Planar Tunnel Research Articles

"Stamp the tunnel"- Innovative tool - for perfection in manual small incision cataract surgery.

Manual small incision cataract surgery (SICS) is a cost-effective and safe procedure offering comparable outcomes to phacoemulsification. It holds significance for outreach and economically disadvantaged patients in developing countries, while also being important for complex cataracts in developed nations. The SICS technique revolves around a three planar self-sealing sclero corneal tunnel (SCT), a critical element for rapid and suture-less healing. The tunnel's components include the incision, side pocket, internal entry, and depth each affecting astigmatism and successful nucleus delivery.[1-3] Various incision types are explored, with the frown incision yielding minimal astigmatism but posing challenges.[2,4] Inappropriate SCT leads on to high induced astigmatism, post op hypotony, and chances of infection. This video introduces "Tunnel stamp" which is a novel device designed to guide the incision length, internal entry line, and side pocket accuracy thus making a perfect SCT particularly for novice surgeons, who often encounter intraoperative and postoperative complications due to inappropriate SCT. The device is produced through 3D printing with thermoplastic polyurethane (TPU), an easily available and economically feasible material. The prototype's practicality is demonstrated through successful wet lab trials on goat eyes and subsequently on human eyes. The device is aligned using a limbus-matching step and a sterilized marker pen. This device has unique advantage to take care of the three aspects of SCT, that is, incision, side pocket, and internal entry. One can have custom-made guarded knife to perform scleral groove in optimum depth, which is another important dimension of SCT. Future developments involve creating the tunnel stamp in transparent flexible silicon to enhance alignment accuracy. Given the diversity of cataract types, multiple sizes of the device are envisioned to accommodate nucleus size variability and different stages of cataract development. To aid novice surgeons, two variations of incision guides (straight and frown) are proposed for immature and harder cataracts reducing induced astigmatism. Overall, this innovative tunnel stamp aims to enhance SICS outcomes, enabling more precise and consistent SCT creation while addressing challenges posed by various cataract types and surgeon experience levels. https://youtu.be/yzV-UC4jwPg.

Tunneling Spectroscopy at Megabar Pressures: Determination of the Superconducting Gap in Sulfur.

The recent discovery of high-temperature, high-pressure superconductors, such as hydrides and nickelates, has opened exciting avenues in studying high-temperature superconductivity. The primary superconducting properties of these materials are well characterized by measuring various electrical and magnetic properties, despite the challenges posed by the high-pressure environment. Experimental microscopic insight into the pairing mechanism of these superconductors is even more challenging, due to the lack of direct probes of the superconducting gap structures at high pressure conditions. Here, we have developed a planar tunnel junction technique for diamond anvil cells and present ground-breaking tunneling spectroscopy measurements at megabar pressures. We determined the superconducting gap of elemental sulfur at 160GPa, a key constituent of the high-temperature superconductor H_{3}S. High quality tunneling spectra indicate that β-Po phase sulfur is a type II superconductor with a single s-wave gap with a gap value 2Δ(0)=5.6 meV. This technique is compatible with superconducting compounds synthesized in diamond anvil cells and provides insight into the pairing mechanism in novel superconductors under high-pressure conditions.

Proposal for All-Electrical Skyrmion Detection in van der Waals Tunnel Junctions.

A major challenge for magnetic skyrmions in atomically thin van der Waals (vdW) materials is reliable skyrmion detection. Here, based on rigorous first-principles calculations, we show that all-electrical skyrmion detection is feasible in two-dimensional vdW magnets via scanning tunneling microscopy (STM) and in planar tunnel junctions. We use the nonequilibrium Green's function method for quantum transport in planar junctions, including self-energy due to electrodes and working conditions, going beyond the standard Tersoff-Hamann approximation. We obtain a very large tunneling anisotropic magnetoresistance (TAMR) around the Fermi energy for a graphite/Fe3GeTe2/germanene/graphite vdW tunnel junction. For atomic-scale skyrmions, the noncollinear magnetoresistance (NCMR) reaches giant values. We trace the origin of the NCMR to spin mixing between spin-up and -down states of pz and dz2 character at the surface atoms. Both TAMR and NCMR are drastically enhanced in tunnel junctions with respect to STM geometry due to orbital symmetry matching at the interface.

