Resonant Elastic X-ray Scattering (REXS)

Number of elements in the periodic table (K and L edges)

Image title

Basic Theory - REXS
Basic steps for sample alignments - REXS

Beamsplitting polarimeter

The polarization analyzer isolates and measures a unique series of diffraction resonances at the different K-edge.

Important SPEC commands for REXS

Opening and closing the shutter

  • opens - Opening the shutter
  • closes - Closing the shutter

Pilatus video on and off

  • pil_von - Turn pilatus video 'on'
  • pil_voff - Turn pilatus video 'off'

Position of the displex

  • wm cryx - where motor for displex in 'x' directions
  • wm cryy - where motor for displex in 'y' directions
  • wm cryy - where motor for displex in 'y' directions

Get the height correct for the sample

  • opens; lup cryz -0.4 0.4 20 0.2; closes - open the shutter and perform the sample scan in the z directions
  • umv cryz CEN- it will go to the center position

Get the theta correct for the sample

  • umv th 10- Move theta to 10 degrees
  • opens; lup cryz -0.4 0.4 20 0.2; closes - open the shutter and perform the sample scan in the z directions

Calulate the motor position in a given point in the reciprocal space

  • setlat - set lattice paramter information (a, b, c, alpha, beta, gamma)
  • pa - it will show the orientation matrix
  • ca - calculate motor settings for a given point in reciprocal space
  • ca 0 0 20 - Calculate the theta, 2theta, chi, and phi for the structural peak (0 0 20)
  • br - br and ubr - move to the reciprocal space coordinates (HKL)
  • ubr 0 0 20 - Go to the peak (0 0 20)
  • or0 0 0 20 - To put the peaks (0 0 20) as first element of the orientation matrix
  • or1 0 0 18 - To put the peaks (0 0 18) as first element of the orientation matrix

Moving energy above and below the resonance, perform energyscan

  • moveE 11.216 - move the energy for the sample Ir L edge
  • getE - Get energy
  • matchUE 3 - the undulator 3rd harmonic match with the energy
  • lscan L-0.1 L+0.1 50 0.5 or lscan 19.9 20.1 50 0.5 - Lscan in a range of 0.2, with 50 steps, and 0.5 sec/step
  • timescan 5 - it is a timescan with 1 datapoint in 5 seconds
  • opens; EUQscan 11.2 11.24 40 3 3; closes : Energyscan to get the edge

Moving the energy to the off-resonance

  • moveE 11.23- Moves to 11.23 keV from current energy
  • matchUE 3 - the undulator 3rd harmonic match with the energy, the h k l values will be different than the previous one
  • ubr H K L - the previous h k l values carried by H K L, we need to do ubr H K L
  • wh - where is every position
  • getE - it gies current energy information

We have two detectors: Pilatus 6 (PIL6) and Pilatus 8 (PIL8). PIL6 is in the beam direction. PIL8 is our sigma-pi channel. The alignment will be based on PIL6.

ROI information

To set the ROI's for PIL6

  • getroi6 - provide information about the roi chosen in the area detector based on the direction beam position, i.e., xmin, ymin, xsize, ysize.
  • setroi6 278 67 1 3 - Changing the vertical and horizontal sizes. Examples: 278 and 67 are minimum pixel dimension along x (vertical) and y (horizontal) axis whereas 1 is vertical pixel size (it is minimum) and 3 is horizontal pixel size.

To set the ROI's for PIL8

  • getroi - provide information about the roi chosen in the area detector based on the direction beam position, i.e., xmin, ymin, xsize, ysize.
  • setroi 278 67 1 3 - Changing the vertical and horizontal sizes. Examples: 278 and 67 are minimum pixel dimension along x (vertical) and y (horizontal) axis whereas 1 is vertical pixel size (it is minimum) and 3 is horizontal pixel size.

After setiing up the two peaks, you can set up the macros to optimize the peak positions

  def alignfine '
        opens
        lup chi -0.2 0.2 50 0.1
        umv chi CEN
        lup th -0.05 0.05 50 0.1
        umv th CEN
        lup tth -0.1 0.1 50 0.1
        umv tth CEN
        lup th -0.03 0.03 30 0.1
        umv th CEN
        lup tth -0.1 0.1 50 0.1
        umv tth CEN
        lup chi -0.2 0.2 50 0.1
        umv chi CEN
        closes
        wh
 ‘

To permform the L scan for (0 1 17) peaks 

  def getlscan '
        wh
        opens
        lscan 16.96 17.04 120 1
        closes
        moveE 11.20
        matchUE 3
        ubr H K L
        opens
        lscan 16.96 17.04 120 1
        closes
        moveE 11.215
        matchUE 3
  ‘

Perform two theta plan

  def gettthscan2 ‘
        wh
        alignfine
        opens
        lup cryz -0.2 0.2 40 0.1
        umv cryz CEN
        alignfine
        opens
        th2th -0.04 0.04 80 1
        closes
  ‘