Radiation Hardness Of Materials Research Articles

Optical manipulation of ultrashort laser pulses for applications in challenging environments

Over the last few years, high throughput ultrashort-pulse laser sources have become increasingly affordable. This facilitated the emergence of many applications that require sub-micron precision material modification. Processes have been demonstrated in applications including micro-structuring semiconductor chips, manufacturing complex 3D parts or inscribing optical materials for data storage. Furthermore, recent progress in techniques for the optical manipulation of ultrashort laser pulses opened up new avenues in applications for challenging environments such as those involving high energy physics or particle beam radiotherapy. These applications require high-resolution 3D structures to be produced in radiation tolerant materials, to make particle sensors with the required sensitivity and resolution. For such processes, accurate spatial and temporal structuring and manipulating of optical parameters such as polarization, wavefront and intensity of laser beams, is essential. This paper presents recent results in advanced optical manipulation including the induction of helical or longitudinal fields at the focus. The resulting laser material coupling interactions are characterized and their suitability for making particle sensors from radiation hard materials considered.

Real-time study of radiation damage in monocrystalline diamond sensors

Being an excellent radiation hard material, diamond is preferred as an ionizing radiation sensor in radiation harsh environments. In this study, radiation damage from a beam of 67.5 MeV protons at the Crocker Nuclear Laboratory on the campus of the University of California, Davis, was used to determine exposure lifetime in detectors made from a thinned (∼ 40 μm) monocrystalline CVD (chemical vapor deposition) diamond substrate. The sensor response was sampled in real time as the sensor was exposed to a total fluence of ∼ 4×1016 / cm2, yielding an overall damage constant of k = (3.3 ± 0.3) × 10-18 cm2 / p-μm. Damage levels were later confirmed using a non-destructive x-ray technique at the LINAC Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory. Results are presented on the real-time degradation of the charge collection efficiency as a function of proton fluence.

Imaging 3D chemistry at 1 nm resolution with fused multi-modal electron tomography

Measuring the three-dimensional (3D) distribution of chemistry in nanoscale matter is a longstanding challenge for metrological science. The inelastic scattering events required for 3D chemical imaging are too rare, requiring high beam exposure that destroys the specimen before an experiment is completed. Even larger doses are required to achieve high resolution. Thus, chemical mapping in 3D has been unachievable except at lower resolution with the most radiation-hard materials. Here, high-resolution 3D chemical imaging is achieved near or below one-nanometer resolution in an Au-Fe3O4 metamaterial within an organic ligand matrix, Co3O4-Mn3O4 core-shell nanocrystals, and ZnS-Cu0.64S0.36 nanomaterial using fused multi-modal electron tomography. Multi-modal data fusion enables high-resolution chemical tomography often with 99% less dose by linking information encoded within both elastic (HAADF) and inelastic (EDX/EELS) signals. We thus demonstrate that sub-nanometer 3D resolution of chemistry is measurable for a broad class of geometrically and compositionally complex materials.

Silicon Carbide Timepix3 detector for quantum-imaging detection and spectral tracking of charged particles in wide range of energy and field-of-view

The hybrid architecture of the Timepix (TPX) family of detectors enables the use of different semiconductor sensors, most commonly silicon (Si), as well as high-density materials such as Cadmium Telluride (CdTe) or Gallium Arsenide (GaAs). For this purpose, we explore the potential of a silicon carbide (SiC) sensor bump-bonded on a Timepix3 detector as a radiation imaging and particle tracking detector. SiC stands as a radiation-hard material also with the ability to operate at elevated temperatures up to several hundreds of degrees Celsius. As a result, this sensor material is more suitable for radiation harsh environments compared to conventional e.g., Si sensors. In this work, we evaluate the response for precise radiation spectrometry and high-resolution particle tracking of newly developed SiC Timepix3 detector which is built and operated as a compact radiation camera MiniPIX-Timepix3 with integrated readout electronics. Calibration measurements were conducted with mono-energetic proton beams with energies of 13, 22, and 31 MeV at the U-120M cyclotron at the Nuclear Physics Institute Czech Academy of Science (NPI CAS), Prague, as well as 100 and 226 MeV at the Proton Therapy Center Czech (PTC) in Prague. High-resolution pattern recognition analysis and single-particle spectral tracking are used for detailed inspection and understanding of the sensor response. Results include distributions of deposited energy and linear energy transfer (LET) spectra. The spatial uniformity of the pixelated detector response is examined in terms of homogeneously distributed deposited energy.

