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Jałochowski M, Zdyb R, Tringides MC. Correlations between In Situ Conductivity and Uniform-Height Epitaxial Morphology in Pb/Si(111)-(7×7). PHYSICAL REVIEW LETTERS 2016; 116:086101. [PMID: 26967427 DOI: 10.1103/physrevlett.116.086101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Indexed: 06/05/2023]
Abstract
The growth of Pb on Si(111)-(7×7) at temperatures from 72 to 201 K has been investigated using in situ electrical resistivity measurements and scanning tunneling microscopy. For temperatures T>140 K the specific resistivity ρ(θ) versus coverage θ shows an unusual "hump," instead of the expected monotonic decrease with θ. This novel result correlates well with the formation of uniform height eight-layer Pb islands and the superdiffusive motion of the wetting layer, despite the low temperatures. A model of the film resistivity as two resistors in series, the amorphous wetting layer and the crystalline islands, explains quantitatively the resistivity dependence on θ.
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Affiliation(s)
- M Jałochowski
- Institute of Physics, M. Curie-Skłodowska University, Place M. Curie-Skłodowskiej 1, PL-20031 Lublin, Poland
| | - R Zdyb
- Institute of Physics, M. Curie-Skłodowska University, Place M. Curie-Skłodowskiej 1, PL-20031 Lublin, Poland
| | - M C Tringides
- Department of Physics and Ames Laboratory-USDOE Iowa State University Ames, Ames, Iowa 50011, USA
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2
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Wu Q, Altman MS. Probing buried magnetic interface structure with the quantum size effect in spin-dependent electron reflectivity. Ultramicroscopy 2015; 159 Pt 3:530-5. [PMID: 25728296 DOI: 10.1016/j.ultramic.2015.02.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2014] [Accepted: 02/09/2015] [Indexed: 11/18/2022]
Abstract
The quantum size effect (QSE) in electron reflectivity from Fe thin films grown on a W(110) surface precovered with a two monolayer Cu film has been investigated using spin polarized low energy electron microscopy. Spin-dependent QSE-induced oscillations in the reflected intensity occur with energy and film thickness. The series of intensity peaks that is observed identifies spin-dependent quantum well resonances in the Fe film that are sensitive to electronic band structure and details of the buried interface. Information about the spin-dependent unoccupied bands of the Fe film in the ΓΝ direction normal to the film plane is obtained by analyzing the observed quantum well resonance conditions. The spin-split bands that are determined are uniformly shifted downward by 1.7 eV compared to bulk-like bands determined previously in Fe films on a bare W(110) substrate by the same method. Evidence is also obtained that the buried interface that defines the thin film quantum well boundary is located one layer above the W(110) surface. These results suggest that the Cu layer in direct contact with the substrate remains largely intact, but the weakly-bound second Cu layer mixes or segregates freely.
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Affiliation(s)
- Qiang Wu
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, PR China
| | - M S Altman
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, PR China
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3
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Wu Q, Altman MS. Spin polarized low energy electron microscopy of quantum well resonances in Fe films on the Cu-covered W(110) surface. Ultramicroscopy 2013; 130:109-14. [PMID: 23628648 DOI: 10.1016/j.ultramic.2013.03.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Revised: 03/13/2013] [Accepted: 03/13/2013] [Indexed: 11/29/2022]
Abstract
Spin polarized low energy electron microscopy has been used to investigate the quantum size effect (QSE) in electron reflectivity from Fe films grown on a pseudomorphic Cu layer on a W(110) surface. Intensity oscillations caused by the QSE as functions of Fe film thickness and incident electron energy identify quantum well resonance conditions in the film. Evaluation of these intensity oscillations using the phase accumulation model provides information on the unoccupied spin polarized band structure in the Fe film above the vacuum level. We also find evidence that the presence of the non-magnetic Cu layer shifts spin polarized quantum well resonances in the Fe layer uniformly downward in energy by 1.1eV compared to Fe/W(110) films without an interface Cu layer, suggesting that the Cu layer gives a small degree of control over the quantum well resonances.
