First-principles modeling of unpassivated and surfactant-passivated bulk facets of wurtzite CdSe: a model system for studying the anisotropic growth of CdSe nanocrystals

Equilibrium geometries, surface energies, and surfactant binding energies are calculated for selected bulk facets of wurtzite CdSe with a first-principles approach. Passivation of the surface Cd atoms with alkyl phosphonic acids or amines lowers the surface energy of all facets, except for the polar 000 facet. On the nonpolar facets, the most stable configuration corresponds to full coverage of surface Cd atoms with surfactants, while on the polar 0001 facet it corresponds only to a partial coverage. In addition, the passivated surface energies of the nonpolar facets are in general lower than the passivated polar 0001 facet. Therefore, the polar facets are less stable and less efficiently passivated than the nonpolar facets, and this can rationalize the observed anisotropic growth mechanism of wurtzite nanocrystals in the presence of suitable surfactants.     

Controlling the reversible wetting capability of smart photochromic-polymer surfaces by micro patterning

We demonstrate the wetting behavior control of polymer surfaces doped with photochromic molecules by modifying the surface patterning features introduced by soft molding lithography. Such surfaces enhance their hydrophilicity upon UV irradiation due to conversion of the non-polar spiropyran dopant molecules to their polar merocyanine isomers. The process is reversed upon visible light irradiation. By changing the topological parameters of the introduced pattern, one achieves surface tuning from hydrophobic to hydrophilic situations. The difference for the contact angles between UV- and green-irradiated surfaces may become significantly higher than for the flat surfaces, for the specific patterning parameters analyzed. PACS 42.62.-b; 68.08.Bc; 83.50.Uv; 42.70.Jk; 42.70.Gi     

Einfluß der Kolloide auf die Dissoziation der Elektrolyte,III

Ohne Zusammenfassung Deutsch von L. Vanzetti (Padua).     

Stimulated photoluminescence of CdTe

Emission spectra of CdTe at low temperature under high intensity optical pumping by means of a tunable dye laser are reported.We show that the optical gain process is enhanced when a high exciton density is achieved by means of quasi-resonant pumping. The mechanism responsible for the amplification process is found to be the well-known exciton-exciton scattering.     

InSe electrical characterization by means of transport parameters

SCLC measurements in single crystals of the layered semiconductor n-type InSe are reported. The measurements were carried out at various temperatures and on samples grown with indium added in excess (from 5 to 10%). The experimental results suggest that the trapping levels location and the charge transport are dependent on the indium excess. Only the samples grown with an indium excess of about 5% show the features typical of intrinsic semiconductors. The anomalous behaviour of samples grown with indium excess between 6 and 10 is explained by means of scattering mechanisms between charge carriers and ionized impurity centers.     

Pmr characterization of diastereomeric forms of acyclic compounds bearing two equivalent chiral atoms in 1,5-positions

Assignment of configurations to diastereomeric pairs was based on anisochronism of diastereotopic protons of suitable probe groups, at various distances from both chiral centers.     

Multiphoton conductivity in KBr

Multiphoton conductivity measurements at room temperature on KBr monocrystals are reported. The experimental results show evidence of two- and four-photon processes and confirm the assignment of the optical gap obtained by means of two-photon spectroscopy.     

On the conduction welding process of steels with the CO2 laser

Experiments on laser conduction seam welding were carried out with a 500 W CO₂ laser. Low carbon and stainless steel samples were butt welded and the optimum working conditions were found. An accurate analysis of these results showed such excellent agreement with the theoretical models that an a priori method could be formulated to calculate the values of all the related parameters, even including the laser focal spot radius to be used to ensure the best utilization of the beam energy.     

Absolute determination of the two photon cross section in NADH

Experimental evidence of two photon absorption in NADH coenzyme at ruby frequency is reported. The γ₂ non linear two photon cross section has been measured by means of two different experimental methods. The high absolute value found (γ₂ = 3.4 x 10^-48cm⁴s) confirms that the reaction rate modifications of NADH under laser irradiation are due to non-linear absorption processes.