Progress in Elastic Recoil Detection Analysis

Elastic recoil detection analysis (ERDA) with heavy ion beams has evolved into a universal ion beam analysis (IBA) method for simultaneous analysis of almost all elements, with an essentially constant detection sensitivity. The method is based on the detection and identification of recoiling atoms that have been elastically scattered from a sample by an incident heavy ion beam. The principal characteristics of heavy-ion ERDA are outlined and illustrated using examples of data obtained with time of flight (TOF) and dE-E detector systems. The potential and limitations of the quantitative analysis were explored. For this purpose, a number of thin layer samples were measured using different projectiles and energies. Desorption of the surface materials during ERDA measurements was determined as a function of the probing ion fluence. As the differential cross-sections for scattering were enhanced for heavy projectiles, the beam dose to which the sample was exposed to during measurements was reduced by using heavy ion beams. However the higher cross-sections caused an increase of the desorption. An essential part of this study was dedicated to study those topics that limit the accuracy of the analysis in heavy ion TOF-ERDA, namely: uncertain stopping forces, quantification accuracy, irradiation induced damage, depth resolution, and the role of multiple and plural scattering. Possible approaches to improve the sample characterisation efficiency and accuracy were studied by using a gas ionisation detector. This study concentrates on the noise reduction, detection characterisation, and analysis procedures. The focus was upon the effect of the large solid angle and position sensitivity on the irradiation induced damage, depth resolution, mass resolution, and elemental sensitivity. The reliability of the concentration distributions obtained with heavy ion ERDA was strongly affected by the surface structure, surface roughness and multiple scattering. These effects were studied by comparing Monte Carlo simulations with the experimental results. The analysis procedure was developed to enable the characterisation of novel materials such as atomic layer deposited thin films and nanoparticles. Data handling and storage was improved to facilitate and speed up the analysis procedures.Nykyteknologian kannalta materiaalien tärkeimmät ominaisuudet sijoittuvat aineen pintakerroksiin. Lisäksi materiaalitutkimuksessa keskitytään enenevässä määrin nanorakenteisiin, kuten nanokiteisiin ja nanoputkiin. Eräs keskeinen materiaalitutkimuksen ongelma on tämän muutamista nanometreistä muutamiin satoihin nanometreihin paksun kerroksen ominaisuuksien analysointi. Ionisuihkuihin perustuvia analysointimenetelmiä (IBA, ion beam analysis) käytetään yleisesti alkuainekoostumuksen analysointiin. Tässä tutkimuksessa keskitytään rekyylispektroskopiaan (ERDA, elastic recoil detection analysis), joka perustuu energeettisten hiukkasten törmäyksessä syntyvän rekyyliatomin havainnointiin. ERDA menetelmässä näytteen analysointiin käytetään usein raskaita ammusioneja, jotka kiihdytetään sähköstaattisella kiihdyttimellä useiden kymmenien megaelektronivolttien energioihin. Kiihdytettyjen hiukkasten ja tutkittavan materiaalin törmäyksessä ammushiukkaset siroavat ja näytteen atomit saavat rekyylin, joka irrottaa atomin näytteestä. ERDA menetelmässä nämä rekyyliatomit ja sironneet ammushiukkaset havainnoidaan sopivalla ilmaisimella. Menetelmässä on mahdollista analysoida näytteen kaikki alkuaineet, aina vedystä raskaimpiin yhdellä mittauksella. Erilaisten havaittavien hiukkasten takia ilmaisinlaitteistolta vaaditaan kykyä tunnistaa hiukkaset ja mitata näiden energia. Tässä tutkimuksessa selvitetään lentoajan mittaukseen perustuvan ERDA ilmaisimen (TOF-ERDA, time-of-flight ERDA) rajoituksiin ja mahdollisiin parannuksiin, jotta menetelmä sopisi nykyisen materiaalitutkimuksen kannalta kiinnostaviin näytteisiin. Keskeisimmät ongelmat TOF-ERDA menetelmässä ovat lentoajan mittauksen tarkkuus (aikaresoluutio) ja ilmaisimen äärelliseen havainnointikulman aiheuttama energian hajonta. Yleisesti IBA menetelmät, joissa määritetään näytteen alkuaineiden syvyysjakaumia, pohjautuvat materiaalin kykyyn jarruttaa varattuja hiukkasia. Aineen jarrutuskyvylle on olemassa erilaisia teoreettisia ja puolikokeellisiin malleja. IBA menetelmissä käytetyimmät mallit pohjautuvat kokeelliseen dataan ja näiden mallien tarkkuus riippuu saatavilla olevan datan määrästä ja tarkkuudesta. Osa tästä tutkimuksesta keskittyy menetelmiin, joilla hiukkasten energian menetys aineessa voidaan mitata ja tästä edelleen materiaalin jarrutuskyky määrittää. Saatuja tuloksia ja parannuksia on käytetty useiden erityyppisten materiaalien alkuaineanalyyseissä

