Influence of grain boundary state on electrical resistivity of ultrafine grained aluminium

An ultrafine grained (UFG) structure has been obtained in commercial purity Al by high-pressure torsion (HPT). Changes in microhardness and electrical resistivity of the UFG material after annealing at various temperatures within a range of 363–673 K have been investigated in correlation with the microstructure evolution. It has been shown that annealing at 363 K leads to substantial decrease in the electrical resistivity while keeping high microhardness level and approximately the same average grain size. The contributions from the various microstructural units (vacancies, dislocations, grain boundaries (GBs)) to the electrical resistivity were analysed. It was shown for the first time that a non-equilibrium state associated with strain-distorted grain boundary (GB) structure strongly affects electrical resistivity of UFG Al. The resistivity of non-equilibrium GBs in UFG structure formed by HPT was evaluated to be at least 50% higher than the resistivity of the thermally equilibrium GBs in a coarse-grained structure.     

Resistivity changes in cold-worked Cd-Mg and Cd-Sn

Experiments on Cd, Cd-0·12 at % Mg, Cd-0·48 at % Mg, Cd-0·056 at % Sn and Cd-0·18 at % Sn wires deformed by torsion in liquid nitrogen have shown that up to 200 K (where in Cd the polygonization and/or recrystallization starts) the form of the isochronous annealing spectrum of electrical resistivity remains unchanged irrespective of the degree of deformation and impurity content. For the Cd-Sn alloy this is in contrast with recent experiments on quenched specimens. It seems at present that this discrepancy is due to the inherent difference of the behaviour of lattice defects in cold-worked and quenched specimens.     

射频溅射Pd薄膜的电阻率研究

本文研究了溅射Pd薄膜的电阻率与膜厚关系和不同溅射功率下Pd薄膜电阻率,结果表明,电阻率与膜厚的关系与现有的薄膜电阻率尺寸效应的理论基本相符,存在的差异主要是由溅射对衬底温度影响而引起的,并显示玻璃衬底上生长膜也有择优取向,溅射功率的变化对电阻率有一定的影响,进一步讨论溅射过程中衬底温度变化的问题,得出膜电阻率随衬底温度变化的定量关系式。 关键词：     

Microstructure evolution of room-temperature-sputtered ITO films suitable for silicon heterojunction solar cells

Thickness influence on structural, optical and electrical properties of sputtered indium tin oxide (ITO) with thickness ranging from 60 up to 430 nm films has been studied. At the increase of the film thickness crystallinity degree and grain size increased, whereas tensile structural distortion as well as resistivity decreased. It was observed that a microstructure evolution takes place: the initial amorphous layer evolved in polycrystalline phase, with a grain–subgrain surface morphology. Carrier concentration increased at the increase of the film thickness and a general relationship between electrical characteristics and structural distortion has been found. In thinner films larger tensile distortion allowed to include larger amount of interstitial O and/or Sn atoms in the lattice. An appreciable impact of the thickness was also observed on electro-optical properties in terms of changes in energy gap, resistivity and optical absorption. Silicon heterojunction solar cells have been produced and J_sc as high as 33.0 mA/cm² has been obtained.     

Low temperature resistivity minimum and its correlation with magnetoresistance in La0.67Ba0.33MnO3 nanomanganites

A systematic investigation of structural, magnetic and electrical properties of nanocrystalline La_0.67Ba_0.33MnO₃ materials, prepared by citrate gel method has been undertaken. The temperature-dependant low-temperature resistivity in ferromagnetic metallic (∼50 K) phase shows upturn behavior and is suppressed with applied magnetic field. The experimental data (<75 K) can be best fitted in the frame work of Kondo-like spin-dependant scattering, electron-electron and electron-phonon interactions. It has been found that upturn behavior may be attributed to weak spin disorder scattering including both spin polarization and grain boundary tunneling effects, which are the characteristic features of extrinsic magnetoresistance behavior, generally found in nanocrystalline manganites. The variation of electrical resistivity with temperature in the high temperature ferromagnetic metallic part of electrical resistivity (75K<T<T_P) has been fitted with grain/domain boundary, electron-electron and magnon scattering mechanisms, while the insulating region (T>T_P) of resistivity data has been explained based on adiabatic small polaron hopping mechanism.     

