A numerical simulation of machining glass by dual CO2-laser beams

In the flat panel display (FPD) industry, lasers may be used to cut glass plates. In order to reduce the possibility of fracture in the process of cutting glass by lasers, the thermal stress has to be less than the critical rupture strength. In this paper, a dual-laser-beam method is proposed, where an off-focus CO₂-laser beam was used to preheat the glass sample to reduce the thermal gradients and a focused CO₂-laser beam was used to machine the glass. The distribution of the thermal stress and the temperature was simulated by using finite element analysis software, Ansys. The thermal stress was studied both when the glass sample was machined by a single CO₂-laser beam and by dual CO₂-laser beams. It was concluded that the thermal stress can be reduced by means of the dual-laser-beam method.     

First-principles calculations on the role of Ni-doping in Cun clusters: From geometric and electronic structures to chemical activities towards CO2

First-principles calculations have been applied to investigate the role of Ni-doping in modifying the geometric and electronic structures of Cu_n clusters (n=1-12), and the chemical activity of clusters towards CO₂. The results reveal that Ni-doping introduces a significant modulation of the electronic structures, such as the density of states, HOMO-LUMO gaps and the d-band centers, which dominate their chemical activities towards CO₂ adsorption. Our findings contribute valuable information for high efficient Cu-Ni alloy nano-catalyst design.     

Planar nano-block structures Tin+1Al0.5Cn and Tin+1Cn (n = 1, and 2) from MAX phases: Structural,electronic properties and relative stability from first principles calculations

Structural, electronic properties and relative stability of quasi-two-dimensional (2D) free-standing planar nano-block (NBs) structures Ti_n+1Al_0.5C_n and Ti_n+1C_n (n = 1 and 2), which can be prepared using the recently developed procedure of exfoliation of corresponding NBs from MAX phases, were examined within first principles calculations in comparison with parent MAX phases Ti₃AlC₂ and Ti₂AlC. We found that in general Ti_n+1C_n and Ti_n+1Al_0.5C_n NBs retain the atomic geometries of the corresponding blocks of the MAX phases, but some structural distortions for the NBs occur owing to the lowering of the coordination number for atoms in the external Ti sheets of the nano-block structures. Our analysis based on their cohesive and formation energies reveals that the stability of the nano-block structures increases with index n (or, in other words, with a growth of the number of Ti–C bonds), the Al-containing NBs becoming more stable than the “pure” Ti–C NBs. Our data show that the magnetization of the simulated planar nano-block structures can be expected; so, for the Ti₃C₂ nano-block the most stable will be the spin configuration, where within each external Ti sheet the spins are coupled ferromagnetically together with antiferromagnetic ordering between opposite external titanium sheets of this nano-block.     

第三族金属氧化物离子对二氧化碳转化的红外光谱研究

本文利用红外光解离光谱研究了第三族金属氧化物离子对二氧化碳分子的转化机制. 研究表明,对于[ScO(CO₂)_n]⁺体系,在n≤4时,形成了溶剂化结构;在n=5时,形成了碳酸盐结构,实现了二氧化碳的转化. 对于[YO(CO₂)_n]⁺体系,需要4个二氧化碳分子就可以实现二氧化碳的转化. 而在[YO(CO₂)_n]⁺体系中,只发现了溶剂化结构,没有观察到碳酸盐结构. 理论计算表明,[YO(CO₂)_n]⁺体系拥有最小的溶剂化结构向碳酸盐结构转化能垒,[LaO(CO₂)_n]⁺体系拥有最大的溶剂化结构向碳酸盐结构转化能垒. 本文从分子水平揭示了不同金属氧化物离子对二氧化碳分子转化的影响规律.     

CO-laser photoacoustic detection of phosgene (COCl2)

Detection of COCl₂, a highly toxic gas in chemical industry, using laser photoacoustic spectroscopy is presented. The spectrophone system used has a broad band LN₂ cooled CW CO laser as a source of radiation, which operates from 4.8–8.4 um in the mid-infrared. Using an extracavity open longitudinal resonant cell, absorption signals to about 30 CO laser lines in the 5.45 um region could be observed. detection sensitivity has been estimated to be ppb order.This work has been supported by the NSFC     

Investigation of chemical decomposition of CCl4 on TiO2 near room temperature

Dissociative adsorption of CCl₄ on TiO₂ at 35 °C has been studied by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance. CCl₄ decompose to form CO, CO₂, and CO₃ on the surface, at such a low temperature, in which CO₂ formation is not from CO oxidation on TiO₂, but CO₃ can be produced by CO and CO₂ adsorption. The Cl generated from CCl₄ decomposition is left on the surface and bonded to titanium ions. Mineralization of CCl₄ on TiO₂ involves the lattice oxygens. Thermodynamical driving force and possible reaction routes for CO and CO₂ formation in the CCl₄ decomposition on TiO₂ are discussed.     

