Focused Ion Beam Machining Research Articles

Graphene-based crack lithography for high-throughput fabrication of terahertz metamaterials

Terahertz (THz) nanoantennas have significant potential for versatile applications in THz spectroscopy because of their capability for strong electromagnetic field localization. Electron-beam lithography or focused ion beam machining is typically employed to fabricate nanoantenna structures. These nanolithography methods present limitations in the widespread utilization of THz nanoantennas because of their high cost and low productivity. In this work, we proposed graphene-based crack lithography as a high throughput fabrication method for nanoantenna structures. A double-layer graphene interface was introduced to enable independent control of the nanoantenna dimensions and provide graphene-based nanoantenna structures. We analyzed the underlying mechanism of graphene-based cracking and developed an analytical model governing the geometric parameters of the fabricated nanostructures. As a vital application of the fabricated nanoantenna structures, we demonstrated the highly sensitive detection of d-Glucose molecules. Graphene-based crack lithography can provide a cost-effective method for generating nanoantenna structures with the desired characteristics and can accelerate the development of practical applications of electromagnetic metamaterials.

Computer-aided manufacturing and focused ion beam technology enable machining of complex micro- and nano-structures

We present a novel framework for the fabrication of geometrically complex structures at the micro- and nano-scale which relies on the synergy of integrated computer-aided design and manufacturing systems (CAD/CAM) and focused ion beam (FIB) technology in a scanning electron microscope. Here we utilise industry standard G-code syntax, for the first time, to FIB machining by designing geometries with CAD, defining machining strategies and exporting G-codes with CAM and generating a coordinate list-based beam path by using a custom-built interpreter program. This allows the fabrication of complex structures from CAD models using syntax which is readily understood in the general fabrication industry. The use of G-code allows optimization of the beam path towards a reduction of beam blanking operations and tracing of contours, leading to minimized re-deposition of material. We give a detailed description of the method, use an application example to demonstrate advantages and prospects of the approach and provide the free and open-source interpreter program CAM2FIB for application of this method. We contrast and compare various existing available milling strategies and demonstrate the versatility of G-code based programming.

Anomalous slip of ZrB2 ceramic grains during in-situ micropillar compression up to 500 °C

The anisotropic deformation behaviour of ZrB2 grains of basal and prismatic orientations in a polycrystalline ZrB2 sample was studied during in-situ micropillar compression at room temperature (RT), 350 °C and 500 °C. Micropillars were milled out of large grains by focused ion beam machining; the basal and prismatic orientations were previously identified using electron backscatter diffraction maps. The basal pillars showed brittle behaviour and cracking on the 101¯0 and 21¯1¯0 type prismatic planes that lead to their collapse. For this orientation, the yield/rupture stress ranged between 8 and 14 GPa and it exceeded 12 GPa even at 500 °C. In the prismatic orientation, considerable plasticity was observed, showing a temperature dependent yield stress from 6 to 8 GPa at room temperature to ~2GPa at 500 °C. The activated slip system family was identified as 101¯0112¯3 type for all of the test temperatures (RT, 350 °C and 500 °C). Analysis of the Schmid-factors revealed that the plasticity of the prismatic micropillars is controlled by the temperature dependence of the critical resolved shear stress of the 101¯0112¯3 slip systems. The brittleness of the basal micropillars was influenced by their defect structure (e.g. microcracks) and it was temperature independent due to the absence of slip activation.

Unconventional magneto-transport in ultrapure PdCoO2 and PtCoO2

The single-band, quasi-two dimensional metals PdCoO2 and PtCoO2 have recently come to prominence because of their extremely long mean free paths, which establish them as some of the most electronically pure materials known, and as potential hosts of previously unobservable regimes of electronic transport. To fully establish their magnetotransport properties, we have studied the magnetoresistance and Hall effect in bulk single crystals to which electrical contacts have been made with high precision using focused ion beam machining. We observe a strong temperature dependence of the Hall resistivity in small applied fields, linked to a large violation of Kohler’s rule in the magnetoresistance. We discuss the extent to which these observations can be accounted for by standard transport theory.

