Ion Beam Bombardment Research Articles

Pulse height decrease in a single-crystal CVD diamond detector under gold ion beam bombardment

A charged-particle detector was fabricated using a single-crystal diamond grown by chemical vapor deposition to examine its radiation hardness under heavy-ion bombardment. The irradiation dose dependence of the output pulse height from the diamond detector during gold ion beam bombardment at an energy of 7 MeV was investigated. The pulse height of output signals decreased with increasing amount of gold ion irradiation, and the pulse height was not recovered after applying a reverse-bias voltage. In addition, although only small amounts of vacancy and charge density generation inside the diamond detector were estimated and were found to be less than those in the Si detector by the Monte Carlo simulation of the Stopping and Range of Ions in Matter, the diamond detector did not show superior radiation hardness to the Si charged-particle detector.

Surface excitation parameter for rough surfaces

In order to assess quantitatively the importance of surface excitation effect in surface electron spectroscopy measurement, surface excitation parameter (SEP) has been introduced to describe the surface excitation probability as an average number of surface excitations that electrons can undergo when they move through solid surface either in incoming or outgoing directions. Meanwhile, surface roughness is an inevitable issue in experiments particularly when the sample surface is cleaned with ion beam bombardment. Surface roughness alters not only the electron elastic peak intensity but also the surface excitation intensity. However, almost all of the popular theoretical models for determining SEP are based on ideal plane surface approximation. In order to figure out whether this approximation is efficient or not for SEP calculation and the scope of this assumption, we proposed a new way to determine the SEP for a rough surface by a Monte Carlo simulation of electron scattering process near to a realistic rough surface, which is modeled by a finite element analysis method according to AFM image. The elastic peak intensity is calculated for different electron incident and emission angles. Assuming surface excitations obey the Poisson distribution the SEPs corrected for surface roughness are then obtained by analyzing the elastic peak intensity for several materials and for different incident and emission angles. It is found that the surface roughness only plays an important role to SEP only for large interaction angle cases (larger than 60°) and large surface roughness (root-mean-square value lager than 15nm). This result is a clear evidence that the SEP database calculated based on ideal plane surface model are still efficient for realistic sample surface with common surface roughness.

The effects of interfacial interactions between Fe–O and Fe–Si induced by ion-beam bombardment on the magnetic properties of Si-oxide/Fe bilayers

Si/Fe and SiO2/Fe thin-film heterostructures are commonly seen in magnetic multilayer devices, whose magnetic properties are strongly influenced by intermixing at the interfaces. In this paper, Si-oxide/Fe bilayers were formed by depositing Si on Fe with in situ O2/Ar ion-beam bombardment during the Si deposition. The surface oxidation conditions were altered by applying different O2/Ar ratios (0–41%) in the ion-beam. The surface and cross-sectional morphologies, and the crystalline structures were characterized by transmission electron microscopy. The formation of Fe–O, Fe–Si and Si–O bonds at the interface of the O2/Ar ion-beam bombarded Si-oxide/Fe bilayers was evidenced by X-ray photoemission spectra. FeO, Fe3O4 and Fe2O3 at the interface resulted in a marked increase in the magnetic coercivity at low temperatures, as characterized by magnetometry.

Ion Beam Induced Modifications of Biocompatible Polymer

Ion beam bombardment has shown great potential for improving the surface properties of polymers. In this paper, the ion beam-polymer interaction mechanisms are briefly discussed. The main objective of this research was to study the effects of H-ion beam on physico-chemical properties of Ultra-high-molecular-weight polyethylene (UHMWPE) as it is frequently used in biomedical applications. UHMWPE was bombarded with 65 keV H-ions to fluences ranging from 1x1014–2x1016 ions/cm2. Changes of surface layer composition produced by ion bombardment of UHMWPE samples were studied. The hydrogen release and oxygen uptake induced by ion beam bombardment were determined by Nuclear reaction analysis (NRA) using the 1H(15N, αγ)12C and Rutherford backscattering spectrometry (RBS), respectively. Tribological and hardness properties at the polymer near surface region were studied by means of friction coefficient and micro-hardness testers, respectively. Wettability of the bombarded surfaces was determined by measuring the contact angle for distilled water. The obtained results showed that the ion bombardment induced hydrogen release increases with the increasing ion fluence. An important effect observed, was the rapid oxidation of samples, which occurs after exposure of bombarded samples to air. These effects resulted in important modifications of the surface properties of bombarded material such as change of friction coefficient, hardness and improved wettability.

