Antibacterial activity of DLC and Ag–DLC films produced by PECVD technique

Diamond-like carbon (DLC) films have been the focus of extensive research in recent years due to its potential application as surface coatings on biomedical devices. Doped carbon films are also useful as biomaterials. As silver (Ag) is known to be a potent antibacterial agent, Ag–DLC films have been suggested to be potentially useful in biomedical applications. In this paper, DLC films were growth on 316L stainless steel substrates by using Plasma Enhanced Chemical Vapour Deposition (PECVD) technique with a thin amorphous silicon interlayer. Silver colloidal solution was produced by eletrodeposition of silver electrodes in distilled water and during the deposition process it was sprayed among each 25 nm thickness layer DLC film. The antibacterial activity of DLC, Ag–DLC and silver colloidal solution were evaluated by bacterial eradication tests with Escherichia coli (E. coli) at different incubation times. With the increase of silver nanoparticle layers in Ag–DLC, the total compressive stress decreased significantly. Raman spectra showed the film structure did not suffer any substantial change due to the incorporation of silver. The only alteration suffered was a slightly reduction in hardness. DLC and Ag–DLC films demonstrated good results against E. coli, meaning that DLC and Ag–DLC can be useful to produce coatings with antibacterial properties for biomedical industry.     

掺银磁铁矿复合薄膜的制备及室温磁电阻效应

采用溶胶-凝胶技术结合旋涂法,以聚乙烯醇作为鳌合剂,选择适当的退火程序,制备了由金属Ag相和Fe3O4相所组成的Agx(Fe3O4)1-x=0,0.1,0.2,0.3)复合薄膜.磁力显微镜观察表明,Fe3O4晶粒为单畴颗粒,其直径为75～85 nm,小于理论计算的单畴,临界尺寸.磁性测量表明:x=0.1和0.3薄膜的矫顽力坼分别为23.1 kA/m和28.6 kA/m,很接近于Fe3O4的磁晶各向异性场HK(27.1 KA/m).室温(300K)下,x=0.1的薄膜具有最大的磁电阻,700 kA/m磁场下为-3.5%,高于纯Fe3O4薄膜的低场磁电阻(-2.2%).随着Ag含量进一步增加,薄膜的室温磁电阻减小.适量金属Ag的掺入有利于提高Fe3O4薄膜的磁电阻,这归因于自旋极化电子在Fe3O4晶粒和Ag颗粒界面处的自旋相关散射以及穿过Fe3O4-Fe3P4晶界的自旋极化隧穿的共同作用.     

Charge carrier lifetime in DLC films

Diamond-like carbon (DLC) layers deposited at room temperature in 13.56 MHz radio-frequency methane (CH₄) plasma have been studied. The results of transient currents for DLC thin films are reported. The carrier's lifetime was determined based on the transient current analysis for the surface and bulk recombinations: t_rs=0.3 ms, t_rv=0.11 ms. These values seem to be relatively high for structures of this type. The diffusion length for DLC films L*=0.67×10⁻⁴ cm. Other parameters such as the diffusion coefficient D*=4×10⁻⁵ cm²/s and surface recombination rate S=0.37 cm/s are exceptionally small here.     

Effects of post-deposition annealing on different DLC films

Amorphous hydrogenated carbon films have been deposited by plasma-enhanced chemical vapour deposition at different process pressures and substrate temperatures, resulting in film properties ranging from polymer-like to diamond-like. The deposition parameter combinations were chosen by experimental design to enable the determination of both deposition pressure and deposition temperature effects on the annealing behaviour. The deposited films have then been annealed in vacuum at successively higher temperatures. Changes in optical band gap, internal stress, film thickness and infrared (IR) absorption spectra have been recorded to assess the influence of deposition parameters on the thermal stability of diamond-like carbon (DLC) and to identify temperature-induced modifications in the bonding structure. The results show a large variation in thermal stability between the different DLC films; samples deposited at low pressure display the greatest stability. The internal stress of the films starts decreasing at very low annealing temperature (<100 °C for the majority of samples), in most cases long before any decrease in the optical band gap can be detected. This is explained by a movement of hydrogen from sp² to sp³ sites as detected by IR measurements.     

Properties of DLC films deposited by an oxyacetylene flame

Diamond-like carbon (DLC) films were obtained by spinning a tungsten carbide substrate at a high speed using an oxyacetylene flame. The films deposited at a typical experimental condition of substrate temperature of 810°C, rotation of 600 rpm and 3 h deposition time, exhibited an uniform, very smooth, hard and glassy surface covering the entire exposed face of the substrate. These films were identified as DLC by their characteristic broad Raman spectra centered at 1554 cm⁻¹ and micro-Vicker's hardness >3400 kg mm⁻². For substrate temperatures <800°C the film started losing the uniform glassy surface and the hardness deteriorated. For temperatures >950°C the film was still hard and shiny, but black in color. DLC films were also obtained in a wide range of speeds of rotation (300–750 rpm), as long as the temperature remained close to 850°C.     

