Site-specific Specimen Preparation Research Articles

Optimizing site-specific specimen preparation for atom probe tomography by using hydrogen for visualizing radiation-induced damage

Atom probe tomography (APT) is extensively used to measure the local chemistry of materials. Site-specific preparation via a focused ion beam (FIB) is routinely implemented to fabricate needle-shaped specimens with an end radius in the range of 50 nm. This preparation route is sometimes supplemented by transmission Kikuchi diffraction (TKD) to facilitate the positioning of a region of interest sufficiently close to the apex. Irradiating the specimen with energetic electrons and ions can lead to the generation of vacancies and even amorphization of the specimen. These extrinsically created vacancies become crucial for probing the hydrogen or deuterium distribution since they act as a strong trap. Here, we investigated the feasibility of site-specific preparation of a two-phase medium-Mn steel containing austenite (fcc) and ferrite (bcc). Following gaseous charging of APT specimens in deuterium (D2), clusters enriched by up to 35 at.% D, are imaged after Pt deposition, conventional Ga-FIB preparation, and TKD conducted separately. These D-rich clusters are assumed to arise from the agglomeration of vacancies acting as strong traps. By systematically eliminating these preparation-induced damages, we finally introduce a workflow allowing for studying intrinsic traps for H/D inherent to the material.

Development of Site Specific Cryogenic Specimen Preparation and Transfer of Frozen Liquids for Complementary High-Resolution Analysis by Scanning Transmission Electron Microscopy and Atom Probe Tomography.

Development of Site Specific Cryogenic Specimen Preparation and Transfer of Frozen Liquids for Complementary High-Resolution Analysis by Scanning Transmission Electron Microscopy and Atom Probe Tomography.

Correlative Site-Specific Sample Preparation for Atom Probe Tomography on Complex Microstructures.

Site-specific specimen preparation for atom probe tomography (APT) is a challenging task. Small features need to be located using a suitable imaging technique and captured within a volume of less than 0.01 μm3. Correlative microscopy has shown to be helpful for target preparation as well as to gain complementary information about the material. Current strategies developed in that direction can be highly time-consuming and not always ensure the correct site extraction in complex microstructures. In this work, we present a methodology to study grain boundaries and interfaces in martensitic steels by combining electron backscattered diffraction, transmission Kikuchi diffraction (TKD), and APT. Furthermore, we include the design of a sample holder that allows to perform TKD and scanning transmission electron microscopy on the specimen during preparation without breaking the vacuum of the scanning electron microscope/focused ion beam workstation. We show a case study where a prior austenite grain boundary is traced from the bulk material to the apex of the APT specimen. The presence of contamination due to the specimen exposure to the electron beam and the use of plasma cleaning to minimize it are discussed.

Xenon plasma focussed ion beam preparation of an Al-6XXX alloy sample for atom probe tomography including analysis of an α-Al(Fe,Mn)Si dispersoid

A Xe plasma Focussed Ion Beam instrument was used to prepare in-situ specimens for Atom Probe Tomography from a bulk sample of an aluminium 6XXX alloy. The nature and distribution of precipitates and solute clusters observed in the alloy are not observed to differ between standard electropolishing methods and Xe plasma preparation. Enabled by site specific specimen preparation, analysis of an α-Al(Fe,Mn)Si dispersoid shows segregation at the phase boundary and in the shell of the dispersoid.

A method for site-specific and cryogenic specimen fabrication of liquid/solid interfaces for atom probe tomography

A site-specific, cryogenic, focused ion beam (FIB) method is presented for the preparation of atom probe tomography (APT) specimens from a frozen liquid/solid interface. As a practical example, the interface between water and a corroded boroaluminosilicate glass has been characterized by APT for the first time. The water/glass interface is preserved throughout specimen preparation by plunge freezing the corroding glass particles with the corrosion solution into slush nitrogen. Site-specific specimen preparation is enabled through a new approach to extract and mount a small volume of material using a cryogenically cooled FIB stage and micromanipulator. The prepared APT specimens are subsequently transferred from the FIB to APT under cryogenic and high-vacuum conditions using a novel FIB/APT transfer shuttle and home-built environmental transfer hub attached to the APT system. Particular focus is given to the technical methods for specimen fabrication under cryogenic conditions. Persistent challenges are discussed in addition to future opportunities for this new specimen preparation method.

