Focused Ion Beam Instrument Research Articles

Ion beam heating of kinetically constrained nanomaterials

The gallium ion beam heating on electron transparent transmission electron microscopy (TEM) samples of Au/Ni bilayer films supported by SiO2 substrates was studied by in-situ TEM combined with energy dispersive X-ray spectroscopy. Brief Ga+ ion beam irradiation during sample transfer inside the focused ion beam instrument was found to induce dewetting of bilayer films. The observed morphological changes of the metal films are complemented by considerable Au diffusion through the underlying polycrystalline Ni film and adsorption at the Ni/substrate interface. In-situ heating experiments confirm that alterations of the metal bilayer films caused by ion beam irradiation are consistent with thermal annealing at 400 °C for several minutes in the absence of any ion bombardment. Ion beam damage effects equivalent to prolonged heating may pose considerable limitations to ion beam microscopy of samples with reduced dimensions. Ex-situ lift-out procedures of electron transparent samples in the absence of any ion beam irradiation lead to successful conservation of sample morphologies.

Cavity-enhanced photoionization of an ultracold rubidium beam for application in focused ion beams

A two-step photoionization strategy of an ultracold rubidium beam for application in a focused ion beam instrument is analyzed and implemented. In this strategy the atomic beam is partly selected with an aperture after which the transmitted atoms are ionized in the overlap of a tightly cylindrically focused excitation laser beam and an ionization laser beam whose power is enhanced in a build-up cavity. The advantage of this strategy, as compared to without the use of a build-up cavity, is that higher ionization degrees can be reached at higher currents. Optical Bloch equations including the photoionization process are used to calculate what ionization degree and ionization position distribution can be reached. Furthermore, the ionization strategy is tested on an ultracold beam of $^{85}$Rb atoms. The beam current is measured as a function of the excitation and ionization laser beam intensity and the selection aperture size. Although details are different, the global trends of the measurements agree well with the calculation. With a selection aperture diameter of 52 $\mu$m, a current of $\left(170\pm4\right)$ pA is measured, which according to calculations is 63% of the current equivalent of the transmitted atomic flux. Taking into account the ionization degree the ion beam peak reduced brightness is estimated at $1\times10^7$ A/(m$^2\,$sr$\,$eV).

A Comprehensive Approach Towards Optimizing the Xenon Plasma Focused Ion Beam Instrument for Semiconductor Failure Analysis Applications

The xenon plasma focused ion beam instrument (PFIB), holds significant promise in expanding the applications of focused ion beams in new technology thrust areas. In this paper, we have explored the operational characteristics of a Tescan FERA3 XMH PFIB instrument with the aim of meeting current and future challenges in the semiconductor industry. A two part approach, with the first part aimed at optimizing the ion column and the second optimizing specimen preparation, has been undertaken. Detailed studies characterizing the ion column, optimizing for high-current/high mill rate activities, have been described to support a better understanding of the PFIB. In addition, a novel single-crystal sacrificial mask method has been developed and implemented for use in the PFIB. Using this combined approach, we have achieved high-quality images with minimal artifacts, while retaining the shorter throughput times of the PFIB. Although the work presented in this paper has been performed on a specific instrument, the authors hope that these studies will provide general insight to direct further improvement of PFIB design and applications.

Nanofluidic Devices with 8 Pores in Series for Real-Time, Resistive-Pulse Analysis of Hepatitis B Virus Capsid Assembly.

To improve the precision of resistive-pulse measurements, we have used a focused ion beam instrument to mill nanofluidic devices with 2, 4, and 8 pores in series and compared their performance. The in-plane design facilitates the fabrication of multiple pores in series which, in turn, permits averaging of the series of pulses generated from each translocation event. The standard deviations (σ) of the pulse amplitude distributions decrease by 2.7-fold when the average amplitudes of eight pulses are compared to the amplitudes of single pulses. Similarly, standard deviations of the pore-to-pore time distributions decrease by 3.2-fold when the averages of the seven measurements from 8-pore devices are contrasted to single measurements from 2-pore devices. With signal averaging, the inherent uncertainty in the measurements decreases; consequently, the resolution (mean/σ) improves by a factor equal to the square root of the number of measurements. We took advantage of the improved size resolution of the 8-pore devices to analyze in real time the assembly of Hepatitis B Virus (HBV) capsids below the pseudocritical concentration. We observe that abundances of assembly intermediates change over time. During the first hour of the reaction, the abundance of smaller intermediates decreased, whereas the abundance of larger intermediates with sizes closer to a T = 4 capsid remained constant.

