The problem of diffusion during charged particle activation analysis; the case of18F in pure germanium single crystals

During ion bombardment, thermal diffusion and radiation enhanced diffusion of atoms occur. These phenomena may be a source of error in ion beam analysis, particularly in radioactivation analysis if contaminant surface atoms are present. It is shown here that penetration of¹⁸F (derived from surface oxygen by nuclear reaction) in germanium single crystals, does not extend appreciably farther than the maximum range of the recoiling¹⁸F nuclei. Since the analyzed depth is over an order of magnitude larger than the recoil, the validity of charged particle activation analysis at the ppb level in the present case (oxygen→¹⁸F in germanium), is clearly demonstrated.     

Characterization of oxygen and argon ion flux interaction with PET surfaces by in-situ XPS and ex-situ FTIR

The effects of low (2.5, 0.2 keV) energy reactive oxygen ion bombardment and argon ion bombardment on poly(ethylene terephthalate) thin film (PET) surface chemical composition were studied. PET films have a high potential as a material for biomedical and electrical industries. The source of ions was an ECR Ion Gun with settable acceleration voltages. PET films were sputtered by ion bombardment for variable process time and the modified films were investigated by in-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Fourier transform infrared spectroscopy (FTIR). The significant changes in the chemical composition of surface layers were quantitatively studied by XPS. The ion bombardment scissions the chains in PET film surface layers. Selective sputtering of oxygen atoms from PET surface was observed when argon ion flux used. The 0.2 keV and 2.5 keV argon ion decreased O/C ratio from 0.37 to 0.25, 0.04 respectively. This phenomenon is responsible for the creation of carbon-rich up 96 at.% surface layer and the oxygen in ester bonds is detached first. The oxygen 2.5 keV ion bombardment had similar effect as argon ion bombardment; the ratio O/C was decreased. The ester bond was broken first. But oxygen 0.2 keV ion flux irradiation created an oxygen rich surface; the O/C ratio was in increased from 0.37 to 0.46. The changes in surface conductivity were investigated by shifts in C1s binding energy. Good agreement with atomic concentration of carbon in C-C bonds on the films surface was found. The FTIR analyses identified changes in chemical composition but with no obvious correlation to surface changes. Photons from the ion source irradiating the PET film during ion bombardment probably caused the observed changes in FTIR spectra.     

Behavior of nitrided and carburized AISI 904 L stainless steels under severe light ion beam irradiation with plasma focus

Superaustenitic stainless steels have become of growing interest in industrial and technological fields, but there is not a complete understanding on their fundamental properties and their performances. For this paper, AISI 904 L superaustenitic samples were nitrided and carburized in order to study the expanded austenite stability under severe deuterium and helium ion bombardment. Surface treatments were conducted using pulsed plasma glow discharges in a low pressure atmosphere, and a dense plasma focus device was used to irradiate the samples. Characterization techniques used were focused ion beam/SEM, energy‐dispersive X‐ray spectroscopy, and grazing incidence X‐ray diffraction. Our results showed in carburized samples lattice expansion growth with the time treatment, but in nitrided samples, an expanded austenite reduction with time treatment was observed due to the formation of nitride nanoagglomerates. Moreover, this ion impingement provoked surface melting and a severe collision cascade, and a damaged bead located under the craters composed solely of minor alloying atoms. Furthermore, nitrided samples were more stable following ion bombardment than the carburized ones. When helium ions were used, the loss of expansion (triggered by diffusion processes of N or C to deeper regions) was more pronounced in the expanded austenite, but when deuterium ions were used to bombard the sample, there was a crystallite development of stressed austenite, which provoked a diffraction peak arousal at 43.3°. Copyright © 2015 John Wiley & Sons, Ltd.     

