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▲ [16p-F203-11] Controlling Morphology of hBN crystals during chemical Vapor deposition synthesis
Keywords:hexagonal boron nitride, Morphology control, chemical vapor deposition
Recently hexagonal boron nitride (hBN) has attracted considerable attention due its closer lattice resemblance with graphene. [1] In hBN lattice, B and N are Sp2 hybridized in honeycomb arrangement. hBN has demonstrated many novel properties like high transparency, thermal conductivity, anti-oxidation behavior and UV emission. Absence of dangling bonds and charge traps also makes hBN better substrate compared to conventionally used SiO2. For graphene case, the shape evolution of graphene crystal has been studied extensively with shapes ranging from hexagonal, triangle, round shape, flower shaped and fractals. [2] In this work we report controlled growth process of hBN with synthesis of triangular and hexagonal hBN crystals and also conversion of hexagonal to triangular crystals with manipulation of growth parameters.
In this work atmospheric pressure chemical vapor deposition (APCVD) is used for the synthesis of hBN on Cu substrate using ammonia borane (H3NBH3) as precursor. Ammonia Borane was heated at 90ºC and 130ºC in two different sets of experiments with other parameters remaining same. It was observed that hBN crystals synthesized at 90ºC were triangular whereas synthesized at 130ºC demonstrated hexagonal morphology. Different set of experiment was designed in which first half part hexagonal crystal was grown by supplying higher rate of BN (at 130ºC) building block and reducing in other half (at 90ºC). It was observed that hexagonal crystal slowly obtained triangular morphology with increase in growth time. These phenomena can be attributed to different growth mechanism depending upon concentration of BN building blocks in growth region. Triangles with zigzag edges are equilibrium shape for hBN crystal under low supply of precursor due to edge attachment as the rate-limiting phenomenon. During high concentration supply of BN radicals, kinetics at edge would be changed, with diffusion becoming rate-limiting phenomenon for crystal growth. Increased diffusion and availability of free B and N radicals makes crystal growth favorable on both B and N terminated edges for maintaining hexagonal morphology. In this work we achieved tuning the growth mechanism from edge attachment limited to diffusion limited by drastic reduction in supply of BN building blocks hence modulating crystal morphology
In this work atmospheric pressure chemical vapor deposition (APCVD) is used for the synthesis of hBN on Cu substrate using ammonia borane (H3NBH3) as precursor. Ammonia Borane was heated at 90ºC and 130ºC in two different sets of experiments with other parameters remaining same. It was observed that hBN crystals synthesized at 90ºC were triangular whereas synthesized at 130ºC demonstrated hexagonal morphology. Different set of experiment was designed in which first half part hexagonal crystal was grown by supplying higher rate of BN (at 130ºC) building block and reducing in other half (at 90ºC). It was observed that hexagonal crystal slowly obtained triangular morphology with increase in growth time. These phenomena can be attributed to different growth mechanism depending upon concentration of BN building blocks in growth region. Triangles with zigzag edges are equilibrium shape for hBN crystal under low supply of precursor due to edge attachment as the rate-limiting phenomenon. During high concentration supply of BN radicals, kinetics at edge would be changed, with diffusion becoming rate-limiting phenomenon for crystal growth. Increased diffusion and availability of free B and N radicals makes crystal growth favorable on both B and N terminated edges for maintaining hexagonal morphology. In this work we achieved tuning the growth mechanism from edge attachment limited to diffusion limited by drastic reduction in supply of BN building blocks hence modulating crystal morphology