Large-Scale Hierarchical Organization of Nanowires for Functional Nanosystems

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1 Jpnese Journl of Applied Physis Vol. 43, No. 7B, 24, pp #24 The Jpn Soiety of Applied Physis Review Pper Lrge-Sle Hierrhil Orgniztion of Nnowires for Funtionl Nnosystems Dongmok WHANG 1, Song JIN 1 nd Chrles M. LIEBER 1;2; 1 Deprtment of Chemistry nd Chemil Biology, Hrvrd University, Cmridge, MA 2138, USA 2 Division of Engineering nd Applied Sienes, Hrvrd University, Cmridge, MA 2138, USA (Reeived My 6, 24; epted My 6, 24; pulished July 29, 24) We review reent studies of solution-sed hierrhil orgniztion of nnowire uilding loks. Nnowires hve een ligned with ontrolled nnometer to mirometer sle seprtion using the Lngmuir-Blodgett tehnique, trnsferred to plnr sustrtes in lyer-y-lyer proess to form prllel nd rossed nnowire strutures over entimeter length sles, nd then effiiently ptterned into repeting rrys of ontrolled dimensions nd pith using photolithogrphy. The hierrhilly-orgnized nnowires open up key opportunities in severl generl res of nnosle siene nd tehnology. First, hierrhilly-ssemled nnowire rrys hve een used s msks to define nnometer sle metl lines nd surfe fetures over lrge res. Seond, hierrhilly-ssemled nnowire rrys hve een used to frite fully-slle entimeter size rrys of field-effet trnsistors in high yields without requiring lignment of individul nnowires to output eletrodes. Diverse pplitions of this pproh for enling rod rnge of funtionl nnosystems, inluding mroeletroni nd sensing pplitions, re desried. [DOI: /JJAP ] KEYWORDS: ssemly, Lngmuir-Blodgett, uilding loks, nnowires, nnolithogrphy, hierrhil rrys, lrge-sle integrtion 1. Introdution Miroeletronis tody hs een driven y innovtions in top-down mnufturing proesses. In order to inrese the density of funtionl devies, improve the proessing power, nd redue the ost of mnufturing, the fetures lithogrphilly ptterned on ulk semiondutor mterils hve een shrunk y more thn two orders of mgnitude over the lst severl dedes. 1) However, this remrkle trend of minituriztion my soon ome to the end due to fundmentl physil nd/or eonomi limittions. 1 3) Alterntively, ottom-up pprohes, 3 6) in whih integrted funtionl devie strutures re ssemled from hemilly synthesized nnosle uilding loks, suh s ron nnotues (NTs) 7 12) nd semiondutor nnowires (NWs), 13 22) hve the potentil to revolutionize the frition of eletroni nd photoni systems nd to enle wide rnge of tehnologil pplitions. It is in this ontext of ottom-up prdigm for nnosiene nd nnotehnology tht we will disuss generl shemes for the hierrhil orgniztion of one-dimensionl nnosle uilding loks for funtionl nnosystems. NWs nd NTs hve een extensively studied s uilding loks for numer of nnosle devies. 4,7 22) Semiondutor NWs re espeilly ttrtive uilding loks sine these mterils n e synthesized in single-rystlline form with preisely ontrolled strutures, dimeters nd lengths, hemil ompositions nd doping/eletroni properties using nnoluster tlyzed vpor-liquid-solid growth proess. 4) This ontrol over the growth of NWs hs enled the ottom-up ssemly of integrted eletroni nd photoni devies, inluding nnometer sle field-effet trnsistors (FETs), 13,14) p-n diodes, 14,15) ipolr juntion trnsistors, 15) istle swithing devies, 16) integrted logi iruits, 16,17) ddress deorders, 18) light-emitting diodes, 14,19) eletrilly driven lsers, 2) sensors. 