Lesson 2

Diffractometers

Nicola Döbelin

RMS Foundation, Bettlach, Switzerland

October 03 – 05, 2016, Maastricht, NL

Repetition: Generation of X-rays / Diffraction

2

Characteristic X-radiation

Anode

Target Sample

SEM: BSE detector, BSED / SAED detector

SEM: SE detector

SEM: EDX detector

EMPA: EDX / WDX

XRF

XPS

XRD (WAXS)

SAXS, XRR

Absorption:

XAS, EXAFS, XANES

3

Repetition: Generation of X-rays

Wavelength (nm)

Inte

nsity

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Cu

Kα1

Kα2

Kβ

Kβ absorption filter

Monochromator Crystal

Digital filtering

Repetition: Powder Diffraction

4

n ∙ λ = 2 ∙ d ∙ sin(θ)

d

λ

θ θ 2θ

(120)

(100)

(010)

Powder sample

Repetition: Powder Diffractometer

5

X-ray tube

Primary Beam

Powder

Sample

Diffraction Cones

«Secondary Beams»

X-ray Detector scanning X-ray intensity

vs. 2θ angle

Analogue Cameras

6

http://adias-uae.com

Debye-Scherrer Camera:

Powder in Glass Capillary

Diffraction pattern recorded

on photographic film

2θ angle

Various alternative setups:

Gandolfi …

Guinier …

Straumanis …

Bradley …

Seemann-Bohlin …

…Camera

Digital Diffractometers

7

Transmission Geometry

Glass Capillary

Foil

Fluid Cell

Capillaries are ideal for:

• Light atoms (Polymers, Pharmaceuticals)

• Small amounts

• Hazardous materials

• Air-sensitive materials

Use characteristic radiation with low absorption coefficient

Flat powder sample

Reflective Geometry

Reflective Geometry is ideal for:

• Absorbing materials (Ceramics, Metals)

• Thin films

• Texture analysis

Use characteristic radiation with high absorption coefficient

Bragg-Brentano Parafocusing Diffractometer

8

Tube and Detector move symmetrically

Sample

X-ray Tube

Detector

Start

Scan

End

Instruments

9

Lab Instrument Monochromator Configuration

RMS Foundation Bruker D8 Energy dispersive Detector

Bragg-Brentano (Reflection) Debye-Scherrer (Capillary)

Uni Bern Panalytical X’Pert Ni-Filter Bragg-Brentano (Reflection)

Uni Bern Panalytical CubiX Graphite Monochromator

Bragg-Brentano (Reflection)

Bruker D8 Panalytical X’Pert Panalytical CubiX

Bragg-Brentano Diffractometer

10

Flat powder sample

More optical elements are required

to control the beam pattern.

X-ray tube

Detector

Kβ filter

Sample holder

Sample surface

Irradiated area

Primary

beam

Bragg-Brentano Parafocusing Diffractometer

11

Sample

X-ray

tube

Detector

Goniometer

circle

Divergence

slit

Soller

slit

Soller

slit

Anti-Scatter

slit

Beam

mask

Anti-Scatter

slit

Receiving

slit

Focusing

circle

Kβ Filter

Typical Configuration (with Kβ filter)

Bragg-Brentano Parafocusing Diffractometer

12

Sample

Detector

Soller

slit Anti-Scatter

slit

Receiving

slit

Secondary

monochromator

Typical Configuration (with secondary monochromator)

Modern instruments are modular.

Configuration can be changed easily.

PANalytical: «PreFIX»

Bruker: «SNAP-LOCK»

Beam Divergence

13

Divergence Slit

Soller Slit

Beam Masks

Instrument Configuration

Many optical elements = many options to

optimize data quality

How to find the best configuration?

14

Tube

Soller Slits

Programmable

Divergence Slit

Beam Mask

Sample Stage

«Spinner»

Anti-Scatter

Slit

Programmable

Anti-Scatter Slit

Soller Slits

Ni-Filter

Detector

Optimum Settings: Divergence Slit

15

80° 2θ

20° 2θ

20° 2θ

80° 2θ

Beam overflow!

