Single Ion Tracks Research Articles

The effect of aluminium concentration on the resistance of Si3N4 to ion track formation

The role of Al impurities on the structural response of polycrystalline silicon nitride to swift Xe and Bi ions at single ion track and overlapped ion track fluences is investigated. Si3N4 with Al impurity concentrations of 3 at.%, 1 at.% and 0.1. at.% were examined by means of high resolution scanning transmission electron microscopy. The threshold electronic energy loss (Set) required to form amorphous tracks was found to decrease with increasing Al fraction from above 33 keV/nm (0.1 at.% Al) to below 22 keV/nm for specimens containing about 3 at.% Al. All specimens were partially amorphized at overlapping ion fluence and the amorphous fraction monotonically increased with increasing Al content at the same ion fluence.

Fabrication of double conical PET nanochannel for molecular detection

Polymer nanochannels based on ion-track etching have attracted increasing interests for molecule detection using current blockage because of the easy control of nanochannel with precise geometry at 1 nm scale in recent years. In this work, polyethylene terephthalate (PET) membranes were irradiated with single ions of 2.15 GeV Kr and then the single latent ion track was developed to fabricate nanochannels of several nanometers for lambda-DNA detection. The ion-track etching with DC or AC provided reliable fabrication of double conical nanochannel with similar size of 48 kb λDNA with symmetrical ion transportation. Current blockage experiments demonstrated that the bi-conical PET nanochannel is sensitive for the translocation of 48 kb λDNA biomolecules with the mean translocation blockage factor Δi/i from 0.02 to 0.10 and the ability to differentiate the number of molecules. The nanochannel is more sensitive for biomolecule detection at lower KCl concentration. This investigation demonstrates that latent track etching of energetic heavy ions is a reliable approach in polymer nanochannel fabrication for biomolecule detection with accurate nanoscale control and low-cost mass production.

Fabrication and Functioning of Magnetically Gated PET Nanochannels

AbstractNanochannel gating exists extensively in biological systems and has wide applications in nanofluidic studies. Magnetic control is non‐contact and penetrative compared to chemical or electrical gating. This work introduces the fabrication of magnetically gated single nanochannels by grafting superparamagnetic nanoparticles, via bridging of DNA single strands, onto the inner surface of the PET nanochannels which were prepared by single ion hit and ion track etching. The nanochannel showed sub‐second magnetic response with an ON/OFF ratio of 18 measured by ionic conductance under control with a permanent magnet. These magnetically gated single PET nanochannel are speficically advantageous for superficial drug‐delivery and non‐contact control in nanofluidic applications.

Optical signatures of single ion tracks in ZnO.

The optical properties of single ion tracks have been studied in ZnO implanted with Ge by combining depth-resolved hyperspectral cathodoluminescence (CL) and photoluminescence (PL) spectroscopy techniques. The results indicate that ZnO is susceptible to implantation doses as low as 108 to 109 cm−2. We demonstrate that the intensity ratio of ionized and neutral donor bound exciton emissions [D+X/D0X] can be used as a tracer for a local band bending both at the surface as well as in the crystal bulk along the ion tracks. The hyperspectral CL imaging performed at 80 K with 50 nm resolution over the regions with single ion tracks permitted direct assessment of the minority carrier diffusion length. The radii of distortion and space charge surrounding single ion tracks were estimated from the 2D distributions of defect-related green emission (GE) and excitonic D+X emission, both normalized with regard to neutral D0X emission, i.e., from the [GE/D0X] and [D+X/D0X] ratio maps. Our results indicate that single ion tracks in ZnO can be resolved up to ion doses of the order of 5 × 109 cm−2, in which defect aggregation along the extended defects obstructs signatures of individual tracks.

