Parallel Electron Energy Loss Spectroscopy Research Articles

Relationships among equivalent oxide thickness, nanochemistry, and nanostructure in atomic layer chemical-vapor-deposited Hf–O films on Si

The relationships among the equivalent oxide thickness (EOT), nanochemistry, and nanostructure of atomic layer chemical-vapor-deposited (ALCVD) Hf–O-based films, with oxide and nitrided oxide interlayers on Si substrates, were studied using x-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) in annular dark-field imaging (ADF), and parallel electron energy-loss spectroscopy (PEELS), capacitance–voltage, and leakage-current–voltage measurements. The XPS (Hf 4f binding energy shift) studies indicated the formation of Hf–O–Si bonds in as-deposited amorphous films, the amount of which was influenced by the interlayer composition and annealing conditions. After post-deposition annealing in N2 and O2, the Hf–O layers were nanocrystalline. Although HRTEM images showed a structurally sharp interface between the Hf–O layer and the interlayer, angle-resolved XPS, ADF imaging, and PEELS in the STEM revealed a chemically diffused HfSiOx region in between. This interdiffusion was observed by the detection of Si (using Si L edge) and Hf (using Hf O2,3 edge) in the Hf–O layer and the interlayer. For an annealed Hf–O/interlayer stack, with an ALCVD target thickness of 4.0 nm for the Hf–O layer on 1.2 nm of nitrided chemical oxide, the experimentally measured EOT and leakage current (at −1 V) were 1.52 nm and ∼10−8 A/cm2. A three-layer (1.2 nm interlayer of nitrided chemical oxide/compositionally graded, 2 nm region of HfSiOx/2 nm HfO2 layer) capacitor model was used to determine the respective contributions to the measured EOT, and the dielectric permittivity of the interlayer was found to be 6.06. These studies clearly indicate that a total EOT of 1 nm and below is attainable in the Hf–N–O–Si/Si–N–O system.

Ultrastructure of the calcium-sequestering gastrodermal cell in the hydroid Hydractinia symbiolongicarpus (Cnidaria, Hydrozoa).

Large, free-floating crystals of calcium carbonate occur in vacuoles of gastrodermal cells of the hydroid Hydractinia symbiolongicarpus. Here, morphological details about the process by which these cells accumulate and sequester calcium are provided by a cytochemical method designed to demonstrate calcium at the ultrastructural level. Electron-dense material presumably indicative of the presence of calcium was EGTA-sensitive and was shown by parallel electron energy loss spectroscopy (EELS) and energy spectroscopic imaging (ESI) to contain calcium. Calcium occurred in only one cell type, the endodermally derived gastrodermal cell. In these cells, the electron-dense material appeared first as a fine precipitate in the cytosol and nucleus and later as larger deposits and aggregates in the vacuole. During the life cycle, gastrodermal cells of the uninduced planula and the planula during metamorphic induction sequestered calcium. In primary polyps and polyps from established colonies, gastrodermal cells sequestered calcium, but the endodermal secretory cells did not. Our observations support the hypothesis that gastrodermal cells function as a physiological sink for calcium that enters the organism in conjunction with calcium-requiring processes such as motility, secretion, and metamorphosis.

The Effects of Vanadium, Niobium, Titanium and Zirconium on the Microstructure and Mechanical Properties of Thin Slab Cast Steels

The evolution of precipitation and microstructure during a simulation of the thin slab direct rolling process, in six vanadium based, low carbon, steels with V, V-N, V-Ti-N, V-Nb, V-Nb-Ti and V-Zr additions was studied by optical microscopy, analytical transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX) and parallel electron energy loss spectroscopy (PEELS). Tensile properties and Charpy vee-notch toughness of the final strip were also determined. The effects of microalloying additions and processing conditions, including equalisation temperature (1 200°C, 1 100°C and 1 050°C) and end water cool temperature, on the austenite and ferrite grain sizes, as well as the type and composition of the precipitates, were determined. The relationship between the microstructure and the properties in the steels was also ascertained.

