Number 219, March 28, 1995 by Phillip F. Schewe and Ben Stein LIQUID CRYSTALS CAN EXHIBIT BOTH SPATIAL AND TEMPORAL PATTERNS. With some of the orderliness of crystalline solids and some of the freedom enjoyed by molecules in a liquid, liquid crystals are important for biology (they form the membranes around the cells in our bodies) and as the basis for the multi-billion-dollar flat-panel-display industry, which depends on a phenomenon in which the rod-like molecules composing liquid crystals can rotate the polarization of light to create an on-or-off shutterlike effect. Liquid crystals are also important for the study of pattern formation in nonequilibrium systems (systems to which energy is being added). Scientists hope thereby to gain a better understanding of turbulence and possibly of morphogenesis (e.g., the question of where tigers get their stripes). Patricia Cladis of AT&T Bell Labs uses liquid crystals as a miniature laboratory for studying phase transitions. Heating one end of a sample and cooling the other end, Cladis has found that the phase interface between a pure liquid state and a liquid crystal state features spatial patterns (stripes with a characteristic "wavelength"); when, furthermore, the liquid crystal is "chiral" (i.e., when it has a handedness or helicity), the interface also oscillates with a characteristic frequency. Speaking at last week's meeting of the American Physical Society in San Jose, Cladis said she wanted to explore the connection between biological systems and the spatial and temporal order of liquid crystal patterns, a connection she calls "the dance of life." THE DENSITY OF DATA stored on magnetic hard disks has been increasing at an annual rate of about 60% over the past few years. If this rate is sustained, areal densities of 10 Gbit/sq in will be achieved by the year 2001, according to Mark Kryder of Carnegie Mellon. He and several other speakers at the APS meeting addressed the subject of future data storage. Continued progress depends on improved recording media. Dieter Weller of IBM Almaden reported on his efforts to enhance the ability of the tiny domains on the film medium to become magnetized, a parameter called magnetic anisotropy. Working with sandwiches of atom-thin layers of iron and platinum, Weller has produced a film with an anisotropy ten times that of materials used in present day hard disks. Even though the storage of data in the form of tiny magnetic orientations on a two-dimensional film keeps getting better, scientists continue to explore alternative methods. Lambertus Hesselink of Stanford described a system in which data is stored in the form of an optical interference pattern in a three-dimensional photorefractive crystal. The merits of such a holographic system would be its high data-transfer rates (data written not in linear streams of bits but in whole 2-dimensional "pages"), a high storage density (perhaps eventually terabits/cc, requiring, in effect, only about a million atoms per bit), and a fast access time (100 microsec). Hesselink has actually transferred data from a computer to a holographic system and then read the data back again. Obstacles remain, however, not least the difficulty of preparing the hologram material and maintaining data for long periods. The bulky apparatus for holographic systems might preclude laptop applications, but the pagelike data format might facilitate delivery of such services as video-on-demand. Finally, Gary Gibson of Hewlett Packard described an even more distant (at least 10 years away) form of data storage, one employing the needle of a scanning probe microscope to write and read bits of data in the form of tiny atom piles or pits (20 nm in size). A typical system would employ arrays of thousands of probe tips, and write data at rates of 10**8 bits/sec.