If thermoplasmonic applications such
as heat-assisted magnetic recording are to be commercially viable,
it is necessary to optimize both thermal stability and plasmonic performance
of the devices involved. In this work, a variety of different adhesion
layers were investigated for their ability to reduce dewetting of
sputtered 50 nm Au films on SiO2 substrates. Traditional
adhesion layer metals Ti and Cr were compared with alternative materials
of Al, Ta, and W. Film dewetting was shown to increase when the adhesion
material diffuses through the Au layer. An adhesion layer thickness
of 0.5 nm resulted in superior thermomechanical stability for all
adhesion metals, with an enhancement factor of up to 200× over
5 nm thick analogues. The metals were ranked by their effectiveness
in inhibiting dewetting, starting with the most effective, in the
order Ta > Ti > W > Cr > Al. Finally, the Au surface-plasmon
polariton response was compared for each adhesion layer, and it was
found that 0.5 nm adhesion layers produced the best response, with
W being the optimal adhesion layer material for plasmonic performance.
SUPPORTING DATAAtomic force microscopy (AFM) was used to characterize the surface topography of the annealed samples of Ta, Ti and W/Au (50nm), and the results are shown in Figure S1. The route mean square roughness values (Ra) for the surface of the samples with 0.5nm adhesion layer are quite similar. The samples with 5nm adhesion layers tend to be rougher, with Ti exhibiting the highest Ra value and W the lowest. This relates to the extent of the diffusion of adhesion metals through the Au films upon annealing, and correlates with other observations (TEM, XPS).
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