Diamond-like Carbon Thin Films Research Articles

Investigating different carbon-based target materials: Can we improve ionization in HiPIMS for the deposition of diamondlike carbon films?

Investigating different carbon-based target materials: Can we improve ionization in HiPIMS for the deposition of diamondlike carbon films?

Enhancing sp3 content in diamond-like carbon thin film electrodes by pulsed laser annealing for durable charge storage performance

In this work, diamond-like carbon (DLC) thin film electrodes were grown on Si substrate by pulsed laser deposition (PLD) technique, and the implication of pulsed laser annealing (PLA) treatment on their electrochemical supercapacitor performance was examined by three electrode systems in 1 M Na2SO4 electrolyte solutions. The SEM micrographs exhibit a sheet-like wrinkled surface of DLC film on Si which later transformed into tiny hierarchical heap-like structures with enhanced surface roughness. The Raman spectra confirm signature of the D and G peaks of pristine DLC film at ~1352 cm−1 (1356 cm−1 after PLA) and 1591 cm−1 (1589 cm−1 after PLA), and appearance of minor T2g (diamond) (1332 cm−1) peaks with an increment of the sp3 content after PLA treatment. The X-ray photoelectron spectroscopy (XPS) spectra were deconvoluted into three different contributions CC (sp2), CC (sp3), and CO, and their sp3 percentages were estimated ~48.9 %, and 64.7 % before and after annealing. The area under cyclic voltammetry (CV) curve and galvanostatic charging discharging (GCD) performance of PLA-treated DLC film were improved and the highest areal-specific capacitance was obtained to be ~48.25 mF/cm2 for scan rate of 5 mV/s and 36.01 mF/cm2 for current density of 2 mA/cm2, respectively. Excellent charging discharging cyclic stability of PLA treated electrode was observed over 5000 cycles, and Coulombic efficiency and capacitance retention were determined to be ~93.5 % and ~ 97.3 %, respectively. The electrochemical impedance spectroscopy (EIS) was performed to obtain the Nyquist plot (Z′vs.Z′′) of both electrodes before and after the stability test, and a small degradation in impedance was observed. The Nyquist plots were fitted with the well-known Randles equivalent circuit model Rs(Cdl(RctZw)) and substantial curtailment of Warburg resistance (Zw) in PLA-induced DLC electrode signifies the dominance of the diffusion-controlled region in the charging-discharging process. Minor changes in the Nyquist plot before and after the stability test manifest the enduring charge kinetics of both electrodes and PLA-treated DLC exhibits better cyclic stability. PLA techniques have a great impact on upgrading the areal-specific capacitance, capacitance retention with high Coulombic efficiency, and stability with negligible impedance loss of the DLC film electrodes.

Effect of doping and preparation parameter on AC conductivity and dielectric modulus formalism of Al doped DLC thin films

Here, we report the composite effect of aluminum doping on the dielectric response of Diamond-Like Carbon (DLC) thin films. In addition, the contribution from preparation parameters like acetylene flow rate is also considered to understand sample behavior. AC conductivity study shows the existence of a nonlinear increase of conductivity with frequency leading toward the Jump Relaxation Model (JRM). The transition frequency (ft) is observed, which increases with conductivity. The study reveals that dielectric response is influenced by space charge conductivity, prompting us to adopt the modified Debye law. Deviation from ideal Debye behavior is also confirmed in dielectric modulus analysis. The deviation is frequency-dependent, and a higher deviation is observed in the high-frequency region. Plotting of the Master curve shows the presence of different relaxation dynamics in different samples. A current-voltage (I-V) study of different samples is also undertaken, showing higher values (greater than unity) of the ideality factor.

Weak oxidant fraction in the microwave plasma influencing the evolution of nanocrystalline-diamond–imbedded diamond–like carbon network at low temperatures and its orbital hybridization dependent wide optical band gaps

