抄録
In this article, we propose a compact absolute length measuring machine (ALMM) with sub-nanometer accuracy and sub-millimeter travel by combining the atomic spacing on the regular crystalline surface and the optical interference fringe, i.e. wavelength. The atomic spacing on the crystalline surface can be obtained with a scanning tunneling microscope (STM). A phase modulation homodyne interferometer (PMHI) can determine displacements between optical interference dark fringes with picometer resolution. The ALMM consists of two piezo-driven sample stages A and B with 1-dimensional motion axes X_A and X_B, atomic force microscope (AFM)/STM heads with tips and YZ scanners, a multi-path PMHI and a thermo-stabilized vacuum cell. A sample of interest and the reference crystal are set on the stage A and B, respectively, which are just beneath AFM and STM heads. 3-dimensional images of the sample and the crystal can be obtained by combining motions of the stages A/B and AFM/STM heads. The stage A and B are independently controlled and their motion axes X_A and X_B are aligned to be parallel with the two arms of the interferometer. The displacement difference between the X_A and X_B axes can be measured and controlled with picometer resolution using the interferometer. Lateral length of the sample along the X_A axis should be measured from the AFM imaging. With the ALMM, an arbitrary scanning length of the stage A, i.e. the sample length, can be determined by utilizing a fine scale (=lattice spacing) and a coarse scale (=wavelength). To asses the possibility of the ALMM, we developed an instrument for direct measurement of lattice spacing on the crystalline surface. In the article, we will discuss the principle of the ALMM and the results of the lattice spacing for graphite crystalline surface.
