Seokhyun Yoon

Surface enhanced Raman spectroscopy (SERS) has been intensively investigated during the past decades for its enormous electromagnetic field enhancement near the nanoscale metallic surfaces. Chemical enhancement of SERS, however, remains rather elusive despite intensive research efforts, mainly due to the relatively complex enhancing factors and inconsistent experimental results. To study details of chemical enhancement mechanism, we prepared various low dimensional semiconductor substrates such

We studied the effects of high-pressure annealing (HPA) on InGaZnO (IGZO) thin-film transistors (TFTs). HPA was proceeded after TFT fabrication as a post process to improve electrical performance and stability. We used N2 as the pressurized gas. The applied pressures were 1 and 3 MPa at 200 °C. For N2 HPA under 3 MPa at 200 °C, field-effect mobility and the threshold voltage shift under a positive bias temperature stress were improved by 3.31 to 8.82 cm(2)/(V s) and 8.90 to 4.50 V, respectively.

Interface engineering is considered the key to improving the device performance and stability of solar cells. In particular, TiO₂ nanostructures, when used as electron transporting layers (ETLs) in metal halide perovskite solar cells (PSCs), led to excellent power conversion efficiencies (PCEs) of over 20%. They effectively transferred charge carriers from the perovskite and suppressed charge recombination at the interfaces. However, the photocatalytic effect of TiO₂ on the

We report a method for fabricating solution-processed quaternary In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) at low annealing temperatures using a vertical diffusion technique (VDT). The VDT is a deposition process for spin-coating binary and ternary oxide layers consecutively and annealing at once. With the VDT, uniform and dense quaternary oxide layers were fabricated at lower temperatures (280 °C). Compared to conventional IGZO and ternary In-Zn-O (IZO) thin films, VDT IGZO thin film had h

Methylammonium lead trihalide perovskites CH₃NH₃PbX₃ (X = Cl, Br, and I) have recently attracted huge attention as a promising candidate for highly efficient solar cell absorber materials. To understand the physical properties of halide perovskites, we investigated the CH₃NH₃PbCl₃ single crystal by Raman scattering spectroscopy from 80 K to room temperature. Benchmarking the phonon modes and their Raman activities obtained by dens

We observed giant enhancement of the Raman intensity from 4-Mpy molecules adsorbed on semiconducting one-dimensional ZnO nanostructures, nanowires and nanocones, without involving any noble metals. Interestingly, the enhancement is strongly dependent on the geometry of ZnO nanostructures and can mainly be explained by the cavity-like structural resonance of the electric field. Our results can be applied to systematically create hot spots for Raman signal enhancement using one-dimensional semicon

We used high-quality ZnO nanostructures/graphene substrates for understanding the mechanisms of charge transfer (CT) that take place under nonplasmonic conditions. As the optimal conditions for CT processes are found, we studied the range of CT normal to the ZnO surface that is coated with nanoscale HfO2 layers with different thicknesses. We could observe that CT decays over a few nanometers. In addition, we also observed a unique oscillation of the SERS intensity in the atomically thin oxide la

Two distinct maxima ${E}_{W}$ and ${E}_{W}^{\ensuremath{'}}$ are observed in the resonant Raman scattering profile for the zone-center longitudinal-optical phonon asymmetric linewidth broadening in ${\mathrm{GaP}}_{1\ensuremath{-}x}{\mathrm{N}}_{x}.$ ${E}_{W}$ originates from the X-point conduction-band state perturbed by isolated nitrogen state ${\mathrm{N}}_{X}$ and the nitrogen-nitrogen (NN) pair and cluster states, and ${E}_{W}^{\ensuremath{'}}$ from the effective band-edge states which are

We report the synthesis of highly crystalline single-phase CoNb2O6 nanofibers using an electrospinning method. Columbite niobate compounds (ANb2O6, A = Ca2+, Mg2+, Zn2+, Ni2+, Sn2+, and Co2+) are promising ceramic materials for many potential applications such as microwave devices and photocatalysts operating at room temperature. The fundamental characteristics including structural and electronic properties at room temperature, however, are not extensively studied at the moment. By combining the

In this letter, we propose a novel packet detection and symbol timing synchronization algorithm for MB-OFDM UWB system over multi-path channel. To find more reliable and exact symbol timing, we utilize the merits of the auto- and cross-correlation at the same time. The auto-correlator can gather the energy of the received signal which is distorted by multipath fading. And, the cross-correlator can estimate symbol timing to sample level precision. We define the detection and symbol timing metric

Vertically-oriented two-dimensional (2D) tungsten disulfide (WS₂) nanosheets were successfully grown on a Si substrate at a temperature range between and 550 °C via the direct chemical reaction between WCl₆ and S in the gas phase. The growth process was carefully optimized by adjusting temperature, the locations of reactants and substrate, and carrier gas flow. Additionally, vertically-oriented 2D WS₂ nanosheets with a few layers were tested as a surface-enhanced

Abstract Hybrid polymer/inorganic nanoparticle blended ternary solar cells are reported. These solar cells have an active layer consisting of PbS colloidal quantum dots (CQDs), poly (3‐hexylthiophene) (P3HT), and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM). Power conversion efficiency (PCE) was improved by incorporating PbS CQDs in the active layer of P3HT:PCBM‐based organic solar cells. As the concentration of PbS CQDs in the hybrid solar cells was increased, PCE was also increased. This