High-Frequency Light Rectification by Nanoscale Plasmonic Conical Antenna in Point-Contact-Insulator-Metal Architecture

Numerous efforts have been undertaken to develop rectifying antennas operating at high frequencies, especially dedicated to light harvesting and photodetection applications. However, the development of efficient high frequency rectifying antennas has been a major technological challenge both due to a lack of comprehension of the underlying physics and limitations in the fabrication techniques. Various rectification strategies have been implemented, including metal-insulator-metal traveling-wave diodes, plasmonic nanogap optical antennas, and whisker diodes, although all show limited high-frequency operation and modest conversion efficiencies. Here a new type of rectifying antenna based on plasmonic carrier generation is demonstrated. The proposed structure consists of a resonant metallic conical nano-antenna tip in contact with the oxide surface of an oxide/metal bilayer. The conical shape allows for an improved current generation based on plasmon-mediated electromagnetic-to-electron conversion, an effect exploiting the nanoscale-tip contact of the rectifying antenna, and proportional to the antenna resonance and to the surface-electron scattering. Importantly, this solution provides rectification operation at 280 THz (1064 nm) with a 100-fold increase in efficiency compared to previously reported results. Finally, the conical rectifying antenna is also demonstrated to operate at 384 THz (780 nm), hence paving a way toward efficient rectennas toward the visible range

IR hot carrier based photodetection in titanium nitride oxide thin film-Si junctions

Hot carrier based methods constitute a valuable approach for efficient and silicon compatible sub-bandgap photodetection. Although, hot electron excitation and transfer have been studied extensively on traditional materials such as Au and Ti, reports on alternative materials such as titanium nitride (TiN) are rare. Here, we perform hot hole photodetection measurements on a p-Si/metal thin film junction using Ti, Au and TiN. This material is of interest as it constitutes a refractory alternative to Au which is an important property for plasmonic applications where high field intensities can occur. In contrast to Au, a TiN/Si junction does not suffer from metal diffusion into the Si, which eases the integration with current Si-fabrication techniques. This work shows that a backside illuminated p-Si/TiN system can be used for efficient hot hole extraction in the IR, allowing for a responsivity of 1 mA/W at an excitation wavelength of 1250 nm and at zero bias. Via a comparison between TiN and other commonly used materials such as Au, the origin of this comparably high photoresponse can be traced back to be directly linked to a thin TiO2-x interfacial layer allowing for a distinct hot-hole transfer mechanism. Moreover, the fabrication of TiN nanodisk arrays is demonstrated which bears great promise to further boost the device efficiency

All-dielectric silicon nanoslots for Er3+ photoluminescence enhancement

We study, both experimentally and theoretically, the modification of Er 3 + photoluminescence properties in Si dielectric nanoslots. The ultrathin nanoslot (down to 5-nm thickness), filled with Er in Si O 2 , boosts the electric and magnetic local density of states via coherent near-field interaction. We report an experimental 20-fold enhancement of the radiative decay rate with negligible losses. Moreover, via modifying the geometry of the all-dielectric nanoslot, the outcoupling of the emitted radiation to the far field can be strongly improved, without affecting the strong decay-rate enhancement given by the nanoslot structure. Indeed, for a periodic square array of slotted nanopillars an almost one-order-of-magnitude-higher Er 3 + PL intensity is measured with respect to the unpatterned structures. This has a direct impact on the design of more efficient CMOS-compatible light sources operating at telecom wavelengths

A Simultaneous Equation Model of Globalization, Corruption, Democracy, Human Development and Social Progress

This study builds a simultaneous equation model that establishes inter-connections among the measures of globalization, measures of democracy, human development, corruption perception index and per capita income, which in turn jointly influence social progress. The model has eleven equations in which the response variables and the predictor variables are log-linearly related. The empirical data used for estimation of the model pertain to the period 2006-2016 for 116 countries distributed over all the continents. The model has been estimated by the conventional Two-Stage Least Squares (2-SLS) and alternatively by a modified 2-SLS in which, at the second stage, Shapley value regression has been used to ameliorate the detrimental effects of collinearity among the predictor variables. It has been found that the modified 2-SLS outperforms the conventional 2-SLS. Empirically, it has been established that globalization, democracy, human development and low level of corruption are reinforcing each other and they together explain social progress quite well

3D coaxial out-of-plane metallic antennas for filtering and multi-spectral imaging in the infrared range

