Cross-sectional Sample Preparation Research Articles

Investigations of local electrical surface characteristics by dynamical scanning force microscopy

A technique is presented that allows to obtain information about sample surface topography and local electrical surface properties simultaneously. A scanning electrical force microscope is used for that purpose which is based on an atomic force microscope (AFM) working in the dynamical mode. Different information channels contained in the cantilever excitation spectrum are separated by a lock-in technique. The physical content of the technique is discussed in detail and the influence of surface topography on the non-topographic imaging is demonstrated. Finally, the real advantages of cross-sectional sample preparation (as known from electron microscopy) for this kind of scanning probe microscopy with respect to various applications is presented.

Cross-Sectional Sample Preparation and Analysis of Intergranular Stress Corrosion Cracks in FE-NI-CR Alloys.

Transmission electron microscopy in its modern high-resolution analytical form has great potential for elucidating mechanisms of environmental cracking in structural alloys and other materials. Apart from a few pioneering efforts, the difficulties of preparing suitable samples with the original corrosion structures preserved in narrow crack tips have limited contributions of TEM in this area. Recent work involving cross-sectional crack preparation has focused on intergranular stress-corrosion cracking of Fe- and Ni-base stainless alloys in high-temperature water. This presentation will illustrate preparation methods that have proven successful, and describe limitations of the analysis.The method for preparing cross-section samples suitable for high-resolution TEM characterization is based on earlier work by Lewis et al. It involves preparing a thin section containing cracks filled with epoxy, dimple grinding selected locations near the crack tip, and ion milling. Figure 1 schematically illustrates this method. The first step is to preserve the crack opening characteristics present under loading and protect the crack surfaces during thinning.

Cross-Sectional Transmission Electron Microscopy Sample Preparation Using Focus Ion Beam Machine and Wedge Technique

Abstract As features on an IC chip become smaller than the resolution power of an optical microscope and of the size of the grinding particles, the trend for preparing cross-sectional transmission electron microscopy (TEM) samples at specific locations (bits) is moving towards using a focused ion beam (FIB) machine. Details on how to use a FIB machine to prepare cross-sectional TEM samples have been outlined in many references.The general procedure is to first mark the specific location (bit) in the FIB machine and then grind the sample down to about 20 microns, 10 microns on each side of the feature of interest. After grinding, the sample is mounted on a pre-cut TEM grid and thinned with the FIB to about 0.1 micron in the region containing the feature of interest. There are several disadvantages to this method. First, the sample goes into the FIB machine at least twice—once for FIB marks on the location and once again for the final thinning.

Transmission Electron Microscopy Observation of 11MEV B5+ Ion Irradiation in Bi2Sr2CaCu2O7-x Single Crystal

Abstract Artificial defects generated by ion irradiation have been considered an efficient method to enhance the critical current density in superconducting materials. The mechanism of producing defects as flux pining centers is still an important issue since the efficiency of irradiation-induced defects in flux pinning strongly depends on their microstructures. Different types of defects have been found in heavy ion irradiation. However, there are few results that show light ion irradiation due to the target material selected, the type of light ion and energy, and the incident ion angle. Another factor is the difficulty of cross-sectional sample preparation. In this paper, a single crystal Bi2Sr2CaCu2O7-x with 11 MeV B5+ ion irradiation was observed by transmission electron microscope (TEM) from both plan and cross-sectional view. The Bi2Sr2CaCu2O7-x single crystals used for ion irradiation were prepared using the floating-zone melting method. The crystals were cleaved into thin sheets of about 20 μm thickness along the a-b plane and cut to about 2mmx2mm size.

Comparison of Focused Ion Beam and Conventional Techniques on Tem Specimen Preparation of Metal-Ceramic Interfaces

Abstract The results of TEM analyses of materials are critically dependent on the quality of the sample prepared. Although numerous techniques have been developed in the last two decades, differential thinning of inhomogeneous materials remains a serious problem. Recently, focused ion beam (FIB) technique has been introduced for cross-sectional sample preparation for TEM and SEM. A novel system for depositing a fine-grain (∼ 200 nm) ceramic coating on a metal surface via a patent pending Small-Particle Plasma Spray (SPPS) technique has been developed at the Basic Industry Research Laboratory of Northwestern University. To understand the properties of the coated surface, the ceramic/metal interface and the microstructure of the ceramic coating must be investigated. This paper presents a comparison of the microstructure of an A12O3 coating on a mild steel substrate prepared using conventional and FEB techniques.