Modern Focused-Ion-Beam-Based Site-Specific Specimen Preparation for Atom Probe Tomography.

Approximately 30 years after the first use of focused ion beam (FIB) instruments to prepare atom probe tomography specimens, this technique has grown to be used by hundreds of researchers around the world. This past decade has seen tremendous advances in atom probe applications, enabled by the continued development of FIB-based specimen preparation methodologies. In this work, we provide a short review of the origin of the FIB method and the standard methods used today for lift-out and sharpening, using the annular milling method as applied to atom probe tomography specimens. Key steps for enabling correlative analysis with transmission electron-beam backscatter diffraction, transmission electron microscopy, and atom probe tomography are presented, and strategies for preparing specimens for modern microelectronic device structures are reviewed and discussed in detail. Examples are used for discussion of the steps for each of these methods. We conclude with examples of the challenges presented by complex topologies such as nanowires, nanoparticles, and organic materials.

Grain boundary study of technically pure molybdenum by combining APT and TKD

Molybdenum is an eligible material for high performance applications. However, its applicability is limited because of a brittle-to-ductile transition around room temperature, depending on the grain size and the content of interstitial impurities present at grain boundaries. The total amount of impurities in the current quality of molybdenum has become very small in the last decades. Therefore, the atom probe with its atomic resolution is the only suitable site-specific analysis technique. Nevertheless, a site-specific specimen preparation by focused ion beam (FIB) is required to study the grain boundary chemistry effectively. With a novel method, which combines re-sharpening of pre-electro-polished tips by FIB with transmission Kikuchi diffraction (TKD), a grain boundary can easily be positioned in the first 200nm of an atom probe sample. Furthermore, the high resolution technique of TKD gives the opportunity to get crystallographic information of the mapped area and, therefore, an analysis of the grain boundary character to support the interpretation of the atom probe data files.In the present study, APT specimens of technically pure molybdenum which contain grain boundaries were prepared by FIB in support of TKD and subsequently were measured in the atom probe. The difference of segregation content at unequal types of grain boundaries in the as-deformed and recrystallized state is discussed.

Site Specific TEM Specimen Preparation for Characterization of Extended Defects in 4H-SiC Epilayers

Silicon carbide (SiC) is an important semiconductor for high temperature, high voltage and high power electronic applications. Unfortunately, SiC still has not reached its potential in these applications due to the presence of extended defects in epilayers, which degrade the performance of SiC-based devices. In this work, focused ion beam (FIB) is employed to prepare site-specific cross-sectional transmission electron microscopy (TEM) specimens allowing direct characterization of unwanted in-grown stacking faults (IGSFs) and basal plane dislocations (BPDs). IGSFs are known to decrease breakdown voltages and increase leakage currents in SiC diodes [1]; however, their nucleation mechanism is currently not established. BPDs can form recombination-induced stacking faults, which lead to device performance degradation over time [2]. Recently, KOH etching of the substrate was reported to cause conversion of BPDs to electrically benign threading edge dislocations (TEDs) in the epilayer. However, for some BPDs this conversion was also associated with a shift in the locations of etch pits [3]. In this study, FIB and TEM are used to explain the nucleation mechanism of IGSFs and the previously observed shift in the locations of BPDs.

A novel approach for site-specific atom probe specimen preparation by focused ion beam and transmission electron backscatter diffraction.