Characteristics of thin p-MCz Si Microstrip Detector Irradiated upto a mixed fluence of 1017neq./cm2for the FCC

Silicon microstrip detectors can be used for the precise particle tracking in the inner tracking region of the detector used in the future high luminosity collider experiment. In the future experiments, hadron collider provides higher luminosities on the strip detector, and therefore, a detector requires very high radiation hardness. Within CERNRD50collaboration, MCz Si is identified as a prime radiation hard material for the fabrication of the p-Si microstrip detector. In this paper, we have used the experimentally verified four level deep-trap mixed irradiation model for p-MCz Si to investigate the effect of heavy irradiations up to a mixed fluence of 1017n eq./cm2 on the full depletion voltage, leakage current, and charge collection efficiency using SRH and CCE modelling.The changes in the characteristics were evaluated, and effect of the traps on the macroscopic performance of the detectors and possible improvement in the design and semiconductor technology of the p-Mcz silicon microstrip detector.

Electron irradiation: From test to material tailoring

In this article, we report some examples of how high-energy electron irradiation can be used as a tool for shaping material properties turning the generation of point-defects into an advantage beyond the presumed degradation of the properties. Such an approach is radically different from what often occurs when irradiation is used as a test for radiation hard materials or devices degradation in harsh environments. We illustrate the potential of this emerging technique by results obtained on two families of materials, namely semiconductors and superconductors.

Mechanism of ion track formation in silicon by much lower energy deposition than the formation threshold

Mechanism of the ion track formation in crystalline silicon (c-Si) is discussed, particularly under 1–9 MeV C60 ion irradiation. In this energy region, the track formation was not expected because the energy E was much lower than the threshold of E th = 17 MeV determined by extrapolation from higher energy data in the past literature. The track formation is different between irradiations of C60 ions and of monoatomic ions: The tracks were observed under 3 MeV C60 ion irradiation but not under 200 MeV Xe ions, while both the irradiations have the same electronic stopping (S e) of 14 keV nm−1 but much higher nuclear stopping (S n) for the former ions. The involvement of S n is suggested for the C60 ions. While the inelastic thermal spike (i-TS) calculations predict that the high energy monoatomic ion irradiation forms the tracks, the tracks have never been experimentally detected, suggesting quick annihilation of the tracks by highly enhanced recrystallization in c-Si. Exceptions are C60 ions of 1–9 MeV, where the track radii are well reproduced by the i-TS theory with assuming the melting transition. Collisional damage induced by the high S n from C60 ions obstructs the recrystallization in c-Si. Then the tracks formed by the melting transition survive against the recrystallization. This is a new type of the synergy effect between S e and S n, different from the already-known mechanisms, i.e., the pre-damage effect and the unified thermal spike. While c-Si was believed as a radiation-hard material in the S e regime with high S e threshold, this study suggests that c-Si has a low S e threshold but with efficient recrystallization.

Simulation of the SiGe use effi-ciency for the production of high-voltage thyristors

Power semiconductor devices often subjected to appreciable terrestrial atmospheric neutron flows. For the improvement of their radiation hardness, the use of silicon doped with Ge (SiGe) was proposed. The stability of last is much higher in comparison with convenient type silicon. Earlier received results confirmed effectiveness of isovalent doping of silicon with germanium at radiation tests of low power (current approx. 100 mA) discrete devices. Power thyristors Т122-25 are used for the transformation and regulation of AC and DC current up to 25А, frequency up to 500 Гц in the circuits with voltage 100 – 1600V (1-16 class). In the data sheets directly indicated that these devices are not suitable for operating in the conditions of ionizing radiation. Therefore, the main practically important mission of the article was the confirmation the technological efficiency of SiGe use, or, in other words, possibility of radiation hard material use for high voltage power devices technology. The purpose of the present work was the modeling of the experimental findings for the informed choice of Ge concentration for manufacturing of high voltage thyristors Т122. The data concern the workable general-purpose power thyristors Т122 type yield, manufactured in accordance with the identical technology, based on CZ-Si и CZ-Si. At SiGe implementation in the technology of power semiconductors was observed no monotonic change of the thyristors gain share for devices of high (10, 11, 12) ranges (classes), the value of pulse recurring voltage in off-state is 1000, 1100 and 1200 V. Simulation of the experimental results was performed in MathCAD. The concentration of Ge, suitable for the manufacture of high-voltage thyristors, is in the range 2 ·1019 - 1·1020 cm-3, i.e. in the linear region of dependence. Previously, the authors have experimentally shown the possibility and mechanism of increasing the radiation resistance of SiGe with a concentration of Ge 5·1019 cm-3. It is allowed to admit the possibility of reaching the radiation resistance of high-voltage power discrete thyristors when tested with γ-quanta in the dose range up to ≅ 3·106 mSv.

