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An obvious blue-shift of the absorption edge in UV-visible absorption spectrum experiments of SiC NWs with length of centimeters and diameters of about 200 nm,which indicates an increase in the band gap of SiC NWs due to the size effect of NWs.From theoretical estimation,only SiC NWs with diameter less than 3nm could exhibit a strong quantum size effect.To our knowledge the higher band gap energy is impossible from defects or weaker doping,the more plausible explanation would seem to be that Nanowires are not single crystal.To confirm the conjecture,HRTEM(High Resolution Transmission Electron Microscopy)images of SiC NWs were studied,shows the SiC NWs was made up of nano-sheets with 3-5nm length which is the reason for the obvious blue-shift of the absorption edge.