown on α-Phase Si(111)√3 × √3R30°-Bi. Materials (Basel) 2022; 15:1730. [PMID: 35268964 DOI: 10.3390/ma15051730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 02/19/2022] [Accepted: 02/21/2022] [Indexed: 11/21/2022]
Abstract
One-monolayer (ML) (thin) and 5-ML (thick) Si films were grown on the α-phase Si(111)√3 × √3R30°-Bi at a low substrate temperature of 200 °C. Si films have been studied in situ by reflection electron energy loss spectroscopy (REELS) and Auger electron spectroscopy, as a function of the electron beam incidence angle α and low-energy electron diffraction (LEED), as well as ex situ by grazing incidence X-ray diffraction (GIXRD). Scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS) were also reported. The REELS spectra, taken at the Si K absorption edge (~1.840 KeV), reveal the presence of two distinct loss structures attributed to transitions 1s→π* and 1s→σ* according to their intensity dependence on α, attesting to the sp2-like hybridization of the silicon valence orbitals in both thin and thick Si films. The synthesis of a silicon allotrope on the α-phase of Si(111)√3 × √3R30°-Bi substrate was demonstrated by LEED patterns and GIXRD that discloses the presence of a Si stack of 3.099 (3) Å and a √3 × √3 unit cell of 6.474 Å, typically seen for multilayer silicene. STM and STS measurements corroborated the findings. These measurements provided a platform for the new √3 × √3R30° Si allotrope on a Si(111)√3 × √3 R30°-Bi template, paving the way for realizing topological insulator heterostructures from different two-dimensional materials, Bi and Si.
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Yang HI, Coyle DJ, Wurch M, Yadav PR, Valentin MD, Neupane MR, Almeida K, Bartels L. Epitaxial Molybdenum Disulfide/Gallium Nitride Junctions: Low-Knee-Voltage Schottky-Diode Behavior at Optimized Interfaces. ACS Appl Mater Interfaces 2021; 13:35105-35112. [PMID: 34259497 DOI: 10.1021/acsami.1c07306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Low turn-on (knee) voltage (∼0.3 V) Schottky-diode behavior of a four-layer (4L) MoS2/GaN junction is achieved by optimizing the in situ interface preparation of the GaN substrate prior to MoS2 overlayer growth in a vacuum system using metallic molybdenum and hydrogen sulfide gas as precursors. The process leads to a clean nitrogen-terminated GaN surface that bonds well to the MoS2 film revealing a 2 × 2 reconstruction at the interface observed in low-energy electron diffraction (LEED). Atomic force microscopy and X-ray photoelectron spectroscopy provide clear images of the GaN terraces through the MoS2 overlayer confirming close adhesion and absence of oxygen and other contaminants. Density functional theory calculations predict the formation of the 2 × 2 superstructure at a clean interface. Transport measurements show diode behavior at an on/off ratio of ∼105 for ±1 V with a forward direction for the positive voltage applied to the MoS2 layer. Combining transport and photoelectron spectroscopy measurements with theory, we deduce a Fermi-level position in the MoS2 gap consistent with interface charge transfer from MoS2 to the substrate. The high performance of the MoS2/Gan diode highlights the technological potential of devices based on GaN/MoS2 interfaces.
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Affiliation(s)
- Hae In Yang
- Department of Chemistry and Materials Science & Engineering Program, University of California-Riverside, Riverside, California 92521, United States
| | - Daniel J Coyle
- Department of Chemistry and Materials Science & Engineering Program, University of California-Riverside, Riverside, California 92521, United States
| | - Michelle Wurch
- Department of Chemistry and Materials Science & Engineering Program, University of California-Riverside, Riverside, California 92521, United States
| | - Prachi R Yadav
- Department of Chemistry and Materials Science & Engineering Program, University of California-Riverside, Riverside, California 92521, United States
| | - Michael D Valentin
- Department of Chemistry and Materials Science & Engineering Program, University of California-Riverside, Riverside, California 92521, United States
| | - Mahesh R Neupane
- Department of Chemistry and Materials Science & Engineering Program, University of California-Riverside, Riverside, California 92521, United States
| | - Kortney Almeida
- Department of Chemistry and Materials Science & Engineering Program, University of California-Riverside, Riverside, California 92521, United States
| | - Ludwig Bartels
- Department of Chemistry and Materials Science & Engineering Program, University of California-Riverside, Riverside, California 92521, United States
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Kundu AK, Barman S, Menon KSR. Role of Surface Termination in the Metal-Insulator Transition of V 2O 3(0001) Ultrathin Films. ACS Appl Mater Interfaces 2021; 13:20779-20787. [PMID: 33887915 DOI: 10.1021/acsami.1c01527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Surface termination is known to play an important role in determining the physical properties of materials. It is crucial to know how surface termination affects the metal-insulator transition (MIT) of V2O3 films for both fundamental understanding and its applications. By changing growth parameters, we achieved a variety of surface terminations in V2O3 films that are characterized by low-energy electron diffraction (LEED) and photoemission spectroscopy techniques. Depending upon the terminations, our results show that MIT can be partially or fully suppressed near the surface region due to the different fillings of the electrons at the surface and subsurface layers and the change of screening length compared to the bulk. Across MIT, a strong redistribution of spectral weight and its transfer from a high-to-low-binding energy regime is observed in a wide energy scale. Our results show that the total spectral weight in the low-energy regime is not conserved across MIT, indicating a breakdown of the "sum rules of spectral weight", signature of a strongly correlated system. Such a change in spectral weight is possibly linked to the change in hybridization, lattice volume (i.e., effective carrier density), and the spin degree of freedom in the system that occurs across MIT. We find that MIT in this system is strongly correlation-driven, where the electron-electron interactions play a pivotal role. Moreover, our results provide better insight into the understanding of the electronic structure of strongly correlated systems and highlight the importance of accounting for surface effects during interpretation of the physical property data mainly using surface-sensitive probes, such as surface resistivity.
