Analysing X-ray data using GudrunX

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X-r

ay i(Q)

Q (Å-1)

Ca60

Mg25

Cu15

Ca60

Mg20

Cu20

Ca60

Mg15

Cu25

Outline• Planning an experiment

– Absorption– Fluorescence– Beam size

• Data required• Outline of analysis process• Step by step guide through analysis• Practice with some data!

– SiO2

– H2O– Tellurite glass

Planning an experiment• Before starting an experiment it is important to have a very good idea of

your sample composition and density.

• This information will help identify any potential problems which may arise, such as:– Absorption +capillary size– Beam size– Measurements required– Fluorescence (We’ll return to this later)

• A good idea of potential problems will help you plan the length of your experiment too.– Strongly absorbing/weakly scattering or strongly fluorescent samples

may require longer data collection

• Consider what your data will be used for and what quality you require.

Planning an experiment: AbsorptionIf we accept 60% loss of

flux, we can estimate the diameter of capillary to use:

H2O : µ = 0.656ln(0.4)/-6.626 = 1.4 cm

d ~ 1.8 cm

Al2O3 : µ = 6.626d ~ 2 mm

GeO2 : µ = 96.906d ~ 0.12 mm

Y2O5 : µ = 186.756d ~ 0.07 mm

TeO2 : µ = 68.607d ~ 0.18 mm

PbO : µ = 549.499d ~ 0.03 mm

Linear (µ) and mass (µ/ρ) absorption coefficients can be calculated from programs

such as XOP(1)

Area = πr2 L =(πr2)/2r = π/4 d ~ 3/4 d

2r

L

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s A

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(Ag

K)

Element

Ag10000 1000000.1

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1000 Ge (32) Y (39) Te (52)

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Energy (eV)

AgIncrease Z → increased energy at

which K edge occurs.

for region around Ag (Z > Ag) µ/ρ < (Z <Ag)

Planning an experiment: Absorption

HOWEVER, there is also density to consider

A Material chosen as a β filter must have an absorption edge which lies between the Kα

and Kβ peaks.For an Ag tube, Rh is used.

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linea

r abs

orpt

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coef

ficie

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m-1

Energy (eV)

K K

Planning an experiment: Absorption

Example: β filter

Planning an experiment: Beam size

Prog. Rec. slit

Anti scatter slit

X-ray tubeKβ filter

Soller slit

Prog. Div. slit

Mask

Soller slit

Detector

Capillary size

PDS ASS

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1 1/4 1/2

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3 1 2Table 1: PDS and ASS

settings

240 mm (r)

PDS angle (θ) Diameter of sample (L)

PDS θ (rad) = L/r

ASS= PDS x 2 PRS (mm) = L

Measurements neededOnce the experimental setup has been decided up, three measurements are required – as with Neutron analysis,

these are:

Background

Sample in capillary

Empty capillary

All these measurements need to be taken under the SAME CONDITIONS.

The current set up is to collect data at 0.2° intervals from 3.2 – 156°.

At each point, data is collected of 30 seconds.

There is the option to collect two sets of data:

Several repeat scans from 3.2 to 156°Additional scans from 35 to 156° to

improve statistics at high Q

GudrunX: What does it do?

Krogh-Moe – Norman normalisation

Polarisation

Absorption

Compton scattering

• Calculating the coherent scattering

Measured data background data

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1x105

2x105

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6x105 raw data corrected for

absorption & polarisation

Inte

nsity

Q (Å-1)

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S(Q

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S(Q)

GudrunX: What does it do?

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Inte

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Experimental data Self scattering

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S(Q

)

Q

S(Q)

sample <f>2 <f2> %diff

SiO2 100 108 8%

Ga2O3 309.7 448 44%

Effect of normalisation:

• Calculating F(Q)

Installing GudrunX

The X-ray diffractometer webpages can be found at http://www.isis.stfc.ac.uk/support-laboratories/xrd/xrd9446.html

OR as a link from the disordered materials group web page.

Instrument panel:The required files are all located in the gudrunX folder.

• User may wish to alter the Q range of the F(Q) produced, depending on the quality of the data.

• The Qmax should be set to the final Qmax you chose for you data.

Beam panel:Requires minimal alteration.

• Edit the beam size if the beam is smaller that the sample.

• Ensure the correct bremsstrahlung file is chosen.

Normalisation panel:

User must choose which method of normalisation they wish to apply to the data.

Altering Breit-Dirac factor and Overlap factor can give some improvements to the extracted F(Q). Maintain default values initially.

Sample background panel:Select an appropriate sample background panel.

‘Read data’ will display the information from the .XRDML file, including number of scans and the range of angles over which the chosen data set has been

measured.

Set sample background factor (between 0.9 and 1)

Sample specific information required:

Once the instrument and background information has been checked, new tabs need to be added to give sample specific information.

As with GUDRUN this includes a sample and a sample container tab.

Information required includes:

Sample specific information:•Composition•Effective density•Sample size•Fluorescence - a problem for elements in the same row as Ag (Rb – Te)•Multiple scattering

Experimental setup:•Polarisation - 0•Compton scattering - 1•Bremsstrahlung - 0.4

Container panel:Composition, container size (inner and outer dimensions), effective density.

For density either the measured effective density can be given, with a tweak factor = 0

Or the bulk density can be used with the tweak factor alteredEffective density = bulk density/tweak factor

Sample panel:Basic information + fluorescence, multiple scattering etc.

Ensure that packing fraction is sensible (measure or estimate it ~60%)Vary effective density and multiple scattering first, then bremsstrahlung.

Only apply fluorescence for samples containing Rb – Te.

GudrunX: Output files

.subcanX = 2θY1 = experimental dataY2 = single atom scatteringY6 = Bremsstrahlung

GudrunX: Output files

.soqX = QY1 = F(Q)

F(Q) will have been normalised to either <f>2 or <f2>. Ensure that you have a record of which you used!

.gofrX = rY1 = G(r)

Quality of G(r) can be improved by varying parameters in GudrunX. Alternatively, the fourier transform software in Open Genie can be used.

Daniel will be discussing the relationship between various correlation functions

GudrunX: Output files

Fluorescence

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10000 Ca Sr Ag K edge

Mas

s ab

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tion

coef

ficie

nt

Energy (eV)

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2 capillary

Inte

nsity

(cps

)

Angle

X-ray energy > absorption edge in sample → Fluorescence

Fluorescence provides a background which is uniformly distributed across

the angular range

Fluorescence

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s ab

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Energy (eV)

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2 capillary

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(cps

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Multiplying the data measured for the empty capillary and Ca/Sr glass data by a scale factor to match the Ca glass data (at high angle) gives:

The shape of the capillary and calcium data are well matched.

Problem with strontium sample.

Fluorescence

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Energy (eV)

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2 capillary

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(cps

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However, if a constant background is subtracting from the Ca/Sr data and THEN the data is scaling:

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The characteristic X-ray shape is onceagain present in the data