Plasma biasing to control the growth conditions of diamond-like carbon

It is well known that the structure and properties of diamond-like carbon, and in particular the sp³/sp² ratio, can be controlled by the energy of the condensing carbon ions or atoms. In many practical cases, the energy of ions arriving at the surface of the growing film is determined by the bias applied to the substrate. The bias causes a sheath to form between substrate and plasma in which the potential difference between plasma potential and surface potential drops. In this contribution, we demonstrate that the same results can be obtained with grounded substrates by shifting the plasma potential. This “plasma biasing” (as opposed to “substrate biasing”) is shown to work well with pulsed cathodic carbon arcs, resulting in tetrahedral amorphous carbon (ta-C) films that are comparable to the films obtained with the conventional substrate bias. To verify the plasma bias approach, ta-C films were deposited by both conventional and plasma bias and characterized by transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS). Detailed data for comparison of these films are provided.     

Structure and blood compatibility of tetrahedral amorphous hydrogenated carbon formed by a magnetic-field-filter plasma stream

Tetrahedral amorphous hydrogenated carbon (ta-C:H) films with various substrate bias voltages were prepared using a magnetic-field-filter plasma stream deposition system. The microstructural and optical properties were studied using ellipsometric spectra. The refractive index n of each sample was obtained by simulating their ellipsometric spectral using Tauc-Lorentz oscillator model, and then the relative sp³ C ratio of each sample was calculated using Bruggeman effective medium approximation. The sp³ C fraction of each sample was quantified by using electron energy-loss spectroscopy (EELS). The blood compatibility of the samples was evaluated by tests of platelet adhesion, kinetic clotting time and thrombin time. The quantity and morphology of the adherent platelets on the surface of these samples were investigated using scanning electron microscopy. Results show that the spectroscopic ellipsometry is a helpful method to evaluate the sp³ carbon fraction of the carbon films. The substrate bias voltage has an obvious effect on sp³ content and blood compatibility of ta-C:H films. The sample prepared with substrate bias voltage of − 20 V showed the best blood compatibility. A simple bio-physical hypothetical model was proposed to explain the experiment results.     

Multi-functional ECR plasma sputtering system for preparing amorphous carbon and Al–O–Si films

A design of cylindrical double-target source with shutter slider which can continuously change the target area ratio was applied to the divergent and mirror-confinement Electron Cyclotron Resonance (ECR) plasma sputtering system in the present study. The deposition process feasibility of several types of films (single-layer of pure and composite film as well as multi-layer film) can be realized by using this multi-functional system. The highly concerned amorphous carbon films were prepared with the Divergent ECR (DECR) and Mirror-Confinement ECR (MCECR) plasma sputtering systems. The tribological properties were compared, which both showed a normally friction coefficient around 0.15. Through adding substrate heating during film preparation, the tribological properties of DECR carbon films were improved with an obvious decreasing of friction coefficient to 0.05 and a much longer wear lifetime. The designed double-target source with shutter slider was used to prepare Al–O–Si films, by which the target area ratio of silicon to aluminum was changed from 0.5 to 2. A composite structure of Al–O–Si film with high transmittance up to 89% at 193 nm wavelength was obtained with the multi-functional ECR plasma sputtering system.     

Cathodic arc plasma deposition of nano-multilayered ZrN/AlSiN thin films

Thin films of ZrN/AlSiN were deposited on SKD 11 tool steel substrate using Zr and AlSi cathodes in an Ar/N₂ gas mixture in a cathodic arc plasma deposition system. The influence of the AlSi cathode arc current and the substrate bias voltage on the mechanical and structural properties of the films was investigated. X-ray diffraction, electron probe micro-analysis, high resolution transmission electron microscopy, nanoindentation and profilometry were used to characterize the films. The ZrN/AlSiN thin films had a multilayered structure by rotating the substrate in which nano-crystalline ZrN layers alternated with amorphous AlSiN layers. The hardness of the films increased as the AlSi cathode arc current was raised from 35 to 40 A, and then decreased with a further increase of the current. The hardness of the films increased with the increase of the bias voltage from − 50 to − 100 V. Further increase in the bias voltage decreased the hardness. The films exhibited a maximum hardness of 38 GPa. With the increase of bias voltage, the residual stress of the films correlated well with the hardness.     

