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An In-Plane Solid-Liquid-Solid Growth Mode for Self-Avoiding Lateral

An In-Plane Solid-Liquid-Solid Growth Mode for Self-Avoiding Lateral Silicon Nanowires Linwei Yu,1Pierre-Jean Alet,1,2Gennaro Picardi,1and Pere Roca i Cabarrocas1

1Laboratoire de Physique des Interfaces et des Couches Minces(LPICM),E′cole Polytechnique,CNRS,91128Palaiseau,France 2CEA,DSM,IRAMIS,SPCSI,Laboratoire de chimie des surfaces et interfaces(LCSI),

Centre de Saclay,91191Gif-sur-Yvette cedex,France

(Received11October2008;published23March2009)

We report an in-plane solid-liquid-solid(IPSLS)mode for obtaining self-avoiding lateral silicon

nanowires(SiNW)in a reacting-gas-free annealing process,where the growth of SiNWs is guided by

liquid indium drops that transform the surrounding a-Si:H matrix into crystalline SiNWs.The SiNWs can

be$mm long,with the smallest diameter down to$22nm.A high growth rate of>102nm=s and rich

evolution dynamics are revealed in a real-time in situ scanning electron microscopy observation.A

qualitative growth model is proposed to account for the major features of this IPSLS SiNW growth mode.

DOI:10.1103/PhysRevLett.102.125501PACS numbers:81.07.Vb,61.46.Km,62.23.Hj,81.16.Dn

One dimensional(1D)semiconductor nanowire struc-tures,with novel electronic,optical,and thermal properties [1,2],are key functional elements for promising applica-tions like nanowire transistors[3],biosensors[4],light emitting[5]and energy harvesting units[6,7].Si nano-wires(SiNW),compatible with the established Si technol-ogy,can be obtained in vertical arrays or bundles via various growth mechanisms like the vapor-liquid-solid (VLS)[8],the solution-liquid-solid[9],the oxide-assisted-growth[10],and the nickel-catalyzed solid-liquid-solid SiNW[11].

The electrical accessibility to SiNWs is one of the most critical issues for SiNW-based device applications[3,4], and in this respect the assembling and connection of SiNWs to prede?ned electrodes is a formidable challenge for large-scale integration of SiNW-based devices. Basically,the main dif?culty in large-scale integration of SiNW-based devices is the incompatibility between the 3D VLS growth mode of SiNWs and the2D planar device architecture,which necessitates an extra rearrangement or manipulation step to integrate vertical SiNWs into a2D layout.From this point of view,a well-controlled in-plane growth of lateral SiNWs with natural connections to pre-designed electrodes could represent an ultimate solution to a planar-architecture-compatible SiNWs-based device integration.

We have discovered an in-plane solid-liquid-solid (IPSLS)growth mode for such lateral SiNWs,where a liquid catalytic indium drop leads their in-plane growth by consuming and transforming surrounding a-Si:H into crystalline SiNW.Indium drops were?rst formed by a H2 plasma treatment on top of a ITO substrate,[12]and then covered by a thin a-Si:H layer.The growth of lateral SiNWs is activated and sustained in a reactive-gas-free low temperature thermal annealing process.All this pro-cess is realized in situ,which avoids the potential oxidation or contamination.The rich growth dynamics of this IPSLS mode SiNW is revealed in a real-time in situ scanning electron microscopy(SEM)observation.

As shown in Figs.1(a)–1(d),the ITO layer on Corning

glass was?rstly treated by using H2plasma in a plasma

enhanced chemical vapor deposition(PECVD)system to

form indium drops on the surface.The typical values for

substrate temperature,treatment time,?ow rate,chamber pressure and rf power density are300 C,5–10min, 100sccm,600mTorr,and$53mW=cm2,respectively.

Then,the substrate with indium drops on top was covered

by a layer of hydrogenated amorphous silicon(a-Si:H,15–

60nm)deposited at100–200 C.Finally,the sample was annealed in vacuum($10à6mbar)at a temperature rang-ing between300–500 C for activating the growth of lat-eral SiNWs.

Figure2(a)shows a typical SEM(Hitachi S4800)image

of the as-grown lateral SiNWs after thermal annealing at 400 C for15h,where the indium drops(the bright spots at the end of the SiNWs)lead the growth of the lateral SiNWs,with typical length of around$20 m.A close side view of a speci?c SiNW,as presented in Fig.2(b), reveals that the SiNW,with a height of3–4times the a-Si:H thickness,sits in a wider‘‘trench’’,which is formed by the catalyst drop.The self-avoiding phenomenon as witnessed in Fig.2(a)can be understood as a consequence of the a-Si:H in the trench region being completely ab-sorbed(or greatly thinned)by the catalyst drop.This interrupts the continuous supply of a-Si:H for the growth of SiNW and thus prevents the crossing of lateral SiNWs. According to the dimensions indicated in Fig.2(b),the cross sectional area of the produced SiNW is roughly85% of that of the trench,which could be due to(i)the volume contraction between amorphous and crystalline silicon, V c=V a,[13]and(ii)the loss of hydrogen from the a-Si:H?lm(which is$10%at.in our case)during the transformation.The smallest IPSLS SiNWs observed so far in our experiment are$22nm in diameter,as shown in Fig.2(c),while lengths up to1mm have been achieved. The crystallinity of the lateral SiNWs was con?rmed by using a confocal back-scattering Raman setup(Labram HR800from Horiba Jobin-Yvon)with633nm laser

exci-

tation(incident at70 )optically coupled to an atomic force

microscope(AFM,XE-100PSIA).A contact mode AFM

image of a SiNW segment is shown in Fig.3(a),with the

corresponding Raman signal intensity mapping on the

same region in Fig.3(b).Pixel color represents the inten-

sity of the Raman signal integrated in the range521?5cmà1,the central position corresponding to the c-Si?rst order phonon band.As shown,the contour of the Raman

mapping in Fig.3(b),which is a convolution of the laser

spot size($2 m)and the real morphology of SiNW,

coincides well with the shape of the SiNW.

