Electrical properties of magnesium-intercalated InSe

Indium monoselenide single crystals have been intercalated with magnesium from the vapor phase, and their electron concentration, electron Hall mobility, anisotropic electrical conductivity, and thermoelectric power have been measured as functions of temperature. The effects of vacuum annealing and Mg intercalation on the electrical properties of InSe are analyzed. Magnesium intercalation has the strongest effect on the conductivity anisotropy in the crystals.     

Electrical behavior of lithium intercalated layered In-Se compounds

InSe and In₂Se₃ was lithium intercalated by mean of a spontaneous intercalation reaction. The electrical conductivity was studied and was found to be altered by 3-orders of magnitude with respect to non-intercalated samples. An interesting time dependent anisotropy appeared during intercalation, associed to the initial non-uniform Li distribution and the movement of Li concentration kinks.     

Physico-chemical and electrical properties of InSe films

Thin films of InSe were obtained by vacuum evaporation of polycrystalline material onto well cleaned glass substrates. After deposition on a cold substrate the samples were placed in a vacuum-sealed Pyrex tube for the annealing process. Physico-chemical and electrical properties of the InSe layers have been investigated. RBS and X-ray diffraction measurements showed that the InSe phase could be obtained. Electrical properties of the InSe layers are studied for different annealing temperatures. Conductivity measurements show that the behaviour of the films is sensitive to their thermal environment. The conductivity is controlled by grain boundaries.     

Self-organization of packing defects and Anderson localization in A3B6—type layered crystals

It is shown that the weakness of interlayered bounds in A³B⁶—type layered crystals leads to layer shift and the self-organization of packing defects, which results in a localization of electron states along the c-axis. The localization of electron states lead to the observation of hopping conductivity with variable range hopping and an Anderson transition at high optical excitation level when the majority carrier quasi-Fermi level crosses the mobility edge. The values of localization width, ΔE₀, in different InSe and GaSe crystals are changing from 10 to 100 meV. Especially, in crystals doped by non-isoelectronic impurity atoms, low values of ΔE₀ are obtained. We assume that this fact is related to structure ordering of doped crystals. The correlation between conductivity anisotropy and localization width was also found.     

Thermal and Electrical Properties of a Suspended Nanoscale Thin Film

This paper reports on measurements of in-plane thermal conductivities, electrical conductivities, and Lorentz number of two microfabricated, suspended, nanosized thin films with a thickness of 28 nm. The effect of the film thickness on the in-plane thermal conductivity is examined by measuring other nanofilm samples with a thickness of 40 nm. The experimental results show that the electrical conductivity, resistance–temperature coefficient, and in-plane thermal conductivity of the nanofilms are much smaller than the corresponding bulk values from 77 to 330 K. However, the Lorentz number of the nanofilms is about two times that of the bulk value at room temperature, and even up to three times that of the bulk value at 77 K. These results indicate that the relation between the thermal conductivity and electrical conductivity of the nanofilms does not follow the Wiedemann–Franz law for bulk metallic materials.     

Anisotropic Thermal Diffusivities of Plasma-Sprayed Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are used to shield the blades of gas turbines from heat and wear. There is a pressing need to evaluate the thermal conductivity of TBCs in the thermal design of advanced gas turbines with high energy efficiency. These TBCs consist of a ceramic-based top coat and a bond coat on a superalloy substrate. Usually, the focus is on the thermal conductivity in the thickness direction of the TBC because heat tends to diffuse from the surface of the top coat to the substrate. However, the in-plane thermal conductivity is also important in the thermal design of gas turbines because the temperature distribution within the turbine cannot be ignored. Accordingly, a method is developed in this study for measuring the in-plane thermal diffusivity of the top coat. Yttria-stabilized zirconia top coats are prepared by thermal spraying under different conditions. The in-plane and cross-plane thermal diffusivities of the top coats are measured by the flash method to investigate the anisotropy of thermal conduction in a TBC. It is found that the in-plane thermal diffusivity is higher than the cross-plane one for each top coat and that the top coats have significantly anisotropic thermal diffusivity. The cross-sectional and in-plane microstructures of the top coats are observed, from which their porosities are evaluated. The thermal diffusivity and its anisotropy are discussed in detail in relation to microstructure and porosity.     

