Browsing by Author "Hsu, Shih-Chieh"

Now showing 1 - 13 of 13

A Study of Mechanical Lift-Off Technology for High-Efficiency Vertical LEDs Using Micro-Porous GaN Template
(2013-01-01)
Lee, Chia-Yu
;
Lin, Da-Wei
;
Liu, Che-Yu
;
Hsu, Shih-Chieh
;
Kuo, Hao-Chung
The high efficiency vertical light emitting diodes (V-LEDs) using mechanical lift-off with Micro-Porous GaN template formed by high temperature molten KOH wet etching process were demonstrated. The average threading dislocation density (TDD) of u-GaN after regrowth was estimated by transmission electron microscopy (TEM) reduced from 2x10(9) to 1x10(8) cm(2). The sapphire substrate was easily removed by mechanical lift-off during wafer bonding process. The light output of V-LEDs are greatly enhanced by 100% compared with Conventional-LEDs at an operating current of 20mA due to the high quality thin GaN and excellent heating dissipation.
Dust transport from non-East Asian sources to the North Pacific
(2012-06-26)
Hsu, Shih-Chieh
;
Huh, Chih-An
;
Lin, Chuan-Yao
;
Chen, Wei-Nai
;
Mahowald, Natalie M.
It is generally thought that East Asia dominates the supply of eolian dust to the North Pacific. Here we show the first data-based evidence of dust primarily from non-East Asian sources even during March 2010 when a super dust storm from East Asia struck the western Pacific. Chemical characteristics of aerosol samples collected at a high-mountain site in Taiwan show variable inputs from eolian dust and biomass burning. From backward trajectory analyses, satellite observation and model simulation, dust origins can be traced to the Middle East and North Africa, suggesting an integrated source from the global dust belt. Our global model results demonstrate that dust deposition in the North Pacific is primarily contributed by non-East Asian sources with an eastward decrease along the Westerlies. Citation: Hsu, S.-C., et al. (2012), Dust transport from non-East Asian sources to the North Pacific, Geophys. Res. Lett., 39, L12804, doi:10.1029/2012GL051962.
Dynamic variations of ultrafine, fine and coarse particles at the Lu-Lin background site in East Asia
(2013-10-01)
Chen, Sheng-Chieh
;
Hsu, Shih-Chieh
;
Tsai, Chuen-Jinn
;
Chou, Charles C. -K.
;
Lin, Neng-Huei
The characteristics of atmospheric ultrafine particles (i.e. <100 nm, nanoparticles or PM0.1), PM2.5 and PM10 were studied at the Lulin Atmospheric Background Station (LABS, 2862 m a.s.l., Taiwan) as part of the 7SEAS/Dongsha campaign. Sampling was conducted in July and August of 2009 and September to November of 2010, during which two 96-h and four 72-h PM samples were taken. Real-time particle size distributions were measured continuously from July to August of 2009 and July to November of 2010. PM0.1, PM2.5 and PM10 were collected by using two MOUDIs (micro-orifice uniform deposit impactor, MSP 110) and a Dichotomous PM10 sampler (Andersen SA-241) while real-time size distributions of particles of 5.5-350 nm in diameter were measured by an SMPS (scanning mobility particle sizer, TSI 3936). Filter samples were analyzed for gravimetric mass and chemical compositions, including organic carbon (OC), element carbon (EC), water-soluble ions and trace elements. Meteorology parameters and gaseous O-3 and CO concentrations were also monitored along with the SMPS data for studying particle nucleation, condensation, SOA (secondary organic aerosol) formation and long-range air pollutant transport at the LABS. SMPS data showed that nanoparticle concentrations at the LABS remained relatively stable at low level (similar to 300-500 #/cm(3)) during the nighttime (22:00-04:00), increased during daytime, and reached a maximum (similar to 2000-4000 #/cm(3)) in the afternoon (12:00-16:00). The NMD (number median diameter) showed an opposite trend with the peak number concentrations observed in the afternoon corresponding to the smallest NMD (20-40 nm). These results indicate the dominance of local sources rather than the transport from other atmospheric air because that the lifetime of nanoparticles was only few minutes. Chemical analysis of filter samples showed that the concentrations of trace elements K and Mn, which serve as biomass burning markers, were elevated in the fine particle fractions during November 9-12th when the air mass passed through South and Southeast Asia prior to reaching the LABS. The concentrations of K and Mn would have been low if the aerosols had local origins The biomass burning derived K was found in all fine particle samples at the LABS suggesting that the free troposphere around Taiwan is frequently impacted by the long-range transport of biomass burning plumes via the westerly winds. (c) 2012 Elsevier Ltd. All rights reserved.
