Gold can be deposited as hemispherical nanoparticles on base metal oxides by coprecipitation, deposition-precipitation, adsorption of organo-gold complexes and so forth. Such Au nanoparticles are usually epitaxially contacted with specific crystal planes of the support metal oxides, for example, Au(111)/anatase TiO2(112). Gold catalysts are superior to Pd and Pt catalysts in many reactions, including low-temperature CO oxidation, water gas shift reaction, and propylene epoxidation. The catalytic behavior dramatically changes at a critical size: 2 nm in diameter and 2 atoms in thickness, where metallic nature is lost. Gold clusters smaller than this can also exhibit interesting reactivities depending on the size and structure.
Formation of multi-twin Au particles on the electrode in electrolyte solution is strictly controlled by electrode potential, which is almost equal to the potential induced reconstruction of Au single crystal surfaces. Lattice shortening caused by negative electrode potential (SCE) is responsible for these two phenomena, which is essentially different from the crystal habit depending on the growth rate of crystal surfaces. Most fcc metals form multi-twin particles when the electrode potential keeps at negative potential (SCE), but the stability of the multi-twin particles formed on the electrode highly depends on the metals. Unstable multi-twin particles react with H2O to form single crystal oxide particles. Cu2O and NiO can not be thermodynamically formed at the potential for the formation multi-twin particle, but single crystals of Cu2O and of NiO are practically formed. When the electrode is kept at the OPD (over potential deposition) for Au ions and UPD (under potential deposition) for Cu ions on Au surface, CuAu alloy particles are grown by layer-by-layer deposition mechanism of Au and Cu ions. Although the electrode potential for the layer-by-layer deposition of Au and Cu is higher than the critical potential for the formation of multi-twin particles of Au and Cu, we can recognize the formation of multi-twin CuAu alloy particles. It is speculated that the adsorption of Cu+ ion on Au layer may induce the lattice contraction so that the multi-twin alloy particles are formed.
When a liquid is irradiated with high intensity ultrasound, unusual and unique reaction-sites are formed. They are attributed to extremely transient and small cavitation bubbles with high temperatures and high pressures. The chemical reactions and their reaction pathways during cavitation are often different from those of conventional thermal-and photo-chemical reactions. We have been investigating the reactivities of active radicals formed from cavitation bubbles and have reported that reduction by radicals could be applied for preparing various noble metal nanoparticles. In this paper, we describe the mechanism of the sonochemical reactions occuring in the formation of metal nanoparticles and theproperties of the synthesized particles.
A new transmission electron microscope-scanning tunneling microscope (TEM-STM) system was developed in order to simultaneously investigate structure and electrical conductance of gold contacts in ultra high-vacuum TEM. We found that the gold contact parallel to the  or  direction of both electrodes became short neck, while the contact parallel to the  direction, long nanowire. When the contact was short neck, the electrical conductance changed stepwise at some points and did discontinuously at the other parts. In this case, the broad conductance peaks appeared in the histogram. On the other hand, when the contact was long nanowire, the conductance changed stepwise and showed an integer times the quantum unit of conductance (G0=2e2/h). In the histogram, the sharp peaks appeared. These experimental results were qualitatively in agreement with the previous theoretical results based on the mesoscopic theory.
Motivated by recent impressive works on high catalytic reactivities of nano-scaled gold particles on oxides, we have investigated the atomic and electronic structures of gold nano-particles adsorbed on MgO(001) by first-principles calculations based on the density functional theory. We show the energetics of various adsorbed structures of Aun (n = 1∼4 and 8) on MgO(001) with or without oxygen vacancies and discuss the effect of vacancy on the stability of nano-particles on the surface.
We introduce a measurement method for measuring the chemical potential of gold nanoclusters, which are bound to Au(111) substrate through tunneling barrier, by using scanning tunneling spectroscopy. Tunneling spectra show Coulomb staircase, by which the chemical potential of nanoclusters can be determined. The statistical analysis is performed on the position of the chemical potential of the nanoclusters relative to the Fermi level of the substrate. We found that the chemical potential of gold nanoclusters distributes around the Fermi level of the substrate and the standard deviation depends on the size of clusters. This size dependence of the deviation clearly shows the process of the charge neutrality breakdown of clusters.
Superparamagnetic behavior of gold nanoparticles which are less than 3 nm in diameter and stabilized by polymers has been reported, although the bulk gold metal has non-magnetic (diamagnetic) properties. However, this observation is somewhat ambiguous because conventional magnetometry may include magnetization from trivial origins such as magnetic impurities. Therefore, it is essential to selectively measure the magnetization of gold atoms to prove that their magnetism is intrinsic. We have performed the element specific magnetization measurement for Au nanoparticles with a mean diameter of 1.9 nm using X-ray magnetic circular dichroism (XMCD). Magnetization of gold atoms estimated by XMCD shows a good agreement with the results obtained by conventional magnetometory and consist of a superparamagnetic part and a Pauli-paramagnetic part. The mixture of these component is reasonably explained by the picture that the surface atoms are ferromagnetic and the core atoms are Pauli-paramagnetic.
One just-focused composite image of a scanning electron microscope (SEM) has been reconstructed from just-focused image areas obtained from different images taken with a series of different focus lengths. The practicable evaluation method for the focus of each image plays an important role for this reconstruction. We selected eight focus-evaluation methods described in the Shape From Focus (SFF) method1∼4) usually used for optical images; the Fourier transform, the gradient magnitude maximization, the high-pass filtering, the gray-level maximization, the gray-level variance, the Sum-Modulus-Difference (SMD), the histogram entropy and the histogram of local variations methods. They were applied to three different series of SEM images and evaluated, where the high-pass filtering method is shown to be the most reliable one for the SEM image. The gray-level variance, the SMD and the gradient magnitude maximization methods are also shown to be the applicable methods.
An odor recorder for recording recipe of smell as well as reproducing it has been developed. It includes an array of sensors with partially overlapping specificities, odor blender and its recipe modification algorithm implemented in a computer. In the odor recorder, the recipe of the blended odor is iteratively modified so that the output pattern of the blended odor can agree with that of the target odor. The real-time reference method was developed to suppress the influence of the environmental change and to record the dynamical change of the odor. The target and blended odors are alternately supplied to the sensors and the recipe of the blended odor is adjusted so that the difference of the sensor responses between the two can be minimized. The dynamical change of the recipe of the four component odors in the apple flavor was successfully recorded without the influence of the environmental disturbance such as temperature and humidity changes.