http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

第12次 아시아ㆍ太平洋 矯政局長會議 參加記

Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjug...

Organic Optoelectronic Materials: Mechanisms and Applications

Creating functional electrical circuits using individual or ensemble molecules, often termed as “molecular-scale electronics”, not only meets the increasing technical demands of the miniaturization of traditional Si-based electronic devices, but also provides an ideal window of exploring the intrinsic properties of materials at the molecular level. This Review covers the major advances with the most general applicability and emphasizes new insights into the development of efficient platform methodologies for building reliable molecular electronic devices with desired functionalities through the combination of programmed bottom-up self-assembly and sophisticated top-down device fabrication. First, we summarize a number of different approaches of forming molecular-scale junctions and discuss various experimental techniques for examining these nanoscale circuits in details. We then give a full introduction of characterization techniques and theoretical simulations for molecular electronics. Third, we highlig...

Molecular-Scale Electronics: From Concept to Function

A possible sighting of Majorana states Nearly 80 years ago, the Italian physicist Ettore Majorana proposed the existence of an unusual type of particle that is its own antiparticle, the so-called Majorana fermion. The search for a free Majorana fermion has so far been unsuccessful, but bound Majorana-like collective excitations may exist in certain exotic superconductors. Nadj-Perge et al. created such a topological superconductor by depositing iron atoms onto the surface of superconducting lead, forming atomic chains (see the Perspective by Lee). They then used a scanning tunneling microscope to observe enhanced conductance at the ends of these chains at zero energy, where theory predicts Majorana states should appear. Science, this issue p. 602; see also p. 547 Scanning tunneling microscopy is used to observe signatures of Majorana states at the ends of iron atom chains. [Also see Perspective by Lee] Majorana fermions are predicted to localize at the edge of a topological superconductor, a state of matter that can form when a ferromagnetic system is placed in proximity to a conventional superconductor with strong spin-orbit interaction. With the goal of realizing a one-dimensional topological superconductor, we have fabricated ferromagnetic iron (Fe) atomic chains on the surface of superconducting lead (Pb). Using high-resolution spectroscopic imaging techniques, we show that the onset of superconductivity, which gaps the electronic density of states in the bulk of the Fe chains, is accompanied by the appearance of zero-energy end-states. This spatially resolved signature provides strong evidence, corroborated by other observations, for the formation of a topological phase and edge-bound Majorana fermions in our atomic chains.

/pdf/observation-of-majorana-fermions-in-ferromagnetic-atomic-5451hode2h.pdf

Observation of Majorana fermions in ferromagnetic atomic chains on a superconductor

Single spins in solid-state systems are often considered prime candidates for the storage of quantum information, and their interaction with the environment the main limiting factor for the realization of such schemes. The lifetime of an excited spin state is a sensitive measure of this interaction, but extending the spatial resolution of spin relaxation measurements to the atomic scale has been a challenge. We show how a scanning tunneling microscope can measure electron spin relaxation times of individual atoms adsorbed on a surface using an all-electronic pump-probe measurement scheme. The spin relaxation times of individual Fe-Cu dimers were found to vary between 50 and 250 nanoseconds. Our method can in principle be generalized to monitor the temporal evolution of other dynamical systems.

/pdf/measurement-of-fast-electron-spin-relaxation-times-with-q7hhrkl3vz.pdf

Measurement of Fast Electron Spin Relaxation Times with Atomic Resolution

1) IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA 2) Institute of the Physics of Nanostructures, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland Experimental Setup: We use an ultra-high-vacuum scanning tunneling microscope (STM) operating at an adjustable temperature of 0.6 K to 10 K. Magnetic fields up to 7 T were applied perpendicular to the sample surface. The fast voltage pulses are applied to the STM tip, but throughout this report we use the commonly employed convention of specifying the voltage of the sample with respect to the tip. For pump-probe measurements the tip-sample distance was fixed by setting the tunnel current to 1 nA at +10.0 mV sample voltage prior to opening the feedback loop. The pump and probe voltage pulses were generated as continous pulse trains by a pulse pattern generator (Agilent 81110A). The pump-probe cycle was repeated every 2 µs and the probe pulse was chopped at 810 Hz. The pump and probe pulses were summed, attenuated by 20 dB and applied to the tip of the STM. The tunnel current is detected at the sample and fed to a current preamplifier (Femto DLPCA-200) with ~1 kHz bandwidth and from there to a lockin amplifier to selectively detect the 810 Hz component of the current corresponding to the tunnel current of the probe pulse. For the measurements shown in Fig. 2C, Fig. 4 and Fig. S2 the pump and probe pulses were 100 ns FWHM long with 50 ns linear-ramp rise and fall times. The amplitude of the pump pulse was −36.5 mV and thereby well above the −16.7 mV threshold for spin excitation. The probe pulse voltage was −4.0 mV leading to a baseline of N = 341 electrons per probe pulse as measured when the probe precedes the pump. The pulse parameters used in Fig. 3A are the same except for a lowered probe-pulse voltage of −1.2 mV and the variable pump-pulse voltage. Spin-polarized STM measurements on Fe-Cu dimers: The spin-polarized tip used in this work has one magnetic atom, Mn, attached to the otherwise non-magnetic Cu-coated apex. The magnetic atom that was used to create spin-polarization in the tip was picked up after the Fe-Cu dimers were assembled by vertical atom manipulation (S1, S2). The magnetic moment of the attached atom is aligned parallel to the external magnetic field. This also determines the direction of the tip's spin-polarization (S3). Since the magnetic atom at the tip apex is adsorbed directly on the metal surface of the tip (without a decoupling layer such as Cu

Supporting Online Material for Measurement of Fast Electron Spin Relaxation Times with Atomic Resolution

We have carried out detailed experimental studies of the exchange bias effect of a series of CoO/Co(111) textured bilayers with different Co layer thickness, using the magneto-optical Kerr effect, superconducting quantum interference device (SQUID) magnetometry, polarized neutron reflectivity, x-ray diffraction, and atomic force microscopy. All samples exhibit a pronounced asymmetry of the magnetic hysteresis at the first magnetization reversal as compared to the second reversal. Polarized neutron reflectivity measurements show that the first reversal occurs via nucleation and domain wall motion, while the second reversal is characterized by magnetization rotation. Off-specular diffuse spin-flip scattering indicates the existence of interfacial magnetic domains. All samples feature a small positive exchange bias just below the blocking temperature, followed by a dominating negative exchange bias field with decreasing temperature.

Interfacial domain formation during magnetization reversal in exchange-biased CoO/Co bilayers

Interfacial domain formation during magnetization reversal in exchange biased CoO/Co bilayers

The realm of high energy, large wave vector spin waves in ultrathin films and at surfaces is unexplored because a suitable method was not available up to now. We present experimental data for an 8 ML thick Co film deposited on Cu(001) which show that spin-polarized electron energy loss spectroscopy can be used to measure spin-wave dispersion curves of ultrathin ferromagnetic films up to the surface Brillouin zone boundary.

/pdf/spin-polarized-electron-energy-loss-spectroscopy-of-high-33d9fddk88.pdf

Markus Etzkorn

Papers

Measurement of Fast Electron Spin Relaxation Times with Atomic Resolution

Supporting Online Material for Measurement of Fast Electron Spin Relaxation Times with Atomic Resolution

Interfacial domain formation during magnetization reversal in exchange-biased CoO/Co bilayers

Interfacial domain formation during magnetization reversal in exchange biased CoO/Co bilayers

Spin-polarized electron energy loss spectroscopy of high energy, large wave vector spin waves in ultrathin fcc Co films on Cu(001).