Papers by Author: Y.T. Wang

Abstract: As aspheric surfaces are more often used in optical systems, suitable error evaluation methods and suitable accuracy calibration methods for related test instruments are urgently required. The two unsolved but important issues are addressed. For evaluation of aspheric surfaces, a scheme is proposed to separate the surface errors into radius error and local error. The effects of the two errors on image quality are discussed. For test instrument calibration, a practical method using a defocused spherical surface is described and verified with an absolute testing instrument based on laser deflectometry, which was developed at Beijing Institute of Technology. The feasibility of the schemes is shown and experimental results are presented.

Abstract: The field electron emission from carbon nanotube films on polycrystalline diamond films was investigated. The carbon nanotubes and diamond films on Si substrates were prepared by a conventional hot filament chemical vapour deposition. The films obtained were characterized by scanning electron microscopy and Raman spectroscopy. The field emission properties of the samples were measured in an ion-pumped vacuum chamber at a pressure of 10-6 Pa.. The experimental results showed that the field emission behaviours of carbon nanotubes/diomond films structure have greatly been improved as compared with carbon nanotubes and diamond films, respectively. A turn-on field of 1.0 V/µm and a maximum current of 500 µA at 1.5 V/µm were observed, which were lower than those of carbon nanotubes and polycrystalline diamond films, respectively. This improvement was attributed to the tip shape of sample surface, which provided an additional local increase in electric field at the tube ends.

Abstract: Electrochemical behaviors of epinephrine and ascorbic acid have been studied at the carbon nanotube electrode using cyclic voltammetry. Electrocatalysis has been found for epinephrine redox reactions at the carbon nanotube electrode in the comparison with the glassy carbon electrode. A well-defined oxidative peak for ascorbic acid was observed at the carbon nanotube electrode with the peak potential negative shift versus the glassy carbon electrode. Low level of epinephrine can be determined at the carbon nanotube electrode selectively with high sensitivity in the presence of a large excess of ascorbic acid in the acidic media and in the physiological pH buffer solution.