A comparative study on the microstructure and tribological properties of Si3N4 and TiN films produced by the IBED method

The tribological properties of Si₃N₄ and TiN thin films produced by ion beam enhanced deposition (IBED) were compared on a SRV friction and wear testing machine. The friction coefficient of all thin films shows a descending tendency with increase in load, and is lower than that of 52100 steel. All the IBED films show a much better wear resistance than 52100 steel, especially in the higher load and frequency ranges; it can reach six times that of the latter. In order to understand the reasons for their excellent properties, the microstructure, microhardness and bonding strength with the substrate were analysed by SEM, X-ray diffraction, Knoop hardness and scratching test methods separately. The results show that the TiN(1) film exhibits the best tribological properties, which are closely related with its greater hardness and bonding strength.     

Structure, Mechanical, and Tribological Properties of MoS2/a-C:H Composite Films

A series of hydrogenated amorphous carbon (a-C:H) films doped with molybdenum disulfide (MoS₂) were deposited by medium frequency unbalanced magnetron sputtering with mixed Ar/CH₄ gases of different volume ratios as the source gases. The effects of Ar/CH₄ ratio on morphology, microstructure, mechanical, and tribological properties of the MoS₂/a-C:H composite films were investigated. Results show that the content of MoS₂ in the as-deposited films decreases with the decreasing Ar/CH₄ ratio, and the highest Ar/CH₄ ratio favors the formation of nanostructured films. Besides, the hardness and internal stress of the composite films first decrease and then increase with decreasing Ar/CH₄ ratio. Furthermore, the film deposited at the highest Ar/CH₄ ratio exhibits excellent antiwear ability in all test environments and shows promising potential as a solid lubricating film in aviation and space industries.     

Tribological behaviors of composite molecular deposition films

Polyallylamine hydrochloride (PAH)/graphite oxides (GO) ultrathin film and the multilayer film of PAH incorporated with TiO₂ enwrapped by polyacrylic acid (PAA), namely PAH/PAA(TiO₂) composite film, were prepared by molecular deposition (MD) method in laboratory. Both of them were heated to change the film forming dynamic force from electrostatic force to covalent bond so as to increase the bonding strength of the films. The structure and nanotribological properties of the films were analyzed by atomic force microscope (AFM) and ultraviolet-visible (UV) spectroscopy. It was found that these films had a much smaller friction force than their substrates and the friction force was dependent on the morphology and/or hardness of the films.     

Tribology and oxidation behavior of TiN/AlN nano-multilayer films

In this study, a series of TiN/AlN nano-multilayer films were prepared using a new sputtering setup, which features a medium frequency (MF) twin unbalanced magnetron sputtering system (UBMS) and a DC balanced magnetron sputtering system (BMS). The MF (6.78 MHz) twin UBMS, which is a modification of single RF power source system, is a special design of this deposition machine. The UBMS was employed to deposit the AlN film, and the BMS the TiN film. The aim of this study was to obtain, through controlling the deposition conditions, a group of TiN/AlN nano-multilayer films with various periods (λ). Then a series of experiments were conducted to understand their wear and oxidation properties.The results revealed that through controlling of the deposition parameters, the TiN/AlN nano-multilayer films with λ ranging from 2.4 to 67.6 nm were obtained. At λ3.6 nm, the nano-multilayers had extremely high hardness and excellent adhesion. The oxidation tests found that the multilayers had obviously better anti-oxidation property, as compared with the single-layer TiN film. The high hardness and good oxidation resistance contributed to very good wear performance of the TiN/AlN nano-multilayer films.     

Tribological and electrical properties of nanocrystalline Cu films deposited by DC magnetron sputtering with varying temperature

Cu films were deposited on Si substrates by direct current (DC) magnetron sputtering at three different substrate temperatures such as room temperature (RT), 100 °C and 200 °C. Possible mechanisms for substrate temperature dependent microstructure evolution in Cu films are discussed in this paper. Enhanced mechanical properties such as high hardness, high elastic modulus, low friction coefficient and high wear resistance of the films were obtained at deposition temperature of 100 °C. However, high friction coefficient as well as high wear rate was measured in films deposited at room temperature and 200 °C.     

Tribological behaviour and microstructure of TiCxN(1−x) coatings deposited by filtered arc

A series of macroparticle-free TiN, TiC_xN_(1−x) and TiC coatings were deposited on 316 austenitic stainless steel using a titanium target in a filtered arc deposition system (FADS) and reactive mixtures of N₂ and/or CH₄ gases. The surface topography, chemical composition and microstructure of these coatings were characterised by optical microscopy (OM), atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The microhardness has been measured and the adhesion of the coatings has been evaluated. Further, the wear and friction behaviour of the coatings were assessed under controlled test conditions in a pin-on-disc tribometer.The results show a significant increase in surface roughness, microhardness and wear resistance as the CH₄:N₂ gas flow rate ratio is increased. The composition of the coatings was strongly dependent on reactive gas flow rate during deposition. Surface particles were observed on high carbon content coatings and subsequently determined to be carbonaceous particles by using OM, AFM and EDS. At lowest load (10 N), all coatings exhibited low friction and wear. At loads of 15 and 25 N, the higher carbon content TiCN and TiC coatings showed a much lower friction and wear compared to TiN and low carbon TiCN.     

