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We present measurements comparing scanning thermal microscopy in air and vacuum. Signal levels are compared and resolution is probed by scanning over the edge of a nanofabricated Ag square embedded in SiO2. Signals measured in air were seen to be 2.5 to 40 times larger than in vacuum. Furthermore, the air signals were stable while the vacuum signals varied significantly. Edge widths measured in air were approximately 39 % larger than those measured in vacuum. Our observations are consistent with the air measurements experiencing heat transfer from the surrounding sample via conduction and convection as well as the formation of a water-related meniscus at the tip-sample junction. These results contribute to the understanding of the complex heat exchange effects that can occur in scanning thermal microscopy when it is conducted in an ambient atmosphere., Comment: 8 pages, 5 figures

We demonstrate that ambient pressure x-ray photoelectron spectroscopy (APXPS) can be used for in situ studies of dynamic changes in surface chemistry in a plasma environment. Hexagonal boron nitride (h-BN) was used in this study as a model system since it exhibits a wide array of unique chemical, optical, and electrical properties that make it a prospective material for advanced electronics. To better understand the stability and surface chemistry of h-BN during plasma-assisted processing, we used polycrystalline Cu foils with single-layer h-BN, grown via chemical vapor deposition (CVD), and tracked in real-time the plasma-induced reduction of the underlying Cu oxide using APXPS equipped with 22 kHz 75 W discharge plasma source operating at 13 Pa. Residual gas analysis (RGA) mass-spectra were concurrently collected during plasma-XPS to track reaction products formed during plasma exposure. A clear reduction of CuxO is seen, while an h-BN layer remains intact, suggesting H radical species can attack the exposed and h-BN-covered Cu oxide patches and partially reduce the underlying substrate. In addition to the demonstration and discussion of plasma-XPS capabilities, our results indicate the h-BN encapsulated metallic Cu interface might be repaired without significantly damaging the overlaying h-BN, which is of practical importance for the development of h-BN encapsulated devices and interfaces

Electrical double layers play a key role in a variety of electrochemical systems. The mean free path of secondary electrons in aqueous solutions is on the order of a nanometer, making them suitable for probing of ultrathin electrical double layers at solid-liquid electrolyte interfaces. Employing graphene as an electron-transparent electrode in a two-electrode electrochemical system, we show that the secondary electron yield of the graphene-liquid interface depends on the ionic strength and concentration of electrolyte and applied bias at the remote counter electrode. These observations have been related to polarization-induced changes in the potential distribution within the electrical double layer and demonstrate the feasibility of using scanning electron microscopy to examine and map electrified liquid-solid interfaces

Additive fabrication of biocompatible 3D structures out of liquid hydrogel solutions has become pivotal technology for tissue engineering, soft robotics, biosensing, drug delivery, etc. Electron and X-ray lithography are well suited to pattern nanoscopic features out of dry polymers, however, the direct additive manufacturing in hydrogel solutions with these powerful tools is hard to implement due to vacuum incompatibility of hydrated samples. In this work, we resolve this principal impediment and demonstrate a technique for in-liquid hydrogel 3D-sculpturing separating high vacuum instrumentation and volatile sample with ultrathin molecularly impermeable membranes transparent to low-energy electrons and soft X-rays. Using either scanning focused electron or synchrotron soft X-ray beams, the principle of the technique, particularities of the in-liquid crosslinking mechanism and factors affecting the ultimate gel feature size are described and validated through the comparison of experiments and simulations. The potential of this technique is demonstrated on a few practical examples such as encapsulation of nanoparticles and live-cell as well as fabrication of mesoscopic 3D-hydrogel structures via modulation of the beam energy, Comment: 24 pages, 11 figures

Recent developments in environmental and liquid cells equipped with electron transparent graphene windows have enabled traditional surface science spectromicroscopy tools, such as X-ray photoelectron spectroscopy (XPS), photoemission electron microscopy (PEEM), and scanning electron microscopy (SEM) to be applied to study solid-liquid and liquid-gas interfaces. Here, we focus on the experimental implementation of PEEM to probe electrified graphene-liquid interfaces using electrolyte-filled microchannel arrays as a new sample platform. We demonstrate the important methodological advantage of these multi-sample arrays: they enable the combination of the wide field of view hyperspectral imaging capabilities from PEEM with the use of powerful data mining algorithms to reveal spectroscopic and temporal behaviors at the level of the individual microsample or the entire array ensemble, Comment: 14 pages 6 figures 47 references

