Preparation of diamond like carbon thin films above room temperature and their properties

Diamond like carbon (DLC) thin films were deposited on p-type silicon (p-Si), quartz and ITO substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) at different substrate temperatures (RT ∼ 300 °C). Argon (Ar: 200 sccm) was used as carrier gas while acetylene (C₂H₂: 20 sccm) and nitrogen (N: 5 sccm) were used as plasma source. Analytical methods such as X-ray photoelectron spectroscopy (XPS), FT-IR and UV–visible spectroscopy were employed to investigate the structural and optical properties of the DLC thin films respectively. FT-IR spectra show the structural modification of the DLC thin films with substrate temperatures showing the distinct peak around 3350 cm^− 1 wave number; which may corresponds to the sp² C–H bond. Tauc optical gap and film thickness both decreased with increasing substrate temperature. The peaks of XPS core level C 1 s spectra of the DLC thin films shifted towards lower binding energy with substrate temperature. We also got the small photoconductivity action of the film deposited at 300 °C on ITO substrate.     

Changes in chemical bonding of diamond-like carbon films by atomic-hydrogen exposure

We have deposited unhydrogenated diamond-like carbon (DLC) films on Si substrate by pulsed laser deposition using KrF excimer laser, and investigated the effects of atomic-hydrogen exposure on the structure and chemical bonding of the DLC films by photoelectron spectroscopy (PES) using synchrotron radiation and Raman spectroscopy. The fraction of sp³ bonds at the film surface, as evaluated from C1s spectra, increased at a substrate temperature of 400 °C by atomic-hydrogen exposure, whereas the sp³ fraction decreased at 700 °C with increasing exposure time. It was found that the sp³ fraction was higher at the surfaces than the subsurfaces of the films exposed to atomic hydrogen at both the temperatures. The Raman spectrum of the film exposed to atomic hydrogen at 400 °C showed that the clustering of sp² carbon atoms progressed inside the film near the surface even at such a low temperature as 400 °C.     

Electrical and optical properties of diamond-like carbon films deposited by pulsed laser ablation

Pulsed laser ablation of a graphite target was carried out by ArF excimer laser deposition at a laser wavelength of 193 nm and fluences of 10 and 20 J/cm² to produce diamond-like carbon (DLC) films. DLC films were deposited on silicon and quartz substrates under 1 × 10^? 6 Torr pressure at different temperatures from room temperature to 250 °C. The effect of temperature on the electrical and optical properties of the DLC films was studied. Laser Raman Spectroscopy (LRS) showed that the DLC band showed a slight increase to higher frequency with increasing film deposition temperature. Spectroscopic ellipsometry (SE) and ultraviolet–visible absorption spectroscopy showed that the optical band gap of the DLC films was 0.8–2 eV and decreased with increasing substrate temperature. These results were consistent with the electrical resistivity results, which gave values for the films in the range 1.0 × 10⁴–2.8 × 10⁵ Ω cm and which also decreased with deposition temperature. We conclude that at higher substrate deposition temperatures, DLC films show increasing graphitic characteristics yielding lower electrical resistivity and a smaller optical band gap.     

Silicon carbide films from polycarbosilane and their usage as buffer layers for diamond deposition

Thin films of polycarbosilane (PCS) were coated on a Si (100) wafer and converted to silicon carbide (SiC) by pyrolyzing them between 800 and 1150 °C. Granular SiC films were derived between 900 and 1100 °C whereas smooth SiC films were developed at 800 and 1150 °C. Enhancement of diamond nucleation was exhibited on the Si (100) wafer with the smooth SiC layer generated at 1150 °C, and a nucleation density of 2 × 10¹¹ cm^− 2 was obtained. Nucleation density reduced to 3 × 10¹⁰ cm^− 2 when a bias voltage of − 100 V was applied on the SiC-coated Si substrate. A uniform diamond film with random orientations was deposited to the PCS-derived SiC layer. Selective growth of diamond film on top of the SiC buffer layer was demonstrated.     

Polymeric semiconducting carbon from fullerene by pulsed laser ablation

The polymeric semiconducting carbon films are grown on silicon and quartz substrates by excimer (XeCl) pulsed laser deposition (PLD) technique using fullerene C₆₀ precursor. The substrate temperature is varied up to 300 °C. The structure and optical properties of the films strongly depend on the substrate temperature. The grain size is increased and uniform polymeric film with improved morphology at higher temperature is observed. The Tauc gap is about 1.35 eV for the film deposited at 100°C and with temperature the gap is decreased upto 1.1 eV for the film deposited at 250 °C and increased to about 1.4 eV for the film deposited at 300 °C. The optical absorption properties are improved with substrate temperature. Raman spectra show the presence of both G peak and D peak and are peaked at about 1590 cm^− 1 and 1360 cm^− 1, respectively for the film deposited at 100 °C. The G peak position remains almost unchanged while D peak has changed only a little with temperature might be due to its better crystalline structure compared to the typical amorphous carbon films and might show interesting in device such as, optoelectronic applications.     