Physical properties of ultrafast deposited micro- and nanothickness amorphous hydrogenated carbon films for medical devices and prostheses

Hydrogenated amorphous carbon films with diamond-like structures have been formed on different substrates at very low energies and temperatures by a plasma-enhanced chemical vapour deposition (PECVD) process employing acetylene as the precursor gas. The plasma source was of a cascaded arc type with argon as the carrier gas. The films grown at very high deposition rates were found to have a practical thickness limit of approximately 1.5 microm, above which delamination from the substrate occurred. Deposition on silicon (100), glass, and plastic substrates has been studied and the films characterized in terms of sp3 content, roughness, hardness, adhesion, and optical properties. Deposition rates of up to 20 nm/s have been achieved at substrate temperatures below 100 degrees C. A typical sp3 content of 60-75 per cent in the films was determined by X-ray-generated Auger electron spectroscopy (XAES). The hardness, reduced modulus, and adhesion of the films were measured using a MicroMaterials NanoTest indenter/scratch tester. Hardness was found to vary from 4 to 13 GPa depending on the admixed acetylene flow and substrate temperature. The adhesion of the film to the substrate was significantly influenced by the substrate temperature and whether an in situ d.c. cleaning was employed prior to the deposition process. The hydrogen content in the film was measured by a combination of the Fourier transformation infrared (FTIR) spectroscopy and Rutherford backscattering (RBS) techniques. From the results it is concluded that the films formed by the process described here are ideal for the coating of long-term implantable medical devices, such as prostheses, stents, invasive probes, catheters, biosensors, etc. The properties reported in this publication are comparable with good-quality films deposited by other PECVD methods. The advantages of these films are the low ion energy and temperature of deposition, ensuring that no damage is done to sensitive substrates, very high deposition rates, relatively low capital cost of the equipment required, and the ease of adjustment of plasma parameters, which facilitates film properties to be tailored according to the desired application.     

Multiferroic behavior of the functionalized surface of a flexible substrate by deposition of Bi2O3 and Fe2O3

Thin films of bismuth and iron oxides were obtained by atomic layer deposition (ALD) on the surface of a flexible substrate poly(4,4′-oxydiphenylene-pyromellitimide) (Kapton) at a temperature of 250°C. The layer thickness was 50 nm. The samples were examined by secondary-ion mass spectrometry, and uniform distribution of elements in the film layer was observed. Surface morphology, electrical polarization, and mechanical properties were investigated by atomic force microscope, piezoelectric force microscopy, and force modulation microscopy. The values of current in the near-surface layer varied in the range of ±80 pA when a potential of 5 V was applied. Chemical analysis was performed by X-ray photoelectron spectroscopy, where the formation of Bi₂O₃ and Fe₂O₃ phases, as well as intermediate phases in the Bi–Fe–O system, was observed. Magnetic measurements were carried out by a vibrating sample magnetometer that showed a ferromagnetic response. The low-temperature method of functionalization of the Kapton surface with bismuth and iron oxides will make it possible to adapt the Bi–Fe–O system to flexible electronics.     

Mechanical and Tribological Properties of Diamond-Like Carbon Films Deposited by Electron Cyclotron Resonance Microwave Plasma Chemical Vapor Deposition

Mechanical and tribological properties of diamond-like carbon (DLC) films deposited by electron cyclotron resonance microwave plasma chemical vapor deposition were analyzed by nanoindentation, nanoscratch and ball-on-disk sliding tests. As the results, hardness and residual stress which depended on the substrate bias voltage had combined effects on the scratch resistance of the films. In sliding friction tests, the transferred layer on the surface of the counterpart accounts for the decrease of friction coefficient with increasing sliding distance. Atomic force microscopic images of the DLC films and the counterpart Si₃N₄ ball surfaces indicate that the sliding friction process could be treated as a periodical scratching process with many indenters.     

