A Very Easy Explanation of Scanning Probe Microscopy
How does an AFM (Atomic Force Microscopy) work?
Which are the operation systems available for AFM and how do they work?
How does an SNOM (Scanning Near-field Optical Microscopy) work?
Taking an extremely close look at science.
A Scanning Probe Microscope (SPM) is an advanced type of computerized microscope used in an very specialized branch of advanced research science. In Scanning Probe Microscopy, this highly sophisticated microscope makes the atoms on the surface of a material clearly visible to a researcher for scientific study.
The particles of matter being examined, the atoms, are so small, they are measured in nanometers (one millionth of a millimeter), and angstroms (one ten millionth of a millimeter). SPM reveal an exotic, hidden world of atomic structures.
What does SPM examine?
What do scanning probe microscopes examine these days? Almost everything that has become part of our daily lives: the surface of the aluminium can for your cool drink; the paint on your bedroom wall; the plastics that you use in the kitchen as packing materials; the microchips that drive your computer; the hip implant that helps grandma walk again; even the DNA that contains the recipe for all living things.
SPM works like an old fashioned record player.
A scanning probe microscope (SPM) basically works like an old fashioned record player, where the up-down movement of the needle sent the recorded impulse through the amplifier and on to the speakers to produce music.
In an SPM, a very sharp "needle", called a probe, scans over the surface of a material. The movement of the needle, due to the forces between the atoms in the needle and the atoms in the surface, are picked up by a computer and sent to produce an image of the surface on a computer screen. Close examination of minute changes occurring with the atoms becomes relatively simple.
We can see clearly now.
This electronic scan of the atom generated onto the computer screen is in color and 3D! It looks like one is plotting the surface of the moon, but this "moon" is so small it cannot be seen by the naked eye. And yet peaks and valleys are seen in clear detail.
SPM is an ever-expanding science.
The areas and opportunities for investigation by SPM are vast, indeed, as they sweep across semiconductor chips, polymers, chemicals, coatings, paper, metals, ceramics, magnetic and recording materials, medicines, biological substances, cells, tissues, films, on and on through the natural and applied sciences. Examining and knowing inner structures ultimately leads scientists to new discoveries, new cures, new ways to improve life and the things of living.
Microscopy Scientists Win Nobel Prize!
SPM technology's ancestor, STM Scanning Tunneling Microscopy, was invented in 1981 by Gerd Binnig and Heinrich Rohrer at IBM in Zurich, Switzerland. They went on to win the Nobel Prize for physics with this discovery. It has formed the basis for all serious in-depth microscopy research worldwide ever since.
The measurement is monitored using the so called optical beam reflection detection system, in which a laser beam is reflected on the backside of the cantilever and onto a four quadrant position-sensitive photo sensor. This detector measures the bending of cantilever during the tip is scanned over the sample. The measured cantilever deflections are used to generate a map of the surface topography.
AFM can be used to study insulators and semiconductors as well as electrical conductors, biological samples, magnetic samples etc..
see also BerMad 2000 AFM
Three imaging modes, contact mode, non-contact mode, and intermittent contact, can be used to produce topographic images of sample surfaces.
In contact mode, the tip makes "physical contact" with the sample, and is essentially dragged across the sample surface to make an topographic image. Contact mode imaging can be performed within a liquid environment, which essentially eliminates problems due to surface moisture such that much lower contact forces can be used.
In Non-contact mode the cantilever is vibrated near the surface of a sample. The spacing between the tip and the sample is on the order of tens to hundreds of angstroms. Like contact mode, the motion of the scanner is used to generate the topographic image.
Intermittent mode is as contact mode except for that the vibrating cantilever tip is brought closer to the sample so that it just barely hits, or "taps" the sample. This mode is applicable to both imaging in liquids and in air, particularly for soft samples, as the resolution is similar to contact mode while the lateral forces applied to the sample are lower and less damaging.
It works by exciting the sample with light passing through a sub-micron aperture formed at the end of a optical fibre. Typically, the aperture is a few tens of nanometers in diameter. The fibre is coated with metal to form the aperture and to prevent light loss, thus ensuring a focused beam from the tip.
see also BioLyser SNOM