Stroomopwaarts

In de elektriciteitsleer en elektronica worden veelvuldig begrippen gebruikt die we kennen van het beschrijven van vloeistoffen. In het bijzonder wordt elektrische stroom vergeleken met.waterstroom. We spreken hier van de hydraulische analogie. De engelse ingenieur, wis- en natuurkundige Oliver Heaviside (1850- 1925), één van de grondleggers van de theorie van het elektro-magnetisme, noemde dit spottend ook wel de “rioolpijptheorie”. De analogie met water komt terug in meer termen. Zo heeft een transistor een “source”, oftewel “bron”, en een “drain”, dat zich laat vertalen als “afvoerputje”. Net als in het geval van mijn lumineuze idee, kan hetgeen wat wegstroomt uit het afvoerputje van de transistor weer nuttig gebruikt worden, bijvoorbeeld voor het voeden van andere componenten in een geïntegreerd circuit, een chip

A photoemission study of interfaces between organic semiconductors and Co as well as Al₂O₃/Co contacts

We have studied the energy-level alignment of ex situ, acetone cleaned Co and Al2O3/Co contacts to the organic semiconductors pentacene and rubrene by combined X-ray and ultraviolet photoemission spectroscopy. Our results demonstrate that the work function under these conditions is smaller than in the in situ cleaned, atomically clean case. Moreover, the studied interfaces are characterized by very small, short range interfaces dipoles and substantial injection barriers for holes. This represents essential information in view of their use in organic spintronic devices. Our core-level photoemission spectroscopy measurements rule out chemical reactions

Highly tuneable hole quantum dots in Ge-Si core-shell nanowires

We define single quantum dots of lengths varying from 60 nm up to nearly half a micron in Ge-Si core-shell nanowires. The charging energies scale inversely with the quantum dot length between 18 and 4 meV. Subsequently, we split up a long dot into a double quantum dot with a separate control over the tunnel couplings and the electrochemical potential of each dot. Both single and double quantum dot configurations prove to be very stable and show excellent control over the electrostatic environment of the dots, making this system a highly versatile platform for spin-based quantum computing

Growth mechanism and interface magnetic properties of Co nanostructures on graphite

We investigated structural, electronic, and magnetic properties of Co adsorbed on highly oriented pyrolytic graphite (HOPG). Distribution and atomic sites of 3d transition-metal Co nanoislands and adatoms on HOPG were experimentally investigated by scanning tunneling microscopy with atomic resolution. In the very low thickness regime (0.6 A° ), a strong nucleation mechanism and a preferred Co nanoisland diameter of ∼3.4 nm have been observed. Co adatoms were found to preferentially occupy β sites of the HOPG surface graphene layer and the atoms aggregated by further occupation of either α or overbond sites. This is in contrast to predictions based on density functional theory, which indicates that the hollow sites are the most energetically stable sites for Co adsorption. The presence of surface hydrocarbon contamination on graphite might be one possible cause of the observed active nucleation and stabilized nanoisland diameter of Co. The formation of Co carbide was evidenced by x-ray absorption spectroscopy. More importantly, the Co magnetic spin moment at the interface of Fe-capped ferromagnetic Co nanostructures and graphite, as determined by x-ray magnetic circular dichroism and sum-rule analysis, was found to be only 63% of the bulk value, implying a magnetically defective spin contact for carbon spintronics applications

Scanning tunnelling miscroscopy/spectroscopy and X-ray absorption spectroscopy studies of Co adatoms and anoislands on highly oriented pyrolytic graphite

In this paper, the scanning tunneling microscopy, scanning tunneling spectroscopy and X-ray absorption spectroscopy of cobalt adatoms and nanoislands were studied on a highly oriented pyrolytic graphite. Local electronic structure were observed by STS.\ud \u

