Focused Ion Beam Machining Research Articles

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.

Microstructure Evolution and Fretting Wear Mechanisms of Steels Undergoing Oscillatory Sliding Contact in Dry Atmosphere.

Variations in the microstructure and the dominant fretting wear mechanisms of carbon steel alloy in oscillatory sliding contact against stainless steel in a dry atmosphere were evaluated by various mechanical testing and microanalytical methods. These included scanning electron microscopy and energy dispersive spectrometry with corresponding elemental maps of the wear tracks, in conjunction with cross-sectional transmission electron microscopy of samples prepared by focused ion beam machining to assess subsurface and through-thickness changes in microstructure, all as a function of applied load and sliding time. Heavily dislocated layered microstructures were observed below the wear tracks to vary with both the load and sliding time. During the accumulation of fretting cycles, the subsurface microstructure evolved into stable dislocation cells with cell walls aligned parallel to the surface and the sliding direction. The thickness of the damaged subsurface region increased with the load, consistent with the depth distribution of the maximum shear stress. The primary surface oxide evolved as Fe2O3 and Fe3O4 with increasing sliding time, leading to the formation of a uniform oxide scale at the sliding surface. It is possible that the development of the dislocation cell structure in the subsurface also enhanced oxidation by pipe diffusion along dislocation cores. The results of this study reveal complex phase changes affecting the wear resistance of steels undergoing fretting wear, which involve a synergy between oxidative wear, crack initiation, and crack growth along dislocation cell walls due to the high strains accumulating under high loads and/or prolonged surface sliding.

Controlling crystal cleavage in focused ion beam shaped specimens for surface spectroscopy.

Our understanding of quantum materials is commonly based on precise determinations of their electronic spectrum by spectroscopic means, most notably angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy. Both require atomically clean and flat crystal surfaces, which are traditionally prepared by in situ mechanical cleaving in ultrahigh vacuum chambers. We present a new approach that addresses three main issues of the current state-of-the-art methods: (1) Cleaving is a highly stochastic and, thus, inefficient process; (2) fracture processes are governed by the bonds in a bulk crystal, and many materials and surfaces simply do not cleave; and (3) the location of the cleave is random, preventing data collection at specified regions of interest. Our new workflow is based on focused ion beam machining of micro-strain lenses, in which shape (rather than crystalline) anisotropy dictates the plane of cleavage, which can be placed at a specific target layer. As proof-of-principle, we show ARPES results from micro-cleaves of Sr2RuO4 along the ac plane and from two surface orientations of SrTiO3, a notoriously difficult to cleave cubic perovskite.

Effect of Refresh Time on XeF2 Gas-assisted FIB Milling of GaAs

Focused ion beam (FIB) machining can be used to fabricate gallium arsenide-based devices, which have a surface finish of several nanometers, and the FIB machining speed and surface finish can be greatly improved using xenon difluoride (XeF2) gas-assisted etching. Although the refresh time is one of the most important parameters in the gas-assisted etching process, its effect on the machining quality of the surface finish has rarely been studied. Therefore, in this work, we investigated the effect of the refresh time on the etching process, including the dissociation process of XeF2, the refresh time dependency of the sputter in yield under different incident angles, and the surface finish under different refresh times. The results revealed that a selective etching mechanism occurred at different refresh times. At an incidence angle of 0°, the sputtering yield increased with the refresh time and reached its maximum value at 500 ms; at an incidence angle of 30°, the sputtering yield reached its minimum value at a refresh time of 500 ms. For surface roughness, the incident angle played a more important role than the refresh time. The surface finish was slightly better at an incidence angle of 30° than at 0°. In addition, both F and Xe elements were detected in the processed area: Xe elements were evenly distributed throughout the processing area, while F elements tended to accumulate in the whole processing area. The results suggest that the optimum surface can be obtained when a larger refresh time is employed.

Enhanced Faraday rotation by a Fano resonance in substrate-free three-dimensional magnetoplasmonic structures.

