Hsi-Chao Chen

Rectangular illumination using a secondary optics with cylindrical lens for LED street light

The illumination pattern of an LED street light is required to have a rectangular distribution at a divergence-angle ratio of 7:3 for economical illumination. Hence, research supplying a secondary optics with two cylindrical lenses was different from free-form curvature for rectangular illumination. The analytical solution for curvatures with different ratio rectangles solved this detail by light tracing and boundary conditions. Similarities between the experiments and the simulation for a single LED and a 9-LED module were analyzed by Normalized Cross Correlation (NCC), and the error rate was studied by the Root Mean Square (RMS). The tolerance of position must be kept under ± 0.2 mm in the x, y and z directions to ensure that the relative illumination is over 99%.

Effect of thermal annealing on the optical properties and residual stress of TiO2 films produced by ion-assisted deposition

The effects of thermal annealing of titanium oxide films deposited by ion-beam assistance at annealing temperatures from 100 degrees C to 300 degrees C on the residual stress and optical properties of the films was investigated. The refractive indices and extinction coefficients increased gradually as the temperature was increased from 100 degrees C to 200 degrees C and then declined gradually as the temperature was increased further from 200 degrees C to 300 degrees C. The film lost oxygen and slowly generated lower suboxides as the annealing temperature was reduced below 200 degrees C, as determined by x-ray photoelectron spectroscopy (XPS). As the annealing temperature increased above 200 degrees C, the lower suboxides began to capture oxygen and form stable oxides. XPS measurements were made to verify both the binding energy associated with the Ti 2p line and the variation of the O 1s line. A Twyman-Green interferometer was employed for phase-shift interferometry to study the residual stress. The residual stress declined as the temperature was reduced from 100 degrees C to 200 degrees C because the lower suboxides reduced the stress in the film. Above 200 degrees C, the film began to capture oxygen, so the residual stress rose. At 300 degrees C, the film was no longer amorphous as the anatase was observed by x-ray diffraction.

Annealing dependence of residual stress and optical properties of TiO2 thin film deposited by different deposition methods.

Titanium oxide (TiO(2)) thin films were prepared by different deposition methods. The methods were E-gun evaporation with ion-assisted deposition (IAD), radio-frequency (RF) ion-beam sputtering, and direct current (DC) magnetron sputtering. Residual stress was released after annealing the films deposited by RF ion-beam or DC magnetron sputtering but not evaporation, and the extinction coefficient varied significantly. The surface roughness of the evaporated films exceeded that of both sputtered films. At the annealing temperature of 300 degrees C, anatase crystallization occurred in evaporated film but not in the RF ion-beam or DC magnetron-sputtered films. TiO(2) films deposited by sputtering were generally more stable during annealing than those deposited by evaporation.

Effects of temperature on columnar microstructure and recrystallization of TiO2 film produced by ion-assisted deposition.

Titanium oxide thin films were deposited by electron-beam evaporation with ion-beam-assisted deposition. The effect of the substrate temperature and annealing temperature on the columnar microstructure and recrystallization of titanium oxide was studied. The values of the refractive index varied from 2.26 to 2.4, indicating that the different substrate temperatures affected the film density. X-ray diffraction revealed that all films were amorphous as deposited. At annealing temperatures from 100 degrees C to 300 degrees C, only the anatase phase was formed. As the substrate temperature increased from 150 degrees C to 200 degrees C to 250 degrees C, the recrystallization temperature fell from 300 degrees C through 250 degrees C to 200 degrees C. Changing the substrate temperature resulted in the formation of various types of columnar microstructure, as determined by scanning-electron microscopy. Different columnar structures resulted in different surface morphologies, as measured by atomic-force microscopy.

Measurement of stress in aluminum film coated on a flexible substrate by the shadow moiré method

This investigation proposes the use of the shadow moiré method (SMM) to measure stress in a thin film that is coated on a flexible substrate. The technique defines the profile of the sample by contour lines without the application of an external force, and the radius of curvature is calculated from these contour lines. The SMM is insensitive to environmental noise and has the same advantages as the interference method, such as being nondestructive and easy to use. For Al film with a thickness of 120 nm coated on a polyimide substrate by a DC magnetron sputtering system (800 W, room temperature), the stress is 0.45 +/- 0.042 GPa.