Luminescence of ZnO:Ga ceramics under sub-threshold electron irradiation

The luminescence of ZnO:Ga ceramics was studied at room temperature under 270 keV electrons irradiation. The near band gap and defects related luminescence intensity independence on irradiation dose up to 9.4 × 1013 e/cm2 as well as absence of thermostimulated luminescence within 300–600 K confirm that ZnO:Ga ceramics is radiation hard material for sub-threshold energy electron irradiation and therefore is prospective as scintillator for sub-threshold electrons detection. The near band gap luminescence peak position is at 393 nm under electron beam irradiation, and it is shifted to the long wave side relative to photoluminescence. The origin of the observed shift could be both – the difference of recharged donor-acceptor pairs created under photoexcitation and electron beam irradiation as well as contribution from host material self-absorption.

Fabrication and First Full Characterisation of Timing Properties of 3D Diamond Detectors

Tracking detectors at future high luminosity hadron colliders are expected to be able to stand unprecedented levels of radiation as well as to efficiently reconstruct a huge number of tracks and primary vertices. To face the challenges posed by the radiation damage, new extremely radiation hard materials and sensor designs will be needed, while the track and vertex reconstruction problem can be significantly mitigated by the introduction of detectors with excellent timing capabilities. Indeed, the time coordinate provides extremely powerful information to disentangle overlapping tracks and hits in the harsh hadronic collision environment. Diamond 3D pixel sensors optimised for timing applications provide an appealing solution to the above problems as the 3D geometry enhances the already outstanding radiation hardness and allows to exploit the excellent timing properties of diamond. We report here the first full timing characterisation of 3D diamond sensors fabricated by electrode laser graphitisation in Florence. Results from a 270MeV pion beam test of a first prototype and from tests with a β source on a recently fabricated 55×55μm2 pitch sensor are discussed. First results on sensor simulation are also presented.

Investigation of Ion Irradiation Effects in Silicon and Graphite Produced by 23 MeV I Beam.

Both silicon and graphite are radiation hard materials with respect to swift heavy ions like fission fragments and cosmic rays. Recrystallisation is considered to be the main mechanism of prompt damage anneal in these two materials, resulting in negligible amounts of damage produced, even when exposed to high ion fluences. In this work we present evidence that these two materials could be susceptible to swift heavy ion irradiation effects even at low energies. In the case of silicon, ion channeling and electron microscopy measurements reveal significant recovery of pre-existing defects when exposed to a swift heavy ion beam. In the case of graphite, by using ion channeling, Raman spectroscopy and atomic force microscopy, we found that the surface of the material is more prone to irradiation damage than the bulk.

Boron doping in gallium oxide from first principles

We study the feasibility of boron doping in gallium oxide (Ga2O3) for neutron detection. Ga2O3 is a wide band gap, radiation-hard material with potential for neutron detection, if it can be doped with a neutron active element. We investigate the boron-10 isotope as possible neutron active dopant. Intrinsic and boron induced defects in Ga2O3 are studied with semi-local and hybrid density-functional-theory calculations. We find that it is possible to introduce boron into gallium sites at moderate concentrations. High concentrations of boron, however, compete with the boron-oxide formation.

Current-voltage characteristics of iron-implanted silicon based Schottky diodes

Current-voltage (I–V) measurements were carried out on undoped and iron (Fe) doped n-silicon (n-Si) to establish and study a change in electrical properties of the material-based diodes with Fe doping concentration. Fe doping was achieved by implantation at the energy of 160 keV to fluences of 1015, 1016 and 1017 ion/cm2. The obtained results indicated that the diodes were well fabricated and Fe doping resulted in a diode behaviour changing from normal exponential to ohmic I–V behaviour. This ohmic behaviour was explained in terms of Fe-induced defect levels that were positioned at the centre of the energy gap. An I–V ohmic region increased with fluence indicating that the density of defect levels has increased with Fe implantation fluence. A change in diode conduction mechanism domination and parameters with fluence were investigated. The obtained I–V properties of Fe doped Si-based diodes were similar to those of the diodes that were fabricated on radiation-hard materials indicating that Fe, too, is a promising dopant in a quest to improve radiation-hardness of Si to be used in high energy physics experiments.

