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Interphase precipitation (IPP) of nanoscale carbides in a vanadium-containing high-strength low-alloy steel has been investigated. Small angle neutron scattering (SANS) and transmission electron microscopy (TEM) were employed to characterize the precipitates and their size distributions in Fe-0.047C-0.2V-1.6Mn (in wt.%) alloy samples which had been austenitized, isothermally transformed at 700 °C for between 3 and 600 min and water quenched. TEM confirms that, following heat treatment, rows of vanadium-containing nanoscale interphase precipitates were present. Model-independent analysis of the nuclear SANS signal and model fitting calculations, using oblate spheroid and disc-shapes, were performed. The major axis diameter increased from 18 nm after 3 min to 35 nm after 600 min. Precipitate volume percent increased from 0.09 to 0.22 vol% over the same period and number density fell from 2 × 10 21 to 5 × 10 20 m −3 . A limited number of measurements of precipitate maximum diameters from TEM images showed the mean value increased from 8 nm after 5 min to 28 nm after 600 min which is in reasonable agreement with the SANS data. [ABSTRACT FROM AUTHOR]

Abstract: The effect of anisotropic strain induced by SrTiO3 (STO) substrate with different orientations on charge ordering (CO) behavior in epitaxial Sm0.5Ca0.5MnO3 (SCMO) films was investigated using cross-sectional transmission electron microscopy at 103K. Incommensurate modulated structure caused by CO transition was observed in the SCMO film grown on a [101]-oriented STO substrate while none were found for SCMO film grown on a [100]-oriented STO substrate. This distinctive orientation-dependent CO transition is correlated with anisotropic strain in the films induced by lattice mismatch, confirming the previous results for growth on different substrates. [Copyright &y& Elsevier]

We have explored the capacity of Cu/V interfaces to absorb helium ion radiation-induced defects spanning a peak damage range of 0.6–18 displacements per atom (dpa). The study provides evidence of alleviated nucleation of He bubbles in the multilayer films from Cu/V 50 nm to Cu/V 2.5  nm. Layer interfaces are retained in all irradiated specimens. Peak bubble density increases monotonically with fluence, and is lower in multilayers with smaller individual layer thickness. Radiation hardening decreases with decreasing layer thickness and appears to reach saturation upon peak radiation damage of 6 dpa. Size- and fluence-dependent radiation damage in multilayers is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline pyrochlore Y2Ti2O7 compounds were irradiated with 400keV Ne2+ ions at cryogenic temperature (∼77K) at fluences ranging from 5×1014 to 1×1016 ions/cm2, corresponding to a peak ballistic damage dose of ∼0.17–3.4 displacements per atom (dpa). Irradiation-induced structural evolution was examined using grazing incidence X-ray diffraction at X-ray incident angles from 0.25° to 3° and cross-sectional transmission electron microscopy. An apparent swelling effect was observed on the irradiation layer prior to the irradiated layer being amorphized. The swelling effect increased with increasing ion irradiation fluence. At an ion induced damage of 1.7dpa, the irradiated layer started to be amorphized. [Copyright &y& Elsevier]

Abstract: The purpose of this study is to investigate the role of stoichiometry in crystalline structure transformations in derivative fluorite compounds known as δ–γ–β phases in Sc2O3–ZrO2 phase diagram. Different composition polycrystalline δ-Sc4Zr3O12, γ-Sc2Zr5O13 and β-Sc2Zr7O17 samples were synthesized by mixing 40% Sc2O3 +60% ZrO2, 16.67% Sc2O3 +83.33% ZrO2, or 12.5% Sc2O3 +87.5% ZrO2, respectively. The pressed and polished pellets of these compounds were then irradiated under liquid nitrogen temperature with 200keV Ne+ ions at a dose rate of ∼1×1012 ions/cm2/s. An order-to-disorder (O–D) transformation was observed for all compositions, as determined using grazing incidence X-ray diffraction (GIXRD) at an incident angle of 0.25°. The O–D transformation threshold dose for δ-Sc4Zr3O12 (∼0.2dpa) was found to be noticeably higher than that for γ-Sc2Zr5O13 and β-Sc2Zr7O17 (∼0.04dpa) based on both GIXRD and cross-sectional transmission electron microscopy (TEM) measurements. However, due to experimental difficulty and uncertainty, our GIXRD and TEM data were unable to conclusively confirm that the O–D transformation threshold dose for γ-Sc2Zr5O13 is in fact slightly higher than that for β-Sc2Zr7O17 as expected from the phase diagram of Sc2O3–ZrO2 system. [Copyright &y& Elsevier]

