Analysis of surface morphological change in PET films induced by tungsten ion implantation

Surface morphological changes and metal nanograin formation of polyethylene terephthalate films with tungsten ion implantation were studied. Tungsten ions were accelerated with a voltage of 40 kV and implanted at fluences from 5 × 10¹⁶ to 2 × 10¹⁷ cm^?2 using a metal vapor vacuum arc implanter. Scanning electron micrographs at the highest fluence show semi-spherical hills, indicating formation of tungsten nanograins on the polymer. The tungsten nanograin formation in the polymer film is confirmed by cross-sectional observation using transmission electron microscopy. Depth profiles of tungsten atoms obtained from energy dispersive X-ray spectra indicate densification and sputtering of the polymer surface layer during implantation. These results indicate that surface morphological change is related with the effects of a critical fluence and tungsten nanograin formation.     

Evaluation of soft error rates using nuclear probes in bulk and SOI SRAMs with a technology node of 90 nm

The difference of soft error rates (SERs) in conventional bulk Si and silicon-on-insulator (SOI) static random access memories (SRAMs) with a technology node of 90 nm has been investigated by helium ion probes with energies ranging from 0.8 to 6.0 MeV and a dose of 75 ions/μm². The SERs in the SOI SRAM were also investigated by oxygen ion probes with energies ranging from 9.0 to 18.0 MeV and doses of 0.14–0.76 ions/μm². The soft error in the bulk and SOI SRAMs occurred by helium ion irradiation with energies at and above 1.95 and 2.10 MeV, respectively. The SER in the bulk SRAM saturated with ion energies at and above 2.5 MeV. The SER in the SOI SRAM became the highest by helium ion irradiation at 2.5 MeV and drastically decreased with increasing the ion energies above 2.5 MeV, in which helium ions at this energy range generated the maximum amount of excess charge carriers in a SOI body. The soft errors occurred by helium ions were induced by a floating body effect due to generated excess charge carriers in the channel regions. The soft error occurred by oxygen ion irradiation with energies at and above 10.5 MeV in the SOI SRAM. The SER in the SOI SRAM gradually increased with energies from 10.5 to 13.5 MeV and saturated at 18 MeV, in which the amount of charge carriers induced by oxygen ions in this energy range gradually increased. The computer calculation indicated that the oxygen ions with energies above 13.0 MeV generated more excess charge carriers than the critical charge of the 90 nm node SOI SRAM with the designed over-layer thickness. The soft errors, occurred by oxygen ions with energies at and below 12.5 MeV, were induced by a floating body effect due to the generated excess charge carriers in the channel regions and those with energies at and above 13.0 MeV were induced by both the floating body effect and generated excess carriers. The difference of the threshold energy of the oxygen ions between the experiment and the computer calculation might be due to the difference between the designed and real structures.     

SHI induced re-crystallization of Ge implanted SiO2 films

Ge nanocrystals embedded in SiO₂ matrix have been synthesized by swift heavy ion irradiation of Ge implanted SiO₂ films. In the present study, 400 keV Ge⁺ ions were implanted into SiO₂ films at dose of 3 × 10¹⁶ ions/cm² at room temperature. The as-implanted samples were irradiated with 150 MeV Ag¹²⁺ ions with various fluences. Similarly 400 keV Ge⁺ ions implanted into Silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au⁸⁺ ions at room temperature (RT). These samples were subsequently characterized by XRD and Raman to understand the re-crystallization behavior. The XRD results confirm the presence of Ge crystallites in the irradiated samples. Rutherford backscattering spectrometry (RBS) was used to quantify the concentration of Ge in the SiO₂ matrix. Variation in the nanocrystal size as a function of ion fluence is presented. The basic mechanism of ion beam induced re-crystallization has been discussed.     

