Electron Incidence Angle Research Articles

Improving the suppression of charge movement by porous chromium oxide coating

A chromium trioxide coating was prepared on the surface of electronic ceramics by screen printing, and solid-phase sintering was carried out at 1350 °C. The surface roughness and surface resistance characteristics of composite coatings with different chromium trioxide contents were studied. The analysis results indicate that the average thickness of Cr2O3 coating is about 19.89 μm. The main crystal phase is (Al0.9Cr0.1)2O3. SEM shows that the surface "pores" and surface roughness of the coating change with the content of Cr2O3. AFM shows that when the Cr2O3 content in the coating is 0.0921 mol, the surface roughness changes the most, and the corresponding surface resistivity of Al2O3 insulating ceramics decreases to the lowest, from 1016 Ω to 1012 Ω. An increase in surface roughness can lead to changes in the incidence angle of electrons, reducing the probability of electron surface collision. The lower the surface resistivity, the better the high-voltage breakdown resistance of vacuum ceramic devices, thereby improving the surface flashover performance of ceramics.

Conductance, spin and valley polarizations through 8-Pmmn borophene magnetic barriers

Conductance, spin and valley polarizations through 8-Pmmn borophene barriers in the presence of external Rashba spin–orbit interaction (RSOI) and magnetic field are investigated theoretically. The spin-dependent conductance shows a strong dependence on the direction of the 8-Pmmn borophene barriers, the strength of RSOI and value of the magnetic field strength. For two barriers unlike to one barrier, the spin-dependent conductance exhibits a prominent oscillatory behavior. For the parallel configuration, the dependence of conductance on the magnetic field is more than for the antiparallel configuration. Transmission probability without and with spin rotation decreases drastically with the increase in the value of the magnetic field, so that for sufficiently large magnetic fields, the transmission probability is zero for most electron incidence angles. The size and direction of the spin and valley polarization can be tuned by the strength of RSOI, direction of the 8-Pmmn borophene barriers, size of the magnetic field and type of parallel or antiparallel configuration. In certain conditions, full valley polarization can be achieved in the proposed structure.

Spin-dependent shot noise in 8-Pmmn borophene based-superlattice

The effect of the Rashba spin-orbit interaction on the shot noise, spin/valley polarization in 8-Pmmn borophene-based superlattice are studied theoretically, by applying the transfer-matrix approach. The spin-dependent transmission probability can be easily controlled by the number of superlattice barriers, the strength of the Rashba, and the incident electron angle. The Fano factor without spin rotation as well as with spin rotation shows an oscillatory pattern versus the strength of the Rashba, and the oscillatory behavior becomes more pronounced as the number of barriers increases. Also, the Fano factor shows a strong dependence on the superlattice direction and number of barriers. The spin and valley polarizations can be easily controlled by the number of barriers and the direction of superlattice. Our findings in this work could provide useful for valleytronics/spintronics systems based on the 8-Pmmn borophene.

Andreev reflection in hybrid [formula omitted] lattices junction

We explore local Andreev reflection and crossed Andreev reflection in a normal metal (N)–superconductor (S)–normal metal (N) hybrid junction based on the α−T3 lattice. Initially, both the left and right sections feature dice lattice structures (α=1). We compute probabilities for electron reflection, local Andreev reflection, electron transmission, and crossed Andreev reflection, as well as local conductance, electron transmission conductance, and crossed Andreev reflection conductance. Subsequently, we analyze structures with the left side featuring dice lattice and the right side graphene (α=0), as well as the reverse configuration. Our findings reveal that crossed Andreev reflections are more prevalent in the graphene–superconductor–dice lattice (GSD) junction, particularly with moderate superconducting region lengths, larger electron incidence angles, and lower electron incidence energy.

Crystallographic rotation effect on the particle and spin across a half metal/semiconductor junction with Dresselhaus spin-orbit interaction

Theoretical studies were conducted on probability, conductance and spin polarization through a junction between a half metal (HM)/semiconductor with Dresselhaus spin-orbit coupling (DSOC), using the scattering theory and the continuous model in a two-dimensional system. The focus was on how the bulk orientation of the DSOC affects the charge and spin polarization. Results showed that the crystal face (100) makes a negative perpendicular to the normal wave vector of the system, resulting in a maximum value of the conductance spectrum and the spin polarization. However, the maximum value of the spin polarization can occur with any crystallographic orientation when the applied voltage reaches the crossing point of the DSOC. Moreover, the electron incident angle injection can cause a gap between in the transmission probability with spin up and spin down, corresponding to higher charge and spin polarization across the junction.

