Scanning Probe Microscope
-is emerging as an important alternative to electron microscopy as a technique for analyzing submicron details on biological surfaces.
-its magnification is up to 100,000,000.
-provides high image magnification for observation of three dimensional shaped specimen.
-the first successful scanning microscope observation was conducted by Dr. Gerd K. Binning and Dr. Heinrich Rohrer.
How does it work?
•A scanning probe microscope has a sharp probe tip on the end of a cantilever, which can scan the surface of the specimen. The tip moves back and forth in a very controlled manner and it is possible to move the probe atom by atom.
•A force deflects the cantilever when the tip gets close to the surface of the sample, which can be measured by a laser reflected from the cantilever into photodiodes. There are many different forces that may cause the deflections, such as mechanical, electrostatic, magnetic, chemical bonds, van der Waals and capillary forces.
•The data from the laser reflections detected by the photodiodes is combined to generate an image by a computer. The image has no color because it is a representation of properties rather than light, although they are often given color by the computer program to assist in differentiating the different properties of the specimen.
Types of Scanning Probe Microscope:
1. Scanning Tunneling Microscopes
-The scanning tunneling microscopes use a piezo-electrically charged wire, a very small space between the charged wire and the surface and the specimen to produce enhanced images of the specimen.
-The charged wire forces energy across the small space and onto the specimen where the current meets with the specimens surface and decays.
-This decay is measured and a high resolution image is produced from the information collected.
-Tunneling microscopy allows imaging at the atomic level to be produced plus different types of information can be obtained by altering the environment that the specimen is observed in such as a gaseous environment, vacuum, or a liquid environment.
2. Atomic Force Microscopy
-Atomic force microscopy uses a cantilever with a sharp probe that scans the surface of the specimen allowing for a resolution that you can measure in fractions of a nanometer; in other words "feeling" the surface of an object in order to produce a visual image.
-The flexibility of these types of microscopes are allowing for additional specialized instruments including the near field scanning optical microscope that utilizes optical fibers to stimulate specimens.
3. Scanning Near-Field Optical Microscopy
-Resolution in classical optical microscopy is limited by diffraction due to the wave nature of light. Therefore a resolution below approx. λ/2 is usually not possible. However, Scanning Near-field Optical Microscopy (SNOM) overcomes the diffraction limit and generates high-resolution optical images. The technique requires only minimal sample preparation if any.
Advantages
•Scanning Probe Microscopy provides researchers with a larger variety of specimen observation environments using the same microscope and specimen reducing the time required to prepare and study specimens.
•Specialized probes, improvements and modifications to scanning probe instruments continues to provide faster, more efficient and revealing specimen images with minor effort and modification.
