Field-emission Scanning Electron Microscope Observation Research Articles

Incorporation of Organic Groups within the Channel Wall of Spin-On Mesostructured Silica Films by a Vapor Infiltration Technique

Organically functionalized mesoporous silica films have been prepared by a novel synthetic procedure that involves spin-coating of mesostructured silica films and a vapor infiltration (VI) technique, using organosiloxanes, before the removal of surfactant. The VI-treated mesostructured films were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and a field emission scanning electron microscope (FE-SEM). Nitrogen adsorption/desorption measurements were performed using films attached with a silicon substrate. The XRD and FE-SEM measurements show that the mesochannel wall, densified and modified with organosilyl groups by the VI treatment, hardly contracts under calcination. FE-SEM observations for the films' cross section support the view that organosiloxane vapor is not deposited on the surface of the film. These results show that organosiloxane molecules penetrate the film and are selectively incorporated into the silica wall. Thus, hydrophobic mesoporous silica films can be synthesized without a reduction in pore size, a result that cannot be attained by conventional grafting and co-condensation methods. The excellent high porosity and hydrophobicity of the mesostructured composite films may be of advantage for next-generation low-k dielectric films.

Analysis of biomass combustion ash behavior at elevated temperatures

Change in tensile strength of a biomass ash powder bed measured by a split-cell type tester at a variety of temperatures up to 900°C was discussed corresponding to the microscopic behavior of ash particles observed by a field emission scanning electron microscope (FE-SEM) with a computer-controlled stage, a heat treatment chamber and an energy dispersive X-ray spectrometer. Tensile strength of a biomass powder bed increased with temperature by two different steps. In temperatures ranging from400 to 700°C, the powder bed had liquid-phase bridging between particles, which caused the relatively large fracture distance in fracture curves. FE-SEM observation showing rounded ash particles after heat treatment at 500°C supported this phenomena. On the other hand, at temperatures higher than 700°C, powder beds showed brittle fracture, which means the absence of any liquid bridge due to evaporation. FE-SEM observation revealed successive evaporation from ash samples in this temperature region.

Effect of using self-etching primer for bonding orthodontic brackets.

Questions over the use of self-etching primers with composite resin adhesives in the bonding of orthodontic brackets remain unsolved. In addition, there are no previous reports on the efficacy of self-etching primers with resin-modified glass ionomer cements for bonding orthodontic brackets in orthodontic dentistry. The purpose of this study was to determine the shear bond strengths of orthodontic brackets bonded with one of four protocols: (1) a composite resin adhesive used with 40% phosphoric acid, (2) the same composite resin used with Megabond self-etching primer, (3) a resin-modified glass ionomer cement adhesive used with 10% polyacrylic acid enamel conditioner, and (4) the same resin-modified glass ionomer cement used with Megabond self-etching primer. The appearance of the tooth surfaces after acid etching or priming was observed with a field-emission scanning electron microscope (FE-SEM). When used with resin-modified glass ionomer cement, Megabond self-etching primer gave no significantly different shear bond strength compared with polyacrylic acid etching. But when used with composite resin adhesive, Megabond self-etching primer gave significantly lower shear bond strength than phosphoric acid etching. However, the shear bond strength of orthodontic brackets bonded with composite resin adhesive after Megabond priming was almost the same as that of brackets bonded with resin-modified glass ionomer cement after polyacrylic acid etching. FE-SEM observation revealed that Megabond self-etching primer produced less dissolution of enamel surface than did phosphoric acid and polyacrylic acid etching. Megabond self-etching primer may be a candidate for bonding orthodontic brackets using the resin-modified glass ionomer cement for minimizing the amount of enamel loss.

Growth mechanism of diamond by laser ablation of graphite in oxygen atmosphere

In this paper, diamond crystals grown on sapphire (0001) substrate by laser ablation in oxygen atmosphere were reported. The experiments were performed at a substrate temperature of \ensuremath{\sim}550 \ifmmode^\circ\else\textdegree\fi{}C and in oxygen pressure of 0.11--0.15 Torr. Field-emission scanning electron microscope (FE-SEM), x-ray diffraction (XRD), and micro-Raman spectroscopy were applied to characterize the products. FE-SEM observation revealed that hexagonal- and triangular-shaped crystals were formed on the sapphire substrate, however, the crystal nucleation and growth were nonuniform and discontinuous. XRD and micro-Raman analyses indicated the coexistence of hexagonal and cubic diamond. Moreover, the secondary nucleation of diamond was observed. The diamond growth mechanism in laser ablation, a physical vapor deposition process, was different than that in chemical vapor deposition process. In an optimum region of carbon energy, carbon species implanted into substrate to form a local high-density region in which the formation of diamond phase ${(sp}^{3}$ bond) rather than graphitic phase ${(sp}^{2}$ bond) was favorable. At suitable substrate temperature and oxygen pressure, the diamond crystals nucleated and grew, while the graphitic phases were excluded by oxygen preferential etching. Compared to diamond synthesized in a hydrogen environment, the conditions for diamond growth in oxygen atmosphere are very critical.