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.

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We present a compact and efficient design for slanted grating couplers (SLGC's) to vertically connect fibers and planar waveguides without intermediate optics. The proposed SLGC employs a strong index modulated slanted grating. With the help of a genetic algorithm-based rigorous design tool, a 20microm-long SLGC with 80.1% input coupling efficiency has been optimized. A rigorous mode analysis reveals that the phase-matching condition and Bragg condition are satisfied simultaneously with respect to the fundamental leaky mode supported by the optimized SLGC.

Perovskite solar cells (PSCs) have achieved a huge success in power conversion efficiency (PCE), although they still suffer from the long-term stability problem caused by the intrinsic sensitivity of perovskites to moisture. 2,2′,7,7′-Tetrakis (N,N-dip -methoxyphenylamine) 9,9′-spirobifluorene (Spiro-OMeTAD) is widely used as the hole transport layer (HTL) in typical PSCs; meanwhile, bis(trifuoromethane)sulfonimide lithium salt (Li-TFSI) is necessary as an additive in the Spiro-OMeTAD HTL to improve the hole mobility. However, the Li + ions bring in high hygroscopicity and a water-uptake effect that both aggravate degradation of the Spiro-OMeTAD HTL and thereby of the perovskite layers. Here, we modify the Li-TFSI-based Spiro-OMeTAD HTL by adding reduced graphene oxide (rGO). We verify that rGO provides adsorption sites for Li + ions and subsequently suppresses Li + migration. The water-uptake effect originating from Li + ions is thus restrained, and unfavorable pinholes in HTL caused by Li + ion migration are eliminated. Consequently, the rGOincorporated HTL remarkably improves the device stability that maintains the initial PCEs within 3% loss after 700 h under 40% humidity; however, the pristine devices almost lose the efficiency after 620 h. In addition, the good conductivity of the rGO favors hole transport in the Spiro-OMeTAD, resulting in a promotion in PCEs from 17.7% to 19.3% by incorporating rGO in HTL. Our work takes an insight into the function of rGO in the HTL and demonstrates an effective way of improving the efficiency and stability of PSCs simultaneously.

Electrocatalytic water splitting is an emerging technique to produce sustainable hydrogen energy. However, it is still challengeable to fabricate a stable, efficient, and cost-effective electrocatalyst that can overcome the sluggish reaction kinetics of water electrolysis. In order to reduce the energy barrier, for the first time, metal−organic framework (MOF)-derived nickel (Ni) and nickel sulfide (NiS) heteronanoparticleembedded semi-MOFs are prepared by a partial sulfurization strategy. These semi-MOF electrocatalysts inherit the advantages associated with MOF architecture and nanoparticles, unlike the traditional OER catalysts such as pristine MOFs or completely pyrolyzed MOFs. Due to the unique nanoarchitecture fabricated by Ni/NiS heteronanoparticles within semi-MOF nanosheets and a carbon nanotube (CNT) network (Ni-M@C-130), it displays exceptional bifunctional activity over the other transition metalbased electrocatalysts ever reported. It requires very small overpotentials for both oxygen evolution reaction (OER; η 10 = 244 mV) and hydrogen evolution reaction (HER; η 10 = 123 mV), with low Tafel slopes of 47.2 and 50.8 mV/dec, respectively. Furthermore, it exhibits overpotential as low as 1.565 V (η 10 ) on nickel foam (1 mg/cm 2 ) substrates for overall water splitting. The outstanding catalytic performance of Ni-M@C-130 is attributed to the combined benefits of MOF nanosheets, synergistic interactions, and improved electrical conductivity and mechanical stability. This study describes the advantages of partial sulfurization of CNT-integrated MOFs in attaining electrochemically active heteronanoparticles within MOF nanosheets to accomplish improved bifunctional activity.