Carbon Nitride Compounds Synthesized by Thermal AnnealingAmorphous Nanostructured Graphite under the Flow of NH3 Gas

Graphitic-C3N4 (g-C3N4) andpseudocubic-C3N4 (p-C3N4) have beensynthesized by thermally annealing high-energy ball milled amorphousnanostructured graphite powders under NH3 atmosphere. Theexperimental results by x-ray, transmission-electron microscopy,selected electron area diffraction and parallel electron energy lossspectroscopy indicated that g-C3N4 grew from the milledgraphite powders in the presence of NH3 gas at a temperature of1050°C. After treatment at a temperature of 1350°C, thepseudocubic-C3N4 phase forms. It was believed that thehigh-energy ball milling generates nanosized amorphous graphitestructures, under subsequent isothermal annealing in a flow ofNH3 gas, the carbon nitride compound can easily form throughreaction of nanostructured carbon with nitrogen of NH3.

Successful application of spatial difference technique to electron energy-loss spectroscopy studies of Mo/SrTiO3 interfaces.

The electron energy-loss near-edge structure (ELNES) of Mo/SrTiO3 interfaces has been studied using high spatial resolution electron energy-loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope. Thin films of Mo with a thickness of 50 nm were grown on (001)-orientated SrTiO3 surfaces by molecular beam epitaxy at 600 degrees C. High-resolution transmission electron microscopy revealed that the interfaces were atomically abrupt with the (110)Mo plane parallel to the substrate surface. Ti-L2,3 ( approximately 460 eV), O-K ( approximately 530 eV), Sr-L2,3 ( approximately 1950 eV) and Mo-L2,3 ( approximately 2500 eV) absorption edges were acquired by using the Gatan Enfina parallel EELS system with a CCD detector. The interface-specific components of the ELNES were extracted by employing the spatial difference method. The interfacial Ti-L2,3 edge shifted to lower energy values and the splitting due to crystal field became less pronounced compared to bulk SrTiO3, which indicated that the Ti atoms at the interface were in a reduced oxidation state and that the symmetry of the TiO6 octahedra was disturbed. No interfacial Sr-L2,3 edge was observed, which may demonstrate that Sr atoms do not participate in the interfacial bonding. An evident interface-specific O-K edge was found, which differs from that of the bulk in both position (0.8 +/- 0.2 eV positive shift) and shape. In addition, a positive shift (0.9 +/- 0.3 eV) occurred for the interfacial Mo-L2,3, revealing an oxidized state of Mo at the interface. Our results indicated that at the interface SrTiO3 was terminated with TiO2. The validity of the spatial difference technique is discussed and examined by introducing subchannel drift intentionally.

Atomic layer chemical vapor deposition of ZrO2-based dielectric films: Nanostructure and nanochemistry

A 4 nm layer of ZrOx (targeted x∼2) was deposited on an interfacial layer (IL) of native oxide (SiO, t∼1.2 nm) surface on 200 mm Si wafers by a manufacturable atomic layer chemical vapor deposition technique at 300 °C. Some as-deposited layers were subjected to a postdeposition, rapid thermal annealing at 700 °C for 5 min in flowing oxygen at atmospheric pressure. The experimental x-ray diffraction, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and high-resolution parallel electron energy loss spectroscopy results showed that a multiphase and heterogeneous structure evolved, which we call the Zr–O/IL/Si stack. The as-deposited Zr-O layer was amorphous ZrO2-rich Zr silicate containing about 15% by volume of embedded ZrO2 nanocrystals, which transformed to a glass nanoceramic (with over 90% by volume of predominantly tetragonal-ZrO2 (t-ZrO2) and monoclinic-ZrO2 (m−ZrO2) nanocrystals) upon annealing. The formation of disordered amorphous regions within some of the nanocrystals, as well as crystalline regions with defects, probably gave rise to lattice strains and deformations. The interfacial layer (IL) was partitioned into an upper SiO2-rich Zr silicate and the lower SiOx. The latter was substoichiometric and the average oxidation state increased from Si0.86+ in SiO0.43 (as-deposited) to Si1.32+ in SiO0.66 (annealed). This high oxygen deficiency in SiOx was indicative of the low mobility of oxidizing specie in the Zr–O layer. The stacks were characterized for their dielectric properties in the Pt/{Zr–O/IL}/Si metal oxide-semiconductor capacitor (MOSCAP) configuration. The measured equivalent oxide thickness (EOT) was not consistent with the calculated EOT using a bilayer model of ZrO2 and SiO2, and the capacitance in accumulation (and therefore, EOT and kZr−O) was frequency dispersive, trends well documented in literature. This behavior is qualitatively explained in terms of the multilayer nanostructure and nanochemistry that evolves.

