34 Crystallization Control of the Photoresponsible Diarylethene …
587
dependence of needle-shaped crystals from either bottom or top of the 1o film was
studied as the first subject. When UV light was irradiated to the 1o film from the
bottom side for 5 min, the irradiation area changed to black. The monochromatic
gradation corresponds to the absorption in the visible range assigned to 1c converted
from 1o [43]. At several hours after UV irradiation, crystals of 1c did not appear
inside and outside the grating, and not even at several days after UV irradiation. On
the other hand, needle-shaped crystals of 1c were observed under the UV irradiation
from the top side. Needle-shaped crystal growth of 1c requires a mobility of 1c
molecules at the center part of a film. Under the UV irradiation from the bottom
side, 1o layer may be still unconverted in the top (film surface) and it can disturb the
molecular alignment in 1c underlayer facing to the substrate.
The irradiation position dependence of crystallization in the film was examined
as the second subject. The film edge was exposed to UV from the bottom side for
10 min (1.1 J/cm
2 ). Exposure area was immediately blacked after UV irradiation.
Then, needle-shaped crystals appeared at several hours with UV irradiation from the
bottom side and grew after several days. Crystallization was induced at the film edge
from the bottom irradiation. This is considered to be attributed to that the mobility of
1c in the film surface and the film edge is higher than that in the center part of the film.
Furthermore, the crystal was never observed at the edge of a too thin-diarylethene 1
film.
In the center part of 1o film exposed to UV for 5 min from the bottom side with a
100× objective, the area of grating pattern corresponds to upper darker part and area
of flat metal corresponds to lower brighter part in Fig. 34.4. The irradiated area was
immediately blackened after UV exposure (Fig. 34.4c). As expected for a center part
exposed to UV light from the bottom, needle-shaped crystals did not appear even
after 20 h incubation (Fig. 34.4d). Then, UV light was irradiated to the film again
from the top side for 3 min with 40× objective, in which the irradiation spot area
exposed from the top (1.6 × 10
−3 cm
2 ) was larger than that from the bottom (9.3 ×
10
−4 cm
2 ) with the 100 × objective. At 7 h after 2nd UV from the top, needle-shaped
crystals were observed at the boundary between the irradiation spots from the top and
bottom sides (Fig. 34.4g). In the region of the boundary, 1o only at the film surface
is isomerized to 1c by the irradiation from the top, whereas 1o at underlayer facing
to the chip surface may still remain without conversion, i.e., the 1o at underlayer
in the boundary may make a role of the platform for alignment of 1c. In contrast,
needle-shaped crystals were not found in the center part completely converted to 1c
due to the UV exposure from both top and bottom sides (Fig. 34.4g). According to
these results, the platform of 1o is required for alignment of 1c and crystals growth.
587
dependence of needle-shaped crystals from either bottom or top of the 1o film was
studied as the first subject. When UV light was irradiated to the 1o film from the
bottom side for 5 min, the irradiation area changed to black. The monochromatic
gradation corresponds to the absorption in the visible range assigned to 1c converted
from 1o [43]. At several hours after UV irradiation, crystals of 1c did not appear
inside and outside the grating, and not even at several days after UV irradiation. On
the other hand, needle-shaped crystals of 1c were observed under the UV irradiation
from the top side. Needle-shaped crystal growth of 1c requires a mobility of 1c
molecules at the center part of a film. Under the UV irradiation from the bottom
side, 1o layer may be still unconverted in the top (film surface) and it can disturb the
molecular alignment in 1c underlayer facing to the substrate.
The irradiation position dependence of crystallization in the film was examined
as the second subject. The film edge was exposed to UV from the bottom side for
10 min (1.1 J/cm
2 ). Exposure area was immediately blacked after UV irradiation.
Then, needle-shaped crystals appeared at several hours with UV irradiation from the
bottom side and grew after several days. Crystallization was induced at the film edge
from the bottom irradiation. This is considered to be attributed to that the mobility of
1c in the film surface and the film edge is higher than that in the center part of the film.
Furthermore, the crystal was never observed at the edge of a too thin-diarylethene 1
film.
In the center part of 1o film exposed to UV for 5 min from the bottom side with a
100× objective, the area of grating pattern corresponds to upper darker part and area
of flat metal corresponds to lower brighter part in Fig. 34.4. The irradiated area was
immediately blackened after UV exposure (Fig. 34.4c). As expected for a center part
exposed to UV light from the bottom, needle-shaped crystals did not appear even
after 20 h incubation (Fig. 34.4d). Then, UV light was irradiated to the film again
from the top side for 3 min with 40× objective, in which the irradiation spot area
exposed from the top (1.6 × 10
−3 cm
2 ) was larger than that from the bottom (9.3 ×
10
−4 cm
2 ) with the 100 × objective. At 7 h after 2nd UV from the top, needle-shaped
crystals were observed at the boundary between the irradiation spots from the top and
bottom sides (Fig. 34.4g). In the region of the boundary, 1o only at the film surface
is isomerized to 1c by the irradiation from the top, whereas 1o at underlayer facing
to the chip surface may still remain without conversion, i.e., the 1o at underlayer
in the boundary may make a role of the platform for alignment of 1c. In contrast,
needle-shaped crystals were not found in the center part completely converted to 1c
due to the UV exposure from both top and bottom sides (Fig. 34.4g). According to
these results, the platform of 1o is required for alignment of 1c and crystals growth.