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Quantum Wells, Nanowires, Nanodots, and Nanoparticles PowerPoint Presentation
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Quantum Wells, Nanowires, Nanodots, and Nanoparticles

Quantum Wells, Nanowires, Nanodots, and Nanoparticles

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Quantum Wells, Nanowires, Nanodots, and Nanoparticles

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  1. Quantum Wells, Nanowires, Nanodots, and Nanoparticles Y. Tzeng ECE Auburn University Auburn, Alabama July 2003

  2. Quantum confinement • Trap particles and restrict their motion • Quantum confinement produces new material behavior/phenomena • “Engineer confinement”- control for specific applications • Structures • Quantum dots (0-D) only confined states, and no freely moving ones • Nanowires (1-D) particles travel only along the wire • Quantum wells (2-D) confines particles within a thin layer (Scientific American)


  4. Energy-band profile of a structure containing three quantum wells, showing the confined states in each well. The structure consists of GaAs wells of thickness 11, 8, and 5 nm in Al0.4  Ga0.6  As barrier layers. The gaps in the lines indicating the confined state energies show the locations of nodes of the corresponding wavefunctions. Quantum well heterostructures are key components of many optoelectronic devices, because they can increase the strength of electro-optical interactions by confining the carriers to small regions. They are also used to confine electrons in 2-D conduction sheets where electron scattering by impurities is minimized to achieve high electron mobility and therefore high speed electronic operation.

  5. Confinement Effects


  7. Commercial TiO2 Nanoparticles All TiNano 40 Series products are in the 30-50 nm primary particle size range. Surface treated products exhibit very littlecrystal growth or change of phase when held in an oxidizing atmosphere at 800º C for over 100 hours. Altium™ TiNano 40 Series slurry products are dispersed to primary crystallites in aqueous media and exhibit specific surface areas (BET) of 40-60 m²/g. The slurry product offers the advantage of requiring no dispersion, and also eliminates the handling of fine powders. A spray-dried product is also available that consists of readily dispersable agglomerates of primary particles.

  8. Nanoparticles have been used in our daily life. • Carbon black ( a nanoscale carbon) is used for writing and painting and is added to rubber to make tires more wear resistance. • Nano phosphors in CRTs display colors. • Polishing compounds for smoothing silicon wafers include nanoscale alumina and silica, etc. • Hard disks in our computers contain nanoscale iron oxide magnetic particles. • Nanoscale zinc oxide and titania block UV light for sunscreens. • Nanoscale platinum particles are critical to the operation of catalytic converters. • Metallic nanoparticles make stained glass and Greek vase colorful. • Nanoscale thin films have also been the heart of our silicon chips for our computers, digital cameras, and photonic devices for quite a while.

  9. The Altair Manufacturing Plant:

  10. The Altair Crystal Phase Growth Process

  11. Application Development Activities • Altair has on-going collaboration projects that specifically address commercial applications using our proprietary nanoparticle technology including: • Battery Materials • Thermal Spray • Solid Oxide Fuel Cell and High Temperature Conductive Oxides • Photo-catalytic Activity • Catalysts and Catalyst Support / Surface Modification • Photovoltaics • Pigment Process • Sunscreen Applications • Arsenic Removal from Drinking Water • Air Purification in HVAC Systems

  12. Nanotechnology may help overcome current limitations of gene therapy Hybrid "nanodevice" composed of a "scaffolding" of titanium oxide nanocrystals attached with snippets of DNA may one day be used to target defective genes that play a role in cancer, neurological disease and other conditions. Nanocomposites not only retain the individual physical and biological activity of titanium oxide and of DNA, but, importantly, also possess the unique property of separating when exposed to light or x-rays. Researchers would attach to the titanium oxide scaffolding a strand of DNA that matches a defective gene within a cell and introduce the nanoparticle into the nucleus of the cell, where the DNA would bind with its "evil twin" DNA strand to form a double-helix molecule. The scientists would then expose the nanoparticle to light or x-rays, which would snip off the defective gene.







  19. February 2003The Industrial Physicist Magazine Quantum Dots for Sale                      Nearly 20 years after their discovery, semiconductor quantum dots are emerging as a bona fide industry with a few start-up companies poised to introduce products this year. Initially targeted at biotechnology applications, such as biological reagents and cellular imaging, quantum dots are being eyed by producers for eventual use in light-emitting diodes (LEDs), lasers, and telecommunication devices such as optical amplifiers and waveguides. The strong commercial interest has renewed fundamental research and directed it to achieving better control of quantum dot self-assembly in hopes of one day using these unique materials for quantum computing. Semiconductor quantum dots combine many of the properties of atoms, such as discrete energy spectra, with the capability of being easily embedded in solid-state systems. "Everywhere you see semiconductors used today, you could use semiconducting quantum dots," says Clint Ballinger, chief executive officer of Evident Technologies, a small start-up company based in Troy, New York...