Oxide Reduction in Advanced Metal Stacks for Microelectronic Applications

ABSTRACTAluminum and copper are widely used for microelectronic interconnect applications. Interfacial oxides can cause device performance degradation and failure by significantly increasing electrical resistance. Interfacial oxide layers found in Al/Ta and Ta/Cu metal stacks were studied using Transmission Electron Microscopy (TEM) combined with Energy Dispersive Spectroscopy (EDS) and Parallel Electron Energy Loss Spectroscopy (PEELS). The analysis indicates that the observed interfacial oxide layers, Al2O3 and mainly Ta2O5, result from spontaneous reductions of Ta oxide and Cu oxide, respectively. Thermodynamics enables interpretation of the results.

Studies of the Ca4Mn3O10 structure obtained using high pressure and hightemperature

An ideal n = 3member of the group of Ruddlesden–Popper (RP) phases Ca4Mn3O10 wasobtained by solid-state reaction under high pressure. This phase has beenstudied by transmission electron microscopy, convergent beam electronmicroscopy, high-resolution transmission electron microscopy, and parallelelectron energy-loss spectroscopy. The lattice parameters are derived asa = b = 0.37 nm andc = 2.69 nm with thespace group I4/mmm,which is the space group of the ideal RP phase.

Transmission electron microscopy studies of C3N4H4 treated at high pressure andhigh temperature

C3N4H4 was treated at 6.0 GPa and 1500 °C for 2.5 min. Powder x-raymeasurement shows that the sample is decomposed and a hexagonal graphitephase forms. Transmission electron microscopy studies show that small amountsof diamond and amorphous carbon phase coexist with the graphite phase. Parallelelectron energy-loss spectroscopy analysis was also carried out for these phases.

Quantitative analysis of complex carbo-nitride precipitates in steels

Two new types of extraction replicas for precipitate analysis in steels have been developed. These replicas, based on alumina, allow accurate quantification of the carbon to nitrogen ratios in carbo-nitride precipitates using parallel electron energy loss spectroscopy in the TEM. Experiments on microalloyed steels show the importance of the nitrogen content in promoting precipitation even at low temperatures.

Detection, distribution, and quantification of carbon in steel microstructures by PEELS.

This work concerns the use of parallel electron energy loss spectroscopy (PEELS) to investigate the detection, distribution, and quantification of carbon in various steel microstructures generated by rapid cooling rates or by isothermal transformation. The feasibility of detecting C in steels containing very small amounts of carbon was first examined by calculating the minimum detectable mass fraction for a variety of binary Fe-C alloy specimen thicknesses and microscope conditions. These theoretical studies indicated that the detection of carbon in steel microconstituents containing about 0.01 wt.% (or even less) was easily possible with an analytical transmission electron microscope equipped with a LaB6 emitter and a PEEL spectrometer. These theoretical calculations seemed to be reasonable, as it proved possible to make a quantitative PEELS study of the partitioning between the microconstituents ferrite, retained austenite, and martensite found in an ultralow carbon (0.03 wt.%) steel weld metal provided care was taken to avoid hydrocarbon contamination. Studies of both carbon and molybdenum segregation to ferrite/martensite interfaces in an isothermally transformed Fe-C-Mo alloy were also carried out in order to investigate the nature of the "solute drag" effect in this alloy system.

Quantitative characterization of biotic iron oxides by analytical electron microscopy

Hydrous ferric oxides (HFO) play a tremendous role in the environment, and as a result, they have often been analyzed for their bulk chemical and mineralogical composition, but rarely at the particle level. This study used a combination of transmission electron microscopy (TEM), parallel electron energy loss spectroscopy (TEM-PEELS), and selected area electron diffraction (TEMSAED), to determine the morphology, stoichiometry, and mineralogy of synthetic biotic HFO and assess the effect of specimen preparation (i.e., dehydration) on their overall chemical composition. A mixture of synthetic lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) was used as reference material for all TEM analyses. HFO were formed by the oxidation of Fe 2+ (pH = 8) in the presence of Bacillus subtilis (bacteria without extracellular polymers) and Bacillus licheniformis cells (with extracellular polymers). Biotic Fe-oxides occurred as small particles (5-10 nm diameter) on the bacterial cell walls and associated exopolymers and were identified as 2-line ferrihydrite by TEMSAED. Quantitative TEM-PEELS results showed that (1) freeze-dried abiotic samples had an Fe/O atomic ratio of 0.54 ± 0.03, whereas the Fe/O ratio of the biotic ferrihydrite formed in the presence of B. licheniformis and B. subtilis was 0.48 ± 0.06 and 0.54 ± 0.08, respectively; (2) air-dried biotic ferrihydrite possessed an Fe/O ratio close to 0.30, whereas the ratio of the abiotic air-dried HFO samples remained unchanged (i.e., 0.51 ± 0.04). These results indicate that quantitative TEM-PEELS can be used for the chemical characterization of Fe-oxides, since the measured Fe/O atomic ratios of the reference HFO are in agreement with their known stoichiometry (i.e., 0.50 for FeOOH). Our results also suggest that ferrihydrite dehydrates during freeze-drying and that specimen preparation is very important when assessing chemical composition

