Effect of substrate temperature on corrosion performance of nitrogen doped amorphous carbon thin films in NaCl solution

Nitrogen doped amorphous carbon (a-C:N) thin films were deposited on p-Si substrates by DC magnetron sputtering at varying substrate temperature from room temperature (RT) to 300 °C. The bonding structure, surface morphology and adhesion strength of the a-C:N films were investigated by using X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, atomic force microscopy (AFM) and micro-scratch testing. The corrosion behavior of the a-C:N films was evaluated by potentiodynamic polarization test in a 0.6 M NaCl solution. The results indicated that the corrosion resistance of the films depended on the sp³-bonded cross-link structure that was significantly affected by the substrate temperature.     

Enhancing the field emission properties of amorphous carbon films by thermal annealing

Polymer-like hydrogenated and nitrogenated amorphous carbon films (a-C:H:N) have been deposited on silicon and glass substrates using a Plasma Technology DP800 radio frequency plasma enhanced chemical vapour deposition system. This equipment was configured with an earthed water-cooled substrate table, allowing the carbon films to grow under low bias conditions yielding films with refractive indices of ∼1.5−1.7, and E₀₄ optical band-gaps of ∼3−4 eV. The field emission properties of these films have been studied using a sphere-to-plane anode–cathode configuration, and the dependence on annealing treatment investigated. A significant lowering of the emission threshold field has been measured after treating the films for 1800 s at 400°C. This has been correlated with a simultaneous study of the change in the films’ microstructural properties. We conclude that the changes commensurate with the onset of graphitization are beneficial for field emission, and that the associated improvements in the films’ mechanical stability will aid incorporation into large-area displays.     

Adherent amorphous hydrogenated carbon films on metals deposited by plasma enhanced chemical vapor deposition

This paper reports the findings of a study of the structural, mechanical, and tribological properties of amorphous hydrogenated carbon (a-C:H) coatings for industrial applications. These thin films have proven quite advantageous in many tribological applications, but for others, thicker films are required. In this study, in order to overcome the high residual stress and low adherence of a-C:H films on metal substrates, a thin amorphous silicon interlayer was deposited as an interface. Amorphous silicon and a-C:H films were grown by using a radio frequency plasma enhanced chemical vapor deposition system at 13.56 MHz in silane and methane atmospheres, respectively. The X-ray photoelectron spectroscopy technique was employed to analyze the chemical bonding within the interfaces. The chemical composition and atomic density of the a-C:H films were determined by ion beam analysis. The film microstructure was studied by means of Raman scattering spectroscopy. The total stress was determined through the measurement of the substrate curvature, using a profilometer, while micro-indentation experiments helped determine the films' hardness. The friction coefficient and critical load were evaluated by using a tribometer. The results showed that the use of the amorphous silicon interlayer improved the a-C:H film deposition onto metal substrates, producing good adhesion, low compressive stress, and a high degree of hardness. SiC was observed in the interface between the amorphous silicon and a-C:H films. The composition, the microstructure, the mechanical and tribological properties of the films were strongly dependent on the self-bias voltages. The tests confirmed the importance of the intensity of ion bombardment during film growth on the mechanical and tribological properties of the films.     

Catalytic CVD growth and properties of a-C:H and a-C:N

Hydrogenated amorphous carbon (a-C:H) and nitrided amorphous carbon (a-C:N) films have been synthesized on quartz substrates at a substrate temperature of 700 °C using a catalytic chemical vapor deposition (Cat-CVD) method. Raman spectra of a-C:H films showed two principal bands, the G-band at 1600 cm⁻¹ and the D-band at 1350 cm⁻¹. Those of a-C:N films showed similar spectra, with a G′ band at 1640 cm⁻¹, the peak energy of which is higher than that of the G-band in a-C:H. The intensity ratio /I_D, which is a measure of the degree of order in a-C:H, decreased for a-C:H with increasing CH₄/H₂ gas-flow ratio. On the contrary, the /I_D ratio increased with increasing CH₄/H₂ gas-flow ratio.     

