• Journal of the Korean Vacuum Society
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• v.17 no.5
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• pp.381-386
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• 2008

Adatom kinetics on the surfaces of Co overlayers, prepared on the W(110) surface, was studied with scanning tunneling microscopy. By counting the number-density of the adatom-islands, we estimated the ratio of adatom diffusion coefficients. The ratio $D_{W(110)}:D_{1ML\;Co}:D_{2ML\;Co}$ was measured to be 1 : 125 : 33000 at room temperature, where $D_{W(110)},\;D_{1ML\;Co}$, and $D_{2ML\;Co}$ are the diffusion coefficients on bare W(110) surface, on one-monolayer Co overlayer, and on two-monolayers Co overlayers, respectively. An increased diffusion coefficient on two-ML Co overlayers, relative to that on one-ML Co overlayers, was explained with the heteroepitaxial strain effect.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.38-38
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• 2011

Covalently bonded halogen ligands possess unusual charge distributions, attracting both electrophilic and nucleophilic molecular ligands to form halogen bonds. In many biochemical systems, halogen bonds and hydrogen bonds coexist. The interplay between halogen and hydrogen bonds has been actively studied in various three-dimensional bulk molecular co-crystals. It was found that halogen bonds could be complementary to hydrogen bonds due to their similar bond strength and dissimilar directionality. In those ensemble-averaging approaches, however, it was not possible to extract local information such as individual bond configurations and nano-level domain structures, which is a crucial part of supramolecular studies. In this study, we directly visualize the individual molecular configuration of a brominated molecule and the role of halogen bonds on Au(111) using scanning tunneling microscopy. The precise arrangement of observed molecular structures was reproduced by first-principle studies and explained in the context of halogen and hydrogen bonds. We discuss the distances and the strengths of the observed halogen bonds and hydrogen bonds, which are consistent with previous bulk data.

• Bulletin of the Korean Chemical Society
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• v.31 no.1
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• pp.162-167
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• 2010

We investigated the adsorption and desorption characteristics of benzene molecules on $Si(001)-2{\times}n$ surfaces using a variable-low temperature scanning tunneling microscopy. When benzene was adsorbed on a $Si(001)-2{\times}n$ surface at a low coverage, five distinct adsorption configurations were found: tight-binding (TB), standard-butterfly (SB), twisted-bridge, diagonal-bridge, and pedestal. The TB and SB configurations were the most dominant ones and could be reversibly interconverted, diffused, and desorbed by applying an electric field between the tip and the surface. The population ratios of the TB and SB configurations were affected by the benzene coverage: at high coverage, the population ratio of SB increased over that of TB, which was favored at low coverage. The desorption yield decreased with increasing benzene coverage and/or density of vacancy defect. These results suggest that the interaction between the benzene molecules is important at a high coverage, and that the vacancy defects modify the adsorption and desorption energies of the benzene molecules on Si(001) surface.

• Bulletin of the Korean Chemical Society
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• v.30 no.2
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• pp.441-444
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• 2009

The formation and structure of self-assembled monolayers (SAMs) by the adsorption of acetyl-protected octylthioacetate (OTA) on Au(111) in a catalytic tetrabutylammonium cyanide (TBACN) solution were examined by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). Molecular-scale STM imaging revealed that OTA molecules on Au(111) in a pure solvent form disordered SAMs, whereas they form well-ordered SAMs showing a c(4 × 2) structure in a catalytic TBACN solution. XPS and CV measurements also revealed that OTA SAMs on Au(111) formed in a TBACN solution have a stronger chemisorbed peak in the S 2p region at 162 eV and a higher blocking effect compared to OTA SAMs formed in a pure solvent. In this study, we clearly demonstrate that TBACN can be used as an effective deprotecting reagent for obtaining well-ordered SAMs of thioacetyl-protected molecules on gold.

• Bulletin of the Korean Chemical Society
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• v.30 no.6
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• pp.1309-1312
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• 2009

Surface potential and growth processes of hexadecanethiol (HDT) self-assembled monolayers (SAMs) on Au(111) surfaces were examined by Kelvin probe method and scanning tunneling microscopy. It was found that surface potential strongly depends on surface structure of HDT SAMs. The surface potential shift for the striped phase of HDT SAMs chemisorbed on Au(111) surface was +0.45 eV, which was nearly the same as that of the flat-lying hexadecane layer physisorbed on Au(111) surface. This result indicates that the interfacial dipole layer induced by adsorption of alkyl chains is a main contributor to the surface potential change. In the densely-packed HDT monolayer, further change of the surface potential was observed, suggesting that the dipole moment of the alkanethiol molecules is an origin of the surface potential change. These results indicate that the work function of a metal electrode can be modified by controlling the molecular orientation of an adsorbed molecule.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.94-94
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• 2010

