Rate constant of free electron-hole recombination in thin cadmium sulfide films

The transient decay kinetics of electrons generated in thin cadmium sulfide films by short laser pulses was studied by the microwave photoconductivity method (9 and 36 GHz) at 295 K. The films were prepared by the pulverization method from thiocarbamide coordination compounds. At the high light intensity I ₀ > 10¹⁴ photon cm^–2 per pulse, the decay kinetics of photoelectrons corresponded to a reaction of the second order. Analysis of the kinetic data made it possible to determine the rate constant of recombination of free electrons and holes: k ₃ 2(±1)·10^–13 cm³ s^–1.     

Rate constant of the recombination of free electrons and holes in AgCl at 295 K

The transient kinetics of the loss of electrons generated by light pulses in powdered AgCl has been studied by the microwave photoconductivity method (36 GHz) at 295 K. At high light intensities,I ₀ > 10¹⁴ photon cm^–2 per pulse, the kinetics obeys the second-order law. The rate constant of the recombination of free electrons and holes is equal to 2·10^–12 cm³ s^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2234–2236, September, 1996.     

Experimental determination of the dependence of the free electron—hole recombination rate constant on the band gap in semiconductors of the AIIBVI and AIBVII types

A correlation between the recombination rate constant of free electrons and holes (k _r) and the band gap (E _g) of semiconductors (AgCl, AgBr, Cd_xZn_1−x S, CdSe, CdTe, and their solid solutions) at 295 K was found. The experimental data were obtained by the UHF photoconductivity (36 GHz) using current carrier generation by laser pulses (λ = 337 nm, pulse duration 8 ns). A decrease in E _g in a range of 1.5–3 eV increases k _r by 1.5 orders of magnitude according to the law close to exponential. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 856–860, May, 2007.     

Chemical surface deposition and growth rate of thin CdSe films

Chemical surface deposition of thin CdSe films was studied. The conditions for preparing thin films were examined, the degrees of Cd conversion in the starting compounds were determined, and the film thicknesses were measured.     

Determination of propagation‐rate constant of vinylidene chloride by emulsion polymerization

The propagation‐rate constant of vinylidene chloride (VDC) was determined at 40 and 50 °C, respectively, by applying the so‐called Ugelstad plot to the polymerization‐rate data of the seeded and unseeded emulsion polymerizations of VDC. The values of the propagation‐rate constant k_p thus determined are k_p = 64 dm³/mol · s at 50 °C and k_p = 52 dm³/mol · s at 40 °C, respectively. From these k_p values, the activation energy for propagation reaction was determined to be E_p = 4.2 kcal/mol, which is close to that of vinyl chloride (3.7 kcal/mol). © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1005–1015, 2001     

Estimation of activation parameters for the propagation rate constant of styrene

For a temperature range of −11.8–92.6°C, the propagation rate constant k_p of styrene has been determined with the use of pulsed-laser polymerization (PLP). The temperature dependency of the obtained k_p data was evaluated using the Arrhenius equation. The NLLS error-in-variables method (EVM) is recommended for this fit. The resulting activation energy is 32.6 kJ mol⁻¹ and the pre-exponential factor is 10^7.66 dm³ mol⁻¹ s⁻¹. A joint confidence interval for these parameters is given. © 1996 John Wiley & Sons, Inc.     

On the Validity of the Steady-State Approximation in Non-Isothermal Kinetics: Part IV. The case of constant rate thermal analysis

The paper investigates the validity of steady-state approximation for the case of constant rate thermal analysis experiments. It is shown that the approximation holds for the experiments run with a controlled rate of either the decomposition of the compound, or the production of gas.This revised version was published online in November 2005 with corrections to the Cover Date.     

Dissociative recombination of electrons and molecular ions

The existing techniques for the calculation of the dissociative recombination (DR) of electrons and molecular ions were compared. The advantages of the method of multichannel quantum defect (MQD), in which equations are formulated directly for the T-matrix of collisions and the unitarity of the scattering S-matrix is thus ensured, were demonstrated. The effect of molecular rotation and of the nonadiabatic electron-rotation coupling on the e^– + H₂ ⁺ , H* + H reaction was investigated. A procedure was suggested based on the use of the adiabatic approximation (with respect to the nuclear rotation) in the near-threshold area while taking into account the contributions of the excited vibronic states of the Rydberg complex formed in an intermediate stage of the reaction. It is notable that the partial rate constants (and the corresponding cross-sections) arc very sensitive to the initial rotation excitation. However, the temperature-averaged rate constants under equilibrium conditions are only slightly affected by rotation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1336–1348, June, 1996.     

