The growth and modification of materials via ion–surface processing

A wide variety of gas phase ions with kinetic energies from 1–10⁷ eV increasingly are being used for the growth and modification of state-of-the-art material interfaces. Ions can be used to deposit thin films; expose fresh interfaces by sputtering; grow mixed interface layers from ions, ambient neutrals, and/or surface atoms; modify the phases of interfaces; dope trace elements into interface regions; impart specific chemical functionalities to a surface; toughen materials; and create micron- and nanometer-scale interface structures. Several examples are developed which demonstrate the variety of technologically important interface modification that is possible with gas phase ions. These examples have been selected to demonstrate how the choice of the ion and its kinetic energy controls modification and deposition for several different materials. Examples are drawn from experiments, computer simulations, fundamental research, and active technological applications. Finally, a list of research areas is provided for which ion–surface modification promises considerable scientific and technological advances in the new millennium.     

Surface channeling of swift light ions

A fast computer code is developed to provide information about the trajectories of swift light particles incident on crystalline targets under surface channeling conditions. The approximations used in the model are tested by comparison of trajectory calculations with the MARLOWE simulation program. The simulation of experimental energy distributions allows discussing various inelastic energy loss models for the interaction of 150 keV protons with a nickel surface. The results suggest that plasmon excitations are not sufficient to account for the measured energy losses. It is found that the Oen-Robinson formula, including inelastic energy losses by single electron excitations in dense materials reasonably well applies to the reflection of light ions from metallic surfaces in channeling conditions. The measured light intensity emitted from 200 keV He⁺ reflected ions in various directions close to compact atomic surface rows is compared with the calculated reflection coefficient. The results suggest that most of the particles reflected in ionic state do not penetrate the target surface. Detailed comparison between light emission measurements and calculated reflection intensities, however, requires accurate modelling of the surface topography as well as of the deexcitation mechanisms involved in the surface reflection of light ions.     

Fragmentation of Ne ions with energy 400 MeV/u behind targets from different materials measured with PNTD

This contribution describes the results of fragmentation of Ne ions with primary energy 400 MeV/u behind different shielding measured with plastic nuclear track detectors in the frame of experiments at HIMAC. The detectors were placed behind 6 different materials (PMMA, Teflon, graphite, Al, Fe, Cu) of various thicknesses, from the entrance up to the depths before the Bragg peak. Spectra of linear energy transfer were obtained for all materials and various thicknesses of the shielding used. Attenuation of primary Ne ions in various materials and the contribution of secondary particles and fragments to the total measured dose are presented.     

Nanostructuring by Energetic Ion Beams

Development of nanostructured materials has become of wide interest due to their exotic properties and interesting physics aspects. Energetic ions play a crucial role in the development of nano materials. Ions of different energy regimes have different roles in growth of nano particles. Low energy ions (typically up to a (kiloelectronvolt) keV) in plasma, have been in use for growth of nano particle thin films. Low energy ions (typically a few hundred (kiloelectronvolt) keV) from ion implanters are used for growth of nano particles in a matrix. High energy heavy ions (swift heavy ions) have been in use in recent years for growth of nanostructures and also for modifying nanostructures. Highly charged slow moving ions and focused ion beams too, have potential for creating nanostructures. Out of these several possible roles of energetic ions, there have been developments at NSC Delhi in growth of nanostructures by RF plasma, low energy ions and swift heavy.     

On the conversion of NDP energy spectra into depth concentration profiles for thin-films all-solid-state batteries

A three-step numerical procedure has been developed, which facilitates the conversion of NDP energy spectra into lithium concentration depth profiles for thin-film Li-ion batteries. The procedure is based on Monte Carlo modeling of the energy loss of charged particles (ions) in the solid media, using the publically available SRIM/TRIM software. For the energy-to-depth conversion, the battery stack has been split into finite volume elements. Each finite volume element becomes a source of ions according to the employed nuclear reaction. Ions loos energy when they move across the battery stack towards the detector. The as-obtained simulated spectra have been compared with the experimentally measured spectra. The thicknesses of the battery stack layers were estimated by minimizing the deviation between the simulated and measured spectra. Subsequently, a relation between the average energy of detected ions and the depth of the corresponding finite volume element, yielding a calibration function, was used to relate that particular part of the spectra with the depth of its source. At the final stage, a Bayesian estimator was used to find the distribution of lithium at a particular depth. The developed procedure was applied to a practically relevant case study of Si immobilization in the LPO electrolyte of all-solid-state thin-film batteries. It is shown that the lithium immobilization process in the LPO electrolyte is responsible for the battery degradation process.     

Negative-ion emission during laser ablation of multicomponent materials

The time of flight technique coupled with an electrostatic energy filter has been used for composition and energy-distribution analysis of the ion species emitted during laser ablation of multicomponent materials Y-Ba-Cu-O, Pb-Sn-Te. The negative-ion output and kinetic-energy distribution as a function of the laser wavelength and the laser fluence on the target were measured. A high output of the negative ions of matrix elements comparable with the positive-ion emission was detected. The barium negative-ion formation was observed in spite of the negative electron affinity of alkaline earth elements in the ground electronic state. The mechanism of negative-ion formation based on the ternary collisional recombination in the laser plasma is analyzed.     

