Introduction to Nanotechnology

CONTENT
• What is Nanotechnology?
– Definition and current status of nanotechnology
• Why needs Nanotechnology?
– Implications of shrinking device size and fundamental limits
to conventional devices
– Technological advancement in fabrication and
characterization
• Misconceptions and Big Promises of Nanotechnology!
• Reality and Potential Applications of Nanotechnology
• Characterization and Fabrication Methods - A primer
• Impact of nanotechnology on economy, society, and
lifestyle
2

What is nanotechnology?
• Definition based on size: Nanoscience and
nanotechnology deal with fabrication and
characterization of structures having
dimensions in the 1-100 nm range.
• Definition based on effects: Nanoscience and
nanotechnology deal with fabrication and
characterization of structures dominated by
quantum effects, size effects, etc. with new or
enhanced properties introduced due to nanosize.
• When did it all start? – 1959 Richard Feynman’s
talk “There is plenty of room at the bottom”.
3

What is nanotechnology?
The size of 1nm
=
1mm
1000000
~ 1/10,000 th of a human hair
~ the dimension of 3 gold atoms
4

What is nanotechnology?
More than meets the eyes in the nano world!
5

Nanotechnology - definition
• Nanotechnology deals with materials and
systems (processing, characterization, testing,
etc.) having following properties:
– Have at least one dimension 1-100 nm.
– Are designed through processes that exhibit
fundamental control over the physical and
chemical attributes of atomic-, molecular-, and
nanometer-scale structures
– Can be combined to form larger structures.
– Exhibit unique, new, novel, enhanced or special
properties due the nanometer size.
– All experimental techniques that are needed to
achieve the above scenarios.
6

Why nanotechnology?
• According to Moore’s law, the number of
components per chip is expected to double
every 18 months.
• According to the International Technology
Roadmap for Semiconductors 2001, by the year
2005 dynamic random access memory (DRAM)
½ pitch and microprocessor unit (MPU) ½
pitch are expected to decrease to 80 nm, while
MPU printed gate length is expected to
decrease to 45 nm.
8

Semiconductor technology – implications of the
shrinking device size
• Fundamental limits of the optical lithography will soon
be reached. New lithographic technologies need to be
developed and implemented. Under development are
extreme UV and X-ray photolithography.
• With downscaling the size of the conventional devices,
quantum effects, such as carrier tunneling resulting in
increased leakage currents, are undesirable but cannot
be avoided with shrinking size.
• MOS scaling – 0.7x feature size reduction per
generation, ~0.44x switching energy reduction
• Gate oxide scaling – current 0.13µm technologies use
1.5 nm SiO 2 (< 7 atomic layers)
• Gate oxide leakage increasing exponentially with size
reduction.
9

Quantum effects
10

Semiconductor technology – implications
of the shrinking device size
• Alternatives – different dielectrics, 3-dimensional
double gate transistor structures, etc.
• Nevertheless, fundamental limits of MOS devices
will soon be reached.
• Alternatives – carbon nanotube FETs, Si, GaN
etc. nanowire FETs, single electron transistors
(main problem – very small size < 5 nm for room
temperature operation), single molecular
switches, quantum dot cellular automata etc.
11

How small can things get?
• Electron microscope
image of world’s
smallest guitar, made by
researchers from Cornell
University.
• The strings are about
100 atom wide, and
would produce high
pitched sound at
inaudible frequency of
about 10MHz.
12

Why nanotechnology?
• Advantages of small size – some examples
– Novel devices whose operating principle is based on quantum
size effects, so that small physical size would be necessary
instead of detrimental to device functioning.
– In electronics, single electron transport devices, such as single
electron transistors, turnstiles, and pumps, offer the advantages
of good scalability and operation with only several instead of
10000-100000 electrons resulting in very low power
consumption, significant decrease in power dissipation, and
faster switching.
– In tribological coatings, nano-mechanics do not involve
dislocation movement, grain boundary rotation and sliding are
the main deformation mechanisms.
– In polymer-clay nanocomposites, they are light weight
materials that rival metals in stiffness and strength while
providing enhanced gas-barrier characteristics, superior
dimensional stability and high heat-distortion temperatures.
13

