Structural and Electronic Properties of ZnWO₄(010) Cleaved Surface

Abstract

A high-quality inclusion-free ZnWO4 crystal 90 mm in diameter and with a mass of up to 8 kg was grown by the low thermal gradient Czochralski technique. Crystallographic properties of ZnWO4(010) cleaved surfaces were evaluated with reflection high energy electron diffraction (RHEED), and the electronic structure of the surface was studied using X-ray photoelectron spectroscopy (XPS). A system of Kikuchi lines was observed for cleaved ZnWO4(010) by RHEED confirming the high crystallographic state of the surface. The XPS valence-band and core-level spectra of ZnWO4(010) have been measured. The XPS measurements reveal that tungsten and zinc atoms are in the formal valences +6 and +2, respectively, on cleaved ZnWO4(010) surface. The 3.0 keV Ar+ bombardment of the surface causes partial transformation of tungsten ions from W6+ to lower valence states; however, no partial loss of oxygen atoms belonging to ZnO6 octahedra occurs due to this bombardment of the ZnWO4(010) surface because after this treatment zinc remains exclusively in the formal valence +2. The W–O chemical bonding is considered in tungstates including ZnWO4.