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

六方氮化硼（hBN）可用作其他2D材料（如石墨烯）上的绝缘阻挡层，或用作带隙为6 eV的半导体[1]。在大多数研究中，使用胶带将hBN从块状晶体剥离并转移到其他基底上。几年来，我们一直在研究通过高温分子外延生长六方氮化硼和石墨烯[2]。我们的目标是以一种可扩展的方式生长hBN，以允许hBN和石墨烯（例如）的受控异质结构生长。目前，我们的重点是了解掺杂剂原子（如碳）如何掺入六方氮化硼并影响层的生长。我们使用原子力显微镜（AFM），椭圆偏振光谱仪和共聚焦荧光显微镜来研究的结构和光学响应的层。例如，在低碳掺杂下，我们已经确定了先前被提出与碳杂质有关的单光子发射体[3]，并且在高碳掺杂下，我们可以在光谱椭圆偏振特征中看到杂质带的形成。我们还与国际上的几个小组[例如参考文献1和3 ]合作，进行额外的测量，例如深紫外荧光研究。该项目的博士生将负责使用高分辨率环境AFM，共聚焦显微镜和光谱椭圆偏振法测量和分析样品。对于共焦显微镜实验，有进一步开发仪器和研究其他类型缺陷的范围，例如硼空位，这些缺陷看起来非常稳定，可以作为单光子发射器，并且是局部磁场传感的候选材料[4]。C. Elias，et al，（2019）Nature Communications 10，26392. Y.J.Cho等人，（2016）Scientific Reports 6，344743. N. Mendelson等人，（2021）Nature Materials 20，3214. H.L. Stern等人，（2022）Nature Communications 13，618

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