Helium Ion Microscopy Research Articles

Denoising Particle Beam Micrographs With Plug-and-Play Methods

In a particle beam microscope, a raster-scanned focused beam of particles interacts with a sample to generate a secondary electron (SE) signal pixel by pixel. Conventionally formed micrographs are noisy because of limitations on acquisition time and dose. Recent work has shown that estimation methods applicable to a time-resolved measurement paradigm can greatly reduce noise, but these methods apply pixel by pixel without exploiting image structure. Raw SE count data can be modeled with a compound Poisson (Neyman Type A) likelihood, which implies data variance that is signal-dependent and greater than the variation in the underlying particle–sample interaction. These statistical properties make methods that assume additive white Gaussian noise ineffective. This article introduces methods for particle beam micrograph denoising that use the plug-and-play framework to exploit image structure while being applicable to the unusual data likelihoods of this modality. Approximations of the data likelihood that vary in accuracy and computational complexity are combined with denoising by total variation regularization, BM3D, and DnCNN. Methods are provided for both conventional and time-resolved measurements, assuming SE counts are available. In simulations representative of helium ion microscopy and scanning electron microscopy, significant improvements in root mean-squared error (RMSE), structural similarity index measure (SSIM), and qualitative appearance are obtained. Average reductions in RMSE are by factors ranging from 2.24 to 4.11.

Helium radiation blistering mechanisms in tungsten: Ion channeling effects

Understanding the radiation damage of low-energy and high-fluence helium ions on tungsten surface is of great interest and significance for developing advanced plasma-facing materials. Here, we investigate the effect of ion channeling on helium radiation blistering using a Helium Ion Microscope. 30 keV helium ions were implanted into individual tungsten grains to a fluence of 1×1018 ions/cm2 at room temperature. The grains of interest were selected based on the grayscale levels of ion channeling contrast image. It has been found that the channeling and non-channeling grains exhibit distinct blistering behaviors in both surface morphology and subsurface microstructure. In contrast with the channeling blister, the non-channeling one is smaller, shallower in irradiated bubble region, and composed of more and larger cracks beneath the surface. The underlying mechanisms were discussed based on the Molecular Dynamic simulations, which might have implications for designing and fabricating plasma-resistant materials through texture and anisotropy tailoring.

Multi-scale imaging of high-pressure hydrogen induced damage in EPDM rubber using X-ray microcomputed tomography, helium-ion microscopy and transmission electron microscopy

Ethylene propylene diene (EPDM) rubber has gained increasing interest for use in hydrogen infrastructure due to its excellent sealing performance and low temperature properties. However, severe structural damage has been observed in EPDM O-rings after exposure to high-pressure hydrogen. The origination and propagation mechanisms of this damage are poorly understood. To address this knowledge gap, multi-scale imaging leveraging X-ray micro-computed tomography (micro-CT), helium ion microscopy (HeIM), and transmission electron microscopy (TEM) were used in this work to study a series of sulfur-cured ethylene propylene diene (EPDM) rubber materials with varying additives that were exposed to different hydrogen environments. Micro-CT captured the substantial structural damage due to hydrogen exposure; it revealed an association between zinc oxide (ZnO) particles and damage initiation. Further studies by TEM and scanning TEM with energy dispersive X-ray spectroscopy (EDS) were focused on these particles at the micro-to nano-scale range. TEM indicated that hydrogen causes void formation at the interface between ZnO and the rubber matrix. HeIM enabled imaging of surface morphology of the material at high resolution pre- and post-hydrogen exposure while providing information on chemical composition and that cannot be captured by either micro-CT or TEM.

Insights into Degradation of the Membrane-Electrode Assembly Performance in Low-Temperature PEMFC: the Catalyst, the Ionomer, or the Interface?

