2.1

Question 1

5 Techniques

Answer 1

SEM
TEM
STM
AFM
XPS

Question 2

SEM

Answer 2

Scanning electron microscopy

Refraction technique

Surface of specimen

Low energy 2ndry electrons emitted from surface of sample

• electron beam in vaccuum concentrated on small area and then rastered across the surface
• electrons detected and reconstructed into an image

morphology of crystals and biological shit not coloured

Resolution 1nm

Question 3

TEM

Answer 3

Transmission electron microscopy
can see atoms pretty mch ish
transmission technique
Sample must be in vassum (e’s are deflected in the air)

sample can be affected by high energy electron beam
->damage to sample
HRES TEM - 0.5 A 4 resolution

Question 4

STM

Answer 4

A conducting tip is brought close to a metallic/semiconducting surface.

Apply small bias electrons tunnel between then

Tunnelling current is proportional to local DOS at fermi level of sample

Variations in current as probe rasters the surface allows an image to be generated

Question 5

STM general

Answer 5

Scanning Tunnelling microscopy
v. high vacuum
lateral res 1A
depth 0.1 A
produces weird looking 3d images etc
tend to look glowy 
sample must conduct

Question 6

AFM

Answer 6

Atomic force microscopy
insulating samples

resolution poorer than STM

a tip mounted on a cantilever rasters a surface

when tip is close to surface
forces between tip and surface result in a deflection of the cantilever

constant height scan or with feedback loop

can do in media

picture is grey white show atoms grey not defined

Question 7

XPS

Answer 7

Xray photoelectron spectroscopy (XPS)

Bombard sample with x rays - many eletron processes can occur
one process is the ionisation of an electron in inner shell
detect the electrons emitted and calculate binding energy and other properties
E=hv-Eo
Eos can be calculated

There are characteristic range of Eo values from different shells for a given element

useful for surfaces but not bulk
as electrons detected are only from top 2-5 nm of surface