Influence of CH4 Flow Rate on Microstructure and Properties of Ti-C:H Films Deposited by DC Reactive Magnetron Sputtering

Nanocomposite Ti-containing hydrogenated carbon films (Ti-C:H) were prepared using a DC reactive magnetron sputtering system. The relationship between CH₄ flow rate and the film characterization and tribological behaviors in both ambient air and deionized water conditions were investigated. Results showed that the Ti content in the as-deposited Ti-C:H films decreased and the sp³ content increased with an increase in CH₄ flow rate. TiC nanocrystallites can be formed at a relatively low CH₄ flow rate, whereas there was almost no formation of TiC in the amorphous carbon matrix at the highest CH₄ flow rate. The hardness, elastic modulus, and internal stress of the films were decreased firstly and then increased as the CH₄ flow rate increased, whereas their adhesion presented an inversely changing trend. The friction coefficients and wear rates of Ti-C:H films in both ambient air and deionized water conditions decreased with increasing CH₄ flow rate from 8 to 12 sccm and then increased as the CH₄ flow rate continually increased. In particular, the nanocomposite Ti-C:H film deposited with a CH₄ flow rate of 12 sccm could achieve superior combining mechanical properties and low friction and high antiwear behaviors in both ambient air and deionized water conditions, indicating potential applications as a protective and lubricating film for mechanical components.     

Sliding friction and wear properties of CNX/TiN composite films

A combined dc magnetron sputtering and multi-arc deposition system was used to grow CN_X/TiN composite films on a high-speed-steel (HSS) substrate. The thickness of these films is about 3 μm, the hardness of the coating exceeds 50 GPa. The sliding friction properties were studied by ball-on-disc tests under different loads and speeds. The wear mode of the films was observed and analyzed. There exist spallation, abrasion and micro-ploughing wear modes under different loads. The critical load value was theoretically determined and tested to be 55 N. The results show that the alternating films have good wear resistance under heavy load and high speed.     

Deposition and Nanotribological Characterization of Sub-100-nm Thick Protective Ti-Based Coatings for Miniature Applications

Ti-based protective thin films with thicknesses below 100 nm, intended for miniature applications were deposited using physical vapor deposition magnetron sputtering. X-ray diffraction (XRD), scanning electron microscopy, and atomic force microscopy were employed for the assessment of microstructure, morphology, film thickness, surface topography, and roughness. XRD pattern showed the formation of f.c.c TiN, TiCN, and TiC phases with different preferred orientations for films prepared in Ar/N₂, Ar/N₂ + C₂H₂, and Ar/C₂H₂ gas mixtures, respectively. Nanotribological performance was investigated using multipass nanoscratch technique at variable applied normal loads (100–400 μN). The nanoscale coefficient of friction was found to be in the 0.08–0.1 range, a sufficiently low value showing the potential of these films for miniature applications, such as microelectromechanical systems. The nanowear resistance at mean contact pressures in the range of 5–8.5 GPa for each sample was evaluated in terms of the average residual wear depth and an abrasive-dominated wear mechanism was found.     

Conventional and ionized magnetron sputter‐deposition of nanocrystalline titanium diboride thin films

Titanium diboride has many interesting physical and chemical properties that make it attractive as a tribological coating material. We focus our study on the relationship between hardness, crystal structure and processing parameters for TiB₂ thin films produced by conventional and ionized magnetron sputtering. When synthesized by conventional magnetron sputtering, TiB₂ films with the highest degree of crystallinity have the highest hardness and are obtainable at an optimum combination of argon pressure and substrate bias. The films also show strong (0001) texture. Such high degree of crystallinity can be obtained without substrate bias by ionized magnetron sputtering, in which enhanced ionization of the plasma is obtained by inductively coupling RF power in the region between the magnetron target and the substrate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural properties of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 relaxor ferroelectric thin films on SrRuO3 conducting oxides

Coating of 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–PT) relaxor ferroelectrics by a sol–gel method is followed by growth of epitaxial SrRuO₃ (SRO) metallic oxide electrodes on SrTiO₃ (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN–PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN–PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed.     

Tribological behavior of plasma-enhanced CVD a-C:H films. Part I: effect of processing parameters

A systematic study was conducted on the effect of plasma-enhanced CVD processing parameters, namely bias voltage, pressure and CH₄/Ar flow ratio, on the characteristics and tribological response of amorphous hydrogenated carbon (a-C:H) films. Film hardness, intrinsic stress, structure, composition and tribological response were characterized. Variation of processing parameters was found to produce a-C:H films with a range of characteristics with the CH₄/Ar ratio exercising a dominant effect. A low ratio produced harder films with more sp³ bonding, low hydrogen content and low wear rate; whereas a high ratio produced softer films, with more sp² bonding, higher hydrogen content and low friction. Film characteristics were found to affect the wear mechanism with softer films showing a layer-by-layer removal and harder films involving formation of fine debris. These two diverse types of films offer the opportunity to synthesize multilayered films combining desirable properties from each component.     

An apparatus for pulse chemical vapor deposition of layers

An apparatus for chemical deposition of layers of different materials with pulsed automated dosing of a hot gas phase of volatile metal-organic compounds (precursors) admitted into a reaction chamber is described. The apparatus has three channels for dosing the gas precursor phase and three channels for dosing reacting gases. As an example, a technique for depositing HfO₂ films on a (100)Si substrate is presented, and the deposited films are analyzed. It is shown, that this apparatus can be used to deposit layers on complex 3D systems with a large aspect ratio using an example of the deposition of HfO₂ layers on the inner surfaces of channels of a microchannel plate.     

