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Surface smoothness of probe tips is critical for applications, such as measuring surface tension of various liquids, oscillatory hydration forces, and interfacial shear strengths from friction experiments. In this study we establish conditions for fabricating tips with smooth surfaces by controlling the electrochemical polishing process throughout the tip evolution rather than following the current practice of producing tips by the drop-off method. Polishing is conducted under a constant voltage, with the wire immersed below the nominal air/electrolyte interface by no more than one-half of the wire diameter and stopping the etching at different current levels. This process provides a tip radius range of approximately 100 nm to 5 μm for a tungsten wire with a 0.2 mm diameter. Alternatively, the wire can be placed above the nominal air/electrolyte interface but within the meniscus until the current drops to zero. In this case, the tip radii range from 5 to 50 μm. In both cases, atomic force microscopy scans of these tips show that the surface rms roughness is about 0.3 nm. [ABSTRACT FROM AUTHOR]

Mono-crystalline silicon single heterojunction solar cells on flexible, ultra-thin (∼25 μm) substrates have been developed based on a kerf-less exfoliation method. Optical and electrical measurements demonstrate maintained structural integrity of these flexible substrates. Among several single heterojunction ∼25 μm thick solar cells fabricated with un-optimized processes, the highest open circuit voltage of 603 mV, short circuit current of 34.4 mA/cm2, and conversion efficiency of 14.9% are achieved separately on three different cells. Preliminary reliability test results that include thermal shock and highly accelerated stress tests are also shown to demonstrate compatibility of this technology for use in photovoltaic modules. [ABSTRACT FROM AUTHOR]