21,22) However, most studies of NWs nd NTs hve een limited to the demonstrtion of single or smll numers of nnodevies using seril lithogrphi proessing, suh s eletron-em Corresponding uthor. E-mil ddress: ml@mliris.hrvrd.edu 4465 lithogrphy, to ontt rndom strutures on sustrte. To provide diretionl ontrol over NW nd NT uilding loks during ssemly severl groups hve used eletrifields 14,23,24) nd fluid flows within mirofluidi hnnels. 25) However, these methods hve only led to reltively smll sle strutures without hierrhil ontrol, nd thus do not ddress mny of the ritil needs required for the ssemly of integrted nnosystems. 4 6) Here we review reent progress 26 28) from the uthors lortory foused on the development of generl nd effiient solution-sed pproh for hierrhilly orgnizing NW uilding loks en msse nd integrtion of the resulting strutures into funtionl devie rrys over lrge res. 2. Assemly of Nnowires Using the Lngmuir-Blodgett Method In order to go eyond the limited suesses hieved previously in the ssemly of NWs nd NTs, 14,23 25) we hve utilized the well-estlished Lngmuir-Blodgett (LB) tehnique for the ssemly of nnosle uilding loks. The LB pproh 29) is ttrtive sine (i) ordered monolyers n e formed over lrge re, (ii) the orgnized monolyers n e esily trnsferred to sustrtes, nd (iii) the ordering nd trnsfer proesses n e repeted to yield multiple lyers of the sme or distint mterils. The underlying onept of our pproh for ssemly of NWs using the LB method is illustrted in Fig ) Stle nonpolr NW suspensions, whih re hieved using surftnts, re dispersed onto n queous suphse in LB trough nd the NW-surftnt monolyer formed on the ir/wter interfe is then unixilly ompressed. During the ompression, diretionl sher flow of the Lngmuir monolyer is indued nd yields NWs ligned perpendiulr to the ompression diretion. In ddition, the verge sping etween NWs n e lso ontrolled y reduing the re of the Lngmuir monolyer, for exmple, y slow dissolution of the surftnt into the wter suphse. The lyer of ligned NWs is then trnsferred in single step to plnr sustrte to yield prllel NWs overing the entire sustrte surfe. Notly, this sequene of steps n e repeted one

2 4466 Jpn. J. Appl. Phys., Vol. 43, No. 7B (24) D. WHANG et l. 2nm Fig. 1. Assemly of NWs. NWs (lines) t the ir-wter interfe re () unixilly-ompressed to speifi pith. () The ligned NWs re trnsferred to sustrte surfe to form uniform prllel rry. () Crossed NW strutures re formed y trnsfer of seond lyer of ligned NWs perpendiulr to the first lyer. or more times with ontrolled orienttion using virtully ny NW uilding lok to produe rossed nd more omplex NW rrys with funtions determined y the NWs hosen for the different ssemly steps. We hve demonstrted this pproh using silion NWs. 3) Snning eletron mirosopy (SEM) imges show tht ligned NWs were trnsferred uniformly onto lrge sustrtes in our experiments (Fig. 2()), nd the spings of the trnsferred NW rrys were lso ontrolled from the mirometer to nnometer sle y the ompression proess (Figs. 2() nd 2()). Our method n e redily extended in slle mnner to ultr-dense NW rrys with ontrolled 1µm 1µm 1µm Fig. 2. Deposition of ontrolled seprtion prllel NWs. () Lrge re SEM imge of prllel NWs deposited uniformly on sustrte. (, ) Imges of ligned prllel NWs trnsferred to sustrtes t different stges of LB ompression, with verge seprtion