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NanoScience & NanoTechnology
Expectations from the New World
As per the
Nanotechnology Initiative (NNI) of
the National Science Foundation
(NSF)
major implications are expected for
• Health
• Wealth
• Peace
M. C. Roco et al., Societal Implications of Nanoscience and Nanotechnology (Kluwer Acad. Publ., Dordrecht, 2001).
Affected Areas
Impact
Manufacturing
- Nanostructuring
- Materials properties
- Materials
- Structure
Electronics
Pharmaceuticals
Chemical Plants
Transportation
Energy (Sustainability)
- Nanostructured catalyst
- Safer and lighter vehicles
(based on materials and
electronics)
- Reduction in energy use
Economical impact per
year (in 10 to 15 years)
$ 340 billion per year
$ 300 billion per year
$ 180 billion per year
$ 100 billion per year
$ 70 billion per year
$ 100 billion per year
(on savings)
NanoScience & NanoTechnology
Bottom-up Approach
To synthesize material from atoms or molecules by means of “self-assembly”.
Spectroscopic Regions:
• Molecule:
Ultra-small clusters: 10 – 100 atoms show strongly deviating
molecular structures from the bulk.
Si13
E.g.: Si13 (metallic-like close packing)
Si45 (distorted diamond lattice)
•
Si45
U. Rothlisberger, et al.,
Phys. Rev. Lett. 72,
665 (1994).
Quantum Dot:
Small clusters: ~103 - 106 atoms (bulk-like structure) but
possess discrete excited electronic states if cluster diameter
less than the bulk Bohr radius, ao, (typically < 10 nm)
 h 


2
ao   2
me
2
NanoScience & NanoTechnology
Cont. Spectroscopic Regions:
• Polariton:
Large “clusters”: > 106 atoms. In this regime the particle acts
as an optical cavity (micro-cavity) due to light matter coupling
-> Polariton Laser
Kinetic Regions:
Consideration of the transport properties in the media.
In semiconductors one experiences in nanocrystals:
< 106 atoms:
Molecular decay kinetics
> 106 atoms:
Many body kinetics (Auger recombinations etc. )
-> important in Si nanocrystal luminescence
NanoScience & NanoTechnology
Quantum Confinement
NanoScience & NanoTechnology
Quantum Devices and
Quantum Effects
200  200 nm2 SFM image of
InAs dots on GaAs
R. Notzel, Semicond. Sci. Techn. 11,
1365 (1996).
White and blue emitting solid-state
devices based on quantum dots
developed in Sandia National
Laboratories.
Sandia National Laboratories, (2003).
NanoScience & NanoTechnology
Molecular Devices / Gates
Use of nanotubes in Field-Effect
Transistors (FET)
Current-Voltage Characteristics
at room temperature (290 K) acts like a FET
IBM: Applied Physics Letters, vol 73, p. 2447
(1998)
at 77K: acts like a single electron transistor
(SET)
NanoScience & NanoTechnology
Top-down Approach
To create and investigate the Nanoscale by means, for instance, of
lithographical methods and high sensitive measurements.
In gates with 2 nm width it
has been shown that the
channel conductance is
quantized in steps of 2e2/h.
100 nm MOSFET (gm=570 mS/mm, fT=110 GHz).
D. M. Tennant, in Nanotechnology, edited by G. Timp (AIP Press, Springer Verlag, New York, 1999), p. 161.
NanoScience & NanoTechnology
Nanofabrication and Lithography
Emission of atomic hydrogen (Lyman-a line)
Nearfield Exposure (not wavelength limited)
Photolithographic contact printing with phase shifting mask.
V. Liberman, M. Rothschild, P. G. Murphy, et al., J. Vac. Sci. Techn. B 20, 2567 (2002).
NanoScience & NanoTechnology
Lithographical Techniques
• Photo emission
• X-rays
• Electrons
• Ions
• SPM (not sketched, see below)
NanoScience & NanoTechnology
Dip-Pen Nanolithography
Submicrometer
arrays of
biomolecules
as screening
tools in
proteomics and
genomics.
Ki-Bum Lee, JACS 2003,
125, 5588
NanoScience & NanoTechnology
Lithographical Techniques
Optical
step and
repeat
reduction
printing
SPM
for 50 % coverage (e.g., equal lines and spaces)
Challenges
be met by
current
laboratory
methods
before they
can be
seriously
considered
D. M. Tennant, in
Nanotechnology,
edited by G. Timp
(AIP Press, Springer
Verlag, New York,
1999), p. 161.
NanoScience & NanoTechnology
Nanoscale Imaging
SFM Study
Lipid Bilayer (LB Technique)
on silicon oxide surface
R.M. Overney, Phys. Rev. Lett. 72, 3546-3549 (1994)
STM Study
Self-assembly of C18ISA on
HOPG surface
S. De Feyter et al. in Organic Mesoscopic Chemistry,
Ed. H. Masuhara et al., Blackwell Science 1999
NanoScience & NanoTechnology
Constraints in the New World
The Nanoscale is not only about small particles or small patterns but also
about material limitation.
e.g. Film Thickness Limitation for the Photoresist in Photo-Lithography
The absorption
coefficient
imposes a max.
thickness on the
photoresist
T. M. Bloomstein, M. Rothschild, R. R. Kunz, et al., J. Vac. Sci. Techn. B 16, 3154 (1998).
NanoScience & NanoTechnology
Other constraints for the Photoresist
Ideally:
A photoresist consists of a Polymer Matrix (e.g., PMMA) consisting of acidlabile groups and “homogeneously” distributed photoacid generators (PAG).
