*2.2.3 Reflection electron microscope (REM)*

Another type of development of the electron microscope is the reflection electron microscope (REM). The REM is an electron microscope that has almost the same way of working as TEM, the difference is that REM uses the detection of electron reflections on the object's surface. The sample is semi-infinite and the surface to be observed is almost parallel to the electron beam. The transmitted spot may or may not be observable, depending on the sample size as shown in **Figure 4**. This technique is specifically used in combination with the Reflection High Energy Electron Diffraction (RHEED) technique and the reflection high-energy loss spectrum (RHELS) technique.

REM could be a combination of imaging, diffraction, and spectroscopy procedures for the characterization of topography, crystal structure, and composition of surfaces of single crystals. High-energy electrons are occurring at looking points to the surface and reflected electrons are utilized to create a REM picture. Utilization of REM in analyzing osteoporosis in bone is still rarely done, because REM has several drawbacks including REM images are shortened in the direction of electron events and high resolution is only achieved in the normal direction, so that in analyzing surface topographic details more than one azimuth is needed. Meanwhile, bones that are not homogeneous can produce different images in each image. These

**Figure 4.** *These ray diagrams illustrate (a) TEM and (b) REM [18].*

techniques are applicable to metal [19], semiconductor [20], crystal surfaces [21], surface reconstructions and phase transformations [22], correlation between topographical features and reconstructions, directions, distribution, and motion of surface steps, dislocations on surfaces, nucleation and growth of films, and surface reactions [23].

Sample preparation for REM is the same as for other types of electron microscopy, i.e., it must be ensured that the surface is sufficiently flat and clean. The size of the sample should fit the microscope sample holder by about 3 mm. Then inserted into the electron microscope with a surface normal perpendicular to the optical axis. The nominal size of a REM sample is no more than 1 mm3 for a sample holder which gets 3 mm grids. Hence, the perceptible surface is about 1 mm or less. The lower restrain of the surface area is approximately 10 μm in diameter.