Specific site cross-sectional sample preparation using focused ion beam for transmission electron microscopy

Sample preparation using focused ion beam (FIB) for transmission Electron Microscopy (TEM) analysis was reviewed. Improving the quality of FIB prepared TEM sample has been an issue in the past. A specific site cross-sectional sample preparation method has been developed using FIB milling for TEM characterization of integrated circuits (ICs). Approach of front side and back side milling has been applied to thin the semiconductor samples for electron transparency. Back side milling has been applied for the first time in our TEM sample preparation using FIB milling. Proper tilting of the stage and use of low beam current are found to be critical for TEM samples quality. Samples prepared during present work are thinner, artifact-free, and of excellent quality for TEM analysis. It is possible to prepare specific site cross-sectional TEM samples of ICs within 2–3 hours using FIB milling. Some examples of specific site cross-sectional TEM analysis of Si based device structures are presented. Final achievable thicknesses of the samples are exemplified from the fact that atomic resolution imaging was possible and microstructure was seen in the tungsten plugs.

Microstructure Characterization of Ni-V Splat Quenched Foils

Abstract Although the thickness of splat quenched (SQ) foils is normally less then 100 μm the solidified microstructure is usually not homogenous, but rather is determined by a cooling rate dependent nucleation and growth behavior of the different phases. The cooling rate and thus the microstructure changes significantly with distance from the edge to the middle of the SQ foils. Rapidly quenched nickel-vanadium (Ni-V) foils consist of three phases formed during solidification, a Ni-fcc, a V-bcc and a intermetallic σ phase [1-3]. To interpret the microstructure evolution in detail, a special TEM cross section sample preparation was applied. The SQ foil was ground to 30 μm, glued on a copper grid and ion-milled parallel to the foils (Fig.1a). In Ni-49V SQ foils seven typical microstructure regions (see Fig. 1 b) could be identified and were analyzed in detail by TEM investigations in plan view and cross section geometries. Furthermore, three solidification pathways were identified.

Preparation of cross-sectional TEM samples for low-angle ion milling.

The ideal ion-milled transmission electron microscope (TEM) sample would contain large, thin areas in selected regions, minimal top and bottom surface amorphization, and minimal preferential etching of adjacent materials. This desire has led to studies of these effects and improvements in designs and techniques for ion mills. Minimizing the incident angle of the ion beam to the surface of the sample has been found to be one of the most effective techniques for fulfilling these requirements. A new generation of ion mills has recently been designed to allow low-angle ion milling for the production of very high quality cross-sectional TEM samples. To take advantage of the low-angle ion milling capabilities and high-powered ion sources in these mills, new sample preparation techniques are required. In this paper, a simple technique of mounting material in a specialized titanium grid for cross-sectional TEM sample preparation is presented. This technique is designed to take full advantage of the powerful capabilities of these new low-angle ion mills.

Cross-Sectional Tem Sample Preparation Method Using Fib Etching for Thin-Film Transistor

AbstractA rapid and precise sample preparation method using focused ion beam (FIB) etching was developed for cross-sectional transmission electron microscopy (X-TEM) analysis of a thin-film transistor (TFT) fabricated on a glass substrate. Gallium (Ga) ions accelerated at 30 kV and at various incident beam angles were applied during FIB etching to create a uniform thin wall. We successfully prepared X-TEM specimens of long and fragile aluminum (Al) whiskers formed on thin Al films in TFT metallization, where a strong charge is built up during FIB etching. The effect of ion-beam-assisted tungsten deposition prior to FIB etching is discussed. A whisker having a length not exceeding approximately 10 #x00B5;m can be successfully etched to a thickness of 200 nm while keeping its original shape. The performance of this technique is demonstrated in applications to etching at other fragile locations related to TFTs.

Cross-sectional TEM sample preparation by FIB

Cross-sectional TEM sample preparation by FIB

Cross-Sectional Tem Sample Preparation of Phase-Change Optical Disk by Ion Milling

AbstractIt is very difficult to prepare cross-sectional TEM samples for phase-change optical disks by conventional argon ion milling because of the difference of ion milling rates between multilayers and the polymer substrate. We have been successful in preparing samples of those optical disks by ion milling method with dissolution of the polymer substrate in advance. The cross-sectional structure was observed more clearly in this method rather than in ultramicrotome method.

