Focused ion beam characterization of plasma-assisted deposition on polymer films at the nanoscale

In this paper, a novel technique is presented for the characterization at the nanoscale of plasma-assisted deposit on polyethylene-terephthalate (PET) polymer films. In previous studies, some microcharacterization and morphology analyses of plasma-assisted deposition were performed by atomic force microscopy (AFM). In the work presented here, we analysed the thickness and homogeneity of plasma-assisted deposits by focused ion beam (FIB). This technique with 5-7 nm resolution requires no sample preparation and relies on a sequence of operations on a relatively fast time scale, so that it is easy to make thorough investigations of the sample. We performed electron and ion imaging of the surface of the material, and a subsequent ionic cutting allowed the study of the morphology of the same sample. We developed a novel approach to the edge detection techniques (EDT) in images for a fast evaluation and monitoring of the deposited layer.     

聚焦离子束电子束系统及其在生物学和医学上的应用

聚焦离子束电子束系统在材料失效分析、纳米材料结构表征与性能分析以及纳米器件研制等方面发挥着重要作用。近年来该系统在生物学和医学领域的应用日益受到人们的重视。本文介绍聚焦离子束电子束系统的组成、性能、相关功能及其在生物学和医学上的若干应用,包括透射电镜生物样品制备、细胞和组织内部结构观察与三维重构等。     

Mechanical characterization of micro/nanoscale structures for MEMS/NEMS applications using nanoindentation techniques

Mechanical properties of micro/nanoscale structures are needed to design reliable micro/nanoelectromechanical systems (MEMS/NEMS). Micro/nanomechanical characterization of bulk materials of undoped single-crystal silicon and thin films of undoped polysilicon, SiO(2), SiC, Ni-P, and Au have been carried out. Hardness, elastic modulus and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Fracture toughness was measured by indentation using a Vickers indenter. Bending tests were performed on the nanoscale silicon beams, microscale Ni-P and Au beams using a depth-sensing nanoindenter. It is found that the SiC film exhibits higher hardness, elastic modulus and scratch resistance as compared to other materials. In the bending tests, the nanoscale Si beams failed in a brittle manner with a flat fracture surface. The notched Ni-P beam showed linear deformation behavior followed by abrupt failure. The Au beam showed elastic-plastic deformation behavior. FEM simulation can well predict the stress distribution in the beams studied. The nanoindentation, scratch and bending tests used in this study can be satisfactorily used to evaluate the mechanical properties of micro/nanoscale structures for use in MEMS/NEMS.     

Far‐reaching geometrical artefacts due to thermal decomposition of polymeric coatings around focused ion beam milled pigment particles

Focused ion beam and scanning electron microscope (FIB‐SEM) instruments are extensively used to characterize nanoscale composition of composite materials, however, their application to analysis of organic corrosion barrier coatings has been limited. The primary concern that arises with use of FIB to mill organic materials is the possibility of severe thermal damage that occurs in close proximity to the ion beam impact. Recent research has shown that such localized artefacts can be mitigated for a number of polymers through cryogenic cooling of the sample as well as low current milling and intelligent ion beam control. Here we report unexpected nonlocalized artefacts that occur during FIB milling of composite organic coatings with pigment particles. Specifically, we show that FIB milling of pigmented polysiloxane coating can lead to formation of multiple microscopic voids within the substrate as far as 5 μm away from the ion beam impact. We use further experimentation and modelling to show that void formation occurs via ion beam heating of the pigment particles that leads to decomposition and vaporization of the surrounding polysiloxane. We also identify FIB milling conditions that mitigate this issue.     

Focused ion beam manipulation and ultramicroscopy of unprepared cells

The focused ion beam (FIB) technique of nanomachining combined with simultaneous scanning electron microscopy (SEM) was used for submicron manipulation and imaging of unprepared (fresh) cells to demonstrate the potentiality of the FIB/SEM technique for ultramicroscopic studies. Sectioning at the nanoscale level was successfully performed by means of ion beam-driven milling operations that reveal the ultrastructure of fresh yeast cells. The FIB/SEM has many advantages over other ultramicroscopy techniques already applied for unprepared/fresh biological samples.     

The complementary use of electron backscatter diffraction and ion channelling imaging for the characterization of nanotwins

On the example of electrodeposited nickel films, it is shown that unique information on twins with dimensions on the nanoscale can be obtained by suitable combination of ion channelling imaging and electron backscatter diffraction analysis, whereas both (routine) single techniques cannot meet the requirements for analysis of these films. High‐resolution electron backscatter diffraction is inadequate for full characterization of nanotwins, but image quality maps obtained from electron backscatter diffraction at least yield a qualitative estimation of the location and number of nanotwins. Complementing this information with ion channelling imaging provides more representative insights into the microstructure, because it supplements the quantitative investigation of the number and width of twin lamellae with additional crystallographic orientation analysis provided by EBSD. To this end, two methods for adjusting EBSD data based on ion channelling images are proposed. Thorough selection of the complementary techniques opens future perspectives for the investigation of other challenging samples with nanoscale features in the microstructure.     

