Atomic and electronic structures of a transition layer at the CrN/Cr interface

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Interfacial atomic and electronic structures of Cu/Al2O3(0001) and Cu/Al2O3(11 ＿ ,20) prepared by a pulsed-laser deposition technique were characterized by high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). It was found that both systems have O-terminated interfaces, irrespective of different substrate orientations. This indicates that Cu-O interactions across the interface play an important role for the Cu/Al2O3 systems.

The local atomic electronic structures of Fe-Mo-C-B metallic glasses are investigated using electron energy-loss spectroscopy (EELS). The fracture behavior of this Fe-based amorphous alloy system undergoes the transition from being ductile to exhibiting brittleness when alloyed with Cr or Er atoms. In addition, the glass-forming ability is also enhanced. This plastic-to-brittle transition is suggested to correlate with the change of local atomic short-range order or bonding configurations. Therefore, the bonding configuration of Fe-Mo-C-B-Er(Cr) amorphous alloys is investigated by studying the electronic structure of Fe and C atoms using electron energy-loss spectroscopy. It is shown that the normalized EELS white line intensities of $\mathrm{Fe}\text{\ensuremath{-}}{L}_{2,3}$ edges decrease slightly with an increasing amount of Er additions, while no noticeable difference is obtained with Cr additions. As for the C $K$ edge, a prominent change of edge shape is observed for both alloy systems, where the first peak corresponding to a $1s\ensuremath{\rightarrow}1{\ensuremath{\pi}}^{*}$ transition increases with increasing Er and Cr additions. Accordingly, it is concluded that changes in the local atomic and electronic structure occur around Fe and C atoms when Er and Cr are introduced into the alloys. Furthermore, it is pointed out that the formation of Er-C and Cr-C carbide like local order inferred from the observed C $K$ edge spectra can provide a plausible explanation for the plastic-to-brittle transition observed in these Fe-based amorphous alloys. In spite of the complexity of electronic and atomic structure in this multicomponent Fe-based metallic glass system, this study could serve as a starting point for providing a qualitative interpretation between electronic structure and plasticity in the Fe-Mo-C-B amorphous alloy system. Complimentary techniques, such as x-ray diffraction and high-resolution transmission electron microscope are also employed, providing a more complete structural characterization.

Polyamide 6 (PA6) and polystyrene (PS) nanotubes were successfully fabricated by polymer solution-wetting method. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and electron energy-loss spectroscopy (EELS) techniques were employed to investigate their crystallization phenomena. It has been found in HRTEM images that the crystalline lattice fringes are observed in some regions of the nanotube walls. XRD analysis showed that these two kinds of polymer nanotubes have a higher degree of crystallinity than that of the bulk materials. PA6 nanotubes dominate in γ phase while bulk PA6 present mainly in α phase. EELS has been used to determine the ratio of C=C and C-C in PS nanotubes, and our result is consistent with the theoretical calculation. HRTEM and EELS will shed light on the microstructural characterization of polymer nanotubes.

Atomic and electronic structures of interfaces in an internally oxidized Pd/ZnO system were studied by high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). {0001}ZnO polar planes tend to be parallel to the interface. A ZnO precipitate was terminated by an oxygen surface at one end of the precipitate and by a zinc (0001) surface at the other end of the precipitate. A pre-edge peak was detected only in O-K energy-loss near-edge spectra (ELNES) acquired from the oxygen-terminated interface. Ab initio calculations indicated that the origin of the pre-edge peak could be attributed to the strong chemical bonding and hybridization of Pd-d and O-p orbitals at the oxygen-terminated polar interface.