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Affiliation(s)
- Asish K Kundu
- Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Kolkata 700064, India
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Sukanta Barman
- Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Kolkata 700064, India
- Department of Physics, Raja Peary Mohan College, Uttarpara, Hooghly 712258, India
| | - Krishnakumar S R Menon
- Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Kolkata 700064, India
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Kelley KP, Sharma V, Zhang W, Baddorf AP, Nascimento VB, Vasudevan RK. Exotic Long-Range Surface Reconstruction on La 0.7Sr 0.3MnO 3 Thin Films. ACS Appl Mater Interfaces 2021; 13:9166-9173. [PMID: 33566561 DOI: 10.1021/acsami.0c20166] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Due to an extremely diverse phase space, La1-xSrxMnO3, as with other manganites, offers a wide range of tunability and applications including colossal magnetoresistance and use as spin-polarized electrodes. Here, we study an unprecedented, exotic surface reconstruction (6 × 6) in La1-xSrxMnO3 (x = 0.3) observed via low-energy electron diffraction (LEED). Scanning tunneling microscopy (STM) shows the surface is relatively flat, with unit-cell step heights, and X-ray photoelectron spectroscopy (XPS) reveals a strong degree of Sr segregation at the surface. By combining electron diffraction and first-principles computations, we propose that the long-range surface reconstruction consists of a Sr-segregated surface with La (6 × 6) ordering. This study expands our understanding of manganite systems and underscores their ability to form interesting surface reconstructions, driven largely by cation segregation that can potentially be controlled for tuning surface ordering.
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Affiliation(s)
- Kyle P Kelley
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Vinit Sharma
- National Institute for Computational Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- Joint Institute for Computational Sciences, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Wenrui Zhang
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Arthur P Baddorf
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Von B Nascimento
- Departamento de Física, Universidade Federal de Minas Gerais, Avenida Antônio Carlos, 6627, Belo Horizonte 31270-901, MG, Brazil
| | - Rama K Vasudevan
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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Belser A, Greulich K, Grüninger P, Bettinger HF, Peisert H, Chassé T. Visualization of the Borazine Core of B 3N 3-Doped Nanographene by STM. ACS Appl Mater Interfaces 2020; 12:19218-19225. [PMID: 32223213 DOI: 10.1021/acsami.0c02324] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Electronic interface properties and the initial growth of hexa-peri-hexabenzocoronene with a borazine core (BN-HBC) on Au(111) have been studied by using X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). A weak, but non-negligible, interaction between BN-HBC and Au(111) was found at the interface. Both hexa-peri-hexabenzocoronene (HBC) and BN-HBC molecules form well-defined monolayers. The different contrast in STM images of HBC and BN-HBC at different tunneling voltages with submolecular resolution can be ascribed to differences in the local density of states (LDOS). At positive and negative tunneling voltages, STM images reproduce the distribution of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) as determined by density functional theory (DFT) calculations very well.
