Influence of bias voltage on diamond like carbon (DLC) film deposited on polyethylene terephthalate (PET) film surfaces using PECVD and its blood compatibility

In this paper, diamond like carbon (DLC) films were coated on polyethylene terephthalate (PET) film substrate as a function of biasing voltage using plasma enhanced chemical vapour deposition. The surface morphology of the DLC films was analyzed by scanning electron microscopy and atomic force microscopy. The chemical state and structure of the films were analyzed by X-ray photoelectrons spectroscopy and Raman spectroscopy. The micro hardness of the DLC films was also studied. The surface energy of interfacial tension between the DLC and blood protein was investigated using contact angle measurements. In addition, the blood compatibility of the films was examined by in vitro tests. For a higher fraction of sp³ content, maximum hardness and surface smoothness of the DLC films were obtained at an optimized biasing potential of ? 300 V. The in vitro results showed that the blood compatibility of the DLC coated PET film surfaces got enhanced significantly.     

Surface energy,wettability, and blood compatibility phosphorus doped diamond-like carbon films

There is an increasing interest in developing novel coatings to improve the biocompatibility of cardiovascular implants. In this work, we fabricated phosphorus-doped (P-doped) diamond-like carbon (DLC) films by plasma immersion ion implantation and deposition (PIII and D) and the structure, physicochemical characteristics, electrical properties, as well as surface biomedical compatibility, were evaluated using different characterization techniques. Microstructures manifesting as dots are visible under optical microscopy while atomic force micrographs disclose that these round and flat islands are distributed evenly on the film surface. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) results show that they are composed of C, P and O while only C and O can be found in the areas away from the islands. Attenuated total-reflection Fourier transform infrared spectroscopy (ATR-FTIR) spectroscopy indicates the presence of many PO_x and CP_xO_x species. In the Raman spectra, the G peak of the P-doped sample shifts to a lower wave-number suggesting that the film is more disordered. The P-doped DLC film exhibits excellent wettability (16.9° water contact angle). In vitro platelet adhesion and coagulation factor experiments were conducted to examine the blood compatibility. Scanning electron microscopy (SEM) and optical microscopy reveal a significant decrease of the number as well as activation of platelets on the P-doped DLC film.     

Preparation and blood compatibility of carbon/TiO2 nanocomposite

A carbon/TiO₂ nanocomposite, which consists of carbon film with various sp³C content and TiO₂ nanowire arrays, has been synthesized, in which the top surface of TiO₂ nanowire arrays prepared using hydrothermal method on fluorine-doped tin oxide glass were coated with carbon thin films. The carbon thin films with a higher, medium and lower sp³C content were deposited by pulsed magnetic filtered cathodic vacuum arc deposition, plasma-enhanced chemical vapor deposition and magnetron sputtering deposition, respectively. The surface morphology and structure of TiO₂ nanowire arrays were investigated by scanning electron microscopy, transmission electron microscope and X-ray diffraction. The sp³C content in carbon films was characterized using Raman spectroscopy. The blood compatibility of the samples including the TiO₂ nanowire arrays, carbon films and carbon/TiO₂ nanocomposite was assessed by tests of platelet adhesion in vitro. Results showed that the carbon/TiO₂ composite can effectively improve the anticoagulant function compared to the single materials. It is believed that the excellent blood compatibility of the carbon/TiO₂ nanocomposite is attributed to a joint function of surface properties adjusted by nanowire arrays and electronic structure of carbon thin films.     

Structure and mechanical properties of oxygen doped diamond-like carbon thin films