Effect of the laser focus position on characteristics of X-ray and ion emission from gold plasmas generated by a sub-nanosecond laser

X-ray and ion emission from gold plasma produced by a sub-nanosecond Nd:glass laser has been studies as a function of distance of the target from the best focus position. Thermal ion (kinetic energy <19 keV) signals and soft X-ray flux (photon energy >0.7 keV) measurements decrease as the target is moved closer to the best focus position in spite of an increase in laser intensity. We observe simultaneously a strong correlation between the onset of this drop in the flux of soft X-ray and the growth of harder X-ray (photon energy 3–5 keV), alongside a growth in fast ion (energy >67 keV) numbers. This is indicative of the onset of non-linear processes at the higher irradiances (～10¹⁴ W/cm²) associated with the best focus position. Our results show that when using laser plasmas as X-ray or ion sources, X-ray and ion emission in a desired spectral range can be optimized by adjusting the focusing on the target.     

Photoluminescence induced from hot Ge implantation into SiO2

Up to the present, by using the ion implantation technique, photoluminescence (PL) from Ge nanocrystals (Ge NCs) was obtained by room temperature (RT) Ge implantation into a SiO₂ matrix followed by a high temperature anneal. In this way two PL bands were observed, one at 310 nm and the second, with much higher yield at 390 nm. In the present work we have used another experimental approach. We have performed the Si implantation at high temperature (T_i) and then, we have done a higher temperature anneal (T_a) in order to nucleate the Ge NCs. With this aim we have changed T_i between RT and 600 °C. By performing the implantation at T_i = 350 °C we found a PL yield four times higher than the one obtained from the usual RT implantation at the same fluence. Moreover, by changing the implantation fluence between Φ = 0.25 × 10¹⁶ and 2.2 × 10¹⁶ Ge/cm² we observed that Φ = 0.5 × 10¹⁶ Ge/cm² induces a PL yield three times higher as compared to the usual RT implantation fluence. In conclusion, using a hot Ge implantation plus an optimal Ge atomic concentration, we were able to gain more than one order of magnitude in the 390 nm PL yield as compared with previous ion implantation results.     

Negative ion beam extraction in ROBIN

The RF based single driver ?ve ion source experiment test bed ROBIN (Replica Of BATMAN like source in INDIA) has been set up at Institute for Plasma Research (IPR), India in a technical collaboration with IPP, Garching, Germany. A hydrogen plasma of density 5 × 10¹² cm^?3 is expected in driver region of ROBIN by launching 100 kW RF power into the driver by 1 MHz RF generator. The cesiated source is expected to deliver a hydrogen negative ion beam of 10 A at 35 kV with a current density of 35 mA/cm² as observed in BATMAN.In first phase operation of the ROBIN ion source, a hydrogen plasma has been successfully generated (without extraction system) by coupling 80 kW RF input power through a matching network with high power factor (cos θ > 0.8) and different plasma parameters have been measured using Langmuir probes and emission spectroscopy. The plasma density of 2.5 × 10¹¹ cm^?3 has been measured in the extraction region of ROBIN. For negative hydrogen ion beam extraction in second phase operation, extraction system has been assembled and installed with ion source on the vacuum vessel. The source shall be first operated in volume mode for negative ion beam extraction. The commissioning of the source with high voltage power supply has been initiated.     

Study of large gap 200 kV breakdowns in vacuum with high stored energy for ITER neutral beam accelerator

In the context of the ITER contract “ITER/CT/07/219–200 kV Stored Energy Tests”, electrical breakdown tests have been performed in vacuum with a stored energy of up to 425 J. The experiments have been conceived and performed with the collaboration of Consorzio RFX. The tests are being performed in the 1 MV test facility at IRFM, CEA-Cadarache. They should simulate the conditions that will be found in the ITER Neutral Beam accelerator, at 200 kV. This paper presents the set-up of the test bed, the choice of critical components, the diagnostic equipments and the results obtained with 200 kV applied on the anode electrode.     

