Process Information

Solid Sample Preparation:

The typical methods of mounting powder samples on the SGM beamline include:

Powders:

(a) pressed into aluminum sample rings, forming a pellet contained in the ring.  Samples must be finely ground to facilitate pellet formation. SGM beamline staff will not grind samples;

(b) pressed onto double-sided carbon tape on either an aluminum, carbon, steel or brass plate.  Surface coverage may not be complete and signatures from the tape may be present;

(c) dispersed in a suitable solvent, usually water, and drop-deposited onto Au coated Si wafers (5 x 5 mm) and air dried.

If there is a preferred method indicate it in the additional information of the sample mail-in form.  Beamline staff will inspect the samples and may recommend an alternative mounting strategy.

Coupons: These are oddly shaped/stand-alone samples (e.g., meteorite, rebar, tooth, carbon paper) or samples affixed to a substrate by the User (e.g., battery component, soil core).  The materials will be attached to either Al, carbon, steel or brass plates using double sided carbon tape.  The size should not exceed 5 x 5 mm to facilitate putting more than one sample on the sample holder or be more than 3 mm thick due to space restrictions imposed by the SDD.  SGM beamline staff will not cut coupons.   IMPORTANT.  Sometimes it is not easy for the beamline staff to tell which side the sample is on when the sample (e.g., carbon sample on carbon paper) is just loose in a vial/bottle.   For these kinds of samples , where cross contamination is not an issue,  we recommend that you mount the samples onto the SGM sample plates in your laboratory and send them that way.  Or alternatively, instead of having them loose in a vial, attach them with double sided C-tape in a petri dish, each sample in its own petri dish if cross contamination is an issue. This way we know which side the sample is on.  You can contact us for the  ordering information for the sample plates (Al, Steel, Brass) we use on the beamline.   We order from McMaster Carr (about $12 to $25/100 plates), depending on the type ordered) and they are usually delivered within 2 or 3 days after they receive the order.

Suspensions: These will be pipetted onto Au coated Si wafers and air-dried. 

For other sample mounting options contact the beamline technical contact. 

Air-Sensitive Samples:  Samples that are air-sensitive can be mounted in an anaerobic chamber in a glove box.   The chamber is then pumped to about 10^-3 Torr, which is then put in the XAS endstation and opened after the endstation is under vacuum (~10^-6 Torr).

X-ray Absorption Spectroscopy (XAS) Data Collection:

Both total electron yield (TEY) and partial fluorescence yield (PFY) will be collected for all samples, references and calibrants.  The TEY signal will be acquired by monitoring the sample drain current.  The PFY signal with energy resolution of ~100 eV will be measured by four silicon drift detectors (SDD) at various angles to the sample.  The beam spot will be between 50 and 100 microns in the vertical and horizontal directions.  The beamline energy will be swept over the desired excitation energy range at a rate determined by beamline staff (typically 1 minute sweeps for 50 eV).  Multiple consecutive scans will be acquired until a sufficient signal to noise (S/N) ratio is achieved up to a maximum of 60 scans.  New or ‘fresh’ spots will be used for each successive scan.  An Excitation-Emission Matrix Spectroscopy (EEMS) measurement will be performed on an arbitrary position of the sample, which involves scanning from 250 to 2000 eV at an energy resolution of about 5 eV, providing elemental information of significant edges and/or diffraction information.

Calibration samples:  The energy scale of the SGM beamline is usually within 2 eV of accepted values.  In order to be consistent between runs so that spectra can be directly compared from different runs to each other, and also to publish XANES spectra usually requires that they be calibrated to spectra from “pure” compounds.  Thus, a calibrant for every edge will be run, at least once per a 24 h shift.    Usually < 10 fly scans will suffice to get an averaged spectrum with good S/N of the calibrating peak energy position.  Note that the User needs to calibrate their spectra based on the actual and expected value of the calibrant.   Ask SGM beamline staff for assistance if required.

The SGM beamline has compiled a calibration document of “pure” compounds that may be used for calibrating of the SGM energy scale.  This document includes the energy positions of a specific peak, usually the white line peak, the associated reference and a figure from the reference indicating the peak used for calibration.  The calibrant document can be found here.  Note that the document is incomplete and if a particular edge is not present it can be added upon request.  Also, if there are more suitable references  for an edge we would like to be informed of them.

Users can supply their own material for calibration purposes and/or suggest another compound be used for calibration.  Regardless, the SGM beamline staff will most likely also run their own calibrant as a form of quality control.  Further quality control scans will be made routinely by beamline staff and will be available to the Users.

Data access and analysis: 

The raw data collected from the User samples, references and calibrants will be in the SGM “User Data Account” indicated on the Sample Mail-in Form.  The data will be displayed in “real-time”.   The raw data will be partially processed, including interpolated, region of interest (ROI) selected from the EEM and the derived spectra averaged, excluding any bad spectra.  The partially processed data and a report on the the processing particulars will be generated and available to the Users in the User Data Account.  To access the raw and processed data Users can login to the SGM data website (https://sgmdata.lightsource.ca) using their CLS User Portal login credentials.  Note that data can be shared between Users listed on the project.  Users can process the raw data using basic tools for reducing the data, such as interpolation,  EEM ROI selection and spectra averaging capabilities.  Please contact the beamline staff for more details on the data collection and  processing of the raw data and for any assistance with the data analysis.  Their contact information is found at https://sgm.lightsource.ca. 

Note Users need to login to their SGM data User Account for the first time at SGM_data_account in order to activate it to receive data.