Scanning tunneling microscopy (STM) was used to study the electronic structure of cobalt(II) tetraphenylporphyrin (CoTPP) on the Fe/W(110) substrate. Clover-like conformation of CoTPP was observed and showed bias dependent STM images. The central Co(II) ion of this porphyrin was protruded on the positive biases, but it was depressed on the negative biases. On the positive biases, the phenyl rings of CoTPP appeared to be bright contrary to the invisible pyrrole rings. These results were compared the first-principles calculations using GGA and GGA+U to elucidate the influence of the Fe substrate. GGA+U results agreed well with the experimental results; however, GGA did not. These results show that proper treatment of the on-site Coulomb repulsion of the Fe ions is crucial to describe the electronic structure of this system. By the comparison between the GGA+U calculations on the Fe substrate and the gas phase calculations, it can be noted that chemical potential shift occurred accompanying charge transfer from the Fe ions of the substrate to the pyrrole ligand of the porphyrin.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.114-114
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• 2011

Graphene is the hottest topic in condensed-matter physics due to its unusual electronic structures such as Dirac cones and massless linear dispersions. Graphene can be epitaxially grown on various metal surfaces with chemical vapor deposition (CVD) processes. Such epitaxial graphene shows modified electronic structures caused by substrates. In the method for removal of the effect of substrate, there are bi, tri-layer graphene, gold intercalation, and oxygen intercalation. Here, We will present the changes of geometric and electronic structure of graphene grown on Ru(0001) by oxygen intercalation between graphene and Ru(0001). Using Scanning tunneling microscopy (STM) and spectroscopy (STS), we observed the aspect that the band gap features near the fermi level of graphene on Ru(0001) system is shifted and narrow. Based on the observed results, two effects by intercalated oxygen were considered.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.344-344
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• 2010

그라핀 나노리본은 독특한 전기적 특성으로 인하여 차세대 나노 소자용 신소재로 주목을 받고 있으며 리본의 폭과 가장자리 구조에 따라 여러 가지 다른 특성을 나타낸다고 알려져 있다. 우리는 Scanning Tunneling Microscopy(STM) 실험을 통하여 기울어진 6H-SiC(0001) 면 위에서 그라핀 나노리본의 성장 가능성을 조사하고 성장된 그라핀 나노구조의 가장자리에서 나타나는 구조에 대하여 연구하였다. 그라핀 성장의 초기 단계에서는 리본 형태의 그라핀 나노 구조를 볼 수 있었으나 그라핀 성장 과정을 거치면서 SiC 기판의 잘 정렬된 계단 구조가 망가져서 그라핀 나노리본 배열의 형성에는 한계가 있음을 확인할 수 있었다. 원자 수준의 STM 이미지를 통해서 그라핀 나노 구조의 가장자리에서 큰 육각형 형태의 양자 간섭 무늬를 관찰하였는데 이러한 형태는 흑연 위의 그라핀 나노 조각에 대한 연구에서 관찰된 것과 동일한 것으로 Armchair 형태의 가장자리 구조의 경우에 형성된다고 알려져 있다.[1] 이로부터 SiC(0001) 표면위에 형성된 그라핀 나노 구조의 경우에도 Armchair 형태의 가장자리 구조가 더 안정적임을 알 수 있었다. 이러한 구조의 국소 전자 구조에 대하여 알아보기 위하여 Scanning Tunneling Spectroscopy 측정도 함께 수행하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.86-86
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• 2010

Water adsorption on Si(001)-c($4{\times}2$) surface is investigated at low temperature by using scanning tunneling microscope (STM) and ab initio pseudopotential calculations. $H_2O$ configurations of single and cluster of two molecules reveal "Y", "X" and "W" depressions as footprints on the surface. Atomic structures of $H_2O$ molecules, which are dissociatively adsorbed on the Si(001)-c($4{\times}2$) surface, are studied with simulated and STM images of the filled states. The generation processes of the growth configurations are systematically considered with elapsed time.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.256-259
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• 2004

[ $V_2O_5$ ] 나노선의 구조 분석을 위해 STM(Scanning Tunneling Microscopy)과 TEM(Transmission Electron Microscopy)을 이용하여 단일 $V_2O_5$ 나노선의 이미지를 얻었다. $V_2O_5$ 나노선은 상온에서 ammonium metavanadate$(NH_4VO_3)$와 양이온 교환수지$(DOWEX50{\times}8-100)$를 2차 증류수에 섞어 합성하였다. STM 시료는 3-APS(3-aminopropyltriethoxysilane)를 전 처리한 실리콘 기판에 $V_2O_5$ 나노선을 올려 만들었고, TEM 시료는 200 mesh/copper 그리드에 침전시켜 준비하였다. STM과 TEM의 결과로부터 $V_2O_5$ 나노선의 기하학적 단면이 $1.5nm{\times}10nm$에 거의 근사하는 것을 확인하였으며 두 이미지의 비교를 통해 $V_2O_5$ 나노선의 표면상태에 대해 논의하였다.