Submillimeter BWO spectroscopy of solids

The potentialities of submillimeter spectroscopy (3–30 cm^–1) based on backward wave oscillators for studying solids are discussed. The scope of the research on this problem made at the Institute of General Physics of the USSR Academy of Sciences is outlined.     

BWO spectroscopy of water spin isomers based on desorption from glycerol

Violation of the normal spin 3: 1 ortho/para ratio in saturated water vapor above a 0.5% water-glycerol solution was detected using the BWO spectroscopy method. The solution was prepared by pumping the initial solution out at room temperature. The effect is supposed to be due to increased fugacity of ortho water molecules from the solution and the corresponding para enrichment of residual water.     

Polarization spectroscopy of a conducting surface

A method of polarization spectroscopy for a conducting surface characterized by a high sensitivity to the state of the surface and its transition layer is proposed. The method uses excitation of surface electromagnetic waves (SEWs) by a linearly polarized probe beam incident on the surface under study and compensation for the phase shift between the p and s components arising upon the SEW excitation. The applicability and competitiveness of the method in both the visible and the IR range is established. The method is tested on an LEF-3M ellipsometer in the visible range by studying the oxidation process in an evaporated copper film.     

Electron-electron scattering in conducting materials

Recent developments are reviewed in the theory and measurement of electron-electron scattering and its contribution to the electrical and thermal resistivities for different types of conducting materials, such as extremely impure metals, one-dimensional and two-dimensional conductors, the simple metals, transition metals, semimetals, organic conductors and the A15 compounds. The discussion includes the following topics: quantum corrections to the Fermi-liquid theory of electron-electron scattering (EES) due to static disorder, the effect of the dimensionality of the system on EES, the measurement and the calculation of the EES contribution to the resistivity of metals, the observed sample dependence of EES for the simple metals, the effect of EES on electron-surface scattering for thin wires, the contribution of EES to the anomalous surface impedance and to the optical relaxation time and the effect of a magnetic field on EES. Comparison is made between theory and recent experimental data for each of these topics.     

Optical spectroscopy of conducting Schiff-base polymer films

Polymer samples of complexes of divalent copper with the H₂msalpn-1,3 ligand have been studied by optical spectroscopy. The optical density spectra of metal-polymer films have been analyzed taking into account the influence of preliminary thermal treatment. The spectral dependences of the absorption coefficient and optical band gap are determined for different experimental conditions.     

Decimeter-Wave Resonant Relativistic BWO

In this paper, we present the results of numerical and experimental studies of a resonant relativistic backward-wave oscillator. Using reflections of the operating TM₀₁ mode from the ends of an electrodynamic system, optimal conditions for the interaction of an electron beam with both the backward (-1)st-order spatial harmonic and the forward fundamental harmonic are reached. Single-mode oscillations at 3.6 GHz with a peak pulse power of 5 GW and an efficiency of 30% were obtained in the experiment. We show the possibility of a 15% oscillation-frequency change corresponding to the FWHM power level by varying the period of a slow-wave structure at constant electron-beam parameters.     

Ion sweeping in conducting dielectric materials

Conductivity-related low-frequency dielectric losses frequently obscure loss peaks arising from dipole relaxations in dielectric materials. The application of moderately large electrical fields to ion containing liquids and solids in combination with temperature cycling enables one to reduce the contribution of conductivity to dielectric loss spectra significantly. Details of this electrical cleaning method are given. Its application is demonstrated and discussed for a diverse array of materials ranging from polymeric and small-molecule supercooled liquids to hydrated proteins and ice-like crystals. The suppression of conductivity-related losses allows one to gain insights into the low-frequency dynamics of such materials. The mobility of the ionic impurities at the base temperature and at the ‘cleaning’ temperature are briefly discussed.     

