Estimation of hole conductivity of AgI through tarnishing studies of silver in iodine vapour at about room temperature

This work reports the hole conductivity data of growing AgI film on silver both for the thicker (5500 to 30 000 Å) and thinner (<6000 Å) ranges at about room temperature. Hole conductivity has been estimated through tarnishing studies of silver in iodine atmosphere and estimation has been based on the fundamental equation of Wagner relating the rate constant and the conductivity of the film. It is revealed that the thinner films show a higher hole conductivity than that of the thicker films under similar temperature and iodine pressure.     

Dependence of the longitudinal strain coefficient of resistivity of silver films on thickness and grain size diameter

A grain boundary model modified by including the Fuchs size effect has been used to derive a general expression for the longitudinal strain coefficient of resistivity of continuous polycrystalline silver films, of thickness greater than the intrinsic mean free path, in terms of the grain size diameter and the film thickness. It has been found that the longitudinal strain coefficient of film resistivity has zero value for very small grain size and attains the bulk value when the grain size and the film thickness are very large. It has also been found that a threshold value of the grain size diameter exists, below which the film thickness has practically no effect on the strain coefficient of film resistivity. However, for grain size diameters greater than the threshold value, thicker films have values of the strain coefficient or resistivity higher than those for thinner films.     

Ferromagnetic films deposited on nanochannel alumina

Interest in artificially grown nanostructures has grown enormously in the last few years because of the potential applications in the magnetic recording industry. In this work we present ferromagnetic resonance investigations performed on Fe films sputter-deposited on nanochannel alumina (NCA). These films form a network-like nanostructure on top of the walls that separate the pores. The geometry is fixed by the channel size, the porosity of the substrate and the film thickness. From the experimental results in NCA of 20 nm pore diameter we have found that thinner films (10 nm or less) are discontinuous and formed by isolated, partially oriented anisotropic particles. An average aspect ratio of ∼1.5 was estimated for the particles forming the film. As the film thickness increases the effective anisotropy (mostly shape anisotropy) tends to reach a saturation value for films thicker than 75 nm. For NCA substrates of larger pore diameter (100 nm and 200 nm pore size) the effective anisotropy is greatly reduced and even changes orientation for the thinner films. This behavior is interpreted as comming from a faster filling of the pores with the sputtered material in the substrates with smaller pore size. Received: 30 March 2000     

Thin liquid films flowing over external aerodynamic surfaces

Boundary-layer theories are constructed to describe the evolution of interfacial waves on thin liquid films which are driven by an air boundary layer. The theories are focused on cases which are most relevant to aircraft icing. It is found that condensed-layer solutions with film inertia adequately describe the linear evolution of interfacial waves for thinner films, whereas a triple-deck pressure displacement interaction is required for thicker films. In all cases it is found that inertia must be retained within the film, even when the film is much more viscous than the air.     

SnO2-x薄膜非化学计量比对气敏性能的影响

采用反应磁控溅射法制备SnO2薄膜经常出现化学计量比的失衡问题。通过控制溅射过程中的氧分压制备不同化学计量比的SnO2-x薄膜,研究非化学计量比对薄膜结构、成分以及气敏性能的影响。XRD结果表明氧分压对材料结构和取向的影响非常显著。薄膜的O／Sn和表面化学成分通过XPS进行确定,分析发现氧分压的增加促使薄膜接近化学计量比,但表面化学吸附氧含量在0．33Pa氧分压下达到最大。气敏性能测试表明,非化学计量比主要影响薄膜表面的化学吸附氧数量,从而影响导电性和气体敏感性。氧分压对薄膜化学吸附氧的影响趋势与对气敏性能的影响趋势一致。0．33Pa氧分压下制备的薄膜拥有最多的表面吸附氧,同时对氢气的灵敏度高达45．6％。另外,在0．2～0．5Pa氧分压下制备的薄膜对氢气具有较好的选择性。     

Influence of calcination ambient and film thickness on the optical and structural properties of sol-gel TiO2 thin films

Influence of both calcination ambient and film thickness on the optical and structural properties of sol-gel derived TiO₂ thin films have been studied. X-ray diffraction results show that prepared films are in an anatase form of TiO₂. Films calcined in argon or in low vacuum (∼2 × 10⁻¹ mbar) are found to be smaller in crystallite size, more transparent at low wavelength region of ∼300-450 nm, denser, have higher refractive index and band gap energy compared to air-calcined films. Scanning electron microscopic study reveals that surfaces of TiO₂ films calcined in argon or in low vacuum are formed by densely packed nano-sized particulates. Presence of voids and signs of agglomeration can be seen clearly in the surface microstructure of air-calcined films. In the thickness range ∼200-300 nm, band gap energy and crystallite size of TiO₂ films remain practically unaffected with film thickness but refractive index of thinner film is found to be marginally higher than that of thicker film. In this work, it has been shown that apart from temperature and soaking time, partial pressure of oxygen of the ambient is also an important parameter by which crystallite size, microstructure and optical properties of the TiO₂ films may be tailored during calcination period.     

