Cross-sectional Sample Preparation Research Articles

Characterization of anisotropic pore structure and dense selective layer of capillary membranes for long-term ECMO by cross-sectional ion-milling method.

Since the COVID-19 pandemic of 2020-2023, extracorporeal membrane oxygenator (ECMO) has attracted considerable attention worldwide. It is expected that ECMO with long-term durability is put into practical use in order to prepare for next emerging infectious diseases and to facilitate manufacturing for novel medical devices. Polypropylene (PP) and polymethylpentene (PMP) capillary membranes are currently the mainstream for gas exchange membrane for ECMO. ECMO support days for COVID-19-related acute hypoxemic respiratory failure have been reported to be on average for 14 or 24days. It is necessary to improve opposing functions such that promoting the permeation of oxygen and carbon dioxide and inhibiting the permeation of water vapor or plasma to develop sufficient durability for long-term use. For this purpose, accurately controlling the anisotropy of the pore structure of the entire cross section and functions of capillary membrane is significant. In this study, we focused on the cross-sectional ion-milling (CSIM) method, to precisely clarify the pore structure of the entire cross section of capillary membrane for ECMO, because there is less physical stress on the porous structure applied during the preparation of cross-sectional samples of porous capillary membranes. We attempted to observe the cross sections of commercially available PMP membranes using the CSIM method. As a result, we succeeded in fabricating fine-scale flat cross-sectional samples of PMP capillary membranes. The pore structures and the degree of anisotropy of the cross sections are quantitatively clarified. The achievements and the approaches of this study are being applied to the development of next-generation gas exchange membranes.

Enabling focused ion beam sample preparation for application in reverse tip sample scanning probe microscopy

Focused ion beam (FIB) has become a powerful tool for transmission electron microscopy sample preparation in the nanoelectronics industry and has in recent years also shown its benefits for specific preparation steps in electrical scanning probe microscopy (SPM). Most recently, a novel SPM approach – so-called reverse tip sample (RTS) SPM – has been proposed in which the position of sample and tip are switched compared to standard SPM; in RTS SPM the sample is attached to the end of a cantilever beam. To achieve this configuration, the region of interest must first be extracted from a substrate and then needs to be reliably fixed to the cantilever by FIB. Therefore, we have explored and developed dedicated FIB preparation methods for RTS SPM in this work. Our established procedures ensure a strong mechanical and good electrical connection of the sample to the cantilever for both cross-section and top view sample preparation. Furthermore, we introduce an approach for mounting samples from a full wafer size workflow. This paper presents the developed FIB procedures and discusses the quality and stability of all mounted samples and their electrical evaluation in RTS SPM.

Preparation of Cross-Sectional Membrane Samples for Scanning Electron Microscopy Characterizations Using a New Frozen Section Technique.

Characterization of the cross-sectional morphologies of polymeric membranes are critical in understanding the relationship of structure and membrane separation performances. However, preparation of cross-sectional samples with flat surfaces for scanning electron microscopy (SEM) characterizations is challenging due to the toughness of the non-woven fabric support. In this work, a new frozen section technique was developed to prepare the cross-sectional membrane samples. A special mold was self-designed to embed membranes orientationally. The frozen section parameters, including the embedding medium, cryostat working temperature, and sectioning thickness were optimized. The SEM characterizations demonstrated that the frozen section technique, using ultrapure water as the embedding medium at a working temperature of -30 °C and a sectioning thickness of 0.5 µm, was efficient for the preparation of the membrane samples. Three methods of preparation for the cross-sectional polymeric membranes, including the conventional liquid nitrogen cryogenic fracture, the broad ion beam (BIB) polishing, and the frozen section technique were compared, which showed that the modified frozen section method was efficient and low cost. This developed method could not only accelerate the development of membrane technology but also has great potential for applications in preparation of other solid samples.

