Site-specific Cross-section Research Articles

Microstructural Characterization of Defects and Chemical Etching for HgCdSe/ZnTe/Si (211) Heterostructures

In this work, transmission electron microscopy has been used to investigate HgCdSe/ZnTe/Si (211) heterostructures grown by molecular beam epitaxy and to study the effects of chemical etchants for measurements of defect density in the HgCdSe epilayers. Both ZnTe/Si and HgCdSe/ZnTe interfaces were decorated with {111}-type stacking faults inclined at angles of ∼ 19° or ∼ 90° with respect to the interface plane. Similar stacking faults were also present in the upper regions of the HgCdSe films. High-resolution imaging and Fourier image analysis revealed dislocations, mostly with $$ \frac{a}{3}\left\langle\bar{1}11\right\rangle $$ Burgers vector, at both ZnTe/Si and HgCdSe/ZnTe interfaces. Etching solutions based on different combinations of nitric acid, hydrochloric acid and lactic acid were tried in attempts to identify an etchant that provided one-to-one correspondence between etch pits and defects in the HgCdSe layer. Focused-ion-beam milling and transmission electron microscopy were used to prepare site-specific cross-section samples from across the etch pits. However, many defects in regions surrounding the etch pits were unaffected by the various different etchants.

Characterisation of the wear mechanisms in retrieved alumina-on-alumina total hip replacements

Due to their superior wear performance and biocompatibility compared to alternative polymer/metal prostheses, alumina-on-alumina total hip replacements (THRs) are extensively used for young and more active patients. However, the understanding of the wear mechanisms of alumina in vivo remains relatively poor, and there remains little quantitative understanding of the structural and chemical changes at the articulating surface. In the current study, the surface and sub-surface microstructures of retrieved in vivo alumina THRs are presented. Severe wear, also called stripe wear, was observed in all cases. The transition between the stripe wear and the mild wear was very sharp. Site-specific cross-section TEM specimens were prepared by Focused Ion Beam (FIB) at the stripe boundary region. The results suggest predominantly intergranular fracture occurred that was restricted to the outer layer of grains below the surface, with transgranular fracture also occurring in the stripe wear region. Cracking was believed to be initiated by extensive dislocation slip. A thin layer of hydroxide was also observed at the extreme surface of the mild wear region by aberration-corrected high resolution transmission electron microscopy (HRTEM). The wear mechanisms are discussed.

On the Oxidation Resistance of Alloy 800HT Exposed in Supercritical Water (SCW)

The purpose of this study was to examine the structure and composition of the oxide scales formed on Alloy 800HT in a supercritical environment after a relatively short exposure time (circa 500 h) to provide a more complete physical description of the metallurgical factors that influence the protectiveness of the scale formed. This was achieved using transmission electron microscopy and associated techniques on site-specific cross-section samples prepared by focused ion beam milling. No physical evidence in support of oxide scale exfoliation was found. Rather, the formation of the discontinuous magnetite (Fe3O4) outer nodular layer is believed to be controlled to a large extent by the underlying microstructure and the presence of ϵ-martensite plates in particular. The formation of a thin compact corundum-type ([Cr,Fe]2O3) base scale is considered to be sufficiently encouraging to justify an effort to reduce or eliminate the small volume fraction of ϵ-martensite from the starting microstructure of Alloy 80...

The effect of alloying additions on the oxide morphologies of super-heater tubes at elevated temperatures

This paper considers the oxidation of boiler tube alloys; viz. 321H which contains titanium, and E1250 which contains niobium and vanadium, at temperatures of 650 and 750°C, under laboratory conditions, for 720 hours. The resulting oxides have been characterised using advanced techniques including scanning electron microscopy, energy dispersive X-ray spectroscopy and site specific crosssections using focused ion beam milling.The results have shown that small concentrations of titanium and vanadium have a pronounced effect on the morphologies of the oxide layers. Where titanium is present, as in alloy 321H, titanium rich nodules form leading to the development of “whisker” growths from the nodules. On the E1250 alloy, vanadium rich, gem like, crystals form on the surface of the chromium/manganese rich scale. Cross-sectional analysis has shown a possible relationship between the surface features and underlying niobium particles.

Order in nanometer thick intergranular films at Au–sapphire interfaces

In recent years extensive studies on interfaces have shown that ∼1 nm thick intergranular films (IGF) exist at interfaces in different material systems, and that IGF can significantly affect the materials’ properties. However, there is great deal of uncertainty whether such films are amorphous or partially ordered. In this study specimens were prepared from Au particles that were equilibrated on sapphire substrates in the presence of anorthite glass, leading to the formation of 1.2 nm thick IGF at the Au–sapphire interfaces. Site-specific cross-section samples were characterized using quantitative high resolution transmission electron microscopy to study the atomistic structure of the films. Order was observed in the 1.2 nm thick films adjacent to the sapphire crystal in the form of “Ca cages”, experimentally demonstrating that ordering is an intrinsic part of IGF, as predicted from molecular dynamics and diffuse interface theory.

