Diamond-like Nanocomposite Films Research Articles

Femtosecond Laser-Induced Periodic Surface Structures in Titanium-Doped Diamond-like Nanocomposite Films: Effects of the Beam Polarization Rotation.

We study the properties of laser-induced periodic surface structures (LIPSS) formed on titanium-doped diamond-like nanocomposite (DLN) a-C:H:Si:O films during ablation processing with linearly-polarized beams of a visible femtosecond laser (wavelength 515 nm, pulse duration 320 fs, pulse repetition rates 100 kHz-2 MHz, scanning beam velocity 0.05-1 m/s). The studies are focused on (i) laser ablation characteristics of Ti-DLN films at different pulse frequencies and constant fluence close to the ablation threshold, (ii) effects of the polarization angle rotation on the properties of low spatial frequency LIPSS (LSFL), and (iii) nanofriction properties of the 'rotating' LIPSS using atomic force microscopy (AFM) in a lateral force mode. It is found that (i) all LSFL are oriented perpendicular to the beam polarization direction, so being rotated with the beam polarization, and (ii) LSFL periods are gradually changed from 360 ± 5 nm for ripples parallel to the beam scanning direction to 420 ± 10 nm for ripples formed perpendicular to the beam scanning. The obtained results are discussed in the frame of the surface plasmon polaritons model of the LIPSS formation. Also, the findings of the nanoscale friction behavior, dependent on the LIPSS orientation relative to the AFM tip scanning direction, are presented and discussed.

Femtosecond laser-induced periodic surface structures on diamond-like nanocomposite films

We study the formation of laser-induced periodic surface structures (LIPSS) on diamond-like nanocomposite (DLN) a-C:H:Si:O films and titanium-doped DLN films during femtosecond (fs) laser ablation processing with linearly-polarized beams of IR and visible fs-lasers (wavelengths 1030 nm and 515 nm, pulse duration 320 fs, pulse repetition rates 100 kHz-2 MHz, scanning beam velocity 0.04–0.4 m/s). The studies are focused on (i) comparison of high spatial frequency LIPSS (HSFL) and low spatial frequency LIPSS (LSFL) formed on DLN and Ti-DLN films by IR fs-laser processing, (ii) effects of the pulse repetition rate on the parameters of LIPSS formed on the DLN and Ti-DLN films, (iii) Raman spectroscopy analysis of the LIPSS-structured films with application for ultrathin surface graphitization, and (iv) relationship between the fs-laser-induced surface graphitization and LIPSS formation on the films. A variety of the HSFL and LSFL have been produced on the surface of DLN and Ti-DLN films, with all the LIPSS being oriented perpendicular to the beam polarization direction. The HSFL periods are varied from ~80 to 240 nm and the LSFL periods are varied from 355 to 840 nm, depending on the fs-laser irradiation conditions (wavelength, fluence, pulse repetition rate) and films properties. Various plasmonic effects such as the superposition of the HSFL and LSFL and emergence of very unusual sinusoid-like structures on the DLN and Ti-DLN films are presented and discussed. • LIPSS fabrication on DLN and Ti-DLN films with IR and visible femtosecond lasers • Effect of surface graphitization on HSFL and LSFL formation thresholds • Raman analysis of ultrathin surface graphitization on LIPSS-structured DLN films • Influence of pulse repetition rate on fs-laser ablation and LIPSS parameters • Plasmonic effects in the fs-LIPSS formation on diamond-like nanocomposite films

Sub-Threshold Fabrication of Laser-Induced Periodic Surface Structures on Diamond-like Nanocomposite Films with IR Femtosecond Pulses.

