Transcript Nanotechnology projects & applications Lecture 5 郭修伯 Frontiers of nanotechnology from Asia-Pacific Nanotech Forum (Tsukuba, 2002)

Nanotechnology projects &
applications
Lecture 5
郭修伯
Frontiers of nanotechnology from
Asia-Pacific Nanotech Forum
(Tsukuba, 2002)
The vision and strategy of the US
national nanotechnology initiative
M.C. Roco
US national science foundation
History
• 1981
– able to measure the size of an atom cluster on a
surface (IBM, Zurich)
• 1991
– able to move atoms on surface (IBM, Almaden)
• 2002
– able to assemble the molecules by physically
positioning the component atoms
Nanotechnology
• National Nanotechnology Initiative (NNI)
– Long-term visionary program since 01/2000
– 22 departments and independent agencies
– 961 million (2004)
• Government investments worldwide ~ 4
billion
– international collaborations and competitions
NNI nanotechnology
• Definition
– Nanotechnology is working - measuring,
manipulating and controlling - at the atomic,
molecular and supramolecular levels, at a
length scale of approximately 1 - 100 nm, in
order to understand and create materials,
devices, and systems with fundamentally new
properties and functions because of their small
structures.
table 4.1
Commercialization
• 1st generation (commercialized)
– passive nanostructure
• applied in coatings, nanoparticles, bulk materials
(nanostructured metals, polymers and ceramics)
– towards systematic design method
• 2nd generation
– active nanostructure
• transistors, amplifier,targeted drugs and chemicals,
and adaptive structures (~2005)
Commercialization
• 3rd generation
– systems of nanosystems
• 3D features, heterogeneous nanocomponents
• specific assembly techniques (such as bio-assembly,
networking at the nanoscale, new architectures)
• ~2010
• 4th generation
– molecular nanosystems
• nanodevices, biomimetics and new molecular
designs (~2020)
Nanotechnology for the next
generation
T.Nakahara & T. Imai
Sumitomo Electric Industries Ltd.
Policies
• Similar projects from
– Nanocarbon materials
– nanoelectronics
– nanobiomaterials
• Others?
– Diamond nanoemitter project
Targets
• Size!
Small size effect
• Compressed ferrous alloy powder
– due to resonance:
• high electromagnetic wave adsorption in the
microwave frequency region
– adjust particle shape and metal composition:
• different absorption peak from 0.5 ~ 5G Hz
– For small and precise communication
• mobilephones, PC, etc.
Nano size effect
• Nanomaterial: diamond
– rigid atomic structure
• high hardness, high thermal conductivity and high
acoustic velocity
– semiconductor properties
• apply as semiconductor devices, optical devices,
electron emission devices
– fabrication and synthesis technology
• manufactured very precisely in a controlled manner
Applications
• Triode vacuum tube (~2000°C) VS. micro vacuum
triode (~30°C)
Vacuum Microelectronic Device
(VMD)
Next generation applications for
polymeric nanofibres
T.C. Lim and S.Ramakrishna
National University of Singapore
Polymeric fibres
• Targets
– high tensile modulus and tensile strength
– UV resistance, electrical conductivity,
biodegradability
– typical: 1-100 m in diameter
• Nanofibres
– decrease in pore size, a drop in structural
defects, enhanced physical behaviour
Nanofibres applications
– Polymer composite reinforcement
• the moduli and fracture resistance improvement in
epoxy resin (300 nm PBI fibres)
– Electrical conductors
• electrochemical rxn rate  electrode’s surface area
• conductive nanofibrous membrane for electrostatic
dissipation, corrosion protection, electromagnetic
interface shielding…
– Sensors
• huge surface area increases the sensitivity
Biomedical applications
• Medical prostheses
– reduce stiffness mismatch / prevent fracture
• a gradient fibrous structure at the tissue/device
interface
• Tissue engineering scaffolds
– biocompatible with the native tissue structure
– design 3D scaffold of synthetic biodegradable
matrices that provide temporary templates for
cell seeding, invasion, proliferation and
differentiation
Biomedical applications
• Drug delivery
– polymeric nanofibres (drug + carrier)
• increase dissolution rate
• increase surface area
• Wound dressing
– biodegradable polymeric fibres spray
• aids the formation of normal skin growth
• prevent the formation of scar tissue
• non-woven nanofibrous membranes with pore
(500~1000 nm)
Filtration applications
• Filter media
– Nano-fabrication of nano filter media
• higher filter efficiency at equal pressure drop
– NonWoven Technologies Inc. of Georgia
• thin-plate die technology for submicron fibres
– Electrospinning process
Filtration applications
• Protective clothing
– lightweight, breathable fabric, permeable to air
and water vapour, insoluble in solvents and
highly reactive with nerve gases and other
chemical agents
– military?
