Interaction of Small Molecules with Carbon Nanotubes by FFB6Vf

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									               Molecular Spintronics



                     S. K. Nayak
Department of Physics, Applied Physics, and Astronomy
       Rensselaer Polytechnic Institute, Troy
             Collaborators

                 Dr. R. Pati
                L. Senapati
                M. Mailmann
                 Y. Zhang
                Physics, RPI

   Professors P. Ajayan and G. Ramanath
          Mat. Sci. and Eng., RPI

  Professor A. M. Rao, Clemson University

  Y. Wu, Dr. P. Giannozzi, Professor R. Car
            Princeton University

         Professor N. Marzari, MIT

Professors R. Reifenberger and Datta, Purdue
                      Scope of the Talk

•   Introduction

•   Fundamental Questions

•   Technological Applications

•   Spintronics at the Molecular Level

•   Experimental results

•   Theoretical Results
                 Nanoelectronics
   Moore’s Law
      Device sizes halve every 5
       years
         This law, observed in
          the 60’s, still holds
          today
      By Moore’s law, devices
       should reach atomic scale by
       2025
         Moore’s law will come
          to an end by 2020.
                          - -- ----           -          ----

                                                          Si
                                          M
                        ---------------           SiO2
          NanoScience and
          NanoTechnology
                       DoD SRA
             http://www.nanosra.nrl.navy.mil


To achieve dramatic, innovative enhancements in the properties and performance of
structures, materials, and devices that have controllable features on the nanometer scale
(i.e., tens of Å).


The ability to affordably fabricate structures at the nanometer scale will enable new
approaches and processes for manufacturing novel, more reliable, lower cost, higher
performance and more flexible electronic, magnetic, optical, and mechanical devices.
                           There's Plenty of Room at the Bottom
                         An Invitation to Enter a New Field of Physics



                 by Richard P. Feynman
                 December 29, 1959, APS Annual meeting

                 Atoms in a small world
What I want to talk about is the problem of manipulating and controlling things on a small scale.

When we get to the very, very small world---say circuits of seven atoms---we have a lot of
new things that would happen that represent completely new opportunities for design.
Atoms on a small scale behave like nothing on a large scale, for they satisfy the laws of
quantum mechanics. So, as we go down and fiddle around with the atoms down there, we
are working with different laws, and we can expect to do different things. We can
manufacture in different ways. We can use, not just circuits, but some system involving the
quantized energy levels, or the interactions of quantized spins, etc.
                  NanoScience and
                  NanoTechnology



Materials and Phenomena at Nanometer-scale (10-100 Å) Offer the Opportunities to
Realize Electronics Devices with Unprecedented Performance


                            Self-assembled InAs QDs on GaAs
                            substract
                                                                  -

                                                              -               +
                    30 nm

                                                30 nm                     -
                      Dot feature size 5-6 nm
          Nano-Enabled
      Revolutionary Capability

   Nanoelectronics and Computer Technology
     Monolithic electro optic devices that detect the
      entire infrared (SWIR-VLWIR) spectrum
     Ultra-high performance massively parallel data
      processors to allow downlinking target
      information directly to the warfighter (e.g.,
      molecular computers)
     Novel communication devices providing
      unheard-of frequencies and bandwidth
                Single-Molecule Electron Devices

•R. Metzger et al., Thin Solid Films, 327-329, 326 (1998)
    •Rectificatoin of current demonstrated by LB films (mono and multilayers) of g-(n-
    hexadecyl)quinolinium tricyanoquinodimethanide, C16H33Q-3CNQ
•Collier et al., Science 285, 391 (1999)
    •Logic operations (AND and OR) demonstrated by Rotaxane monolayer sandwitched
    between Ti and Al2O3
•Moresco et al., Phys. Rev. Lett. 86, 672 (2000)
    •Current switching by STM manipulation of Cu-tetra-3,5 di-ter-butyl-phenyl porphyrin (Cu-
    TBPP) on Cu (211) surface: Possibly change in intra-molecular conformation
•J. Chen, et al, Appl. Phys. Lett. 77, 1224 (2000)
    •Room temperature negative differential resistance (NDR) exhibited by self-assembled
    monolayers of nitroamine and nitro substituted di(ethenylphenyl-benzene thiolate
                      Single-Molecule Devices

•C-Nanotube Based Electronic Devices
    •Explosion in the field: Andriotis et al, Phys. Rev. Lett. 87, (Aug 2001)

•Bio-molecules Based Electronic Devices
    •Fink and Schoenenberger, Nature 398, 407 (1999)
    Conduction through DNA molecules
•Photo-activated Molecular Devices
    •A. P. de Silva et al., J. Am. Chem. Soc. 122, 3965 (2000)
    Fluoresecent based moleular logic and arithmatic

    •Nagatoshi et al., Nature 401, 152 (1999)
    Light-driven mono-directional molecular rotor

    •Bermudez, et al., Nature 406, 608 (2000)
    AC-field induced molecular rotor
                         WHY ORGANICS?