Far infrared stimulated emissions from CO2 laser excited dichloromethane

Six new far-infrared laser frequencies have been obtained in CO₂-laser excited dichloromethane. Competing transitions have enabled assignments to be made to the v₇ band.     

Laser spectroscopic monitoring of gas emission and measurements of the C/C isotope ratio in CO2 from a wood-based combustion

We report on the application of a compact and field-deployable instrument, based on a continuous-wave fiber-coupled Telecom external cavity diode laser, to measure the ¹³C/¹²C isotope ratio in CO₂ from a wood-based combustion. Carbon dioxide, the most important greenhouse gas, is a major product of combustion. The measurements of the ¹³C/¹²C isotopic ratio in CO₂ from combustion emission permit one to identify the CO₂ source and to study the temporal and spatial variations of pollution in the atmosphere. The average value of the ¹³CO₂/¹²CO₂ ratio is found to be (1.1011±0.0024)%. The corresponding δ-value relative to PDB standard is (−20.17±2.14)‰, which is in good agreement with the typical value of (−25±2)‰ for wood. Simultaneous monitoring of multiple species from gas emission has been performed using direct-absorption spectroscopy. The concentrations of C₂H₂, CO, CO₂ and H₂O were determined on the basis of integrated absorbance measured by least-squares fitting a Voigt lineshape to experimental absorption spectra.     

Far-Infrared Laser Assignments for Methylamine

Reported far-infrared laser lines for five different transition systems of CH₃NH₂ optically pumped by a CO₂ laser have been identified spectroscopically through a high-resolution Fourier transform infrared study of the C-N stretching band together with CO₂-laser/microwave-sideband broad-scan and Lamb-dip measurements. From the infrared analysis plus previous far-infrared (FIR) results for the ground vibrational state, quantum numbers have been assigned for seven methylamine FIR laser transitions and their C-N stretching pump absorptions coincident with the CO₂ laser lines. The assignments are confirmed through the use of closed frequency combination loops that also provide improved FIR laser frequencies to spectroscopic accuracy.     

Characterization of mesoporous VOx/MCM-41 composite materials obtained via post-synthesis impregnation

Spherical-particle MCM-41 was synthesized at room temperature, and, then, impregnated with aqueous solutions of NH₄VO₃ to produce variously loaded VO_x/MCM-41 composite materials. Bulk and surface properties of the materials thus produced were characterized by means of X-ray powder diffractometry (XRD), infrared spectroscopy (FTIR), N₂ sorptiometry and X-ray photoelectron spectroscopy (XPS). Results obtained indicated that subsequent calcination at 550 °C (for 2 h) of the blank and impregnated MCM-41 particles, results in materials assuming the same bulk structure of MCM-41, and exposing uniformly mesporous, high area surfaces (P_w = 2.0-2.3 nm; 974-829 m²/g), except for the material obtained at 20 wt%-V₂O₅ that was shown to suffer a considerable loss on surface area (down to 503 m²/g). XPS results implied that the immobilization of the VO_x species occurs via interaction with surface OH/H₂O groups of MCM-41, leading to the formation of vanadate (VO₃⁻) surface species, as well as minor V-O-Si and V₂O₅-like species. However, in all cases, the vanadium sites remained pentavalent and exposed on the surface.     

A novel demonstration of photoacoustic Raman spectroscopy with combined stimulated Raman pumping in H2 molecule

We present the experimental demonstration of a novel, efficient, and vibrational selective technique to prepare population in vibrational level v″ = 1 using the stimulated Raman pumping. Photoacoustic Raman signal has been studied in non-radiative transitions in the molecule H₂ (v″ = 0) and (v″ = 1). The population fraction in the v″ = 1 level can be estimated by using combined photoacoustic Raman spectroscopy with stimulated Raman pumping for the first time.     

