Papers by Peter Schattschneider
arXiv (Cornell University), Nov 22, 2018
In optics, mode conversion is an elegant way to switch between Hermite Gaussian and Laguerre Gaus... more In optics, mode conversion is an elegant way to switch between Hermite Gaussian and Laguerre Gaussian beam profiles and thereby impart orbital angular momentum onto the beam and to create vortices. In optics such vortex beams can be produced in a setup consisting of two identical cylinder lenses. In electron optics, quadrupole lenses can be used for the same purpose. Here we investigate generalized asymmetric designs of a quadrupole mode converter that may be realized within the constraints of existing electron microscopes and can steer the development of dedicated vortex generators for high brilliance electron vortex probes of atomic scale.
Scanning microscopy, 1992
Plasmon spectrometry is an important method to obtain information on many-body effects in the sol... more Plasmon spectrometry is an important method to obtain information on many-body effects in the solid state. The plasmon halfwidth and the dispersion coefficient are well investigated for a number of materials, and compare well with quantum mechanical predictions. The excitation strength of the coherent double plasmon has been investigated to a lesser extent. Experimental results are at variance with one another and with theory. This is partly due to the plural scattering which masks the coherent double plasmon. Accurate analysis of plasmon spectra requires not only to remove the inelastic plural processes but also to take into account the coupling between Dragg and plasmon scattering at high scattering angles. It is shown that the excitation strength of the coherent double plasmon in forward direction falls below the detection limit when this correction is applied.
Journal of Microscopy, 1997
This work uses electron energy loss spectroscopy (EELS) to study the excitation of interface and ... more This work uses electron energy loss spectroscopy (EELS) to study the excitation of interface and bulk plasmons in artificial, nonmagnetic metallic multilayers. We obtain EELS spectra for W/Si and Ta/Si multilayers with layer periodicity d using an off‐axis acquisition technique and compare the results with dispersion relations and energy loss probability distributions predicted from dielectric theory. Our energy loss spectra, taken for a fixed out‐of‐plane wavevector kz = π/d and low in‐plane wavevectors ky < 1/d, contain features which are identified as coupled interface modes by solving the appropriate superlattice dispersion relation. These interface modes are accompanied by bulk plasmons of the individual media. We find that dielectric theory greatly overemphasizes these bulk modes. This behaviour is interpreted phenomenologically as a finite size effect and is modelled by introducing a cut‐off for the long‐wavelength bulk modes.
Zeitschrift für Operations Research, 1980
Zusarnmenfassung: Drei Modellans~itze zur hydrodynamischen Besehreibung yon Verkehrsstr6men werde... more Zusarnmenfassung: Drei Modellans~itze zur hydrodynamischen Besehreibung yon Verkehrsstr6men werden an einem Beispiel beschrieben. Es wird gezeigt, dafS der iiblicherweise angenommene Zusammenhang zwischen Stromdichte und Stromgeschwindigkeit im allgemeinen zu mehrdeutigen L6sungen ffihrt. Ein umfassender Ansatz liefert eindeutige L6sungen, wenn man Unstetigkeiten im Dichteverlauf zulS_gt. Stetige, eindeutige L6sungen erh~ilt man schlieglich, wenn die Geschwindigkeit nicht nut in Abh~ingigkeit vonder Dichte, sondern auch vom Dichtegradienten angesetzt wird. Die auf der Basis der drei Modelle errechneten Gruppenformen werden diskutiert und an Hand eines hypothetischen Beispiels verglichen. Der erste AnSatz ist geeignet zur Beschreibung gut organisierter, homogener Gruppen, wogegen der zweite vorgezogen werden sollte, wenn SchockweUen erwartet werden. Jedoch k6nnen zufgllige Schwankungen im Dichteverlauf Instabilit~iten wNtrend der Berechnung verursachen. Dies wird bei der Anwendung des dritten diskutierten Ansatzes vermieden. Hinsichtlich der Beschreibung verschiedener Gruppenformen ist letzterer am vielseitigsten.
