Methods for atom probe analysis of microgradients in functionally graded cemented carbides

Methods to prepare needle-shaped specimens for atom probe field ion microscopy from near surface regions have been developed. The material used was a cemented carbide with a composition gradient towards the surface, but the method is equally applicable for other materials. The preparation technique involves dimple grinding, electropolishing and focused ion beam (FIB) milling. The use of FIB milling allows for specimen preparation of materials which due to the preferential etching of different phases are difficult to electropolish. The technique also allows for preparation of specimens at well defined depth from the sample surface, selection of phase to be analysed, and to sharpen and re-use already analysed specimens.

Atom probe analyses of the near surface zone region in a gradient sintered WC–Ti(C,N)–TaC–Co cemented carbide are presented.     

On the Precision Preparation of Samples for Atom Probe Tomography Using a Focused Ion Beam in a SEM

Atom probe tomography is a modern and dynamically developing method of material investigation. It allows studies of the structure of matter at the atomic scale. The physical fundamentals of this method require a specific size, shape and conductivity type of the sample. To expand the analytical capabilities of atom probe tomography, a technique for preparing samples using a focused ion beam in a scanning electron microscope is studied and implemented in this work. The basic principles of this approach are demonstrated; its advantages, disadvantages and important practical aspects are described. To protect a fabricated sample from the influence of environment upon its transport to an atom probe tomograph, it is suggested a platinum coating be used. The atom-probe-tomography analysis of samples prepared with a focused ion beam is carried out. The effects of using such a sample preparation technique are studied.     

A methodology for the fabrication by FIB of needle-shape specimens around sub-surface features at the nanometre scale

A novel methodology for the preparation by focused ion beam (FIB) of needle-shape specimens in specific sites underneath the sample surface for their study by electron tomography (ET) is proposed. In particular, we demonstrate this methodology for the fabrication of needles containing InAs/InP quantum dots (QDs). The main challenge of this methodology is the location of specific QDs in the FIB equipment, as they are not visible with the secondary electrons detector. In order to overcome this difficulty, a series of marks visible both in conventional transmission electron microscopy and in the FIB are introduced before the preparation of the needles. The conditions for the fabrication by FIB of needles with optimized characteristics for their study by ET are also detailed.     

Preparation of micro-foils for TEM/STEM analysis from metallic powders

A technique has been developed which facilitates the preparation of electro-polished micro-foil transmission electron microscopy (TEM) specimens, which have previously been machined out of ≈100 μm diameter metallic powder particles using a Focussed Ion Beam (FIB) instrument. The technique can be used to create small volume TEM specimens from most metallic powder particles and bulk metal samples. This is especially useful when the matrices are ferritic steels, which are often difficult to image in the electron microscope, since the necessary aberration corrections change as the sample is tilted in the magnetic field of the objective lens.Small samples, such as powder particles, were attached to gold support grids using deposited platinum and were then ion milled to approximately 2 μm thickness in a focussed ion beam (FIB) instrument. Subsequently, the specimen assemblies were electropolished for short durations under standard conditions, to produce large (5 μm × 5 μm) electron transparent regions of material. The specimens produced by this technique were free from FIB related artefacts and facilitated atomic resolution scanning-TEM (STEM) imaging of ferritic and nickel matrices containing, for example, yttrium rich oxide nano-dispersoids.     

Redeposition effects in transmission electron microscope specimens of FeAl-WC composites prepared using a focused ion beam

Artifacts associated with transmission electron microscope (TEM) specimens prepared using a focused ion beam (FIB) are not well understood, especially those in non-semiconductor materials. In this paper the extent and origins of artifacts associated with redeposition of milled material in TEM specimens of a FeAl--WC metal matrix composite prepared by FIB were investigated. Cross-sections were prepared normal to an initial FIB cut that allowed direct observation of any damage layers, which are believed to be associated with both redeposition of sputtered material and amorphisation of the surface of the specimen by the ion beam. Techniques for the minimisation of redeposition using either final cleaning mills at low accelerating voltages or plasma cleaning were also investigated and found to be ineffective in removing or reducing these damaged layers. TEM cross-sections of specimens treated using low energy mills and plasma cleaning, further confirmed that these techniques did little to reduce any redeposited or amorphous material.     

