J. Appl. Cryst.の発刊に際して

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

Exchange bias in nanostructures

The engineering of highly organized systems from instructed molecular building blocks opens up new vistas for the control of matter and the exploration of nanodevice concepts. Recent investigations demonstrate that well-defined surfaces provide versatile platforms for steering and monitoring the assembly of molecular nanoarchitectures in exquisite detail. This review delineates the principles of noncovalent synthesis on metal substrates under ultrahigh vacuum conditions and briefly assesses the pertaining terminology-self-assembly, self-organization, and self-organized growth. It presents exemplary scanning-tunneling-microscopy observations, providing atomistic insight into the self-assembly of organic clusters, chains, and superlattices, and the metal-directed assembly of low-dimensional coordination architectures. This review also describes hierarchic-assembly protocols leading to intricate multilevel order. Molecular architectonic on metal surfaces represents a versatile rationale to realize structurally complex nanosystems with specific shape, composition, and functional properties, which bear promise for technological applications.

Molecular architectonic on metal surfaces.

In the field of molecular spintronics, the use of magnetic molecules for information technology is a main target and the observation of magnetic hysteresis on individual molecules organized on surfaces is a necessary step to develop molecular memory arrays. Although simple paramagnetic molecules can show surface-induced magnetic ordering and hysteresis when deposited on ferromagnetic surfaces, information storage at the molecular level requires molecules exhibiting an intrinsic remnant magnetization, like the so-called single-molecule magnets (SMMs). These have been intensively investigated for their rich quantum behaviour but no magnetic hysteresis has been so far reported for monolayers of SMMs on various non-magnetic substrates, most probably owing to the chemical instability of clusters on surfaces. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism synchrotron-based techniques, pushed to the limits in sensitivity and operated at sub-kelvin temperatures, we have now found that robust, tailor-made Fe(4) complexes retain magnetic hysteresis at gold surfaces. Our results demonstrate that isolated SMMs can be used for storing information. The road is now open to address individual molecules wired to a conducting surface in their blocked magnetization state, thereby enabling investigation of the elementary interactions between electron transport and magnetism degrees of freedom at the molecular scale.

http://www.molspinqip.org/wp-content/uploads/file/magnetic%20memory_1.pdf

Magnetic memory of a single-molecule quantum magnet wired to a gold surface.

This self-contained, comprehensive book describes the fundamental properties of soft x-rays and extreme ultraviolet (EUV) radiation and discusses their applications in a wide variety of fields, including EUV lithography for semiconductor chip manufacture and soft x-ray biomicroscopy. The author begins by presenting the relevant basic principles such as radiation and scattering, wave propagation, diffraction, and coherence. He then goes on to examine a broad range of phenomena and applications. The topics covered include EUV lithography, biomicroscopy, spectromicroscopy, EUV astronomy, synchrotron radiation, and soft x-ray lasers. He also provides a great deal of useful reference material such as electron binding energies, characteristic emission lines and photo-absorption cross-sections. The book will be of great interest to graduate students and researchers in engineering, physics, chemistry, and the life sciences. It will also appeal to practicing engineers involved in semiconductor fabrication and materials science.

X-Rays and Extreme Ultraviolet Radiation: Principles and Applications

Pasteur's separation of the optical antipodes of ammonium sodium tartrate tetrahydrate in 1848 and the concept of the asymmetrically substituted carbon atom, introduced by van't Hoff and le Bel, marked the birth of stereochemistry. Although the Fischer–Rosanoff convention based on d-(+)glyceraldehyde got general acceptance, it was not possible to link the optical rotary power to the absolute configuration of chiral molecules. In 1951, however, Bijvoet and co-workers determined the absolute configuration of (+)-sodium rubidium tartrate through anomalous X-ray scattering and showed that the arbitrary d-/l-convention matches reality. Increasing computational power and improved quantum mechanical codes nowadays allow to connect chiroptical spectra with absolute configuration, but this approach is still limited to relatively small or rigid molecules. Other methods for determining the absolute configuration, such as wetting or enantioselective adsorption on polar crystals and measurements of the electric polarization in ferroelectric liquid crystals, have been reported. The conformation of chiral molecules adsorbed on a surface plays an important role in biomineralization and in stereoselective heterogeneous catalysis. For example, tartaric acid serves as chiral modifier for the enantioselective hydrogenation of b-ketoesters over supported nickel catalysts. To gain deeper insight into the mechanisms of enantioselective surface chemistry and biomineralization, a detailed analysis of the local adsorbate structure is necessary. The absolute chirality of molecules adsorbed on surfaces has been inferred from scanning tunneling microscopy (STM) images. However, in most cases of molecular adsorption it is very difficult to correlate the observed electron densities with the absolute atomic positions, and modeling of STM images requires extensive theoretical and computational effort. Herein we demonstrate that the absolute configuration of chiral molecules adsorbed on single-crystal surfaces can be determined in a straightforward fashion by means of anglescanned X-ray photoelectron diffraction (XPD), a method delivering direct real-space structural information. For our study we chose the classic tartaric acid molecule adsorbed on the Cu(110) surface. This adsorbate system has been studied in great detail. At low coverages and after activation at 405 K, tartaric acid becomes doubly deprotonated, with the resulting bitartrate species forming long-range ordered chiral structures on the surface. Based on IR spectroscopy results, a local C2 symmetry for the bitartrate adsorbate complex has been proposed. Figure 1 illustrates the basic principles of the XPD experiment for the case of the adsorbed bitartrate species.

