Transcript Material Chemistry

無機化學特論(四)
授課老師：林寬鋸 教授
http://web.nchu.edu.tw/pweb/users/kjlin
Advanced Inorganic Chemistry (IV): Material Chemistry
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Overview of Solid State Chemistry (two weeks)
Synthesis methods in solid sate (three weeks)
Electronic conductivity (2 weeks)
Magnetic (2 weeks)
Electronic transfer and energy transfer (2 weeks)
Functional hybrid systems for biosensing (3 weeks)
Home works
• Semiconductor quantum dots (q-dots)
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Submitted q-dots you prefer (2/27)
Energy levels for q-dots (3/6)
Syntheses and characterizations (3/20)
Absorption and emission spectra (3/27, 4/10)
Electrical transport properties (4/17, 4/24)
Single electron tunneling (5/1)
Optical gain and Lasing (5/8)
Application in Bio-imaging (5/15, 5/22,)
Application in solar-cell (5/29)
• Nanopartilces, core-shell colloidal, 1D-wires, 1Darrangements
NANOCHEMISTRY
• Nanochemistry is an active new field that deals with
confinement of chemical reactions on nanometer length
scale to produce chemical products that are of
nanometer dimensions (generally in the range of 1100nm). The challenge is to be able to use chemical
approaches that would reproducibly provide a precise
control of composition, size, and shape of the nanoobjects formed. These nanomaterials exhibit new
electronic, optical, and other physical properties that
depend on their composition, size, and shape.
Nanoscale chemistry also provides an opportunity to
design and fabricate hierarchically built multilayer
nanostructures to incorporate multifunctionality at
nanoscale.
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Nanochemistry offers the following
capabilities:
• Preparation of nanoparticles of a wide range of
metals, semiconductors, glasses, and polymers
• Preparation of multilayer, core-shell-type
nanoparticles
• Nanopatterning of surfaces, surface
functionalization, and self-assembling of
structures on this patterned template
• Organization of nanoparticles into periodic or
aperiodic functional structures
• In situ fabrication of nanoscale probes, sensors,
and devices
Nanotechnology for Biophotonics：
Bionanophotonics
• Nanophotonics is an emerging field that
describes nanoscale optical science and
technology.
• the use of nanoparticles for optical
bioimaging, optical diagnostics, and lightguided and activated therapy
two classes of nanoparticle emitters
• (1) semiconductor nanoparticles, also known as
quantum dots, whose luminescence wavelength
is dependent on the size and the nature of the
semiconductors. These nanoparticle emitters
can be judiciously selected to cover the visible to
the IR spectral range. They can also be surfacefunctionalized to be dispersable in biological
media as well as to be conjugated to various
biomolecules.
• (2) up-converting nanophores comprised of rareearth ions in a crystalline host.
Quantum Dots
Semiconductor Quantum Dots
• Quantum dots (also frequently abbreviated as Qdots) are
nanocrystals of semiconductors that exhibit quantum
confinement effects, once their dimensions get smaller
than a characteristic length, called the Bohr’s radius.
• This Bohr’s radius is a specific property of an individual
semiconductor and can be equated with the electronhole distance in an exciton that might be formed in the
bulk semiconductor.
• For example, it is 2.5nm for CdS. Below this length scale
the band gap (the gap between the electron occupied
energy level, similar to HOMO, and the empty level,
similar to LUMO) is size-dependent
Qdots
When the particle size decreases below the Bohr’s
radius, the absorption and the emission wavelengths of
the nanoparticles shift to a shorter wavelength (toward
UV).
• The quantum dots, therefore, offer themselves as
fluorophores where the emission wavelength can be
tuned by selecting appropriate-size nanocrystals.
• By appropriate selection of the materials and the size of
their nanocrystals, a wide spectral range of emission can
be covered for biolimaging.
• Also, a significantly broad range of emission covered by
many sizes of nanocrystals of a given material can be
excited at the same wavelength. The typical line widths
are20-30nm, thus relatively narrow, which helps if one
wants to use the quantum dots more effectively for
multispectral imaging.
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Qdots
• Compared to organic fluorophores, the major
advantages offered by quantum dots for bioimaging are:
1. Quantum dot emissions are considerably narrower
compared to organic fluorophores, which exhibit broad
emissions. Thus, the complication in simultaneous
quantitative multichannel detection posed by cross-talks
between different detection channels, derived from
spectral overlap, is significantly reduced.
2. The lifetime of emission is longer (hundreds of
nanoseconds) compared to that of organic fluorophores,
thus allowing one to utilize time-gated detection to
suppress autofluorescence, which has a considerably
shorter lifetime.
3. The quantum dots do not readily photobleach.
4. They are not subject to microbial attack.
• A major problem in the use of quantum
dots for bioimaging is the reduced
emission efficiency due to the high surface
area of the nanocrystal. enhance the
emission efficiency of the core quantum
dot.
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CdSe
B
PbSe
J. Phys. Chem. B, Vol. 106, No. 41, 2002
Partuicles size：3.5 nm
J. Am. Chem. Soc., Vol. 115. No. 19. 1993