Layer-Dependent Hydrazine Adsorption Properties in Few-Layer WS₂

Abstract

We have developed a lithography free technique for the fabrication of two-dimensional material based devices for electrical characterization. We fabricated few-layer and multilayer WS2 devices using a transmission electron microscope (TEM) grid as a shadow mask, and its transport characteristics were studied by electrical measurements. WS2 samples were synthesized by first depositing WO3 followed by sulfurization and characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy. Each sample was exposed to hydrazine at varying pressures, and their electrical resistances were monitored during adsorption (exposing to hydrazine vapor) and subsequent desorption (by pumping). The WS2 sample consisting of two layers showed a decrease of resistance upon exposure to hydrazine vapor and showed complete reversibility upon pumping. The WS2 sample with three layers showed a decrease of resistance during exposure but showed only partial recovery during desorption. In contrast, the multilayered (12 layers) WS2 sample showed an initial decrease followed by a continued increase of the resistance upon exposure to hydrazine with little or no reversibility upon pumping. The charge transfer from N2H4 to WS2 is believed to be responsible for the decrease of the resistance. Trapping of N2H4 molecules within the multilayers of WS2 causing charge redistribution and possible chemical reactions may be responsible for the increase in resistance during the adsorption and complete irreversibility of resistance during desorption. The experimental results are explained with the help of computational calculations performed by employing the density functional theory (DFT) framework, as implemented in the Vienna Ab-initio Simulation Package (VASP).

Pressure-Induced SERS-Enhanced Sensing of 4-Mercaptobenzoic Acid Using Few-Layer WS2 Nanosheets

“…The three-dimensional (3D) AFM height image in Figure d shows that the thickness of FL-WS 2 nanosheets is 6.2 nm; thus, it can be inferred that the layer number is ∼8 by reference to the 0.75 nm thickness of monolayer WS 2 . Furthermore, the Raman spectrum in Figure e reveals that the intensity of the out-of-plane mode (A 1g ) is obviously stronger than that of the in-plane mode (E 2g 1 ), indicating that the layer number of FL-WS 2 nanosheets is more than 3, which is in good agreement with the AFM result . Ultraviolet–visible (UV–vis) spectra were adopted to unveil the optical properties of the FL-WS 2 materials.…”

“…37 Furthermore, the Raman spectrum in Figure 1e reveals that the intensity of the out-ofplane mode (A 1g ) is obviously stronger than that of the inplane mode (E 2g 1 ), indicating that the layer number of FL-WS 2 nanosheets is more than 3, which is in good agreement with the AFM result. 38 Ultraviolet−visible (UV−vis) spectra were adopted to unveil the optical properties of the FL-WS 2 materials. As shown in Figure 1f, the UV−vis spectrum of FL-WS 2 exhibits three peaks A, B, and C at 635, 527, and 459 nm, respectively.…”

Direct fabrication and characterization of vertically stacked Graphene/h-BN/Graphene tunnel junctions

“…The AFM topography images were obtained in tapping mode in air with the aid of Si tips with a typical tip radius of 25 nm, tip length of ∼240 μm, spring constant range 1.8−12.5 N m −1 , and frequency range 58−97 kHz. The average thicknesses of samples were found to be 2.23, 4.04, and 6.85 nm respectively [83] Figure 5 shows the tunneling I-V characteristic curves of three Graphene/h-BN/Graphene based single tunnel junctions with varying h-BN thicknesses (tunnel barrier widths). All three curves show exponential dependence of the current (I) with the bias voltage (V) at higher voltages.…”

Insight the process of hydrazine gas adsorption on layered WS2: a first principle study

“…Detecting hydrazine with high sensitivity is crucial for many industries. Our recent experimental study [28] has found that the electrical resistance of 2D WS 2 layered materials decreases when they are exposed to hydrazine at varying pressures (i.e. varying N 2 H 4 concentration).…”

“…While, 3-4 layers of WS 2 showed only partial recovery during desorption. In contrast, multi-layered WS 2 showed a little or no reversibility upon pumping [28]. To shed light into such interesting response behaviors of 2D WS 2 exposed to N 2 H 4 gas molecule, we carried out a comprehensive study at the first principle level.…”