of. ().8 nd ().4 mm. 2nm Fig. 3. High-density prllel NW rrys. () Shemti illustrting lose-pked NW rry on sustrte, where the NWs onsist of funtionl ore (gry) nd srifiil shell (lk), nd susequent removl of the shell to yield ultrhigh density NW rry. (, ) SEM imges of high-density prllel NW rrys with verge pithes of () 9 nd (d) 45 nm. regulr sping. Our pproh for hieving this ontrol on the nnometer sle involves oting NWs with srifiil lyer of ontrolled thikness prior to LB ssemly, ompression of the nnowires to n ligned lose-pked struture, trnsfer to sustrte, nd then removl of the srifiil lyer (Fig. 3()). Well-ligned prllel NWs with ontrolled pithes of smller thn 1 nm (Figs. 3() nd 3()) were mde following deposition of lose-pked Si/ SiO 2 ore/shell NWs, 31) in whih the SiO 2 shell thikness ws preisely ontrolled, nd susequent ething to remove the oxide, though the rrys ould e sled to even higher densities using smller dimeter NWs. 3. Assemled Nnowires s Msks for Nnolithogrphy The development of novel methods for ptterning strutures on nnometer length sles n mke possile fundmentl investigtions of new devies nd ould help to enle pplitions in nnoeletronis, photonis nd nno-iotehnology. It is possile to pttern nnometer sle fetures using the NW rrys s msks for deposition nd ething. 27) Following trnsfer of unixilly-ligned NWs with ontrolled seprtion to sustrte, the NWs n e used s msks to trnsfer the line-pttern to the underlying sustrte surfe y ething, or lterntively, other mterils, suh s metls, n e deposited using the ligned NWs s shdow msks to rete rrys of nnosle wires. The NW msks re removed y isotropi wet ething nd sonition to expose the ethed or deposited prllel line fetures t the end of these steps. A ler illustrtion of the flexiility of this pproh is illustrted in Fig. 4, where ssemled NWs were used to define the deposition of prllel metl lines with verge widths nd pithes s smll s 4 nd 9 nm, respetively. Thin metl films were deposited using the ligned NWs s shdow msks to rete rrys of nnosle wires. These studies demonstrted severl importnt hrteristis of our NW-sed lithogrphy pproh using lrgesle ssemled NWs. First, the line width nd pith n e well-ontrolled vi the synthesis of NWs nd susequent

3 Jpn. J. Appl. Phys., Vol. 43, No. 7B (24) D. WHANG et l µm 5nm d 5nm 2nm Fig. 4. SEM imges of Cr-metl stripes with pithes of () 6, () 3, () 2, nd (d) 9 nm. Brighter res in the imges orrespond to the 15 nm thik Cr-metl lines. ssemly steps. This offers the potentil for rpidly nd independently hnging the line width nd pith down to the nnometer sle. Seond, the smllest feture sizes defined y our method re omprle to stte-of-rt extreme UV lithogrphy nd pproh the limit of eletron-em lithogrphy. Third, LB pproh n e used to ssemle NWs in one-step over res of t lest 2 m 2, whih exeeds most other unonventionl lithogrphy methods. Hene, this nnolithogrphy method represents highly slle nd flexile pproh for defining nnometer sle lines on multiple lengths sles nd thus hs sustntil potentil for enling the frition of mny types of periodi nnostrutures nd integrted nnosystems. 