Diamond-like Carbon Structure Research Articles

Effects of thermal annealing and Si incorporation on bonding structure and fracture properties of diamond-like carbon films

The effects of thermal annealing and Si incorporation on the structure and properties of diamond-like carbon (DLC) films were investigated. As-deposited DLC film (DLC) and Si incorporated DLC film (Si-DLC), both with and without thermal annealing, were analyzed for bonding structure, residual stress, film thickness, elastic modulus and fracture properties using Raman spectroscopy, wafer curvature, nanoindentation, four-point bend fracture testing, and X-ray photoelectron spectroscopy (XPS). Raman spectroscopy clearly showed that thermal annealing of DLC films promotes more sp 2 bonding character, whereas Si incorporation into the films promotes more sp 3 bonding character. Interfacial fracture energies, film hardness and elastic modulus, and residual film stress were all found to vary strongly with the degree of sp 3 bonding in the DLC film. These changes in mechanical properties are rationalized in terms of the degree of three dimensional inter-links within the atomic bond network.

Resistivity change of the diamondlike carbon, deposited by focused-ion-beam chemical vapor deposition, induced by the annealing treatment

Diamondlike carbon (DLC) deposited by focused-ion-beam chemical vapor deposition (FIB-CVD) has the interesting material characteristics because DLC deposited by FIB-CVD using the gallium (Ga) FIB contained Ga. The DLC wires were subjected to annealing, and it was found that their resistivity and the Ga content of DLC decreased. To understand the reason for the decrease in resistivity, changes in the fine structure and composition of DLC due to annealing were examined by transmission electron microscope electron energy loss spectroscopy and Rutherford backscattering spectroscopy/elastic recoil detection analysis, respectively. The results revealed that the graphite content of DLC increased due to hydrogen (H) elimination induced by annealing. Thus, it was concluded that the resistivity of the annealed DLC wires decreased due to the increase in the graphite content of DLC.

Graphitization of thin films formed by focused-ion-beam chemical-vapor-deposition

The effect of annealing on the structure of diamond-like carbon (DLC) thin film fabricated by focused-ion-beam chemical-vapor deposition (FIB–CVD) was investigated. The near-edge x-ray absorption fine-structure spectrum of the carbon K-edge over the excitation energy range of 275–320 eV was measured on the FIB–CVD DLC thin film by annealing for 1 h in a temperature region from room temperature (RT) to 1273 K. The sp 2/( sp 2 + sp 3) ratio maintained ≈ 0.4 in an annealing temperature region from room temperature to 523 K and steeply increased from ≈ 0.4 to ≈ 0.7 with annealing temperature from 523 K to 773 K. The I( D)/ I( G) ratio, which was obtained from the Raman spectrum, also indicated a similar dependence on annealing temperature. The graphitization of thin film fabricated by focused-ion-beam chemical-vapor deposition (FIB–CVD) by annealing was confirmed to start at ≈ 600 K.

Photoluminescence enhancement induced by nanoparticles from La 2O 3 and CeO 2 doped diamond-like carbon films

La 2O 3 and CeO 2 doped composite hydrogen-free diamond-like carbon (DLC) films with thickness of 230–280 nm were deposited by unbalanced magnetron sputtering. Nanoparticles are formed on the surface of deposited films. Auger electron spectroscopy shows the C, O, La and Ce elements distribute uniformly along the depth direction, and they diffuse into the Si(1 0 0) substrate. X-ray photoelectron spectroscopy confirms the forming of La 2O 3 and CeO 2 within the DLC films, and the amorphous DLC structure is not changed with the doping of rare earth oxides. G peak positions shift to higher wave numbers, and relative intensities ratio I D/ I G increase of DLC films with the doping of La 2O 3 and CeO 2, indicating the coherence between the I D/ I G and G peak position. Furthermore, the photoluminescence (PL) obviously increase with the forming of nanoparticles and doping of La 2O 3 and CeO 2. Specially, the PL intensity of 4% La 2O 3 and 4% CeO 2 doped composite DLC films is 18.4 times of that of pure DLC films, which is beneficial for the increase of photoconversion efficiency of solar cells.