Performance comparison of planar and cylindrical ferroelectric tunnel junctions

A comprehensive comparison of the electrical characteristics between the planar (P-FTJ) and cylindrical ferroelectric tunnel junction (C-FTJ) is conducted based on physical modeling and simulation. The FTJ architecture consists of metal-ferroelectric–dielectric-metal stacks. Two configurations of C-FTJ are considered depending on whether the position of the ferroelectric (FE) layer is close or away from the inner electrode. The differences between the P-FTJ and C-FTJs in the distributions of the electric field and FE polarization are analyzed. The resultant tunneling electroresistance (TER) is explored as a function of the inner radius, FE thickness, dielectric thickness, and remnant polarization. These simulation results offer physical insights into achieving highly integrated three-dimensional storage structures by improving the TER ratio.

Bosonic excitation spectra of superconducting Bi2Sr2CaCu2O8+δ and YBa2Cu3O6+x extracted from scanning tunneling spectra

A detailed interpretation of scanning tunneling spectra obtained on unconventional superconductors enables one to gain information on the pairing boson. Decisive for this approach are inelastic tunneling events. Due to the lack of momentum conservation in tunneling from or to the sharp tip, those are enhanced in the geometry of a scanning tunneling microscope compared to planar tunnel junctions. This work extends the method of obtaining the bosonic excitation spectrum by deconvolution from tunneling spectra to nodal d-wave superconductors. In particular, scanning tunneling spectra of slightly underdoped Bi2Sr2CaCu2O8+δ with a Tc of 82 K and optimally doped YBa2Cu3O6+x with a Tc of 92 K reveal a resonance mode in their bosonic excitation spectrum at Ωres≈63 meV and Ωres≈61 meV respectively. In both cases, the overall shape of the bosonic excitation spectrum is indicative of predominant spin scattering with a resonant mode at Ωres<2Δ and overdamped spin fluctuations for energies larger than 2Δ. To perform the deconvolution of the experimental data, we implemented an efficient iterative algorithm that significantly enhances the reliability of our analysis.

Magnetic field orientation dependence of planar tunneling spectroscopy in the superconducting state of NbSe2

Layered superconductors exhibit strong anisotropic responses to magnetic fields in out-of-plane and in-plane orientations, due to their distinct vortex structures and upper critical field values. Here, we utilize the planar tunnel junction technique to perform continuous magnetic field-dependent dI/dV spectroscopy measurements on 2H-NbSe2 under different field orientations. We observe characteristic kink features for weak in-plane magnetic fields, but the overall behaviors are quite similar for different field orientations despite the distinct vortex generation processes and widely different upper critical field values. Especially, the generic square root dependence of the Fermi level density of state on magnetic field indicates that the Doppler shift plays a central role in the low energy excitations of 2H-NbSe2 in the presence of magnetic field.

Role of optical rectification in photon-assisted tunneling current

Emission of light and conversely rectification of an optical signal using an all-metallic electronic device is of fundamental and technological importance for nano-optics. However despite recent experimental efforts in the development of electrically-driven plasmonic sources, the interplay between quantum transport and optics is still under debate. Here, we measure the photon-assisted current in a planar tunnel junction under infrared illumination. To address the microscopic mechanism at the origin of the optical rectification, we compare the photon-assisted current and the current-voltage characteristic of the junction measured on a voltage range much greater than {V}_{0}=frac{hc}{elambda }=0.825,{{{{{{{rm{V}}}}}}}}, previously unexplored. The experimental results do not agree with the theory based on the existence of a non-thermal distribution function corresponding to the exchange of energy quanta between electrons and photons. We show instead that the illumination power mainly goes into heating and that the rectification results from the tunneling Seebeck effect.

Planar tunneling spectroscopy on van der Waals superconductors with AlOx junction grown by atomic layer deposition

We demonstrate a method for fabricating a high-quality AlOx-based planar tunnel junction using atomic layer deposition, integrated with the exfoliation and transfer techniques for van der Waals (vdW) materials. The tunneling spectroscopy results on exfoliated Bi2Sr2CaCu2O8+δ and 2H-NbSe2 vdW superconductors are highly consistent with that obtained by ultrahigh vacuum scanning tunneling spectroscopy on atomically clean surfaces. The planar tunneling devices enable high-precision spectroscopy over a wide range of temperatures and magnetic fields and reveal novel features and stark contrast between high-TC cuprates and conventional superconductors. This method represents a universally applicable technique for probing the electronic structure of various two-dimensional vdW materials.

