Pulsed Plasma-enhanced Chemical Vapor Deposition Research Articles

Probing the ultra-low friction mechanism of hydrogenated carbon films with controllable fullerene-like nano-structures grown with different bias voltage

Tribological properties of hydrogenated amorphous carbon films (HACFs) are strongly affected by external atmospheres stimulus. This greatly limited its applications in fields that require special trans-atmospheric environments. Here, a unique fullerene-like (FL) nanostructure was designed to embed in amorphous carbon matrix to improve the friction behavior of HACFs in ambient air. High-frequency pulsed plasma-enhanced chemical vapor deposition was employed to deposit the films. The HACFs with fullerene-like (FL) characteristics are fabricated with the ‘amorphous to FL’ evolutions. At bias voltage of − 950 V, HACF has the highest odd ring fraction (57.3%) and exhibit the lowest coefficient of friction (0.039) and wear rate (2.2 ×10−8 mm3/Nm) in ambient air. This may provide potential strategies for HACFs to expand the tribology application environments.

Mechanism of protein biofilm formation on Ag-DLC films prepared for application in joint implants

Silver-doped diamond-like carbon (Ag-DLC) films offer low residual stress, good adhesion, and excellent wear resistance, and thus are promising materials for surface modification of joint prostheses. Further, as proteins are the most abundant component of joint fluid, the wear performance of Ag-DLC films in protein environments warrants investigation. We prepared DLC and 10.0 at.% Ag-DLC films using hybrid deposition technique by combining high-power pulsed magnetron sputtering and high-power pulsed plasma-enhanced chemical vapor deposition. The wear performance of the films was tested using bovine serum albumin (BSA) solution. A biofilm of denatured proteins formed at the friction interface of the Ag-DLC film, which improve wear resistance. Subsequent protein adsorption, Ag+ ions release, and spectroscopic evaluation of the interaction between Ag+ ions and BSA molecules revealed the mechanism of biofilm formation. Ag doping promoted the protein adsorption on film surface and friction interface of Ag-DLC films. Meanwhile, Ag-DLC films released Ag+ ions when exposed in physiological solutions. The released Ag+ ions break the hydrogen bonds and disulfide bonds in proteins and transform the α-helix structure to β-sheet and β-turn structure, thus unfolding the protein, exposing the inner hydrophobic groups, and inducing protein deposition and biofilm formation. The study elucidates the biofilm formation mechanism at the friction interface of Ag-DLC films and counterparts and can aid in design of hardwearing joint implants.

Low Temperature Growth of Wafer-Scale 2D MoS2 Thin Films By Pulsed Plasma-Enhanced Chemical Vapor Deposition

Layered two-dimensional molybdenum sulfide (MoS2) has attracted great interest for a promising candidate material for opto-electronic, sensing and catalysis applications due to its outstanding mechanical, electrical and optical properties. In order to apply MoS2 to the industrial field, significant efforts have been placed in obtaining a wafer-scale uniform MoS2. There have been many progressions in various methods such as thermal-CVD [1] and ALD [2], but these methods have crucial limitation that they demand either high growth temperature or post-thermal treatment. In the present study, to overcome the limitation of traditional method, pulsed plasma-enhanced chemical vapor deposition was adopted for the growth of MoS2 thin films. By using H2S plasma reactant, the growth temperature could be significantly lower than in the previous way. The pulsing of Mo precursor injection properly regulates the Mo precursor partial-pressure ratio that is crucial for the synthesis of MoS2. Through these strategies, mono to few layers of MoS2 thin films was deposited uniformly on SiO2/Si substrates. X-ray photoelectron spectroscopy and transmission electron microscopy demonstrated the composition and crystallinity of MoS2 thin films depends on the plasma conditions. Furthermore, through optimizing the plasma conditions, the potential of MoS2 for electric device component was investigated.Fig1. (a) Raman spectra of MoS2 thin films (b) XPS spectra of Mo 3d(left), S 2p(right) obtained from MoS2 thin films deposited by pulsed PECVD.

