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Abstract: This paper reports on a four-terminal dual-emitter heterojunction phototransistor (4T-DEPT) with a base biased by a current source in comparison with a three-terminal dual-emitter heterojunction phototransistor (3T-DEPT). While only voltage can be used to tune the optical performance of the 3T-DEPT, voltage- and current-control modes are considered for the 4T-DEPT. One emitter (E2) serves as the voltage (V E21)-controlled terminal at a fixed base biasing current while the other one (E1) is at the ground state. On the other hand, the base terminal controls the operation by applying an additional current (I Bdc) bias when the V E21 is constant. Therefore, voltage- and current-dependent characteristics will be detailed. Four operating regions exist in the voltage-dependent characteristics for both 3T- and 4T-DEPTs: negative-saturation, negative-tuning, positive-tuning, and positive-saturation regions. When the 4T-DEPT operates at the bias condition of V E21 =0.4V, I Bdc =0.001μA, and the incident optical power (P in) of 0.423μW, it shows the maximum current-dependent current-tuning efficiency and gain-tuning efficiency of 21.40 and 73.87μA−1, respectively. In addition to the power- and voltage-tunable optical gains, a current-tunable one is also available in the 4T-DEPT. [Copyright &y& Elsevier]

Abstract: A new SnO2/mesoporous silica composite was synthesized by a facile method, ‘tin vapor reduction method’, in which mesoporous silica SBA-15 was treated with tin vapor at temperature above 700°C under inert atmosphere. This material displays enhanced room-temperature photoluminescence (RT-PL) at increased treatment temperature. It is proved that RT-PL properties of this composite are closely related to twofold-coordinated tin oxygen-deficient centers. [Copyright &y& Elsevier]

The spontaneous formation of surface electron accumulation (SEA) was observed in synthesized molybdenum diselenide (MoSe 2) layered crystals with two-hexagonal (2 H) structure. An anomalously high electron concentration at the surface up to 1019 cm−3 is several orders of magnitude higher than that (3.6 × 1012 cm−3) of the inner bulk. The SEA is found to be generated easily by mechanical exfoliation and room temperature deselenization. Se-vacancies have been confirmed to be the major source resulting in SEA and n-type conductivity, and also the active sites for electrochemical catalysis in MoSe 2. Noted that the SEA conjugated with the Se-vacancy-related surface defects enhances the electrochemical hydrogen evolution reaction (HER) activity substantially. The optimized HER efficiency with an overpotential at 0.17 V and Tafel slope at 60 mV/dec of the basal plane of 2 H-MoSe 2 was achieved by the nitrogen plasma treatment, which has outperformed several nanostructures, thin films, and hybrid counterparts. This study reveals the intriguing surface-dominant electronic property and its effect on the HER enhancement of the basal plane, which is crucial for development of a stable, low-cost and highly efficient catalyst using 2 H-MoSe 2. [Display omitted] • Anomalous surface electron accumulation (SEA) was discovered in synthesized MoSe 2. • Se-vacancies caused by spontaneous deselenization have been confirmed to be the origin of the SEA and n-type conductivity in MoSe 2. • The SEA conjugated with surface defects substantially enhances the electrochemical hydrogen evolution reaction (HER) activity. • The HER efficiency of nitrogen plasma-treated 2H-MoSe 2 outperforms several nanostructure and hybrid counterparts. [ABSTRACT FROM AUTHOR]

Numerical simulations are performed to investigate the effect of aerosol on microphysical and electrification in thunderstorm clouds. A two-dimensional (2-D) cumulus model with electrification scheme including non-inductive and inductive charge separation is used. The concentration of aerosol particles with distribution fitted by superimposing three log-normal distributions rises from 50 to 10,000 cm −3 . The results show that the response of charge separation rate to the increase of aerosol concentration is nonmonotonic. When aerosol concentration is changed from 50 to 1000 cm −3 , a stronger formation of cloud droplet, graupel and ice crystal results in increasing charge separation via non-inductive and inductive mechanism. However, in the range of 1000–3000 cm −3 , vapor competition arises in the decrease of ice crystal mixing ratio and the reduction of ice crystals size leads to a slightly decrease in non-inductive charge rate, while inductive charging rate has no significant change in magnitude. Above aerosol concentration of 3000 cm −3 , the magnitude of charging rate which keeps steady is insensitive to the increase in aerosol concentration. The results also suggest that non-inductive charge separation between ice crystal and graupel contributes to the main upper positive charge region and the middle negative charge region. Inductive graupel–cloud droplet charge separation, on the other hand, is found to play an important role in the development of lower charge region. [ABSTRACT FROM AUTHOR]