Atomic and electronic structure of diamond grain boundaries analyzed by HRTEM and EELS

Crystallographic and interfacial characteristics of polycrystalline-Si/ZrO 2 / SiO 2 /Si metal-oxide-semiconductor (MOS) structures were investigated at the atomic scale by high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS) combined with the annular dark-field scanning transmission electron microscopy. The HRTEM and electron diffraction results showed that the ZrO 2 film exhibited a mixed structure of the tetragonal (P4m2) and the monoclinic (P2 1 /c) phases. Moreover, Zr-Si nodules formed by the reaction of Zr with polycrystalline-Si were evaluated to be ZrSi 2 of the orthorhombic phase or Zr 5 Si 4 of the tetragonal phase. From the EELS results, Zr atoms were detected at the upper and bottom interfaces of the SiO 2 film, and the interfacial SiO 2 layer with thickness <1 nm was observed at the polycrystalline-Si/ZrO 2 interface. The interfacial reactions directly influence the electrical properties of the MOS structures.

Thin Cu films were grown on single crystalline α-Al2O3 by molecular beam epitaxy at a substrate temperature of T = 800°C. The nominally 100 nm thin film consists of islands, which have diameters of 0.5-1 μm. High-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS) were applied to obtain information about the atomic and electronic structure of the interface. HRTEM studies were performed on the Jeol JEM ARM 1250 operated at 1250 kV (point resolution of 0.12 nm). Analytical studies were conducted on a dedicated scanning TEM (VG HB 501) operated at 100 kV and equipped with a parallel EELS (Gatan 666). HRTEM of the Cu/ Al2O3-interface shows an atomically abrupt interface and reveals an epitaxial orientation relationship (1120)s[0001]s || (111)Cu &amp;lt;211&amp;gt;Cu (S denotes sapphire) (FIG.l). Close-packed planes and directions in both crystals are parallel to each other resulting in misfits of 2% and 7% in &amp;lt;211&amp;gt;Cu- and &amp;lt;110&amp;gt;Cu-directions, respectively. The interface is not coherent, but in both directions no misfit dislocations are detectable.

The field-emission characteristics of individual ropes made of B–C–N nanotubes were measured in situ in a low-energy electron point source microscope. The tungsten field emission tip of the microscope was used as a movable electrode, approaching the rope, and acting as an anode during field-emission measurements. The atomic structure and chemical composition of the ropes were analyzed by high-resolution transmission electron microscopy and electron energy-loss spectroscopy. The tubes assembled within the ropes typically revealed open-tip ends, a small number of layers and zigzag chirality. We found that the field-emission properties of the B–C–N nanotube ropes are competitive with conventional C nanotubes, with the expected additional benefit that the B–C–N ropes exhibit higher environmental stability.

We have synthesized quaternary chalcogenide-based misfit nanotubes LnS(Se)-TaS2(Se) (Ln = La, Ce, Nd, and Ho). None of the compounds described here were reported in the literature as a bulk compound. The characterization of these nanotubes, at the atomic level, has been developed via different transmission electron microscopy techniques, including high-resolution scanning transmission electron microscopy, electron diffraction, and electron energy-loss spectroscopy. In particular, quantification at sub-nanometer scale was achieved by acquiring high-quality electron energy-loss spectra at high energy (∼between 1000 and 2500 eV). Remarkably, the sulfur was found to reside primarily in the distorted rocksalt LnS lattice, while the Se is associated with the hexagonal TaSe2 site. Consequently, these quaternary misfit layered compounds in the form of nanostructures possess a double superstructure of La/Ta and S/Se with the same periodicity. In addition, the interlayer spacing between the layers and the interatomic distances within the layer vary systematically in the nanotubes, showing clear reduction when going from the lightest (La atom) to the heaviest (Ho) atom. Amorphous layers, of different nature, were observed at the surface of the nanotubes. For La-based NTs, the thin external amorphous layer (inferior to 10 nm) can be ascribed to a Se deficiency. Contrarily, for Ho-based NTs, the thick amorphous layer (between 10 and 20 nm) is clearly ascribed to oxidation. All of these findings helped us to understand the atomic structure of these new compounds and nanotubes thereof.

