Focused Ion Beam Research Articles

Tight focusing of terahertz vortex beams formed by laser dielectric resonator

Wave characteristics of vortex laser beams during their tight focusing have been theoretically studied. The Rayleigh–Sommerfeld theory was used to describe propagation in free space of laser beams excited by the modes of a waveguide dielectric resonator. It is shown that at the topological charge of the spiral phase plate n = 0, the studied EH11 mode has a maximum of radiation intensity on the axis. Introduction of a topological charge leads to the appearance of a minimum of radiation intensity on the axis as well as to the increase in the size of the focal spot. However, for the TE01 mode with the topological charges n = 0 and n = 2, the intensity distribution retains a ring shape, while at n = 1 the beam profile turns into the Gaussian-like one. The wave front in the focal region of the lens for the components of the EH11 and TE01 modes transforms from spherical to spiral one with increasing the topological charge.

Design of a long depth of focus Gaussian beam shaping system via aspheric lenses

This paper presents a beam shaping system that uses a Galilean beam shaper. The light mapping function and the aspherical coefficient, which determines the characteristics of the aspheric lens, are derived based on the law of conservation of energy. Furthermore, optical software (i.e., ZEMAX) was utilized to simulate the design of the shaping system. In addition, a spherical collimation system is introduced to achieve the shaping system with long depth of focus. The results show that the output flat-top beam has the uniformity over 90% within the 300mm depth of focus range and the divergence angle no more than 0.6°, which is in line with the theoretical expectation. Compared to the previous works, our beam shaping system is characterized by long depth of focus, simple structure and good beam shaping effect, which makes the present shaping beam more flexible for the application in the field of laser processing.

Microstructure of Gilsocarbon graphite revealed by a correlative study of optical texture and FIB-TEM

Transmission Electron Microscopy (TEM) alongside Polarized Optical Microscopy (POM), is used to investigate the microstructure of nuclear graphite, specifically Gilsocarbon coke, fillers, binders, and flour. Detailed analyses revealed domain structures, domain boundaries, sub-domains and two types of microcracks: intra-domain and inter-domain cracks. Analysis of TEM images, from samples prepared via Focused Ion Beam (FIB), showed domain sizes in coke filler and flour regions ranged from 1 to 3 μm, whereas binder regions had larger domains of up to tens of micrometers, with correspondingly longer Mrozowski cracks. Within these domains, sub-domain boundaries further constrained Mrozowski cracks, resulting in crack lengths significantly shorter than the domain size. Domain boundaries were classified into small-angle and large-angle boundaries based on orientation differences, with large-angle boundaries arising from multiple small-angle transformations facilitated by polygonal microcracks. This microstructural data obtained from virgin Gilsocarbon graphite provides essential inputs for an experimentally informed model predicting the deformation and fracture properties of this material at the micrometer length scale, which may offer improved insights to enhance our understanding of how these properties may evolve under reactor operating conditions.

Advanced multi-scale characterization of loess microstructure: Integrating μXCT and FIB-SEM for detailed fabric analysis and geotechnical implications

Loess, a Quaternary wind-blown deposit, is a problem soil that gives rise to frequent geohazards such as landslides and water-induced subsidence. The behaviour of loess is controlled by its microstructure, consisting of silt-sized skeleton particles and complex bonding structures formed by clay-sized particles. Achieving a deep understanding and precise modelling of loess behaviour necessitates comprehensive knowledge of the realistic 3D microstructure. In this paper, a correlative investigation of the 3D loess microstructure is performed using X-ray micro-computed tomography (μXCT) and focused ion beam scanning electron microscope (FIB-SEM). Details of clay structures in loess, such as clay coatings, clay bridges and clay buttresses, are visualized and characterized in 3D based on FIB-SEM images with a voxel size of 10 × 10 × 10 nm3. The clay structures exhibit a diverse degree of complexity and their impact on the mechanical properties of loess is highlighted. Statistical analysis of the skeleton particles, including size, shape and orientation, are derived from μXCT images with a voxel size of 0.7 × 0.7 × 0.7 μm3. The findings provide insights into the collapse mechanism and particle-scale modelling of loess. The combination of μXCT and FIB-SEM proves to be a powerful approach for characterizing the intricate micro-structures of loess, as well as other geomaterials.

