第一次文献报告

第一次文献报告,报告人：导师：2014年10月25日,主要内容,场发射简介,一,文献报告,二,一.场发射简介,1.场发射：是在外加电场的作用下使其表面电子发生隧穿效应，从而使电子发射到真空中的一种物理过程,2.特点：,FE显示器,X射线管,纳米玻璃,3.应用：,FE扫描电子显微镜,4.场发射理论：,电场作用下半导体表面的势垒曲线,场致电子发射是利用加在物体表面的强电场削弱阻碍电子逸出物体的力，并利用隧道效应使固体向真空发射出电子，由于外加强电场使表面势垒高度降低，宽度变窄，电子穿透势垒的几率增加，因而发射电流随之迅速增加，电子就可顺利地穿透表面势垒进入到真空。,二.文献报告,Thefirsttime,well-alignedandhigh-densityZnOnanoconearraysweresynthesizedusingasimpleandinexpensiveelectricfield-assistedchemicalbathdeposition(FECBD)method,ZnOisawidebandgapsemiconductorwithexcellentchemicalstabilityandhighexcitonbindingenergy.,ZnOnanostructuresofdifferentmorphologieswererecentlysynthesizedbyvarioustechniques,includingpulsedlaserdeposition,hydrothermalmethod,electrochemicalmethod,sonicatedsolgelimmersion,andsoon.,thecone-shapedZnOnanostructuresfabricatedbyasimpleandinexpensiveFECBDarepromisingforapplicationasfieldemission(FE)electronsources,以陶瓷氧化锌为靶材料，100、P型硅基底上，功率为100W,射频磁控溅射1小时，沉积出ZnO晶种层。将六水合硝酸锌（Zn（NO3）26H2O）和六次甲基四胺（C6H12N4）被分别溶解于去离子水中，配成等摩尔浓度的溶液，在室温下，将覆有氧化锌晶种层的硅基底和铂电极浸入溶液中分别作为阴极和阳极。控制电流密度为0.5毫安/平方厘米，电化学沉积1小时，生成ZnO纳米锥阵列，将该样品用去离子水冲洗，并在氮气中干燥。对样品进行SEM,XPD,PL表征，并检测场发射特性。,Fig.1.FE-SEMimagesoftheZnOnanorodgrowthatdifferenttemperatures.(a)55,(b)80,(c)Topview(inset:ahighmagnificationimage)and(d)Sideviewat105(inset:crystalgrowthhabitofwurtziteZnOhexagonalrod,Fig.2.(a)PLspectraand(b)XRDpatternsofZnOnanostructuresatdifferentgrowthtemperatures.,单斜晶体SnO2纳米线,Fig.3.FEcharacteristicsofcone-shapedZnOnanorads(a)JEplot(inset:FNplot)(b)Stabilityoftheemissioncurrent,k=,=2654,(1)FE-SEManalysisshowedthatthecone-shapedZnOnanorodswerepreparedusingtheelectrochemicalmethodat105,(2)Thecone-likeZnOnanorodsexhibitedexcellentFEproperties,withaturn-onelectricfieldof3.2V/m,alargefield-enhancementfactorof2654,andgoodFEstability,ThealignedSnO2nanotubearraysonSisubstratehavebeenpreparedvialiquid-phasedepositionwiththesolutionsystemofSnF2utilizingZnOnanorodarraysassacrificialtemplate.TheSnO2nanotubesaredistributeduniformlyandgrownperpendicularlytothesubstrate,SnO2isann-typesemiconductingoxidewithawideband-gap(Eg=3.6eV),theSnO2nanotubes(SnNTs)withhighsurface-to-volumeratiosaresuggestedtobeidealobjectsforthenanodevicesusedinphotoelectronicfields,(2)AvarietyofefficientsyntheticstrategieshavebeenreportedtofabricateSnO2nanotubes,suchaschemicalvapordepositionsolidvaporgrowthandtemplate-assistedsynthesis,(3)However,theSnO2nanotubespreparedbytheabovementionedmethodswerenormallyfreestanding,whicharedifficultfordirectlyusinginnanodevices.,(4)TheSnNTswerefabricatedbytwo-stepmethodusingZnOnanorodarraysasthesacrificialtemplates.,利用磁控溅射在硅基底上沉积10nm厚的ZnO晶种层。将硅基底浸入等摩尔的（0.025M）二水合醋酸锌与六亚甲基四水溶液，置于内衬为聚四氟乙烯的不锈钢高压釜中，95下水热反应4h，生成ZnO纳米棒阵列。室温下，将ZnO模板浸入（0.0075M）SnF2溶液中液相沉积4h，将该样品用去离子水冲洗，在600下焙烧2h，得到SnO2纳米管阵列。对样品进行SEM,XPD,TEM,EDX,拉曼表征，并检测场发射特性。,Fig.1.(a)Plain-viewand(b)cross-sectionSEMimagesofZnOnanorodarraystemplates,ThehighlyalignedanddenseZnOnanorodarraysweregrownonSisubstrate.Thesenanorodshavenearlyuniformlengthsof1.5mwithadiameterregionof150280nm,Fig.1(c)plain-viewand(d)cross-sectionSEMimagesofSnNTsonSisubstrate,theend-cappedSnNTsarefoundwithanaveragelengthof1.3mandoutsidediametersof190310nm,Fig.1(e)EDXspectrumofSnNTs,(f)XRDpatternsofSnNTs(up)andZnOnanorods(bottom)onSisubstrate,Fig.2.TEMimagesof(a)aZnOnanorod,(b)SnO2nanotubes.Theinsetsaretheassociatedselectedareaelectrondiffractionpatterns,theZnOnanorodsaresinglecrystalgrowingalongthe(0001)axis，andtheSnO2sampleshaveatubularandend-closedstructurewithawallthicknessof45nm,Theaveragegrainsizeis6.5nmforSnO2nanotubes,estimatedfromthe(110)peakbyScherrerformula:d=0.89/Dcos,thedissolutionrateofZnOishigherthanthatoftheSnO2formationintheinitialstage,andconsequently,thelengt(1.3m)ofSnNTsbecomesshorterthanthatoftheoriginalZnOnanorods(length:1.5m),Fig.4.