Number 74, April 2, 1992 by Phillip F. Schewe and Ben Stein THE INFRARED GALAXY IRAS 10214+4724 may consist mostly of molecular gas rather than stars. 10214+4724 is estimated to have a luminosity 3 x 1014 times greater than our sun, a luminosity rivaling that of the brightest quasars. Last year, the galaxy's spectrum was found to contain a prominent emission line for CO; the redshift of this spectrum, 2.286, is a factor of 10 larger than the redshift for any previous CO emission line. Such a redshift places the galaxy in an epoch of high quasar density; but this era may also have been a time of galaxy mergers, in which molecular gas could have fueled star formation. So, is the prodigious production of infrared radiation the result of star formation, or is a quasar lurking at the core of the galaxy? A new comparison of IRAS 10214+4724 with relatively nearby IR-luminous galaxies does not settle this issue, but does suggest that CO may account for as much as 90% of the mass of 10214+4724. The mass of CO, 2--6 x 1011 solar masses, is as much as that of many large nearby spiral galaxies. (Nature, 26 Mar. 1992.) PAIRS OF SILICON ATOMS are arranged like teeter-totters on certain silicon surfaces, recent STM measurements indicate. Like diamonds, silicon crystals can be cleaved in many different ways, but these bonded pairs, known as "dimers," are formed on only one type of silicon surface, the so-called Si(100) surface, which is widely used in electronics devices because of its favorable electronic properties. Room-temperature STM images had previously suggested that the dimers lie flat on the Si(100) surface. But low-temperature (120K) STM images taken by Robert Wolkow of AT&T show that the dimers are tilted with respect to the surface, implying that the room-temperature STM images are actually time-averaged views of thermally-excited dimers bobbing up and down between extreme positions. X-ray spectroscopy measurements by Gunther Wertheim and co-workers at AT&T show that the upper atom in the dimer has 0.3 electronic charge units more than its partner. The properties of surface atoms on Si(100) are believed to be important factors in processes which involve surface reactions, such as semiconductor etching, oxide film formation, and chemical vapor deposition. (Chemical & Engineering News, 30 March 1992.) TYPE II-VI SEMICONDUCTOR device performance is improving. Silicon (residing in column IV of the Periodic Table) does not readily emit light; compounds using column III and V elements (such as GaAs) produce light, but chiefly in the infrared. To get shorter wavelengths in the visible range, scientists have been studying compounds (such as ZnSe) which combine elements from columns II and VI; bandgap energies in these compounds usually exceed 2 eV. Problems with doping and with establishing a suitable crystalline matchup between the light-emitting material (II-VI) and substrate material (III-V) have hindered the development of devices. New epitaxial techniques have partially changed this. For example, type II-VI lasers have operated at power levels up to 700 mW, at temperatures up to room temperature, and at duty cycles (the fraction of time the laser is on) as high as 40%. Light emitting diodes made from type II-VI semiconductors have radiated at wavelengths as short as 490 nm. (Physics World, Mar. 1992.)