Direct evidence is provided for the transition from surface conduction (SC) to electro-osmotic flow (EOF) above a critical channel depth (d) of a nanofluidic device. The dependence of the overlimiting conductance (OLC) on d is consistent with theoretical predictions, scaling as d −1 for SC and d 4=5 for EOF with a minimum around d ¼ 8 μm. The propagation of transient deionization shocks is also visualized, revealing complex patterns of EOF vortices and unstable convection with increasing d. This unified picture of surface-driven OLC can guide further advances in electrokinetic theory, as well as engineering applications of ion concentration polarization in microfluidics and porous media.

Silicon nanocrystals were in situ grown in a silicon nitride film by plasma-enhanced chemical vapor deposition. The size and structure of silicon nanocrystals were confirmed by high-resolution transmission electron microscopy. Depending on the size, the photoluminescence of silicon nanocrystals can be tuned from the near infrared (1.38eV) to the ultraviolet (3.02eV). The fitted photoluminescence peak energy as E(eV)=1.16+11.8∕d2 is evidence for the quantum confinement effect in silicon nanocrystals. The results demonstrate that the band gap of silicon nanocrystals embedded in silicon nitride matrix was more effectively controlled for a wide range of luminescent wavelengths.

Current in vitro skin models do not recapitulate the complex architecture and functions of the skin tissue. In particular, on-chip construction of an in vitro model comprising the epidermis and dermis layer with vascular structure for mass transport has not been reported yet. In this study, we aim to develop a microfluidic, three-dimensional (3D) skin chip with fluidic channels using PDMS and hydrogels. Mass transport within the collagen hydrogel matrix was verified with fluorescent model molecules, and a transport-reaction model of oxygen and glucose inside the skin chip was developed to aid the design of the microfluidic skin chip. Comparison of viabilities of dermal fibroblasts and HaCaT cultured in the chip with various culture conditions revealed that the presence of flow plays a crucial role in maintaining the viability, and both cells were viable after 10 days of air exposure culture. Our 3D skin chip with vascular structures can be a valuable in vitro model for reproducing the interaction between different components of the skin tissue, and thus work as a more physiologically realistic platform for testing skin reaction to cosmetic products and drugs.

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The photoluminescence (PL) property of crystalline silicon quantum dots (Si QDs) in silicon nitride grown by using ammonia and silane gases is reported. The peak position of PL could be controlled in the wavelength range from 450 to 700 nm by adjusting the flow rates of ammonia and silane gases. The PL intensity of Si QDs grown by ammonia was more intense compared to that of Si QDs grown by nitrogen gas. To investigate the role of hydrogen in the PL enhancement, the Si QDs grown by nitrogen gas were postannealed under hydrogen ambient. The enhancement in PL intensity was attributed to the hydrogen passivation of dangling bonds related to silicon and/or nitrogen at the interface of Si QDs and silicon nitride.