Focused Ion Beam Micromachining Research Articles

Solvent-free microfabrication of thin film device using the focused ion beam

We introduce a novel fabrication technique for thin film devices, utilizing Focused Ion Beam micro-machining. Unlike conventional methods requiring post processes such as etching or solvent treatment, this method involves creating a pre-patterning step-like structure on the substrate before growing the thin film, achieving the desired device pattern right after thin film deposition. As an example, we fabricated devices with VO2 thin film of which electrical transport properties are examined. The VO2 devices exhibit robust metal-insulator transition behavior and V-I characteristics, indicating the high quality of the patterned devices. The results indicate that our approach enables intricate patterning, comparable to conventional e-beam lithography, without the risk of sample degradation. The simplicity, stability, and versatility of this technique suggest new possibilities for thin film device fabrication.

Temperature effects on electrospray current from an externally wetted EMI-Im ionic liquid ion source

Ionic liquid ion sources are expected to be used in a wide range of applications such as space electric propulsion and focused ion beam micromachining. It is known that the backstreaming of secondary charged species generated by ion beam impacts can cause unexpected temperature rise and chemical changes in ionic liquids. This paper reports on results of heating experiments using a sharp needle emitter wetted with an ionic liquid, 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)amide, at temperatures in a range from room temperature to 120 °C. Current measurements show that positive and negative electrospray currents from the heated emitter increased as the temperature increased. Time-of-flight (TOF) mass spectrometric measurements reveal that the beam composition changed significantly with increasing temperature, indicating that charged droplets as well as ions were emitted from the heated emitter. The TOF data show that a significant fraction of the current is due to droplets at higher temperatures. On the basis of the results obtained, the size and charge of the emitted droplets are discussed. The beam is roughly estimated to contain charged droplets with a diameter of around 20 nm at 120 °C.

Interaction Study of Anti‐E. coli Immobilization on 1DZnO at Nanoscale for Optical Biosensing Application

AbstractDeveloping low‐cost biosensing platforms for robust detection response and sensitivity at low concentrations is of great interest. This work reports synthesizing 1D ZnO nanostructured materials (1DZnO) with controllable properties utilizing a metal catalyst‐assisted vapor phase growth technique (VLS). The obtained materials are functionalized with (3‐aminopropyl) trimetoxysilane (APTMS) and immobilized with anti‐Escherichia coli enteropathogenic (EPEC) antibodies. Characterization results show changes in the optical and structural properties of 1DZnO that are correlated with the biofunctionalization methodologies. Further, the biofunctionalization process is assessed on 1DZnO surface platforms to obtain acceptable antibody immobilization efficiencies (52%, 96%, and 100%) using a low‐concentration antibody solution (30 µg ml−1). Special techniques such as focused ion beam micromachining and scanning tunneling electron microscopy are proposed to appreciate the semiconductor biofunctionalization layer around 1DZnO and explain the physics of the interaction process. It is found that morphology obtained from distinct synthesis methods, solvents, and functionalization agents can generate functional groups for biomolecule attachment. Remarkably, it is demonstrated that biofunctionalization on 1DZnO takes place all over a single nanostructure. This work presents a proof‐of‐concept focused on generating pathogen sensing platforms using 1DznO semiconducting materials, providing new insights into bio‐analytes interaction with structures at the nanoscale.

Microbiology: And Amoebophilus Invented the Machine Gun!

Bacterial contractile injection systems are fascinating particles that usea spring-like mechanism to inject an effector-loaded needle into target cells. A recent study shows that the intracellular bacterium Amoebophilus asiaticus uses arrays of contractile structures to escape from the amoeba phagosome.

Fiber Optic Fabry–Perot Optofluidic Sensor With a Focused Ion Beam Ablated Microslot For Fast Refractive Index and Magnetic Field Measurement

A compact fiber-optic Fabry–Perot interferometric sensor with an embedded microfluidic channel for static magnetic field measurement is proposed and implemented. Fabrication of the Fabry–Perot structure involved cascading two silica capillary tubes with different inner diameters, followed by milling of a microslot directly on the sidewall of the large inner diameter silica capillary tube, by focused ion beam micromachining. The microslot, together with the hollow structure of the small inner diameter silica capillary tubes forms an open Fabry–Perot cavity to function as a microfluidic channel. The microslot was found to improve the response time of the Fabry–Perot sensor to changes in refractive index (RI) of the cavity. Magnetic fluid was introduced in the Fabry–Perot cavity, thereby, enabling implementation of an optofluidics system for magnetic field measurement. The sensing scheme is based on the magnetic field strength induced RI change of the magnetic fluid which in turn modulates the interference spectrum of the sensor. Wavelength shifts were monitored real time for the continuous measurement of magnetic field strength. The sensor calibration curves with respect to magnetic field were plotted and the sensor exhibits a relative high magnetic field sensitivity of ∼418.7 pm/Oe relative to the dip wavelength around 1590 nm.

