Effects of sapphire substrates surface treatment on the ZnO thin films grown by magnetron sputtering

The surface treatment effects of sapphire substrate on the ZnO thin films grown by magnetron sputtering were studied. The sapphire substrates properties have been investigated by means of atomic force microscopy (AFM) and X-ray diffraction rocking curves (XRCs). The results show that sapphire substrate surfaces have the best quality by CMP with subsequent chemical etching. The surface treatment effects of sapphire substrate on the ZnO thin films were examined by X-ray diffraction (XRD) and photoluminescence (PL) measurements. Results show that the intensity of (0 0 2) diffraction peak of ZnO thin films on sapphire substrates treated by CMP with subsequent chemical etching was strongest, FWHM of (0 0 2) diffraction peak is the narrowest and the intensity of UV peak of PL spectrum is strongest, indicating surface treatment on sapphire substrate preparation may improve ZnO thin films crystal quality and photoluminescent property.     

Structural properties of TiN films grown on stainless steel substrates by a reactive radio-frequency sputtering technique at low temperature

TiN thin films were grown on stainless steel substrates by using the reactive radio-frequency magnetron-sputtering technique at relatively low temperature (200°C) using Ti and N₂. The deposition rate of the TiN film increased linearly with increasing applied radio-frequency power, and it decreased with increasing partial-pressure ratio of the N₂ gas to the Ar gas. Scanning electron microscopy (SEM) showed that the surfaces of the TiN films had very smooth morphologies. The TiN thin film had good stoichiometry for a partial-pressure ratio of 0.05. The stoichiometry of the TiN films and the interface qualities of the TiN/stainless steel heterostructures were investigated by Auger electron spectroscopy (AES) measurements. Auger depth profiles indicated that the compositions of the as-grown films consisted of titanium and nitrogen uniformly distributed throughout the films and that the films exhibited smooth interfaces. The interface quality of the TiN films to the stainless steel substrates were improved by annealing. These results indicate that annealed TiN thin films grown on stainless steel substrates hold promise for potential applications in advanced ceramic devices.     

Microstructure, optical and electrical properties of nitrogen doped sp-rich a-C thin films grown by facing-target magnetron sputtering

N atoms were incorporated into sp²-rich a-C networks using DC facing-target reactive sputtering at various N₂ fraction (P_N2) and their structure and opto-electrical properties were investigated systematically. As P_N2 increases, the fraction of CN bonded carbons (or the N content) increases primarily at the expense of the CC bonded carbons and then reaches its saturated value at P_N2 > 40%. The incorporated N preferentially forms different kinds of non-aromatic CN phase, leading to more localization of π electrons and the loss of the connectivity of nanographite fragments in the films, which is different from the case in N-doped sp³-rich a-CN_x films. Hence, with increasing P_N2, the a-C(:N) film converts from a semiconductor with a narrower optical band gap to an insulator-like material with a wider gap. Additionally, the variation of optical constants (n and k) and spin defects are related to the enhancement of the non-aromatic CN phase.     

Structural and optical properties of ZnO thin films on (111) CaF2 substrates grown by magnetron sputtering

ZnO thin films were grown on (111) CaF₂ substrates by magnetron sputtering at room temperature. Structural and optical properties of the ZnO thin films were studied. XRD analysis showed that the ZnO thin films had the (002) preferential orientation. The transmittance of ZnO thin films was over 80% in the visible range. The optical band gap of the ZnO thin films was 3.26 eV. The optical constants (n,k)$(n,k)$ of the ZnO thin films in the wavelength range 300–1000 nm were obtained by infrared spectroscopic ellipsometry measurement. PL spectra of ZnO thin films showed strong UV near-band-edge emission peak at 376.5 nm and weak visible red emission at 643.49 nm using He–Cd laser as the light source, using a synchrotron radiation light source PL spectra showed three emission peak at 320 nm, 410 nm and 542 nm respectively.     

Structural and morphological properties of thin ZnO films grown by pulsed laser deposition

The pulsed laser deposition technique was used to produce zinc oxide thin films onto silicon and Corning glass substrates. Homogeneous surfaces exhibiting quite small Root Mean Square (RMS) roughness, consisting of shaped grains were obtained, their grain diameters being 40-90 nm at room temperature and at 650 °C growth respectively. Films were polycrystalline, even for growth at room temperature, with preferential crystallite orientation the (0 0 2) basal plane of wurtzite ZnO. Temperature increase caused evolution from grain to grain agglomeration structures, improving crystallinity. Compressive to tensile stresses transition with temperature was found while the lattice constant decreased.     

