Increasing Incident Energy Research Articles

Light-modulated 8-Pmmn borophene-based pure crossed Andreev reflection

Abstract We investigate the off-resonant circularly polarized light-modulated crossed Andreev reflection in an 8-Pmmn borophene-based normal conductor/superconductor/normal conductor junction. When the signs of Fermi energies in two normal regions are opposite, the pure crossed Andreev reflection without the local Andreev reflection and the elastic cotunneling occurs. By using the Dirac-Bogoliubov-de Gennes equation and the Blonder-Tinkham-Klapwijk formula, the pure crossed Andreev reflection conductance and its oscillation as a function of the junction length and the Fermi energy in the superconducting regions are discussed. It is found that the value of pure crossed Andreev reflection conductance peak value and its corresponding value of light-induced gap increase with the increase of incident energy of electron. Furthermore, the valley splitting for the transmitted hole is found due to the presence of tilted velocity of borophene. Our findings are beneficial for designing the high efficiency 8-Pmmn borophene-based nonlocal transistor and nonlocal valley splitter without local and non-entangled processes.

A DFT study of the CaMg2As2 material for photovoltaic applications

The research focused on investigating the structural, elastic, electronic, optical, and thermoelectric characteristics of the CaMg2As2 compound. To inspect these properties, the density functional theory (DFT) method has been applied via the Wien2K code. The electronic analysis revealed that the CaMg2As2 compound demonstrates semiconductor behavior with an indirect band gap of 1.781 eV. Additionally, its elastic properties were examined, revealing a 1.980 % AVR, indicating a variation in elasticity depending on the direction of load or stress applied. We have also studied various optical properties of CaMg2As2, including the refractive index, extinction coefficient, electron energy loss, dielectric tensor, and optical conductivity. the absorption coefficient value is zero for energy levels below 2.60 eV, meaning there is no energy absorption by the material at lower energy levels. However, as the energy surpasses 2.60 eV, the absorption coefficient increases and shows multiple peaks. This signifies that as the incident radiation's energy increases, the material starts absorbing more energy at specific energy levels. In addition, one significant finding is that the thermal conductivity of the lattice (κL) in CaMg2As2 decreases exponentially as the temperature rises. This means that as the material gets hotter, its ability to conduct heat becomes less effective. In simple terms, the material becomes less efficient at transferring heat at higher temperatures. These findings suggest that CaMg2As2 has potential as a thermoelectric material with interesting properties that deserve further investigation.

A Molecular Dynamics Study on the Defect Formation and Mechanical Behavior of Molybdenum Disulfide under Irradiation.

Due to its appealing characteristics, molybdenum disulfide (MoS2) presents a promising avenue for the exploration of lubrication protection materials in high-energy irradiation scenarios. Herein, we present a comprehensive investigation into the defect behavior of multilayer MoS2 under argon (Ar) atom irradiation leveraging molecular dynamics simulations. We have demonstrated the energy shifts and structural evolution in MoS2 upon irradiation, including the emergence of Frenkel defects and intricate defect clusters. The structural damage exhibits an initial increase followed by a subsequent decrease as the incident kinetic energy increases, ultimately peaking at 2.5 keV. Moreover, we investigated the effect of postannealing on defect recovery and conducted the uniaxial tensile and interlayer shearing simulation in order to provide valuable insights for the defect evolution and its impact on mechanical and tribological properties. Furthermore, we have proposed the optimal annealing temperature. The current study reveals the atomic mechanisms underlying irradiation-induced damage on the structural integrity and mechanical performance of MoS2, thereby providing crucial guidance for its vital application in nuclear reactors and aerospace industries.

