3 nst-c60-cnt

Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, Pakistan

Thursday, April 13, 2023

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 Emitters SiGe Quantum Cascade Emitters

Quantum Dots, Quantum Wire, Quantum WellQuantum Dots, Quantum Wire, Quantum Well BUCKY BALL – BuckminsterfullereneBUCKY BALL – Buckminsterfullerene



Mainstream nanoelectronic Mainstream 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 applicationsCOMPLEMENTARY METAL-OXIDE-SEMICONDUCTOR (COMPLEMENTARY METAL-OXIDE-SEMICONDUCTOR (CMOS)CMOS)

The largest section of the The largest section of the micro- and nanoelectronics micro- and nanoelectronics market is in the production of market is in the production of CMOS circuits. For the last 40 CMOS circuits. For the last 40 years, the gate length on years, the gate length on transistors, Ltransistors, Lgg has been scaled has been scaled

to smaller dimensions to to smaller dimensions to improve the on-current of the improve the on-current of the transistor, Itransistor, Ionon for a given gate for 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



Mainstream nanoelectronic applicationsMainstream nanoelectronic applicationsResonant 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.



Mainstream nanoelectronic applicationsMainstream nanoelectronic applicationsSiGe 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.



Mainstream nanoelectronic applicationsMainstream nanoelectronic applications

Heterojunction bipolar transistors (HBTs)Heterojunction bipolar transistors (HBTs) 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 – BUCKY BALL – BuckminsterfullereneBuckminsterfullerene



BUCKY BALLBUCKY BALLBuckminsterfullereneBuckminsterfullerene

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



BUCKYBALLBUCKYBALLThe 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 C6060In 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 evacuatedtubes 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 showingrhodium 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 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



Synthesis of Carbon NanotubesSynthesis of Carbon Nanotubes• Growth mechanism



Synthesis of Carbon Synthesis 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)



Synthesis of Carbon NanotubesSynthesis of Carbon Nanotubes• Laser ablation



Synthesis of Carbon NanotubesSynthesis of Carbon NanotubesUltra fast Pulses from a free electron laser (FEL) method

Schematic drawings of the ultra fast-pulsed laser ablation apparatus.



Synthesis of Carbon NanotubesSynthesis of Carbon NanotubesChemical vapour deposition (CVD)



Synthesis of Carbon NanotubesSynthesis of Carbon NanotubesChemical vapour deposition (CVD)

375.04

Mass Flow Meter(Gas Flow Meter)

SCCMPirani Gauge

Thermocouple

Vacuum Pump

Flang Quartz Tube

Bubbler

2-Phase Furnace Controller

Heating Zone

Analytical GradeAr Gass Cylender

Valve

Valve



Synthesis of Carbon NanotubesSynthesis of Carbon Nanotubes



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.


3 nst-c60-cnt

Education

quantum wire

central quantum

nm si quantum

quantum wellquantum

university of azad jammu

useful nanoelectronic

gate voltage

mainstream use