Research On The Fabrication Of Ag/Cu/Diamond Nanostructures And The Corresponding Surface Enhanced Raman Scattering Factor

Metal nanoarrays,such as Ag nanowire arrays,are widely used in the filed of electrochemical detection,catalysis,optics,microfluidics,and surface enhanced Raman scattering（SERS）.However,it always requires complex experimental processes and equipment for preparing ordered metal nanoarrays.This study investigated the wetting ability of Ag-based alloy in porous anodized aluminum oxide（AAO）,developing a new method for preparing Ag nanoarrays.The reaction mechanism between Ag-based alloy and AAO was analyzed.The Ag/Cu composite nanostructures were achieved by using hydrothermal and reduction methods.The AAO-assisted synthesis of diamond nanoarrays was also studied,obtaining Ag/Cu/diamond composite nanostructures with excellent SERS performance.AgCuTi and Ag-CuO brazing alloys were selected to investigate the reactive wetting in the AAO templates for fabricating Ag nanoarrays.In a vacuum,Ti could react with AAO and promote the infiltration of AgCuTi into the AAO nanopores.After infiltration,the Na OH aqueous solution was used to treat the sample for removing AAO and obtaining nanostructures.However,a large amount of Ti-O compounds was generated on the sample surfaces,leading to undesirable SERE performance.On the other hand,the molten Ag-CuO had a good infiltration in the AAO nanopores at 970℃.As increasing the CuO content,the height of Ag infiltration increased gradually.Adding too much CuO into Ag could result in cracks in AAO templates owing to the violent reaction.When increasing the size of AAO nanopores,the height of Ag infiltration increased obviously.After cooling,the Ag nanowires were embedded in the AAO templates,which can be released by hydrothermal treatment in Na OH solution.The as-obtained Ag nanowire arrays exhibited good mechanical properties and SERS performance with the enhancement factor of（8.9±2.1）×10⁵.After preparing Ag nanowire array by the reactive wetting of Ag-CuO and AAO,the Ag/Cu nanostructures were fabricated by introducing Cu nanostructures and used as SERS substrates.The products of AAO skeleton and Ag-CuO were first studied.After heating at 970℃for 30 min,CuO and AAO skeleton reacted to generate a Cu-Al-O compound with spinel structures.With the increase in CuO content,the atomic proportion of the products was close to Cu Al₂O₄.CuO nanowires were obtained by hydrothermal treatment of the Cu-Al-O skeletons in low concentration Na OH solution.The effects of parameters on the CuO morphology were studied.Cu nanowires with good SERS performance could be achieved by reducing CuO nanowires.After Ag-CuO infiltrates into the AAO template,Ag/Cu composite nanostructures were obtained by hydrothermal treatment and subsequent reduction.Based on the reaction mechanism of Ag-CuO and AAO,rare earth oxide CeO₂ was proposed to enhance the wettability of Ag-CuO.A small amount of CeO₂ could promote the infiltration height of Ag in AAO nanopores.The obtained shows the enhancement factor of（4.8±0.9）×10⁶.With the increase of CeO₂,the Ag infiltration height decreased obviously,because the fluidity of Ag-CuO-CeO₂was affected.The Ag/Cu/diamond composite nanostructures were fabricated as SERS substrates by introducing diamond nanopillars into Ag/Cu nanostructures.The diamond nanostructures were explored as SERS substrates.First,hot filament CVD was used to synthesize diamond films,which could not exhibit acceptable SERS properties due to the wide band gap of pure diamond.The Raman laser could not generate the charge transfer between diamond films and probe molecules.Subsequently,diamond nano-arrays were grown by using AAO as templates.The diffusion of active CVD gas in AAO nanopores was analyzed.As decreasing the AAO thickness,the active gas was easier to pass through the nanopores and reach the substrate surface.The interaction between AAO and the substrates was then discussed.The smooth and thin diamond film was easier for the AAO adhesion and reduced the damage of AAO caused by thermal expansion mismatch.Diamond nanopillars with diameters of 300 nm and 70 nm were prepared using AAO templates with different nanopore sizes.The～300 nm diamond nanopillars had an appropriate amount of sp² carbon doping,indicating a suitable band gap.The charge transfer between probe molecules and substrates can be excited,leading to a good SERS performance.Finally,the composite substrates combining Ag/Cu composite nanostructures with diamond nanopillars exhibited excellent SERS performance with the enhancement factor of（8.1±2.6）×10⁷.