4. Hierrhil Ptterning of Nnowire Arrys The ligned, ontrolled sping NW strutures produed y LB ssemly method exhiit fetures similr to nemti liquid rystl phse, inluding flututions in the verge lignment diretion nd poor end-to-end registry (Fig. 2()). These non-uniform fetures re distint from the preise strutures fmilir to onventionl top-down frition; however, these fetures do not represent serious impediments to mking integrted nd interonneted devies. Speifilly, interonneted finite-size rrys of nnosle devies re more desirle thn monolithi strutures for integrted nnosystems, euse hierrhil orgniztion redues the proility tht smll numers of defets will use tstrophi filure in the whole system. Hene, y djusting the rry size to e less thn the verge NW length it is possile to minimize the numer of NWs tht fil to spn the width of n rry due to poor end-to-end registry. We hve implemented this desired hierrhil ptterning of the trnsferred NW strutures using photolithogrphy (Fig. 5()). Following uniform trnsfer of NWs of speified sping onto sustrte, photolithogrphy is used to define pttern over the entire sustrte surfe, whih sets the rry dimensions nd rry pith, nd then the NWs outside the ptterned rry re removed y gentle sonition. An imge of 1 mm 1 mm squre rry with 25 mm rry pith (Fig. 5()) shows tht this method provides redy nd slle ess to ordered rrys over lrge res. This rry exhiits order on multiple length sles 4 nm dimeter NWs,.5 mm NW sping, 1 mm rry size, 25 mm rry pith repeted over entimeters tht is representtive of the sustntil ontrol enled y our pproh. In Fig. 5. () Hierrhil ptterning of prllel nd rossed NW rrys. () SEM imge of ptterned 1 mm 1 mm prllel NW rrys. () SEM imge of ptterned 1 mm 1 mm rossed NW rrys. ddition, this pproh n e used to define rry geometries nd tiling ptterns more omplex thn the ove squre strutures. Our method n lso e used to deposit sequentil lyers of ligned NWs in whih the speifi nnowire properties nd rry orienttion re vried. This pility, whih is dvntgeous over trnsfer lithogrphy pprohes, ould enle lrge rossed NW rrys needed for implementing eletroni nd photoni nnosystems sed upon previously reported rossed NW juntions. 15,17,18) To this end we hve rried out ssemly nd hierrhil ptterning of rossed NW rrys using the lyer-y-lyer sheme illustrted in Fig. 5(). First, ligned, prllel NWs were trnsferred in sequentil orthogonl diretions onto sustrte surfe. Seond, rossed NW rrys nd tiling ptterns were defined using photolithogrphy, nd NWs outside the pttern were removed to produe regulr squre rrys over lrge res, in whih eh squre rry onsists of lrge numer of rossed NW juntions (Fig. 5()). In this generl proess, the different levels of hierrhy nd ptterning n e redily hnged nd different NW uilding loks n e sustituted in file mnner, oth of whih re essentil for the generl ssemly of integrted nd funtionl nnosystems. 4,5) 5. Lrge-Sle Integrtion of Nnowire Devies without Registrtion Devie integrtion pprohes tht re fully slle in terms of devie density nd re of overge re essentil for the development of funtionl nnosystems ssemled from the ottom-up. 3 6) Previously reported studies of NW nd NT FETs hve used seril eletron em lithogrphy to define interonnets, nd hve thus preluded studies of lrge systems. 8 1,12 14) To overome this sustntil issue, we developed new strtegy tht hs enled prllel nd slle integrtion of NW devies over lrge res without the need to register individul nnowire-eletrode interonnets. 28) This pproh exploits the Lngmuir-Blodgett method desried ove to orgnize NWs with ontrolled lignment nd sping over lrge res, nd prllel photolithogrphy to define interonnets in sttistil mnner.

