S. S. Kim

Correlation between photoelectric and optical absorption spectra of thermally evaporated pentacene films

We have measured the spectral photoresponse of Al/pentacene Schottky junction photodiodes and optical absorption spectra of pentacene films thermally evaporated on glass. The photoelectric response exhibited the genuine highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) transition at 1.97 eV and interband absorption peaks at 2.3 and 2.5 eV. These peaks are also identified in the optical absorption spectra, but they are dominated by additional strong exciton peaks at 1.82 and 2.1 eV. By comparing these complementary measurements, we determine the HOMO–LUMO gap energy of 1.97 eV and the fundamental exciton binding energy of 0.15 eV for thin solid pentacene.

Optical and luminescence characteristics of thermally evaporated pentacene films on Si

We report on the optical and luminescence properties of pentacene films deposited on n-Si by thermal evaporation at room temperature, 40, 60, 80, and 120u200a°C. Ellipsometric spectra of the films deposited at room temperature and 60u200a°C exhibited a main absorption peak at 1.82 eV and additional weak features at higher energy levels. Photoluminescence spectra taken at room temperature revealed band-to-exciton and band-to-acceptor transitions at 1.7 and 1.76 eV, respectively. An electroluminescence band was also observed near 1.65 eV under a forward bias from p-pentacene/n-Si diodes which show strong rectifying behavior.

Fabrication of p-pentacene/n-Si organic photodiodes and characterization of their photoelectric properties

We have fabricated p-pentacene/n-Si organic photodiodes by thermal evaporation of pentacene films at 25 (RT), 60, and 80u200a°C. Our pentacene films exhibit the main absorption peak (highest occupied molecular orbital-lowest unoccupied molecular orbital gap transition) at 1.82 eV and photoelectric effects were clearly observed from our p-pentacene/n-Si diodes when illuminated by a monochromatic red light of 1.85 eV (670 nm). Excellent photoresponsivity of 2.6 A/W and the photoresponse time of less than 40 ns have been demonstrated. The photodiodes exhibited typical rectifying behavior in the dark and the leakage current increases with the deposition temperature.

Optical Properties of Solid Pentacene

We have prepared pentacene films on Si, Al2O3, and glass substrates by thermal evaporation and have investigated their optical properties at room temperature over a wide range of frequencies from infrared to ultraviolet (5 meV to 6.5 eV). A series of optical phonon modes and electronic transitions have been observed. The internal vibrational modes in the infrared region match well their molecular counterparts but the electronic transitions show substantial changes from those of a free pentacene molecule. The HOMO–LUMO gap energy of the pentacene films deposited on Al2O3 and glass substrates is 1.85 eV.

Photoelectric and optical properties of pentacene films deposited on n-Si by thermal evaporation

Abstract The optical and photoelectric properties of pentacene films deposited on n-Si by thermal evaporation at room temperature, 60 and 80 °C are investigated. Ellipsometric spectra of the films deposited at room temperature and 60 °C exhibited a main absorption peak at 1.82 eV and additional weak features at higher energy levels. Photoelectric effects were well observed from p-pentacene/n-Si diodes, which showed a maximum photoresponsivity of 3.87 A/W under a monochromatic red light of 1.85 eV (670 nm) at 5 V reverse bias. All the diodes exhibited typical rectifying behavior but a higher dark current leakage level was observed from the p-pentacene/n-Si diodes prepared at a higher deposition temperature.

Synthesis of crystalline polyimide film by ionized cluster-beam deposition

Polyimide thin films were deposited by the ionized cluster-beam deposition technique. Imidization and crystallization of polyimide films were investigated using transmission electron microscopy and Fourier transform infrared spectroscopy. Polyimide films deposited under optimum conditions showed a maximum imidization and good crystal structure, which is superior to that of films fabricated by other techniques.

