| 摘要 |
<p>A novel apparatus/method for directly detecting a light-absorbing substance on the order of nanometers by using a scanning tunnel microscope (STM) probe. When the surface of a semiconductor where band bending (BB) occurs for some cause is irradiated with light of energy more than the bandgap width, generated photocarriers drift because of the electric field produced by the BB, thereby causing charge separation that lowers the BB. The decrease of the BB is called a surface photovoltage (SPV). If an SPV is produced in a specimen being observed by an STM, the PPV is effectively added to the bias voltage applied between the probe and the specimen, varying the tunneling current. If a modulator (12) modulates the surface electric field by modulating the bias voltage, this modulates the band structure. During the modulation, if light causing interband transition is continuously applied, the SPV produced by the light application varies synchronously with the electric field modulation. Therefore, if the amplitude of a tunneling current modulation signal as a function of the wavelength of continuous light is measured, a spectrum equivalent to that obtained by the ER (electro-reflectance) method widely used as means for examining the electronic structure of the band deep part.</p> |