Enhanced electrical stability of flexible indium tin oxide films prepared on stripe SiO2 buffer layer-coated polymer substrates by magnetron sputtering

The electrical stability of flexible indium tin oxide (ITO) films fabricated on stripe SiO₂ buffer layer-coated polyethylene terephthalate (PET) substrates by magnetron sputtering was investigated by the bending test. The ITO thin films with stripe SiO₂ buffer layer under bending have better electrical stability than those with flat SiO₂ buffer layer and without buffer layer. Especially in inward bending text, the ITO thin films with stripe SiO₂ buffer layer only have a slight resistance change when the bending radius r is not less than 8 mm, while the resistances of the films with flat SiO₂ buffer layer and without buffer layer increase significantly at r = 16 mm with decreasing bending radius. This improvement of electrical stability in bending test is due to the small mismatch factor α in ITO-SiO₂, the enhanced interface adhesion and the balance of residual stress. These results indicate that the stripe SiO₂ buffer layer is suited to enhance the electrical stability of flexible ITO film under bending.     

Crystalline silicon films sputtered on molybdenum: A study of the silicon–molybdenum interface

Polycrystalline silicon films were grown on molybdenum (Mo)-coated substrates at high deposition rate using the pulsed magnetron sputtering technique. Our study investigates the silicon–molybdenum interface of these films to elucidate stimulating mechanisms for an ordered crystalline silicon thin film growth. Both Auger electron spectroscopy and Rutherford backscattering reveal that at a substrate temperature as low as T_S=450 °C during the deposition process intermixing of Si and Mo at the Si–Mo interface takes place leading to a compositional ratio Mo:Si of about 1:2. By Raman spectroscopy hexagonal β-MoSi₂ could be identified as the dominant phase in this intermixed region. The dependence of the resulting thickness of the reacted interface layer on the deposition conditions is not fully understood yet.     

Dependence of intermediated noble metals on the optical and electrical properties of ITO/metal/ITO multilayers

Sn doped In₂O₃ (ITO) single layer and a sandwich structure of ITO/metal/ITO (IMI) multilayer films were deposited on a polycarbonate substrate using radio-frequency and direct-current magnetron sputtering process without substrate heating. The intermediated metal films in the IMI structure were Au and Cu films and the thickness of each layer in the IMI films was kept constant at 50 nm/10 nm/40 nm. In this study, the ITO/Au/ITO films show the lowest resistivity of 5.6 × 10⁻⁵ Ω cm.However the films show the lower optical transmission of 71% at 550 nm than that (81%) of as deposited ITO films. The ITO/Cu/ITO films show an optical transmittance of 54% and electrical resistivity of 1.5 × 10⁻⁴ Ω cm. Only the ITO/Au/ITO films showed the diffraction peaks in the XRD pattern. The figure of merit indicated that the ITO/Au/ITO films performed better in a transparent conducting electrode than in ITO single layer films and ITO/Cu/ITO films.     

Deposition of MgO films by pulsed mid-frequency magnetron sputtering

MgO films were deposited by pulsed mid-frequency magnetron sputtering from metallic targets in the mixture of Ar and O₂ gas. The surface morphology, crystalline structure, and optical properties were characterized by using atomic force microscopy (AFM), X-ray diffraction (XRD), and spectroscopic ellipsometry, respectively. The secondary electron emission coefficients of MgO films were measured by using a self-made apparatus in He gas. A pronounced hysteresis phenomenon of target voltage, current, and deposition rate with increasing and decreasing O₂ flow rate was observed. The structure of films deposited at a metallic mode changes from Mg phase to the mixed Mg and MgO phase, and the films have a very rough surface. All the films deposited at oxide mode have high transparency and smooth surface, and show (2 2 0) preferred orientation growth. The refractive index and extinction coefficient at a wavelength of 670 nm for MgO films deposited at oxide mode with a O₂ flow rate of 3 sccm are 1.698 and 1.16×10⁻⁴, respectively. The secondary emission coefficient at a E/p of 57.8 V/(cm Torr) for MgO films deposited at a O₂ flow rate of 3 sccm is 0.16, which is higher than that of MgO films deposited by e-beam evaporation.     

Optical and electrical properties of nanocrystal zinc oxide films prepared by dc magnetron sputtering at different sputtering pressures

The nanocrystal thin films of zinc oxide doped by Al (ZnO:Al) were deposited by dc reactive magnetron sputtering on the glass substrates, in the pressure range of 33-51 Pa. From the X-ray diffraction patterns, the nanocrystalline structure of ZnO:Al films and the grain size were determined. The optical transmission spectra depend from the sputtering pressure, but their average value was 90% in the range from 33 Pa to 47 Pa. Also, the sputtering pressure changes the optical band gap of ZnO:Al films, which is highest for films deposited at 37 Pa, 40 Pa and 47 Pa. The obtained films at room temperature have a sheet resistance of 190 Ω/cm² which increases with time, but the films annealed at temperature of 400 °C have constant resistance. The surface morphology of the films was studied by Scanning electron microscopy. XPS spectra showed that the peak of O1s of the as-deposited films is smaller than the peak of the annealed ZnO:Al films.     

