518 research outputs found
Cationic ordering control of magnetization in Sr2FeMoO6 double perovskite
The role of the synthesis conditions on the cationic Fe/Mo ordering in
Sr2FeMoO6 double perovskite is addressed. It is shown that this ordering can be
controlled and varied systematically. The Fe/Mo ordering has a profound impact
on the saturation magnetization of the material. Using the appropriate
synthesis protocol a record value of 3.7muB/f.u. has been obtained. Mossbauer
analysis reveals the existence of two distinguishable Fe sites in agreement
with the P4/mmm symmetry and a charge density at the Fe(m+) ions significantly
larger than (+3) suggesting a Fe contribution to the spin-down conduction band.
The implications of these findings for the synthesis of Sr2FeMoO6 having
optimal magnetoresistance response are discussed.Comment: 9 pages, 4 figure
InGaAs/InP double heterostructures on InP/Si templates fabricated by wafer bonding and hydrogen-induced exfoliation
Hydrogen-induced exfoliation combined with wafer bonding has been used to transfer ~600-nm-thick films of (100) InP to Si substrates. Cross-section transmission electron microscopy (TEM) shows a transferred crystalline InP layer with no observable defects in the region near the bonded interface and an intimately bonded interface. InP and Si are covalently bonded as inferred by the fact that InP/Si pairs survived both TEM preparation and thermal cycles up to 620 °C necessary for metalorganic chemical vapor deposition growth. The InP transferred layers were used as epitaxial templates for the growth of InP/In0.53Ga0.47As/InP double heterostructures. Photoluminescence measurements of the In0.53Ga0.47As layer show that it is optically active and under tensile strain, due to differences in the thermal expansion between InP and Si. These are promising results in terms of a future integration of Si electronics with optical devices based on InP-lattice-matched materials
The 2016 oxide electronic materials and oxide interfaces roadmap
Lorenz, M. et al.Oxide electronic materials provide a plethora of possible applications and offer ample
opportunity for scientists to probe into some of the exciting and intriguing phenomena
exhibited by oxide systems and oxide interfaces. In addition to the already diverse spectrum
of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown
phenomena due to the increased surface-to-volume ratio.
Oxide electronic materials are becoming increasingly important in a wide range of
applications including transparent electronics, optoelectronics, magnetoelectronics, photonics,
spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and
environmental waste management. Synthesis and fabrication of these materials, as well as
processing into particular device structures to suit a specific application is still a challenge.
Further, characterization of these materials to understand the tunability of their properties
and the novel properties that evolve due to their nanostructured nature is another facet of the
challenge. The research related to the oxide electronic field is at an impressionable stage, and
this has motivated us to contribute with a roadmap on ‘oxide electronic materials and oxide
interfaces’.
This roadmap envisages the potential applications of oxide materials in cutting edge
technologies and focuses on the necessary advances required to implement these materials,
including both conventional and novel techniques for the synthesis, characterization,
processing and fabrication of nanostructured oxides and oxide-based devices. The
contents of this roadmap will highlight the functional and correlated properties of oxides
in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theoretical
considerations behind both present and future applications in many technologically
important areas as pointed out by Venkatesan.
The contributions in this roadmap span several thematic groups which are represented
by the following authors: novel field effect transistors and bipolar devices by Fortunato,
Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff,
and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic
materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan,
and Prellier; and concepts for topological oxide electronics by Kawasaki, Pentcheva, and
Gegenwart. Finally, Miletto Granozio presents the European action ‘towards oxide-based
electronics’ which develops an oxide electronics roadmap with emphasis on future nonvolatile
memories and the required technologies.