In this study, structure and mechanical properties of doped diamond-like carbon (DLC) films with oxygen were investigated. A mixture of methane (CH₄), argon (Ar) and oxygen (O₂) was used as feeding gas, and the RF-PECVD technique was used as a deposition method. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and a combination of elastic recoil detection analysis and Rutherford backscattering (ERDA-RBS). Nano-indentation tests were performed to measure hardness. Also, the residual stress of the films was calculated by Stoney equation. The XPS and ERDA-RBS results indicated that by increasing the oxygen in the feeding gas up to 5.6 vol.%, the incorporation of oxygen into the films' structure was increased. The ratio of sp² to sp³ sites was changed by the variation of oxygen content in the film structure. The sp²/sp³ ratios are 0.43 and 1.04 for un-doped and doped DLC films with 5.6 vol.% oxygen in the feeding gas, respectively. The Raman spectroscopy (RS) results showed that by increasing the oxygen content in doped DLC films, the amount of sp² CC aromatic bonds was raised and the hydrogen content reduced in the structure. The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the decrease of hydrogen content and the increase the ratio of CC aromatic to olefinic bonds. Hardness and residual stress of the films were raised by increasing the oxygen content within the films' structure. The maximum hardness (19.6 GPa) and residual stress (0.29 GPa) were obtained for doped DLC films, which had the maximum content of oxygen in structure, while the minimum hardness (7.1 GPa) and residual stress (0.16 GPa) were obtained for un-doped DLC films. The increase of sp³ CC bonds between clusters and the decrease of the hydrogen content, with a simultaneous increase of oxygen in the films' structure is the reason for increase of hardness and residual stress.     

The effect of CNT content on the surface and mechanical properties of CNTs doped diamond like carbon films

The carbon nanotubes (CNTs) doped diamond like carbon films were carried out by spinning coating multi-walled carbon nanotubes (CNTs) on silicon covered with diamond like carbon films via PECVD with C₂H₂ and H₂. The results show that the I_D/I_G and sp²/sp³ ratios are proportional to the CNT contents. For wettability and hydrogen content, the increase of CNT content results in more hydrophobic and less hydrogen for CNT doped DLC films. As for mechanical properties, the hardness and elastic modulus increases linearly with increasing CNT content. The residual stress is reduced for increasing CNT content. As for the surface property, the friction coefficient is reduced for higher CNT content. For CNT doped DLC films, the inclusion of horizontal CNT into DLC films increases the hardness, elastic modulus and reduces the hydrogen content, friction coefficient and residual stress. Like the light element and metal doping, the CNT doping has effects on the surface and mechanical properties on DLC which might be useful to specific application.     

Leakage current and dielectric breakdown in lanthanum doped amorphous aluminum oxide films prepared by sol–gel

Dielectric Al_2−2xLa_2xO₃ (x=0.00, 0.005, 0.02, 0.05, and 0.10) thin films were fabricated on Pt/Ti/SiO₂/Si substrates by sol–gel spin coating. The surface morphology of Al_2−2xLa_2xO₃ thin film was observed by field emission scanning electron microscopy. The chemical state of the lanthanum in aluminum oxide films was analyzed using X-ray photoelectron spectroscopy (XPS), indicating that lanthanum reacts with absorbed water to form lanthanum hydroxide. J–E measurements were used to investigate the current conduction mechanism and breakdown behavior. The results show that La doping changes the conduction mechanism and makes influences on leakage current. The dominating conduction process of 10% La doped Al₂O₃ films turns into the space charge limited current (SCLC) mechanism in the field region ranging from 25 to 150 MV/m. The leakage current of the films with 10% La doping decreases by three orders of magnitude from 10⁻⁶ to 10⁻⁹ at the electric field of 25 MV/m. The breakdown strength increases with the increasing content of lanthanum.     

Diamond-like carbon thin films by microwave surface-wave plasma CVD aimed for the application of photovoltaic solar cells

