Precise fabrication of large areas of ordered nanoscale structures is essential for microelectronic and information technology, the broad scope of top-down processes, including conventional immersion lithography, extreme ultraviolet lithography, and soft lithography have been proposed to meet the demands of devices miniaturization, these endeavors have enabled the lateral dimensions of devices to be readily shrunk below 100 nm [1–3]. However, as the lateral dimension goes smaller and smaller, these ‘top-down’ approaches become extremely difficult and expensive, hence, other methodologies of creating nanostructures are of great interesting if they can offer advantages in reduced production cost, smaller feature sizes, and more complex nanopatterns. Nanofabrication via block copolymer self assembly represents one of the most powerful candidates, and is now taking as the most promising methodology for next-generation lithography [4–6], mainly due to their intrinsic nanoscale dimensions, facile synthesis, and strict control of architecture. Ever since the self assembly of block copolymers was introduced as a powerful ‘bottom-up’ route to well-organized nanostructures decade ago, many efforts have been devoted: as through chemical modification of the block copolymer structure to achieve special functionalities, exploring electric fields, and interfacial interactions to control the orientation, and utilizing solvent induced ordering, salt complexes, and shear fields to achieve ordered arrays [7–10]. Among which solvent annealing is of particularly beneficial mainly due to their mild process condition and no need for additional complicated apparatus, and now it has turn out to be a very simple while robust approach to generate almost defect-free microphase separation structures in BCP thin films [11–13]. Even more, it appears to be the single possible way for thermal lible systems such supramolecular block copolymers based on noncovalently bonding. Further research revealed the use of a co-solvent atmosphere, will enables one to enhancing the ordering process ever further [14, 15]. However, a critical drawback of solvent annealing is that BCP thin film often de-wets its substrate during solvent exposure as have been already pointed out by several researchers [16–19]. This makes it is very difficult to obtain uniform and ordered BCP thin film over a macroscopic area without the direction of additional external fields. In many cases, realizing the vast technological potential of block copolymers requires both the precise controlling of the orientation and long-range ordering, however, weakness still remains, so far, only few works have reported to achieve highly ordered thin film nanotemplates, and the control of well-organized structures over large scale is still a challenging topic.
In recent decade, Ikkala and ten Brinke have thoroughly demonstrated that well-ordered nanostructures in the bulk may be fabricated through supramolecular assemblies (SMA) of low molecular amphiphiles and block copolymers [20, 21]. The amphiphiles can be physically bonded to homopolymers and block copolymers using noncovalent interactions, this complexation can lead to the formation of supramolcecular block copolymer which can further assembled into hierarchy nanostructures with various responsive properties. More recently, we have demonstrated that ordered nanoporous thin film can be fabricated from a similar approach based on the supramolecular assemblies of block copolymers PS-PVP and small molecule (2,4-Hydroxybenzeneazo benzoic acid, HABA) [22–26], the SMA thin films demonstrated hexagonal cylindrical morphology with PS form the matrix. Solvent annealing in dioxane can enhance the ordering of thin films microphase separation, following extraction of HABA with selective solvent methanol results in a nanoporous thin films. The channels can be filled with metal, for example, nickel, by electrochemical deposition to fabricate an array of ordered metal nanodots or nanowires with some defects appear in the array due to the nonuniform electrodeposition kinetics of the metal clusters in nanochannels .
In this article, we further investigate the PS-PVP/HABA supramolecular assembly system in order to achieve a highly ordered morphology and to explore a high definition nanotemplate replication method for fabrication of highly ordered polymeric nanodots and nanowire arrays. We will demonstrate that under a mixture solvent annealing atmosphere (with the dedicating choosing of an additional nitromethane as a selective solvent for the minor component), a near-defect-free nanoporous thin films with long-range ordering over a large areas can be achieved. Taking aim at high definition nanotemplate transfer technique which is another daunting obstacle to the application of the nanoporous template, we will further show that under the direction of the capillary action and hydrogen bonding, this ordered nanoporous template can be perfectly transferred, and thus achieved a methodology for the preparation of highly ordered sub-30 nm polymeric nanodot and nanowire arrays.