# Presentation: 716340

## M. Meyyappan

- Introduction to
- Nanotechnology

## Nanotechnology is the creation of USEFUL/FUNCTIONAL materials, devices and systems (of any useful size) through control/manipulation of matter on the nanometer length scale and exploitation of novel phenomena and properties which arise because of the nanometer length scale:

- Nanotechnology is the creation of **USEFUL/FUNCTIONAL** materials, devices and systems (of any useful size) through control/manipulation of matter on the nanometer length scale and exploitation of novel phenomena and properties which arise because of the nanometer length scale:

- •	Physical
- •	Chemical
- •	Electrical
- •	Mechanical
- •	Optical
- •	Magnetic
- •
- •

- _Nanometer_
- •	One billionth (10-9) of a meter
- •	Hydrogen atom 0.04 nm
- •	Proteins ~ 1-20 nm
- •	Feature size of computer chips 90 nm
- 	(in 2005)
- •	Diameter of human hair ~ 10 μm

## •	Examples

- •	Examples
- 	-	Carbon Nanotubes
- 	-	Proteins, DNA
- 	-	Single electron transistors
- •	Not just size reduction but phenomena 		intrinsic to nanoscale
- 	-	Size confinement
- 	-	Dominance of interfacial phenomena
- 	-	Quantum mechanics
- •	New behavior at nanoscale is not 			necessarily predictable from what we 		know at macroscales.

- AFM Image of DNA

## What is Special about Nanoscale?

- •	Atoms and molecules are generally less than a nm and we study 		them in chemistry.  Condensed matter physics deals with solids
- 	with infinite array of bound atoms.  Nanoscience deals with the
- 	in-between meso-world
- •	Quantum chemistry does not apply (although fundamental laws
- 	hold) and the systems are not large enough for classical laws of
- 	physics
- •	Size-dependent properties
- •	Surface to volume ratio
- 		-	A 3 nm iron particle has 50% atoms on the surface
- 		-	A 10 nm particle             20% on the surface
- 		-	A 30 nm particle             only 5% on the surface

## What is new about Nanoscience?

- •	Many existing technologies already depend on nanoscale materials
- 	and processes
- 		-	photography, catalysts are “old” examples
- 		-	developed empirically decades ago
- •	In existing technologies using nanomaterials/processes, role of
- 	nanoscale phenomena not understood until recently; serendipitous
- 	discoveries
- 		-	with understanding comes opportunities for improvement
- •	Ability to design more complex systems in the future is ahead
- 		-	designer material that is hard and strong but low weight
- 		-	self-healing materials

## •	Recently, there has been an explosion of research 	on the nanoscale behavior

- •	Recently, there has been an explosion of research 	on the nanoscale behavior
- 	-	Nanostructures through sub-micron self 			assembly creating entities from “bottom-up” 		instead of “top-down”
- 	-	Characterization and applications
- 	-	Highly sophisticated computer simulations to 		enhance understanding as well as create 			‘designer materials’

- •	1959 Feynman Lecture *“There is Plenty of Room at the **	**Bottom” *provided the vision of exciting new discoveries if 	one could fabricate materials/devices at the atomic/molecular 	scale.
- •	Emergence of instruments in the 1980s; STM, AFM 		providing the “eyes”, “fingers” for nanoscale manipulation, 	measurement...

- STM

- Image of Highly Oriented Pyrolitic Graphite

## Nanotechnology R & D

**Materials**

**Applications**

## Various Nanomaterials and

- Nanotechnologies

- •	Nanocrystalline materials
- •	Nanoparticles
- •	Nanocapsules
- •	Nanoporous materials
- •	Nanofibers
- •	Nanowires
- •	Fullerenes
- •	Nanotubes
- •	Nanosprings
- •	Nanobelts
- •	Dendrimers
- •

- •	Molecular electronics
- •	Quantum dots
- •	NEMS, Nanofluidics
- •	Nanophotonics, Nano-optics
- •	Nanomagnetics
- •	Nanofabrication
- •	Nanolithography
- •	Nanomanufacturing
- •	Nanomedicine
- •	Nano-bio
- •
- •

