Shao-Ren Deng

Cu adhesion on tantalum and ruthenium surface: Density functional theory study

This work reports a first-principles study of copper adhesion on Ta(110) and Ru(0001) surface with the density functional theory. Adsorption energy, electron density difference, and geometrical structures of Cu on pure, oxygen, and nitrogen doped Ta(110), Ru(0001) surfaces, and Ru doped Ta(110) surface were investigated. By analyzing the calculated results and the existing experimental results, it is found that although Ta has stronger chemical interaction with Cu, its larger lattice mismatch with Cu, and easy oxidation and nitridation make Ta a poorer Cu adhesion layer in comparison with Ru. The adhesion ability of Cu on Ta can be improved by doping Ru in Ta. The agglomeration of Cu on Ta or Ru is also studied. The calculation results show that Cu adsorbed on Ta(110) surface is more likely to be desorbed and agglomerated on the top of the second Cu atom layer. The substitutional oxygen O Ta in Ta will stimulate the agglomeration of Cu on the Ta surface.

Duplication of nanoimprint templates by a novel SU-8/SiO2/PMMA trilayer technique

In this work, a trilayer technique used in the nanoimprint lithography process to replicate the templates is developed. The SU8/SiO2/PMMA trilayer was used. The photosensitive epoxy (SU8 resist) which has a low glass transition temperature was used as the imprint layer. Polymethylmethacrylate (PMMA) was used as the transfer layer. A SiO2 layer is placed between the SU8 and PMMA to act as a protective layer due to its strong resistance to oxygen reactive ion etching. By optimizing imprint and etching processes, master templates with minimum feature size of 150 nm and period of 300 nm can be successfully duplicated.

The EL properties of well-aligned n-ZnO nanorods / p-GaN structure

Well-aligned ZnO nanorods were grown on the p-GaN substrate by a hydrothermal method and n-ZnO nanorods/p-GaN heterojunction LED structures were formed. The electroluminescence (EL) properties of this structure were studied under both forward and reverse bias. The nanorod LED device only has light output under reverse bias. The I–V characteristic results show that the nanosized junction can increase the carrier injection efficiency of the n-ZnO nanorods/p-GaN LED device.

The effects of high work function electrodes on the electrical properties of solution processed ZnO thin film transistor

In this work, the effects of electrodes on the performance of sol-gel fabricated ZnO thin film transistor were investigated. The metal with high work function such as Pt was employed as the source-drain electrodes. Compared to the device with Al electrodes as reported before, the transistor fabricated with Pt electrode exhibited lower saturation voltage and current, which was due to the Schottky contact between the Pt electrode and the ZnO film. The result has also been proved by the current-voltage (IV) measurement of the Pt-ZnO-Pt structure. For the Schottky contact between the electrodes and the channel layer, the current saturated when the source was depleted. This kind of device reduced the operation voltage and power dissipations effectively.

Highly ordered growth of ZnO nanostructures by combination of nanoimprint lithography and hydrothermal method

By combining nanoimprint lithography and traditional hydrothermal growth method of ZnO nanorods, vertical and well patterned ZnO nanostructures were successfully fabricated. The imprinted SU-8 resist deep trenches above the ZnO seed layer prohibit the lateral growth of ZnO nanorods. Various patterned vertical ZnO nanostructures like nanorods and nanowalls can be obtained. The improvement of photoluminescence property of ZnO nanorods was observed after removing the SU-8 resist from the substrate by O2 reactive ion etching (RIE).

Trilayer nanoimprint fabrication and simulation of the silicon nanowire sensor for gas detection

In this work, we demonstrate a novel SU8/SiO2 /PMMA trilayer nanoimprint technique to fabricate the silicon nanowire (SiNW) sensor used for gas detection. The SiNW sensor fabricated in our experiment is based on the silicon on insulator (SOI) substrate which is doped by boron with a dopant concentration of 8×1017cm−3. Two nanowire sensors with different linewidths as well as a thin-film plane device were fabricated for comparison. The fabricated devices were then used for detecting 250ppm NO2 and 250ppm NH3. The results show a large enhanced sensitivity especially for the narrower device. Finally, a computer simulation work was done to qualitatively explain our experimental results.