SIMS using O−, F−, Cl−, Br− and I− primary ion bombardment

The success of secondary ion mass spectrometry (SIMS) analyses depends largely on the ionization probability of the analyzed elements. The chemical state of the surface changes with the chemical nature and the concentration of implanted ions. The positive ionization probability can be enhanced by bombarding the surface with electronegative elements. In view of such an enhancement of the positive secondary ion yield, we present SIMS analyses carried out with O^?, F^?, Cl^?, Br^? and I^? primary ion beams. Useful yields were experimentally determined for metal (Al, Ni, Cu, Ag and Ta) and semiconductor samples (Si, Ge, InP and GaAs). For metal samples, an enhancement of the useful yield under halogen bombardment, compared with O^? bombardment, was observed for Ni, Cu and Ag under F^? bombardment (enhancement of up to two orders of magnitude). For semiconductors, lower useful yields are obtained under halogen bombardment as compared with O^? bombardment. The observed results are discussed in terms of the surface concentration of the implanted primary ion species and their electronegativity. Copyright © 2012 John Wiley & Sons, Ltd.     

Understanding gold-thiolate cluster emission from self-assembled monolayers upon kiloelectronvolt ion bombardment

This article focuses on the emission of organometallic clusters upon kiloelectronvolt ion bombardment of self-assembled monolayers. It is particularly relevant for the elucidation of the physical processes underlying secondary ion mass spectrometry (SIMS). The experimental system, an overlayer of octanethiols on gold, was modeled by classical molecular dynamics, using a hydrocarbon potential involving bonding and nonbonding interactions (AIREBO). To validate the model, the calculated mass and energy distributions of sputtered atoms and molecules were compared to experimental data. Our key finding concerns the emission mechanism of large clusters of the form MxAuy up to M6Au5 (where M is the thiolate molecule), which were not observed under sub-kiloelectronvolt projectile bombardment. Statistically, they are predominantly formed in high-yield events, where many atoms, fragments, and (supra)molecular species are desorbed from the surface. From the microscopic viewpoint, these high-yield events mostly stem from the confinement of the projectile and recoil atom energies in a finite microvolume of the sample surface. As a result of the high local energy density, molecular aggregates desorb from an overheated liquidlike region surrounding the impact point of the projectile.     

Ion‐beam‐induced morphology on the surface of thin polymer films at low current density and high ion fluence

The effect of Xe⁺ bombardment on the surface morphology of four different polymers, polystyrene (PS), poly(phenylene oxide), polyisobutylene, and polydimethylsiloxane, was investigated in ion energy and fluence ranges of interest for secondary ion mass spectrometry depth‐profiling analysis. Atomic force microscopy (AFM) was applied to analyze the surface topography of pristine and irradiated polymers. AFM analyses of nonirradiated polymer films showed a feature‐free surface with different smoothness. We studied the influence of different Xe⁺ beam parameters, including the incidence angle, ion energy (660–4000 eV), current density (0.5 × 10² to 8.7 × 10² nA/cm²), and ion fluence (4 × 10¹⁴ to 2 × 10¹⁷ ion/cm²). Xe⁺ bombardment of PS with 3–4 keV at a high current density did not induce any change in the surface morphology. Similarly, for ion irradiation with lower energy, no surface morphology change was found with a current density higher than 2.6 × 10² nA/cm² and an ion fluence up to 4 × 10¹⁶ ion/cm². However, Xe⁺ irradiation with a lower current density and a higher ion fluence led to topography development for all of the polymers. The roughness of the polymer surface increased, and well‐defined patterns appeared. The surface roughness increased with ion irradiation fluence and with the decrease of the current density. A pattern orientation along the beam direction was visible for inclined incidence between 15° and 45° with respect to the surface normal. Orientation was not seen at normal incidence. The surface topography development could be explained on the basis of the balance between surface damage and sputtering induced by the primary ion beam and redeposition–adsorption from the gas phase. Time‐of‐flight secondary ion mass spectrometry analyses of irradiated PS showed strong surface modifications of the molecular structure and the presence of new material. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 314–325, 2001     

Tailoring and investigation of surface chemical nature of virgin and ion beam modified muscovite mica

We report that the surface chemical properties of muscovite mica [KAl₂(Si₃Al)O₁₀(OH)₂] like important multi-elemental layered substrate can be precisely tailored by ion bombardment. The detailed X-ray photoelectron spectroscopic studies of a freshly cleaved as well as 12-keV Ar⁺ and N⁺ ion bombarded muscovite mica surfaces show immense changes of the surface composition due to preferential sputtering of different elements and the chemical reaction of implanted ions with the surface. We observe that the K atoms on the upper layer of mica surface are sputtered most during the N⁺ or Ar⁺ ions sputtering, and the negative aluminosilicate layer is exposed. Inactive Ar atoms are trapped, whereas chemically reactive N atoms form silicon nitride (Si₃N₄) and aluminum nitride (AlN) during implantation. On exposure to air after ion bombardment, the mica surface becomes more active to adsorb C than the virgin surface. The adsorbed C reacts with Si in the aluminosilicate layer and forms silicon carbide (SiC) for both Ar and N bombarded mica surfaces. Besides the surface chemical change, prolonged ion bombardment develops a periodic ripple like regular pattern on the surface.     

