• Bulletin of the Korean Chemical Society
• /
• v.24 no.6
• /
• pp.763-770
• /
• 2003

The $BH_5$ molecule, which is suggested as an intermediate of the acidolysis of $BH_4^-$, contains a weak two-electron-three-center bond and it requires extremely high-level of theories to calculate the energy and structure correctly. The structures and energies of $BH_5$ and the transition state for the hydrogen scrambling have been studied using recently developed multi-coefficient correlated quantum mechanical methods (MCCMs). The dissociation energies and the barrier heights agree very well with the previous results at the CCSD(T)/ TZ(3d1f1g, 2p1d) level. We have also calculated the potential energy curves for the dissociation of $BH_5$ to $BH_3$ and $H_2$. The lower levels of theory were unable to plot correct potential curves, whereas the MCCM methods give very good potential energy curves and requires much less computing resources than the CCSD(T)/ TZ(3d1f1g,2p1d) level. The potential energy of the $BH_5$ scrambling has been obtained by the multiconfiguration molecular mechanics algorithm (MCMM), and the rates are calculated using the variational transition state theory including multidimensional tunneling approximation. The rate constant at 300 K is 2.1 × $10^9s^{-1}$, and tunneling is very important.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.35D no.6
• /
• pp.15-20
• /
• 1998

The linewidth enhancement factor $\alpha$ and fiber dispersion of 1.55 ${\mu}{\textrm}{m}$ strained multi-quantum well laser diodes are measured using small signal power modulation transfer function in a dispersive fiber. The measured fiber dispersion values are between 16.766 and 16.786ps/nm/km and these are the expected values from standard single mode fiber. To measure the $\alpha$ parameter in the actual operational range of the laser diodes, the dependence of $\alpha$ on laser output power is measured. The $\alpha$ parameter increases linearly as the power of the laser diode increases. This result can explain the non-linear gain effect on the $\alpha$ parameter more accurately than any other measurements.

• Applied Microscopy
• /
• v.41 no.2
• /
• pp.89-98
• /
• 2011

Atom Probe Tomography (APT) can provide 3-dimensional information such as position and chemical composition with atomic resolution. Despite the ability of this technique, APT could not be applied for poor conductive materials such as semiconductor. Recently APT has dramatically developed by applying the laser pulsing and combining with Focused Ion Beam (FIB). The invention and combination of these techniques make possible site-specific sample preparation and permit the investigation of various materials including insulators. In this paper, we introduced the recently achieved state of the art applications of APT focusing on Si based FET devices, LED devices, low dimensional materials.

• Applied Microscopy
• /
• v.41 no.3
• /
• pp.215-222
• /
• 2011

We discuss the experimental procedure for extracting reliable phase information from a defocus series of transmission electron microscopy (TEM) dark-field images using the transport of intensity equation (TIE). Taking InGaN/GaN multi-quantum well light-emitting diode as a model system, various factors affecting the final result of reconstructed phase such as TEM sample preparation, TEM imaging condition, image alignment, the correction of defocus values and the use of high frequency pass filter are evaluated. The obtained phase of wave function was converted to the geometric phase of the corresponding lattice planes, which was then used for the two-dimensional mapping of lattice strain following the dark-field inline holography (DIH) routine. The strain map obtained by DIH after optimized image processing is compared with that obtained by the geometric phase analysis of high resolution TEM (HRTEM) image, manifesting that DIH yields more accurate and reliable strain information than HRTEM-based GPA.

• Journal of the Semiconductor & Display Technology
• /
• v.10 no.4
• /
• pp.131-138
• /
• 2011

We fabricated distributed feedback InGaAsP/InP laser diodes for optical fiber communication module and characterized the lasing properties in continuous wave operation. The active layer of 7-period InGaAsP(1.127 eV)/InGaAsP(0.954 eV) multi-quantum well structure was grown by the metal-organic chemical vapor deposition. The grating for waveguide was also fabricated by the implementation of the Mach-Zehender holographic method of two laser beams interference of He- Cd laser and the fabricated laser diode has the dimension of the laser length of $400{\mu}m$ and the ridge width of $1.2{\mu}m$. The laser diode shows the threshold current of 3.59 mA, the threshold voltage of 1.059 V. For the room-temperature operation with the current of 13.54 mA and the voltage of 1.12 V, the peak wavelength is about 1309.70 nm and optical power is 13.254 mW.

• Korean Journal of Materials Research
• /
• v.6 no.6
• /
• pp.651-656
• /
• 1996

InGaAs/InGaAsP 다층박막을 corrugation이 형성된 InP 기판위에 MOVPE 방법을 이용하여 성장 시킨 후 성장조건에 따른 corrugation 높이의 변화와 석출상에 대하여 투과전자현미경을 이용하여 시킨 후 성장조건에 따른 corrugation 높이의 변화와 석출상에 대하여 투과전자현미경을 이용하여 연구하였다. Corrugation이 형성된 InP 기판을 PH3 및 AsH3가스를 동시에 공급해 주었는데 AsH3 가스의 압력이 높으면(1.8x10-2torr)많은 양의 As를 포함한 In1-xAsxP(x=0.3)석출상이 격자결함과 더불어 형성되었다. 반면에 AsH3 가스의 압력이 낮을때는 (1.0x10-3torr) corrugation의 높이가 30nm이었고, 적은 양의 As를 포함한 In1-xAsxP(x<0.1)석출상이 격자결함이 없이 형성되었다.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.9
• /
• pp.2581-2587
• /
• 2010

