Characterization of superconducting YBaCuO-films by low temperature scanning electron microscopy

Low-temperature scanning electron microscopy has been performed for imaging the spatial distribution of the critical current densityj _c(x,y) and of the critical temperatureT _c(x,y) in polycrystalline superconducting YBaCuO films. Strongly inhomogeneous behavior has been observed, and the spatial resolution limit has been found to be 1–2 m. The local temperature increment in the specimen film caused by the electron beam scanning has been demonstrated experimentally as the underlying mechanism of the imaging principle, and the beam-induced thermal perturbation of the high-T _c film/substrate configuration is discussed in detail. The radiation hardness of the sample films against the electron beam irradiation in our imaging experiments has been evaluated. No radiation damage could be detected up to the maximum applied dose of well above 10²⁰ electrons/cm² for a typical beam energy of 26 keV.     

Microstructure, hardness, and electrical behavior of Y-doped CaZrO3 films prepared by chemical solution deposition

CaZr_0.9Y_0.1O_3???δ films were fabricated by chemical solution deposition on single-crystalline YSZ (ZrO₂ doped by 10 mol% of Y₂O₃) substrates. Mechanical hardness and morphology of the films were studied using nano-indentation and atomic force microscopy techniques. Grain microstructure of the films has been shown to depend upon thermal treatment duration and film thickness. Thin films with grains a few times greater than the film thickness have been obtained. It has been shown that thickness of films can be evaluated by comparing of the indentation curves for the clean and coated by the film substrates. Mechanical hardness of the film has been found to be sensitive to the film grain microstructure. Electrical behavior of CaZr_0.9Y_0.1O_3???δ films studied by impedance spectroscopy strongly depends on the film microstructure.     

Emission characteristics of a barrier discharge in an Ar-H2O mixture

We have experimentally studied the UV radiation of a low-temperature barrier discharge plasma in an Ar-H₂O mixture. The spectral interval 300–400 nm has been examined in detail. Addition of argon with a pressure of 24 kPa to a barrier discharge in water vapor at a pressure of ～0.1 kPa leads to a ninefold increase in the UV radiation power of excited hydroxyl molecules. An increase in the duration of the UV radiation pulse of the mixture in the longitudinal discharge decay has been achieved for the first time, which may be direct evidence of energy transfer from metastable argon atoms to water molecules. An estimate of the upper boundary of the dissociative excitation rate constant of hydroxyl molecules OH*(A ²Σ⁺) upon interaction of metastable argon atoms with water molecules has been obtained.     

Microstructure, chemical bonds, and friction properties of nanocrystalline diamond films deposited in two different plasma media

Nanocrystalline diamond films with the properties dependent on the composition of the gaseous medium have been prepared using the microwave plasma enhanced chemical vapor deposition (MPECVD) method. A nanocrystalline film formed in the Ar/CH₄ plasma is characterized by a high crystallinity factor, a small grain size, a large fraction of sp ²-amorphous carbon, and, consequently, by an increase in the hardness and elastic modulus. The low value of the friction coefficient of this film is associated with the small grain size and large fraction of the sp ²-amorphous carbon boundary phase that ensures an easy sliding. The contact angle of the film is small (hydrophilic properties) in the case when the plasma consists of an Ar/CH₄ mixture. It has been shown that the wetting properties of the films are provided by a thin layer of carboxyl and hydroxyl functional groups passivating the dangling bonds at the surface that are responsible for the boundary lubrication mechanism. It has also been found that the friction coefficient of these films is inversely proportional to the contact pressure dependent on the diameter of the sliding counterbody ball.     

