RESUMEN
Laser beam (He-Ne - 6328 A0) induced deflection in uncoated, Au, and Al coated Si microcantilevers (MCs) of various dimensions was studied, using an AFM head, to examine the induced stress contribution from photothermal and photostriction phenomenon. The laser beam was made to incident sequentially on front and back surfaces of the MC, by flipping it, and results were compared in terms of deflection magnitude, direction of bending and response time. In case of uncoated MCs, it was observed that the induced deflection was always in the direction of the incident laser beam with a fast response. In contrast, in metal (Au, Al) coated MCs, deflection direction was found to be dependent on laser beam exposure side with two orders of enhanced deflection sensitivity and slow response time. The former is attributed to photostriction effect while the latter is explained on the basis of photothermal effect in bimetallic MCs. Flipping experiments on bimettalic MCs, further revealed that stress contribution from these two source mechanisms crucially depends on MC dimensions and direction of laser exposure.
RESUMEN
This Letter reports on nanomechanical and optical properties of yttrium thin films deposited on an Si (100) wafer. Elemental depth profiling by a secondary ion mass spectrometer revealed absence of formation of yttrium hydride, both on the surface and beneath. The optical properties were investigated by spectroscopic ellipsometry, and the refractive indices extracted after suitable modeling were found to be 2.51 at 546 nm. Hardness and elastic modulus of these films were found to be 7 and 142 GPa, respectively. These studies indicate that yttrium thin films are suitable for x-ray mirrors, photocathode emitters in e-beam lithography, electron microscopes, and free-electron lasers.
RESUMEN
Thin films of nanocrystalline TiO2 were synthesized by spray pyrolysis technique in the temperature range 300 degrees C to 550 degrees C in steps of 50 degrees C. The films were coated on glass and quartz substrates by ultrasonic nebulization of titanium-oxy-acetyl acetonate followed by pyrolysis. The structure and morphology of the thin films were characterized by X-ray Diffraction (XRD), Raman Spectroscopy (RS) and Scanning Electron Microscopy (SEM), while the optical band gaps were measured by Spectroscopic Ellipsometry (SE) and UV-Visible spectroscopy. XRD investigations revealed distinct crystal structures of the films synthesized above and below 300 degrees C. While films grown at substrate temperature 300 degrees C were amorphous, those grown at 350 dgrees C and above showed tetragonal anatase crystal structure. The morphological investigations from SEM showed that the films deposited at 350 degrees C were porous and exhibited flower like morphology. The microstructures of the films grown on quartz at 450 degrees C were found to be uniform and dense. The nominal grain sizes evaluated from High Resolution SEM (HRSEM) studies were approximately 20 nm and compared well with the grain sizes calculated from XRD. The band gap values calculated from ellipsometry studies were approximately 3.7 eV and 3.95 eV for the films grown at 450 degrees C and 350 degrees C, respectively. This is in good agreement with those obtained from UV-Visible spectroscopy.