Sample preparation by focused ion beam micromachining for transmission electron microscopy imaging in front-view

This article deals with the development of an original sample preparation method for transmission electron microscopy (TEM) using focused ion beam (FIB) micromachining. The described method rests on the use of a removable protective shield to prevent the damaging of the sample surface during the FIB lamellae micromachining. It enables the production of thin TEM specimens that are suitable for plan view TEM imaging and analysis of the sample surface, without the deposition of a capping layer. This method is applied to an indented silicon carbide sample for which TEM analyses are presented to illustrate the potentiality of this sample preparation method.     

Integration of correlative Raman microscopy in a dualbeam FIB SEM

We present an integrated confocal Raman microscope in a focused ion beam scanning electron microscope (FIB SEM). The integrated system enables correlative Raman and electron microscopic analysis combined with focused ion beam sample modification on the same sample location. This provides new opportunities, for example the combination of nanometer resolution with Raman advances the analysis of sub‐diffraction‐sized particles. Further direct Raman analysis of FIB engineered samples enables in situ investigation of sample changes. The Raman microscope is an add‐on module to the electron microscope. The optical objective is brought into the sample chamber, and the laser source, and spectrometer are placed in a module attached onto and outside the chamber. We demonstrate the integrated Raman FIB SEM function with several experiments. First, correlative Raman and electron microscopy is used for the investigation of (sub‐)micrometer‐sized crystals. Different crystals are identified with Raman, and in combination with SEM the spectral information is combined with structurally visible polymorphs and particle sizes. Analysis of sample changes made with the ion beam is performed on (1) structures milled in a silicon substrate and (2) after milling with the FIB on an organic polymer. Experiments demonstrate the new capabilities of an integrated correlative Raman–FIB–SEM. Copyright © 2016 John Wiley & Sons, Ltd.     

Combining TEM and APFIM techniques to study the microstructure of steels and hardmetals

This paper describes the benefits of combining transmission electron microscopy (TEM) and atom probe field ion microscopy (APFIM) techniques to study the microstructure of steels and hardmetals. In addition to energy dispersive X-ray spectrometry (EDS), recent experience of electron energy loss spectroscopy (EELS) and energy filtered TEM (EFTEM) is treated. Topics covered are: phase composition (APFIM, TEM/EDS and TEM/EELS); precipitate size distribution (EFTEM); precipitate volume fraction (APFIM); and compositional gradients (APFIM, EFTEM and SEM). Examples given include precipitate composition and size distribution in creep resistant 9–12% chromium steels, phase distribution and composition in nitrogen containing hardmetals (cermets) after sintering and heat treatment, and boron grain boundary segregation in austenitic stainless steels.     

Focused ion beam milling and ultramicrotomy of mineralised ivory dentine for analytical transmission electron microscopy

The use of focused ion beam (FIB) milling for preparation of sections of mineralised ivory dentine for transmission electron microscopy (TEM) is investigated. Ivory dentine is essentially composed of fibrillar type-I collagen and apatite crystals. The aim of this project is to gain a clearer understanding of the relationship between the organic and inorganic components of ivory dentine using analytical TEM, in order to utilise these analytical techniques in the context of common skeletal diseases such as osteoporosis and arthritis. TEM sections were prepared in both single and dual beam FIB instruments, using two standard lift-out techniques, in situ and ex situ. The FIB sections were systematically compared with sections prepared by ultramicrotomy, the traditional preparation route in biological systems, in terms of structural and chemical differences. A clear advantage of FIB milling over ultramicrotomy is that dehydration, embedding and section flotation can be eliminated, so that partial mineral loss due to dissolution is avoided. The characteristic banding of collagen fibrils was clearly seen in FIB milled sections without the need for any chemical staining, as is commonly employed in ultramicrotomy. The FIB milling technique was able to produce high-quality TEM sections of ivory dentine, which are suitable for further investigation using electron energy-loss spectroscopy (EELS) and energy-filtering TEM (EFTEM) to probe the collagen/apatite interface.     

The application of FIB milling for specimen preparation from crystalline germanium

The effectiveness of focused ion beam (FIB) for preparation of crystalline germanium specimens has been studied. FIB milling results in strong cellular relief of the germanium surfaces on bulk specimens. This cellular relief, associated with the generation of high densities of point defects during interaction of the specimen with the high-energy gallium beam, can be reduced by using either a lower ion beam currents or a lower beam energy. Even under these milling conditions the cellular relief is, however, still evident on the surface of the TEM specimens as evidenced by so-called 'curtaining' relief. Nevertheless good quality specimens for both conventional and high-resolution imaging may be prepared using FIB milling if low currents are employed for final milling.     

