Showing papers on "Focused ion beam published in 2013"

Synthesis and characterization of Cu-doped ZnO one-dimensional structures for miniaturized sensor applications with faster response

Abstract: Detection of chemicals and biological species is an important issue to human health and safety. In this paper, we report the hydrothermal synthesis at 95 °C of Cu-doped ZnO low-dimensional rods for room-temperature (RT) sensing applications and enhanced sensor performances. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman and photoluminescence are used to characterize the material properties. To demonstrate the suitability of the Cu-doped ZnO rods for gas sensor applications and for comparison with pure ZnO, we fabricated a double rod device using Focused Ion Beam. The responses of pure-ZnO and Cu-doped ZnO rods studied in exactly the same condition are reported. We found that Cu-ZnO sensors have enhanced RT sensitivity, faster response time, and good selectivity. Miniaturized Cu-ZnO rod-based sensors can serve as a good candidate for effective H2 detectors with low power consumption.

Elevated temperature, nano-mechanical testing in situ in the scanning electron microscope

Abstract: A general nano-mechanical test platform capable of performing variable temperature and variable strain rate testing in situ in the scanning electron microscope is described. A variety of test geometries are possible in combination with focused ion beam machining or other fabrication techniques: indentation, micro-compression, cantilever bending, and scratch testing. The system is intrinsically displacement-controlled, which allows it to function directly as a micro-scale thermomechanical test frame. Stable, elevated temperature indentation/micro-compression requires the indenter tip and the sample to be in thermal equilibrium to prevent thermal displacement drift due to thermal expansion. This is achieved through independent heating and temperature monitoring of both the indenter tip and sample. Furthermore, the apex temperature of the indenter tip is calibrated, which allows it to act as a referenced surface temperature probe during contact. A full description of the system is provided, and the effects of indenter geometry and of radiation on imaging conditions are discussed. The stabilization time and temperature distribution throughout the system as a function of temperature is characterized. The advantages of temperature monitoring and thermal calibration of the indenter tip are illustrated, which include the possibility of local thermal conductivity measurement. Finally, validation results using nanoindentation on fused silica and micro-compression of ⟨100⟩ silicon micro-pillars as a function of temperature up to 500 °C are presented, and procedures and considerations taken for these measurements are discussed. A brittle to ductile transition from fracture to splitting then plastic deformation is directly observed in the SEM for silicon as a function of temperature.

Sub-5 nm hard x-ray point focusing by a combined Kirkpatrick-Baez mirror and multilayer zone plate

Abstract: Compound optics such as lens systems can overcome the limitations concerning resolution, efficiency, or aberrations which fabrication constraints would impose on any single optical element. In this work we demonstrate unprecedented sub-5 nm point focusing of hard x-rays, based on the combination of a high gain Kirkpatrick-Baez (KB) mirror system and a high resolution W/Si multilayer zone plate (MZP) for ultra-short focal length f. The pre-focusing allows limiting the MZP radius to below 2 μm, compatible with the required 5 nm structure width and essentially unlimited aspect ratios, provided by enabling fabrication technology based on pulsed laser deposition (PLD) and focused ion beam (FIB).

Nanometallic Glasses: Size Reduction Brings Ductility, Surface State Drives Its Extent

Abstract: We report tensile experiments on Ni80P20 metallic glass samples fabricated via a templated electroplating process and via focused ion beam milling, which differed only in their surface energy states: Ga-ion-irradiated and as-electroplated. Molecular dynamics simulations on similar Ni80Al20 systems corroborate the experimental results, which suggest that the transition from brittle to ductile behavior is driven by sample size, while the extent of ductility is driven by surface state.

A FIB/TEM study of butterfly crack formation and white etching area (WEA) microstructural changes under rolling contact fatigue in 100Cr6 bearing steel

Abstract: Butterflies are microscopic damage features forming at subsurface material imperfections induced during rolling contact fatigue (RCF) in rolling element bearings. Butterflies can lead to degradation of the load bearing capacity of the material by their associated cracks causing premature spalling failures. Recently, butterfly formation has been cited to be related to a premature failure mode in wind turbine gearbox bearings; white structure flaking (WSF). Butterflies consist of cracks with surrounding microstructural change called ‘white etching area’ (WEA) forming wings that revolve around their initiators. The formation mechanisms of butterflies in bearing steels have been studied over the last 50 years, but are still not fully understood. This paper presents a detailed microstructural analysis of a butterfly that has initiated from a void in standard 100Cr6 bearing steel under rolling contact fatigue on a laboratory two-roller test rig under transient operating conditions. Analysis was conducted using focused ion beam (FIB) tomography, 3D reconstruction and transmission electron microscopy (STEM/ TEM) methods. FIB tomography revealed an extensive presence of voids/cavities immediately adjacent to the main crack on the non-WEA side and at the crack tip. This provides evidence for a void/cavity coalescence mechanism for the butterfly cracks formation. Spherical M3C carbide deformation and dissolution as part of the microstructural change in WEA were observed in both FIB and STEM/TEM analyses, where TEM analyses also revealed the formation of superfine nano-grains (3–15 nm diameter) intersecting a dissolving spherical M3C carbide. This is evidence of the early formation of nano-grains associated with the WEA formation mechanism.