Study on diamond wire wear, surface quality, and subsurface damage during multi-wire slicing of c-plane sapphire wafer

This paper aims on slicing of c-plane mono-crystalline aluminum oxide using reciprocating electroplated diamond wire in rocking mode sawing process. Effect of process parameters and wire characteristics on the surface morphology, surface roughness, and subsurface damage had been investigated. The machined wafer topography, wire wear, and subsurface damage are observed using scanning confocal microscopy (CCI), electron microscopy (SEM), and focused ion beam machining (FIB) respectively. Raman spectroscopy is used to observe the distribution of amorphous regions as a measure of dominant material removal mode. Results show that with reduced diamond size, higher wire speed, and uniform grit distribution, the wafer exhibits lower surface roughness and subsurface damage. The effect of wire speed is more pronounced than abrasive size and distribution density on surface quality. The wafers have shown lower roughness and greater evidence of ductile removal with increased wire wear. However, subsurface cracks are more and slightly deeper for wafers with increased wire wear. The wire characteristics in the form of abrasive size and distribution have dominant effect on subsurface damage. Wire wear analysis has shown that the pulled out diamond abrasive from the nickel bonding layer is the main reason for wire wear. Higher wire speed, lower ingot feed rate, and lower diamond grits size are suggested for lower subsurface damage.

Testing Method for Determination of Microscopic Fracture Toughness for Rock Materials

Abstract The fracture behavior of rocks is known to depend on the microstructures of the rocks: the distribution and orientation of the microcracks, and the type, size, and shape of mineral grains. To explain quantitatively the effect of the microstructures on the fracture of rocks, the determination of the fracture toughness of grain and grain boundaries, namely, the microscopic fracture toughness (MFT), is necessary. The authors developed a testing method for determination of MFT for rock materials. A microsized specimen of a cantilever beam type with dimensions of 10 by 10 by 50 μm was used in this testing method, and we built a special testing machine for this specimen. Microsized specimens were made within grains of Iksan granite by Focused Ion Beam machining, and the MFT of its constituents—plagioclase, alkali feldspar, and quartz—was determined using this testing method at room temperature. The MFT varied widely and the results are discussed based on the mineralogical knowledge. This testing method will be helpful to more accurately interpret the fracture behavior.

전자 빔과 이온 빔 가공기술의 현황

Energy beam machining is a type of micro/nano-manufacturing technology for advanced materials. The energy beam is composed of the matter which exhibits not only particle but also wave-like behaviors. In this paper, we focused on the energy beam machining using the charged particles, which is classified into electron beam and ion beam machining. The equipment and principles of irradiation of electron beam and ion beam are investigated, and the range of technologies according to the energy beam characteristics is summarized. For the electron beam machining, recent studies for equipment development of surface heat treatment process and electron beam melting process using low-power electron beam are summarized. For the ion beam machining, recent studies on focused ion beam machining with various materials, such as high hardness materials, optical materials and semiconductor materials, are summarized. The studies for improving the accuracy and productivity of focused ion beam machining was is summarized. It was found that numerous technologies using the energy beam have been achieved for manufacturing of micro/nano-components with high precision. It is expected that the energy beam machining becomes a promising manufacturing technology for advanced materials.

Fracture of Silicon: Influence of rate, positioning accuracy, FIB machining, and elevated temperatures on toughness measured by pillar indentation splitting

The pillar indentation splitting test is a novel technique for assessing the fracture behavior of materials using micro-scale pillar samples. One typical limitation of this technique is the necessity of fabricating samples using focused ion beam (FIB) machining, which both creates damage to the samples and limits the number of samples which can be manufactured in a set timeframe. An alternative fabrication technique, lithography, is used here to fabricate a large number of (100)-oriented, Silicon micro-pillar samples. This allowed parametric studies of pillar splitting to be performed to study the influence of testing rate and positioning accuracy. Further, it allows the comparison of samples produced using different methods (lithography, Gallium FIB, and Xenon FIB) as a function of size. FIB damage was found to significantly increase the apparent toughness at smaller pillar sizes, but the influence diminishes to negligibility at pillar diameters > 10 μm. Lastly, the fracture behavior of Silicon was investigated as a function of temperatures up to 300 °C. Apparent toughness values began increasing at 175 °C due to crack blunting due to partial dislocation-mediated plasticity. At temperatures > 250 °C, the plasticity was sufficient to prevent splitting – requiring elastic-plastic fracture mechanics methods for further analysis.

Hydrogen-enhanced-plasticity mediated decohesion for hydrogen-induced intergranular and “quasi-cleavage” fracture of lath martensitic steels

Hydrogen embrittlement of lath martenistic steels is characterized by intergranular and “quasi-cleavage” transgranular fracture. Recent transmission electron microscopy (TEM) analyses (Nagao et al., 2012a, 2014a, 2014b, 2014c) of samples lifted from beneath fracture surfaces through focused ion beam machining (FIB) revealed a failure mechanism that can be termed hydrogen-enhanced-plasticity mediated decohesion. Fracture occurs by the synergistic action of the hydrogen-enhanced localized plasticity and decohesion. In particular, intergranular cracking takes place by dislocation pile-ups impinging on prior austenite grain boundaries and “quasi-cleavage” is the case when dislocation pile-ups impinge on block boundaries. These high-angle boundaries, which have already weakened by the presence of hydrogen, debond by the pile-up stresses. The micromechanical model of Novak et al. (2010) is used to quantitatively describe and predict the hydrogen-induced failure of these steels. The model predictions verify that introduction of nanosized (Ti,Mo)C precipitates in the steel microstructure enhances the resistance to hydrogen embrittlement. The results are used to discuss microstructural designs that are less susceptible to hydrogen-induced failure in systems with fixed hydrogen content (closed systems).