Annealing effect on the chemical structure of diamondlike carbon

The effect of annealing in an ultrahigh vacuum on the chemical structure of diamondlike carbon (DLC) was investigated using photoelectron spectroscopy, thermal desorption spectroscopy, electrical resistivity, and micro-Raman spectroscopy measurements. The line shapes of the C 1s photoelectron spectra depended on annealing temperature. The relative intensities of four chemical components in the spectra were quantitatively evaluated: sp3 carbon with carbon-carbon bonds (C–C sp3 carbon), sp2 carbon with carbon-carbon bonds (C–C sp2 carbon), sp2 carbon with hydrogen-carbon bonds (H–C sp2 carbon), and sp3 carbon with hydrogen-carbon bonds (H–C sp3 carbon). The variation of the ratio of the components demonstrated that hydrogen in DLC is emitted to the outside in between 450 and 600 °C, and the remaining DLC is graphized above 600 °C. The increase in the asymmetry of the C 1s spectra and the decrease in the electrical resistivity of the DLC film with annealing temperature agree with the picture that the H–C bonds in DLC produces large free spaces in the structure, which inhibit conductive routes and lead to high electrical resistivity.

Towards the use of diamond-like carbon solid lubricant coatings in vacuum and space environments

Owing to the increasing demand in tribological performance for vacuum- and space-related applications, development of new solid lubricant coatings is necessary. Diamond-like carbon (DLC) coatings have been successfully used in many conventional mechanical applications to reduce both friction and wear. The potential use of these new solid lubricants under vacuum becomes then a critical question, which this article will attempt to address. DLC deposition, structure, and properties are first introduced to the reader. The exceptional tribological behaviour of DLC coatings is also discussed, in comparison with other tribological coatings. Attention is focused on the vacuum tribology of DLC films, pointing out the very low friction and wear that may be achieved with these materials. Phenomena accounting for establishment and lifetime of such low-friction regime are proposed. Finally, some open issues concerning vacuum- and space-related applications are discussed.

Transparent polymer and diamond-like hydrogenated amorphous carbon thin films by PECVD technique

Optical, electrical and structural properties of hydrogenated amorphous carbon films deposited by radio frequency plasma enhanced chemical vapour deposition technique (RF-PECVED) have been investigated thoroughly. The films were deposited using a mixture of hydrogen and acetylene gases at a low substrate temperature of 200 °C. The electrical resistivities of the films are ⩾ 109 Ω cm. The ratio of hydrogenated sp3 to sp2 bonded carbon atoms in the films is obtained by deconvoluting the infrared spectra over the 2800 cm−1–3100 cm−1 range. Polymer-like hydrogenated amorphous carbon films are grown at a low power (50 mW cm−2) having a high hydrogen content (30.3–46.1 at%). Increase in hydrogen dilution increases the total hydrogen content as well as the ratio of hydrogenated sp3 to sp2 carbon bonding and it becomes a maximum at an optimum hydrogen dilution. Similarly the grain density also increases with the increase in hydrogen dilution. On the other hand, at a higher RF power of 150 mW cm−2 much stronger C–C sp3 and C–C sp2 bonds are formed and the total hydrogen content drastically reduces to a very low value of 1.1–1.8 at%. This indicates the growth of hydrogenated diamond-like carbon (DLC) structure. The stronger C–C sp3 bonds present in the DLC film make the films harder as well as Raman active.