Kinetics of intermetallic compound formation in thermally evaporated Ag-In bilayers

The kinetics of intermetallic compound (IMC) formation in thermally evaporated Ag-In bilayers, with In on top of Ag, was investigated using X-ray diffractometry, applied to the surfaces of the bilayer specimens, as well as scanning electron microscopy, applied to cross-sections of the bilayer specimens, prepared by a focused ion beam instrument. IMC formation was followed at room temperature as well as at elevated temperatures of 50 °C, 60 °C, and 70 °C. Two distinct growth regimes were observed coinciding with the availability of pure In. The AgIn2 IMC nucleated initially, followed by nucleation of the Ag2In IMC. The growth of AgIn2 was found to be controlled by both diffusional processes as well as interfacial reactions. The growth of the Ag2In IMC is dominantly diffusion-controlled. An interdiffusion coefficient of D=1.1±3.9·10−4 cm2 s−1 exp(−60.5±9.2 kJ mol−1R−1T−1) was obtained for the Ag2In IMC. The observations were discussed in terms of the interplay of thermodynamic and kinetic constraints.

B12-O-17Microsecond Time-Scale In Situ Observations of Electron-Irradiation-Induced Crystallization in an Amorphous Antimony Nanoparticle by Ultra-High Voltage Electron Microscopy

In-situ compression tests in a transmission electron microscope were carried out to investigate the deformation behavior of δ-ferrite nanopillars of 2205 duplex stainless steel. Nanopillars of ~600 nm in length, ~300 nm in width, and ~100 nm in thickness were fabricated by a focused ion beam instrument (JEOL JEM-9320 FIB). The pillars were compressed uniaxially along the [001] direction at room temperature in a JEOL 2010F transmission electron microscope with a Hysitron PicoIndenter installed. The δferrite with spinodal nanostructure, which formed due to aging at 475oC for 64 h [1], obviously retarded the progress of serrated yielding (intermittent short strain bursts with a discrete large burst [2]), which occurred in the unaged pillars without spinodal nanostructures. A typical example is illustrated in Fig. 1. The detailed defomation structures have been examined through the in-situ videos and snapshots. The different trends in the deformation behavior clearly indicate that the spinodal structure in the aged nanopillar strongly confined the movement of dislocations during the course of compression, leading to a notable strengthening effect. [1] T.H. Chen, K.L. Weng, J.R. Yang, Mater. Sci. Eng., A 338 (2002) 259-270. [2] K.Y. Xie et al, Scripta Mater. 65 (2011) 1037-1040. B12-O-17 doi:10.1093/jmicro/dfv104

Enhancement of XeF2-assisted gallium ion beam etching of silicon layer and endpoint detection from backside in circuit editing

Within the semiconductor industry, backside circuit editing is the process of modifying individual nanometer-scale devices after they have been fabricated by conventional mass production techniques. The technique includes the removal of bulk silicon, to reach the devices, followed by the removal of small and precisely defined volumes of silicon and other materials. It also includes the ability to deposit precise patterns of conductors or insulators to modify the devices in question. Essential to the circuit edit processes are the focused ion beam (FIB) instruments, usually providing a gallium ion beam, to sputter away the volumes which need to be removed. When used in conjunction with specific “precursor” gases, the FIB instrument can deposit metals and insulators in arbitrary patterns to achieve the desired circuit repair or modification. Other gases, such as xenon difluoride (XeF2), can work in conjunction with the FIB to improve the effectiveness and the rate of material removal. Our experimental investigation found that the removal rate of backside silicon by a gallium FIB could be enhanced by 100 times when used in conjunction with the XeF2 gas. The XeF2 also reduced the redeposition of the removed silicon material, making the removal more effective. And importantly, the production of secondary electrons was found to offer a viable endpoint signal to indicate the transition to a new material.

A state-of-the-art review of micron-scale spatially resolved residual stress analysis by FIB-DIC ring-core milling and other techniques

