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2. Molecular Electronics

2. Molecular Electronics. Molecular-scale electronics Molecular materials for electronics. Molecular wire Diode, rectifier Molecular switches Molecular memory Sensors Optics and optical switches Displays Electrochemical devices Molecular heterostructure and quantum well devices.

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2. Molecular Electronics

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  1. 2. Molecular Electronics • Molecular-scale electronics • Molecular materials for electronics • Molecular wire • Diode, rectifier • Molecular switches • Molecular memory • Sensors • Optics and optical switches • Displays • Electrochemical devices • Molecular heterostructure and quantum well devices

  2. Molecular Electronic Switching Devices • Electric-field controlled molecular switching devices including quantum-effect molecular electronic devices • Electromechanicalmolecular electronic devices • Photoactive/photochromic molecular switching devices • Electrochemical molecular devices Bistability Eb>kT

  3. 강의 순서 • Information transfer • Interconnections • Electron transport • Molecular wire • Molecular rectifier • Molecular switches • Molecular RTD • Molecular memory • Atom relay

  4. Computational Limits • Rolf Landauer • Nonreversible computer performing Boolean • logic operation requires minimum energy for a • bit operation, P = nkBT ln2 Ex) energy required to add two 10 digit decimal numbers ? P ~ 100kT ln2 ~ 3x10-18 joule per additions 1018 additions per joule This is roughly the equivalent of 109 Pentiums !

  5. Why Molecular electronics ? ENIAC, 1947 HP Jornada, 2000 17,468 vacuum tubes 60,000 pounds 16,200 cubic feets 174 kilowatts (233 horsepower) • Popular Mechanics (1949, March issue) predict that • someday ENIAC would contain only 1500 vacuum tubes • Now, Improve power efficiency by 108 and shrink by 108 • Their prediction was based wrong foundation(vacuum-tube • technology)

  6. Technology and Biology • Technology Biology • Artificial Natural • Si-based C-based • Manufactured Self-assembled • Short history Long history • Function:logical Replication, adaptation… • numercal operation • Room temp Room temp

  7. Microprocessor vs Brain • MPU Brain • # of MOSFET ~ 107 # of cells ~ 1012 • # of switches ~ 107 # of switches ~ 1011 neurons • # of connections ~107 # of connections ~ 1015 synapses • Wiring: fixed flexible • Architecture: serial parallel

  8. DRAM vs DNA DRAM DNA

  9. Advantages of Molecular Electronics • Nano-scaled structures with identical size • Ultra High density: 106 times denser than Si logic circuits • Very cheap

  10. Critical issues on Molecular Electronics • What device types can provide bistable operation ? • How can these devices be organizedinto high • density 2D and 3D arrays ? • How can these devices be connectedin large number • to input/output lines?

  11. Dynamic Random Access Memory (DRAM) W1 W2 CMOS FET D1 D2 (bit line)

  12. Interconnection Dilemma • Today’s chip densities are such that the wires consume some 70% of the real estate → they cause some 70% of the defects that lower chip yield • The rate of defects in a chemically fabricated nanocircuit : ppb level → million defects in a system containing 1015 components

  13. Several Fascinating Possibilities • Defect-tolerant computing architecture: Heath, and Stoddart at UCLA, teamed up with Williams at HP • Nanocell: Tour at Rice, Reed at Yale teamed up with Penn State in Nov. 1999 • Switching with nanotubes: Lieber at Harvard University • DNA assembly, computation: Seeman at New York University

  14. Defect-Tolerant Computing Architecture • Fat tree architecture enable one to route around and avoid the defect. • Manufacturing by chemical assembly is feasible.

