Ion Milling Research Articles

Fabrication and Evaluation of Catalyst Layers in Polymer Electrolyte Fuel Cells: A Comparison of Decal and Inkjet Printing Techniques

In polymer electrolyte fuel cells (PEFCs), an enhancement of oxygen transport with excess water removal in membrane electrode assemblies can lead to better cell performance especially in high current density operation. Controlling porous structure in the catalyst layers is of great concern, satisfying these demands as well as achieving less precious catalyst loading and reduction of overpotential that are necessitated for automobile application of PEFCs. Depositing and engineering the catalyst layers have been gathering much attention intensively in these two decades [1-2]. Porous electrodes in PEFCs are generally fabricated by either coating or spraying the electrode slurry on substrate materials. Mixing, coating and drying processes of the slurry inherently affect the structural formation of the porous electrode and thus cell performance [3].In this study, we focused our attention on the inkjet printing technique as a versatile method to control catalyst layer structure. Catalyst layers (CL) with micro-grooves, which potentially provide liquid water channels in the electrodes, were fabricated by adjusting an electrode slurry injectable from a single capillary nozzle in a printing device (Fig.1). Catalyst layers made by a decal transfer technique were also prepared for comparison. The catalyst layers prepared by each method were controlled to gain the same amount of contents, i.e. platinum, ionomer and carbon, within 5% variation.Porous structure and cell polarization of each catalyst layer were examined. A two-stage ion-beam method using ion milling and focused ion beam (FIB) [4] was applied to analyze the spatial distribution of both ionomer and pore in the catalyst layers as shown in Fig.1. In this technique, a relatively wide cross-section of the CL was firstly formed by a broad ion beam and then, the ionomer impregnated in the CL was removed selectively by a focused ion beam. It was revealed that the electrode thickness was affected by fabrication methods, presumably due to mixing and coating processes. Cell performance shows its variation, depending on fabrication methods and this suggests an optimized electrode structure for further cell performance improvements. Acknowledgements This work was supported by JSPS KAKENHI Grant Number 18H01383.

Influence of Microstructure on Initial Corrosion Behavior of Steel Materials Using Kelvin Force Microscope

Improvement of the efficiency of power engines and reduction of the vehicles weight are important to boost the fuel efficiency of transportation equipment such as automobiles. One of the countermeasures is to expand the application of ultra-high tensile steel materials to structural members. However, the surface of ultra-high tensile steel becomes often non-uniform due to the metallographic control during manufacturing. Surface non-uniformities are more likely to lead to corrosion. Therefore, in order to further expand the application of ultra-high tensile steel materials, it is necessary to fully understand local corrosion behavior such as selective corrosion depending on the metal structure and grain boundaries. The purpose of this study is to research an influence of the non-uniformity of surface microstructure on corrosion of steel material, and the surface potential of each metallographic structures was measured by the Kelvin force microscope (KFM).Carbon steel (S45C) was heat-treated under conditions of holding it at 1250°C for 30 minutes and cooling in the furnace. After the sample surface was mirror-polished, the sample surface was smoothed by performing ion milling as a pretreatment for the KFM measurement. The KFM measurement was conducted for a predetermined range with 0.30 Hz of a scanning frequency, and the surface shape image was also measured in AFM mode. Furthermore, a corrosion test was conducted by immersion in a borate buffer containing 0.01 mol dm-3 NaCl for 1 hour, in order to clarify the relationship between the surface potential distribution obtained by KFM measurement and the initial corrosion behavior. After that, the sample surface was thoroughly washed with distilled water, dried, and KFM measurement was performed again.The surface morphology and the potential of the samples before the corrosion test changed periodically corresponding to the ferrite and cementite phases in pearlite. The potential of the cementite phase was about 10 mV lower than that of the ferrite phase. It was suggested that the interface between the cementite phase and the ferrite phase becomes an origin of corrosion, since the place showing the large potential difference is likely to be the starting point of corrosion. In comparing the surface morphology of the samples before and after the corrosion test, the width of the cementite phase was clearly narrower than that before the corrosion test. The surface potential of this part of the sample before the corrosion test showed more negative potential than the surroundings, which is considered that the shape change is attributed to the dissolution of the metal. Therefore, it was concluded that the potential distribution of the sample before the corrosion test is closely related to the corrosion behavior.

