Manuales

 Here we describe our procedure to obtain the vector magnetization in XMCD-PEEM (and SPLEEM). 

howto triangles 06 3DVector XMCD-PEEM relies on measuring XMCD images of the same place on a surface, along different relative orientations of the x-ray beam and the surface under study. Each orientation gives the dichroic signal along the x-ray beam direction. Combining three components along three non-coplanar directions, the full dichroic vector, proportional to the magnetization, can be obtained. In SPLEEM something similar can be done by measuring the spin-assymetry for three (non-coplanar) spin-polarizations of the electron beam relative to the sample. The problem with XMCD-PEEM is that rotating the sample guarantes that the imaging conditions and thus the image distortions are not the same for each angle, so images have to be corrected afterwards (step 3). Also rotating the azimuthal angle in a typical XMCD-PEEM setup involves a substantial amount of time (typically half-an-hour per rotation) due to the need to keep the same area centered and to readjust the tilt, so a full 3D sequence requires easily several hours. In contrast, SPLEEM allows to acquire a triplet in seconds, albeit without chemical sensitivity. However, if you want to do SPLEEM the available instruments are fewer than for XMCD-PEEM. One possibility is to apply for time at the SPLEEM of the National Center for Electron Microscopy at Berkeley Lab with Andreas K. Schmid. The images show here have been acquired at the CIRCE beamline in the Alba synchrotron in collaboration with Michael Foerster and Lucía Aballe.

ImageJ plugins 

ImageJ is a really neat program for image processing, so it is very useful if you work with LEEM/PEEM images. And it runs in Linux, MacOSX, Windows, you name it. Nowadays it might be more fun to use the Fiji compilation (https://fiji.sc/), which is actually based on ImageJ2. One problem is that, for me at least, Fiji is just too slow reading images, so we are stuck with using the two versions. Or using the raw import.

The file format of the proprietary UView format of Elmitec files with the original data of the Nanoscale manuscript includes a header of variable length depending on the version, and a block of  nx*ny (if the file has only one image of dimensions nx,ny) 16-bit integers with little endian byte order, i.e. the header is (total_file_size-2*nx*ny). As such it can be used by open source programs that open the format natively: 
  • Gxsm  (use menu option File->Open to Free Channel)
  • ImageJ with the plugins described below.
Or with any program that can open 16-bit images skipping a header such as ImageJ/Fiji using the Import->Raw option, selecting 16-bit, 1024x1024 pixels, 520 offset, little-endian bye order.
 

I finally made a plugin in the "new-style" good for Fiji and ImageJ2, whose source you can find in the github repository: https://github.com/jufiba/scifio-UView. Just copy the .jar file under into the plugins folder and restart Fiji/ImageJ2. You should be able to open the Elmitec .dat files without any import option. Regretably, Fiji is a moving target at lately the plugin has stopped working.

 

Cámara: FlyCap2 (software)
STM: SPM Controller

 

2013-01-18 16.43.16

 

Dosers:

1. Connect water.

2. Connect filament and doser power supplies (Delta and FUG).

3. Check that minus output of doser power supply is grounded.

4. Check that shutter is closed.

5. Turn on doser power supply.

6. Apply required high voltage.

7. Make sure filament current is 0 A.

8. Turn on filament power supply.

9. Increase filament current until required emission.

10. Leave some time warming (5-15 min, depending on doser).

11. Heat sample during warming time *

12. Open shutter for a given time. Record emission current (and HV voltage), background pressure, filament current and voltage, sample temperature.