Diamond-like Carbon Interlayer Research Articles

Interface Engineering of a Silicon/Graphene Heterojunction Photodetector via a Diamond-Like Carbon Interlayer.

Silicon/graphene nanowalls (Si/GNWs) heterojunctions with excellent integrability and sensitivity show an increasing potential in optoelectronic devices. However, the performance is greatly limited by inferior interfacial adhesion and week electronic transport caused by the horizontal buffer layer. Herein, a diamond-like carbon (DLC) interlayer is first introduced to construct Si/DLC/GNWs heterojunctions, which can significantly change the growth behavior of the GNWs film, avoiding the formation of horizontal buffer layers. Accordingly, a robust diamond-like covalent bond with a remarkable enhancement of the interfacial adhesion is yielded, which notably improves the complementary metal oxide semiconductor compatibility for photodetector fabrication. Importantly, the DLC interlayer is verified to undergo a graphitization transition during the high-temperature growth process, which is beneficial to pave a vertical conductive path and facilitate the transport of photogenerated carriers in the visible and near-infrared regions. As a result, the Si/DLC/GNWs heterojunction detectors can simultaneously exhibit improved photoresponsivity and response speed, compared with the counterparts without DLC interlayers. The introduction of the DLC interlayer might provide a universal strategy to construct hybrid interfaces with high performance in next-generation optoelectronic devices.

Tribological and thermal stability study of nanoporous amorphous boron carbide films prepared by pulsed plasma chemical vapor deposition

In this work, the thermal stability and the oxidation and tribological behavior of nanoporous a-BC:H films are studied and compared with those in conventional diamond-like carbon (DLC) films. a-BC:H films were deposited by pulsed plasma chemical vapor deposition using B(CH3)3 gas as the boron source. A DLC interlayer was used to prevent the a-BC:H film delamination produced by oxidation. Thermal stability of a-BC:H films, with no delamination signs after annealing at 500 °C for 1 h, is better than that of the DLC films, which completely disappeared under the same conditions. Tribological test results indicate that the a-BC:H films, even with lower nanoindentation hardness than the DLC films, show an excellent boundary oil lubricated behavior, with lower friction coefficient and reduce the wear rate of counter materials than those on the DLC film. The good materials properties such as low modulus of elasticity and the formation of micropores from the original nanopores during boundary regimes explain this better performance. Results show that porous a-BC:H films may be an alternative for segmented DLC films in applications where severe tribological conditions and complex shapes exist, so surface patterning is unfeasible.

The diamond radiation detector with an Ohmic contact using diamond-like carbon interlayer

A diamond-like carbon thin layer was used as an interlayer between a free-standing diamond substrate grown by microwave plasma enhanced chemical vapour deposition and a Pt/Au layer. The dark-current of about 5·0 pA cm−2 was found for this detector at an electric field of 200 V cm−1. Ohmic contact was achieved by this diamond-like carbon/Pt/Au trilayer structure as evidenced by a linear dark I-V curve. The ratios of photocurrent to dark-current were about 26 and 35 for diamond detectors with Ti/Pt/Au and diamond-like carbon/Pt/Au trilayer electrodes, respectively. The energy resolution for the diamond detector with diamond-like carbon/Pt/Au electrode was about 3·30%, better than 4·56% for the detector with Ti/Pt/Au electrode.

Nitrogen doping for adhesion improvement of DLC film deposited on Si substrate by Filtered Cathodic Vacuum Arc (FCVA) technique

Abstract Diamond-like carbon (DLC) films have been used in many applications due to their attractive combination of properties including chemical inertness, corrosion protection, biocompatibility, high hardness, and low wear rates. However, they still have some limitations such as high internal stresses and low toughness which lead to poor adhesion of films. Synthesis of nitrogen-doped DLC (N-DLC) offers the possibility of overcoming these limitations. In this study, DLC films, namely tetrahedral amorphous carbon (ta-C) and nitrogen doped tetrahedral amorphous carbon (ta-C:N) were deposited on single crystalline Si wafer substrates using the Filtered Cathodic Vacuum Arc (FCVA) technique. Film characterizations were carried out by Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), triboindenter tester and nano-scratch tester. Measurement results showed that intentionally doping with nitrogen reduced the carbon sp 3 content and increased the surface roughness in comparison with that of pure ta-C films. The hardness measurement confirmed the Raman and AFM analyses that adding nitrogen in ta-C films decreased the hardness, especially with high nitrogen content. However, the nano-scratch test revealed the increasing of the critical load with nitrogen. This work, then, extended its scope to investigate the properties of double-layer ta-C films which were composed of ta-C:N interlayer of various thickness around 10–30 nm and ta-C top-layer with thickness of around 80 nm. Microstructure characterization demonstrated that a ta-C:N interlayer gradually decreased the sp 3 fraction in the films and increased film roughness whenever the ta-C:N interlayer thickness increased. In this structure, the tribological property in terms of adhesion to the Si substrate was significantly improved by about 20–90%, but the mechanical property in terms of hardness was gradually degraded by about 2–10%, compared to pure ta-C film, when the ta-C:N interlayer thickness increased from around 10–30 nm. This indicates that the nitrogen-doped DLC interlayer may sacrifice the mechanical strength of the films but gain benefits in terms of the adhesion property.