Three-dimensional atomic scale analysis of nanostructured materials

The 3-dimensional atom probe (3DAP) has been used to provide atomic-scale microcharacterisation of a number of nanostructured materials. Grain boundary segregation has been investigated in electrodeposited nanocrystalline nickel and Ni-P. In the nanocrystalline nickel, there was no observable grain boundary segregation in the as-deposited condition. After annealing, carbon and sulphur contamination was found at the boundary of an abnormally-grown grain. In the as-deposited Ni-P alloy, only limited grain boundary segregation of P is seen, but annealing produces significant segregation and the formation of Ni₃P precipitates at grain boundaries. The phase chemistry in a melt-spun amorphous Fe-Si-Cu-Nb-B-Al (FINEMET-type) alloy has also been studied, and the hetereogeneous nucleation of Fe-Si nanocrystals at Cu precipitates shown conclusively. It is found that at early stages of crystallisation, there is only limited partitioning of the Si between the nanocrystals and the amorphous matrix. Atom probe studies of thin layered films have historically been limited by specimen preparation problems, but recent advances have now yielded data on metallic multilayer films. This has allowed atomic-scale measurements of interface chemistry in these films for the first time.     

Highly regular nanometer-sized hexagonal pipes in 6H-SiC(0001)

An array of troughs was prepared on a 6H-SiC(0001) surface using focused ion beam (FIB) patterning. Troughs were etched with various ion doses and close-to-circular voids of increasing depths for larger ion doses were obtained. The samples were then etched in a hot-wall reactor at a hydrogen partial pressure of 13 mbar at 1800 °C. The resulting morphological reorganizations have been studied by scanning electron and atomic force microscopy. Very regular hexagonal voids with facets oriented perpendicular to the surface were obtained after hydrogen etching. The voids were surrounded by regular secondary facets of lower inclination. Whereas the depth of the voids increases with ion dose, the void diameter and facet sizes stay constant. This effect is explained by surface diffusion during hydrogen etching. The FIB technique in combination with hydrogen etching allows the preparation of very regular surface patterns and highly ordered wells and tubes for nanometer-sized sieves and photonic crystals. PACS 47.70.Fw; 68.37.-d; 68.37.Hk; 68.37.Ps; 81.65.Cf     

Serial sectioning methods for 3D investigations in materials science

A variety of methods for the investigation and 3D representation of the inner structure of materials has been developed. In this paper, techniques based on slice and view using scanning microscopy for imaging are presented and compared. Three different methods of serial sectioning combined with either scanning electron or scanning ion microscopy or atomic force microscopy (AFM) were placed under scrutiny: serial block-face scanning electron microscopy, which facilitates an ultramicrotome built into the chamber of a variable pressure scanning electron microscope; three-dimensional (3D) AFM, which combines an (cryo-) ultramicrotome with an atomic force microscope, and 3D FIB, which delivers results by slicing with a focused ion beam. These three methods complement one another in many respects, e.g., in the type of materials that can be investigated, the resolution that can be obtained and the information that can be extracted from 3D reconstructions. A detailed review is given about preparation, the slice and view process itself, and the limitations of the methods and possible artifacts. Applications for each technique are also provided.     

Grain boundary misorientation changes during grain growth in pure aluminium

A new method is described for data-logging large amounts of grain boundary misorientation information from channelling patterns in the scanning electron microscope (SEM). The method relies on producing specimens where the grain size is larger than the specimen thickness and where the grain boundary planes are perpendicular to the specimen plane (the so-called columnar structure). Results for grain growth in pure aluminium at 460 and 500°C are presented. There is an increase in the proportion of low angle boundaries at the expense of high angle boundaries during growth times of up to a few hours. The reasons are thought to be partly connected with lower low angle boundary mobility compared with high angle boundaries. However, the growth kinetics appear to be normal over the entire growth time range.     

Transformation of Slip Dislocations in Σ3 Grain Boundary

Grain boundary processes during plastic deformation of bicrystals were studied by TEM. Two methods were used. In situ straining in the electron microscope followed by post mortem examination and post mortem observation of specimens previously deformed by in situ synchrotron radiation X-ray topography. Two mechanisms governing slip propagation across a coherent twin boundary in a Fe-Si alloy bicrystal were identified. The first mechanism is a dissociation of a slip dislocation with the Burgers vector lying parallel to the boundary into three equal grain boundary dislocations. The second mechanism is a decomposition of a slip dislocation with Burgers vector inclined to the boundary into a dislocation mobile in the other grain and two screw grain boundary dislocations.     