Boundary Lubrication Properties of Nanoperiod Solid Lubricant Multilayer Films Composed of Diamond-Like Carbon and Gold Layers

To develop electroconductive and high-endurance solid lubricant nanoperiod multilayer (DLC/Au)_n films, diamond-like carbon (DLC) and gold layers were deposited while controlling the time the substrate was exposed graphite and gold targets. The electrical resistivity of the (DLC/Au)_n multilayer films was ~12.4 Ω cm. The hardness of the (DLC/Au)_n multilayer films was similar to that of DLC films and much higher than that of gold monolayer films. According to the results of oscillating sliding tests under water boundary lubrication and dry conditions, (DLC/Au)_n multilayer films exhibited the low friction coefficient, little damage, and high sliding durability than the monolayer films. (DLC/Au)_n films also have a lower friction coefficient and exhibit less damage than a Au monolayer under polyalphaolefin boundary lubrication.     

Mechanical and Tribological Properties of Thin Remote Microwave Plasma CVD a-Si:N:C Films from a Single-Source Precursor

Silicon carbonitride (a-Si:N:C) films produced by remote plasma chemical vapor deposition (RP-CVD) were investigated. Tetramethyldisilazane as a single-source precursor and (H₂+N₂) upstream gas mixture for plasma generation were used. The influence of the upstream gas composition on the structure, density, mechanical and tribological properties of the films deposited on p-type Si (001) wafers (both heated—T _s =300°C and unheated—T _s =30°C) are reported. The H₂ RP-CVD process was found to result in the formation of outstanding low friction (0.04) and high hardness (H=27-31 GPa) a-Si:N:C films exhibiting promisingly high H/E values.     

Structural, optical and mechanical properties of nanostructure diamond synthesized by chemical vapor deposition

Nanostructure diamond (NSD) films on Si substrate are prepared by microwave plasma enhanced chemical vapor deposition (MPECVD) using methane and hydrogen as the reactants with two-step negative substrate bias (SB). The dependencies of the NSD film morphology, grains, surface roughness, crystal and bonding structures and hardness on the negative SB at the bias-enhanced growth (BEG) step and substrate temperature during growth have been investigated by conducting atomic force microscopy (CAFM), X-ray diffraction (XRD), Raman spectroscopy and nanoindentation. The hardness of the NSD film is found to be as high as 80 GPa with CAFM average and root mean square roughness of 7 and 9 nm, respectively, under optimal negative SB at the BEG step. From the studies of substrate temperature effect, the hardness of the NSD film is as high as 70 GPa, with average and root mean square CAFM roughness of 9 and 11 nm, respectively, which were obtained at a substrate temperature of 500 °C. In both cases, the film hardness was found to be affected by the size of clusters, which are composed of many small NSD particles, the amount of NSD in an amorphous matrix as well as surface roughness. We also synthesized transparent NSD films by MPECVD under optimized single-step growth conditions on quartz substrates, which are scratched with several micrometers diamond powder. A hardness as high as 60 GPa and a maximum transmittance of 60% in the visible light region are achieved for an NSD coating of 1.0 μm thickness with small surface roughness.     

Atomistic Insights into the Running-in,Lubrication, and Failure of Hydrogenated Diamond-Like Carbon Coatings

The tribological performance of hydrogenated diamond-like carbon (DLC) coatings is studied by molecular dynamics simulations employing a screened reactive bond-order potential that has been adjusted to reliably describe bond-breaking under shear. Two types of DLC films are grown by CH₂ deposition on an amorphous substrate with 45 and 60 eV impact energy resulting in 45 and 30% H content as well as 50 and 30% sp³ hybridization of the final films, respectively. By combining two equivalent realizations for both impact energies, a hydrogen-depleted and a hydrogen-rich tribo-contact is formed and studied for a realistic sliding speed of 20 m s⁻¹ and loads of 1 and 5 GPa. While the hydrogen-rich system shows a pronounced drop of the friction coefficient for both loads, the hydrogen-depleted system exhibits such kind of running-in for 1 GPa, only. Chemical passivation of the DLC/DLC interface explains this running-in behavior. Fluctuations in the friction coefficient occurring at the higher load can be traced back to a cold welding of the DLC/DLC tribo-surfaces, leading to the formation of a transfer film (transferred from one DLC partner to the other) and the establishment of a new tribo-interface with a low friction coefficient. The presence of a hexadecane lubricant leads to low friction coefficients without any running-in for low loads. At 10 GPa load, the lubricant starts to degenerate resulting in enhanced friction.