In situ electrical conductivity and the amorphous-crystalline transition in vacuum deposited thin films of Se80Te20 alloy

The electrical conductivity of thin films of Se₈₀Te₂₀ polycrystalline alloy vacuum-deposited at room temperature on glass substrates has been studied duringin situ heating and cooling cycles. From the electron diffraction of as-grown films it is seen that the studied films are amorphous at room temperature. The electrical conductivity and electron diffraction studies showed that the as-grown amorphous thin films undergo an amorphous-crystalline transition in the temperature range 340 to 360 K. Upon cooling, the films appear to undergo a crystalline crystalline transition around the same temperatures. There does not appear to be any dependence of the amorphous-crystalline transition temperature on the thickness of the films. However, high-resistance films (thinner films) have a well-defined transition temperature while the low-resistance films (thicker films) have a broader transition. The electrical conductivity of polycrystalline Se₈₀Te₂₀ films above 360 K appears to be an exponential function of reciprocal temperature.     

Structure of chemically deposited polycrystalline-silicon films

The influence of the deposition conditions on the structure of chemically deposited, polycrystalline-silicon films has been examined. The films were deposited primarily onto oxidized silicon wafers by the thermal decomposition of silane over temperature and thickness ranges of 650°–1200°C and 0.6–15 microm, respectively. After an initial induction period, which exhibits an activation energy of about 1.0 eV, island-type nucleation was observed for deposition temperatures of 850° and 1025°C; however, no islands could be resolved for a deposition temperature of 650°C. Although {110}- and {111}-texture are both important in the thinner films, {110}-texture becomes dominant over most of the temperature range as the film thickness increases. The {100}-texture is important in thicker films deposited at higher temperatures. Transmission electron microscopy indicated that the grain size increases with increasing film thickness and deposition temperature, ranging from less than 0.05 microm to more than 1 microm in the films studied. An investigation of the influence of the initial stages of deposition on the development of the texture indicated that the highly twinned {110}-grains, once nucleated, grow most rapidly. An anomalous, low-temperature structure, the effect of the reactant gas, and the influence of the substrate have been briefly investigated.     

Measurement of the Temperature Coefficient of Resistance in Metallic Films with Nano-thickness

The temperature coefficient of resistance (TCR) values of gold and aluminum films deposited on glass substrates were obtained in the range of thickness from 20 nm to 200 nm at 298 K and atmospheric pressure conditions. Applying an electrical current and measuring simultaneously the corresponding changes of voltage (i.e., electrical resistance), and the change of temperature on the thin films, the TCR value was estimated. The measured TCR values show a decrement with the film thickness reduction, and their values are approximately 13.0 % lower than their corresponding bulk values mainly for thinner films. A comparison with previously reported cooper TCR values and the values estimated with the Tellier–Tosser model show good agreement with differences of about 5.0 % between them.     

Interplay of the influence of oxygen partial pressure and rf power on the properties of rf-magnetron-sputtered AZO thin films

The complex interplay between the influence of oxygen partial pressure and that of rf power on the structural, electrical and optical properties of rf-magnetron-sputtered aluminium-doped zinc oxide, AZO, thin films is illustrated. The dependence of film electrical resistance and interplanar spacing of film crystallites on rf power seems to be different at higher oxygen partial pressure values than at lower ones. Film preparation was performed at room temperature (without extra heating) and low pressure p \(=\) 0.5 mTorr, varying the rf power density between P \(=\) 0.57 and 2.83 W \(\hbox {cm}^{-2}\) at different relative oxygen partial pressure values. An explanation of film properties has been sought in terms of changes in the chemical properties of the films due to the bombardment of the films during film formation with negative oxygen ions.     

