Nanotechnology and Nanomaterials

Andrew Pratt Senior Research Fellow York Institute for Materials Research (Nanophysics Group) Science in an Engineering Context, 18 th March 2009

Outline

• Introduction - what is nanotechnology?

- history - public perception/media • Tools of Nanotechnology - microscopy - spectroscopy • Nanofabrication - bottom up – self-assembly – nanowires - top down – nanolithography – atom lithography • Summary

Introduction – the nanoscale

• 1 nanometre = 10 -3 mm = 10 -9 m µm = 10 -6 • If the width of your finger (~1 cm) represented 1 nm, then 1 metre would be 10,000 km (diameter of Earth ~ 12,000 km) • Diameter of a silicon atom = 0.234 nm • Atomic dimensions measured in Angstroms (Å) 1 Å = 0.1 nm = 10 -10 m • Magnification needed to “see” atoms ~ 1,000,000

Introduction – nanotechnology

Nanoscience and nanotechnologies: opportunities and uncertainties

, Royal Society/Royal Academy of Engineering report (2004):

Nanoscience

“the study of phenomena and manipulation of materials at atomic and molecular scales”

Nanotechnology

“the design, characterisation, production and application of structures, devices and systems by controlling shape and size at nanometre scale” Electronic properties change at the nanoscale, for example • opaque substances become transparent (Cu) • inert materials become catalysts (Pt) • stable materials become combustible (Al) • solids turn into liquids (Au) • insulators become conductors (Si)

Introduction – size matters

• At the nanoscale, the surface of a material determines its properties: - Volume decreases as the 3 rd power of linear dimensions - Surface area decreases as 2 nd power of linear dimensions • Surface-to-volume ratio extremely important in nanotechnology and nanomaterials • Consider the power-to-friction ratio at the nanoscale, for example in drills, gears and bearings Microelectromechanical systems (MEMS) – also NEMS http://mems.sandia.gov/scripts/images.asp

History of nanotechnology

• Scientific revolutions: • 1959 – “There’s plenty of room at the bottom” Richard Feynman (won the Nobel Prize in 1965) gives his famous talk “There’s plenty of room at the bottom” "The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, and to do things on an atomic level, is ultimately developed – a development which I think cannot be avoided.“ Feynman prize for advances in Nanotechnology

History of nanotechnology

• 1965 – Moore’s law Gordon Moore – co-founder of Intel – observes that the number of transistors that can be inexpensively placed on an integrated circuit is increasing exponentially, doubling approximately every two years.

• 1974 – “Nano-Technology” Prof. Nario Taniguchi (Tokyo) coins the term nanotechnology in his paper “On the Basic Concept of Nano Technology” “’Nano-technology’ mainly consists of the processing of, separation, consolidation, and deformation of materials by one atom or molecule”

History of nanotechnology

History of nanotechnology

• 1980 – Molecular nanotechnology K. Eric Drexler starts a molecular engineering software company called Nanorex and describes nanotechnology as deterministic rather than stochastic leading to the concept of “molecular nanotechnology” Small bearing Molecular gear train Planetary gear http://www.nanoengineer-1.com

• Late 1980s Development of cluster science (fullerenes, carbon nanotubes) and the scanning tunnelling microscope (STM)

Applications

Nanostructures and Nanomaterials

Length scales <100 nm - 1-D – nanotextured surface – thickness - 2-D – nanotubes/nanowires – long - 3-D – nanoparticles Racetrack memory Iron atoms on a copper surface Catalysis Integrated circuits Magnetic storage

Applications

•Nanotechnology gives sensitive read-

out heads for compact hard disks

• This year's physics prize is awarded for the technology that is used to read data on hard disks. It is thanks to this technology that it has been possible to miniaturize hard disks so radically in recent years. Sensitive read-out heads are needed to be able to read data from the compact hard disks used in laptops and some music players, for instance.

• The GMR effect was discovered thanks to new techniques developed during the 1970s to produce very thin layers of different materials. If GMR is to work, structures consisting of layers that are only a few atoms thick have to be produced. GMR can also be considered one of the first real applications of the a promising field of nanotechnology .

