Recent Progress on Ligand-Protected Metal Nanoclusters in Photocatalysis.

The reckless use of non-replenishable fuels by the growing population for energy and the resultant incessant emissions of hazardous gases and waste products into the atmosphere have insisted that scientists fabricate materials capable of managing these global threats at once. In recent studies, photocatalysis has been employed to focus on utilizing renewable solar energy to initiate chemical processes with the aid of semiconductors and highly selective catalysts. A wide range of nanoparticles has showcased promising photocatalytic properties. Metal nanoclusters (MNCs) with sizes below 2 nm, stabilized by ligands, show discrete energy levels and exhibit unique optoelectronic properties, which are vital to photocatalysis. In this review, we intend to compile information on the synthesis, true nature, and stability of the MNCs decorated with ligands and the varying photocatalytic efficiency of metal NCs concerning changes in the aforementioned domains. The review discusses the photocatalytic activity of atomically precise ligand-protected MNCs and their hybrids in the domain of energy conversion processes such as the photodegradation of dyes, the oxygen evolution reaction (ORR), the hydrogen evolution reaction (HER), and the CO2 reduction reaction (CO2RR).

Radio Frequency Transistors and Circuits Based on CVD MoS2.

We report on the gigahertz radio frequency (RF) performance of chemical vapor deposited (CVD) monolayer MoS2 field-effect transistors (FETs). Initial DC characterizations of fabricated MoS2 FETs yielded current densities exceeding 200 µA/µm and maximum transconductance of 38 µS/µm. A contact resistance corrected low-field mobility of 55 cm(2)/(V s) was achieved. Radio frequency FETs were fabricated in the ground-signal-ground (GSG) layout, and standard de-embedding techniques were applied. Operating at the peak transconductance, we obtain short-circuit current-gain intrinsic cutoff frequency, fT, of 6.7 GHz and maximum intrinsic oscillation frequency, fmax, of 5.3 GHz for a device with a gate length of 250 nm. The MoS2 device afforded an extrinsic voltage gain Av of 6 dB at 100 MHz with voltage amplification until 3 GHz. With the as-measured frequency performance of CVD MoS2, we provide the first demonstration of a common-source (CS) amplifier with voltage gain of 14 dB and an active frequency mixer with conversion gain of -15 dB. Our results of gigahertz frequency performance as well as analog circuit operation show that large area CVD MoS2 may be suitable for industrial-scale electronic applications.

Light trapping in ultrathin 25 µm exfoliated Si solar cells.

The optical absorption in 25-µm-thick, single-crystal Si foils fabricated using a novel exfoliation technique for solar cells is studied and improved in this work. Various light-trapping and optical absorption enhancement schemes implemented show that it is possible to substantially narrow the gap in optical absorption loss between the 25 µm Si foils and industry-standard 180-µm-thick Si wafer solar cells. An improvement of absorption by 58% in the near-infrared (740-1200 nm) range is observed for the 25 µm monocrystalline Si substrates with the use of antireflective coating and texturing. The back reflectance of the metal foil that provides mechanical support to the ultrathin Si semiconductor-on-metal foils is extracted to be ∼51.5%, based on the reflectance matching with the simulated escape reflectance in the sub-bandgap region. The back reflectance is enhanced to ∼58% by incorporating an intermediate silicon nitride layer on the back between the Si and the metal. The incorporation of Al as an improved metal reflector on top of the silicon nitride at the backside of the solar cell results in a 5.8 times enhancement in optical path length as a consequence of the improved effective back reflectance of ∼95%. A thin Si foil solar cell with an unoptimized amorphous Si/crystalline Si heterojunction with intrinsic-thin-layer design with implementation of such light-trapping schemes shows an efficiency of 13.28% with a short-circuit current density (JSC) of 35.97 mA/cm2, which approaches the JSC of industrial wafer-based Si solar cells.

High-performance flexible thin-film transistors exfoliated from bulk wafer.

Mechanically flexible integrated circuits (ICs) have gained increasing attention in recent years with emerging markets in portable electronics. Although a number of thin-film-transistor (TFT) IC solutions have been reported, challenges still remain for the fabrication of inexpensive, high-performance flexible devices. We report a simple and straightforward solution: mechanically exfoliating a thin Si film containing ICs. Transistors and circuits can be prefabricated on bulk silicon wafer with the conventional complementary metal-oxide-semiconductor (CMOS) process flow without additional temperature or process limitations. The short channel MOSFETs exhibit similar electrical performance before and after exfoliation. This exfoliation process also provides a fast and economical approach to producing thinned silicon wafers, which is a key enabler for three-dimensional (3D) silicon integration based on Through Silicon Vias (TSVs).