Effect of rapid thermal annealing treatment on the field-emission characteristics of nanocrystalline diamonds grown on various metal/silicon substrates

In this study, nanocrystalline diamond (NCD) films were deposited on various metal/silicon substrates using a microwave plasma chemical vapor deposition system. Metal layers used are chromium, titanium, aluminum and were used as the electron source for field emitters. These NCD/metal/silicon structures were subsequently annealed at 500 °C in a rapid thermal annealing (RTA) furnace. After RTA treatment, the surface of NCD films becomes flat and the grain boundaries can no longer be clearly seen. The intensity of graphitic peak is substantially decreased and the sp³ content of NCD films is increased. The chemical composition of NCD film remains unchanged after RTA treatment, but the sp³/sp² ratio in C 1s has been increased. It is found that the field-emission characteristics of diamond emitter not only can be effectively controlled by the metal used in the metal/NCD/Si structure, but also can be further enhanced by the improved microstructure of the NCD film obtained after RTA treatment.     

Effects of applied power on hydrogenated amorphous carbon (a-C:H) film deposition by low frequency (60 Hz) plasma-enhanced chemical vapor deposition (PECVD)

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass substrates using low frequency (60 Hz) plasma-enhanced chemical vapor deposition and the effects of the applied power on a-C:H films deposition were investigated. During deposition, the electron temperature and the density of CH₄-H₂ plasma were 2.4-3.1 eV and about 10⁸ cm⁻³, respectively. The main optical emission peak of the carbon species observed in the CH₄-H₂ plasma is shown to be excited carbon CH* at 431 nm. The sp³/sp² ratio, band gap, hydrogen content, and refractive index of a-C:H films gradually increased up to a power of 25 W and then saturated at higher power. This tendency is similar to the variation of plasma parameters with varying applied power, thereby indicating that a strong relationship exists between the properties of the films and the plasma discharge.     

The influence of methane/argon plasma composition on the formation of the hydrogenated amorphous carbon films

The quality of the a-C:H films was particularly correlated with the mixed ratio of methane/argon plasma. For a constant supply of energy and flowing rate, the optical emission from H_α intensity linearly increased with the addition of methane in argon plasma, while that from intensities of radiation of diatmoic radicals (CH^?and C₂^?) exponentially decreased. For the a-C:H films, the added methane in argon plasma tended to raise the quantity of hydrogenated carbon or sp³ C-H structure, which exponentially decreased the nano-hardness and friction coefficient of the films. In contrast, the electric resistance of the films enlarged dramatically with the increase of the methane content in argon plasma. It is therefore advantageous to balance the mechanical properties and electrical resistance of the a-C:H film by adjusting plasma composition in the course of the film-growing process.     

Amorphous carbon-silicon heterojunctions by pulsed Nd:YAG laser deposition

Amorphous carbon (a-C) films were deposited at 10^− 4 Pa on n-Si (Si-111) and p-Si (Si-100) substrates using a pulsed Nd:YAG laser with fundamental, second- and third-harmonic outputs. These unhydrogenated and undoped a-C films were characterized by visible and UV Raman spectroscopy which indicated the presence of substantial amount of sp³ hybridized carbon network depending on the laser wavelength. The bulk resistivity in the Au/a-C/indium tin oxide structure varied between (10⁹-10¹³) Ω cm — the lowest resistivity was obtained for films deposited by the fundamental laser output at 1064 nm while the highest value was by the third-harmonic laser output at 355 nm. All the a-C/Si heterostructures exhibited a nonlinear current density-voltage characteristic. Under light illumination, by taking into consideration the fill factor of ~ 0.2 for a-C/n-Si, the conversion efficiency at the highest photovoltage and photocurrent, at an illumination density of 0.175 mW/cm² was estimated to be ~ 0.28%.     

