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Giacomo JA, Mullet CH, Chiang S. Growth, phase transition, and island motion of Au on Ge(111). J Chem Phys 2021; 155:054701. [PMID: 34364342 DOI: 10.1063/5.0048882] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Using low energy electron microscopy, Au on Ge(111) is determined to follow a Stranski-Krastanov growth mode consisting of a single layer up to one monolayer (ML), followed by three-dimensional Au-Ge alloy droplets. Near 600 °C, we report the first observation of a reversible first-order phase transition that occurs from the (3 × 3)R30° phase to a (1 × 1) phase, which has a coverage of 0.367 ML. The transition gradually occurs through a coexistence region with a temperature range of about 2 °C and weakly depends on coverage, varying from 640 °C at 1 ML down to 580 °C at 0.8 ML. The phase transition is accompanied by phase fluctuations of small domains or the fluctuations of phase boundaries of large domains. At coverage >1 ML and above 250 °C, the 3D droplets move with stick-slip hopping behavior that has previously been explained by dissolution of Ge at step edges into the alloy droplet, which then comes to concentration and thermal equilibrium via the island motion.
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Affiliation(s)
- J A Giacomo
- Department of Physics, University of California, Davis, 1 Shields Avenue, Davis, California 95616-5270, USA
| | - C H Mullet
- Department of Physics, University of California, Davis, 1 Shields Avenue, Davis, California 95616-5270, USA
| | - S Chiang
- Department of Physics, University of California, Davis, 1 Shields Avenue, Davis, California 95616-5270, USA
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Zarshenas M, Gervilla V, Sangiovanni DG, Sarakinos K. Room-temperature diffusion of metal clusters on graphene. Phys Chem Chem Phys 2021; 23:13087-13094. [PMID: 34059869 DOI: 10.1039/d1cp00522g] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We study the diffusion dynamics, the diffusion mechanisms, and the adsorption energetics of Ag, Au, Cu, and Pd dimers, as well as of Ag trimers on single-layer graphene (SLG) by means of ab initio molecular dynamics (AIMD) simulations and density-functional theory (DFT) calculations. The simulations show that Ag, Cu, and Au clusters exhibit a super-diffusive pattern characterized by long jumps, which can be explained by the flat potential energy landscape (PEL) (corrugation of a few tens of meV) encountered by those clusters on SLG. Pd dimers, instead, diffuse in a pattern that is reminiscent of conventional random walk, which is consistent with a significantly rougher PEL of the order of 100 meV. Moreover, our data show that all clusters exhibit diffusion mechanisms that include both concerted translation and rotation. The overall results of the present study provide key insights for modeling the growth of metal layers and nanostructures on graphene and other van der Waals materials, which is a prerequisite for the directed growth of multifunctional metal contacts in a broad range of enabling devices.
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Affiliation(s)
- Mohammad Zarshenas
- Nanoscale Engineering Division, Department of Physics, Chemistry and Biology, Linköping University, SE-58183, Linköping, Sweden.
| | - Victor Gervilla
- Nanoscale Engineering Division, Department of Physics, Chemistry and Biology, Linköping University, SE-58183, Linköping, Sweden.
| | - Davide G Sangiovanni
- Theoretical Physics Division, Department of Physics, Chemistry and Biology, Linköping University, SE-58183, Linköping, Sweden
| | - Kostas Sarakinos
- Nanoscale Engineering Division, Department of Physics, Chemistry and Biology, Linköping University, SE-58183, Linköping, Sweden.