Structure and properties of hard carbon films depending on heat treatment temperatures via polymer precursor

Phenylcarbyne polymer films were coated on silicon substrates and heat treated in 1 atm pressure of argon at various temperatures. The structural changes occurring during the heat treatment process of the polymer were investigated by Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The Raman and FTIR spectra features of the polymer showed a dependence on the heat treatment temperatures. At low temperatures (below 400°C), the Raman and IR spectra of the polymer were similar to those of the original polymer. The hardness and Young's modulus of the polymer films were below 1 and 50 GPa, respectively. With increasing temperature (above 400°C), thermal decomposition of the polymer occurred, resulting in structural changes of the polymer from soft amorphous hydrocarbon (400–600°C) phases to hard carbon phases (above 600°C). The hardness and Young's modulus increased from 1.5 and 65 GPa at 600°C to 9 and 120 GPa at 1000°C, respectively. It is assumed that the hard carbon film converted from the polymer might contain sp² and sp³ carbon phases; high temperature of heat treatment resulted in increasing sp² (glassy) carbon phase in the films.     

Synthesis and mechanical properties of carbon nanotube/diamond-like carbon composite films

Diamond-like carbon (DLC) coatings were successfully deposited on carbon nanotube (CNT) films with CNT densities of 1 × 10⁹/cm², 3 × 10⁹/cm², and 7 × 10⁹/cm² by a radio frequency plasma-enhanced chemical vapor deposition (CVD). The new composite films consisting of CNT/DLC were synthesized to improve the mechanical properties of DLC coatings especially for toughness. To compare those of the CNT/DLC composite films, the deposition of a DLC coating on a silicon oxide substrate was also carried out. A dynamic ultra micro hardness tester and a ball-on-disk type friction tester were used to investigate the mechanical properties of the CNT/DLC composite films. A scanning electron microscopic (SEM) image of the indentation region of the CNT/DLC composite film showed a triangle shape of the indenter, however, chippings of the DLC coating were observed in the indentation region. This result suggests the improvement of the toughness of the CNT/DLC composite films. The elastic modulus and dynamic hardness of the CNT/DLC composite films decreased linearly with the increase of their CNT density. Friction coefficients of all the CNT/DLC composite films were close to that of the DLC coating.     

Structural and electrical properties of Sr2NaNb4O13 thin film grown by electrophoretic method using nanosheets synthesized from K(Sr2Na)Nb4O13 compound

Sr₂NaNb₄O₁₃⁻ (SNNO⁻) nanosheets were exfoliated from the K(Sr₂Na)Nb₄O₁₃ compound that was synthesized at 1200 °C. The SNNO⁻ nanosheets were deposited on a Pt/Ti/SiO₂/Si substrate at room temperature by the electrophoretic method. Annealing was conducted at various temperatures to remove organic defects in the SNNO film. A crystalline SNNO phase without organic defects was formed in the film annealed at 500 °C. However, a SrNb₂O₆ secondary phase was formed in the films annealed above 600 °C, probably due to the evaporation of Na₂O. The SNNO thin film annealed at 500 °C showed a dielectric constant of 74 at 1.0 MHz with a dielectric loss of 2.2%. This film also exhibited a low leakage current density of 9.0 × 10⁻⁸ A/cm² at 0.6 MV/cm with a high breakdown electric field of 0.72 MV/cm.     

Pulsed laser deposition of hard and superhard carbon thin films from C60 targets

In the present study, carbon films were deposited by a pulsed laser deposition method. A C₆₀ fullerene target has been irradiated by a frequency doubled Nd:YAG laser with a pulse duration of 7 ns. The carbon films grown on Si(111) substrates at different substrate deposition temperatures (30, 300 and 500 °C) were characterized by Raman, X-ray Photoelectron and X-ray Auger Electron Spectroscopies, Energy Dispersive X-Ray Diffraction, Scanning Electron and Atomic Force Microscopies, and Vickers microhardness technique. The composition, structure, morphology and mechanical properties of films were found to be strongly dependent on the substrate temperature. At 30 °C and 300 °C deposition temperature, superhard and hard diamond-like films have been obtained, respectively. In the case of 500 °C deposition, a hard film, composed of crystalline C₆₀ and diamond-like carbon, has been prepared.     