A Combinatorial Approach for the Solution Deposition of Thin Films

Optimization of thin film deposition is often the limiting step in the discovery of new materials and device development. Over the years, high-throughput combinatorial methods were developed for the deposition of thin films from the gas phase. However, very few reports focused on combinatorial thin film deposition from solution. Here, we introduce a combinatorial approach for the deposition of thin films from solution. The flow deposition setup allows for simultaneously studying the effect of two critical parameters, deposition time and deposition temperature, on a single sample. As a proof of concept, we demonstrate the solution deposition of PbS thin films, which resulted in a library of 25 deposition condition combinations on a single GaAs (100) substrate. X-ray diffraction and scanning electron microscopy combined with focused ion beam cross-sectional sample preparation confirmed the formation of high-quality PbS films and showed the morphology evolution as a function of these two deposition parameters. This method can be easily adapted for cost-effective and rapid combinatorial studies of a large variety of solution-deposited thin film materials.

Electropolishing—A Practical Method for Accessing Voids in Metal Films for Analyses

In many applications, voids in metals are observed as early degradation features caused by fatigue. In this publication, electropolishing is presented in the context of a novel sample preparation method that is capable of accessing voids in the interior of metal thin films along their lateral direction by material removal. When performed at optimized process parameters, material removal can be well controlled and the surface becomes smooth at the micro scale, resulting in the voids being well distinguishable from the background in scanning electron microscopy images. Compared to conventional cross-sectional sample preparation (embedded mechanical cross-section or focused ion beam), the accessed surface is not constrained by the thickness of the investigated film and laterally resolved void analyses are possible. For demonstrational purposes of this method, the distribution of degradation voids along the metallization of thermo-mechanically stressed microelectronic chips has been quantified.

Estimation of needle height using relative parallax between two SIM images in single-column focused ion beam instrument

Gallium liquid metal ion source focused ion beam (FIB) instruments are widely used for cross-sectional sample preparation of specific areas of interest for scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Most FIB instruments are equipped with a metal needle for manipulation of the sample in the sample chamber most commonly as a micro-sampling probe for preparing TEM samples. Automatic needle manipulation has not yet been achieved for a conventional single-column FIB instrument without an SEM column because a reliable method for measuring needle height has not been established yet. This study investigated the use of scanning ion microscope (SIM) image processing to measure needle height from the sample surface in a conventional single-column FIB instrument without an SEM column. The needle height is measured using the relative parallax between two SIM images in which the needle is observed from two directions using a conventional aligner without the use of any special devices. It was demonstrated that the relative parallax was proportional to the needle height. The estimation precision was about several 10 μm, which is sufficient for automatic manipulation and safe touchdown of a needle in practical micro-sampling.

Garnet-Type Li7La3Zr2O12 / Lithium Metal Interface: Microstructure and Electrochemical Properties in Solid State Batteries

All-solid-state lithium ion batteries may overcome safety issues in future energy storage systems, when a non-flammable solid electrolyte instead of a liquid electrolyte is applied. Garnet-type Li7La3Zr2O12 (LLZO) is an encouraging choice due to its high Li+ conductivity and its chemical stability against lithium metal [1]. However, low-resistance LLZO/Li interfaces are deteriorated by incomplete adhesion of lithium metal onto LLZO and by surface contamination [2]. The resulting inhomogeneous distribution of contact areas may be more prone to dendrite formation. Previous studies [3,4] indicate that LLZO/Li interface quality is significantly improved by metallic buffer layers.In this study, we aim for a reliable preparation of low-resistance interfaces between solid electrolyte and lithium metal. At first, magnetron sputtering is applied to deposit an indium buffer layer of 50 to 500 nm thickness onto the polished and cleaned electrolyte surface. For cell assembly, lithium foil is put on both sides of an In-coated LLZO pellet and the test cell is heated to 220°C in argon atmosphere. After that, microstructure and electrochemical properties of the symmetric cells are analyzed. We improved cross-section sample preparation to inspect the quality of LLZO/In/Li interfaces over hundreds of µm. Scanning electron microscopy (SEM, cf. figure 1) confirms excellent adhesion between lithium and LLZO. We use a dry inert atmosphere during preparation, handling and transfer of our samples to avoid artifacts and sample degradation. The FEI Helios G4 FX microscope enables correlative SEM imaging by simultaneous acquisition of up to four different detector signals for interface topography and material contrast. Local chemical composition at the interface is analyzed by energy dispersive X-ray spectroscopy and electron-beam damage is minimized for SEM imaging by selecting optimum electron energies.Electrochemical impedance spectroscopy (EIS) followed by data evaluation via the distribution of relaxation times (DRT) and equivalent circuit modelling [5] deliver the proportional contributions of grain, grain boundaries and interfaces to the total impedance of symmetric cells (Li/In/LLZO/In/Li). Interface microstructures and EIS measurements are correlated for samples with different buffer layer characteristics to allow targeted optimization. We compare the pristine state of the test cells to samples that have been cycled with different current densities.

