Guosheng Shao

Prediction of amorphous phase stability in the metal–silicon systems

The stability of the amorphous phase with respect to the liquid phase in metal–silicon systems is modeled thermodynamically as a second-order phase transformation. The glass transition temperature of amorphous silicon is estimated according to the experimentally determined heat of crystallization and the Third Law of Thermodynamics. The feasibility of the model has been demonstrated using the Pd–Si, Co–Si, and Au–Si systems as examples. The predicted glass transition temperatures and heat of formation of the amorphous phase are consistent with available experimental data. The predicted amorphization stabilization at low temperatures in the Co–Si systems agrees with experimental observations.

Microwave-assisted growth of In2O3 nanoparticles on WO3 nanoplates to improve H2S-sensing performance

Hierarchical In2O3@WO3 nanocomposites, consisting of discrete In2O3 nanoparticles (NPs) on single-crystal WO3 nanoplates, were synthesized via a novel microwave-assisted growth of In2O3 NPs on the surfaces of WO3 nanoplates that were derived through an intercalation and topochemical-conversion route. The techniques of XRD, SEM, TEM and XPS were used to characterize the samples obtained. The gas-sensing properties of In2O3@WO3 nanocomposites, together with WO3 nanoplates and In2O3 nanoparticles, were comparatively investigated using inorganic gases and organic vapors as the target substances, with an emphasis on H2S-sensing performance under low concentrations (0.5–10 ppm) at 100–250 °C. The results show that the In2O3 NPs with a size range of 12–20 nm are uniformly anchored on the surfaces of the WO3 nanoplates. The amounts of the In2O3 NPs can be controlled by changing the In3+ concentrations in their growth precursors. The In2O3@WO3 (In/W = 0.8) sample has highest H2S-sensing performance operating at 150 °C; its response to 10 ppm H2S is as high as 143, 4 times higher than that of WO3 nanoplates and 13 times that of In2O3 nanocrystals. However, the responses of the In2O3@WO3 sensors are less than 13 upon exposure to 100 ppm of CO, SO2, H2, CH4 and organic vapors, operating at 100–150 °C. The improvement in response and selectivity of the In2O3@WO3 sensors upon exposure to H2S molecules can be attributed to the synergistic effect of In2O3 NPs and WO3 nanoplates, hierarchical microstructures and multifunctional interfaces.

Amorphous-iron disilicide: A promising semiconductor

We report here the synthesis and the measurements of the microstructural and optical properties of a promising semiconductor, amorphous-iron disilicide. The material was obtained by ion-beam mixing of Fe layers on Si, with Ar8+ ions, at 300 °C. Optical absorption measurements indicate a semiconductor with a direct band gap of 0.88 eV. The significance of this discovery is that it demonstrates the existence of such a material. It should be possible to synthesize by other techniques and could be applied in large-area electronics.

Prediction of amorphous phase stability in metallic alloys

The stabilization of the amorphous solid with respect to the high temperature liquid phase is modeled thermodynamically as a second order phase transformation. The model proposed in this work incorporates the thermodynamic description of the high temperature liquid phase, the glass transition temperature, and the maximum entropy of amorphization in an explicit formalism. The predicted heat of formation of the amorphous solid in the Cu–Zr and Ni–Zr systems agrees well with experimentally determined data.

Thermodynamic and kinetic aspects of intermetallic amorphous alloys

The glass transition in metallic alloy systems can be modelled thermodynamically, using the Calphad approach, as a second-order transition from the supercooled liquid phase, giving good predictability for glass transition temperatures and the thermodynamic stability of the amorphous phase in intermetallic alloy systems. The resultant thermodynamic database can also be used for calculating crystallisation temperatures for the glass devitrification, and the Calphad approach is a powerful tool for designing bulk metallic glass alloys.

Spontaneous Growth and Chemical Reduction Ability of Ge Nanoparticles

Forming colloidal solutions containing semiconductor quantum-sized nanoparticles (NPs) with clean surface has been a long-standing scientific challenge. In this contribution, we report a “top-down” method for the fabrication of Ge NPs by laser ablation of a Ge target in deionized water without adding any stabilizing reagents. The initial Ge NPs in amorphous structure showed spontaneous growth behavior by aging Ge colloids in deionized water under ambient temperature, which gradually evolved into a metastable tetragonal structure as an intermediate phase and then transformed into the stable cubic structure, being consistent with the Ostwalds rule of stages for the growth in a metastable system. The laser-induced initial Ge NPs demonstrate a unique and prominent size-dependent chemical reductive ability, which is evidenced by the rapid degradation of organic molecules such as chlorinated aromatic compounds, organic dyes, and reduction of heavy metal Cr(VI) ions.

