The scanning transmission electron microscopy (STEM) laboratory in National Taiwan University represents the first dedicated electron energy-loss spectroscopy (EELS) group in Taiwan. Our major expenditure in the past five years has been the development of the conjunction of STEM and EELS, STEM-EELS, enabling an electronic characterization at nanometer-scale spatial resolution. Using this combined technique of STEM-EELS, we have unraveled the intriguing surface-plasmon properties in individual gold nanoparticles, popularly known as plasmonics, and revived a class of surface resonances, surface exciton polaritons that had been largely ignored in the past. As what we will discuss through this article, STEM-EELS is not only an indispensable tool for nano-characterizations, but also an avenue for unexpected physics.
In this paper, we summarize our initial efforts in combining optical techniques and in situ electron microscopy in order to achieve comprehensive characterization of individual one dimensional nanostructures. Two straightforward approaches have been adapted. Firstly, we employ different characterization techniques to locate and measure the same individual nanostructure in a compatible sample for the involved instruments. Secondly, we combine optical fiber probe detector and nanoprobe technique inside a scanning electron microscope to assemble a comprehensive characterization system. Above techniques have been applied to the studies of the origin of the “green” emission and the waveguiding behavior in 1D ZnO nanostructures. The integrated characterization system also enables in situ assembly and characterization of nanostructures for optoelectronic device purposes. Using these examples, we demonstrate that the combination of optical techniques and in situ electron microscopy can be powerful for the studies of optoelectronic nanomaterials and nanodevices.
Structural phase transition in cubic GaN layers grown by metalorganic vapor phase epitaxy on GaAs (001) substrates using AlGaAs as an intermediated layer was analyzed by transmission electron microscopy. Roles of the AlGaAs intermediated layer on structural phase transition in nano-scale of cubic GaN layers have been focused. The inserted AlGaAs layer is found to play as a protection layer to prevent the GaAs substrate from thermal decomposition at higher growth temperatures (>900°C) of GaN. This enables us to grow GaN layer on GaAs substrate without a generation of voids at the GaN/AlGaAs interface. On the other hand, the generation of voids, which was observed from the cubic GaN/GaAs/AlGaAs/GaAs (001) structure, was found to stop by the AlGaAs intermediate layer. It is evidenced that, however, the AlGaAs intermediated layer induced the structural phase transition from cubic to hexagonal phases in the GaN top layer. The existence of nano-scale structural phase transition from cubic to cubic/hexagonal mixed phases and their epitaxial relationship in the cubic GaN layer were analyzed through the observation with TEM measurements. This result was confirmed by the results obtained from photoluminescence and Raman scattering measurements.
The important of ceramic foam in technological applications initiate the R & D in producing controllable properties of ceramic foam to meet the requirement for emerging applications in environmental and engineering such as catalytic converter, diesel particulate filters, porous biomaterials, solid oxide fuel cell and lightweight core materials for sandwich structures. In this study, ceramic foam with controllable properties has been produced using commercially available polymeric sponges as template materials. SEM observation revealed the microstructure of ceramic foam produced is the replication of template materials and also confirmed the effect of the various solid loadings and template density to the microstructure of porous porcelain. The amount of pores and pore sizes are decreased, the thickness cell wall or struts was increased as solid loading increased. These changes can also be determined by the amount of porosity and density through Archimedes technique. The porosity decreased from 82 to 12% and density increased from 0.40 to 1.99g/cm3 with the ceramic solid loading increased from 20 to 45%. Further evidence can be observed as the flexural strength increases from 0.59 to 14.20 MPa. Ceramic foam with controllable properties was successfully produced using this simple and relatively cheaper fabrication method. The low density of porous porcelain makes it suitable as alternative core materials for sandwich structures construction.