Silicon nanowire lithium-ion battery anodes with ALD deposited TiN coatings demonstrate a major improvement in cycling performance

Abstract: We demonstrate that nanometer-scale TiN coatings deposited by atomic layer deposition (ALD), and to a lesser extent by magnetron sputtering, will significantly improve the electrochemical cycling performance of silicon nanowire lithium-ion battery (LIB) anodes. A 5 nm thick ALD coating resulted in optimum cycling capacity retention (55% vs. 30% for the bare nanowire baseline, after 100 cycles) and coulombic efficiency (98% vs. 95%, at 50 cycles), also more than doubling the high rate capacity retention (e.g. 740 mA h g−1vs. 330 mA h g−1, at 5 C). We employed a variety of advanced analytical techniques such as electron energy loss spectroscopy (EELS), focused ion beam analysis (FIB) and X-ray photoelectron spectroscopy (XPS) to elucidate the origin of these effects. The conformal 5 nm TiN remains sufficiently intact to limit the growth of the solid electrolyte interphase (SEI), which in turn both improves the overall coulombic efficiency and reduces the life-ending delamination of the nanowire assemblies from the underlying current collector. Our findings should provide a broadly applicable coating design methodology that will improve the performance of any nanostructured LIB anodes where SEI growth is detrimental.

Surface-Plasmon Resonance-Enhanced Multiphoton Emission of High-Brightness Electron Beams from a Nanostructured Copper Cathode

Abstract: We experimentally investigate surface-plasmon assisted photoemission to enhance the efficiency of metallic photocathodes for high-brightness electron sources. A nanohole array-based copper surface was designed to exhibit a plasmonic response at 800 nm, fabricated using the focused ion beam milling technique, optically characterized and tested as a photocathode in a high power radio frequency photoinjector. Because of the larger absorption and localization of the optical field intensity, the charge yield observed under ultrashort laser pulse illumination is increased by more than 100 times compared to a flat surface. We also present the first beam characterization results (intrinsic emittance and bunch length) from a nanostructured photocathode.

Correlative in vivo 2 photon and focused ion beam scanning electron microscopy of cortical neurons.

Abstract: Correlating in vivo imaging of neurons and their synaptic connections with electron microscopy combines dynamic and ultrastructural information. Here we describe a semi-automated technique whereby volumes of brain tissue containing axons and dendrites, previously studied in vivo, are subsequently imaged in three dimensions with focused ion beam scanning electron microcopy. These neurites are then identified and reconstructed automatically from the image series using the latest segmentation algorithms. The fast and reliable imaging and reconstruction technique avoids any specific labeling to identify the features of interest in the electron microscope, and optimises their preservation and staining for 3D analysis.

Electrokinetically-driven transport of DNA through focused ion beam milled nanofluidic channels.

Abstract: The electrophoretically driven transport of double-stranded λ-phage DNA through focused ion beam (FIB) milled nanochannels is described. Nanochannels were fabricated having critical dimensions (width and depth) corresponding to 0.5×, 1×, and 2× the DNA persistence length, or 25 nm, 50 nm, and 100 nm, respectively. The threshold field strength required to drive transport, the threading mobility, and the transport mobility were measured as a function of nanochannel size. As the nanochannel dimensions decreased, the entropic barrier to translocation increased and transport became more constrained. Equilibrium models of confinement provide a framework in which to understand the observed trends, although the dynamic nature of the experiments resulted in significant deviations from theory. It was also demonstrated that the use of dynamic wall coatings for the purpose of electroosmotic flow suppression can have a significant impact on transport dynamics that may obfuscate entropic contributions. The nonintermitt...

