Some electrical properties of diamond-like carbon thin films

Diamond-like carbon (DLC) belongs to very interesting materials used for a number of practical applications. It was noted that the electrical properties of DLC films obtained by RF PCVD discharge depend substantially on the deposition conditions. The results and discussion of the electrical properties of DLC films and DLC/Si heterostructures is presented. The electrical conductivity results are explained in terms of hopping mechanism. The relation between charge transport, structure of the energy gap and the deposition conditions is discussed.     

Optical study of ion-deposited diamond-like carbon films using spectroscopic ellipsometry

Spectroscopic ellipsometry was used for the characterization of ion-deposited diamond-like carbon (DLC) films, including the determination of film thickness and optical properties of DLC. The measured spectra in the wavelength range from 300 to 850 nm were analyzed with an appropriate fitting model, which was constructed according to the nominal sample structure in which the optical properties of DLC were described by a Cauchy dispersion model. Reasonably good agreement was found between the measured and calculated spectra for all samples studied, indicating that the models used were appropriate and that the calculated results were reliable. The results of our analysis suggest that, under the same deposition conditions (i.e., same substrate temperature and same chamber pressure), the optical properties of ion-deposited DLC film did not change much even if the film was prepared with quite different gas flow ratios.     

氟化类金刚石薄膜介电性能研究

采用射频等离子体增强化学气相沉积法制备了氟化类金刚石薄膜。利用俄歇电子能谱、绝缘电阻测试仪、耐压测试仪和QS电桥对样品组分和介电性能进行了表征、分析。结果表明:薄膜的介电常数εr在2.07~2.65之间,绝缘电阻在245 MΩ左右,击穿场强在2.1 MV/cm以上,它们与膜内F的含量密切相关。     

掺硅类金刚石薄膜的制备及其光学性质研究

利用直流磁控溅射技术在单晶硅和光学玻璃表面制备了掺硅类金刚石薄膜,采用紫外-可见光光谱仪、原子力显微镜、X射线光电子能谱(XPS),荧光光谱仪考察了不同硅含量对类金刚石薄膜的光学透过、表面形貌、电子结构和光学带隙的影响.结果表明,掺硅后的类金刚石薄膜的表面粗糙度先变大后变小,光学带隙变宽,但当掺硅达到一定量时,光学带隙有所降低.随着硅掺入量的增加,薄膜的红外透过率显著提高;光的发射中心"蓝移"并且强度增加.XPS的结果表明薄膜的sp3/sp2的比率随着硅含量的增加而变大.     

氟化类金刚石膜结构、性能及应用

氟化类金刚石膜是基于传统类金刚石膜的基础上发展起来的一种改性材料,该膜具有许多良好的性能,包括疏水性能、电学性能、光学性能、机械性能、热稳定性以及生物相容性,因此引起了人们的极大关注.本文介绍了氟化类金刚石膜的结构、性能、应用领域和发展趋势.     

Diamond and diamond-like carbon films

Polycrystalline diamond films are grown from low pressure gas mixtures, the deposition techniques are Microwave Plasma Chemical Vapour Deposition and Hot filament Chemical Vapour Deposition, in both techniques the deposition temperature is close to 900°C. The film growth process is strongly dominated by the initial nucleation stage, after this stage, the film grows at a rate of one micron per hour. The carbon atoms in the diamond film are fully fourfold (sp³) co-ordinated and the film properties are close to those of single crystalline diamond: extremely hard, resistant and transparent from UV to IR.Diamond-like carbon (DLC) films are amorphous and contain a variable amount of hydrogen in their structure, the carbon atoms are partially threefold (sp²) co-ordinated. Films are obtained at temperatures below 250°C and deposited on almost any substrate. Film composition, structure and functional properties are strongly dependent on the level of ionic bombardment of the film during growth. DLC films are very hard, have a low friction coefficient and good wear resistance, are chemically inert and are transparent in the IR.     

Optical properties of graphite-like carbon films

A model of the electronic structure of graphite-like carbon films, describing the semiconductor properties of this material, is presented. Spectra of optical constants of microcrystalline carbon films in the region λ = 0.4–8.0 μm were studied by the spectral ellipsometry and IR reflection methods. A number of distinctive features of the spectra, associated with both the appearance of C---C- and C---H_n-type bonds and direct energy gaps, were found. Analysis of the optical data using the proposed model makes possible a common interpretation of our results and literature data. Values of a parameter Θ, which is an averaged qualitative parameter of structural distortions within carbon microcrystallites as compared with crystalline graphite, are determined from comparison of theoretical results and experimental data.     

