氧化锌纳米棒阵列的生长.docx
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氧化锌纳米棒阵列的生长
AlignedZnONanorodArraysGrownDirectlyonZincFoilsandZincSpheresbyaLow-TemperatureOxidizationMethod
用低温氧化方法直接在锌箔和锌颗粒培养排列有序的氧化锌纳米棒阵列
ABSTRACTVerticallyaligned,denseZnOnanorodarraysweregrowndirectlyonzincfoilsbyacatalyst-free,
low-temperature(450_500°C)oxidizationmethod.ThezincfoilsremainconductiveevenafterthegrowthofZnO
nanorodsonitssurface.Thesuccessofthissynthesislargelyreliesonthelevelofcontroloveroxygenintroduction.
Byreplacingzincfoilswithzincmicrospheres,uniqueandsophisticatedurchin-likeZnOnanorodassembliescanbereadilyobtained.
摘要
垂直有序密排的氧化锌纳米棒阵列直接通过无催化剂,低温(450~500°C)氧化法在锌箔上生长。
在氧化锌纳米棒生长在它表面上后,锌箔仍然具有导电性。
合成能够成功在很大程度上依赖于对引导氧气控制程度。
通过将锌箔更换成锌微球,独特和复杂的海胆样氧化锌纳米棒组件很容易获得。
Zincoxide(ZnO)isrecognizedasone
ofthemostimportantphotonicmaterials
forapplicationsintheblue_ultravioletregionowingtoitsdirect
widebandgap(_3.37eV)andlargeexcitation
bindingenergy(60meVatroom
temperature).Stimulatedbytherecent
discoveryofbeltlikemorphologyandthe
realizationofroom-temperatureUVlasing
fromZnOnanowires,ZnOnanostructures
intheformofnanorods,nanowires,and
nanobeltshaveattractedagreatdealofattention
fromtheresearchcommunity.
Especially,
substantialefforthasbeendevoted
tothefabricationofverticallyalignedZnO
nanowirearraysbecausethesearraysdemonstrated
superioropticalandfieldemission
propertiesthatmakethempromising
candidatesforapplicationsinUVlasers,
light-emittingdiodes(LED),solarcells,
andfieldemissiondisplays.
TofabricateverticallyalignedZnOnanorod
arrays,threemaintechniqueswereusually
usedsofar.Thefirsttechniqueisbased
onthewell-knownvapor_liquid_solid
(VLS)growthmechanism,10inwhichgold
nanoparticleswereusedasthecatalystto
directthenanowiregrowth,a-planesapphire
whichhasperfect
latticematchup
withZnOcplanewas
usedasthegrowth
substrates,andthe
growthwasconducted
atrelatively
hightemperaturesof
由于其直宽禁带和大的激励结合能,氧化锌是公认的应用于蓝紫外地区最重要的光子材料之一,由于带状形态发现的促进和室温紫外激光发射的实现,氧化锌纳米线,以纳米棒,纳米线,和纳米带形式存在的纳米氧化锌吸引了研究机构大量的注意力。
尤其是,大量努力已投入垂直有序排列的氧化锌纳米线阵列的制备中,因为这些阵列显示优越的光学和场发射性能,使他们有望应用于紫外激光器,发光二极管(发光二极管),太阳能电池,和led。
为了制造垂直有序排列氧化锌纳米棒阵列,至今为止三个主要的技术通常被
使用。
第一种技术是在著名的气液固增长机制,其中黄金纳米粒子被用作催化剂引导纳米线的生长,蓝宝石状晶面具有完美的晶格匹配,它用氧化锌晶面被用作生长基质,并且生长在相对温度高850_1000°c的情况下进行
Thesecondtechnique
ismetal_
organicchemicalvapor
deposition
(MOCVD),inwhich
metal_organiczinc
precursor(diethylzinc,
Et2Zn)wasusedasthe
zincsourceand
alignedZnOnanowires
wereepitaxially
substrates(orsiliconwafers)at400_500°Cinalowpressure
MOCVDsystem.13_15第二种方法是金属有机化学气相沉积,其中金属有机锌前体被用作锌源,有序排列的纳米氧化锌在400~500°时在低压有机金属化学气相沉积技术培养基(或硅晶片)外延生长
Thethirdtechniqueis
basedonsolutionmethod,inwhichZnOnanocrystals
(5_10nmindiameter)werecoatedonasubstrate(e.g.,
siliconwafer)toactastheseedsfollowedbyhydrothermal
ZnOgrowthinanaqueoussolutionofzincnitrate
hydrateat90°C.Thesolutionprocessisfavoredfor
itslowcostandtheeaseofscale-up(arraysonfourinch
siliconwaferandtwo-inchplasticsubstrateswere
reported17)butsuffersfromthelowcrystallinequality
comparedwiththeVLS-andMOCVD-grownnanowires.