Applications

Carbon nanotubes and fullerenes Aerogels Hard materials

Applications

Cosmetics Biology and medicine

Public perception

Public perception

Carbon nanotubes Self-replicating nanobots Grey-goo SCIENCE FICTION!

Asbestos fibres

Public perception

Characterisation

Materials Science

Structure Characterisation Properties Preparation Structure Curiosity?

(physics)

Surface Science

Properties Structure Performance Processing Characterisation Properties Processing

Nanotechnology

Performance

Surface properties

• A clean surface has a different atomic structure to that of the bulk.

• Therefore the surface has different electronic, chemical, magnetic, and physical properties.

• These properties can be modified with the adsorption of other atomic species.

A bulk-terminated silicon surface A bulk-terminated silicon surface Holmium on silicon

Tools of nanotechnology - microscopy

• Due to diffraction optical microscopy limited to a resolution of ~200 nm and magnifications of 2,000 – shortest wavelength is for blue light at ~450 nm  

h p



h mv

 = wavelength, h = Planck’s constant, p = momentum, m = mass, v = velocity • Using electrons overcomes this limit to allow resolutions as low as 0.05 nm and magnifications of up to 2,000,000

Scanning Electron Microscopy (SEM) Transmission Electron Microscopy (TEM)

An SEM image of pollen TEM

Tools of nanotechnology - microscopy

• A recently established £5M world-class research facility for performing electron microscopy, surface analysis and nanolithography • Includes one of the world’s most powerful microscopes – 1 Å resolution • Allows atomic imaging of advanced nanomaterials in semiconductor, chemical and electronics technologies • Studying key interfaces in electronics devices, stability of catalytic nanoparticles and magnetic nanoclusters JEOL JEM 2200FS

Scanning tunnelling microscopy (STM)

• Developed in the early 1980s along with atomic force microscopy (AFM) • STM – an atomically sharp tip is brought extremely close to a surface until an electrical current flows between the two – this is quantum mechanical tunnelling • The detected current usually depends on where the atoms are located on the surface A 1-100 nA Tip 0.1-3 V Surface Tunnelling current • Ideally the STM tip will be atomically sharp • This can be achieved by electro chemically etching tungsten wire in a strong base (KOH or NaOH)

Scanning tunnelling microscopy (STM)

Silicon STM image

Silicon

• Most widely studied surface due to its technological importance • Model of the atomic positions at the surface developed 3 nm

30 nm

Silicon(111)7x7 STM image

Single atomic step.

Brighter region is 0.34 nm higher than darker region.

e e 10 keV

Material Properties - Microscopy

1-100 nA e 200 keV A 0.1-3 V e SEM

Earwig’s claw

TEM e e -

Si dumbbells

AFM

Fe nanoclusters

STM

Si(111) 7x7

Electron microscopy Scanning probe microscopy

Electrons

e Information Depth < 5 nm e -

Material Properties - Spectroscopy

h n

Photons

e ID: 1 nm (UV) 1 – 5 nm (X-ray) e -

Atoms

He* ~3 – 5 Å

Permalloy Post Cleaning

41000 36000 31000 26000 21000 16000 Data C O O2 Ar Ar2 Fe Fe2 Fe3 Ni Ni2 Ni3 AES03 AES04 Ni4 Ni5 Next Day Permalloy 11000 0 100 200 300 400 500

Energy (eV)

600 700 800 900 1000 Auger electron Si(111)-SiO Photoemission (UPS or XPS) 2 Metastable de-excitation (MDS)

Nanofabrication

• Two general approaches to nanofabrication: •

Bottom up

, i.e. building things atom by atom • Examples: DNA molecular construction, molecular and atomic self-assembly •

Top down

, e.g. lithography • Examples: fabrication of microprocessors using deep-UV lithography (now sub-100 nm), atomic-layer deposition, MEMs, dip-pen nanolithography using AFM, spintronics Molecular gear – bottom-up Integrated circuit – top-down

Nanofabrication – bottom up

Quantum Corral

Arrangement of 48 iron atoms on Copper(111). Temperature = 4 K IBM California

Nanofabrication – bottom up Arrangement of 48 iron atoms on Copper(111). Temperature = 4 K IBM California

