MRCI studies on the electronic structure of AlN and AlN, and the electron affinity of AlN

Using multireference configuration-interaction methods and double to triple-zeta basis sets with semidiffuse and polarization functions, potential energies and spectroscopic constants for low-lying doublet, and quartet states of AlN⁻ were calculated. has R_e=3.280 bohr and . lies 0.17 eV above the ground state. Using an estimated electron affinity of 2.1 eV for AlN, four states of AlN⁻ are found to be stable, namely , , , and . Comparisons with the isovalent anions BN⁻ (three stable states) and AlP⁻ (seven stable states) are made. Photo-detachment of an electron from the state of AlN⁻ can lead to an accurate determination of the energy difference between the two close-lying lowest states of AlN, and , predicted here to be 0.09 eV apart.     

Photoisomerization dynamics study on cis-azobenzene derivative using ultraviolet-to-visible tunable femtosecond pulses

We performed the transient absorption measurement and the first rate equation (RE) analysis for cis isomer of 4-carboxy-2′,6′-dimethylazobenzene to clarify the quantitative difference between the photoisomerization process and the thermal relaxation process from the excited state. The RE analysis enabled us to determine the cis-to-trans photoisomerization rate per each pump pulse to be 3% under the condition of the 430 nm, 150 fs pump pulse with energy of 200 nJ. Moreover, the signal due to the yielded trans molecules appearing in the transient absorption was assigned from the following observed result: the transient absorbance change at the 380 nm probe mostly decreased within 300 fs after the 430 nm pulse pumping and then slowly decreased to zero, while the absorbance change at the 350 nm probe had a positive constant component in the over one picosecond time region. The RE analysis showed that this constant component is due to the yielded trans molecules, and its positive value is due to the fact that the absorption cross-section of the -to- transition in their trans molecules is larger than that of the -to- transition in the original cis molecules.     

Electrolytic coloration and spectral properties of OH-doped KBr polycrystals

OH⁻-doped KBr polycrystals were colored electrolytically by using a pointed cathode and a flat anode. Characteristic O⁻, OH⁻, U, Cu⁺ and absorption peaks were observed in resolved absorption spectrum of uncolored polycrystals. Herein the position of the absorption peak at room temperature was determined by using a Mollwo-Ivey plot. Characteristic V₂, V₃, Cu⁺, , I₂ and F spectral bands were observed in Kubelka-Munk functions of colored polycrystals. Current-time curve for electrolytic coloration of an OH⁻-doped KBr polycrystal and its relationship with electrolytic coloration process were given. Formation and conversion of color centers were explained.     

First CRDS-measurements of water vapour continuum in the 940 nm absorption band

Measurements of near-infrared water vapour continuum using continuous wave cavity ring down spectroscopy (cw-CRDS) have been performed at around 10611.6 and . The continuum absorption coefficients for N₂-broadening have been determined to be and at , and and at , respectively.These results represent the first near-IR continuum laboratory data determined within the complex spectral environment in the 940 nm water vapour band and are in reasonable agreement with simulations using the semiempirical CKD formulation.     

Preparation-dependent properties of Ca(Cu,Mn)7O12 CMR materials

Both magnetic ordering temperatures and lattice constants were observed to be a function of preparation temperature for single-phase CaCuMn₆O₁₂ CMR ceramics of the same cation, oxygen composition and crystal structure. It was found for the first time that higher preparation temperatures result in a linear increase of a cubic cell parameter a, , and in a sharp decrease of magnetic ordering temperatures , by about , for quenched samples. High resolution NPD experiments have shown the presence of antisite defects resulting in partial occupation of octahedral (8c) sites by Cu²⁺ at higher preparation temperatures as never assumed for an ideal structure. The data obtained give a new insight to the problem of functional properties reproducibility suggesting stronger requirements for the production control of CMR materials.     

Experimental and theoretical studies on X-ray induced secondary electron yields in Ti and TiO2

Generation of X-ray induced secondary electrons in Ti and TiO₂ was studied from both experimental and theoretical approaches, using X-ray photoelectron spectroscopy (XPS) attached to a synchrotron radiation facility and Monte Carlo simulation, respectively.The experiment revealed that the yields of secondary electrons induced by X-rays (electrons/photon) at photon energies to 4950 and 5000 eV for Ti and TiO₂ are δ_Ti(4950 eV) = 0.002 and δ_Ti(5000 eV) = 0.014 while those for TiO₂ are δTiO₂(4950 eV)=0.003 and δTiO₂(5000 eV)=0.018.A novel approach to obtain the escape depth of secondary electrons has been proposed and applied to Ti and TiO₂. The approach agreed very well with the experimental data reported so far. The Monte Carlo simulation predicted; and while and .An experimental examination on the contribution of X-ray induced secondary electrons to photocatalysis in TiO₂ has also been proposed.     

