Danilo Barrionuevo

Thickness dependent functional properties of PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3 heterostructures

The ultra thin ferroelectric PbZr0.52Ti0.48O3 (PZT) films with various thicknesses ranging from 100 (P100) to 10 (P10) nm were grown on La0.67Sr0.33MnO3/(LaAlO3)0.3(Sr2AlTaO6)0.7 (LSMO/LSAT) (001) substrates deposited by pulsed laser deposition technique. The x-ray diffraction patterns of the heterostructures show only (00l) (l = 1 and/or 2) reflections corresponding to the LSAT substrate, PZT, and LSMO layers. The atomic force microscopy studies show that the root mean square surface roughnesses of P100 and P10 films are 2.39 and 0.99 nm, respectively. An increase of both real (e′) and imaginary (e″) permittivities was observed when thickness of PZT increases from 10 nm to 100 nm. Temperature dependent e′ presents an anomaly, related to ferromagnetic-metal to paramagnetic-insulator transition of the LSMO, in the range of 350–500 K. The dielectric anomalies and magnetic phase transition temperature shifted to the lower temperature values with decrease in the PZT films thicknesses. The values of the remane...

Ferroelectric photovoltaic properties in doubly substituted (Bi0.9La0.1)(Fe0.97Ta0.03)O3 thin films

Doubly substituted [Bi0.9La0.1][Fe0.97Ta0.03]O3 (BLFTO) films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition. The ferroelectric photovoltaic properties of ZnO:Al/BLFTO/Pt thin film capacitor structures were evaluated under white light illumination. The open circuit voltage and short circuit current density were observed to be ∼0.20 V and ∼1.35 mA/cm2, respectively. The band gap of the films was determined to be ∼2.66 eV, slightly less than that of pure BiFeO3 (2.67 eV). The PV properties of BLFTO thin films were also studied for various pairs of planar electrodes in different directions in polycrystalline thin films.

Ferroelectric capped magnetization in multiferroic PZT/LSMO tunnel junctions

This article was originally published online on 31 March 2015 with an incorrect author’s address. The address is correct as it appears above. All online versions were corrected on 3 April 2015 and the address was correct as it appeared in the printed version of the journal.

Optical, ferroelectric, and piezoresponse force microscopy studies of pulsed laser deposited Aurivillius Bi5FeTi3O15 thin films

Bi5FeTi3O15 (BFTO) based Aurivillius ferroelectric thin films were fabricated on strontium ruthanate coated amorphous fused silica substrates using pulsed laser deposition technique. Optical, ferroelectric, and piezoresponse properties of these thin films were investigated. The estimated refractive index (n) and extinction coefficient (k) for these films were in the range from 2.40 to 2.59 and 0.012 to 0.19, respectively. The bandgap of the BFTO thin layers was estimated to be 2.88 eV. Domain switching and hysteresis loops of BFTO films were studied utilizing piezoresponse force microscopy (PFM). The measured apparent polarization (Pr) and coercive field (Ec) for the samples were 20 μC/cm2 and 250 kV/cm, respectively. The amplitude and phase hysteresis curves obtained from PFM characterization reveal that these films can be switched below 5 V. These results suggest that BFTO in thin film form is a promising material for photo ferroelectric and optoelectronic devices applications.

Study on the optical and electrical properties of tetracyanoethylene doped bilayer graphene stack for transparent conducting electrodes

We report the optical and electrical properties of chemically-doped bilayer graphene stack by tetracyanoethylene, a strong electron acceptor. The Tetracyanoethylene doping on the bilayer graphene via charge transfer was confirmed by Raman spectroscopy and Infrared Fourier transform spectroscopy. Doped graphene shows a significant increase in the sheet carrier concentration of up to 1.520 × 1013 cm−2 with a concomitant reduction of the sheet resistance down to 414.1 Ω/sq. The high optical transmittance (ca. 84%) in the visible region in combination with the low sheet resistance of the Tetracyanoethylene-doped bilayer graphene stack opens up the possibility of making transparent conducting electrodes for practical applications.

Studies on structural, optical, magnetic, and resistive switching properties of doped BiFe1-xCrxO3 thin films

We report the effect of multivalent Cr-ion doping on the structural, optical, magnetic, and resistive switching properties of BiFe1-xCrxO3 (BFCO) thin films (where, 0 ≤ x ≤ 0.15). BFCO thin films were deposited on Pt/TiO2/SiO2/Si (100) substrate using pulsed laser deposition technique. X-ray diffraction and micro-Raman analysis revealed the presence of a secondary phase in BFCO thin films, above 5% Cr doping concentrations. Enhanced magnetization was observed in BFCO films owing to ferromagnetic superexchange interaction between Fe and Cr-ions. X-ray photoelectron spectroscopy measurements revealed the multivalent states of Cr and Fe-ions, where suppression of oxygen vacancies due to Cr-ion doping in BFCO films was discussed based on the defect chemistry viewpoint. Moreover, current conduction and resistive switching properties were studied and the dominant switching mechanism was explained in the light of oxygen vacancies assisted filamentary conduction model.

Ferroelectric/Multiferroic Tunnel Junctions for Multifunctional Applications

Ferroelectric and multiferroic tunnel junctions (FTJ/MFTJs) are a novel class of next generation nonvolatile memories devices that display simultaneous magnetic spin, electric dipole ordering, and tunneling with cross coupling and have drawn increasing interest due to their multifunctionality for a variety of device applications. With the rapid development of thin-film growth techniques and characterization tools in the last decade, it is possible to do extensive research in the area of polar barrier tunnel junctions (TJ). This chapter summarizes how the ferroelectric (FE) (polar) nature of the barrier changes the tunneling probability, and briefly, we expose several aspects to be considered in the synthesis of FTJ and MFTJ, such as critical thickness for ferroelectricity, effect of the depolarization field, and the role of interface on ferroelectricity at the nanoscale level. In addition, we include recent research results in FTJ/MFTJ. We focus in particular on PZT (lead zirconate titanate) and BTO (barium titanate) in case of ferroelectric tunnel junction (FTJ), and BFO (bismuth ferrite) and BMO (bismuth manganite) single-phase multiferroics (MFs) used as barriers in multiferroic tunnel junctions (MFTJ). The variety of interesting physical phenomena of these TJ and their multifunctional properties for various technological applications make the research in this field challenging and promising. Keywords: Tunnel junctions; multiferroic; ferroelectric; ultrathin films; magnetoelectric