Helium focused ion beam fabricated plasmonic antennas with sub-5 nm gaps

Abstract: We demonstrate a reliable fabrication method to produce plasmonic dipole nanoantennas with gap values in the range of 3.5–20 nm. The method combines electron beam lithography to create gold nanorods and helium focused ion beam milling to cut the gaps. Results show a reproducibility within 1 nm. Scattering spectra of antennas show a red shift of resonance wavelengths and an increase of the intensity of resonance peaks with a decrease of the gap size, which is in agreement with finite element simulations. The measured refractive index sensitivity was about 250 nm per refractive index unit for antennas with gap values below 5 nm.

Comprehensive structural, surface-chemical and electrochemical characterization of nickel-based metallic foams.

Abstract: Nickel-based metallic foams are commonly used in electrochemical energy storage devices (rechargeable batteries) as both current collectors and active mass support. These materials attract attention as tunable electrode materials because they are available in a range of chemical compositions, pore structures, pore sizes, and densities. This contribution presents structural, chemical, and electrochemical characterization of Ni-based metallic foams. Several materials and surface science techniques (transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), focused ion beam (FIB), and X-ray photoelectron spectroscopy (XPS)) and electrochemical methods (cyclic voltammetry (CV)) are used to examine the micro-, meso-, and nanoscopic structural characteristics, surface morphology, and surface-chemical composition of these materials. XPS combined with Ar-ion etching is employed to analyze the surface and near-surface chemical composition of the foams. The spe...

Measuring the fracture resistance of hard coatings

Abstract: A way of characterizing cracking in a hard coating is described Microscale double cantilever beams have been made by focused ion beam milling and compressed in situ using a nanoindenter The method can account for frictional effects and is demonstrated first on single crystals of SiC and GaAs of known toughness, before studying cracking in CrN-based hard coatings It is found that ultra-fine grained CrAlN/Si3N4 coatings have a toughness approximately twice that of a conventional CrN coating Although grain-size effects are still unclear, in situ observations directly show crack interactions with particles of Cr and voids in the film

High capacity cathode materials for Li–S batteries

Abstract: To enhance the stability of sulfur cathode for a high energy lithium–sulfur battery, sulfur–activated carbon (S–AC) composite was prepared by encapsulating sulfur into micropores of activated carbon using a solution-based processing technique. In the analysis using the prepared specimen of S–AC composite by the focused ion beam (FIB) technique, the elemental sulfur exists in a highly dispersed state inside the micropores of activated carbon, which has a large surface area and a narrow pore distribution. The S–AC composite was characterized through X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) method, selected area electron diffraction (SAED), energy dispersive X-ray spectrometry (EDX), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TGA), and field emission scanning electron microscopy (FESEM). A lithium–sulfur cell using the S–AC composite has a high first discharge capacity over 800 mA h g−1 S even at a high current density such as 2C (3200 mA g−1 S) and has good cycleability around 500 mA h g−1 S discharge capacity at the 50th cycle at the same current density.

Mapping the Complex Morphology of Cell Interactions with Nanowire Substrates Using FIB-SEM

Abstract: Using high resolution focused ion beam scanning electron microscopy (FIB-SEM) we study the details of cell-nanostructure interactions using serial block face imaging. 3T3 Fibroblast cellular monolayers are cultured on flat glass as a control surface and on two types of nanostructured scaffold substrates made from silicon black (Nanograss) with low- and high nanowire density. After culturing for 72 hours the cells were fixed, heavy metal stained, embedded in resin, and processed with FIB-SEM block face imaging without removing the substrate. The sample preparation procedure, image acquisition and image post-processing were specifically optimised for cellular monolayers cultured on nanostructured substrates. Cells display a wide range of interactions with the nanostructures depending on the surface morphology, but also greatly varying from one cell to another on the same substrate, illustrating a wide phenotypic variability. Depending on the substrate and cell, we observe that cells could for instance: break the nanowires and engulf them, flatten the nanowires or simply reside on top of them. Given the complexity of interactions, we have categorised our observations and created an overview map. The results demonstrate that detailed nanoscale resolution images are required to begin understanding the wide variety of individual cells’ interactions with a structured substrate. The map will provide a framework for light microscopy studies of such interactions indicating what modes of interactions must be considered.

Chemical and structural properties of conducting nanofilaments in TiN/HfO2-based resistive switching structures

Abstract: Structural, chemical and electronic properties of electroforming in the TiN/HfO2 system are investigated at the nanometre scale. Reversible resistive switching is achieved by biasing the metal oxide using conductive atomic force microscopy. An original method is implemented to localize and investigate the conductive region by combining focused ion beam, scanning spreading resistance microscopy and scanning transmission electron microscopy. Results clearly show the presence of a conductive filament extending over 20?nm. Its size and shape is mainly tuned by the corresponding HfO2 crystalline grain. Oxygen vacancies together with localized states in the HfO2 band gap are highlighted by electron energy loss spectroscopy. Oxygen depletion is seen mainly in the central part of the conductive filament along grain boundaries. This is associated with partial amorphization, in particular at both electrode/oxide interfaces. Our results are a direct confirmation of the filamentary conduction mechanism, showing that oxygen content modulation at the nanometre scale plays a major role in resistive switching.