Defect distribution in boron doped silicon nanostructures characterized by means of scanning spreading resistance microscopy

Scanning spreading resistance microscopy (SSRM) was applied on boron (B) doped bulk and nanostructured silicon (Si) samples. Finite element simulations are performed to calculate the expected resistance profile based on secondary ion mass spectrometry data of the chemical B profile. Differences between experimental and simulated resistance scans are consistently described by the interaction of electrically active dopants with defect states. These states are strongly correlated to the cross-sectional sample preparation applied before the SSRM analysis. Whereas the B-doped bulk sample only reveals preparation induced bulk and surface defects, the SSRM scan of B-doped Si pillars is additionally affected by interface defects at the outer shell of the pillar. These interface defects do not only affect the concentration of charged carriers in the Si pillar but could also influence dopant diffusion in nanostructured Si.

Cross-sectional nanoprobing sample preparation on sub-micron device with fast laser grooving technique

Cross-sectional sample preparation is one of the most important failure analysis (FA) techniques in the semiconductor industry. It was commonly used for film stack critical dimension measurement, defect identification, electrical fault isolation and etc. However, cross-sectional sample preparation to a specific target location on a sub-micron device is very challenging and time-consuming. This is because of mechanical polishing easily caused metal smear, delamination, film peel-off, micro-cracked and etc. This paper focused on cross-sectional nanoprobing (XNP) sample preparation improvement in quality and quantity. A laser blast to deprocess or create a groove at near to target location before conventional mechanical polishing and focus ion beam (FIB) fine milling. The proposed technique not only reduces the sample preparation time to the sub-micron target location but also prevent mechanical damages that caused by mechanical polishing technique.

Study of the austenitic stainless steel with gradient structured surface fabricated via shot peening

A gradient-structured layer with initially nanoscale grain size increased gradually to original coarse microscale (∼50 μm) was fabricated on the surface of austenitic (γ) stainless steel SS304 via ultrasonic nanocrystallization surface modification (UNSM) peening. Modified cross-sectional and depth-specific plan-view (DSPV) sample preparation methods were explored with the analysis scales from macro to atom by synchrotron radiation XRD, EBSD, and TEM to determine the depth (strain) dependent deformation microstructures and grain refinement mechanism. The depth-dependent deformation microstructures were ascribed to strain-induced martensitic-transformed (SIMT) α′- and ε-martensite, deformation nanotwins (NT), and dislocation grids. The grain nanocrystallization mechanism was suggested as the formation of α′ and ε grain boundaries that divided the original coarse grains (CG) to the nanoscale. The strains also appeared to play a key role in the crystallographic orientation relationship (OR) of the γ/α′: Kurdjumov-Sachs (K-S) and Pitsch in low strain region and Nishiyama-Wassermann (N-W) in the high strain region.

Cross-Sectional Transmission Electron Microscopy Sample Preparation of Soldering Joint Using Ultramicrotomy