Computer processing of electronic absorption spectra of rare-earth elements in inorganic laser media

Algorithms and program modules are developed for calculation of the Judd-Ofelt parameters on modern computers. These programs can be used to perform numerical analysis of the energy absorption by rareearth ions in laser media.     

Properties of strongly interacting matter and the search for a mixed phase at the JINR nuclotron

A physical program is formulated for new facilities opening in Dubna for the acceleration of heavy ions with an energy up to 5A GeV. The text was submitted by the authors in English.     

Effect of ion velocity on SHI-induced mixing in Ti/Bi system

Energetic ion beams are proving to be versatile tools for modification and depth profiling of materials. The energy and ion species are the deciding factor in the ion-beam-induced materials modification. Among the various parameters such as electronic energy loss, fluence and heat of mixing, velocity of the ions used for irradiation plays an important role in mixing at the interface. The present study is carried out to find the effect of the velocity of swift heavy ions on interface mixing of a Ti/Bi bilayer system. Ti/Bi/C was deposited on Si substrate at room temperature by an electron gun in a high-vacuum deposition system. Carbon layer is deposited on top to avoid oxidation of the samples. Eighty mega electron volts Au ions and 100?MeV Ag ions with same value of S_e for Ti are used for the irradiation of samples at the fluences 1?×?10¹³–1?×?10¹⁴ ions/cm². Different techniques like Rutherford backscattering spectroscopy, atomic force microscopy and grazing incidence X-ray diffraction were used to characterize the pristine and irradiated samples. The mixing effect is explained in the framework of the thermal spike model. It has been found that the mixing rate is higher for low-velocity Au ions in comparison to high-velocity Ag ions. The result could be explained as due to less energy deposition in thermal spike by high-velocity ions.     

水杨酸-Tb3+(Gd3+)络合物的高效发光

合成了水杨酸-Tb3+和水杨酸-Tb3+(Gd3+)高效发光材料.通过发射光谱、激发光谱和荧光衰减时间的测定,观察到了水杨酸根与Tb3+之间的能量传递,并获得了高效发光.以Gd3+代替4/5摩尔的Tb3+也得到较好的结果.     

Temperature dependent spall threshold of four metal alloys

Many aerospace components operate at elevated temperature. Such components are more vulnerable to impact and radiation environments than if cold. To evaluate the effects of these environments, an experimental program was undertaken in which four candidate missile structural materials were tested at various temperatures. The materials studied were 2024 aluminum alloy, 304 stainless steel, Haynes 25 cobalt alloy, and AZ-31B magnesium. A carbon foil radiative heater was used to provide initial temperatures up to 1300°K. The heated test specimens were then exposed to a high energy (~3 MeV) electron beam with a deposition time of 50nsec in the Boeing FX-75 facility. The results of these tests provided spall thresholds as a function of internal energy (temperature) for the various materials. Impact tests in the Boeing gas gun were also conducted to provide data on spall behavior at room temperature.     

Effective stopping of relativistic composite heavy ions colliding with atoms

A nonperturbative theory of energy loss by relativistic composite heavy highly charged ions colliding with atoms is developed. A simple formula for effective stopping is derived. By composite ions, we mean partially ionized atoms of heavy elements consisting of the ion core and several bound electrons that incompletely neutralize the ion core charge. Such ions, which have, as a rule, a high charge (for example, partly stripped uranium atoms), are used in many experiments performed with modern heavy ion accelerators.     

Effect of lithium thiocyanate addition on the structural and electrical properties of biodegradable poly(ε-caprolactone) polymer films

Polymer electrolyte films of biodegradable poly(ε-caprolactone) (PCL) doped with LiSCN salt in different weight ratios were prepared using solution cast technique. The effect of crystallinity and interaction between lithium ions and carbonyl groups of PCL on the ionic conduction of PCL:LiSCN polymer electrolytes was characterized by X-ray diffraction (XRD), optical microscopy, Fourier transform infrared spectroscopy (FTIR) and AC impedance analysis. The XRD results revealed that the crystallinity of the PCL polymer matrix decreased with an increase in LiSCN salt concentration. The complexation of the salt with the polymer and the interaction of lithium ions with carbonyl groups of PCL were confirmed by FTIR. The ionic conductivity was found to increase with increasing salt concentration until 15 wt% and then to decrease with further increasing salt concentration. In addition, the ionic conductivity of the polymer electrolyte films followed an Arrhenius relation and the activation energy for conduction decreased with increasing LiSCN concentration up to 15 wt%. UV–vis absorption spectra were used to evaluate the optical energy band gaps of the materials. The optical energy band gap shifted to lower energies with increasing LiSCN salt concentration.     