An optimized TEM specimen preparation method of quantum nanostructures

Electron transparent TEM lamella with unaltered microstructure and chemistry is the prerequisite for successful TEM explorations. Currently, TEM specimen preparation of quantum nanostructures, such as quantum dots (QDs), remains a challenge. In this work, we optimize the sample-preparation routine for achieving high-quality TEM specimens consisting of SrRuO3 (SRO) QDs grown on SrTiO3 (STO) substrates. We demonstrate that a combination of ion-beam-milling techniques can produce higher-quality specimens of quantum nanostructures compared to TEM specimens prepared by a combination of tripod polishing followed by Ar+ ion milling. In the proposed method, simultaneous imaging in a focused ion-beam device enables accurate positioning of the QD regions and assures the presence of dots in the thin lamella by cutting the sample inclined by 5° relative to the dots array. Furthermore, the preparation of TEM lamellae with several large electron-transparent regions that are separated by thicker walls effectively reduces the bending of the specimen and offers broad thin areas. The final use of a NanoMill efficiently removes the amorphous layer without introducing any additional damage.

Multiple Long Wavelength Infrared MOCVD Grown HgCdTe Photodetectors for High Temperature Conditions

This paper presents large area multiple photodetectors of the MOCVD grown HgCdTe heterostructures for operation at temperatures of (200-300)K in the long wavelength infrared range. Conventional long wavelength photovoltaic detectors operating at higher temperatures suffer from low dynamic resistance and multiple photodetectors idea solves this problem. Particular experimental steps are demonstrated starting from MOCVD technology, through etching, angled ion milling, angled contact metal deposition, assembly and electro-optical measurements. MOCVD technique with wide range of composition and donor/acceptor doping and without post growth annealing provides HgCdTe heterostructures for uncooled multiple detectors. CdTe buffer layer deposition allows HgCdTe heterostructure growth on GaAs substrates. Angled ion Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> milling optimal selection parameters is crucial for proper junction formation and conductivity type conversion. Theoretical modelling using APSYS platform supports designing of the detector's structures. Presented technology enable to fabricate large area (4 × 4mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) multiple photodetectors with detectivity D* exceeding 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 10.6 μm and room temperature operation useful for many applications.

Electrical characteristics, stability, electromigration, Joule heating, and reliability aspect of focused ion beam fabricated gold and copper nanobar interconnects on SiO2 and glass substrates

The electrical characteristics and stability of rectangular nanobar interconnects are investigated owing to their importance and reliability concern in electronic devices. One dimensional gold and copper nanobars (cross section 150–180 × 80–150 nm2 and length 3.0–5.0 μm), fabricated by milling of respective thin films with a 30 keV Ga+ ion probe (size 10–20 nm) at a current of ∼1 nA, are studied for their current bearing capacity and temperature profile caused by Joule heating. The temperature attained is shown to depend on the length with a maximum lying at the bar center. The electromigration of species (drift velocity for gold being ∼0.92 nm/s) forms void and induces breakage in the bar at a current density of ∼1011 A m−2. The phenomenon is governed by the bar length, prevailing temperature gradient, crystal defects, and grain boundaries. The thermo-migration process facilitates or impedes the electromigration effects depending upon the direction of the thermal gradient and electric field. The I–V characteristics of a gold bar with a gap of ∼44 nm under a vacuum of ∼10−6 mbar follow a classical Child–Langmuir V3/2 law in the voltage range of 10–45 V, but the copper electrodes with a large gap of ∼250 nm (created by ion milling) demonstrate V0.05-dependence up to 32 V, V1/2-law at 39–58 V, and Fowler–Nordheim emission [with an effective area of 1600 nm2 and a field enhancement factor of 8.1] above 66 V.

