High-resolution electron microscopy of a microporous carbon

The structure of a microporous carbon prepared by the carbonization of sucrose was examined using high-resolution electron microscopy. It was found to be disordered and isotropic and primarily made up of tightly curved individual carbon layers, enclosing pores typically about 1nm in size. Completely closed carbon particles were also present. These observations suggest that the carbon may have a fullerene-related structure, in which pentagons and heptagons are distributed randomly throughout a hexagonal network, producing continuous curvature.     

Real temperature of nanoparticles in electron microscope beams

Abstract

This Letter presents a solution of the problem of the real temperature of nanoparticles under conditions of electron microscope beam irradiation. It is shown that the average temperature of the nanoparticles (NPs) may increase to several hundred degrees depending on contact conditions with the substrate, the intensity of the beam and the size of the NPs. The temperature increases with NP size a according to the dependence: T α a² for sufficiently small particles.     

Solid-phase epitaxy of implanted silicon at liquid nitrogen and room temperature induced by electron irradiation in the electron microscope

Abstract

Electron-beam-induced solid-phase epitaxy (SPE) has been obtained on cross-sections of implanted Si layers, by in situ irradiation in the electron microscope, with electrons of energies of 200, 250 and 300 keV, at both room and liquid-nitrogen temperature. The, absence of a transition from SPE to layer-by-layer amorphization (which is observed during ion-beam irradiation on decreasing the temperature below a certain critical value) and the athemal nature of the electron-induced crystallization process below room temperature, indicate that, although elastic displacement is the basic mechanism of both processes, the models which describe ion-beam-induced epitaxy in the temperature range 200≤T≤400°C cannot be extrapolated to explain the results of electron irradiation below room temperature.     

High-resolution electron microscopy observations of microplastic fracture in SiC under ball milling at room temperature

Nanometre-sized kinks and cracks formed in 6H SiC under ball milling (BM) at room temperature have been observed and characterized on the atomic scale using high-resolution electron microscopy (HREM). Observations of the kinks show that numerous positive and negative partials are aligned at either of the kink boundaries, and the stacking sequences in the kink band are considerably different from those in the other areas. It was also observed that the (0001) lattice planes in the kink band are kinked, indicating that microplasticity occurs in the normally brittle material SiC under BM even at room temperature. HREM observations of cracks show that cracks previously observed by transmision electron microscopy are not completely open but are at the initiation stage of fracture. Inside a crack, one residual kink region can be clearly observed, which indicates a correlation between kink and crack, that is a crack evolves from a kink.     

High-resolution in situ electron microscopy of a silicon surface modification by molten aluminium at high temperatures

High-resolution in situ heating experiments in a transmission electron microscope have been applied to a study of the surface modification of Si by molten Al in a vacuum of 1 10^-5 Pa. Transformation from an atomically rough to an atomically flat surface was induced by wetting of molten Al atoms. Si {110}, {112}, {115} and {773} surfaces show sawtooth-like structures composed of nanofacets. It is concluded that molten Al atoms remove a native amorphous oxide layer which existed on the original Si surface, making the surface 'clean' even in a non-ultra-high vacuum such as 10^-5Pa.     

Modelling of irradiation-induced hardening in metals using dislocation dynamics

A new simulation technique (three-dimensional dislocation dynamics) enabling the capture of a hardening effect in metals due to irradiation is reported. When bombarded with high-energy particles, metals accrue internal damage. In irradiated Pd, for example, damage takes the form of interstitial loops. Such loops are nano-sized and typically have a high number density. The stress field of a loop is given from dislocation theory. It is shown here the hardening is due to the elastic interaction of gliding dislocations with a high number of spatially dispersed interstitial loops. Results are found to correlate well with experiments.     

High-resolution electron-microscopy analysis of splitting patterns in Ni alloys

The late stages of coarsening of coherent solid particles is strongly influenced by the reduction of elastic strain energy. This produces migration and alignment of particles as well as some other effects. In this investigation, the origin of the so-called splitting pattern arrangement of γ′ precipitate particles, an arrangement which has often been interpreted as being due to splitting of a larger particle into smaller ones, has been studied. The two-particle relationship as to whether they are in-phase or out-of-phase is examined by means of a translation order domain analysis of high-resolution electron-microscopy images along a zone axis parallel to [001]. Ni alloys have been used for the investigation including a binary Ni–Al alloy (producing different volume fractions) and two commercial multicomponent alloys with high volume fraction. About 72% of two-particle pairs forming the splitting configuration are in the out-of-phase relationship, indicating that adjacent pairs are randomly formed and that they are not formed by the splitting of a large particle. In addition, an elasticity analysis shows that the elastic interaction energy of two γ′ particles exhibits a minimum at a certain separation distance along???100?.     

Evidence of carbon ordering and morphology change in a cubic carbide phase

Abstract

The crystallographic and microstructural changes of the ordered cubic carbide (K) phase on ageing have been studied in rapidly solidified Fe-30.9 wt% Mn-8.9 wt% AI-2.8 wt%C ((Fe_0.65, Mn_0.35)_0.83 Al_0.17–12 at.%C) alloy. In the as-rapidly solidified condition, an austenitic phase coexists with the carbide phase which is composed of antiphase domains in the interior of the solidification cell. The antiphase domain boundaries were aligned nearly parallel to the {100} planes. By visually comparing the intensity ratio (I₁₁₀/I₁₀₀) of the selected-area diffraction pattern in the transmission electron microscope and by quantitatively comparing the same X-ray diffraction intensity ratio, we have deduced that the K phase tends to consolidate into the L'1₂ structure on ageing at 450°C but into the L1₂ structure on ageing at 700°C.     