Unraveling the Dynamic Properties of New-Age Energy Materials Chemistry Using Advanced In Situ Transmission Electron Microscopy.

The field of energy storage and conversion materials has witnessed transformative advancements owing to the integration of advanced in situ characterization techniques. Among them, numerous real-time characterization techniques, especially in situ transmission electron microscopy (TEM)/scanning TEM (STEM) have tremendously increased the atomic-level understanding of the minute transition states in energy materials during electrochemical processes. Advanced forms of in situ/operando TEM and STEM microscopic techniques also provide incredible insights into material phenomena at the finest scale and aid to monitor phase transformations and degradation mechanisms in lithium-ion batteries. Notably, the solid-electrolyte interface (SEI) is one the most significant factors that associated with the performance of rechargeable batteries. The SEI critically controls the electrochemical reactions occur at the electrode-electrolyte interface. Intricate chemical reactions in energy materials interfaces can be effectively monitored using temperature-sensitive in situ STEM techniques, deciphering the reaction mechanisms prevailing in the degradation pathways of energy materials with nano- to micrometer-scale spatial resolution. Further, the advent of cryogenic (Cryo)-TEM has enhanced these studies by preserving the native state of sensitive materials. Cryo-TEM also allows the observation of metastable phases and reaction intermediates that are otherwise challenging to capture. Along with these sophisticated techniques, Focused ion beam (FIB) induction has also been instrumental in preparing site-specific cross-sectional samples, facilitating the high-resolution analysis of interfaces and layers within energy devices. The holistic integration of these advanced characterization techniques provides a comprehensive understanding of the dynamic changes in energy materials. This review highlights the recent progress in employing state-of-the-art characterization techniques such as in situ TEM, STEM, Cryo-TEM, and FIB for detailed investigation into the structural and chemical dynamics of energy storage and conversion materials.

Interdependence of Support Wettability ‐Electrodeposition Rate ‐ Sodium Metal Anode and SEI Microstructure

This study examines how current collector support chemistry (sodiophilic intermetallic Na2Te vs. sodiophobic baseline Cu) and electrodeposition rate affect microstructure of sodium metal and its solid electrolyte interphase (SEI). Capacity and current (6 mAh cm‐2, 0.5‐3 mA cm‐2) representative of commercially relevant mass loading in anode‐free sodium metal battery (AF‐SMBs) are analyzed. Synchrotron X‐ray nanotomography and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) are combined with cryogenic focused ion beam (cryo‐FIB) microscopy. Highlighted are major differences in film morphology, internal porosity, and crystallographic preferred orientation e.g. (110) vs. (100) and (211) with support and deposition rate. Within the SEI, sodium fluoride (NaF) is more prevalent with Te‐Cu versus sodium hydride (NaH) and sodium hydroxide (NaOH) with baseline Cu. Due to competitive grain growth the preferred orientation of sodium crystallites depends on film thickness. Mesoscale modelling delineates the role of SEI (ionic conductivity, morphology) on electrodeposit growth and onset of electrochemical instability.

Stress-strain curve estimation from micropillar compression with transverse contraction effect

