Expandable fluorine micas were synthesized using talc and Na2SiF6 at 800°C for 2 hours in air, nitrogen, argon, and under vacuum. Gaseous SiF4, generated from Na2SiF6, and the resultant amorphous sodium silicofluoride formed during the reaction between talc and Na2SiF6 below 900°C are taking active part in the formation of expandable micas because the intensity of the 12.5 Å reflection of expandable micas decreases as the gas flow increases in the furnace. Expandable micas seem to be formed by the transformation from talc taking place without the entire disruption of the original atomic arrangement. This takes place with the loss of one Mg2+ from an octahedral site and by the intercalation of every two Na+ into the interlayer site of talc. Infrared absorption and thermal analyses show that expandable micas include a small amount of OH− in their structures.

In this paper, we will discuss our recent approaches for improving the mechanical stability of free-standing bilayer lipid membranes (BLMs) by combining with BLM formation and microfabrication techniques. BLMs were prepared across a microaperture fabricated in a silicon (Si) chip and their mechanical stability and electric properties were investigated. BLMs suspended in a thin Si3N4 septum showed a dramatic improvement of BLM stability. The BLMs were resistant to voltage of ±1 V and the membrane lifetime was 15- ~40 h with and without incorporated channels. The membrane containing gramicidin channel exhibited tolerance to repetitive solution exchanges. At first, electric properties of the BLMs, such as noise level and current transient, were necessary to be improved. However, after coating the chip with insulator layers of Teflon and SiO2, total chip capacitance was reduced, leading to noise reduction (1-2 pA in peak-to-peak after low-pass filtering at 1 kHz) and elimination of current transients (< 0.5 ms). Since the vicinity of the aperture edge was remained uncoated, the BLMs formed in the Si chips still showed high mechanical stability after the insulator coatings. The mechanically stable BLMs having electric properties suitable for recording activities of biological channels will open up a variety of applications including high-throughput analysis of ion-channel proteins.

On the assumption that the diameter of the reference vessel might determine the thickness of neointimal coverage of stents placed in the pulmonary arteries, we analyzed the angiograms of 28 lesions in 17 patients who underwent follow-up cardiac catheterization. Excluding 2 lesions where late stenosis was determined mainly by recoil of greater than 30%, we investigated the neointimal thickness of 26 lesions in 16 patients. Several factors that might contribute to late re-stenosis were also analyzed. Age and body weight at implantation ranged from 0.8 to 20 years, with a median of 6 years, and from 6.8 to 77.5 kg, with a median of 17.6 kg. Follow-up interval was from 6 to 15 months, with a median of 6 months.

There was a significant increase in diameter, as well as a reduction in pressure gradient, immediately after the implantation of stents. Although there was no significant difference between the achieved diameter and the diameter of the stent at follow-up, the diameter of the lesion at follow-up was significantly smaller than the diameter achieved by stenting. The increase in the pressure gradient at follow-up was slightly greater in 4 lesions where the late reduction in diameter was greater than 30% than in the 18 lesions where this was less than 30% (p = 0.05). The diameter of the reference vessel, and the diameter by stenting correlated with the late reduction in diameter. All lesions with diameter reduced greater than 30% had a reference diameter of less than 6.1 mm, and a diameter achieved by stenting of less than 6.5 mm. Late loss in luminal diameter directly correlated with the thickness of the neointimal coverage. In conclusion, close observation should be mandatory following implantation of stents in small pulmonary arteries.

We implanted either large or medium Palmaz stents, or a Palmaz Corinthian stent, in various stenotic vessels, such as the pulmonary arteries, pulmonary veins, aorta, or superior caval vein. Using angiograms, we measured the diameter of the stenotic vessel before or after the implantation, the minimal diameter of the lumen, the minimal diameter of the largest fully expanded balloon used to expand the stent, and the diameter immediately after withdrawal of the balloon.