Nanofabrication – bottom up Arrangement of 48 iron atoms on Copper(111). Temperature = 4 K National Institute of Standards and Technology

http://www.physics.nist.gov/Divisions/Div841/Gp3/epg_home.html

Self-assembly - nanowires

• Rare-earth metals deposited on to silicon and germanium leads to the growth of nanowires • Potential for use in nanocircuits 700 x 700 nm 2 • The nanowires here have thicknesses in the range 1.5 – 5.3 nm and lengths of up to 300 nm 29 x 12 nm 2 • Imaging between the nanowires shows the surface properties and atomic positions are modified

Self-assembly - nanowires

Clean germanium surface Nanowires naturally form when holmium added to surface. Rods are 0.15 nm wide 120 nm x 120 nm

Self-assembly - nanowires

Nanorods formed with a low (0.1 ML) coverage of Ho on Ge. Top image: 14 nm x 33 nm Measured (top) and simulated filled-states STM images for the Ge-Ho nanowires

Nanolithography – top down

• The fabrication of integrated circuits currently uses deep-UV photolithographic techniques • Feature sizes are limited by diffraction of the light source • De broglie:  

h p



h mv

• Therefore the heavier a particle is the smaller the diffraction limit • Electron beam lithography also used although electron-solid interactions restrict feature size • Atoms!

Photolithography

Nanolithography – laser cooling

• One approach to atom lithography is to use the energy of metastable atoms to damage a resist and produce nanostructures  Neutral atom lithography • Electric and magnetic fields have a negligible effect on the trajectories of atoms • Laser-cooling has developed into a huge field in atomic physics (ultra-cold atoms, Bose-Einstein condensates, atomic clocks, atom optics, etc)

Nanolithography – York set-up

-60 0 450 600 The York apparatus for producing a metastable helium beam 2500 mm Collimation Focussing A scanning atomic lens

Atom lithography laboratory

Neutral atom nanolithography

• Photolithography uses physical masks and light optics (lenses) to produce nanostructures • Atom lithography uses light masks to produce the desired pattern • Atom optics Physical mask Light mask NIST

Neutral atom nanolithography

• A resist-coated surface is exposed to a metastable beam • This beam is selectively quenched (de excited) with a light mask • Pattern then transferred to a surface using etching SEM images of pillars etched using Ne* atoms

Summary

Nanoscience

“the study of phenomena and manipulation of materials at atomic and molecular scales”

Nanotechnology

“the design, characterisation, production and application of structures, devices and systems by controlling shape and size at nanometre scale” • Nanotechnology on scales of 100 nm or less • Applications in a huge number of areas relevant to our daily lives

Summary

• Various approaches to fabricating structures on the nanoscale •

Top down

, e.g. lithography.

•

Advantages

: massive parallelism possible, very fast, relatively simple •

Disadvantages

: theoretical limits on feature size, lack of control. For neutral atom lithography arbitrary structures a problem •

York research

: atom lithography •

Bottom up

, i.e. building things atom by atom.

•

Advantages

: deterministic control of individual atoms •

Disadvantages

: extremely slow, laborious, and time consuming •

York research

: nanowires

Further reading

Research Articles

• P Ball,

Natural strategies for the molecular engineer

, Nanotechnology

13

, R15 (2002) • K E Drexler

Engines of Creation

(New York, Anchor) (1986) • C Phoenix and E Drexler,

Safe exponential manufacturing

, Nanotechnology

15

, 869 (2004) • N C Seeman and A M Belcher,

Emulating biology: building nanostructures from the bottom up,

Proc. Natl. Acad. Sci. USA

99

, 6451 2002

Links

www.nano.gov – US National Nanotechnology Initiative www.nanotechweb.org – nanotechnology news and information www.nanotec.org.uk – Royal Society survey of nanotechnology www.nano.org.uk – Institute of Nanotechnology

“Course they will, the Ferret yawned; Dorian says they'll do it with nannywhatsit, little robot thingies - isn't that it, Dorian? Nanotechnology, Fergus - you're quite right; they'll have tiny hyperintelligent robots working in concert to repair our damaged bodies.” Dorian

– Will Self