X-ray photoelectron spectroscopy study of the initial growth of transition metal nanoscale films on (100) Si substrates

The initial growth stages of materials non-active to a substrate has been extensively studied for decades, whereas there had been fewer studies on the initial growth of active metals on silicon substrate, despite its technological importance. In this paper the very early growth stages of transition metal (Ti, V and Nb) films deposited by rf sputtering on unheated (100) Si substrate were studied by in situ X-ray photoelectron spectroscopy. The following sequence of the phase composition and the growth mechanism changes during deposition process was revealed. Initially in a submonolayer regime, small 3D TiO₂ islands are formed via reduction of a native silicon oxide layer on a substrate followed by formation of a TiO phase between TiO₂ islands and on their top. After deposition of ca. 2 monolayers a metallic Ti phase appears and later only the metal Ti film grows. The same growth behavior takes place at Nb and V deposition with a difference that in the case of Nb the above changes occur at earlier stages what can be explained by the highest niobium activity to the reduction of silicon oxide in the row V, Nb, Ti.     

Characterization of metal films on corundum substrates

Gold layers on corundum, -Al₂O₃, substrates, with intermediate sputtered copper and chromium layers, are used for microwave integrated circuit applications. The existance of islands of monocrystalline Au and Cu in otherwise polycrystalline material has been verified using X-ray and electron diffraction techniques. In these monocrystalline regions, a discrete Cr layer, under the Au and Cu layers, is no longer present. Investigations on specially prepared samples established the monocrystalline Cu to be a twinned epitaxic layer with (111)Cu//(0001)-Al₂O₃; [¯1¯12] Cu//[2¯1¯10]-Al₂O₃. In a sample consisting of a single Cr layer on -Al₂O₃, the Cr was found to be epitaxic with (110) Cr//(0001)-Al₂O₃. Epitaxic islands are detrimental to device performance, and their formation has been suppressed by reducing the sputtering power density.     

Deposition of diamond films on metal substrates

In this paper we report on the growth of polycrystalline diamond films on Mo, W, and Ni substrates using oxy-acetylene combustion flame technique. Effect of substrate temperature on the growth of diamond films has been studied in the temperature range 600–1100°C. The deposits and their surface morphology has been characterized by X-ray diffraction and scanning electron microscopy (SEM). A short duration pretreatment of Mo substrates by outer zone of the oxy-acetylene flame at lower substrate temperatures, results in the improvement of quality and adherence of the films. Growth of diamond as well as other intermediate compounds depending on the nature of substrates and interface layers is discussed. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

An investigation of the growth of nickel ferrite films on magnesium oxide substrates

Nickel ferrite films have been prepared by chemical vapour deposition and by the oxidation of sputtered and vacuum deposited films at high temperature. The interaction of magnesium oxide substrates with these films has been investigated using a wide range of electron optical techniques. Considerable interdiffusion is observed, which is likely to alter the magnetic properties of these films.     

X-ray absorption and Raman study of GaN films grown on different substrates by different techniques

Raman scattering and polarization-dependent synchrotron radiation X-ray absorption, in combination, have been employed to examine the residual stress of undoped GaN epitaxial layers grown on Si by molecular beam epitaxy and Si-doped n-type GaN layers grown on sapphire by metalorganic chemical vapor deposition. Values of the lattice constant of different GaN films can be deduced from the interatomic distances in the second coordination shell around Ga by polarization-dependent extended X-ray absorption fine structure analysis and the strain of the films can be obtained. This result is further confirmed by Raman scattering spectra in which the phonon modes show a significant shift between different GaN epitaxial layers with different growth conditions.     

Adhesion testing of glass-ceramic thick films on metal substrates

The adhesion of thick glass-ceramic films bonded to metal substrates was measured using five different tests: tensile delamination using a bonded stud, scratch testing, an interfacial shear test, indentation and a bend test. All the tests proved to have limitations, and no test gave a fully quantitative measure of adhesion. However, the different tests did rank the samples in the same order of adhesion strength. This indicates that although a fully quantitative method of testing the adhesion of thick films has not yet been developed, many of the published tests can be used to obtain qualitative data.     