High quality vertical light emitting diodes fabrication by mechanical lift-off technique
(2011)
Tu, Po-Min
;
Hsu, Shih-Chieh
;
Chang, Chun-Yen
;
光電工程學系
;
Department of Photonics
We report the fabrication of mechanical lift-off high quality thin GaN with Hexagonal Inversed Pyramid (HIP) structures for vertical light emitting diodes (V-LEDs). The HIP structures were formed at the GaN/sapphire substrate interface under high temperature during KOH wet etching process. The average threading dislocation density (TDD) was estimated by transmission electron microscopy (TEM) and found the reduction from 2x10(9) to 1x10(8) cm(-2). Raman spectroscopy analysis revealed that the compressive stress of GaN epilayer was effectively relieved in the thin-GaN LED with HIP structures. Finally, the mechanical lift-off process is claimed to be successful by using the HIP structures as a sacrificial layer during wafer bonding process.
Learning Based Mesh Generation for Thermal Simulation in Handheld Devices with Variable Power Consumption
(2019-01-01)
Lo, Wen-Sheng
;
Chiou, Hong-Wen
;
Hsu, Shih-Chieh
;
Lee, Yu-Min
;
Cheng, Liang-Chia
This work utilizes machine learning techniques to achieve learning based mesh generation for the thermal simulator. In the learning stage, first, we generate many power value sets of application processors and apply the superposition technique to obtain the temperature raw data of material blocks. We, then, use these thermal data and several defined thermal gradient ranges to obtain different appropriate mesh-size sets of material blocks for each power value set. We construct the regressions that are capable of predicting targets as a supervised learning task, and the architecture of regression model includes seven hidden layers. After the learning stage, we integrate the learning based mesh decision engine into a developed system-level thermal simulator, which is built by the finite difference method. The experimental results show that the temperature profiles of the handheld device calculated by the developed thermal simulator with learning based mesh generation fits the results obtained by a commercial tool pretty well with less runtime usages. Moreover, the learning based mesh decision engine is much more efficient than the artificial mesh decision.
Natural substrate lift-off technique for vertical light-emitting diodes
(2014-04-01)
Lee, Chia-Yu
;
Lan, Yu-Pin
;
Tu, Po-Min
;
Hsu, Shih-Chieh
;
Lin, Chien-Chung
Hexagonal inverted pyramid (HIP) structures and the natural substrate lift-off (NSLO) technique were demonstrated on a GaN-based vertical light-emitting diode (VLED). The HIP structures were formed at the interface between GaN and the sapphire substrate by molten KOH wet etching. The threading dislocation density (TDD) estimated by transmission electron microscopy (TEM) was reduced to.1 x 10(8) cm(-2). Raman spectroscopy indicated that the compressive strain from the bottom GaN/sapphire was effectively released through the HIP structure. With the adoption of the HIP structure and NSLO, the light output power and yield performance of leakage current could be further improved. (C) 2014 The Japan Society of Applied Physics
Output Power Enhancement of Light Emitting Diodes with Defect Passivation layer
(2010)
Lo, Ming-Hua
;
Tu, Po-Min
;
Cheng, Yuh-Jen
;
Wang, Chao-Hsun
;
Hung, Cheng-Wei
We demonstrate high efficiency blue light emitting diodes with defect passivation layers. The defect passivation layers were formed by defect selective wet etching, SiO(2) deposition, and chemical mechanical polishing process. The process does not require photolithography patterning. The threading dislocation density of grown sample was reduced down to similar to 4x10(7) cm(-2). The defect passivated epi-wafer is used to grow light emitting diode (LED) and the output power of the fabricated chip is enhanced by 45% at 20 mA compared to a reference one without using defect passivation.
