Focused Ion Beam Machining Research Articles

Uniaxial compression of fcc Au nanopillars on an MgO substrate: The effects of prestraining and annealing

The size-dependent strength of face-centered cubic (fcc) metals, as revealed by uniaxial compression of nanopillars, suggests that plasticity is dislocation source-controlled, with fewer sources in smaller pillars producing a “smaller is stronger” effect. To further investigate this phenomenon we have studied the effects of prestraining and annealing on the deformation properties of [0 0 1] Au nanopillars. By making pillars from an epitaxial film of [0 0 1] Au on [0 0 1] MgO, using focused ion beam machining, we are able to create both puck-shaped pillars that can be stably prestrained and pillars with a high aspect ratio, which can be tested in uniaxial compression. We find that prestraining dramatically reduces the flow strength of nanopillars while annealing restores the strength to the pristine levels. These unusual effects are not seen in bulk fcc metals, which behave in the opposite way. We discuss their possible causes in terms of dislocation densities using transmission electron microscopy.

Development of a local vacuum system for focused ion beam machining

A local vacuum system for focused ion beam (FIB) processing, with a workpiece set in the air, has been developed. The local vacuum apparatus had a double-wall cylinder structure, used a differential exhaust, and each cylinder was connected to a vacuum exhaust pump. When the gap between the workpiece and the apparatus was 10 microm, the pressure of beam line in the machining head achieved 2.1 x 10(-3) Pa. In addition, a visualization system was developed by visualizing the current flow out from a sample by FIB irradiation. With this system, it is possible to conduct focus adjustments of the FIB and shape recognition on a workpiece in the order of microns.

Focused Ion Beam Fabrication of Boron-Doped Diamond Ultramicroelectrodes

The fabrication of ultramicroelectrodes (UMEs) for analytical electrochemical applications has been explored, using boron-doped diamond as the active electrode material in an insulating coating formed by deposition of electrophoretic paint. Because of the rough nature of the diamond film, the property of such coatings that is normally exploited in the fabrication of UMEs, namely the tendency to retract automatically from sharp protrusions, cannot be used in the present instance. Instead focused ion beam (FIB) sputtering was employed to controllably produce UMEs with well-defined geometry, critical dimension of a few micrometers, and very thin insulating coatings. If the FIB machining is carried out at normal incidence to the diamond electrode surface, significant ion beam damage reduces the yield of successful electrodes. However, if a parallel machining geometry is employed, high yields of ultramicroelectrodes with a flat disk geometry can be obtained very reliably. The electrochemical properties of diamond UMEs are characterized. They show much lower background currents than the equivalent Pt or carbon fiber electrodes but more varied electrochemical response than macroscopic diamond electrodes.

Micromechanical testing of stress corrosion cracking of individual grain boundaries

Grain boundaries of different misorientation and chemistry have differing susceptibilities to stress corrosion cracking but carrying out mechanical tests on individual grain boundaries of known character has until now been very difficult. We present a method for manufacturing specimens containing a single grain boundary (in 304 stainless steel) using focused ion beam machining. A nanoindenter/atomic force microscope was used to drive controlled grain boundary crack growth under load in an active solution. Scanning electron microscopy examination confirmed the growth of the crack along the grain boundary.

Transformation-induced plasticity during pseudoelastic deformation in Ni–Ti microcrystals

[1 1 0]-oriented microcrystals of solutionized 50.7 at.% Ni–Ti were prepared by focused ion beam machining and then tested in compression to investigate the stress-induced B2-to-B19′ transformation in the pseudoelastic regime. The compression results indicate a sharp onset of the transformation, consistent with little prior plasticity. Post-mortem scanning transmission electron microscopy reveals no apparent retained martensite but rather a macroscopic band of dislocation activity within which are planar arrays of ∼100 nm dislocation loops involving a single a〈0 1 0〉{1 0 1} slip system. Micromechanics analyses show that the angle of the band is consistent with activation of a favored martensite plate. Further, the stress from the individual variants within the plate is shown to favor activation of the observed slip system. The work done by the applied stress during the B2-to-B19′ transformation is estimated to be ∼34 MJ m −3 at ambient temperature.

