M.L.Terranova Dip. di Scienze e Tecnologie Chimiche Interdisc. MIcro- and NAno-Structured Systems...
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Transcript of M.L.Terranova Dip. di Scienze e Tecnologie Chimiche Interdisc. MIcro- and NAno-Structured Systems...
M.L.Terranova
Dip. di Scienze e Tecnologie Chimiche Interdisc. MIcro- and NAno-Structured Systems – MINASlab Universita’ di Roma “TOR VERGATA”
PREPARAZIONI, PROPRIETA’, APPLICAZIONI di SISTEMI a BASE di NANOTUBI di CARBONIO
A SINGLE GRAPHITE SHEET: GRAPHENE
An example of mono-dimensional system
TWO DIFFERENT CLASSES
S. Iijima Nature 354: 56 (1991)
Dext.= 20÷200 ÅDint. = 10÷100 Å
Multi-wall (MWNTs)Multi-wall (MWNTs)
Single-wall (SWNTs)Single-wall (SWNTs)
D = 10÷20 Å
S. Iijima, T. Ichihashi Nature, 363: 603 (1993)
PROPERTIES
• ELECTRONIC• MECHANICAL• CHEMICAL• THERMAL
OPTICAL
MAGNETIC
SPINTRONICS
High chemical stability (inertness against oxidation..)
Structural integrity after intercalation and de-
intercalation
High performances of gas storage
Feasibility to attach foreign species or chemical groups
Thermal stability (up to 2000 C under vacuum)
Low density (1.33-1.40 g/cm3) (1/6 the weight of steel)
Mechanical Resistance (Young modulus ~1.8 TPa)
Breaking strength : 13-50 GPa (a strain of 6%)
Volume compressibility : 2 x 10 –3 1/kbar
Reversible deformation modes (bending, axial
compression, torsion)
The highest thermal conductivity (2000-6000 W/m·K)
Metallic or semiconducting behaviour
Electrical conductivity (1 GA/cm2 )
High efficiency of Field Emission (FE)
continues………..
ELECTRONIC STRUCTURE of GRAPHITE
In 3D graphite the inter-planar interactions are weak with respect to the in-plane C-C interactions
The electronic structure of 2D graphite is similar (in first approximation) to that of 3D graphite
The e * bands of graphene “touch” in 6 points (at the corners of hexagonal Brillouin zone ) and equal the Fermi energy for onespecial wavevector
K- POINT
HOW TO ROLL GRAPHENE
Indexing scheme
Chiral vector : O-A = Ch= na1+ma2
A set of 1D energy states, corresponing to sections of the band structure of 2D graphite .
kc·Ch=2j
Confinement of electrons along the tube circumference
SEMICONDUCTOR
ELECTRONIC STRUCTURE of SWNT
Depending on the position of allowed wavevector with respect to k-point
METAL-LIKE
The nanotubes (n,n) and (n,m) with n-m=3i behave as 1D metals : the density of states at the Fermi level has a finite value.
(n,n)(n,m) | n-m=3i
Metal-like Nanotubes (zero-gap)
In metal-like SWNTs the conduction is due to discrete 1-D electronic states (spaced of about 0.4 meV) which extend along the whole tube length
Dependance of the gap on the diameter
Eg~1/R,
0.2 Eg 1.2 eV
(n,m) | n-m3i
T.W. Odom, J.L. Huang, P. Kim e C.M. Lieber, Nature 391 (1998): 62
DOS= 0 at the Fermi level
Semiconducting Nanotubes
The gap decreases with diameter increasing .
SWNTs represent the ideal 1D QUANTUM WIRE
The transport properties are dependent on the geometrical characteristics: HELICITY -DIAMETER
Depending on the structure the nanotubes canhave a metal-like or semiconducting behaviour
The electrons are confined along the circumference and propagate exclusively along the axis of the cylinder . The conduction is ballistic.