Different Deformation Behaviour Between Zirconia and Yttria Particles in Dispersion Strengthened Platinum-20% Rhodium Alloys

Platinum-20% rhodium strengthened by oxides of zirconium and yttrium were prepared by solidification of platinum-rhodium-(zirconium)-yttrium powder which had been internally oxidised. After forging, rolling and annealing, 1 mm plates were obtained. Then the plates were mechanically ground to 50–70 μm from rolling-normal direction, followed by argon ion milling until a hole appeared on the centre of the foil to obtain samples which were characterised by transmission electron microscopy (TEM), combined with thermodynamic analysis. The existence of spherical ZrO2 and Y2O3 particles was verified with platinum and rhodium present as pure metals at the same time. It was found that the deformation behaviour of ZrO2 and Y2O3 particles was quite different during processing, where the former basically maintain their spherical shape and were bonded tightly to matrix, while the latter were compressed along normal direction and form two cracks on both sides of Y2O3 particles along the rolling direction. The differences in hardness and interface bonding properties of these two types of particles are supposed to be the main causes of different deformation behaviour during hot forging and cold rolling.

Surface treatment and electron backscatter diffraction (EBSD) analysis of the body-centered cubic phase in Mg-Li based alloys processed by severe plastic deformation

Although electron backscatter diffraction (EBSD) analysis for Mg-Li based alloys is difficult to conduct, this technique is necessary to understand the properties of these alloys. Numerous studies have addressed the use of electron backscatter diffraction (EBSD) analysis as an effective technique for quantifying Mg-Li based alloys. However, a crystallographic orientation determination of β-Mg by EBSD has not been achieved thus far. In this study, to conduct EBSD analysis of the body-centered cubic (BCC) phase in Mg-Li based alloys with various applied equivalent strains prepared by severe plastic deformation, surface treatment techniques were established. By the use of both Ar+ ion milling and Ar+ ion etching under ultra-high vacuum conditions, the Kikuchi patterns of Mg-Li based alloys were detected. According to the results of the EBSD analysis, it was concluded that the structural evolution of BCC Mg-Li based alloys can be understood with this approach. From the results of the EBSD analysis, it is clarified that the high strength of this alloy is attributed to the combination of Hall–Petch relationship and Bailey–Hirsch relationship.

Fabrication of hybrid artificial spin ice arrays with periodic site-specific local magnetic fields

We describe the microfabrication and magnetic behavior of a composite/hybrid, two-dimensional, magnetostatically interacting array of nanomagnets of Fe and exchange-biased bilayer Fe/IrMn heterostructures. Such an interacting array of nanomagnets, forming an artificial spin ice lattice but with a hybrid structure, has not been demonstrated before. These devices are fabricated of epitaxially grown Fe/IrMn thin films by a two-stage electron beam lithography process involving metal mask transfer and controlled ion milling. Following the epitaxial deposition of Fe/IrMn bilayer films, the first step involves electron beam lithography fabrication of nanomagnet arrays, followed by selective removal of exchange-bias by etching away IrMn layer at specific nanomagnet elements by ion milling. The technique described provides a way to apply a site-specific magnetic field at the nanometer length scale, utilizing the phenomenon of exchange-bias, as demonstrated here for an array with local fields applied at twice the period of the artificial spin ice lattice. This technology can also be readily extended to different spintronic devices requiring spatial distribution of exchange-bias fields.

Sequential plan-view imaging of sub-surface structures in the transmission electron microscope

Transmission electron microscopy (TEM) is a central technique for the characterisation of materials at the atomic scale. However, it requires the sample to be thin enough to be electron transparent, imposing strict limitations when studying thick structures in plan-view. Here we present a method for sequential plan-view TEM that allows one to image complex structures at various depths. The approach consists of performing an iterative series of front-side ion milling followed by TEM imaging. We show it is possible to image how the sample properties vary with depth up to several microns below the surface, with no degradation of the sample and imaging conditions throughout the experiment. We apply this approach to 3D cavities in mesoporous GaN distributed Bragg reflectors, demonstrating the ability to characterise the morphology of the pores, local crystal features and chemical composition through the multilayer structure. The same workflow can be applied to a variety of complex micron-scale systems which are by nature too thick for standard TEM analysis, and can also be adapted for profiling samples in cross-section.