Ultramicroscopy, 2014
The origin of post-peak spectra in electron energy loss near edge structure (ELNES) spectra of pu... more The origin of post-peak spectra in electron energy loss near edge structure (ELNES) spectra of pure Ni and NiO is investigated through ab initio calculation. Contrary to the general view that post-peak spectra in ELNES are generated by transitions to continuum states, it is found that orbit hybridization is the main cause of post-peak spectra in the low energy range above the Fermi level based on the calculation of electronic structure and ELNES. Reasons for the intensity differences of the simulated and experimental spectra are discussed. This work contributes to the understanding of ELNES and to the quantification of ELNES spectra.
Acta Crystallographica Section A Foundations and Advances, Dec 1, 2017
Microscopy and Microanalysis, 2016
The European project METEOR aims at the development of large-grained poly-Si thin-film solar cell... more The European project METEOR aims at the development of large-grained poly-Si thin-film solar cells on foreign substrates. A two step process has been used to form the poly-Si films: (1) a thin large-grained poly-Si film (seed layer) is prepared by the aluminium-induced layer exchange (ALILE) process and (2) this seed layer is subsequently used as a template for an epitaxial thickening process. Two different concepts have been investigated: (i) a low-temperature approach using glass substrates (T < 600°C) and (ii) a high-temperature approach using ceramic substrates (T > 1000°C). The surface roughness of the ceramic substrates has a negative impact on the ALILE process. The surface roughness can be reduced by the deposition of an additional oxide layer. At high temperatures thermal CVD has successfully been used for epitaxy. At low temperatures about 73% of the area under investigation have been epitaxially thickened by a 400nm ECRCVD grown film because of the preferential (100) orientation of the seed layer. First poly-Si thin-film solar cells have been prepared at low and high temperatures. The best solar cell so far has reached an open circuit voltage of 428mV and an efficiency of 4.2%.
The European Physical Journal Applied Physics, 2011
ABSTRACT In this work two aspects of momentum-dependent electron energy loss spectrometry are stu... more ABSTRACT In this work two aspects of momentum-dependent electron energy loss spectrometry are studied, both in the core-loss and in the low-loss region. In the case of core losses, we focus on the demonstration and the interpretation of an unexpected non-Lorentzian behavior in the angular part of the double-differential scattering cross-section. The silicon L3 edge is taken as an example. Using calculations we show that the non-Lorentzian behavior is due to a change in the wavefunction overlap between the initial and the final states. In the case of low losses, we first analyze the momentum-dependent loss functions of coinage metals Cu, Ag, and Au. We then demonstrate how advanced electronic structure calculations can be used to build simple models for the dielectric function that can then serve as a basis for the calculation of more complicated sample geometries.
Acta Metallurgica Sinica (English Letters), 2007
Antimony induced crystallization of PVD (physics vapor deposition) amorphous silicon can be obser... more Antimony induced crystallization of PVD (physics vapor deposition) amorphous silicon can be observed on sapphire substrates. Very large crystalline regions up to several tens of micrometers can be formed. The Si di%action patterns of the area of crystallization can be observed with TEM (transmission electron rnicrosc0p.y). Only a few and much smaller crystals of the order of I p.m were formed when the antimony layer was deposited by MBE (molecular beam epitaq) compared with a layer formed by thermal evaporation. The use of high vacuum is essential in order to observe any Sb induced crystallization at all. In addition it is necessary to take measures to limit the evaporation of the antimony.
Science and Fiction, 2021
Cornell University - arXiv, May 16, 2020
We propose to use the topological charge instead of the spin variable to span a two-dimensional H... more We propose to use the topological charge instead of the spin variable to span a two-dimensional Hilbert space for beam electrons in a transmission electron microscope (TEM). In this basis, an electron can be considered as a qbit freely floating in vacuum. We show how a combination of magnetic quadrupoles with a magnetic drift tube can serve as a universal device to manipulate such qbits at the experimenter's discretion. High-end TEMs with aberration correctors, high beam coherence and utmost stability are a promising platform for such experiments, allowing the construction of quantum logic gates for single beam electrons in a microscope.
In this work, the transition matrix elements for inelastic electron--electron scattering are inve... more In this work, the transition matrix elements for inelastic electron--electron scattering are investigated. The angular part is given by spherical harmonics. For the weighted radial wave function overlap, analytic expressions are derived in the Slater-type and the hydrogen-like orbital models. These expressions are shown to be composed of a finite sum of polynomials and elementary trigonometric functions. Hence, they are easy to use, require little computation time, and are significantly more accurate than commonly used approximations.
