Analysis of microscopic parameters of surface charging in polymer caused by defocused electron beam irradiation

The relationship between microscopic parameters and polymer charging caused by defocused electron beam irradiation is investigated using a dynamic scattering-transport model. The dynamic charging process of an irradiated polymer using a defocused 30 keV electron beam is conducted. In this study, the space charge distribution with a 30 keV non-penetrating e-beam is negative and supported by some existing experimental data. The internal potential is negative, but relatively high near the surface, and it decreases to a maximum negative value at z = 6 μm and finally tend to 0 at the bottom of film. The leakage current and the surface potential behave similarly, and the secondary electron and leakage currents follow the charging equilibrium condition. The surface potential decreases with increasing beam current density, trap concentration, capture cross section, film thickness and electron–hole recombination rate, but with decreasing electron mobility and electron energy. The total charge density increases with increasing beam current density, trap concentration, capture cross section, film thickness and electron–hole recombination rate, but with decreasing electron mobility and electron energy. This study shows a comprehensive analysis of microscopic factors of surface charging characteristics in an electron-based surface microscopy and analysis.     

Propagation of Plasma Generated by Intense Pulsed Ion Beam Irradiation

Taking the calculation results based on the established two-dimensional ablation model of the intense-pulsed-ionbeam （IPIB） irradiation process as initial conditions, we build a two-dimensional hydrodynamic ejection model of plasma produced by an IPIB-irradiated metal titanium target into ambient gas. We obtain the conclusions that shock waves generate when the background pressure is around 133 mTorr and also obtain the plume splitting phenomenon that has been observed in the experiments.     

Effect of modifying a methyl siloxane-based dielectric by a polymer thin film for pentacene thin-film transistors

We report on the fabrication of pentacene thin-film transistors (TFTs) utilizing a spun methyl siloxane-based spin-on-glass (SOG) dielectric and show that these devices can give a similar electrical performance as achieved by using pentacene TFTs with a silicon dioxide (SiO₂) dielectric. To improve the electrical performance of pentacene TFTs with the SOG dielectric, we employed a hybrid dielectric of an SOG/cross-linked poly-4-vinylphenol (PVP) polymer. The PVP film was deposited onto the spun SOG dielectric prior to pentacene evaporation, resulting in an improvement of the saturation field effect mobility (μ_sat) from 0.01 cm²/(V s) to 0.76 cm²/(V s). The good surface morphology and the matching surface energy of the SOG dielectric that was modified with the polymer thin film allow the optimized growth of crystalline pentacene domains whose nuclei are embedded in an amorphous phase.     

Self-organization of ripples on Ti irradiated with focused ion beam

30 keV focused Ga⁺ ions were used to raster the metallographically polished surface of commercially pure Ti (CP Ti) at various FIB incidence angles over a wide range of doses (10¹⁶-10¹⁸ ions/cm²) at room temperature. The sputtered surfaces were observed in situ using FIB imaging and later carefully characterized ex situ under scanning electron microscope (SEM) and atomic force microscope (AFM). Ripples were observed on the irradiated surfaces even at the normal FIB incidence angle. The ripple evolution is analyzed as functions of surface diffusion, surface crystallographic orientation, ion dose and incidence angle. It is found that the ripple orientation was progressively influenced by the ion beam direction with incidence angle increasing and in some cases curved ripples or fragmented rods viewed from different angles occurred at high ion doses. The morphological evolution from the well-developed straight ripples to the curved ones is never observed. The formation of ripples is attributed to the competition between the formation of ripples due to anisotropic surface diffusion and the formation of incidence-angle dependent ripples determined by Bradley-Harper (BH) model.     

The effect of contamination of dielectric target surfaces under electron irradiation

The influence of the contamination film formed under the electron bombardment of the sample surface on the conditions of experimental studies using analytical electron-probe apparatus (scanning electron microscopes, X-ray microanalyzers) is considered. The accompanying artifacts, namely the decreased effective value of the secondary electron emission coefficient and the shifted value of the second crossover energy of primary electrons are calculated.     

Mechanisms of small clusters production by short and ultra-short laser ablation

The mechanisms involved into the formation of clusters by pulsed laser ablation are studied both numerically and experimentally. To facilitate the model validation by comparison with experimental results, the time and length scales of the simulation are considerably increased. This increase is achieved by using a combination of molecular dynamics (MD) and the direct simulation Monte Carlo (DSMC) methods. The combined MD-DSMC model is then used to compare the relative contribution of the two channels of the cluster production by laser ablation: (i) direct cluster ejection upon the laser-material interaction, and (ii) collisional sticking and aggregation in the ablated gas flow. Calculation results demonstrate that both of these mechanisms play a role. The initial cluster ejection provides cluster precursors thus eliminating the three-body collision bottleneck in the cluster growth process. The presence of clusters thus facilitates the following collisional condensation and evaporation processes. The rates of these processes become considerable, leading to the modification of not only the plume cluster composition, but also the dynamics of the plume expansion. Calculation results explain several recent experimental findings.     

