Lesson 1 - X-rays and Diffractionprofex.doebelin.org/wp-content/uploads/2015/01/... · Lesson 1...
Transcript of Lesson 1 - X-rays and Diffractionprofex.doebelin.org/wp-content/uploads/2015/01/... · Lesson 1...
Lesson 1
X-Rays & Diffraction
Nicola DöbelinRMS Foundation, Bettlach, Switzerland
January 14 – 16, 2015, Bern, Switzerland
Electromagnetic Spectrum
2
X rays:
Wavelength λ: 0.01 – 10 nm
Energy: 100 eV – 100 keV
Generation of X-radiation:
Shoot electrons on matter
Interatomic distances in crystals:
typically 0.15 – 0.4 nm
Interference phenomena only
for features ≈ λ
X-ray Tube
3
e‒
Filament (W)
Target (Cu, Mo, Fe, Co, ...)
Be window
Acceleration
VoltageV
acu
um
Filament
Current
X-ray Tube
4
e‒
Filament (W)
Target (Cu, Mo, Fe, Co, ...)
Point focus
Line focus
Generation of X-rays
5
Accelerated electron impinges on matter:
Electron is deflected and decelerated by the atomic nucleus.
(Inelastic scattering)
Deflected electron emits electromagnetic radiation.
Wavelength depends on the loss of energy.
Bremsstrahlung (Deceleration radiation)
Bremsstrahlung
6
Wavelength (nm)
Inte
nsity
0.00 0.05 0.10 0.15 0.20
20 kV, 20 mA
30 kV, 20 mA
40 kV, 20 mA
Continuous spectrum
0.25 0.30
Acceleration Voltage:
� Speed / Energy of Electrons
Bremsstrahlung
7
Wavelength (nm)
Inte
nsity
0.00 0.05 0.10 0.15 0.20
30 kV, 20 mA
Continuous spectrum
0.25 0.30
30 kV, 30 mA
30 kV, 40 mA Generator Current:
� Number of Electrons
Characteristic Radiation
8
KLM
Eb (eV)
0
76
122
933952
1097
8979
M4,5 (3d)
M2,3 (3p)
M1 (3s)
L3 (2p3/2)
L1 (2p1/2)
L1 (2s)
K1 (1s)
Kα1 Kα2 Kβ
Cu
Wavelength of Kα1, Kα2, Kβ, Lα... are characteristic for the atomic species.
X-rays: Spectrum
9
Wavelength (nm)
Inte
nsity
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Cu
Kα1
Kα2
Kβ
Kα1
Kα2
Kβ
Mo
Old X-ray tubes
10
Caution:
Beryllium is toxic & carcinogenic!
- Never touch the windows!
- Use appropriate covers!
Caution:
Beryllium is toxic & carcinogenic!
- Never touch the windows!
- Use appropriate covers!
Lifetime of a few years:
- Vacuum decreases� loss of intensity
- Tungsten from filament depositson target� contaminated spectrum (characteristicW spectrum starts to appear)
- Monitor the intensity
- Replace old tubes
X-rays: Summary
11
• Generated in an X-ray tube
• Spectrum contains Bremsstrahlung (continuous) and
characteristic radiation (Kα1, Kα2, Kβ) of target material
• Tube is characterized by:• Target material• Size and shape of target• Aceleration voltage and
current
Diffraction Basics
12
Interaction of X-rays with matter:
- Absorption (photoelectric effect, giving rise to fluorescence)
- Elastic scattering (Thomson scattering)
- Inelastic scattering (Compton scattering)
Absorption Photoelectric effect, Fluorescence
1. Absorption and ionization
2. Relaxation and emission of characteristic radiation
CuKα1
FeKα1
Fe atom
Elastic Scattering
13
Electron oscillates in the electric field,
emits photons of the same wavelength as
the incoming radiation (λs = λp).
λp
λs
CuKα1
CuKα1
Fe atom
Secondary wave is in phase
(+ 180°) with primary wave.
