Low Ion Fluences Research Articles

Fabrication and characterization of a co-planar detector in diamond for low energy single ion implantation

We demonstrate low energy single ion detection using a co-planar detector fabricated on a diamond substrate and characterized by ion beam induced charge collection. Histograms are taken with low fluence ion pulses illustrating quantized ion detection down to a single ion with a signal-to-noise ratio of approximately 10. We anticipate that this detection technique can serve as a basis to optimize the yield of single color centers in diamond. The ability to count ions into a diamond substrate is expected to reduce the uncertainty in the yield of color center formation by removing Poisson statistics from the implantation process.

Structure of ion tracks in ceria irradiated with high energy xenon ions

Structure and accumulation behavior of ion tracks in CeO2 irradiated with 200 MeV Xe ions were examined by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) to obtain fundamental knowledge on the microstructure evolution induced by fission fragments in nuclear fuels and transmutation targets, which is of importance for the development of advanced fuel/target materials at high burn-up conditions. Bright-field (BF) TEM images of ion tracks from an inclined direction showed Fresnel contrast along penetrating path of incident ions. The signal intensity of high-angle annular dark-field (HAADF) STEM images was decreased at the core damage region of ion tracks along the path of ions, revealing the reduction of atomic density inside the ion track. Preferential formation of smaller and larger ion tracks was observed at a high ion fluence of 1 × 1014 cm−2 compared to a low ion fluence of 1 × 1011 cm−2. Results were discussed due to the coalescences and incomplete recovery of the core damage regions during the overlap of high density electronic excitation damage, which is induced during the repetition of the formation and recovery of ion tracks within an influence region.

A 3D feature point tracking method for ion radiation

A robust and computationally efficient algorithm for automated tracking of high densities of particles travelling in (semi-) straight lines is presented. It extends the implementation of (Sbalzarini and Koumoutsakos ) and is intended for use in the analysis of single ion track detectors. By including information of existing tracks in the exclusion criteria and a recursive cost minimization function, the algorithm is robust to variations on the measured particle tracks. A trajectory relinking algorithm was included to resolve the crossing of tracks in high particle density images. Validation of the algorithm was performed using fluorescent nuclear track detectors (FNTD) irradiated with high- and low (heavy) ion fluences and showed less than 1% faulty trajectories in the latter.

Structural, surface potential and optical studies of AlGaN based double heterostructures irradiated by 120 MeV Si9+ swift heavy ions

The Al0.33Ga0.77N/Al0.14Ga0.86N based double heterostructure was irradiated using Si9+ ion at room temperature (RT) and liquid nitrogen temperature (LNT) with four dissimilar ion fluence. The effect of Si9+ ion irradiation in dislocation densities and in-plane strain of GaN layer were discussed. The in-plane strain values of AlxGa1-xN layers were calculated from asymmetric reciprocal space mapping (RSM). The surface modification and the variation in phase shift on Al0.33Ga0.77N surfaces due to the irradiation were measured by Electrostatic Force Microscopy (EFM). The capacitance of the tip-sample system was determined from EFM. The band edge emissions of heterostructures were measured by the room temperature phototluminescence (PL) and the shift in the Al0.14Ga0.86N active layer emission peaks towards the low energy side at low fluence ion irradiation has been noted.

Ionoluminescence of fused silica under swift ion irradiation

Ion beam induced luminescence spectra have been in-situ recorded during He+ (2.5MeV), O4+ (13.5MeV) and Si4+ (24.4MeV) irradiations for three vitreous silica grades with different OH content (KU1, KS-4V and Infrasil 301). Remarkable changes in the ionoluminescence spectra of the three silica grades were observed for low ion fluences. He+ irradiated samples exhibited higher luminescence than equivalent ones irradiated with heavier O4+ and Si4+ ions. KU1 samples with the highest OH content showed the lowest blue luminescence. Blue luminescence maximum during ion irradiations with O4+ and Si4+ ions is correlated with structural changes.