Chemical Structural Analysis of Diamondlike Carbon Films with Different Electrical Resistivities by X-ray Photoelectron Spectroscopy

The chemical structure of diamondlike carbon (DLC) has been clarified by means of the quantitative analysis of the C 1s X-ray photoelectron spectra of the DLC films with different electrical resistivities prepared by the unbalanced magnetron sputtering (UBMS) method. The observed C 1s spectra showed asymmetric shapes and shifts of peak positions depending on the electrical resistivity of the films. Every spectrum was decomposed into four chemical components that were represented by the Doniach–Šunjić (DŠ) function convoluted with a Gaussian function. The structures corresponding to the chemical components were analyzed by considering that the electrical resistivity of DLC increases as the amount of hydrogen increases. The assignments of the chemical components are as follows: in order of binding energy, sp3 carbon with carbon–carbon bonds (C–C sp3 carbon, 283.7–283.8 eV), sp2 carbon with carbon–carbon bonds (C–C sp2 carbon, 284.2–284.3 eV), sp2 carbon with hydrogen–carbon bonds (H–C sp2 carbon, 284.7–284.8 eV), and sp3 carbon with hydrogen–carbon bonds (H–C sp3 carbon, 285.3–285.4 eV).

Modification of amorphous DLC films induced by MeV photon irradiation

Modification of the properties of amorphous diamond-like carbon (DLC) coatings irradiated by MeV photons from medical linear accelerator has been investigated. DLC structures of different content and thickness, synthesized under different technological parameters at room temperature using direct ion deposition (cold cathode) method were used for the investigation. Properties of the irradiated carbon films were studied using UV/VIS spectrometry and laser ellipsometry. Bonding structure of the samples was analyzed by Fourier transform infrared (FTIR) spectrometry and Raman scattering (RS) spectroscopy. Investigated DLC films indicated increased optical transparency which was different for the films with different networking structure. No significant structural changes were found in irradiated SiOx-containing and additionally N2 co-doped DLC films. Reduction of permittivity was observed in all irradiated samples.The results of investigation are analyzed in accordance with the registered radiation induced changes in investigated samples and possible model of the X-ray photon interaction with amorphous DLC films is discussed.

Influence of compressive load on microstructure of micro-scaled DLC structures produced by FIB-CVD

Influence of compressive load on microstructure of micro-scaled diamond-like carbon (DLC) structures was investigated by high-resolution electron transmission microscopy (HRTEM) analyses. The micro-scaled structures were produced by the focused ion-beam chemical vapor deposition method. The compressive loads were applied by a dynamic ultra micro hardness tester equipped with a flat-tip diamond indenter. Microgrid images in HRTEM observation and selected area diffraction patterns were varied by the compressive loads. The variations revealed that constituent atoms arranged disorderly in DLC were clustered by compressive loads. Electron energy loss spectroscopy measurements indicated that sp3 fraction in DLC was decreased by the compressive load. Consequently, it was suggested that graphitic clusters were formed in the microstructure of DLC by the compressive loads.

Improvement of the wiggling profile of spin-on carbon hard mask by H[sub 2] plasma treatment

The H2 plasma treatment for spin-on carbon (SOC) hard mask in the trilayer resist process is expected to serve as a reliable alternative to single layer resist process for 45nm nodes and beyond. The authors have investigated this treatment with a view to suppress the deformation of SOC by oxide etching. The wiggling profile of SOC drastically improves due to the formation of a thicker diamondlike amorphous carbon structure by the H2 plasma treatment with higher-energy hydrogen ions.

Active immobilization of biomolecules on a hybrid three-dimensional nanoelectrode bydielectrophoresis for single-biomolecule study

We propose and experimentally demonstrate a method of active immobilization forbiomolecules on a three-dimensional nanometre-scale electrode (3D nanoelectrode) usingdielectrophoresis to immobilize the biomolecules at predetermined locations forsingle-biomolecule study. We have developed a novel two-step fabrication process forobtaining a 3D nanoelectrode having a sharp top, which is necessary for immobilizing asingle biomolecule at a single point. The first step is to fabricate the backbonestructure, which is rigid and defines the shape of the 3D nanoelectrode. It wasfabricated with diamond-like carbon (DLC) obtained using focused ion beam assistedchemical vapour deposition followed by post-plasma etching, which reshapes the DLCstructure. The second step coats the DLC structure with a thin layer of aluminium,which supplies electrical conductivity to the DLC structure. By applying a highfrequency (of the order of megahertz) and high intensity (greater than or equalto a few megavolts per metre) electric field using the 3D nanoelectrodes, thegenerated dielectrophoresis attracted and then immobilized target biomolecules ontothe tops of 3D nanoelectrodes, as a demonstration of active immobilization ofbiomolecules.

