In the case of high-fluence implantations, the approximation that every new incoming particle interacts with a pristine substrate material no longer holds. Dynamical changes to the substrate can induce different phenomena, one of which is self-sputtering. Self-sputtering occurs when incoming ions remove previously implanted ions from the implantation substrate. This phenomenon is significant in target production for nuclear structure studies and medical radionuclide separation, where self-sputtering limits can be reached during isotope implantation. Self-sputtering can be modeled using TRIDYN simulations in order to guide implantations. This work explores the ability of TRIDYN to give order-of-magnitude estimates for the onset of self-sputtering for these nuclear physics applications. This is performed through the implantation of Yb in Zn and Al, relevant to both fundamental and medical nuclear physics research. Our findings indicate that TRIDYN predicts general dependencies reasonably well. However, it is important to carefully consider input parameters and validity of the TRIDYN simulations. Copyright M. Heines et al. This work is licensed under the Creative Commons Attribution 4.0 International License. Published by the SciPost Foundation.

Scandium-based silicides have attracted attention as new contact materials for ultimately scaled CMOS devices. Excellent contact properties in combination with P-doped Si have been demonstrated. However, unlike conventional Ti, Co, and Ni silicides, little is known about the formation mechanisms and properties of Sc silicides. This manuscript, therefore, reports on the formation and structural properties of orthorhombic ScSi silicide formed by solid state reaction between a sputter deposited 15 nm Sc film and a Si(001) substrate. Synchrotron x-ray diffraction (XRD) pole figures, in combination with cross-sectional transmission electron microscopy, are leveraged to determine the texture of ScSi. An epitaxial texture with two different components is evidenced. Large (≳20 nm) grains, having a minimal defectivity originating from the lattice mismatch between the silicide and the substrate, are distinguished from small (≲5 nm) nanotwinned grains. The formation of these two sets of grains is investigated by in situ XRD. Due to a solid state amorphization reaction between Sc and Si, the formation of orthorhombic ScSi is preceded by the formation of an amorphous ScSi phase. Orthorhombic ScSi formation is initiated at ∼320 °C by the crystallization of small nuclei at the interface with Si, as evidenced for the first time by cross-sectional transmission electron microscopy. These nuclei share a singular epitaxial orientation, corresponding to the one of the large grains in the final ScSi film. Further crystallization occurs anisotropically in the lateral direction. Along the c axis, the initial epitaxial orientation is maintained. However, along the a axis, twin defects are generated, resulting in the small grain size.

We report on the implementation of a radiotracer photoluminescence spectroscopy setup at the ISOLDE radioactive ion beam facility at CERN, enabling element-specific identification of optically active defects in solids. The method combines radioactive ion implantation with optical spectroscopy, allowing the temporal evolution of photoluminescence signals to be correlated directly with nuclear decay. The setup is currently optimized for color centers in diamond and related wide-bandgap materials and enables room-temperature measurements. The system consists of an optical microscope coupled to a fiber-fed Czerny-Turner spectrometer with a liquid-nitrogen-cooled CCD detector, providing the stability required for long-duration measurements. As a proof-of-principle, radioactive ^75Ga was implanted into diamond as a precursor to produce ^75Ge impurities. The photoluminescence band extending from 600 nm, corresponding to the well-known GeV^- center, exhibits an exponential decay with a half-life of 82.3^+2.5_-2.3min, in agreement with the known β^- decay half-life of ^75Ge of 82.78(4) min. This establishes a direct and unambiguous correlation between the observed spectral feature and its germanium origin. These results demonstrate the capability of the setup to perform element-specific optical spectroscopy and extend radiotracer methods to color centers in wide-bandgap materials, taking advantage of the uniquely broad range of radioactive isotopes available at ISOLDE.

