In this contribution, we use heavy ion irradiation and photoluminescence (PL) spectroscopy to demonstrate that defects can be used to tailor the optical properties of two-dimensional molybdenum disulfide (MoS2). Sonicated MoS2 flakes were deposited onto Si/SiO2 substrate and subjected to 3 MeV Au2+ ion irradiation at room temperature to fluences ranging from 1 × 1012 to 1 × 1016 cm−2. We demonstrate that irradiation-induced defects can control optical excitations in the inner core shell of MoS2 by binding A1s- and B1s-excitons, and correlate the exciton peaks to the specific defects introduced with irradiation. The systematic increase of ion fluence produced different defect densities in MoS2, which were estimated using B/A exciton ratios and progressively increased with ion fluence. We show that up to the fluences of 1 × 1014 cm−2, the MoS2 lattice remains crystalline and defect densities can be controlled, whereas at higher fluences (≥1 × 1015 cm−2), the large number of introduced defects distorts the excitonic structure of the material. In addition to controlling excitons, defects were used to split bound and free trions, and we demonstrate that at higher fluences (1 × 1015 cm−2), both free and bound trions can be observed in the same PL spectrum. Most importantly, the lifetimes of these states exceed trion and exciton lifetimes in pristine MoS2, and PL spectra of irradiated MoS2 remains unchanged weeks after irradiation experiments. Thus, this work demonstrated the feasibility of engineering novel optical behaviors in low-dimensional materials using heavy ion irradiation. The insights gained from this study will aid in understanding the many-body interactions in low-dimensional materials and may ultimately be used to develop novel materials for optoelectronic applications.

Porphyrins are a class of conjugated molecules that structurally and functionally resemble natural photosynthetic and enzymatic chromophores. Crystalline solids self-assembled from anionic and cationic porphyrins yield a new class of multifunctional optoelectronic micro- and nanomaterials. In this article, we provide details on the concept of binary ionic self-assembly (ISA) and ionized forms of porphyrins, as well as formation of hierarchical structures, including nanotubes, rods and ribbons, sheets, and three-dimensional clover-like shapes, spheres, and sheaf-like structures. We summarize key physical properties from ultraviolet–visible characterizations of J-aggregate, exciton delocalization and extended π–π stacking, and related electronic and light-harvesting properties of the structures. Depending on the molecular subunits, the functionalities of the ISA materials are altered. These ISA nanostructures possess attractive light-harvesting and charge- and energy-transport functionalities and allow access to a novel class of nanomaterials with potential for applications in sensors, photovoltaics, photocatalysis, and solar power.

We use irradiation with 50-MeV Cu-ions to create vortex pinning defects in high-temperature superconducting Y1Ba2Cu3O7-x coated conductors using a beam-rastering approach that allows for the uniform irradiation of large ample areas. Our samples contain barium zirconate nanorods as pre-existing vortex pinning defects. By irradiating the samples at angles of 0o, 15oand 30o from the crystallographic c-axis we explore the interplay between pre-existing and irradiation-induced pinning and find that irradiation at 30o leads to a moderate enhancement of Jc at 5 K at high fields (greater than 2 Tesla). In contrast, Jc was suppressed for all temperatures and fields for other angles of irradiation. Optimized particle irradiation procedures offer a way for improving the performance of high-temperature superconducting wires for use in high magnetic fields without the need for changing wire synthesis protocols.

The role of oxide nanoparticles in cavity formation of a nano-oxide-dispersed ferritic steel subjected to (Fe + He) dual-ion and (Fe + He + H) triple-ion irradiations has been studied using transmission electron microscopy to elucidate the synergistic effects of helium and hydrogen on radiation tolerance of nano-oxide-dispersed ferritic steel for fusion energy systems. The effect of oxide nanoparticles on suppressing radiation-induced void swelling is clearly revealed from the observation of preferred trapping of helium bubbles at oxide nanoparticles, which results in a unimodal distribution of cavities in the (Fe + He) dual-ion irradiated specimen. An adverse effect of hydrogen implantation, however, is revealed from the observation of a bimodal distribution of cavities with large and facetted voids in association with the formation of HFe5O8-based hydroxide in local regions of the (Fe + He + H) triple-ion irradiated specimen.