This reacting-gas-free IPSLS growth mode enables a

real-time in situ observation of the growth of SiNWs in a

SEM system(FEI Quanta600F)equipped with a heating

stage.The H2plasma treatment and a-Si:H covering pro-cesses were?rst done in a PECVD system,and then the sample was transferred to a heating stage in the SEM chamber for real-time characterization.Figures4(a)–4(f) show a series of six frames captured in sequential order from a real-time observation of a SiNW,which is activated by thermal annealing at$500 C and guided by a running indium drop that keeps absorbing and transforming the a-Si:H matrix into crystalline SiNW behind.A close scru-

tiny of the frame series reveals a rich growth dynamics, which arises from the interplay between the front In=a-Si:H interface(at speed v ma)and the rear SiNW=In interface(at speed v cm).Speci?cally,the SiNW=In inter-face is found to be moving slightly faster than the In=a-Si:H interface(v cm>v ma),which leads to a two-step response of the liquid catalyst drop:?rst,the drop is gradually squeezed by the faster-moving SiNW

from FIG.2(color online).(a)A typical SEM image of the lateral SiNWs,(b)a side-view of a SiNW sitting in a trench structure in the a-Si:H matrix,and(c)one of the smallest lateral

SiNWs.

FIG.3(color online).(a)AFM image of a single SiNW with vertical scale from black to white of160nm,and(b)its corresponding crystalline Si Raman peak signal mapping(inte-grated in the spectral window521?5cmà1).The inset in (a)shows the Raman spectrum recorded from the position marked with an x in(b).

FIG.1(color online).(a)–(d)the basic experimental procedure for the growth of IPSLS SiNWs;(e)illustrates the IPSLS growth mode of SiNW,with J out Si(J in Si),R m,L m,R SiNW and H a,the?ux of Si atoms from In drop to SiNW(from a-Si:H into In drop),the cross section and length of the In catalyst drop,the cross section of SiNW and the thickness of a-Si:H layer,respectively.(f)and (g)depict two possible situations for the actual absorbed a-Si:H thickness(H?a).(h)illustrates the origin of the drawing force at the imbalanced triple phase line due to continuous absorption at the In=a-Si:H interface.

behind and deforms into a half spherical shape [Figs.4(a)–4(d)];then,it comes to a rapid change of moving direction and restores a spherical shape [Fig.4(e)].The details of the quick restoration process seem to be driven by the surface tension of the liquid drop to restore a more energetically favorable shape.This dynamic process repeats periodically during the growth to counteract the speed mismatch of the two interfaces and produces a bending trajectory of the as-produced SiNW [Fig.4(f)].According to the experimental observation,the diameter of the SiNWs R SiNW is roughly proportional to the lateral cross section size of the catalyst

drops R m ,with f R 2SiNW =R 2m %0:045?0:015being de-termined by the contact angle between SiNW and catalyst.

Note that this periodic deformation/restoration of the cata-lyst drop also causes the surface corrugations on the SiNWs surface and trench sides.

The opposite case of v cm

Before a more detailed discussion of the dynamic be-havior,it is interesting to make a comparison with the well-known VLS process.Similarly,the growth of IPSLS SiNW also consists of three steps:(i)the Si atoms are absorbed from the a -Si:H matrix at the front interface;then,(ii)the Si atoms diffuse across the catalyst drop and (iii)de-posit at the SiNW =In interface.From an energetic point of view,the major driving force comes from the Gibbs energy difference between the crystalline and amor-phous Si phases,which is about áE Si ?E a Si àE c Si ?

0:12–0:15eV =atom [14,15].In contrast to the VLS mode

where the growth is basically ‘‘friction-free’’,the catalyst drop in IPSLS mode has to overcome an extra friction between the liquid drop and the solid substrate.Nevertheless,the typical growth rate observed here,ac-cording to Figs.4(a)–4(d)and 4(f),is as high as v ?1:2?102nm =s at 500 C ,which is almost 2orders of magnitude higher than the highest growth rate of 3–4nm =s (at 600 C )achieved in our previous study of the In-catalyzed vertical VLS SiNWs.This much higher growth rate in the IPSLS mode can be related to the fact that the catalyst drop in IPSLS mode is in direct contact with a solid state a -Si:H precursor,with a 106–107higher density than that achiev-able in gas phase.This guarantees a high in?ux rate of Si

atoms (J in

)into the catalyst.Moreover,the absorption of Si atoms from the a -Si:H matrix involves only the ‘‘Si-Si’’bond breaking that is energetically less demanding than the ‘‘Si-H’’bond breaking (silane decomposition)at the cata-lyst surface in VLS mode.

