REPORTS heig 4B)shows that the pillars are standing face, a point that suggests these thin sheets 1. S Helveg et al. Nature 427, 426(2004) lose to I mm. A close examination bility allowed it to bow and touch the sur- eferences and Notes available as supporting a cross section of the SWNT structure corre- by mechanical forces, gas flows, or electric 3 H Choi et al., Nano Lett. 3, 157(2003) sponds well with the patterned catalyst(inset fields. 4. M. Cinke et al, Chem. Phys. Lett. 365, 69(2002) of Fig. 4A), and thus it is possible to Our approach is applicable to other 5. w. L Chiang et aL, J. Phys. Chem. B 105. 8297 fabricate arbitrary shapes of organized hesis methods developed for the mass 6M].o' Conn aL., Science297.593(2002) SWNT structures in which the base is litho- fuction of SWNTs, such as rotary kiln, K. Tohji et aL., Nature 383, 679(1996) graphically defined and the height is con- floating catalyst, and fluidized bed, address. 8 K Tohji et al, /. Phys. Chem.8101,1974(1997) trolled by the growth time. To further explore ing simultaneously such critical problems this unusual opportunity, we templated rows scalability, purity, and cost. Thus, our ap- 10. We thank Y Kak analyses, T. Yokoi for M observations, an in growing pseudo two-dimensional orga- realization of large-scale SWNT material L. Okazaki and ka for helpful discussions. nized SWNT structures(Fig 4, C and D)that Additionally, our SWNTs are pure enough resemble sheets. A close investigation of a for use in various fields ranging from Technology Development Organization(NEDO) Nano sheet face(Fig. 4F)reveals that the SWNTs biology and chemistry to magnetic research Nano-Processing Facility are acknowledged. are well aligned, with high uniformity. Some Highly pure SWNTs could be grown into of these sheets are curved like pages in a scaled-up macroscopic organized structures Supporting Online Material book, which demonstrates their flexibility. with defined shape, be it a three-dimensional dC1 sciencemag org/cgi/content/fulL/306/5700/1362/ thick was fabricated. Although this sheet optical polarizers and field-emitter arrays for Move nd s ethods This aspect is highlighted in Fig. 4E, in complex structure or a two-dimensional Materials and which an isolated thin SWNT sheet 5 um flexible sheet; potential applications include formed a well-organized structure, its flexi- flat-panel displays 7 September 2004: accepted 21 October 2004 Two of the three instruments Mars South polar al the gamma ray spectrometer(GRS)on Mars 后 Odyssey (5-7) can study CO, frost accumu- 5 Enhancement: A Tracer for South of aln nn cond mulative effects of the sum densables at southern latitudes Polar Seasonal Meridional Mixing by measuring the count rates of thermal neu- o ons, which show slightly lower values as oncondensables accumulate in the atmo- 8 A.L. Sprague,W. V Boynton,KE. Kerry. D M. Janes, sphere( 8). The GRS has the ability to mea- S D. M. Hunten, K.J. Kim,R. C. Reedy, A E. Metzger sure Ar alone from the flux of the 1294-kev gamma ray associated with the 110-min half- The gamma ray spectrometer on the Mars Odyssey spacecraft measured an life decay of Ar following neutron capture enhancement of atmospheric argon over southern high latitudes during au- (9) [see supporting online material(SOM) tumn followed by dissipation during winter and spring. Argon does not freeze at text for details of this emission]. The instru- o0333Eo temperatures normal for southern winter (145 kelvin) and is left in the at- ment has a circular footprint on Mars with a osphere enriched relative to carbon dioxide(Co, ), as the southern seasonal diameter equal to about 240 km (10). We cap of CO, frost accumulates Calculations of seasonal transport of argon into compute the fractional content of Ar relative and out of southern high latitudes point to meridional(north-south) mixing to the total atmosphere in the polar region throughout southern winter and spring [mass mixing ratio ()] by dividing the 3 mass of Ar measured by the grs over the Between autumn(areocentric longitude of the pole, they are turned in the direction of the polar area by the mass of CO, in the pola Sun L, 0o to 90o)(n)and winter in the south- planet,'s rotation and form a vortex. This phe- atmosphere as predicted by the National ern hemisphere of Mars, about 25% of the nomenon has received attention in connection Aeronautics and Space Administration Ames atmosphere accumulates as a thick southen with the terrestrial polar ozone holes, the Research Center Mars Global Circulation polar cap of CO, frost. Argon, a noncondens- chemistry of which is connected to the iso- Model(MGCM) run 2002.17(11, 12) able gas, is left behind in the polar