STM/AFM - overview
Some twenty years ago at IBM's Almaden Research Center in San Jose, in a small lab packed with high-tech equipment in the hills of Silicon Valley, IBM researchers achieved a landmark in mankind's ability to build small structures. On September 29, 1989 they demonstrated the ability to manipulate individual atoms with atomic-scale precision, and went on to write I-B-M with individual Xenon atoms, an event likened to the Wright brother’s first flight at Kitty Hawk.
Now, a new crop of researchers in that same lab -- with help from the University of Regensburg -- have taken the extraordinary step of measuring the tiny forces needed to manipulate the atoms.
Understanding the force necessary to move specific atoms on specific surfaces is one of the keys to designing and constructing the small structures that will enable future nanotechnologies. The problem is akin to what scientists and engineers needed to learn about construction at macroscopic sizes many decades ago. For example, building a modern bridge would be impossible without first measuring the strength of different materials, understanding the relevant forces, and comprehending how everything interacts. In the nanotechnology realm, to make structures that you want to remain rigidly in place you would use strongly bonded ("sticky") atoms while for groups of atoms that need to move you would use atoms held in place only by weak chemical bonds.
In the paper, "The Force Needed to Move an Atom on a Surface", published in Science on February, 22nd 2008, the scientists show that the force required to move a cobalt atom over a smooth platinum surface is 210 piconewtons, while moving a cobalt atom over a copper surface takes only 17 piconewtons. To put this in perspective, the force required to lift a copper penny that weighs just three grams is nearly 30 billion piconewtons -- 2 billion times greater than the force to move a single cobalt atom over a copper surface.
The pages accessed from the panel on the right explain in some detail how these measurements were performed and what further information can be derived from such experiments.