Search

The long stagnation of the photo-conversion efficiency of kesterites below 13% is a source of frustration in the scientific community. In this study, we investigated the effects of sodium on the passivation of grain boundaries and defects in Cu 2 ZnSnSe 4 (CZTSe) grown on a soda-lime glass (SLG) and borosilicate (BS) glass. Because BS glass does not inherently contain sodium, we placed a thin layer of NaF between CZTSe and Mo. The composition of the samples is Cu-poor and Zn-rich. The distribution of sodium and its contributions to phase formation and defects were examined by cross-sectional energy-dispersive X-ray profiling, Raman scattering spectroscopy and imaging, surface potential and photoluminescence. From the experimental results, it can be strongly claimed that sodium ions segregate predominantly near the grain boundaries and reduce Cu Zn -related defects. These local surface imaging analyses provided the exact locations of the secondary phases. In particular, the photo-assisted scanning probe method enabled us to observe the changes in the optoelectrical properties of the thin films and the carrier behavior within the materials. Further studies with distinct alkali ions and optimal processing conditions will pave a way to improve the performance of kesterite solar cells.

High quality gallium sulfide II (GaS) and gallium sulfide III ([Formula: see text]) thin films on [Formula: see text]/Si substrates were simultaneously grown by using physical vapor deposition with GaS powder as a single precursor. By controlling the substrate temperature, we can selectively grow either GaS or Ga 2 S 3 thin films on SiO 2 /Si substrates. Relatively high and low substrate temperature conditions resulted in Ga 2 S 3 and GaS thin films, respectively. The synthesized thin films were characterized by x-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy analyses.

The covalently bonded in-plane heterostructure (HS) of monolayer transition-metal dichalcogenides (TMDCs) possesses huge potential for high-speed electronic devices in terms of valleytronics. In this study, high-quality monolayer MoSe 2 -WSe 2 lateral HSs are grown by pulsed-laser-deposition-assisted selenization method. The sharp interface of the lateral HS is verified by morphological and optical characterizations. Intriguingly, photoluminescence spectra acquired from the interface show rather clear signatures of pristine MoSe 2 and WSe 2 with no intermediate energy peak related to intralayer excitonic matter or formation of Mo x W (1-x) Se 2 alloys, thereby confirming the sharp interface. Furthermore, the discrete nature of laterally attached TMDC monolayers, each with doubly degenerated but nonequivalent energy valleys marked by (K M , K' M ) for MoSe 2 and (K W , K' W ) for WSe 2 in k space, allows simultaneous control of the four valleys within the excitation area without any crosstalk effect over the interface. As an example, K M and K W valleys or K' M and K' W valleys are simultaneously polarized by controlling the helicity of circularly polarized optical pumping, where the maximum degree of polarization is achieved at their respective band edges. The current work provides the growth mechanism of laterally sharp HSs and highlights their potential use in valleytronics.

Nanoscale sensors based on single-walled carbon nanotube (SWNT) networks have been considered impractical due to several fundamental limitations such as a poor sensitivity and small signal-to-noise ratio. Herein, we present a strategy to overcome these fundamental problems and build highly-sensitive low-noise nanoscale sensors simply by controlling the structure of the SWNT networks. In this strategy, we prepared nanoscale width channels based on aligned SWNT networks using a directed assembly strategy. Significantly, the aligned network-based sensors with narrower channels exhibited even better signal-to-noise ratio than those with wider channels, which is opposite to conventional random network-based sensors. As a proof of concept, we demonstrated 100 nm scale low-noise sensors to detect mercury ions with the detection limit of approximately 1 pM, which is superior to any state-of-the-art portable detection system and is below the allowable limit of mercury ions in drinking water set by most government environmental protection agencies. This is the first demonstration of 100 nm scale low-noise sensors based on SWNT networks. Considering the increased interests in high-density sensor arrays for healthcare and environmental protection, our strategy should have a significant impact on various industrial applications.

RNase E (Rne) plays a major role in the decay and processing of numerous RNAs in E. coli, and protein inhibitors of RNase E, RraA and RraB, have recently been discovered. Here, we report that coexpression of RraA or RraB reduces the ribonucleolytic activity in rne-deleted E. coli cells overproducing RNase ES, a Streptomyces coelicolor functional ortholog of RNase E, and consequently rescues these cells from growth arrest. These findings suggest that the regulators of ribonuclease activity have a conserved intrinsic property that effectively acts on an RNase E-like enzyme found in a distantly related bacterial species.