Solution-Derived Zn-Doped GaO Films as Alignment Layers for Twisted-Nematic Liquid Crystal Displays Using Ion-Beam Bombardment

This letter demonstrates liquid crystal (LC) alignment on solution-derived Zn-doped GaO (ZnGaO) films using an ion beam (IB) method. Homogeneous and uniform LC alignment was achieved on IB-irradiated ZnGaO films. X-ray photoelectron spectroscopy was used to analyze the chemical bonding states of the IB-irradiated ZnGaO surfaces to verify the compositional behavior for LC alignment. In addition, ZnGaO films with twisted nematic cells exhibited electro-optical characteristics comparable with those of a conventional polyimide layer for potential LC display applications.

Control of the wrinkle structure on surface-reformed poly(dimethylsiloxane) via ion-beam bombardment.

We investigated the surface reformation of poly(dimethylsiloxane) (PDMS) elastomers by means of ion beam bombardment for fabricating wrinkle structures. Oxidation on the PDMS surface formed a silica-like outer layer that interacted with the inner PDMS layer, leading to the formation of wrinkle structures that minimized the combined bending energy of the outer layer and stretching energy of the inner layer. In addition, we controlled the amplitude and period of the wrinkle structures by adjusting the PDMS annealing temperature. As the PDMS annealing temperature was increased, the amplitude and period of the wrinkles formed by IB irradiation changed from 604.35 to 69.01 nm and from 3.07 to 0.80 μm, respectively.

Surface morphological evolution and nanoneedle formation of 18Cr-ODS steel by focused ion beam bombardment

Morphological evolution upon intense energetic particle–matter interactions is of fundamental importance for materials utilized in extreme radiation environment, and controlling surface morphology by radiation also provides a new pathway for exploring non-equilibrium process at surface. In this work, surface morphology and microstructural evolution upon low energy ion irradiation of 18Cr-ODS, a candidate structural material for cladding and first wall of future fission and fusion reactors, were investigated by in situ focused Ga+ ion beam/scanning electron microscopy and ex situ transmission electron microscopy. A surface roughening through pore formation, coalescence and eventually nanoneedle formation was induced on 18Cr-ODS steel surface. Cross-section microstructure analysis indicates that the formation of nanoneedle was not a result of grain recrystallization or chemical composition change. Pre-irradiated materials by He+ and Fe+ ions displays enhanced kinetics for surface morphological evolution and lower fluences of focused Ga+ are required for the nanoneedle formation. These results suggest that the surface roughening and morphological evolution of 18Cr-ODS under low energy ion irradiation is an interplay between a curvature-dependent sputtering and defect accumulation near the surface.

Nonuniversality due to inhomogeneous stress in semiconductor surface nanopatterning by low-energy ion-beam irradiation

A lack of universality with respect to ion species has been recently established in nanostructuring of semiconductor surfaces by low-energy ion-beam bombardment. This variability affects basic properties of the pattern formation process, like the critical incidence angle for pattern formation, and has remained unaccounted for. Here, we show that nonuniform generation of stress across the damaged amorphous layer induced by the irradiation is a key factor behind the range of experimental observations, as the form of the stress field is controlled by the ion/target combination. This effect acts in synergy with the nontrivial evolution of the amorphous-crystalline interface. We reach these conclusions by contrasting a multiscale theoretical approach, which combines molecular dynamics and a continuum viscous flow model, with experiments using ${\text{Xe}}^{+}$ and ${\text{Ar}}^{+}$ ions on a Si(100) target. Our general approach can apply to a variety of semiconductor systems and conditions.

Novel hydrophilic SiO2 wafer bonding using combined surface-activated bonding technique

Low-temperature hydrophilic SiO2–SiO2 wafer bonding has been performed in vacuum by a new combined surface-activated bonding (SAB) technique. In this technique, wafers are irradiated by ion beam bombardment and simultaneously deposited with silicon by in situ silicon sputter deposition, and then terminated with Si–OH groups by water vapor exposure prior to bonding in vacuum. A surface energy of more than 1 J/m2 was achieved by 200 °C postbonding annealing. A void-free oxide intermediate layer with a thickness of about 15 nm was observed at the bonding interface by transmission electron microscopy (TEM). The increased bonding energy can be attributed to the greater number of Si–OH formed through hydroxylation of the silicon deposited on the SiO2 surfaces.