In-Situ Transmission Electron Microscopy of the Solid-Phase Epitaxial Growth of GaAs: Sample Preparation and Artifact Characterization

AbstractIn-situ transmission electron microscopy (TEM) has been used to characterize the solidphase epitaxial growth of amorphized GaAs at a temperature of 260°C. To maximize heat transfer from the heated holder to the sample and minimize electron-irradiation induced artifacts, non-conventional methodologies were utilized for the preparation of cross-sectional samples. GaAs (3xI) mm rectangular slabs were cut then glued face-to-face to a size of (6x3) mm stack by maintaining the TEM region at the center. This stack was subsequently polished to a thickness of ~ 200 ýtm. A 3 mm disc was then cut from it using a Gatan ultrasonic cutter. The disc was polished and dimpled on both sides to a thickness of ~15 mimT.h is was ion-beam milled at liquid nitrogen temperature to an electron-transparent layer. From a comparison of in-situ and ex-situ measurements of the recrystallization rate, the actual sample temperature during in-situ characterization was estimated to deviate by ≤ 20°C from that of the heated holder. The influence of electron-irradiated was found to be negligible by comparing the recrystallization rate and microstructure of irradiated and unirradiated regions of comparable thickness. Similarly, the influence of “thin-foil effect” was found to be negligible by comparing the recrystallization rate and microstructure of thick and thin regions, the former determined after the removal of the sample from the microscope and further ion-beam milling of tens of microns of material. In conclusion, the potential influence of artifacts during in-situ TEM can be eliminated by the appropriate choice of sample preparation procedures.

Preparation of cross section samples of ferrimagnetic iron garnet thin films for EM structural characterization

Ferrimagnetic iron garnet thin film multilayered heterostructures were deposited by pulsed laser deposition on paramagnetic [111]-oriented single crystalline GdGa-garnet (GGG) substrates. Bismuth and rare-earth substituted iron garnet thin films are being presently considered as good potential candidates for the next generation of thermo-magneto-optical (TMO) permanent memories, due to their improved magneto-optical (MO) response to the green laser radiation. As reported previously, improved magnetic and MO properties were shown by multilayered Y3Fe5O12/Bi3Fe5O12 (YIG/BIG) and Y3Fe5O12/Eu1Bi2Fe5Ol2 (YIG/EBIG) heterostructures when compared to their single layer counterparts. The present study tries to elucidate the relationship between the films microstructure and their improved properties. Along with x-ray structural characterization, scanning electron microscopy for topographical characterization and analytical transmission electron microscopy for chemical and microstructural analysis are being used.Due to the brittleness of both films and substrates, conventional cross section sample preparation becomes extremely difficult. Samples under roughly 20 μm thickness break under the lowest load of the dimpler.

Two-dimensional profiling by selective etching: the role of implant induced secondary defects

We have investigated the selective chemical etching of B-doped n-type silicon in a HF:HNO 3 mixture either under illumination with ultraviolet light or using an electrolytic cell. The etching profiles are observed by transmission electron microscopy after a double cross section sample preparation. They extend up to the junction depth with a regular shape if no crystallographic defects are present in the sample. Extended defects affect the etching profiles and steps appear. The experimental results are interpreted by taking into account the role of the free carriers generated by light or by an external current source. This information is of fundamental importance to develop a two-dimensional junction profiling technique for micrometer size features by selective etching and transmission electron microscopy observations.

Ion beam etching technique in the preparation of samples for cross-sectional microscopy studies of thin films and hard coatings

The scanning tunneling microscope has proved to be an effective tool in the structure characterization of interfaces and interlayers in thin films and coatings. However, since it lacks the deep profiling capabilities sufficient to penetrate hard coatings, an ion beam etching method has been developed for cross-sectional sample preparation. The sample preparation method is developed keeping in mind the image formation of a scanning tunneling microscope which is based on the topographical differences of the inspected surface. Thus the sample preparation process includes three main parts. Firstly, a mechanical grinding and polishing step, secondly, an ion beam polishing step for producing a smooth surface and, thirdly, an ion beam etching step for producing a topography related to the bulk microstructure of the sample. Examples of results obtained with TiN hard coatings are given, including X-ray scanning force microscopy pictures of a tribofilm grown on a TiN-coated cast iron sample during a high temperature wear test; the usefulness of the developed technique is discussed. The results achieved are compared with the structural information obtained by X-ray transmission electron microscopy analysis from the same samples.

