Preparation Of ZnO Nanotower Arrays And Study On Its SERS Performance

Surface-enhanced Raman scattering?SERS?spectroscopy technology has great potential in chemical and biological sensing applications owing to its fast response,high sensitivity,and fingerprint effects.Among a variety of SERS substrate materials,the hybrid noble metal/semiconductors hybrid substrates can produce a higher SERS effect than single noble metal substrates due to the electromagnetic enhancement and the chemical enhancement of the electron transfer resonance between the semiconductor and the noble metal.The Ag/ZnO hybrid SERS substrates have received particular attention due to electron transfer?ET?resonance aroused by the work function difference between ZnO and Ag,and the tunability of the morphology of ZnO and Ag-nanoparticles?Ag-NPs?.Thus,this paper designed and synthesized the Ag-NPs/ZnO nanotower array?AZT?SERS substrate,which exhibited excellent Raman activity.The main contents are as follows:Firstly,the Zn O nanotower arrays were successfully prepared via a chemical bath deposition?CBD?method,and the influence of various factors on the morphology of the nanotower was explored.The concentration of Zn?NH₃?₄²⁺and the direct growth unit Zn?OH?₄^2-in the precursor solution can be adjusted by the amount of ammonia,thereby changing the diameter and apex angle of the nanotower.The dosage of ZnCl₂ and the area of the Si substrates affect the concentration of Zn?OH?₄^2-in the precursor solution and the number of nucleation sites,respectively,and the diameter of the nanotower changes accordingly.The main reason for the nanotower steps are that the Cl^-ions selectively adsorb on the?001?surface of the ZnO nanorods and inhibit the crystal growth rate in the[0001]direction.The anti-reflection performance test of ZnO nanotower arrays prepared with different experimental parameters obtained the most suitable conditions for SERS substrates preparation.Then,a silver colloid composed of cubes and tetrahedral Ag-NPs with an average diameter of about 60 nm was prepared by a solvothermal method,and the colloid was dropped onto the ZnO nanotower array to prepare the AZTsubstrate.Using rhodamine 6G ?R6G?as a probe molecule,the detection limit of the AZT substrate is as low as 1×10^-18M,and the EF is as high as 6.9×10¹³.The repeatability test results of the AZT substrate show that the RSD value of the Raman peak at 611 cm^-1 of R6G is 0.08,which meets the actual test requirements.The AZT substrate exhibits such high Raman activity due to the electromagnetic enhancement and the chemical enhancement between ZnO and Ag-NPs.It is also attributed to:a lot of Ag-NPs loaded on ZnO nanotowers;high hot-spots density and Raman scattering efficiency brought by cubic or tetrahedral Ag-NPs with a average diameter of about 60 nm;Ag-NPs and the molecules can simultaneously retain on the nanosteps of the nanotower,making the molecules access the hot-spots regions;the inclination of the nanotower and the apex nanosteps increase the laser excitation rate of the free electrons on the Ag-NPs surface.