Very hard ZrC thin films grown by pulsed laser deposition

Thin ZrC films were grown on (1 0 0) Si substrates at temperatures from 30 to 500 °C by the pulsed laser deposition technique. Auger electron spectroscopy investigations found that films contained oxygen concentration below 2.0 at%, while X-ray photoelectron spectroscopy investigations showed that oxygen is bonded in an oxy-carbide type of compound. The films’ mass densities, estimated from X-ray reflectivity curve simulations, and crystallinity improved with the increase of the substrate temperature. Williamson–Hall plots and residual-stress measurements using the modified sin² ψ method for grazing incidence X-ray diffraction showed that the deposited films are nanostructured, with crystallite sizes from 6 to 20 nm, under high micro-stress and compressive residual stress. Nanoindentation investigations found hardness values above 40 GPa for the ZrC films deposited at substrate temperatures higher than 300 °C. The high density of the deposited films and the nm-size crystallites are the key factors for achieving such high hardness values.     

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.     

Thermal stability and mechanical properties of HVOF/PVD duplex ceramic coatings produced by HVOF and cathodic vacuum arc

Duplex ceramic coatings, consisting of an inner NiCr-Cr₃C₂-based coating and an outmost AlCrN film, were produced on the steel substrate in succession by velocity oxygen-fuel spraying (HVOF) and cathodic vacuum arc methods, and then isochronally annealed at annealing temperatures below 900 °C for 2 h. The thermal stability and mechanical properties of the annealed samples were systematically studied by means of X-ray diffraction, Optical microscope and transmission electron microscope, in association with mechanical property measurements. The results show that the microstructure, phase evolution and mechanical properties of duplex ceramic coatings are significantly dependent on the annealing temperature. Metastable fcc-AlCrN solid solution in AlCrN film first decomposes to rich-Al and rich-Cr domains by spinodal decomposition at 700 °C, leading to a notable increase in hardness due to its smaller grain size and high elastic strain field, and then to equiaxed hcp-AlN and Cr₂N by the nucleation and growth at 900 °C, leading to a notable decrease in hardness due to the recrystallization and the formation of hcp-AlN. Meanwhile, the both decarburization of Cr₃C₂ to Cr₇C₃ occurs at 800 °C, but becomes more intensive at 900 °C, leading to a notable loss in hardness. In addition, the dissolution of Cr₃C₂ produces high density of porosity, which also reduces the hardness. The hardness tests show the following ordering of load-bearing capacity for the duplex ceramic coatings: 700 °C>As-deposited >800 °C>900 °C. Tribological property measurements demonstrate that the wear resistance of the tested duplex ceramic coatings obeys the following ordering: 700 °C>As-deposited >800 °C>900 °C. The improved wear resistance is due to high surface hardness, load-bearing capacity and thermal stability. In addition, the wear mechanisms are shown.     

Structural,optical, and electrical properties of conducting p-type transparent Cu–Cr–O thin films

Cu–Cr–O films were prepared by DC magnetron co-sputtering using Cu and Cr targets on quartz substrates. The films were then annealed at temperatures ranging from 400 °C to 900 °C for 2 h under a controlled Ar atmosphere. The as-deposited and 400 °C-annealed films were amorphous, semi-transparent, and insulated. After annealing at 500 °C, the Cu–Cr–O films contained a mixture of monoclinic CuO and spinel CuCr₂O₄ phases. Annealing at 600 °C led to the formation of delafossite CuCrO₂ phases. When the annealing was further increased to temperatures above 700 °C, the films exhibited a pure delafossite CuCrO₂ phase. The crystallinity and grain size also increased with the annealing temperature. The formation of the delafossite CuCrO₂ phase during post-annealing processing was in good agreement with thermodynamics. The optimum conductivity and transparency were achieved for the film annealed at approximately 700 °C with a figure of merit of 1.51×10⁻⁸ Ω⁻¹ (i.e., electrical resistivity of up to 5.13 Ω-cm and visible light transmittance of up to 58.3%). The lower formation temperature and superior properties of CuCrO₂ found in this study indicated the higher potential of this material for practical applications compared to CuAlO₂.     

The influence of ion beam assisted deposition parameters on the properties of boron nitride thin films

We studied ion beam assisted deposition of cubic boron nitride thin films on silicon (100) and high speed steel. The boron nitride films were grown by the electron beam evaporation of pure boron (99.4%) and the simultaneous ion bombardment of a mixture of nitrogen and argon ions from a Kaufman ion source. At a constant boron evaporation rate, the ion energy, ion current density, substrate temperature and process gas mixture was varied. The thickness of the films was kept between 200 and 300 nm. Boron nitride films with >80% of the cubic phase (determined by Fourier transform infrared spectroscopy) were obtained with nitrogen/argon mixtures of 50/50 at ion energies of 450 eV and substrate temperatures of 400°C. The current density amounted to 0.45 mA cm⁻² at a nominal boron rate of 200 pm s⁻¹. Cubic boron nitride films were deposited on high speed steel by introducing a titanium interlayer for adhesion improvement.     

