Due to size, computational and power limitations an integrated nanosensor device needs to be redesigned with a limited number of components. A sensorless event detection node can overcome these limitations where such node can be powered using energy harvested from various events. The harvested energy could also be a significant factor for events detection without using any sensors. This study presents a detailed description of a sensorless event detection node which consists of two components — an energy harvester and a pulse generator. We discuss the state of the art configurations for these two components. However, due to the low complexity of the nanoscale device, the pulse generator should be kept simple. We, therefore, theoretically investigate different approaches for the pulse generator to generate Surface Plasmon Polaritons (SPPs) which reasonably resemble femtoseconds long pulses in graphene. Based on our analysis, we find that SPPs can be excited using a near-field excitation method for the THz band which is simple and can produce Electromagnetic (EM) radiation with a wide range of high wavenumber. Hence, the coupling condition can be easily satisfied and consequently, the SPP wave can be excited. However, such method excites SPPs locally, which requires improvement in practice. Thus we numerically investigate how operating frequency, the doping amount of graphene and the properties of the evanescent source affect the plasmon resonance of SPPs. We also studied different evanescent sources such as electric dipole, and hexapole, and find that the former provides better SPP resonance. We also observe that through fine-tuning of the chemical potential, frequency and source phase angle, higher amplitude SPPs can be excited on graphene surface in the THz band. The proposed model can be a good candidate for a low-complexity realization of a THz pulse generator in self-powered sensorless events detection node.
Graphene as well as more generally Dirac solids constitute two dimensional materials where the electronic flow is ultra relativistic. When a Dirac solid is deposited on a different substrate surface with roughness, a local random potential develops through an inhomogeneous charge impurity distribution. This external potential affects profoundly the charge flow and induces a chaotic pattern of current branches that develops through focusing and defocusing effects produced by the randomness of the surface. An additional bias voltage may be used to tune the branching pattern of the charge carrier currents. We employ analytical and numerical techniquesin order to investigate the onset and the statistical properties of carrier branches in Dirac solids. We find a specific scaling-type relationship that connects the physical scale for the occurrenceof branches with the characteristic medium properties, such as disorder and bias field. We usenumerics to test and verify the theoretical prediction as well as a perturbative approach that gives a clear indication of the regime of validity of the approach. This work is relevant to deviceapplications and may be tested experimentally.
Although plasmon modes exist in doped graphene, the limited range of doping achieved by gating restricts the plasmon frequencies to a range that does not include the visible and infrared. Here we show, through the use of first-principles calculations, that the high levels of doping achieved by lithium intercalation in bilayer and trilayer graphene shift the plasmon frequencies into the visible range. To obtain physically meaningful results, we introduce a correction of the effect of plasmon interaction across the vacuum separating periodic images of the doped graphene layers, consisting of transparent boundary conditions in the direction perpendicular to the layers; this represents a significant improvement over the exact Coulomb cutoff technique employed in earlier works. The resulting plasmon modes are due to local field effects and the nonlocal response of the material to external electromagnetic fields, requiring a fully quantum mechanical treatment. We describe the features of these quantum plasmons, including the dispersion relation, losses, and field localization. Our findings point to a strategy for fine-tuning the plasmon frequencies in graphene and other two-dimensional materials.
We demonstrate analytically and numerically that the dispersive Dirac cone emulating an epsilon-near-zero (ENZ) behavior is a universal property within a family of plasmonic crystals consisting of two-dimensional (2D) metals. Our starting point is a periodic array of 2D metallic sheets embedded in an inhomogeneous and anisotropic dielectric host that allows for propagation of transverse-magnetic (TM) polarized waves. By invoking a systematic bifurcation argument for arbitrary dielectric profiles in one spatial dimension, we show how TM Bloch waves experience an effective dielectric function that averages out microscopic details of the host medium. The corresponding effective dispersion relation reduces to a Dirac cone when the conductivity of the metallic sheet and the period of the array satisfy a critical condition for ENZ behavior. Our analytical findings are in excellent agreement with numerical simulations.