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last update 15/02/2010
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 SPELEEM DESCRIPTION 

Introduction | Specifications | Operation modes | XPEEM and LEEM methods

The scheme of the SPELEEM microscope is illustrated in the figure below: (1) the main chamber; (2) the preparation chamber with load lock; (3) the image column; (4) the illumination colummn; (5) the beam separator; (6) the connection to the beamline. There are valves between the main chamber and the beamline, between the main chamber and the preparation chamber, between the preparation chamber and the load lock, and between the main chamber and the beam separator.

beamline layout
Layout of the SPELEEM microscope.

(1) The Main Chamber
Overall, there are eight ports pointing at the sample, which sits in front of the objective lens. One horizontal port connects the main chamber to the beamline, another allows illumination of the sample with Hg-lamp. The latter can also be used to read the sample temperature with an optical pyrometer. The other six ports are generally used for e-beam evaporators (two inclined 45° from above, two 45° from below, one from top, one from bottom).
A schematics drawing of the instrument main chamber can be found here.
The main chamber is pumped by a Varian Starcell ion pump (300l/s) coupled with a titanium sublimator pump, assuring a base pressure in the low tens. Alternatively a magnetic bearing turbo pump with vibration insulation can be used. In the latter configuration, the microscope can be operated using the main chamber as a gas flow reactor, up to a maximum pressure of 1·10-6 mbar when the beamline is open. This figure can be increased to 1·10-5 mbar when the microscope is isolated from the beamline (LEEM operation mode).
Available facilites are a gas line with precision leak valves, Omicron e-beam evaporators, a quadrupole mass spectrometer, a magnetisation stage, and a sample parking stage.

(2) The preparation chamber
A small preparation chamber is available for sample treatment. The sample is hosted on a small manipulator allowing heating, facing the sputter gun. The sample preparation chamber is equipped with a load-lock that allows to transfer samples in 45 minutes from air to a vacuum of better than 10-8 mbar. The preparation chamber is pumped by an ion pump and a Ti sublimation pump. Base pressure is about 10-9 mbar.

(3) The image column
The image column consists of imaging optics (transfer lens, field lens, intermediate lens, projector lens), the imaging energy analyser, a double projector, and a chevron channelplate/screen detector (Burle). Images are taken with a video camera (PCO SensiCAM).

(4) The illumination column
The illumination column consists of an LaB6 electron gun and capacitor lenses. It provides the electron beam used to probe the sample in LEEM and µ−LEED operation. It illuminates an area of about 80 µm on the sample. Apertures can be used to illuminate smaller regions (20, 5, 2µm).

(5) The Beam Separator
The beam separator connects the image column and the electron gun with the main chamber. It acts as a magnetic prism which separates incident and reflected beams, when the microscope is operated in LEEM or LEED modes.

(6) The Connection to the Beamline
It hosts the beamline diagnostics, a Au coated Mo mesh to measure I0 and a photodiode.