The diamond-like carbon (DLC) thin films having intrinsic nanocrystalline diamond (NCD) components were synthesized on bare glass substrates at 300 °C, employing a (C2H2/CO2/H2/) gas mixture in MW-PECVD. Relevant influence of the weak oxidant fraction [F = CO2/(CO2 + C2H2)] in the plasma on the specific hybridized constituents (sp3 and sp2) in the C-network, optical transmission characteristics of the film, and its accomplished degree of nanocrystallinity were investigated. A substantial segment of the NCD was achieved in the DLC matrix. An optimized diamond-phase component corresponding to the minimized bond angle disorder in the matrix was accounted from the manifestation of the maxima of IDia/IG and IDia/ID simultaneous to the minimum of ID/IG ratio in Raman response, along with an allied diamond peak appearing near 1332 cm−1. The optimal DLC film at F = 0.23 revealed a wide optical band gap (Eg) of ∼3.60 eV, ∼59% sp3-hybridized C component of the diamond phase, and a significant sp3/sp2 ratio of ∼2.1. The film microstructure seemed homogeneous with uniformly distributed NCDs of average diameter ∼7.5 nm and dominant 〈111〉 crystallographic orientation. The sp3/sp2 fraction in the film matrix has been correlated directly to the IDia/IG and IDia/ID, and inversely to ID/IG ratios of the Raman data. Atomic-O, including atomic-H, remains instrumental in chemical reactions, facilitating the etching of graphitic and a-C phases while preserving the superior sp3-hybridized NCD component growing uninterruptedly in the DLC network that subsists shielded from the high-energy ion impact within secondary plasma under the shadow mask.

Using AFM to measure the elastic modulus of Diamond-Like Carbon thin films

In contemporary technological landscapes, a multitude of applications necessitate the fabrication of structures and mechanisms at exceptionally diminutive scales, prominently within the realm of Nano and Micro-Electro-Mechanical Systems (NEMS and MEMS). The comprehension of mechanical properties inherent in materials tailored for deployment in these applications assumes paramount significance. Consequently, an array of methodologies has been devised with the explicit purpose of delineating material properties at nano or micrometric scales. This report delves into select scholarly contributions aligned with this objective, and specifically, it explores a technique leveraging the capabilities of Atomic Force Microscopy (AFM) for the precise determination of the elastic modulus of Diamond-Like Carbon (DLC) films. The exploration of such methodologies is indispensable for advancing the understanding of material behavior at minute scales and facilitating the development of innovative technologies with enhanced structural integrity and performance characteristics.

Effect of Gas Flow Rate and Ratio on Structure and Properties of Nitrogen-Doped Diamond-like Carbon Films

Diamond-like carbon (DLC) has attracted much attention due to its unique properties such as high chemical inertness, optical transparency, and high biocompatibility. In this study, the total gas flow rate was kept constant, while the ratio of reactive gases was varied to deposit nitrogen-doped diamond-like carbon thin films on glass substrates using radiofrequency plasma-enhanced chemical vapor deposition. The effects of the gas flow ratio on the composition, microstructure, surface morphology, and optical properties of the thin films were investigated through extended deposition times. It was found that with an increase in the nitrogen-to-methane gas flow ratio, the film surface became smoother and more compact. The maximum transmittance in the visible range reached 90%, and the highest and lowest transmittance in the same ultraviolet wavelength region differed by up to 25.62% among several sample groups. The optical bandgap decreased from 3.58 eV to 3.46 eV, contrary to the trend of the sp2 fraction variation. Compared with other studies, this study considered the preparation of nitrogen-doped diamondoids using a chemical vapor deposition method with a lesser total gas flow rate passed into it, which provides practical data reference value for the preparation of N-DLC.

Effect of deposition temperature on the tribo-mechanical properties of nitrogen doped DLC thin film

The tribomechanical characteristics of diamond-like carbon (DLC) coatings are notably superior to other hard coatings, making them highly desirable for industrial applications. This study focuses on the synthesis of nitrogen-doped DLC (N-DLC) films through chemical vapor deposition (CVD) methods, with an emphasis on varying the deposition temperature. Comprehensive characterization techniques such as atomic force microscopy (AFM), scanning electron microscopy (SEM), and nanoindentation were employed to investigate the morphological and mechanical attributes of these coatings. The thickness of the films, measured using a Dektak profilometer, demonstrated an increase from 1.9 to 2.8 µm as the deposition temperature rose. Nanoindentation testing revealed that the film deposited at 900°C exhibited the highest hardness (H) and modulus of elasticity (E), measuring 21.95 and 208.3 GPa, respectively. Conversely, the film deposited at 1,000°C showed the lowest values, with H and E at 14.23a and 141.9 GPa, respectively. The H/E ratio of the coatings initially rose from 0.096 to 0.106 as the deposition temperature increased from 800°C to 900°C. However, for deposition temperatures exceeding 900°C the H/E ratio began to decline.

