Laser-assisted scanning tunneling microscopy

Abstract

Infrared laser radiation is coupled via the tip into the tunneling junction of a scanning tunneling microscope. Rectification and difference frequency generation of the laser light caused by the nonlinearity in the current-voltage characteristic of the junction are observed. Images with atomic resolution are obtained either by recording the rectified signal or by measuring the intensity at the difference frequency when the tip is scanned across the surface. These images are compared with others obtained in the conventional way by observing the tunneling current.

Effect of tip geometry on contrast and spatial resolution of the near-field microwave microscope

“…The third class of combined microscopes [18][19][20][21][22] couples an STM tunnel junction with laser light. The tunnel junction is illuminated with two fine-tuned optical frequencies.…”

High-frequency near-field microscopy

“…Both point-contact ''cat whisker'' antennas [102][103][104][105] and metalbarrier-metal diodes 106 were used to rectify or mix incident far-field FIR or IR radiation. Closely related are mixing experiments in a STM junction [107][108][109] that are discussed in detail in Sec. V A 3.…”

“…102 . Völcker et al [107][108][109] have investigated frequency mixing of two IR lasers at the junction of a STM and found the resulting rectified current and difference frequency signal at 9 GHz dependent on sample conductivity. In a related experiment, Bragas, Land, and Martínez 182 determined the optical field enhancement in a STM junction by measuring the rectified current.…”

Classification of Scanning Probe Microscopies

“…Other modifications of the STM involve electromagnetic radiation [27][28][29][30][31][32][33][34][35][36][37][38][39]. We must distinguish between two basic concepts: measuring photons generated in the tunneling gap by inelastic tunneling effects [31,35,37,38] and generation of electrical currents by irradiation of the tunneling gap [28][29][30][32][33][34].…”

“…We must distinguish between two basic concepts: measuring photons generated in the tunneling gap by inelastic tunneling effects [31,35,37,38] and generation of electrical currents by irradiation of the tunneling gap [28][29][30][32][33][34]. For the first group of methods the term photon emission scanning tunneling microscopy (PESTM) is recommended, for the second one photon assisted scanning tunneling microscopy (PASTM).…”