- Wrong peak intensities

- Artifact signal from sample holder

Reduced beam

divergence angle

Optimum Settings: Divergence Slit

16

20° 2θ 80° 2θ

Low incident angle:

- Low penetration depth

- Large illuminated area

High incident angle:

- Deep penetration depth

- Small illuminated area

Fixed divergence slit:

Irradiated Volume

is constant

Constant intensity of

diffraction pattern

20° 2θ

Low incident angle:

- Narrow divergence slit

- Low penetration depth

Variable divergence slit:

80° 2θ

High incident angle:

- Wide divergence slit

- Deep penetration depth

Irradiated Area

is constant

Higher diffracted intensity

at high 2θ angle

Fixed vs. Variable Divergence Slit

17

20 30 40 50 60 70 80 90

Inte

nsity [a

.u.]

Diffraction Angle [°2]

fixed

variable

More than 2x higher

intensity at 90° 2θ

with variable DS

Divergence Slit: Irradiated Length

18

30.2 30.3 30.4 30.5 30.6 30.7

0

500

1000

1500

2000

2500

3000

Inte

nsity [co

un

ts]

Diffraction Angle [°2]

5mm

10mm

15mm

Soller Slits: 0.02 rad, Beam Mask: 10mm

30.2 30.3 30.4 30.5 30.6 30.7

0

20

40

60

80

100

Inte

nsity [%

]

Diffraction Angle [°2]

5mm

10mm

15mm

15 mm

10 mm

5 mm

Optimum Settings: Divergence Slit

19

Sample holder

Sample surface

Irradiated area

Primary

beam

Correct! Wrong! Wrong!

Reduce «irradiated length»

of divergence slit Use a smaller Beam Mask

Beam Mask

Beam Mask

20

30.2 30.3 30.4 30.5 30.6 30.7

0

500

1000

1500

2000

2500

3000

3500

Inte

nsity [co

un

ts]

Diffraction Angle [°2]

5mm

10mm

20mm

Soller Slits: 0.02 rad, Irradiated Length: 10mm

30.2 30.3 30.4 30.5 30.6 30.7

0

20

40

60

80

100

Inte

nsity [%

]

Diffraction Angle [°2]

5mm

10mm

20mm20 mm

10 mm

5 mm

Optimum Settings: Divergence Slit

21

Using sample holders of various sizes?

Match your Divergence Slit and Beam Mask!

Or else: Waste of intensity Beam spill-over or

30.2 30.3 30.4 30.5 30.6 30.7

0

20

40

60

80

100

Inte

nsity [%

]

Diffraction Angle [°2]

0.02rad

0.04rad

Soller Slits / Collimators

22

30.2 30.3 30.4 30.5 30.6 30.7

0

1000

2000

3000

4000

5000

6000

7000

Inte

nsity [co

un

ts]

Diffraction Angle [°2]

0.02rad

0.04rad

In primary & secondary beam, Beam Mask: 10mm, Irradiated Length: 10mm

0.04 rad

0.02 rad

Receiving Slit / Detector Slit

23

Al2O3, 15 mm irradiated length, 2.5° soller slit

34.9 35.0 35.1 35.2 35.3 35.4

0

1000

2000

3000

4000

5000

6000

7000

Inte

nsity [co

un

ts]

Diffraction Angle [°2]

0.075 mm

0.225 mm

0.375 mm

34.9 35.0 35.1 35.2 35.3 35.4

0

20

40

60

80

100

Inte

nsity [%

]

Diffraction Angle [°2]

0.075 mm

0.225 mm

0.375 mm

Summary: Monochromators

24

Optical Element Effect on Spectrum Effect on Intensity

Kβ Filter Reduces Kβ peaks Moderate loss

Graphite Monochromator Eliminates Kβ peaks Eliminates Fluorescence

Strong loss

Multi-bounce Monochromator Eliminates Kβ and Kα2 Eliminates Fluorescence

Massive loss (mostly used on Synchrotrons)

Energy dispersive Detector Reduces Kβ peaks Eliminates Fluorescence

No loss

Cu Radiation

Kβ absorption filter

filtered Radiation

Cu Radiation

Monochromator Crystal

(Graphite, d = 0.3352 nm)

CuKα1/2 Radiation

Cu Radiation Energy dispersive

Detector

Digital filtering

Summary: Optical Elements

25

Optical Element Effect Too Small Too Large

Divergence Slit Adjusts beam length on the sample

Loss of intensity Beam spills over sample

Soller Slit Reduces peak asymmetry

Loss of intensity, Better resolution

More asymmetry, Less resolution

Anti-Scatter Slit Reduces background signal

Loss of intensity High background

Beam Mask Adjusts beam width on the sample

Loss of intensity Beam spills over sample

Receiving Slit Adjusts peak width / resolution

Loss of intensity Better resolution

Loss of resolution Higher intensity

Kβ Filter Reduces Kβ peaks - -

Graphite Monochromator

Eliminates Kβ peaks - -

Bragg-Brentano Parafocusing Diffractometer

26

Sample

X-ray

tube

Detector

Detectors

27

Detector’s

window

Receiving

slit

Point Detector (0D) Linear Detector (1D) Area Detector (2D)

