RD-fli56 671 POLYMER ENGINEERING: POLYMERIC AND MOLECULAR ELECTRONIC /DIELECTRIC AND OPTICAL PROPERTIES FOR DEVICEAPPLICATIONS(U) NAVAL AIR SYSTEMS COMMAND WASHINGTON DC

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V I Devices: Matterias Cq-side!-tftiorns, 32

'X ~PnrIwer Inte-faco, . ..

x Anplic~at' . 37

0 ~pn',c 4t!ir of Advaficpl Devices . - 4!

AlChlteCtUreS . 47

x Other Applications including Advanced sf rs 50

XPy Derense & Aerosprice Applicef ions -

i~et1rb se& Aer' ..f'!-kq~t Cons'ertons.. 56

GLOSSARY

Introduction

-n'* t 'n' Vchnongy tAwj ii re& is no b'd -of l'~'~~4- ewhIch C211- Dr;: ide a__iumbyU.I Vo" th rlp'ilete suite to that utse 3. the p:resent. timne. Desr.ite

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Thr is MY) the isu of whrether rnat4 fil s with nonlinear susceptibility of* *± in 7 ?I' ofl1 inorgani ng ar. z.I-SI4lable for use in optical devices. In the

1'm univars't- or arim-mvQ MIS -Can finid champions of both types ofi~lfl>--c- ns Ithis issue wihll be decided case-tbw ase on

4' Lao A petimanc and 'h'nlVi-_, Optical phase conjiuga tion us~ing thle

*n.. -a- nirroris for Arim reversed" signal clean-up, f,' r opticalOn i, t andj Oi(A'r Ve 512- , hc dot inot rjerlebt the .eerg of the

wni ave Whout WASdw' e:d~tv~ttcass of That9IIIsval goiie Me no~nlirnear coptical pt'p'etties recquired, one can nevertheless

*e a--n imporitant use for the - i-'i&9s '4ii'4i. rely on those pi-opertis.7it -r i. numrber cit thrusts in Doivrrier science which, if riot yet "lad

Wse do :Eow. qjteat deal cit ,oftia i~i C'n exmple 15 hei pyicilized 'A' ~;~ ~r-itzA i - . -, P - ~ ~ .-~ft .ipplic-atioiti ti:) dielt.-niW' -

' ~hrj -er ,c .-' n j* and r-monent. rragits (Pohl and Pollak, 1947T,i''i 'nl! A 1o i vn'ith !- the~'li' e ife- saltsc- which -P '!'1~ns fori I' ' ~ i- -ui'i to iilit--jithsse w. IImouhfes andl analog -digital

±±:0an WF bo tW Tyiii 146j itiI -± is e::wteci tha. both of thi--irograms 70 to11 r~.h ra2rK- *p.i i

:, "'IS 1 ±.tt pr-:S-A pf lyni-qt' -'l have~ a majo'r imrpact.0 a s - - m a s i:~ t 11 realizedI tha j -a - .-ci1a., -. jf~t n be - ie in

a, moon - 1.i at- rial -u apaiie andj' the~ task t):', be

performe d. The pycof polyer 'andC molecuaI r d ynamical function-f,

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tetbook dlelsign mechanisns for non-von-Neumarmr pr,--1r, illormaat.nfusion and cnrter*t-ddressable resonanc.e .r'c on The enormous variety -.-

-- 7.--r,"'c oes.vn;er:ter variety fYf polymer ald molecular .. rl.... offers i al e .. e-architectural designs once the mind-set is discr:arded of the classical digital-4swit.h as the Inly building liock for architectures. New ,-olymer-based.-

-rchitectures cff-er more efficient analog transformations and silnp'iP&{ morerobust architectures dedicated to function. O ptical (boson) processing, unlike'. electronic r i:,. prOCe.- also resistant to electromagnetic.*: nterieren,::e..-"-:.-

The use of laser-induced cemt irc" heri'al synthesis techniques, -L;Eguir-Bl..dett monolayer sel.f -r...rin and precision chemical reartion-oping , offer chemical device fabrication and lithographic te.chniques withadvantages over current etch lithog:raphy. Precision in the achievement ofelectron mobilities and Ferni-levels can be obtained with chemical synthesisof donor-accept-r compounds Multiple-quantum-well structures can also be-.Clieved-with monolayer techniques and electrodeposition.

The fields of polymer and molecular physics and chemistry offer anenormous variety of material properties usable in polymer engineering.Pre.sently, there is a requirement for fundamental studies of (a) barriersmade from thin films and (b) methods to achieve molecular order. The use ofelectric and magnetic fields in polvmer processing for ordered materials is a*-subject under study.

in the first five chapters the theoretical physics and chemistry whichunderpin evice function is introduced. Chapters six to nine address theproblems of material orga zation. Chapters ten to fifte.en addressapplications. An attempt has been made in these chapters to indicate thepossibilities and opportunities in this emerging field but. at t2e same tire,

to:: indic::ate the difficultie-s. There are roses to be pi:ked in this field, but theyare surrounded by thorns. Guarding against, scratches, how.. ever, does not

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References:

(C I) Basic Properties of Optical Materials, NRational Bureau of Standards.I.ithersbrg, Maryland, 7-9 May 1 c4%:

((2 Topical Meeting on Optical Computing, March 18-20. 1985, InclineVillage. Nevada, s:ponsored by the pticai ciety of America, the Computer . -.-Sk,ety, of the inctitute of Electrical and Electronics Engineers and the LocietyAf t,-'.:,til-. Instrurmentati.on Engineer's.

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'C3) The 3rd International Conference on Solid-State Sensors andActuators (Transducers "85), -::pon:-red by tnhe IEEE Elecc: . eviesSociety and the Electr,oc.hermical Soiety, h. ld.h.., - .Pohl H.A. , Pollak, M ., .T. Chem. Pliys., 6. (I377) ,,.-... ,kum,8•1 . P.. and F'pi, HA.. J. P.lymer In., P -lymer Phys. Ed.., 23'

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I Polymer Semiconductors

In 1964 Little suggested the possibility of synthesizing a polymeric, organicconductor of high transition temperature. The mechanism suggested forachieving, this superconductivity at. room temperature was an electron-electron coupling or one involving the exchange of molecular excitationsinstead of phonons. The suggestion was thus named an "exciton" mechanism(Ginzburg, 1968) and can be contrasted with the BCS tleory involvinge -lectron pairs coupled to phonons. If not at room temperature (but at O.90Kelvin). the first organic superconductors have at least appeared. Theyconsist primarily of stacks of tetrarmethiyltetraselenafulvalene (TMTSF), themolecules of which are said to be donors in that they tend to give up theirvalence electrons. Crystals are grown in which the TMTSF molecules are

*. adjacent to acceptor ions, and they have paths of easy electrical conductionwhich are essentially molecular corridors. Along the favored direction, anelectron is scattered appro:dmately once every 1000 molecules, which is ten

* to twenty times less frequently than in a typical metal. These materials arenow known as Bechgaard salts.

The search for the true room temperature superconductor continues (Little,1963), but in the meantime, polymeric organic semiconductors and metalsand even organic superconductors of moderately low transition temperature(Jerome et al.. 1900; Chaikin et al 1903) have come along. The first organiccompound shown to display metallic conductivity is also now intensively

*.-"- . studied (tetrathiafulvalene -tetracyanoquinodimethane (TTF-TCNQ)). -"-It has been known for many years that organic molecules can be

semiconductors (Kallmann & Silver, 1960; Gutman & Lyons, 1967; Katon,19681 Meier, 1974; Kao & Hwa.ng, 1981; Pope & Swenberg, 1902, Seanor,192) but sustained interest began with the experimental studies of dark

-conductivity in phthalocyanines by Eley (194) in England and Vartanyan(9I 4' in the Soviet. Union. The phthalocyanines (Moser & Thomas, 1983)and the porphyrins (Lever & Gray, 1963) continue to be of interest and sodoes photoconductivity (Bube, 1960). The organic conducting field in general

* .-. _... has attracted numerous investigators and some of the important results havebeen summarized in recent reviews (Wegner, 1901; Baughman et al, 1982;Simionescu and Perec, 1902; Duke & Gibson, 190 2 Etemad & Neeger, 1902).

_* There will continue to be theoretical difficulties in the treatment ofpolymer semiconductors. This is because the conductance is dependent upondelocalized pi-orbitals, which are treated by many approximation methodswith varying degrees of success, e.g., valence band theory, molecular orbital

* : theory, free electron theory, etc. It is instructive, therefore, to trace ther development of free electron theory and note the problems still to be solved.

In the 1920s the band theory of crystals was developed resulting in theBloch scheme describing independent motion of charge carrying electrons

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and hjoles. In 19.31 the ,concept of exciton arose (Frenkel, 1931; Peierls,1932), which is an electronic excitation wave which does not carry electriccurrent - but does carry energy - and involves correlated motion of electronsand holes. Excitons have been found in all basic types of nonmetallic crystals,as well as certain rare earths and intermetallics. There are three basic typesof excitons: (1) the Frenkel type, which have no energy levels; (2) thecharge-transfer type, where an electron exists on a different atom to ahole; anid (3) the Wannier type (Wannier, 1()937), where there are energylevels of charge transfer in analogy to the energy levels of the hydrogenatom. Excitons can be associated with any critical point in the band structure,the criterion for existence being that the electron and hole have equalvelocity.

A related concept is that of polaron, which had an initial meaning of anelectron interacting with long-wave optic vibrations. The wider meaning isnow of a self-trapped electron or exciton and it is this meaning which is usedin descriptions of conduction in organics with nondegenerate ground states.Another concept is that of polariton, which arises when an e.m. fieldinteracts with an exciton in a very specific way. The conditions for thisinteraction come about because the exciton has a polarization which can beeither longitudinal or transverse and only the transverse exciton can interactwith the e.m. field. The polariton is created by an exciting photon and thetransverse exciton mix in a crossover region, both losing their identity in acombined particle of the polariton.

If one wishes to study polymeric semiconduction, one should be aware atthe start that there is even a difficulty in knowing, theoretically, what ismeant by semiconduction. For the delocalized states of the pi-electronsthere are a number of theories of carrier transport, all of which haveadvantages and disadvantages (Kao & Hw/ang. 1981). For example, there isthe energy band model - which is only appropriate for high mobilities.Then there is the tunneling model - which has failed to explain negative

_, temperature dependence of mobility and the difference between electronand hole mobilities. Or the hopping model - which only succeeds if theelectron-phonon interaction is strong. Or the polaron theory - the validity -.-.of which is in doubt for the cases in which the interaction between electronand surroundings depends on electron velocity. There is also a fundamentaldifference between semiconduction in inorganics and organics. It is knownthat the basic mechanism of charge transport depends on the nature of the

--.- electron exchange interactions and the electron phonon interactions.Whereas, on the one hand, in inorganic semiconductors the electroninteractions are much larger than the electron-phonon interactions, so thatthe electrons behave as quasi-free particles occasionally scattered byphonons causing the charge transport to be coherent, in organic -.-semiconductors, on the other hand, the electron exchange interactions are -.

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much smaller, while the electron-phonon interactions may be the same. sothat electron-phonon interactions may dominate. There are furtherdifficulties.

For en.mple, in order to describe the dielectric susceptibilities of these-organics there are a variety of models, e g., the resonance oscillator modeland the self-consistent solution mod..lel Unfortunately, there is no single._unique form for the spatially dispersive dielectric function. In 1 957Pekar, in the Soviet Union, pointed out the wave-vector dependence of the

i,, dielectric r ; s, no, fntion. Thi < m......dilecri repos funcion his. mreans that" the cornstitutive relation."--

-" between induced polarization and inducing electric field is not spatiallylocal. The determination of the correct linear combination of exciton-fieldcan be reduced to a boundary value problem, which is known as the problemof additional boundary conditions or the "abc problem". The origin of thisproblem (of nonlocality) is due to the propagation of the excited state.