Source Characterization and Apportionment of PM10, PM2.5 and PM0.1 by Using Positive Matrix Factorization
(2012-08-01)
Gugamsetty, Balakrishnaiah
;
Wei, Han
;
Liu, Chun-Nan
;
Awasthi, Amit
;
Hsu, Shih-Chieh
Ambient Particulate Matters (PM10, PM2.5 and PM0.1) were investigated at Shinjung station in New Taipei City, Taiwan. Samples were collected simultaneously using a dichotomous sampler (Andersen Model SA-241) and a MOUDI (MSP Model 110) over a 24-h period from May 2011 to November 2011 at Shinjung station. Samples were analyzed for metallic trace elements using ion coupled plasma mass spectroscopy (ICP-MS) and ionic compounds by ion chromatography (IC). The average concentrations of PM10, PM2.5 and PM0.1 were found to be 39.45 +/- 11.58, 21.82 +/- 7.50 and 1.42 +/- 0.56 mu g/m(3), respectively. Based on the chemical information, positive matrix factorization (PMF) was used to identify PM sources. A total of five source types were identified, including soil dust, vehicle emissions, sea salt, industrial emissions and secondary aerosols, and their contributions were estimated using PMF. The crustal enrichment factors (EF) were calculated using Al as a reference for the trace metal species to identify the sources. Conditional probability functions (CPF) were computed using wind profiles and factor contributions. The results of CPF analysis were used to identify local point sources. The results suggest a competitive relationship between anthropogenic and natural source processes over the monitoring station.
"Source Characterization and Apportionment of PM10, PM2.5 and PM0.1 by Using Positive Matrix Factorization"
(2012-08-01)
Gugamsetty, Balakrishnaiah
;
Wei, Han
;
Liu, Chun-Nan
;
Awasthi, Amit
;
Hsu, Shih-Chieh
"Ambient Particulate Matters (PM10, PM2.5 and PM0.1) were investigated at Shinjung station in New Taipei City, Taiwan. Samples were collected simultaneously using a dichotomous sampler (Andersen Model SA-241) and a MOUDI (MSP Model 110) over a 24-h period from May 2011 to November 2011 at Shinjung station. Samples were analyzed for metallic trace elements using ion coupled plasma mass spectroscopy (ICP-MS) and ionic compounds by ion chromatography (IC). The average concentrations of PM10, PM2.5 and PM0.1 were found to be 39.45 +/- 11.58, 21.82 +/- 7.50 and 1.42 +/- 0.56 mu g/m(3), respectively. Based on the chemical information, positive matrix factorization (PMF) was used to identify PM sources. A total of five source types were identified, including soil dust, vehicle emissions, sea salt, industrial emissions and secondary aerosols, and their contributions were estimated using PMF. The crustal enrichment factors (EF) were calculated using Al as a reference for the trace metal species to identify the sources. Conditional probability functions (CPF) were computed using wind profiles and factor contributions. The results of CPF analysis were used to identify local point sources. The results suggest a competitive relationship between anthropogenic and natural source processes over the monitoring station."
The size effect of titania-supported Pt nanoparticles on the electrocatalytic activity towards methanol oxidation reaction primarily via the bifunctional mechanism
(2015-04-15)
Ting, Chao-Cheng
;
Liu, Chung-Hsuan
;
Tai, Chun-Yen
;
Hsu, Shih-Chieh
;
Chao, Chih-Shuan
We prepared Pt nanoparticles of different particle sizes by plasma enhanced atomic layer deposition (PEALD) on the native oxide surface layer of Ti thin films, and investigated the Pt particle size effect on the electrocatalytic activity towards methanol oxidation reaction (MOR) in acidic media. The average Pt nanoparticles size ranges from 3 nm to 7 nm depending on the number of the PEALD reaction cycles. The electronic interaction between Pt nanoparticles and the TiO2 support is insignificant according to x-ray photoelectron spectroscopy analyses, suggesting that the influence of the Pt particle size on the electrocatalytic activity can be mainly described by the bifunctional mechanism. From cyclic voltammetry measurements, Pt particles of smaller size have a better CO tolerance in MOR. We proposed the reaction steps for the electrooxidation of CO adspecies on Pt nanoparticles on the basis of the bifunctional mechanism. The electrode with Pt nanoparticles of similar to 5 nm in size shows the best electrocatalytic performance in terms of CO tolerance and electrochemical stability. (C) 2015 Elsevier B.V. All rights reserved.
