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08/11/2010
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Introduction to Nanomaterials, Nanoscience, and Nanotechnology (Cont’)
Dr Montree Sawangphruk (DPhil)
Chemical Engineering, Kasetsart University, Room #1209-5, email:[email protected]
http://pirun.ku.ac.th/~fengmrs/ https://course.ku.ac.th/
Surface Reconfigurations
In a perfect crystal, the equilibrium position of an atom is
determined by minimizing the total energy.
We usually call it surface relaxation when atoms in the
entire surface layer shift either vertically or laterally
relative to the layer underneath, while their relative
position within the surface layer remains unchanged.
On the other hand, if there is a surface structure or
symmetry change in addition to a position shift, we
usually refer to it as a surface reconstruction.
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Surface Relaxation
Relaxations are slight changes in bond lengths and angles.
Surface Reconstructions
Image of surface reconstruction on a clean Au(100) surface
Reconstructions are changes in the periodicity of
the surface or the symmetry.
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Applications of Nanomaterials
Nano is an enabling technology for the future
Nanochips
Nanocapsules
Nanofilms
Handheld computer, watchphone
Electronic transdermal drug delivery patch
Flexible thin screen
Na
no
tech
no
log
y
NOW FUTURE
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Microfluidics
Lab-on-a-chip
Microfluidics
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What are Limits to Smallness?
Particle (Quantum) Nature of Matter: Photons, Electrons, Atoms,
Molecules
Biological Examples of Nanomotors and Nanodevices
How Small can you Make it?
What are the Methods for Making Small Objects?
How Can you See What you Want to Make?
How Can you Connect it to the Outside World?
If you Can’t See it or Connect to it, Can you Make it Self-assemble and
Work on its Own?
Particle (Quantum) Nature of Matters:
Photons, Electrons, and Atoms
No transistor smaller than an atom, about 0.1 nm, is possible.
In practice, of course, there are all sorts of limits on assembling small things to an engineering specification.
At present there is hardly any systematic approach to making arbitrarily designed devices or machines whose parts are much smaller than a millimetre!
A notable exception is the photolithographic technology of the semiconductor electronics industry which make very complex electronic circuits with internal elements on a much smaller scale, down to about 100 nm.
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Photons
The most surprising early recognition of the granularity of
nature was forced by the discovery that light is composed
of particles, called photons, whose precise energy is hʋ.
Here h is Planck‟s constant, 6.6x10–34 J·s, and ʋ is the light
frequency in Hz.
The energy of a particle of light in terms of its
wavelength, λ, is E = h ʋ = hc/ λ.
Biological Examples of Nanomotors and
Nanodevices
Biology provides examples of nanometer scale motors and electrical devices, which can be seen as limits of smallness.
If nature can make these (only recently perceived) nanoscale machines, why, some ask, cannot human technology meet and eventually exceed these results? It is certainly a challenge.
The contraction of muscle occurs through the concerted action of large numbers of muscle myosin molecules, which “walk” along actin filaments in animal tissue.
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How Small can you Make it?
The fundamental limits to the sizes of machines and devices, presented by the size of atoms and as represented by the molecular machines of biology, are clear.
The conventional machine tools that make small mechanical parts scarcely work below millimetre size at present.
Making many identical small molecules, or even many very large molecules is easy for today‟s chemist and chemical engineer.
The challenge of nanotechnology is much harder, to engineer (design and make to order) a complex structure out of molecular sized components.
What are the Methods for Making Small
Objects?
Top-down
Bottom-up
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How Can you See What you Want to Make? Photons
Dynamics Light Scattering (laser)
UV-absorption/fluorescent
Electrons STM
SEM
TEM
X-radiation (composed of X-rays) is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nm. XPS
XRD
etc
If you Can’t See it or Connect to it, Can you
Make it Self-assemble and Work on its Own?
The genius of biology is that complex structures assemble
and operate autonomously, or nearly so.
Self-assembly of a complex nano-structure is completely
beyond present engineering approaches, but the example
of DNA-directed assembly in biology is understood as an
example of what is possible.
George M. Whitesides (H-index=159, total citation =102,566 ) ref: web of science (07 Sep 2010)
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Introduction to Quantum Mechanics
Montree Sawangphruk
Chemical Engineering, Kasetsart University
„„Understanding electron as a wave‟‟
„„Quantum is the best tool to explain
the behaviours of nanomaterials‟‟ Erwin Rudolf Josef Alexander Schrödinger
Born: 12 Aug 1887 in Erdberg, Vienna, Austria
Died: 4 Jan 1961 in Vienna, Austria
Nobel Prize in Physics 1933
"for the discovery of new productive forms of atomic theory"
Movement of the Electron around the
Nucleus
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Time Dependent
Wave Equation!
EH Schrodinger equation
Time Independent
EH Schrodinger equation
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Spherical Coordinates
q
f
r
Energy of the electron
Energy is related to the Principle Quantum
number, n.
This gives 3 of the 4 quantum numbers, the
last one is the spin quantum number, s, either
+½ or – ½.
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Wave
Functions
Probability to
find an electron
Energy of the electron
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Electron Transitions give off Energy as
Light/Xrays
E=hc/l
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Red/Blue Clouds in Space
Zeeman Effect
Light Emission in Magnetic Field
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Light Emission from Elements Predicted
Quantum Dot White LEDs
An example of Nanodevices
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Light Emitting Diode Structure
LEDs are p-n junction
devices constructed of
gallium arsenide (GaAs),
gallium arsenide
phosphide (GaAsP), or
gallium phosphide (GaP).