Nano-scale and surface precipitation of metallic particles in laser interference patterned noble metal-based thin films

Laser interference patterning (also known as “laser interference metallurgy”) is used to locally tailor the microstructure of oxide (Pd_0.25Pt_0.75O_x) and nitride (Cu₃N) thin films to induce a chemical decomposition, which is responsible for a decrease of electrical resistivity. This technique allows hereby a laser-induced chemical decomposition of as-deposited oxide and nitride films, resulting locally in a porous microstructure due to the simultaneous emission of gaseous nitrogen and oxygen. The process locally generates at the nanometer scale metal precipitatation of Pt or Cu in the oxide or nitride matrix. Thus, isolated metallic clusters with low resistivity coexist with a high resistivity phase, establishing a preferential electrical conduction path and giving the system a lower effective resistivity. The decomposition process is investigated by four-point probe method, X-ray diffraction, spectrophotometry, white light interference, scanning and transmission electron microscopies.     

Fabrication and structural characterization of metal films coated on cenosphere particles by magnetron sputtering deposition

Metal films were successfully coated on cenosphere particles using a magnetron sputtering deposition system in which a newly designed sample stage equipped with an ultrasonic vibration generator was used for the tumbling of cenosphere particles. It was found by FE-SEM and AFM results that the films were well compacted and highly uniform in thickness. Due to the difference in sputtering rate, the film thicknesses estimated from FE-SEM characterizations in backscattered mode were <10, 39, 50 and 134 nm for Co, Ni, Cu and Ag films, respectively, under the same sputtering deposition conditions. The RMS values derived from the AFM measurements were 1.94, 4.31, 10.92 and 18.33 nm for Co, Ni, Cu and Ag films, respectively, which can ascribe to the different crystallization behaviors for the four metals. The experiment results indicate that the coating method can be applicable for the fabrication of many other films on cenosphere particles which can be sputter deposited.     

Studies on sprayed lanthanum sulphide (La2S3) thin films from non-aqueous medium

Thin films of lanthanum sulphide (La₂S₃) have been deposited onto glass substrates by spray pyrolysis technique from non-aqueous (methanol) medium. The structural, morphological, optical, dielectric, electric and thermoemf properties were studied. The films were polycrystalline with an irregular shaped particles present over the porous structure within a fibrous network structure. The optical band gap was estimated to be 2.50 eV. The dielectric properties were measured in the range 100 Hz-1 MHz. The electrical resistivity was of the order of 10⁴ to 10⁵ Ω cm. Thermoemf study revealed that the La₂S₃ films exhibit p-type electrical conductivity.     

Photoluminescence of polycrystalline CuIn0.5Ga0.5Te2 thin films grown by flash evaporation

Polycrystalline CuIn_0.5Ga_0.5Te₂ films were deposited by flash evaporation from ingot prepared by reacting, in stoichiometric proportions, high purity Cu, In, Ga and Te elements in vacuum sealed quartz. The as-obtained films were characterized by X – ray diffraction (XRD), transmission electron microscopy (TEM) combined with energy dispersive spectroscopy (EDS). XRD and TEM results showed that the layer has a chalcopyrite-type structure, predominantly oriented along (112) planes, with lattice parameters a?=?0.61?nm and c?=?1.22?nm. The optical properties in the near - infrared and visible range 600–2400?nm have been studied. The analysis of absorption coefficient yielded an energy gap value of 1.27?eV. Photoluminescence analysis of as-grown sample shows two main emission peaks located at 0.87 and 1.19?eV at 4?K.     

The influence of using different substrates on the structural and optical characteristics of ZnO thin films

ZnO thin films with thikness d = 100 nm were deposited onto different substrates such as glass, kapton, and silicon by radio frequency magnetron sputtering. The structural analyses of the films indicate they are polycrystalline and have a wurtzite (hexagonal) structure.The ZnO layer deposited on kapton substrate shows a stronger orientation of the crystallites with (0 0 2) plane parallel to the substrate surface, as compared with the other two samples of ZnO deposited on glass and silicon, respectively.All three layers have nanometer-scale values for roughness, namely 1.7 nm for ZnO/glass, 2.4 nm for ZnO/silicon, and 6.8 nm for ZnO/kapton. The higher value for the ZnO layer deposited on kapton substrate makes this sample suitable for solar cells applications. Transmission spectra of these thin films are strongly influenced by deposition conditions. With our deposition conditions the transparent conducting ZnO layer has a good transmission (78-88%) in VIS and NIR domains. The values of the energy gap calculated from the absorption spectra are 3.23 eV for ZnO sample deposited onto glass substrate and 3.30 eV for the ZnO sample deposited onto kapton polymer foil substrate. The influence of deposition arrangement and oxidation conditions on the structural, morphological, and optical properties of the ZnO films is discussed in the present paper.     

