Silicon-to-steel bonding using rapid thermal annealing

This paper presents the rapid, low-temperature bonding between silicon and steel using the rapid thermal annealing process. Three different thin-film adhesion layer systems including silver, gold, and nickel were utilized as the intermediate bonding material to assist the eutectic Pb/Sn bonding between silicon and steel. The bonding temperature was set at 220/spl deg/C for 20 s, with a 20-s ramp-up time. Five experiments were conducted to determine the strength of the bond, including static tensile and compressive four-point bend tests, axial extension tests, tensile bending fatigue tests, and corrosion resistance tests. The test results have shown that the gold adhesion layer is the most robust, demonstrating minimal creep during fatigue tests, no delamination during the tensile or compressive four-point bend tests, and acceptable strength during the axial extension tests. Additionally, all adhesion layers have withstood four months of submersion in various high-temperature solutions and lubricants without failure. Simulations of the axial stresses and strains that developed during the four-point bend and axial extension tests were performed and showed that the presence of the silicon die provides a local reinforcement of the bond as observed in the experimental tests.     

Local vapor transport synthesis of zinc oxide nanowires for ultraviolet-enhanced gas sensing

A novel local vapor transport technique via induction heating is presented to enable selective, localized synthesis and self-assembly of nanowires, providing a simple and fast method for the direct integration of nanowires into functional devices. The single-crystalline zinc oxide (ZnO) nanowires are grown locally across the silicon-on-insulator microelectrodes within minutes, and the enhancement of gas sensing of ZnO nanowires is demonstrated under ultraviolet (UV) illumination at room temperature. Experiments indicate that when suspended nanowires are exposed to UV light, a twelve-fold increase in conductance and a near five-fold improvement in oxygen response are measured. Furthermore, the UV-enhanced transient responses exhibit a two-level photocurrent decay attributed to carrier recombination and oxygen readsorption. As such, the local vapor transport synthesis and UV-enhanced sensing scheme could provide a promising approach for the construction of miniaturized and highly responsive nanowire-based gas sensors.     

An electrothermal carbon nanotube gas sensor

We show both gas pressure and species sensing capabilities based on the electrothermal effect of a multiwalled carbon nanotube (MWCNT). Upon exposure to gaseous environments, the resistance of a heated MWCNT is found to change following the conductive heat-transfer variances of gas molecules. To realize this mechanism, a suspended MWCNT is constructed by synthesis and assembly in localized chemical vapor deposition that is accomplished within seconds via real-time electrical feedback control. Vacuum pressure sensitivity and gas species differentiability are observed and analyzed. Such MWCNT electrothermal sensors are compact, fast and reversible in responses, and fully integratable with microelectronics.     

Titanium dioxide nanoswords with highly reactive, photocatalytic facets

Titanium dioxide (TiO(2)) is one of the most widely studied and important materials for catalysis, photovoltaics, and surface science applications, but the ability to consistently control the relative exposure of higher surface energy facets during synthesis remains challenging. Here, we present the repeatable synthesis of highly reactive, rutile {001} or {101} facets on broad, sword-shaped TiO(2) nanostructures rapidly synthesized in minutes. Growth occurs along planes of lower surface energy, repeatedly yielding nanostructures with large, high energy facets. The quantitative photocatalytic reactivity of the nanoswords, demonstrated by the photoreduction of silver, is over an order of magnitude higher than reference low energy TiO(2){110} substrates. Therefore, the higher surface energy dominated TiO(2) nanoswords are ideal structures for characterizing the physicochemical properties of rutile TiO(2), and may be used to enhance a variety of catalytic, optical, and clean-technology applications.