Angle-Dependent Measurement of Near Edge X-ray Absorption Fine Structure of Annealing Effect on Local Structure of Focused-Ion-Beam Chemical Vapor Deposition Diamond-Like Carbon

The annealing effect on the local structure of diamond-like carbon (DLC) formed by Ga+ focused-ion-beam chemical vapor deposition (FIB-CVD) was investigated by the incidence angle-dependent measurement of the C K-edge near edge X-ray absorption fine structure (NEXAFS) from 0 to 60°. The peak intensity corresponding to the resonance transition of 1s →σ* originating from carbon–gallium bonding markedly increased with incidence angle in the spectra of a FIB-CVD DLC film annealed at 400 °C. This angle dependency was attributable to the movement of residual Ga atoms from the bottom to the neighboring surface of the FIB-CVD DLC film.

Characterization of diamond-like carbon coatings prepared by pulsed bias cathodic vacuum arc deposition

Hydrogen free diamond-like carbon (DLC) coatings have been deposited on Si(100) and stainless steel substrates by cathodic vacuum arc plasma deposition with pulse voltage. Adherent deposits on silicon can be obtained through applying gradient Ti/TiC/DLC layers. A pulse bias of − 100 V was applied to the substrate in order to obtain a denser structure of DLC coating approximately 1 μm thick. The microstructure and hardness value of DLC films were analyzed by using X-ray photoelectron spectroscopy and nano-indenter. The experimental results show that the duty cycle strongly influenced the hardness and sp 3 content of the DLC coatings. We observed that when the duty cycle was raised from 2.5% to 12.5%, the hardness increased from 26 GPa to 49 GPa, and the sp 3 fraction of the DLC films measured by XPS increased from 39% to 50.8 % as well. But at constant duty cycle, say 12.5%, the hardness is dropped from 49 to 14 GPa in proportion to the increase of residual gas pressure from 3 × 10 − 3 Pa to 1 Pa. As the residual gas pressure increased, collisional phenomenon will decrease the energy of the ions. Ions with low energy make more graphitic carbon links and result in a low hardness value.

Femtosecond-laser-induced nanostructure formation and surface modification of diamond-like carbon film

This paper reports the pump and probe experiment for in situ reflectivity measurements in the femtosecond laser ablation that brings about nanoscale modification of diamond-like carbon (DLC) film. The characteristic reflectivity changes observed demonstrate that the formation of periodic nanostructure is preceded by a change in bonding structure of DLC in the ablation at low fluences. We have observed a coherent nonlinear wave-mixing signal that can resolve the ultrafast interaction processes for the nanoscale modification on the film surface. Based on the results obtained, a model of the interaction process is proposed.

Deposition of Diamond-like Carbon Films using Graphite Sputtering in Neon Dense Plasma

This paper reports the deposition of diamond-like carbon (DLC) films on Si , using a low energy (1.45 kJ) dense plasma focus assisted sputtering of graphite insert at the tip of the tapered anode. The substrates are placed in front of the anode at different axial and angular positions and are exposed to multiple focus shots. The information regarding the DLC structure is acquired by using Raman spectroscopy. The spectra are characterized by two broad bands known as “G-band” and “D-band”. The results point towards the formation of DLC films with both sp3 (diamond like) and sp2 (graphite like) domains. In X-ray diffraction (XRD) pattern, no additional peak is observed except a peak at 2θ = 69° which corresponds to the silicon (Si) substrate. The intensity of Si peak is reduced after treatment indicating the deposition of amorphous carbon. Scanning electron microscopy (SEM) results demonstrate that the smoothness of the film increases with increasing the substrate angular positions with respect to the anode axis. Energy dispersive X-ray (EDX) analysis reveals that the films deposited at lower axial and angular positions are thicker which is complemented by the cross-sectional views of the films.

