Influence of UV light irradiation on film thickness distribution of tin oxide films by photochemical vapour deposition

Tin oxide (non-doped) films have been prepared by a photochemical vapour deposition (photo-CVD) from Tetramethyltin (TMT) (Sn(CH₃)₄) and O₂ (containing O₃). A low-pressure mercury lamp was used as the light source. The effect of the UV light irradiation on the film thickness distribution along 5 cm×5 cm area was examined. By piling Teflon films on the surface of the suprasil window, the light intensity of 184.9 nm UV wavelength of the low-pressure mercury lamp was controlled, while that of 253.7 nm wavelength through the Teflon hardly changed. As a result, the uniformity of the film thickness distribution was improved as the light intensity (184.9 nm) increased. The UV 184.9 nm light irradiation may have improved the uniformity of the reactive species distribution in the vapour phase, which may result in the formation of the uniform thickness distribution.     

Monte-Carlo study of reactive ion-beam assisted film growth

A Monte-Carlo computer program which is composed of ion implantation simulation and deposition calculation is described. It is applied to study TiN film growth by reactive ion-beam assisted deposition in a N₂ gas environment. The relationship between film composition and nitrogen partial pressure in the processing chamber is established. The influence of ion energy, atomic arrival rate ratio and ion species on the thickness of the film is studied. We also investigated the intermixing at the interface region between the film and substrate. The calculated data are compared with experimental results.The work was supported by National Hi-Tech Projects     

Ionic conductivity of epitactic MBE-grown BaF2 films

We studied parallel conductivities of pure BaF₂ films with thicknesses ranging from 35 to 300 nm, epitaxially grown on Al₂O₃(0 1 2) substrates by molecular beam epitaxy technique. The overall conductivities of the films are found to increase with decreasing thickness. The detailed investigation of the overall conductance as a function of the thickness permits the deconvolution of bulk and boundary effects, the latter being attributed to distinct space charge effects in the interface between BaF₂ film and Al₂O₃ substrate. The (extrinsic) Debye length (λ) is estimated to be about 8 nm at T=593 K, which corresponds to an impurity content of 10¹⁸/cm³ (singly ionized dopant assumed). This is consistent with the fact that we observed a constant boundary contribution for all investigated films (film thickness >4λ). It is also consistent with the Debye length observed in a previous report on CaF₂/BaF₂ heterolayers fabricated by the same technique, in which the low temperature enhancement was also attributed to space charges in BaF₂ [Nature 408 (2000) 946]. Only at low temperatures (below 370 °C), the conductance seems to be influenced by strain effect.     

Probing charge transport in manganite film through switching parameters

We have investigated the bipolar resistive switching of Y_0.95Ca_0.05MnO₃ (YCMO) thin film on Si substrate using pulsed laser deposition. Simulation of Mn L_3,2 near-edge X-ray absorption fine structure has been executed by CTM4XAS to corroborate the presence of a mixed-valence state of Mn ions and oxygen vacancies. The charge transport in the film is described by the space charge limited mechanism. Murgatroyd and space charge limited mechanism relations are used to calculate the mobility and other switching parameters at high resistance state. With a decrease in the switching layer (near to positively biased electrode) thickness, better resistive switching was observed. This work indicates that the localized switching thickness and temperature strongly affect the resistive switching of the YCMO film.     

High temperature characteristics of ZnO-based MOS-FETs with a photochemical vapor deposition SiO2 gate dielectric

The authors report the fabrication of ZnO-based metal-oxide-semiconductor field effect transistors (MOSFETs) with a high quality SiO₂ gate dielectric by photochemical vapor deposition (photo-CVD) on a sapphire substrate. Compared with ZnO-based metal-semiconductor FETs (MESFETs), it was found that the gate leakage current was decreased to more than two orders of magnitude by inserting the photo-CVD SiO₂ gate dielectric between ZnO and gate metal. Besides, it was also found that the fabricated ZnO MOSFETs can achieve normal operation of FET, even operated at 150 °C. This could be attributed to the high quality of photo-CVD SiO₂ layer. With a 2 μm gate length, the saturated I_ds and maximum transconductance (G_m) were 61.1 mA/mm and 10.2 mS/mm for ZnO-based MOSFETs measured at room temperature, while 45.7 mA/mm and 7.67 mS/mm for that measured at 150 °C, respectively.     

