静電気力と表面粗さの影響を低減したカシミール力の解析及び測定法に関する研究

The summary of this research work is as follows.1. In the Casimir force measurement, surface roughness causes the deviation of the Casimir force, and the evaluation on the force becomes complicated. In addition, the contact point between tip and sample may differs from the theoretical contact point due to the roughness. Thus, it is hard to de ne the separation and measure the force in a shorter distance. The preparation of the sample in an UHV environment is important in order to reduce the surface roughness especially in a shorter distance. 2. We prepare the sample in the ultrahigh-vacuum condition of 1.5×10-8 Pa to obtain an atomically at surface. The sample was outgassed by heating at 833K over two days to remove surface contaminants. After that treatment, it was ashed at 1453 K and cooled from 1173 K to 873 K to remove the SiO2 layer and obtain 7 7 reconstructed surface. From this procedure, atomically at Si surface was obtained which is con rmed by AFM images. 3. We measured the interaction force between a spherical Au tip and an atomically at Si(111)-(7 7) surface at tip-sample distances from 15 to 50 nm in an ultrahigh vacuum of 1:5 10􀀀8 Pa by means of FM-AFM. The experimental conditions enable us to measure the distance dependence of the Casimir force in the shorter distance of 15 nm. From these results, it is elucidated that the theory described in Ref. [30] enables good understanding of the distance dependence in the shorter distance of 15 nm. 4. In an AFM measurement, the measured force is the net force including the Casimir force and the electrostatic force which is caused by CPD. Thus, in the Casimir force measurement, the electrostatic force is an issue. To obtain the distance dependence of the Casimir force from the measured force, the effect of the electrostatic force should be evaluated or minimized. To investigate the electrostatic force, the value of CPD should be known since the theoretical electrostatic force cannot be calculated correctly without the accurate value of the CPD. However, the accurate CPD cannot be obtained with the conventional FM-AFM system when it depends on the distance [45]. Thus, the method to measure the Casimir force and the electrostatic force separately or the method to obtain accurate value of CPD is required for the Casimir force measurement. 5. We have proposed the analytical method to obtain the distance dependence of the Casimir force and the electrostatic force separately with an conventional FM-AFM. It is based on the analysis of the two measurements which are the distance dependence of the frequency shift and the distance dependence of applied bias voltage. From the difference of the two results, the distance dependence of the Casimir force and electrostatic force was obtained. 6. By comparing the measured electrostatic force and theoretical one, the accurate value of CPD can be evaluated from our proposed method in the distance where the roughness of the tip and sample surface is negligible. This method can be used for the Casimir force measurement or the force microscopy with FM-AFM.