Unveiling the interaction regimes between atomic oxygen and amorphous carbon surface depending on incident energy

The chemical reactions between atomic oxygen (AO) and solid surface are particularly crucial for numerous fundamental fields. However, it is lack of clearly understanding the reaction mechanisms between AO and the solid surface because the complex interaction dynamics are extremely difficult to be measured experimentally and to be modelled theoretically. In this work, the reactive molecular dynamics simulations are conducted to fully reveal the interactive mechanisms of AO irradiation on the amorphous carbon surface. As the incident energy (E) increases, our simulations demonstrate three distinct interaction regimes: (I) surface oxidation without carbon removal, (II) surface oxidation accompanied by minor material removals, and (III) continuous material removal. The first critical energy (E1) of ∼3.5 eV as the boundary between regime I and II is related to the dissociative energy of C–C bonds. The second critical energy (E2) of ∼6.5 eV as the boundary between regime II and III corresponds to the largest repulsion energy that the oxidized surface could provide. We further establish a phenomenological model to quantitatively describe how the rebound ratio varies with incident energy and surfacial oxygen density, which not only fit all simulation data perfectly but also give a very precise prediction of E2 value.

Impact of temperature on residual stress and bonding in diamond-like carbon film: A molecular dynamics study under various deposition conditions

Diamond-like carbon (DLC) films exhibit excellent frictional properties; however, the high residual stress within the film, which causes detachment issues, limits their application in mechanical sliding surfaces. We have previously clarified via molecular dynamics (MD) simulations that the growth of sp3 clusters after the transition from sp2 to sp3 bonds during film formation causes the in-plane compressive stress in DLC films. In this study, we investigated whether this stress generation mechanism holds under various deposition conditions in the MD simulations, wherein incident energy, atomic flux, and substrate temperature were systematically changed. The results of the MD simulations consistently revealed that the compressive stress generation mechanism remains unchanged across different deposition conditions. With increasing incident energy and atomic flux and decreasing substrate temperature, in-plane compressive stress in the film increased owing to increased sp3 content. Conversely, when the incident energy was further increased, both stress and sp3 content decreased. Based on a molecular statistical calculation, it was shown that the stable bonding state changed from sp3 to sp2 at high temperatures. Because the temperature monotonically increased with increasing incident energy, it was concluded that the change in the stable bonding state caused the non-monotonic change in the stress and sp3 content at high temperatures.

Molecular dynamics simulation of effect of nickel transition layer on deposition of carbon atoms and graphene growth on cemented carbide surfaces

<sec>WC-Co cemented carbide has excellent cutting performance, which is a potential tool material. But when it is used as cutting ultra-high strength and high hardness materials, the machining accuracy and service life of the tool are significantly reduced. Graphene is a potential coating material for cemented carbide cutting tools due to its excellent mechanical properties. In this work, molecular dynamics (MD) is used to simulate the deposition of nickel transition layer and high-temperature catalytic growth of graphene in cemented carbide. The Ni and C atomic deposition process and the high temperature annealing process are simulated, and a combination of potential functions is adopted to continuously simulate these two deposition processes. The effect of deposition temperature and the effect of incident energy on the growth of graphene are analyzed. The healing mechanism of nickel-based catalytic defective graphene under high-temperature annealing is explored in detail.</sec><sec>The simulation results show that at the deposition temperature of 1100 K, the coverage of graphene is higher and the microstructure is flat. The higher temperature helps to provide enough kinetic energy for carbon atoms to overcome the potential energy barrier of nucleation, thereby promoting the migration and rearrangement of carbon atoms and reducing graphene growth defects. Too high a temperature will lead to continuous accumulation of carbon atoms on the deposited carbon rings, forming a multilayered reticulation and disordered structure, which will cause a low coverage rate of graphene. The increase of incident energy helps to reduce the vacancy defects in the film, but excessive energy leads to poor continuity of the film, agglomeration, the more obvious stacking effect of carbon atoms and the tendency of epitaxial growth. When the incident energy is 1 eV, the surface roughness of the film is lower, and more monolayer graphene can be grown. During annealing at 1100 K, the carbon film dissolves and nucleates simultaneously in the Ni transition layer, and the nickel transition layer catalyzes the repair of defective graphene. The graphene film becomes more uniform, and the number of hexagonal carbon rings increases. Appropriate high-temperature annealing can help to repair and reconstruct defective carbon rings and rearrange carbon chains into rings. Therefore, when the deposition temperature is 1100 K and the incident energy is 1 eV, graphene can be deposited and annealed to grow a high-quality graphene coatings. The simulation results provide the reference for preparing the cemented carbide graphene coated tools.</sec>