Characterization of TiCr(C,N)/amorphous carbon coatings synthesized by a cathodic arc deposition process

Ternary TiCrN and nanocomposite TiCr(C,N)/amorphous carbon (a-C) coatings with different carbon contents (0-26.6 at.%) were synthesized by cathodic arc evaporation with plasma enhanced duct equipment. The structural, chemical, and mechanical properties of the deposited films were studied by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and nanoindentation measurement. The atomic content ratios of carbon/(Ti + Cr) and carbon/nitrogen increased with increasing C₂H₂ flow rate. A nanocomposite structure of coexisting metastable hard TiCr(C,N) crystallites and amorphous carbon phases was found in the TiCr(C,N)/a-C coatings, those possessed smaller crystallite sizes than the ternary TiCrN film. XPS analyses revealed the concentration of a-C increased with increasing carbon content from 8.9 at.% to 26.6 at.%. Exceeding the metastable solubility range of carbon within the TiCrN lattice, the carbon formed a-C phase in the deposited coatings. The nanocomposite TiCr(C,N)/a-C coatings exhibited higher hardness value of 29-31 GPa than the deposited TiCrN coating (26 ± 1 GPa). It has been found that the structural and mechanical properties of the films were correlated with the carbon content in the TiCr(C,N)/a-C coatings.     

Crystalline carbon nitride films prepared by microwave plasma chemical vapour deposition

Crystalline carbon nitride films have been synthesized on Si (100) substrates by a microwave plasma chemical vapour deposition technique, using mixture of N₂, CH₄ and H₂ as precursor. Scanning electron microscopy shows that the films consisted of hexagonal bars, tetragonal bars, rhombohedral bars, in which the bigger bar is about 20 μm long and 6 μm wide. The X-ray photoelectron spectroscopy suggests that nitrogen and carbon in the films are bonded through hybridized sp² and sp³ configurations. The x-ray diffraction pattern indicates that the films are composed of α-, β-, pseudocubic and cubic C₃N₄ phase and an unidentified phase. Raman spectra also support the existence of α- and β-C₃N₄ phases. Vickers microhardness of about 41.9 GPa measured for the films.     

Deposition and characterization of magnetron sputtered amorphous Cr-C films

Thin films in the Cr-C system with carbon content of 25-85 at.% have been deposited using non-reactive DC magnetron sputtering from elemental targets. Analyses with X-ray diffraction and transmission electron microscopy confirm that the films are completely amorphous. Also, annealing experiment show that the films had not crystallized at 500 °C. Furthermore, X-ray spectroscopy and Raman spectroscopy show that the films consist of two phases, an amorphous CrC_x phase and an amorphous carbon (a-C) phase. The presence of two amorphous phases is also supported by the electrochemical analysis, which shows that oxidation of both chromium and carbon contributes to the total current in the passive region. The relative amounts of these amorphous phases influence the film properties. Typically, lower carbon content with less a-C phase leads to harder films with higher Young’s modulus and lower resistivity. The results also show that both films have lower currents in the passive region compared to the uncoated 316L steel substrate. Finally, our results were compared with literature data from both reactively and non-reactively sputtered chromium carbide films. The comparison reveals that non-reactive sputtering tend to favour the formation of amorphous films and also influence e.g. the sp²/sp³ ratio of the a-C phase.     

Surface etching effects of amorphous C:H and CNx:H films formed by supermagnetron plasma for field emission use

Supermagnetron plasma was used to deposit amorphous hydrogenated carbon (a-C:H) and hydrogenated carbon nitride (a-CN_x:H) films for field-emission devices using i-C₄H₁₀/(H₂ or N₂). It was also used to improve the field-emission characteristics by surface etching using N₂/H₂ plasma. The best emission threshold electric field (E_TH) was 13 and 12 V/μm for devices using as-deposited a-C:H and as-deposited a-CN_x:H films, respectively, while they were remarkably improved to 11 and 8 V/μm by surface etching using N₂/H₂ (120/40 sccm) gas, though surface roughness was slightly increased by the surface etching. The hardness of as-deposited films was higher than 22 GPa.     