イオンビーム援用傾斜機能性TiNコーティングを施したチタン合金の摩耗およびフレッティング疲労特性

The effect of functionally graded TiN coating on the wear and fretting fatigue behavior of titanium alloy was investigated. The two kinds of monolayer TiN coatings and three kinds of functionally graded TiN coatings were deposited on Ti-6Al-4V alloy substrate using an ion beam assisted deposition technique. Monolayer TiN coating was fabricated by an electron beam evaporation of titanium and simultaneous nitrogen ion bombardment at the acceleration voltage of 0.2 or 2.0 keV. The later consisted of top TiN layer and functionally graded layer. During the fabrication of functionally graded layer, the mixing ratio of nitrogen and argon gas that were used for the generation of ion beam increased stepwisely. The mixed layer formed by ion beam bombardment became thicker by an increase in acceleration voltage. The adhesion and wear resistance improved with an increase in the acceleration voltage. Moreover, inserting the functionally graded layer with the layer thickness of 250 nm improved them significantly. However, further increase in graded layer thickness deteriorated the adhesion and wear resistance. The fretting fatigue life was evaluated by a four-point bending fatigues test. The fretting fatigue life of specimen coated with monolayer TiN film was longer than that of uncoated specimen. The TiN coating with functionally graded layer was the most effective to improve the fretting fatigue life. It was concluded that the insert of functionally graded layer with appropriate layer thickness is effective way for improvement of wear and fretting fatigue behavior.

Effect of ion-beam surface modification technology on the variation of surface texture

Ion-beam surface bombardment modification technology is successfully used to manufacture different kinds of nano-textures on the surface of silicon substrate. Relationship between the morphology and arrangement patterns of nano-textures and the bombarding parameters is studied. Results show that the ion-beam bombardment has a significant impact on surface morphology. Different kinds of textures on silicon substrate can be formed according to the variation of bombardment time. The nanodot array texture is observed on the surface of silicon substrate when the duration of argon ion-beam bombardment is 15 minutes. Simultaneously, the tetrahedral amorphous carbon film is deposited on the silicon substrates that have different kinds of nano-texture. The microstructure of ta-C film deposited on unprocessed and nano-textured silicon substrate is analyzed by X-ray photoelectron spectroscopy. Results indicate that the content of sp3 bonds decreases with increasing bombardment time, and thereafter keeps a steady value. The ta-C films deposited on the nanodot-textured substrate shows the lowest sp3 fraction. It is also observed by friction and wear test that the wear time is enhanced from 10 to 70 min. The tribological properties is highly improved when the coating is deposited on the nano-textured substrate.

Thermoelectric Figures of Merit of Zn4Sb3 and Zrnisn-based Half-heusler Compounds Influenced by Mev Ion-beam Bombardments

Semiconducting β-Zn4Sb3 and ZrNiSn-based half-Heusler compound thin films with applications as thermoelectric (TE) materials were prepared using ion beam assisted deposition (IBAD). High-purity solid zinc (Zn) and antimony (Sb) were evaporated by electron beam to grow the β-Zn4Sb3 thin film while high-purity zirconium (Zr) powder and nickel (Ni) tin (Sn) powders were evaporated by electron beam to grow the ZrNiSn-based half-Heusler compound thin film. Rutherford backscattering spectrometry (RBS) was used to analyze the composition of the thin films. The grown thin films were subjected to 5 MeV Si ions bombardment for generation of nanostructures in the films. We measured the thermal conductivity, Seebeck coefficient, and electrical conductivity of these two systems before and after 5 MeV Si ions beam bombardment. The two material systems have been identified as promising TE materials for the application of thermal-to-electrical energy conversion, but the efficiency still limits their applications. The electronic energy deposited due to ionization in the track of MeV ion beam couldcause localized crystallization. The nanostructures produced by MeV ion beam can cause significant change in both the electrical and the thermal conductivity of thin films, thereby improving the efficiency. We used the 3ω-method (3rd harmonic) measurement system to measure the cross-plane thermal conductivity, the van der Pauw measurement system to measure the electrical conductivity, and the Seebeck-coefficient measurement system to measure the cross-plane Seebeck coefficient. The thermoelectric figures of merit of the two material systems were then derived by calculations using the measurement results. The MeV ion-beam bombardment was found to decrease the thermal conductivity of thin films and increase the efficiency of thermal-to-electrical energy conversion.

