RESUMEN
Laser ablation of bulk target materials in liquids has been established as an alternative method for the synthesis of nanoparticles colloidal solutions mainly due to the fact that the synthesized nanoparticles have bare, ligand-free surfaces since no chemical precursors are used for their synthesis. InSb is a narrow band gap semiconductor which has the highest carrier mobility of any known semiconductor and nanoparticles of this material are useful in optoelectronic device fabrication. In this paper a bulk InSb target was ablated in deionized (DI) water or ethanol using a nanosecond (20 ns) or a femtosecond (90 fs) pulsed laser source, for nanoparticles synthesis. In all four cases the largest percentage of the nanoparticles are of InSb in the zincblende crystal structure with fcc lattice. Oxides of either In or Sb are also formed in the nanoparticles ensembles in the case of ns or fs ablation, respectively. Formation of an oxide of either element from the two elements of the binary bulk alloy is explained based on the difference in the ablation mechanism of the material in the case of ns or fs pulsed laser irradiation in which the slow or fast deposition of energy into the material results to mainly melting or vaporization, respectively under the present conditions of ablation, in combination with the lower melting point but higher vaporization enthalpy of In as compared to Sb. InSb in the metastable phase with orthorhombic lattice is also formed in the nanoparticles ensembles in the case of fs ablation in DI water (as well as oxide of InSb) which indicates that the synthesized nanoparticles exhibit polymorphism controlled by the type of the laser source used for their synthesis. The nanoparticles exhibit absorption which is observed to be extended in the infrared region of the spectrum.
RESUMEN
The automation of the mica surface displacement of a surface force apparatus (SFA) increases the accuracy of the intermolecular force measurements that is obtained without the presence of the experimenter. The automatic device cancels any thermal drift and the stability of the mica surfaces is optimum. The distance between the mica surfaces is measured by Tolansky multiple-beam interferometry (FECO method) which offers a sensitivity of 0.1 nm in the direction perpendicular to the plane of contact area. The mean refractive index of the medium between the mica plates is computed from simultaneous measurements of the wavelengths of two successive fringes of equal chromatic order (FECO). A conversion of an isotropic molecule to another anisotropic molecule can be identified from the variations of the refractive index. In good conditions, we can compute the local concentration of the molecules in the gap of the device, and estimate the Young's modulus of a protein.