Emitter Arrays Research Articles

A first-principles study of the electronic, mechanical, vibrational, and optical properties of the zirconium carbide under high pressure

Zirconium carbide is a compound widely used in cutting tools, nuclear reactors, field emitter arrays and solar energy receivers; additionally, combined with other materials, it can be used in rocket technology and the aerospace industry. For this work was studied the effect of the high hydrostatic pressure on the electronic, mechanical, vibrational, and optical properties of the ZrC, from first principles calculations based on the Density Functional Theory. The calculated enthalpy and cohesive energy data show a B1 (NaCl) to B2 (CsCl) phase transition at 297 GPa. For the B1 phase, results for the calculated equilibrium lattice parameters, bands structure, electron and phonon densities of states, elastic moduli constants, entropy, enthalpy, Gibbs free energy, heat capacity, reflectivity, loss function, conductivity, and dielectric function are consistent with the available experimental and theoretical data. Our results for phonons show that the B1 phase is dynamically stable; in contrast, the B2 phase is not stable. Furthermore, when pressure is applied, the calculated density of electronic states shows that the C 2p-orbitals around the Fermi energy contribute significantly to the conduction band, turning the compound into a ductile the material, with a mixture of metallic and ionic-covalent bonds. On the other hand, the study of the mechanical properties of the B1 phase shows a highest mechanical resistance and maximum thermal absorption, above 356 K and 638 K, respectively; but these switch to higher temperatures as pressure is applied. Finally, the B1 phase of the ZrC is a good coating material and a photon detector at low frequencies in the UV region, but also at the visible and infrared regions; although, increasing the pressure, the values of the optical properties increase. The increase of the parameters’ values of the studied properties, as the pressure increases, indicates that the ZrC could be more efficient in a wider range of applications.

Passive Joint Emitter Localization with Sensor Self-Calibration

This paper studies the problem surrounding distributed passive arrays (sensors) locating multiple emitters while performing self-calibration to correct possible errors in the assumed array directions. In our setting, only the angle-of-arrival (AoA) information is available for localization. However, such information may contain bias due to array directional errors. Hence, localization requires self-calibration. To achieve both, the key element behind our approach is that the received signals from the same emitter should be geometrically consistent if sensor arrays are successfully calibrated. This leads to our signal model, which is built on a mapping directly from emitter locations and array directional errors to received signals. Then we formulate an atomic norm minimization and use group sparsity to promote geometric consistency and align ‘ghost’ emitter locations from calibration errors. Simulations verify the effectiveness of the proposed scheme. We derive the Cramér Rao lower bound and numerically compare it to the simulations. Furthermore, we derive a necessary condition as a rule of thumb to decide the feasibility of joint localization and calibration.

Circularly Polarized Photoluminescence from Nanostructured Arrays of Light Emitters

Strategically designed metamaterials can influence the properties of light emitters in several ways, including shaping of the directionality and polarization of luminescence. These properties, however, are limited in systems where the luminophores uniformly coat the metamaterial. Here, we study and design metamaterials composed of both Au nanobars and nanopatterned light emitters. We systematically investigate the role of spatial averaging, dipole orientation, chirality, near-field effects, and other factors for these multimaterial systems. Finally, we discuss multiple design routes to create metasurfaces that can emit photoluminescence of any circular polarization at any arbitrary angle. These systems simultaneously exhibit high photoluminescence intensity and tailored, directional, and polarized photoluminescence.

Image classification with a fully connected opto-electronic neural network

Optical approaches have made great strides enabling high-speed, scalable computing necessary for modern deep learning and AI applications. In this study, we introduce a multilayer optoelectronic computing framework that alternates between optical and optoelectronic layers to implement matrix-vector multiplications and rectified linear functions, respectively. The system is designed to be real-time and parallelized, utilizing arrays of light emitters and detectors connected with independent analog electronics. We experimentally demonstrate the operation of our system and compare its performance to a single-layer analog through simulations.

Water soluble non-conjugated fluorescent polymers: aggregation induced emission, solid-state fluorescence, and sensor array applications

In this work, two water soluble fluorescent non-conjugated polymers have been designed and synthesized.