The nitrogen doped diamond-like carbon (DLC) thin films were deposited on quartz and silicon substrates by a newly developed microwave surface-wave plasma chemical vapor deposition, aiming the application of the films for photovoltaic solar cells. For film deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor (C₁₀H₁₆O) dissolved with ethyl alcohol (C₂H₅OH), methane (CH₄), ethylene (C₂H₄) and acetylene (C₂H₂). The optical and electrical properties of the films were studied using X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, atomic force microscope, electrical conductivity and solar simulator measurements. The optical band gap of the films has been lowered from 3.1 to 2.4 eV by nitrogen doping, and from 2.65 to 1.9 eV by experimenting with different hydrocarbon source gases. The nitrogen doped (flow rate: 5 sccm; atomic fraction: 5.16%) film shows semiconducting properties in dark (i.e. 8.1 × 10^{− 4} Ω^{− 1} cm^{− 1}) and under the light illumination (i.e. 9.9 × 10^{− 4} Ω^{− 1} cm^{− 1}). The surface morphology of the both undoped and nitrogen doped films are found to be very smooth (RMS roughness ≤ 0.5 nm). The preliminary investigation on photovoltaic properties of DLC (nitrogen doped)/p-Si structure show that open-circuit voltage of 223 mV and short-circuit current density of 8.3 × 10^{− 3} mA/cm². The power conversion efficiency and fill factor of this structure were found to be 3.6 × 10^{− 4}% and 17.9%, respectively. The use of DLC in photovoltaic solar cells is still in its infancy due to the complicated microstructure of carbon bondings, high defect density, low photoconductivity and difficulties in controlling conduction type. Our research work is in progress to realize cheap, reasonably high efficiency and environmental friendly DLC-based photovoltaic solar cells in the future.     

Tribological properties of DLC films with different hydrogen contents in water environment

Diamond-like carbon (DLC) films were deposited on silicon wafers by thermal electron excited chemical vapor deposition (CVD). To change the hydrogen content in film, we used three types of carbon source gas (C₇H₈, CH₄, and a CH₄+H₂) and two substrate bias voltages. The hydrogen content in DLC films was analyzed using elastic recoil detection analysis (ERDA). Tribological tests were conducted using a ball-on-plate reciprocating friction tester. The friction surface morphology of DLC films and mating balls was observed using optical microscopy and laser Raman spectroscopy.Hydrogen content in DLC films ranged from 25 to 45 at.%. In a water environment, the friction coefficient and specific wear rate of DLC films were 0.07 and in the range of 10⁻⁸–10⁻⁹ mm³/Nm, respectively. The friction coefficient and specific wear rate of DLC film in water were hardly affected by hydrogen content. The specific wear rate of DLC film with higher hardness was lower than that of film with low hardness. Mating ball wear was negligible and the friction surface features on the mating ball differed clearly between water and air environments, i.e., the friction surface on mating balls in water was covered with more transferred material than that in air.     

Tailoring the room temperature ferromagnetism in TiO2 nanoparticles by modulating the concentration of surface oxygen vacancy via La incorporating

La-incorporated TiO₂ nanoparticles (Ti_1-xLa_xO₂) were synthesized by a sol-gel method followed by vacuum annealing at 500 °C for 4 h, and were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman scattering spectroscopy, and vibrating sample magnetometer (VSM), respectively. The results indicated that La ions were incorporated with TiO₂ without distorting the tetragonal anatase structure, and a small amount of La ions were doped into TiO₂ lattice by substituting the surface Ti sites, whereas most of the La atoms evenly distribute into TiO₂ matrix in the form of La₂O₃. The incorporation of La ions with TiO₂ matrix modulates the concentration of surface oxygen vacancy in Ti_1-xLa_xO₂ nanoparticles. The room temperature ferromagnetism (RTFM) in Ti_1-xLa_xO₂ nanoparticles varies with the concentration of surface oxygen vacancy due to ferromagnetic coupling interactions between singly ionized oxygen vacancy, thus RTFM can be tailored by modulating the concentration of surface oxygen vacancy via La ions incorporating.     

Microstructure and mechanical properties of CeO2 doped diamond-like carbon films

A kind of rare earth oxide, CeO₂, was doped into the diamond-like carbon (DLC) films with thickness of 180–200 nm, using unbalanced magnetron sputtering. All the adhesion strength of CeO₂ doped DLC films is increased, while the residual compressive stress is obviously decreased compared to pure DLC film. Specially, the residual compressive stress of the deposited films are reduced by 90%, when the CeO₂ content is in the range of 5–7%, from a value of about 4.1 GPa to 0.5 GPa. When the CeO₂ content is increased to 10%, the deposited films possess the highest adhesion strength of 85 mN, 37% higher than that of pure DLC film. The nanohardness and elastic modulus exist a transition point at 8% of CeO₂ content within the DLC film. Before this value, nanohardness and elastic modulus of CeO₂ doped DLC films are lower than those of pure DLC film, and after this value, they are higher or adjacent to those of pure DLC film. Auger electron spectroscopy shows a more widened interface of 6% CeO₂ doped DLC film compared to pure DLC film. The enhancement of adhesion strength is mainly attributed to the widening of the film-substrate interface, as well as the decrease of residual compressive stress.     

