Michael P. Zach

Self-assembled monolayer-enhanced hydrogen sensing with ultrathin palladium films

Resistive-type palladium structures for hydrogen sensing remains as a research focus for their simplicity in device construction. We demonstrate that a siloxane self-assembled monolayer placed between a substrate and an evaporated ultrathin Pd film promotes the formation of small Pd nanoclusters and reduces the stiction between the palladium and the substrate. The resulting Pd nanocluster film can detect 2%H2 with a rapid response time of ∼70ms and is sensitive to 25 ppm hydrogen, detectable by a 2% increase in conductance due to the hydrogen-induced palladium lattice expansion.

Size-selective electrodeposition of meso-scale metal particles: a general method

Metal nano- and microparticles that are narrowly dispersed in diameter can be electrodeposited on graphite basal plane surfaces using the two-step method: First, a voltage pulse with a duration of 5 ms and an overpotential η = - 500 mV was used to nucleate metal particles on the graphite surface. Then, a growth pulse with an overpotential, η, of -20 to -250 mV was applied to grow the metal particles obtained in step 1 to the desired final diameter. For a variety of metals including silver, gold, platinum, molybdenum, and nickel, this slow-growth method yielded dispersions of particles ranging in diameter from 50 nm to 2 μm having a relative standard deviation (RSD dia = σ dia / ) as low as 7%.

Electronic devices from electrodeposited metal nanowires

Abstract Based on their electronic conductivity behavior, metallic nanowires may have electronic applications ranging from interconnects to sensors. We have recently developed an electrochemical method for synthesizing metal nanowires (Pd, Cd, Mo, Au, Ag, Cu,…) ranging in diameter from a few tens of nanometer to 1 μm with millimeter lengths. These nanowires are prepared by the electrodeposition of metal at step edges present on a graphite surface. These nanowires can be used to connect metal nanoparticles (Ni, Au…) or, once transferred in a polymer cast, can operate as sensors. In this paper, we shall describe the general method of preparation of such naked and beaded nanowires as well as how may these nanowires be manipulated to make electronic devices. As an example of such nanodevice, a brief overview of the characteristics of the first nanowire-based sensor for hydrogen gas (H 2 ) will be given.

Electrodeposition of portable, metal nanowire arrays

Parallel arrays of long (> 500 m), dimensionally uniform nanowires composed of molybdenum, copper, nickel, gold, and palladium were electrodeposited. Nanowires with diameters in the range from 15 nm to 750 nm were obtained by electrodepositing these metals, or metal oxides, selectively at the step edges present on the surface of a highly oriented pyrolytic graphite electrode. Depending on the metal, either of two methods were used to carry out electrochemical step edge decoration (ESED): Nanowires of Ni, Cu or Mo were prepared by electrodepositing nanowires of a conductive metal oxide such as NiO, Cu2O, or MoO2. Nanowires of the parent metal were then obtained by reducing the metal oxide nanowires in hydrogen at elevated temperature. Nanowires composed of noble metals and some coinage metal can be obtained by direct electrodeposition of the metal at step edges. Direct electrodeposition involved the application of three voltage pulses in succession: An oxidizing activation pulse, a large amplitude, reducing nucleation pulse, and a small amplitude reducing growth pulse. These nanowires arrays were portable: After embedding the nanowires in a polymer film, arrays of nanowires could be lifted off the graphite surface thereby facilitating the incorporation of these arrays in devices such as sensors.

Electroplate and Lift Lithography for Patterned Micro/Nanowires Using Ultrananocrystalline Diamond (UNCD) as a Reusable Template

A fast, simple, scalable technique is described for the controlled, solution-based, electrochemical synthesis of patterned metallic and semiconducting nanowires from reusable, nonsacrificial, ultrananocrystalline diamond (UNCD) templates. This enables the repeated fabrication of arrays of complex patterns of nanowires, potentially made of any electrochemically depositable material. Unlike all other methods of patterning nanowires, this benchtop technique quickly mass-produces patterned nanowires whose diameters are not predefined by the template, without requiring intervening vacuum or clean room processing. This technique opens a pathway for studying nanoscale phenomena with minimal equipment, allowing the process-scale development of a new generation of nanowire-based devices.