Metal oxide resistive switches are increasingly important as possible artificial synapses in next generation neuromorphic networks. Nevertheless, there is still no codified set of tools for studying properties of the devices. To this end, we demonstrate electron beam induced current measurements as a powerful method to monitor the development of local resistive switching in TiO2 based devices. By comparing beam-energy dependent electron beam induced currents with Monte Carlo simulations of the energy absorption in different device layers, it is possible to deconstruct the origins of filament image formation and relate this to both morphological changes and the state of the switch. By clarifying the contrast mechanisms in electron beam induced current microscopy it is possible to gain new insights into the scaling of the resistive switching phenomenon and observe the formation of a current leakage region around the switching filament. Additionally, analysis of symmetric device structures reveals propagating polarization domains., Comment: 27 Pages 10 figures

Photoelectron emission microscopy PEEM is a powerful tool to spectroscopically image dynamic surface processes at the nanoscale but is traditionally limited to ultra high or moderate vacuum conditions. Here, we develop a novel grapheme capped multichannel array sample platform that extends the capabilities of photoelectron spectromicroscopy to routine liquid and atmospheric pressure studies with standard PEEM setups. Using this platform, we show that graphene has only a minor influence on the electronic structure of water in the first few layers and thus will allow for the examination of minimally perturbed aqueous phase interfacial dynamics. Analogous to microarray screening technology in biomedical research, our platform is highly suitable for applications in tandem with large-scale data mining, pattern recognition, and combinatorial methods for spectro temporal and spatiotemporal analyses at solid liquid interfaces. Using Bayesian linear unmixing algorithm, we were able to discriminate between different X-ray induced water radiolysis scenarios and observe a metastable wetting intermediate water layer during the late stages of bubble formationformation, Comment: 20 pages, 4 figures

We present a field theory approach to study changes in local temperature due to an applied electric field (the electrocaloric effect) in electrolyte solutions. Steric effects and a field-dependent dielectric function are found to be of paramount importance for accurate estimations of the electrocaloric effect. Interestingly, electrolyte solutions are found to exhibit negative electrocaloric effects. Overall, our results point toward using fluids near room temperature with low heat capacity and high salt concentration for enhanced electrocalorics., Comment: 25 pages, 5 figures

Sensing response of individual single-crystal titania nanowires configured as chemiresistors for detecting reducing (CO, H2) and oxidizing (O2) gases is shown to be sensitive to visible light illumination. It is assumed that doping of the TiO2 nanowires with C and/or N during carbon assisted vapor-solid growth creates extrinsic states in the band gap close to the valence band maximum, which enables photoactivity at the photon energies of visible light. The inherently large surface-to-volume ratio of nanowires, along with facile transport of the photo-generated carriers to/from the nanowires surface promote the adsorption/desorption of donor/acceptor molecules, and therefore open the possibility for visible light assisted gas sensing. The photo-catalytic performance of TiO2 nanowire chemiresistors demonstrates the prospect of combining light harvesting and sensing action in a single nanostructure.

We performed self-consistent modelling of electrotransport and electromechanical response of solid electrolyte thin films allowing for steric effects of mobile charged defects (ions, protons or vacancies), electron degeneration and Vegard stresses. We establish correlations between the features of the space-charge dynamics, current-voltage and bending-voltage curves in the wide frequency range of applied electric voltage. The pronounced ferroelectric-like hysteresis of bending-voltage loops and current maxima on double hysteresis current-voltage loops appear for the electron-open electrodes. The double hysteresis loop with pronounced humps indicates the resistance switching of memristor-type. The switching occurs due to the strong coupling between electronic and ionic subsystem. The sharp meta-stable maximum of the electron density appears near one open electrode and moves to another one during the periodic change of applied voltage. Our results can explain the nature and correlation of electrical and mechanical memory effects in thin films of solid electrolytes. The analytical expression proving that the electrically induced bending of solid electrolyte films can be detected by interferometric methods is derived., Comment: 28 pages including 8 figures, 3 tables and supplement