AFM and Optical Studies of Boron Nitride and Graphene Grown By High Temperature Molecular Beam Epitaxy

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Hexagonal boron nitride (hBN) can be used as an insulating barrier layer on other 2D materials such as graphene or as a semiconductor with a 6 eV band gap [1]. In most research the hBN is exfoliated from bulk crystals using adhesive tape and transferred to other substrates. We have been investigating the growth of hexagonal boron nitride and graphene by high temperature molecular epitaxy for several years [2]. The aim is to grow hBN in a way that is scalable to allow controlled heterostructures of hBN and graphene (for instance) to be grown.At present our focus is on understanding how dopant atoms such as carbon are incorporated into the hexagonal boron nitride and affect the growth of the layers. We use atomic resolution atomic force microscopy (AFM), spectroscopic ellipsometry and confocal fluorescent microscopy to study the structure and optical response of the layers. For example, at low carbon doping we have identified single photon emitters that have previously been proposed as being related to carbon impurities [3] and at high carbon doping we can see the formation of impurity bands in the spectroscopic ellipsometry signatures. We also collaborate with several groups internationally [e.g. refs 1 and 3 ] to make additional measurements e.g. fluorescence study in the deep UV.The PhD student in this project will be responsible for measuring and analysing the samples using high resolution ambient AFM, confocal microscopy and spectroscopic ellipsometry. For the confocal microscopy experiments there is scope to further develop the instrumentation and to study other types of defects e.g. boron vacancies that appear to be very stable, can act as single photon emitters and are candidate materials for local sensing of magnetic fields [4].References1. C. Elias, et al, (2019) Nature Communications 10, 26392. Y.J. Cho, et al, (2016) Scientific Reports 6, 344743. N. Mendelson, et al, (2021) Nature Materials 20, 3214. H.L. Stern, et al, (2022) Nature Communications 13, 618