Quantitative analysis of a structure means to determine which atoms are where. The where is restricted by the lateral resolution, and the which is related to the sensitivity against differences of the atomic species. Electron holography is on the move to tackle both questions.

• where - Lateral Resolution Electron holography has surmounted conventional electron microscopy in that it has reached atomic resolution both in the amplitude and phase images: with our CM30FEG/UT Special Tuebingen electron microscope, the information limit of 0.09nm and the pixel number of the 2048_ - CCD camera allow to take holograms with image details smaller than 0.095nm; the quality of correction of the aberrations allows an interpretable resolution approaching 0. lnm both in amplitude and phase [1].

• which - Phase Detection Limit (PDL) The phase detection limit describes the minimum phase difference detectable well above a given noise level.

During the last five years the technique focal-series reconstruction has evolved to a powerful tool for investigating materials science problems in high-resolution transmission electron microscopy. Compared to the conventional interpretation of one single high-resolution image, the quantum mechanical electron wave function at the exit plane of the object (exit-plane wave function, EPW) is in many cases a better starting point for the materials analysis. The retrieval of the EPW is achieved on a routine basis by applying automated numerical procedures to a series of images taken from the same specimen area at different objective lens defocus values. The application of the reconstruction procedure allows one to remove numerically all the well known instrumental artifacts, such as nonlinear contrast formation or delocalisation effects due to spherical aberration and other parasitic aberrations. The reconstructed EPW gives thus direct insight into the atomic structure in the case of sufficiently thin objects and renders tedious image simulations of complicated defects unnecessary in many cases.

Recent progress in High Resolution Transmission Electron Microscopy makes it possible to investigate crystalline materials by phase contrast microscopy with a resolution close to the 80 pm information limit of a 300 kV field emission microscope'"". A reconstruction of the electron exit wave from a focal series of lattice images converts the recorded information into interpretable resolution. The present contribution illustrates some recent applications of this technique to interfaces.

Fig. 1 shows a reconstructed electron exit wave of a heterophase interface between GaN and sapphire. The experiment takes advantage of three factors: First, we resolved the GaN lattice in projection, which requires at least 0.15 nm resolution. The projection eliminates the stacking fault contrast that usually obscures lattice images in the commonly recorded projection. Thus, image interpretation is drastically simplified. Second, all atom columns at the interface and in the sapphire are resolvable with a smallest projected aluminum - oxygen spacing of 85 pm in the sapphire.

Polycrystalline ZnO was sintered with 5 mol.% Ga2O3 at 1350°C for lhour in air. Samples for transmission electron microscopy (TEM) were prepared by cold pressing, grinding, dimpling and Argon ion-milling.

ZnO crystallizes in the hexagonal wurtzite structure. Bright field and dark field images reveal lamellar defect structures which are not observed in undoped ZnO. Electron diffraction shows that the lamellar regions consist of heavily twinned ZnO. The twin boundaries (TB) of both twin variants are parallel to lattice planes of type { }. Lattice images along reveal narrow planar twin boundaries as well as a diffuse image contrast within the twin lamellae (Fig. la). to characterize the nature of the boundaries we recorded dark field images of the twinned regions using reflections of type ±{0002}. in combination with microdiffraction it can be shown that the diffuse boundaries are inversion domain boundaries (IDB) which alternate with the sharp TB. This microstructure is related to the polarity of ZnO.

In polycrystalline materials the trapping of charge at interfaces has a decisive influence on the electrical transport properties through the formation of electrostatic potential barriers. This can either be an intrinsic phenomenon or can be related to impurity segregation leading to complex defect centers. This plays a key role in technologically important systems, especially those having electrically active interfaces, e.g.,p-n junctions in semiconductors and grain boundaries in electroceramics.

Electroceramic oxides such as ZnO and SrTiO3 are common systems that exhibit the tendency of current control by internal potential barriers. While bulk measurements, either electrical (e.g. P-E, C-V, I-V), or optical (e.g. Raman) have contributed significantly to the understanding of charged interfaces, there are a very few direct observations of electrical activity at a nanometer level. For instance, it has been recognized that space charge and dopant segregation at the grain boundary are inter-related.