A study of crystallographic phases in non-stoichiometric (oxygen deficiency) indium oxide thin films

Indium oxide is a well-known transparent conductive oxide (TCO) in its stoichiometric composition (In₂O₃). Its electrical and optical properties are strongly influenced by the chemical composition. This work focuses on an experimental investigation of the crystallographic phases in non-stoichiometric (oxygen deficiency) compositions of indium oxide thin films. The thin films were deposited at 300 °C by reactive sputtering of pure indium target at different oxygen gas flow rates on Si substrates. Two different phases are identified only in the non-stoichiometric compositions: metallic indium- and crystalline indium-rich oxide. The metallic indium phase appears as nano-crystals, a few nano-meters in diameter, evenly dispersed and occupies only 1 vol. % of the film. These metallic nano-particles have a negligible effect on the optical transparency and electrical conductivity of the films. The indium-rich oxide (In_xO_y) phase which occupies about 99 vol. % of the film has the bixbyite crystallographic structure and average grain size of about 50 nm. This phase has a pronounced effect on improving the TCO figure-of-merit (FM) relative to stoichiometric crystalline In₂O₃ films due to a higher increase of the electrical conductivity than the decrease of the optical transparency.     

Gas-tight alumina films on nanoporous substrates through oxidation of sputtered metal films

The fabrication of ultrathin oxide films without gas leakage was investigated for the application to low-temperature solid oxide fuel cells (SOFCs). Aluminum thin films were deposited onto two types of anodic nanoporous alumina substrates with pore diameter of 20 and 200 nm, respectively, using dc-magnetron sputter at room temperature. By subsequent oxidation at temperatures over 500 °C, the metal films were successfully transformed into oxide films with thickness of about 35 and 410 nm. Volume expansion induced from oxidation of metal resulted in dense thin films that are free from hydrogen permeation.     

Vertical ZnO nanowire growth on metal substrates

Vertical growth of ZnO nanowires is usually achieved on lattice-matched substrates such as ZnO or sapphire using various vapor transport techniques. Accomplishing this on silicon substrates requires thick ZnO buffer layers. Here we demonstrate growth of vertical ZnO nanowires on FeCrAl substrates. The pre-annealing prior to growth appears to preferentially segregate Al and O to the surface, thus leading to a self-forming, thin pseudo-buffer layer, which then results in vertical nanowire growth as on sapphire substrates. Metal substrates are more suitable and cheaper than others for applications in piezoelectric devices, and thin self-forming layers can also reduce interfacial resistance to electrical and thermal conduction.     

柔性衬底氧化物半导体透明导电膜的研究进展

回顾和评述了柔性衬底氧化物透明导电膜（包括锡掺杂的三氧化二铟ITO薄膜、铝掺杂的氧化锌AZO薄膜等）的研究进展情况。报道了在柔性衬底上制备的ITO膜、ZnO膜的光电性质对衬底种类、制备工芑及制备参数的依赖关系,给出了在此领域内应进一步进行的工作。     

Reflection X-ray topography of ZnO thin films on non-orienting substrates

Thin or moderately thick polycrystalline films of ZnO with preferentially oriented crystallites deposited on non-orienting substrates can in some cases be investigated using conventional X-ray topography. Examples of such reflection topographs are presented and their characteristic features are discussed. In particular, it is often possible to observe the texture, the film inhomogeneity and the influence of the deposition conditions on the preferred orientation.     

Catalyst-free growth of nanographene films on various substrates

We have developed a new method to grow uniform graphene films directly on various substrates, such as insulators, semiconductors, and even metals, without using any catalyst. The growth was carried out using a remote plasma enhancement chemical vapor deposition (r-PECVD) system at relatively low temperatures, enabling the deposition of graphene films up to 4-inch wafer scale. Scanning tunneling microscopy (STM) confirmed that the films are made up of nanocrystalline graphene particles of tens of nanometers in lateral size. The growth mechanism for the nanographene is analogous to that for diamond grown by PECVD methods, in spite of sp2 carbon atoms being formed in the case of graphene rather than sp3 carbon atoms as in diamond. This growth approach is simple, low-cost, and scalable, and might have potential applications in fields such as thin film resistors, gas sensors, electrode materials, and transparent conductive films.     

Nanostructuring thin Au films on transparent conductive oxide substrates

Fabrication processes of Au nanostructures on indium-tin-oxide (ITO) surface by simple, versatile, and low-cost bottom-up methodologies are investigated in this work. A first methodology exploits the patterning effects induced by nanosecond laser irradiations on thin Au films deposited on ITO surface. We show that after the laser irradiations, the Au film break-up into nanoclusters whose mean size and surface density are tunable by the laser fluence. A second methodology exploits, instead, the patterning effects of standard furnace thermal processes on the Au film deposited on the ITO. We observe, in this case, a peculiar shape evolution from pre-formed nanoclusters during the Au deposition stage on the ITO, to holed nanostructures (i.e. nanorings), during the furnace annealing processes. The nanorings depth, height, width, and surface density are shown to be tunable by annealing temperature and time.     

