• Journal of Microbiology and Biotechnology
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• v.12 no.1
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• pp.46-52
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• 2002

As a functional additive for intestinal microflora, panose ($6^2-{\alpha}$-D-glucopyranosylmaltose) was synthesized during kimchi fermentation using the glucose transferring reaction of glucansucrase from Leuconostoc mesenteroides. For the glucose transferring reaction, sucrose and maltose were added ($2\%$ each, w/v) to dongchimi-kimchi as the glucosyl donor and acceptor molecule, respectively. After five days of incubation at $10^{\circ}C$, referring to the initial phase for the production of lactic acid in kimchi, over $60\%$ (w/v) of the total sugars were converted into panose and other branched oligosaccharides. Thereafter, the kimchi was stored at $4^{\circ}C$ and the amount of panose remained at a constant level for three weeks, thereby indicating the stability of panose to microbial degradation during the period of kimchi consumption. The use of maltose as the acceptor molecule in the kimchi also facilitated a lower viscosity in the kimchi-juice by preventing the synthesis of a dextran-like polymer which caused an unfavorable taste. Accordingly, the application of this new method of simultaneous biocatalytic synthesis of oligosaccharides during lactate fermentation should facilitate the extensive development of new function-added lactate foods.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.41-44
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• 2014

In this paper, we will investigate the activation energies of Nb for $TiO_2$ using Hall effect measurement and photoluminescence (PL) system. Nb-doped $TiO_2$ thin film was grown on $SrTiO_3$ substrate by pulsed laser deposition (PLD) technique. After measurements, activation energies of niobium donor were 14.52 meV in Hall effect measurement, and 6.72 meV in PL measurement, respectively. These results showed different tendencies which are measured from the samples with acceptor materials. Therefore, it is thought that more research on activation energies for dopants of shallow donor level is expected.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.509-514
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• 2020

The two key variables of an Si solar cell, i.e., emitter (n-type window layer) and base (p-type substrate) doping levels or concentrations, are studied using Medici, a 2-dimensional semiconductor device simulation tool. The substrate is p-type and 150 ㎛ thick, the pn junction is 2 ㎛ from the front surface, and the cell is lit on the front surface. The doping concentration ranges from 1 × 10¹⁰ cm^-3 to 1 × 10²⁰ cm^-3 for both emitter and base, resulting in a matrix of 11 by 11 or a total of 121 data points. With respect to increasing donor concentration (Nd) in the emitter, the open-circuit voltage (Voc) is little affected throughout, and the short-circuit current (Isc) is affected only at a very high levels of Nd, exceeding 1 × 10¹⁹ cm^-3, dropping abruptly by about 12%, i.e., from Isc = 6.05 × 10^-9 A·㎛^-1, at Nd = 1 × 10¹⁹ cm^-3 to Isc = 5.35 × 10^-9 A·㎛^-1 at Nd = 1 × 10²⁰ cm^-3, likely due to minority-carrier, or hole, recombination at the very high doping level. With respect to increasing acceptor concentration (Na) in the base, Isc is little affected throughout, but Voc increases steadily, i.e, from Voc = 0.29 V at Na = 1 × 10¹² cm^-3 to 0.69 V at Na = 1 × 10¹⁸ cm^-3. On average, with an order increase in Na, Voc increases by about 0.07 V, likely due to narrowing of the depletion layer and lowering of the carrier recombination at the pn junction. At the maximum output power (Pmax), a peak value of 3.25 × 10^-2 W·cm^-2 or 32.5 mW·cm^-2 is observed at the doping combination of Nd = 1 × 10¹⁹ cm^-3, a level at which Si is degenerate (being metal-like), and Na = 1 × 10¹⁷ cm^-3, and minimum values of near zero are observed at very low levels of Nd ≤ 1 × 10¹³ cm^-3. This wide variation in Pmax, even within a given kind of solar cell, indicates that selecting an optimal combination of donor and acceptor doping concentrations is likely most important in solar cell engineering.