Crystal Lattice
14
Crystal: Periodic arrangement of atoms/ions/molecules in 3 dimensions.
Electrons of each atom become a source of
scattered radiation (spherical waves)
15
Interference pattern
n=2
+ =
Positive / constructive
interference
Amplification
+ =
Negative / destructive
interference
Extinction
16
Interference pattern
n=4n=8n=12n=25n=50
Bragg’s Law
17
n · λ = 2 · d · sin(θ)
d
λ
θθδ
2δ = n · λ δ = d · sin(θ)
d = (n · λ) / (2 · sin(θ))
Lattice Planes and Miller Indices
18
a
b
Definition:
A lattice plane is a plane
which intersects atoms of
a unit cell across the whole
3‐dimensional lattice.
d(100)
d(010)
d(110)
d(-210)
- Each lattice plane
generates a diffraction
peak.
- The 2θ angle of thepeak depends on the plane’s d-spacing.
- Diffraction peaks canbe labelled with the plane’s Miller index.
Bragg’s Law
19
CuKα1 = 0.154056 nm
a = 0.2 nm
b = 0.5 nm
ba
b
a
2θ = 45.30°2θ = 17.72°
d = 0.2 nm
d = 0.5 nm
θ = 22.65°θ = 8.86°
Single Crystal
20
A single crystal must be rotatedto bring each lattice plane indiffraction condition.
2θ 2θ
2θ
Polycrystals, Powders
21
In an ideal powder everypossible orientation ofcrystals occurs.
In a random powderno orientation is preferred.
In an ideal powder all possible diffraction peaksare generated, regardless of sample orientation.
Diffraction Cones
22
Diffraction at an angle 2θ° fromthe primary beam
All possible rays form a cone = diffraction cone = Debye cone
Diffraction Cones
23
(120)
(100)
(010)
One Debye Cone for each lattice plane spacing (d value)
Powder sample:
Debye Ring
24
Gra
y V
alu
e
2θ Angle
Gra
y V
alu
e
2θ Angle
Powder Diffractometer
25
X-ray tube
Primary Beam
Powder
Sample
Diffraction Cones
«Secondary Beams»
X-ray Detectorscanning X-ray intensity
vs. 2θ angle
Powder Diffraction Pattern
26
10 20 30 40 50 60
0
500
1000
1500
2000In
ten
sity (
cts
)
Diffraction Angle (°2θ)
Lesson 2: All about powder diffractometers
Monochromatic X-radiation
27
n · λ = 2 · d · sin(θ)
http://fineartamerica.com
Diffraction angle θ depends on wavelength λ:
Polychromatic X-ray Beam
We need monochromatic X-radiation!
28
Monochromatic X-Radiation
Cu Radiation
Kβ absorption filter
filtered Radiation
Ideally: Isolate Kα1
Reality: Suppress Kβ and Bremsstrahlung
Wavelength (nm)
Inte
nsity
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Cu
Kα1
Kα2
Kβ
BremsstrahlungCu Radiation
Monochromator Crystal
(Graphite, d = 0.3352 nm)
CuKα1/2 Radiation
n · λ = 2 · d · sin(θ)
Cu RadiationEnergy dispersive
Detector
Digital filtering
Kβ-filtered Diffraction Pattern
29
27 28 29 30 31 32
0
100000
200000
300000
400000
500000
Inte
nsity
Diffraction Angle (°2θ)
CuKα1
CuKα2
LaB6 pattern, Cu radiation, Ni filter in primary beam (Bruker D8 Advance)
Kβ-filtered Diffraction Pattern
30
27 28 29 30 31 32
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
Inte
nsity
Diffraction Angle (°2θ)
CuKβ
CuKα1 & CuKα2 duplet
Remaining Bremsstrahlung
Absorption Edge
Impurity
CuKα Satellites
