Preparation and Characterization of DLC Films by Twinned ECR Microwave Plasma Enhanced CVD for Microelectromechanical Systems (MEMS) Applications

Diamond-like carbon (DLC) films have recently been pursued as the protection of MEMS against their friction and wear.Plasma enhanced chemical vapor deposition (PECVD) technique is very attractive to prepare DLC coating for MEMS.This paper describes the preparation of DLC films using twinned electron cyclotron resonance (ECR) microwave PECVD process.Raman spectra confirmed the DLC characteristics of the films.Fourier-transform infrared (FT-IR)characterization indicates the carbon is bonded in the form sp~3 and sp~2 with hydrogen participating in bonding.The surface roughness of the films is as low as approximately (0.093)nm measured with an atomic force microscope.A CERT microtribometer system is employed to obtain information about the scratch resistance,friction properties,and sliding wear resistance of the films.The results show the deposited DLC films have low friction and good scratch/wear resistance properties.

Plasma Diagnosis for Microwave ECR Plasma Enhanced Sputtering Deposition of DLC Films

Application of the Langmuir probe in plasma circumstance for deposition of diamond-like carbon （DLC） thin films usually faces the problem of rapid failure of the probe due to surface insulative coating. In this paper, we circumvent the problem by using the floating harmonic probe technique. In the real circumstance of DLC film deposition, the floating harmonic probe worked reliably over 3 hours, correctly indicating the ion density and electron temperature. The technique was practically used to measure the ion density and electron temperature in DLC film deposition processes using the microwave ECR plasma enhanced sputtering. Combined with the Raman spectroscopic characterization of the films, the conditions for deposition of DLC films were investigated.

STUDY ON COMPOSITION, MICROSTRUCTURE AND HARDNESS OF DLC FILMS BY VCAD

DLC super-hard films have been deposited on the substrates of single crystalline Si, pure Ti and stainless steel 18-8 by a method of vacuum cathode arc deposition (VCAD). The composition, microstructure and micro-hardness of the films have been studied in this paper. The results indicate that hardness of the DLC films is different on the different substrates. Hardness of the films increases with decreasing in surface roughness of the films. The maximum value of micro-hardness belongs to the DLC films deposited under the hydrogen pressure of 0.35Pa and the negative bias of 100V.

Tuning C-C sp2/sp3 ratio of DLC films in FCVA system for biomedical application

Diamond like carbon(DLC)films with different C-C sp2/sp3 ratios were prepared by tuning the N2 flow rate in a filtered cathodic vacuum arc(FCVA)system.The increase of N2 flow rate facilitated the increase of C-C sp2/sp3 ratio(1.09-2.66),the growth of particle size(0.78-1.58 nm)and the improvement of surface roughness.The SBF immersion results,as well as WCAs(77.57°~71.71°),hemolysis rate(0.14-1.00%)and cytotoxicity level(0)demonstrated that the as-fabricated DLC film was promising for biomedical application.As a result of surface charge effect,the apatite layers formed in the SBF increased with the increase of C-C sp2/sp3 ratio until 1.74 and then showed a tiny decrease during 1.74-2.66.A raise of hemolysis and cytotoxicity was observed when sp2/sp3 ratio was increased.Moreover,a decrease of friction coefficient of Si surface induced by increasing sp2/sp3 ratio was respectively evidenced in ambient air and SBF lubrication environments.

Field emission properties of a-C and a-C：H films deposited on silicon surfaces modified with nickel nanoparticles

The a-C and a-C：H films are deposited on silicon surfaces modified with and without nickel nanoparticles by using mid-frequency magnetron sputtering. The microstructures and morphologies of the films are analyzed by Raman spec- troscopy and atomic force microscopy. Field emission behaviors of the deposited films with and without nickel nanopar- ticles modification are comparatively investigated. It is found that the hydrogen-free carbon film exhibits a high field emission current density and low turn-on electric field compared with the hydrogenated carbon film. Nickel modifying could increase the current density, whereas it has no significant effect on the turn-on electric field. The mechanism of field electron emission of a sample is discussed from the surface morphologies of the films and nickel nanoparticle roles in the interface between film and substrate.

Study on the Stress of DLC/MCT Interface by Finite Element Method

Micro-indention and finite element method (FEM) are used to study the stress at the interface between diamond-like carbon (DLC) film and mercury cadmium telluride (MCT) substrate, with different coating thickness, deposition temperature and indention load. The FEM simulation results show that when Young's modulus ratio of the coating to the substrate Ec/Es<1, Whether a load was applied or not, the interfacial maximum shear stress decreased with the increase of coating thickness. The Von mises stress always concentrated at the interface. The maximum value of the stress locates at the edge of the interface for thin film (h1/h2<0. l), however, it will locate at the center of the interface while the film become thick (h1/h2>0. 1 ). The stress also increased with raising the film deposition temperature, and the temperature affected the strain obviously. When a load was applied, the stress would concentrate where the load was applied, and the stress value is much larger than that of unloading. When the film stress exceeds the film fracture strength, film cracking occurs at the location where load is applied.

