Two-phase structure of ultra-thin La-Sr-MnO films

The structural, electrical and magnetic properties of ultra-thin La_0.83Sr_0.17MnO₃ (LSMO) films, deposited on NdGaO₃ substrate by using the MOCVD technique, were studied. The film thickness d varied in the range from 4 to 140 nm. X-ray and RHEED measurements demonstrated that the films had a two-phase structure. One phase had an orthorhombic face centred structure (a = 0.406 nm and c = 0.46 nm), while the other one had a cubic perovskite-like structure with a = 0.388 nm. Low field dc resistance and magnetization vs. temperature dependences were investigated in the temperature range from 5 to 300 K using a conventional four-probe method and a SQUID magnetometer. It was found that the temperature of the resistivity maximum, T_m, increases with increasing film thickness and that the value of the Curie temperature T_C estimated from the temperature dependence of magnetization is very close to T_m. Modelling of the remanent magnetization vs. temperature dependence based on a two-phase model was in agreement with experimental results. This model also explains the T_m shift to lower temperatures with decreasing film thickness.     

Preparation and characterization of ultra-thin sol-gel films

The formation and characterization of nanometer thick sol-gel films are reported. The films were prepared by spin-coating of a diluted solution of a silane precursor on a number of different substrates. The effect of dilution, rotation speed and nature of substrate on the thickness and homogeneity of the films was examined. Characterization of the films was carried out by profilometry, reflectance spectroscopy, atomic force microscopy, adhesion test and electrochemistry. We find that the dilution factor has a pronounced effect on the film thickness. Moreover, the time of dilution, namely, whether dilution was carried out before or after a period of hydrolysis, has a noticeable effect on the thickness as well as on the permeability of embedded species.     

Non-ohmic transport behavior in ultra-thin gold films

Structure and local lateral electrical properties of Au films of thicknesses ranging from 10 to 140 nm are studied using conductive atomic force microscopy. Comparison of current maps taken at different thicknesses reveals surprising highly resistive regions (10¹⁰-10¹¹ Ω), the density of which increases strongly at lower thickness. The high resistivity is shown to be directly related to discontinuities in the metal sheet. Local I-V curves are acquired to show the nature of electrical behavior relative to thickness. Results show that in Au films of higher thickness the electrical behavior is ohmic, while it is non-ohmic in highly discontinuous films of lower thickness, with the transition happening between 34 and 39 nm. The non-ohmic behavior is explained with tunneling occurring between separated Au islands. The results explain the abrupt increase of electrical resistivity at lower thin film thicknesses.     

非晶氧化铝超薄膜中的电荷输运特性

研究了反应射频磁控溅射制备的非晶氧化铝薄膜中电荷输运过程,发现交流和直流电导导电机制是明显不同的。对直流输运,以Poole-Frenkel发射发射模式为主,而新样品的直流电导则常常是带陷阱的空间电荷限制电流模式。交流电导则是由所谓的声子辅助的定域载流子的跳跃引起的。电导的温度特性表明,交流电导有两种不同的导电机制,即低温区的浅陷阱发和 高温区的因氧缺陷导致的深陷阱的发射过程,直流电导与交流电导在高温区趋于一致。     

A dynamic bistability in two-layer magnetically-coupled films

The dynamic behavior of magnetic moments in a two-layer magnetically coupled film system was studied in the region of ferromagnetic resonance with large amplitudes of the precession angle. The system exhibits manifestations characteristic of the nonlinear phenomena, including (i) a shift in the resonance frequency with increasing microwave field strength and (ii) the existence of dynamic bistability regions with respect to the microwave frequency and the magnetizing field strength.     

FTIR and ellipsometry characterization of ultra-thin ALD TaN films

In this paper, Fourier-transform infrared (FTIR) spectroscopy and ellipsometric spectroscopy were used to characterize the optical properties of atomic layer-deposited (ALD) ultra-thin TaN films on a Si(1 0 0) single crystal. The analysis of FTIR spectra indicates that the incorporated impurities are in the form of radicals of NH_x, CH_x and OH_x. SiH_x is also detected due to interfacial reactions between NH_x and the Si substrate native oxide. These H-containing radicals can be removed by post-annealing the samples. The vibration of Ta–N bonding is at the wavenumber of 1190 cm⁻¹, which is independent of the film thickness and post-annealing temperature. The results of ellipsometric spectra show that the band gaps are 3.28 eV, 2.65 eV and 2.50 eV as the films thicknesses are 1 nm, 5 nm and 10 nm, respectively. A slight red-shift of the band gap takes place after annealing the ultra-thin films. The mechanisms of the film optical properties were analyzed in the paper.     