Three-dimensional magnetoplasmonic nanostructures possess more novel and richer optical and magneto-optical (MO) behaviors compared with planar nanostructures, and exhibit attractive potential applications in micro-nano non-reciprocal photonic devices. However, fabrication of three-dimensional magnetoplasmonic nanostructures is difficult using the usual nanofabrication methods. This work constructs three-dimensional substrate-free Au/Co/Au structures prepared using focused ion beam (FIB) technology. In the three-dimensional split-ring structure, with y-polarized light normal incidence, a three-dimensional coupling current is formed between the vertical split-ring and the bottom square hole, which causes excitation of the Fano resonance. The Fano resonance causes a significant enhancement of the local magnetic field, resulting in a larger Faraday rotation (FR). The resonance also brings about a sign reversal of FR, which is related to the direction of the Lorentz force on electrons. Similar effects also exist in the three-dimensional nanopillar structure and the three-dimensional nanoring structure in the simulation results. Due to the high flexibility of FIB machining, the height and shape of the three-dimensional split-ring can be arbitrarily changed, which means the FR intensity and the position of the FR null point are tunable. The designed three-dimensional structures provide a new route to regulate the Faraday effect, and broaden the possibilities for the design and construction of MO devices.

Fabrication of sinusoidal-shaped multi-tip diamond tools by a focused ion beam machining process

Multi-tip diamond (MTD) tools have remarkable advantages in scratching micro-nano structures. A key component of inertial confinement fusion is a glass capsule with a periodic sinusoidal ripple nanostructure, and its processing requires very low surface roughness and a consistent nanostructure. Using MTD tools for force servo machining is an efficient method, and the focused ion beam (FIB) method has been effective in machining multi-tip diamond tools. To machine an MTD tool with high precision and efficiency, experiments were conducted to explore the influence of FIB machining parameters on tip geometries. The tip of a MTD tool with a three-dimensional periodic sinusoidal ripple was successfully prepared using optimized processing parameters. The results demonstrated that the estimated amplitude and period machining error was less than 1.71% and 1.63%, respectively, for nanoscale structured tips. Related research provides a new solution for the cross-scale and efficient processing of nanostructures.

Multi-scale three-dimensional analysis on local arrestability of intergranular crack in high-strength martensitic steel

The present study investigated the local arrestability of intergranular crack in high-strength martensitic steel through multi-scale three-dimensional (3D) analysis using X-ray computed tomography and focused ion beam machining (FIB)-scanning electron microscopy (SEM) serial sectioning combined with electron backscattering diffraction (3D EBSD). Macroscopic analysis using X-ray computed tomography demonstrated discontinuous propagation of the intergranular cracks, indicating local arrest of the crack propagation. An analysis of the opening displacement of each crack component revealed that the resolved normal stress was not the only factor determining the intergranular crack propagation path. The relationship between the microstructure and local crack-arrestability was microscopically analyzed using FIB-SEM serial sectioning. The 3D EBSD analysis clearly suggested that the crack propagations were arrested at the low-angle grain boundary plane segments and at the grain boundary triple junctions surrounded by relatively large martensite variants. Moreover, the larger martensite variants around grain boundaries contributed to the plastic accommodation of stress concentration and promoted crack-tip blunting. We propose that increasing the fraction of low-angle grain boundary plane segments as well as that of large martensite variants existing around grain boundaries can enhance local crack-arrestability and retard intergranular fracture of high-strength martensitic steels.

Cold photo-carving of halogen-bonded co-crystals of a dye and a volatile co-former using visible light.

The formation of co-crystals by the assembly of molecules with complementary molecular recognition functionalities is a popular strategy to design or improve a range of solid-state properties, including those relevant for pharmaceuticals, photo- or thermoresponsive materials and organic electronics. Here, we report halogen-bonded co-crystals of a fluorinated azobenzene derivative with a volatile component-either dioxane or pyrazine-that can be cut, carved or engraved with low-power visible light. This cold photo-carving process is enabled by the co-crystallization of a light-absorbing azo dye with a volatile component, which gives rise to materials that can be selectively disassembled with micrometre precision using low-power, non-burning laser irradiation or a commercial confocal microscope. The ability to shape co-crystals in three dimensions using laser powers of 0.5-20 mW-substantially lower than those used for metals, ceramics or polymers-is rationalized by photo-carving that targets the disruption of weak supramolecular interactions, rather than the covalent bonds or ionic structures targeted by conventional laser beam or focused ion beam machining processes.