X-ray reflectivity studies on DLC films deposited by microwave ECR CVD: Effect of substrate bias

Diamond like carbon (DLC) films were deposited at room temperature on Si (111) substrates by microwave electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) process using plasma of methane diluted with argon gas. During deposition, dc self bias (− 25 V to − 200 V) on substrate was varied by application of RF power to the substrate. The influence of substrate bias on density of the deposited films was studied by X-ray reflectivity (XRR). The results from these measurements are further correlated with the results from UV and visible Raman spectroscopy. DLC film is modeled as a structure having three different layers such as low density surface, bulk and interface with the substrate. This three-layer model is used to fit the measured XRR data to evaluate the surface, interface and interlayer roughness, thickness and density of these films. The surface roughness obtained from XRR is correlated with the results from Atomic Force Microscopy (AFM) measurements. The observed results are explained based on the subplantation model for DLC film growth.     

基片负偏压对Cu膜纳米压入硬度及微观结构的影响

测试了不同溅射偏压下Cu膜的纳米压入硬度，探讨了溅射偏压、残余应力及压痕尺寸效应对Cu膜硬度的影响。结果表明，随着溅射偏压的增大，薄膜晶粒尺寸及残余压应力均减小，导致薄膜的硬度增大，并在-80V达到最大值，随后有所降低。同时薄膜中的压痕尺寸效应对薄膜硬度随压入深度的分布有很大的影响。     

加氮对直流电弧等离子体喷射金刚石膜显微组织和断裂强度的影响

利用DcArcP1asmaJetcVD法制备搀杂氮的金刚石厚膜。研究了在反应气体cH。／Ar／H：中加入N!对金刚石膜显微组织和力学性能的影响。在固定H2、Ar、CH4流量的情况下改变N2的流量，即反应气体中氮原子和碳原子的变化比例(N／C比，范围从0．06～0．68)，同时在固定的腔体压力(4kPa)和衬底温度(800℃)下进行金刚石膜生长。用扫描电镜(SEM)观察金刚石膜形貌、用X射线衍射表征晶体取向，用三点弯曲的方法来测量金刚石膜的断裂强度。结果表明，氮气在反应气体中的大量加入，对直流等离子体喷射制备金刚石膜的显微组织和力学性能有显著的影响。     

Density changes with substrate negative bias for ta-C films deposited by filter cathode vacuum arc

Specular X-ray reflectivity (XRR) measurements were used to study the density and cross-section information of tetrahedral amorphous carbon (ta-C) films deposited by filter cathode vacuum arc(FCVA) system at different substrate bias. According to the correlation between density and substrate negative bias, it is found that the value of density reaches a maximum at -80 V bias. As the substrate bias increases or decreases, the density tends to lower gradually. Based on the density of diamond and graphite, sp3 bonding ratio of ta-C films was obtained from their corresponding density according to a simple equation between the two. And a similar parabolic variation was observed for ta-C films with the sp3 content changes with substrate negative bias. The mechanical properties such as hardness and elastic modulus were also measured and compared with the corresponding density for ta-C films. From the distribution of data points, a linear proportional correlation between them was found, which shows that the density is a critical parameter to characterize the structure variation for ta-C films.     

Nucleation of highly oriented diamond on silicon

Highly oriented diamond particles were deposited on the mirror-polished (100) silicon substrates in the belljar type microwave plasma deposition system. The diamond films were deposited by a three-step process consisting of carburization, bias-enhanced nucleation and growth. The bias-enhanced nucleation was performed under the deposition conditions such as 2-3% of methane concentration in hydrogen, 1333-2666 Pa of total pressure, the negative bias voltage below 200V and the substrate temperature of 1073 K. By adjusting the geometry of the substrate and substrate holder, very dense disc-shaped plasma was formed on the substrate when the bias voltage was below 200V. As characterized by transmission electron microscopy (TEM), almost perfectly oriented diamond particles were obtained only in this dense plasma. From the results of the optical emission spectra of disc-shaped dense plasma, it was found that the concentrations of atomic hydrogen and hydrocarbon radicals were increased with negative bias voltage. As a result, it was suggested that the highly oriented diamonds were obtained by the combination of the high dose of hydrocarbon radicals and the increased hydrogen etching effects.     