A simple method for residual stress measurements in thin films by means of focused ion beam milling and digital image correlation

Abstract: Hydrogenated amorphous carbon (a-C:H) coatings contain substantial residual stresses which particularly influence the failure behaviour of the coating system. However, measuring their residual stresses with conventional methods is not trivial. In this work, a simple method is presented to determine residual stresses of thin films locally by using stress relaxation tests by means of focused ion beam (FIB) milling and digital image correlation (DIC). It is shown, that the H-bar geometry, as it is used for TEM lamella preparation, is especially suitable for such measurements. Displacements due to relaxation of residual stresses are tracked using DIC and the stresses are obtained by correlation with finite element analysis. The method is applied to determine residual stresses of two a-C:H coatings processed with different deposition processes and parameters. It was found, that the coatings differ in their mechanical properties as well as in their residual stress state. The proposed method offers therefore a simple way for analysing residual stresses in thin amorphous coatings.

Influence of bulk pre-straining on the size effect in nickel compression pillars

Abstract: Micro-compression tests were performed on pre-strained nickel (Ni) single crystals in order to investigate the influence of the initial dislocation arrangement on the size dependence of small-scale metal structures. A bulk Ni sample was grown using the Czochralski method and sectioned into four compression samples, which were then pre-strained to nominal strains of 5, 10, 15 and 20%. Bulk samples were then characterized using transmission electron microscopy (TEM), micro-Laue diffraction, and electron backscatter diffraction. TEM results show that a dislocation cell structure was present for all deformed samples, and Laue diffraction demonstrated that the internal strain increased with increased amount of pre-straining. Small-scale pillars with diameters from 200 nm to 5 μm were focused ion beam (FIB) machined from each of the four deformed bulk samples and further compressed via a nanoindenter equipped with a flat diamond punch. Results demonstrate that bulk pre-straining inhibits the sample size effect. For heavily pre-strained bulk samples, the deformation history does not affect the stress–strain behavior, as the pillars demonstrated elevated strength and rather low strain hardening over the whole investigated size range. In situ TEM and micro-Laue diffraction measurements of pillars confirmed little change in dislocation density during pillar compression. Thus, the dislocation cell walls created by heavy bulk pre-straining become the relevant internal material structure controlling the mechanical properties, dominating the sample size effect observed in the low dislocation density regime.

Cold atomic beam ion source for focused ion beam applications

Abstract: We report measurements and modeling of an ion source that is based on ionization of a laser-cooled atomic beam. We show a high brightness and a low energy spread, suitable for use in next-generation, high-resolution focused ion beam systems. Our measurements of total ion current as a function of ionization conditions support an analytical model that also predicts the cross-sectional current density and spatial distribution of ions created in the source. The model predicts a peak brightness of 2 × 107 A m−2 sr−1 eV−1 and an energy spread less than 0.34 eV. The model is also combined with Monte-Carlo simulations of the inter-ion Coulomb forces to show that the source can be operated at several picoamperes with a brightness above 1 × 107 A m−2 sr−1 eV−1. We estimate that when combined with a conventional ion focusing column, an ion source with these properties could focus a 1 pA beam into a spot smaller than 1 nm. A total current greater than 5 nA was measured in a lower-brightness configuration of the ion source, demonstrating the possibility of a high current mode of operation.

A Step-By-Step Analysis of the Polishing Process for Tungsten Specimens

Abstract: The different stages of the polishing process of polycrystalline tungsten samples were investigated by scanning electron microscopy of both the sample surface and of cross-sections prepared with the help of a focused ion beam It is shown that a distortion layer is present at the sample surface after mechanical fine grinding and even after polishing with diamond suspension, although the sample has a mirror-like finish A sufficiently long chemo-mechanical polishing step using an alkaline colloidal silica suspension was able to remove this distortion layer Although electropolishing produced an even smoother surface, the microstructure quality after chemo-mechanical polishing is comparable to that of an electropolished sample

Effect of surface modification on the corrosion resistance of austenitic stainless steel 316L in supercritical water conditions