Yttrium (Y) is a promising candidate for low-resistance NMOS contacts due to the low n-type Schottky barrier height of its silicide and its high charge carrier effective mass. However, previous attempts to achieve a low contact resistivity have failed because of severe oxygen contamination during sputter deposition. This study therefore investigates Y silicide formation in sputtered TiN/Y stacks on Si(001), Si(110), and Si(111) substrates. Upon annealing, hexagonal YSi1.7 forms through a three-step process: (i) metallic Y reacts with Si by solid-state amorphization (SSA), producing amorphous a-YSi, (ii) a-YSi crystallizes into hexagonal YSi1.7 at the interface with Si and (iii) grows in thickness until the reaction is fully completed. X-ray diffraction pole figure analyses confirm epitaxial texturing, with Si(001) and Si(111) exhibiting a single epitaxial component. Consistent with a nucleation-controlled formation, hexagonal YSi1.7 starts to form at a significantly lower temperature on Si(111) compared to Si(001) and Si(110) due to the superior YSi1.7/Si epitaxial relationship. The formation of pinholes during crystallization further supports nucleation-limited formation but results in a partial oxidation of the Y film. These findings clarify the role of nucleation and diffusion during YSi1.7 formation and highlight the challenges that must be addressed should Y be integrated in CMOS devices.

Determining the laser-induced specimen apex temperature in atom probe tomography is fundamental to understanding and ensuring analytical accuracy and reliability. This study reviews the existing protocols and assesses their applicability to experimentally determine the apex temperature rise of silicon specimens under ultraviolet laser pulsing in the LEAP 5000 XR. We demonstrate that the method that incorporates the temperature-dependent specific heat of Si offers the best approach, which even works in the athermal field-evaporation regime of this material. Apex temperature increases of 51-146 K are found for laser pulse energies of 1-6 pJ at a base temperature of 50 K. The subsequently extracted field-evaporation barrier of (110 ± 10) meV for a field reduction ≳0.9 aligns with field-evaporation model predictions. From the review of the literature across different materials and methods, inconsistent apex temperature estimates between methods based on voltage and laser mode were found. However, a reasonably consistent trend between the laser-induced temperature rise and the zero-barrier evaporation field is observed. This suggests a simplified protocol for estimating the rise in specimen apex temperature with increasing laser energy, potentially offering a straightforward and practical route for broader application in atom probe tomography studies.

Scandium (Sc) silicides, formed through solid-state reactions between thin Sc films and Si, have recently gained attention for their potential in low-resistance metal/semiconductor contacts. In this work, in situ x-ray diffraction is used to investigate the phase evolution of Sc thin films deposited on Si(001), Si(110), and Si(111) substrates. As-deposited, Sc crystallizes in the hexagonal P6(3)/mmc structure, while a thin amorphous silicide interlayer exists at the Sc/Si interface. Upon annealing, this interlayer thickens via a solid-state amorphization reaction between Sc and Si. At higher temperatures, orthorhombic ScSi nucleates at the interface, while residual Sc transforms into the metastable P6(1)22 hexagonal phase before fully reacting. The formation of orthorhombic ScSi from the amorphous precursor phase is nucleation-controlled. As a result, the crystallization temperature, textural disorder, and interface roughness depend on the Si substrate orientation. On Si(001) and Si(111), ScSi exhibits multiple epitaxial texture components associated with smooth interfaces. In contrast, Si(110) shows the highest crystallization temperature, a rough interface, and a highly disordered axiotaxial texture. Surprisingly, this axiotaxy occurs despite the absence of one-dimensional lattice matching between the film and the substrate.

In semiconductor technology, boron-doped silicon-germanium compounds have attracted significant attention due to their application in strain engineering to enhance the carrier mobility. One of the current challenges in this context is the accurate quantification of the concentration of boron, since many analytical techniques require a reference standard with a known and traceable concentration. In this study, we present a method to quantify the absolute amount of boron in thin films by combining substrate-less Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). First, a substrate-less boron pellicle is realized for which the absolute amount of boron is quantified with RBS. Then, the obtained absolute standard is used as a reference for the analysis with the 11B(p,alpha 1)2 alpha nuclear reaction at a proton energy of 640 keV. The strength of the RBS-NRA hybrid approach is illustrated with the analysis of a boron-doped SiGe epilayer, demonstrating the traceable uncertainty and an accuracy of 1.5%. More generally, the method can be employed to certify standards of 11B in various compounds that are needed for other analytical techniques, such as secondary ion mass spectrometry (SIMS).