FCVA法制备的超薄类金刚石薄膜的结构分析

用真空阴极过滤电弧(Filtered Cathode Vacuum Arc,FCVA)法制备厚度分别为50 nm,30 nm,10 nm,5 nm,2 nm的类金刚石(DLC)薄膜,利用拉曼光谱和电子能量损失谱研究了薄膜的结构,分析了硬度和内应力的变化趋势。结果表明,随着薄膜厚度的减小,可见光拉曼光谱高斯分解的G峰位置向低波数方向移动,D峰和G峰强度之比Id/Ig不断增大,G峰面积与D峰面积之比Ag/Ad减小;说明随着薄膜厚度的减小,DLC薄膜中的sp3键含量减少,有序化的sp2团簇增加。电子能量损失谱的结果也表明薄膜厚度的减小会引起薄膜中sp3键含量的减少。当薄膜的厚度由50 nm变为30 nm时,薄膜硬度由53.85 GPa减小为39.64 GPa,内应力由4.63 GPa降低为3.47 GPa,随着厚度降低,薄膜的硬度和内应力呈下降趋势。     

An X-ray photoelectron spectroscopy study of ultra-thin oxynitride films

Oxynitrides prepared by nitridation of 2 to 5 nm SiO₂ films on silicon, were studied by X-ray photoelectron spectroscopy at two analyser exit angles. An iterative procedure was applied to obtain simultaneously the average nitrogen content and the thickness of the nitrided layer, mutually dependent via the electron transport properties of the layer matrix. Inelastic mean free paths and elastic corrections thereof were determined in accordance with ISO18118:2004(E), whereas a set of empirical relative sensitivity factors was used. The results reveal a significant increase of the 2 nm film thickness upon nitrogen incorporation of the order of 50 at.%, whereas the 5 nm films retain their thickness upon comparable extent of nitridation.     

超薄磁盘保护膜的制备技术

类金刚石薄膜和氮化硅薄膜都是性能很好的绝缘材料,可以用于对磁盘进行保护,在本文中主要讨论了它们各自的制备方法.随着巨磁阻读写磁头(giant magneto-resistive heads)技术的引入,磁盘的存储密度以每年100%的速度在增加,这就要求磁盘保护膜的厚度要尽量的小,所以对制备方法有一定的要求.对类金刚石磁盘保护膜,可以使用等离子体磁控溅射沉积、磁过滤阴极弧沉积、等离子体化学气相沉积来制备;对氮化硅磁盘保护膜,可以使用射频反应溅射沉积来制备.     

Titanium monoxide ultra-thin coatings evaporated onto polycrystalline copper films

We evaporated polycrystalline copper thin films of thickness between 10 and 100 nm on silicon substrates with their native oxide under ultra-high-vacuum conditions. Some of them were exposed to air for a period ranging from 1 day to 2 weeks. X-ray photoelectron spectroscopy (XPS) revealed a clean copper surface with a trace of oxygen. These films that were exposed to air presented oxides in the state Cu(II), the amount of CuO depended on the time that the film was exposed to air. Subsequently, we deposited TiO ultra-thin films on polycrystalline copper substrates. Both these thin films were formed by electron beam evaporation. XPS spectra showed that the surface of the titanium monoxide (TiO) films was contamination-free. An evaporation of 0.3 nm of TiO reduced the native oxide of the copper substrates from Cu(II) to Cu(I) or Cu(0) and transformed the TiO into TiO₂ at the interface. Low-energy ion spectroscopy showed that the complete coverage of the substrates depends on the thickness of the copper films. For 10 nm copper thin films the complete coverage occurred at 1.5 nm of TiO, and for 100 nm it occurred at 2.0 nm of TiO. In samples exposed to air, the complete coverage occurred at a film thickness slightly higher than those treated under ultra-high-vacuum conditions.     

Fabrication of unbacked ultra-thin films of beryllium and other metals

A method is given for preparing ultra-thin unbacked metal films by evaporating the metal onto rock-salt platelets coated with a thin layer of a soluble thermoplastic resin. Beryllium films have been made with thickness ranging from 0.2 to 0.5 μm and free from “optical” pinholes. The beryllium was rapidly and continuously evaporated from a tungsten crucible with very little corrosion of the crucible. Deposition rates of 100 nm s^-1 were achieved with a source-to-substrate distance of 140 mm.     

Epitaxial growth of Bi ultra-thin films on GaAs by electrodeposition

We report on the growth of thin bismuth films on GaAs substrates with different orientations by means of electrochemical deposition. Atomic force microscopy reveals that the films are continuous and exhibit low roughness when they are grown under the appropriate overpotential. ω–2θ X-ray diffraction scans only show reflections that can be indexed as (0 1 L), meaning that Bi grows onto GaAs only in combinations of the (0 0 1) and (0 1 0) orientations. The matching between the GaAs substrate and the Bi layer has been studied by asymmetric X-ray scans, finding that Bi grows epitaxially on GaAs(1 1 0) and GaAs(1 1 1)B, both As-terminated surfaces. We explain these results by structural and chemical considerations.     

Dynamics of helium films

We present quantitative calculations for the static structure and the dynamics of quantum liquid films on a translationally invariant substrate. The excitation spectrum is calculated by solving the equations of motion for time-dependent one- and two-body densities. We find significant corrections to the Feynman spectrum for the phonon-like collective excitations.     

Supramolecular organization in ultra-thin films of alpha-sexithiophene on silicon dioxide.

The supramolecular organization of organic semiconductors on the dielectric layer of thin-film field-effect transistors is a crucial factor in achieving good device performance. Charge transport in these devices occurs near the interface with the gate dielectric. By confocal spectroscopy and microscopy we study the supramolecular organization in ultra-thin films of a prototype organic semiconductor, alpha-sexithiophene, on silicon dioxide, a widely used transistor gate dielectric. We demonstrate that in submonolayer films of sexithiophene (T6), regions where the molecules stand on their long molecular axis coexist with regions where the molecules lie flat on the substrate. When the first monolayer is completed, all T6 molecules stand on the substrate, and the flat molecules detected in the submonolayer films are no longer present. In films thicker than two monolayers, the photoluminescence spectra of standing molecules show a molecular H-like aggregation as in the single crystal.