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Tiny lights enable molecular-scale imaging Arrays of nanoscale light-emitting diodes (LEDs) offer an energy-efficient means for achieving microscopic imaging with resolution below the diffraction limit. Microscale LEDs are already poised to have a transformative impact on display technology, but it remains challenging to construct arrays of individually controllable LEDs at the nanometer scale. Daria Bezshlyakh of the Technische Universität Braunschweig in Germany and colleagues have developed a fabrication approach that enabled them to manufacture a compact super-resolution imaging system based on such arrays. Their device employs gallium nitride nano-LEDs that generate precisely structured patterns of illumination, which make it possible to image specimens at spatial resolutions smaller than the wavelength of light. Based on the performance and stability of this initial prototype, the authors conclude that similar devices could offer a promising platform for future molecular imaging applications.

The electronics for monolithically integrated gas sensor arrays fabricated using a compatible CMOS process have been developed. Circuitry includes the heater driver for temperature control and an interface circuit for inspection of the four sensors in the array. The operating temperature of the sensing resistors is between 200° and 400°C. The proposed temperature controller is capable of regulating the temperature of a 2100 × 2100 μm hotplate up to 400°C with a resolution of 2°C with 5 V supply voltage. A readout circuit based on a ring-oscillator has been included to measure the sensing resistance change upon gas exposure over a high dynamic range. Because it is robust, small, low priced and offers future capabilities with adequate signal processing, the system would be able to cover most of today's gas sensor markets.

Nanocrystalline thick-film SnO2 sensors with different dopants were fabricated by an optimized screen printing process and subsequent annealing. Powders were used as starting materials which were prepared by a wet chemical process from SnCl4. Microanalysis was performed of both, the precursors and the final sensor materials with their different annealing conditions. Gas sensing tests with CO, CH4 and NO2 in air with controlled humidity were correlated with results from X-ray photoemission spectroscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). As an interesting result, the distribution of the transition metal dopants Pd and Pt (as deduced from TEM and XPS data) rules out the existence of metallic clusters or even atoms in the metallic state at the surface. This finding does not allow to explain the sensor effects on SnO2 based materials as usually done by means of spill-over effects or Fermi energy control.