Receiving slit

determines

active height

Linear array of

solid state

detectors

2D array of

solid state

detectors

Scintillation counter (various)

SOL-XE (Bruker)

XFlash (Bruker)

X’Celerator (PANalytical)

PIXcel1D (PANalytical)

LynxEye (Bruker)

LynxEye XE (Bruker)

Våntec-1 (Bruker)

D/teX Ultra (Rigaku)

PIXcel3D (PANalytical)

Våntec-500 (Bruker)

SOL-XE:

Energy dispersive

XFlash:

Combines XRD + XRF

Fast

LynxEye XE:

Energy dispersive

Fast

2D image of

Debye rings

Detector

Type

Example

Key

Features

Position-sensitive

«bins»

Instruments

28

Lab Instrument Monochr. Detector

RMS Foundation Bruker D8 Energy dispersive Detector

1D LynxEye XE

Uni Bern Panalytical X’Pert Ni-Filter 1D X’Celerator

Uni Bern Panalytical CubiX Graphite 0D Scintillation Counter

Bruker D8 Panalytical X’Pert Panalytical CubiX

10 20 30 40 50 60

0

20

40

60

80

100In

ten

sity [%

]

Diffraction Angle [°2theta]

Measurement parameters

29

• Angular Range

• Step Size

• Counting Time

0 10 20 30 40 50 60

0

2000

4000

6000

8000

10000

12000

14000

Inte

nsity [C

ou

nts

]

Diffraction Angle [° 2theta]

Angular Range

30

Start before first peak

End at ≥ 60° (higher = better)

Typical Ranges:

5-60° 2θ

Angular Range

31

0 10 20 30 40 50 60

0

5000

10000

15000

20000

Inte

nsity [C

ou

nts

]

Diffraction Angle [° 2theta]

Avoid the primary beam!

Angular Range

32

0 10 20 30 40 50 60

0

5000

10000

15000

20000

25000

30000

Inte

nsity [C

ou

nts

]

Diffraction Angle [° 2theta]

No need to measure

empty background

35.0 35.1 35.2 35.3

0

5000

10000

15000

20000

25000

Inte

nsity [C

ou

nts

]

Diffraction Angle [° 2theta]

Step Size

33

At least 5 data

points per peak

Typically ≤ 0.02° 2θ

Here: 0.0122°

Time per Step

34

10 20 30 40 50 60

0

1000

2000

3000

4000

5000

6000

7000

Inte

nsity [co

un

ts]

Diffraction Angle [°2theta]

10 20 30 40 50 60

0

20

40

60

80

100

120

140

160

180

Inte

nsity [co

un

ts]

Diffraction Angle [°2theta]

12.5 min 12.5 min

1D Energy dispersive Detector 0D Detector

Examples

35

30 31 32 33 34 35

0

1000

2000

3000

4000

5000

6000

7000

Inte

nsity [co

un

ts]

Diffraction Angle [°2theta]

30 31 32 33 34 35

0

20

40

60

80

100

120

140

160

180

Inte

nsity [co

un

ts]

Diffraction Angle [°2theta]

Jagged peak shape

Noise or peak?

No recommendation!

Check your S/N ratio and peak shape!

Data Quality Checklist

36

Sample

X-ray

tube

Detector Divergence

slit

Soller

slit

Soller

slit

Anti-Scatter

slit

Beam

mask

Anti-Scatter

slit

Receiving

slit

Kβ Filter

Check beam paths Tube Sample Detector

Data Quality Checklist

37

Optical Element Ideal setup

Divergence Slit Automatic Max irr. length w/o beam overflow

Soller Slit Installed Small opening

Mask Installed (if available) Max irr. width w/o beam overflow

Anti-scatter slit Identical to divergence slit

Sample Spinning

Anti-scatter slit Wide open

Soller slit Installed Small opening

Additional slits Wide open

Kβ filter Installed

For linear detector with Kβ filter

Incid

en

t b

ea

m p

ath

D

iffr

acte

d b

eam

path