Combining Ar ion milling with FIB lift-out techniques to prepare high quality site-specific TEM samples

Focused ion beam (FIB) techniques can prepare site‐specific transmission electron microscopy (TEM) cross‐section samples very quickly but they suffer from beam damage by the high energy Ga⁺ ion beam. An amorphous layer about 20–30 nm thick on each side of the TEM lamella and the supporting carbon film makes FIB‐prepared samples inferior to the traditional Ar⁺ thinned samples for some investigations such as high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). We have developed techniques to combine broad argon ion milling with focused ion beam lift‐out methods to prepare high‐quality site‐specific TEM cross‐section samples. Site‐specific TEM cross‐sections were prepared by FIB and lifted out using a Narishige micromanipulator onto a half copper‐grid coated with carbon film. Pt deposition by FIB was used to bond the lamellae to the Cu grid, then the coating carbon film was removed and the sample on the bare Cu grid was polished by the usual broad beam Ar⁺ milling. By doing so, the thickness of the surface amorphous layers is reduced substantially and the sample quality for TEM observation is as good as the traditional Ar⁺ milled samples.     

双束聚焦离子束工作原理及微电子领域的应用

聚焦离子束系统以其超强的微加工及微分析能力在微电子领域的地位越来越重要。随着聚焦离子束系统的发展,离子束和电子束结合的双束聚焦离子束系统已经普遍被使用。双束聚焦离子束系统结合了高能离子束和电子束的优点,采用液态镓离子源通过高压引出,并经偏转会聚为离子束实现样品加工,利用高能电子束扫描样品成像,可以做到边加工边观察。本文介绍了双束聚焦离子束系统的组成,主要部件的工作原理及在微电子领域的主要应用,并详述了主要应用的操作方法。     

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. Microsc. Res. Tech. 76:476–480, 2013. © 2013 Wiley Periodicals, Inc.     

Preparation of site-specific cross-sections of heterogeneous catalysts prepared by focused ion beam milling

Focused ion beam (FIB) milling offers a novel approach to preparation of site‐specific cross‐sections of heterogeneous catalysts for examination in the transmission electron microscope (TEM). Electron‐transparent sections can be obtained without the need to embed or grind the original sample. Because the specimen can be imaged in the FIB with submicrometre resolution before, during and after milling it is possible to select precisely the region from which the section is removed and to control the thickness of the section to within tens of nanometres. The ability to produce sections in this way opens the possibility of studying a range of catalyst systems that have previously been impossible to examine with the TEM.     

Making the practically impossible “Merely difficult”—Cryogenic FIB lift‐out for “Damage free” soft matter imaging

The preparation of thinned lamellae from bulk samples for transmission electron microscopy (TEM) analysis has been possible in the focussed ion beam scanning electron microscope (FIB‐SEM) for over 20 years via the in situ lift‐out method. Lift‐out offers a fast and site specific preparation method for TEM analysis, typically in the field of materials science. More recently it has been applied to a low‐water content biological sample (Rubino 2012). This work presents the successful lift‐out of high‐water content lamellae, under cryogenic conditions (cryo‐FIB lift‐out) and using a nanomanipulator retaining its full range of motion, which are advances on the work previously done by Rubino (2012). Strategies are explored for maintaining cryogenic conditions, grid attachment using cryo‐condensation of water and protection of the lamella when transferring to the TEM. Microsc. Res. Tech. 79:298–303, 2016. © 2016 Wiley Periodicals, Inc.     

Surface damage formation during ion-beam thinning of samples for transmission electron microscopy

All techniques employed in the preparation of samples for transmission electron microscopy (TEM) introduce or include artifacts that can degrade the images of the materials being studied. One significant cause of this image degradation is surface amorphization. The damaged top and bottom surface layers of TEM samples can obscure subtle detail, particularly at high magnification. Of the techniques typically used for TEM sample preparation of semiconducting materials, cleaving produces samples with the least surface amorphization, followed by low-angle ion milling, conventional ion milling, and focused ion beam (FIB) preparation. In this work, we present direct measurements of surface damage on silicon produced during TEM sample preparation utilizing these techniques. The thinnest damaged layer formed on a silicon surface was measured as 1.5 nm thick, while an optimized FIB sample preparation process results in the formation of a 22 nm thick damaged layer. Lattice images are obtainable from all samples.     

Reducing the formation of FIB-induced FCC layers on Cu-Zn-Al austenite

The irradiation effects of thinning a sample of a Cu-Zn-Al shape memory alloy to electron transparency by a Ga(+) focused ion beam were investigated. This thinning method was compared with conventional electropolishing and Ar(+) ion milling. No implanted Ga was detected but surface FCC precipitation was found as a result of the focused ion beam sample preparation. Decreasing the irradiation dose by lowering the energy and current of the Ga(+) ions did not lead to a complete disappearance of the FCC structure. The latter could only be removed after gentle Ar(+) ion milling of the sample. It was further concluded that the precipitation of the FCC is independent of the crystallographic orientation of the surface.     

