1-x-ray introduction

8/7/2019 1-X-ray Introduction

1/13

9/23/20

ADVANCED

NANOMATERIALS CHARACTERIZATION

I

UNIT I XRAY DIFFRACTION

Xraypowderdiffraction

Singlecrystaldiffractiontechniques

Determinationofaccuratelatticeparameters

Nanostructural analysis

ParticlesizeanalysisusingSchererformula

9/23/2009 1


2/13


3/13

9/23/20

Moretools

Otherstakepicturesinthemomentumspaceorwavevectorspaceratherthaninrealspace:

XRD (XRayDiffraction)

LEED(Low EnergyElectron Diffraction)

RHEED (Reflection High EnergyElectron Diffraction)

NEUTRONDIFFRACTION

Aswith

any

camera,

information

isreadily

obtained

about

thestaticstructureofthematerial,althoughblurrinessalsoconveyssomedynamicalinformation

9/23/2009 5

Somemore!

Additionally, therearesomeothertoolsalsothatworkintherealtimeandinthefrequencyvariablespace

Intherealtime timede endentluminescentstudiescanbeusedtostudythedynamicalevolutionofthesystem

Inthefrequencyspacearetheopticalspectrospcopies:

IR,VIS andUV Spectroscopies

Light Scattering,Ellipsometry,IRabsorption,Raman Scattering,

P oto uminescencean NonLinear Optica Spectroscopy

EELS(Electron EnergyLoss Spectroscopy)

AES (Auger Electron Spectroscopy)

INS(Inelastic Neutron Scattering)9/23/2009 6


4/13

9/23/20

Evenmore!!

Techniquesinwhichbothelectronsandphotonsplayasignificantrole:

EXAFS(ExtendedXrayAbsorption FinestructureSpectroscopy)

XPS (XrayPhotoemission Spectroscopy)

UVPS (UV Photoemission Spectroscopy)

NMR(Nuclear Ma netic Resonance)

ESR(Electron Spin Resonance)

NQR(Nuclear Quadrupole Moment )

MOSSBAUEREFFECT9/23/2009 7

Herewe

go

again!!!

Usin ionic robessomemoretechni ues:

o SIMS (SecondaryIon Mass Spectrometry)

o RBS (Rutherford Back Scattering)

o PAS (PositronAnnihilation Spectroscopy)

o uon recess on pec roscopy

9/23/2009 8


5/13

9/23/20

WilhelmConradWilhelmConrad

RntgenRntgen((1845184519231923))

Wilhelm Conrad Rntgen

discovered the X-rays in

1895.

n e was onoure wthe Nobel prize for physics.

In 1995 the German FederalMail edited a stamp dedicated

to W. C. Rntgen.A modern radiograph

of a handBertha Rntgens Hand

8 Nov, 18959/23/2009 10


6/13

9/23/20

Radiographsliketheonesinthelastslidearesimplyshadowgrams.

TheXrayseitherpassstraightthroughorarestoppedbytheob ect.

Thediagramontheupperleftillustratestheprincipleandshowsaperfectshadow.

Inreality,alargefractionoftheXraysarenotsimplyabsorbedortransmittedbytheobjectbutarescattere .

Thediagramonthebottomleft

illustratesthiseffectandillustratesthefuzzyedgeoftheobjectthatisproducedintheimagebythescatteredXrays.

9/23/2009 11

Thefirstkindofscatterprocesstobe

recognisedwasdiscoveredbyMaxTheodorFelixMaxTheodorFelixvonvon LaueLaue

LauewasawardedtheNobelprizefor

physicsin1914"forhisdiscoveryoftheforhisdiscoveryofthe

diffractionofXdiffractionofXraysbycrystalsraysbycrystals".

HiscollaboratorsWalterFriedrichandPaul

Knipping in1912,tookthepictureof a

characteristicpatternofacrystal(copper

sulphateinthiscase)whenitscattereda

beamofXrays.