Mechanical strength problem of thin silicon wafers (120 and 140 [formula omitted]) cut with thinner diamond wires (Si kerf 120 → 100 [formula omitted]) for photovoltaic use

We compared the mechanical strength of as-sawn thin silicon wafers (120 and 140 μm) cut by thinner diamond wires (Si kerf 120 → 100 μm). The fracture strength was evaluated by applying uniaxial mechanical loads on the fresh- and worn-wire sides of the wafers. The loads were applied parallel and perpendicular to the direction of the wire saw marks. Under parallel loading, wafers from both the fresh- and worn-wire sides had approximately the same low fracture strength, whereas under perpendicular loading, wafers from the fresh-wire side had a larger strength distribution compared to that of wafers from the worn-wire side. Observation by laser microscope revealed deeper pits in the lower strength wafers compared to the higher strength wafers. Observation by ion milling and subsequent scanning electron microscope revealed several cracks below the deeper pits whereas few cracks appeared below the shallower pits. Since the cracks were thought to be the deciding factor in the wafer fracture, we conducted a fractographic study on the fractured surfaces from the perspective of crack propagation. We found that the mechanical strength of the wafers cut by thinner wires showed a larger strength distribution. Although this variation was probably caused by the motion of the thin wire during the sawing process, further study is required for confirmation.

An investigation on the adsorption capacity of carbon particle for the removal of Fe3+ ion from water

Carbon particle was prepared from Sugarcane Bagasse by using carbonization method. The surface morphology of carbon particle was characterized by SEM and EDX. The results from EDX showed that this adsorbent is not a pure carbon. The iodine number suggests that this is a good activated charcoal. The capacity of SB charcoal to remove Fe3+ ion from water by adsorption technique was studied by Langmuir and Freundlich adsorption isotherm. Adsorption isotherm testing suggest the formation of multilayer and having heterogeneous surface energy. The Fe3+ ion adsorption capacity of SB charcoal was moderately satisfactory. The degree of elimination of Fe3+ ion was found to be dependent on pH, adsorbent dosage, initial metal ion concentration and milling time of adsorbent. Result shows that the optimum pH is 8 for about 74.75% Fe3+ ion adsorption onto the SB charcoal for 130 minutes contact time.

Low damage lamella preparation of metallic materials by FIB processing with low acceleration voltage and a low incident angle Ar ion milling finish

Metallic materials are known to be very sensitive to Gallium (Ga) focused ion beam (FIB) processing. Crystal defects formed by FIB irradiation degrade the transmission electron microscope image quality, and it is difficult to distinguish original defects from FIB process-induced damage. A solution to this problem is the low acceleration voltage and low incident angle (LVLA) Argon ion milling, which can be incorporated as an extensional countermeasure for FIB damage removal and eventually for preparation of high-quality lamellae. The transmission electron microscope image quality of iron single crystal could be improved by removing crystal defects using the low acceleration voltage and low incident angle Argon ion milling finish. Lamella quality of the processing result was almost similar with that of the conventional electrolytic polishing. As a practical application of the process, low damage lamella of stainless cast steel could be prepared. Effectiveness of the FIB system equipped with the low acceleration voltage and low incident angle Argon ion milling function as a tool to make high-quality metallic material lamellae is illustrated.

Focused ion beam preparation of microbeams for in situ mechanical analysis of electroplated nanotwinned copper with probe type indenters