The origination of ill-defined layer in organic spin valves

The origination of ill-defined layer in organic spin valves was investigated by using atomic force microscopy (AFM) and Rutherford backscattering (RBS) analysis. It was found that conductive bulges of LSMO film and self-grown pinholes in Alq₃ film other than Co inclusions could lead to the formation of ill-defined layer. The morphology of LSMO substrate had a strong influence on that of Alq₃ film, LSMO/Alq₃ and Alq₃/Co interfaces. Moreover, Alq₃ film with the thickness of 1-4 nm could be barriers which was explained by small active area and added insulated layer in organic magnetic tunnel junctions.     

Study of atomic transport mechanisms during thermal nitridation of silicon in ammonia using 15N and D labelled gas

Thermal silicon nitridation mechanisms in ammonia gas at 950°C and under 2 × 10⁻⁵ Torr were investigated by using ¹⁵N as a tracer. Nitride layers first grown in ¹⁴NH₃ were further grown in ¹⁵NH₃. ¹⁵N profiling was obtained by combining nuclear microanalysis with step-by-step chemical dissolution of the nitride layer. Thus one can show that the nitride film consists of a ¹⁴N layer located near the Si/nitride interface and a ¹⁵N layer located near the external surface of the film. It was also shown that there is no isotope exchange between the nitrogen of the nitride network and of the NH₃ gas. These results indicate that the growth does not occur by interstitial transport through the nitride film of the NH₃ molecules nor by any other nitrogenated species resulting from a decomposition of the ammonia gas. A possible incorporation of hydrogenated species was also examined using ND₃ nitridation. As the relative concentration of deuterium in such a film was less than 10⁻⁴, ammonia most probably dissociates at the outer surface and hydrogenated species do not react appreciably with the network.From these experiments, it can be concluded that the growth of the silicon nitride layer occurs by either:

• -transport of silicon atoms through the layer which then react with the nitridant gas;
• -or a step-by-step migration of a nitrogen network defect (vacancy or interstitialcy) in only one direction. In such a case, the defect should be electrically charged and the hoping direction should be imposed by a strong electrical field arising from the charging of nitrogenated species adsorbed at the external nitride surface by electrons coming from the silicon substrate because of the very small thickness of the nitride film (< 40 Å) (tunnel or thermionic effects)

.     

Gas barrier properties of diamond-like carbon films coated on PTFE

Diamond-like carbon (DLC) films were deposited on polytetrafluoroethylene (PTFE) using radio frequency (RF) plasma-enhanced chemical vapour deposition (PE-CVD). Before the DLC coating, the PTFE substrate was modified with a N₂ plasma pre-treatment to enhance the adhesive strength of the DLC to the substrate. The influences of the N₂ plasma pre-treatment and process pressure on the gas permeation properties of these DLC-coated PTFE samples were investigated. In the Raman spectra, the G peak position shifted to a lower wave number with increasing process pressure. With scanning electron microscopy (SEM), a network of microcracks was observed on the surface of the DLC film without N₂ plasma pre-treatment. The density of these cracks decreased with increasing process pressure. In the film subjected to a N₂ plasma pre-treatment, no cracks were observed at any process pressure. In the gas barrier test, the gas permeation decreased drastically with increasing film thickness and saturated at a thickness of 0.2 μm. The DLC-coated PTFE with the N₂ plasma pre-treatment exhibited a greater reduction in gas permeation than did the samples without pre-treatment. For both sample types, gas permeation decreased with increasing process pressure.     

Integrated structural color array enabled by ultrathin silver film via cavity-enhanced absorption

In this work, we experimentally demonstrate enhanced absorption resonance enabled by the deconstructive interference of the reflected light in a sandwiched nanostructures composing of the ultrathin silver layer, transparent SiO₂ cavity, and the opaque metallic substrate (e.g., 300-nm Ag). Such cavity-enhanced absorption is tunable via modulating the thickness of the absorptive ultrathin silver layer or the embedded transparent SiO₂ cavity, giving rise to tunable structural coloration. Through five deposition processes, a 32-channel colorful sample is successfully fabricated. We believe the concepts and results make it evident that such ultrathin absorptive film offers us unprecedented opportunities on developing various photonic applications such as labeling, visual arts, and optical filters.     

