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Due to its electronic-grade quality and potential for scalability, two-dimensional (2D) MoS2 synthesized by chemical vapor deposition (CVD) has been widely explored for electronic/optoelectronic applications. As 2D MoS2 can be considered a 100% surface, its unique intrinsic properties are inevitably altered by the substrate upon which it is grown. However, systematic studies of substrate-layer interactions in CVD-grown MoS2 are lacking. In this study, we have analyzed builtin strain and charge doping using Raman and photoluminescence spectroscopy in 2D MoS2 grown by CVD on four unique substrates: SiO2/Si, sapphire, Muscovite mica, and hexagonal boron nitride. We observed decreasing strain and charge doping in grown MoS2 as the substrates become less rough and more chemically inert. The possible origin of strain was investigated through atomic force microscopy roughness measurements of the as-grown layer and substrate. Our results provide direction for device optimization through careful selection of the growth substrate and pave the way for further investigations to unravel the complex nature of the 2D monolayer-substrate interface. [ABSTRACT FROM AUTHOR]

Plasmonic phenomena in metals have garnered significant scientific and technological interest in the past decade. Despite many promising applications based on plasmonics, one remaining challenge is to control the surface geometry or morphology of the metallic structures, which can significantly affect the plasmonic properties of nanostructures. Here, we report the morphological modulation of gold (Au) nanopatterns on atomically thin layered molybdenum disulfide (MoS2), compared to Au nanopatterns grown on SiO2/Si substrate. We have used electron energy loss spectroscopy in a scanning transmission electron microscope to probe the locally enhanced surface plasmons in nanoporous Au patterns grown on SiO2/Si substrate as well as on single- and few-layer MoS2 flakes. Thin flakes of MoS2 as substrates significantly influence the morphology of Au patterns, which locally alters the plasmonic behavior. Features such as nanoscale pores exhibit plasmon localization with strong near fields, akin to "hot spots." Boundary element method simulations demonstrate that the dipolar and breathing modes can be excited at different positions of the nanopatterns. [ABSTRACT FROM AUTHOR]

The generation and presence of strain around nanostructures of oxides is a key to their growth, properties, and functions, but it has been a challenge to experimentally measure its sign, magnitude, and spatial distribution. Combining diffuse scattering with scanning x-ray nanodiffraction, we have mapped the strain distribution in an oxide-on-oxide nanopatterned structure with a high sensitivity (10-4) and a submicrometer spatial resolution. An edge-induced strain distribution is observed from a sample of CoFe2O4 nanolines epitaxially grown on MgO substrate, which agrees quantitatively with the numerical simulations. [ABSTRACT FROM AUTHOR]

We report on high resolution imaging of self assembled monolayers using atomic force microscopy (AFM) in aqueous environment using thermal drift corrected cantilevers. Thermal drift of the AFM probes limit the possibilities of experiments that are designed to resolve single macromolecule dynamics in aqueous conditions. We present a method of minimizing the thermal drift of the AFM cantilevers under aqueous conditions, thus paving way for getting high resolution images of molecular self assembly. This methodology, which is based on a very high resolution silicon probe attached to silicon cantilever, low-force touch due to tapping mode at each pixel in the AFM field, enables the high resolution nondestructive imaging with minimal thermal drift. [ABSTRACT FROM AUTHOR]

The effects of UV illumination on the electronic properties and gas sensing performance of ZnO are reported. It is found that UV light improves the sensitivity and the sensor response and recovery rate. By investigating the photoresponse behavior of ZnO, we observe that the electrons generated by UV light promote the adsorption of oxygen and form the photoinduced oxygen ions [O2-(hv)]. These ions [O2-(hv)] are responsible for the room-temperature gas sensing phenomena and promise enhanced sensor performance through further optimization. [ABSTRACT FROM AUTHOR]

We explore various metal-oxide-semiconductor field-effect transistor (MOSFET)-embedded microcantilever designs to assess their performance as an efficient nanomechanoelectronic signal transduction platform for monitoring deflection in microcantilever-based phenomena such as biochemical sensing and actuation. The current-voltage characteristics of embedded MOSFETs show current noise in the nanoampere range with a large signal-to-noise ratio sufficient to provide measureable output signal. The change in drain current with cantilever deflection is consistent with the effect of stress on carrier mobility and drain current reported in previous studies, validating that the MOSFET cantilevers can directly transduce deflection of a microcantilever into reproducible change in electrical signal. [ABSTRACT FROM AUTHOR]