Deposition of nanolayered CrN/AlBN thin films by cathodic arc deposition: Influence of cathode arc current and bias voltage on the mechanical properties

Thin films of CrAlBN were deposited on SKD 11 tool steel substrate using Cr and AlB cathodes in a cathodic arc plasma deposition system. The influence of AlB cathode arc current and substrate bias voltage on the mechanical and the structural properties of the films was investigated. The CrAlBN thin films had a multilayered structure in which the nano-crystalline CrN layer alternated with the amorphous AlBN layer. The hardness of the films increased as the AlB cathode arc current was raised from 35 to 45 A, and then decreased with further increase of the current. The hardness of the films increased rapidly with the increase of the bias voltage from − 50 to − 150 V. Further increase in the bias voltage decreased the hardness. The maximum hardness of 48 GPa was obtained at the bias voltage of − 150 V. With the increase of bias voltage, a good correlation between the residual stress and the hardness of the films was observed.     

偏压对DLC薄膜结构及摩擦学性能的影响

目的通过调节偏压,改善无氢DLC薄膜的微观结构,提高其力学性能和减摩抗磨性能。方法采用离子束辅助增强磁控溅射系统,沉积不同偏压工艺的DLC薄膜。采用原子力显微镜(AFM)观察薄膜表面形貌,采用拉曼光谱仪对薄膜的微观结构进行分析,采用纳米压痕仪测试薄膜硬度及弹性模量,采用表面轮廓仪测定薄膜沉积前/后基体曲率变化,并计算薄膜的残余应力,采用大载荷划痕仪分析薄膜与不锈钢基体的结合力,采用TRB球-盘摩擦磨损试验机评价薄膜的摩擦学性能,采用白光共聚焦显微镜测量薄膜磨痕轮廓,并计算薄膜的磨损率。结果偏压对DLC薄膜表面形貌、微观结构、力学性能、摩擦学性能都有不同程度的影响。偏压升高导致碳离子能量升高,表面粗糙度呈现先减小后增加的趋势,-400V的薄膜表面具有最小的表面粗糙度且C─C sp^3键含量最多,这也导致了此偏压下薄膜的硬度最大。薄膜的结合性能与碳离子能量大小呈正相关,-800 V时具有3.98 N的最优结合性能。不同偏压工艺制备的薄膜摩擦系数随湿度的增加,均呈现减小的趋势,偏压为-400V时,薄膜在不同湿度环境中均显示出最优的摩擦学性能。结论偏压为-400 V时,DLC薄膜综合性能最优,其表面粗糙度、硬度、结合力和摩擦系数分别为2.5 nm、17.1 GPa、2.81 N和0.11。     

Cross-linked graphene layer embedded carbon film prepared using electron irradiation in ECR plasma sputtering

A new path to prepare cross-linked graphene layers embedded carbon (GLEC) films has been reported by introducing electron irradiation during the mirror-confinement electron cyclotron resonance (ECR) plasma sputtering process. The electron irradiation in the ECR plasma was identified by using Langmuir single probe equipped with a designed simulated substrate and the irradiation mode was found to be controlled directly by altering the substrate bias voltage. Cross-linked GLEC film was prepared using the electron irradiation in the pressure of 0.04 Pa and positive bias voltage of 50 V, and the nanostructure and binding configuration of the film were analyzed by high resolution transmission electron microscope (HRTEM) and X-ray photoelectron spectroscopy (XPS). The results showed that GLEC film contains cross-linked graphene layers grown normally to the substrate surface when the content of sp² hybridized carbon atoms in the film is more than 70%. The tribological behaviors of both cross-linked GLEC films and amorphous carbon films were compared using a Pin-on-Disk tribometer, and the mechanism for low friction coefficient was discussed by using HRTEM observation on wear track. The HRTEM results indicated that the cross-linked GLEC film has the potential to achieve low friction at the beginning of the friction.     

Composition and structure of Ti-C/DLC graded composite films

The Ti-C→DLC gradient composite films were characterized systematically.The elemental depth profile and elemental chemical state evolution were determined by X-ray photoelectron spectroscopy (XPS).The transmission electron microscope (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to study the structure of interfacial zone between DLC film and Ti-C layers.Results show that there are composition transition zone between DLC film and either Ti-C layer or steel substrate on condition that pre-deposited Ti layers on the steel substrate then plasma based bias deposited DLC films.In Ti-C graded layer,the chemical state of titanium and carbon are changed gradually.The structures of zone in Ti-C layer near the DLC film is consisted of random oriented nanocrystallines TiC dispersed in amorphous DLC matrix.The structure of the zone between DLC film and Ti-C graded layer is gradually changed too.     