Motivation
•Energy
efficient
•Long life
•Durable
•Small size
•Design
flexibility
Replacement for incandescent and
fluorescent lighting
Improve White LED performance
Quantum dot white LED
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White LEDS
Multichip devices (red-,green-
,blue-emitting chips)
Single-chip devices
(phosphors)
• Electroluminescence (EL)
– Light emitted in response to an
electric current
– Result of radiative
recombination
(Charge injection)
– Photon is released
http://www.science24.com/resources/paper/15507/images/OLED_2.JPG
Quantum Dots
http://chem.ps.uci.edu/~lawm/Barriers%20and%20wells.pdf
Colloidal inorganic semiconductor nanocrystal
II-VI semiconductor materials (i.e. CdS, CdSe)
2-10 nm in diameter
Exhibit strongly size-dependent optical and electrical properties
Quantum confinement effects
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Quantum Confinement
Light-Emitting Diode (LED)
is a PN junction
Recombination of an electron
and hole
Electron-hole pair known as
an exciton
e- h+
• Size of semiconductor
crystal on the order of
Exciton Bohr Radius
• Discrete energy levels
• Tunable band gapExciton Bohr Radius
http://www.science24.com/resources/paper/15507/images/OLED_2.JPG
Quantum Confinement
CdSe: Size tunable energy gap provides size
dependent emission
Term Small1
4
1
8
Coulombic
0
2
tConfinemen Quantum
2
2
R
e
REE
eh
gap
Optical properties of nano-materials depend on the size (Quantum Dots)
Visible light carries the photon
energies 1.7eV~3eV.
Size of nano particles
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InGaN-CdSe-ZnSe Quantum Dot White LEDs
InGaN CdSe-ZnSe
IEEE Photonics Technology Letters 2006 18 [1] 193
• Single-chip InGaN used as
excitation source
• CdSe-ZnSe QDs used as
phosphor
WLED from Ternary Nanocrystal Composites
Advanced Materials (2006) 18 2545-2548
Charge transfer mechanisms:
-Charge trapping
-Forster energy transfer
QDs: CdSe/ZnS
-Red λ =618 nm
-Green λ =540 nm
-Blue λ =490 nm
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RGB Colloidal Quantum Dot
Monolayer
Nano Letters (2007) 7 [8] 2196-2200
Electron transport layer
Cathode
Hole blocking layer
Quantum dot layer
Hole transport layer
Hole injection layer
Anode
Red: CdSe/ZnS (λ=620
nm)
Green: ZnSe/CdSe (λ=540 nm)
Blue: ZnCdS (λ=440 nm)
Charge injection into blue QDs more
efficient at higher applied biases
References X. Zhao, “Commercialization of Quantum Dot White Light Emitting Diode Technology,” M.Eng.
Thesis (2006).
A.P. Alivisatos, “Semiconductor Clusters, Nanocrystals, and Quantum Dots,” Science, 271
[5251], 933-937 (1996).
Y. Li, A. Rizzo, R. Cingolani, and G.Gigli, “White-light-emitting diodes using semiconductor
nanocrystals,” Microchim Acta, 159, 207-215 (2007).
H.S. Chen, C.K. Hsu, and H.Y. Hong, “InGaN-CdSe-ZnSe Quantum Dots White LEDs,” IEEE
Photonics Technology Letters, 18 [1], 193-195 (2006).
Y.Li, A. Rizzo, R. Cingolani, and G. Gigli, “Bright White-Light-Emitting Device from Ternary
Nanocrystal Composites,” Advanced Materials, 18 2545-2548 (2006).
P.O. Anikeeva, J.E. Halpert, M.G. Bawendi, and V. Bulovi, “Electroluminescence from a Mixed
Red-Green-Blue Colloidal Quantum Dot Monolayer,” Nano Letters, 7 [8] 2196-2200 (2007).
http://www.evidenttech.com
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Exercise 1
Moore‟s Law. The number of transistors in successive generations of computer chips has risen exponentially, doubling every 1.5 years
or so. The notation “mips” on right ordinate is “million instructions per second”. Gordon Moore, co-founder of Intel, Inc. predicted this
growth pattern in 1965, when a silicon chip contained only 30 transistors! The number of Dynamic Random Access Memory (DRAM)
cells follows a similar growth pattern. The growth is largely due to continuing reduction in the size of key elements in the devices, to
about 100 nm, with improvements in optical photolithography. Clock speeds have similarly increased, presently around 2 GHz.
Referring to Moor‟s Figure: if there are 10 million transistors uniformly
distributed on a one centimetre square silicon chip, what is the linear size
of each unit?
Question 1
Referring to Moor‟s Figure: if there are 20 million transistors uniformly
distributed on a one centimetre square silicon chip, what is „‟mips‟‟?
Question 1I
Transistors (millions) mips
0.01 0.10.1 11 25
10 500
y = 49.749xR² = 0.9965
0
100
200
300
400
500
600
0 2.5 5 7.5 10 12.5
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Question III
Extrapolate the line in Moor‟s Figure, to estimate in which year the size of the transistor cell
will be 10 nm.
Question IV
Calculate the density of Au nanostructures with bcc, fcc,
and hcp crystalline structures?