A comparative vacuum ultraviolet spectroscopy study conducted at ISOLDE-CERN of the radiative decay of the ^{229m}Th nuclear clock isomer embedded in different host materials is reported. The ratio of the number of radiative decay photons and the number of ^{229m}Th embedded are determined for single crystalline CaF_{2}, MgF_{2}, LiSrAlF_{6}, AlN, and amorphous SiO_{2}. For the latter two materials, no radiative decay signal was observed and an upper limit of the ratio is reported. The radiative decay wavelength was determined in LiSrAlF_{6} and CaF_{2}, reducing its uncertainty by a factor of 2.5 relative to our previous measurement. This value is in agreement with the recently reported improved values from laser excitation.

An approach to characterize dopant spatial inhomogeneity at the nanoscale along with its local chemical environment has been developed using atom probe tomography. We achieve this through the combination of a local composition analysis using the nearest-neighbor atoms combined with a nonparametric Kolmogorov-Smirnov or Anderson-Darling statistical test. Using an in situ highly boron-doped silicon germanium layer we demonstrate that all three elements have an inhomogeneous distribution. Moreover, by subdividing the local dopant composition distribution, a correlation between the boron doping level and variations in the surrounding matrix composition was determined. These atomic-scale measurements provide new experimental insights into the dopant incorporation behavior in technologically relevant semiconductors and its relationship to the epitaxial growth processes.

Muonic atom spectroscopy is a method that can determine absolute nuclear charge radii with typical relative precision of $$10^{-3}$$ . Recent developments have enabled to extend muonic atom spectroscopy to microscopic target quantities as low as $$5\,{\upmu }\text {g}$$ . This substantial reduction from the traditional limit of the order of $$100\,\text {mg}$$ is based on a transfer mechanism in a high-pressure hydrogen gas cell, which transports the muon to the surface of the target material rather than stopping it over a broad depth range. This approach enables the measurement of absolute nuclear charge radii of long-lived radioactive isotopes (half-life above $$\sim$$ 20 years), but the production of appropriate targets for the technique has presented some major challenges, such as the formation of organic layers on the substrate. This study presents a systematic investigation of the stopping efficiency for different target preparation methods: ion implantation, drop-on-demand printing, and molecular plating. Notable differences between the three methods were discovered in terms of their performance allowing to further fine tune the method of choice for future target preparations. Our findings show that implantation provides appropriate targets for our method with negligible losses. This achievement opens the landscape of potential measurements to isotopes where high mass separation is required not achievable with other methods. Furthermore, molecular plated targets performed substantially better than those prepared using drop-on-demand printing.

InP/ZnSe core-shell quantum dots (QDs) can emit spectrally narrow light with high efficiency, but the relation between the QD properties and the composition of the core-shell interface remains unclear. Here, we compare 4 different batches of InP/ZnSe QDs, formed with or without intermediate purification and InP surface oxidation before shell growth. Elemental analysis and solid-state NMR show that the presence of InCl3 during ZnSe shell growth leads to indium incorporation into the ZnSe shell, while interfacial oxidation creates a polyphosphate at the core/shell interface. The sample in which both interfacial engineering approaches were applied features a higher photoluminescence quantum yield and the slowest biexciton Auger recombination rate. These findings support emerging insights on the InP/ZnSe core/shell interface in the literature and pave the way for further improving the optoelectronic properties of these materials by adjusting the interfacial composition.

