Deutsche Gesellschaft für Materialkunde / German Materials Science Society

The physical foundations for the use of electron energy loss spectroscopy towards analytical purposes, seem now rather well established and have been extensively discussed through recent publications. In this brief review we intend only to mention most recent developments in this field, which became available to our knowledge. We derive also some lines of discussion to define more clearly the limits of this analytical technique in materials science problems.The spectral information carried in both low ( 0<ΔE<100eV ) and high ( >100eV ) energy regions of the loss spectrum, is capable to provide quantitative results. Spectrometers have therefore been designed to work with all kinds of electron microscopes and to cover large energy ranges for the detection of inelastically scattered electrons (for instance the L-edge of molybdenum at 2500eV has been measured by van Zuylen with primary electrons of 80 kV). It is rather easy to fix a post-specimen magnetic optics on a STEM, but Crewe has recently underlined that great care should be devoted to optimize the collecting power and the energy resolution of the whole system.

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Electron holography in materials science

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100087665 ◽

1991 ◽

Vol 49 ◽

pp. 670-671

Author(s):

Hannes Lichte ◽

Edgar Voelkl

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Materials Science ◽

Fourier Spectrum ◽

Object Wave ◽

Electron Holography ◽

Reconstruction Procedure ◽

Numerical Reconstruction ◽

Transmission Electron ◽

Unique Interpretation

The object wave o(x,y) = a(x,y)exp(iφ(x,y)) at the exit face of the specimen is described by two real functions, i.e. amplitude a(x,y) and phase φ(x,y). In stead of o(x,y), however, in conventional transmission electron microscopy one records only the real intensity I(x,y) of the image wave b(x,y) loosing the image phase. In addition, referred to the object wave, b(x,y) is heavily distorted by the aberrations of the microscope giving rise to loss of resolution. Dealing with strong objects, a unique interpretation of the micrograph in terms of amplitude and phase of the object is not possible. According to Gabor, holography helps in that it records the image wave completely by both amplitude and phase. Subsequently, by means of a numerical reconstruction procedure, b(x,y) is deconvoluted from aberrations to retrieve o(x,y). Likewise, the Fourier spectrum of the object wave is at hand. Without the restrictions sketched above, the investigation of the object can be performed by different reconstruction procedures on one hologram. The holograms were taken by means of a Philips EM420-FEG with an electron biprism at 100 kV.

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Zero-loss omega-filtered REM and RHEED on the new Zeiss 912

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100087392 ◽

1991 ◽

Vol 49 ◽

pp. 616-617

Author(s):

J.C.H. Spence ◽

J. Mayer

Keyword(s):

Electron Microscopy ◽

Materials Science ◽

Surface States ◽

Ccd Camera ◽

Dark Field ◽

Ion Pump ◽

Magnetic Imaging ◽

Reflection Electron Microscopy ◽

Diffraction Patterns ◽

Large Background

The Zeiss 912 is a new fully digital, side-entry, 120 Kv TEM/STEM instrument for materials science, fitted with an omega magnetic imaging energy filter. Pumping is by turbopump and ion pump. The magnetic imaging filter allows energy-filtered images or diffraction patterns to be recorded without scanning using efficient parallel (area) detection. The energy loss intensity distribution may also be displayed on the screen, and recorded by scanning it over the PMT supplied. If a CCD camera is fitted and suitable new software developed, “parallel ELS” recording results. For large fields of view, filtered images can be recorded much more efficiently than by Scanning Reflection Electron Microscopy, and the large background of inelastic scattering removed. We have therefore evaluated the 912 for REM and RHEED applications. Causes of streaking and resonance in RHEED patterns are being studied, and a more quantitative analysis of CBRED patterns may be possible. Dark field band-gap REM imaging of surface states may also be possible.

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