No abstract

The hydrogen sensing characteristics of a single nanotrench fabricated by focused ion beam milling (FIB) in an evaporated palladium microwire are presented. In situ atomic force microscopy (AFM) measurements proved that, in the presence of H(2), the trench closes and electrically connects the initially separated parts of the wire due to the increase in volume of the material. Therewith, an electrical current can be switched through the wire. With experiments under various H(2) concentrations and a mathematical model, we describe the closing mechanism of the trench with respect to various parameters, including the substrate material, film thickness, trench size and wire dimensions. Results have been compared with those from equivalent continuous wires. Thin SiO(2) and polyimide (PI) layers on silicon were used to study the effect of substrate elasticity. Sufficient lateral expansion of Pd to close trenches of up to 70 nm in width has only been observed on PI, which we attribute to its advantageous elastic properties. The scale of the response times allowed the observation of two superposing effects: the chemical conversion of Pd to PdH(x) and the mechanical closing of the trench.

No abstract

Employing higher oscillation modes of microcantilevers promises higher sensitivity when applied as sensors, for example, for mass detection or in atomic force microscopy. Introducing a special cantilever geometry, we show that the relation between the resonance frequencies of the first and second resonance modes can be modified to separate them further or to bring them closer together. In atomic force microscopy the latter is of special interest as the photodiode of the beam deflection detection limits the accessible frequency range. Using finite element simulations, we optimized the design of the modified cantilever geometry for a maximum reduction of the frequency of the second oscillation mode with respect to the first mode. Cantilevers were fabricated by silicon micromachining and subsequently utilized in an ultrahigh vacuum Kelvin probe force microscope imaging the surface potential of C 60 on graphite.

No abstract