A comprehensive open-access database of electron backscattering coefficients for energies ranging from 0.1KeV to 15MeV.

The characterization of electron backscattering is essential in medical physics for accurately assessing dose deposited around inhomogeneities where backscattering alters the spatial energy distribution pattern and for determining Monte-Carlo code's ability to effectively describe electron scattering and does calculation in a target volume. Recent machine learning advances have provided physicists with powerful tools for effectively extracting information and trends from extensive experiment observations if sufficiently sizeable datasets are available for data mining. We report on the development of a publicly accessible database on electron backscattering coefficients for solid targets. The first database on electron-solid interactions was assembled in 1995. Data for bulk materials, limited to normal incidence and energies up to 100keV, were primarily focusing on electron microscopy. To accommodate broad high-energy applications and include the most recent publications we have created a comprehensive database of electron backscattering coefficients, listed as a function of target atomic number and thickness, electron energy, and incidence angle. These additions resulted in a database of 3566 data points, compared to the previous database of 1430. The data collection includes only published experimental observations (no calculations or results fitting) with no attempt to judge their accuracy or quality. A limited number of data points were compared to recently published Monte-Carlo results. The presented database provides values of electron backscattering coefficients for 50 elements and 19 compounds at electron energies ranging from 0.1keV to 15MeV, presented in ASCII files. Each file contains the electron energy and backscattering coefficient with target thickness or electron incidence angle included where available, and the reference number shown in the last column. Additionally, the presented data were shown in the graphs for better visualization. The online database can be accessed from the website https://doi.org/10.5281/zenodo.7810951. The database provides the most up-to-date source of experimentally obtained electron backscattering coefficients that can be used in theoretical and MC calculations and modeling validations. The data availability is still very limited for many solids and almost non-existent for compounds. Novel machine learning methods should be well adapted to predict these unknown values for various targets, thicknesses, energies, and incident angles utilizing the presented cleaned dataset.

Effect of the Rashba interaction on the tunneling time and Hartman effect in an 8-Pmmn borophene superlattice

The spin-dependent group delay time and Hartman effect as well as the valley/spin polarization in an 8-Pmmn borophene superlattice under Rashba interaction are investigated theoretically, by using the stationary phase and the transfer matrix approaches. The group delay time depends on the spin degree of freedoms, and can be effectively controlled by changing the direction of superlattice, incident electron angle and Rashba strength. Both the valley and spin polarization reveal a strong dependence on the number of the superlattice barriers. Furthermore, group delay time oscillates as the width of the potential barriers increases, but in special conditions, the dependence on the width of the potential barriers will disappear. Interestingly, by increasing the angle of the direction of the superlattice the Hartman effect can be observed for most electron incidence angles. Our study show that, the 8-Pmmn borophene superlattice can be useful for future electronics and spintronics applications.

Spin-valley-dependent transport in a monolayer MoS2 under strain and time-oscillating potential

The effect of the external strain and time-periodic potential on the spin/valley transmission probability are studied theoretically in the monolayer MoS2. It is found that, the probability of transmission shows oscillatory pattern with strain strength. Also, the probability of transmission strongly depends on the direction of the strain, incident electron angle, amplitude of the oscillating potential, and sideband orders. By increasing the order of the sideband, the transmission probability decreases. Therefore, the higher order of the sidebands have a smaller contribution to the probability of transmission. Remarkably, when the time-dependent potential is applied to the monolayer MoS2 under armchair direction strain, unlike the strain in the zigzag direction, the transmission probability will be an even function in terms of the incident electron angle. Our results provides a new structure, which can be useful to future spintronic, valleytronic and electronic devices.

Comment on "Spin- and angle-resolved inverse photoemission setup with spin orientation independent from electron incidence angle" [Rev. Sci. Instrum. 93, 093904 (2022)

The paper under discussion promises a spin- and angle-resolved inverse-photoemission (IPE) setup, where the spin-polarization direction of the electron beam used for excitation "can be tuned to any preferred direction" while "preserving the parallel beam condition." We support the idea to improve IPE setups by introducing a three-dimensional spin-polarization rotator, but we put the presented results to the test by comparing them with the literature results obtained by existing setups. Based on this comparison, we conclude that the presented proof-of-principle experiments miss the target in several aspects. Most importantly, the key experiment of tuning the spin-polarization direction under otherwise allegedly identical experimental conditions causes changes in the IPE spectra that are in conflict with existing experimental results and basic quantum-mechanical considerations. We propose experimental test measurements to identify and overcome the shortcomings.

