M. S. Wong

Analytical electron microscopy and Raman spectroscopy studies of carbon nitride thin films

Deposition of carbon nitride thin films on Si(100) and polycrystalline Zr substrates was performed by dc magnetron sputtering of a graphite target under a pure nitrogen ambient. The resulting carbon nitride films (CNx) are primarily amorphous with a small volume fraction of nanocrystallites. Both energy‐dispersive x‐ray analysis and electron energy loss spectroscopy measurements showed that the amorphous matrix has uniform nitrogen‐to‐carbon ratios ∼0.4–0.8 depending on deposition conditions. Carbon and nitrogen K edge structures obtained from electron energy loss spectroscopy studies suggest that the amorphous carbon nitride matrix is primarily sp2 bonded. Apart from the carbon–nitrogen stretching vibration, Raman spectra of CNx films closely resemble those of diamondlike carbon films. Intensity and peak width changes of Raman features in the 1300–1600 cm−1 range due to inorganic carbon (D and G peak) under different deposition conditions are explained in terms of the extent of structural disorder in the...

Nano‐indentation studies of ultrahigh strength carbon nitride thin films

Carbon nitride (CNx) thin films were prepared by dc magnetron sputtering of a graphite target in a nitrogen ambient onto Si(100) substrates held at ambient temperatures. The films are amorphous with a small volume fraction of nanocrystallites. All CNx coatings grown to a thickness of 1.5 μm are adherent and smooth. Nanoindentation studies showed clear dependence of hardness and effective modulus on deposition process parameters (nitrogen pressure, target power, and substrate bias). Most striking is the observation that CNx films can be synthesized with yield strength exceeding 5 GPa.

Deposition and properties of polycrystalline TiN/NbN superlattice coatings

Polycrystalline TiN/NbN superlattice coatings were deposited on M2 tool steel substrates using an opposed dual‐cathode unbalanced magnetron sputtering system. Superlattice deposition was achieved by placing the substrates on a cylindrical holder that rotated on an axis equidistant between, and parallel to, the faces of opposed Ti and Nb targets. Cross contamination of the targets and the alternating superlattice layers was minimized using a baffle or an extra‐large cylindrical substrate holder. The superlattice period was determined by the substrate holder rotation speed. Analytical techniques including x‐ray diffraction, energy‐dispersive spectroscopy and transmission electron microscopy were used to characterize the structure of the superlattice coatings. Microhardness values for the superlattice coatings as high as 5200 kg/mm2 Hv0.05 have been achieved, comparable to the reported highest hardness values of single crystal TiN/VN, TiN/V0.6Nb0.4N and TiN/NbN superlattice coatings. The results indicate that the hardness of the polycrystalline TiN/NbN superlattice coatings is affected not only by superlattice period, but also by nitrogen partial pressure and ion bombardment during deposition.

Synthesis of superhard carbon nitride composite coatings

Crystalline carbon nitride/TiN composite coatings have been deposited using a dual‐cathode magnetron sputtering system onto polished silicon and M2 steel substrates held at room temperature. We propose that TiN provides a lattice‐matched structural template to seed the growth of carbon nitride crystallites. The resulting coatings are smooth, fully crystalline, with nanoindentation hardness in the range of 45–55 GPa. This hardness is in the low‐end range of diamond films. Suggestions for better seeding materials to further improve the hardness are proposed.

Structure and hardness studies of CNx/TiN nanocomposite coatings

Crystalline CNx/TiN multilayer composite coatings have been synthesized using an opposed cathode unbalanced magnetron sputtering system. Electron microscopy studies showed that the CNx/TiN coatings were fully crystalline and dense at small bilayer thicknesses. An amorphous phase was formed when the CNx layer thickness exceeded 4–5 nm. Two new d spacings extracted by Fourier transform of digitized images of the crystalline CNx region cannot be matched by known compounds formed by the detected elements. This provides limited evidence for the possible formation of a new carbon–nitrogen compound. Nanoindentation hardness about 45–55 GPa was reproducibly achieved for coatings produced under low nitrogen partial pressure and high substrate bias (−150 to −250 V). TiN (111) preferred orientation was strongly correlated to the high coating hardness.