Characteristics of a silicon carbide field emission array under pre-breakdown conditions

This study assesses promising field electron sources based on silicon carbide monolithic field emission array (FEA). FEA is fabricated on single-crystal wafers of silicon carbide (0001C) 6H-SiC of n-type conductivity using the technology of two-stage reactive ion etching in SF6/O2/Ar atmosphere. To implement conditions close to breakdown, an experimental setup based on high-voltage narrow pulses generating device GKVI-300 was used. A series of nanosecond voltage pulses with amplitudes from 120 to 250 kV was generated. To study the characteristics of the FEA in the pre-breakdown state, the beam of field emitted electrons was separated from the ion torch or cathode plasma, formed in the following breakdown phases, by placing a 50-μm-thick titanium foil under zero potential into the interelectrode gap. Current-voltage characteristics of peak-currents vs. peak-voltages passing through the foil are close to rectilinear in the Fowler-Nordheim coordinates. The current-voltage characteristics plotted for each of the pulses along increasing and decreasing branches show a discrepancy (hysteresis). After the experiments, the silicon carbide cathode FEA was studied in a scanning electron microscope. Keywords: field electron emission, field emitter array, silicon carbide, pre-breakdown, high-voltage narrow pulses.

Характеристики матричного катода из карбида кремния в предпробойных и пробойных условиях

This study assesses promising field electron sources based on silicon carbide monolithic field emission array (FEA). FEA is fabricated on single-crystal wafers of silicon carbide (0001C) 6H-SiC of n-type conductivity using the technology of two-stage reactive ion etching in SF6/O2/Ar atmosphere. To implement conditions close to breakdown, an experimental setup based on high-voltage narrow pulses generating device GKVI-300 was used. A series of nanosecond voltage pulses with amplitudes from 120 to 250 kV was generated. To study the characteristics of the FEA in the pre-breakdown state, the beam of field emitted electrons was separated from the ion torch or cathode plasma, formed in the following breakdown phases, by placing a 50-μm-thick titanium foil under zero potential into the interelectrode gap. Current-voltage characteristics of peak-currents vs. peak-voltages passing through the foil are close to rectilinear in the Fowler-Nordheim coordinates. The current-voltage characteristics plotted for each of the pulses along increasing and decreasing branches show a discrepancy (hysteresis). After the experiments, the silicon carbide cathode FEA was studied in a scanning electron microscope.

A fast-modeling algorithm to predict the thermo-field emission and thermal stability of field emitter arrays

In the last decades, numerical simulation has become a precious tool to assist the design and study of electron sources based on regular arrays of field emitters. Simulations of field emitter arrays (FEAs) require 3D treatment to account for the interactions between neighbor emitters. Therefore, modeling the thermal evolution of FEAs involves high computational resources due to the multi-physics approach and time dependency. The present paper proposes an algorithm which gives a fast prediction of the self-heating of a large array of N axisymmetric field emitters. It consists in finding for each emitter the equivalent 2D axisymmetric situation yielding the same electron current at 300 K as in the 3D array. The 3D modeling is thus efficiently split into N simulations in 2D, with a significant computation time reduction by at least one order of magnitude. The proof of concept uses 3×3 arrays of ideal emitters. Our results show a correct prediction, within a few percent, of the array thermo-field current and maximum temperature—two quantities of high interest for thermal failure and breakdown voltage considerations. The algorithm paves the way for including thermal effects in future optimization studies of realistic FEAs.

Research on the influence mechanism and modification technology of UV-curing adhesive on the HPLD thermal-induced misalignment

The demand for output performance and reliability of the HPLD (high-power laser diode) has become increasingly stringent with the development of application requirements. The thermal effect of the HPLD will lead to optical components' thermal-induced misalignment, which will significantly affect the output quality and power of the laser. In this paper, the influence of the thickness and uniformity of UV-curing adhesive on the thermal-induced misalignment of the bonding module is revealed. Then the thermal stability of UV-curing adhesive is optimized by the microparticles composite modification method. Finally, the single emitter array laser is packaged with the optimized modified UV-curing adhesive, the thermal-induced misalignment of beam-shaping components can be reduced by 8 times, and the power reduction ratio of the laser is reduced from 3.8% to 0.72%. This research supports efficient control of the thermal-induced misalignment which to ensures high-performance packaging and manufacturing for HPLD.

Close-packed silicon field emitter arrays with integrated anode fabricated by electron-beam lithography

Design, fabrication, and characterization of close-packed field emitter tips enclosed in an Si trench and stand-alone arrays are presented. The two types of field emitter arrays (FEAs) are fabricated using a combination of high-throughput electron-beam lithography, plasma etching, and anode bonding integration technology. The field emitter array inside the trench shows a higher turn-on voltage compared to the stand-alone array. Without any tip sharpening, a current of 7.5 μA was observed at 300 V from FEAs inside the trench, while a higher current of 12.5 μA was observed at the same voltage for the stand-alone array.