Tailoring the properties of copper nanowires by ion beam irradiation

Abstract In the present paper, we investigated the change in the properties of copper nanowires under the irradiance of 80 MeV Si 7+ ion beam. The nanowires were electrodeposited in the cylindrical pores of the track-etched polycarbonate membranes. The phase, morphology and optical absorbance of the fabricated nanowires were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy, respectively. The XRD study showed a face centered cubic crystal structure of copper nanowires. Further measurements with FESEM revealed that nanowires were continuous, aligned with uniform diameter having high aspect ratio. The XRD spectra of irradiated nanowires indicated an improved crystalinity at low ion fluences while it declines at higher ion fluences. The optical absorbance properties of the irradiated copper nanowires were also examined. The absorption spectra exhibited a peak at 568 nm which was attributed to the surface plasmon resonance. A significant increase in absorbance after irradiation accounts for the possibility of defects formation. The electrical properties measured from I – V characteristics showed an increase in resistivity of irradiated nanowires.

Impact of 100 MeV Ag7+ SHI irradiation fluence and N incorporation on structural, optical, electrical and gas sensing properties of ZnO thin films

In the present study, we have investigated the influence of Ag7+ ion irradiation fluence and N incorporation on structural, optical, electrical and gas sensing properties of ZnO thin films. The X-ray diffraction analysis reveals the retainment of ZnO wurtzite structure even at higher fluence irradiation with slight decrease in crystallinity. Photoluminescence and Hall effect measurement analysis showed an increase in density of defects for high ion fluence irradiation. Atomic force microscope analysis shows that the films irradiated at high ion fluence have vertical standing needle-like morphology and also have high value of roughness compared with the films irradiated at low ion fluence. The ammonia and methanol gas sensing properties of the films have been studied at different operating temperature and gas concentration. It conveys that the films have selectivity towards ammonia than methanol and also that the films irradiated at high ion fluence exhibit better sensitivity, low response and recovery times compared with the films irradiated at low ion fluence. The film grown in oxygen ambience and irradiated at high ion fluence showed good sensing characteristics at all temperatures even at room temperature.

Ar+ ion irradiation-induced reorganization of colloidal silica nanoparticles in Langmuir–Blodgett monolayers

The Ar+ ion irradiation-induced reorganization of Langmuir–Blodgett monolayers of colloidal silica nanoparticles with a diameter of 220nm and 450nm deposited on silicon substrate is investigated in a wide range of ion fluences. The cluster formation, average cluster size, ion beam-induced charging and discharging of particles, heating effects, the ion beam-induced viscous flow as well as the swelling of the Si substrate as a function of the ion fluence are discussed. Inhomogeneous particle distribution causes strong nonlinear Si swelling inside wide defect-channels between the clusters and linear Si swelling inside narrow channels between the particles. At low ion fluences particle charging and Coulomb repulsion forces govern the particle reorganization process, while at high ion fluences ion beam-induced viscous flow and hydrodynamic forces between the particles and the underlying substrate play major role. Two different types of patterns: smaller compact clusters of few particles and longer chain-like clusters of dozens of particles are observed. The dynamics of the reorganization process in both cases is treated analogous to the dynamics of colloidal suspensions based on the Tanaka–Araki model. The results of the model are comparable to the experimentally observed cluster characteristics.

Irradiation effect on deuterium behaviour in low-dose HFIR neutron-irradiated tungsten

