skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Studies of Local and Intermediate Range Structure in Crystalline and Amorphous Materials at High Pressure Using High-Energy X-rays

Abstract

The method of high-energy total elastic X-ray scattering to determine the atomic structure of nanocrystalline, highly disordered, and amorphous materials is presented. The current state of the technique, its potential, and limitations are discussed with two successful studies on the pressure induced phase transition in mackinawite (FeS) and the high-pressure behavior of liquid gallium.

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930509
Report Number(s):
BNL-80469-2008-JA
Journal ID: ISSN 0885-7156; PODIE2; TRN: US200904%%759
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Powder Diffraction; Journal Volume: 22; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AMORPHOUS STATE; CRYSTAL STRUCTURE; GALLIUM; IRON SULFIDES; LIQUIDS; MATERIALS; PRESSURE RANGE MEGA PA 10-100; SCATTERING; X RADIATION; national synchrotron light source

Citation Formats

Ehm,L., Antao, S., Chen, J., Locke, D., Michel, F., Martin, D., Yu, T., Parise, J., Lee, P., and et al. Studies of Local and Intermediate Range Structure in Crystalline and Amorphous Materials at High Pressure Using High-Energy X-rays. United States: N. p., 2007. Web. doi:10.1154/1.2737456.
Ehm,L., Antao, S., Chen, J., Locke, D., Michel, F., Martin, D., Yu, T., Parise, J., Lee, P., & et al. Studies of Local and Intermediate Range Structure in Crystalline and Amorphous Materials at High Pressure Using High-Energy X-rays. United States. doi:10.1154/1.2737456.
Ehm,L., Antao, S., Chen, J., Locke, D., Michel, F., Martin, D., Yu, T., Parise, J., Lee, P., and et al. Mon . "Studies of Local and Intermediate Range Structure in Crystalline and Amorphous Materials at High Pressure Using High-Energy X-rays". United States. doi:10.1154/1.2737456.
@article{osti_930509,
title = {Studies of Local and Intermediate Range Structure in Crystalline and Amorphous Materials at High Pressure Using High-Energy X-rays},
author = {Ehm,L. and Antao, S. and Chen, J. and Locke, D. and Michel, F. and Martin, D. and Yu, T. and Parise, J. and Lee, P. and et al.},
abstractNote = {The method of high-energy total elastic X-ray scattering to determine the atomic structure of nanocrystalline, highly disordered, and amorphous materials is presented. The current state of the technique, its potential, and limitations are discussed with two successful studies on the pressure induced phase transition in mackinawite (FeS) and the high-pressure behavior of liquid gallium.},
doi = {10.1154/1.2737456},
journal = {Powder Diffraction},
number = 2,
volume = 22,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The method of high-energy total elastic X-ray scattering to determine the atomic structure of nanocrystalline, highly disordered, and amorphous materials is presented. The current state of the technique, its potential, and limitations are discussed with two successful studies on the pressure induced phase transition in mackinawite (FeS) and the high-pressure behavior of liquid gallium.
  • Extended x-ray-absorption (EXAFS) and electron-energy-loss fine-structure (EXELFS) measurements have been performed on amorphous unhydrogenated silicon carbide, a-SiC, and amorphous hydrogenated silicon carbide, a-SiC:H. Two hydrogenated samples with hydrogen concentrations corresponding, respectively, to H flows of 4 sccm (20% of argon flow) and 8 sccm (40% of argon flow) during the reactive sputtering process, were analyzed (sccm denotes standard cubic centimeters per minute at STP). It is found that short-range order (SRO), consisting of the same tetrahedrally coordinated units present in cubic crystalline c-SiC (zinc-blende structure), where a Si atom is surrounded by nearly four C atoms and vice versa, doesmore » exist in all the amorphous samples. This SRO, however, is detected only at a level of the first C and Si coordination shells in a-SiC and a-SiC:H. The structural disorder of the first Si and C coordination shells in all forms of amorphous SiC is somewhat greater than c-SiC, and it decreases appreciably as hydrogen is added. The a-SiC sample exhibits large Si and C coordination numbers, almost identical to c-SiC, a low atomic density, and virtually the same Si-C bond length as c-SiC. These results indicate that a relatively small concentration of large voids exist in a highly disordered a-SiC matrix.« less
  • Typically only dilute (up to {approx}10%) highly mismatched alloys can be grown due to the large differences in atomic size and electronegativity of the host and the alloying elements. We have overcome the miscibility gap of the GaN{sub 1-x}As{sub x} system using low temperature molecular beam epitaxy. In the intermediate composition range (0.10 < x < 0.75), the resulting alloys are amorphous. To gain a better understanding of the amorphous structure, the local environment of the As and Ga atoms was investigated using extended x-ray absorption fine structure (EXAFS). The EXAFS analysis shows a high concentration of dangling bonds comparedmore » to the crystalline binary endpoint compounds of the alloy system. The disorder parameter was larger for amorphous films compared to crystalline references, but comparable with other amorphous semiconductors. By examining the Ga local environment, the dangling bond density and disorder associated with As-related and N-related bonds could be decoupled. The N-related bonds had a lower dangling bond density and lower disorder.« less
  • We describe an approach for acquiring high quality x-ray absorption fine structure (XAFS) spectroscopy spectra with wide energy range at high pressure using diamond anvil cell (DAC). Overcoming the serious interference of diamond Bragg peaks is essential for combining XAFS and DAC techniques in high pressure research, yet an effective method to obtain accurate XAFS spectrum free from DAC induced glitches has been lacking. It was found that these glitches, whose energy positions are very sensitive to the relative orientation between DAC and incident x-ray beam, can be effectively eliminated using an iterative algorithm based on repeated measurements over amore » small angular range of DAC orientation, e.g., within {+-}3{sup o} relative to the x-ray beam direction. Demonstration XAFS spectra are reported for rutile-type GeO{sub 2} recorded by traditional ambient pressure and high pressure DAC methods, showing similar quality at 440 eV above the absorption edge. Accurate XAFS spectra of GeO{sub 2} glass were obtained at high pressure up to 53 GPa, providing important insight into the structural polymorphism of GeO{sub 2} glass at high pressure. This method is expected be applicable for in situ XAFS measurements using a diamond anvil cell up to ultrahigh pressures.« less