The Focused Ion Beam (FIB) technique and the associated compression testing capabilities provide versatile access to understanding the microstructural behaviour of materials. Among many objectives, determining the stress-strain relationship from experimental or numerical force-displacement data remains a fundamental challenge. However, for micropillers under compression, the inside deformation constraint is complex like in components and the transformation of a measured force-displacement curve into an accurate uniaxial stress-strain curve is not straightforward. In this context, in a previous numerical based analysis for perfect volume constancy or incompressibility the determination of reliable and accurate stress-strain curves from nonlinear load-deformation curves of micropillers was already verified. In the case of transverse contractions, however, numerical simulations of micropillers provide unexpected force-displacement behaviour, i.e. their force-displacement curves are almost superimposing and are very close to the force-displacements for incompressibility. This effect implies, that transverse contraction would have no contributions in micropillar compression. In contrast, independent simulations using a single finite element accurately explore the true uniaxial stress-strain behaviour for the whole range of transverse contractions. These are considered as the reference behaviour and are also treated by an analytical expression. With the presented new stress-strain estimation approach, including transverse contraction, any force-displacement curve from a micropillar under compression can be stepwise corrected. The first step of the new stress-strain curve estimation method, including transverse contraction, is carried out in the same way as in the preceding analysis for incompressibility, followed by further steps to obtain the final true stress-strain curve. Although the presented numerical analysis is exemplarily performed for the behaviour of fused silica, but the stress-strain approach is in the same manner generally applicable for a material behaviour with other stress-strain curves. The assumption behind is isotropic and nonlinear material behaviour.

A mechanism study of thermal resistance formation and post-fire strength recovery in cement paste with carbon nanotubes and nanosilica via focused ion beam/scanning electron microscopy tomography

Although carbon nanotubes (CNT) and nanosilica (NS) have shown substantial potential for enhancing the thermal resistance and post-fire mechanical recovery of cementitious composites, their combined synergistic effects remain unclear. This study aimed to elucidate the influence of CNT and NS double-hybrids on the physicochemical properties of cementitious composites under different heating temperatures (200, 500, and 800 °C) and re-curing conditions (25 °C/65 % RH and water immersion). We assessed the changes in the compressive and tensile strengths, bulk density, surface morphology, hydration products, and pore characteristics using focused ion beam scanning electron microscopy to visualize the evolving nanoscale pore structures. Our findings reveal a remarkable synergistic effect on the thermal resistance and strength recovery properties of the CNT/NS hybrid samples, owing to the stable matrix observed after heating to 800 °C. Following exposure to 800 °C, the tensile strength exhibited a remarkable 69.6 % increase compared to its pre-heating state, without any indication of crack formation. The CNT served as nucleation sites, expediting the pozzolanic reaction of NS during heating and resulting in a homogenized pore structure with interconnected hydrates. The CNT/NS hybrid samples exhibited uniform shrinkage of hydrates without creating nanoscale rod-like pores typical in ordinary cement paste, while the increase in pore volume was predominantly attributed to the expansion of existing pores and the formation of nearby new pores.

Alterable fracture toughness of amorphous silica by injection and removal of electrostatic charge

In this study, we demonstrate that the fracture toughness of amorphous silica, an electrical insulator, can be dramatically increased and restored via injecting and removing the electrical charge content. Micropillar specimens of amorphous silica were fabricated using focused ion beam machining. The specimens were charged by electron-beam irradiation (charged specimens), and the charge was removed from the specimens by exposure to atmospheric conditions and annealing (charge-removed specimens). Fracture toughness testing was conducted on non-charged, charged, and charge-removed micropillar specimens. The fracture toughness of the charged specimen was 2.4 times higher than that of the non-charged specimens. Furthermore, the fracture toughness of the charge-removed specimens was restored to a level similar to that of the non-charged specimens, but not completely restored. These results indicate that the fracture toughness of amorphous silica can be controlled by injecting and removing electrostatic charges.

Rubidium and Cesium Ion-Induced Electron and Ion Signals for Scanning Ion Microscopy Applications.

Scanning ion microscopy applications of novel focused ion beam (FIB) systems based on ultracold rubidium (Rb) and cesium (Cs) atoms were investigated via ion-induced electron and ion yields. Results measured on the Rb+ and Cs+ FIB systems were compared with results from commercially available gallium (Ga+) FIB systems to verify the merits of applying Rb+ and Cs+ for imaging. The comparison shows that Rb+ and Cs+ have higher secondary electron (SE) yields on a variety of pure element targets than Ga+, which implies a higher signal-to-noise ratio can be achieved for the same dose in SE imaging using Rb+/Cs+ than Ga+. In addition, analysis of the ion-induced ion signals reveals that secondary ions dominate Cs+ induced ion signals while the Rb+/Ga+ induced signals contain more backscattered ions.