Rapid growth of ultra thin SiO2 films by a large-area electron beam

Rapid growth of ultra thin oxide films (40–180Å) of silicon using a low-energy large-area electron beam has been performed with a pressure ratio of 31 (O₂/He) and a total pressure of 0.5–0.7 Torr. A higher oxidation rate of about 625Ų/s is found for shorter irradiation time of the e-beam in the e-beam dose range 0.75–3 Coulomb/cm² and at lower substrate temperature 540–740°C. AES and XPS demonstrated a rapid electron-stimulated oxidation process of the Si surface. For the grown ultra thin oxide films, C-V characteristics, dielectric strength, uniformity of the film over the entire Si wafer and its thickness as a function of the processing time of the e-beam are also presented.     

Synthesis of nanoclusters by nanosecond laser ablation: Direct simulation Monte Carlo modelling

Collisional processes leading to the formation of nanoparticles in a laser-ablated plume are numerically simulated with the aid of an atomistic-level model based on direct simulation Monte Carlo (DSMC) method. The formation of nanoparticles in nanosecond laser ablation of a mono-atomic target is investigated in the presence of an inert background gas. The DSMC procedure is modified in order to account for numerous plume species and to describe several reactions (i.e., recombination/dissociation, sticking, evaporation) taking place in the plume and affecting the size and spatial distribution of the produced nanoclusters. Calculation results allow us to visualize the nanoparticles and to correlate their space distributions with plume dynamics. In addition, cluster size distributions are investigated at different pressures. The effects of the background gas on cluster formation within the plume are furthermore shown.     

Improvement in piezoelectric effect of violet InGaN laser diodes

The laser performance of violet InGaN laser diodes is investigated numerically. The polarization-dependent properties, including overlap of electron and hole wavefunctions, threshold current, and slope efficiency, are studied through the use of step-like quantum well structure. Furthermore, the electron and hole wavefunctions, band diagrams, and emission wavelength are compared and analyzed. The simulation results show that the lowest threshold current and the highest slope efficiency are obtained when the step-like quantum well structure is designed as In_0.12Ga_0.88N (2.5 nm)-In_0.18Ga_0.82N (1 nm) or In_0.18Ga_0.82N (2.5 nm)-In_0.12Ga_0.88N (1 nm) for violet laser diodes due to sufficiently enhanced overlap of electron and hole wavefunctions.     

Study of the charge build up and transport in electron beam irradiated dielectric films

The Pulsed Electro Acoustic– PEA –method is used to perform space charge measurements in organic dielectrics subjected to electron beam irradiation as also during relaxation, under short-circuit and open-circuit conditions. A model based on GEANT 4 libraries for electron transport analysis has been developed in order to understand the behavior of space charge in space environment. Examples of measurements recorded on Polyimide films using various configurations are analyzed in the paper. A comparison between experimental data and simulated results shows that various complex phenomena are occurring simultaneously.     

The dynamic natures of microscopic particles described by nonlinear Schrödinger equation

There are a lot of difficulties and troubles in quantum mechanics, when the linear Schrödinger equation is used to describe microscopic particles. Thus, we here replace it by a nonlinear Schrödinger equation to investigate the properties and rule of microscopic particles. In such a case we find that the motion of microscopic particle satisfies classical rule and obeys the Hamiltonian principle, Lagrangian and Hamilton equations. We verify further the correctness of these conclusions by the results of nonlinear Schrödinger equation under actions of different externally applied potential. From these studies, we see clearly that rules and features of motion of microscopic particle described by nonlinear Schrödinger equation are greatly different from those in the linear Schrödinger equation, they have many classical properties, which are consistent with concept of corpuscles. Thus, we should use the nonlinear Schrödinger equation to describe microscopic particles.     

The surface potential of insulating thin films negatively charged by a low-energy focused electron beam

We report on the surface potential characteristics in the equilibrium state of the grounded insulating thin films of several 100 nm thickness negatively charged by a low-energy (<5 keV) focused electron beam, which have been simulated with a newly developed two-dimensional self-consistent model incorporating electron scattering, charge transport and charge trapping. The obtained space charge is positive and negative within and outside the region, respectively, where the electron and hole densities are greater than the trap density. Thus, the surface potential is relatively high around the center, then it decreases to a maximum negative value and finally tends to zero along the radial direction. The position of the maximum value is far beyond the range of e-beam irradiation as a consequence of electron scattering and charge transport. Moreover, a positive electric field can be generated near the surface in both radial and axial directions. The surface potential at center exhibits a maximum negative value in the condition of the ～2 keV energy non-penetrating e-beam in this work, which is supported by some existing experimental data in scanning electron microscopy. Furthermore, the surface potential decreases with the increase in beam current, trap density and film thickness, but with the decrease in electron mobility.     

