Broadband Setup for Magnetic-Field-Induced Domain Wall Motion in Cylindrical Nanowires

In order to improve the precision of domain wall dynamics measurements, we develop a coplanar waveguide-based setup where the domain wall motion should be triggered by pulses of magnetic field. The latter are produced by the Oersted field of the waveguide as a current pulse travels toward its termination, where it is dissipated. Our objective is to eliminate a source of bias in domain wall speed estimation while optimizing the field amplitude. Here, we present implementations of this concept for magnetic force microscopy (MFM) and synchrotron-based investigation

Magnetism in nanometer-thick magnetite

The oldest known magnetic material, magnetite, is of current interest for use in spintronics as a thin film. An open question is how thin can magnetite films be and still retain the robust ferrimagnetism required for many applications. We have grown 1-nm-thick magnetite crystals and characterized them in situ by electron and photoelectron microscopies including selected-area x-ray circular dichroism. Well-defined magnetic patterns are observed in individual nanocrystals up to at least 520 K, establishing the retention of ferrimagnetism in magnetite two unit cells thick

adsorbate induced self ordering of germanium nanoislands on si 113

The impact of Ga preadsorption on the spatial correlation of nanoscale three-dimensional (3D) Ge-islands has been investigated by low-energy electron microscopy and low-energy electron diffraction. Submonolayer Ga adsorption leads to the formation of a 2D chemical nanopattern, since the Ga-terminated (2×2) domains exclusively decorate the step edges of the Si(113) substrate. Subsequent Ge growth on such a partially Ga-covered surface results in Ge 3D islands with an increased density as compared to Ge growth on clean Si(113). However, no pronounced alignment of the Ge islands is observed. Completely different results are obtained for Ga saturation coverage, which results in the formation of (112) and (115) facets regularly arranged with a periodicity of about 40 nm. Upon Ge deposition, Ge islands are formed at a high density of about 1.3×1010 cm−2. These islands are well ordered as they align at the substrate facets. Moreover, the facet array induces a reversal of the Ge islands' shape anisotropy as compared to growth on planar Si(113) substrates

Spillover Reoxidation of Ceria Nanoparticles

Interest in resolving the mechanisms behind ceria's activity has been intense due to the numerous industrial applications including those in heterogeneous catalysis. In this work, we study the reduction and reoxidation of ultrathin CeO2(111) nanoislands on Rh(111) and Pt(111) substrates, so-called inverse model catalysts, with a combination of real and reciprocal space techniques based on X-ray photoemission electron microscopy (XPEEM) and low energy electron microscopy. Soft X-ray microfocused illumination was employed to reduce the ceria islands, which we are able to control by varying the oxygen partial pressure within the measurement chamber. Low energy electron diffraction measurements of the irradiated ceria films demonstrate the formation of an ordered array of oxygen vacancies leading to a (√7 × √7)R19.1° superstructure attributed to the ι-phase (Ce7O12)(111). Resonant photoelectron spectroscopy provides the required high sensitivity to detect small changes in Ce3+ concentration. The high spatial resolution of the XPEEM allows us to determine that the reduction of the ceria occurs initially at the interface of the islands with the Rh support. Reoxidation of the CeO2–x(111) to CeO2(111) proceeds via spillover of activated oxygen adsorbed on the Rh(111) surface as a (2 × 2) overlayer. Our results highlight the important role that the noble metal plays in the regeneration of the stoichiometric ceria surface, a vital step in many reactions on ceria. This differs from the commonly proposed Mars–van Krevelen model in which reoxidation involves direct reaction of the ceria with O2