Surface Analysis and Photoelectrochemical Studies of Mixed Polycrystals of p ‐ WSe2 /  WS 2

Abstract

Mixed polycrystals of p-WS%/WS2 with varied composition have been grown by the physical vapor transport technique by using the original compounds as starting materials. Three atomic ratios of WSe2/WS2, I(1:2), II(1:1), and III(2:l), were used. The mixed polycrystals were studied by scanning electron microscopy, x-ray fluorescence, and Auger electron spectroscopy. For the three syntheses, two types of polycrystals, rough (r) and smooth (s), were observed. The rough side had axial planes at the surface, while the smooth side had basal planes. The average size of the hexagonal single-crystal flakes, which form the polycrystal array, increased with a decrease in the sulfur content; Ir (118 ~m) < IIr (256 ixm) < IIIr (2 95 ixm). Direct energy bandgaps of 1.78, 1.71, and 1.66 eV were calculated for compounds I, II, and III, respectively. These p-type semiconductors have been characterized as electrode materials in nonaqueous systems by using cyclic voltammetry and photovoltammetry. Without illumination compound Ir showed a diffusion control cyclic voltammogram with the highest dark current. This is due to the high density of axial to basal plane ratio. The ilatband potential in acetonitrile in the dark decreased with a decrease in the sulfur content, from 1.12 for compound Ir to 0.78 V vs. SSCE for compound IIIr. The compound with the highest sulfur concentration (It) presented the highest underpotential in all the redox systems, while the compound with the lowest sulfur concentration showed the highest photocurrent. Compound IIr combines a large crystal size with an adequate sulfur concentration to present the highest conversion efficiency (0.36%) in a chlorani107+~ (O.OIOM/O.OOIM) and TBAP 0.25M solution.

Temperature dependences of energies and broadening parameters of the band-edge excitons of Re-doped WS2and 2H-WS2single crystals

“…WS 2 has been the subject of great interest, because its bandgap is well matched to the solar spectrum [9]. It can act as an efficient photoconductive layer in photovoltaic devices and photoelectrochemical solar cells [10][11][12]. The main advantage of WS 2 is the prevention of photocorrosion, because the phototransitions involve nonbonding d-d orbitals of W atoms [13].…”

Basal Plane Functionalization of Niobium Disulfide Nanosheets with Cyclopentadienyl Manganese(I) Dicarbonyl

“…While TMDs have a wide range of electronic properties ranging from semiconducting (WS 2 , WSe 2 , MoS 2 , MoSe 2 ) or semimetallic (WTe 2 , , NbS 2 1 ) to superconducting (NbS 2 ), introducing new functionality into them without disrupting their structure and electronic properties has proven to be challenging. Apart from isoelectronic substitutions, − it is difficult to incorporate other atoms, such as electronic dopants or magnetic elements, into the sheets without introducing unintentional defects or producing undesirable side products. While there has been measured success in tuning transition-metal dichalcogenide (TMD) properties via local gating − and novel CVD heterostructures, ,, these techniques struggle with limited scalability.…”

Study of the hydrostatic pressure dependence of the Raman spectrum of W/WS2 fullerene-like nanosphere with core–shell structure

“…Tungsten disulfide (WS 2 ) has an anisotropic layered structure, which is characterized by strong covalent bonds between the atoms within the molecular layer and weak van der Waals (vdW) forces between the layers. The structural anisotropy of this material has shown wide applications, such as photovoltaic solar cells [1], solid lubricants [2], battery cathodes and hydride sulfurization catalysis etc [3]. As a solid-state lubricant, WS 2 inorganic fullerenelike (IF-WS 2 ) nanoparticles show superior tribological performance over traditional platelet crystal analogues, and a low coefficient of friction and a low rate of wear, especially under high loads [4].…”