In the paper, we study the formation of laser-induced periodic surface structures (LIPSS) on diamond-like nanocomposite (DLN) a-C:H:Si:O films during nanoscale ablation processing at low fluences—below the single-pulse graphitization and spallation thresholds—using an IR fs-laser (wavelength 1030 nm, pulse duration 320 fs, pulse repetition rate 100 kHz, scanning beam velocity 0.04–0.08 m/s). The studies are focused on microscopic analysis of the nanostructured DLN film surface at different stages of LIPSS formation and numerical modeling of surface plasmon polaritons in a thin graphitized surface layer. Important findings are concerned with (i) sub-threshold fabrication of high spatial frequency LIPSS (HSFL) and low spatial frequency LIPSS (LSFL) under negligible surface graphitization of hard DLN films, (ii) transition from the HSFL (periods of 140 ± 30 and 230 ± 40 nm) to LSFL (period of 830–900 nm) within a narrow fluence range of 0.21–0.32 J/cm2, (iii) visualization of equi-field lines by ablated nanoparticles at an initial stage of the LIPSS formation, providing proof of larger electric fields in the valleys and weaker fields at the ridges of a growing surface grating, (iv) influence of the thickness of a laser-excited glassy carbon (GC) layer on the period of surface plasmon polaritons excited in a three-layer system “air/GC layer/DLN film”.

Tribological Performance of Diamond-like Nanocomposite Coatings: Influence of Environments and Laser Surface Texturing

Diamond-like nanocomposite (DLN) films (a-C:H:Si:O films) are characterized by their unique structure and remarkable tribological properties to be pronounced under various environmental and surface modification conditions. In this paper, we investigated the effects of environments (humid air, water and oil lubrication, elevated temperatures) and laser surface texturing on tribological performance of DLN coatings. Femtosecond laser (wavelength 515 nm) was used for surface texturing. Comparative tests of DLN films sliding against different counterbodies (steel, Si3N4) in humid air and water demonstrated the low-friction and low-wear performance under water, in the absence of chemical interaction of water with the counterbody surface. The wear rates of the film and Si3N4 ball in water, 7.5 × 10−9 and 2.6 × 10−9 mm3/(Nm), were found to be considerably lower than the corresponding values 6.8 × 10−7 and 3.8 × 10−8 mm3/(Nm) in humid air, in spite of higher friction in water-lubricated sliding. Laser surface texturing of DLN films was performed to fabricate microcrater arrays, followed by tribological testing under oil lubrication at different temperatures, from 23 to 100 °C. The lubricated friction performance of laser-textured films was improved at both the room temperature and elevated temperatures. The friction coefficient was reduced from 0.1 (original film) to 0.083 for laser-textured film at room temperature, and then to 0.068 at 100 °C. The nano-/microfriction behavior of laser-structured surface characterized by lower friction forces than the original surface was demonstrated using friction force microscopy in ambient air. The obtained results demonstrate excellent tribological properties of DLN coatings in various environments, which can be further improved by femtosecond-laser-surface texturing.

Effect of diamond-like nanocomposite as antireflection layer on multi-crystalline silicon solar cells

Silicon nitride (SiNX) is conventionally used as antireflection coating (ARC) on p-type Silicon solar cells. But synthesis of SiNX involves two toxic and highly flammable gases ammonia (NH3) and silane (SiH4). To overcome this, an alternative material instead of SiNx was investigated. Diamond-like nanocomposite (DLN) is such a material whose deposition as ARC follows less hazardous pathway and produces better performance in many respect compare to SiNX. DLN film is deposited by a radio frequency plasma enhanced chemical vapour deposition (rfPECVD) process by using liquid precursor Hexamethyl disilazane (HMDSN) in argon (Ar) plasma. In this paper, the authors have compared electrical and optical parameters of multicrystalline silicon solar cells (mc-Si) for two different antireflection coatings SiNx and DLN. DLN film is characterized by FTIR and Raman spectroscopy. Optical properties are estimated by UV–Vis-NIR spectrophotometer. Electrical properties are measured by I-V simulator under 1.5 AM condition. The minimum reflection has been achieved 4.86% at 797 nm wavelength. The short circuit current density, JSC and open circuit voltage, VOC have been achieved from finished mc-Si solar cell are 32.54 mA/cm2 and 0.582 V respectively. Results prompt to conclude that DLN as ARC is comparable to SiNX. Thus silane and ammonia free DLN deposition as ARC, could be a good alternative of SiNX.

