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Shafqat Ali Muzaffarabad Azad kashmir 03465409202

Shafqat Ali Muzaffarabad Azad kashmir 03465409202

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3 nst-c60-cnt 3 nst-c60-cnt Presentation Transcript

  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Quantum StructuresQuantum Structures
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Mainstream 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
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Mainstream nanoelectronicMainstream nanoelectronicapplicationsapplications Heterojunction bipolar transistors (HBTs)Heterojunction bipolar transistors (HBTs)The first major use of SiGe alloys in amicroelectronics application was in theheterojunction bipolar transistor (HBT) that wasfirst demonstrated by Patton et al. (1988) andentered 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 thebase of the transistor. This reduction of energysignificantly improves the injection efficiency ofelectrons from the emitter into the base as most ofthe reduction of bandgap occurs in the conductionWhere thickness of the Si1−xGex heterolayer in the basehas now been scaled to below 10 nm. Furtherscaling of these devices is likely to further increasethe 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 andVBE = voltage applied across the base emitter interface
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Mainstream nanoelectronic applicationsMainstream nanoelectronic applicationsCOMPLEMENTARY METAL-OXIDE-SEMICONDUCTOR (COMPLEMENTARY METAL-OXIDE-SEMICONDUCTOR (CMOS)CMOS)The largest section of theThe largest section of themicro- and nanoelectronicsmicro- and nanoelectronicsmarket is in the production ofmarket is in the production ofCMOS circuits. For the last 40CMOS circuits. For the last 40years, the gate length onyears, the gate length ontransistors, Ltransistors, Lgg has been scaledhas been scaledto smaller dimensions toto smaller dimensions toimprove the on-current of theimprove the on-current of thetransistor, Itransistor, Ionon for a given gatefor a given gatewidth W aswidth W asHere, μ is the mobility of the carriers in thechannel, Vg is the gate voltage applied tothe transistor and current flows or thetransistor is switched on when Vg is abovethe threshold voltage, VTTransistor gate lengths were 35 nm in production in 2008Transistor gate lengths were 35 nm in production in 2008
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Mainstream nanoelectronic applicationsMainstream nanoelectronic applicationsResonant Tunnelling Diodes (RTDs)Resonant Tunnelling Diodes (RTDs)• Resonant tunnelling diodes (RTDs) are a true quantum nanoelectronic device and operate usingquantum-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 isaligned to a subband state in the quantum well.• Therefore, electrons can only tunnel from source to drain when the source contact is resonant with asubband state in the central quantum well.Transmission electron micrograph of the 2-nmSi0.4Ge0.6 barriers and a 3-nm Si quantum well in aSi/SiGe RTD. 10-nm Si cladding layers are usedeither side of the RTD structure to improve thebarrier height.10 nm10 nm3 nm2 nm2 nmRTDs are very common in the III–V material systems suchas GaAs/AlGaAs RTDs but as the diodes are only twoterminal, most useful nanoelectronic circuit designsrequire the RTDs to be integrated with transistors to formtunnelling static random access memories (TSRAMs) orlogic circuits.
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Mainstream nanoelectronic applicationsMainstream nanoelectronic applicationsSiGe quantum cascade emittersSiGe quantum cascade emittersThe terahertz (THz) region of the electromagnetic spectrumpotentially has a large number of applications including medicaland security imaging, pollution monitoring, proteomics andbioweapons detection.The major limitation to the mainstream use of the technologyhas been the lack of cheap and practical THz sources. Mostapplication demonstrations to date have used photoconductiveantenna with pulsed femtosecond lasers but such systems arestill far too expensive for many of the markets THz has thepotential 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 sourcesbut to date these still typically operate with tens of mW powerbelow 100K (Williams et al. 2005).Higher-temperature operation has recently been demonstratedby the use of a double metal-reflector technology, but at thecost of reduced power.
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Mainstream nanoelectronic applicationsMainstream nanoelectronic applications 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
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013BUCKY BALLBUCKY BALLBuckminsterfullereneBuckminsterfullereneThe term Buckminsterfullerene was inspired by the geodesic dome structure designedby Buckminster Fuller, which was the center piece of the Expo ‘67 exhibition inMontreal, Canada
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013BUCKYBALLBUCKYBALLFig. The structures of the three known forms ofcrystalline carbon:(a) hexagonal structure of graphite,(b) Modified face-centered cubic (fcc) structure(two interpenetrating fcc lattices displaced by aquarter of the cube diagonal) of diamond (eachatom is bonded to four others that form thecorners of a tetrahedron), and(c) the structures of the two most commonfullerenes: a soccer ball C60 and a rugby ballC70 molecules
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013BUCKYBALLBUCKYBALLThe C60 molecule has been named fullerene after the architect andinventor R. Buckminister Fuller, who designed the geodesicdome that resembles the structure of C60.Originally the molecule was called buckminsterjiullerene, but thisname 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 amolecular ball. In fact a soccer ball has the same geometricconfiguration as fullerene.These ball-like molecules bind with each other in the solid state toform a crystal lattice having a face centered cubic structure. In thelattice each C60 molecule is separated from its nearest neighbor by1 nm (the distance between their centers is 1 nm), and they areheld together by weak forces called van der Waals forces.Because C60 is soluble in benzene, single crystals of it can begrown by slow evaporation from benzene solutions.
