Nanoscience – working small, thinking big

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Key text

Nanoscience involves working with objects on a very very small scale. How small? Well, have a look at the back of your hand. Using just your eyes you can focus down to a scale of 1 centimetre to 1 millimetre. At this scale the skin looks flat. However, get out a magnifying glass and you can see it's actually wrinkly with cracks and folds. The magnifying glass allows you to study the fine structure of the skin at less than a millimetre (or one-thousandth of a metre).

If you were to look closer with a microscope you could examine the cells that make up your skin. Now you're working at the scale of micrometres (one-thousandth of a millimetre), sometimes referred to as the microworld. Cells and bacteria are measured in micrometres, and electronic components on a silicon chip are usually around 1 micrometre in size.

Related site: Back to basics – Atoms and molecules Provides a number of annotated links to sites that introduce concepts related to atoms and molecules. (Australian Academy of Science)

To reach the nanoworld you have to go smaller again. A nanometre (nm) is one-thousandth of a micrometre (or one-billionth of a metre). This is the scale at which we measure atoms and the molecules they make.

For example, ten hydrogen atoms laid side by side measure a nanometre across and a pin head is around a million nanometres wide. The 'machines' inside our cells and the molecular constructions they put together are measured in nanometres.

Working at the nanoscale

The prospect of changing the big world by working in the nanoworld was first proposed by Richard Feynman back in 1959 (Box 1: Room at the bottom). But it's only been in the last decade that science and technology has given scientists sufficient mastery to enable them to start working directly in this strange world.

While it might be right under our noses, the world of the ultra small, in practical terms, is a distant place. It exists beyond any of our senses. We can't see or touch it. Light microscopes can't provide images of anything smaller than the wavelength of visible light (ie, nothing smaller than 380 nanometres) so they don't help much.

Physical and chemical properties change

Related site: Scanning Probe Microscopy (SPM) Describes common scanning probe microscopy techniques and provides links to images of the materials scanned using these techniques. (Missouri Botanical Garden, USA)

Recent developments in technology are only now allowing scientists to understand what is happening down at this level. While we can't literally see the atomic landscapes of molecules, we can model their composition and structure by using a variety of techniques such as X-ray crystallography, nuclear magnetic resonance spectroscopy and scanning probe microscopy.

Part of the challenge of operating in the nanoworld is that things behave differently when you go ultra small. Consider a lump of gold, yellowy gold in colour. If you were to break that lump into nanosize chunks, the gold changes colour depending on the size of the chunks. In the 10 to 100 nanometre range it can appear reddish. Indeed, by breaking down a 'bulk' material into nanosized particles you can often change many of its properties. By controlling the manner in which nanometre-scale molecular structures are formed, it is possible to control the fundamental properties of the materials these molecules build: properties such as colour, electrical conductivity, melting temperature, hardness, crack-resistance and strength.

Related site: Introduction to nanoscience A slide show explaining that the shape, properties and colour of a nanosolid are different from the bulk material. (Rice University, USA)

This is quite amazing when you think we are not changing the chemical composition of the substance. We're not adding a red pigment to the gold, just breaking it into smaller pieces. The physical and chemical properties change because we're opening up and exposing more surface area of the material. For example, if you break a cube of ice in half you increase its surface area without adding any extra volume of ice.

When particle sizes are reduced to the nanoscale, the ratio of surface area to volume increases dramatically. Since many important chemical reactions – including those involving catalysts – occur at surfaces, it is not too surprising that very small particles are staggeringly reactive. This is one of the reasons that chemists are very excited about nanoscience – if they can make more surface area, they get more catalytic action, giving the potential to speed up almost all physical and manufacturing processes.

Nanoscale construction

Constructing things on the nanoscale requires new ways of operating – ways that make a complete break from traditional construction techniques. One good example of this is the move away from traditional 'top-down' manufacturing processes in favour of 'bottom-up' approaches. This is best explained by considering work on nano-electronics.

