Transcript Slide 1

Common scanning probe modes
• Basic mode: surface morphology
– Contact mode
– Non-contact
– Tapping mode
• Secondary modes:
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Surface potential
Capacitance derivative and actual Capacitance
Surface conductivity
Scanning gate
Magnetic force microscopy
Thermal conductivity and temperature
Trivia: AFM was discovered after the inventor of STM (Gerd Binnig and Heinrich Rohrer were awarded
Nobel Prize in1986) wanted to develop a technique for mapping non-conductive samples.
Slide
# 1
Scanning probe microscopy
• Atomic force microscopy (AFM) and associated
modes: Applicable for conductive and nonconductive samples. Not as high resolution as STM.
Best resolution possible in conductive AFM.
• Scanning tunneling microscopy (STM): Only
applicable for conductive samples. True atomic
resolution possible.
Slide # 2
Picture of a typical AFM machine
A larger view of the system
A close-up of the
scanning chamber
Slide # 3
Parts of an AFM system
• A microcantilever to transduce changes in physical
parameters
• A probe tip to obtain nanoscale resolution
• A transduction method to quantify the change in
deflection or the oscillation amplitude of the cantilever
• Environment control chamber
• Noise cancellation schemes
• The sample with proper connections
Slide # 4
Contact mode AFM schematic
Basic idea: In contact mode, the probe tip is in physical contact with the sample,
within few Å from the surface, and operates in the repulsive region of the interatomic force curve (explained later). In contact mode the cantilever deflection is
measured to track the surface morphology using a feedback loop.
Slide # 5
Non-contact mode AFM schematic
Basic idea: In non-contact mode, the probe tip oscillates in resonance frequency with
an amplitude of several tens of nm, and operates in the attractive region of the interatomic force curve (explained later). In non-contact mode the oscillation amplitude of
the cantilever is measured to track the surface morphology by a feed back loop.
Laser deflection from cantilever sensed
with 4 quadrant photo-diode
Slide # 6
Tapping mode
(Intermittent contact mode)
This mode was developed (patented by Veeco Instruments) to take care
of some of the problems of both the contact and intermittent contact
modes.
Specifically, it takes care of the lateral force problem of the contact mode,
and the “water layer sticking” problem of the non-contact mode.
In this mode the tip intermittently comes in contact with the sample and
thus can provide much better imaging results, especially in liquid
environments.
Slide # 7
Amplitude
Basics of AFM modes
Curve 2 (near)
Change in amplitude
Curve 1(far)
d
Frequency
Non-contact mode amplitude vs. frequency
curve for the tip, far from and near the surface
k  k
0 
m
For van der Waals force region of the F-d curve, the
slope dF/dz is positive. Hence 0 decreases as the tip
comes closer to the surface, i.e. the curve shifts left
Slide # 8
Associated modes with contact and noncontact /Intermittent contact modes
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Scanning gate (Contact)
Scanning capacitance and capacitance derivative (Contact)
Scanning conductivity (Contact)
Scanning thermal conductivity and temperature (non-contact)
Magnetic force microscopy (non-contact)
Scanning Kelvin probe (non-contact)
Slide # 9