• Journal of the Korean Chemical Society
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• v.18 no.2
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• pp.85-96
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• 1974

Extended H ckel Theory and CNDO/2 MO calculation methods have been applied to $C_6H_5YCH_2Cl$(Y = None, -$CH_2$-, -O-, -S-, -CO-, -$SO_2$-). It has been shown that charge distributions in molecules are mainly controlled by the migration of valence inactive electron, giving the order of ${\sigma}$-acceptor and ${\pi}$-donor effects -O- > -S- > -$CH_2$- > -$SO_2$-. The -CO- group exceptionally acts as ${\sigma}$-donor and ${\pi}$-acceptor. It was also predicted that, $S_N2$ reactivities of C$C_6H_5YCH_2Cl$ would be in the order of -O-${\thickapprox}$-CO- >>-S-${\thickapprox}$None > -$CH_2$-, neglecting solvent effect. From the results of our studies, we conclude that the structural factors influencing 의 $S_N$ reactivities will be: (1) positive charge developments on reaction center carbon atom (2) energy level of ${\sigma}$-antibonding unoccupied MO with respect to C-Cl bond. (3) ${\sigma}$-antibonding strength of C-Cl bond at that level.

• Applied Science and Convergence Technology
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• v.23 no.6
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• pp.351-356
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• 2014

The electronic structure at organic-organic interface gives essential information on device performance such as charge transport and mobility. Especially, the molecular orientation of organic material can affect the electronic structure at interface and ultimately the device performance in organic photovoltaics. The molecular orientation is examined by the change in ionization potential (IP) for metal phthalocyanines (MPc, M=Zn, Cu)/fullerene ($C_{60}$) interfaces on ITO by adding the CuI templating layer through ultraviolet photoelectron spectroscopy measurement. On CuPc/$C_{60}$ bilayer, the addition of CuI templating layer represents the noticeable change in IP, while it hardly affects the electronic structure of ZnPc/$C_{60}$ bilayer. The CuPc molecules on CuI represent relatively lying down orientation with intermolecular ${\pi}-{\pi}$ overlap being aligned in vertical direction. Consequently, in organic photovoltaics consisting of CuPc and $C_{60}$ as donor and acceptor, respectively, the carrier transport along the direction is enhanced by the insertion of CuI templaing layer. In addition, optical absorption in CuPc molecules is increased due to aligned transition matrix elements. Overall the lying down orientation of CuPc on CuI will improve photovoltaic efficiency.

• Transactions on Electrical and Electronic Materials
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• v.9 no.2
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• pp.67-72
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• 2008

Al-doped p-type ZnO thin films were fabricated by RF magnetron sputtering on n-Si (100) and homo-buffer layers in pure oxygen ambient. ZnO ceramic mixed with 2 wt% $Al_2O_3$ was selected as a sputtering target. XRD spectra show that the Al-doped ZnO thin films have ZnO crystal structure. Hall Effect experiments with Van der Pauw configuration show that p-type carrier concentrations are arranged from $1.66{\times}10^{16}$ to $4.04{\times}10^{18}\;cm^{-2}$, mobilities from 0.194 to $198\;cm^2V{-1}s^{-1}$ and resistivities from 0.0963 to $18.4\;{\Omega}cm$. FESEM cross section images of different parts of a p-type ZnO:Al thin film annealed at $800^{\circ}C$ show a compact structure. Measurement for same sample shows that density is $5.40\;cm^{-3}$ which is smaller than theoretically calculated value of $5.67\;cm^{-3}$. Photoluminescence (PL) spectra at 10 K show a shoulder peak of p-type ZnO film at about 3.117 eV which is ascribed to electron transition from donor level to acceptor level (DAP).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.419-420
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• 2008