The potential variation, charge transfer and lattice distortion across grain boundaries in polycrystalline superconductors play a crucial role in the transport properties of the material. in particular, the grain interfaces often act as weak links to the superconducting current, which limits the critical current densities that may be obtained. in the case of the high Tc superconductor Bi2Sr2CaCu2O8 (Bi-2212), special interest is paid to (001) twist boundaries since, in part, they are dominant in c-axis aligned tapes and wires, but more interestingly because the superconducting critical current is found to be independent of twist angle for this system. Such grain boundary behavior is presently not understood, and is further puzzling since “impurity phases” of Bi-2223 or Bi-2201 (consisting of additional or missing Cu-Ca-0 planes, respectively) are commonly observed at the (001) twist boundaries. with the rich structure found at these types if interfaces, understanding the potential distribution may lead to new insight about the boundary properties.

EELS fine structures on characteristic core edges are closely related to the bonding type and structural environment around the excited atoms. Consequently, they constitute useful hints for investigating the electronic properties at interfaces. One major difficulty then lies in the extraction of the information relevant to the involved atoms, from that due to neighbouring atoms on both sides of the selected interface seen end on by the impinging electrons. We have investigated possible ways to reach this goal, using the spectrum-line method, which consists in acquiring sequences of spectra at well defined increments (0.3 nm) while scanning a subnanometer electron probe (0.7 nm) across the interface. This approach constitutes one step forward with respect to the spatial-difference (SD) method which processes spectra acquired on two adjacent areas, one encompassing the interface, the other one on a reference area nearby. A normalized version (NSD) has been introduced to extend its field of application from grain boundaries to heterophase interfaces in order to enhance their specific ELNES contribution

Grain boundary Cr segregation provides magnetic isolation between the crystals in sputtered Co thin films used for longitudinal magnetic recording. Magnetic isolation decouples individual grains in order to increase coercivity, lower media noise, and allow for higher recording densities. These sputtered Co alloys grow with a strong [1120] texture owing to a body centered cubic (BCC) Cr underlayer. The sputtered Cr seed-layer has a [001]BCC growth texture and the BCC {110}cr planes lattice match with the hexagonal (0002)cr planes. This produces the desired condition of the easy axis of magnetization, [0001]co, in the plane of the magnetic layer. However, since two orthogonal orientations of the {110}cr planes exist parallel to the [001]cr growth direction, it is possible to nucleate two hexagonal Co grains with orthogonal variants of the c-axis that will impinge to form a 90° grain boundary. The well defined crystallographic texture of the Co-alloy thin film with random angle and 90° grain boundaries presents an opportunity to study the effects of boundary character on Cr segregation in hexagonal crystals.

Temper-embrittlement in low-alloy steel has been attributed to the segregation of elements to the prior austenite grain boundary (PAGB). Auger electron spectroscopy (AES) has shown that the embrittlement of the PAGB is due to phosphorus segregation. The problem with this type of analyses is that only the PAGBs that fracture can be analyzed. More recent X-ray studies in a field emission gun scanning transmission microscope have shown that molybdenum, nickel, chromium manganese and phosphorus all segregate to PAGBs, and that these elements can be classified into two segregation groups; those PAGBs that contain nickel, manganese and phosphorus and those PAGBs that contain molybdenum, chromium and phosphorus. AES cannot determine conclusively, which segregation group is responsible for the embrittled PAGBs. The measurement of how embrittled the low-alloy steel has become, requires the knowledge, which PAGBs are embrittled and the percentage of these boundaries within a given volume.

In recent years, electron energy loss spectroscopy has provided high spatial resolution information on the elemental composition of interfacial reactions. with the use of field emission guns in conventional TEM or STEM, additional information on the chemical, structural and electronic state at grain boundaries and interfaces can also be obtained (e.g. Ref. 1 and 2). in the study of new types of materials for semiconductor applications such as high-K dielectrics, high spatial resolution information of this type is of critical importance as the dimensions of the structures are reduced and the ultimate electronic properties become size dependent. This paper discusses the analysis of near edge structure information obtained at the Si-Gd2O3 interface, a system with great potential for the next generation of gate material.

The preparation of the thin films and the sample preparation details are given elsewhere3 and only a summary of the characterization method and results are described here.