Effect of nitrogen content on the properties of CrNxOyCz coating prepared by DC reactive magnetron sputtering

The CrN_xO_yC_z coatings were deposited by planar DC reactive magnetron sputtering onto AZ31 Mg alloy and high speed tool steel (HSTS) substrates at a substrate temperature of 200 °C. The effect of N₂ content on composition and structure of the CrN_xO_yC_z coatings was investigated. The structure of the CrN_xO_yC_z coatings was analyzed by a glancing angle X-ray diffraction (GXRD). The cross-section morphology and thickness of the CrN_xO_yC_z coatings were checked by a field emission scanning electron microscope (FESEM), and the composition profile and chemical state were carried out by an X-ray photoelectron spectroscopy (XPS). The experimental results showed that the structure and phase composition of the CrN_xO_yC_z coatings depended on N₂ content. The evolution of the structure of CrN_xO_yC_z coatings was consistent with CrN_x-based coatings, and the CrN_xO_yC_z coatings contained Cr₂O₃, CrO₂, CrO, Cr₃C₂, CrN_x (Cr, CrN, Cr₂N), as well as different chromium oxynitride. However, the carbide and oxynitride were oxidized after annealing.     

Observation of the K2 4Δg state by cw perturbation-facilitated optical-optical double resonance spectroscopy

This paper reports for the first time both, an experimental observation and theoretical calculations of the K₂ 4³Δ_g state. For the experiment we used cw perturbation-facilitated optical-optical double resonance (PFOODR) spectroscopy. A single mode Ti-sapphire laser and a dye laser served as the pump and probe lasers, respectively. A total of 55 PFOODR signals have been assigned to the 4³Δ_g ← b³Π_u transitions. Absolute vibrational numbering was determined by using quantum defect analysis combined with comparing observed intensities with calculated Franck-Condon factors (FCF). For the former we used known parameters from the 2³Δ_g state since the 2³Δ_g and the 4³Δ_g states belong to the same Rydberg series. We report here our experimental and calculated spectroscopic constants, the corresponding RKR potential energy curve, the Franck-Condon table for the 4³Δ_g ↔ b³ Π_u system, as well as a comparison with the theoretical potential energy curve. The T_e value is found to be 28408.938(52) cm⁻¹.     

In situ Raman spectroscopy of phase transformation in CrOx-Y2O3 system at elevated temperatures

A CrO_x-Y₂O₃ sample was prepared by a deposition-precipitation method and phase transformation of the sample under N₂ and air atmospheres was characterized by in situ Raman spectroscopy and X-ray diffraction (XRD) techniques. It was found that when the CrO_x-Y₂O₃ sample was heated, CrO₃ transformed to YCrO₄ and then to YCrO₃ and Cr₂O₃. Also, the transformation started from the surface region of the sample and then extended to the bulk, due to the fact that the phase transformation was detected by Raman spectroscopy at lower temperature compared to that by XRD. In addition, both atmosphere and temperature had influence on the phase transformation in the surface region, while the phase transformation in the bulk was merely dependent on the temperature. It was also found that low oxidation state Cr(III) species on the surface could be re-oxidized to high oxidation state Cr(V) or Cr(VI) species when the thermal treated sample was exposed to ambient air.     

Effects of Li2CO3 on the sintering behavior and piezoelectric properties of Bi2O3-excess (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramics doped with Li₂CO₃ and Bi₂O₃ as sintering aids were manufactured, and their micro structural, dielectric and piezoelectric properties were investigated. All specimens could be well sintered at a low-temperature of 1080 °C. The bulk density of the specimens doped with a small amount of Li₂CO₃ was enhanced. The dielectric and piezoelectric properties of ceramics were investigated with different amounts of Li₂CO₃ substitutions. High electrical properties of d₃₃ = 167 pC/N, k_p = 0.34, P_r = 40 μC/cm² and E_c = 38 kV/cm were obtained from the specimen containing 0.1 mol% of Li₂CO₃ sintered at 1080 °C.     

Thermal expansion and magnetostriction in Pr(n+2)(n+1)Nin(n−1)+2Sin(n+1) compounds

Thermal expansion and magnetostriction of members of a homologous series of compounds based on the alloy series Pr_(n+2)(n+1)Ni_n(n−1)+2Si_n(n+1) have been measured. The crystal structures of these compounds are closely interrelated because they form trigonal prismatic columns in which the number of trigonal prisms that form the base of the trigonal columns is determined by the value of n in the chemical formula. Two compositions were investigated, Pr₅Ni₂Si₃ and Pr₁₅Ni₇Si₁₀, corresponding to n=3$n=3$ and n=4,$n=4,$ respectively. The results were analyzed and used to determine the location of magnetic phase transitions by calculating the magnetic contribution to thermal expansion using the Gruneisen–Debye theory. This allowed more precise determination of the magnetic transition temperatures than could be achieved using the total thermal expansion. The results show two phase transitions in each material, one corresponding to the Curie temperature and the other at a lower temperature exhibiting characteristics of a spin reorientation transition.     

