X-ray diffractionX-ray diffractionAntony D. HanAntony D. Han

Chem 750/7530Chem 750/7530

Feb. 21, 2006Feb. 21, 2006

OutlineOutline

History and background information of X-History and background information of X-ray diffraction.ray diffraction.

Theory behind the equipmentTheory behind the equipment Challenges of applying traditional XRD to Challenges of applying traditional XRD to

nano-technologynano-technology Summary Summary

History of X-ray and XRDHistory of X-ray and XRD

Wilhelm Conrad Röntgen discovered Wilhelm Conrad Röntgen discovered X-Rays in 1895.X-Rays in 1895.

1901 Nobel prize in Physics1901 Nobel prize in Physics

Wilhelm Conrad Röntgen (1845-1923)

A modern radiograph of a hand Bertha Röntgen’s Hand 8 Nov, 1895

History of X-ray and XRDHistory of X-ray and XRD Radiographs like the ones in the Radiographs like the ones in the

last slide are simply shadowgrams. last slide are simply shadowgrams. The X-rays either pass straight The X-rays either pass straight

through or are stopped by the through or are stopped by the object. The diagram on the upper object. The diagram on the upper left illustrates the principle and left illustrates the principle and shows a perfect shadow.shows a perfect shadow.

In reality, a large fraction of the X-In reality, a large fraction of the X-rays are not simply absorbed or rays are not simply absorbed or transmitted by the object but are transmitted by the object but are scattered. The diagram on the scattered. The diagram on the bottom left illustrates this effect and bottom left illustrates this effect and illustrates the fuzzy edge of the illustrates the fuzzy edge of the object that is produced in the image object that is produced in the image by the scattered X-rays. by the scattered X-rays.

The first kind of scatter process to be The first kind of scatter process to be recognised was discovered by Max recognised was discovered by Max vonvon Laue Laue who was awarded the Nobel prize for who was awarded the Nobel prize for physics in 1914 physics in 1914 "for his discovery of the "for his discovery of the diffraction of X-rays by crystals". diffraction of X-rays by crystals". His His collaborators Walter Friedrich and Paul collaborators Walter Friedrich and Paul Knipping took the picture on the bottom left in Knipping took the picture on the bottom left in 1912. It shows how a beam of X-rays is 1912. It shows how a beam of X-rays is scattered into a characteristic pattern by a scattered into a characteristic pattern by a crystal. In this case it is copper sulphate.crystal. In this case it is copper sulphate.

The X-ray diffraction pattern of a pure The X-ray diffraction pattern of a pure substance is like a fingerprint of the substance is like a fingerprint of the substance. The powder diffraction method is substance. The powder diffraction method is thus ideally suited for characterization and thus ideally suited for characterization and identification of polycrystalline phases.identification of polycrystalline phases.

History of X-ray and XRDHistory of X-ray and XRD

Max von Laue (1897-1960)

Bragg’s LawBragg’s Law

The father and son team of Sir The father and son team of Sir William Henry and William Lawrence William Henry and William Lawrence Bragg were awarded the Nobel prize Bragg were awarded the Nobel prize for physics for physics "for their services in the "for their services in the analysis of crystal structure by means analysis of crystal structure by means of Xrays“ in 1915.of Xrays“ in 1915.

Bragg's law was an extremely Bragg's law was an extremely important discovery and formed the important discovery and formed the basis for the whole of what is now basis for the whole of what is now known as crystallography. This known as crystallography. This technique is one of the most widely technique is one of the most widely used structural analysis techniques used structural analysis techniques and plays a major role in fields as and plays a major role in fields as diverse as structural biology and diverse as structural biology and materials science.materials science.

William LawrenceBragg (1890-1971)

Sir William HenryBragg (1862-1942)

EquipmentEquipment

Bruker D8 Analytical X-ray Systems

GoniometerGoniometer

2-Theta:Theta Setup

GoniometerGoniometer

Theta:Theta Setup

FundamentalsFundamentals How it works?How it works?

An electron in an alternating electromagnetic field will oscillate with the An electron in an alternating electromagnetic field will oscillate with the same frequency as the field. When an X-ray beam hits an atom, the same frequency as the field. When an X-ray beam hits an atom, the electrons around the atom start to oscillate with the same frequency as electrons around the atom start to oscillate with the same frequency as the incoming beam. In almost all directions we will have destructive the incoming beam. In almost all directions we will have destructive interference, that is, the combining waves are out of phase and there is interference, that is, the combining waves are out of phase and there is no resultant energy leaving the solid sample. However the atoms in a no resultant energy leaving the solid sample. However the atoms in a crystal are arranged in a regular pattern, and in a very few directions we crystal are arranged in a regular pattern, and in a very few directions we will have constructive interference. The waves will be in phase and there will have constructive interference. The waves will be in phase and there will be well defined X-ray beams leaving the sample at various will be well defined X-ray beams leaving the sample at various directions. Hence, a diffracted beam may be described as a beam directions. Hence, a diffracted beam may be described as a beam composed of a large number of scattered rays mutually reinforcing one composed of a large number of scattered rays mutually reinforcing one another. another.