An improved preparation method for cross‐sectional TEM specimens of films deposited on metallic substrates

Cross‐sectional TEM analysis is one of the most important techniques to characterize microstructures of films. However, the complex process, low efficiency, and low success rate of specimen preparation limit its application. This paper analyzed the main causes of low success rate and proposed an improved method for specimen preparation of films deposited on metallic substrates. This method consisting of twin‐jet electropolishing and one‐sided rocking ion milling is high in efficiency and success rate. Microsc. Res. Tech. 79:276–279, 2016. © 2016 Wiley Periodicals, Inc.     

Microstructural characterization of Ti‐6Al‐4V alloy subjected to the duplex SMAT/plasma nitriding

In this study, microstructural characterization of Ti‐6Al‐4V alloy, subjected to the duplex surface mechanical attrition treatment (SMAT)/nitriding treatment, leading to improve its mechanical properties, was carried out through novel and original samples preparation methods. Instead of acid etching which is limited for morphological characterization by scanning electron microscopy (SEM), an original ion polishing method was developed. Moreover, for structural characterization by transmission electron microscopy (TEM), an ion milling method based with the use of two ions guns was also carried out for cross‐section preparation. To demonstrate the efficiency of the two developed methods, morphological investigations were done by traditional SEM and field emission gun SEM. This was followed by structural investigations through selected area electron diffraction (SAED) coupled with TEM and X‐ray diffraction techniques. The results demonstrated that ionic polishing allowed to reveal a variation of the microstructure according to the surface treatment that could not be observed by acid etching preparation. TEM associated to SAED and X‐ray diffraction provided information regarding the nanostructure compositional changes induced by the duplex SMAT/nitriding process. Microsc. Res. Tech. 76:897–903, 2013. © 2013 Wiley Periodicals, Inc.     

Two‐In‐one sample preparation for plan‐VIew TEM

Transmission electron microscopy (TEM) sample preparation requires special skills, it is time consuming and costly, hence, an increase of the efficiency is of primary importance. This article describes a method that duplicates the yield of the conventional mechanical and ion beam preparation of plan‐view TEM samples. As a modification of the usual procedures, instead of one two different samples are comprised in a single specimen. The two pre‐cut slabs, one from each samples, are embedded side by side in the window of a 3 mm dia Ti disk and the specimen is thinned mechanically and by ion milling until perforation that occurs at the interface of the two different slabs. That, with proper implementation, provides acceptable size thin area for the TEM study of both samples. The suitability of the two‐in‐one method has been confirmed through examples. Microsc. Res. Tech. 78:599–602, 2015. © 2015 Wiley Periodicals, Inc.     

Use of permanent marker to deposit a protection layer against FIB damage in TEM specimen preparation

Permanent marker deposition (PMD), which creates permanent writing on an object with a permanent marker, was investigated as a method to deposit a protection layer against focused ion beam damage. PMD is a simple, fast and cheap process. Further, PMD is excellent in filling in narrow and deep trenches, enabling damage‐free observation of high aspect ratio structures with atomic resolution in transmission electron microscopy (TEM). The microstructure, composition, gap filling ability and planarization of the PMD layer were studied using dual beam focused ion beam, transmission electron microscopy, energy dispersive X‐ray spectroscopy and electron energy loss spectroscopy. It was found that a PMD layer is basically an amorphous carbon structure, and that such a layer should be at least 65 nm thick to protect a surface against 30 keV focused ion beam damage. We suggest that such a PMD layer can be an excellent protection layer to maintain a pristine sample structure against focused ion beam damage during transmission electron microscopy specimen preparation.     

A method for preparing cross sections of films on wear surfaces for transmission electron microscopy study

A method for preparing cross sections of surface layers which exist on bulk metal substrates for transmission electron microscopy (TEM) study is described. The surface layer or film is protected by a vacuum-deposited or sputtered coating of a suitable metal. A mask is placed over the surface and non-masked areas are subjected to ion beam etching until the substrate is exposed. A thick electroplated layer is then applied to the surface. This layer adheres well to the ion-etched substrate and seals the coated surface film against damage during the usual slicing and grinding steps which are required for the preparation from bulk materials of thin foils for TEM study. The method was developed specifically for the analysis of boundary and extreme pressure lubrication films on wear surfaces together with the near-surface region of the substrate. However, it is also applicable to the investigation of oxide, corrosion and other surface films.     

