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Saito, R., M. lower ͑ Dresselhaus, is M. S. from Eq.
minus sign the Fujita, G. ␲͒ band. Itand clear Dresselhaus, ͑6͒
that Tight	
  bspectrum is Lett. 60, 2204. around zero energy if tЈ
 lectronic propertiespproxima0on	
  
        the inding	
  a of graphene
         1992a, Appl. Phys. symmetric
       Saito,finite values graphite”	
  by	
  Wallace	
  Phys.	
  Rev.	
  Le<.	
  71,	
  622,	
  1947	
  is
= 0. For
             	
  “The	
  band	
  theory	
  of	
  
                    R., M. Fujita, of tЈ, the electron-hole symmetry 	
  
                                                  G. Dresselhaus, and M. S. Dresselhaus,
broken and theRev.and ␲1804.
 ,       1992b, Phys.
                                    ␲ B 46, * bands become 1asymmetric. In
       San-Jose, P., E. Prada, and D. Golubev,k2007,bPhys. Rev. B 76,
-
Fig. 3, we show theAfullBband structure of graphene with            y
         195445.
 ,
both t and S.,. 2007, Phys. Rev.figure, we also show a zoom in
       Saremi, tЈ δ 3 the1 same B 76, 184430.
                             In δ                                                K
 ,
of the band D., E. H. Hwang, and W. K.ofΓ the Dirac points ͑at
       Sarma, S. structure close to one Tse, 2007, Phys. Rev. B
s
the K or KЈ a 1
         75, 121406. pointδ 2in the BZ͒. This dispersion can be                  M          kx
c      Schakel, A. M.2J., 1991, the full band structure, Eq. ͑6͒,
obtained by expanding Phys. Rev. D 43, 1428.
                                  a
                                                                                K’
t
close to the K ͑orGeim, vector, Eq. ͑3͒, as kE. H. + q, P.
       Schedin, F., A. K. KЈ͒ S. V. Morozov, D. Jiang, = K Hill, with
                                                                          b2
a        Blake, and K. S. Novoselov, 2007, Nature Mater. 6, 652.
͉q ͉ Ӷ ͉K͉ ͑Wallace, 1947͒,
n      Schomerus, H., 2007, Phys. Rev. B 76, 045433.
-      Schroeder,͑ColorM. + O͓͑q/K͒2͔, and A. Javan, 1968, Phys. ͑7͒
        FIG. 2.                        online͒ Honeycomb lattice and its Brillouin
       E±͑q͒ Ϸ P. R., ͉q͉ S. Dresselhaus,
                            ± vF
 ;      zone.Lett. 20, 1292.structure of graphene, made out of two in-
         Rev. Left: lattice
       Semenoff, G. momentumRev. ͑a1 53, a2 are
where q is theW.,triangular latticesLett. and 2449. the latticethe
        terpenetrating 1984, Phys. measured relatively to unit
-      Sengupta, and ␦i G. 1 , 2the are the nearest-neighbor by vF
        vectors, and
Dirac pointsK., and, viF=Baskaran, 2008, Phys. Rev. B given vectors͒.
                                                  is , 3 Fermi velocity, 77, 045417.
       Seoanez, C., a value vandf	
  1raphene”	
   The This result are lo-
       “The	
  electronic	
  proper0es	
  o A. H. Castro Neto, 2007, Phys.
                                  F. Guinea, Ӎ g ϫ 106 m / s. Dirac cones was
        Right: corresponding Brillouin zone.
= 3ta / 2,.	
  Castro	
  Neto	
  Rev.	
  Mod.	
  Phys.	
  81,	
  109	
  2009	
  
-      A.	
  H with 125427. KЈ F
        catedB 76, K and
         Rev. at the                                 points.
first obtained by Wallace ͑1947͒.
-
form Left: energy spectrum ͑in units of t͒ for finite values of
lattice. ͑Wallace, 1947͒
t and tЈ, with t = 2.7 eV and tЈ = −0.2t. Right: zoom in of the
     E±͑k͒ = ± tͱ3 + f͑k͒ − tЈf͑k͒,
energy bands close to one of the Dirac points.


 1
     f͑k͒ = 2 of tЈ is not 4 cos ͩ ͪ ͩ ͪ
                                   ͱ3
                                     ky cos kxa
                                                  3
   The valuecos͑ͱ3kya͒ + well knownabut ab initio , calcula
                                                          ͑6͒
͑Reich et al., 2002͒ find 0.02t Շ tЈ2 0.2t depending on the t
                                   Շ              2
binding parametrization. These the upperet͑al.:alsoelectronic pro
where the plus sign applies to      calculations␲*Theand the
                                      Castro Neto
                                                    ͒ include
effect of a third-nearest-neighbors hopping, which has a v
minus sign the lower ͑␲͒ band. It is clear from Eq. ͑6͒
of around 0.07 eV. A tight-binding fit to cyclotron reson
that the spectrum is symmetric around zero energy if tЈ
experiments ͑Deacon et al., 2007͒ finds tЈ Ϸ 0.1 eV.
= 0. For finite values of tЈ, the electron-hole symmetry is
broken and the ␲ and ␲* bands become asymmetric. In
Fig. 3, we show the full band structure of graphene with
both t and tЈ. In the same figure, we also show a zoom in
of the band structure close to one of the Dirac points ͑at
the K or KЈ point in the BZ͒. This dispersion can be
anប = 1͒ ͚ e−ik·Rna͑k͒,
      ͑we use units such that = ͱN k
                 ͑15͒
                                    c

           H=−t    ͚is
  by A = 3ͱ3a / 2.͗i,j͘,␴
               2
                   It
                              †
                            ͑a␴,ib␴,j + H.c.͒
                               where Nc is the number of unit cells.
         c
  tates for graphene is        mation, we write the field an as a
  . Dirac fermions
                      ͚         †          †
                               coming+ b␴,ib␴,j + H.c.͒, Fourier s
   of carbon nanotubes ͑a␴,ia␴,j
                 − tЈ                   from expanding the
  er shows 1 / ͱE singu- ␴ K. This produces an Јapproximation
                      ͗͗i,j͘͘,
    We consider the Hamiltonian ͑5͒ withas a sum of two ne
                               tion of the field an t = 0 and the
 their electronic spec- the electron operators,
  ourier transform of ͒ annihilates ͑creates͒ an electron
       where the ͑ai,␴   †
antization of ai,␴ mo-
  ular spin ␴ tube axis. ͒ on site Ӎ i −iK·RsublatticeЈ·Rna ͑an equ
        to the ͑␴ = ↑ , ↓          an e
                                       R on na + e−iK A ,
                                                1,n          2,n
   nanoribbons, whichis used for sublattice B͒, t͑Ϸ2.8 eV͒ i
       lent definition
             1
         =     ͚   e−ik·Rna͑k͒,
      anearest-neighbor hopping energy ͑hopping between
            ͱN c k
   perpendicular to the
       n                                                       ͑16͒
milar ferent sublattices͒, and t is the next −iKЈ·Rn
        to carbon nano-
                                   bn Ӎ e−iK·Rnb1,n + e nearest-neig
                                       Ј                    b2,n ,
      hopping energy1 ͑hopping in the same sublattice͒.
where Nc is the number of unit cells. Using this transfor-
      energy bands derived from this Hamiltonian have
mation, we write the field an as a sum of two terms,
 2009
      form ͑Wallace, 1947͒
ͩ
  ͑ai bi ͒ ͱ = 1
    † †
    − ,3a͑i −͑i 3͒/4, 2͒.
                                                         y               ͪͬ
                                                     guage,1 the two-component
                                     It 0is clear that around K has the fo
                                                     mentum the effective Ham
                                    ͫͩ               ͪ ͬͪ
oniant ͵ dxdy⌿ is madeͱ of 3a͑1 − iͱclose to of ͱthe3a͑− i − ͱ3͒/4 /2 ⌿Di
                                             two 3͒/4 ‫ + ץ‬the K massless ˆ ͑r͒   ͪ ͩ                        ͪͬ
                                                                          point, obeys
                                                                                                   ͩͪ ͬ ͪ
    H Ӎ − ͑18͒3a͑i − ͱ3͒/4                            copies 0
                                   0
                   ˆ ͑r͒
   0                       †
                                                                               −i␪k ‫ץ‬
                                          ‫ץ‬y holding for − 3͒/4 1 e K and
                           1                                                      x                             y   1
                           − 3a͑1 + i 3͒/4       ˆ0
                                                ⌿2͑r͒         − 3a͑i         0
 ke− Hamiltonian, 3a͑1 + iͱ3͒/4      one                             p around E␺
        ͱ3͒/4
− i + ⌿ ͑r͒ˆ      †
 ther for p 3a͑1 − i  ͫͩ 0 0
                  − around
                  2
                                                           −±,K͑k͒ ·=ٌ ͱ3͒/4
                            ͱ3͒/4 K0 . Note− 3a͑− i − ͱ3͒/4 first ‫ץ‬
                                          Ј       ‫+ ץ‬
                                                          that, in 0 x       ͩ
                                                           ␺0ivF␴ 3a͑i −␺͑r͒ =iˆ␪ /2 ͑r͒.
                                                                        ͱ2 quantized
                                                                             ±e⌿ k ͑r͒              y   2

