Extracting the effective mass of fewer layers 2D h-BN nanosheets using the Fowler-Nordheim tunneling model

Hexagonal boron nitride(h-BN)is found to have widespread application,owing to its outstanding properties,including gate dielectrics,passivation layers,and tunneling layers.The current studies on the funda⁃mental physical properties of these ultrathin h-BN films and the electron tunneling effect among them are inade⁃quate.In this work,the effective mass in h-BN was successfully determined through a combined approach of ex⁃perimental and theoretical research methods by fitting the current-voltage curves of metal/insulator/metal struc⁃tures.It was observed that within a range of 4-22 layers,the effective mass of h-BN exhibits a monotonic de⁃crease with an increase in the number of layers.The physical parameters of the Fowler-Nordheim tunneling model in the context of electron tunneling in h-BN are precisely ascertained by utilizing the extracted effective mass.Ad⁃ditionally,the impact of fixed charges at the metal/h-BN interface and various metal electrode types on FowlerNordheim tunneling within this structure is investigated utilizing this physical parameter in Sentaurus TCAD soft⁃ware.This work is informative and instructive in promoting applications in the fields of h-BN related infrared physics and technology.

Capturing CO2 Emissions in the George C. Wallace Tunnel: A Case Study

This paper describes the design of a ventilation system to be paired with a carbon capture system. The ventilation system utilizes the geometry of the George C. Wallace tunnel, located in the City of Mobile, Alabama, USA to capture and redirect emissions to a direct air capture (DAC) device to sequester 25% of the total CO2 mass generated from inside the tunnel. The total CO2 mass rate for the westbound traffic between the week-day hours of 7 a.m. and 6 p.m. has been estimated between 2,300 to 3,000 lbs./hr. By sequestering these emissions, the overall surrounding air quality was shown to be improved to a level that mirrors that from the pre-US industrial era of 270 ppm.

Geomechanics model test and numerical simulation of 2G-NPR bolt support effect in an active fault tunnel

Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel.In this paper,the grade IV rock surrounding the cross-fault tunnel with poor geological conditions has been chosen for the study.The support capacity of 2^(nd) Generation-Negative Poisson’s Ratio(2G-NPR)bolt in an active fault tunnel has been carried out on the basis of relevant results obtained from the geomechanical model test and numerical investigations of failure model for existing unsupported fault tunnel.The investigation shows that surrounding rock of the tunnel is prone to shear deformation and crack formation along the fault,as a result,the rock mass on the upper part of the fault slips as a whole.Furthermore,small-scale deformation and loss of blocks are observed around the tunnel;however,the 2G-NPR bolt support is found to be helpful in keeping the overall tunnel intact without any damage and instability.Due to the blocking effect of fault,the stress of the surrounding rock on the upper and lower parts of the fault is significantly different,and the stress at the left shoulder of the tunnel is greater than that at the right shoulder.The asymmetrical arrangement of 2G-NPR bolts can effectively control the asymmetric deformation and instability of the surrounding rock.The present numerical scheme is in good agreement with the model test results,and can reasonably reflect the stress and displacement characteristics of the surrounding rock of the tunnel.In comparison to unsupported and ordinary PR(Poisson’s Ratio)bolt support,2G-NPR bolt can effectively limit the fault slip and control the stability of the surrounding rock of the fault tunnel.The research findings may serve as a guideline for the use of 2G-NPR bolts in fault tunnel support engineering.

Possible Nodeless Superconducting Gaps in Bi_2Sr_2CaCu_2O_(8+δ) and YBa_2Cu_3O_(7-x) Revealed by Cross-Sectional Scanning Tunneling Spectroscopy

Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/spectroscopy, we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi2Sr2CaCu2O8＋δ （Bi2212） and YBa2Cu3O7-x （YBCO） along their c-axes on a scale shorter than the interlayer spacing. By tunneling into the （100） plane of a Bi2212 single crystal and a YBCO film, we observe both U-shaped tunneling spectra with extended fiat zero-conductance bottoms, and V-shaped gap structures, in different regions of each sample. On the YBCO film, tunneling into a （110） surface only reveals a U-shaped gap without any zero-bias peak. Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap. The V-shaped gap has a very small amplitude, and is likely proximity-induced by regions having the larger U-shaped gap.

