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Field ion microscopy of silicon

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.

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.

The decomposition of Fe–C martensite (α') was studied using conventional transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffractometry and differential scanning calorimetry. The ageing and tempering of α' at temperatures between room temperature and 423 K result in changes in the atomic structure of α' and subsequently precipitation of iron carbide. In an early stage of decomposition, carbon enrichments develop in the iron matrix. At temperatures below about 363 K. this development of carbon-enriched and carbon-depleted zones leads gradually to the formation of a modulated structure, as revealed by the observation of specific diffraction phenomena. The carbon enrichments possess variable carbon content. Their misfit with the matrix is, at least initially, accommodated elastically. At temperatures above about 363 K. the transition carbide precipitates. It could be shown that the transition carbide has the η-carbide crystal structure and the orientation re...

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.

The halophilic bacterium Halomonas smyrnensis from a modern salt lake used in experiments to induce biomineralization has resulted in the precipitation of monohydrocalcite and other carbonate minerals. In this study, a Halomonas smyrnensis WMS-3 (GenBank:MH425323) strain was identified based on 16S rDNA homology comparison, and then cultured in mediums with 3% NaCl concentration to induce monohydrocalcite at different Mg/Ca molar ratios of 0, 2, 5, 7, and 9. The growth curve of WMS-3 bacteria, pH values, NH4+ concentration, HCO3− and CO32− concentration, carbonic anhydrase (CA) activity, and the changes in Ca2+ and Mg2+ ion concentration were determined to further explore the extracellular biomineralization mechanism. Moreover, the nucleation mechanism of monohydrocalcite on extracellular polymeric substances (EPS) was analyzed through studying ultrathin slices of the WMS-3 strain by High resolution transmission electron microscopy (HRTEM), Selected area election diffraction (SAED), Scanning transmission electron microscopy (STEM), and elemental mapping, besides this, amino acids in the EPS were also analyzed. The results show that pH increased to about 9.0 under the influence of ammonia and CA activity. The precipitation ratio (%, the ratio of the mass/volume concentration) of the Ca2+ ion was 64.32%, 62.20%, 60.22%, 59.57%, and 54.42% at Mg/Ca molar ratios of 0, 2, 5, 7, and 9, respectively, on the 21st day of the experiments, and 6.69%, 7.10%, 7.74%, 8.09% for the Mg2+ ion concentration at Mg/Ca molar ratios 2, 5, 7, and 9, respectively. The obtained minerals were calcite, Mg-rich calcite, aragonite, and hydromagnesite, in addition to the monohydrocalcite, as identified by X-ray diffraction (XRD) analyses. Monohydrocalcite had higher crystallinity when the Mg/Ca ratio increased from 7 to 9; thus, the stability of monohydrocalcite increased, also proven by the thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) analyses. The C=O and C–O–C organic functional groups present in/on the minerals analyzed by Fourier transform infrared spectroscopy (FTIR), the various morphologies and the existence of P and S determined by scanning electron microscope-energy dispersive spectrometer (SEM-EDS), the relatively more negative stable carbon isotope values (−16.91‰ to −17.91‰) analyzed by a carbon isotope laser spectrometer, plus the typical surface chemistry by XPS, all support the biogenesis of these mineral precipitates. Moreover, Ca2+ ions were able to enter the bacterial cell to induce intracellular biomineralization. This study is useful to understand the mechanism of biomineralization further and may provide theoretical reference concerning the formation of monohydrocalcite in nature.

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.

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

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.

Interfacial reactions of ultrahigh vacuum deposited yttrium thin films on atomically clean (111)Si at low temperatures have been studied by both conventional and high-resolution transmission electron microscopy, Auger electron spectroscopy, and x-ray diffraction. A 10-nm-thick yttrium thin film, deposited onto (111)Si at room temperature, was found to completely intermix with Si to form an 11-nm-thick amorphous interlayer. Crystalline Y5Si3 and Si were observed to nucleate first within the amorphous interlayer in samples annealed at temperatures lower than 200 °C. Epitaxial YSi2−x was found to be the only phase formed at the interface of amorphous interlayer and crystalline Si in samples annealed at temperatures higher than 250 °C. In as deposited 20- to 60-nm-thick Y thin films on silicon samples, crystalline Y5Si3, Si, and YSi and a 2.5-nm-thick amorphous layer were found to be present simultaneously. Good correlations were found among difference in atomic size between metal and Si atoms, the calculated free energy of mixing as well as the critical and maximum amorphous interlayer thickness for the Y/Si and a number of refractory metal/Si systems. The Y/Si system is the only system found up to date among all metal/Si systems that the a interlayer can be grown to a thickness exceeding 10 nm during deposition at room temperature.

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

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).