SummaryA site‐specific xenon plasma focused ion beam preparation technique for microcantilever samples (1–20 µm width and 1:10 aspect ratio) is presented. The novelty of the methodology is the use of a chunk lift‐out onto a clean silicon wafer to facilitate easy access of a low‐cost probe type indenter which provides bending force measurement. The lift‐out method allows sufficient room for the indenter and a line of sight for the electron beam to enable displacement measurement. An electroplated nanotwinned copper (NTC) was cut to a 3 × 3 × 25 µm microbeam and in situ mechanically tested using the developed technique. It demonstrated measured values of Youngs modulus of 78.7 ± 11 GPa and flow stress of 0.80 ± 0.05 GPa, which is within the ranges reported in the literature.Lay DescriptionIn this paper a site specific method is present for making particularly small mechanical tests samples, of the order of 100th the size of a human hair. These small samples can then be used to determine the mechanical properties of the bulk material. Copper with a nano twinned grain structure is used as a test medium.Ion milling was used to cut the sample to shape and a micro probe was used for mechanical testing. Ion milling can cut away very small volumes of material as it accelerates ions at the surface of the sample, atomically machining the sample. Micro probes are a cost‐effective small‐scale load measurement devices, however, they require a large area for accessing the sample. The indenter requirements are a problem when making you samples with ion milling as ion millers are best at making small cuts. Our aim was to design a cutting strategy which reduces the amount of cutting required while allowing samples to be fabricated anywhere on the sample.We used a chunk lift out technique to remove a piece of material which is then welded to a wafer of silicon this gives sufficient space around the sample for ion milling and testing. The additional space allowed easy access for the probe. A 3 × 3 × 10 µm micro cantilever beam was cut out from copper, this beam was then bent. The force from bending and distance bent was measured and converted into Youngs modulus which is a measure of flexibility. The modulus value measured was comparable to the values reported in other papers.

A machining of the tool edge shape by the Ar ion milling process

A machining of the tool edge shape by the Ar ion milling process

In-situ time resolved spectrographic measurement using an additively manufactured metallic micro-fluidic analysis platform.

IntroductionMicrofluidic reactionware allows small volumes of reagents to be utilized for highly controlled flow chemistry applications. By integrating these microreactors with onboard analytical systems, the devices change from passive ones to active ones, increasing their functionality and usefulness. A pressing application for these active microreactors is the monitoring of reaction progress and intermediaries with respect to time, shedding light on important information about these real-time synthetic processes.ObjectiveIn this multi-disciplinary study the objective was to utilise advanced digital fabrication to research metallic, active microreactors with integrated fibre optics for reaction progress monitoring of solvent based liquids, incompatible with previously researched polymer devices, in combination with on-board Ultraviolet-visible spectroscopy for real-time reaction monitoring.MethodA solid-state, metal-based additive manufactured system (Ultrasonic Additive Manufacturing) combined with focussed ion beam milling, that permitted the accurate embedment of delicate sensory elements directly at the point of need within aluminium layers, was researched as a method to create active, metallic, flow reactors with on-board sensing. This outcome was then used to characterise and correctly identify concentrations of UV-active water-soluble B-vitamin nicotinamide and fluorescein. A dilution series was formed from 0.01–1.75 mM; which was pumped through the research device and monitored using UV-vis spectroscopy.ResultsThe results uniquely showed the in-situ ion milling of ultrasonically embedded optical fibres resulted in a metallic microfluidic reaction and monitoring device capable of measuring solvent solutions from 18 μM to 18 mM of nicotinamide and fluorescein, in real time. This level of accuracy highlights that the researched device and methods are capable of real-time spectrographic analysis of a range of chemical reactions outside of those possible with polymer devices.

Gas cluster ion beam SEM for imaging of large tissue samples with 10 nm isotropic resolution

We demonstrate gas cluster ion beam scanning electron microscopy (SEM), in which wide-area ion milling is performed on a series of thick tissue sections. This three-dimensional electron microscopy technique acquires datasets with <10 nm isotropic resolution of each section, and these can then be stitched together to span the sectioned volume. Incorporating gas cluster ion beam SEM into existing single-beam and multibeam SEM workflows should be straightforward, increasing reliability while improving z resolution by a factor of three or more.

Au-Nanoparticle-Embedded Open-Ended Freestanding TiO2 Nanotube Arrays in Dye-Sensitized Solar Cells for Better Electron Generation and Electron Transport.