In this study, high quality (Al,N)-codoped p-type ZnO thin films were obtained by DC magnetron sputtering. The film on buffer layer grown in 80% $N_2$ ambient shows highest hole concentration of $2.93\times10^{17}cm^{-3}$. The films show hole concentration in the range of $1.5\times10^{15}$ to $2.93\times10^{17}cm^{-3}$, resistivity of 131.2 to 2.864 $\Omega$cm, mobility of 3.99 to 31.6 $cm^2V^{-1}s^{-1}$. The films on Si show easier p-doping in ZnO than those on buffer layer. The film on Si shows the highest quality of optical photoluminescence (PL) characteristics. The donor energy level $(E_d)$ of (Al,N)-codoped ZnO films is about 50 meV and acceptor energy level $(E_a)$ is in the range of 63 to 71 meV. It will help to improve p-type ZnO films.

• Korean Journal of Materials Research
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• v.8 no.6
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• pp.526-531
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• 1998

A hydride vapor phase epitaxy (HVPE) method was performed to grow the $10~240\mu{m}$ thick GaN films on (111) spinel $MgAl_2O_4$ substrate. The GaN films on $MgAl_2O_4$ substrate revealed a photoluminescence (PL) characteristics of the impurity doped GaN by the out-diffusion and auto-doping of Mg from $MgAl_2O_4$ substrate during GaN growth. The PL spectrum measured at 10K consists of free and bound excitons related recombination transitions and impurity-related donor-acceptor pair recombination and its phonon replicas. However, the deep-level related yellow band emission was not observed. The peak energy of neutral donor bound excitonic emission and the frequency of Raman $E_2$ mode were exponentially decreased with increasing the GaN thicknesses. and the frequency of E, Raman mode was shifted with the relation of $\Delta$$\omega$=3.93$\sigma$($cm^{-1}$/GPa), where l1 (GPa) is the residual strain in the GaN epilayers.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.95-98
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• 2013

The photoluminescence (PT) properties of Al-doped ZnO thin films grown by the sol-gel dip-coating method have been investigated. At 12 K, nine distinct PL peaks were observed at 2.037, 2.592, 2.832, 3.027, 3.177, 3.216, 3.260, 3.303, and 3.354 eV. The deep-level emissions (2.037, 2.592, 2.832, and 3.027 eV) were attributed to native defects. The near-band-edge (NBE) emission peaks at 3.354, 3.303, 3.260, 3.216, and 3.177 eV were attributed to the emission of the neutral-donor-bound excitons ($D^0X$), two-electron satellite (TES), free-to-neutral-acceptors (e,$A^0$), donor-acceptor pairs (DAP), and second-order longitudinal optical (2LO) phonon replicas of the TES (TES-2LO), respectively. According to Haynes' empirical rule, we calculated the energy of a free exciton (FX) to be 3.374 eV. The thermal activation energy for $D^0X$ in the nanocrystalline ZnO thin film was found to be ~25 meV, corresponding to the thermal dissociation energy required for $D^0X$ transitions.

• Rapid Communication in Photoscience
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• v.3 no.4
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• pp.61-63
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• 2014

3,7-bis(4-(diphenylamino)phenyl)-5-phenyl-5H-benzo[b]phosphinedole 5-sulfide (DBPPS-TPA) and 3,7-bis(4-(diphenylamino)phenyl)-5-phenyl-5H-benzo[b]phosphinedole 5-selenide (DBPPSe-TPA) are newly synthesized D-A-D type molecules based on dibenzophospholes and their physic-chemical properties are studied in comparison with a P=O type compouond, 3,7-bis(4-(diphenylamino)-5-phenyl-5H-benzo[b]phosphinedole 5-oxide (DBPPO-TPA). Fluorescence emission and electrochemical redox properties of these compounds are investigated regarding results of density functional theory (DFT) calculations, X-ray crystallographic structures and UV-vis absorption spectra. These results exhibit systematic variation in optical properties of these compounds having P=O, P=S, and P=Se units. LUMO energy level is systematically modulated with different chalcogenide atoms.