The binary alloy system Au/Pd; a SIMS study

Sputtering yields, positive secondary ion yields and relative degrees of ionization of sputtered atoms under bombardement of 10keV O₂⁺-ions have been determined for the single-phase binary alloy system Au/Pd. A weak minimum of the total sputtering yields was observed at a Pd-concentration around 75% atomic.Strong surface topography was found after high-dose ion bombardment. Sputtering yields, together with surface enrichment factors determined by Auger Electron Spectroscopy have been used to calculate surface binding energies for both alloy components.The apparent degree of ionization for positive ions shows a different behaviour for the two alloy components; whereas an almost constant value was found for Au, a distinct maximum at a Pd-concentration of about 40% was observed for Pd. The measurements indicate that, in the concentration range investigated, the concept of constant relative sensitivity factors would yield large analytical errors when applied to the quantization of secondary ion mass spectra of Au/Pd alloys.     

覆氧或氧离子轰击下固体表面二次正离子发射的研究

通过对离子轰击下固体表面电离过程重新考虑认为，在固体表面覆氧或氧离子轰击下除表面原子的直接电离外，激发态双原子间电子交换和断键亦起重要作用。在此基础上修正了局部热力学平衡模型，得到了一个包含各类离子内配分函数、电离能、金属－氧原子键断键能以及表面金属原子与氧原子结合份数等参数决定的新电离几率分析表达式。应用该分析表达式解释了金属表面覆氧、氧离子轰击金属、化合物半导体表面二次离子发射中氧增强效应、充氧量对二次离子发射的影响及其基体效应等实验现象。并由此得到了元素相对灵敏度因子的分析表达式，对化合物半导体及一些陶瓷材料表面二次离子质谱分析中元素灵敏度因子随元素电离能变化曲线给予了相应的物理解释。     

Atomic, molecular and cluster dynamics on flat and stepped surfaces

Surface diffusion is responsible for transport of atoms at the surface. It is therefore essential for understanding many surface phenomena where transport of atoms and molecules are involved. Using the field ion microscope and scanning tunneling microscope, we have directly observed many elementary surface atomic and molecular processes at terraces and steps and have measured the activation barrier heights of these processes, and have also studied their atomic mechanisms in detail. For Si(111) surface, transport of atoms above 450°C appears to be achieved by magic clusters of about 10–15 atoms in size, and their diffusion behavior is very different from those of individual atoms and molecules. We discuss how atom dynamics affects the growth behavior, island shape transitions, and growth modes in the growth of crystals and epitaxial films.     

Ion beam modification of metals: Compositional and microstructural changes

Ion implantation has become a highly developed tool for modifying the structure and properties of metals and alloys. In addition to direct implantation, a variety of other ion beam techniques such as ion beam mixing, ion beam assisted deposition and plasma source ion implantation have been used increasingly in recent years. The modifications constitute compositional and microstructural changes in the surface of the metal. This leads to alterations in physical properties (transport, optical, corrosion, oxidation), as well as mechanical properties (strength, hardness, wear resistance, fatigue resistance). The compositional changes brought about by ion bombardment are classified into recoil implantation, cascade mixing, radiation-enhanced diffusion, radiation-induced segregation, Gibbsian adsorption and sputtering which combine to produce an often complicated compositional variation within the implanted layer and often, well beyond. Microstructurally, the phases present are often altered from what is expected from equilibrium thermodynamics giving rise to order-disorder transformations, metastable (crystalline, amorphous or quasicrystalline) phase formation and growth, as well as densification, grain growth, formation of a preferred texture and the formation of a high density dislocation network. All these effects need to be understood before one can determine the effect of ion bombardment on the physical and mechanical properties of metals. This paper reviews the literature in terms of the compositional and microstructural changes induced by ion bombardment, whether by direct implantation, ion beam mixing or other forms of ion irradiation. The topics are introduced as well as reviewed, making this a more pedogogical approach as opposed to one which treats only recent developments. The aim is to provide the tools needed to understand the consequent changes in physical and mechanical properties.     