The Effect of Substrate Temperature on the Properties of Nanostructured Silicon Carbide Films Deposited by Hypersonic Plasma Particle Deposition

Nanostructured silicon carbide films have been deposited on molybdenum substrates by hypersonic plasma particle deposition. In this process a thermal plasma with injected reactants (SiCl₄ and CH₄) is expanded through a nozzle leading to the nucleation of ultrafine particles. Particles entrained in the supersonic flow are then inertially deposited in vacuum onto a temperature-controlled substrate, leading to the formation of a consolidated film. In the experiments reported, the deposition substrate temperature T_s has ranged from 250°C to 700°C, and the effect of T_s on film morphology, composition, and mechanical properties has been studied. Examination of the films by scanning electron microscopy has shown that the grain sizes in the films did not vary significantly with T_s. Micro-X-ray diffraction analysis of the deposits has shown that amorphous films are deposited at low T_s, while crystalline films are formed at high T_s. Rutherford backscattering spectrometry has indicated that the films are largely stoichiometric silicon carbide with small amounts of chlorine. The chlorine content decreases from 8% to 1.5% when the deposition temperature is raised from 450°C to 700°C. Nanoindentation and microindentation tests have been performed on as-deposited films to measure hardness, Young's modulus and to evaluate adhesion strength. The tests show that film adhesion, hardness and Young's modulus increase with increasing T_s. These results taken together demonstrate that in HPPD, as in vapor deposition processes, the substrate temperature may be used to control film properties, and that better quality films are obtained at higher substrate temperatures, i.e. T_s700°C.     

Studies on the effect of nozzle-to-substrate distance on the structural, electrical and optical properties of spray deposited CdIn2O4 thin films

The physical, chemical, electrical and optical properties of as-deposited and annealed CdIn₂O₄ thin films deposited using spray pyrolysis technique at different nozzle-to-substrate distances are reported. These films are characterized by X-ray diffraction, XPS, SEM, PL, Hall effect measurement techniques and optical absorption studies. The average film thickness lies within 600-800 nm range. The X-ray diffraction study shows that films exhibit cubic structure with orientation along (3 1 1) plane. The XPS study reveals that CdIn₂O₄ films are oxygen deficient. Room temperature PL indicates the presence of green shift with oxygen vacancies. The typical films show very smooth morphology. The best films deposited with optimum nozzle-to-substrate distance (NSD) of 30 cm, has minimum resistivity of 1.3 × 10⁻³ Ω cm and 2.6 × 10⁻⁴ Ω⁻¹ figure of merit. The band gap energy varies from 3.04 to 3.2 eV with change in NSD for annealed films. The effect of NSD as well as the annealing treatment resulted into the improvement of the structural, electrical and optical properties of the studied CdIn₂O₄ thin films.     

Synthesis and characterization of superhard Ti-Si-N films obtained in an inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) with magnetic confinement

Using a novel inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) with magnetic confinement system, Ti-Si-N films were prepared on single-crystal silicon wafer substrates by sputtering Ti and Si (5 at.%:1 at.%) alloyed target in argon/nitrogen plasma. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), atomic force microscopy (AFM) and Nano Indenter XP tester were employed to characterize nanostructure and performances of the films. These films were essentially composed of TiN nanocrystallites embedded in an amorphous Si₃N₄ matrix with maximum hardness value of 44 GPa. Experimental results showed that the film hardness was mainly dependent on the TiN crystallite size and preferred orientation, which could be tailored by the adjustment of the N₂/Ar ratio. When the N₂/Ar ratio was 3, the film possessed the minimum TiN size of 10.5 nm and the maximum hardness of 44 GPa.     

微波ECR磁控溅射制备SiNx薄膜的XPS结构研究

利用微波电子回旋共振等离子体增强非平衡磁控溅射法在不同N₂流量下制备无氢SiN_x薄膜.通过X光电子能谱、纳米硬度仪等表征技术,研究了不同N₂流量下制备的SiN_x薄膜的化学键结构、化学键含量、元素配比及各元素沿深度分布.研究结果表明,N₂流量是影响SiN_x薄膜化学键结构、元素配比、元素延深度分布等性质的主要因素.在N_{2关键词： x}')" href="#">SiN_x 磁控溅射 XPS 化学键结构     

Ionizing radiation effects on electrical and reliability characteristics of sputtered Ta2O5/Si interface