Constructing electronic circuits from the top down

The miniaturisation of electronic circuits is a testament to the power of science and technology in the twentieth century. The best computer chips around these days can pack in around 40 million transistors, each measuring around a micrometre (one-thousandth of a millimetre) or less. This is electronics on a microscale, and it is done using what is called a top-down approach. It involves taking a large chunk of material, usually silicon, and slicing it up into many wafers. Patterns (circuits consisting of many transistors) are drawn on light-sensitive films on the surface of each wafer, using light, and then unwanted material between the circuits is etched away with acid.

This approach is called top down because you start with a large piece of material and whittle, cut and etch it down to the product you want. Most traditional manufacturing processes follow a top-down process.

When you start getting down to the nanoscale with electronics, the traditional top-down techniques using light-generated patterns aren't precise enough to draw and cut the circuits (for the same reasons you can't see the nanoworld – visible light is simply too 'big' to work with, with wavelengths ranging upwards from 380 nanometres). Although it is possible to pattern the circuits at the nanoscale without using visible light (eg, using X-rays or electron beams with much smaller wavelengths than visible light), there is a completely new way of building circuits.

Constructing electronic circuits from the bottom up

A possible way forward for nanocircuits was put forward by IBM scientists more than 25 years ago. They proposed that by tailoring the atomic structure of organic molecules it should be possible to create a molecular-sized transistor. However, it has only been in the last few years that a variety of nanoscale electronic components made from molecules have been designed and created by researchers. They are now able to build transistors and other electronic components from organic molecules, carbon nanotubes and semiconductor nanowires. But building individual molecular components is only part of the problem. The next challenge is how to assemble these nano-components into integrated devices.

This is a completely different way of building circuits. Instead of whittling down a big block of silicon, you're building from the ground up: creating molecules on a surface and then allowing them to assemble into larger structures. This approach is referred to as the bottom-up approach and it's one of the characteristics of a lot of the new nanoscience.

Manipulating atoms

Related site: A beginner's guide to nanotechnology Provides an overview of molecular nanotechnology. (Rocky Angelucci, 10 September 2001, Dallas Business Journal, USA)

Scientists are now attempting to manipulate individual atoms and molecules. (To get an idea of how difficult this is, try building something from LEGO blocks while wearing oven mitts.) But techniques for manipulating atoms are being refined and building with individual atoms is becoming easier. Eventually it could be possible to precisely construct any object using individual atoms and molecules (Box 2: Nanomanipulation).

Building by modules (just like living cells do)

Researchers already have some capacity to control many aspects of the nanoworld. However, many of the structures being built are in two dimensions and are relatively simple compared to some of nature's handiwork. Living cells, for example, are nanoscale devices that are constantly assembling complex structures one or two molecules at a time (eg, DNA synthesis).

Increasingly scientists are looking to see how the machinery found within living cells manufactures natural molecules and structures. An Australian company has combined several of nature's devices to create a biosensor that enables doctors to obtain results from blood samples in less than five minutes and diagnose patients more quickly (Box 3: In nature's footsteps).

Applications of nanoscience

The biosensor is not the only product to come from Australian nanoscience. An Australian company has used knowledge about the altered reflective ability of nanoparticles to produce a sunscreen that is effective in filtering UV radiation, yet does not leave a coloured film on the skin. Australian scientists have also been involved in the construction of nanosize capsules that could be used as an effective drug delivery system.

Dreams or nightmares?

Related site: Nanotechnology – the issues Outlines potential applications and some of the ethical concerns relating to nanotechnology. (Royal Society of Chemistry, UK)

As investment in nanoscience and nanotechnology continues, some people are voicing ethical, environmental and economic concerns. Media headlines have warned of the 'grey goo' (millions of self-replicating nanomachines) that could engulf the world, and Michael Crichton based his 2002 novel, Prey, on this concept. While this science fiction scenario is far-fetched, there are valid concerns, such as the effect of nanoparticles on health and the environment. But most scientists believe that nanoscience will lead to huge advances in medicine, biotechnology, manufacturing, information technology and other equally diverse areas.

