Electron transport in solids and liquids

We review our recent experimental studies of the excess electron states in insulating solids and liquids. We use a muon spin relaxation technique to explore the phenomenon of delayed muonium formation: excess electrons liberated in the μ⁺ ionization track converge upon the positive muons and form Mu (μ⁺e^?) atoms in which the μ⁺ polarization is partially lost. The spatial distribution of such electrons with respect to the muon is shown to be highly anisotropic: the μ⁺ thermalizes well “downstream” from the center of the electron distribution. Measurements in electric fields up to 30 kV/cm allow one to estimate the characteristic muon-electron distance in different insulators: the results range from 10^?6 to 10^?4 cm. Such a microscopic length scale enables the electron to sometimes spend its entire free lifetime in a state which may not be detected by conventional macroscopic techniques. This circumstance illustrates the potential of μ⁺SR techniques in studies of electron transport in matter. The muonium formation process in condensed matter is shown to depend critically upon whether the excess electron forms a polaron or remains in a delocalized state. Different mechanisms of electron transport in insulators are discussed.     

Photoacoustic spectroscopy of solids immersed in transparent liquids

A method is developed to obtain the photoacoustic spectra of solids by immersing them in a liquid cell with a submersed tranducer and detecting the acoustic pulse generated due to bulk absorption of pulsed laser radiation in the solids. Proper choice of liquids enables spectra to be obtained which are independent of the optical properties of the solid surfaces of the surrounding liquid. This technique is compared to other established PAS methods.     

Muonium formation via charge transport in solids and liquids

We review our recent experimental studies on delayed muonium formation in insulators and semiconductors. This involves the positive muon capturing one of the excess electrons liberated in its own ionization track and competes with recombination or escape of the electrons. The muon is generally found to thermalise well “downstream” from the center of the electron distribution, so that the transport mechanism of the electrons is a crucial factor. This is discussed in terms of the different tendencies to localization (as polarons in solids or in bubbles in liquids) vs. band‐like propagation. Studies of Van der Waals cryocrystals and cryoliquids are reviewed and some preliminary results reported for sapphire and silicon. Transport distances and times are determined from the variation of μSR signal amplitudes with applied electric and magnetic fields, respectively, enabling the development of a new technique for measuring electron mobilities on a microscopic scale. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electronic transport and localization in low mobility solids and liquids

This article is concerned with the electronic transport properties of the large group of solids (and also some liquids) which possess carrier mobilities from 10 cm²V^-1sec^-1 to many orders below that value. Its main aim is to trace the close relation between transport and localization. To this end the physical basis of three important localization models is discussed and the predicted transport mechanisms are reviewed in the light of the experimental information. After a brief summary of the experimental methods, the first subject is the localization arising from strong electron-phonon interaction. Here we consider in some detail the formation of a small polaron in a molecular crystal and its transport by phonon-assisted intermolecular hopping. The second part of the paper deals with the localization of an electron in a so-called electronic bubble, which occurs for example in simple liquids such as Ne or He. The stability and transport of this entity is discussed. The third section is devoted to non-crystalline solids. In these localization is associated with the lack of long-range order and does not depend on phonon interaction. The transport through the various parts of the density of states spectrum is summarized and the suggested models are reviewed on the basis of recent experimental work on amorphous silicon. Finally, the possibility of polaron formation and transport in some chalcogenide alloy glasses is briefly considered. The paper leads to the conclusion that available experimental evidence supports the general validity of the above three models, although it must be emphasized that this is based on an as yet limited range of experimental information.     

Nanoparticle formation during laser ablation of solids in liquids

The experimental data on the generation of metal and semiconductor nanoparticles during their laser ablation in liquids is reviewed. The dependence of the morphology of noble metal nanoparticles on the liquid type and laser parameters is discussed. The data on the kinetics of the formation of alloyed Au-Ag nanoparticles under laser irradiation of a mixture of colloid solutions of individual nanoparticles are presented. The effect of femtosecond laser beam self-action during metal ablation in liquids via the second harmonic generation at Ag nanoclusters is discussed. The data on the generation of core-shell nanoparticles during laser ablation of alloys and in the presence of the chemical interaction of formed nanoparticles with surrounding liquid are presented. It was shown that laser ablation of CdS and ZnSe crystals leads to the formation of quantum dots of these semiconductors in solution. The parameters controlling the properties of nanoparticles during ablation in liquids and possible applications of the method are discussed.     

Dissipation functions and conservation laws of molecular liquids and solids

Thermodynamics of molecular liquids (anisotropic liquids, liquid crystals, etc.) and molecular solids (e.g. dielectrics, pyroelectrics, molecular crystals) are treated in a unified way, using an internal energy potentialU and a dissipation functionD. Assuming that the motion of the mass points making up the molecule is essential in determiningU we write down the appropriate field equations of motion and the entropy equation. With the assumed invariance ofU under a group of space-time transformations and the invariance ofD under rigid body uniform motions, we derive the conservation laws of mass, momentum, energy and angular momentum. In particular, we show that the total stress tensor is asymmetric.Furthermore, a symmetric stress tensor does not guarantee angular momentum conservation. The complete specification ofD leads to symmetry relations between the dissipative coefficients in an unambiguous way, without invoking the concept of so called forces and fluxes, in contrast to the conventional Onsager approach. Our formalism allows for a class of different dissipation functions, and is applicable to linear or nonlinear molecular media of arbitrary symmetry. It covers simple materials as special cases.     