Tungsten samples were irradiated by neutrons in the High Flux Isotope Reactor (HFIR), Oak Ridge National Laboratory at reactor coolant temperatures of 50–70 °C to low displacement damage of 0.025 and 0.3 dpa. After cooling down, the HFIR neutron-irradiated tungsten samples were exposed to deuterium plasmas in the Tritium Plasma Experiment, Idaho National Laboratory at 100, 200 and 500 °C twice at the ion fluence of 5 × 1025 m−2 to reach the total ion fluence of 1 × 1026 m−2 in order to investigate the near-surface deuterium retention and saturation via nuclear reaction analysis. Final thermal desorption spectroscopy was performed to elucidate the irradiation effect on total deuterium retention. Nuclear reaction analysis results showed that the maximum near-surface (<5 µm depth) deuterium concentration increased from 0.5 at% D/W in 0.025 dpa samples to 0.8 at% D/W in 0.3 dpa samples. The large discrepancy between the total retention via thermal desorption spectroscopy and the near-surface retention via nuclear reaction analysis indicated the deuterium was trapped in bulk (at least 50 µm depth for 0.025 dpa and 35 µm depth for 0.3 dpa) at 500 °C cases even in the relatively low ion fluence of 1026 m−2.

Helium behaviour in UO2 through low fluence ion implantation studies

In this work we focus on experiments involving implantation of 500keV 3He ions in sintered polycrystalline material. Samples are implanted at low fluences (∼2×1013ions/cm2) and subsequently isothermally annealed in a highly sensitive thermal desorption spectrometry (TDS) device PIAGARA (Plateforme Interdisciplinaire pour l’Analyse des GAz Rares en Aquitaine). The helium fluencies studied are two to three orders of magnitude lower than previous Nuclear Reaction Analysis (NRA) experiments carried out on identical samples implanted at identical energies. The fractional release of helium obtained in the TDS experiments is interpreted using a three-dimensional axisymmetric diffusion model which enables results to be quantitatively compared to previous NRA data. The analysis shows that helium behaviour is qualitatively independent of ion fluency over three orders of magnitude: helium diffusion appears to be strongly inhibited below 1273K within the centre of the grains presumably as a result of helium bubble precipitation. The scenario involving diffusion at grain boundaries and in regions adjacent to them observed at higher fluencies is quantitatively confirmed at much lower doses. The main difference lies in the average width of the region in which uninhibited diffusion occurs.

Effect of ion irradiation on the surface, structural and mechanical properties of brass

Modifications to the surface, structural and mechanical properties of brass after ion irradiation have been investigated. Brass targets were bombarded by carbon ions of 2MeV energy from a Pelletron linear accelerator for various fluences ranging from 56×1012 to 26×1013 ions/cm2. A scanning electron microscope and X-ray diffractometer were utilized to analyze the surface morphology and crystallographic structure respectively. To explore the mechanical properties e.g., yield stress, ultimate tensile strength and microhardness of irradiated brass, an universal tensile testing machine and Vickers microhardness tester were used. Scanning electron microscopy results revealed an irregular and randomly distributed sputter morphology for a lower ion fluence. With increasing ion fluence, the incoherently shaped structures were transformed into dendritic structures. Nano/micro sized craters and voids, along with the appearance of pits, were observed at the maximum ion fluence. From X-ray diffraction results, no new phases were observed to be formed in the brass upon irradiation. However, a change in the peak intensity and higher and lower angle shifting were observed, which represents the generation of ion-induced defects and stresses. Analyses confirmed modifications in the mechanical properties of irradiated brass. The yield stress, ultimate tensile strength and hardness initially decreased and then increased with increasing ion fluence. The changes in the mechanical properties of irradiated brass are well correlated with surface and crystallographic modifications and are attributed to the generation, augmentation, recombination and annihilation of the ion-induced defects.