Filtered vacuum arc deposition of undoped and doped ZnO thin films: Electrical, optical, and structural properties

Filtered vacuum (cathodic) arc deposition (FVAD, FCVD) of metallic and ceramic thin films at low substrate temperature (50-400 °C) is realized by magnetically directing vacuum arc produced, highly ionized, and energetic plasma beam onto substrates, obtaining high quality coatings at high deposition rates. The plasma beam is magnetically filtered to remove macroparticles that are also produced by the arc. The deposited films are usually characterized by their good optical quality and high adhesion to the substrate. Transparent and electrically conducting (TCO) thin films of ZnO, SnO₂, In₂O₃:Sn (ITO), ZnO:Al (AZO), ZnO:Ga, ZnO:Sb, ZnO:Mg and several types of zinc-stannate oxides (ZnSnO₃, Zn₂SnO₄), which could be used in solar cells, optoelectronic devices, and as gas sensors, have been successfully deposited by FVAD using pure or alloyed zinc cathodes. The oxides are obtained by operating the system with oxygen background at low pressure. Post-deposition treatment has also been applied to improve the properties of TCO films.The deposition rate of FVAD ZnO and ZnO:M thin films, where M is a doping or alloying metal, is in the range of 0.2-15 nm/s. The films are generally nonstoichiometric, polycrystalline n-type semiconductors. In most cases, ZnO films have a wurtzite structure. FVAD of p-type ZnO has also been achieved by Sb doping. The electrical conductivity of as-deposited n-type thin ZnO film is in the range 0.2-6 × 10^− 5 Ω m, carrier electron density is 10²³-2 × 10²⁶ m^− 3, and electron mobility is in the range 10-40 cm²/V s, depending on the deposition parameters: arc current, oxygen pressure, substrate bias, and substrate temperature. As the energy band gap of FVAD ZnO films is ∼ 3.3 eV and its extinction coefficient (k) in the visible and near-IR range is smaller than 0.02, the optical transmission of 500 nm thick ZnO film is ∼ 0.90.     

Physical properties of chemical vapour deposited nanostructured carbon thin films

A simple thermal chemical vapour deposition technique is employed for the deposition of carbon films by pyrolysing the natural precursor “turpentine oil” on to the stainless steel (SS) and FTO coated quartz substrates at higher temperatures (700-1100 °C). In this work, we have studied the influence of substrate and deposition temperature on the evolution of structural and morphological properties of nanostructured carbon films. The films were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), contact angle measurements, Fourier transform infrared (FTIR) and Raman spectroscopy techniques. XRD study reveals that the films are polycrystalline exhibiting hexagonal and face-centered cubic structures on SS and FTO coated glass substrates respectively. SEM images show the porous and agglomerated surface of the films. Deposited carbon films show the hydrophobic nature. FTIR study displays C-H and O-H stretching vibration modes in the films. Raman analysis shows that, high ID/IG for FTO substrate confirms the dominance of sp³ bonds with diamond phase and less for SS shows graphitization effect with dominant sp² bonds. It reveals the difference in local microstructure of carbon deposits leading to variation in contact angle and hardness, which is ascribed to difference in the packing density of carbon films, as observed also by Raman.     

实验参数对金刚石薄膜内应力的影响研究

采用热丝化学气相沉积法(HFCVD)在硬质合金基体上制备金刚石薄膜涂层,采用SEM观察金刚石薄膜形貌,采用Raman光谱法分析制备的金刚石薄膜与基体的内应力。变化丝基间距、偏流、碳浓度等参数,通过测定拉曼光谱单一谱峰的位移Δω计算涂层的内应力,从而得到制备内应力较小的金刚石膜的工艺参数范围。     

