Electro-optical properties of a graphene device on a tip-enhanced Raman spectroscopy system.

This paper investigates the impact of graphene on tip-enhanced Raman spectroscopy (TERS) by developing an electromagnetic characterization of the TERS-graphene device system. The study focuses on the interaction between the tip, the gate voltage, and the sample, specifically examining the electromagnetic effects in the system. Employing a finite element method (FEM)-based simulation model, we meticulously dissect the electric field distribution and the Raman amplification when graphene is introduced into the system. Our findings reveal that including graphene results in a marginal reduction in Raman amplification and a negligible variation in the induced charges within the system. To reinforce our simulations, we employ a simplified capacitor model, which corroborates our results, showcasing negligible induced charges and validating the obtained capacitance values. In this manuscript, we also explore the influence of the setup on the electro-optical properties of graphene, revealing a slight variation in conductivity despite strong changes in chemical potential. Overall, this work contributes to understanding TERS's electromagnetic aspects in the presence of graphene.

Spatially Coherent Tip-Enhanced Raman Spectroscopy Measurements of Electron-Phonon Interaction in a Graphene Device.

Coherence length (Lc) of the Raman scattering process in graphene as a function of Fermi energy is obtained with spatially coherent tip-enhanced Raman spectroscopy. Lc decreases when the Fermi energy is moved into the neutrality point, consistent with the concept of the Kohn anomaly within a ballistic transport regime. Since the Raman scattering involves electrons and phonons, the observed results can be rationalized either as due to unusually large variation of the longitudinal optical phonon group velocity vg, reaching twice the value for the longitudinal acoustic phonon, or due to changes in the electron energy uncertainty, both properties being important for optical and transport phenomena that might not be observable by any other technique.

Photonic crystal integrated logic gates and circuits.

This paper presents and demonstrates the three logic processing levels based on complementary photonic crystal logic devices through photonic integrated circuit modeling. We accomplished a set of logic circuits including AND, OR, NAND, NOR, XOR, FAN-OUT, HALF ADDER, and FULL ADDER based on photonic crystal slab platforms. Furthermore, we achieved efficient all-optical logic circuits with contrast ratios as high as 5.5 dB, demonstrated in our simulation results, guaranteeing well-defined output power values for logic representations; a clock-rate up to 2 GHz; and an operating wavelength at λ ≈ 1550 nm. Thus, we can now switch up for high computing abstraction levels to build photonic integrated circuits rather than isolated gates or devices.

Electro-Optical Biosensor Based on Embedded Double-Monolayer of Graphene Capacitor in Polymer Technology.

In this work, we present an interferometric polymer-based electro-optical device, integrated with an embedded double-monolayer graphene capacitor for biosensing applications. An external voltage across the capacitor applies an electric field to the graphene layers modifying their surface charge density and the Fermi level position in these layers. This in turn changes the electro-optic properties of the graphene layers making absorption in the waveguide tunable with external voltages. Simultaneously, it is possible to appreciate that this phenomenon contributes to the maximization of the light-graphene interaction by evanescent wave in the sensing area. As a result, it is obtained large phase changes at the output of the interferometer, as a function of small variations in the refractive index in the cladding area, which significantly increasing the sensitivity of the device. The optimum interaction length obtained was 1.24 cm considering a cladding refractive index of 1.33. An absorption change of 129 dB/mm was demonstrated. This result combined with the photonic device based on polymer technology may enable a low-cost solution for biosensing applications in Point of Care (PoC) platform.

The limits of near field immersion microwave microscopy evaluated by imaging bilayer graphene moiré patterns.

Near field scanning Microwave Impedance Microscopy can resolve structures as small as 1 nm using radiation with wavelengths of 0.1 m. Combining liquid immersion microscopy concepts with exquisite force control exerted on nanoscale water menisci, concentration of electromagnetic fields in nanometer-size regions was achieved. As a test material we use twisted bilayer graphene, because it provides a sample where the modulation of the moiré superstructure pattern can be systematically tuned from Ångstroms up to tens of nanometers. Here we demonstrate that a probe-to-pattern resolution of 108 can be obtained by analyzing and adjusting the tip-sample distance influence on the dynamics of water meniscus formation and stability.

Complementary photonic crystal integrated logic devices.

We theoretically propose and demonstrate through numerous simulations complementary photonic crystal integrated logic (CPCL) devices. Simulation results provide demonstration of a highly efficient clock rate, higher than 20 GHz, guaranteeing operation at both input and output with the same wavelength (around λ=1550nm). The proposed devices show well-defined output power values representing the two logic states 1 and 0, with a contrast ratio as high as 6 dB. The results presented here provide countless possibilities for future research, targeting the development of photonic crystal logic and communications systems with CPCLs acting as the core hardware devices.

Trimodal Waveguide Demonstration and Its Implementation as a High Order Mode Interferometer for Sensing Application.

This work implements and demonstrates an interferometric transducer based on a trimodal optical waveguide concept. The readout signal is generated from the interference between the fundamental and second-order modes propagating on a straight polymer waveguide. Intuitively, the higher the mode order, the larger the fraction of power (evanescent field) propagating outside the waveguide core, hence the higher the sensitivity that can be achieved when interfering against the strongly confined fundamental mode. The device is fabricated using the polymer SU-8 over a SiO2 substrate and shows a free spectral range of 20.2 nm and signal visibility of 5.7 dB, reaching a sensitivity to temperature variations of 0.0586 dB/ ∘ C. The results indicate that the proposed interferometer is a promising candidate for highly sensitive, compact and low-cost photonic transducer for implementation in different types of sensing applications, among these, point-of-care.

Dielectric barrier discharge plasma treatment of modified SU-8 for biosensing applications.

In this work we demonstrate the use of a dielectric barrier discharge plasma for the treatment of SU-8. The resulting hydrophilic surface displays a 5° contact angle and (0.40 ± 0.012) nm roughness. Using this technique we also present a proof of concept of IgG and prostate specific antigen biodetection on a thin layer of SU-8 over gold via surface plasmon resonance detection.

Last Advances in Silicon-Based Optical Biosensors.

We review the most important achievements published in the last five years in the field of silicon-based optical biosensors. We focus specially on label-free optical biosensors and their implementation into lab-on-a-chip platforms, with an emphasis on developments demonstrating the capability of the devices for real bioanalytical applications. We report on novel transducers and materials, improvements of existing transducers, new and improved biofunctionalization procedures as well as the prospects for near future commercialization of these technologies.

Study of a low-cost trimodal polymer waveguide for interferometric optical biosensors.

A novel evanescent wave biosensor based on modal interaction between the fundamental mode and the second order mode is proposed and numerically demonstrated. By taking advantage of their symmetries, it is possible to design a device where only the fundamental and the second order modes can propagate, without excitation of the first order mode. With this selection of modes it is possible to achieve a high sensitivity behavior in the biosensor configuration, due to the strong interaction between the evanescent field and the outer surface as compared to previous evanescent wave-based biosensor designs.