Surface redox induced bipolar switching of transition metal oxide films examined by scanning probe microscopy

The bipolar resistive switching mechanisms of a p-type NiO film and n-type TiO₂ film were examined using local probe-based measurements. Scanning probe-based current–voltage (I–V) sweeps and surface potential/current maps obtained after the application of dc bias suggested that resistive switching is caused mainly by the surface redox reactions involving oxygen ions at the tip/oxide interface. This explanation can be applied generally to both p-type and n-type conducting resistive switching films. The contribution of oxygen migration to resistive switching was also observed indirectly, but only in the cases where the tip was in (quasi-) Ohmic contact with the oxide.     

Nanosecond laser ablation and deposition of silicon

Nanosecond-pulsed KrF (248 nm, 25 ns) and Nd:YAG (1064 nm, 532 nm, 355 nm, 5 ns) lasers were used to ablate a polycrystalline Si target in a background pressure of <10⁻⁴ Pa. Si films were deposited on Si and GaAs substrates at room temperature. The surface morphology of the films was characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Round droplets from 20 nm to 5 μm were detected on the deposited films. Raman Spectroscopy indicated that the micron-sized droplets were crystalline and the films were amorphous. The dependence of the properties of the films on laser wavelengths and fluence is discussed.     

Synthesis of 2-amino-3-cyano-4H-chromen-4-ylphosphonates and 2-amino-4H-chromenes catalyzed by tetramethylguanidine

Synthesis of 2-amino-4H-chromen-4-ylphosphonates and 2-amino-4H-chromenes has been accomplished by the reaction of salicylaldehyde, malononitrile, dialkyl/diphenylphosphites catalyzed by 1,1,3,3-tetramethylguanidine (TMG) under neat conditions at room temperature. The applicability of catalytic TMG for the synthesis of 2-amino-4H-chromenes also has been described. The mild reaction conditions, simple work-up procedure, and use of TMG as an inexpensive catalyst provides an economical protocol for the preparation of important phosphorus-containing compounds.     

Hierarchically‐ordered electroactive silica‐polyaniline nanohybrid: A novel material with versatile properties

Poly(trimethoxy silylpropylaniline), a nanoporous (pore diameter of 2.4 nm), electroactive (stable reversible redox characteristics), electrochromic (yellow at ?0.10 V, blue green at +0.50 V, and dark green at +0.70 V), and pH‐sensitive, silica–polyaniline (PANI) hybrid material (designated as KGM‐1) has been synthesized in powder form by a simple one‐pot chemical synthesis as well as a “thin nanolayered film” by cyclic voltammetry. High‐resolution transmission image of KGM‐1 informs that the particles are spherical, with diameters in the range of 0.5–1.5 μm. X‐ray diffraction pattern of pristine KGM‐1 confirms the combined presence of ordered silica network and PANI chains. The surface area of calcined KGM‐1 is 40 m²/g (～15 times higher than KGM‐1), and the average pore size is 2.4 nm. The N₂ adsorption features also inform that PANI is present as a uniform layer within the pores of silica and because of that the silica pores are not completely blocked. The reversible redox transitions in PANI units and nanoporosity of KGM‐1 are effectively used for the electro‐driven loading/release of DNA or adenosine 5′‐triphosphate. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Mechanism of light emission in low energy ion implanted silicon

A silicon wafer implanted with a single low energy (42 keV) silicon ion beam results in strong luminescence at room temperature. The implantation results in the formation of various luminescent defect centers within the crystalline and polymorphous regions of the wafer. The resulting luminescence centers (LC) are mapped using fluorescence lifetime imaging microscopy (FLIM). The emission from the ion-implanted wafer shows multiple PL peaks ranging from the UV to the visible; these emissions originate from bound excitonic states in crystal defects and interfacial states between crystalline/amorphous silicon and impurities within the wafer. The LCs are created from defects and impurities within the wafer and not from nanoparticles.