Why nanotechnology?
– In optoelectronics, quantum dot lasers offer the advantages of
low threshold current density, suppressed temperature
dependence of the threshold current, and large differential
gain (which enables large modulation bandwidth).
– In sensing applications, nanosensors and nanoprobes are
enabling detection of extremely low concentrations of
molecules in chemical and biological applications and
opening the possibility of intracellular measurements for
biomedical applications which can lead to minimally invasive
diagnostic techniques.
– Other applications of nanosize (quantum) dots, such as
ferromagnetic dots for magnetic memories, quantum dots as
spin filter and spin memory, or quantum dot cellular
automata for quantum computing, have also been proposed.
– In biotechnology, new drug delivery systems and devices can
be made to improve efficiency and functionality
14

Misconceptions about nanotechnology
• With nanotechnology everything is possible.
FALSE
• With nanotechnology, we will be able to
eliminate cancer and diseases and live forever.
FALSE
• With nanotechnology, we can easily clean up
the pollution and colonize space. FALSE
• Nanotechnology is dangerous. A mistake with
nanomachines can destroy the entire planet
and just leave grey goo behind. FALSE
15

Big promises
• Nano-machines which can build anything you
want starting from atoms.
• Nano-machines which can swim in your
bloodstream and kill viruses and cancer cells.
• Prosperity, pollution-free industry, almost eternal
life, cure for all diseases, cryonics….
• Smart paints for military applications which can
change camouflage on command and even become
invisible.
• Smart walls in which windows and doors can be
moved on command.
• Growing buildings from “seeds”.
16

Illustration of “nano-machines”
pump
17

Candidate for “nano-motor”
From Nanozine:
“Researchers Don Noid, Robert
Tuzund and Bobby Sumpter of Oak
Ridge National Laboratory show
nanotubes can become
extraordinarily simple motors, when
exposed to a oscillating polarized light
source. “
18

Reality
• Nanotechnology is rapidly developing field, and its
future is hard to predict.
• We are already benefiting from products based on
nanotechnology:
– Tennis balls with 1nm sheets of clay
– Sunscreen with ZnO particles
– Quantum dots for immunoassays
– Carbon nanotube tips for surface probe microscopy
– Textile products (wrinkle resistant, odor dissipating
etc.)
19

Some examples of products already on the market
Application: Catalysts
Company: Exxonmobil
Description: Zeolites, minerals with pore sizes of less than one nanometer,
serve as more efficient catalysts to break down, or crack, large hydrocarbon
molecules to form gasoline.
Application: Data storage
Company: IBM
Description: In the past few years, disk drives have added nanoscale layeringwhich
exploits the giant magnetoresistive effect to attain highly dense data
storage.
Application: Drug delivery
Company: Gilead Sciences
Description: Lipid spheres, called liposomes, which measure about 100
nanometers in diameter, encase an anticancer drug to treat the AIDS-related
Kaposi's sarcoma.
Application: Manufacture of raw materials
Company: Carbon Nanotechnologies
Description: Co-founded by buckyball discoverer Richard E. Smalley, the
company has made carbon nanotubes more affordable by exploiting a new
manufacturing process.
Company: Carbolex Inc.
Description: single wall carbon nanotubes
20

Some examples of products already on the market
Application: Materials enhancement
Company: Nanophase Technologies
Description: Nanocrystalline particles are incorporated into other materials to
produce tougher ceramics, transparent sunblocks to block infrared and
ultraviolet radiation, and catalysts for environmental uses, among other
applications.
Application: Immunoassays
Company: Quantum Dot Corporation
Description: Qdot nanocrystals can be used instead of fluorescent-tagged
molecules, colorimetric enzymes, or colloidal gold. Nanocrystals can be
covalently linked using standard conjugation chemistry to biomolecules, and
thus used to detect binding partners of these molecules in a wide range of
assays. Quantum dots can also be attached to antibodies and oligonucleotides.
Application: Surface Probe Microscopy
Company: Piezomax technologies
Description: carbon nanotube SPM tips
Application: Nanocomposite Superhard Coating
Company: Teers
Description: Superhard coatings of Ti-Si-N nanocomposites
21

