• Bulletin of the Korean Chemical Society
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• v.33 no.9
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• pp.3139-3141
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• 2012

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.240.2-240.2
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• 2007

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.140.2-140.2
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• 2016

Despite the growing interest in GeTe as a archetypal displacive ferroelectric material as well as the basis of related materials used in data-storage applications, atom-resolved study of single crystalline GeTe surface been lacking. Using low temperature scanning tunneling microscopy (STM) and spectroscopy (STS), we investigated as-cleaved and annealed surfaces of GeTe. We found that as-cleaved GeTe(111) surface is composed of at least two kinds of terraces at 78 K. While two terraces show metallic characteristics, they also exhibit distinctive I-V spectra and imaging conditions, with each being attributed to Ge-terminated, and Te-terminated surfaces respectively. GeTe(111) surfaces annealed at moderately elevated temperature introduces intricate networks of extended defect structures. We will present these data and discuss the role of vacancies in the formation of these structures.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.2
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• pp.51-54
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• 2005

In this work, the attempt has been made to investigate the morphology of self-assembled dipyridinium dithioacetate on Au(111) substrate by Scanning Tunneling Microscopy(STM). Also, we measured electrical properties(I-V) using Scanning Tunneling Spectroscopy(STS). Sample used in this experiment is dipyridinium dithioacetate, which contains thiol functional group, this structure that can be self-assembled easily to Au(111) substrate. The self-assembly procedure was used for two different concentrations, 0.5 mM/ml and 1 mM/ml. Dilute density of sample by 0.5 mM/ml, 1 mM/ml and observed dipyridinium dithioacetate's image by STM after self-assembled on Au(111) substrate. The structure of STM tip-SAMs-Au(111) substrate has been used measurement for electrical properties(I-V) using STS. The current-voltage(I-V) measurement result, observed negative differential resistance(NDR) properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.181-181
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• 2011

The adsorption structure and the electronic property of azidotrimethyltin (ATMT) on monolayer graphene was investigated using scanning tunneling microscopy and core-level photoemission spectroscopy. We also confirmed the n-type doping effect by scanning tunneling spectroscopy and work function measurements. We will systematically demonstrate the variation of characteristic of graphene induced by the chemical functionalized molecule as we confirmed the results using scanning tunneling microscopy in conjunction with core-level photoemission spectroscopy.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.125-125
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• 2012

Graphene was epitaxially grown on a 6H-SiC(0001) substrate by thermal decomposition of SiC under ultrahigh vacuum conditions. Using scanning tunneling microscopy (STM), we monitored the evolution of the graphene growth as a function of the temperature. We found that the evaporation of Si occurred dominantly from the corner of the step rather than on the terrace. A carbon-rich $(6{\sqrt{3}}{\times}6{\sqrt{3}})R30^{\circ}$ layer, monolayer graphene, and bilayer graphene were identified by measuring the roughness, step height, and atomic structures. Defect structures such as nanotubes and scattering defects on the monolayer graphene are also discussed. Furthermore, we confirmed that the Dirac points (ED) of the monolayer and bilayer graphene were clearly resolved by scanning tunneling spectroscopy (STS).

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.390-390
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• 2010

Superconducting proximity effects of Nb/Si(111) were investigated with scanning tunneling microscopy(STM) and scanning tunneling spectroscopy(STS). A highly-doped($0.002\;{\omega}{\diamondsuit}cm$) Si wafer pieces were used as substrate and Nb source was thermally evaporated onto the atomically clean silicon substrate. The temperature of the silicon sample was held at $600^{\circ}C$ during the niobium deposition. And the sample was annealed at $600^{\circ}C$ for 30 minutes additionally. Volmer-Weber growth mode is preferred in Nb/Si(111) at the sample temperature of $600^{\circ}C$. With proper temperature and annealing time, we can obtain Nb islands of lateral size larger than Nb coherence length(~38nm). And outside of the islands, bare Si($7{\times}7$) reconstructed surface is exposed due to the Volmer-Weber Growth mode. STS measurement at 5.6K showed that Nb island have BCS-like superconducting gap of about 2mV around the Fermi level and the critical temperature is calculated to be as low as 6.1K, which is lower than that of bulk niobium, 9.5K. This reduced value of superconducting energy gap indicates suppression of superconductivity in nanostructures. Moreover, the superconducting state is extended out of the Nb island, over to bare Si surface, due to the superconducting proximity effect. Spatially-resolved scanning tunneling spectroscopy(SR-STS) data taken over the inside and outside of the niobium island shows gradually reduced superconducting gap.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.307-307
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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 processes. Such epitaxial graphene shows modified electronic structures caused by substrates. Here, local geometric and electronic structures of graphene grown on Ru(0001) will be presented. Scanning tunneling microscopy (STM) and spectroscopy (STS) was used to reveal energy dependent atomic level topography and position-dependent differential conductance spectra. Both topography and spectra show variations from three different locations in rippled structures caused by lattice mismatch between graphene and substrate. Based on the observed results, structural models for graphene on Ru(0001) system were considered.

• Journal of the Korean Vacuum Society
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• v.15 no.2
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• pp.139-144
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• 2006

Using scanning tunneling microscopy (STM) measurements, we studied the adsorption of hydrogen on the Si(111)$4{\times}1$-In surface at room temperature. The H atom features are found to be located between the two protrusions in one side of the $4{\times}1$ chain. The adsorbed H preferentially occupies one of the two zigzag In subchains, suggesting that the adsorption of H is influenced by the subsurface structure. The adsorbed H atom induces not only a localized distortion but also perturbs the distant region and results in a period-doubling modulations in the STM images. This H-induced perturbation differs from the Na-Induced perturbation on the same surface.

• Bulletin of the Korean Chemical Society
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• v.32 no.8
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• pp.2623-2627
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• 2011

We investigated the surface structure and wetting behavior of octaneselenolate self-assembled monolayers (SAMs) on Au(111) formed in a 50 ${\mu}M$ ethanol solution according to immersion time, using scanning tunneling microscopy (STM) and an automatic contact angle (CA) goniometer. Closely-packed, well-ordered alkanethiol SAMs would form as the immersion time increased; unexpectedly, however, we observed the structural transition of octaneselenolate SAMs from a molecular row phase with a long-range order to a disordered phase with a high density of vacancy islands (VIs). Molecularly resolved STM imaging revealed that the missing-row ordered phase of the SAMs could be assigned as a $(6{\times}{\surd}3)R30^{\circ}$ superlattice containing three molecules in the rectangular unit cell. In addition, CA measurements showed that the structural order and defect density of VIs are closely related to the wetting behaviors of octaneselenolate SAMs on gold. In this study, we clearly demonstrate that interactions between the headgroups and gold surfaces play an important role in determining the physical properties and surface structure of SAMs.