  20. Quantum Dots for SaleThe Industrial Physicist reports that quantum dots are emerging as a bona fide industry. Evident NanocrystalsEvident's nanocrystals can be separated from the solvent to form self-assembled thin films or combined with polymers and cast into films for use in solid-state device applications. Evident's semiconductor nanocrystals can be coupled to secondary molecules including proteins or nucleic acids for biological assays or other applications.

  21. EviArrayCapitalizing on the distinctive properties of EviDots™, we have devised a unique and patented microarray assembly. The EviArray™ is fabricated with nanocrystal tagged oligonucleotide probes that are also attached to a fixed substrate in such a way that the nanocrystals can only fluoresce when the DNA probe couples with the corresponding target genetic sequence.


  23. EviDots - Semiconductor nanocrystalsEviFluors- Biologically functionalized EviDotsEviProbes- Oligonucleotides with EviDotsEviArrays- EviProbe-based assay system Optical Transistor- All optical 1 picosecond performanceTelecommunications- Optical Switching based on EviDotsEnergy and Lighting- Tunable bandgap semiconductor





  28. Properties and Advantages of Silicon Nanoparticles Comparison of Particle Size and Resulting Photoluminescence • High quantum efficiency: 50% to 60%. • Ultrabright: several times greater than that of fluorescein or other biological markers. • Long-lasting: Silicon nanoparticles fluoresce up to 100 times longer than other materials used in biological applications. • Selectable photoluminescence: The wavelength varies according to the size of the particles • Easy to use: Differently sized silicon nanoparticles can be excited with a single laser to obtain various colors. • Easy to manufacture: Large quantities of uniformly sized silicon nanoparticles can be produced by making small modifications to the fabrication process.

  29. Silicon nanoparticles are • incredibly bright, are • highly photostable, and • can be sized to emit varying photoluminescence in response to a single light source. • Their emission brightness exceeds that of fluorescein in the blue wavelength (400 nm). • Biological Applications • Biosensors, • Imaging, • Targeted drug delivery, • Destruction of pathogens • This technology is an ideal alternative to • common dyes, which can be • toxic, • burn out quickly, and are • difficult to use when labeling multiple biological materials.

  30. Silicon Nanoparticles for Optical Applications • Lasers, • Frequency doublers/mixers, • Light amplifiers, • Optical interconnects • Bulk silicon and porous silicon are indirect bandgap materials and poor emitters of light. • Silicon nanoparticles produce stimulated emissions significantly greater than Group III-V sources. • Furthermore, they allow luminescent superlattices and microelectronic architectures to be integrated, combining optical and electronic circuits within silicon.

  31. UIUC’s Electrochemical Process for Producing Silicon Nanoparticles The process for making the silicon nanoparticles uses highly catalyzed electrochemical etching in hydrofluoric acid (HF) and hydrogen peroxide (H2O2) to disperse crystalline silicon into ultrasmall nanoparticles. The wafer is laterally anodized while being advanced slowly into the etchant, producing a large meniscus-like area. Because HF is highly reactive with silicon oxide, H2O2 catalyzes the etching, producing smaller particles. Moreover, the oxidative nature of the peroxides produces high-quality chemical and electronic samples.

  32. The pulverized wafer is then transferred to an • ultrasound bath for a brief treatment, under which • the film crumbles into colloidal suspension of ultrasmall blue particles. • Larger particles are less amenable to dispersion due to stronger interconnections. • A post-HF treatment weakens those particles, and then • an ultrasound treatment disperses the particles. • The mix is centrifuged, and the resulting residue contains the largest red particles, while • the suspension contains the green/yellow particles. • The residue is redissolved and sonicated. • The red-emitting particles stay in suspension, while • the green particles may be separated by additional sonication and/or the addition of a drop of HF. • Commercial gel permeation chromatography may be used to separate the particles further, if necessary, or to obtain additional accuracy in separation of the other particles. • The particles are separated into several vials, each containing particles of uniform size, with near 90% to 100% efficiency.

  33. Quantum dots for detection of low energy single photon • Quantum dots are nano-sized deposits of one semiconductor embedded in another semiconductor that has a larger energy bandgap than that of the core. • Since the dot material has an energy bandgap that is smaller than that of the surrounding material, it can trap charge carriers. • When a photon arrives at the first dot of two electrically connected quantum dots made of gallium arsenide and aluminum gallium arsenide, it excites an electron into the conduction band of the dot. • A strong bias voltage between these two quantum dots transfers this electron to the second quantum dot. • This dot acts as a single-electron transistor, which is switched by the electron to register the photon. • This one-way transfer of single electrons is crucial because it prevents an excited electron returning to its ground state in the first quantum dot before it can be registered.