Non-linear Shubnikov-de Haas oscillations in the self-heating regime

We demonstrate a non-linear measurement scheme of the Shubnikov–de Haas effect based on Joule self-heating that builds on ideas of the 3ω-method used in thin films. While the temperature dependence of the resistance, R(T), of clean metals at low temperatures saturates, a significant temperature dependence, dR/dT, appears at high fields due to Landau quantization. We experimentally demonstrate this effect in the semi-metal CoSi, resolving well quantum oscillations at low magnetic fields in the non-linear channel, which appear as 3rd harmonics of the current drive frequency. To ensure the dominant self-heating originates in the crystal, not at the contacts, we fabricate crystalline microbars using focused ion beam machining. These oscillations in non-linear channel encode the ratio between the dR/dT and the thermal conductivity of the material, rendering it an interesting probe in situations of the broken Wiedemann–Franz law. Our results present a quantitative methodology that is particularly suited to investigate the electronic structure of micro- and nano-materials at intermediate temperatures.

Bending strain in 3D topological semi-metals

We present an experimental set-up for the controlled application of strain gradients by mechanical piezoactuation on 3D crystalline microcantilevers that were fabricated by focused ion beam machining. A simple sample design tailored for transport characterization under strain at cryogenic temperatures is proposed. The topological semi-metal Cd3As2 serves as a test bed for the method, and we report extreme strain gradients of up to m−1 at a surface strain value of at 4 K. Interestingly, the unchanged quantum transport of the cantilever suggests that the bending cycle does not induce defects via plastic deformation. This approach is a first step towards realizing transport phenomena based on structural gradients, such as artificial gauge fields in topological materials.

Determination of fracture toughness of a platinum-modified nickel aluminide coating by micromechanical testing

The fracture toughness of an industry benchmark platinum-modified nickel aluminide coating (RT22LT) is determined by microcantilever bending tests. Cantilevers are prepared in three microstructurally-different zones across the coating cross-section by focused ion beam machining and then bent in-situ by a nanoindenter in a scanning electron microscope. Elastic-plastic fracture mechanics, combined with finite element analysis, are implemented to compute the fracture toughness. It is found that the fracture toughness of the coating varies through its thickness: the middle zone has the highest toughness (7.62 MPam), followed by the surface zone (6.59 MPam), and the interdiffusion zone has the lowest toughness (4.89 MPam). The main reason for such difference is the amount of plastic deformation prior to fracture and its corresponding contribution to the energy release rate vary from zone to zone. Observations of fracture surface show that fracture in the β-phase matrix is predominantly transgranular. However, the fracture morphology depends on the precipitate content of each zone and a higher precipitate content gives rise to more interfacial decohesion between the β-matrix and the precipitates. Analysis of microstructural-compositional features and their correlation with the plastic component of the energy release rate suggests that the precipitate content plays a major role in variation of the fracture toughness between the three zones. The fracture behaviours of the coating are compared with those reported in the literature and their difference is rationalised by the Weibull analysis.

Measurement of critical current flow and connectivity in systems of joined square superconducting plates

A method to measure the electrical connectivity between square superconducting plates joined by weak link interfaces is presented. It is based on observation of lines where the flow of critical current abruptly changes direction due to the presence of weak links, and the confinement created by the shape of the sample. The method is demonstrated using magneto-optical imaging (MOI) of systems consisting of up to 2×2 plates joined to form a larger square. The samples used in this study are Nb films with weak links created by focused ion beam machining. Common features are found in the current flow patterns, which allow to measure the electrical connectivity between the plates by observing an angle between pairs of lines indicating where the current abruptly changes flow direction, so-called discontinuity, or d-lines.