Preparation of Single Cu Nanowire and in-situ Study of Its Electrical Properties

Metal nanowires, as one of the most crucial components of nanoelectronic devices in the future, have attracted enormous attention. Therefore, it is of great significance to investigate the electrical properties of single metal nanowires. Herein, the single Cu nanowire with diameter of 64 nm was successfully prepared by using single-ion track template method combined with electrochemical deposition approach, and its I-V curve was measured. Such a diameter represents the thinnest one as comparing the reported ones obtained by the same method. The results illustrated that the process of formation and growth, as well as the final diameter of single nanochannel in template can be monitored and measured by conductance method. During the electrochemical deposition, the dynamic evolution of the deposition of nanowire can be clearly reflected through the deposition current and deposition time. At the same time, I-V measurements reveal that the Cu nanowire has typical metallic characteristic. For the first time, the resistivity of such a thin nanowire is obtained and its resistivity is 3.46 μΩ·cm which is around twice that of Cu bulk materials. The increase of resistivity is believed coming from finite size effects and may be related to the electrons scattering at the grain boundaries and surfaces.

Diffusion of Vacancies Created by High‐Energy Heavy Ion Strike Into Diamond

A novel technique is proposed to measure how far vacancies diffuse from the initial damaged region with sub‐micrometer resolution. Vacancies created by a single heavy ion with high energy are considered. The most important feature of the single ion track is the quasi‐one‐dimensional vacancy distribution with high volume density, which exceeds 1019 vacancies cm−3. After annealing, the vacancies combine with nitrogen impurities to form nitrogen vacancy (NV) centers. With increasing annealing temperature and time, the distribution of NV centers becomes wider. Therefore, the vacancies created by a single heavy ion are suitable to investigate vacancy diffusion. The activation energy of vacancy migration in diamond is determined to be 2.12 eV, which is in reasonable agreement with reported values.

Visualization of air and metal inhomogeneities in phantoms irradiated by carbon ion beams using prompt secondary ions

PurposeNon-invasive methods for monitoring of the therapeutic ion beam extension in the patient are desired in order to handle deteriorations of the dose distribution related to changes of the patient geometry. In carbon ion radiotherapy, secondary light ions represent one of potential sources of information about the dose distribution in the irradiated target. The capability to detect range-changing inhomogeneities inside of an otherwise homogeneous phantom, based on single track measurements, is addressed in this paper. MethodsAir and stainless steel inhomogeneities, with PMMA equivalent thickness of 10mm and 4.8mm respectively, were inserted into a PMMA-phantom at different positions in depth. Irradiations of the phantom with therapeutic carbon ion pencil beams were performed at the Heidelberg Ion Beam Therapy Center. Tracks of single secondary ions escaping the phantom under irradiation were detected with a pixelized semiconductor detector Timepix. The statistical relevance of the found differences between the track distributions with and without inhomogeneities was evaluated. ResultsMeasured shifts of the distal edge and changes in the fragmentation probability make the presence of inhomogeneities inserted into the traversed medium detectable for both, 10mm air cavities and 1mm thick stainless steel. Moreover, the method was shown to be sensitive also on their position in the observed body, even when localized behind the Bragg-peak. ConclusionsThe presented results demonstrate experimentally, that the method using distributions of single secondary ion tracks is sensitive to the changes of homogeneity of the traversed material for the studied geometries of the target.

Three dimensional reconstruction of therapeutic carbon ion beams in phantoms using single secondary ion tracks

Carbon ion beam radiotherapy enables a very localised dose deposition. However, even small changes in the patient geometry or positioning errors can significantly distort the dose distribution. A live, non-invasive monitoring system of the beam delivery within the patient is therefore highly desirable, and could improve patient treatment. We present a novel three-dimensional method for imaging the beam in the irradiated object, exploiting the measured tracks of single secondary ions emerging under irradiation.The secondary particle tracks are detected with a TimePix stack—a set of parallel pixelated semiconductor detectors. We developed a three-dimensional reconstruction algorithm based on maximum likelihood expectation maximization. We demonstrate the applicability of the new method in the irradiation of a cylindrical PMMA phantom of human head size with a carbon ion pencil beam of MeV u−1. The beam image in the phantom is reconstructed from a set of nine discrete detector positions between and from the beam axis. Furthermore, we demonstrate the potential to visualize inhomogeneities by irradiating a PMMA phantom with an air gap as well as bone and adipose tissue surrogate inserts.We successfully reconstructed a three-dimensional image of the treatment beam in the phantom from single secondary ion tracks. The beam image corresponds well to the beam direction and energy. In addition, cylindrical inhomogeneities with a diameter of cm and density differences down to g cm−3 to the surrounding material are clearly visualized.This novel three-dimensional method to image a therapeutic carbon ion beam in the irradiated object does not interfere with the treatment and requires knowledge only of single secondary ion tracks. Even with detectors with only a small angular coverage, the three-dimensional reconstruction of the fragmentation points presented in this work was found to be feasible.