Influence of Ag doping on the microstructure, mechanical properties, and adhesion stability of diamond-like carbon films

Silver (Ag)-doped diamond-like carbon (Ag-DLC) films were deposited on Si wafer and Co-Cr-Mo alloy substrates using a hybrid deposition technique that combined high-power pulsed magnetron sputtering (HPPMS) and high-power pulsed plasma-enhanced chemical vapor deposition (HPP-PECVD). The Ag concentration (0.0–10.0 at.%) in Ag-DLC films was controlled by adjusting the number of Ag rods in the mosaic silver-graphite target. The effects of Ag doping on the microstructure, chemical bonding, mechanical properties, and adhesion stability of DLC films were systematically investigated. The results demonstrated that Ag doping could refine the columnar structure in DLC films and change the shape and size of DLC surface hillocks. The residual stress in the DLC films decreased as the Ag concentration increased, which effectively improved the adhesion between the films and substrates. The fraction of sp3 bonds in the carbon structure decreased with increasing Ag concentration, which resulted in a reduction in the film hardness when the Ag concentration was higher than 3.2 at.%. Ag doping could improve the wear performance of DLC films, and the Ag-DLC film with 3.2 at.% Ag had excellent wear resistance. Compared with pure DLC films, the Ag-DLC films had better adhesion stability in physiological solutions, which is beneficial for the long-term service of DLC films in vivo applications.

CVD-diamond nanoparticle synthesis for DLC film application

Diamond-like carbon (DLC) films have been extensively applied as a solid lubricant and as a protective coating due to their attractive chemical, mechanical, and tribological properties. Furthermore, these properties of DLC coatings can be improved with the incorporation of nanoparticles of different materials, especially diamond nanoparticles (DNPs). Herein, the incorporation of chemical vapor deposition (CVD) DNPs was done from a deionized aqueous colloidal solution by using a controlled pulsed valve, which is an innovative aspect of this work. The CVD DNPs were pulverized into the plasma region and incorporated in the DLC films bulk with controllable size particle distribution and density. In addition, an enhanced process to obtain DNPs with suitable size distribution was established by using a high energy ball milling technique, centrifugation, and a special chemical cleaning process. The DLC films were deposited on a metallic substrate via a modified, pulsed DC plasma-enhanced chemical vapor deposition (PECVD) technique, with an additional cathode. X-ray diffractometry (XRD) and scanning electronic microscopy (SEM) techniques showed that an aqueous colloidal solution of high-purity DNPs with a mean diameter of 32 nm was obtained. Dynamic light scattering (DLS) results showed that it is possible to control particle size distribution by varying the milling and centrifugation time lengths. Therefore, a valuable result was that DLC films could be deposited with DNPs by using clean water without affecting deposition rate, the adhesion between the DLC films and substrates, the structural quality of the film, and keeping lower coefficient of friction.

Surface modification of 316L stainless steel by diamond-like carbon films

The diamond-like carbon (DLC) film on 316L stainless steel substrate was prepared by pulsed plasma-enhanced chemical vapor deposition, and the performance of the films was optimized by regulating the pulse voltage. Microstructure and properties of DLC film on 316L stainless steel were characterized by atomic force microscopy, field-emission scanning electron microscopy, Raman spectra, nano-indenter and electrochemical workstations. The results showed that DLC films with smooth and dense morphology have a low friction coefficient and high nano-indentation hardness, and the surface hardness of 316L stainless steel substrate was enhanced by more than 3 times. The mechanical properties of DLC films and their bond with 316L stainless steel could be further optimized by increasing pulse voltage. DLC films on 316L stainless steel substrate increased the self-corrosion potential by 0.173 V and decreased self-corrosion current by 99%, which significantly improved the anti-corrosive properties of 316L substrate.