Quantification of residual stress gradients can provide great improvements in understanding the complex interactions between microstructure, mechanical state, mode(s) of failure and structural integrity. Highly focused local probe non-destructive techniques such as X-ray diffraction, electron diffraction or Raman spectroscopy have an established track record in determining spatial variations in the relative changes in residual stress with respect to a reference state for many structural materials. However, the interpretation of these measurements in terms of absolute stress values requires a strain-free sample often difficult to obtain due to the influence of chemistry, microstructure or processing route. With the increasing availability of focused ion beam instruments, a new approach has been developed which is known as the micro-scale ring-core focused ion beam-digital image correlation technique. This technique is becoming the principal tool for quantifying absolute in-plane residual stresses. It can be applied to a broad range of materials: crystalline and amorphous metallic alloys and ceramics, polymers, composites and biomaterials. The precise nano-scale positioning and well-defined gauge volume of this experimental technique make it eminently suitable for spatially resolved analysis, that is, residual stress profiling and mapping. Following a summary of micro-stress evaluation approaches, we focus our attention on focused ion beam-digital image correlation methods and assess the application of micro-scale ring-core methods for spatially resolved residual stress profiling. The sequential ring-core milling focused ion beam-digital image correlation method allows micro- to macro-scale mapping at the step of 10–1000 μm, while the parallel focused ion beam-digital image correlation approach exploits simultaneous milling operation to quantify stress profiles at the micron scale (1–10 μm). Cross-validation against X-ray diffraction results confirms that these approaches represent accurate, reliable and effective residual stress mapping methods.

Probe Optimization studies For High current Focused Ion Beam Instruments

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In Situ Mechanical Testing in Electron Microscopes: Current Progress and Future Opportunities in Small-Scale Experimentation

The overriding motivation behind conducting small-scale in situ experiments in electron microscopes is to establish a one-to-one correlation between the changes within the microstructure (in real time) of a specimen ‘‘in its original place’’ and its overall deformation response (stress–strain, fracture, etc.). This can enable precise spatial and temporal correlation of slip, fracture, and failure events as a result of plastic flow anywhere within the entire test specimen. This stands in contrast to macroscopic in situ experiments that characterize a fraction of the entire volume undergoing deformation. Much of the in situ mechanical testing conducted on small volumes has been directed toward testing specimens in the form of thin fibers and whiskers, microcompression and nanocompression pillars, and thin films. This is sometimes driven by the need to characterize the mechanical properties of a material at intrinsically small volumes for specific applications, e.g., electronics [microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS)], aerospace (coating and superalloys), energy (solid oxide fuel cell and filtration), etc. Other mechanistic investigations of small scale deformation have benefitted from recent progress in specimen fabrication made possible by the advancement of focused ion beam (FIB) technology with its versatile milling capabilities at the micron and submicron scale. So what is next for in situ mechanical testing? The coming years will see the integration of various experimental techniques accelerating our realtime study of deformation mechanisms. Investigations have now been focused on novel microscale specimen preparation techniques—e.g., batch fabrication—thereby reducing the cost and/or improving statistical sampling of test results. The new plasma FIB instruments also offer dramatic improvements in specimen production throughput while employing an inert ion sputtering source. Perhaps first and foremost, we can expect to observe the convergence of nanoscale and microscale (5 nm to 10 lm) and macroscale (>1000 lm) specimen testing in the form of mesoscale specimen (10– 1000 lm) testing. Specimens tested at these length scales can return properties representative of the bulk, while at the same time allowing for observation of the entire specimen volume (or representative bulk volume) in the electron microscope. These tests not only provide bulk property measurement but are amenable to full volume plasticity modeling where calculations of explicit, discrete grain configurations composed of tens or hundreds of grains have become a tractable problem. All these advancements will also promote the use of in situ testing within the electron microscope for industry where results can directly influence design considerations. This special topic of ‘‘In Situ Mechanical Testing in Electron Microscopes’’ presents a collection of selected articles from well-known researchers all across the world. This topic covers a broad area in the recent advances in in situ testing, techniques, and recent results. In addition, review articles will certainly hold the interest of readers. Details of the articles in this topic are mentioned below. To download any of the papers, follow the URL: http:// link.springer.com/journal/11837/67/8/page/1 to the table of contents page for the August 2015 issue (vol. 67, no. 8).

The effects of metal surface geometry on the formation of uranium hydride

The present work examines the effect of surface geometry on the reaction between hydrogen gas and uranium metal, forming uranium hydride (UH3), a pyrophoric compound of significance to the civil nuclear industry. Hydride formation was initiated on uranium samples that had been patterned with a focused ion beam instrument to form surface arrays of triangular prisms and pillars with differing apex angles. Post reaction analysis indicated preferential hydride formation at the apex of these features. Additionally, once hydride formation had commenced the observed growth rate on the prisms appeared to accelerate in comparison to the rate exhibited on the surrounding surface.

Single-particle electrophoresis in nanochannels.

