Microstructure and magnetic properties of Co(Cr)/Ti(Cr)/ZnO films prepared by laser ablation on Si substrates

High-quality Co(Cr)(50–66 nm)/Ti(Cr)(25–30 nm)/ZnO(165–225 nm) films were grown on Si substrates by the pulsed-laser deposition technique at 450–500°C. The microstructure of the films and their magnetic properties were investigated by X-ray diffraction, transmission electron microscopy and a vibrating sample magnetometer. It was found that the Co(Cr)/Ti(Cr)/ZnO thin films had a highly preferential c-axis direction normal to the surface of the substrate, and the ZnO sublayer had columnar structures in the growth direction. The interface of the multi-layer films is smooth without interface reaction. The as-produced films had in-plane easy magnetization. It indicates that the enhancements of the magnetic properties of the films are mainly ascribed to the grain structure and multi-domain state of the Co-alloy layer, which can be controlled by the ZnO sublayer.     

Growth of ZnO nanostructures by vapor–liquid–solid method

Zinc oxide nanorods have been grown by vapor–liquid–solid (VLS) catalytic growth. The optical properties and structures properties of the grown ZnO nanostructures have been studied by photoluminescence, high resolution X-ray diffraction and scanning electron microscopy. The results show that the formation of ZnO nanostructures is strongly influenced by the growth conditions and used substrates. It was found that oriented ZnO nanorods are grown more easily on a substrate with a similar crystalline structure as ZnO. By optimizing growth conditions, oriented-ZnO nanorods grown on Si(001) substrate with a diameter of around 300 nm and lengths of 20 to 35 μm have been achieved, and they show excellent optical properties. Laser action has been observed at room temperature by using optical pumping. PACS 81.05.Dz; 81.10.Bk; 81.16.Hc     

Laser ablation and micropatterning of thin TiN coatings

Laser ablation of thin TiN films deposited on steel substrates has been studied under wide-range variation of irradiation conditions (pulsewidth, wavelength, energy density and spot size). It has been demonstrated that both picosecond (150–300 ps) and nanosecond (5–9 ns) laser pulses were suitable for controllable ablation and microstructuring of a 1-μm-thick TiN film unlike longer 150-ns pulses. The ablation rate was found to be practically independent of the wavelength (270–1078 nm) and pulsewidth (150 ps–9 ns), but it increased substantially when the size of a laser spot was reduced from 15–60 μm to 3 μm. The laser ablation technique was applied to produce microstructures in the thin TiN films consisting of microcraters with a typical size of 3–5 μm in diameter and depth less than 1 μm. Tests of lubricated sliding of the laser-structured TiN films against a steel ball showed that the durability of lubricated sliding increased by 25% as compared to that of the original TiN film. Received: 28 July 1999 / Accepted: 17 April 2000 / Published online: 20 September 2000     

Transparence and electrical properties of ZnO-based multilayer electrode

Three-layered ZnO/Ag–Ti/ZnO structures were prepared using both the sol-gel technique and DC magnetron sputtering. This study focuses on the electrical and optical properties of the ZnO/Ag–Ti/ZnO multilayers with various thicknesses of the Ag–Ti layer. The ZnO thin film prepared by the sol–gel method was dried at 300°C for 3 minutes, and a fixed thickness of 20 nm was obtained. The thickness of the Ag–Ti thin film was controlled by varying the sputtering time. The Ag–Ti layer substantially reduced the electrical resistivity of the sol–gel-sprayed ZnO thin films. The sheet resistance of the Ag–Ti layer decreased dramatically and then became steady beyond a sputtering time of 60 s. The sputtering time of Ag–Ti thin film deposition was determined to be 60 s, taking into account the optical transmittance. Consequently, the transmittance of the ZnO/Ag–Ti/ZnO multilayer films was 71% at 550 nm and 60% at 350 nm. The sheet resistance was 4.2 Ω/sq.     

