An attempt to correlate surface physics with chemical properties: molecular beam and Kelvin probe investigations of Ce1-xZrxO2 thin films.

What is the correlation between physical properties of the surfaces (such as surface potential, electronic nature of the surface), and chemical and catalysis properties (such as chemisorption, sticking probability of surface)? An attempt has been made to explore any correlation that might exist between the physical and chemical properties of thin film surfaces. Kelvin probe microscopy (KPM) and the molecular beam (MB) methods were employed to carry out the surface potential, and oxygen adsorption and oxygen storage capacity (OSC) measurements on Ce1-xZrxO2 thin films. A sol-gel synthesis procedure and spin-coating deposition method have been applied to make continuous nanocrystalline Ce1-xZrxO2 (x = 0-1) (CZ) thin films with uniform thickness (35-50 nm); however, surface roughness and porosity inherently changes with CZ composition. MB studies of O2 adsorption on CZ reveal high OSC for Ce0.9Zr0.1O2, which also exhibits highly porous and significantly rough surface characteristics. The surface potential observed from KPM studies varied between 30 and 80 mV, with Ce-rich compositions exhibiting the highest surface potential. Surface potential shows large changes after reduction or oxidation of the CZ film demonstrating the influence of Ce3+/Ce4+ on surface potential, which is also a key to catalytic activity for ceria-based catalysts. The surface potential measured from KPM and the OSC measured from MB vary linearly and they depend on the Ce3+/Ce4+ ratio. More and detailed studies are suggested to arrive at a correlation between the physical and chemical properties of the surfaces.

Curcumin-Loaded, Self-Assembled Aloevera Template for Superior Antioxidant Activity and Trans-Membrane Drug Release.

Fine combination of natural botanical extracts to evaluate and maximize their medicinal efficacy has been studied for long. However, their limited shelf-life, complicated extraction protocols, and difficult compositional analysis have always been a problem. It is due to this that such materials take time to convert them into a proper pharmaceutical technology or product. In this context, we report on synthesis of self-assembled template of one of the most popular natural product, aloevera. This forms a fine porous membrane like structure, in which a natural drug, curcumin has been immobilized/trapped. The so-made curcumin-loaded-aloevera (CLA) structures have been carefully evaluated using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), atomic force microscopy (AFM), UV-vis spectroscopy and fluorescence microscopy. While FTIR shows that there is no chemical interaction between aloevera and curcumin, the pores are finely occupied by curcumin molecules. Fine microscopy structures reveal their distribution and fluorescence microscopy confirm the presence of curcumin within the pores. TGA shows 15% loading of the curcumin in the template and UV-visible spectroscopy data shows independent peaks of both, aloevera (196 nm and 256 nm) and curcumin (423 nm), respectively. When subjected to antioxidant studies, using DPPH assays, CLAs show a synergistically superior DPPH radical scavenging activity as compared to only curcumin and only aloevera extract. Same is true for hydroxyl and NO2 radicals. Trans-membrane release study reveals that there is no significant difference in the amount of curcumin release from CLAs till initial 30 min, however, it increases steadily thereafter. CLA is found to facilitate efficient release of curcumin in 5 h, which is higher as compared to the curcumin alone.

Electron transport in dodecylamine capped gold nanocluster films using current sensing atomic force microscope (C-AFM).

Electron transport across cataphoretically deposited dodecylamine capped gold nanocluster rough films on Si(111) substrate is investigated using current sensing atomic force microscopy. Contact mode images depict uniform deposition of agglomerates of gold nanoparticles. The current images display strong correlation with topographic images. The I-V measurement on a single agglomerate of approximately = 250 nm size at different forces exhibits force dependent threshold voltage. The electron transport from tip to sample is found to be ohmic in contrast to that from sample to tip which, exhibits Fowler-Nordheim behavior up to 35 nN force. At higher forces, the I-V behavior could be attributed to other electron transfer processes such as Schottky/Poole-Frenkel or trapping/detrapping, although no exact mechanism could be identified. The results are discussed in the light of models based on Coulomb blockaded collective charge transport in nanoparticle arrays duly accounting for the potential role of the capping layer.

Some aspects of pulsed laser deposited nanocrystalline LaB(6) film: atomic force microscopy, constant force current imaging and field emission investigations.

Nanocrystalline lanthanum hexaboride (LaB(6)) films have been deposited on molybdenum foil by the pulsed laser deposition (PLD) technique. The as-deposited films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD pattern shows the cubic crystallinity of the LaB(6) film. The AFM studies reveal that the conical shaped LaB(6) nanostructures have height 60 nm, base 800 nm, and a typical radius of curvature ∼20 nm. A comparison of force and in situ current imaging AFM studies reveals that current contrast does not originate from the surface topography of the LaB(6) film. Field emission studies have been performed in the planar diode configuration. A current density of 4.4 × 10(-2) A cm(-2) is drawn from the actual emitting area. The Fowler-Nordheim plot is found to be linear, in accordance with the quantum mechanical tunneling phenomenon. The field enhancement factor is estimated to be 3585, indicating that the field emission is from LaB(6) nanocrystallites present on the emitter surface, as confirmed by the AFM. The emission current-time plots show current stability to the extent of 5% fluctuation about the average current over a period of 3 h.