Etching of mercuric iodide in cation iodide solutions

The surface properties of mercuric iodide after etching in various cation iodide solutions have been investigated in terms of dissolution rate, morphology, electrical properties and reaction with water vapour. No significant differences have been observed in the etching rates. However, dissolution of HgI₂ in NH₄I, NaI, KI or RbI leaves the surface more or less covered with a residual iodo mercurate compound whose electrical properties and stability with regard to humidity may noticeably influence the behaviour of mercuric iodide devices. The smallest effect has been observed for etching in NaI.     

Synthesis of β-Ga2O3 nanowires through microwave plasma chemical vapor deposition

In this study, we demonstrate the large-scale synthesis of beta gallium oxide (β-Ga₂O₃) nanowires through microwave plasma chemical vapor deposition (MPCVD) of a Ga droplet in the H₂O and Ar atmosphere at 600 W. Unlike the commonly used MPCVD method, the H₂O, not mixture of gas, was employed to synthesize the nanowires. The ultra-long β-Ga₂O₃ nanowires with diameters of about 20-30 nm were several tens of micrometers long. The morphology and structure of products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM). The growth of β-Ga₂O₃ nanowires was controlled by vapor-solid (VS) crystal growth mechanism.     

Vacuum ultraviolet photoionization of the 5d elements in the region of the 5p and 4f excitation

The results of recent VUV photoionization experiments of the 5d elements Ta, W, Re, Ir and Pt using atomic beam technique, excitation with monochromatized synchrotron radiation and detection of singly and doubly charged photoions are discussed. Special attention is given to the resonances caused by discrete transitions of the 5p and 4f electrons into the unfilled 5d subshells. As there is a crossover of the 5p and 4f levels along the series of the 5d elements the result is a complicated structure of the corresponding interacting resonances. The photoion spectra are compared with theoretical calculations carried out within the relativistic time dependent local density and the relativistic Hartree-Fock approximation. Received: 9 October 1997 / Accepted: 3 November 1997     

Recent results on Auger resonant Raman spectroscopy of free atoms and molecules

Accepted: 6 March 1997     

Relativistic and correlation effects in the anisotropy of near-threshold Kr 3d and Xe 4d photoionization

Angular distributions of the spin–orbit split components and their branching ratios have been studied experimentally and theoretically for the 3d photoelectrons of Kr and 4d photoelectrons of Xe. The focus was on the electron dynamics near the ionization threshold of each spin–orbit split component and its behaviour as a function of Z   in passing from Kr to Xe. The experimental spectra were measured with high photon and electron energy resolutions with photon energies at about 3–12 eV above the 3d_3/2$3{\text{d}}_{3/2}$ and 3d_5/2$3{\text{d}}_{5/2}$ thresholds for Kr and at about 5–12 eV above the Xe 4d_3/2$4{\text{d}}_{3/2}$ and 4d_5/2$4{\text{d}}_{5/2}$ thresholds. Experimental results for the angular distribution parameters have been compared with theoretical values obtained with relativistic Dirac–Fock method and results from independent particle approximation with a modified Hartree potential [A. Derevianko, W. Johnson, K. Cheng, Atom. Data Nucl. Data Tables 73 (1999) 153]. The branching ratios were compared with theoretical predictions from Dirac–Fock and relativistic random-phase approximation [K. Cheng, W. Johnson, Phys. Rev. A 28 (1983) 2820].     

Isothermal nanocrystallization kinetics during polymorphic transformation

The experimental value of Avrami exponent during polymorphic nanocrystallization deviates from the theoretical prediction of the Kolmogorov-Johnson-Mehl-Avrami (KJMA) isothermal kinetics. The assumption of negligible nuclei volume, implicit in KJMA, is violated for all such transformations involving nano-sized grains. A discrete adaptation of the KJMA model is used to study the effect of the non-zero nuclei volume on nanocrystallization kinetics. Transformations initiated by homogeneous and heterogeneous nucleation are analyzed under constant nucleation and growth rate conditions. For homogeneous nucleation, a universal scaling relation with respect to finite nuclei size is found. In contrast to this, for the heterogeneous case a series of linear scaling relations are observed with respect to the nucleation conditions.     

Structural and electrical transport properties of Nb-doped TiO2 films deposited on LaAlO3 by rf sputtering

We have investigated the structural and electrical transport properties of Nb-doped TiO₂ films deposited on (1 0 0) LaAlO₃ substrates by rf magnetron sputtering at temperatures ranging from 873 K to 1073 K. Films deposited below 998 K are anatase, and mixed phases between anatase and rutile exist in the film grown at higher temperatures. We find that films deposited at low temperatures exhibit semiconductor behavior, while metallic conductivity is observed in the most conducting film deposited at 998 K. For this sample, compared to electron-phonon scattering mechanism, electron-phonon-impurity interference effect plays an important role in its electron transport process. Moreover, the temperature coefficient of the resistivity for the film deposited at 1073 K is negative from 2 K to 300 K. The temperature dependence of resistivity for the film is described by ∼exp(b/T)^1/2 at temperatures from 80 K down to 30 K, and by the fluctuation induced tunneling model from 80 K to 300 K.     

Facile synthesis and phase control of copper chalcogenides with different morphologies

A series of stoichiometric and nonstoichiometric copper–chalcogenide nanocrystallines with different morphologies, e.g., extremely high aspect ratio nanofibers (Cu₉S₈), tubular structure (Cu _x S (x=∼1.86–1.96), nanorods (CuS, Cu₃₁S₁₆), platelets (β-CuSe, Cu₃Se₂), rope-like Cu₃Se₂, as well as spherical nanoparticles (Cu₇Se₄, Cu_2−x Se), have been successfully synthesized in 20 vol% water and 80 vol% organic solvents mixture under mild conditions. The products were characterized by various techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electronic diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). The studies of the optical properties revealed that the copper chalcogenides have a wide absorption in the range of about 400–700 nm, with accessional IR band. Systematic studies showed that the mixture of 20 vol% water and 80 vol% organic solvents played a key role in controlling the copper chalcogenides with different morphologies and phases.     

Luminescence properties of β-FeSi2 and its application to photonics

We have investigated the photoluminescence properties of β-FeSi₂ and have subsequently reported many studies on the enhancement of luminescence efficiency. We have further discussed a limit for the luminescence efficiency based on the weak confinement theory of excitons in β-FeSi₂ nanocrystals. Moreover, we have reported an application of β-FeSi₂ with a high refractive index to photonic crystals.