Max Theodor Felix von Laue

(1897-1960)

TheXraypowderdiffractionpatternofa

puresubstanceislikeafingerprintofthe

substanceandisthusideallysuitedfor

characterizationandidentificationof

polycrystallinephases.9/23/2009 12


7/13

9/23/20

X rays are invisible, highly penetrating electromagnetic radiationof much shorter wavelength (higher frequency) than visible light

The wavelength range for X rays is from about 10 m to about1011 m and the corresponding frequency range is from about3 1016 Hz to about 3 1019 Hz

9/23/2009 14


8/13

9/23/20

X-RAY ENERGY Electromagnetic radiation is described as having packets of

energy, or photonsphotons

E=hE=h

andand

= c/= c/

The energy of the photon is related to its frequency by the

following formula

E=E=hchc//xxrrayay 1010

1010 11AA E E 101044eVeV

=Wavelength,=Wavelength, =Frequency, c=Velocityoflight=Frequency, c=Velocityoflight

E=

9/23/200915

9/23/2009 16


9/13

9/23/20

X rays can be produced in a highly evacuated glass bulb,called an Xray tube, that contains essentially twoelectrodesan anode made of platinum, tungsten, oranother heav metal of hi h meltin oint and a cathode.

X-RAY TUBE

Evacuatedglassbulb

When a high voltage is applied between the electrodes,streams of electrons (cathode rays) are accelerated from thecathode to the anode and produce Xrays as they strike theanode.

17

Anode Cathode

Xrays9/23/2009

K-shell knockout The free electron collides with the tungsten atom, knocking an electron out

of a lower orbital.

An electron in a higher orbital immediately falls to the lower energy level,

releasing its extra energy in the form of a photon. It's a big drop, so thehoton has a hi h ener level it is an X-ra hoton.

189/23/2009


10/13

9/23/20

Monochromatic and Broad Spectrum of X-rays

For X-rays to be generated, electrons of high energy (> 104)are required.

Some of these electrons may excite electrons from the corestates in the target metal, which then recombine, producinghighly monochromatic X-rays. These are referred to ascharacteristic X-ray lines.

Other electrons, which are decelerated by the periodicpotential of the metal, produce a broad spectrum of X-rayfrequencies (BremsstrahlungBremsstrahlung- stopping potential).

Depending on the diffraction experiment, either or both ofthese X-ray spectra can be used.

19 9/23/2009

Continuous

Radiation

(BremsstrahlungBremsstrahlung)

9/23/2009 20


11/13

9/23/20

CharacteristicRadiation

9/23/2009 21

XraySpectrum

9/23/2009 22


12/13

9/23/20

CharacteristicRadiation

9/23/2009 23

Absorption of X-rays The atoms that make up your body tissue absorb

visible light photons very well. The energy level ofthe photon fits with various energy differencesbetween electron positions.

Radio waves don't have enough energy to moveelectrons between orbitals in larger atoms, so theypass through most stuff.

X-ray photons also pass through most things, butfor the opposite reason: They have too muchenergy.

...somethingyouwon'tseeveryoften(Visible light)

Xray

e a sorp on o -rays s g ven yI (I () = ) = IIoo (( ) exp ( ) exp (xx))

Where,Where, absorption coefficient of the materialabsorption coefficient of the material

density of the materialdensity of the material

xx distance travelled by the Xdistance travelled by the X--rays through the materialrays through the material

Note that mass absorption coefficients are additive functions ofthe weights fractions of elements.

249/23/2009


13/13

9/23/20

Absorption of X-rays A largerlarger atomatom is more likelylikely toto absorbabsorb anan XXrayray photonphoton in

this way, because larger atoms have greater energy

matches the energy of the photon.

SmallerSmaller atomsatoms, where the electron orbitals are separated byrelatively low jumps in energy, are lessless likelylikely toto absorbabsorb XXrayrayphotonsphotons.

The soft tissue in your body is composed of smaller atoms,and so does not absorb Xray photons particularly well.

The calcium atoms that make up your bonesbones are much larger,so they are better at absorbing Xray photons.

259/23/2009

1-x-ray introduction

Documents