L to M shell transitions and model comparisons for radiative opacities of sodium fluoride plasma

The radiative opacities of hot dense sodium fluoride (NaF) plasma have been studied in the case of local thermodynamic equilibrium (LTE). The spectrally resolved opacity in the case of and is taken as an example to illustrate the absorption structures of the NaF plasma. The transitions from L to M shells of sodium and fluoride are the main contributions for the plasma absorptions. The isodense opacities of NaF plasma are studied at a density of and temperatures of 20-60 eV. Detailed comparisons among the results of the detailed term accounting (DTA), detailed configuraion accounting (DCA), unresolved transition array (UTA) and average atom (AA) model codes, which have been developed independently in China in the past few years, are performed for both the spectral resolved and mean opacities. Good agreements are found at a temperature of 40 eV and a density of , but discrepancies appear at a temperature of 50 eV and a density of .     

Hydrothermal synthesis of ZnO nanobelts and gas sensitivity property

The ZnO nanobelts were synthesized by a hydrothermal method. The XRD spectrum indicates that the sample is wurtzite (hexagonal) structured ZnO with lattice constants of , . SEM and TEM images show the nanobelts to have lengths of 10-20 μm, widths of 50-500 nm, thicknesses of about 30-60 nm, and growth direction of [0001]. Gas sensitivity experiments on ZnO nanobelts were carried out under different temperatures. The results indicated high sensitivities with an operating temperature of only 220 ^°C for the oxidative gas O₂, and 305 ^°C for the gas N₂. The mechanism of gas sensitive effects is analyzed in detail.     

High-temperature UV absorption of methyl radicals behind shock waves

The absorption of ultraviolet narrow-line laser radiation by methyl radicals (CH₃) in the electronic system has been studied at high temperatures behind shock waves. Methyl radicals at high temperatures were generated by the shock heating of methyl precursors: azomethane, methyl iodide, and ethane. The spectral shape and intensity of the broadband absorption feature from 211.5 to 220 nm at high temperature (1565 K) has been measured. The absorption coefficient of CH₃ at 216.62 nm, the wavelength of peak absorption at high temperatures in the P+Q band, has been determined from 1200 to 2500 K. Additionally, the absorption coefficients of several interfering UV-absorbing combustion species (, and C₃H₆) have been determined at 216.62 nm.     

Near-infrared diode laser spectroscopy of the HCSi radical

The , , and band spectra of HCSi radical were investigated by means of near-infrared diode laser spectroscopy to determine precise molecular constants for the and states. The detailed analysis of the rotationally resolved band spectra, studied for the first time in the present investigation, leads to the precise determination of molecular constants for the state associated with the Renner-Teller interaction. We obtained −0.15126663(53) and 495.00698(30) cm⁻¹ as the Renner-Teller parameter ε and the bending vibrational frequency ω₂, respectively. Based on the molecular constants for the and states, the rotational levels of the state were analyzed to obtain molecular constants and information on upper state perturbations. Using the available spectroscopic data, valence force fields for both the and states were estimated to aid in understanding the vibrational energy levels of the HCSi radical.     

First-principles study of arsenic impurity clusters in molecular beam epitaxy (MBE) grown HgCdTe

The understanding of the microstructures of the arsenic tetramer , dimer , and singlet of HgCdTe is important to explain the high electrical compensation of molecular beam epitaxy (MBE) samples and the conversion to p-type behavior. The stable configurations were obtained from the first-principles calculations for the arsenic cluster defects [ (n=1, 2, and 4)] in as-grown HgCdTe. According to the defect formation energies calculated under Te-rich conditions, the most probable configurations of , , and have been established. For the optimized and the energy is favorable to combine in a nearest neighboring mercury vacancy , and the corresponding configurations can be used to explain the self-compensated n-type characteristics in as-grown materials. is likely to be more abundant than in as-grown materials, but arsenic atoms are more strongly bounded in than in , thus more substantial activation energy is needed for than that for . The atomic relaxations as well as the structural stability of the arsenic defects have also been investigated.     

Surface phase diagram and temperature induced phase transitions of Sn/Cu(1 0 0)

Room temperature deposition of Sn on Cu(1 0 0) gives rise to a rich variety of surface reconstructions in the submonolayer coverage range. In this work, we report a detailed investigation on the phases appearing and their temperature stability range by using low-energy electron diffraction and surface X-ray diffraction. Previously reported reconstructions in the submonolayer range are p(2 × 2) (for 0.2 ML), p(2 × 6) (for 0.33 ML), ()R45° (for 0.5 ML), and c(4 × 4) (for 0.65 ML). We find a new phase with a structure for a coverage of 0.45 ML. Furthermore, we analyze the temperature stability of all phases. We find that two phases exhibit a temperature induced reversible phase transition: the ()R45° phase becomes ()R45° phase above 360 K, and the new phase becomes p(2 × 2) also above 360 K. The origin of these two-phase transitions is discussed.