Many studies have reported the interfacial reaction of Sn-Ag/ electroless nickel immersion gold (ENIG). Various analysis techniques, such as scanning electron microscopy, electron probe microanalyzer, and transmission electron microscopy (TEM), have been used to examine interfacial reaction. Among them, TEM equipped with analytical attachments offers the most complete tool for characterizing the formation of intermetallic compounds (IMCs) at the interface. However, solders are typically soft and ductile, while IMCs tend to be quite hard and brittle, which has limited the level of success in preparing TEM samples. We utilized ultramicrotomy since it might offer a reasonable and relatively quick alternative in this case. Ultramicrotomy has been used for the preparation of TEM specimens from biological materials and extending a range of materials including polymers, coating layer, particles, and even metals (Becker & Bange, 1993; Glanvill, 1995; Howell et al., 1995). TEM sample making to section hard materials by ultramicrotomy are not new. Besides, it has been traditionally considered that the mechanical damage during sectioning by diamond knife might hinder unambiguous specimen characterization. However, this technique also has many advantages such as no ion beam irradiation damage, no chemical mixing, no differential thinning rate and the ease of preparation of many serial sections with large, thin areas of uniform thickness in a relatively short time (Quintana, 1997). The increasing acceptability of ultramicrotomy in materials science is evidenced by a number of recent paper giving results for different hard materials (Hwang & Suganuma, 2003).

Fabrication of high aspect ratio AFM probes with different materials inspired by TEM “lift-out” method

The most commonly used materials in all commercially available high-aspect-ratio (HAR) nanowire's (NW) tips are made of silicon and carbon nanotube which limit their applications in other types of atomic force microscopy (AFM), such as conducting AFM and magnetic force microscope. Therefore, a simple process inspired by cross-sectional transmission electron microscopy sample preparation method was used to demonstrate the feasibility of fabricating HAR AFM probes, which can easily define the tilt angle of the NW tip with respect to the direction that is normal to the axis of the cantilever to which it is attached by simply tilting the sample stage where the cantilever is placed. This is very important as it enables precise control of the inclination angle of the NW tip and allows the tip to be made perpendicular to the probed surface for scanning with different AFM mounts. Two different tips were fabricated, one attached parallel and the other attached at an angle of 13° with respect to the normal of the cantilever axis. These tips were used to profile the topography of a silicon nanopillar array. Only the probe attached at an angle of 13° allowed mapping of the topography between nanopillars. This is the first successful demonstration of an HAR AFM tip being used to map the topography of a nanopillar array. In addition, the authors also demonstrated that this method can be extended to fabricate HAR AFM tips of different materials such as copper with a slightly modified approach.

Cross-sectional atom probe tomography sample preparation for improved analysis of fins on SOI

Sample preparation for atom probe tomography of 3D semiconductor devices has proven to significantly affect field evaporation and the reliability of reconstructed data. A cross-sectional preparation method is applied to state-of-the-art Si finFET technology on SOI. This preparation approach advantageously provides a conductive path for voltage and heat, offers analysis of many fins within a single tip, and improves resolution across interfaces of particular interest. Measured B and Ge profiles exhibit good correlation with SIMS and EDX and show no signs of B clustering or pile-up near the Si/SiGe interface of the fin.

Detection and Analysis of Subsurface Cracks of Single Crystal SiC Wafers Based on Cross-Sectional Microscopy Method

For subsurface crack detection of single crystal SiC wafer, this paper proposed a cross-sectional cleavage detection method and compared with traditional cross-sectional sample preparation method. The characteristics and detection results of two cross-sectional sample preparation methods were compared and the subsurface crack characteristics in SiC wafer grinding were researched. The results show that the configurations and depth of subsurface cracks measured by two cross-sectional sample preparation methods were similar. The cross-sectional cleavage sample preparation method is simpler and more rapid in subsurface crack detection. The subsurface crack system of single crystal SiC wafer grinding mainly includes lateral crack and median crack.

Cross-sectional analysis of W-cored Ni nanoparticle via focused ion beam milling with impregnation.

Tungsten and nickel bimetallic nanoparticle is synthesized by radio frequency thermal plasma process which belongs to the vapor phase condensation technology. The morphology and chemical composition of the synthesized particle were investigated using the conventional nanoparticle transmission electron microscopy (TEM) sample. A few part of them looked like core/shell structured particle, but ambiguities were caused by either TEM sample preparation or TEM analysis. In order to clarify whether a core/shell structure is developed for the particle, various methodologies were tried to prepare a cross-sectional TEM sample. Focused ion beam (FIB) milling was conducted for cold-compacted particles, dispersed particles on silicon wafer, and impregnated particles with epoxy which is compatible with electron beam. A sound cross-sectional sample was just obtained from cyanoacrylate impregnation and FIB milling procedure. A tungsten-cored nickel shell structure was precisely confirmed with aid of cross-sectional sample preparation method.