Atom probe tomography (APT) is a suitable technique for chemical analyses with almost atomic resolution. However, the time-consuming site-specific specimen preparation can be improved. Recently, transmission electron backscatter diffraction (t-EBSD) has been established for high resolution crystallographic analyses of thin foils. In this paper we present the first successful application of a combined focused ion beam (FIB)/t-EBSD preparation of site-specific APT specimens using the example of grain boundary segregation in technically pure molybdenum. It will be shown that the preparation of a grain boundary can be substantially accelerated by t-EBSD analyses in-between the annular milling FIB procedure in the same microscope. With this combined method, a grain boundary can easily be recognized and positioned in the first 220nm of an APT sample much faster than e.g. with complementary investigations in a transmission electron microscope. Even more, the high resolution technique of t-EBSD gives the opportunity to get crystallographic information of the mapped area and, therefore, an analysis of the grain boundary character to support the interpretation of the APT data files. To optimize this newly developed technique for the application on needle-shaped APT specimens, a parameter study on enhanced background correction, acceleration voltage, and tilt angle was carried out. An acceleration voltage of 30kV at specimen surface tilt angles between -45° and -35° from horizontal plane leads to the best results. Even for molybdenum the observation of crystal orientation data up to about 200nm specimen thickness is possible.

Atom probe study of grain boundary segregation in technically pure molybdenum

Molybdenum, a metal with excellent physical, chemical and high-temperature properties, is an interesting material for applications in lighting-technology, high performance electronics, high temperature furnace construction and coating technology. However, its applicability as a structural material is limited because of the poor oxidation resistance at high temperatures and a brittle-to-ductile transition around room temperature, which is influenced by the grain size and the content of interstitial impurities at the grain boundaries. Due to the progress of the powder metallurgical production during the last decades, the amount of impurities in the current quality of molybdenum has become so small that surface sensitive techniques are not applicable anymore. Therefore, the atom probe, which allows the detection of small amounts of impurities as well as their location, seems to be a more suitable technique. However, a site-specific specimen preparation procedure for grain boundaries in refractory metals with a dual focused ion beam/scanning electron microscope is still required.The present investigation describes the development and successful application of such a site-specific preparation technique for grain boundaries in molybdenum, which is significantly improved by a combination with transmission electron microscopy. This complimentary technique helps to improve the visibility of grain boundaries during the last preparation steps and to evidence the presence of grain and subgrain boundaries without segregants in atom probe specimens. Furthermore, in industrially processed and recrystallized molybdenum sheets grain boundary segregation of oxygen, nitrogen and potassium is successfully detected close to segregated regions which are believed to be former sinter pores.

Effect of grain boundary orientation on radiation-induced segregation in a Fe–15.2 at.% Cr alloy

Ferritic chromium steels are important structural materials for future nuclear fission and fusion reactors due to their advantages over traditional austenitic steels, such as higher thermal fatigue resistance, lower thermal expansion coefficients and reduced swelling. However radiation-induced segregation or depletion (RIS/RID) of solute atoms at grain boundaries in these materials is a concern because these phenomena could adversely affect their mechanical properties. In an effort to develop a full mechanistic understanding of RIS/RID, a systematic approach combining orientation imaging, site-specific specimen preparation and three-dimensional atomic-scale analysis has been developed to characterize the behaviour of Cr and C at grain boundaries during irradiation. This methodology has been applied to a Fe–15.2at.% Cr alloy to investigate the effects of grain boundary misorientation, irradiation depth and impurities. Systematic differences in Cr segregation are reported as a function of grain boundary character and irradiation conditions. The similar properties demonstrated by grain boundaries of similar type means that it should be possible to apply relatively simple models to predict the long-term behaviour of these materials under irradiation conditions.

Micro/nanometric investigations of the effects of laser ablation in the generation of micro-tools from solid CVD diamond structures

Using pulsed laser ablation, a novel method has been successfully developed for the generation of micro-features in diamond thus enabling the production of precision abrasive like micro-cutting elements into solid diamond micro-grinding tools. This paper examines the effects of the laser ablation on the generation of abrasive micro-features in diamond by using electron energy loss spectroscopy (EELS) and transmission electron microscopy (TEM). Site specific specimen preparation by a focus ion beam (FIB) material removal process has been made possible by the application of platinum and tungsten protective layers, providing the necessary specimen surface stability during the ion beam milling and lift-out operations. The prepared thin section orientated orthogonally to the cutting edge of a laser generated abrasive feature, has allowed the identification of the graphite and diamond allotropes across the ablated interface using EELS. A sequence of TEM images has revealed the extent of surface graphitisation and the high integrity of the diamond substructure. TEM examinations at nanometric resolutions have allowed the visualisation of the diamond and graphite allotropes at molecular level while depicting the abrupt graphite to diamond transition resulting in a highly defined boundary, thereby endorsing the capabilities of the laser ablation process to generate cutting edges with minimal structural damage.