We have developed high-speed AFM capable of directly visualizing dynamic processes played by protein molecules at high spatial and temporal resolution. It was achieved by increasing the response speed of all devices contained in AFM and by developing techniques for damping scanner vibrations and for reducing the tip-sample interaction force. Thereby, the imaging speed reached 40-70 ms/frame. Moreover, the high-speed imaging does not disturb delicate protein-protein interactions. Using this new microscopy, we succeed in directly imaging dynamic behaviors of functioning proteins. We also exemplified that the functional mechanisms of proteins can be elucidated straightforwardly from the dynamic imaging. In this review, we first mention our motivation of developing high-speed AFM, and then describe the outline of the instrument development, obtained dynamic images, and the future prospects of high-speed AFM.
Irradiation damage is an intrinsic problem for TEM especially during the observation of organic molecules. A large number of incident electrons is required in order to achieve high resolution and high contrast for single molecular imaging. We show here several examples for individual molecular imaging by HR-TEM and discuss the reasons why it is possible even though higher dose than the known tolerant dose is required.
Single particle analysis is a TEM application to structural biology. While it has a favorable feature which does not require crystallization of the target particle, it also has an undesirable feature which needs to collect a huge number of data. In the present field, a thin layer of vitreous ice is formed in holes of the supporting film and an appropriate specimen area is selected by DIFF shadow imaging. Their low signal-to-noise ratio and pincushion or barrel distortion prevent automation of searching. An automated data acquisition system JADAS, which can overcome those problems, will be described.
Recently electron cryo-tomography provides new possibilities of structural analysis of biological molecules and organelles in vitro and in vivo. Frozen specimen is continuously tilted in the transmission electron microscope. Micrographs are taken at various tilt angles and backprojected into 3D reconstruction. Here in this article we will review our recent knowledge on the structure of outer and inner dynein arms, which is responsible for bending motion and its regulation, by making sliding among nine microtubule doublets in eukaryotic flagella using electron cryo-tomography. Three outer arm dyneins and eight inner arm dyneins have been identified by biochemistry, while physiological analysis of mutants characterized the outer dynein arm as a force generator and the inner dynein arm as a regulator of wave forms. 3D structural analysis by electron cryo-tomography revealed the location and conformation of dyneins in flagella. Three outer arm dyneins stack vertically, while eight inner arm dyneins array horizontally. All the dyneins have N-terminal tail domains at the distal side of flagella and head rings at the proximal side. Interestingly composition of inner arm dyneins is not identical among nine microtubule doublets from green algae Chlamydomonas. This might indicate the mechanism of planar asymmetrical bending motion of Chlamydomonas flagella.
At first, mechanical atom manipulation by atomic force microscope is introduced. Then, discovery of heterogeneous-atom interchange vertical manipulation, where tip apex works as an advanced interchangeable single-atom pen, is demonstrated. At last, by the construction of the embedded atom letters “Si”, possible high speed nano-pattering by an advanced interchangeable single-atom pen is revealed.
The measurements of vibration of high-voltage electron microscopes (HVEM) installed on some institutes and universities, including the HVEM of Nagoya University, were carried out to examine the environmental vibration characteristics of the ground and foundation as well as the transmission properties of vibration through the support structure. In particular, the performance for the vibration reduction was investigated on two different types of vibration isolation systems, that is, the suspended mount type (HITACHI) and the double foundation type (JEOL).
As a result, it was clarified that the HVEM of Nagoya University is located on the place of high ground vibration level due to a traffic condition in comparison with the other sites. And it was also confirmed that the countermeasures to the vibration amplification of the support structure and the rocking vibration mode caused by the vibration isolation system are necessary further to realize the higher operability of HVEM.
To apply cellulose as an industrial resource, a novel method for pulverization of crystalline cellulose by water-jet was developed. Morphology of cellulose treated with the method was examined by electron microscopic observations. The quick-freeze, deep-etch replica technique combined with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron tomography was useful to visualize the fine structures of cellulose in water. The result demonstrated that the treatment dispersed cellulose to nanofibers (20-40nm wide) which formed three-dimensional networks in water.