Specific Process Knowledge/Thin film deposition/Deposition of Gold/Adhesion layers: Difference between revisions

The samples with the adhesion layers and 20 nm Au layer were also analyzed. The addition of the adhesion layer had in both cases a profound impact on grain size and orientation of the Au film, as visible in Fig. 7a and 7c. The image shows small grains mainly oriented in the [111] crystal direction, with an average grain size of 40 nm for Ti (Fig. 7b) and 36 nm for Cr (Fig. 7d). During the collection of the TKD maps, only the Kikuchi patterns produced by the electron scattering from the Au layer were recorded and indexed. Cr and Ti layers did not contribute to the pattern formation due to two main reasons: i) they are too thin to produce enough scattered electrons and ii) they are

The smaller grain size is attributed to an enhanced wetting of the deposited Au promoted by the adhesion layer. The enhanced wetting behaviour increases the number of nucleation sites compared to the pure Au film case, where Au is evaporated directly onto the SiO2 surface. This eventually leads to a much denser nucleation of the Au grains, which at the

same time facilitates the inter-diffusion of Au atoms. The enhanced wetting might be due to the formation of Ti-Au and Cr-Au bonds. The very dominant [111] crystal orientation observed implies a decrease of the energy barrier for the formation of the energetically most favourable Au crystal structure. This is promoted by the denser nucleation and stronger inter-diffusion of Au atoms described above. In contrast to the pure Au case, all the grains have the same diffusion rate of the (111) exposed planes, and therefore the grains grow with a narrow grain size distribution. Since the film has been deposited at room temperature, the system did not have enough energy to overcome the energy barrier for grain coalescence, hence resulting in grains with a small average size. For the Cr case, also small grains with [100] and [110] crystal orientations were detected. This might suggest that for Au on Cr the [111] orientation is energetically less favored with respect to the [100] and [110] orientations compared to the Ti/Au case.