                                                         The wave function, in m
      = − i ͵ dxdy͓⌿ ͑r͒␴ · ٌ⌿ ͑r͒ + ⌿ ͑r͒␴ · ٌ⌿ ͑r͔͒,
uage,v the two-componentfor HK = vFwave where the ␺
                     ˆ          †ˆ      ˆ           ˆ electron ␴ · k, function
                                                         †
                                                                              ͑18͒
                                                     mentum around K has the
              F                              1                   *       2
                                1                        2

lose to the K point, obeyseigenenergies E = ± vFk, that the 2D Dirac equation,
      − ivF␴ · ٌ␺͑r͒ = E␺͑r͒. tion ␺±,Kthe = ͱ
                                                     respectively, and
with Pauli matrices ␴ = ͑␴ , ␴ ͒, ␴ = ͑␴ , −␴ ͒, and ⌿
                                                 *    ˆ
                                                                         1 ␪k −i␪kgiven
                                                            for 1 p 2 ±ei␪k  †
                                                                               e is /2
                                                                  ͑k͒ momentum/2arou      ͑      ͩ ͪ
                                                                                                 ͩ ͪ
                                     x   y           x       y ˆ
                                                              h= ␴· .        i
= ͑a† , b†͒͑i = 1 , 2͒. It is clear that the effective Hamil-
 The wave function, in momentum ͉p͉space, for/2the m
    i    i                        2
                                                e i␪k
                                          1 where the
 onian ͑18͒ is made of two copies of the massless Dirac-
                        for HK =͑k͒␴thek,
                            ␺±,KЈ vF =· definition −i␪ that the
        ˆ = around· Kp Note that, in first quantized lan-
               1
mentum around K has the formis clear from
 ike Hamiltonian, one holding for p around K and the
                                                                                               ͱ
                            It                        ˆ
                                                   of h /2
other h p
       for         ␴ Ј. .                    ͑22͒ ˆk
                                             ±e
                                              eigenenergies E = ± vof k, tha2

                                             ͩ ͪ
               2          ͉p͉
guage, the two-component electron wave function ␺͑r͒,  and ␺ Ј͑r͒ are also eigenstates F h,
                                                                                       K

                                              respectively, ␺ ͑r͒, ␪k is given
                                           −i␪ /2
  lose to the K point, obeys the 2D Dirac equation,
                            1 e k                                       and
                                                           h␺= v= ␴ * · k. Note that t
       ␺±,K͑k͒ = the definition offor thatЈthe Fstates ␺ ͑r͒ aro
                                                           ˆ ͑r͒ ±
                                              ͑19͒ H K
                                                                                           1
    − iv ␴ · ٌ␺͑r͒ = E␺͑r͒.
   is clear from ͱ ±ei␪k for tion and equivalent by K
          F
                                                 h for the momentum
                                                 ˆ
                                                                                       K

t The wave function, in momentum space,/2 the mo-Ј areanrelatedequation for ␺ ͑r͒ with in
                                                                                           2   K
                                                                                                   ͑
                             2                 K                                 time-rever
                                                                                         Ј                  K
mentum around K has the form                       ˆ , Therefore, electrons ͑holes͒ haveka/2
 nd ␺KЈ͑r͒ are also eigenstates of h helicity. Equation ͑23͒ impliesethat mom
                                               origin of coordinates in ␴positive      i␪
              1 e ␪    −i k/2                                               1                has its
ed, leading to a new term to the original Hamilto
5͒,  Hod = ͚ ͕␦t͑ab͒͑a†bj + H.c.͒ + ␦t͑aa͒͑a†aj + b†bj͖͒,
                ij    i               ij    i      i
               i,j

   Hod = ͚ ͕␦t͑ab͒͑a†bj + H.c.͒ + ␦t͑aa͒͑a†aj + b†bj͖͒,
              ij    i               ij    i      i
                                                     ͑14
             i,j
 or in Fourier space,
                                                                             ͑1
          ͚space,͚     †                                  ជ
                                         ͑ab͒ i͑k−kЈ͒·Ri−i␦aa·kЈ
     Hod =           a kb kЈ           ␦ti e                       + H.c.
r in Fourier     ជ
              k,kЈ             i,␦ab


   Hod = ͚                     ͚␦ ͚        ͑aa͒ i͑k−k ·kЈ ជ
                     ††                             ជ
                               † ͑ab͒ i͑k−kЈ͒·R −i␦ Ј͒·Ri−i␦ab·kЈ
         +         ͑akakЈ +
                    a kb kЈ   bkbtiЈ͒ e ␦ti e i aa + H.c.
                                 k                                ,         ͑14
                             ជ         ជ
                                     i,␦aa
           k,kЈ            i,␦   ab

 where ␦t͑ab͒ ͑† a͑aa͒+ is †the ͒change of i͑k−khopping·kenerg
                ␦tij ͒ b b
                                            ͚
                                                         ជ
                                         ͑aa͒ the Ј͒·Ri−i␦ab Ј
          ij ͑a
           + k kЈ                      ␦ti e                   , ͑
                           k kЈ
 between orbitals on lattice ជsites Ri and Rj on the sam
                                 i,␦aa
 ͑different͒ sublattices ͑we have written R = R + ␦, whe   ជ
                                                               j      i
͚
  ange a similar expression ␦t͑ab͒͑r͒e−i␦but ,
   with of the Coulomb
   by A
                         A͑r͒ =
               Two	
  Dirac	
  cones	
  a
  hklovskii, 2007͒ and,
                                         ab           ͵
                                            for cone 2 ab·K with A replaced
                                                  Hod = d2r͓⌿†    ˆ
         Castro Neto et al.: The ជelectronic properties of graphene
                                                                    1
                                                                                ជ     ˆ
          *, where ͑Fogler, ␦ re	
  not	
  coupled	
  by	
  disorder	
   ͑r͒␴ · A͑r͒⌿1͑
  in graphene
 007͒. In fact, transport −i␦ab·K
                    experimentsជ
 pretation = ͚ ␦t͑ab͒͑r͒e
         A͑r͒ of                                , A͑r͒aa·K x͑r͒ + iAy͑r͒.
                                                         ជ=A                    ͑147͒
                  ជ
                  ␦
                         ␾ San-   ͚           ͑aa͒     −i␦
mura et al., ofabgraphene= et ␦t In͑r͒e of .the Dirac Hamilton
 s properties 2007; ͑r͒
nic͑Chen, Jang, Fuhrer,
                                                   terms
                                                     ជ
                                                                                      135
  ures in the transport that where A = ͑Ax , Ay͒. This result sh
   2008͒.
                                      ជ
                                     ␦aa
  impurities. Screening ef-                     Eq. ͑146͒ as
   oneA͑r͒ = A ͑r͒͑aa͒the −i␦ hopping amplitude lead to ͑149͒
         that changes iA ͑r͒. ·K                                                   the a
         ␾͑r͒ = ͚ ␦t case,
                                                          ͵
nd range of Note that y aa .+ ͑r͒ewhereas ␾͑r͒ = ␾*͑r͒, because of th
                  the Coulomb
                                          ជ
   orbitals. In this ͑Fogler, and scalar = potentials␴ ͑148͒ D
                    x
  ial in graphene                                   Hod ⌽ d2r͓⌿†͑r͒ in A͑r͒⌿
                 symmetry of the two triangular sublattices in
                 ជ
                 ␦are modi- Hamiltonian ͑18͒, we 1 potential
                                                                        ˆ         the ˆ
                                                                                · ជ th
7; terms of
 In Shklovskii,the Dirac presence of a vector can rewrite
 ferent sites aa 2007͒ and,
   original as of honeycomb *lattice, A is complex becauseB
                 the
 Eq. ͑146͒Hamiltonian
  terpretation           transport ␾ ͑r͒, because of the inversion ជ
   Note that whereas ␾͑r͒ = that an effective magnetic field
                 inversion symmetry for nearest-neighbor

