Microscopes Flashcards
two types of scanning probe microscopes
scanning tunneling microscopy (STM)
atomic force microscopy (AFM)
two types of AFM
contact and non contact
in scanning probe microscopes, what happens
sharp probe tip is scanned across a surface
in scanning probe microscopes, what controls the x, y, z motion
piezoelectric materials
what is required for scanning probe microscopes
good vibration isolation
what does the scanning probe microscope detect
signal that reflects topography or other property of interest
STM can operate in
air, liquid or vacuum
for STM the sample and tip must be what
conducting
most common STM tips
electrochemically etched Tungsten wire
mechanically cut Pt-Ir wire
desirable properties of STM tips
conducting, hard, inert (for imaging in air)
in STM the anode is
the tungsten wire
in STM in liquid, the cathode is submerged in aqueous solution of
NaOH or KOH
The tungsten wire etches and breaks at
the air/solution interface
AFM measures what
deflection of a cantilever of known spring constant due to tip-surface interaction forces
AFM can operate in
air, liquid or vacuum
IN AFM sample and tip must be
conduction or insulating
Contact AFM operates in what region
repulsive tip sample forces
in contact AFM scanning at constant cantilever deflection results in what
contour map of constant force, representing topography
In contact AFM, what is twisting the cantilever a measure of
lateral (friction) forces
Disadvantage of AFM contact mode
can be damaging to surface
non contact AFM operates in what region
van der waals forces (attractive forces)
in non contact AFM the cantilever is forced to
oscillate at its resonant frequency (100-300 kHz)
in non contact AFM what does the change in force experienced by tip changes what
the resonant frequency
in non contact AFM what is the change in resonant frequency used as
the feedback signal
advantages of non contact AFM
ideal for delicate samples. and can give atomic resolution
