Rodolfo Fernandez, Xiaohua Wang, Peter Rogen, and A. La Rosa Near-field Microscopy Group Department...
-
date post
19-Dec-2015 -
Category
Documents
-
view
215 -
download
1
Transcript of Rodolfo Fernandez, Xiaohua Wang, Peter Rogen, and A. La Rosa Near-field Microscopy Group Department...
Rodolfo Fernandez, Xiaohua Wang, Peter Rogen, and A. La RosaNear-field Microscopy Group
Department of Physics, Portland State University, P.O. Box 751; Portland, Oregon 97207
INTRODUCTION EXPERIMENTAL SETUP
GND
Ref
TF
Signal generator
Acoustic feedback
control signal
Acoustic Signal from mesoscopic
film
Piezo-Electric
tube
Lock-in #1
Lock-in #2
WORKING PRINCIPLE -1
3.2 10-8
3.4 10-8
3.6 10-8
3.8 10-8
4 10-8
4.2 10-8
4.4 10-8
0
1
2
3
4
5
-50 0 50 100 150 200 250
Shear-forceAcousto
Probe retracts from the sample Ultrasonic S
ignal (a. u.)
(Arb
. uni
ts)
Probe displacement z (nm)
amplitude of probe's oscillations
Ultrasonicsignal
WORKING PRINCIPLE -2
Left: The lateral oscillations of the probe (few nm amplitude), while immersed into the mesoscopic film, engenders acoustic waves, which are sensitively detected by a acoustic sensor located underneath the sample. Right: The intensity of the acoustic wave depends sensitively on the probe-substrate separation distance (z). The results
shown above constitute an unprecedented detection of shear-forces via acoustic means.
~ nm
Acoustic sensor #1
Solidsubstrate
Probe’s lateral oscillations
Confined mesoscopicfluid
z
Mechanical motion driver
Listening to the nanowaves engendered at confined fluids
under shear
Exploiting the microscope frame as acoustic cavity to sense probe-sample surface interactions
We have developed a compact and versatile Shear-force/Acoustic Near-field Microscope (SANM), fully operated by acoustic sensory devices (U.S. Patent No. 11/809,196). It provides :a)An alternative method (acoustic) for characterizing surface phenomena (nanotribology, adhesion, wetting).b) a suitable characterization platform towards the development of surface related technologies ( industrial and bio-engineering lubricants,) and •c) potential capability for imaging sub-surface materials properties. Further, unique to its novel development, the SANM operates using its own acoustic-based feedback control, which allows topographic characterization of the sample.
S H E A R- F OR C E / A CO U S T I C N E A R – F I E L D M I C R O S C O P E (SANM)
S A N M L I S T E N S T O S U R F A C E I N T E R A C T I O N S at the N A N O - S C A L E
SubstrateAcoustic sensor #1
Substrate
PSU Near-field Microscopy Group
Pictorially, SANM uses a simple “audiphone”, (placed around the microscope’s frame) for listening to the probe-sample interactions, allowing the probe to “walk” safely across the sample’s surface.
Acoustic-based feedback control for scanning probe microscopy
Probe
Vx
Vy
TF
Acoustic sensor # 2
Resonant Cavity
Set point
XYZ scanner To image
processing
Topographic image
Ref
Vz Feedback
control
Sample Lock-in
SANM acoustic feedback for controlling the probe’s vertical position. SANM acoustic feedback for controlling the probe’s vertical position. The inset shows the acoustic signal decreasing monotonically as the probe approaches the sample in the last 35 nm proximity. This behavior is exploited by the SANM to implement its own probe-sample distance feedback control and, hence, image the sample’s topography. SANM is the first scanning probe microscope operated via acoustic transducer.
Principle: The probe-sample interactions affect the lateral motion of the probe. The latter, in mechanical contact
Acousticcavity
Acoustic sensor #2
XYZ scanner
Acousticwaves
Probe
Fluid film
Probe-filmInteraction region
Tic, tac,
tic
, tac
Tic, tac,
Probe
Acoustic sensor 2
Acousticresonant
cavity
SampleTic, ta
c,
Tic, tac,
Sample
0
1.1 10-5
2.2 10-5
3.3 10-5
140 105 70 35 0
File-15_(Feb-2005)Approaching_first_interval
UST
TF
0
1.1
2.2
3.3
Arb
. un
its
Probe-sample distance z (nm)
Acousticsignal #2
2 cm
Acoustic sensor
Acoustic cavity
with the cavity, sets waves that travel upwards towards the cavity where they interfere (see interference pattern). The acoustic is placed judiciously at the location of o constructive node for maximum sensitivity.