Seung-Han Park

Synthesis of Si Nanosheets by a Chemical Vapor Deposition Process and Their Blue Emissions

We synthesized free-standing Si nanosheets (NSs) with a thickness of about <2 nm using a chemical vapor deposition process and studied their optical properties. The Si NSs were formed by the formation of frameworks first along six different <110> directions normal to [111], its zone axis, and then by filling the spaces between the frameworks along the <112> directions under high flow rate of processing gas. The Si NSs showed blue emission at 435 nm, and absorbance and photoluminescence (PL) excitation measurements indicate that enhanced direct band transition attributes to the emission. Time-resolved PL measurement, which showed PL emission at 435 nm and a radiative lifetime of 1.346 ns, also indicates the enhanced direct band gap transition in these Si NSs. These outcomes indicate that dimensionality of Si nanostructures may affect the band gap transition and, in turn, the optical properties.

The electronic structure of C60/ZnPc interface for organic photovoltaic device with blended layer architecture

The interfacial electronic structures of fullerene (C60)/zinc-phthalocyanine (ZnPc) and C60/ZnPc:C60 (50 wt %) containing a blended layer were investigated by in situ ultraviolet photoelectron spectroscopy (UPS), in an attempt to understand the role of the blended layer in improving the performance of organic photovoltaic devices that contain such layers. From the UPS spectra, the band bending found to be 0.30 eV in the ZnPc layer and 0.43 eV in the C60 layer at the C60/ZnPc interface. On the other hand, the band bending was 0.25 eV in both of the organic layers at the ZnPc:C60/ZnPc interface and no significant band bending in the C60 layer at the C60/ZnPc:C60 interface was found. The observed interface dipole was 0.06 eV at the C60/ZnPc interface and 0.26 eV at the ZnPc:C60/ZnPc interface. The offset between the highest unoccupied molecular orbital of ZnPc and the lowest occupied molecular orbital of C60 was 0.75 eV at C60/ZnPc and was 1.04 eV at the ZnPc:C60/ZnPc interface. The increased offset can be a...

Numerical analysis of an annular-aperture solid immersion lens

A physical model of an annular-aperture solid immersion lens (SIL) is proposed, and its attractive features are presented numerically with the finite-difference time-domain method. Placing an appropriate annular aperture in front of the SIL shows that the focal depth can evidently be improved, combining the virtues of the annular-aperture technique and the SIL technique. With this proposed method the rigorous distance control condition in related devices can be relaxed, preventing scratches or collisions between the optical head and the recording medium. Potentially, this technique could have great prospects for applications in optical data recording, lithography, and other applications that depend on immersion media to meet the resolution criteria across the image field.

Laparoscopic cholecystectomy only could be an appropriate treatment for selected clinical R0 gallbladder carcinoma.

BackgroundLaparoscopic cholecystectomy (LC) for gallbladder carcinoma still is controversial except for the early stages of gallbladder carcinoma (Tis). This study was designed to evaluate and revisit the role of LC in treating gallbladder carcinoma.MethodsAvailable medical records of patients with surgeries for gallbladder carcinoma were retrospectively investigated from August 1992 to February 2005.ResultsAmong 219 patients treated for gallbladder carcinoma, 57 (26%) underwent LC. A total of 16 patients (28.1%) underwent subsequent radical cholecystectomy (LC–RC), and 41 (71.9%) were only followed up without radical surgery (LC). Tis was found in 11 patients (19.3%), T1a in 3 patients (5.3%), T1b in 8 patients (14%), T2 in 19 patients (33.3%), and T3 in 16 patients (28.1%). The findings showed R0 in 14 cases of the radical cholecystectomy group, and clinical R0 was noted in 30 cases of the LC-only group. No survival differences were noted between LC and LC–RC (p = 0.2575), especially in the case of T2 lesions (p = 0.6274), nor between the R0 and clinical R0 (p = 0.5839). However, significant survival differences were noted between the R2 and R0 groups, and between R2 and clinical R0, respectively (p < 0.001).ConclusionsThe findings show that LC could be appropriate treatment for gallbladder carcinoma only in selected cases of clinical R0 lesions.

Phase-shifting lateral shearing interferometer with two pairs of wedge plates

We present a compact and robust phase-shifting lateral shearing interferometer that produces shearing fringes in orthogonal directions without any mechanical rotation or precise alignment. It consists of two pairs of wedge plates, a beam splitter, and a single CCD camera. Both phase-shifting and tilt for lateral shearing are achieved with two pairs of wedge plates, which can reduce systematic errors caused by external vibration and atmospheric disturbance.

Indirect energy transfer of Ce3+ → Eu2+ in CaAl12O19 phosphor

Photoluminescence characteristics and the energy transfer between Ce3+ and Eu2+ in CaAl12O19 host lattice have been investigated. A series of concentrations of Ce3+ ion with a fixed Eu2+ concentration in doubly doped CaAl12O19 : Ce3+Eu2+ have been studied. The indirect energy transfer has been observed between Ce3+ and Eu2+ through the Ce3+OMe complex in CaAl12O19 host lattice. The two nonradiative relaxation processes from the excited levels of Ce3+OMe complex; one, to the lower emitting level of Ce3+OMe complex themselves and the other, to the Eu2+ site are competing processes.

MEASUREMENT OF FREE-CARRIER NONLINEARITIES IN ZNSE BASED ON THE Z-SCAN TECHNIQUE WITH A NANOSECOND LASER

Self-defocusing and nonlinear absorption resulting from two-photon-excited free charge carriers were observed in polycrystalline ZnSe at the low power density of ~ 30 MW/cm(2) by use of the Z-scan technique with nanosecond laser pulses. The total carrier absorption cross section and the variation of refractive index per unit of photoexcited carrier density were estimated to be 0.80 +/- 0.10 x 10(-18) cm(2) and 0.60 +/- 0.15 x 10(-21) cm(3), respectively.

Coupling of semiconductor nanowires with neurons and their interfacial structure.

We report on the compatibility of various nanowires with hippocampal neurons and the structural study of the neuron–nanowire interface. Si, Ge, SiGe, and GaN nanowires are compatible with hippocampal neurons due to their native oxide, but ZnO nanowires are toxic to neuron due to a release of Zn ion. The interfaces of fixed Si nanowire and hippocampal neuron, cross-sectional samples, were prepared by focused ion beam and observed by transmission electron microscopy. The results showed that the processes of neuron were adhered well on the nanowire without cleft.

Evolution of electromagnetic interference through nano-metallic double-slit

We investigated the characteristics of the near- and far-field regions of the interference for nano-metallic double-slits using a two-dimensional finite-difference time-domain (FDTD) method. We have found that the patterns in the near-field region have a phase difference of pi with respect to those in the far-field region. A boundary, which separates the interference patterns of the two regions exists as a half circle and grows as the distance between the two slits increase. It is also found that evanescent waves can be enhanced and confined by coating the double-slit with a dielectric cladding.

Finite-difference time-domain analysis of self-focusing in a nonlinear Kerr film.

By using a finite-difference time-domain method, we analyze self-focusing effects in a nonlinear Kerr film and demonstrate that the near-field intensity distribution at the film surface can reach a stable state at only a few hundred femtoseconds after the incidence of the beam. Our simulations also show that the formation of multiple filamentations in the near-field is quite sensitive to the thickness of the nonlinear film and the power of the laser beam, strongly indicating the existence of nonlinear Fabry-Perot interference effects of the linearly polarized incident light.