原位XPS技术研究碳化铀的表面氧化

采用X射线光电子能谱(XPS)原位分析研究了298 K时烧结UC的清洁表面在O₂气氛中的初始氧化过程. UC试样清洁表面通过氩离子束长时间溅射获取. 初始反应各阶段U4f, O1s和C1s芯能级谱的变化显示样品表面的氧化产物为UO₂和自由碳. 当O₂饱和吸附后, UC表面氧化膜的增长呈抛物线型, 氧透过氧化膜的扩散为UC进一步氧化的速率控制步骤. 定量分析表明, 反应过程中U, C原子均未出现明显的表面偏析.     

Structure and reactivity of GaAs surfaces

First the analytical tools, preparation methods and surface crystallography of clean GaAs surfaces are briefly reviewed. Besides the usual methods of cleaving, ion bombardment and annealing, molecular beam epitaxy is mainly used as a growth method under UHV conditions, and has brought a manifold of differently reconstructed structures on the same crystallographic surface, depending on the exact experimental conditions during growth. Quantitative analysis of the surface composition by AES gives the result that these structures differ only in the amount of As in the topmost layer. From the combination of theoretical LEED analysis, UPS results and arguments considering the different physicochemical nature of Ga and As atoms, rehybridisation of the surface atomic bonds emerges as the driving force for reconstruction: the surface Ga atoms try to assume a trivalent planarsp² and the As atoms a trivalentp³ configuration with three mutually perpendicularp-bonds. The better this rehybridised configuration can be achieved, the better is the chemical stability of the respective structure. The sticking coefficient for oxygen, although generally low, thus varies between ～10^-4 and <10^-9, depending on the crystallographic surface and, on the same surface, on the degree of surface bond saturation given by the respective structure. However, it emerges that, at least on As-depleted polar surfaces, adsorption proceeds via a mechanism of removal of Ga atoms during exposure and adsorption on the defect sites created in this way. The existence of such a complicated mechanism is consistent with the difficulties arising with the preparation of thick stoichiometric oxide layers, the preparation methods and properties of which are reviewed briefly in the last section.     

A time-dependent molecular orbital approach to electron transfer in ion–metal surface collisions

A time-dependent molecular orbital method has been developed to study charge transfer in collisions of ions with metal surfaces at energies between 1 and 100 au. A set of localized basis functions consisting of generalized Wannier functions for the surface and s- and p-atomic functions for the ion, is used to separate the system into primary and secondary regions. An effective Hamiltonian and time-dependent equations for the electron density matrix are obtained in the primary region, where most charge transfer occurs. The equations for the electron density matrix are solved with a linearization scheme. The method is suitable to study atomic orbital orientation for collisions of ions and surfaces. A model calculation for Na⁺ + W(110) collisions with a prescribed trajectory is presented. The interaction potentials between the W(110) surface and Na⁺ 3s and 3p orbitals are calculated from Na⁺ pseudopotentials. Results show that the yield of neutralized atoms in 3p states changes as the collision energy is lowered.     

Cr-AlN界面的二次离子质谱研究

采用电子束蒸发的方法在２００℃抛光的氮化铝（ＡｌＮ）陶瓷衬底上淀积２００ｎｍ的Ｃｒ膜，并在高真空中退火。利用ＭＣｓ＋－ＳＩＭＳ技术（在Ｃｓ＋一次离子轰击下检测ＭＣｓ＋型二次离子）对样品进行了深度剖析，给出了界面组分分布随退火温度与时间的变化关系。结果表明，ＭＣｓ＋－ＳＩＭＳ技术是研究金属－陶瓷界面扩散与反应的有效方法。     

Rapid surface functionalization of poly(ethersulphone) foils using a highly reactive oxygen‐plasma treatment

We present a study of the oxygen‐plasma functionalization of polyethersulphone (PES). PES samples were exposed to a weakly ionized, highly dissociated oxygen plasma, with an electron temperature of 5 eV and a positive ion density of 8 × 10¹⁵ m^?3, and its afterglow, in which the density of charged particles was negligibly low and the density of neutral oxygen atoms was 4 × 10²¹ m^?3. The wettability of the samples was determined by measuring the contact angle of a water drop, while the appearance of the functional groups on the surface of the samples was determined using high‐resolution conventional XPS. The samples were saturated with surface functional groups, both in the plasma and in the afterglow region, after 1 s of treatment time. The results are explained by the high flux of oxygen atoms on the sample surface and the characteristics of the oxygen plasma. Copyright © 2007 John Wiley & Sons, Ltd.     

