| Fabrication of ordered semiconductive, optical or magnetic metal and metal oxide nanostructure arrays has attracted great attention due to the potential applications of these unique materials in photocatalytic, photoelectronic, sensors, solar cells, nanogenerator and data storage devices. The properties and applications of these unique nanomaterials are influenced by their components, shape, size and interfacial spacing. Therefore, development of general approaches for fabricating ordered nanostructure arrays with controlled shape, size and position is very important. Recently, some methods for the fabrication of nanostructure arrays have been developed. But most of them have inherent limitation in achieving sub-30 nm features and sub-100 nm interfeature spacing, and they are also time-consuming, complicated and expensive, which restrict their applications in large-scale production of high density and ordered nanostructure arrays. Block copolymer lithography has recently received considerable attention due to the advantages of self-assembly to provide arrays of periodic patterns of 5～50 nm length scales with a simple process, low cost and easy scale-up.In this study, we demonstrate series of novel and flexible approaches for fabricating ordered nanostructure arrays via block copolymer lithography. Firstly, self-assembly of PS-b-P4VP block copolymer on silicon substrate was studied. The results were that PS-b-P4VP cylindrical thin films with ordered P4VP nanodomains surrounded by PS matrix were obtained when the concentration of PS-b-P4VP chloroform solution between 0.2 wt% and 0.6 wt%. Moreover, it was found that the size and center-to-center distance of P4VP nanodomains can be adjusted by adding homopolymer. When adding PS homopolyer, the size of the cylindrical nanodomains and the center-to-center distance of the nanodomains decreased, but the density of the nanodomains increased with the amounts of PS homopolymer increasing. However, When the PS homopolymer content was above 60 wt%, the ordered pattern of the thin film was disturbed.Ordered PS-b-P4VP nanoporous film can be obtained by immering PS-b-P4VP cylindrical thin film in HF solution due to the selective protonation of the pyridyl groups of P4VP blocks with HF, and the best concentration of HF solution is 0.5 wt% with 40 min and methanol as solvent. Additionally, the adsorption of metal nanoparticle, such as Ag, on PS-b-P4VP cylindrical thin film was studied because the pyridyl groups of P4VP blocks not only have incorporation with metal nanoparticles but also have responsive to pH. It was found that pH has serious influence on the adsorption of Ag nanoparticles on PS-b-P4VP cylindrical thin film. When the pH of the solutin was about 5～6, Ag nanoparticles can be adsorbed uniformly on PS-b-P4VP cylindrical thin film.PS-b-P4VP diblock copolymers have two blocks with different solubility for the same solvent. When a good solvent for P4VP blocks but non-solvent for PS blocks, such as methanol, is chosen as the reactant solvents, the patterned P4VP nanocores in the PS-b-P4VP thin film can be used as nanoreactors to in-situ synthesize different nanoparticle arrays with different reactions, and then in-situ transferred to silicon substrate by a two-step calcination method. The ordered Au nanoparticle or nanocluster arrays were obtained by reducing HAuCl4 with sodium citrate dihydrate, and the number of the nanoparticles formed in each P4VP nanocore can also be adjusted by addition of PS homopolymer to PS-b-P4VP diblock copolymer. When the homopolystyrene content increased to 40 wt%, single Au nanoparticle was observed in each P4VP nanocore. Based on the same principle, ordered ZnO and FexOy nanoparticle arrays were also synthesized with thermal decomposition and double decomposition reactions, respectively. In principle, this approach can be a general and versatile approach for fabricating functional nanoparticle arrays.When the PS-b-P4VP cylindrical thin film was exposed into the vapor of methanol at 40℃, the P4VP core swells by absorbing methanol vapor, which is a good solvent for P4VP. However, the PS matrix is unaffected because methanol is a non-solvent for PS. With the absorbed methanol in the core evaporating, the P4VP molecules shrink, pulling the P4VP molecules towards the interfacial region of PS and P4VP, resulting in the formation of nanopores. Combining the novel technology of reconstruction of patterned block copolymer thin film with salt precipitation reaction, ordered nanoring arrays of metals, metal oxides, and other inorganic materials with diameter of sub-50 nm and center-to-center distance of nanorings below100 nm were in-situ fabricated, such as ZnO, TiO2, Fe2O3, Au, etc. And the formation mechanism was further studied.Different kinds of ordered polymeric nanostructure arrays were obtained via selective and sequential re-assembly of cylindrical block copolymer thin film. When the PS-b-P4VP cylindrical thin film is exposed to toluene vapor （a good solvent for PS block, but non-solvent for P4VP.）, PS blocks shrink, pulling the PS molecules towards the P4VP nanodomains and resulting in the formation of polymeric nanoislands of PS-b-P4VP. After that, the polymeric nanoisland array is exposed to methanol vapor. Based on the same principle, the P4VP blocks in the nanodomain move to the interfacial region of PS and P4VP, resulting in the formation of ordered polymeric nanoring array. Moreover, the size and distance of polymeric nanorings can be adjusted by adding homopolymer. It was found that the average center-to-center distance of the PS-b-P4VP polymeric nanorings was found to be 103±3 nm, and on average, the inner and outer diameters of the nanorings were around 22±2 nm and 58±3 nm, respectively. When 20 % P4VP was added, the average center-to-center distance of the polymeric nanorings was about 115 ? 4 nm with the average inner and outer diameters of 39 ? 3 nm and 73 ? 4 nm, respectively. When 20 % PS was added, the average center- to-center distance of the polymeric nanorings was about 86? 3 nm, and the average inner and outer diameters were about 19 nm and 54 nm, respectively. Besides, metal or other inorganic nanoparticles that were randomly pre-loaded inside or on the PS-b-P4VP thin film can be pulled to the rim of PS and P4VP along the movements of PS and P4VP blocks respectively via the novel method of selective and sequential re-assembly of cylindrical block copolymer thin film. As a result, ordered sub-50 nm inorganic/polymeric composite nanoring arrays were fabricated for the first time. |