In summary, we do hope that this oxide roadmap appears as an interesting up-to-date
snapshot on one of the most exciting and active areas of solid state physics, materials science,
and chemistry, which even after many years of very successful development shows in short
intervals novel insights and achievements.This work has been partially supported
by the TO-BE COST action MP1308. J F acknowledges
financial support from the Spanish Ministry of Economy and
Competitiveness, through the ‘Severo Ochoa’ Programme
for Centres of Excellence in R&D (SEV-2015-0496) and
MAT2014-56063-C2-1R, and from the Catalan Government
(2014 SGR 734). F.M.G. acknowledges support from MIUR
through the PRIN 2010 Project ‘OXIDE’.Peer reviewe
Role of hydrogen in hydrogen-induced layer exfoliation of germanium
The role of hydrogen in the exfoliation of Ge is studied using cross-sectional transmission electron microscopy, atomic force microscopy, and multiple-internal transmission mode Fourier-transform infrared absorption spectroscopy and compared with the mechanism in silicon. A qualitative model for the physical and chemical action of hydrogen in the exfoliation of these materials is presented, in which H-implantation creates damage states that store hydrogen and create nucleation sites for the formation of micro-cracks. These micro-cracks are chemically stabilized by hydrogen passivation, and upon annealing serve as collection points for molecular hydrogen. Upon further heating, the molecular hydrogen trapped in these cracks exerts pressure on the internal surfaces causing the cracks to extend and coalesce. When this process occurs in the presence of a handle substrate that provides rigidity to the thin film, the coalescence of these cracks leads to cooperative thin film exfoliation. In addition to clarifying the mechanism of H-induced exfoliation of single-crystal thin Ge films, the vibrational study helps to identify the states of hydrogen in heavily damaged Ge. Such information has practical importance for the optimization of H-induced layer transfer as a technological tool for materials integration with these materials systems
Spectroscopic studies of the mechanism for hydrogen-induced exfoliation of InP
The motion and bonding configurations of hydrogen in InP are studied after proton implantation and subsequent annealing, using Fourier transform infrared (FTIR) spectroscopy. It is demonstrated that, as implanted, hydrogen is distributed predominantly in isolated pointlike configurations with a smaller concentration of extended defects with uncompensated dangling bonds. During annealing, the bonded hydrogen is released from point defects and is recaptured at the peak of the distribution by free internal surfaces in di-hydride configurations. At higher temperatures, immediately preceding exfoliation, rearrangement processes lead to the formation of hydrogen clusters and molecules. Reported results demonstrate that the exfoliation dynamics of hydrogen in InP and Si are markedly different, due to the higher mobility of hydrogen in InP and different implant-defect characteristics, leading to fundamental differences in the chemical mechanism for exfoliation
Hall-Effect Sign Anomaly and Small-Polaronic Conduction in (La_{1-x}Gd_x)_{0.67}Ca_{0.33}MnO_3
The Hall coefficient of Gd-doped La_{2/3}Ca_{1/3}MnO_3 exhibits Arrhenius
behavior over a temperature range from 2T_c to 4T_c, with an activation energy
very close to 2/3 that of the electrical conductivity. Although both the doping
level and thermoelectric coefficient indicate hole-like conduction, the Hall
coefficient is electron-like. This unusual result provides strong evidence in
favor of small-polaronic conduction in the paramagnetic regime of the
manganites.Comment: 11 pages, 4 figures, uses revtex.st
Growth and magnetic properties of multiferroic LaxBi1-xMnO3 thin films
A comparative study of LaxBi1-xMnO3 thin films grown on SrTiO3 substrates is reported. It is shown that these films grow epitaxially in a narrow pressure-temperature range. A detailed structural and compositional characterization of the films is performed within the growth window. The structure and the magnetization of this system are investigated. We find a clear correlation between the magnetization and the unit-cell volume that we ascribe to Bi deficiency and the resultant introduction of a mixed valence on the Mn ions. On these grounds, we show that the reduced magnetization of LaxBi1-xMnO3 thin films compared to the bulk can be explained quantitatively by a simple model, taking into account the deviation from nominal composition and the Goodenough-Kanamori-Anderson rules of magnetic interactions
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