Temperature dependent infrared spectroscopy of proton conducting alkali thio-hydroxogermanates

We have investigated the thermal stability and reversibility upon dehydration and re-hydration of a novel class of proton conducting alkali thio-hydroxogermanates. The results indicate that no phase transitions or structural degradation occur in the temperature range 25 to 300 °C, and that repeated dehydration and subsequent re-hydration is a reversible process. The dehydration occurs gradually with increasing temperature, starting at about 80 °C. For temperatures above 180 °C the materials are dry, as all molecular water has been dried off. The dehydration process is shown to be reversible and the material can be rehydrated by exposure to air. The thermal stability and reversibility of the dehydration–rehydration process are attractive properties of functional materials, making the proton conducting alkali thio-hydroxogermanates to potential fuel cell electrolytes.     

Impedance spectroscopy of Na+ conducting zeolite ZSM-5

The electrochemical impedance of Na⁺ ion conducting zeolite Na-ZSM-5 contacted with gold electrodes is measured. Complementary impedance measurements of the same material contacted with Na⁺ ion conducting Na₂CO₃ enabled the separation of volume and electrode parts of the impedance. Both volume and electrode impedances consisted of multiple components. Possible underlying mechanisms are discussed in view of the application of zeolites as sensitive materials in solid-state ionic gas sensors.     

Autodyne Effect in Weak-Resonant BWO with Chaotic Dynamics

An autodyne phenomenon in the O-type Weak-Resonant Backward Wave Oscillator of K _a-band working in chaotic oscillatory regime is under investigation. The main attention is paid to the studying of the action of decorrelated reflected signals on the modulation of the power spectral density of the chaotic oscillations. Physical mechanisms are revealed and phenomenological model is suggested to explain the strong PSD modulation observed under the affect of the small refelected signal. The PSD modulation index has been introduced and its anomalous increase with the enlargement of the distance to the load is revealed experimentally, as well as the physical explanation for that effect is presented. All physical results obtained are valid for the autodyne effect in any chaotic oscillator. The results obtained can be used for the design of different autodyne based devices for the remote sensing, microwave telemetry and control systems.     

Raman spectroscopy characterization of two-dimensional materials

Two-dimensional(2D) materials have become a hot study topic in recent years due to their outstanding electronic,optical, and thermal properties. The unique band structures of strong in-plane chemical bonds and weak out-of-plane van der Waals(vdW) interactions make 2D materials promising for nanodevices and various other applications. Raman spectroscopy is a powerful and non-destructive characterization tool to study the properties of 2D materials. In this work, we review the research on the characterization of 2D materials with Raman spectroscopy. In addition, we discuss the application of the Raman spectroscopy technique to semiconductors, superconductivity, photoelectricity, and thermoelectricity.     

Alternative transparent conducting electrode materials for flexible optoelectronic devices

Transparent Conductive Electrode (TCE) is an essential part of the optoelectronic and display devices such as Liquid Crystal Displays (LCDs), Solar Cells, Light Emitting Diodes (LEDs), Organic Light Emitting Diodes (OLEDs) and touch screens. Indium Tin Oxide (ITO) is a commonly used TCE in these devices because of its high transparency and low sheet resistance. However, scarcity of indium and brittle nature of ITO limit its use in future flexible electronics. In order to develop flexible optoelectronic devices with improved performance, there is a requirement of replacing the ITO with a better alternate TCE. In this work, several alternative TCEs including transparent conductive oxides, carbon nanotubes, conducting polymers, metal nanowires, graphene and composites of these materials are studied with their properties such as sheet resistance, transparency and flexibility. The advantage and current challenges of these materials are also presented in this work.     

SrZrO3-based proton conducting materials with La additions

The behaviour of La-containing strontium zirconate based ceramics is revised. La additions contribute to improve the sinterability of these materials, but transport properties are also affected. Sr_1−xLa_xZrO_3+δ show some unusual changes in transport properties when samples are exposed to H₂-containing atmospheres and then reoxidized. Nevertheless, the transport properties of (Sr,La)(Zr,Y)O_3−δ, are still mainly dependent on Y additions, at least for cases when the fraction of Y exceeds the fraction of La. In addition, lanthanum causes significant changes in lattice parameters. A combination of conductivity measurements in different atmospheres, ion blocking experiments, and emf measurements has been used to demonstrate that electron hole conductivity increases with temperature, and the protonic contribution drops. The transport properties at temperatures lower than about 800 °C might be affected by structural changes. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Oxygen-ion conducting electrolyte materials for solid oxide fuel cells