三氯乙烷与氟原子的反应机理研究和速率常数计算

采用双水平直接动力学方法研究了反应CH3CCl3+F→CH2CCl3+HF的反应机理和动力学性质;在MPW1K/6-311+G(d,p)水平上优化了所有稳定点的几何构型,并通过频率分析进行了验证;随后在MCG3-MPWPW91//MPW1K水平上进行了能量校正,并利用变分过渡态理论,在MCG3-MPWPW91//MPW1K/6-311+G(d,p)水平上计算了反应在200～2 000K温度区间内的速率常数.结果表明,反应物CH3CCl3属于Cs点群,-CH3基团上的3个H原子等同,反应存在单个氢迁移反应通道.     

Self-assembly and optical properties of water-soluble porphyrin alternating CdSe nanoparticulate films

A new type of self-assembled film was prepared by alternating deposition of oppositely charged meso-tetra-(4-trimethylaminophenyl) porphyrin nickel iodide (NiTAPPI) and citrate-stabilized CdSe nanoparticles. The stepwise deposition process was monitored by means of UV–vis spectroscopy. The interaction between the porphyrin and CdSe nanoparticles was characterized with UV–vis and fluorescence spectra. The SEM images showed the formation of densely packed two-dimensional array and the conversion of disorder-to-order of CdSe nanoparticles on the quartz substrate modified by PDDA when depositing positively charged NiTAPPI. The self-assembled film placed in ambient air exhibited significant enhancement of fluorescence intensity. The effects of heat treatment and UV-light irradiating on fluorescence properties of the composite films were investigated in details.     

The inelastic mean free paths of auger electrons in thin films of copper and nickel

The inelastic mean free paths of 600–1000 eV Auger electrons have been determined in Cu and Ni films. Thin films of known thickness were produced by the vapor deposition of Cu on Ni substrates and vice versa. The strengths of the characteristic Auger signals of Cu and Ni were monitored as a function of film thickness. Values of the mean free paths are presented and compared to values previously published by other workers. By monitoring the strengths of the Auger signals from the condensate, it is concluded that backscattering factors for a Ni substrate carrying a Cu film are higher than the backscattering factors for a Cu substrate carrying a Ni film.     

Low dielectric constant nanocomposite thin films based on silica nanoparticle and organic thermosets

Low dielectric constant (low-k) nanocomposite thin films have been prepared by spin coating and thermal cure of solution mixtures of one of two organic low-k thermoset prepolymers and a silica nanoparticle with an average diameter of about 8 nm. The electrical, the mechanical, and the thermomechanical properties of these low-k nanocomposite thin films have been characterized with 4-point probe electrical measurements, nanoindentation measurements with an atomic force microscope, and specular X-ray reflectivity. Addition of the silica nanoparticle to the low-k organic thermosets enhances both the modulus and the hardness and reduces the coefficient of thermal expansion of the resultant nanocomposite thin films. The enhancements in the modulus of the nanocomposite thin films are less than those predicted by the Halpin-Tsai equations, presumably due to the relatively poor interfacial adhesion and/or the aggregation of the hydrophilic silica nanoparticles in the hydrophobic organic thermoset matrices. The addition of the silica nanoparticle to the low-k organic thermoset matrices increases the relative dielectric constant of the resultant nanocomposite thin films. The relative dielectric constant of the nanocomposite thin films has been found to agree fairly well with an additive formula based on the Debye equation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1482–1493, 2007     

Kinetic study of the nitric oxide oxidation between 288 and 323 K,under pressure,focus on the oxygen influence on the reaction rate constant

The sequestration of carbon dioxide fumes from oxyfuel combustion is used to reduce significantly the carbon dioxide emissions from coal-fired power plants. Impurities like nitric oxide, present in the fumes, can cause technical difficulties during the capture, the treatment, the transport, and the storage steps of the CO₂ fumes. The purpose of this study is to better understand the oxidation of nitric oxide under pressure in the presence of carbon dioxide and in the experimental condition of flue gas treatment. This reaction is known to be a third-order reaction, two order in nitric oxide and first order in oxygen. To examine the effect of the temperature, the pressure and the volume fraction of oxygen on the rate constant of oxidation, k₁, an autoclave is used. The first experiment studies the influence of the temperature between 288 and 323 K. The results found are in the form of an Arrhenius-type equation: k₁ = 810 exp^(620/T) and are in agreement with the literature. Carbon dioxide does not seem to have an influence on the rate constant, whereas our experimental measurements indicate an influence of the volume fraction of oxygen. The rate constant decreases when the oxygen volume fraction increases by up to 10%. Then the rate constant remains constant. This observation allows us to conclude that the mechanism involving the mechanism with a dimer of NO as an intermediate is more likely to be the mechanism involved in the nitric oxide oxidation in our experimental conditions: high pressure and ambient temperature. The rate constant k₂, k_–2, and k₃ were also estimated in these conditions.     

