Electronic and Chemical Analysis of a Metal-Insulator Interface Utilizing Transmission Electron Energy Loss Spectroscopy at 5Å Spatial Resolution

AbstractUsing a 0.5 nm diameter probe of 100 keV electrons, we have been able to detect significant changes in the transmission electron energy loss spectra in the region of valence shell and L23 shell excitation within a spatial extent of 0.4 nm of an Al-AlF3 interface. The spectra have been recorded with a dose significantly less than the critical dose for destruction of the AlF3.</jats:p

Surface Magnetic Microstructural Analysis using Scanning Electron Microscopy with Polarization Analysis (SEMPA)

High resolution imaging of magnetic microstructure has important ramifications for both fundamental studies of magnetism and the technology surrounding the magnetic recording industry. In SEMPA, a focused beam of electrons excites secondary electrons on a ferromagnet's surface. The secondaries leave the solid with an electron spin polarization which is characteristic of the net spin density in the ferromagnet. This is related directly to the sample magnetization. By scanning the beam and analyzing the secondary electron spin polarization at each point, a magnetization map of the ferromagnet's surface is generated.As SEMPA is a surface sensitive, magnetic microstructural analysis technique, the environment local to the specimen must be ultra-high vacuum. A schematic of our SEMPA instrument is shown in figure 1. The probe forming electron optical column of a SEMPA system must produce small probes with high currents (&gt; 1 nA) at long working distances ( &gt; 10 mm). The SEMPA system may be equipped with a single, or multiple spin detectors as in figure 1. Two detectors are used for the acquisition of all three orthogonal components of the polarization vector signal. The inefficiency of all polarimeters makes SEMPA time consuming when compared to conventional SEM. The polarized secondary electrons must be extracted efficiently without introducing any deleterious effects into the focused incident electron beam. This imposes limits on incident beam energies and extraction voltages for the transport optics. Additionally, the transport optics must map the scanned spot of the secondary electrons produced under the incident rastered beam, to a (stationary) position on the spin detector such that undesirable instrumental asymmetries are not introduced.</jats:p

High-Resolution X-Ray Photoemission Electron Microscopy at the Advanced Light Source

ABSTRACTX-ray Photoemission Electron Microscopy (X-PEEM) is a full-field imaging technique where the sample is illuminated by an x-ray beam and the photoemitted electrons are imaged on a screen by means of an electron optics. It therefore combines two well-established materials analysis techniques - photoemission electron microscopy (PEEM) and x-ray spectroscopy such as near edge x-ray absorption fine structure (NEXAFS) spectroscopy. This combination opens a wide field of new applications in materials research and has proven to be a powerful tool to investigate simultaneously topological, elemental, chemical state, and magnetic properties of surfaces, thin films, and multilayers at high spatial resolution. A new X-PEEM installed at the bend magnet beamline 7.3.1.1 at the Advanced Light Source (ALS) is designed for a spatial resolution of 20 nm and is currently under commissioning. An overview of the ongoing experimental program using X-PEEM in the field of materials research at the ALS is given by elemental and chemical bonding contrast imaging of hard disk coatings and sliders, field emission studies on diamond films as possible candidates for field-emission flat-panel displays, and the study of dewetting and decomposition phenomena of thin polymer blends and bilayers.</jats:p

Vortex Flux Channeling in Magnetic Nanoparticle Chains

International audienceA detailed understanding of the formation of magnetic vortices in closely spaced ferromagnetic nanoparticles is important for the design of ultra-high-density magnetic devices. Here, we use electron holography and micromagnetic simulations to characterize three-dimensional magnetic vortices in chains of FeNi nanoparticles. We show that the diameters of the vortex cores depend sensitively on their orientation with respect to the chain axis and that vortex formation can be controlled by the presence of smaller particles in the chains

Off-Axis Electron Holography of Self-Assembled Co Nanoparticle Rings

AbstractWe use off-axis electron holography in the transmission electron microscope (TEM) to study magnetic flux closure (FC) states in self-assembled nanoparticle rings that each contain between five and eleven 25-nm-diameter Co crystals. Electron holograms are acquired at room temperature in zero-field conditions after applying chosen magnetic fields to the samples in situ in the TEM by partially exciting the conventional microscope objective lens. Mean inner potential contributions to the phase shift are determined by turning the samples over, and subsequently subtracted from each recorded phase image to obtain magnetic induction maps. Our results show that most nanoparticle rings form FC remanent magnetic states, and occasionally onion-like states. Although the chiralities (the directions of magnetization) of the FC states are determined by the shapes, sizes and positions of the constituent nanoparticles, reproducible magnetization reversal of each ring can be achieved by using an out-of-plane magnetic field of between 1600 and 2500 Oe.</jats:p

Origin of Magnetization Decay in Spin-Dependent Tunnel Junctions

Spin-dependent tunnel junctions based on magnetically hard and soft ferromagnetic layers separated by a thin insulating barrier have emerged as prime candidates for information storage. However, the observed instability of the magnetically hard reference layer, leading to magnetization decay during field cycling of the adjacent soft layer, is a serious concern for future device applications. Using Lorentz electron microscopy and micromagnetic simulations, the hard-layer decay was found to result from large fringing fields surrounding magnetic domain walls in the magnetically soft layer. The formation and motion of these walls causes statistical flipping of magnetic moments in randomly oriented grains of the hard layer, with a progressive trend toward disorder and eventual demagnetization.</jats:p