Shang-Chou Chang

Low-temperature process in growing carbon nanotube

Nickel particles, converted from film by microwave hydrogen plasma at a low temperature of 250^oC, were used as the catalyst for growing carbon nanotubes (CNTs). Low-temperature process is desirable for CNT application in flat panel display industry. We found that the processing pressure and microwave power can greatly influence the nickel particle size and density. The processing pressure during pretreatment affects the CNT to be grown or not at all. The microwave power affects the particle size of the catalyst and the diameter of the grown CNT. It was also found that after pretreatment, the diameter of the grown CNT is proportional to the catalyst particle size. The threshold electric field of CNT field emission was found reduced as the diameter of the CNT became smaller.

Thermal effect on the structural, electrical, and optical properties of in-line sputtered aluminum doped zinc oxide films explored with thermal desorption spectroscopy

This work investigates the thermal effect on the structural, electrical, and optical properties of aluminum doped zinc oxide (AZO) films. The AZO films deposited at different temperatures were measured using a thermal desorption system to obtain their corresponding thermal desorption spectroscopy (TDS). In addition to obtaining information of thermal desorption, the measurement of TDS also has the effect of vacuum annealing on the AZO films. The results of measuring TDS imply part of the doped aluminum atoms do not stay at substituted zinc sites in AZO films. The (002) preferential direction of the AZO films in X-ray diffraction spectra shifts to a lower angle after measurement of TDS. The grain size grows and surface becomes denser for all AZO films after measurement of TDS. The carrier concentration, mobility, and average optical transmittance increase while the electrical resistivity decreases for AZO films after measurement of TDS. These results indicate that the AZO films deposited at 200°C are appropriate selections if the AZO films are applied in device fabrication of heat-produced process.

Thermal stability of hydrogen annealed aluminum doped zinc oxide films investigated by thermal desorption spectroscopy

To investigate thermal stability of hydrogen annealed aluminum doped zinc oxide (AZO) films, hydrogen annealed AZO films were measured with thermal desorption system and their thermal desorption spectroscopy (TDS) were analyzed. The measured TDS results indicate all three elements in AZO films: oxygen, aluminum and zinc are observed. The result indicates the aluminum impurity in hydrogen annealed AZO films is thermally unstable, and implies the doped aluminum does not stay in the substituted zinc site in AZO films to some extent. The hydrogen annealed AZO films prepared at 200°C substrate is recommended to apply since it shows relatively good thermal stability considering total atomic desorption amount, electric resistivity and average optic transmittances percentage variation.

Anisotropic Stress Effect on Aluminum Doped Zinc Oxide Films Produced from in-line Sputtering

In this study, aluminum doped zinc oxide (AZO) films were prepared by in-line DC sputtering with different substrate temperatures in order to produce large area and high throughput transparent conductive oxide films applied in thin film solar cells. It was found that apparent time instability of carrier concentration and mobility for the AZO films prepared with substrate temperature higher than 50℃. Moreover, not only the measured X-ray diffraction intensity with respect to ZnO preferential (002) plane decreases but also for substrate temperature higher than 50℃. Both cases are believed to relate with anisotropic stress for the prepared AZO films produced during in-line sputtering process.

Heating rate of post-annealing on microstructure/electrical/optical properties of gallium and aluminum co-doped zinc oxide films

To investigate whether heating rate of post-annealing can affect the microstructure, electrical and optical properties of gallium and aluminum co-doped zinc oxide (GAZO) films or not, GAZO films were post-annealed with 9°C/min and 30°C/min heating rate. The GAZO films post-annealed with 9°C/min heating rate appears smaller full width at half maxima of (002) diffraction peak, more uniform and bigger grain size, higher mobility, lower resistivity, higher average optical transmittance and higher figure of merit than those with 30°C/min heating rate. Low heating rate like 9°C/min in post-annealing can provide more time in thermal reaction for GAZO films at a certain heating temperature. This scenario may explain the above phenomena.

Microwave hydrogen plasma annealing to improve electrical and optical properties of aluminum doped zinc oxide films

To investigate whether microwave hydrogen plasma can improve the electrical and optical properties of aluminum doped zinc oxide (AZO) films or not, AZO films prepared with different substrate temperature were treated with microwave hydrogen plasma. The AZO films were post-treated by one 2.45 GHz microwave hydrogen plasma system with 25 torr, 700 W and 10 minutes. It was observed the electrical and optical properties of all AZO films prepared with different substrate temperatures were apparently improved with microwave hydrogen plasma. Taking 200°C produced AZO films as an example, the electrical resistivity decreases 43% and the average optical transmittance increases 7% respectively. Microwave hydrogen plasma makes AZO films recrystallization like process from measured results of X-ray diffraction, scanning electron micrograph and transmission electron micrograph. The oxygen adsorption on grain boundary of AZO films after microwave hydrogen plasma apparently decreases observed from results of X-ray photoelectron spectroscopy. The above two phenomena may be the mechanism why microwave hydrogen plasma cam improve the electrical and optical properties of AZO films. This work contributes to industries like touch panel, solar cells. etc. which transparent conductive films belong to the industry products component.

Carbon nano tubes grown on glass substrate with different interface layer

Microwave plasma enhanced chemical vapor deposition (MPECVD) was applied in growing carbon nano tubes (CNTs) on sodium free glass with different interface layer materials. Surface morphology and field emission characteristics of as grown CNTs were measured. Three different materials: titanium(Ti), gold(Au) and indium tin oxide (ITO) thin films were prepared on glass first as the interface role between CNTs and glass. Nickel(Ni) films were sputtered on three different interface films and also direct on glass. After hydrogen plasma pretreatment on nickel films, CNTs were tried to grow on four kinds of glass combination: Ni/glass, Ni/ITO/glass, Ni/Au/glass and Ni/Ti/glass, three substrate temperatures: unheated, 300°C and 500 °C, with the mixture of methane and hydrogen microwave plasma. It was found CNTs can be grown with high CNTs density, high adhesion and 2.5V/ µ m turn on electric field corresponding to Ni/Ti/glass and 500 °C process condition. The same MPECVD system with same pretreatment and process gas can be used to grow CNTs on silicon substrate without extra substrate heating. It is proposed the electrical conductivity of substrate has strong influence on CNTs growth. The interface material like Ti can modify the electrical conductivity of the substrate surface.