Microstructure and optical properties of chromium containing amorphous hydrogenated carbon thin films (a-C:H/Cr)

Chromium containing amorphous hydrogenated carbon thin films was deposited using a dc sputter deposition technique under various mixtures of methane and Ar. The microstructure, composition, and optical properties of the resulting films were investigated. We show that a-C:H/Cr thin films exhibiting absorptance in certain wavelengths are greater than 95% and the average absorptance was 86% in the 0.3 to 2.5 µm wavelength can be obtained by using appropriate methane/Ar ratios and deposition times.     

Tribological behaviour a-C and a-C:H films doped with Ti in biological solutions

The coatings were deposited in a multi magnetron Teer sputtering device with two C targets and a Ti target in Ar atmosphere, on steel and Si substrates. To deposit hydrogenated coatings methane was introduced in the discharge atmosphere. The films were deposited in a range of 7-14 at.% Ti content. X-ray diffraction patterns revealed the presence of a nanocrystalline TiC phase. The hardness varied from 8 to 9 GPa. The tribological tests were performed under dry sliding and lubricated (0.9% NaCl water solution, physiological solution, PS, and 10% fetal bovine serum dissolved in Ringer’s saline solution, FBS) conditions, using a 100Cr6 steel balls with a diameter of 6 mm, in a pin-on-disc wear test apparatus.     

Mechanical properties of a-C:H thin films deposited by r.f. PECVD method

Internal stress, hardness and deposition rate were evaluated for hydrogenated amorphous carbon (a-C:H) films prepared by conventional r.f. plasma-enhanced chemical vapour deposition. The internal stress, hardness and deposition rate of 0.9, 18 and 58 nm/min, respectively, achieved at 40 Pa gas pressure for negative self-bias voltages (V_b) window (from −370 to −550 V). It was found that the negative self-bias voltage window was associated with the existence of two turning points, which shift to higher wavenumber of G band peak position of Raman spectroscopy (Raman) at different V_b in relation to the internal stress and hardness, and rapid decreasing of the relative total peak areas of Fourier Transform Infra-red absorption spectroscopy (FT-IR).The internal stress relaxed from approximately 35 eV ion energy when the energy is increased and rapidly decreased in comparison with the stress relaxation equation.     

Mid-frequency deposition of a-C:H films using five different precursors

The plasma-enhanced chemical vapour deposition (PECVD) of amorphous hydrogenated carbon films from pulsed discharges with frequencies in the range from 50 kHz to 250 kHz was investigated. Five different hydrocarbons (acetylene C₂H₂, isobutene C₄H₈, cyclopentene C₅H₈, toluene C₇H₈ and cycloheptatriene C₇H₈) were probed as film growth precursors. In addition, two types of pulse-generators with somewhat different waveforms were used to power the discharges in the so called mid-frequency range. The a-C:H films deposited in a parallel-plate reactor were characterised for their thickness/deposition rate, hardness and hydrogen content. The hydrogen concentration in the films varied between 19 at.-% and 37 at.-%. With the substrate temperature held constant, it is roughly in inverse proportion to the hardness. The film with the highest hardness of 25 GPa was formed at a deposition rate of 0.8 μm/h in the C₂H₂ discharge at the lowest investigated pressure of 2 Pa. With increasing molecular mass of the precursor mostly weaker films were deposited. Relatively high values of both deposition rate and hardness were achieved using the precursor isobutene: a hardness of 21 GPa combined with a deposition rate of 4.1 μm/h. From the probed precursors, isobutene is also most advantageous for a-C:H deposition at higher pressures (up to 50 Pa investigated). But, as an over-all trend, the a-C:H hardness decreases with increasing deposition rate.     