Diagnostic efficiency of single source dual energy CT in differentiating adrenal adenoma from adrenal metastasis

Background: The distinction between incidental adrenal lesions is still difficult in diagnostic imaging whereas Dual energy CT has not been thoroughly tested for its ability to diagnose adrenal lesions. This study utilizes dual energy CT to identify between the two most prevalent adrenal neoplasms, adrenal metastasis and adrenal adenomas.Objective:To evaluate the efficacy of non-enhanced single-source dual-energy computed tomography (ssDECT) in differentiating metastases from adenomas in adrenal glands Materials and methods :This is a retrospective study conducted in the department of radio diagnosis of Mysore medical college and research institute after receiving the approval from our institutional ethical committee.A total of fifty six patients (32 men,24 women) with 31 adrenal metastases (AMs) and 32 adrenal adenomas (AAs) underwent a plain dual-energy CT imaging from March 2021 to October 2022 were included. The CT number from the virtual monochromatic spectral (VMS) image sets were measured for the AMs and AAs. The difference of CT numbers between AMs and AAs was statistically compared by P value and the box plot curve. Results: The CT number (medium, range) of metastases (50.47, 29.93 HU at 40 keV and 29.00, 9.36 HU at 140 keV) was significantly higher than that of adenomas (0.76, 33.04 to 13.73, 18.96 HU) at each energy level from 40 to 140 keV (P <.05).Conclusion: Using CT numbers obtained from virtual monochromatic images of single source dual energy CT can be used to differentiate adenomas from adrenal metastasis. The Median CT number of metastases was higher than that of adenomas at 40 Kev and 140 Kev. The median CT number of metastases decreased with increase in incident photon energy in Kev and median CT number of adenomas increased with increase in incident photon energy in Kev. Keywords- Virtual monochromatic spectral (VMS) image,Dual energy computed tomography, adrenal lesions, differential diagnosis.

Study on the Duration of Laser-Induced Thin Film Plasma Flash

The accuracy of judging whether the film is damaged directly affects the accuracy of the measurement of the film laser damage threshold. When judging the film damage by the traditional plasma flash method, there is a problem of misjudgment caused by the failure to distinguish the film and air plasma flash. In order to eliminate misjudgment, the two flashes are accurately distinguished by the difference in the duration of the air and film plasma flash. This paper aims to obtain the theoretical and experimental values of the duration of the film plasma flash (tf) and analyze the factors affecting it. Firstly, taking single-layer hafnium oxide and aluminum oxide thin films as examples, when the wavelength of the incident laser is 1064 nm, the diameter of the laser focusing spot is 0.08 cm, the energy of the incident laser is 100 mJ, and the pulse width of incident laser is 10 ns, the tf of hafnium oxide, and aluminum oxide thin films are 542.7 and 299.6 ns, respectively. Secondly, the experimental study of tf was carried out. Through six experiments, the following results were obtained: (1) With the increase in incident laser energy, the tf of both films increases; (2) The tf of the hafnium oxide film is longer than that of the aluminum oxide film. (3) The experimental parameters are put into the calculation model, and the theoretical results are in good agreement with the experimental tf values. Finally, it is found that tf increases with the increase in incident laser energy and incident laser pulse width, and decreases with the increase in focusing spot diameter.

Electron, Photon, and Neutron Dose Conversion Coefficients of Lens and Non-Lens Tissues Using a Multi-Tissue Eye Model to Assess Risk of Cataracts and Retinitis.

