Atomic-registry-dependent electronic structures of sulfur vacancies in ReS2 studied by scanning tunneling microscopy/spectroscopy

정성준,정태환,심재우,박상우,박진홍,신봉규,송영재 한국물리학회 2019 Current Applied Physics Vol.19 No.3

Rhenium disulfide (ReS2) is regarded as a promising candidate for optoelectronic applications (e.g., infrared photodetector), as it maintains a direct bandgap regardless of the number of layers unlike other typical transition metal dichalcogenides. Therefore, it is very important to understand and control the defects of ReS2 for enhancing the performance of photodevices. In this work, we studied the electronic structures of ReS2 affected by sulfur vacancies of different atomic registries at the atomic scale. The atomic and electronic structures of the mechanically exfoliated ReS2 flakes were investigated using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS), and were confirmed using density functional theory (DFT) calculations. The atomic structural models indicate four distinguishable atomic registries of sulfur vacancies on one face of ReS2. Energetically, these atomic vacancies prefer to locate on the bottom side of the top monolayer of ReS2 flakes. Only two among four possible kinds of vacancies could be observed using STM and STS, and they were identified using additional DFT calculations. We believe that our results regarding the identification of the defects and understanding the corresponding effects for electronic structures will provide important insights to enhance the performances of ReS2-based optoelectronic devices in the future.

Geometric and Electronic Structure of Passive CuN Monolayer on Cu(111) : A Scanning Tunneling Microscopy and Spectroscopy Study

백홍우,전상준,서정필,국양 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.2

An insulating CuN monolayer was grown on a Cu(111) surface; subsequently, the dynamic growth process, the reconstructed geometric structure and the electronic structure were studied using scanning tunneling microscopy. Confirmation of the atomic model of the pseudo-(100) layer, proposed by Higgs et al. and Driver et al. was made. In addition, we observed a small misalignment of the super cell away from the <110> direction of the Cu substrate, resulting in long range distortion. A large insulator-like band gap of ~ 3.3 eV was measured through the CuN surface. The CuN monolayer can be used as a model surface on which the electronic structure of an atom or a molecule is explored by scanning tunneling microscopy. This electronic structure can not be perturbed by the metallic substrate, despite the tunneling of electrons through the surface layer.

Atomic-Scale Spectroscopy of Gated Monolayer MoS₂

Zhou, Xiaodong,Kang, Kibum,Xie, Saien,Dadgar, Ali,Monahan, Nicholas R.,Zhu, X.-Y.,Park, Jiwoong,Pasupathy, Abhay N. American Chemical Society 2016 NANO LETTERS Vol.16 No.5

<P>The electronic properties of semiconducting monolayer transition-metal dichalcogenides can be tuned by electrostatic gate potentials. Here we report gate-tunable imaging and spectroscopy of monolayer MoS<SUB>2</SUB> by atomic-resolution scanning tunneling microscopy/spectroscopy (STM/STS). Our measurements are performed on large-area samples grown by metal–organic chemical vapor deposition (MOCVD) techniques on a silicon oxide substrate. Topographic measurements of defect density indicate a sample quality comparable to single-crystal MoS<SUB>2</SUB>. From gate voltage dependent spectroscopic measurements, we determine that in-gap states exist in or near the MoS<SUB>2</SUB> film at a density of 1.3 × 10<SUP>12</SUP> eV<SUP>–1</SUP> cm<SUP>–2</SUP>. By combining the single-particle band gap measured by STS with optical measurements, we estimate an exciton binding energy of 230 meV on this substrate, in qualitative agreement with numerical simulation. Grain boundaries are observed in these polycrystalline samples, which are seen to not have strong electronic signatures in STM imaging.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2016/nalefd.2016.16.issue-5/acs.nanolett.6b00473/production/images/medium/nl-2016-004733_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl6b00473'>ACS Electronic Supporting Info</A></P>

Atomic and Electronic Structures of the Ni-induced Phases on Si(111): Scanning Tunneling Microscopy and Spectroscopy Study

