Experimental observations on metal-like carrier transport and Mott hopping conduction behaviours in boron-doped Si nanocrystal multilayers.

Studies on the carrier transport characteristics of semiconductor nanomaterials are the important and interesting issues which are helpful for developing the next generation of optoelectronic devices. In this work, we fabricate B-doped Si nanocrystals/SiO2multilayers by plasma enhanced chemical vapor deposition with subsequent high temperature annealing. The electronic transport behaviors are studied via Hall measurements within a wide temperature range (30-660 K). It is found that when the temperature is above 300 K, all the B-doped Si nanocrystals with the size near 4.0 nm exhibit the semiconductor-like conduction characteristics, while the conduction of Si nanocrystals with large size near 7.0 nm transforms from semiconductor-like to metal-like at high B-doping ratios. The critical carrier concentration of conduction transition can reach as high as 2.2 × 1020cm-3, which is significantly higher than that of bulk counterpart and may be even higher for the smaller Si nanocrystals. Meanwhile, the Mott variable-range hopping dominates the carrier transport when the temperature is below 100 K. The localization radius of carriers can be regulated by the B-doping ratios and Si NCs size, which is contributed to the metallic insulator transition.

First principles study on modulating electronic and optical properties with h-BN intercalation in AlN/MoS2heterostructure.

The van der Waals (vdW) heterostructures formed by stacking layered two-dimensional materials can improve the performance of materials and provide more applications. In our paper, six configurations of AlN/MoS2vdW heterostructures were constructed, the most stable structure was obtained by calculating the binding energy. On this basis, the effect of external vertical strain on AlN/MoS2heterostructure was analyzed, the calculated results show that the optimal interlayer distance was 3.593 Å and the band structure was modulated. Then the h-BN intercalation was inserted into the AlN/MoS2heterostructure, by fixing the distance between h-BN and AlN or MoS2, two kinds of models were obtained. Furthermore, the electronic properties of AlN/MoS2heterostructure can be regulated by adding h-BN intercalation layer and adjusting its position. Finally, the optical properties show that the absorption coefficient of AlN/MoS2heterostructure exhibits enhancement characteristic compared with that of the individual monolayers. Meantime, compared with AlN/MoS2, the AlN/h-BN/MoS2shows a redshift effect and the light absorption peak intensity increased, which indicated that h-BN intercalation layer can be used to regulate the electronic and optical properties of AlN/MoS2heterostructure.

Adjustable electronic and optical properties of BlueP/MoS2 van der Waals heterostructure by external strain: a first-principles study.

Blue phosphorene (BlueP) has been widely researched recently as a potential material for novel photocatalytic and electronic devices. In this letter, due to its similar in-plane hexagonal lattice structure to MoS2, BlueP/MoS2 van der Waals heterostructures were built in six configurations. The II-stacking configuration was the most stable due to the lowest binding energy obtained from the calculation results. Furthermore, by controlling the external vertical strain, the geometry structures were optimized and the electronic structures of the BlueP/MoS2 heterostructure were modulated. We found that when the interlayer distance was 3.71 Å, the structure was the most optimized. In addition, as the result of charge transfer at the interlayer, a built-in electric field was formed in the BlueP/MoS2 heterostructure, which explained the formation of the type-II band alignment structure. The optical properties results show that the BlueP/MoS2 heterostructure has a wide optical response range and good light absorption ability, which indicated significant potential for BlueP/MoS2 heterostructure use in the next generation of photovoltaic devices and water-splitting materials.

Interface-Enhanced SiOx/Ru Heterocatalysts for Efficient Electrochemical Water Splitting.

Developing a bifunctional electrocatalyst with remarkable performance viable for overall water splitting is increasingly essential for industrial-scale renewable energy conversion. However, the current electrocatalyst still requires a large cell voltage to drive water splitting due to the unsuitable adsorption/desorption capacity of reaction intermediates, which seriously hinders the practical application of water splitting. Herein, a unique SiOx/Ru nanosheet (NS) material was proposed as a high-performance electrocatalyst for overall water splitting. The SiOx/Ru NSs show superior performance in the hydrogen evolution reaction with a low overpotential of 23 mV (@ 10 mA cm-2) and excellent stability for nearly 200 h (@ 10 mA cm-2) in 1 M KOH. By means of the introduction of SiOx, it is beneficial for balancing the local charge density of the surrounding Ru sites. The suitable electronic coupling between the d-band electrons of Ru and the adsorbed species effectively balances the adsorption and desorption of reaction intermediates on the surface. As a result, the catalyst also exhibits overall water splitting activity with a cell voltage of only 1.496 V to reach the current density of 10 mA cm-2. The present work opens up a new strategy for designing high-performance electrocatalysts for water splitting.

Enhanced Electroluminescence from a Silicon Nanocrystal/Silicon Carbide Multilayer Light-Emitting Diode.

Developing high-performance Si-based light-emitting devices is the key step to realizing all-Si-based optical telecommunication. Usually, silica (SiO2) as the host matrix is used to passivate silicon nanocrystals, and a strong quantum confinement effect can be observed due to the large band offset between Si and SiO2 (~8.9 eV). Here, for further development of device properties, we fabricate Si nanocrystals (NCs)/SiC multilayers and study the changes in photoelectric properties of the LEDs induced by P dopants. PL peaks centered at 500 nm, 650 nm and 800 nm can be detected, which are attributed to surface states between SiC and Si NCs, amorphous SiC and Si NCs, respectively. PL intensities are first enhanced and then decreased after introducing P dopants. It is believed that the enhancement is due to passivation of the Si dangling bonds at the surface of Si NCs, while the suppression is ascribed to enhanced Auger recombination and new defects induced by excessive P dopants. Un-doped and P-doped LEDs based on Si NCs/SiC multilayers are fabricated and the performance is enhanced greatly after doping. As fitted, emission peaks near 500 nm and 750 nm can be detected. The current density-voltage properties indicate that the carrier transport process is dominated by FN tunneling mechanisms, while the linear relationship between the integrated EL intensity and injection current illustrates that the EL mechanism is attributed to recombination of electron-hole pairs at Si NCs induced by bipolar injection. After doping, the integrated EL intensities are enhanced by about an order of magnitude, indicating that EQE is greatly improved.

Alkali Activation of Copper and Nickel Slag Composite Cementitious Materials.

Alkali-activated copper and nickel slag cementitious materials (ACNCMs) are composite cementitious materials with CNS (copper and nickel slag) as the main materials and GGBFS (ground-granulated blast-furnace slag) as a mineral admixture. In this paper, the activity indexes of CNS with different grinding times were studied using CNS to replace a portion of cement. NaOH, Na2SO4, and Na2SiO3 activators were used to study the alkaline solution of the CNS glass phase. The effects of the fineness of CNS and the type of activator on the hydration of ACNCMs were investigated via physical/mechanical grinding and chemical activation. The hydration products of ACNCMs were analyzed via XRD, SEM, FT-IR, TG, and MIP. The results of the study revealed that the activity indexes of CNS ground with different grinding times (10, 30 and 50 min) were 0.662, 0.689, and 0.703, respectively. When Na2SiO3 was used as the activator, the glass phase dissolved the most Si4+, Al3+, and Ca2+, and the respective concentrations in the solution were found to be 2419, 39.55, and 3.38 mg/L. Additionally, the hydration products of ACNCMs were found to have a 28-day compressive strength of up to 84 MPa.