Synchrotron-based spectroscopic analysis of diamond-like carbon films from different source gases

Diamond-like carbon (DLC) films were deposited using the pulsed plasma-enhanced chemical vapor deposition (PECVD) method with different source gases such as methane (CH4), acetylene (C2H2), acetylene with methane (C2H2:CH4), ethylene (C2H4), and ethylene with methane (C2H4:CH4). The chemical characteristics of these DLC films were investigated using suitable spectroscopic techniques. Raman spectroscopy analysis illustrated decrease of the ID/IG ratio with the addition of CH4. Importantly, X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy not only enabled evaluation of the relative content of sp2 and sp3, but also clarified the chemical bonding of the films with different source gases. The XPS results showed lower sp2 content than the NEXAFS results. Moreover, glow discharge optical emission spectrometry (GD-OES) illustrated increase in the hydrogen content, which is in good agreement with increase of the sp3 content based on Raman, XPS, and NEXAFS analyses. Consequently, the synthesis and characterization indicate a significant role for differences of chemical composition of the films. The study described herein provides useful information for preparing high-quality DLC films, as well as for evaluating appropriately the distribution of the carbon sp2/(sp2 + sp3) ratio and the hydrogen content in the films with different source gases.

Stable super-hydrophobic lauryl methacrylate film fabrication on the surface of cotton fabrics in plasma-enhanced chemical vapor deposition with different duty cycles

In this paper, stable super-hydrophobic lauryl methacrylate (LMA) film on the surface of cotton fabrics was fabricated by a simple process of pulsed plasma-enhanced chemical vapor deposition (PECVD) with different duty cycles. The influence of duty cycles on the surface structure and properties of cotton fabrics was analyzed after a series of measurements. The results showed that water contact angles (WCAs) of samples were inversely proportional to the duty cycle values and exhibited the highest WCA (162°) at a duty cycle of 2%. The optimized washing durability of samples was obtained under the treatment of duty cycle of 25% and the WCA could still reach 127° after 15 laundering cycles. The formation of a micro-nano-composite structure and evenness of film could be observed by atomic force microscopy and scanning electron microscopy. Nevertheless, the sample, which was treated by plasma with a 25% duty cycle, had the best uniformity of film deposition. The results of attenuated total reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy illustrated that the LMA monomer was grafted and deposited on the surface of cotton fabrics successfully in covalent binding after PECVD treatment, and this was supposed to be the cause of the washing stability of the films. The results indicated that cotton fabrics modified with the proposed method can exhibit excellent super-hydrophobicity and washing durability, while the duty cycle was an appreciable effect factor in the modification.

The effects of phase transformation on the structure and mechanical properties of TiSiCN nanocomposite coatings deposited by PECVD method

In the present study, the effects of phase transformations on the structure and mechanical properties of TiSiCN coatings were investigated. TiSiCN nanocomposite coatings were deposited on AISI H13 hot-work tool steel by a pulsed direct current plasma-enhanced chemical vapor deposition process at 350 or 500 °C, using TiCl4 and SiCl4 as the precursors of Ti and Si, respectively, in a CH4/N2/H2/Ar plasma as the source of carbon and nitrogen and reducing environment. Some samples deposited at 350 °C were subsequently annealed at 500 °C under Ar atmosphere. Super hard self-lubricant TiSiCN coatings, having nanocomposite structure consisting of TiCN nanocrystals and amorphous carbon particles embedded in an amorphous SiCNx matrix, formed through spinodal decomposition in the specimens deposited or annealed at 500 °C. In addition, it was revealed that either uncomplete or relatively coarse phase segregation of titanium compounds was achieved during deposition at 350 °C and 500 °C, respectively. On the contrary, by deposition at 350 °C followed by annealing at 500 °C, a finer structure was obtained with a sensible improvement of the mechanical properties of coatings. Accordingly, the main finding of this work is that significant enhancement in key properties of TiSiCN coatings, such as hardness, adhesion and friction coefficient, can be obtained by deposition at low temperature and subsequent annealing at higher temperature, thanks to the formation of a fine grained nanocomposite structure.