Investigation of Tibetian Plateau varnish: new findings at the nanoscale using focused ion beam and transmission electron microscopy techniques

Dual-beam focused ion beam microscopy (FIB/SEM) preparation of rock varnish for high-resolution transmission electron microscopy (HR-TEM) has enabled us to characterize unreported nanostructures. Fossils, unreported textures, and compositional variability were observed at the nanoscale. These techniques could provide a method for studying ancient terrestrial and extra-terrestrial environments to better understand geological processes at the nanoscale.     

Nano/Microtribological Properties of Ultrathin Functionalized Imidazolium Wear-Resistant Ionic Liquid Films on Single Crystal Silicon

Ionic liquids (ILs) are considered as a new kind of lubricant for micro/nanoelectromechanical system (M/NEMS) due to their excellent thermal and electrical conductivity. However, so far, only few reports have investigated the tribological behavior of molecular thin films of various ILs. Evaluating the nanoscale tribological performance of ILs when applied as a few nanometers-thick film on a substrate is a critical step for their application in MEMS/NEMS devices. To this end, four kinds of ionic liquid carrying methyl, hydroxyl, nitrile, and carboxyl group were synthesized and these molecular thin films were prepared on single crystal silicon wafer by dip-coating method. Film thickness was determined by ellipsometric method. The chemical composition and morphology were characterized by the means of multi-technique X-ray photoelectron spectrometric analysis, and atomic force microscopic (AFM) analysis, respectively. The nano- and microtribological properties of the ionic liquid films were investigated. The morphologies of wear tracks of IL films were examined using a 3D non-contact interferometric microscope. The influence of temperature on friction and adhesion behavior at nanoscale, and the effect of sliding frequency and load on friction coefficient, load bearing capacity, and anti-wear durability at microscale were studied. Corresponding tribological mechanisms of IL films were investigated by AFM and ball-on-plane microtribotester. Friction reduction, adhesion resistance, and durability of IL films were dependent on their cation chemical structures, wettability, and ambient environment.     

Evolution of residual stress and crack morphologies during 3D FIB tomographic analysis of alumina

Three‐dimensional focused ion beam (FIB) tomography is increasingly being used for 3D characterization of microstructures in the 50 nm–20 μm range. FIB tomography is a destructive, invasive process, and microstructural changes may potentially occur during the analysis process. Here residual stress and crack morphologies in single‐crystal sapphire samples have been concurrently analyzed using Cr³⁺ fluorescence spectroscopy and FIB tomography. Specifically, maps of surface residual stress have been obtained from optically polished single‐crystal alumina [surface orientation (1 ī 0 2)], from FIB milled surface trenches, from Vickers micro‐indentation sites (loads 50 g–300 g), and from Vickers micro‐indentation sites during FIB serial sectioning. The residual stress maps clearly show that FIB sputtering generates residual stress changes. For the case of the Vickers micro‐indentations, FIB sputtering causes significant changes in residual stress during the FIB tomographic serial sectioning. 3D reconstruction of the crack distribution around micro‐indentation sites shows that the cracks observed are influenced by the location of the FIB milled surface trenches due to localized stress changes.     

Imaging damage evolution in a small particle metal matrix composite

It is difficult to study effectively microstructural damage in metal matrix composites (MMCs) due to artefacts arising from traditional metallographic sample preparation techniques. The sectioning and imaging capabilities of the focused ion beam (FIB) microscope provide an excellent method for studying damage accumulation in MMCs.
The capabilities of the FIB system have been used to carry out a study of damage evolution in a powder-processed/hot-extruded Al2080/SiC_p MMC. Microvoid damage is found to be preserved accurately during FIB sectioning, allowing measurements of the fraction of decohered particles and the void area fraction. These microscopic damage measurements are correlated with the macroscopic damage parameter, D , as determined by density measurements.
Using transmission electron microscopy, the evolution of dislocation structures at the SiC–matrix interfaces has been examined. A previously unreported decohesion mechanism has been observed.     

A new method for the reconstruction of micro- and nanoscale planar periodic structures

In recent years, the micro- and nanoscale structures and materials are observed and characterized under microscopes with large magnification at the cost of small view field. In this paper, a new phase-shifting inverse geometry moiré method for the full-field reconstruction of micro- and nanoscale planar periodic structures is proposed. The random phase shift techniques are realized under the scanning types of microscopes. A simulation test and a practical verification experiment were performed, which demonstrate this method is feasible. As an application, the method was used to reconstruct the structure of a butterfly wing and a holographic grating. The results verify the reconstruction process is convenient. When being compared with the direct measurement method using point-by-point way, the method is very effective with a large view field. This method can be extended to reconstruct other planar periodic microstructures and to locate the defects in material possessing the regular lattice structure. Furthermore, it can be applied to evaluate the quality of micro- and nanoscale planar periodic structures under various high-power scanning microscopes.     