Controlled lateral positioning of NV centres in diamond by CVD overgrowth

A challenge to this day in the development of diamond devices for quantum applications is the laterally defined and closely spaced positioning of nitrogen-vacancy centres with exceptional coherence properties. Here, we demonstrate a maskless, implantation-free method for the controlled in-plane positioning of NV centres using a combination of focused ion beam (FIB) milling, plasma etching and nitrogen-doped diamond growth. The Ga+ ion beam milling resulted in 1 μm × 1 μm cavities with depths of up to 450 nm, each cavity exhibiting the four [111]-oriented diamond facets after pure hydrogen plasma treatment and a depth of 700 nm. Low-methane, nitrogen-doped chemical vapour deposition (CVD) overgrowth resulted in in situ formation of oriented NV ensembles, exclusively perpendicular to the {111}-planes.

Investigation of Mode-Induced Spin Wave Transmission Blockage by In Situ Nanoscale Grooves.

In the pursuit of advancing spin-wave optics, the propagation of magnetostatic surface spin-waves is investigated in a uniform permalloy waveguide with in-situ nanopatterned grooves created through Atomic Force Microscopy nanolithography and Focused Ion Beam etching. The study unveils that the introduction of narrow constrictions and grooves leads to a non-monotonic reduction of the transmitted spin-wave signal intensity as the spin-wave pathway is shrinked. The remarkable feature that a stronger signal extinction is obtained for a narrow groove compared to a spin-waveguide interrupted by a full gap, where only inefficient transport through dipolar coupling is allowed, is highlighted. Combining experimental and numerical analyses, the intricate interplay between spin-wave diffraction and reflection at the waveguide edges is unraveled, being at the origin of a transverse-mode variation responsible for the signal extinction when detected using coplanar antennas. The findings offer insights into the controllable manipulation of detected spin-wave intensity, thereby opening promising avenues for the improvement of spin-wave switches and interferometers, and for the nanopatterning of graded indexmagnonics.

Terahertz Metasurfaces for Polarization Manipulation and Detection: Principles and Emerging Applications

AbstractTerahertz frequencies locating between microwave and infrared regions can record and process optical information for next‐generation information technology such as 6G communication. Metasurfaces, as emerging planar optical components built with micro‐ or nanostructures, enable precise control, and manipulation of electromagnetic waves from near fields to far fields. These subwavelength artificial structures can be engineered to exhibit specific polarization responses, thus holding significant potential for applications in polarization detection. In the terahertz (THz) region, polarization information is crucial for identifying and analyzing the properties of materials in the terahertz. In this review, we focus on recent advances in terahertz metasurfaces for polarization manipulation and detection, including principles and emerging applications. New polarization detection methods such as polarization state conversion, polarization‐selective absorption, polarization‐selective focusing, and vector beam construction are discussed. Finally, it is concluded with a few perspectives on emerging trends and existing challenges in the fields of terahertz polarization manipulation and detection.

Transformations in laser track microstructures for a quasicrystal-reinforced Al-Cu-Fe-Cr alloy

Aluminum-quasicrystal composites are attractive candidate alloys for additive manufacturing, but the cost of evaluating such systems can be prohibitive. Recently, surface laser glazing studies have been used to show that desirable composite microstructures can be formed in an Al85Cu6Fe3Cr6 alloy under a wide range of laser processing parameters. Here the thermal stability of these laser track microstructures has been evaluated by performing in situ scanning transmission electron microscopy heating experiments on specimens produced by focused ion beam milling from the center of the tracks. The initial track microstructures exhibited a uniform phase mixture with 70 % by volume of I-phase quasicrystalline dispersoids in a FCC Al matrix with a film of Al2Cu at the interface. Preliminary ramped heating experiments were used to identify the temperatures at which transformations occurred and then isothermal experiments on fresh samples were used to monitor the progress of these processes. For temperatures of up to 450 °C the only significant changes were a redistribution and coarsening of the Al2Cu phase with a gradual increase in the Fe content of the phase. At higher temperatures, the I-phase decomposed to form a mixture of crystalline ω-Al7Cu2Fe and μ-Al4Cr phases. The I-phase decomposition proceeded by ejection of Cu and Fe with the remaining Cr-rich regions transforming to the Al4Cr approximant phase. The implications of these phenomena for use of the alloy in additive manufacturing are discussed.

