Ion Beam Tool Research Articles

Ion beam tools for nondestructive in-situ and in-operando composition analysis and modification of materials at the Tandem Laboratory in Uppsala

Ion accelerators have demonstrated tremendous versatility in their research applications throughout several decades. Starting predominantly as nuclear physics tools, they subsequently provided novel insights into fundamental atomic physics. Nowadays small and medium size accelerators are routinely employed in several branches of materials science. As research questions increasingly drive the need for analyses and material modification experiments performed in-situ and/or in-operando, facilities must adapt to service such a need. In this work, we highlight capabilities for in-situ and in-operando composition depth profiling and materials modification, developed with instrumentation at the Tandem Laboratory at Uppsala University. An overview of available ion sources and accelerators is given. We then exemplify the specific capabilities of the available end stations for materials synthesis, sample modification and device operation either during simultaneous ion beam based characterization or with such characterization performed in-situ before and after the application of various modification steps. Describing specific recent examples and potential future applications, we illustrate the impact of the present national research infrastructure.

True 3D-AFM sensor for nanometrology

A new three dimensional (3D) atomic force microscopic (AFM) probe, referred to as the 3D-Nanoprobe, is introduced. The 3D-Nanoprobe is realized by introducing flexure hinge structures to the cantilever of a conventional critical dimension AFM (CD-AFM) probe. It has quasi-isotropic stiffness in 3D directions and is thus more powerful for detecting 3D tip-sample interaction forces in AFM measurements. In addition, the stiffness of the 3D-Nanoprobe is balanced to the bending stiffness of slender CD-AFM tips, offering improved 3D sensitivity. In this paper, a design example of a 3D-Nanoprobe based on a CD-AFM probe with a tip nominal diameter of 70 nm is presented. The design parameters are optimized via analytic modelling and the finite element analysis (FEA) method. The simulation results indicate that the designed 3D-Nanoprobe has much better performance than that of the original CD-AFM probe, for instance, its stiffness’ anisotropy ratio (including the tip contribution) has been improved from 8:8:1 (x, y, z) to 0.9:0.9:1 (x, y, z). The probing sensitivity is improved by a factor of more than 106, 128 and 1.6 in x-, y- and z-direction, respectively. Moreover, the designed 3D-Nanoprobe has the first bending mode eigenfrequency of 84.4 kHz and the first torsional mode eigenfrequency of 346 kHz. The 3D-Nanoprobe has been manufactured by applying a focused ion beam (FIB) tool. Finally, to detect the full 3D interaction forces by the 3D-Nanoprobe, a new AFM-head prototype which consists of two independently adjustable dual optical levers have been developed.

Effect of multiple laser shock processing on nano-scale microstructure of an aluminum alloy

In this study, nano-scale microstructural evolution in 6061-T6 alloy after laser shock processing (LSP) was studied. 6061-T6 alloy plate was subjected to multiple LSP. The LSP treated area was characterized by X-ray diffraction and the microstructure of the samples was analyzed by transmission electron microscopy. Focused Ion Beam (FIB) tools were used to prepare TEM samples in precise areas. It was found that even though aluminum had high stacking fault energy, LSP yielded to formation of ultrafine grains and deformation faults such as dislocation cells, stacking faults. The stacking fault probability (PSF) was obtained in LSP-treated alloy using X-Ray diffraction. Deformation induced stacking faults lead to the peak position shifts, broadening and asymmetry of diffraction. XRD analysis and TEM observations revealed significant densities of stacking faults in LSP-treated 6061-T6 alloy. And mechanical properties of LSP-treated alloy were also determined to understand the hardening behavior with high concentration of structural defects.

Design guidelines for on-chip unstable resonator cavity to suppress filamentation in GaSb-based diode lasers

We demonstrate GaSb-based diode lasers emitting near 2.7 μm that are fabricated as on-chip unstable resonator cavities using the focused ion beam tool. A near-diffraction-limited lateral beam is observed in broad-area devices where the reflection from the cylindrical mirror at the back facet overrides direct counterpropagation in the cavity to suppress the formation of filaments. We identify a geometric parameter that can be used as a general guide to optimizing the on-chip unstable resonator cavity for maximum brightness. This parameter is the aperture within the unstable resonator cavity, a measure of the angular divergence contained within the device, and is shown to correlate with the onset of filament suppression.

