3 nst-c60-cnt

Prof. Dr. Abdul Majid
Department of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, Pakistan
Wednesday, May 15, 2013
Quantum StructuresQuantum Structures

Mainstream Nanoelectronic ApplicationsMainstream Nanoelectronic Applications
 Heterojunction Bipolar Transistors (HBTS)Heterojunction Bipolar Transistors (HBTS)
 Complementary Metal-Oxide-SemiconductorComplementary Metal-Oxide-Semiconductor (CMOS)CMOS)
 Resonant Tunnelling Diodes (RTDS)Resonant Tunnelling Diodes (RTDS)
 SiGe Quantum Cascade EmittersSiGe Quantum Cascade Emitters
 Quantum Dots, Quantum Wire, Quantum WellQuantum Dots, Quantum Wire, Quantum Well
 BUCKY BALL – BuckminsterfullereneBUCKY BALL – Buckminsterfullerene

Mainstream nanoelectronicMainstream nanoelectronic
applicationsapplications
 Heterojunction bipolar transistors (HBTs)Heterojunction bipolar transistors (HBTs)
The first major use of SiGe alloys in a
microelectronics application was in the
heterojunction bipolar transistor (HBT) that was
first demonstrated by Patton et al. (1988) and
entered production in late 1998.
The addition of a small amount of Ge to the base of Si n-
p-n bipolar transistor will reduce the bandgap in the
base of the transistor. This reduction of energy
significantly improves the injection efficiency of
electrons from the emitter into the base as most of
the reduction of bandgap occurs in the conduction
Where thickness of the Si1−xGex heterolayer in the base
has now been scaled to below 10 nm. Further
scaling of these devices is likely to further increase
the performance.
where Dn = diffusion constant for minority electrons in the base,
q = electron charge, niB = intrinsic carrier density in the base,
WB = base width, NA = acceptor doping density in the base and
VBE = voltage applied across the base emitter interface

Mainstream nanoelectronic applicationsMainstream nanoelectronic applications
COMPLEMENTARY METAL-OXIDE-SEMICONDUCTOR (COMPLEMENTARY METAL-OXIDE-SEMICONDUCTOR (CMOS)CMOS)
The largest section of theThe largest section of the
micro- and nanoelectronicsmicro- and nanoelectronics
market is in the production ofmarket is in the production of
CMOS circuits. For the last 40CMOS circuits. For the last 40
years, the gate length onyears, the gate length on
transistors, Ltransistors, Lgg has been scaledhas been scaled
to smaller dimensions toto smaller dimensions to
improve the on-current of theimprove the on-current of the
transistor, Itransistor, Ionon for a given gatefor a given gate
width W aswidth W as
Here, μ is the mobility of the carriers in the
channel, Vg is the gate voltage applied to
the transistor and current flows or the
transistor is switched on when Vg is above
the threshold voltage, VT
Transistor gate lengths were 35 nm in production in 2008Transistor gate lengths were 35 nm in production in 2008

Resonant Tunnelling Diodes (RTDs)Resonant Tunnelling Diodes (RTDs)
• Resonant tunnelling diodes (RTDs) are a true quantum nanoelectronic device and operate using
quantum-mechanical tunnelling.
• The device is fabricated using two tunnel barriers with a quantum well sandwiched between the barriers.
Electrons can only tunnel through the whole device when the chemical potential of the source contact is
aligned to a subband state in the quantum well.
• Therefore, electrons can only tunnel from source to drain when the source contact is resonant with a
subband state in the central quantum well.
Transmission electron micrograph of the 2-nm
Si0.4Ge0.6 barriers and a 3-nm Si quantum well in a
Si/SiGe RTD. 10-nm Si cladding layers are used
either side of the RTD structure to improve the
barrier height.
10 nm
10 nm
3 nm
2 nm
2 nm
RTDs are very common in the III–V material systems such
as GaAs/AlGaAs RTDs but as the diodes are only two
terminal, most useful nanoelectronic circuit designs
require the RTDs to be integrated with transistors to form
tunnelling static random access memories (TSRAMs) or
logic circuits.