Heavy ion induced luminescence studies of YAlO3:Tb3+, Tm3+ single crystals

Ionoluminescence (IL), photoluminescence (PL) and thermoluminescence (TL) studies of YAlO3:Tb3+, Tm3+ (1 at %) single crystals are carried out using 100 MeV Si7+ ions for the fluence 3.91 × 1012 ions cm−2. IL peaks are recorded in the range 385–450, 493, 544, 585 and 624 nm in Tb3+- and 353, 459, 523, 651 and 763 nm in Tm3+-doped YAlO3 single crystals, respectively. PL studies also show similar characteristic emission peaks. The variation of IL intensity is studied in a YAlO3:Tb3+ crystal for a wide fluence range of 3.91 × 1012 –17.57 × 1012 ions cm−2. The IL intensity is found to be higher in lower ion fluences, and it decreases with the increase of ion fluence. Thermoluminescence (TL) studies are carried out for ion fluence– (3.91 × 1012 ions cm−2) and UV-exposed (05–60 min) single crystals. A single well-resolved glow peak at 242 °C, along with a shouldered peak at 272 °C, is recorded in the Tm3+-doped sample. In the Tb3+-doped samples, a well-resolved glow peak at 218 °C, along with a shouldered peak at 147 °C, is recorded at the lower temperature side. In the UV-exposed crystals, two glow peaks at 168 °C and 223 °C are recorded. The glow peaks are found to be shifted towards the lower temperature side with an increase in UV exposure time. Good linearity over a large span of UV exposure time and a single glow peak with a simple trap distribution are observed in YAlO3:Tb3+ single crystals, which makes them suitable as a dosimeter for UV-rays. The kinetic parameters (E, b, s) are estimated using the glow peak shape method for both ion and UV-exposed crystals, and the results are discussed in detail.

Evolution of defects in silicon carbide implanted with helium ions

Effects of accumulation of radiation damage in silicon carbide are important concerns for the use of silicon carbide in advanced nuclear energy systems. In the present work lattice damage in silicon carbide crystal (4H type) implanted with 100keV 4He+ ions was investigated with Rutherford backscattering spectrometry in channeling geometry (RBS/c) and positron beam Doppler broadening spectrometry (PBDB). Helium implantation was performed at the specimen temperature of 510K to avoid amorphization of the SiC crystal. Fluences of helium ions were selected to be in the range from 1×1016 to 3×1016ionscm−2, around the dose threshold for the formation of observable helium bubbles under transmission electron microscopes (TEM).The RBS/c measurements show distinctly different annealing behavior of displaced Si atoms at doses below or above the threshold for helium bubble formation. The RBS/c yield in the peak damage region of the specimen implanted to 3×1016He-ionscm−2 shows an increase on the subsequently thermal annealing above 873K, which is readily ascribed to the extra displacement of Si atoms due to helium bubble growth. The RBS/c yield in the specimen implanted to a lower ion fluence of 1.5×1016He-ionscm−2 decreases monotonously on annealing from ambient temperatures up to 1273K. The PBDB measurements supply evidence of clustering of vacancies at temperatures from 510 to 1173K, and dissociation of vacancy clusters above 1273K. The similarity of annealing behavior in PBDB profiles for helium implantation to 1×1016 and 3×1016ionscm−2 is ascribed to the saturation of trapping of positrons in vacancy type defects in the damaged layers in the specimens helium-implanted to the two dose levels.

Fabrication of nanopores in a graphene sheet with heavy ions: A molecular dynamics study

Molecular dynamics simulations were performed to study the formation process of nanopores in a suspended graphene sheet irradiated by using energetic ions though a mask. By controlling the ion parameters including mass, energy, and incident angle, different kinds of topography were observed in the graphene sheet. Net-like defective structures with carbon atom chains can be formed at low ion fluences, which provide the possibility to functionalize the irradiated sample with subsequent chemical methods; finally a perfect nanopore with smooth edge appears when the ion fluence is high enough. We found that the dependence of ion damage efficiency on ion fluence, energy, and incident angle are different from that predicted by the semi-empirical model based on the binary-collision approximation, which results from the special structure of graphene. Our results demonstrate that it is feasible to fabricate controlled nanopores/nanostructures in graphene via heavy ion irradiation.

The impact of the discreteness of low-fluence ion beam processing on the spatial architecture of GaN nanostructures fabricated by surface charge lithography

We show that the descrete nature of ion beam processing used as a component in the approach of surface charge lithography leads to spatial modulation of the edges of the GaN nanostructures such as nanobelts and nanoperforated membranes. According to the performed Monte Carlo simulations, the modulation of the nanostructure edges is caused by the stochastic spatial distribution of the radiation defects generated by the impacting ions and related recoils. The obtained results pave the way for direct visualization of the networks of radiation defects induced by individual ions impacting a solid-state material.