Surface damage induced by FIB milling and imaging of biological samples is controllable

Focused ion beam (FIB) techniques are among the most important tools for the nanostructuring of surfaces. We used the FIB/SEM (scanning electron microscope) for milling and imaging of digestive gland cells. The aim of our study was to document the interactions of FIB with the surface of the biological sample during FIB investigation, to identify the classes of artifacts, and to test procedures that could induce the quality of FIB milled sections by reducing the artifacts. The digestive gland cells were prepared for conventional SEM. During FIB/SEM operation we induced and enhanced artifacts. The results show that FIB operation on biological tissue affected the area of the sample where ion beam was rastering. We describe the FIB-induced surface major artifacts as a melting-like effect, sweating-like effect, morphological deformations, and gallium (Ga(+)) implantation. The FIB induced surface artifacts caused by incident Ga(+) ions were reduced by the application of a protective platinum strip on the surface exposed to the beam and by a suitable selection of operation protocol. We recommend the same sample preparation methods, FIB protocol for milling and imaging to be used also for other biological samples.     

Embossed‐carving processing of cytoskeletons of cultured cells by using focused ion beam technology

The focused ion beam (FIB) technology has drawn considerable attention in diverse research fields. FIB can be used to mill samples at the nanometer scale by using an ion beam derived from electrically charged liquid gallium (Ga). This powerful technology with accuracy at the nanometer scale is now being applied to life science research. In this study, we show the potential of FIB as a new tool to investigate the internal structures of cells. We sputtered Ga⁺ onto the surface or the cross section of animal cells to emboss the internal structures of the cell. Ga⁺ sputtering can erode the cell surface or the cross section and thus emboss the cytoskeletons quasi‐3 dimensionally. We also identified the embossed structures by comparing them with fluorescent images obtained via confocal laser microscopy because the secondary ion micrographs did not directly provide qualitative information directly. Furthermore, we considered artifacts during the FIB cross sectioning of cells and propose a way to prevent undesirable artifacts. We demonstrate the usefulness of FIB to observe the internal structures of cells. Microsc. Res. Tech. 76:290–295, 2013. © 2013 Wiley Periodicals, Inc.     

Current SEM techniques for de- and re-construction of centromeres to determine 3D CENH3 distribution in barley mitotic chromosomes

Combined light microscopic (LM) and field emission scanning electron microscopic (FESEM) techniques with FluoroNanogold labelling allowed quantification and high resolution analysis of 3D distribution of the centromere-specific histone H3 variant CENH3 in barley mitotic chromosomes. Chromosomes were investigated with fluorescence LM, conventional FESEM, low-voltage FESEM and combined FIB/FESEM techniques for unprecedented comprehensive analysis to determine chromatin distribution patterns in the centromere. Using data from FIB/FESEM sectioning of centromeric regions of chromosomes, it was possible to render 3D reconstruction of the CENH3 distribution with highest resolution achieved to date. Complementary data derived from each approach show that CENH3 localizes not only to the primary constriction, but also in the pericentric regions and is distributed exclusively in the interior, rather than on the surface, of the centromere. This is relevant for understanding kinetochore assembly and digresses from current models of centromere structure. We emphasize here this broad microscopic approach, focusing on technical aspects of combined FESEM techniques, for which advantages and limitations are discussed, providing a relevant example--in the field of centromeric research--for application to investigations of other subcellular biological structures.     

Focused ion beam scanning electron microscopy in biology

Since the end of the last millennium, the focused ion beam scanning electron microscopy (FIB‐SEM) has progressively found use in biological research. This instrument is a scanning electron microscope (SEM) with an attached gallium ion column and the 2 beams, electrons and ions (FIB) are focused on one coincident point. The main application is the acquisition of three‐dimensional data, FIB‐SEM tomography. With the ion beam, some nanometres of the surface are removed and the remaining block‐face is imaged with the electron beam in a repetitive manner. The instrument can also be used to cut open biological structures to get access to internal structures or to prepare thin lamella for imaging by (cryo‐) transmission electron microscopy. Here, we will present an overview of the development of FIB‐SEM and discuss a few points about sample preparation and imaging.     

An electron microscopy three‐dimensional characterization of titania nanotubes

To characterize complex, three‐dimensional nanostructures, modern microscopy techniques are needed, such as electron tomography and focused ion beam (FIB) sectioning. The aim of this study was to apply these two techniques to characterize TiO₂ nanotubes in terms of their size, shape, volume, porosity, geometric surface area, and specific surface area (SSA). For these experiments, titania nanotubes were fabricated by means of the electrochemical oxidation of titanium at a voltage of 20 V for 2 hr followed by heat treatment at 450°C for 3 hr to change the amorphous structure into a crystalline anatase structure. The quantitative data obtained from the FIB and electron tomography reconstructions show a high similarity in porosity and some differences in SSA. These might be the result of differences in resolution between the two reconstruction techniques.     

