Application of image processing techniques for analysis of nano- and micro-spaces in carbon materials K. Oshida a,* , T. Nakazawa a , T. Miyazaki a , M. Endo b a Nagano National College of Technology, 716 Tokuma, Nagano 381-8550, Japan b Faculty of Engineering, Shinshyu University, Nagano 380-8553, Japan Received 7 May 2001; received in revised form 2 June 2001; accepted 9 July 2001 Abstract Transmission electron microscopy TEM) is one of the most useful methods to clarify the structure in carbon materials. We developed quantitative analysis methods for the texture and structure of carbon materials containing the micro- and nano-spaces by using electron microscopy combined with image processing technique. The relations between phase transfer functions and TEM images of amorphous carbon ®lms which consist of random arrangement of carbon layers were investigated using image processing. The similar patterns as the laser diffraction are obtained by the two-dimensional 2D) fast Fourier transform FFT) of the digitized TEM images. The details of frequencydistributioncanbeanalyzedbyintegrationaroundthecentralpointofthepowerspectrumimages.Weappliedthisnewtechnique to the study of microtexture and structure of graphite intercalation compounds GICs). As a result of application of the frequency analysis using2DFFTtotheCuCl 2 -GIC,acharacteristicpowerspectrumpatterncalledstreak,whichwassimilartotheelectrondiffractionpattern, was obtained. The images corresponding to the speci®c frequencies were reconstructed by 2D inverse FFT IFFT). The stage structure of CuCl 2 -GICs was discussed by using this technique. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Amorphous carbon ®lms; Graphite intercalation compounds; Transmission electron microscopy; Image analysis; Fast Fourier transform 1. Introduction Many kinds of carbon-based materials have been con- tributing to develop the current engineering technology, which have been reinforced by analysis techniques of their structures.X-raydiffraction,variousspectroscopyandtrans- port measurements have been widely used as quantitative techniques for analyzing carbon-based materials [1]. How- ever,itisdif®culttoattainresultswithatomicresolution.On theotherhand,wholeandpartialimagesofmaterialscanbe observed by means of transmission electron microscopy TEM), though it is not quantitative by itself. In this study, we tried to analyze microtexture and struc- ture of carbon materials, using TEM combined with image analysis. Contrast in TEM image mainly consists of two elements, extinction contrast and phase difference one. In highresolutionregion,thephasedifferencecontrastismore effective. Therefore, arbitrary magni®cation image is obtained by modulating acceleration voltage and defocus value Df onrealhighresolutionTEMobservation.Wereport here the investigation of TEM image of amorphous carbon ®lm, which does not have any particular oriented structure, under the different conditions of Df. The results of char- acterization of the materials structure by using image ana- lysis of the TEM image are also reported. Anewapproachtothestudyofmicrotextureandstructure of acceptor-type graphite intercalation compounds GICs) with CuCl 2 was shown using the technique of high resolu- tion TEM combined with image analysis. We used a two- dimensional 2D) fast Fourier transform FFT) for our frequencyanalysis.Fromtheanalysisofthepowerspectrum obtained by the 2D FFT, we extracted some speci®c fre- quencies. The power spectrum was then analyzed by 2D inverse FFT IFFT), and real space image associated with the speci®c frequencies was reproduced. The relationship between the electron diffraction streak patterns and the microstructure of the GICs was further analyzed. 2. Relation between phase transfer function and TEM image of amorphous carbon films 2.1. Experimental We surveyed quantitative analysis method for random structure by using amorphous carbon ®lm. Amorphous Synthetic Metals 125 2002) 223±230 * Correspondingauthor.Tel.: 81-26-295-7092; fax: 81-26-295-4950. E-mail address: oshida@ei.nagano-nct.ac.jp K. Oshida). 0379-6779/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0379-677901)00535-5