Influence of drying conditions on the optical and structural properties of sol–gel-derived ZnO nanocrystalline films

Zinc oxide nanothin films were prepared on glass substrate by sol–gel dip-coating method using zinc acetate dihydrate, methanol, and monoethanolamine as precursor, solvent, and stabilizer, respectively. The relationship between drying conditions and the characteristics of ZnO nanocrystalline films (c-axis orientation, grain size, roughness and optical properties) was studied. The films were dried in an oven at different temperatures and by IR radiation. Then, the films were annealed at 500°C in a furnace. The chemical composition, transmission spectra, structure, and morphology of the samples were studied using infrared (IR) and UV–visible spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM), respectively. The XRD results show that the drying conditions affect the orientation of crystallization along the (0 0 2) plane. AFM images show that the thicknesses of the films decrease from 128 to 93 nm by changing the drying conditions. The photoluminescence (PL) of ZnO nanothin films shows the UV emission at near band edge and broad green radiation at about 465 nm wavelength.     

Electrodeposition of polyaniline–carbon nanotubes composite films and investigation on their role in corrosion protection of austenitic stainless steel by SNIFTIR analysis

Composite films of polyaniline (PANI) and carbon nanotubes (CNTs) were prepared by electrochemical co-deposition from solutions of the corresponding monomer containing two different kinds of CNTs. The first type was commercial (diameter = 110–170 nm, length = 5–9 μm) and the second one was home-made (diameter = 30 nm, length = 5–20 μm). The electrochemical behaviour of PANI–CNTs composite films was investigated with Cyclic Voltammetry and the surface morphology was analysed by Scanning Electron Microscopy (SEM). Subtractively Normalised Interfacial FT-IR procedure was used to investigate the presence of corrosion products when the films were deposited on stainless steel substrates and exposed to acid environment. The spectral investigations were utilised to understand the role of composite films in the corrosion protection and to discriminate the best performance CNTs.     

Impurity effects on the laser-induced crystallization of thin amorphous silicon film on glass substrate

Crystallization of 100 nm thick amorphous silicon (a-Si) films deposited on glass substrates was carried out using a dual-green-laser method. Depending on a-Si deposition method, either low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD), the density of impurities such as Al, K, and Na within the a-Si thin films significantly varied. For the high impurity case of LPCVD, grains of 200–300 nm in size were obtained, whereas for the PECVD case a maximum grain size of about 4 μm was achieved, satisfying the requirements for applications in commercial TFT devices. These results confirm that for the use of glass substrates in polycrystallization of a-Si, controlling the impurity density during substrate preparation is critical.     

Structural and photoluminescent properties of ZnO films deposited by radio frequency reactive sputtering

Zinc oxide films with c-axis preferred orientation were deposited on silicon (100) substrates by radio frequency (RF) reactive sputtering. The properties of the sam- ples were characterized by X-ray diffractometer, X-ray photoelectron spectroscopy and fluorescent-spectrophotometer. The effect of sputtering power and substrate temperature on the structural and photoluminescent (PL) properties of the ZnO films was investigated. The results indicated that when the sputtering power is 100 W and the substrate temperature is 300-400℃, it is suitable for the growth of high c-axis orientation and small strain ZnO films. A violet peak at about 380 nm and a blue band at about 430 nm were observed in the room temperature photolumines- cence spectra, and the origin of blue emission was investigated.     

Characterization of dip-coated ITO films derived from nanoparticles synthesized by␣low-pressure spray pyrolysis

In₂O₃:Sn (Indium Tin Oxide; ITO) films were prepared from a sol solution with highly crystalline ITO nanoparticles (less than 20 nm in size with 10 at.% Sn) which had been prepared by low-pressure spray pyrolysis (LPSP) in a single step. The ITO sol solution was prepared by dispersing LPSP-prepared ITO nanoparticles into ultra pure water. The nanoparticle ITO film was deposited on a glass substrate using a dip-coating method and then annealed in air at various temperatures. The optical transmittances of the ITO films were measured by UV–Vis spectrometry, and the films were found to have a high transparency to visible light (in the case of a film thickness of 250 nm annealed at 400°C, the transparency was in excess of 95% over the range λ=450–800 nm, with a maximum value near 100% at wavelengths above λ=700 nm). The optical transmittances of the films were influenced by the size of the ITO particle used, the film thickness and the annealing temperature. The ITO films showed a minimum resistivity of 9.5×10⁻² Ω cm, and their resistivity was affected by both the ITO particle size and the annealing temperature used.     

