Oxide removal and desorption of oxygen from partly oxidized thin films of copper at low pressures

Partly oxidized copper films were annealed in a controlled vacuum of 10^–7 Pa at a temperature of 450° C. The changes discussed below were observed in situ with a specially designed high-resolution transmission electron microscope. The thin, (100)-oriented, single-crystal films of copper had been oxidized immediately prior to the annealing studies at the same temperature and at an oxygen partial pressure of 7×10 ^–1 Pa, until the desired fraction of the copper film was converted to oxide. It was observed that the oxide disappeared during annealing as long as some copper was left unoxidized. The disappearance of the oxide is explained as being due to dissociation of the oxide at the oxide-metal interface followed by diffusion of oxygen into the metal and desorption of oxygen from the surface of the unoxidized copper. The rate of disappearance of the oxide was found to be proportional to the surface area of unoxidized copper, i.e., the desorption was found to be the rate — limiting step. In the case of heavily oxidized films (>50%), holes were observed to develop in the oxide near the oxide-metal interface after an annealing period of 2–3 hr. Upon resumption of the oxidation, these holes first disappeared, and the normal oxidation behavior was then resumed. The formation of holes may be explained by vacancy clustering. When completely oxidized films were annealed, recrystallization of the oxide was observed.This work was performed at the Ames Research Center and funded by NASA Grants Nos. NCA2-OP390-403 and NSG-2025.     

Preparation and electrochemical performance of copper foam-supported amorphous silicon thin films for rechargeable lithium-ion batteries

Amorphous Si thin films, which have been deposited on copper foam by radio-frequency (rf) magnetron sputtering, are employed as anode materials of rechargeable lithium-ion batteries. The morphologies and structures of the as-prepared Si thin films are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). Electrochemical performance of lithium-ion batteries with the as-prepared Si films as the anode materials is investigated by cyclic voltammetry and charge-discharge measurements. The results show that the electrode properties of the prepared amorphous Si films are greatly affected by the deposition temperature. The film electrode deposited at an optimum temperature of 300 °C can deliver a specific capacity of ∼2900 mAh/g and a coulombic efficiency above 95% at charge/discharge current density of 0.2C after 30 cycles. The Li⁺ diffusion coefficiency in copper foam-supported Si thin films is determined to be 2.36 × 10⁻⁹ cm²/s.     

Structure and phase separation of Ag–Cu alloy thin films

We report an in situ electron diffraction study and microscopy observation of phase separation in Ag–Cu solution alloy thin films of different compositions and film thicknesses. The results show that the as-deposited films consist of nanocrystalline Ag- and Cu-rich phases of a few nanometers in size. Upon annealing, two stages of thin-film transitions are observed. In the first stage, the growth of Cu crystallites is responsible for phase separation in Ag₅₀Cu₅₀ or Ag-rich alloy. For the Cu-rich samples, the phase separation process is much slower. The second stage transition involves thin film dewetting. A combination of Z-contrast scanning transmission electron microscopy imaging and electron diffraction reveal grain growth and phase separation between Ag and Cu in both stages. Atomic force microscopy results show the surface morphology of thin films only changes significantly at the late stage of phase separation when the thin film dewets.     

Influence of CeO2-coating on the high-temperature oxidation of chromium

The reactive-element effect on high-temperature oxidation of chromium metal was studied at oxygen pressures of 10⁵ Pa (1 atm) and 0.67 Pa and at temperatures of 800 and 1050°C under both isothermal and cyclic conditions. The reactive element, cerium, was applied as a cerium-oxide coating by sol-gel deposition. Growth and adherence of the chromia scale on the metallic substrate were investigated by kinetic weight-gain measurements, and the microstructure was characterized by scanning electron microscopy, transmission electron microscopy, EDX-analysis, X-ray diffraction, and Auger analysis. The study of the oxidation kinetics under isothermal conditions at 800°C clearly showed a reduction in the growth rate of the oxide film when cerium oxide was present. Improvement of the oxide-scale adhesion was also observed when ceria-coated chromium was subjected to thermal cycling. The applicability of a number of models which have been used to explain the reactive-element effect is discussed.     