Evaluation of mechanical properties and tribological behavior of DLC/WC/WCN/W multilayer coatings deposited by HiPIMS

In the present research, thin films of diamond-like carbon (DLC), tungsten carbide (WC), tungsten carbonitride (WCN) and tungsten (W) were deposited onto the surface of an AISI 52100 steel using the PVD process by HiPIMS. A (DLC/WC/W), B (DLC/WCN/W) and C (DLC/WC/WCN/W) coating systems were evaluated through mechanical and tribological tests to establish the optimal system for its application in the bearing industry. The physicochemical characterization was carried out using SEM and EDS. On the other hand, the mechanical properties were obtained by Berkovich instrumented indentation tests, where it was observed that the synergy between the WC/WCN intermediate bilayer in Coating C increased the hardness and elastic modulus concerning the WC and WCN intermediate monolayers. Finally, the coating systems were evaluated through the linear reciprocating wear test. Coating C presented the highest wear resistance and the lowest values of coefficient of friction, due to the positive synergy between the WC/WCN intermediate bilayer.

A temperature-based synthesis and characterization study of aluminum-incorporated diamond-like carbon thin films

The present work deals with the study of various properties of aluminum (Al)-incorporated diamond-like carbon (DLC) thin films synthesized using the atmospheric pressure chemical vapor deposition (APCVD) technique by varying the deposition temperature (Td) and keeping the N2 flow rate constant. Surface morphology analysis, resistance to corrosion, nanohardness (H), and Young’s modulus (E) of the coatings were carried out using atomic force microscopy (AFM), corrosion test, scanning electron microscopy (SEM), and nanoindentation test, respectively. SEM results showed a smoother surface morphology of the coatings grown at different process temperatures. With an increase in process temperature, the coating roughness (Ra) lies in the range of 20–36 µm. The corrosion resistance of the coating was found to be reduced with a consecutive increase in the deposition temperature from 800℃ to 880℃. However, above 880℃, the resistance increases further, and it may be due to the presence of more Al weight percentage in the coating. The nanoindentation result revealed that H and E of the coating increase with an increase in the CVD process temperature. The elastic–plastic property indicated by H/E and H3/E2, which are also indicators of the wear properties of the coating, were studied using the nanoindentation technique. The residual stresses (σ) calculated using Stoney’s equation revealed a reduction in residual stress with an increase in the process temperature.

Electron cyclotron resonance chemical vapor deposited diamond-like carbon thin films with various acetylene flow rates for heterojunction solar cells with anti-reflective coating

Electron cyclotron resonance chemical vapor deposited diamond-like carbon thin films with various acetylene flow rates for heterojunction solar cells with anti-reflective coating

Structure and Optical Characteristics of DLC Films

SummaryUsing a RF‐Plasma Enhanced Chemical Vapor (RF‐PECVD) Depositions method, employing hydrogen and methane gas, Diamond like carbon (DLC) films were fabricated on glass and silicon substrates. The impact of varying CH4 to H2 ratios on the resulting film's structure, optical characteristics, and mechanical properties was investigated. The deposition process occurred at methane flow rates spanning 5 to 40 sccm. The films' surface morphology, and roughness were analyzed through Atomic Force Microscopy. Moreover, the Vickers hardness tests was employed to determine the hardness of produced films. The optical behavior of the DLC thin films was explored utilizing UV‐visible spectrometry and ellipsometry. A thorough investigation was conducted to understand how the CH4 flow rate influences layer growth, morphology, topography, and how these factors relate to the films' transmittance, reflectance, refractive index, and optical band gap.

Dielectric response and current-voltage characteristic of Mo-doped diamond-like carbon thin films at room temperature

Herein we have reported the effect of molybdenum (Mo) doping and acetylene (C2H2) gas flow rate, during deposition, on the electrical properties of diamond like carbon (DLC) films. The frequency dependent dielectric response of the undoped and doped DLC films has been discussed in details. Mo doping also increases the dielectric constant value owing to interfacial polarization and the corresponding change with C2H2 gas flow rate has been attributed to the formation of sp2 bonding over sp3 bonding, favoring the emergence of a graphite-like phase. The ac conductivity of DLC films has been observed to increase with frequency following a power law behavior. However, with 29 % Mo doping we have noticed two plateau regions having different slopes which has been explained on the basis of the jump relaxation model (JRM). The theoretical fitting of the experimental data indicates occurrence of ionic conduction along with polaron hoping. The dc contribution part (σdc) of the measured ac conductivity is found to vary with the acetylene (C2H2) gas flow dependent sp2 bonding formation. The σdc is extracted to be 2351 S/m for the 29 % Mo doped DLC films. From the Nyquist plot in impedance spectroscopy single relaxation phenomena have been observed for the no or low Mo doping but with 29 % Mo doping both the grain and grain boundary effect are prominent. This also suggests the presence of sp2 hybridization and formation of dangling bonds between the metal carbide and DLC film. From the current voltage characteristics, the development of high sp2 bonding and high electron injection into the DLC matrix with subsequent change in nature of the DLC from semiconducting to metallic with high Mo doping has been reported. From the capacitance voltage characteristics study it has been found that either increase in acetylene gas flow during deposition or Mo doping increases the space charge and trap carrier densities.

