Wang, Jian Wang, Zhiqiang Cho, Hyunjin Kim, Myung Jong Sham, T. K. Sun, Xuhui 2024-01-20T08:00:50Z 2024-01-20T08:00:50Z 2021-09-04 2015-02 2040-3364 https://pubs.kist.re.kr/handle/201004/125839 Chemical imaging, thickness mapping, layer speciation and polarization dependence have been performed on single and multilayered (up to three layers and trilayered nanosheets overlapping to form 6 and 9 layers) hexagonal boron nitride (hBN) nanosheets by scanning transmission X-ray microscopy. Spatially-resolved XANES directly from freestanding regions of different layers has been extracted and compared with sample normal and 30 degrees tilted configurations. Notably a double feature sigma* excitonic state and a stable high energy sigma* state were observed at the boron site in addition to the intense pi* excitonic state. The boron projected sigma* DOS, especially the first sigma* exciton, is sensitive to surface modification, particularly in the single layered hBN nanosheet which shows more significant detectable contaminants and defects such as tri-coordinated boron/nitrogen oxide. The nitrogen site has shown very weak or no excitonic character. The distinct excitonic effect on boron and nitrogen was interpreted to the partly ionic state of hBN. Bulk XANES of hBN nanosheets was also measured to confirm the spectro-microscopic STXM result. Finally, the unoccupied electronic structures of hBN and graphene were compared. English ROYAL SOC CHEMISTRY TRANSMISSION BN SPECTROSCOPY Layer speciation and electronic structure investigation of freestanding hexagonal boron nitride nanosheets Article 10.1039/c4nr04445b 1 NANOSCALE, v.7, no.5, pp.1718 - 1724 NANOSCALE 7 5 1718 1724 scie scopus 000348348300022 2-s2.0-84921755346 Chemistry, Multidisciplinary Nanoscience & Nanotechnology Materials Science, Multidisciplinary Physics, Applied Chemistry Science & Technology - Other Topics Materials Science Physics Article TRANSMISSION BN SPECTROSCOPY h-BN X-ray analysis