Effect of tungsten doping on laser ablation and graphitization of diamond-like nanocomposite films

Laser surface microstructuring of diamond-like nanocomposite (DLN) films is a promising technique to improve their properties. For industrial applications, UV excimer or IR lasers with high pulse repetition rate are commonly used. In this paper, we investigate the influence of metal (tungsten) doping of DLN film on the ablation and graphitization behavior of the films using KrF laser (λ = 248 nm, τ = 20 ns) and Yb:Yag laser (λ = 1030 nm, τ = 8 ps). The response is found to be sensitive to the laser wavelength and pulse duration. For UV ns-pulses, the ablation threshold is insensitive to W-doping, showing only a slight increase for the highest tungsten concentration of 27 at.%, while the ablation rate decreases. Conversely, an increase of tungsten content in the case of the irradiation by IR ps-pulses induces a drop in the ablation threshold and an increase in the ablation rate. The structural modification of the films is analyzed by Raman spectroscopy, which also allows us to estimate the thickness of a residual graphitized layer on the surface after laser irradiation. It is found that laser-induced graphitization is stronger for doped DLN films after multipulse irradiation.

Effects of titanium doping on the structure and mechanical properties of diamond-like nanocomposite films

In this paper, we report on comparative studies of mechanical properties of diamond-like nanocomposite (DLN) a-C:H:Si:O films and titanium-doped DLN films, which were focused on (i) nanoindentation and internal stress examination of DLN films of different thickness (up to 10 μm) and (ii) structural transformations and mechanical properties changes with increasing titanium content in Ti-DLN films. The DLN films were found to combine high hardness of 22–24 GPa, high elastic recovery, and low compressive stresses of 100–160 MPa. For Ti-DLN films, the hardness, elastic modulus, and residual stress were found to exhibit similar behavior vs Ti content: an initial decrease at low Ti contents was followed by gradual increase of the hardness, elastic modulus and compressive stresses. The mechanical properties changes were shown to correlate with the structure modifications induced by titanium incorporation into the DLN matrix. Raman spectra of Ti-DLN films revealed three peaks in the low-frequency region from 200 to 700 cm−1, attributed to the TiC phase. An additional evidence of the formation of TiC nanocrystals of several nanometers size was obtained using transmission electron microscopy (TEM) of Ti-DLN films. The findings of Raman spectroscopy along with the TEM data have demonstrated the main factors – formation of TiC nanocrystals and increase of the sp2-carbon content, responsible for the mechanical behavior of Ti-DLN films.

Femtosecond-laser-ablation induced transformations in the structure and surface properties of diamond-like nanocomposite films

Femtosecond laser ablation processing is applied for surface modification and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films). Using a visible femtosecond laser (wavelength 515 nm, pulse duration 320 fs), microgroove patterns have been fabricated on the DLN films, aimed at further studies of their properties. The studies were focused on (i) structural transformations in the surface layers using Raman spectroscopy and transmission electron microscopy (TEM), (ii) wettability of laser-patterned films, and (iii) nano/microscale friction properties of laser-patterned DLN films using lateral force microscopy. Raman spectroscopy and TEM data showed characteristic features of the surface graphitization during ultrashort-pulse ablation. High resolution TEM study of the microgrooves revealed the formation of cubic SiC nanocrystals (4–8 nm size) on the laser-ablated surface. The water contact angle measurements showed anisotropic wetting behavior of the grooved surfaces (the contact angle was different in the directions parallel and perpendicular to microgrooves), depending on the groove depth (aspect ratio). Lateral force microscopy examination (with micro-sized Si tips) showed that the laser-patterned regions exhibited low friction properties compared to the original surface. The obtained results demonstrate that femtosecond laser processing is an effective technique to generate new properties of hard DLN coatings at the micro and macroscale.

Low temperature growth of diamond-like nanocomposite films prepared by PACVD from Ar diluted siloxane plasma

Here, the diamond-like films in composite of nanostructure form are grown at low temperature (∼100 °C) from siloxane precursor incorporating silicon oxide (SiOx) moiety in amorphous carbon hydrogen (a-C:H) network using radio frequency plasma assisted chemical vapour deposition (rf-PACVD) method on various substances including ultra high molecular weight polyethylene (UHMWPE) substrates with the change in argon (Ar) carrier gas flow rate. The deposited diamond-like nanocomposite (DLN) films have been characterized using different spectroscopic techniques and tribological tests to understand the optimum deposition condition. The biocompatible nature of superior DLN film makes it a promising articulate knee and hip joint coating material.