Abstract: This work summarizes the results of corrosion studies of a surface treated austenitic stainless steel 316L at relevant operating conditions of SCWR (Supercritical Water Reactor). Different surface treatments were conducted for austenitic stainless steel 316L tube samples in order to study the effect of cold work in sample surface on corrosion resistance. Samples were exposed in supercritical water (SCW) at 650 °C/25 MPa, up to 3000 h. The corrosion rate was evaluated by measuring the weight change of the samples and by cross-section examinations using a Scanning Electron Microscope (SEM) in conjunction with Energy Dispersive X-ray Spectroscopy (EDS). Additional investigations using a Focused Ion Beam (FIB) microscope and a Transmission Electron Microscopy (TEM) were also performed on selected samples. It is observed that in machined sample, with a fine-grained microstructure and higher dislocation density in the sub-surface zone formed a very thin Cr-rich oxide film which suppresses the inward oxygen and outward iron diffusion.

Maskless and targeted creation of arrays of colour centres in diamond using focused ion beam technology

Abstract: The creation of nitrogen-vacancy (NV) centres in diamond is nowadays well controlled using nitrogen implantation and annealing. Although the high-resolution placement of NV centres has been demonstrated using either collimation through pierced tips of an atomic force microscope (AFM) or masks with apertures made by electron beam lithography, a targeted implantation into pre-defined structures in diamond may not be achieved using these techniques. We show that a beam of nitrogen ions can be focused to approximately 100 nm using focused ion beam (FIB) technology. The nitrogen ion beam is produced using an electron cyclotron resonance (ECR) plasma source. Combined with a scanning electron microscope, the nitrogen-FIB offers new possibilities for the targeted creation of single defects in diamond. This maskless technology is suitable for example for the creation of optical centres in the cavities of photonic crystals or in diamond tips for scanning magnetometry.

Oxidation of Co- and Ce-nanocoated FeCr steels: A microstructural investigation

Abstract: The effect of novel Co and Ce nanocoatings on oxidation behaviour and chromium volatilization from a commercial Fe-22Cr steel (Sanergy HT) developed for solid oxide fuel cell interconnect applications is investigated. Three different coatings (10 nm Ce, 640 nm Co and 10 nm Ce + 640 nm Co) are studied. Uncoated and nanocoated samples are exposed isothermally at 850 C in the air with 3% H2O for 168 h. The detailed microstructure of the different coatings is investigated. The surface morphology and microstructure of the oxide scales are characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX). Cross-section TEM thin foils are prepared by using a combined FIB/SEM (focused ion beam/scanning electron microscope) instrument. A 640 nm cobalt coating strongly inhibits Cr volatilization but has only minor effects on oxidation rate. In contrast, a 10 nm Ce coating decreases the oxidation rate but has no significant effects on chromium volatilization. Combining the two coatings, i.e., applying a 640 nm Co coating on top of the 10 nm Ce, effectively reduces Cr evaporation and slows down the rate of alloy oxidation.

Growth defect density in PVD hard coatings prepared by different deposition techniques

Abstract: Growth defects are imperfections which form during coating growth. In this work stylus profilometer was used to measure the defect surface density of a given coating surface on smaller areas (typically 2 mm 2 ) and larger areas (several tens of mm 2 ). From a large number of defect density measurements on samples from industrial production batches, we performed statistical analysis in order to evaluate the influence of deposition parameters on the defect surface density. We analyzed various PVD hard coatings (TiN, TiAlN, CrN, TiAlN/a-CN, nanostructured AlTiN/TiN and TiAlSiN/TiSiN/TiAlN layers) prepared by different PVD deposition techniques (thermionic arc evaporation, magnetron sputtering) at various deposition conditions. The surface morphology of the coated substrates was examined by field emission scanning electron microscope in combination with focused ion beam and 3D stylus profilometer. We found that the defect density on various samples in the same batch scatters a lot. There can also be a substantial difference (up to 50% in the peak density) on the two faces of the same 3-fold rotated sample. This suggests that the formation of growth defects is sporadic and spatially localized. For this reason a statistical approach for presentation of defect density was used. We found that the defect density depends on sample position, deposition time, type of coating material, and batching material. However, there is no significant difference in peak density distributions for 1-, 2- and 3-fold rotated samples prepared in the same batch. The substrate material type does not have an unambiguous influence. The influence of steel inclusions on coating growth was also analyzed. In order to understand the effects of different inclusions and other irregularities the substrate surface morphology was followed from the cleaning to ion etching and deposition. By transformation of the local (sample-based) coordinate system to the current instrumental coordinate system we were able to locate any defect and followed it through sample preparation. Shallow craters and voids were observed at positions of MnS inclusions, while the growth of TiAlN/CrN nanolayer coating on SiO 2 inclusions was coherent.