Ni, Pd and Cr thin films were grown on (100)SrTiO3 surfaces by molecular beam epitaxy at substrate temperatures of TNJ, pd=650°C and Tcr =150°C. Electron energy-loss spectroscopy (EELS) and high resolution transmission electron microscopy (HRTEM) were applied to investigate the local electronic structure and the atomic structure of the interfaces, respectively. Analytical microscopy was carried out with a parallel energy-loss spectrometer (PEELS766) attached to a dedicated scanning transmission electron microscope (STEM) operated at 100keV, which has a point resolution of 0.22 nm. HRTEM studies were performed on a Jeol JEM ARM 1250 operated at 1250keV (0.12 nm point resolution). Conventional TEM and HRTEM experiments showed epitaxial orientation relationships between the thin metal films and the substrate for each interface.

The electronic structure of the interfaces in terms of the site- and symmetry projected density of states (PDOS) above the Fermi-level can be extracted from the electron energy-loss near-edge structures (ELNES).

Z-contrast images and electron energy loss spectra (EELS) were obtained from low angle grain boundaries in SrTiO3 and YBa2Cu3O7-x (YBCO). Z-contrast images are easy to interpret and especially useful for positioning the beam to acquire EELS data from small sample areas [1], because both these techniques can be performed simultaneously.

In high-temperature superconductors even a single grain boundary can reduce the critical current by up to four orders of magnitude. The band-bending model can quantitatively explain this phenomenon. YBCO is a hole-doped superconductor with about one hole per unit cell for optimum doping at x close to zero. It has a structure closely related to the perovskite structure, and Z-contrast images have shown that the dislocation cores are made up of similar structural units as in SrTiO3.[2,3] Our EELS measurements show clear evidence for band bending effects around isolated dislocation cores in an undoped 8° low angle grain boundary.

The properties of ceramic oxides being developed for such varied applications as fuel cells, ionic transporting membranes, high-Tc superconductors, ferroelectrics and varistors are dominated by the presence of grain boundaries. Key to controlling the electronic properties of the grain boundaries in these materials is a fundamental understanding of the complex relationship between structure, composition and local electronic structure. The ability to characterize and directly correlate these parameters on the atomic scale is afforded by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM). Furthermore, the recent development of in-situ heating capabilities in the JEOL 201 OF STEM/TEM permits atomic resolution analysis to be performed at elevated temperatures and the interactions of grain boundaries with the oxygen vacancies determined.

Figure 1 shows an example of the type of experiment that can be performed using these methods.

High resolution transmission electron microscopy (HREM) is an excellent experimental method to image grain boundary structures with atomic resolution. The advantage of the method is the short exposure time of only about one second that is needed to record an image. Other methods like Z-contrast imaging require much longer exposure times and are therefore much more prone to specimen drift during recording. However there is the remaining difficulty to HREM that the evaluation of experimental images is not straightforward and a thorough analysis of the images is necessary in order to deduce quantitative information with small error bars of only a few pm (10-15m). A second inherent difficulty common to all atomic resolution imaging techniques is that the information is retrieved from a very small area of a specimen. The question arising from that is: can we nevertheless be sure to obtain a representative answer to a “real world” material science problem? A positive answer to this question is given by the investigations presented here.

Extended structural defects in α-Al2O3 (alumina), a technologically important, complex ceramic material were quantitatively analyzed with respect to grain boundary segregation, atomic and electronic structures using spatially resolved electron energy-loss spectroscopy (EELS), energy dispersive X-ray spectroscopy (EDS) and first-principles local-density-functional (LDFT) calculations. in this study the results of analytical investigations will be compared with the outcome of LDFT calculations.

The analytical measurements were performed with a dedicated scanning transmission electron microscope (TEM) VG HB501UX, operating at 100 kV and with a typical beam diameter of lnm. For the spatially resolved EELS a parallel electron energy-loss spectrometer (Gatan model 666) with an energy resolution of better than 0.8 eV was used. For the chemical analysis an EDS system (Noran-Gresham with a Si(Li) detector and a Norvar window) was applied. The detection limit of the EDX system for measuring interface excess is in the range of 0.3 atoms/nm2.

