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51.
Tae Ho Yeom 《Journal of Physics and Chemistry of Solids》2011,72(1):56-59
The variations with temperature of the relaxation mechanisms of the 9Be, 27Al, and 29Si nuclei in emerald (Be3Al2Si6O18:Cr3+) single crystals were investigated by using a pulse NMR spectrometer. The values of the spin-lattice relaxation rates for the three nuclei are different, and these differences are attributed to the differences between their Larmor frequencies and their local nuclear environments. The relaxation rates of the 9Be and 27Al nuclei undergo no abrupt changes within the temperature range 180-400 K, which indicates that there are no phase transitions within this temperature range. The spin-lattice relaxation rates of 9Be and 27Al were found to be proportional to temperature. Therefore, the nuclear spin-lattice relaxation processes of these two nuclei proceed via single-phonon processes. 相似文献
52.
53.
Cho WB Kim JW Lee HW Bae S Hong BH Choi SY Baek IH Kim K Yeom DI Rotermund F 《Optics letters》2011,36(20):4089-4091
High-quality monolayer graphene as large as 1.2×1.2?cm2 was synthesized by chemical vapor deposition and used as a transmitting saturable absorber for efficient passive mode-locking of a femtosecond bulk solid-state laser. The monolayer graphene mode-locked Cr:forsterite laser was tunable around 1.25?μm and delivered sub-100?fs pulses with output powers up to 230?mW. The nonlinear optical characteristics of the monolayer graphene saturable absorber and the mode-locked operation were then compared with the case of the bilayer graphene saturable absorber. 相似文献
54.
CuSbS2‐Sensitized Inorganic–Organic Heterojunction Solar Cells Fabricated Using a Metal–Thiourea Complex Solution
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Dr. Yong Chan Choi Eun Joo Yeom Prof. Tae Kyu Ahn Prof. Sang Il Seok 《Angewandte Chemie (International ed. in English)》2015,54(13):4005-4009
The device performance of sensitizer‐architecture solar cells based on a CuSbS2 light sensitizer is presented. The device consists of F‐doped SnO2 substrate/TiO2 blocking layer/mesoporous TiO2/CuSbS2/hole‐transporting material/Au electrode. The CuSbS2 was deposited by repeated cycles of spin coating of a Cu‐Sb‐thiourea complex solution and thermal decomposition, followed by annealing in Ar at 500 °C. Poly(2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene)‐alt‐4,7(2,1,3‐benzothiadiazole)) (PCPDTBT) was used as the hole‐transporting material. The best‐performing cell exhibited a 3.1 % device efficiency, with a short‐circuit current density of 21.5 mA cm?2, an open‐circuit voltage of 304 mV, and a fill factor of 46.8 %. 相似文献
55.
M.H. Jeon A.K. Mishra S.-K. Kang K.N. Kim I.J. Kim S.B. Lee T.H. Sin G.Y. Yeom 《Current Applied Physics》2013,13(8):1830-1836
60 MHz pulsed radio frequency (rf) source power and 2 MHz continuous wave rf bias power, were used for SiO2 etching masked with an amorphous carbon layer (ACL) in an Ar/C4F8/O2 gas mixture, and the effects of the frequency and duty ratio of the 60 MHz pulse rf power on the SiO2 etch characteristics were investigated. With decreasing duty ratio of the 60 MHz pulse rf power, not only the etch rate of SiO2 but also the etch rate of ACL was decreased, however, the etch selectivity of SiO2 over ACL was improved with decreasing the duty ratio. On the other hand, when the pulse frequency was varied at a constant duty ratio, no significant change in the etch rate and etch selectivity of both materials could be observed. The variation of the etch characteristics was believed to be related to the change in the gas dissociation characteristics caused by the change in the average electron temperature for different pulsing conditions. The improvement in the etch selectivity with the decrease of duty ratio, therefore, was related to the decreased gas dissociation of C4F8 by the decrease of average electron temperature and, which resulted in a change in composition of the fluorocarbon polymer on the etched materials surface from C–C rich to CF2 rich. With decreasing the duty ratio, not only the etch selectivity but also the improvement in the SiO2 etch profile could be observed. 相似文献
56.
We report >13 MHz/mW pump power efficiency in increasing the repetition rate of passive harmonic mode-locking by engineering the soliton pulse energy in Er fiber lasers incorporating carbon nanotube saturable absorber. Stable pulses with a ~5 GHz repetition rate and 40 dB of super-mode suppression are demonstrated with only ~400 mW pump power in a single-clad fiber laser. 相似文献
57.
Van Tu Nguyen Seongju Ha Dong-Il Yeom Yeong Hwan Ahn Soonil Lee Ji-Yong Park 《Current Applied Physics》2019,19(10):1127-1131
Large-scale growth of mostly monolayer molybdenum disulfide (MoS2) on quartz, sapphire, SiO2/Si, and waveguide substrates is demonstrated by chemical vapor deposition with the same growth parameters. Centimeter-scale areas with large flakes and films of MoS2 on all the growth substrates are observed. The atomic force microscopy and Raman measurements indicate the synthesized MoS2 is monolayer with high quality and uniformity. The MoS2 field effect transistors based on the as-grown MoS2 exhibit carrier mobility of 1–2 cm2V?1s?1 and On/Off ratio of ~104 while showing large photoresponse. Our results provide a simple approach to realize MoS2 on various substrates for electronics and optoelectronics applications. 相似文献
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59.
Chang-Eun Yeom 《Tetrahedron letters》2007,48(51):9035-9039
Ionic liquid was found to be an excellent medium for asymmetric Diels-Alder reaction catalyzed by chiral bis(oxazoline)-copper complex. The reactivity and selectivity of reactions were highly dependent upon the property of the ionic liquids. Reactions of β-substituted acryloyl dienophiles in [Bmim]SbF6 at ambient temperature provided remarkably enhanced reactivity and stereoselectivity compared to homogeneous reactions in non-ionic liquid solvent at −78 °C. Due to the increased reactivity, the amount of metal catalyst could be reduced down to 0.6 mol % without any significant selectivity compromise. Additionally, recycling of the ligand-metal complex was achieved efficiently up to 18 times. 相似文献
60.
Poly(vinyl alcohol) (PVA) membranes crosslinked with glutaraldehyde (GA) were prepared by a solution method for the pervaporation separation of acetic acid-water mixtures. In the solution method, dry PVA films were crosslinked by immersion for 2 days at 40°C in reaction solutions which contained different contents of GA, acetone and a catalyst, HCl. In order to fabricate the crosslinked PVA membranes which were stable in aqueous solutions, acetone was used as reaction medium in stead of aqueous inorganic salt solutions which have been commonly used in reaction solution for PVA crosslinking reaction. The crosslinking reaction between the hydroxyl group of PVA and the aldehyde group of GA was characterized by IR spectroscopy. Swelling measurements were carried out in both water and acetic acid to investigate the swelling behavior of the membranes. The swelling behaviour of a membrane fabricated at different GA content in a reaction solution was dependent on crosslinking density and chemical functional groups created as a result of the reaction between PVA and GA, such as the acetal group, ether linkage and unreacted pendent aldehydes in PVA. The pervaporation separation of acetic acid-water mixtures was performed over a range of 70–90 wt% acetic acid in the feed at temperatures varying from 35 to 50°C to examine the separation performances of the PVA membranes. Permeation behaviour through the membranes was analyzed by using pervaporation activation energies which had been calculated from the Arrhenius plots of permeation rates. 相似文献