For decades now, silicon has been the workhorse of the microelectronics revolution and a key enabler of the information age. Owing to its excellent optical properties in the near- and mid-infrared, silicon is now promising to have a similar impact on photonics. The ability to incorporate both optical and electronic functionality in a single material offers the tantalizing prospect of amplifying, modulating and detecting light within a monolithic platform. However, a direct consequence of silicon's transparency is that it cannot be used to detect light at telecommunications wavelengths. Here, we report on a laser processing technique developed for our silicon fibre technology through which we can modify the electronic band structure of the semiconductor material as it is crystallized. The unique fibre geometry in which the silicon core is confined within a silica cladding allows large anisotropic stresses to be set into the crystalline material so that the size of the bandgap can be engineered. We demonstrate extreme bandgap reductions from 1.11 eV down to 0.59 eV, enabling optical detection out to 2,100 nm.
Synergetic experimental and DFT insights of energy band structures and photogenerated reactive intermediates are indispensable to design impurity-doped photocatalysts for photocatalytic environment remediation and solar fuels. Herein, despite the larger bandgap (Eg), Zn-doped BiOBr samples exhibited superior activity to BiOBr in the photocatalytic water splitting but adverse in photodegradation of Rhodamine B under visible-light illumination. Based on the spectral and electrochemical impedance characterisations and DFT simulations, the broader bandgap of Zn-doped BiOBr was explicitly assigned to more positive valence band maximum (VBM) and more negative conduction band minimum (CBM). The enhanced photocatalytic water splitting on Zn-doped BiOBr was assigned to the higher redox chemical potentials of charge carriers on respective CBM and VBM, suppressed back reaction and reduced recombination of photogenerated charge carriers. However, the reduced e-h + recombination on Zn-doped BiOBr cannot cancel the adverse influences of its weaker light absorption and dye-sensitisation effects, leading to slower RhB photodegradation.
͑͒We describe a technique for surface domain engineering in congruent lithium niobate single crystals. The method is based on conventional electric-field poling, but involves an intentional overpoling step that inverts all the material apart from a thin surface region directly below the patterned photoresist. The surface poled structures show good domain uniformity, and the technique has so far been applied to produce domain periods as small as ϳ1 m. The technique is fully compatible with nonlinear optical integrated devices based on waveguide structures. ͓͔
We report the experimental measurements for etch rates of the zz and 2z faces of single crystal lithium niobate immersed in HF and HNO 3 acid mixtures of varying ratios. We find that pure HF produces an etch rate that is a factor of 2 higher than the rate obtained for the more frequently used mixture of HF/HNO 3 in a 1 : 2 ratio. We further observe that the quality of etching is improved for either pure HF or HF/HNO 3 in a 1 : 4 ratio, again by comparison with use of a 1 : 2 ratio. These results lead to a discussion of the etch chemistry involved, and an explanation for the observed high degree of differential etching between the zz and 2z crystal faces.
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