Determination of the optimal parameters for the fabrication of ZnO thin films prepared by spray pyrolysis method

In this work, ZnO thin films have been prepared by spray pyrolysis deposition method on the glass substrates. The effect of deposition parameters, such as deposition rate, substrate temperature and solution volume has been studied by X-ray diffraction (XRD) method, UV–Vis–NIR spectroscopy, scanning electron microscopy (SEM), and electrical measurements. The XRD patterns indicate polycrystalline wurtzite structure with preferred direction along (0 0 2) planes. Thin films have transparency around 90% in the visible range. The optical band gap was determined at 3.27 eV which did not change significantly. Evolution of electrical results containing the carriers’ density, sheet resistance and resistivity are in agreement with structural results. All the results suggest the best deposition parameters are: deposition rate, R = 3 ml/min, substrate temperature, T _s = 450°C and thickness of the thin films t = 110–130 nm.     

Electrodeposition of ZnO nanorods for device application

We report the electrochemical growth of zinc oxide nanorods in a zinc nitrate/hexamethylenetetramine solution at 70 °C. High-density vertical nanorods were grown on Au films on silicon substrates with a texture coefficient better than 99.9%. By varying the reactant concentration the diameter can be varied between 100 and 250 nm, with corresponding lengths of 1 to 4 μm. Furthermore, this approach was used for the selective growth on Ti/Au strip conductors ordered in an interdigitated structure on an insulating substrate. We achieved the growth of ZnO nanorods between neighbouring strip conductors bridging the gap between them. In this configuration the nanorods are already contacted and electrical measurements can be directly performed. First I–V measurements show a good conductivity of the as-grown nanorods and the resistance could be estimated to be 0.1 Ω cm. Under UV illumination the ZnO nanorods demonstrate a photoconductivity, but only after annealing the sample at 300 °C in N₂. PACS 61.05.cp; 73.63.-b; 78.55.Et; 81.15.Pq; 82.45.Yz     

Structure–conductivity relations of simulated highly porous nanoparticle aggregate films

Electrical conductivity of porous films composed of nanoparticle aggregates is theoretically evaluated with respect to aggregate structure and film packing density. The aggregates are fractals composed of 5–30 primary particles with diameter of 10 nm. The film properties are derived from simulated boxes in the range of 0.5–1 μm. The electrical conductivity across the films of packing densities ranging from 0.01 to 0.15 was studied. All films prepared by an aerosol deposition technique, which uses nanoparticle aggregates, exhibited percolation behavior between planes parallel to the moving direction of the aggregates. They also followed the classical percolation relation for electrical conductivity while the critical percolation packing density depends on the aggregate size and structure used to build the films. Films using larger aggregates as building blocks have higher electrical conductance than smaller aggregates close to the percolation limit. For validation and supplementary information, two independent models are developed: one model follows the percolation theory to get detailed physical insights and another one computes the exact conductivities but at the cost of some details. This analysis gives new insights into the conduction backbone structures of these films with regard to neck contacts within an aggregate and grain boundary contacts between aggregates. The results shown are important for solar application of these films and especially for gas sensors where high sensitivity is often counteracted by low conductivity.     

