Abu Samah Zuruzi

Highly sensitive gas sensor based on integrated titania nanosponge arrays

Highly sensitive gas sensors were fabricated using nanostructured titania pad arrays. Nanostructured titania (NST) formed is sponge-like consisting of interconnected nanoscale wires and walls, which are made up of anatase nanocrystals. Electrical characterization indicates that contacts were ohmic and NST was highly sensitive to O2. Variations of hundreds of oxygen molecules over a 20μm NST square pad sensing element were detected at 250°C. The NST-based sensor operates at lower temperatures, has fast response time, and superior sensitivity relative to oxygen sensors based on porous undoped titania reported in the literature.

ROUGHNESS EVOLUTION OF CU6SN5 INTERMETALLIC DURING SOLDERING

The roughness evolution of the Cu6Sn5 intermetallic compound during the soldering reaction of 40/60% (by wt %) PbSn solder on Cu and its effects on wettability were studied due to their importance in the reworking of microelectronic components. The roughness parameters investigated were Rrms and the ratio, Rrms/λa, where Rrms is the root mean square roughness and λa is the average distance between asperities. It was found that Rrms increased with soldering time for the range of soldering times studied. The evolution of Rrms was found to follow a parabolic relation with soldering time—which is similar to that observed for the intermetallic thickness. However, the ratio Rrms/λa was found to increase very gradually for the range of soldering times investigated. From the ratio Rrms/λa obtained, the average inclination of the intermetallic morphology was calculated. The average inclination of the Cu6Sn5 intermetallic morphology was found to be greater than the apparent contact angle observed during the wetting...

Nanostructured TiO2 thin films as porous cellular interfaces

We report the use of nanostructured TiO2 (NST) as porous cellular adhesion interfaces for microsystems. Integrated NST films and pad arrays with sponge-like morphology were fabricated by aqueous oxidation of Ti films followed by thermal annealing. Cell culture studies indicate significantly (t<0.02 from the students t-test) greater initial attachment of mouse fibroblast cells on porous NST than on silicon dioxide and nitride films for up to 18?h seeding time. Fibroblasts seeded on NST have flat morphology with numerous processes attaching to walls of NST. These results indicate the potential of using NST as porous cell adhesion films and membranes for bioMEMS applications.

Electrical conductivity of porous silver made from sintered nanoparticles

Electrical conductivity of open cell porous silver (Ag) with sub-micrometer features was studied. Porous Ag was formed from annealing Ag nanoparticles at 150°C up to 5 minutes. Porous Ag is a network of cylindrical ligaments joined at their ends to spherical vertices. Electrical conductivity of porous Ag was ~20% of bulk value after 5 mins annealing. Kelvin cells (truncated octahedrons) with cylindrical ligaments and spherical vertices (CLSV) were used to compute electrical conductivity which is in agreement with experimental data, without any fitting parameter. Results of the CLSV model are also in agreement with the well-established Koh-Fortini empirical relation.

Fabrication and characterization of patterned micrometre scale interpenetrating Au–TiO2 network nanocomposites

Integrated micrometre scale interpenetrating Au–nanostructured TiO2 (Au–NST) network nanocomposites have been fabricated using a two-step process. First, NS Tp adarrays were prepared by reacting patterned Ti surfaces with aqueous H2O2 .N ST formed is porous with pores 50–200 nm in diameter and walls about 75–125 nm thick. Second, Au was infiltrated into pores of NST using electroless deposition to form the nanocomposite. SEM studies indicate that Au was deposited into pores of NST with little void formation. Selective deposition of Au on NST pads was confirmed using XRD and area-mode XPS. This process is a general route to forming micrometre-scale nanocomposite features consisting of NST and metals that are amenable to electroless deposition. (Some figures in this article are in colour only in the electronic version)

Superhydrophilicity on microstructured titanium surfaces via a superficial titania layer with interconnected nanoscale pores.