(a)UVvisabsorptionspectrumoftheSnNTsonSisubstrate.Theinsetisthecorrespondingplotof(hv)2versusphotonenergy,hv=D(hv-Eg)1/2theopticalabsorptioncoefficient()andthebandgapenergy(Eg),hisPlancksconstant,isthefrequencyoftheincidentphoton,Disconstant,Eg=3.850.05eV，ThiscanbeattributedtothelargeraveragesizeofthegrainsofSnNTs(6.5nm)thantheexcitonBohrradiusof2.7nmforSnO2,(b)Field-emission(FE)currentdensityofSnNTsonSisubstrateasafunctionoftheappliedelectronicfield.TheinsetshowsthecorrespondingFNplot,TheFNplotisapproximatelylinearathigh-appliedfields,indicatingthattheemittingelectronsmainlyresultfrombarriertunnelingelectronsextractedbytheelectricfield,Theturn-onelectricfield(definedastheEcorrespondingtotheJof0.75Acm-2)isestimatedtobe5.4Vcm-1,UtilizingZnOnanorodarraysasasacrificialtemplatetoobtainalignedSnNTs，theFEpropertyissuperiortothoseofthereportedSnO2nanorodsandnanowiresThereasonfortheefficientFEpropertyismainlyduetoalignedstructure,goodelectricalcontactwiththeconductingsubstrate,andweakerfield-screeningeffect,Anovelthree-dimensional(3D)prickly-likeSnO2nanostructurehasbeeneffectivelysynthesizedbyahydrothermalmethod.Thefield-emissionpropertiesofprickly-likeSnO2nanostructureshavebeenmeasuredtoexhibitalowerturn-onelectricfieldof0.87V/m,thresholdelectricfieldof1.2Vm.,配制15ml的蒸馏水和甲醇（3:2）溶液，将5mg的SnCl22H2O加入15ml的人溶液中，磁力搅拌2h。然后再加入5ml氨水修改溶液的pH值，搅拌1h，之后，通过离心机收集该混合物并用水洗涤。将混合物分散在约20毫升水中，然后把该溶液密封在60毫升聚四氟乙烯内衬的不锈钢高压釜中，在180下水热反应12小时，离心收集产物，用水洗涤并冻干。作为对照，用相同的方法不加氨水溶液合成二氧化锡纳米棒。,Fig.1.SEMimagesofprickly-likeSnO2nanostructuresatalowmagnification(a),highmagnification(b,Eachofprickly-likenanostructuresconsistsoftheSnO2nanosheetandarrayedSnO2shortrodshapes.ThesearrayedSnO2shortrodsappeartobenearlyuniforminsize.TheSnO2shortrodshavediametersof20-30nmandlengthsupto30-50nm.TheseSnO2shortrodsgrownearlyuniformlyonbothupperandlowersurfacesoftheSnO2sheets.SnO2nanorodsalsohaveaverysharptipwherethediameteris10-20nm,XRD(c),andEDX(d)patternsofprickly-likeSnO2nanostructures,Allthediffractionpeaksatdifferent2-thetadegreevaluescanbeindexedtoatetragonalrutile-likeSnO2withlatticeconstantsofA=0.4742nmandC=0.3182nm,consistentwiththestandarddata.EDXresultsrevealthatthestructureconsistsofSnandOelements,Theobservedvibrationpeakslocatedat116,134,and163cm-1correspondtoEg,A1g,andB2gvibrationmodes,respectively.TheresultsareingoodagreementwiththoseoftherutilecrystalofSnO2structures,Fig.3.Field-emissionpropertiesofprickly-likeSnO2nanostructures,(a)currentdensitiesvs.theappliedelectricfields,theemissioncurrentdensityofthesamplesincreasesmonotonicallywiththeappliedfield.Theprickly-likeSnO2nanostructurefilmrequiresamuchlowerdrivingelectricfieldthantheSnO2nanorodsTheturnonfieldEtooftheprickly-likeSnO2nanostructuresandSnO2nanorodsoccursat0.87,and1.2Vm-1,comparedwiththeSnO2nanorodsandotherSnO2nanostructures14-19,theturn-onfieldvaluefortheprickly-likeSnO2nanostructuresisfoundtobelower,indicatingthattheprickly-likeSnO2nanostructureisabletogeneratehigherfield-emissioncurrentatlowervoltages.,(b)Fowler-Nordheimplotsofthefieldemissioncurrentdensities,thefieldenhancementfactorofprickly-likeSnO2nanostructuresandSnO