Optical and electrical properties of zinc oxide thin films with low resistivity via Li-N dual-acceptor doping

Zinc oxide thin films with low resistivity have been deposited on glass substrates by Li-N dual-acceptor doping method via a modified successive ionic layer adsorption and reaction process. The thin films were systematically characterized via scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction, ultraviolet-visible spectrophotometry and fluorescence spectrophotometry. The resistivity of zinc oxide film was found to be 1.04 Ω cm with a Hall mobility of 0.749 cm² V⁻¹ s⁻¹ and carrier concentration of 8.02 × 10¹⁸ cm⁻³. The Li-N dual-acceptor doped zinc oxide films showed good crystallinity with prior c-axis orientation, and high transmittance of about 80% in visible range. Moreover, the effects of Li doping level and other parameters on crystallinity, electrical and ultraviolet emission of zinc oxide films were investigated.     

An analysis of the temperature-induced supersaturation effects on structure and properties of sono-electrodeposited copper thin films

The mechanism of electrodeposition of copper thin film on aluminum has been studied under the influence of power ultrasound using cyclic voltammetry. The deposited thin films were characterized by X-ray diffraction, scanning electron microscopy and atomic force microscopy. Films are crystalline in structure. The spherical copper domains of the deposits without sonication have been converted to mushroom structures in the presence of ultrasound. Properties, including thermal and mechanical are further analyzed using differential scanning calorimeter and nano-indentation. There is a significant change in the variation of thermal stability for films that were deposited at different bath temperatures. The observed hardness values are closely conforming to the reported data available in the open literature. Further the soft films are found to have good wear properties.     

The growth and structure of oxide films on Fe. II. Oxidation of polycrystalline Fe at 240–320°C

The influence of surface pretreatment and metal orientation on the oxidation of coarse-grained polycrystalline Fe has been studied at 240 to 320°C in 5×10^–3 Torr O₂ using electron diffraction, electron microscopy, and Mössbauer spectroscopy to complement kinetic data. Consistent with previous studies on Fe single crystals, differences in oxidation kinetics for surfaces covered with an electropolish film from those with a similar thickness prior oxide formed by dry oxidation at room temperature are interpreted in terms of differing densities of leakage paths in the oxide layers. The more complex kinetics for electropolished polycrystalline Fe are a result of the leakage path density, the degree of oxide separation, and the extent of -Fe₂O₃ formation varying with substrate orientation. Where adherent Fe₃O₄ layers are formed on polycrystalline and single-crystal Fe surfaces, the parabolic rate constants give an activation energy which is consistent with a previous value of 32 kcal · mole^–1, suggesting that at these low temperatures the transport mechanism for magnetite growth is cation diffusion via easy diffusion paths in the oxide.     

The nature of the copper sulfide film grown on copper in aqueous sulfide and chloride solutions

In this paper, the properties of copper sulfide films formed both anodically and naturally in deaerated/anoxic aqueous sulfide and chloride solutions were investigated using a series of electrochemical and surface analytical techniques. A combination of cyclic voltammetric, corrosion potential (E_corr), and cathodic stripping voltammetric experiments showed that the sulfide film growth kinetics and film morphologies were controlled by the supply of SH⁻ from the bulk solution to the copper surface. There was no passive barrier layer observed on the copper surface under either electrochemical or corrosion conditions. The film morphology was dependent on the type and concentration of anions (SH⁻, Cl⁻) present in the solution. Scanning electron microscopy on both surfaces and focused ion beam-cut cross-sections showed the growth of a thin, but porous, base layer of chalcocite (Cu₂S) after short immersion periods (up to 2 hr) and the continuous growth of a much thicker crystalline outer deposit over longer immersion periods (≥36 hr), suggesting a solution species transport-based film formation process and the formation of an ineffective thin “barrier-type” layer on copper.     