The study of wet etching on GaN surface by potassium hydroxide solution
(2017-06-01)
Lai, Yung-Yu
;
Hsu, Shih-Chieh
;
Chang, Hua-Sheng
;
Wu, YewChung Sermon
;
Chen, Ching-Hsiang
Potassium hydroxide solution was used to etch un-doped GaN grown on the sapphire substrate at 180 and 260 A degrees C. We illustrated the etching phenomenon in detail and probed its mechanism in the wet etching process. By multiplying the planar density and the number of dangling bonds on the N atom, we proposed the etching barrier index (EBI) to describe the difficulty degree of each lattice facet. The raking of EBI will be +c-plane > a-plane > m-plane > -c-plane > (10-1-1) plane > r-plane. Combining the EBI with SEM results, we thoroughly studied the whole etching process. We confirmed that in our research, KOH wet etching on GaN starts from the r-plane instead of the +c-plane or -c-plane, which differs from other studies. We also found that during the high-temperature etching process, there are two etching approaches. In one, the etching begins vertically from the top to the bottom, then horizontally, and finally reversely from the bottom to the top. In the other, etching pits will develop into a hexagonal hole of the sidewall of m-plane.
Thermodynamics and regeneration of CO(2) adsorption on mesoporous spherical-silica particles
(2009-12-01)
Lu, Chungsying
;
Su, Fengsheng
;
Hsu, Shih-Chieh
;
Chen, Wenfa
;
Bai, Hsunling
Mesoporous spherical-silica particles (MSPs) were modified by N-[3-(trimethoxysilyl) propyllethylenediamine (EDA) solution and were employed as sorbents to study thermodynamics and regeneration Of CO(2) adsorption from gas streams. The thermodynamic analysis gave low isosteric heats of adsorption, which are typical for physical adsorption. The cyclic CO(2) adsorption on MSP(EDA) showed that the adsorbed CO(2) could be effectively desorbed via thermal treatment at 120 degrees C for 25 min while the adsorbed CO(2) due to physical interaction could be effectively desorbed via vacuum suction at 0.145 bar for 30 min. If a combination of thermal treatment and vacuum suction was conducted at 120 degrees C and 0.145 bar, the time for effectively desorbing CO(2) could be shortened to 7.5 min and thus reduces a significant amount of energy penalty. The adsorption capacities and the physicochemical properties of MSP(EDA) were preserved after 15 cycles of adsorption and regeneration. These results suggest that the MSP(EDA) can be stably employed in the prolonged cyclic adsorption and that they are thus possibly cost-effective sorbents for CO(2) capture from flue gases. (C) 2009 Elsevier B.V. All rights reserved.
Thermodynamics and regeneration of CO2 adsorption on mesoporous spherical-silica particles
(2009-12-01)
Lu, Chungsying
;
Su, Fengsheng
;
Hsu, Shih-Chieh
;
Chen, Wenfa
;
Bai, Hsunling
Mesoporous spherical-silica particles (MSPs) were modified by N-[3-(trimethoxysilyl) propyllethylenediamine (EDA) solution and were employed as sorbents to study thermodynamics and regeneration Of CO2 adsorption from gas streams. The thermodynamic analysis gave low isosteric heats of adsorption, which are typical for physical adsorption. The cyclic CO2 adsorption on MSP(EDA) showed that the adsorbed CO2 could be effectively desorbed via thermal treatment at 120 degrees C for 25 min while the adsorbed CO2 due to physical interaction could be effectively desorbed via vacuum suction at 0.145 bar for 30 min. If a combination of thermal treatment and vacuum suction was conducted at 120 degrees C and 0.145 bar, the time for effectively desorbing CO2 could be shortened to 7.5 min and thus reduces a significant amount of energy penalty. The adsorption capacities and the physicochemical properties of MSP(EDA) were preserved after 15 cycles of adsorption and regeneration. These results suggest that the MSP(EDA) can be stably employed in the prolonged cyclic adsorption and that they are thus possibly cost-effective sorbents for CO2 capture from flue gases. (C) 2009 Elsevier B.V. All rights reserved.