New developments in manufacturing and automation, from three-dimensional printing to the “Internet of things,” signify dramatic changes in our society. The push toward quantum materials is driving device fabrication toward atomic precision. Recent results suggest that scanning transmission electron microscopy (STEM) with sub-angstrom scale beams could offer a solution. However, a detailed theoretical understanding of the interaction of the electron beam with solids is needed to form a basis for new technology. This article summarizes the existing literature on electron-beam interactions with solids with a focus on irreversible transformation. We further suggest that the theoretical framework of a two-temperature model developed for fast ion damage in solids could be applicable to predicting the effects of fast electrons. Recent results from STEM-directed epitaxial growth on crystalline–amorphous interfaces are discussed in detail. Finally, perspectives on the development of this field in the near future are offered.

An in-depth look at diffusion mechanics within lithium-ion electrodes under fast charging conditions is presented. Electrochemical impedance spectroscopy is used as the primary technique to investigate lithium diffusion within electrode material and in electrolyte near the electrode-electrolyte interface. Half-cells of silicon are charged under varying galvanostatic rates while obtaining impedance data. Collected data is analyzed with the help of an electrical equivalent circuit model that provides mechanical and electrochemical parameters for each instance. The novelty of this equivalent circuit partly lies in its ability to resolve between solid-phase diffusion and liquid-phase diffusion, both of which occur during cycling of a lithium-ion electrode. Observed patterns in the parameters of this circuit provide insight into impact of fast charging on mechanics of lithium diffusion, both inside the electrode matrix and within electrolyte.

Electric-field noise from the surfaces of ion-trap electrodes couples to the ion’s charge causing heating of the ion’s motional modes. This heating limits the fidelity of quantum gates implemented in quantum information processing experiments. The exact mechanism that gives rise to electric-field noise from surfaces is not well-understood and remains an active area of research. In this work, we detail experiments intended to measure ion motional heating rates with exchangeable surfaces positioned in close proximity to the ion, as a sensor to electric-field noise. We have prepared samples with various surface conditions, characterized in situ with scanned probe microscopy and electron spectroscopy, ranging in degrees of cleanliness and structural order. The heating-rate data, however, show no significant differences between the disparate surfaces that were probed. These results suggest that the driving mechanism for electric-field noise from surfaces is due to more than just thermal excitations alone.

Ternary Fe-Co-Si B20 phase structure was formed by implanting Fe and Co ions consecutively into Si(100) substrate at 50 keV energy, each with a fluence of 1.0 × 1017 atoms/cm2 and post-thermal vacuum annealing at 500 oC for 60 minutes. An in-situ magnetic field was used to enhance the formation of the ternary phase in the Si substrate during the implantation process. The magnetic field of 0.05 T was applied perpendicular to the incoming ion beam direction and parallel to the substrate surface to form elongated clusters in the transverse direction of the sample. Prior to the implantation of ions, the implant ions depth profiles were simulated using a dynamic ion-solid interaction code (TRIDYN). The TRIDYN simulation predicted a saturation in the peak concentration of the Fe and Co ions at a fluence of 1.0 × 1017 atoms/cm2. XPS measurement at the peak concentration depth (40 nm) showed the presence of Fe (23 %) and Co (32 %) in the Si matrix. XRD characterization confirmed the presence of stable Fe-Co-Si B20 phase structure in the annealed samples implanted with the in-situ magnetic field.

Potassium titanyl phosphate crystals in both x-cut and z-cut were irradiated with 185 MeV Au ions. The morphology of the resulting ion tracks was investigated using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). SAXS measurements indicate the presence of cylindrical ion tracks with abrupt boundaries and a density contrast of 1 ± 0.5% compared to the surrounding matrix, consistent with amorphous tracks. The track radius depends on the crystalline orientation, with 6.0 ± 0.1 nm measured for ion tracks along the x-axis and 6.3 ± 0.1 nm for those along the z-axis. TEM images in both cross-section and plan-view show amorphous ion tracks with radii comparable to those determined from SAXS analysis. The protruding hillocks covering the sample surface detected by AFM are consistent with a lower density of the amorphous material within the ion tracks compared to the surrounding matrix. Simulations using an inelastic thermal-spike model indicate that differences in the thermal conductivity along the z- and x-axis can partially explain the different track radii along these directions.