Optical and electrical properties of ZnO films deposited by activated reactive evaporation

ZnO films having good transmittance and conductivity were deposited by activated reactive evaporation of Zn metal on glass and Si substrates at room temperature. Optical constants and thickness of ZnO films deposited under different deposition conditions were determined both by spectroscopic ellipsometry (SE) and spectrophotometry. Structural studies showed that the films exhibited a polycrystalline wurtzite structure with the preferential oriented along the (002) plane. Electrical studies by four probe technique showed that the sheet resistance of the films varied from 10⁶ to 50 Ω/square depending upon the oxygen partial pressure used during deposition, and this sheet resistance value increased with time. The increase in sheet resistance with time was found to be dependent on the surface morphology of the film and on the substrate over which they were deposited.     

Electrospray deposition of silver nanowire films for transparent electrodes

Silver nanowire (AgNWs) films were fabricated as transparent electrodes by electrostatic spray deposition (ESD) at atmospheric pressure and room temperature. The effects of solution concentration, spray flow rate, applied high voltage, and annealing temperature were characterized to obtain uniform films. AgNWs thin film was produced with ca. 20 Ω/[square] sheet resistance and 83% transparency in the visible range. Morphologies, optical and electrical properties, and stabilities of the films were investigated in this work. A maximum ratio of DC to optical conductivity of 288 was achieved in a 120 nm thick AgNW thin film. Chemical stability was evaluated in various solvents and we found that solvents had little effect on conductivity.     

铜膜碘化法制备p型CuI薄膜及其用作空穴传输层的反型钙钛矿电池性能

γ相碘化亚铜(γ-CuI)是一种带隙为3.1 eV的p型半导体材料, 适合应用于发光二极管和太阳能电池等光电子器件。本研究利用简单的铜膜碘化法制备了CuI薄膜, 探究了碘化时间、温度及铜/碘比等生长条件对其透明导电性能的影响。在最优碘化时间(30 min)和碘化温度(120℃)下, 制备出了高透过率(可见光范围>75%)、导电性能好(电阻率4.4×10^-2 Ω·cm)的CuI薄膜。利用CuI薄膜作为空穴传输层, 组装了CuI/CH₃NH₃PbI₃/PCBM反型平面钙钛矿电池, 获得的最高光电转换效率为8.35%, 讨论了CuI薄膜透明导电性能对钙钛矿电池光电转换效率的影响机理。     

The effect of film thicknesses on craze microstructure

Transmission electron microscopy of the fibrillar microstructure of air crazes grown in polystyrene (PS) films thicker than 150 nm, shows this microstructure to consist of fine fibrils 4 to 10 nm in diameter with a mean value of 6 nm, in excellent agreement with recent small angle X-ray scattering measurements on crazes in bulk PS. For films 100 nm and thinner, the crazes have a much coarser microstructure, often resembling a perforated sheet more than a set of discrete fibrils. Where fibrils exist they are much larger in diameter (up to 150 nm) than those in thick film crazes. This change in craze micro-structure with decreasing film thickness is attributed to the absence of plastic constraint in the direction of film thickness. Even in much thicker films the absence of plastic constraint at the film surface gives rise to a surface plastic zone producing a surface groove of depth ∼ 25 nm which can extend up to 1000 nm ahead of the craze tip. The absence of lateral stresses in these films increases the wavelength of the meniscus instability (the mechanism of craze tip advance and fibril formation) until for a film thickness less than this wavelength a true fibril structure can no longer form.     

Effects of metallic, semiconducting, and insulating substrates on the coupling involving radiative polaritons in thin oxide films

Through simulations, this work explores the effects of conducting, semiconducting, and insulating substrates on the absorption of infrared radiation by radiative polaritons in oxide layers with thicknesses that range from 30 nm to 9 μm. Using atomic layer deposition, oxide layers can be formed in the nanometer scale. Our results suggest that the chemistry and conductivity of the substrate determine the amount of absorption by radiative polaritons in oxide layers thinner than the skin depth. The effects of the chemistry and conductivity of the substrate are especially effective for oxide films thinner than about 250 nm, which we label as the substrate sensitive thickness of the oxide film.     

Ellipsometry-based conductivity extraction in case of phosphorus doped polysilicon

In this work, we investigated a new method for thin films electrical conductivity extraction based on spectroscopic ellipsometry. This has been enabled through the correlation between the films conductivity and their ellipsometric properties. Indeed, it has been demonstrated that numerous ellipsometric fitting-based approaches can provide, in an indirect way, the electrical characteristics of thin films. The study was focused on electrical conductivity, but doping level or carriers’ mobility can also be extrapolated from ellipsometric measurements. Among various possibilities leading to electrical properties extraction, we can cite the extremal values of Ψ and Δ ellipsometric angles, their associated wavelengths, the mean square error and the maximal and minimal reflectivities ratio. Otherwise, the correlation between extrinsic conductivity and ellipsometric parameters evolution has been confirmed in case of low doping levels with particular behavior after annealing. This contactless method has been successfully applied to polycrystalline silicon films deposited on oxidized, p-type monocrystalline substrates, by low pressure chemical vapor deposition technique, and lightly or heavily phosphorus doped by diffusion. The feasibility of the method has been proven in this case, but also in other cases like implanted polysilicon layers or silicon-on-insulator (not included here).     