This paper describes the effect of ionizing radiation on the interface properties of Al/Ta₂O₅/Si metal oxide semiconductor (MOS) capacitors using capacitance–voltage (C–V) and current–voltage (I–V) characteristics. The devices were irradiated with X-rays at different doses ranging from 100?rad to 1?Mrad. The leakage behavior, which is an important parameter for memory applications of Al/Ta₂O₅/Si MOS capacitors, along with interface properties such as effective oxide charges and interface trap density with and without irradiation has been investigated. Lower accumulation capacitance and shift in flat band voltage toward negative value were observed in annealed devices after exposure to radiation. The increase in interfacial oxide layer thickness after irradiation was confirmed by Rutherford Back Scattering measurement. The effect of post-deposition annealing on the electrical behavior of Ta₂O₅ MOS capacitors was also investigated. Improved electrical and interface properties were obtained for samples deposited in N₂ ambient. The density of interface trap states (D_it) at Ta₂O₅/Si interface sputtered in pure argon ambient was higher compared to samples reactively sputtered in nitrogen-containing plasma. Our results show that reactive sputtering in nitrogen-containing plasma is a promising approach to improve the radiation hardness of Ta₂O₅/Si MOS devices.     

Patterning of gold nano-octahedra using electron irradiation combined with thermal treatment and post-cleaning process

A novel approach to pattern nanocrystalline gold (Au) octahedra is presented based on electron irradiation combined with thermal treatment and post-cleaning process using HAuCl₄-loaded poly(styrene-b-2-vinyl pyridine) (PS-b-P2VP) block copolymer (BCP) as a precursor material. The BCP tends to cross-link under electron irradiation, and thus a patterned film can be prepared by selectively irradiating an electron beam onto a precursor film using a shadow mask. A post-thermal treatment leads to the formation of crystalline Au nano-octahedra inside the patterned film with a help of the BCP acting as a capping agent. Subsequently, the BCP can be removed by O₂ plasma etching combined with oxidative degradation, with the Au nanoparticles remaining. As a result, a patterned film consisting of high-purity nanocrystalline Au octahedra is fabricated. The sizes of the Au octahedral nanoparticles can be readily controlled from 49 to 101 nm by changing the thickness of the precursor film. The patterned Au nano-octahedra films exhibit excellent surface-enhanced Raman scattering behavior with the maximum enhancement factor of ~10⁶.     

Silver macro‐texture substrates fabricated by plasma selective etching for surface‐enhanced Raman scattering

We have demonstrated a novel method to generate the nanostructured substrate that shows a large enhancement with a spatially uniform enhancement factor of approximately 10⁶ in surface enhanced Raman scattering (SERS). The substrates are fabricated using plasma selective etching. First, the Al₂O₃–TiC template which contains mixed Al₂O₃ and TiC grains with the diameters of ~400 nm is selected as a base plate. The Al₂O₃ and TiC grains have different physical properties, such as hardness, which corresponds to different etching rate in a plasma gas. Then, the Al₂O₃–TiC substrate is selectively etched to generate a random macro‐texture (MT) with different depths using the plasma of mixed gas of Ar and C₂H₄. Third, the MT substrate is deposited with a silver film (Ag). We further demonstrate that by varying the thickness of Ag layer, the EF is different which is confirmed by the plasmonic localized electric fields calculations using finite difference time domain. Finally, we combine this novel Ag MT substrate with ultrathin dielectric film, and the prepared substrates are coated with a 10 Å ta‐C film. The 10 Å ta‐C film can protect the oxygen‐free Ag in air and prevent Ag ionizing in aqueous solutions. More importantly, the ultrathin ta‐C can release the strongest plasmonic electric field to the outside of ta‐C layer and get a higher electric field than the uncoated Ag substrate. We expect that this method has more potential applications in analytic assays using SERS technology. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanical response of proton beam irradiated nitinol

The present investigation deals with the study of mechanical behavior of proton beam irradiated nitinol at room temperature. The specimens in austenitic phase were irradiated over periods of 15, 30, 45 and 60 min at room temperature using 2 MeV proton beam obtained from Pelletron accelerator. The stress-strain curves of both unirradiated and irradiated specimens were obtained using a universal testing machine at room temperature. The results of the experiment show that an intermediate rhombohedral (R) phase has been introduced between austenite and martensite phase, which resulted in the suppression of direct transformation from austenite to martensite (A-M). Stresses required to start R-phase (σ_RS) and martensitic phase (σ_MS) were observed to decrease with increase in exposure time. The hardness tests of samples before and after irradiation were also carried out using Vickers hardness tester. The comparison reveals that the hardness is higher in irradiated specimens than that of the unirradiated one. The increase in hardness is quite sharp in specimens irradiated for 15 min, which then increases linearly as the exposure time is increased up to 60 min. The generation of R-phase, variations in the transformation stresses σ_RS and σ_MS and increase in hardness of irradiated nitinol may be attributed to lattice disorder and associated changes in crystal structure induced by proton beam irradiation.     

