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We report on the performance of our aberration-corrected JEOL-JEM2200FS electron microscope. This high-resolution field-mission TEM/STEM is equipped with a Schottky field-emission gun operated at 200 kV, a CEOS probe corrector, and an in-column energy filter. We focus on the performance of the probe corrector and show that the Si [110] dumbbell structure can be routinely resolved in STEM mode with the power spectrum indicating a probe size of ~1 Å. Ronchigram analysis suggests that the constant phase area is extended from 15 mrad to 35 mrad after corrector tuning. We also report the performance of our newly installed JEOL-JEM2200MCO, an upgraded version of the JEM2200FS, equipped with two CEOS aberration correctors (and a monochromator), one for the probe-forming lens and the other for the postspecimen objective lens. Based on Young's fringe analysis of Au particles on amorphous Ge, initial results show that the information limit in TEM mode with the aberration correction (Cs = −3.8 μm) is ~0.12 nm. Materials research applications using these two instruments are described including atomic-column-resolved Z-contrast imaging and electron energy-loss spectroscopy of oxide hetero-interfaces and strain mapping of a SrTiO3 tilt-grain boundary. The requirements for a high-precision TEM laboratory to house an aberration-corrected microscope are also discussed.
The hardmetal composites are generally produced from powders of tungsten carbide (WC) and of metal elements, belonging to group 8-10 of the periodic table, which are mixed together by wet milling. News processes, alternatives to milling, have been developed, aiming a higher uniformity of the metallic binder distribution in WC based composites, together with other technological benefits. One of those methods consists of the sputter deposition of metal binder onto the WC powder leading to powder particles coated with the metallic elements. The particles coating showed to be chemically and morphologically very uniform and possesses a nanocrystalline structure and improved surface properties, such as powder's flowability, pressing behaviour, sinterability and thermal reactivity.
Following is a list of microscopy-related meetings and courses. The editors would greatly appreciate input to this list via the electronic submission form found in the MSA World-Wide Web page at http://www.msa.microscopy.com. We will gladly add hypertext links to the notice on the web and insert a listing of the meeting in the next issue of the Journal. Send comments and questions to Nan Yao, nyao@Princeton.edu.
Nickel aluminides can be formed by thermal annealing of alternate layers of Ni and Al that react exothermically. These metals have medium/high energy of mixing and when in adiabatic conditions the reaction could become self-propagating. The first phase to form in Ni/Al reactions has been widely investigated, but there is no consensus regarding this subject. Depending on the overall chemical composition and modulation period of the multilayer, and on the processing history, the first phase to form could be NiAl3, NiAl and Ni2Al9.
Ultrafast Electron Microscopy and Ultrafast Science
The continuous miniaturization of the mechanical components and devices push to microfabrication techniques such as μPIM (micro-Powder Injection Moulding) and laser sintering, particularly DMLS (Direct Metal Laser Sintering).
Ultrafast Electron Microscopy and Ultrafast Science
Chromium dioxide (CrO2) has been extensively used in the magnetic recording industry. However, it is its ferromagnetic half-metallic nature that has more recently attracted much attention, primarily for the development of spintronic devices. CrO2 is the only stoichiometric binary oxide theoretically predicted to be fully spin polarized at the Fermi level. It presents a Curie temperature of ∼ 396 K, i.e. well above room temperature, and a magnetic moment of 2 mB per formula unit. However an antiferromagnetic native insulating layer of Cr2O3 is always present on the CrO2 surface which enhances the CrO2 magnetoresistance and might be used as a barrier in magnetic tunnel junctions.
Materials mechanical resistance is known to depend on the size of structural features, accordingly to the familiar HallPetch equation. For the nanometer range of grain sizes, this relationship breaks down and a change of the grain size exponent is needed to satisfy this dependency. Nevertheless, the superior strength of the nanocrystalline material relays on the small dimension of its grains. Characterization of the thermal stability of these materials becomes relevant since a large fraction of atoms are in the grain boundaries and, as a result, its structure posses a large excess of energy that promotes grain growth. Grain growth in nanocrystalline metals has been observed well below the temperatures needed to promote grain growth in coarse grained materials; in some cases, even at room temperature. From this perspective, the study of grain growth in nanocrystalline metals is crucial for the development of new nanocrystalline materials with outstanding mechanical properties. There are many studies that propose models to explain the mechanism of nucleation and growth of annealing twins in F.C.C. materials. In-situ TEM and SEM techniques are invaluable for understanding and characterizing dynamic microstructural changes like nucleation and growth of grains and twins. This is an important observation because twinning affects the properties of materials and so is essential to comprehend the mechanism of twin formation. Other advantage of the in-situ TEM technique is the study of grain growth in ultra fine film with a thickness in the range of 50 to 100 nm. With these techniques, the mechanisms and kinetics of grain growth in nanocrystalline thin films can be observed and studied in real time.
Ferroelectric films with a composition gradient have attracted much attention because of their large polarization offset present in the hysteresis loops. Lead Zirconate Titanate (PZT) films were deposited on Pt/TiO2/SiO2/Si substrates by Pulsed Laser Deposition (PLD) technique, using a Nd:YAG laser (Surelite) with a source pulse wavelength of 1064 nm and duration of 5-7 ns delivering an energy of 320 mJ per pulse and a laser fluence energy about 20 J/cm2. The film growth is performed in O2 atmosphere (0,40 mbar) while the substrate is heated at 600°C by a quartz lamp. Starting from ceramic targets based on PZT compositions and containing 5% mol. of excess of PbO to compensate the lead evaporation during heat treatment, three films with different compositions Zr/Ti 55/45, 65/35 and 92/8, and two types of complex structures were produced. These complex structures are in the case of the up-graded structure (UpG), with PZT (92/8) at the bottom, PZT (65/35) on middle and PZT (55/45) on the top, and for down-graded (DoG) one, that order is reversed.