The authors report fabrication of multiferroic BiFeO3 (BFO) by the soft electron beam lithography technique. BiFeO3 nanopatterns with less than 100 nm characteristic dimension are fabricated from its liquid-phase precursor on diverse substrates. The chemical constituents and phase purity are characterized by transmission electron microscopy. The ferroelectric behavior is confirmed by piezoresponse force microscopy. A saturation magnetization of about 10 emu/cm3 is observed, demonstrating the multiferroic characteristic of the BFO nanopatterns. Furthermore, the BFO nanolines pattened on SrTiO3 substrate exhibit a bamboolike structure, which can serve as an excellent model system for investigating the contribution of grain boundaries to the leakage current. [ABSTRACT FROM AUTHOR]

In oxide grain boundaries (GBs), oxygen ions and their vacancies serve as a common denominator in controlling properties such as GB barrier height and capacitance. Therefore, it is critical to analyze, control and manipulate oxygen and vacancies at oxide interfaces as most of the practical devices are almost always influenced by the presence of electrostatic potential barriers at interfaces. Here, we report adjustment of a single GB potential barrier via manipulation of oxygen vacancy concentration using simple oxidation and reduction treatments. We validate our analysis with aberration-corrected HAADF imaging and column-by-column EELS coupled with macroscopic transport measurements of isolated GBs to gain important insight into the physical attributes of GB potential barriers. [ABSTRACT FROM AUTHOR]

Controlled patterning of conducting polymers at a micro- or nanoscale is the first step towards the fabrication of miniaturized functional devices. Here, we introduce an approach for the nanopatterning of conducting polymers using an improved monomer “ink” in dip-pen nanolithography (DPN). The nominal monomer “ink” is converted, in situ, to its conducting solid-state polymeric form after patterned. Proof-of-concept experiments have been performed with acid-promoted polymerization of pyrrole in a less reactive environment (tetrahydrofuran). The ratios of reactants are optimized to give an appropriate rate to match the operation of DPN. A similar synthesis process for the same polymer in its bulk form shows a high conductance and crystalline structure. The miniaturized conducting polymer sensors with light detection ability are fabricated by DPN using the improved ink formula, and exhibit excellent response, recovery, and sensitivity parameters. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A scaleable and site-specific patterning approach with individual addressability is demonstrated via an electropolymerization process within the gap of electrodes. The method can pattern conducting polymer structures by applying a bias between desired electrodes in a monomer vapor. The reaction is proposed to happen in a thin water film condensed inside the electrode gap at ambient environment. It is possible to pattern different conducting polymers on the same substrate by exposing to different monomers. Proof-of-concept experiments on pyrrole and thiophene have shown the generality of this simple and robust method, which enables the real-time monitoring of the resistance and deposition of the conducting polymers. Finally, chemical sensing of the patterned polypyrrole structures to ethanol vapor and ammonia gas are presented. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

AC four-point impedance spectroscopy has been applied to Nb-doped SrTiO[sub 3] bicrystals. Due to the simplified geometry and highly conductive bulk of the bicrystal, the reference impedance of the electrode was significantly reduced, validating the applicability of ac four-point impedance spectroscopy for electroceramics. DC current-voltage characteristics without any interference due to electrodes confirmed these ac measurements. Using ac four-point impedance spectroscopy, grain boundary contributions are isolated and the corresponding grain boundary thickness and resistivity are estimated. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Due to its electronic-grade quality and potential for scalability, two-dimensional (2D) MoS2 synthesized by chemical vapor deposition (CVD) has been widely explored for electronic/optoelectronic applications. As 2D MoS2 can be considered a 100% surface, its unique intrinsic properties are inevitably altered by the substrate upon which it is grown. However, systematic studies of substrate-layer interactions in CVD-grown MoS2 are lacking. In this study, we have analyzed builtin strain and charge doping using Raman and photoluminescence spectroscopy in 2D MoS2 grown by CVD on four unique substrates: SiO2/Si, sapphire, Muscovite mica, and hexagonal boron nitride. We observed decreasing strain and charge doping in grown MoS2 as the substrates become less rough and more chemically inert. The possible origin of strain was investigated through atomic force microscopy roughness measurements of the as-grown layer and substrate. Our results provide direction for device optimization through careful selection of the growth substrate and pave the way for further investigations to unravel the complex nature of the 2D monolayer-substrate interface. [ABSTRACT FROM AUTHOR]

We report here the direct observation of high resolution structures of assemblies of Alzheimer beta-amyloid oligomers and monomers using liquid atomic force microscopy (AFM). Visualization of nanoscale features of Abeta oligomers (also known as ADDLs) was carried out in tapping mode AFM in F12 solution. Our results indicate that ADDL preparations exist in solution primarily as a mixture of monomeric peptides and higher molecular mass oligomers. Our study clearly reveals that the size and shape of these oligomer aggregates exhibit a pronounced dependence on concentration. These studies show that wet AFM enables direct assessment of oligomers in physiological fluids and suggests that this method may be developed to visualize Abeta oligomers from human fluids.