Thermally activated diffusion of indium into layered materials 2H‐TaSe 2 , and TaS 2

We have studied the thermal diffusion of indium in single crystals of the layered compounds 2H‐TaSe 2 , and TaS 2 parallel to the layers. Measurements were done in situ in a scanning electron microscope equipped with an X‐ray energy dispersive system. The distance of the diffusing indium front into the crystal was determined as a function of time from secondary electron image as well as from X‐ray line scans for indium taken at different time intervals. The diffusion coefficients D were found by fitting the data to 〈 r 2 〉 = 2 Dt , where 〈 r 2 〉 is the mean square displacement in time t . The diffusion coefficients thus obtained were 1.5 × 10 –12 , 3.8 × 10 –12 , 7.7 × 10 –12 , and 17.5 × 10 –12 m 2 /s with an uncertainty of about 10 percent at 351, 375, 411, and 458 K respectively for TaSe 2 . The values for TaS 2 were 5.3 × 10 –11 , 9.5 × 10 –11 , 1.7 × 10 –10 , and 3.6 × 10 –10 m 2 /s at 345, 369, 388, and 437 K respectively. The activation energy E 0 of indium diffusion, using D = D 0 e   – E   0 / kT , were determined to be (0.32 ± 0.04) eV, and (0.27 + 0.03) eV for TaSe 2 and TaS 2 respectively. The results show that diffusing indium atoms put severe stress on the layers as they intercalate between them. This stress is relieved by buckling of the layers and these buckling features are clearly visible in secondary electron images. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)