Fabrication and validation of fused silica NIL templates incorporating different length scale features

A cost effective methodology for pattering of Nano Imprint Lithography (NIL) templates incorporating different length scale features is proposed. The approach relies on selecting the optimum processing window of different technologies for cost effective micro- and nano-patterning. Very promising results were obtained when first fused silica templates were structured by F2 laser ablation at 157 nm. It was demonstrated that nano-scale features and complex 3D micro-scale features could be machined with a Focused Ion Beam (FIB) over the existing topography produced by laser ablation. Thus, a large area (up to several square centimeters) of the NIL templates is easily patterned with micro- and even meso-scale features by laser ablation while nano- and micro-scale features could be introduced locally by FIB machining. Through S-FIL process such templates were validated and the nano- and micro-structures were accurately replicated in one imprinting step.

Microscale Fracture Testing of Mg-Zn-Y

AbstractA microfracture testing technique was applied for investigating the fracture properties of Mg-Zn-Y alloys with a long-period stacking ordered (LPSO) phase. Microsized cantilever beam specimens with dimensions ≈ 10×20×50 μm3 were prepared from Mg-Zn-Y alloys by focused ion beam (FIB) machining. Notches with widths of 0.5 μm and depths of 3.5–5 μm were also introduced into the specimens by FIB machining. In this study, three types of Mg-Zn-Y alloys―Mg99.2Zn0.2Y0.6, Mg97Zn1Y2, and Mg88Zn5Y7―were used. Fracture tests were successfully conducted using a mechanical testing machine for microsized specimens at room temperature. The fracture toughness values (KIC) could not be obtained as the specimen size was too small to satisfy the plane strain condition. Hence, provisional KQ values were considered. The KQ values of the Mg97Zn1Y2 alloy were 0.8–1.2 MPam½, and those of the Mg88Zn5Y7 alloy were 1.2–3.0 MPam½. As the fracture in the Mg99.2Zn0.2Y0.6 alloy specimen occurred in a ductile plastic deformation, it was impossible to evaluate KQ values of this specimen. The increasing volume fraction of the LPSO phase indicates that the fracture toughness of Mg-Zn-Y alloys increases in LPSO phase.

A31 Focused ion beam machining of silicon carbide(M4 processes and micro-manufacturing for science)

Focused ion beam can remove hard materials such as diamond, sapphire, and silicon carbide (SiC). SiC is very useful for glass molding because of high temperature toughness and high hardness, however, fine patterning of SiC is very difficult. Therefore, ion beam machining properties of SiC were investigated and 3D fabrication of SiC using dwell time machining method was also carried out. The machining properties, submicron patterns and 3D patterns of SiC were obtained.

Cleaving of solid single mode polymer optical fiber for strain sensor applications

Single mode polymer optical fibers (smPOFs) can be applied for measuring large strains in numerous applications, such as civil engineering infrastructure assessment and health monitoring. Because of the large light attenuation of solid smPOFs, small lengths of the fiber would need to be coupled to silica optical fibers (SOFs) for practical applications of the smPOF as a strain sensor. This coupling requires smooth cleaving of the smPOFs. In this work, several cleaving techniques previously demonstrated to provide smooth cross-sections of multimode POFs were applied to the smPOF. From these techniques, hot-knife cutting was determined to be a feasible method for cleaving when the blade was heated to 80°C and the smPOF heated in the range of 30°C to 40°C. In addition, focused ion beam machining which produces high-precision cleaves of the solid smPOF cross-section, was performed to set a bench mark and thus evaluate the quality of cleaving from other methods used in this study.

Fracture Toughness Test with a Sharp Notch Introduced by Focussed Ion Beam

The validity of fracture toughness data obtained from tests with V-notched bending bars is affected by the notch root radius and the presence of R-curve behavior. A macroscopic test specimen has been developed that contains a notch introduced by focused ion beam machining. This produces a notch root radius of less than 0.1 μm, so that notch effects can be ignored for most ceramics. Also, due to the very small notch depths the influence of a rising R-curve should be very close to that of natural cracks. First tests, carried out on a Ce-doped zirconia ceramic resulted in a toughness of KIc ≈ 5.9 MPa√m.

