Time-resolved High-resolution Transmission Electron Research Articles

Visualization of oscillatory behaviour of Pt nanoparticles catalysing CO oxidation.

Many catalytic reactions under fixed conditions exhibit oscillatory behaviour. The oscillations are often attributed to dynamic changes in the catalyst surface. So far, however, such relationships were difficult to determine for catalysts consisting of supported nanoparticles. Here, we employ a nanoreactor to study the oscillatory CO oxidation catalysed by Pt nanoparticles using time-resolved high-resolution transmission electron microscopy, mass spectrometry and calorimetry. The observations reveal that periodic changes in the CO oxidation are synchronous with a periodic refacetting of the Pt nanoparticles. The oscillatory reaction is modelled using density functional theory and mass transport calculations, considering the CO adsorption energy and the oxidation rate as site-dependent. We find that to successfully explain the oscillations, the model must contain the phenomenon of refacetting. The nanoreactor approach can thus provide atomic-scale information that is specific to surface sites. This will improve the understanding of dynamic properties in catalysis and related fields.

In situ observation of the initial growth process of carbon nanotubes by time-resolved high resolution transmission electron microscopy.

We succeeded in plan-view dynamic observation of the initial formation process of carbon nanotubes from beta-SiC( 1 1 1) surfaces by time-resolved high resolution transmission electron microscopy. At 1360 degrees C, the flakes of graphite layers of a fibre orientation were formed on the SiC( 1 1 1) surfaces. From the graphite layers, carbon nanotubes were formed perpendicular to the ( 1 1 1) plane of the SiC. A scanning tunnelling microscopy observation showed that the end of carbon nanotube was closed. These results indicate that the caps of the carbon nanotubes are formed by a lift of a part of the graphene along the [ 1 1 1] direction of the SiC through generation of pentagons and heptagons. Two types of carbon nanotube, single-wall and double-wall, were observed in plan-view images. Different image intensity between an outer ring and an inner ring in double-wall nanotubes suggests that the inner layers of multiwall nanotubes are formed after the outer ones.

Time-resolved high-resolution transmission electron microscopy and high-angle annular dark field scanning transmission electron microscopy of metal-mediated crystallization of amorphous germanium films

Metal mediated crystallization of amorphous germanium (a-Ge) films was studied through ‘in-situ’ heating by time-resolved high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), mainly on a-Ge films with nanometer-sized gold clusters on the surfaces. It was revealed from the dynamic HRTEM observations that the interface between crystalline gold and a-Ge was a bit melted due to alloying even at 70°C and liquid-like gold-rich alloys migrate on the a-Ge films to initiate the crystallization, which was confirmed also through the static observations with HAADF-STEM.

Direct atomistic observation of deformation in multiwalled carbon nanotubes

The deformation process of individual multiwalled carbon nanotubes was directly observed by time-resolved high-resolution transmission electron microscopy using a piezo-driving specimen holder at a spatial resolution of 0.2 nm and a time resolution of 1/60 s. High elasticity and the subsequent atomistic damage process of the nanotubes were demonstrated.

Direct Atomistic Observation of Grain Boundary Sliding II. Silicon Including Boundary Glass Phase

A silicon (Si) grain boundary including a glass phase was produced by the bonding of nanometer-sized Si tips which surfaces were coated with glass Si oxide layers inside a 200 kV electron microscope using a piezo-driving specimen holder Atomistic grain boundary sliding was then caused at room temperature The sliding process was directly observed by time-resolved high-resolution transmission electron microscopy at spatial resolution of 0.2 nm and time resolution of 1160 s. The glass phase at the center of the grain boundary showed viscous flow-like deformation during the boundary sliding. The thickness of the glass phase decreased and relative shift of the tips was varied during the grain boundary sliding The internal regions of the Si tips were not deformed plastically or fractured when the thickness of the glass phase was more than about 1 nm corresponding to a few atomic layers. It was shown that the stress introduced during the sliding was relived by the deformation of the glass phase at the boundary.

Direct Atomistic Observation of Grain Boundary Sliding I. Gold

Grain boundary sliding in gold was caused at room temperature and directly observed inside a 200 kV high-resolution transmission electron microscope using a piezo-driving specimen holder. The grain in one side of the grain boundary was displaced at an atomic level along the boundary plane. The grain boundary sliding occurred by the displacement. The atomic process of the grain boundary sliding was in situ observed by time-resolved high-resolution transmission electron microscopy at spatial resolution of 0.2 nm and time resolution of 1/60 s. It was found that so-called grain boundary sliding contained four elemental processes; the sliding parallel to boundary plane, the boundary migration perpendicular to boundary plane, the variation in the direction of boundary plane, and the rotation of crystallites beside the boundary.

