Molecular layers attached to a silicon nanowire field effect transistor (SiNW FET) can serve as antennas for signal transduction of volatile organic compounds (VOCs). Nevertheless, the mutual relationship between the molecular layers and VOCs is still a puzzle. In the present paper, we explore the effect of the molecular layer's end (functional) groups on the sensing properties of VOCs. Toward this end, SiNW FETs were modified with tailor-made molecular layers that have the same backbone but differ in their end groups. Changes in the threshold voltage (ΔVth) and changes in the mobility (Δμh) were then recorded upon exposure to various VOCs. Model-based analysis indicates that the interaction between molecular layers and VOCs can be classified to three main scenarios: (a) dipole-dipole interaction between the molecular layer and the polar VOCs; (b) induced dipole-dipole interaction between the molecular layers and the nonpolar VOCs; and (c) molecular layer tilt as a result of VOCs diffusion. Based on these scenarios, it is likely that the electron-donating/withdrawing properties of the functional groups control the dipole moment orientation of the adsorbed VOCs and, as a result, determine the direction (or sign) of the ΔVth. Additionally, it is likely the diffusion of VOCs into the molecular layer, determined by the type of functional groups, is the main reason for the Δμh responses. The reported findings are expected to provide an efficient way to design chemical sensors that are based on SiNW FETs to nonpolar VOCs, which do not exchange carriers with the molecular layers.

It is still challenging to develop sulfur electrodes for Li−S batteries with high electrical conductivity and fast kinetics, as well as efficient suppression of the shuttling effect of lithium polysulfides. To address such issues, herein, polar MoTe 2 with different phases (2H, 1T, and 1T′) were deeply investigated by density functional theory calculations, suggesting that the 1T′-MoTe 2 displays concentrated density of states (DOS) near the Fermi level with high conductivity. By optimization of the synthesis, 1T′-MoTe 2 quantum dots decorated threedimensional graphene (MTQ@3DG) was prepared to overcome these issues, and it accomplished exceptional performance in Li−S batteries. Owing to the chemisorption and high catalytic effect of 1T′-MoTe 2 quantum dots, MTQ@3DG/S exhibits highly reversible discharge capacity of 1310.1 mAh g −1 at 0.2 C with 0.026% capacity fade rate per cycle over 600 cycles. The adsorption calculation demonstrates that the conversion of Li 2 S 2 to Li 2 S is the rate-limiting step where the Gibbs free energies are 1.07 eV for graphene and 0.97 eV for 1T′-MoTe 2 , revealing the importance of 1T′-MoTe 2 . Furthermore, in situ Raman spectroscopy investigation proved the suppression of the shuttle effect of LiPSs in MTQ@3DG/S cells during the cycle.

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We report on the sensing of different polar and nonpolar volatile organic compounds (VOCs) in an atmosphere with background humidity (relative humidity: 40%), using molecularly modified silicon nanowire field effect transistors (SiNW FETs). In this endeavor, a systematic comparative analysis is performed with: (i) SiNW FETs that were functionalized with a series of molecules having different electron-withdrawing and electron-donating end groups; and (ii) SiNW FETs that are functionalized with a series of molecules having similar functional groups but different backbone lengths. The analysis of the sensing signals are focused on three main FET parameters: (i) changes in the threshold voltage, (ii) changes in the carrier mobility, and (iii) changes in the on-current, compared to the baseline values under vacuum. Using discriminant factor analysis, the performance of the molecularly modified SiNW FETs is further analyzed as sensors array. The combination of sensors having the best discriminative power between the various VOCs are identified and discussed in terms of their constituent surface modifications.