STEM is an important tool for the study of material by forming Z-contrast ADF images. Studies of strain fields suggest that strain can cause extra contrast in ADF images. Since strain fields exist in many TEM samples, especially interfaces of two different materials, it is necessary to study the contrast effect of strain fields in more detail. in this paper, we study the contrast effect of strain fields by STEM experiments and multislice simulations.

Sample thickness and the dimensions of ADF detector can both affect strain contrast. We first study the influence of sample thickness. A cross-section TEM sample of an interface of crystal silicon and amorphous silicon was prepared by typical tripod polishing and was studied with the 100 kV Cornell VG 5.0 UHV STEM. The sample was tilted so that the crystal was on the (110) zone axis and ADF images of the interface were recorded.

Annular Dark Field imaging has the potential to be directly quantifiable. By this I mean that with careful measurement, the absolute image intensity has physical meaning. Unlike Bright Field TEM, the ADF image has no contrast reversals with focus and with the exception of thick specimens there are no contrast reversals with changes in thickness. Thus, image intensity is related to thickness, composition, orientation, and structure of local regions whose size is determined by the electron probe. The ability to extract quantitative information about the specimen from the intensity requires careful collection of the intensity data and a solid understanding of how that intensity will change with thickness, composition, orientation, and structure. The qualitative effect of thickness and composition has been well shown in the literature but more quantitative approaches have been lacking.

The simplest models of ADF imaging treat each atom interacting

Many of the topics in valence spectroscopy originally pioneered with TEM equipment have now been taken over by STEM. Notable exceptions are the studies by J. Silcox and his colleagues of plasmon dispersion and of the guided modes in thin slabs where retardation and other relativistic effects arise. The growing use of STEM valence EELS on increasingly complex nanostructures and the development of dielectric excitation theory for quantitative interpretation of the results were recently reviewed. The spatial resolution approaches the atomic scale, exceeding by orders of magnitude the capability of near field spectroscopy. By using the cathodoluminescence (CDL) signal, optical precision in STEM energy loss measurement can also be achieved, particularly in the difficult region below 5 eV or even 1 eV. High spatial resolution can be preserved provided that an intermediate stage of carrier diffusion is not involved in the radiative decay of excitations.

Figure 1 shows STEM CDL images of an Ag particle obtained from the dipole l=1 and quadrupole l=2 surface plasmon excitations

Carbon nanotubes (CNT) have great potential as one-dimensional quantum conductors in future molecular electronic applications. Local electronic property determinations at low energies in CNT have been confined to those made by scanning probe microscopy techniques (SPM). Although SPM measurements provide unprecedented electronic property information, they suffer from substrate coupling and a limited ability to measure structural characteristics of nanotubes. A high-resolution transmission electron microscope (TEM) coupled with an electron energy loss spectrometer (EELS) offers electronic property determination as well as structural (imaging and diffraction) and spectroscopic analysis of truly isolated nanotubes. Here we report measurements of EEL spectra of single-walled CNT, both singly and in bundles. The experiments were performed in a VG HB501 STEM at Cornell University, operating at 100 kV. CNT samples chosen for analysis include isolated single-walled tubes with diameters 1.2-1.3 nm and bundles of ∼3-150 single-walled tubes. Many of the spectra were obtained in the aloof mode, i. e. with the beam not penetrating the material.

There is an intimate connection between the electronic structure of a material and its physical properties. to change one, is to change the other. Some of the most striking illustrations of this relationship can be found at grain boundaries in metals and their alloys. Here, the most important changes in cohesion can be described by changes in the local density of states (LDOS), which in turn can be measured using EELS [1]. The first demonstration that EELS could be used to connect the electronic and mechanical properties of a material was in revealing the role that boron has in restoring a bulk-like bonding to grain boundaries in Ni3Al [2,3]. Boron was known to change the fracture mode in Ni3Al from intergranular to transgranular, possibly by enhancing grain boundary cohesion.

What interested me in this project, when John Silcox first suggested it as a thesis topic, was the potential of using the EELS fine structure to measure materials properties directly.