## See www.nano.gov

- As Recommended by the IWGN (Interagency Working Group on Nanotechnology) Panel
- •	Nanostructure Properties
- 	-	Biological, chemical, electronic, magnetic, optical, structural...
- •	Synthesis and Processing
- 	-	Enable atomic and molecular control of material building blocks
- 	-	Bioinspired, multifunctional, adaptive structures
- 	-	Affordability at commercial levels
- •	Characterization and manipulation
- 	-	New experimental tools to measure, control
- 	-	New standards of measurement
- •	Modeling and simulation
- •	Device and System Concepts
- 	-	Stimulate innovative applications to new technologies
- •	Application Development

## This is NOT an exhaustive list

- 1.	What novel quantum properties will be enabled by nanostructures  (at room temp.)?
- 2.	How different from bulk behavior?
- 3.	What are the surface reconstructions and rearrangements of atoms in nanocrystals?
- 4.	Can carbon nanotubes of specified length and helicity be synthesized as pure 	species?  Heterojunctions in 1-D?
- 5.	What new insights can we gain about polymer, biological...systems from the 	capability to examine single-molecule properties?
- 6.	How can one use parallel self-assembly techniques to control relative arrangements 	of nanoscale components according to predesigned sequence?
- 7.	Are there processes leading to economic preparation of nanostructures with control 	of size, shape... for applications?

## Some 'Nano' Definitions

- •	Cluster
- 		-	A collection of units (atoms or reactive molecules) of up to 				about 50 units
- •	Colloids
- 		-	A stable liquid phase containing particles in the 1-1000 nm 				range.  A colloid particle is one such 1-1000 nm particle.
- •	Nanoparticle
- 		-	A solid particle in the 1-100 nm range that could be 					noncrystalline, an aggregate of crystallites or a single 				crystallite
- •	Nanocrystal
- 		-	A solid particle that is a single crystal in the nanometer range

## Percentage of Surface Atoms

- Source: Nanoscale Materials in Chemistry, Wiley, 2001

## Surface to Bulk Atom Ratio

- •	Spherical iron nanocrystals
- •	J. Phys. Chem. 1996, 	Vol. 100, p. 12142

## Size Dependence of Properties

- •	In materials where strong chemical bonding is present, delocalization of valence 	electrons can be extensive.  The extent of 	delocalization can vary with the size 	of the system.
- •	Structure also changes with size.
- •	The above two changes can lead to different physical and chemical
- 	properties, **depending on size**
- 		-	Optical properties
- 		-	Bandgap
- 		-	Melting point
- 		-	Specific heat
- 		-	Surface reactivity
- 		-
- 		-
- •	Even when such nanoparticles are consolidated into macroscale solids, new 		properties of bulk materials are possible.
- 		-	Example:  enhanced plasticity

## Some More Size-Dependent

- Properties

- •	For semiconductors such as ZnO, CdS, and Si, the bandgap 		changes with size
- 		-	Bandgap is the energy needed to promote an electron 				from the valence band to the conduction band
- 		-	When the bandgaps lie in the visible spectrum, changing 				bandgap with size means a change in color
- •	For magnetic materials such as Fe, Co, Ni, Fe3O4, etc., magnetic 	properties are size dependent
- 		-	The ‘coercive force’ (or magnetic memory) needed to 				reverse an internal magnetic field within the particle is 				size dependent
- 		-	The strength of a particle’s internal magnetic field can be 			size dependent

## Color

- •	In a classical sense, color is caused by the partial absorption of 		light by electrons in matter, resulting in the visibility of the 		complementary part of the light
- •	On a smooth metal surface, light is totally reflected by the high 		density of electrons           no color, just a mirror-like appearance.
- •	Small particles absorb, leading to some color.  This is a size 		dependent property.
- 	_Example_: Gold, which readily forms nanoparticles but not easily 	oxidized, exhibits different colors depending on particle size.
- 		-	Gold colloids have been used since early days of glass 				making to color glasses.  Ruby-glass contains finely 				dispersed gold-colloids.
- 		-	Silver and copper also give attractive colors