Data-Driven Prediction of Stability of Rock Tunnel Heading: An Application of Machine Learning Models

In this paper, Artificial Neural Networks (ANN) have been utilized to predict the stability of a planar tunnel heading in rock mass based on the well-defined Hoek-Brown (HB) yield criterion. The HB model was developed to capture the failure criterion of rock masses. To provide the datasets for an ANN model, the numerical upper bound (UB) and lower bound (LB) solutions obtained from the finite element limit analysis (FELA) with the HB failure criterion for the problem of tunnel headings are derived. The sensitivity analysis of all influencing parameters on the stability of rock tunnel heading is then performed on the developed ANN model. The proposed solutions will enhance the dependability and preciseness of predicting the stability of rock tunnel heading. Note that the effect of the unlined length ratio has not been explored previously but has been found to be of critical importance and significantly contributes to the failure of rock tunnel heading. By utilizing the machine learning-aided prediction capability of the ANN approach, the numerical solutions of the stability of tunnel heading can be accurately predicted, which is better than the use of the classic linear regression approach. Thus, providing a better and much safer assessment of mining or relatively long-wall tunnels in rock masses.

Source pocket-engineered hetero-gate dielectric SOI Tunnel FET with improved performance

In this paper, we have studied and proposed a planar Tunnel FET device with source side SiGe pocket and hetero-gate dielectric structure that works by utilizing quantum mechanical Band-to-Band tunnelling (BTBT) mechanism. Simulation results obtained using a calibrated SILVACO TCAD device simulator show that the device exhibits good ambipolar performance because of the hetero-gate dielectric and the use of source pocket leads to steep point subthreshold swing of 4.90 mV/dec., an average subthreshold swing of 25.31 mV/dec. and a threshold voltage of 0.23 V. For including the hetero-gate dielectric, the variation in drain current values with high-κ dielectric length is analysed. The change in transfer characteristics with pocket parameters including pocket length and pocket doping is also reported. A 4 nm Si0.7Ge0.3 n+ pocket with doping concentration of 5 × 1019 cm−3 is found to show the maximum ON-OFF current ratio of 5.23 × 1011. This paper also performs a comparative study between different TFET structures and the analysis clearly highlights the potential of proposed Source Pocket-Engineered Hetero Gate Dielectric (SPE-HGD) TFET device for low-power and energy-efficient applications.

The influence of the magnetic configuration on the charge current generated by the temperature gradient in the double planar ferromagnetic tunnel junctions

The charge current generated by the temperature gradient applied to the double planar tunnel junctions with ferromagnetic external electrodes and central layer is investigated in the free-electron model. The situation when the bias voltage is applied to the junction is also considered. It has been shown that the analyzed current may depend on the orientation of magnetic moments in the ferromagnetic external electrodes and the central layer. The influence of the magnetic configuration on the tunnel current can be enhanced due to the resonant tunneling by the resonant states. Especially strong modifications of the current flowing through the junction can be observed as a result of changing the orientation of the magnetic moments in the central layer in junctions where the tunneling by the resonant states located below the bottom for the spin-down electrons in the source electrode is observed. The studied effects are strongly depended on the thickness of the central layer, spin splitting of the electron bands in the external electrodes and in the central layer, and the bias voltage applied to the junctions, but are also sensitive to the average temperature of the junction and the height and width of the barriers, whereas they are less sensitive to the temperature difference between the electrodes.

Physics-based stitching of multi-FOV PIV measurements for urban wind fields

Particle image velocimetry (PIV) is commonly used to measure multiple field-of-views (FOVs) of the flow in large urban domains, performed in wind tunnels using an array of cameras located at fixed positions or a single camera setup that traverses during the measurements. With respect to the large amount of data produced in this type of measurement, traditional stitching approaches are no longer adequate to efficiently merge the image data. A physics-based flow field stitching method is proposed for stitching flows in urban wind fields, named regional-flow stitching. It matches the flow characteristics within neighboring FOVs of flow using a vorticity-based reference window. The method is based on finding the optimal similarity between a reference window in one FOV and another possible matching window in the other FOV. The matching window rolls in both directions at the interval of two adjacent data points, which determines the stitching resolution. The matching in flow similarity is evaluated using the normalized root-mean-squared error (NRMSE) between reference and possible matching windows, which is evaluated by comparison to a traditional stitching method and further verified using planar and stereo wind tunnel PIV measurement results. A comparison of computational cost with 8 FOVs and approximate 7% surface overlap between FOVs shows that our method is faster, taking about 46% of processing time, than a traditional stitching method. 3D visualization of the merged FOVs is further demonstrated with ParaView. The proposed stitching method may serve as a powerful tool for experimental studies involving large domains of urban wind flow fields.

