• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.397-404
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• 2006

Effects of surface defect distribution on flame instability during flame-surface interaction are experimentally investigated. To examine chemical quenching phenomenon which is caused by radical adsorption and recombination processes on the surface, thermally grown silicon oxide plates with well-defined defect density were prepared. ion implantation technique was used to control the number of defects, i.e. oxygen vacancies. In an attempt to preferentially remove oxygen atoms from silicon dioxide surface, argon ions with low energy level from 3keV to 5keV were irradiated at the incident angle of $60^{\circ}$. Compositional and structural modification of $SiO_2$ induced by low-energy $Ar^+$ ion irradiation has been characterized by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). It has been found that as the ion energy is increased, the number of structural defect is also increased and non-stoichiometric condition of $SiO_x({\le}2)$ is enhanced.

• Journal of the Korean Chemical Society
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• v.28 no.2
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• pp.102-108
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• 1984

The catalytic oxidation of CO has been investigated on $ZnCe_{1+y}O_2$ at temperatures from 300 to $500^{\circ}C$ under various P_{CO} and PO_2 conditions. The oxidation rates have been correlated with 1.5-order kinetics: first order with respect to CO and 0.5 order with respect to O2. CO appears to be absorbed essentially on the O lattice of $ZnCe_{1+y}O_2$ as a molecular species, while $O_2$ adsorbs on an O vacancy as an ionic species. The conductivity data show that CO adsorption contributes electron to the conduction band and the adsorption process of $O_2$ withdraws it from an O vacancy. The oxidation mechanism and the defect model of $ZnCe_{1+y}O_2$ are inferred at given temperature and $PO_2'$s from the agreement between the conductivities and kinetic data. It is suggested that CO absorption is the rate-controlling.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.84-84
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• 2003

The ZnSe epilayers were grown on the GaAs substrate by hot wall epitaxy. After the ZnSe epilayers treated in the vacuum-, Zn-, and Se-atmosphere, respectively, the defects of the epilayer were investigated by means of the low-temperature photoluminescence measurement. The dominant peaks at 2.7988 eV and 2.7937 eV obtained from the PL spectrum of the as-grown ZnSe epilayer were found to be consistent with the upper and the lower polariton peak of the exciton, I$_2$ (D$^{\circ}$, X), bounded to the neutral donor associated with the Se-vacancy. This donor-impurity binding energy was calculated to be 25.3meV The exciton peak, lid, at 2.7812 eV was confirmed to be bound to the neutral acceptor corresponded with the Zn-vacancy. The I$_1$$\^$d/ peak was dominantly observed in the ZnSe/GaAs:Se epilayer treated in the Se-atmosphere. This Se-atmosphere treatment may convert the ZnSe/GaAs:Se epilayer into the p-type. The SA peak was found to be related to a complex donor like a (V$\sub$se/ - V$\sub$zn/) - V$\sub$zn-/

• Journal of the Korean Society of Combustion
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• v.10 no.2
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• pp.1-8
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• 2005

Incomplete combustion due to quenching in a narrow confinement has been a major problem for realization of a reliable micro combustion device. In most micro combustors, effects of flows are absent in the quenching because the flow is laminar and no severe stretch is present. In such circumstance, quenching is caused either by heat loss or by removal of active radicals to the wall surface of the confinement. An experimental investigation was carried out to investigate the relative significance of these two causes of quenching of a premixed flame. A premixed jet burner with a rectangular cross section at the exit was built. At the burner exit, the flame stands between two walls with adjustable distance. The gap between the two walls at which quenching occurs was measured at different wall surface conditions. The results were analyzed to estimate the relative significance of heat loss to the wall and the removal of radicals at the surface. The measurements indicated that the quenching distance was independent of the wall surface characteristics such as oxygen vacancy, grain boundary, or impurities at low temperature. At high temperature, however, the surface characteristics strongly affect the quenching distance, implying that radical removal at the wall plays a significant role in the quenching process.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.3
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• pp.105-110
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• 2003

