Synthesis and characterization of boron incorporated diamond-like carbon thin films

Abstract

Diamond-like carbon (DLC) thin films have been attracting significant interest from both academic and industrial communities due to their unique structures and properties. Boron (B) incorporation is very promising to modify DLC properties for electronic and mechanical applications. However, the current techniques suffer from their limitations and it’s difficult to use them to prepare high quality B incorporated DLC (B-DLC) films to meet application demands. A recently developed biased target ion beam deposition (BTIBD) technique has been applied to produce high quality DLC based films, but no work has been reported on synthesis of B-DLC films by BTIBD and their characteristics. In this work, B-DLC films were synthesized on silicon wafers using BTIBD technique, where DLC was deposited by ion beam deposition and B was simultaneously incorporated by ion beam sputtering of boron carbide (B4C) under different conditions. DLC films and B-carbon (B-C) films were also synthesized by ion beam deposition and ion beam sputtering of B4C under similar conditions, respectively, as reference samples and for estimation of B4C sputtering rate and DLC deposition rate to control the B content in B-DLC. Scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy, synchrotron-based X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure were applied to investigate morphology, microstructure, chemical composition and bonding state of the films. Nanoindentation and ball-on-disc tests were conducted using a Universal Mechanical Tester to measure hardness, Young’s modulus and friction coefficient of the synthesized films. The preliminary relationships between processing conditions, film structures and properties were investigated. B-DLC thin films with different B doping levels (up to 8 wt. %) have been successfully synthesized by the BTIBD technique and the B concentration incorporated increases with the increase of target bias voltage and sputtering ion current density. It has been found that B exists in different states in B-DLC, including carbon-rich and B-rich boron carbides, boron suboxide and boron oxide, and the oxidation of B probably occurs during the film deposition. The incorporation of B into DLC leads to the increase of sp3 bonded carbon in the films, the increase of both film hardness and elastic modulus, and the decrease of both surface roughness and friction coefficient. Furthermore, the content of sp3 bonded carbon, film hardness and elastic modulus increase, and the film surface roughness and friction coefficient decrease with the increase of B-rich B-C bonding content in the B-DLC films. The results demonstrate a good promise to synthesize quality B-DLC films using BTIBD.