So the desired characteristic of excitation propagation due to delocalizedelectrons brings with it theoretical intransigence. There are theoretical

o- attempts on the abc problem, e.g., the "semirnlacroscopic solution" of Pekarand the Hopfield and Thomas (1963) solution, but each is based onunverifiable assumptions and is also macroscopic, so a complete solutionmust await the development of combined Maxwell-Schr6dingerequations. Attempts in this direction include Zeyher et al (1974) andHyzhnyakov et al(1975), both having found limited success (Birman, 1982).

There are two types of conducting polymers (Wynne & 'treet., 1962). Thefirst category is a category of one - (SN)3, which is an intrinsicallyconducting polymer, and the only one. (SN), has open shell electronic

structure and has metallic conductivity. The more numerous second classincludes those in which the pi-bonding system, (not the closed valence.shells), have been modified by oidation or reduction. Oxidation leads to apartial emptying of previously filled bands, while reduction leads tQ partialfilling of previously empty bands giving rise to p- and n-type conductivity,respectively. The conducting polymers include. poly(sulfur nitride),polyacetylene, poly(1,6-heptadiyne), polypyrrole, polythiophene, poly(p-phenylene), poly (p -phenylene sulfide), poly (p -phenylene vinylene,poly (pyrrole tetrafluoroborate) and bridge-st.cked phthalocyanines.

References:

Baughman, R., Bredas, J.L., Chance, R.R., Elsenbaumer, R.L. & Shaklette, L.W.,SChem. Rev., 62 (1962) 209.

*1 Birman, J.L., pp. 29-81 in Rashba, El. & Sturge, M.D. (eds) Excitons,North-Holland Publishing Co, New York (196 2).

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83Braun, .L. -.5T. in Keler.D.aun. . ,:_--7.- in Keller. S.P (ec) Materials, Properties and

* .. Preparation, North -Holland Publ. Co., New York (1960).Bube, RH., Photoconductivity of Solids, Wiley., New York (191.haikin, P.M., hoi, M-Y. , Greene, R.L., Pl y .Colloque ., 4 (11 ..:' 78 j:'.

Duke, C.F& Gison, H. in Encyclopaedia of Chemical TechnologyA. iF 7 Q

Ele, [iD.., N atu re 162 (19 4A) 8 1 i.. Fren1Ikel, J1 Pys. Rev., '7 (1 1) 17 : 127 -

Gii! in u'' r :: ntetr Mp. Ph ysics 9 '(' ) ,-

-. Gutman, G LF T y ns, L.E., Organic Semiconductors Wiley, New York

Hopfield, .J. 8, Thomas, D.G., Phys. Rev., 1:')2 1::1.% 56 .Hvzhnyakov V.,V Maradudin, A, A Mills, D.L., Phys• Rev. , B I i (1975 10.Jerome, D., Mazaud, A., Ribault., M. &Bechgaard, K, .Ph ; - aris)I, Lett 41

.. k i1:% : 0) Lc95."

K alman, H. & Silver, M. Symposium on Electrical Conductivity inOrganic Solids. Interscienc New er 1960)Ka, K C Hwan,.g,- I-.... ., Electrical Transport in Solids, withParticular Reference to Organic Semiconductors, Perga:mon.New Xork ::I

Katon, E, ', Organic Semiconducting Polymers., Marcel Dekker., New,ork (1 '4:)

Lever, AB.P. & Gray, HB., (eds) Iron Porphyrins, Part I, Addison-Wesley,.--.-Reading, Massachusetts ( ' 3)Little, WA., Phys. Rev., A 14 (19 6 41416Little, W A, J. Phy-s. Colloque 03 44 (1 i : ,) .1 9

- Meier, H., Organic Semiconductors, Dark and Photoconductivity ofOrganic Solids, VerlaQ Chermie (19 74).

-- Mser, F.H. & Thomas, A.L., The Phthalocyanines, Vol 1, Properties, "R CRC Preis Inc., Boca Raton, Florida (1. 8.

Peierls, R. Ann. Phys. eipzg) 13(1.) 905. tPekar S.31, JETP 3.3 (195>7) 1022 (So. Phys. JETP 6 (1957) 735)" .Pope.. M. & Swenberg, C.E., Electronic Processes in Organic Crystals,-l:f ord University Press, New York (1 .2)Seanor, D.R., (ed) Electrical Properties of Polymers, Academic, New

. York (1982). S •Simionescu, C.1. & Perec, V., Prog. Polym. S"- 12: 133Vartanyan, A.T., Zh. Fiz. Khim., 22 (1948) 769.Wannier, GH., Phys• Rev., 52(1937) 191. - -. ,.-.Wegner, G., Angew. (Cherm. It. Ed. Eng.., 2 0 ' 981) t6 1. ...- .Wynne, K.J. & Street, G.D., Id. Eng Chrem. Pri. Res. Dev., 2 1 (l') zZeyher, R., Ting C.. & Birman, .L., Phys. Re., B 10 (1974) 1725.

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II Physical Bases of Excitons

A half a century ago the concept of e:tonwas conceived and since thenthere have been many attempts toc? refine the concept. with work still inprogress (Rashba., Sturge., 1W32). However, there are few unambigu,:us_exp eriments which d'.remonstrate the most important property of the exitc'rn.namely its ability t:) transport energy over large distances large in

. cormnparisor with atomic dirrienslons.. vie shall commence then with some* definitions off what at exciton is It is:

0 a quanturn of electronic e:xcitation energy traveling in a periodicstructure (nearly impossible to --achieve enpirically). ,,hose motion ischaracterized by a wave vector (De.ter & H-.. I 9().(.2 a particle able t.: transfer er'Er: y, but no.t charge, in "wave n.r.cets" Offe .- ,c.itatiort. C:ncernirig this latter one may ,bserve that although there aree:.-perinent.:s to show that art excitorn moves, there are none to show how far

* it moves. Given these definitions, and comments, the reader will realiseimediately that the concept of e.:lton is an idealised theoretcl c, ne

However, if the exciton :oncep t is not actuaHly an -.-rTbeon hn hrce an. "* , ser, -abler-e then there"-:.--__

are, at least, many experients requiring interprettion which urgently needto invoke it-s ep-:lanatory power.

P'robes of e:,citors in .semlti,:,duc.,:tors include resonant Raman and Brillouin-> .spectroscopy (Yu, 1979, and the rtonraarnagnetic nature of electrical

rtconduction in most polymers indicate. the existence of charged Boseparticles which may be excitons or polarorts or bipolarors (E.-razovskii ,Kirova. 196 1). From the theorist.s point of view, the field is a unique meeting

place of transport theory from a non-equilibriurn statistic:al mechanicsorientation, which addresses the movement. of the excitons, as well as theinteract.:ion of light with matter and the creation and radiative decay ofexcit" n s (Kenkre & Reireker, 19 62 '.. s rrent major theme e, :iton theory'

is the development c:f an account of the absct pti cn of light in materials(Davydov, 1962, Knox, 1963, 196.).

More recently, a new field has been created for the study of excitons at"'".- high density irn semiconductors (Haken & Nikitine, 1975) These consist. of

..hydrogen-like e-citorns which are made up of an electro," n in the c::Onductio-band and a hole in the valence band coupled together by Coulomb

-- interaction and perhaps modified by polarization effects The creation of high- concentratiors of excit,:o.,ns (by shining laser light. on insulating crystals) has

* -:-: resulted in the st.udy of different species of excitoris There are excitcnic-: n~, molecules (" biec:itors"), possibly Bose condensation of excitons; possibly* such condensation c4 be.'tns, electron-hole droplets whtich are bound .

maly by W l e a. ,:Winge intera:tion between electrons aind holes:- - p....il. .plye'..r itcn- and e 'er :y,.-.. excitons in ,7hich a quantum

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crystal is formed within a Crystal. All of sUh species are possible, recausethe mass ratio between the exciton and hole may vary over a wide range. -

Returning now tn the theoretical underpinning for the concept., andassumirg purely electronic states in perfectly periodic systems, the two

jorimgs a a solid, nar ely, the "ticht-binding approximation" and the

"Bloch description both lead to the conclusion that there must exist low- - _i tigIenery, excited 0ta.te of insulating crystals. The "tight-binding ..

appro:mation" picture is of a periodic array of atoms or molecules. The"Bloch description" emphasizes electrons traveling around in a periodicthe ucurs only -leipotential provided by the positive nuclei. In biological structures, onlychlorophyll arrays have shown clear-cut evidence of delocalization ofelectronic energy., perhaps some nucleic acids, and perhaps also, the purplemembrane of some salt-loving bacteria (Perlstein, 1962). Excitons confinedto a single molecule without charge-transfer and without energy levels areFrenkel excitons, and intramolecular vibrational excitations may beconsidered as vibrational Frenkel excitations (Belousov, 1932). Such excitonsmay also be of importance in conduction in organics.

For example, associated with the charge-densicy wave in organics is alocalized electronic state or states within the bandgap. Before doping, theorganic polymer isi sometes paramagnetic, indicating the e:dstence of spin. ..-__..The rationale is that if the localized state contains one electron, a soliton (or .c:harge-density wave) is neutral, with spin 1/2, and therefore is .---.paramagnetic. On the other hand, if the localized state is empty (doubly 'occupied) the soliton is positively (negatively) charged, with spin 0 and .-nonmagnetic. Therefore: doping results in conductivity or the ability to - -transfer charge, an absence of spin (the socalled charge-spin exchange), andeffectively a "hole" or "holes" created in the bandgap. If these "holes" arepaired with electrons of the dopant, then one has a type of exciton. This -would necessarily stretch the definition, as in the past the concept of excitonhas been associated with energy transfer but not charge.

References:

Belousov, M.V., pp. 771-607 in Rasiba, E.I. and Sturge, M.D., (eds) Excitons,North-Holland Publishing Co, Amsterdam (1982).Brazovskii, S.A. & Kirova, N.N., JETP Letters 33 (196 1) 6.Davydov, A.S., Theory of Molecular Excitons, McGraw-Hill,. New York(11962).

Deater, D.L. & Knox, R.S., Excitons, Interscience, New York (1 965).Haken, H. and Nikitine, S. (eds) Excitons at High Density, Springer, New • -York (1975). -

- Kenkre, V.M. & Reineker, P., Exciton Dynamics in Molecular Crystal andAggregates, Springer, New York ( 19 2)... - ,

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Knox, R.S.. Theory of Excitons, A,;:der,, New York (19C 7,) '-Knox, R.S, Introduction to E,':tn Ph :.s , iii f ,:i sirtnh :E. :1 1 Dnuacn ; cA:1Collective Excitations In Solids, v.:.luFm , N IAT'I' series New Yrk,Plenum.Perist in, R.M. 7 5-770 in Rashba, E.I, in,: tr,-e, vn .J ':ed Excitons.-North-Holland Publishing Co, Amsteram :, -HIr' Iu .., .; 21-, I Aiyi up 1 - 1 in I, (ho (ed) Excitons, pringer, New Nork (. II:Yi.

