Influence of interdiffusion on the electrical conductivity of multilayered metal films

The annealing-time dependence of the electrical conductivity of multilayered single-crystal and polycrystalline metal films has been analyzed theoretically within the frame of the semi-classical approach. It is demonstrated that changes in the electrical conductivity which are caused by the diffusion annealing allow for investigating the processes of the bulk and grain-boundary diffusion, and for estimating the coefficients of the diffusion. The electrical conductivity was calculated and the numerical analysis of the diffusion-annealing time dependence was performed at various parameters.     

Electrical conductivity and diffusion coefficient of electrons in a graphene bilayer

The electron diffusion coefficient and the electrical conductivity of a graphene bilayer in an external electric field with a strength vector directed along the graphene sheet are calculated theoretically. The evolution of the electron system is simulated using the Boltzmann kinetic equation in the relaxation-time semi-classical approximation. Analytic expressions are obtained for the electron diffusion coefficient and the electrical conductivity, and the nonlinear dependences of these quantities on the electric field are established. The dependences of these quantities on the control electrostatic potential between graphene layers are analyzed.     

Grain Boundary Diffusion in Polycrystalline Ferrites with Different Intergranular Potential Barrier

Using the method of layer-by-layer measurements of the electrical conductivity activation energy, an investigation is performed of grain-boundary diffusion of oxygen in polycrystalline Li–Ti-ferrites in the range of temperatures 873–1073 K. A correlation relation is established between the value of the intergranular potential barrier and the parameters of grain-boundary diffusion of oxygen in polycrystalline ferrites. An increase in this value gives rise to a growth in the diffusion activation energy. The grain-boundary diffusion coefficient increases with the value of the intergranular potential barrier.     

Size dependence of the activation energy of diffusion in multilayer Cu-Ni films

The results of studying the effect of the characteristic size on the rate of diffusion processes in nanometer Cu-Ni film systems have been reported. The film system has been prepared by sequential vacuum deposition of the components, and the activation energy of diffusion has been determined from a change in the electrical resistance of the film system in a heating-cooling cycle. It has been shown that the activation energy of grain-boundary diffusion decreases with decreasing characteristic size of the system and amounts to 0.25 eV for the film system with a characteristic size of 5 nm, which corresponds to an increase in the grain-boundary diffusion coefficient by 10 orders of magnitude with respect to massive samples.     

Ionic conductivity of ThO2- and ZrO2-based electrolytes between 300 and 2000 K

A conductivity vs temperature relationship is derived which results from simplified geometrical considerations of a polycrystalline solid electrolyte, assuming that oxygen ion diffusion only takes place through the grains or along the grain boundaries. The relationship proves to be capable of describing conductivity data of YDT, CDT, YSZ and CSZ between 300 and 2000 K. The data analysis reveals that the activation enthalpy as well as the activation entropy of grain conductivity are significantly higher in comparison with grain-boundary conductivity. It may be concluded that BAUERLE's electrical equivalent circuit which underlies the interpretation of dispersive type measurements aiming at separate determination of grain and grain-boundary conductivity ought to be revised.     

Effect of grain-boundary electron scattering in magnetic layers on the magnetoresistive ratio of a polycrystalline sandwich under transverse charge transfer

For a polycrystalline magnetic sandwich, an analytical expression that relates the electron scattering by grain boundary roughness, the conductivity of ferromagnetic layers, and the grain size is derived for the case of a transverse charge transfer. The effect of this scattering mechanism on the giant magnetoresistance of the sandwich is studied with account taken for the dispersity of the ferromagnetic layers and the length of grain-boundary diffusion of nonmagnetic spacer atoms into the layers.     

金纳米薄膜导电和导热性质的实验研究

由于尺寸效应和晶界效应的影响,纳米薄膜在导电和导热方面呈现出与体材料不同的性质.本文实验研究了不同厚度(20～54 nm)金薄膜在不同温度(100～340 K)的导电、导热性质.测量结果显示,薄膜的电导率和热导率比体材料小,洛伦兹数比体材料大,Wiedemann-Franz定律不再成立.随着厚度增加,薄膜的电导率,热导率和电阻温度系数都增加.薄膜热导率随温度变化趋势与体材料相反,随着温度升高而升高.电导率随温度变化趋势与体材料相同,随着温度升高而降低;但薄膜没有体材料对温度变化敏感,导致电阻温度系数下降.     

Étude expérimentale de la diffusion des électrons de conduction par les défauts superficiels de couches minces d'or

Polycrystalline thin gold films are grown under vacuum by successive depositions of metal layers. Their electrical resistivity is interpreted in terms of Fuchs-Sondheimer and Cottey-Halpern theories. For recrystallised samples, these models yield values near 0.3 for the diffusion parameter of conduction electrons by the surfaces. Their bulk resistivity at 20°C is found to exceed that for pure perfect gold by some tenth of microΩ cm.Unrecrystallized layers have large thickness inhomogeneities; consequently their electrical resistance cannot be directly described by the theoretical models used here.The variations of electrical resistance measured when adding a small amount of gold on the free surface of a recrystallized gold film are studied in details. They are explained in terms of diffusion of the conduction electrons by the surface defects created in this. process.The growth mechanism of the film is shown to depend on the state of the free surface, residual gas in the vacuum chamber and substrate temperature. A schematic model for growth process is given to account for oscillations of the diffusion parameter observed during the deposition of the first monolayers of metal.     

