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Barton AT, Walsh LA, Smyth CM, Qin X, Addou R, Cormier C, Hurley PK, Wallace RM, Hinkle CL. Impact of Etch Processes on the Chemistry and Surface States of the Topological Insulator Bi 2Se 3. ACS APPLIED MATERIALS & INTERFACES 2019; 11:32144-32150. [PMID: 31416305 DOI: 10.1021/acsami.9b10625] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The unique properties of topological insulators such as Bi2Se3 are intriguing for their potential implementation in novel device architectures for low power and defect-tolerant logic and memory devices. Recent improvements in the synthesis of Bi2Se3 have positioned researchers to fabricate new devices to probe the limits of these materials. The fabrication of such devices, of course, requires etching of the topological insulator, in addition to other materials including gate oxides and contacts which may impact the topologically protected surface states. In this paper, we study the impact of He+ sputtering and inductively coupled plasma Cl2 and SF6 reactive etch chemistries on the physical, chemical, and electronic properties of Bi2Se3. Chemical analysis by X-ray photoelectron spectroscopy tracks changes in the surface chemistry and Fermi level, showing preferential removal of Se that results in vacancy-induced n-type doping. Chlorine-based chemistry successfully etches Bi2Se3 but with residual Se-Se bonding and interstitial Cl species remaining after the etch. The Se vacancies and residuals can be removed with postetch anneals in a Se environment, repairing Bi2Se3 nearly to the as-grown condition. Critically, in each of these cases, angle-resolved photoemission spectroscopy (ARPES) reveals that the topologically protected surface states remain even after inducing significant surface disorder and chemical changes, demonstrating that topological insulators are quite promising for defect-tolerant electronics. Changes to the ARPES intensity and momentum broadening of the surface states are discussed. Fluorine-based etching aggressively reacts with the film resulting in a relatively thick insulating film of thermodynamically favored BiF3 on the surface, prohibiting the use of SF6-based etching in Bi2Se3 processing.
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Affiliation(s)
- Adam T Barton
- Department of Materials Science and Engineering , University of Texas at Dallas , Richardson , Texas 75080 , United States
| | - Lee A Walsh
- Department of Materials Science and Engineering , University of Texas at Dallas , Richardson , Texas 75080 , United States
- Tyndall National Institute , University College Cork , Lee Maltings Complex , Cork T12R5CP , Ireland
| | - Christopher M Smyth
- Department of Materials Science and Engineering , University of Texas at Dallas , Richardson , Texas 75080 , United States
| | - Xiaoye Qin
- Department of Materials Science and Engineering , University of Texas at Dallas , Richardson , Texas 75080 , United States
| | - Rafik Addou
- Department of Materials Science and Engineering , University of Texas at Dallas , Richardson , Texas 75080 , United States
| | - Christopher Cormier
- Department of Materials Science and Engineering , University of Texas at Dallas , Richardson , Texas 75080 , United States
| | - Paul K Hurley
- Tyndall National Institute , University College Cork , Lee Maltings Complex , Cork T12R5CP , Ireland
| | - Robert M Wallace
- Department of Materials Science and Engineering , University of Texas at Dallas , Richardson , Texas 75080 , United States
| | - Christopher L Hinkle
- Department of Materials Science and Engineering , University of Texas at Dallas , Richardson , Texas 75080 , United States
- Department of Electrical Engineering , University of Notre Dame , Notre Dame , Indiana 46556 , United States
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Liu TH, Zhou J, Li M, Ding Z, Song Q, Liao B, Fu L, Chen G. Electron mean-free-path filtering in Dirac material for improved thermoelectric performance. Proc Natl Acad Sci U S A 2018; 115:879-884. [PMID: 29339475 PMCID: PMC5798353 DOI: 10.1073/pnas.1715477115] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recent advancements in thermoelectric materials have largely benefited from various approaches, including band engineering and defect optimization, among which the nanostructuring technique presents a promising way to improve the thermoelectric figure of merit (zT) by means of reducing the characteristic length of the nanostructure, which relies on the belief that phonons' mean free paths (MFPs) are typically much longer than electrons'. Pushing the nanostructure sizes down to the length scale dictated by electron MFPs, however, has hitherto been overlooked as it inevitably sacrifices electrical conduction. Here we report through ab initio simulations that Dirac material can overcome this limitation. The monotonically decreasing trend of the electron MFP allows filtering of long-MFP electrons that are detrimental to the Seebeck coefficient, leading to a dramatically enhanced power factor. Using SnTe as a material platform, we uncover this MFP filtering effect as arising from its unique nonparabolic Dirac band dispersion. Room-temperature zT can be enhanced by nearly a factor of 3 if one designs nanostructures with grain sizes of ∼10 nm. Our work broadens the scope of the nanostructuring approach for improving the thermoelectric performance, especially for materials with topologically nontrivial electronic dynamics.
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Affiliation(s)
- Te-Huan Liu
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Jiawei Zhou
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Mingda Li
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
- Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Zhiwei Ding
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Qichen Song
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Bolin Liao
- Department of Mechanical Engineering, University of California, Santa Barbara, CA 93106
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Gang Chen
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139;
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Wismer MS, Kruchinin SY, Ciappina M, Stockman MI, Yakovlev VS. Strong-Field Resonant Dynamics in Semiconductors. PHYSICAL REVIEW LETTERS 2016; 116:197401. [PMID: 27232043 DOI: 10.1103/physrevlett.116.197401] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2015] [Indexed: 06/05/2023]
Abstract
We predict that a direct band gap semiconductor (GaAs) resonantly excited by a strong ultrashort laser pulse exhibits a novel regime: kicked anharmonic Rabi oscillations. In this regime, Rabi oscillations are strongly coupled to intraband motion, and interband transitions mainly take place when electrons pass near the Brillouin zone center where electron populations undergo very rapid changes. The asymmetry of the residual population distribution induces an electric current controlled by the carrier-envelope phase of the driving pulse. The predicted effects are experimentally observable using photoemission and terahertz spectroscopies.
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Affiliation(s)
- Michael S Wismer
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
| | | | - Marcelo Ciappina
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
| | - Mark I Stockman
- Center for Nano-Optics (CeNO) and Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30340, USA
| | - Vladislav S Yakovlev
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
- Center for Nano-Optics (CeNO) and Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30340, USA
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d-Wave Superconductivity and s-Wave Charge Density Waves: Coexistence between Order Parameters of Different Origin and Symmetry. Symmetry (Basel) 2011. [DOI: 10.3390/sym3040699] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
A review of the theory describing the coexistence between d-wave superconductivity and s-wave charge-density-waves (CDWs) is presented. The CDW gapping is identified with pseudogapping observed in high-Tc oxides. According to the cuprate specificity, the analysis is carried out for the two-dimensional geometry of the Fermi surface (FS). Phase diagrams on the σ0 − α plane—here, σ0 is the ratio between the energy gaps in the parent pure CDW and superconducting states, and the quantity 2α is connected with the degree of dielectric (CDW) FS gapping—were obtained for various possible configurations of the order parameters in the momentum space. Relevant tunnel and photoemission experimental data for high-Tc oxides are compared with theoretical predictions. A brief review of the results obtained earlier for the coexistence between s-wave superconductivity and CDWs is also given.
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