The effect of alloying additions on the oxide morphologies of super-heater tubes at elevated temperatures

This paper considers the oxidation of boiler tube alloys; viz. 321H which contains titanium, and E1250 which contains niobium and vanadium, at temperatures of 650 and 750°C, under laboratory conditions, for 720 hours. The resulting oxides have been characterised using advanced techniques including scanning electron microscopy, energy dispersive X-ray spectroscopy and site specific crosssections using focused ion beam milling.The results have shown that small concentrations of titanium and vanadium have a pronounced effect on the morphologies of the oxide layers. Where titanium is present, as in alloy 321H, titanium rich nodules form leading to the development of “whisker” growths from the nodules. On the E1250 alloy, vanadium rich, gem like, crystals form on the surface of the chromium/manganese rich scale. Cross-sectional analysis has shown a possible relationship between the surface features and underlying niobium particles.

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.

Recent Developments in CrossBeam® Technology

Abstract Recent developments in nano- and semiconductor technology have substantially increased the demand for accurate and efficient site specific cross-sectioning of specimens and preparation of TEM samples. Moreover, nano-research is facing new challenges for manipulation, observation, and modification of devices on a submicron scale. At the same time in materials science a new focus on analytical nanoscale investigations—not only of specimen surfaces and cross sections—but on sample volumes is emerging. These demanding requirements can be met if a focused ion beam (FIB) column for nanoscale structuring is combined with a high resolution SEM that is used to monitor the FIB milling and deposition process on a nanometer scale. Such an integrated Cross-Beam® system enables the high resolution observation and direct control of the FIB milling process in real time. Using this concept it is possible to prepare site specific TEM samples and cross sections with nano-scale accuracy. Such a system can be complemented with a gas injection system (GIS), for deposition and enhanced etching of specific materials, as well as, in-situ micro manipulation systems, and analytical detectors such as EDX and EBSP systems.

Nanoscale Structuring and Investigation

Recent developments in nano- and semiconductor technology have substantially increased the demand for accurate and efficient site specific cross-sectioning of specimens and preparation of TEM samples. Moreover, nano-research is facing new challenges for manipulation, observation, and modification of devices on a submicron scale.

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.

Site-specific cross-sectioning of carbon nanotube-to-metal junctions for high spatial resolution chemical and structural analysis

AbstractIn this study, we have demonstrated successful site-specific cross-sectioning of carbon-nanotube - metal junctions which provided samples suitable for high resolution transmission electron microscopy and electron energy loss spectroscopy. For the cross-sectioning, we have suggested a modified technique based on combination of the Focused Ion Beam (FIB) lift-out and the conventional Ar+ ion milling techniques. Electron-transparent cross-sections of multiwall carbon nanotubes showing no significant surface amorphization or Ga contamination (typical artifacts of conventional FIB lift-out technique) were obtained. High-resolution transmission electron microscopy and electron energy loss spectroscopy of a multi-wall carbon nanotube cross-section have been carried out.

Site-specific cross-sectioning of carbon nanotube-to-metal junctions for high spatial resolution chemical and structural analysis

ABSTRACTIn this study, we have demonstrated successful site-specific cross-sectioning of carbon-nanotube - metal junctions which provided samples suitable for high resolution transmission electron microscopy and electron energy loss spectroscopy. For the cross-sectioning, we have suggested a modified technique based on combination of the Focused Ion Beam (FIB) lift-out and the conventional Ar+ ion milling techniques. Electron-transparent cross-sections of multiwall carbon nanotubes showing no significant surface amorphization or Ga contamination (typical artifacts of conventional FIB lift-out technique) were obtained. High-resolution transmission electron microscopy and electron energy loss spectroscopy of a multi-wall carbon nanotube cross-section have been carried out.

TEM FIB Lift-Out of Mount Saint Helens Volcanic Ash

Focused Ion Beam (FIB) specimen preparation for both scanning and transmission electron microscopy (SEM and TEM respectively) has seen an increase in usage over the past few years. The advantage to the FIB is that site specific cross sections (or plan view sections) may be fabricated quickly and reproducibly from numerous types of materials using a finely focused beam of Ga+ ions [1,2]. It was demonstrated by Prenitzer et al. that TEM specimens may be acquired from individual Zn powder particles by employing the FIB LO specimen preparation technique [3]. In this paper, we use the FIB LO technique to prepare TEM specimens from Mount Saint Helens volcanic ash.Volcanic ash from Mount Saint Helens was obtained at the Microscopy and Microanalysis 1998 meeting in Atlanta. TEM analysis of the ash was performed using the FIB lift out technique [1]. Ash powders were dusted onto an SEM sample stud that had been coated with silver paint.