High Temperature Characterization of a MIS Schottky Diode Based on Diamond-Like Carbon Nanocomposite Film

Many kind of materials have been inserted between metals and semiconductors to obtain metal–interlayer–semiconductor (MIS) Schottky diodes with higher barrier height. It is well known that the interlayer materials have to meet some requirements such as hold on the substrate, thermal stability and wear resistance. In this context, the diamond-like carbon (DLC) films seem good candidates as a material that can fulfill these requirements due to their superior properties. In this study, sulfur doped diamond-like carbon (S-DLC) nanocomposite film was deposited electrochemically, and it was used as an interlayer to fabricate an Au/S-DLC/p-Si MIS Schottky diode. An Au/p-Si metal semiconductor diode was also fabricated for comparison. The electrodeposited S-DLC film was characterized by scanning electron microscopy, Raman spectroscopy and x-ray photoelectron spectroscopy. Temperature dependence of the current–voltage (I–V) characteristic of the diodes was studied in the range of 300–700 K. The ideality factors (n) and barrier heights (Φb) were calculated from the forward bias I–V characteristics. It was observed that both parameters showed temperature dependence. Barrier height values were increased with increasing temperature, while ideality factors values were decreased. The observed non-linearity in Richardson plots were explained by Gaussian distributions of inhomogeneities of barrier heights. Modified Richardson plots were used to obtain actual values of barrier height. It was shown that S-DLC film can be a good candidate for the high temperature diode applications.

Heat accumulation effects in laser processing of diamond-like nanocomposite films with bursts of femtosecond pulses

In this paper, we have investigated the burst mode (BM) ablation and surface structuring of diamondlike nanocomposite (DLN) a-C:H:Si:O films with femtosecond laser pulses (wavelength λ = 515 nm, pulse duration τ = 320 fs, and pulse repetition rate f = 100 kHz) under different scanning conditions (single spots and linear structures). The pulse separation in the bursts is 25 ns (intraburst frequency f = 40 MHz), and the pulse number is varied from 1 to 8. The ablation depth and specific ablation rates (μm3/μJ) are found to be higher for the burst mode compared to single-pulse irradiation, increasing with the pulse number in the burst. The obtained experimental data of the higher ablation efficiency are shown to correlate with computer simulations of the BM ablation. In correlation with the ablation findings, Raman spectra of single spots and microgrooves have evidenced a growing graphitization of the amorphous film structure with the pulse number in the bursts (at an equal energy deposited into the films). Contact-mode atomic force microscopy (AFM) is applied to reveal an influence of the BM processing on the surface properties (nanoscale relief, friction) of laser-structured films. Based on the ablation and Raman data analysis, AFM examination of ablated/redeposited layers, and computer simulations of the burst mode ablation, the heat accumulation is identified as the main factor responsible for the enhanced ablation efficiency during the BM processing of DLN films. In addition, results of the high precision surface microstructuring of DLN films in the burst mode are presented.

Femtosecond laser surface texturing of diamond-like nanocomposite films to improve tribological properties in lubricated sliding

We report on femtosecond laser ablation and surface micropatterning (texturing) of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films), aimed to improve tribological properties of laser-patterned films under lubricated sliding conditions. Femtosecond laser system generating pulses of 320-fs duration at the wavelength 515 nm is applied. Femtosecond laser ablation of 2.7-μm-thick DLN films is studied to determine optimum irradiation parameters for laser surface texturing with the requirements of the minimal spot size, high ablation rate, surface quality and pattern depth less than the film thickness. Periodic microcrater patterns (with 10 μm diameter, 2.2 μm depth, and different area density of microcraters) have been fabricated on the DLN films over the areas of 6 mm × 10 mm size. Tribological tests of the original and laser-patterned DLN films are performed using a ball-on-flat tribometer under linear reciprocating sliding against 100Cr6 steel balls in the presence of oil lubrication (engine oils of low and high viscosity). The ball-on-flat investigations have demonstrated the reduced friction and wear properties of the laser-textured DLN films, depending on the area density of microcraters and lubrication conditions. The obtained results evidence that femtosecond laser surface texturing is an effective technique to improve lubricated sliding performance of the DLN coatings.