Visualizing the Molecular Socialogy at the HeLa Nucleus in Situ

Cellular functions arise from an intricate network of macromolecular interactions. Hence it is of fundamental importance to be able to decipher the ‘molecular sociology’ of cells, ideally by direct visualization - the goal of visual proteomics. Traditional electron microscopy has established cellular ultrastructure as we know it, but falls short of revealing the molecular landscape of cells. Cryo-electron tomography (ET) provides three-dimensional images of unperturbed cellular environments at increasingly higher resolutions. Hitherto there were a number of limitations which can now be overcome: Only peripheral thin regions of cells were accessible but thicker regions including nuclear volumes, remained inaccessible; their thickness rendered them non transparent. Focused ion beam micromachining (FIB) changed this and virtually opened ‘windows’ into frozen-hydrated cells. Direct detectors improve the quality of the tomograms substantially and the recently developed Volta phase plate improves (phase) contrast especially for lower spatial frequencies without the need of defocusing. In-focus phase contrast avoids the need of correcting for the contrast transfer function and renders the tomograms directly interpretable. Here we demonstrate that these developments can be used in a synergistic manner to produce 3D images of HeLa cells in situ of unprecedented quality, allowing for direct visualization of macromolecular complexes and their spatial coordination in unperturbed eukaryotic cellular environments.

Realization of a diamond based high density multi electrode array by means of Deep Ion Beam Lithography

In the present work we report about a parallel-processing ion beam fabrication technique whereby high-density sub-superficial graphitic microstructures can be created in diamond. Ion beam implantation is an effective tool for the structural modification of diamond: in particular ion-damaged diamond can be converted into graphite, therefore obtaining an electrically conductive phase embedded in an optically transparent and highly insulating matrix.The proposed fabrication process consists in the combination of Deep Ion Beam Lithography (DIBL) and Focused Ion Beam (FIB) milling. FIB micromachining is employed to define micro-apertures in the contact masks consisting of thin (<10μm) deposited metal layers through which ions are implanted in the sample. A prototypical single-cell biosensor was realized with the above described technique. The biosensor has 16 independent electrodes converging inside a circular area of 20μm diameter (typical neuroendocrine cells size) for the simultaneous recording of amperometric signals.

Efficient and flexible Focused Ion Beam micromachining of Solid Immersion Lenses in various bulk semiconductor materials – An adaptive calibration algorithm

Focused Ion Beam (FIB) micromachining of Solid Immersion Lenses (SILs) in substrate material offers optical analysis solutions for current and future technologies without the limitations of external SIL systems. This work presents an efficient single iteration calibration algorithm. This algorithm enables the implementation of FIB created SILs using a variety of substrate materials, process chemistries and most importantly different SIL shapes to match sample thicknesses. The successful application on silicon and silicon carbide is presented by creating a 50μm wide refractive lens segment with a radius of curvature of 60μm. Laser scanning microscope images of a silicon sample demonstrate the optical benefit with a measured resolution of 274nm.

Ultra-high-strain-rate shearing and deformation twinning in nanocrystalline aluminum

Nanocrystalline aluminum films with grain sizes of 50–100 nm were made through E-beam evaporation. The films were then subjected to high-rate shearing deformations with strain rates of 105–106 s−1, with local shear stresses of the order of 10 GPa. The experimental configuration is that of a compression–torsion Kolsky bar, where the specimen is a thin film (thickness 200 nm) mounted on a silicon wafer ring. Strain rates during the shearing are determined from the measured torsional waves in the bars. Site-specific TEM samples are prepared using focused ion beam micromachining to investigate the regions of large plastic deformation. Deformation twins and stacking faults are found to develop under the high-strain-rate shearing. The formation of twinning in pure aluminum with comparatively large grain sizes and the high-strain-rate promotion of twinning are discussed, and possible mechanisms are considered.