Application of Time-of-Flight Secondary Ion Mass Spectrometry to study diamond-like carbon films

Chemical composition and some differences between surface and bulk structure of diamond-like carbon (DLC) thin films studied with Time-of-Flight Secondary Ion Mass Spectrometry (ToF SIMS) are the subject of this paper. The DLC films were deposited using radio-frequency plasma-chemical vapor deposition (RF PCVD) method by the decomposition of CH 4 gas in high-frequency plasma. The negative self-bias voltage defining the power used for deposition was in the range of − 100 V to − 400 V. The results obtained show that the DLC films primarily contain carbon and hydrogen. The collected depth profiles also show that all samples contain considerable amount of Fe, Ni, Cr and some other elements introduced during the deposition process. These elements are mainly placed at the interface region of the substrate and deposited in the DLC film. The mass spectra obtained show that the amount of hydrogen in the surface layer is much greater than in the sample bulk which is consistent with widely accepted models of deposition of hydrogenated DLC films. The structure of the studied DLC samples was characterized by the analysis of negative carbon cluster ions in the mass spectra obtained. Some significant differences in the surface and bulk energy of fragmentation of carbon clusters are registered. The results suggest that the fragmentation pattern is independent of the self-bias voltage used during film deposition.

Plasma biasing to control the growth conditions of diamond-like carbon

It is well known that the structure and properties of diamond-like carbon, and in particular the sp 3/sp 2 ratio, can be controlled by the energy of the condensing carbon ions or atoms. In many practical cases, the energy of ions arriving at the surface of the growing film is determined by the bias applied to the substrate. The bias causes a sheath to form between substrate and plasma in which the potential difference between plasma potential and surface potential drops. In this contribution, we demonstrate that the same results can be obtained with grounded substrates by shifting the plasma potential. This “plasma biasing” (as opposed to “substrate biasing”) is shown to work well with pulsed cathodic carbon arcs, resulting in tetrahedral amorphous carbon (ta-C) films that are comparable to the films obtained with the conventional substrate bias. To verify the plasma bias approach, ta-C films were deposited by both conventional and plasma bias and characterized by transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS). Detailed data for comparison of these films are provided.

Surface characterization of ion-enhanced implanted photoresist removal

We characterize the chemical constitutents of high dose implanted deep ultraviolet photoresist before and after dual-mode oxygen plasma processing, where a remote rf-plasma source is operated simultaneously with rf bias. Raman spectroscopy indicates that the organic composition of the crust comprises a mixture of sp2 graphite and sp3 diamondlike carbon structures. High dose ion implantation reduces the hydrogen content by about 50 at. % as measured by hydrogen forward scattering and explains the reduced optical emission signal intensity observed during crust removal. The crust thicknesses extracted from the secondary-ion-mass spectroscopy profile correspond well to prior scanning electron microscopy characterization [Kawaguchi et al., J. Vac. Sci. Technol. B (submitted)] and support the existence of a transitional layer between the hardened crust and the underlying photoresist. Angle-resolved x-ray photoelectron spectroscopy analysis of arsenic implanted photoresist shows that dual-mode plasma processing causes substantial oxidation deep into the bulk. This result contrasts with downstream plasma processing, which proceeds by a near-surface mechanism. In addition, surface arsenic levels increase by an order of magnitude, which suggests that ion bombardment does not significantly sputter the dopant.

Structure and morphology of diamond-like carbon coated on nylon 66/poly(phenylene ether) alloy

In order to investigate the structure and morphology of diamond-like carbon (DLC) film coated on a polymer alloy prepared by a particular four-steps method in the plasma-based ion implantation and deposition (PBIID) process, studies were made on the structure and properties of the DLC film with special reference to its surface morphology by scanning (SEM) and transmission (TEM) electron microscopies. It is revealed from TEM microscopy that the amorphous structure of the DLC film consists of a silicon-implanted layer on the polymer substrate, a hard acetylene-implanted layer and a flexible acetylene/toluene-deposited layer. Some properties of the DLC film can be accounted for by the morphology examined in this study.