The ZnSe epilayers were grown on the GaAs substrate by hot wall epitaxy. After the ZnSe epilayers treated in the vacuum-, Zn-, and Se-atmosphere, respectively, the defects of the epilayer were investigated by means of the low-temperature photoluminescence measurement. The dominant peaks at 2.7988 eV and 2.7937 eV obtained from the PL spectrum of the as-grown ZnSe epilayer were found to be consistent with the upper and the lower polariton peak of the exciton, $I_{2}$ ($D^{\circ}$, X), bounded to the neutral donor associated with the Se-vacancy. This donor-impurity binding energy was calculated to be 25.3 meV, The exciton peak, $I_{1}^{d}$ at 2.7812 eV was confirmed to be bound to the neutral acceptor corresponded with the Zn-vacancy. The $I_{1}^{d}$ peak was dominantly observed in the ZnSe/GaAs : Se epilayer treated in the Se-atmosphere. This Se-atmosphere treatment may convert the ZnSe/GaAs : Se epilayer into the p-type. The SA peak was found to be related to a complex donor like a $(V_{se}-V_{zn})-V_{zn}$.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.35-35
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• 2010

Understanding the mechanistic details of heterogeneous catalytic reactions will provide a way to tune the selectivity between various competing reaction channels. In this regard, catalytic decomposition of alcohols over the rutile $TiO_2$(110) surface as a model oxide catalyst has been studied to understand the reaction mechanism employing the temperature-programmed desorption (TPD) technique. The $TiO_2$(110) model catalyst is found to be active toward alcohol dehydration. We find that the active sites are bridge-bonded oxygen vacancies where RO-H heterolytically dissociates and binds to the vacancy to produce alkoxy (RO-) and hydroxyl (HO-). Two protons adsorbed onto the bridge-bonded oxygen atoms (-OH) readily react with each other to form a water molecule at ~500 K and desorb from the surface. The alkoxy (RO-) undergoes decomposition at higher temperatures into the corresponding alkene. Here, the overall desorption kinetics is limited by a first-order decomposition of intermediate alkoxy (RO-) species bound to the vacancy. We show that detailed analysis on the yield and the desorption temperatures as a function of the alkyl substituents provides valuable insights into the reaction mechanism. After the catalytic role of the oxygen vacancies has been established, we employed x-ray photoelectron spectroscopy to further study the surface electronic structure related to the catalytically active defective sites. The defect-related state in valence band has been related to the chemically reduced $Ti^{3+}$ defects near the surface region and are found to be closely related to the catalytic activity of the $TiO_2$(110) surface.

• Bulletin of the Korean Chemical Society
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• v.15 no.8
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• pp.616-622
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• 1994

The oxidation of carbon monoxide by gaseous oxygen in the presence of a powdered $Nd_{1-x}Sr_xCoO_{3-y}$ solid solution as a catalyst has been investigated in the temperature range from 150$^{\circ}$C to 300$^{\circ}$C under various CO and $O_2$ partial pressures. The site of Sr substitution, nonstoichiometry, structure, and microstructure were studied by means of powder X-ray diffraction and infrared spectroscopy. The electrical conductivity of the solid solution has been measured at 300$^{\circ}$C under various CO and $O_2$ partial pressures. The oxidation rates have been correlated with 1.5-and 1.2-order kinetics with and without a $CO_2$ trap, respectively; first-and 0.7 order with respect to CO and 0.5-order to $O_2$. For the above reaction temperature range, the activation energy is in the range from 0.25 to 0.35 eV/mol. From the infrared spectroscopic, conductivity and kinetic data, CO appears essentially to be adsorbed on the lattice oxygens of the catalyst, while $O_2$ adsorbs as ions on the oxygen vacancies formed by Sr substitution. The oxygen vacancy mechanism of the CO oxidation and the main defect of $Nd_{1-x}Sr_xCoO_{3-y}$ solid solution are supported and suggested from the agreement between IR data, conductivities, and kinetic data.