Response to "Comment on 'Spin- and angle-resolved inverse photoemission setup with spin orientation independent from electron incidence angle'" [Rev. Sci. Instrum. 93, 093904 (2022)

We reply to the Comment by Donath et al. on our setup, which allows a total 3D control of the polarization direction of the electron beam in an inverse photoemission spectroscopy (IPES) experiment, a significant advance with respect to previous setups with partial polarization control. Donath et al. claim an incorrect operation of our setup after comparing their results, treated to enhance the spin asymmetry, with our spectra without the same treatment. They also equal spectra backgrounds instead of equaling peak intensities above the background. Thus, we compare our Cu(001) and Au(111) results with the literature. We reproduce previous results, including spin-up/spin-down spectral differences observed for Au and not observed for Cu. Also, spin-up/spin-down spectral differences appear at the expected reciprocal space regions. In the Comment, it is also stated that our tuning of the spin polarization misses the target because the spectra background changes when tuning the spin. We argue that the background change is irrelevant to IPES since the information is contained in peaks produced by primary electrons, those having conserved their energy in the inverse photoemission process. Second, our experiments agree with previous results from Donath et al. [Wissing et al., New J. Phys. 15, 105001 (2013)] and with a zero-order quantum-mechanical model of spins in vacuum. Deviations are explained by more realistic descriptions including the spin transmission through an interface. Consequently, the operation of our original setup is fully demonstrated. Our development corresponds to "the promising and rewarding angle-resolved IPES setup with the three-dimensional spin resolution," as indicated in the Comment, after our work.

Extreme Ultraviolet Lighting Using Carbon Nanotube-Based Cold Cathode Electron Beam.

Laser-based plasma studies that apply photons to extreme ultraviolet (EUV) generation are actively being conducted, and studies by direct electron irradiation on Sn for EUV lighting have rarely been attempted. Here, we demonstrate a novel method of EUV generation by irradiating Sn with electrons emitted from a carbon nanotube (CNT)-based cold cathode electron beam (C-beam). Unlike a single laser source, electrons emitted from about 12,700 CNT emitters irradiated the Sn surface to generate EUV and control its intensity. EUV light generated by direct irradiation of electrons was verified using a photodiode equipped with a 150 nm thick Zr filter and patterning of polymethyl methacrylate (PMMA) photoresist. EUV generated with an input power of 6 W is sufficient to react the PMMA with exposure of 30 s. EUV intensity changes according to the anode voltage, current, and electron incident angle. The area reaching the Sn and penetration depth of electrons are easily adjusted. This method could be the cornerstone for advanced lithography for semiconductor fabrication and high-resolution photonics.

Electron tunneling through HgTe/CdTe quantum wells with all-electrical superlattice structures

We theoretical investigate the electron transport through HgTe/CdTe quantum wells (QWs) heterostructure interfaces with periodic electrical potential modulations in this work. We find Fabry–Pérot resonant tunneling with perfect transmission through a two dimensional topological insulator superlattice structure in HgTe/CdTe QWs, which is supposed to be experimentally observable. This unique feature indicates potential applications of Fabry–Pérot interferometers device. The transport properties of electrons tunneling through the superlattice structures can be adjusted by tuning the Fermi energy, electron incident angle, the electrical modulation numbers and modulation amplitude. We also find the enhanced Fabry–Pérot resonance tunneling due to the electric-induced Rashba spin–orbit interaction (RSOI). This all-electrical mechanism may pave a realistic way to control the electron transport in two dimension topological insulator from a device application perspective.

Spin- and angle-resolved inverse photoemission setup with spin orientation independent from electron incidence angle.

A new spin- and angle-resolved inverse photoemission setup with a low-energy electron source is presented. The spin-polarized electron source, with a compact design, can decouple the spin polarization vector from the electron beam propagation vector, allowing one to explore any spin orientation at any wavevector in angle-resolved inverse photoemission. The beam polarization can be tuned to any preferred direction with a shielded electron optical system, preserving the parallel beam condition. We demonstrate the performances of the setup by measurements on Cu(001) and Au(111). We estimate the energy resolution of the overall system at room temperature to be ∼170meV from kBTeff of a Cu(001) Fermi level, allowing a direct comparison to photoemission. The spin-resolved operation of the setup has been demonstrated by measuring the Rashba splitting of the Au(111) Shockley surface state. The effective polarization of the electron beam is P = 30% ± 3%, and the wavevector resolution is ΔkF ≲ 0.06 Å-1. Measurements on the Au(111) surface state demonstrate how the electron beam polarization direction can be tuned in the three spatial dimensions. The maximum of the spin asymmetry is reached when the electron beam polarization is aligned with the in-plane spin polarization of the Au(111) surface state.