Magnetic tunnel junctions (MTJ) which consist of two ferromagnetic electrodes separated by a thin (∼10Å) tunnel barrier can exhibit a magnetoresistance of greater than 40% at 295 K. They hold substantial potential for application as computer memory and magnetic field sensors. Much about the spin-dependent tunneling process is still not understood. in order to identify features that may affect the spin-polarization of the tunnel current, we have used the UHV STEM at Cornell University to perform atomic-scale imaging and EELS on an MTJ system. The MTJ was sputter deposited on (100) Si with layer sequence Co 60Å/Al 12AÅO2 exposure/Co 100Å.

The annular dark field (ADF) image (Fig. la) shows the A10x barrier layer has a fairly uniform thickness of about 15 Å. Its profile (Fig. 1c) appears diffuse partly due to layer roughness rather than atomic mixing. in bright field (BF) the appearance of strong Fresnel fringes (Figs. 1b,c), due to a large difference in average electrostatic potential between Co and AlOx, complicates interpretation.

For failure analysis and process control it is critical to perform comprehensive microanalysis. The desire to perform this analysis thoroughly but quickly is the ultimate goal. Typical analyses of this sort have been performed by collecting x-ray spectra at points, along lines, by mapping, and more recently by spectrum imaging where a complete x-ray spectrum is collected over a 2D array of points. Spectrum imaging is perhaps of greatest interest for its potential to thoroughly and comprehensively sample a given area of a microstructure. The problem is that the techniques available for analyzing large (> 1000 spectra) spectrum image (SI) data sets have been limited to mapping after the fact and perhaps thresholding the maps and summing the resultant spectra from those pixels. As a result, there is a need for more sophisticated SI analysis tools, capable of reducing the SI to its essence-the chemical components. Software is currently commercially available for the automated analysis of x-ray spectrum images (SIs) from the SEM

Energy Dispersive Spectrometry (EDS) is an ubiquitous method of elemental analysis for SEM, TEM, and STEM applications. The elements of interest are generally quantified without standards using theoretical calculations or by using standards that are high purity specimens of the elements measured. However, EDS is often used to determine a small percentage of an element in a matrix. The accuracy and limit of detection of these low concentration measurements has not been established. An earlier report proved the concept that a cross section high dose BF2 implanted specimen could provide a standard for EDS measurement of F. This study extends this quantification approach to transition elements of importance to the semiconductor industry.

The Fe and Co standards were created by high dose ion implantation. For ions implanted into silicon, a dose of lxl016 atoms/cm2 results in a peak concentration of approximately lxl021 atoms/cm3 or 2% atomic. The exact concentration can be determined using methods such as Rutherford Backscattering Spectrometry (RBS) and Secondary Ion Mass Spectrometry (SIMS).

CdSe/ZnSe based semiconductor quantum dot (Q D) structures are a promising candidate for optoelectronic device applications. However, key to the luminescence properties is the cation distribution and ordering on the atomic level within the CdSe QDs/agglomerates. Here the Z contrast imaging technique in the scanning transmission electron microscope (STEM) is employed to study multisheet (Cd,Zn,Mn)Se QD structures. Since Z-contrast is an incoherent imaging technique, problems associated with strain contrast in conventional TEM are avoided an accurate size and composition determinations can be made.

For this work we used a JEOL JEM 201 OF field emission STEM/TEM. The sample was grown by molecular beam epitaxy in order to achieve vertical self-ordering of Cd rich quasi-2D platelet This sample comprises 8 sequences of 10 ML (2.83 nm)Zn0.9Mn0.1Se cladding layer and 0.3 ML (0.09 nm) CdSe sheet, a further 10 ML of Zn0.9Mn0.1Se, and a 50 nm ZnSe capping layer.

The electron beam broadening in specimens is a important issue to obtain a high spatial resolution expected by using a fine electron probe of nanometer order in analytical electron microscopy. Beam broadening mainly depends on electron diffusion in specimens. The theoretical equation on the beam broadening, which is based on single scattering approximation model for incident electrons, has been proposed by Goldstein et al.. in this work, the beam broadening was estimated experimentally by a TEM equipped with a field emission gun and the results were compared with the values theoretically obtained.

The sizes of the beam diameter with and without specimens were measured by using JEM-2010F and JEM 3000F TEMs, which are equipped with a field emission gun, being operated at 200 and 300 kV, respectively. The beam diameter was defined as the diameter containing 90% of the total electrons. The specimens used were amorphous SiO2, crystalline MgO and Si.