Evaluation of tritium retention in plasma facing components during JET tritium operations

An assessment of the tritium (T) inventory in plasma facing components (PFC) during JET T and deuterium-tritium (DT) operations is presented based on the most comprehensive ex situ fuel retention data set on JET PFCs from the 2015-2016 ILW3 operating period is presented. The global fuel retention is 4.19 x 10(23) D atoms, 0.19% of injected fuel. The inner divertor remains the region of highest fuel retention (46.5%). The T inventory in PFCs at the end of JET operations is calculated as 7.48 x 10(22) atoms and is informative for accountancy, clean-up efficacy and waste liability assessments. The T accumulation rate at the upper inner divertor during JET DT operations has been used to assess the requirements and frequency of operation of a new laser induced desorption diagnostic to be installed on JET for the final DT experiments in 2023.Peer reviewe

Thermal diffusivity degradation and point defect density in self-ion implanted tungsten

Using transient grating spectroscopy (TGS) we measure the thermal diffusivity of tungsten exposed to different levels of 20 MeV self-ion irradiation. Damage as low as 3.2 × 10−4 displacements per atom (dpa) causes a measurable reduction in thermal diffusivity. Doses of 0.1 dpa and above, up to 10 dpa, give a degradation of ̴55% from the pristine value at room temperature. Using a kinetic theory model, the density of irradiation-induced point defects is estimated based on the measured changes in thermal diffusivity as a function of dose. These predictions are compared with point defect and dislocation loop densities observed in transmission electron microscopy (TEM). Molecular dynamics (MD) predictions are combined with the TEM observations to estimate the density of point defects associated with defect clusters too small to be probed by TEM. When these “invisible” defects are accounted for, the total point defect density agrees well with that estimated from TGS for a range of doses spanning 3 orders of magnitude. Kinetic theory modelling is also used to estimate the thermal diffusivity degradation expected due to TEM-visible and invisible defects. Finely distributed invisible defects appear to play a much more important role in the thermal diffusivity reduction than larger TEM-visible dislocation loops. This work demonstrates the capability of TGS, in conjunction with kinetic theory models, to provide rapid, quantitative insight into defect densities and property evolution in irradiated materials.Peer reviewe

Modified deformation behaviour of self-ion irradiated tungsten : A combined nano-indentation, HR-EBSD and crystal plasticity study