                 ͵
Nomura et al., the two triangular sublattices that make up
   symmetry of 2007; San- also be present, naively implying
                 Hence, †
                        2 ˆ                        ˆ ជ because†of the result
                                             ជ ͑r͒⌿ ͑r͒ + ͑Ax , Ay͒. This͑r͔͒, s
                                                where A =
        2008͒.
  ͑aa͒ honeycomb lattice, A is
   the †         †                          A complex ␾͑r͒⌿1 aˆlack of
   al., Hod = d r͓⌿1͑r͒␴ · symmetry, although͑r͒⌿1 origina
                                                     1
                                                                   ˆ
 the͑ai aj + bi symmetrythe reversal invariant. This broken t
  ij
   inversion          j͖͒,
        one thatbchanges                  for hopping amplitude lead to the
                                                 nearest-neighbor hopping.
    pz orbitals. In Mod. Phys., Vol. 81, No. 1, January–March ͑150͒͑150͒
   Hence,        Rev. this case, is and real since Eq. 2009 in is th
                                                not scalar ⌽ potentials              the
                           ͑144͒
   different sites are modi- only one of of a Dirac cones. Th
                                                presence the vector potential
  the original Hamiltonian related an effective by time-revers
            ជ
 where A = ͑Ax , Ay͒. This result shows that changes infield
                                                that to the first magnetic the
   Rev. Mod. Phys., Vol. 81, No. 1, January–March 2009
Sca<ering	
  mechanisms	
  in	
  graphene	
  
	
  
	
  
	
  
•  Suspended	
  graphene	
  at	
  4K	
  μ	
  ~200,000	
  	
  cm2/V	
  	
  [1]	
  
	
  
	
  
•  Suspended	
  graphene	
  at	
  300K	
  	
  μ	
  ~10,000	
  	
  cm2/V	
  s	
  
     ü  Out-­‐of-­‐plane	
  flexural	
  phonons	
  limit	
  [2]	
  
	
  
•  Suspended	
  graphene	
  in	
  non-­‐polar	
  liquid	
  	
  	
  
       μ	
  ~60,000	
  	
  cm2/V	
  s	
  
	
  
•  Effect	
  of	
  liquids	
  on	
  the	
  flexural	
  phonons	
                                                  Image	
  from	
  Meyer,	
  J.	
  C	
  .	
  
     ü  Vacuum	
  

       ü  Hexane	
  C6H14	
  

       ü  Toluene	
  C6H5CH3	
                                            	
  
                                                                           1.     Bolo0n,	
  K.	
  I.	
  et	
  al.	
  Solid	
  State	
  Comm.	
  	
  2008	
  
                                                                           2.     Castro,	
  E.	
  V.	
  et	
  al.	
  Phys	
  Rev	
  Le<.	
  2010	
  
kk                   kk       kk

 ponds to theElectron	
  sca<ering	
  due	
  to	
  flexural	
  ripples	
   h is the
 ponents of in-planeofatomic displacements by a
                 solution    the Boltzmann equation and
 (Ziman 2001) or, equivalently, using the modifies the hopping
   o a graphene sheet. This curvature Mori formula
  in which only intra-band matrix elements of the current
                            
 o account. For the case of a small concentration of either
                          vg
          g Z one
 mb scatterers,g0 Ccan check u ij : direct calculations that
                                
                                by                                            ð4:2Þ
  he same concentrationudependence of resistivity approxima0on	
  
                         vij 0                      Harmonic	
   as the
   ach described in §2.
                                                  T
 st-neighbour hopping parameters is equivalent to the          2
        Fourier	
  components	
  of	
  	
   hq ~
                                             
      bending	
  correla0on	
  func0on	
  
       4. Scattering by ripples                  κ q4
 field (Morozov et al. 2006) described by a ‘vector potential
   1                          ðyÞ    1
Zgraphene sheetK g3 Þ; interatomic00K	
  	
   2 K g3and angles
                                  Z ðg
     ð2g1 K g2 changes V h	
   at	
  3 distances Þ;                         ð4:3Þ
 ds2and can be described by the following nonlinear term in
                                     2
 r and 3 label 2004):
   (Nelson et al. the nearest neighbours that correspond to
      pffiffiffi 1  vu vu ffiffiffi vh vh 
                     p                  pffiffiffi
 K uij Z; 0Þ, ða=2 j3;K
   a= 3
                i
                   C     C a=2Þ and ða=2 3; a=2Þ, ð4:1Þ
                                  ;                respectively
           2 vxj     vxi  vxi vxj
 nearest-neighbour hopping also lead to an electrostatic
  fluctuates in a randomly rippled graphene sheet
   2007). However, as follows from equations (3.2) and
To estimate scattering on such ripples, we note that, in the simpl
  approximation, the averagersta.royalsocietypublishing.org on February 22, 20
                             Downloaded from potential energy per individual ben
  Eq Z kq 4 hjhq j2 i=2sis equal to kdue	
  to	
  flexural	
  phonons	
   stiffness of
             Electron	
   caering	
   BT/2 (kz1 eV is the bending
  which yields
 200                                                                k BT
                                                    M. I. Katsnelson and :A. K. Geim
                                                                2
Hopping	
  integrals	
  γ	
  are	
  modified	
  	
         hjhq j i Z 4
                                                                     kq
                                                                                2	
  
 Poten0al	
  perturba0on	
  due	
  to	
  ripples	
  a	
  	
  realistic atomicatomic displacement
   Numerical simulations using 	
  -­‐
  where u i are the components of in-plane interaction potential                 1	
  
 random	
  sign-­‐changing	
  this result graphene sheet. This curvature modifi
   directly confirm ‘magne0c	
  field’	
   the case of bending fluctuations wit
  displacements normal to a                     for
   length scale smaller than l Ãz7–10 nm (Fasolino et al. 2007). Th
 integrals g as conductivity is experimentally 
                                               2                           3	
   observed for doping
1 2π Ã
   dependence of                           2
                   ( )
   that F l E 1, VqV−q ~ h g Z g C vg
   ≈ kN O F which justifiesq the use of the harmonic approximatio
τ then use equation (4.8) for the pair correlationufunction and find
          h                                            0                               ij :
                                                                                  u
                                                                                vij 0
   resistivity as                2
 The change in    1        2 nearest-neighbour ðk T=kaÞ2parameters is equ
                                                     h hopping
ρappearance ofha gauge field (Morozov etB al. 2006) described by a ‘v
  ripple
            ~ ~ q                         rr z 2
                                                    4e                      n
                                                                                      L;
                  τ
   where the factor L is of the order of unity for k F l à y1 1
                                     1 1. The above equationðyÞ and weakly, a
                            V ðxÞ [
                                   Ã
   depends on n for k F l Z ð2g1 K g2 K g3 Þ; V shows ðg2 Ktherma                        Z that g3 Þ;
                                     2
   ripples lead to charge-carrier mobility m practically independen
Effect	
  of	
  liquids	
  
