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Nanospectroscopy Beamline Description

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The schematics diagram of the SPELEEM microscope is illustrated in the figure on the right hand side: (1) main chamber; (2) preparation chamber with load lock; (3) image column; (4) illumination column; (5) beam separator; (6) 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.

The Main Chamber (1)

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 sample temperature cn be read through the objective lens using 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). The main chamber is pumped by a Varian Starcell ion pump (300 l/s) coupled with a titanium sublimation pump, assuring a base pressure in the low 10-10 mbar range. 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 value can be increased to 1·10-5 mbar when the microscope is isolated from the beamline (LEEM operation mode). Available facilities are a gas line with precision leak valves, e-beam evaporators (Focus - Omicron GmbH), a quadrupole mass spectrometer, a magnetization stage, and a sample parking stage.

The preparation chamber (2)

A small preparation chamber allows simple treatments such as annealing and exposure to gas. A small heating facility allows annealing and flash up to temperatures of about 2000 K. An Ar ion gun facing the sample is provided for sputtering.  There are also two precision leak valves for traetent with gases. 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 through theairlock turbo or with a dedicated ion pump . Base pressure is in10-9 mbar range.

The image column (3)

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

The illumination column (4)

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 with a maximum total current of about 100 nA. Apertures can be used to illuminate smaller regions (20, 5, 2µm).

The Beam Separator (5)

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.

The Connection to the Beamline (6)

It hosts the beamline diagnostics, a Au coated Mo mesh to measure I0, a photodiode and a phosphor screen.

Last Updated on Thursday, 15 November 2018 10:31