Pulsed laser ablation of borax target in vacuum and hydrogen DC glow discharges

The aim of our experiment was to produce a material with BH bonds for applications in hydrogen storage and generation. By using KrF excimer laser (λ = 248 nm) ablation of borax (Na₂B₄O₇) target, thin films were deposited on KBr and silicon substrates. Ablation was performed both in vacuum and in hydrogen atmosphere. DC glow discharge technique was utilized to enhance hydrogen gas ionization. Experiments were performed using laser fluence from 5 to 20 J/cm². Films were deposited under gas pressure of 1 × 10⁻⁵ to 5 × 10⁻² mbar and substrate temperatures of 130-450 °C. Scanning electron microscopy analysis of films showed presence of circular particulates. Film thickness, roughness and particulates number increased with increase in laser fluence. Energy dispersive X-ray spectroscopy analysis shows that sodium content in the particulates is higher than in the target. This effect is discussed in terms of atomic arrangements (both at surface and bulk) in systems where ionic and covalent bonds are present and by looking at the increased surface/bulk ratio of the particulates with respect to the deposited films. The Fourier transform infrared spectroscopy measurements showed presence of BO stretching and BOB bending bonds. Possible reasons for absence of BH bonds are attributed to binding enthalpy of the competing molecules.     

Crystallization and surface morphology evolution of erbium fluoride films on different substrates

Erbium fluoride (ErF₃) films were thermally deposited on Ge(1 1 1), Si(0 0 1) and copper mesh grid with different substrate temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the films. The structure of ErF₃ films deposited on germanium and silicon changed from amorphous to crystalline with increasing the substrate temperature, while the crystallization temperature of the films on silicon is higher than that of on germanium. The infrared optical properties of the films change greatly with the evolution of crystal structure. It is also found that the morphology of ErF₃ film on Ge(1 1 1) at 200 °C is modulated by the stress between the substrate and film. The SEM and TEM results confirmed that the ErF₃ films on copper mesh grid were crystalline even at 100 °C. Interestingly, the ErF₃ films show flower-like surface morphology when deposited on copper mesh at 200 °C. The crystallization temperature (T_c) of ErF₃ films on the three substrates has the relation which is which is induced by the wetting angle of ErF₃ films on different substrates.     

The study of ion mixed amorphous carbon films on single crystal silicon by C ion implantation

Amorphous-carbon (a-C) films were deposited on a single-crystal silicon substrate by vacuum vapor deposition system and these amorphous carbon films were implanted with 110 keV C⁺ at fluences of 1 × 10¹⁷ ions/cm². The effect of ion mixing on the surface morphology, friction behavior and adhesion strengths of amorphous carbon films was examined making use of atomic force microscopy (AFM), ball-on-disk reciprocating friction tester, nano-indentation system and scanning electron microscope (SEM). The changes in chemical composition and structure were investigated by using X-ray photoelectron spectroscopy (XPS). The results show that the anti-wear life and adhesion of amorphous carbon films on the Si substrates were significantly increased by C ion implantation. The SiC chemical bonding across the interface plays a key role in the increase of adhesion strength and the anti-wear life of amorphous carbon film. The friction and wear mechanisms of amorphous carbon film under dry friction condition were also discussed.     

Influence of radiofrequency power on compositional, structural and optical properties of amorphous silicon carbonitride films

The silicon carbonitride (SiCN) films were deposited on n-type Si (1 0 0) and glass substrates by the radiofrequency (RF) reactive magnetron sputtering of polycrystalline silicon target under mixed reactive gases of acetylene and nitrogen. The films have been characterized by energy dispersive spectrometer (EDS), atomic force microscope (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectrophotometer (UVS). The influence of RF power on the compositional, morphological, structural and optical properties of the SiCN films was investigated. The SiCN films deposited at room temperature are amorphous, and the C, Si and O compositions except N in the films are sensitive to the RF power. The surface roughness and optical band gap decrease as the RF power increases. The main bonds in the SiCN films are C-N, N-H_n, C-H_n, C-C, CN, Si-H and Si-C, and the intensities of the CN, Si-H and C-H_n bonds increase with increment of the RF power. The mechanisms of the influence of RF power on the characteristics of the films are discussed in detail.     

