Ultra-thin Diamond-like Carbon Research Articles

Ultra-thin DLC diaphragm-based optical fiber sensor achieving a highly sensitive and broadband acoustic response.

In the design of an extrinsic Fabry-Perot interferometer (EFPI) acoustic sensor, broadband response and high-sensitivity sensing are usually conflicting and need to be carefully balanced. Here, we present a novel, to the best of our knowledge, optical fiber acoustic sensor based on an ultra-thin diamond-like carbon (DLC) film, fabricated using the plasma-enhanced chemical vapor deposition method, and transferred by a surface-energy-assisted method. The sensor exhibits a broadband response ranging from 200 Hz to 100 kHz, maintains an average sensitivity of 457.3 mV/Pa within the range of 6 to 30 kHz, and can detect weak acoustic signals down to 3.23 µPa/Hz1/2@16.19 kHz. The combination of an ultra-thin DLC film with a relatively high Young's modulus and internal stresses results in a trade-off between high sensitivity and a broadband response. This performance demonstrates that our sensor is among the most advanced in the EFPI acoustic sensor family, with significant potential for applications such as photoacoustic spectroscopy, defect diagnosis, and bio-imaging.

Diamond-like carbon conversion surfaces for space applications

We present diamond-like carbon (DLC) conversion surfaces to detect particles with energy below 2 keV. Conversion surfaces have been widely applied in measurements of low-energy particles by instruments onboard planetary and heliophysics missions. Their effectiveness is characterized by the efficiency in changing the charge state of the incident particles while maintaining a narrow angular distribution for the reflected particles. DLC as a conversion surface coating material has high conversion efficiency. We developed a conversion surface production process that provides ultra-smooth and ultra-thin DLC conversion surfaces. The process includes substrate preparation through precision cleaning, plasma immersion ion deposition of the DLC film, and diagnostics of the film parameters. The latter includes the measurement of the coating thickness, surface roughness, and the conversion efficiency for ion beams with energy below 2 keV. The process we developed provides the DLC conversion surface coating of repeatable parameters with a mean surface roughness of 3.4 ± 0.2 Å and a mean film thickness of 46.7 ± 0.8 nm uniform across the sample area. Ion beam measurements showed a negative ion yield of 1%–2% for hydrogen atoms and 8%–15% for oxygen atoms with an angular scatter distribution of 10°–20° at full width of half maximum. These results agree with those of other conversion surface coatings in the literature. The DLC conversion surfaces presented here are implemented in the conversion surface subsystem of the Interstellar Mapping and Acceleration Probe (IMAP)-Lo instrument of the IMAP mission scheduled for launch in 2025.

Effects of sp3 bond and modulation ratios on ultra-thin diamond-like carbon coatings using molecular dynamics nanoindentation

Effects of sp3 bond and modulation ratios on ultra-thin diamond-like carbon coatings using molecular dynamics nanoindentation

Structural characterization of ultrathin diamond-like carbon overcoats for high areal density magnetic recording

This paper reports a comprehensive study on chemical structures of ultrathin diamond-like carbon (DLC) overcoats for high areal density magnetic recording. The DLC overcoats were fabricated in a range of thicknesses between 0.5 and 5.0 nm with Si interlayer on NiFe substrates using a pulsed filtered cathodic vacuum arc (PFCVA) technique. The overcoat thicknesses were accurately determined by high–resolution transmission electron microscopy and wavelength dispersive X-ray fluorescence techniques. The surface morphology, chemical composition, microstructure, and tribological properties were systematically investigated by atomic force microscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, Raman spectroscopy techniques, and a reciprocating wear test. The results showed that the surface morphologies of DLC overcoats were atomically smooth with a root mean square surface roughness below 0.23 nm. The DLC overcoats had high sp3 bonds fraction. However, as the overcoat thickness was thinner than 1 nm, the sp2 bonds fraction suddenly increased resulting in a significant increase in the coefficient of friction. The obtained results demonstrated the limitation of the thickness of the DLC overcoat fabricated by the PFCVA technique as a protective coating for high–density magnetic storage devices.

Electrostatic and tribological properties of hydrogenated diamond-like carbon on anodic aluminium oxide

The electrostatic and tribological properties of three types of anodic aluminium oxide (alumite) and hydrogenated Diamond-Like Carbon (DLC) on alumites were investigated. It was first proven that an ultrathin DLC at 5 nm on an insulative surface exhibits slow discharge. For alumites, clear electrostatic discharge behaviour was not observed in spite of the fact that surface resistance was in the dissipative region of 1010 Ω. Upon coating alumites with a hydrogenated DLC, slow charge and discharge were observed. DLC coatings on alumites significantly improved dielectric strength and hardness due to DLC's intrusion into the porous structure of the alumites. The coefficient of friction on alumites, which stood at 0.9 against Al2O3 and E52100 balls, was much improved to 0.1 with a DLC coating, and so was wear loss and life time.