Inaddition,someelectricalandopticalapplicationsof
theabove-mentionedZnOnanowiresremainconstrained
bytheexpensiveand/ornonconductingsubstrates
(suchassapphire).
Inthispaper,wereportthecontrolledgrowthofvertically
alignedZnOnanorodarraysonmetalzincfoils
(10cmlongby1cmwide)byacatalyst-free,lowtemperature
(450_500°C)oxidizationmethod.More
amazingly,bysubstitutingtheflatzincfoilswithhighly
curvedzincmicrospheres,sophisticatedurchin-like
ZnOnanorodsuperstructures,suchasZnOnanorod
balls/bowlswhosesurfaceswerecoveredwithdense,
uniformZnOnanorods,canbereadilyobtained.
第三种是基于溶液的方法,其中纳米氧化锌(5_10纳米直径)被涂覆在衬底(例如,硅晶片)来充当种子,随后在90°c时将水热氧化锌生长在锌盐水合物溶液中.溶液生长过程成本低,易于规模化(报道的四英寸硅晶片阵列和2寸塑料衬底)备受青睐,但与气液固和金属有机化学沉积法制造的纳米线相比,其结晶度低。
此外,上述提及的的氧化锌纳米线一些在电光学上的应用仍然是受昂贵和/或不导电衬底制约(如蓝宝石)。
在本文中,我们报告了,通过无催化剂,低温(450_500°丙)氧化法,在金属锌箔(10厘米长1厘米宽)上,可控制生长垂直排列氧化锌纳米棒阵列的方法
令人惊讶的是,用曲率高的的锌微球,复杂的海胆样氧化锌纳米棒的超结构,如表面覆盖着致密均匀氧化锌纳米棒氧化锌纳米棒球/碗,取代平面锌箔可以很容易获得。
Thegrowthwasconductedinsideatubefurnace
system(Figure1).Zincpowderwasusedasthesource
materialandzincfoils(orzincmicrospheres)wereused
asthegrowthsubstrates.Toensurethesuccessofthe
synthesis,theintroductionofoxygenneedstobecarefully
controlled.生长过程是在管式炉系统中进行(图1)。
锌粉末用作源材料。
锌箔(或锌微球)被用来作为生长基质。
为确保合成成功,氧的引入需要小心控制。
Theissuesrelatedtooxygenintroduction
include(i)thepositionoftheoxygentube,(ii)the
oxygenflowrate,and(iii)thetimewhentheoxygenis
introduced,whichcanbesummarizedasfollows.
氧引入相关的问题包括
(一)氧气管的位置,
(二)氧气流量,(三)氧气导入时间,这可概括如下
First,theoutletoftheoxygentubeshouldbepositioned
downstreamofthesourcezincpowderbutright
abovethemiddleofthezincfoil.Thisavoidstheoxidization
ofzincpowder,whilegeneratinganefficient,
wideoxidizingregionoverthezincfoiltofacilitatethe
ZnOnanorodgrowth.
Second,theoxygengasflowrateneedstobecontrolled
below5sccm(standardcubiccentimeterper
minute).Iftheoxygenflowrateistoohigh,theconcentration
ofreactantspeciesinthevaporwillbesohigh
thatathicklayerofbyproduct(suchasrandomZnO
nanorods,ZnOtetrapods,20orZnOnanocombs21,22)will
bedepositedonthesurfaceofthenanorodarrays.
Theoptimumoxygenflowrateswerefoundtobein
therangeof3_5sccm.
Third,theoxygengasneedstobeintroducedas
soonasthefurnacetemperaturereaches600°C.At
thistemperaturethezincpowderlocatedatthefurnace
centercanbeefficientlyevaporatedtofeedthe
ZnOnanorodgrowth.Becauseofthetemperaturegradient
ofthefurnace,thetemperatureinthegrowthregion
wasmeasuredtobeabout450_500°C,atwhich3
结果与讨论
第一,氧气管出口应定位在锌粉源下游但锌箔的中等以上。
这避免了氧化锌粉的氧化,而在氧化锌箔上产生一个有效的宽区以促进氧化锌纳米棒生长。
其次,氧气流量需要被控制低于5sccm。
如果氧气流量太高,在蒸气反应物浓度会很高以至于产生
一层厚厚的副产品将沉积纳米棒阵列的表面上。
最佳氧流量被认为是在3~5的范围。
第三,当温度达到600℃时°氧气需要迅速引入炉内这个温度在位于炉中心锌粉可以很快的被蒸发掉,以支持氧化锌纳米棒生长。
因为该炉温度梯度,在生长区测量温度约为450_500°C,在图三中可以观察到。
pointthesurfaceofthezincfoil(orzincballs)wasin
themeltingstateandthuscanbeimmediatelyoxidized
byoxygentoformathinlayer(1_mthick)ofdense
ZnOnanopillars(Figure2).LiketheZnOnanocrystal
seedsusedinsolutionmethod,17theZnOnanopillars
formedatthisinitialgrowthstagearebelievedtoact
astheseedsforsubsequentnanorodgrowth.Thisassumption
wasverifiedbythefollowingtwofacts.