Enhanced blue emission of ZnO films deposited on AlN substrates

Taking into account the individual excellent optical properties of ZnO and AlN, the combination of ZnO with AlN may give the enhanced performances. Based on similar lattice constants between ZnO and AlN, considering that AlN is a promising high power integrated circuit substrate material, ZnO films are deposited on AlN substrates using magnetron sputtering. We find that AlN substrate shows an excellent transparency with an average transmittance of about 80%. As ZnO films are deposited on AlN substrate, average transmittance still maintain above 80% except for the UV absorption edge shifted to the longer wavelength. In addition, AlN substrate shows two emission peaks at 420 and 468 nm ascribed to Al vacancies with different charge states. As ZnO films are deposited on AlN substrates in pure Ar gas, the intensity of both peaks attain the maximum. After introducing O₂ gas, they conversely decreases and attains the minimum. PL emissions increase again as the sample is annealed in vacuum. Excellent blue emissions are obtained due to the synergistic effect between ZnO and AlN. This work may help the development of the practical optoelectronic devices based on ZnO and AlN materials.     

Properties of dc magnetron sputtered Cu2O films prepared at different sputtering pressures

The sputtering pressures maintained during the deposition of Cu₂O films, by dc reactive magnetron sputtering, influence the structural, electrical and optical properties. The crystalline orientation mainly depends on the sputtering pressure. The films deposited at a sputtering pressure of 4 Pa showed single-phase Cu₂O films along (1 1 1) direction. The electrical resistivity of the films increased from 1.1 × 10¹ Ω cm to 3.2 × 10³ Ω cm. The transmittance of the films increased from 69% to 88% with the increase of sputtering pressure from 2.5 Pa to 8 Pa.     

Electrochemical characteristics of alumina dielectric layers

The electrochemical characteristics of alumina dielectric layers were studied using a surface roughness factor and an impedance spectroscopy. From the limiting diffusion current method, the surface area factor of the dielectric anodic layer with low electrical conductivity was estimated to be 1.03. As alumina dielectric films on Al have a variable stoichiometry, the electrochemical behavior of Al₂O₃ layer can be monitored by evaluating an equivalent circuit with Young impedance of dielectric constant with a vertical decay of conductivity.     

Structural and optical characterization of DC magnetron sputtered molybdenum oxide films

Thin films of molybdenum trioxide were deposited on glass substrates employing direct current (DC) magnetron sputtering by sputtering of molybdenum at different oxygen partial pressures in the range 8 × 10⁻⁵–1 × 10⁻³ mbar and at a substrate temperature of 473 K. The glow discharge characteristics of magnetron cathode target of molybdenum were studied. The influence of oxygen partial pressure on the structural and optical properties of molybdenum trioxide films was investigated. The films formed at an optimum oxygen partial pressure of 2 × 10⁻⁴ mbar were polycrystalline in nature with orthorhombic α- phase and an optical band gap of 3.16 eV. The refractive index of the films formed at an oxygen partial pressure of 2 × 10⁻⁴ mbar decreased from 2.08 to 1.89 with increase of wavelength from 450 to 1,000 nm, respectively. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Properties of barium hexa-ferrite thin films dependent on sputtering pressure

M-type barium ferrite thin films were deposited onto sapphire (0 0 l) substrates by radio frequency magnetron sputtering. An ultra-thin layer about 20 nm was deposited and annealed before continuous deposition of the films up to 500 nm under different sputtering pressures: 0.2, 0.5, 0.8 and 1.0 Pa, respectively. It was found that the atomic ratios of Fe to Ba increased from 9.3 to 15.0 with the increase of the pressure. The films sputtered at all pressures have c-axis normal to the film plane by a four circle X-ray diffractometer, which is an improvement of the films directly sputtered on the substrate. Needle-like grains were formed on the surface of the films under higher sputter pressure with bubble domains, which is originated from high magnetocrystalline anisotropy of the film. Magnetic hysteresis loops recorded by vibrating sample magnetometer agree with them, where in-plane and out-of-plane loops of the samples prepared under high sputtering pressures are quite different, while they are almost identical of the samples under low pressures. The influence of the sputtering pressure was understood by that with the increase of the pressure, resputtering of the films was increased. Nucleation with c-axis normal to the film plane was deteriorated. Thus samples prepared under high pressure have more needle-like crystallites which have c-axis parallel to the film plane.