High aspect ratio contact hole etching using relatively transparent amorphous carbon hard mask deposited from propylene

In this study, a high aspect ratio contact pattern, beyond 70 nm technology, in a very-large-scale integrated circuit, was achieved using hydrogenated amorphous carbon (a-C:H) film as the dry etching hard mask. The effect of temperature on the a-C:H deposits prepared by plasma enhanced chemical vapor deposition was studied. The a-C:H films resulting from propylene (C₃H₆) decomposition exhibited high transparency incorporated rich hydrogen concentration with a decreasing deposition temperature. A matrix of dispersed cross-linked sp³ clusters in a-C:H films, which has an increasing optical band gap and higher hydrogen content, is attributed to reduce the defect density of status and obtain high transmittance rate. Moreover, the higher transparency of a-C:H films could afford lithographic aligned capability as well as compressive stress and dry etching resistance. These explorations provided insights into the role of hydrogen in a-C film and also into the practicality of its future nano-scale device applications.     

Characteristics of nano-crystalline diamond films prepared in Ar/H2/CH4 microwave plasma

Characteristics of nano-crystalline diamond (NCD) thin films prepared with microwave plasma chemical vapor deposition (CVD) were studied in Ar/H₂/CH₄ gas mixture with a CH₄ gas ratio of 1-10% and H₂ gas ratio of 0-15%. From the Raman measurements, a pair of peaks at 1140 cm^− 1 and 1473 cm^− 1 related to the trans-polyacetylene components peculiar to nano-crystalline diamond films was clearly observed when the H₂ gas ratio of 5% was added in Ar/H₂/CH₄ mixture. With an increase of H₂ gas content up to 15%, their peaks decreased, while a G-peak at roughly 1556 cm^− 1 significantly increased. The degradation of NCD film quality strongly correlates with the decrease of C₂ optical emission intensity with the increase of hydrogen gas contents. From the surface analysis with atomic force microscopy (AFM), it was found that grain sizes of NCD films were typically of 10-100 nm in case of 5% H₂ gas addition.     

Nanocrystalline diamond film as cathode for gas discharge sensors

Nanocrystalline diamond (NCD) film was deposited on a silicon substrate utilizing microwave plasma-enhanced chemical vapor deposition in a mixed flow of methane, hydrogen and argon. The deposited film had a cauliflower-like morphology, and was composed of NCD, carbon clusters and mixed sp²- and sp³-bonded carbon. Electron field emission (EFE) in vacuum and electrical discharges in Ar, N₂ and O₂ using the NCD film as the cathode were characterized. The turn-on field for EFE and the geometric enhancement factor for the NCD film were 8.5 V/μm and 668, respectively. The breakdown voltages for Ar, N₂ and O₂ increased with pressures from 1.33 × 10⁴ Pa to 1.01 × 10⁵ Pa, following the right side of the normal Paschen curve.     

Superior hardness and Young's modulus of low temperature nanocrystalline diamond coatings

Nanocrystalline diamond (NCD) coatings with thickness of about 3 μm were grown on silicon substrates at four deposition temperatures ranging from 653 to 884 °C in CH₄/H₂/Ar microwave plasmas. The morphology, structure, chemical composition and mechanical and surface properties were studied by means of Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD), Raman spectroscopy, nanoindentation and Water Contact Angle (WCA) techniques. The different deposition temperatures used enabled to modulate the chemical, structural and mechanical NCD properties, in particular the grain size and the shape. The characterization measurements revealed a relatively smooth surface morphology with a variable grain size, which affected the incorporated hydrogen amount and the sp² carbon content, and, as a consequence, the mechanical properties. Specifically, the hydrogen content decreased by increasing the grain size, whereas the sp² carbon content increased. The highest values of hardness (121 ± 25 GPa) and elastic modulus (1036 ± 163 GPa) were achieved in NCD film grown at the lowest value of deposition temperature, which favored the formation of elongated nanocrystallites characterized by improved hydrophobic surface properties.     