Organic molecules offer a natural medium for controlled electron transport




                                                     Can be used as
                                          q
                     q                                 Basic Device Elements
    D
        d+                                A    d-    -wire (connectors)
                                                     -insulator
   H2N-                                       -NO2   -diode (switch, memory)
                                                     -transistor


               p-electron medium
                 benzene ring

                para-nitroaniline (PNA)
                         Molecular Electronics

                                  CHALLENGES
•Understanding electron transport and device physics in molecular systems
    •Conduction different from bulk: 1-electron, overlap of localized wavefunction,
    involvement of discrete energy levels, tunneling
•Interface with microscopic and real world
    •Physics and chemistry of molecule-metal contact, assembly, fabrication,
    measurements and interpretation
                                 OPPORTUNITIES
•True breakthroughs: Exploration of new science ==> Engineering
•Device Concepts
    •Traditional electronics vs. new devices based on new physical mechanisms
      Spintronics- (Spin Electronics): Telling the electron to
                        remember its spin

   Electron has negative charge and spin (magnetic moment: 1/2).


   Electron seen by an electronician:




   So far electronics industry are taking advantage of only its charge
    character to store and process information.
                      Electronics Application
   Primary electronic device: MOSFET




   Disadvantage
               volatile of information
               limited density information
               reaching the fundamental limit
       Spin Alone Phenomena- Magnetism



Electrons seen by magnetician




Store information using spin
Alignment of spins are important
                         Magnetic Application

   Primary magnetic Application: storage information




   Disadvantage
               mechanical access
        Spin-electronics- Time for electron to take a spin


 Exploit the quantum nature



 Combine charge and spin to



                store information in terms of spin orientation
               (up/down)

                 the spins will be attached to mobile electrons which
               will carry the information along with wire

                  the information will be read at the terminal

                  Spin coherence length is large (~nm to m)
                     New Challenges


Fundamental Questions-
 Injection of spins into semiconductors

 Spin coherence length (spin relaxation)

 Spin entanglement

 Interface effect



New Phenomena:
 Giant Magnetic Resistance: (GMR)

 Tunneling Magnetic Resistance (TMR)
                      New Technology


   magnetic disk heads (used in computer)
   magnetic random access memories (M-RAM) (non volatile)
Forming Integrated Circuits- Ferromagnetic
metal+semiconductor (still a challenge)
   Spin-transistor
   Spin Valve
   Quantum Computer         Magnetic Tunneling
                             Junction- Motorola
         Giant Magnetic Resistance (GMR)


Baibich et al., PRL 61, 2472 (1988)
Binasch et al., PRB 39, 4828 (1989)
                GMR Mechanism




                     RF  RAF
Ferromagnetic
                     GMR Ratio = (RAF+RF)/(RAF-RF)
                     could be larger than 50 %




Anti-Ferromagnetic
        Tunneling Magnetic Resistance (TMR)

Moodera et al., PRL 74, 3273 (1995)




Applications of TMR: magnetic random access memories (M-RAM)
Injecting Spin Polarized Electrons in Semiconductor

Awschalom, Nature, 397 (1999)
Spin-electronics at Nanoscale




                  Size of magnetic drive is
                  also shrinking!
                  Reading the data through
                  GMR needs to go to
                  molecular scale
Spin-electronics at Nanoscale
Magnetic Reading Head




        Size of magnetic drive is also shrinking!
        Reading the data through GMR needs to go
        to molecular scale
             New Questions and New Challenges

Fundamental Interest:

   Can we inject spins into molecules

   Spin coherence length

   Heating and time scale involved

   Just a beginning ...
Coherent Spin polarized transport through carbon nanotube




 Tsukagoshi Nature, 401, 572 (1999)
                    Molecules goes Spintronics


Schon, J. H., Science, Published online,
I:10.1126/science.1070563 (2002).

                                                V               I



                                                        H




                                                            S
                                                    C
                                           Ni
                                                                    Gold

 Challenges-
 How to apply local magnetic field?
First Principles Quantum Conductance Calculations of
Spin Polarized Electron Transport in a Molecular Wire
                   THEORETICAL PROCEDURE

   We solve Schrödinger equation:
                Hψ(x1, x2, x3 …) = E ψ(x1, x2, x3 …)
                  ψ is an N-electron wave function.