Electronic structures of new tunnel barrier spinel MgAl_2O_4:first-principles calculations

The electronic structures of spinel MgAl 2 O 4 and MgOtunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are found for the MgAl 2 O 4 and MgO tunneling barriers. The calculated direct energy gaps at the Γ-point are about 5.10 eV for MgAl 2 O 4 and 4.81 eV for MgO, respectively. Because of the similar feature in band structures from Γ high-symmetry point to F point ( band), the coherent tunneling effect might be expected to appear in MgAl 2 O 4-based MTJs like in MgO-based MTJs. The small difference of the surface free energies of Fe (2.9 J m 2 ) and MgAl 2 O 4 (2.27 J m 2 ) on the {100} orientation, and the smaller lattice mismatch between MgAl 2 O 4 and ferromagnetic electrodes than that between MgO and ferromagnetic electrodes, the spinel MgAl 2 O 4 can substitute MgO to fabricate the coherent tunneling and chemically stable magnetic tunnel junction structures, which will be applied in the next generation read heads or spintronic devices.

Effect of SiO_(2) Aerogel-cement Mortar Coating on Strength of Self-Compacting Concrete after Simulated Tunnel Fire

In order to facilitate self-compacting concrete to be better used in tunnel linings that can resist fires,a SiO_(2) aerogel-cement mortar coating was prepared.Based on the HC curve,a self compacting concrete cube specimens coated and uncoated with SiO_(2) aerogel-cement mortar(SiO_(2)-ACM)were heated to simulate tunnel fire for 0.5,1,1.5,2,2.5,3 and 4 h,respectively.The residual compressive strength was tested after the specimens were cooled to room temperature by natural cooling and water cooling.The results show that,the damages of specimens become more serious as fire time goes on,but the residual strength of specimens coated with SiO_(2)-ACM is always higher than that of uncoated with SiO_(2)-ACM.In addition,the residual strength of specimens cooled by water cooling is lower than that of natural cooling.However,for the specimens coated with SiO_(2)-ACM,the adverse effects of water cooling are lessened.With the increase of fire time,the protective effect of SiO_(2)-ACM is still gradually improved.Finally,a formula was established to predict the residual 150 mm cube compressive strength of specimens protected by SiO_(2)-ACM after a simulated tunnel fire.

Image charge effect on the light emission of rutile TiO2(110) induced by a scanning tunneling microscope

The plasmon-enhanced light emission of rutile TiO2（110） surface has been investigated by a low-temperature scanning tunneling microscope （STM）. We found that the photon emission arises from the inelastic electron tunneling between the STM tip and the conduction band or defect states of TiO2（110）. In contrast to the Au（111） surface, the maximum photon energy as a function of the bias voltage clearly deviates from the linear scaling behavior, suggesting the non-negligible effect of the STM tip on the band structure of TiO2. By performing differential conductance （dl/dV） measurements, it was revealed that such a deviation is not related to the tip-induced band bending, but is attributed to the image charge effect of the metal tip, which significantly shifts the band edges of the TiO2（110） towards the Femi level （EF） during the tunneling process. This work not only sheds new lights onto the understanding of plasmon-enhanced light emission of semiconductor surfaces, but also opens up a new avenue for engineering the plasmon-mediated interfacial charge transfer in molecular and semiconducting materials.

Anisotropic refraction and valley-spin-dependent anomalous Klein tunneling in a 1T'-MoS_(2)-based p–n junction

We investigate the transport properties of electron in a 1T'-MoS_(2)-based p–n junction.The anisotropic refraction of electron is found when the electron beam crosses the p–n junction,which brings the phenomenon of valley splitting without any external fields.Moreover,it is found that the valley-spin-dependent anomalous Klein tunneling,i.e.,the perfect transmission exists at a nonzero incident angle of valley-spin-dependent electron,happens when the vertical electric field is equal to the critical electric field.These two peculiar properties arise from the same reason that the tilted band structure makes the directions of wavevector and velocity different.Our work designs a special valley splitter without any external fields and finds a new type of Klein tunneling.