Characterization of Ultra-Thin Diamond-Like Carbon Films by SEM/EDX

A novel, high throughput method to characterize the chemistry of ultra-thin diamond-like carbon films is discussed. The method uses surface sensitive SEM/EDX to provide substrate-specific, semi-quantitative silicon nitride/DLC stack composition of protective films extensively used in the hard disk drives industry and at Angstrom-level. SEM/EDX output is correlated to TEM to provide direct, gauge-capable film thickness information using multiple regression models that make predictions based on film constituents. The best model uses the N/Si ratio in the films, instead of separate Si and N contributions. Topography of substrate/film after undergoing wear is correlatively and compositionally described based on chemical changes detected via the SEM/EDX method without the need for tedious cross-sectional workflows. Wear track regions of the substrate have a film depleted of carbon, as well as Si and N in the most severe cases, also revealing iron oxide formation. Analysis of film composition variations around industry-level thicknesses reveals a complex interplay between oxygen, silicon and nitrogen, which has been reflected mathematically in the regression models, as well as used to provide valuable insights into the as-deposited physics of the film.

Dependence of Optimum Thickness of Ultrathin Diamond-like Carbon Coatings over Carbon Nanotubes on Geometric Field Enhancement Factor

The generation of a field emission (FE) cathode electron source has attracted wide attention for its miniaturization, high-frequency operability, and low energy consumption. However, the FE performance of cold cathodes is limited by poor current stabilities of carbon nanotube (CNT) emitters. Coating CNTs with sp3-bonded carbon coatings is considered as a successful approach to stabilize the FE currents. High-quality ultrathin diamond-like carbon (DLC) films, which serve as sp3 carbon coatings, are deposited uniformly on CNTs by filtered cathodic vacuum arc evaporation in this research. The thicknesses of DLC coatings and the field enhancement factors of pristine CNTs affect to a large extent the FE properties. An optimum coating thickness of DLC layers corresponding to the lowest threshold field exists due to space-charge-induced band bending, at which the depletion region of the DLC layer in equilibrium is maximized. The optimum coating thickness increases with the geometric field enhancement factor of p...

Diamond-like carbon as gate dielectric for metal–insulator–semiconductor applications

Diamond-like carbon (DLC) has been studied as a dielectric material for future metal–insulator–semiconductor (MIS) technology. In this paper, ultrathin DLC films were deposited on silicon substrates by using the dc magnetron sputtering technique at various deposition voltages. The current–voltage characteristics indicated that the leakage currents of the MIS devices decreased with an increase in deposition voltages, and that a low leakage current ([Formula: see text] A/cm2) was achieved at −2 V bias voltage. The deposition voltage effects on the structures of films were investigated through Raman spectroscopy, which indicated that the sp3 bonding fraction decreased with an increase in the deposition voltage. The ramp-voltage breakdown test revealed high effective breakdown electric field ([Formula: see text]85 MV/cm) for the MIS device with the DLC film deposited at 1100-V deposition. Stress-induced leakage current measurement indicated that the DLC film exhibited excellent reliability.

Single-shot laser-induced damage threshold of free-standing nanometer-thin diamond-like carbon foils

Single-shot laser-induced damage threshold (LIDT) of free-standing nanometer-thin diamond-like carbon (DLC) foils was measured in vacuum environment for pulse durations from 50 fs to 200 ps. It is found that, due to higher surface defects density, the LIDT of free-standing ultrathin DLC foils is lower than that of bulk DLC by a factor of 3, and the damage fluence is almost a constant of about 0.1 J/cm2 when the pulse duration is longer than 500 fs. Different from DLC films coated on silicon wafer, the damage fluence of free-standing DLC has a weak dependence on their thickness. Based on the measurement, the damage mechanism is illustrated by virtue of the carrier population analysis, and the requirement on the temporal laser contrast when DLC targets are used in relativistic laser-plasma experiment is discussed.

Quantifying adhesion of ultra-thin multi-layer DLC coatings to Ni and Si substrates using shear, tension, and nanoscratch molecular dynamics simulations

Ultra-thin diamond-like carbon (DLC) coatings are used in many engineering applications including hard disk drives, automobile engines, and MEMS/NEMS devices to protect delicate substrates against wear and corrosion. However, they are susceptible to brittle cracking and delamination due to high intrinsic stress and poor adhesion to many substrates. Inclusion of an intermediate layer can prevent delamination of the coating. We perform simple shear and tension loading and nanoscratch molecular dynamics simulations to quantify the effect of coating layer thickness and composition on the adhesion of the ultra-thin multi-layer DLC coatings used in hard disk drives to their substrate. We observe that an intermediate Si layer improves adhesion of DLC coatings to Ni substrates compared to coatings without one, and that an optimum thickness of the Si layer exists. We also find that an intermediate DLC layer with sp3 fraction lower than the outermost DLC coating layer protects the substrate from plastic deformation under external loading, and that it improves adhesion to Si but not Ni substrates compared to coatings with no intermediate layer.