Magnetron sputtered nanocrystalline metastable (V,Al)(C,N) hard coatings

Nanocrystalline hard coatings of the system V-Al-C-N with an f.c.c. metastable solid solution (V,Al)(N,C) microstructure were deposited by non-reactive r.f.-magnetron sputtering of a ceramic compound target (composition: 60 mol.% VC and 40 mol.% AIN) in a pure argon discharge at 1.1 Pa. The chemical composition of the as-deposited coatings was determined by electron probe micro analysis (EPMA). The microstructure of the thin films was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The influence of a moderate argon ion bombardment during thin film deposition, realized through the variation of the argon ion energy in the range 20 eV-170 eV, as a means to adjust the adatom surface mobility and surface diffusion processes, on the microstructure evolution and on the Vickers micro-hardness is discussed. The conditions for the formation of a metastable solid solution f.c.c. (V,AI)(C,N) thin film microstructure are described in terms of surface processes during film growth and thermodynamic considerations. It was demonstrated, that a metastable phase formation in the quaternary material system V-Al-C-N can easily be adjusted in magnetron sputter deposition.     

Process–structure–property relations of micron thick Gd2O3 films deposited by reactive electron-beam physical vapor deposition (EB-PVD)

Thick polycrystalline gadolinium oxide (Gd₂O₃) films up to 11 μm in thickness were deposited via reactive electron beam-physical vapor deposition (EB-PVD) on silicon (111) substrates for use in neutron radiation detection. The effects of coating thickness, substrate temperature, and oxygen flow on film structural, electrical and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), capacitance–voltage (C–V) measurements, and ultraviolet–visible (UV–Vis) spectroscopy. Films were characterized as either monoclinic or mixed monoclinic and cubic phase depending on deposition parameters. Increasing the deposition temperature resulted in increased film crystallinity and cubic phase volume while decreasing the O₂ flow rate resulted in increased volume of the monoclinic phase. Evidence of a thickness dependent crystallography is also presented. Electrical property measurements showed thin film dielectric constant could be tailored between 12 and 20 at 1 MHz frequency by decreasing the oxygen flow rate at deposition temperatures of 250 °C which is attributed to an increased presence of the monoclinic phase and increased film density. Band gap values were calculated from transmission measurements and ranged between 5.44 and 5.96 eV.     

Influence of oxidation on the composition and structure of the surface layer of hot-pressed boron carbide

The oxidation of hot-pressed boron carbide under isothermal conditions and under conditions of programmed heating up to 1500°C was investigated. Oxidized samples were studied by secondary-ion mass spectrometry, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray microanalysis, X-ray diffraction, and other methods. It has been demonstrated that oxidation starts above 600°C and results in the formation of a thin transparent B₂O₃ film that is cracked after cooling. Up to 1200°C, the oxidation process is limited by the diffusion of reagents through the oxide layer; at higher temperatures, it is determined by the rate of chemical reaction of carbide with oxygen in the air. During boron carbide oxidation the etching of grain boundaries occurs, it results in strength degradation at higher temperatures.     

New process for synthesis of nickel oxide thin films and their characterization

Sol-gel spin coating method has been successfully employed for the deposition of nanocrystalline nickel oxide (NiO) thin films. The films were annealed at 400-700 °C for 1 h in an air and changes in the structural, morphological, electrical and optical properties were studied. The structural properties of nickel oxide films were studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis shows that all the films are crystallized in the cubic phase and present a random orientation. Surface morphology of the nickel oxide film consists of nanocrystalline grains with uniform coverage of the substrate surface with randomly oriented morphology. The electrical conductivity showed the semiconducting nature with room temperature electrical conductivity increased from 10⁻⁴ to 10⁻² (Ω cm)⁻¹ after annealing. The decrease in the band gap energy from 3.86 to 3.47 eV was observed after annealing NiO films from 400 to 700 °C. These mean that the optical quality of NiO films is improved by annealing.     

