Thermal effect of ion implantation with ultra-short ion beams

Ion implantation with plasma guns operated in the detonation mode presents several differences from normally used low current ion implanter systems.

The most important differences are the high power of the beams generated with the plasma guns owing to their pulsed nature on one hand, and the plasma environment in which the target is immersed during the process of implantation on the other hand. Both effects were studied in this work.

The temperature profiles and their evolutions during and after nitrogen implantation in pure titanium, stainless steel and copper were investigated by using the finite differences method. The calculation for nitrogen ion implantation (fluence of 10¹³ cm⁻² and pulse time of 400 ns) in pure titanium, shows melting layers of 20 ns after the first 200 ns of implantation, with a fast cooling after the end of implantation. Thermal gradients of 1000 K μm⁻¹ and a heating rate of 5 K ns⁻¹ were also observed.

Optical spectroscopy observations (real time spectroscopy) of the implantation region show a highly activated nitrogen plasma.

Both effects can be of extreme importance in several applications such as, for example, titanium nitriding because of an extra temperature assisted absorption by the getter effect.     

等离子体浸没离子注入(PⅢ)在材料表面改性中的应用及发展

等离子体浸没离子注入(PⅢ)是一种用于材料表面改性的新的离子注入技术.系统地分析和讨论了等离子体浸没离子注入技术的原理和特点:该技术直接将待处理材料浸没在等离子体中进行注入,保留了常规束线离子注入(CBⅡ)技术的主要特点,消除了常规束线离子注入所固有的视线限制,克服了保持剂量问题,使注入装置变得简单和价廉.综述了等离子体浸没离子注入技术在金属材料、半导体材料和高分子材料改性方面的应用.展示了等离子体浸没离子注入技术应用的发展前景.     

Improve retained dose and impact energy of inner surface plasma immersion ion implantation using long pulse duration with deflecting electric field

Not restricted by the line-of-sight process, plasma immersion ion implantation (PIII) has shown great potential for inner surface modification, but the impact energy and retained dose turned to be very low. The process was investigated numerically and experimentally in this paper. The results show that a high percentage of low impact energy ions was the key factor that resulted in low impact energy on the inner surface. This was caused by sheath overlapping and appearance of the dead zone during inner surface PIII. Long pulse duration could alleviate this problem and increase ion impact energy on the inner surface, hence the implant depth, which was key factor for the modifying effect of PIII. Also, long pulse duration was helpful in improving the retained dose on the inner surface.     

Effect of Sn ion implantation on electrochemical behavior of zircaloy-4

In order to study the effect of tin ion implantation on the aqueous corrosion behavior of zircaloy-4, specimens were implanted by tin ions with a dose range from 1×10¹⁶ to 5×10¹⁷ ions/cm² at an extracted voltage of 40 kV. The valence and element penetration distribution of the surface layer were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES), respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the micro-morphology and microstructure of tin-implanted samples. When the dose is 5×10¹⁶ ions/cm² or higher, a large number of small tin balls are produced in the implanted surface. The potentiodynamic polarization measurement was employed to evaluate the aqueous corrosion resistance of zircaloy-4 in a 0.5 M H₂SO₄ solution. It was found that a significant improvement was achieved in the aqueous corrosion behavior of zircaloy-4 implanted with tin when the dose is 1×10¹⁶ ions/cm². When the dose is higher than 1×10¹⁶ ions/cm², the corrosion resistance of zircaloy-4 implanted with tin ions decreased compared with that of the as-received zircaloy-4. Finally, the mechanism of the corrosion behavior of the tin-implanted zircaloy-4 is discussed.     

Ionic implantation at low energy: application to the shallow junction accomplishment and surface functionalization

The proposed work deals with rapid thermal processing of ionic boron (¹¹B⁺) and boron difluoride (BF₂⁺), implanted in phosphorusdoped Cz-(100) silicon substrates through protecting oxide films, under different technological parameters. After implantation, the samples were rapidly thermally annealed at temperatures ranging from 900 to 1100 °C, in argon ambient gas, for different annealing durations. The rapid thermal annealings (RTAs) are carried out also, for some samples, after oxide mask removal. The total boron, fluorine as well as oxygen concentrations versus depth profiles, before and after annealing steps, in the SiO₂/Cz-(100) silicon systems were determined using secondary ion mass spectrometry (SIMS). Using a background concentration, the junction depth in the substrate has been investigated under different annealing experimental conditions. The kinetic diffusion process of implanted boron into oxide and monocrystalline silicon during rapid thermal treatments has also been investigated. The reported results show that boron diffusion in the BF₂⁺ case is widely reduced during rapid thermal treatments. Discussions of this are based on the effect of both knocked-on oxygen and fluorine on the boron diffusion kinetics.     