Effects of deposition temperature and post-annealing on structure and electrical properties in (La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>)CoO<Subscript>3</Subscript> films grown on silicon substrate

(La_0.5Sr_0.5)CoO₃ (LSCO) thin films have been fabricated on silicon substrate by the pulsed laser deposition method. The effects of substrate temperature and post-annealing condition on the structural and electrical properties are investigated. The samples grown above 650°C are fully crystalline with perovskite structure. The film deposited at 700°C has columnar growth with electrical resistivity of about 1.99×10⁻³ Ω cm. The amorphous films grown at 500°C were post-annealed at different conditions. The sample post-annealed at 700°C and 10⁻⁴ Pa has similar microstructure with the sample in situ grown at 700°C and 25 Pa. However, the electrical resistivity of the post-annealed sample is one magnitude higher than that of the in situ grown sample because of the effect of oxygen vacancy. The temperature dependence of resistivity exhibits semiconductor-like character. It was found that post-annealing by rapid thermal process will result in film cracks due to the thermal stress. The results are referential for the applications of LSCO in microelectronic devices.     

Ordering properties and interpretation of radiation damage IN Au–15 at.% Ag alloys

The equilibrium value of the electrical resistivity of Au–16.25 at.% Ag has been determined as a function of temperature. In addition, isochronal annealing of quenched Au–15 at.% Ag alloys has been studied by means of resistivity measurements. Both types of experiments indicate that in these alloys a decrease of the degree of order gives rise to an increase of the electrical resistivity. This result confirms the previous interpretation of the radiation damage and its recovery in low-temperature electron-irradiated Au–15 at.% Ag alloys in terms of the two-interstitial model.     

Effects of deposition parameters on tantalum films deposited by direct current magnetron sputtering in Ar–O2 mixture

The structure, composition, and temperature coefficient of resistance of tantalum films sputtered in Ar–O₂ mixture were studied as a function of deposition parameters and substrates temperature. As the sputtering power increased from 25 to 100 W, the samples deposited at 300 °C only consisted of the β phase, the preferred-growth orientation of films changed from (2 0 0) to (2 0 2) and the temperature coefficient of resistance reduced from −289.8 to −116.7 ppm/°C. The decrease of the oxygen and other impurity in the films was observed as the increase of the sputtering power. In addition, the O/Ta ratio decrease and grain size reduction in the films related to a change of electrical resistivity were observed at substrate temperatures in the range of 300–500 °C. These results suggested that the electrical properties were due to the oxygen and other impurity content and grain size in the films rather than to growth orientation. At 650 °C, the deposited films contained both partial stable body-centered-cubic α phase with low resistivity and tetragonal β phase of Ta. The presence of α phase of Ta causes a sharp decrease of the electrical resistivity and a significant change in the microstructure of the samples.     

The change in properties of the alloy MgC d at the order-disorder phase transformation

The mechanical properties and structure of the alloy MgCd have been investigated in the ordered and quenched states and so has the kinetics of the change in yield point and electrical resistivity of the alloy quenched from T > T_c in water at room and elevated temperatures. The reasons for the hardening of the alloy in the quenched state are discussed.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 8, pp. 44–48, August, 1968.     

Structure property correlations in superconducting Ti-Nb alloys

Titanium-rich transition metal alloys are metastable in their quenched boc β phase. The instability is relieved by low temperature structural transformations. We have investigated this in a series of Ti-Nb alloys, through the measurements of electrical resistivity (ρ), superconducting transition temperature and upper critical field. Supporting structural evidence has been obtained from transmission electron microscopy (tem) and x-ray studies. It is shown that both ρ and dρ/dT can be used as useful indices of this instability. The enhanced value of resistivity on account of the instability results in the enhancement of upper critical field as shown from dH _c2/dT measurements.     