Comparative studies of SIMS and SNMS analyses during the build up of sputter equilibrium under oxygen and rare gas ion bombardment

Sputtering of solid surfaces by using a focused ion beam is the basis for secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS). The ion bombardment initiates not only redistribution of sample atoms but also massive changes in the surface and near surface composition of the bombarded area due to the sputter process and implantation of the primary ions. Changes in the matrix-composition affects the secondary ion yields and therefore a steady state (sputter equilibrium) has to be reached before SIMS data can give quantifiable results. SNMS is much less affected by those yield effects and therefore a combination of SIMS and SNMS can establish a basis for interpretation of SIMS data before the steady state is reached. In order to determine the effects of primary ion incorporation, we applied different primary ion species successively to generate different equilibria. An oxygen ion beam oxidizes the sample surface and by using a rare gas primary ion (PI) this oxide can be removed and analyzed.     

Detection of surface atoms by energy analysis of scattered primaries and recoiled secondaries from CsBr under Ar+ and Ar+ bombardment

Time-of-flight (TOF) and electrostatic sector analysis (ESA) have been used to measure particles scattered and sputtered by direct recoils and surface recoils during 3 keV Ar⁺ and 6 keV Ar²⁺ bombardment of CsBr at forward and backscattering angles. Charge fractions of scattered argon and recoiling surface atoms are obtained. Hydrogen and oxygen surface impurities are detected predominantly as directly recoiled neutrals.     

Mass Distribution and Diffusion of [1‐Butyl‐3‐methylimidazolium][Y] Ionic Liquids Adsorbed on the Graphite Surface at 300–800 K

The structure and diffusion behavior of 1‐butyl‐3‐methylimidazolium ([bmim]⁺) ionic liquids with [Cl]^?, [PF₆]^?, and [Tf₂N]^? counterions near a hydrophobic graphite surface are investigated by molecular dynamics simulation over the temperature range of 300–800 K. Near the graphite surface the structure of the ionic liquid differs from that in the bulk and it forms a well‐ordered region extending over 30 Å from the surface. The bottom layer of the ionic liquid is stable over the investigated temperature range due to the inherent slow dynamics of the ionic liquid and the strong Coulombic interactions between cation and anion. In the bottom layer, diffusion is strongly anisotropic and predominantly occurs along the graphite surface. Diffusion perpendicular to the interface (interfacial mass transfer rate k_t) is very slow due to strong ion–substrate interaction. The diffusion behaviors of the three ionic liquids in the two directions all follow an Arrhenius relation, and the activation barrier increases with decreasing anion size. Such an Arrhenius relation is applied to surface‐adsorbed ionic liquids for the first time. The ion size and the surface electrical charge density of the anions are the major factors determining the diffusion behavior of the ionic liquid adjacent to the graphite surface.     

Study of in-situ surface cleaning for Si and SiGe epitaxy on Si with a novel ion beam vapor/assisted deposition technique

Ion beam vapor deposition is a new technique to grow Si and SiGe layers on Si substrates at low temperatures. The in situ surface cleaning prior to the deposition is a crucial step in the epitaxial growth of Si and SiGe films and is achieved by Ar ion bombardment with substrates kept at ambient temperature. A high temperature annealing (800 °C) is needed to repair the damage caused by this bombardment. We studied the effects of ion beam energy and the substrate temperature during the in situ cleaning on the quality of the grown films. An ion beam energy of 150–200eV is found to be sufficient to clean the surface for epitaxial growth. While the films deposited on properly cleaned surfaces are epitaxially grown, the inadequately cleaned surface leads to the formation of polycrystalline layers especially at low substrate temperatures.