Metasurface-based Monolayer Molecular Detection

In recent years,great progresses have been made in the area of metamaterials.With the rapid development of metamaterials in both theory and experiment,more and more studies start to address the device applications of metamaterials.Molecular fingerprint detection is one of these applications,which attracts considerate interest in the community due to its potential value in health,environment and biochemical studies.To address the fabrication difficulty and challenge associated with existing metasurace molecular sensors,we demonstrate two molecular sensors with significantly simplified structure and fabrication in this thesis.The main results of research in this thesis are summarized as following:?1?We proposed a molecular detection mechanism based on the field discontinuity boundary condition between Au and air.A theoretical model using numerical FDTD method is built to simulate the molecular detection properties.Using an analytical approach,expression of the surface field between Au and air is also derived,which suggests that there is a field enhancement of 1.94 at the Au surface for p-polarization at at angles close to grazing incidence.This field enhancement can be used for increasing molecular fingerprint absorptions.?2?A molecular sensor made of an Au film is fabricated,which exhibits monolayer sensitivity for Bovine Serum Albumin?BSA?molecules.Using e-beam evaporation technique and molecular self-assembling process,we fabricated a protein sensor using a180 nm thick Au film on a Si substrate.Infrared spectroscopy measurements show that there are two reflection dips at 1664 cm^-11 and 1546 cm^-1 for p-polarization at 80°angle,whose magnitudes are 1.14%and 0.5%,respectively.These two absorption features correspond to the vibration modes of amide I and amide II in BSA protein molecules.,which are consistent with the simulated results.?3?Based on local surface plasmon resonance,a molecular sensor made of Au disk arrays is also designed.Using a numerical model with HFSS software,we simulated the resonant modes and molecular detection properties of the structure.The results show that two resonances occur at 1533.3cm^-1and 2786.7cm^-1,which are attributed to the fundamental mode and a coupled mode,respectively.Frequency of the coupled mode matches the fingerprint absorption lines of target octadecathiol?ODT?molecules,and thus it is suitable for molecule detection purpose.?4?An Au disk array sensor is fabricated,which exhibits monolayer sensitivity of for representative octadecathiol?ODT?molecules as designed.Using photolithography and molecular self-assembling techniques,we fabricated an Au disk array sensor which is made of bottom Au layer,an ZnSe dielectric film and top Au disk array.Infrared spectral measurements show that the sensor exhibits two absorption lines at 2850cm^-11 and2918cm^-1,whose magnitudes are 0.9%and 2.1%,corresponding to symmetric and antisymmetric virbration modes of CH2 in the ODT.These experimental results are in good agreement with theoretical calculations.