Qualitative Evaluation of Ultra-thin Multi-layer Diamond-Like Carbon Coatings Using Molecular Dynamics Nanoindentation Simulations

Ultra-thin diamond-like carbon (DLC) coatings are used in hard disk drives to protect the intricate magnetic structures from wear and corrosion. The coating on the recording head consists of a hard DLC layer and a silicon (Si) layer that improves adhesion between the DLC layer and the substrate. Damage to this protective coating can expose the magnetic structures to corrosion and compromise the reliability and functionality of the hard disk drive. Hence, it is critical to understand how coating design parameters affect the mechanical properties of these protective DLC coatings. We have used molecular dynamics simulations to determine the hardness and Young’s modulus of the ultra-thin multi-layer protective DLC coating of a recording head as a function of coating design parameters. We have found that hardness and Young’s modulus of the multi-layer coating increase with increasing DLC layer and decreasing Si layer thickness. Furthermore, hardness and Young’s modulus of the multi-layer coating are a function of the sp3 fraction and, thus, the hardness of the DLC layer. In addition, the mismatch between the hardness of the DLC layer and the substrate determines whether plastic deformation occurs in the coating or the substrate, and significantly affects the hardness of the multi-layer protective coating.

Nanomechanical and nanotribological behavior of ultra-thin silicon-doped diamond-like carbon films

Diamond-like carbon (DLC) film with ultra-thin thickness displays high internal stress, thereby resulting in the failure of protection to the substrate. Incorporation of silicon into DLC films, which has higher adhesion to substrate and extraordinary thermal stability, can be potentially used in heat assisted magnetic recording (HAMR). The nanomechanical and nanotribological behavior of Si doped DLC films is investigated using molecular dynamic simulation method. Effects of the Si content and density of Si-DLC films on the frictional behavior and wear resistance of Si-DLC films are investigated. Surface profiles at the contact interface are identified before and after sliding.

Materials Selection for Ultra-Thin Diamond-Like Carbon Film Metrology and Structural Characterization by TEM

Materials Selection for Ultra-Thin Diamond-Like Carbon Film Metrology and Structural Characterization by TEM

Conductive Atomic Force Microscopy Characterization of Ultra-Thin Diamond-Like Carbon Films on Magnetic Recording Heads

Journal Article Conductive Atomic Force Microscopy Characterization of Ultra-Thin Diamond-Like Carbon Films on Magnetic Recording Heads Get access Shirley Mejia, Shirley Mejia Western Digital Corporation, Magnetic Heads Operations, Metrology & Materials Characterization, Ayutthaya, Thailand, 13160 Search for other works by this author on: Oxford Academic Google Scholar Sean P Leary, Sean P Leary Western Digital Corporation, Magnetic Heads Operations, Metrology & Materials Characterization, Ayutthaya, Thailand, 13160 Search for other works by this author on: Oxford Academic Google Scholar Guilherme P Souza, Guilherme P Souza Western Digital Corporation, Magnetic Heads Operations, Metrology & Materials Characterization, Ayutthaya, Thailand, 13160 Search for other works by this author on: Oxford Academic Google Scholar Kurt C Ruthe Kurt C Ruthe Western Digital Corporation, Magnetic Heads Operations, Metrology & Materials Characterization, Ayutthaya, Thailand, 13160 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 21, Issue S3, 1 August 2015, Pages 1613–1614, https://doi.org/10.1017/S1431927615008843 Published: 23 September 2015

Deformation of Ultra-Thin Diamond-Like Carbon Coatings Under Combined Loading on a Magnetic Recording Head

Ultra-thin diamond-like carbon (DLC) coatings are used in precision engineering applications, such as magnetic storage devices, to protect intricate structures from wear and corrosion. A DLC coating typically consists of hard amorphous carbon in combination with an interlayer such as silicon (Si), to improve adhesion to the substrate material. Deformation and delamination of these coatings, even in part, could expose the substrate material and compromise its integrity and functionality. We have implemented a molecular dynamics model to quantify the strength of the interface between an ultra-thin tetrahedral amorphous carbon coating, a Si layer, and a permalloy (NiFe) substrate, under combined normal and tangential loading that mimics accidental contact between the recording head and the disk of a hard drive. We have evaluated the effect of the thickness of the different coating layers on deformation and interfacial strength of the coating during combined loading. The results indicate that deformation occurs primarily in the Si layer, and at the interface between the Ni–Si and the Si–C layers. Permanent separation of the Si and ta-C layers is observed, which gradually increases with multiple combined loading cycles. We find that increasing the Si and carbon layer thickness strengthens the DLC coating. However, increasing the carbon layer thickness has a larger effect on coating strength than increasing the Si layer thickness.