Sm(Co,Cu,Fe,Zr)z 2:17 based permanent magnets have the highest Curie temperature and the most excellent temperature stability among the current rare-earth permanent magnets. in recent years, the Sm(Co,Cu,Fe,Zr)z magnets have attracted again considerable attention due to the demand of the Department of Defense for high temperature applications such as aircraft, spacecraft and ship systems. Our recent studies have led to the development of new precipitation hardened Sm(Co,Fe,Cu,Zr)z magnets with operating temperatures above 400°C and with coercivities as high as 10 kOe at 500°C. The microstructure of the Sm(Co,Cu,Fe,Zr)z high temperature magnets consists of a cellular structure (2:17 rhomobohedral cells surrounded by 1:5 hexagonal cell walls) superimposed on a lamella phase (2:17 hexagonal). This microstructure is sensitive to processing and to the alloy chemical composition. Magnetic domain structure studies play a critical role in understanding the magnetic hardening behavior of the magnets. in this paper, HREM and magnetic domain structure were studied in these Sm(Co,Cu,Fe,Zr) high temperature permanent magnets.

Similar to graphite and carbon fullerenes, the physical properties of carbon nanotubes (NTs) can be altered by ex-situ doping or by functionalizing the nanotube walls. Such mechanisms for tailoring the properties of carbon NTs expand their potential utility in electronic, optical and structural applications. Both acceptor (e.g. I2, Br) and donor-type (e.g. K, Rb) dopants have been successfully intercalated into single-wall NT (SWNT) bundles, and the transport properties of these doped species are greatly altered. For example, iodine-doped SWNTs exhibit a 40% decrease in DC conductivity. Doped SWNTs are a completely new class of nanostructured materials, and there is a large demand for understanding the structure of the various doped-compounds as well as the ramifications for the electronic properties of the material.

In this paper we demonstrate the utility of Z-contrast scanning transmission electron microscopy (STEM) for elucidating the structure of doped nanotubes.

The advancement of metal-oxide-semiconductor (MOS) technology towards sub- 100nm device dimensions presents several technical difficulties. Nanoscaling in MOS devices is specifically governed by difficulties in the formation of ultrashallow junctions for the source/drain regions with the requirement of low resistance and low leakage currents. The use of a silicide (forming Schottky contacts at the source and drain) instead of the conventional ion implanted Si for the contacts allows a reduction in the contact area to be made, due to lower serial resistance per unit area of the silicide. According to the specific contact resistance dependence on the Schottky barrier height (ΦSB) and active dopant concentration (ND),

Current commercial analytical electron microscopes (AEMs) including scanning transmission electron microscopes (STEMs) are a compromise design between the highest spatial, analytical and energy resolutions. in contrast, a VG HB603 STEM at Lehigh University has been designed with a 300 kV cold field-emission gun and twin X-ray detectors to maximize X-ray generation and collection efficiencies [1]. in addition, instrumental features of almost no stray radiation, ultra-high vacuum (<10−7 Pa in the stage and <10−7 Pa in the gun), beam blanking and direct probe-current measurement in the HB 603 have transformed the approaches to quantitative analysis. By using such modern AEMs, it is now possible to perform X-ray microanalysis with the spatial resolution as low as 1.5 nm and the detectability limits of∽2 atoms in the analyzed volume [2]. Furthermore, even quantitative X-ray mapping becomes achievable, while maintaining, high spatial resolution (the original aim of such instruments) [3].

Mixed conductors have been the focus of many studies in the last decade, leading to a detailed understanding of many of the macroscopic bulk properties of these materials. in particular, although the reduced low temperature phase in rare earth perovskite oxides is commonly explained in terms of ordered brownmillerite structured micro domains, its transition to the high temperature phase remains elusive. in this presentation an investigation of (La, Sr)FeO3, prepared under different reducing conditions through correlated atomic resolution annular dark field imaging and electron energy loss spectroscopy will be shown.

We investigate the (La, Sr)FeO3 material by atomic resolution Z-contrast imaging and EELS using a 200 keV STEM/TEM JEOL2010F with a post column GIF. The combination of these techniques allows us to obtain direct images from the atomic structure of the bulk sample and to correlate this with the atomically resolved EELS information. In-situ heating of the material in a heating double tilt holder in the microscope columns allows us to simulate the highly reducing operating conditions for this oxygen conducting membrane material.