Sample preparation by focused ion beam micromachining for transmission electron microscopy imaging in front-view

This article deals with the development of an original sample preparation method for transmission electron microscopy (TEM) using focused ion beam (FIB) micromachining. The described method rests on the use of a removable protective shield to prevent the damaging of the sample surface during the FIB lamellae micromachining. It enables the production of thin TEM specimens that are suitable for plan view TEM imaging and analysis of the sample surface, without the deposition of a capping layer. This method is applied to an indented silicon carbide sample for which TEM analyses are presented to illustrate the potentiality of this sample preparation method.

Facile fabrication of ZnO nanowire-based UV sensors by focused ion beam micromachining and thermal oxidation

ZnO nanowire UV sensors were fabricated by using focused ion beam micromachining and thermal oxidation of metallic zinc microstructures. A metallic zinc “micro-strip” was first deposited by thermal evaporation with the aid of a shadow mask on SiO2/Si substrate. A 3-μm wide “trench” was cut across the metallic strip by focused ion beam; the subsequent thermal oxidation at 450°C results in the growth of single crystalline [110] ZnO nanowires across the trench. The ZnO nanowire sensor was completed by patterning silver ohmic contacts on the two ends of the metallic strip. Our photoluminescence (PL) spectroscopic studies show that the room temperature emission of the ZnO nanowire is due to the recombination of free exciton and free to bound transition, while at 10K, the PL is dominated by the recombination of surface excitons. Irradiated at 300nm, the rise time, decay time and normalized photoconductive gain of the ZnO sensor were determined to be 200ms, 400ms and 3×10−6m2V−1, respectively. The fast sensor response is due to the high crystalline quality of the nanowire, which facilitates a rapid equilibrium of absorption and desorption of molecular oxygen on the surface.

Application of Focused Ion Beam Micromachining: A Review

Fabrication of micro and nanoscale components are in high demand for various applications in diversified fields that include automotive, electronics, communication and medicine. Focused ion beam (FIB) machining is one of the techniques for microfabrication of micro devices. This paper presents a review of FIB machining technology that include its parameter, responses, its important component systems, as well as the fundamentals of imaging, milling (etching) and deposition techniques. The application of FIB in micromachining is also presented.

Three‐dimensional nanofabrication of polystyrene by focused ion beam

Focused ion beam micromachining provides a maskless and resistless technique for prototyping of structures from thermoplastic polymers, an example being the production of polystyrene microcantilevers with potential applications as micro/nanoelectromechanical systems sensors and actuators. The applicability of FIB technology is, however, often restricted by the damage created by high energy gallium ion bombardment and local beam heating, which can affect the desired properties and limit the minimum achievable size of the fabricated structure. To investigate the ion-induced damage and determine the limitations of the technique for polymer nanofabrication, we have exposed thin polystyrene film to the ion beam at varying ion doses, ion energies and specimen temperatures. Ion doses ranging from 10(16) to 10(18) ions cm(-2) show significant gallium implantation, redeposition of sputtered material and chemical degradation in the polymer. Raman results show that the local heating in polymer during milling is severe at room temperature, damaging the aromatic carbon bonding (C = C) in particular. These observations are supported by the results of a beam heating model and Monte Carlo simulations. The chemical degradation caused by local beam heating is found to be significantly reduced by cooling the specimen to -25°C during milling. This is consistent with observations that reversible and repeatable thermal actuation of a fabricated polystyrene-platinum microcantilever is only observed when the cantilever is prepared at low temperature milling. Using this cooling approach, polymer structures can be fabricated with dimensions as low as 200 nm and still retain a sufficient volume of material unaffected by the ion beam.

Direct observation of sintering mechanics of a single grain boundary

A method to analyze the mechanics of sintering of a single grain boundary was developed by using specimens fabricated by focused ion beam micro-machining. The translational motion and rotation of particles in sintering are influenced by the grain boundary diffusion coefficient and grain boundary energy; both are dependent on crystallographic orientation. Three-dimensional computer simulation was used to analyze the shrinkage and rotation as a response to sintering force and torque, respectively. The model experiments on gold were compared with the simulation results to determine the depth of the cusps on the plot of grain boundary energy vs. misorientation angle, the grain boundary diffusion coefficients, and the surface diffusion coefficient.