The structure of ion beam amorphised zirconolite studied by grazing angle X-ray absorption spectroscopy

Ti K edge X-ray absorption spectroscopy (XAS) was applied to determine the Ti co-ordination environment in the surface amorphised layer formed on zirconolite ceramics by 2 MeV Kr⁺ irradiation, to a fluence of 5 × 10¹⁵ ions cm^?2. The application of XAS in a grazing angle geometry was demonstrated to be essential in order to probe only the surface damaged layer (<1000 nm thick), in isolation of the undamaged interior of the specimen. 2 MeV Kr⁺ irradiation induced a change in the Ti co-ordination environment from majority six fold to majority five fold in the amorphised surface layer. This finding is consistent with the formation of five fold Ti in metamict natural zirconolite, as reported previously and confirmed in this study, despite the difference in dose rate of at least 10¹² between ion beam irradiated and naturally metamict materials. This study therefore opens the door to systematic investigation of composition – structure – property relations in materials designed for radioactive waste immobilisation, through the combined application of ion beam irradiation and grazing angle XAS.     

Effect of He-pre-injection on dislocation loop formation and irradiation-induced segregation of Fe–12%Cr–15%Mn austenitic steel

The effect of He-injection on irradiation-induced segregation of aging treated Fe–12%Cr–15%Mn austenitic steels, which are candidate materials as the reduced radio-activation of structure material for nuclear and/or fusion reactors was investigated by using the 1250 kV high voltage electron microscope (HVEM) connected with an ion accelerator. The Fe–Mn–Cr steel has been irradiated at 573 K by three irradiation modes of single electron-beam irradiation, electron-beam irradiation after He-injection and electron/He⁺-ion dual-beam irradiation in a HVEM. Irradiation-induced segregation analyses were carried out by an energy dispersive X-ray analyzer (EDX) in a 200 kV FE-TEM with beam diameter of about 0.5 nm. Dislocation loops with strain contrast were formed during irradiation and the loop numbers density increased rapidly with irradiation dose for He-pre-injected specimens. Voids were not observed after irradiations with three irradiation modes up to 5.4 dpa at 573 K. Irradiation-induced segregations of Cr and Mn near grain boundary were observed in each irradiation condition, but the amounts of Mn segregation decreased in the cases of electron/He⁺-ion dual-beam irradiation compared with single electron-beam and electron-beam irradiation after He-injection conditions.     

Conceptual design of a high-voltage compact bushing for application to future N-NBI systems of fusion reactors

The energy of future neutral beam injector (NBI) heating systems of fusion power plants ranges from 1 to 2 MeV. They are based on powerful (several tens of MW) hydrogen negative ion electrostatic accelerators where electrodes are polarized by DC high-voltage. The beam line under vacuum is supplied by HV power supplies via a transmission line pressured under SF₆ and a high voltage feedthrough called bushing. The paper presents results obtained over experimental campaigns dedicated to high voltage vacuum insulation for future NBI systems (ITER). It addresses the problematic of the electron field emission and the high voltage breakdown limit under vacuum between large electrode surfaces. The paper highlights the dependence of the electron emission (dark current) with the voltage and the background tank pressure: at low pressure (～1E?3 Pa in hydrogen), an important dark current of I ～ 100 mA has been measured at 500 kV, while at higher pressure (～0.3 Pa in helium), the dark current has been nearly suppressed (less than 3 mA of dark current at 970 kV). The paper shows that a field induced gas adsorption process could occur on the emitting surfaces (cathode), and this process tends to lower the electron field emission current by increasing the work function of the electrode surface. The Fowler–Nordheim law applied to the measured dark current indicates about 70% of work function increase at 0.3 Pa in helium. Finally, a new high-voltage bushing concept relevant to the future NBI systems is presented; it is based on these experimental findings in high voltage vacuum insulation; the main feature of the new bushing concept is to take benefit of the field induced adsorption effect, i.e., the suppression of the dark current with helium gas, in the inner part of the bushing where the electric field intensity is highest.     