Patterning of Silicon Substrate with Self-Assembled Monolayers Using Vertically Aligned Carbon Nanotube Electron Sources.

We introduce a novel patterning technique based on e-beam lithography using vertically aligned carbon nanotube (VACNT) emitters with self-assembled monolayers (SAMs). A 20 μm line width of silicon wafer patterning was successfully demonstrated using octadecyl trichlorosilane (OTS) as a photoresist. To investigate surface modification by the irradiated electrons from the emitters, both contact angle measurement and energy dispersive X-ray (EDX) analysis were conducted. The patterning mechanism of the electron beam irradiated on OTS-coated substrate by our cold cathode electron beam (C-beam) was demonstrated by the analyzed results. The effect of current density and exposure time on the OTS patterning was studied and optimized for the Si wafer patterning in terms of the electronic properties of the VACNTs. The authors expect the new technique to contribute to the diverse applications to microelectromechanical (MEMS) technologies owing to the advantages of facile operation and precise dose control capability based on field electron emission current from the VACNT emitter arrays.

Coherence Properties of Electron-Beam-Activated Emitters in Hexagonal Boron Nitride Under Resonant Excitation

Lattice defects in two-dimensional materials are compelling sources of single photons for applications in quantum information processing. However, the range of emission wavelengths is broad, the defect types vary and the atomic structures of most are unknown, and the inability to fabricate defects systematically on demand has limited progress. This work leverages a robust, site-specific fabrication technique to produce arrays of blue quantum emitters for study via cryogenic spectroscopy. The authors characterize processes that limit emitter coherence and observe Rabi oscillations, demonstrating the potential of these defects for scalable quantum technologies.

Theoretical Analysis of Self-Heating and Cooling Processes in the Pulsed Field Emission From ZnO Nanowire for Achieving High Emission Current

Quasi-one-dimensional (Q1D) nanowire field emitter arrays (FEAs) have important applications in vacuum microelectronics. Investigation on its pulsed field emission characteristics is important for not only avoiding self-heating-induced vacuum breakdown but also achieving high emission current. In this work, a model for quantitative calculation of the transient emission current and temperature distribution of individual nanowire during pulsed field emission has been established by considering the time-dependent thermal conduction equation. Taking ZnO nanowire as an example, the influences of the pulsewidth, the nanowire length, the nanowire radius, and the electrical properties of nanowire on its maximum transient emission current have been investigated. Besides, the cooling process is found to be mainly related on the nanowire length when the nanowire temperature is below 1000 K. By calculating the average emission current under different pulsewidths and duty ratios, it is found that its maximum is determined by the maximum emission current in the steady state that the nanowire is self-heating steadily to the critical temperature below the melting point. Finally, discussions for improving the emission current in different potential applications of FEAs are given. The results provide guidelines for designing Q1D nanowire FEAs.

Submicron-Size Emitters of the 1.2–1.55 μm Spectral Range Based on InP/InAsP/InP Nanostructures Integrated into Si Substrate

We study photoluminescence of InP/InAsP/InP nanostructures monolithically integrated to a Si(100) substrate. The InP/InAsP/InP nanostructures were grown in pre-formed pits in the silicon substrate using an original approach based on selective area growth and driven by a molten alloy in metal-organic vapor epitaxy method. This approach provides the selective-area synthesis of the ordered emitters arrays on Si substrates. The obtained InP/InAsP/InP nanostructures have a submicron size. The individual InP/InAsP/InP nanostructures were investigated by photoluminescence spectroscopy at room temperature. The tuning of the emission line in the spectral range from 1200 nm to 1550 nm was obtained depending on the growth parameters. These results provide a path for the growth on Si(100) substrate of position-controlled heterojunctions based on InAs1-xPx for nanoscale optical devices operating at the telecom band.

Multi-pixel photoconductive emitters for the controllable generation of azimuthal and radial terahertz beams.

