The scanning tunneling microscope (STM) has become one of the most powerful tools used in studying the surface structure of electrically conducting solid-state materials at an atomic resolution. Since its conception, the STM has had the greatest impact in the field of modern surface science because of its superior capability of characterizing and resolving the surface atomic structures and defects. Surface features such as atomic point defects, dislocations, and grain boundary identification can routinely be studied using a STM. Furthermore, STMs also allow the characterization of step structures at the atomic level during the processes of surface preparation and growth of semiconductors, such as epitaxial growth on semiconductor structures.
Unfortunately, STMs have been generally unable to resolve amorphous structures atomically. Many other types of probing microscopes — such as atomic force microscopes (AFM), magnetic force microscopes (MFM), and optical tunneling microscopes (OTM) — have also been developed in the industry. Generally, these other types of probing microscopes are based on the interaction between single probing tips and the sample surface. Moreover, these other types of probing microscopes also generally face the same challenge of the interpretation of results as found in conventional STMs. Therefore, there remains a need for a novel probing microscope capable of facilitating the interpretation of experimental results of sample surface probing.
An improvement to standard STMs that overcomes well-known limitations of conventional, single-tip STM systems was developed. In place of the single-tip configuration, a dual-tip probe comprises two single-atom protrusions on a single-crystal metal wire. As the dual-tip probe scans across the surface of a sample material, an interference electron-wave function formed by the two protruding atoms interacts with electron wave functions of the sample surface. This creates an electron wave density as high as four times that of a single-atom tip, resulting in a much more accurate and better resolved microscopic image of the sample surface.
In addition to higher sensitivity, the probe is compatible with current STMs, and can be fabricated using available industry processes, including focused ion beam milling.