(i)锌箔表面上的点(或锌球)是在熔融状态,因此可以立即在氧化锌表面形成薄薄的一层致密的(1m密厚)氧化锌奈米柱(图2)。
如在溶液法中氧化锌纳米晶体种子,在这个初期增长阶段形成的氧化锌奈米柱当做随后纳米棒生长的种子。
这一假设由以下两点验证。
Whensiliconwafersoraluminaplateswereusedasthe
substrates,onlyrandomZnOnanorodsweredeposited
onthesubstratesurfaces(inanrecentreportby
Shenetal.)quasi-alignedZnOnanonailsandnanopencils
weregrownonsiliconwafersurfacebyheating
zincpowderat600_700°Cinatubefurnacesystem,
wheretheoxygenwasprobablyfromthesystemleaking).
(ii)Whennoexternalzincsourcewasprovided,the
thicknessoftheZnOnanopillarskeptat_1_mregardless
ofthegrowthtime.
当硅片或氧化铝板被用作衬底,只有随机氧化锌纳米棒沉积在衬底表面(据沈等人最近报告,通过在600~700°C碳管炉系统中加热锌粉,准定向排列氧化锌钉和纳米笔生长在硅晶片表面,那里的氧气可能是从系统泄漏)。
ThelaterfactalsoindicatesthattheZnOnanocrystalthinlayerisseamlesslyformed
andfirmlyattachedtothezincfoilsurface,whichprotects
innerzincfrombeingevaporatedandoxidized
duringthenanorodgrowthprocess.随后的现象说明氧化锌纳米晶体薄层是无缝生成的并紧紧地贴在锌箔表面,这可以保护内部的锌免受蒸发和氧化。
Indeed,whenthefoilisintentionallybrokenafter10_30mingrowth,unreacted
metalzinclayercanbeeasilyseen.事实上,在经过10_30分钟的生长后箔会被有意的损坏,没有反应的金属锌层能够清晰的看见。
Afterthegrowth,thesurfaceofthe10cm_1cm
zincfoilwascoveredwithathinwhite-graylayer.X-ray
diffraction(XRD)analysis(Figure3)showsthatthedeposit
iswurtzite(hexagonal)-structuredZnOwithlattice
constantsofa_3.249andc_5.206Å(JCPDScard
No.35-1451).生长后,距其表面10厘米_1厘米表面锌箔被一层薄薄的白灰色覆盖了。
X射线衍射(X射线衍射)分析(图3)显示,沉积的(六)纤锌矿结构氧化锌晶格常数是,A=3.249和c=5.206(JCPDS卡片第35-1451)。
Thestrongintensityofthe(002)peakindicates
thattheZnOstructurehasapreferentialgrowth
directionalongthec-axisorientation.
Scanningelectronmicroscopy(SEM)observations
revealthattheentiresubstratesurfaceiscoveredwith
dense,highlyalignedZnOnanorodswithgrowthdirection
perpendiculartothesubstratesurface(Figures4).
Becauseofthedifferencesintemperature(from500°
to450°C)andoxygenconcentration(fromlowtohigh)
fromtheleftendtotherightendofthezincfoil,the
morphologiesandsizesoftheas-synthesizedZnO
nanorodsacrossthe10cmlongfoilvarygradually.
高强度的(002)峰表明该氧化锌的结构沿c轴方向择优生长。
扫描电子显微镜(扫描电镜)观察显示,整个衬底表面被垂直于衬底表面生长方向(图4)密集,高度定向氧化锌纳米棒所覆盖。
因为温度不同(从500°450°丙)和从左到右端锌箔的氧浓度(从低到高),在长10厘米箔上合成的氧化锌纳米棒的形态和大小变化缓慢。
Althoughthereisnoapparentboundarybetweenadjacentregions,fourdistinctivedepositionzonescanbeidentifiedonthebasisofthemorphologiesandsizesof
thenanorods,asthatlabeledinFigure4a.虽然在相邻的区域没有明显的界限,四个不同的沉积区域可以凭借纳米棒形态尺寸上的差异区分开来,如图四所示.Fromthe
leftendtotherightend,themorphologiesoftheproducts
changefromnanoneedles(zone1;Figure4b),to
uniformnanorods(zone2;Figure4c,d),nanonails(zone
3;Figure4e),andfinallymicronails(zone4;Figure4f,g).
Whilethelengthsofthenanorodsformedindifferent
zonesarealmostthesame(_5_m),theaveragediameters
ofthenanorodsincreasesignificantlyfromabout
50nmofthenanoneedles(Figure4b)toabout200nm
oftheuniformnanorods(Figure4d)andnanonails(Figure
4e),andtoabout500nmofthemicronails(Figure
4f,g;thediametersofthenailcapsare