Polycrystalline methylammonium-lead bromide perovskite films for photonic metasurfaces

Polycrystalline films of organo-inorganic perovskite semiconductors are promising as a foundation for creating functional optical metasurfaces. The requirements for film structural perfection, thickness uniformity, and defect-free characteristics are much more stringent compared to perovskite films for photovoltaics. This work presents the results of searching for optimal conditions for one-step synthesis of lead methylammonium bromide films using centrifugation, and describes the successful fabrication of subwavelength optical gratings from these films through focused ion beam processing. The measured spectra of light transmission through the gratings demonstrated their excellent optical quality and confirmed the possibility of creating semiconductor photon metasurfaces with submicrometer periodicity and high-Q dielectric resonances.

Patterning damage mechanisms for two-dimensional crystalline polymers and evaluation for a conjugated imine-based polymer

High-quality patterning determines the properties of patterned emerging two-dimensional (2D) conjugated polymers and is essential for potential applications in future electronic nanodevices. However, the most suitable patterning method for 2D polymers has yet to be determined because we still do not have a comprehensive understanding of their damage mechanisms by visualizing the structural modification that occurs during the patterning process. Here, the damage mechanisms during patterning of 2D polymers, induced by various patterning methods, are unveiled based on a systematic study of structural damage and edge morphology in an imine-based 2D polymer (polyimine). Patterning using a focused electron beam, focused ion beam (FIB) and mechanical carving is evaluated. The focused electron beam successively introduces a sputtering effect, knock-on displacement damage and massive radiolysis with increasing electron dose from9.46×107electrons nm-2to1.14×1010electrons nm-2. Successful patterning is enabled by knock-on damage but impeded by carbon contamination beyond a critical sample thickness. A FIB creates current-dependent edge morphologies and extensive damage from ion implantation caused by the tail of the unfocused beam. A precisely controlled tip can tear the polyimine film through grain boundaries and hence create a patterning edge with suitable edge roughness for certain application scenarios when beam damage is avoided. Taking structural damage and the resulting quantitative edge roughness into consideration, this study provides a detailed instruction on the proper patterning techniques for 2D crystalline polymers and paves the way for tailored intrinsic properties and device fabrication using these novel materials.

Study by transmition electron microscopy of Co-WC/Ni interface produced by solid state bonding

The microstructure of the interface and inter-diffusion behavior during bonding plays an important role to understand and to control the joining process for better mechanical properties of an interface. In this work, the microstructure of the formed interlayer between cermet WC-Co and metallic Ni after solid state bonding (the WC-Co/Ni interface) was analyzed by scanning (SEM) and transmission (TEM) electron microscopy, and characteristic energy dispersive x-ray spectroscopy (EDS). The WC-Co/Ni joint was produced at 980°C for 25 minutes in argon atmosphere. For SEM observation, the samples were mechanically polished and etched. TEM samples were produced parallel (sample P), perpendicular (sample T) and oblique (sample TP) to the interface by focused ion beam (FIB). The EDS results indicate the inter-diffusion at the interface of W, Ni, Co and C and the segregation of Ni and Co, together with the formation of crystalline phases and an amorphous carbon layer. W follows a homogeneous diffusion while Ni and Co show a non-homogeneous diffusion behavior.