Previous publications describe the estimation of the dose from ionizing radiation to the whole lens or parts of it but have not considered other eye tissues that are implicated in cataract development; this is especially critical for low-dose, low-ionizing-density exposures. A recent review of the biological mechanisms of radiation-induced cataracts showed that lenticular oxidative stress can be increased by inflammation and vascular damage to non-lens tissues in the eye. Also, the radiation oxygen effect indicates different radiosensitivities for the vascular retina and the severely hypoxic lens. Therefore, this study uses the Monte Carlo N-Particle simulations to quantify dose conversion coefficients for several eye tissues for incident antero-posterior exposure to electrons, photons, and neutrons (and the tertiary electron component of neutron exposure). A stylized, multi-tissue eye model was developed by modifying a model by Behrens etal. (2009) to include the retina, uvea, sclera, and lens epithelial cell populations. Electron exposures were simulated as a single eye, whereas photon and neutron exposures were simulated employing two eyes embedded in the ADAM-EVA phantom. For electrons and photons, dose conversion coefficients are highest for either anterior tissues for low-energy incident particles or posterior tissues for high-energy incident particles. Neutron dose conversion coefficients generally increase with increasing incident energy for all tissues. The ratio of the absorbed dose delivered to each tissue to the absorbed dose delivered to the whole lens demonstrated the considerable deviation of non-lens tissue doses from lens doses, depending on particle type and its energy. These simulations demonstrate that there are large variations in the dose to various ocular tissues depending on the incident radiation dose coefficients; this large variation will potentially impact cataract development.

Laser-induced modification in structural, morphological, linear and non-linear optical parameters of Ge20Ag10Te10Se60 thin films for optoelectronic applications

The current study reveals the time dependent laser irradiation induced modifications in structural and optical properties of the thermally evaporated Ge20Ag10Te10Se60 thin films. The amorphous nature of the films is unchanged with irradiation time. The morphological study depicts very small changes in the microstructure of the films. The average particle size is found to be 8.24 nm from transmission electron microscopy for the high irradiated film. The indirect optical bandgap of the films increased while the refractive index decreased with increase in irradiation time. The dispersion parameters decreased along with the decrease in dielectric loss with increase in irradiation time, making the material useful for various electrical applications. The non-linear refractive index (n2) and susceptibilities (χ(1) and χ (3)) are found to be decreased with increased irradiation time. The non-linear absorption coefficient increased with increase in incident energy. The surface wettability study shows the hydrophobicity nature of the films which enables it for application in different coating materials. The observed changes in different optical parameters of the films under laser irradiation makes it eligible for various optoelectronics applications.

Experimental Study on the Dynamic Tensile Characteristics of Coal Samples.

As coal mines continue deep mining, the frequency of coal and rock dynamic disasters has also gradually increased. In this paper, dynamic tensile strength deformation, energy evolution, and crack development under an impact test were studied on Brazilian coal samples, using a split Hopkinson pressure bar (SHPB) test device. A high-speed camera was adopted to capture the failure process of the coal specimens. The research results demonstrate that when the impact velocity is greater than 4.75 m/s, the dynamic tensile strength of the vertical bedding direction is higher than that of the parallel bedding direction of the coal samples. With the increase in the impact velocity, the dynamic strain and ultimate strain rate of two types of coal samples are increased, and the average value of the first and second dynamic deformation moduli of coal samples shows decreasing characteristics. As the incident energy increases, the sum of reflected and transmitted energy increases, and the absorbed energy also increases in the two types of coal samples. The two types of Brazilian disc coal samples mainly showed tensile and shear failure characteristics. The dynamic tensile deformation characteristics of the two types of coal specimens are less affected by the impact angles. However, the crack propagation of coal samples was mainly influenced by the impact angles. The test results can be used for the prediction of coal and rock outburst in deep underground coal excavation.

Study on the mechanism of surface pressure of optical films formed by laser plasma shock wave

In a high-power laser system, when the surface pressure of the optical film caused by laser plasma shock wave is greater than the adhesion per unit area of the film layer, the film will produce mechanical damage, and in serious cases, the whole system may not work. Therefore, studying the formation mechanism of optical film surface pressure caused by laser plasma shock wave and calculating the pressure is the key to ensure the normal operation of high power laser system. In this paper, by studying the relaxation process of shock wave on optical film surface pressure, a theoretical calculation model of shock wave on optical film pressure is established, and the variation law of pressure with different parameters is obtained, which reveals the mechanism of forming the optical film surface pressure. The calculation and simulation results show that the maximum pressure is 108 N m−2 during the laser pulse, and the pressure decreases with the increase of laser pulse time after the pulse, and the total action time of laser plasma and shock wave on the film is in the order of microseconds. The pressure increases with the increase of incident laser energy, focal length of focusing lens and incident laser pulse width, which increases with the decrease of the distance between the film surface and the focal plane of the focusing lens. The pressure changes more obviously with the incident laser energy and the distance between the film surface and the focal plane of the focusing lens than with the focal length of the focusing lens and the incident laser pulse width.

