Papers by Author: Yu Li Lin

Abstract: A simple, fast, and reliable characterization method for measuring junction temperature (Tj) on high power GaN-based light emitting diodes (LED) was presented in this study. Thermal characteristics of high power Light-emitting-diode have been analyzed by using a three-dimensional thermal conduction model. Maximum operation temperature has also been calculated. The induced thermal behaviors of the best package processes for LED device with diamond film were investigated by finite element analysis (FEA) and by experimental measurement. The large change of forward operation voltage with temperature in light emitting diodes is advantageously used to measure junction temperature. Using this method, junction temperature (Tj) of LED under various structures and chip mounting methods was measured. It was found that the junction temperature can be reduced considerably by using diamond film substrates to replace sapphire substrate. In this study, the junction temperature can be decreased by about 14.3% under 1.5W power and decreased by about 15.9% under 1W power for 1mm square die. The thermal resistance (RT) can be measured to be 14.8°C/W under 1.5W power and 16.6°C/W under 1.W power.

Abstract: The task of this study is to prepare the TiO2 film electrode for dye-sensitized solar cells (DSSC) on ITO PET substrate using a general jet-printer. The results were compared with that obtained using ITO glass substrate. In this study, the dispersion of TiO2 slurry was manipulated by changing the pH value of the solution to avoid agglomeration of TiO2 particles. The average TiO2 particles used in this study were measured about 130nm. The experimental results show that it has the best performance when the thickness of the TiO2 film was about 10μm. In ITO glass substrate, the measured short circuit current was about 5.03mA, the open circuit voltage was measured to be 0.65V. In ITO-PET substrate, the measured short circuit current was about 2.73mA, the open circuit voltage was measured to be 0.68V.

Abstract: The task of this study is to find the optimal condition of designed High Concentration Reflected Photovoltaic (HCRPV) module by simulation method whose concentration ratio is set to be 872 and 78.5. This simulated optimal condition was then utilized to fabricate HCRPV module. From simulation results, the light collective efficiency, the energy uniformity, the shape of light spot diagrams can be obtained. It was found that square based pyramid light guide tube can effectively improve the uniformity of light on model A structure. When the slope angle of square based pyramid shape of light guide tube is set to be 3 degree, the focal length of the first mirror is 60mm and the secondary mirror vertex distance is designed to be 93.1mm, the HCRPV module have the best performance. It was also found that the light collective efficiency can be reached to about 97.7% with these conditions. On model B structure, the size was reduced to 9 times without light guide comparing to model A structure. It was also found that the light collective efficiency can also be reached to about 97.1%. The Aluminum HCRPV module was then fabricated according to the optimal simulated conditions. When the HCRPV module was coated with silver material, the voltage on the multi-junction solar cell was measured to be 2.7V and 2.68V, the current was measured to be 2.83A and 0.63A corresponding to model A and B structures, as the solar energy of illumination is 800 W/m2. The power is measured to about 7.64W and 1.7W corresponding to model A and B structures.

Abstract: Efficiency is a critical performance for a high-power ultrasonic transducer composed of 1-3 piezocomposites and geometric parameters of the composites can influence the efficiency of the transducer. The effect of inter-rod responses in the composite matrix on the efficiency was experimentally investigated in this study. For analyses, four PZT4-epoxy composite ultrasonic transducers with various volume fractions and inter-rod spacing were fabricated in-house. The experimental results demonstrated that the inter-rod coupling of the 0.1-mm spacing could significantly degrade the efficiency of the composite probe at about 1.0 MHz resonance since the 0.1-mm spacing between PZT4 rods was so small as to cause a high interference. At the same volume fraction, the transducer engineer should take the inter-rod coupling into account for the design of the high-power ultrasonic transducer.

Abstract: The task of this study is to find the optimal condition of designed High Concentration Reflected Photovoltaic (HCRPV) module by simulation method whose concentration ratio is set to be 872. This simulated optimal condition was then utilized to fabricate HCRPV module. In simulation, the focal length of first and secondary mirror, the slope angle and the length of light guide tube were the main parameters to be optimized. From simulation, the light collective efficiency, the energy uniformity, the shape of light spot diagrams can be obtained. It was found that square based pyramid light guide tube can effectively improve the uniformity of light. When the slope angle of square based pyramid shape of light guide tube is set to be 3 degree, the focal length of the first mirror is 60mm and the secondary mirror vertex distance is designed to be 93.1mm, the HCRPV module have the best performance. It was also found that the light collective efficiency can be reached to about 97.7% with these conditions. The Aluminum HCRPV module was then fabricated according to the optimal simulated conditions. As the solar energy of illumination is 650 W/m², the voltage on the multi-junction solar cell was measured to be 2.56V, the current was measured to be 0.68A. The corresponding power was about 1.74W. When the HCRPV module was coated with silver material, the voltage on the multi-junction solar cell was measured to be 2.7V, the current was measured to be 2.83A, as the solar energy of illumination is 800 W/m². The corresponding power is about 7.64W.