Here, we report a study on the structural characteristics of membrane electrode assembly (MEA) samples obtained from a low-temperature (LT) polymer electrolyte membrane (PEM) fuel cell (FC) stack subjected to long-term durability testing for ∼18,500 h of nominal operation along with ∼900 on/off cycles accumulated over the operation time, with the total power production being 3.39 kW h/cm2 of MEA and the overall degradation being 87% based on performance loss. The chemical and physical states of the degraded MEAs were investigated through structural characterizations aiming to probe their different components, namely the cathode and anode electrocatalysts, the Nafion ionomer in the catalyst layers (CLs), the gas diffusion layers (GDLs), and the PEM. Surprisingly, X-ray diffraction and electron microscopy studies suggested no significant degradation of the electrocatalysts. Similarly, the cathode and anode GDLs exhibited no significant change in porosity and structure as indicated by BET analysis and helium ion microscopy. Nevertheless, X-ray fluorescence spectroscopy, elemental analysis through a CHNS analyzer, and comprehensive investigations by X-ray photoelectron spectroscopy suggested significant degradation of the Nafion, especially in terms of sulfur content, that is, the abundance of the -SO3- groups responsible for H+ conduction. Hence, the degradation of the Nafion, in both of the CLs and in the PEM, was found to be the principal mechanism for performance degradation, while the Pt/C catalyst degradation in terms of particle size enlargement or mass loss was minimal. The study suggests that under real-life operating conditions, ionomer degradation plays a more significant role than electrocatalyst degradation in LT-PEMFCs, in contrast to many scientific studies under artificial stress conditions. Mitigation of the ionomer degradation must be emphasized as a strategy to improve the PEMFC's durability.

Blister formation in dynamic release mirror structures using femtosecond laser pulses.

Blister formation occurs when a laser pulse interacts with the underside of a polymer film on a glass substrate and is fundamental in Laser-Induced Forward Transfer (LIFT). We present a novel method of controlling blister formation using a thin metal film situated between two thin polymer films. This enables a wide range of laser pulse energies by limiting the laser penetration in the film, which allows us to exploit nonlinear interactions without transmitting high intensities that may destroy a transfer material. We study blisters using a helium ion microscope, which images their interiors, and find that laser energy deposition is primarily in the metal layer and the top polymer layer remains intact. Blister expansion is driven by laser-induced spallation of the gold film. Our work shows that this technique could be a viable platform for contaminant-free LIFT using nonlinear absorption beyond the diffraction limit.

Ordered Bose Glass of Vortices in Superconducting YBa2Cu3O7-δ Thin Films with a Periodic Pin Lattice Created by Focused Helium Ion Irradiation.

The defect-rich morphology of YBa2Cu3O7−δ (YBCO) thin films leads to a glass-like arrangement of Abrikosov vortices which causes the resistance to disappear in vanishing current densities. This vortex glass consists of entangled vortex lines and is identified by a characteristic scaling of the voltage–current isotherms. Randomly distributed columnar defects stratify the vortex lines and lead to a Bose glass. Here, we report on the observation of an ordered Bose glass in a YBCO thin film with a hexagonal array of columnar defects with 30 nm spacings. The periodic pinning landscape was engineered by a focused beam of 30 keV He+ ions in a helium-ion microscope.

Epitaxial Lateral Overgrowth of Tin Spheres Driven and Directly Observed by Helium Ion Microscopy

Epitaxial Lateral Overgrowth of Tin Spheres Driven and Directly Observed by Helium Ion Microscopy

Fire safety performance of 3D GFRP nanocomposite as a cladding material

Vertical fire spread along highly flammable claddings is a major safety issue for buildings. In this project, a potential new type of cladding material, 3D Glass Fibre Reinforced Polymer (3D GFRP) with improved thermal stability, and fire performance is developed. 3D GFRP nanocomposite samples were fabricated with different percentages of Sepiolite (Sep), Sepiolite-phosphate (SepP), Ammonium Polyphosphate (APP) flame retardant, and 3D glass fabrics. Synthesis of SepP, dispersion analysis of nanoparticles, and manufacturing process have been studied. The characterisation of materials was conducted using Scanning Electron Microscopy, Helium Ion Microscopy, Transmission Electron Microscopy, Thermogravimetric Analysis (TGA), and X-ray Diffraction Analysis. The thermal stability and fire behaviour of the 3D GFRP nanocomposite was studied via TGA and cone calorimeter test. TGA results showed that the optimum amount of additives that improved the thermal stability is 15% flame retardants. Results of cone calorimeter tests showed that different percentages of APP, Sep, and SepP decreased the peak of the heat release rate between 4% and 42%. Also, the effects of APP flame retardant in improving thermal and fire reaction properties were more than Sep and SepP. The test results of 3D GFRP nanocomposite also showed a prospective cladding that can benefit the construction industry in near future.