High-quality graphene as a coating for polycrystalline tungsten in low-energy helium and deuterium plasma exposures

• Graphene acts as a sputter shield against low energy helium and deuterium plasmas. • High ion fluences can limit the functional range for graphene coatings. • Tungsten fuzz growth can be slowed down by coating polished surfaces with graphene. In the presence of irradiation by energetic ions, plasma facing components (PFCs) tend to develop surface morphologies that lead to mass loss of the wall material, potentially diminishing their lifetime and plasma performance. We explore the performance of graphene as a coating for plasma facing components to protect against sputtering due to low-energy ions. We show that graphene can slow changes in surface morphology of tungsten subjected to energetic-helium and deuterium ion bombardment over a wide range of energies, as tested in the PISCES-A facility at UC-San Diego. We exposed tungsten samples half-coated with graphene in the PISCES-A facility, at energies of 40 and 140 eV and fluences ranging from 1 × 10 24 - 3.6 × 10 25 ions/m 2 . We found that tungsten “fuzz” growth at high fluences (10 24 –10 25 He-D/m 2 ) can be reduced by approximately 30%. At the lower fluence and energy, no fuzz formed. Using scanning electron microscopy and focused-ion beam machining, we investigate these changes in surface morphology. Deuterium results do not show the graphene defect production to be as energy or fluence dependent as helium bombardment. We determine damage to and the lifetime of the graphene membrane with Raman spectroscopy for vacuum components subjected to such extreme environmental conditions.

Investigation Into Low Frequency Response of Acoustic MEMS for Determination of Failure Modes

Frequency response to stimuli applied to acoustic micro-electro-Mechanical Systems (MEMS) yield meaningful information of certain defects affecting such devices. This article presents the effects of three distinct root causes of failures affecting the low-frequency response of MEMS microphones: lid attach holes, die attach holes and broken vents with experimental inductions of these effects for the lid attach holes and broken vents. Methods to create such defects are presented which include laser drilling and focused ion beam machining of holes. A complete characterization of induced broken vents is presented. Alternative locations for defects induction are proposed and demonstrated on 34 devices, 16 with lid attach holes and 18 with induced broken vents. The information obtained from the frequency response of the devices is shown to be insufficient to separate the root causes of failures as their effects on the frequency response is similar and the magnitudes of the variations of the observed response overlap. Additional information about the circumstances regarding the onset of defects such as location of the fault and its occurrence in the device manufacturing/assembly/operation timeline is however sufficient for root cause identification.

Fabrication of microtool for micromachining: A review

Nowadays, every component is getting miniature. For machining of these micro components, micromachining have to be performed either on soft or hard materials. To machine at micron range, the tool has to be also in the micron range. But the fabrication of the tool at the micron range is very challenging because of its size, shape, strength, etc. Several researchers have utilized non-conventional machining to fabricate microtools using different techniques such as Electrical discharge machining (EDM), Electrochemical machining (ECM), Focused ion beam machining (FIB), etc. In this paper, a detailed explanation of all these processes for the fabrication of micro tools has been discussed with the advantages and disadvantages associated with these processes. The shape and size of the fabricated microtool are also discussed with their applications.

Femtosecond laser machining of hollow-core negative curvature fibres.

Hollow core negative curvature fibres (NCFs) are a relatively new class of microstructured optical fibre with potential applications in areas such as the delivery of high power laser light and gas sensing. For sensing, it is necessary for the measurand to interact with the guided mode. To facilitate this, a novel femtosecond laser-based machining protocol has been developed that allows the precision sculpting of access slots into the NCF core along the length of the fibre. The process is a direct-write process using a digitally defined scanning strategy with no need for physical masks or additional processing such as wet etchants and/or focussed ion beam machining. Due to the inherent flexibility of the machining strategy and the high level of control over the depth of material removal, it is likely that this new technique will be transferable to a wide range of microstructured fibres.

Generation of Core-Sheath Polymer Nanofibers by Pressurised Gyration.