Onset of pressure gradient on collective flow through balance and transition geometry

The impression of mean field and spectator matter has been studied through the collision geometry dependence of reduced flow and elliptical flow in heavy-ion collisions (HICs) at intermediate energies using Isospindependent Quantum Molecular Dynamics (IQMD) model for the reaction of $$_{20}^{50}{\rm{Cu + }}_{20}^{50}{\rm{and}}_{79}^{197}{\rm{Au + }}_{79}^{197}{\rm{Au}}$$ at incident energy between 50 MeV/nucleon and 450 MeV/nucleon. The collision geometry at which the reduced flow and elliptical flow changes its sign is termed as balance geometry $$({\hat b_{bal}})$$ and transition geometry $$({\hat b_{trans}})$$ of flow, respectively. Our study reveals that $$({\hat b_{bal}})$$ and $$({\hat b_{trans}})$$ increases with increase in incident energy. In addition to this, the effect of nuclear charge radius has also been studied by using the isospin-independent as well dependent nuclear charge radii parameterizations.

Enhancing the radiation absorption ability of the glass system with the contamination of Heavy Metal Oxide (PbO, CuO, and Bi2O3)‏

Containing the molar percentage recipe of 55B2O3–x PbO–(45-x) CuO [ where, x = 5, 10,15, 20, 25 and 30 mol%] glass systems were particularized in this present study. To detect the radiation shielding features such as linear attenuation coefficients (LAC), mass attenuation coefficients (MAC), half value layer (HVL), mean free path (MFP), effective atomic number (Zeff) of these six glasses by using Phy-X software. The obtained results indicate that the value of the studied glass systems represented the highest value of LAC, MAC, and Zeff whereas the lowest value has found for HVL, and MFP. The value of these parameters represented the utmost shielding ability displayed by the studied glass containing the highest mol percentage of the PbO and CuO. Additionally, it has been seen that the density of the glass systems upsurges due to the greater addition of wt% of the PbO and CuO. The studied glass system S6 (30PbO-15CuO-55B2O3) represented a 5.3 times lower value than sample S1(5PbO-40CuO-55B2O3). That means the highest percentage of PbO and CuO enhances the shielding ability. Noteworthy, it has been found from the studied results that with the increase of incident photon energy the value of HVL has increased. Like at energy 1.33 MeV, the half value layer for studied glass sample S1 (5PbO-40CuO-55B2O3) is approximately 3 cm while S6 is 2 cm. In view of the above facts, it can be easily stated that the studied sample S6 (30PbO-15CuO-55B2O3) has the best shielding ability among the six studied glass samples.

Experimental study on energy dissipation of layered backfill under impact load

• The dynamic characteristics of layered cemented tailings backfill(LCTB) were studied by SHPB test system. • The failure of LCTB mainly occurs at the delamination of the specimen. • The reflected and absorbed energy of specimens gradually increases and the transmitted energy gradually decreases as the number of layers increases. • The specific energy absorption value (J EA ) and dissipation rate were significantly positively correlated with the number of layers. The failure of the cemented tailing backfill (CTB) under the impact load is mainly related to the absorption and dissipation of energy; in order to obtain the corresponding dynamic characteristics and energy evolution law, The diameter is 50 mm split Hopkinson pressure bar (SHPB) test system was conducted to investigate the influence of different layers, cement tailing ratios (CTR) and impact rates on the failure mode, dynamic stress–strain curve and energy evolution of the LCTB. The results show that: (1) with the increase in the number of layers, impact rate and CTR, the dynamic peak stress of the CTB gradually increases. When the impact rate is constant, the strength of the CTB gradually decreases with the increase of the number of layers. (2) With the increase in the number of layers, the reflection energy and absorption energy, specific energy absorption value (JEA) and dissipation rate of the CTB gradually increase while the transmission energy decreases gradually; with the increase of incident energy, the energy increment and dissipation rate of the CTB increase first and then decrease, suggesting that the energy absorption of the CTB will not change greatly when the incident energy increases to a certain extent. (3) Due to the filling layer, the basic particles forming the CTB will slip relatively at the layer while the stress wave acting on the layer, which intensifies the dynamic process at the layer and eventually induces the fracture of the CTB specimen along with the layer. With the increase in impact rate, the failure mode of the CTB without delamination mainly includes shear failure and axial splitting failure. Finally, this research can provide important theoretical support for the further study of underground LCTB.

