In this work, we report the feasibility of the silver nanowire (AgNW) foils as highly-sensitive, reproducible and facile detection tools for surface-enhanced Raman spectroscopy (SERS) applications. These flexible and free-standing AgNW foils, fabricated by vacuum filtration method following a modified polyol synthesis of AgNWs, are adequately structured for both biological specimen filtering and trace amount of molecule detection simultaneously. The compatibility of AgNW foil in SERS is investigated by using a Raman active molecule of different steric volumes across the filter cross-section. We have shown that AgNW foils exhibit extremely strong SERS activity with detection limit up to 10-9 M of crystal violet (CV) molecule with 20% variation over ~cm2, revealing reliable homogeneity of the acquired signal. While naturally occurring polyvinylpyrrolidone (PVP) layer during polyol synthesis contribute to controlled aggregation, oxidation prevention, and size - shape control purposes, it also creates a major challenge for obtaining enormous enhancement factors. However, controlled thickness of aluminum oxide (Al2O3) coating on PVP@AgNW foils affords to achieve higher enhancement factors than the uncoated ones. What is interesting is that the maximum intensity is achieved from two cycles of Al2O3 deposited on AgNW foils. This is attributed to the two different origins: first, a higher adsorption affinity of CV molecules to Al2O3 layer than PVP layer; second, tunneling barrier formation against quantum tunneling effects.
In this work, the electron-carrier-selectivity of ALD deposited TiO2 contact on n-type and p-type c-Si wafers is presented. The optical, compositional, and diode quality dependence of TiO2 on the ALD deposition temperature were analyzed using spectroscopic ellipsometry, AFM, XPS, GI-XRD, and CV measurements. By optimizing the ALD process parameters, an impressive effective minority carrier lifetime of up to 2.3 milliseconds corresponding to an iVoc of ~700 mV was obtained from wet chemical oxide-SiO2/TiO2 passivation stack layers. Finally, the asymmetry in C-V and J-V measurements betweenTiO2/n-type and TiO2/p-type c-Si heterojunctions was examined and the electron transport selectivity of TiO2 was revealed.
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