Improved ion beam tools for ultraprecision figure correction of curved aluminum mirror surfaces (Erratum)

Improved ion beam tools for ultraprecision figure correction of curved aluminum mirror surfaces (Erratum)

Improved ion beam tools for ultraprecision figure correction of curved aluminum mirror surfaces

Aluminum mirrors offer great potential for satisfying the increasing demand in high-performance optical components for visible and ultraviolet applications. Ion beam figuring is an established finishing technology and in particular a promising technique for direct aluminum figure error correction. For the machining of strongly curved or arbitrarily shaped surfaces as well as the correction of low-to-mid spatial frequency figure errors, the usage of a high-performance ion beam source with low tool width is mandatory. For that reason, two different concepts of ion beam generation with high ion current density and narrow beam width are discussed. (1) A concave ion beam extraction grid system is used for apertureless constriction of ion beams in the low millimeter range. An oxygen ion beam with a full-width at half-maximum (FWHM) of 4.0 mm with an ion current density of 29.8 mA / cm2 was achieved. (2) For even smaller ion beams, a conic aperture design with a submillimeter-sized exit opening was tested. A nitrogen ion beam with an FWHM down to 0.62 mm with an ion current density of 4.6 mA / cm2 was obtained. In situ ion current density mapping is performed by scanning Faraday probe measurements. Special interest is set on the data evaluation for submillimeter ion beam analysis.

Atomic force microscope integrated with a scanning electron microscope for correlative nanofabrication and microscopy

More than 40 years after its invention, the atomic force microscopy (AFM) can be integrated with scanning electron microscope (SEM) instruments as an increasingly capable and productive characterization tool with sub-nanometer spatial resolution. The authors have designed and developed an AFM instrument capable to be integrated into any SEM or in a combination of SEM with a focused ion-beam (FIB) tool. The combination of two or more different types of techniques like SEM, energy dispersive x-ray spectroscopy, and AFM is called correlative microscopy because analytical information from the same place of the sample can be obtained and correlated. For the first time, they introduced to the SEM/FIB tool correlative nanofabrication methods like field-emission scanning probe lithography, tip-based electron beam induced deposition, and nanomachining. The combination of all these methods provides a completely new nanotechnology instrument, which should be seen as a tool for correlative nanofabrication and microscopy. Thus, it provides for the first time the capabilities of a stand-alone instrument with the capabilities of nondestructive three-dimensional tip-based metrology and nanofabrication into the combined SEM/FIB tool. In this article, the authors describe all these methods in detail and present a brief example of the results obtained. They demonstrate that the self-sensing, self-actuating cantilevers (called active cantilevers) equipped with Diamond tip are a versatile toolkit for fast imaging and emerging nanofabrication. The AFM integrated into SEM is using active cantilevers that can characterize and generate nanostructures all in situ without the need to break-vacuum or contaminate the sample.

Effect of multiple laser shock processing on nano-scale microstructure of an aluminum alloy

In this study, nano-scale microstructural evolution in 6061-T6 alloy after laser shock processing (LSP) were studied. 6061-T6 alloy plate were subjected to multiple LSP. The LSP treated area was characterized by X-ray diffraction and the microstructure of the samples was analyzed by transmission electron microscopy. Focused Ion Beam (FIB) tools were used to prepare TEM samples in precise areas. It was found that even though aluminum had high stacking fault energy, LSP yielded to formation of ultrafine grains and deformation faults such as dislocation cells, stacking faults. The stacking fault probability (PSF) was obtained in LSP-treated alloy using X-Ray diffraction. Deformation induced stacking faults lead to the peak position shifts, broadening and asymmetry of diffraction. XRD analysis and TEM observations revealed significant densities of stacking faults in LSP-treated 6061-T6 alloy. And mechanical properties of LSP-treated alloy were also determined to understand the hardening behavior with high concentration of structural defects.