金属薄膜厚度小于电子自由程对其光反射率的影响

提出了金属薄膜厚度对薄膜中自由电子的平均自由程影响的物理模型,并给出了薄膜中自由电子的平均自由程的修正公式.理论研究表明:当膜厚小于自由电子的平均自由程时,薄膜中电子平均自由程随膜厚的减小而减小|当膜厚大于或等于自由电子的平均自由程时,薄膜中电子的平均自由程与块状材料一样.利用薄膜中电子平均自由程的计算公式,修正了薄膜导电率的基本理论表达式,再利用金属薄膜的反射率与薄膜导电率的关系,得出金属薄膜厚度对其光反射率的影响.计算机模拟表明:当薄膜厚度小于电子自由程时,金属薄膜反射率随薄膜厚度变化而呈非线性关系.     

Diffraction profiles of thin film diffusion couples

On the basis of hypothetical thin film couples in which a grain-boundary supported diffusion process is simulated, it is shown that the concentration spectrum may contain maxima which would not occur if the process were governed by lattice diffusion only. As such maxima consequently appear in the diffraction pattern, real diffraction profiles of interdiffusion layers must be interpreted carefully, keeping in mind that diffraction peaks need not necessarily be associated with a particular phase. The thin-film diffusion system Au-Cu is chosen as an example to demonstrate experimentally the generation of diffraction maxima which must not be attributed to phase formation.Dedicated to Prof. Dr. F. Lihl on the occasion of his 75^th birthday     

Electrical properties of bilayer heterojunctions in a strong magnetic field

The electrical properties of bilayer heterojunctions in a strong magnetic field at low temperatures have been considered. It has been shown that both the ohmic and Hall conductivities decrease exponentially due to the formation of neutral pairs if the electric fields in the two layers are parallel. In the antiparallel fields, the Hall conductivity is still determined by the activation energy of the excited electrons and decreases exponentially, but the ohmic conductivity decreases much slower, proportional to the temperature square.     

Determination of the Oxygen Diffusion Coeficient in Polycrystalline Li-Ti Ferrites

Two independent methods, the isotope method based on nuclear microanalysis and the method based on measuring the electronic-conductivity activation energy, are used to determine the grain-boundary diffusion and volume diffusion of an oxygen isotope ¹⁸O in a polycrystalline lithium-titanium ferrite at the thermal annealing temperature 1073 K. A comparative analysis is conducted of the potential of the methods in studying oxygen diffusion in the material concerned. It is shown that the technique for obtaining the diffusion parameters from the electronic conductivity measurements allows a comparatively precise determination of both the volume and grain-boundary diffusion coefficients of oxygen in polycrystalline ferrites.     

Thermoelectric effect in laser annealed printed nanocrystalline silicon layers

Nanocrystalline boron and phosphorus doped silicon particles were produced in a microwave reactor, collected, and dispersed in ethanol. Pulsed laser annealing of spin‐coated films of these particles resulted in p‐ and n‐type conductive layers on flexible substrates if a threshold laser energy density of 60 mJ/cm² was exceeded. The thermopower of the laser sintered layers exhibits a distinct maximum at a doping concen‐ tration around 10¹⁹ cm^–3 for both boron and phosphorus doping with an absolute value of the Seebeck coefficient of about 300 µV/K. Since the thermal conductivity of the layers is reduced by nearly the same factor compared to bulk crystalline silicon as the electrical conductivity, these results are promising for the application of such nanocrystalline layers in thin film thermoelectric devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Er3+注入CdTe薄膜的结构和光电性能研究

采用离子注入技术对近距离升华制备的CdTe薄膜进行Er³⁺掺杂研究.讨论了不同掺Er³⁺浓度对CdTe薄膜的结构和光电性能的影响.利用X射线衍射仪、扫描电子显微镜、紫外-可见分光光度计、霍耳效应测试系统和复阻抗分析仪对样品进行测试.结果表明，适当的掺杂量可以改善CdTe薄膜的结晶性能，降低晶界势垒高度，提高其导电性能.在一定掺杂范围内掺Er³⁺对CdTe薄膜的光能隙影响不大. 关键词： CdTe薄膜 离子注入 晶界势垒 光能隙     

Antimony thin-film transport properties and size effect

Antimony thin films were vacuum deposited on glass substrates at room temperature. X-ray structural studies were performed. The thickness dependence of both the de electrical resistivity and the Hall coefficient were earried out at room temperature over a thickness range from 29 nm to 216 nm. The type of conduction, the concentration and the mobility of charge carriers were revealed.Analysis incorporating the electrical resistivity and the Hall effect data has led to the determination of the specular and non-specular size-effect parameters. Parameters such as the bulk resistivity ( ₀), bulk mean free path ( ₀), grain-boundary transmission coefficient (t), external surface parameters (U), surface scattering factor (p) and grain-boundary parameter (V), were all evaluated without using any adjusting parameters.Beside the background contribution to the film resistivity, an estimation of the contribution of the surface and grain-boundary to the film resistivity was also carried out.     