Note that the a -Si:H layer in the trench region could be completely or partially consumed by the catalyst drop,as indicated in Figs.1(e)and 1(f),which corresponds to the

cases of H ?a

?H a or H ?a

The typical time scale for the Si atoms diffusing through an indium drop of L m ?200–500nm is t d %L 2m =D Si ?

0:02–0:1ms (at 400 C ),with D Si %2?10à9

m 2=s the binary diffusion coef?cient of Si atom in indium [16].To sustain a growth rate of v %102nm =s (equivalent to a Si atom ?ux of J SiNW ?v= Si ,with Si the atom volume of Si),the concentration gradient áC Si across a catalyst drop of 500nm (for driving a Si atom ?ux

FIG.4.(a)–(f)a series of six frames captured in sequential order (with t ?0,1,2,4,5,47s)in a real-time in situ SEM observation.A gradual squeezing of the In drop by the SiNW behind can be clearly witnessed in (a)–(d),followed by a quick restoration

(d)–(e).

FIG.5.shows three SiNWs (A,B,and C)obtained on the same sample but with different morphologies.

J Si ?D Si áC Si =L m )can be estimated,with the continuity

condition at the SiNW =In interface J SiNW R 2SiNW ?J Si R 2

m ,to be

áC Si ?vL m f=eD Si Si T%1016at :=cm 3;

(1)

which,according to the solubility of Si in In [17],accounts for only $2%($0:3%)of the equilibrium Si concentration

C c eq ?3?10

at :=cm 3at 400 C (2?1019at =cm 3at 500 C )at the c -Si =In interface.So,the diffusion mass transport is still a quick process.

The speeds of the front In =a -Si :H interface (v cm )and the rear SiNW =In interface (v ma )are related to the absorp-tion ?ux from a -Si:H (J a -Si )and the deposition ?ux onto SiNW (J SiNW ),respectively.In a balanced condition,one obtains

S SiNW v cm % R m H ?

v ma ;(2)

with S SiNW ?R 2SiNW ?fR 2

m being the cross section area of SiNW.Thus,the relative speed of the two moving inter-faces can be de?ned as

v cm =v ma % H ?a R m f

?AH ?

a =R SiNW ;with A ? f à1=2:

(3)

As can be seen,the relative speed ratio is proportional to H ?a =R SiNW .In principle,for >1(v cm >v ma ),the grow-ing SiNW pushes the catalyst drop from behind and squeezes it,causing the swaying response of catalyst drop and producing relatively bending SiNWs,as shown in Fig.4;On the contrary for <1(v cm

To provide a qualitative test of the in?uence of ,let us examine the three SiNWs (A ,B and C )shown in Fig.5,

and compare their different absorbed a -Si:H thickness H ?

and size R SiNW .We can see that H ?a àA ?H ?a àC

>H ?

àB (since the a -Si:H in the trench of SiNW àB is only par-tially consumed)and R A SiNW %R B SiNW %80nm

SiNW %180nm ,as indicated in Fig.5.According to the ratio $H ?a =R SiNW ,the SiNW trajectory can be changed by either

reducing H ?

a or by increasing R SiNW .The ?rst case is justi?ed by the straighter trajectory of the SiNW àB ,with H ?a àB

with R B SiNW %R A SiNW and thus B < A ;The second assumption is also supported by comparing SiNWs

A and C .Indeed,we see that SiNW àC ,with H ?a àC

?H ?a àA ?H a and R C SiNW >R A

SiNW and thus C < A ,is al-most perfect straight.We suggest that this simple but useful relation indicates an effective way to tune the morphology (and even the strain state)of the IPSLS SiNWs.

We propose that the drawing force on the front catalyst =a -Si:H interface results from the imbalanced tri-

ple phase line.As illustrated in Fig.1(h),during the growth of SiNWs,the catalyst =a -Si:H interface (immersed in the catalyst)is continuously weakened as Si atoms are ab-sorbed into the indium catalyst.As a consequence,the balance in the horizontal direction between the surface/interface tensions,In/vacuum (f In ),a -Si:H =vacuum (f a Si )and In =a -Si:H (f In -a Si ),which in case of no absorption should be f In -a Si ?f a Si tf In cos ,is broken due to the ‘‘disappearing’’of f In -a Si interface tension.As a result,the triple-phase-line is drawn forward to form a new In =a -Si:H interface and to reestablish the balance,which however will soon be broken again due to the continuous absorption process.So,a drawing force will always be exerted on the triple-phase-line interface (given that the absorption is continuous).Moreover,since the bottom interface of the catalyst drop is subject to a larger friction than the top surface,it is possible that the liquid catalyst could be forced into a rolling forward movement,as indicated by the dashed blue line in Fig.1(e).

In summary,we report an in-plane solid-liquid-solid (IPSLS)growth mode of lateral SiNW obtained in an all-in situ process.The growth of SiNW is promoted by indium catalyst drops which transform the surrounding a -Si:H matrix into crystalline SiNW.An ultrahigh growth rate (>102nm =s )and rich growth dynamics are directly observed in a real-time in situ SEM observation.This IPSLS growth mode of SiNWs opens new opportunities for large-scale integration of SiNWs-based nanodevices.The authors gratefully thank Daniel Caldemaison from

Laboratoire de Me

′canique des Solides (LMS)for his help with the real-time in situ SEM

characterizations.