Tribological Characteristic of Diamond-like Carbon Films Investigated by Lateral Force Microscope

Tribological characteristic of different thick diamond-like carbon (DLC) films was studied. A geometrical method was applied to calibrate the cantilever spring constant and to calculate the normal and lateral forces, respectively. Experimental results show that the lateral force under different applied loads is proportional to the normal force for the DLC films with the thickness of 153.4nm and 64.9nm. However, for the thickness of 4.48nm and 2.78nm DLC films, lateral force is nonlinear to normal force, which is opposed to the Amonton's law.The single asperity regime and the DMT model were put forward to predict the possible nanotribological mechanism between the probe and DLC film.

Tribological Properties of DLC Film Prepared by C^+ Ion Beam-assisted Deposition (IBAD)

C ^＋ ion beam-assisted deposition was utilized to prepare deposit diamond-like carbon （ DLC ） film. With the help of a series of experiments such as Raman spectroscopy, FT-IR spectroscopy, AFM and nanoindentation , the DLC film has been recognized as hydrogenated DLC film and its tribologicul properties have been evaluated. The bull-on-disc testing results show that the hardness and the tribologicul properties of the DLC film produced by C^ ＋ ion beam- assisted deposition are improved significantly. DLC film produced by C ^＋ ion beam- assisted deposition is positive to have a prosperous tribologicul application in the near future.

Microstructure and Mechanical Property of Magnetron Sputtering Deposited DLC Film

A diamond-like carbon（DLC） film was deposited on YT14 substrate using magnetron sputtering（MS）. The surface morphologies, roughness and bonding spectra of obtained film were characterized using scanning electron microscopy（SEM）, atomic force microscopy（AFM）, and X-ray photoelectron spectroscopy（XPS）, respectively, and its mechanical property and bonding strength were measured using a nanoindentation and scratch tester, respectively. The results show that the C-enriched DLC film exhibits a denser microstructure and smoother surface with lower surface roughness of 21.8 nm. The ratio of C sp2 at 284.4 e V that corresponds to the diamond（111） and the C sp3 at 285.3 e V that corresponds to the diamond（220） plane for the as-received film is 0.36： 0.64, showing that the C sp3 has the high content. The hardness and Young＇s modulus of DLC film by nanoindentation are 8.534 41 and 142.158 1 GPa, respectively, and the corresponding bonding strength is 74.55 N by scratch test.

Optimizing the tribological performance of DLC-coated NBR rubber:The role of hydrogen in films

Diamond-like carbon(DLC)films directly deposited on rubber substrate is undoubtedly one optimal option to improve the tribological properties due to its ultralow friction,high-hardness as well as good chemical compatibility with rubber.Investigating the relationship between film structure and tribological performance is vital for protecting rubber.In this study it was demonstrated that the etching effect induced by hydrogen incorporation played positive roles in reducing surface roughness of DLC films.In addition,the water contact angle(CA)of DLC-coated nitrile butadiene rubber(NBR)was sensitive to the surface energy and sp?carbon clustering of DLC films.Most importantly,the optimum tribological performance was obtained at the 29 at%H-containing DLC film coated on NBR,which mainly depended on the following key factors:(1)the DLC film with appropriate roughness matched the counterpart surface;(2)the contact area and surface energy controlled interface adhesive force;(3)the microstructure of DLC films impacted load-bearing capacity;and(4)the generation of graphitic phase acted as a solid lubricant.This understanding may draw inspiration for the fabrication of DLC films on rubber to achieve low friction coefficient.

Effects of the ion-beam voltage on the properties of the diamond-like carbon thin film prepared by ion-beam sputtering deposition

Diamond-like carbon （DLC） thin film is one of the most widely used optical thin films. The fraction of chemical bondings has a great influence on the properties of the DLC film. In this work, DLC thin films are prepared by ion-beam sputtering deposition in Ar and CH4 mixtures with graphite as the target. The influences of the ion-beam voltage on the surface morphology, chemical structure, mechanical and infrared optical properties of the DLC films are investigated by atomic force microscopy （AFM）, Raman spectroscopy, nanoindentation, and Fourier transform infrared （FTIR） spec- troscopy, respectively. The results show that the surface of the film is uniform and smooth. The film contains sp2 and sp3 hybridized carbon bondings. The film prepared by lower ion beam voltage has a higher sp3 bonding content. It is found that the hardness of DLC films increases with reducing ion-beam voltage, which can be attributed to an increase in the fraction of sp3 carbon bondings in the DLC film. The optical constants can be obtained by the whole infrared optical spectrum fitting with the transmittance spectrum. The refractive index increases with the decrease of the ion-beam voltage, while the extinction coefficient decreases.