SiGe quantum cascade emittersSiGe quantum cascade emitters
The terahertz (THz) region of the electromagnetic spectrum
potentially has a large number of applications including medical
and security imaging, pollution monitoring, proteomics and
bioweapons detection.
The major limitation to the mainstream use of the technology
has been the lack of cheap and practical THz sources. Most
application demonstrations to date have used photoconductive
antenna with pulsed femtosecond lasers but such systems are
still far too expensive for many of the markets THz has the
potential to address.
The demonstration of GaAs quantum cascade lasers (QCLs)
operating at terahertz frequencies (Kohler et al. 2002)
potentially opens up much cheaper, high-power THz sources
but to date these still typically operate with tens of mW power
below 100K (Williams et al. 2005).
Higher-temperature operation has recently been demonstrated
by the use of a double metal-reflector technology, but at the
cost of reduced power.

 Heterojunction bipolar transistors (HBTs)Heterojunction bipolar transistors (HBTs)
 CMOSCMOS
 Resonant tunnelling diodes (RTDs)Resonant tunnelling diodes (RTDs)
 SiGe quantum cascade emittersSiGe quantum cascade emitters
 Quantum Dots, Quantum Wire, Quantum WellQuantum Dots, Quantum Wire, Quantum Well
 BUCKY BALL –BUCKY BALL – BuckminsterfullereneBuckminsterfullerene

BUCKY BALLBUCKY BALL
BuckminsterfullereneBuckminsterfullerene
The term Buckminsterfullerene was inspired by the geodesic dome structure designed
by Buckminster Fuller, which was the center piece of the Expo ‘67 exhibition in
Montreal, Canada

BUCKYBALLBUCKYBALL
Fig. The structures of the three known forms of
crystalline carbon:
(a) hexagonal structure of graphite,
(b) Modified face-centered cubic (fcc) structure
(two interpenetrating fcc lattices displaced by a
quarter of the cube diagonal) of diamond (each
atom is bonded to four others that form the
corners of a tetrahedron), and
(c) the structures of the two most common
fullerenes: a soccer ball C60 and a rugby ball
C70 molecules

BUCKYBALLBUCKYBALL
The C60 molecule has been named fullerene after the architect and
inventor R. Buckminister Fuller, who designed the geodesic
dome that resembles the structure of C60.
Originally the molecule was called buckminsterjiullerene, but this
name is a bit unwieldy, so it has been shortened to fullerene.
In Fig. a sketch of the molecule. It has 12 pentagonal (5 sided)
and 20 hexagonal (6sided) faces symmetrically arrayed to form a
molecular ball. In fact a soccer ball has the same geometric
configuration as fullerene.
These ball-like molecules bind with each other in the solid state to
form a crystal lattice having a face centered cubic structure. In the
lattice each C60 molecule is separated from its nearest neighbor by
1 nm (the distance between their centers is 1 nm), and they are
held together by weak forces called van der Waals forces.
Because C60 is soluble in benzene, single crystals of it can be
grown by slow evaporation from benzene solutions.

BUCKYBALLBUCKYBALL
Th e C60 molecule is perhaps best described as a hollow cage with a molecular diameter on the order of 1 nm,
consisting of 60 carbon atoms that are arranged as a truncated icosahedron, * 12 pentagons and 20 hexagons
An icosahedron contains 12 vertices, 20 faces, and 30 edges. In this structure the vertices have a five fold
symmetry axis. A truncated icosahedron contains 12 pentagonal faces, 20 hexagonal faces, 60 vertices, and 90
edges.
The pentagons are arranged so that no two are adjacent to one another. Each carbon atom lies at the vertex of
one pentagon and two hexagons. Th e C60 molecule has a ground-state geometry that corresponds to the
Icosahedra point group Ih. A carbon atom occupies each vertex in C60, and each carbon is three-connected to
other carbon atoms by one double bond and two single bonds. Carbon atoms with this kind of connectivity are
called “sp carbons” because the orbitals used to sigma-bond the three adjacent carbons are hybrids of the 2s
orbital and the two 2p orbitals (2p and 2p). Th e remaining 2p orbital (2p) is responsible for the π-bond. Each
carbon atom is bonded to 3 other carbon atoms to form sp2 hybridization, and consequently the C60 molecule is
surrounded by π electron clouds. Examination of the illustration of a C60 molecule reveals that it resembles a
soccer ball, resulting in it commonly being referred to as a buckyball.