Effects of thermal annealing in oxygen plasma for buffer layers on properties of ZnO thin films

ZnO thin films with ZnO buffer layers were grown by plasma-assisted molecular beam epitaxy (PA-MBE) on p-type Si(100) substrates. Before the growth of the ZnO thin films, the ZnO buffer layers were deposited on the Si substrates for 20 minutes and then annealed at the different substrate temperature ranging from 600 to 800 degrees C in oxygen plasma. The structural and optical properties of the ZnO thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and room-temperature (RT) photoluminescence (PL). A narrower full width at half maximum (FWHM) of the XRD spectra for ZnO(002) and a larger grain are observed in the samples with the thermal annealed buffer layers in oxygen plasma, compared to those of the as-grown sample. The surface morphology of the samples is changed from rugged to flat surface. In the PL spectra, near-band edge emission (NBEE) at 3.2 eV (380 nm) and deep-level emission (DLE) around 1.77 to 2.75 eV (700 to 450 nm) are observed. By increasing the annealing temperatures up to 800 degrees C, the PL intensity of the NBEE peak is higher than that of the as-grown sample. These results imply that the structural and optical properties of ZnO thin films are improved by the annealing process.     

Characterization of TiCr(C,N)/amorphous carbon coatings synthesized by a cathodic arc deposition process

Ternary TiCrN and nanocomposite TiCr(C,N)/amorphous carbon (a-C) coatings with different carbon contents (0-26.6 at.%) were synthesized by cathodic arc evaporation with plasma enhanced duct equipment. The structural, chemical, and mechanical properties of the deposited films were studied by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and nanoindentation measurement. The atomic content ratios of carbon/(Ti + Cr) and carbon/nitrogen increased with increasing C₂H₂ flow rate. A nanocomposite structure of coexisting metastable hard TiCr(C,N) crystallites and amorphous carbon phases was found in the TiCr(C,N)/a-C coatings, those possessed smaller crystallite sizes than the ternary TiCrN film. XPS analyses revealed the concentration of a-C increased with increasing carbon content from 8.9 at.% to 26.6 at.%. Exceeding the metastable solubility range of carbon within the TiCrN lattice, the carbon formed a-C phase in the deposited coatings. The nanocomposite TiCr(C,N)/a-C coatings exhibited higher hardness value of 29-31 GPa than the deposited TiCrN coating (26 ± 1 GPa). It has been found that the structural and mechanical properties of the films were correlated with the carbon content in the TiCr(C,N)/a-C coatings.     

Deposition of silicon doped and pure hydrogenated amorphous carbon coatings on quartz crystal microbalance sensors for protein adsorption studies

In this study hydrogenated amorphous carbon films (a-C:H) and silicon doped hydrogenated amorphous carbon films (a-C:H:Si) with different hydrogen and silicon contents were deposited onto sensors of a quartz crystal microbalance with dissipation detection (QCM-D). The resulting films were investigated with regard to their structural and elemental compositions using Raman spectroscopy, elastic recoil detection analysis and Rutherford backscattering spectroscopy. Furthermore the surface free energy (SFE) of the films was determined using contact angle measurements. The polar part of SFE of the a-C:H:Si films was found to be adjustable by the silicon content in these films and increased by increasing amounts of silicon. Carbon films with a broad range of chemical composition showed similar structure and properties when deposited on QCM-D sensors as compared with the deposition on silicon wafers. Subsequently, the amorphous carbon coated QCM-D sensors were used to study the adsorption of human serum albumin. These QCM-D results were related to the surface properties of the films.     

退火温度对a-C:H膜结构及摩擦学性能的影响

为研究环境温度对含氢无定形碳(a-C:H)膜结构和性能的影响,将a-C:H膜在大气环境中进行高温退火处理,并借助红外光谱、拉曼光谱、X射线光电子能谱、3D表面分析仪和球盘摩擦试验机等手段对退火前后a-C:H膜的结构、组成和性能进行了系统地考察.研究发现,在较低的退火温度下(300℃),a-C:H膜结构无明显变化,而其内应力降低,摩擦学性能显著提高;在400℃和500℃下退火,膜结构发生明显变化并伴随严重氧化,同时摩擦学性能降低甚至完全失效.结果表明,退火温度的选择对a-C:H膜的结构、组成及性能具有重要影响.     

