| 1. |
- Kawasaki, Jason K., et al.
(author)
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A simple electron counting model for half-Heusler surfaces
- 2018
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In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 4
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Journal article (peer-reviewed)abstract
- Heusler compounds are a ripe platform for discovery and manipulation of emergent properties in topological and magnetic heterostructures. In these applications, the surfaces and interfaces are critical to performance; however, little is known about the atomic-scale structure of Heusler surfaces and interfaces or why they reconstruct. Using a combination of molecular beam epitaxy, core-level and angle-resolved photoemission, scanning tunneling microscopy, and density functional theory, we map the phase diagram and determine the atomic and electronic structures for several surface reconstructions of CoTiSb (001), a prototypical semiconducting half-Heusler. At low Sb coverage, the surface is characterized by Sb-Sb dimers and Ti vacancies, while, at high Sb coverage, an adlayer of Sb forms. The driving forces for reconstruction are charge neutrality and minimizing the number of Sb dangling bonds, which form metallic surface states within the bulk bandgap. We develop a simple electron counting model that explains the atomic and electronic structure, as benchmarked against experiments and first-principles calculations. We then apply the model to explain previous experimental observations at otherhalf-Heusler surfaces, including the topological semimetal PtLuSb and the half-metallic ferromagnet NiMnSb. The model provides a simple framework for understanding and predicting the surface structure and propertiesof these novel quantum materials.
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| 2. |
- Kawasaki, Jason K., et al.
(author)
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Cross-sectional scanning tunneling microscopy and spectroscopy of semimetallic ErAs nanostructures embedded in GaAs
- 2011
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In: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1520-8567 .- 1071-1023. ; 29:3, s. 03-104
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Conference paper (peer-reviewed)abstract
- The growth and atomic/electronic structure of molecular beam epitaxy-grown ErAs nanoparticles and nanorods embedded within a GaAs matrix are examined for the first time via cross-sectional scanning tunneling microscopy and spectroscopy. Cross sections enable the interrogation of the internal structure and are well suited for studying embedded nanostructures. The early stages of embedded ErAs nanostructure growth are examined via these techniques and compared with previous cross-sectional transmission electron microscopy work. Tunneling spectroscopy I(V) for both ErAs nanoparticles and nanorods was also performed, demonstrating that both nanostructures are semimetallic. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3547713]
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| 3. |
- Kawasaki, Jason K., et al.
(author)
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Epitaxial growth and surface studies of the Half Heusler compound NiTiSn (001)
- 2013
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In: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 31:4
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Journal article (peer-reviewed)abstract
- The Half Heuslers are currently an attractive family of compounds for high temperature thermoelectrics research, and recently, there has been renewed interest since some of these compounds are proposed to be topological insulators. NiTiSn belongs to the family of 18 valence electron Half Heuslers that are predicted to be semiconducting, despite being composed entirely of metallic elements. The growth of the Half Heusler compound NiTiSn by molecular beam epitaxy is demonstrated. The NiTiSn films are epitaxial and single crystalline as observed by reflection high-energy electron diffraction and x-ray diffraction. Temperature dependent transport measurements suggest the films may be semiconducting, but with a high background carrier density indicative of a high density of electrically active defect states. Methods of protecting the sample surface for synchrotron-based photoemission measurements are explored. These methods may be applied to the study of surface electronic structure in unconventional materials. (C) 2013 American Vacuum Society.
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| 4. |
- Patel, Sahil J., et al.
(author)
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Surface and electronic structure of epitaxial PtLuSb (001) thin films
- 2014
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:20
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Journal article (peer-reviewed)abstract
- The surface and electronic structure of single crystal thin films of PtLuSb (001) grown by molecular beam epitaxy were studied. Scanning tunneling spectroscopy (STS), photoemission spectroscopy, and temperature dependent Hall measurements of PtLuSb thin films are consistent with a zero-gap semiconductor or semi-metal. STS and photoemission measurements show a decrease in density of states approaching the Fermi level for both valence and conduction bands as well as a slight shift of the Fermi level position into the valence band. Temperature dependent Hall measurements also corroborate the Fermi level position by measurement of p-type carriers. (C) 2014 AIP Publishing LLC.
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