Electrochromic materials from the visible to the infrared region: an example WO<Subscript>3</Subscript>

Herein, the example of the most typical electrochromic material, namely WO₃, is used to illustrate the potential of electrochromic materials for controlling infrared reflectance and hence, emissivity. Playing with various growth parameters, contrast in reflectance between the inserted H _xWO₃ and deinserted WO₃ states as high as 73% in mid-wavelength band (MW, 3–5 μm) was achieved for 320 nm WO₃ films. The latter electrochromic materials were radio frequency sputtered on Au substrate at ambient temperature in 6 Pa of chamber pressure. In comparison, for long wavelength band (LW, 8–12 μm), the contrast in reflectance did not exceed 30%. The origins of the various electrochromic behaviours are correlated to the film structure, morphology and composition, indicating better properties for porous, nonstoichiometric films. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Photoluminescence properties of thin nitrogen- and phosphorus-doped ZnO films fabricated using pulsed laser deposition

The production of n- and p-type high-quality film structures is a foreground task in tackling the problem of growing the light-emitting p-n junctions based on zinc oxide. The ZnO:N and ZnO:P thin-film samples are produced from ceramic targets using the pulsed laser deposition. Zn₃N₂, MgO, and Zn₃P₂ are introduced in the ZnO ceramic targets for the fabrication of the p-type ZnO films. Gases O₂ and N₂O are used as buffer gases. The thermal annealing of the ZnO films is employed. The resistance and photoluminescence (PL) spectra of the ZnO films are measured prior to and after annealing. The dependence of the ZnO PL peak amplitude and position prior to and after annealing on the level of doping with nitrogen and phosphorus is established. The PL characteristics of the films are studied at cw optical excitation using a He-Cd laser with a radiation wavelength of 325 nm. The PL spectra in the interval 300–700 nm are recorded by an HR4000 Ocean Optics spectrometer in the temperature range 10–400 K. The effect of the conditions for the film deposition on the PL spectra is analyzed. The effect of the N- and P-doping level of the ZnO films on the PL intensity of the films and the position of the PL bands in the UV region is investigated. The short-wavelength (250–400 nm) transmission spectra of the ZnO:P films are measured. The effect of the P-doping level on the band gap of the ZnO films is studied.     

以表面等离子体为媒介的ZnO薄膜发光增强特性研究

采用两步法制备Si基Ag/ZnO双层结构薄膜,研究了Ag覆盖层的厚度和生长温度T对ZnO近带边发光强度的影响.对于厚度为100 nm的ZnO薄膜,发现Ag覆盖层的最佳厚度仅为8 nm,此时双层薄膜相对于单层ZnO薄膜的发光增强因子η达到最大值8.1;同时还发现,在最佳Ag层厚度下,生长温度T≥300 ℃时生长Ag所获Ag/ZnO双层薄膜的ZnO发光强度比生长温度T≤200 ℃时生长的双层薄膜样品大一倍以上,η ≈ 18.结合对双层薄膜表 关键词： 表面等离子体共振 复合薄膜     

Nanostructuring of thin Au films by means of short UV laser pulses

The particle size distribution, morphology and optical properties of the Au nanoparticle (NP) structures for surface enhanced Raman signal (SERS) application are investigated in dependence on their preparation conditions. The structures are produced from relatively thin Au films (10–20 nm) sputtered on fused silica glass substrate and irradiated with several pulses (6 ns) of laser radiation at 266 nm and at fluencies in the range of 160–412 mJ/cm². The SEM inspection reveals nearly homogeneously distributed, spherical gold particles. Their initial size distribution of the range of 20–60 nm broadens towards larger particle diameters with prolonged irradiation. This is accompanied by an increase in the uncovered surface of the glass substrate and no particle removal is observed. In the absorption profiles of the nanostructures, the broad peak centred at 546 nm is ascribed to resonant absorption of surface plasmons (SPR). The peak position, halfwidth and intensity depend on the shape, size and size distribution of the nanostructured particles in agreement with literature. From peak intensities of the Raman spectra recorded for Rhodamine 6G in the range of 300–1800 cm⁻¹, the relative signal enhancement by factor between 20 and 603 for individual peaks is estimated. The results confirm that the obtained structures can be applied for SERS measurements and sensing.     