Influence of nanocrystalline structure and composition on hardness of thin films based on TiO<Subscript>2</Subscript>

In this work, the influence of Tb-doping on structure, and especially hardness of nanocrystalline TiO₂ thin films, has been described. Thin films were formed by a high-energy reactive magnetron sputtering process in a pure oxygen atmosphere. Undoped TiO₂-matrix and TiO₂:Tb (2 at. % and 2.6 at. %) thin films, had rutile structure with crystallite sizes below 10 nm. The high-energy process produces nanocrystalline, homogenous films with a dense and close packed structure, that were confirmed by X-ray diffraction patterns and micrographs from a scanning electron microscope. Investigation of thin film hardness was performed with the aid of a nanoindentation technique. Results of measurements have shown that the hardness of all manufactured nanocrystalline films is above 10 GPa. In the case of undoped TiO₂ matrix, the highest hardness value was obtained (14.3 GPa), while doping with terbium results in hardness decreasing down to 12.7 GPa and 10.8 GPa for TiO₂:(2 at. % Tb) and TiO₂:(2.6 at. % Tb) thin films, respectively. Incorporation of terbium into TiO₂-matrix also allows modification of the elastic properties of the films.     

TiO2/polyaniline nanocomposite films prepared by magnetron sputtering combined with plasma polymerization process

Radiofrequency plasma polymerization in combination with direct current reactive magnetron sputtering is utilized for the synthesis of TiO₂/plasma polymerized aniline nanocomposite thin films. In the composite film, X-ray diffraction measurements reveal formation of nanocrystalline rutile TiO₂ of crystallite size 3.6 nm. Due to continuous bombardment of plasma species during simultaneous magnetron sputtering and plasma polymerization, the precursors of polymerization are broken and few functional groups are retained in the composite film. The plasma polymerized aniline has the direct optical band gap of 3.55 eV and the nanocrystalline rutile TiO₂ is wide gap semiconductor with indirect gap of 3.20 eV which suggests the existence of an energy barrier at the interface in the composite form. The ac conductivity of composite film shows significant improvement as compared to plasma polymerized aniline film and sputtered rutile TiO₂ film. The composite film may find potential application as antistatic coatings.     

Formation of TiO2 film with lower electrical resistance by aerosol beam and fiber laser irradiation

Titanium dioxide (TiO₂) is a functional ceramic with unique photoconductive and photocatalytic properties. In our previous study, a TiO₂ film was formed by aerosol beam irradiation. The films were darkened by femtosecond laser irradiation in air. Then electrical resistance of the darkened area on the film decreased. The heating process is also a useful method to vary the TiO₂ film property. Local heating can be performed by using a continuous wave (CW) fiber laser. In this study, the film was irradiated with a commercial CW fiber laser in vacuum. Laser irradiated area on the film was also darkened after CW fiber laser irradiation. The electrical resistance of the darkened area on the films was decreased as laser fluence was increased. Electrical resistance of the darkened area after CW fiber laser irradiation in vacuum was much smaller than that after femtosecond laser irradiation.     