Effects of synthesis temperature on CuIn(S,Se)2 thin films prepared by one-step evaporation of Cu–In precursors

CuIn(S,Se)₂ thin films were grown on soda-lime glass substrates by one-step evaporation Cu–In precursors processes. Effects of synthesis temperature on the structural and optical properties of CuIn(S,Se)₂ absorption layers were studied. The changes of surface morphology among different samples were observed by field-emission scanning electron microscopy. From X-ray diffraction images and Raman spectra, the CuIn(S,Se)₂ films had good crystallinity quality when the synthesis temperature was 550 °C. The FWHM of (112) peaks decreased from 0.537° to 0.180°, and secondary phase Cu_x(S,Se) disappeared when the synthesis temperature increased from 300 to 550 °C. The Raman spectra of the films also showed the CuIn(S,Se)₂ A₁ mode peaks existed chalcopyrite, and the blue shift of the CuIn(S,Se)₂ A₁ mode peaks from 289 to 284 cm^?1. The optical properties of the films were showed by transmission spectra, and the energy band gap of the CuIn(S,Se)₂ thin films fabricated at 550 °C is 1.34 eV.     

Investigation into the thermal annealing effects on CuIn(S,Se)2 thin films prepared by solution processes

CuIn(S,Se)₂ polycrystalline films were grown on soda-lime glass substrates by a solution process. Different annealing temperatures led to the variations of structural and electrical properties of the thin films. The pre-annealing temperatures changed from room temperature (RT) to 250°C, and all the post-annealing temperatures were set at 550°C. High quality film was obtained after post-annealing when the pre-annealing temperature increased to 250°C. The (112) X-ray diffraction peak’s position shifted at different pre-annealing temperatures after post-annealing, and the intensity of the (112) orientation increased with the pre-annealing temperature rising. Raman spectra exhibited A₁ mode was stable and the mixed B₂-E modes disappeared gradually with pre-annealing temperature increasing. The band gap energy of the film pre-annealed at 250°C is about 1.29 eV. The resistivity of the films without pre-annealing was 1230 Ω·cm, and 1.5 Ω·cm was achieved when the pre-annealing temperature was 250°C.     

Effect of substrate temperature and precursor ratio on properties of thin ZnS films sprayed by improved method

Zinc sulphide (ZnS) thin films were prepared by improved spray pyrolysis (ISP) method. The ISP parameters, such as carrier gas flow rate, solution flow rate and substrate temperature, were controlled with an accuracy of ±0.25 lpm, ±1 ml/h and ±1 °C, respectively. The solution was sprayed in a pulsed mode. The substrate temperature was optimized by analyzing substrate temperature dependent properties of thin films. The thin film deposited at a temperature of 450 °C was dense and fairly smooth with satisfactory crystallinity and very small impurity content. The effect of precursor ratio in the solution on structural, compositional and optical properties of thin ZnS films, deposited at a temperature of 450 °C, was studied. A gradual increase in band gap energy from 3.524 eV to 3.634 eV, refractive index from 2.5 to 2.9 and dielectric constant from 6.6 to 8.7 were observed with the variation of solution precursor (Zn:S) ratio from (1:2) to (1:6). The structural and compositional studies support this kind of enhancement in optical properties. The results show that the thin ZnS film prepared by ISP at the substrate temperature of 450 °C from a solution with specific precursor ratio can be used for optoelectronic and photovoltaic applications.     

