Nam-Suk Lee

Formation and Superlattice of Long-Range-Ordered Self-Assembled Monolayers of Pentafluorobenzenethiols on Au(111)

The formation and surface structure of pentafluorobenzenethiol (PFBT) self-assembled monolayers (SAMs) on Au(111) formed under various experimental conditions were examined by means of scanning tunneling microscopy (STM). Although it is well known that PFBT molecules on metal surfaces do not form ordered SAMs, we clearly revealed for the first time that the adsorption of PFBT on Au(111) at 75 degrees C for 2 h yields long-range, well-ordered self-assembled monolayers having a (2 x 5 square root(13))R30 degrees superlattice. Our results will provide new insight into controlling the structural order of PFBT SAMs, which will be very useful in precisely tailoring the interface properties of metal surfaces in electronic devices.

Measurement of Negative Differential Resistance Properties of Dipyridinium Self-Assembled Monolayers by Ultrahigh-Vacuum Scanning Tunneling Microscopy

We fabricated organic monolayers onto a Au(111) substrate by the self-assembly method using 4-{4[4-(4-{1-[4-(4-acetylsulfanyl-phenylethynyl)-phenyl]-2,6-diphenyl-pyridinium-4-yl}-phenyl)-2,6-diphenyl-pyridinium-1-yl]-phenylethynyl}-phenylthioacetate (dipyridinium). Also, we selected an organic single molecule in the organic monolayers and measured their current–voltage (I–V) properties by ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). Self-assembly monolayers (SAMs) were prepared on a Au(111) substrate that had been thermally deposited onto freshly cleaved, heated mica. The Au substrate was exposed to a 1 mM solution of 1-dodecanethiol in ethanol for 24 h to form a monolayer. After thoroughly rinsing the sample, it was exposed to a 0.3 mM solution of dipyridinium in tetrahydrofuran (THF) for 30 min. Finally, the electrical property of the organic monolayers was investigated by UHV-STM. The applied voltages were from -2.0 to +2.0 V at 299 K. The vacuum condition is 6×10-8 Torr. As a result, we confirmed the property of a negative differential resistance (NDR) in the positive-voltage region in between 1.5 and 2.0 V.

A study on conformational changes by electron charges in viologen single molecules by using STM.

The topography of self-assembled viologen derivatives (VC(8)SH, VC(10)SH, HSC(8)VC(8)SH, and HSC(10)VC(10)SH) molecules on an octanethiol (C(8)) self-assembled monolayer (SAM) modified gold surface was measured using ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). We demonstrate here a novel matrix SAM appropriate for isolation of the viologen molecules. The C(8) was used for a matrix SAM, in which the VC(8)SH, VC(10)SH, HSC(8)VC(8)SH, and HSC(10)VC(10)SH were inserted at molecular lattice defects. The isolated single molecules of viologen derivatives inserted in the matrix SAM were observed as protrusions in STM topography using a constant current mode. We measured the topographic heights (VC(8)SH: 1.53 nm, VC(10)SH: 2.01 nm, HSC(8)VC(8)SH: 2.71 nm, and HSC(10)VC(10)SH: 3.3 nm) of the molecular protrusions using STM. Also, changes in the central axis of viologen molecules were observed as VC(8)SH (0.5-0.73 nm), VC(10)SH (0.4-0.74 nm), HSC(8)VC(8)SH (0.67-0.84 nm), and HSC(10)VC(10)SH (0.67-0.99 nm), respectively.

Study on tunneling current through barrier height using scanning tunneling microscopy

The electrical properties of viologen derivatives were studied of the tunneling current characteristics on the length of the viologen derivatives using self-assembling techniques and ultra high vacuum scanning tunneling microscopy (UHV-STM). The current-voltage (I-V) and differential conductance (dl/dV-V) characteristics were measured while the electrical properties of the formed monolayer were scanned by using a scanning tunneling spectroscopy (STS). Also, we investigated to study electrons movement which is caused by height variation because we can see the organic materials barrier height and STM tip by organic materials energy gap (Eg). The total effective barrier height Phi of viologen derivatives VC8SH, VC10SH, HSC8VC8SH, and HSC10VC10SH SAMs were calculated to be 1.076 eV, 1.86 eV, 1.85 eV, 2.28 eV, respectively.

CURRENT–VOLTAGE PROPERTIES OF SELF-ASSEMBLY MONOLAYERS ON AU(111) SUBSTRATE USING SCANNING TUNNELING MICROSCOPY

This study observes the morphology of self-assembled organic thin film that is formed at room temperature using a Scanning Tunneling Microscopy (STM) and examines its electrical properties using a Scanning Tunneling Spectroscopy (STS). The specimen used in this experiment that has a functional group for both sides and will be controlled to make self-assembled onto the Au(111) substrate. After the dilution of the specimen by 1 mM/ml and self-assembled onto the Au(111) substrate. Using a STM, the images of organic thin film can be observed. In addition, the electrical properties of organic thin film can also be examined by the junction structure of STM–organic thin film–Au(111) substrate by using a STM tip. As a result, we measured current–voltage (I–V) curve using STS, I–V curve also clearly shows several current peaks between the negative bias region (-1.42 V) and the positive bias region (1.30 V), respectively.

A Study on the Current-voltage Properties of Dipyridinium Molecule using Scanning Tunneling Microscopy

In this study, electrical properties of self-assembled dipyridinium dithioacetate molecule onto the Au(111) substrate is observed using Scanning Tunneling Microscopy(STM) by vortical structure of STM probe. At first, the Au(111) substrate is cleaned by piranha solution

UV-ozone surface treatment of indium-tin-oxide in organic light emitting diodes

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