碳纤维/聚醚醚酮单向带各向异性导电行为的尺度效应

具有导电各向异性的高分子复合材料(ACPCs)在场发射装置及传感器设计领域具有重要应用。常规的ACPCs很难获得超大导电各向异性系数,且力学性能有限。本文采用碳纤维(CF)宽展、表面浸润与树脂复合一体化超薄热塑性单向带制备方法,制备厚度为0.04 mm和0.1 mm的CF增强聚醚醚酮(CF/PEEK)复合材料单向带,以PEEK纤维为纬线制备CF/PEEK复合材料单向编织布,采用热成型工艺制备CF/PEEK复合材料单向层合板。利用数字万用表和霍尔效应系统测试层合板面内及厚度方向的电阻率和面内的电子迁移率;采用超景深显微镜观察CF/PEEK复合材料单向层合板面内和厚度方向的纤维排列形貌。结果表明,超薄CF/PEEK复合材料单向层合板面内(纤维方向与横向)导电率之比高达377,而面内横向和厚度方向的导电率之比接近1,表明CF/PEEK复合材料获得了良好的横观各向同性;超薄化CF/PEEK复合材料的面内电子迁移行为同样具有巨大的各向异性,这一结果为CF/PEEK复合材料在场发射器件、传感器设计及其灵敏度调控方面提供了实验基础。      

Effect of the addition of milled carbon fiber as a secondary filler on the electrical conductivity of graphite/epoxy composites for electrical conductive material

In this work, carbon composite bipolar plates consisting of synthetic graphite and milled carbon fibers as a conductive filler and epoxy as a polymer matrix developed using compression molding is described. The highest electrical conductivity obtained from the described material is 69.8 S/cm for the in-plane conductivity and 50.34 S/cm for the through-plane conductivity for the composite containing 2 wt.% carbon fiber (CF) with 80 wt.% filler loading. This value is 30% greater than the electrical conductivity of a typical graphite/epoxy composite with 80 wt.% filler loading, which is 53 S/cm for the in-plane conductivity and 40 S/cm for the through-plane conductivity. The flexural strength is increased to 36.28 MPa compared to a single filler system, which is approximately 25.22 MPa. This study also found that the General Effective Media (GEM) model was able to predict the in-plane and through-plane electrical conductivities for single filler and multiple filler composites.     

高优值系数In4Se3多晶的制备及其热电输运特性

分别采用不同的熔炼、退火工艺, 结合放电等离子烧结方法制备了块状多晶In₄Se₃热电材料。研究了熔炼时间和退火时间对材料物相、成分、显微结构及热电性能的影响。熔炼后铸锭中存在In及InSe杂相, Se缺失量随熔炼时间的延长而增加, 使得样品载流子浓度增大, 电导率有所提高, 熔炼48 h样品ZT值相对较高。在确定熔炼工艺的基础上, 进行不同时间的退火处理后, InSe相消失, 显微结构中分布有较大尺寸的台阶状结构, 这种台阶状结构有利于降低热导率, 而对电导率无明显影响。实验结果表明: 一定程度延长熔炼时间、退火时间对提高样品的热电性能有积极作用, 其中熔炼48 h再退火96 h后的样品ZT值最高, 在702 K达到0.83, 比文献值提高约32%。     

Prediction of size effect on thermal conductivity of nanoscale metallic films

Incorporating both the scattering mechanisms of the rough film surfaces and the microscopic grain boundaries, we report on a realistic simulation of the in-plane thermal conductivity of nanoscale gold, copper and aluminum films on the basis of non-interacting electron and kinetic theory. The results are consistent with previous theoretical analyses and molecular dynamic simulations, as well as available experimental data. The thermal conductivity of metallic films is found to drop much below the bulk value, even showing dielectric effects. As with the size effect on the electrical conductivity of metallic films, the fine-grain structure has a greater effect on the thermal conductivity than the film surface properties. The influence of temperature on the thermal conductivity is also investigated.     