A variety of semiconductor and metal nanoparticles can be synthesized and tunable in size from about 10 to 200 Å using size-selective separation technique. Preparation of monodisperse samples enables systematic characterization of the structural, electron, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close-packed, glassy and ordered nanocrystal. At inter-particle separations 5-100 Å, dipole-dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. The fabrication of monodisperse ordered nanoarrays with the inter-particle separations less than 5Å will be very important to study its physical properties since interaction between neighboring nanocrystals cause otherwise insulating assemblies to become semiconducting, metallic, or superconducting depending on nanocrystals composition. Here we present the fabrication of monodisperse PbSe nanoarrays with inter-particle distance less than 5 Å and its nanostructure study.

Patterned nanostructures and nanodots are attracting increasing interest in the information storage industry. The ultimate recording density of a magnetic medium will have single domain dots aligned in arrays and each dot in such an array acts as a recording bit. The ideal structure is that the dots are magnetic and the surrounding medium is non-magnetic so that each dot can switch magnetization direction freely without the interference from other dots. This paper presents the nanostructure of the nano-dot array investigated by transmission electron microscopy and magnetic force microscopy. The Co:C film was deposited by alternatively sputtering Co target and C target. The as-deposited specimen has an amorphous structure as revealed by electron diffraction in TEM. Such films transform to ferro-magnetic ones after heat treatment [1]. A laser beam of wavelength of 308 nm and a flux of 0.24 J/cm2 was split into two beams of an approximately equal intensity and then recombined, generating an interference pattern and a periodic modulation of the light intensity.

The growth of self-organized nanoislands and nanowires on a substrate has been extensively studied with a view to fabricating the new functional materials and advanced electric devices. in the present work, Pd silicide islands and wires grown on Si (111) 7x77×7surface were observed in situ by ultrahigh vacuum transmission and reflection electron microscopy (UHV-TEM/REM). Pd was deposited on Si (111) 7×7 surface at about 700 K using an electron beam evaporator attached to the column of a UHV microscope. Two kinds of specimens were prepared: a <111> oriented rectangular specimen with a thin area, whose (111) top surface was observed by plan viewed TEM, and a <110> oriented bulk rectangular specimen, whose (111) side surface was observed by REM

Figure la shows a REM image of Si (111) 7×7 surface. An incident electron beam is directed from the top to the bottom of the figure, which is foreshortened in the beam direction.

Y2O3 is a super refractory oxide with high thermal stability and finds various applications in optics and microelectronic devices. Recently, Eu-activated Y2O3 films attracted much research interest due to its promising applications in flat panel field emission displays. Epitaxial Y2O3:Eu thin films have been grown on LaA1O3(LAO). in this paper we report a transmission electron microscopy (TEM) study of Y2O3 nano tip-structure grown on LAO by pulsed laser deposition using stoichiometric YBa2Cu3O7-σ.a target under a low oxygen pressure. The experimental work was conducted within a JEOL2010F TEM equipped with an ED AX system.

Fig.l is a low magnification cross-section TEM image of the nano-tip structure grown on (001) LAO. The lattice parameters of the tips were calculated to be that of Y2O3 by using LAO as a standard for indexing the diffraction patterns. Nano electron beam diffraction patterns from the tips along [100] and [110] axis are shown in Fig.2a and Fig.2b, respectively, in agreement with the simulated ones using bulk Y2O3 structure.

Molybdenum-based alloys possess a unique combination of physical properties including high strength at elevated temperatures, high thermal conductivity, low coefficient of thermal expansion, and excellent performance in neutron flux environments. However, welds in commercial grade molybdenum alloys typically exhibit low (∼3%) ductility which limits their application. Bryhan has shown that controlled additions of substitutional and interstitial alloying elements can provide almost 20% elongation from gas-tungsten arc welds in 6.35-mm-thick material. Therefore, molybdenum alloys may be considered for use in fusion reactors and other high temperature applications.

The molybdenum alloy was vacuum arc-cast with 0.16 at % Zr intended to getter the O (250 appm) and N (178 appm) impurities together with 53 appm B and 96 appm C intended to strengthen the grain boundaries. The 4-pass welding process was performed on a 6.35-mm plate in a controlled atmosphere chamber where the O, N and water vapor impurity levels were < 10 wppm each.