Papers by Author: Yi Shi

Abstract: A novel precursor, 6FAPB-PMDA type polyimide, was developed to prepare carbon membranes and carbon nanotube (CNT) composite carbon membranes. The thermal stability of precursors was characterized by TGA. The morphology of carbon membrane was observed by SEM. The microstructure was measured by XRD and nitrogen adsorption technique. Results have shown that 6FAPB-PMDA type polyimide is a promising precursor, and the introduction of CNT can obviously modify the thermal stability, as well as the carbon and porous structure of resultant carbon membranes.

Abstract: The influence of Mn content on the structure and magnetic permeability of Nd3Fe68-xMnxCo18B11 (x = 0, 1, 2) amorphous soft magnetic alloys was studied. The ribbons were prepared by melt-spining. The permittivity–frequency and permeability–frequency properties were determined in the microwave frequency regime of 2-18 GHz by vector network analysis. XRD spectra showed that only α-Fe diffraction peak was observed in the as-spun alloy. It is found that the acquired complex permittivity and permeability values match the microwave frequency when the 1at% Mn content doped. The results suggest a new design of microwave absorbers based on electromagnetic wave absorbing materials.

Abstract: GaN films are grown on Si(111) with low-temperature GaN (LT-GaN) layers as buffer layers by hydride vapor phase epitaxy (HVPE). The LT-GaN layers are deposited at different temperatures ranging from 400 to 900 °C. The surface property, the structure and optical properties of the GaN films with different LT-GaN layers are studied. When deposition temperature of LT-GaN layer is 600 °C, the GaN film shows the best properties.

Abstract: Fe films have been grown on different oriented Si substrates by metal organic chemical vapor deposition (MOCVD), and then samples are put in the air without any protection for nearly fifteen years. In this paper, using methods such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM), we make a detailed research on the samples. We identify the composition and structure of the epitaxial films on different oriented substrates and compare the difference both in composition and magnetic properties. Different orientation of the substrates results in different epitaxial film with different characteristic. We also confirm the existence of single crystal iron in the heteroepitaxial film grown on Si (001), and discuss the possible reason why the single crystal iron film still exists without complete oxidation in air for such a long time.