Crystal systems, space groups, reciprocal lattice, Miller indices…Crystal systems, space groups, reciprocal lattice, Miller indices…

Planes going through areas with high electron density will reflect Planes going through areas with high electron density will reflect strongly, planes with low electron density will give weak intensities.strongly, planes with low electron density will give weak intensities.

Sample preparation Sample preparation Single crystal X-ray diffractionSingle crystal X-ray diffraction

The single crystal sample is a perfect crystal (all unit cells The single crystal sample is a perfect crystal (all unit cells aligned in a perfect extended pattern) with a cross section of aligned in a perfect extended pattern) with a cross section of about 0.3 mm. about 0.3 mm.

The single crystal diffractometer and associated computer The single crystal diffractometer and associated computer package is used mainly to elucidate the molecular structure of package is used mainly to elucidate the molecular structure of novel compounds.novel compounds.

Powder (polycrystalline) X-ray diffractionPowder (polycrystalline) X-ray diffraction It is important to have a sample with a smooth plane It is important to have a sample with a smooth plane

surface. If possible, we normally grind the sample surface. If possible, we normally grind the sample down to particles of about 0.002 mm to 0.005 mm down to particles of about 0.002 mm to 0.005 mm cross section. The ideal sample is homogeneous and cross section. The ideal sample is homogeneous and the crystallites are randomly distributed. The sample the crystallites are randomly distributed. The sample is pressed into a sample holder so that we have a is pressed into a sample holder so that we have a smooth flat surface.smooth flat surface.

Data collection and analysisData collection and analysis

Collecting data: computer and softwareCollecting data: computer and software Analysis: Analysis:

ICDD database – IdentificationICDD database – Identification Structure refinement – GSASStructure refinement – GSAS Quantitative phase analysis – GSASQuantitative phase analysis – GSAS Novel structure – single crystalNovel structure – single crystal

ApplicationsApplications

IdentificationIdentification Polymer crystallinityPolymer crystallinity Residual stressResidual stress Texture analysisTexture analysis

Challenge of applying to Challenge of applying to nanotechnologynanotechnology

Traditional X-ray powder-diffraction techniques rely on Traditional X-ray powder-diffraction techniques rely on the long-range order in crystals to produce sharp "Bragg the long-range order in crystals to produce sharp "Bragg peaks" in a diffraction pattern. By examining these Bragg peaks" in a diffraction pattern. By examining these Bragg peaks, which result from X-ray scattering, scientists can peaks, which result from X-ray scattering, scientists can determine the material's atomic structure. determine the material's atomic structure.

But nanocrystals lack long-range order and often But nanocrystals lack long-range order and often incorporate a large number of defects. As a result, their incorporate a large number of defects. As a result, their diffraction patterns are much more diffuse with few, if diffraction patterns are much more diffuse with few, if any, Bragg peaks. any, Bragg peaks.

"This poses a real challenge to the traditional techniques "This poses a real challenge to the traditional techniques for structure determination," -- Valeri Petkov of Michigan for structure determination," -- Valeri Petkov of Michigan State. State.

Breakthroughs for diffraction Breakthroughs for diffraction

RTMS detection technology and the RTMS detection technology and the implementation of mono-capillary have reduced implementation of mono-capillary have reduced measurement times and minimum amounts of measurement times and minimum amounts of material required considerably. material required considerably.

Many X-ray diffraction techniques are at disposal Many X-ray diffraction techniques are at disposal of the nanoscientist now for the structural of the nanoscientist now for the structural characterization of the nanomaterials, such as characterization of the nanomaterials, such as high-resolution diffraction, reflectometry, small-high-resolution diffraction, reflectometry, small-angle X-ray scattering and line profile analysis. angle X-ray scattering and line profile analysis. 

SummarySummary

X-ray diffraction provides a powerful tool to X-ray diffraction provides a powerful tool to study the structure and composition of the study the structure and composition of the materials which is a key requirement for materials which is a key requirement for understanding materials properties understanding materials properties

An X-ray diffraction system should not be An X-ray diffraction system should not be missing in a modern laboratory for missing in a modern laboratory for research on nano- and advanced research on nano- and advanced materials. – materials. – www.panalytical.comwww.panalytical.com

Some useful linksSome useful links GSAS:GSAS:

http://www.ncnr.nist.gov/xtal/software/gsas.htmlhttp://www.ncnr.nist.gov/xtal/software/gsas.html ICDD:ICDD:

http://www.icdd.com/http://www.icdd.com/ CCP14CCP14

http://ccp14.sims.nrc.ca/http://ccp14.sims.nrc.ca/ Diffraction tutorialsDiffraction tutorials

http://www.uni-wuerzburg.de/mineralogie/crystal/teaching/http://www.uni-wuerzburg.de/mineralogie/crystal/teaching/basic.htmlbasic.html

Paper addressed the problemPaper addressed the problem Phase TransitionsPhase Transitions, 2003, Vol , 2003, Vol 7676, Nos. 1-2, pp. 171-185, Nos. 1-2, pp. 171-185