Related Nova topics:

Buckyballs – a new sphere of science

Nanotechnology – taking it to the people

Box 1. Room at the bottom

'Up till now,' he said, 'we've been content to dig in the ground to find minerals. We heat them and we do things on a large scale with them...But we must always accept some atomic arrangement that nature gives us...I can hardly doubt that when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do.'

This was a momentous prediction: Feynman was forecasting that we would one day be creating and modifying materials at their fundamental level as opposed to just reworking nature's products.

The term 'nanotechnology' was first coined by Eric Drexler in 1986, in a book called Engines of Creation. Drexler imagined molecular manufacturing being carried out by tiny machines called 'nanoassemblers'. These would build self-replicating nanomachines – robots that would produce copies of themselves if supplied with the right materials.

Related sites

• There's plenty of room at the bottom by Richard P. Feynman (Zyvex, USA)

• Engines of creation – the coming era of nanotechnology by K Eric Drexler (Foresight Institute, USA)

Box 2. Nanomanipulation

Moving atoms

One aspect of manipulation at the nanoscale involves the ability to move atoms from one location to another to build different structures. This is much easier said than done. There are no tweezers small enough to pick up an atom. However, the tip of a scanning probe microscope (SPM) can be used to the same effect. One method simply involves placing the tip of the probe between two atoms and pushing one aside.

Another method involves picking up an atom on the tip of the probe and moving it to the desired location. In a famous example that was published in 1990, researchers moved 35 xenon atoms to spell the letters IBM on top of a crystal of nickel. The entire logo measured less than 3 nanometres. But the challenge is to construct useful materials and structures using this technique. This will involve not single SPM tips but whole arrays of tips working in parallel.

Researchers at Cornell University in the USA recently created an ultra-tiny SPM with a silicon tip only 20 nanometres wide and powered by a motor one-fifth of a millimetre in diameter. An army of these tiny SPMs could be used for patterning computer circuits on an incredibly fine scale, allowing millions of bits of information to be stored in an area no larger than the width of a human hair.

Spray painting with atoms

Another form of nanomanipulation involves laying down atoms in precise arrangements as atom-thin coatings. There are a variety of techniques that allow scientists to lay down multiple thin layers of different atoms in a carefully controlled way. Individual layers might only be a couple of atoms thick. It's like spray painting with atoms.

Semiconductor wafers made of silicon or compound semiconductors like gallium arsenide are coated in a variety of layers. The layers then have circuits cut into them using acids, lasers or ultraviolet radiation. Depending on the optical and electrical properties of individual layers, it is possible to create an enormous range of devices ranging from the laser-emitting semiconductors that read your CDs to computer chips and advanced memory chips.

Related sites

• Biotechnology as a route to nanotechnology (Ralph C Merkle, July 1999, Trends in Biotechnology, USA)

• Laboratory for Molecular Robotics, University of Southern California, USA
  • Nanorobotics
  • Layered nanoassembly of three-dimensional structures

Box 3. In nature's footsteps

One day our science might match nature in its ability to self-assemble wonderful structures that possess incredible properties. However, until that day, why not borrow from nature's library of success stories to build our own nano-devices? That's just how the Australian biosensor, one of the world's first nanomachines, came to be. This biosensor can detect vanishingly small concentrations of a substance. Its sensitivity is such that it could detect whether a sugar cube had been added to Sydney Harbour!

The biosensor is an amalgam of biological structures. First, it detects the substance being searched for with an antibody, just like in our immune systems. The antibody is connected to an ion channel switch which is contained within a membrane anchored to a gold electrode. When the antibody latches onto the substance being detected, an electrical current can be measured at the gold electrode. This approach promises a revolution in accurate, sensitive and inexpensive chemical detection. For example it could be used to detect environmental pollutants or bacteria used as biological weapons.

Approaches like this may one day have an armoury of sensors testing for all sorts of things on a tab the size of an icy pole stick. A drop of your blood or saliva might be placed on this tab and in moments you would be tested for a whole range of diseases and disorders. It really would be a revolution in diagnosis.