Some Vacuum-Arc-Based Plasma and Ion Beam Tools for Surface Modification

Some Vacuum-Arc-Based Plasma and Ion Beam Tools for Surface Modification

A direct differential method for measuring thermal conductivity of thin films.

Over the past two decades, significant progress in the thermal metrology for thin films and wires has enabled new understanding of the thermal conductivity of nanostructures. However, a large variation in the measured thermal conductivity of similar nanostructured samples has been observed. In addition to potential differences from sample-to-sample, measurement uncertainty contributes to the observed variation in measured properties. Many now standard micro/nanoscale thermal measurement techniques require extensive calibration of the properties of the substrate and support structures and this calibration contributes to uncertainty. Within this work, we develop a simple, direct differential electrothermal measurement of thermal conductivity of micro/nanoscale sample films by extending conventional steady state electrothermal approaches. Specifically, we leverage a cross-beam measurement structure consisting of a suspended, composite heater beam (metal on silicon) with the sample structure (silicon) extending at a right angle from the center of the heater beam, in a configuration similar to the T-type measurements used for fibers and nanotubes. To accurately resolve the thermal conductivity of the sample, the steady-state Joule heating response of the cross-beam structure is measured. Then, the sample is detached from the heater beam with a Focused Ion Beam (FIB) tool enabling direct characterization of the composite heater beam thermal properties. The differential measurement of the structure before and after FIB cut enables direct extraction of the sample thermal conductivity. The effectiveness of this differential measurement technique is demonstrated by measuring thermal conductivity of a 200 nm silicon layer. Additionally, this new method enables investigation of the accuracy of conventional approaches for extracting sample thermal conductivity with the composite beam structure and conventional comparative approaches. The results highlight the benefits of the direct differential method for accurate measurements with minimal assumptions.

Microstructural Characterization of SOFC Electrodes: Observations and Simulations

SOFC electrodes are typically porous composite materials bringing ionic, electronic and pore phases into intimate contact. These electrodes must fulfill a broad range of criteria from diffusion and electrocatalysis to mechanical support and redox tolerance. Historically design and optimisation has been largely empirical and characterisation of electrode microstructures at sub-micron length scales has been restricted to two-dimensional electron microscopy. In recent years, the development and application of focused ion beam and X-ray nano tomography tools has enabled characterisation of electrode microstructures in three dimensions providing unprecedented access to a wealth of microstructural information . As well as improving our understanding of existing electrode geometries, these tools have also been successfully applied to evaluate design and manufacturing strategies. With improved availability and functionality of high-resolution tomography tools, we can start to explore the effects of processing and operation on microstructure and performance. Using the unique benefits of non-destructive synchrotron X-ray nano-CT we have explored microstructural evolution processes in-situ using so-called "4D tomography" - facilitating an improved understanding of electrode aging and durability. These tomography platforms are however most powerful when used in conjunction with relevant simulation tools. Here we present the results of finite element simulations, exploring coupled electrochemistry and transport and stress in composite SOFC electrodes, utilising experimentally derived microstructural frameworks.

Focused Ion Beam Induced Microstructural Alterations: Texture Development, Grain Growth, and Intermetallic Formation

Copper, gold, and tungsten thin films have been exposed to 30 kV Ga+ ion irradiation, and the resulting microstructural modifications are studied as a function of ion dose. The observed microstructural changes include texture development with respect to the easy channeling direction in the target, and in the case of Cu, an additional intermetallic phase is produced. Texture development in these target materials is a function of the starting materials grain size, and these changes are not observed in large grained materials. The accepted models of differential damage driven grain growth are not supported by the results of this study. The implications of this study to the use of focused ion beam tools for sample preparation are discussed.