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图表与口诀记忆when、as、while的区别

图表与口诀记忆when、as、while的区别 1.图表与口诀前知识关键是比较主从句子的动词，看其动词的持续性。瞬间的理解成点，持续的理解成线。主从关系有：点（点点、点线），线线，线点。点：为瞬间动词，准确地称为“终止性动词”，指动词具有某种内在界限的含义，一旦达到这个界限，该动作就完成了。如come（来），一旦“到来”，该动作就不再继续下去了。瞬间动词：arrive, begin, borrow, become, buy, catch, come, die, find, go，give, graduate, join, kill, lose, leave, marry, realize… 线：为非瞬间动词，准确地称为叫“延续性动词”。包括动态动词静态动词。动态动词：live, sit, stand, study, talk, work, write… 静态动词（状态动词）：情感、看法、愿望等。Be, belong, consist, exist, feel, hate, have, hope, love, want… 兼有瞬时和非瞬时的动词：feel，look，move，run，work，write…，需要根据不同的语境判断。 2. when、as、while的区别一览表【表格说明】：第一个点或者线表示从句谓语动词的持续性特征，黑点表示从句所表示的动作持续短，为瞬间动词，线表示持续长，为非瞬间动词。1~7为主句与从句所表示的动作时间有重合，第8为主句与从句所表示的动作不是同时发生，而是有先后顺序。线线重相并发生，长线” 【主句谓语为非瞬间动词中的动态动词】【记忆：等线动，相并发生，但：【主句谓语为非瞬间动词中的静态动词】【记忆：等线动，

when,while,as的区别

一、根据从句动作的持续性来区分 1.“主短从长”型：即主句是一个短暂性的动作，而从句是一个持续性动作，此时三者都可用。如： Jim hurt his arm while [when, as] he was playing tennis. 吉姆打网球时把手臂扭了。 As [When, While] she was waiting for the train, she became very impatient. 她在等火车时，变得很不耐烦。注意：as用于引出一个持续性动词表示“在……期间”时，其谓语通常只能是那些含有动作和发展意味的动词，一般不能是那些不用于进行时态的动词(如be, seem, love, want, agree, see, know, have 等)，所以下面一句中的while不能换为as： A：I’m going to the post office. 我要去邮局。 B：While you are there, can you get me some stamps? 当你在邮局时，能帮我买几张邮票吗? 若主句与从句表示的是两个几乎同时发生的动作，含有类似汉语“刚要……就”“正要……却”的意思，英语一般要用as(也可用when)，且此时通常连用副词just。且此时，从句一般用进行时，主句用短暂性动词的一般时态。【注意与六区别】 I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住了。 Just as [when] the two men were leaving, a message arrived. 就在这两个人要离开的时候，突然有了消息。 2.“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态，且强调主句动作或状态延续到从句所指的整个时间，此时通常要用while。如： I always listen to the radio while I’m driving. 我总是一边开车一边听收音机。 He didn’t ask me in; he kept me standing at the door while he read the me ssage. 他没有让我进去，他只顾看那张条子，让我站在门口等着。但是，若主句和从句所表示的两个同时进行的动作含有“一边……一边”之意时，则习惯上要用as。如： He swung his arms as he walked. 他走路时摆动着手臂。 I couldn’t remember a story to tell the children, so I made one up as I went along. 我想不出有什么故事可给孩子讲了，只好现编现讲。 3.“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用a s或when，但不能用while。如：

while、when和as的用法区别

as when while 的区别和用法 as when while的用法一、as的意思是“正当……时候”,它既可表示一个具体的时间点，也可以表示一段时间。as可表示主句和从句的动作同时发生或同时持续，即“点点重合”“线线重合”；又可表示一个动作发生在另一个动作的持续过程中，即“点线重合”，但不能表示两个动作一前一后发生。如果主句和从句的谓语动词都表示持续性的动作，二者均可用进行时，也可以一个用进行时，一个用一般时或者都用一般时。 1、As I got on the bus，he got off. 我上车，他下车。（点点重合）两个动作都是非延续性的 2、He was writing as I was reading. 我看书时，他在写字。（线线重合）两个动作都是延续性的 3、The students were talking as the teacher came in. 老师进来时，学生们正在讲话。（点线重合）前一个动作是延续性的，而后一个动作时非延续性的二、while的意思是“在……同时（at the same time that )”“在……期间(for as long as, during the time that）”。从while的本身词义来看，它只能表示一段时间，不能表示具体的时间点。在时间上可以是“线线重合”或“点线重合”，但不能表示“点点重合”。例如： 1、He was watching TV while she was cooking. 她做饭时，他在看电视。（线线重合） 2、He was waiting for me while I was working. 我工作的时候，他正等着我。（线线重合） 3、He asked me a question while I was speaking. 我在讲话时，他问了我一个问题。（点线重合）

第七--when-while-as-区别及练习.