Tuning magnetic properties of BiFeO3 thin films by controlling Mn doping concentration

Mn-doped BiFeO₃ (BiFe_1–xMn_xO₃, x = 0, 0.03, 0.05, 0.10, 0.15 and 0.20) polycrystalline multiferroic thin films were successfully synthesized using the facile sol-gel spin-coating method. The crystal structures, surface features, elements valences, and magnetic properties of as-prepared samples were systematically explored. X-ray diffraction and Raman spectroscopy studies revealed the substitutions of Mn into the Fe site and a rhombohedral-to-orthorhombic phase transition. The Field Emission Scanning Electron Microscopy showed a decrease in the average particle sizes and an improvement of surface morphology with increasing the concentration of the substitutes. Energy-dispersive X-ray spectroscopy confirmed the doping concentration of Mn²⁺ in the samples. X-ray photoelectron spectroscopy indicated the co-existence of Mn²⁺/Mn³⁺ ions in the doped films. The remnant magnetization value of BiFe_0.90Mn_0.10O₃ thin film was found to be approximately six times than that of pure BiFeO₃ thin film under a magnetic field of 10 kOe. The enhanced magnetic property of BiFe_0.90Mn_0.10O₃ thin film was mainly ascribed to the structural distortion of spin cycloid and the enhancement of super-exchange interaction between the Fe³⁺ (Mn²⁺) and O^2- ions.     

Characteristics and surface energy of silicon-doped diamond-like carbon films fabricated by plasma immersion ion implantation and deposition

Diamond-like carbon (DLC) films doped with different silicon contents up to 11.48 at.% were fabricated by plasma immersion ion implantation and deposition (PIII-D) using a silicon cathodic arc plasma source. The surface chemical compositions and bonding configurations were determined by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results reveal that the sp³ configuration including Si–C bonds increases with higher silicon content, and oxygen incorporates more readily into the silicon and carbon interlinks on the surface of the more heavily silicon-doped DLC films. Contact angle measurements and calculations show that the Si-DLC films with higher silicon contents tend to be more hydrophilic and possess higher surface energy. The surface states obtained by silicon alloying and oxygen incorporation indicate increased silicon oxycarbide bonding states and sp³ bonding states on the surface, and it can be accounted for by the increased surface energy particularly the polar contribution.     

A comparative study on lanthanum oxide and holmium oxide doped borate glasses

We have synthesized La₂O₃ and Ho₂О₃ doped borate glasses using conventional rapid melt quench method. The amorphous nature was identified using the XRD pattern. Photoluminescence spectrum and IR spectrum were used to analyze the spectral properties and differentiate the various vibrational modes. Also Raman spectroscopy of La₂O₃ and Ho₂О₃ doped borate glass was studied. The electrical properties such as the dielectric constant and the dielectric loss, of the La₂O₃ and Ho₂О₃ doped borate glass were studied at different frequencies and different temperatures.     

Characterization of luminescent SrAl2O4 films doped with terbium and europium ions deposited by ultrasonic spray pyrolysis technique

SrAl₂O₄, SrAl₂O₄:Tb³⁺ and SrAl₂O₄:Eu³⁺:Eu²⁺ films were synthesized by means of the ultrasonic spray pyrolysis technique. These samples, characterized by X-Ray Diffraction, showed the monoclinic phase of the strontium aluminate. Images of the surface morphology of these films were obtained by SEM and the chemical composition was measured by EDS and XPS. The photoluminescence and cathodoluminescence characteristics of the films were studied as a function of the terbium and europium concentrations. The optimal PL emission intensities were reached at 8?at% for terbium doped films and 6?at% for europium doped samples. The CL emission spectra for europium doped films showed the typical bands of Eu³⁺ ions and also a broadband centered at 525?nm which is attributed to Eu²⁺ ions. XPS measurements confirm the presence of Eu³⁺ and Eu²⁺ in europium doped SrAl₂O₄ films, without having been subjected to a reducing atmosphere. Chromatic diagrams exhibited green color for SrAl₂O₄:Tb³⁺ films, red and yellow colors for SrAl₂O₄:Eu³⁺:Eu²⁺ films. The PL decay curves were also obtained: the averaged decay time was 2.7?ms for SrAl₂O₄:Tb³⁺ films and 1.9?ms for SrAl₂O₄:Eu³⁺ films. Similar results were obtained by the stretched exponential model.     