Magnetron sputtering process for deposition of multilayered thin diamond-like carbon films with silver nanoparticles for anti-reflective coatings and refractometric sensing

Multilayered film stacks serving optical applications usually require multiple target sources for deposition. In this work, we present a convenient method for the deposition of single- and multilayered thin films with varying diamond-like carbon (DLC) and silver content employing a single magnetron in the deposition system. For this, a reactive magnetron sputtering system was utilized and the silver target was poisoned based on desired structure: clean target and argon gas resulted in a pure silver film, completely poisoned target and acetylene and argon gas resulted in a DLC film, and anything in between resulted in a nanocomposite DLC:Ag film. The films were deposited on fused quartz, crystalline silicon, and porous anodized aluminum oxide substrates. We investigated the optical properties of these films and showed their applications for anti-reflective, black-appearing coatings and refractometric sensors, both experimentally and by simulation methods.

Increased body fluid repellency and electrochemical corrosion resistance of intravascular stent materials by ICP-CVD-based DLC thin-film deposition

Intravascular stents face adhesion- and corrosion-based challenges causing In-stent Restenosis (ISR). This study analyzes the influences of thin-film Diamond-Like-Carbon (DLC) deposition on body fluid repellency and corrosion behavior in Simulated Body Fluid (SBF) at 37 °C for intravascular stent materials. The stent specimens of 316 L and 316 LVM stainless steel, Ti-Alloy, and CoCr-Alloy were coated with DLC thin-films by Inductively Coupled Plasma Chemical Vapor Deposition (ICP-CVD). The repellencies of bare and DLC-coated specimens to body fluids, including the blood, plasma, glycerol, and distilled water (DIW) were analyzed by their Contact Angles (CA). Electrochemical impedance spectroscopy (EIS) and corrosion analysis in simulated body fluid were conducted using a potentiostat system. Bare specimens exhibited hydrophilic behavior with 51° CA for distilled water and lower body fluid repellencies with 69°, 64°, and 57° CAs for total blood, blood plasma, and glycerol, respectively. DLC coating improved blood repellency to 88° CA and hydrophobic feature to 81° CA. The electrochemical corrosion analysis exhibited that ICP-CVD based DLC thin-film deposition increased the electrochemical polarization resistance of BMS specimens from 22.02 kΩ.cm2 to 386.6 kΩ.cm2 for 316 L SS, 408.8 kΩ.cm2 for 316 LVM SS, 1703.0 kΩ.cm2 for CoCr-Alloy, and 1748 kΩ.cm2 for Ti-Alloy. The obtained values reduced the corrosion rate from 447.1 μm/year to 0.241 μm/year and the mass loss rate from 357.1 mg/cm2year to 0.165 mg/cm2year. This study concludes that DLC thin-film structures can lower the risk of ISR by adhesion and corrosion inhibition in BMS specimens, and they have a potential application in fluid-repellent and anti-corrosive drug-free stents.

Study on properties of diamond-like carbon films deposited by RF ICP PECVD method for micro- and optoelectronic applications

In this paper, a comparison of Diamond-like Carbon (DLC) films with different sp3 fraction content prepared by Radio Frequency Inductively Coupled Plasma Enhanced Chemical Vapour Deposition (RF ICP PECVD) was presented. Structural, surface, optical, and mechanical properties of deposited DLC films were analyzed with the use of awide range of measurement techniques. The investigated films were deposited on silicon (Si), amorphous silica (SiO2), and metallic (Ti6Al4V) substrates at room temperature. The deposited DLC films have sp3 fraction content ranging from 35 % to 70 %, uniform, compact and dense microstructure. The investigation indicates that the properties of DLC films required for micro- and optoelectronic applications improve with the sp3 fraction content. The refractive index (n) increased from 1.976 to2.086, packaging density (PD) from 0.964 to 0.744, electrical resistivity (ρ) from 2.1 ∙ 1010 to 4.4 ∙ 1011 Ωcm, hardness (H) from 16.4 19.1 to GPa and elastic modulus (E) from 109 to 129 GPa. However, the 50 % sp3 DLC thin film exhibited the highest resistance to cracking (H3/E2 = 0.44). The decrease of Urbach energy (EU) from 0.75 to 0.46 eV was observed for the DLC film with the highest sp3 fraction content, while all investigated DLC samples had similar optical bandgap energy (Egopt ≈ 1.3 eV). The research has shown that it is possible to obtain DLC coatings using the RF ICP PECVD technique that has better properties than films deposited by the classic PECVD technique.

