Imaging and Moving Individual Atoms

The tunneling current, as Binnig and Rohrer discovered that night in their laboratory at IBM, is extremely sensitive to distance, making it possible to maintain a precise separation between the tip and the surface by moving the tip up or down to compensate 

The tip of a seaming tunneling microscope (STM) moves across an atomic surface. 

Movement of tip is used to create an image with atomic resolution. 

Tip is scanned across surface and moved up and down to maintain constant tunneling current. 

As we discussed in Chapter 1, it was only 200 years ago that John Dalton proposed his atomic theory. Today we can image atoms, move them, and even build tiny machines out of just a few dozen atoms (an area of research called nanotechnology). These atomic machines, and the atoms that compose them, are almost unimaginably small. 

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A little over two hundred years ago the atomic theory was broadly accepted for the first time in history (in part because of John Dalfon). Today we can "fake picfures" of them. In 1986 Gerd Binnig of Germany and Heinrich Rohrer of Switzerland shared the Nobel Prize for fheir discovery of the scanning tunneling microscope (STM), a microscope that can image and move individual atoms and molecules. Figure 1-12 shows "NANO USA" written with 112 individual molecules. The ability to see and move individual atoms has created fantastic possibilities. It may be possible some day to construct microscopic... 

Nanotechnology has looked possible since the discovery of the scanning tunneling microscope, which can image and move individual atoms. This and other recent advances, such as the discovery of buckyballs and buckytubes, have helped move nanotechnology from merely an idea into the laboratory. 

Alternatives to photolithography are needed if we are to achieve smaller circuits and,hence, more powerful computers. The obvious solution is nanotechnology,through which circuits may be built atom by atom. One of the pioneering tools that will allow this to happen is the scanning probe microscope. As discussed in Chapter 5, scanning probe microscopes are not only able to produce images of individual atoms, they allow the operator to move individual atoms into desired positions. 

One approach to avoid cluster artifacts is tlie use of periodic boundary conditions (PBCs). Under PBCs, the system being modeled is assumed to be a unit cell in some ideal crystal (e.g., cubic or orthorhombic, see Theodorouo and Suter 1985). In practice, cut-off distances are usually employed in evaluating non-bonded interactions, so the simulation cell need be surrounded by only one set of nearest neighbors, as illustrated in Figure 3.6. If tlie trajectory of an individual atom (or a MC move of that atom) takes it outside tlie boundary of the simulation cell in any one or more cell coordinates, its image simultaneously enters the simulation cell from tlie point related to the exit location by lattice symmetry. 

It is increasingly important to understand nature on a scale in between the quantum and classical worlds. Technological methods have moved into this transitional realm with dramatic results. Scanning tunneling microscopes can image individual atoms and reveal the atomic character of surfaces of solids. Individual atoms can be moved about and materials tailored for specific purposes. Electronic circuit elements have been reduced to dimensions of molecules. As scientists come to understand how the quantum domain gives way to the classical domain, these technologies will... 

This chapter has been reorganized to place greater emphasis on the physical structure of the atom, as determined from the classic experiments of Thomson, Millikan, and Rutherford. The chapter ends with direct scanning tunneling microscopy images of individual atoms in chemical reactions. Section 1.6 in Principles of Modern Chemistry, fifth edition (mole, density, molecular volume), has been moved to Chapter 2, which now gives a comprehensive treatment of formulas, stoichiometry, and chemical equations. 

Today, the evidence for the atomic theory is overwhelming. Recent advances in microscopy have allowed scientists not only to image individual atoms but also to pick them up and move them ( Figure 4.2). Matter is indeed composed of atoms. 

A computer then generates a contour map of the surface and the outline of individual atoms can be detected. The atoms resemble the hard spheres proposed by Dalton (Figure 2.10), but the STM images are in fact showing the electrons. The fuzziness occurs because the electrons move in a cloud and are not in fixed energy levels or orbits. Previous generations of chemists believed in atoms, but the STM provides empirical evidence for the existence of atoms. 

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