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Title: Band gap opening in strongly compressed diamond observed by x-ray energy loss spectroscopy

The extraordinary mechanical and optical properties of diamond are the basis of numerous technical applications and make diamond anvil cells a premier device to explore the high-pressure behavior of materials. However, at applied pressures above a few hundred GPa, optical probing through the anvils becomes difficult because of the pressure-induced changes of the transmission and the excitation of a strong optical emission. Such features have been interpreted as the onset of a closure of the optical gap in diamond, and can significantly impair spectroscopy of the material inside the cell. In contrast, a comparable widening has been predicted for purely hydrostatic compressions, forming a basis for the presumed pressure stiffening of diamond and resilience to the eventual phase change to BC8. We here present the first experimental evidence of this effect at geo-planetary pressures, exceeding the highest ever reported hydrostatic compression of diamond by more than 200 GPa and any other measurement of the band gap by more than 350 GPa. We here apply laser driven-ablation to create a dynamic, high pressure state in a thin, synthetic diamond foil together with frequency-resolved x-ray scattering as a probe. The frequency shift of the inelastically scattered x-rays encodes the optical properties and,more » thus, the behavior of the band gap in the sample. Using the ultra-bright x-ray beam from the Linac Coherent Light Source (LCLS), we observe an increasing direct band gap in diamond up to a pressure of 370 GPa. This finding points to the enormous strains in the anvils and the impurities in natural Type Ia diamonds as the source of the observed closure of the optical window. Our results demonstrate that diamond remains an insulating solid to pressures approaching its limit strength.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [1] ;  [4] ;  [5] ;  [1] ;  [1] ;  [1]
  1. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States); Univ. of Michigan, Ann Arbor, MI (United States)
  3. High-Energy Density Science Group, Hamburg (Germany)
  4. Univ. of Warwick (United Kingdom)
  5. Helmholtz Association of German Research Centres, Dresden (Germany)
Publication Date:
OSTI Identifier:
1241296
Report Number(s):
SLAC-PUB--16488
TRN: US1600693
DOE Contract Number:
AC02-76SF00515
Resource Type:
Technical Report
Research Org:
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Sponsoring Org:
US DOE Office of Science (DOE SC)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; DIAMONDS; X RADIATION; PRESSURE RANGE GIGA PA; WINDOWS; ENERGY-LOSS SPECTROSCOPY; PRESSURE DEPENDENCE; X-RAY DIFFRACTION; OPTICAL PROPERTIES; COMPRESSION; EXCITATION; ABLATION; EMISSION; FOILS; IMPURITIES; LASERS; STRAINS; LIGHT TRANSMISSION PHYS