When while as区别一、根据从句动作的持续性来区分 1、“主短从长”型：即主句是一个短暂性动作，而从句是一个持续性动作，此时三者都可用。如： Jim hurt his arm while［when， as］ he was playing tennis. 吉姆打网球时把手臂扭伤了。 2、“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态，且强调主句动作或状态延续到从句所指的整个时间，此时通常要用while。 I always listen to the radio while I’m driving. 我总是一边开车一边听收音机。 He didn’t ask me in; he kept me standing at the door while he read the message. 他没有让我进去，他只顾看那张条子，让我站在门口等着。但是，若主句和从句所表示的两个同时进行的动作含有“一边……一边”之意时，则习惯上要用as。如： He swung his arms as he walked. 他走路时摆动着手臂。 3、“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用as 或when，但不能用while。如： It was raining hard when [as] we arrived. 我们到达时正下着大雨。二、根据主句与从句动作是否同时发生来区分 1、若主句与从句表示的是两个同时发生的短暂性动作，含有类似汉语“一……就”的意思，英语一般要用as (也可用when)。如： The ice cracked as [when] I stepped onto it. 我一踩冰就裂了。 2、若主句与从句表示的是两个几乎同时发生的短暂性动作，含有类似汉语“刚要……就”“正要……却”的意思，英语一般要用as(也可用when)，且此时通常连用副词just。如： I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住了。三、根据是否具有伴随变化来区分若要表示主句动作伴随从句动作同时发展变化，有类似汉语“随着”的意思，英语习惯上要用as，而不用when或while。如： The room grew colder as the fire burnt down. 随着炉火逐渐减弱，房间越来越冷。注：若不是引导从句，而是引出一个短语，则用with，不用as。如： With winter coming on, it’s time to buy warm clothes. 随着冬天到来，该买暖和衣裳了。四、根据从句动作的规律性来区分若暗示一种规律性，表示“每当……的时候”，英语一般要用when。如： It’s cold when it snows. 下雪时天冷。五、根据主从句动作的先后顺序来区分若主句与从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when。

When while as的区别和用法(综合整理)

When while as的区别和用法 when的用法当主句使用持续性动词时. Dave was eating,when the doorbell rang.门铃响时,大卫在吃饭. 2.一个动作紧接着另一个动作发生. When the lights went out, I lit some candles.灯灭了,我赶紧点上一些蜡烛. 3.谈论生命中的某一阶段,或过去的某段时间. His mother called him Robbie when he was a baby. 在他很小时,他妈妈叫他Robbin. 4.指"每一次" When I turn on the TV, smoke comes out the back. 每当我打开电视,就有烟从后面冒出. while/as 的用法从句多为进行时,而且为持续性动词. I'll look after the children while you are making dinner. 你做饭,我来照顾孩子. 注意事项: (1) “主短从长”型：主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。 Jim hurt his arm while［when，as］he was playing tennis. 吉姆打网球时把手臂扭伤了。 As［When，While］she was waiting for the train，she became very impatient. 她在等火车时，变得很不耐烦。 (2) “主长从长”型：若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as：

when,while,as引导时间状语从句的区别

when，while，as引导时间状语从句的区别 when，while，as显然都可以引导时间状语从句，但用法区别非常大。一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as只能和延续性动词连用。 ①Why do you want a new job when youve got such a good one already？（get 为短暂性动词）你已经找到如此好的工作，为何还想再找新的？ ②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。 ③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。 ④The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while 和as从句的谓语动作必须是和主句谓语动作同时发生。 1．从句动作在主句动作前发生，只用when。 ①When he had finished his homework，he took a short rest．（finished先发生）当他完成作业后，他休息了一会儿。 ②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。 2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。 ①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。 ②When ／While ／As she was making a phonecall，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。 3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用as。这时，as常表示“随着……”；“一边……，一边……”之意。 ①As the time went on，the weather got worse．（as表示“随着……”之意） ②The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。 ③As years go by，China is getting stronger and richer．随着时间一年一年过去，中国变得越来越富强了。 ④The little girls sang as they went．小姑娘们一边走，一边唱。 ⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。 4．在将来时从句中，常用when，且从句须用一般时代替将来时。 ①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。 ②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。三、when用于表示“一……就……”的句型中（指过去的事情）。 sb．had hardly（＝scarcely）done sth．when．．．＝Hardly ／Scarcely had sb．done sth．when．．．

When,While,As引导时间状语从句的区别

When，While，As引导时间状语从句的区别 when，while，as显然都可以引导时间状语从句，但用法区别非常大。一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as 只能和延续性动词连用。 ① Why do you want a new job when you’ve got such a good one already？（get为短暂性动词）你已经找到如此好的工作，为何还想再找新的？ ②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。 ③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。 ④ The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while 和as从句的谓语动作必须是和主句谓语动作同时发生。 1．从句动作在主句动作前发生，只用 when。 ①When he had finished his homework，he took a short rest．（finished 先发生）当他完成作业后，他休息了一会儿。 ②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。 2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。 ①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。 ②When ／While ／As she was making a phone call，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。 3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用 as。这时，as常表示“随着……”；“一边……，一边……”之意。 ① As the time went on，the weather got worse．（as表示“随着……”之意） ② The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。 ③As years go by，China is getting stronger and richer．随着时间一年一年过去，中国变得越来越富强了。 ④The little girls sang as they went．小姑娘们一边走，一边唱。 ⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。 4．在将来时从句中，常用when，且从句须用一般时代替将来时。 ①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。 ②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。三、when用于表示“一……就……”的句型中（指过去的事情）。

