조문호 교수

van der Waals layered materials have large crystal anisotropy and crystallize spontaneously into two-dimensional (2D) morphologies. Two-dimensional materials with hexagonal lattices are emerging 2D confined electronic systems at the limit of one or three atom thickness. Often these 2D lattices also form orthorhombic symmetries, but these materials have not been extensively investigated, mainly due to thermodynamic instability during crystal growth. Here, we show controlled polymorphic growth of

In general, in thermoelectric materials the electrical conductivity σ and thermal conductivity κ are related and thus cannot be controlled independently. Previously, to maximize the thermoelectric figure of merit in state-of-the-art materials, differences in relative scaling between σ and κ as dimensions are reduced to approach the nanoscale were utilized. Here we present an approach to thermoelectric materials using tin disulfide, SnS2, nanosheets that demonstrated a negative correlation betwee

Two-dimensional stacks of dissimilar hexagonal monolayers exhibit unusual electronic, photonic and photovoltaic responses that arise from substantial interlayer excitations. Interband excitation phenomena in individual hexagonal monolayer occur in states at band edges (valleys) in the hexagonal momentum space; therefore, low-energy interlayer excitation in the hexagonal monolayer stacks can be directed by the two-dimensional rotational degree of each monolayer crystal. However, this rotation-dep

We report a diameter-dependent photoconduction gain in intrinsic Ge nanowire (NW) photodetectors. By employing a scanning photocurrent imaging technique, we provide evidence that the photocarrier transport is governed by the hole drift along the Ge NWs, ensuing the higher internal gain up to approximately 10(3) from the thin NWs. It is found that the magnitudes of both gain and photoconductivity are inversely proportional to the NW diameter ranging from 50 to 300 nm. We attribute our observation

We have fabricated spin polarized tunneling devices based upon half-metallic manganites $({\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3})$ incorporating ${\mathrm{NdGaO}}_{3}$ as a barrier material. These devices show high tunnel magnetoresistance (TMR) values above 77 K and coherent switching with a qualitatively different dependence of resistance on magnetic field to previous devices. The electron polarization deduced from measurements at 77 K is higher than the directly measured val

2D vertical stacking and lateral stitching growth of monolayer (ML) hexagonal transition-metal dichalcogenides are reported. The 2D heteroepitaxial manipulation of MoS2 and WS2 MLs is achieved by control of the 2D nucleation kinetics during the sequential vapor-phase growth. It enables the creation of hexagon-on-hexagon unit-cell stacking and hexagon-by-hexagon stitching without interlayer rotation misfits.

We report the energy band-gap modulation of single-crystalline Si1-xGex (0 <or= x <or= 1) nanowires ranging from near-infrared (NIR) to visible regions by optical band-edge absorption. Single-crystalline Si1-xGex nanowires were grown by an Au catalyst-assisted chemical vapor synthesis using SiH4 and GeH4 precursors, and the relative composition of Si and Ge was reproducibly directed in the whole range of 0 <or= x <or= 1 by controlling the kinetics of catalytic decomposition of precursors near th

A simple and controlled growth of metallic NiSi nanowires at low temperatures (< 400 °C) by a chemical vapor deposition using SiH4 at a low supersaturation limit is reported. It is demonstrated that the simple and low temperature synthesis of metallic nanowires is compatible with conventional Si processing and provide interesting strategies for their possible applications as interconnects in Si microelectronics and as field emitters in field emission displays.

The 1s exciton--the ground state of a bound electron-hole pair--is central to understanding the photoresponse of monolayer transition metal dichalcogenides. Above the 1s exciton, recent visible and near-infrared investigations have revealed that the excited excitons are much richer, exhibiting a series of Rydberg-like states. A natural question is then how the internal excitonic transitions are interrelated on photoexcitation. Accessing these intraexcitonic transitions, however, demands a fundam

A low dielectric constant material for an intermetal dielectric (IMD) is imperative to reduce power dissipation, cross talk, and interconnection delay in the deep submicron device regime. SiO2 aerogel is one of the possible candidate with an inherent low dielectric constant. This article reports on the results of the successful fabrication of a SiO2 aerogel film as well as its material properties and electrical properties. Fundamental physical, chemical, and electrical material properties were e