Investigation Of Plasmonic Devices For Biosensing And Energy Harvesting

Nowadays,petrochemical energy tends to be exhausted,and cancer seriously threatens human life.Developing new energy and curing cancer have become two urgent problems facing mankind.Solar radiation energy is rich and inexhaustible.It is an ideal new energy for human beings.The first problem to be solved in developing solar energy is to improve the efficiency of solar radiation energy collection,but the current collection efficiency is not ideal.The first problem in curing cancer is to find cancer cells as early as possible.The earlier the cancer cells are diagnosed,the greater the chance of cure.Therefore,it is of great academic and applied value to develop energy collection techniques for solar energy utilization as the main purpose and biosensor research with high sensitivity detection of cancer cells as the main purpose.Theoretically plasmonic nanostructures and absorber designs for different devices are investigated using the finite-element method.Multiple Fano resonances are obtained with high-quality factor and FoM values in various spatial designs.Symmetry breaking technique is applied to excite multiple high-order dark modes.Plasmon-induced anti-transparency?PIAT?and transparency?PIT?are obtained in relatively simple geometry.The mechanism of reduced symmetry is used through incorporating nano-splits and rotating/moving the nanogaps in opposite directions.Absorber designs are used to obtain input-voltage based highly tunable and flexible perfect absorption.The electro-optic substrate based absorbers are very sensitive which can be used to shift the resonance wavelength to the desired wavebands without changes in the line-shape of spectra.Our incident-angle less-independent results cover broad wavebands which are highly sensitive to variations in applied voltage,which can be used for sensing,detection,energy harvesting and imaging.In developing the absorber,multi-open-ring plasmonic structures were constructed and multi Fano modes,PIAT modes,and PIT modes are found.As it is known that these modes have many new applications,especially for sensors,therefore,we did some research on sensors based on the plasmonic structures proposed.High refractive index based sensitivity for Fano,PIAT and PIT resonances are calculated to evaluate the designs for biosensing.For background materials the refractive indices of different solvents,both healthy and cancerous tissues are used.Our designs demonstrate the highest figure-of-merit?FoM?,single side quality factor(Q_ss)of 808 and 654 respectively.For voltage tunability,the relative sensitivity is calculated as high as 4.802e-4 V^-1.The refractive index sensitivity?S?,resolution???and very small limit of refractive index detection(?n_min)are calculated about 964 nm/RIU,1.1 nm,and0.001,respectively.Our designs can also pave significant applications in switching,filtering,line-shape engineering,and slow-light devices.Main work and achievements are as follows:i)Q-shaped metasurface,a relatively simple design,is used to achieve high-quality factor and high FoM values for detection purposes.Symmetry is reduced by rotating the nanorod and incorporating nanogaps.The Q_ss value as high as 196and FoM of 105 are observed.ii)Two metallic nested circle nanorings each with opposite nanogaps are used to compose a unit cell for a metasurface structure on a dielectric substrate.Nanogaps are introduced and rotated in opposite directions to break the symmetry of resonators.The refractive indices of healthy and cancerous tissues are utilized as background materials to evaluate the metasurface for biosensing.High Q_ss and FoM values of 566 and 391 are obtained.iii)Square nanorings with nano-cuts in opposite sides placed on a thick dielectric substrate are employed to comprise the unit cell for a metasurface.The nanoscale aperture results in narrow PIT and PIAT resonances as we exploit the symmetry by displacing the nano-cuts in opposite directions.A unified mechanism for generating the PIAT resonances and plasmon-induced transparency?PIT?resonances are studied and it agrees with the simulation results.Different refractive indices are used to change the background molecules to weight-up the design for biosensing.FoM and Q_ss are boosted to 808 and 654 respectively.iv)Cross-shaped parallel metallic nanorods placed at the top of an electro-optic layer backed over a thick metallic substrate are designed to form a metasurface.For applications,we applied different background refractive indices for biosensing and voltages to adjust the resonances to desired wavebands with relative sensitivity as high as 4.802e-4 V^-1.v)An excellent plasmonic absorber is designed to achieve absorption in the waveband of 500 nm to 2000 nm and above.In the form of Metal-Dielectric-Metal structure,electro-optic material is introduced as dielectric layer to shift the resonant wavelengths to the range of interest.In the resonator,metallic split rings and disks are arranged.To check the validity of the simulated results,the some analysis is carried out which agrees well with the simulation results.Actual solar energy absorption efficiency of the absorber is calculated by taking the integration of solar spectrum and absorption spectra.The total efficiency is calculated as high as 76.35%,approaching to the 96%efficiency of about 88-layered design?300-2000 nm waveband?reported in literature.