Nanotechnology in textiles
www.nano-tex.com
• Nano-Tex is an advanced materials company which uses molecular
engineering to improve textiles.
• By manipulating the architecture and chemistry of structures of
nano-meter to sub-micron dimensions, novel and unique
properties of fabrics can be achieved.
• NANO-PEL, NANO-CARE TM fabric technology – wrinkle
resistant and liquid repellent fabrics.
• NANO-TOUCH fabric technology, cotton-like sheath wrapped
around a durable synthetic core to combine durability of
synthetics with softness of cotton.
• NANO-DRY enhanced fabrics absorb perspiration into the
fabric and pull it away from the skin. Nano-net absorbent
structure around fibers provides moisture management.
22

Bio-nano-technology
• AFM for biological sample testing – strands
of DNA attached on cantilevers,
complementary sequence binds to anchored
strands and bends the cantilever and gets
detected.
• Dendrimers – globular molecules with many
branches. They have voids and can serve as
drug or DNA delivering vehicles.
• Nanoshells – gold coated glass beads. Can be
injected into the body and heated by outside
strong IR source to release drugs or kill
cancer cells. – research at Rice University.
• Repair of damaged tissues – building
scaffolding for bone growth etc.
23

Drug delivery
• Targeted drug therapy is of enormous interest
for medicine. This provides opportunity to
deliver drugs, radioactive particles or toxins to
specifically kill affected cells without damaging
surrounding healthy tissue.
• Implications – significant reduction in side
effects of treatments such as chemotherapy
which also kills healthy cells or stops cell
growth.
24

Nano-medicine
• Applications in biomedical research, disease
diagnosis and therapy.
• Faster, more sensitive and more flexible
biological tests measuring the presence of
activity of selected substances with
nanostructures as tags, labels or sensors.
• Nanoparticles can be used for drug delivery
just where the drugs are needed. Minimization
of therapy side effects.
• Artificial nanoscale building blocks for tissue
repair and organ regeneration.
25

Quantum dot corporation
26

Nanocrystals for solid state lighting
• Alternative to size controlled emission – localized
impurity inside a nanocrystal. [J. Crystal Growth, 214-
215, 926 (2000)].
• Emitted wavelength depends on the localized impurity
atom – less stringent control of size needed. As the size
of nanocrystal decreases, efficiency of light emission
increases.
• Dopants – rare earth atoms, europium for red, terbium
for green and thulium for blue.
• Nanocrystals Technology Inc., organized nanocrystal
Lighting Corporation in April 2002 to exploit
nanocrystals for solid state lighting.
27

Carbon nanotube applications
• Applications: SPM tips, field emission displays,
prototype memories and electronic devices
reported.
• Nantero, Woburn, Mass. – non-volatile random
access memory – based on carbon nanotubes.
Pairs of carbon nanotubes store data by locking
together when current runs through them.
They remain linked until separated by counter
current, so memory is retained.
28

Carbon nanotubes-displays application
• Field emission display
using carbon nanotubes.
• Choi et al. Appl. Phys.
Lett., 15 Nov., 1999.
• Samsung Advanced
Institute of Technology
29

Piezomax Technologies
30

Piezomax Technologies
31

Nanotechnology applications
• Cleaner energy
– Hydrogen fuel cells – energy produced from
hydrogen and oxygen, byproduct – water.
– Needs nanoscale catalyst (platinum) particles.
– Needs hydrogen extraction or storage. Carbon
nanotubes promising for this application.
• Coatings
– Nanocrystalline or nanocomposite:
• Superhardness (> 40 GPa)
• anti-corrosion,
• wear protective,
• decorative or functional, etc.
32

Polymer-clay nanocomposites
Lightweight materials containing nanocomposites promise to rival metals in stiffness and
strength, while providing superior dimensional stability and heat distortion properties.
TEM micrographs of
polyethylene/4% verniculite
(a clay) nanocomposite
showing the formation of
exfoliated vermiculite layers
in the composite.
33

Nanobalance
• P. Poncharal et al.,
Science March 5,
1999.
• Principle of
operation – mass
attached at the end
of nanotube shifts its
resonant frequency.
From frequency
shift, mass can be
determined.
34

AFM applications
• Lutwyche et al. Appl. Phys.
Lett. 13 Nov. 2000
• An array of 1024 tips is
scanned over a thin
polymer film used as a
storage medium.
• Each tip can be addressed
individually by a timemultiplexing
system which
was adapted from DRAM
technology.
35