Recombination lifetime of charge carriers in DLC thin films

Decay of photocurrent in diamond-like carbon (DLC) thin films and broadband dielectric measurements of rectifying n-Si/DLC junctions were used to find the recombination lifetime of charge carriers in DLC films. The recombination lifetime found from the two methods was between 10⁻⁴ and 10⁻³ s.     

Sulphur doped DLC films deposited by DC magnetron sputtering

Diamond‐like carbon (DLC) and sulphur doped diamond‐like carbon (S‐DLC) films were synthesised at different sulphur molar percentage of 0%, 2%, 5%, 8% and 10% by direct current (DC) magnetron sputtering process using novel compressed sulphur‐graphite targets at relatively low power density. Films were characterised for their morphologies, structural, electrical and optical properties. Scanning electron microscope images reveal changes in the quality of the obtained films shown by the denser packing of DLC grains at different sulphur percentage. The conductivities of S‐DLC films were found to be in the range of 6.0 × 10^?3–0.6/Ω cm. The optical band gap energies were found to be in the range of ～1.4–2.0 eV. Both electrical and optical measurements exhibit nonlinear responses with optimum at around 5% sulphur molar percentage (minimum for conductivity and maximum for optical band gap energy). These trends of change in both conductivity and optical band gap energy are consistent with the variation in bond characters of the films indicated by Raman spectroscopy. © 2011 Canadian Society for Chemical Engineering     

Diamond-like carbon (DLC) films as electrochemical electrodes

Amorphous carbon can be any mixture of carbon bonds of sp³, sp², and even sp¹, with the possible presence of hydrogen. The group of mixture, of which there is a high fraction of diamond-like (sp³) bonds, is named diamond-like carbon (DLC). Unlike the crystalline carbon materials: diamond, graphite, carbon nanotube, fullerene and graphene, DLC can be deposited at room temperature without catalyst or surface pretreatment. Furthermore, its properties can be tuned by changing the sp³ content, the organization of sp² sites and hydrogen content, and also by doping. This paper firstly reviewed the electrochemical properties of DLC films and their applications.     

Capabilities of combined studies of DLC films by X-ray methods

We demonstrate the possibility of determining a large group of physical properties of DLC films using only one group of methods based on X-ray interference studies. These include methods the determination of the film thickness, material density and roughness of the surface. We present the analysis of possibilities to use the method of the two-crystal X-ray spectrometer to evaluate internal stress and to deduce the modules of elasticity and thermal expansion coefficients of the film. It is shown that this method can be used for the in-situ control of the film parameters during the film deposition in the technological chamber.     

Antibacterial activity of silver-doped hydroxyapatite nanoparticles against gram-positive and gram-negative bacteria

Ag-doped nanocrystalline hydroxyapatite nanoparticles (Ag:HAp-NPs) (Ca_10-xAg_x(PO₄)₆(OH)₂, x_Ag = 0.05, 0.2, and 0.3) with antibacterial properties are of great interest in the development of new products. Coprecipitation method is a promising route for obtaining nanocrystalline Ag:HAp with antibacterial properties. X-ray diffraction identified HAp as an unique crystalline phase in each sample. The calculated lattice constants of a = b = 9.435 Å, c = 6.876 Å for x_Ag = 0.05, a = b = 9.443 Å, c = 6.875 Å for x_Ag = 0.2, and a = b = 9.445 Å, c = 6.877 Å for x_Ag = 0.3 are in good agreement with the standard of a = b = 9.418 Å, c = 6.884 Å (space group P6₃/m). The Fourier transform infrared and Raman spectra of the sintered HAp show the absorption bands characteristic to hydroxyapatite. The Ag:HAp nanoparticles are evaluated for their antibacterial activity against Staphylococcus aureus, Klebsiella pneumoniae, Providencia stuartii, Citrobacter freundii and Serratia marcescens. The results showed that the antibacterial activity of these materials, regardless of the sample types, was greatest against S. aureus, K. pneumoniae, P. stuartii, and C. freundii. The results of qualitative antibacterial tests revealed that the tested Ag:HAp-NPs had an important inhibitory activity on P. stuartii and C. freundii. The absorbance values measured at 490 nm of the P. stuartii and C. freundii in the presence of Ag:HAp-NPs decreased compared with those of organic solvent used (DMSO) for all the samples (x_Ag = 0.05, 0.2, and 0.3). Antibacterial activity increased with the increase of x_Ag in the samples. The Ag:HAp-NP concentration had little influence on the bacterial growth (P. stuartii).     