Mechanistic details of the formation and growth of nanoscale voids in Ge under extreme conditions within an ion track

The formation of nanoscale voids in amorphous-germanium (a-Ge), and their size and shape evolution under ultra-fast thermal spikes within an ion track of swift heavy ion, is meticulously expatiated using experimental and theoretical approaches. Two step energetic ion irradiation processes were used to fabricate novel and distinct embedded nanovoids within bulk Ge. The ‘bow-tie’ shape of voids formed in a single ion track tends to attain a spherical shape as the ion tracks overlap at a fluence of about 1 × 1012 ions cm−2. The void assumes a prolate spheroid shape with major axis along the ion trajectory at sufficiently high ion fluences. Small angle x-ray scattering can provide complementary information about the primary stage of void formation hence this technique is applied for monitoring simultaneously their formation and growth dynamics. The results are supported by the investigation of cross-sectional transmission and scanning electron micrographs. The multi-time-scale theoretical approach corroborates the experimental findings and relates the bow-tie shape void formation to density variations as a result of melting and resolidification of Ge within the region of thermal spike generated along an ion track, plus non-isotropic stresses generated towards the end of the thermal spike.

Single event upset characteristics and physical mechanism for nanometric SOI SRAM induced by space energetic ions

Based on Monte-Carlo method, the characteristics and physical mechanisms for deposited-energy spectra in sensitive volume (SV), single event upset cross sections, and on-orbit error rates in 65-32 nm silicon-on-insulator static random access memory (SOI SRAM) devices induced by space energetic ions are investigated. Space ions on geostationary earth orbit exhibit a flux peak at an energy point of about 200 MeV/n. In consequence, the single event response of nanometric SOI SRAMs under 200 MeV/n heavy ions is studied in detail. The results show that 200 MeV/n space ions exhibit the large straggling of deposited-energy in the device SV with thickness ranging from 60 nm to 40 nm, which causes the single event upsets to occur in the sub-LETmth region. The device SV can only partially collect the electron-hole pairs in the single ion track with a wide distribution of secondary electrons. As a result, the maximum and average deposited-energy in the SV decrease by 25% and 33.3%, respectively. Further, the single event upset probability decreases and the on-orbit error rate decreases by about 80%. With the downscaling of feature size, the per-bit saturated cross sections and on-orbit error rates of nanometric SOI SRAM devices decrease dramatically. The phenomenon of constant-increasing single event upset cross section with higher ion linear energy transfer (LET) is not observed, owing to the fact that (a) the density of electron-hole pairs in the track of 200 MeV/n space ion is relatively low and (b) the SOI device has thin sensitive volume, which results in the fact that the secondary-electron effect cannot upset nearby sensitive cells. Besides, it is found that the direct-ionization process of trapped protons leads to an increase of on-orbit error rate of 65 nm SOI SRAM by one to two orders of magnitude.

Swift heavy ion irradiation of CaF2 – from grooves to hillocks in a single ion track

A novel form of ion-tracks, namely nanogrooves and hillocks, are observed on CaF2 after irradiation with xenon and lead ions of about 100 MeV kinetic energy. The irradiation is performed under grazing incidence (0.3°–3°) which forces the track to a region in close vicinity to the surface. Atomic force microscopy imaging of the impact sites with high spatial resolution reveals that the surface track consists in fact of three distinct parts: each swift heavy ion impacting on the CaF2 surface first opens a several 100 nm long groove bordered by a series of nanohillocks on both sides. The end of the groove is marked by a huge single hillock and the further penetration of the swift projectile into deeper layers of the target is accompanied by a single protrusion of several 100 nm in length slowly fading until the track vanishes.By comparing experimental data for various impact angles with results of a simulation, based on a three-dimensional version of the two-temperature-model (TTM), we are able to link the crater and hillock formation to sublimation and melting processes of CaF2 due to the local energy deposition by swift heavy ions.