Micro-Machined Optical Fiber Side-Cantilevers for Acceleration Measurement

We propose an accelerometer based on a micro-cantilever fabricated onto the side of a single mode optical fiber using a combination of ps-laser machining and focused ion beam (FIB) processing. FIB machining is also used to fabricate a 45° mirror onto the end of the fiber that is accurately aligned with optical fiber core. This provides a reliable means to optically address components attached to the side of the fiber, such as the cantilever. Using interferometry to accurately monitor the deflection of the side cantilever results in a device that is capable of measuring two-axis acceleration. Acceleration up to 6 g is measured with a resolution of ~0.01 g and a frequency range from dc to 500 Hz has been demonstrated. The cross-axis sensitivity is below −32 dB.

Material interface detection based on secondary electron images for focused ion beam machining

A method for interface detection is proposed for focused ion beam (FIB) processes of multilayered targets. As multilayers have emerged as promising structures for nanodevices, the FIB machining of multilayers has become a challenging issue. We proposed material interface detection by monitoring secondary electron (SE) images captured during the FIB process. The average of the gray-levels and the skewness coefficient of gray-level histograms of the SE images were evaluated to recognize endpoints for the FIB processes. The FIB process control with the proposed method was demonstrated by fabricating the nanostructures on the multilayered target without thickness information. It was also demonstrated on a curved surface. Grooves with a desired depth into the target and an aperture as an opening window were precisely fabricated by the FIB process control. The proposed strategy of the FIB process can be used for complex substrates such as curved or flexible targets.

A method to improve the quality of 2.5 dimensional micro-and nano-structures produced by focused ion beam machining

The present work deals with a new technique to produce complex micro- and nano-scale patterns with high accuracy by FIB micro machining. The proposed method is related to the production of stream file, which is optimized through a software interface. A unique sampling approach is used to optimize the conversion from a 3D meshed CAD object to the focused ion beam (FIB) digital to analogue converter (DAC). The method uses a novel scan strategy, sensitive to the pattern local geometry and size, to define the optimal ion beam path, dwell time and the scanning pitch. This not only allows to minimize the redeposition but also to obtain accurate and scalable milling routines. In order to show the applicability of the method, a hemisphere and a pyramid shape are milled and compared to the shapes obtained using the conventional techniques. Results show that the method is very effective in producing complex shapes while overcoming the detrimental effect of conventional raster/serpentine FIB strategies, such as redeposition. Lastly, a fish-net structure with a pitch of ∼200nm as well as a series of truncated cones with sub-micrometrical details are realized to show the potential impact of this new method. Results show that a spatial resolution of less than 100nm is achievable with the help of this method.

Measuring notch toughness of thin film metallic glasses using focused ion beam-based microcantilever method: Comparison with Ti and TiN crystalline films

This study measured the notch toughness of Zr- and W-based thin film metallic glasses (TFMGs), and compared the results with those data obtained from crystalline Ti and TiN thin films as well as bulk metallic glass (BMG). Deflection testing was conducted using microcantilevers fabricated by focused ion beam machining. The resulting load vs. deflection curves revealed that Zr-based TFMG, BMG, and Ti films exhibited non-linear curves after yielding, which represented the ductile deformation characteristics. Higher notch toughness values of 3.84 and 5.13MPam for Zr- and W-based TFMGs, respectively, than TiN (2.15MPam) and Ti (0.74MPam) films were obtained. Thus, at micro-scales, metallic glasses present relatively better fracture behavior than do crystalline materials. This paper presents a direct comparison of works related to the notch toughness of amorphous and crystalline materials.

Cold Spray: Advanced Characterization Methods—Focused Ion Beam Machining and Electron Probe Microanalysis

Abstract Focused ion beam (FIB) systems are selectively used in cold spray coating characterization to gather information on the nature of splat formation, single splats, multiple splats, or the coating-substrate interface. Electron probe microanalysis has been used in cold-sprayed coating characterization primarily to understand the bonding mechanism at the coating-substrate interface.