KEY POINTS
Use of synthesis techniques for the control of architecture:
Alignment
Chemical state
Orientation
PlacementDensity of bundles
Definition of post-synthesis protocols for control of :
PRODUCTION METHODS
Sublimation or evaporation of carbon targets
LASER ABLATION
ARC DISCHARGE
Decomposition of hydrocarbons , alcools … PYROLYSIS VAPOUR DEPOSITION
ALL THE PROCESSES MUST BE CATALYSED BY USING
TRANSITION METALS
LASER ABLATION Sources: pulsed Nd:YAG lasers ( = 532 nm)
pulsed CO2 lasers ( = 10.6 m)
cw CO2 lasers ( = 10.6 m)
double-pulsed laser systems: 532 nm pulse followed
by a coaxial 1064 nm pulse
Targets : graphite
metal/graphite
T ~ 10 4 K v ~ 10 6 cm s -1
ARC DISCHARGE
Advantages : low-cost process
Disavantages : low yields of SWNTs bad quality of nanotubes
dispersed material (all round the walls)V = 20-25 V I = 50-120 A
graphite
metal/graphite
Targets :
PYROLYSISCarbon sources :
hydrocarbons
Advantages : continuous production at low cost low process temperatures easy to scale-up
Disadvantages : large amounts of amorphous C large amounts of residual catalysts
T = 700-1000 C P = 1 Atm
CHEMICAL VAPOUR DEPOSITION
Activation of reactants in vapour phase by :
# PLASMAS (RF,MW..) ,
# FLAMES
# HOT FILAMENTS
T = 700-1000 C
P < 1 Atm
Carbon sources:
hydrocarbons , acetone, alcools, ferrocene…
BUT ALSO: C powders (graphite, amorphous nanoparticles….)
Production of aligned and oriented bundles Growth onto selected areas Straightforward scaling up Easy collection of the material from substrate
Advantages
Hot Filament CVDHot Filament CVD
Microwave Plasma Enhanced CVDMicrowave Plasma Enhanced CVD Thermal CVDThermal CVD
CVD APPARATUSES at MINASlab
T HE GROWTH
Control of density and orientation
10m10m
Deposition on shaped substrates
Deposition on patterned surfaces
Filling- with metals , oxides, salts, carbides, semiconductors , enzymes…. (wet chemistry, molten materials )- with a gasMixing -to prepare nanocomposites
Purification-to separate catalyst particles-to suppress contamination by other C forms
Opening - to increase the reactivity at the open edges- to make easier filling of nanotubes with gases Chemical functionalization - to solubilize nanotubes - to selective modificate the intrinsic properties
POST-SYNTHESIS TREATMENTS
FUNCTIONALIZATION
At an open endOn sidewalles
The scope :
SOLUBILIZATION in POLAR MEDIALINKING of COMPLEX STRUCTURES MODIFICATION of the PROPERTIES PREPARATION OF NANOCOMPOSITES
CNT-BASED COMPOSITES
Mineral oils
metals
Glasses-ceramics
The techniques:
Polymers
BLENDINGMIXINGELECTROPOLYMERIZATION
The matrices:
Mechanical properties
Charge transport
Energy storage
Optical properties
flexible layers
fibers
pastes
films
» Conducting Polymers: polythiophene, polyaniline, polypirrole,…
» Thermoplastic Polymers: polystyrene, polyamides, …
» Thermally Conductive Polymers: silicones, epoxy resins … » Liquid crystals thermotropic, lyotropic polymer …
» Conducting Polymers: polythiophene, polyaniline, polypirrole,…
» Thermoplastic Polymers: polystyrene, polyamides, …
» Thermally Conductive Polymers: silicones, epoxy resins … » Liquid crystals thermotropic, lyotropic polymer …
POLYMER-BASED NANOCOMPOSITES
A critical issue in nanocomposites: A critical issue in nanocomposites: control of distribution A critical issue in nanocomposites: A critical issue in nanocomposites: control of distribution
POLYMER-ENWRAPPED NANOTUBES
CONTROL of DISTRIBUTION
CONDUCTING NETWORKS
The homogeneity and uniformity of the nanotube dispersion inside the matrices can be checked using the microscopy techniques AFM and AFAM (Atomic Force Acousitc Microscopy).
.
AFAM map AFAM map
AFMAFMAFAMAFAM
FILLER-MATRIX DISPERSIONS
The maps enable to evaluate the quality of the nanotube dispersion inside the host
matrix
HOW TO CHARACTERIZE THE NANOTUBES
MORPHOLOGY -Scanning Electron Microscopy (SEM)-Transmission Electron Microscopy (TEM)-Scanning Tunnelling Microscopy (STM)-Atomic Force Microscopy (AFM)
STRUCTURE -Nanodiffraction Techniques :
*Reflection High Energy Electron Diffr. (RHEED) *X-Ray Diffraction (XRD) -Raman Spectroscopy
NANOTUBES in ACTION
CHARGE TRANSPORT in CNT SYSTEMS
But the properies of nanotube systems depends on their aggregation . Membranes Pressed tablets Ribbons/wires Oriented arrays
EXHIBIT DIFFERENT ELECTRICAL BEHAVIOUR
-Low electrical resistance : in a 1D system the electrons travelling only forward or backward have few possibilities to scatter-Energy dissipated is very small-Carried currents per given cross-sectional areas larger with respect to common metals (Cu, Al..) -No electromigration of atoms (covalent bonds vs. metal bonds)
CNT ribbons CNT ribbons
CNT aligned by electrical fields (multifinger device) CNT aligned by electrical fields (multifinger device)
0 1 2 3 4 5 6-1
0
1
2
3
4
5
6
7 2mm 3mm 5mm
Cur
rent
(mA
)
Voltage (V)
CNT coated by NiCNT coated by Ni
MICRO-NANO-WIRES and CIRCUITS
As deposited nanotubes Aligned bundles
(AC field 1MHz)
0 1 2 3 4 5 6-100
0
100
200
300
400
500
600
700 without Electric Field Electric Field at 1MHz, Vpp=20V
Curre
nt (
A)
Voltage (Volt)
The orientation of SWNT bundles strongly improves the conductivity
of the material.