Electrophoretic mobilities and particle sizes of individual Hepatitis B Virus (HBV) capsids were measured in nanofluidic channels with two nanopores in series. The channels and pores had three-dimensional topography and were milled directly in glass substrates with a focused ion beam instrument assisted by an electron flood gun. The nanochannel between the two pores was 300 nm wide, 100 nm deep, and 2.5 μm long, and the nanopores at each end had dimensions 45 nm wide, 45 nm deep, and 400 nm long. With resistive-pulse sensing, the nanopores fully resolved pulse amplitude distributions of T = 3 HBV capsids (32 nm outer diameter) and T = 4 HBV capsids (35 nm outer diameter) and had sufficient peak capacity to discriminate intermediate species from the T = 3 and T = 4 capsid distributions in an assembly reaction. Because the T = 3 and T = 4 capsids have a wiffle-ball geometry with a hollow core, the observed change in current due to the capsid transiting the nanopore is proportional to the volume of electrolyte displaced by the volume of capsid protein, not the volume of the entire capsid. Both the signal-to-noise ratio of the pulse amplitude and resolution between the T = 3 and T = 4 distributions of the pulse amplitudes increase as the electric field strength is increased. At low field strengths, transport of the larger T = 4 capsid through the nanopores is hindered relative to the smaller T = 3 capsid due to interaction with the pores, but at sufficiently high field strengths, the T = 3 and T = 4 capsids had the same electrophoretic mobilities (7.4 × 10–5 cm2 V–1 s–1) in the nanopores and in the nanochannel with the larger cross-sectional area.

Electroosmotic flow in nanofluidic channels.

We report the measurement of electroosmotic mobilities in nanofluidic channels with rectangular cross sections and compare our results with theory. Nanofluidic channels were milled directly into borosilicate glass between two closely spaced microchannels with a focused ion beam instrument, and the nanochannels had half-depths (h) of 27, 54, and 108 nm and the same half-width of 265 nm. We measured electroosmotic mobilities in NaCl solutions from 0.1 to 500 mM that have Debye lengths (κ–1) from 30 to 0.4 nm, respectively. The experimental electroosmotic mobilities compare quantitatively to mobilities calculated from a nonlinear solution of the Poisson–Boltzmann equation for channels with a parallel-plate geometry. For the calculations, ζ-potentials measured in a microchannel with a half-depth of 2.5 μm are used and range from −6 to −73 mV for 500 to 0.1 mM NaCl, respectively. For κh > 50, the Smoluchowski equation accurately predicts electroosmotic mobilities in the nanochannels. However, for κh < 10, the electrical double layer extends into the nanochannels, and due to confinement within the channels, the average electroosmotic mobilities decrease. At κh ≈ 4, the electroosmotic mobilities in the 27, 54, and 108 nm channels exhibit maxima, and at 0.1 mM NaCl, the electroosmotic mobility in the 27 nm channel (κh = 1) is 5-fold lower than the electroosmotic mobility in the 2.5 μm channel (κh = 100).

Subgrain boundary analyses in deformed orthopyroxene by TEM/STEM with EBSD-FIB sample preparation technique

High-resolution structure analyses using electron beam techniques have been performed for the investigation of subgrain boundaries (SGBs) in deformed orthopyroxene (Opx) in mylonite from Hidaka Metamorphic Belt, Hokkaido, Japan, to understand ductile deformation mechanism of silicate minerals in shear zones. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analysis of Opx porphyroclasts in the mylonitic rock indicated that the crystal orientation inside the Opx crystals gradually changes by rotation about the b-axis by SGBs and crystal folding. In order to observe the SGBs along the b-axis by transmission electron microscopy (TEM) or scanning TEM (STEM), the following sample preparation protocol was adopted. First, petrographic thin sections were slightly etched with hydrofluoric acid to identify SGBs in SEM. The Opx crystals whose b-axes were oriented close to the normal of the surface were identified by EBSD, and the areas containing SGBs were picked and thinned for (S) TEM analysis with a focused ion beam instrument with micro-sampling system. High-resolution TEM imaging of the SGBs in Opx revealed various boundary structures from a periodic array of dissociated (100) [001] edge dislocations to partially or completely incoherent crystals, depending on the misorientation angle. Atomic-resolution STEM imaging clearly confirmed the formation of clinopyroxene (Cpx) structure between the dissociated partial dislocations. Moreover, X-ray microanalysis in STEM revealed that the Cpx contains a considerable amount of calcium replacing iron. Such chemical inhomogeneity may limit glide motion of the dislocation and eventually the plastic deformation of the Opx porphyroclasts at a low temperature. Chemical profiles across the high-angle incoherent SGB also showed an enrichment of the latter in calcium at the boundary, suggesting that SGBs are an efficient diffusion pathway of calcium out of host Opx grain during cooling.

