Electrical and optical properties of as-deposited, ion beam sputtered, Al-doped ZnO films have been studied as a function of film thickness and carrier concentration. Hall effect measurements reveal that the bulk electrical resistivity of the film generally decreases with increasing film thickness. Additionally, it is observed that the rate of decreasing resistivity depends on the particular film thickness regime. For thinner films (100–200 nm), the resistivity decreases rapidly with increasing film thickness and is due to increases in both carrier concentration and Hall mobility. However, for thicker films, the resistivity decreases more slowly with increasing film thickness and approaches a nearly constant value at a thickness of 1100 nm. In this thickness regime, the slight decrease in resistivity with increasing film thickness is found to be due to an increase in carrier concentration alone. The above observations suggest the presence of at least two scattering mechanisms. It is speculated that grain boundary and ionized impurity are the most likely mechanisms. These issues, together with observed optical properties of the films, are discussed.

Optically induced dielectrophoresis (ODEP) has been proved experimentally as a powerful method for efficiently manipulating some micro-scale, or even nano-scale objects. However, few ODEP platforms have been demonstrated towards the fully automatic wafer-scale manipulation and rapid fabrication of micro and nano sensors and devices. That would be of great significance to the application and industrialization of micro and nano materials. In this paper, an innovative ODEP platform for reconfigurable and automatic micro/nano-scale material manipulation is presented by combining microactuation and microvision analysis with ODEP technology. The ODEP chip consists of a typical photoconductive layer of amorphous silicon, which generates a nonuniform electric field at the light-illuminated region to induce dielectrophoretic (DEP) force for manipulating particles within the chip. A high resolution 3D motorized stage enables an accurate and rapid movement of the chip in wafer-scale. The microvision analysis program automatically recognizes the positions and sizes of randomly distributed particles and creates direct image patterns to manipulate the selected particles to form a predetermined pattern in predesired position. The programmed dynamic reconfigurable optical patterns provide increased functionality and versatility in particle manipulation. The patterning of polystyrene beads with different sizes is accomplished. This platform may be promising for rapid and wafer-scale fabrication of micro and nano sensors and devices, high-throughput bio-sample pretreatment and other applications requiring massively parallel manipulation.

This paper describes the assembly of 2 nm gold nanoparticles between micro-fabricated planar electrodes by using dielectrophoresis (DEP). The optimal conditions for effectively dieletrophoretic manipulation have been established through theoretical analysis and experimental validation. In the theoretical analysis, the effect of Brownian motion was taken into consideration, as well as the electrothermal flow and the AC electroosmosis flow. For effective manipulation of nanoparticles using DEP, proper high electric field strength is desired to give rise to dominate DEP effect, since the higher electric field strength increases the Joule heating and the lower strength reduces the DEP force. The current results indicate that the input voltage of 16Vp-p, 150 kHz leads to effective assembly of 2 nm gold nanoparticles. Our study proved that the DEP is capable of consistently assembling gold nanoparticles down to 2 nm in diameter with micro-fabricated electrodes, which was thought to be extremely difficult in the past.