## Specific Heat

- •	C = ∆Q/m∆T; the amount of heat ∆Q required to raise the 		temperature by ∆T of a sample of mass m
- •	J/kg ·K or cal/g ·K; 1 calorie is the heat needed to raise the temp. of 	1 g of water by 1 degree.
- •	Specific heat of polycrystalline materials given by Dulong-Petit law
- 	 -	C of solids at room temp. (in J/kg ·k) differ widely from one to 		another; but the molar values (in J/moles ·k) are nearly the 			same, approaching 26 J/mol ·K; Cv = 3 Rg/M
- 			     where M is molecular weight
- •	Cv of nanocrystalline materials are higher than their bulk 		counterparts.  Example:
- 		-  Pd: 48%  from 25 to 37 J/mol.K at 250 K for 6 nm crystalline
- 		-  Cu: 8.3%  from 24 to 26 J/mol.K at 250 K for 8 nm
- 		-  Ru: 22%  from 23 to 28 J/mol.K at 250 K for 6 nm

## The melting point decreases dramatically as the particle 

- Melting Point of Gold Particles

- The melting point decreases dramatically as the particle
- size gets below 5 nm

- Source: Nanoscale Materials in Chemistry, Wiley, 2001

## Melting Point Dependence on

- Particle Size

- •	Lowering of the melting point is proportional to 1/r
- •	 can be as large as couple of hundred degrees when the 		particle size gets below 10 nm!
- •	Most of the time,  the surface tension coefficient is unknown;
- 	by measuring the melting point as a function of radius,  can be
- 	estimated.
- •	Note: For nanoparticles embedded in a matrix, melting point may 	be lower or higher, depending on the strength of the interaction 		between the particle and matrix.

## •	For metals, conductivity is based on their band structure.  If the 		conduction band is only partially occupied by electrons, they can 		move in all directions without resistance (provided there is a perfect 	metallic crystal lattice).  They are not scattered by the regular 		building blocks, due to the wave character of the electrons.

- •	For metals, conductivity is based on their band structure.  If the 		conduction band is only partially occupied by electrons, they can 		move in all directions without resistance (provided there is a perfect 	metallic crystal lattice).  They are not scattered by the regular 		building blocks, due to the wave character of the electrons.

*v*  = electron speed
- o = dielectric constant in vacuum

- 	 , mean time between collisions, is /*v*
- •	For Cu, *v* = 1.6 x 106 m/s at room temp.;  = 43 nm,  = 2.7 x 10-14s

- Electrical Conductivity

## •	Scattering mechanisms

- •	Scattering mechanisms
- 	(1)	By lattice defects (foreign atoms, vacancies, interstitial 				positions, grain boundaries, dislocations, stacking disorders)
- 	(2)	Scattering at thermal vibration of the lattice (phonons)
- •	Item (1) is more or less independent of temperature while item #2 	is independent of lattice defects, but dependent on temperature.
- •	Electric current        collective motion of electrons; in a bulk metal,
- 					      Ohm’s law:  V = RI
- •	Band structure begins to change when metal particles become 		small. Discrete energy levels begin to dominate, and Ohm’s law is 	no longer valid.

- Electrical Conductivity
- (continued)

## I-V of a Single Nanoparticle

- Source: Nanoscale Materials in Chemistry, Wiley, 2001

## I-V of a Single Nanoparticle

- •	Consider a single nanoparticle between two electrodes, but 	cushioned by a 		capacitance on each side
- 		-	If an electron is transferred to the particle, its coulomb energy        by
- 						Ec = e2/2c
- 		-	Thermal motion of the atoms in the particle can initiate a charge & Ec, 				leading to further electrons tunneling uncontrollably
- 		-	So, kT << e2/2c
- 		-	Tunneling current I = V/RT
- 		-	Current begins at coulomb voltage Vc = ± e/2c which is called coulomb 			blockade
- 		-	Further electron transfer happens if the coulomb energy of the ‘quantum 			dot’ is compensated by an external voltage Vc = ± ne/2c where n is an 				integer
- -	Repeated tunneling results in a ‘staircase’ with step height in current, e/Rc
- -	Possible to charge and discharge a quantum dot in a quantized manner        		principle behind some future computers

## •	If a bulk metal is made thinner and thinner, until the electrons can 	move only in two dimensions (instead of 3), then it is “2D quantum 	confinement.”