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10'T -tt and1 and ual ence

, , ',. a Yz' :l sd i n lesicriing -,i in in, fo ex mple,'it f p-t-t if ainal1 ou - -P.ll' - ..- in for tran -

I -, -r t' tip- .. . l .. nt.. .. ,,r,".nd :tats There is thusiS.1 ,- i sin tals and

" f.2, t±er. that tar-ns-pdlyaietylene at certaint dopant1 i . : -. r Vi s n-,:ond uc tor . aV. t other dc pant levels '1nducts

* --ilI vep n indj th-at, whereas? anac; e Can be madeS..- ,, b : t_,ctre mrodel, fhr example, between metals, semi-

0 i'.I "- i th , ie h,:ind :rid oro.arii:-, on the other, at the physical1.- ri level,.x, t-h other hand, -all three are different And again:

.... iiak se--'_. ;&-ns e. when the temperature-dependence cf thei. . .. ., ,hlv dop.ed tr.11-p-cyacetvlere is considered, to call such

=.: m_n:. a nth-etic metal", at the level of the physical mechanism,'t" - 1.-,lipon I,:n.r:tIe Wtates- in the case of trans-polyacetylene andg Iffere,,:es bet'een filled and unfilled electronic levels in the case of

rh. metf: 1,,1 the physcral mechanism is nonetheless different. Nor shouldIi- rr te Iounci states be considered the defining attribute of organic

,,nits, as examples will be noted below of organic conductors withoutI,- ,4fr4ate g::t~round states Furthermore, the soliton mechanism itself is

-I-ritiV not oni-dered to be the sine qua non of organic conduction atall d,-,pant levels and in all organics (see Chien, 1984b) And finally: the

-- in lion. ',,h.h -an be defined so rigorously as a moving, dynamicmathematical entity, is sometimes used in the literature to refer to a---,-astationary dislocation The reader may, at least., remain assured that

ra _, do, indeed, conduct (even with conductivities as high as IM'.ohm rn ) and await a completed theory of conduction so necessary to ""

craft{ in'g2 of., viv::,rner to funcstion. -" "

Nw, the HarniltoIinan derived by .u et al (1979, 1980) which vas written ..in terms of creatioi and annihilation operators and is now known as the SSHHamiltonian, ,:an be rewritten in the partial differential equation form to " --ojbtain the Cointinun limit (Brazovsku, 7 ,, 1980. Takayama et al. 1980). , - -From this Hamilt,::,nian one obtains a pair of Bogoliubov-de Gennesequations (inetic equations) the solution of which is the total mean fieldener!y C arnpbell arid Bishop (19611 1982at) Bishop, 1980) observed thatthese bugliu~v-de Gennes equattions deronstrate that the conductionmec,1ti"hanisr is polaron-like Using the analogy of the relativistic-field-

theory of ss and Neveu (Gross & Neveu, 1974, Dashen et al, 1974,1 9a b, Andrei & Lowenstein., 1979), they further demonstrated that the Su

-4 sl (slitor) kink-anti-kink pair has a single electron spectrum with twostatps syrnmetrically placed at the band-gap These states only est when

*A

thr w I: h r oitv sta th- Pj4. fi on :,-r the hol1 I is

Tim- n aol flf± 1J j T.): Pf' suid&Tiwp1' mIPn f

n~iien~d i' ymes.ondu~til-ri anisotropy is to be- exece ard hsbe

Slt1 ')prfisdan itrsitn foimcinmcaim obth rim-, n us -mindied: a n i nte r-s to. tion~ r -d omain -wal cnduc tion

zi n cisiinIii . The- , e~-es the , 'n f bott- a. ta solitori and

I_111P1 ~fr I t s7.ite

ii! Lida ii v n I has(-* two decenerat-k:

thus iritrinsK t, the ,rganv polymer. in doped inorganic semionductrs, cnthe other han, the st-at-es in the tanngap are dcopant levels (Bredas et :1,1964b) In the case .of p-ty,-,pe doping .f organics, the bipolaron levels in thegap are empty Contr-ely. in the case of n-type doping of organics, theI::polaron levels in the ga.p are fully oc:cupied. The bipolarons are thus

spinless

References:

Andrei, N. and Lowenst.e H, Phys. R v Lett-, 4 (1979) l.Bishop,. A.R, Solid State Comm 5 955Boudreaux, I. S., Chance, R R , Elsenbaurner, R.L., Fromrner, J.E., B6das, JL. andSilbey R,:'hys Rev. B 1, l '... in pressFrazcvskii, ,.. JETP Lett, 2a (1978) 6 N-::- .Bred:, I L Mol. Cryst Liq Cryst in preE;- (19 14Breias, j L, Chance, K.R and Silbey, R., Phys Rev , B26 (1982) 5843.__3Bredas. J L " ''tt. Sl .YaC uhi, K and Street, J ,.. Phys Rev B30 (1964a)1023SBredas, J.L., Themans, B, Fripiat, JG, Andre, J M and Chance, R.R., Phys.Rev. B2'4 ( 14 b) 6761Braz,.vskii, S, v Phys JETP 51 (190) 342.

Campbell, D K. and Fshop., A.R., *ys1 Rev., B24 (19 ) 97. -Campbell, E C. and Bishop, A cl.ar hysc B200 (1 2..1)6 97. -Canpbell. LK and Bishop, AR., " inolarc in Polyacetylene", preprint

:: ,: 1962b) '::

-hiarn:, (IC. Fncher, C R, Park, Y.W Heeger, A.J, Shirakawa, H., Louis, E.J., '* . au, S C and Maciarmid, A', Phys. Rev. Lett ., (1977) 10.-

Chien, IC.M, Polyacetylene: Chemistry, Physics and Material Science,A,: adernic, New York ( I 98' a)'Chien, j C N , Am-. Chen So. Annual Meeting, August 26th-3 1st,

* Philadelphia, PA, Paper 153 'Mechanisrms of Electionic Conduction in 7"Organic "Metals ' (1984b)Dashen. R F. Hasslacher. B and Neveu, A., Phys Rev,. 10 (1974a) 4114; I 101970) 4 130, 10 (197c) 436., 11 ( 1975a) 342; 12 (1975b) 2443.

Dlavvdov, A S. I Theor hol. 66 (977) 379,DaL yQv. A S, Phys StRt Sol (b) 90 1978) 457.Davyd, v. A S, Int I Quant (hen, 16 (1979) 5La.vydcv, A S, Sov Phs JETP 51 19a .- Oa,3,.L .vydo , A S, Ph, Sta-t Zol (b) 102 (190b) 275K Iivel n, S ., Iol Cryst LTiq Cryst 7 7 ( 1 1 a) g 5Ki, i'..I ... . Pn S Tys Rev Lett, 4!6 (1, IN I344

vFelson, S, Phys Rev '- 2 1 %.Ri M J, Phys Lpt , AT I l171) I,2

- . . - : . . . . . ., . . . .. . -. . . _ . . .7

17

Scott., A.C., pp. 9-82 in Enns. R.H., Jones, B.L., Miura, R.M. and Rangnekkar,S... (eds) Nonlinear Phenomena in Physics and Biology. Plenum,New York (1981).Shirakawa, H., Louis, E.J., MacDiarmid, A.G., Chiang, C.K. and Heeger, A.J., J.

Chem. Soc. Them. Comm. (1977) p 578.Su, W.P., Schrieffer, J.R. and Heeger, A.J., Phys. Rev. Lett., 42 (1979) 1698.Su, W.P,. Schrieffer, J.R. and Heeger, AJ., Phys• Rev. B 22 (1980) 2099.Takayama, H. Lin-Liu, Y.R. and Maki, K., Phys• Rev., B2 1 (1980) 233.Zabusky, N.J. and Kruskal, M.D., Phys. Rev. Let.t. 13 (1965) 240.

* S

. .-.-.. ..*.- ... . . .... . . . . .

. . .. . . . . . . . . . . . . . ..

18-.

IV Photon Molecular Switching

IV.I. Bistable Molecules and Photon Switching

Optical bistability requires some combination of microscopic nonlinearitywith some microscopic feedback We shall first. consider nonlinearity inpolymeric materials and then address how the feedback may be achieved.

Recent developments in the field of nonlinear optics hold promise forapplications in optical information processing. This field has emerged fromsolid-state physics and has become of great interest since the realizationthat organic and polymeric materials with very large delocalized pi-electronsystems can exhibit extremely large nonlinear responses (chi( 3), for example) ...- larger, in some instances, than those of most inorganic materials. It is nowrecognized that thin films of organic materials with even second-ordernonlinearities offer the possibility of novel phenomena and devices for lasermodulation, frequency conversion, deflection, power limiting andinformation control in optical circuitry, When large third-order nonlinearitiesare available, then degenerate four-wave mixing (DFWM) is possible foruse in integrated circuits with for a variety of purposes. The physicalmechanisms underlying the large responses of organics are different fromthose underlying the responses of inorganics (Williams, 1963). The origin ofthe nonlinear effects in organics is the polarization of the pi-electron cloudas opposed to displacement or rearrangement of nuclear coordinates foundin inorganic materials. An additional benefit of this circumstance is thatthere is a potential use of organics in very high frequency applications(due to the relative fast response time of the electron cloud) versus therelatively slower response time of nuclear rearrangements (Franck-Condonprinciple).

The theoretical prediction that a particular polymer in bulk will possesslarge nonlinear character is difficult. This is because a theoretical analysis atthe single polymer level is difficult to extrapolate to the macroscopic or bulkmaterial. For example, the second order molecular hyperpolarizability is zeroin centrosymmetric media and is related to the bulk material second ordersusceptibility through summations over the number of contributing atoms ormolecules per unit volume corrected for contributions from neighboringmolecular fields. Therefore, a molecule which is asymmetric and possessing asecond order hyperpolarizability may still exist in a centrosymmetric crystalor a molecular environment in which orientations are averaged (liquid oramorphous polymer). The bulk material, in this instance, will exhibit a small

U second order susceptibility despite the large single molecular or polymer,"- - .hyperpolarizability-

Despite this theoretical difficulty., the organics offer an empiricalopportunity to tailor charge asymmetry and provide the polymeric

-.- ,. . , . . ... - • . .'.. ' J,. -- -.... -. . . ....'° "...........................................................................................................A.. - ,

19. -

conditions for radiation induced nonlinear effects in one part of the radiationspectrum but transparency in another.

. Examples of optically nonlinear single crystal polymers possessing three-dimensional long range order include diacetylene (Garito & Singer, 1982),

. 1,6-bis(2,4-dinitro-phenoxy)-2.4-hexadiyne or DNP (McGhie et al, 198 1) and2-methyl-4-nitroaniline or MNA substituted diacetylenes known as NTDAand MNADA (Garito & Singer, 1982). Flytzanis (1983) has observed that inpolyacenes and polydiacetylenes Pople-Walmsley (1962) defects can occ urwhich are the conditions for soliton-type motion. The electron delocalizationlength determines the optical third order susceptibility of polydiacetyleneand its dynamical behavior is dictated by soliton mechanics. These defects(optical solitons) can be created by excitation near the main visibleabsorption peak.

Such organics are, however, essentially one-dimensional and their uniqueproperties arise from this one-dimensionality. The nonlinear responserequires response times longer than 1-4 psec. which are the diffusion timesof conjugation defects along the constraints of th9 polymer chain. In three-dimensional semiconductors, on the other hand, the response is almostinstantaneous.

An interesting technique for the investigation of the third-order nonlinearsusceptibility of multilayers of polydiacetylene has been reported by Carter-0t 31 (1983). This measurement technique has possible device applications.Polydiacetylene was deposited to a thickness of 5000 A one monolayer at atime using the Langmuir-Blodgett technique on a silver overcoated gratingetched on a silicon wafer. The third order effect was measured indirectly byits effect on the refractive index. The grating permitted coupling of a freelypropagating laser beam into the planar waveguide structure formed by thepolydiacetylene on the metal. The third order susceptibility is intensitydependent, so changing the intensity of the laser beam permitted the.observation of a change in coupling angle to the waveguide mode. From thisan estimate of the nonlinear index of refraction of the polydiacetylene near -- .the absorption edge was obtained.