Adhesion and friction performance of DLC/rubber:The influence of plasma pretreatment

Diamond-like carbon(DLC)films are deposited on rubber surfaces to protect the rubber components,and surface pretreatment of the rubber substrates prior to the film deposition can improve the adhesion between the DLC films and the rubber.Thus,the principal purpose of this work concentrates on determining the effects of argon(Ar),oxygen(O_(2)),nitrogen(N_(2)),and hydrogen(H_(2))plasma pretreatments on the adhesion and friction performance of the DLC films deposited on rubber(DLC/rubber).The results indicated that the Ar plasma pretreatment promoted the formation of a compact layer on the rubber surface.By contrast,massive fillers were exposed on the rubber surface after oxygen or nitrogen plasma pretreatments.Moreover,the typical micrometer-scale patches divided by random cracks were observed on the surface of DLC/rubber,except for the sample pretreated with oxygen plasma.The adhesion of DLC/rubber was found to strengthen with the removal of weak boundary layers and the generation of free radicals on the rubber surface after plasma pretreatment.The tribo-tests revealed that DLC/rubber with O_(2),N_(2),and H_(2) plasma pretreatments cannot achieve optimal friction performance.Significantly,DLC/rubber with Ar plasma pretreatment exhibited a low and stable friction coefficient of 0.19 and superior wear resistance,which was correlated to the high adhesion,good load-bearing of the rubber surface,and the approximate sine function of the surface profile of the DLC film.

Effects of platinum content on tribological properties of platinum/nitrogen doped diamond-like carbon thin films deposited via magnetron sputtering

Platinum(Pt)and nitrogen(N)were co-incorporated in diamond-like carbon(DLC)thin films using a magnetron sputtering system to form PtN-DLC thin films for tribological applications.The Pt content in the PtN-DLC films prepared on Si substrates was controlled by varying RF power applied to a Pt target at a fixed N2 flow rate.The tribological properties of the PtN-DLC films were investigated with respect to the Pt content in the films.The uncoated Si substrate surface tested against a steel ball of 6 mm in diameter had significant abrasive and fatigue wear,while no significant wear was found on the N-DLC coated sample surface,indicating that the N-DLC film effectively prevented its underlying Si substrate from wear.However,the incorporation of Pt in the N-DLC films reduced the wear resistance of the films by degrading sp3-bonded cross-linking structures of the films so that significant wear tracks were found on the surfaces of the PtN-DLC films.Therefore,the increased radio frequency(RF)power applied to the Pt target decreased the wear resistance of the PtN-DLC films as a result of the increased Pt content.

Tribological properties of platinum/ruthenium/nitrogen doped diamond-like carbon thin films deposited with different negative substrate biases

The platinum/ruthenium/nitrogen doped diamond‐like carbon(PtRuN‐DLC)thin films were deposited on Si substrates via DC magnetron sputtering by varying negative substrate bias.The tribological performance of the PtRuN‐DLC films was systematically investigated using ball‐on‐disc microtribological test.The Raman results showed that the increased negative substrate bias significantly increased the number of sp3 bonds in the PtRuN‐DLC films as a result of the increased kinetic energies of impinging ions.The adhesion strength of the PtRuN‐DLC films apparently decreased with increased negative substrate bias due to the promoted residual stress in the films.The tribological results clearly revealed that the increased negative substrate bias decreased the friction and wear of the PtRuN‐DLC films by improving the sp3 bonded cross‐linking structures of the films.It can be concluded that the PtRuN‐DLC films could effectively prevent their underlying Si substrates from wear as the negative substrate bias had a significant influence on the tribological properties of the PtRuN‐DLC films.

Running-in behavior of a H‒DLC/Al_(2)O_(3) pair at the nanoscale

Diamond-like carbon(DLC)film has been developed as an extremely effective lubricant to reduce energy dissipation;however,most films should undergo running-in to achieve a super-low friction state.In this study,the running-in behaviors of an H–DLC/Al_(2)O_(3) pair were investigated through a controllable single-asperity contact study using an atomic force microscope.This study presents direct evidence that illustrates the role of transfer layer formation and oxide layer removal in the friction reduction during running-in.After 200 sliding cycles,a thin transfer layer was formed on the Al2O3 tip.Compared with a clean tip,this modified tip showed a significantly lower adhesion force and friction force on the original H–DLC film,which confirmed the contribution of the transfer layer formation in the friction reduction during running-in.It was also found that the friction coefficient of the H–DLC/Al_(2)O_(3) pair decreased linearly as the oxygen concentration of the H–DLC substrate surface decreased.This phenomenon can be explained by a change in the contact surface from an oxygen termination with strong hydrogen bond interactions to a hydrogen termination with weak van der Waals interactions.These results provide new insights that quantitatively reveal the running-in mechanism at the nanoscale,which may help with the design optimization of DLC films for different environmental applications.