Characterization of CMOS programmable multi-beam blanking arrays as used for programmable multi-beam projection lithography and resistless nanopatterning

Multi-beam projection lithography and resistless direct nanopatterning techniques provide decisive advantages compared to existing single electron and ion beam tools. Aperture plate systems (APS) including CMOS addressable programmable blanking arrays serve as pattern generators within these tools. An APS test stand was designed to achieve 0.08 µrad for measuring lateral/angular beamlet movements. For CMOS programmable APS units, providing 43 000 programmable beams, nearest-neighbour cross talk measurements have shown 5.5 µrad influence. This is well below the target spec for the charged particle multi-beam projection technology.

Ion beam assisted crystallization of amorphous silicon layers using high current density Gallium beams

We have investigated ion beam assisted crystallization as a possible method for the creation of crystalline Si layers on amorphous substrates. Ion beam assisted crystallization has previously been characterised with pulsed and modest continuous beam current densities, but not at the high densities that would be required for high throughput processes. In this study, amorphous Si layers were implanted with Ga using a focused ion beam (FIB) tool and with Ga, Ar, Ge and As using beamline implanters. Crystallization was only observed for Ga, implying Ga alone was acting to reduce the activation energy. The observed rates of crystallization also implied that the relaxation state of the a-Si, influenced by the beam conditions, was an important driver for the phase transformation.

Atomic layer deposition enabled interconnect technology for vertical nanowire arrays

We have demonstrated an atomic layer deposition (ALD) enabled interconnect technology for vertical, c-axis oriented gallium nitride (GaN) nanowire (NW, 5–10 μm in length, 80–200 nm in diameter) arrays encapsulated by benzocyclobutene (BCB). The nano-scaled ALD multilayer is essential to provide conformal co-axial dielectric (ALD-alumina)/conductor (ALD-tungsten) coverage and precise thickness control for nanowire metallization. Furthermore, we have successfully developed a fabrication process to locally remove and connect tungsten (W) interconnect on NWs. Cross-sectional image taken in a focused ion beam (FIB) tool confirms the conformality of ALD interconnects. Photoluminescence (PL) wavelengths of the nanowires array can be tuned dynamically by changing the input current supplied to ALD-tungsten interconnect which heats nanowires. Such an experiment also demonstrated the quality of interconnect. This interconnect technology can be applied to various vertical nanowire-based devices, such as nanowire light emitting diodes, nanowire-based field effect transistors, resonators, batteries or biomedical applications.

Emerging Methods in Mechanical Behavior

Over the week of March 9–13, 2008, at the TMS Annual Meeting in New Orleans, Louisiana, a symposium was held on the topic of “Emerging Methods in Mechanical Behavior.” While this topic is a common theme in the Society for Experimental Mechanics’ meetings, this particular symposium was somewhat unusual because the host venue, TMS, is a materials society rather than a mechanics society. The TMS meeting holds symposia ranging from aluminum refining to phase transformations. A subset of materials scientists specialize in understanding the mechanical properties of materials. It is this group of researchers that the symposium had targeted: metallurgists, materials scientists, and mechanical engineers who are developing or employing new techniques to gain insight into the mechanical behavior of materials. Materials Scientists typically come from a background that is strong in advanced characterization tools. For this reason, it is no surprise that this symposium on ‘Emerging Methods in Mechanical Behavior’ was laced with the quantitative application of characterization techniques in materials mechanics. Based on the contributions to this symposium, it is clear that diffraction techniques are expanding as a tool in experimental mechanics. While conventional x-ray diffraction has been used for decades as in the measurement of residual stresses, recently developed diffraction methods are becoming increasingly prevalent, including electron backscattered diffraction (also known as orientation imaging microscopy), synchrotron microdiffraction, and neutron diffraction. New microscopy techniques are also becoming prevalent. The dual-beam focused ion beam tool, which has emerged as a workhorse research tool in materials science over the past decade, permits microdissection, microwelding, ion channeling imaging, and many other creative new approaches to interrogation. Quantitative in-situ loading stages in scanning and transmission electron microscopies enable the connection between mechanical response and microscale evolution. In-situ imaging is providing valuable insight into nanoindentation and micropillar compression experiments. Another significant advance in quantitative experimental mechanics over the past decade has been the proliferation of digital image correlation (DIC) techniques. This surface deformation and strain mapping capability provides a tool for experimental mechanics that is loosely analogous to the advent of the finite element method for computational mechanics. Early applications of DIC were in the area of structural mechanics of lab-scale components. However, it is now clear that the DIC algorithm can also have applicability at the microscale through atomic force and scanning electron microscopies. Microscale DIC brings a powerful new tool to understand mechanical behavior at the microstructural scale. As shown in the collection of papers that are represented in this Special Issue of Experimental Mechanics, these emerging advanced characterization techniques are now providing crucial new insights into the mechanical behavior of materials. B.L. Boyce (*, SEM member) Sandia National Laboratories, Albuquerque, NM, USA e-mail: blboyce@sandia.gov