We turn now to the use of these organic nonlinearities in optical switchesbased on the principle of optical bistability Optical bistability requires acombination of microscopic (material) nonlinearity, which we have alreadydiscussed, with some macroscopic feedback, so that a device's tiansmissiondepends upon the output intensity. This occurs when a nonlinear opticalmedium interacting with a coherent. driving field has more than one stablesteady state. Now, the nonhinearities discussed above are intensity .. "

* dependent, thus it should come as no surprise that the current problemswith optically bistable switches involve the difficulty of obtaining

-..:. adequately fast switching times at sufficiently low powers or switching -K energy to make useful devices Attempts t.o minimize switching energy have_ 0

involved the use of Fabry-Perot res nant cavities (Agrawal & Carmichael,c)7(" Git:, et ". _. , gr-- FvtI-)7., :.s et al, I N)0; Aorawal & Flytzanis, 1981), but, of course, thisincreases the difficulty of fabrication.The quantum theory of optical bistability has undergone some recent

ieveloprnernt (Drurnrnond Walls, 19'81 Carmichael et al, 1983). TheObservatiorn of bistability can occur either in the absorptive operation, or indispersive operation with detuning of the laser and interferometer from theatc,mic t-ansition. Cooperative effects- in resonance fluorescence are alsopossible (F.cnifacio & Lugiato, 1978 Donifacio et al. 1979). Radiative andc*6:lhsional damping of atoms and losses at cavity mirrors are modeled bycoupling the atoms and cavity mode to thermal reservoirs resulting in aFokker-Planck equation or quantum-statistical treatment. Thetheory remains, however, without empirical confirmation.

Recently, however, a new type of optical bistabilitv has been discovered,which requires only on a material whose absorption increases as theimaterial becomes excited (Miller et al, I 94a). No mirrors or other externalfeedback are required, as the feedback is internal and positive. Furthermore,new electroabsorptive processes, 1arger than those in conventionalserniconductors, are seen in room-temperature GaAs/GaAIAs multiplequantum well (MQW) material (Chemla et al, 1983; Wood et al 1964).These new developments have been combined to make a hybrid version ofoptical bistabilitv in which a micron-thick piece of MQ is used as bothdetector and electroabsorptive modulator (Miller et al, 1984b). With only aseries resistor and a constant voltage bias added to a p-i-n diode (where irefers to the MQW material) the resulting device is referred to as a self-electro-optic effect device (SEED). The switch is activated by incidentlight at a vavelength near the exciton resonance position for zero voltage

.- -. across the diode.With low optical power, nearly all the supply voltage of the SEED is dropped

-- across the diode as there is little photocurrent. This voltage shifts theexcitation absorption to longer wavelengths, i.e., lower energies, and therethe optical absorption is relatively low. Increasing the optical power . -increases the photocurrent, reducing the voltage across the diode. Thisreduced voltage, however, gives increased absorption as the excitonresonances move back, resulting in further increased photocurrent. This canlead to regenerative feedback and switching. Switching time has beendemonstratted in the nanosecond range.

There is a large family of organo-metallic compound semiconductorsthich possess threshold and memory switching. The electron acceptor

molecules 7,7.6,-tetracyanoquinodimethane (TCNQ) and 11, 11, 12,12-0 tetracyano -2,6 -napthoquinodimethane (TNAP) have been shown to produce• - -electrically conducting solids with aromatic heterocyclics, as well as with

alkali, and divalent transition metal counterions. The electrical conductivities . -

.'.."'-. .,... -'-

-. • . .r r. -1

oV --

Of TCNrf and TN A P Cirlexed ,,,ith e1e,letron donfo rs su ch as

tetrathiofulvalene (TTF) have also been intensively investigated. Sharpchanges hav been report d in electrical conductivity due to phasetransition, in both TCNO. and TNAP complexes induced by varying the

.tperature :f the material. More remarkably,, a reversible electric field(light or em. field) induced phase transition has been observed in films ofeither copper or silver complexed wlth the electron acceptors TCNQ, TNAP or

* ~~oth~er TONY derivatives (P:oternber et al, lI -?" Poeleetl,194:Besoet al.. 1983). Thi; remarkable t-ransition is accompanied by an abruptincrease in the electrical conductivity of the organic semiconductor ,.hen theapplied field surpasses a threshold value. The highly conductive stateremains intact as long as the field is present. On removal of the field, the

- .: system can either return to the high impedance state, or, if a voltagesignificantly higher than the threshold voltage was used to induce the highlyconductive state, the material will remain in the low-impedance state after .

0 the applied field is removed.For inte,:rmediat field stretths,. it is p ssible to operate a device using,

e .g., Cu-TCNQ, as either a memory switch or a threshold switch by varyingthe strength or duration of the applied field in the low-impedance state.Although the limiting speed of response is not presently known, a Cu-TNAPsample was able to switch and follow the rise time of a 4 nanosec. pulse(Potember &C Poehler, 192). It has also been demonstrated that opticalswitching in such sermiconducting organometallic films can be erased using

-" " the heat from C02 laser radiation (Benson et al, 1933). Of special interest isthe possibility that below threshold a device using these films might addinputs algebraically, a capability offering the possibility of the fabrication ofanalog-digital hybrid computer elements.

WI.. Switches Activated by Polarized Light.Refraction is one consequence of the scattering of light by the electrons

and nuclei in the constituent molecules of the medium, and can be- accompanied by Rayleigh and Raman scattering in all directions. Raman

-.- activity is dependent upon an induced polarizability due, almost alavys, toan induced electric dipole moment. An induced magnetic dipole

.-.. moment also can occur, but. usually at. a magnitude I06 less than the- induced electric dipole (Chiu, 1970). An exception to this magnitude

differential occurs if the incident light is (a) in resonance with a magneticsubstate split in zero field, and (tb) an effective magnetic field able to interact.

* with magnetic states, i.e., the light is circularly polarized. When conditions (a)and (b) apply, the ratio of induced electric to magnetic dipole is 1:1 (Barrett,191 1, 1932)

- - - i . .. . . . .. - .-- .s.-*- -7 - " - -- . - "- - . . , ""- , "

,-:

If the itera,ction of light and magnetic substa'te is of the kid in 'hich thesubstate is filled by an electron from a donating molecule, then a specialinteraction occurs in which the substate, populated by circularly polarizedlight photon energy, is "otherwi se occu.pied", and cannot play the role ofelectron acceptor If the electron ,jonlatinc, molecule, now prevented frorr.donating, becoimes a p-semiconductor when it is able to:, donate, the molecule -now be,::omes less of ; conductor.

This. situation was reported to oc,ur in the phthalocyanines (Pc), whi,.ch arethe lec tror donating species, ard o xygen, which was the electron acceptingspe.ies, and the magnetic sutbstates of w,,,hich were filled by incidentcircularly polarized radiation (Barrett.. 196.3; Barrett, Wohlt.jen & Snow,..-

Light interaction with the Pcs in an oxygen or electron-acceptingat osphere is possible from two points of view. On the one hand, magneticincular dichroism studies of the metal Pcs indicate resonance interaction

with the central metal in the red (long wavelength) end of the visible'E:ectruI , On the other hand, light interaction with 02 adsorbed t.. the Pcring o -c.-urs over most of the visible spectrum. However, the two effects weredissociated by studying both metal substituted and metal-free Pcs. Thedemnstrated ability to modulate, with circularly polarized (versus linearlypolarized) light, the electrical conductance of Pc films sublimed onto an 0interdigital electrode surface is due to light interaction with the electron

-- . acceptor, 02, rather than with metal d electrons. The effect offers the-.: possibility of fast light-induced switching in electron- donating/electron-

, accepting sandwiches. More investigation is required with monolayersandwiches and other semiconducting organics.

References:

• " _ Agrawal, G.P. & Carmichael, H.J., Phys. Rev., A 19 (1979) 2074.Agrawal, G.P. & Flytzanis, C., IEEE J. Quant. Electr. QE-17 (198 1) 374.Barrett, T.W., Chem. Phys. Lett, 78 (1981) 125.

" ' -Barrett, T.W., Chem. Comm. J. Chem. Soc., 1 (1962) 9.Barrett, T.W., Thin Solid Films 102 (1983) 23 1.

re Barrett, T.W., Wohltjen, H. & Snow, A., Nature 30 1 (1983) 694. -Benson, R.C., Hoffman, R.C., Potember, R.S., Bourkoff, E. & Poehler, T.O., Appl.Phys. Let... 42 (1963) 5.,Bonifacio, R. & Lugiato, L.A., Phys. Rev., A 18 (1978) 1129.Bonifacio, R., Lugiato, L.A. & Gronchi, M., pp. 426-4 50 in H. Walther & K.W.

Rothe (eds) Laser Spectroscopy IV Springer Verlag, New York (1979).Carmichael, H.J, Walls, D.F., Drummond, PD. & Hassan, S.S., Phys. Rev., A27

(1983) 3112.

- ....A . . .. ..

'atr li. he;n .. & Tr ipathy. 5. pp "I'. 213 -2 -)In Wii Di -ej

* (hrnia)., D S , Dmen, T C . iller D.A.E. -,- Tard, A. . Wiegmann, 'A, Appi.Phivs Let:lt I 1O;:

1-i iu., Y -N I 'Ihearr Phvs, .52 :1 7): 7 .'± 1D"rurrmn,J P.D. C& Walls, 1).F_, Phvs, R-evy 'A r1.,)

Iftan: 7-p 1 [;E in Wliiilliamns, D J lcr I'-- . Jet! ait ATF & t 'ii L i ou,; O

Gil -1Iill, L. 6t Vf1:at4s an. T.N.Cup t. Enr1( 3''4MTi- F'Lip'-' mr ' F G a,b F. ,J De-o-ai, K.N. ILIynaan'n

MillerD A. F Li Ua.-'t Foc,-us 16 1 O4 1 2 (4.* ~ ~ ~ ~ ~ ~ ~ ~ Y Milr I -td l: i-rn,-i tnn W' Opt. Le:t., I (19 4.)b2

Miller, D.A.B.. Ih'-inla, D.S., Din, T.' Gos krw-& V! A ,: C f Wi nW.WodT.H. CS Burlu (i. C.. Appl. Phts LAt4't cj (Il.n'wPoe~hier, Tt' , futember, R.-. Hlfrdn, R. Be nson, K.C, 11Iol. Cryst. Liq.Crys Tt. .10 7 ( 19P4)91P'ople, I.A 1W amnslIEy , , S. H., Mlol1. P hv.( 1 9215Potember, P. S., Poehier, T.O. 8/ Cowian, D.C., Appi. Phys. Lett., 34 (199) 405l.

PoebR. PS., Poehier, TO1 ., Rapoa, A., Cowrv,7.-an-, D.CO. B loch, AN.R, j. Amn.Chem-rn So'::., 102 (19 0)%5.___Po te,rn be r. K. S., Poebhleir, T.O., Cow7an,. D.O &Bloch, AN., ppl. 419-4268 in L.

