science/technology
MOISTUREANALYSIS GIVING YOU A PAIN?
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SEPTEMBER 4, 2000 C&EN
World's Smallest Crystal Imaged Scientists in England have synthesized and characterized one-dimensional potassium iodide crystals encapsulated in single-walled carbon nanotubes (SWNTs). The work opens up possibilities for the design of new materials with novel and unexpected properties, the team suggests. "We have succeeded in imaging and characterizing the world's smallest single-crystal wires using a new state-of-theart high-resolution transmission electron microscope," says Jeremy Sloan, a postdoctoral researcher at Oxford University, who carried out the work with Angus I. Kirkland, senior research fellow at Cambridge University, and coworkers at both universities [Science, 289,1324, (2000)]. "The crystals, which were grown in Oxford, are made up of three-by-three atomic arrays of KI extended along the capillaries of 1.6-nm-diameter SWNTs," Sloan explains. The group measured the interatomic dimensions of the encapsulated KI crystals with a resolution of 0.1 nm from image data obtained with a Japan Electron Optics Laboratory (JEOL) JEM-3000F field emission gun transmission electron microscope that was installed at Oxford earlier this year. An image restoration technique developed in Cambridge was used to obtain images of individual atom columns of potassium and iodine inside the nanotubes. 'This work reports very exciting developments in a forefront area of materials chemistry and physics," comments Peter P. Edwards, professor of inorganic and materials chemistry at the University of Birmingham, England. "What
is particularly impressive is the authors' development and combination of both advanced synthesis and advanced structural instrumentation; namely, the synthesis and complete crystallography of a 1-D crystal of KI contained within a single-walled nanotube." Imaging of the encapsulated KI crystals reveals that the lattice spacings within the crystals are substantially different from those in bulk KI. According to the team, the results show that a SWNT with a preselected diameter could be used to template particular strain states of encapsulated 1-D crystals and therefore be used to tailor their physical properties. "New and breathtaking possibilities now wait," Edwards remarks. "Perhaps most spectacular will be the encapsulation of elements and other materials which are metallic in their bulk form. Constrained within a 1-nm nanotube, such materials may well find themselves as insulators. On the other hand, it is quite possible that semiconductors such as silicon could become metals when encapsulated." Malcolm Green, professor of inorganic chemistry at Oxford and a member of the team, points out that the accurate determination of interatomic distances of nano-dimensioned crystals will also provide a challenge to theoretical chemists to understand the bonding energies of the crystals. The Oxford and Cambridge group is now working on the total crystallographic characterization of other electronic, ceramic, semiconducting, and metallic materials encapsulated within nanotubes. Michael Freemantle