Localized DLC etching by a non-thermal atmospheric-pressure helium plasma jet in ambient air

Using a versatile atmospheric-pressure helium plasma jet, diamond-like carbon (DLC) films were etched in ambient air. We observed that the DLC films are etched at a nominal rate of around 60 nm/min in the treated area (230 μm in diameter) during a 20-min exposure. The etching rate increased after the initial 10-min exposure. During this period, the flat DLC surface was structurally modified to produce carbon nanostructures with a density of ~ 2.4 × 10¹¹ cm^− 2. With this increase in surface area, the etching rate increased. After 20 min, the DLC film had a circular pattern etched into it down to the substrate where silicon nanostructures were observed with sizes varying from 10 nm to 1 μm. The initial carbon nanostructure formation is believed to involve selective removal of the sp²-bonded carbon domains. The carbon etching results from the formation of reactive oxygen species in the plasma.     

High-temperature deformation behavior in SrTiO3 ceramics

The high-temperature deformation behavior of a polycrystalline strontium titanate (SrTiO₃) ceramic (6 μm grain size) was investigated at temperatures of 1200–1345 °C in an argon atmosphere. Compressive deformation tests were conducted at strain rates ranging from 5 × 10⁻⁶ to 5 × 10⁻⁵ s⁻¹. Steady-state flow stresses were 0.05–30 MPa and increased with increasing strain rates. Stress exponents of ≈1, at temperatures >1200 °C, indicated a viscous diffusion-controlled deformation with an activation energy of ≈628 ± 24 kJ/mol. Comparison of activation energy with literature data suggests diffusion of cations as the rate-controlling mechanism. Absence of cavitation and grain-shape changes were consistent with grain-boundary sliding as the principal deformation mechanism. The electron back-scattered diffraction (EBSD) technique was used to determine the grain orientation as a function of applied strain. The results indicate that some of the grains rotate with cumulative rotation as large as 7° at a strain of 4%.     

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.     

Sputtering deposition of transparent conductive F-doped SnO2 (FTO) thin films in hydrogen-containing atmosphere

F-doped SnO₂ (FTO) thin films have been prepared by sputtering SnO₂-SnF₂ target in Ar+H₂ atmosphere. The effects of H₂/Ar flow ratio on the structural, electrical and optical properties of the films were investigated at two substrate temperatures of 150 and 300 °C and two base pressures of 3.5×10⁻³ and 1.5×10⁻² Pa. The results show that introducing H₂ into sputtering atmosphere can lead to the formation of a FTO film with a (101) preferred orientation and produce oxygen vacancy (V_O) at lower H₂/Ar flow ratios, but SnO phase at higher H₂/Ar flow ratios in the films. Accordingly, the resistivity of the films first decreases and then increases, but the transmittance decreases continuously with increasing H₂/Ar flow ratio. When H₂/Ar flow ratio is increased above a certain value, more amorphous SnO phase forms in the films, resulting in a big decrease in conductivity, transmittance, and band gap (E_g). Increasing substrate temperature can increase the Hall mobility due to the improvement of film crystallinity, but decrease the carrier concentration due to outward-diffusion of fluorine in the films. At a base pressure of 3.5×10⁻³ Pa, high substrate temperature (300 °C) can hinder the formation of SnO and thus improve the transparent conductive properties of the films. At a base pressure of 1.5×10⁻² Pa, the range of H₂/Ar flow ratio for forming the SnO₂ phase and hence for obtaining high transparent conductive FTO films is widened at both substrate temperatures of 150 and 300 °C.     

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.     

Fabrication of fluorine-terminated diamond-like carbon thin film using a hyperthermal atomic fluorine beam

Surface modification of diamond-like carbon (DLC) film was performed using a hyperthermal atomic fluorine beam on the purpose of production of hydrophobic surface by maintaining the high hardness of DLC film. By the irradiation of atomic fluorine beam of a 1.0 × 10²⁰ atoms/cm², the contact angle of a water drop against the DLC surface increased from 73° to 111°. The formation of CF₃, CF₂ and CF bonding on the modified DLC surface was confirmed from the measurements of X-ray photoelectron spectra and near-edge X-ray absorption fine structure spectra. Irradiation of hyperthermal atomic fluorine beam was concluded to produce insulator fluorine-terminated DLC film, which has high F content on the surface, by the taking of the use of neutral atomic beam as a fluorine source.