Multiple-fiber collection system for scanning tunneling microscope light emission spectroscopy

We have constructed an optical fiber system for collecting light emission ( LE) from the gap between a sample and the tip of a scanning tunneling micro scope (STM). The collection system consists of four optical fibers with a c ore diameter of 600 mum and a numerical aperture (NA) of 0.2. The four opti cal fibers point radially at the tip-sample gap from four directions. To de monstrate the performance of the collection system, we evaluated its effect ive solid angle of collection by measuring the STM-LE from a Au evaporated film, The effective solid angle was estimated to be 0.33 +/- 0.03 sr, which corresponds to about 2.6 times that of a single optical fiber determined b y the INA (0.13 sr). Although the solid angle of collection did not increas e by a factor of four, the increase of the collection solid angle will impr ove the detection limit by reducing the accumulation time for spectral meas urements.