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Affiliation(s)
- Qiang Wu
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, PR China
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4
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Locatelli A, Knox KR, Cvetko D, Menteş TO, Niño MA, Wang S, Yilmaz MB, Kim P, Osgood RM, Morgante A. Corrugation in exfoliated graphene: an electron microscopy and diffraction study. ACS NANO 2010; 4:4879-4889. [PMID: 20681631 DOI: 10.1021/nn101116n] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Low-energy electron microscopy and microprobe diffraction are used to image and characterize corrugation in SiO(2)-supported and suspended exfoliated graphene at nanometer length scales. Diffraction line-shape analysis reveals quantitative differences in surface roughness on length scales below 20 nm which depend on film thickness and interaction with the substrate. Corrugation decreases with increasing film thickness, reflecting the increased stiffness of multilayer films. Specifically, single-layer graphene shows a markedly larger short-range roughness than multilayer graphene. Due to the absence of interactions with the substrate, suspended graphene displays a smoother morphology and texture than supported graphene. A specific feature of suspended single-layer films is the dependence of corrugation on both adsorbate load and temperature, which is manifested by variations in the diffraction line shape. The effects of both intrinsic and extrinsic corrugation factors are discussed.
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Affiliation(s)
- Andrea Locatelli
- Elettra, Sincrotrone Trieste SCpA, 34149 Basovizza, Trieste, Italy.
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5
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Han Y, Ünal B, Jing D, Thiel PA, Evans JW, Liu DJ. Nanoscale "Quantum" Islands on Metal Substrates: Microscopy Studies and Electronic Structure Analyses. MATERIALS 2010; 3:3965-3993. [PMID: 28883318 PMCID: PMC5445798 DOI: 10.3390/ma3073965] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Revised: 06/22/2010] [Accepted: 07/06/2010] [Indexed: 11/16/2022]
Abstract
Confinement of electrons can occur in metal islands or in continuous films grown heteroepitaxially upon a substrate of a different metal or on a metallic alloy. Associated quantum size effects (QSE) can produce a significant height-dependence of the surface free energy for nanoscale thicknesses of up to 10–20 layers. This may suffice to induce height selection during film growth. Scanning STM analysis has revealed remarkable flat-topped or mesa-like island and film morphologies in various systems. We discuss in detail observations of QSE and associated film growth behavior for Pb/Cu(111), Ag/Fe(100), and Cu/fcc-Fe/Cu(100) [A/B or A/B/A], and for Ag/NiAl(110) with brief comments offered for Fe/Cu3Au(001) [A/BC binary alloys]. We also describe these issues for Ag/5-fold i-Al-Pd-Mn and Bi/5-fold i-Al-Cu-Fe [A/BCD ternary icosohedral quasicrystals]. Electronic structure theory analysis, either at the level of simple free electron gas models or more sophisticated Density Functional Theory calculations, can provide insight into the QSE-mediated thermodynamic driving force underlying height selection.
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Affiliation(s)
- Yong Han
- Institute of Physical Research & Technology, Iowa State University, Ames, IA 50011, USA.
| | - Bariş Ünal
- Ames Laboratory, Departments of Materials Science & Engineering and Chemistry, Iowa State University, Ames, IA 50011, USA.
| | - Dapeng Jing
- Ames Laboratory, Departments of Materials Science & Engineering and Chemistry, Iowa State University, Ames, IA 50011, USA.
| | - Patricia A Thiel
- Ames Laboratory, Departments of Materials Science & Engineering and Chemistry, Iowa State University, Ames, IA 50011, USA.
| | - James W Evans
- Ames Laboratory, Departments of Physics & Astronomy and Mathematics, Iowa State University, Ames, IA 50011, USA
| | - Da-Jiang Liu
- Ames Laboratory, Iowa State University, Ames, IA 50011, USA.
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6
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Altman MS. Trends in low energy electron microscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:084017. [PMID: 21389393 DOI: 10.1088/0953-8984/22/8/084017] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Low energy electron microscopy (LEEM) and spin polarized LEEM (SPLEEM) are two powerful in situ techniques for the study of surfaces, thin films and other surface-supported nanostructures. Their real-time imaging and complementary diffraction capabilities allow the study of structure, morphology, magnetism and dynamic processes with high spatial and temporal resolution. Progress in methods, instrumentation and understanding of novel contrast mechanisms that derive from the wave nature and spin degree of freedom of the electron continue to advance applications of LEEM and SPLEEM in these areas and beyond. We review here the basic imaging principles and recent developments that demonstrate the current capabilities of these techniques and suggest potential future directions.