Structure and tribological properties of amorphous carbon films deposited by electrochemical method on GCr15 steel substrate

Amorphous carbon films were deposited on GCr15 steel substrates by electrolysis of methanol, dimethylsulfoxide (DMSO) and the methanol-DMSO intermixture electrolytes, respectively, under high voltage and low temperature conditions. The microstructure and wear morphology of the deposited films were analyzed using X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) combined with energy dispersive X-ray fluorescence spectrometer (EDX), respectively. The tribological properties of the films were evaluated using a ball-on-disk rotating friction tester under dry friction condition. The results show that the films deposited by electrodeposition technique on GCr15 steel substrates are amorphous carbon films. It is also found that the electrolytes have an obvious influence on the tribological properties of the deposited films with the electrodeposition method. The tribological properties of the films deposited with the intermixture electrolyte are better than those of the films deposited by other pure electrolytes. The related growth mechanism of the films in the liquid-phase electrodeposition is discussed as well in this study. Via the reaction of the CH₃ groups with each other to form carbon network and reaction of the CH₃ and SO²⁺ groups to achieve the doping of sulfur atom in the carbon network, respectively, in other words, amorphous carbon films can be obtained on GCr15 steel substrates by electrodeposition technique.     

Structural and optical properties of the SiCN thin films prepared by reactive magnetron sputtering

Silicon carbonitride (SiCN) thin films were deposited on n-type Si (1 0 0) and glass substrates by reactive magnetron sputtering of a polycrystalline silicon target in a mixture of argon (Ar), nitrogen (N₂) and acetylene (C₂H₂). The properties of the films were characterized by scanning electron microscope with an energy dispersive spectrometer, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry and ultraviolet-visible spectrophotometer. The results show that the C₂H₂ flow rate plays an important role in the composition, structural and optical properties of the films. The films have an even surface and an amorphous structure. With the increase of C₂H₂ flow rate, the C content gradually increases while Si and N contents have a tendency to decrease in the SiCN films, and the optical band gap of the films monotonically decreases. The main bonds are Si-O, N-H_n, C-C, C-N, Si-N, Si-C and Si-H in the SiCN films while the chemical bonding network of Si-O, C-C, C-O, C-N, N-Si and CN is formed in the surface of the SiCN films.     

Patterned uniformly orientated silicon nanocrystallite films and efficient field emission characteristics

Patterned uniformly (100)-orientated silicon nanocrystallite (SiNC) films were fabricated based on hydrogen ion implantation technique and typical electrochemical anodic etching method. The surface morphology and microstructure characteristics of the films were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and atomic force microscopy. The efficient field emission with low turn-on field of about 3.2 V/μm at current density of 0.1 μA/cm² was obtained. The emission current density from the SiNC films reached 1 mA/cm² under a bias field of about 11 V/μm. The experimental results demonstrate that the SiNC films have great potential applications for flat panel displays.     

Preparation of silicon carbide film by a plasma focus device

Silicon carbide (SiC) films were grown on the silicon (100) substrate by a 20 kJ Mather-type dense plasma focus device. The preparation method and characterization data are presented. X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (SEM) and nano-indentor were employed for the characterization of the samples obtained at different axial position of 50 mm, 90 mm, 130 mm and 170 mm, respectively. Polycrystalline 3CSiC were obtained at the position of 90 mm and 130 mm from XRD and FTIR spectra. SEM image showed that the silicon carbide films obtained at the position of 90 mm are porous on surface layer. Nano-indentor indicates that the film obtained at the position of 130 mm has the highest mechanical hardness.     