Drug delivery
• Challenge in drug delivery – crossing the
cellular barrier. Important in the case of
nose, intestine, and the skin. For lung,
main difficulty is in getting the drug to
the deep lung.
• Microchips containing nanosized drug
reservoirs (image on the left) could
deliver drugs in controlled manner over
prolonged period of time.
Science 293, 58 (2001)
36

DNA self-assembly
• G. C. L. Wong et al. Appl.
Phys. Lett. Oct. 5, 1998.
• J. O. Rädler et al. Science 275,
810 (1997).
• Negatively charged DNA on
positively charged artificial
membranes.
• Uses – delivery vehicles in
gene therapy, templates for
fabrication of inorganic
nanostructures,
electrophoretic media for
sorting molecules.
37

DNA – a semiconductor
• D. Porath et al. Nature,
10 Feb. 2000.
• DNA – large bandgap
semiconductor.
• Experiment performed
at DIMES institute, Delft
Institute of Technology.
38

Quantum coral
• Manorahan et al. Nature, Feb.
3, 2000. 36 cobalt atoms in
quantum corral structure on
copper substrate, one cobalt
atom at focus of the ellipse.
Electron waves moving in the
copper substrate interact with
magnetic cobalt atom at one
of the foci. At another focus
there is a “mirage” of another
cobalt atom which isn’t really
there.
• Don Eigler, IBM. STM
picture of quantum corral
made by positioning iron
atoms on a copper surface.
39

Helical nanowires
• Zhang et al., Nanoletters
2, 941 (2002).
• SiC nanowires covered
with silicon oxide sheath.
Diameter of SiC core 10-
40 nm with helical
periodicity 40-80 nm,
covered by 30-60 nm
amorphous SiO 2 .
40

Key issues in nano-manufacturing
• Precursor nanomaterials and nanoparticles
• Fabrication of nanostructures
• Characterization and processing
• Theory, modeling, simulation, and control
• Design and integration of nanodevices and
systems
• Nano-manufacturing education and
dissemination strategies
41

Fabrication of nanostructures
There are two approaches:
• Approach I: Assembly of prefabricated nanocomponents
(clusters, tubes, wires)
1. nanocomponent fabrication,
2. nanocomponent sorting and selection, and
3. nanocomponent assembly into devices.
Can produce large quantities of nanocomponents in
inexpensive manner, steps 2 and 3 are problematic.
• Fabrication of the individual nanocomponents is typically low
cost, high speed process. There are numerous fabrication
methods, such as different methods of gas phase synthesis,
colloidal synthesis etc. Main disadvantages of this process are
poor purity and composition control, and wide size and shape
distribution. In addition, post-synthesis processing of these
nanostructures is very difficult.
42

Fabrication of nanostructures
• Approach II: Direct deposition of nanostructures on
the substrate.
QD lasers based on InGaAs material system have
been demonstrated.
• Advantage: compatible with conventional device
processing technologies. The disadvantages: higher
cost and the need to develop novel solutions to
achieve good size control of the fabricated
nanostructures.
43

Growth of nanostructures
• Early quantum dot (QD) works were based on
etched QDs. The PL efficiency of such QD
devices was low and decreasing with dot size, so
that PL spectra of 60 nm QDs was only about
1% of the PL of the mesa structure.
• Majority of QDs fabricated by self-assembly.
• Free standing nanostructures fabrication – selfassembly
• Various organic nanostructures – self-assembly.
44

Free standing nanostructures
• Free standing
nanostructures (nanowires,
nanoribbons, nanotubes,
nanorings) can be
synthesized in relatively
simple and inexpensive
manner.
SnO 2 nanoribbons
Solid State
Communications 118, 351
(2001).
45

GaN nanorings
Free standing nanostructures
Appl. Phys. A 72, 629 (2001)
GaN 1D nanostructures
Appl. Phys. A 71, 587 (2000).
46

Free standing nanostructures
FESEM - ZnO nanorods
47

Science 297,787 (2002)
Carbon nanotubes
• A,B, C – schematic
representation of single
wall CNTs
• D) TEM of 1.3 nm
SWNT
• E) TEM of multiwall
CNT
• F) TEM image of lateral
packing of 1.4 nm
SWNTs
• G) SEM image of
MWNT array
48