Atomistic simulations of focused ion beam machining of strained silicon

The focused ion beam (FIB) technique has established itself as an indispensable tool in the material science community, both to analyze samples and to prepare specimens by FIB milling. In combination with digital image correlation (DIC), FIB milling can, furthermore, be used to evaluate intrinsic stresses by monitoring the strain release during milling. The irradiation damage introduced by such milling, however, results in a change in the stress/strain state and elastic properties of the material; changes in the strain state in turn affect the bonding strength, and are hence expected to implicitly influence irradiation damage formation and sputtering. To elucidate this complex interplay between strain, irradiation damage and sputtering, we perform TRIM calculations and molecular dynamics simulations on silicon irradiated by Ga+ ions, with slab and trench-like geometries, whilst simultaneously applying uniaxial tensile and compressive strains up to 4%. In addition we calculate the threshold displacement energy (TDE) and the surface binding energy (SBE) for various strain states. The sputter rate and amount of damage produced in the MD simulations show a clear influence of the strain state. The SBE shows no significant dependence on strain, but is strongly affected by surface reconstructions. The TDE shows a clear strain-dependence, which, however, cannot explain the influence of strain on the extent of the induced irradiation damage or the sputter rate.

Multi-sample loading technique for comparative physical property measurements in the diamond-anvil cell

ABSTRACT We present a method to perform improved measurements of the effects of chemical variability on physical properties of single-crystal samples in the diamond-anvil cell by employing a multi-sample approach. By customizing the sizes and shapes of the samples using a focused ion beam machine the simultaneous loading of relatively large crystals into a single sample chamber becomes feasible. To illustrate the potential of this approach, elastic properties of four single crystals of ringwoodite with different chemical compositions have been measured at high pressure. Our results suggest that the multi-sample approach allows for the quantification of small effects of chemical variations, such as iron and hydrogen incorporation, on physical properties. Furthermore, we discuss the possibility of using the multi-sample approach to load several crystals with different crystallographic orientations of the same material into one sample chamber in order to map out the direction dependence of anisotropic physical properties.

Micromechanical behavior of single-crystalline Cu6Sn5 by picoindentation

The micromechanical behavior of single-crystalline Cu6Sn5 is studied by micropillar compression in a picoindenter. The compound Cu6Sn5 is important because it is used as a structural material in microbumps of advanced electronic packages. Micropillars of Cu6Sn5 with known crystallographic orientations were fabricated by focused ion beam machining. Pillars with the c-axis perpendicular to the load direction tended to possess higher strain to failure and lower Young’s modulus. Measured Young’s modulus from micropillar compression was compared with results from nanoindentation measurements. The modulus values from micropillar compression were consistently smaller than those from nanoindentation measurements.

Nanopatterning on Nano-Polycrystalline Diamond and Cubic Boron Nitride Using Focused Ion Beam and Heat Treatment to Fabricate Textured Cutting Tools

Texturing on the surface of cutting tools is an effective method to improve the friction and resultant machining performances of the tool. In this study, to fabricate nanotextures on various tools used for precision cutting, a patterning method on nanopolycrystalline diamond and cubic boron nitride tools was investigated using focused ion beam (FIB) irradiation and heat treatment. Patterning was possible using this method, and the patterning characteristics were different from those of single-crystal diamond. This method was more suitable for cutting tools compared with direct FIB machining because of its high efficiency and significantly low affected layer.

Investigation of the deformation behavior of aluminum micropillars produced by focused ion beam machining using Ga and Xe ions

Sample geometries for micro-mechanical testing, e.g. micro-pillars and micro-cantilevers are primarily produced using gallium focused ion beam technology. However, the effects of the gallium ions on the mechanical properties of metals which are embrittled by liquid metal gallium are still unknown. In this work, micro-compression samples from single crystalline and ultrafine-grained aluminum are fabricated using both xenon and/or gallium ions. The different ions have little effect on the yield strength of single crystalline aluminum. However, for the ultrafine-grained aluminum, the strength is reduced with increasing Ga dose, and considerable differences in the deformation morphology and resulting microstructures are observed.

High-Temperature In situ Deformation of GaAs Micro-pillars: Lithography Versus FIB Machining

The plasticity of silicon-doped GaAs was investigated between 25°C and 400°C using microcompression to prevent premature failure by cracking. Micropillars with diameters of ~2.5 μm were fabricated on a $$\langle 100\rangle $$ -oriented GaAs single crystal by means of both conventional lithographic etching techniques and focused ion beam machining and then compressed in situ in the scanning electron microscope (SEM). A transition in deformation mechanisms from partial dislocations to perfect dislocations was found at around 100°C. At lower temperatures, the residual surface layer from lithographic processing was found to provide sufficient constraint to prevent crack opening, which resulted in a significant increase in ductility over FIB-machined pillars. Measured apparent activation energies were found to be significantly lower than previous bulk measurements, which is mostly attributed to the silicon dopant and to a lesser extent to the size effect.