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Affiliation(s)
- M S Altman
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
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7
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Kaganer VM, Jenichen B, Shayduk R, Braun W, Riechert H. Kinetic optimum of volmer-weber growth. PHYSICAL REVIEW LETTERS 2009; 102:016103. [PMID: 19257216 DOI: 10.1103/physrevlett.102.016103] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2008] [Revised: 11/27/2008] [Indexed: 05/27/2023]
Abstract
We find that the molecular beam epitaxy of Fe3Si on GaAs(001) observed by real-time x-ray diffraction begins by the abrupt formation of 3 monolayer (ML) high islands and approaches two-dimensional layer-by-layer growth at a thickness of 7 ML. A surface energy increase is confirmed by ab initio calculations and allows us to identify the growth as a strain-free Volmer-Weber transient. Kinetic Monte Carlo simulations incorporating this energy increase correctly reproduce the characteristic x-ray intensity oscillations found in the experiment. Simulations indicate an optimum growth rate for Volmer-Weber growth in between two limits, the appearance of trenches at slow growth and surface roughening at fast growth.
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Affiliation(s)
- Vladimir M Kaganer
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin, Germany
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8
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Man KL, Tringides MC, Loy MMT, Altman MS. Anomalous mass transport in the Pb wetting layer on the Si(111) surface. PHYSICAL REVIEW LETTERS 2008; 101:226102. [PMID: 19113491 DOI: 10.1103/physrevlett.101.226102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2008] [Indexed: 05/27/2023]
Abstract
The temporal evolution of nonequilibrium coverage profiles in the Pb wetting layer on the Si(111) surface is studied using low energy electron microscopy. The initial coverage step profile propagates rapidly at a constant velocity with an unperturbed shape. A model is proposed that attributes this nonclassical equilibration behavior to the diffusion of thermally generated adatoms on top of the wetting layer. This model can account for the observed convectionlike mass transport, as well as its dramatic dependence on Pb coverage. Such anomalous mass transport is believed to facilitate the remarkably efficient self-organization of uniform Pb quantum island height on the Si(111) surface that was observed previously.
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Affiliation(s)
- K L Man
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
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9
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Han Y, Unal B, Qin F, Jing D, Jenks CJ, Liu DJ, Thiel PA, Evans JW. Kinetics of facile bilayer island formation at low temperature: Ag/NiAl(110). PHYSICAL REVIEW LETTERS 2008; 100:116105. [PMID: 18517802 DOI: 10.1103/physrevlett.100.116105] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2007] [Indexed: 05/26/2023]
Abstract
Facile nucleation and growth of bilayer Ag(110) islands on NiAl(110) is observed by STM for Ag deposition at temperatures as low as 127 K. Density functional theory analysis for supported Ag films determines adatom adsorption energies (which favor bilayer islands), interaction energies, and diffusion barriers. Analysis of an atomistic lattice-gas model incorporating these energies elucidates the role of strongly anisotropic interactions in enabling the upward mass transport needed for bilayer island formation.
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Affiliation(s)
- Yong Han
- Institute of Physical Research and Technology, Iowa State University, Ames, IA 50011, USA
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10
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Wu YZ, Schmid AK, Qiu ZQ. Spin-dependent quantum interference from epitaxial MgO thin films on Fe(001). PHYSICAL REVIEW LETTERS 2006; 97:217205. [PMID: 17155772 DOI: 10.1103/physrevlett.97.217205] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2006] [Indexed: 05/12/2023]
Abstract
Spin-dependent electron reflection from MgO thin films grown on Fe(001) was measured using spin-polarized low energy electron microscopy. The electron reflectivity exhibits quantum interference from which two MgO energy bands with Delta1 symmetry were determined in experiment. We found that a bulklike MgO energy gap is fully established for MgO film thicker than 3 atomic monolayers and that the electron reflectivity from the MgO/Fe interface exhibits a spin-dependent amplitude and a spin-independent phase change.
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Affiliation(s)
- Y Z Wu
- Surface Physics Laboratory (National Key Laboratory), Fudan University, Shanghai 200433, China.
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11
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Morgenstern K, Laegsgaard E, Besenbacher F. Quantum size effects in adatom island decay. PHYSICAL REVIEW LETTERS 2005; 94:166104. [PMID: 15904250 DOI: 10.1103/physrevlett.94.166104] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2005] [Indexed: 05/02/2023]
Abstract
The decay of hexagonal Ag adatom islands on top of larger Ag adatom islands on a Ag(111) surface is followed by a fast-scanning tunneling microscope. Islands do not always show the expected increase in decay rate with decreasing island size. Rather, distinct quantum size effects are observed where the decay rate decreases significantly for islands with diameters of 6, 9.3, 12.6, and 15.6 nm. We show that electron confinement of the surface state electrons is responsible for this enhancement of the detachment barrier for adatoms from the island edge.
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Affiliation(s)
- Karina Morgenstern
- Institut für Festkörperphysik, Universität Hannover, Appelstrasse 2, D-30167 Hannover, Germany
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