ORGANIZATION & CONDUCTIVITY
An example: bundles aligned between electrodes by dielectroforesys
*Integrated nanocircuits*Inverters*Interconnections*Intramolecular junctions
WORK in PROGRESS
FIELD-EMISSION
Thermoionic emission Field emission
A mechanism for electron emission alternative to thermoionic emission
F.E. is a quantum tunnelling: the electrons pass through a barrier in the presenceof a high E.F. F.E. does not require any heat to extract electronsF.E. advantages: higher efficiency, less scatter, faster turn-on times, building of robust and compact devicesF.E. disadvantages: dependence on the materials properties and on the shape of the cathode
THE Fowler-Nordheim LAW
E
bE
aJ
2/322 exp
• Emitting area A
• Current density J = I/A• Macrosc. electrical fieldc. E• Enhancement Factor
• Work function
L.W.Nordheim Proc.Royal Soc.London A121(1928)626
Density of emitted current
• STRATEGIES to IMPROVE FIELD EMISSION
• Increase of A Organized Arrays • Decrease of Specific materials• Increase of β High form factors
Very high emission current densities : up to 1 A/cm2 at 5 V/m Low values of : turn-on and threshold ( few V/ m )
Energy spread 0.2 eV Long term stability
FIELD EMISSION from SWNT
NANOTUBES
F.E : GEOMETRICAL REQUIREMENTS
The F.E efficiency depends on the structure : SW,MW,open/closed tips…
…but also on density and organization of nanotube arrays
COLD CATHODES for …
• Flat panel displays (FPD)• MEMS systems• Light sources (lamps)• Coherent electron sources • AFM tips• X-rays tubes • Vacuum microelectronics (tube
amplifier)
J Wei et al. Appl. Phys. Lett. 84 (2004) 4869
CNT-BASED LIGHT SOURCES
BUILDING a CNT-BASED DISPLAY
Diode configuration C.A.Spindt et al. J.Appl.Phys.47(1976)5248
In a FED, each pixel has its individual electron source (no electron scanning required ).
1,5 – 3 W!1,5 – 3 W!
CheMin spectrometer 2009 Mars Science LaboratoryCheMin spectrometer 2009 Mars Science Laboratory
COLD CATHODES for X-RAY SOURCES
X-ray emission from a metallic anode bombarded by electronsThe use of a triode-type architecture increases the performances(reduced threshold voltage, improved emission control )
Sarrazin et al Adv. X-Ray Anal. 48 (2005) 194] Sarrazin et al Adv. X-Ray Anal. 48 (2005) 194]
The quick response of CNT-based cold cathodes can be used for 3D X-ray imaging, obtained irradiating the object from different angles , activatingsequentially different e- sources (without moving and precision mechanics)
Transistors are the basic building blocks of integrated circuits.
In the generic CNFET a CNT is placed between two electrodes :a In the generic CNFET a CNT is placed between two electrodes :a separate gate electrode controls the flow of current in the separate gate electrode controls the flow of current in the channel.channel.
CNT-BASED FIELD EFFECT TRANSISTORS
This devices can operate at R.T. with efficiency similar to that of conventional Si transistors, but with extremely riduced dimensions and shorter commutation times .
CNFET
R. Martel et al APL 73 (1998):2447 IBM Research Division
THE FABRICATION of a CNFET
The amount of current flowing through the nanotube channel can The amount of current flowing through the nanotube channel can be varied by a factor of 100,000 by changing the voltage applied be varied by a factor of 100,000 by changing the voltage applied to the gate (VG).to the gate (VG).