A reproducible method for damage‐free site‐specific preparation of atom probe tips from interfaces

Atom probe tomography (APT) is a mass spectrometry method with atomic-scale spatial resolution that can be used for the investigation of a wide range of materials. The main limiting factor with respect to the type of problems that can be addressed is the small volume investigated and the randomness of common sample preparation methods. With existing site-specific specimen preparation methods it is still challenging to rapidly and reproducibly produce large numbers of successful samples from specifically selected grain boundaries or interfaces for systematic studies. A new method utilizing both focused ion beam (FIB) and transmission electron microscopy (TEM) is presented that can be used to reproducibly produce damage-free atom probe samples with features of interest at any desired orientation with an accuracy of better than 50 nm from samples that require very little prior preparation.

Broadening the applications of the atom probe technique by ultraviolet femtosecond laser

Laser assisted field evaporation using ultraviolet (UV) wavelength gives rise to better mass resolution and signal-to-noise ratio in atom probe mass spectra of metals, semiconductors and insulators compared to infrared and green lasers. Combined with the site specific specimen preparation techniques using the lift-out and annular Ga ion milling in a focused ion beam machine, a wide variety of materials including insulating oxides can be quantitatively analyzed by the three-dimensional atom probe using UV laser assisted field evaporation. After discussing laser irradiation conditions for optimized atom probe analyses, recent atom probe tomography results on oxides, semiconductor devices and grain boundaries of sintered magnets are presented.

FIB/DualBeam Techniques for Quantitative Analyses

Lucille A. Giannuzzi FEI Company, 5350 NE Dawson Creek Drive, Hillsboro, OR 97124 The use of Focused ion beam (FIB) and combined FIB plus scanning electron microscope (SEM) dual platform instruments have continued to increase in popularity over the past decade in both the physical and biological sciences. FIB based techniques enable site specific regions to be prepared for direct quantitative analysis and/or extracted for quantitative analyses using other analytical instruments in material systems that were once too difficult or unfeasible to observe by other means. In addition, since FIB techniques in general offer higher throughput than conventional methods, more samples may be quantified than previously possible. In this paper, quantitative techniques facilitated by either direct FIB imaging or FIB-based specimen preparation methods are discussed. One of the most popular uses of focused ion beams is for transmission electron microscopy (TEM) specimen preparation. The ubiquitous FIB lift-out techniques allow for site-specific extraction of interfaces, inclusions, failure sites, etc., from a wide range of materials [1]. Therefore, quantitative x-ray energy dispersive spectrometry (XEDS) techniques can be directly applied to e.g., interdiffusion studies [2], or grain boundary segregation effects on grain boundary diffusion [3]. A particular advantage to FIB-based imaging is the channeling contrast generated by ion induced secondary electron imaging which is unsurpassed compared to conventional SEM imaging. Thus, FIB imagining can provide direct capabilities for quantification of microstructural features. This ability to use FIB channeling contrast imaging on a mechanically polished Cu-Ni diffusion couple revealed regions where diffusion induced recrystallization (DIR) occurred at the diffusion couple interface [2]. Site specific TEM specimen preparation of DIR and non-DIR regions allowed for direct quantitative analysis of the Cu-Ni diffusion couple showing an enhancement of lattice interdiffusion due to grain boundary contributions [2]. FIB channeling across grain boundaries was also used to prepare TEM specimens for the quantification of the effects of Bi segregation on the Ni diffusion through Cu twist boundaries [3]. In addition, dopant profiles of p/n junctions within Si-based transistor gates can be quantified using electron holography methods with the utilization of back-side FIB milling plus low energy polishing steps [4]. The basic FIB lift-out techniques have also been employed to prepare samples for quantification in surface science instruments such as x-ray photoelectron spectroscopy [5], Auger electron spectroscopy [6], secondary ion mass spectroscopy (SIMS) [6], as well as 3D atom probe [7,8]. The same techniques used to prepare atom probe specimens can be used to make pillar-shaped TEM specimens for on-axis TEM tomography [9,10].

