Biomedical subjects

G Schönhense

Publications and source records attributed to G Schönhense.

At least 19 recordsLinked to original sources

PubMed2005

Self-trapping of magnetic oscillation modes in Landau flux-closure structures.

We investigated the magnetodynamics in rectangular Permalloy platelets by means of time-resolved x-ray photoemission microscopy. 10 nm thick platelets of size 16 x 32 microm were excited by an oscillatory field along the short side of the sample with a fundamental frequency of 500 MHz and considerable contributions of higher harmonics. Under the influence of the oscillatory field, the Néel wall in the initial classical Landau pattern shifts away from the center, corresponding to an induced magnetic moment perpendicular to the exciting field. This phenomenon is explained by a self-trapping effect of the dominating spin-wave mode when the system is excited just below the resonance frequency. The basic driving mechanism is the maximization of entropy.

Journal Article↗

PubMed2005

Photoemission electron microscopy as a tool for the investigation of optical near fields.

Photoemission electron microscopy was used to image the electrons photoemitted from specially tailored Ag nanoparticles deposited on a Si substrate (with its native oxide SiO(x)). Photoemission was induced by illumination with a Hg UV lamp (photon energy cutoff homega(UV) = 5.0 eV, wavelength lambda(UV) = 250 nm) and with a Ti:sapphire femtosecond laser (homega(l) = 3.1 eV, lambda(l) = 400 nm, pulse width below 200 fs), respectively. While homogeneous photoelectron emission from the metal is observed upon illumination at energies above the silver plasmon frequency, at lower photon energies the emission is localized at tips of the structure. This is interpreted as a signature of the local electrical field therefore providing a tool to map the optical near field with the resolution of emission electron microscopy.

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PubMed2003

Measurement of the electric field distribution and potentials on the object surface in an emission electron microscope without restriction of the electron beams.

An emission electron microscope without restriction of the electron beams was used to visualize and measure the distribution of electric fields and potentials on the surface under study. Investigations of this kind can be performed in an emission electron microscope without any aperture diaphragm. The potentialities of this method have been demonstrated using measurements with a silicon p-n junction to which a voltage has been applied in the reverse direction. The quantitative analysis becomes more complicated if the specimen is characterized by a heterogeneous intensity distribution of the electron emission from different areas of its surface. In the latter case two images obtained at different accelerating voltages (i.e. different voltages of the microscope extractor) provide the information necessary for an analysis of electric field and potential distributions.

Beta Particles↗

PubMed2002

Use of emission electron microscope for potential mapping in semiconductor microelectronics.

An emission electron microscope was used for visualization and measurement of the distribution of electric fields and potentials on the surface under study. The contrast of microfields is caused by the fact that slow-moving electrons emitted from the object surface are deflected by these fields. The measurements were performed on a p-n junction to which a voltage was applied. It is shown that the type of contrast from the p-n junction can be reversed depending on the position of the contrast aperture restricting the electron beam. The same result was obtained by means of a computer simulation.

Journal Article↗

PubMed2001

Imaging of three-dimensional objects in emission electron microscopy.

Under investigation by emission electron microscopy, the shape and size of three-dimensional objects are distorted because of the appearance of a characteristic potential relief and a possible contact potential difference between the particles and the substrate. An estimation of these effects for spherical particles is made. It is shown that the apparent size of particles observed in an emission electron microscope (EEM) could be increased as well as decreased depending on the relation between the work functions of the particle and the substrate. The corresponding formulae are given and several possibilities are shown which permit us to determine from the EEM image the real size of particles and their work function relative to the substrate.

Journal Article↗

PubMed2001

Peculiarities of imaging one- and two-dimensional structures using an electron microscope in the mirror operation mode.

Measurements performed in an electron microscope with the mirror operation mode are most sensitive to local electric fields and geometrical roughness of any kind of the object being studied. The object with a geometrical relief is equivalent to a smooth surface with an effective distribution of microfields. Electrons forming the image interact with the local microfields for an extended time: during approach to the object, deceleration and acceleration away from the object. As a result, the electron trajectories can be strongly distorted, and the contrast changes essentially, leading to image deformation of details of the object under investigation and to lowering of the resolution. These effects are theoretically described and are illustrated by experiments. An analysis of these effects enables the real size and the shape of the object involved to be reconstructed.

Journal Article↗

PubMed2000

Magneto-optical linear dichroism in threshold photoemission electron microscopy of polycrystalline Fe films.

Magnetic linear dichroism in threshold photoemission has been exploited to obtain magnetic contrast in a photoemission electron microscope using a mercury arc lamp. The dichroism at threshold can be described similar to the magneto-optical Kerr effect in the region of visible light. The asymmetry of electron intensity observed for a 100 nm polycrystalline Fe film on silicon is A=(0.37+/-0.05)%. The asymmetry occurs for the geometry of the transverse Kerr effect. For unpolarized light the asymmetry was about half the value observed for linearly polarized light. Threshold photoemission microscopy has a large potential for high resolution magnetic domain imaging with fast data acquisition.

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PubMed1995