The Tools of Nanotechnology

Universeum28th March 2006

The Science Behind Nanotechnology

The Tools to Make and Analyse Nanostructures

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Matter consists of atoms

Each atom contains positively charged protons and an equal number of negatively charged electrons (protons are much heavier than electrons)

Charged particles interact via the Coulomb Interaction

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Opposite charges: negative (attractive force); Like charges: positive (repulsive force)If the number of protons is different from the number of electrons we have an ion

But: atoms are not really like miniature solar systems and electrons can behave like particles or like waves!

Classical Mechanics needs to be replaced by Quantum Mechanics at the atomic level

How big is an atom? 0.1 – 0.2 nm

On the atomic / nm scale energy and charge cannot be added continuously to matter, but can only be added in small pieces. Quanta for energy, electrons for charge.

The charge of an ion is quantised – it is not possible to add or subtract less than one electron.

(Money is quantised with the fundamental quantum of 50 ore)

Characteristic emission from atoms - e.g. Yellow Na lines

Energy levels too close to observe quantisation within a band

Manipulate the energy levels by changing the size of the particle

Bulk semiconductor

Gold and Silver Particles: Plasmon Resonance

Semiconductor Nanoparticles: Fluorescence

Size-dependent frequency of collective electron oscillations

Molecules are formed when atoms are brought together in a fixed structure.

All chemical bonds are caused by interactions between the electrons of the atoms.

The electrons are responsible for the chemical properties of atoms and molecules.

Electron interactions are key to nanotechnology. They combine atoms into molecules or nanoparticles. The bonds themselves can act as mechanical devices such as hinges or bearings.

Molecular switch – controlled by electric field direction or light or chemical environment..

On: conducting

Off: insulating

4,4'-Di(ethinylphenyl)-2'-nitro-1-benzothiolate

Different kinds of material important for nanotechnology:

Metals: Electrons are ”free” to move beween the metal atoms in the bulk. Good conductors of electricity. Free elecrons also scatter light efficiently.

Bulk metals follow Ohm’s law. V = IR.

This is not necessarily the case on the nanoscale.

Polymers or Macromolecules: usually based on carbon. Single molecules formed of repeating patterns in a chain. Generally they do not conduct electricity (but some special ones do and can be used e.g. as molecular wires or to make electronic devices, NP in chemistry 2000).

Biopolymers: DNA, proteins, polysaccharides

Ceramics:

Composed of different kinds of atoms (usually containing oxygen). Electrons are localised so do not conduct electricity.

Carbon Nanostructures:

Pure carbon materials, localised electrons produce a strong and stable structure. Delocalised electrons responsible for electronic properties.

Each carbon atom has 4 electrons that can interact with neighbouring atoms: for nanotubes, fullerenes and graphite, 3 electrons form localised strong bonds and 1 electron is delocalised

Molecular Recognition: ”Self-Assembly”

Molecules have shapes and charges. Often the electrons are distributed unevenly.

Because Coulomb’s law tells us that positive charges are attracted to negative charges, molecules can interact with one another by electrical (Coulomb) forces.

The ability of one molecule to attract and bind specifically to another is often referred to as molecular recognition.

Biological Systems make great use of molecular recognition e.g. Smell or taste detection.

Biomimetics: copying biology (e,g. Making sensors based on moelcular recognition, artificially producing surfaces with the same behaviour as lotus leaves,.....)

Related to molecular recognition is making use of the intermolecular interactions to induce self-assembly of interesting nanosystems

Large biological molecules can recognise one another and, in so doing, build the cells by which higher biological organisms are structured.

Molecular recognition combined with self-assembly is a key feature of Nanotechnology. Because much of nanotechnology depends on building from the bottom up, making molecules that can organise themselves on their own or with a supporting surface is a key strategy for manufacturing nanostructures.

To manipulate material on the atomic level it helps to ”see” the atoms

High resolution electron microscopy has made great advances and it is now possible to see individual atoms, even as smal as Li (1Å resolution).

High resolution Transmission Electron Microscope

Transmission electron microscopes use high electric voltages — as much as 400,000 volts — to accelerate a beam of electrons within a vacuum chamber. The beam is then aimed at a thin slice of the material under study. After the powerful beam of electrons passes through the sample, it is focused and projected onto either a monitor or photographic film to provide an image of the structure. Transmission electron microscopes can provide magnification as much as 1.5 million times. Since the electron beam must pass through it, preparation of the sample is critical.

Scanning Tunnel Microscope

Binnig and Röhrer, NP 1986

Possible to ”see” and MANIPULATE individual

atoms

STM scan of graphite

STM scans of carbon nanotubes

Atomic Force Microscope

Principle of AFM based data storage system

Actual image of data bits written on

PMMA

MILLIPEDE- 2D array of cantilevers

Image from: http://www.research.ibm.com/journal/rd/

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IBM’s Millipede

Magnetic Force Microscopy

MFM picture of the bits of a hard disk (30µm x 30 µm)

STM: Electron waves on a CNT Peapod

D. Hornbaker and A. Yazdani

STM studies of the electronic structure of carbon nanotube ”peapods”

Captured molecules influence the electronic structure and behaviour without changing the atomic structure of the surrounding carbon cylinder

How to make ”top down” nanostructures

Llithography in clean room conditions (MC2 Chalmers)

• Chalmers logo made by electron beam lithography.

• Gold on a silicon surface.

• 8 m in diameter and the narrowest linewidth is 30 nm.

• About 100 of these may fit in on the cross section of a hair.

Bengt Nilsson SnL (Swedish nanometer laboratory)

”Large” structures can be made with photolithography. Small structures with electron beam lithography but principle is the same

LOL2000

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Mask

Expose the desired structure to radiation using a mask

Develop the Resist

Irradiation damages the photoresist polymer

The damaged part can be removed with chemicals

Evaporate a thin layer of metal onto the structure

LOL

Dissolve the LOL layer

Photolithography for the large structures. E-beam lithography for the small electrodes

For commercial production of nanostructures, we need something quicker and much less expensive:

Nano-imprint Lithography: back to the SPM

Lithography is a complicated and time-consuming but very powerful technique for making nano structures in a controlled way

But very expensive!

Top down nanostructure processing at Chalmers MC Lab.

Access to lithography facilities, SPM and electron microscopes

Some links:

Slightly more scientifically advanced book:

”Nanotechnology: basic science and emerging technologies” Wilson et al. (Chapman & Hall 2004)

Web Links:

Exploring the nanworld with LEGO:http://mrsec.wisc.edu/Edetc/LEGO/index.html

Self-Assembly: http://www.math.udel.edu/MECLAB/Projects/SelfAssembly/selfassembly1.htm

General: http://www.nano.gov/html/edu/eduteach.html

http://www.mrsec.wisc.edu/Edetc/index.html

http://www.sciencemuseum.org.uk/antenna/nano/