Registration procedure for spatial correlation of physical energy deposition of particle irradiation and cellular response utilizing cell-fluorescent ion track hybrid detectors

The hybrid technology cell-fluorescent ion track hybrid detector (Cell-Fit-HD) enables the investigation of radiation-related cellular events along single ion tracks on the subcellular scale in clinical ion beams. The Cell-Fit-HD comprises a fluorescent nuclear track detector (FNTD, the physical compartment), a device for individual particle detection and a substrate for viable cell-coating, i.e. the biological compartment. To date both compartments have been imaged sequentially in situ by confocal laser scanning microscopy (CLSM). This is yet in conflict with a functional read-out of the Cell-Fit-HD utilizing a fast live-cell imaging of the biological compartment with low phototoxicity on greater time scales. The read-out of the biological from the physical compartment was uncoupled. A read-out procedure was developed to image the cell layer by conventional widefield microscopy whereas the FNTD was imaged by CLSM. Point mapping registration of the confocal and widefield imaging data was performed. Non-fluorescent crystal defects (spinels) visible in both read-outs were used as control point pairs. The accuracy achieved was on the sub-µm scale. The read-out procedure by widefield microscopy does not impair the unique ability of spatial correlation by the Cell-Fit-HD. The uncoupling will enlarge the application potential of the hybrid technology significantly. The registration allows for an ultimate correlation of microscopic physical beam parameters and cell kinetics on greater time scales. The method reported herein will be instrumental for the introduction of a novel generation of compact detectors facilitating biodosimetric research towards high-throughput analysis.

Structural response of titanate pyrochlores to swift heavy ion irradiation

The structure, size, and morphology of ion tracks resulting from irradiation of five different pyrochlore compositions (A2Ti2O7, A = Yb, Er, Y, Gd, Sm) with 2.2 GeV 197Au ions were investigated by means of synchrotron X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Radiation-induced amorphization occurred in all five materials analyzed following an exponential rate as a function of ion fluence. XRD patterns showed a general trend of increasing susceptibility of amorphization with increasing ratio of A- to B-site cation ionic radii (rA/rB) with the exception of Y2Ti2O7 and Sm2Ti2O7. This indicates that the track size does not necessarily increase with rA/rB, in contrast with results from previous swift heavy ion studies on Gd2Zr2-xTixO7 pyrochlore materials. For Y2Ti2O7, this effect is attributed to the significantly lower electron density of this material relative to the lanthanide-bearing pyrochlores, thus lowering the electronic energy loss (dE/dx) of the high-energy ions in this composition. An energy loss normalization procedure was performed which reveals an initial increase of amorphous track size with rA/rB that saturates above a cation radius ratio larger than Gd2Ti2O7. This is in agreement with previous low-energy ion irradiation experiments and first principles calculations of the disordering energy of titanate pyrochlores indicating that the same trends in disordering energy apply to radiation damage induced in both the nuclear and electronic energy loss regimes. HRTEM images indicate that single ion tracks in Yb2Ti2O7 and Er2Ti2O7, which have small A-site cations and low rA/rB, exhibit a core-shell structure with a small amorphous core surrounded by a larger disordered shell. In contrast, single tracks in Gd2Ti2O7 and Sm2Ti2O7, have a larger amorphous core with minimal disordered shells.

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.

A simple and rapid method for high-resolution visualization of single-ion tracks

Prompt determination of spatial points of single-ion tracks plays a key role in high-energy particle induced-cancer therapy and gene/plant mutations. In this study, a simple method for the high-resolution visualization of single-ion tracks without etching was developed through the use of polyacrylic acid (PAA)-N, N’-methylene bisacrylamide (MBAAm) blend films. One of the steps of the proposed method includes exposure of the irradiated films to water vapor for several minutes. Water vapor was found to promote the cross-linking reaction of PAA and MBAAm to form a bulky cross-linked structure; the ion-track scars were detectable at a nanometer scale by atomic force microscopy. This study demonstrated that each scar is easily distinguishable, and the amount of generated radicals of the ion tracks can be estimated by measuring the height of the scars, even in highly dense ion tracks. This method is suitable for the visualization of the penumbra region in a single-ion track with a high spatial resolution of 50 nm, which is sufficiently small to confirm that a single ion hits a cell nucleus with a size ranging between 5 and 20 μm.