Growth and characterization of stoichiometric BCN films on highly oriented pyrolytic graphite by radiofrequency plasma enhanced chemical vapor deposition

Hexagonal boron carbonitride (h-BCN) hybrid films have been synthesized on highly oriented pyrolytic graphite by radiofrequency plasma enhanced chemical vapor deposition using tris-(dimethylamino)borane as a single-source molecular precursor. The films were characterized by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopic measurements. XPS measurement showed that the B atoms were bonded to C and N atoms to form the sp²-B-C-N atomic hybrid chemical environment. The atomic composition estimated from the XPS of the typical sample was found to be almost B₁C₁N₁. NEXAFS spectra of the B K-edge and the N K-edge had the peaks due to the π* and σ* resonances of sp² hybrid orbitals implying the existence of the sp² hybrid configurations of h-BCN around the B atoms. The G band at 1592 and D band at 1352 cm^− 1 in the Raman spectra also suggested the presence of the graphite-like sp²-B-C-N atomic hybrid bonds. The films consisted of micrometer scale crystalline structure of around 10 µm thick has been confirmed by the field emission scanning electron microscopy.     

Synthesis of carbon coatings employing a plasma torch from an argon-acetylene gas mixture at reduced pressure

Amorphous hydrogenated carbon films (a-C:H) were formed on Si (1 1 1) wafers from an argon-acetylene gas mixture at a reduced pressure of 1000 Pa using a direct current (DC) plasma torch discharge. The Ar/C₂H₂ gas volume ratio varied from 1:1 to 8:1, the distance between plasma torch exit and the samples 0.04-0.095 m. The DC plasma torch technique allows the production of thick (∼90 μm) coatings at 0.3 μm/s growth rates. Raman spectra shape, D and G peak positions and the intensity ratio (I_D/I_G) show an increase of sp³ bond fraction with decreasing acetylene flow in argon plasma. Reflectance of the coatings deposited at Ar/C₂H₂=8:1 is high (∼97%) and slightly increases with increasing distance between samples and plasma torch exit.     

Laser-induced transformation of a-C:H thin films

In this work, we report the laser irradiation effects on the properties of various types of amorphous hydrogenated carbon (a-C:H) films. The influence of the initial carbon film (hydrogen concentration, sp³/sp² ratio, and sp² clustering) is studied. The results show that a loss of hydrogen and an increase of the sp² phase are the main processes in the laser power range between 1.8 and 5 MW/cm². Only these processes are stronger for “more polymer-like” and “graphite-like” films than for “more diamond-like” films.     

Nanocrystalline diamond/amorphous carbon composite films for applications in tribology,optics and biomedicine

Nanocrystalline diamond/amorphous carbon (NCD/a-C) composite thin films have been deposited by microwave plasma chemical vapour deposition from methane-rich CH₄/N₂ mixtures. The films have been thoroughly characterized with respect to basic properties such as growth rates, morphology and structure, composition, crystallinity, and bonding environment. They consist of diamond nanocrystals with diameters of 3–5 nm, which are embedded in an amorphous carbon matrix. Further studies are aimed at application relevant properties. I/V and Hall measurements showed that the films are p-type conductive with a resistitivity of 0.14 Ω cm, a carrier concentration of 1.9 × 10¹⁷ cm^− 3, and a carrier mobility of 250 cm²/Vs. Reflection, scattering and ellipsometric measurements revealed a refractive index of 1.95–2.1 in the visible region and an rather high extinction coefficient of about 0.14 at 400 nm. The films possess a hardness of ca. 40 GPa and a Young's modulus of ca. 390 GPa. Nano tribo test and nano scratch tests proved a low friction coefficient, and a strong protective effect and good adhesion on silicon substrates. First biomedical tests showed that the films are not cytotoxic but bioinert. Finally, the deposition of multilayers nano/polycrystalline diamond with improved properties is demonstrated.     

