A single molecule switch based on two Pd nanocrystals linked by a conjugated dithiol

Tunneling spectroscopy measurements have been carried out on a single molecule device formed by two Pd nanocrystals (dia, $\sim$5 nm) electronically coupled by a conducting molecule, dimercaptodiphenylacetylene. The I-V data, obtained by positioning the tip over a nanocrystal electrode, exhibit negative differential resistance (NDR) on a background M-I-M characteristics. The NDR feature occurs at $\sim$0.67 V at 300 K and shifts to a higher bias of 1.93 V at 90 K. When the tip is held in the middle region of the device, a coulomb blockade region is observed ($\pm\sim$0.3 V).Comment: Accepted in Praman

Optimization and Development of Swellable Controlled Porosity Osmotic Pump Tablet for Theophylline

Purpose: To develop swellable controlled porosity osmotic pump tablet of theophylline and to define the formulation and process variables responsible for drug release by applying statistical optimizationtechnique.Methods: Formulations were prepared based on Taguchi Orthogonal Array design and Fraction Factorial design for core and coating, respectively. The tablets were prepared by direct compression and wet granulation methods; spray coated with ethyl cellulose solution containing varying amounts ofPEG 400 and plasdone. Drug release from the osmotic drug delivery system was studied using USP Type I paddle type apparatus. The membrane morphology of the delivery system was determined byscanning electron microscopy (SEM).Results: Optimization results indicated that the release rate of theophylline from the swellable controlled porosity osmotic pump tablet is directly proportional to the levels of osmotic agent, solubilizing agent andpore former in the tablet core and the membrane, respectively. SEM showed the formation of pores in the membrane through which drug release occurred. The best formulation showed 98.2 % drug releaseand complied with USP requirements.Conclusion: The results confirmed that the factors responsible for drug release were osmotic agents (core) and pore former (membrane). Also, the preparation of swellable controlled porosity osmotic pumptablet was facilitated by coating the core tablet with pore forming agent, thus eliminating the need for the more expensive laser drilling

In situ carbon coated Li2MnSiO4/C composites as cathodes for enhanced performance li-ion batteries

An in-situ carbon coated Li2MnSiO4/C composite was synthesized by a nanocomposite gel precursor route using starch as the carbon source. Our approach enabled a uniform coating of amorphous carbon on Li 2MnSiO4 with an orthorhombic crystalline structure, which was confirmed by electron microscopy, X-ray diffraction and Raman studies. Conducting-atomic force microscopy (C-AFM) images also revealed the presence of high current interconnected domains in the composite, indicating the ability of the carbon coating to facilitate electron movement. Galvanostatic charge-discharge studies demonstrated outstanding initial charge and discharge capacities, respectively, of 330 and 195 mAh g-1 at 0.05 C-rate for the composite, and after 30 cycles a reversible capacity of 115 mAh g -1 was retained. The electrochemical performance of the neat silicate was dismal (10.6 mAh g-1 at 0.05 C-rate), which again reiterated the role of carbon in improving the conduction and Li-ion storage capacity of the silicate. An insignificant change in charge transfer resistance, with cycling, as inferred from impedance spectroscopy illustrated that charge transfer and transport processes remain facile with cycling, thus demonstrating Li 2MnSiO4/C to be promising cathode Li-ion batteries

Ferromagnetism as a universal feature of nanoparticles of the otherwise nonmagnetic oxides

Room-temperature ferromagnetism has been observed in the nanoparticles (7 - 30 nm dia) of nonmagnetic oxides such as CeO2, Al2O3, ZnO, In2O3 and SnO2. The saturated magnetic moments in CeO_2 and Al_2O_3 nanoparticles are comparable to those observed in transition metal doped wide band semiconducting oxides. The other oxide nanoparticles show somewhat lower values of magnetization but with a clear hysteretic behavior. Conversely, the bulk samples obtained by sintering the nanoparticles at high temperatures in air or oxygen became diamagnetic. As there were no magnetic impurities present, we assume that the origin of ferromagnetism may be due to the exchange interactions between localized electron spin moments resulting from oxygen vacancies at the surfaces of nanoparticles. We suggest that ferromagnetism may be a universal characteristic of nanopartilces of metal oxidesComment: 6 pages, 4 figure

A novel method of preparing thiol-derivatised nanoparticles ofgold, platinum and silver forming superstructures

Thiol-derivatised nanoparticles of Au, Pt and Ag (diameter 1-10 nm) forming superstructures, are prepared by the acid-facilitated transfer of well characterized particles in a hydrosol to a toluene layer containing the thiol

Experimental and theoretical electronic charge densities in molecular crystals

Electronic charge density distribution in molecular systems has been described in terms of the topological properties. After briefly reviewing methods of obtaining charge densities from X-ray diffraction and theory, typical case studies are discussed. These studies include rings and cage systems, hydrogen bonded solids, polymorphic solids and molecular NLO materials. It is shown how combined experimental and theoretical investigations of charge densities in molecular crystals can provide useful insights into electronic structure and reactivity

Effect of size on the Coulomb staircase phenomenon in metal nanocrystals

The Coulomb staircase in polymer-covered Pd and Au nanocrystals of varying diameters in the 1.7-6.4 nm has been investigated by employing tunneling conductance measurements. Charging up to several electrons is observed at room temperature in the I-V data. Small nanocrystals show charging steps exceeding 200 mV while the larger ones exhibit smaller steps. Significantly, the charging energies follow a scaling law of the form, U=A+B/d, where d is the diameter of the nanocrystal. Furthermore, the line widths in the derivative spectra also vary inversely with the diameter

Dip-pen lithography using aqueous metal nanocrystal dispersions

Dip-pen lithography has been successfully demonstrated on mica substrates employing hydrosols of polyvinylpyrrolidone-capped Pd nanocrystals as well as Au nanocrystals stabilized by tetrakishydroxymethyl phosphonium chloride. Lines of widths as small as 30 nm and various aspect ratios have been successfully drawn by this method