Abstract: Ba0.75Sr0.25TiO3 film was epitaxially grown on a (001) LaAlO3 substrate using single-target pulsed laser deposition. The dissociation of misfit and threading dislocations in the epitaxial Ba0.75Sr0.25TiO3 film was investigated using high-resolution transmission electron microscopy (HRTEM). For a misfit dislocation with a Burgers vector of [200], it was shown that it could dissociate into four partial dislocations with Burgers vector of type 1/2 <110>. For the threading dislocations, it was found that they usually coexist with stacking faults. The formation mechanism for the dissociated dislocations was discussed. All the dislocations can relieve the local strain in the Ba0.75Sr0.25TiO3 epitaxial film. [Copyright &y& Elsevier]

Abstract: Faceting has been observed in some Si nanocrystals (Si nc) embedded in SiO2 using high-resolution transmission electron microscopy (HRTEM). Statistical analyses of the interface-energy (Si nc/SiO2) ratios for different facets of the single-crystalline Si nc have been carried out. For these single-crystalline Si nc, the interfacial energy ratios of {100} and {113} relative to {111} facets, are 1.1 and 0.89, respectively. The influences of planar defects such as twins and stacking faults on the faceting and interfacial energy of Si nc/SiO2 are discussed in terms of their possible contribution to the interfacial energy. [Copyright &y& Elsevier]

Si nanocrystals were formed by implantation of Si+ into SiO2 film on (1 0 0) Si, followed by high-temperature annealing. Transmission electron microscopy (TEM) was used to examine the effect of hydrogen passivation on the microstructure of the Si nanocrystals (nc) in SiO2 film. The size and spatial distribution of the Si nc in both non-passivated and passivated samples were investigated using dark-field imaging technique. It is shown that the size and spatial distribution of the Si nc are much similar for both samples. The concentration of Si nc in SiO2 film was determined from the dark field images taken under different diffraction conditions. Selected area electron diffraction pattern shows that there is no preferential orientation for the Si nc in the SiO2 film. For the passivated sample, the increase of photoluminescence intensity is attributed to the elimination of the optically inactive defects in SiO2 matrix and around the Si nc/SiO2 interface. [Copyright &y& Elsevier]

Titanium dioxide nanotubes are synthesized using sol–gel method. Electron energy-loss spectroscopy has been used to investigate the chemical composition of the nanotubes. The results show that the atomic ratio of O/Ti is very close to two. Electron diffraction studies indicate that the nanotubes have the anatase structure. High-resolution transmission electron microscopy studies show that the nanotubes possess a layered structure with layer spacing of about 7.1 A˚. The tube axis is determined to be along [0 1 0] direction of the anatase phase. The formation mechanism of the nanotubes can be explained as 3D→2D→1D. The two-dimensional lamellar TiO2 is essential for the formation of the nanotubes. [Copyright &y& Elsevier]

Electron energy-loss spectroscopy in the transmission electron microscope has been used to determine the valence state of manganese in La0.5Ca0.5MnO3 at room temperature and at 93 K. An incommensurate charge ordering modulation in La0.5Ca0.5MnO3 was detected by transmission electron microscopy. A structural model, based on the selected area electron diffraction and high-resolution electron microscopy observation, is proposed for the incommensurate modulation. [Copyright &y& Elsevier]

Abstract: Bi0.4Ca0.6MnO3 (BCMO) film with a thickness of 110nm was epitaxially grown on a (110) SrTiO3 (STO) substrate using pulsed laser ablation technique. The microstructure of the epitaxial films was investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) in details. Two different kinds of dislocations, one being perpendicular to the BCMO/STO interface, the other being parallel to the interface, have been commonly observed. The formation mechanism for these dislocations has been discussed. All the dislocations are thought to relieve the local strain in the epitaxial film. [Copyright &y& Elsevier]