Electrodeposited Au-CdTe-Au Nanowires: Solution-based Control Over Cd/Te Stoichiometry

Heterostructured, composition-adjusted Au-CdTe-Au nanowires were fabricated via templated electrodeposition. Cd/Te ratios were modified in the wires by varying the Te4+ concentration in the deposition electrolyte. These wires were characterized by energy-dispersive x-ray spectroscopy (EDS); subsequently, they were deposited onto Si/SiO2 substrates and electrically contacted using Pt deposition in a focused ion beam tool. EDS and photoelectron x-ray spectroscopy (XPS) were used to characterize the composition and surface chemistry of CdTe films deposited from the various electrolytes.

Dual-beam focused ion beam/electron microscopy processing and metrology ofredeposition during ion–surface 3D interactions, from micromachining to self-organizedpicostructures

Focused ion beam (FIB) tools have become a mainstay for processing and metrology ofsmall structures. In order to expand the understanding of an ion impinging a surface(Sigmund sputtering theory) to our processing of small structures, the significance of 3Dboundary conditions must be realized. We consider ion erosion for patterning/lithography,and optimize yields using the angle of incidence and chemical enhancement, but we findthat the critical 3D parameters are aspect ratio and redeposition. We consider focused ionbeam sputtering for micromachining small holes through membranes, but we find that thecritical 3D considerations are implantation and redeposition. We consider ion beamself-assembly of nanostructures, but we find that control of the redeposition by ionand/or electron beams enables the growth of nanostructures and picostructures.

Shrinking solid-state nanopores using electron-beam-induced deposition

Solid-state nanopores of only a few nanometres in size show a great potential forapplications such as molecule detection and DNA sequencing. In most cases, thefabrication of such a nanopore requires the high energy beam of a transmission electronmicroscope (TEM) or focused ion beam (FIB) tool to drill or reshape a small hole in afreestanding membrane. Here, we present a novel method to reduce the size of existingnanopores using electron-beam-induced deposition (EBID) of carbon in a conventionalscanning electron microscope (SEM). The existing nanopores are etched in asilicon membrane using anisotropic wet etching and can be shrunk down to afew nanometres using EBID. This paper discusses the parameters that influencethe rate of shrinking and provides an insight into the underlying mechanism.

Cryogenic vitrification and 3D serial sectioning using high resolution cryo‐FIB SEM technology for brine‐filled grain boundaries in halite: first results

AbstractThe structure of brine films in grain boundaries of halite has been the subject of much controversy over the past 20 years; although a number of innovative methods have been developed to study these structures, much is still unknown and fundamental information is missing. In this study, we investigated different methods of plunge‐freezing to vitrify the brine fill of grain boundaries for natural salt polycrystal. This was followed by a preliminary study of the 3D morphology of a vitrified grain boundary in a natural rock salt sample with a focused ion beam (FIB) excavation system. We have shown that brine‐filled grain boundaries in rock salt can be efficiently well frozen when dimensions are less than about 1 mm. Coupled with an ion beam tool, cryo‐SEM allows 3D observation of the well‐frozen grain boundaries in large volumes and high resolution. Initial results of brine‐filled natural halite grain boundaries show non‐faceted crystal–brine interfaces and unexpectedly low dihedral angles at room temperature and pressure.