심형준,이근섭,김도환,홍석륜,김세훈 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.6

The atomic and electronic structures of Ni-induced phases formed on a Si(111) surface were investigated using scanning tunneling microscopy (STM) and spectroscopy (STS). STM images show the presence of two kinds of the ring clusters ('1x1'-RCs and √19-RCs) which are related to the known '1x1' and √19×√19 phases, respectively. In addition, a new ordered structure having a √7×√7 periodicity with a considerable domain size was also observed to form on the surface. Islands of the √7×√7 structure embedded in the surface of the √19×√19 structure are found to be made by regular packing of the '1x1'-RCs. High-resolution, dual-bias STM images reveal unprecedented atomistic details of both the ring clusters forming the ordered √19×√19 and √7×√7 structures. STS data indicate that the local √7×√7 phase is semiconducting with a gap of about 1 eV. The √19×√19 structure is either metallic or semiconducting with a gap smaller than 0.2 eV. The peaks in the (dI/dV)/(I/V) curves were attributed to the density of the states expected from the existing atomic models of the two ordered structures.

Controlling Spin State of Magnetic Molecules by Oxygen Binding Studied Using Scanning Tunneling Microscopy

Soon-hyeong Lee,Yun Hee Chang,Howon Kim,Kyung Min Kim,Yong-Hyun Kim,Se-Jong Kahng 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.2

Phase Segregation in the Mixed Alkyl Thiol Self-assembled Monolayers on a Gold Surface at a High Incubation Temperature in a Sealed Container

마문,Ali A. S. M. Zahid,이인섭,강홍석,한재량 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.11

Self-assembled monolayers (SAMs) of mixed 1-octanethiol (OT) and 1-decanethiol (DT) that were formed on gold substrates at a high incubation temperature in a sealed container were characterized using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In mixed-composition monolayer films, self-assembly of the mixture could induce phase separation into discrete molecular domains at higher incubation temperatures. Mixtures of the alkanethiol molecules affected the domain size, defect density, packing density, and binding features of the resultant SAMs prepared on gold substrates. Single-molecule-resolved STM images of mixed SAMs revealed both c(4 × 2) − ns (non-shifted) for DT and c(4 × 2) − s (shifted) for OT domains. For the mixed SAMs, the peak S2 (XPS) increased in intensity relative to the peak S1, reflecting significant modifications in the binding characteristics of the thiols and surface roughness upon mixing.

Switching and Sensing Spin States of Co–Porphyrin in Bimolecular Reactions on Au(111) Using Scanning Tunneling Microscopy

Kim, Howon,Chang, Yun Hee,Lee, Soon-Hyeong,Kim, Yong-Hyun,Kahng, Se-Jong American Chemical Society 2013 ACS NANO Vol.7 No.10

<P>Controlling and sensing spin states of magnetic molecules at the single-molecule level is essential for spintronic molecular device applications. Here, we demonstrate that spin states of Co–porphyrin on Au(111) can be reversibly switched over by binding and unbinding of the NO molecule and can be sensed using scanning tunneling microscopy and spectroscopy (STM and STS). Before NO exposure, Co–porphryin showed a clear zero-bias peak, a signature of Kondo effect in STS, whereas after NO exposures, it formed a molecular complex, NO–Co–porphyrin, that did not show any zero-bias feature, implying that the Kondo effect was switched off by binding of NO. The Kondo effect could be switched back on by unbinding of NO through single-molecule manipulation or thermal desorption. Our density functional theory calculation results explain the observations with pairing of unpaired spins in d<SUB><I>z</I><SUP>2</SUP></SUB> and ppπ* orbitals of Co–porphyrin and NO, respectively. Our study opens up ways to control molecular spin state and Kondo effect by means of enormous variety of bimolecular binding and unbinding reactions on metallic surfaces.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-10/nn4039595/production/images/medium/nn-2013-039595_0007.gif'></P>

Atmospheric Oxygen Binding and Hole Doping in Deformed Graphene on a SiO₂ Substrate

Ryu, Sunmin,Liu, Li,Berciaud, Stephane,Yu, Young-Jun,Liu, Haitao,Kim, Philip,Flynn, George W.,Brus, Louis E. American Chemical Society 2010 NANO LETTERS Vol.10 No.12

