Hyunwook Song

Investigation of inelastic electron tunneling spectra of metal-molecule-metal junctions fabricated using direct metal transfer method

We measured the inelastic electron tunneling spectroscopy (IETS) characteristics of metal-molecule-metal junctions made with alkanethiolate self-assembled monolayers. The molecular junctions were fabricated using a direct metal transfer method, which we previously reported for high-yield metal-molecule-metal junctions. The measured IETS data could be assigned to molecular vibration modes that were determined by the chemical structure of the molecules. We also observed discrepancies and device-to-device variations in the IETS data that possibly originate from defects in the molecular junctions and insulating walls introduced during the fabrication process and from the junction structure.

Electrical characterization of benzenedithiolate molecular electronic devices with graphene electrodes on rigid and flexible substrates

We investigated the electrical characteristics of molecular electronic devices consisting of benzenedithiolate self-assembled monolayers and a graphene electrode. We used the multilayer graphene electrode as a protective interlayer to prevent filamentary path formation during the evaporation of the top electrode in the vertical metal-molecule-metal junction structure. The devices were fabricated both on a rigid SiO2/Si substrate and on a flexible poly(ethylene terephthalate) substrate. Using these devices, we investigated the basic charge transport characteristics of benzenedithiolate molecular junctions in length- and temperature-dependent analyses. Additionally, the reliability of the electrical characteristics of the flexible benzenedithiolate molecular devices was investigated under various mechanical bending conditions, such as different bending radii, repeated bending cycles, and a retention test under bending. We also observed the inelastic electron tunneling spectra of our fabricated graphene-electrode molecular devices. Based on the results, we verified that benzenedithiolate molecules participate in charge transport, serving as an active tunneling barrier in solid-state graphene-electrode molecular junctions.

Investigation of molecular junctions with inelastic electron tunneling spectroscopy

ABSTRACT Molecular junctions in which individual molecules are utilized as active electronic components constitute a promising approach for the ultimate miniaturization and integration of electronic devices through the bottom-up strategy. A study on charge transport through the constituent molecules attached to two metallic electrodes is a very challenging task, but advances have been made in recent years. Especially, inelastic electron tunneling spectroscopy (IETS) has recently become a premier analytical tool for investigating nanoscale molecular junctions. The IETS spectrum provides invaluable information about the correlation between charge carriers and molecular vibrations in the junctions. This review discusses how IETS is used to investigate molecular junctions and presents an overview of recent experimental and theoretical studies.

Combing non-epitaxially grown nanowires for large-area electronic devices

A facile route for aligning randomly oriented nanowires synthesized by a vapor-liquid-solid method for the fabrication of nanoelectronic devices was achieved using a polymer combing technique. By controlling the Youngs modulus of the polymer combs, van der Waals interactions and shearing forces between the combs and nanowires can be manipulated and thus the nanowire density and alignment can be controlled. Using the proposed method, field-effect transistors were directly fabricated on as-grown substrates after aligning the nanowires, thereby demonstrating the feasibility of the scheme for the production of nanoelectronic devices.

Transition voltage spectroscopy analysis of charge transport through molecular nanojunctions

ABSTRACT Probing the position of frontier molecular orbitals (the highest occupied molecular orbital, HOMO or the lowest unoccupied molecular orbital, LUMO) with respect to the Fermi levels of the electrodes in the molecular junctions is of crucial importance to understand the charge transport behavior and realize the functions of the molecular junctions. Recently, transition voltage spectroscopy (TVS) has been presented to provide insight into the energy offset between the contact Fermi level and the nearest frontier molecular orbital energy responsible for molecular charge transport; this is accomplished by measuring the transition voltage required to generate the inflection behavior of a Fowler–Nordheim plot, i.e., the corresponding analysis of ln(I/V2) against 1/V for I(V) characteristics. One of the key advantages of the TVS is that it requires lower electric fields, which accordingly can avoid the breakdown of the junctions (due to very large electric fields reaching “resonant” condition). This review describes theoretical interpretations of TVS, and then covers the major advances regarding TVS as a promising spectroscopic tool for charge transport experiments in molecular-scale junctions.

Electrostatic Gate Control in Molecular Transistors

Molecular transistors, in which single molecules serve as active channel components in a three-terminal device geometry, constitute the building blocks of molecular scale electronic circuits. To demonstrate such devices, a gate electrode has been incorporated in several test beds of molecular electronics. The frontier orbitals’ alignments of a molecular transistor can be delicately tuned by modifying the molecular orbital energy with the gate electrode. In this review, we described electrostatic gate control of solid-state molecular transistors. In particular, we focus on recent experimental accomplishments in fabrication and characterization of molecular transistors.

Spectroscopic interrogation and charge transport properties of molecular transistors

ABSTRACT Molecular transistors have been extensively investigated as the building blocks for the ultimate miniaturization of electronic devices. They are assembled from single molecules and molecular monolayers serving as a current-carrying channel in a conventional field-effect transistor configuration, in which gate electrodes have been electrically or electrochemically implemented in several types of test beds such as electromigration junctions, mechanically controllable break junctions, and devices with carbon-based electrodes. The energy level alignments of the component molecules incorporated into the transistor can be tuned using molecular orbital gating and it can ultimately control the flow of charge carriers. Herein, we review recent progress in studying spectroscopic characterization techniques and charge transport properties of molecular transistors.

Erratum to: Branch length similarity entropy-based descriptors for shape representation (Journal of the Korean Physical Society, (2017), 71, 10, (727-732), 10.3938/jkps.71.593)

Regrettably, due to a technical error during the production process, there were discrepancies in DOI of the mentioned articles between HTML and PDF files. The DOIs are correct in the PDF files but were incorrect in HTML. The original articles have been corrected. The Publisher apologizes for any inconvenience and confusion caused.