When, while, as的区别和用法

When, while, as的区别和用法版本一 (1) 若主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。【注】as 用于引出一个持续性动词表示“在……期间”时，其谓语通常只能是那些含有动作(action)和发展(development) 意味的动词，一般不能是那些不用于进行时态的动词(如be, seem, love, want, agree, see, know, have 等)，所以下面一句中的while 不能换为as： A：I’m going to the post office. 我要去邮局。 B：While you’re there, can you get me some stamps? 当你在邮局时，能帮我买几张邮票吗? (2) 若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as： She sang as she went along. 她边走边唱。 (3) 若从句是一个短暂性动作，主句是一个持续性动作，可用as / when 但不用while： It was raining hard when [as] we arrived. 我们到达时正下着大雨。 (4) 若主从句表示的是两个同时(或几乎同时)发生的短暂性动作，用as / when： I thought of it just when [as] you opened your mouth. 就在你要说的时候，我也想到了。 (5) 若要表示两个正在发展变化的情况，相当于汉语的“随着”，一般用as： Things are getting better and better as time goes on. 随着时间的推移，情况越来越好。 As it grew darker, it became colder. 天色越晚，天气越冷。 (6) 表示“每当…的时候”(暗示一种规律性)，一般要用when： It’s cold when it snows. 下雪时天冷。 He smiles when you praise him. 你夸奖他时他总是笑笑。 (7) 若主从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when： I will go home when he comes back. 他回来时，我就回家去。 (8) when 可用作并列连词，表示“这时(突然)”；while 也可以用作并列连词，表示“而”、“却”(表示对比)；但as 则没有类似用法： We were about to start when it began to rain. 我们正要出发，这时天开始下雨了。 He likes coffee, while she likes tea. 他喜欢咖啡，而她却喜欢茶。 (9) as 和when 后均可直接跟一个名词，构成省略句，但while 一般不这样用： As [When] a boy, he lived in Japan. 他小时候在日本。

第七whenwhileas区别及练习

When while as 区别一、根据从句动作的持续性来区分 1、“主短从长”型：即主句是一个短暂性动作，而从句是一个持续性动作，此时三者都可用。如： Jim hurt his arm while ［ when， as］ he was playing tennis. 吉姆打网球时把手臂扭伤了。 2、“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态，状态延续到从句所指的整个时间，此时通常要用while 。且强调主句动作或 I always listen to the radio while I ’ m driving. 我总是一边开车一边听收音机。 He didn ’ t ask me in; he kept me standing at the door while he read the message. 他没有让我进去，他只顾看那张条子，让我站在门口等着。但是，若主句和从句所表示的两个同时进行的动作含有“一边,, 一边”之意时，则习惯上要用 as。如： He swung his arms as he walked. 他走路时摆动着手臂。 3、“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用as 或when，但不能用 while 。如： It was raining hard when [as] we arrived.我们到达时正下着大雨。二、根据主句与从句动作是否同时发生来区分 1、若主句与从句表示的是两个同时发生的短暂性动作，含有类似汉语 “一英语一般要用 as (也可用 when)。如： ,, 就的”意思，The ice cracked as [when] I stepped onto it. 我一踩冰就裂了。 2、若主句与从句表示的是两个几乎同时发生的短暂性动作，含有类似汉语“刚要“正要 ,, 却”的意思，英语一般要用 as(也可用 when)，且此时通常连用副词 ,, just。如：就” I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住了。三、根据是否具有伴随变化来区分若要表示主句动作伴随从句动作同时发展变化，有类似汉语“随着”的意思，英语习惯上要用as，而不用 when 或 while 。如： The room grew colder as the fire burnt down.随着炉火逐渐减弱，房间越来越冷。注：若不是引导从句，而是引出一个短语，则用with ，不用 as。如： With winter coming on, it ’ s time to buy warm clothes. 随着冬天到来，该买暖和衣裳了。四、根据从句动作的规律性来区分若暗示一种规律性，表示“每当,, 的时候”，英语一般要用when 。如：It ’s cold when it snows. 下雪时天冷。五、根据主从句动作的先后顺序来区分若主句与从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when 。

when while as区别用法详解

when/while/as区别用法详解 when, while, as都可作"当……的时候"解，但它们之间也有差别。若主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用。 He fell asleep when/while/as he was reading. 他看书时睡着了。 when只表示一般的时间关系，它既可指时间的一点，也可指一段时间。用when时，从句的动作可与主句的动作同时发生，也可先于主句的动作，因此when用得最多。如： He was playing basketball when I saw him. 当我看见他的时候，他正在打篮球。 Don't forget to return this book for me, when you go to the library. 你去图书馆时，不要忘记替我还这本书。 while只能指一段时间，而不能指时间的一点。用while时，从句的动作或者与主句的动作同时发生，或者主句的动作是在从句的动作的进展过程中发生的。因此，从句中的谓语必须是表示延续性动作或状态的动词。这是while与when的主要差别。如： When we arrived in Beijing, it was raining. (arrive不是延续性的动词)我们到达北京时，天正在下雨。 Please do not trouble me while I am writing my homework. 我写作业时请不要打扰我。在用when和while连接的从句中，常省略与主句相同的主语和相应的be，而在as连接的从句中一般则不省略。如： He fell asleep while(he was)studying his grammar book.他在阅读语法书的时候睡着了。While in London,he studied music.他在伦敦的时候，研究音乐。 when 可用作并列连词，表示“这时(突然)”；while 也可以用作并列连词，表示“而”、“却”(表示对比)；但as 则没有类似用法： We were about to start when it began to rain. 我们正要出发，这时天开始下雨了。 He likes coffee, while she likes tea. 他喜欢咖啡，而她却喜欢茶。