The influence of atomic displacements on the electrical resistivity due to vacancies in simple metals

The influence of atomic displacements around a vacancy on the electrical resistivity due to vacancies in simple metals has been calculated by the pseudopotential method. The influence of atomic displacements on the electrical resistivity was very large and the resistivity has a minimum at an appropriate relaxation. Therefore it is very important to take into account the effect of the lattice distortions considering the individual atomic displacements around vacancies in the calculation of the electrical resistivity due to vacancies.     

Galvanomagnetic effects of dilute nitrogen-iron alloys

Galvanomagnetic effects of the dilute nitrogen-iron alloys have been investigated in detail between 4.2 and 250 K. The specific resistivity increment by solute nitrogen in pure iron is determined experimentally as 8.9 μΩcm/at.%. It is revealed that Kohler plots for the transverse magnetoresistance of quenched and unquenched specimens lie on the same curve, while it is not so for the longitudinal magnetoresistance, and Kohler plots for the longitudinal effect of single crystals containing solute nitrogen, are different from one another for each crystal axis (100), (110) and (111). Furthermore, a substantial deviation from Matthiessen's rule was found out by the measurement of the temperature dependence of the electrical resistivity of the alloy between 4.2 and 250 K.The Matthiessen's rule parameter is about seven.Kohler's rule holds for the Hall resistivity. In the low-field limit the plots do not go through the origin. The tangent of the Hall angle is 1.0 × 10^?2 for quenched specimens. This non-zero value can be explained with the asymmetric scattering proposed by Smit. The extraordinary Hall constant is proportional to the ohmic resistivity.     

Temperature dependence of the optical properties of ion-beam sputtered ZrN films

The reflectivity of sputtered Zirconium nitride films on glass substrate has been investigated in the spectral energy range of 0.8–6.1 eV as a function of deposition temperature varying between 373 and 723 K. Optical constants of the prepared films have been determined using the Drude analysis. Experimental results showed strong dependency of optical properties of the films, such as optical resistivity on the substrate temperature. The temperature increase of the substrate has shown an increase in both the plasmon frequency and electron scattering time. The electrical behavior of the films showed a good agreement between their optical and electrical resistivity.     

铝纳米晶的低温导电特性研究

采用真空热压技术将电磁感应加热-自悬浮定向流法制备的铝纳米粉末压制成块体样品.通过X射线衍射、透射电子显微镜、扫描电子显微镜及X射线能谱分析了铝纳米晶的微观结构,并用四探针法测量了不同温度下(8—300 K)样品的电阻率,研究了铝纳米晶的电阻率(ρ)随温度的变化规律.结果表明:由于晶界(非晶氧化铝)对电子的散射以及晶界声子对电子的散射效应,低温(40 K)下,铝纳米晶的本征电阻率随温度变化关系明显不同于粗晶铝,不仅呈现出T~4变化,还表现出显著的T3变化规律.因晶界等缺陷和非晶氧化铝杂质对电子的散射,铝纳米晶残余电阻率比粗晶铝电阻率大5—6个数量级.     

Magnetic and magnetoresistive properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sr<Subscript>2</Subscript>FeMoO<Subscript>6–δ</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoheterostructures

A method has been developed for fabricating nanoporous matrices based on anodic aluminum oxide for the deposition of ferromagnetic nanoparticles in them. The modes of deposition of strontium ferromolybdate thin films prepared by the ion-plasma method have been worked out, and the magnetic and magnetoresistive properties, structure, and composition of the films have been investigated. It has been revealed that the microstructure and properties of the strontium ferromolybdate films deposited by ionplasma sputtering depend on the deposition rate and the temperature of the substrate. Based on the measurement of the electrical resistivity of nanoheterostructures in a magnetic field, it has been found that the magnetoresistance reaches 14% at T = 15 K and B = 8 T, which is due to the manifestation of tunneling magnetoresistance.     

Current voltage analysis and band diagram of Ti/TiO2 nanotubes Schottky junction

We report variable temperature resistivity measurements and mechanisms related to electrical conduction in 200 keV Ni²⁺ ion implanted ZnO thin films deposited by vapor phase transport. The dc electrical resistivity versus temperature curves show that all polycrystalline ZnO films are semiconducting in nature. In the room temperature range they exhibit band conduction and conduction due to thermionic emission of electrons from grain boundaries present in the polycrystalline films. In the low temperature range, nearest neighbor hopping (NNH) and variable range hopping (VRH) conduction are observed. The detailed conduction mechanism of these films and the effects of grain boundary (GB) barriers on the electrical conduction process are discussed. An attempt is made to correlate electrical conduction behavior and previously observed room temperature ferromagnetism of these films.     