  15. HPL Teramac1THz multi-architecture computer • Tera: 1012 operations per sec • Mac: Multiple architecture computer • 106 gates operating at 106 cycle/sec • Largest defect-tolerant computer • Contains 256 effective processors • Computes with look-up tables • 220,000 (3%) defective components

  16. Nanotube Interconnects • Molecular scale wire with atomic perfection • Interconnect at high density • High thermal conductivity • Very stiff materials Lieber et al

  17. Wire conductance vs. Electron transfer Molecular wire Intramolecular electron transfer Potential Energy Obsevablecurrent rate constant Continuum electrode vibronic levels Process electron tunneling electron tunneling Theory I = (2pe/h)∫dE T2(E,V) k =(2p/h)T2DA(FC) [fD(E)(1-fA(E+eV)) R(DA) P(D+A- ) Ef Eg

  18. Conductance : Landauer formula m2 eVmol eV m1 m2 m1 I = (2e/h)∫dE T(E,V) [f(E-m1)-f(E- m2)] • F(E): Fermi function • T(E,V): transmission function • molecular energy levels and their coupling • to the metallic contacts • m1, m2 : electrochemical potentials • m1= Ef- eVmol • m2 =Ef+eV- eVmol W. Tian et al, J. Chem. Phys. 109, 2874(1998)

  19. Intramolecular Electron Transfer D Bridge A R(DA) P(D+A- ) Eg RDA k = (2p/h)V2DA(FC) VDA = aexp(-bRDA), b= -(1/a)ln(2t/Eg) VDA : electronic coupling through direct and superexchange FC: Frank-Condon factor RDA : DA distance a: length between electronic basis function in the bridge structure T: matrix elements between those bridge structure Eg : energy gap Chap1 and 2 in Molecular Electronics ed. J. Jortner and M. Ratner

  20. Fabrication: Self-Assembled Monolayer (SAM)

  21. Fabrication:Langmuir-Blodgett Technique Setup for Langmuir-Blogett Deposition Transferring Monolayers & Multilayer Film P-Area Isotherms http://www.public.iastate.edu/~miller/nmg/lbfilms.html

  22. Conductance of molecular wire: STM • Tip bias voltage = 1V, • Tunnling current = 10 pA L. A. Bumm et al , Science 271, 1705 (1996).

  23. Conductance of Molecular Wire: MBJ • Mechanically controllable break junction • Energy gap Gap: 0.7 eV • Conductance = 0.45 mS (R=22 MW) MA REED,C Zhou, CJ Muller, TP Burgin, JM Tour, Science 278, 252 (1997)

  24. Structural Effects on Conductance:Theory • Resistance increases exponentially with the # of the rings • Relative orientation of the rings • The bonding between them. MP Samanta et al, Phys. Rev. B53, R7626 (1996)

  25. Temperature Effects : Theory 0 90 • Unusual temperature induced large shift (~1eV) in is due to: • - The rotation property of the NO2 group • - Different symmetry of the states localized on the NO2 group • with respect to the orbitals of the carbon ring M Di Ventra, SG Kim, ST Pantelides, ND Lang, PRL86, 288(2001)

  26. Comparison of Conductivity 1,4 benzene polyphenylene carbon copper wire ditiol wire (3ring) nanotube App. Vol 1 1 1 2x10–3 (10cm) Current (A) 2x10-8 3.2x10 -5 1x10 -7 1 Cross section (nm2) ~0.05 ~0.05 ~3.1 ~3.1x1012 r=1nm r=1mm Current density 2x1012 4x1012 2x1011 2x106 (e/sec-nm2)

  27. I A. Aviram and M.A. Ratner, Chem. Phys. Lett. 29, 277 (1974) V Molecular Rectifier Forward bias electron donor electron acceptor p n B P - + - + - + + - TTF TCNQ Tetrathiofulvalene tetracyanoquinodimethane πD* πA* EF πD πA

  28. Energy Levels of Molecular Orbitals DELUMO =ELUMO (D)- ELUMO (A) Vacuum f Unoccupied No bias Off resonance Ef Occupied Transmitted electron eVb Forward bias In resonance

  29. R. M. Metzger et al, J. Am. Chem. Soc. 119, 10455 (1997) Electrical Rectification of LB films

  30. Energy levels Electron affinity Ionization potential LUMO HOMO • Ionization potetials ID for D end must be small and match as closely as • possible work function (f1) of metal layer (M1). • - If ID is too low, the molecule would oxidize in air • Electron affinity AA for A end must be as large as possible, match with • the work function metal layer M2(f2): this is not easy !