A multi-pixel photoconductive emitter is reported that generates THz beams with either azimuthal, radial or linear polarization states. Switching between the different polarization states was purely electrical, via the bias voltage applied, circumventing the need for mechanical polarization optics or different THz emitters to change the polarization. Dipole array modelling was performed to validate emitter array designs, and to explore their optimal bias configuration, while spatially-resolved electro-optic detection of the generated beams confirmed that cylindrical-vector beams were produced. We further demonstrate that the spatial beam profile was optimized by adjusting the bias level on particular pixels, improving the polarization purity of the beam.

Cavity-Enhanced 2D Material Quantum Emitters Deterministically Integrated with Silicon Nitride Microresonators.

Optically active defects in 2D materials, such as hexagonal boron nitride (hBN) and transition-metal dichalcogenides (TMDs), are an attractive class of single-photon emitters with high brightness, operation up to room temperature, site-specific engineering of emitter arrays with strain and irradiation techniques, and tunability with external electric fields. In this work, we demonstrate a novel approach to precisely align and embed hBN and TMDs within background-free silicon nitride microring resonators. Through the Purcell effect, high-purity hBN emitters exhibit a cavity-enhanced spectral coupling efficiency of up to 46% at room temperature, exceeding the theoretical limit (up to 40%) for cavity-free waveguide-emitter coupling and demonstrating nearly a 1 order of magnitude improvement over previous work. The devices are fabricated with a CMOS-compatible process and exhibit no degradation of the 2D material optical properties, robustness to thermal annealing, and 100 nm positioning accuracy of quantum emitters within single-mode waveguides, opening a path for scalable quantum photonic chips with on-demand single-photon sources.

Chirality-driven delocalization in disordered waveguide-coupled quantum arrays

We study theoretically the competition between directional asymmetric coupling and disorder in a one-dimensional array of quantum emitters chirally coupled through a waveguide mode. Our calculation reveals a highly nontrivial phase diagram for the eigenstates' spatial profile, nonmonotonously depending on the disorder and directionality strength. The increase of the coupling asymmetry drives the transition from Anderson localization in the bulk through delocalized states to chirality-induced localization at the array edge. Counterintuitively, this transition is not smeared by strong disorder but becomes sharper instead. Our findings could be important for the rapidly developing field of waveguide quantum electrodynamics, where chiral interactions and disorder play crucial roles.

Effects of the emitters density on the performance of an atmospheric ionic thruster

A laboratory study on the performance of corona thrusters as a function of the spatial arrangement of the emitting electrodes is presented. The setup consists in arrays of emitters and collectors with independently adjustable spacings. This thruster is tested in different benches, for output velocity and direct thrust measurements. The measured velocity is also used to determine thrust by momentum balance, comparing it with direct readings. Electric measurements complete the dataset. The parameter space consists of two different collector spacings and several emitter spacings, with fixed interelectrode gap and voltage. Within this space lies an optimal collector–emitter spacing ratio 2:1.

Regulation of Thermal Emission Position in Biased Graphene.

A very attractive advantage of graphene is that its Fermi level can be regulated by electrostatic bias doping. It is of great significance to investigate and control the spatial location of graphene emission for graphene thermal emitters, in addition to tuning the emission intensity and emission spectrum. Here, we present a detailed theoretical model to describe the graphene emission characteristics versus gate voltages. The experimentally observed movement of the emission spot and temperature distribution of graphene emitters are basically in agreement with those from the theoretical model. Our results provide a simple method to predict the behavior of graphene emitters that is beneficial for achieving the spatial dynamic regulation of graphene infrared emission arrays.

Improving the Response Speed of an Active-Current Controlled Field Emitter Arrays by Modifying the Controlled Current

Using an active-current control (ACC) component such as MOSFET in field emitter arrays (FEAs) is an important way to achieve stable emission current. However, the controlled current of ACC may reduce the response speed of FEAs due to the longer charging process, which limits its application. In this work, a general model for the field emission of MOSFET-controlled FEAs has been established to study the influence of controlled saturation current on its response speed. It is found that the response speed which decreases nearly linearly as the saturation current decreases can be reduced down by above 1 order of magnitude comparing to the intrinsic value. The field emission characteristics of a MOSFET-controlled ZnO nanowire FEAs under different saturation current and duty ratio have been investigated, in which the result is in consistency with the model. A solution using a controlled current which is larger than the induced current during the charging process and can rapidly reduce down to the field emission current has been proposed for balancing the stability and response speed in MOSFET-controlled FEAs. All the results provide a method for obtaining fast response ACC-FEAs, which should be useful in the application that requires pulsed driving FEAs.