Single-layer Diamond-like Carbon Research Articles

Effects of sp3 bond ratio and modulation ratios on nanotribology behaviors of diamond-like carbon coatings investigated using atomistic nanoscratching simulations.

Diamond-like carbon (DLC) films are amorphous solids in which carbon atoms are linked by hybridized sp3, sp2, and sp bonds. The mechanical and tribological properties of DLC films can be adjusted by tuning the sp2/sp3 bond ratio. These films are typically used as protective coatings for components such as dies, automotive engines, mechanical seals, hard disk drives, biological engineering devices, and micro/nano-electromechanical systems. Further exploration of the mechanical and tribological behavior of DLC films is important for enhancing functional design for the above applications. The simulation results show that single-layer DLC with a higher sp3 ratio has better resistance to indentation. Single-layer DLC with a lower initial sp3 ratio has lower friction and a shorter repeated cycle in the friction force curve due to an increase in the graphitization of the friction interface. Single-layer DLC with a higher sp3 ratio has a higher coefficient of friction because compared with the normal force, the friction force is much more sensitive to an increase in the sp3 ratio. Molecular dynamics simulations based on the Tersoff potential were performed using the open-source code LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator).

A comparative study of microstructural and tribological properties of N-DLC/DLC double layer and single layer coatings deposited by DC-pulsed PACVD process

Diamond-like carbon (DLC) coatings have been attractive for their unique properties such as high wear resistance, high hardness, chemical inertness, and biocompatibility. The double layer N-DLC/DLC coating was deposited by the D.C. Pulsed Plasma Assisted Chemical Vapour Deposition (PACVD) technique on the H13 Tool Steel. The structural, mechanical, and tribological properties of the double layer coating were compared with the single layer DLC and N-DLC coatings. The tribological behavior of the coatings was evaluated by the rotational ball-on-disk tribometer and the contact profilometer. The structural changes in the coatings were investigated by Attenuated-Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectroscopy, Visible Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS). The N-DLC/DLC coating showed excellent wear properties compared to single layer coatings. High stability and low friction coefficient are the most important characteristics of the double layer coating. It was found that the gradient properties in the mechanical and chemical composition of the N-DLC/DLC coating improve tribological properties and adhesion to the substrate compared to single layer.

Development of diamond-like carbon (DLC) coatings with alternate soft and hard multilayer architecture for enhancing wear performance at high contact stress

Diamond-like carbon (DLC) coatings have attracted overwhelming interest due to a wide range of exceptional mechanical and tribological properties. Unfortunately, they have limited tribological applications where high contact stresses are required due to high residual stresses. We proposed that multilayer DLC coatings may have potential for tribological applications at high stresses. In this study, DLC coatings consisting of alternate soft-layer and hard-layer were deposited onto M2 steel substrates using unbalanced magnetron sputtering technique. The tribological performance at high contact stresses (2.5GPa, 3.2GPa, and 4GPa) was evaluated by a ball-on-disc tribometer. The residual stress, the hardness and reduced modulus are increased with percentage of hard-layer thickness. Multilayer coatings with the soft-top layer improve wear performance compared with single-layer DLC coatings. In contrast, multilayer coatings without the soft-top layer show poor wear performance under high stresses. The soft-top layer reduces the wear volume during run-in period by forming a transfer layer so that decreases the total wear. The 50% hard multilayer coating with the soft-top layer provides the best wear performance at an extreme stress of 4GPa among all coatings in this study because it combines the low magnitude of the residual stress with the acceptable hardness value. Such carbon/carbon multilayer structure offers an alternative to deposit low stress and high wear resistance DLC coatings without introducing other elements.

Resistance Switching Induced by Hydrogen and Oxygen in Diamond-Like Carbon Memristor

In this letter, one single-layer diamond-like carbon (DLC) resistive random access memory (RRAM) and two opposite stacking double-layer DLC/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> RRAMs were prepared to investigate the resistance switching mechanism of DLC-based memristors. The RRAM devices were fabricated by sandwiching the active-layers between Pt top and TiN bottom electrodes. Based on the analyses for Pt/DLC/TiN and Pt/DLC/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiN structures, we demonstrated the resistance switching in DLC RRAM is induced by hydrogen reaction near the Pt electrode. In addition, the resistance switching in Pt/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /DLC/TiN structure is attributed to oxygen reaction near the TiN electrode. Based on the results of HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> stacked with DLC devices, we demonstrated for the first time the resistance switching of DLC at inactive electrode side (Pt) and active electrode side (TiN) is attributed to hydrogen and oxygen-induced redox of C-C bonds, respectively.

Fabrication of High Transparency Diamond-Like Carbon Film Coating on D263T Glass at Room Temperature as an Antireflection Layer

This study intends to deposit high transmittance diamond-like carbon (DLC) thin films on D263T glass substrate at room temperature via a diamond powder target using the radio frequency (RF) magnetron sputtering technique. Moreover, various process parameters were used to tune the properties of the thin films by using the Taguchi method. Experimental results show that the content of sp3bonded carbon decreases in accordance with the effect of the substrate temperature. In addition, the hardness of all as-deposited single-layer DLC films ranges from 13.2 to 22.5 GPa, and the RMS surface roughness was improved significantly with the decrease in sputtering pressure. The water repellent of the deposited DLC films improved significantly with the increase of the sp3content, and its contact angle was larger than that of the noncoated one by 1.45 times. Furthermore, the refraction index (n) of all as-deposited DLC films ranges from 1.95 to 2.1 atλ= 600 nm. These results demonstrate that the thickness increased as the reflectance increased. DLC film under an RF power of 150 W possesses high transmissive ability (&gt;81%) and low average reflectance ability (&lt;9.5%) in the visible wavelengths (atλ= 400–700 nm).

