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不需要加热，低能耗时间没有迟滞发射电流稳定方向性和单色性好易于小型化和集成化高的电流密度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HighlightsThefirsttime,well-alignedandhigh-densityZnOnanoconearraysweresynthesizedusingasimpleandinexpensiveelectricfield-assistedchemicalbathdeposition(FECBD)methodIntroductionZnOisawidebandgapsemiconductorwithexcellentchemicalstabilityandhighexcitonbindingenergy.ZnOnanostructuresofdifferentmorphologieswererecentlysynthesizedbyvarioustechniques,includingpulsedlaserdeposition,hydrothermalmethod,electrochemicalmethod,sonicatedsol–gelimmersion,andsoon.thecone-shapedZnOnanostructuresfabricatedbyasimpleandinexpensiveFECBDarepromisingforapplicationasfieldemission(FE)electronsourcesExperimental(1)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。(2)将六水合硝酸锌（Zn（NO3）2·6H2O）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。(3)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。(4)对样品进行SEM,XPD,PL表征，并检测场发射特性。ResultsanddiscussionFig.1.FE-SEMimagesoftheZnOnanorodgrowthatdifferenttemperatures.(a)55℃,(b)80℃,(c)Topview(inset:ahighmagnificationimage)and(d)Sideviewat105℃(inset:crystalgrowthhabitofwurtziteZnOhexagonalrodFig.2.(a)PLspectraand(b)XRDpatternsofZnOnanostructuresatdifferentgrowthtemperatures.单斜晶体SnO2纳米线Fig.3.FEcharacteristicsofcone-shapedZnOnanorads(a)J–Eplot(inset:F–Nplot)(b)Stabilityoftheemissioncurrentk=β=2654Conclusion(1)FE-SEManalysisshowedthatthecone-shapedZnOnanorodswerepreparedusingtheelectrochemicalmethodat105℃(2)Thecone-likeZnOnanorodsexhibitedexcellentFEproperties,withaturn-onelectricfieldof3.2V/μm,alargefield-enhancementfactorof2654,andgoodFEstabilityHighlightsThealignedSnO2nanotubearraysonSisubstratehavebeenpreparedvialiquid-phasedepositionwiththesolutionsystemofSnF2utilizingZnOnanorodarraysassacrificialtemplate.TheSnO2nanotubesaredistributeduniformlyandgrownperpendicularlytothesubstrateIntroduction(1)SnO2isann-typesemiconductingoxidewithawideband-gap(Eg=3.6eV),theSnO2nanotubes(SnNTs)withhighsurface-to-volumeratiosaresuggestedtobeidealobjectsforthenanodevicesusedinphotoelectronicfields(2)AvarietyofefficientsyntheticstrategieshavebeenreportedtofabricateSnO2nanotubes,suchaschemicalvapordepositionsolid–vaporgrowthandtemplate-assistedsynthesis(3)However,theSnO2nanotubespreparedbytheabovementionedmethodswerenormallyfreestanding,whicharedifficultfordirectlyusinginnanodevices.(4)TheSnNTswerefabricatedbytwo-stepmethodusingZnOnanorodarraysasthesacrificialtemplates.Experimental(1)利用磁控溅射在硅基底上沉积10nm厚的ZnO晶种层。(2)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。(3)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。(4)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-sectionSEMimagesofZnOnanorodarraystemplatesThehighlyalignedanddenseZnOnanorodarraysweregrownonSisubstrate.Thesenanorodshavenearlyuniformlengthsof1.5μmwithadiameterregionof150–280nmFig.1(c)plain-viewand(d)cross-sectionSEMimagesofSnNTsonSisubstratetheend-cappedSnNTsarefoundwithanaveragelengthof1.3μmandoutsidediametersof190–310nmFig.1(e)EDXspectrumofSnNTs,(f)XRDpatternsofSnNTs(up)andZnOnanorods(bottom)onSisubstrateFig.2.TEMimagesof(a)aZnOnanorod,(b)SnO2nanotubes.TheinsetsaretheassociatedselectedareaelectrondiffractionpatternstheZnOnanorodsaresinglecrystalgrowingalongthe(0001)axis，andtheSnO2sampleshaveatubularandend-closedstructurewithawallthicknessof45nm,Theaveragegrainsizeis6.5nmforSnO2nanotubes,estimatedfromthe(110)peakbyScherrerformula:d=0.89λ/DcosθthedissolutionrateofZnOishigherthanthatoftheSnO2formationintheinitialstage,andconsequently,thelengt(1.3μm)ofSnNTsbecomesshorterthanthatoftheoriginalZnOnanorods(length:1.5μm)Fig.4.(a)UV–visabsorptionspectrumoftheSnNTsonSisubstrate.Theinsetisthecorrespondingplotof(hv)2versusphotonenergyαhv=D(hv-Eg)1/2theopticalabsorptioncoefficient(α)andthebandgapenergy(Eg),hisPlanck'sconstant,υisthefrequencyoftheincidentphoton,DisconstantEg=3.85±0.05eV，ThiscanbeattributedtothelargeraveragesizeofthegrainsofSnNTs(6.5nm)thantheexcitonBohrradiusof2.7nmforSnO2(b)Field-emission(FE)currentdensityofSnNTsonSisubstrateasafunctionoftheappliedelectronicfield.TheinsetshowsthecorrespondingF–NplotTheF–Nplotisapproximatelylinearathigh-appliedfields,indicatingthattheemittingelectronsmainlyresultfrombarriertunnelingelectronsextractedbytheelectricfield,Theturn-onelectricfield(definedastheEcorrespondingtotheJof0.75μAcm-2)isestimatedtobe5.4Vcm-1ConclusionsUtilizingZnOnanorodarraysasasacrificialtemplatetoobtainalignedSnNTs，theFEpropertyissuperiortothoseofthereportedSnO2nanorodsandnanowiresThereasonfortheefficientFEpropertyismainlyduetoalignedstructure,goodelectricalcontactwiththeconductingsubstrate,andweakerfield-screeningeffectHighlightsAnovelthree-dimensional(3D)prickly-likeSnO2nanostructurehasbeeneffectivelysynthesizedbyahydrothermalmethod.