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121.
Seulah Lee Ja Hoon Koo Jungmok Seo Sung-Dae Kim Kwang Hyun Lee Seongil Im Young-Woon Kim Taeyoon Lee 《Journal of nanoparticle research》2012,14(5):840
Although the aqueous electroless etching (AEE) method has received significant attention for the fabrication of silicon nanowires
(SiNWs) due to its simplicity and effectiveness, SiNWs grown via the AEE method have a drawback in that their surface roughness
is considerably high. Thus, we fabricated surface-modified p–n
+ junction SiNWs grown by AEE, wherein the surface roughness was reduced by a sequential processes of oxide growth using the
rapid thermal oxidation (RTO) cycling process and oxide removal with a hydrofluoric acid solution. High-resolution transmission
electron microscopy analysis confirmed that the surface roughness of the modified SiNWs was significantly decreased compared
with that of the as-fabricated SiNWs. After RTO treatment, the wettability of the SiNWs had dramatically changed from superhydrophilic
to superhydrophobic, which can be attributed to the formation of siloxane groups on the native oxide/SiNW surfaces and the
effect of the nanoscale structure. Due to the enhancement in surface carrier mobility, the current density of the surface-modified
p–n
+ junction SiNWs was approximately 6.3-fold greater than that of the as-fabricated sample at a forward bias of 4 V. Meanwhile,
the photocurrent density of the surface-modified p–n
+ junction SiNWs was considerably decreased as a result of the decreases in the light absorption area, light absorption volume,
and light scattering. 相似文献
122.
Sang Jin LeeTae Jong Baek Min HanSeok Gyu Choi Dong Sik KoSam Dong Kim Jin Koo Rhee 《Current Applied Physics》2012,12(3):773-777
We present a high isolation W-band MMIC drain type cascode single balanced mixer of high LO-to-RF isolation and wide band with conversion characteristic using the high directivity monolithic tandem couplers and 0.1 μm GaAs-based metamorphic high electron mobility transistors (MHEMTs). The fabricated mixer consists of two cascode MHEMT mixers and two tandem couplers using the air-bridge crossovers. We establish a drain type cascode mixer structure where the LO signal is applied to the drain port in the mixing component of common source MHEMT circuit. The tandem coupler exhibits good couplings (2.92-3.8 dB), low return losses (−32.7 dB), and isolations (15.4-39.2 dB) in a wide bandwidth of 75-110 GHz. The mixer shows a conversion loss of 9.8 dB at 94 GHz, an output P1dB of −14.8 dBm at LO frequency of 94.542 GHz, and LO-to-RF isolations of 29.5-39.5 dB at 94-100 GHz. 相似文献
123.
Hyun-Joo Koo 《Solid State Communications》2012,152(13):1116-1118
The causes for the three-dimensional magnetic ordering and the observed spin orientation of the layered oxides Sr2MnSi2O7 and Ba2MnGe2O7 were investigated by evaluating the spin exchange interactions and the preferred spin orientation on the basis of density functional calculations and by calculating the magnetic dipole–dipole interaction energies. 相似文献
124.
Park SJ Shin S Koo OJ Moon JH Jang G Ahn C Lee BC Yoo YJ 《Experimental & molecular medicine》2012,44(1):20-25
Transplantation of islet cells into diabetic patients is a promising therapy, provided that the islet cells are able to evade host immune rejection. With improved islet viability, this strategy may effectively reverse diabetes. We applied 2% calcium alginate to generate small and large capsules to encapsulate porcine neonatal pancreatic cell clusters (NPCCs) using an air-driven encapsulator. After encapsulation, the viability was assessed at 1, 4, 7, 14 and 28 days and secretion of functional insulin in response to glucose stimulation were tested at days 14 and 28. Selective permeability of the small alginate capsules was confirmed using various sizes of isothiocyanate-labeled dextran (FITC-dextran). Encapsulation of NPCCs was performed without islet protrusion in the small and large capsules. The viability of NPCCs in all experimental groups was greater than 90% at day 1 and then gradually decreased after day 7. The NPCCs encapsulated in large capsules showed significantly lower viability (79.50 ± 2.88%) than that of naïve NPCCs and NPCCs in small capsule (86.83 ± 2.32%, 87.67 ± 2.07%, respectively) at day 7. The viability of naïve NPCCs decreased rapidly at day 14 (75.67 ± 1.75%), whereas the NPCCs encapsulated in small capsules maintained (82.0 ± 2.19%). After 14 and 28 days NPCCs' function in small capsules (2.67 ± 0.09 and 2.13 ± 0.09) was conserved better compared to that of naïve NPCCs (2.04 ± 0.25 and 1.53 ± 0.32, respectively) and NPCCs in large capsules (2.04 ± 0.34 and 1.13 ± 0.10, respectively), as assessed by a stimulation index. The small capsules also demonstrated selective permeability. With this encapsulation technique, small capsules improved the viability and insulin secretion of NPCCs without islet protrusion. 相似文献
125.