Nanocrystalline materials are known to possess excellent radiation resistance due to high fraction of grain boundaries that act as defect sinks, provided they are microstructurally stable at such extreme conditions. In this work, radiation response of a stable nanocrystalline Cu-Ta alloy is studied by irradiating with 4 MeV copper ions to doses (close to the surface) of 1 displacements per atom (dpa) at room temperature (RT); 10 dpa at RT, 573 and 723 K; 100 and 200 dpa at RT and 573 K. Nanoindentation results carried out for samples irradiated till 100 dpa at RT and 573 K show exceptionally low radiation hardening behavior compared to various candidate materials from literature. Results from microstructural characterization, using atom probe analysis and transmission electron microscopy, show a stable nanocrystalline microstructure with minimal grain growth and a meagre swelling in samples irradiated to 100 dpa (~0.2%) and 200 dpa at RT, while no voids in those at 573 K. This radiation tolerance is partly attributed to the stability of Ta nanoclusters due to phase separating nature of the alloy. Additionally, the larger tantalum particles are observed to undergo ballistic dissolution at doses greater than 100 dpa and are eventually precipitated as nanoclusters, replenishing the sink strength, which enhanced material's radiation tolerance when exposed to high irradiation doses and elevated temperatures. Image, graphical abstract [ABSTRACT FROM AUTHOR]

FeCrAl ferritic alloys are excellent cladding candidates for accident tolerant fuel systems due to their high resistance to oxidation as a result of formation of a protective Al 2 O 3 scale at high temperatures in steam. In this study, we report the irradiation response of the 10Cr and 13Cr FeCrAl cladding tubes under Fe 2+ ion irradiation up to ∼16 dpa at 300 °C. Dislocation loop size, density and characteristics were determined using both two-beam bright field transmission electron microscopy and on-zone scanning transmission electron microscopy techniques. 10Cr (C06M2) tube has a lower dislocation density, larger grain size and a slightly weaker texture compared to the 13Cr (C36M3) tube before irradiation. After irradiation to 0.7 dpa and 16 dpa, the fraction of <100> type sessile dislocations decreases with increasing Cr amount in the alloys. It has been found that there is neither void formation nor α′ precipitation as a result of ion irradiations in either alloy. Therefore, dislocation loops were determined to be the only irradiation induced defects contributing to the hardening. Nanoindentation testing before the irradiation revealed that the average nanohardness of the C36M3 tube is higher than that of the C06M2 tube. The average nanohardness of irradiated tube samples saturated at 1.6–2.0 GPa hardening for both tubes between ∼3.4 dpa and ∼16 dpa. The hardening calculated based on transmission electron microscopy was found to be consistent with nanohardness measurements. [ABSTRACT FROM AUTHOR]

Dislocation loop rafting and dislocation decoration have been previously observed in neutron and heavy ion irradiated materials. Understanding the fundamental aspects of these phenomena assist in evaluating irradiation damage of nuclear materials. Multiple different mechanisms have been suggested to explain loop rafting. Here, we performed a detailed transmission electron microscopy study on dislocation loop rafts in heavy ion irradiated tungsten. Different imaging conditions showed that the rafts are of <111> Burgers vector type and specifically the same <111> Burgers vector variant (<1 1 ¯ 1>) in the particular grain analyzed. Some rafts were associated with dislocation lines while some form as a result of alignment of dislocation loops. They were shown to form at both room temperature (RT) and high temperature with stronger rafts forming at RT. These observations confirm the mechanism previously suggested by Wen et al. which explains raft formation due to loop glide, cluster-cluster and grown-in dislocation-cluster interaction with subsequent Burgers vector rotation. Similar irradiation studies on nanocrystalline tungsten showed that these materials are more resistant to raft formation at RT irradiations. [ABSTRACT FROM AUTHOR]