Electrical and switching properties of InSe amorphous thin films

In this work electrical and switching properties of InSe thin films have been studied.

The semiconductor compound InSe was obtained by direct synthesis from stoichiometric amounts of spectroscopically pure indium and selenium. By slow cooling of the synthesized InSe a polycrystalline material is obtained. The amorphous films were obtained by thermal evaporation under vacuum of the polycrystalline material on glass or pyrographite substrates.

From electrical measurements, it was found that for all films the dark electrical resistivity decreases with an increase in film thickness and temperature. The InSe compound exhibits non-linear I–V characteristics and switching phenomena. The threshold voltage decreases with increasing annealing temperature and increases with increasing film thickness.     

Factors affecting the magnitudes and anisotropies of the thermal and electrical conductivities of poly(l-lactic) acid composites with carbon fibers of various sizes

Investigation of the thermal and electrical conductivities of poly(l-lactic acid) composites containing carbon fibers (CFs) of various sizes has revealed that the thermal conductivity depends largely on the length of the CFs in the composites and that the electrical conductivity depends largely on the aspect ratio of the CFs. These different dependencies are due to the effect of the number of interfaces between the CFs in a percolation network formed in the composites, where electron transport is enhanced but phonon thermal conduction is limited by phonon scattering at the interfaces between the CFs. The anisotropy of each conductivity is also influenced by the length of the CFs, which could determine the alignment of the CFs in the molded composites.     

Electrical conductivity,structure and hall effect measurements of InSe films

Stoichiometric InSe films were prepared by discrete evaporation using spectrally pure (99.999%) InSe powder in a residual pressure of about 4×10^?6 Torr. The thickness of the films was varied from 500 to 3000 Å. The elctrical conductivity of the films was measured by Van der Pauw's method. The as-deposited films had an amorphous structure as observed with an electron microscope. Thermal annealing was carried out through a number of annealing cycles and a transformation to a crystalline state during the process was evidenced by the electron micrographs. Conductivity measurements were made on the amorphous films from the transition temperature to liquid air temperature and the activation energies were calculated from the variation in conductivity with temperature. The density of states at the Fermi level was also calculated at low temperatures. Hall effect measurements were made on the annealed films and the Hall mobility μ_H, the Hall coefficient R_H and the carrier concentration n were evaluated.     

The effect of substrate and post annealing temperature on the electrical properties of polycrystalline InSe thin films

The correlation between the electrical properties of vacuum evaporated InSe thin films and the growth conditions as well as post depositional annealing has been investigated. The electrical properties of the deposited films have been studied in the temperature range of 50–320 K. The donor levels present in the InSe films have been analysed by applying the single donor-single acceptor model to the electrical data.     

In-plane anisotropic electrical and optical properties of gold-doped rhenium disulphide

Au-doped ReS₂ layer crystals were grown by chemical vapour method with iodine as the transport agent. Room temperature Hall effect measurement showed p-type semiconducting character for the doped sample. The electrical conductivities parallel and perpendicular to the crystal b-axis were investigated. The near band-edge temperature-dependent in-plane anisotropic optical properties were studied by the polarization-dependent photoconductivity measurements, with the incident light beam parallel and perpendicular to the crystal b-axis, in the temperature range from 20 to 300 K. The influence of Au in the measured conductivity anisotropy and photoconductivity spectra of doped ReS₂ were analysed and discussed.     