Structure and optical properties of nanocrystalline NiO thin film synthesized by sol–gel spin-coating method

NiO thin film was prepared by sol–gel spin-coating method. This thin film annealed at T = 600 °C. The structure of NiO thin film was investigated by means of X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). The optical properties of the deposited film were characterized from the analysis of the experimentally recorded transmittance and reflectance data in the spectral wavelength range of 300–800 nm. The values of some important parameters of the studied films are determined, such as refractive index (n), extinction coefficient (k), optical absorption coefficient (α) and band energy gap (E_g). According to the analysis of dispersion curves, it has been found that the dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters and high-frequency dielectric constant were determined. In such work, from the transmission spectra, the dielectric constant (_∞), the third-order optical nonlinear susceptibility χ⁽³⁾, volume energy loss function (VELF) and surface energy loss function (SELF) were determined.     

Synthesis and characterization of neodymium oxide nanoparticles

The nanometric precursors of neodymium oxide of various morphology from fibrous to well-dispersed spheroidal were prepared via a solvothermal reaction routes. The precursors and their thermal evolution to neodymium oxide phase were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the reaction parameters, kind of solvent as well as neodymium salt used played a key role for the product formation of desired morphology and structure. Similarly, kind of neodymium oxide precursor determined the morphology and the crystal structure (haxagonal or cubic) of the final oxide. The potential application of Nd₂O₃ precursors prepared by solvothermal method as convenient material for preparation of homogeneous thin coatings on planar substrates is shown.     

纳米结构Ni-TiN复合薄膜的电沉积及腐蚀行为

采用电沉积方法在黄铜基底上制备纳米结构的Ni-TiN复合薄膜。用扫描电镜（SEM）及透射电镜（TEM）对其微观结构进行表征,利用X射线衍射（XRD）分析其平均晶粒尺寸,采用极化曲线及电化学阻抗谱（EIS）研究其腐蚀行为。结果表明,电沉积的电流密度、TiN纳米粒子的浓度、搅拌速度、溶液温度及pH值对电沉积薄膜形貌的影响较大。制备的Ni-TiNi电沉积薄膜的平均晶粒尺寸约为50nm。纳米结构的Ni-TiNi电沉积薄膜的耐腐蚀性能远优于纯Ni沉积薄膜的。     

Charge-discharge induced phase transformation of RuO<Subscript>2</Subscript> electrode for thin film supercapacitor

We report on the preparation of an all solid-state thin film micro-supercapacitor using RuO₂ electrode film and LiPON electrolyte film on a Pt/Ti/Si substrate with dual target dc and rf reactive sputtering. Room temperature charge-discharge measurements based on a symmetrical RuO₂/LiPON/RuO₂ structure clearly demonstrated the cyclibility dependence of the RuO₂ electrode on the microstructure. Using both glancing angle X-ray diffraction (GXRD) and transmission electron microscopy (TEM) analysis, it was found that the characteristics of the thin film supercapacitor are dependent on the microstructure of the RuO₂ film. In addition, high-resolution electron transmission microscopy (HREM) analysis after cycling demonstrates that the interface layer formed by interfacial reaction between the LiPON and RuO₂ acts as the main factor in the degradation of the performance of the thin film micro-supercapacitor. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials”, organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

Structural, morphological and electrical properties of spray deposited nano-crystalline CeO2 thin films