The influence of Er and Si nanoclustering on near-infrared (NIR) Er emission is investigated in fused silica samples exposed to proton beams, used to reproduce the space radiation conditions at low-Earth orbit (LEO). Bulk silica glasses are used as model systems that mimic optical fibers. The growth of Er/Si nanoclusters, synthesized in co-implanted fused silica after thermal annealing between 1000 °C and 1200 °C, was analyzed by transmission electron microscopy (TEM) and energy-dispersive x-ray spectroscopy analysis. Photoluminescence measurements of Er 3 + optical emission indicate that its 4 I 13/2 → 4 I 15/2 transition around 1.54 μm can still be used for optical communication after proton irradiation doses equivalent to over 50 years of exposure at LEO. Using a phenomenological model supported by Monte Carlo simulations, our results can be described in terms of an increase of the photocarrier transfer occurring between Si nanocrystals and NIR Er emitting levels, which partially compensates for the optical losses induced by structural damage. Our work demonstrates an alternative approach for the development of advanced Er light sources with superior radiation resistance and longer operating times in space environment. [ABSTRACT FROM AUTHOR]

Interface engineering is an important strategy for developing radiation tolerant materials. In prior work, bulk nanolayered composites fabricated by accumulative roll bonding (ARB) showed outstanding radiation resistance. However, the effects of layer thickness and radiation conditions on damage distributions and their effect on hardness have not been explored. Here, we use transmission electron microscopy (TEM) and nanoindentation to investigate the effects of radiation on the distribution of radiation-induced cavities and post-radiation hardness in ARB nanolayered Cu-Nb composites. We show that whether the cavities cross the interface depends on layer thickness and temperature, and that, remarkably, radiation could generate softening, not always hardening. We posit that the softening mainly results from the recovery of dislocations stored in the crystal after the bulk forming ARB processing due to He radiation and this phenomenon offsets radiation-induced hardening as layers become finer and temperatures rise. [ABSTRACT FROM AUTHOR]

The precipitate evolution, strength and corrosion resistance of an Al–Zn–Mg–Cu alloy processed by cryorolling, warm rolling and final aging have been investigated. A large number of spherical Zn-rich GP zones formed after warm rolling. In-situ transmission electron microscopy (TEM) observation indicated that the GP zones are stable during aging treatment and can serve as nuclei for subsequent precipitates, leading to homogeneous distribution of precipitates in the matrix after aging. TEM results also showed that ultrafine subgrains were developed in the deformed microstructure during aging. The high density of precipitates and dislocations combined with grain refinement contribute to the higher strength of the thermo-mechanically treated alloy compared with the peak-aged alloy. On the other hand, the η phase with C15 cubic structure having ‧‧‧RR‧‧‧ stacking is found in the thermo-mechanically treated alloy and is different from one with C14 hexagonal structure having ‧‧‧RR−1‧‧‧ stacking that is commonly observed in conventionally aged alloys, where R and R−1 represent rhombic layer and the relatively 180°-rotated rhombic layer, respectively. The transition from ill-defined stacking to C15 stacking and further to C14 stacking is observed in the structure of a η phase. Besides, the combination of warm rolling and aging can avoid the formation of continuous grain boundary precipitates, which is beneficial to the corrosion resistance of the alloy. [ABSTRACT FROM AUTHOR]

A potentially enhanced radiation resistance of nanocrystalline materials, as a consequence of the high density of interfaces and surfaces, has attracted much attention both to understand the fundamental role of these defect sinks and to develop them for high-radiation environments. Here, irradiation response of nanocrystalline A 2 Ti 2 O 7 (A = Gd, Ho and Lu) pyrochlore powders with grain sizes of 20–30 nm was investigated by 1-MeV Kr 2+ ion bombardment. In situ transmission electron microscopy (TEM) revealed that the critical amorphization fluence for each nanocrystalline compound at room temperature was greater than that for their coarse-grained counterparts, indicating an enhanced amorphization resistance. The effect of temperature on the irradiation response of one of these compounds, nanocrystalline Lu 2 Ti 2 O 7 , was further examined by performing ion irradiation at an elevated temperature range of 480–600 K. The critical amorphization temperature ( T c ) was found to be noticeably higher in nanocrystalline Lu 2 Ti 2 O 7 (610 K) than its coarse-grained counterpart (480 K), revealing that nanocrystalline Lu 2 Ti 2 O 7 is less resistant to amorphization compared to its coarse-grained phase under high temperatures. We interpret these results with the aid of atomistic simulations. Molecular statics calculations find that cation antisite defects are less energetically costly to form near surfaces than in the bulk, suggesting that the nanocrystalline form of these materials is generally less susceptible to amorphization than coarse-grained counterparts at low temperatures where defect kinetics are negligible. In contrast, at high temperatures, the annealing efficiency of antisite defects by cation interstitials is significantly reduced due to the sink properties of the surfaces in the nanocrystalline pyrochlore, which contributes to the observed higher amorphization temperature in the nano-grained phase than in coarse-grained counterpart. Together, these results provide new insight into the behavior of nanocrystalline materials under irradiation. [ABSTRACT FROM AUTHOR]

