Comparison of Metal Adhesion Layers for Au Films in Thermoplasmonic Applications

Abstract

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.

Combining Sub-nanometer Adhesion and Capping Layers for Thermally Stable Nanometer-Thick Au Films

“…In Figure 3, the normalized degradation curves for 0.5 nm Ti/50 nm Au films with varying thickness of the Al capping layer are shown. The capping layers follow a trend similar to that of the adhesion layers studied previously 21 in that thinner layers result in an increase in the dewetting resistance, with 0.5 nm being the optimal thickness. The falloff in stability for the 5 nm capping layer is extreme.…”

“…We have recently shown that there is little difference between these two adhesion layers at this thickness. 21 Quartz substrates were cleaned by means of sonication in acetone and then isopropanol, followed by a short plasma clean in oxygen before deposition. Samples were fabricated using a SHAMROCK 19608 DC sputtering system, which has a base pressure of 5 × 10 −7 Torr.…”

Gold surface cleaning by etching polishing: Optimization of polycrystalline film topography and surface functionality for biosensing

“…However, heat treatment does not exclude subsequent contamination by strongly binding molecules and is hence not ideal where high purity or biochemical modification is required. In contrast, chemical cleaning such as electrochemical polishing [37][38][39] and dissolution of contamination by common solvents and detergents suffer from the risk of damaging the adhesive chromium layer [40,41]. The widely spread use of hydrogen peroxide (so-called Piranha solution made of a 3:1 v/v mixture of hydrogen peroxide and sulfuric acid) can remove nearly all organics [42], but often leads to extensive and uncontrolled etching of the surface [43].…”

Pseudoequilibrium between Etching and Selective Grain Growth: Chemical Conversion of a Randomly Oriented Au Film into a (111)-Oriented Ultrathin Au Film

“…X-ray diffraction (XRD) (Figure e) and electron backscatter diffraction (EBSD) (Figure f,g) exhibit a change in the crystallographic orientation of the grains by the TOABr treatment. Some grains were delaminated, which resulted from the weak adhesion between Au and SiO 2 and also from the continuous growth of the (111) grains in the lateral direction, which caused mechanical strain in the Au film. , The Au thin film was flattened by gentle pressing for EBSD analysis. The black regions in Figure f,g were caused by grain detachment during the gentle pressing.…”

“…Some grains were delaminated, which resulted from the weak adhesion between Au and SiO 2 and also from the continuous growth of the (111) grains in the lateral direction, which caused mechanical strain in the Au film. 35,36 The Au thin film was flattened by gentle pressing for EBSD analysis. The black regions in Figure 1f,g were caused by grain detachment during the gentle pressing.…”