It is known that wurtzite III-V nitrides are highly polarized in the c-direction, which is usually the growth direction. This polarization (spontaneous and piezoelectric) in GaN/AlxGa1-xN heterostructure field effect transistors (HFET) results in high carrier concentrations at the interfaces, in addition to the large conduction band offset. This high-density 2D electron gas formed at a GaN/AlxGa1-xN heterointerface in its turn increases the mobility of the heterostructure. Therefore, questions about the measurement of the physical width of a GaN/AlxGa1-xN interface and the calculation of its effects on the physical characteristics of devices naturally arise. Since the electrical field distribution, as well as the location and density of the 2D electron gas, depends on the width of the GaN/AlxGa1-xN heterointerface, accurate determination of the width is critical.

Measurements with high spatial resolution EELS using transmission electron spectroscopy with a ∽2Å focused electron beam permits atomic-level studies of such specimens.

High spatial resolution information on the structure and composition of semiconductor quantum dots is necessary to relate microstructure to macroscopic electron-optical properties [1]. Scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) can be used to determine the elemental composition of nanometer-sized particles. Applying these techniques to quantum dots is challenging because the dot nucleates on a very thin wetting layer of similar composition and is embedded in a matrix. Here we present a strategy to extract absolute compositional information on InGaAs dots. The method relies on modeling both the dot shape and the electron probe profile.

Samples were prepared by depositing four monolayers of In0.5Ga0.5As onto a GaAs substrate giving a nominal wetting layer thickness of 1.2 nm [2]. STEM was performed on a Vacuum Generator's HB501 equipped with a GATAN parallel electron energy-loss spectrometer. An ES Vision system was used to acquire spatially resolved electron energy-loss spectra from the wetting layer and the quantum dots.

The study of magnetic thin films by Lorentz microscopy in the transmission electron microscope (TEM) is a well-established technique. However, in many instances, images are recorded with the specimen in its as-grown state or in a single remanent state following application of a magnetic field outside the microscope. Although such images can provide valuable information, they rarely produce insight into the mechanism by which the magnetic material reverses nor do they show the magnetic structures that form during the reversal process. Furthermore, it is not possible to determine, for example, the field range over which a reversal takes place. Given the importance of such elements for magnetic sensing and storage applications, there is considerable incentive to develop techniques which not only yield the magnetisation loop for an individual element but which reveal how the spatial distribution of magnetisation evolves as a function of field.

The study of magnetic materials using electron column instruments has been a fruitful area of research for microscopists/microanalysts for nearly 4 decades. A number of techniques have been developed for both the SEM and TEM which enable visualization of magnetic fields ranging from Fresnel imaging (Fuller and Hale, Silcox), Differential Phase Contrast (Chapman), through to Electron Holography (Tonomura). The latter are generally qualitative, while the former quantitative, albeit at the price of significant complexity. The advent of microprocessor control of modern instruments, CCD detectors, and experimental diligence allows us to revisit and in fact revitalize this area of measurement.

The experimental work reported here is being carried out in the ANL AAEM HB603Z 300 kV FEG instrument. in this instrument, the electron optical column was operated in a zero field mode (figure 1), where the objective lens is turned off and the probe forming lens functions were reallocated to the C1, C2, and C3 lenses.

In this paper, we discuss the advantage of combining STEM imaging with diffraction. in addition, we present a set of accurately calculated convergent beam electron diffraction (CBED) patterns for Si, which highlights the sensitivity of electron diffraction to structure. The calculation takes the full account of crystal bonding by including known experimental structure factors in simulation. Such calculated patterns can be used for accurate determination of the sample thickness, crystal orientation and polarity (for acentric crystals). Calculations with and without crystal bonding show significant difference in calculated intensities, equivalent to a change in thickness about several nanometers for thick samples.

The annual dark field (ADF) imaging mode in scanning transmission electron microscopes offers the unique advantage of combining high-resolution electron imaging and spectroscopy with diffraction. The large cutoff angle used in ADF imaging allows simultaneous recording of diffraction patterns for quantitative structural information, while ADF imaging gives the precise position of the probe and the image of the sample.