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Theoretical Study of the Bias-Dependent Scanning Tunneling Microscopy Images of Pyridine on Ge(001)
Suklyun Hong,Hanchul Kim 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
We have studied the electronic structure of a pyridine-adsorbed Ge(001) surface using ab initio pseudopotential calculations. Examining the projected density of states, we found that the N lone-pair state, which is the highest occupied molecular orbital, and the down-Ge dangling bond disappear in forming a dative bond. Other molecular orbitals of pyridine are found to rigidly shift downwards due to the surface potential with some degree of broadening. Such changes in the electronic structure induced by the pyridine adsorption explain well the bias dependence of the scanning tunneling microscopy images, and the simulated images are in accordance with the experimental observation.
Theoretical Demonstration of the Ionic Barristor
Nie, Yifan,Hong, Suklyun,Wallace, Robert M.,Cho, Kyeongjae American Chemical Society 2016 Nano letters Vol.16 No.3
<P>In this Letter, we use first-principles simulations to demonstrate the absence of Fermi-level pinning when graphene is in contact with transition metal dichalcogenides (TMDs). We find that formation of either an ohmic or Schottky contact is possible. Then we show that, due to the shallow density of states around its Fermi level, the work function of graphene can be tuned by ion adsorption. Finally we combine work function tuning of graphene and an ideal contact between graphene and TMDs to propose an ionic barristor design that can tune the work function of graphene with a much wider margin than current barristor designs, achieving a dynamic switching among p-type ohmic contact, Schottky contact, and n-type ohmic contact in one device.</P>
Structure of Glycine on Ge(100): Ab Initio Study of Its Scanning Tunneling Microscopy Images
Park, Jinwoo,Hong, Suklyun American Chemical Society 2012 The Journal of Physical Chemistry Part C Vol.116 No.26
<P>We have performed ab initio calculations to study the atomic and electronic structure of glycine on the Ge(100) surface. Previously, adsorption configurations of glycine on Ge(100) was studied using scanning tunneling microscopy (STM), density functional theory (DFT) calculations, and high-resolution core-level photoemission spectroscopy (HRCLPES), where the most probable structure observed in experiment was assigned to an “intrarow O–H dissociated and N dative bonded structure”. Using DFT calculations with van der Waals corrections, we find that the intrarow structure is less stable by about 0.23 eV than another structure called “interrow O–H dissociated and N dative bonded structure”, different from the previous study. Furthermore, comparing the energetics and theoretical STM images with the experimental images for glycine on Ge(100), we conclude that the structure observed in the STM experiment is clearly identified as the interrow O–H dissociated and N dative bonded structure. Finally, these results for glycine on Ge(100) are compared with those on Si(100).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-26/jp2038224/production/images/medium/jp-2011-038224_0006.gif'></P>
Kim, Gunn,Park, Jinwoo,Hong, Suklyun Elsevier 2012 Chemical physics letters Vol.522 No.-
<P><B>Graphical abstract</B></P><P><ce:figure id='f0025'></ce:figure></P><P><B>Highlights</B></P><P>► We study the substitutional carbon pair and Stone–Wales defect complexes in boron nitride nanotubes. ► Formation energy of SW defect of the carbon dimer is lower than that of a B–N pair. ► This phenomenon may be experimentally observed with a higher probability. ► We discuss the localized states originating from the carbon pair impurities.</P> <P><B>Abstract</B></P><P>Using density functional theory, we study physical properties of boron nitride nanotubes (BNNTs) with the substitutional carbon pair defect. We also consider the Stone–Wales (SW) rearrangement of the C–C pair defect in the BNNT. The formation energy of an SW defect of the carbon dimer is approximately 3.1eV lower than that of the SW-transformed B–N pair in the undoped BNNT. The activation energies show that the SW defect in the C-doped BNNT may be experimentally observed with a higher probability than in the undoped BNNT. Finally, we discuss the localized states originating from the carbon pair impurities.</P>