AFM tip. This may be either Unmounted or pre-mounted. Note that mounted tips may be too large to fit between the poles of a TEM.
Lateral force calibration grid, for example, that available from MikroMasch, number TGG01.
• In the Signal access Control connect the Mon10 Z(T-B) to AUX1-
• Open SPM Cockpit
• Set Channels:
Channel 1: Z(HGT)
Channel 2: Z(ERR)
Channel 3: Z(L-R)
Channel 4: AUX(IN)
• Align laser
• Go into contact
• Record a force distant curve monitoring the AUX(IN) signal and record pull-off force.
• Set the resolution to the desired value
• Set the scan size. Example: 10 μm.
Based on a method by D. Flater and R. Cannara
I. Calibrating F versus L data- Calibration Experiments
A. Lateral calibration (Based on a method suggested by Ogletree et al., Rev. Sci. Instrum. 67, 9 (1996))
1. After performing FvL experiments, the tip should be scanned across a lateral calibration grating. This sample has long parallel ridges of well-defined crystallographic orientation, such as a SrTiO3 sample or Mikro Masch’s TGG01.
The TGG01 works best for all types of tips, even tips with a large radius.
2. Scan an image with load variation so that at least 2 sloped facets (one up, one down) can be seen during the scan.
Scanning at loads between - FPO and 2FPO, where FPO is the pull-off force, is sufficient.
B. Normal calibration (Based on a method suggested by Sader et al. Rev. Sci. Instrum. 70, 10 (1999))
1. Determine the resonance frequency of the cantilever.
a) Measure amplitude of oscillation of the cantilever as a function of frequency of forced oscillation. Find the
first significant resonance peak. This can be performed by the Pacific Nanotechnology software. This should
correspond to the first resonance of the cantilever. Record the frequency at which the amplitude is a maximum
within this resonance peak.
b) Double check this frequency with that which is given by the manufacturer.
(1) Your measured frequency should be in the same range as the manufacturer’s value.
(2) If not, you may have found a harmonic of the resonance frequency. Change the frequency range so that
this resonance frequency may be found.
2. Determine the Q factor of the cantilever.
a) Some software programs can calculate Q automatically.
b) If it is not calculated automatically, record the resonance peak to be imported into a graphing software
package (e.g. KaleidaGraph).
(1) Determine the full width at half the maximum.
(2) Q = w/δw, where w is the resonance frequency and δw is the full width at half maximum of the
resonance peak.
3. If possible, record ambient temperature and relative humidity, during the above steps.
4. Measure in-plane dimensions of the cantilever.
a) Use an optical microscope with a calibrated measuring device to determine the length and width of the
cantilever.
b) Be careful to measure the length from the appropriate base of the cantilever; this position is not always
obvious, and it may be necessary to check with the manufacturer (or obtain a side-view image
in an SEM or TEM).
II. Analyzing F versus L Data
A. Normal Force Constant Calibration
1. To determine the normal spring constant of the cantilever.
a) Go to http://www.ampc.ms.unimelb.edu.au/afm/calibration.html
b) Input values for the resonance frequency, Q factor, and the in-plane dimensions of the cantilever.
c) The program will automatically calculate the normal spring constant of your cantilever, in N/m. If you know
the torsional resonance properties, the section at the bottom will calculate the torsional spring constant.
2. Determine the normal sensitivity of the cantilever.
a) From force distance curves measured on a stiff surface, such as silicon or diamond, calculate the
normal sensitivity of the cantilever (i.e., the slope of deflection voltage versus z displacement). Some AFMs
calculate this slope for you from a force distance plot.
b) The normal sensitivity, SN, is basically the conversion factor between the number of vertical nanometers
traveled by the piezo and the change in volts measured by the movement of the laser spot on the photodiode.
Units: [nm/V]
C. Lateral Force Constant Calibration
1. Take the friction_v_load.m file, including friction calibration images (rev.txt, for.txt, revaux.txt), and place them in the same file folder.
2. Open up MatLab and make the current directory the same as the one that holds the above files.
3. Run friction_v_load.m to calibrate the lateral sensitivity of the cantilever. (The prompts for the program should
be self-explanatory, but here are the step-by-step actions. Italics here indicate what you see in the MatLab
command window, or what you should type.)
a) Type the following at the MatLab prompt, where for.txt, rev.txt and revaux.txt are the files that you wish to
analyze: friction_v_load(‘auxrev.txt’,’for.txt’,’rev.txt’)
(1) A window will appear showing a force distance curve obtained from the variation of the load. Forces
should be given here in volts and there will be an offset due to the initial alignment of the photodiode.
The out-of-contact region of the force curve should be at 0V but may be offset due to this alignment
issue. Therefore the data need to be shifted accordingly.
(2) Enter the value in volts that this line is away from 0. You can use the zoom-in tool to help with this.
(3) For example, if the out-of-contact line is at –1.2V, type in –1.2 at the prompt.