4 4468 Jpn. J. Appl. Phys., Vol. 43, No. 7B (24) D. WHANG et l. produe devies in the nnometer size regime over lrge res. Sine the verge NW sping n e ontrolled down to the nnometer sle during the Lngmuir-Blodgett ompression, muh smller devie size nd higher density of devie integrtion n e redily hieved when existing high resolution prllel lithogrphy tehniques, suh s sumiron photolithogrphy, extreme-uv lithogrphy 32) or nnoimprint lithogrphy, 33) re pplied to define eletrodes following this interonnetion strtegy. To demonstrte this key point of sling, we used eletron em lithogrphy to define regulr nnometer sle ontt eletrodes without registering to individul NWs to produe individul NW devies with 3 nm (Fig. 7(d)) nd 15 nm (Fig. 7(e)) pith in high-yield. High performne devies were hieved in high yields for the mssive rrys of FETs frited vi this pproh. Eletril hrteriztion of rndomly hosen NW devies within the lrge rrys (Fig. 8) show expeted 34) urrentvoltge hrteristis for high performne p-type fieldeffet trnsistors tht rivl stte-of-the-rt plnr silion devies: 35) on/off urrent rtios greter thn 1 6 nd susthreshold slopes of elow 25 mv/dede. A histogrm of the oserved pek trnsondutne vlues (Fig. 8() inset) shows most prole vlue lose to 1 na/v nd mximum vlue of 43 na/v orresponding to lulted hole moility of 37 m 2 /Vs. We hve lso frited pixel-like rrys (Fig. 9()), in whih interdigitted eletrodes were used s ontts to the ptterned NWs so tht the numer of NW devies per pixel trnsistor n e redily vried y ontrolling the NW sping prior to deposition of the ontt eletrodes. Sine the NW devies ehve reproduily, it is possile to sle key devie hrteristis, suh s the trnsistor on-urrent, in this wy. Trnsfer of ligned NWs with reltively lrge (Fig. 9()) nd smll (Fig. 9()) verge NW spings yielded devies with few NWs nd 3 4 NWs, respetively, ridging eh set of interdigitted eletrodes. The signifint differenes in on-urrents (6 ma vs 37 ma) demonstrte exellent sling of properties in the multi 4µm 1mm 3µm d e PL, Deposition 3nm 3nm Fig. 6. Prllel nd slle interonnetion of NW devies without registrtion. () Centrl eletrode region of single rry emphsizing the high frtion of interonneted NWs otined without the registrtion of individul eletrodes. () Shemeti illustrting key step of the deposition of repeting metl eletrode rry defined using photolithogrphy (PL). Our pproh to lrge-sle nd prllel interonnetion exploits the ft tht the seprtion etween NWs ssemled y the Lngmuir-Blodgett method hs defined verge vlue ut vries on the lol sle. In this ontext, it is possile to hieve high yield of metl eletrode-tonnowire ontts simply y setting the verge NW seprtion to vlue omprle to the eletrode width (Fig. 6()); tht is, the lol flututions in seprtion led to n effiient formtion of ontts. There re two key fetures in this pproh. First, it is not neessry to register the metl eletrodes, whih re defined y onventionl lithogrphy, to individul NWs in n rry to hieve high yield of ontts; only the position of the eletrodes reltive to group of ligned NWs needs to e fixed. Seond, the pproh is intrinsilly slle to lrge res sine eh of the key steps (Fig. 6()) n e rried out over n entire sustrte or wfer in prllel. This pproh hs een demonstrted with the frition of lrge rrys of NW FETs in whih eh tive devie onsists of single p-type silion NW. 28) Optil nd eletron mirosopy imges (Figs. 7() 7()) demonstrte the key fetures nd hierrhy of strutures produed y our pproh, inluding (1) FET su-rrys with 1 mm rry pith repeted over the entire sustrte, (2) entrl eletrode rrys on 3 mm eletrode pith, nd (3) individul 2 nm dimeter NWs onneted etween the finger eletrodes. Figure 7() illustrtes tht single NWs n fll etween two metl eletrodes s expeted sttistilly, lthough the overll NW lignment prevents suh defetive devies from dversely ffeting properly interonneted NWs. Using this method, pproximtely 8% of the 3 possile eletrode onnetions ville on typil test hip ould e ridged y NWs when the sping of the ligned NWs ws losely mthed to the eletrode width. Our si pproh is slle nd thus n e used to Fig. 7. () Optil mirogrph of integrted metl eletrode rrys deposited on top of ptterned prllel NW rrys defined y photolithogrphy. () SEM imge of the entrl tive region of repet unit of the eletrode rry show in prt. () Imge of three NW devies onneted etween the ommon nd finger eletrodes. (d, e) Imges of higher-density NW devies defined y eletron een lithogrphy.