Study of Electrode Fabrication in Diamond with a Femto‐Second Laser

Diamond is a radiation hard material, which makes it suitable for its use in high energy physics experiments as a particle detector. To further reduce the effects of radiation damage, diamond detectors can be fabricated by inscribing graphitic electrodes perpendicular to the surface—the so‐called 3D detectors. This can be done via processing with a femtosecond laser. Herein, a systematic study of the cross section of the graphitic wires inscribed into diamond is shown as a function of laser pulse energy, stage translational speed and, for the first time, polarization for a single crystal and polycrystalline chemical vapour deposition (CVD) diamond samples. No dependence of the electrode width with speed polarization and sample for the same pulse energies within uncertainties are observed. The graphitic content of the electrodes is studied in terms of Raman spectrometry: no clear dependence on the fabrication parameters studied is observed.

Determination of radiation hardness of silicon diodes

In this paper, we describe an experiment aimed to measure the physical observables, which can be used for the assessment of the radiation hardness of commercially available silicon photo diodes commonly used as nuclear detectors in particle accelerator laboratories. The experiment adopted the methodology developed during the International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP No. F11016) “Utilization of Ion Accelerators for Studying and Modelling Ion Induced Radiation Defects in Semiconductors and Insulators”.This methodology is based on the selective irradiation of micrometer-sized regions with different fluences of MeV ions using an ion microbeam and on the measurement of the charge collection efficiency (CCE) degradation by Ion Beam Induced Charge (IBIC) microscopy performed in full depletion condition, using different probing ions.The IBIC results are analyzed through a theoretical approach based on the Shockley-Read-Hall model for the free carrier recombination in the presence of ion-induced deep traps. This interpretative model allows the evaluation of the material radiation hardness in terms of recombination parameters for both electrons and holes.The device under study in this experiment was a commercial p-i-n photodiode, which was initially characterized by i) standard electronic characterization techniques to determine its doping and ii) the Angle-Resolved IBIC to evaluate its effective entrance window. Nine regions of (100 × 100) µm2 were irradiated with 11.25 MeV He ions up to a maximum fluence of 3·1012 ions/cm2. The CCE degradation was measured by the IBIC technique using 11.25 MeV He and 1.4 MeV He as probing ions.The model presented here proved to be effective for fitting the experimental data. The fitting parameters correspond to the recombination coefficients, which are the key parameters for the characterization of the effects of radiation damage in semiconductors.

Evolution of Diamond based Microdosimetry

The requirements for solid state micro- dosimetry particularly within the context of medical and space environments necessitate a tissue equivalent and radiation hard material, for which diamond is uniquely suited. An overview of the current status of diamond based microdosimetry is given. This overview will explore previous and current technologies developed by the Centre for Medical Radiation Physics (CMRP). The overview will analyse technologies in terms of their advantages and disadvantages within the context of microdosimetry. Using this as a basis, recommendations with respect to fabri- cation methodologies/techniques are provided in order to direct the course and progress of development so as to achieve true diamond based microdosimetry.

Underlying role of mechanical rigidity and topological constraints in physical sputtering and reactive ion etching of amorphous materials

Analytical expressions describing ion-induced sputter or etch processes generally relate the sputter yield to the surface atomic binding energy $({U}_{\mathrm{sb}})$ for the target material. While straightforward to measure for the crystalline elemental solids, ${U}_{\mathrm{sb}}$ is more complicated to establish for amorphous and multielement materials due to composition-driven variations and incongruent sublimation. In this regard, we show that for amorphous multielement materials, the ion-driven yield can instead be better understood via a consideration of mechanical rigidity and network topology. We first demonstrate a direct relationship between ${U}_{\mathrm{sb}}$, bulk modulus, and ion sputter yield for the elements, and then subsequently prove our hypothesis for amorphous multielement compounds by demonstrating that the same relationships exist between the reactive ion etch (RIE) rate and nanoindentation Young's modulus for a series of $a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{N}}_{x}$:H and $a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{x}{\mathrm{C}}_{y}$:H thin films. The impact of network topology is further revealed via application of the Phillips--Thorpe theory of topological constraints, which directly relates the Young's modulus to the mean atomic coordination $(\ensuremath{\langle}r\ensuremath{\rangle})$ for an amorphous solid. The combined analysis allows the trends and plateaus in the RIE rate to be ultimately reinterpreted in terms of the atomic structure of the target material through a consideration of $\ensuremath{\langle}r\ensuremath{\rangle}$. These findings establish the important underlying role of mechanical rigidity and network topology in ion--solid interactions and provide additional considerations for the design and optimization of radiation-hard materials in nuclear and outer space environments.