Nitration of tyrosine and tryptophan residues is common in cells under nitrative stress. However, physiological consequences of protein nitration are not well characterized on a molecular level due to limited availability of the 3D structures of nitrated proteins. Molecular dynamics (MD) simulation can be an alternative tool to probe the structural perturbations induced by nitration. In this study we developed molecular mechanics parameters for 3-nitrotyrosine (NIY) and 6-nitrotryptophan (NIW) that are compatible with the AMBER-99 force field. Partial atomic charges were derived by using a multi-conformational restrained electrostatic potential (RESP) methodology that included the geometry optimized structures of both $\alpha$- and $\beta$-conformers of a capped tripeptide ACE-NIY-NME or ACE-NIW-NME. Force constants for bonds and angles were adopted from the generalized AMBER force field. Torsional force constants for the proper dihedral C-C-N-O and improper dihedral C-O-N-O of the nitro group in NIY were determined by fitting the torsional energy profiles obtained from quantum mechanical (QM) geometry optimization with those from molecular mechanical (MM) energy minimization. Force field parameters obtained for NIY were transferable to NIW so that they reproduced the QM torsional energy profiles of ACE-NIW-NME accurately. Moreover, the QM optimized structures of the tripeptides containing NIY and NIW were almost identical to the corresponding structures obtained from MM energy minimization, attesting the validity of the current parameter set. Molecular dynamics simulations of thioredoxin nitrated at the single tyrosine and tryptophan yielded well-behaved trajectories suggesting that the parameters are suitable for molecular dynamics simulations of a nitrated protein.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.153-153
• /
• 2010

Recently, to develop GaN-based light-emitting diodes (LEDs) with better performances, various approaches have been suggested by many research groups. In particular, using the patterned sapphire substrate technique has shown the improvement in both internal quantum efficiency and light extraction properties of GaN-based LEDs. In this paper, we discuss the influences of the direction of the hexagonal-structure arrays of lens-shaped patterns (HSAPs) formed on sapphire substrates on the crystal, optical, and electrical properties of InGaN/GaN multi-quantum-well (MQW) LEDs. The basic direction of the HSAPs is normal (HSAPN) with respect to the primary flat zone of a c-plane sapphire substrate. Another HSAP tilted by 30o (HSAP30) from the HSAPN structure was used to investigate the effects of the pattern direction. The full width at half maximums (FWHMs) of the double-crystal x-ray diffraction (DCXRD) spectrum for the (0002) and (1-102) planes of the HSAPN are 320.4 and 381.6 arcsecs., respectively, which are relatively narrower compared to those of the HSP30. The photoluminescence intensity for the HSAPN structure was ~1.2 times stronger than that for the HSAP30. From the electroluminescence (EL) measurements, the intensity for both structures are almost similar. In addition, the effects of the area of the individual lens pattern consisting of the hexagonal-structure arrays are discussed using the concept of the planar area fraction (PAF) defined as the following equation; PAF = [1-(patterns area/total unit areas)] For the relatively small PAF region up to 0.494, the influences of the HSAP direction on the LED characteristics were significant. However, the direction effects of the HSAP became small with increasing the PAF.

• The Transactions of the Korea Information Processing Society
• /
• v.5 no.10
• /
• pp.2686-2703
• /
• 1998

The widening pClformnnce gap between processor and memory causes an emergence of the promising architecture, processor-memory (PM) integration In this paper, various design issues for P-M integration are studied, First, an analytical model of the DRAM access time is constructed considering both the bank conflict ratio and the DRAM page hit ratio. Then the points of both the performance improvement and the perfonnance bottle neck are found by the proposed model as designing on-chip DRAM architectures. This paper proposes the new architecture, called the delayed precharge bank architecture, to improve the perfonnance of memory system as increasing the DRAM page hit ratio. This paper also adapts an efficient bank interleaving mechanism to the proposed architecture. This architecture is verified !II he better than the hierarchical multi-bank architecture as well as the conventional bank architecture by executiun driven simulation. Eight SPEC95 benchmarks are used for simulation as changing parameters for the cache architecture, the number of DRAM banks, and the delayed time quantum.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.5 no.2
• /
• pp.131-135
• /
• 2005

The effect of different surface passivation films on blue or green (465-505 nm) InGaN/GaN multi-quantum well light-emitting diodes (LEDs) die were examined. $SiO_2$ or $SiN_x$ deposited by plasma enhanced chemical vapor deposition, or $Sc_2O_3$ or MgO deposited by rf plasma enhanced molecular beam epitaxy all show excellent passivation qualities. The forward current-voltage (I-V) characteristics were all independent of the passivation film used, even though the MBE-deposited films have lower interface state densities ($3-5{\times}10^{12}\;eV^{-1}\;cm^{-2}$) compared to the PECVD films (${\sim}10^{12}\;eV^{-1}\;cm^{-2}$), The reverse I-V characteristics showed more variation, hut there was no systematic difference for any of the passivation films, The results suggest that simple PECVD processes are effective for providing robust surface protection for InGaN/GaN LEDs.