Graphene oxide monolayers as supporting films for high resolution transmission electron microscopy

A novel kind of TEM support composed of graphene oxide monolayers was fabricated by a facile solution-cast method. Compared to the conventional carbon supporting films, such graphene oxide film (GO-film) performed better stability under high-energy electron beams and better dispersion effect for water-soluble nanoparticles. Quantitative improvement in TEM imaging resolution for nanomaterials on such GO-films compared to the commercial ultrathin carbon films was demonstrated.     

Spin polarized low energy electron microscopy investigations of magnetic transitions in Fe/Cu(1 0 0)

Magnetic transitions in ultrathin Fe films on the Cu(1 0 0) surface have been studied with spin polarized low energy electron microscopy. By monitoring averaged image intensity oscillations and the evolution of magnetization and magnetic domain structure simultaneously and continuously during growth, magnetism and film thickness are correlated with unprecedented precision. The thickness range over which ferromagnetism exists in films grown at room temperature generally increases as the deposition rate is decreased. This trend is attributed to the influence of residual hydrogen. The two-dimensional Ising model with finite size scaling of the Curie temperature accurately describes the evolution of magnetization with increasing film thickness.     

Adsorption geometry of glycine on Cu（001） determined with low—energy electron diffraction and scanning tunnelling microscopy

Using low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) it has been found that glycine molecules adsorbed on Cu(001) can form but only the (2×4) and c(2×4) superstructures. On the basis of the missing LEED spots of the surface, it has been concluded that: each (2×4) unit cell consists of two molecules, one being the mirror image of the other; the C－C axis of both molecules lies in the mirror plane of the Cu substrate without a significant shift and twist from the plane; and the two O atoms of the carboxylate group of both molecules locate at the same height level without significant buckling. According to these conclusions, a structural model has been proposed for the (2×4) superstructure (a model for the c(2×4) superstructure already exists). We argue that the (2×4) and c(2×4) superstructures must have similar specific surface free energy, that their hydrogen bonds must be of N-H-O_II type, and that their local adsorption geometry must be similar or even the same. The advantage of combining STM with LEED to determine surface structures is clearly demonstrated.     

Initial oxidation of Ni(1 1 1) observed by electron emission microscopy: PEEM and MEEM

The initial oxidation of Ni(1 1 1) in the temperature range of 550-700 K has been monitored by photoelectron emission microscopy (PEEM) and metastable-atom electron emission microscopy (MEEM). The PEEM and MEEM images show uniform patterns for the chemisorbed overlayer, reflecting the electronic homogeneity as seen at the μm scale. During the nucleation and lateral growth of oxide, however, the μm-scale pattern due to the formation of oxide domains appears and its evolution depends strongly on the substrate temperature and dose pressure of gaseous O₂. Our data indicate that the high-temperature oxidation is regarded as a successive multi-nucleation process in a reaction-diffusion field.     

Evolution of long-period stacking order (LPSO) in Mg97Zn1Gd2 cast alloys viewed by HAADF-STEM multi-scale electron tomography

We have studied three-dimensional (3D) structures and growth processes of 14H-type long-period stacking order (LPSO) formed in Mg₉₇Zn₁Gd₂ cast alloys by single tilt-axis electron tomography (ET) using high-angle annular dark-field scanning transmission electron microscopy. Evolution of the solute-enriched stacking faults (SFs) and the 14H LPSO by ageing were visualised in 3D with a high spatial resolution in multi-scale fields of views from a few nanometres to ~10 μm. Lateral growth of the solute-enriched SFs and the LPSO in the (0?0?0?1)_Mg plane is notable compared to the out-of-plane growth in the [0?0?0?1]_Mg direction. The 14H LPSO grows at the cost of decomposition of the (Mg, Zn)₃Gd-type precipitates, and accompany a change of in-plane edge angles from 30 to 60°. We have updated the Time–Temperature–Transformation diagram for precipitation in Mg₉₇Zn₁Gd₂ alloys: starting temperatures of both solute-enriched SFs and LPSO formation shifted to a shorter time side than those in the previous diagram.     

Use of confocal laser scanning microscopy (CLSM) for depthwise resolved microscale-particle image velocimetry (μ-PIV)

A novel use of confocal laser scanning microscopy (CLSM) makes the truly focused field-of-view with well-defined depthwise resolution possible for microscale particle image velocimetry (μ-PIV) applications. The operating principle of the CLSM is presented using the point spread function (PSF) that describes diffracted images of extremely small particles. The implemented high-speed CLSM system using a Nipkow rotating disk is applied to measure the microscale rotating Couette flow field confined between two parallel horizontal disks that are 180-μm apart, with the bottom one stationary and the top one rotating and seeded by 200-nm fluorescent spheres. The CLSM provides much distinct particle images in comparison with the conventional wide-field microscopy (WFM) and the measured vector profiles are more concentric and accurate depicting closer to an ideal Couette flow.