NT-MDT Solver PRO User manual

Solver PRO
Scanning Probe Microscope
Atomic Force Acoustic Microscopy
Instruction Manual
22 April 2010
Copyright © NT-MDT
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Read me First!
Observe safety measures for operation with devices containing sources of laser radiation.
Do not stare into the beam. A label warning about the presence of laser radiation is
attached to the measuring head (Fig. 1), laser sources.
Fig. 1
Before you start working with the instrument, get acquainted with the basic safety
measures and the operation conditions for the instrument!
If you are a beginner in scanning probe microscopy, we recommend you to familiarize with
basic SPM techniques. “Fundamentals of Scanning Probe Microscopy” by V.L. Mironov
gives a good introduction to the subject. This book is available on the Internet,
http://www.ntmdt.com/manuals.
Feedback
Should you have any questions, which are not explained in the manuals, please contact the
Service Department of the company ([email protected]) and our engineers will give you
comprehensive answers. Alternatively, you can contact our staff on-line using the ask-on-
line service (http://www.ntmdt.com/online).

User’s documentation set
The following manuals are included into the user’s documentation set:
−Instruction Manual – is the guidance for the preparation of the instrument and other
equipment for operation on various techniques of Scanning Probe Microscopy. The
contents of the user’s documentation set may differ in dependence on the delivery set
of the instrument.
−SPM Software Reference Manual – is the description of the control program
interface functions, all commands and functions of the menu and, also a description of
the Image Analysis module and the Macro Language “Nova PowerScript”.
−Control Electronics. Reference Manual – is the guide to SPM controller,
Thermocontroller and Signal Access module.
Some equipment, which is described in the manuals, may not be included into your
delivery set. Read the specification of your contract for more information.
The manuals are updated regularly. Their latest versions can be found in the site of the
company, in the section “Customer support” (http://www.ntmdt.com/support).

Atomic Force Acoustic Microscopy
SPM Solver PRO. Instruction Manual.
Atomic Force Acoustic Microscopy
Table of Contents
1. PREPARATION OF THE INSTRUMENT FOR OPERATION.........................................................5
1.1. ULTRASOUND TRANSDUCER INSTALLATION .................................................................................... 6
1.2. FIXING THE SAMPLE ......................................................................................................................... 6
1.3. CHOOSING THE PROBE...................................................................................................................... 7
2. CONDUCTING THE MEASUREMENTS............................................................................................8
3. FINISHING THE OPERATION ..........................................................................................................16

Chapter 1. Preparation of the Instrument for Operation
SPM Solver PRO. Instruction Manual.
Atomic Force Acoustic Microscopy
1. Preparation of the Instrument for Operation
The instrument preparation procedure is specified in section “Instrument preparation for
AFM modes” (see Performing Measurements, chapter 3). The list of the basic operations is
given below together with the description of the features of preparing the instrument for
AFAM measurements:
−Electromechanical configuration for “Scanning by probe” excluding the installation of
the sample holder.
−Ultrasound Transducer Installation (see i. 1.1on page 6).
−Fixing the Sample (see i. 1.2 on page 6).
−Turning on the instrument.
−Loading scanner calibration parameters.
−Preparing the measuring head (see i. “Preparing the instrument for ‘Scanning-by-
probe’ configuration” in Performing Measurements):
-Probe installation;
-Adjustment of the system for detecting the cantilever deflections;
-Installation of the scanning measuring head.
−Protective hood installation.
−Turning on the Vibration Isolation System (see the manual on the Vibration Isolation
System).
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Atomic Force Acoustic Microscopy
1.1. Ultrasound Transducer Installation
1. Unbend the spring supports and mount the ultrasound transducer in the positioning
device of the approach unit with the rounded part of the transducer base facing the user,
see Fig. 1-1.
a) ultrasound transducer b) ultrasound transducer mounted
in the positioning device
Fig. 1-1
2. Using the adapter shown in Fig. 1-2 plug the transducer to the EXTENSION socket of
the SPM Controller.
Fig. 1-2. Adapter
1.2. Fixing the Sample
Before fixing the sample make sure that it has a fairly flat and smooth surface on the side
by which it is to be fixed on the transducer. It means that the surface shall be free from
large prominence and irregularities that might impede tight contact with the transducer. A
material with good acoustic conductivity shall be used for fixing the sample. Common
liquid honey is one of the cheapest and easily available materials suitable for this purpose.
1. Put a small drop of honey on the ultrasound transducer surface (see Fig. 1-3).
2. Spread the honey evenly on the part of the transducer surface that is to contact the
sample.
6