結晶境界挙動の原子直視観察

Atomistic visualization of behavior of internal crystalline boundaries, such as grain boundaries and interfaces, was realized by time-resolved high-resolution transmission electron microscopy at a spatial resolution of 0.1 nm and a time resolution of 1/60 s. Various types of atomic processes in mechanical interaction including approach, contact, bonding deformation and fracture, grain boundary migration, and interface formation in gas-phase epitaxial growth, were demonstrated in this review.

Atomic Process of Point Contact in Gold Studied by Time-Resolved High-Resolution Transmission Electron Microscopy

Contact and subsequent retraction between nanometer-sized gold tips were controlled at an atomic scale using a piezoelectric device at room temperature inside a high-resolution transmission electron microscope. The atomic process of the point contact was observed in situ at a spatial resolution of 0.2 nm and at a time resolution of $\frac{1}{60}\mathrm{s}$. It was shown that an atomistic pillarlike elongated neck is formed by lattice slip and structural relaxation during retraction.

Atomistic Visualization of Mechanical Interaction in Gold Crystalline Boundaries by Time-Resolved High Resolution Transmission Electron Microscopy

The atomic processes in mechanical interaction were visualized by time-resolved high resolution transmission electron microscopy at a spatial resolution of 0.2 nm and a time resolution of 1/60 s. Nanometer-sized tips of gold were approached, contacted, bonded, deformed and fractured inside a 200 kV electron microscope using a piezo-driving specimen holder. The crystallographic boundary formed after the contact. A few layers near the surfaces and bonding boundaries were responsible for the approach, contact and bonding processes. Atomic scale mechanical tests, such as the friction test, compressing, tensile and shear deformation tests, were proposed. A new type of mechanical processing at one-atomic-layer resolution was demonstrated. Atomic scale contact or noncontact type surface scanning similar to that in atomic force microscopy was also performed with the gold tips.

Time-Resolved High-Resolution Transmission Electron Microscopy Using a Piezo-Driving Specimen Holder for Atomic-Scale Mechanical Interaction.

: Time-resolved high-resolution transmission electron microscopy at a spatial resolution of 0.2 nm and a time resolution of 1/60 sec using a piezo-driving specimen holder is reported here. Various types of atomic processes in mechanical interaction, such as contact, bonding, deformation, and fracture, in nanometer-sized gold crystallites and carbon nanotubes are demonstrated.

原子間力顕微鏡チップ 表面間相互作用の原子直視型透過電子顕微鏡観察

Atomic processes of mechanical interaction between a tip of atomic force microscopy (AFM) and surfaces were directly observed by time-resolved high-resolution transmission electron microscopy at spatial resolution of 0.2 nm and time resolution of 1/60 s.A piezo-driving specimen holder of transmission electron microscopy (TEM) was develoved for the observation of AFM tip-surface interaction. Nanometer-sized tips of gold were allowed to be approached, contacted, bonded, deformed and fractured inside a 200 kV TEM using the specimen holder. Atomic scale contact or non-contact type surface-scanning corresponding to AFM operation was performed using the gold tip. No structural modulation was observed during the non-contact type scanning. On the other hand, the crystallographic boundary formed between the tip and surface during the contact-type scanning. It was found that stick-slip motion appears due to the boundary formation. A few atomic layers near the surfaces and the boundaries were responsible for the contact-type scanning. The surface structure changed after the scanning.

Atomistic visualization of epitaxial growth process using a new TEM specimen holder for vacuum-deposition

A side-entry-type specimen holder for a high-resolution transmission electron microscope (HRTEM) was developed for the atomistic visualization of the vapor-phase epitaxial growth process. Gold was vacuum-deposited on a (001) surface of a magnesium oxide substrate inside the HRTEM using the specimen holder. It was found that structural modification of a gold cluster and an interface can be observed corss-sectionally by time-resolved high-resolution transmission electron microscopy at a spatial resolution of 0.2 nm and a time resolution of 1 60 s .

Cross-sectional time-resolved high-resolution transmission electron microscopy of atomic-scale contact and noncontact-type scannings on gold surfaces

Atomic-scale contact and noncontact scannings on gold surfaces were performed by gold tips in time-resolved high-resolution transmission electron microscopy (HRTEM) using a piezodriven specimen holder. The structural variations of atomic arrangements in the scanning process were observed in situ with a time resolution of 1/60 s. Possibility of combination-type microscopy of HRTEM and scanning-probe microscopy was shown. Mechanical processing at one atomic-layer scale was demonstrated.

TIME-RESOLVED ATOMIC OBSERVATION OF FRAGMENTATION PROCESS IN GOLD CLUSTERS BY HIGH-RESOLUTION TRANSMISSION ELECTRON MICROSCOPY

Fragmentation in gold clusters was for the first time observed by the time-resolved high-resolution transmission electron microscopy at 0.2-nm spatial resolution and 1/60 s time resolution. A gold cluster of about 1.5-nm diameter made asymmetrical fragmentation on a magnesium oxide (001) surface. It was suggested that the present fragmentation process was similar to the Coulomb explosion process.