Computational Predictions and Microwave Plasma Synthesis of Superhard Boron-Carbon Materials

Abstract

Superhard boron-carbon materials are of prime interest due to their non-oxidizing properties at high temperatures compared to diamond-based materials and their non-reactivity with ferrous metals under extreme conditions. In this work, evolutionary algorithms combined with density functional theory have been utilized to predict stable structures and properties for the boron-carbon system, including the elusive superhard BC5 compound. We report on the microwave plasma chemical vapor deposition on a silicon substrate of a series of composite materials containing amorphous boron-doped graphitic carbon, boron-doped diamond, and a cubic hard-phase with a boron-content as high as 7.7 at%. The nanoindentation hardness of these composite materials can be tailored from 8 GPa to as high as 62 GPa depending on the growth conditions. These materials have been characterized by electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, and nanoindentation hardness, and the experimental results are compared with theoretical predictions. Our studies show that a significant amount of boron up to 7.7 at% can be accommodated in the cubic phase of diamond and its phonon modes and mechanical properties can be accurately modeled by theory. This cubic hard-phase can be incorporated into amorphous boron-carbon matrices to yield superhard materials with tunable hardness values.

First-principles study of the surface structure and stability of BC5

“…Later, Xi et al [16] claimed that Pmma was more stable than I-4m2. The same conclusion has been obtained by Li et al [2], Alp et al [3], and Baker et al [14]. Using thorough structural searches with an evolutionary algorithm, Li et al [2] proposed the orthorhombic Pmma structure was thermodynamically the most favorable among the P3m1, Imm2, I-4m2, and Pmma phases and agreed well with the experimental x-ray diffraction and Raman data.…”

“…They also proposed that for diamond-like B-C materials, cubic-BC 5 represented the metastable limit solubility of boron in diamond (16 at% of B) [1]. Recently, Baker et al [14] synthesized a superhard d-BC x with a boron-content up to 7.7 at% using the microwave plasma chemical vapor deposition on a silicon substrate. The Scanning Electron Micrograph of the sample (2.9 at% boron) revealed a (100) plane and a further increased boron content to 7.7 at% causes a less faceted structure.…”

“…The Scanning Electron Micrograph of the sample (2.9 at% boron) revealed a (100) plane and a further increased boron content to 7.7 at% causes a less faceted structure. They proposed that the most stable bulk BC 5 presents an orthorhombic phase with Pmma symmetry employing evolutionary algorithms combined with DFT [14]. However, due to the lack of important information such as atomic coordinates in experiments, it is necessary to use first-principles calculations to determine the possible stable bulk and surface structures.…”

Modulating Band Gap of Boron Doping in Amorphous Carbon Nano-Film

“…Semiconductor films are the most common form of amorphous carbon (a-C) films, owing to the superior mechanical, optical, and opto-electronic properties [1,2,3,4,5]. Even though the carbon atoms are disordered in a-C, the optical band gap (E opt ) is still controllable, and the E opt can be changed over a quite large range from 1 eV to 4 eV [6,7].…”

Teknologi Material Maju : Prinsip Dasar dan Aspek Rekayasa

“…1.Baker PA, Catledge SA, Harris SB, Ham KJ,Chen WC, et al 2018. Computational Predictions and Microwave Plasma Synthesis of Superhard Boron-Carbon Materials.…”