Theoretically, everything that can be done in a synchrotron is also feasible in an electron micro... more Theoretically, everything that can be done in a synchrotron is also feasible in an electron microscope. In practice, however, electron and photon probes behave quite differently. In this respect, the EMCD technique (energy loss magnetic chiral dichroism) in the electron microscope [1,2] the equivalent of the synchrotron based XMCD, a standard technique for the study of atom specific magnetism has the intrinsic advantage of high spatial resolution. But there are many obstacles in taking a dichroic energy loss spectrum that do not exist for synchrotron radiation. The main difficulty with EMCD is the notoriously low signal intensity, asking for exposure times of the order of minutes, and the very particular scattering conditions necessary to observe a chiral dichroic signal. Nevertheless, much progress was made in the last years. The signal strength could be considerably increased, and some innovations such as using a convergent beam have been introduced. EMCD has evolved into several techniques, now utilising either energy filtering, spectroscopy, TEM or STEM conditions. After a synopsis of the present situation in EMCD, we highlight recent results such as nanometric resolution [3], the applicability of XMCD sum rules [4,5], and a new image simulation software [6]. Furthermore we discuss potential applications of this technique like the investigation of magnetism of individual magnetic nanoparticles. Such nanoparticles, which can be made e.g. of Fe3O4, are due to their magnetic properties interesting for a variety of applications like magnetic markers in biotechnology or as magnetic ink for printable magnetic bar codes. In Fig. 1 an example of recently obtained EELS spectra of an 8 nm sized magnetite particle showing a dichroic signal at the Fe edge is given. The observation that chiral electronic transitions break certain mirror symmetries in energy spectroscopic diffraction (ESD) led to the prediction that this chirality pertains in the energy filtered HR image [7], thus opening a road to mapping electron spins of individual atomic columns under HR-TEM conditions see Fig. 2. We discuss the necessary conditions to do so and present a feasibility experiment on the SuperSTEM facility.
Microscopy and Microanalysis, 2003
For measuring the degree of coherence across plasmons in more detail, we used a Philips CM30FEG e... more For measuring the degree of coherence across plasmons in more detail, we used a Philips CM30FEG electron microscope with an electron biprism for holography, and a GIF with a wide slit for energy selection. A [110]-oriented Aluminum specimen area with a thickness of was selected ...
Basic Concepts Momentum Resolved ELNES, C. Hebert , J.-C. LeBosse Relativistic Effects and the Ma... more Basic Concepts Momentum Resolved ELNES, C. Hebert , J.-C. LeBosse Relativistic Effects and the Magic Angle, J.-C. LeBosse, C. Hebert An Introduction to XMCD, G.Schutz Chirality in EELS and the Role of the Angular Momentum, P. Schattschneider) Calculation Methods Multiplet Methods, L. Calmels, J. Rusz DFT Methods, C. Ambrosch, L. Pardini, F. Manghi Multiple-Scattering Theory of Circular Dichroism, J. Rehr , H. Wende Experimental Chiral/Circular Dichroism EMCD Techniques and Geometries, S. Rubino et al. Data Treatment, Artefacts, Noise, K. Leifer, C. Gatel, B. Warot-Fonrose et al. The Role of the Crystal, J. Verbeeck, J. Rusz, S. Rubino Sum Rules in EMCD and XMCD, J. Rusz, J. Rehr, L. Calmels Related Techniques and Perspectives Magnetic Dichroism in X-Ray Holography, S. Eisebitt Prospects for Spin Mapping with Atomic Resolution, M. Stoger-Pollach , J. Verbeeck, P. Schattschneider
Physical Review B, 1992
The efFects of an angle-limiting aperture on electron-energy-loss spectra are studied for paralle... more The efFects of an angle-limiting aperture on electron-energy-loss spectra are studied for parallel and convergent incident beams. The angular distribution of multiply scattered electrons is calculated by means of Bessel functions. The residual intensity of multiple scattering after deconvolution is calculated. The infiuence of a cutog angle for plasmon excitation to deconvolution and simulation is investigated showing that the cutofF efFect reduces the accuracy of deconvolution, but if the anglelimiting aperture is much larger than the characteristic scattering angle the relative error in the deconvolution is less than 3'.
Uploads
Papers by Peter Schattschneider