Patterns of affectivity in the transition to adolescence

The present paper reports the findings of a factor analytic investigation of adolescent affect in a cross-sectional sample of 483 male and female fifth through ninth graders. Following the ESM method, adolescents carried electronic pagers and self-report booklets for one week. Students were paged seven times daily and completed self-report forms after each signal describing their moods and feelings. Principal components analysis yielded two internally consistent factors which were virtually identical to the positive and negative affect dimensions described in the literature on adult emotion. Contrary to findings reported in the developmental literature, arousal did not emerge as a dimension of adolescent affect. Further, the bipolar structure obtained for the entire sample, positive and negative affect, consistently emerged in separate analyses of adolescent gender and school groups. MANOVA analysis of estimated positive and negative affect scores indicated that while the underlying dimensions of adolescent affect were comparable to those observed for adults, variation along those dimensions may have been related to the social transitions (e.g., schooling) which punctuate adolescence.     

Microstructural characterization of the M23C6 carbide in a long-term aged Ni-based superalloy

The microstructural features of M₂₃C₆ carbide in a long-term aged heat- and corrosion-resistant Ni-based superalloy have been investigated in detail using various kinds of transmission electron microscope (TEM) techniques. It is found that TEM contrast, which is related to structural and chemical inhomogeneities inside the grains, always exists in the interior of grains in the alloy. The structure of these inhomogeneous regions has been determined to be the same as that of the γ′ and t-M₂₃C₆ phases, where t-M₂₃C₆ indicates a transitional and metastable phase. Although possessing the same structure as the M₂₃C₆ phase, the chemical composition of the t-M₂₃C₆ is different from that of the M₂₃C₆ phase. Compared with M₂₃C₆, t-M₂₃C₆ is richer in Ni, Co, Al and Ti but poorer in W, Mo and Cr. This phenomenon of structural and chemical inhomogeneity demonstrates that pristine M₂₃C₆ carbide (p-M₂₃C₆) precipitated in standard heat-treated samples is unstable. Therefore, upon long-term ageing treatment, Ni, Co, Al and Ti may locally enrich inside the p-M₂₃C₆ phase, finally forming the γ′ phase, which can be described by the decomposition reaction p-M₂₃C₆ → M₂₃C₆ + γ′.     

Transmission electron microscopy of dislocations in SrTiO3

Dislocations have been introduced in SrTiO₃ by Vickers indentation at room temperature and analysed by transmission electron microscopy. The slip systems in SrTiO₃ were identified as ?110?-{110}. ?110? dislocations are dissociated into two partial dislocations. The stacking-fault energy γSF was determined to be 136 ± 15 mJm^-2.     

Transmission electron microscopy observations of low-load indents in GaAs

Nanoindentations have been made on (001) surfaces of GaAs single crystals at room temperature and the indents observed by transmission electron microscopy. The permanent deformation, generated by a Berkovitch indentor submitted to maximum loads ranging between 600 to 1700 muN, was analysed and interpreted as a function of the loading curves. The plastic zone size was measured as a function of the maximum load to determine the yield strength of GaAs at room temperature. Finally, the fine structure of the dislocations generated by the indenter has been analysed and this is compared with previously reported structures for higher indenting loads.     

Verbal imprecision as an index of knowledge in transition.

Children can be verbally imprecise when they are learning, but this phenomenon is not well documented. Verbal imprecision, anecdotally referred to as "hemming and hawing," may be indexed by restatements, comments on one's lack of knowledge, deletions of sentence constituents, and pauses. The authors examined whether they could quantify indexes of verbal imprecision and use them to predict changes in problem-solving performance. Four types of verbal imprecision were found to predict improved performance. Results were used to make inferences about processes of knowledge change. In particular, evidence suggests that adopting a new approach and rejecting an old one may be independent, and ordered, processes. Although others have drawn similar conclusions, using verbal imprecision as the data source is a relatively unique and readily accessible method for lending support to this model of knowledge change.     

Moods in transition: Theorizing the affective-dynamic constitution of situatedness

In this paper we draw from Gilbert Simondon's work in order to develop a conceptual perspective on moods as transitory, dynamic, and holistic affective processes, manifesting the persistence of pre-individual tensions throughout processes of individuation. In defending our proposal we focus on two features of mood experiences that have traditionally proven conceptually challenging: (1) the intentionality of moods and (2) their phenomenal status. By revisiting Colombetti's theory of moods as affectively scaffolded and Slaby's theory of moods as disclosive postures we show how a Simondonian approach might enrich current enactive as well as phenomenological theorizing about moods.     

The role of self-enhancing evaluations in a successful life transition

The objective of the study was to investigate how self-enhancing evaluations, obtained via positive social comparisons and reflected appraisals, were related to mental health in a later life transition. The sample consisted of 266 women who were interviewed once before and 3 times after the experience of community relocation. Results extended prior findings suggesting the dynamic impact of self-enhancing evaluative processes on psychological well-being and depressive symptoms. Additional analyses showed evidence for reverse causality, that is, that mental health also influenced self-evaluative processes. This study underscores the significance of holding a positive view of self vis-à-vis others in negotiating life challenges as well as the reciprocal influence of well-being on social self-evaluative processes.     

Universality of the reversal transition in growth phenomena of molecular crystals

ABSTRACT

The fundamental origin of the reversal transition during crystal growth has been investigated by Monte Carlo simulations. Evidence is provided supporting the geometrical nature of the transition, arising from the broken translational invariance at the growth front and the interactions of multipoles of opposed parity. The range of interactions, the details of the force field and model are irrelevant to the occurrence and only determine the functional behaviour of the relevant physical quantities like the localisation of the critical point and the morphology of the phase diagram.