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Atomically thin WO3is fabricated using a three-step process, involving wet-chemical synthesis of hydrated-WO3, mechanical exfoliation of fundamental layers and dehydration by annealing at 300 °C. Atomic force microscopy reveals that the minimum resolvable thickness of the hydrated flakes to be ∼1.4 nm, which corresponds to the unit-cell height. The subsequent annealing temperature determines the degree of dehydration and thereby the crystallographic structure of the resultant WO3. The hydrated and dehydrated flakes are characterized by Raman spectroscopy to reveal spectroscopic fingerprints of flake thickness. Thin flakes are also shown to have higher propensity for lithium intercalation, which is also evidenced in Raman planar peak intensity. [ABSTRACT FROM AUTHOR]

Active droplets play important roles in microfluidics, robotics, and micro-electromechanical systems. As a special class of active droplets that are conductive, reactive, and of high surface tension, liquid metal droplets (LMDs) can be driven by electric-field-induced surface (Marangoni) flows to function as reconfigurable components in actuators, sensors, catalytic reactors, and antennas. Stimulating LMDs using an electric field induces concurrent electro-hydrodynamic flows and electrochemical surface oxidation (passivation). It is however difficult to decouple these two effects which brings complexity in controlling LMD motions. To address this challenge, pulse time modulation (PTM) signals are used. PTM enables controlled LMD displacement by propelling the droplets forward during the voltage-on phases and facilitating surface recovery from oxidation during the voltage-off phases. Counterintuitively, by taking such intermittent "rests", the LMDs effectively inhibit the unfavorable impact of oxidation, granting high motion controllability. Combining high-speed imaging, motion tracking, machine learning, and electrochemical analysis, the study reveals how electro-hydrodynamic flows and surface oxide formation/dissolution interplay to generate well-defined motion regimes. The study further develops a quasi-analytical model to describe droplet motions and designs a rotary LMD motor to showcase the versatility of the approach. This work provides the fundamental framework and viable strategy for designing innovative liquid metal-based systems. [ABSTRACT FROM AUTHOR]

We demonstrate a facile localized reduction approach to synthesizing a Au nanoparticle-decorated Keggin ion/TiO2photococatalyst for improved solar light photocatalysis application. This has been achieved by exploiting the ability of TiO2-bound Keggin ions to act as a UV-switchable, highly localized reducing agent. Notably, the approach proposed here does not lead to contamination of the resultant cocatalyst with free metal nanoparticles during aqueous solution-based synthesis. The study shows that for Keggin ions (phosphotungstic acid, PTA), being photoactive molecules, the presence of both Au nanoparticles and PTA on the TiO2surface in a cocatalytic system can have a dramatic effect on increasing the photocatalytic performance of the composite system, as opposed to a TiO2surface directly decorated with metal nanoparticles without a sandwiched PTA layer. The remarkable increase in the photocatalytic performance of these materials toward the degradation of a model organic Congo red dye correlates to an increase of 2.7-fold over that of anatase TiO2after adding Au to it and 4.3-fold after introducing PTA along with Au to it. The generalized localized reduction approach to preparing TiO2–PTA–Au cocatalysts reported here can be further extended to other similar systems, wherein a range of metal nanoparticles in the presence of different Keggin ions can be utilized. The composites reported here may have wide potential implications toward the degradation of organic species and solar cell applications. [ABSTRACT FROM AUTHOR]

An initiator is applied to synthesize single-walled carbon nanotube/polyaniline composite nanofibers for use as high-performance chemosensors. The composite nanofibers possess widely tunable conductivities (10−4to 102S/cm) with up to 5.0 wt % single-walled carbon nanotube (SWCNT) loadings. Chemosensors fabricated from the composite nanofibers synthesized with a 1.0 wt % SWCNT loading respond much more rapidly to low concentrations (100 ppb) of HCl and NH3vapors compared to polyaniline nanofibers alone (120 s vs 1000 s). These nanofibrillar SWCNT/polyaniline composite nanostructures are promising materials for use as low-cost disposable sensors and as electrodes due to their widely tunable conductivities. [ABSTRACT FROM AUTHOR]

A microfluidic dielectrophoresis platform consisting of curved microelectrodes was developed and integrated with a Raman spectroscopy system. The electrodes were patterned on a quartz substrate, which has insignificant Raman response, and integrated with a microfluidic channel that was imprinted in poly-dimethylsiloxane (PDMS). We will show that this novel integrated system can be efficiently used for the determination of suspended particle types and the direct mapping of their spatial concentrations. We will also illustrate the system's unique advantages over conventional optical systems. Nanoparticles of tungsten trioxide (WO3) and polystyrene were used in the investigations, as they are Raman active and can be homogeneously suspended in water. [ABSTRACT FROM AUTHOR]

Among the available metal oxide nanostructures, tungsten oxide has remained, at times, troublesome to fabricate, with many synthetic methods often requiring exotic equipment and or reagents. In this work, we present a systematic investigation demonstrating a new method for the deposition of anhydrous and hydrated nanostructured tungsten oxide thin films via spin coating. The attributes of these materials include the following: high surface area, controllable deposition, and compatibility with existing semiconductor fabrication infrastructure making this method a suitable candidate for application in the manufacture of gas sensors and dye sensitized solar cells. We will show that it is possible to form micrometer thick highly crystalline nanostructured thin films and, using Raman, SEM, XRD, XPS, and TEM analysis, will prove that these nanostructures can be rendered into anhydrous or partially or fully hydrated tungsten oxides. We further demonstrate the application of these materials in the fabrication of an inexpensive NO2gas sensor, capable of sensing sub-ppm levels of NO2concentrations at a modest operating temperature of 175 °C. [ABSTRACT FROM AUTHOR]

We have investigated several key aspects for the self-organization of nanotubes in RF sputtered titanium (Ti) thin films formed by the anodization process in fluoride-ion-containing neutral electrolytes. Ti films were deposited on indium tin oxide (ITO) glass substrates at room temperature and 300 °C, and then anodized. The films were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV−vis spectrometry before and after anodization. It was observed that anodization of high temperature deposited films resulted in nanotube type structures with diameters in the range of 10−45 nm for an applied voltage of 5−20 V. In addition, the anatase form of TiO2is formed during the anodization process which is also confirmed using photocurrent measurements. However, the anodization of room temperature deposited Ti films resulted in irregular pores or holes. [ABSTRACT FROM AUTHOR]

This paper reports the electrowetting properties of ZnO nanorods. These nanorods were grown on indium tin oxide (ITO) substrates using different liquid-phase deposition techniques and hydrophobized with sputtered Teflon. The surfaces display superhydrophobic properties. When the applied voltages are less than 35 V, the contact angle change is small and exhibits instant reversibility. For higher voltages, larger contact angle changes were observed. However, the surface was not reversible after removing the applied voltage and required mechanical agitation to return to its initial superhydrophobic state. [ABSTRACT FROM AUTHOR]