                                                                                                2
   agreement with experiments. Importantly, equation (4.9) also yiel
 where the C6Hof	
   magnitudepffiffiffi labelet.	
  apffiffinearest 2006	
  
     ü  Hexane	
   indices 1, 2 and 3 S.	
  V.	
   thePhys.	
  Rev.	
  Le	
   neighbours that
   same order 14                          as observed ffi experimentally. One can
                                        Morozov	
                  l,	
                                pffiffiffi
     ü  Toluene	
  2C6H5CH3	
  
 translational vectors K2 as M.	
  3.	
  ;Keffectivend	
  A3K.	
  Geim,	
  Phil.	
  Trans.	
  R.	
  Soc.	
  A,	
  	
  2defec
   ðk B Tq =kaÞ z1012 cm ðKa= Castro,	
  E.	
  V.	
  et.	
  aa Phys	
  Rev	
  Le	
  (2010)	
   of static ;008	
  
                                          I atsnelson	
                    .	
   ;Ka=2Þ and
                                         an 0Þ, ða=2 concentration ða=2 3 a=2
                                                             l	
  
Molecular	
  dynamics	
  with	
  classical	
  poten0als	
  

•  Large	
  system	
  10,000-­‐50,000	
  atoms	
  L	
  ~10nm	
  

•  Large	
  0me	
  scale	
  ~ns	
  

•  Bond-­‐order	
  poten0als	
  	
  for	
  C-­‐H	
  

•  Boundary	
  condi0ons	
  
    ü  NPT	
  –	
  constant	
  pressure	
  
    ü  NVT	
  –	
  constant	
  volume,	
  corresponding	
  to	
  P~0	
  

     	
  	
  
Strain-­‐free	
  suspended	
  graphene	
  

 T	
  =	
  300	
  K	
  
                                          h	
  




                                 h2               = 0.89 Å2	
  	
  
                                      vacuum




                          	
  
                          	
  
                          	
  
Suspended	
  graphene	
  in	
  hexane	
  
                   Hexane	
  molecules	
  envelopes	
  graphene	
  sheet	
  




C	
  chain	
  aligned	
  parallel	
  to	
  the	
  plane	
               Mean	
  square	
  displacement	
  

                                                                      h2            = 0.39 Å2	
  	
  
                                                                           hexane
Suspended	
  graphene	
  in	
  toluene	
  


    Toluene	
  molecules	
  envelopes	
  graphene	
  sheet	
  

C	
  ring	
  aligned	
  parallel	
  to	
  the	
  plane	
         Mean	
  square	
  displacement	
  

                                                                    h2           = 0.42 Å2	
  	
  
                                                                         toluene
Preferred	
  molecule	
  posi0on:	
  DFT	
  calcula0on	
  



              ΔE	
  =	
  0.21	
  eV	
                             ΔE	
  =	
  0.37	
  eV	
  

                                                                                3	
  Å	
  

3	
  Å	
                  Van	
  der	
  Waals	
  interac0on	
  
Ripple	
  height	
  analysis	
  

                                               h	
  




h2             = 0.89 Å2	
  	
  
     vacuum



h2           = 0.42 Å2	
  	
  
     toluene

h2            = 0.39 Å2	
  	
  
     hexane
dependence of conductivity is experimentally observed for
 that k F l à O 1, which justifies the use of the harmonic appro
                     Bending	
  s0ffness	
  of	
  graphene	
  in	
  liquid	
  
 then use equation (4.8) for the pair correlation function a
 resistivity as
        2           TN                                h ðk B T=kaÞ2
   hq =
     
                κ A0q4                      rr z 2                            L;
                                                     4e            n
 where the factor L is of the order of unity for k F l à y1 and w
 depends uppresses	
  	
   k F l à [ 1. The above equation shows that
    Liquid	
  s on n for                                Bending	
  S)ffness	
  
    flexural	
  phonons	
  
 ripples lead to charge-carrier mobility m practically ind
 agreement with experiments. Importantly, equation (4.9) a
 same order of magnitude as observed experimentally. O
 ðk B Tq =kaÞ2exural	
  	
   12 cmK2 as an effective concentration of stat
  Out-­‐of-­‐plane	
  fl z10
phonons	
  limit	
  at	
  room	
  T	
  
 induced at the quench temperature Tq of 300 K. We emphas
 disorder,μthat is,	
  cin2/V	
  s	
   Born approximation, the above forma
 ü  Vacuum	
   	
  ~10,000	
   m the
 describe electron scattering by both static (quenched) and
 assuming 	
  200,000	
  	
  first, sthey are classical scatterers and, secon
 ü  Liquid	
  μ	
  ~ that, cm2/V	
   	
  
 relevant q is smaller than the energy of scattered Dirac ferm
 2001). The former condition means that kk 2 a2 / kB Tq and           F
Conclusion	
  
	
  
•  Liquid	
  dielectric	
  environment	
  suppresses	
  flexural	
  phonons	
  


•  Phonon	
  suppression	
  affects	
  mobility	
  through	
  bending	
  s0ffness	
  
current for a resistor (blue), capacitor (red), inductor (green) and memristor (purple). The lower figur
Четвертый	
  основной	
  компонент	
  электрической	
  цепи	
  
                      show the current-voltage characteristics for the four devices, with the characteristic pinched hysteresis
                      loop of the memristor in the bottom right. It is nearly obvious by inspection that the memristor curve
                      cannot be constructed by combining the others.




                      There are also arguments that there are far more than four fundamental electronic circuit elements. In
                      fact, Chua has shown that there are essentially an infinite number of two-terminal circuit elements tha
                      can be defined via various integral and differential equations that relate voltage and current to each oth
                      [L. O. Chua, Nonlinear Circuit Foundations for Nanodevices, Part I: The Four-Element Torus. Proc.
                      IEEE 91, 1830-1859 (2003) – this is an interesting tutorial for the beginner], to which the memcapacit
                      and meminductor belong. It comes down to whether one wants to think of all of these possible circuit
                      elements as being on an equal footing or choose the four lowest order relations to be a fundamental se
                      with a large number of higher order cousins. Similar considerations apply in other fields – do we
                      consider electrons, protons and neutrons fundamental or quarks or what?

                      Who 'Discovered' the Memristor?
The	
  nonlinearity	
  exists	
  because	
  of	
  coupled	
  
 electronic	
  and	
  ionic	
  conducOon,	
  the	
  laPer	
  being	
  
    mediated	
  by	
  defects,	
  typically	
  vacancies	
  or	
  
                         intersOOals.	
  	