XPS study of the a-C:H/Ti and a-C:H/a-Si interfaces

In this study ultrathin hydrogenated amorphous carbon (a-C:H) films have been grown onto the titanium and amorphous silicon (a-Si) overlayers by direct ion beam deposition using acetylene gas as a hydrocarbon source. X-ray photoelectron spectroscopy (XPS) was used for study of the DLC-Ti and DLC-Si interfaces. It was revealed that a-Si is a good interlayer for improvement of adhesion in the case of diamond-like carbon film deposition onto the steel substrate at room temperature. a-C:H film growth without substantial intermixing occurred on the a-Si. On the other hand, adhesion between the Ti interlayer and the diamond like carbon film was very sensitive to the deposition conditions (presence of the pump oil) as well as structure and stress level of the Ti film. It was explained by strong intermixing between the growing carbon film and Ti. Bad adhesion between the growing DLC film and Ti interlayer was observed despite formation of the TiC. At the same time, formation of the TiO_x was not an obstacle for good adhesion. It is shown that composition of the used hydrocarbon gas, structure of the Ti thin film and mechanical stress in it had greater influence on adhesion with a-C:H film than elemental composition of the Ti interlayer surface.     

Mid-frequency deposition of a-C:H films using five different precursors

The plasma-enhanced chemical vapour deposition (PECVD) of amorphous hydrogenated carbon films from pulsed discharges with frequencies in the range from 50 kHz to 250 kHz was investigated. Five different hydrocarbons (acetylene C₂H₂, isobutene C₄H₈, cyclopentene C₅H₈, toluene C₇H₈ and cycloheptatriene C₇H₈) were probed as film growth precursors. In addition, two types of pulse-generators with somewhat different waveforms were used to power the discharges in the so called mid-frequency range. The a-C:H films deposited in a parallel-plate reactor were characterised for their thickness/deposition rate, hardness and hydrogen content. The hydrogen concentration in the films varied between 19 at.-% and 37 at.-%. With the substrate temperature held constant, it is roughly in inverse proportion to the hardness. The film with the highest hardness of 25 GPa was formed at a deposition rate of 0.8 μm/h in the C₂H₂ discharge at the lowest investigated pressure of 2 Pa. With increasing molecular mass of the precursor mostly weaker films were deposited. Relatively high values of both deposition rate and hardness were achieved using the precursor isobutene: a hardness of 21 GPa combined with a deposition rate of 4.1 μm/h. From the probed precursors, isobutene is also most advantageous for a-C:H deposition at higher pressures (up to 50 Pa investigated). But, as an over-all trend, the a-C:H hardness decreases with increasing deposition rate.     

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.     

Kinetic modeling of laser annealing processes in a-C:H films

In this research work, a nanosecond-pulsed YAG:Nd laser was used to modify the properties of an amorphous hydrogenated carbon film, which was deposited on c-Si substrate. Experimental examination has revealed that the primary effect of irradiation is diamond-to-graphite transformation or, more specifically, carbon sp³-to-sp² hybridization transition. These findings were qualitatively verified by numerical simulation of kinetic processes that proceed in the film under laser irradiation.     

Multilayer amorphous hydrogenated carbon (a-C:H) and SiOx doped a-C:H films for optical applications

In this study SiO_x doped amorphous hydrogenated carbon (a-C:H) films were formed from hexamethyldisiloxane (with hydrogen transport gas) by closed drift ion beam deposition applying variable ion beam energy (300-800 eV). The band gap dependence on the deposition energy was determined and used in production of SiO_x doped a-C:H and a-C:H (formed from acetylene gas) multilayer (two and four layers) stack. Optical properties of the multilayer structures as well as individual layers were analysed in the UV-VIS-NIR range (200-1000 nm). It was shown that employing double or four layer systems, the reflectivity of the multilayer structure-crystalline silicon can be tuned to almost 0% at specific wavelength range (550-950 nm), important in solar cell applications.     