Controlling the growth dynamics of carbon nanotips on substrates irradiated by a focused electron beam

The dynamics of nanopillar growth on a variety of substrates as a result of the deposition of hydrocarbon molecules by a sharply focused electron beam is studied. The growth rate is found to depend strongly on the substrate’s material, thickness, and surface condition. The results are explained through the dissociation of adsorbed molecules by scattered and secondary electrons far from the point of beam incidence, thereby reducing the flow of diffusion to a nanotip’s peak.     

Ion-induced secondary electron emission from ZnS thin films deposited by closed-spaced sublimation

ZnS thin films were deposited on soda lime glass and aluminum substrates by close-spaced sublimation technique. The change in composition, structural and optical properties of the films was investigated as a function of the substrate temperature. The deposited films were stoichiometric and crystalline in nature having cubic structure oriented only along (1 1 1) plane. The energy band gap of the films deposited at the substrate temperature of 150, 250 and 350 °C was 3.52, 3.58 and 3.63 eV respectively. These films were then bombarded with 2-10 keV energy pulsed Ar⁺ beam and their electron yield was determined from impinging ion and emitted electron currents. The electron yield of ZnS films was much high as compared to the metals. The electron yield of ZnS films increased with energy of the incident ion and got saturated at about 8 keV. The most important result of this study was that the electron yield of ZnS films having same composition was different. Monte Carlo simulations performed to interpret these experimental findings showed that the dissimilar electron yields of ZnS films is due to the combined effect of energy band gap, surface barrier potential and density of the films.     

Numerical Simulation of Electromagnetic Waves Scattering by Discrete Exterior Calculus

We show how to construct discrete Maxwell equations by discrete exterior calculus. The new scheme has many virtues compared to the traditional Yee＇s scheme： it is a multisymplectic scheme and keeps geometric properties. Moreover, it can be applied on triangular mesh and thus is more adaptive to handle domains with irregular shapes. We have implemented this scheme on a Java platform successfully and our experimental results show that this scheme works well.     

Numerical Simulation of the Elastic Shrinkage Induced by Portevin-Le Chatelier Effect

A new one-dimensional phenomenological model based on the dynamic strain aging mechanism is developed. In order to account for the elastic shrinkage induced by the Portevin-Le Chatelier effect, elastic deformation is considered under the boundary conditions of the present model. The simulated results are found to be in good agreement with the experimental observations.     

Maintaining the stability of nonlinear differential equations by the enhancement of HPM

Homotopy perturbation method is an effective method to find a solution of a nonlinear differential equation. In this method, a nonlinear complex differential equation is transformed to a series of linear and nonlinear parts, almost simpler differential equations. These sets of equations are then solved iteratively. Finally, a linear series of the solutions completes the answer if the convergence is maintained. In this Letter, the need for stability verification is shown through some examples. Consequently, HPM is enhanced by a preliminary assumption. The idea is to keep the inherent stability of nonlinear dynamic, even the selected linear part is not.     

On uniqueness of solution of a reverse problem of magnetic location

An analysis of solution uniqueness for a problem of magnetic dipole localization based on known values of magnetic field strength vectors at two points is presented. It is shown that a usage of two triples (pairs) of sensors is sufficient to solve a 3D (2D) problem of arbitrary magnetic dipole localization with a satisfactory number of crude errors.     

Electrical and optical properties of ZnO films grown by molecular beam epitaxy

Zinc oxide (ZnO) films have been grown on sapphire by molecular beam epitaxy (MBE), and it is found that the grain size of the ZnO films increased with increasing the growth temperature. Photoluminescence (PL) study shows that the intensity ratio of near-band-edge emission to deep-level-related emission (NBE/DL) of the ZnO is significantly enhanced with increasing the growth temperature, and the dependence of the carrier mobility on the growth temperature shows very similar trend, which implies that there is a community factor that determines the optical and electrical properties of ZnO, and this factor is suggested to be the grain boundary. The results obtained in this paper reveal that by reducing the grain boundaries, ZnO films with high optical and electrical properties may be acquired.     

Well-aligned ZnO nanocolumns grown by reactive electron beam evaporation

We report on the reactive electron beam evaporative growth of well-aligned ZnO nanocolumns on Si (001) wafers in the environment of NH₃/H₂ gas mixture by using polycrystalline ZnO ceramic target as source material. The growth was carried out at low temperatures (400-450 °C) without employing any metal catalysts. Field emission scanning electron microscopy (FESEM) revealed that nanocolumns with uniform distributions in their diameters, lengths, and densities were grown vertically from the substrates and terminated by smooth hexagonal (0001) facets with no terrace-like steps emerged, which should render potential applications such as inherent resonance cavities in fabricating ultraviolet-laser arrays. X-ray diffraction measurements revealed that ZnO nanocolumns were highly c-axis oriented, which is well consistent with the FESEM observations. More importantly, photoluminescence investigations of the nanocolumns demonstrated the strong excitonic emission and extremely weak deep level emission, indicating the high crystalloid and optical quality of the nanocolumns.