Improvement in micro-structural and mechanical properties of zinc film by surface treatment with low temperature argon plasma

Nanocrystalline zinc films were deposited on gold coated borosilicate glass substrates by thermal evaporation method using zinc powders as the source material and then treated with argon plasma at various temperatures. From X-ray diffraction study, the as-deposited films are found to be metallic Zn and polycrystalline in nature. The crystalline nature improves with the increase of temperature up to 200 °C and decreases with the further increase of temperature to 300 °C. The binding energy observed for Zn 2p_3/2, and the binding energy separation between Zn 2p_3/2 and Zn 2p_1/2 in the X-ray photoelectron spectrum indicate that the films are metallic zinc films. Transmission electron microscopic study shows hexagonal shaped grains having size ∼58 nm upon treatment with Ar plasma. It is clearly shown the grain growth and distinct grain boundary with the increase in temperature. The average Young's modulus (E) and hardness (H) are measured to be 84 GPa and 4.0 GPa for as-deposited film, whereas 98 GPa and 5.8 GPa for plasma treated film at 200 °C. The enhancement in mechanical properties is attributed to improvement in crystalline nature of the film and better interlinking between grains and boundaries.     

碳氮膜的红外光谱特性分析

用射频直流磁控溅射法在硅、石英基片上制备碳氮膜;采用傅里叶变换红外光谱(FTIR)技术,对基片上的碳氮膜进行红外光吸收谱测量,发现所制备的膜中有β相的C3N4;用硬度计测量镀膜后的硬度,均比镀膜前有所增强;对所制备的膜进行热处理,结果发现热处理前膜的红外吸收谱与热处理后的红外吸收谱相比没有变化,说明膜的热稳定性较好,可以作为红外光学材料.     

Effects of laser irradiation on optical properties of a-Se100−x Te x thin films

The effect of laser irradiation on the optical properties of thermally evaporated Se_100?x Te _x (x=8, 12, 16) chalcogenide thin films has been studied. The result shows that the irradiation causes a shift in the optical gap. The results have been analyzed on the basis of laser irradiation-induced defects in the film. The width of the tail of localized state in the band gap has been evaluated using the Urbach edge method. As the irradiation time increases, the values of the optical energy gap for all compositions decrease, while tail energy width increases. It is also observed that the optical energy gap decreases with increasing Te content in the alloy. These changes are a consequence of an increment in disorder produced by laser irradiation in the amorphous structure of thin film.     

Direct conversion of a metal organic compound to epitaxial Sb-doped SnO2 film on a (0 0 1) TiO2 substrate using a KrF laser, and its resulting electrical properties

Epitaxial Sb-doped SnO₂ (0 0 1) thin film on a TiO₂ (0 0 1) substrate was successfully prepared by laser-assisted metal organic deposition at room temperature. The effects of the precursor thin film and laser fluence on the resistivity, carrier concentration, and mobility of the Sb-doped SnO₂ film were investigated. The resistivity of the Sb-doped SnO₂ film prepared by direct irradiation to metal organic film is one order of magnitude lower than that of film prepared by irradiation to amorphous Sb-doped SnO₂ film. From an analysis of Hall measurements, the difference between the resistivity of the Sb-doped SnO₂ film prepared using the metal organic precursor film and that of amorphous precursor film appears to be caused by the mobility. Direct conversion of the metal organic compound by excimer laser irradiation was found to be effective for preparing epitaxial Sb-doped SnO₂ film with low resistivity.     

Role of carbon in the formation of hard Ge1−xCx thin films by reactive magnetron sputtering

We have deposited germanium carbide (Ge_1−xC_x) films on Si(1 0 0) substrate via radio-frequency (RF) reactive magnetron sputtering in a CH₄/Ar mixture discharge, and explored the effects of carbon content (x) on the chemical bonding and hardness for the obtained films. We find that x significantly influences the chemical bonding, which leads to a pronounced change in the hardness of the film. To reveal the relationship between the chemical bonding and hardness, first-principles calculations have been carried out. It is shown that as x increases from 0 to 0.33, the fraction of sp³ C-Ge bonds in the film increases at the expense of Ge-Ge bonds, which promotes formation of a strong covalently bonded network, and thus enhances the hardness of the film. However, as x further increases from 0.33 to 0.59, the fraction of sp³ C-Ge bonds in the film gradually reduces, while that of sp³ C-H and graphite-like sp² C-C bonds increases, which damages the compact network structure, resulting in a sharp decrease in the hardness. This investigation suggests that the medium x (0.17<x<0.40) is most favorable to the preparation of hard Ge_1−xC_x films due to the formation of dominant sp³ C-Ge bonds.