Flow and evaporation in single micrometer and nanometer scale pipes

We report measurements of pressure driven flow of fluids entering vacuum through a single pipe of micrometer or nanometer scale diameter. Nanopores were fabricated by etching a single ion track in polymer or mica foils. A calibrated mass spectrometer was used to measure the flow rates of nitrogen and helium through pipes with diameter ranging from 10 μm to 31 nm. The flow of gaseous and liquid nitrogen was studied near 77 K, while the flow of helium was studied from the lambda point (2.18 K) to above the critical point (5.2 K). Flow rates were controlled by changing the pressure drop across the pipe in the range 0–31 atm. When the pressure in the pipe reached the saturated vapor pressure, an abrupt flow transition was observed. A simple viscous flow model is used to determine the position of the liquid/vapor interface in the pipe. The observed mass flow rates are consistent with no slip boundary conditions.

Radial distribution of dose within heavy charged particle tracks – Models and experimental verification using LiF:Mg,Cu,P TL detectors

A new method of experimental verification of radial dose distribution models using solid state thermoluminescent (TL) detectors LiF:Mg,Cu,P has been recently proposed. In this work the method was applied to verify the spatial distribution of energy deposition within a single 131Xe ion track. Detectors were irradiated at the Department of Physics of the University of Jyväskylä, Finland. The obtained results have been compared with theoretical data, calculated according to the Zhang et al., Cucinotta et al. and Geiss et al. radial dose distribution (RDD) models. At the lowest dose range the Zhang et al. RDD model exhibited the best agreement as compared to experimental data. In the intermediate dose range, up to 104 Gy, the best agreement was found for the RDD model of Cucinotta et al. The probability of occurrence of doses higher than 104 Gy within a single 131Xe ion track was found to be lower than predicted by all the studied RDD models. This may be a result of diffusion of the charge, which is then captured by TL-related trapping sites, at the distances up to dozens of nanometers from the ionization site.

Structural and optical characterization of SiO2 under irradiation with swift heavy ions

SiO2 single crystals irradiated with 600keV, 4 and 5MeV Kr ions using the 320kV High Voltage Experimental Platform (IMP, Lanzhou) were investigated with infrared, fluorescence spectroscopes and TEM. In the low-energy regime, single ion tracks are well separated and the damage process is dominated by the formation of simple color centers such as F+ and F2 centers. For the high energy ions, the energy density in ion tracks produced at a high stopping power is larger, and consequently the defect concentration increases significantly. At higher defect densities, the distance between single defects is smaller facilitating the aggregation of individual electron center to defect cluster and defect annihilation by recombination of hole and electron centers. The latter process determines the limited efficiency of color-center creation under heavy-ion irradiation. Using the unified thermal spike model, a combination of the elastic collision spike model and the inelastic thermal spike model based on electronic energy losses, it is possible to fully describe the experimental data, which clearly demonstrate a synergy between the nuclear energy loss and the electronic energy loss processes.

Modeling of defect accumulation in lithium fluoride crystals under irradiation with swift ions

In many materials electronic excitations created around the trajectories of swift ions result in defect creation. Experimental observations often yield information on integral damage effects. The presented approach suggests a theoretical model to correlate integral damage results with microscopic effect produced by overlapping of individual single ion tracks. The model is applied to ion-beam induced defects in LiF crystals. Two aspects are treated separately viz. the ion-deposited energy distribution for a given fluence and the material response to the absorbed energy. The first problem is treated within the framework of stochastic superposition of ion tracks, taking into account the radial distribution of the energy transfer of a single ion. For lithium fluoride the creation of color centers is considered as the materials response. The dependence of the defect concentration on the absorbed energy is included in order to obtain the integral defect production.

Scale Invariance of Nanosize Structures Arising from the Overlap of Single Ion Tracks

Nanosize structures that may arise from the multiple overlapping of single tracks with growth in the irradiation dose have been modeled without account of the process of formation of the single tracks themselves. It has been established that the percolation cluster of the structure of overlapped ion tracks is a physical fractal. The surface area of such a cluster nonmonotonically depends on the angle of irradiation with fast heavy ions. It has been determined that the percolation irradiation dose depends on the dimension of the sample by a power law. The power of this dependence is inversely p roportional to the critical exponent which is determined by the track shape and by the distribution of the tracks over the sample’s depth.