Nanocrystalline, uniform, dense, and adherent cerium oxide (CeO₂) thin films have been successfully deposited by a simple and cost effective spray pyrolysis technique. CeO₂ films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. Films were characterized by differential thermal analysis, X-ray diffraction, scanning electron microscopy, atomic force microscopy; two probe resistivity method and impedance spectroscopy. X-ray diffraction analysis revealed the formation of single phase, well crystalline thin films with cubic fluorite structure. Crystallite size was found to be in the range of 10-15 nm. AFM showed formation of smooth films with morphological grain size 27 nm. Films were found to be highly resistive with room temperature resistivity of the order of 10⁷ Ω cm. Activation energy was calculated and found to be 0.78 eV. The deposited film showed high oxygen ion conductivity of 5.94 × 10⁻³ S cm⁻¹ at 350 °C. Thus, the deposited material shows a potential application in intermediate temperature solid oxide fuel cells (IT-SOFC) and might be useful for μ-SOFC and industrial catalyst applications.     

LiCoO2 cathode thin film fabricated by RF sputtering for lithium ion microbatteries

Thin films of lithium cobalt oxide were deposited on Pt or Pt/Ti/quartz glass substrates by radio frequency (RF) magnetron sputtering at the substrate temperatures from room temperature to 500 °C. As the substrate temperature increased, the film structure changed from amorphous structure to crystallinity with a strong (003) texture as characterized by X-ray diffraction. The surface morphology and cross-section were observed using scanning electron microscopy. It was found that the films tended to crack at a high substrate temperature. Charge-discharge tests of these films were conducted and compared. The different electrochemical characteristics of these films were attributed to the modified crystallography, morphology, and thermal stress. The LiCoO₂ film deposited at 400 °C showed a well-defined 4.0 V voltage plateau on charge and a 3.9 V plateau on discharge, and delivered 54.5 μAh/cm² μm at the first discharge capacity, with good cycling performance, giving evidence that such films could be used as the thin film cathodes for lithium microbatteries.     

Characterization of rapid thermally processed LiMn204 thin films derived from solution deposition

Cathode material LiMn₂O₄ thin films were prepared through solution deposition followed by rapid thermal annealing. The phase identification and surface morphology were studied by X-ray diffraction and scanning electron microscopy. Electrical and electrochemical properties were examined by four-probe method, cyclic voltammetry and galvanostatic charge-discharge experiments. The results show that the film prepared by this method is homogeneous, dense and crack-free. As the annealing temperature and annealing time increase, the electronic resistivity decreases, while the capacity of the films increases generally. For the thin films annealed at different temperatures for 2 min, the thin film annealed at 800 °C has the best cycling behavior with the capacity loss of 0.021% per cycle. While for the thin films annealed at 750 °C for different times, the film annealed for 4 min possesses the best cycling performance with a capacity loss of 0.025% per cycle. For the lithium diffusion coefficient in LiMn₂O₄ thin film, its magnitude order is 10⁻¹¹ cm²·s⁻¹.     

The effects of defects in purple AuAl2 thin films

Sputter deposited thin films consisting of the intermetallic phase AuAl₂ are known to display a different color than their bulk counterparts, gray or faint pink, instead of the intense purple the phase is famous for. Only after heat treatment is the typical color apparent. The reason for this behavior is assumed to be point defects in the film, a consequence of the deposition method. Heat treatment at 350 °C of 500 nm thin films results in a steady reduction in defects and the color becomes more intense. Ion irradiation by 3.5 MeV Au⁺ ions with fluences between 10¹² and 5 × 10¹⁵ ions cm^–2 reintroduces point defects in the material and thus gradually removes the color again. Interestingly, the color can be brought back to a very similar shade with subsequent thermal treatments, demonstrating reversibility in the process. The samples were investigated by means of X-ray diffraction, reflectometry, electron backscattered diffraction, scanning electron microscopy, light microscopy, transmission electron microscopy and resistivity measurements to obtain information about the correlation between color and the number of defects within the samples. The measured resistivity values were compared with values calculated using the combined Fuchs–Sondheimer/Mayadas–Shatzkes model. Vacancy concentrations were determined from the difference between the model and the measurements.