固态金属中声子热传递的分子动力学模拟研究

固态金属中的热传递是声子和自由电子共同作用的结果。自由电子引起的热导率可以通过电导率,利用Wiedemann-Franz定律得到,声子引起的热导率目前仍然不能进行实验测量,只能借助其他方法来研究。本文采用非平衡分子动力学(NEMD)方法,用镶嵌原子方法(EAM)势能模型,模拟计算了不同厚度(1.760-10.56nm)金属镍薄膜中由于声子-声子作用引起的热导率。然后根据纳米厚度金属薄膜的热导率借助关联式推到宏观尺度下由于声子-声子作用引起的热导率。结果表明,对于纳米厚度金属薄膜,由于声子-声子作用引起的热导率比块体金属镍的热导率小一个数量级;薄膜厚度越小,声子-声子作用引起的热导率越小;对于块体金属镍,由于声子-声子作用引起的热导率约占其总热导率的33.0%左右。     

Structural, morphology and electrical properties of layered copper selenide thin film

Thin films of copper selenide (CuSe) were physically deposited layer-by-layer up to 5 layers using thermal evaporation technique onto a glass substrate. Various film properties, including the thickness, structure, morphology, surface roughness, average grain size and electrical conductivity are studied and discussed. These properties are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ellipsometer and 4 point probe at room temperature. The dependence of electrical conductivity, surface roughness, and average grain size on number of layers deposited is discussed.      

Understanding nitrogen-induced effects on the performance of ultra low-k dielectric systems through ab initio simulations

Large scale ab initio molecular dynamics simulations were performed to investigate how Cu/ultra low-k systems are improved when N is incorporated into the pore-sealing layers. It was found that the high affinity of N to Ta and H gives rise to new phases that prevent H atoms from penetrating the Ta diffusion barrier layer. Consequently, the Ta layer forms organized structures with good barrier performance and electrical conductivity. Furthermore, a continuous ductile film is formed to seal the highly porous polymer dielectrics. Interfacial adhesion between the pore-sealing layer and the dielectrics is also enhanced by inter-diffusion.     

Improving hole injection ability using a newly proposed WO3/NiOx bilayer in solution processed quantum dot light-emitting diodes

We propose a novel device structure with a WO₃/NiO_x bilayer to improve the hole injection ability in QLEDs fabricated mainly by a solution-based process. First, we employed a spin-coated NiO_x thin film as a hole injection layer (HIL) to replace Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) PEDOT:PSS which corrodes indium tin oxide (ITO) used as an anode in QLEDs. We showed a simply optimized annealing process, instead of a rather complicated process like doping, can improve the electrical conductivity of the NiO_x thin film. The reason for the dependency of conductivity on the post-metallization annealing is because of the change of the total amount of Ni vacancy in the NiO_x thin film as a function of annealing temperature: The electrical conductivity of the NiO_x thin film annealed at 275 °C was the best in this work. Second, we inserted the WO₃ thin film in between ITO electrode and NiO_x HIL to form an ITO/WO₃/NiO_x structure which reduces the hole injection barrier to 0.35 eV, resulting in the excellent characteristic in view of charge balance. Finally, we measured the properties of QLEDs with the WO₃/NiO_x bilayer to check the effects of the proposed device structure and showed the substantial improvement of the electrical conductivity of NiO_x, the luminance, and the current efficiency of the QLEDs.     

Diffusion of nickel in single- and polycrystalline Cr2O3

Chromia protective layers are formed on many industrial alloys to prevent corrosion by oxidation. Their role is to limit the inward diffusion of oxygen and the outward diffusion of cations. A number of chromia-forming alloys contain nickel as a component, such as steels, FeNiCr and NiCr alloys. To ascertain if chromia is a barrier to outward diffusion, nickel diffusion in chromia was studied in both single crystals and polycrystals in the temperature range 900–1100°C at an oxygen pressure of 10^?4 atm (argon + 100 ppm O₂). A nickel film of ～35 nm thick was deposited on the chromia surface and, after diffusing treatment, nickel penetration profiles were established by secondary ion mass spectrometry (SIMS). Two diffusion domains appear in polycrystals, the first domain is assigned to bulk diffusion and the second is due to diffusion along grain boundaries. For the bulk diffusion domain and diffusion in single crystals, using a solution of Fick's second law for diffusion from a thick film, bulk diffusion coefficients were determined at 900 and 1000°C. At the higher temperature, a solution of Fick's second law for diffusion from a thin film could be used. For the second domain in polycrystals, Le Claire's model allowed the grain boundary diffusion parameter (αD _gb δ) to be established. Nickel bulk diffusion does not vary significantly according to the microstructure of chromia. The activation energy of grain boundary diffusion is slightly greater than the activation energy of bulk diffusion, probably on account of segregation phenomena. Nickel diffusion was compared with cationic self-diffusion and with literature data on Fe and Mn heterodiffusion in the bulk and along grain boundaries. All results were analyzed in relation to the oxidation process of stainless steel.