Related sites

• Critters on a chip (Scientific American Explorations)

• An introduction to the Ambri biosensor (Ambri Ltd, Australia)

• Australia considers threat of biological warfare (transcript of Lateline, 3 October 2001, Australian Broacasting Corporation)

• A biosensor that uses ion-channel switches (letters to Nature 5 June 1997)

Activities

• AccessNano (Australian Government Department of Innovation, Industry, Science and Research)
  
  • Provides a series of 13 teaching resources on nanotechnology. These include PowerPoint presentations, experiments, activities, animations and links to interactive websites.


• Molecular expressions (Florida State University, USA)
• Perspectives: powers of 10 – students draw the same object at different magnifications.
• Virtual scanning electron microscopy – an interactive Java tutorial that allows students to view specimens (eg, grasshopper, jellyfish) at different magnifications with a virtual scanning electron microscope.
• Powers of 10 – provides a series of pictures (from the Milky Way to electrons), each of which is an image of something that is 10 times smaller than the one before it.

• Interactive Nano-visualization in Science and Engineering Education (USA)
  • List of modules – a number of web-based educational modules about materials. 'Size and scale' includes topics such as 'Defining dimensions' and 'Does size matter?'  with links to relevant online activities. Scanning probe microscope – introduces the theory and application of these microscopes as tools of nanotechnology. The module 'Is smaller better?' has information that is relevant to nanoscience, but there are no online activities.

• Science NetLinks (American Association for the Advancement of Science)
  • Structure matters – explores the molecular structure of matter and how it can affect the physical characteristics of a specific material.

• Sciencemax (Reed International Books, Australia)
  • Small wonders – this activity is on the last page of this PDF file and asks students to design a prototype of a nanomachine. There are also a number of other tasks asking students to find out more about different aspects of nanotechnology.

• Discovery School (USA)
  • Future body – students investigate how electrical signals are used in the human nervous system. They look at how computer chips or electrodes might be used to repair or augment the system.

• Nanobiotechnology Center (Cornell University, USA)
  • Nanosmores and photolithography – students make an edible, layered biscuit to represent the process used to create a patterned silicon wafer using a substrate and a photosensitive chemical.

• NteQ Lesson Plan Builder (USA)
  • From little atoms grow giant molecules – students find out more about the periodic table and use the knowledge they have gained about atomic structure to answer questions about the development of nanoscale computer chips.

• Exploring the nanoworld (Materials Research Science and Engineering Center on Nanostructured Materials and Interfaces, University of Wisconsin, USA)
  • Structures at the nanoscale – shows how students can use LEGO bricks to demonstrate the nanostructure of solids.
  • Self-assembly: Building structures at the nanoscale – students make a square pattern of magnetic LEGO bricks using a 'top-down' and a 'self-assembly' approach.
  • Educator resources – provides a variety of activities related to nanoscale technology. The activities are presented under three headings – Nanoscale activities, Applications activities, and Societal implications activities.
  • Interdisciplinary education group – provides a variety of resources in addition to those mentioned above (eg, 'Nanoworld cineplex of movies' and 'Nanoscale video lab manual').

Further reading

• What colour is gold (by Paul Mulvaney)
• Pollution's sweet solution (by Michael Moylan)
• Nanoengineering smart particles (by Frank Caruso)
• Manipulating viruses to grow semiconductors (by Angela Belcher)
• Thermodynamic limits to nanomachines (by Denis Evans)
• Nanotechnology raises big issues (by Vijoleta Braach-Maksvytis)

• Down to the nearest billionth
  
• Treating and healing on three fronts
  
• The miracle and the infinite
  
• Toxicity under nano-surveillance
  

Useful sites

• Nanotechnology: Nature's toy box (Background Briefing, 14 November 2004)
  Looks at both the remarkable possibilities and potential risks of nanotechnology.
  http://www.abc.net.au/rn/talks/bbing/stories/s1241931.htm