5 Jpn. J. Appl. Phys., Vol. 43, No. 7B (24) D. WHANG et l I sd (µa) 5-5 I sd (µa) V sd (V) Count 1 1 Trnsondutne (ns) V g (V) Fig. 8. () Fmily of soure-drin urrent (I sd ) vs soure-drin voltge (V sd ) plots t different gte voltges (V g ) for typil devie in the rry; V g vries from 5 (red) to þ3 V (mgent). () I sd vs V g plots t V sd of 1 V for smpling of devies from the lrge rrys; (inset) Histogrm of the trnsondutne vlues oserved for smpling of devies in the lrge-sle rry Isd (µa) V g (V) Isd (µa) V g (V) Fig. 9. () Optil mirogrph of lrge-sle pixel-like eletrode rrys deposited on hierrhilly ptterned NW rrys. Sle r, 1 mm. (inset) SEM imge of severl devie units frited on the ptterned NWs. Sle r, 1 mm. () I sd vs V g plots t V sd of 1 V for typil devie ridged with low-density of ligned NWs; (inset) SEM imge of typil low-density NW devie with out two ligned NWs ridging the interdigitted eletrodes. Sle r, 1 mm. () I sd vs V g reorded t V sd of 1 V (red) nd 4 V (lue) for typil devie ridged with highdensity of ligned NWs; (inset) SEM imge of typil high-density NW devie with out nine ridging NWs. Sle r, 1 mm. 4 NW devies sine there re. 6 times more tive devies (35 vs 6) in the high versus low density rrys, respetively. In ddition, histogrm of the threshold voltges determined from mesurements on lrge numer of devies, exhiits men of 1.4 V nd stndrd devition of.36 V. This reltively nrrow distriution is promising for pplitions, where uniformity of devie hrteristis is importnt. 6. Summry nd Perspetives We hve outlined generl strtegy for hierrhil ssemly of NWs into integrted devie rrys. Overll, our prllel nd slle pproh enles NWs to e ligned with ontrolled pith nd hierrhilly ssemled into repeting rrys, in whih the speifi NW uilding loks, NW pith, NW orienttion, rry size, rry orienttion, nd rry pith n e ontrolled independently. We hve lso demonstrted tht the hierrhil ssemly pproh n e redily pplied to the frition of lrge-sle rrys of high performne nnowire FETs with high reproduiility nd slility. These highly reproduile nnowire devie rrys ould e of gret interest in numer of pplitions, inluding multiplexed hemil nd iosensors 21) nd informtion displys. 36) In this ltter mroeletroni pplition, distint dvntge of our pproh ompred to those using high-performne thin-film devies is the room temperture proessing, mking it omptile with low-ost nd flexile glss nd plsti sustrtes. 37) More generlly, this solution-sed ottom-up ssemly pproh ould enle file integrtion of diverse NW uilding loks with more omplex struturl hierrhy nd flexile eletrode designs, nd thus provide pthwy for the ssemly of rod rnge of integrted funtionl nnosystems. We elieve, for exmple, tht rossed NW rrys ould e redily implemented to yield ddressle nnosle light-emitting diode rrys nd highly integrted logi/memory rrys tht re needed for nnoomputing. 