Optical Techniques and Experimental Investigation of Diffusion Processes in Disordered Media
Different diffusion processes in disordered media will be investigated using optical methods and interpreted in the light of new theoretical approaches based on fractals:
We will investigate heat diffusion processes in disordered materials by heating the surface of the sample with a pulsed laser and by determining the time dependence of the surface temperature. Much care will be taken to describe the properties of the surface temperature when this surface is either tortuous or fractal. New theoretical results will be given.
In the case of naphthalene D8 crystal doped with naphthalene H8, two triplet excitations which meet together fuse in a singlet state which instantaneously luminesces. Time resolved spectroscopy will allow us to determine the time dependence of the rate of fusion. The results will be interpreted in the light of the percolation theory inside and outside the critical region.
Time resolved spectroscopy and transient grating experiments will be used to investigate the geometry of the pore space of a porous material which is called vycor. We will discuss the efficiency fo each of these two methods to determine the tortuosity of the pore space.
Determination of the state density of an amorphous semiconductor will be performed by a photothermal detection of absorption. This technique is more sensitive than classical ones when absorption is small. It is then peculiarly efficient in the case of the state density in the forbidden gap.
KeywordsFractal Dimension Malachite Green Heat Diffusion Percolation Model Energy Migration
Unable to display preview. Download preview PDF.
- 1.H.S. Carlsraw, and J.C. Jaeger, “Conductor of heat in solids”, Oxford Clarendon (1959)Google Scholar
- 4.B. Mandelbrot, “The fractal geometry of nature”, Freeman, New York (1983) and “Les objets fractals”, Flammarion, Paris (1975)Google Scholar
- 6.R. Rammal, G. Toulouse, J. de Physique (Paris) Lettres, 44, L-13 (1983)Google Scholar
- 7.R. Pynn, and A. Skjeltorp, “Scaling phenomena in disordered systems”, edit. NATO, ASI series Plenum (1985)Google Scholar
- 8.H.E. Stanley, and N. Ostrowsky, “On growth and form” edit. NATO ASI series, Nijhoff Amsterdam (1985)Google Scholar
- 9.R. Zallen, “The Physics of amorphous materials”, John Wiley (1983)Google Scholar
- 10.S. Alexander, and R. Orbach, J. de Physique (Paris) Lettres, 43, L-625 (1982)Google Scholar
- 32.P.G. de Gennes, C.R. Acad. Sc. Ser. B 296, 881 (1983)Google Scholar
- 35.K. Kadukora, Ph.D. Dissertation, University of California, Los Angeles (1983)Google Scholar
- C.L. Yang, P. Evesque, J. Duran, and A. Bourdon, J. Phys. (Paris) C7, 45 (1985)Google Scholar
- 42.A. Rosencwaig, “Photoacoustic and photothermal spectroscopy”, John Wiley and Son, New York (1980)Google Scholar
- 44.W.B. Jackson, N.M. Amer, A.C. Boccara, and D. Fournier, 20, 1333 (1981)Google Scholar
- 46.M.L. Theye, A. Georghia, K. Driss-Khodja, and A.C. Boccara, “11th Conf. on Amorphous and Liquid Semiconductors”, Rome (1985)Google Scholar
- 47.W. Jackson, N. Amer, D. Fournier and A.C. Boccara, “Technical Digest 2nd Int. topical mentions on photoacoustic spectroscopy” (1981)Google Scholar