Rough Surfaces give a more complete "picture"of the sample. One of the key advantages of the SEM with respect to other types of microscopy is its large depth of Composition field.This ability makes it Both SEM and SPM provide possible to image very rough compositional information surfaces with millimeters of through a variety of techniques. vertical information within a SEM is the only one of the two single image.A SEM image of techniques which provides non-woven polyethylene oxide elemental analysis,however,both fibers can be seen in Figure 8a. SEM and AFM are associated with The depth of field and small beam techniques which can provide size makes it possible to image the compositional information fibers far below the top layer.This through analyzing materials and ability also makes it possible to physical properties of the sample. measure very rough surfaces over Some of the most common of larger lateral areas as well.Al- these methods are described though the AFM can measure below. vertical surface variations below 0.5A,its ability to measure a tall SEM structure comes from how far the scanner can move vertically. Along with the secondary electron Standard scanners typically have 5 emission which is used to form a (b) NCSU 5ku×18.66815mL81 to 6um of vertical range,however, morphological image of the in some configurations the vertical surface in the SEM,a number of range approaches 10um or larger. other signals are emitted as a result Figure 8.(a)SEM image of a non-woven textile For scanning areas that have of the electron beam impinging sample of polyethylene oxide fibers.The large depth heights of greater than 5 to 10um's on the surface,as shown in Figure of field of the SEM makes it possible to image fibers of variation,the SEM would be 9.Each of these signals carries which are 10's of um's below the upper layer of fibers. better suited for the analysis. Bar=10um;(b)SEM image of Y,O crystal.Bar=1um. information about the sample which provide clues to its compo- Another example of a complex sition three-dimensional surface struc- ture which shows how the SEM Two of the most commonly used and AFM can complement each signals for investigating composi- other can be seen in Figure 8b. tion are x-rays and backscattered The convoluted three dimensional electrons.X-ray signals are Y,O,oxide crystal shown growing commonly used to provide out of a relatively flat Y,O,thin elemental analysis by the attach- film on a Si substrate is easily ment of an Energy-Dispersive imaged in the SEM(Figure 8b). Spectrometer (EDS)or Wave- Although the AFM would have length-Dispersive Spectrometer probelms imaging the obtuse (WDS)to the SEM system.X- angels and enclosed areas of this ray emission results from inelastic surface,the roughness of the Y,O scattering between the beam film can be measured whereas in electrons and the electrons of the the SEM image the surface sample atoms.This interaction roughness is not evident.There- results in the ejection of an inner fore,the two techniques together shell electron from the atom, 66 Rough Surfaces One of the key advantages of the SEM with respect to other types of microscopy is its large depth of field. This ability makes it possible to image very rough surfaces with millimeters of vertical information within a single image. A SEM image of non-woven polyethylene oxide fibers can be seen in Figure 8a. The depth of field and small beam size makes it possible to image the fibers far below the top layer. This ability also makes it possible to measure very rough surfaces over larger lateral areas as well. Al￾though the AFM can measure vertical surface variations below 0.5Å, its ability to measure a tall structure comes from how far the scanner can move vertically. Standard scanners typically have 5 to 6µm of vertical range, however, in some configurations the vertical range approaches 10µm or larger. For scanning areas that have heights of greater than 5 to 10µm’s of variation, the SEM would be better suited for the analysis. Another example of a complex three-dimensional surface struc￾ture which shows how the SEM and AFM can complement each other can be seen in Figure 8b. The convoluted three dimensional Y2 O3 oxide crystal shown growing out of a relatively flat Y2 O3 thin film on a Si substrate is easily imaged in the SEM (Figure 8b). Although the AFM would have probelms imaging the obtuse angels and enclosed areas of this surface, the roughness of the Y2 O3 film can be measured whereas in the SEM image the surface roughness is not evident. There￾fore, the two techniques together give a more complete "picture" of the sample. Composition Both SEM and SPM provide compositional information through a variety of techniques. SEM is the only one of the two techniques which provides elemental analysis, however, both SEM and AFM are associated with techniques which can provide compositional information through analyzing materials and physical properties of the sample. Some of the most common of these methods are described below. SEM Along with the secondary electron emission which is used to form a morphological image of the surface in the SEM, a number of other signals are emitted as a result of the electron beam impinging on the surface, as shown in Figure 9. Each of these signals carries information about the sample which provide clues to its compo￾sition. Two of the most commonly used signals for investigating composi￾tion are x-rays and backscattered electrons. X-ray signals are commonly used to provide elemental analysis by the attach￾ment of an Energy-Dispersive Spectrometer (EDS) or Wave￾length-Dispersive Spectrometer (WDS) to the SEM system. X￾ray emission results from inelastic scattering between the beam electrons and the electrons of the sample atoms. This interaction results in the ejection of an inner shell electron from the atom, Figure 8. (a) SEM image of a non-woven textile sample of polyethylene oxide fibers. The large depth of field of the SEM makes it possible to image fibers which are 10’s of µm’s below the upper layer of fibers. Bar=10µm; (b) SEM image of Y2 O3 crystal. Bar=1µm. (a) (b)