Study on the diamond-like carbon multilayer films for tribological application

In this paper, DLC multilayer films consisting of alternating layers of soft and hard carbon films were deposited on Si wafer by a plasma CVD deposition system. Different DLC multilayer films were prepared by varying the sub-layer thickness (from 1000 to 25 nm) and the ratio of hard to soft sub-layer (H/S) thickness (from 1:1 to 4:1). By using a ball-on-disk tribo-tester, the friction and wear properties of the DLC multilayer films were measured in vacuum, O₂ and dry-air environments respectively. By comparing with single-layer DLC film, the change of the multilayer structure has little influence on friction coefficient of the multilayer films. However, the wear rate of the DLC multilayer films is restricted effectively by constructed the multilayer structure in the film. The wear rate of the multilayer films is lower than that of the single film in reactive (O₂ and dry-air) environments. An DLC multilayer film with excellent wear resistance, approximately in the level of 10⁻⁸ mm³/Nm in different environments (dry-air, O₂ and vacuum), is obtained as the DLC multilayer film at a certain sub-layer thickness and ratio.     

Tribological performance of hydrophilic diamond-like carbon coatings on Ti–6Al–4V in biological environment

Tribological performance of diamond-like carbon (DLC) and Si doped DLC (Si-DLC) films on Ti–6Al–4V under bovine serum as well as water and ambient air condition has been studied in terms of surface modification with O₂ plasma treatment for superhydrophilic surface. A tribo-test revealed that bovine serum significantly enhanced the tribological performance on all DLC surfaces in comparison with those under water or in air medium. Especially, O₂ plasma treated Si-DLC coatings with superhydrophilic nature were found to lower the wear and increase coating stability associated with macromolecules especially proteins in the bovine serum and their interactions with surfaces.     

Chemical grafting of sulfobetaine onto poly(ether urethane) surface for improving blood compatibility

Poly(ether urethane)s (PEUs) are widely used as blood‐contact biomaterials because of their good biocompatibility and mechanical properties. Nevertheless, their blood compatibility is still not adequate for more demanding applications. Surface modification is an effective way to improve blood compatibility and retain bulk properties of biomaterials. The purpose of the present study was to design and synthesis a novel non‐thrombogenic biomaterial by modifying the surface of PEU with zwitterionic monomer. In this study, sulfobetaine was grafted onto PEU surface through the following reaction steps: (1) Poly(propylene oxide) (PPO) was reacted at both chain ends with hexamethylene diisocyanate (HDI), and OCN–PPO–NCO was obtained; (2) OCN–PPO–NCO was reacted at one chain end with N,N‐dimethylethanolamine (DMEA) and OCN–PPO–N(CH₃)₂ was formed; (3) the sulfobetaine was prepared by a ring‐opening reaction between OCN–PPO–N(CH₃)₂ and 1,3‐propanesultone (PSu); (4) the sulfobetaine was grafted onto PEU surface by the reaction between NCO and the N–H bonds of PEU. The surface composition of films and the hydrophilicity on the PEU surface were investigated by X‐ray photoelectron spectroscopy analysis and contact angle measurements, respectively. The blood compatibility of PEU was evaluated by platelet‐rich plasma contact experiments and the results were observed by scanning electron microscopy. The state of platelet adhesion and shape variation for the attached platelets was described. The modified surface showed excellent blood compatibility, featured by low platelet adhesion. Copyright © 2003 Society of Chemical Industry     

Electrochemical properties of N-doped hydrogenated amorphous carbon films fabricated by plasma-enhanced chemical vapor deposition methods

