Page 137 - Photoreactive Organic Thin Films

116 ZOUHEIR SEKKAT AND WOLFGANG KNOLL

0.0
35.0 37.5 40.0 42.5 45.0 47.5 50.0 52.5 55.0
External Angle (Degrees)
0.460
.Blue On I Blue On Blue On

0.455 - Blue

0.450-

0.445- IJVOn UVOn

UV UVOff
0.440-
240 480 720 960 1200 1440
Time, t / sec
FIG. 4.5 (Top) Surface plasmon resonance of the Bare Ag/SiO x substrate before (black circles) and
after (white circles) coating with a SAM of azo-silane; the inset shows the fitted geometrical thickness
of the Ag, SiO x, and azo-silane SAMThe full lines are theoretical fits from Fresnel calculations. (Bottom)
Optical thickness change as obtained by recording the reflected intensity of the azo-silane SAM sample
at a fixed angle of incidence (6 = 45 degrees) during irradiation; the moments of turning the irradiation
light on and off are indicated by arrows. After reference 39, redrawn by permission of ACS.

can be restored by switching to visible light (450 nm), which isomerizes the
azobenzenes back into the trans form. These reaction cycles can be conducted
many times. It is important to note that, given the signal-to-noise level of
these data, index changes smaller than 0.001 can be monitored in refractive
layers that are only 9 A thick.