Increasing the in-situ active doping level is a primary method for reducing source-drain resistance1. The impact of this approach is dependent on the dopant atoms spatial distribution and their local chemical environment. To measure and optimize these parameters is a characterization challenge although atom probe tomography (APT) has the potential to capture the required data. Likewise, extracting the relevant information and its interpretation still requires development. In this presentation, we show how a 3D APT dataset can be analyzed using a statistical algorithm to characterize the spatial (in)homogeneity of all the elements present. Moreover, the influence of the dopant atoms on their local chemical environment is also revealed. For demonstration purposes, a 43 nm thick in-situ highly boron-doped (~4 at.%) epitaxially grown SiGe layer with an intended site fraction of 0.7:0.3 (Si:Ge) was utilized. A custom Python code, developed upon a similar algorithm to that proposed by Stephenson et al. 2, alongside a significance test to evaluate the element spatial inhomogeneity within our dataset was employed. The code utilized a fixed number (500) of nearest neighbor atoms surrounding each dopant element, thereby establishing the local composition pertaining to the dopant element. A two-sample Kolmogorov-Smirnov test3 was conducted to validate the spatial (in)homogeneity. This involved comparing the resulting composition frequency of the experimental dataset with a randomized version of the same dataset featuring shuffled chemical identities. A significance threshold of α ≤ 0.01 was applied to reject the null hypothesis for a random distribution of elements throughout the dataset. The empirical cumulative distribution functions (CDF) for the B-B, along with the B-Si and B-Ge site fractions are presented in Fig. 1. Statistical analysis of the data supports all three elements being spatially inhomogeneous i.e., p value < 0.01. The B-B distribution also shows a notable deviation towards higher concentration relative to the randomized version and indicated ~10% of the B was aggregating. Sub-dividing the B-B composition distribution (Fig. 2a) into three regions, with the division points being where the two composition distributions (measured and randomized data) intersected, enabled further insight about the localized matrix behavior (Fig. 2b, c). The Si site fraction was found to monotonically shift from a lower to higher level with increasing B composition, while the Ge exhibited the opposite trend. This implies that the B incorporation modifies the matrix at a localized scale and leads to an enhanced Si site fraction around the B. This finding is consistent with a recent DFT simulation for B doped SiGe4. The 3D-APT metrology presented here enhances our ability to study the spatial distribution of dopants on an atomic scale and could be used, for example, to refine the epitaxial growth or link it to the performance of devices. J.-L. Everaert et al., in 2017 Symposium on VLSI Technology, p. T214–T215, IEEE, Kyoto, Japan (2017). L. T. Stephenson et al., MethodsX, 1, 12–18 (2014). J. N. Miller, J. C. Miller, and R. D. Miller, Statistics and chemometrics for analytical chemistry, Seventh edition., Pearson Education Limited, Harlow, United Kingdom, (2018). G. Rengo et al., J. Phys. Chem. C (submitted) Figure 1

We have investigated the elastic backscattering which occurs during ion implantation, and its impact on the retained implantation dose. A series of Si1-xGex (0 <= x <= 1) alloy films were implanted with 5 x 1014 atoms/cm2 of 11B at an energy of 10 keV. Nuclear reaction analysis (NRA) was used to characterize the retained boron dose within the Si1-xGex (0 <= x <= 1) samples by means of the 11B(p,alpha 1)2 alpha 12 nuclear reaction. The experimental results show that the elastic backscattering effect is significant in this case, with the retained boron dose decreasing linearly as the target matrix varies from pure silicon to pure germanium. Our findings are in good agreement with simulations carried out using the SRIM-2013 software. Our study indicates that the backscattering effect during implantation must be accounted for when a specific concentration is targeted, or when adopting an implanted film as a reference standard, for example, in secondary ion mass spectrometry.

We introduce a machine learning approach designed for the self-consistent analysis of data acquired through simultaneous Rutherford backscattering spectrometry (RBS) in multiple scattering geometries, with subsequent determination of the analysis uncertainty. Using a simulated data set, the successful self-consistent evaluation of up to six simultaneous RBS data collections was achieved by employing artificial neural networks (ANN). The results demonstrate enhanced accuracy and precision when concatenating multiple RBS spectra as input to the ANN. The precision was quantified through the combined uncertainty, encompassing the ANN random uncertainty, the ANN systematic uncertainty, and the model robustness. While applied to only RBS analysis, this approach holds promise for advancing the analysis of data collected by next-generation RBS equipment and Total ion beam analysis, offering a robust and efficient framework for future research.

In order to study the structural formation yield of germanium-vacancy (GeV) centers from implanted Ge in diamond, we have investigated its lattice location by using the β ^− emission channeling technique from the radioactive isotope ^75 Ge ( t _1/2 = 83 min) produced at the ISOLDE/CERN facility. ^75 Ge was introduced via recoil implantation following 30 keV ion implantation of the precursor isotope ^75 Ga (126 s) with fluences around 2 × 10 ^12 –5 × 10 ^13 cm ^−2 . While for room temperature implantation fractions around 20% were observed in split-vacancy configuration and 45% substitutional Ge, following implantation or annealing up to 900 °C, the split-vacancy fraction dropped to 6%–9% and the substitutional fraction reached 85%–96%. GeV complexes thus show a lower structural formation yield than other impurities, with substitutional Ge being the dominant configuration. Moreover, annealing or high-temperature implantation seem to favor the formation of substitutional Ge over GeV. Our results strongly suggest that GeV complexes are thermally unstable and transformed to substitutional Ge by capture of mobile carbon interstitials, which is likely to contribute to the difficulties in achieving high formation yields of these optically active centers.