Subwavelength light focusing of plasmonic lens with dielectric filled nanoslits structures

A plasmonic lens composed of a dielectric-filled nanoslits structure on an aluminum film is proposed and experimentally demonstrated. The slits' structure is designed with equal distance, length, and width, but filled with variant thickness SiO2 dielectric for specific phase retardations. A dual focused ion beam instrument is employed to mill the slits and deposit SiO2 into the slits. The phase modulation by SiO2-filled slits is illustrated by a double slits interference experiment. The light focusing behavior of the fabricated plasmonic lens is experimentally characterized by a scanning near-field optical microscope. Experimental results show good agreement with the simulations. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE).

NanoSIMS imaging alteration layers of a leached SON68 glass via a FIB‐made wedged crater

Currently, nuclear wastes are commonly immobilized into glasses because of their long‐term durability. Exposure to water for long periods, however, will eventually corrode the waste form and is the leading potential avenue for radionuclide release into the environment. Because such slow processes cannot be experimentally tested, the prediction of release requires a thorough understanding of the mechanisms governing glass corrosion. In addition, because of the exceptional durability of glass, much of the testing must be performed on high‐surface area powders. A technique that can provide accurate compositional profiles with nanometer scale depth resolution for non‐flat samples would be a major benefit to the field. In this study, NanoSIMS was used to image the cross section of the corrosion layers of a leached SON68 glass sample. A wedged crater was prepared by a focused ion beam instrument to obtain a five‐fold improvement in depth information for NanoSIMS measurements. This improvement allowed us to confirm that the breakdown of the silica glass network is further from the pristine glass than a second dissolution front for boron, another glass former, despite only ~50 nm distance between them. More importantly, NanoSIMS images show that the roughness majorly exists in Si corrosion layer. This novel sample geometry will be a major benefit to efficient NanoSIMS sampling of irregular interfaces at the nanometer scale that would otherwise be obscured within time‐of‐flight secondary ion mass spectroscopy depth profiles. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Fabrication of high quality plan-view TEM specimens using the focused ion beam

We describe a technique using a focused ion beam instrument to fabricate high quality plan-view specimens for transmission electron microscopy studies. The technique is simple, site-specific and is capable of fabricating multiple large, >100μm2 electron transparent windows within epitaxially grown thin films. A film of La0.67Sr0.33MnO3 is used to demonstrate the technique and its structural and functional properties are surveyed by high resolution imaging, electron spectroscopy, atomic force microscopy and Lorentz electron microscopy. The window is demonstrated to have good thickness uniformity and a low defect density that does not impair the film's Curie temperature. The technique will enable the study of in-plane structural and functional properties of a variety of epitaxial thin film systems.

Laser-Deposited In Situ TiC-Reinforced Nickel Matrix Composites: 3D Microstructure and Tribological Properties

A new class of Ni-Ti-C based metal matrix composites has been developed using the laser engineered net shaping (LENS) process. These composites consist of an in situ formed and homogeneously distributed titanium carbide (TiC) phase reinforcing the nickel matrix. Additionally, by tailoring the Ti/C ratio in these composites, an additional graphitic phase can also be engineered into the microstructure. The microstructure of these composites has been characterized in detail in three dimensions, via serial-sectioning in a dual-beam focused ion beam instrument followed by appropriate 3D reconstructions, to determine the true morphology and spatial distribution of the TiC and graphite phases as well as the phase evolution sequence. These three-phase Ni-TiC-C composites exhibit excellent tribological properties, in terms of extremely low coefficient of friction while maintaining a relatively high hardness, and these will be discussed in the presentation.

Advances in source technology for focused ion beam instruments

Abstract

Focused Ion Beam nano-patterning from traditional applications to single ion implantation perspectives

AbstractIn this article we review some fundamentals of the Focused Ion Beam (FIB) technique based on scanning finely focused beams of gallium ions over a sample to perform direct writing. We analyse the main limitations of this technique in terms of damage generation or local contamination and through selected examples we discuss the potential of this technique in the light of the most sensitive analysis techniques. In particular we analyse the limits of Ga-FIB irradiation for the patterning of III-V heterostructures, thin magnetic layers, artificial defects fabricated onto graphite or graphene and atomically thin suspended membranes. We show that many of these earlypointed “limitations” with appropriate attention and analysis can be valuable for FIB instrument development, avoided, or even turned into decisive advantages. Such new methods transferable to the fabrication of devices or surface functionalities are urgently required in the emerging nanosciences applications and markets.