No abstract

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 ferroelectricoxide 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 BaTiO 3 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.

Effects of silicon-hydrogen bond characteristics on the crystallization of hydrogenated amorphous silicon films prepared by plasma enhanced chemical vapor deposition 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 ͑IR͒ absorption at ϳ 1990 cm Ϫ1 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 ͓H͔Ͼ6 at. % causes the appearance of an additional IR absorption band at ϳ2080 cm Ϫ1 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.

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.

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.