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Discover the SPA-LEED
The spot profile analysis low energy electron diffraction (SPA-LEED) instrument was developed in the 1980s by Prof. Martin Henzler and coworkers at the university of Hannover. Its advantages are:
- Very high dynamic range
7 orders of magnitude, (0.1 … 2*10^6 electrons per second) - Very high lateral resolution
transfer width >1000 Angstroms - Background intensity without artefacts
neither grid nor suppressor Moiré - No obstruction in images
no electron gun shadow visible
It is thus particularly well suited for high resolution, high dynamic range measurements of LEED spot profiles for detailed analysis of the spot shape (hence its name), which allows to derive quantitative information on roughness, defects, etc. impossible to infer from other methods.
(SPA-LEED data 1&2 courtesy of Dr. Rüdiger Hild, #3 Dr. Christian Wiedhoff, #4 Dr. Peter Kury)
In addition to the quality of the diffraction data in terms of dynamic range and resolution, a SPA-LEED produces very beautiful and esthetically satisfying LEED images due to absence of moirès, gun shadows, and the ability to choose false color tables for display.
The SPA-LEED combines two electrostatic deflection systems to bend the trajectories of the incoming electron beam (originating at the electron gun) on an S-shaped path onto the sample, as well as that of the diffracted electrons in the same fashion on the way back to a single electron detector.
The deflection of incoming and diffracted trajectory leads to a favorable Ewald construction with almost twice the length of the (k_f - k_i) vector and thus a larger accessible k_par range and less Ewald sphere curvature (green) in comparison to an optical LEED instrument (blue).
The instruments were made in the past by Leybold and later by Omicron Nanotechnology (now ScientaOmicron), and we are proud to continue the legacy of this powerful tool for surface analysis.
The latest (3rd generation) design includes a conical front of the instrument, which improves the access to the sample for molecular beam epitaxy, ion sources, etc. and thus enables the method to be used for structural anaylses during growth experiments (similar to RHEED).
References
The original SPA-LEED paper
U. Scheithauer, G. Meyer, M. Henzler
A new LEED instrument for quantitative spot profile analysis
Surf. Sci. 178(1–3): 441-451, 1986 [download]
Classics on LEED
M. G. Lagally, J. A. Martin
Instrumentation for low-energy electron diffraction
Rev. Sci. Instrum. 54: 1273, 1983 [download]
M. A. Van Hove, S. Y. Tong
Surface Crystallography by LEED
Springer Series in Chemical Physics, Vol. 2, Springer, Berlin, 1979
K. Müller, K. Heinz
The Structure of Surfaces
Springer Series in Surface Sciences, Vol. 2, 105, Springer, Berlin, 1985
Spot profile analysis
J. Wollschläger, J. Falta, M. Henzler
Electron diffraction at stepped homogeneous and inhomogeneous surfaces
Appl. Phys. A 50(1): 57-68, 1990 [download]
M. Horn-von Hoegen
Growth of semiconductor layers studies by spot profile analysing low energy electron diffraction
Z. Kristallogr. 214:1-75, 1999 [abstract]
[download]
W. Moritz, G. Chiarotti, P. Chiaradia (eds.)
Physics of Solid Surfaces · 5.4 SPA-LEED
Landolt-Börnstein - Group III Condensed Matter 45A (Springer Materials), 2015
[Springer] [DOI]
Reciprocal space maps
F.-J. Meyer zu Heringdorf, M. Horn-von Hoegen
Reciprocal space mapping by spot profile analizing low energy electron diffraction
Rev. Sci. Instrum. 76(8):085102/1-5, 2005 [download]
F.-J. Meyer zu Heringdorf, K. L. Roos, Ch. Wiethoff, M. Horn-von Hoegen, K. R. Roos
Growth of Ag nanowires on Au-pre-facetted 4 vicinal Si(0 0 1)
Surf. Sci. 602: 1852–7, 2008[download]
Pulse heating
P. Kury, P. Zahl, M. Horn-von Hoegen, C. Voges, H. Frischat, H. Pfnür, M. Henzler
Chopped sample heating for quantitative profile analysis of low energy electron diffraction spots at high temperatures
Rev. Sci. Instrum. 75(11):4911-5, 2004 [download]
SPA-RHEED
B. Müller, M. Henzler
SPA-RHEED — A novel method in reflection high-energy electron diffraction with extremely high angular and energy resolution
Rev. sci. Instrum. 66(11): 5232, 1995 [download]
ELS-LEED
H. Claus, A. Büssenschütt, M. Henzler
Low-energy electron diffraction with energy resolution
Rev. Sci. Instrum. 63(4):2195-9, 1992 [download]
T. Nagao, S. Hasegawa
Construction of an ELS-LEED: an electron energy-loss spectrometer with electrostatic two-dimensional angular scanning
Surf. Interf. Anal. 30: 488-92, 2000 [download]
Latest developments
P. Zahl, M. Horn-von Hoegen
Third-generation conical spot profile analyzing low-energy electron diffraction
Rev. Sci. Instrum. 73(8):2958-62, 2002 [download]