Applications of image analysis in plant chromosome and chromatin structure study

BackgroundThe use of image analysis to understand the structure of chromosome and chromatin is critical to the study of genetic evolution and diversification. Furthermore, a detailed chromosome map and the structure of chromatin in the nucleus may contribute to the plant breeding and the study of fundamental biology and genetics in organisms.ResultsIn plants with a fully annotated genome project, such as the Leguminosae species, the integration of genetic information, including DNA sequence data, a linkage map, and the cytological quantitative chromosome map could further improve their genetic value. The numerical parameters of chromocenters in 3D can provide useful genetic information for phylogenetic studies of plant diversity and heterochromatic markers whose epigenetic changes may explain the developmental and environmental changes in the plant genome. Extended DNA fibers combined with fluorescence in situ hybridization revealed the highest spatial resolution of the obtained genome structure. Moreover, image analysis at the nano‐scale level using a helium ion microscope revealed the surface structure of chromatin, which consists of chromatin fibers compacted into plant chromosomes.ConclusionsThe studies described in this review sought to measure and evaluate chromosome and chromatin using the image analysis method, which may reduce measurement time and improve resolution. Further, we discussed the development of an effective image analysis to evaluate the structure of chromosome and chromatin. An effective application study of cell biology and the genetics of plants using image analysis methods is expected to be a major propeller in the development of new applications.

Maskless Generation of Single Silicon Vacancy Arrays in Silicon Carbide by a Focused He+ Ion Beam

Precise generation of spin defects in solid-state systems is essential for nanostructure fluorescence enhancement. We investigated a method for creating single silicon vacancy defect arrays in silicon carbide using a helium-ion microscope. Maskless and targeted generation can be realized by precisely controlling the focused He+ ion beam with an implantation uncertainty of 60 nm. The generated silicon vacancies were identified by measuring the optically detected magnetic resonance spectrum and room temperature photoluminescence spectrum. We systematically studied the effects of the implantation ion dose on the generated silicon vacancies. After optimization, a conversion yield of ~ 6.95 % and a generation rate for a single silicon vacancy of ~ 35 % were realized. This work paves the way for the integration and engineering of color centers to photonic structures and the application of quantum sensing based on spin defects in silicon carbide.

Cellulose-inorganic hybrids of strongly reduced thermal conductivity

The employment of atomic layer deposition and spin coating techniques for preparing inorganic–organic hybrid multilayer structures of alternating ZnO-CNC layers was explored in this study. Helium ion microscopy and X-ray reflectivity showed the superlattice formation for the nanolaminate structures and atomic force microscopy established the efficient control of the CNCs surface coverage on the Al-doped ΖnO by manipulating the concentration of the spin coating solution. Thickness characterization of the hybrid structures was performed via both ellipsometry and X-ray reflectivity and the thermal conductivity was examined by time domain thermoreflectance technique. It appears that even the incorporation of a limited amount of CNCs between the ZnO laminates strongly suppresses the thermal conductivity. Even small, submonolayer amounts of CNCs worked as a more efficient insulating material than hydroquinone or cellulose nanofibers which have been employed in previous studies.

Supercritical adsorptive precipitation of coenzyme Q10 on sodium alginate aerogel

Supercritical adsorptive precipitation (SAP) can be employed to load hydrophobic bioactives onto aerogels formed using the Pressurized Gas eXpanded liquid (PGX) Technology to prepare novel delivery systems. The objective of this study was to investigate the effects of SAP parameters on the coenzyme-Q10 (CoQ10) loading onto PGX-processed sodium alginate (PGX-SA) and its physicochemical properties. Within the ranges tested, higher recirculation time (50 min) and flow rate (262 mL/min), lower pressure (200 bar), and higher surface area biopolymer resulted in higher CoQ10 loading (46.9 ± 3.0% w/w). Helium ion microscopy revealed a rather uniform coating of PGX-SA fibrils, covering the porous structure. Thermal and crystallinity analyses demonstrated a decrease in CoQ10 crystallinity. CoQ10-loaded PGX-SA suspension in water remained stable for 50 days at 4 °C. These findings demonstrate the potential of PGX Technology combined with SAP for developing delivery systems for hydrophobic bioactives to increase water dispersibility and suspension stability, which can boost their bioavailability.