Study of the products of C 3N 4H 4 treated by high pressure–high temperature

C 3N 4H 4 was treated at 6.0 GPa and 1500 °C for 2.5 min. The powder X-ray measurement shows that the sample is decomposed and a hexagonal graphite phase forms. Transmission electron microscopy studies show that a small amount of diamond and amorphous carbon phases coexists with the graphite phase. Parallel electron energy loss spectroscopy analysis was also carried out for these phases.

Hurlbutite, the first Be mineral from Västanå iron mine, Skåne, Sweden

Hurlbutite has been identified as the first Be mineral from the Västanå iron mine, Skåne, Sweden. The mineral is yellowish to whitish and its microscopic habit is platy and porous. Associated minerals are pinkish apatite, hematite, quartz and svanbergite. The unit cell dimensions calculated from powder X-ray diffraction data are: a = 8.321(8) Å, b = 8.834(8) Å, c = 7.881(7) Å, β = 90.38(6)°. Energy dispersive X-ray analyses of Ca, Sr and P indicated the formula (Ca0.93Sr0.07)Be2(PO4)2. The presence of Be and O was qualitatively confirmed by parallel electron energy loss spectroscopy, and traces of B were also detected.

Microstructural, compositional, and microhardness variations across a gas-metal arc weldment made with an ultralow-carbon consumable

An experimental gas-metal arc (GMA) weldment of HSLA-100 steel fabricated with an ultralowcarbon (ULC) consumable of interest for United States Navy applications, designated “ARC100,” was studied to determine the relationships among the microstructure, the solute redistributions at various positions across the weldment, and the local properties (microhardness). These relationships were investigated by a variety of techniques, including microhardness mapping, optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) (including compositional X-ray mapping), and parallel electron energy-loss spectroscopy (PEELS). The microconstituents observed in this weld include lath ferrite, degenerate ferrite, lath martensite, retained austenite, and oxide inclusions; no carbides or other solid-state precipitates are present within the weld metal. Microhardness mapping indicates an undermatched weld metal (lower hardness as compared to the base plate) in which the hardest regions are in the first and last top beads, the root passes, and between highly ferritic soft bands associated with the outer portion of each weld bead’s heat-affected zone (HAZ) (within the fusion zone). The majority of the gradient in the substitutional alloying elements (Ni, Cu, Mn, and Cr) occurs within a region of less than about 0.5 mm of the fusion boundary, but the composition still changes even well into the fusion zone. Appreciable segregation of Ni and Cu to solidification cell boundaries occurs, and there is appreciable enrichment of C, Ni, Cu, and Mn in thin films of interlath retained austenite. This ULC weld metal is softer than the base plate due to the preponderance of lath ferrite rather than lath martensite, even at the high cooling rates experienced in this low-heat-input weld. Alternatively, the strength of the weld metal is due to the presence of at least some untempered lath martensite and the fact that the majority of the ferrite is lath ferrite and not polygonal ferrite. The interlath retained austenite might enhance toughness, but might also serve as a source of hydrogen in solution, which could potentially contribute to hydrogen-assisted cracking.

EELS studies of MgB 2 superconductor obtained under high pressure

The MgB 2 intermetallic superconductor obtained under high pressure, which has the transition temperature of above 39 K, has been studied by scanning electron microscopy (SEM), transmission electron microscopy and parallel electron energy-loss spectroscopy (EELS). From the SEM, it can be seen that the bulk compound is highly dense and the grains are connected compactly. The size of single crystal is at the magnitude of ∼μm. The high resolution transmission electron microscopy image of [0 0 1] zone axis clearly shows the hexagonal planes of the constituent atoms. The EELS spectrum of B shows the peaks of σ and antibonding bonds. The EELS results show a good agreement with the theoretical band structure calculations and the hole doping in the B σ(p xy ) bonding bands.

