There is a high demand for compact low-cost ozone sensors. It has been shown recently that In2O3 nanolayers can act as ozone sensitive films activated at room temperature by ultraviolet light. In the present work, the authors integrate ultrathin layers of In2O3 nanoparticles and a GaInN∕GaN based blue light emitting diode (LED) on a single sensor chip. The integrated sensor was found to be sensitive to O3 concentrations as low as ∼40ppb. These results demonstrate that by integrating GaInN∕GaN based blue LEDs and metal oxide sensing layers back to back on a single chip, compact and robust gas sensors can be realized.
Single crystalline tungsten nanowires were prepared from directionally solidified NiAl-W alloys by a chemical release from the resulting binary phase material. Electron back scatter diffraction (EBSD) proves that they are single crystals having identical crystallographic orientation. Mechanical investigations such as bending tests, lateral force measurements, and mechanical resonance measurements were performed on 100–300 nm diameter wires. The wires could be either directly employed using micro tweezers, as a singly clamped nanowire or in a doubly clamped nanobridge. The mechanical tests exhibit a surprisingly high flexibility for such a brittle material resulting from the small dimensions. Force displacement measurements on singly clamped W nanowires by an AFM measurement allowed the determination of a Young's modulus of 332 GPa very close to the bulk value of 355 GPa. Doubly clamped W nanowires were employed as resonant oscillating nanowires in a magnetomotively driven resonator running at 117 kHz. The Young's modulus determined from this setup was found to be higher 450 GPa which is likely to be an artefact resulting from the shift of the resonance frequency by an additional mass loading.
One-step device fabrication through the integration of nanowires (NWs) into silicon microchips is still under intensive scientific study as it has proved difficult to obtain a reliable and controllable fabrication technique. So far, the techniques are either costly or suffer from small throughput. Recently, a cost-effective method based on thin-film fracture that can be used as a template for NW fabrication was suggested. Here, a way to integrate NWs between microcontacts is demonstrated. Different geometries of microstructured photoresist formed by using standard photolithography are analyzed. Surprisingly, a very simple "stripe" geometry is found to yield highly reproducible fracture patterns, which are convenient templates for fault-tolerant NW fabrication. Microchips containing integrated Au, Pd, Ni, and Ti NWs and their suitability for studies of conductivity and oxidation behavior are reported, and their suitability as a hydrogen sensor is investigated. Details of the fabrication process are also discussed.
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