Improved crystallization characteristics of ZnO thin film grown onto a-C:H film used as a buffer layer

We employed a-C:H buffer layer to improve the crystalline property of ZnO thin film for the membrane film bulk acoustic resonator (FBAR). The a-C:H film as a buffer layer is prepared by applying dc bias of 200 V and also this sample showed a smoother surface roughness, higher hardness and Young's modulus when compared to the other samples. In addition, the FWHM value was improved from 7.5 to 4.3° on a-C:H film. The fabricated FBAR device showed the resistivity of 0.73 × 10⁸ Ω when compared with no buffer layer and the frequency characteristics of the FBAR were finally confirmed to be 1.15 GHz and 21.24 dB, respectively.     

a-C∶H/a-Se 复合膜结构的红外及喇曼谱研究

a-C∶H/a-Se/Al 是一种优良的新型复印感光体。我们在 KCl 和 Si 单晶上制备了 a-C∶H/a-Se 复合膜,以进行红外和喇曼谱分析。结果表明,a-Se 上 a-C∶H 层中 CH_n 键型(n=1～3)的比例为:sp~1∶sp~2∶sp~3=0.10∶0.09∶0.81;而 sp~3键型中各功能团比例为:sp~3CH∶sp~3CH_2∶sp~3CH_3=0.28∶0.38∶0.34。在同样工艺条件下制备的 KCl 上 a-C∶H 中的相应比例则为 sp~1∶sp~2∶sp~3=0∶0∶1;sp~3CH∶sp~3CH_2∶sp~3CH_3=0.45∶0.33∶0.22。二者相比,可认为 a-Se(?)衬底上的 a-C∶H 层中主要由 sp~3CH_2和 sp~2CH 构成的“长链型”近程有序成分大大增加。由此可解释复合膜的性能并寻找改进复合膜的途径。     

a-C∶H/a-Se复合膜非平衡晶化分形特征的SEM观测

a-C∶H/a-Se/Al 感光体的 a-C:H 层在能流密度的6.4×10~(14)eV/mm~2·s 的离子流轰击下发生了非平衡晶化凝聚。晶体凝聚物为“链环状分形”。用盒子计数法测得其分数维 D_0=1.35±0.04;用相关函数法测得其关联维为 D_2=1.39±0.03。这与我们用计算机模拟的结果很好地符合。本文同时讨论了这一系列文章([2][3]及本文)对发展一种新的非平衡晶化分析方法的意义。     

a-C∶H/a-Se复合膜晶化分形凝聚的计算机模拟研究

本文基于红外透射及喇曼谱分析的结果提出了一个 a-C:H/a-Se 复合膜的 a-C∶H 层非平衡晶化凝聚模型,并做了计算机模拟研究。模拟得到的图形是具有良好的无标度性的链环状分形。其分维值为1.37±0.02,此结果得到了实验的肯定。这对非晶膜的结构及晶化机理的研究均富有价值。     

低介电常数a-C:F薄膜结构和热稳定性研究

采用电子回旋共振等离子体化学气相沉积的方法以C4F8和CH4为源气体制备了非晶氟化碳(a-C:F)薄膜.采用傅里叶变换红外光谱(FTIR)和X光电子能谱(XPS)技术分析了a-C:F薄膜化学组分.FTIR分析表明a-C:F薄膜中存在CF=C(1680 cm-1)和位于a-C:F薄膜交联结构末端的CF2=CF (1780 cm-1)结构.C1s峰高斯解叠后结合态与结合能对应关系为:CF3(295 eV),CF2(293 eV),CF(291 eV),C-O(289 eV),C-CFx(x=1～3)(287 eV),以及位于a-C:F薄膜交联结构末端的C-C结合态(285 eV).位于a-C:F薄膜交联结构末端的CF3和C-C结构热稳定性较差,退火后容易生成气态挥发物并导致a-C:F薄膜厚度减小.当C-CFx交联结构增多,且位于a-C:F薄膜交联结构末端的CF3和C-C结构减少时,a-C:F薄膜热稳定性提高.     

Preparation and comparison of a-C:H coatings using reactive sputter techniques

Amorphous hydrogenated carbon (a-C:H) coatings are widely used in several industrial applications. These coatings commonly will be prepared by plasma activated chemical vapor deposition (PACVD). The main method used to prepare a-C:H coating in industrial scale is based on a glow discharge in a hydrocarbon gas like acetylene or methane using a substrate electrode powered with medium frequency (m.f. — some 10 to 300 kHz). Some aims of further development are adhesion improvement, increase of hardness and high coating quality on complex geometries. A relatively new and promising technique to fulfil these requirements is the deposition of a-C:H coatings by a reactive d.c. magnetron sputter deposition from a graphite target with acetylene as reactive gas. An advancement of this technique is the deposition in a pulsed magnetron sputter process. Using these three mentioned techniques a-C:H coatings were prepared in the same deposition machine. For adhesion improvement different interlayer systems were applied. The effect of different substrate bias voltages (d.c. and d.c. pulse) was investigated. By applying the magnetron sputter technique in the d.c. pulse mode, plastic hardness values up to 40 GPa could be reached. Besides hardness other mechanical properties like resistance against abrasive wear were measured and compared. Cross sectional SEM images showed the growth structure of the coatings.     