Determination of the absolute chirality of adsorbed molecules.

The optical design and performance expectations of a Fresnel zone plate based scanning transmission x‐ray microscopy (STXM) beamline at a bending magnet of the Swiss Light Source is described. The instrument allows microspectroscopy in polymer science in the water window and the study of magnetic materials with circularly polarized light. The beamline is based on a spherical grating monochromator with two gratings at a constant deviation angle and covers a photon energy range from 200 eV to 1000 eV.

/pdf/the-pollux-microspectroscopy-beam-line-at-the-swiss-light-4yku1qdqbs.pdf

The PolLux Microspectroscopy Beam line at the Swiss Light Source

Periodic square arrays of antidots in 10 nm-thick cobalt films have been investigated with antidot periods, p, ranging from 2 μm down to 200 nm and various ratios of antidot size to antidot separation, w/d. For p=2 μm, the extent of modification of the thin film magnetic domain structure increases with increasing w/d, forming domains pinned diagonally between antidots for w/d⩾0.2 and resulting in a two-dimensional periodic checked domain contrast commensurate with the antidot lattice for w/d⩾0.9. As p is decreased while maintaining d≈w, we observe a dramatic change in the magnetic domain configuration at p=400 nm resulting in chains of magnetic domains running parallel to the intrinsic hard axis and with lengths corresponding to a multiple of the antidot period.

/pdf/x-ray-photoemission-electron-microscopy-investigation-of-17pui2u9wi.pdf

X-ray photoemission electron microscopy investigation of magnetic thin film antidot arrays

A fascinating property of micromagnetism comes from the possibility to control the domain and vortex configuration through the sample shape and size. For instance, in a rectangular platelet a configuration containing a stable combination of vortices and an antivortex can be created. Such a single cross-tie wall can be understood as being a coupled micromagnetic system with three static solitons. Here we report on its magnetization dynamics including the vortex-antivortex interactions. The spectrum of eigenmodes is investigated as well as the effect of different vortex core orientations. We show that the vortex dynamics can be used to identify the core configuration, which is not directly accessible to x-ray microscopy because of its limited spatial resolution.

/pdf/dynamic-vortex-antivortex-interaction-in-a-single-cross-tie-21pu54ze12.pdf

Dynamic vortex-antivortex interaction in a single cross-tie wall.

The element specific domain configuration of a microstructured Co86Fe10B4∕Mn77Ir23∕Ni80Fe20∕Si3N4 exchange bias film was studied by photoemission electron microscopy using x-ray magnetic circular dichroism. In the dots the magnetization shows less preferred orientation along the exchange bias direction than in unstructured areas. Uncompensated Mn spins at the CoFeB/MnIr interface with an antiferromagnetic coupling between the Mn and the Co magnetic moments could be studied by imaging and spectromicroscopy.

/pdf/uncompensated-spins-in-a-micro-patterned-cofeb-mnir-exchange-4h6zdla0ao.pdf

Christoph Quitmann

Papers

Determination of the absolute chirality of adsorbed molecules.

The PolLux Microspectroscopy Beam line at the Swiss Light Source

X-ray photoemission electron microscopy investigation of magnetic thin film antidot arrays

Dynamic vortex-antivortex interaction in a single cross-tie wall.

Uncompensated spins in a micro-patterned CoFeB / MnIr exchange bias system