Thermal behavior of size-selected Pt clusters, Pt30 and Pt10, bound to a Si (111)-7×7 surface was investigated by means of scanning-tunneling microscopy. The Pt clusters were prepared by cluster-impact deposition of sizeselected cluster ions onto the substrate at the collision energy of 1 eV per Pt atom. The clusters, Pt30 and Pt10, are stably bound to the Si surface at room temperature as a monatomic layered Pt30 disk with a close-packed arrangement of Pt atoms and a Pt10Six disk with insertion of Si atoms into the Pt10, respectively. The Pt30 disk is stable at a temperature as high as 673 K and changes to a protrusion between 673 K and 873 K by insertion of Si atoms by a mechanism similar to the phase transition of Pt thin films prepared on a Si substrate. The protrusion disappears through in-diffusion of Pt atoms into the bulk Si by heating at 973 K. On the other hand, the Pt10Six disk starts to decompose between 623 K and 673 K by further insertion of Si atoms into the disk as PtSi thin films do at similar temperatures. The higher thermal stability of Pt30 than Pt10Six is explained by higher barrier for the Si insertion into the close-paced Pt30 disk than the platinum-silicide disk of Pt10Six. Indeed, a Pt atom on the Si (111)- 7×7 surface prepared by collision of Pt+ at 1 eV is unstable at 500 K. This result also supports that the multiple bonding between the cluster and the substrate increases the thermal stability.
Inorganic nanorods have attracted great attention owing to the potential application to nanoscale functional devices based on their unique properties quite different from bulk materials. Regularly aligned structures of nanorods are required to utilize their fascinating anisotropic properties. Though top-down lithography technologies and selective growth methods have been applied to fabricate well-defined nanorod structures, it is still desired to develop sophisticated methods for having presynthesized nanorods aligned over a large area to adopt nanorods with various materials. In this study, we demonstrate the facile methods for aligning inorganic nanorods unidirectionally on a substrate. Nematic liquid crystalline (LC) polymers were grafted from nanorod surfaces. The modification density of polymerization initiator moieties on nanorod surfaces were regulated to design nematic LC polymergrafted nanorods interacting to small nematic LC molecules effectively. Consequently, unidirectional orientation of nanorods owing to molecular ordering of nematic LC materials was achieved by a conventional LC alignment technologies.
Dynamics of Li+ ions encapsulated in C60 cages in [Li+@C60](PF6 –) crystal was investigated by terahertz (THz) absorption spectroscopy (0.5–9.5 THz) between 10 K and 300 K. Four peaks were found at ~1.3 THz, 2.2 THz, 8.0 THz and 9.2 THz at 300 K. The first one was assigned to the rotational bands of Li+ ion in the C60 cage. The features of the bands were successfully explained by a free rotation model of Li+ ion circulating with radius of ~1.5 Å. The spectrum dramatically changed at low temperature: As the temperature was lowered from 300 K to 120 K, the rotational bands shifted to lower frequency, and started disappearing below 120 K. In addition, new peaks appeared at 2.2 THz, 2.6 THz, 7.8 THz and 8.0 THz below 120 K. It is concluded that the Li+ ions do not rotate at low temperature. Several models describing the motions of the Li+ ions and corresponding energy schemes were proposed.
Chitin and Chitosan have been studied for biomedical applications, such as wound dressing, drug delivery
systems and space-filling implants because of their non-toxicity, biocompatibility,
and biodegradability. The authors have prepared biodegradable organic-inorganic
hybrid based on chitosan and investigated their microstructure, mechanical
property, biodegradability, and cytocompatibility, etc. The chitosan-inorganic
hybrids have good potential for tissue engineering fields. In this paper,
chitosan-siloxane hybrid microparticles prepared by microfluidic system
for drug delivery vehicle and microfiber of chitosan –hydroxyapatite hybrids
used by coagulation method are introduced.
Unique Photochemical characteristics of organic molecules upon a complexation with inorganic nanosheets are briefly reviewed. Absorption spectrum of molecules often shifts to longer wavelength regions by the expansion of π–conjugation systems due to the molecular flattening upon the complexation with atomically flat surfaces. Moreover, a strong fluorescence enhancement is frequently observed on the nanosheet surfaces mainly due to the suppression of non-radiative deactivation pathways. Mechanisms of these unique behaviors are described.
Chemical methods to create thin and extensive film of well-organized colloidal
nanocrystals with a various shape have been developed because collective
properties of the nanocrystals are thought to lead to the development of
functional materials. Previously reported methods are basically applied
to isotropically shaped nanoparticles and cannot be applicable to anisotropically
shaped nanoparticles such as rod-shaped nanoparticles due to the difficulty
of the control of their orientation. Therefore, it is still challenging
to prepare two dimensional thin film composed of vertically aligned nanorods
over large areas.
Here, we introduce an approach to achieve a vertical alignment of extensive
nanorod arrays. Our approach uses a charged polymer brush, which is a collection
of charged polymer chains grafted onto an interface, as a scaffold to align
nanorods vertically. Charged polymer chains condensed in a confined area
are forced to stretch perpendicularly to the grafted plane due to interactions
between adjacent polymer chains including osmotic pressure and excluded
volume effects. Therefore, we considered that oppositely charged nanorods
(positively charged gold nanorods) can be adsorbed to the charged polymer
brush (double-stranded DNA brush) along the axis of the extended polymer
chains. Interestingly, the nanorods could align vertically when the nanorods
were modified with a cationic ligand and a nonionic ligand in a ratio of
1:4. The present results open up the possibility of producing thin film
composed of vertically aligned nanorods over large areas, which is expected
to lead to development of a device with unprecedented functions.