纳米材料课件7.pdf

Natotubes for ElectronicsSWNTs can be used in faster,more efficient and more durable electronic devicesImportant property:A SWNT can either be metallic or semiconducting depending on its diameter and helix.M.S.Fuhrer et al.,SCIENCE VOL 288 21 APRIL 2000S-S Fan et al.,SCIENCE VOL 283 22 JANUARY 1999FEASIBILITYTHE IDEAOBSTACLESRAT-INGSChemical andGenetic ProbesA nanotube-tipped AFM can trace astrand of DNA and identifychemical markers that reveal whichof several possible variants of a geneis present in the strand.This is the only method yetinvented for imaging the chemistryof a surface,but it is not yet usedwidely.So far it has been used onlyon relatively short pieces of DNA3MechanicalMemoryA screen of nanotubes laid onsupport blocks has been tested as abinary memory device,withvoltages forcing some tubes tocontact(the“on”state)and others toseparate(the“off”state)The switching speed of the devicewas not measured,but the speedlimit for a mechanical memory isprobably around one megahertz,which is much slower thanconventional memory chips.2NanotweezersTwo nanotubes,attached toelectrodes on a glass rod,can beopened and closed by changingvoltage.Such tweezers have beenused to pick up and move objectsthat are 500 nm in size.Although the tweezers can pick upobjects that are large comparedwith their width,nanotubes are sosticky that most objects cant bereleased.And there are simplerways to move such tiny objects.2Beyond Electronics Other uses of nanotubesNote:0=Science Fiction,2=Demonstrated,4=Ready for marketsupersensitiveSemiconducting nanotubes changetheir sensors electrical resistancedramatically when exposed toalkalis,halogens and other gases atroom temperature,raising hopes forbetter chemical sensors.Nanotubes are exquisitely sensitiveto so many things(includingoxygen and water)that they maynot be able to distinguish onechemical or gas from another3Hydrogen andIon StorageNanotubes might store hydrogen intheir hollow centers and release itgradually in efficient andinexpensive fuel cells.They can alsohold lithium ions,which could leadto longer-lived batteries.So far the best reports indicate 6.5percent hydrogen uptake,which isnot quite dense enough to makefuel cells economical.The workwith lithium ions is stillpreliminary.1SharperScanningMaterialsAttached to the tip of a scanningprobe microscope,nanotubes canboost the instrumemts lateralresolution by a factor of 10 or more,allowing clearer views of proteinsand other large moleculesAlthough commercially available,each tip is still made individually.The nanotube tips dont improvevertical resolution,but they doallow imaging deep pits innanostructures that were previouslyhidden.4SuperstrongMaterialsEmbedded into a composite,nanotubes have enormous resilienceand tensile strength and could beused to make cars that bounce in awreck or buildings that sway ratherthan crack in an earthquakeNanotubes still cost 10 to 1,000times more than the carbon fiberscurrently used in composites.Andnanotubes are so smooth that theyslip out of the matrix,allowing it tofracture easily0SupersensitiveChemical SensorsCarbon Nanotube used as sharper scanning probesScientific Fiction by Richard E.Smalley1996 Nobel laureate P.Kim,C.M.Lieber,SCIENCE VOL 286 10 DECEMBER 1999