纳米材料与微型机器外文文献翻译中英文翻译.docx
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纳米材料与微型机器外文文献翻译中英文翻译
外文资料
NanotechnologyandMicro-machine
原文
(一):
Nanomaterial
Nanomaterialsandnanotechnologyhavebecomeamagicwordinmodernsociety.
Nanomaterialsrepresenttoday’scuttingedgeinthedevelopmentofnoveladvancedmaterialswhichpromisetailor-madefunctionalityandunheardapplicationsinallkeytechnologies.Sonanomaterialsareconsideredasagreatpotentialinthe21thcenturybecauseoftheirspecialpropertiesinmanyfieldssuchasoptics,electronics,magnetics,mechanics,andchemistry.Theseuniquepropertiesareattractiveforvarioushighperformanceapplications.Examplesincludewearresistantsurfaces,lowtemperaturesinterablehigh-strengthceramics,andmagneticnanocomposites.Nanostructuresmaterialspresentgreatpromisesandopportunitiesforanewgenerationofmaterialswithimprovedandmarvelousproperties.
Itisappropriatetobeginwithabriefintroductiontothehistoryofthesubject.Nanomaterialsarefoundinbothbiologicalsystemsandman-madestructures.Naturehasbeenusingnanomaterialsformillionsofyears,asDiscksonhasnoted:
“Lifeitselfcouldberegardedasananophasesystem”.Examplesinwhichnanostructuredelementsplayavitalrolearemagnetotacticbacteria,ferritin,andmolluscanteeth.Severalspeciesofaquaticbacteriausetheearth’smagneticfieldtoorientthenselves.Theyareabletodothisbecausetheycontainchainsofnanosized,single-domainmagnetiteparticles.Becausetheyhaveestablishedtheirorientation,theyareabletoswimdowntonutrimentsandawayfromwhatislethaltothem,oxygen.Anotherexampleofnanomaterialsinnatureisthatherbivorousmollusksuseteethattachedtoatonguelikeorgan,theradula,toscrapetheirfood.Theseteethhaveacomplexstructurecontainingnanocrystallineneedles.Wecanutilizebiologicaltemplatesformakingnanomaterials.Apoferritinhasbeenusedasaconfinedreactionenvironmentforthesynthesisofnanosizedmagnetiteparticles.Somescholarsconsiderbiologicalnanomaterialsasmodelsystemsfordevelopingtechnologicallyusefulnanomaterials.
Scientificworkonthissubjectcanbetracedbackover100years.In1861theBritishchemistThomasGrahamcoinedthetermcolloidtodescribeasolutioncontaining1to100nmdiameterparticlesinsuspension.Aroundtheturnofthecentury,suchfamousscientistsasRayleigh,Maxwell,andEinsteinstudiedcolloids.In1930theLangmuir-Blodgettmethodfordevelopingmonolayerfilmswasdeveloped.By1960Uyedahadusedelectronmicroscopyanddiffractiontostudyindividualparticles.Ataboutthesametime,arc,plasma,andchemicalflamefurnaceswereemployedtoprouducesubmicronparticles.Magneticalloyparticlesforuseinmagnetictapeswereproducedin1970.By1980,studiesweremadeonclusterscontainingfewerthan100atoms.In1985,ateamledbySmalleyandKrotofoundspectroscopicevidencethat
clusterswereunusuallystable.In1991,Lijimareportedstudiesofgraphiticcarbontubefilaments.
Researchonnanomaterialshasbeenstimulatedbytheirtechnologicalapplications.Thefirsttechnologicalusesofthesematerialswereascatalystsandpigments.Thelargesurfaceareatovolumeratioincreasesthechemicalactivity.Becauseofthisincreasedactivity,therearesignificantcostadvantagesinfabricatingcatalystsfromnanomaterials.Thepeopertiesofsomesingle-phasematerialscanbeimprovedbypreparingthemasnanostructures.Forexample,thesinteringtemperaturecanbedecreasedandtheplasticityincreasedonsingle-phase,structuralceramicsbyreducingthegrainsizetoseveralnanometers.Multiphasenanostructuredmaterialshavedisplayednovelbehaviorresultingfromthesmallsizeofheindividualphases.
Technologicallyusefulpropertiesofnanomaterialsarenotlimitedtotheirstructural,chemical,ormechanicalbehavior.Multilayersrepresentexamplesofmaterialsinwhichonecanmodifyoftuneapropertyforaspecificapplicationbysensitivelycontrollingtheindividuallayerthickness.ItwasdiscoveredthattheresistanceofFe-CrmultilayeredthinfilmsexhibitedlargechangesinanappliedmagneticfieldofseveraltensofkOe.Thiseffectwasgiventhenamegiantmagnetoresistance(GMR).Morerecently,suitablyannealedmagneticmultilayershavebeendevelopedthatexhibitsignificantmagnetoresistanceeffectseveninfieldsaslowas5to10Oe(Oersted).Thiseffectmayprovetobeofgreattechnologicalimportanceforuseinmagneticrecordingreadheads.