Ion beam induced stress formation and relaxation in germanium

Ion irradiation of crystalline solids leads not only to defect formation and amorphization but also to mechanical stress. In the past, many investigations in various materials were performed focusing on the ion beam induced damage formation but only several experiments were done to investigate the ion beam induced stress evolution. Especially in microelectronic devices, mechanical stress leads to several unwanted effects like cracking and peeling of surface layers as well as changing physical properties and anomalous diffusion of dopants. To study the stress formation and relaxation process in semiconductors, crystalline and amorphous germanium samples were irradiated with 3MeV iodine ions at different ion fluence rates. The irradiation induced stress evolution was measured in situ with a laser reflection technique as a function of ion fluence, whereas the damage formation was investigated by means of Rutherford backscattering spectrometry. The investigations show that mechanical stress builds up at low ion fluences as a direct consequence of ion beam induced point defect formation. However, further ion irradiation causes a stress relaxation which is attributed to the accumulation of point defects and therefore the creation of amorphous regions. A constant stress state is reached at high ion fluences if a homogeneous amorphous surface layer was formed and no further ion beam induced phase transition took place. Based on the results, we can conclude that the ion beam induced stress evolution seems to be mainly dominated by the creation and accumulation of irradiation induced structural modification.

Roughness formation in (100) silicon during low‐energy Cs+ bombardment

In secondary ion mass spectrometry, high depth resolution for the characterization of ultra‐shallow junctions can only be obtained when making use of low‐energy primary ion bombardment. However, such analysis conditions often lead to roughness formation at the crater bottoms.In this paper, roughness formation has been studied on silicon for Cs+ bombardment on the Cameca (Gennevilliers, France)SC‐Ultra instrument. Impact energies have been changed from 250 eV up to 5 keV working in positive secondary ion polarity.The surface morphology has been characterized by atomic force microscopy. Surface roughening appeared at low primary ion fluence and continued growing at higher fluences. Ripples formed perpendicular to the plane containing the beam and the normal to the surface. Their wavelength and correlation length have been studied as a function of the experimental conditions. Both parameters increase with increasing ion fluence, and higher values of ion energy promoted more ordered rippled structures and lower values of roughness. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Evolution of superconducting and normal state properties of YBa2Cu3O7−y thick films under 200 MeV Ag ion irradiation

Temperature dependent resistivity of YBa2Cu3O7−y (YBCO) thick films irradiated with 200MeV Ag ions has been investigated. The YBCO thick films were prepared by solid state diffusion reaction technique. In contrast to the general perception that the energetic ion induces defects and disorders, which lead to decrease of Tc and increase of normal state resistivity in a superconductor, 200MeV Ag ions in the present case led to an increase in Tc and decrease in normal state resistivity at low ion fluence (1011 ions cm−2) in YBCO. At this fluence, the electronic energy loss, Se induced amorphous ion tracks are well separated from each other and hence are not expected to influence the Tc. The observed changes in transport properties is explained as being caused by irradiation-induced chain oxygen ordering of the oxygen defects in the CuO chains. Subsequent increase of irradiation fluence leads to decrease of Tc and increase of normal state resistivity.

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.

Empirical modeling of the cross section of damage formation in ion implanted III-V semiconductors

In this letter, the cross section of damage formation per individual ion is measured for III-V compound semiconductors ion implanted at 15 K, applying Rutherford backscattering spectrometry. An empirical model is proposed that explains the measured cross sections in terms of quantities representing the primary energies deposited in the displacement of lattice atoms and in electronic interactions. The resulting formula allows the prediction of damage formation for low temperatures and low ion fluences in these materials and can be taken as a starting point for further quantitative modeling of damage formation including secondary effects such as temperature and ion flux.