Comparison of Ar+ Monoatomic and Cluster Ion Sputtering of Ta2O5 at Different Ion Energies, by XPS: Part 2 - Cluster Ions

A standard 30 nm thick Ta2O5 oxide layer grown on Ta was examined by XPS after Arn+ cluster ion bombardment at ion energies of 4 keV, 5 keV and 6 keV, with a cluster size of 1000 atoms. The reduction of Ta2O5, resulting from the preferential sputtering of oxygen after ion beam bombardment at different energies has been investigated. Survey spectra, C 1s, Ta 4f and O 1s spectra are presented for each profile at three stages: native surface, after reaching the steady-state oxide composition, and from the underlying metal substrate. It is necessary to reach a voltage of 6 keV to obtain a good sputter rate. The use of the cluster source seems to be promising to reduce the preferential sputtering phenomenon.

Comparison of Ar+ Monoatomic and Cluster Ion Sputtering of Ta2O5 at Different Ion Energies, by XPS: Part 1 - Monoatomic Ions

A standard 30 nm thick Ta2O5 oxide layer grown on Ta was examined by XPS after Ar+ ion bombardment at ion energies of 200 eV, 500 eV, and 3 keV. The reduction of Ta2O5, resulting from the preferential sputtering of oxygen after ion beam bombardment at different energies has been investigated. Survey spectra, C 1s, Ta 4f and O 1s spectra are presented for each profile at three stages: native surface, after reaching the steady-state oxide composition, and from the underlying metal substrate. Reducing the Ar+ energy from 3 keV to 200 eV makes no substantial difference in the degree of Ta2O5 reduction observed following ion bombardment.

Microstructural and magnetic characterization of ion-beam bombarded [Ni80Fe20-Cr]50 thin films

Ion-beam bombardment during thin film deposition can effectively change the microstructure and thus influence the magnetic properties of the thin film system. In this paper, we studied plain (un-bombarded) and argon ion-beam bombarded multilayered [Ni80Fe20-Cr]50 thin films fabricated using a dual ion-beam deposition technique. The atomic force microscopy images of the bombarded thin films showed a much rougher surface and an increased average grain size. No noticeable exchange bias phenomenon was observed in the thin films deposited with or without bombardment, indicating that the interfacial uncompensated spins were prevented from providing the necessary unidirectional anisotropy due to interfacial intermixing. This significant intermixing between Ni80Fe20 and Cr layers, and the etching process caused by the bombardment, led to the formation of an nano-composite [Ni80Fe20-Cr]50 thin film with a reduced Curie temperature. An enhancement of the coercivity attributed to the stronger NiFe–Cr coupling was also found, which was the result of additional pinning sites created by the bombardment. The bombarded thin film also exhibited a higher ZFC/FC divergence temperature compared to the un-bombarded film, which indicated a much stronger NiFe–Cr coupling and more coordinated alignment of the magnetization of the film's larger crystallites.

Large-scale nanotwins in Cu films/Cu nanowires via stress engineering by a high-energy ion beam bombardment process: growth and characterization

Dense nanoscale twins were introduced into Cu films and nanowires through bombardment with high-energy Ar+ ions at low temperatures. Both the twin boundary density and indentation hardness of the ion-irradiated Cu films increased with decreases in the bombardment temperature. The improved mechanical strength in the ion-irradiated Cu films is attributed to twin boundary–dislocation and dislocation–dislocation interactions. The strengthened region is several hundreds of nanometers beneath the surface of the bombarded nanowires and thin strips. A mechanism based on irradiation-induced thermal spike cascades is proposed to explain the influence of the energy of the Ar+ ions and bombardment temperature on nanoscale twinning in crystalline Cu. This study provides a route to developing advanced interconnection technology for micro- and nanoelectronic devices.