Photoresist with “Homogeneous”
PAG distribution
However, the reality of photolithographical
imperfections (see below) suggests PAG
distribution inhomogeneities.
SUBSTRATE
T - tops
Fat Bottoms
NanoScience & NanoTechnology
Spincoated Ultrathin Films
In polymeric systems, the molecular mobility is of particular concern
if length scales below ~ 100 nm are involved
Illustrated with a
study on:
NanoScience & NanoTechnology
Spin Coating Effect on Polymer Mobility
below the 100 nm Film Thickness Regime
Scan Size
50  50 mm2
tPEP 400 nm
Scan Size
10  10 mm2
tPEP 4 nm
R.M. Overney et al., J. Vac. Sci. Techn. B 14(2), 1276-1279 (1996).
NanoScience & NanoTechnology
Dewetting and Spincoated Ultrathin Films
Dewetting hole velocities
as function of the PEP
film thickness
Dewetting Velocity
Lateral
Force
PEP
Si
Lateral Force and dewetting
kinetics suggest the formation of a
rheologically modified boundary
layer of PEP towards the silicon
substrate → “glassification” of PEP
Normalized Lateral Force
(▲ Poly(vinyl pyridine (PVP) screener to silicon substrate)
1.0
0.8
0.6
0.4
0.2
0.0
0
100
200
300
400
R.M. Overney et al., J. Vac. Sci. Techn. B 14(2), 1276-1279 (1996).
NanoScience & NanoTechnology
Confined Boundary Layer of Spincoated Ultrathin Films
BULK
Lateral Force and Dewetting Studies suggest that the PEP phase is
rheological modified within a 100 nm boundary region that exceeds by two
orders of magnitude the theoretically predicted pinning regime of annealed
elastomers at interfaces with negative spreading coefficient.
SRZ
~ 100 nm
ICZ
S
S
~ 1 nm
ICZ
BULK
Mean field theories consider
the effect of pinning at
interfaces only within a
pinning regime (0.6 – 1 nm
« Rg)
NanoScience & NanoTechnology
Entanglement Strength and Spincoated Ultrathin Films
Entanglement strength studies on poly (ethylene-propylene) (PEP) films
revealed interfacial confinement effects on the transition load from 3D
viscous shear to 2D chain sliding.
t = 520 nm
Transition Point Pt
 Entanglement
Strength
(a) low load sliding regime
(b) high friction coefficient
m1 = 2.1
3D flow
(c) low friction coefficient
m2 = 0.3
2D sliding
C. K. Buenviaje, S. Ge, M. Rafailovich, J. Sokolov, J. M. Drake, R. M. Overney,
Confined Flow in Polymer Films at Interfaces, Langmuir, 19, 6446-6450, (1999).
• No transition, only 2D chain sliding is observed on films < ~ 20 nm thick (ICZ).
• Transition load increases with thickness up to ~230nm (SRZ).
• Transition load is constant for films thicker than ~230 nm (BULK).
NanoScience & NanoTechnology
Interfacially Confined Spincoated Ultrathin Films
Structural Model
• At a thickness of 20 nm the polymer films are in a
gel-like state (“porous structure”). [ X-ray reflection data of L.W. Wu]
Chains are fully disentangled due to high shear
stresses.
• The polymers adjacent to the sublayer diffuse into the
porous structure of the sublayer. [Neutron Reflectivity studies on
polystyrene, X. Zheng et al. Phys. Rev. Lett. 74, 407 (1995)]
two-fluid system
• The anisotropy generated in normal direction
recovers slowly over a distance of about 7-10 Rg.
• Temperature annealing causes the gel to shrink and
to “freeze” the anisotropic boundary structure. [Neutron
Reflectivity studies on polystyrene, X. Zheng et al. Phys. Rev. Lett. 74, 407 (1995)]
NanoScience & NanoTechnology
Material Property Engineering
Engineering with Molecular Weight
FILM THICKNESS, d ( nm )
50
100
150
200
250
12.0 kDa PS
17.5 kDa PS-BCB
21.0 kDa PS-BCB
300
100
12.0 kDa PS
FOX-FLORY (BULK)
95
180
130
90
95
80
30
10
14
18
22
MW (kDa)
85
0
90
50
100
150
200
250
300
FILM THICKNESS, d ( nm )
Engineering with Crosslinking
85
115
110
Tg ( o C )
o
Tg ( C )
100
T g ( oC )
105
d MAX (nm)
0
105
105
100
95
CROSSLINKED Tg
90
S
ICZ
SRZ
BULK
INITIAL Tg
85
0
50
100
150
200
250
FILM THICKNESS d (nm)
300