• Journal of the Korean Vacuum Society
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• v.19 no.3
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• pp.199-205
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• 2010

The electrical properties and defect states in ZnO substrates were studied during high-energy electron beam irradiations. 1 MeV and 2 MeV electron-beam with dose of $1{\times}10^{16}$ electrons/$cm^2$ were irradiated on Zn-surface of the sample. In the sample irradiated by 1 MeV, the leakage current was increased by electron-beam induced surface defects, while the enhancement of on/off property and the decrease of leakage current appeared in the 2 MeV irradiated sample. From the deep level transient spectroscopy measurements for these samples, it showed that the defect states with the activation energies of $E_c$-0.33 eV and $E_v$+0.8 eV are generated during the high energy electron-beam irradiation. Especially, it considered that the $E_c$-0.33 eV state related with O-vacancy affects to their electrical properties.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1830-1832
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• 1999

고에너지 이온주입(1)에 기인한 격자 손상 발생 및 열처리에 따라 이들의 회복이 어느정도 가능한지에 대하여 측정 및 분석방법을 통하여 조사하였다. 그리고 본 실험에서는 이온주입시 형성되는 빈자리 결함(Vacancy defect)과 격자간 결함(interstitial defect)의 재결할(recombination)을 이용 점결합(point defect)를 감소 시킬 수 있는 effective RTA조건을 설정하여 well 특성을 개선하고자 하였다. 8inch p-type Si(100)기판에 pad oxide 100A을 형성한 후 NMOS 형성하기 위해 vtn${\sim}$p-well과 PMOS 형성을 위해 vtp$\sim$n-well을 이온주입 하였다. Mev damage anneal은 RTA(2)(Rapid Thermal Anneal)로 $1000\sim1150C$ 온도에서 $15\sim60$초간 spilt 하여 실험후 suprem-4 simulation data를 이용하여 실제 SIMS측정 분석결과를 비교하였으며 이온주입에 의해 발생된 격자손상이 열처리후 damage 정도를 알아보기 위해 T.W(Therma-Wave)을 이용하였으며 열처리후 면저항값은 4-point probe를 사용하였다. 이온주입후 열처리 전,후에 따른 불순물 분포를 SIMS(Secondary ion Mass Spectrometry)를 이용하여 살펴보았다. SIMS 결과로는 열처리 온도 및 시간의 증가에 따라서 dopant확산 및 활성화는 큰차이는 보이지 않고 오히려 감소하는 경향을 볼 수 있으며 또한 접합깊이와 농도가 약간 낮아지는 것을 볼 수 있었다. 결점(defect)을 감소시키기 위해서 diffusivity가 빠른 임계온도영역($1150^{\circ}C$-60sec)에서 RTA를 실시하여 dopant확산을 억제하고 점결점(point defect)의 재결합(recombination)을 이용하여 전위 (dislocation)밀도를 감소시켜 이온주입 Damage 및 면저항을 감소 시켰다. 이와 같은 특성을 process simulation(3)(silvaco)을 통하여 비교검토 하였다.

• Bulletin of the Korean Chemical Society
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• v.13 no.2
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• pp.127-131
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• 1992

Changes in network structures of ${\alpha}-Nb_2O_5$ in the X MgO+(1-X) ${\alpha}-Nb_2O_5$ solid solutions occurring as the MgO doping level (X) was varied were investigated by means of infrared spectroscopy and X-ray analysis. X-ray diffraction revealed that all the synthesized specimens have the monoclinic structure. The FT-IR spectroscopy showed that the system investigated forms the solid solutions in which $Mg^{2+}$ ions occupy the octahedral sites in parent crystal lattice. Electrical conductivities were measured as a function of temperature from 600 to $1050{\circ}$ and $P_{O2}$ form $1{\times}10^{-5}$ to $2{\times}10^{-1}$ atm. The defect structure and conduction mechanism were deduced from the results. The $1}n$ value in ${\alpha}{\propto}{P_{O2}^{1}n}}$ is found to be -1/4 with single possible defect model. From the activation energy ($E{\alpha}$ = 1.67-1.73 eV) and the1/n value, electronic conduction mechanism is suggested with a doubly charged oxygen vacancy.