Alkali-Doped CAlkali-Doped C6060
In the face-centered cubic fullerene structure of C60 has 26% of the
volume of the unit cell is empty, so alkali atoms can easily fit into
the empty spaces between the molecular balls of the material.
When C60 crystals and potassium metal are placed in evacuated
tubes and heated to 400°C, potassium vapor diffuses into these
empty spaces to form the compound K3C6O.
The C60 crystal is an insulator, but when doped with an alkali
atom it becomes electrically conducting.
Figure shows the location of the alkali atoms in the lattice where
they occupy the two vacant tetrahedral sites and a larger
octahedral site per C60 molecule. In the tetrahedral site the alkali
atom has four surrounding C60 balls, and in the octahedral site
there are six surrounding C60 molecules. When C60 is doped with
potassium to form K3C60, the potassium atoms become ionized to
form K+
and their electrons become associated with the C60, which
becomes a C60
3-
triply negative ion. Thus each C60, has three extra
electrons that are loosely bonded to the C60, and can move
through the lattice making C60 electrically conducting. In this case
the C60 is said to he electron-doped.

Larger and Smaller FullerenesLarger and Smaller Fullerenes
Larger fullerenes such as C70, C76, C 80, and C84 have also been
found.
A C20 dodecahedral carbon molecule has been synthesized by
gas-phase dissociation of C20HBr13.
C36H4 has also been made by pulsed laser ablation of graphite.
A solid phase of C22 has been identified in which the lattice
consists of C20 molecules bonded together by an intermediate
carbon atom.
One interesting aspect of the existence of these smaller fullerenes
is the prediction that they could be superconductors at high
temperatures when appropriately doped.
Because K3C60 show superconductivity at 18K.
Cs2RbC60, show superconductivity at 33K.

Carbon NanotubesCarbon Nanotubes
Figure Illustra tion of some possible structures of
carbon nanotubes, depending on how graphite
sheets are rolled: (a) armchair structure; (b) zigzag
structure; (c) chiral structure.
Sketches of three different SWNT structures that are
examples of (a) a zig-zag-type nanotube, (b) an armchair-
type nanotube, (c) a helical nanotube

Transmission electron microscopy image showing
rhodium nanoparticles supported on the surface of an
MWNT

Carbon Nanotube depending on how the graphene sheet rolls determines the type of nanotube.

Figure: Structural relation between a graphene sheet and a nanotube. The
vectors a1, a2 form a basis pair for the graphene lattice.
The chiral vector Ch = n a1 + m a2 is specified by the ordered pair (n, m). By
limiting the chiral angle θ between 0º and 30º, every value of Ch defines a
unique nanotube.

The honeycomb lattice of graphene. The hexagonal unit cell contains two carbon atoms (A and B). The
chiral vector determining the structure of a carbon nanotube is given by L, and its length gives the
circumference. The chiral angle is denoted by η, with η = 0 corresponding to zigzag nanotubes and
η = π/6 to armchair nanotubes.

Diagram explaining the relationship of a SWNT to a graphene sheet. The wrapping vector for an (8,4)
nanotube, which is perpendicular to the tube axis, is shown as an example. Those tubes which are
metallic have indices shown in red. All other tubes are semiconducting.

Synthesis of Carbon NanotubesSynthesis of Carbon Nanotubes
• Growth mechanism
• Arc disc
• Synthesis of SWNT
• Synthesis of MWNT
• Laser ablation
• SWNT versus MWNT
• Large scale synthesis of SWNT
• Ultra fast Pulses from a free electron laser (FEL) method
• Continuous wave laser-powder method
• Chemical vapour deposition
• Plasma enhanced chemical vapour deposition
• Thermal chemical vapour deposition
• Alcohol catalytic chemical vapour deposition
• Vapour phase growth
• Aero gel-supported chemical vapour deposition
• Laser-assisted thermal chemical vapour deposition
• CoMoCat process
• High pressure CO disproportionation process
• Flame synthesis

• Growth mechanism

Synthesis of CarbonSynthesis of Carbon Buckyballs (C60)Buckyballs (C60)
• ARC DISC
Kratschmer et al. (1990a) reported on a novel method for the production of C60 in much larger quantities by
creating an electric arc between two graphite rods placed in a helium atmosphere macroscopic amounts of carbon
soot consisting of crystallized buckyballs (i.e., solid state C60)

• Laser ablation

Ultra fast Pulses from a free electron laser (FEL) method
Schematic drawings of the ultra fast-pulsed laser ablation apparatus.

Chemical vapour deposition (CVD)

Chemical vapour deposition (CVD)
375.04
Mass Flow Meter
(Gas Flow Meter)
SCCM
Pirani Gauge
Thermocouple
Vacuum Pump
Flang Quartz Tube
Bubbler
2-Phase Furnace Controller
Heating Zone
Analytical Grade
Ar Gass Cylender
Valve
Valve

3 nst-c60-cnt

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