Antibacterial Zirconia Surfaces from Organocatalyzed Atom-Transfer Radical Polymerization.

Antibacterial coatings are becoming increasingly attractive for application in the field of biomaterials. In this framework, we developed polymer coating zirconia with antibacterial activity using the "grafting from" methodology. First, 1-(4-vinylbenzyl)-3-butylimidazolium chloride monomer was synthesized. Then, the surface modification of zirconia substrates was performed with this monomer via surface-initiated photo atom transfer radical polymerization for antibacterial activity. X-ray photoelectron spectroscopy, ellipsometry, static contact angle measurements, and an atomic force microscope were used to characterize the films for each step of the surface modification. The results revealed that cationic polymers could be successfully deposited on the zirconia surfaces, and the thickness of the grafted layer steadily increased with polymerization time. Finally, the antibacterial adhesion test was used to evaluate the antibacterial activity of the modified zirconia substrates, and we successfully showed the antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa strains.

Artificial Aging of Thin Films of the Indium-Free Transparent Conducting Oxide SrVO3.

SrVO3 (SVO) is a prospective candidate to replace the conventional indium tin oxide (ITO) among the new generation of transparent conducting oxide (TCO) materials. In this study, the structural, electrical, and optical properties of SVO thin films, both epitaxial and polycrystalline, are determined during and after heat treatments in the 150-250 °C range and under ambient environment in order to explore the chemical stability of this material. The use of these relatively low temperatures speeds up the natural aging of the films and allows following the evolution of their related properties. The combination of techniques rather sensitive to the film surface and of techniques sampling the film volume will emphasize the presence of a surface oxidation evolving in time at low annealing temperatures, whereas the perovskite phase is destroyed throughout the film for treatments above 200 °C. The present study is designed to understand the thermal degradation and long-term stability issues of vanadate-based TCOs and to identify technologically viable solutions for the application of this group as new TCOs.

Strong Magnetic Anisotropy of Epitaxial PrVO3 Thin Films on SrTiO3 Substrates with Different Orientations.

We have probed the structural and magnetic properties of PrVO3 (PVO) thin films grown on the (001)-, (110)-, and (111)-oriented SrTiO3 (STO) substrates. By changing the substrate orientation, the film out-of-plane orientation can be tuned to [110], [100]/[010], and [011]/[311], with different in-plane crystallographic variants. Accommodation of these variants on the different substrates implies different strain states, which have direct influence on the magnetic properties of PVO films. The magnetic moment of PVO films radically enhances from 0.4 µB/f.u. for STO(001) to 2.3 µB/f.u. for STO(111). While films on the (001)-oriented STO substrate display out-of-plane anisotropy, an in-plane anisotropy is observed for films grown on the (110)- and (111)-oriented STO substrates. In addition, a strong uniaxial magnetic anisotropy is also extracted for a partially relaxed film on the (110)-oriented STO substrate. Such findings can help oxide community for the better understanding of magnetic anisotropy in vanadate thin films, a subject that still suffer from significant lack of scientific investigations.

Transfer of Epitaxial SrTiO3 Nanothick Layers Using Water-Soluble Sacrificial Perovskite Oxides.

The integration of functional thin film materials with adaptable properties is essential for the development of new paradigms in information technology. Among them, complex oxides with perovskite structures have huge potential based on the particularly vast diversity of physical properties. Here, we demonstrate the possibility of transferring perovskite oxide materials like SrTiO3 onto a silicon substrate using an environmentally friendly process at the nanoscale by means of a water-soluble perovskite sacrificial layer, SrVO3. Based on in situ monitoring atomic force microscopy and photoemission studies, we reveal that the dissolution is initiated from a strontium-rich phase at the extreme surface of SrVO3. The nanothick SrTiO3-transferred layer onto silicon presents appropriate morphology and monocrystalline quality, providing a proof of concept for the integration and development of all-perovskite-oxide electronics or "oxitronics" onto any Si-based substrate.

Textured Manganite Films Anywhere.

New paradigms are required in microelectronics when the transistor is in its downscaling limit and integration of materials presenting functional properties not available in classical silicon is one of the promising alternatives. Here, we demonstrate the possibility to grow La0.67Sr0.33MnO3 (LSMO) functional materials on amorphous substrates with properties close to films grown on single-crystalline substrates using a two-dimensional seed layer. X-ray diffraction and electron backscatter diffraction mapping demonstrate that the Ca2Nb3O10- nanosheet (NS) layer induces epitaxial stabilization of LSMO films with a strong out-of-plane (001) texture, whereas the growth of LSMO films on uncoated glass substrates exhibits a nontextured polycrystalline phase. The magnetic properties of LSMO films deposited on NS are similar to those of the LSMO grown on SrTiO3 single-crystal substrates in the same conditions (which is used as a reference in this work). Moreover, transport measurements take advantages of the texture and polycrystalline properties to induce low-field magnetoresistance at low temperature and also a high value of 40% magnetoresistance from 10 to 300 K, making it interesting for sensor applications. Therefore, the NS seed layer offers new perspectives for the integration of functional materials grown at moderate temperatures on any substrate, which will be the key for the development of oxitronics.

Spontaneous ordering, strain control, and multifunctionality in vertical nanocomposite heteroepitaxial films.

Two-phase nanocomposite heteroepitaxial films with vertical microstructures hold great promise for various (multi)functional (e.g., multiferroic) electronic device applications. With the aim of creating addressable arrays, it is necessary to form spontaneously ordered structures over large areas. However, such structures have not, so far, been demonstrated. We have recently produced remarkable spontaneously ordered phase assemblies and find that these structures form concomitantly with 2-D vertical strain control, i.e., strain in the 2 phases is controlled along the vertical interface between them rather than being influenced by the substrate. In this paper, we report on our findings in the BiFeO3 and BaTiO3 ferroelectric systems.

Strain control and spontaneous phase ordering in vertical nanocomposite heteroepitaxial thin films.

Two-phase, vertical nanocomposite heteroepitaxial films hold great promise for (multi)functional device applications. In order to achieve practical devices, a number of hurdles need to be overcome, including the creation of ordered structures (and their formation on a large scale), achieving different combinations of materials and control of strain coupling between the phases. Here we demonstrate major advances on all these fronts: remarkable spontaneously ordered structures were produced in newly predicted compositions, vertical strain was proven to dominate the strain state in films above 20 nm thickness and strain manipulation was demonstrated by selection of phases with the appropriate elastic moduli. The work opens up a new avenue for strain control in relatively thick films and also promises new forms of ordered nanostructures for multifunctional applications.