Improved characteristics of sprayed CdO films by rapid thermal annealing

We report the influence of rapid thermal annealing (RTA) on optical, electrical and structural properties of sprayed undoped CdO thin films. XRD investigation revealed that as-grown films are polycrystalline in nature with cubic structure; and pronounced improvement in crystallinity of the films have been noticed after annealing. RTA-treated films showed preferred orientation in the (2 0 0) direction. The optical band gap was deduced from transmittance data for as-grown and annealed films and found to be 2.51 eV for as-grown film and ranged between 2.25 and 2.48 eV for annealed films. Figure of merit was calculated and found its maximum value (1.2 × 10^?2 Ω^?1) was for film annealed with of 6 min. Thermoelectric power (TEP) measurements revealed that the CdO films are having n-type conductivity. Furthermore, the activation energy was calculated for films from TEP data. The lowest electrical resistivity was found to be 6 × 10^?4 Ω cm for CdO film annealed with time ≥6 min. The observed changes demonstrated that RTA is a viable technique for improving characteristics of sprayed CdO films.     

Properties of nitrogen diluted hydrogenated amorphous carbon (n-type a-C:H) films and their realization in n-type a-C:H/p-type crystalline silicon heterojunction diodes

Nitrogen incorporated hydrogenated amorphous carbon (a-C:N:H) films were grown in an asymmetric rf PECVD system using C₂H₂ and N₂ gaseous mixture. Deposition rate, stress, hardness, optical bandgap, refractive index, and electrical characteristics have been studied as a function of self bias. Microstructures of these films were also studied using LASER Raman technique. Finally nitrogen diluted a-C:H films were realized as n-type semiconductor in n-type a-C:H/p-type crystalline silicon hetrojunction diodes. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics have also been studied as a function of self bias on these heterojunction diodes.     

Relative fraction of sp bonding in boron incorporated amorphous carbon films determined by X-ray photoelectron spectroscopy

Boron incorporated amorphous carbon (a-C:B) films were deposited by a filtered cathodic vacuum arc system using various percentage of boron mixed graphite cathodes. X-ray photoelectron spectroscopy (XPS) was employed to determine the properties of the films as a function of boron concentration. Deconvolutions of the XPS C 1s core level spectra were carried out using four different components. The relative fraction of sp³ bonding was then evaluated from the area ratio of the peaks at 285.0, 284.1 eV which were individually attributed to sp³ C-C, sp² CC hybridizations. The results showed that the sp³ content of a-C:B film decreases from 73.8 to 58.6% for the films containing boron from 0.59 to 2.13 at.%, and then gradually reduced to 42.5% at a slower rate with boron concentration up to 6.04 at.%. Furthermore, a series of a-C:B films with fixed boron content (2.13 at.%) were prepared to identify the relationship between sp³ bonding and substrate bias. It was found that the fraction of sp³ bonding increased from 50.28% at the bias voltage of 0 V and reached a maximum value of 66.3% at −150 V. As the bias voltage increased up to −2000 V, the sp³ content decreased sharply to 43.9%.     

Microstructure, mechanical and tribological properties of Ti(C, N)/a-C gradient composite films

Ti(C, N)/a-C composite films with compositional gradient from Ti-TiN-Ti(C, N) to Ti-containing a-C layers have been prepared by closed-field unbalanced magnetron sputtering. Within the composite films, the carbon contents gradually increase and achieve maximum in the a-C layer by increasing the power applied to the graphite targets, the nitrogen contents gradually decrease to zero from Ti(C, N) layer of the interface to a-C layer of the films. In order to achieve a good combination of the mechanical and tribological properties in the composite films, a designed experimental parameter basing on various substrate rotation speeds is also selected. Results show that the compositional gradient result in the microstructure change of composite films where the Ti(C, N) layers consist of fine nanocolumnar Ti(C, N) grains and the a-C layers consist of 2-7 nm TiC nanocrystallites embedded in an amorphous C matrix. The Ti(C, N) layers also exhibit clear multilayer structure where the period thickness gradually decreases as substrate rotation speed increases. Under higher rotation speed, disappearance of the multilayer structure is accompanied with simultaneous increase in the crystallinity of Ti(C, N) layer and also the Ti(C, N) grain size. In the a-C layer, the TiC nanocrystallites embedded in the a-C matrix is produced by the high rotation speeds. The Ti(C, N)/a-C gradient composite films exhibit high microhardness values (~5000 H_V) and low friction coefficient (~ 0.15), which is related to the hard Ti(C, N) layer and self-lubricate a-C layer, respectively. The combination of the Ti(C, N) layer with a-C layer increases the load and the wear resistance capacity of the composite films, which gives satisfactory friction performance in the pin-on-disk tests with a wear rate of 3.7 × 10^− 17 m³/mN.     