Quantum oscillations and quasiparticle properties of thin film Sr2RuO4

We measure the Shubnikov--de Haas effect in thin-film ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ grown on an $({\mathrm{LaAlO}}_{3}{)}_{0.29}\text{\ensuremath{-}}({\mathrm{SrAl}}_{1/2}{\mathrm{Ta}}_{1/2}{\mathrm{O}}_{3}{)}_{0.71}$ substrate. We detect all three known Fermi surfaces and extract the Fermi surface volumes, cyclotron effective masses, and quantum lifetimes. We show that the electronic structure is nearly identical to that of single-crystal ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, and that the quasiparticle lifetime is consistent with the ${T}_{\mathrm{c}}$ of comparably clean, single-crystal ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$. Unlike single-crystal ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, where the quantum and transport lifetimes are roughly equal, we find that the transport lifetime is $1.3\ifmmode\pm\else\textpm\fi{}0.1$ times longer than the quantum lifetime. This may suggest that extended (rather than point) defects could be the dominant source of quasiparticle scattering in these films. To test this hypothesis, we perform cross-sectional scanning transmission electron microscopy and find that out-of-phase boundaries extending the entire thickness of the film occur with a density that is consistent with the quantum mean free path. The long quasiparticle lifetimes make these films ideal for studying the unconventional superconducting state in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ through the fabrication of devices---such as planar tunnel junctions and superconducting quantum interference devices.

Programmable Organic-Free Negative Differential Resistance Memristor Based on Plasmonic Tunnel Junction.

A novel negative differential resistance (NDR) phenomenon is reported herein based on planar plasmonic tunnel junction, resulting from plasmon-assisted long-range electron tunneling (P-tunneling) and electronic caching effect of Au@SiO2 nanoparticles. The tunnel junction is made of shell-insulated Au@SiO2 nanoparticle nanomembrane, in which SiO2 shells act as a tunable tunneling barrier, while the Au core not only support the plasmonic effect to enable P-tunneling, but also act as electronic caches to render NDR responses. The NDR peak voltage and current can be programmably controlled by varying the thickness of SiO2 shell and the size of Au core to tune barrier level for electron transport. In addition, light induced plasmonic effect can be further managed to regulate the NDR behavior by fine-tuning P-tunneling. The phenomenon is exploited for robust use as memristors. The work provides a new mechanism for the generation of NDR effect and may open a way for the development of robust and new conceptual nanoelectronic devices.

Abrupt degenerately-doped silicon nanowire tunnel junctions

We have confirmed the presence of narrow, degenerately-doped axial silicon nanowire (SiNW) p-n junctions via off-axis electron holography (EH). SiNWs were grown via the vapor-solid-liquid (VLS) mechanism using gold (Au) as the catalyst, silane (SiH4), diborane (B2H6) and phosphine (PH3) as the precursors, and hydrochloric acid (HCl) to stabilize the growth. Two types of growth were carried out, and in each case we explored growth with both n/p and p/n sequences. In the first type, we abruptly switched the dopant precursors at the desired junction location, and in the second type we slowed the growth rate at the junction to allow the dopants to readily leave the Au catalyst. We demonstrate degenerately-doped p/n and n/p nanowire segments with abrupt potential profiles of 1.02 ± 0.02 and 0.86 ± 0.3 V, and depletion region widths as narrow as 10 ± 1 nm via EH. Low temperature current-voltage measurements show an asymmetric curvature in the forward direction that resemble planar gold-doped tunnel junctions, where the tunneling current is hidden by a large excess current. The results presented herein show that the direct VLS growth of degenerately-doped axial SiNW p-n junctions is feasible, an essential step in the fabrication of more complex SiNW-based devices for electronics and solar energy.

Design and Sensitivity Analysis of Steep-Slope Bi-Channel Vertical Tunnel Field Effect Transistor

In this paper, the electrical characteristics of a low power steep-slope vertical tunnel field effect transistor (VTFET) is introduced with dual lateral channel in the source sidewall, which can considerably improve the device performance in comparison with the planar tunnel field effect transistor (TFET). The results demonstrate that unlike the conventional TFET with limited tunneling junction at the source/channel interface, the band to band tunneling area in VTFET is created along the entire length of the source region from the both sides, which amplifies the tunneling rate. The results demonstrate that on/off current ratio of 8.36e+7 and subthreshold swing (SS) of 10 mV/dec has been achieved for the VTFET in comparison with the on/off current ratio of 9.79e+5 and SS = 31 mV/dec for the planar TFET, respectively. Sensitivity analysis is conducted via calculating the standard deviation and mean value of main electrical measures as a function of various design parameters. It is indicated that gate workfunction and source doping density are critical design parameters that may fundamentally affect the efficiency of the device. An important feature of the proposed device is the insensitivity of the off-state current and subthreshold swing to the channel length scaling and drain bias, which exhibits VTFET promising potential for future low-power circuits.