   A simple but accurate way of solving the above equation is to
    use density functional theory.
   Here we work with ρ(r) : 3N to 3



   Remarkable!
                         DENSITY FUNCTIONAL THEORY

 HOHENBERG-KOHN (1964):
 Total energy of an interacting electron gas in presence of an external
 potential Vext (r):
             E   V ( r )  ( r ) dr  F [  ]
                          ext




                                   functional independent of Vext
 KOHN-SHAM (1965):

E  T [  ]   V ( r )  ( r ) dr  1
                                               ( r )  ( r )drdr   E [  ]
                                          
       s           ext
                                     2         |r-r |                        XC




    kinetic energy                                              exchange
    non interacting                                            correlation

 Local Density Approximation (LDA):                       ( r ) [  ( r )]dr
                                                                 XC




                                                      ( r ) F [  ,  ( r )]dr
 Gradient Corrected Approximation (GGA):
                        WORKING SCHEME

   1-electron equations:

{- 1  2 - Z 
                  dr  F [  ,  ]} ( r )    ( r )
   2       r   |r-r |                i         i i

where           (r)       |       |
                                      2

                            i
                                  i
   These equations are known as Kohn-Sham orbital equations.


KS equations have the similar form as Hartree equations- but have
correlation, in principle can work for all systems.


In practice, the present formalism works great for systems where
bonding is primarily chemical.


   Not successful for weakly bound systems- attempts are underway.
                Calculation of Current
Non-equilibrium Green’s Function Methoda

                G  (E  I - H Mol - Left - Right )-1
  HMol: Molecular Hamiltonian
  T: Transmission function                  : Self-energy function
                                                     
        Tmn  tr (mGn G  )             left  Cleft Gleft Cleft
                                                                    
          i( -  )                    right  Cright Gright Cright

                E f  eV 
           2e
      I           dE )T ( E,V )  [ f ( E - 1 ) - f ( E -  2 )]
           h E f -eV (1-

aW.   Tian, et al., J. Chem. Phys. 109, 2874 (1998)
                     Ferromagnetic

                                                AF is lower in energy !




                      Anti-Ferromagnetic
Electron Spin Density Plot for anti-parallel Spin Alignment
I-V Characteristics For Different Spin Alignment

               45
                        Ni-(ll)-Spin Up
               40       Ni-(ll)-Spin Down
                        Ni-(ll)-Total
               35
                        Ni-(anti)-Spin Up
               30       Ni-(anti)-Spin Down
                        Ni-(anti)-Tot                    Down spins
Current (A)




               25                                        majority carriers
               20

               15

               10

                5

                0
                    0    1              2        3   4
                                   Voltage (V)
                     Conductance-Voltage Curve


             50

             45
                                              Ni-(ll)-Spin Up
             40                               Ni-(ll)-Spin Down
                                              Ni-(anti)-Spin Up
             35                               Ni-(anti)-Spin Down

             30
DOS (1/eV)




             25

             20

             15

             10

             5

             0
              -6.5          -6         -5.5              -5         -4.5
                                    Energy (eV)
Conductance-Voltage Curve
   EF




             (A)




              

    EF




              (B )
                                         Spin Up
                        Conductance-Voltage Curve        are majority carriers-
                                                Spin valve effect is less.

               70
                         Mn-(ll)-Spin Up
               60        Mn-(ll)-Spin Down
                         Mn-(ll)-Total
                         Mn-(anti)-Spin Up
               50
                         Mn-(anti)-Spin Down
                         Mn-(anti)-Total
Current (A)




               40


               30


               20


               10


               0
                    0     1            2                 3   4        5
                                           Voltage (V)
Oscillatory MR is Atomic Wires



                    A. I. Yanson et al ,
                    “Formation of atomic
                    gold wires” al, “Quantized
                   H. Ohnishi etNature, 395
                   Conductance through a
                    783 (1998).
                   chain of Gold atoms” Nature
                   395, 780 (1998).
          0.35

           0.3

          0.25

           0.2
E (eV)




          0.15

           0.1

          0.05

            0
                 0   1        2         3         4         5   6
                         Number of C-atoms in Atomic wire
Ferro- - 1.687 Å       1.294 Å      1.294 Å    1.687 Å
Anti ferro-1.692 Å      1.293 Å      1.293 Å    1.692 Å




