Influence of Ti and Cr Adhesion Layers on Ultrathin Au Films

Abstract

Efficient adhesion of gold thin films on dielectric or semiconductor substrates is essential in applications and research within plasmonics, metamaterials, 2D materials, and nanoelectronics. As a consequence of the relentless downscaling in nanoscience and technology, the thicknesses of adhesion layer and overlayer have reached tens of nanometers, and it is unclear if our current understanding is sufficient. In this report, we investigated how Cr and Ti adhesion layers influence the nanostructure of 2-20 nm thin Au films by means of high-resolution electron microscopy, complemented with atomic force microscopy and X-ray photoelectron spectroscopy. Pure Au films were compared to Ti/Au and Cr/Au bilayer systems. Both Ti and Cr had a striking impact on grain size and crystal orientation of the Au overlayer, which we interpret as the adhesion layer-enhanced wetting of Au and the formation of chemical bonds between the layers. Ti formed a uniform layer under the Au overlayer. Cr interdiffused with the Au layer forming a Cr-Au alloy. The crystal orientation of the Au layers was mainly [111] for all thin-film systems. The results showed that both adhesion layers were partially oxidized, and oxidation sources were scrutinized and found. A difference in bilayer electrical resistivity between Ti/Au and Cr/Au systems was measured and compared. On the basis of these results, a revised and more detailed adhesion layer model for both Ti/Au and Cr/Au systems was proposed. Finally, the implications of the results were analyzed, and recommendations for the selection of adhesion layers for nano-optics and nanoelectronics applications are presented.

Ultrathin and Ultrasmooth Gold Films on Monolayer MoS2

“…To reduce the percolation threshold of ultrathin gold films, adhesion or seed layers of Ti, Cr, Ni, Pt, or Ge are commonly used. However, these adhesion layers significantly affect the optical and electrical properties of ultrathin metal nanostructures . Recently, the organosilane‐based adhesion layers (mercaptosilanes and aminosilanes) were used for the deposition of sub‐10 nm thick continuous Au films on silicon and glass surfaces .…”

“…Recently, the organosilane‐based adhesion layers (mercaptosilanes and aminosilanes) were used for the deposition of sub‐10 nm thick continuous Au films on silicon and glass surfaces . However, organosilanes are not compatible with nonoxidized silicon surfaces and poorly compatible with standard lift‐off procedures, that imposes severe limitations to their use as adhesion layers . Adhesion layers based on organosilanes are also inefficient for the deposition of atomically thin metal films and does not move us closer to the deposition of 2D layers from bulk plasmonic metals.…”

Broadband Magnetic Composite Energy Harvester

“…DC sputtering in argon ambient was used to deposit a 20 nm thick titanium adhesion layer . Subsequently, a 120 nm thick layer of platinum was deposited without breaking the vacuum.…”

Plasmonic-Active Nanostructured Thin Films

“…More importantly, removing 10 nm thick titanium adhesion layer from nanohole array by etching drastically decreases the optical resonance bandwidths. Another study has found that Cr can interdiffuse more with Au to form Cr-Au alloy than Ti, suggesting Ti is the optimal adhesion layer for Au-based PANTFs [33]. The adhesion layer has been engineered to minimize the plasmonic damping by depositing less than 1 nm adhesive, which prevents the layer to overlap with the hotspots of PANTFs [34]; however, thinner layer of adhesive also means low stability of PANTFs.…”