Diabetes, a global health problem, necessitates precise blood glucose measurement for effective management. Despite their prevalence, enzymatic glucose sensors suffer from sensitivity to temperature and pH and limited lifetime of the enzyme, thus requiring replacement every two weeks (Teymourian et al., 2020). In contrast, non-enzymatic sensors offer enhanced durability, superior sensitivity, and ease of miniaturization, making them promising for the so-called "fourth generation" glucose sensors (Aun et al., 2021). Noble metals like Pt (Kim et al., 2012), Au (Shen et al., 2022), Pd (Elkholy et al., 2019), and Ir (Dong et al., 2018) have emerged as prospective candidates for glucose sensing due to their ability to oxidize glucose at a physiological pH of 7.4. Among these, Au has gained attention due to its remarkable electroactivity for glucose electro-oxidation (Vassilyev et al., 1985), despite its weak chemisorptive properties arising from filled d-orbitals (Hammer & Nørskov, 1995). Various methods have been employed to fabricate nanostructured gold electrodes, encompassing direct electrostatic assembly, covalent linking, polymer entrapment or co-mixing, sol-gel processes, electrochemical etching, and electrodeposition (Dahan et al., 2023). Nevertheless, many of these fabrication approaches entail the use of hazardous chemicals or involve cumbersome procedures, de facto limiting their practical application. As a result, scalable solutions to catalyst fabrication and deposition are needed to seamlessly integrate with the cleanroom process flows to build non-enzymatic glucose sensors. In this study, 7x7mm glassy carbon electrodes (GCs) served as working electrodes in a three-electrode system, with a reversible hydrogen electrode employed as a reference and a Pt mesh as a counter electrode. The GCs underwent meticulous polishing using alumina slurry of varying sizes (1μm, 0.3 μm, and 0.01 μm). Subsequently, they were anodized in 1M KOH at 1.8V for 2 hours in ambient air conditions. The electroactive area of the GCs was determined by measuring the capacitance with EIS before and after anodization, and by later dividing by the specific capacitance (13 μF/cm 2 ). A remarkable tenfold increase in surface area was observed after anodization. With a custom-built cluster deposition apparatus (Figure 1a), four monolayers of gold clusters were deposited on three bare GCs (BareGC) and three anodized ones (AnGC). Field Emission Scanning Electron Microscopy (FE-SEM) images captured the morphology of BareGC and AnGC, both with and without clusters (Figure 1b). Atomic force microscopy was also utilized to complement the morphology study of the electrodes' surface. Grazing Incidence X-ray Diffraction (XRD) at 0.5 degrees revealed a peak corresponding to the Au(111) plane in Au+BareGC (Figure 1c). Rutherford backscattering was employed to quantify the gold loading on the samples. To facilitate the generation of active Au-OH species on the nanoclusters, the electrodes underwent cycling between 0.43V and 1.53V in 0.1M PBS, devoid of chlorides. Subsequently, the sensing performance towards glucose was evaluated via chronoamperometric methods, maintaining the potential at 0.884V under stirring conditions (250 rpm). Gradual increases in glucose concentration were applied in steps of 0.25 mM and later in 1 mM increments up to 7 mM (Figure 1d). Both Au+BareGC and Au+AnGC electrodes exhibited an extremely linear response (R²=0.99) within the 0.25 mM to 7 mM linear range. After calibration, the electrodes underwent cycling in 0.5 M H 2 SO 4 between 0.015V and 1.715V ( vs RHE). The gold oxide reduction peak was integrated (Figure 1e), allowing estimation of the electroactive surface area (ESA) using the formula ESA=(Integrated charge)/(scan rate*0.386 mC/cm -2 ). A comparative analysis with similar nanostructured Au samples (Table 1) revealed that Au+AnGC displayed a four times higher sensitivity and substantially lower detection limits.The impact of chlorides was explored by repeating the chronoamperometric calibration in a PBS+0.1M KCl buffer. Chloride adsorption led to complete catalyst deactivation and eventually to gold loss from both samples. Notably, Au+BareGC displayed higher sensitivity to Cl etching, experiencing a 50% reduction in gold ESA compared to a 30% drop in Au+AnGC. This work has proved that the deposited nanoclusters possess an extremely high density of active sites towards glucose electro-oxidation. In addition, the deposition on highly porous electrodes decreases the poisoning effect of chlorides. These findings show significant promise as a scalable fabrication strategy to glucose sensor development. References in Table 1: [1] https://www.sciencedirect.com/science/article/pii/S001346861400766X#bib0060 [2] https://pubs.acs.org/doi/10.1021/jp810235v [3] https://www.sciencedirect.com/science/article/pii/S0925400515007133?via%3Dihub [4] https://www.sciencedirect.com/science/article/pii/S0039914012008971 [5] https://pubs.acs.org/doi/10.1021/ac035143t Figure 1

