Photochemically Grafted Polystyrene Layer Assisting Selective Au Electrodeposition

Abstract

We describe the selective electrodeposition of submicrometer gold (Au) patterns achieved by a thin film resist layer of polystyrene (PS) that was exposed to ultraviolet (UV) light on a photoreactive monolayer of a benzophenone-containing alkylthiol formed on a Au-plated substrate and patterned by thermal nanoimprint lithography. The presence of a PS graft layer caused by the benzophenone monolayer photochemistry at an interface between the PS resist layer and photoreactive monolayer played the important role of suppressing the unfavorable growth of tiny Au grains in regions masked with the PS resist layer, resulting in the selective Au electrodeposition in aperture regions of PS resist patterns. The suppressive effect on selective Au electrodeposition depended on the molecular weight of PS used as a resist material. Among unimodal PSs having weight-average molecular weights (M(w)'s) of 2100, 10,900, and 106,000 g mol(-1), the PS of M(w) = 10,900 g mol(-1) functioned most effectively as the resist layer. Au electrodeposition at a low current density allowed the preparation of Au lines having widths of submicrometers and a uniform height independent of line widths in resist aperture regions. Submicrometer bump structures of Au lines could be fabricated on transparent silica substrates by the subsequent wet etching of a Au electrode layer and then a chromium adhesive layer.

Reactive-monolayer-assisted Thermal Nanoimprint Lithography

“…Electrodeposited Au grew only at aperture regions without PS resist masks, and the growth of Au grains at masked regions were hardly observed. In contrast, a lot of Au grains with sizes of several tens of nanometers grew in the case of PS resist mask formed on a bare Au surface [14] and on an unexposed PrM-modified Au surface [24]. It is worthy to note that the presence of a PS graft layer formed by a benzopehnone-containing PrM upon exposure to UV light suppresses undesired growth of Au grains at regions masked with PS resist layers.…”

“…This is because wet etching occurs in an isotropic manner. We investigated R-TNIL involving Au electrodeposition and subsequent etching for the fabrication of Au patterns applicable to optical devices [24].…”

“…The suppressive effect on the growth of tiny Au grains was dependent on a molecular weight of monodisperse PS used as resist materials. The detail will be published [24].…”

“…9(b). We demonstrated that Au line bump structures could be fabricated by R-TNIL involving Au electrodeposition and subsequent wet etching of Au and Cr layers used as an electrode [24].…”

Conducting polymer–gold co-patterned surfaces via nanosphere lithography

“…In the case of the conjugated polymer and substrate, significant differences in conductivity might enable the patterned polycarbazole film to act as a resist and re-direct further electrodeposition of Au to more electrochemically accessible surfaces. Similar studies have used ultraviolet photolithographic techniques to create patterns composed of either self-assembled monolayers or polymers acting as electrochemical shields for metal deposition [36,37]. Employing the poly(G 1 cbz-TEG) inverse opal film as the working electrode, Au was electrodeposited on the macropores of the inverse honeycomb structure by electrochemical reduction of Au 3+ .…”