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This work describes morphological and crystalline properties of the InAs islands grown on templates created by focused ion beam (FIB) on indium phosphide (InP) substrates. Regular arrangements of shallow holes are created on the InP (001) surfaces, acting as preferential nucleation sites for InAs islands grown by Metal-Organic Vapor Phase Epitaxy. Ion doses ranging from 1015 to 1016 Ga+/cm2 were used and islands were grown for two sub-monolayer coverages. We observe the formation of clusters in the inner surfaces of the FIB produced cavities and show that for low doses templates the nanostructures are mainly coherent while templates created with large ion doses lead to the growth of incoherent islands with larger island density. The modified island growth is described by a simple model based on the surface potential and the net adatom flow to the cavities. We observe that obtained morphologies result from a competition between coarsening and coalescence mechanisms. more...

Ag/TiO 2 thin films have been prepared on glass substrates by the dip-coating technique and sol–gel process using a precursor solution containing titanium alkoxide and silver nitrate in an Ag/Ti atomic ratio of 1:6 and 1:100. These films were annealed at 100 °C and 400 °C and cooled rapidly to obtain silver nanoparticles dispersed in an amorphous TiO 2 matrix, confirmed by X-ray diffraction (XRD) analyses. Ag/TiO 2 nanocrystalline films were also prepared using slow cooling. Silver nanoparticles coalesced and migrated to the thin film surfaces with increasing annealing temperature as observed by high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and scanning probe microscopy (SPM). A transmission electron microscope (TEM) was used to induce phase transition in the amorphous matrix into anatase and rutile crystalline phases using a 200 kV electron beam. The variation of the Ag/Ti atomic ratio changed the plasmon resonance absorption and band gap values of the Ag/TiO 2 films due to the change in the Ag nanoparticle sizes formed on the surface of films, as verified by UV–vis absorption spectroscopy and spectroscopic ellipsometry. more...

Ag-doped TiO2 wet gels were prepared by sol–gel process using a mixture of titanium isopropoxide and silver nitrate as precursor solution, with Ag:Ti molar ratio of 1:6. After drying, the titanium oxide xerogels were used as template in the preparation of nano and microcrystals of metallic silver. The porous network and the structure of the titania matrix influenced the type and distribution of silver crystal produced on the composite surface. Silver nanoparticles segregated to the surface of titania xerogel during the heating step, giving rise to nanocrystals that coalesced forming microcrystals with different shapes and faceting. The microcrystals grew on the composite surface, reaching sizes between 5 and 20 microns and self-organized of different ways. The xerogel heated at 600 °C formed by anatase, rutile and silver nanoparticles exhibited considerable photocatalytic activity to degrade methylene blue. more...

Iron silicide samples were grown on Si (111) substrates by solid phase epitaxy and reactive deposition epitaxy. The different iron silicide phases and their correlations with the growth parameters were analyzed by x-ray photoelectron spectroscopy, conversion electron Mossbauer spectroscopy, x-ray diffraction, atomic force microscopy, and magnetic force microscopy. The authors investigated the potential of each technique for identifying and quantifying of the phases. In particular, the authors used a semiquantitative analysis of magnetic force microscopy images to spatially resolve the semiconductor β-FeSi2 phase. more...

Iron silicides were grown on Si (111) substrates by Solid Phase Epitaxy (SPE) and Reactive Deposition Epitaxy (RDE) to identify the optimum conditions to obtain the semiconduting β-FeSi2 phase. The films were produced under different growth and annealing conditions and analyzed in situ and ex situ by X-ray Photoelectron Spectroscopy, and ex situ by Conversion Electron Mossbauer Spectroscopy. The use of these techniques allowed the investigation of different depth regions of the grown layer. Films of the ɛ-FeSi and β-FeSi2 phases were obtained as well as the mixtures Fe3Si + ɛ-FeSi and ɛ-FeSi + β-FeSi2. The sequence Fe3Si→ɛ-FeSi→β-FeSi2 was found upon annealing, where the phase transformation occurred due to the migration of silicon atoms from the substrate to the surface region of the grown layer. The best conditions for the phase transformation in SPE samples were met after annealing in the range 700 – 800 °C. For the RDE samples, the transition to the beta phase occurred between 600 and 700 °C, but pure β-FeSi2 was obtained only after two hours of annealing at 700 °C. more...

The epitaxial growth by reactive deposition of $\ensuremath{\epsilon}\text{-FeSi}$ and $\ensuremath{\beta}{\text{-FeSi}}_{2}$ nanodots on Si(111) is studied as a function of Fe coverage. The nanodots density, size, and strain were analyzed by atomic force microscopy and x-ray diffraction. Almost single phase $\ensuremath{\epsilon}\text{-FeSi}$ and $\ensuremath{\beta}{\text{-FeSi}}_{2}$ were formed at low and high iron coverage, respectively. A $\ensuremath{\epsilon}\text{-FeSi}$ to $\ensuremath{\beta}{\text{-FeSi}}_{2}$ change in phase formation is observed at Fe coverage of 5.5 nm, which is coincident with the coalescence of the nanodots, the relaxation of the strain in both phases and a discontinuous increase of the grain size of the $\ensuremath{\beta}{\text{-FeSi}}_{2}$ phase. A direct comparison of the diffraction and microscopy data shows that nanodots of different phases also exhibit different shapes, being the $\ensuremath{\epsilon}\text{-FeSi}$ $(\ensuremath{\beta}{\text{-FeSi}}_{2})$ nanodots smaller (larger) and with a low (high) aspect ratio. more...

We study the influence on the photocurrent of the final state in bound-to-quasibound transitions in self-assembled quantum dot infrared photodetectors. We investigate two structures designed to explore different mechanisms of carrier extraction and therefore achieve a better insight on these processes. We observe photocurrent in opposite directions, with positive and negative sign, for different incident frequencies at the same applied external electric field. This phenomenon is attributed to the asymmetry of the potential barriers surrounding the quantum dots. more...