when,while和as引导时间状语从句的用法

when, while 和 as 引导时间状语从句的用法这三个词的意思很简单，都有“当……时候”的意思。但学生经常会问三个词的区别在哪儿，特别是在做选择题的时候。别说是学生，就我个人而言，做这样的选择题要保证百分之百的正确也是不可能的。现根据大量的实例和个人的思考，做一点小结，供大家参考。一、when 的用法如果只从现象来看，when 从句用的最多的是一般过去时，而主句的时态没有限制，根据具体情况而定。 When he was a child he was always trying out new ideas. 他小时候就常常试验一些新的设想。 when she came into my room I was just reading a book. 她走进我房间时，我正在看书。 Were you writing when the teacher came in? 老师进来的时候，你在写信吗？ Sorry，I was out when you called me. 对不起，你打电话来的时候我出去了。 He was on the point of leaving when someone knocked at the door. 他正要走,这时有人敲门。 I thought of it just when you opened your mouth. 就在你要说话的时候,我也想到了。 I had hardly[scarcely] closed my eyes when someone knocked at the door. 我刚一闭上眼，就有人在敲门了。根据以上的例句，我们可以总结出一点：when 从句的A事件，相当于另一个事件B发生的时间点。也就是说，when 从句的重点不在动作本身发生的状态，而只是把它作为一个时间点，所以when 多数情况下用的是一般过去时，则不用正在进行时。因为如果用正在进行时，它表示的就是一段时间而不是一个时间点了。根据这一点，有的文章补充说：when 从句的动词大多是瞬时动词。这种说法也可以参照。实际上，when 从句也可以有其它的时态，但几乎也不用进行时，因为它也只是作为一个时间参照点。例如： When I got to the airport，the guests had left. 当我赶到飞机场时，客人们已经离开了。 When he had finished his homework，he took a short rest．当他完成作业后，他休息了一会儿。 Why do you want a new job when you have got such a good one already？你已经找到如此好的工作，为何还想再找新的？ You shall borrow the book when I have finished reading it.

状语从句中的when,while ,as用法汇总

状语从句中的when, while和as的用法一．when，while，as在时间状语从句中的区别： ①三者均可表示“当……的时候”，如果主句表示的是短暂的动作，而从句表示的是一段时间，三者可通用。如： I met Kang Li as／when／while I was walking along the street．当我沿街散步时碰见了康丽。 ②when可以和延续性动词连用，也可以和短暂性动词连用；而while和as只能和延续性动词连用。如： It was snowing when we got to the airport．当我们到达机场时，天正下着雪。（不能用while） ③as强调主句与从句表示的动作同时发生，as常表示“随着……”；“一边……，一边……；while强调主句表示的动作持续于while所指的整个时间内；when 可指主、从句所述动作同时或先后发生。如： As the time went on，the weather got worse．（as表示“随着……”之意） He sang as he went along．他边走边唱。 Please write while I read．我读的时候，请写下来。 When he reached home，he had a little rest．回到家后，他休息了一会儿。 ④when用于表示“一……就……”的句型中（指过去的事情）。 somebody had hardly（＝scarcely）done …when．．．＝Hardly ／Scarcely had somebody done …when．．． ①I had hardly ／scarcely closed my eyes when someone knocked at the door．＝Hardly ／Scarcely had I closed my eyes when someone knocked at the door．我刚一闭上眼，就有人在敲门了。二.when, while和as都可引导让步状语从句： ①when引导让步状语从句，意为“尽管，虽然”相当于though或although: They stopped trying when they might have succeeded next time. ②while引导让步状语从句，相当于although ，是较为正式的书面语: While I am willing to go, I would like it better that you went. ③as引导让步状语从句必须倒装，从句中的表语，状语或动词原形置于句首，若表语为名词，前置时省略冠词。 Child as he is, he knows a lot. Much as I like it, I will not buy it, for it’s too expensive.

When_ _while _as的区别和用法

When while as的区别和用法一 (1) 若主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。【注】as 用于引出一个持续性动词表示“在……期间”时，其谓语通常只能是那些含有动作(action)和发展(development) 意味的动词，一般不能是那些不用于进行时态的动词(如be, seem, love, want, agree, see, know, have 等)，所以下面一句中的while 不能换为as： A：I’m going to the post office. 我要去邮局。 B：While you’re there, can you get me some stamps? 当你在邮局时，能帮我买几张邮票吗? (2) 若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as： She sang as she went along. 她边走边唱。 (3) 若从句是一个短暂性动作，主句是一个持续性动作，可用as / when 但不用while： It was raining hard when [as] we arrived. 我们到达时正下着大雨。 (4) 若主从句表示的是两个同时(或几乎同时)发生的短暂性动作，用as / when： I thought of it just when [as] you opened your mouth. 就在你要说的时候，我也想到了。 (5) 若要表示两个正在发展变化的情况，相当于汉语的“随着”，一般用as： Things are getting better and better as time goes on. 随着时间的推移，情况越来越好。 As it grew darker, it became colder. 天色越晚，天气越冷。 (6) 表示“每当…的时候”(暗示一种规律性)，一般要用when： It’s cold when it snows. 下雪时天冷。 He smiles when you praise him. 你夸奖他时他总是笑笑。 (7) 若主从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when： I will go home when he comes back. 他回来时，我就回家去。 (8) when 可用作并列连词，表示“这时(突然)”；while 也可以用作并列连词，表示“而”、“却”(表示对比)；但as 则没有类似用法： We were about to start when it began to rain. 我们正要出发，这时天开始下雨了。 He likes coffee, while she likes tea. 他喜欢咖啡，而她却喜欢茶。 (9) as 和when 后均可直接跟一个名词，构成省略句，但while 一般不这样用： As [When] a boy, he lived in Japan. 他小时候在日本。 (10) when 和while 后可接现在分词、介词短语、形容词等构成省略句，但as 一般不这样用： When [While] reading, he fell asleep. 他看书时睡着了。 When [While] in trouble, ask her for help. 遇到麻烦的时候你就去找她帮忙。