The sensitivity and dynamic response of field ionization gas sensor based on ZnO nanorods

Field ionization gas sensors based on ZnO nanorods (50–300 nm in diameter, and 3–8 μm in length) with and without a buffer layer were fabricated, and the influence of the orientation of nano-ZnO on the ionization response of devices was discussed, including the sensitivity and dynamic response of the ZnO nanorods with preferential orientation. The results indicated that ZnO nanorods as sensor anode could dramatically decrease the breakdown voltage. The XRD and SEM images illustrated that nano-ZnO with a ZnO buffer layer displayed high c-axis orientation, which helps to significantly reduce the breakdown voltage. Device A based on ZnO nanorods with a ZnO buffer layer could distinguish toluene and acetone. The dynamic responses of device A to the NO _x compounds presented the sensitivity of 0.045 ± 0.007 ppm/pA and the response speed within 17–40 s, and indicated a linear relationship between NO _x concentration and current response at low NO _x concentrations. In addition, the dynamic responses to benzene, isopropyl alcohol, ethanol, and methanol reveals that the device has higher sensitivity to gas with larger static polarizability and lower ionization energy.     

Synthesis and field emission of two kinds of ZnO nanotubes: taper-like and flat-roofed tubes

Two kinds of ZnO nanotubes, including taper-like and flat-roofed tubes, have been successfully fabricated using a simple aqueous solution route by changing the experimental conditions. All the obtained nanotubes have a uniform size of 500 nm in diameter, 10–50 nm in wall thickness, and 2–5 μm in length. The growth mechanism of two kinds of ZnO nanotubes was investigated. Field emission measurements showed that tapering nanotubes have the good field emission performance with a low turn-on field of ∼ 2.1 V μm^-1 and a low threshold field of ∼ 3.8 V μm^-1, which suggests the possible applications of the ZnO tubular structures in field emission microelectronic devices. PACS 73.61.Ga; 73.63. Fg; 85.45.Db     

Effects of preannealing temperature of ZnO thin films on the performance of dye-sensitized solar cells

The preferred (002) orientation zinc oxide (ZnO) nanocrystalline thin films have been deposited on FTO-coated glass substrates by sol–gel spin-coating technology and rapid thermal annealing for use in dye-sensitized solar cells (DSSC). The effects of preannealing temperature (100 and 300°C) on the microstructure, morphology and optical properties of ZnO thin films were studied. The ZnO thin films were characterized by X-ray diffraction (XRD), scanning electron microscopic (SEM) and Brunauer–Emmett–Teller (BET) analysis. The photoelectric performance of DSSC was studied by I–V curve and the incident photon-to-current conversion efficiency (IPCE), respectively. From the results, the intensities of (002) peaks of ZnO thin films increases with increasing preannealing temperature from 100°C to 300°C. The increase in pore size and surface area of ZnO films crystallized at the increased preannealing temperature contributed to the improvement on the absorption of N3 dye onto the films, the short-circuit photocurrent (J _sc) and open-circuit voltage (V _oc) of DSSC. The higher efficiency (η) of 2.5% with J _sc and V _oc of 8.2 mA/cm² and 0.64 V, respectively, was obtained by the ZnO film preannealed at 300°C.     

Surface relief and structure of electroexplosive composite surface layers of the molybdenum-copper system

The surface topography and structure of copper layers exposed to multiphase plasma jets of products of electrical explosion of molybdenum and copper foils are studied using profilometry and scanning electron and light microscopy. Such treatment allows deposition of either layered coatings or alloyed composite layers. It is found that the surface layer roughness parameter is R _a = 3.2−4.0 μm. The thickness of some copper and molybdenum layers of coatings is 15–20 μm. Electroexplosive alloying produces layers 25 μm thick. Sizes of copper inclusions in the molybdenum matrix near the surface of such layers vary from 30 nm to 1–2 μm.