Tribological properties and hardness of silicon nitride ceramics after ion implantation and subsequent annealing

Silicon nitride ceramic (β-Si₃N₄) with Y₂O₃ and Al₂O₃ as sintering additives was implanted with Cr or Ti ions to a fluence of 10¹⁷ cm⁻² at energies ranging from 200 keV to 2 MeV. Changes in the phase composition in the near surface layer due to the implantation and subsequent annealing at 1000 and 1200 °C and their correlation with the behaviour of hardness and wear were investigated. Implantation results in amorphization of the near surface layer, which is buried for MeV implantations. For Ti-implanted samples, annealing leads to oxidation, resulting in the formation of γ-YSi₂O₇ and cristobalite besides the β-Si₃N₄. In the case of Cr implantation with MeV energies, the amorphous layer recrystallizes to -Si₃N₄ already at 1000 °C catalyzed by the chromium. This causes a significant suppression of the oxidation. Consequently, the hardness and the tribological behaviour of Ti- and Cr-implanted samples, respectively, are affected differently by the annealing process. For chromium, the improved wear behaviour due to the high-energy implantation remains after annealing while the reduced hardness as result of the amorphized surface is partly recovered. For titanium, the oxide formation leads to a poorer hardness and tribological behaviour.     

Surface analysis and corrosion behavior of zirconium samples implanted with yttrium and lanthanum

Zirconium specimens were implanted with yttrium and lanthanum ions with a fluence ranging from 1×10¹⁶ to 1×10¹⁷ ions/cm² at approx. 130 °C, using a metal vapor vacuum arc source at an extraction voltage of 40 kV. The surfaces of the implanted samples were then analysed. The valence states of elements in implanted surface layer were analysed by X-ray photoelectron spectroscopy (XPS), which showed that yttrium existed in the form of Y₂O₃, and lanthanum existed in the form of La₂O₃. Depth distributions of elements in the implanted surface of samples were obtained by Auger electron spectroscopy (AES), which showed that the oxide film of zirconium substrate became thicker with increasing implantation fluence, the thicknesses of the oxide films reached the maximum approximately to the fluence of 1×10¹⁷ ions/cm². Rutherford back-scattering indicates that a profile of La appears in Zr around the depth of 30 nm, which also indicates that a serious sputtering occurred during the (La+Y) 1×10¹⁷ ions/cm² implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of the implanted-zirconium samples in 0.6 M H₂SO₄. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zirconium compared with that of as-received zirconium when the fluence is smaller than 5×10¹⁶ (Y+La)/cm². The mechanism of the corrosion behavior of the implanted-zirconium samples was discussed.     

TA2钛板掺杂钒离子渗碳层的耐腐蚀性能

为提高钛基双极板的耐腐蚀性能和导电性,在TA2纯钛的表面进行双辉离子渗碳,另外为降低渗碳温度,在渗碳过程中掺杂钒。使用扫描电镜和能谱分析、X射线衍射对改性层的组织结构、化学成分、物相组成进行研究,并测得改性层的界面接触电阻率、耐腐蚀性能。结果表明,在优化的制备工艺参数下,在TA2表面生成结构致密的TiC改性层、钒掺杂渗碳改性层。当压实力为140 N/cm²时,730℃下制备的钒掺杂渗碳改性层、850℃下制备的TiC改性层、TA2基体的界面接触电阻率分别是1.17、3.66、14.71 mΩ/cm²。在模拟双极板的工作环境中,测得730℃下制备的钒掺杂渗碳改性层、850℃下制备的TiC改性层的自腐蚀电流密度分别是5.238、7.563μA/cm²,均比TA2基体的腐蚀电流密度低1个数量级。在离子渗碳的过程中掺杂钒可以有效降低渗碳的工艺温度,并且提高TA2基体的导电性和耐腐蚀性能。     

Structure and properties of amorphous diamond-like carbon films produced by ion beam assisted plasma deposition

The microstructure and tribological properties of carbon film produced by ion beam assisted plasma deposition in a plasma source ion implantation (PSII) chamber with energies varied from 0 to 30 keV are examined. The process is illustrated schematically, and Raman spectra as well as TEM images and corre-sponding diffraction patterns of carbon films are shown.     

