X-Ray Diffraction

Question 1

What is X-ray Diffraction?

Answer 1

Collimated beam of X-rays diffracted by crystalline structure within specimen. Diffraction follows Bragg’s Law Lambda = 2dsin(theta) where d is the spacing b/w atomic planes in the crystal.

Question 2

What are shifts in positions of peaks used to calculate?

Answer 2

change in d spacing

Question 3

What causes changes in d spacing

Answer 3

which can occur due to a change of lattice spacing constants under strain

Question 4

How do inhomogeneous strains appear?

Answer 4

as broadening of peaks that increase with sin(theta)

Question 5

What is Small Angle X-ray Scattering?

Answer 5

Constructive interference of X-rays scattered from ordered arrays of atoms and molecules.

Question 6

What is the benefit of smaller scattering angles in SAXS?

Answer 6

Can probe larger objects

Question 7

What is SAXS useful for?

Answer 7

quantifying nanoscale differences as they deliver structural info at that scale

Question 8

What does each diffraction pattern represent?

Answer 8

Circular/Ring: spherically symmetric crystalline assemblies
Point/Line: oriented stacks of lamellar crystallites
Multi-point: lamellar crystallites stacked in different orientations

Question 9

Give 3 points comparing XRD with SAXS

Answer 9

Different scales
SAXS: scattering due to existence of inhomogeneity regions at NP scale
XRD: determines atomic structures (e.g. atoms within a NP)

Question 10

Comparison of X-ray with neutrons and electrons

Answer 10

see table in notes