Surface Enhanced Raman Scattering Spectroscopy On Diamond-based Substrates

Surface-enhanced Raman scattering?SERS?is an important spectral analysis technology,which can be used to identify chemistry,biology and other components,and the detection limit has reached the level of single molecule.SERS substrates general use noble and transition metals.In recent years,the materials expanded to semiconductor?TiO₂,ZnO,Si,graphene?,which is called semiconductor SERS substrate.The advantages of semiconductor substrates are?I?spectral uniformity,?ii?energy level adjustable,etc.But there are also disadvantages,such as poor enhancement effect.New type of semiconductor SERS substrate needs further research.Wide bandgap semiconductor diamond has the advantages of high chemical stability,semiconductor doping,surface functionalization,single Raman peak and biological compatibility.In this paper,microwave plasma chemical vapor deposition?MPCVD?method was used to grow boron-doped diamond?BDD?,which was used as SERS substrate.We have proved that diamond broadened the selection range of SERS substrate materials.It also has high enhancement factor,reproducibly,recycling and stability.In addition,Au thin films and nanoparticles were deposited on BDD which used as SERS substrates,and the enhanced mechanism attribute to electromagnetic enhancement.The main research of this paper are as follows:?1?Using BDD semiconductor as SERS substrate.Methylene blue?MB?was used as the probe molecule to obtain the enhancement factor of 10⁵,and the detection limit reached 10^-7M.The enhancement factor is three to four times orders of magnitude higher than other single element semiconductors?silicon,germanium,and graphene?.The mechanism of semiconductor enhancement is studied in detail.By comparing the hydrogen terminated boron-doped diamond and oxygen terminated boron-doped diamond boron-doped,three different wavelength lasers of 514nm,633nm and 785nm were selected to SERS test for a variety of probe molecules.It was observed that when the laser energy,substrate and probe molecule energy matched,and the charge transfer could occur,SERS phenomenon was generated;When the energy of substrate and probe molecules did not match and no charge transfer occurred,there was no obvious SERS phenomenon.The mechanism of BDD enhancement can be attributed to the chemical enhancement.The charge transfer between the substrate and the probe molecule enhances the polarizability of the probe molecule,leading to the enhancement of Raman signal.Diamonds as SERS substrates,has the advantages of stability,uniformity and cycling.?2?Using Au film/BDD and nanostructure Au/BDD composite structure as the substrate,using R6G as the probe molecule and 633nm wavelength laser excitation to test the SERS.The results of Au film/BDD SERS substrate different spraying time?10s,20 and 40s?has been discussed,the best Au sprayed time is 20s.Then different spray time of Au film/BDD under800^oC in air annealing 2 min,and got nanostructure Au/BDD substrate,the detection limit of R6G probe molecule reached to 10^-9M.The substrate enhanced mechanism was derived from electromagnetic field enhancement.FDTD software was used to calculate the electromagnetic field distribution of gold particles with different sizes,which proved that the electromagnetic field enhanced the SERS response.In this paper,boron-doped polycrystalline diamond and metal/semiconductor BDD were used to prepare SERS substrate with excellent properties.New ideas and methods were provided for exploring high performance SERS.