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A nanocrystalline Si layer can be formed by the surface structure chemical transfer (SSCT) method in which a platinum mesh is instantaneously contacted with polycrystalline Si wafers immersed in hydrogen peroxide plus hydrofluoric acid solutions. The polycrystalline Si surface after the SSCT method possesses an ultra-low reflectivity. The nanocrystalline Si layer possesses a 100–150 nm thickness, and gives a photoluminescence with a peak maximum at ∼670 nm, indicating band-gap widening. The minority carrier lifetime of as-sliced Si wafers greatly increases after the SSCT method most probably due to the enlargement of the nanocrystalline Si band-gap.

The metal-binding capabilities of the spiropyran family of molecular switches have been explored for several purposes from sensing to optical circuits. Metal-selective sensing has been of great interest for applications ranging from environmental assays to industrial quality control, but sensitive metal detection for field-based assays has been elusive. In this work, we demonstrate colorimetric copper sensing at low micromolar levels. Dimethylamine-functionalized spiropyran ( SP1 ) was synthesized and its metal-sensing properties were investigated using UV–vis spectrophotometry. The formation of a metal complex between SP1 and Cu 2+ was associated with a color change that can be observed by the naked eye as low as ≈6 μM and the limit of detection was found to be 0.11 μM via UV–vis spectrometry. Colorimetric data showed linearity of response in a physiologically relevant range (0–20 μM Cu 2+ ) with high selectivity for Cu 2+ ions over biologically and environmentally relevant metals such as Na + , K + , Mn 2+ , Ca 2+ , Zn 2+ , Co 2+ , Mg 2+ , Ni 2+ , Fe 3+ , Cd 2+ , and Pb 2+ . Since the color change accompanying SP1 –Cu 2+ complex formation could be detected at low micromolar concentrations, SP1 could be viable for field testing of trace Cu 2+ ions.

Chemical modifications through substitution are observed to be effective in controlling the optoelectronic properties of various polymers for different applications. In this study, density functional theory–based calculations are employed to investigate the optoelectronic properties of several oligothiophenes based on poly(3-hexylthiophene-2,5-diyl) by varying the number of fluoro and cyano substituents attached. The resulting structures of the polymer derivatives are affected by the electrostatic interactions between the cyano or fluoro groups and the adjacent thiophene unit. Of the two, cyano substitution results in much lower frontier orbital energies for the same number of substituents. It was observed that a decrease in the highest occupied molecule orbital and lowest unoccupied molecular orbital energies correlates very strongly with the number of cyano and fluoro substituents. The effect of the cyano and fluoro groups on the frontier orbitals is also demonstrated and observed to correlate strongly with a lowering of the highest occupied molecule orbital and lowest unoccupied molecular orbital energies as the number of substituents is varied. The predicted solar cell characteristics reveal that most cyano and fluoro derivatives will have improved characteristics compared to unsubstituted poly(3-hexylthiophene-2,5-diyl). This theoretical study shows that by varying the number of electron-withdrawing substituents, the optoelectronic properties may be tuned for solar cell applications.