Relative fraction of sp bonding in boron incorporated amorphous carbon films determined by X-ray photoelectron spectroscopy

Boron incorporated amorphous carbon (a-C:B) films were deposited by a filtered cathodic vacuum arc system using various percentage of boron mixed graphite cathodes. X-ray photoelectron spectroscopy (XPS) was employed to determine the properties of the films as a function of boron concentration. Deconvolutions of the XPS C 1s core level spectra were carried out using four different components. The relative fraction of sp³ bonding was then evaluated from the area ratio of the peaks at 285.0, 284.1 eV which were individually attributed to sp³ C-C, sp² CC hybridizations. The results showed that the sp³ content of a-C:B film decreases from 73.8 to 58.6% for the films containing boron from 0.59 to 2.13 at.%, and then gradually reduced to 42.5% at a slower rate with boron concentration up to 6.04 at.%. Furthermore, a series of a-C:B films with fixed boron content (2.13 at.%) were prepared to identify the relationship between sp³ bonding and substrate bias. It was found that the fraction of sp³ bonding increased from 50.28% at the bias voltage of 0 V and reached a maximum value of 66.3% at −150 V. As the bias voltage increased up to −2000 V, the sp³ content decreased sharply to 43.9%.     

Hydrogen influence on the structure and properties of amorphous hydrogenated carbon films deposited by direct ion beam

The present work provides results for amorphous hydrogenated carbon (a-C:H) films grown by direct ion beam deposition method. Acetylene and its mixtures with hydrogen were used. The films were characterized by Rutherford backscattering spectrometry, elastic recoil detection, Raman spectroscopy, ellipsometry, infrared spectroscopy, and microhardness measurements. These techniques indicated that an admixture of hydrogen yields a lower deposition rate, a higher content of total and bounded hydrogen in the a-C:H films, and a lower film density. The optical and mechanical properties depend on both, hydrogen concentrations in the gas phase and in the films, and show a strong diamond-like component, which reaches maximum at 34 at.% of hydrogen. Further hydrogen dilution enhanced only sp² clustering and possible reduced a number of both sp³ and C-C sp³ bonds. We suppose that these effects (in the high hydrogen concentration range) are not only related to the ion irradiation difference between the light hydrogen and the much heavier carbon but also to the diffusion in the a-C:H films.     

Effect of substrate temperature on corrosion performance of nitrogen doped amorphous carbon thin films in NaCl solution

Nitrogen doped amorphous carbon (a-C:N) thin films were deposited on p-Si substrates by DC magnetron sputtering at varying substrate temperature from room temperature (RT) to 300 °C. The bonding structure, surface morphology and adhesion strength of the a-C:N films were investigated by using X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, atomic force microscopy (AFM) and micro-scratch testing. The corrosion behavior of the a-C:N films was evaluated by potentiodynamic polarization test in a 0.6 M NaCl solution. The results indicated that the corrosion resistance of the films depended on the sp³-bonded cross-link structure that was significantly affected by the substrate temperature.     

Evaluation of microstructures and mechanical properties of diamond like carbon films deposited by filtered cathodic arc plasma

Diamond-like carbon (DLC) films were deposited by a cathodic arc plasma evaporation (CAPD) process, using a mechanical shield filter combined with a magnetic filter with enhanced arc structure at substrate-bias voltage ranging from − 50 to − 300 V. The film characteristics were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). The mechanical properties were investigated by using a nanoindentation tester, scratch test and ball on disc wear test. The Raman spectra of the films showed that the wavenumber ranging from 900 to 1800 cm^− 1 could be deconvoluted into 1140 cm^− 1, D band and G band. The bias caused a significant effect on the sp³ content which was increased with the decreasing of I_D/I_G ratio. The XPS spectra data of the films which were etched by H⁺ plasma indicated the sp³ content are higher than those of the as-deposited DLC films. This implied that there is a sp²-rich layer present on the surface of the as-deposited DLC films. The nanoindentation hardness increased as the maximum load increased. A 380 nm thick and well adhered DLC film was successfully deposited on WC-Co substrate above a Ti interlayer. The adhesion critical load of the DLC films was about 33 N. The results of the wear tests demonstrated that the friction coefficient of the DLC films was between 0.12 and 0.2.