-. -. Ac~cer ed)The Physics and Chemistry of Low Dimensional Solids,Keide l (1960)Potemrber . . 84& Po'ehler. T.O0, Materials Science 7 (19(:) 39Potember, R. S. &, Poehler, T.O pp. 233'-46( in E.D. Felt &C. 'Wilkins (e'i)Polymer Materials for Electronic Applications, ASSymposium SeriesNo 164, Amnerican Chemical Society (1062)Poteniber, R.S., Poebl- er, T.O., kappa, A.., Cowan, D.'. &% [lochi. AN , SynteicMel~tals, 419,2) 7 1.Po-tebr S.Pohr TO. &Benson, P. C., Appl. Phys, Lett., 4116)54t_Poternber, R.S., Poehier, T.O. &Benson., P. C, Appi. Phv.s. Lett, 4 1 (19254Potember. P.S5 Poehier, J. Phys. (Paris- ' Colloque C 44 (19 33) 17160villiarns, D.J.ed Nonlinear Optical Properties of Organic andPolymeric Materials ACS, Symrposu Series 2J American Chemnical

* Society, Washiington D.C. (1963).Wooxi, T H., Burrus, CA.. Mliller, D.A.B., Crhemla, .S ,[amn T.C., GlossardAC: 7YY iE & ;-, Wi j nn W, App Phys. Lett , 44 (194)1

* - V. Properties of Bioconductors -

Thep term bicn ductr c:an b~e uewihtodfrntmeaningsc. TIhefirst rr ~jn'~ refr tolhiprenl udcidIseofw thr.

bicPci~r~r m in i -n ll% ~ ernvnn t r Th c fjmaflr 4--;t

to-it tflu A I i ntn thf(AE1 - i t, rUt kdm t ' l t v.7t -ii 1uh'ae1.' la t1-1

natura-l tl-i 11, -a t~o': .ni,'~ 1 1-i;. as it a nt j tW-e i mip-tmnmight be dcoped ti'- o r n n't'n qit ohe.1 than in its naturallyA

ea 1lhtt Of HI if U 1 lift n di 9'2n1, th is i the? h ar dest to

*have_- the p.roFj> t~-t - -.-If . aQlJc c iii Ii q I4 1- i;t- '; 'a -otltd th-t-C T1 TMit 0LWf't 1-~4 i'prten nY2 beav Iil' -. ~ T -. ,

- ~ ~ P ..1-' 'c:nlitin bads notitherI -1io' dj 0. ice thtat. -4'" t mcexiainenergy migrate betwee n rrii. amr~ino acid n__J ~r

Sze~ ~ ~ ~ ~~~~~~~~~..- ntGo 15smr~d inie wsc ticsc i hCg'uiruds that..bancL-l rina a1 tct sytm asprtin naciroolcules- is o f the; Orde -r o-ftCVso that under normal tjemperatur-e 'conditionis, there- would- be, no nigntiori- o.,f

elcrosa(t.1 h J:'anc.p, and hlencke n 'co di xdction . Fu rthe+mn-,re,thAene 01lwligevs of elestfottic ne tral x(1it'tK 01 pet1:b~d

is ncn p~troco'ialyhence there woculd appear to bep little interactionbet.w~en the-'rn. In1 .li:ni~fl h itac ewe lcV h lcccie iy-anitd n~ux:pe bad ehul beofth cdef the--rm-al entkT

Fut-h~- in 'I-. p-elctins te artili deloc (aliZed o,:nly in sin:iH r'-tv'I,rii .l -T ~hare separated by insul-atiit, ou

H -. ithe-- ar-gumntn oewter potis eruonu ll,ad dresse d the spesial. .cai s(:'f intrinsic ciu(:,.nrI ucti~lr- c~~.il n, rea . a

proteins c ti tan t -i -t V -' - -irfuiy .* ide groulps; etc.+ If thesce side grcoups were dope~d in vit-ro, then the questiojn

f1 servicoduct.ion mnight be ;answvered quite difrn l o the. argumnertapearsI still c:F:en' Yet. ag a In,. Sc Me fel that the Multitude of electron aridhoetiaplcAtlcos to a prten' C:ncli xont ds mmaht preclue the

motio'n o-f ch-arge c-arrie.rs over larne d is tane (l I umen- 11fe Ld I d. I*CerTtainilyV, the_: primnary-7 igcah t poesin photosynthetic systems

cl~rfc'usratessinscf'EntC~oCIc~~i:'. u-rhrmore. in hlighet- Plantclornpl.actc mcI baterial c _hrorna torpho>r-:4 thev itatmn rrri'' m rni)ate

thr'u~ah an enserntle cf dye -p a c ked moeue er - q ehns

*~~~~ ~ ~- -* ,*9, **

sera;.3rIn m-r hh r CteKsstm

Turninc! tob rP th5-f3 et biunu)tt as exepliti i~'11nr bioircdyr

1ffl ~ TI4 T1ft j - u4F ~ni ~rain n I tl a

peIci -r np-Mi riFM ~~ 1~h''t~-mwdepr 14! f, tr4 ~ -i in f 1- - -lic nat)--U -tu IFn te

I-,van -1 s-tin iiC~ '.tn -*it F) h A4. tt FijiJ in it- o4 Ft i I (ITj T ,

is that "nmuFr:rtitetujrPs, n eercgent of 'a miateri-alsphsia

* maE-I iN nl npni iuP'in their refiiefEn. fr the tiuan i 1n

oiir dnt if 'a tinacmvio nn-on Ne-um-ann proce .ssi;nojrutht mr 'A, ml' Lc -d iF 'ital h, btrtJd 1 rn enrt c-omputaton may be sueiri-

mi - --n 1-nt t-t i IF - in -:1: whc euire COMPfIXWiItI'i~F 1FtiIfi F 'l!V im i' ~i~F!liKF ( -iomatio and Oc'ylaAnE

f jp.1li 11'1~~fl ' B ~.C~} i 07lthre1 tenerve impuls ofte

iti -mn~lI-I-; h Ut1 kn eleit of rlervrus sv-'ste rnc;SJ-{ 1 F Un--h t r .II .Intf i;- unlikelyJT tD b'- e d inf-, pue

- tI&~ 'Ii E i P' Lf)F iI /1 I -I,-eC n ioi cocntration grradient.

breal~~~~ 3, -~rrlaere:hsn St~ o slo w, arid requires met~abolic.i: rj Jt'li-U the : Iii-jj_- I ! -hr i nlu.t'hera impulse. I t worjuI l seem tha t

in Ih~I -- al 1bI.II utL n'

diversity. Just bees use struc aral independJece is pr-eset7a does 170t mean that tuncetional inadepen0dence of eeet

tfl4i~i7'tiY: :.(f the solid state physics of the contact junction ofthin materials TPt- lirctxmtntintj;ujY ii1'- tip- c'ht-nn

n~ar~t~a-dp~xtxt.minimum thickness Schottky barriers, Ti-

>ictra t esign preIc- I ated nn th- trat-ria CFls '-s prpeti 1 inanalg-dgita hyridmicreleenKThere: is lsoth questin-Ti 01

r~~erdvieTToldb had sa le Ty t h t h k- e rsr Itlv- E? 'sf (-)- t 11tY* fesibetut if it is" it 'acull s-till bet~ ±th-aeo te JI

mer~~one ada ritge

References:

U flnEonfeld, L.A., Problems of Biological Physics, Spiner.aw Yo-rk,I p

FoseT_ Ann ., 2 KiY't .

P. , *".%ASA~ f~*14 Ia. 6

ANature 14 1.A4t) IcUzgiris., E. E anid Kornbt,-rg. F: VD. NaW'-.n '1(9jY17

7 it,

1 h -1 th

j' t7' , t

1''t''

r j4 4.4, 4~~r 2,~t-.. *tj4 ,t r

1 T1* ,41 ~~ - ~ $ - ~ pti4..u I E, fil 4h .44 , iL. h are

45j iA,t jKrr- .cs-

$t TI . .

44, ..Z* -Atj 4'.

I~' A

pr ii ty "~-*.. supe..'.t* ites ~ V r~' b ,~ 4 r.,

:1-

-- t-1 T' 7 fj J4 I ee~17 v~r.:l. AI n - t ~ ~ 1 Sili a b

~nJ j.i~:' ' - n~ 4 Ea xe' aiV-

maeral nt-V'IV. ~; a .m A , auPle n ttY

1 1 1d £n o n ti ni --if~t n on ;if

. ..-- °±

-_;,:. :.- e, _ L 1,., Insoluble Monolayers at Ltquid--Gas Interlaces :': 0,,,- V , ,

t , r

I

ilS

-n S

* S b - -

w J - -, -' . : .

VI I Organization of Polymeric Conductors

In ecet yars nuieruspt'l eK materials have been synthe~evn 1, on r clwi il complexes with codciiisin the

semiin n to -t-me~l rrlr~Tb nzato oYf these cofliup;3tk.d V.akb-ne..-7ol _ni- -. 1Cheel1 1lt n' lectr,::n donor or acceiptors to,. po-lyr.- ti -- ti k:, I l-i jj-:ra-phe&nylenei, polypyrrole.pold p1t ~peyte uiA ~Jp ltphene The simnilarity of thne

dc~~~ ~~ 1t11 f yerisI i ~ -irsreslte in a search for a unif inQ.un1i> Fmdlt. t I- ~it'dc io propertles. The concept. ofcnn n -i in',x ~lrP -h f V asIntroduced byv Su, Schrieffer and

Hee' :-'1 ' r *'ppli-- tcf rt -in-plvcetln This model wa-S extendedto pp'1V lA-:r~-vl~rn: 1 f' -las t al, 1 (4 '2, to polyparaphenylene

1: Bdri's t al, ~ 1 4 -'~ vai aIv p.'vho rie (ea-1 ,t, al, I C1 a, 1 'vw:Th ~ ~ ~ n( -)fi t 1 11tu tu-i the model4 have aIso been explored

17~akauarna tA al. Ic 1it a k: 1a, 1 y2a b~c. E-aensvyl and Maki, I19W')It appar ta t trnpo ?ctyli;ne (ard also the as:- ye(t unyt e

r,- lX~eeehce Dura 4~11 1cfl qijte differerint frorn other,nFuatd olmers'_ in that. the grround -4ate -~~dn ge, et, is

I enrteOe oseunc f this uiqueness is that in the dopedVimpla:eyeecomplex the". possicbility exiusts fo--r intrachain transport

Ic islae c re soiton rs Howver, thei lack ofsiilar degenerate& groundV tsin otheir do-ped- polymrs leadsI to a des--cription of mobile defects as

cope2airs of s olito*1nlike1 defects, referred o a pL arons or Lolarons;The eplanaion o el~triaonut in or-ganics is even more

c r sd in that nt a-ll the-- empricl vidne related to conrduction in thesecrg'ainic 1 s in a,2reement with the sci~nmodel (Chien, 194.In fact, the

tnitthat canbe-:ai frtiw 3 ha cnuctio by roditon -like mnechanismslii, atf dt I pint levels, but pro bably not all At. the time of

wri~~~~~inu~~~ i''- f--i7'iico leewch sup~posedly c-onduct usingsolb i ii i ii Ii IdliiLAJth ft-t cV~'cv-f conductors descrbed

Vip -V ac 1afitnishTed tb&eoretical picture of

Thzr 'i.~nin :,eit (6o1110- by th us;ual lithographicI I1 ju~ ~ ~o l ih i - tha--t the: condtcting mnatierial is a

complex, t1 V is,, the or:onI tin-2. a u rer kurcor re-quires ionizationari tisluI. nc i dpin D pii~ iy c~ivntlorinal mnetho,-ds would preclude

any; cheicial svnthesr;l for A- hrv de~vice fabrication Attempt; in this* liectin wuld e gratl ad .jnced if the organic complex could be-

Iri t-;eI J E~ Luri the oanic coplx could be synthesized, thecnp~ue ml: lewilbe-1 onet: of many sucvh, w,,hich together form a

"- ..-. r C ." r r

1 :ductn elenient of a device Inter-corplex electron h-,.:,ppizg must a!W:,'7:,:::,c,::'sir therefore. -

The organization of different organic complexes in one device mustencounter the Iifficu.ltie.s of interfacing materials of different latticeconstants Thfe great, advantage of superlattvCes is that lattice constants d"not have t, be rnat :lhed, but their methodi of conduction is not solitonlike. Itis clear, therefore, that the organization of soliton conductors requiresfurther research,

References:

Baerisyl, I. and Maki, K., Phys. Rev., B26 (1983) 206d.Boudreaux, DS, Chance R., Elsenbaumer, R.L., Frommer J.E., Br.das .L.and Silbey. R.. Phys. Rev. B31 (1985)

Bredas, J.L.., Chance. R.R. and Silbey, R... Phys. Rev., B26 (1962) 5643.0 Bredas, I.L., Scott, J.C.., Yakushi, K. and Street.. G.B., Phys. Rev., B30 (1984a)

102 3.: Dr~das, J.L., Themans, B., Fripiat., J.G., Andre, JM. and Chance., R.R., Phys.

Rev., B29 (1 64b) 6761.Ch ien, J.C.w.W, Mechanism of Conduction in Organic "Metals", paperread at the American Chemical Society Annual Meeting, Philadelphia,

-:::.- Pa, August, 194.*Maki, K., Phys. Rev., B26 (1984a) 2 18 .