The role of a ZnO buffer layer in the growth of ZnO thin film on Al2O3 substrate

A ZnO buffer layer and ZnO thin film have been deposited by the pulsed laser deposition technique at the temperatures of 200 C and 400 C, respectively. Structural, electrical and optical properties of ZnO thin films grown on sapphire (Al₂O₃) substrate with 1, 5, and 9 nm thick ZnO buffer layers were investigated. A minute shift of the (101) peak was observed which indicates that the lattice parameter was changed by varying the thickness of the buffer layer. High resolution transmission electron microscopy (TEM) was used to investigate the thickness of the ZnO buffer layer and the interface involving a thin ZnO buffer between the film and substrate. Selected area electron diffraction (SAED) patterns show high quality hexagonal ZnO thin film with 30 in-plane rotation with respect to the sapphire substrate. The use of the buffer can reduce the lattice mismatch between the ZnO thin film and sapphire substrate; therefore, the lattice constant of ZnO thin film grown on sapphire substrate became similar to that of bulk ZnO with increasing thickness of the buffer layer.     

Effects of interface between SnO2 thin film and Si substrate on growth time

SnO₂ thin film was grown on Si substrate using the low pressure chemical vapor deposition (LPCVD) method. The SnO₂ thin film was grown in the direction of (110) as deposition time increased. The atomic ratio of O decreased by 62.4, 57.6, and 45.6%, and the thickness of the thin film increased to 0.2, 0.3, and 0.7 ? as the deposition time increased to 10, 20, and 30 min, respectively. The interface of the thin film was examined using high-resolution transmission electron microscope (HRTEM) and energy dispersive spectroscopy (EDS) analysis. The SiO₂ layer was observed at between the SnO₂ thin film and the Si substrate. This layer decreased in thickness as the deposition time increased, which indicates that the deposition time affected the interface of the thin film.     

Determination of the refractive index and thickness of a transparent film on a transparent substrate from the angles of incidence of zero reflection-induced ellipticity

Linearly polarized light incident on a transparent film coating a transparent substrate remains linearly polarized after reflection only at a set of discrete angles of incidence φ_m (m integer). Measurement of these angles of incidence for zero reflection-induced ellipticity (ZRIE) allows simple, direct and explicit determination of the refractive index and thickness of the film, independent of the substrate refractive index. The latter can be separately and easily determined from the azimuths of the incident and reflected linear vibrations at one of the angles of incidence φ_m or, alternatively, from the angle of refraction of light into the substrate using Snell's law. The proposed technique requires that the thickness of the film exceed one-fourth the wavelength of light in the medium of the film, and that it does not fall in a “higher-order” thickness gap when the ratio of the refractive index of the film to that of the ambient is greater than $\text{2}\text{√3}$.     

Formation of textured Ni(200) and Ni(111) films by magnetron sputtering

The effect of the working gas pressure (P ≈ 1.33–0.09 Pa) and the substrate temperature (T_s ≈ 77–550 K) on the texture and the microstructure of nickel films deposited by magnetron sputtering onto SiO₂/Si substrates is studied. Ni(200) films with a transition type of microstructure are shown to form at growth parameters P ≈ 0.13–0.09 Pa and T_s ≈ 300–550 K, which ensure a high migration ability of nickel adatoms on a substrate. This transition type is characterized by a change of the film structure from quasi-homogeneous to quasi-columnar when a film reaches a critical thickness. Ni(111) films with a columnar microstructure and high porosity form at a low migration ability, which takes place at P ≈ 1.33–0.3 Pa or upon cooling a substrate to T_s ≈ 77 K.     

Homogeneous Si films on CaF2/Si(1 1 1) due to boron enhanced solid phase epitaxy

The structure and morphology of Si/CaF₂/Si(1 1 1) structures have been investigated by X-ray diffraction (XRD, GIXRD) and X-ray photoelectron spectroscopy (XPS). While CaF₂ films were grown via molecular beam epitaxy (MBE), Si films on CaF₂/Si(1 1 1) are fabricated by surfactant enhanced solid phase epitaxy (SE-SPE). Here Boron was used as a surfactant to obtain semiconductor films of homogeneous thickness. The Si films are entirely relaxed while the CaF₂ films have both pseudomorphic and relaxed crystallites. After exposure to ambient conditions, the Si films have a very thin native oxide film. The homogeneous Si film partially prevents the incorporation of impurities at the interface between the Si substrate and CaF₂ via migration along residual defects of the CaF₂ film.     