  


Pd/WO3/W	
  	
                                       TiO2	
  
4                      fit experimental  RC
 current,                                                        to appe
      2                      data using
        900 K                equivalent
      0                                           RON
     -2       •  R(w(t))=RONw(t)/D+ROFF(1-­‐w(t)/D)	
  	
  
                             circuit
                                                   extract
     -4
        -2.0 -1.0 0.0 1.0                          geometry
             voltage, V                            from fitting
perature on I-V                    OFF state       ON state
                                       dOUT           z dON
                                               r
                 perform 3D              wOFF
                                                       0
                 coupled      TiO2      dC                   wON
                 electro-    ( I I) metallic  L
                                     channel
                 thermal              ( C C)
                 simulations
                               electrode (   E   E)


                                     D.Strukov et al. MRS (2009)

ort required for high retention, even more for half
Однополярный	
     Биполярный	
  
Биполярный	
  механизм	
  	
  
поверхностного	
  переключения	
  	
  
The	
  most	
  common	
  type	
  of	
  insulators	
  in	
  the	
  sandwich	
  structures	
  
are	
  metal	
  oxides	
  with	
  high	
  concentra0ons	
  of	
  oxygen	
  vacancies,	
  
such	
  as	
  NiO,	
  HfO2,	
  ZnO,,	
  Al2O3,	
  WO3,	
  and	
  TiO2	
  	
  
Электронная	
  плотность	
  	
  
                                                	
  
                            Разложение	
  по	
  функциям	
  Гаусса	
  

                                                         q %
                                                                            
                                
ρ r =()
                N atoms

                ∑                (
                            ρn r − Rn    )            (      ) $ Q '
                                                               #   A
                                                                          (
                                                   ρn r − Rn = $1− n ' ρ0A r − Rn   )
                 n=1
                 	
  	
  




        Перенос	
  заряда	
   	
  	
  
          M gauss
                   −γ m r 2
        ()
         2
ρn r = ηr ∑ cme
                             m=1

             
 ∫
Ωcell
            (                )
        ρn r − Rn d 3r = QA − qn
                               *
Полная	
  энергия 	
  	
  


                                                                    
                             !             $
 Etotal =        ∫             () ()
                         W r #ρ r           ρ r d 3r + ∫ W q !ρ q $ ρ q d 3q + Eion−ion
                                                              #     () ()
            Ω
                                          %           Ω
                                                                  %
                volume                                 volume




                                                     
      !              $     !                 $      !    $
  W r #ρ r
           ()       
                     %
                       = T #ρ r
                                      ()    
                                             %        ()
                                               +Vex #ρ r 
                                                         %
                                	
  	
  


                            
     !    $
            ()                ()
 W q #ρ q  =V ps q +Vhartree q
         %                                         ()          Vps ( q ) = S ( q ) w pseudo ( q )
Кинетическая энергия
                                                             corr   corr
                                        T = TWang −Teter + TLDA + Tatom

                                                 5 
                  % 45          2       5
              ()
 TWang−Teter $ρ r ' =
             #      128 ( )
                          3π 2     3
                                     ∫∫   () ( ) ( )
                                        ρ 6 r w1 r − r ' ρ 6 r ' d 3rd 3r '−

                     21      2        5        1       1        1   
                  −
                    250
                       ( )
                        3π 2   3
                                  ∫    ()       () ()
                                     ρ 3 r d r − ∫ ρ 2 r ∇ ρ 2 r d 3r
                                            3

                                                2
                                                              2




Теория линейного отклика


                                      1 (q               − 4)
                                                     2
     5 ⎛ −1      3 2       3 ⎞                                   2−q
 w1 = ⎜ w ( q ) − q       + , and w = +
                                ⎟                              ln
     8 ⎝         4           5 ⎠           2       8q            2+q
        N grid
                      )6
                      +     n    -
                                  +
  corr !     $
       ()
TLDA #ρ r    =
             %    ∑ *∑ cnΔρ ri .
                  i=1 + n=1
                      ,
                              2
                                  +
                                  /
                                   ()
                           3
  corr
              6 π % 2  k2 %
     ()
Tatom k = ∑ cn $ ' exp $ −
                $ξ '
                # n
                       $ 4ξ '
                       #
                               '
            n=1              n
                 
                  
             k %       
                           
   ()
S A ki = ∑ $1− α ' exp −ikα iRα
              $ N '
         α ∈A #    α 
                               (        )
λ=1   upper limit von Weizsäcker
λ=1/9 gradient expansion second order
λ=1/5 computational Hartree-Fock
1. Phase Diagram

