GISAXS @ D-line: Procedures
Line-up
mode: Rock & Roll
- disable CCD macros > ccdoff
- reset all sample positions and chose a new filename > new
- provide filename for sample
- provide scan number (hit return for default)
- provide sample thickness (hit return, if unchanged)
- note : new moves
the ion chamber into the beam automatically
- go into hutch and change sample
- 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
- for rough samples: do rock at
least twice and then skip to ccd mode
- reflectivity line-up (for smooth samples with
good reflectivity)
- measure a calibration reflectivity curve >
roll
- 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
- optional : measure
a proper reflectivity curve
> xrfine
- xrfine automatically takes a 10 sec dark current measurement before each actual scan
- in order to change scan parameters, use
> set_xrfine
- redo xrfine with
the new settings
- new setting will be remembered until changed with set_xrfine again
( 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
- check current sample position using wsam
- choose sample position (samth, samx, samaz)
- a samth
value of 0.25 deg at 10 keV x-ray energy usually is
a good starting point
- samx=0
is the default line-up point; make sure to take images at 2 other samx
values at least
- enable ccd macros >
ccdon
- moves ccd into the scattering position
- enables ccd macros
- 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 (suggestions)
- 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
- note : 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 reflected
beam position
shift (in pixels) vs. samth
offset
- fine scan: choose a variety of
samaz values (+/-180 deg)
- the ex-situ goniometer with the crossed arcs works best
for this, in conjunction with a laser beam line-up
- laser line-up: adjust arcs
such that the reflected laser beam ends up in the same spot independent
of samaz
- using azimuth angle pairs with a 180deg difference in
the azimuth of a specific arc is most efficient.
- please be careful when you spin samaz
manually to disengage the worm gear properly
- when you re-engage samaz please check with your
hand first that the worm gear is properly aligned
- tighten the set screw only after motor is properly
engaged - this may require moving samaz +/-1deg
- a line-up laser can be supplied
- if any of this procedure does not make sense to you,
please ask for help / training