光学塑料零件粘接用胶的选择与改性

光学塑料和其它工程塑料一样，由于表面能低，胶液在其表面难以润湿和粘合。为提高光学塑料零件的粘接性能，需寻求适合于光学塑料零件的粘接材料。根据相似相溶的原理，趋向于选用与光学塑料材料分子结构相似的树脂作为光学胶的基本粘料。本文介绍了聚甲基丙烯酸甲酯（ＰＭＭＡ）和聚本乙烯醇薄膜（ＰＶＡＬ）等光学塑料零件与光学玻璃零件粘接时的有关情况。作为光学粘接材料主要选用ＪＮ－７９１光学环氧树脂胶并掺入［Ｎ·Ｓ］硅烷偶联剂的改性胶和以环氧丙烯酸酯为光敏树脂的ＧＢＮ－５０１光学光敏胶。本文着重就相似相溶原理以及为提高粘接性能的作用机理作了初步的探讨。     

Monitoring dissolved active trace elements in biogas plants using total reflection X-ray fluorescence spectrometry

Generally, full-scale biogas plants require trace elements supplementation to sustain a stable process. The aim was to apply total reflection X-ray fluorescence (TXRF) to monitor the dissolved, active elements, for the first time, at μg/L levels in biogas plants. The digester liquid is comparable to sludge with high solids content and high salt concentrations. The ions are usually measured in the dried fermenter slurry after acid digestion in its inactive bound form, although microorganisms can take up only dissolved ions as active agent. In this study, a procedure was developed to monitor dissolved ions in such environmental processes to prevent an overdose or underdose. The analytical figures of merit considered were the lowest possible limit of detection, the recovery of spiked ions and linearity. Samples were spiked with nickel, selenium and tungsten in the range of 10–200 μg/L. Highest recovery rates of >93% for concentrations of 10 to <100 μg/L were obtained after the samples were centrifugated twice, followed by application of microwave-assisted acid digestion. The calculated lowest limit of detection was 2–4 μg/L. The developed method was first tested in laboratory-scale biogas digesters with wheat straw as substrate. Successful application of TXRF was also achieved in a full-scale biogas plant to estimate the dynamics of “active” trace element ions in the range of 2–1,000 μg/L for several months. Therefore, cost-effective biogas plant management is possible through the application of TXRF spectrometry to monitor trace elements.     

Electronic stopping power calculation method for molecular dynamics simulations using local Firsov and free electron-gas models

Molecular dynamics simulations have proven to be accurate in predicting depth distributions of low-energy ions implanted in materials. Free parameters adjusted for every ion-target combination are conventionally used to obtain depth profiles in accordance with the experimental ones. We have previously developed a model for predicting depth profiles in crystalline Si without free parameters. The electronic stopping power was calculated using local total electron density. The model underestimated the stopping in the ?1 1 0? channeling direction. We have now taken a new approach to calculate the electronic stopping power. We use the local valence (3p²) electron density to account for the electronic energy loss between collisions and the Firsov model to account for the electronic energy loss during collision. The lowest electron densities are adjusted with a parametrization that is same for all ions in all implanting directions to correct the problems in the ?1 1 0? channeling direction.     

High‐energy polarized‐beam EDXRF for trace metal analysis of vegetation samples in environmental studies

The aim of this work was to achieve improved instrumental sensitivity and detection limits for the determination of several trace elements (Cd, Pb, As, Cu, Fe and Zn) in different vegetation species collected at two mining areas in Spain (Aran Valley and Cartagena) by using new instrumentation based on high‐energy polarized‐beam energy‐dispersive x‐ray fluorescence analysis. Cd was determined by using its Kα line, while the mutual interference of As and Pb was solved by employing selective excitation conditions with targets of different materials. The use of a standardless fundamental parameter approach (IAEA QXAS) allowed the determination of other metals in the absence of suitable certified reference materials and to compensate accurately for self‐attenuation effects in the sample. The proposed methodology provides an alternative analytical tool to classical destructive analytical methods, commonly applied for the determination of these toxic elements in vegetation matrices, with accuracy and precision levels fulfilling the requirements for environmental studies. Copyright © 2006 John Wiley & Sons, Ltd.     

Superexchange mechanism of energy transfer between neighboring lanthanide ions in dielectric crystals

It is shown that unusually rapid energy transfer between neighboring lanthanide ions in dielectric crystals is caused by the efficient short-range interaction, which is similar to the magnetic superexchange interaction. Both these interactions are related to virtual transition of electrons between lanthanide ions via common bridge ligands. A general method is developed for calculating matrix elements of the effective superexchange Hamiltonian, and the rates of energy transfer in exchange-coupled pairs of lanthanide ions are estimated. The possibility of using the superexchange model of energy transfer for analysis of up-conversion in lanthanide crystals is discussed.     

A finite element method for damped acoustic systems: An application to evaluate the performance of reactive mufflers

The approximate equations governing the forced harmonic motion of a damped acoustic system are set up by using a variational principle. Acoustic finite elements are then used in a computer program to study the transmission loss and insertion loss performance of some expansion chamber mufflers. The manner in which the equations are set up allows a number of input and output nodes, and two-dimensional effects involving the influence of transverse acoustic modes to be taken into account. Although only the simplest of elements and coarse mesh sizes are used the resulting accuracy of the solutions is extremely good; thus the method should be a viable one for studying the performance of more complicated mufflers, having variable cross-sections and internal energy dissipation.