Photo of a homemade STM

SPM Research

Scanning probe
microscopy (SPM) is a class of microscopy that uses a sharp probe or needle to push, pull, and/or scan the surface of a material. Two common examples of SPM include scanning tunneling microscopy (STM) and atomic force microscopy (AFM), both of which were invented in the 1980s. Invented first, the STM operates by measuring the electron tunnel current between a sharp metal tip and a metallic or semiconducting surface and can routinely obtain atomic-resolution images of clean surfaces.
Photo of the tip-sample region of an
  Omicron STM head.

The microscope consists of a "head," which is the electro-mechanical system for carefully controlling the relative separation and position of the tip and sample, and the controller, which processes the electrical signals using hardware and software to create the image of the surface. A simple STM head can be made fairly easily (see image of a brass STM head at upper right), and more sensitive heads can be made or purchased, such as the Omicron STM1 head shown at left.

The AFM operates by measuring the electrostatic forces between the tip and the surface and can image the surfaces of metals, semiconductors, and insulators. While obtaining atomic-resolution images with AFM can be challenging, its use for imaging all material types at the nano to micro-meter scales has made AFM very popular for characterizing material surfaces.

The term SPM can be used to encompass all of the many imaging techniques that have extended or enhanced basic STM and AFM. These SPM techniques have been enable a range of surface material properties to be mapped or "imaged" qualitatively and sometimes quantitatively. In our research, we commonly use the SPM techniques to learn more about the structure, composition, and properties of new materials that we make in the lab.

Below are SPM images from our research. Click the images to see a larger version.

SPM Images