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STM images at top reveal a propeller-like molecule in an immobilized state when close to four adjacent molecules (left) and in a rotating state when shifted away by one-quarter of a nanometer (right). Computer simulations at bottom show the locked and free positions of the molecular wheel. Each of the six lobes on each molecule corresponds to a tert-butyl group.
ing a reversible change in the shape of specifically designed molecules triggered by a voltage pulse from the STM tip." The molecular wheel compound is hexa-tert-butyldecacyclene. Three propeller-like outer naphthalene rings—each terminated by two bulky tert-butyi legs—are linked to a central benzene ring. When deposited as a monolayer on a copper surface, the molecules are immobilized by steric interactions with their neighbors and form a two-dimensional supramolecular lattice. When the surface coverage is less complete, however, a random array of nanoscopic voids occurs in the lattice and STM images of the surface reveal ringlike objects in the spaces. The doughnut-shaped forms are timeaveraged images of molecules rotating at speeds higher than the scan rate used for imaging, according to Gimzewski's team. The wheels "work dry in the sense that there is no lubricant," says Gimzewski, and appear to be wearless. The molecular wheels can be switched between rotating and an immobilized state by moving the molecular rotor axis only a quarter of a nanometer with the microscope tip. In the monolayer, the immobilized rotor molecule is locked in by four sister molecules. When the position of the molecule is shifted slightiy, a vacant space is created. This allows it to escape, although its lateral movement is limited by a fifth molecule opposite the other four molecules. The liberated molecule, although confined within the vacant space, is free to choose between several binding sites. It 14 JULY 27, 1998 C&EN
thus rotates within a supramolecular bearing formed by the surrounding molecules. "Our calculations show that the thermal energy at room temperature is sufficient for the molecule to rotate in a bearing as observed, whereas the proximity of molecules in a fully ordered lattice stops such movement," notes team member Christian Joachim, director of research at the National Center for Scientific Research, Toulouse, France. According to J. Fraser Stoddart, professor of organic chemistry at the University of California, Los Angeles, "The findings reported by Gimzewski's team could bring scientists one step nearer to realizing functioning molecular machines— that is, molecular computers in the next millennium. "Rotary motion is encountered ubiquitously in the molecular machines deployed in biological systems," he continues. "The fabrication and operation of a man-made, single-molecule rotor in a dry state without wear and tear show that artificial analogs of these machines are close at hand." Michael Freemantle
Honors go to 'real' materials innovations A dozen R&D efforts that have led to commercially useful new materials in the past few years were honored with "Innovations in Real Materials" awards last week at the Innovations in Materials Conference in Washington, D.C. The conference, sponsored by the International Union of Materials Research Societies, is the brainchild of materials science professor Rustum Roy of Pennsylvania State University, University Park. The purpose of the conference and the awards was to focus attention on "stepfunction"—as opposed to incrementaladvances in the creation and use of new materials. An international committee selected the winners from nominations made by the materials sections of various national science and engineering academies. Among the award recipients were: • Dinesh K. Agrawal and coworkers at Perm State's Materials Research Laboratory, who developed a microwave process for sintering ceramics, metal carbide composites, and powdered metals to full
Wl&M': ' density in five to 30 minutes—less than one-tenth the time required by conventional sintering methods. Along with saving time and energy, the new process leads to improved materials properties. • Amitabha Kumar and colleagues at E. Khashoggi Industries, Santa Barbara, Calif., who developed a process for manufacturing environmentally friendly foam composites for use as food packaging. The biodegradable composites are made largely from starch, ground limestone, wood pulp, and water. "EarthShell" containers cost less to manufacture than Styrofoam or paperboard containers, and consumers seem to prefer them. McDonald's is very interested. • Shuji Nakamura of Nichia Chemical Industries, Anan, Japan, who found a reliable way to grow high-quality doped gallium nitride films and high-quality single-crystal indium gallium nitride films. Incorporating these films into devices, he produced the first high-brightness blue and green light-emitting diodes for use in large-area displays and traffic lights. More recently, he has produced violet laser diodes suitable for high-density recording of next-generation digital versatile disks. His work caused a sensation in the optoelectronics world. • Joseph R. Pickens of Concurrent Technologies Corp., Johnstown, Pa., who developed ultra-high-strength Weldalite aluminum-lithium-based alloys for space and other applications. One of these alloys was used to make a superlightweight external fuel tank that was used for the first time on a space shuttle flight early last month and "was a complete success," Pickens said. • Kazuhito Hashimoto and coworkers at the University of Tokyo, who developed photocatalytic titanium dioxide (Ti02) coatings with self-cleaning, antifogging, and sterilizing properties. The coatings, which can be applied to almost any material, including plastics, decompose carbonbased impurities at room temperature. "Our dream," Hashimoto said, is to coat buildings with Ti0 2 to make them selfcleaning. • Richard P. Wool, a chemical engineering professor at the University of Delaware, Newark, whose team developed a family of high-strength resins based on soybean triglycerides. These resins, combined with glass, carbon, or natural fibers such as hemp, straw, flax, jute, and wood, have led to inexpensive thermosetting composites for agricultural, automotive, construction, and other uses. Ron Dagani
