Introduction

The scanning tunneling microscope (STM) is the youngest member of the electron microscopy family, developed only a little over ten years ago. The STM has its own unique list of assets and capabilities to apply to the study of high Tc superconducting materials that distinguishes it from the other family members. The data obtainable by STM can duplicate, surpass, or complement those extracted by the other electron microscopes. The STM has the advantage of having a higher vertical resolution than the scanning electron microscope and can achieve atomic resolution without the extensive and potentially damaging sample preparation techniques required for transmission electron microscopy. A disadvantage is that STM measurements are limited to the near surface region. Its realm is truly the atomic-to-nanometer world of the surface.

In addition to the extremely high vertical resolution (less than a 1 Å) routinely attainable by scanning tunneling microscopy and the often limited sample preparation required as noted above, the STM's additional advantages lie in (1) its sensitivity to both local electronic and structural properties, (2) the variety of measurements possible, (3) the low, generally nondestructive, energy range in which it operates, and (4) its environmental flexibility, i.e. its ability to operate under a wide range of temperatures and atmospheric conditions.

The STM's roots lie in electron vacuum tunneling spectroscopy. In the context of measuring electronic properties, it is more correctly described as a spectrometer, for it is the electronic properties of the surface that are being probed in the STM experiment. The correspondence between the electronic and topographic properties is responsible for the microscope label.