Fabrication of nanodot plasmonic waveguide structures using FIB milling and electron beam‐induced deposition

Fabrication of metallic Au nanopillars and linear arrays of Au‐containing nanodots for plasmonic waveguides is reported in this article by two different processes—focused ion beam (FIB) milling of deposited thin films and electron beam‐induced deposition (EBID) of metallic nanostructures from an organometallic precursor gas. Finite difference time domain (FDTD) modeling of electromagnetic fields around metallic nanostructures was used to predict the optimal size and spacing between nanostructures useful for plasmonic waveguides. Subsequently, a multi‐step FIB fabrication method was developed for production of metallic nanorods and nanopillars of the size and geometry suggested by the results of the FDTD simulations. Nanostructure fabrication was carried out on planar substrates including Au‐coated glass, quartz, and mica slides as well as cleaved 4‐mode optical fibers. In the second fabrication process, EBID was utilized for the development of similar nanostructures on planar Indium Tin Oxide and Titanium‐coated glass substrates. Each method allows formation of nanostructures such that the plasmon resonances associated with the nanostructures could be engineered and precisely controlled by controlling the nanostructure size and shape. Linear arrays of low aspect ratio nanodot structures ranging in diameter between 50–70 nm were fabricated using EBID. Preliminary dark field optical microscopy demonstrates differences in the plasmonic response of the fabricated structures. SCANNING 31: 139–146, 2009. © 2009 Wiley Periodicals, Inc.     

Towards better 3-D reconstructions by combining electron tomography and atom-probe tomography

Scanning transmission electron microscope tomography and atom-probe tomography are both three-dimensional techniques on the nanoscale. We demonstrate here the combination of the techniques by analyzing the very same volume of an Al-Ag alloy specimen. This comparison allows us to directly visualize the theoretically known artifacts of each technique experimentally, providing insight into the optimal parameters to use for reconstructions and assessing the quality of each reconstruction. The combination of the techniques for accurate morphology and compositional information in three dimensions at the nanoscale provides a route for a new level of materials characterization and understanding.     

Large-scale process optimization for focused ion beam 3-D nanofabrication

With the ever-decreasing size of manufactured objects, fabrication processes driven by charged particle beams, such as focused ion beam (FIB), become important for a wide spectrum of interdisciplinary applications. A designed three-dimensional (3-D) pattern to fabricate may contain millions of pixels, which will require solving an unprecedented large-scale problem for planning. This paper proposes a general framework of planning FIB milling for fabricating 3-D nanostructures, including model formulations to enable FIB for scalable and automated applications and a corresponding optimization model to support the process planning. The implementation of proposed work does not affect the fabrication quality and yet tremendously reduces the required computational time and data storage during planning. The proposed framework of process planning is further illustrated and verified by simulation and milling experiments of submicron features on Si and Si₃N₄. This research offers an accurate and economical solution to the realization from designs to actual micro/nanoscale models and builds a scientific foundation for immediate development of complex, yet more accurate and cost-effective, beam scanning techniques.     

Comparison of different preparation methods of biological samples for FIB milling and SEM investigation

When a new approach in microscopy is introduced, broad interest is attracted only when the sample preparation procedure is elaborated and the results compared with the outcome of the existing methods. In the work presented here we tested different preparation procedures for focused ion beam (FIB) milling and scanning electron microscopy (SEM) of biological samples. The digestive gland epithelium of a terrestrial crustacean was prepared in a parallel for FIB/SEM and transmission electron microscope (TEM). All samples were aldehyde-fixed but followed by different further preparation steps. The results demonstrate that the FIB/SEM samples prepared for conventional scanning electron microscopy (dried) is suited for characterization of those intracellular morphological features, which have membranous/lamellar appearance and structures with composition of different density as the rest of the cell. The FIB/SEM of dried samples did not allow unambiguous recognition of cellular organelles. However, cellular organelles can be recognized by FIB/SEM when samples are embedded in plastic as for TEM and imaged by backscattered electrons. The best results in terms of topographical contrast on FIB milled dried samples were obtained when samples were aldehyde-fixed and conductively stained with the OTOTO method (osmium tetroxide/thiocarbohydrazide/osmium tetroxide/thiocarbohydrazide/osmium tetroxide). In the work presented here we provide evidence that FIB/SEM enables both, detailed recognition of cell ultrastructure, when samples are plastic embedded as for TEM or investigation of sample surface morphology and subcellular composition, when samples are dried as for conventional SEM.