Excess conductivity analysis of heavy ions irradiated TlBa2(Ca2−yMgy)Cu3O10−δ superconductor

The excess conductivity analysis of resistivity versus temperature data of TlBa2(Ca2−yMgy)Cu3O10−δ (y=0.5, 1.0, 1.5) superconductor samples have been performed in the light of Aslamasov-Larkin and Lawrence-Doniach theories before and after irradiation with a beam of gold (Au4+) ions of energy 20MeV having a fluence of 1×1015 ions/cm2. The microscopic parameters such as zero temperature coherence length {ξc(0)}, inter-plane coupling constant (α), and Fermi velocity (VF) have been calculated from the ln-ln plot of excess conductivity (Δσ) versus reduced temperature (ε) using the Lawrence and Doniach model. The cross-over temperatures separating different fluctuation regions in the ln-ln plot are also determined. It is observed from the excess conductivity analysis that all the microscopic parameters have been decreased after the irradiations. Whereas, calculations have shown that critical magnetic fields (Bc) and critical current density (Jc) are increased after the ion irradiation, which, confirms the validity of the results because Bc and Jc are increased by the formation of artificial pinning centers after bombardment of energetic heavy ion beam.

Surface modifications of PADC polymeric material by ion beam bombardment for high technology applications

Surface modification of Poly (allyl diglycol carbonate) (PADC) is induced by 150 keV Ag ions of different fluences. The pristine as well as bombarded samples were investigated by UV–Vis spectroscopy, Fourier transform-infrared analysis (FTIR) and micro-hardness tester. The variations of wettability and surface free energy were determined by the contact angle measurements. The obtained results showed that ion beam bombardment induced increase in the absorption spectra of the UV–Vis with increase of ion fluence as well. The direct and indirect optical band gap decreased from 4.2 to 3.6 eV for pristine sample to 3.2 and 2.5 eV for those bombarded with Ag ion beam at the highest fluence, respectively. Changes in chemical properties were observed by Fourier transform infrared spectroscopy. Increase in the wettability, surface free energy and work of adhesion with increase the ion fluence were observed. Ion bombardment inducing increasing in a micro-hardness surface due to the high carbon surface concentration and cross-linking effects in the polymeric chains. The bombarded PADC surfaces may find special applications to the field of the micro-electronic devices and printing process.

Engineering the activity and lifetime of heterogeneous catalysts for carbon nanotube growth via substrate ion beam bombardment.

We demonstrate that argon ion bombardment of single crystal sapphire leads to the creation of substrates that support the growth of vertically aligned carbon nanotubes from iron catalysts with a density, height, and quality equivalent to those grown on conventional, disordered alumina supports. We quantify the evolution of the catalyst using a range of surface characterization techniques and demonstrate the ability to engineer and pattern the catalyst support through control of ion beam bombardment parameters.

Post-CMOS Integration of MEMS Inertial Sensors Using Oxidized Porous Silicon Technique

At present, MEMS inertial sensor technology has an exhaustive range of applications in the field of mass-produced commercial products, such as smart phones, PDAs, automobiles, and pedometers, which cause a strong demand for small, robust, low-cost and CMOS- integrated inertial sensors. DRIE process has been widely used in the post-CMOS approach to create high aspect ratio structures [1], but the high expense and long consuming time are usually unacceptable for the mass manufacturing. In addition, during the ion beam bombardment, CMOS structures inevitably suffers from a certain amount of damages which might reduce the device performance [2]. Here we demonstrate a low-cost and CMOS compatible production method to fabricate CMOS-MEMS inetial sensors. A thick oxidized prous silicon (OPS) layer is selectively grown on the silicon substate before the standard CMOS processes for dielectric isolation and thermal isolation. The OPS techique has a substantial cost advantage over DRIE techniqe and can produce very thick layers without severe stress problems. Lowly-doped p-type wafers (20-40 Ωcm, 500 μm-thick, [100] -oriented and polished) were used in our experiments. The whole process includes three main steps: formation of OPS layers, CMOS sturctures fabrication, and the MEMS structures fabrication. To create thick porous silicon layer, ohmic contact was achieved by sputtering an 800 nm-thick Al film on the backside of samples. The electrolytes used for anodization contained 48 wt.% aqueous HF and DMF. Galvanostatic current densities of 500 mAcm-2 were applied from an Agilent power source with a tolerance up to 60 V. Macropore arrays with depth of about 48 μm were obtained, followed by an optimized oxidation process to form OPS layers. After that, standard CMOS process steps were used to produce electronic components. Finally, the MEMS structures are completely built on top of the finished CMOS substrate by partely removing the OPS layers, leaving the CMOS layers unthouched. Figure 1 show SEM pictures of the cantilever beam-mass structure (Figure 1a) and comb structure (Figure 1b) released by removing the OPS layer. Figure 1c shows the MEMS inertial stuctures and CMOS electronic components obtained on the same chip. This represents an effective method to integrate MEMS sensors with electronic circuits.