Freestanding TiO2 nanotube arrays (TNTAs) were prepared by an electrochemical method, and dye-sensitized solar cells (DSSCs) were fabricated with the open-ended freestanding TNTAs incorporated with Au nanoparticles (NPs). Open-ended freestanding TNTAs were prepared by etching the barrier layer of closed-ended freestanding TNTAs using an ion milling method, and Au NPs were incorporated into the channel of the open-ended freestanding TNTAs by an electrodeposition method. The Au-NP-embedded open-ended freestanding TNTAs were applied to DSSCs to improve the energy conversion efficiency (ECE) by better electron generation and electron transport. The ECE of DSSCs based on the closed-ended freestanding TNTAs with Au NPs increased to 6.116% from 5.502% for DSSCs based on the closed-ended freestanding TNTAs without Au NPs, an enhancement of 11.16% because of better electron generation by the plasmonic and charging effects of the Au NPs. However, the ECE of DSSCs based on the closed-ended freestanding TNTAs incorporated with Au NPs for 40 s decreased from 6.116 to 5.336% because aggregation of the Au NPs led to a decrease in the open-circuit voltage (Voc) and fill factor. For enhanced ECE of DSSCs, the barrier layer of closed-ended freestanding TNTAs was etched by an ion milling method for 0, 30, 60, or 90 min to provide “open-ended freestanding TNTAs”. Then, Au NPs were incorporated into the open-ended freestanding TNTAs. After the barrier layer was completely removed by the ion milling method for 90 min, the ECE of the DSSCs reached 7.120% because the electron transport and electrolyte diffusion were improved by the elimination of the barrier layer of the freestanding TNTAs.

Controlled Focused Ion Beam Milling of Composite Solid State Nanopore Arrays for Molecule Sensing.

Various nanoscale fabrication techniques are elaborated to form artificial nanoporous/nanochannel membranes to be applied for biosensing: one of the most prevalent is the micro-electromechanical systems (MEMS) compatible focused ion beam (FIB) milling. This technique can be easily adopted in micro- and nanomachining process sequences to develop composite multi-pore structures, although its precision and reproducibility are key points in the case of these thick multi-layered membranes. This work is to demonstrate a comprehensive characterisation of FIB milling to improve the reliability of the fabrication of solid state nanopore arrays with precisely predetermined pore geometries for a targeted molecule type to be recognised. The statistical geometric features of the fabricated nanopores were recorded as the function of the process parameters, and the resulting geometries were analysed in detail by high resolution scanning electron microscope (SEM), transmission electron microscope (TEM) and ion scanning microscopy. Continuous function of the pore diameter evolution rate was derived from the experimental results in the case of different material structures, and compared to former dissentient estimations. The additional metal layer was deposited onto the backside of the membrane and grounded during the ion milling to prevent the electrical charging of dielectric layers. The study proved that the conformity of the pore geometry and the reliability of their fabrication could be improved significantly. The applicability of the developed nanopore arrays for molecule detection was also considered by characterising the pore diameter dependent sensitivity of the membrane impedance modulation based measurement method.

Post-FIB Cleaning of TEM Specimens from 14 nm and Other FinFETs by Concentrated Argon Ion Milling

Abstract TEM specimens prepared using a Ga FIB are susceptible to artifacts, such as surface amorphization and ion-implanted layers, that can be problematic in advanced technology nodes, particularly for FinFETs. As this article shows, however, post-FIB cleaning via concentrated argon ion milling makes for a fast and effective specimen preparation process for FinFET devices controlled to a thickness of less than 20 nm. Although the results presented here are based on 14 nm node FinFETs, the method is also applicable to the 10 and 7 nm FinFET technologies currently in production.

Double-Gap Magnetic Flux Concentrator Design for High-Sensitivity Magnetic Tunnel Junction Sensors.

To improve the sensitivity of the magnetic tunnel junction(MTJ)sensor, a novel architecture for a double-gap magnetic flux concentrator (MFC) was studied theoretically and experimentally in this paper. The three-dimensional finite element model of magnetic flux was established to optimize the magnetic field amplification factor, with different gaps. The simulation results indicate that the sensitivity of an MTJ sensor with a double-gap MFC can be significantly better than that of a sensor with a traditional single-gap MFC, due to the fact that the magnetic magnification sharply increases with the decrease in effective gap width. Besides this, the half-bridge MTJ sensors with the double-gap MFC were fabricated using photolithography, ion milling, evaporation, and electroplating processes. Experimental results show that the sensitivity of the MTJ sensor increased by ten times compared to the sensor without the double-gap MFC, which underlines the theoretical predictions. Furthermore, there is no significant increase in the sensor noise. The work in this paper contributes to the development of high-performance MTJ sensors.