Ferro—1.736 Å        1.269 Å     1.317 Å 1.269 Å     1.736 Å
Anti ferro-1.82 Å    1.245 Å     1.353 Å 1.245 Å    1.82 Å
         4
                                                     (ll)-Spin Up
        3.5                                          (ll)-Spin Down
                                                     (anti)-Spin Up
         3                                           (anti)-Spin Down
                                                     (ll)-Total
        2.5                                          (anti)-Total
G(Ef)




         2

        1.5


         1

        0.5


         0
              0   1        2          3         4         5             6
                      Number of C- Atoms in Atomic wire
  Transistor with different Oxidation State
       State- Experimental Results:
 [Co(tpy-(CH2)5-SH)2]2+ (longer molecule)
  I–V et. al. the single-electron
Park, curves ofNature, 417, transistor as gate voltage is varied: from -0.4
  V (2002)
722,(red) to -1.0 V (black) in increments of -0.15 V.
                                               Why Nanotube ?




                                                                                 
                                                                        c  na1  ma2
                                                                       Metallic:n=m, and n-m=3i
                                                                       Semiconducting:n-m     3i
                                                                                                   
       Unique molecular structure, Highly Stable (Thermally and Chemically)
       Very small dimension (nm-mm)
       Some are metallic ;J~ 1011 Electrons per Sec-nm2 (Copper Wire, J~ 106
       Electrons per Sec-nm2); Some are semi-conducting (Eg~1/DNT)
       Technological applications: Nanoelectronic devices.

aJ.   Kong et al, Science 287 (2000) 622.
                                  Motivation
Molecular and Nano-electronics
* Progress Towards Miniaturization
* Searching for New Device Architectures
* Developing Compatible Technology




Carbon Nanotubes
Metallic and Semiconducting

Conductivity found to be higher compared to
the best metal

Transconductance of the nanotube is found to
be twice that of conventioanal MOSFET

Arrays of nanotube transistors are shown to
exhibit logic circuits.
                                              New Devices and Geometries: Challenges
                                              • 3-D Architectures, Growth, Integration
                                              • Tailoring Nanotube Structure, Properties
                                              • Making and Characterizing Junctions, Networks
  Achievements of Last Two Years




Fabricated aligned carbon nanotube
arrays at desired locations on planar
substrates using substrate templating and
CVD with control over:
           * Nucleation & Termination
Sites of Nanotubes
          * Surface-selectivity
                                          Effect of Molecular Adsorbate on Transport Property: Nano Sensor




                                                                                                               40




                                                                                   Partial Pressure (Pa*10 )
                                                                                   -6
                               1.02                                                                                                           H2
Resistance normalized (Ohms)




                                                                                                               30                 CO2

                                                                                                                    H2O

                               1.00
                                                                                                               20


                                                                                                                                       CO

                                                                                                               10
                               0.98


                                                                                                                                  O2
                                                                                                               0
                                      0         200                    400   600                                0   200                 400        600
                                                                                                                                        o
                                                                   o
                                                      Temperature ( C)                                                    Temperature ( C)
Theory: Effect of Molecular Adsorbate on Transport Property: Nano
Sensor




               200
               150         Ideal (3x3)
               100         Ideal (3x3-3O2)
Current (A)




                50
                 0
                -50
               -100
               -150                                          Oxygen doping increases conductance.
               -200
                                                             Water decreases conductance.
                      -6   -4     -2     0      2   4   6
                                    Voltage (V)
                    Endohedral Doping-Magnetic atom inside nano-tube




                                                                  This shows that C60 provides additional path for current.
K. Harihara et al. PRL,85(2000)5384 has shown that GdC82 can be   Applied Physics Letters -- February 25, 2002 -- Volume 80,
encapsulated inside nanotube. Experiment done by HRTEM.           Issue 8, pp. 1450-1452
                    Transport through Peapod
                                           90.00

                                                                      80.00
                                                                                          17x0
                                                                      70.00               17x0-C60

                                                                      60.00




                                                       Current (A)
                                                                      50.00
17x0 nanotube with buckyball inside                                   40.00
                V                                                     30.00

                                                                      20.00

                                                                      10.00

                                                                       0.00
                                                                          0.00     0.20      0.40        0.60           0.80     1.00
                                                                                              Voltage (V)




                                                        70


                                                        60                                                      17x0
                                                                                                                17x0-C60
                                                        50




                                          DOS (1/eV)
                                                        40


                                                        30


                                                        20


                                                        10


                                                               0
                                                                  -6.53          -6.03        -5.53             -5.03          -4.53
                                                                                           Energy (eV)
 Summary


• Spintronics offer a new way of store and transmit
information.
• Molecules, Wires, Carbon Nanotubes are good
examples of studying spin assisted transport at the
molecular level
Funding:
NSF
NASA
SRC

								
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