Self-assembled Cubic Boron Nitride Nanodots

Alireza Khanaki,Hao Tian,Jianlin Liu,Jian-Guo Zheng,Zhongguang Xu,Zheng Zuo,Renjing Zheng

doi:10.1038/s41598-017-04297-1

Abstract

One of the low-dimensional Boron Nitride (BN) forms, namely, cubic-BN (c-BN) nanodots (NDs), offers a variety of novel opportunities in battery, biology, deep ultraviolet light emitting diodes, sensors, filters, and other optoelectronic applications. To date, the attempts towards producing c-BN NDs were mainly performed under extreme high-temperature/high-pressure conditions and resulted in c-BN NDs with micrometer sizes, mixture of different BN phases, and containing process-related impurities/contaminants. To enhance device performance for those applications by taking advantage of size effect, pure, sub-100 nm c-BN NDs are necessary. In this paper, we report self-assembled growth of c-BN NDs on cobalt and nickel substrates by plasma-assisted molecular beam epitaxy. It is found that the nucleation, formation, and morphological properties of c-BN NDs can be closely correlated with the nature of substrate including catalysis effect, lattice-mismatch-induced strain, and roughness, and growth conditions, in particular, growth time and growth temperature. The mean lateral size of c-BN NDs on cobalt scales from 175 nm to 77 nm with the growth time. The growth mechanism of c-BN NDs on metal substrates is concluded to be Volmer-Weber (VW) mode. A simplified two-dimensional numerical modeling shows that the elastic strain energy plays a key role in determining the total formation energy of c-BN NDs on metals.

Highlights

Boron nitride (BN) is a III-V compound and isoelectronic to the structured carbon lattice, i.e., can possess sp2- and sp3-bonded phases
As the self-assembly formation of dots represents a process of strain relaxation due to lattice mismatch between the dots and substrate, the degree of strain relaxation may vary from dots with different sizes and shapes, and from near the substrate-NDs interface to the upper part within the same dot, as shown in Transmission electron microscopy (TEM) imaging later
We report self-assembled growth of c-Boron Nitride (BN) NDs on Co and Ni metal substrates by plasma-assisted molecular beam epitaxy (MBE)

Summary

Introduction

Boron nitride (BN) is a III-V compound and isoelectronic to the structured carbon lattice, i.e., can possess sp2- and sp3-bonded phases. This feature leads to a variety of crystalline BN forms including hexagonal (h-BN), rhombohedral (r-BN), turbostratic (t-BN), cubic (c-BN) and wurtzite (w-BN) Among all these crystalline forms, bulk c-BN is most thermodynamically stable, which has excellent physical and chemical properties such as super high hardness (>70 GPa), wide direct band-gap energy (Eg ≈ 6.4 eV), doping ability for both p- and n-type conductivity, very high isotropic thermal conductivity (13 Wcm−1K−1) along with very low linear thermal expansion (1.2 × 10−6 °C−1), low dielectric constant (7.1), high breakdown field (~0.7 Vnm−1), high-oxidation resistant (>1300 °C), and high structural and chemical stability. A simplified numerical model is introduced to simulate the formation energy behaviour of c-BN NDs on metal substrates

Methods

Results

Conclusion