Chapter 1. Preparation of the Instrument for Operation
3. Put the sample on the transducer. Slightly pressing the sample with tweezers make
several short movements along the transducer surface to ensure optimal spread of the
honey and better contact between the surfaces.
After completing the manipulations described above it is strongly recommended to wait for
some time (about one hour) before starting the measurements. This would allow the sample
to glue better to the transducer surface and would also minimize vertical drift of the sample
that can make the measurements difficult or even impossible.
Fig. 1-3
1.3. Choosing the Probe
When choosing the probe it is recommended:
−to use “rigid” probes (k~30 N/m) for measurements on rigid surfaces (semiconductors,
metals, etc.);
−to use “soft” probes (k~1 Н/м) for soft surfaces such as polymers.
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Atomic Force Acoustic Microscopy
2. Performing Measurements
The user is supposed to have detailed knowledge of the contact and semicontact mode
AFM (see Performing Measurements, chapter 3) before conducting the AFAM
measurements.
In AFAM method the phase, the amplitude or the frequency of the cantilever bending
oscillations is measured near the contact resonance frequency simultaneously with
recording the topography map by the contact technique.
To obtain the AFAM image the follow the procedure below:
1. Select Contact in the menu for choosing the electrical configuration of the instrument
(Fig. 2-1).
Fig. 2-1
2. Perform the approach the same way as in the standard contact technique:
a. Switch to Approach tab;
b. Activate Auto SetPoint option;
c. Click on Landing button.
3. Make a trial measurement of the sample topography map and choose an area for
scanning.
4. Switch to Resonance tab.
5. Determine resonance frequencies for the cantilever bending oscillations in a free state
(i.e. when the feedback is turned off and the probe is far enough from the surface):
f0, f1, f2. For that:
a. Turn off the feedback ( button is not pressed in).
b. Energize the piezodrive in the probe holder with voltage from the generator. To this
purpose, open the instrument block scheme and commute the key as shown on
Fig. 2-2.
8

Chapter 2. Performing Measurements
Fig. 2-2
c. In the control panel of Resonance tab make the following changes (Fig. 2-3):
-In Response signal drop-down list select Mag.
-Set the range (From … To)to include several cantilever resonance frequencies.
The second and third resonance frequencies are related to the first one as
f1/f0=6.22 and f2/f0=17.5. So, with the exemplary frequency f0=28 of the contact
probe the operating range should be taken as From = 0 kHz, To = 600 kHz.
-Clear the Auto peak find check box.
-Set Amplitude parameter equal to 1V × 1.
-Set the lock-in amplifier gain (Gain parameter) equal to 10.
Fig. 2-3
d. Click
Run button to plot the frequency response of cantilever oscillation amplitude
(Mag signal), see Fig. 2-4, Fig. 2-5. On the resulting response apart from the peaks
corresponding to the cantilever resonance frequencies, spurious peaks may appear
owing to resonance oscillations of the piezodriver exciting the cantilever.
e. By narrowing From … To range adjust it to cover the frequency range
corresponding to a chosen AFAM resonance mode (n=1, n=2, …). In the given
example the range was chosen between the first, f0, and the second, f1 , resonance
peaks related to the first mode. The cantilever contact resonance frequencies
( , ) shall lie between the resonance frequencies of the cantilever
oscillations in the free state: f0< < f1; f1< < f2.
AFAM
n
f1
AFAM
n
f2
AFAM
n
f1
AFAM
n
f2
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Atomic Force Acoustic Microscopy
Fig. 2-4. Frequency response of the cantilever oscillations amplitude
in the frequency range below 55 kHz
Fig. 2-5. Frequency response of the cantilever oscillations amplitude
in the frequency range above 55 kHz
10

Chapter 2. Performing Measurements
6. In the range chosen determine the contact resonance frequency of the cantilever
( , …). For that:
AFAM
n
f1
AFAM
n
f2
a. Turn on the feedback ( button is pressed in).
b. Open the instrument block scheme with the Scheme button in the Additional
Operations Panel. Supply voltage from the generator to the ultrasound transducer
by turning the key to Ex6 position (Fig. 2-6).
Fig. 2-6
c. In the control panel of Resonance tab make the following changes (Fig. 2-7):
-In Generator Output drop-down box select Ex6 (Fig. 2-7). At this the generator
output voltage is applied to the transducer.
Fig. 2-7
-Set the gain factor of the lock-in amplifier equal to 10 (Fig. 2-8) since the
response in AFAM is much smaller than in the semicontact technique.
Fig. 2-8
d. Click Run button to plot the frequency response of cantilever oscillation amplitude
(Mag signal).
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Atomic Force Acoustic Microscopy
7. Adjust the amplitude of the generator output signal (Amplitude parameter) and the
lock-in amplifier gain (Gain parameter) so that the maximum of Mag signal is within
the range of 5-10 nA and the resonance peak is symmetrical. If the peak is tilted or
truncated Amplitude shall be decreased.
A criterion for the right choice of Amplitude value is approximate linearity of the
dependence between Mag signal and Amplitude signal. This can be checked by first
increasing and then decreasing Amplitude signal by a factor of ~2.
Fig. 2-9
8. Adjust
Set Point as follows: for several values of Set Point notice the shift in the
position of the resonance peak with minor variations in Set Point (the peak should go
to the right (i.e. the resonance frequency should rise) with increasing the Set Point
value and to the left with decreasing the Set Point value). Choose the Set Point value
that corresponds to the maximum shift in the position of the resonance peak. In this
case the best contrast of the AFAM image will be achieved.
NOTE: Invariability of the peak position with changing Set Point means that
the contact stiffness does not vary (reaches saturation) as a function of the
pressure applied to the cantilever. This can result in poor contrast of the
AFAM image for a given sample region.
12