Defect formation in the samples of graphene, graphene oxide and silicon irradiated with Ar cluster and highly-charged ion irradiations were studied. Ar cluster ions, with acceleration energy E = 30 kV (Exogenesis nAccel00, Boston, USA) and total Ar cluster ion fluences ranged from 1x109 cm-2 to 1x1013 cm-2 were directed toward various surfaces. Highly-charged ions (HCI) bombardment on surfaces with highly charged Xeq+ (q = 22) was employed at Eurasian National University, Kazakhstan, using a DC-60 cyclotron accelerator. Multi-layer graphene oxide, single-layer graphene- (SLG), few-layer of graphene (FLG) and polished Si are used for irradiation experiments. The study of irradiated samples was conducted by Raman spectroscopy, atomic force microscopy (AFM). Uniformly distributed defects and craters were observed on the surfaces of graphene, graphene oxide and silicon irradiated with cluster and HCI beams in our experiments. Ab-initio density-functional theory (DFT) was used to study point defects and molecular-dynamics (MD) simulations were used for studying formation of craters due to gas cluster ion impacts in graphene. The results of simulations were compared with experimental craters and surface shape.

The formation and stability of radiation-induced defects in structural materials in reactor environments significantly effects their integrity and performance. Hydrogen, which may be present in significant quantities in future reactors, may play an important role in defect evolution. To characterize the effect of hydrogen on cascade damage evolution, in-situ TEM self-ion irradiation and deuterium implantation was performed, both sequentially and concurrently, on nickel. This paper presents preliminary results characterizing dislocation loop formation and evolution during room temperature deuterium implantation and self-ion irradiation and the consequence of the sequence of irradiation. Hydrogen isotope implantation at room temperature appears to have little or no effect on the final dislocation loop structures that result from self-ion irradiation, regardless of the sequence of irradiation. Tilting experiments emphasize the importance of precise two-beam conditions for characterizing defect size and structure.

Development of new materials for current and advanced reactor concepts is hampered by long lead times and high cost of reactor irradiations coupled with the paucity of test reactors. Ion irradiation offers many advantages for emulating the microstructures and properties of materials irradiated in reactors but also poses many challenges. Nevertheless, there is a growing body of evidence, primarily for light ion (proton) irradiation showing that many, if not all of the features of the irradiated microstructure and properties, can be successfully emulated by careful selection of irradiation parameters based on differences in the damage processes between ion and neutron irradiation. While much less has been done to benchmark heavy- or self-ion irradiation, recent work shows that under certain conditions, the complete suite of features of the irradiated microstructure can be emulated. This study summarizes the contributions of ion irradiation to our understanding of irradiation effects, the options for emulating radiation effects in reactors, and experience with both proton irradiation and heavy ion irradiation.

Lumbar intervertebral disc (IVD) degeneration is the leading cause of lower back pain. While lumbar IVDs have low cellularity and limited capacity of regeneration, they bear high mechanical loads. Accelerated disc degeneration may happen because of undue cell stimulation, and cell nutrition also seems to be particularly influent in the disc. Cell nutrition depends on exchange of oxygen, glucose, and lactate between the periphery and the various regions of the IVD, which in turn depends on mechanical deformations. The mechanical regulation of disc cell nutrition, known as indirect mechanotransduction, is difficult to study in vivo or in vitro. This review reports on an important alternative in the form of numerical methods, which are based on the ability of poromechanical models to be coupled to solute transport-reaction models. Models need to address intricate nonlinear and time-dependent phenomena, but have allowed for important mechanisms to be proposed, complementing current knowledge gained from in vivo or in vitro observations.

Electrochemical performance of hybrid supercapacitor (HSC) utilizing surface sculpted Li4Ti5O12 (LTO) insertion electrode having nanoplatelet-like morphology and activated carbon (AC) electrode is investigated for energy storage application. Cyclic voltammetry (CV) at variable scan rates 0.5 to 60 mV.s-1 in the 0-3.2 V range show pseusocapacitive behavior and fast rate of current change indicating rapid Faradaic kinetics. Nyquist impedance study show charge transfer resistance due to kinetic effects of electron transfer and Li+ de-intercalation process at the LTO anode. Low capacity (0.2 C-1C) charge-discharge (CD) curves show high Coulomb efficiency with marginal reduction at high 5-10 C rates due to irreversibility of adsorbed PF6 anions at the electrolyte-AC interface. Galvanostatic CD cycling tests over 50 cycles at different C-rates show decline in storage capacity due to electrode polarization effects. Reduction, broadening and shift of the Raman line at 678 cm-1 from Ti-O bonds in TiO6 octahedra after cycling indicates Li insertion reactions in functioning of hybrid supercapacitor. The hybrid supercapacitor cells have shown energy density, 29 Wh.kg-1 and power density, 350 W.kg-1.