(= CuKα3)
LaB6 pattern, Cu radiation, Ni filter in primary beam (Bruker D8 Advance)
Graphite Monochromator
31
27 28 29 30 31 32
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Inte
nsity
Diffraction Angle (°2θ)
CuKα1
CuKα2
LaB6 pattern, Cu radiation, Graphite monochromator, secondary beam (PANalytical CubiX3)
Graphite Monochromator
32
27 28 29 30 31 32
0
100
200
300
400
500
Inte
nsity
Diffraction Angle (°2θ)
CuKα1 & CuKα2 duplet
CuKα Satellites
(= CuKα3)
LaB6 pattern, Cu radiation, Graphite monochromator, secondary beam (PANalytical CubiX3)
31 32 33 34 35 36
0
10000
20000
30000
40000
50000
Inte
nsity (
co
unts
)
Diffraction Angle (°2θ)
Energy-Dispersive Detector
33
Al2O3 pattern, Cu radiation, LynxEyeXE detector (Bruker D8 Advance)
CuKα1
CuKα2
31 32 33 34 35 36
0
1000
2000
3000
4000
5000
Inte
nsity (
co
un
ts)
Diffraction Angle (°2θ)
Energy-Dispersive Detector
34
CuKβ
CuKα1 & CuKα2 duplet
Edge of
Energy Window
Al2O3 pattern, Cu radiation, LynxEyeXE detector (Bruker D8 Advance)
31 32 33 34 35 36
0
5000
10000
15000
20000
25000
30000
Inte
nsity (
co
un
ts)
Diffraction Angle (°2θ)
Energy-Dispersive Detector + Kβ filter
35
CuKα1
CuKα2
50% loss of intensity(0.0125 mm Ni filter)
Al2O3 pattern, Cu radiation, LynxEyeXE detector (Bruker D8 Advance)
31 32 33 34 35 36
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Inte
nsity (
co
un
ts)
Diffraction Angle (°2θ)
Energy-Dispersive Detector + Kβ filter
36
CuKα1 & CuKα2 duplet
Al2O3 pattern, Cu radiation, LynxEyeXE detector (Bruker D8 Advance)
Edge of
Energy Window
50% loss of intensity(0.0125 mm Ni filter)
Monochromators
37
Kβ Filter:Selectively suppresses Kβand parts of Bremsstrahlung
Monochromator crystal andenergy dispersive detector:Suppress everything BUT Kα
Important difference forfluorescent samples
«Notch filter»
«Bandpass filter»
38
Ni-Filtered Cu Radiation, Fe Fluorescence
10 20 30 40 50 60 70 80
0
500
1000
1500
2000
Inte
nsity [cts
]
Diffraction Angle [°2θ] Cu radiation, Ni filter in 2nd beam
(PANalytical X’Pert Pro)
100% TiO2
95% TiO2
+ 5% NiFe2O4
90% TiO2
+ 10% NiFe2O4
75% TiO2
+ 25% NiFe2O4
50% TiO2
+ 50% NiFe2O4
25% TiO2
+ 75% NiFe2O4
Secondary-monochromated Cu-Radiation
39
10 20 30 40 50 60 70 80
0
200
400
600
800
1000
Inte
nsity [cts
]
Diffraction Angle [°2θ] TiO2 + NiFe2O4,
Cu radiation, 2nd graphite monochromator
(PANalytical CubiX3)
95% TiO2
+ 5% NiFe2O4
90% TiO2
+ 10% NiFe2O4
75% TiO2
+ 25% NiFe2O4
50% TiO2
+ 50% NiFe2O4
25% TiO2
+ 75% NiFe2O4
100% NiFe2O4
In case of Fluorescence, use:
- Secondary-beam monochromator
- Energy-dispersive Detector
- Different X-ray tube (Cr / Fe / Co)
Summary: Monochromators
40
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
Overview of Instruments
41
Lab Instrument Monochromator
RMS Foundation Bruker D8 Energy dispersive
Detector
Uni Bern Panalytical X’Pert Kβ-Filter
Uni Bern Panalytical CubiX Graphite
Monochromator
Bruker D8 Panalytical X’Pert Panalytical CubiX