Comparison of glancing-angle scatterings on different materials in a high aspect ratio plasma etching process using molecular dynamics simulation

In plasma etching for microelectronics fabrication, one of the objectives is to produce a high aspect ratio (HAR) via and trench structures. A principal contributor to the HAR feature shape is the manner in which energetic ions interact with sidewalls inside the feature. The scattering angle and energy loss of ions reflecting from sidewalls determine the sidewall slope and can lead to defects such as microtrenching and bowing. Understanding how ions interact with sidewalls can improve our control of the critical dimensions of HAR features. Ions accelerated in the plasma sheath arrive in the feature with energies as large as a few keV and initially strike the sidewalls at glancing angles. These scattering events extend to the photolithographic mask. Scattering from the mask at glancing angles can produce ions incident into the underlying feature with a broader angular distribution, leading to less desirable feature properties. In this work, results are discussed from Molecular Dynamics (MD) simulations of glancing-angle scattering of argon ions from three materials common to HAR etch: polystyrene (as a photoresist surrogate), amorphous carbon (a hard mask material), and SiO2 (a common insulating material used in microelectronics devices). Results from simulations reveal a transition from specular scattering to diffuse scattering as the angle of the incident ion decreases (90° being glancing incidence) and incident energy increases. Scattering from polystyrene is more diffuse compared to amorphous carbon and SiO2 for identical incident ion conditions.

Preparation of Core–Shell Structure W/Gd2O3 and Study on the Properties of Radiation Protection Materials

W/Polydopamine (PDA) was prepared by adding W powder into the dopamine (DA) solution and adjusting the pH value of the solution. PDA contains several phenolic hydroxyl and amino groups, which provide abundant active sites for the complexation of metal ions. Therefore, we prepared W/Gd2O3 with core–shell structure by self-assembly method and homogeneous precipitation method, respectively. At the same time, polyurethane (PU) coating fabrics with W and Gd2O3 mixed powder and core–shell W/Gd2O3 powder were prepared, and their X-ray protection performance was tested. Results show that compared with W and Gd2O3 mixed powder PU coating fabrics, the protection efficiency and lead equivalent of core–shell structure W/Gd2O3 powder PU coating fabrics against different energy rays are obviously improved. With the increase in incident energy, the protective efficiency of core–shell structure W/Gd2O3 powder PU coating fabric decreases more slowly than that of W/Gd2O3 mixed powder PU coating fabric. When the incident energy is 65–100 keV, the protective efficiency of the core–shell structure W/Gd2O3 powder PU coating fabric is above 60%, showing a good synergistic protective effect. When the incident energy is 83 keV, the X-ray protection efficiency of core–shell W/Gd2O3 powder PU coating fabric is 65.5%, and the lead equivalent is 0.4051 mmPb.

Adsorption of hydrogen isotopes on graphene

We investigated the possibility of using graphene for control of hydrogen isotopes by exploring adsorption, reflection, and penetration of hydrogen isotopes on graphene using molecular dynamics. Reflection is the dominant interaction when hydrogen isotopes have low incident energy. Adsorption rates increase with increasing incident energy until 5 eV is reached. After 5 eV, adsorption rates decrease as incident energy increases. At incident energies greater than 5 eV, adsorption rates increase with the number of graphene layers. At low incident energies (<1 eV), no isotopic effects on interactions are observed since the predominant interaction is derived from the force of π electrons. Between 1 eV and 50 eV, heavier isotopes exhibit higher adsorption rates and lower reflection rates than lighter isotopes, due to the greater momentum of heavier isotopes. Adsorption rates are consistently higher when the incident angle of the impacting atoms is smaller between 0.5 eV and 5 eV. At higher energies (>5 eV), larger incident angles lead to higher reflection and lower penetration rates. At high incident energies (>5 eV), crumpled graphene has higher adsorption and lower penetration rates than wrinkled or unwrinkled graphene. The results obtained in this research study will be used to develop novel nanomaterials that can be employed for tritium control.