Tunneling Conductance in d_(x^2-y^2)+id_(xy) Mixed Wave Superconductor Graphene Junctions

Using the extended Blonder-Tinkham-Klapwijk formalism, we investigate the conductance spectra of normal metal/dx2-y2 ＋ idxy mixed wave superconductor graphene junctions. It is found that the conductance spectra vary strongly with the orientation of the gap and the amplitude ratio （Δ1/Δ0） of two components for dx2-y2 ＋ idxy mixed wave. The zero bias conductance is nearly 2 and the conductance peak vanishes in doped graphene for a = 0 and Δ1/Δ0 = 1. The conductance increases with increasing the amplitude ratio of two components for α =π/4 and Δ1/Δ0 -- 1. The ZBCP becomes observable wide with 1 〈 EF/Δ0 〈 100 for α= π/4 and Δ1/Δ0 = 1. This property is different from that in normal metal/dx2-y2 wave superconductor graphene junctions.

Tunneling conductance in quantum wire/insulator/d_(x2-y2) + id_(xy) mixed wave superconductor junctions

Using the extended Blonder-Tinkham-Klapwijk （BTK） theory, this paper calculates the tunnelling conductance in quantum wire/insulator/dx2-y2 ＋ idly mixed wave superconductor （q/I/dx2-y2 ＋ idly） junctions. That is different from the case in d- and p-wave superconductor junctions. When the angle α between a-axis of the dx2-y2 wave superconductor and the interface normal is π/4, there follows a rather distinctive tunnelling conductance. The zero-bias conductance peak （ZBCP） may or may not appear in the tunnelling conductance. Both the interface potential z and the quasi-particle lifetime factor F are smaller, there is no ZBCP. Otherwise, the ZBCP will appear. The position of bias conductance peak （BCP） depends strongly on the amplitude ratio of two components for dx2-y2 ＋ idxy mixed wave. The low and narrow ZBCP may coexist with the BCP in the tunnelling conductance. Using those features in the tunnelling conductance of q/I/dx2-y2 ＋ idxy junctions, it can distinguish dx2-y2 ＋ idxy mixed wave superconductor from d- and p-wave one.

Intrinsic tunneling study of underdoped Bi_2Sr_(2-x)La_xCuO_(6+δ) superconductors

We report on a tunneling study of underdoped submicron Bi2Sr2_xLasCuO_6＋δ （La-Bi2201） intrinsic Josephson junctions （IJJs）, whose self-heating is sufficiently suppressed. The tunneling spectra are measured from 4.2 K up to the pseudogap opening temperature of T＊ = 260 K. The gap value found from the spectral peak position is about 35 meV and has a weak temperature dependence both below and above the superconducting transition temperature of Tc = 29 K. Since the superconducting gap should have a value of 10-15 meV, our results indicate that the pseudogap （～35 meV） plays an important role in the underdoped La-Bi2201 intrinsic tunneling spectroscopy down to the lowest temperature of 4.2 K. However, the contribution of the superconducting gap can be separated by normalizing the spectra to the one near and above Tc, which shows that the IJJs can be a useful tool for the study of the electronic properties of the La-Bi2201 cuprate superconductors.