Analysis of polished polycrystalline diamond using dual beam focused ion beam microscopy

This paper presents a study on polycrystalline diamond (PCD) polished by dynamic friction polishing (DFP) with the aid of advanced dual beam FIB (focused ion beam) microscopy. After disclosing a variety of wear tracks by DFP using electron imaging in combination with the ion channelling effect, a dual beam FIB was successfully employed at wear track sites to specifically create both the large cross-sectional specimen for microanalysis and thin foil for nanoanalysis. The study concluded that the polished PCD subsurface was free from microscale cracking. However, the attached debris layer on the top surface contained metal oxides and non-diamond carbon phase with inhomogeneous distributions of C, Fe, Cr, Ni, Si and O across the layer. An attached layer directly above a diamond grain was composed of essentially amorphous carbon, suggesting that a direct phase transformation from diamond crystalline to amorphous occurred during DFP.     

Optimized FIB silicon samples suitable for lattice parameters measurements by convergent beam electron diffraction

The aim of this paper is to check the effect of artefacts introduced by focused ion beam (FIB) milling on the strain measurement by convergent beam electron diffraction (CBED). We show that on optimized silicon FIB samples, the strain measurement can be performed with a sensitivity of about 2.5 × 10⁻⁴ which is very close to the theoretical one and we conclude that FIB preparation can be suitable for such measurements in microelectronic devices.

To achieve this, we first used CBED and electron energy loss spectroscopy (EELS) which provide a procedure permitting an exact knowledge of the sample geometry, i.e. the thickness of both amorphous and crystalline layers. This procedure was used in order to measure the FIB-amorphized sidewall layer. It was found that if the FIB preparation is optimized one can reduce this amorphous layer down to around 7 nm on each side. Secondly different preparation techniques (cleavage, Tripod™ and FIB) permit to check if the surface damaged layer introduced by FIB influences the strain state of the sample. Finally, it was found that the damaged layer does not introduce measurable strain in pure silicon but reduces appreciably the quality of the CBED patterns.     

Initial electron back-scattered diffraction observations of cerium

The first electron back-scattered diffraction Kikuchi patterns and grain orientation maps were captured for pure n-phase (fcc) Ce. The sample preparation technique used for electron back-scattered diffraction orientation mapping of this surface-reactive metal included ion sputtering the surface using a scanning Auger microprobe followed by vacuum transfer of the sample from the scanning Auger microprobe to the scanning electron microscope. The effect of ion sputtering on the microstructure as well as preliminary electron back-scattered diffraction microstructural characterization is presented. Based on the sputtering data, the room-temperature diffusivity of O in n-Ce was estimated.     

Crystallographically-dependent ripple formation on Sn surface irradiated with focused ion beam

The metallographically polished polycrystalline Sn surface was sputtered by 30 kV focused Ga⁺ ions at room temperature. The experiment was carried out using various FIB incidence angles (0°, 15°, 30°, and 45°) over a wide range of doses (10¹⁶–10¹⁸ ions/cm²). The surface morphology was carefully characterized under the optical microscope, scanning electron microscope (SEM) and atomic force microscope (AFM). Ripples were observed on the irradiated areas even at the normal FIB incidence angle, which is not consistent with the Bradley–Harper (BH) rippling model. The orientation of ripples relies on crystallographic orientation rather than projected ion beam direction as predicted by BH model. The ripple wavelength is independent of ion dose, while ripple amplitude increases with ion dose. It is found that the ripples are formed by self-organization due to anisotropic surface diffusion in the low melting point metal.     

PED沉积La-Sr-Cu-O薄膜表面的有序纳米结构

采用脉冲电子束沉积(PED)技术在Si(100)衬底上生长La_Sr_Cu_O薄膜，在750℃生长温度下获得具有有序纳米结构的表面形貌.采用聚集离子束(FIB)技术对获得的纳米结构进行表征，结果表明，这种有序的纳米结构是由于Si衬底和La_Sr_Cu_O薄膜之间的热膨胀系数和晶格的 失配引起的纳米裂纹.在这些纳米裂纹处，La_Sr_Cu_O成核生长获得独立的纳米线.通过控制 这种有序的纳米结构的生长，这种有序的纳米结构可以用来构造弱连接形成的器件. 关键词： 脉冲电子束沉积 La_Sr_Cu_O薄膜 纳米结构