Maki. K., Phys. Rev.. B26 (1984b) 2 187.Maki, K., Phys. Rev., 52 2 (1 (j 4c 45 9SM., W.P., Schrieffer, J.R. and Heeger, A.J., Phys. Rev., 522 (1960) 2209.Takayama, H., Lin-Liu, YR. and Maki, K., Phys. Rev., B21 (1960) 2303.

.. .. ...... .. -. .

• >°.- .. * j-l ',w

VIII Devices- Materials Considerations

A broad classfic-atior: of ,roa.nic ds with enhared eletrica .rpertiesinto two tyes,,. has been attemted Vay:i.kurnar and Pohl, 198i The firsttype consists Af the charge-transfer complexes ;and w,uid-include the-charge-transfer salts arid also those organio. with slitc r propertes wose"conductivity also depends upon spin- hare eha.ie, eg. trans-

.. .r aIc e I ". I .. / . .lyti.phe e, olypyr ,tc. ''"h prn , pnly 7e nyleresulfide). Correlated t lectrn-hole stt. t-it ha - _patial x-etent of one ortwo lattice constants w,,-ere termed onic .tat,.' by Lris l 1'67) and are nowcalled charge-transfer eZcitons (P.ope and Swenberg, 1".)- Theseinterm..ediate ec.ons can be thought of as distorted Wannier -like 'excitornsdue to the anistropic nature of the molecular crystals. The second typeconsists of those polymers with inherent long-range delocalization andthese include the polyphthalocyanines and the polyacen e quirione radical(,PAQR) polymers (Pohl and Pollak, 1977). The giant polarization observed inthis second type is due to long-ranging travel of freed c,::harges or 'nomadic: -polarization" or the res,ponse of highly delocalized carrier-- as they tw-lusually as polarons, over the long molecular domains provided by the

associated pi orbitals of properly conjugated polymers.No, although polaron-type conduction is postulated for some cases of the

first type - in particular, for those with solit-n-like mechanisms - the -polarn miechanisrn, in this instance, irolves degeneracies in ground statesor Franck-Condon-like.sttes, both in short-ranging orbitals coupled byphorons. It seems reasonable, therefcre, t assume the aforementionedbroad two part classification, and it is the -e,:d type, cr those with highly adelccalized carriers w+:hich will be considered here.

A case .can be. made that this seconl type is much more stable than thefirst. The first type includes many which are thermally nsta ble and aresensitive to atmospheric attack. The second type are highly stable dow n to,.770 K and highly conductive. It includes ickel-doped pyropolyrers (Wyhof

and Pohl, 1970) and other pyrolized polymers. The term "ekaconjugation"(as opposed to "rubiconjugation" was proposed for these polymericsystems (Pohl 1 966). An ekaconiugated structure is one in which, as thedegree of polymerization increases, the energy difference between theground state and the first excited electronic ionized state approaches zero. Onthe other hand, in rubiconjugated structures, the difference in such energystates remains nonzero as the molecular size is i:::reased To cbtalnri

-:-:_:-- enhanced electoactive c.aracter, materials must possess con;ugated spineswith stabilized orbital delocalriaton pt er nttin- critinuous intramolecularoverlap of pi orbitals extending over lonig dIhciti Accordirg t the tnomaddic W

polarization theory of Pollal' and Pohl 1 97C the dielectric c::ornstarnt slou. 11-,vary with the intensity Of the af..lied field.."th thme square of the chan

%*7 -,1 .97

A

l&:nc'th 'A th& p ler, a-nd, w- i a-ppliedl freuev y T i prd cLhascee

These~~~~~~~ hihy-;at-d~~flr ' rpare 1wa yrlizatiente biqu nd fin, 2ondt't They,, are? thus in an"ams

rapieiestat He- ti?- ih in r.nough fI tbi:-t "b'ase sttnCk",pro-.pe rties, that diletrc o tta i ts frr I- t, ci ionutvis

As the py1iair prduc a r inras In thi AZz. the e~yfW thI; inlt a:I C th mntan§m ronu ti, r Fo : xipe the hopTpirf of a

* ~ ~ 1' eetroCn-hode. Pair (eior)!cmmreue v l- 'vb- isthe migratic-n ftth* xio.When the; electron andi the; hole 17umrnp **~ter frommoeuet

rricc ule rtI(a --s they mnic-rate. ehv the ihtLmdn '- and the nwaif.?1-itaticn is ai FE-enikel e:xcitonr. It is also.. p si I I fto tht- el arnamd holE- to-bea on dIifferennt mlcls but in eachter .1 ' vi ity this is the 'weak-

bidn aeandI the miprating excitation ic, ow spre.,ad ove ?r sTeeralmnolecule (or ioris) is A Wannie:_r ezioiAi m od~nresult.,:fromn incre_:asedI p::dyrneriza--tiori (with p-yrolizatic i), it is likely that some type;:1 Frnlckel excitations are? involved- It is beS-t to4:ll oetees thla~t the;W,4annier-t\p andi Frenkel -type exiosare proba,_ibly e:ftees f a

These:; eka con u Qat ted polymers cl-eazirly offer advantages in stability, highrid tivi tvadh:hdeetric ccnsta ri ts. The ir pre-;paration v a

pyrolAizatiori process p)r EcIude them howver s rm anIheia* ~ ~ ~ ~ i-hrrtpyo uling fromn smrall up;'i.ards in analogy to theMriiec

synith-sii techniquje TheyT culdI be: usCV v"- ahbi thdw-thezn -C; u" chnlique. 1earlv, the? t.vyt -(rl:::I.tvmEr ;c, norotth

Sp-Ad 4f .ondui-ction nor, prsnlthe envir:nrne'ntal stabilityV of thtese* ty'- t m'except. perha3ps, in the, .ase of polypyrro'-le, andI alsoplaeyln

* ~ r oc corin, to reetunverified lain frm apanese company).TI It is likelthe-re fore-, that the EkaCorjiiuates have: adv1arita yes?--: too glreat to. a2nrJnd

4 w~ill never te superceded ( by the yp-oe ontheestetw ye* materials each havea their advanae and disadvan tage.

References -

Lyons, LB ., Aust. 1. (tern., 1 1' (1 7i7*Pcohl, HA,,,,.Chap. 2 in J.E. Keaton (ed) Organic Superconducting Polymers,

DEkkemr New Yor'k(1'6.Pol, H.A. and Poll.ak, M., J.t:Iirln P'hv ,-. u 7)40

olaM. arid Poll, H.A J. Chern Phv'. 6.1 (1 ~%'2:t~!ope., andl S7wenbeng(, 1- E, Electronic Processes in Organic Crystals..

(lanendon Press, Qzxford 1 ('i/2

an Plymerl. Hd. oymr hs.E

Wuhfjo J.R -and Pohl. H.A. . Polvmn. Scl., A-2.. b~ (1970), 174

IX Polymer Interfaces-S

A distinction wacs made above between conduction in (1) -h - -ta sf2?complexes which include those to which soliton-like properties a.-- tattributed and w hich possess distorted Wannier-like excitonic st-M s., -andthose polyrners with inherent long-range delocalization for which the-conductivity is attributed to the response of highly delocalized carriers ardwhich possess Frenkel-like excitons traveling usually as polarons. Type (1),,,5- identified with advanced device conduction, and Type 2),, it"intermediate-stage device conduction. The interfacing of intermediate-stage .-

devices with advanced devices is equivalent to the interfacing of Frenkel-like excitons with Wannier-like excitons, i.e., of strong-binding, excitons withweak-binding e:.:cito.,ns (Knox, 1963). We now consider the problemsassociated with this interfacing.

Weo, can commence by eiamining the range of validity of the FrEn' el andWannier models. The Frenkel exciton problem obtains a quick solutionbecause an assumption is made that the excited electron shares- a unit cell

• with the hole. Physically, a single exciton is a good eigenstate of themolecular Hamiltonian if it can be correctly argued that it lies well below allhigher excitations and does not interact strongly with then. This is true onlyof molecular excitcns. Formally, it is possible to solve any exciton problem •

- with Frenkel states, but a very large radius exciton would then be an-._. enormously complicated mixture of highly interacting, high-energy atomtic

states. Thus, large radius excitons are usually treated in terms of the-. Wannier model.

The Wannier model, on the other hand, is not appropriate for small radius-.. excitons nor is it appropriate for orbits which attain the dimensions-: . comparable with the "crystal". The excitons will then interact with the

surface of the material. Thus, whereas the strict-sense Frenkel model isbased on excited states of individual atoms, the strict-sense Wannrier model"

* requires large Bohr radii for the excitons treated. It should be re.lized then..that strict-sense Wannier and Frenkel excitons are hard to find' In fact, thetype (1) and (2) conductors exhibit intermediate-type Freinkl :;,. Wid nierexcitons.

Given, however, two distinctive ly different types of excitons, even if bothare rare in the trictest. sense, an, interface will involve barriers. We maytry an energy band picture of this interface. When a type I semiconduct or ismaking contact wihth a type 2 sericonduct.r, the Fermi levels in the twomaterials must be coincident at thermal equilibrium. On contact, the Fermilevel of the lesser conductor is lowered by an amount equal to the differencebetween the two wo::,rk functions. the work function being the energydifference between the vacuum level and the Fermi level. The contactpotential will be the difference between electron affinities and band g,aps.

"* 4

1,aS.e -II vj - l.- t"- ,lt n l '

This t 111 i * 1 ztr , .. Ae an answer n12 a 1a Tla- t -'

"Yci.L f tI i I:- -1 l-'i W LIit-i r ' l irni:1ts A

ilP nh-jhc t g petti priapi lflrflt 'f t 5r.rj I -A

ih tt if t Itxu , t - ta ll? Condctio but.4a 1:j 11t 'l t I ifl-rt. I ~-4-f h a' aridll

References:

noR. , Theory of Excitons, AVaei P.-s NwfrkCI(I, u Taku Y P'ro' 1 Theore P'hv (Ev.o7to 1 ) I f :77) ''1

W 'K V 17 ''1

X Applications

.t'~~,1 1 4+i' r 1 . 14~ -A I .'" vt-:4c~tcn '~jl~'

tre- it- Itherait 1 l1 Ilirult. 1 Sc dj;.trlaj th 1 ne from the othe TheATP11.i flr Inc.if li-d tli Ii

ocranir p: 'lIn.M,- -, I Pnm n igril latti c sructure: tc b~e dispiaced. Howee

'' -VF s the point is a ;.Illlf' There are tq::cj -ii 'j1' i n-r-lbe.: -7ufitti wt, to I em i n 1mn '~ osdriri'ped-'f

4- T

ot- t$at 1n it-ruM shol i tn h)71i 111: r ofch rdering.- a n n

I l.,-.j4I ylns ad om i l!~'l '. dfr-iYi? di -ol f m .o ut T prcs-- in-l iAto

* A-' I-IT Y r ralr dnr~ r1 P-t- A rn~sb~t tnclau-. Al. d-c 1, Atit unet4 Qtxt. nemthtf mtma eim

letona ta 3-ari ant i II eUl c ain g- -o,- sipstifIir~atE

* ' ivan:' ftI~ivme ad) lifolen in2~fitif tot-- devie /fflat.flalf f.(cC

rea i:-i 1' IJ i- ~U hat reve-aled pf '1. ni new tecnolcoies by wh

-~~~. -. J- --ni .,uco - i-i .A on ..~ fi. ca :e -lre

r~r1t*. aala' h sru~ctures, d"rtle, strained superlattces- , hell-I'- tti uii t1 h~ftetetn 4 Anl e3ml ipa.:t1 use 1s to ta

'b-y hi' 'P m-iri urit''ocntai in Tie of the sandc.wich maIias Uei 1iniii' i m 4ilitv ian I the n sel ft fh other rria.teraziI St6 be- c,.f hilgh To ivi

