Effect of Au/HfS₃ interfacial interactions on properties of HfS₃-based devices

Abstract

N-type HfS3in vacuo (left) versus p-type HfS3 in air (right); O2 chemisorption changes the n-type EF to p-type EF.

What happens when transition metal trichalcogenides are interfaced with gold?

“…The higher binding energy of the Hf 4f doublet in blue, in comparison with the binding energy value of the doublet in red, implies more charge donation in the former case compared to the latter. Therefore, in accordance with the existing literature [91][92][93][94][95], the lower intensity Hf 4f core-level doublet at the higher binding energy value is attributed to the Hf-O bonding environment; whereas the Hf 4f core-level doublet at the lower binding energy is characteristic of the Hf-S bonding environment [73]. These results imply facile dissociative chemisorption of oxygen on HfS 3 .…”

“…While isostructural with TiS 3 and ZrS 3 , unlike TiS 3 and ZrS 3 , the photoemission spectroscopy data of HfS 3 show signature of oxidation of hafnium that appears to occur upon exposure of HfS 3 to ambient air [73], implying that the surface of HfS 3 is nontrivial. Figure 4 shows the XPS data of the Hf 4f core-level of HfS 3 .…”

“…Likewise, the ZrS 3 crystals were obtained as the product of a chemical reaction between vapors of sulfur and metallic zirconium, in vacuum-sealed quartz ampules at 800°C [69][70][71]. For the synthesis of HfS 3 crystals, just like its titanium and zirconium counterparts, metallic hafnium was made to react with sulfur vapors in a vacuum-sealed quartz ampule at 600°C [72,73]. Eventually, after annealing the HfS 3 ampules at 600°C for 2 weeks [72, 73], a few-millimeter long crystals of HfS 3 were gathered.…”

“…The XPS spectra of TiS 3 , ZrS 3 , and HfS 3 were collected using an Al K α SPECS X-ray anode, with the X-ray photon energy of 1486.6 eV, and a PHI hemispherical electron analyzer (Model: 10-360). All the XPS measurements were carried out in an ultrahigh vacuum chamber as the base pressure was always better than 1.9 × 10 -10 Torr, as described elsewhere [73][74][75]. To extract the information about the individual S 2p core-level components, the fits to all the XPS spectra were performed using the XPST curve fitting package available in Igor Pro.…”

“…Chemisorption of oxygen at the HfS 3 is also consistent with the electrical transport data shown in refs. [73,96], and explains how the exposure of HfS 3 to ambient air makes it transition from being an n-type semiconductor, in its as-synthesized form, to a p-type semiconductor.…”