FIB Plan and Side View Cross-Sectional TEM Sample Preparation of Nanostructures

Focused ion beam is a powerful method for cross-sectional transmission electron microscope sample preparation due to being site specific and not limited to certain materials. It has, however, been difficult to apply to many nanostructured materials as they are prone to damage due to extending from the surface. Here we show methods for focused ion beam sample preparation for transmission electron microscopy analysis of such materials, demonstrated on GaAs-GaInP core shell nanowires. We use polymer resin as support and protection and are able to produce cross-sections both perpendicular to and parallel with the substrate surface with minimal damage. Consequently, nanowires grown perpendicular to the substrates could be imaged both in plan and side view, including the nanowire-substrate interface in the latter case. Using the methods presented here we could analyze the faceting and homogeneity of hundreds of adjacent nanowires in a single lamella.

Novel techniques of preparing TEM samples for characterization of irradiation damage

Focus ion beam preparation of transmission electron microscopy (TEM) samples has become increasingly popular due to the relative ease of extraction of TEM foils from specific locations within a larger sample. However the sputtering damage induced by Ga ion bombardment in focus ion beam means that traditional electropolishing may be a preferable method. First, we describe a special electropolishing method for the preparation of irregular TEM samples from ex-service nuclear reactor components, spring-shaped spacers. This method has also been used to prepare samples from a nonirradiated component for a TEM in situ heavy ion irradiation study. Because the specimen size is small (0.7 × 0.7 × 3 mm), a sandwich installation is adopted to obtain high quality polishing. Second, we describe some modifications to a conventional TEM cross-section sample preparation method that employs Ni electroplating. There are limitations to this method when preparing cross-section samples from either (1) metals which are difficult to activate for electroplating, or (2) a heavy ion irradiated foil with a very shallow damage layer close to the surface, which may be affected by the electroplating process. As a consequence, a novel technique for preparing cross-section samples was developed and is described.

Cross‐section metal sample preparations for transmission electron microscopy by electro‐deposition and electropolishing

A cross-section sample preparation technique is described for transmission electron microscopy studies of metallic materials. The technique uses jet electro-polishing for the final perforation. Examples are provided of using this technique for copper-support/copper-films/copper-support multilayer structures, grown by electro-deposition. The samples prepared by our current technique are compared with the ones made by ion-milling. The technique is also applicable to materials which are susceptible to ion beam and thermal damages.

Optimized Ar+-ion milling procedure for TEM cross-section sample preparation

High-quality samples are indispensable for every reliable transmission electron microscopy (TEM) investigation. In order to predict optimized parameters for the final Ar(+)-ion milling preparation step, topographical changes of symmetrical cross-section samples by the sputtering process were modeled by two-dimensional Monte-Carlo simulations. Due to its well-known sputtering yield of Ar(+)-ions and its easiness in mechanical preparation Si was used as model system. The simulations are based on a modified parameterized description of the sputtering yield of Ar(+)-ions on Si summarized from literature. The formation of a wedge-shaped profile, as commonly observed during double-sector ion milling of cross-section samples, was reproduced by the simulations, independent of the sputtering angle. Moreover, the preparation of wide, plane parallel sample areas by alternating single-sector ion milling is predicted by the simulations. These findings were validated by a systematic ion-milling study (single-sector vs. double-sector milling at various sputtering angles) using Si cross-section samples as well as two other material-science examples. The presented systematic single-sector ion-milling procedure is applicable for most Ar(+)-ion mills, which allow simultaneous milling from both sides of a TEM sample (top and bottom) in an azimuthally restricted sector perpendicular to the central epoxy line of that cross-sectional TEM sample. The procedure is based on the alternating milling of the two halves of the TEM sample instead of double-sector milling of the whole sample. Furthermore, various other practical aspects are issued like the dependency of the topographical quality of the final sample on parameters like epoxy thickness and incident angle.

FIB TEM Cross-Section Sample Preparation of Thin Metal Films Deposited on Polymer Substrates

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.