Microstructure and mechanical properties of Mo/DLC nanocomposite films

Mo-doped diamond-like carbon (Mo/DLC) films were deposited on stainless steel and Si wafer substrates via unbalanced magnetron sputtering of molybdenum combined with inductively coupled radio frequency (RF) plasma chemical vapor deposition of CH₄/Ar. The effects of Mo doping and sputtering current on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), and nano-indentation. It was found that Mo doping led to increase in the content of sp² carbon, and hence decreased the hardness and elastic modulus of Mo/DLC films as compared with that of DLC films. The content of Mo in the films increased with the increasing sputtering current, and most of Mo reacted with C atoms to form MoC nanocrystallites at a higher sputtering current. Moreover, the Mo-doped DLC films had greatly decreased internal stress and increased adhesion to the substrate than the DLC film, which could be closely related to the unique nanocomposite structure of the Mo-doped films. Namely, the Mo/DLC film was composed of MoC nanoparticles embedded in the cross-linked amorphous carbon matrix, and such a kind of nanostructure was beneficial to retaining the loss of hardness and elastic modulus.     

Direct formation of amine functionality on DLC films and surface cyto-compatibility

Hydrogenated diamond-like carbon (H-DLC) films were synthesized on a p-type silicon wafer using radio frequency plasma composed of a mixture of Ar and C₂H₂ (ratio of 7 to 28). NH₃ plasma treatment was carried out to generate surface-terminal amino groups. The treated surfaces were characterized by Raman scattering, atomic force microscopy (AFM), water contact angle, and X-ray photoelectron spectroscopy (XPS). MC₃T₃-E₁ mouse pre-osteoblasts were cultured on the samples, and cell morphology and proliferation were investigated to evaluate the cyto-compatibility. Cell–surface interactions were investigated by fluorescence microscopy in terms of spreading and proliferation. A cell count kit-8 (CCK-8 Beyotime) was employed to determine quantitatively the viable pre-osteoblasts. The formation of the amine functionality led to better cyto-compatibility on the DLC.     

Growth and properties of hydrogen-free DLC films deposited by surface-wave-sustained plasma

Hydrogen-free diamond-like carbon (DLC) films were deposited by a new surface-wave-sustained plasma physical vapor deposition (SWP-PVD) system in various conditions. Electron density was measured by a Langmuir probe; the film thickness and hardness were characterized using a surface profilometer and a nanoindenter, respectively. Surface morphology was investigated using an atomic force microscope (AFM). It is found that the electron density and deposition rate increase following the increase in microwave power, target voltage, or gas pressure. The typical electron density and deposition rate are about 1.87 × 10¹¹–2.04 × 10¹² cm^− 3 and 1.61–14.32 nm/min respectively. AFM images indicate that the grain sizes of the films change as the experimental parameters vary. The optical constants, refractive index n and extinction coefficient k, were obtained using an optical ellipsometry. With the increase in microwave power from 150 to 270 W, the extinction coefficient of DLC films increases from 0.05 to 0.27 while the refractive index decreases from 2.31 to 2.11.     

Etching of DLC films using a low intensity oxygen plasma jet

This article describes the characteristics of the etching process of diamond-like carbon (DLC) films using a new plasma system based on an oxygen plasma jet which comprises charged particles and activated neutral species in a range of energies and fluxes suitable for the etching process. This plasma source was used to etch DLC films which were grown on silicon substrates by magnetron sputtering technique. Prior to etching these films were characterized by different methods, namely Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), current×voltage curves and atomic force microscopy (AFM). Etch rates in the range 7.0–25 nm/min were measured for substrates placed at different positions along the axis of the plasma jet. An attractive feature observed in this work was the influence of an axial magnetic field applied to improve the confinement of the plasma stream. An increase by a factor of 3.4 in the etch rate was verified when the magnetic field increased from 2.5 to 6.0 mT. Raman spectra features (line shapes, frequencies and line width) of the etched films were compared with those obtained before etching. The results show that this plasma jet etching is a reliable technique for DLC film processing.     

Characterization of DLC:Si films by the gas effusion technique

In this work an investigation of hard DLC:Si films by the gas effusion technique is presented. Effusion of hydrogen, methane and higher hydrocarbons was studied for films with silicon contents of up to 40 at%. Three major contributions to the effusion spectra could be identified: (i) a desorption-limited mechanism from the internal surfaces of a network of voids which could be observed even for large hydrocarbon molecules, indicating that low silicon content material possesses a porous structure; (ii) a sharp peak related to the abrupt graphitization of the films which dominates the spectra for hydrogen and methane effusion in the low concentration range and is gradually shifted to high temperatures as the silicon content is increased; and (iii) a diffusion-limited mechanism that appears for high silicon content films, suggesting that the films undergo a transition from porous to a relatively compact structure.     