Improving diamond coating on Ti6Al4V substrate using a diamond like carbon interlayer: Raman residual stress evaluation and AFM analyses

We used the micro-Raman spectroscopy to evaluate residual stresses developed in deposited diamond films on Ti6Al4V substrates. A comparison is made between specimens with and without a diamond like carbon (DLC) interlayer. The effect of seeding the specimens prior to the deposition of the diamond coating is also investigated. In addition, AFM analysis is carried out to evaluate the quality of the surface roughness. The results show that the introduction of a DLC interlayer lowered the residual stress intensity compared to the specimens without DLC. The seeding process enabled the generation of smaller grains compared to the specimens without seeding. The measured averaged residual stresses on specimens with a DLC interlayer were about half of those measured on specimens without DLC. However the seeding process, which led to a better surface finish, had a partial opposite effect on the stress intensities. This is probably due to the grain growth depending on the nucleation sites available from the seeding process.

Influence of Interlayer on Wear and Corrosion Resistance of DLC Film

Diamond-like carbon (DLC) films have many excellent characteristics such as low friction coefficient, wear resistance, gas barrier property and biocompatibility. These many positive characteristics enable DLC coatings to be applied to a lot of fields from metallic materials to polymer materials for overcoatings. However, usual DLC film has a lot of micro-pores or pinholes, and those defects become problems as DLC film is not able to make the best use of abrasion resistance effectively due to the substrate corrosion. In addition, the DLC films deposited directly on the steel substrates often encountered the problem of poor adhesion. It has been attempted to overcome the negative effect by means of multilayer structure using metal and ceramic layers. In this study, we aim to deposit DLC films satisfied with both antiwear and anticorrosion characteristics. This time, we attempted to improve those properties by enhancing adhesion strength between DLC film and substrate. Interlayers used were a Si modified DLC (Si-C:H) interlayer deposited by using Si(CH3)4 gas and a Cr interlayer deposited with magnetron sputtering method. These interlayered DLC films were deposited on austenite stainless steel substrates. DLC films with Si-C:H and/or Cr interlayer were deposited by a pulse plasma CVD method using C2H2 gas. Three kinds of coatings: (1) substrate/Si-C:H/DLC, (2) substrate/Cr/DLC and (3) substrate/Cr/Si-C:H/DLC had been done. As fundamental tests, Raman spectroscopy, nano indentation, X-ray reflectometer analysis and rutherford back scattering spectrometry/elastic recoil detection analysis were carried out to reveal both mechanical and anticorrosion characteristics. Then, ball-on-disk tests and electrochemical measurements also had been running. These results lead us to conclusion that the effects of the DLC coating had been confirmed and an optimal structure to improve both tribological property and anticorrosion property was substrate/Si-C:H/DLC. Moreover, in the case of emphasizing tribological property, substrate/Cr/Si-C:H/DLC structure was recommended.

S0401-1-1 DLC成膜したステンレス鋼の耐摩耗性及び耐腐食性評価([S0401-1]表面改質および薄膜コーティング(1))

DLC (Diamond-like carbon) film shows low friction coefficient against various materials and has high wear-resistance. However, usual DLC film has micro-pores or pinholes, and those defects become problems that DLC film is not able to make the best use of abrasion resistance effectively due to the corrosion of the substrate. In this study, we aim to deposit DLC films satisfied with both antiwear and anticorrosion characteristics. This time, we focused on the interlayer. We use Si modified DLC (Si-DLC) interlayer deposited by using Si(CH_3)_4 gas and Cr interlayer. As a fundamental test, the adhesion strength between DLC film and a steel substrate was investigated by a scratch test. Then, with measuring the pitting potential as well as the tribological properties, the effects of the DLC coating had been confirmed. A ball-on-disk (BoD) test and an electrochemical measurement lead us to conclusion that an optimal structure to improve both tribological property and anticorrosion property was substrate/Cr/Si-C:H/DLC.

A quantitative in vitro method to predict the adhesion lifetime of diamond-like carbon thin films on biomedical implants

A quantitative method using Rockwell C indentation was developed to study the adhesion of diamond-like carbon (DLC) protective coatings to the CoCrMo biomedical implant alloy when immersed in phosphate-buffered saline (PBS) solution at 37 °C. Two kinds of coatings with thicknesses ranging from 0.5 up to 16 microns were investigated, namely DLC and DLC/Si-DLC, where Si-DLC denotes a 90 nm thick DLC interlayer containing Si. The time-dependent delamination of the coating around the indentation was quantified by means of optical investigations of the advancing crack front and calculations of the induced stress using the finite element method (FEM). The cause of delamination for both types of coatings was revealed to be stress-corrosion cracking (SCC) of the interface material. For the DLC coating a typical SCC behavior was observed, including a threshold region (60 J m −2) and a “stage 1” crack propagation with a crack-growth exponent of 3.0, comparable to that found for ductile metals. The DLC/Si-DLC coating exhibits an SCC process with a crack-growth exponent of 3.3 and a threshold region at 470 J m −2, indicating an adhesion in PBS at 37 °C that is about eight times better than that of the DLC coating. The SCC curves were fitted to the reaction controlled model typically used to explain the crack propagation in bulk soda lime glass. As this model falls short of accurately describing all the SCC curves, limitations of its application to the interface between a brittle coating and a ductile substrate are discussed.

