Sheet-like Fig. 5. Schematic pictures of typical shaped domains Des of domains the e ted mesophase pitch-based graphitized fiber with transverse section. In the SEM photograph, the ribbon shaped fibril was not observed anymore, bi fibers showed circular cross-sectional shapes all fibrils appeared to be composed of round sha with no open wedges in the OM photograph. Blue stacked along the tiber axis. Particularly, such disks achromatic regions were located in I and Ill regions are defined as the pleat shaped units as observed in hich were 90 different from those of F-A and F-b the fibril of liquid crystal polymers [19 fibers, indicating a radial orientation in the fiber. HR-SEM photographs of the longitudinal sections Complete symmetry of blue and yellow regions indi- obviously showed very definitely developed plea cated that such an orientation developed in the whole shaped units, indicating such units as a unique and core area carried domains of radial orientation, in Fig. 7. The length of the pleat shaped unit wa whcrcas only the outcr of 2-3 um thick showed an conjectured from 20 to 40 nm [20]. Such a pleat onion type orientation. HR-SEM photographs more shaped unit also appeared in the surface of the clearly showed size, shapes and micro-domains of the mesophase pitch-based graphitized fiber. Figure 8 domain.In a HR-SEM photograph of small magnifi- shows the STM images of mesophase pitch-based cation, the area 2-3 um thick from the surface clearly carbon fibers graphitized at 2000 C. In a lower showed the onion type domain alignments, whereas domains of the radial orientation dominated in the magnified imagc, cach fibril appcarcd as a rod of core area. HR-SEM confirmed such features. In the stacked coins. The size of such stacking layers was ore area, most domains had a loop or bent shape, conjectured as around 20 the higher magnified being aligned in an approximately radial orientation STM image. Such units are also found in the photo- The thickness and length of domains appeared under graph in the literature [21] 100 nm and above 200 nm, respectively. In the middle Figure 6(c) and (d) shows TEM photographs of area,domains showed more loop shapes than in the BF and DF images along the fiber axis. BF and DF ore area, being weakly oriented in a radial manner. images of low magnification also showed well devel The length and thickness were almost same in the oped fibrils along the fiber axis, and a discontinuity core areas. In the outer area. domains of multi-folded of each fibril, which might reflect defects induced by shape were basically oriented in onion-like stacking cutting. In the BF image of high magnification, the equence. There were no linear shaped domains in cluster units (see black arrows)which formed the the outer part. The length of domains was found micro-domains (see white arrows)were well defined above 400 nm rather uniformly. as illustrated in Fig 9. Micro-domains which were arranged in the same direction along the fiber axis 3.2 The longitudinal sections of mesophase pitch- formed the fibrils. The thickness of the fibrils was based graphitized fiber assessed above 100 nm. From close examination. each Figures 6(a)and(b)showed OM, SEM photo- micro-domain and cluster unit showed a smooth graphs of longitudinal sections in F-A fiber. In the wave along the fiber axis, Fig. 10. No pleat-shaped OM photograph, ribbon-like belt-fibrils with lengths unit was identified in the TEM images of our observa-950 I. MOCHIDA et al. 8. Direction of shrinkage Sheet-like Bent Looped Fig. 5. Schematic pictures of typical shaped domains. 3.1.4 Fiber with quasi-onion transverse tex￾ture Figure 1 (d) showed OM, SEM and HR-SEM photographs of transverse sections in the naphthalene derived mesophase pitch-based graphitized fiber with the quasi onion texture (F-D). All fibers showed circular cross-sectional shapes with no open wedges in the OM photograph. Blue isochromatic regions were located in I and III regions which were 90” different from those of F-A and F-B fibers, indicating a radial orientation in the fiber. Complete symmetry of blue and yellow regions indi￾cated that such an orientation developed in the whole area. A SEM photograph of F-D showed that the core area carried domains of radial orientation, whereas only the outer of 2-3 ltrn thick showed an onion type orientation. HR-SEM photographs more clearly showed size, shapes and micro-domains of the domain. In a HR-SEM photograph of small magnifi￾cation, the area 2-3 pm thick from the surface clearly showed the onion type domain alignments, whereas domains of the radial orientation dominated in the core area. HR-SEM confirmed such features. In the core area, most domains had a loop or bent shape, being aligned in an approximately radial orientation. The thickness and length of domains appeared under 100 nm and above 200 nm, respectively. In the middle area, domains showed more loop shapes than in the core area, being weakly oriented in a radial manner. The length and thickness were almost same in the core areas. In the outer area, domains of multi-folded shape were basically oriented in onion-like stacking sequence. There were no linear shaped domains in the outer part. The length of domains was found above 400 nm rather uniformly. 3.2 The longitudinal sections of mesophase pitch￾based graphitized$bers Figures 6(a) and (b) showed OM, SEM photo￾graphs of longitudinal sections in F-A fiber. In the OM photograph, ribbon-like belt-fibrils with lengths over 30 pm were observed as often reported [ 181. The width of each fibril was variable, reflecting the variable cross-sectional shapes of domains in the transverse section. In the SEM photograph, the ribbon shaped fibril was not observed anymore, but all fibrils appeared to be composed of round shapes stacked along the fiber axis. Particularly, such disks are defined as the pleat shaped units as observed in the fibril of liquid crystal polymers [ 191. HR-SEM photographs of the longitudinal sections obviously showed very definitely developed pleat shaped units, indicating such units as a unique and universal structure which formed each fibril as shown in Fig. 7. The length of the pleat shaped unit was conjectured from 20 to 40 nm [20]. Such a pleat shaped unit also appeared in the surface of the mesophase pitch-based graphitized fiber. Figure 8 shows the STM images of mesophase pitch-based carbon fibers graphitized at 2000°C. In a lower magnified image, each fibril appeared as a rod of stacked coins. The size of such stacking layers was conjectured as around 20 nm in the higher magnified STM image. Such units are also found in the photo￾graph in the literature [21]. Figure 6(c) and (d) shows TEM photographs of BF and DF images along the fiber axis. BF and DF images of low magnification also showed well devel￾oped fibrils along the fiber axis, and a discontinuity of each fibril, which might reflect defects induced by cutting. In the BF image of high magnification, the cluster units (see black arrows) which formed the micro-domains (see white arrows) were well defined, as illustrated in Fig. 9. Micro-domains which were arranged in the same direction along the fiber axis formed the fibrils. The thickness of the fibrils was assessed above 100 nm. From close examination, each micro-domain and cluster unit showed a smooth wave along the fiber axis, Fig. 10. No pleat-shaped unit was identified in the TEM images of our observa-