The minimal diameter of the fully expanded balloon, and the minimal diameter of the lumen subsequent to expansion, were 8.2 ± 2.4, and 7.7 ± 2.3 mm, giving an absolute recoil of 0.5 ± 0.4 mm, and a proportional recoil of 7 ± 4%. There was no significant difference in either the absolute or proportional recoil for any of the stents, or for any of the different stenotic vessels. The proportional recoil correlated linearly with the minimal diameter of the lumen prior to the procedure, and with the ratio of the stenosis to the balloon, while the diameter of the stenotic vessels, the minimal diameter of the largest fully expanded balloon, the proportional stenosis prior to the procedure, and the ratio of the balloon to the diameter of the stenotic vessel, had no significant correlation with proportional recoil. The proportional recoil exceeded more than one-tenth when the minimal diameter of the lumen prior to the dilation was less than 3 mm, or the ratio of the balloon to the stenosis was greater than 3.0.

An absolute recoil of around 1 mm is common when a large or medium Palmaz, or a Palmaz Corinthian stent, is implanted in great vessels. Balloons with a diameter of approximately one-tenth greater than that of the adjacent vessel may be needed if the minimal diameter of the lumen is small prior to the procedure.

We investigated formation processes of a porous anodic alumina film on a p-type silicon (Si) substrate using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We observed drastic IR spectral changes when porous anodic alumina film approached interfaces between an aluminum (Al) layer and a Si substrate. The intensity of the IR absorption peaks due to water (H2O) molecules and silicon oxides (SiO2) increased simultaneously with a spike of anodic current density. The IR spectral changes indicated that the penetration of electrolytes brought about inhomogeneous oxidation of a Si substrate surface. We observed that the arrangement of the SiO2 nanodots closely reflected that of pores of a porous anodic alumina film. IR absorption peaks due to porous anodic alumina finally disappeared. The formation of SiO2 nanodots on a Si substrate promoted penetration of electrolytes to peel the porous anodic alumina film off it.

Recently we found high and persistent spontaneous buildup of the surface potential upon vacuum vapor deposition of tris(8-hydroxyquinolinato) aluminum(III)(Alq3) on Au substrate under dark conditions (28 V for 560 nm thick Alq3 film). Such giant potential is removed by visible-light irradiation. These natures of the film suggest the possible applications to various organic devices such as memory devices. In this study, we investigated the retention time of the giant potential and the mechanism of the light-induced depolarization in order to discuss the feasibility of the device applications. The observed decay rate of the surface potential in vacuum condition was roughly 10 % loss in 10 years, which is enough for memory devices. As to the decay rate by light-irradiation, the observed rate was successfully reproduced by a theoretical simulation based on the photo-induced randomization of oriented Alq3 molecules.

We have investigated the method of fabricating microstructures on a Si surface that is covered with a patterned gold (Au) mask, by electrochemical etching (anodization) in dilute hydrofluoric acid (HF) solution. We found that at electrode potentials below approximately 0.5 V, the Si surface is preferentially etched on the fringe of the Au mask, where a number of pores are formed. At higher electrode potentials, Au microwires with about 1 µm in width form along the fringe of the Au mask overlayer. We suggest that electromigration of Au towards the fringe of the Au mask induces self-assembling of Au atoms to form microwires. The observed self-formation of metal microwires would be beneficial to the fabrication of metal micro- or nano-structures on Si.

The chemical nature of Si(100) and (111) surfaces during immersion in dilute hydrofluoric acid (HF) solution and water was investigated “in-situ” and in real time using infrared absorption spectroscopy in the multiple internal reflection geometry. We demonstrate that in dilute HF solution, Si surfaces are not perfectly terminated by hydrogen, but are covered in part with hydrogen-associated Si fluorides, such as SiH2(SiF). We find that the hydrogen coverage of the surface during storage in dilute HF solution depends on the HF concentration of the solution. It is shown that rinsing in water following HF treatment leads to complete hydrogen termination of the surface. We also show that hydrogen exchange reaction occurs on the hydrogen-terminated Si surface during storage in water.