Comparative study on growth characteristics and electrical properties of ZrO2 films grown using pulsed plasma-enhanced chemical vapor deposition and plasma-enhanced atomic layer deposition for oxide thin film transistors

The deposition of high-quality ZrO2 films has been achieved using both pulsed plasma-enhanced chemical vapor deposition (P-PE-CVD) and plasma-enhanced atomic layer deposition (PE-ALD) with (C5H5)Zr[N(CH3)2]3 as a Zr precursor. The authors compared the growth characteristics, chemical compositions, and electrical properties of P-PE-CVD and PE-ALD ZrO2 prepared under various deposition conditions. The ZrO2 films prepared using both methods showed high purity and good stoichiometry. Electrical characterization of a metal-oxide-semiconductor capacitor utilizing the ZrO2 films showed that PE-ALD films have a relatively lower leakage current than P-PE-CVD films, whereas the dielectric constant, interface trap density, and hysteresis of both films are similar. Applying both methods, the electrical properties of ZrO2 films were also evaluated using In–Ga–Zn–O thin-film transistors (TFTs), which showed a good device performance in terms of high Ion-Ioff ratios (>108) and low off-currents (<10−11 A). In addition, ZrO2-based TFT showed high reliability against a negative Vth shift. Based on the self-limiting growth characteristics and electrical properties of P-PE-CVD, the authors found that the P-PE-CVD process results in electrical properties comparable to those of PE-ALD ZrO2 films. Thus, the authors believe that P-PE-CVD can be an alternative process to PE-ALD for future electronic device applications, especially for display applications due to its good electrical properties with high throughput.

Evaluation of Vapor Deposition Techniques for Membrane Pore Size Modification

The suitability of three vapor deposition techniques for pore size modification was evaluated using polycarbonate track etched membranes as model supports. A feature scale model was employed to predict the pore geometry after modification and the resulting pure water flux. Physical vapor deposition (PVD) and pulsed plasma-enhanced chemical vapor deposition (PECVD), naturally, form asymmetric nanopores that retain high flux as pore size is reduced. But PVD-modified supports exhibited poor control and reproducibility. In contrast, pulsed PECVD and plasma-enhanced atomic layer deposition (PEALD) were shown to deliver digital control over pore size. Moreover, good agreement was obtained between model predictions and flux measurements. Exposure limitations during PEALD introduce a degree of asymmetry, though net growth rates were 1-2 orders of magnitude smaller than pulsed PECVD and PVD. Filtration experiments using bovine serum albumin as a model solute showed that pulsed PECVD-modified membranes can be engineered to simultaneously deliver both high flux and high selectivity. For example, pulsed PECVD-modified supports were demonstrated to deliver high retention (~ 75%) while maintaining 70% of their initial pure water flux.

パルスDC-PCVD法による各種硬質皮膜の金型への応用

パルスDC-PCVD法による各種硬質皮膜の金型への応用

Feature scale modeling of pulsed plasma-enhanced chemical vapor deposition

A two dimensional feature scale model has been developed to predict film profile evolution during pulsed plasma enhanced chemical vapor deposition (PECVD). The model employs a diffusion reaction framework with a spatially variable Knudsen diffusion coefficient to account for molecular transport in evolving feature geometries. The transient model accounts for the alternating atomic layer deposition (ALD) and PECVD growth modes that contribute to deposition. A scaling analysis is used to account for diffusion limitations that affect the ALD component in high aspect ratios due to insufficient precursor exposure. The model predictions have been validated using cross section micrographs of nanostructures produced by pulsed PECVD of aluminum oxide on patterned substrates. The model provides a tool to design the fabrication of nanostructures with digital precision. By varying the relative contributions of the two modes pulsed PECVD provides an opportunity engineer the degree of conformality to produce unique morphologies that are distinct from either steady state vapor deposition processes or conventional ALD.