when,while,as讲解与练习

时间状语从句讲解与练习 when, while 和as 引导时间状语从句的用法这三个词的意思很简单，都有“当……时候”的意思, 但又有区别。一、when 的用法观察下面的句子: 1. When he was a child he was always trying out new ideas. 他小时候就常常试验一些新的设想。 2. When she came into my room, I was just reading a book. 她走进我房间时，我正在看书。 3. Were you writing when the teacher came in? 老师进来的时候，你在写信吗？ 4. Sorry, I was out when you called me. 对不起，你打电话来的时候我出去了。 5. He was leaving when someone knocked at the door. 他正要走，这时有人敲门。 6. I thought of it just when you opened your mouth. 就在你要说话的时候，我也想到了。根据以上的例句，我们可以总结出一点：when 从句中的A事件，相当于主句中B事件发生的时间点。也就是说，when 从句的重点不在动作本身发生的状态，而只是把它作为一个时间点，所以when从句多数情况下用的是一般过去时，而不用进行时, 而且, when 从句的动词大多是短暂性动词。这种说法也可以参照。实际上，when 从句也可以有其它的时态，但几乎也不用进行时，因为它也只是作为一个时间参照点。例如： When the manager comes here for a visit next week, I’ll talk with him about this. 下周，经理来这参观时，我会和他谈谈此事。 When的特殊用法：主句（进行时）when 从句（一般时） I was walking along the street when a ball hit me on the head. 我正沿着路边着，就在这时一个球打在了头上。此句中的when=at that time, 表示“突然性” 二、while 的用法 while 从句的侧重点在于描述动作正在发生的状态，它的意思是：当while 事件正在发生的时候，另一件事如何如何。所以，while 从句一般用的是正在进行时。而另一件事的状态没有硬性的要求，根据具体情况而定。例如： 1. While my wife was reading the newspaper, I was watching TV. 当妻子正在看报纸的时候，我正在看电视。 2. While Jim was mending his bike, Lin Tao came to see him. 正当吉姆修自行车时，林涛来看他。 3. While they were talking, the bell rang. 正在他们谈话的时候，上课铃响了。 4. You can’t do your homework while you’re watching TV. 你不能看着电视做着作业。从时间的角度来看，while 表示的是一段时间，是一个过程。这是while 的侧重点。因此，如果含有“一段时间”的含义的时候，就可以用while。例如：Strike while the iron is hot. 趁热打铁。这句话中，是说趁着铁是热的这段时间，赶紧打铁。再例： —I'm going to the post office. —While you're there, can you get me some stamps? while的特殊用法：表示微弱的对比性转折“而” I like English while my sister likes math. 我喜欢英语而我姐姐喜欢数学。三、as 的用法 as从句表达的事件，往往只是主句动作发生的背景或条件时，也就是说，主句的动作是伴随着as从句中的动作发生的。因此，as 从句一般可以翻译成“边……边……”，或者“随着……”之意。但与while 从句不同的是，as 从句用的一般不用正在进行时，而只是一般过去时。例如：

when,while和as引导时间状语从句的用法

when, while 和as 引导时间状语从句的用法一、when 的用法如果只从现象来看，when 从句用的最多的是一般过去时，而主句的时态没有限制,根据具体情况而定。 1. When he was a child he was always trying out new ideas. 他小时候就常常试验一些新的设想。 2. When she came into my room, I was just reading a book. 她走进我房间时，我正在看书。 3. Were you writing when the teacher came in? 老师进来的时候，你在写信吗？ 4. Sorry, I was out when you called me. 对不起，你打电话来的时候我出去了。 5. He was on the point of leaving when someone knocked at the door. 他正要走，这时有人敲门。 6. I thought of it just when you opened your mouth. 就在你要说话的时候，我也想到了。 7. I had hardly[scarcely] closed my eyes when someone knocked at the door. 我刚一闭上眼，就有人在敲门了。根据以上的例句，我们可以总结出一点：when 从句的A事件，相当于另一个事件B发生的时间点。也就是说，when 从句的重点不在动作本身发生的状态，而只是把它作为一个时间点，所以when 多数情况下用的是一般过去时，则不用正在进行时。因为如果用正在进行时，它表示的就是一段时间而不是一个时间点了。根据这一点，有的文章补充说：when 从句的动词大多是瞬时动词。这种说法也可以参照。实际上，when 从句也可以有其它的时态，但几乎也不用进行时，因为它也只是作为一个时间参照点。例如： 1. When I got to the airport, the guests had left. 当我赶到飞机场时，客人们已经离开了。 2. When he had finished his homework, he took a short rest. 当他完成作业后，他休息了一会儿。 3. Why do you want a new job when you have got such a good one already? 你已经找到如此好的工作，为何还想再找新的？ 4. You shall borrow the book when I have finished reading it. 在我读完这本书后，你可以借阅。 5. When the manager comes here for a visit next week, I’ll talk with him about this. 下周，经理来这参观时，我会和他谈谈此事。