Abstract: This study systematically investigates the interface structure of Nb films grown on MgO substrates with different orientations ((100) and (111)) by experiments and simulations. X-ray diffraction, transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were used to characterize the structure of Nb films and the structure of interfaces between Nb films and MgO substrates. The results show that thin films exhibit different preferred planes on different orientations of MgO substrates. First-principles calculations were used to understand the interface configuration through a coherent interface model. The combination of experiments and simulations shows that the work of separation, together with substrate orientation and lattice mismatch, determines the interface structure between films and substrates. [Copyright &y& Elsevier]

Abstract: The accumulation of radiation-induced defect clusters and He bubble formation in He+ ion irradiated nanocrystalline TiO2 and Fe–TiO2 multilayer thin films were investigated using transmission electron microscopy (TEM). Prior to ion irradiation it was found that the crystallinity of TiO2 layers depends on the individual layer thickness: While all TiO2 layers are amorphous at 5nm individual layer thickness, at 100nm they are crystalline with a rutile polymorph. After He+ irradiation up to ∼6dpa at room temperature, amorphization of TiO2 layers was not observed in both nanocrystalline TiO2 single layers and Fe–TiO2 multilayers. The suppression of radiation-induced amorphization in TiO2 is interpreted in terms of a high density of defect sinks in these nano-composites in the form of Fe–TiO2 interphase boundaries and columnar grains within each layer with nano-scale intercolumnar porosity. In addition, a high concentration of He is believed to be trapped at these interfaces in the form of sub-nanometer-scale clusters retarding the formation of relatively larger He bubbles that can be resolved in TEM. [Copyright &y& Elsevier]

Abstract: The dependence of the width of void-denuded zones (VDZs) on grain boundary (GB) characters was investigated in Cu irradiated with He ions at elevated temperature. Dislocation loops and voids formed near GBs during irradiation were characterized by transmission electron microscopy, and GB misorientations and normal planes were determined by electron back-scatter diffraction. The VDZ widths at Σ3〈110〉 tilt GBs ranged from 0 to 24nm and increased with the GB plane inclination angle. For non-Σ3 GBs, VDZ widths ranged from 40 to 70nm and generally increased with misorientation angle. Nevertheless, there is considerable scatter about this general trend, indicating that the remaining crystallographic parameters also play a role in determining the sink efficiencies of these GBs. In addition, the VDZ widths at two sides of a GB show different values for certain asymmetrical GBs. Voids were also observed within GB planes and their density and radius also appeared to depend on GB character. We conclude that GB sink efficiencies depend on the overall GB character, including both misorientation and GB plane orientation. [Copyright &y& Elsevier]

Abstract: Epitaxial anatase films with thickness of around 300nm were deposited on and irradiated with 250keV Ne ions at room temperature. X-ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy were used to characterize the microstructural changes under irradiation. Two primary features are observed in the irradiated material: a damaged layer with a high density of nano-sized defects including dislocation loops was observed in the film and, near the interface, a defect denuded zone formed on the side while an amorphous layer formed on the side. Atomistic calculations attribute the formation of both the defect-denuded zone and the interfacial amorphous layer not to the interaction between the irradiation induced defects and the hetero-interface but rather differences in chemical potential and mobilities for defects in each of the two phases. [Copyright &y& Elsevier]

The microstructural evolution of Ne-ion-irradiated anatase TiO2/SrTiO3 films was investigated. A defect denuded layer formed in the TiO2 film near the TiO2/SrTiO3 interface after irradiation. The accumulation of defects at the TiO2/SrTiO3 interface led to the formation of a continuous interfacial amorphous layer on SrTiO3. Both observations are attributed to the interaction of defects with the interface. Present results reveal that a hetero-epitaxial interface between two different oxides can act as an effective sink to absorb irradiation-induced defects. [Copyright &y& Elsevier]

