A palladium (Pd) nanowire-based hydrogen (H2) sensor has been fabricated with a novel viral-templated assembly route. A filamentous M13 bacteriophage was used as the viral-template for assembly of Pd nanowires at ambient conditions.
Scanning electron microscopy determined Pd nanowire distribution and morphology with the devices. The phage
template concentration controlled the number of physical and electrical nanowire connections across the device. A
greater phage concentration resulted in a higher connection density and thicker Pd deposition. A lower phage
concentration generated devices which formed chain-like nanowires of Pd nanocrystals, whereas a higher phage
concentration formed devices with a continuous mesh-like structure. The lower concentration devices showed 51-78%
instantaneous response to 2000 ppm H2 and response time less than 30 s.
Preliminary studies toward the assembly of a gold-polypyrrole (PPy) peapod-like chemiresistive ammonia (NH3) gas
sensors are presented. The proposed synthesis process will use electropolymerization to embed gold nanoparticles in
polypyrrole nanowires. Viral-templating of gold nanoparticles and PPy electrodeposition via cyclic voltammetry are the
focus of this investigation. A gold-binding M13 bacteriophage was used as a bio-template to assemble continuous
chains of gold nanoparticles on interdigitated Pt working electrodes. The dimensions of the resulting nanowire-like
structures were examined and the electrical resistance measured. PPy films were electropolymerized using an
interdigitated planar, Pt electrode integrated counter and reference electrode. Morphological characterization of the
polymer films was completed.
We report a fabrication technique that is potentially capable of producing arrays of individually addressable nanowire sensors with controlled dimensions, positions, alignments, and chemical compositions. The concept has been demonstrated with electrodeposition of palladium wires with 75 nm to 350 nm widths. We have also fabricated single and double conducting polymer nanowires (polyaniline and polypyrrole) with 100nm and 200nm widths using electrochemical direct growth. Using single Pd nanowires, we have also demonstrated hydrogen sensing. It is envisioned that these are the first steps towards nanowire sensor arrays capable of simultaneously detecting multiple chemical species.
Alumina nanotemplates integrated on silicon substrate with pore diameters of 12 nm to 100 nm were prepared by galvanostatic anodization. High current density (e.g. 100 mA.cm-2) promoted a highly ordered hexagonal pore structure with fast formation rate independent of anodizing solutions, where 2000 nm/min, 1000 nm/min were achieved at current densities of 100 mA.cm-2 and 50 mA.cm-2, respectively. These rates were approximately two orders of magnitude greater than other reports in the literature.
Different electrolytes of sulfuric acid (1.8 to 7.2 M), oxalic acid (0.3 M) and mixed solutions of sulfuric and oxalic acid were evaluated as anodizing solutions. Sulfuric acid promoted smaller pore diameter with lower porosity than mixed acids and oxalic acid. The I-V characteristics strongly depend on solution composition, temperature, and bath agitation. In the case of sulfuric acid, the breakdown voltage (UB) varied linearly with logarithmic of sulfuric acid concentration (UB = 24.5-11 log [H2SO4]) and it decreased at higher temperature.
The pore diameter of silicon-integrated alumina nanotemplate varied linearly with measured voltage with a slope of 2.1 nm/V, which is slightly smaller than reported data on bulk aluminum (2.2 nm/V and 2.77 nm/V). Thermoelectric Bi2Te3 nanowires with diameter of 43 nm were electrodeposited.
A design concept for nanowire-based sensors and arrays is described. The fabrication technique involves electrodeposition to directly grow nanowires between patterned thin film contact electrodes. To prove our concept, we have electrodeposited 1-μm diameter Pd single wires and small arrays. To demonstrate nanowire sensors, we have
electrochemically grown metal (Pd, Au, Pt), metal oxide (Sb2O3), and conducting polymer (polyaniline) bundled nanowires. Using Pt bundled nanowires surface modified with glucose oxidase, we have demonstrated glucose detection as a demonstration of a biomolecular sensor.
A 3X3 array of hyperboloid quadrupole mass filters with a 3 mm pole length was fabricated using the LIGA (LIthographic Galvanoformung and Abformung) process. Electrical connectivity and spatial orientation are established by bonding the pole array to a low temperature co-fired ceramic (LTCC) substrate. A miniature scroll pump for vacuum pumping with a scroll height of 3 mm was also fabricated using the LIGA process. New LIGA fabrication steps (e.g. expose and developed freestanding PMMA, compression bonding of electroplating base and PMMA, low-stress electroplated films) have been developed to fabricate ultra thick PMMA molds with high aspect ratios (70:1) and high precision. Computational analysis was performed to estimate the miniature scroll pump performance characteristics.