A comparison of the proto-dolomite induced by cyanobacteria and halophilic bacteria: implications for dolomite-inducing microbe identification

This study investigates the morphological and mineralogical characteristics of proto-dolomite induced by two specific microorganisms with varying lifestyles: the extremely halophilic bacterium Vibrio harveyi QPL2 and the cyanobacterium Leptolyngbya boryana. Halophilic bacterially-induced proto-dolomite (HBD) and cyanobacterially-induced proto-dolomite (CBD) were subjected to comprehensive characterization techniques, including X-ray diffraction, scanning electron microscopy, Focused Ion Beam, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The results indicate that both HBD and CBD exhibit a low degree of crystallinity and possess comparable molar ratios of MgCO3 to CaCO3. Moreover, neither of them exhibits the ordered structure of ideal dolomite. HBD and CBD exhibit notable distinctions in external morphology and internal structure. HBD forms a subunit aggregate with a less dense surface and numerous pinhole structures resulting from bacterial survival. In contrast, CBD adopts a bispherical shape with a relatively dense surface and minimal indications of cyanobacterial survival. Both HBD and CBD have an internal hollow structure. However, HBD is characterized by sparse population and loosely arranged subunits, while CBD features only a central cavity. Additionally, HBD particles are smaller compared to CBD particles. These morphological differences suggest that HBD primarily grows through bacterial surface-dependent processes, whereas the growth of CBD is not directly reliant on the surface of cyanobacteria. Compositionally, the weight percentage of crystalline water in CBD exceeded that of HBD with a value of 29.42 % compared to 5.9 %. This increase in internal crystalline water enables a faster conversion of CBD to the ordered ideal dolomite in a specific diagenetic environment. This study implies that the morphology and composition of microbial proto-dolomite may aid in identifying the type of dolomite-inducing microbes.

Study of curtaining effect reduction methods in Inconel 718 using a plasma focused ion beam.

The curtaining effect is a common challenge in focused ion beam (FIB) surface preparation. This study investigates methods to reduce this effect during plasma FIB milling of Inconel 718 (nickel-based superalloy). Platinum deposition, silicon mask and XeF2 gas injection were explored as potential solutions. These methods were evaluated for two ion beam current conditions; a high ion beam intensity condition (30kV-1µA) and a medium one (30kV-100nA) and their impact on curtaining reduction and resulting cross-section quality was assessed quantitatively thanks to topographic measurements done by atomic force microscopy (AFM). XeF2 assistance notably improved cross-section quality at medium current level. Pt deposition and Si mask individually mitigated the curtaining effect, with greater efficacy at 100nA. Both methods also contributed to reducing cross-section curvature, with the Si mask outperforming Pt deposition. However, combining Pt deposition and Si mask with XeF2 injection led to deterioration of these protective layers and the reappearance of the curtaining effect after a quite short exposure time.

On the preparation and mechanical testing of nano to micron-scale specimens

Over the past two decades, means allowing to probe experimentally the mechanical behavior of materials specimens only a few micrometers or less in diameter have multiplied, largely owing to the widespread adoption and versatility of focused ion beam (FIB) milling for the preparation of small-scale test specimens. Despite its remarkable capabilities, the ion bombardment that is employed during FIB milling operations does not leave machined surfaces unscathed: it may induce a series of alterations in the near-surface microstructure of materials, which vary in severity depending on the material being milled, or milling parameters, or the type of ion used. These alterations in turn can strongly influence the local behavior, and as a result measured mechanical properties, of the milled material. In the first part of this manuscript, we review the different forms that FIB-induced microstructural alterations can take and their influence on small-scale mechanical test results. In the second part, we present alternative strategies that have been used to circumvent the issue. These include the use of entirely different small-scale sample fabrication processes, as well as approaches that do use FIB-milling but put effort in the test design to minimize or avoid the formation of FIB-induced defects in regions where micromechanical test data are collected. The advent of such methods can enhance our understanding of FIB-induced defects on the mechanical behavior of microsamples by comparing the results with those from ion-milled samples. This, in turn, should improve our ability to interpret test data when FIB-milling is the only method available for microsample production.