Abstract: We have systematically studied Ar-ion-milling-induced microstructural evolution in Cu50Zr45Ti5 metallic glass (MG) during specimen preparation for transmission electron microscopy (TEM). We have observed the formation of a Cu10Zr7 intermetallic phase in samples prepared using low energy ion milling (2keV) but without evident crystallization. We also observed the formation of nanocrystalline Cu10Zr7 phase (with a possibility of being mixed with other minor phases) in samples prepared using high energy ion milling (⩾3keV). In contrast, the MG samples remained in the glassy state without any microstructural changes when prepared by either electropolishing or low energy ion milling with liquid nitrogen cooling (2keV). Further, our study suggests that chemical decomposition might be a necessary intermediate stage for crystallization. In situ TEM electron irradiation shows ion-milling-induced phase segregation and preferred nanocrystallization in the precipitated regions. [Copyright &y& Elsevier]

Abstract: Ion irradiation can be used to induce partial crystallization in metallic glasses to improve their surface properties. We investigated the microstructural changes in ribbon Zr55Cu30Al10Ni5 metallic glass after 1MeV Cu-ion irradiation at room temperature, to a fluence of 1.0×1016 cm−2. In contrast to a recent report by others that there was no irradiation induced crystallization in the same alloy [S. Nagata, S. Higashi, B. Tsuchiya, K. Toh, T. Shikama, K. Takahiro, K. Ozaki, K. Kawatusra, S. Yamamoto, A. Inouye, Nucl. Instr. and Meth. B 257 (2007) 420], we have observed nanocrystals in the as-irradiated samples. Two groups of nanocrystals, one with diameters of 5–10nm and another with diameters of 50–100nm are observed by using high resolution transmission electron microscopy. Experimentally measured planar spacings (d-values) agree with the expectations for Cu10Zr7, NiZr2 and CuZr2 phases. We further discussed the possibility to form a substitutional intermetallic (Ni x Cu1− x )Zr2 phase. [Copyright &y& Elsevier]

Microstructural evolution of Zr55Cu30Al10Ni5 and Cu50Zr45Ti5 metallic glasses under 200keV electron irradiation has been studied in situ by transmission electron microscopy. Zr55Cu30Al10Ni5, which has a wider supercooled liquid region, is found to be stable under electron irradiation and no crystallization is observed up to an irradiation fluence of 8.7×1026 electronsm−2. In contrast, nanometer size crystalline Cu10Zr7 phases are formed in Cu50Zr45Ti5 under electron irradiation. The partial crystallization is attributed to irradiation enhanced atomic mobility. [Copyright &y& Elsevier]

The heavy-ion irradiation behavior of bulk zirconium-niobium multilayered composites was investigated up to large doses. Multilayers with an average individual layer thicknesses ranging between 15 and 80 nm were synthesized by accumulative roll bonding technique. The irradiation was performed with a defocused 7 MeV Zr2+ ion beam at 500 °C. The maximum dose achieved was ∼145 dpa at the depth of ∼1.5 μm from the irradiated surface. Sub-surface microstructural damage and the chemical redistribution were characterized by transmission electron microscopy and energy dispersive spectroscopy, respectively. Irrespective of the layer thicknesses, the irradiation condition caused layer instability and the extent of damage varied with the dose levels. Doses lesser than ∼60 dpa caused layer fragmentation and greater than ∼60 dpa resulted in layer dissolution. The chemical mixing of layers occur to a depth of ∼1 μm, consuming multiple bi-layer periods. Despite the elevated irradiation temperature (500 °C) and a slightly positive heat of mixing (+6 kJ/mol), no phase separation was observed and single-phase was retained in the mixed region. The results demonstrate that chemical mixing was facilitated by the liquid phase miscibility of Zr and Nb, which propelled the interdiffusion within the thermal spikes towards mixing. [ABSTRACT FROM AUTHOR]

