EE235 Nanofabrication TechnologyMultifunctional Nanowire Evanescent Optical Sensors By By Donald J. Sirbuly, Andrea Tao, Matt Law, Rong Fan, and Peidong Yang
Multifunctional Nanowire Evanescent Optical Sensors • Optical sensor • Use nanowire to define the solution type and detect the solution concentration. • Goal • Reusable • Small • Multifunctional Nanowire works as a sensor Setup of the microchannel and the optical sensor Setup of the microchannel and the optical sensor Setup of the microscope
Agenda • Agenda • Work function • Experimental results • Determine concentration • Influence of Ag nanocube • Influence of cladding refraction index • Clean and reuse (remove metallic containment) • Conclusion Sketch of the microchannel Optical sensor in the microchannel
Work Function • Nanowire • Made by single crystal SnO2 • High refractive indices (n>2) • High aspect ratios (>103) to allow longer device • Chemical and mechanical properties to withstand harsh cleaning conditions • Molecule of the solution influence the evanescent field • Emit photons from one side of the nanowire and collect the output from the other side • calculate the absorbance to gain the concentration and type of the solution Clean PL Sense PL PL Intensity Absorbance Absorbance
Concentration (I) • EITC is the dye of the absorption measure. • Absorbance varies with the concentration of the solution and the wavelength • Peak absorbance is a linear function of concentration of EITC Absorbance increases with concentration of EITC Absorbance for different concentration Linear!! 3 mM solution of EITC pass through a single sensing channel Peak absorbance v.s concentration
Concentration (II) • Different nanowire size • Thinner nanowire (d<150nm) has a decreased absorbance in longer wavelength • Photons emitted near the ribbon surface are recaptured • Thicker nanowire (d>200nm) has a larger linewidth • Penetration depth of evanescent field is a function of wavelength A decreased absorbance Larger linewidth
Nanocube and Cladding Type • Work function • Nanocube is absorbed to the waveguide surface • Nanocube scatter 5-10 % waveguide light • Complete attenuation occurred when 10-15 nanoparticle • Scattering is stronger if the evanescent has a larger refraction index The inverse dependence of intensity of the index of refraction is cased by the increase in waveguide loss as the cladding index increase Attach NPs The PL intensity for different evanescent refraction index SnO2 waveguid bridge a single sensing channel
Metallic Containment (Resue) • Reuse can be achieved • Remove metal nanostructures and regain the original waveguiding properties • Use solution of aqua(1:1 HNO3/HCl:H2O) Scattering images of a metal-decorated waveguide upon introduction of a 1:1 HCl/HNO3:H2O solution. The time elapsed is 30 sec.
Conclusion • Nanowire is used to make a optical sensor • Concentration and type of the solution can be easily determined with this new setup • Reuse of this optical sensor can be achieved by removing the metallic containment with aqua.