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.     

Mechanical properties of a-C:H and a-C:H/SiOx nanocomposite thin films prepared by ion-assisted plasma-enhanced chemical vapor deposition

a-C:H and a-C:H/SiO_x nanocomposite thin films were deposited on silicon, aluminum and polyimide substrates at 25 °C in an asymmetric 13.56 MHz r.f.-driven plasma reactor under heavy ion bombardment. Fourier transform infrared spectra of the films indicate that the nanocomposite filmsappears to consist of an atomic scale random network of a-C:H and SiO_x. Raman spectroscopy revealed that the sp² carbon fraction in the nanocomposite film was reduced compared with the a-C:H film. The intrinsic stress of both films increased with increasing negative bias voltage (−V_dc) at the substrate. However, the nanocomposite films exhibited lower intrinsic stress compared w with a-C:H-only films. Especially, a thin SiO_x-rich interlayer was very effective in reducing the film stress and enhancing the bonding strength at the interface. The interlayer allowed deposition of thick films of up to 5 μm. Also, the nanocomposite films were stable in 0.1 M NaOH solution and showed good microhardness.     

a－C：H膜折射率的变化规律及红外应用

本文对ａ－Ｃ：Ｈ膜的性质如折射率和生长速率的变化规律进行了研究，并且在增透原理的指导下制备了具有高红外透过率的单波段、双波段和宽波段的ａ－Ｃ：Ｈ增透保护膜     

Recrystallization and grain growth of nanocomposite Ti–B–N coatings

Nanocomposite Ti–B–N coatings with different chemical composition were prepared by non-reactive co-sputtering of a segmented TiN–TiB₂ target. The coatings investigated are primarily composed of nanocrystalline TiN and TiB₂ phases. Increasing boron content results in a decreasing grain size from approximately 6 to 2 nm. During a thermal treatment of such coatings solely recovery and recrystallization with subsequent grain growth would appear, since the two phases are in thermodynamic equilibrium. Differential scanning calorimetry (DSC) and X-ray diffraction analysis were used to investigate the recrystallization behavior and subsequent grain growth of the nanocomposite Ti–B–N coatings. On heating the coating samples, which were removed chemically from their low alloyed steel substrates, an exothermal peak appeared during the DSC measurements indicating grain growth. From the onset temperature of this peak the recrystallization temperature was found which increases with increasing boron content from 1032 to 1070 °C. Activation energies for grain growth are obtained from Kissinger plots and yield values decreasing from 7.9 to 4.4 eV with increasing boron content. After heat treatment up to 1400 °C during the DSC measurements the coatings showed grain sizes within the range of 15–30 nm. It was found that the highest recrystallization temperature does not imply the highest activation energy for grain growth.     

Deposition of a-C:N films and evaluation of their robustness in electrochemical applications

A multilayer a-C:N film electrode deposition process has been developed using the filtered cathodic vacuum arc (FCVA) system based on the highly conductive silicon wafer with a Ti interlayer for ohmic contacts. Its robustness has been evaluated under the practical electrochemical conditions and shows that it has no pin-hole and no breaking point happened when voltages are applied on it. Extremely large errors will arise in the electrochemical characterizing a-C:N film electrodes (hydrogen and oxygen evolutions and oxygen reduction) when there is a pin-hole or a broken point in the films. And the error caused by the non-ohmic contact amplifies at a high potential range. It is expected that non-robust a-C:N film electrodes and non-ohmic contacts mislead the electrochemical characterizing on a-C:N films.