Abstract: Implantation of Si+ in excess into SiO2 followed by annealing produces Si nanocrystals (Si-nc) embedded in the SiO2 layer, which can emit a strong photoluminescence (PL) signal. Several samples have been characterized by means of ellipsometry and transmission electron microscopy (TEM). For local Si concentrations in excess of ∼2.4×1022 Si+/cm3, the Si-nc diameter ranges from ∼2 to ∼22nm in the whole sample, the Si-nc in the middle region of the implanted layer being bigger than those near the surface or the bottom of the layer. The depth distribution of the Si-nc agrees relatively well with the SRIM simulation as well as with the depth distribution of the n and k components of the complex refractive index. For SiO2 layers thermally grown on a Si wafer, the PL spectrum is modulated by optical interference of the pump laser and of the light emitted by the Si-nc in this layer. The good agreement between the results of the model calculations and experimental measurements indicates that for low and moderate Si concentration in excess (<8×1021 cm−3) the PL light emitters are localized in a layer situated at the same depth as the Si-nc depth distribution. However, for a Si concentration in excess of ∼2.3×1022 cm−3, the depth distribution of light emitters is narrow and situated mostly in the first half (relative to the surface) of the Si-nc depth distribution. This observation indicates that the recombination of the electron–hole pair at the interfaces could be responsible for the emitted PL spectrum. [Copyright &y& Elsevier]

Abstract: Si nanocrystals (Si-nc) embedded in a SiO2 layer have been characterized by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). For local Si concentration in excess ⩽8×1021 Si+/cm3, the size of the Si-nc was found to be ∼3nm and comparatively homogeneous throughout the whole implanted layer. For local Si concentration in excess of ∼2.4×1022 Si+/cm3, the Si-nc diameter ranges from ∼2 to ∼12nm in the sample, the Si-nc in the middle region of the implanted layer being bigger than those near the surface and the bottom of the layer. Also, Si-nc are visible deeper than the implanted depth. Characterization by XPS shows that a large quantity of oxygen was depleted from the first ∼25nm in this sample (also visible on TEM image) and most of the SiO2 bonds have been replaced by Si–O bonds. Experimental and simulation results suggest that a local Si concentration in excess of ∼3×1021 Si/cm3 is required for the production of Si-nc. [Copyright &y& Elsevier]

We report the transmission electron microscopy (TEM) study of the microstructure of wurtzitic GaN films grown on Si(1 1 1) substrates with AlN buffer layers by metalorganic chemical vapor deposition (MOCVD) method. An amorphous layer was formed at the interface between Si and AlN when thick GaN film was grown. We propose the amorphous layer was induced by the large stress at the interface when thick GaN was grown. The In0.1Ga0.9N/GaN multiple quantum well (MQW) reduced the dislocation density by obstructing the mixed and screw dislocations from passing through the MQW. But no evident reduction of the edge dislocations by the MQW was observed. It was found that dislocations located at the boundaries of grains slightly in-plane misoriented have screw component. Inversion domain is also observed. [Copyright &y& Elsevier]

As-quenched microstructure in a low carbon and low alloy steel has been examined by transmission electron microscopy and atom probe tomography. The coarsening kinetics of the cementite was investigated for the tempered steel. The results show that a number of nanosized auto-tempered transition‑iron-ε' carbide and cementite precipitate in the coarse lath martensite during quenching. The carbon concentrations of auto-tempered transition‑iron-carbide are typically around 10–15 at.%, lower than that for stoichiometric Fe 2.4 C or Fe 2 C transition ε carbide. Partitioning of Mn, Cr and Mo into the cementite occurs during tempering. The coarsening rate of the cementite is governed by volume diffusion of Mn, Cr and Mo, and Cr retards cementite coarsening more effectively than Mn and Mo. More stable M 7 C 3 type carbide transforms from the cementite partially, and retains smaller size than the cementite during tempering with prolonged time. • Auto-tempered ε' carbides and cementite precipitate in martensite during quenching. • Carbon concentrations of auto-tempered carbides are typically around 10–15 at.%. • Coarsening rate of cementite is governed by volume diffusion of Mn, Cr and Mo. • Cr retards cementite coarsening more effectively than Mn and Mo. • More stable M 7 C 3 transforms from cementite partially and retains smaller size. [ABSTRACT FROM AUTHOR]