S. Holgado

Piezoelectric ultrathin lead titanate films prepared by deposition of aquo-diol solutions

We report on the preparation of continuous ultrathin ferroelectric films of pure lead titanate by chemical solution deposition (CSD) methods. Aquo-diol solutions highly diluted have been used to obtain films with thickness down to 13 nm, the lowest reported for CSD films. The formation of islands instead of continuous coatings, which has been reported when CSD is used to prepare ultrathin films, is avoided here. The piezoelectric activity of the films has been characterized by piezoresponse force microscopy, showing that the thinnest film obtained retains a significant piezoelectric activity at the nanoscale, which is promising for their use as transducer elements in nanoelectromechanical systems (NEMS)

Fabrication of continuous ultrathin ferroelectric films by chemical solution deposition methods

The integration of ferroelectrics in nanodevices requires firstly the preparation of high-quality ultrathin films. Chemical solution deposition is considered a rapid and cost-effective technique for preparing high-quality oxide films, but one that has traditionally been regarded as unsuitable, or at least challenging, for fabricating films with good properties and thickness below 100 nm. In the present work we explore the deposition of highly diluted solutions of pure and Ca-modified lead titanates to prepare ultrathin ferroelectric films, the thickness of which is controlled by the concentration of the precursor solution. The results show that we are able to obtain single crystalline phase continuous films down to 18 nm thickness, one of the lowest reported using these methods. Below that thickness, the films start to be discontinuous, which is attributed to a microstructural instability that can be controlled by an adequate tailoring of the processing conditions. The effect of the reduction of thickness on the piezoelectric behavior is studied by piezoresponse force microscopy. The results indicate that films retain a significant piezoelectric activity regardless of their low thickness, which is promising for their eventual integration in nanodevices, for example, as transducer elements in nanoelectromechanical systems.

Passivation, structural modification, and etching of amorphous silicon in hydrogen plasmas

Atomic hydrogen from plasma discharges dissolves in silicon previously amorphized by ion implantation (aSi) in the form of Si–H bonds, giving rise to infrared (IR) absorption at ∼1990 cm−1 and causing partial activation of implanted dopants. Passivation of aSi does not affect the rate at which the material subsequently undergoes solid phase epitaxy. Exposure giving rise to [H]>6 at. % causes the appearance of an additional IR absorption band at ∼2080 cm−1 and coloration of the layer. Despite annealing, the Si–H defects, normal solid phase epitaxy does not occur during subsequent heat treatment. The structural modification by H-plasma exposure coincides with etching of the layer. The observations can be understood in terms of void formation in aSi resulting from the clustering of Si–H.

Rapid solid phase crystallization of nanocrystalline silicon deposited by electron cyclotron plasma chemical vapor deposition

Nanocrystalline silicon films were deposited in an electron cyclotron resonance plasma of Ar+H2+SiH4 on (100) and (111) oriented Si substrates without external heating. Before deposition, the substrates were cleaned in situ in an Ar+H2 plasma. This cleaning process caused surface roughness particularly on (100) substrates. Apparently, the excessive roughness of the interface with (100) Si surface prevented complete crystallization of the subsequently deposited films. In contrast, rapid solid phase crystallization of the films deposited on (111) surfaces occurred at around 1000 °C.

Regrowth-process study of amorphous BF2+ ion-implanted silicon layers through spectroscopic ellipsometry

The recrystallization kinetics of BF2+ ion-implanted silicon has been studied by means of spectroscopic ellipsometry. It has been found that the dielectric constant of the implanted layers depends on the energy, dose and ion-beam current. The activation energy of the regrowth process increases with ion peak concentration becoming saturated for the largest implanted doses. In the largest-dose samples implanted at low current a significant decrease of the regrowth rate was detected when the recrystallization front crosses the peak of the impurity distribution.

Thin Film Multiferroic Nanocomposites by Ion Implantation

Thin film multiferroic nanocomposites might enable a range of potentially disruptive integrated magnetoelectric devices for information storage, spintronics, microwave telecommunications, and magnetic sensing. With this aim, we have investigated ion implantation of magnetic species into ferroelectric single crystal targets as a radically novel approach to prepare film nanoparticulate magnetic-metal ferroelectric-oxide composites. These materials are an alternative to multiferroic oxide epitaxial columnar nanostructures that are under intensive research, but whose magnetoelectric response is far from expectations. Here, we unambiguously demonstrate the preparation of such a thin film multiferroic nanocomposite of Co and BaTiO3 by ion implantation of a high dose of the magnetic species, followed by rapid thermal processing under tailored conditions. Results thus constitute a proof of concept for the feasibility of obtaining the materials by this alternative approach. Ion implantation is a standard technique for the microelectronic industry in combination with well-established patterning procedures.

Use of the solvent chemistry for the control of the critical thickness of PbTiO 3 ultrathin films

The preparation of high-quality ferroelectric PbTiO 3 -based ultrathin films by chemical solution deposition, using a diol-based sol-gel method, has proved to be successful. However, there is a critical thickness below which the films break up into isolated structures. According to previous studies, above a certain grain size to thickness ratio a microstructural instability occurs and the coatings are no longer continuous. We explore the use of the solvent chemistry to control this phenomenon, as an alternative to the more conventional variation of the crystallization parameters. The use of diols with short C chain lengths leads to films with smaller grain sizes, whose critical thicknesses are lower. A reduction from 40 to 15 nm is achieved by reducing the number of C of the diol used from 5 to 2. A critical value of G / t

Multiferroic nanoparticulate thin film composites by Co implantation of ferroelectric Pb(Mg1/3Nb2/3)O3?PbTiO3 single crystal targets

Two-phase magnetostrictive–piezoelectric thin film composites are key materials to the development of a range of potentially disruptive magnetoelectric technologies, such as electrical-writing magnetic-reading random access memories. However, multiferroic thin film composites prepared so far show neither magnetoelectric switching nor magnetoelectric responses comparable to those of related bulk ceramic materials and cermets. Here we show that ion implantation of magnetic species into ferroelectric single crystal targets can be an effective alternative means of obtaining nanoparticulate thin film composites of this type. Concept is proved by the implantation of Co into a Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal with ultrahigh piezoelectricity. Formation of an ensemble of ferromagnetic nanoparticles embedded in an amorphized layer within the ferroelectric crystal is clearly shown.

Functional Ultrathin Capacitors Obtained By Chemical Solution Deposition with Tailored Grain Size

In this work we present a study on the preparation of functional capacitors, i.e. without electrical shorts, from ultrathin PbTiO3 films obtained by Chemical Solution Deposition methods with tailored grain sizes. The use of different diols during the synthesis stage prove to be successful to produce fine grained films at the optimum crystallization conditions that prevent the presence of detrimental secondary phases. Besides the importance of avoiding any film damage during the electrode deposition, we show that the grain size to thickness ratio is a determinant factor to successfully prepare functional capacitors down to a thickness of 34 nm.

MPI and Non-MPI Simulations for Epitaxial Surface Growth

Usually, theories of surface growth are based on the study of global processes without taking in account the local behaviour of atoms. We have implemented two Monte-Carlo simulations. In this work we present these two simulations. Both makes use of local principles of thermodynamic for atomic deposition, relaxation and diffusion of a growing surface, and are based on a simple model that allows us to simulate the growing process of a surface of a certain material. The first one is a quasi-static model whereas the second recreates the atomic interaction. The obtained results agree with those that use global theories and with experimental results of scanning tunneling microscopy (STM)