2. Elastic Properties

3. Defect Formation Energies
Ширина	
  запрещенной	
  зоны	
  
G0W0	
                                         GaN	
  

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лекция 5 memristor

  • 1. Saito, R., M. lower ͑ Dresselhaus, is M. S. from Eq. minus sign the Fujita, G. ␲͒ band. Itand clear Dresselhaus, ͑6͒ that Tight  bspectrum is Lett. 60, 2204. around zero energy if tЈ lectronic propertiespproxima0on   the inding  a of graphene 1992a, Appl. Phys. symmetric Saito,finite values graphite”  by  Wallace  Phys.  Rev.  Le<.  71,  622,  1947  is = 0. For  “The  band  theory  of   R., M. Fujita, of tЈ, the electron-hole symmetry   G. Dresselhaus, and M. S. Dresselhaus, broken and theRev.and ␲1804. , 1992b, Phys. ␲ B 46, * bands become 1asymmetric. In San-Jose, P., E. Prada, and D. Golubev,k2007,bPhys. Rev. B 76, - Fig. 3, we show theAfullBband structure of graphene with y 195445. , both t and S.,. 2007, Phys. Rev.figure, we also show a zoom in Saremi, tЈ δ 3 the1 same B 76, 184430. In δ K , of the band D., E. H. Hwang, and W. K.ofΓ the Dirac points ͑at Sarma, S. structure close to one Tse, 2007, Phys. Rev. B s the K or KЈ a 1 75, 121406. pointδ 2in the BZ͒. This dispersion can be M kx c Schakel, A. M.2J., 1991, the full band structure, Eq. ͑6͒, obtained by expanding Phys. Rev. D 43, 1428. a K’ t close to the K ͑orGeim, vector, Eq. ͑3͒, as kE. H. + q, P. Schedin, F., A. K. KЈ͒ S. V. Morozov, D. Jiang, = K Hill, with b2 a Blake, and K. S. Novoselov, 2007, Nature Mater. 6, 652. ͉q ͉ Ӷ ͉K͉ ͑Wallace, 1947͒, n Schomerus, H., 2007, Phys. Rev. B 76, 045433. - Schroeder,͑ColorM. + O͓͑q/K͒2͔, and A. Javan, 1968, Phys. ͑7͒ FIG. 2. online͒ Honeycomb lattice and its Brillouin E±͑q͒ Ϸ P. R., ͉q͉ S. Dresselhaus, ± vF ; zone.Lett. 20, 1292.structure of graphene, made out of two in- Rev. Left: lattice Semenoff, G. momentumRev. ͑a1 53, a2 are where q is theW.,triangular latticesLett. and 2449. the latticethe terpenetrating 1984, Phys. measured relatively to unit - Sengupta, and ␦i G. 1 , 2the are the nearest-neighbor by vF vectors, and Dirac pointsK., and, viF=Baskaran, 2008, Phys. Rev. B given vectors͒. is , 3 Fermi velocity, 77, 045417. Seoanez, C., a value vandf  1raphene”   The This result are lo- “The  electronic  proper0es  o A. H. Castro Neto, 2007, Phys. F. Guinea, Ӎ g ϫ 106 m / s. Dirac cones was Right: corresponding Brillouin zone. = 3ta / 2,.  Castro  Neto  Rev.  Mod.  Phys.  81,  109  2009   - A.  H with 125427. KЈ F catedB 76, K and Rev. at the points. first obtained by Wallace ͑1947͒. -
  • 2. form Left: energy spectrum ͑in units of t͒ for finite values of lattice. ͑Wallace, 1947͒ t and tЈ, with t = 2.7 eV and tЈ = −0.2t. Right: zoom in of the E±͑k͒ = ± tͱ3 + f͑k͒ − tЈf͑k͒, energy bands close to one of the Dirac points. 1 f͑k͒ = 2 of tЈ is not 4 cos ͩ ͪ ͩ ͪ ͱ3 ky cos kxa 3 The valuecos͑ͱ3kya͒ + well knownabut ab initio , calcula ͑6͒ ͑Reich et al., 2002͒ find 0.02t Շ tЈ2 0.2t depending on the t Շ 2 binding parametrization. These the upperet͑al.:alsoelectronic pro where the plus sign applies to calculations␲*Theand the Castro Neto ͒ include effect of a third-nearest-neighbors hopping, which has a v minus sign the lower ͑␲͒ band. It is clear from Eq. ͑6͒ of around 0.07 eV. A tight-binding fit to cyclotron reson that the spectrum is symmetric around zero energy if tЈ experiments ͑Deacon et al., 2007͒ finds tЈ Ϸ 0.1 eV. = 0. For finite values of tЈ, the electron-hole symmetry is broken and the ␲ and ␲* bands become asymmetric. In Fig. 3, we show the full band structure of graphene with both t and tЈ. In the same figure, we also show a zoom in of the band structure close to one of the Dirac points ͑at the K or KЈ point in the BZ͒. This dispersion can be
  • 3. anប = 1͒ ͚ e−ik·Rna͑k͒, ͑we use units such that = ͱN k ͑15͒ c H=−t ͚is by A = 3ͱ3a / 2.͗i,j͘,␴ 2 It † ͑a␴,ib␴,j + H.c.͒ where Nc is the number of unit cells. c tates for graphene is mation, we write the field an as a . Dirac fermions ͚ † † coming+ b␴,ib␴,j + H.c.͒, Fourier s of carbon nanotubes ͑a␴,ia␴,j − tЈ from expanding the er shows 1 / ͱE singu- ␴ K. This produces an Јapproximation ͗͗i,j͘͘, We consider the Hamiltonian ͑5͒ withas a sum of two ne tion of the field an t = 0 and the their electronic spec- the electron operators, ourier transform of ͒ annihilates ͑creates͒ an electron where the ͑ai,␴ † antization of ai,␴ mo- ular spin ␴ tube axis. ͒ on site Ӎ i −iK·RsublatticeЈ·Rna ͑an equ to the ͑␴ = ↑ , ↓ an e R on na + e−iK A , 1,n 2,n nanoribbons, whichis used for sublattice B͒, t͑Ϸ2.8 eV͒ i lent definition 1 = ͚ e−ik·Rna͑k͒, anearest-neighbor hopping energy ͑hopping between ͱN c k perpendicular to the n ͑16͒ milar ferent sublattices͒, and t is the next −iKЈ·Rn to carbon nano- bn Ӎ e−iK·Rnb1,n + e nearest-neig Ј b2,n , hopping energy1 ͑hopping in the same sublattice͒. where Nc is the number of unit cells. Using this transfor- energy bands derived from this Hamiltonian have mation, we write the field an as a sum of two terms, 2009 form ͑Wallace, 1947͒
  • 4. ͩ ͑ai bi ͒ ͱ = 1 † † − ,3a͑i −͑i 3͒/4, 2͒. y ͪͬ guage,1 the two-component It 0is clear that around K has the fo mentum the effective Ham ͫͩ ͪ ͬͪ oniant ͵ dxdy⌿ is madeͱ of 3a͑1 − iͱclose to of ͱthe3a͑− i − ͱ3͒/4 /2 ⌿Di two 3͒/4 ‫ + ץ‬the K massless ˆ ͑r͒ ͪ ͩ ͪͬ point, obeys ͩͪ ͬ ͪ H Ӎ − ͑18͒3a͑i − ͱ3͒/4 copies 0 0 ˆ ͑r͒ 0 † −i␪k ‫ץ‬ ‫ץ‬y holding for − 3͒/4 1 e K and 1 x y 1 − 3a͑1 + i 3͒/4 ˆ0 ⌿2͑r͒ − 3a͑i 0 ke− Hamiltonian, 3a͑1 + iͱ3͒/4 one p around E␺ ͱ3͒/4 − i + ⌿ ͑r͒ˆ † ther for p 3a͑1 − i ͫͩ 0 0 − around 2 −±,K͑k͒ ·=ٌ ͱ3͒/4 ͱ3͒/4 K0 . Note− 3a͑− i − ͱ3͒/4 first ‫ץ‬ Ј ‫+ ץ‬ that, in 0 x ͩ ␺0ivF␴ 3a͑i −␺͑r͒ =iˆ␪ /2 ͑r͒. ͱ2 quantized ±e⌿ k ͑r͒ y 2 The wave function, in m = − i ͵ dxdy͓⌿ ͑r͒␴ · ٌ⌿ ͑r͒ + ⌿ ͑r͒␴ · ٌ⌿ ͑r͔͒, uage,v the two-componentfor HK = vFwave where the ␺ ˆ †ˆ ˆ ˆ electron ␴ · k, function † ͑18͒ mentum around K has the F 1 * 2 1 2 lose to the K point, obeyseigenenergies E = ± vFk, that the 2D Dirac equation, − ivF␴ · ٌ␺͑r͒ = E␺͑r͒. tion ␺±,Kthe = ͱ respectively, and with Pauli matrices ␴ = ͑␴ , ␴ ͒, ␴ = ͑␴ , −␴ ͒, and ⌿ * ˆ 1 ␪k −i␪kgiven for 1 p 2 ±ei␪k † e is /2 ͑k͒ momentum/2arou ͑ ͩ ͪ ͩ ͪ x y x y ˆ h= ␴· . i = ͑a† , b†͒͑i = 1 , 2͒. It is clear that the effective Hamil- The wave function, in momentum ͉p͉space, for/2the m i i 2 e i␪k 1 where the onian ͑18͒ is made of two copies of the massless Dirac- for HK =͑k͒␴thek, ␺±,KЈ vF =· definition −i␪ that the ˆ = around· Kp Note that, in first quantized lan- 1 mentum around K has the formis clear from ike Hamiltonian, one holding for p around K and the ͱ It ˆ of h /2 other h p for ␴ Ј. . ͑22͒ ˆk ±e eigenenergies E = ± vof k, tha2 ͩ ͪ 2 ͉p͉ guage, the two-component electron wave function ␺͑r͒, and ␺ Ј͑r͒ are also eigenstates F h, K respectively, ␺ ͑r͒, ␪k is given −i␪ /2 lose to the K point, obeys the 2D Dirac equation, 1 e k and h␺= v= ␴ * · k. Note that t ␺±,K͑k͒ = the definition offor thatЈthe Fstates ␺ ͑r͒ aro ˆ ͑r͒ ± ͑19͒ H K 1 − iv ␴ · ٌ␺͑r͒ = E␺͑r͒. is clear from ͱ ±ei␪k for tion and equivalent by K F h for the momentum ˆ K t The wave function, in momentum space,/2 the mo-Ј areanrelatedequation for ␺ ͑r͒ with in 2 K ͑ 2 K time-rever Ј K mentum around K has the form ˆ , Therefore, electrons ͑holes͒ haveka/2 nd ␺KЈ͑r͒ are also eigenstates of h helicity. Equation ͑23͒ impliesethat mom origin of coordinates in ␴positive i␪ 1 e ␪ −i k/2 1 has its