Oxygen-ion conducting solid electrolyte systems have been reviewed with specific emphasis on their use in solid oxide fuel cells. The relationships between phase assemblage, electrolyte stability and ionic conductivity have been discussed. The role of parameters such as sintering temperature and atmosphere which influence the segregation of impurities, present in the starting ceramic powders, at grain boundaries and at the external surface of the electrolyte compacts has been emphasised. The stability of various electrolyte materials in contact with other fuel cell components and in fuel environments has been discussed in detail. The ageing behaviour at fuel cell operating temperatures has been described. Data on ionic conductivity, mechanical and thermal properties have been presented for a number of electrolyte materials.     

Remote laser spectroscopy of building materials

We describe specific features of an optical-fiber-based method of remote identification of the type of material and demonstrate the possibility of determining the main types of building materials from spectrograms of a plasma plume produced by a laser beam acting upon a material surface.     

Appearance potential spectroscopy of layer materials

It has been shown that soft X-ray appearance potential spectroscopy (SXAPS) can be used as a probe of the conduction band density of states in several of the layer transition metal dichalcogenides, where the pronounced structure seen for TiS₂ agrees well with X-ray absorption data. In contrast, the complex structure seen in the SXAPS of pyrolytic graphite has previously been interpreted in terms of strong plasmon coupling. However, we find that the SXAP spectrum for vacuum cleaved pyrolytic graphite shows details not readily explicable by such an argument but which agree well with what would be expected on the basis of a conduction band self-convolution model. Further strong support for this interpretation is derived from XPS and SXAPS studies of the isostructural, isoelectronic boron nitride.     

Excitation of the chaotic oscillations in millimeter BWO

In the paper the characteristic properties of the chaotic oscillation excitation in millimeter Backward-Wave Oscillators are investigated. To enhance the interaction efficiency and provide the strong nonlinear working regimes of the oscillator the weak-resonant oscillatory system with large electrical length is proposed to use. It is shown, that in this case the oscillation automodulation with complicated power spectrum are developed for the smaller values of the working current to starting current ratio in comparison with BWO having matched oscillatory system. This allows to oscillate with high efficiency the continuous millimeter chaotic (noise) signals which have a wide enough power spectrum and integral power of about several watts.     

Two-dimensional2H NMR exchange spectroscopy on conducting ionic crystals

The two-dimensional (2-D) deuterium nuclear magnetic resonance (NMR) exchange spectroscopy is applied to two types of conducting ionic crystals for the study of hydrogen mobility and conductivity, viz. partially deuterated ammonium hydrogen selenate, NH₄HSO₄ (AHSe), and partially deuterated mixed crystals of betaine phosphate (DBP) and betaine phosphite (DBPI), DBP_1?x DBPI_x. In both crystals chemical exchange processes of deuterons between different hydrogen bridges occur which are studied by the 2-D-₂H-NMR technique over a wide temperature range in the slow-exchange regime. For AHSe exchange only occurs between two sites which are involved in hydrogen bonds. Two Arrhenius-like exchange processes were found the activation energies of which could be determined. For the case of DBP_1?x DBPI_x, with several deuteron sites taking part in the exchange, the analysis of the quantitative exchange behavior required a combination of time-domain analysis of our 2-D NMR data with mixing-time- and temperature-dependent measurements. Different exchange rates for each two-site exchange, all showing Arrhenius behavior, were obtained for DBP_0.3, DBPI_0.7. For crystals with different phosphite concentrationx the differences towards DBP_0.3, DBPI_0.3 were established. With the help of conductivity data from dielectric measurements quantitative relations between the exchange and conductivity processes are obtained for AHSe as well as for DBP_1?x DBPI_x. Finally, an estimation of effective charge carrier densities is discussed in view of possible conductivity models for both crystals.     

Study on the dispersion characteristic of the plasma-loaded relativistic BWO

The dispersion characteristic of the plasma-loaded relativistic backward wave oscillator has been analyzed. The theoretical model has been established and the numerical calculations accord with the experimental results, which provides some useful suggestions on the designing of slow-wave structure of BWO.