Fern Lan Ng

Influence of Crystal Structure, Morphology and Sodium Ion on the Photocatalytic Reactivity of Spray Deposited Titanium Dioxide Film

In this paper, three types of titanium dioxide structures (anatase, heated amorphous and amorphous) from peroxo titanium complex were deposited on glass and wafer substrates by spraying technique. Influences of crystal structure, morphology and sodium ion on UV induced hydrophilicity were studied. X-ray diffraction revealed that crystalline anatase coatings are extremely hydrophilic (<10°) under UV irradiation (indoor) while the amorphous coatings are still hydrophobic on both glass and wafer substrate with contact angles as high as 70º. When amorphous coating was heated at 450°C, its structure was converted into crystalline anatase, and hence its UV induced hydrophilicity behavior on wafer substrate became similar to that of anatase. However, this UV induced hydrophilicity was inhibited on heated glass (450°C), suggesting that sodium ions in the glass might be responsible for the differences between silicon wafer and glass. With increasing coating thickness, such inhibition effect was reduced, but the hydrophilicity still could not reach the level of anatase. After 6 months of outdoor exposure, water contact angle for amorphous, heated amorphous and anatase were 61°, 26.6° and 12.1°, respectively. Also, X-ray diffraction suggested that amorphous is not converted into anatase after long period of UV exposure, although coating morphologies are changed based on Scanning Electron Microscopic observation. It is concluded that the crystal structure, coating morphology and sodium ion concentration have key impact on the photocatalytic properties on glass substrate.

X-Ray Microanalysis of Metallic Thin Films

Nickel and gold films are widely used for microsystems fabrication and packaging, as well as under bump metallization. In this paper, x-ray microanalysis was used to measure the thickness of Ni and Au films. Au and Ni films with varied thicknesses were deposited on silicon (Si) substrate by magnetron sputtering method. Incremental electron beam energy ranging from 4 keV to 30 keV was applied while other parameters were kept constant to determine the electron beam energy required to penetrate the metallic films. The effects of probe current at a fixed electron beam energy on the penetration depth were investigated too. With higher energy applied, the electron beam can penetrate deeper and more Si signal can be detected. The Ni and Au film thicknesses almost have linear relationship with the required penetration electron beam energy. The probe current has minimal effect on the specimen once it has reached the critical excitation probe current. For Ni and Au films with same thickness, higher energy or probe current is needed to penetrate the Au film to reach Si substrate due to the higher Au atomic weight.Copyright

THERMAL STABILITY STUDY OF TANTALUM NITRIDE THIN FILMS BY SPECTROSCOPIC ELLIPSOMETRY

Spectroscopic ellipsometry was successfully applied in the evaluation of the thermal stability of thin films in air by detecting the changes in film optical properties and thickness. Tantalum nitride (TaxNy) films with a nominal thickness of 30 nm were deposited on silicon wafer and annealed at different temperatures from 200°C to 700°C. Annealing-induced changes in thickness and optical properties of TaxNy were detected and determined by spectroscopic ellipsometry. Different approaches were adopted in the modeling and analysis of spectroscopic ellipsometric data. The results are consistent with the findings from Fourier Transform Infrared Spectroscopy (FTIR).