Pulsed laser deposition of amorphous carbon nitride thin films and their electrical properties

Amorphous carbon nitride thin films were deposited by pulsed laser deposition combined with a nitrogen rf radical beam source. A structural characterization of the deposited films was performed using X-ray photoelectron and Raman-scattering spectroscopy. The Raman spectra showed that the dominant hybridization state of carbon atoms in the deposited film is sp². N 1s electron spectra were deconvoluted into three components, N bonded to pyridine-like N and/or N-sp³C (N1), substitutional N in graphite (N2), and N-O and/or N-N (N3). The proportion of N1 increased with increasing N/C atomic ratio in the film. The electrical conductivity at room temperature decreased and the Tauc optical band gap increased with increasing N/C atomic ratio. The temperature dependence of the electrical conductivity indicated that electronic conduction occurred by variable range hopping between electron localized states. The decrease in electrical conductivity with increasing N/C atomic ratio was caused by a strong electron localization due to the increased proportion of N1. PACS 81.05.Uw; 81-15.Fg; 73.61.Jc     

Si-nanostructures formation in amorphous silicon nitride SiNx:H deposited by remote PECVD

The formation of silicon nanoclusters embedded in amorphous silicon nitride (SiN_x:H) can be of great interest for optoelectronic devices such as solar cells. Here amorphous SiN_x:H layers have been deposited by remote microwave-assisted chemical vapor deposition at 300 °C substrate temperature and with different ammonia [NH₃]/silane [SiH₄] gas flow ratios (R=0.5−5). Post-thermal annealing was carried out at 700 °C during 30 min to form the silicon nanoclusters. The composition of the layers was determined by Rutherford back scattering (RBS) and elastic recoil detection analysis (ERDA). Fourier transform infrared spectroscopy (FTIR) showed that the densities of SiH (2160 cm⁻¹) and NH (3330 cm⁻¹) molecules are reduced after thermal annealing for SiN:H films deposited at flow gas ratio R>1.5. Breaking the SiH bonding provide Si atoms in excess in the bulk of the layer, which can nucleate and form Si nanostructures. The analysis of the photoluminescence (PL) spectra for different stoichiometric layers showed a strong dependence of the peak characteristics (position, intensity, etc.) on the gas flow ratio. On the other hand, transmission electron microscopy (TEM) analysis proves the presence of silicon nanoclusters embedded in the films deposited at a gas flow ratio of R=2 and annealed at 700 °C (30 min).     

Study of interfacial oxide layer of LaAlO3 gate dielectrics on Si for metal–insulator–semiconductor devices

Lanthanum aluminate (LAO) thin films were deposited on silicon by pulsed-laser deposition. It was found that oxygen partial pressure played an essential role in the formation of an interfacial layer. The films deposited in nitrogen at a pressure of 20 Pa had no interfacial layer. However, an interfacial layer was observed in the films deposited in 1×10^-2 Pa atmosphere. According to the thickness of the LAO film and interfacial layer and the measured capacitance, it could be deduced that the interfacial layer was not pure SiO₂. Auger electron spectroscopy, secondary ion mass spectroscopy and X-ray photoelectron spectroscopy depth analyses indicated that the interfacial layer was La–Al–silicate rather than pure silicon oxide and that the La and Al concentrations in the interfacial layer had gradients from the LAO layer to the substrate. PACS 79.61.Jv; 77.55.+f; 81.15.Gh     

Synthesis of molybdenum silicide by both ion implantation and ion beam assisted deposition

Two groups of Mo/Si films were deposited on surface of Si(1 0 0) crystal. The first group of the samples was prepared by both ion beam assisted deposition (IBAD) and metal vapor vacuum arc (MEVVA) ion implantation technologies under temperatures from 200 to 400 °C. The deposited species of IBAD were Mo and Si, and different sputtering Ar ion densities were selected. The mixed Mo/Si films were implanted by Mo ion with energy of 94 keV, and fluence of Mo ion was 5 × 10¹⁶ ions/cm². The second group of the samples was prepared only by IBAD under the same test temperature range. The Mo/Si samples were analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), sheet resistance, nanohardness, and modulus of the Mo/Si films were also measured. For the Mo/Si films implanted with Mo ion, XRD results indicate that phase of the Mo/Si films prepared at 400 and 300 °C was pure MoSi₂. Sheet resistance of the Mo/Si films implanted with Mo ion was less than that of the Mo/Si films prepared without ion implantation. Nanohardness and modulus of the Mo/Si films were obviously affected by test parameters.     