- •	If a bulk metal is made thinner and thinner, until the electrons can 	move only in two dimensions (instead of 3), then it is “2D quantum 	confinement.”
- •	Next level is ‘quantum wire
- •	Ultimately ‘quantum dot’

- Source: Nanoscale Materials in Chemistry, Wiley, 2001

## Adsorption

## Adsorption:  Some Background

- •	Adsorption is like absorption except the adsorbed material is held 	near the surface rather than inside
- •	Bulk solids, all molecules are surrounded by and bound to 		neighboring atoms and forces are in balance.  Surface atoms are 		bound only on one side, leaving unbalanced atomic and molecular 	forces on the surface.  These forces attract gases and molecules 
- 	Van der Waals force,  physical adsorption or physisorption
- •	At high temperatures, unbalanced surface forces may be satisfied by 	electron sharing or valence bonding with gas atoms  chemical 	adsorption or chemisorption
- 		-	Basis for hetergeneous catalysis (key to production of 				fertilizers, pharmaceuticals, synthetic fibers, solvents, 				surfactants, gasolines, other fuels, automobile catalytic 				converters...)
- 		-	High specific surface area (area per unit mass)

## Physisorption

- •	Physisorption of gases by solids increases with decreasing T and with increasing P
- •	Weak interaction forces; low heats of adsorption
- 	< 80 KJ/mole; physisorption does not affect the
- 	structure or texture of the absorbent
- •	Desorption takes place as conditions are reversed
- •	Mostly, testing is done at LN2 temperature
- 	(77.5 K at 1 atm.).  Plot of gas adsorbed as
- 	volume Va at 0° C and 1 atm (STP) vs. P/Po
- 	(Po is vapor pressure) is called adsorption
- 	isotherm.

## Chemisorption

- •	Much stronger interaction than physisorption
- •	Heat of adsorption up to 800 KJ/mole
- •	Adsorbing gas or vapor molecule splits into atoms, radicals or ions
- 	which form a chemical bond with the adsorption site.  Sharing of 	electrons between the gas and solid surface; may be regarded as the 	formation of a surface compound.
- •	Simple reversal is not possible like in physisorption
- 		-	O2 chemisorbed on charcoal  application of heat and 				vacuum will result in CO desorption instead of O2.
- •	Under favorable T & P, physisorption takes place on all surfaces.  	But chemisorption is localized and occurs on only certain surface sites
- •	Physisorption  with  in T; chemisorption  with  in T
- •	Same surface can exhibit physiosorption at low T and chemisorption 	at high T.  Example: N2 chemisorption on Fe at 800° C to form iron
- 	nitride but physisorption at LN2 temperatures.

## Chemisorption: Langmuir Theory

- •	Assumes gases form only one monolayer on a solid
- •	Gas molecule collision with solid  inelastic, so the gas molecule stays in contact 	with solid, for a time before desorbing
- •	Writing a balance between the rate at which molecules strike the surface and rate 	at which they leave:
- 					 Vm=  quantity of gas absorbed when the
- 					          entire surface is covered with a
- 					           monolayer
- •	Rearranging,
- •	Plot of         vs. P should yield a straight line if the equation applies  evaluate
- 	Vm and b
- •	Specific surface area

- Vm=  molar volume of the gas (22414 cm3);
-          NA = Avog. #
-   =  surface area occupied by single adorbed
-          molecule, 16.2 A2 for N2
- m =  mass of the adsorbing sample

## Nanomaterials in Catalysis

- •	Surface chemistry is important in catalysis.  Nanostructured materials have some
- 	advantages:
- 		-	Huge surface area, high proportion of atoms on the surface
- 		-	Enhanced intrinsic chemical activity as size gets smaller which is likely
- 			due to changes in crystal shape
- 		-	Ex:  When the shape changes from cubic
- 			to polyhedral, the number of edges
- 			and corner sites goes up
- 			significantly
- 		-	As crystal size gets smaller, anion/cation
- 			vacancies can increase, thus affecting
- 			surface energy; also surface atoms can be
- 			distorted in their bonding patterns
- 		-	Enhanced solubility, sintering
- 			at lower T, more adsorptive
- 			capacity

## Nanoporous Materials

- •	Zeolite is an old example which has been around a long time and 	used by petroleum industry as catalysts
- •	The surface area of a solid increases when it becomes nanoporous; 	this improves catalyst effects, adsorption properties
- •	‘Adsorption’ is like ‘absorption’ except the absorbed material is 		held near the surface rather than inside
- •	How to make nanopores?
- 		-	lithography followed by etching
- 		-	ion beam etching/milling
- 		-	electrochemical techniques
- 		-	sol-gel techniques

