Improvement in Tribological Properties by Modification of Grain Boundary and Microstructure of Ultrananocrystalline Diamond Films

Abstract

Grain boundaries and microstructures of ultrananocrystalline diamond (UNCD) films are engineered at nanoscale by controlling the substrate temperature (TS) and/or by introducing H2 in the commonly used Ar/CH4 deposition plasma in a microwave plasma enhanced chemical vapor deposition system. A model for the grain growth is proposed. The films deposited at low TS consist of random/spherical shaped UNCD grains with well-defined grain boundaries. On increasing TS, the adhering efficiency of CH radical onto diamond lattice drops and trans-polyacetylene (t-PA) encapsulating the nanosize diamond clusters break due to hydrogen abstraction activated, rendering the diamond phase less passivated. This leads to the C2 radical further attaching to the diamond lattice, resulting in the modification of grain boundaries and promoting larger sized clustered grains with a complicated defect structure. Introduction of H2 in the plasma at low TS gives rise to elongated clustered grains that is attributed to the presence of atomic hydrogen in the plasma, preferentially etching out the t-PA attached to nanosized diamond clusters. On the basis of this model a technologically important functional property, namely tribology of UNCD films, is studied. A low friction of 0.015 is measured for the film when ultranano grains are formed, which consist of large fractions of grain boundary components of sp(2)/a-C and t-PA phases. The grain boundary component consists of large amounts of hydroxylic and carboxylic functional groups which passivates the covalent carbon dangling bonds, hence low friction coefficient. The improved tribological properties of films can make it a promising candidate for various applications, mainly in micro/nanoelectro mechanical system (M/NEMS), where low friction is required for high efficiency operation of devices.

Enhanced strength of nano-polycrystalline diamond by introducing boron carbide interlayers at the grain boundaries

“…cBN) at the grain boundaries. 3,13,[26][27][28] Thus, the simultaneous enhancement of fracture toughness and stability in this work primarily depends on the existence of the so grain boundary phase, B 4 C domains (shown in Fig. 5), which is of great help in releasing the residual stress formed during the HPHT sintering process.…”

“…3 Extensive experimental and theoretical studies had been devoted to further strengthening polycrystalline superhard materials, involving controlled creation of composted phases, internal defects, stacking faults and interface boundaries. 13,14,[26][27][28][29] Diamond particles can be sintered into strong masses in crystalline forms directly by HPHT methods, consisting of easily controllable physical dimensions, shape and ne grain size. 1,10 The introduction of other superhard materials (cBN) in the npdiamond was found to effectively improve its mechanical and stability properties.…”

An Insight into Grain Refinement Mechanism of Ultrananocrystalline Diamond Films Obtained by Direct Current Plasma-Assisted Chemical Vapor Deposition

“…The emission peaks at 388.8, 486.7, and 656.3 nm were attributed to CH (B 2 Σ − X 2 Π), H β , and H α emissions, respectively (see Figure ) . Using the ratio of the H β versus H α emissions, the electron temperatures were calculated according to the procedure reported by Suzuki et al and Larijani et al The resulting electron temperature variation at the three important locations of the discharge was plotted against the IEEF in Figure .…”

Anisotrpic friction behavior of charcoal and the influence of humidity

“…However, the quantum of lubricity associated with these materials is anisotropic and low friction is exhibited only under certain specific conditions. Some of carbon allotropes and carbonbased advanced materials prepared by physical and chemical vapor deposition also signifies advanced tribological properties [5][6][7][8]. However, there are several limitations in realizing practical applications of thin film deposited by physical and chemical means.…”