A Tutorial of the Fib Lift-Out Technique for TEM Specimen Preparation

Abstract The focused ion beam (FIB) instrument has been developed and exploited by the microelectronics arena for specimen preparation for both scanning and transmission electron microscopy (TEM). The inception [1] and subsequent development [2] of the FIB TEM lift-out (LO) technique has enabled electron transparent membranes of generally uniform thickness to be produced for TEM analysis. The primary advantage of the FIB technique is that site specific cross sections (or plan view sections [3]) may be fabricated quickly and reproducibly. The FIB LO technique has been used extensively in our laboratory for a wide range of materials [4] and biological applications [5] which are summarized in figure 1. The FIB LO method consists of milling a series of trenches around an area of interest. Then the bulk sample is tilted up to ∼60 degrees to allow the beam to impinge on the lower portion of the specimen surface so that cuts can be made along the bottom edge and the lower 2/3 of the distance up one side of the specimen.

Material Dependence of Sputtering Behavior During Focused Ion Beam Milling: A Correlation Between Monte Carlo Based Simulation and Empirical Observation

Abstract The focused ion beam (FIB) lift-out method is a high precision technique by which site-specific cross-section transmission electron microscopy (TEM) specimens may be rapidly prepared from virtually any material. The technique is particularly useful when the sample geometry or composition is complex (e.g., fibers, powders, composites and interfaces). In addition to the preparation of TEM specimens, FIB milling has also found widespread utility in micromachining and microfabrication applications as well as specimen preparation for scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS). As the applications of the FEB instrument continue to become more universally recognized, the need to understand the interrelationships between the target material, processing parameters, and process efficiency of the milling phenomena becomes more critical. Incident ion attack angle, target material stopping efficiency and sputtering yield, Y, are important variables governing the milling process. TRIM, a binary collision approximation Monte Carlo simulation code, is used to physically model variables that influence FIB sputtering behavior.

Focused Ion Beam Milling and Micromanipulation Lift-Out for Site Specific Cross-Section Tem Specimen Preparation

AbstractA site specific technique for cross-section transmission electron microscopy specimen preparation of difficult materials is presented. Focused ion beams are used to slice an electron transparent sliver of the specimen from a specific area of interest. Micromanipulation lift-out procedures are then used to transport the electron transparent specimen to a carbon coated copper grid for subsequent TEM analysis. The experimental procedures are described in detail and an example of the lift-out technique is presented.

Site-Specific Cross-sectioning of IC Devices for Failure Analysis by SEM/TEM: Specimen Preparation Challenge and Approach

Abstract Cross-sectioning of microelectronic devices for the purpose of construction or failure analysis by SEM and/or TEM has always been considered a major challenge. The ever increasing complexity and shrinking dimensions of these devices have pushed the art and science of the related specimen preparation beyond their conventional limits. The need for SEM failure analysis of sub-micron elements of a failed device requires the capability of cross-sectioning the sample with a high spatial-resolution within a specific transverse piane. An image of the device structure obtained at sufficiently high magnification from the above specimen generally reveals the defect(s) responsible for the failure. If the imaging resolution and contrast offered by an SEM prove to be inadequate for the above purpose, device structure will be inspected via TEM. Analysis of such device by TEM imposes the additional requirement of back-thinning the above specimen to electron transparency at the site of failure.

Measurements and significance of bio-optical parameters for remote sensing in two subalpine lakes of different trophic state

Bio-optical measurements were carried out on eutrophic Lake Zug and oligotrophic Lake Lucerne, to provide data and models for thein situ calibration of multispectral imagery collected in 1991, during an AVIRIS flight over Central Switzerland. The results indicate that Secchi depth, chlorophyll and total suspended solid concentrations, vertical extinction coefficient, absorption coefficient and irradiance reflectance in the PAR region can be used to discriminate between the two lakes. Dissolved organics concentration, scattering and total attenuation coefficients estimates, as well as backscattering probability, are less acceptable, because of instrumental limitations. Relationships between optical and water quality parameters were investigated and found to behave according to accepted theoretical frameworks. Both lakes exhibited vertical and horizontal heterogeneities in chlorophyll and turbidity, and had contrasting mean bio-optical characteristics: although suspended solid concentrations were similar, transparency was lower in Lake Zug, but reflectance was substantially higher in Lake Lucerne. Water colour determined by chromaticity analysis was blue-green in Lake Lucerne and green in Lake Zug. Reflectance spectra simulated through a three-component optochemical model did not completely match those derived fromin situ measurements, because of lack of site-specific optical cross-sections for suspended minerals and dissolved organics. The monitoring of water quality in subalpine lakes by remote sensing, both with present and future technology, is discussed and considered as possible, provided that their optical behaviour is known, and preferably expressed by a valid optochemical model.