Effects of Ion Assistance and Substrate Temperature on Optical Characteristics and Microstructure of MgF2 Films Formed by Electron-Beam Evaporation

Magnesium fluoride thin films were prepared by electron-beam evaporation and ion-assisted deposition (IAD). The effects of ion assistance and substrate temperature during deposition on the optical properties and microstructure were studied. The grain size, the crystallinity and the surface roughness of MgF2 films deposited without ion assistance all decreased with substrate temperature. MgF2 films deposited with IAD exhibited small grains, rough surfaces, fluorine deficiencies and large optical losses in the 200–500 nm wavelength range when bombarded with argon ions.

Investigation of thermal annealing of optical properties and residual stress of ion-beam-assisted TiO2 thin films with different substrate temperatures.

Titanium oxide films were prepared by ion-beam-assisted deposition on glass substrates at various substrate temperatures. The effect of the temperature of thermal annealing from 100 degrees C to 300 degrees C on the optical properties and residual stress was investigated. The influence on the stoichiometry and residual stress of titanium oxides deposited at different substrate temperature was discussed. The residual-stress was minimum and the extinction coefficient was maximum at an annealing temperature of 200 degrees C with a substrate temperature of 150 degrees C. However, when the substrate temperature was increased to 200 degrees C and 250 degrees C, the residual stress was minimum and the extinction coefficient was maximum at an annealing temperature of 250 degrees C. The spectra of x-ray photoelectron spectroscopy reveal that the films lost oxygen and slowly generated lower suboxides at the annealing temperature at which the residual stress was minimum and the extinction coefficient was maximum. As the annealing temperature increased above the temperature at minimum stress, the lower suboxides began to capture oxygen and form stable oxides. TiO2 films deposited at substrate temperatures of 200 degrees C and 250 degrees C were more stable than films deposited at 150 degrees C.

Electrochromic and optical properties of tungsten oxide films deposited with DC sputtering by introducing hydrogen

Research was undertaken to investigate the electrochromic and optical properties of tungsten oxide (WO3) films deposited by introducing hydrogen with a direct current (DC) and pulsed DC sputtering. The results show that WO3 films have optimum electrochromic properties at a hydrogen flow of 4 and 3 sccm for DC and pulsed DC, respectively. In the Raman spectra, the peak intensity increased with the increase of hydrogen flow at both 770  cm1 and 950  cm(-1) peaks, which resulted in bonds of W(6+)-O and W(6+)=O, respectively. Simultaneously, the transmittance (ΔT550  nm) variations were 65.6% and 64.4%, and the average transmittance (ΔT400-500  nm) variations were 56.7% and 56.4% for DC and pulsed DC, respectively. The bleached/colored ability of the cyclic voltammograms (CVs) was DC>pulsed DC, and the resistances of AC impedance were pulsed DC>DC.

Measurement of residual stress for ITO/PET substrates by the double beam shadow moiré interferometer

This study constructed a measurement system that can quickly and accurately analyze the residual stress of flexible electronics. A double beam shadow moiré interferometer was set up to measure and evaluate the residual stress of tin-doped indium oxide films on a polyethylene terephthalate substrate. However, this system required only two symmetrical fringes to evaluate the residual stress of transparent conductive oxide films on flexible substrate. Applying the grating translation techniques to the double beam shadow moiré interferometer greatly improved the measurement resolution and accuracy, and the relative error was reduced to 1.2%.

Improving the illumination efficiency and color temperature for a projection system by depositing thin-film coatings on an x-cube prism

A new x-cube prism with small polarizing dichroic filters was made for an optical projection system. The x-cube prism was used to combine the three primary colors, which were divided by the preset dichroic mirrors. A coating was designed and fabricated such that s- and p-polarized light was shifted to be obliquely incident in the x-cube prism: the shift was the same as that at the dividing dichroic mirrors. Hence, energy loss was lower than that associated with the conventional x-cube prism, and the brightness of the projection system was 33.2% higher and the color temperature was 18.2% higher than those of the conventional x-cube prism.