We fabricated and investigated a new configuration of 3D coaxial metallic antennas working in the infrared which combines the strong lateral light scattering of vertical plasmonic structures with the selective spectral transmission of 2D arrays of coaxial apertures. The coaxial structures are fabricated with a top-down method based on a template of hollow 3D antennas. Each antenna has a multilayer radial structure consisting of dielectric and metallic materials not achievable in a 2D configuration. A planar metallic layer is inserted normally to the antennas. The outer dielectric shell of the antenna defines a nanometric gap between the horizontal plane and the vertical walls. Thanks to this aperture, light can tunnel to the other side of the plane, and be transmitted to the far field in a set of resonances. These are investigated with finite-elements electromagnetic calculations and with Fourier-transform infrared spectroscopy measurements. The spectral position of the resonances can be tuned by changing the lattice period and/or the antenna length. Thanks to the strong scattering provided by the 3D geometry, the transmission peaks possess a high signal-to-noise ratio even when the illuminated area is less than 2 × 2 times the operation wavelength. This opens new possibilities for multispectral imaging in the IR with wavelength-scale spatial resolution

Light Rectification with Plasmonic Nano-Cone Point Contact- Insulator-Metal Architecture

Numerous efforts have been recently undertaken towards the development of rectifying devices operating at high frequencies especially dedicated to light harvesting and photo detection applications. To this end various rectification strategies have been implemented, such as laser-induced STM tunneling, metal-insulator-metal (MIM) travelling wave diodes, plasmonic nanogap optical antennas, antenna-diode coupled planar MIM, and MIM point-contact sharp-tip or whisker diodes. However, developing high frequency rectifying antennas (rectennas) remains a major technological challenge, as only recent progresses enabled the fabrication of efficient tunable nano-antennas at near infrared and visible frequencies. Here we report on a new type of rectenna based on plasmonic carrier generation. The proposed rectifying structure consists of a broadly resonant gold conical nano-tip antenna in contact with a metal-oxide/metal sample surface, forming a point-contact tunneling diode. The nano-sized antenna apex, designed to maximize the Surface Plasmon Polaritons (SPPs) damping, allows for an efficient power conversion from the light field into excited charges above the Fermi level, the latter ones collectable from the point-contact location through an electronic tunneling process. We demonstrated rectification operation at 280 THz with a power conversion efficiency one order of magnitude higher than the state-of-the-art which we attribute to efficient plasmonic carrier generation and collection

Combination of scanning probe technology with photonic nanojets

Light focusing through a microbead leads to the formation of a photonic nanojet functional for enhancing the spatial resolution of traditional optical systems. Despite numerous works that prove this phenomenon, a method to appropriately translate the nanojet on top of a region of interest is still missing. Here, by using advanced 3D fabrication techniques we integrated a microbead on an AFM cantilever thus realizing a system to efficiently position nanojets. This fabrication approach is robust and can be exploited in a myriad of applications, ranging from microscopy to Raman spectroscopy. We demonstrate the potential of portable nanojets by imaging different sub-wavelength structures. Thanks to the achieved portability, we were able to perform a detailed optical characterization of the resolution enhancement induced by the microbead, which sheds light into the many contradictory resolution claims present in literature. Our conclusions are strongly supported by rigorous data analysis and by numerical simulations, all in perfect agreement with experimental results

Quasi-BIC Modes in All-Dielectric Slotted Nanoantennas for Enhanced Er3+ Emission

In the quest for new and increasingly efficient photon sources, the engineering of the photonic environment at the subwavelength scale is fundamental for controlling the properties of quantum emitters. A high refractive index particle can be exploited to enhance the optical properties of nearby emitters without decreasing their quantum efficiency, but the relatively modest Q-factors (Q ∼ 5–10) limit the local density of optical states (LDOS) amplification achievable. On the other hand, ultrahigh Q-factors (up to Q ∼ 109) have been reported for quasi-BIC modes in all-dielectric nanostructures. In the present work, we demonstrate that the combination of quasi-BIC modes with high spectral confinement and nanogaps with spacial confinement in silicon slotted nanoantennas lead to a significant boosting of the electromagnetic LDOS in the optically active region of the nanoantenna array. We observe an enhancement of up to 3 orders of magnitude in the photoluminescence intensity and 2 orders of magnitude in the decay rate of the Er3+ emission at room temperature and telecom wavelengths. Moreover, the nanoantenna directivity is increased, proving that strong beaming effects can be obtained when the emitted radiation couples to the high Q-factor modes. Finally, via tuning the nanoanntenna aspect ratio, a selective control of the Er3+ electric and magnetic radiative transitions can be obtained, keeping the quantum efficiency almost unitary