Source: Delft University and IBM
The world’s first single-electron transistor : two sharp bends (i.e., large potential barriers) placed in a CNT 20 nm apart to create a “conducting island” that electrons must tunnel in to.
AF
M n
ano
man
ipu
lati
on
SINGLE-ELECTRON CNT TRANSISTOR
Source: Delft University
CNFETs have already been used, at research lab level, to implement basic logic circuits such as the inverter.
Circuit example : CNTFET inverter
1904 ,Sir Flemming discovers the thermoionic effect and develops the first vacuum tube.
1904-1930 Different kinds of vacuum tubes: • Diode • Triode • Tetrode • Pentode
VACUUM TUBES
BUT…..development of high frequency/high power electronic components require compact and efficient valves assembled with material with specific properties : radiation hardness
possibility to operate over a wide range of temperatures
reduced dimensions
After : the “era” of solid state devices
Propagation of electrons in vacuum : with respect to solids Longer mean-free path Lower energy loss
CNT-BASED VACUUM TUBES
Miniaturized efficient and compact devices No heating requiredOperational extension to higher frequencies (THz region )
AMPLIFIERS : Starting from an initial electrical signal,the aim is to obtain
-special gains -shape modifications
Integrated gated F.E. devices based on CNT electron emitters brings together the advantages of vacuum tubes and solid state power transistors Last generation of vacuum tubes competitive with solid-state devices Vacuum tubes represent the amplifier of choice for radar, telecommunications and space-based communications
MW and THz AMPLIFIERS
THz sources for :
radar telecommunications space-based communications security applications
security
communications
medical applications
THz SOURCES for …..
PLANNING a TECHNOLOGY FOR A CNT-TRIODE
-PREPARATION BY LITOGRAPHY of LOCATIONS -DEPOSITION OF THE CATALYST INSIDE THE PATTERNS-IN SITU CVD GROWTH OF ORDERED CNT ARRAYS
Measured output characteristic of the triode
OPTHER- FP7 project
OPTOELECTRONICS TECHNOLOGY
CNT-based transistors can be made ambipolar : the current is conducted by
Electronically controlled light sources
Under appropriate bias conditions electrons and holes can enter the nanotube channel simultaneously from opposite ends.When electron/holes meet, they release energy in form of heat or light
electrons for positive gate voltageholes for negative gate voltage
An array of carbon nanotube An array of carbon nanotube transistors partially suspended from a transistors partially suspended from a silicon dioxide substratesilicon dioxide substrate
UNIPOLAR TRANSPORT CONDITIONSUNIPOLAR TRANSPORT CONDITIONS
Electrons were injected ( gate : -2.1 Electrons were injected ( gate : -2.1 V) from the contacting electrodes into V) from the contacting electrodes into the nanotube and gained enough the nanotube and gained enough energy at the suspended/supported energy at the suspended/supported substrate interface to generate substrate interface to generate tightly-bound electron-hole pairs, tightly-bound electron-hole pairs, which subsequently neutralize each which subsequently neutralize each other and emit lightother and emit light. .
An array of carbon nanotube An array of carbon nanotube transistors partially suspended from a transistors partially suspended from a silicon dioxide substratesilicon dioxide substrate
UNIPOLAR TRANSPORT CONDITIONSUNIPOLAR TRANSPORT CONDITIONS
Electrons were injected ( gate : -2.1 Electrons were injected ( gate : -2.1 V) from the contacting electrodes into V) from the contacting electrodes into the nanotube and gained enough the nanotube and gained enough energy at the suspended/supported energy at the suspended/supported substrate interface to generate substrate interface to generate tightly-bound electron-hole pairs, tightly-bound electron-hole pairs, which subsequently neutralize each which subsequently neutralize each other and emit lightother and emit light. .
EXTRA-BRIGHT BEAMS of IR LIGHT
courtesy of IBM
P.Avouris (IBM) Science
3 A current generated 107 photons /nm2 s
Source: Stony Brook University
The basic idea of CMOL circuits is to combine the advantages of CMOS technology (including its flexibility and high fabrication yield) with theextremely high potential density of molecularscale two-terminal nanodevices.
CMOL Architecture : hybrid CMOS/nanowire/nanodevice
The challenge: precise alignment of nanowires
CMOS : complementary metal oxide semiconductor
Source: Stony Brook University
The density of active devices in CMOL may be up to 10The density of active devices in CMOL may be up to 1012 12
cmcm22 and could provide unparalleled information and could provide unparalleled information processing performance up to 10processing performance up to 102020 operations/cm operations/cm22/s./s.