Technique for mounting SiC fibers for cross-sectional microscopic examination

Silicon carbide (SiC) fibers are commonly used in many composite and other material applications. It is often of interest to examine cross sections of such fibers microscopically, prior to composite manufacturing processes, to ensure diameter consistency. However, SiC fibers are difficult materials to metallographically mount and polish, because the fibers are harder than most epoxy mounting materials. The difference in hardness between the SiC and the mounting epoxy usually causes rounding of the fibers during final polishing. It is also difficult to position a large group of fibers for cross-sectioning, because a group of closely spaced fibers will have poor bonding to the epoxy. The following technique was developed to improve the preparation of cross-sectional samples of SiC fibers. In this study, fibers of SiC plated with electroless nickel were used to demonstrate the technique. The following outline describes the steps that were taken in preparing a cross-sectional specimen of the plated fibers.

Selected area polishing for precision TEM sample preparation.

A selected area mechanical polishing technique has been developed to improve the precision of cross-sectional TEM sample preparation, based upon the early work of Benedict and colleagues [Benedict et al. (1990) MRS Symp. Proc. Vol. 199, p. 189]. TEM samples were made from a pre-selected section through the middle of a 1 micron wide band of transistors extending laterally for more than 1 mm by precise control over the plane of polish with a corresponding reduction in sample preparation time. To illustrate the application of this technique, a uniformly thin, electron transparent TEM sample of a single, specific, failed transistor is obtained from a 4 mm by 10 mm device array.

Sample preparation technique for cross-sectional transmission electron microscopy of quantum wire structures.

A novel cross-sectional sample preparation technique for quantum wire (QWR) structures is described. By coating a thin layer of Au with a designed pattern on the sample as a marker to indicate the position of the wire pattern, the location of the thinned area can be controlled precisely. An example of applying this technique to an InGaAs/GaAs QWR structure is demonstrated. This technique can also be applied to any other small dimensional structures or devices with specific regions of interest.

HREM applications to industrial products: Observation of thick-film resistors with very large electron transparent area

HRTEM is a very powerful tool for structural characterization of materials. However, its role in industry is still very limited and electron microscopy is generally considered as a secondary support technique, although it can uniquely provide microstructural information leading to understanding and improvement of product quality, especially for those materials in the form of films. An example in the semiconductor industry is recendy described by Anderson. He points out that the main concerns of imaging using a conventional cross-section sample preparation method are too small imaged areas, not representative of the product, and artifacts that may be introduced during the ion-milling process. Here we apply HREM to thick film resistors and attempt to overcome these obstacles.

A technique for the preparation of cross-sectional TEM samples of ZnSe/GaAs heterostructures which eliminates process-induced defects

Cross-sectional transmission electron microscopy (TEM) sample preparation of ZnSe/GaAs epitaxial films is investigated. Conventional argon ion milling is shown to produce a high density (approximately 5-8 x 10(11)/cm2) of small (diameter approximately 60-80 A) extended defects (stacking faults, microtwins, double positioning twins, etc.). In addition, transmission electron diffraction results indicate a thin ZnO layer can also occasionally form upon ion milling or electron-beam irradiation although the exact conditions for ZnO formation are not well understood. Conventional TEM (amplitude contrast) and high-resolution TEM (phase contrast) imaging in combination with transmission electron diffraction studies were performed to determine the optimum method of removing the ion milling related damage and ZnO layers during sample preparation. HF/HCl, NaOH/H2O, H2SO4/H2O2/H2O and Br2/CH3OH etching mixtures as well as low voltage argon or iodine ion milling were studied. A low energy (2 keV) iodine or argon ion milling step was shown to remove the ZnO layer and reduced the density of the extended defects associated with Ar+ ion milling, but was unsuccessful in removing all of the defects. Auger electron spectroscopy results indicate residual iodine was either left on the surface or implanted beneath the surface during iodine ion milling. Etching the XTEM samples in HF/HCl was shown to be effective in removing the ZnO layer but had little or no effect on the ion milling induced defects. Etching the samples in a 0.5% Br2/CH3OH solution resulted in complete elimination of the ion milling induced extended defects including the residual defects associated with iodine ion milling. In addition the Br2/CH3OH etch produced the best surface morphology. Thus a brief (1-2 seconds) Br2/CH3OH etch after conventional preparation (argon ion milling) of cross-sectional ZnSe/GaAs TEM samples appears to be an inexpensive and superior alternative to iodine ion milling.