Mechanical properties and thermal stability of nitrogen incorporated diamond-like carbon films

The nitrogen incorporated diamond-like carbon films were deposited on Si (100) substrates by arc ion plating (AIP) under different N₂ content in the gas mixture of Ar and N₂. The influence of N₂ content on the film microstructure and mechanical properties was studied by atomic force microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and nanoindentation. It was found that the hardness (H), elastic modulus (E), elastic recovery (R) and plastic resistance parameter (H/E) decrease with increasing the nitrogen content. The decrease of mechanical properties of DLC films resulted from nitrogen incorporation was associated with total sp³ carbon bond content and N-sp³C bond content. The structural modification as well as mechanical properties of the annealed nitrogen incorporated diamond-like carbon films was investigated as a function of annealing temperature. Raman spectra indicate that the I_D/I_G ratio starts to increase and G peak position shifts upward at the annealing temperature over 500 °C. The hardness and elastic modulus of thermally annealed nitrogen incorporated DLC films decreased slightly at lower annealing temperature and then significantly decreased at higher annealing temperature. The strong covalent bonding between C and N atoms is expected to be effective on their thermal stability enhancement.     

Influence of PECVD parameters on the properties of diamond-like carbon films

The properties of diamond-like carbon (DLC) are strongly affected by the amount of carbon atoms bonded in sp² and sp³ electronic hybridizations. Also the amount of incorporated hydrogen and oxygen plays an important role in the final properties of DLC films. Usually, the structure and chemical composition of thin DLC films can be changed by varying the deposition parameters. Therefore, the influence of PECVD process parameters on the properties of DLC films, grown on Si substrates, was investigated in this work.Thin DLC films were deposited in a CH₄/H₂ plasma by using Ar as a gas carrier. Different ratios of gas flows were used as a variable parameter of the PECVD process. The effect of cathodic ion bombardment was also investigated.The chemical composition of DLC specimens was studied by X-ray photoelectron spectroscopy (XPS). The ratio of carbon in sp² and sp³ hybridizations was determined by analyzing the first derivative of Auger C KLL spectra. These results were also confirmed by the measurements of electrical resistivity. The changes of surface morphology and microadhesion were analyzed by Atomic Force Microscopy (AFM).     

Characterization of ion-beam-deposited diamond-like carbon films

Diamond-like carbon (DLC) films are excellent prospects for a wide range of high-technology applications but their precise structure and properties are not well understood. The purpose of the present work was to use several complementary techniques to characterize the nature, structure and microstructure of DLC films. Thin DLC films were deposited on various substrates in the presence of a Si interlayer (500 Å thick) using CH₄ ion-beam deposition at an acceleration energy of 750 eV and a current density of about 2.5 mA cm⁻². The Si interlayer was deposited by either e-beam evaporation or Si evaporation enhanced by Ar⁺ beam bombardment (1 keV). The produced DLC films were featureless, very smooth and of high hardness (2900–3300 kg mm⁻²). Auger electron spectroscopy and electron diffraction showed that the films were mainly amorphous. Their microstracture was characterized by a three-dimensional network structure with a medium-range order of about 25 nm. Fourier transform infrared and Raman spectroscopies showed that the films were mainly composed of sp³ and sp² carbon-bonded hydrogen. The sp³/sp² ratio varied from 3.2 to 4.1 and was found to depend on the nature of the Si bond layer. The results showed that the nucleation of the diamondlike structure was promoted on the Si interlayer that was deposited under Ar⁺ beam bombardment. This effect can be explained by the higher surface roughness produced in this interlayer as suggested by the reflectivity measurements. Spectroscopic ellipsometry revealed that the films had an optical band gap between 1.56–1.64 eV. The present results are consistent with previous proposals suggesting that the DLC structure is composed of small graphitelike clusters (involving fused six-fold rings) that are interconnected by sp³-bonded carbon.     