The ability to generate core–sheath bicomponent polymer nanofibers in a single-step with scale-up possibilities is demonstrated using pressurised gyration manufacturing. This is the first time that nanofiber containing more than one polymer having a core–sheath configuration has been generated in this way. Water-soluble polymers polyethylene oxide (PEO) and polyvinyl pyrrolidone (PVP) are used as the core and sheath layers, respectively. Core–sheath nanofibers with a diameter in the range of 331 to 998 nm were spun using 15 wt % PEO and 15 wt % PVP polymer solutions. The forming parameters, working pressure and rotating speed, had a significant influence on the size, size distribution and the surface morphology of the nanofibers generated. Overall, fibre size decreased with increasing working pressure and rotating speed. The fibre size was normally distributed in all cases, with 0.2 MPa working pressure in particular showing narrower distribution. The fibre size distributions for 0.1 and 0.3 MPa working pressure were broader and a mean fibre size of 331 nm was obtained in the latter case. The fibre size was evenly distributed and narrower for rotating speeds of 2000 and 4000 RPMs. The distribution was broader for rotating speed of 6000 RPM with a mean value obtained at 430 nm. Continuous, smooth and bead-free fibre morphologies were obtained in each case. The fibre cross-section analysis using a focused ion beam machine showed a solid core surrounded by a sheath layer. Our findings demonstrate that the pressurised gyration could be used to produce core–sheath polymer nanofibers reliably and cost-effectively with scale-up possibilities (~4 kg h−1).

Study of different materials response in micro milling using four edged micro end mill tools

Fabrication of micro channels with a width of less than 200 μm is always challenging as the available cutting tools are costly and not adequate for machining for a longer time. Popular tool fabrication processes like tool grinding experience high scrap rate as the micro features in the cutting tools cannot withstand the grinding forces. Other non-contact tool fabrication processes like focused ion beam machining (FIB) and wire electro-discharge machining (wire EDM) are very slow and need high capital investment. In this paper, micro end mill tools with high dimensional accuracy are fabricated by a sequential EDM method and the performance analysis is conducted by milling micro channels of different depth on aluminium 6061, brass 340, AISI 1040 and poly methyl methacrylate (PMMA). The cutting tools are proven to be capable of producing micro channels of high dimensional accuracy (100 ± 4 μm), nanometer surface finish (29−120 nm), high surface integrity, and less post-milling tool damages.

Femtosecond Laser Ablation for Mesoscale Specimen Evaluation

Focused ion beam machining revolutionized the way samples are studied in materials science. The introduction of this tool enabled researchers to break into new frontiers of research. While this method focused on the nanometer length scale, the mesoscale manufacturing of samples has not seen such advances. It remains a challenge to manufacture sample geometries too large for focused ion beam milling yet too small for conventional machining. Femtosecond laser ablation opens this length scale of sample space and allows the fabrication of numerous useful geometries. This paper outlines a state-of-the-art femtosecond laser machining system that can be used for rapid, micro- and mesoscale sample preparation. To illustrate the utility of this system, stress–strain data are presented for single-crystal Cu micropillars and three microscale tensile test specimens prepared from physical-vapor-deposited Cu and Ni foils.

Effect of focused ion beam process parameter on Tin-Nickel-Copper micropillars microfabrication

ABSTRACTIn this work, the mechanism of focused ion beam (FIB) milling as an advanced manufacturing technique is studied to pattern micropillars at different diameter sizes of 5, 10 and 20 μm. Under the same type of ion source which is Ga ion, the main ion beam parameters that influenced the FIB machining to produce micropillars are the ion beam scanning, dose, profile, and incident angle. The mathematical modeling is presented to describe the micropillars’ production by crater sputtering of the FIB milling. The effect of sputtering and redeposition on the final geometrical micropillars suggest the arrangement of the multilayer sample (Sn/Ni/Cu) that close to the ion irradiation gets highly sputtered and redeposited despite the surface binding energy and sputtering yield, ϒ of each element is known. Results show that the highest aspect ratio values are derived from the lowest diameter size of the micropillars produced from the FIB machining.