Field cooled annular Josephson tunnel junctions

We investigate the physics of planar annular Josephson tunnel junctions quenched through their transition temperature in the presence of an external magnetic field. Experiments carried out with long Nb/Al-AlOx/Nb annular junctions showed that the magnetic flux trapped in the high-quality doubly-connected superconducting electrodes forming the junction generates a persistent current whose associated magnetic field affects the both the static and dynamics properties of the junctions. More specifically, the field trapped in the hole of one electrode combined with a d.c. bias current induces a viscous flow of dense trains of Josephson vortices which manifests itself through the sequential appearance of displaced linear slopes, Fiske step staircases and Eck steps in the junction’s current-voltage characteristic. Furthermore, a field shift is observed in the first lobe of the magnetic diffraction pattern. The effects of the persistent current can be mitigated or even canceled by an external magnetic field perpendicular to the junction plane. The radial field associated with the persistent current can be accurately modeled with the classical phenomenological sine-Gordon model for extended one-dimensional Josephson junctions. Extensive numerical simulations were carried out to disclose the basic flux-flow mechanism responsible for the appearance of the magnetically induced steps and to elucidate the role of geometrical parameters. It was found that the imprint of the field cooling is enhanced in confocal annular junctions which are the natural generalization of the well studied circular annular junctions.

A comprehensive analysis of Auger generation impacted planar Tunnel FETs

Tunnel Field Effect Transistors (TFETs) are known to be compromised by higher order processes that downgrade their performance compared to ballistic projections. Using a quasi-analytical model that extends the chemistry based Simmons equation to include finite temperature effects, potential variations and scattering, we exhibit that non-idealities like trap-assisted tunneling and Auger generation can explain the observed performance discrepancy. In particular, Auger generation is the dominant leakage mechanism in TFETs at low trap densities. Our studies suggest that possible ways of reducing Auger generation rate are reducing source carrier concentration and increasing the valence band transport effective mass of the source material. In this paper, we specifically investigate the impact of variations of these factors on device performance of staggered bandgap planar III-V heterojunction Tunnel FETs.

The Influence of the Ferroelectric and Magnetic Configuration on the Tunnel Current in Double Planar Tunnel Junctions with Ferromagnetic Electrodes and Ferroelectric Barriers

Herein, the tunnel current in double planar tunnel junctions, consisting of ferromagnetic external electrodes and a central ferromagnetic layer separated by ferroelectric barriers, is analyzed. Different orientations of magnetic moments in the electrodes and electric polarization in the barriers are considered. The influence of the thickness of the central layer, the spin splitting of the electron bands, and the Thomas–Fermi screening length in the electrodes and the central layer on the obtained results is analyzed. The modification of the results caused by the change of the width and electric polarization of the barriers is also discussed. The influence of the change of the ferroelectric configuration on the magnitude of the tunnel current can be enhanced in the junctions with different Thomas–Fermi screening lengths in the central layer and external electrodes as well as in the junctions in which the resonant states in the central layer are located near the Fermi level in the source electrode or near the band edge for electrons of minority spin in the drain electrode. It is possible to find the junctions in which electron transport is sensitive to both ferroelectric and magnetic configurations, which can be used as multibit memories.

Confocal Annular Josephson Tunnel Junctions with Large Eccentricity

Confocal Annular Josephson Tunnel Junctions (CAJTJs) which are the natural generalization of the circular annular Josephson tunnel junctions, have a rich nonlinear phenomenology due to the intrinsic non-uniformity of their planar tunnel barrier delimited by two closely spaced confocal ellipses. In the presence of a uniform magnetic field in the barrier plane, the periodically changing width of the elliptical annulus generates a asymmetric double-well for a Josephson vortex trapped in a long and narrow CAJTJ. The preparation and readout of the vortex pinned in one of the two potential minima, which are important for the possible realization of a vortex qubit, have been numerically and experimentally investigated for CAJTJs with the moderate aspect ratio 2:1. In this work we focus on the impact of the annulus eccentricity on the properties of the vortex potential profile and study the depinning mechanism of a fluxon in more eccentric samples with aspect ratio 4:1. We also discuss the effects of the temperature-dependent losses as well as the influence of the current and magnetic noise.