Silver nanoparticle film induced photoluminescence enhancement of near-infrared emitting PbS and PbS/CdS core/shell quantum dots: observation of different enhancement mechanisms.

The photoluminescence (PL) enhancement of a Ag nanoparticle and near-infrared quantum dots (QD) plasmon/fluorophore system was investigated. Different enhancement mechanisms were obtained by tuning surface plasmon resonance of the Ag film and PL of the QDs. A maximum enhancement factor of 2.8 was achieved.

Photovoltaic effect in multiphase Bi-Mn-O thin films.

We report an external solar power conversion efficiency of ~0.1% in Bi-Mn-O thin films grown onto (111) oriented Niobium doped SrTiO3 (STO) single crystal substrate by pulse laser deposition (PLD). The films contain BiMnO3 (BMO) and Mn3O4 (MO) phases, which both grow epitaxially. The growth conditions were tailored to obtain films with different Bi/Mn ratios. The films were subsequently illuminated under a sun simulator (AM 1.5 G). We find that the Bi/Mn ratio in the film affects the magnitude of the photo induced voltage and photocurrent and therefore the photovoltaic conversion efficiency. Specifically, a higher Bi/Mn ratio (towards unity) in the film increases the power conversion efficiency. This effect is described in terms of a more favorable energy band alignment of the film/substrate hetero-structure junction, which controls photo carrier separation.

Mechanical and electrical properties of epitaxial Si nanowires grown by pulsed laser deposition.

We report on the elastic and piezoresistive properties of individual epitaxial Si-NWs grown on n-doped Si(111) by pulsed laser deposition. Using scanning probe microscopy, we obtained a Young's modulus between 82 and 900 GPa for the nanowires, unaffected by the nanowire shape. A relative resistivity change is observed in the prestrained (curved) Si-NWs, which we attribute to a large piezoresistance coefficient in the NW along its axis. Assuming that for the bent NWs the effect of longitudinal stress on resistivity is compensated, the piezoresistance coefficient originating in the shear strain alone, we found a piezoresistance gauge factor (GF) of 600, which is close to the values reported in literature for Si-NWs.

Multiferroic nanoscale Bi2FeCrO6 material for spintronic-related applications.

We report the control of the growth mode of Bi(2)FeCrO(6) thin and ultrathin films by either tuning the pulsed laser deposition parameters or by using a buffer layer. The films are epitaxial and the heterostructures exhibit very smooth interfaces, thus eliminating the main obstacle in the realization of tunnel junctions. By characterizing the functional properties of thin films we find that Bi(2)FeCrO(6) retains its room temperature multiferroic character even at the nanoscale. The coexistence of these properties in ultra-thin Bi(2)FeCrO(6) films will pave the way to design multifunctional devices for applications in spintronics and electronics, such as ferroelectric tunnel junctions or magnetic tunnel junctions with ferroelectric barriers.

Multiferroic properties-structure relationships in epitaxial Bi(2)FeCrO(6) thin films: recent developments.

We report recent developments in the growth and characterization of epitaxial Bi(2)FeCrO(6) (BFCO) thin films. The body of experimental data stemming mostly from our investigations, and also considering the few available reports from other groups, allows us to explain the origin(s) of the thickness dependence of the multiferroic properties observed. A drastic reduction of the films' magnetization is observed for film thicknesses larger than 80 nm. This decrease in magnetization is attributed to the formation of defects, such as antisites and antiphase boundaries, in the BFCO films. The change in magnetization is accompanied by a BFCO cell expansion, a consequence of the volume increase of the oxygen octahedra surrounding the Fe cations induced by the defects. BFCO films are ferroelectric for all the thicknesses investigated, ferroelectricity being only moderately affected by the film thickness.

Modified Stranski-Krastanov growth in Ge/Si heterostructures via nanostenciled pulsed laser deposition.

The combination of nanostenciling with pulsed laser deposition (PLD) provides a flexible, fast approach for patterning the growth of Ge on Si. Within each stencilled site, the morphological evolution of the Ge structures with deposition follows a modified Stranski-Krastanov (SK) growth mode. By systematically varying the PLD parameters (laser repetition rate and number of pulses) on two different substrate orientations (111 and 100), we have observed corresponding changes in growth morphology, strain and elemental composition using scanning electron microscopy, atomic force microscopy and µ-Raman spectroscopy. The growth behaviour is well predicted within a classical SK scheme, although the Si(100) growth exhibits significant relaxation and ripening with increasing coverage. Other novel aspects of the growth include the increased thickness of the wetting layer and the kinetic control of Si/Ge intermixing via the PLD repetition rate.