Characterization of the microstructures produced by different solutionizing quench rates in aluminum-lithium alloys

New and interesting physical phenomena are being observed via thin film depositions using a variety of processing techniques in different material systems. The present study describes Pb-Zr-Ti-O pyrochlore thin films which were deposited onto (100) MgO substrates using an ion beam sputtering technique. These films are of interest because of their unique microstructure which may provide valuable information in better understanding the epitaxial growth of thin films. Characterization were performed using conventional transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Special TEM sample preparation procedures have been developed, which will be reported elsewhere.The as-deposited pyrochlore thin film is near epitaxial and is oriented with both (100) and (111) parallel to the (100) of the MgO substrate. Figure 1(a) shows the selected area diffraction pattern (SADP) of the pyrochlore thin film taken parallel to the [100] zone axis of the substrate.

The structure of hydrogen-induced platelets (HIPs) in silicon has been examined with conventional transmission electron microscopy (CTEM) and high-resolution transmission electron microscopy (HRTEM). Hrtem was utilized to clarify the atomic structure in which hydrogen atoms are assumed to saturate the broken bonds between adjacent (111) planes. The structural model was refined by introducing a reliability factor in real space for quantitative comparison between experimental and simulated images. Some contrast variations in HRTEM images can be well explained by allowing for atomic ledges on the (111) plane with broken bonds. Furthermore it is found from the strain contrast in a CTEM image that a considerable amount of H2 gas is contained in the open space of the HIP, which results in an internal pressure as large as 1 GPa. The formation process of Hips is discussed.

Quantitative TEM study of the precipitation microstructure in aluminium alloy Al(MgSiCu) 6056 T6

Investigation of the atomic structure of a (111) Zr/ZrN interface shows that it is a type-3 incoherent interface (i.e., high-index orientation relationship with a low-index interface plane in only one phase), as determined from conventional transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images, image simulations, and near-coincidence-site atomic modeling of the interface. Long facets and atomic ledges several {111}ZrN planes high form at the interface, indicating that such features cannot be used as criteria to define partial coherency at interfaces. These results also indicate that ledgewise growth is possible during the phase transformation from Zr to ZrN. Composition profiles taken across the interface using energy-filtering TEM and the N K-edge show that the composition changes abruptly at the interface, in accord with the structural transformation. Simulation results on an inclined (111) Zr/ZrN interface indicate that it is possible to judge whether an interface is inclined and faceted at the same time. A rough interface can look faceted in a HRTEM image due to projection effects, but only under a very strict set of conditions. Conversely, an interface cannot be faceted if it looks rough in an HRTEM image.

Effect of quench-induced precipitation on microstructure and mechanical properties of 7085 aluminum alloy

Thin Nb films were grown by MBE in a UHV chamber at two different temperatures (50°C and 950°C) on the (110) surface of TiO2 (rutile).At a growth temperature of 50°C, reflection high energy electron diffraction (RHEED) revealed epitaxial growth of Nb on rutile: (110)[001] TiO2 ¦¦ (100)[001] Nb. In addition, investigations with Auger electron spectroscopy (AES) revealed that a chemical reaction took place between the Nb overlayer and the TiO2 substrate at the initial growth stage. A 2 nm thick reaction layer at the Nb/TiO2 interface has been identified by means of conventional transmission electron microscopy (CTEM) and high-resolution transmission electron microscopy (HRTEM).At a substrate temperature of 950°C, during growth, the Nb film was oxidized completely, and NbO2 grew epitaxially on TiO2. The structure and the chemical composition of the overlayers have been investigated by RHEED, AES, CTEM and HRTEM. Furthermore, it was determined that the reaction of Nb with TiO2 is governed by the defect structure of the TiO2 and the relative oxygen affinities of Nb and TiO2.

Laminated (Fe/sub 0.7/Co/sub 0.3/)/sub 88/Zr/sub 7/B/sub 4/Cu/sub 1/ amorphous HITPERM/SiO/sub 2/ multilayer thin films have been studied by room-temperature (RT) pulsed inductive microwave magnetometry (PIMM) in single, bilayer, and trilayer films. Switching has been measured in a multilayer film with six (50 nm) HITPERM layers, separated by five (2 nm) SiO/sub 2/ layers. Films were investigated by conventional transmission electron microscopy (TEM), high-resolution TEM (HREM), and superconducting quantum interference device (SQUID) magnetometry. HREM and TEM show BCC FeCo nanocrystals to nucleate on top of SiO/sub 2/ layers. Plan view TEM on the top layer reveals FCC nanocrystals that align in chains with spacing of /spl sim/50-100 nm. SQUID magnetometry shows reversal to begin by rotation in a single layer for H<14.4 kA/m (180 Oe) followed by nearly simultaneous reversal of several layers. A final switching event is thermally activated, requiring fields in excess of 8 kA/m (100 Oe) to switch at 2 K, but switching at the same field as other layers for elevated temperatures (RT).

Electron microscope techniques provide very powerful tools to investigate nanometer scaled structures in solids, especially by using high resolution electron microscopy (HREM) and conventional transmission electron microscopy (TEM). The present overview describes the possibilities of investigating quantum dot (QD) structures by TEM and HREM, discussing advantages and disadvantages, presuppositions needed, limitations, and the problems of contrast analysis and interpretation in comparison with other structure analyzing methods.

