There is some confusion about phase imaging. Phase imaging is not really an operation mode in itself. It is carried out in intermittent contact mode (IC-AFM). In commercial AFMs. depending on the instrument, IC-AFM may be referred to as AC-AFM, vibrating mode, tapping, etc. If you carry out IC-AFM and monitor the phase signal, you are doing what is referred to as "phase imaging", i.e. generating a phase-contrast AFM image. Further confusion can occur because of the unrelated optical microscopy technique "phase contrast microscopy". There is also a technique in TEM called "phase-contrast imaging". Even more confusingly, with heterogeneous materials samples, researchers often refer to the different materials in the sample as forming different phases. Thus, many users are confused about what phase imaging in AFM really is. However, it is a powerful technique, for producing contrast on heterogeneous samples. In this shortened extract from Atomic Force Microscopy. The origin of the signal and its use is described in this article. phase

 

 

I am adding some short articles about different AFM Modes. These should describe how the mode works, and what it can do. They will all be extracted from my book "Atomic Force Microscopy.

The first article is about Phase Imaging, an often misunderstood technique in AFM.

phase

 


 

The second "modes" article is about Magnetic Force microscopy, MFM. This technique allows MFM to measure magnetic fields. 

MFM IMage

 


 

book coverThe articles in the book all contain a full reference list.

Images in this article come from the book, and are Copyright Peter Eaton/ OUP 2010.

At the moment, I have disabled user registration and login. Most of you never login, and the only advantage to do so, is that you can submit pictures to the gallery, so it wont have much negative effect. I did this because the user registraiton was getting spammed with fake accounts. If I figure out how to add some effective captcha to stop this heppening, I may re-enable the user menu in the future.

-Pete

Magnetic Force Microscopy

Magnetic force microscopy (MFM), is a family of techniques used to measure magnetic fields using an AFM. In fact there are a large number of different  techniques used to measure magnetic properties, but in general, they all use the AFM to measure the oscillation of a magnetically sensitive probe when it is far (5-100 nm) from the sample surface. MFM probes are usually made by coating normal silicon probes with a thin magnetic coating. The magnetic coating means that the oscillation of the probe will change when in a magnetic field. However, when the probe is touching the sample, the short range tip-sample forces will obscure the magnetic forces (which are much weaker). Fortunately, since magnetic forces can be measured at a distance, it is possible to remove the probe from the surface, and still measure magnetic forces, while removing these short range forces. In order to make accurate measurements, the probe should be at the same distance from the sample throughout the image. There are a number of techniques to do this, which are reviewed in [1], but in most commercial implementations, the so-called “Lifting” method first used by Bard [2] is used. This method is illustrated schematically below.

 

How MFM lifting modes work

In order to make MFM measurements with this lifting mode, an oscillating mode is used, typically intermittent contact mode AFM. For each line of the image, two scans are made. In the first line, the topography is measured as usual. The probe is then lifted a user-defined distance above the surface (typically in the range 5 to 50 nm). The second line will then be measured, but the topography measured in the first line is added to the height of the probe as it scans along the line. In this way, the instrument attempts to keep the probe at exactly the same distance from the sample surface at each point in the MFM image. MFM is widely used to generate images of magnetic fields associated with small domains, and is particularly of use in the development of magnetic recording technology . It can also show magnetic fields associated with individual magnetic nanoparticles[3]. However, interpretation of MFM signals is complicated by the unknown nature of the probe, and it is limited to measuring fairly intense fields[4,1].

mfm

The image above shows topogrpahic (left) and magnetic field (right) images of a cluster of magnetic nanoparticles.

 

References

Eaton P et al. (2010) Atomic force microscopy. OUP, Oxford

Lin CW et al. (1987). J Electrochem Soc 134:1038-1039.

 Neves CS et al. (2010). Nanotechnology 21:305706.

Schreiber S et al. (2008). Small 4:270-278.


book coverThis article was condensed from “Atomic Force Microscopy” by Eaton and West, OUP, 2010. The article comes from Chapter 3, which describes all of the commonly used modes in Atomic Force Microscopes. The Article in the book also contains a full reference list.

 


Images in this article come from the book, and are Copyright Peter Eaton/ OUP 2010.

This instrument is supervised by: Peter Eaton; Please contact Peter for any enquiries regarding access to the lab, or training or use of the instruments. Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

TTAFM at porto

 

Instrument #1: Long Beach

This instrument is a modified TT-AFM from AFM Workshop.

It is equipped with two scanners, enabling large (low resolution) or small (high resolution) sample imaging. It has an standard liquid cell for in-situ measurements, and a custom-made liquid heater cell (ambient to 60 celcius), with 0.1 degree accuracy. It has been upgraded with two new ADC cards, so it's now capable of recording 12 channels simultaneously, and displaying a life feed of height, scanner voltage, amplitude, etc (see left image above). It's installed in a custom-made vibration and acoustic isolation cabinet.

Here are more detailed specifications:

  • Instrument Configuration: Optical lever - based sample-scanning AFM
  • Sample Size: Maxmium ca. 20x20x5 mm
  • Imaging Modes: vibrating (tapping), non-vibrating (contact), phase imaging, lateral force microscopy (friction force microscopy)*
  • Imaging Environment: Air or Liquid.
  • Imaging temperature ambient to 60 ºC
  • Z-translation: Vertical direct drive (1 micron resolution)
  • XY Translation: Manual
  • Video Optical Microscope: Zoom to 400X, 3 micron resolution (3M pixel camera)
  • Scan Range: 50x50x17 microns or 20x20x7 microns
  • Linearisation: All axes (x, y and z) with strain guages, can be turned off for enhanced signal to noise ratio
  • Z noise level: less than 0.2 Angstrom
  • Vibration isolation: Passive vibration isolation, with acoustic shielding

 

Instrument #2: San Diego

This is a Life Sciences AFM (model B) from AFM Workshop. It is a probe-scanning AFM with maximum 50 micron scan range. it is mounted on an inverted optical microscope, equipped for brightfield, phase, and fluorescence microscopy. We have both air and liquid scanning-capable probe holders. It is typically used for cell studies and other transparent samples. UPDATE: This instrument currently not available.



Booking Schedules and Calendars:

Click the link below to see the Longbeach Google calendar

TT-AFM - Longbeach

 

 

LS-AFM -San Diego - Calendar currently not available



Example Images
Here are just a few example images measured with the TT-AFM instrument on a variety of samples.

More images can be found in the LS-AFM image gallery and the TT-AFM image gallery.

many bacteria amplitude e. coli
Grid spores in phase cells and spore
leishmania cell epithelial cell  



TT-AFM Protocols



Troubleshooting

There is a Google Docs file I have created which contains the solutions to some problems that might crop up using the TT-AFM. This could also apply to other TT-AFM instruments. You can reach it (for viewing) via this link: TT-AFM troubleshooting. If you have something to add to the document, and wish to contribute, just email me (This email address is being protected from spambots. You need JavaScript enabled to view it.) for access.

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