Morphology-Controlled Synthesis of Hexagonal Boron Nitride Crystals by Chemical Vapor Deposition

Abstract

Synthesis of hexagonal boron nitride (hBN) crystals with a controlled morphology is a major challenge due to various kinetic and thermodynamic factors at the edge. Supplying BN building blocks by heating precursor ammonia borane at a temperature of 90 °C produced triangular crystals, whereas, at higher heating (130 °C), hBN crystals with a hexagonal morphology were observed. The shape of crystals could also be modulated from hexagonal to triangular under a continuous reduced supply of BN building blocks. We attributed these phenomena to a different growth mechanism dependent on the concentration of BN radicals in the growth region. With a low supply of BN building blocks, crystal growth is the edge attachment limited, producing triangles, whereas, under higher concentration of BN building blocks, crystal growth is limited by diffusion producing hexagons. The presence of alternating B and N terminated vertices in hexagonal hBN crystals offers the possibility of hBN/graphene in-plane heterostructure synthesis with B-C and N-C bonding at the interface, which is not possible with N terminated triangular crystals. Supplying the controlled amount of BN building blocks to synthesize triangular and hexagonal crystals and modulation from hexagons to triangles is a major achievement (in the present work) due to single parameter control over the experiment.

Atomically Thin Hexagonal Boron Nitride and Its Heterostructures

“…Furthermore, the content of precursor in feedback is vital for the growth of 2D materials, [ 90–97 ] it can be also employed to tune the growth behaviors of h‐BN crystals. [ 80,82,98 ] This phenomenon is attributed to the modulated ratio of diffusion and availability of active N and B radicals, which makes crystal growth for either favorable triangular shape with N terminated edges or hexagonal shape with alternating N and B terminated edges. [ 80,82,98 ] It has been reported that the shapes of h‐BN single crystals can be tailored from triangular to truncated triangular and further to hexagonal by simple moving away the Cu substrate from the CVD tube inlet.…”

“…[ 80,82,98 ] This phenomenon is attributed to the modulated ratio of diffusion and availability of active N and B radicals, which makes crystal growth for either favorable triangular shape with N terminated edges or hexagonal shape with alternating N and B terminated edges. [ 80,82,98 ] It has been reported that the shapes of h‐BN single crystals can be tailored from triangular to truncated triangular and further to hexagonal by simple moving away the Cu substrate from the CVD tube inlet. [ 82 ] The shape variation of h‐BN crystals was attributed to different ratios of boron to nitrogen active species concentrations inside the CVD reactor.…”

“…[ 80 ] Similar phenomenon has also been reported by Tanemura and co‐workers, the morphology of h‐BN crystals could also be modulated from triangular to hexagonal by increasing heating temperature of precursor. [ 98 ]…”

Fundamentals of Chemical Vapor Deposited Graphene and Emerging Applications

“…hBN can be considered as a structural analogue of graphene, which is composed of alternating boron and nitrogen atoms in a honeycomb lattice rather than the carbon atoms. Graphene with a zero bandgap is a semimetallic as discussed in Section 1, while hBN with a bandgap of ~6 eV is insulating [100][101][102][103][104][105][106][107]. Significant carrier mobility of graphene has been achieved on atomically flat hBN as a dielectric layer for the FET device.…”

A high-throughput synthesis of large-sized single-crystal hexagonal boron nitride on a Cu–Ni gradient enclosure

“…1. [5][6][7][9][10][11][12][13][14][15][16][17][18][19][20][21][22] It is in order to grow h-BN with a higher growth rate and simultaneously guarantee the lateral size.…”