38) Aknowledgments This work ws supported y the Defense Advned Reserh Projets Ageny, Air Fore Offie of Sientifi Reserh, the Ntionl Cner Institute, nd the Ellison Medil Foundtion. 1) M. Lundstrom: Siene 299 (23) 21. 2) J. D. Meindl, Q. Chen nd J. A. Dvis: Siene 293 (21) ) C. M. Lieer: Si. Am. (21) Septemer, p ) C. M. Lieer: MRS Bull. 28 (23) ) G. Y. Tseng nd J. C. Ellenogen: Siene 294 (21) ) P. Yng: Nture 425 (23) ) P. L. MEuen: Phys. World 13 (2) 31. 8) Ph. Avouris: A. Chem. Res. 35 (22) ) S. J. Tns, A. R. M. Vershueren nd C. Dekker: Nture 393 (1998)

6 447 Jpn. J. Appl. Phys., Vol. 43, No. 7B (24) D. WHANG et l ) V. Deryke, R. Mrtel, J. Appenzeller nd Ph. Avouris: Nno Lett. 1 (21) ) T. Ruekes, K. Kim, E. Joselevih, G. Y. Tseng, C.-L. Cheung nd C. M. Lieer: Siene 289 (2) ) A. Jvey, H. Kim, M. Brink, Q. Wng, A. Url, P. MIntype, P. MEuen, M. Lundstrom nd H. Di: Nture Mter. 1 (22) ) Y. Cui, Z. Zhong, D. Wng, W. U. Wng nd C. M. Lieer: Nno Lett. 3 (23) ) X. Dun, Y. Hung, Y. Cui, J. Wng nd C. M. Lieer: Nture 49 (21) ) Y. Cui nd C. M. Lieer: Siene 291 (21) ) X. Dun, Y. Hung nd C. M. Lieer: Nno Lett. 2 (22) ) Y. Hung, X. Dun, Y. Cui, L. J. Luhon, K. Kim nd C. M. Lieer: Siene 294 (21) ) Z. Zhong, D. Wng, Y. Cui, M. W. Bokrth, C. M. Lieer: Siene 32 (23) ) M. S. Gudiksen, L. J. Luhon, J. Wng, D. C. Smith nd C. M. Lieer: Nture 415 (22) ) X. Dun, Y. Hung, R. Agrwl nd C. M. Lieer: Nture 421 (23) ) Y. Cui, Q. Wei, H. Prk, C. M. Lieer: Siene 293 (21) ) J.-I. Hhm nd C. M. Lieer: Nno Lett. 4 (24) ) P. A. Smith, C. D. Nordquist, T. N. Jkson, T. S. Myer, B. R. Mrtin, J. Mindyo nd T. E. Mllouk: Appl. Phys. Lett. 77 (2) ) M. R. Diehl, S. N. Ylirki, R. A. Bekmn, M. Brhon nd J. R. Heth: Angew. Chem. Int. Ed. 41 (22) ) Y. Hung, X. Dun, Q. Wei nd C. M. Lieer: Siene 291 (21) ) D. Whng, S. Jin, Y. Wu nd C. M. Lieer: Nno Lett. 3 (23) ) D. Whng, S. Jin nd C. M. Lieer: Nno Lett. 3 (23) ) S. Jin, D. Whng, M. C. MAlpine, R. S. Friedmn, Y. Wu nd C. M. Lieer: Nno Lett. 4 (24) ) A. Ulmn: An introdution to ultrthin orgni films: from Lngmuir- Blodgett to self-ssemly (Ademi Press, New York, 1991). 3) Y. Cui, L. J. Luhon, M. S. Gudiksen, J. Wng nd C. M. Lieer: Appl. Phys. Lett. 78 (21) ) L. J. Luhon, M. S. Gudiksen, D. Wng nd C. M. Lieer: Nture 42 (22) ) G. Mrsh: Mter. Tody (23) ) S. Y. Chou, P. R. Kruss nd P. J. Renstrom: Siene 272 (1996) ) S. M. Sze: Physis of Semiondutor Devies (Wiley, New York, 1981). 35) B. S. Doyle, S. Dtt, M. Dozy, S. Hrelnd, B. Jin, J. Kvlieros, T. Linton, A. Murthy, R. Rios nd R. Chu: IEEE Eletron Devie Lett. 24 (23) ) E. Lueder: Liquid Crystl Displys: Addressing Shemes nd Eletrooptil Effets (Wiley & Sons, Chihester, 21). 37) M. C. MAlpine, R. S. Friedmn, S. Jin, K.-H. Lin, W. U. Wng nd C. M. Lieer: Nno Lett. 3 (23) ) A. DeHon: IEEE Trns. Nnoteh. 2 (23) 23.