Tiling the Silicon for Added Functionality: PLD Growth of Highly Crystalline STO and PZT on Graphene Oxide-Buffered Silicon Surface.

The application of two-dimensional (2D) materials has alleviated a number of challenges of traditional epitaxy and pushed forward the integration of dissimilar materials. Besides acting as a seed layer for van der Waals epitaxy, the 2D materials─being atom(s) thick─have also enabled wetting transparency in which the potential field of the substrate, although partially screened, is still capable of imposing epitaxial overgrowth. One of the crucial steps in this technology is the preservation of the quality of 2D materials during and after their transfer to a substrate of interest. In the present study, we show that by honing the achievements of traditional epitaxy and wet chemistry a hybrid approach can be devised that offers a unique perspective for the integration of functional oxides with a silicon platform. It is based on SrO-assisted deoxidation and controllable coverage of silicon surface with a layer(s) of spin-coated graphene oxide, thus simultaneously allowing both direct and van der Waals epitaxy of SrTiO3 (STO). We were able to grow a high-quality STO pseudo-substrate suitable for further overgrowth of functional oxides, such as PbZr1-xTixO3 (PZT). Given that the quality of the films grown on a reduced graphene oxide-buffer layer was almost identical to that obtained on SiC-derived graphene, we believe that this approach may provide new routes for direct and "remote" epitaxy or layer-transfer techniques of dissimilar material systems.

Correlating Structural Properties with Electrochemical Behavior of Non-graphitizable Carbons in Na-Ion Batteries.

We report on a detailed structural versus electrochemical property investigation of the corncob-derived non-graphitizable carbons prepared at different carbonization temperatures using a combination of structural characterization methodology unique to this field. Non-graphitizable carbons are currently the most viable option for the negative electrode in sodium-ion batteries. However, many challenges arise from the strong dependence of the precursor's choice and carbonization parameters on the evolution of the carbon matrix and its resulting electrochemistry. We followed structure development upon the increase in carbonization temperature with thorough structural characterization and electrochemical testing. With the increase of carbonization temperature from 900 to 1600 °C, our prepared materials exhibited a trend toward increasing structural order, an increase in the specific surface area of micropores, the development of ultramicroporosity, and an increase in conductivity. This was clearly demonstrated by a synergy of small- and wide-angle X-ray scattering, scanning transmission electron microscopy, and electron-energy loss spectroscopy techniques. Three-electrode full cell measurements confirmed incomplete desodiation of Na+ ions from the non-graphitizable carbons in the first cycle due to the formation of a solid-electrolyte interface and Na trapping in the pores, followed by a stable second cycle. The study of cycling stability over 100 cycles in a half-cell configuration confirmed the observed high irreversible capacity in the first cycle, which stabilized to a slow decrease afterward, with the Coulombic efficiency reaching 99% after 30 cycles and then stabilizing between 99.3 and 99.5%. Subsequently, a strong correlation between the determined structural properties and the electrochemical behavior was established.

An investigation on focused electron/ion beam induced degradation mechanisms of conjugated polymers.

Irradiation damage, caused by the use of beams in the electron microscopes, leads to undesired physical/chemical material property changes or uncontrollable modification of structures that are being processed. Particularly, soft matter such as polymers or biological materials is highly susceptible and very much prone to react on irradiation by electron and ion beams. The effect is even higher when materials are subjected to energetic species such as ions that possess high momentum and relatively low mean path due to their mass. Especially when Ga(+) ions (used as the ion source in Focused Ion Beam (FIB) instruments) are considered, the end-effect might even be the total loss of the material's properties. This paper will discuss the possible types of degradation mechanisms and defect formations that can take place during ion and electron beam irradiation of the conjugated polymers: e.g. polyfluorene (PF) and poly-3-hexylthiophene (P3HT) thin films. For the investigation of the irradiation induced degradation mechanisms in this study, complementary analytical techniques such as Raman Spectroscopy (RS), Infrared Spectroscopy (IR), Electron Energy Loss Spectroscopy (EELS), Atomic Force Microscopy (AFM), and Fluorescence Microscopy including Photoluminescence (PL) and Electroluminescence (EL) Microscopy were applied.

Modifying the Silver-Titania Nanocomposites with Carbonaceous Materials to Remove the Pollutants from Domestic Waste Water.

The aim of this study was to prepare and characterize nanostructured composites based of TiO2, carbonaceus materials (GN or GO) and Ag and the test their capacity to remove the pollutants from domestic wastewater. The composites were characterized by IR and UV-Vis spectroscopy, X-ray diffraction, electron microscopy and nitrogen adsorption-desorption measurements. The photocatalytic activity was measured from the experiment of salicylic acid (SA) degradation. The capacity to remove the pollutants from domestic wastewater was performed by considering the absorbance of residual solution at 200 nm. The non-calcined composites have high specific surface area (˜300 m²/g), but nitrogen adsorption-desorption isotherms showed a porous structure with closed pores. The porosity of the thermal treated composites is about 10 times less, but the pores are open. The salicylic acid was 94% degraded over all composites, showing their efficient photoactivity. A percent of 70% of pollutants were removed over the calcined composites with GN and ˜67% on those with GO. It was no statistically significant difference between the photocatalytical efficiency of GN- and GO-based composites. Even if the calcined composites have the specific surface area about 10 times lower, their lower gap energy, higher degree of crystallinity and photocatalytic activity make them efficient candidates for removal of pollutants from domestic waste water. The photodegradation mechanism occurred mostly by π-π interactions between GN/GO and pollutant molecules.

Compositional and structural study of a (K0.5Na0.5)NbO3 single crystal prepared by solid state crystal growth.

In this work we investigated the chemical composition and structure of (K0.5Na0.5)NbO3 (KNN) single crystals grown by the solid state crystal growth method. The optical, scanning, and transmission electron microscopies were employed for the analysis of the chemical homogeneity and domain structure of the KNN crystal. No compositional inhomogeneities within experimental error were encountered in the KNN single crystals. The domain structure of the KNN single crystal, with a monoclinic unit cell, is composed of large 90 degrees domains of up to 100 microm width, which further consist of smaller 180 degrees domains with widths from 50 to 300 nm.