Izabela Szafraniak

Nanoshell tubes of ferroelectric lead zirconate titanate and barium titanate

Wafer-scale fabrication of ferroelectric oxide nanoshell tubes as well as ordered nanotube arrays have been accomplished using a simple and convenient fabrication method that allows full tailoring of tube dimensions as well as array pattern and size. Using different silicon and alumina templates, barium titanate and lead zirconate titanate tubes with diameters ranging from 50 nm up to several micrometers meter and lengths of more 100 μm have been fabricated. Ferroelectric switching of submicrometer tubes has been shown using piezoresponse scanning probe microscopy.

Ferroelectric epitaxial nanocrystals obtained by a self-patterning method

Lead zirconate titanate nanoislands were obtained by a self-patterning method making use of the instability of ultrathin films during high-temperature treatments. After high-temperature annealing, the as-deposited film breaks into islands with a narrow size distribution. The single-crystal nanoislands were studied by scanning and high-resolution transmission electron microscopy, atomic force microscopy, and x-ray diffraction. They show an epitaxial relationship with the Nb-doped (001) SrTiO3 substrate. The ferroelectric switching of several individual islands was investigated by piezoresponse force microscopy.

Self-patterning of arrays of ferroelectric capacitors: description by theory of substrate mediated strain interactions

Self-patterning presents an appealing alternative to lithography for the production of arrays of nanoscale ferroelectric capacitors for use in high density non-volatile memory devices. However current levels of registration achieved experimentally are far from adequate for this application. To provide a guide for experiment we have applied the theories developed for self-patterning of semiconductor nanocrystals to two self-patterning systems of potential interest for ferroelectric memory applications, metallic bismuth oxide on bismuth titanate and ferroelectric lead zirconate titanate on strontium titanate.

Ferroelectric Lead Zirconate Titanate and Barium Titanate Nanotubes

Wetting of the pore walls of porous templates is a simple and convenient method to prepare nanotubes. Ferroelectric lead zirconate titanate and barium titanate nanotubes were fabricated by wetting of porous silicon templates of polymeric precursors. The ferro- and piezoelectric properties of an individual ferroelectric either of a PZT or a BaTiO3 nanotube were electrically characterized by measuring the local piezoelectric hysteresis. A sharp switching at the coercive voltage of about 2 V was shown from the hysterisis loop. The corresponding effective remnant piezoelectric coefficient is about 90 pm/V. We also expect that free-standing ferroelectric nanotubes obtained by partial etching of the silicon template will be used as building blocks of miniaturized devices and can have a significant impact in the field of nano-electromechanical systems.

GaAs on Si heterostructures obtained by He and/or H implantation and direct wafer bonding

Transfer of GaAs layers onto Si by helium and/or hydrogen implantation and wafer bonding was investigated. The optimum conditions for achieving blistering/splitting only after postimplantation annealing were experimentally obtained. It was found that specific implantation conditions induce large area exfoliation instead of blistering after annealing of unbonded GaAs. This effect is related to a narrow size and/or a depth distribution of the platelets in as-implanted GaAs and their evolution with annealing. The influence of substrate orientation in blistering/splitting of GaAs was also investigated. Thin GaAs layers were transferred onto silicon by a combination of He and/or H implantation, wafer bonding and low temperature annealing.

Low-temperature layer splitting of (100) GaAs by He+H coimplantation and direct wafer bonding

The present letter introduces a low-temperature GaAs layer splitting approach by He+H coimplantation which—in combination with direct wafer bonding—enables monolithic integration of GaAs with different substrates. The influence of He+H coimplantation on blistering and layer splitting of GaAs is studied and the optimum coimplantation conditions are determined. Thin GaAs layers are transferred onto Si after bonding of He+H coimplanted GaAs and Si substrates via a spin-on glass intermediate layer and subsequent annealing at only 225 °C for 14 h. Cross-sectional transmission electron microscopy investigations show a high quality of the GaAs/SOG bonding interface.

Single-Crystalline Ferroelectric Thin Films by Ion Implantation and Direct Wafer Bonding

Layer splitting by helium and/or hydrogen implantation and wafer bonding was applied to transfer thin single-crystalline ferroelectric layers onto different substrates. The optimum conditions for achieving blistering/splitting after post-implantation annealing were experimentally obtained for LiNbO3, LaAlO3, SrTiO3 single crystals and PLZT ceramic. Under certain implantation conditions large area exfoliation instead of blistering occurs after annealing of as-implanted substrates. Small area single-crystalline layer transfer was successfully achieved.

Thermodynamics of the phase transitions in ferroelectric pyridinium perchlorate, [C5NH6]+ClO4-

Calorimetry, linear thermal expansion, volumetric dilatometry and dielectric methods were applied to investigate the phase transitions of pyridinium perchlorate, [C5NH6]+ClO4-. Anomalies of the physical properties measured, related to the first-order phase transitions, were observed at T1 = 248?K and T2 = 233?K. The values of the entropy change indicate their order-disorder character. An additional thermal anomaly observed at T3 = 236?K is connected with the next continuous phase transition. The mechanism of the phase transitions is proposed in this paper. The results suggest that the character of the phase transitions do not change up to 800?MPa. On the basis of the high-pressure studies the p-T phase diagram is obtained. The pressure dependences of the phase transition temperatures agree well with the values estimated from the Clausius-Clapeyron relationship. The uniaxial pressure dependences of the phase transition temperatures are estimated.

Hydrothermal Growth of Nanosize Ferroelectrics

Hydrothermal growth was used to fabricate single crystal ferroelectric nanostructures. PbTiO 3 nanocrystals were synthesised in alkaline solution from mixture of TiO 2 (anatase) and Pb(NO 3 ) 2 . Nanocrystals were grown on single-crystal SrTiO 3 and LaAlO 3 substrates at different temperature ranging from 130 to 180C. The ferroelectric nanostructures were characterised by scanning electron microscopy, atomic force microscopy and X-ray diffraction. The ferroelectric nanocrystals show the epitaxial relationship with substrates. The dependence of the size on the reaction time together with the influence of the substrates and substrate orientations are presented.

Epitaxial Lead Zirconate Titanate Nanocrystals Obtained by a Self-Patterning Method

Epitaxial lead zirconate titanate nanoislands were obtained by a self-patterning method using the instability of ultrathin films during high-temperature treatments. After high-temperature annealing, the as-deposited film breaks into islands with a narrow size distribution. Nanostructures, as small as 20 nm lateral size with a height of 9 nm, were epitaxially grown on Nb-doped (001) SrTiO3 substrates. The formation of nanostructures was investigated as a function of the initial film thickness and crystallisation condition. Single-crystal nanoislands were studied by scanning and high-resolution transmission electron microscopy, atomic force microscopy and X-ray diffraction. Ferroelectric switching of several individual islands was investigated by piezoresponse force microscopy.