Modified Casimir force measurement using high vacuum FM (Frequency Modulation)-AFM based short coherence interferometer

 

1. Investigation of the impact of the impurity type, concentration and distribution in semiconductor boundary surfaces on the Casimir force;

2. Demonstration of novel Casimir force through patterned doping of semiconductors;

3. Studying the role of the metal to insulator transition on the Casimir force.

 

 

After improved measurements using metals, we made the first precision measurements of the material dependences of the Casimir force using silicon surfaces and showed that it is 30% lower compared to gold. This required development of a special high vacuum AFM and surface protection to prevent oxidation of the silicon. New consistency checks had to be developed given the decreased conductivity of silicon. With these improvements we were even able to demonstrate the role of the carrier density in the Casimir force by measuring the difference in the Casimir force between two materials with different dopant densities.

 

The boundary material dependences of the Casimir force are taken into account through the permittivity with the Lifshitz theory.  In 2000, it was realized that the calculation of the Casimir force using the Lifshitz theory at non-zero temperature is non trivial due to the combined roles of zero point and real photons which interact with lossy metallic boundaries.  We tested this through an experiment which was the first demonstration of the optical modulation of the Casimir force. Here, light was used to change the carrier density of a specially designed silicon membrane and the corresponding change in the Casimir force was measured through a phase dependent technique. The silicon carrier density was changed from the dielectric phase to above critical (metallic phase).  The inclusion of the dc conductivity of the silicon in the Lifshitz theory was found to disagree with the experiment. These developments have led recently to suggested modifications of the Lifshitz theory which are still not conclusive. 

The Casimir force with the semiconductor