Geometric reduction of dynamical nonlocality in nanoscale quantum circuits

Nonlocality is a key feature discriminating quantum and classical physics. Quantum-interference phenomena, such as Young’s double slit experiment, are one of the clearest manifestations of nonlocality, recently addressed as dynamical to specify its origin in the quantum equations of motion. It is well known that loss of dynamical nonlocality can occur due to (partial) collapse of the wavefunction due to a measurement, such as which-path detection. However, alternative mechanisms affecting dynamical nonlocality have hardly been considered, although of crucial importance in many schemes for quantum information processing. Here, we present a fundamentally different pathway of losing dynamical nonlocality, demonstrating that the detailed geometry of the detection scheme is crucial to preserve nonlocality. By means of a solid-state quantum-interference experiment we quantify this effect in a diffusive system. We show that interference is not only affected by decoherence, but also by a loss of dynamical nonlocality based on a local reduction of the number of quantum conduction channels of the interferometer. With our measurements and theoretical model we demonstrate that this mechanism is an intrinsic property of quantum dynamics. Understanding the geometrical constraints protecting nonlocality is crucial when designing quantum networks for quantum information processing

Low-temperature solution synthesis of chemically functional ferromagnetic FePtAu nanoparticles

Magnetic nanoparticles are of great scientific and technological interest. The application of ferromagnetic nanoparticles for high-density data storage has great potential, but energy efficient synthesis of uniform, isolated, and patternable nanoparticles that remain ferromagnetic at room temperature is not trivial. Here, we present a low-temperature solution synthesis method for FePtAu nanoparticles that addresses all those issues and therefore can be regarded as an important step toward applications. We show that the onset of the chemically ordered face-centered tetragonal (L10) phase is obtained for thermal annealing temperatures as low as 150 C. Large uniaxial magnetic anisotropy (107 erg/cm3) and a high long-range order parameter have been obtained. Our low-temperature solution annealing leaves the organic ligands intact, so that the possibility for postanneal monolayer formation and chemically assisted patterning on a surface is maintained

Highly ordered C₆₀ films on epitaxial Fe/MgO(001) surfaces for organic spintronics

Hybrid interfaces between ferromagnetic surfaces and carbon-based molecules play an important role in organic spintronics. The fabrication of devices with well defined interfaces remains challenging, however, hampering microscopic understanding of their operation mechanisms. We have studied the crystallinity and molecular ordering of C-60 films on epitaxial Fe/MgO(001) surfaces, using X-ray diffraction and scanning tunneling microscopy (STM). Both techniques confirm that fcc molecular C-60 films with a (111)-texture can be fabricated on epitaxial bcc-Fe(001) surfaces at elevated growth temperatures (100-130 degrees C). STM measurements show that C-60 monolayers deposited at 130 degrees C are highly ordered, exhibiting quasi-hexagonal arrangements on the Fe(001) surface oriented along the [100] and [010] directions. The mismatch between the surface lattice of the monolayer and the bulk fcc C-60 lattice prevents epitaxial overgrowth of multilayers. (C) 2012 Elsevier B.V. All rights reserved

Single-hole tunneling through a two-dimensional hole gas in intrinsic silicon

In this letter we report single-hole tunneling through a quantum dot in a two-dimensional hole gas, situated in a narrow-channel field-effect transistor in intrinsic silicon. Two layers of aluminum gate electrodes are defined on Si/SiO$_2$ using electron-beam lithography. Fabrication and subsequent electrical characterization of different devices yield reproducible results, such as typical MOSFET turn-on and pinch-off characteristics. Additionally, linear transport measurements at 4 K result in regularly spaced Coulomb oscillations, corresponding to single-hole tunneling through individual Coulomb islands. These Coulomb peaks are visible over a broad range in gate voltage, indicating very stable device operation. Energy spectroscopy measurements show closed Coulomb diamonds with single-hole charging energies of 5--10 meV, and lines of increased conductance as a result of resonant tunneling through additional available hole states.Comment: 4 pages, 4 figures. This article has been submitted to Applied Physics Letter