Surface Structure Determination

Question 1

reconstruction

Answer 1

reorganisation of the surface to lower gibbs free energy

Question 2

lattice types

Answer 2

body centered, face centered and hexagonal

Question 3

low index

Answer 3

most ordered surface, smallest number of sites for adsorption and atoms have relatively high coord no

Question 4

commensurate

Answer 4

adatoms/admolecles all adopt same sites

Question 5

Ewald construction steps

Answer 5

determine magnitudes of reciprocal lattice vectors, sketch reciprocal lattice to scale, calculate magnitude of wavevector of incident radiation, at origin draw circle of radius |K0| and no. of lattice points enclosed in circle = no of diffracting beams emerging from surface

Question 6

Determining angle of diffracted beams

Answer 6

do Ewald construction, draw set of perpendicular lines at each lattice point, draw line from origin to intersection of sphere and diffraction line, calculate angle

Question 7

determining energy of x-rays

Answer 7

E=hc/lambda

Question 8

determining energy of electrons and He atoms

Answer 8

quantum particles, use de Broglie relationship

Question 9

Adv of SXRD

Answer 9

x-rays interact weakly with matter therefore only observe single scattering events so simple data analysis and measurement in any environment

Question 10

Disadv of SXRD

Answer 10

not surface sensitive, need to work at graving angle to avoid bulk and need intense source

Question 11

Adv of LEED (low energy e- diffraction)

Answer 11

only probe surface and lab based

Question 12

Disadv of LEED

Answer 12

strong interaction means possible multiple scattering giving detailed analysis and needs UHV

Question 13

Adv of He atom diffraction (HAD)

Answer 13

surface specific as cant penetrate bulk, single scattering events means easy analysis and lab based