We present a theoretical approach for modeling electrolyte solutions at interfaces that reaches into the mesoscale while retaining molecular detail. The total Hamiltonian of the system includes interactions arising from density and charge density (ion correlation) fluctuations, direct Coulomb interactions between ions, and at interfaces the image interactions, ion-solid and ion-water dispersion interactions. The model was validated against its ability to reproduce ion activity in 1:1 and 2:1 electrolyte solutions in the 0-2 M concentration range, its ability to capture the ion-specific effect in 1:1 electrolytes at the air-water interface, and solvent structure in a confined environment between hydrophobic surfaces, revealing the central role of ion hydration interactions in specific ion thermodynamic properties in the bulk solutions and at interfaces. The model is readily extensible to treat electrolyte interactions and forces across charged solid-water interfaces.

Calculations based on Poisson-Boltzmann theory are used to investigate the equilibrium properties of an electrolyte containing TcO4− and SO42− ions near the surface of amorphous silica. The calculations show that the concentration of TcO4− is greater than SO42− at distances less than 1 nm from the surface due to the negative charge density caused by deprotonation of the amorphous silica silanol groups. At lower pH, the surface becomes protonated and the magnitude of this effect is reduced. These results have implications for the potential use of oxyanion-SAMMS for the environmental remediation of water contaminated with 99Tc.

Over the last few years, significant improvements in sources, columns, detectors, control software, and accessories have enabled a wealth of new focused ion beam applications. In addition, modeling has provided many insights into ion-sample interactions and the resultant effects on the sample. With the knowledge gained, the community has found new ion-beam induced chemistries and ion-beam sources, allowing extending nanostructure fabrication and material deposition to smaller dimensions and better control for direct write and patterning. Insignificant proximity effects in resist-based ion beam lithography, combined with the availability of sub-nm ion spot sizes, opens the way to sub-10 nm structures and dense patterns. Additionally, direct-write ion beam nanomachining can process multilevel structures with arbitrary depths in one single process step, with all the information included in a single standard design file, thus enabling fabrication applications not achievable with any other technique.

Focused ion beam microscopes are extremely versatile and powerful instruments for materials research. These microscopes, when coupled in a system with a scanning electron microscope, offer the opportunity for novel sample imaging, sectioning, specimen preparation, three-dimensional (3D) nano- to macroscale tomography, and high resolution rapid prototyping. The ability to characterize and create materials features in a site-specific manner at nanoscale resolution has provided key insights into many materials systems. The advent of novel instrumentation, such as new ion sources that encompass more and more of the periodic table, in situ test harnesses such as cryogenic sample holders for sensitive material analyses, novel detector configurations for 3D structural, chemical, and ion contrast characterization, and robust and versatile process automation capabilities, is an exciting development for many fields of materials research.

The MIAMI* facility at the University of Huddersfield is one of a number of facilities worldwide that permit the ion irradiation of thin foils in-situ in a transmission electron microscope. MIAMI has been developed with a particular focus on enabling the in-situ implantation of helium and hydrogen into thin electron transparent foils, necessitating ion energies in the range 1 – 10 keV. In addition, however, ions of a variety of species can be provided at energies of up to 100 keV (for singly charged ions), enabling studies to focus on the build up of radiation damage in the absence or presence of implanted gas.

This paper reports on a number of ongoing studies being carried out at MIAMI, and also at JANNuS (Orsay, France) and the IVEM / Ion Accelerator Facility (Argonne National Lab, US). This includes recent work on He bubbles in SiC and Cu; the former work concerned with modification to bubble populations by ion and electron beams and the latter project concerned with the formation of bubble super-lattices in metals.

A study is also presented consisting of experiments aimed at shedding light on the origins of the dimensional changes known to occur in nuclear graphite under irradiation with either neutrons or ions. Single crystal graphite foils have been irradiated with 60 keV Xe ions in order to create a non-uniform damage profile throughout the foil thickness. This gives rise to varying basal-plane contraction throughout the foil resulting in almost macroscopic (micron scale) deformation of the graphite. These observations are presented and discussed with a view to reconciling them with current understanding of point defect behavior in graphite.

*Microscope and Ion Accelerator for Materials Investigations

Among the new non-volatile memories gaining attention as a potential replacement for flash technology is the programmable metallization cell (PMC) that works by creating and dissolving a conductive bridge across a solid electrolyte film. This enables switching between a high resistance state (HRS) and a low resistance state (LRS). The dominant mechanism for resistance switching is field dependent ion transport in the film. In this work, we examine, through numerical simulation, the effects of process variation on the impedance characteristics of the PMC in both HRS and LRS, by changing key parameters of the device. These parameters include the material bandgap, affinity and permittivity of each device layer. Finally, we show which parameters have the greatest effects on the impedance behavior.