Minimization of focused ion beam damage in nanostructured polymer thin films

Focused ion beam (FIB) instruments have proven to be an invaluable tool for transmission electron microscopy (TEM) sample preparation. FIBs enable relatively easy and site-specific cross-sectioning of different classes of materials. However, damage mechanisms due to ion bombardment and possible beam heating effects in materials limit the usefulness of FIBs. Materials with adequate heat conductivity do not suffer from beam heating during FIB preparation, and artifacts in materials such as metals and ceramics are primarily limited to defect generation and Ga implantation. However, in materials such as polymers or biological structures, where heat conductivity is low, beam heating can also be a problem. In order to examine FIB damage in polymers we have undertaken a systematic study by exposing sections of a PS-b-PMMA block copolymer to the ion beam at varying beam currents and sample temperatures. The sections were then examined by TEM and scanning electron microscopy (SEM) and analyzed using electron energy loss spectroscopy (EELS). Our empirical results show beam heating in polymers due to FIB preparation can be limited by maintaining a low beam current (≤100 pA) during milling.     

Site-specific structural investigations of oxidized nickel samples modified by plasma erosion processes

A focused ion beam was employed for local target preparation for EBSD analysis. The volume of the ion‐solid interaction is well below 50 nm at glancing incidence for metallic and transition metal oxide samples. Therefore, focused ion beam can successfully be used for electron backscatter diffraction (EBSD) sample preparation. The sample investigated consists of Ni covered with a NiO layer of ～5 μm thickness. Focused ion beam cross‐sectioning of these layers and subsequent electron imaging in addition to EBSD maps shows a bimodal structure of the oxide layer. In order to test the potential of such oxidized samples as electrode materials, single spark erosion experiments were performed. The erosion craters have diameters up to 40 μm and have a depth corresponding to the thickness of the oxide layer. In addition, a deformation zone produced by thermoshock accompanies the formation of the crater. This deformation zone was further investigated by EBSD analysis using a new way of sample preparation employing the focused ion beam technology. This target preparation routine is called Volume of Interest Transfer and has the potential of providing a full three‐dimensional characterization.     

Preparation of TEM foils from Nb-10 a/o Si.

Ductile phase toughened composites contain phases with significantly different physical properties. Consequently, these phases thin at different rates depending on the sample preparation procedure. A new TEM foil preparation method for the ductile phase toughened Nb-10 a/o Si material has been developed. The method involves chemical thinning in a 70% nitric acid/30% hydrofluoric acid solution followed by electropolishing in a 12.5% sulfuric acid/87.5% methanol electrolyte at -40 degrees C. This procedure for making TEM foils results in large thin areas with the minimum of artifacts. Mechanical grinding of a sample followed by either ion milling, dimpling, or electropolishing produced foils with large electron transparent areas, but with uncharacteristic features of the original Nb-10 a/o Si alloy microstructure. These artifacts were identified as dislocations, surface mottling, and antiphase domains.     

Micro‐CT scouting for transmission electron microscopy of human tissue specimens

Transmission electron microscopy (TEM) provides sub‐nanometre‐scale details in volumetric samples. Samples such as pathology tissue specimens are often stained with a metal element to enhance contrast, which makes them opaque to optical microscopes. As a result, it can be a lengthy procedure to find the region of interest inside a sample through sectioning. We describe micro‐CT scouting for TEM that allows noninvasive identification of regions of interest within a block sample to guide the sectioning step. In a tissue pathology study, a bench‐top micro‐CT scanner with 10 μm resolution was used to determine the location of patches of the mucous membrane in osmium‐stained human nasal scraping samples. Once the regions of interest were located, the sample block was sectioned to expose that location, followed by ultra‐thin sectioning and TEM to inspect the internal structure of the cilia of the membrane epithelial cells with nanometre resolution. This method substantially reduced the time and labour of the search process from typically 20 sections for light microscopy to three sections with no added sample preparation.     

Revealing local variations in nanoparticle size distributions in supported catalysts: a generic TEM specimen preparation method

The specimen preparation method is crucial for how much information can be gained from transmission electron microscopy (TEM) studies of supported nanoparticle catalysts. The aim of this work is to develop a method that allows for observation of size and location of nanoparticles deposited on a porous oxide support material. A bimetallic Pt‐Pd/Al₂O₃ catalyst in powder form was embedded in acrylic resin and lift‐out specimens were extracted using combined focused ion beam/scanning electron microscopy (FIB/SEM). These specimens allow for a cross‐section view across individual oxide support particles, including the unaltered near surface region of these particles. A site‐dependent size distribution of Pt‐Pd nanoparticles was revealed along the radial direction of the support particles by scanning transmission electron microscopy (STEM) imaging. The developed specimen preparation method enables obtaining information about the spatial distribution of nanoparticles in complex support structures which commonly is a challenge in heterogeneous catalysis.     