The ion-beam processing of powders

Many of the properties of a powder are determined by the its surface. Therefore, surface modification is one useful tool for modifying powder properties. Ion-beam techniques have the advantage of being highly controllable, single-step processes. One problem, however, is that ion beams are line-of-sight processes; hence, rather sophisticated devices must be used to agitate the powder in the beam. In this review, different facilities for the ion-beam treatment of powder, including ion implantation and ion-beam-assisted deposition, are described. Basic results on radiation damage, annealing behavior, degree of doping, and resulting properties are discussed. As examples for potential applications, results on the catalytic activity of ion-beam-modified powders for gas-phase reactions and electrocatalysis in aqueous systems are discussed.     

Improvement of tribological properties by ion implantation

Many different measurements confirm that ion implantation changes the friction and wear behaviour, which are the most important properties of tribological systems. Unfortunately, these properties will not always be improved. In industrial application, very often different results of the effects of ion implantation into tools or machine components can be observed, even if the same materials are used. A very important reason for this is the different stresses on the tribological systems. Our own practical experience has so far proved ion implantation to be advantageous in the fields of cutting and milling tools, injection moulds, calibration tools for plastics extrusion, punches and dies, surgical instruments, and wear parts of combustion engines.

Year by year, experience of the effective industrial use of ion implantation is gained. However, many investigations of tribometers and real engines using the on-line radionuclide wear measurement technique show us more and more that we are not yet able to understand the complicated physical and chemical reasons for the changes in tribological properties. We do not have a useful theory for the wear processes, so it is not possible to deduce the effects of ion implantation. Predictions can only be made from experience, and are poorly defined. This situation is the main reason for the slow introduction of ion implantation in industry.

To find a new applicable theory of friction and wear, much more attention must be given to the following aspects of fundamental importance.

1. (1) The energy input caused by friction, which is a function of the stress and other parameters of the tribosystem, within a short time leads to the appearance of energy islands, which are statistically distributed over the surfaces. The density of energy within these tiny energy islands is very high.

2. (2) One result of these high energy densities is a mutation of the material's composition and structure within a very thin layer of less than 100 nm underneath the surface. Another result is wear.

3. (3) Ion implantation also changes the composition and structure of the bulk material close to the surface.

4. (4) Together with the wearing surfaces, the mutating compositions and structures migrate into the depth of the material.

Thus there is urgent need to increase our knowledge of the tribo-induced mutations of ion-implanted materials and their influence on the tribological properties. For that reason surface analyses have to be carried out to determine the composition and structure of the materials and the mutation caused by friction and wear. Complementary sensitive wear analysis will then enable new models and theories to be developed and corroborated.

This is a difficult but interesting challenge to modern physicists, chemists and engineers.     

Spectroscopic properties of Yb: LuLiF4 crystal grown by the Czochralski method for laser applications and evaluation of quenching processes: a comparison with Yb: YLiF4

Spectroscopic properties of Yb³⁺ ion in LuLiF₄ (LLF) laser host are presented here for the first time. Czochralski technique was used to grow undoped and Yb³⁺-doped LLF single crystals under CF₄ atmosphere. Detailed analysis of Yb³⁺-doped LLF spectroscopy were made to contribute to the determination of energy levels in this host and a comparison with the isomorphic YLiF₄ (YLF) laser host is done. We are dealing with temperature and concentration dependences of both π and σ polarizations of the infrared (IR) absorption and emission spectra. Raman spectra were also used to give an attempt for the interpretation of electronic and vibronic levels. Concentration dependence of fluorescence lifetimes allows the measurement of the high radiative lifetime in the range of 2–3 ms and shows a strong self-trapping process. Self-quenching was not seen by the reduction of the decay times but observed by non-radiative up-conversion energy transfer due to the presence of Er³⁺ and Tm³⁺ ions as unexpected impurities. Contrary to oxide crystals this process still remains lower than the self-trapping process. Yb³⁺ pairing and clustering were investigated as well. Evaluation of the laser potentiality of this host by the evaluation of figure-of-merit developed by our group is presented.     