Silicon carbide synthesis with energy pulses

Polycrystalline SiC layers were synthesized through nanosecond pulse heating of thin carbon films deposited on single-crystalline silicon wafers. The samples were submitted to electron beam irradiation (25 keV, 50 ns) at various current densities in vacuum (10^–4mbar) and to XeCl excimer laser pulses (308 nm, 15ns) in air. Rutherford backscattering spectrometry (RBS) showed that in the e-beam annealed samples mixing of the elements at the interface starts at current densities of about 1200 A/cm². The mixed layer thickness increases almost linearly with current density. From the RBS spectra a composition of the intermixed layers close to the SiC compound was deduced. Transmission electron microscopy (TEM) and electron diffraction studies clearly evidenced the formation of SiC polycrystals. Using the XeCl excimer laser, intermixing of the deposited C film with the Si substrate was observed after a single 0.3 J/cm² pulse. Further analysis evidenced the formation of SiC nanocrystals, embedded in a diamond film.     

Effect of ambient hydrogen sulfide on the physical properties of vacuum evaporated thin films of zinc sulfide

Evaporated thin films of zinc sulfide (ZnS) have been deposited in a low ambient atmosphere of hydrogen sulfide (H₂S ∼10⁻⁴ Torr). The H₂S atmosphere was obtained by a controlled thermal decomposition of thiourea [CS(NH₂)₂] inside the vacuum chamber. It has been observed that at elevated substrates temperature of about 200 °C helps eject any sulfur atoms deposited due to thermal decomposition of ZnS during evaporation. The zinc ions promptly recombine with H₂S to give better stoichiometry of the deposited films. Optical spectroscopy, X-ray diffraction patterns and scanning electron micrographs depict the better crystallites and uniformity of films deposited by this technique. These deposited films were found to be more adherent to the substrates and are pinhole free, which is a very vital factor in device fabrication.     

Laser deposition of amorphous diamond films from liquid aromatic hydrocarbons

6 H₅CH₃, C₆H₆, and C₆H₅CH(CH₃)₂) to pulsed visible laser radiation of a copper vapor laser (λ=510.6 nm). The X-ray Auger electron spectroscopy (XAES), reflection high energy electron diffraction (RHEED), and Raman analysis are employed to characterize the deposited films. The sp³ fraction in deposited films amounts to 60–70% and depends on the precursor. The average film thickness on a glass substrate is about 100 nm. The films show excellent adherence, are transparent in the visible and have microhardness of 50–70 GPa, as measured by nanoindentor. Received: 28 September 1998 / Accepted: 13 January 1999     

辉光放电等离子体辅助XeCl准分子激光溅射沉积碳氮薄膜

利用直流辉光放电等离子体辅助的脉冲激光沉积技术在Si衬底上生长了碳氮薄膜.通过扫描电子显微镜、X射线衍射、X射线光电子能谱、俄歇电子能谱等多种手段,对薄膜的形貌、成分、晶体结构、价键状态等特性进行了分析和确定.结果表明,沉积薄膜为含有非晶SiN和晶态氮化碳颗粒结构,晶态成分呈多晶态,主要为α-C₃N₄相、β-C₃N₄相,晶粒大小为40—60nm.碳氮之间主要以C-N非极性共价键形式相结合. 关键词： 脉冲激光沉积 直流辉光放电 碳氮薄膜     

