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Scanning electron microscopy (SEM) of nanoscale objects in dry and fully hydrated conditions at different temperatures is of critical importance in revealing details of their interactions with an ambient environment. Currently available WETSEM capsules are equipped with thin electron-transparent membranes and allow imaging of samples at atmospheric pressure, but do not provide temperature control over the sample. Here, we developed and tested a thermoelectric cooling/heating setup for WETSEM capsules to allow ambient pressure in situ SEM studies with a temperature range between −15 and 100°C in gaseous, liquid, and frozen conditions. The design of the setup also allows for correlation of the SEM with optical microscopy and spectroscopy. As a demonstration of the possibilities of the developed approach, we performed real-time in situ microscopy studies of water condensation on a surface of Morpho sulkowskyi butterfly wing scales. We observed that initial water nucleation takes place on top of the scale ridges. These results confirmed earlier discovery of a preexisting polarity gradient of the ridges of Morpho butterflies. Our developed thermoelectric cooling/heating setup for environmental capsules meets the diverse needs for in situ nanocharacterization in material science, catalysis, microelectronics, chemistry, and biology.
Gold nanoclusters were successfully deposited in the interior of TiO2 nanotubes fabricated as ordered arrays. This approach is a useful fabrication platform for miniature planar fuel cells, gas sensors, and heterogeneous catalysts. A pressure impregnation process was used to inject the titania and Au precursors into mesoporous alumina. After thermal treatment, Au nanoclusters were well-dispersed on the interior walls of nanotubular TiO2. The TiO2 nanotubes were shown by x-ray diffraction to be entirely anatase. Transmission electron microscopy imaging confirmed that 80% of the Au particles were 4.1 nm ± 2.0 nm in diameter. This material exhibited catalytic CO oxidation activity at low temperatures.
Using a novel low-temperature process, we demonstrate the facile integration of crack-free nanostructured titania (NST) as sensing elements in microsystems. Unlike conventional sol-gel methods, NST layers of interconnected nano-walls and nano-wires were formed by reacting Ti surfaces with aqueous hydrogen peroxide solution. Cracks were observed in NST layers formed on blanket Ti films but absent on arrays of patterned Ti pads below a threshold dimension. Analyses using TEM, high resolution SEM, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveal that NST consists of anatase TiO2 nano-crystals. NST pads were found able to detect oxygen gas of a few ppm. NST pad arrays were integrated on rigid and flexible substrates with potential applications in low cost and wearable sensing systems.
MgO thin films having different defect densities are explored in this study using metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), temperature programmed desorption (TPD), and scanning tunneling microscopy (STM). Surface point defects on MgO exhibit themselves in both the MIES and UPS spectra as a feature approximately 2 eV above the valance band, whereas extended defects are only observed spectroscopically as a broadening of the O 2p band. The interaction of NO and N2O with the MgO surface as a function of surface defect density is explored. Upon adsorption on MgO thin films at 100K, both NO and N2O show the development of three features which coincide with a standard gas phase N2O spectrum. The saturation coverage of N2O from NO adsorption increases with increasing defect density, indicating that defect sites are mainly responsible for N2O formation. STM images confirm the increase of thin film defect density upon thermal quenching.
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