Formation of germanium nanoparticles in silica glass studied by optical absorption and X-ray absorption fine structure analysis

We examined the relation between the 3.1 eV emission band and local structure for Ge⁺ implanted silica glass by means of photoluminescence, optical and X-ray absorption spectroscopies. In the 2 × 10¹⁵ cm^?2 implanted sample, a new emission band around 2.7 eV was observed, the origin of which was assigned to the B_2α oxygen deficient center and/or small Si clusters in silica. When the Ge⁺ fluence exceeded 2 × 10¹⁶ cm^?2, a sharp and intense 3.1 eV emission band replaced the 2.7 eV band. We found that the intense 3.1 eV PL occurred by the prolonged X-ray irradiation onto the 2 × 10¹⁵ cm^?2 implanted sample. UV–vis absorption and XAFS spectroscopies suggested that the aggregation of atomically dispersed tetravalent (Ge(IV)) atoms into Ge(0) clusters of ～1 nm exhibit strongly correlation with the generation of the 3.1 eV PL. Such nano- and/or subnano-size Ge(0) clusters formed by the X-ray radiation were oxidized and decomposed again to the isolated Ge(IV) atoms, while those produced by the higher Ge⁺ fluence were stable against the exposure to air.     

Empirical approach to the description of spectral performance degradation of silicon photodiodes used as particle detectors

The spectral deterioration of Hamamatsu S5821 silicon photodiodes for ion types and energies frequently used in Ion Beam Analysis was investigated. Focused proton beams with energies 430 keV and 2 MeV were applied to generate radiation damage via an area selective ion implantation in unbiased diodes at room temperature. The variations of spectroscopic features were measured “in situ” by Ion Beam Induced Current (IBIC) method as a function of fluence, within the 10⁹–5 × 10¹² ion/cm² range and diode bias voltages, between 0 and 100 V.An empirical model has been developed to describe the radiation damage. Equations are derived for the variations of the normalized peak position and peak width. The derived empirical equations are physically correct, as far as they account for the superposition of the influence of charge carrier trapping by native and radiation-induced defects and for the effect of charge carrier velocity saturation with electric field strength, as well.     

Ion beam characterization of Fe-implanted GaN

Fe ion implantation in GaN has been investigated by means of ion beam analysis techniques. Implantations at an energy of 150 keV and fluences ranging from 2 × 10¹⁵ to 1 × 10¹⁶ cm^?2 were done, both at room temperature and at 623 K. Secondary Ions Mass Spectrometry was used to determine the Fe implantation profiles, whereas Rutherford Backscattering in channeling conditions with a 2.2 MeV ⁴He⁺ beam allowed us to follow the damage evolution. Particle Induced X-ray Emission in channeling conditions with a 2 MeV H⁺ beam was employed to study the lattice location of Fe atoms after implantation. The results show that a high fraction of Fe-implanted atoms are located in high symmetry sites in low fluence implanted samples, where the damage level is lower, whereas the fraction of randomly located Fe atoms increases by increasing the fluence and the resulting damage. Moreover, dynamical annealing present in high temperature implantation has been shown to favor the incorporation of Fe atoms in high symmetry sites.     

Design of neutral beam injection system for KSTAR tokamak

The neutral beam injection (NBI-1) system has been designed for providing a 300 s deuterium beam of 120 kV/65 A as an auxiliary heating and current drive system of the KSTAR (Korea Superconducting Tokamak Advanced Research) tokamak. The deuterium beam is produced from a long pulse ion source composed of a bucket-type plasma generator and a multi-aperture tetrode accelerator with the help of discharge power supplies and high voltage (HV) power supplies. The beamline components (BLCs) include a neutralizer with an optical multi-channel analyzer (OMA) section, a bending magnet (BM), an ion dump assembly, a movable calorimeter, beam scrapers, and a cryo-sorption pump system in a rectangular vacuum tank. A beam duct equipped with bellows and a voltage break is placed between the NBI vacuum tank and the KSTAR vacuum vessel. All data and parameters of the NBI system are controlled by a control and data acquisition (CODAQ) system through the EPICS based Ethernet interface.     