Electrical properties of aluminum oxide films deposited on indium-tin-oxide glasses

We report on the electrical properties of amorphous aluminum oxide films which are the potential gate dielectric material of organic thin-film transistors. The oxide films were deposited on indium-tin-oxide glasses using rf magnetron sputtering at room temperature under various Ar/O2 ambient of 6:1, 10:1, and Ar only. As measured by Rutherford backscattering spectrometry, the stoichiometry (x:y) of the AlxOy oxide films approaches up to 2:3.5 when the gas ratio increases. The highest breakdown electric field (∼3u2009MV/cm) was obtained from the samples deposited at the Ar only condition. According to capacitance–voltage measurements, all of our aluminum oxide films show ∼7 as their dielectric constant, k.

Initial phase wall conditioning in KSTAR

The initial phase wall conditioning in KSTAR is depicted. The KSTAR wall conditioning procedure consists of vessel baking, glow discharge cleaning (GDC), ICRH wall conditioning (ICWC) and boronization (Bz). Vessel baking is performed for the initial vacuum conditioning in order to remove various kinds of impurities including H2O, carbon and oxygen and for the plasma operation. The total outgassing rates after vessel baking in three successive KSTAR campaigns are compared. GDC is regularly performed as a standard wall cleaning procedure. Another cleaning technique is ICWC, which is useful for inter-shot wall conditioning under a strong magnetic field. In order to optimize the operation time and removal efficiency of ICWC, a parameter scan is performed. Bz is a standard technique to remove oxygen impurity from a vacuum vessel. KSTAR has used carborane powder which is a non-toxic boron-containing material. The KSTAR Bz has been successfully performed through two campaigns: water and oxygen levels in the vacuum vessel are reduced significantly. As a result, KSTAR has achieved its first L–H mode transition, although the input power was marginal for the L–H transition threshold. The characteristics of boron-containing thin films deposited for boronization are investigated.

Interfacial properties of ion beam mixed Cu/SiO2 system

Abstract A thin Cu layer (35 nm) deposited on SiO 2 has been mixed with 80 keV Ar + at room temperature, 550 and 650 K. Interfacial properties of irradiated samples were investigated with Rutherford backscattering spectroscopy, grazing angle X-ray diffraction and scratch test. Adhesion of Cu films was improved by a factor of 3 at a dose of 1.5 × 10 16 Ar 4 /cm 2 in the case of ion beam mixing at room temperature, while the high temperature ion beam mixing enhanced the adhesion by a factor of 5. The ballistic mixing effects on the improvement of adhesion for the room temperature ion mixing and the creation of Cu 2 O phase at the interface, which contributes to the enhancement of adhesion induced by ion beam mixing at high temperature, are described in the present paper.

Transventricular Endoscopic Fenestration of Intrasellar Arachnoid Cyst

BACKGROUNDnTo manage arachnoid cysts, incorporation with the normal circulation is the single most important determinant of success. Although the postoperative cerebrospinal fluid leakage rate is 3.9% for all cases of transsphenoidal surgery, it is 21.4% for intrasellar arachnoid cysts.nnnOBJECTIVEnTo present a safe, relatively easy, and effective treatment option for very rare intrasellar arachnoid cysts.nnnMETHODSnWe performed a prospective study of intrasellar cystic lesions without a solid portion. Endoscopic exploration and fenestration were performed for all lesions under neuronavigational guidance. We analyzed presenting symptoms, endocrinological status, and magnetic resonance images.nnnRESULTSnThere were 2 male and 4 female patients with a mean age of 45 years (range, 27-67 years). All patients presented with the visual disturbance of bitemporal hemianopsia. Four patients had endocrinological symptoms including galactorrhea, dysmenorrhea, and diabetes insipidus. Endoscopic fenestration of the cyst was successfully performed in all patients. All patients were confirmed to have a pure cystic lesion, namely an arachnoid cyst. The follow-up period was 10 months on average (range, 6-12 months). Visual disturbance improved in 5 patients. Endocrinological problems persisted in all patients for 3 months and then normalized, with the exception of the patient with diabetes insipidus. There was no evidence of recurrence in any of the 6 patients in the 12-month postoperative imaging studies (median follow-up of 10 months). Two patients showed syndrome of inappropriate antidiuretic hormone at 2 and 4 weeks after the operation, but antidiuretic hormones recovered to normal levels after this time point.nnnCONCLUSIONnEndoscopic fenestration of an intrasellar arachnoid cyst is a safe and simple procedure without serious complications.