Using the Helium Ion Microscope for Imaging and Modification of Nanostructures, 2D Materials, and SARS-CoV-2 Infected Cells

Using the Helium Ion Microscope for Imaging and Modification of Nanostructures, 2D Materials, and SARS-CoV-2 Infected Cells

Scanning Transmission Helium Ion Microscopy- How Does It Compare to TEM?

Scanning Transmission Helium Ion Microscopy- How Does It Compare to TEM?

Experimental study of the influence of geochemical features on the viscoelasticity of organic matter in shale

Understanding time-dependent mechanical properties is critical to perform geomechanical risk quantification and reduce the environmental impact of fracking operations. In this study, vitrinite reflectance test, scanning electron microscope (SEM)/helium ion microscope (HIM) observation, atomic force microscopy (AFM)-based nanoscale dynamic mechanical analysis (AFM-nDMA), and micro-Raman analysis were combined as a chemo-mechanical method to investigate the role of thermal maturation in affecting nanoscale viscoelasticity of organic matter with maceral classification. The results of 208 tested areas demonstrated that viscosity is negatively correlated with thermal maturity, while storage modulus is positively correlated with maturity, suggesting that such polymer-like to mineral-like process might be prone to fracture initiation. Moreover, chemical structure changes during the thermal evolution exhibited by micro-Raman analysis were found to contribute to the abovementioned mechanical variations. Characterization of viscoelasticity of organic matter considering geochemical features is a highly promising aspect for inclusion in petrophysical workflows, leading to improved design of hydraulic fracturing and homogenization modeling.

Use of the helium ion microscope in small crack fractography

Highly stressed aerospace structures, such as the wing attachment points and load carry-through bulkheads of fighter aircraft, often grow fatigue cracks from micro-scale discontinuities. These cracks spend much of their lives close to these discontinuities in the small crack regime. The accurate prediction of fatigue crack growth in this small crack regime leads to setting realistic inspection thresholds for the aircraft and assisting in accurate risk-based assessment of the lives of such cracks. Fractography can greatly aid the assessment of the growth of small cracks. It has traditionally been carried out using optical and Scanning Electron Microscopes to gather the necessary small crack growth rate data, however, limitations on the resolution and the surface sensitivity of these instruments restricts the gathering of crack growth rate data at small crack lengths. As an extension to the current capabilities, the newly introduced Helium Ion Microscope offers improved nano-scale resolution and topographical sensitivity. As a result, the Helium Ion Microscope offers the potential for both quantitative and qualitative analysis of small fatigue crack growth about nucleating discontinuities at resolutions previously unobtainable. This paper presents an overview of the technology and gives three different fractographic examples of its possible applications to failure analysis. These examples include extension of small crack fractography, extension of near initiation fractographic feature analysis, and extension of nano-scale feature analysis. To demonstrate these capabilities, fatigue fractures produced by experimental loading spectra that were applied to the aluminium alloy AA7050-T7451 have been investigated.

Electron transport tuning of graphene by helium ion irradiation

This article reviews charge carrier transport phenomena in single-layer graphene, in which crystalline defects are generated by helium-ion-beam irradiation using a helium-ion microscope. Crystalline defects work as electron scatterers, and the conductivity drastically decays as ion dose increases. Moreover, real-time conductivity monitoring during ion beam scans over the graphene surface is demonstrated. In cryogenic measurements under magnetic fields, defective graphene exhibits negative magnetoresistance, suggesting that strong localization occurred in this two-dimensional electron system, which survived even at room temperature. The localized state contributes to inducing a transport gap around the Dirac point, where the density of states is at its minimum, and it enables field-effect control of the carrier transport by tuning the carrier density. The fabrication and operation of field-effect transistors with defective graphene channels are demonstrated.