Vacuum system of SST-1 Tokamak

Vacuum chambers of Steady State Superconducting (SST-1) Tokamak comprises of the vacuum vessel and the cryostat. The plasma will be confined inside the vacuum vessel while the cryostat houses the superconducting magnet systems (TF and PF coils), LN₂ cooled thermal shields and hydraulics for these circuits. The vacuum vessel is an ultra-high (UHV) vacuum chamber while the cryostat is a high-vacuum (HV) chamber. In order to achieve UHV inside the vacuum vessel, it would be baked at 150 °C for longer duration. For this purpose, U-shaped baking channels are welded inside the vacuum vessel. The baking will be carried out by flowing hot nitrogen gas through these channels at 250 °C at 4.5 bar gauge pressure. During plasma operation, the pressure inside the vacuum vessel will be raised between 1.0 × 10^?4 mbar and 1.0 × 10^?5 mbar using piezoelectric valves and control system. An ultimate pressure of 4.78 × 10^?6 mbar is achieved inside the vacuum vessel after 100 h of pumping. The limitation is due to the development of few leaks of the order of 10^?5 mbar l/s at the critical locations of the vacuum vessel during baking which was confirmed with the presence of nitrogen gas and oxygen gas with the ratio of ～3.81:1 indicating air leak. Similarly an ultimate vacuum of 2.24 × 10^?5 mbar is achieved inside the cryostat. Baking of the vacuum vessel up to 110 °C with ±10 °C deviation was achieved with a net mass flow rate of 0.8 kg/s at 1.5 bar gauge inlet pressure and supply temperature of 230 °C at the heater end. Also during gas feed system installation, the pressure inside the VV was raised from 3.01 × 10^?5 mbar to 1.72 × 10^?4 mbar by triggering a pulse of lower amplitude of 25 voltage direct current (VDC) for 100 s to piezoelectric valve. This paper describes in detail the design and implementation of the various vacuum subsystems including relevant experimental results.     

Er+ medium energy ion implantation into lithium niobate

Erbium-doped lithium niobate (Er:LiNbO₃) is a prospective photonics component, operating at 1.5 μm, which could find its use chiefly as an optical amplifier or waveguide laser. In this study, we have focused on the properties of the optically active Er:LiNbO₃ layers, which are fabricated by medium energy ion implantation under various experimental conditions. Erbium ions were implanted at energies of 330 and 500 keV with fluences of 1.0 × 10¹⁵, 2.5 × 10¹⁵ and 1.0 × 10¹⁶ cm^?2 into LiNbO₃ single-crystalline cuts of various orientations. The as-implanted samples were annealed in air at 350 °C for 5 h. The depth distribution and diffusion profiles of the implanted Er were measured by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He⁺ ions. The projected range R_P and projected range straggling ΔR_P were calculated employing the SRIM code. The damage distribution and structural changes were described using the RBS/channelling method. Changes of the lithium concentration depth distribution were studied by Neutron Depth Profiling (NDP). The photoluminescence spectra of the samples were measured to determine whether the emission was in the desired region of 1.5 μm. The obtained data made it possible to reveal the relations between the structural changes of erbium-implanted lithium niobate and its luminescence properties important for photonics applications.     