Conductance and shot noise in a silicene-based superconducting superlattice with two ferromagnetic electrodes

Using the scattering matrix method and the Blonder–Tinkham–Klapwijk formalism, we theoretically study the transport properties and the shot noise in a silicene-based superconducting superlattice (SCSL) with two ferromagnetic electrodes . It is found that for the antiparallel (AP) magnetization configuration, the crossed Andreev reflection (CAR) probability for spin-up electron from the K valley shows the nearly perfect transmission peak at the superconducting energy gap. With increasing the exchange splitting energy, the transmission probabilities of the elastic cotunneling and CAR processes for spin-up electron from the K valley around zero incident angle show the valley–peak–valley transitions. For the AP magnetization configuration, the local Fano factor shows the super-Poissonian value and the nonlocal Fano factor forms a Poissonian value plateau with weak oscillation within a suitable parameter regime. Compared to the local Fano factor, the nonlocal Fano factor is always sub-Poissonian for the parallel magnetization configuration, but for the AP magnetization configuration its maximum value increases and becomes super-Poissonian as the number of layers in the SCSL increases. • The crossed Andreev reflection probability shows nearly perfect transmission peak. • The transmission probabilities are symmetric about the incident angle of electron. • The super-Poissonian Fano factor is found. • The Poissonian value plateaus of the local and nonlocal Fano factors are formed. • The energy range with pure crossed Andreev reflection is robust to layer number.

Strain-modulated anisotropic Andreev reflection in a graphene-based superconducting junction

We investigate the Andreev reflection across a uniaxial strained graphene-based superconducting junction. Compared with pristine graphene-based superconducting junction, three opposite properties are found. Firstly, in the regime of the interband conversion of electron–hole, the Andreev retro-reflection happens. Secondly, in the regime of the intraband conversion of electron–hole, the specular Andreev reflection happens. Thirdly, the perfect Andreev reflection, electron–hole conversion with unit efficiency, happens at a nonzero incident angle of electron. These three exotic properties arise from the strain-induced anisotropic band structure of graphene, which breaks up the original relation between the direction of velocity of particle and the direction of the corresponding wavevector. Our finding gives an insight into the understanding of Andreev reflection and provides an alternative method to modulate the Andreev reflection.

Rashba-split image-potential state and unoccupied surface electronic structure of Re(0001)

The influence of spin-orbit interaction on the unoccupied electronic structure of the Re(0001) surface is investigated by spin- and angle-resolved inverse photoemission and density-functional theory calculations. In the two high-symmetry azimuths $\overline{\mathrm{\ensuremath{\Gamma}}}\phantom{\rule{0.16em}{0ex}}\overline{\text{K}}$ and $\overline{\mathrm{\ensuremath{\Gamma}}}\phantom{\rule{0.16em}{0ex}}\overline{\text{M}}$, we identify transitions into $d$-derived bulk states as well as different types of surface states. The Rashba-type spin-split hole pocket around $\overline{\mathrm{\ensuremath{\Gamma}}}$ finds continuation in empty spin-split surface states for higher ${\mathbf{k}}_{\ensuremath{\parallel}}$, thereby forming $\mathsf{W}$-shaped states whose lower parts are partially occupied. A large energy gap below and above the vacuum energy around $\overline{\mathrm{\ensuremath{\Gamma}}}$ hosts image-potential-induced surface states. The $n=1$ member of the Rydberg-like series exhibits a free-electron-like $E({\mathbf{k}}_{\ensuremath{\parallel}})$ dispersion with an effective mass of ${m}^{*}/{m}_{e}=1.2\ifmmode\pm\else\textpm\fi{}0.1$. Careful spin-resolved measurements for several angles of electron incidence allow us to detect Rashba-type spin-dependent energy splittings of this state with a Rashba parameter of ${\ensuremath{\alpha}}_{\text{R}}=105\ifmmode\pm\else\textpm\fi{}33\phantom{\rule{0.16em}{0ex}}\text{meV}\phantom{\rule{0.16em}{0ex}}\AA{}$.

