Uncapped silver nanoparticles synthesized by DC arc thermal plasma technique for conductor paste formulation

Uncapped silver nanoparticles were synthesized by DC arc thermal plasma technique. The synthesized nanoparticles were structurally cubic and showed wide particle size variation (between 20–150 nm). Thick film paste formulated from such uncapped silver nanoparticles was screen-printed on alumina substrates and the resultant ‘green’ films were fired at different firing temperatures. The films fired at 600 °C revealed better microstructure properties and also yielded the lowest value of sheet resistance in comparison to those corresponding to conventional peak firing temperature of 850 °C. Our findings directly support the role of silver nanoparticles in substantially depressing the operative peak firing temperature involved in traditional conductor thick films technology.     

Oxidation of Ni(Pt)Si by molecular vs. atomic oxygen

X-ray photoelectron spectroscopy (XPS) has been used to characterize the oxidation of a clean Ni(Pt)Si surface under two distinct conditions: exposure to a mixed flux of atomic and molecular oxygen (O + O₂; PO+O₂ = 5 × 10⁻⁶ Torr) and pure molecular oxygen (O₂; PO₂ = 10⁻⁵ Torr) at ambient temperatures. Formation of the clean, stoichiometric (nickel monosilicide) phase under vacuum conditions results in the formation of a surface layer enriched in PtSi. Oxidation of this surface in the presence of atomic oxygen initially results in formation of a silicon oxide overlayer. At higher exposures, kinetically limited oxidation of Pt results in Pt silicate formation. No passivation of oxygen uptake of the sample is observed for total O + O₂ exposure <8 × 10⁴ L, at which point the average oxide/silicate overlayer thickness is 23 (3) Å (uncertainty in the last digit in parentheses). In contrast, exposure of the clean Ni(Pt)Si surface to molecular oxygen only (maximum exposure: 5 × 10⁵ L) results in slow growth of a silicon oxide overlayer, without silicate formation, and eventual passivation at a total average oxide thickness of 8(1) Å, compared to a oxide average thickness of 17(2) Å (no silicate formation) for the as-received sample (i.e., exposed to ambient.) The aggressive silicon oxidation by atomic oxygen, results in Ni-rich silicide formation in the substrate and the kinetically limited oxidation of the Pt.     

Photon polarisation asymmetries in (p,p′γ) experiments

The Stokes parameters characterising the polarization of the photon in theγ-decay of¹²C*(1⁺) are examined in correlation with the scattered proton in¹²C(p,p′)¹²C*(1⁺). This opens up the possibility of efficiently determining empirically the six inelastic scattering amplitudes utilizing only 13 measurements. We identify several alternative sets of such measurements to encourage experimental efforts in this direction.     

Divergent stereoselectivity in the photoaddition of alkanals and medium ring cycloalkenes

Photocycloaddition of alkanals and cycloheptene, cyclooctene, and 1,5-cyclooctadiene results in stereoisomeric oxetanes, the composition of which depends on the concentration of starting alkene.     

Left-handed and ambidextrous helices in the gas phase

We have used ion mobility mass spectrometry to study the effect of d-residues on helix formation in unsolvated alanine-based peptides. The right-handed helix of AC-A15K + H+ is significantly disrupted when five or more of the natural L-residues are randomly replaced with D-residues. On the other hand, when a block of L-residues is replaced with D-residues, an unusual ambidextrous structure with helical segments of opposite chirality is formed. A peptide with all D-residues forms a left-handed helix.     

Cyclic chlorophosphites as scaffolds for the one-pot synthesis of α-aminophosphonates under solvent-free conditions

New α-aminophosphonates of the type (OCH₂CMe₂CH₂O)P(O)CH(NHCO₂R)(R′) [6a-i, 7a-e, and 8a-c] have been synthesized in high yields by a three-component reaction using (OCH₂CMe₂CH₂O)PCl (3), benzamide (or urethane or benzyl carbamate), and an aldehyde without using any catalyst under solvent-free conditions. This route can be readily adapted for bis-aminophosphonates as well as optically active binaphthoxy α-aminophosphonates; it also tolerates the phenolic -OH group as shown by the synthesis of hydroxy functionalized aminophosphonates. Partial hydrolysis of compounds 7a-d leads to products in which the phosphorinane ring is cleaved first. Compounds (OCH₂CMe₂CH₂O)P(O)CH[NHC(O)Ph](9-anthryl) (6f) and optically pure (R,S)-(−)-(C₂₀H₁₂O₂)P(O)CH(NHCO₂Et)(Ph) (14a) were characterized by X-ray crystallography.