Raman spectra of iron-modified amorphous carbon

Raman spectra of amorphous carbon films containing encapsulated iron (a-C:Fe) have been measured in the frequency range 200–1000 cm⁻¹. The concentration of encapsulated iron atoms (3, 26, 38, and 54 at. %) was controlled by changing the relative areas of iron and graphite targets during the film deposition by RF magnetron sputtering and checked by Rutherford backscattering. The Raman spectra of a-C:Fe films display a series of almost equidistant bands spaced by approximately 110 cm⁻¹. This character of the spectrum is explained in terms of the atomic vibrations in short carbon nanotubes formed during the introduction of iron into an amorphous carbon matrix.     

Piezoresistive effect in amorphous carbon thin films

Abstract

In this contribution amorphous carbon (a-C) films are integrated as strain gauges in micromachined silicon boss membranes. Sputter deposited a-C films have high hardness and <2 % hydrogen content in it. The tribological properties of the a-C films are comparable with diamond and can be used for hard coatings. The films have very low resistivity which decreases with the temperature. Current voltage characteristics of a-C/oxide Si shows Ohmic behaviour. Variable range hopping mechanism is dominant at low temperatures and is thermally activated at room temperature and at higher temperatures. Piezoresistive gauge factor are measured in the temperature range 23–50°C.     

Structural and optical properties of wurtzite InN grown on Si(111)

We report the structural and optical properties of InN films on Si(111) prepared by ion-beam-assisted filtered cathodic vacuum arc technique. X-ray diffraction and Raman spectroscopy measurements indicated that all the InN films were hexagonal crystalline InN. The InN films deposited at substrate temperature of 475 °C exhibited highly (0001) preferred orientation and texturing (cratered) surface morphology. The oxygen incorporated in the InN films was segregated in the form of amorphous indium oxide or oxynitride phases at the grain boundaries. Photoluminescence emission of ∼ 1.15 eV was observed at room temperature from the InN films.     

Influence of annealing temperature on the properties of polycrystalline silicon films formed by rapid thermal annealing of a-Si:H films

In this work, rapid thermal annealing (RTA) was employed to crystallize the amorphous silicon films deposited by hot-wire chemical vapor deposition. The influence of annealing temperature on structural and electrical properties was studied by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and temperature-dependent conductivity measurement. The results show that the amorphous silicon films can be successfully crystallized by RTA in a very short time. The crystallinity and electrical properties of the poly-Si films was greatly improved as the RTA temperature increasing. When the temperature higher than 900 °C, the poly-Si films obtained the crystalline fraction above 95 %, and the hydrogen atoms almost disappeared in the poly-Si films. At the temperature of 1,100 °C, polycrystalline silicon films with conductivity of 16.4 S cm^?1 is obtained, which is seven orders in magnitude higher than that of the film annealed at 700 °C.     

氮掺杂氟化非晶碳薄膜光学性质的研究

用射频等离子体增强化学气相沉积(RF-PECVD)法制备氮掺杂氟化非晶碳(a-C:F:N)薄膜.用紫外-可见分光光谱仪、椭偏仪、傅立叶变换红外光谱仪对薄膜进行了检测.结果表明:随源气体中氮气含量的增加,光学带隙先减小后升高,折射率变化情况与之相反.在其它条件相同的情况下,升高沉积温度使得薄膜的光学带隙和折射率降低.光学带隙的大小与sp2键含量密切相关,sp2键浓度越大,薄膜的光学带隙越小.