Influence of the thickness on structural,magnetic and electrical properties of La0.7Ca0.3MnO3 thin film

We have studied the effect of thickness on the structural, magnetic and electrical properties of La_0.7Ca_0.3MnO₃ thin films prepared by pulsed laser deposition method using X-ray diffraction, electrical transport, magneto-transport and dc magnetization. X-ray diffraction pattern reflects that all films have c-axis epitaxial growth on LaAlO₃ substrate. The decrease in out-of-plane cell parameter specifies a progressive relaxation of in the plane compressive strain as the film thickness is increases. From the dc magnetization measurements, it is observed that ferromagnetic to paramagnetic transition temperature increases with increase in the film thickness. Magneto-resistance and temperature coefficient of resistance increases with film thickness and have maximum value near its metal to insulator transition temperature.     

Doping properties of microcrystalline silicon prepared by mercury sensitized photochemical vapor deposition

Conductivity of photo-CVD microcrystalline silicon (c-Si:H) in wide range of dopant gas concentration (10^–53/SiH₄, B₂H₆/SiH₄<10^–2) is investigated. As compared with a-Si:H, the conductivity of the film is improved more than two orders of magnitude by microcrystallization for a wide range of dopant concentration at a deposition temperature of as low as 150°C. This indicates the suitability of photo-CVD for low temperature processing. A conductivity minimum is found at a doping ratio of about B₂H₆/SiH₄=1×10^–5.     

Sputter deposition of high transparent TiO2−xNx/TiO2/ZnO layers on glass for development of photocatalytic self-cleaning application

In this study, TiO_2−xN_x/TiO₂ double layers thin film was deposited on ZnO (80 nm thickness)/soda-lime glass substrate by a dc reactive magnetron sputtering. The TiO₂ film was deposited under different total gas pressures of 1 Pa, 2 Pa, and 4 Pa with constant oxygen flow rate of 0.8 sccm. Then, the deposition was continued with various nitrogen flow rates of 0.4, 0.8, and 1.2 sccm in constant total gas pressure of 4 Pa. Post annealing was performed on as-deposited films at various annealing temperatures of 400, 500, and 600 °C in air atmosphere to achieve films crystallinity. The structure and morphology of deposited films were evaluated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). The chemical composition of top layer doped by nitrogen was evaluated by X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of samples was measured by degradation of Methylene Blue (MB) dye. The optical transmittance of the multilayer film was also measured using ultraviolet-visible light (UV-vis) spectrophotometer. The results showed that by nitrogen doping of a fraction (∼1/5) of TiO₂ film thickness, the optical transmittance of TiO_2−xN_x/TiO₂ film was compared with TiO₂ thin film. Deposited films showed also good photocatalytic and hydrophilicity activity at visible light.     

Some aspects of interactions between HTSC-films and substrates

Different aspects of the interaction between YBa₂Cu₂O_y(YBCO) films and (100) ZrO₂〈Y〉 (YSZ) substrates have been investigated. It was determined using X-ray diffraction methods that the structural mismatch between the film and the substrate leads to a film deformation throughout its thickness. At the same time a strained layer appears in the substrate, whose thickness is proportional to the film thickness. The surface morphology changes of YBCO films which take place with variation of the growth temperaturet_sin the vicinity of the optimum temperature lead to changes of the film grain structure probably connected with nucleation centers. Tl₂Ba₂CaCu₂O_y(TBCCO) films on YSZ substrates were also synthesized. It was found that the dependence of the TBCCO film surface morphology changes with annealing temperature and the dependence of YBCO film surface morphology changes ont_sare similar.     

直流磁控溅射YBCO非晶薄膜的卢瑟福背散射研究

利用直流磁控溅射(D.C.Magnetron Sputtering)法,选取总气压为80Pa,沉积时间为60min,溅射靶尺寸为φ80,在磁场强度、靶与基片之间的距离及Ar/O₂比等参数变化的情况下,制备了四组YBCO/Al₂O₃非晶薄膜样品。用MeV Li卢瑟福背散射(RBS)分析技术,测量了各块样品中Ba和Cu相对Y的含量和薄膜厚度随基片的横向分布。分析结果表明:在不同的沉积条件下,薄膜中各点的Ba和Cu相对浓度差别较大,薄膜厚度分布也 关键词：     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.