The free flexural vibration of a hanged clamped-free cylindrical shell with various boundary conditions partially submerged in a fluid is investigated. Specifically, the effects of the boundary conditions such as the existence of the external wall, internal shaft, and bottom on the natural vibration characteristics of the partially submerged cylindrical shell are investigated both theoretically and experimentally. The fluid is assumed to be inviscid and irrotational. The cylindrical shell is modeled by using the Rayleigh–Ritz method based on the Sanders shell theory. The kinetic energy of the fluid is derived by solving a boundary-value problem related to the fluid motion. The theoretical predictions were in good agreement with the experimental results validating the theoretical approach developed in this study. The effects of the external wall, internal shaft, and bottom on the natural vibration characteristics can be neglected when its boundaries are not very close to the shell structure. 相似文献
126.
Jung CY Kim JS Kim HS Ha JM Kim ST Lim HJ Koo SM 《Journal of colloid and interface science》2012,367(1):257-263
Monodispersed, submicron-sized Janus ORMOSIL particles with multiple functional groups were prepared by the selective surface reaction of a monolayer film formed at a hexane-water interface. A well-ordered monolayer film was obtained by self-assembly of ORMOSIL particles with multiple functional groups at hexane-water interface. The photopolymerization of an ordered monolayer containing ORMOSIL particles yields a rigid film strong enough to maintain its integrity for transfer and further chemical reaction. The chemical reaction of this ordered film with organic and inorganic functional groups produced Janus ORMOSIL particles with multiple functional groups. The morphologies, structures, and chemical compositions of monolayer films and Janus ORMOSIL particles were characterized by FT-IR, solid state NMR, X-ray diffraction (XRD), optical microscopy (OM), electron microscopies (SEM and TEM), and confocal laser scanning microscopy. 相似文献
127.
Characterization of Hydrophobic SiO2 Powders Prepared by Surface Modification on Wet Gel 总被引:2,自引:0,他引:2
Ae-Young Jeong Sang-Man Koo Dong-Pyo Kim 《Journal of Sol-Gel Science and Technology》2000,19(1-3):483-487
Hydrophobic porous silica has been prepared by surface modification of TEOS (tetraethylorthosilicate) wet gel with 6 and 12 vol.% of TMCS (trimethylchlorosilane). We characterized the products by using FT-IR, TGA, DTA, N2 adsorption/desorption, contact angle and SEM. Surface silanol groups of the gel were widely replaced by–Si(CH3)3 to result in a hydrophobic SiO2 powder as confirmed by contact angle measurements with H2O, 1-butanol and ethanol. The modified dried gels had a surface area of 950–1000 m2/g (average pore size 120 Å), compared to the non-modified surface which had a surface area of 690 m2/g (average pore size 36 Å). The adsorption/desorption isotherm curves indicated they had similar pore characteristics as aerogels prepared by the supercritical drying process. 相似文献
128.
High-Resolution Infrared-Vacuum Ultraviolet Photoion and Pulsed Field Ionization-Photoelectron Methods for Spectroscopic Studies of Neutrals and Cations
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Xi Xing Beth Reed Mi Kyung Bahng Peng Wang Hin Koo Woo Sun Jong Baek Chee Shing Lam Cheuk Yiu Ng¤ 《化学物理学报(中文版)》2008,21(3):193-201
We show that by scanning the frequency of a single mode infrared (IR) optical parametric oscillator (IR-OPO) laser to excite the molecular species of interest and fixing the frequency of a vacuum ultraviolet (VUV) laser to photoionize the IR excited species, high-resolution IR spectra of polyatomic neutrals can be obtained with high sensitivity. The fact that this IR-VUV-photoion (IR-VUV-PI) method is based on VUV photoionization probe, and thus, allows the identification of the neutral IR absorber, makes it applicable for IR spectroscopy measurements of isotopemers, radicals, and clusters, which usually exist as impure samples. The highly resolved IR-VUV-PI measurements achieved using the single mode IR-OPO laser have made possible the selection of single rovibrational states of CH3X (X=Br and I), C2H4, and C3H4 for VUV-pulsed field ionization-photoelectron (VUV-PFI-PE) measurements, resulting in rovibrationally resolved photoelectron spectra for these polyatomic molecules. These experiments show that the signal-to-noise ratios of the IR-VUV-PI and IR-VUV-PFI-PE spectra obtained by employing the high-resolution IR-OPO laser are significantly higher than those observed in previous IR-VUV-PI and IR-VUV-PFI-PE studies using a low-resolution IR-OPO laser. Further improvement in sensitivity of IR-VUV-PI and IR-VUV-PFI-PE measurements by using the collinear arrangement of IR-VUV lasers and molecular beam is discussed. 相似文献
129.
130.
Boo Rim Choe Hyungwoon Koo Wayne Smith 《Transactions of the American Mathematical Society》2003,355(7):2829-2855
We study the action of composition operators on Sobolev spaces of analytic functions having fractional derivatives in some weighted Bergman space or Hardy space on the unit disk. Criteria for when such operators are bounded or compact are given. In particular, we find the precise range of orders of fractional derivatives for which all composition operators are bounded on such spaces. Sharp results about boundedness and compactness of a composition operator are also given when the inducing map is polygonal.