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Hershberger MT, Hupalo M, Thiel PA, Wang CZ, Ho KM, Tringides MC. Nonclassical "explosive" nucleation in Pb/Si(111) at low temperatures. PHYSICAL REVIEW LETTERS 2014; 113:236101. [PMID: 25526139 DOI: 10.1103/physrevlett.113.236101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Indexed: 06/04/2023]
Abstract
Classically, the onset of nucleation is defined in terms of a critical cluster of the condensed phase, which forms from the gradual aggregation of randomly diffusing adatoms. Experiments in Pb/Si(111) at low temperature have discovered a dramatically different type of nucleation, with perfect crystalline islands emerging "explosively" out of the compressed wetting layer after a critical coverage Θ_{c}=1.22 ML is reached. The unexpectedly high island growth rates, the directional correlations in the growth of neighboring islands and the persistence in time of where mass is added in individual islands, suggest that nucleation is a result of the highly coherent motion of the wetting layer, over mesoscopic distances.
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Affiliation(s)
- M T Hershberger
- Ames Laboratory-U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - M Hupalo
- Ames Laboratory-U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA
| | - P A Thiel
- Ames Laboratory-U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA and Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA and Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA
| | - C Z Wang
- Ames Laboratory-U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA
| | - K M Ho
- Ames Laboratory-U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - M C Tringides
- Ames Laboratory-U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
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Matetskiy AV, Bondarenko LV, Gruznev DV, Zotov AV, Saranin AA, Tringides MC. Structural transformations in Pb/Si(111) phases induced by C₆₀ adsorption. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:395006. [PMID: 24013200 DOI: 10.1088/0953-8984/25/39/395006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Structural transformations at the Pb/Si(111) surface occurring upon C₆₀ adsorption onto Pb/Si(111)1 × 1 phase at room temperature and Pb/Si(111)[Formula: see text] at low temperatures between 30 and 210 K, have been studied using scanning tunneling microscopy and low-energy electron diffraction observations. Typically, C₆₀ fullerenes agglomerate into random molecular islands nucleated at the surface defects. C₆₀ island formation is accompanied by expelling Pb atoms to the surrounding surface area where more dense Pb/Si(111) phases form. Productivity of C₆₀-induced expelling of Pb atoms is controlled by surface defects and is suppressed dramatically when regular ('crystalline') C₆₀ islands self-assemble at the defect-free Pb/Si(111) surface. When Pb atoms are ejected by the random C₆₀ islands, extended structural transformations involving reordering of numerous Pb atoms are fully completed at the surface within the shortest possible time (a few dozen seconds) to reapproach and image the surface after C₆₀ deposition. Estimations show that the observed transformations cannot be controlled by random walk diffusion of Pb adatoms, which implies a highly correlated motion of the Pb atom displacements within the layer.
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Affiliation(s)
- A V Matetskiy
- Institute of Automation and Control Processes FEB RAS, 690041 Vladivostok, Russia. School of Natural Sciences, Far Eastern Federal University, 690950 Vladivostok, Russia
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Ohtsubo Y, Muto H, Yaji K, Hatta S, Okuyama H, Aruga T. Structure determination of Pb/Ge(111)-β-(√3 × √3)R30° by dynamical low-energy electron diffraction analysis and first-principles calculation. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:435001. [PMID: 21926457 DOI: 10.1088/0953-8984/23/43/435001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We have determined the atomic structure of the Pb/Ge(111)-β-(√3 × √3)R30° surface, which was shown to exhibit a large Rashba spin splitting in a metallic surface state by dynamical low-energy electron diffraction analysis. The Pb coverage for the optimized atomic structure is 4/3 with one Pb atom located at every third H(3) site of the bulk-truncated Ge(111) surface and the other three near the T(1) sites but slightly displaced towards the T(4) sites. The determined atomic structure agrees well with the energetically optimized one obtained from the first-principles calculation. The calculation also revealed that the potential for the Pb atoms on the H(3) sites is very soft along the surface normal, suggesting that their vertical position is distributed within a range of about 0.2-0.3 Å. The previously proposed phase transition associated with the surface melting is discussed.
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Affiliation(s)
- Yoshiyuki Ohtsubo
- Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto, Japan
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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: 16] [Impact Index Per Article: 1.1] [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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