Space-charge capacitance in thin semiconductor monocrystalline films

The paper describes the solution for the space-charge capacitance in thin semiconductor films under general boundary conditions. The influence of both surfaces and film thickness on this capacitance is discussed in more detail and it is shown that cases exist in which the space-charge capacitance depends on the properties of one surface or on the film thickness only.Notation E _s2 dimensionless surface field intensity - F ₁, F₂, F₃ space-charge functions - k Boltzmann's constant - n bulk electron density - p _b bulk hole density - q electron charge - T absolute temperature - _o permittivity of free space - _s relative permittivity of semiconductor - dimensionless thicknessd/L _D - dimensionless coordinate perpendicular to the surfacez/L _D - dimensionless potential (multiples ofkT/q).     

Variations in thermoelectric power of thin monocrystalline films with conductivity

Starting from the bi-dimensional model for grain boundaries in monocrystalline thin films, the difference in thermoelectric power is expressed in terms of conductivity and energy dependence of the bulk electronic mean free pathU. A new procedure is suggested for measuringU.     

Activation conduction in metallic island films

The differential conductivity of metallic island films of Ti, Co, W, and FeNi is investigated in the vicinity of liquid nitrogen temperatures. It is found that the temperature dependence of the conductivity of metallic island films in the insulator phase varies in accordance with the activation law σ ∝T ⁿ exp(?E/kT). It is shown that the power of temperature in the preexponential factor varies from n = 2 to 1 upon an increase in the film thickness. In thicker films, in which a transition from the insulator to the metal conductivity phase takes place, the temperature dependence of the conductivity increases in proportion to temperature. The mechanism of conduction in metallic island films is discussed.     

Non-Ohmic conduction in polydiacetylene thin films

We have studied the current–voltage (I–V) characteristics of polydiacetylene (PDA) thin films in the temperature region 300–1.7 K. It was found that at electric fields higher than 2 × 10⁴ V/cm, the I–V characteristics are strongly super-linear with negative temperature coefficient of starting voltage. Negative gate voltage increases the source-drain current (the effect is more pronounced at low temperature), whereas the magnetic field up to 7 T does not affect it. The results demonstrate that at low temperature the charge transport is mainly supported due to a charge injection and tunneling from the metallic banks, whereas at higher temperatures the activation energy is related to the band gap mismatch between the different polymer chains or granules.     

Dynamics of Skyrmion crystals in metallic thin films

We study the collective dynamics of the Skyrmion crystal in thin films of ferromagnetic metals resulting from the nontrivial Skyrmion topology. It is shown that the current-driven motion of the crystal reduces the topological Hall effect and the Skyrmion trajectories bend away from the direction of the electric current (the Skyrmion Hall effect). We find a new dissipation mechanism in noncollinear spin textures that can lead to a much faster spin relaxation than Gilbert damping, calculate the dispersion of phonons in the Skyrmion crystal, and discuss the effects of impurity pinning of Skyrmions.     

Electrical conductivity of multi-layered metallic thin films

Multi-layered metallic thin films have quite unique properties such as electrical conductivity because of their enhanced interactions at the interfaces between different metals. A theoretical solution has been derived for the distribution functions of the conduction electrons, through Boltzmann's equation and certain interface boundary conditions. The solution of the electrical conductivity for the multi-layered metallic thin films is given.     

Size-dependent electrical conduction of thin nickel films

The electrical resistivity of thin nickel films, thermally evaporated on freshly cleaved mica and smooth glass at 160 °C is studied. The measurements were taken in situ before and after annealing at 420 °C.The values of resistivity of thinner films are reduced by few orders of magnitude after annealing. A sharp reduction in the resistivity is noticed for films prepared on mica compared with those prepared on glass under the same conditions. The resistivity of films with thickness less than 200 Å on glass is irreversible with reduction, while on mica it is reversible. A tunnelling mechanism in the absence of Fuchs theory is adapted to explain the abrupt increase in resistivity of the island-films. The data recorded for thicker films was fitted to Fuchs theory withp=0.The authors would like to acknowledge Prof. Dr. K. R.Wassif for his kind cooperation and interest.     

Phonon emission spectra of thin metallic films

Thin metallic films evaporated on an Al₂O₃-single crystal and cooled to liquid helium temperatures are heated by short electric current pulses. The high frequency part of the emitted phonons is detected by calibrated superconductive tunneling junctions on the opposite surface of the substrate. The observed phonon detector signal amplitude is compared with theoretical models taking account of the boundary conditions for elastic waves in the film. It is found that the phonon spectrum emitted perpendicularly to the substrate-film boundary depends strongly on the thickness of the heater film.     

金属薄膜中的逆自旋霍尔效应

自旋流的产生和测量是自旋电子学面临的重大挑战．逆自旋霍尔效应提供了对自旋流进行电学测量的有效手段．文章总结了近年来人们对金属薄膜中的逆自旋霍尔效应的研究,从非局域电注入、铁磁共振注入、声波共振注入和圆偏振光注入这四种不同的自旋流注入方式来介绍逆自旋霍尔效应的物理机制、实现方式和影响因素．     

Intrinsic nonlinear ferromagnetic relaxation in thin metallic films

We propose an intrinsic mechanism for ferromagnetic relaxation in thin films that can dominate competing linear mechanisms even for rapidly relaxing metals. In particular, we use an analytic theory of four-magnon scattering to demonstrate rapid decay for technologically important systems involving high moment materials subject to large rotations. A micromagnetic simulation is used to verify the results.     

