Preparation And Characteristics Of Hexagonal Boron Nitride Single Crystal Based On Metal Flux Method

Hexagonal boron nitride(h BN)has a structure similar to graphene,but its band gap is about 5.9 e V,which means it has excellent dielectric properties.Its was thus used to reduce effectively the charge scattering in two-dimensional semiconductor devices.Single-layer or few-layer hexagonal boron nitride is one of the best choices for high-performance twodimensional material device substrates,gate insulators or tunneling layers.It also has broad applications in deep ultraviolet detectors,emitters and neutron detectors.Currently,the main problem hindering the research and application of hexagonal boron nitride is the preparation of high quality and large size single crystals.As the hexagonal boron nitride has very high melting point and low vapor pressure,it is not easy to be fabricated under normal environmental conditions.My work focuses on the growth of high quality and large sized hexagonal boron nitride single crystal material using the metal flux method,that is,the raw materials are dissolved in the metal flux at a high temperature,and then slowly cooled down to induce the crystal grow on the metal flux surface.The main results are as follows:1.h BN single crystals were successfully grown by using nickel-chromium alloy as the metal flux.The feasibility of the metal flux method was verified using our own apparatus.At the same time,we made some improvements on equipment setup,raw material selection,etc.We have also studied on sample post-processing methods such as single crystal thickness measurement method,single crystal separation(from the metal flux),and transfer methods.2.Carbon powder was added in the metal flux in order to obtain a high yield of h BN single crystal.1.8% carbon was found to increase greatly the yield of the h BN single crystal while keep its quality.3.More metal flux systems,such as cobalt-chromium,nickel-tungsten,cobalt-tungsten and 301 stainless steel alloy,were used to grow large-size and high-quality single crystals.Among them,the maximum crystal size grown by 301 stainless steel alloy reaches 1.2 cm.4.The mechanism of h BN crystal growth using metal flux method was studied.A possible crystal growth model was proposed.It provides new ideas for subsequent researches.During this research,we used many advanced methods such as SEM,TEM,RAMAN,XRD,and EELS in order to achieve some fundamental insights in the metal flux h BN technique.After a large number of experiments and a series of optimization,the hexagonal boron nitride single crystal we finally grow has high quality and large size,which may meet various applications.