Teck Yaw Tiong

Electrochemically deposited and etched membranes with precisely sized micropores for biological fluids microfiltration

This paper presents simple and economical, yet reliable techniques to fabricate a micro-fluidic filter for MEMS lab-on-chip (LoC) applications. The microporous filter is a crucial component in a MEMS LoC system. Microsized components and contaminants in biological fluids are selectively filtered using copper and silicon membranes with precisely controlled microsized pores. Two techniques were explored in microporous membrane fabrication, namely copper electroplating and electrochemical etching (ECE) of silicon. In the first technique, a copper membrane with evenly distributed micropores was fabricated by electroplating the copper layer on the silicon nitride membrane, which was later removed to leave the freestanding microporous membrane structure. The second approach involves the thinning of bulk silicon down to a few micrometers thick using KOH and etching the resulting silicon membrane in 5% HF by ECE to create micropores. Upon testing with nanoparticles of various sizes, it was observed that electroplated copper membrane passes nanoparticles up to 200?nm wide, while porous silicon membrane passes nanoparticles up to 380?nm in size. Due to process compatibility, simplicity, and low-cost fabrication, electroplated copper and porous silicon membranes enable synchronized microfilter fabrication and integration into the MEMS LoC system.

Influence of growth temperature on SnO2 nanowires

Abstract Tin oxide (SnO2) nanowires have been synthesised using a thermal evaporation approach on quartz (SiO2) substrates in nitrogen atmosphere with a mixture of milled SnO2 powder and graphite as reactants. The substrates were placed vertically right above the reactants during the growth at 850, 900, 950 and 1000°C. A SnO2 thin film layer has been used as the nucleation site which is different from the conventional methods of using metal catalyst as seed for growth. SnO2 thin films have self-catalysed to form SnO2 nanowires at 950°C. At 850 and 900°C, plenty of SnO2 clusters landed on the substrates which were originated from the non-vaporised SnO2 powder. An optimum range of temperature was obtained for growth of clean SnO2 nanowires which were free from metal catalysts and non-vaporised SnO2 clusters.

Butane Sensing Property of Si-ZnO Nanowires p-n Junction

The p-n junction has been formed by using p-type boron doped silicon and n-type ZnO nanowires (NWs). It was prepared by using simple vapour-transport deposition method. Gas sensing property has been examined by measuring the resistance change of the junction sample towards 1 % of butane gas at room temperature. Significant improvement of sensing behaviour was observed from the fabricated junction sample when it was compared to sample of non-p-n junction ZnO NWs. The increase in the sensitivity of the p-n junction ZnO NWs and the ability to regain the sensing power by returning back to the initial state at room temperature are useful for future sensing device with minimum power consumption. Keywords: ZnO nanowires, Si-ZnO nanowires p-n junction, room temperature sensing and butane gas

Synthesis and characterization of sn doped ZnO nanowires

This paper reports on synthesis and characterizations of Sn doped ZnO nanowires. Sn doped ZnO nanowires was successfully been grown using carbothermal reduction method. Morphological and structures were characterized using FESEM, revealed that nanowires grown on random direction with diameter around 30 – 60 nm. EDX analysis was used to confirm composition element, Sn element was found in the nanowires in less than 1% of total composition. XRD was applied to examine structure quality of Sn doped ZnO nanowires, XRD spectra shown the structure have high crystallinity and it is wurtzite structure. No contrast different were found between pure and Sn doped ZnO nanowires. I-V measurement shown that using Sn as dopant may decrease the resistance of ZnO nanowires.

The growth of pine-leaf-like hierarchical SnO2 nanostructures

Pine-leaf-like SnO2 hierarchical nanostructures (NSs) were grown by a two-step vapour transport deposition process with a combination of vapour–solid and vapour–liquid–solid mechanisms at the primary and secondary processes, respectively. This type of hierarchical structure consisted of SnO2 trunk with homo-branching nanowires (NWs). The branched NWs connected the trunk NWs at included angles of 56° and 90° for two different types of hierarchical NSs. Based on the thermodynamic calculation, the formation of branched NWs at those angles are all energetically favourable.

Study of the contact properties of ZnO nanowires with Ag and Au/Ag

Zinc oxide (ZnO) nanowires have been synthesized using thermal evaporation approach on quartz (SiO2) substrates in nitrogen atmosphere with a mixture of milled ZnO and graphite powder as reactants. Ohmic behavior has been obtained for both Ag and Au/Ag contact to ZnO nanowires. The samples were re-examined after annealing at 300degC, 400degC and 500degC. The optimum annealing temperature for obtaining minimum resistance of Ag and Au/Ag contact with ZnO nanowires are 400degC and 300degC respectively. The contact is dominated by Metal-Zinc bonds rather than Metal-Oxygen bonds which cause the formation of ohmic behavior.

The growth of Sn doped ZnO nanobelts and their properties

Sn doped ZnO nanobelts have been synthesized by using thermal evaporation method. Sn powder was mixed with the ZnO and graphite grain powder as the growth reactant for obtaining doped ZnO nanobelts. This nanobelts was prepared under nitrogen ambient and at temperature 1000°C. The nanobelts formed were observed under X-ray diffraction (XRD), scanning electron microscope (SEM) and analysis of its electrical and optical properties also was determined. The growth mechanisms of the Sn doped ZnO nanobelt and its potential applications are further discussed.

Study of the properties of indium doped ZnO nanowires

Indium doped ZnO nanowires were synthesized by carbothermal reduction method in a quartz tube. The nanowires were characterized by FESEM for morphological structure, the results showed a hexagonal structure with diameter around 40 – 100 nm, and lengths from hundreds of nanometers to a few microns. EDX was also used for materials composition and all the composition were found in the spectrum. XRD was then used for checking crystallinity of the structure. ZnO nanowires were than measured for electrical properties. The results show that the indium doped ZnO nanowires has lower resistivity compare to the undoped ZnO nanowires. Gas sensing characterization has also been performed.