<P>Using micro-Raman spectroscopy and scanning tunneling microscopy, we study the relationship between structural distortion and electrical hole doping of graphene on a silicon dioxide substrate. The observed upshift of the Raman G band represents charge doping and not compressive strain. Two independent factors control the doping: (1) the degree of graphene coupling to the substrate and (2) exposure to oxygen and moisture. Thermal annealing induces a pronounced structural distortion due to close coupling to SiO<SUB>2</SUB> and activates the ability of diatomic oxygen to accept charge from graphene. Gas flow experiments show that dry oxygen reversibly dopes graphene; doping becomes stronger and more irreversible in the presence of moisture and over long periods of time. We propose that oxygen molecular anions are stabilized by water solvation and electrostatic binding to the silicon dioxide surface.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-12/nl1029607/production/images/medium/nl-2010-029607_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl1029607'>ACS Electronic Supporting Info</A></P>

Local Atomic and Electronic Structure of Boron Chemical Doping in Monolayer Graphene

Zhao, Liuyan,Levendorf, Mark,Goncher, Scott,Schiros, Theanne,Pá,lová,, Lucia,Zabet-Khosousi, Amir,Rim, Kwang Taeg,Gutié,rrez, Christopher,Nordlund, Dennis,Jaye, Cherno,Hybertsen, Mar American Chemical Society 2013 Nano letters Vol.13 No.10

<P>We use scanning tunneling microscopy and X-ray spectroscopy to characterize the atomic and electronic structure of boron-doped and nitrogen-doped graphene created by chemical vapor deposition on copper substrates. Microscopic measurements show that boron, like nitrogen, incorporates into the carbon lattice primarily in the graphitic form and contributes ∼0.5 carriers into the graphene sheet per dopant. Density functional theory calculations indicate that boron dopants interact strongly with the underlying copper substrate while nitrogen dopants do not. The local bonding differences between graphitic boron and nitrogen dopants lead to large scale differences in dopant distribution. The distribution of dopants is observed to be completely random in the case of boron, while nitrogen displays strong sublattice clustering. Structurally, nitrogen-doped graphene is relatively defect-free while boron-doped graphene films show a large number of Stone-Wales defects. These defects create local electronic resonances and cause electronic scattering, but do not electronically dope the graphene film.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-10/nl401781d/production/images/medium/nl-2013-01781d_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl401781d'>ACS Electronic Supporting Info</A></P>

Surface Structures and Thermal Desorption Behaviors of Cyclopentanethiol Self-Assembled Monolayers on Au(111)

Kang, Hun-Gu,Kim, You-Young,Park, Tae-Sun,Park, Joon-B.,Ito, Eisuke,Hara, Masahiko,Noh, Jae-Geun Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.4

The surface structures, adsorption conditions, and thermal desorption behaviors of cyclopentanethiol (CPT) self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). STM imaging revealed that although the adsorption of CPT on Au(111) at room temperature generates disordered SAMs, CPT molecules at $50^{\circ}C$ formed well-ordered SAMs with a $(2{\surd}3{\times}{\surd}5)R41^{\circ}$ packing structure. XPS measurements showed that CPT SAMs at room temperature were formed via chemical reactions between the sulfur atoms and gold surfaces. TDS measurements showed two dominant TD peaks for the decomposed fragments ($C_5H_9^+$, m/e = 69) generated via C-S bond cleavage and the parent molecular species ($C_5H_9SH^+$, m/e = 102) derived from a recombination of the chemisorbed thiolates and hydrogen atoms near 440 K. Interestingly, dimerization of sulfur atoms in n-alkanethiol SAMs usually occurs during thermal desorption and the same reaction did not happen for CPT SAMs, which may be due to the steric hindrance of cyclic rings of the CPT molecules. In this study, we demonstrated that the alicyclic ring of organic thiols strongly affected the surface structure and thermal desorption behavior of SAMs, thus providing a good method for controlling chemical and physical properties of organic thiol SAMs.