Terabit scale memoriesTerabit scale memories
Reconfigurable digital circuits with multi tera-flops Reconfigurable digital circuits with multi tera-flops scale performancescale performance
Mixed signal Neuromorphic networks that may Mixed signal Neuromorphic networks that may compete with biological neural systems in area compete with biological neural systems in area density, exceeding their speed at acceptable power density, exceeding their speed at acceptable power dissipationdissipation
time-to-market > 15-20 years!
CMOL : advantages and applications
Non-linear optical properties are evidenced in nanocomposites , suspended–solubilized nanotube systems or in specific nanotube aggregates .
*STRONG LUMINESCENCE (UV-Vis) for SWNTs embedded in varius polymeric matrices
*OPTICAL LIMITING BEHAVIOUR of SWNTs functionalized with selected groups or chains
* HIGH ORDER HARMONIC GENERATION produced by specific solid aggregates
OPTICAL PROPERTIES
2nd armonics
3nd armonics
S.Botti et al. Appl. Phys.Lett (2004)
Pressed SWNT tablets: a Q-switched Nd:Yag laser (1064 nm) laser pulse : 10 Hz, 100-200 mJ (nanosecond time scale)
The generation of 2° and 3°-order harmonics is due to quantum confinement of the electrons and is related to the helicity of the SWNT samples.
Centrosymmetric materials do not generate 2° harmonics .
The generation of 2°hamonics indicate partial anysotropy (chiral CNT or disorientation )
HIGH-ORDER HARMONIC GENERATION
Nanotubes functionalized with selected groups or chains
The fluence optical limiting of pulsed lasers is due to non –linear scattering of the nanotube dispersions
Z.Jin et al, Chem.Phys.Lett 2002
OPTICAL LIMITING BEHAVIOUR
Promising systems for:
-Manipulation of optical beams-Optical switchers -Devices for fast processing of optical signals
MAGNETIC and SPINTRONICS PROPERTIES
The encapsulation of: MAGNETIC & FERROMAGNETIC nanoparticles
For SWNT systems in a magnetic field the changes of electron spin signals depend on the orientation with respect to the field and on the SWNT organization (dispersed/aggregates) .
1-ferromagnetic contacts and coherent transport of spin-electrons througtht nanotubes 2-protection of nanoparticles against oxidation and reduction of dipolar particle-particle interactions
High-density magnetic record mediaNon-volatile magnetic memories Spin- electronic magnetic sensors
TOWARDS CNT-BASED FLEXIBLE ELECTRONICS It is possible to integrate the nanotubes in different matrices :
using polymers different plastic/flexible devices can be produced
ElectrodesTransistorsLight-emitting diodesPlastic solar cells
-ease production
-flexibility
-versatility
-miniaturization
POLYMER/CNTs HYBRID DEVICES
PolyimidPEDOT:PSS
PentacenePEDOT:PSS PVA
How to fabricate a flexible transistor
nanocompositenanocomposite
Patterned electrodePatterned electrode
Polymide Support
PHOTOVOLTAIC CELLS
General scheme of a “DYE SENSITIZED SOLAR CELL” DSSC based on donor-acceptor systems
The interaction of SWNTs with conjugated polymers allows charge separation of the photo-generated excitons in the polymer and efficient electron transport to the electrode through the nanotubes.
Michael Grätzel , Nature 414 (2001) 338
Cathode: PlatinumCathode: Platinum
SWNT/conjugated polymer nanocomposites represent efficient cathodes for the assembling of high performance flexible photovoltaic cells
SWNT-BASED CATHODES for DSSC
Cathode: CNT+polymersCathode: CNT+polymers
The thermal conductivity increases up to 40%The thermal conductivity increases up to 40%
THERMAL MANAGEMENT
Thermal Interface Materials
THEORY (#) : predicts K = 6000 W/mK ( S.Berber Phys.Rev.Lett. 84 (2000) 4613 )EXPERIMENTS : values between 1000 and 3000 W/mK
Die Substrate
Package
Heat Sink: polymeric or epoxy matrices with CNTs
Chip
Resina Epossidica + SWCNTs1%p
Resina Epossidica
Potenza (W)
11
22
33
44
NANOTUBES for INTERCONNECTS
Flip-Chip configuration : charge and heath transport
CNT: multifunctional structural materials which open a series of technological opportunities for micro- and nano-electronics.
These exciting carbon nanomaterials are providing the scientific community with many interesting ideas and potential applications, some of them practical and some simply dreams for the future
But to obtain the expected benefits a lot of research work is still needed !
But to obtain the expected benefits a lot of research work is still needed !
CONCLUSIONS?