Self limiting deposition of pyrite absorbers by pulsed PECVD

Self-limiting growth of pyrite thin films was accomplished by pulsed plasma-enhanced chemical vapor deposition (PECVD) with continuous delivery of iron pentacarbonyl diluted in a mixture of H2S and argon. The growth rate per cycle was controlled between 0.1 and 1 Å/pulse by adjusting the duty cycle and/or plasma power. The onset of thermal chemical vapor deposition was identified at ∼300 °C, and this process resulted in films containing substoichiometric pyrrhotite. In contrast, pulsed PECVD produced stoichiometric FeS2 films without the need for postdeposition sulfurization. Films contained a mixture of pyrite and marcasite, though the latter could be attenuated using a combination of high duty cycle, low temperature, and low plasma power. Pulsed PECVD films displayed similar optical properties with a band gap of ∼1 eV and an absorption coefficient of ∼105 cm−1, regardless of the pyrite:marcasite ratio.

Structural and optical properties of Au-catalyzed SiNWs grown using pulsed plasma-enhanced chemical vapour deposition

Silicon nanowires (SiNWs) were grown on indium tin oxide-coated glass substrates using pulsed plasma-enhanced chemical vapour deposition (PPECVD) with gold (Au) as a catalyst. Various thicknesses of Au thin films ranging from 10nm to 100nm were deposited on the substrates by thermal evaporation. The surface morphological study of the prepared wires showed that the wire diameter increased as the catalyst film thickness increased. The X-ray diffraction patterns of the prepared SiNWs illustrated that the grown wires had cubic phase, and the crystallinity was enhanced as the catalyst thickness increased. The photoluminescence spectra of the SiNWs had a red emission band whose band location and shape were found to be dependent on catalyst thickness. The Raman spectra of the prepared nanowires showed that the first order transverse band shifted toward lower frequencies compared with the c-Si band location. The first order transverse band approached the c-Si band location as the wire diameter increased due to the increasing catalyst film thickness.

FTIR analysis of a-SiCN:H films deposited by PECVD

Hydrogenated amorphous silicon carbonitride films (a-SiCN:H) have been deposited at low temperature by mid-frequency pulsed plasma enhanced chemical vapour deposition (PECVD) from systematically varied mixtures of trimethylsilane (SiH(CH3)3), nitrogen, hydrogen and argon. The elemental composition of the films was measured by elastic recoil detection analysis (ERDA). The film stoichiometry was varied in a wide range, i.e. between nitrogen-free and nitrogen rich films, but typically carbon was the most abundant element.The main effort was aimed at getting information about the various chemical bonds in the films by Fourier transform infrared spectrometry (FTIR) in the range 400–7000 cm−1. For the analysis of the transmission spectra optical modelling of the layer stack “vacuum/a-SiCN:H/monocrystalline silicon/vacuum” was used. The applied dielectric function model describing the amorphous a-SiCN:H material comprises Sellmeier dispersion, Urbach absorption and a superposition of Kim oscillator susceptibilities, representing the different infrared active modes of network bonds (e.g. Si–C, Si–N) and terminal hydrogen bonds (e.g. Si–Hx, Si–CHx, C–Hx). The FTIR analysis showed systematic changes in the optical film properties (refractive index, absorption coefficient) as a function of the deposition conditions. The oscillator strengths are well correlated with the a-SiCN:H film composition. Furthermore, the wave number positions of absorption peaks also shift in a systematic manner. The FTIR results were interpreted in terms of the chemical environment of the bonds.

Characterization of silicon nanowires grown on silicon, stainless steel and indium tin oxide substrates

Silicon nanowires (SiNWs) have been grown on crystalline silicon (Si), indium tin oxide (ITO) and stainless steel (SS) substrates using a gold catalyst coating with a thickness of 200 nm via pulsed plasma-enhanced chemical vapor deposition (PPECVD). Their morphological, mineralogical and surface characteristics have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman analysis. SiNWs growth is accompanied by oxidation, thus yielding partially (SiO x ) and fully oxidized (SiO2) Si sheaths. The mean diameters of these SiNWs range from 140 to 185 nm. Si with (111) and (220) planes exists in SiNWs grown on all three substrates while Si with a (311) plane is detected only for Si and ITO substrates. Computational simulation using density functional theory (DFT) has also been conducted to supplement the experimental Raman analyses for crystalline Si and SiO2. XPS results reveal that ca. 30 % of the SiNWs have been oxidized for all substrates. The results presented in this paper can be used to aid selection of appropriate substrates for SiNW growth, depending on specific applications.

