Dynamic High-resolution Transmission Electron Microscopy Research Articles

In situ dynamic HR-TEM and EELS study on phase transitions of Ge 2Sb 2Te 5 chalcogenides

The phase transition phenomena of Ge 2Sb 2Te 5 chalcogenides were investigated by in situ dynamic high-resolution transmission electron microscopy (HR-TEM) and electron energy loss spectroscopy (EELS). A 300 kV field emission TEM and a 1250 kV high voltage TEM were employed for the in situ heating experiments from 20 to 500 °C for undoped and 3 wt% nitrogen-doped Ge 2Sb 2Te 5 thin films deposited by DC sputtering. Crystallization of amorphous Ge 2Sb 2Te 5 to its cubic structure phase started at 130 °C and then rapid crystal growth developed from cubic to hexagonal phase in the range of 130–350 °C; finally, the hexagonal crystals started to melt at 500 °C. For nitrogen-doped Ge 2Sb 2Te 5, its crystallization from amorphous film occurred at higher temperature of ca. 200 °C, and the cubic and hexagonal phases were usually formed simultaneously without significant growth of crystals at further heating to 400 °C. EELS measurements showed that the electronic structures of Ge, Sb and Te stayed almost the same regardless of the amorphous, FCC and hexagonal phases. The nitrogen doped in Ge 2Sb 2Te 5 was confirmed to exist as a nitride. Also, the doped nitrogen distributed homogeneously in both amorphous and crystalline phases. Localization of doped nitrogen was not found in the grain boundary of crystallized phases. The dynamic process of phase transition was enhanced by high-energy electron irradiation. Peeling of atomic layers in nitrogen-doped Ge 2Sb 2Te 5 film was detected during heating assisted with electron beam irradiation.

Magnesium Hydroxide Dehydroxylation: In Situ Nanoscale Observations of Lamellar Nucleation and Growth

Lamellar dehydroxylation mechanisms are important in understanding highly reactive nanocrystal oxide formation as well as a variety of applied lamellar hydroxide reaction processes. These mechanisms have been observed for the first time via in situ nanoscale imaging for the prototype lamellar hydroxide: Mg(OH)2. Environmental-cell, dynamic high-resolution transmission electron microscopy was combined with advanced computational modeling in discovering that lamellar nucleation and growth processes govern dehydroxylation. The host lamella can guide the formation of a solid solution series of lamellar oxyhydroxide intermediates en route to oxide formation. This investigation opens the door to a deeper, atomic-level understanding of lamellar dehydroxylation reaction processes, nanocrystal oxide formation, and the range of potential new intermediate materials and third component reaction pathways they can provide.

Atomic processes of grain-boundary migration and phase transformation in zinc oxide nanocrystallites

Grain-boundary and interface migration during phase transformation in zinc oxide nanometre-gained polycrystals have been observed by dynamic highresolution transmission electron microscopy. The migration of a [21.0] tilt grain boundary was found to proceed by the shift of ledges corresponding to the structural units of the boundary. The phase transformed from a wurtzite to a zincblende structure after the migration of the interface. The interface migration also proceeded by the shift of ledges on it. The product of the lattice misfits at the grain boundary and interface along two directions was reduced from 5.2 to 1.0% after the grain-boundary migration and phase transformation.

Atomistic visualization of deformation in gold

Atomistic visualization of deformation was realized by dynamic high-resolution transmission electron microscopy. Compression, tensile, and shear deformation in nanometer-sized gold was carried out at room temperature inside a 200-kV transmission electron microscope using a piezodriving specimen holder. The atomic process of the deformation was observed in situ at a spatial resolution of 0.2 nm and at a time resolution of $\frac{1}{60}$ s. It was shown that slip and twinning are attributed to the deformation and proceed at every atomic layer in dislocation-free nanometer-sized gold. A dislocationlike line defect is observed during the slip and twinning processes.

Atomic Level Observation of Early Events in Molecular Intercalation: Preintercalation Host-Layer “Loosening” and the Role of Elastic Strain

Dynamic high-resolution transmission electron microscopy (DHRTEM) has been used to follow the early events in ammonia/2H-TaS2 intercalation. This molecular intercalation process is characterized by two intriguing transient partial gallery expansions of 0.6 and 1.4 Å, prior to and during intercalation, respectively. These expansions do not persist throughout the intercalation process, eventually yielding to full gallery expansions of 3.0 Å. The former partial expansion was observed prior to intercalation during preintercalation ammonia adsorption on the basal planes and can be associated with a charge-transfer-induced host-layer “loosening” of the outermost guest gallery via octahedral-to-trigonal prismatic restacking of the adjacent host layers. The latter expansion is associated with the formation of a near planar ammonia species, which reduces the elastic strain energy for molecular intercalation.

In Situ Dynamic Atomic-Level Investigation of a Weak Charge Transfer Lamellar Intercalation Process

AbstractEnvironmental-cell dynamic high-resolution transmission electron microscopy (DHRTEM) has been used to provide atomic-level insight into lamellar reaction processes for the model weak- charge-transfer intercalation reaction of NH3with 2H-TaS2.In situintercalation was induced by exposing 2H-TaS2crystallites to controlled pressures of NH3(g) and recorded on videotape with 0.03 second time resolution. The intercalation processes observed possess a strong similarity to nucleation and growth processes. Onset occurs in either outermost or internal guest galleries, with further intercalation of the galleries progressing away from the onset layers. Randomly staged regions, containing occasional packages of short-range order, were observed to form during the growth process.

In-situ dynamic high-resolution transmission electron microscopy: application to Pt/GaAs interfacial reactions

In-situ annealing high-resolution transmission electron microscopy (HRTEM) is a powerful technique for the observation of dynamic events in materials at the atomic scale. This paper discusses its use, and applies it to the study of the interfacial reactions in the Pt/GaAs system. We observed that initially a solid-state amorphization process occurs, by the dominant diffusion of Pt to the GaAs. The correlation of the kinetic data with the microstructural changes reveals that the diffusion kinetics are changed after the transformation of the amorphous phase to a crystalline product. During the high-temperature reaction which produces crystalline platinum gallide and platinum di-arsenide, we observed that GaAs substrate is dissociated in a layer-by-layer manner via a ledge mechanism. The whole reaction process and kinetic data are consistent with those of parallel ex-situ annealing experiments.

In-Situ Dynamic High-Resolution Transmission Electron Microscopy Investigation of Guest-Layer Behavior During Deintercalation of Mercury Titanium Disulfide

ABSTRACTDeintercalation processes for the model neutral intercalation system HgxTiS2 (1.25≥x>0.00) have been investigated using dynamic high-resolution transmission electron microscopy. X-ray powder diffraction and thermogravimetric analysis demonstrated the intercalation process is thermally reversible, both structurally and compositionally. In situ deintercalation of stage- 1 compounds was induced by thermal/electron-beam heating during DHRTEM observation. The resulting deintercalation processes were followed with 0.03 second time resolution. The deintercalation processes observed possess a strong similarity to nucleation and growth processes. Deintercalation was observed to “nucleate” by the initial deintercalation of an external-most or internal guest layer, with further deintercalation of the guest “growing” away from the onset layers. This results in generally randogmuelsyt lsatyaegresd greengeiroanllsy, occasionally containing regions of short-range order, that expand away from the deintercalation onset layers.