Abstract: In this study, single-wall carbon nanotube (SWCNT) mixed with hydrous ruthenium oxide was co-deposited on titanium substrate by cathodic deposition method. Titanium substrate was first cleaned thoroughly by acetone and followed by chemical etching of 5%HF for 5 minutes and 50%HCl for 15 minutes. The purpose of acid etching is to increase the adhesion between the coating layer and the Ti substrate. SWCNT has been dispersed by ultrasonic method to avoid agglomeration during deposition processes. The concentration of SWCNT added in the deposition process was 0.05 wt%. The time of specimens which were immersed into the deposition bath is varied from 5minutes to 60 minutes. The electrical capacity characteristics of specimen were examined by cyclic voltammetry. The microstructure of hydrous ruthenium oxide coating is elucidated by high resolution transmission electron microscopy (HRTEM). Combination of amorphous and nanocrystalline structure of hydrous ruthenium oxide was investigated in this study. Nano-sized particles (about 2-3nm) were found embedded in the amorphous matrix. The capacitance was found increased when the deposition time was increased. The maximum capacitance of hydrous ruthenium oxide coating was measured to be 556.7F/g.

Abstract: Microstructure of 0.63C-12.7Cr martensitic stainless steel during various tempering treatments was investigated in this study. Results demonstrate that finely distributed primary carbides were observed on 0.63C-12.7Cr martensitic stainless steel. The matrix phase of 0.63C-12.7Cr martensitic stainless steel when tempered below 500 °C was identified as martensite. However, the matrix structure when tempered at 500 °C and 600 °C was found containing of both ferrite and martensite. On carbide particles, mixed of M7C3 and M23C6 particles were observed on all specimens when tempered at 200-600 °C. The amount of M7C3 carbides was found decreased as the tempered temperature was increased.

Abstract: In this study, hydrous ruthenium oxide was deposited on titanium(Ti) and carbon nanotube(CNT) substrate by cathodic deposition method. Combination of amorphous and nanocrystalline structure of hydrous ruthenium oxide was investigated by high resolution electron microscopy. The measured capacitance was found keeping nearly constant through charge/discharge processes for hydrous ruthenium oxide coating on Ti substrate. On the other hand, thin and uniform layer of hydrous ruthenium oxide coating can be deposited on CNT substrate. The thickness of the coating layer was found less than 10nm. Combination of amorphous and nanocrystalline structure of hydrous ruthenium oxide was also investigated on this specimen. The consumption of coating was found very effective for this specimen after 105 charge/discharge cycles which lead to the tremedenously decreasing in the measured capacitance.

Abstract: The 16Cr-1C martensitic stainless steel can provide the higher hardness and better wear resistance for 440C steel. The microstructure of DLC coatings were observed by optical microscope and field-emission scanning electron microscope (FE-SEM). The compositional depth profile of DLC films were measured by field-emission Auger electron spectroscopy (Fe-AES). In addition, the micro-hardness and elastic modulus of DLC films were measured by nano-indentation tests. Experimental results show that the total thickness of coating was in the range of 600nm~1100nm. This coating was included of Ti/TiC transition layer and DLC layer. The Ti/TiC transition layer was grown on the 440C stainless steel substrate, and the upper layer was DLC layer. This layer structure was confirmed by the FE-AES analysis. The micro-hardness of DLC coating was measured in the range of 24.2GPa~26.0GPa, and the elastic modulus was measured in the range of 264GPa~313GPa in the nanoindentation test. The nanoscratch results show that DLC films have lower friction coefficients than 440C substrate.

Abstract: In this study, the microstructure and mechanical properties of 0.63C-12.7Cr martensitic stainless steel during various tempering treatments were investigated. Experimental results demonstrate that finely distributed primary carbides can be observed in 0.63C-12.7Cr martensitic stainless steel. It was also found that the measured hardness of 0.63C-12.7Cr martensitic stainless steel after 300°C tempered treatment for 60 minutes can still reach to 677Hv. The variation of measured hardness was found not significant during tempering treatments (200°C-500°C). Moreover, owing to lower concentration of C and Cr, the matensitic transformation temperature Ms can be increased to 96.4°C comparing to -127°C of SUS440C materials.