Effects of ion beam processing parameters on the adherence of DLC films

Scratch testing of hydrogenated DLC films applied via an energetic ion beam is used to demonstrate that critical failure loads are increased primarily by increasing a Si bond layer thickness. These loads also increase as DLC layer thickness is increased to a few micrometers and as ion energy is reduced below ca 500 eV. Processing temperatures <200°C have a negligible effect on the loads.     

Influence of nitrogen doping on photoconductivity properties of a: DLC films

We present photoconductivity, photosensitivity and decay time of photocurrent measured as a function of temperature for both nitrogen-doped and undoped a:DLC films. The a:DLC films were deposited using radio-frequency (RF) glow discharge of methane gas (CH₄) as a source of carbon. Several films were doped employing nitrogen (N₂) as the doping gas. The doped and undoped a:DLC films have shown photoconductivity effects in a wide range of temperatures. All photoconductivity parameters, i.e. spectral response, photosensitivity, decay time and photocurrent, were measured for both undoped and doped films. The maximum spectral photosensitivity of doped films shifts to a higher energy, similar to the optical energy-gap measurements. The photocurrent of the doped film is larger by two orders of magnitude than that of undoped film, while the photosensitivity shows an opposite effect. The mobility of doped films (2.43 × 10⁻⁵) is larger by two orders of magnitude than that of undoped films (5.64×10⁻⁷) at room temperature. In order to provide nanoscale information about the morphological properties of the undoped a:DLC films surface, we have used atomic force microscopoy (AFM). It was found that the roughness of our films increased with increasing thickness of the films, from 0.3 to 1.5 μm.     

Influence of UV-laser radiation on the synthesis of DLC films by ECR-plasma-CVD

Simultaneous UV-laser irradiation during the deposition of DLC films has been found to significantly influence the growth process and to favourably modify the film properties. The influence of the spectral and energetic parameters of laser radiation was investigated with respect to the optical, structural and mechanical properties of DLC films. Detailed investigations on the mechanism of laser-induced structural transformations in DLC films are presented, as studied by Raman spectroscopy. Further, the characteristic peak for the nanocrystalline diamond phase at 1140 cm⁻¹ was evident for irradiated films. Noteworthy is the increase in film microhardness with increasing energy of the deposited carbon ions with a simultaneous reduction in internal stresses, caused by photolytically induced modification of the film structure by UV-laser radiation. As a result, hard (up to 30 GPa) and thick (up to 3 μm) defect-free DLC films without cracks have been synthesized.     

DLC films by plasma assisted chemical vapor deposition near room temperature

This work concentrates on the preparation of diamond-like amorphous carbon films using a d.c. glow discharge with and without coupling to a microwave source. Films were deposited on single crystal silicon, glass and several plastics at temperatures between room temperature and 150°C. A variety of carbon containing feed gases have been used at pressures ranging from few milliTorrs to 1 Torr with an applied electric field up to 3300 V in⁻¹. The films obtained range from transparent to semi-transparent and can be very hard as observed by an ASTM scratch tester. The visible, IR and Raman spectra of the films have been obtained, and these are related to their structure and hardness. The DLC films grown on plastics were found to suffer from deformations due to the flexibility of the underlying material, and hence their performance was judged to be less than ideal despite the hardness of the overlying material. The results are discussed in terms of chemical composition and growth kinetics of the films.     

Characteristic of silver doped DLC films on surface properties and protein adsorption

Ag-incorporated diamond-like carbon (DLC) films were prepared on Si substrate using a hybrid deposition system composed of an end-Hall-type hydrocarbon ion gun and a silver DC magnetron sputter source. Ag was selected due to their potential values of biomaterial. The concentration of Ag in the films was varied from 0.1 to 9.7 at.% by controlling the fraction of Ar in the reaction gas mixture with benzene. In order to understand the influence of incorporated Ag on wettability, the surface energy and the protein adsorption as an indirect haemo-compatibility were measured. The surface energy of the Ag-incorporated DLC film decreased gradually with the increase of the Ag concentration. The haemo-compatibility was examined by the adsorption ratio of albumin/fibrinogen as an indirect method and improved with the increase of Ag concentration. The surface and biological behaviors of the films will be discussed in terms of the atomic bond characteristic and microstructure induced by Ag incorporation. Our results demonstrate that the Ag-incorporated DLC films are potentially useful as biomedical devices having good haemo-compatibility and hydrophobic characteristics.