Spin and valence state equilibria of cobalt and magnetic properties of LaCoO3

On the basis of the spin and valence state equilibria and superexchange interaction of the various cobalt ions in LaCoO₃, an approximate semiempirical formula has been proposed and used to calculate magnetic susceptibilities of LaCoO₃ over a wide temperature range (100–1200 K). The results indicate that there are thermodynamic equilibria between the low spin state Co^III (t_2g⁶e_g⁰) ion, the high spin state Co³⁺ (t_2g⁴e_g²) ion, the Co^II (t_2g⁶e_g¹) ion and the Co^IV (t_2g⁵e_g⁰) ion in LaCoO₃. The energy difference between the low spin state Co^III and the high spin state Co³⁺ is about 0.006 eV. The content of the low spin state Co^III ion is predominant in LaCoO₃ and the content of the high spin state Co³⁺ ion varies with temperature, reaching a maximum at about 350 K, then decreasing gradually with increasing temperature. At low temperature the contents of the Co^II ion and the Co^IV ion in LaCoO₃ are negligible, while above 200 K the contents of both the Co^II ion and the Co^IV ion increase with increasing temperature; however, the content of the Co^II ion always is larger than that of the Co^IV ion at any temperature. These calculated results are in good agreement with experimental results of the Mössbauer effect, magnetic susceptibility and electrical conductivity of LaCoO₃.     

Application of lanthanide ion doped alkaline metal sulfates to ESR imaging

Imperfections and defects are well known to form in the alkaline metal sulfates after X-ray irradiation. The paramagnetic radicals (SO₃⁻ and SO₄⁻) were produced by the irradiation of X-ray in the Gd ion doped K₃Na(SO₄)₂. The ESR signal of SO₃⁻ radical in the Gd ion doped K₃Na(SO₄)₂ was isotropic and thermally stable. The ESR signal intensity depended on an absorbed dose range of X-ray from 10⁻⁵ to 10² Gy. We planned to apply lanthanide (Ln) ion doped K₃Na(SO₄)₂ rods to ESR imaging. Two-dimensional ESR image shows clearly a distribution of SO₃⁻ radical formed in the Gd ion doped K₃Na(SO₄)₂ rod by the irradiation of X-ray. The results obtained in this study suggest that the Gd ion doped K₃Na(SO₄)₂ rod is available to two-dimensional ESR dosimetry.     

Plasma immersion ion implantation into cylindrical bore using internal inductively-coupled radio-frequency discharge

Plasma immersion ion implantation (PIII) is a potentially excellent interior surface treatment technique due to no line-of-sight restriction. However, some problems have been encountered due to the low ion energy and ion fluence non-uniformity especially for treatment of the interior wall of a thin tube. In this paper, a new method for inner surface PIII using internal inductively-coupled radio-frequency (RF) discharge is described. A cylindrical inductive coil inserted inside the tube serves as both the plasma source and grounded electrode to avoid overlapping of the plasma sheath fronts propagating from opposite sides. The effects of the gas species, gas pressure, RF power, and number of coil turns are investigated. Our results demonstrate the feasibility of this novel inner surface treatment method and the number of turns in the coil has a critical influence on the discharge behavior. If the number of turns is little, the plasma density is low and non-uniform inside the tube due to the relatively intense capacitively-coupled RF discharge at the two ends. In contrast, the plasma density and uniformity are evidently improved by using more turns in the coil.     

Converting polycrystals into single crystals – Selective grain growth by high-energy ion bombardment

Common failure mechanisms in microelectronics such as electromigration, creep and fatigue can be positively influenced by microstructure optimization. In this paper a new mechanism of microstructure optimization in thin metal films is proposed. Post-deposition ion bombardment can produce an in-plane texture in originally highly fiber textured thin metal films by a selective grain growth process. In extreme cases the in-plane texture becomes as sharp as the out-of-plane fiber texture. A subset of grains oriented for ion channeling was found to grow significantly at the expense of the remaining grain fraction. We studied the selective grain growth as a function of ion species (N⁺, Ne⁺, Ar⁺), ion energy (1–3.5 MeV) and target temperature (liquid nitrogen to 400 °C). In a textured thin film the degree of preferred in-plane orientation can be strongly influenced by ion bombardment, and therefore this technique has the potential to become a powerful tool for the enhancement of reliability in micro- and nanosystems.     