High-resolution transmission electron microscopy and electron energy loss spectroscopy (EELS) were used to study the interfacial layers formed in Gd2O3 films on Si(001) during rapid thermal annealing at 780 °C in an O2 ambient. Oxygen diffuses through the films and reacts with the substrate to form a SiO2 layer and an intermediate layer containing Gd2O3 and SiO2. Singular value decomposition was used to profile the Si, SiO2, and Gd2O3 components through the film from the characteristic spectra observed in the Si L2,3, Gd N4,5 and O K-edge EELS. The profiling results support the results of x-ray photoelectron spectroscopy sputter profiling measurements and contribute to a complete picture of the chemical bonding within the films. The ab initio multiple scattering method was used to simulate the observed EELS spectra at the Si L2,3 and O K edges and provide further insight into the chemical bonding of the film and the origin of spectral features. For SiO2, the Si L2,3 EELS is due only to the first-neighbor oxygen atoms. The O K-edge EELS for Gd2O3 is also due only to Gd first neighbors, while the SiO2 EELS is very sensitive to the number of O second neighbors as well as the Si first neighbors.

In this study, we have demonstrated successful site-specific cross-sectioning of carbon-nanotube - metal junctions which provided samples suitable for high resolution transmission electron microscopy and electron energy loss spectroscopy. For the cross-sectioning, we have suggested a modified technique based on combination of the Focused Ion Beam (FIB) lift-out and the conventional Ar+ ion milling techniques. Electron-transparent cross-sections of multiwall carbon nanotubes showing no significant surface amorphization or Ga contamination (typical artifacts of conventional FIB lift-out technique) were obtained. High-resolution transmission electron microscopy and electron energy loss spectroscopy of a multi-wall carbon nanotube cross-section have been carried out.

ABSTRACTIn this study, we have demonstrated successful site-specific cross-sectioning of carbon-nanotube - metal junctions which provided samples suitable for high resolution transmission electron microscopy and electron energy loss spectroscopy. For the cross-sectioning, we have suggested a modified technique based on combination of the Focused Ion Beam (FIB) lift-out and the conventional Ar+ ion milling techniques. Electron-transparent cross-sections of multiwall carbon nanotubes showing no significant surface amorphization or Ga contamination (typical artifacts of conventional FIB lift-out technique) were obtained. High-resolution transmission electron microscopy and electron energy loss spectroscopy of a multi-wall carbon nanotube cross-section have been carried out.

We have investigated the growth and atomic interface structures of diamond on aluminum nitride (AlN). The two-step chemical vapor deposition technique is used to control diamond nucleation density, crystal size, and AlN surface orientation and polarity. Highly uniform diamond layers with a nucleation density in the range of 105–1011 cm–2 and a grain size of 0.1–5 μm are fabricated. Crystallographically abrupt interfaces between polycrystalline diamond and single-crystal AlN(0001) layers have been observed via high-resolution transmission electron microscopy and electron energy-loss spectroscopy. A majority of the diamond crystals have been found to have the diamond(111)/AlN(0001) interface relationship. Atomistic models of the bonding mechanism at the heterointerface are used to elucidate experimental observations and the role of hydrogen plasma on the growth of diamond on AlN. Nonpolar and semipolar AlN surfaces have been found to have higher resistance to process plasma and led to better crystallinity o...

Grain boundaries (GBs) modulate the macroscopic properties in polycrystalline materials because they have different atomic and electronic structures from the bulk. Despite the progress on the understanding of GB atomic structures, knowledge of the localized electronic band structures is still lacking. Here, we experimentally characterized the atomic structures and the band gaps of four typical GBs in α-Al2O3 by scanning transmission electron microscopy and valence electron energy-loss spectroscopy (EELS). It was found that the band gaps of the GBs are narrowed by 0.5-2.1 eV compared with that of 8.8 eV in the bulk. By combing core-loss EELS with first-principles calculations, we elucidated that the band gap reductions directly correlate with the decrease of the coordination numbers of Al and O ions at the GBs. These results provide in-depth understanding between the local atomic and electronic band structures for GBs and demonstrate a novel electronic-structure analysis for crystalline defects.