  • 5. ed, leading to a new term to the original Hamilto 5͒, Hod = ͚ ͕␦t͑ab͒͑a†bj + H.c.͒ + ␦t͑aa͒͑a†aj + b†bj͖͒, ij i ij i i i,j Hod = ͚ ͕␦t͑ab͒͑a†bj + H.c.͒ + ␦t͑aa͒͑a†aj + b†bj͖͒, ij i ij i i ͑14 i,j or in Fourier space, ͑1 ͚space,͚ † ជ ͑ab͒ i͑k−kЈ͒·Ri−i␦aa·kЈ Hod = a kb kЈ ␦ti e + H.c. r in Fourier ជ k,kЈ i,␦ab Hod = ͚ ͚␦ ͚ ͑aa͒ i͑k−k ·kЈ ជ †† ជ † ͑ab͒ i͑k−kЈ͒·R −i␦ Ј͒·Ri−i␦ab·kЈ + ͑akakЈ + a kb kЈ bkbtiЈ͒ e ␦ti e i aa + H.c. k , ͑14 ជ ជ i,␦aa k,kЈ i,␦ ab where ␦t͑ab͒ ͑† a͑aa͒+ is †the ͒change of i͑k−khopping·kenerg ␦tij ͒ b b ͚ ជ ͑aa͒ the Ј͒·Ri−i␦ab Ј ij ͑a + k kЈ ␦ti e , ͑ k kЈ between orbitals on lattice ជsites Ri and Rj on the sam i,␦aa ͑different͒ sublattices ͑we have written R = R + ␦, whe ជ j i
  • 6. ͚ ange a similar expression ␦t͑ab͒͑r͒e−i␦but , with of the Coulomb by A A͑r͒ = Two  Dirac  cones  a hklovskii, 2007͒ and, ab ͵ for cone 2 ab·K with A replaced Hod = d2r͓⌿† ˆ Castro Neto et al.: The ជelectronic properties of graphene 1 ជ ˆ *, where ͑Fogler, ␦ re  not  coupled  by  disorder   ͑r͒␴ · A͑r͒⌿1͑ in graphene 007͒. In fact, transport −i␦ab·K experimentsជ pretation = ͚ ␦t͑ab͒͑r͒e A͑r͒ of , A͑r͒aa·K x͑r͒ + iAy͑r͒. ជ=A ͑147͒ ជ ␦ ␾ San- ͚ ͑aa͒ −i␦ mura et al., ofabgraphene= et ␦t In͑r͒e of .the Dirac Hamilton s properties 2007; ͑r͒ nic͑Chen, Jang, Fuhrer, terms ជ 135 ures in the transport that where A = ͑Ax , Ay͒. This result sh 2008͒. ជ ␦aa impurities. Screening ef- Eq. ͑146͒ as oneA͑r͒ = A ͑r͒͑aa͒the −i␦ hopping amplitude lead to ͑149͒ that changes iA ͑r͒. ·K the a ␾͑r͒ = ͚ ␦t case, ͵ nd range of Note that y aa .+ ͑r͒ewhereas ␾͑r͒ = ␾*͑r͒, because of th the Coulomb ជ orbitals. In this ͑Fogler, and scalar = potentials␴ ͑148͒ D x ial in graphene Hod ⌽ d2r͓⌿†͑r͒ in A͑r͒⌿ symmetry of the two triangular sublattices in ជ ␦are modi- Hamiltonian ͑18͒, we 1 potential ˆ the ˆ · ជ th 7; terms of In Shklovskii,the Dirac presence of a vector can rewrite ferent sites aa 2007͒ and, original as of honeycomb *lattice, A is complex becauseB the Eq. ͑146͒Hamiltonian terpretation transport ␾ ͑r͒, because of the inversion ជ Note that whereas ␾͑r͒ = that an effective magnetic field inversion symmetry for nearest-neighbor ͵ Nomura et al., the two triangular sublattices that make up symmetry of 2007; San- also be present, naively implying Hence, † 2 ˆ ˆ ជ because†of the result ជ ͑r͒⌿ ͑r͒ + ͑Ax , Ay͒. This͑r͔͒, s where A = 2008͒. ͑aa͒ honeycomb lattice, A is the † † A complex ␾͑r͒⌿1 aˆlack of al., Hod = d r͓⌿1͑r͒␴ · symmetry, although͑r͒⌿1 origina 1 ˆ the͑ai aj + bi symmetrythe reversal invariant. This broken t ij inversion j͖͒, one thatbchanges for hopping amplitude lead to the nearest-neighbor hopping. pz orbitals. In Mod. Phys., Vol. 81, No. 1, January–March ͑150͒͑150͒ Hence, Rev. this case, is and real since Eq. 2009 in is th not scalar ⌽ potentials the ͑144͒ different sites are modi- only one of of a Dirac cones. Th presence the vector potential the original Hamiltonian related an effective by time-revers ជ where A = ͑Ax , Ay͒. This result shows that changes infield that to the first magnetic the Rev. Mod. Phys., Vol. 81, No. 1, January–March 2009
  • 7. Sca<ering  mechanisms  in  graphene         •  Suspended  graphene  at  4K  μ  ~200,000    cm2/V    [1]       •  Suspended  graphene  at  300K    μ  ~10,000    cm2/V  s   ü  Out-­‐of-­‐plane  flexural  phonons  limit  [2]     •  Suspended  graphene  in  non-­‐polar  liquid       μ  ~60,000    cm2/V  s     •  Effect  of  liquids  on  the  flexural  phonons   Image  from  Meyer,  J.  C  .   ü  Vacuum   ü  Hexane  C6H14   ü  Toluene  C6H5CH3     1.  Bolo0n,  K.  I.  et  al.  Solid  State  Comm.    2008   2.  Castro,  E.  V.  et  al.  Phys  Rev  Le<.  2010  
  • 8. kk kk kk ponds to theElectron  sca<ering  due  to  flexural  ripples   h is the ponents of in-planeofatomic displacements by a solution the Boltzmann equation and (Ziman 2001) or, equivalently, using the modifies the hopping o a graphene sheet. This curvature Mori formula in which only intra-band matrix elements of the current o account. For the case of a small concentration of either vg g Z one mb scatterers,g0 Ccan check u ij : direct calculations that by ð4:2Þ he same concentrationudependence of resistivity approxima0on   vij 0 Harmonic   as the ach described in §2. T st-neighbour hopping parameters is equivalent to the 2 Fourier  components  of     hq ~  bending  correla0on  func0on   4. Scattering by ripples κ q4 field (Morozov et al. 2006) described by a ‘vector potential 1 ðyÞ 1 Zgraphene sheetK g3 Þ; interatomic00K     2 K g3and angles Z ðg ð2g1 K g2 changes V h   at  3 distances Þ; ð4:3Þ ds2and can be described by the following nonlinear term in 2 r and 3 label 2004): (Nelson et al. the nearest neighbours that correspond to pffiffiffi 1 vu vu ffiffiffi vh vh p pffiffiffi K uij Z; 0Þ, ða=2 j3;K a= 3 i C C a=2Þ and ða=2 3; a=2Þ, ð4:1Þ ; respectively 2 vxj vxi vxi vxj nearest-neighbour hopping also lead to an electrostatic fluctuates in a randomly rippled graphene sheet 2007). However, as follows from equations (3.2) and
  • 9. To estimate scattering on such ripples, we note that, in the simpl approximation, the averagersta.royalsocietypublishing.org on February 22, 20 Downloaded from potential energy per individual ben Eq Z kq 4 hjhq j2 i=2sis equal to kdue  to  flexural  phonons   stiffness of Electron   caering   BT/2 (kz1 eV is the bending which yields 200 k BT M. I. Katsnelson and :A. K. Geim 2 Hopping  integrals  γ  are  modified     hjhq j i Z 4 kq 2   Poten0al  perturba0on  due  to  ripples  a    realistic atomicatomic displacement Numerical simulations using  -­‐ where u i are the components of in-plane interaction potential 1   random  sign-­‐changing  this result graphene sheet. This curvature modifi directly confirm ‘magne0c  field’   the case of bending fluctuations wit displacements normal to a for length scale smaller than l Ãz7–10 nm (Fasolino et al. 2007). Th integrals g as conductivity is experimentally 2 3   observed for doping 1 2π à dependence of 2 ( ) that F l E 1, VqV−q ~ h g Z g C vg ≈ kN O F which justifiesq the use of the harmonic approximatio τ then use equation (4.8) for the pair correlationufunction and find h 0 ij : u vij 0 resistivity as 2 The change in 1 2 nearest-neighbour ðk T=kaÞ2parameters is equ h hopping ρappearance ofha gauge field (Morozov etB al. 2006) described by a ‘v ripple ~ ~ q rr z 2 4e n L; τ where the factor L is of the order of unity for k F l à y1 1 1 1. The above equationðyÞ and weakly, a V ðxÞ [ à depends on n for k F l Z ð2g1 K g2 K g3 Þ; V shows ðg2 Ktherma Z that g3 Þ; 2 ripples lead to charge-carrier mobility m practically independen Effect  of  liquids   2 agreement with experiments. Importantly, equation (4.9) also yiel where the C6Hof   magnitudepffiffiffi labelet.  apffiffinearest 2006   ü  Hexane   indices 1, 2 and 3 S.  V.   thePhys.  Rev.  Le   neighbours that same order 14 as observed ffi experimentally. One can Morozov   l,   pffiffiffi ü  Toluene  2C6H5CH3   translational vectors K2 as M.  3.  ;Keffectivend  A3K.  Geim,  Phil.  Trans.  R.  Soc.  A,    2defec ðk B Tq =kaÞ z1012 cm ðKa= Castro,  E.  V.  et.  aa Phys  Rev  Le  (2010)   of static ;008   I atsnelson   .   ;Ka=2Þ and an 0Þ, ða=2 concentration ða=2 3 a=2 l  