  31. Molecular Switches • Chemical switching • Electrochemical switching • Photochemical switching V.Balzani et al, Acc. Chem. Res. 31, 405 (1998)

  32. 4PF6- O O O O O O O O O O O O O O O O + + N N N N N N + + CH2OH Molecular Switches and Gates: Rotaxane • Closed at reducing voltage(-2V): current flow due to resonant tunneling • Open at oxidizing voltage(>0.7V): irreversible C.P. collier et al, Science 285, 391(1999)

  33. Electron Transport in Single molecule I Ef B1 B2 V LUMO I Ef Ef V M M HOMO V I V=VLUMO I V=0 VOLT V DELUMO-HOMO V=-VHOMO

  34. Electron Transport in Single molecule M  M* M  M* Ef V I . . . . . . . . . . . . . . . . . . . . . . . . I V DELUMO-HOMO Molecule switches V = -VSWITCH V = -VLOMO Then, reset at the opposite bias V = -VRESET

  35. Configurable Molecular AND Gate 4 +V high L 2 out low 0 Current (10-9 Amps) 1 0 0 1 1 0 1 0 A= B= B A AND Gate Address Levels A B C 0 0 0 1 0 0 0 1 0 1 1 1 A B A B C C R V+ • Difference between high • and low current levels: • 15 ~30 C.P. Collier, E.W. Wong et al.

  36. Collier et al, Science, 289,1172 (2000) Ti/Al : top electrode LB monolayer Reversible Molecular Switches: [2]Catenane n-type ploy Si film: bottom electrode Si SiO2 Ox. Red. Close Open • Upon oxidation, the TTF become positively charged, the Coulombic repulsion between TTF+ and the tetracationic cyclophane causes to circumrotate. • Reversible switching :Opened >+2V, closed <-1.5V

  37. Molecular Field Effect TransistorR.A. Reed and J.M. Tour, Sci. Amer. 282,86 (2000) Source Gate Drain

  38. Reversible Molecular Switch with NDR Effect • Negative Differential Resistance ~ 400 MWcm2 • Peak current denisty: 50A/cm2 • Peak to valley ratio = 1030:1 (typical device=30:1) • Temperature induced shift : rotation of ligand(JACS,122,3015 (2001)) J Chen, MA Reed, AM Rawlett, JM Tour, Science 286, 1550 (1999)

  39. NDR Effect (continued) Q=0 -1 -2 A B C - + I B A C V • Anion conduction state • ON • Dianion insulatingstate • OFF

  40. Diodes Using the nanopore process and a 4-thioacetatebiphenyl SAM we constructed a diode. Molecular Diode • The prominent rectifying behavior is due to the asymmetry of • the molecular heterostructure. • The barrier from the bottom electrode is higher than the barrier for • electrons from the top T electrode C. Zhou, M. R. Deshpande, M. A. Reed, L. Jones II, and J. M. Tour, Appl. Phys. Lett., 71, 611 (1997).

