Nitrogen (N)-doped graphitic layers were deposited as shells on pregrown silicon nanowires by chemical vapor deposition. Graphite-like and pyridine-like structures were selectively chosen for 3 and 10% N doping, respectively. Increasing the thickness of the undoped graphitic layers from 20 to 50 nm led to an increase in the charge capacity of the lithium ion battery from 800 to 1040 mA h/g after 45 cycles. Graphitelike 3% N-doping in the 50 nm-thick shell increases the charge capacity by 21% (i.e., to 1260 mA h/g), while pyridine-like 10% N-doping in the 20 nm-thick shell increases it by 36% (i.e., to 1090 mA h/g). This suggests that both pyridine-and graphitelike structures can be effective for lithium intercalation. First principles calculations of the graphene sheets show that the large storage capacity of both N-doping structures comes from the formation of dangling bonds around the pyridine-like local motives upon lithium intercalation.

Vertically aligned ZnO--CdSSe core-shell nanocable arrays were synthesized with a controlled composition and shell thickness (10-50 nm) by the chemical vapor deposition on the pregrown ZnO nanowire arrays. They consisted of a composition-tuned single-crystalline wurtzite structure CdS1-xSex (x=0, 0.5, and 1) shell whose [0001] direction was aligned along the [0001] wire axis of the wurtzite ZnO core. The analysis of structural and optical properties shows the formation of Zn containing alloy in the interface region between the ZnO core and shell, which can facilitate the growth of single-crystalline shell layers by reducing both the lattice mismatch and the number of defect sites. In contrast, the TiO2 (rutile) nanowire array can form the polycrystalline shell under the same condition. The photoelectrochemical cell using the ZnO--CdS photoelectrode exhibits a higher photocurrent and hydrogen generation rate than that using the TiO2-CdS one. We suggest that the formation of the CdZnSSe intermediate layers contributes to the higher photoelectrochemical cell performance of the ZnO--CdSSe nanocables.

In x Ga 1Àx As (0 e x e 1) alloy nanowires (average diameter = 50 nm) were synthesized at 800 °C with complete composition tuning by the thermal evaporation of GaAs/InAs powders. X-ray diffraction and Raman spectroscopy confirmed the complete composition tuning over the whole range. They exhibit exclusively a superlattice structure composed of zinc blende phase twinned octahedral slice segments having alternating orientations along the axial [111] direction and wurtzite phase twin planes. When the mole fraction (x) approaches 0.5, the period of the twinned superlattice structures becomes shorter, showing a controlled wurtziteÀzinc blende polytypism. At x = 0.5, the wurtzite phase is dominant with the shortest superlattice periodicity (∼2 nm). The smaller diameter consistently induces shorter periodic superlattice structures. This unique polytypism shows that the incorporation of In (or Ga) and the smaller diameter promotes the crystallization of the nanowires in the wurtzite phase. These In x Ga 1Àx As nanowires produce an efficient THz emission, showing minimized carrier mobility at x = 0.5, where the superlattice stacking faults are maximized.

Abstract:We investigate the mode of action and classification of antibiotic agents (ceftazidime, patulin, and epigallocatechin gallate; EGCG) on Pseudomonas aeruginosa (P. aeruginosa) biofilm using Raman spectroscopy with multivariate analysis, including support vector machine (SVM) and principal component analysis (PCA). This method allows for quantitative, label-free, non-invasive and rapid monitoring of biochemical changes in complex biofilm matrices with high sensitivity and specificity. In this study, the biofilms were grown and treated with various agents in the microfluidic device, and then transferred onto gold-coated substrates for Raman measurement. Here, we show changes in biochemical properties, and this technology can be used to distinguish between changes induced in P. aeruginosa biofilms using three antibiotic agents. The Raman band intensities associated with DNA and proteins were decreased, compared to control biofilms, when the biofilms were treated with antibiotics. Unlike with exposure to ceftazidime and patulin, the Raman spectrum of biofilms exposed to EGCG showed a shift in the spectral position of the CH deformation stretch band from 1313 cm −1 to 1333 cm −1 , and there was no difference in the band intensity at 1530 cm −1 (C = C stretching, carotenoids). The PCA-SVM analysis results show that antibiotic-treated biofilms can be detected with high sensitivity of 93.33%, a specificity of 100% and an accuracy of 98.33%. This method also discriminated the three antibiotic agents based on the cellular biochemical and structural changes induced by antibiotics with high sensitivity and specificity of 100%. This study suggests that Raman spectroscopy with PCA-SVM is potentially useful for the rapid identification and classification of clinically-relevant antibiotics of bacteria biofilm. Furthermore, this method could be a powerful approach for the development and screening of new antibiotics.

Complete composition-tuned CdS x Se 1Àx alloy layers (avg. thickness ¼ 50 nm) were deposited on pregrown TiO 2 nanowires by the thermal vapor transport of CdS/CdSe powders, producing core-shell nanocable arrays. CdS x Se 1Àx alloy nanowires were also synthesized with full composition tuning by the same method for comparison. The CdSSe nanowires consisted of Se-rich and S-rich pseudo binary phases, while the nanocable shell consisted of more complex multinary phases including CdSe and CdS. Remarkably, unique CdS-CdSSe-CdSe multishell structures were produced in the Se-rich composition range. The photoelectrochemical (PEC) cells fabricated using the as-grown nanocable arrays show higher solar photocurrents and hydrogen generation rates for the Se-rich shelled TiO 2 nanocable arrays. This suggests that the CdS-CdSSe-CdSe multishell structures increase greatly the PEC performance by producing novel band alignment for efficient electron-hole separation following enhanced visible-range photon absorption.