Spectroscopy XRD

(X-Ray Diffraction on powders)

Dr. Chris UP, Feb. 2016

Energy regions of electromagnetic waves

Different principles (1) Energy absorption

E1 and E2 are different states of a molecule: Vibrational states -> IR spectroscopy Nuclear spin states -> NMR spectroscopy electronic states -> UV/VIS spectroscopy

(2) Energy emission

Raman (infrared) Fluorescence (uv)

(3) XRD “spectroscopy”

Different principle: reflection of X-Rays on a sample

Generation of X-Rays The target metal

defines the energy of the x-rays

Excitation of INNER electrons, falling back emits X-Rays Typical metals are Mo (λ = 0.07 nm) and Cu (λ = 0.154 nm)

XRD Principle

Different planes in a crystal give different signals = positive interference of waves

Why 2 ϴ ? The Bragg diffraction condition contains only one

factor of θ: 2dsinθ=nλ It should be noted that θ refers to the incidence angle of the x-ray beam, and the beam is actually deflected

by an angle of 2θ, as illustrated in the image below:

Bragg’s Law

PLANES IN CRYSTALS MILLER INDICES

Crystal lattices – 3 cubic structures

NaCl type

Movie clip: youtube.com/watch?v=pMTA_wiY784

Indices h k l

http://slideplayer.org/slide/792387/#

Identify crystal layers Miller indices h k l

http://www.iue.tuwien.ac.at/phd/dhar/node17.html

Practice Miller layers

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Negative indices

Examples

Miller Indices Example

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Cubic structure – interplanar distances

Calculate plane distances

Examples

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What is the unit cell dimension a of NaCl ? Use plane 111 with 2x theta = 27 deg and λ = 1.54 nm (Cu-Kα)

Which plane will give a signal at 2x theta = 46 deg when the cubic constant a = 0.5 nm and λ = 1.54 nm ?

X-rays with wavelength 1.54 Å are “reflected” from the (1 1 0) planes of a cubic crystal with unit cell a = 6 Å. Calculate the Bragg angle, ϴ, for orders of reflection, n = 1-5.

Use Braggs Law to calculate possible values for ϴ :

Solution:

Indexing Example

constant

Find out which hkl combinations using in this formula will give a constant value.

ESTIMATED PARTICLE SIZES

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AG NANOPARTICLES

From jcpds database http://comptech.compres.us/tools/jcpds/

In Angstrom = 10 x nm

VERSION: 4 COMMENT: Silver (04-0783, shock wave) K0: 120.800 K0P: 4.84000 SYMMETRY: CUBIC A: 4.08620 ALPHAT: 0.000000 DIHKL: 2.3590 100. 1.00 1.00 1.00 DIHKL: 2.0440 52. 2.00 0.00 0.00 DIHKL: 1.4450 32. 2.00 2.00 0.00 DIHKL: 1.2310 36. 3.00 1.00 1.00 DIHKL: 1.1760 12. 2.00 2.00 2.00 DIHKL: 1.0215 6. 4.00 0.00 0.00 DIHKL: 0.9375 23. 3.00 3.00 1.00 DIHKL: 0.9137 22. 4.00 2.00 0.00 DIHKL: 0.8341 23. 4.00 2.00 2.00

Ag Nanoparticles XRD

http://www.azonano.com/article.aspx?ArticleID=2318#5

Particle size estimation

Debye-Scherrer Formula:

λ = 0.154 nm , W = width at half maximum = 0.011 rad, Theta = 45 deg

Plane distance

http://pubs.rsc.org/en/content/articlehtml/2013/ce/c3ce40497h

a = b = c = 0.4081 nm Distance between 111 planes

between 100 planes

GRAPHITE AND GRAPHENE OXIDE (GO)

JCPDS Database VERSION: 4 COMMENT: Graphite K0: 100.000 K0P: 4.00000 SYMMETRY: HEXAGONAL A: 2.456 C: 6.696 VOLUME: 34.9786 ALPHAT: 00.00E0 DIHKL: 3.3480 100. 0 0 2 DIHKL: 2.1270 3. 1 0 0 DIHKL: 2.0271 17. 1 0 1 DIHKL: 1.7953 3. 1 0 2 DIHKL: 1.6740 7. 0 0 4 DIHKL: 1.5398 5. 1 0 3 DIHKL: 1.2280 2. 1 1 0 DIHKL: 1.1529 3. 1 1 2 DIHKL: 1.1333 2. 1 0 5 DIHKL: 1.1160 2. 0 0 6

It needs 4 indices to describe the planes in hexagonal structure

Indices for HCP structures http://www.materials.ac.uk/elearning/matter/crystallography/indexingdirectionsandplanes/indexing-of-hexagonal-systems.html

https://www.youtube.com/watch?v=vK913oWl_XI

Graphite and Graphene Oxide

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Reduced GO: 2θ = 26.29 degree With λ = 0.154 nm the distance between the planes: The close d-spacing of RGO to pristine graphite and disappearance of peak at 2θ = 12.43 degree indicate that the oxygen containing group of graphite oxide have been efficiently removed

From: Nanomaterials 2015, 5, 826-834 Graphene Oxide Synthesis from Agro Waste

The peak at 2θ = 11.6° indicates an interlayer distance of 0.79 nm fully oxidized graphite sheets

FT-IR spectrum of GO

In the IR spectrum typical peaks of functional groups can be identified: Around 3500 cm-1: O-H stretching 1700 cm-1: typical for C=O stretching 1600 cm-1: C-C vibrations of graphite 1210 cm-1: C-OH stretching

From: Chem. Commun., 2011,47, 12370-12372 One-pot reduction of graphene oxide at subzero

temperatures

From: J. Chil. Chem. Soc. vol.58 no.4 Concepción dic. 2013 http://dx.doi.org/10.4067/S0717­97072013000400067

GREEN SYNTHESIS AND CHARACTERIZATION OF GRAPHITE OXIDE BY ORTHOGONAL EXPERIMENT

Different oxidation parameters for graphite

From: SENSORS AND ACTUATORS B CHEMICAL 199:190–200 · AUGUST 2014

ZINC OXIDE NANOPARTICLES

Hexagonal Closest Packing

Zinc oxide XRD – Wurzite Structure

http://www.hindawi.com/journals/isrn/2012/372505/

Estimate particle sizes

Nanoscience and Nanotechnology 2015, 5(1): 1-6 Synthesis of Zinc Oxide Nanoparticles via Sol – Gel

Route and Their Characterization

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