NANO-CRYSTALS OF c-DIAMOND, n-DIAMOND AND i-CARBON GROWN IN CARBON-ION IMPLANTED FUSED QUARTZ

Combined high-resolution transmission electron microscopy, selected area electron diffraction and parallel electron energy loss spectroscopy are used to characterise carbon nano-phases found embedded in fused quartz. These appear after implantation of 1 MeV carbon ions, followed by annealing in argon, oxygen and forming gas for 1 hour at 1100°C. For Ar, virtually all of the carbon diffuses out of the substrate with no observable carbon clusters for all doses studied. After annealing in oxygen, a crystalline CO x phase is identified at the end of range, following a dose of 5×1017 C/cm 2. Three nano-crystalline carbon phases, including diamond, appear after annealing in forming gas: these form a layer 170 nm beneath the fused quartz surface for all ion doses. The average size of these clusters and the corresponding phases depend on the ion dose; the smallest size of 5–7 nm diameter crystallise as fcc [Formula: see text] diamond following a dose of 0.5× 1017 C/cm 2, whereas clusters of 8–13 nm diameter, for a higher dose of 2× 1017 C/cm 2, have a [Formula: see text] modified phase of diamond known as n-diamond. The largest clusters, diameter 15–40 nm, for a dose of 5× 1017 C/cm 2, have the cubic P2 13 (or P4 232) structure known as i-carbon. These buried layered diamond and diamond-related materials may have applications for field emission and optical waveguide type devices.

Ion beam synthesis of gallium nitride

This work investigates the synthesis of amorphous and poly-crystalline gallium nitride by ion implantation of Ga ions into AlN substrates at 140 keV. Cross-sectional transmission electron microscopy (XTEM) of AlN layers implanted with Ga to a dose of 1×10 17 cm −2 into unheated substrates showed that a layer of precipitates was present within the AlN layer. Parallel electron energy loss spectroscopy (PEELS) was used to show that the precipitates largely contain A1. X-ray photoelectron spectroscopy (XPS) provided evidence that GaN-type bonds were present in the Ga-implanted AlN. Auger parameters indicated that Ga exists both in elemental and nitride forms. A ternary phase diagram has been proposed based on the experimental data.

Reaction of magnesium boride particles in mechanically alloyed Ti-4wt%MgB2

A Ti-4wt%MgB2 alloy was produced by mechanical alloying (MA) Ti and MgB2 powders for 48 hours in a Spex 8000 mill. TEM analysis of the alloy showed it to consist of a nanocrystalline (10–20 nm) Ti matrix, which enclosed 20–300 nm MgB2 particles. Following heat treatments at 600°C, plate like structures of a previously unknown compound were observed to have extended into the crystals. Convergent beam electron diffraction (CBED) confirmed the new phase to have the same basic arrangement of atom sites as in the NiAs structure. Parallel electron energy loss spectroscopy (PEELS) and energy dispersive X-ray analysis (EDX) measurements identified the elements Ti, Mg and B within these plates. However, the exact proportions of these elements and their distribution within the unit cell could not be determined.

Silicide Formation by Pulsed Excimer Laser Annealing

AbstractSilicide formation may occur at the interface of metal and a-Si films upon annealing with a pulsed excimer laser (XeCl 308 nm; 30 ns). During laser-induced melting, the melt front reaches the Si/metal interface, where liquid phase kinetics allow reaction to occur to form a silicide, despite the <100 ns time-scale. It is thought that silicide reaction would occur if TM, metal ≍ TM, a-Si (1480 ± 50K). The a-Si/metal film stacks that have been investigated include a-Si/Al/Cr, a-Si/Ti, and a-Si/W on thermally oxidized Si. Samples were laser-annealed at varying energy densities in order to determine the onset of melt, and the fluence at which Si/metal interface reaction and film ablation occurs. Rutherford backscattering (RBS), optical inspection, cross-sectional scanning transmission electron microscopy (STEM), as well as parallel and serial electron energy loss spectroscopy (EELS) were used to analyze the films. For the a-Si/Al/Cr and a-Si/W films, no reaction is observed at the Si/metal interface. With a-Si/Ti, intermixing of Si and Ti at the interface is observed, as indicated by RBS and parallel EELS analysis. Laser annealing at higher fluences and further characterization is needed to determine if this mechanism does allow for silicide reaction to take place.