Carbon nanotubes
• Types – single wall and multiwall (several
layers rolled into cylinders. Single wall carbon
nanotubes can be either metals or
semiconductors depending on the chirality
(chiral angle between hexagons and tube axis).
• Band gap is inversely proportional to the
diameter for same chirality.
• Manufacturing methods: arc discharge, laser
ablation and chemical vapor deposition.
49

Carbon nanotube
• Laser ablation & arc discharge – high quality nanotubes
with low number of defects, but many byproducts.
• CVD – metal catalysts as seeds, hydrocarbon gases as
sources.
• None of the methods produces bulk materials with same
diameters and chirality.
• CVD growth on patterned substrates – ordered arrays of
nanotubes. Electric field can be used to control the growth
directions.
• For details on CNTs, see: Science 297,787 (2002), Critical
Reviews in Solid State and Materials Sciences 26(3), 145
(2001), H. Dai, Acc. Chem. Res. 2002.
50

Carbon nanotubes
• Small diameter, single wall CNTs have high
Young’s modulus and high tensile strength –
light, stiff and strong material.
• Impurities – carbon coated metal particles,
amorphous carbon, fullerene. Typically
removed with acid and/or heating, which can
damage tubes and introduce other impurities.
51

Field emission
• Potential applied between nanotube or
nanowire coated surface and anode produces
high local fields as a result of small radius of
nanostructure.
• High local fields cause tunneling of electrons
from nanotube (nanowire) tip into vacuum.
• Electric fields direct electrons to anode, where
a phosphor produces light.
52

Carbon nanotubes-display application
Science 297,787 (2002)
• A) Schematic illustration
of a carbon nanotube
display
• B) SEM image of an
electron emitter
• C) 5 inch nanotube field
emission display made
by Samsung.
53

Science 297,787 (2002)
Nanoelectronic devices
A) schematic diagram of carbon
nanotube FET
B) STM image of SWNT FET
C) Image and schematic
representation of electrical
pulses removing layers of
MWNT to reveal layers with
desired transport properties.
D) STM image of a nanotube
having different helicity on
opposite sides of a kink – one
side is metallic, the other is
semiconducting.
54

Hurdles to overcome:
Lack of size uniformity and order
Control of shape of nano-objects
Substance purity
Control of crystal structure
55

Nanotechnology- present and future
• Efforts of past 10 years have identified
important consequences and applications of
nano science and technology
• To reap these benefits, R&D in the future
need to master ways to control the shape,
size and placement of nano objects
• In order to accomplish this aim, joint efforts
and fabrication ideas from fields of physics,
engineering, chemistry and biology are
needed.
56

Impact of nanotechnology
• If self-replicating universal assemblers and medical nanobots could be
achieved, impact would be enormous.
• Economic implications – no limits to growth, does not conform to
conventional supply and demand. Obsolescence, substitution and
aftermarket driving the demand.
• Societal implications – no value of labour in basic industries. Increased
leisure will not necessarily result in pursuit of knowledge.
• Geopolitical implications – use of nanomachines as weapons, in wars and by
terrorists and “rogue leaders” (Iraq etc.).
• Longevity implications – limiting population growth and limiting evolution
potential, socio-legal problems (crime and punishment, suicide), eugenics,
and superhumanism.
• Fortunately – realizations of self-replicating universal assemblers and
universal repair medical nanobots are not likely.
• For detailed discussion on “nanotechnology what ifs”, see: NanoTechnology Magazine, 3:5, June-July,
1997, 1-6, NanoTechnology Magazine, 2:4, April, 1996, pp. 2-3; NanoTechnology Magazine , 2:5, May,
1996, pp. 4-6; NanoTechnology Magazine, 2:6, June, 1996, pp. 7-10; NanoTechnology Magazine, 2:7,
July, 1996, pp. 6-9; and NanoTechnology Magazine, 2:8, August, 1996, pp. 3-5.
57

Economic growth
Impact of nanotechnology
Better, cheaper products
Advances in diagnostic
techniques
Improved disease and cancer
treatment
+
Benefits to
individuals
Benefits to
society
58