Pulsed laser deposition of hydroxyapatite-diamondlike carbon multilayer films and their adhesion aspects

We have developed a layered hydroxyapatite/diamondlike carbon/functionally gradient diamondlike carbon-silver/titanium carbide/titanium carbonitride/titanium nitride composite film using pulsed laser deposition. A diamondlike carbon interlayer between a hydroxyapatite coating and the Ti-6Al-4V alloy can serve several purposes, including preventing corrosion of Ti-6Al-4V alloy, overcoming poor adhesion between the hydroxyapatite coating and the titanium oxide surface, and reducing inflammation at the implant/tissue interface. Titanium nitride, titanium carbonitride (TiC x N y ), titanium carbide and functionally gradient diamondlike carbon-silver layers were used to improve the adhesion of diamondlike carbon films to Ti-6Al-4V alloy. We envision several potential medical applications for these multilayer materials, including use in orthopedic and dental devices.

DLC/Hydroxyapatite Nanocomposites

ABSTRACTStudies of orthopaedic implant failures have shown that mechanical failure of an implant almost exclusively occurs at the biomaterial-tissue interface. Hydroxyapatite (HA) mimics the behavior of natural bone, and provides a strong, long-lasting adhesive interface between a bone replacement implant and the surrounding tissue. Currently, thin film HA is not commonly used because it contains defects, porosity, and cracks. Delamination of the hydroxyapatite film and formation of hydroxyapatite particles may lead to implant wear and loosening. Furthermore, the coating also acts only as a temporary barrier to ion release from the bulk biomaterial. One method to improve the tribological properties of a bioactive coating is to strengthen the microstructure of the coating through the placement of a DLC (hydrogen-free diamondlike carbon) interlayer. DLC coatings possess properties close to diamond in terms of hardness, atomic smoothness, and chemical inertness. We have developed a diamondlike carbon/HA bilayer, in which the bilayer surface (HA) is bioactive and the interlayer (diamondlike carbon) is biocompatible, wear resistant, and corrosion resistant. We have successfully deposited nanocrystalline hydroxyapatite and DLC films by ablating a hydroxyapatite target and a graphite target using a KrF laser. A novel target design was adopted to incorporate alloying atoms into the films during pulsed laser deposition. These alloying elements possess unique biological properties. Surface morphology was studied using SEM, interfacial structure was studied using TEM, and HA phase microstructure was studied using XRD. The DLC/nanocrystalline HA bilayer material is potentially useful for several orthopedic implant designs.

Adhesion improvement of diamond coating on silicon nitride substrate

Abstract Adherent diamond coating on sintered silicon nitride substrate was prepared by a microwave plasma enhanced chemical vapor deposition (CVD) in the CO and H 2 reactant system. The substrate was pretreated in a hot and strong acid solution and microflawed ultrasonically with diamond grains suspended in ethanol. The effects of diamond-like carbon (DLC) interlayer on the adhesion strength of diamond film was investigated in relation to the formation of the graded texture and characteristic C–C bonding varied from substrate side to diamond film. The DLC interlayer was grown by RF plasma enhanced CVD in the CH 4 –H 2 system. Adhesion strength of the diamond film were evaluated by a compression topple test and the subsequent observation of the fractured surface. Adhesion was found to increase considerably by the insertion of DLC layer, which would relax the residual stress in the interfacial region between diamond film and substrate. Actual cutting test by milling the Al–20 wt%Si alloy work revealed an excellent long tool life in using a thick diamond coated specimen inserted with DLC interlayer.

ＣＶＤダイヤモンド膜‐窒化ケイ素基板の密着性に及ぼすＤＬＣ中間層の効果

Effects of a diamond-like carbon (DLC) interlayer on the interfacial microstructure and adherence between diamond film and a silicon nitride substrate were investigated. The substrate was pretreated in a strong acid solution, followed by ultrasonic microflawing pretreatment. DLC was found to be deposited into etched micropores and to form a uniform film for 2h by rf plasma CVD using CH4-H2 reactant gas. Diamond film was then coated subsequently by microwave plasma CVD using CO-H2 reactant gas. Fine-grained diamond was nucleated onto microflawed DLC film by first-stage CVD for 1h, and diamond film 35μm thick was prepared by second-stage CVD for 29h. Milling tests of the coated specimen using Al-20wt% Si alloy as the work material exhibited higher adherence and longer tool life than the diamond-coated specimen without the DLC interlayer.