Investigations of electron emission from DLC thin films deposited by means of RF PCVD at various self-bias voltages

The aim of this paper is to report the results of field emission experiments on undoped, flat diamond-like carbon (DLC) thin films deposited at various self-bias voltages using radio frequency plasma chemical vapor deposition (RF PCVD) technique. It has been observed that the emission properties improve when the absolute value of self-bias voltage becomes higher, e.g., the turn-on field value decreases. The correlation between electron field emission and sp2 content in these films showed improvement of electron emission properties of DLC films for higher amount of sp2 phase.

Fabrication of plane-type axon guidance substrates by applying diamond-like carbon thin film deposition

This research aims to fabricate plane-type substrates for evaluating the axon behaviors of neuronal cells in vitro toward the development of brain-on-chip models by applying the functions of diamond-like carbon (DLC) thin film deposition, which helped to eliminate the costly and time-consuming lithography process by utilizing a shadow mask. The DLC thin films were partially deposited on stretched polydimethylsiloxane (PDMS) substrates covered with a metal mask by the plasma chemical vaper deposition method, and using the substrates culture teats with human neuroblastoma cells (SH-SY5Y) were performed. Three patterns of interconnection structures of axons were created on the substrates with disordered and regular linear wrinkle structures with several μm size formed by the depositions. The patterns were characterized by the structure that the aggregations of axons formed on the linear DLC thin film deposited areas were separately placed in regular intervals and connected each other by plenty of axons, which were individually taut in a straight line at about 100 to over 200 μm in length. The substrates expected of uses for evaluation of axon behaviors are available without fabricating guiding grooves by conventional soft lithographic methods requiring multiple stages and their treating times.

Influence of Fluorine Doping on Hardness and Compressive Stress of the Diamond-Like Carbon Thin Film

Influence of Fluorine Doping on Hardness and Compressive Stress of the Diamond-Like Carbon Thin Film

The effect of coated diamond-like carbon thin films on polymer tooth based denture: Micro-morphology and fractal feature studies

To consider improving the micromorphology study of dentures combined with biocompatibility in recent years, we study hybrid organic–inorganic materials and diamond-like carbon coated on tooth-based dentures by the sol–gel and the RF sputtering method, respectively. Afterward, the effect of such material coating on the surface roughness and surface topography of dentures was evaluated. Aimed at this, 3D atomic force microscope images were analyzed via MountainsMap® Premium software, which divided the surface into peaks and pits through the watershed segmentation algorithm. This method made motif analysis possible by detecting the surface dimensions, curvature, volume, perimeters, shape, structure, etc., and the obtained statistics indicate interesting results for the regular and irregular topography and the surface of the prepared samples. In addition, the energy-dispersive x-ray spectrum illustrates the existence of N, C, O, Na, and Si in all samples, with the maximum value of C in the diamond-like carbon coated sample, which is because of the highest value of carbon in diamond-like carbon. Scanning electron microscope images also present a series of grooves on the surface with small randomly oriented cracks. The linear interpolation type shows that the surface of diamond-like carbon coated on the hybrid-control sample has the most irregular topography while the most regular topography was found in the hybrid coated control sample.

Nickel concentration dependent mechanical and tribological properties of subsurface layer of electrodeposited Ni-C nanocomposite thin films

Electrodeposited nickel- carbon (Ni-C) nanocomposite thin films are found to have varying mechanical and tribological properties. Ni-C nanocomposites thin films of varying nickel content were synthesized by a simple electrodeposition method. Annealed thin films possess a relatively hard and adherent subsurface layer. In order to have an understanding of the mechanical and tribological characteristics of the subsurface layer, the relatively soft and fragile outer layer of the thin films was removed by scraping. The sp2 and sp3 bondings of carbon atoms in the thin films were explored by Raman spectroscopy. The Fourier- transform infrared spectra of the diamond-like carbon (DLC) and Ni-C thin films also consist of sp2 and sp3 hybridized carbon bonds. Nanocrystalline nickel nanoparticles distributed in carbon matrix were observed in Transmission electron microscopy study of the films. Decrease in coefficient of friction of the films is observed with increase in nickel content in thin films having DLC structure. The highest nickel content Ni-C composite thin film shows the maximum hardness of 7.6 GPa while the amorphous DLC thin film possesses the least hardness of 2.19 GPa. The subsurface layers demonstrate a clear demarcation of mechanical properties with unmodified overlayer pointing towards an extra care must be exercised before applying these electrodeposited coating on technological appliances.