Measurement of wurtzite ZnO/rutile TiO2 heterojunction band offsets by x-ray photoelectron spectroscopy

Four novel dmit complexes: [(C₂H₅)₄N][Ni (dmit)₂], [(C₃H₇)₄N][Ni(dmit)₂], [(C₂H₅)₄N][Au(dmit)₂] and [(C₃H₇)₄N][Au(dmit)₂], abbreviated as EtNi, PrNi, EtAu, and PrAu, were synthesized. The third-order nonlinear optical properties of them in acetonitrile solutions were investigated by using the Z-scan technique with 20 ps pulses width at 1064 nm. When the on-axis irradiance at focus I ₀ was 5.025 GW/cm², the nonlinear refraction coefficient n ₂, the third-order nonlinear susceptibility χ ⁽³⁾, the molecular second-order hyperpolarizability γ of the four types of material were obtained with subject to Z-scan curves, and these indexes were with the magnitudes of 10⁻¹⁸ m²/W, 10⁻¹³ esu, and 10⁻³¹ esu, respectively. The nonlinear absorption coefficient β of Ni samples had the 10⁻¹² m/W scale. The impact of different metals and cations on the third-order nonlinear optical properties of materials was analyzed. Through the derivation, the result suggests that these dmit complexes are promising candidates for applications to nonlinear optical devices manufacture in the near-infrared waveband.     

Measurement of GaN/Ge（001） Heterojunction Valence Band Offset by X-Ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset （VBO） at the GaN/Ge heterostructure interface. The VBO is directly determined to be 1.13 ±0.19 eV, according to the relationship between the conduction band offset AEc and the valence band offset △Ev：△Ec =EgGaN -EgGe - △Ev, and taking the room-temperature band-gaps as 3.4 and 0.67eV for GaN and Ge, respectively. The conduction band offset is deduced to be 1.6±0.19 eV, which indicates a type-I band alignment for GaN/Ge. Accurate determination of the valence and conduction band offsets is important for the use of GaN/Ge based devices.     

Decline of nucleation in the heating process with a high heating rate

The effect of the heating rate on the nucleation of metallic glass in a rapid heating process starting from the glass transition temperature is investigated. The critical nucleus radius increases with the increase of the temperature of the undercooling liquid. If the increment rate of the critical nucleus radius, owing to the heating process, is higher than the growth rate of the nuclei, the nuclei generated at the low temperature will become the embryos at the high temperature. This means that the high heating rate can make no nucleation happen in the heating process. In consideration of the interfacial energy, the growth rate of the nuclei increases with the increase of their size and the growth rate of the critical nucleus is zero. Thus, the lower heating rate can also make the nuclei decline partially. Finally, this theory is used to analyze the nucleation process during laser remelting metallic glass.