Diamond-like Carbon Films Deposited at Room Temperature on Flexible Plastics Substrates for Antireflection Coating

In this present work, diamond-like carbon (DLC) films were coated onto polycarbonate (PC) substrates as a protective layer at room temperature by radio frequency (rf) magnetron sputtering technique. The ID/IG ratio, roughness (Ra), and contact angle of amorphous DLC films could be controlled by regulating deposition power. The DLC films deposited at 150 W with a good hardness of as high as 13.74 GPa were realized with a surface roughness and contact angle of 0.63 nm (Ra) and 103°, respectively. Ultraviolet/visible (UV/vis) spectrophotometry of single-layer DLC films showed a high transmissive ability (>80%) in the visible wavelengths. No cracks occurred on the surface of DLC films after the flexibility test 500 times at a frequency of 8.6 min-1. This confirms the excellent adhesion of DLC films on PC plastic substrates with potential applications in flexible optoelectronic devices.

Optical Properties of Diamond-like Carbon Films for Antireflection Coating by RF Magnetron Sputtering Method

Diamond-like Carbon (DLC) film has the ability to change the refractive index (n) value achieved high transmittance for potential applications of antireflection coating. The DLC films were coated onto D263T glass substrates at room temperature by radio frequency (RF) magnetron sputtering method. From the results of UV/VIS spectrophotometer analysis of single-layer DLC film, which shows an absorption wavelength (λ) ranged from 380nm to 950nm, the average reflectance of the film is 12.66% with the deposition time of 3hrs. It was found that DLC film with high transmittance was due to the highest ID/IG ratio of 1.71.

イオン化蒸着法によるTi-6Al-4V基板上へのダイヤモンドライクカーボン系二層膜の作製

A double-layers film, in which the top layer was a diamond-like carbon (DLC) film and the bottom layer was a compositionally graded film of silicon and carbon compounds with decreasing C/Si atomic ratio to a substrate, was successfully formed on a Ti-6Al-4V substrate by an ionization deposition method. In the film deposition process, a benzene vapor was used for the DLC deposition, and hexamethyldisiloxane and benzene vapors were used for the compositionally graded film of silicon and carbon compounds, as source gasses. The results of ball-on-disk and scratching tests showed that the double-layers film with graded composition provided a low friction coefficient, high wear resistance and good adhesion with the Ti-6Al-4V substrate compared to a single-layer DLC film. The DLC-based double-layers film developed in this study is very effective in extending the applications of the Ti-6Al-4V alloy for antifriction components.

Formation of Diamond-Like Carbon Based Double-Layer Film on Ti-6Al-4V Substrate by Ionization Deposition

A double-layer film, in which the top layer was a diamond-like carbon (DLC) film and the bottom layer was a compositionally graded film of silicon and carbon compounds with decreasing C/Si atomic ratio to a substrate, was successfully formed on a Ti-6Al-4V substrate by an ionization deposition method. In the film deposition process, a benzene vapor was used for the DLC deposition as a source gas, and hexamethyldisiloxane and benzene vapors were used as source gasses for the compositionally graded film of silicon and carbon compounds. The results of ball-on-disk and scratching tests showed that the double-layer film with graded composition provided a low friction coefficient, high wear resistance and good adhesion with the Ti-6Al-4V substrate compared to a single-layer DLC film. The DLC-based double-layer film developed in this study is much effective in wide applications of the Ti-6Al-4V alloy for which the use to antifriction components has been difficult.

Tribological characterization of diamond-like carbon (DLC) coatings sliding against DLC coatings

Two different qualities (single-layer and multi-layer) of thick diamond-like carbon (DLC) coatings were prepared on both extremely polished ( R a ∼0.01 μm) stainless steel disks and 6 mm diameter stainless steel balls. Morphological and micro-structural evaluations reveal that multi-layer DLC coatings are superior in nature compared to the single-layer coatings. Tribological characterisations using a pin (ball)-on-disk tribometer shows that, even though the multi-layer DLC coating exhibits superior qualities, when it slides against the same displays relatively higher friction and wear compared to that of single-layer DLC sliding against the same. Multi-layer DLC coated steel ball sliding against the single-layer DLC coated disk displays the best tribological performance. However, stress cracking was observed very rarely at the sliding edge of the multi-layer film prepared on the ball and is believed to be due to the relatively higher compressive stress in the film combined with the applied stress. The tribological performance of the single-layer DLC sliding against the same is also found to be excellent, and is comparable to that of the multi-layer DLC coated ball against the single-layer DLC coated disk. No cracks were observed on the low stress single-layer DLC coated ball after the friction test. The study reveals that the single-layer DLC sliding against the same would provide the best tribological DLC pair for relatively higher load applications such as in orthopaedic implants.