COMPUTATIONAL SCHEME FOR SIMULATING PLASMA DYNAM-ICS DURING PLASMA-IMMERSION ION IMPLANTATION

Plasma--immersionionimplantation(Pill)isapowerfultechniqueforsurfacemodificationofmaterials[1'2].InthePillprocess)theobjectbeingimplantedisimmersedinaplasmaandrepeatedlypulsedtoahigh,negativevoltage(scallto--100kV).AtypicaltargetgeometryisshowninFig.la.Theapplicationofthisbiascreatesasheaththatexpandsintothesurroundingplasma,uncoveringpositiveionsandacceleratingthemtothetargetsurfaCe,wheretheymaybeimplanted.Theseimplantedionsmodifythesurfacewhiletightdimensionaltolerancesaremaintained.Aprin…     

Calculation of the ligand–lanthanide ion energy transfer rate in coordination compounds: contributions of exchange interactions

Recently, one of us (O.L.M.) developed a theoretical approach to the energy transfer process between a ligand and a lanthanide ion in luminescent compounds. This approach takes into account the direct Coulomb interaction only. Here we present further calculations which also include the exchange Coulomb interaction (isotropic and anisotropic). The selection rules on the total angular momentum, J, of the lanthanide 4f states, derived from each interaction are different. They are in fact complementary. We discuss the case of energy transfer to the ⁵D₁ manifold of the Eu³⁺ ion, which is forbidden when only the direct Coulomb interaction is considered but becomes allowed through the exchange interaction. In this case numerical estimates show that, depending on resonance conditions and the nature of the ligand donor state, the transfer rate may assume very high values. It is also emphasised that, according to the present approach, energy transfer to the ⁵D₀ level of the Eu³⁺ ion is forbidden by both mechanisms, provided J-mixing between the ⁷F₀ and ⁷F₂ manifolds is neglected.     

Bulk and surface modifications of insulating poly (paraphenylene sulphide) films by ion bombardment

Thin poly(paraphenylene sulphide) (PPS) films (2 μm thick), bombarded with He⁺ (380 keV), B⁺ (350 keV) and Ar²⁺ (700 keV) at fluences ranging from 10¹² to 2 × 10¹⁶ ions cm⁻², were analysed by X-ray diffractometry, UV-visible absorption spectroscopy, electrical resistance measurements and solubility tests. The polymer gradually underwent an amorphization process indicated by the decrease in the main X-ray diffraction peak area and also lost its solubility with increasing ion fluence. This behaviour revealed the formation of cross-linking and amorphous structures. A red shift of the optical absorption threshold with increasing fluence was also observed by UV-visible spectroscopy. This trend is usually attributed to the conjugation of unsaturated carbon bonds which gives rise to non-localized π electrons. From these spectral data the gap between valence band and conduction band (optical gap E_g) using a model for amorphous semiconductors can be obtained. The conjugation process increased with fluence resulting in a decrease in the optical gap. For Ar²⁺ -bombarded samples the optical gap saturated at 0.9 eV for fluences around 10¹⁵ cm⁻². The decrease in E_g with increasing fluence is a direct indication that a new group of conducting structures is being formed in the polymeric material. Electrical measurements made immediately after 2 × 10¹⁶ Ar²⁺ cm⁻² bombardment revealed that the electrical resistivity decreased by 18 orders of magnitude in relation to the original PPS. When the bombarded samples were exposed to air the electrical conductivity decreased. This electrical instability was assigned to the free radicals present in the polymer chain after ion bombardment. This work shows that different hydrogenated amorphous carbon films can be obtained from one common polymeric matrix by judicious choice of the projectile ion stopping mechanism.     

Reduction in surface resistivity of polymers by plasma source ion implantation

The surface resistivity of several polymers such as poly(styrene/butadiene copolymer), modified poly(phenyleneoxide), poly(ethylene terephthalate), and polyimide was improved by the argon gas plasma source ion implantation (Ar-PSII) technique equipped with a mesh-type conducting grid. With the grid, the surface resistivities of the modified polymers decreased up to 11 orders of magnitudes at a high ion dose, and remained nearly at the same values after 3 months. The PSII treated polymer sample with the grid provided more uniformly modified surface and lower surface resistivity than that treated without the grid. The extent of the decrease in surface resistivity depended on the polymer structures and physical properties. However, the surface resistivity was independent of the sample thickness, the grid size, and the grid height. Surface analyses using scanning electron microscopy, time-of-flight secondary ion mass spectrometry, and Raman spectroscopy provided the useful information on modified surfaces.