Biocompatible film deposition by using Nd:YAG pulsed laser

A Nd:YAG laser operating at the fundamental wavelength (1064 nm) and at the second harmonic (532 nm), with 9 ns pulse duration, 100–900 mJ pulse energy, and 30 Hz repetition rate mode, was employed to ablate in vacuum (10^?6 mbar) biomaterial targets and to deposit thin films on substrate backings. Titanium target was ablated at the fundamental frequency and deposited on near-Si substrates. The ablation yield increases with the laser fluence and at 40 J/cm ² the ablation yield for titanium is 1.2×10¹⁶ atoms/pulse. Thin film of titanium was deposited on silicon substrates placed at different distance and angles with respect to the target and analysed with different surface techniques (optical microscopy, scanning electron spectrosopy (SEM), and surface profile).

Hydroxyapatite (HA) target was ablated to the second harmonic and thin films were deposited on Ti and Si substrates. The ablation yield at a laser fluence of 10 J/cm ² is about 5×10¹⁴ HA molecules/pulse. Thin film of HA, deposited on silicon substrates placed at different distance and angles with respect to the target, was analysed with different surface techniques (optical microscopy, SEM, and Raman spectroscopy).

Metallic films show high uniformity and absence of grains, whereas the bio-ceramic film shows a large grain size distribution. Both films found special application in the field of biomaterial coverage.     

Optical properties of single-phase β-FeSi2 films fabricated by electron beam evaporation

Single-phase semiconducting iron disilicide (β-FeSi₂) films on silicon substrate were fabricated by electron beam evaporation (EBE) technique. For preventing the oxidation of Fe film, silicon/iron/silicon sandwich structure films with different thickness of silicon and iron were deposited and then annealed at different temperatures. X-ray diffraction (XRD), Raman and Fourier transform infrared spectroscopy (FTIR) measurements were carried out to study the phase distribution and crystal quality of the films. Single-phase β-FeSi₂ with high crystal quality was achieved after annealing at 800 °C for 5 h. An apparent direct bandgap E_g of approximately 0.85-0.88 eV was observed in the β-FeSi₂ films. It is considered that the silicon/iron/silicon sandwich structure is suited for formation of single-phase β-FeSi₂ with high crystal quality.     

Study on structural properties of epitaxial silicon films on annealed double layer porous silicon

In this paper, epitaxial silicon films were grown on annealed double layer porous silicon by LPCVD. The evolvement of the double layer porous silicon before and after thermal annealing was investigated by scanning electron microscope. X-ray diffraction and Raman spectroscopy were used to investigate the structural properties of the epitaxial silicon thin films grown at different temperature and different pressure. The results show that the surface of the low-porosity layer becomes smooth and there are just few silicon-bridges connecting the porous layer and the substrate wafer. The qualities of the epitaxial silicon thin films become better along with increasing deposition temperature. All of the Raman peaks of silicon films with different deposition pressure are situated at 521 cm⁻¹ under the deposition temperature of 1100 °C, and the Raman intensity of the silicon film deposited at 100 Pa is much closer to that of the monocrystalline silicon wafer. The epitaxial silicon films are all (4 0 0)-oriented and (4 0 0) peak of silicon film deposited at 100 Pa is more symmetric.     

微波ECR等离子体增强磁控溅射制备SiNx薄膜及其性能分析

利用微波ECR磁控反应溅射法在室温下制备无氢SiN_x薄膜.通过傅里叶红外光谱 、X射线电子谱、膜厚仪、纳米硬度仪、原子力显微镜等分析手段，分析了N₂流 量、Si靶溅射功率等实验参数对SiN_x薄膜结构、化学配比以及机械性质的影响. 结果表明，SiN_x薄膜中Si-N结构、化学配比及机械性质与等离子体中的Si元素 含量关系密切，随着N₂流量的增加或者Si靶溅射功率的降低，等离子体中的Si 元素含量降低，SiN_x薄膜结构、化学配比及硬度发生变化，红外光谱发生偏移 ，硬度下降，沉积速率降低. 关键词： x')" href="#">SiN_x 磁控溅射 傅里叶变换红外吸收光谱 X射线电子谱