• electrospun nanofibres prevent lower impedance to
moisture vapour diffusion and maximum efficiency
in trapping aerosol particles as compared to
conventional textiles
Application of nanomaterials
G.Z. Cao
University of Washington, Seattle
Nanomaterial application based on
– peculiar physical properties
• gold nanoparticles used as inorganic dye to
introduce colors into glass and as low temp. catalyst
– huge surface area
• mesoporous titania for photoelectrochemical cells
and nanoparticles for sensors
– small size
• offer extra possibilities for manipulation and room
for accommodation multiple functionalities
Catalysis by gold nanoparticles
• Catalyst
– Clean gold nanoparticles are extremely active
in the oxidation of CO if deposited on partly
reactive oxides (e.g. MnO2).
– Extraordinary high activity for partial oxidation
of hydrocarbons, hydrogeneration of
unsaturated hydrocarbons, and Nox.
– The 6s2 and 5d electrons helps!
Gold catalysts
• Essential requirements:
– small particle size (< 4 nm)
– use of “reactive” support
– particles in intimate contact with the support
• carefully designed chemical functionality of
the ligand shell (not the potential catalytic
activity of a nanostructured clean metal
surface)
Band gap engineered quantum
device
• Band gap engineering
– synthetic tailoring of band gaps with the intent
to create unusual electronic transport and
optical effects
– most of the devices based on semiconductor
nanostructures are band gap engineered
quantum devices
Quantum well device
• Quantum well lasers
– III-V semiconductors
• GaAs or GaAsP
– lower threshold current
– lower spectra width
– single or multiple quantum wells
• allow the possibility of independently varying
barriers and cladding layer compositions and widths
• higher threshold carrier and current densities for
single quantum well lasers
Quantum well device
• Light emitting diodes (LED)
– Based on nanostructures of wide-band gap
– quantum well heterostructure configuration
– II-VI semiconductor materials
• ZnSe or ZnTe
– direct energy band gap to achieve high internal
radiative efficiency
Quantum dot device
• The key parameter that controls the
wavelength is the “dot size”
– large sized dots emit at longer wavelength
• quantum dot heterostructures synthesis
– molecular beam epitaxy (取向附生) at the
initial stages of strained heteroepitaxial growth
via the laser-island or Stranski-Krastanov
growth model
Quantum dot device
• Quantum dot lasers
– ultralow-threshold current densities
– low sensitivity to temperature variations
• Quantum dot detectors
– not sensitive to normal-incident light
Nanomechanics
• Cantilevers (懸臂樑)
– a nanomechanical sensor device for detecting
chemical interactions between binding partners
on the cantilever surface and in its environment
– detection modes
• static, dynamic, heat
– AFM applications
Photoelectrochemical cells
• Also “photovoltaic cells” or “solar cells”
• device
– need for higher conversion efficiency of solar
energy to electrical power
– silicon-based p-n junction materials or other
heterojunction materials
– InGaP/GaAs (~20% efficiency)
– difficulties: high cost of production, expensive
equipment, necessary clean-room facilities
Other photoelectrochemical cells
• O’Regan and Grätzel, 1991
– dye-sensitized solar cell
– low product cost device with >10% efficiency
– Sol-gel-derived titania films with a crystal
structure of anatase and mesoporous structure
– porous nanocrystalline TiO2 film + efficient
light-absorbing dye
dye-sensitized solar cell
• Mechanism
– TiO2 functions as a electron-capturing and
electron-transporting material
– the dye adsorbed to TiO2 is exposed to a light
source, absorbs photons upon exposure, and
injects electrons into the conduction band of the
TiO2 electrode
• Nanostructure
– large surface area
TiO2 film
• Methods
–
–
–
–
Chemical vapor deposition
Gas-phase hydrothermal crystallization
Powder compression
Sol-Gel (coating?)
• efficiency
– ~ <10%