Diode laser absorption spectroscopy measurement of linestrengths and pressure broadening coefficients of the methane 2ν3 band at elevated temperatures

A diode laser sensor based on absorption spectroscopy has been developed for the measurement of spectroscopic parameters in the R (3) and R (4) manifolds of 2ν₃ band of CH₄. Individual linestrengths of each transition are determined for a range of temperatures. In addition, collision-broadened half-widths for CO₂, N₂, H₂O, CH₄, and CO collision partners are measured as a function of temperature and pressure for these strongly overlapped transitions. From this, temperature dependence of the collision half-width for each collision partner is determined. Using a new method for calculation of collisional broadening at high temperatures for strongly overlapped transitions makes these transitions accessible for spectroscopy.     

Methyl concentration time-histories during iso-octane and n-heptane oxidation and pyrolysis

Methyl radical concentration time-histories were measured during the oxidation and pyrolysis of iso-octane and n-heptane behind reflected shock waves. Initial reflected shock conditions covered temperatures of 1100-1560 K, pressures of 1.6-2.0 atm and initial fuel concentrations of 100-500 ppm. Methyl radicals were detected using cw UV laser absorption near 216 nm; three wavelengths were used to compensate for time- and wavelength-dependent interference absorption. Methyl time-histories were compared to the predictions of several current oxidation models. While some agreement was found between modeling and measurement in the early rise, peak and plateau values of methyl, and in the ignition time, none of the current mechanisms accurately recover all of these features. Sensitivity analysis of the ignition times for both iso-octane and n-heptane showed a strong dependence on the reaction C₃H₅ + H = C₃H₄ + H₂, and a recommended rate was found for this reaction. Sensitivity analysis of the initial rate of CH₃ production during pyrolysis indicated that for both iso-octane and n-heptane, reaction rates for the initial decomposition channels are well isolated, and overall values for these rates were obtained. The present concentration time-history data provide strong constraints on the reaction mechanisms of both iso-octane and n-heptane oxidation, and in conjunction with OH concentration time-histories and ignition delay times, recently measured in our laboratory, should provide a self-consistent set of kinetic targets for the validation and refinement of iso-octane and n-heptane reaction mechanisms.     

The effect of PVA (Bi2O3-doped) interfacial layer and series resistance on electrical characteristics of Au/n-Si (110) Schottky barrier diodes (SBDs)

Two types of Schottky Barrier Diodes (SBDs) with and without PVA (Bi₂O₃-doped) polymeric interfacial layer, were fabricated and measured at room temperature in order to investigate the effects of the PVA (Bi₂O₃-doped) interfacial layer on the main electrical parameters such as the ideality factor (n), zero-bias barrier height (Φ_B0), series resistance (R_s) and interface-state density (N_ss). Electrical parameters of these two diodes were calculated from the current-voltage (I-V) characteristics and compared with each other. The values of Φ_B0, n and R_s for SBDs without polymeric interfacial layer are 0.71 eV, 1.44 and 4775 Ω, respectively. The values of Φ_B0, n and R_s for SBDs with PVA (Bi₂O₃-doped) polymeric interfacial layer are 0.74 eV, 3.49 and 10,030 Ω, respectively. For two SBDs, the energy density distribution profiles of interface states (N_ss) were obtained from forward-bias I-V measurements by taking the bias dependence of R_s of these devices into account. The values of N_ss obtained for the SBD with PVA (Bi₂O₃-doped) polymeric interfacial layer are smaller than those of the SBD without polymeric interfacial layer.     

Optoacoustic Laser Stark spectroscopy and FIR laser action on CH3Br using a waveguide CO2 laser

The optoacoustic spectrum of CH₃Br around 10 m band lines of a tunable cw waveguide CO₂ laser is investigated. Several new infrared absorptions are observed and most of the correspond ing molecular transitions are assigned. Far infra red laser action is reported by pumping with the same CO₂ laser: pump offsets are given using the Transferred Lambs dip (TLD) technique. A new FIR laser emission is obtained and assigned. An optoacoustic Laser Stark spectroscopy technique is used to investigate off resonance infrared tran sitions.