• The house that nano built (The Buzz, 31 March 2003)
  An interview with the coordinator of the nano-house project at the University of Technology, Sydney.
  http://www.abc.net.au/rn/science/buzz/stories/s820758.htm

• Nanotechnology – mind the gap (The Buzz, 24 February, 2003)
  Covers the social and ethnical consequences of nanotechnology.
  http://www.abc.net.au/rn/science/buzz/stories/s791611.htm

• Bachelor of nanotechnology (The Buzz, 15 October, 2001)
  Discusses the nanotechnology degree being offered at the University of New South Wales.
  http://www.abc.net.au/rn/science/buzz/stories/s391251.htm

• Nanotechnology (The Science Show, 24 February, 2001)
  Features comments from two scientists working with nanometre-scale electronic computers.
  http://www.abc.net.au/rn/science/ss/stories/s250676.htm

Glossary

antibody. A protein produced by the body’s immune system in response to a foreign substance (antigen). An antibody reacts specifically with the antigen that induced its formation and inactivates the antigen. Our bodies fight off an infection by producing antibodies.

atom. The fundamental unit of all matter consisting of a nucleus of protons and neutrons surrounded by orbiting electrons (or in the case of hydrogen, just one electron). For more information see Back to Basics: Atoms and molecules (Australian Academy of Science).

catalyst. A substance that increases the rate of a chemical reaction without actually undergoing any change itself.

ion channel. A protein-coated pore in a cell membrane that selectively regulates the diffusion of ions into and out of the cell. An ion channel switches between open and closed when the protein undergoes a conformational change. For more information see Ions cannot cross membranes (University of Washington, USA).

membrane. A thin, pliable sheet or layer. Biological membranes consist of a double layer of lipids – organic molecules that are not soluble in water – and associated proteins. Biological membranes are selectively permeable – not all molecules can pass through the membrane. For more information see Structure of plasma membranes (British Broadcasting Corporation, UK) and Cell membranes (Kimball's Biology Pages, USA).

molecule. The smallest unit of a chemical compound that can exist. It consists of two or more atoms held together by chemical bonds. Molecules can vary greatly in size and complexity.

nanotubes. Extremely small tubes made from pure carbon. For more information see IPE nanotube primer (Institut de Physique des Nanostructures, Switzerland).

nuclear magnetic resonance (NMR) spectroscopy. Nuclear magnetic resonance (NMR) spectroscopy provides information on the position of specific atoms within a molecule by using the magnetic properties of nuclei. For more information see Nuclear Magnetic Resonance Spectroscopy (University of Calgary, Canada).

scanning probe microscopy. Scanning probe microscopes (SPMs) pass a needle-like probe over the surface of a molecule and record an image of that surface. Different SPMs can not only map the topography but also determine the type of atoms and their thermal and magnetic properties. Scanning tunnelling microscopes and atomic force microscopes are types of SPMs. For more information see Scanning probe microscopy (SPM) (Missouri Botanical Garden, USA).

semiconductor wafer. A tiny complex of electronic components and their connections, produced in or on a small slice of material (like silicon). For more information see Semiconductor manufacturing: How a chip is made (Texas Instruments, USA).

wavelength. The distance between two adjacent wave crests. Visible light and X-rays are both electromagnetic waves and differ from each other only in the length of the wave. The wavelength of visible light ranges from 400 to 700 nanometres while the wavelength of X-rays ranges from about 0.01 to 10 nanometres. The relatively long wavelength of visible light sets the limit of how small an image it can produce. For more information see Electromagnetic radiation (Back to basics, Australian Academy of Science).

X-ray crystallography. X-ray crystallography involves firing X-rays through the crystal of a molecule to produce a diffraction pattern. This pattern provides information on the structure of that crystal. For example, X-ray crystallography helped scientists discover that the DNA molecule exists as a double helix. For more information see Introduction to crystallography (Matter, UK) and X-ray crystallography (The British Biophysical Society, UK).