April 5, 1990, Section B, Page 11Buy Reprints View on timesmachine TimesMachine is an exclusive benefit for home delivery and digital subscribers. About the Archive This is a digitized version of an article from The Times’s print archive, before the start of online publication in 1996. To preserve these articles as they originally appeared, The Times does not alter, edit or update them. Occasionally the digitization process introduces transcription errors or other problems. Please send reports of such problems to [email protected]
Hiram Maxim, the inventor of the machine gun, used to demonstrate his marksmanship by firing patterns of bullets into walls to spell out the initials of potential customers. In a similar vein, I.B.M. announced yesterday that its scientists had spelled out the company's initials by dragging single atoms into the desired pattern on the surface of a crystal of nickel.
One result of I.B.M.'s tour de force was the cover photograph of the British journal Nature today. In a letter published by the journal, Dr. Donald M. Eigler and Dr. Erhard K. Schweizer of the I.B.M. Almaden Research Center at San Jose, Calif., reported that using an instrument that can discern individual atoms, they had positioned single atoms of xenon into various patterns, including the letters I.B.M.
Although single atoms have been manipulated by other laboratories using lasers and electromagnetic fields, this marked the first time atoms had been precisely positioned, one at a time, on a flat surface, like dominoes on a playing table. Next, Custom Molecules? An I.B.M. spokesman said the technique had no immediate applications but might eventually open the way to assembling custom-designed molecules atom by atom, and to building atom-sized transistors, which might operate at a much higher speed than is now possible.
The instrument the scientists used, a scanning tunneling microscope, was developed in the mid-80's by Dr. Gerd Binnig and Dr. Heinrich Rohrer, both of I.B.M., who received the 1986 Nobel Prize in Physics for their work. The microscope, which is now widely used to study crystal structures and biological material, uses a fine tungsten needle whose tip can be moved to within a few atoms' distance of the surface of an object under examination. A slight difference in voltage between the tip and the object creates a tiny flow of current when the needle approaches the object, even though they never touch.
A delicate mechanism scans the needle over the surface of the object, a single line at a time. The mechanism raises or lowers the needle to maintain a constant flow of current. The vertical movements of the needle, which reflect the bumps caused by single atoms over which it passes, are recorded electronically. From this recording, computers construct a picture of the surface of the sample, showing the position and size of each atom.
Dragging a Single Atom
Dr. Eigler and Dr. Schweizer discovered that when the needle is brought to just the right distance from a particular atom that has come to rest on the surface of a crystal, the needle attracts the atom. By carefully moving the needle, researchers can pull the atom along behind it to any desired position. When the needle is raised, the atom is released.
To conduct the experiment, the investigators chilled their samples with liquid helium. With a temperature of 452 degrees below zero Fahrenheit, less than 7 degrees above absolute zero, the liquid helium reduces the natural motion of atoms so they can be held in place once captured.
To start, Dr. Eigler and Dr. Schweizer sprayed a beam of xenon atoms at a chilled crystal of nickel, leaving a random pattern of the atoms on the surface. Then they manipulated these atoms into desired patterns using the scanning tunneling microscope. Besides spelling out I.B.M., they succeeded in creating chains of xenon atoms similar in form to molecules.
Such xenon chains are stable only at ultra-cold temperatures, and only when they are held in place by the metal surface on which they are resting. Dr. Eigler said in an interview that xenon atoms would ordinarily never arrange themselves in such a pattern.
The I.B.M. scientists said they could only speculate on the nature of the force the microscopic needle exerts on the xenon atoms, which are electrically neutral. They surmised that the main force might be the Van der Waals attraction, a fluctuating magnetic field that can be created between atoms or molecules.
''Many new avenues of investigation are open to us,'' the scientists said in the letter to Nature. ''It should be possible to assemble or modify certain molecules in this way. We can build novel structures that would otherwise be unobtainable.'' Potentially, that could include atomic-scale transistors and other electronic devices.