Hierarchical Fe2O3@WO3 nanostructures with ultrahigh specific surface areas: microwave-assisted synthesis and enhanced H2S-sensing performance

Hierarchical Fe2O3@WO3 nanocomposites with ultrahigh specific areas, consisting of Fe2O3 nanoparticles (NPs) and single-crystal WO3 nanoplates, were synthesized via a microwave-heating (MH) in situ growth process. WO3 nanoplates were derived by an intercalation and topochemical-conversion route, and the Fe2O3 NPs were in situ grown on the WO3 surfaces via a heterogamous nucleation. The water-bath-heating (WH) process was also developed to synthesize a Fe2O3@WO3 nanocomposite for comparison purposes. The techniques of X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the samples obtained. The results show that α-Fe2O3 NPs with a size range of 5–10 nm are uniformly, tightly anchored on the surfaces of WO3 nanoplates in the Fe2O3@WO3 samples obtained via the MH process, whereas the α-Fe2O3 NPs are not uniform in particle-sizes and spatial distribution in the Fe2O3@WO3 samples obtained via the WH process. The BET surface area of the 5wt%Fe2O3@WO3 sample derived by the MH process is as high as 1207 m2 g−1, 5.9 times higher than that (203 m2 g−1) of the corresponding WO3 nanoplates. The dramatic enhancement in the specific surface area of the Fe2O3@WO3 samples should be attributed to the hierarchical microstructure, which makes the internal surfaces or interfaces in aggregated polycrystals be fully outside surfaces via a house-of-cards configuration, where the single-layered and disconnected Fe2O3 NPs are tightly anchored on the surfaces of the WO3 nanoplates. The gas-sensing properties of the Fe2O3@WO3 sensors were investigated. The gas-sensors based on the Fe2O3@WO3 obtained via the MH process show a high response and selectivity to H2S at low operating temperatures. The 5%Fe2O3@WO3 sample shows the highest H2S-sensing response at 150 °C. Its response to 10 ppm H2S is as high as 192, 4 times higher than that of the WO3-nanoplate sensor. The improvement in the gas-sensing performance of the Fe2O3@WO3 nanocomposites can be attributed to the synergistic effect in compositions and the hierarchical microstructures with ultrahigh specific surface areas.

Effect of Chromium and Niobium Doping on the Morphology and Electrochemical Performance of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Material

Undoped, Cr-doped, and Nb-doped LiMn(1.5)Ni(0.5)O4 (LNMO) is synthesized via a PVP (polyvinylpyrrolidone)-combustion method by calcinating at 1000 °C for 6 h. SEM images show that the morphology of LNMO particles is affected by Cr and Nb doping. Cr doping results in sharper edges and corners and smaller particle size, and Nb doping leads to smoother edges and corners and more rounded and larger particles. The crystal and electron structure is investigated by XRD- and synchrotron-based soft X-ray absorption spectroscopy (sXAS). Cr doping and light Nb doping (LiNb(0.02)Ni(0.49)Mn(1.49)O4) improve the rate performance of LNMO. To explore the reason for rate-performance improvement, we conducted potential intermittent titration technique (PITT) and electrochemical impedance spectroscopy (EIS) tests. The Li(+) chemical diffusion coefficient at different state of charge (SOC) is calculated and suggests that both Cr and light Nb doping speeds up Li(+) diffusion in LNMO particles. The impedance spectra show that both R(SEI) and R(ct) are reduced by Cr and light Nb doping. The cycling performance is improved by Cr or Nb doping, and Cr doping increases both Coulombic efficiency and energy efficiency of LNMO at 1 C cycling. The LiCr(0.1)Ni(0.45)Mn(1.45)O4 remains at 94.1% capacity after 500 cycles at 1 C, and during the cycling, the Coulombic efficiency and energy efficiency remain at over 99.7% and 97.5%, respectively.

Ion beam synthesis of superconducting MgB2 thin films

Superconducting MgB2 thin films have been fabricated by 80 keV 11B ion implantation into commercial Mg ribbon with 11B doses up to 1018 ions/cm2, followed by thermal annealing at 500 °C. Temperature dependent dc magnetization measurements confirmed superconducting phase transitions between 11 and 18 K for samples containing nanocrystalline MgB2 grains embedded in Mg substrate with a small amount of MgO inclusion.

Three-dimensional Porous Networks of Ultra-long Electrospun SnO2 Nanotubes with High Photocatalytic Performance

Recent progress in nanoscience and nanotechnology creates new opportunities in the design of novel SnO2 nanomaterials for photocatalysis and photoelectrochemical. Herein, we firstly highlight a facile method to prepare three-dimensional porous networks of ultra-long SnO2 nanotubes through the single capillary electrospinning technique. Compared with the traditional SnO2 nanofibers, the as-obtained three-dimensional porous networks show enhancement of photocurrent and photocatalytic activity, which could be ascribed to its improved light-harvesting efficiency and high separation efficiency of photogenerated electron–hole pairs. Besides, the synthesis route delivered three-dimensional sheets on the basis of interwoven nanofibrous networks, which can be readily recycled for the desirable circular application of a potent photocatalyst system.