RESEARCH PROJECT

• Null Transmission Ellipsometry

• Differential Optical Reflectivity

• Surface Tension by Direct Force Measurement/Heat Capacity/Optical Reflectivity

• Surface Tension by Drumhead Resonance/Optical Reflectivity

• Surface Tension by Deflected String/Optical Reflectivity

• Depolarized Reflected Light Microscopy

The experimental setup is shown on the left. The sample geometry is free-standing film. A linear polarized light illuminates the film at nearly normal incidence. Due to the optical anisotropy, the polarization of the light will rotate slightly toward the direction which has a larger index of refraction. The reflected light is analyzed by another polarizer (analyzer) and a CCD camera is used to record the image.

The following movies show the observation from 7-layer and ~200-layer films of a hockey stick-shaped compound. The molecular structure of this compond can be found in PRL 90, 025502(2003). For the 7-layer (~200-layer) film the temperature decreased quickly (at 0.1K/min) from the SmC1 to the SmC2 phase. There are 4 transitions occurring in the 7-layer films and the following sequence is obtained: nonferroelectric-ferroelectric-nonferroelectric-ferroelectric-nonferroelectric.

For the ~200-layer film, a 70V/cm square electric field with period of ~17 second was applied. The first movie shows that there is no polarization in the SmC1 phase. We show the movie in a "fast forward" way, so the direction of the electric field switches every second in the movie. The second movie shows the first observed surface transition occurring at a temperature 3.6K above the bulk SmC1-SmC2 transition. In the movie, you will see a transtition front move across the film. After this transition, it can be seen from the third movie that now the film is ferroelectric. The next movie presents the bulk SmC1-SmC2 transition which is characterized by many transition fronts appearing at the same time. The last movie shows that the film is ferroelectric in the SmC2 phase indicating that this is an even-layer film.

• 7-layer film, first transition from nonferroelectric to ferroelectric (file size: 18Mbytes)
• 7-layer film, second transition from ferroelectric to nonferroelectric(file size: 9Mbytes)
• 7-layer film, last two transitions from nonferroelectric to ferroelectric to nonferroelectric(file size: 3Mbytes)
• ~200-layer film, in the SmC1 phase, nonferroelectric(file size: 5Mbytes)
• ~200-layer film, first observed surface transition(file size: 13Mbytes)
• ~200-layer film, after first surface transition, the film becomes ferroelectric(file size: 3Mbytes)
• ~200-layer film, bulk transition(file size: 12Mbytes)
• ~200-layer film, in the SmC2 phase, ferroelectric(file size: 2Mbytes)