Synthesis and characterization of vanadium oxide thin films on different substrates

In this study, the V₈O₁₅ derivative of vanadium oxide was produced on plain glass, indium tin oxide and silicon wafer substrate layers by taking advantage of wet chemical synthesis which is an easy and economical method. The structural properties of the produced films were examined by XRD and SEM analyses. Besides, Al/VO_x/p-Si metal-oxide-semiconductor (MOS) structure was obtained by the same synthesis method. Doping densities of these MOS structures were calculated from frequency dependent capacitance–voltage measurements. It was determined that the interface states which were assigned with the help of these parameters vary according to frequency.     

Effect of crystallographic orientations on electrical properties of sputter-deposited nickel oxide thin films

Nickel oxide thin films of various preferred orientations were deposited by radio-frequency (RF) magnetron sputtering process in different gas ratios of oxygen atmosphere at RF power 200 W on unheated and heated for (673 K) substrates. The relationships among substrate temperature, preferred orientation and electrical properties of the NiO films were investigated. The resulting films were analyzed by grazing-incidence X-ray diffraction, high-resolution transmission electron microscopy (HR-TEM), and ultrahigh resolution scanning electron microscopy (HR-SEM). The electrical properties were measured using four probe and Hall effects measurements. The results show that films deposited at room temperature with the ratio of oxygen varying from 0 to 100% develop a (111) preferred orientation. At temperature of 673 K, while the (111)-orientated film was obtained under a low ratio of oxygen (<50% O₂), a (200) preferred orientation was developed under 100% oxygen. The lowest sheet resistance 0.01 MΩ/□, resistivity 0.83 Ω-cm and higher carrier density 7.35 × 10¹⁸ cm⁻³ could be obtained on (111) preferred orientation samples prepared on unheated substrates in pure oxygen atmosphere. The relationship between preferred orientation and electrical properties was proposed in this paper.     

原子层淀积制备金属氧化物薄膜研究进展

原子层淀积(ALD)技术作为一种先进的薄膜制备方法近年来越来越得到重视,它能精确地控制薄膜的厚度和组分,实现原子层级的生长,生长的薄膜具有很好的均匀性和保形性,因而在微电子和光电子等领域有广泛的应用前景。本文综述了ALD技术的基本原理,及其在金属氧化物薄膜制备上的研究进展。     

Nucleation and growth of GeTe films on KCl and SnTe substrates

The nucleation and growth of GeTe films on KCl or SnTe substrates is found to follow the same mechanism on both substrates. Nucleation occurs through the formation of three-dimensional nuclei of almost equal sizes, bounded by edges along the [110] and [1$\text{1}$0] directions. The growth continues through the lateral extension of the nuclei. The overgrowth layer is anisotropic strainwise, due to the difference in lattice misfit along [110] and [1$\text{1}$0]. This angular misfit is responsible for an increase in the equilibrium energy by 5%. The excess strain is accommodated by misfit dislocations forming a network parallel to the [110] and [1$\text{1}$0] directions, the dislocations being of the edge orientation with Burger's vector equal to $\text{1}\text{2}\text{a<110>}$ and with a different linear density in the two directions. Annealing the system GeTe/SnTe results in a substantial decrease in the density of dislocations due to cross diffusion of Ge and Sn respectively, which forces the dislocations to climb to the surface.     

Permeation barrier properties of thin oxide films on flexible polymer substrates

Solar cells and organic electronic devices require an encapsulation to ensure sufficient lifetime. Key parameters of the encapsulation are permeation barrier, UV stability, temperature stability, optical transmission spectra and mechanical stability. The requirements depend very much on the specific application. Many work groups suggest multilayer stacks to meet the permeation requirements. In this paper the permeation barrier properties of the different constituents of such a multilayer stack are characterized. Different layer materials are compared regarding their water vapour and oxygen permeability as well as the influence of process parameters is examined. Finally temperature dependent permeation measurements are used to characterize the permeation mechanisms in the different constituents of the multilayer barrier.