Effect of oxygen partial pressure on the electrical and optical properties of highly (200) oriented p-type Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O films by DC sputtering

Thin films of NiO (bunsenite) with (200) preferential orientation were synthesized on glass substrates by direct current sputtering technique in Ar+O₂ atmosphere. Nanostructural properties of the NiO films were investigated by X-ray diffraction and also by atomic force microscopic (AFM) studies. Electrical and optical properties of the deposited films were investigated as a function of different partial pressure of oxygen in the sputtering gas mixture during deposition. The films showed p-type electrical conduction and the conductivity depends on the partial pressure of oxygen. The electrical conductivity (σ_RT) was found to be .0615 S cm⁻¹ for films deposited with 100% O₂ and its value sharply decreased with the decrease the partial pressure of O₂; for example σ_RT for 50% O₂ was 6.139 × 10⁻⁵ S cm^-1. The mechanism of the origin of p-type electrical conductivity in the NiO film is discussed from the viewpoint of nickel or oxygen vacancies, which generate holes and electrons respectively. X-ray photoelectron spectroscopic studies supported the above argument. Corresponding optical properties showed that the transparency decreases with increasing oxygen partial pressure and the bandgap also decreases.     

X-ray photoelectron spectroscopy and conducting atomic force microscopy investigations on dual ion beam sputtered MgO ultrathin films

Ultrathin films of MgO (~ 6 nm) were deposited on Si(100) using dual ion beam sputtering in different partial pressures of oxygen. These thin films were characterized by X-ray photoelectron spectroscopy (XPS) for chemical state analysis and conducting atomic force microscopy for topography and local conductivity map. No trace of metal Mg was evidenced in these MgO films. The XPS analysis clearly brought out the formation of oxygen interstitials and Mg(OH)₂ primarily due to the presence of residual water vapors in the chamber. An optimum value of oxygen partial pressure of ~ 4.4 × 10^− 2 Pa is identified with regard to homogeneity of film and stoichiometry across the film thickness (O:Mg::0.93-0.97). The local conductivity mapping investigations also established the film homogeneity in respect of electrical resistivity. Non-linear local current-voltage curves revealed typical tunneling characteristics with barrier width of ~ 5.6 nm and barrier height of ~ 0.92 eV.     

Transferable thin films of pristine carbon nanotubes

We describe here a simple and low-cost method to prepare ultra-thin, homogeneous, and transferable films of pristine carbon nanotubes (CNTs). The highly efficient chemical vapor deposition (CVD) growth method involves silica supported catalysts and alcohol vapor as gaseous carbon source. By varying the amount of catalysts, the thickness of synthesized films can be easily tuned from 20 nm (sub-monolayer) to 150 nm in a controlled fashion. High-resolution transmission electron microscopy (HRTEM) revealed that the films are composed primarily of single-walled and a small fraction of double-walled CNTs. A nonlinear relationship between film conductivity and thickness was observed. Our sub-monolayer ( 20 nm) film, which is noticeably thinner than conductive CNT films synthesized using other methods (typically > 50 nm and up to 100 microm), shows the highest conductivity of 400 mho x cm(-1) with 90% transparency in the visible range and close to 100% transparency in the infrared range. This ultra-thin film can also be transferred carrier-film free to a wide range of substrates including low-cost plastics for flexible electronics. Compared to CNT films prepared by filtration techniques, our films demonstrated superior stability against mechanical bending.     

Measurement technique for thermal conductivity of thin polymer films

We present a modified steady-state heat flow technique, which allows measuring the thermal conductivity of films applied on a substrate. The measurement technique with the here presented setup provides an accuracy (overestimation) of 5-10% for film thickness up to 100 μm. For thicker films a correction factor based on finite-element simulations has to be used or the geometry has to be adapted. The technique is validated with thin glass plates of known thermal conductivity. To demonstrate the application of the technique the thermal conductivity of a thin polymer film of fluorinated acrylate is determined as 0.19 ± 0.02 W/mK.