A reconfigurable narrow and wide band multi bias graphene based THz absorber

A three layers graphene-based THz absorber composed of multi-bias graphene ribbons is presented. The structure is described using equivalent circuit model and design methodology is developed via impedance matching concept. Also, relatively heavy optimization is utilized to obtain two sets of chemical potential values. Two operational behaviors are expressed corresponding to each bias set. Leveraging both equivalent circuit representation and impedance matching concept, the proposed structure is able to show both narrow multi band and wide band absorption over 0.1 THz to 5 THz frequency range. The first mode of operation can perfectly absorb THz incident waves in 0.5 THz, 1.4 THz, 2.35 THz, 3.23 THz and 4.11 THz while the second mode of operation absorbs THz incident waves between 0.5 THz to 2.5 THz as wide band response. Additionally, to investigate device dependency against geometrical parameters, electron relaxation time, chemical potentials and incident angle, ample simulations are reported for both modes of operations. Achieving both multi band and wide band absorption via a unique structure, makes the proposed device an ideal candidate to be used in optical systems and sensors for medical imaging, indoor communications and security.

Super-Klein tunneling and electron-beam collimation in the honeycomb superlattice

The honeycomb superlattice model from the nearly commensurate charge-density-wave phase of $1\mathrm{T}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ has been shown to host multiple robust flat bands that depends on the number $(m)$ of extra atoms residing on each edge of the hexagon [Lee et al., Phys. Rev. Lett. 124, 137002 (2020)]. In this work we numerically study the transport phenomenon of the single-valley Dirac electrons around the band center $E=0$ where a flat band crosses. A super-Klein tunneling (SKT) phenomenon is found for $m=1$ that the Dirac electrons can tunnel through a rectangle barrier with a unity transmission irrespective of the incident angle of electrons. For the case of $m=3$, a super electron-beam collimation instead of the SKT phenomenon is identified that the Dirac electrons are allowed to tunnel through the barrier only within nearly zero incident angle, and such perpendicular transmission probability is optimal in the low-energy regime but suppressed in the high-energy regime.

Effect of Differences in Insert Materials of Cutout Block on Dose Distribution in Electron Radiotherapy: Comparison between Measurements and Monte Carlo Simulation

In electron beam radiotherapy, an irradiation field is created with a cutout block using a low melting point lead alloy. The block can be replaced with a lead plate as a shield. Dose distribution is expected to be affected by differences in the material and thickness of the shield. Thus, this study aimed to investigate the cause of differences in dose distribution by reproducing the electron beam irradiation condition via Monte Carlo simulation, comparing dose distribution when each shield is used and analyzing energy fluence distribution. Radiation interaction in the treatment device manufactured by Varian was assessed using the general-purpose simulation code, and the dose distribution in the water was calculated. Electron energy fluence and incident angle of the electron fluence incident on the water surface were analyzed, and the effect of the difference in the shield was investigated in the irradiation field limited to 3 cm or less. Regarding dose distribution, the deviation in the buildup area became larger when the lead plate was made thinner. A difference of 1.6-6.8% was observed on an average when comparing the buildup region of depth dose distributions except for 1×1 cm2 field. In electron energy fluence, the lower the lead thickness, the higher the low energy component, which affected the buildup region. The effect was greater as the electron beam energy increased. It was possible to evaluate the difference in scattered radiation between the low melting point lead alloy and the lead plate by MC simulation. Based on the study findings, the effect of scattered electrons generated from the block was strong as a factor.

Atypical secondary electron emission yield curves of very thin SiO2 layers: Experiments and modeling

The secondary electron emission phenomenon often refers to the emission of electrons as a result of the interaction of impinging energetic electrons with the surface of a material. Although it is fairly well described for metals, with a typical shape of the total electron emission yield (TEEY) first increasing to reach a maximum and then decreasing along with the energy increase in the primary electrons, there is still a lack of data and detailed analysis for dielectrics, in particular thin layers. The present work proposes a new insight into the electron emission phenomenon from very thin dielectric layers. It reports on the TEEY from very thin SiO2 layers, less than 100 nm. It is found that a departure from the typical shape of the TEEY curve occurs for primary electrons with energy of around 1 keV. The TEEY curve presents a dip, a local minimum that might be as deep as below 1. This atypical shape depends substantially on the layer thickness. The measured TEEY is compared to an electron emission 1D-model in which we consider the combined effect of the space-charge electric field induced by trapped charges in the dielectric layer and of the processes of field-dependent conductivity and radiation-induced conductivity on the fate of secondary electrons. Those mechanisms govern the charge transport in the dielectric and, consequently, the electron emission. The effects of the SiO2 layer thickness, an incidence angle of the primary electrons, and an applied external electric field on the TEEY curves are reported.