region lation of the winter polar stratosphere and the The relative Ar abundance (grs)over (along with N2, O2, and CO)and becomes special chemistry that takes place in this cold Mars southern polar latitudes from 75to more enriched relative to CO,, the main con- dark region. On Mars, very low temperatures 90s peaked at 4,98,193 solar days(3) stituent in the atmosphere, as autumn prog. above the southen polar winter night were after CO, frost accumulation had begun(Fig resses. The atmosphere near the poles tends discovered from analysis of Infrared Temper- 1). The Ar abundance then decreased con to be isolated from the equatorial regions ature Mapper measurements made from the tinuously throughout winter even thou because of the conservation of angular mo- Viking Orbiters(2, 3). A substantial depletion CO, frost accumulation continued. A mini- mentum. If winds attempt to flow toward a in CO, might be the cause of the localized mum in Ar mass mixing ratio occurred after very low temperatures. Such a depletion solid CO, began to sublime off the cap in niver- would be accompanied by a large enhance- early spring. Although the increase and de- ment of the noncondensables Ar and N,, and crease in Ar abundance are notable, the real rsity of New Mexico, NM these were suggested to be enhanced by as surprise is that the data indicate transport of USA. Jet Propulsion Laboratory, Pasa- much as a factor of 20(4), particularly if co, Ar equatorward throughout winter and pole- dena, CA 91109, USA depletion was the cause of the localized cold ward in spring. The Ar mixing ratio drops To whom correspondence should be addressed. spots. Here, we describe measurements of Ar below the Viking Lander 2(VL2)value(14) E-maiL: sprague@lpL. arizona. edu in the polar region of the southem hemisphere. but is still measurable, despite rapid dilution 1364 19NovemBer2004voL306SciEncewww.sciencemag.orgheight close to 1 mm. A close examination (Fig. 4B) shows that the pillars are standing vertically from the substrate. Notably, the cross section of the SWNT structure corre￾sponds well with the patterned catalyst (inset of Fig. 4A), and thus it is possible to fabricate arbitrary shapes of organized SWNT structures in which the base is litho￾graphically defined and the height is con￾trolled by the growth time. To further explore this unusual opportunity, we templated rows of catalytic stripe patterns and succeeded in growing pseudo two-dimensional orga￾nized SWNT structures (Fig. 4, C and D) that resemble sheets. A close investigation of a sheet face (Fig. 4F) reveals that the SWNTs are well aligned, with high uniformity. Some of these sheets are curved like pages in a book, which demonstrates their flexibility. This aspect is highlighted in Fig. 4E, in which an isolated thin SWNT sheet 5 mm thick was fabricated. Although this sheet formed a well-organized structure, its flexi￾bility allowed it to bow and touch the sur￾face, a point that suggests these thin sheets could be arbitrarily laid down, for example, by mechanical forces, gas flows, or electric fields. Our approach is applicable to other synthesis methods developed for the mass production of SWNTs, such as rotary kiln, floating catalyst, and fluidized bed, address￾ing simultaneously such critical problems as scalability, purity, and cost. Thus, our ap￾proach represents an advance toward a realization of large-scale SWNT material. Additionally, our SWNTs are pure enough for use in various fields ranging from biology and chemistry to magnetic research. Highly pure SWNTs could be grown into scaled-up macroscopic organized structures with defined shape, be it a three-dimensional complex structure or a two-dimensional flexible sheet; potential applications include optical polarizers and field-emitter arrays for flat-panel displays. References and Notes 1. S. Helveg et al., Nature 427, 426 (2004). 2. Material and methods are available as supporting material on Science Online. 3. H. Choi et al., Nano Lett. 3, 157 (2003). 4. M. Cinke et al., Chem. Phys. Lett. 365, 69 (2002). 5. W. I. Chiang et al., J. Phys. Chem. B 105, 8297 (2001). 6. M. J. O’Connell et al., Science 297, 593 (2002). 7. K. Tohji et al., Nature 383, 679 (1996). 8. K. Tohji et al., J. Phys. Chem. B 101, 1974 (1997). 9. A. Cao, X. Zhang, C. Xu, D. Wu, B. Wei, J. Mater. Res. 16, 3107 (2001). 