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Affiliation(s)
- Axel Belser
- Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Katharina Greulich
- Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Peter Grüninger
- Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
- Institute of Organic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Holger F Bettinger
- Institute of Organic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
- Center for Light-Matter Interaction, Sensors & Analytics (LISA+) at the University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Heiko Peisert
- Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Thomas Chassé
- Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
- Center for Light-Matter Interaction, Sensors & Analytics (LISA+) at the University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
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Harbers R, Heepenstrick T, Perepichka DF, Sokolowski M. Pure and mixed ordered monolayers of tetracyano-2,6-naphthoquinodimethane and hexathiapentacene on the Ag(100) surface. Beilstein J Nanotechnol 2019; 10:1188-1199. [PMID: 31293856 PMCID: PMC6604726 DOI: 10.3762/bjnano.10.118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Accepted: 05/16/2019] [Indexed: 06/09/2023]
Abstract
We report on mixed ordered monolayers of the electron acceptor-type molecule tetracyano-2,6-naphthoquinodimethane (TNAP) and the electron donor-type molecule hexathiapentacene (HTPEN). This investigation was motivated by the general question which type of mixed stoichiometric structures are formed on a surface by molecules that are otherwise typically used for the synthesis of bulk charge-transfer materials. The layers were obtained by vacuum deposition on the Ag(100) surface and analyzed by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The formation of the mixed structure occurs spontaneously. An important motif for the structure formation is given by hydrogen bonds between the TNAP molecules. Both molecules, TNAP and HTPEN also form well-ordered monolayers on the Ag(100) surface on their own. In all structures, the molecules are adsorbed in a planar orientation on the surface. We discuss the influence of intermolecular charge transfer on the ordering in the mixed structure.
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Affiliation(s)
- Robert Harbers
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstraße 12, 53115 Bonn, Germany
| | - Timo Heepenstrick
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstraße 12, 53115 Bonn, Germany
| | - Dmitrii F Perepichka
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, H3A 0B8, Quebec, Canada
| | - Moritz Sokolowski
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstraße 12, 53115 Bonn, Germany
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Luches P, Valeri S. Structure, Morphology and Reducibility of Epitaxial Cerium Oxide Ultrathin Films and Nanostructures. Materials (Basel) 2015; 8:5818-5833. [PMID: 28793536 PMCID: PMC5512658 DOI: 10.3390/ma8095278] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [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: 07/30/2015] [Revised: 08/18/2015] [Accepted: 08/21/2015] [Indexed: 11/17/2022]
Abstract
Cerium oxide is a very interesting material that finds applications in many different fields, such as catalysis, energy conversion, and biomedicine. An interesting approach to unravel the complexity of real systems and obtain an improved understanding of cerium oxide-based materials is represented by the study of model systems in the form of epitaxial ultrathin films or nanostructures supported on single crystalline substrates. These materials often show interesting novel properties, induced by spatial confinement and by the interaction with the supporting substrate, and their understanding requires the use of advanced experimental techniques combined with computational modeling. Recent experimental and theoretical studies performed within this field are examined and discussed here, with emphasis on the new perspectives introduced in view of the optimization of cerium oxide-based materials for application in different fields.
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Affiliation(s)
- Paola Luches
- Istituto Nanoscienze, Consiglio Nazionale delle Ricerche, Via G. Campi 213/a, Modena 41125, Italy.
| | - Sergio Valeri
- Istituto Nanoscienze, Consiglio Nazionale delle Ricerche, Via G. Campi 213/a, Modena 41125, Italy.
- Dipartimento di Scienze Fisiche Informatiche e Matematiche, Università degli Studi di Modena e Reggio Emilia, Via G. Campi 213/a, Modena 41125, Italy.
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Li L, Lu SZ, Pan J, Qin Z, Wang YQ, Wang Y, Cao GY, Du S, Gao HJ. Buckled germanene formation on Pt(111). Adv Mater 2014; 26:4820-4824. [PMID: 24841358 DOI: 10.1002/adma.201400909] [Citation(s) in RCA: 266] [Impact Index Per Article: 26.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 04/14/2014] [Indexed: 06/03/2023]
Abstract
Germanene, a 2D honeycomb lattice analogous to graphene, is fabricated on a Pt(111) surface. It exhibits a buckled configuration with a (3 × 3) superlattice coinciding with the substrate's (√19 × √19) superstructure. Covalent bonds exist throughout the germanene layer. The resulting high-quality germanene enables researchers to explore the fundamentals of germanene and its potential applications.
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Affiliation(s)
- Linfei Li
- Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, PR China
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Hlawacek G, Khokhar FS, van Gastel R, Poelsema B, Teichert C. Smooth growth of organic semiconductor films on graphene for high-efficiency electronics. Nano Lett 2011; 11:333-7. [PMID: 21207968 PMCID: PMC3036005 DOI: 10.1021/nl103739n] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2010] [Indexed: 05/23/2023]
Abstract
High-quality thin films of conjugated molecules with smooth interfaces are important to assist the advent of organic electronics. Here, we report on the layer-by-layer growth of the organic semiconductor molecule p-sexiphenyl (6P) on the transparent electrode material graphene. Low energy electron microscopy and micro low energy electron diffraction reveal the morphological and structural evolution of the thin film. The layer-by-layer growth of 6P on graphene proceeds by subsequent adding of {111} layers.
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Affiliation(s)
- Gregor Hlawacek
- Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands.
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