染料敏化太阳电池中的电子传输及复合*

电子传输与复合是染料敏化太阳电池中仍然存在争议的基本物理过程,解决这些争议对于进一步提高染料敏化太阳电池的光伏性能及稳定性是至关重要的。多缺陷理论模型用扩散系数及电子寿命这两个基本物理量准确地描述了染料敏化太阳电池中的电子传输及复合。为了对扩散系数及电子寿命等物理参数进行实验测量,近年来,人们发展出了频域、时域以及稳态等多种实验方法和技术手段,本文对这些方法进行了综述,并分别从纳晶半导体光阳极、电解质以及敏化染料等方面评述了近年来电子传输及复合的相关研究进展。     

Determination of the epimerization rate constant of amygdalin by microemulsion electrokinetic chromatography

A new method for separation and determination of amygdalin and its epimer (neoamygdalin) in the epimerization of amygdalin by MEEKC is proposed. For the chiral separation of amygdalin and neoamygdalin, a running buffer composed of 80 mM sodium cholate, 5.0% v/v butan‐1‐ol, 0.5% v/v heptane and 94.5% v/v 30 mM Na₂B₄O₇ buffer (pH 9.00) is proposed. Under optimum conditions, the basic separation of amygdalin and neoamygdalin can be achieved within 7 min. The calibration curve for amygdalin showed excellent linearity in the concentration range of 20–1000 μg/mL with a detection limit of 5.0 μg/mL (S/N=3). The epimerization rate constant of amygdalin in basic microemulsion was first determined by monitoring the concentration changes of amygdalin, and the epimerization rate constant of amygdalin was found to be 2×10^?3 min^?1 at 25°C under the above optimum microemulsion conditions.     

Lowering the dielectric constant of polyimide thin films by swelling with supercritical carbon dioxide

The swelling with supercritical carbon dioxide (sc‐CO₂) of thin films of polyimides having various structures was investigated. It was shown that the degree of swelling is significantly influenced by the solvent which was used for the synthesis of those polyimides, by the solvent which was used for the preparation of thin films and by the conformational rigidity of the polymers. The presence of hexafluoroisopropylidene groups in the main chain of a polymer prevents its swelling with sc‐CO₂. The best results were obtained for polyimide film ULTEM, based on m‐phenylene‐diamine and isopropylidene‐diphenoxy‐bis(phthalic anhydride), synthesized in benzoic acid, whose free volume increased twice and its dielectric constant decreased from 3.15 to 2.45 by swelling with sc‐CO₂. Copyright © 2013 John Wiley & Sons, Ltd.     

Kinetics and mechanisms in carbocationic polymerization: The quest for true rate constants

This article is a critical analysis of kinetic dataavailable on carbocationic polymerizations. A survey of published propagation rate constant (k_p) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6‐trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, k_p = 1.35 × 10⁴ L mol^?1 s^?1 was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded k_p = 1.01 × 10⁷ L mol^?1 s^?1, close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2‐ chloro‐2,4, 4‐ trimethylpentane (TMPCl)/TiCl₄ from various laboratories yielded of ΔH ～?25 and ?34.5 kJ/mol for high and low TMPCl/TiCl₄ ratios, respectively. Aromatic (cumyl‐type) initiators show ΔH ～ ?40 kJ/mol, whereas H₂O/TiCl₄ in the presence of the strong electron‐ pair donor dimethylacetamide gave ΔH = ?12 kJ/mol. The significant differences indicate different underlying mechanisms with complex elementary reactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5394–5413, 2005     

Full rate constant matrix contraction method for obtaining branching ratio of unimolecular decomposition

The branching ratio of unimolecular decomposition can be evaluated by solving the rate equations. Recent advances in automated reaction path search methods have enabled efficient construction of the rate equations based on quantum chemical calculations. However, it is still difficult to solve the rate equations composed of hundreds or more elementary steps. This problem is especially serious when elementary steps that occur in highly different timescales coexist. In this article, we introduce an efficient approach to obtain the branching ratio from a given set of rate equations. It has been derived from a recently proposed rate constant matrix contraction (RCMC) method, and termed full‐RCMC (f‐RCMC). The f‐RCMC gives the branching ratio without solving the rate equations. Its performance was tested numerically for unimolecular decomposition of C₃H₅ and C₄H₅. Branching ratios obtained by the f‐RCMC precisely reproduced the values obtained by numerically solving the rate equations. It took about 95 h to solve the rate equations of C₄H₅ consisting of 234 elementary steps. In contrast, the f‐RCMC gave the branching ratio in less than 1 s. The f‐RCMC would thus be an efficient alternative of the conventional kinetic simulation approach. © 2016 Wiley Periodicals, Inc.     

CdS和CdSe薄膜的制备及其光电化学性质

本文采用简易的化学水浴沉积法和自牺牲模板法制备CdS、CdSe薄膜,对两种薄膜进行了XRD表征,比较了两种薄膜的紫外吸收光谱并研究了CdS、CdSe薄膜作为太阳能电池中的光阳极时所产生的光电流和光电压,对两种薄膜的电化学性能进行了比较.