Preparation and characterization of silicon nanowires catalyzed by aluminum

Silicon nanowires (SiNWs) were grown on indium tin oxide coated glass substrates by a pulsed plasma-enhanced chemical vapor deposition (PPECVD) method using aluminum as a catalyst. The thin films of the catalyst, with thicknesses ranging from 10nm to 100nm, were deposited on the substrates by thermal evaporation. The effect of the thickness of the thin film catalyst on the morphology of the silicon nanowires was investigated. The surface morphology study of the prepared wires showed that the modal wire diameter increased as the catalyst film thickness increased. The X-ray diffraction patterns of the prepared silicon nanowires had no silicon peaks, indicating that the wires had low crystallinity. The photoluminescence spectra of the SiNWs showed that all samples had more than one emission band. The emission band location and shape were found to be dependent on catalyst thickness. The Raman spectra of the prepared nanowires showed that the first order transverse band shifted toward lower frequencies compared with the c-Si band location.

Mid-frequency PECVD of a-SiCN:H films and their structural, mechanical and electrical properties

The mid-frequency pulsed plasma enhanced chemical vapour deposition (PECVD) of hydrogenated amorphous silicon carbonitride (a-SiCN:H) was investigated to prove the suitability of these films as a mechanical stiff insulator for the integration of piezoelectric fibres in microstructured aluminium plates. For the a-SiCN:H deposition trimethylsilane (SiH(CH3)3; 3MS) and nitrogen in mixture with argon were used. The films were characterised regarding their deposition rate, elastic modulus and hardness (nanoindentation), mechanical stress, elemental composition (ERDA) and electrical insulating properties.The breakdown field strength of μm-thick a-SiCN:H films is in the range of 2–4 MV/cm. At pressures of a few Pa the deposition rate reached values up to 6 μm/h. It is limited by the power absorption in the 100 kHz bipolar-pulsed discharge. Varying the pressure from 2 Pa to 15 Pa has only little influence on the film composition. With increasing pressure during deposition the elastic modulus of the films decreases from about 146 GPa to 100 GPa and the compressive film stress from 1.2 GPa to 0.55 GPa. By reducing the 3MS flow rate from 50 sccm to 10 sccm (at 8 Pa deposition pressure), the carbon and the hydrogen concentrations in the films were reduced by about 10 at. %. The Si-content is only slightly reduced but the N-content is more than tripled. In contrast, the changes in the mechanical film properties are comparatively small. The mechanical properties of a-SiCN:H films are not simply correlated to the stoichiometry but are rather controlled by the ion bombardment during growth.

Dielectric performance of hybrid alumina-silicone nanolaminates synthesized by plasma enhanced chemical vapor deposition

Plasma enhanced chemical vapor deposition (PECVD) was used to deposit hybrid nanolaminates comprising silicone and alumina at low temperature. Hexamethyldisiloxane was used as the sole precursor for silicone, and alumina synthesis was accomplished via pulsed PECVD using trimethyl aluminum and oxygen. Digital control over the nanolaminate structure and composition was demonstrated through spectroscopic ellipsometry and cross-sectional microscopy. The dielectric performance of alumina–silicone nanolaminates was examined as a function of the dyad composition and thickness. The effective dielectric constant could be tuned between those of the parent compounds, achieving high specific capacitance values ranging from 20 to 80 nF/cm2. Current-voltage measurements showed that the leakage current was a strong function of the thickness of the individual alumina layers, and nanolaminates with Al2O3 layers >10 nm displayed excellent performance. The leakage current density at a field strength of 1 MV/cm was ∼10−9 A/cm2, whereas breakdown required applied electrical fields in excess of 5 MV/cm.