Effects of AFM tip wear on frictional images of laser-patterned diamond-like nanocomposite films

Effects of AFM tip wear on frictional images of laser-patterned diamond-like nanocomposite films

Effects of AFM tip wear on frictional images of laser-patterned diamond-like nanocomposite films

Contact-mode atomic force microscopy (AFM) techniques (lateral force microscopy, force-distance curves) are applied to study the effects of femtosecond-laser ablation and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films) on the friction behavior at the nano and microscale. A femtosecond laser (wavelength 515 nm, pulse duration 320 fs, pulse repetition rate 101 kHz) is used to fabricate line-like micropatterns (microgrooves) on the DLN films under ablation conditions with a scanning beam. Lateral force microscopy (LFM) studies of the laser-ablated microgrooves have revealed wearing-tip-induced nanofriction changes during AFM imaging with Si tip, characterized by much lower friction forces inside and around the microgrooves compared to the original surface (due to strong influence of the capillary forces on friction forces with increasing radius of the worn tip). Using wear-resistant diamond-coated tips, the friction contrast is found to reverse to higher friction in the laser-modified regions. The increased nanoscale roughness of the ablated DLN surface and redeposited surface layers is considered responsible for the observed nanofriction behavior of both the Si and diamond-coated tips.

Nanostructuring of Titanium-Doped Diamond-Like Nanocomposite Films via Electric Probe Lithography

The influence of titanium doping of diamond-like nanocomposite films a-C:H,Si:O on the process of their structuring by the technique of bias-induced probe nanolithography of the scanning probe microscope (SPM) was studied. It has been found that titanium doping suppresses formation of dendritic-like structures that grow in undoped a-C:H,Si:O films at relative humidity above 50%. Instead of dendritic-like nanostructures, hill-like protrusions arise. At the same time, a decrease in the electrical conductivity and an increase in the friction forces in the modified region are close to those on films without metal. The mechanisms of the observed effects are discussed.

Femtosecond-laser surface modification and micropatterning of diamond-like nanocomposite films to control friction on the micro and macroscale

Laser surface micropatterning (texturing) of hard materials and coatings is an effective technique to improve tribological systems. In the paper, we have investigated the laser-induced surface modifications and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H,Si:O) using IR and visible femtosecond (fs) lasers, focusing on the improvement of frictional properties of laser-patterned films on the micro and macroscale. The IR and visible fs-lasers, operating at λ = 1030 nm and λ = 515 nm wavelengths (pulse duration 320 fs and pulse repetition rate 101 kHz), are used to fabricate different patterns for subsequent friction tests. The IR fs-laser is applied to produce hill-like micropatterns under conditions of surface graphitization and incipient ablation, and the visible fs-laser is used for making microgroove patterns in DLN films under ablation conditions. Regimes of irradiation with low-energy IR laser pulses are chosen to produce graphitized micropatterns. For these regimes, results of numerical calculations of the temperature and graphitized layer growth are presented to show good correlation with surface relief modifications, and the features of fs-laser graphitization are discussed based on Raman spectroscopy analysis. Using lateral force microscopy, the role of surface modifications (graphitization, nanostructuring) in the improved microfriction properties is investigated. New data of the influence of capillary forces on friction forces, which strongly changes the microscale friction behaviour, are presented for a wide range of loads (from nN to μN) applied to Si tips. In macroscopic ball-on-disk tests, a pair-dependent friction behaviour of laser-patterned films is observed. The first experimental data of the improved friction properties of laser-micropatterned DLN films under boundary lubricated sliding conditions are presented. The obtained results show the DLN films as an interesting coating material suitable for laser patterning applications in tribology.

