Considerations on the kinetic correlation between SiC nitridation and etching at the 4H-SiC(0001)/SiO2 interface in N2 and N2/H2 ambient

Kinetics of SiC surface nitridation process of high-temperature N2 annealing was investigated with 4H-SiC(0001)/SiO2 structure based on the correlation between the rates of N incorporation and SiC consumption induced by SiC etching. During the early stage of the annealing process, the rate-limiting step for N incorporation would be the removal of the topmost C atoms in the slow-etching case, while it would be another reaction step, probably the activation process of nitrogen in the fast-etching case. The SiO2 layer thickness and the annealing ambient which serve as the parameters to affect the SiC etching rate, would determine the N incorporation rate according to the kinetic correlation between the N incorporation and SiC etching. The SiC consumption observed during high-temperature annealing in N2 or N2/H2 ambient would be induced by the active oxidation by residual O2 or H2O in the ambient, which would lead to the SiC surface roughening.

Nitrogen-incorporation activates NiFeOx catalysts for efficiently boosting oxygen evolution activity and stability of BiVO4 photoanodes

Developing low-cost and highly efficient catalysts toward the efficient oxygen evolution reaction (OER) is highly desirable for photoelectrochemical (PEC) water splitting. Herein, we demonstrated that N-incorporation could efficiently activate NiFeOx catalysts for significantly enhancing the oxygen evolution activity and stability of BiVO4 photoanodes, and the photocurrent density has been achieved up to 6.4 mA cm−2 at 1.23 V (vs. reversible hydrogen electrode (RHE), AM 1.5 G). Systematic studies indicate that the partial substitution of O sites in NiFeOx catalysts by low electronegative N atoms enriched the electron densities in both Fe and Ni sites. The electron-enriched Ni sites conversely donated electrons to V sites of BiVO4 for restraining V5+ dissolution and improving the PEC stability, while the enhanced hole-attracting ability of Fe sites significantly promotes the oxygen-evolution activity. This work provides a promising strategy for optimizing OER catalysts to construct highly efficient and stable PEC water splitting devices.

The Effect of Nitrogen Incorporation on the Optical Properties of Si-Rich a-SiCx Films Deposited by VHF PECVD

The influence of N incorporation on the optical properties of Si-rich a-SiCx films deposited by very high-frequency plasma-enhanced chemical vapor deposition (VHF PECVD) was investigated. The increase in N content in the films was found to cause a remarkable enhancement in photoluminescence (PL). Relative to the sample without N incorporation, the sample incorporated with 33% N showed a 22-fold improvement in PL. As the N content increased, the PL band gradually blueshifted from the near-infrared to the blue region, and the optical bandgap increased from 2.3 eV to 5.0 eV. The enhancement of PL was suggested mainly from the effective passivation of N to the nonradiative recombination centers in the samples. Given the strong PL and wide bandgap of the N incorporated samples, they were used to further design an anti-counterfeiting label.

Study of patterned GaAsSbN nanowires using sigmoidal model

This study presents the first report on patterned nanowires (NWs) of dilute nitride GaAsSbN on p-Si (111) substrates by self-catalyzed plasma-assisted molecular beam epitaxy. Patterned NW array with GaAsSbN of Sb composition of 3% as a stem provided the best yield of vertical NWs. Large bandgap tuning of ~ 75 meV, as ascertained from 4 K photoluminescence (PL), over a pitch length variation of 200–1200 nm has been demonstrated. Pitch-dependent axial and radial growth rates show a logistic sigmoidal growth trend different from those commonly observed in other patterned non-nitride III–V NWs. The sigmoidal fitting provides further insight into the PL spectral shift arising from differences in Sb and N incorporation from pitch induced variation in secondary fluxes. Results indicate that sigmoidal fitting can be a potent tool for designing patterned NW arrays of optimal pitch length for dilute nitrides and other highly mismatched alloys and heterostructures.

Boosting the efficiency and stability of CoMoS4 by N incorporation for electrocatalytic hydrogen evolution

In situ N incorporation was developed to greatly improve the efficiency and stability of sulfide electrocatalyst for hydrogen evolution by electronic density modulation.

Revisiting the Site-Competition Doping of 4H-SiC: Cases of N and Al

Because the well-known site-competition and step-controlled epitaxy rules cannot reasonably describe all the incorporation processes of the main impurities (Al and N) into 4H-SiC during epitaxy, the concept of replacement incorporation was proposed and applied to explain the experimental results published so far. In this model, the transient formation of C or Si vacancies at the surface or sub-surface of terraces is proposed to play a key role by destabilizing the impurities sitting on them. In addition to the availability of these vacancies at the surface, desorption was proposed to be a very important limiting process for Al incorporation while only occasionally relevant for N incorporation. The main 4H-SiC epitaxial growth parameters are reviewed and discussed according to the proposed replacement model.

Np4A alarmones function in bacteria as precursors to RNA caps

Stresses that increase the cellular concentration of dinucleoside tetraphosphates (Np4Ns) have recently been shown to impact RNA degradation by inducing nucleoside tetraphosphate (Np4) capping of bacterial transcripts. However, neither the mechanism by which such caps are acquired nor the function of Np4Ns in bacteria is known. Here we report that promoter sequence changes upstream of the site of transcription initiation similarly affect both the efficiency with which Escherichia coli RNA polymerase incorporates dinucleoside polyphosphates at the 5′ end of nascent transcripts in vitro and the percentage of transcripts that are Np4-capped in E. coli, clear evidence for Np4 cap acquisition by Np4N incorporation during transcription initiation in bacterial cells. E. coli RNA polymerase initiates transcription more efficiently with Np4As than with ATP, particularly when the coding strand nucleotide that immediately precedes the initiation site is a purine. Together, these findings indicate that Np4Ns function in bacteria as precursors to Np4 caps and that RNA polymerase has evolved a predilection for synthesizing capped RNA whenever such precursors are abundant.