Chapter 2. Performing Measurements
9. Set the working frequency of the generator accounting for the entity to be recorded
(phase, amplitude, or frequency).
-When recording amplitude change: set the value of the piezodriver working
frequency (Frequency parameter) at one of the resonance peak slopes. In case of
the right slope lighter region would correspond to larger cantilever response signal
Mag and, consequently, to greater sample stiffness since the resonance peak shifts
to the right as stiffness increases. On the contrary, lighter regions correspond to
smaller stiffness in case of the left slope.
-When recording phase change: set the value of the piezodriver working
frequency (Frequency parameter) corresponding to a maximum Mag signal.
-When recording frequency change: set the value of the piezodriver working
frequency (Frequency parameter) corresponding to a maximum Mag signal.
10. Set the phase in a chosen point equal to 90° using a special script. For this select in the
main window sequentially Tools Script Scripts Phase_Auto_Ajustment_1_5.
11. Define the phase containment range for scanning:
NOTE. This step is unnecessary with recording amplitude or phase of the
cantilever bending oscillation.
a. In Response signal drop-down box select Phase.
b. Click Run button to plot phase response (Fig. 2-10).
c. Select the phase containment range by placing two vertical markers in desired
positions in the vicinity of the resonance (between extremum).
Fig. 2-10
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Atomic Force Acoustic Microscopy
12. Switch to Scan tab.
Now the procedure branches out to account for the recorded entity (phase, amplitude,
or frequency).
For recording the frequency change, select the AFAM mode. Skip this step if the
phase change or the amplitude change are recorded.
a. Select the measurement mode in the Mode drop down list. The AFAM panel
appends the Control Panel to the right (Fig. 2-11). The input fields Freq Min, Max
are filled with values defined by the markers in the plot. The Set Point field is filled
with the phase value of 90. The Gain field sets the gain coefficient to its negative
extremum.
Fig. 2-11. AFAM Control Panel
b. Select the Freq FB Enabled box.
For recording the phase change or the amplitude change, the corresponding entity
should be selected as the measured signal:
a. Open Scan Settings dialog window (Settings button).
b. For signals measured on the direct scan set:
-when recording amplitude change: Height and Mag,
-when recording phase change: Height and Phase (Fig. 2-12).
c. Close Scan Settings dialog window (OK button).
Fig. 2-12. Scan settings for AFAM measurement of amplitude
14

Chapter 2. Performing Measurements
Scanning
1. Select scan area and set scanning.
2. For recording the frequency change, set a moderate scanning speed for the feedback to
follow phase changes. The recommended scanline rate is Frequency 0.5 kHz.
3. Start scanning by clicking Run button.
Fig. 2-13 shows an example of a scanned image for the surface of polyethylene-
oxide/carbon nanotube nanocompisite. It is seen that regions with greater stiffness (carbon
nanotubes) correspond to darker areas in the AFAM-image.
Fig. 2-13 Image of the surface of polyethylene-oxide/carbon nanotube nanocomposite. Left:
topography map; right: AFAM phase contrast.
ScanSize – 40x40 μm2, Frequency – 1 Hz, f=67.95 kHz
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Atomic Force Acoustic Microscopy
3. Finishing the Operation
1. Rise the probe 2-3 mm above the sample.
2. Turn off the feedback ( button is not pressed in).
3. Turn off the SPM controller.
4. Turn off the Vibration Isolation System.
5. Close the control program.
6. Remove the sample from the transducer.
NOTE: Thin inflexible samples might require the application of small side force,
see Fig. 3-1. The sample will start moving gradually and then it can be easily
removed. When honey is used little heating may be recommended to facilitate the
sample removal.
Fig. 3-1
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