Nitrogen-doped hydrogenated amorphous carbon thin films (a-C:N:H, N-doped DLC) were synthesized with microwave-assisted plasma-enhanced chemical vapor deposition widely used for DLC coating such as the inner surface of PET bottles. The electrochemical properties of N-doped DLC surfaces that can be useful in the application as an electrochemical sensor were investigated. N-doped DLC was easily fabricated using the vapor of nitrogen contained hydrocarbon as carbon and nitrogen source. A N/C ratio of resulting N-doped DLC films was 0.08 and atomic ratio of sp³/sp²-bonded carbons was 25/75. The electrical resistivity and optical gap were 0.695 Ω cm and 0.38 eV, respectively. N-doped DLC thin film was found to be an ideal polarizable electrode material with physical stability and chemical inertness. The film has a wide working potential range over 3 V, low double-layer capacitance, and high resistance to electrochemically induced corrosion in strong acid media, which were the same level as those for boron-doped diamond (BDD). The charge transfer rates for the inorganic redox species, Fe^2+/3+ and Fe(CN)₆^4−/3− at N-doped DLC were sufficiently high. The redox reaction of Ce^2+/3+ with standard potential higher than H₂O/O₂ were observed due to the wider potential window. At N-doped DLC, the change of the kinetics of Fe(CN)₆^3−/4− by surface oxidation is different from that at BDD. The rate of Fe(CN)₆^3−/4− was not varied before and after oxidative treatment on N-doped DLC includes sp² carbons, which indicates high durability of the electrochemical activity against surface oxidation.     

Multi-electrochromism behavior and electrochromic mechanism of electrodeposited molybdenum doped vanadium pentoxide films

Molybdenum doped vanadium pentoxide (Mo doped V₂O₅) films are prepared by cathodic electrodeposition on indium tin oxide substrate from Mo doped V₂O₅ sol. As an anodic and cathodic coloration electrochromic material, the electrodeposited Mo doped V₂O₅ film presents a better cycling stability, reversibility and multi-electrochromic behavior (orange-yellow-green-blue) with an optical modulation of 60-90% in the spectral region 550-900 nm, which can be expected as a result of enhanced electron intervalence transfer between Mo⁶⁺ and V⁵⁺, V⁴⁺ states, in addition to V⁵⁺ and V⁴⁺ transition. The electrochromic mechanism of Mo doped V₂O₅ films is investigated with atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. The surface roughness of the film increase at the different coloration states due to the increasing crystallinity degree. The change of the interlayer spacing for the host V₂O₅ and the change of the C and Li element states verify the insertion of organic solvent into the interlayer of the host V₂O₅ and some of the Li⁺ ions into the sites in the V-O layers. The electrochromic kinetics process indicates that the electrochromism of Mo doped V₂O₅ films can be considered as a reversible reduction/oxidation process accompanying the insertion/extraction of Li⁺ ions and electrons.     

The upconverted luminescence and chemical stability of morphologically controllable La2O3:Yb3+/Er3+ nanoparticles

Morphology and size controls are critical for the research of luminescent nanomaterials. In this work, La₂O₃:18%Yb³⁺/2%Er³⁺ nanoparticles were synthesized by a urea-assisted coprecipitation process, where the morphology and size of nanoparticles could be precisely controlled by adjusting the doping concentration, urea dosage and reaction time. With increasing Yb³⁺ doping concentration and reaction time, morphological evolution processes from nanosheets to nanospheres to nanofibers were observed. The experimental results revealed that the nanospheres could only be synthesized when 18%Yb³⁺ and 2%Er³⁺ were doped into the La₂O₃ host, where the size of the nanospheres could be precisely controlled by adjusting the urea dosage. The effects of the particle morphology and size on the upconversion luminescence of La₂O₃:18%Yb³⁺/2%Er³⁺ nanoparticles were investigated. In addition, the chemical stability of La₂O₃:18%Yb³⁺/2%Er³⁺ nanospheres in air was investigated by recording XRD and upconversion luminescence spectra after exposure to air for different periods. The experimental conclusions were useful for further probing the effects of the particle morphology and size on the upconversion emission of Er³⁺.