* t 1 - i -' liir- - minsinth-( ndih the? rnlob:ility is then Ty e', hi~p 1-* ~~~ Pu Vi, i Ii is due- t 't~vr ml iesosprntit

~ ~~ V i ~-t~1p f the- cI t

u~- Tericc- of the, sujperlattic. n0 An Thi4ch- is raly2 t ime sln:thA latc mnstant of the hiost. material, butt shorter than the electron

mean t ree path.. is exnamined, a series ctnr'w)f ~ ~ ad obde!arnds ma~b :etd duie to the subdivision of the Brillouin zoneinto a series of minizones. W1hen the sameseironucin material1 is

dtI .: p1 and n tyethe lattice constants of the two types ofmaterial need not be matched. Tithe motcrucial property of,

~uperlatt~c~s, promise .:iEultcl'.iJ processin o inatio-n atdifrn

The- wthof each mriiancl in the 5lpe'rlattdcE rar: bDe des-igner, Tiwidh i deermnedby hetrenrrt of int-eraction b-etw,,een neighboring

,Fotcn-t-, al welarid iricreases vh wth decreasin2, width of the layeiVrs 0f that.~orrnicoridiictc'r fin the supernittice whoe andgap isc, grea-:ter. Ec

.ecillatLon occud'ie to thw -, i ti-ic fgacj; th ireliriaticri of wohichl isJut- toj thek applic--ationi of an eletric field. In -a conventional semi c ond u cto r,the& ;eectrons in the conduction band are? driven tow/.ard the upper edge of

* te tilte:d biand. Howe iver,. du-e t tiit- relaifvelyT lafrge Width Of the bnthleynee eahtenrd arid lose ~eergy by7 emitting thermal vib~rations in the

:rsa.In the suiperlattie., on the other, hand, the minib~and:.s are narrow,~in te 'rbaultyof arnectd lcio reachinfg ti-i edge of the b~and is

high. A--t ti-ic utpe-ir edge, ti -iclectrons are reflecfted (Bragg reflectio-n) andre;turn tc'the bottomr cdeoi ti-c ba--nd for possible repeate d relcinAsthe? b-)and is tilted.1 mfore (with increas ing, apidvoltage) the? iJZioUis effect isl otained of negative resistance (Esaki and Tsu, 1970). due to an increasedD ragg re4 f I: tin bu - t with d rc asin enlergy loss orestac

In crdnarv nu: * x~u.. ~r; o~inQresuilts in a decrease i toiiyI* uperlathtces-, the rev erse is the ^,cse This, is becauise a doping of donors is. -* -onfined to the: layers-: of t1-ic crinductor with ti-i largcst .ban:ga r) As ..-

each do--no-r onfbtsa fre eecro to the rystal, arid as thie ele+ctro-ns -:ee te valalestte tat have- the lowest energy, U-ic elcrnmobility

inceaesThe? inrastself is ue to the, state-s of lowest energy re:-siding Inthe bands of the otter semniconductor in the? sandwichi, anid separation will be?a(:eed t-V'etween thie donor laye r and meelcton ,-'riateclTheSpeati:e architetr le1nds t:fto i ng by () cirganids with lange

mo lecular orbtal ove,,rlap ace to obained the desired suiperlattice* carctritisand (ii) organics contr-olled by), incident. 1:-ght, so that ti-i S

tuaiiyof the? (harateristics nitioriecl in 1.i) is obtained A periodic array.4f n and p oe aesseparate~d byj tndoped laye-rs is knownrr as a nipisuperstructure (Liohlem, l'92a,b), whiere i met -ansc intr-insic This intrisil aye r of the: rnipi strucfture can be organic mnaterial, wyhich, as the pro-pertiesc

*of orglanic mnaterial-s are limnite ,d only by the, exen rt of thLe srnthe-tv.hrci1-* r prrnv-&* : a gfreat viariety of designed siperlatti1ce mater.ials

Th' esl11fti; 1piAt~ will ilZlie ma-ultiple a_-nd tunable? ia~Sin9 Ilie-LIrorn diode lasers; lA proceingi c-apajbilities) simpleriarctn

inegrabte chips 3n:( denser electrnic arrays -

'crptrsdecad t' tas;k with nfraonintieu ation cpblte

T he:;re- -are-- m--any sit+Uatio*nsrake fi orn the- rml11itarTy com1ba3t 5 l~ ntrom Z the Qtu _: enonee by th arieplt, t~he automrobile: drive Aand te '7 nc~V an s1rta(: tri dormv in Wich accur-ate 4 lffOrmi.a+,

LI ~lurei.but f :t ilie af terI a. set trime, the.Zn a. tcat.srtpocmr an lH- inf'maic pcsi r no Matter- how aturat th o)utco-me

nee rio mi tknace I otte wrssoe itation reqir

II t( b accur te, bu have he J.:v r im-, recluirernerit that.t el-: dvriplis hel wthin a f irut tiesan.k O f what. Rgood is cuayi t

arrives to lat-fr it to be- a c n7It~ ~ * is fo-uhcmuainl eurmnstah analog-digital1 hybrid

*, elresf rnrl ~;I u a1- deice ofe:r a dv7 an ta ge s. The informational furnelingCn . an fusicri frorn differentl sensors7 ari.d devices can, by arnalc'g method.J:_., be.;

summated for a final judgment w,.ithin a. specified time span. This time-hrinitei:d inform-ational comresin al proceeld in parallel with the1:ret4ainme nt- ofA soure? ot input The; o)rganic co~mpcrnents off-er the 'gneatest

* - versaZtilityT in dic ti .to task inj the, mos,.t Copc form.

q~) Ih MoeuarTaisso arnd MoleA.cular A rn pl1if 1CiConv

Moleula an p:-lyme t rc dynm v iI: are quite df fenrent fromn ele ri 41.l andItr sstcr .-lrcuit dy ,namics Hm,111all-en,. in one, rev pard there rs a. sim la r~t

betee tem nmeyIn the hnmnn fanlfi.ti' in whfichb a sm-all

Thrv~o nitQCr input. variable4 resuilts in a. lan%# chan9; in an ouftmut1 varialei

* ~ ~ ~ : __thmny oye n oeua ystm hc function 1 arfo1 ceaequhbrur (Knepd.>fjKndpd a rid PriQ,~cg inc I Q $1Rn 2pudl

-3.~i~.ti'-~r n C 1 , I- ia reAA .kn onerely t

* hcc i-rt'* !&p4 44 r 'hr : StfCOe; tjp..1 h o rln icsaei)C", :1 t -:-

the bifut 'd '.1 r~A uiI 1 utcn h4 it nb the cspa ti,.-temicirarl ivi ns if th.j* -An ~t i the- reac ttn Inohrwrds, if

there is iii-i -il -iri±--t,-i. 1) It .f onir :trnnth o 111 kon PH.I C:iC( ticfied trn m'mU 4 ~ -~I - tj H the_:n .:virin -t r lec; than -a critial

* value I h' d r ~ tI I: 1-1,2 A Ij , ! A. 1 1r' ..., 1 _itrim i w e, t.j ±S

- I ~vale to -'~jvd~ci tq t n V- anothlet .tit- ur u )c beavior iswell-known for mnole:culs in srd,,ut(.n in the- case ofl the ex-o-ci

7-0

h.rn n~ l tn i1- n all U-i , i v.. flC.; i

~~Ill t- t4 1! 1-i . h 71 , U-j 1 :i 1± 1-1 t~'di i-.* *f lj t b

It I- hri t. e111t i~ L1~ Ttr nttire JIv r -Afi r, i2±,~ e ped:

Ref erences

h±iH Pbss ta Si ) 2 1-11.

-Jhi-' L 14v Sc-Aieni R i~ra c~rbr A 1i

~ ~i-i iiLi, p 2 -vin REs-i hi L E J Siiv:c IInstabilities, Bifurcations, and Fluctuations in Chemical Systems _S

ij t Tex v Pires Autin 4 1- 2n~~pudi Li and Nelsonj R;WPhv ,,,7~ Le:tt,5.(i

i. D C :1K - . . jyi.i

* N: s-r Han Weatung 7 ntdSae aet~1?O>J1;

A. -

Xl Application of Advanced Pevicc";

sTt.1.. 1"-1 t1 Ii 1 .Tn " ": 'n "-- .. . . . . . . . .. - " ""

K - jj 1 .i,-,tt i * *'. -1 jp , - ji, 1.' ,: "** .- 0...