Research on the Planar Electrical Anisotropy of Conductive Woven Fabrics

The main aim of the research is to determine electrical anisotropy of woven fabrics to describe the multidirectional dependence of the electrical resistance of woven fabrics. The van der Pauw electrodes configuration is used to determine the electrical resistance. Scanning electron microscope–energy-dispersion X-ray spectroscopy (SEM–EDS) analysis is carried out to identify the real amount of conductive elements on a fabric surface as a result of yarns or fabric metallization and to explain the electrical conductivity of the textile materials. The planar electrical anisotropy of electroconductive woven fabrics is observed. The maximum and minimum values of resistances of woven fabric are connected with the weft/warp of which direction coincides with the direction of the longitudinal and transversal axes in the sample plane. SEM–EDS analysis confirms that the electrical conductivity of fabrics depends on the samples elemental composition and the amount of metals deposited on yarns or woven fabrics. It is observed that the sample metallization with thick coating gives a better solution than weaving textiles from coated yarns from the point of view of electrical properties.     

Thermal conductivity and electrical resistivity of cadmium arsenide (Cd3As2) in the temperature range 4.2–40 K

Results on electrical resistivity and thermal conductivity measured in the temperature range 4.2–40 K are presented for single-crystal and polycrystalline samples of Cd₃As₂. Hall effect has been studied at temperatures of 4.2, 77, and 300 K. The calculated value of the conduction electron concentration was in the range 1.87–1.95 10²⁴m^–3. Electrical resistivity of all investigated samples was independent of temperature up to about 10K and increased slowsly at higher temperatures. The thermal conductivity shows a maximum in the region in which the lattice component of thermal conductivity dominates. The strong anisotropy of the lattice component determines the anisotropy of the total thermal conductivity. The electronic component of thermal conductivity does not exhibit any anisotropy and shows a maximum at a temperature of about 300 K.Paper submitted to the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Conductivity measurements of various yttria-stabilized zirconia samples

Samples of yttria-stabilized zirconia manufactured by the following fabrication procedures, were obtained from commercial sources: (i) hot isostatic pressing; (ii) tape casting; (iii) vacuum plasma spraying, and (iv) calendering. The ionic conductivities of these samples were measured by (a) impedance spectroscopy; (b) the four-point probe method; (c) the current-interruption technique, and (d) the van der Pauw technique. The tape-cast and hot pressed samples showed good and very reproducible conductivity values. The vacuum plasma sprayed samples showed an anisotropy in their conductivity, with the cross-plane value being several times lower than the in-plane value. A simple model based on the porous microstructure of these samples can explain this observation. Sintering of the plasma sprayed samples minimized the anisotropy and significantly improved their conductivity values. The calendered samples also showed a similar anisotropy in their conductivity data when they were inadequately sintered.     

Domains and domain nucleation in magnetron-sputtered CoCr thinfilms

The magnetic domain configurations in magnetron-sputtered CoCr thin films have been examined by Lorentz transmission electron microscopy. The thinnest (10 nm) films display in-plane 180° domain walls, while thicker (50 nm) films exhibit out-of-plane dot-type domain structures. The dot domains were observed even in films that had not yet developed a columnar morphology. Intermediate thickness films show a featherlike contrast, indicating that both in-plane and out-of-plane magnetization components are present. Magnetization reversal is seen to occur by domain wall motion in films displaying in-plane anisotropy and by rotation for perpendicular anisotropy films. Intrinsic film stress was found to play a major role in determining the preferred magnetization direction, and thus the resulting magnetic domain configurations     

影响磁性纳米颗粒膜吸波性能的主要因素

基于Landau-Lifshitz-Gilbert方程、Bruggeman有效媒质理论及纳米颗粒膜的电输运和介电理论,通过计算磁性纳米颗粒膜的有效磁导率、有效介电常数、计算分析饱和磁化强度、各向异性场、电导率和阻尼系数对纳米颗粒膜吸波性能的影响.结果表明,饱和磁化强度、各向异性场、电导率和阻尼系数均对纳米颗粒膜的微波吸收特性产生显著影响,通过调控纳米颗粒膜的电磁特性可以有效提高其吸波性能,可以应用于薄层吸波材料的设计中.