Materials Science Forum Vols. 475-479

Abstract: In this study, severe plastic straining through equal-channel angular pressing (ECAP) is imposed on age-hardenable Al-Mg-Si alloys having two different compositions of excess Si or Mg in the Al-Mg2Si pusedo-binary system. Thereafter, the alloys are subjected to aging and the microstructures are examined using transmission electron microscopy. It is shown that the precipitation behavior is significantly changed through application of ECAP.

Abstract: The precursor of LaMnO3 obtained by the reaction of metal salt with potassium hydroxide was subjected to hydrothermal condition in an autoclave then the precipitate was treated in different temperatures (600-900°C). The effect of precursor type and hydrothermal crystallization conditions on the morphology of lanthanide manganese grains was investigated. The morphology and the structure of the products was studied by transmission electron microscope (TEM) and X-ray diffraction (XRD). Different shapes of LaMnO3 can be obtained by controlling prepare condition and treated temperature. The XRD results showed the formation of perovskite-type LaMnO3.

Abstract: Ultrafine-grained (UFG) pure Cu processed by equal channel angular pressing (ECAP) was subjected to cyclic deformation and subsequent ageing treatment at room temperature (RT) in order to investigate the stability of defects and grain size. Cyclic deformation for 1000 cycles at RT leads to a large decrease of internal stress. X-ray diffraction (XRD) shows that the stability of defects and grain size at RT in as-cyclic deformed sample is lower than that in as-processed sample and that a reduction of internal stress takes place prior to grain growth. TEM observations show that the microstructural evolution during ageing is characterized by normal grain growth accompanied with recovery within grain interior.

Abstract: A new procedure is proposed for the exit electron wave reconstruction using a small set of high-resolution electron microscopy (HREM) images. This procedure is similar to that proposed by van Dyck and coworkers, but the relative shifts between different HREM images are obtained via the genetic algorithm instead of the more widely used cross-correlation function (XCF) method. The new procedure is demonstrated using simulated HREM images with added noise, and shown to be able to deal with situation where the scheme based on the method of XCF is not applicable.

Abstract: A novel EELS technique was developed to study bonding of grain boundary in many kinds of steels. We measured the normalized intensities of Fe white lines and calculated the occupancies of 3d states of iron, and then analyzed the relationship of the occupancies of 3d states of iron and the fracture property of the steels. We found that if the grain boundary has a different occupancy of 3d state of iron from that of the bulk, the steel tends to have an intergranular fracture, whereas if the grain boundary has almost the same occupancy of 3d state as the bulk, the steel tends to have a transgranular fracture. Our result shows that the difference in the occupancy of 3d state between bulk and grain boundary can be used to study the fracture mode at grain boundary in steel.

Abstract: We have demonstrated the preparation of the almost defect-free homoepitaxial layer and the defective layer, respectively, with and without applying the in-situ cleaning of the silicon substrate surface using electron cyclotron resonance hydrogen plasma. Secondary ion mass spectroscopy indicated that the interfacial oxygen and carbon concentrations, respectively, decreased and increased with the in-situ cleaning. We have investigated the effect of process parameters such as microwave power, d.c bias, and cleaning time, on the epitaxial growth, by evaluating the cross-sectional transmission electron microscopy images of the subsequently deposited Si homoepitaxial film.

Abstract: The failure of individual multiwall carbon nanotubes (CNTs) during electron field emission was investigated in situ inside the transmission electron microscope (TEM). Long time emission of a single CNT at the level of tens µA or higher may lead to unrecoverable damage to the CNT. High-resolution TEM observations of the emission failure process shown that the failure was usually companied by structure damage or break of the CNT, and the failure or degradation of the emission characteristics of the CNT was typically initiated at the CNT/substrate contact, defect site or at the open end via the field evaporation or oxidation of the tip of the CNT.

Abstract: The potential barrier at the metal/oxide junction in a specular spin valve structure with nano-oxide layers has been mapped by off-axis electron holography in a field emission gun transmission electron microscope. A potential jump of ~3V across the metal/oxide junction was detected. Presence of the potential barrier confirms formation of metal/insulator/metal structure, which contributes to confinement of conductance electrons with spin polarity characteristic in the key SV structure by the specular reflection of the spin-polarized electrons at the metal/oxide junction and leads to nearly double enhancement of magnetoresistance (MR) ratio from 8% to ~16%.

Abstract: Using a nanoprobe system, we have studied the wetting and the contact properties of Ga with Au, TiN on Al, SiO2 and carbon nanotubes in micro and nano meter scale. Some new phenomena have been observed.

Abstract: In core-level electron energy loss spectroscopy (EELS) for anisotropic systems, the applied electric field is determined by the momentum transfer vector q, therefore the collection solid angle range for the scattering electrons and sample orientation will affect the measured EELS spectra.. Using the spatially resolved C 1s core excitation in carbon nanotube as an example, we show that the EELS measurement can be understood by a simple dipole theory of anisotropic core loss spectroscopy which decomposes the spectral contribution in terms of orientationelly averaged isotropic spectrum and linear dichrotic spectrum. In addition, we point out the Magic Angle (MA) conditions that allow the direct determination of the averaged spectra acquired independent of the exact sample orientation.