Inmicroelectronics,theneedforfasterswitchingtimesandeverlargerintegrationhasmotivatedconsiderableefforttoreducethesizeofelectroniccomponents.Increasingthecomponentdensityincreasesthedifficultyofsatisfyingcoolingrequirementsandreducestheallowableamountofenergyreleasedonswitchingbetweenstates.Itwouldbeidealiftheswitchingoccurredwiththemotionofasingleelectron.Onekindofsingle-electrondeviceisbasedonthechangeintheCoulombicenergywhenanelectronisaddedorremovedfromaparticle.Forananoparticlethisenerychangecanbelargeenoughthataddingasingleelectronwilleffectivelyblockstheflowofotherelectrons.TheuseofCoulombicrepulsioninthiswayiscalledCoulombblockade.
Inadditiontotechnology,nanomaterialsarealsointerestingsystemsforbasicscientificinvestigations.Forexample,smallparticlesdisplaydeviationsfrombulksolidbehaviorsuchasreductiosinthemeltingtemperatureandchanges(usuallyreductions)inthelatticeparameter.Thechangesnthelatticeparameterobservedformetalandsemiconductorparticlesresultfromtheeffectofthesurfacefreeenergy.Boththesurfacestressandsurfacefreeenergyarecausedbythereducedcoordinationofthesurfaceatoms.Bystudyingthesizedependenceofthepropertiesofparticles,itispossibletofindthecriticallengthscalesatwhichparticlesbehaveessentiallyasbulkmatter.Generally,thephysicalpropertiesofananoparticleapproachbulkvaluesforparticlescontainingmorethanafewhundredatoms.
Newtechniqueshavebeendevelopedrecentlythathavepermittedresearcherstoproducelargerquantitiesofothernanomaterialsandtobettercharacterizethesematerials.Eachfabricationtechniquehasitsownsetofadvantagesanddisadvantages.Generallyitisbesttoproducenanoparticleswithanarrowsizedistribution.Inthisregard,freejetexpansiontechniquespermitthestudyofverysmallclusters,allcontainingthesamenumberofatoms.Ithasthedisadvantageofonlyproducingalimitedquantityofmaterial.Anotherapproachinvolvestheproductionofpelletsofnanostructuredmaterialsbyfirstnucleatingandgrowingnanoparticlesinasupersaturatedvaporandthenusingacoldfingertocollectthenanoparticle.Thenanoparticlesarethenconsolidatedundervacuum.Chemicaltechniquesareveryversatileinthattheycanbeappliedtonearlyallmaterials(ceramics,semiconductors,andmetals)andcanusuallyproducealargeamountofmaterial.Adifficultywithchemicalprocessingistheneedtofindtheproperchemicalreactionsandprocessingconditionsforeachmaterial.Mechanicalattrition,whichcanalsoproducealargeamountofmaterial,oftenmakeslesspurematerial.Oneproblemcommontoallofthesetechniquesisthatnanoparticlesoftenformmicron-sizedagglomerates.Ifthisoccurs,thepropertiesofthematerialmaybedeterminedbythesizeoftheagglomerateandnotthesizeoftheindividualnanoparticles.Forexample,thesizeoftheagglomeratesmaydeterminethevoidsizeintheconsolidatednanostructuredmaterial.
Theabilitytocharacterizenanomaterialshasbeenincreasedgreatlybytheinventionofthescanningtunnelingmicroscope(STM)andotherproximalprobessuchastheatomicforcemicroscope(AFM),themagneticforcemicroscope,andtheopticalnear-fieldmicroscope.SMThasbeenusedtocarefullyplaceatomsonsurfacestowritebitsusingasmallnumberofatmos.Ithasalsobeenemployedtoconstructacirculararrangementofmetalatomsonaninsulatingsurface.Sinceelectronsareconfinedtothecircularpathofmetalatoms,itservesadaquantum‘corral’ofatoms.Thisquantumcorralwasemployedtomeasurethelocalelectronicdensityofstatesofthesecircularmetallicarrangements.Bydoingthis,researcherswereabletoverifythequantummechanicaldescriptionofelectronsconfinedinthisway.
Othernewinstrumentsandimprovementsofexistinginstrumentsareincreasinglybecomingimportanttoolsforcharacterizingsurfacesoffilms,biologicalmaterials,andnanomaterials.Thedevelopmentofnanoindentorsandtheimprovedabilitytointerpretresultsfromnanoindentationmeasurementshaveincreasedourabilitytostudythemechanicalpropertiesofnanostructuredmaterials.Improvedhigh-resolutionelectronmicroscopesandmodelingoftheelectronmicroscopeimageshaveimprovedourknowledgesofthestructureofthetheparticlesandtheinterphaseregionbetweenparticlesinconsolidatednanomaterials.
Nanotechnology
1.Introduction
Whatidnanotechnology?
itisatermthatenteredintothegeneralvocabularyonlyinthelate1970’s,mainlytodescribethemetrologyassociatedwiththedevelopmentofX-ray,opticalandotherveryprecisecomponents.Wedefinednanotechnologyasthetechnologywheredimensionsandtolerancesintherange0.1~100nm(fromthesizeoftheatomtothewavelengthoflight)playacriticalrole.
Thisdefinitionistooall-embracingtobeofpracticalvaluebecauseitcouldinclude,forexample,topicsasdiverseasX-raycrystallography,atomicphysicsandindeedthewholeofchemistry.Sothefieldcoveredbynanotechnologyislaternarroweddowntomanipulationandmachiningwithinthedefineddimensionalrange(from0.1nmto100nm)bytechnologi