Sc-based contacts to Si:P have shown great potential for NMOS devices. However, the promising properties of this material system are not yet fully understood. This work provides new insights into the crystallinity and composition of annealed TiN/Sc/Si:P stacks. After silicidation, two distinct phases are evidenced, with orthorhombic ScSi lying atop a thin Sc1-x-y SixPy interfacial layer that shares a commensurate interface with the underlaid Si:P, hypothetically resulting in a low interface defectivity. The formed ScSi phase is observed to be thermally stable between similar to 450 degrees C and 700 degrees C, which is suitable for most device applications. The impact of additional thermal budgets within this temperature range is investigated, revealing potential origins for thermally induced degradation of the contact properties. (c) 2024 The Japan Society of Applied Physics

The magnetization direction of a ferromagnetic (FM) film deposited onto a ferroelectric (FE) substrate undergoes significant changes when it is subjected to applied electric fields. These are mainly due to the strain-mediated magnetoelectric effects associated with the FE switching behavior of the substrates. Here, we report on the magnetoelectric response of the magnetization direction at two different depths within the FM film in an artificial multiferroic heterostructure consisting of a 5 nm FM Fe film deposited onto a 0.7Pb(Mg1/3Nb2/3)O-3-0.3PbTiO(3) (PMN-PT) FE single-crystal substrate. The overall magnetic anisotropy of the Fe (5 nm)/PMN-PT system was studied by using magneto-optic Kerr effect (MOKE) magnetometry. On the other hand, the isotope-specific nuclear forward scattering (NFS) of synchrotron radiation was used to study the magnetization direction at two specific depths within the Fe film. Our results reveal that magnetic anisotropy is significantly influenced by the Fe/PMN-PT interface. Additionally, the magnetoelectric response of the easy magnetization direction when the layer is simultaneously subjected to electric and magnetic fields is different at (1st nm of Fe) as compared to away (3rd nm of Fe) from the Fe/PMN-PT interface. At the interface, the magnetization direction is influenced by the electric field-induced strain and charge effects originating in PMN-PT. Away from the interface, a weaker magnetoelectric response of the magnetization direction consistent with previous reports is observed. These results provide insight in understanding the magnetoelectric coupling behavior of such FM/PMN-PT heterostructures, which is crucial to recognize their potential in developing (multi)functional devices based on such systems.

We address the high accuracy and precision demands for analyzing large in situ or in operando spectral data sets. A dual-input artificial neural network (ANN) algorithm enables the compositional and depth-sensitive analysis of multinary materials by simultaneously evaluating spectra collected under multiple experimental conditions. To validate the developed algorithm, a case study was conducted analyzing complex Rutherford backscattering spectrometry (RBS) spectra collected in two scattering geometries. The dual-input ANN analysis excelled in providing a systematic analysis and precise results, showcasing its robustness in handling complex data and minimizing user bias. A comprehensive comparison with human supervision analysis and conventional single-input ANN analysis revealed a reduced susceptibility of the dual-input ANN analysis to inaccurately known setup parameters, a common challenge in material characterization. The developed multi-input approach can be extended to a wide range of analytical techniques, in which the combined analysis of measurements performed under different experimental conditions is beneficial for disentangling details of the material properties.