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This research was performed to quantify the atomic-level dynamic behavior and the nature of Cu segregation to a crystalline Si/liquid Al-alloy interface in a partially molten Al-Si-Cu-Mg alloy. The results show that in contrast to atomistic simulations, no characteristic fluctuations were observed at a {113} Si/liquid Al-alloy interface other than a tendency to advance/recede by one or two {113} interplanar spacings. Segregation of Cu to the interface was found to occur by the formation of nano-scale fluctuating Cu islands, which had a highly reproducible orientation relationship with the crystalline Si. The fluctuating Cu islands had an approximately Gaussian distribution of heights while the widths displayed a log-normal distribution, indicative of high interfacial mobility and coalescence among islands. The presence of Cu islands was found to suppress the dynamic motion of the {113} Si solid-liquid interface. These findings reveal new and unexpected behavior about both the dynamic behavior of, and possible segregation mechanisms to, solid-liquid interfaces. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a systematic study comparing experimental in situ transmission electron microscopy observation of microstructural and compositional evolution with complementary thermodynamic calculations, to better understand the redistribution of solute elements and the nucleation behavior of different phases in a commercial Al-alloy powder (AA390). The results show that Cu segregation to the solid Si–liquid Al interface, as well as the significant undercooling achieved in the liquid under non-equilibrium conditions because the Al phase cannot nucleate homogeneously, play a important roles in nucleating Al2Cu at the interface prior to the Mg2Si phase in the alloy. Although Cu segregation can occur at various locations along the interface, the Al2Cu phase appears to preferentially nucleate at a high-index Si–liquid interface as opposed to a low-index one. The Cu concentration during segregation remains essentially constant with time, indicating that the observed segregation behavior is a thermodynamic and not a kinetic phenomenon. These in situ observations and complementary thermodynamic calculations substantially enhance our understanding of potential crystal nucleation and growth processes. [Copyright &y& Elsevier]

Abstract: Positively answering the question in the title, we demonstrate in this work single electron beam trapping and steering of 20–300nm solid Al nanoparticles generated inside opaque submicron-sized molten Al–Si eutectic alloy spheres. Imaging of solid nanoparticles and liquid alloy in real time was performed using energy filtering in an analytical transmission electron microscope (TEM). Energy-filtering TEM combined with valence electron energy-loss spectroscopy enabled us to investigate in situ nanoscale transformations of the internal structure, temperature dependence of plasmon losses, and local electronic and optical properties under melting and crystallization of individual binary alloy particles. For particles below 20nm in size, enhanced vibrations of the dynamic solid–liquid interface due to instabilities near the critical threshold were observed just before melting. The obtained results indicate that focused electron beams can act as a tool for manipulation of metal nanoparticles by transferring linear and angular mechanical momenta. Such thermally assisted electron tweezers can be utilized for touchless manipulation and processing of individual nano-objects and potentially for fabrication of assembled nanodevices with atomic level sensitivity and lateral resolution provided by modern electron optical systems. This is by three orders of magnitude better than for light microscopy utilized in conventional optical tweezers. New research directions and potential applications of trapping and tracking of nano-objects by focused electron beams are outlined. [Copyright &y& Elsevier]

Abstract: This investigation uses in situ high-resolution transmission electron microscopy to quantify the atomic-level dynamic behavior of a diffuse interphase boundary between ordered and disordered phases in an Au–Cu alloy at elevated temperature. It is found that both the interphase boundary position and thickness fluctuate with time and that the behavior of the disordered side of the interphase boundary differs from that of the ordered side. Analysis of the interphase boundary shape shows that it fluctuates by a mechanism involving the collective motion of many atoms rather than by single-atom jumps. These features are explained in terms of the physical properties of the different phases at the interphase boundary. [Copyright &y& Elsevier]

Abstract: The effects of spatial and temporal averaging on high-resolution transmission electron microscope (HRTEM) images and associated intensity profiles of a solid–liquid Al interface were investigated using atomic coordinates obtained from molecular dynamics simulations. It was found that intensity profiles obtained by spatial averaging across the solid–liquid interface capture the variation in structural features nearly as well as time-averaged intensity profiles. This suggests that adequate spatial averaging of a single HRTEM image can be used to study the contrast from interfaces, and thereby, the structural details, without the need for more time-consuming, computer-intensive time averaged analyses. The limitations of this method are also discussed. [Copyright &y& Elsevier]

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Electron energy-loss near-edge structure (ELNES) analysis using in situ heating in a transmission electron microscope (TEM) was performed to compare the electronic structure of crystalline and liquid Al versus temperature. It was found that the ELNES features in the L 2,3 edges of crystalline and liquid Al are qualitatively similar, but that the edge threshold is modified and certain features in the energy range between 102 and 115 eV vanish in the liquid, indicating that partial DOS is quantitatively different. Broadening of the L 2,3 edge maximum for Al with temperature indicates a decay in the centrifugal barrier for the 2p electrons with increasing temperature. Comparison between the ELNES edge in supercooled liquid and crystalline Al at the same temperature of 600 °C shows that the degree of order, i.e., crystallinity, plays an important role in determining the DOS. The ELNES edge of supercooled liquid Al closely resembles that of superheated liquid Al. [ABSTRACT FROM AUTHOR]

Atomic structures of ordered monolayer Guinier-Preston (GP) zones in Mg-Zn-X (X = Ca, Nd) systems are predicted based on first-principles calculations combined with the statistical-mechanical approach of cluster expansion. Multiple metastable GP zones with various compositions are identified in both systems. The predicted metastable structures in both systems show striking similarities and are all structurally related to monolayer Mg 2 X with each X atom 6-fold coordinated by Mg atoms on the HCP basal plane. An increased number of Mg atoms in monolayer Mg 2 X are replaced by Zn atoms to form ordered GP zones at an increased Zn/X ratio due to strong attractive interactions between Zn and X solutes, which ultimately leads to lower formation energies of the GP zones. Simulated TEM images and diffraction patterns of the predicted structures agree well with prior experimental observations. [Display omitted] [ABSTRACT FROM AUTHOR]