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013BUCKYBALLBUCKYBALLTh 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 hexagonsAn icosahedron contains 12 vertices, 20 faces, and 30 edges. In this structure the vertices have a five foldsymmetry axis. A truncated icosahedron contains 12 pentagonal faces, 20 hexagonal faces, 60 vertices, and 90edges.The pentagons are arranged so that no two are adjacent to one another. Each carbon atom lies at the vertex ofone pentagon and two hexagons. Th e C60 molecule has a ground-state geometry that corresponds to theIcosahedra point group Ih. A carbon atom occupies each vertex in C60, and each carbon is three-connected toother carbon atoms by one double bond and two single bonds. Carbon atoms with this kind of connectivity arecalled “sp carbons” because the orbitals used to sigma-bond the three adjacent carbons are hybrids of the 2sorbital and the two 2p orbitals (2p and 2p). Th e remaining 2p orbital (2p) is responsible for the π-bond. Eachcarbon atom is bonded to 3 other carbon atoms to form sp2 hybridization, and consequently the C60 molecule issurrounded by π electron clouds. Examination of the illustration of a C60 molecule reveals that it resembles asoccer ball, resulting in it commonly being referred to as a buckyball.
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Alkali-Doped CAlkali-Doped C6060In the face-centered cubic fullerene structure of C60 has 26% of thevolume of the unit cell is empty, so alkali atoms can easily fit intothe 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 theseempty spaces to form the compound K3C6O.The C60 crystal is an insulator, but when doped with an alkaliatom it becomes electrically conducting.Figure shows the location of the alkali atoms in the lattice wherethey occupy the two vacant tetrahedral sites and a largeroctahedral site per C60 molecule. In the tetrahedral site the alkaliatom has four surrounding C60 balls, and in the octahedral sitethere are six surrounding C60 molecules. When C60 is doped withpotassium to form K3C60, the potassium atoms become ionized toform K+and their electrons become associated with the C60, whichbecomes a C603-triply negative ion. Thus each C60, has three extraelectrons that are loosely bonded to the C60, and can movethrough the lattice making C60 electrically conducting. In this casethe C60 is said to he electron-doped.
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Larger and Smaller FullerenesLarger and Smaller FullerenesLarger fullerenes such as C70, C76, C 80, and C84 have also beenfound.A C20 dodecahedral carbon molecule has been synthesized bygas-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 latticeconsists of C20 molecules bonded together by an intermediatecarbon atom.One interesting aspect of the existence of these smaller fullerenesis the prediction that they could be superconductors at hightemperatures when appropriately doped.Because K3C60 show superconductivity at 18K.Cs2RbC60, show superconductivity at 33K.
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Carbon NanotubesCarbon NanotubesFigure Illustra tion of some possible structures ofcarbon nanotubes, depending on how graphitesheets are rolled: (a) armchair structure; (b) zigzagstructure; (c) chiral structure.Sketches of three different SWNT structures that areexamples of (a) a zig-zag-type nanotube, (b) an armchair-type nanotube, (c) a helical nanotube
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Carbon NanotubesCarbon NanotubesTransmission electron microscopy image showingrhodium nanoparticles supported on the surface of anMWNT
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Carbon Nanotube depending on how the graphene sheet rolls determines the type of nanotube.Carbon NanotubesCarbon Nanotubes
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Figure: Structural relation between a graphene sheet and a nanotube. Thevectors 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). Bylimiting the chiral angle θ between 0º and 30º, every value of Ch defines aunique nanotube.Carbon NanotubesCarbon Nanotubes
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013The honeycomb lattice of graphene. The hexagonal unit cell contains two carbon atoms (A and B). Thechiral vector determining the structure of a carbon nanotube is given by L, and its length gives thecircumference. The chiral angle is denoted by η, with η = 0 corresponding to zigzag nanotubes andη = π/6 to armchair nanotubes.Carbon NanotubesCarbon Nanotubes
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Diagram 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 aremetallic have indices shown in red. All other tubes are semiconducting.Carbon NanotubesCarbon Nanotubes
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Synthesis 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
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Synthesis of Carbon NanotubesSynthesis of Carbon Nanotubes• Growth mechanism
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Synthesis of CarbonSynthesis of Carbon Buckyballs (C60)Buckyballs (C60)• ARC DISCKratschmer et al. (1990a) reported on a novel method for the production of C60 in much larger quantities bycreating an electric arc between two graphite rods placed in a helium atmosphere macroscopic amounts of carbonsoot consisting of crystallized buckyballs (i.e., solid state C60)
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Synthesis of Carbon NanotubesSynthesis of Carbon Nanotubes• Laser ablation
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Synthesis of Carbon NanotubesSynthesis of Carbon NanotubesUltra fast Pulses from a free electron laser (FEL) methodSchematic drawings of the ultra fast-pulsed laser ablation apparatus.
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Synthesis of Carbon NanotubesSynthesis of Carbon NanotubesChemical vapour deposition (CVD)
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Synthesis of Carbon NanotubesSynthesis of Carbon NanotubesChemical vapour deposition (CVD)
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Synthesis of Carbon NanotubesSynthesis of Carbon NanotubesChemical vapour deposition (CVD)375.04Mass Flow Meter(Gas Flow Meter)SCCMPirani GaugeThermocoupleVacuum PumpFlang Quartz TubeBubbler2-Phase Furnace ControllerHeating ZoneAnalytical GradeAr Gass CylenderValveValve
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013Synthesis of Carbon NanotubesSynthesis of Carbon Nanotubes
  • Prof. Dr. Abdul MajidDepartment of Physics, University of Azad Jammu and Kashmir, Muzaffarabad-13100, PakistanWednesday, May 15, 2013The honeycomb lattice of graphene. The hexagonal unit cell contains two carbon atoms (A and B). Thechiral vector determining the structure of a carbon nanotube is given by L, and its length gives thecircumference. The chiral angle is denoted by η, with η = 0 corresponding to zigzag nanotubes andη = π/6 to armchair nanotubes.Carbon NanotubesCarbon Nanotubes