le-r" u-ia C'j i I )' ,,-', 1 - " --- . -

• -,r,,t ' ,:* '-ir -9r .. ...' -* :,-4 ...... .1 ' " icj. . . .. ..II

~~~~organization "- " ' . .~ " i ..." . .. . * , :: - ' - - .'

.1:':" I .1-$ 1 ' 4 - I~t f- ., f 4,: 44 -T .I,- -:1 _.b:: " :

I1terdsciphnary scientists

the ?ppIlYt-lo-8 7rid Jtose pr,?ppr!10-" - .. _:-":--

* p+ " -.'€ " - ' V ' I '' -~ .. ... .. ,*. . . - . . . .

* ' . 't + I ";,.. - .l. -, * -... •

m ernl...wo mrn- ajor resus,,

orgt i zat .'" ion *I]:_t" !r ,,_ .. -rn .'i *1 ''i: - r .. _" ... :, .

+' 1 T

9 V- ': .. :I1,. + l i. ,i

Ii ] 1 ' , : ' ' *" 'i" - '.1, ft-' ...... ' .. .fir' . ..... .

I I - I " m ' " u4m .4,..,.,...,,,,,,,.-,,-,.- ,-,..,,.-,r .... . -r.... .. .... .. ,-

C'.. ! [ -a* .. . - ..mm 6 q l jl •m . .

- . ,, -. S

cm . ".".,

, ' . ai '

- .. ... .

. . . . . . . . . . . . . .

* ' .-. . .°-..18

. ' . - -. . . .

. ,.

O'1 -- 7

*4 ...

: " i -" .. .. .i'

• S S: : ... .

Ur IfI n Ir Ii p---.

Table 1, From Roberts (1983)Potential Applications of L-B Films

JEItOfl Boam Mnrolithography J,'t/5! aJ

.';I cr~ r -r ~ sattrinIo elecronis fromw substratep anid4a tj vt ozi~n dT 'ir poitve reosi st s. jr ;S I

Ia I egra ted Op tic s Kitad. W~ 96197Jufk

2Y tt 24 r-a a t a 1

- OJ"7* ' "biy~L.ib -. trolle of ie sj mito podi!

-of 44t.' oil fi,4cL94 juro~g dI );hg I~g eeJLI-c j

-i tome ts dion tic voi ulec!ulari amit .t are so astc rdc

DlucteRaictsive SorePo t at IaIJ*; 960) 3j'Cominen ts. kadca t1 ye n ild ?crJcatdincn;Vt na

*-v lv"I- -- 5 YM -S% LU '; 0~r cil Y~ of lo Lenei..

Ltd .a.9l% Z-eh-4 etal

Is.444. 41.. 4 N,

tte mdoavers c;a ite be tt actv ecrolu'MIZ~Sct aOIeai s edL. to v e nv a ' r av fi . ,~ rozv A ino r dide, rasi L"' Sapplic3Ja^,n9rn ~ t alit! liqJ7 idYI rstl~q displa Deoito ci!iyLi

7Two -dimenfsional Mafgnetic A rrays L'P'mr:fi n t LI)

A s P jV*tL

Batey. I Robert. T 1- arid Petty. M .C. Thin Sclid Films, 99cl ( I5 A)i3faner ic-, A. and Landjo, I F , Thi-n Solid FJ 1ms:, 5 J r 1 (tiogner, U.T, Roska, GT and Oyralf, F., Thin Solid Films, 4 1-t 2 7.

rerAV Naid Pome)r nEtz, M., Thin 'Solid Filnn.is CM Ia c) 2 1Daie, MF. Lethnrj:t.nI C n Sr 11, v Thin VfiFilm- 19 A

u-ty F R. and Lando 4.. F 11 rorfole: 1l1e; 1 .' 1 0b)*' I 1 ±Dj9, D R -sld bind EF I ppl. PolyM u(i u

L''yi- D.R Fn mlin"' lrU. H Ivlkrornol Chem.r, 1(5 0 1:' 1) 91094'' r, f- Tf Tr Slr i., oly '-em Ed. I- C( 1f

Rmricc, G, Lando, .T l P'd Ricet, Thin Soldid Filmi. 9~9 (195 A ) O&0jFlainuin, M.T., Thin Solid Filmes t M '196v 1 )'an!iL-, AF. and. Sinu~f: i i Tt SoF Am. 7 0p s '1 '1 f.5 1 %y9.fruihE-ld F.adtt., Tfint SA-id Films, 9(j1 2 249

Hiz-1rfan, S-rI-1,C. ndEaeS T hin Soid Films,'j (193I)W 2V5.* Kcn. KIIK Potty .v -mu. ad Rutt. LG.. Proc. Rcvleig~h Cont. lon the Pyv

_) 1M0 TIcmtnr; Pernmn Newi, York, 1()6!0, P. 344. __r. SKan,, K.K. Petty,,, M.' and Roberts. .. Thin Solid Films. 99 f 21 ) 21.Larkuins) 'UTL. Th -rnpsiin ED., Ortiz, E., Burkhart, C.1W-. and Larido f!. Ti

-, 2)11(1 Fii&lm,4 I it 'j

Lohe., a~1- H. Tie ke, F

sq 46

Roberts, G.G., McGinnity, T.M., Barlcw, W.A. and Vincett, P.S.., Thin SolidFilms, 68 (1960) 223.Roberts. 6.G., Pande, K.P. and Barlow, WA., Proc. IEE Part I, Solid Sat.e andElectronic Devices, 2 (1978) 169.Roberts, G.G., Petty, M.C. and Dharmadasa, I.M., Proc. IEE Part I, Solid Statearid Electronic Devices 128 (1981) 197.Sarkar, M. and Lando, J.B., Thin Solid Films, 99 (1983) 119.Tieke, B. and Wegner, G., Makromol. Chem., 179 (1973) 16.39.Tredgold, R.H. and Jones, R., Proc. LEE Part I, Solid State and Electronic

" " Devices, 126 (1981) 197. ":Vincett, P.S. and Roberts, G.G., Thin Solid Films, 66 (1980) 135.

I! 00A

FS

,: D 0

K _ • _.*o .. .. .

47

XI1 Architectures

The ENIAC.. the UNIVAC and today's pocket. calculators are based on a singlecent-al processor perforrinig operations sequentially to produce the desiredresult, which is the traditional view of computer design as put forward byCharles Babbage, Alan Turing and ohn von Neumann. Such designs, whichare referred to as von Neurann computers, are constrained to perform onetask at. a time in real time. If they are programmed to perform more thanone task., then they do not. perform the additional tasks in parallel real timesbut switch between tasks rapidly, so that the central processor is "timeshared" with a concomitant loss in speed for each task time. This observationis not absolute, because every computer has a word of eight. bits or more,which enables it. t,:, address eipiht questions, but relatively speaking, mostpresent computers are serial processors, with some notable exceptions (suchas COLCSSUS, ILLIAC-IV, PARALLEL ELEMENT PROCESSING ENSEMBIE,DISTRIBUTED ARRAY PROCESSO1R and HETEROGENEOUS ELEMENT PrFOCESSC.;

* (HEP) among others).Multiprogramming enables some of today's computers to perform

operations in parallel and vector architectures permit a single operation tobe performed on several components of a vector simultaneously (Browne,1964). Knowing in advance the sequence of operations permits the some

* programs to order some data, while the central processing unit is working onother data, an operation known as pipelining. However, there is still a singlecentral processing unit. Thus, among digital architectures one can distinguishthree basic types: (a) The computer applies a single stream of instructions toa single stream of data; (b) The computer applies a single stream of

-*- instructions to multiple streams of data.: and (c) The computer applies .multiple sti-eams of instructions to multiple streams of data. The analog-digital hybrid, based on molecular components-, is yet another approachwhich we consider later.

* Further advances being considered are: use of gallium arsenide for higherspeeds, further use of parallelism in the software, such as that describedabove, and other non-von Neumann architectures using standardcomponents. Yet another influence on computer performance, quite apart

" " from the individual processors, is their organization into a network. Acurrent theory now being considered is that. by Hopfield ( 192, 1984) This isa content addressa.ible memory, admitto.edly difficult. to construct in standard -digital hardware, but which is a collective property of a set of devicesconceived in analogy to biological nerve cells. Particular memories are storednonlocally in many interconnecticns with recall a collective dcision made bythe network as a whole in a single settling time, withi the decision about thememory to reconstruct made in the analog domain and with the memorydeveloping its full digital representation. At the present. time small matrix

- .. , fu ll .-.

the CudTNkcag-rnse at Ufljt unto

Here, themn in abtat da tsi~ y1hi rLi$v rV t hrWi* mu~t r- h :u~ f:)r i .lecula componnts if it isto eom i opeiiv

size ~ ~ ' frie, ee s h eand for I izIoa eleent in th ftteALo- ithe tatsi: to b.e p44-me by 1.a particular computrbcn

mnat -i t' byii1 the capabilities of a partiulr ular lar mael otat t-earc" ut. tut A- is deWdt on (ind(i Tu s. th tra_-dition.-A mtho c

c~d(I~lifq te tti4Ktt~ede~~inerwtth ( )the t.s11nd 1) tfld21I1n1il

ar -jilll- 1. th C: 1.y. Ih njt1 'I th chi:' avial U fed -e-r

1~~~ *s ehnlc' - t I C., g-- mb'- br (:,W a futv. c-rmpiutitcnl4Li dmrs -n ) rn zm nc even CI umn Aemnt may,,

£- 1 Hf V/ver,4 t~- 1-'h71 ensco-iu n te vai.) Mi1u, energies cifr -1~ i'' mutipl F) 1 7P T, t) tunnPng thirough- th in Qatrv Oi T laeS.

I'slcti f I~ uht u nsti in thesol volhI arS; :n-mv devicves due tol " r tit", 1 1- ir a t 11I~ btU'r nsie h resistance of a-- few mmni of meItal Irt,- Ii'. I& n', t h -it -t he Wire 6-Canrc b-e t-reated as an equ)Jipot-eritni. So tha r *

hn-'-p v-tvrI o signals occui:rs (3* itz & Matsoo). A -uib.idiar-DI ffis p-t if interco nneilction w~iring Bipcolar trnitrcircits have& an

e~c MCC' circuits in speed but chip integraton is poo-rer due to .'C.

Theus c olefa eerits instea-d of irgncelements wil also runmt.- these?, difficulties, if the same trnitr htlybarrier element

deis: ae oloe How ever, due to the a,_rialog nat-ure of the (haire-rJ t1ansfer dpnetsicngof, for-A examnple Cu-TCNQ arid thel possibilities

* ~~ ...f Mih-(: trcl of upratcsfromoanc lmn; both resulting in >mnultiple, input;- to* -a si1ngle emnt,& heqsme desigS nfeed nOLt be .folio wed The;1 oppo-rtuntiesc for simultaneous inform-ation integratiorn andre -c er-ra ton are aviae in molecuolar element- and such designs do not

* even obey the same logic truth tables as the digital transistor -switch. Thus, it is tnappnopriac.te t~o acsuine the? sacme limiting constraints,and due- to' the OVD(ortunitv for Manalo2 intera:ctiori betwee swt-chu S1

elmnsas well 1 as thea g~ret:-. ve *rsatility fee in moclec..ular econtrol andinasr~j fd'ictin, those limi,1tinQ, cns-tra ints are riot the am Only arn.-.

i ris -N rjh - store-thr'.wer would reruirc the? saeardstick fo(r the- twoj,phy/sic -ally distinct devicetchocis

References--

Hopfield i Pre.: Nat. A(-- :: )L,7> 'Q)2V5Hcmfiel:1 j I c'lcat.-1~r - n 0IAe-i~ ~mris ae CAFie

--- Marc 1 'iA at ti-j Amri PITcal L9C. ~iwmLeorvlichicgar±, I'tarc-h,1~;

- Se!::, anJ Mi;tEt~ .Z Ff~1S cay.7 'l93'

- -V -W l p * . .. *-. .. uq

XIlI Other Applications Including Advanced Sensors

The applications of molecular transducers for information gathering _.purposes are many and include those to biomedical diagnostics, sensoryprosthetic devices, sensory systems in robotics, chemical sensing infermentation systems, and sensing in airframes and engines. In manyinstances, the molecular transducer technology will be integrated withoptical fiber and wave guide technology and in the biomedical field willinclude patch clamping techniques.

Already optical fibers are being used in aircraft structures to determine theorientation of composite fibers and to assess excessive strain on aircraftparts. In the future, even jet engine temperatures will be monitored byoptical fiber sensors. In a day not too distant, one can foresee an aircraft'ssystems and airframe being routinely tested by a computer controlledinterrogation of an optical fiber bus which links to all the aircraft sensingcomponents.

The sensing of molecules for diagnostic purposes in the medical diagnostics "Ofield will depend a great deal on coating technology and the ability tominiaturize. Hirschfeld (1983) has pointed out that as the scale ofengineering grows smaller, so does the importance of phenomena which varyas a high power of size. For example, gravity, inertia and magnetism, varyin increasing importance as the third power of size; flow phenomena as the -fourth power; and thermal emission as the second to the fourth power.

- . .: Electrostatics and surface tension vary directly with size; diffusion as thesquare root and Van der Waals forces as the negative fourth power. Thelatter, unimportant for bulk material dynamics, may become predominant at "0

• small size. Ouantum effects, a minor consideration at bulk size, become

preeminent small scales causing tunneling and nonlinear behavior.*~i Hirschfeld's point is summed up in the observation that "you don't get a

workable ant. by scaling down an eleph:ant."* _His other point is, however, that by scaling down an elephant you obtain

unelephant-like dynamics which you may be able to use for quite different .devices than ants, i.e., scaling laws sometimes produce different functions.This other point should always be kept in mind together with thefirst.

Fiber optic sensors are devices that. provide optical signals in response tophysical, chemical or other stimuli In a typical sensor of this type., light froma solid state optical source is coupled into an optical fiber which thentransmits it to the sensing region In the sensing region, some property ofthe light (intensity, phase, polarization or spectral content) is modulated by

0 the phenomenon of interest. The modulated optical signal is then returned .via the optical fiber to a processing location, where it is converted to anelectrical signal by a solid state detector.

.. .- '

,, • . ~ ~~~. . ........- ,..,,......

' . d. - i . . - -, :. . :: :. .. . .

There ar tw,-Yo generic classes of fiber optic. sensors -intrinsic- sensors tnUnderhrtT -.

optical fiber itself, and 'extrinsic' sensors in whic P the op-tical fier ismerely used toc tiranstt light. to, arid frrurn the sE-nin_: mueur:on The.: 'eJ.ecan bea pot*:nt-ially as; small as the fibers: themselvs '~.1 etan0and can be configiurEd eithe r as distrib-ute.dse ponsnsn

elmnsAll of the- publicized advantages of fiber optv ti: rY fioIg aplytfiber Optic sen-rsors as welThese include: Irlt1Vj fredm ro

electromagne tic- interferenice arid pulseii effects,- larc ,7-nt: lrl(: jandw,,idth.arid the ability toperfLOrm in hostile environmenI ts. In -adlt.n, a number ometh11ods e:'ilst for multiple:azng such sensors onto a single cpticatl fiber,thereby pro-viding a