Dirk Preikszas

XPEEM WITH ENERGY-FILTERING: ADVANTAGES AND FIRST RESULTS FROM THE SMART PROJECT

The second development step of the SMART project, i.e. an energy-filtered but not yet corrected photoelectron emission microscope, operates at the undulator U49/1-PGM beamline at BESSY II. It already demonstrates the variety of methods of the final version: microscopy, spectroscopy and electron diffraction. Some recent experimental results are reported for these three operation modes. In addition, the theoretical improvement of lateral resolution and transmission of PEEMs in general by using an energy filter is discussed for systems without and with aberration correction.

SMART: An Aberration-Corrected XPEEM/LEEM with Energy Filter

A new UHV spectroscopic X-ray photoelectron emission and low energy electron microscope is presently under construction for the installation at the PM-6 soft X-ray undulator beamline at BESSY II. Using a combination of a sophisticated magnetic beam splitter and an electrostatic tetrode mirror, the spherical and chromatic aberrations of the objective lens are corrected and thus the lateral resolution and sensitivity of the instrument improved. In addition a corrected imaging energy filter (a so-called omega filter) allows high spectral resolution (ΔE=0.1 eV) in the photoemission modes and back-ground suppression in LEEM and small-spot LEED modes. The theoretical prediction for the lateral resolution is 5 A; a realistic goal is about 2 nm. Thus, a variety of electron spectroscopies (XAS, XPS, UPS, XAES) and electron diffraction (LEED, LEEM) or reflection techniques (MEM) will be available with spatial resolution unreached so far.

Double aberration correction in a low-energy electron microscope

The lateral resolution of a surface sensitive low-energy electron microscope (LEEM) has been improved below 4 nm for the first time. This breakthrough has only been possible by simultaneously correcting the unavoidable spherical and chromatic aberrations of the lens system. We present an experimental criterion to quantify the aberration correction and to optimize the electron optical system. The obtained lateral resolution of 2.6 nm in LEEM enables the first surface sensitive, electron microscopic observation of the herringbone reconstruction on the Au(111) surface.

Outline of the Mirror Corrector for SMART and PEEM3

Extended abstract of a paper presented at the Pre-Meeting Congress: Materials Research in an Aberration-Free Environment, at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, July 31 and August 1, 2004.

Corrected Electron Optics‐Improved Resolution and New Analysis Capabilities

Innovative charged particle imaging instruments overcome many of the limitations of conventional analysis methods. Resolution improvements and enhanced analysis capabilities are provided by advanced SEM and TEM electron optics as well as innovative detector schemes. In this paper we will discuss various embodiments of corrected electron optics employed in SEMs and TEMs, respectively.

Concept and Design of the SMART Spectromicroscope at BESSY II

The concept of a new spectromicroscope (SMART = spectromicroscope for all relevant techniques) currently under construction for an undulator beam line at BESSY II is discussed. The design of the optical system is described as well as the modes of operation and the experiments that can be performed. Monochromatic XUV-radiation (tunable within the energy range 20 to 2000 eV) will be provided by a planegrating monochromator and focussed onto the sample by means of an ellipsoidal mirror. In addition, an electron gun will be installed allowing LEEM, MEM and other forms of microscopy as well as small spot LEED to be performed. With an aberration corrector we expect to achieve a lateral resolution better than 5 nm and to increase considerably the transmission of the optical system compared to previous instruments. An imaging band pass filter corrected to second order will select the energy and the energy band width for the image-forming electrons. The instrument will also allow spectroscopy of photoelectrons from selected small areas of the sample (5–500 nm) with an energy resolution of 0.1 eV.