Microstructured titanium (Ti) surfaces often suffer from poor hydrophilicity which makes the realization of open microfluidic devices difficult. Here, we investigate the effect of a superficial porous titania (TiO2) layer on the hydrophilicity of microstructured surfaces. High aspect ratio Ti micropillars were micromachined from bulk Ti sheets. Porous TiO2 was subsequently grown on Ti micropillars by a wet oxidation route followed by thermal annealing. Porous TiO2 was characterized using atomic force microscopy, x-ray diffraction and x-ray photoelectron spectroscopy. Detailed morphology study and pore size analysis were carried using focused ion beam machining coupled with scanning electron microscopy. Static contact angle and dynamic spreading studies clearly demonstrate enhanced hydrophilicity of microstructured Ti surfaces with a superficial porous TiO2 layer. Such enhancement promises interesting applications in the microfluidics and microsystems fields.

A simple strategy to incorporate Pt into TiO2 nanosponges via wet oxidation of multilayered films

Addition of noble metals has been shown to enhance the properties of TiO2 for a wide range of applications. Methods to incorporate Pt into TiO2 usually involve the use of chloride-containing precursors. Here we present an alternative chloride-free method to incorporate Pt through aqueous oxidation of multilayered Ti/Pt/Ti films in a simple manner. In this contribution, we demonstrate this route using sputtered Ti/Pt/Ti films either in blanket layer or micrometer scale features patterned using lithography. A mechanism for Pt incorporation into TiO2 based on formation of Pt hydroxides is proposed. We demonstrate the utility of this technique to incorporate Pt into TiO2 nanosponges by constructing prototype sensors which exhibit a faster response time and a current increase of 2 orders of magnitude larger than sensors using pristine TiO2 nanosponges. This method is a simple route to integrate Pt-modified TiO2 (Pt-TiO2) nanosponge features into devices such as lab on a chip and integrated power sources.

Tailored nanostructured titania integrated on titanium micropillars with outstanding wicking properties.

A novel wicking material using nanostructured titania grown on high aspect ratio titanium micropillars is demonstrated. High aspect ratio titanium micropillars were micromachined from bulk titanium sheets. Nanostructured titania was then grown on the surface of titanium micropillars by oxidation in aqueous hydrogen peroxide solution followed by thermal annealing. The nanostructured titania formed has an open porous structure with a nanoscale pore diameter and wall thickness. X-ray diffraction and pole figure studies indicate the formation of anatase phase of titania and the absence of a preferred orientation in the porous film. The hybrid nanostructured titania on titanium micropillars has excellent hydrophilic properties with a water capillary speed comparable to or exceeding that of conventional wick materials commonly used in heat pipes for the thermal management of electronic devices.

Interdiffusion of high-Sn/high-Pb (SnPb) solders in low-temperature flip chip joints during reflow

We carried out experiments and numerical simulations to investigate the transport of Sn in a composite solder joint, comprising of high-Pb and high-Sn (SnPb) alloys, in a chip-composite solder-organic substrate package during the reflow process. Both the experimental and simulation results demonstrate that surface diffusion causes the transport of Sn on the surface to be faster than that inside the solder joint. Surface diffusion also accelerates the homogenization process of the composite solder joint.

Tailored nanostructured titania grown on titanium micropillars with outstanding wicking properties for thermal management of microelectronics devices

This paper discusses a novel thermal management approach using nanostructured titania formed on high-aspect ratio micromachined titanium structures. A recently developed dry etching technology, with etch rates of more than 2 μm/min, enables bulk micromachining of titanium using an inductively coupled plasma to define high aspect ratio structures. This technology allows for the development of three-dimensional architectures through the successive stacking and bonding of through-etched titanium foils. Nanostructured titania was formed on high aspect ratio titanium structures using a simple technology involving oxidation in aqueous hydrogen peroxide followed by annealing. These high aspect ratio structures with nanostructured titania surface and titanium core have excellent hydrophilic properties which bodes well for thermal management applications. Compared to those using copper based wick materials, heat pipes using nanostructured titania/Ti ones have better capillary speed characteristics which decays at a slower rate.