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SUMMARY:Near-surface regions of chalcopyrite studied using XPS\, HAXPES\, 
 XANES and DFT
DTSTART;VALUE=DATE-TIME:20160707T050000Z
DTEND;VALUE=DATE-TIME:20160707T052000Z
DTSTAMP;VALUE=DATE-TIME:20260419T151659Z
UID:indico-contribution-1246@indico.inp.nsk.su
DESCRIPTION:Speakers: Yuri Mikhlin (Institute of Chemistry and Chemical Te
 chnology of the Siberian Branch of the Russian Academy of sciences)\nChalc
 opyrite CuFeS2\, is the most common mineral of copper\; chalcopyrite and r
 elated compounds are of interest for thermoelectric\, photovoltaic and oth
 er applications. We also examined valleriite (Fe\,Cu)S(Mg\,Al)(OH)2\, natu
 ral nanocomposite composed of chalcopyrite-like Fe\,Cu sulfide layers and 
 brucite-like oxide layers\, which is important mineral of Norilsk ore depo
 sits. Conventional XPS and synchrotron-based hard photoemission spectrosco
 py (HAXPES)\, surface-sensitive Cu L-\, Fe L-\, S L-edge TEY XANES and S K
 -\, Fe K-edge TEY and PFY XANES spectroscopy were used along with some oth
 er experimental techniques and DFT+U calculations in order to characterize
  near-surface regions of the initial (in fact\, oxidized in air) minerals 
 and the ones chemically oxidized in Fe(III) solutions. The synchrotron irr
 adiation experiments were performed at Russian-German laboratory and HIKE 
 endstations at BESSY II facility (Helmholtz Zentrum Berlin). Both the elem
 ent concentrations and the chemical state of atoms\, e.g.\, mono-\, di-\, 
 polysulfide and other S species\, as a function of the probing depth and t
 he reaction conditions\, were studied. The near-surface regions of chalcop
 yrite are generally consist of (i) a thin\, no more than 1-4 nm\, strongly
  metal-depleted outer layer containing polysulfide species\, (ii) a layer 
 with smaller stoichiometry deviations and low\, if any\, concentrations of
  polysulfide\, which composition and dimensions strongly depend on the che
 mical treatment conditions\, and (iii) an about stoichiometric underlayer 
 extended to at least several dozen of nanometers. The latter shows Fe K-ed
 ge TEY spectra altered probably due to a high content of defects\, even if
  only oxidized in ambient air. In contrast to other spectra\, Cu L-XANES p
 atterns were surprisingly insensitive to the changes of the composition of
  the reacted near-surface layers. DFT+U analysis of the iron-deficient str
 uctures formed shows that polysulfide species are stable only near the sur
 face\, copper remains 4-fold coordinated to S in the layers with disulfide
  anions\, the layer with iron deficiency transforms from antiferromagnetic
  and semiconducting state into paramagnetic metallic state. Moreover\, the
  formation of these structures is generally energy-favorable under the oxi
 dative conditions. The lengthy regions are expected to heavily affect the 
 electronic characteristics and processes involving surface and interfacial
  charge transfer.\n\nhttps://indico.inp.nsk.su/event/3/contributions/1246/
LOCATION:Budker INP Conference Hall
URL:https://indico.inp.nsk.su/event/3/contributions/1246/
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