金属薄膜中的逆自旋霍尔效应

自旋流的产生和测量是自旋电子学面临的重大挑战.逆自旋霍尔效应提供了对自旋流进行电学测量的有效手段.文章总结了近年来人们对金属薄膜中的逆自旋霍尔效应的研究,从非局域电注入、铁磁共振注入、声波共振注入和圆偏振光注入这四种不同的自旋流注入方式来介绍逆自旋霍尔效应的物理机制、实现方式和影响因素.     

Ferromagnetic-antiferromagnetic coupling: NiFe thin films deposited on monocrystalline CoO substrates

NiFe thin films have been deposited on monocrystalline CoO substrates cut out from a single crystal and carefully polished. A loop displacement and a large increase of the easy axis coercive force are found below the Néel temperature of the oxide. At the same time, the torque curves show residual rotational hysteresis in large applied fields, unidirectional anisotropy and an anomalous increase of the uniaxial anisotropy. The results do not depend on the orientation, (111) or (100), of the substrates, because of surface roughness. Unidirectional anisotropy and rotational hysteresis are due to exchange coupling at the interface between the two materials. The increase inK _u andH _c might result from strain effects or from ferro-antiferromagnetic exchange coupling.Supported by DGRST, Contract No 69-01-908, and by CNRS.The authors wish to thank M. Schlenker and R. Perrier de in bâthie for supplying the CoO single crystals and for helpful discussions, J. L. Fraimbault for his valuable advices in the preparation of samples and N. Vejllet for her help in the mechanical polishing.     

Size effects of static conduction in thin tantalum films

In thin tantalum films grown by pulsed laser deposition in a vacuum, the resistivity versus thickness dependence is found to oscillate. The oscillation periods equal 5.0 and 5.6 nm for α-and β-Ta films, respectively. This observation is interpreted as the quantum-size effect in thin tantalum films.     

Temperature dependence of SSW linewidth in metallic thin films

Measurements of the standing spin wave linewidth H _n at 17·6 GHz from 6 °K to 400 °K are presented for two permalloy films whose structure is either polycrystalline or epitaxial. It is shown that in both films, H _n is proportional ton ² (n is the mode number). Although H _n is little modified by temperature (20% variation maximum over the entire temperature range), we experimentally state that the slopep of H _n (n ²) is a linear function of the saturation magnetizationM which agrees with a planar inhomogeneity model.The authors wish to thank H. Pascard and F. Hoffmann who have prepared and selected the films as also E. Villain and A. Gatineau for invaluable technical assistance.     

Hopping conduction in GeCr amorphous thin films

Thin amorphous films of germanium and GeCr alloys have been prepared by vacuum evaporation. Their electrical resistivity is studied in function of temperature for concentrations of chromium up to 13.5%. The results are analysed and compared to Mott and Ambegaokar theories of electrical conduction in amorphous materials.     

Resistance changes in thin metallic films under ion bombardment

Resistance changes in thin films of copper, aluminium and bismuth have been studied under the bombardment of nitrogen, carbon and argon ions. Variations in resistance with implantation dose have been observed upto doses of ∼ 3 × 10¹⁷ ions/cm² for ion energies in the range 40 to 120 keV. The results are discussed in terms of desorption of gases from the film and a composite action of sputter removal of the film and its structural changes upon ion bombardment. A simple theoretical model is discussed which can qualitatively explain the experimental observations.     

A contribution to the theory of the space-charge region in thin semiconductor monocrystalline films

The potential distribution in films the thickness of which is equal to or smaller than the Debye length is derived from Poisson's equation under general boundary conditions. It is shown that there exist three basic forms of this distribution depending on the densities and character of charges on both surfaces, on the geometrical thickness of the thin film and on the Debye length of the semiconductor.Notation E _S 1,E _S 2 dimensionless surface field intensities - F ₁ F ₂ space-charge functions - L _D Debye length - k Boltzmann's constant - n _b bulk electron density - N _S 1,N _S 2 concentration of surface charges - p _b bulk hole density - q electron charge - T absolute temperature - thickness of thin film measured in Debye lengths - coordinate perpendicular to the surface measured in Debye lengths - ₀ permittivity of free space - _s relative permittivity of semiconductor - dimensionless potential (multiples of kT/q) - E _cb energy of bulk conduction-band edge - E _c energy of conduction-band edge - E _i energy line that runs parallel to band edges and coincides in the bulk (assumed homogeneous) withE _ib , the intrinsic Fermi level - E _v energy of valence-band edge - E _vd energy of bulk valence-band edge - V potential     

On defects in aluminium single crystal thin films

Defects in Al single crystal thin films prepared by epitaxial growth on mica were investigated by transmission electron microscopy. Dislocations, subgrain boundaries, grain of different orientation and separated polycrystalline regions were observed in the single crystal matrix with density dependent on the pressure of residual gases.