Micron-scale polymer–metal cantilever actuators fabricated by focused ion beam

Polymer–metal microcantilever actuators have been fabricated using an innovative approach based on focused ion beam micromachining technology. The fabrication involves depositing a thin metal film onto the surface of the polymer and machining using the ion beam. The microcantilever created is then extracted and transferred to a desirable support using a micromanipulator. This approach demonstrates the potential for maskless and resistless prototyping of cantilevers that can be evaluated for use as MEMS/NEMS actuators. Nanometer-scale displacement of the resulting polystyrene–platinum bimorph microactuator with respect to temperature change is demonstrated via visual monitoring in a scanning electron microscope with a heating stage. The performance of the bimorph cantilever microactuators is verified using both analytical and finite element modeling.

Uniform tensile elongation in framed submicron metallic glass specimen in the limit of suppressed shear banding

Metallic glasses (MGs) normally plastically deform via severe strain localization in the form of shear banding at room temperature. Here we show that, in the event of much delayed shear banding, submicron-scale MG specimens can elongate homogeneously in tension to a uniform plastic strain as large as 12% before failure, plus an estimated elastic strain of ∼5%, at a temperature close to room temperature (below 70 °C). This high deformability of MGs well below the glass transition temperature, revealed in situ using tensile testing inside a transmission electron microscope and specimens prepared via focused ion beam micromachining, is attributed to the suppression of shear banding instability due to the nanoscale samples together with a sample frame design that imparts high effective machine stiffness and confinement. We also point out that the pronounced “homogeneous” deformation reported here is a form of non-localized deformation that is different from the homogeneous viscous flow for superplastic forming at high temperatures (in the supercooled liquid state), and from the intrinsic tensile ductility (stable uniform elongation) resulting from inherent strain hardening and strain-rate hardening mechanisms in free-standing conventional crystalline metals under uniaxial tension.

Investigation of Microholes Produced by Focused Ion Beam Micromachining

This paper discusses the microfabrication of microholes using focused ion beam and investigation of geometrical integrity of microholes. Different combination of aperture size, probe current, acceleration voltage was applied for micromachining and optimized based on taper angle. Microholes with 3.0 μm of diameter were milled according to the optimized parameter using bitmap mode. The depth range of microholes was 1.0-5.5 μm. The hole’s depth and taper angle were investigated for characterization. Each of the microholes was cross sectioned for investigation. A relationship of taper angle (θ), depth and aspect ratio were plotted. Low aspect ratio (less than 1) would give the lower taper angle and hence better integrity. Acceleration voltage of 25 kV, probe current of 41.5 pA and aperture size of 4 nm produced lower taper angle for different aspect ratio.

Focused Ion Beam Fabricated Polystyrene-Platinum Thermal Microactuator

Individually released polystyrene-platinum bimorph microcantilevers that have potential applications as MEMS/NEMS thermal actuators are produced using focused ion beam micromachining technique. The microcantilevers are sharply defined and triangular in cross-section, and are about 20µm long, 2 µm wide and 1.5 µm thick. The fabrication process is fast (&lt; 3 hours) and does not require any mask or resist. The nanometer-scale displacement of the resulting bimorph microactuator with respect to temperature change is recorded via imaging in a scanning electron microscope, equipped with a heating stage. By increasing the temperature to ca. 55 °C, a tip deflection of ca. 380 nm was measured. This result is compared with the numerical result obtained from a finite element analysis (FEA).

Microfiber-probe-based ultrasmall interferometric sensor

We report an ultrasmall microfiber-probe-based reflective interferometer for highly sensitive liquid refractive index measurement. It has a 3.5 microm micronotch cavity fabricated by focused ion beam micromachining. A sensitivity of 110 nm/RIU (refractive index unit) in liquid is achieved with over 20 dB extinction ratio. Theoretical analysis shows this kind of device is a hybrid of Fabry-Perot and modal interferometers. In comparison with normal fiber interferometers, this probe sensor is very compact, stable, and cheap, offering great potentials for detecting inside sub-wavelength bubbles, droplets, or biocells.

Quantitative measurements of small scaled grain sliding in ultra-fine grained Al–Zn alloys produced by friction stir processing

An Al-15 wt.% Zn alloy was processed by friction stir processing to produce grain sizes of ~ 0.5 μm, ~ 1 μm, and ~ 2 μm. A simple and effective method was developed to determine the true strain by scribing marker lines with scaled division using focused ion beam micromachining prior to deformation. The “microscopic” grain boundary sliding, with displacements of adjacent grains of the order of a nanometer, can easily be detected by the proposed technique, providing a surface analysis with high accuracy that could be used to observe the changes in relief with increasing strains. Moreover, the occurrence of grain boundary sliding at room temperature was considered a major cause for higher strain rate sensitivity in fine-grained Al–Zn alloys.