Engineering topics
Paltiel, Yossi
Publications and source records attributed to Paltiel, Yossi.
Optical Activity and Spin Polarization: The Surface Effect
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Chiral Induced Spin Selectivity Gives a New Twist on Spin-Control in Chemistry
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Effect of Chiral Molecules on the Electron’s Spin Wavefunction at Interfaces
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3D strain-induced superconductivity in La 2 CuO 4+δ using a simple vertically aligned nanocomposite approach
A long-term goal for superconductors is to increase the superconducting transition temperature, T C . In cuprates, T C depends strongly on the out-of-plane Cu-apical oxygen distance and the in-plane Cu-O distance, but there has been little attention paid to tuning them independently. Here, in simply grown, self-assembled, vertically aligned nanocomposite thin films of La 2 CuO 4+δ + LaCuO 3 , by strongly increasing out-of-plane distances without reducing in-plane distances (three-dimensional strain engineering), we achieve superconductivity up to 50 K in the vertical interface regions, spaced ~50 nm apart. No additional process to supply excess oxygen, e.g., by ozone or high-pressure oxygen annealing, was required, as is normally the case for plain La 2 CuO 4+δ films. Finally, our proof-of-concept work represents an entirely new approach to increasing >T C n cuprates or other superconductors.
Broad-band high-gain room temperature photodetectors using semiconductor–metal nanofloret hybrids with wide plasmonic response
We present an optoelectronic device for broad spectral detection using SiGe nanowires coupled to a plasmonic antenna.
Chiral molecules and the electron spin
The electron’s spin is necessary to the stability of matter, and control over the spin opens up avenues for manipulating the properties of molecules and materials. The Pauli exclusion principle requires that two electrons in a single spatial eigenstate have opposite spins, and this fact dictates basic features of atomic states and chemical bond formation. The energy associated with interacting electron clouds changes with their relative spin orientation, and by manipulating the spin directions, one can guide chemical transformations. However, controlling the relative spin orientation of electrons located on two reactants (atoms, molecules or surfaces) has proved challenging. Recent developments based on the chiral-induced spin selectivity (CISS) effect show that the spin orientation is linked to molecular symmetry and can be controlled in ways not previously imagined. For example, the combination of chiral molecules and electron spin opens up a new approach to (enantio)selective chemistry. Our Review describes the theoretical concepts underlying the CISS effect and illustrates its importance by discussing some of its manifestations in chemistry, biology and physics. Specifically, we discuss how the CISS effect allows for efficient long-range electron transfer in chiral molecules and how it affects biorecognition processes. Several applications of the effect are presented, and the importance of controlling relative spin orientations in multi-electron processes, such as electrochemical water splitting, is emphasized. We describe the enantiospecific interaction between ferromagnetic substrates and chiral molecules and how it enables the separation of enantiomers with ferromagnets. Lastly, we discuss the relevance of CISS effects to biological electron transfer, enantioselectivity and CISS-based spintronics applications.
Electric Field-Controlled Magnetization in GaAs/AlGaAs Heterostructures–Chiral Organic Molecules Hybrids
Here, we study GaAs/AlGaAs devices hostinga two-dimensional electron gas and coated with a monolayer of chiral organic molecules.We observe clear signatures of room temperature magnetism, which is induced in these systems by applying a gate voltage. We explain this phenomenon as a consequence of the spin-polarized charges that are injectedinto the semiconductor through the chiral molecules. The orientation of the magnetic moment can be manipulated by low gate voltages, with a switching ratein the MHz range. Therefore, our devices implement an efficient, electric field controlled magnetization, which has long been desired for their technical prospects.
Single Domain 10 nm Ferromagnetism Imprinted on Superparamagnetic Nanoparticles Using Chiral Molecules
The rapid growth in demand for data and the emerging applications of Big Data require the increase of memory capacity. Magnetic memory devices are among the leading technologies for meeting this demand; however, they rely on the use of ferromagnets that creates size reduction limitations and poses complex materials requirements. Typically magnetic memory sizes are limited to 30–50 nm. Reducing the size even further, to the ≈10–20 nm scale, destabilizes the magnetization and its magnetic orientation becomes susceptible to thermal fluctuations and stray magnetic fields. In the present work, it is shown that 10 nm single domain ferromagnetism can be achieved. Using asymmetric adsorption of chiral molecules, superparamagnetic iron oxide nanoparticles become ferromagnetic with an average coercive field of ≈80 Oe. The asymmetric adsorption of molecules stabilizes the magnetization direction at room temperature and the orientation is found to depend on the handedness of the chiral molecules. These works point to a novel method for the miniaturization of ferromagnets (down to ≈10 nm) using established synthetic protocols.
Probing Molecular‐Transport Properties using the Superconducting Proximity Effect
Molecular electronics research focuses on the study and application of molecular building blocks for the fabrication of nanoscale electronic devices, and on utilizing their self‐organization properties to achieve large‐scale electronic circuits. One of the key issues in molecular electronics is to identify the mechanism governing the electrical conductivity along the molecules. More specifically, the problem is to determine whether the junction behaves as a tunnel barrier, or the junction provides electron or hole conduction channels through the molecule. Due to the large energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), it is usually assumed in calculations that the molecule may contain only one conducting channel either for electrons or for holes. Experimentally, measurements using a local‐probe tip or a small gap between two metallic leads strongly depend on the nature of the linkage between the molecules and the contacts, which is hard to optimize. Here, a new approach is presented to study the electronic and transport properties of molecules using the superconducting proximity effect. Insight into these properties is gained by monitoring the modifications of the superconducting properties upon linking nanoparticles to a superconductor via the studied molecules.
Atomic structure and composition distribution in wetting layers and islands of germanium grown on silicon (001) substrates
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Atomic-scale mapping of quantum dots formed by droplet epitaxy
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Morphology and growth of capped Ge/Si quantum dots
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Surface X-Ray Diffraction Results on the III-V Droplet Heteroepitaxy Growth Process for Quantum Dots: Recent Understanding and Open Questions
In recent years, epitaxial growth of self-assembled quantum dots has offered a way to incorporate new properties into existing solid state devices. Although the droplet heteroepitaxy method is relatively complex, it is quite relaxed with respect to the material combinations that can be used. This offers great flexibility in the systems that can be achieved. In this paper we review the structure and composition of a number of quantum dot systems grown by the droplet heteroepitaxy method, emphasizing the insights that these experiments provide with respect to the growth process. Detailed structural and composition information has been obtained using surface X-ray diffraction analyzed by the COBRA phase retrieval method. A number of interesting phenomena have been observed: penetration of the dots into the substrate ('nano-drilling') is often encountered; interdiffusion and intermixing already start when the group III droplets are deposited, and structure and composition may be very different from the one initially intended.
Structure of droplet-epitaxy-grown InAs/GaAs quantum dots
We have used a direct x-ray phasing method, coherent Bragg rod analysis, to obtain sub-angstrom resolution electron density maps of the InAs/GaAs dot system. The dots were grown by the droplet heteroepitaxy (DHE) technique and their structural and compositional properties are compared with those of dots grown by the strain-driven Stranski-Krastanov method. Our results show that the Ga diffusion into the DHE-grown dots is somewhat larger; however, other characteristics such as the composition of the dots uppermost layers, the interlayer spacing, and the bowing of the atomic layers are similar.