MoS_(2)/Si tunnel diodes based on comprehensive transfer technique

Due to the pristine interface of the 2D/3D face-tunneling heterostructure with an ultra-sharp doping profile, the 2D/3D tunneling field-effect transistor(TFET) is considered as one of the most promising low-power devices that can simultaneously obtain low off-state current(IOFF), high on-state current(ION) and steep subthreshold swing(SS). As a key element for the 2D/3D TFET, the intensive exploration of the tunnel diode based on the 2D/3D heterostructure is in urgent need.The transfer technique composed of the exfoliation and the release process is currently the most common approach to fabricating the 2D/3D heterostructures. However, the well-established transfer technique of the 2D materials is still unavailable.Only a small part of the irregular films can usually be obtained by mechanical exfoliation, while the choice of the chemical exfoliation may lead to the contamination of the 2D material films by the ions in the chemical etchants. Moreover, the deformation of the 2D material in the transfer process due to its soft nature also leads to the nonuniformity of the transferred film,which is one of the main reasons for the presence of the wrinkles and the stacks in the transferred film. Thus, the large-scale fabrication of the high-quality 2D/3D tunnel diodes is limited. In this article, a comprehensive transfer technique that can mend up the shortages mentioned above with the aid of the water and the thermal release tape(TRT) is proposed. Based on the method we proposed, the MoS_(2)/Si tunnel diode is experimentally demonstrated and the transferred monolayer MoS_(2) film with the relatively high crystal quality is confirmed by atomic force microscopy(AFM), scanning electron microscopy(SEM), and Raman characterizations. Besides, the prominent negative differential resistance(NDR) effect is observed at room temperature, which verifies the relatively high quality of the MoS_(2)/Si heterojunction. The bilayer MoS_(2)/Si tunnel diode is also experimentally fabricated by repeating the transfer process we proposed, followed by the specific analysis of the electrical characteristics. This study shows the advantages of the transfer technique we proposed and indicates the great application foreground of the fabricated 2D/3D heterostructure for ultralow-power tunneling devices.

Activated dissociation of H_(2) on the Cu(001)surface:The role of quantum tunneling

The activation and dissociation of hydrogen molecules(H_(2))on the Cu(001)surface are studied theoretically.Using first-principles calculations,the activation barrier for the dissociation of H_(2) on Cu(001)is determined to be~0.59 eV in height.It is found that the electron transfer from the copper substrate to H_(2) plays a key role in the activation and breaking of the H–H bond,and the formation of the Cu–H bonds.Two stationary states are identified at around the critical height of bond breaking,corresponding to the molecular and the dissociative states,respectively.Using the transfer matrix method,we also investigate the role of quantum tunneling in the dissociation process along the minimum energy pathway(MEP),which is found to be significant at or below room temperature.At a given temperature,the tunneling contributions due to the translational and the vibrational motions of H_(2) are quantified for the dissociation process.Within a wide range of temperature,the effects of quantum tunneling on the effective barriers of dissociation and the rate constants are observed.The deduced energetic parameters associated with the thermal equilibrium and non-equilibrium(molecular beam)conditions are comparable to experimental data.In the low-temperature region,the crossover from classical to quantum regime is identified.

Tunneling via surface dislocation in W/β-Ga_(2)O_(3) Schottky barrier diodes

In this work,W/β-Ga_(2)O_(3)Schottky barrier diodes,prepared using a confined magnetic field-based sputtering method,were analyzed at different operation temperatures.Firstly,Schottky barrier height increased with increasing temperature from 100 to 300 K and reached 1.03 eV at room temperature.The ideality factor decreased with increasing temperature and it was higher than 2 at 100 K.This apparent high value was related to the tunneling effect.Secondly,the series and on-resistances decreased with increasing operation temperature.Finally,the interfacial dislocation was extracted from the tunneling current.A high dislocation density was found,which indicates the domination of tunneling through dislocation in the transport mecha-nism.These findings are evidently helpful in designing better performance devices.

Bilateral carpal tunnel syndrome and motor dysfunction caused by gout and type 2 diabetes:A case report

BACKGROUND Carpal tunnel syndrome(CTS)has been associated with gout and type 2 diabetes mellitus(T2DM).However,due to insufficient clinical understanding of goutrelated CTS and reliance on the diagnostic importance of elevated serum uric acid levels,such cases are prone to missed diagnosis,misdiagnosis,and delayed treatment.In addition,the effect of T2DM on gout-induced carpal tunnel syndrome has not been reported.CASE SUMMARY Herein,we present an unusual case of CTS and motor dysfunction caused by miliary tophaceous gout and T2DM.The patient presented to the hand and foot clinic with paresthesia of the fingers of both hands,especially at night.The patient was diagnosed with type 2 diabetes a month ago.Ultrasonography revealed bilateral transverse carpal ligament thickening with median nerve compression during hospitalization.The patient was successfully treated with carpal tunnel decompression and tendon release.The postoperative pathological examination revealed typical gout nodules.This case suggests that the presence of T2DM could accelerate tophi formation and worsen CTS symptoms,although no definitive proof in this regard has been described previously.CONCLUSION Tophi formation may most likely cause the co-occurrence of CTS and flexor dysfunction in gout and incipient diabetes patients.

