Scanning tunneling microscopy and scanning electron microscopy can be applied to examine the fiber surface topography (shape, width, and depth of porosity).  The fiber surface area is important in considering the lock and key configuration between fiber and matrix.
       In SEM, the probing mechanism for the topographical analysis is electrons which have a better resolution than an optical microscope.  The SEM technique also gives a 3-dimensional feature due to its larger depth of field (4-5 nanometers) on the surface.  Pictured below is an actual Environmental Scanning Electron Microscope (ESEM).

      STM can provide quantitative information on the depth as well as the width and length of a surface feature of a fiber such as a pore.  Atomic level resolution can be achieved with STM and atomic force microscopy, with AFM being useful on nonconductive surfaces.  The exact depth of exploration has not yet been fully exploited for STM and AFM instrumentation.  Pictured below is a Atomic Force Microscope (AFM) at the USM School of Polymers and High Performance Materials.

      An ESEM image is shown below of a fiber reinforced composite.  The material was broken and the insides looked at (like and autopsy).  Notice the fibers (long white cylinders) surrounded by the matrix.  It is difficult to see by this SEM, but some fibers have pulled out of the matrix and it looks like dowell rod pulled out of a jar of hard glue.

      The last SEM image below represents another fiber reinforced matrix composite, however, in this material, the adhesion between fiber and matrix is stronger (good interphase).  As you can see it appears as though the fiber has broken out of its hole and brought some of the matrix with it.

Below is a table of technique properties for each of the methods mentioned in this area of surface analysis techniques.
 

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