Simulation of radiation effects on In0.52Al0.48As and In0.53Ga0.47As by low energy He ion

"In this article, influence of He ions irradiation on In0.52Al0.48As and In0.53Ga0.47As materials with the energies ranging from 50 to 200 keV at normal incidence, including the distributions of the He ions, ionizing energy loss, vacancy, and backscattering ion number, is studied through the simulation. The calculated results show that the peak position of He ion distribution moves to the deeper depth with increasing incident energy and the distribution curve conforms to Bragg distribution. The distribution of the ionizing energy loss induced by He ions is almost constant first and then sharply drops with increasing energy induced by recoil atoms conforms to Bragg distribution. The numbers of vacancies increase with increasing energy and the As vacancy is the prominent vacancy for these two materials. The number of phonons induced by recoil atoms is much higher than that induced by the He ions. The total numbers of the backscattering for the In0.52Al0.48As and In0.53Ga0.47As all decline as the energy is increases and the value for InGaAs is always higher than that the He ions. The higher numbers of backscattering ions are obtained for InAlAs. "

Secondary electron emission of Al&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; and MgO nanofilms fabricated by atomic layer deposition

<p indent="0mm">Electron multiplier devices are widely applied in many electronic instruments like mass spectrometers and atomic clocks. It is considerably crucial for a multiplier to possess a high electron gain, and this index can be directly determined by secondary electron yield (SEY) of the dynodes. Al₂O₃ and MgO possess a relatively high SEY level among majority of dynode materials, and their film products are excellent dynode candidates. Whereas, for some multipliers like microchannel plate (MCP), only an ultrathin film of several nanometers is allowed to be coated onto the inner wall of the micro channels to avoid the variation of the channel diameter. Therefore, SEY characteristics of the ultrathin films are necessary to be figured out. Here, by using the technology of atomic layer deposition, 7 groups of ultrathin Al₂O₃ and MgO nanofilms with increase thickness (1, 3, 5, 7, 10, 30, and <sc>50 nm)</sc> are fabricated on silicon (Si) substrates. As well as, 5 groups of Al₂O₃ nanofilms (1, 2, 3, 4, and <sc>20 nm)</sc> are deposited on MgO film <sc>(20 nm)</sc> substrate. Surface composition, morphology, film thickness, and SEY have been characterized in detail. Via the experiments, it is found that SEY of the Al₂O₃/Si and MgO/Si samples largely depends on the film thickness, namely, SEY increases obviously as the film thickness rises, meanwhile, the increment of SEY decreases gradually. The SEY tendency indicates that the effect of top film on SEY becomes enhanced, and the influence of bottom substrate on SEY becomes weakened. When the film thickness increases beyond <sc>30 nm,</sc> SEY increment approaches to 0, and SEY tends to be saturated. This phenomenon demonstrates that the penetration depth of incident electrons is less than the film thickness under the circumstances. To interpret the experimental results, the SEE semi-physical theory developed for double layer structures is utilized. The calculation results indicate that the film thickness has a remarkable impact on SEY, especially when the incident energy becomes lower and the film becomes thicker, the results also reveal that the dielectric surface film possesses a great ability to modulate the surface SEY. However, SEY becomes less dependent on film thickness as the incident energy increases, and it results from the increase of penetration depth for the incident electrons. This work reveals the mechanism of the SEE characteristics for ultrathin Al₂O₃ and MgO nanofilms, which is of great significance for the subsequent research on the use of nanoscale high SEY dielectric films as the SEE functional layer in electron multipliers.