偏压对GLC镀层的结构及应力的影响研究

采用磁控溅射离子镀技术制备了类石墨镀层（GLC）,利用扫描电子显微镜（SEM）测量了镀层的厚度、X射线衍射仪（XRD）研究了材料的物相和应力,并结合透射电子显微镜（TEM）观察和分析了材料的组织结构。研究结果表明：不同偏压下得到的镀层结构相同,均为非晶为主的类石墨镀层,并且随着偏压增大,膜厚逐渐减小;在所研究的偏压下,应力变化规律是随着偏压的增加,样品与基体的复合应力先增大,后减小,其中～65V时达到最大值。     

Cathodic arc plasma deposition of nano-multilayered Zr-O/Al-O thin films

Thin films of Zr-O/Al-O were deposited on SKD 11 tool steel substrate using Zr and Al cathodes in a cathodic arc plasma deposition system. The substrates were mounted on a rotating holder which alternatively exposed them to plasma from the two cathodes. The influence of the Zr and Al cathode arc currents and the substrate bias on the mechanical and the structural properties of the films were investigated. Films with a nano-layered structure of alternating Al-rich and Zr-rich layers were obtained. The Zr layers contained nano-crystallites of (101) oriented t-ZrO structure. Crystallites with α-Al₂O₃ structure were observed only when the substrate was negatively biased in the 100-150 V range. The hardness of the film decreased with the increase of Zr cathode current from 60 to 80 A, increased when the Al cathode current increased from 25 to 30 A, and decreased when the Al cathode current increased from 30 to 35 A. The hardness of the film increased with the increase of bias voltage up to − 150 V and then decreased with further increase of the negative bias. The film structure was elucidated by HRTEM microscopy. Good correlation between the residual stress and the hardness enhancement of the films was observed.     

高功率脉冲磁控溅射制备的TiN薄膜 应力释放及其结合稳定性研究

目的 探究高功率脉冲磁控溅射（HPPMS）制备的氮化钛（TiN）薄膜在自然时效过程中,应力、薄膜/基体结合性能随时间的变化规律。方法 采用高功率脉冲磁控溅射（HPPMS）技术,通过调控基体偏压（-50、-150 V）,制备出具有不同残余压应力（3.18、7.46 GPa）的TiN薄膜,并采用基片曲率法、X射线衍射法、划痕法和超显微硬度计评价了薄膜的应力、薄膜/基体结合性能、硬度随时间的变化规律。结果 在沉积完成后1 h内,-50 V和-150 V基体偏压下制备的TiN薄膜压应力分别在3.12~3.39 GPa和7.40~7.55 GPa范围内波动,薄膜压应力没有发生明显变化;沉积完成后1~7天,平均每天分别下降28.57 MPa和35.71 MPa;7~30天,平均每天分别下降2.08 MPa和2.50 MPa;30~60天内,平均每天分别下降1.67 MPa和7.00 MPa。其压应力连续下降,且均表现出前期下降速率快,后期下降逐渐放缓的趋势。自然放置60天后,应力基本释放完毕,薄膜性质基本保持稳定。同时,薄膜/基体结合性能随时间逐渐变差,薄膜硬度下降。结论 HPPMS制备的TiN薄膜在自然时效过程中,其残余应力会随时间增加,连续下降,进而影响薄膜的力学性能。     

Deposition of dense and smooth Ti films using ECR plasma-assisted magnetron sputtering

We report high quality Ti films grown in a novel electron cyclotron resonance (ECR) plasma-assisted magnetron sputtering (PMS) deposition system. The films are compared with films deposited by conventional direct current (DC) magnetron sputtering. Using ECR-PMS, the argon plasma bombardment energy and Ti film deposition rate can be controlled separately, with the substrate bias voltage under feedback control. Results from SEM, AFM, XRD and PAS (scanning electron microscopy, atomic force microscopy, X-ray diffraction and positron annihilation spectroscopy) show that the properties of Ti films prepared by ECR-PMS are greatly improved compared with conventional sputtering. SEM and AFM confirmed that ECR-PMS Ti films have a dense, smooth, mirror-like surface. Increasing the substrate bias of the ECR plasma from − 23 V to − 120 V while keeping a fixed sputtering bias voltage of − 40 V, the intensity of the (100) reflection of Ti film was a little strengthened, but (002) remained strongly preferred orientation. The XRD peak broadening of ECR-PMS Ti films is more than for conventional magnetron sputtering, due to grain refinement induced by Ar ion bombardment. Doppler broadening of PAS analysis reveals that the Ti films have fewer vacancy defects compared with films prepared by the conventional magnetron.