高压下ZnSe直流和交流电学性质的研究

采用高压原位测量技术在0–35 GPa压力范围内对ZnSe直流和交流电学性质进行了研究. 通过分析直流电学测量结果可知,在实验压力区间内ZnSe经历了由纤锌矿转变为朱砂相再转变为岩盐相的两次相结构转变. 分析温度与材料电阻率的变化关系表明ZnSe在高压下的相变为金属化相变,并通过交流阻抗谱的测量实验证实了这个结论. 进一步比较低压条件下晶粒和晶界电阻的变化,表明朱砂相结构的ZnSe更接近各向同性材料. 关键词： 高压 ZnSe 电学     

Van der Pauw resistivity measurements on evaporated thin films of cadmium arsenide, Cd3As2

Cadmium arsenide is a II-V semiconductor, exhibiting n-type intrinsic conductivity with high mobility and narrow bandgap. It is deposited by thermal evaporation, and has shown the Schottky and Poole-Frenkel effects at high electric fields, but requires further electrical characterisation. This has now been extended to low-field van der Pauw lateral resistivity measurements on films of thickness up to 1.5 μm. Resistivity was observed to decrease with increasing film thickness up to 0.5 μm from about 3 × 10⁻³ Ω m to 10⁻⁵ Ω m, where the crystalline granular size increases with film thickness. This decrease in resistivity was attributed to a decrease in grain boundary scattering and increased mobility. Substrate temperature during deposition also influenced the resistivity, which decreased from around 10⁻⁴ Ω m to (10⁻⁵ to 10⁻⁶) Ω m for an increase in substrate deposition temperature from 300 K to 423 K. This behaviour appears to result from varying grain sizes and ratios of crystalline to amorphous material. Resistivity decreased with deposition rate, reaching a minimum value at about 1.5 nm s⁻¹, before slowly increasing again at higher rates. It was concluded that this resulted from a dependence of the film stoichiometry on deposition rate. The dependence of resistivity on temperature indicates that intercrystalline barriers dominate the conductivity at higher temperatures, with a hopping conduction process at low temperatures.     

Preparation of porous (Ba,Sr)TiO3 by adding corn-starch

A new method of preparing porous (Ba,Sr)TiO₃ ceramics has been introduced, using an ordinary ceramics processing technique. The effect of corn-starch on the positive temperature coefficient of resistivity characteristics and microstructure of the porous (Ba,Sr)TiO₃ ceramics has been investigated. When the corn-starch addition was 1-20 wt%, the PTCR jump was over 10⁶ and 1-2 orders higher than that of samples without corn-starch. Also, it was found that the (Ba,Sr)TiO₃ ceramics had porous microstructure by the addition of corn-starch. The porosity of the ceramics with 20 wt% corn-starch was 44%. The electrical properties of the (Ba,Sr)TiO₃ ceramics have been discussed, based on the microstructure, resistivity of grain boundaries, donor concentration of grains and the electrical potential barrier of grain boundaries.     

Structure of Be films quenched from the vapour

The crystallite boundary mismatch in crystalline films leads to tensile stresses which act on the substrate. Due to these stresses the substrate is bended. In the dense random packing of atoms in an amorphous film local tensile- and compressive stresses compensate and thus the films seem to be free of stresses with regard to the substrate. From this point of view the measurement of mechanical stresses produced by vapour quenched films can be used for structural analysis. Thus an apparatus is described which allows in situ measurements of mechanical stresses and electrical resistivity of vapour quenched films from 1.2 K to 400 K.An investigation of beryllium films revealed that stresses are produced even by films with a superconducting transition temperature of 9.6 K. From this fact it can be concluded that vapour quenched Be is not completely amorphous. Furthermore, it is shown that inhomogeneous films exist with a two phase double layer structure which is responsible for some peculiarities reported in the literature.