Experimental investigation of change in sheet resistance and Debye temperatures in metallic thin films due to low-energy ion beam irradiation

We present a systematic experimental investigation of low-energy (0-1 kV) ion irradiation induced changes in sheet resistivity and Debye temperatures in metallic nano-films of Ag, Cu and Al of thickness d/lambda(o) similar to 2-5, where d is the film thickness and lambda(o) is the bulk mean free path, as a function of ion beam induced defects and impurities in a controlled manner. Ions of both atomic (Ne, Ar and Kr) and molecular (H-2, N-2) gases are employed in the investigation and the number of defects and impurities in the nano-film can be varied in a controlled manner by varying the ionic mass number (1-84) and beam fluence (8.7 x 10(15)-1.4 x 10(16) ions cm(-2)). Low-temperature measurements are carried out for pristine and irradiated films to obtain the residual sheet resistance (R-RS). An empirical formula relating the variation of R-RS with beam fluence and ionic mass number is proposed for the first time. The change in R-RS is due to the large diffusion of the impurities inside the nano-films as confirmed from energy dispersive x-ray spectroscopy. The Debye temperature (Theta(D)) is determined from Bloch-Gruneisen fitting of the temperature variation of sheet resistance data and it is found that Theta(D) decreases with increase in both fluence and ionic mass number arising primarily from the change in bulk modulus of the nano-film.