Ultra-thin nano-patterned wear-protective diamond-like carbon coatings deposited on glass using a C60 ion beam

The wear resistance and optical properties of ultra-thin diamond-like carbon (DLC) coatings deposited on glass substrates at room temperature were investigated. The coatings were deposited using a C60 ion beam. A sequence of surface treatments including ion-beam etching, molecular-beam deposition and ion-beam deposition were used for production of ultra-thin DLC coatings with a nano-patterned surface. The goal of the surface nano-patterning was to improve the wear resistance of the DLC coatings while maintaining a low thickness to obtain a high optical transparency. The experimental results demonstrated the excellent ability of the ultra-thin DLC coatings to improve the wear resistance of the glass substrates. A comparison between the wear rate for the DLC coating with nano-patterns and that of a more smooth coating revealed that the nano-patterned surface shows a 39% higher wear resistance. Furthermore, the coatings demonstrated a high transparency (94–97%) in the visible-light wavelength range.

Multifunctional three-dimensional nanodiamond-nanoporous alumina nanoarchitectures

Hybrid composite nanomaterials provide an attractive and versatile material platform for numerous emerging nano- and biomedical applications by offering the possibility to combine diverse properties which are impossible to obtain within a single material. In this work, we present the fabrication of novel hybrid diamond and amorphous diamond-like carbon (DLC) coated nanoporous alumina materials that exhibit multiple functionalities, such as high surface area, quasi-ordered nanopore structure, tunable surface chemistry and electrical conductivity, excellent biological, chemical and corrosion resistance. These multifunctional nanohybrid materials are fabricated using the plasma-induced carbonization method that effectively modifies the surface and the inside of the nanopores of anodic alumina, producing a homogenous ultrathin DLC protecting layer over the whole external and internal surfaces of the membranes. We demonstrate that the interplay between internal and external carbon supply is a critical factor for the formation of the ultrathin sp3-bonded carbon layer in the nanopores. This study brings new insights in the DLC growth mechanisms in confined nanospaces and opens new avenues to fabricate hybrid, chemically resistant and biocompatible carbon-coated nanoarchitectures on other inorganic supports.

Structural stability of nanometer thick diamond-like carbon films subjected to heating for thermally assisted magnetic recording

In this study, the structural stability of ultra-thin diamond-like carbon (DLC) films subjected to heating was investigated experimentally. The thermal robustness of nanometer thick DLC films for thermally assisted magnetic recording was demonstrated, and their damage mechanisms were elucidated using chemical vapor deposition and filtered cathodic vacuum arc DLC films. In addition, the refractivity of disk substrates with heated DLC thin films was evaluated using a scanning microellipsometer. This measurement system is suggested to be an effective method for evaluating the thermal stability of DLC films. The effect of the heating duration on the thermal stability of DLC films was also investigated by this method. Further, it was suggested that DLC thin films on an air bearing surface may be affected by laser heating because this surface may be heated for a significantly longer duration owing to the magnetic head read/write operation. However, the DLC thin films on the disk substrate may not be affected as severely by laser heating.

Magnetically enhanced plasma coating of nanostructures with ultrathin diamond-like carbon films

Coating using magnetically enhanced plasma deposition gives smooth diamond-like carbon films that increase hardness and wear resistance of nanostructures.

Gas Permeation, Mechanical Behavior and Cytocompatibility of Ultrathin Pure and Doped Diamond-Like Carbon and Silicon Oxide Films

Protective ultra-thin barrier films gather increasing economic interest for controlling permeation and diffusion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was a benchmarking of the mechanical oxygen permeation barrier, cytocompatibility, and microbiological properties of inorganic ~25 nm thin films, deposited by vacuum deposition techniques on 50 µm thin polyetheretherketone (PEEK) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit pure and nitrogen doped diamond-like carbon films, while physical vapor deposition (magnetron sputtering in pulsed DC mode) was used for the formation of silicon as well as titanium doped diamond-like carbon films. Silicon oxide films were deposited by radio frequency magnetron sputtering. The results indicate a strong influence of nanoporosity on the oxygen transmission rate for all coating types, while the low content of microporosity (particulates, etc.) is shown to be of lesser importance. Due to the low thickness of the foil substrates, being easily bent, the toughness as a measure of tendency to film fracture together with the elasticity index of the thin films influence the oxygen barrier. All investigated coatings are non-pyrogenic, cause no cytotoxic effects and do not influence bacterial growth.