SIMS

Question 1

3 steps in SIMS

Answer 1

1. ion generation - ionisation
2. Ion analysis - mass separation
3. Ion detection - micro channel plates

Question 2

Method for ion generation

Answer 2

desorption ionisation, best because sample can remain in solid phase

Question 3

methods for mass analysis

Answer 3

time of flight
Quadrupole
Magnetic

Question 4

MCP?

Answer 4

Microchannel plates
million independent channel and each channel acts as an electron multiplier
2D periodic array of channels fused together and sliced into a thin plate

Question 5

Types of analysis in SIMS

Answer 5

surface spectroscopy (mass spectra, static SIMS, mass resolution
surface imaging - ion mapping
depth profiling - dynamic SIMS/ ion beam broadening

Question 6

UHV, what and whyq

Answer 6

Ultra high vacuum,
monolayers form easily on samples that could inhibit analysis - we need to know how quickly it’ll form
gives us high sensitivity
smaller pressure - lower density of molecules present, higher mean free path of electrons, lower force - reduced collisions with surface to be analysed

Question 7

Strength of SIMS

Answer 7

Can analyse all elements
molecular species can also be detected
info form solid surface - we know where it came from
UHV - gives sensitivity so high detection levels
analysis can be performed both on surface and in bulk

Question 8

what do O2+ and Cs2+ favour (ion species)

Answer 8

O - positive ions

Cs - negative ions

Question 9

chemical effect due to the presence of oxygen

Answer 9

1. oxide surface layer
2. oxygen primary ion beam
3. oxygen flood

2+3 can be done if a layer of oxygen doesn’t form naturally

Question 10

depth of altered region depends on…

Answer 10

type of ion beam
its energy and
angle of incidence

Question 11

ion beam interactions

Answer 11

1. recoil mixing
2. cascade mixing

both result in feature such as interfaces, or buried features broadening

Question 12

SRIM

Answer 12

Stopping and range of ions in matter

model impact on matter

Question 13

Reducing ion beam interaction

Answer 13

reduce ion impact per atom
for inorganic materials low energy beam are good such as O2+ or Cs2+

For organic materials Ar clusters are needed

Question 14

depth profiling vs mass spectromerty modes

Answer 14

depth - dynamic mode

mass - static mode

Question 15

surface spectrometry - interferences

Answer 15

become greater with larger mass

C-H interactions become more visible as well

Question 16

surface spectrometry

Answer 16

mass spectra - static SIMS - fragmentation - mass resolution

fragmentation - if charge spread around molecule - less likely to fragment
lowest Energy C-H bonds broken
oxygen bonds, and benzene rings stable

Question 17

mass resolution

Answer 17

typically 28 amu

R=M/deltam

Question 18

depth profiling intricacies

Answer 18

chemical effects - correct ion beam has to be selected
physical effects - suitable ion beam energy and ion beam current
speed of analysis - appropriate area chosen

Ion beam effects play a role

Question 19

charging - what if a sample is insulating?

Answer 19

+ve charge builds up on surface
Cover it with a conductive layer gold
Use a flood gun - low beam of ions directed over surface to dissipate charge

Question 20

RSF

Answer 20

relative sensitivity factor