Determination of the temperature distribution in liquids and solids using holographic interferometry

It is shown that holographic interferometry can be applied to solve two problems: heating of a glass plate by a complex heat source and nonisothermal flow of a submerged jet around a wedge. The process of isolating and numbering the skeletal lines on the interferograms is automated and direct calculations are made of the temperature fields. Zh. Tekh. Fiz. 69, 106–111 (June 1999)     

Rate spectra of small deformations in solids

The method of constructing the temperature dependence for the rate of small creep deformation (strain-rate spectra) is applied to determine relaxation transitions in solids. This method is based on precision measurements of the rate using a laser interferometer and is distinguished by its high resolution. The possibility of using the spectra for predicting critical temperatures in the fracture kinetics of polymers and metals, as well as changes in the electrical properties (for example, the superconducting transition in Y-Ba-Cu-O ceramics) is pointed out. Fiz. Tverd. Tela (St. Petersburg) 41, 848–850 (May 1999)     

Relativistic corrections and very small g-shifts in solids

The relativistic Breit-Margenau correction to the Zeeman-interaction has been calculated for a group of atoms in the periodic table with Herman Skillman wave functions and potentials. The results are applied to the S-state ions Mn²⁺ and Gd³⁺, to the F-center and V_k-center, and to the shallow donors in Si.     

Spectrophotometric determination of vanadium in crude oil

Spectrophotometric method has been developed for the determination of vanadium after derivatization with 2-pyrrolealdehyde phenylsemicarbazone (PPS). The linear calibration curve was obtained with 2.5- vanadium. Copper(II), cobalt(II), iron(II) and palladium(II) could also be determined separately using PPS with linear calibration curves within 2.5-12.5, 5-15, 2.5-15 and 1- at 362, 355, 355 and 365 nm, respectively. The vanadium in crude oil was determined with relative deviation (RSD) of 2.5-5.0%. The methods have been applied for the analysis of copper from copper wires, cobalt from pharmaceutical preparation and palladium from palladium on barium sulphate with RSD within 2.6-4.5%.     

Generation of picosecond light continua by parametric four-photon interactions in liquids and solids

Light continua extending from the i.r. to the u.v. are generated with picosecond laser pulses in liquids and solids. It is demonstrated that the light spectra in water are produced by stimulated parametric fourphoton interactions, which are resonantly enhanced by single and difference frequency resonances of the non-linear susceptibility ⁽³⁾. A theory of the various parametric four-photon interaction processes is developed and the resonant structure of ⁽³⁾ is discussed. The experimental results are compared with theoretical calculations. The generation of light continua by other nonlinear optical processes is briefly discussed.     

Photo-acoustic and photo-refractive detection of small absorptions in liquids

The sensitivities of pulsed photo-acoustic and photo-refractive (e.g., thermal lensing) techniques for the measurement of small absorptions in liquids have been evaluated both theoretically and experimentally. Electrostriction limits the sensitivity of both techniques, this limitation is less severe for the photo-refractive technique. The minimum absorption constants observed experimentally, for a 200-μm laser spot size in liquid N₂, are 4 × 10^-5 cm^-1 for the photo-acoustic measurement and 6 × 10^-7 cm^-1 for the photo-refractive measurement. The calculated electrostrictive limits are 2 × 10^-5 cm^-1 and 7 × 10^-11 cm^-1, respectively.     

近红外光谱检测蜂蜜中可溶性固形物含量和水分的应用研究

提出了一种利用近红外光谱技术定量分析蜂蜜中可溶性同形物含量(SSC)的新方法,同时对蜂蜜中的水分也进行了研究.在不同光谱范围内,通过对原始光谱的不同预处理,用偏最小二乘法分别建立了SSC和水分的近红外透反射光谱校正模型,所有模型都有高的的预测精度和水分的最优模型都为在全谱范围内,光谱预处理采用Norris平滑+一阶微分+多元信号校正,SSC模型的交互验证决定系数(RCV2)、交互验证误差均方根(RMSECV)、验证集决定系数(RP2)、验证误差均方根(RMSEP).SSC模型分别为0.998 6,0.190,0.998 5和0.127,水分模型分别为0.998 4,0.187.0.998 6和0.125.近红外光谱能实现蜂蜜中SSC和水分的准确测定.水分模型预测结果略好于相关文献的报道.     

Spectrophotometric determination of sparfloxacin in pharmaceutical formulations and urine samples

A simple and sensitive spectrophotometric method has been developed for the determination of sparfloxacin in bulk and pharmaceutical formulations, and in artificial urine. Sparfloxacin was oxidized into a red colored product using ammonium monovanadate in acidic media. The proposed method was successfully applied to the determination of sparfloxacin in different pharmaceutical formulations (tablets) and in a spiked urine sample. The influence of commonly used excipients on the determination of sparfloxacin was studied. Percentage recoveries in the range of 98.0 ± 0.14 % to 100.0 ± 0.20 % were obtained. The observed data have been evaluated statistically which showed high accuracy and precision.