ABSTRACT
We report the successful demonstration of a hybrid system that combines pulsed laser deposition (PLD) and magnetron sputtering (MS) to deposit high quality thin films. The PLD and MS simultaneously use the same target, leading to an enhanced deposition rate. The performance of this technique is demonstrated through the deposition of titanium dioxide and bismuth-based perovskite oxide Bi2FeCrO6 (BFCO) thin films on Si(100) and LaAlO3 (LAO) (100). These specific oxides were chosen due to their functionalities, such as multiferroic and photovoltaic properties (BFCO) and photocatalysis (TiO2). We compare films deposited by conventional PLD, MS and PLD combined with MS, and show that under all conditions the latter technique offers an increased deposition rate (+50%) and produces films denser (+20%) than those produced by MS or PLD alone, and without the large clusters found in the PLD-deposited films. Under optimized conditions, the hybrid technique produces films that are two times smoother than either technique alone.
ABSTRACT
We demonstrate the promising potential of using perovskite Bi2FeCrO6 (BFCO) for niche applications in photovoltaics (PV) (e.g. self-powered sensors that simultaneously exploit PV conversion and multiferroic properties) or as a complement to mature PV technologies like silicon. BFCO thin films were epitaxially grown on silicon substrates using an MgO buffer layer. Piezoresponse force microscopy measurements revealed that the tensile strained BFCO phase exhibits a polarization predominantly oriented through the in-plane direction. The semiconducting bandgap of the ordered BFCO phase combined with ferroelectric properties, opens the possibility of a ferroelectric PV efficiency above 2% in a thin film device and the use of ferroelectric materials simultaneously as solar absorber layers and carrier separators in PV devices. A large short circuit photocurrent density of 13.8 mA cm(-2) and a photovoltage output of 0.5 V are typically obtained at FF of 38% for BFCO devices fabricated on silicon. We believe that the reduced photovoltage is due to the low diffusion length of photogenerated charge carriers in the BFCO material where the ferroelectric domains are predominately oriented in-plane and thus do not contribute efficiently to the photocharge separation process.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
We report the local electronic and magnetic properties of Bi(2)FeCrO(6) nanostructures by element-specific polarized x-ray techniques. Sizable magnetic ordering in the remanent state is observed at room temperature for both Fe and Cr ions. The Bi(2)FeCrO(6) system offers an example of d(5)-d(3) magnetic superexchange interaction with a magnetic order for both Fe and Cr, which are both formally in the + 3 valence state. The results suggest a coexistence of antiferromagnetic and ferromagnetic superexchange interaction between Fe and Cr spins in the nanostructures at the remanent state and at room temperature.
Subject(s)
Bismuth/chemistry , Iron Compounds/chemistry , Magnets/chemistry , Nanostructures/chemistry , Oxides/chemistry , Algorithms , Materials Testing , Temperature , X-Ray DiffractionABSTRACT
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.