Anatomical analysis of turgescent and semi‐dry resurrection plants: The effect of sample preparation on the sample,resolution, and image quality of X‐ray micro‐computed tomography (μCT)

Computer tomography has been used frequently for the 3‐D visualization of plant anatomical traits but sample preparation has been widely neglected. Without any preparation smaller (i.e., up to 1 × 1 cm²) turgescent or semi‐dry plant samples (especially leaf samples) diminish the image quality of a scan due to gradual water loss and therefore constant movement. A suitable preparation for scans of turgescent and semi‐dry plant samples with a high resolution μCT (<1–5 μm) has to be very thin, heat‐resistant (up to 35°C), have a low attenuation coefficient, and should not alter the water content and structure of the sample. Several agents have been tested, but only a coating with vaseline conserved the water content of a plant sample efficiently. However, water molecules and vaseline both attenuate the X‐ray beam, which decreases the image quality of scans of turgescent or semi‐dry plant samples. Therefore, trade‐offs between the spatial resolution, sample water content, sample size, and image quality have to be considered: larger samples have to be placed further away from the X‐ray tube, which leads to a lower spatial resolution; water and preparation agents attenuate the X‐ray beam, causing low‐quality images which may be accompanied by motion artifacts compared to a scan of a dry sample, where no preparation is necessary. Microsc. Res. Tech., 2011. © 2010 Wiley‐Liss, Inc.     

Novel method for the plan-view TEM preparation of thin samples on brittle substrates by mechanical and ion beam thinning

A new preparation method has been developed in order to avoid the breaking of brittle samples for plan-view TEM investigation during and after mechanical and ion beam thinning. The thinning procedure is carried out on a reduced size piece of the sample (about 1.6 x 0.8 mm(2) or about 1-1.6 mm diameter) that is embedded into a 3-mm-diameter Ti disk, which fits the sample holder of the TEM. The small sample size and the supporting metal disk assure the mechanical stability and minimize the possibility of breaking during and after the preparation: The Ti disk is placed on adhesive kapton tape, a cut piece of the sample is put into the slot of the disk, pressed onto the tape and embedded with glue. The tape keeps the parts in place and in the same plane, keeps the sample surface safe from the embedding glue and can be removed easily after the glue solidifies. Subsequently, the embedded sample is thinned from the rear by well-known mechanical and ion beam techniques until electron transparency. This simple solution lowers the risk of failed sample preparation remarkably and makes it possible to reduce the thickness of the sample to about 50 microm by mechanical thinning. As a result, dimpling becomes unnecessary and low angle ion milling gives a large transparent area for TEM. Its efficiency has been proved by successful preparation of numerous thin film samples on Si, sapphire, and glass substrates. The method is compatible with the widespread cross-sectional thinning procedures, and can be easily adopted by TEM laboratories.     

Argon broad ion beam tomography in a cryogenic scanning electron microscope: a novel tool for the investigation of representative microstructures in sedimentary rocks containing pore fluid

The contribution describes the implementation of a broad ion beam (BIB) polisher into a scanning electron microscope (SEM) functioning at cryogenic temperature (cryo). The whole system (BIB‐cryo‐SEM) provides a first generation of a novel multibeam electron microscope that combines broad ion beam with cryogenic facilities in a conventional SEM to produce large, high‐quality cross‐sections (up to 2 mm²) at cryogenic temperature to be imaged at the state‐of‐the‐art SEM resolution. Cryogenic method allows detecting fluids in their natural environment and preserves samples against desiccation and dehydration, which may damage natural microstructures. The investigation of microstructures in the third dimension is enabled by serial cross‐sectioning, providing broad ion beam tomography with slices down to 350 nm thick. The functionalities of the BIB‐cryo‐SEM are demonstrated by the investigation of rock salts (synthetic coarse‐grained sodium chloride synthesized from halite‐brine mush cold pressed at 150 MPa and 4.5 GPa, and natural rock salt mylonite from a salt glacier at Qom Kuh, central Iran). In addition, results from BIB‐cryo‐SEM on a gas shale and Boom Clay are also presented to show that the instrument is suitable for a large range of sedimentary rocks. For the first time, pore and grain fabrics of preserved host and reservoir rocks can be investigated at nm‐scale range over a representative elementary area. In comparison with the complementary and overlapping performances of the BIB‐SEM method with focused ion beam‐SEM and X‐ray tomography methods, the BIB cross‐sectioning enables detailed insights about morphologies of pores at greater resolution than X‐ray tomography and allows the production of large representative surfaces suitable for FIB‐SEM investigations of a specific representative site within the BIB cross‐section.