  34. Activate neurons with quantum dots Put peptide molecules that have very specific protein sequences into semiconductor quantum dots, which then very specifically bind to particular locations on cell surfaces. By using the molecular-recognition capabilities of peptide molecules, scientists have made selective electrical contacts to neurons. The cadmium sulfide contacts act as photodetectors, allowing researchers to communicate with the cells using precise wavelengths of light. In the past, a variety of objects have been attached to cells using biorecognition, such as fluorescent dyes, enzymes and radioactive labels. Relatively large electrode grids have also been implanted into patients to encourage neuron growth over the grid arrays. There was still about a 1-micron gap between the neurons and the electrodes. The quantum dot (Schmidt's) method slims that down to 3 nanometers.

  35. Nanoparticles Well Studied in Isolation…Why Nanoparticle Arrays?A: Device IntegrationA: New Functionality in Ordered Ensembles

  36. Si nanocrystal synthesis and classification by size silicon source rod graphite crucible and silicon melt • Silicon evaporated in an atmosphere of ultra pure Ar, creating an aerosol • Nanocrystals synthesized in a clean environment to avoid oxidation nanocrystal aerosol excess aerosol water cooled Cu electrodes Turbo pump Ar inlet particle trajectories excess flow, Qe • Size classification done with a radial differential mobility analyzer (RDMA) • Before entering RDMA particles are charged • After classification, particles are deposited on a Si substrate or SiO2 film electric field lines aerosol flow, Qa VDMA sheath flow, Qsh sample flow, Qs S.-H. Zhang et al. Aerosol Science and Technology, 23:357-372(1995)

  37. Dp2 10.0 V 24.5 V 54.1 V 111 V 8.0 2.8 nm x 3 x 7 x 4 (0.6 nm) 10.8 nm (1.8 nm) 6.0 8.0 nm 5.2 nm 4.0 (1.6 nm) (1.4 nm) 2.0 0.0 0 2 8 10 12 14 6 4 Nanocrystal Diameter, Dp (nm) Details of size classification Aerosol particles (charge q) ve2 Dp2 > Dp1 ve1 ve2 < ve1 Sheath flow E Dp1 DN/DDp (1010 nm-1 cm-2) R.P. Camata et. al. Appl. Phys. Lett. 68 (22), 27 May 1996

  38. h h D D Caltech Nanoparticle Memory Project • 1 transistor/cell nonvolatile memory with Si nanoparticle floating gate: • thin tunnel oxide • fast • greater reliability Previous work: (Tiwari et al Appl. Phys. Lett. 68 (10), 4 March 1996) Materials: AFM Charging of Si Nanoparticles, and Nanoscale Charge Imaging via Electrostatic Force Microscopy Devices: Improved Performance Nonvolatile Memory

  39. -V Tip charging of Single Si nanocrystals • Scanning tip first brought to rest above particle • Tip lowered toward sample (change set point) • Voltage pulse of • -10- -25V applied • Tip set point returned to precharging value and height changes monitored

  40. Single Particle Discharge 15 minutes 21 minutes 4 minutes 29 minutes 38 minutes

  41. Where is the charge stored? nanocrystals? surface states? defects in oxide? Ec Si/SiO2 interface states? Ef Efm Ev nanoparticle/oxide interface states? • Charging trapping state not known in detail • Transport mechanism not well characterized

  42. Flatband Lineup of Si Nanocrystals in SiO2 Si Substrate Si AFM tip SiO2 Energy Position

  43. Performance of Leff = 0.2 mm Nanoparticle Memory

  44. Industry News about Nanoparticle Memory

  45. Industry estimates forecast thatflash memoryrevenue will hit $13 billion this year, up from $7.7 billion in 2002, according to Jim Handy, a memory services executive with Semico Research. By 2007, flash memory is expected to be a $43 billion industry. Chip giant Intel is experimenting with Ovonics Unified Memory, which uses the same material as DVD discs. Motorola, meanwhile, is looking atsilicon nanocrystals, which replace a solid layer inside the transistor with a lattice of silicon atoms. Nanocrystal chips could hit the market by 2006. Other alternatives being developed include: magnetic RAM (MRAM), which isn't really magnetic; ferroelectric RAM (FeRAM), which involves shifting atoms in a crystal; and polymer memory, which is made from the stuff used in liquid-crystal display screens. By Michael KanellosStaff Writer, CNET News.comMarch 27, 2003, 4:00AM PT

  46. Nanocrystal Shape Control Boosts Efficiency of New Solar Cells Hybrid nanocrystal-polymer solar cell is made by blending CdSe nanocrystals with P3HT, a conducting polymer, to form a 200 nm thick film sandwiched between an aluminum top contact (orange) and a transparent bottom contact (blue). Nanocrystal shape affects the cell efficiency. Monochromatic quantum efficiencies of over 50% are achieved by using rod-like nanocrystals that are partially aligned with the path of current flow in the device.