  41. Lowest Unoccupied Molecular Orbital (LUMO) No LUMO states on the ring

  42. Molecular RAM On Off • 15min hold time DRAM at room temperature • Reversible molecular memory • Over one billion cycles and counting with no degradation M.A. Reed et al, Appl. Phys. Lett. 78, 3735 (2001), Z.J. Donahuer et al, Science 292, 2305 (2001)

  43. Molecular Resonant Tunneling Diode (MRTD) Unoccupied Off Occupied 1nm On • Peak to valley ratio = 1.3 :1 • Electrically active device by molecular orbital engineering M.A.Reed, Proc. IEEE , Volume: 87, 652 (1999)

  44. Synthesis of Molecular Devices Source Drain Gate • Nano-scaled structures with identical size and shape • High density and low power J.A Tour, Acc. Chem. Res. 33, 391 (2000)

  45. Logic Gate : OR A B C 0 0 0 1 0 1 0 1 1 1 1 1 A B A B C C R V- CH2 Donor Acceptor wire CH2 Donor Acceptor Long HC Conjugated aromatic organic molecules

  46. Electromechanical Molecular Electronics • Single molecule electromechanical amplifier: • Joachim and Gimzewski Chem Phys. Lett. 265, 353 (1997) • - conductance modulation due to • electromechnical deformation of C60 cage 2. Atom relay transistor Y. Wada, JVST A17, 1399 (1999) • Upon charging a gate, a mobile switching atom move into • a line of atomic wire

  47. Inroganic-Organic Hybrid Circuits: Nanocell • Molecular wire having alligator clip Metallic nanoparticles which are connected by functional molecules 1mm

  48. Further challenges • Combining individual devices • Mechanisms of conductance • Nonlinear I/V behavior • Energy dissipation • Necessity of gain in molecular electronic circuits • Slow speed • New computer architecture • Synthesis of new molecules

  49. 숙제 1. Read Feyman’s lecture “There is plenty of room at the bottom” listed at www.zyvex.com/nanotech/feynman.html • 공고 • 금주 20일 (목요일): 휴강 • 스케쥴 변경 • week 7 : 10.16-10.18 Macromolecular nanostructures (김상율 교수) • week 8 : 10.20-26 중간고사 switch

  50. CH712 물리화학특강 II 가을학기 강의 진도표 주제: Nano Science and Technology ㅇ 강의담당: 김세훈, 유룡, 김상율, 김진백, 이윤섭, 이억균, 곽주현, 천진우 ㅇ 주관교수: 김세훈 ㅇ 연락처:전화: x2831; email:sehkim@kaist.ac.kr ㅇ 강의시간: 화,목 16:00-17:30 ㅇ 강의실: 자연과학동 2124호 ㅇ 참고문헌: Nanotechnology Research Directions: IWGN Workshop Report(1999) http://itri.loyola.edu/nano/IWGN.Research.Directions/ ㅇ 강의내용: 기능성 나노구조의 합성, 제조, 물리 화학적 성질과 나노구조에 대한 특성분석 방법 등을 다루고 나노구조를 응용한 나노센서 및 나노소자의 개념을 소개함. ------------------------------------------------------------------------------------------ week 1 : 9. 4 Introduction (김세훈 교수) week 1/2 : 9.6-9.11 Nano-characterization (김세훈 교수) week 2/3 : 9.13-9.18 Nano dvice I (김세훈 교수) week 3/4 : 9.20-9.25 Template based nanostructures (유룡 교수) week 4/5 : 9.27-10.4 Template based nanostructures (유룡 교수) week 6 : 10.9-10.11 Macromolecular nanostructures (김상율 교수) week 7 : 10.16-10.18 휴강 week 8 : 10.20-26 Macromolecular nanostructures (김상율 교수) week 9 : 10.30-11.1 Nano-fabrication and nano-lithography (김진백 교수) week 10 : 11.6-11.8 Nano-quantum chemistry (이윤섭 교수) week 11 : 11.13-11.15 Nano-thermodynamics (이억균 교수) week 12 : 11.20-11.22 Nano-sensor and nano-device II (곽주현 교수) week 13: 11.27-11.29 Nano-sensor and nano-device II (곽주현 교수) week 14: 12.4-12.6 Nanoparticles and nanowires (천진우 교수) week 15: 12.11-12.13 Nanoparticles and nanowires (천진우 교수) week 16 : 12.15-12.21 기 말 고 사

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