Tunneling spectra of underdoped Bi_2Sr_2Ca_(1-x)Y_xCu_2O_(8+δ) intrinsic Josephson junctions

Mesa-structured submicron intrinsic Josephson junctions are successfully fabricated and well characterized on underdoped Bi2Sr2Ca1-xYxCu2O8＋δ single crystals with a Tc of 80 K. Tunneling spectra at the temperatures ranging from 4.2 K to 295 K are measured. A pulse technique is used to reduce sample heating for the measurement near pseudogap opening temperature T^＊ - 280 K. Our experimental results show that the superconducting gap, the peakdip separation, and the pseudogap opening temperature are all increased as compared with those from near optimally doped samples, which requires further theoretical analysis in the future.

Molecular Beam Epitaxy Growth and Scanning Tunneling Microscopy Study of Pyrite CuSe2 Films on SrTiO3

We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide （CuSe2 ） films on SrTiO3 （001）. Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski-Krastanov （layer-plus-island） mode with a preferential orientation of （111）. Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures 2 ×√3 and √x ×√3-R30°. The Cu termi- nation is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films.

Research on Tunneling Techniques in Virtual Private Networks

It is a trend of virtual private networks (VPNs) to be used for information exchange between enterprises, branches of enterprises and enterprises and their employees instead of traditional dial networks and leased lines. The tunneling technique is the key technique to implement VPN. In this paper, with the VPN implementation requirements in mind, we perform a comparative research on the existing tunneling protocols including GRE, L2TP, IPSec and IP/IP. We also propose an integrated scheme of tunneling mechanism that supports VPN under the current condition.

Nano-buffer controlled electron tunneling to regulate heterojunctional interface emission

Interface emission from heterojunction is a shortcoming for electroluminescent devices.A buffer layer introduced in the heterojunctional interfaces is a potential solution for the challenge.However,the dynamics for carrier tunneling to control the interface emission is still a mystery.Herein,the low-refractive HfO_(2)with a proper energy band configuration is em-ployed as the buffer layer in achieving ZnO-microwire/HfO_(2)/GaN heterojunctional light-emitting diodes(LEDs).The optic-ally pumped lasing threshold and lifetime of the ZnO microwire are reduced with the introduced HfO_(2)layer.As a result,the interface emission is of blue-shift from visible wavelengths to 394 nm whereas the ultraviolet(UV)emission is en-hanced.To regulate the interface recombination between electrons in the conduction band of ZnO and holes in the valence band of GaN,the tunneling electrons with higher conduction band are employed to produce a higher tunneling current through regulation of thin HfO_(2)film causing blue shift and interface emission enhancement.Our results provide a method to control the tunneling electrons in heterojunction for high-performance LEDs.

Wind tunnel tests on aerodynamic characteristics of vehicles on same-storey highway and rail bridge under crosswind

In recent years,the safety and comfort of road vehicles driving on bridges under crosswinds have attracted more attention due to frequent occurrences of wind-induced disasters.This study focuses on a container truck and CRH2 high-speed train as research targets.Wind tunnel experiments are performed to investigate shielding effects of trains on aerodynamic characteristics of trucks.The results show that aerodynamic interference between trains and trucks varies with positions of trains(upstream,downstream)and trucks(upwind,downwind)and numbers of trains.To summarize,whether the train is upstream or downstream of tracks has basically no effect on aerodynamic forces,other than moments,of a truck driving on windward sides of bridges(upwind).In contrast,the presence of trains on the bridge deck has a significant impact on aerodynamic characteristics of a truck driving on leeward sides(downwind)at the same time.The best shielding effect on lateral forces of trucks occurs when the train is located downstream of tracks.Finally,the pressure measuring system shows that only lift forces on trains are affected by trucks,while other forces and moments are primarily affected by adjacent trains.