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Title: Optical measure of disorder: Why Urbach analysis works for amorphous silicon but fails for amorphous carbon

Abstract

We investigate the basis for the Paradox where the Urbach-slope disorder parameter disagrees with the Raman width in amorphous diamond-like carbon (DLC) materials (lower Urbach-Eo yet greater Raman width). We examined the bandgap and Urbach-slope measurement issues. While significant errors are identified, ultimately these cannot resolve the Paradox. This resolution involves large changes in shape of DLC's absorption band resulting from large energy shifts. To solidify the understanding of band energy shifts, we examined their properties using a-Si:H, well known for its agreement between Raman and Urbach-slope disorder parameters. Using Tauc-Lorentz (T-L) dispersion functions, the Urbach method works for a-Si:H because small changes in shape occur, as measured by (i) peak position, (ii) peak width, (iii) peak amplitude, and (iv) and gap energies. Moreover, for a-Si:H, a 5th condition (v) there is no other feature below the principal band to interfere with its fall. All 5 of these conditions fail for DLCs. Because T-L dispersions accommodate asymmetry, we traced the Paradox to a steepening of the band shape as it pushes toward lower energy. This steepening is unrelated to disorder, but to a boundary value problem where energy cannot be negative. We conclude that Urbach analysis is invalid for DLCmore » materials, but the T-L width is a good measure instead. We also examined another disorder measure, where π bonds should be considered as disorder relative to the σ bonds in an idealized “amorphous diamond” sp3 network: superconvergence can be used to quantify these π transitions. Finally, further molecular orbital calculations are needed to properly interpret the changes in T-L widths.« less

Authors:
 [1];  [2];  [1]
+ Show Author Affiliations
  1. The Mackinac Technology Co. (United States)
  2. Fraunhover (United States)
Publication Date:
Research Org.:
Mackinac Technology Company, Kentwood, MI (United States)
Sponsoring Org.:
USDOE Advanced Research Projects Agency - Energy (ARPA-E)
OSTI Identifier:
1848235
Alternate Identifier(s):
OSTI ID: 1778283
Grant/Contract Number:  
AR0000682
Resource Type:
Accepted Manuscript
Journal Name:
Diamond and Related Materials
Additional Journal Information:
Journal Volume: 110; Journal Issue: C; Journal ID: ISSN 0925-9635
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Materials Science; Physics; Urbach; Tauc; Disorder; Amorphous; Silicon, a-Si:H; Carbon; DLC; Raman

Citation Formats

Tsu, David V., Schuelke, Thomas, and Slagter, John. Optical measure of disorder: Why Urbach analysis works for amorphous silicon but fails for amorphous carbon. United States: N. p., 2020. Web. doi:10.1016/j.diamond.2020.108137.
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Tsu, David V., Schuelke, Thomas, & Slagter, John. Optical measure of disorder: Why Urbach analysis works for amorphous silicon but fails for amorphous carbon. United States. https://doi.org/10.1016/j.diamond.2020.108137
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Tsu, David V., Schuelke, Thomas, and Slagter, John. Thu . "Optical measure of disorder: Why Urbach analysis works for amorphous silicon but fails for amorphous carbon". United States. https://doi.org/10.1016/j.diamond.2020.108137. https://www.osti.gov/servlets/purl/1848235.
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@article{osti_1848235,
title = {Optical measure of disorder: Why Urbach analysis works for amorphous silicon but fails for amorphous carbon},
author = {Tsu, David V. and Schuelke, Thomas and Slagter, John},
abstractNote = {We investigate the basis for the Paradox where the Urbach-slope disorder parameter disagrees with the Raman width in amorphous diamond-like carbon (DLC) materials (lower Urbach-Eo yet greater Raman width). We examined the bandgap and Urbach-slope measurement issues. While significant errors are identified, ultimately these cannot resolve the Paradox. This resolution involves large changes in shape of DLC's absorption band resulting from large energy shifts. To solidify the understanding of band energy shifts, we examined their properties using a-Si:H, well known for its agreement between Raman and Urbach-slope disorder parameters. Using Tauc-Lorentz (T-L) dispersion functions, the Urbach method works for a-Si:H because small changes in shape occur, as measured by (i) peak position, (ii) peak width, (iii) peak amplitude, and (iv) and gap energies. Moreover, for a-Si:H, a 5th condition (v) there is no other feature below the principal band to interfere with its fall. All 5 of these conditions fail for DLCs. Because T-L dispersions accommodate asymmetry, we traced the Paradox to a steepening of the band shape as it pushes toward lower energy. This steepening is unrelated to disorder, but to a boundary value problem where energy cannot be negative. We conclude that Urbach analysis is invalid for DLC materials, but the T-L width is a good measure instead. We also examined another disorder measure, where π bonds should be considered as disorder relative to the σ bonds in an idealized “amorphous diamond” sp3 network: superconvergence can be used to quantify these π transitions. Finally, further molecular orbital calculations are needed to properly interpret the changes in T-L widths.},
doi = {10.1016/j.diamond.2020.108137},
journal = {Diamond and Related Materials},
number = C,
volume = 110,
place = {United States},
year = {Thu Oct 15 00:00:00 EDT 2020},
month = {Thu Oct 15 00:00:00 EDT 2020}
}
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Works referenced in this record:

Structural information from the Raman spectrum of amorphous silicon
journal, July 1985

Spectroscopic ellipsometry of thin film and bulk anatase (TiO2)
journal, June 2003

  • Jellison, G. E.; Boatner, L. A.; Budai, J. D.
  • Journal of Applied Physics, Vol. 93, Issue 12
  • DOI: 10.1063/1.1573737

Deposition of silicon oxynitride thin films by remote plasma enhanced chemical vapor deposition
journal, July 1987

  • Tsu, D. V.; Lucovsky, G.; Mantini, M. J.
  • Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, Vol. 5, Issue 4
  • DOI: 10.1116/1.574902

Determination of energy barrier for structural relaxation in a-Si and a-Ge by Raman scattering
journal, July 1984

  • Tsu, R.; Hernandez, J. G.; Pollak, F. H.
  • Journal of Non-Crystalline Solids, Vol. 66, Issue 1-2, p. 109-114
  • DOI: 10.1016/0022-3093(84)90307-7

Mechanism of Properties of Noble ZnS–SiO 2 Protection Layer for Phase Change Optical Disk Media
journal, August 2006

  • Tsu, David V.; Ohta, Takeo
  • Japanese Journal of Applied Physics, Vol. 45, Issue 8A
  • DOI: 10.1143/JJAP.45.6294

Ion and neutral argon temperatures in electron cyclotron resonance plasmas by Doppler broadened emission spectroscopy
journal, May 1995

  • Tsu, David V.; Young, R. T.; Ovshinsky, S. R.
  • Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, Vol. 13, Issue 3
  • DOI: 10.1116/1.579654

Superconvergence and Sum Rules for the Optical Constants
journal, December 1972

  • Altarelli, M.; Dexter, D. L.; Nussenzveig, H. M.
  • Physical Review B, Vol. 6, Issue 12
  • DOI: 10.1103/PhysRevB.6.4502

Optical constants of a hydrogenated amorphous carbon film
journal, February 1984

  • Smith, F. W.
  • Journal of Applied Physics, Vol. 55, Issue 3
  • DOI: 10.1063/1.333135

The absorption edge of amorphous As2S3
journal, January 1970

  • Kosek, F.; Tauc, J.
  • Czechoslovak Journal of Physics, Vol. 20, Issue 1
  • DOI: 10.1007/BF01698111

Reversible Electrical Switching Phenomena in Disordered Structures
journal, November 1968

Diamond-like amorphous carbon
journal, May 2002

Effects of the nearest neighbors and the alloy matrix on SiH stretching vibrations in the amorphous SiO r :H (0< r <2) alloy system
journal, July 1989

Obtaining optical constants of thin GexSbyTez films from measurements of reflection and transmission
journal, July 1999

  • Tsu, David V.
  • Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, Vol. 17, Issue 4
  • DOI: 10.1116/1.581904

Spectroscopic ellipsometry and Raman study of fluorinated nanocrystalline carbon thin films
journal, July 2001

  • Lee, Hosun; Kim, In-Young; Han, S. -S.
  • Journal of Applied Physics, Vol. 90, Issue 2
  • DOI: 10.1063/1.1378337
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