GISAXS @ D-line: Procedures
Line-up
mode
- disable CCD macros > ccdoff
- reset all sample positions and chose a new filename > new
- go into hutch, put ion chamber in, and change samples
- direct beam line-up
- make sample parallel to beam > rock
- if the angular scan shows the "shark tooth" profile,
you can proceed
- if the angular file has a flat top, or does not go to
zero on one side, redo rock
- reflectivity line-up
- measure a calibration reflectivity curve >
xr
- extrapolate the onset of samth scan to find the proper
zero value [ZERO]
using pencil & ruler on the print-out
- reset the zero of samth
>
mv samth [ZERO]; set samth 0
- measure
a proper reflectivity curve > xrfine
- in order to change scan parameters, use
> set_xrfine
- redo xrfine with
the new settings
( note: after ">" follows the spec command,
as it is
typed in )
( note: [ZERO] denotes the numerical value of the zero offset )
Switch
to CCD
mode
- enable ccd macros >
ccdon
- go into hutch and remove ion chamber
- open garage door
- take a test image for 0.1 sec >
corr 1
0.1
- finetune beamstop position , if needed
- step of +/- 0.1 mm in bsx
> mvr bsx
0.1
- whenever you move the beam stop: take a test image after
each step >
corr 1 0.1
- set the new bsx position
to zero >
set bsx 0
- collect images
- increase the exposure time - please no more than a factor
of 10 per step
- check that dark image exists > ls dark
- if not, collect a dark image first > dark [new exposure time]
- it is sufficient to update dark images once a day
- check image in fit2d
: maximum linear range of CCD is 15,000 units, the CCD saturates above
16,000 units
- recommended z-scaling in fit2d
: logarithmic with user min/max of 15 and 15,000
- choose a variety of samth
values, to optimize contrast
- choose a couple of samx
values, to check homogeneity of the sample
- within +/- 2 mm all remains well-aligned
- if you need a larger samx
range (>5mm) use the level macro
in connection with samtilt
- for anisotropic samples
- coarse check: turn sample 90
deg on holder and redo line-up, before collecting images
- fine scan: choose a variety of
samaz values (+/-20 deg)
- the samaz
axis is unfortunately not well aligned
- hence samth
should be corrected so that the reflected beam or the horizon or the
Yoneda band appear at the same position in the image
- it is useful to make a little calibration of position
shift (in pixels) vs. samth
offset