A Method for Site-specific Specimen Preparation of Si Device after 65 nm-node Technology using FIB-STEM/TEM System

A Method for Site-specific Specimen Preparation of Si Device after 65 nm-node Technology using FIB-STEM/TEM System

Site-specific specimen preparation for atom probe tomography of grain boundaries

Atom probe tomography is a powerful technique that is highly suited to the study of low-level grain boundary segregation. However, difficulties in preparation of the required needle-shaped specimens containing the area of interest have precluded detailed studies of this nature to date. Two new methods are presented to manufacture atom probe tips from site-specific areas using a dual-beam focused ion beam (FIB)/scanning electron microscope (SEM). One involves the use of electropolished blanks, which are resharpened using the ion beam, and the second utilises micromanipulators to lift the area of interest directly from a bulk specimen before ion beam fabrication of the tip. The advantages and drawbacks of each technique are compared.

FIB and TEM studies of interface structure in diamond–SiC composites

The microstructure of diamond–SiC interfaces was studied by transmission electron microscopy (TEM). Specimens were prepared by focused ion beam (FIB) etching from a diamond–SiC composite bulk material. The diamond–SiC interfaces were easily located by high contrast in FIB images of the bulk surface, and site-specific specimen preparation was possible. The possible origin of this high contrast in FIB images compared to SEM images is discussed. TEM images and electron diffraction patterns showed that the diamond and SiC crystals away from the interface region are relatively defect-free, but numerous defects are present at the diamond–SiC interface over a dimension of 600 nm, much larger than the physical interface.

Site-specific specimen preparation by focused ion beam milling for transmission electron microscopy of metal matrix composites.

This work describes the application and usefulness of the focused ion beam (FIB) technique for the preparation of transmission electron microscopy (TEM) samples from metal matrix composite materials. Results on an Aldiamond composite, manufactured by the squeeze casting infiltration process, were chosen for demonstration. It is almost impossible to prepare TEM specimens of this material by any other conventional method owing to the presence of highly inhomogeneous phases and reinforcement diamond particles. The present article gives a detailed account of the salient features of the FIB technique and its operation. One of the big advantages is the possibility to prepare site-specific TEM specimens with high spatial resolution. The artifacts occurring during the specimen preparation, for example, Ga-ion implantation, curtain effects, amorphous layers, bending of the lamella, or different milling behaviors of the materials have been discussed. Furthermore, TEM examination of the specimens prepared revealed an ultrafine amorphous layer of graphite formed at the interface between the Al and diamond particles that may affect the interfacial properties of the composite materials. This may not have been feasible without the successful application of the FIB technique for production of good quality site-specific TEM specimens.

Microstructure of as-coated thermal barrier coatings with varying lifetimes

The microstructures of the thermally grown oxide (TGO) in as-coated electron beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) were examined by scanning transmission electron microscopy (STEM) as a function of demonstrated TBC lifetime in a thermally cycled environment. As-coated TBC specimens were selected for analysis based on individual statistical significance in overall lifetime variation (i.e. early failures to long-lasting). Weibull probability distribution developed through cyclic furnace tests (CFT) served as the medium to determine statistical significance. For selected TBC specimens that represent the variation in lifetime, site-specific specimen preparation for STEM was carried out by focused ion beam (FIB) equipped with in-situ lift-out (INLO) technique. Differences in microstructure of TGO particularly in the mixed-oxide and continuous-oxide zone were examined and correlated to the lifetime characteristics of the TBCs. The TGO for durable TBC consisted of fine grained, uniformly thick, and dense mixed-oxide zone in addition to a uniform and smooth microstructural transition into the continuous oxide zone.