This Project aims at both theoretical and experimental investigation of polar metasurfaces and metamaterials for managing of surface phonon polaritons (SPhPs). The development of a photonic platform in the mid-infrared (MIR) range is an active field of research motivated by applications, such as detection of traces of biomolecules and harmful/explosive substances, passive radiative cooling as well as devices for thermal imaging and for medical diagnostics.
Most of the advances in this field have been achieved by excitation of SPPs supported by doped semiconductors or in graphene. Our approach is based on the exploitation of different polaritonic modes called surface phonon polaritons (SPhPs) in van der Waals (vdW) materials and in polar materials based on their nanostructuration with randomly dispersed subwavelength dielectric elements.
Different materials will be exploited, such as innovative and extremely promising 2D vdW materials as hexagonal boron nitride (hBN) and molybdenum trioxide (MoO3), displaying multiple Reststrhalen bands along two (hBN) or three different (MoO3) crystallographic directions. Dynamic control of surface phonon polaritons (SPhPs) resonances will be also investigated by adding a layer of thermochromic vanadium dioxide, VO2. Finally, more insight into materials crystalline structure and further resonances tunability will be achieved using optical second harmonic generation nonlinear optical effects.
This proposal addressing key challenges in mid-IR polaritonic platforms involves several novel and creative ideas that will push the field forward and highly benefit the scientific community. In particular use of polar oxides for controllable, tunable and flexible mid-IR polaritonic metamaterial and metastructure platforms are poised to play significant role in advancement of key application areas including biosensing, novel IR photonic components (filters, polarizers, emitters, switches).
Significant progresses beyond the state-of-the-art are envisioned in fields such as polaritonics, materials growth technology, 2D polar metamaterials and mid-IR light sources as well as IR sensing. Substantial advancements are connected with the project objectives and involve: extending the use of surface waves in polar materials beyond having multiple Reststrahlen bands (Ga2O3, hBN, MoO3); enabling dynamic control of surface waves by combining phase change material (VO2) with hyperbolic materials (MoO3); exploring the conditions for surface waves hybridization such as longitudinal and transverse phonon polaritons; investigating nonlinear optical effects (second harmonic generation) from polar metamaterials and metasurfaces.
The possibility of exciting different surface waves, by nanostructuring different patterns and areas onto the same polar matrix film, paves the way to a wide operational wavelength, spanning in those ranges where real part of dielectric constants allows the existence of SPhPs (negative values). This wide wavelength range offer a plethora of potential applications, such as sensing the number of IR active vibrational fingerprints for the identification of trace levels of chemical and biological contaminants pollutants or harmful substances, coherent directional sources of IR light, thermal logic gates to name some.
The development of polaritonic metamaterials and metasurfaces with tunable spectral response will result in deep impact in fields such as chemical and bio- sensing where the design of MIR optical elements with sharp absorption resonances produce increased sensitivity of conventional bulk spectroscopic techniques. Furthermore, the possibility to get nanostructured polar materials where the conditions of surface modes hybridization can be fulfilled would allow energy transfer from nonradiating to radiating modes. This challenging task opens the way to the development of phonon polariton-based electrically pumped mid-IR emitters.
Last not least, the increasing need of high-throughput virus sensing is emerging due to the Coronavirus pandemic (COVID-19). Spectroscopic techniques, such as Raman and FTIR are emerging methods to perform
real-time, non-invasive analysis of biofluids. Specifically, attenuated total reflectance (ATR) FTIR spectroscopy is extremely sensitive to the interlayer between prism and a sample acting as a source for surface waves.
Biofluids such as saliva droplets or tears, contain specific disease biomarkers such as proteins, nucleic acids, lipids, carbohydrates, to name some. These biomarkers can be targeted by molecular specific diagnostic tests
such as ATR FTIR spectroscopy, to strengthen the potential of virology studies.