Yun Park

With its electrical carrier type as well as carrier densities highly sensitive to light, graphene is potentially an ideal candidate for many optoelectronic applications. Beyond the direct light-graphene interactions, indirect effects arising from induced charge traps underneath the photoactive graphene arising from light-substrate interactions must be better understood and harnessed. Here, we study the local doping effect in graphene using focused-laser irradiation, which governs the trapping an

We observed bipolar switching behavior from an epitaxial strontium cobaltite film grown on a SrTiO3 (001) substrate. The crystal structure of strontium cobaltite has been known to undergo topotactic phase transformation between two distinct phases: insulating brownmillerite (SrCoO2.5) and conducting perovskite (SrCoO3−δ) depending on the oxygen content. The current–voltage characteristics of the strontium cobaltite film showed that it could have a reversible insulator-to-metal transition trigger

For the first time, vertically suspended and stretched carbon nanotube network junctions were fabricated in large quantity via the directed assembly strategy using only conventional microfabrication facilities. In this process, surface molecular patterns on the side-wall of the Al structures were utilized to guide the assembly and alignment of carbon nanotubes in the solution. We also performed extensive experimental (electrical and mechanical) analysis and theoretical simulation about the verti

Utilizing lattice-matched GaAs∕InGaP∕GaAs heterostructures, clean micromechanical resonators are fabricated and characterized. The nearly perfect selectivity of GaAs∕InGaP is demonstrated by realizing paddle-shaped resonators, which require significant lateral etching of the sacrificial layer. Doubly clamped beam resonators are also created, with a Q factor as high as 17 000 at 45mK. Both linear and nonlinear behaviors are observed in GaAs micromechanical resonators. Furthermore, a direct relati

Nanoconfined waters exhibit low static permittivity mainly due to interfacial effects that span about one nanometer. The characteristic length scale may be much longer in the terahertz (THz) regime where long-range collective dynamics occur; however, the THz dynamics have been largely unexplored because of the lack of a robust platform. Here, we use metallic loop nanogaps to sharply enhance light-matter interactions and precisely measure real and imaginary THz refractive indices of nanoconfined

We investigated the resistance switching (RS) phenomenon in epitaxial NiO (epi-NiO) films by employing different types of top electrodes (TEs). Epi-NiO showed successive bipolar RS when Pt and CaRuO 3 (CRO) were used as the TEs, but not when Al and Ti were used. We studied the temperature dependence of the current–voltage ( I – V ) characteristics for various TEs and resistance states to understand the conduction properties of TE/epi-NiO. Pristine CRO/epi-NiO showed metallic behavior, while pris

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

Results on the synthesis of ferromagnetic GaMnN and GaMnP by both Molecular Beam Epitaxy or implantation of Mn directly into p-GaN or GaP(C) at elevated temperatures to avoid amorphization will be described. There is a relatively broad range of growth conditions under which single-crystal, single-phase material may be obtained with significant Mn concentrations. The effects of background doping level are discussed, along with a comparison of results on direct implantation of Fe and Ni instead of

The realization of high-yield, stable molecular junctions has been a long-standing challenge in the field of molecular electronics research, and it is an essential prerequisite for characterizing and understanding the charge transport properties of molecular junctions prior to their device applications. Here, we introduce a new approach for obtaining high-yield, vertically structured metal-molecule-metal junctions in which the top metal electrodes are formed on alkanethiolate self-assembled mono

A high quality epitaxial SrRuO3(SRO)/BaTiO3(BTO)/SRO/SrTiO3 (001) heterostructure was grown by pulsed laser deposition with in situ re ection high-energy electron diraction. The growth mode and crystallinity of the heterostructure were veried by X-ray diraction and atomic force microscopy. Ferroelectric (FE) hysteresis loops could be observed down to 9 nm of BTO thickness. Remanent polarization decreased as the FE layer thickness decreased. In addition, all the capacitors showed imprint phenomen

Recent research on nanomechanical resonators has shown that their mechanical motion can be controlled via the interactions between different flexural modes, in diverse structures. Strong coupling in flexural modes has been attributed to strain mediation, but further study is needed to harness the dynamics for applications. The authors use a doubly clamped resonator to demonstrate coupling between flexural modes of different parity, and then use theory to show that the thermomechanical motion of

We report on an investigation of the applicability of the skew scattering model for the anomalous Hall Effect in (Ga,Mn)As prepared using low-temperature molecular beam epitaxy. Specifically, we study the relationship between the Hall resistivity (xy) and the longitudinal resistivity (xx) for differing Mn concentrations incorporated into the IIIGa site. The growth conditions for single-phase (Ga,Mn)As were carefully determined by using in-situ reflection high-energy electron diffraction, exsitu

Carbon nanotubes (CNTs) have great potential in the development of high-power electron beam sources. However, for such a high-performance electronic device, the electric and thermal contact problem between the metal and CNTs must be improved. Here, we report graphene as an interfacial layer between the metal and CNTs to improve the interfacial contact. The interfacial graphene layer results in a dramatic decrease of the electrical contact resistance by an order of 2 and an increase of the interf