  • 10. Molecular  dynamics  with  classical  poten0als   •  Large  system  10,000-­‐50,000  atoms  L  ~10nm   •  Large  0me  scale  ~ns   •  Bond-­‐order  poten0als    for  C-­‐H   •  Boundary  condi0ons   ü  NPT  –  constant  pressure   ü  NVT  –  constant  volume,  corresponding  to  P~0      
  • 11. Strain-­‐free  suspended  graphene   T  =  300  K   h   h2 = 0.89 Å2     vacuum      
  • 12. Suspended  graphene  in  hexane   Hexane  molecules  envelopes  graphene  sheet   C  chain  aligned  parallel  to  the  plane   Mean  square  displacement   h2 = 0.39 Å2     hexane
  • 13. Suspended  graphene  in  toluene   Toluene  molecules  envelopes  graphene  sheet   C  ring  aligned  parallel  to  the  plane   Mean  square  displacement   h2 = 0.42 Å2     toluene
  • 14. Preferred  molecule  posi0on:  DFT  calcula0on   ΔE  =  0.21  eV   ΔE  =  0.37  eV   3  Å   3  Å   Van  der  Waals  interac0on  
  • 15. Ripple  height  analysis   h   h2 = 0.89 Å2     vacuum h2 = 0.42 Å2     toluene h2 = 0.39 Å2     hexane
  • 16. dependence of conductivity is experimentally observed for that k F l à O 1, which justifies the use of the harmonic appro Bending  s0ffness  of  graphene  in  liquid   then use equation (4.8) for the pair correlation function a resistivity as 2 TN h ðk B T=kaÞ2 hq =  κ A0q4 rr z 2 L; 4e n where the factor L is of the order of unity for k F l à y1 and w depends uppresses     k F l à [ 1. The above equation shows that Liquid  s on n for Bending  S)ffness   flexural  phonons   ripples lead to charge-carrier mobility m practically ind agreement with experiments. Importantly, equation (4.9) a same order of magnitude as observed experimentally. O ðk B Tq =kaÞ2exural     12 cmK2 as an effective concentration of stat Out-­‐of-­‐plane  fl z10 phonons  limit  at  room  T   induced at the quench temperature Tq of 300 K. We emphas disorder,μthat is,  cin2/V  s   Born approximation, the above forma ü  Vacuum    ~10,000   m the describe electron scattering by both static (quenched) and assuming  200,000    first, sthey are classical scatterers and, secon ü  Liquid  μ  ~ that, cm2/V     relevant q is smaller than the energy of scattered Dirac ferm 2001). The former condition means that kk 2 a2 / kB Tq and F
  • 17. Conclusion     •  Liquid  dielectric  environment  suppresses  flexural  phonons   •  Phonon  suppression  affects  mobility  through  bending  s0ffness  
  • 18. current for a resistor (blue), capacitor (red), inductor (green) and memristor (purple). The lower figur Четвертый  основной  компонент  электрической  цепи   show the current-voltage characteristics for the four devices, with the characteristic pinched hysteresis loop of the memristor in the bottom right. It is nearly obvious by inspection that the memristor curve cannot be constructed by combining the others. There are also arguments that there are far more than four fundamental electronic circuit elements. In fact, Chua has shown that there are essentially an infinite number of two-terminal circuit elements tha can be defined via various integral and differential equations that relate voltage and current to each oth [L. O. Chua, Nonlinear Circuit Foundations for Nanodevices, Part I: The Four-Element Torus. Proc. IEEE 91, 1830-1859 (2003) – this is an interesting tutorial for the beginner], to which the memcapacit and meminductor belong. It comes down to whether one wants to think of all of these possible circuit elements as being on an equal footing or choose the four lowest order relations to be a fundamental se with a large number of higher order cousins. Similar considerations apply in other fields – do we consider electrons, protons and neutrons fundamental or quarks or what? Who 'Discovered' the Memristor?
  • 19. The  nonlinearity  exists  because  of  coupled   electronic  and  ionic  conducOon,  the  laPer  being   mediated  by  defects,  typically  vacancies  or   intersOOals.     Pd/WO3/W     TiO2  
  • 20. 4 fit experimental RC current, to appe 2 data using 900 K equivalent 0 RON -2 •  R(w(t))=RONw(t)/D+ROFF(1-­‐w(t)/D)     circuit extract -4 -2.0 -1.0 0.0 1.0 geometry voltage, V from fitting perature on I-V OFF state ON state dOUT z dON r perform 3D wOFF 0 coupled TiO2 dC wON electro- ( I I) metallic L channel thermal ( C C) simulations electrode ( E E) D.Strukov et al. MRS (2009) ort required for high retention, even more for half
  • 21. Однополярный   Биполярный  
  • 22. Биполярный  механизм     поверхностного  переключения    
  • 23. The  most  common  type  of  insulators  in  the  sandwich  structures   are  metal  oxides  with  high  concentra0ons  of  oxygen  vacancies,   such  as  NiO,  HfO2,  ZnO,,  Al2O3,  WO3,  and  TiO2    
  • 24.
  • 25.
  • 26. Электронная  плотность       Разложение  по  функциям  Гаусса     q %         ρ r =() N atoms ∑ ( ρn r − Rn ) ( ) $ Q ' # A ( ρn r − Rn = $1− n ' ρ0A r − Rn ) n=1     Перенос  заряда        M gauss −γ m r 2 () 2 ρn r = ηr ∑ cme m=1    ∫ Ωcell ( ) ρn r − Rn d 3r = QA − qn *
  • 27. Полная  энергия         ! $ Etotal = ∫ () () W r #ρ r ρ r d 3r + ∫ W q !ρ q $ ρ q d 3q + Eion−ion # () () Ω % Ω % volume volume    ! $ ! $ ! $ W r #ρ r () % = T #ρ r () % () +Vex #ρ r %        ! $ () () W q #ρ q =V ps q +Vhartree q % () Vps ( q ) = S ( q ) w pseudo ( q )
  • 28. Кинетическая энергия corr corr T = TWang −Teter + TLDA + Tatom     5  % 45 2 5 () TWang−Teter $ρ r ' = # 128 ( ) 3π 2 3 ∫∫ () ( ) ( ) ρ 6 r w1 r − r ' ρ 6 r ' d 3rd 3r '− 21 2 5  1 1  1  − 250 ( ) 3π 2 3 ∫ () () () ρ 3 r d r − ∫ ρ 2 r ∇ ρ 2 r d 3r 3 2 2 Теория линейного отклика 1 (q − 4) 2 5 ⎛ −1 3 2 3 ⎞ 2−q w1 = ⎜ w ( q ) − q + , and w = + ⎟ ln 8 ⎝ 4 5 ⎠ 2 8q 2+q
  • 29. N grid )6 + n  - + corr ! $ () TLDA #ρ r = % ∑ *∑ cnΔρ ri . i=1 + n=1 , 2 + / () 3 corr 6 π % 2 k2 % () Tatom k = ∑ cn $ ' exp $ − $ξ ' # n $ 4ξ ' # ' n=1 n    k %    () S A ki = ∑ $1− α ' exp −ikα iRα $ N ' α ∈A # α ( )
  • 30. λ=1 upper limit von Weizsäcker λ=1/9 gradient expansion second order λ=1/5 computational Hartree-Fock
  • 31. 1. Phase Diagram 2. Elastic Properties 3. Defect Formation Energies