Structural evolution of amorphous and nanocrystalline TiAl films under helium implantation

The structure evolution and mechanism of the material during helium ion implantation are directly related to their performance and service life, towards the nuclear application. Despite the growing interest in amorphous and nanocrystalline films for a range of nuclear applications, many specifics about how their structure evolves during helium implantation are unclear. Here, the amorphous and nanocrystalline TiAl films produced by magnetron sputtering were in situ observed in a helium ion microscope to further understand the mechanism of microstructural evolution under severe ion implantation of two distinct structured nanomaterials. The result shows that a blister suddenly appeared on the surface of the nanocrystalline TiAl film, caused by a laterally ordered distribution of bubbles along the 〈111〉 crystal direction when the implantation dose reached 3.5 × 1017 ions cm−2. Instead, significant swelling of the whole implantation region of amorphous TiAl film was observed. At the final dose (9 × 1017 ions cm−2), the swelling thickness of the amorphous film was 200 nm and no exfoliation and cracking occurred. Due to long-range disorder, the degradation processes of amorphous TiAl film significantly differ from those of nanocrystalline TiAl film. This research has the potential to classify applications of materials in the nuclear field while providing a new viewpoint on the material structure design.

Renewable energy powered membrane technology: Impact of osmotic backwash on organic fouling during solar irradiance fluctuation

Organic fouling is a major issue of nanofiltration/reverse osmosis (NF/RO) membranes because it causes severe and usually irreversible flux decline. Consequently, NF/RO requires frequent chemical cleaning and/or replacement. In directly coupled photovoltaic (PV) powered NF/RO systems for brackish water desalination, solar energy fluctuations can induce a spontaneous osmotic backwash (OB) process, which may mitigate organic fouling. In this study, the feasibility of spontaneous OB as a self-cleaning method for organic fouling (humic acid with calcium) control under fluctuating conditions was evaluated with an online total organic carbon (TOC) analyser. The OB cleaning mechanisms with different solar energy fluctuating conditions, relevant feedwater chemistry (salinity, pH, and hardness) and membrane type (NF270 and BW30) were investigated. The visualisation of fouling layers by a helium ion microscope (HIM), a cryo scanning electron microscope equipped with a focused ion beam (FIB-SEM) and energy dispersive X-Ray spectroscopy (EDS) showed that partial foulants were removed by spontaneous OB, and the remaining layer was not uniform. Periodic solar irradiance step-response experiments’ results showed that spontaneous OB cleaning restored 46%–98% flux, depending on solar irradiance fluctuating conditions, feedwater chemistry, and membrane type. Specifically, low-level solar irradiance (i.e., more cloud coverage) and short operating time (i.e., high cleaning frequency) showed high OB cleaning efficiency. High salinity was found to enhance the OB performance but it was still ineffective for the enhanced organic fouling layer. Extremely pH (e.g. pH 2 or pH 12) weakened OB efficiency via a compact fouling layer/mixed fouling layer structures (calcite participation) in presence of calcium. Although spontaneous OB cleaning is promising to mitigate organic fouling, it is ineffective for severe organic fouling (e.g. 12.5 mM humic acid with 2.5 mM CaCl2). This work provides the contribution of process and water quality variables that make spontaneous OB effective for fouling control, which facilitates the further development and application of the OB technique in decentralised PV-NF/RO systems.

High-Resolution Topographic and Chemical Surface Imaging of Chalk for Oil Recovery Improvement Applications

Chalk is a very fine-grained carbonate and can accommodate high porosity which is a key characteristic for high-quality hydrocarbon reservoirs. A standard procedure within Improved Oil Recovery (IOR) is seawater-injection which repressurizes the reservoir pore pressure. Long-term seawater-injection will influence mineralogical processes as dissolution and precipitation of secondary minerals. These secondary minerals (<1 micrometer) precipitate during flooding experiments mimicking reservoir conditions. Due to their small sizes, analysis from traditional scanning electron microscopy combined with energy dispersive X-ray spectroscopy is not conclusive because of insufficient spatial resolution and detection limit. Therefore, chalk was analyzed with high-resolution imaging by helium ion microscopy (HIM) combined with secondary ion mass spectrometry (SIMS) for the first time. Our aim was to identify mineral phases at sub-micrometer scale and identify locations of brine–rock interactions. In addition, we wanted to test if current understanding of these alteration processes can be improved with the combination of complementary imaging techniques and give new insights to IOR. The HIM-SIMS imaging revealed well-defined crystal boundaries and provided images of excellent lateral resolution, allowing for identification of specific mineral phases. Using this new methodology, we developed chemical identification of clay minerals and could define their exact location on micron-sized coccolith grains. This shows that it is essential to study mineralogical processes at nanometer scale in general, specifically in the research field of applied petroleum geology within IOR.