Long-life bismuth liquid metal ion source for focussed ion beam micromachining application

Liquid metal ion sources (LMISs) with Ga as ion species are widely used in focused ion beam (FIB) technology for micromachining and surface treatment on the sub-micron and nano-scale. Key features of a LMIS for investigating mechanical properties and 3D-microfabrication of materials are long life-time, high brightness, stable ion current and a highly effective milling ability for the material to be modified. In order to increase the material removal rate, heavier ions than Ga and their clusters should be applied. Bismuth (Bi) is the heaviest, non-radio-active element in the periodic table, is non-toxic and exhibits a low melting point. We have thus produced a long-life (about 1000 h) Bi LMIS with a good beam performance, applicable in any FIB system. Since Bi is the only element in this source, it is not necessary to separate it from other ions by a mass filter. Investigation of the sputtering rate of NiTi shape memory alloys using Ga and Bi LMIS showed that, for the same experimental conditions, the material removal rate with using of Bi n k+ ions in a standard FIB machine without a mass separator is about five times larger compared to Ga + ions. This use of Bi as LMIS-species is the ultimate breakthrough in sputtering applications.

Development of Focused Ion Beam Machining Systems for Fabricating Three-Dimensional Structures

We designed a focused ion beam (FIB) machining system for fabricating three-dimensional (3-D) micro- and nano-structures. The system used an automatic sample stage that can tilt up to 93°. By tilting the sample stage, a pattern of the bridge width from the top direction and bridge height from the lateral direction is possible for machining 3-D structures. The exact size of the structures is etched by scanning the sample images from the top and lateral views. These etching methods using the first in situ FIB micromachining system showed many advantages for fabricating 3-D structures including transistor configuration.

Resolution enhancing using cantilevered tip-on-aperture silicon probe in scanning near-field optical microscopy

Scanning near-field optical microscopy (SNOM) achieves a resolution beyond the diffraction limit of conventional optical microscopy systems by utilizing subwavelength aperture probe scanning. A problem associated with SNOM is that the light throughput decreases markedly as the aperture diameter decreases. Apertureless scanning near-field optical microscopes obtain a much better resolution by concentrating the light field near the tip apex. However, a far-field illumination by a focused laser beam generates a large background scattering signal. Both disadvantages are overcome using the tip-on-aperture (TOA) approach, as presented in previous works. In this study, a finite difference time domain analysis of the degree of electromagnetic field enhancement is performed to verify the efficiency of TOA probes. For plasmon enhancement, silver is deposited on commercially available cantilevered SNOM tips with 20 nm thicknesses. To form the aperture and TOA in the probes, electron beam-induced deposition and focused ion beam machining were applied at the end of the sharpened tip. The results show that cantilevered TOA probes were highly efficient for improvements of the resolution of optical and topological measurement of nanostructures.

Effect of sample size on deformation in amorphous metals

Uniaxial compression tests were performed on micron-sized columns of amorphous PdSi to investigate the effect of sample size on deformation behavior. Cylindrical columns with diameters between 8μm and 140nm were fabricated from sputtered amorphous Pd77Si23 films on Si substrates by focused ion beam machining and compression tests were performed with a nanoindenter outfitted with a flat diamond punch. The columns exhibited elastic behavior until they yielded by either shear band formation on a plane at 50° to the loading axis or by homogenous deformation. Shear band formation occurred only in columns with diameters larger than 400nm. The change in deformation mechanism from shear band formation to homogeneous deformation with decreasing column size is attributed to a required critical strained volume for shear band formation.

Characterization of the charging effect in a ZrO2 sintered body by Ga ion beam irradiation

The charging effect in a ZrO2 sintered body was investigated by using scanning ion microscope (SIM) images. In this study, we report interesting features caused by the charging effect in the ZrO2 sintered body during the Ga ion beam irradiation: a bright contrast with a distorted net shape appears around the positively charged specimen. From this feature in the SIM image, it is clarified that the Ga ion beam is strongly deflected and the wide area of the internal parts of the focused ion beam machine is irradiated by the Ga ion beam, depending on the extent to which the specimen is charged. We discuss the mechanism of the characteristic charging effect through observing SIM images by varying the intensity of the Ga ion beam.