The interphase boundary between the front of a cubic and tetragonal matrix grown in a yttria-stabilized tetragonal zirconia polycrystal was investigated by conventional transmission electron microscopy (CTEM) and high-resolution transmission electron microscopy (HRTEM). Periodic contrasts with a regular spacing were clearly observed on the boundary. CTEM and HRTEM observation revealed that there are misfit dislocations with a Burgers vector of 1/2〈110〉. The yttrium cation distribution across the interphase boundary was measured by energy-dispersive X-ray spectroscopy using a probe size <1 nm. The yttrium cation content changes sharply at the c/t interphase boundary with a transition width of about 10 nm.

In 4H–SiC, damage created by helium implantation at high fluence (5×1016 ions cm−2) and high energy (1.6 MeV) was studied using different techniques of electron microscopy all along the ion path. Around the end of range, conventional transmission electron microscopy was used to observe the fine microstructure of defects in the as-implanted and 1500 °C annealed samples. No bubbles were found in the as-implanted sample while numerous cavities with different shape, size and density are present after annealing. The amorphous-crystalline (a/c) transition region was checked by high resolution transmission electron microscopy. The strain profile, determined using the large angle convergent beam electron diffraction, shows a strong correlation with the nuclear stopping curve given by SRIM simulation. The dilatation of the c axis measured all along the ion path is in agreement with the value of the observed swelling. Relaxation volumes for interstitial and vacancy do not cancel. After annealing the cavity parameters are found to be dependent on both the helium density and the as-implanted microstructure.

Scanning transmission electron microscope (STEM) is a combination of the scanning electron microscope and the transmission electron microscope (TEM). Thin specimens are viewed in transmission, while images are formed serially by the scanning of an electron probe. In recent years, through the successful correction of Q2 the intrinsically high aberrations of electron lenses it has become possible to form probes well below atomic dimensions, and as a result, atomic resolution images showing sub‐angstrom resolution may now be routinely achieved in this instrumentThe nature of the images obtained in the STEM can differ in significant ways from those formed by the conventional TEM, in particular, multiple signals can be acquired in the STEM including bright field, annular dark field (ADF) images, and spectroscopic images using either electrons that have lost energy by exciting specific inner shell or valence band levels or by detecting emitted characteristic x‐rays. A key difference between STEM and TEM imaging is that the ADF image available on the STEM represents almost perfect incoherent imaging, while the bright field image represents almost perfect coherent imaging, equivalent to the image provided by a conventional high‐resolution TEM. The latter technique has often been simply referred to as high‐resolution electron microscopy (HREM). This article focuses on Z‐contrast imaging of materials at atomic resolution and associated techniques such as electron energy loss spectroscopy (EELS).

Conventional and high resolution TEM investigation of the microstructure of compositionally graded TiAlSiN thin films

IntroductionCurrently, the resolution of structural detail in conventional transmission electron microscopy (CTEM) of organic materials is limited by the electron beam damage suffered by the sample. It has recently been shown that the imaging modes now available in scanning transmission electron microscopy (STEM) provide the potential for improvements in resolution over CTEM methods. However, the effect of the sensitivity of an organic sample itself to beam damage has not been compared in STEM versus CTEM. In STEM each element of the sample area is briefly illuminated with a small diameter, high flux, scanning electron beam, whereas in CTEM the entire sample area is continuously illuminated with a large diameter, lower flux, static electron beam. Although it has been shown that the amount of sample damage in CTEM is independent of dose rate(2), the electron flux in STEM may range from 3 to 4 orders of magnitude greater than that in CTEM, with a possible influence on damage rate. Generally, the effects of beam size, high flux, and short dwell time of the scanning electron beam on sensitivity of the sample to damage in STEM are not known.

The paper reports structural and microchemical investigations of low-dimensional semiconducting materials by combined imaging and spectroscopical techniques of transmission electron microscopy (TEM). The materials systems under investigation comprise graded (Al,Ga)As layers, (In,Ga)As quantum wires in V-grooved (001)InP, and (In,Ga)As quantum dots in GaAs. In order to elucidate structural peculiarities of these objects conventional and high-resolution TEM (CTEM/HRTEM) were performed, whereas information about the chemical composition and element distribution was obtained through electron energy loss spectroscopy (EELS), energy-filtered TEM (EFTEM), and energy-dispersive X-ray spectroscopy (EDXS). Particularly, the application possibilities of EFTEM are here demonstrated for revealing the local element content at high lateral resolution in a semi-quantitative manner.

Precipitation and age hardening processes in A1 alloy 6061 and Comral-85™ metal matrix composite have been investigated and compared. A number of sophisticated techniques were used to characterise fine-scale precipitation in these materials. These included atom-probe field ion microscopy (APFIM), high resolution transmission electron microscopy (HRTEM), conventional transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). A dark-field high resolution technique was developed that enabled imaging of the crystal structures of fine-scale precipitates. The precipitation sequence in alloy 6061 was found to be: independent clusters of Mg and Si atoms >> co-clusters that contained both Mg and Si atoms >> small precipitates of unknown structure precipitates >> mostly B' and some s' precipitates It was found that the Mg:Si ratio in the small precipitates, precipitates and B' precipitates was close to 1. A new structure was proposed for the precipitate: base-centred monoclinic, a = 15.34Â, b = 4.05A, c = 6.83A, s = 106°. The development of hardness during ageing of alloy 6061 was related to different types of precipitates that formed in the precipitation sequence. The clusters of atoms and also the small precipitates had a negligible effect on hardness. Themajority of age hardening was provided by needle-shaped precipitates. The formation of B' precipitates resulted in substantial overageing of the alloy.