Comparison of 41Ca analysis on 0.5 MV and 5 MV-AMS systems

A comparative study was made between the compact AMS system at the PSI/ETH Laboratory of Ion Beam Physics in Zurich with 0.5 MV terminal voltage and the 5 MV-AMS system at the Scottish Universities Environmental Research Centre (SUERC), Glasgow. Overall 34 urinary samples with ⁴¹Ca/⁴⁰Ca ratios in the range from 4 × 10^?11 to 3 × 10^?10 were processed to CaF₂ and aliquots of the same material were measured on both instruments.Measurements on the compact AMS system were performed in charge state 3+ achieving a transmission of 4% at 1.7 MeV beam energy. Under these conditions a suppression of the interference ⁴¹K is virtually impossible. However, samples with an excess of potassium can be identified by a shift of the ⁴¹Ca/⁴¹K peak in the ΔE ? E histogram of the gas ionization detector employed and a criterion for data rejection can be defined. An overall precision of ～4% and a ⁴¹Ca/⁴⁰Ca background level of 5 × 10^?12 have been reached.For studies with higher demands on the detection limit AMS systems like the one at SUERC are attractive: in charge state 5+ and using a gas stripper beam energy of 27 MeV, a transmission of 5%, a ⁴¹K suppression factor of ～500 and a ⁴¹Ca/⁴⁰Ca background level of 3 × 10^?14 are achieved.We demonstrate that both systems are well suited for large-scale ⁴¹Ca biomedical applications.     

Homogeneously size distributed Ge nanoclusters embedded in SiO2 layers produced by ion beam synthesis

500 nm SiO₂ layers were implanted with 450 keV (F=3 × 10¹⁶ at./cm²) and 230 keV (F=1.8 × 10¹⁶ at./cm²) Ge ions at room temperature to obtain an almost constant Ge concentration of about 2.5 at.% in the insulating layer. Subsequently, the specimens were annealed at temperatures between 500°C and 1200°C for 30 min in a dry N₂ ambient atmosphere. Cross-sectional TEM analysis reveal homogeneously distributed Ge nanoclusters arranged in a broad band within the SiO₂ layer. Their mean cluster size varies between 2.0 and 6.5 nm depending on the annealing conditions. Cluster-free regions are always observed close to the surface of the specimens independent of the annealing process, whereas a narrow Ge nanocluster band appears at the SiO₂/Si interface at high annealing temperatures, e.g. ⩾1000°C. The atomic Ge redistribution due to the annealing treatment was investigated with a scanning TEM energy dispersive X-ray system and Rutherford back scattering (RBS).     

Measuring the generation lifetime profile modified by MeV H+ ion implantation in silicon

A silicon wedge mask with thickness varying from approximately 5 μm to a few hundred μm has been used for converting the depth distribution of defect concentration induced by 4 MeV H⁺ ion implantation in silicon to a lateral scale on the surface, i.e. the distance from the edge of the wedge mask. Thus, using proper devices fabricated on bulk Si prior to ion implantation, depth profiles of the generation lifetime of minority charge carriers and of the different defect densities can be measured by the transient capacitance method and by Deep Level Transient Spectroscopy (DLTS), respectively. The distribution of lifetime follows well that of the implantation induced vacancies calculated by the TRIM code in the applied dose range (from 1 × 10¹⁰ to 3 × 10¹¹ H⁺/cm²). The correlation between implantation dose and lifetime decrease is also discussed.     

BioMICADAS: Compact next generation AMS system for pharmaceutical science

The next generation Accelerator Mass Spectrometer system specifically designed to address the needs of the growing pharmaceutical science market has passed validation testing. The system dubbed BioMICADAS is based on a previously developed compact carbon dating instrument, the MICADAS. Like its predecessor, it has an overall footprint of only 2.5 × 3 m² and uses a 200 kV high voltage platform for tandem based ion acceleration. The ion source can accommodate samples as graphite or gaseous CO₂. It is equipped with two independently operating vacuum locks, allowing continuous measurement sequence and providing a capacity of ～20,000 samples per annum. A barcoded cathode tracking system allows data capture into Laboratory Information Management System (LIMS) for Good Laboratory Practices (GLP) regulated work. It can be housed in research laboratories alongside other complementary bioanalytical equipment and operated by general laboratory staff as the system is designed to be robust and user-friendly.The system has undergone rigorous validation over the range from 0.1 to 100 Modern Carbon, including accuracy, linearity, robustness, and precision experiments over the course of 7 months. It has been shipped and installed at the site of our collaborative partner, Vitalea Science in Davis, California. The installation process took ～2 weeks from boxes to beam. The feasibility of the system to determine the absolute specific activity of biogenic samples was also shown by using the method of isotopic dilution.