Femtosecond laser microstructuring of diamond-like nanocomposite films

We report on femtosecond laser surface modification and microstructuring of diamond-like nanocomposite (DLN) films (a-C:H,Si:O), and investigation of the frictional properties of laser-micropatterned DLN films on the nano, micro and macroscale. DLN films of 2–3μm thickness were irradiated using a femtosecond laser (wavelength 1030nm, pulse duration 320fs, pulse repetition rate 101kHz) to produce periodic linear micropatterns over the areas of 40mm2. Laser irradiation was performed at low fluences (below the single-pulse ablation threshold) corresponding to the conditions of surface graphitization and incipient ablation developing during the multipulse irradiation. Frictional properties of laser-micropatterned DLN films were studied using (i) lateral force microscopy (LFM) and (ii) ball-on-flat tribometer under linear reciprocating sliding against 100Cr6 steel and Si3N4 balls. The LFM measurements revealed significant changes in the friction behavior of the laser-patterned films during transition from nano to microscale, demonstrating much lower friction forces within laser-graphitized strips than on the original film. Such microfriction behavior was attributed to (i) higher hydrophobicity of laser-graphitized nanostructured surface and (ii) strong influence of capillary forces of adsorbed water layers on friction under the ‘nano’ loads. Macroscopic friction properties of the fs-laser-patterned DLN films were shown to depend on the friction pair (DLN vs steel ball, DLN vs Si3N4 ball), both at the initial stage of sliding and during prolonged sliding tests.

Effects of UV laser micropatterning on frictional performance of diamond-like nanocomposite films

We report on UV laser modification and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H,Si:O) with nanosecond pulses and effects of laser surface microstructuring on the frictional performance of DLN films on the nano- and macroscale. A technique of direct laser interference patterning was applied to produce arrays of periodic linear microstructures on the DLN films. The UV laser irradiation was performed at low fluences corresponding to the regime of surface graphitization and incipient ablation. At the initial stage of the thin film modification, the laser-induced spallation and graphitization in the surface layers were found to strongly influence the nanoscale topography and mechanical properties of the DLN surface. Frictional properties of the laser-patterned DLN films were studied using (1) atomic force microscopy in lateral force mode and (2) a ball-on-flat tribometer under linear reciprocating sliding against a 100Cr6 steel ball. The lateral force microscopy measurements revealed that the laser-irradiated regions were characterized by increased friction forces due to microspallation effects and enhanced surface roughness, correlating with tribotests at the initial stage of sliding. During prolonged sliding in ambient air, both the original and laser-patterned DLN surfaces exhibited low-friction performance at the friction coefficient of 0.07–0.08.

Studies on the influence of argon flow rate on PECVD grown diamond-like nanocomposite film

Diamond like nanocomposite film is grown using PECVD method for its use as IR window. It is seen that the argon flow rate variation can change the surface quality and the film thickness and these changes are also not linear. So, depending upon application, argon flow rate is to be optimized. Moreover, an interferometric technique to measure the phase variation of the film surface has been proposed. This phase variation is comparable with the surface quality as obtained from AFM images and can thus be considered as a cheap alternative technique to measure surface quality.

Anti-reflective nanocomposite based coating for crystalline silicon solar cells with noticeable significance

Novel Diamond-like Nanocomposite (DLN) thin film as Anti-Reflective Nanocomposite Based (ARNAB) coating for crystalline silicon (c-Si) solar cell is the main objective of this paper. The DLN film was deposited by plasma assisted chemical vapour deposition (PACVD) method and characterized by Fourier transform infrared, field emission scanning electron microscope, and high resolution transmission emission microscope. Results show that c-Si3N4 and c-SiC nanoparticle (3–5 nm) were embedded in a-C:H matrix, and they were interpenetrated by Si-C bonding, i.e., typical DLN structure. The optical properties of the film were investigated by UV-VIS-near-infrared and photoluminescence spectroscopy. The performance of ARNAB coating was evaluated by measuring the reflectance, external quantum efficiency (EQE), and conversion efficiency. The solar weighted average reflection from textured c-Si was reduced to 2.25% in wavelength range 300 nm–1100 nm, and more than 90% EQE of the solar cell was achieved within the broad wavelength range 560 nm–870 nm. The result has been also compared with conventional silicon nitride anti-reflection coating (ARC). Finally, 0.8% absolute increased of efficiency was achieved with ARNAB layer in comparison with silicon nitride AR coating. The ARNAB thin film has a great potential to be used as ARC for silicon based solar cell.