Tuning the Crystallinity and Coverage of SiO2-ZnIn2S4 Core-Shell Nanoparticles for Efficient Hydrogen Generation.

The coverage, thickness, and crystallinity of ZnIn2S4 (ZIS) shells on SiO2 core nanoparticles (SiO2@ZIS) were systematically investigated using microwave-assisted solvothermal methods aided by the addition of acid in ethanolic medium. The surface modification of the SiO2 cores with (3-mercaptopropyl)trimethoxysilane was found to be critical to generate a homogeneous coverage of ZnIn2S4. The SiO2@ZIS core-shell nanoparticles exhibited the best coverage but poor crystallinity when synthesized in pure ethanol, whereas best crystallinity but poor coverage was observed when synthesized in an aqueous solution. The addition of selected amounts of acid (HCl) led to improved crystallinity in the ethanolic medium. The thickness of the ZIS shell could be controlled in an ethanolic solution by judiciously varying the amounts of acid and the concentration of the ZIS precursor. Increasing the concentration of the ZIS precursor to twice the standard concentration in ethanolic solution with the addition of 100 µL of HCl afforded better crystallinity, homogeneous coverage, and optimal photocatalytic hydrogen production.

Forced flow atomic layer deposition of TiO2 on vertically aligned Si wafer and polysulfone fiber: Design and efficacy of conduit plates and soak function.

The effectiveness of three different designs of conduit plates was verified for even distribution of precursors in a voluminous forced-flow atomic layer deposition (ALD) chamber designed to hold macroscopic elongated substrates vertically. Furthermore, a new "soak function" was introduced in the controlling software of the ALD instrument. This function enabled increase in residence time of the precursor in the chamber without escalating the dosage. The flow of precursors guided by the conduit plates with and without application of the soak function was simulated using computational fluid dynamics. A conformal coating of TiO2 with good uniformity on Si and porous polysulfone fibers was achieved to evidence the design and efficacy of conduit plates and soak function.

Uniform coating of Ta2O5 on vertically aligned substrate: A prelude to forced flow atomic layer deposition.

Uniform tantalum oxide thin films, with a growth rate of 0.6 Å/cycle, were fabricated on vertically aligned, 10 cm-long, silicon substrates using an innovative atomic layer deposition (ALD) design. The ALD system, with a reaction chamber depth of 13.3 cm and 18 vertical enclosed channels (inner diameter 1.3 cm), was coupled with a shower-head type precursor conduit plate bearing 6 radial channels. This design enabled deposition on 6 silicon substrates at a time. The degrees of non-uniformity of deposits along the length of the silicon wafer and across different positions in the ALD chamber were found to be 1.77%-6.21% and 3.27%-5.45%, respectively. A further advantage of the design is that the conduit plate may be modified and the number of channels increased to process 18 substrates simultaneously, thus moving toward efficient and expedited ALD systems.

Enabling higher photoelectrochemical efficiency of TiO2via controlled formation of a disordered shell: an alternative to the hydrogenation process.

A simple one-step and low-temperature process was developed to form an amorphous overlayer on the crystalline TiO2 film by atomic layer deposition. This composite structure is beneficial for improved photoelectrochemical efficiency since the as-deposited amorphous layer showed unique properties such as local disorder and presence of oxygen vacancies.