Predicting the dramatic changes in mechanical and physical properties caused by irradiation damage is key for the design of future nuclear fission and fusion reactors. Self-ion irradiation provides an attractive tool for mimicking the effects of neutron irradiation. However, the damaged layer of self-ion implanted samples is only a few microns thick, making it difficult to estimate macroscopic properties. Here we address this challenge using a combination of experimental and modelling techniques. We concentrate on self-ion-implanted tungsten, the frontrunner for fusion reactor armour components and a prototypical bcc material. To capture dose-dependent evolution of properties, we experimentally characterise samples with damage levels from 0.01 to 1 dpa. Spherical nano-indentation of grains shows hardness increasing up to a dose of 0.032 dpa, beyond which it saturates. Atomic force microscopy (AFM) measurements show pile-up increasing up to the same dose, beyond which large pile-up and slip-steps are seen. Based on these observations we develop a simple crystal plasticity finite element (CPFE) model for the irradiated material. It captures irradiation-induced hardening followed by strain-softening through the interaction of irradiation-induced-defects and gliding dislocations. The shear resistance of irradiation-induced-defects is physically-based, estimated from transmission electron microscopy (TEM) observations of similarly irradiated samples. Nano-indentation of pristine tungsten and implanted tungsten of doses 0.01, 0.1, 0.32 and 1 dpa is simulated. Only two model parameters are fitted to the experimental results of the 0.01 dpa sample and are kept unchanged for all other doses. The peak indentation load, indent surface profiles and damage saturation predicted by the CPFE model closely match our experimental observations. Predicted lattice distortions and dislocation distributions around indents agree well with corresponding measurements from high-resolution electron backscatter diffraction (HR-EBSD). Finally, the CPFE model is used to predict the macroscopic stress-strain response of similarly irradiated bulk tungsten material. This macroscopic information is the key input required for design of fusion armour components.Peer reviewe

Highly Material Selective and Self-Aligned Photo-assisted Atomic Layer Deposition of Copper on Oxide Materials

There is a growing need for bottom-up fabrication methods in microelectronic industry as top-down, lithography-based methods face increasing challenges. In Photo-assisted atomic layer deposition (Photo-ALD), photons supply energy to the deposition reactions on the surface. Here, a process and patterning for Photo-ALD of copper is reported, with inherently selective, self-aligned film growth without any photomasking or additive layers. Highly conductive and pure copper films are selectively deposited on tantalum oxide for over hundred nanometers of film thickness, while no copper deposits on silicon or aluminum oxide. On anatase titanium dioxide, copper deposition is crystal-facet selective. Selective deposition of a metal is realized on oxides, which has been especially challenging for ALD. This study indicates that the growth mechanism is closely related to photocatalysis: the photons interact with the material under the growing copper film, enabling the inherent selectivity. The findings provide promising material engineering schemes for microelectronics, photocatalysis, and photovoltaics.Peer reviewe

Ionic conductivity in LixTaOy thin films grown by atomic layer deposition

The material system Li-Ta-O is a promising candidate for thin-film solid-state electrolytes in Li-ion batteries. In the present study, we have varied the Li content x in LixTaOy thin films grown by atomic layer deposition (ALD) with the aim of improving the Li-ion conductivity. The amorphous films were grown at 225 degrees C on insulating sapphire and on conductive Ti substrates using tantalum ethoxide (Ta(OEt)(5)), lithium tert-butoxide ((LiOBu)-Bu-t) and water as reactants. The film composition was determined by time-of-flight elastic recoil detection analysis (TOF-ERDA), displaying an almost linear relationship between the pulsed and deposited Li content. The ionic conductivities were determined by in-plane and cross-plane AC measurements, exhibiting an Arrhenius-type behaviour and comparatively weak thickness-dependence. Increasing Li content x from 0.32 to 0.98 increases the film conductivity by two orders of magnitude while higher Li content x = 1.73 results in decreased conductivity. A room-temperature conductivity ciRT of similar to 10(-8) S cm(-1) is obtained for a 169 nm thick Li0.98TaOy film. The evolution of conductivity and activation energy suggests a competing effect between the concentration and the mobility of mobile Li ions when more Li are incorporated. The compositional dependence of Li transport mechanism is discussed. (C) 2020 The Author(s). Published by Elsevier Ltd.Peer reviewe

A low-temperature thermal ALD process for nickel utilizing dichlorobis(triethylphosphine)nickel(ii) and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine

In this work, we developed a new ALD process for nickel metal from dichlorobis(triethylphosphine)nickel(ii) (NiCl2(PEt3)(2)) and 1,4-bis(trimethylgermyl)-1,4-dihydropyrazine ((Me3Ge)(2)DHP). A series of phosphine adducts of nickel and cobalt halides were synthesized and characterized for their volatility and thermal stability. Also (Me3Ge)(2)DHP is a novel reducing agent in ALD. Smooth nickel films were deposited on different substrate materials at 110 degrees C, which is the lowest deposition temperature for Ni metal found in the literature. The growth rate is 0.2 angstrom per cycle when the film is not continuous and decreases to 0.1 angstrom per cycle after the film becomes pinhole-free. Besides a small amount (7 at%) of carbidic carbon, the films have only small amounts of impurities. Most notably, the chlorine content is below 0.2 at%, indicating efficient reduction. Furthermore, we think that (Me3Ge)(2)DHP can open new avenues for the ALD of other metals at low temperatures.Peer reviewe

Effect of interstitial carbon on the evolution of early-stage irradiation damage in equi-atomic FeMnNiCoCr high-entropy alloys

Owing to their excellent radiation tolerance, some of the high-entropy alloys (HEAs) are considered as potential candidates for structural materials in extreme conditions. In order to shed light on the early-stage irradiation damage in HEAs, we performed positron annihilation spectroscopy on hydrogen implanted equiatomic FeMnNiCoCr and interstitial carbon-containing FeMnNiCoCr HEAs. We reveal primary damage as monovacancies in low dose irradiated HEAs. The enhancement of Frenkel pair recombination by C addition is observed in C-containing HEAs. In addition, the C interstitials suppress the vacancy cluster formation in high dose irradiated HEAs.Peer reviewe

Thermal diffusivity recovery and defect annealing kinetics of self-ion implanted tungsten prob e d by insitu transient grating spectroscopy

Tungsten is a promising candidate material for plasma-facing armour components in future fusion reactors. A key concern is irradiation-induced degradation of its normally excellent thermal transport properties. In this comprehensive study, thermal diffusivity degradation in ion-implanted tungsten and its evolution from room temperature (RT) to 1073 K is considered. Five samples were exposed to 20 MeV self-ions at RT to achieve damage levels ranging from 3.2 x 10(-4) to 3.2 displacements per atom (dpa). Transient grating spectroscopy with insitu heating was then used to study thermal diffusivity evolution as a function of temperature. Using a kinetic theory model, an equivalent point defect density is estimated from the measured thermal diffusivity. The results showed a prominent recovery of thermal diffusivity between 450 K and 650 K, which coincides with the onset of mono-vacancy mobility. After 1073 K annealing samples with initial damage of 3.2 x 10(-3) dpa or less recover close to the pristine value of thermal diffusivity. For doses of 3.2 x 10(-2) dpa or higher, on the other hand, a residual reduction in thermal diffusivity remains even after 1073 K annealing. Transmission electron microscopy reveals that this is associated with extended, irradiation-induced dislocation structures that are retained after annealing. A sensitivity analysis shows that thermal diffusivity provides an efficient tool for assessing total defect content in tungsten up to 10 0 0 K. (c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc.Peer reviewe

Atomic layer deposition of GdF3 thin films

doi: 10.1116/6.0001629Gadolinium fluoride is an attractive optical material with applications in, e.g., deep-UV lithography, solar cells, and medical imaging. Despite the interest toward this material, no atomic layer deposition (ALD) process has been published. In this article, an ALD process for GdF3 using Gd(thd)(3) and NH4F as precursors is presented. The deposition was studied at temperatures 275-375 & DEG;C, but 285-375 & DEG;C produce the purest films. The saturation of the growth per cycle (GPC) with respect to precursor pulses and purges was proved at 300 & DEG;C. The GPC value at this temperature is & SIM;0.26 & ANGS;, and the deposition temperature has very little effect on the GPC. According to x-ray diffraction, all the films consist of orthorhombic GdF3. The impurity contents, evaluated by time-of-flight elastic recoil detection analysis, is low, and the films are close to stoichiometric. The nitrogen content is less than < 0.04 at. %. The antireflection properties were qualitatively evaluated by UV-vis spectrometry in a transmission mode at a 190-1100 nm range: on sapphire substrates, GdF3 serves as an antireflective coating. Dielectric properties of the films were studied, and for example, a permittivity value of 9.3 was measured for a & SIM;64 nm film deposited at 300 & DEG;C.Peer reviewe