Space Environment Effects on Flexible, Low-Voltage Organic Thin-Film Transistors.

Organic electronic devices fabricated on flexible substrates are promising candidates for applications in environments where flexible, lightweight, and radiation hard materials are required. In this work, device parameters such as threshold voltage, charge mobility, and trap density of 13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)-based organic thin-film transistors (OTFTs) have been monitored for performing electrical measurements before and after irradiation by high-energy protons. The observed reduction of charge carrier mobility following irradiation can be only partially ascribed to the increased trap density. Indeed, we used other techniques to identify additional effects induced by proton irradiation in such devices. Atomic force microscopy reveals morphological defects occurring in the organic dielectric layer induced by the impinging protons, which, in turn, induce a strain on the TIPS-pentacene crystallites lying above. The effects of this strain are investigated by density functional theory simulations of two model structures, which describe the TIPS-pentacene crystalline films at equilibrium and under strain. The two different density of states distributions in the valence band have been correlated with the photocurrent spectra acquired before and after proton irradiation. We conclude that the degradation of the dielectric layer and the organic semiconductor sensitivity to strain are the two main phenomena responsible for the reduction of OTFT mobility after proton irradiation.

The Co-60 gamma-ray irradiation effects on the Al/HfSiO4/p-Si/Al MOS capacitors

In this work, the initial interface trap density (Nit) to examine device compability for microelectronics and then the Co-60 gamma irradiation responses of Al/HfSiO4/p-Si/Al (MOS) capacitors were investigated in various dose ranges up to 70Gy. Pre-irradiation response of the devices was evaluated from high frequency (HF) and low frequency (LF) capacitance method and the Nit was calculated as 9.91 × 1011cm−2 which shows that the HfSiO4/p-Si interface quality is convenient for microelectronics applications. The irradiation responses of the devices were carried out from flat-band and mid-gap voltage shifts obtained from stretch of capacitance characteristics prior to and after irradiation. The results show that the flat band voltages very slightly shifted to positive voltage values demonstrating the enhancement of negative charge trapping in device structure. The sensitivity of the Al/HfSiO4/p-Si/Al MOS capacitors was found to be 4.41mV/Gy for 300nm-thick HfSiO4 gate dielectrics. This value approximately 6.5 times smaller compared to the same thickness conventional SiO2 based MOS devices. Therefore, HfSiO4 exhibits crucial irradiation tolerance in gamma irradiation environment. Consequently, HfSiO4 dielectrics may have significant usage for microelectronic technology as a radiation hard material where radiation field exists such as in space applications.

Effect of microstructure on irradiated ferroelectric thin films

This work investigates the role of microstructure on radiation-induced changes to the functional response of ferroelectric thin films. Chemical solution-deposited lead zirconate titanate thin films with columnar and equiaxed grain morphologies are exposed to a range of gamma radiation doses up to 10 Mrad and the resulting trends in functional response degradation are quantified using a previously developed phenomenological model. The observed trends of global degradation as well as local rates of defect saturation suggest strong coupling between ferroelectric thin film microstructure and material radiation hardness. Radiation-induced degradation of domain wall motion is thought to be the major contributor to the reduction in ferroelectric response. Lower rates of defect saturation are noted in samples with columnar grains, due to increased grain boundary density offering more sites to act as defect sinks, thus reducing the interaction of defects with functional material volume within the grain interior. Response trends for measurements at low electric field show substantial degradation of polarization and piezoelectric properties (up to 80% reduction in remanent piezoelectric response), while such effects are largely diminished at increased electric fields, indicating that the defects created/activated are primarily of low pinning energy. The correlation of film microstructure to radiation-induced changes to the functional response of ferroelectric thin films can be leveraged to tune and tailor the eventual properties of devices relying on these materials.