Bridging the micronanomanufacturing gap

New facilities have been established at the Manufacturing Engineering Centre at Cardiff University to provide an open access service to UK industry known as 'MicroBridge'. This will provide its customers with a suite of equipment and facilities based on a focused ion beam machine, a picosecond laser ablation system and nano imprinting lithography. In this paper, we will outline the key requirements for micronanomanufacturing and show how MicroBridge will provide an essential provision for design engineers and manufacturers who wish to have a competitive advantage in the markets for micronanotechnology-based products and systems, estimated to be $1 trillion within the next decade. Examples will be given of microtooling that can be developed for manufacturing products made from a range of non-silicon materials.

パルス通電焼結法で作製されたＳＵＳ／ＷＣ表面硬化材料の微細領域における機械的性質の評価

In order to improve wear properties of austenite stainless steel, we applied powder composite process to obtain thick hard layer on stainless steel. The raw alloy powder was prepared by planetary ball milled tungsten carbide (WC) powder and SUS316L stainless steel powder. Sintering process was performed by pulsed current sintering (PCS) method. Wear properties were evaluated by pin-on-disk wear testing machine, and a remarkable improvement was confirmed in wear resistance property. In this investigation, we applied micro-sized testing technique to evaluate mechanical properties of WC layer and Stainless interface of layer. Micro-sized cantilever specimens with a size of 10×20×50μm3 were prepared by focused ion beam machining system. Micro-sized bending tests were successfully completed using a mechanical testing machine for micro-sized specimens. The maximum bending stresses were different for stainless matrix, interface layer, and SUS/WC composite. Ductile rapture surface was observed at stainless matrix, and brittle rapture surfaces at interface of WC layer and Stainless layer and SUS/WC composite layer.

Data preparation for focused ion beam machining of complex three-dimensional structures

The realization of complex three-dimensional structures at micro- and nanometre scale in various materials is of great importance for a number of micromechanical, microoptical, and microelectronic applications. Focused ion beam (FIB) patterning is one of the promising technologies for producing such three-dimensional structures utilizing layer-by-layer fabrication methods. A novel and efficient data preparation approach is proposed in this paper for layer-based FIB processing. By applying it, complex surfaces can be designed easily in any three-dimensional computer-aided design (CAD) package and then converted into GDSII streams for FIB sputtering or deposition. To validate the proposed CAD/CAM approach an experimental study was conducted. The factors that can affect the accuracy of the structures produced by layer-based FIB processing are also discussed. By assessing all stages of the proposed approach and the results of its experimental validation, conclusions are drawn about its applicability.

A guide on FIB preparation of samples containing stress corrosion crack tips for TEM and atom-probe analysis

The preparation of samples containing stress corrosion crack tips for 3D atom-probe tomography and transmission electron microscopy is of ultimate importance for understanding the mechanisms controlling crack propagation. In this paper, it will be shown that a focused ion beam machine equipped with an in situ micromanipulator is an ideal tool to systematically prepare such demanding samples. The methodology is described and discussed in detail, and several results are presented to demonstrate the potential of the technique.

Frequency tuning AFM optical levers using a slot

Presented here is a theoretical analysis and experimental validation for the passive frequency tuning of atomic force microscope (AFM) optical levers. The natural frequencies of the optical lever are a function of material, geometry, and elastic properties of the microstructure. In this regard, the geometry of the structure can be altered in post-fabrication using such methods as laser drilling or focused ion beam machining. Several slot sizes are investigated and the eigenvalues obtained are mapped as a function of the slot length and width. In this regard, the elastic property of the optical lever can be tuned through material removal in either a mass or stiffness reduction arrangement in which a particular slot size and configuration is machined into the optical lever structure. In this work a slot cut into the optical lever using focused ion beam machining is used to passively tune the natural frequencies and mode shapes of suspended microcantilever structures used for optical lever scanning such as in AFM probes. This analysis will contribute to the performance optimization of AFM probes and microresonators. The Rayleigh–Ritz energy method is used for the theoretical analysis and a non-contact optical test method is used to obtain the natural frequency of several slotted AFM optical levers.