The document discusses atom probe field ion microscopy, a technique combining field ion microscopy and time-of-flight mass spectrometry for atomic-level analysis. It highlights the process of removing and analyzing individual atoms, the benefits of high spatial resolution, and its ability to map elemental and isotopic identities in volumes up to 100 nm. Additionally, it details the operational conditions, imaging systems, and advantages of field evaporation for achieving reliable chemical identification.

1. -PRESENTED BY
A.Akila
1st yr M.TECH
Nano Science and Technology
Anna University –BIT Campus
Trichy

2.  Atom probe field ion microscopy is a combination
of field ion microscopy and time of flight mass
spectrometer.
 FIM is a projection type microscope of atomic
resolution.
 Time of flight : atom go through a small apecture
in the centre of screen makes it possible to
determine the mass to charge ratio.
 The atom probe microscope operates by removing
and analyzing individual atoms.

4.  The precursor to the atom probe microscope was
the field ion microscope (FIM)
 During FIM analysis, gas atoms adsorbed to the
surface of a sharply pointed specimen are ionized
by means of a strong electric field.
 They are then accelerated toward a phosphor
screen or other position-sensitive detector placed at
some distance from the specimen.

5. • Extremely high spatial resolution
• Equal detection efficiency for light elements
• The atom probe’s unique atom-by-atom analysis
provides a map of the elemental and isotopic
identity and position of individual atoms in
volumes of material of up to 100 nm in diameter
and 100 nm in depth.

6.  The atom probe analyzes three-dimensional
volumes of material, whereas the AFM analyzes
surface features only.
 The atom probe provides both imaging and
chemical analysis, whereas AFM provides imaging
only.

9.  Basic technique of preparing sample is electro
polishing technique.
 Advanced techniques - focused ion beam technique.

12.  Image is produced by applying high voltage to specimen
with respect to channel plate screen in presence of
imaging gas .
 The field strength required at the sample surface
reaches approximately 50v/nm.
 In order to achieve this order of magnitude needle
shaped specimens are prepared with average radius of
curvature R=10-100nm.
 The whole setup is kept in ultra high vacuum at a
pressure of 10ˆ-7 pa.
 During the operation tip is kept at temperature of 10-
150k
 Imaging system comprises of micro channel plate and
phosphor screen.

13.  The applied field at which field image results is called Best
Image Field (BIF) and the corresponding voltage is called
Best Image Voltage(BIV).
 Advantages of field evaporation
> Removal of oxides and impurities on the surface of
sample.
> smoothens the irregular surface of the sample until
the hemispherical surface is obtained.

16.  Chemical identification of the sample is achieved by
measuring the time of flight when used in combination
with the FIM.
 Difference between the BIF and evaporation field strength
is created by superimposing a short pulse Vp with respect
to width and amplitude of to that of the permanent
BIV.
 Vp must be high enough to remove the specimen atoms by
field evaporation.
 Pulse fraction is the ratio of pulse to permanent voltage.
 By the correction of selection of Vp and setting of the
analysis temperature the preferential evaporation of any
constituent with respect to the others is avoided and a
reliable analysis can be achieved.

17.  Synchron pulse in TDC (Time to digital converter) is used
to reset and start the clock
 When the field evaporation ion reaches the drift velocity ,
surface atoms are evaporated
 After the time of flight T , the ion hits the detector and the
pulse is used to stop the clock.
 Conversion of energy for drifting ion is given by
 From the above relation mass to charge ratio can be
measured for the field evaporation ion
 So the whole analysis is performed by adjusting the pulse
frequency
 The projection of probe hole onto the surface of the tip
defines the diameter of the sample and the length of the
sample is given by the hkl plane

18.  The resolution depends on the shape of applied pulse and
kind of TOF.
 The information obtained from the data is that only the
composition of the sample and it could not specify the
different distribution of the constituents.
 This can be overcome by using position sensitive detector.