Scanning probe microscopy

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Scanning Probe Microscopy (SPM) is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. An image of the surface is obtained by mechanically moving the probe in a raster scan of the specimen, line by line, and recording the probe-surface interaction as a function of position. SPM was founded with the invention of the scanning tunneling microscope in 1981.

Many scanning probe microscopes can image several interactions simultaneously. The manner of using these interactions to obtain an image is generally called a mode.

The resolution varies somewhat from technique to technique, but some probe techniques reach a rather impressive atomic resolution. They owe this largely to the ability of piezoelectric actuators to execute motions with a precision and accuracy at the atomic level or better on electronic command. One could rightly call this family of technique 'piezoelectric techniques'. The other common denominator is that the data are typically obtained as a two-dimensional grid of data points, visualized in false color as a computer image.

Contents

[edit] Established types of scanning probe microscopy

Of these techniques AFM and STM are the most commonly used followed by MFM and SNOM/NSOM.

[edit] Probe tips

Probe tips are normally made of platinum/iridium or gold. There are two main methods for obtaining a sharp probe tip, acid etching and cutting. The first involves dipping a wire end first into an acid bath and waiting until it has etched through the wire and the lower part drops away. The remained is then removed and the resulting tip is often one atom in diameter. An alternative and much quicker method is to take a thin wire and cut it with a pair of scissors or a scalpel. Testing the tip produced via this method on a sample with a known profile will indicate whether the tip is good or not and a single sharp point is achieved roughly 50% of the time. The problem with this method is that you can end up with a tip that has more than one peak but this will be immediately obvious when you start scanning due to the high level of ghost images.

[edit] Advantages of scanning probe microscopy

  • The resolution of the microscopes is not limited by diffraction, but only by the size of the probe-sample interaction volume (i.e., point spread function), which can be as small as a few picometres. Hence the ability to measure small local differences in object height (like that of 135 picometre steps on <100> silicon) is unparalleled. Laterally the probe-sample interaction extends only across the tip atom or atoms involved in the interaction.
  • The interaction can be used to modify the sample to create small structures (nanolithography).
  • Unlike electron microscope methods, specimens do not require a partial vacuum but can be observed in air at standard temperature and pressure or while submerged in a liquid reaction vessel.

[edit] Disadvantages of scanning probe microscopy

  • The detailed shape of the scanning tip is sometimes difficult to determine. Its effect on the resulting data is particularly noticeable if the specimen varies greatly in height over lateral distances of 10 nm or less.
  • The scanning techniques are generally slower in acquiring images, due to the scanning process. As a result, efforts are being made to greatly improve the scanning rate. Like all scanning techniques, the embedding of spatial information into a time sequence opens the door to uncertainties in metrology, say of lateral spacings and angles, which arise due to time-domain effects like specimen drift, feedback loop oscillation, and mechanical vibration.
  • The maximum image size is generally smaller.
  • Scanning probe microscopy is often not useful for examining buried solid-solid or liquid-liquid interfaces.

[edit] Programs

[edit] References

  1. ^ Morita, Seizo. Roadmap of Scanning Probe Microscopy. 3 January 2007
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[edit] External links

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Scanning probe microscopy
Common
Typical atomic force microscopy set-up
Other
Applications
See also
Retrieved from "http://en.wikipedia.org/wiki/Scanning_probe_microscopy"
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