类金刚石碳膜的热稳定性

总结了各种ＤＬＣ膜的热稳定性及分析手段,概述了加热退火情况下ＤＬＣ膜结构,内应力的变化,评述了国内的最新研究进展,并提出了有等进一步研究的问题。     

Influence of nitrogen on the optical and mechanical properties of diamond-like carbon films

Optical and mechanical properties of diamond-like carbon films grown by chemical vapor deposition were investigated as a function of the nitrogen content in the gas mixture. The nonmonotonic variation of the optical band gap and the microhardness of the films are interpreted using a model which allows for the influence of nitrogen on their structure. It is shown that nitrogen-containing diamond-like carbon films hold out promise as protective and antireflection coatings for silicon solar cells. Pis’ma Zh. Tekh. Fiz. 24, 87–92 (May 26, 1998)     

PECVD法制备类金刚石薄膜的结构和摩擦学性能研究

采用射频一直流等离子体增强化学气相沉积技术在单晶硅衬底上沉积了类金刚石薄膜。用激光拉曼光谱仪和原子力显微镜对薄膜的结构和表面形貌进行了表征，并用纳米压痕仪测定了薄膜的硬度。用UMT微摩擦磨损试验机考察了薄膜在不同的滑行速度下薄膜的摩擦学性能。结果表明：所沉积的薄膜具有典型类金刚石薄膜的结构特征，薄膜表面光滑致密，硬度较高；薄膜与氧化铝陶瓷球对磨显示出良好的摩擦学性能，随着滑行速度的增加，薄膜的摩擦系数单调降低，但磨损寿命先增加后降低。     

Photoelectron spectroscopy characterization of diamond-like carbon films

The electronic states of diamond-like hydrogenated carbon (DLC) films were studied by synchrotron radiation photoelectron spectroscopy. The valence band spectra measured at different excitation energies show the gradual emergence of the p-pi band in relation to the sample annealing and ion bombardment amorphization. The p-pi band of the annealed DLC was characterized by localized p(z) states, while the formation of the amorphous carbon surface was accompanied by appearance of the delocalized p(z) states, which reduce the optical gap. A simple approach permitting the extraction of the 2p band shape from the photoelectron spectra is proposed.     

Electrochemical performance of diamond-like carbon thin films

Diamond-like carbon (DLC) thin films used in this study were intended for their electrochemical properties. The DLC films were deposited by a filtered cathodic vacuum arc (FCVA) process on p-type silicon (100) substrates biased at different pulse voltages (0-2000 V). The chemical bonding structures of the DLC films were characterized with micro-Raman spectroscopy and the electrochemical properties were evaluated by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The DLC films showed high impedance, high polarization resistance and high breakdown potential in a 0.5 M H₂SO₄ aqueous solution, which were attributed to the high sp³ content and uniformity of the films. The excellent chemical inertness of the DLC films made them promising corrosion resistant coating materials.     

Optical properties of hydrogenated hard carbon thin films

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass, silicon and germanium substrates. The films are transparent in the IR and are extremely hard (Mohs' hardness of about 8). The a-C:H coatings were prepared in an r.f.-excited discharge sustained by various hydrocarbon gases.The thickness, density, refractive index (at 0.3 μm and 2–10 μm) and relative hydrogen content were determined. Variations in the IR refractive index and the relative hydrogen content could be correlated with the deposition conditions. With a refractive index of approximately 2 a-C:H is an ideal antireflection coating for germanium (n = 4).Laser calorimetric measurements of optical absorption at 10.6 μm give a loss as low as 3% for a coating 1.3 μm thick on germanium (λ/4 for n = 2 at 10.6 μm).     

激光辐照对类金刚石薄膜改性及损伤研究

介绍了激光损伤的检测及损伤阈值的测量方法.讨论激光辐照对类金刚石结构和性质的影响规律.并论述不同工作参数的激光对类金刚石薄膜的激光破坏行为及其损伤阈值.在此基础上分析类金刚石薄膜激光损伤的机理.还从物理特性及制备技术方面着手,比较分析金刚石及类金刚石薄膜各自的优缺点和实际应用状况,并提出类金刚石薄膜的应用前景和有待进一步研究的问题.     

Field emission from diamond and diamond-like carbon films

Field emission from diamond and diamond-like carbon thin films deposited on silicon substrates has been studied. The diamond films were synthesized using hot filament chemical vapor deposition technique. The diamond-like carbon films were deposited using the radio frequency chemical vapor deposition method. Field emission studies were carried out using a sphere-to-plane electrode configuration. The results of field emission were analyzed using the Fowler-Nordheim model. It was found that the diamond nucleation density affected the field emission properties. The films were characterized using standard scanning electron microscopy, Raman spectroscopy, and electron spin resonance techniques. Raman spectra of both diamond and diamond-like films exhibit spectral features characteristic of these structures. Raman spectrum for diamond films exhibit a well-defined peak at 1333cm^?1. Asymmetric broad peak formed in diamond-like carbon films consists of D-band and G-band around 1550 cm^?1 showing the existence of both diamond (sp³ phase) and graphite (sp² phase) in diamond-like carbon films.