Reactive direct current magnetron sputtering of aluminum oxide coatings

Aluminum oxide coatings were reactively direct current magnetron sputtered using an arc suppression unit to stop arcing on the cathode. The process was very controllable when the arc suppression unit was used, and it did not produce any debilitating arcing as is commonly found with conventional reactive direct current magnetron sputtering. Arc suppression is a major advancement in reactive dc magnetron sputtering technology. With the automatic feedback partial pressure control of the reactive gas, all compositions of AlOx, where 0≤x≤1.5, are possible. There are no forbidden compositions as there are with flow control of the reactive gas. All coatings were deposited with a floating substrate bias, and the color of the AlOx films ranged from metallic when there was no or a small partial pressure of oxygen during deposition to a very clear film when the oxygen partial pressure was 0.08 mTorr. The clear film was amorphous, and its average index of refraction, n, was 1.6. The Vickers hardness of the clear film...

Ionized magnetron sputter deposition of amorphous carbon nitride thin films

Carbon nitride thin films were prepared using an ionized magnetron sputtering system. An inductively coupled rf plasma was generated in the region between the sputtering source (high purity graphite) and the substrate table. An argon–nitrogen mixture was used as the sputtering gas. Sputtered atoms which pass through the radio frequency (rf) plasma may be ionized, and the degree of ionization depends on several processing variables, such as the gas total pressure, reactive gas partial pressure, and applied rf power. Pulsed substrate bias voltage was varied up to −500 V. Chemical bonding and composition of the deposited films were studied by infrared and Auger electron spectroscopy, respectively. An ultramicroindentation system was used to measure the hardness. Nitrogen was found to be bonded to carbon in various configurations. The dependence of the nitrogen‐to‐carbon ratio and film hardness on the deposition conditions was studied. Under optimum conditions, films with nitrogen‐to‐carbon ratio ∼0.3–0.4 and...

Growth and characterization of C-N thin films

Abstract Our preliminary studies showed that carbon nitride in amorphous and crystalline forms can be synthesized using reactive magnetron sputtering with substrates held at ambient temperatures. The films were evaluated by a wide range of diagnostic techniques (Auger spectroscopy, IR spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, atomic force microscopy, transmission electron microscopy and tribo-testing). The most important finding is that we can deposit smooth, continuous C-N films on a variety of substrates. Unlike previous work, we were able to incorporate significant amounts of nitrogen into these films (N:C ratio exceeding 0.4 in the bulk). More importantly, IR studies show that nitrogen exists not merely as gaseous species but is chemically bonded to carbon in the film. Transmission electron microscopy studies showed clearly the coexistence of amorphous and crystalline C-N phases. When deposited on polycrystalline zirconium substrates, these films appear to be very adherent and wear resistant under lubricated sliding conditions. In dry sliding against 52100 steels, carbon nitride gives friction coefficients as low as 0.16, comparable with that of diamond.

Nanoindentation hardness, abrasive wear, and microstructure of TiN/NbN polycrystalline nanostructured multilayer films grown by reactive magnetron sputtering

TiN, NbN, and TiN/NbN polycrystalline nanostructured multilayer films were deposited on high-speed steel substrates by unbalanced reactive magnetron sputtering of Ti and Nb targets in Ar–N2 discharges. Two techniques were used for obtaining a series of multilayers with compositional modulation period, Λ, in the range 3.8–100 nm; rotation of a cylindrical substrate holder between two opposing cathodes or by positioning inclined cathodes above the substrate and using shutters. For the two setups, ions were accelerated from the discharge by a negative substrate bias Vs=120–150 V and Vs=100 V, respectively, with an ion-to-metal arrival rate ratio of ∼1. The nanoindentation hardness and abrasive wear resistance by dimple grinding test of the coatings were compared between the sample series and related to the microstructure, phase composition, and residual stress σres obtained by transmission electron microscopy, x-ray diffraction, and substrate curvature technique, respectively. All films exhibited a dense and...

Early stages of plasma synthesis of diamond films

The early stages of diamond film nucleation and growth in a microwave plasma have been studied in detail as a function of important deposition parameters. The influence of the substrate temperature on the diamond nucleation rate, quality, and final film morphology has been elucidated through Raman spectroscopy and scanning electron microscopy measurements. Using transmission infrared spectroscopy and x‐ray diffraction, it is found that a carbide layer is initially formed on the substrate prior to the growth of the diamond film. Furthermore, the final film morphology is also a strong function of the plasma starting condition, the gas composition, and the substrate temperature.