10. We thank Y. Kakudate for x-ray analyses, T. Yokoi for assistance with spectrofluorimetric measurements, K. Suenaga, K. Urita for some TEM observations, and T. Okazaki and M. Yudasaka for helpful discussions. Partial support by the New Energy and Industrial Technology Development Organization (NEDO) Nano Carbon Technology project and the use of the AIST Nano-Processing Facility are acknowledged. Supporting Online Material www.sciencemag.org/cgi/content/full/306/5700/1362/ DC1 Materials and Methods Figs. S1 and S2 Movie S1 7 September 2004; accepted 21 October 2004 Mars’ South Polar Ar Enhancement: A Tracer for South Polar Seasonal Meridional Mixing A. L. Sprague,1 * W. V. Boynton,1 K. E. Kerry,1 D. M. Janes,1 D. M. Hunten,1 K. J. Kim,2 R. C. Reedy,2 A. E. Metzger3 The gamma ray spectrometer on the Mars Odyssey spacecraft measured an enhancement of atmospheric argon over southern high latitudes during au￾tumn followed by dissipation during winter and spring. Argon does not freeze at temperatures normal for southern winter (È145 kelvin) and is left in the at￾mosphere, enriched relative to carbon dioxide (CO2), as the southern seasonal cap of CO2 frost accumulates. Calculations of seasonal transport of argon into and out of southern high latitudes point to meridional (north-south) mixing throughout southern winter and spring. Between autumn (areocentric longitude of the Sun Ls 0- to 90-) (1) and winter in the south￾ern hemisphere of Mars, about 25% of the atmosphere accumulates as a thick southern polar cap of CO2 frost. Argon, a noncondens￾able gas, is left behind in the polar region (along with N2, O2, and CO) and becomes more enriched relative to CO2, the main con￾stituent in the atmosphere, as autumn prog￾resses. The atmosphere near the poles tends to be isolated from the equatorial regions because of the conservation of angular mo￾mentum. If winds attempt to flow toward a pole, they are turned in the direction of the planet_s rotation and form a vortex. This phe￾nomenon has received attention in connection with the terrestrial polar ozone holes, the chemistry of which is connected to the iso￾lation of the winter polar stratosphere and the special chemistry that takes place in this cold dark region. On Mars, very low temperatures above the southern polar winter night were discovered from analysis of Infrared Temper￾ature Mapper measurements made from the Viking Orbiters (2, 3). A substantial depletion in CO2 might be the cause of the localized very low temperatures. Such a depletion would be accompanied by a large enhance￾ment of the noncondensables Ar and N2, and these were suggested to be enhanced by as much as a factor of 20 (4), particularly if CO2 depletion was the cause of the localized cold spots. Here, we describe measurements of Ar in the polar region of the southern hemisphere. Two of the three instruments comprising the gamma ray spectrometer (GRS) on Mars Odyssey (5–7) can study CO2 frost accumu￾lation and the cumulative effects of the sum of all noncondensables at southern latitudes by measuring the count rates of thermal neu￾trons, which show slightly lower values as noncondensables accumulate in the atmo￾sphere (8). The GRS has the ability to mea￾sure Ar alone from the flux of the 1294-keV gamma ray associated with the 110-min half￾life decay of Ar following neutron capture (9) Esee supporting online material (SOM) text for details of this emission^. The instru￾ment has a circular footprint on Mars with a diameter equal to about 240 km (10). We compute the fractional content of Ar relative to the total atmosphere in the polar region Emass mixing ratio ( f GRS)^ by dividing the mass of Ar measured by the GRS over the polar area by the mass of CO2 in the polar atmosphere as predicted by the National Aeronautics and Space Administration Ames Research Center Mars Global Circulation Model (MGCM) run 2002.17 (11, 12). The relative Ar abundance ( f GRS) over Mars_ southern polar latitudes from 75- to 90-S peaked at Ls 98-, 193 solar days (13) after CO2 frost accumulation had begun (Fig. 1). The Ar abundance then decreased con￾tinuously throughout winter even though CO2 frost accumulation continued. A mini￾mum in Ar mass mixing ratio occurred after solid CO2 began to sublime off the cap in early spring. Although the increase and de￾crease in Ar abundance are notable, the real surprise is that the data indicate transport of Ar equatorward throughout winter and pole￾ward in spring. The Ar mixing ratio drops below the Viking Lander 2 (VL2) value (14) but is still measurable, despite rapid dilution R EPORTS 1 Lunar and Planetary Laboratory, 1629 East Univer￾sity Boulevard, University of Arizona, Tucson, AZ 85721–0092, USA. 2 Institute of Meteoritics, MSC03- 2050, University of New Mexico, Albuquerque, NM 87131–0001, USA. 3 Jet Propulsion Laboratory, Pasa￾dena, CA 91109, USA. *To whom correspondence should be addressed. E-mail: sprague@lpl.arizona.edu 1364 19 NOVEMBER 2004 VOL 306 SCIENCE www.sciencemag.org on January 23, 2008 www.sciencemag.org Downloaded from