## Fine Particle Technology

- •	Frequently encountered powders:
- 		-	Cement, fertilizer, face powder, table salt, sugar, detergents, coffee 				creamer, baking soda...
- •	Some products in which powder incorporation is not obvious
- 		-	Paint, tooth paste, lipstick, mascara, chewing gum, magnetic recording 				media, slick magazine covers, floor coverings, automobile tires...
- •	For most applications, there is an optimum particle size
- 		-	Taste of peanut butter affected by particle size
- 		-	Extremely fine amorphous silica is added to control the ketchup flow
- 		-	Medical tablets dissolve in our system at a rate controlled by particle size
- 		-	Pigment size controls the saturation and brilliance of paints
- 		-	Effectiveness of odor removers controlled by the surface area of 				adsorbents.

- From: Analytical methods in Fine Particle Technology, Webb and Orr

## •	Ability to synthesize nanoscale building blocks with control on size,

- •	Ability to synthesize nanoscale building blocks with control on size,
- 	composition etc. 	     further assembling into larger structures with
- 	designed properties will revolutionize materials manufacturing
- 	-	Manufacturing metals, ceramics, polymers, etc. at exact shapes without 			machining
- 	-	Lighter, stronger and programmable materials
- 	-	Lower failure rates and reduced life-cycle costs
- 	-	Bio-inspired materials
- 	-	Multifunctional, adaptive materials
- 	-	Self-healing materials

- •	Challenges ahead
- 	-	Synthesis, large scale processing
- 	-	Making useful, viable composites
- 	-	Multiscale models with predictive capability
- 	-	Analytical instrumentation

## •	Carbon Nanotubes

- •	Carbon Nanotubes
- •	Nanostructured Polymers
- •	Optical fiber preforms through sol-gel
- 	processing of nanoparticles
- •	Nanoparticles in imaging systems
- •	Nanostructured coatings
- •	Ceramic Nanoparticles for netshapes

- Source:  IWGN Report

## More Examples of Nanotech in

- Materials and Manufacturing

- •	Nanostructured metals, ceramics at exact shapes without machining
- •	Improved color printing through better inks and dyes with  		nanoparticles
- •	Membranes and filters
- •	Coatings and paints (nanoparticles)
- •	Abrasives (using nanoparticles)
- •	Lubricants
- •	Composites (high strength, light weight)
- •	Catalysts
- •	Insulators

## Nanoelectronics and Computing

- _Past_
- Shared computing	     thousands of people sharing a mainframe computer

- _Present_
- Personal computing

- _Future_
- Ubiquitous computing	             thousands of computers sharing each
- and everyone of us; computers embedded in walls, chairs, clothing,
- light switches, cars....; characterized by the connection of things in
- the world with computation.

## •	Quantum Computing

- •	Quantum Computing
- 		-	Takes advantage of quantum mechanics 				instead of being limited by it
- 		-	Digital bit stores info. in the form of ‘0’ and 				‘1’; qubit may be in a superposition state of 				‘0’ and ‘1’ representing both values
- 			*simultaneously* until a measurement is made
- 		-	A sequence of N digital bits can represent 				*one* number between 0 and 2N-1; N qubits 				can represent *all* 2N numbers simultaneously

- •	Carbon nanotube transistors by several groups
- •	Molecular electronics: Fabrication of logic gates
- 	from molecular switches using rotaxane
- 	molecules
- •	Defect tolerant architecture, TERAMAC computer
- 	by HP 	              architectural solution to the
- 	problem of defects in future molecular electronics

- - Stan Williams

## •	DNA microchip arrays using advances for IC industry

- •	DNA microchip arrays using advances for IC industry
- •	‘Gene gun’ that uses nanoparticles
- 	to deliver genetic material	to
- 	target cells
- •	Semiconductor nanocrystals
- 	as fluorescent biological labels

- Source:  IWGN Report

## Summary

- •	Nanotechnology is not about simply shrinking the dimensions to
- 	1- 100 nm level nor is the routine top-down miniaturization as we 	do in silicon CMOS fabrication.  If that is the case, we do not 		need new terminologies and funding to continue the old stuff.
- •	Instead, it is about exploring novel properties that arise because 		of the nanoscale - properties that differ from their bulk 			counterparts.
- •	Once we identify such properties, the next big question is: What 	useful things can we do with that?
- •	There are several areas in which researchers have been able to 		answer positively to this question, leading to the evolution of the 	field.