SLIDE 1 High Resolution X-ray Diffraction
Nina Heinig with data from Dr. Zhihao Donovan Chen, Panalytical and slides from Colorado State University
Outline
- Watlab’s new tool: Panalytical MRD system
- Techniques:
– introduction to XRD – high resolution XRD – glancing incidence XRD – x-ray reflectometry
SLIDE 2
X-ray source Detector 4-circle goniometer Panalytical’s Materials Research Diffraction System (MRD-Pro)
SLIDE 3
SLIDE 4
Introduction to X-ray diffraction Bragg's Law: nλ = 2d sinθ
λ = x-ray wavelength, CuKα1=1.540562 Å d = crystal lattice spacing θ = incident angle
For a single crystal sample, Bragg’s law will result in diffracted spots in space. These can be mapped onto an Ewald sphere, and assigned to various diffraction planes. For a multi-crystal powder sample, the large number of diffracted spots form rings.
SLIDE 5 Powder Diffraction is widely used to determine unknown inorganic phases.
A powder scan involves moving the incident angle (called θ or ω), and the detector angle (called 2θ), simultaneously, so that ω is ½(2θ). This will satisfy the Bragg condition for a range of d-spacings.
22-0346 (Q) - Iron Hydroxide - Fe(OH)3 - Y: 20.83 % - d x by: 1. - WL: 1.5406 - Cubic - 40-1139 (I) - Iron Oxide - Fe2O3 - Y: 19.19 % - d x by: 1. - WL: 1.5406 - Hexagonal - Karan1 - File: Karan1.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 40.950 ° - Step: 0.050 ° - Step time:
100 200 300
2theta (degree)
20 30 40
04- 0836 ( * ) - Copper , s y n - Cu - Y: 10. 04 %
L: 1. 5406 - Cubi c - 04- 0784 ( * ) - G
- l d, s yn - Au - Y: 10. 04 %
- d x by : 1. - W
L: 1. 5406 - Cubi c - Oper at i ons : I m por t M ar k 1 - Fi l e: M ar k1. r aw - Type: 2Th/ Th l oc k ed - St ar t : 35. 000 ° - End: 52. 000 ° - St ep: 0. 020 ° - St ep t i me: 1. s
Lin (Counts)
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250
2-Theta - Scale
35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52
Cu nanoparticles on Si/Au/PPy. Only Au peaks are seen. Fe nanoparticles on Si. Signal/noise is bad.
SLIDE 6
Single crystal diffraction is used widely for drug discovery and to analyze large biomolecules.
Large molecules can have thousands of diffracted spots, making it a challenge to determine the structure. This technique also requires “large” single crystals of the biomolecule.
SLIDE 7 High Resolution X-ray Diffraction
What affects how accurately Bragg’s law is followed?
- monochromacity of the x-ray beam
(i.e. how accurately do we know λ?)
- dispersion of the x-ray beam
(i.e. how parallel is the beam?)
- accuracy and step-size of the goniometer
- noise in the detector
- Sample Artifacts:
small sample size defects/impurities in the crystal lattice diffuse scattering from amorphous material
SLIDE 8
SLIDE 9 High resolution XRD : SrTiO3 (002) Rocking Curve
FWHM = 0.269˚
Fix 2θ at a known Bragg reflection, and move (rock) ω about ½(2θ). The width of the peak indicates the perfection
This single crystal film is highly crystalline (i.e. few defects), but contains some mis-aligned grains.
SLIDE 10
SrTiO3 (002) Reciprocal Space Map A more detailed look at the Bragg reflection seen in the rocking curve.
SLIDE 11
SrTiO3 (002) In-Plane Rocking Curve
FWHM = 0.868° YBa2Cu3O7-x SrTiO3 Most of the film has the STO (002) crystal axis perpendicular to the film surface. An in-plane rocking curve shows part of the STO film consists of mis-aligned grains that have the STO (002) crystal axis parallel to the film surface. AFM or SEM shows small nano-crystals in the film.
SLIDE 12
Glancing Incidence X-ray Diffraction (GIXRD)
GIXRD can determine the diffraction pattern from a very thin film or layer. This is sometimes difficult with ordinary diffraction, because
1) small volume of material in the film 2) strong contribution from the substrate swamps out film data
SLIDE 13
When the angle of incidence of the x-ray beam decreases, the beam will not penetrate (refract) as deeply into the sample. Any light hitting an interface can have a reflected and refracted component. Below a critical angle, αc, total external reflection will occur. Much of the x-ray beam is reflected, and the refracted beam propogates parallel to the interface, while being exponentially damped below the interface. This refracted beam is what is used by GIXRD. The exact details of penetration depth, intensities etc., are found by solving Maxwell’s equations for the case with a boundary condition.
SLIDE 14
GIXRD shows Au and Cu phases for Cu nanoparticle on PPy/Au/Si
SLIDE 15 Au nano-particles on Si, seen using GIXRD
Au (111) Au (200)
SLIDE 16
X-ray Reflectivity (XRR)
X-ray reflectivity occurs when x-rays hit the sample at low incident angles The reflection occurs at the interface.
So the film does not have to be crystalline. Amorphous, disordered films are also ok.
SLIDE 17 X-ray reflectivity limitations
If the films are rough, or do not have even thickness, the interference are washed
Also, the film layers must have different electron densities to get reflection from the interface. Many orders of magnitude in x-ray intensity are needed. Therefore, big samples are better.
SLIDE 18
XRR on Cr/Glass sample (8x4 cm2)
SLIDE 19 Summary
- Thin film XRD system has varied
capability.
- Complete analysis of SrTiO3 structure in
reciprocal space using HRXRD.
- Accurate phase identification of
nanoparticles using GIXRD.
- Can determine of film thickness, density
and roughness by XRR method
