Questions for P. Alex Greaney

Learn more about my research In January, 2007, P. Alex Greaney answered visitors questions about nano sensors.

Your Comments, Thoughts, Questions, Ideas

Anonymous's picture
Anonymous says:

What are nano sensors?

posted on Mon, 01/15/2007 - 4:10pm
P. Alex Greaney's picture
P. Alex Greaney says:

In my research group, when we talk about sensors we mean chemical
sensors, that is, sensors designed to detect the presence of a
particular type of molecule or biological agent. By "nano-sensors" we
mean that the sensor "works" by exploiting phenomena that only
occur at the nano-scale. In general nanotechnology is not about making
things small for the sake of having smaller things, rather, it is that
when things are very small (billionths of a meter across) they behave

There are many types of nanoscale behavior that can be used to detect
different types of molecules, and there are many scientists working to
understand them and make use of them. In fact there are several types
of nano-sensors already in operation. At U.C Berkeley researchers have
developed sensors that make use of tiny cantilevers to detect the
explosive TNT in concentrations as low as parts per trillion. Sensors
based on networks of carbon nanotubes have also been developed. Theseare used to detect hydrogen by measuring the change in the electricalproperties of the nanotubes. In my research I am studying if
vibrational interactions at the nanoscale can be used to "finger
print" and detect different types of molecules. While all of these
sensors work in different ways they all take advantage of nanoscale

posted on Mon, 01/29/2007 - 11:00am
Anonymous's picture
Anonymous says:

How are you going to collect data from these devices if they are scattered into the air to detect pathogens. A transmitter or energy source would be too large to be attached to the device. How would this process be feasible.

posted on Mon, 01/15/2007 - 6:37pm
P. Alex Greaney's picture
P. Alex Greaney says:

The idea of a nano-sensors is not that the whole sensor be on the
nanometer length-scale but rather that the sensor used phenomena that
only occur on the nanoscale in order to do its sensing. However, you
are correct that a sensor by itself is useless, a low-cost
self-contained detector unit (that might be wildly distributed to
collect environmental data) also requires: some kind of computer to
decide when something had been detected, a way of communicating that
it has detected something, and finally a power supply to run all of
this. The incorporation of each of these processes into one package is
not science fiction, in fact, there many research groups and even
several companies that make such a thing. At the moment these "motes"
as they are called are not terribly small---only a couple of
millimeters in length along each side. These motes are not just for
sensing chemicals either but can be for measuring many other things
such as temperature, humidity, pressure, light intensity and so on.

To further miniaturize motes---to make truly useful as distributable
detectors---each of the components must be made smaller and less
expensive. Luckily nanotechnology may be able to help us here too. In
fact my work on nano-sensor is only one part of a program at
Berkeley devoted to just this task. This research program includes
scientists developing nanotechnology-based solar cells for energy
scavenging, developing nano-scale wireless transmitters
for communication, and developing ways to integrate all
of this into a single self-contained package.

posted on Mon, 01/29/2007 - 11:00am
karina's picture
karina says:

I want to know If you think it is possible to creat ozone by any nano method, I say this because lack Ozone is affecting the wether and overheating the world, if Im not wrong, it will mealt the north and south pols and so, the level of water in the oceans is going to grow up destroying cities and creating a big mundial problem

posted on Thu, 01/18/2007 - 2:50pm
P. Alex Greaney's picture
P. Alex Greaney says:

Ozone is the tri-atomic molecular form of oxygen (the oxygen that we use when we breath is the more stable diatomic form). It actually occurs naturally and is being produced continuously in the atmosphere by reaction of diatomic oxygen with sunlight. Ozone is also an undesirable by-product of all sorts of human activities, so much so that the main problem with ozone is not making more of it but making less of it.

Most of the ozone in the atmosphere resides at a very high altitude in a region of the stratosphere called the ozone layer. Up there, the ozone absorbs much of the high energy ultra violet light from the sun that is harmful to living things, and so a thinning of the ozone layer is indeed worrying. The reduction of the ozone layer is caused by chlorine and bromine radicals in the stratosphere which can breakdown ozone. Small quantities of these chemicals occur naturally in the stratosphere, and normally the destruction of ozone that they cause is balanced by its continued creation by the sunlight. The problem is that over the last century we humans have released a lot of chlorine and bromine containing chemicals into the environment. Some of these have made it to the upper atmosphere and are now destroying the ozone faster that is being created. The remedy to this problem is not to make more ozone but to reduce the amount of chlorine and bromine. If this is done the ozone layer will come back into balance by its self.

At ground level, where we live, an excess of ozone is in fact harmful. It is produced by (amongst other things) electrical discharges such as thunderstorms and in high voltage electrical equipment. It is very reactive, particularly in the presence of sunlight and is one of the key ingredients in the photochemical smog that shroud many industrialized cities. It is also somewhat toxic, especially to plants. This is not all bad as ozone is sometimes used to sterilize the both drinking water and the air in hospitals.

So are there ways in which nanotechnology can help reduce the ozone destroying chemicals in the upper atmosphere and are there ways in which nanotechnology can ameliorate the problems from low lever ozone?

The answer is yes. nanotechnology has the potential to help in a couple of ways. Firstly nanotechnology may permit us to make efficient thermoelectric materials. These are materials that can be made to cool down by running an electric current through them. This would permit efficient refrigeration devices that don't require the chlorine and bromine containing compounds that cause the damage to the ozone layer. In the lower atmosphere, nanotechnology may permit us to develop small inexpensive detectors that can monitor your personal environment. Being able to know if there are harmful levels of ozone of ultraviolet light environmental enables us to safely manage the risk that they pose.

posted on Tue, 03/20/2007 - 3:32pm
Anonymous's picture
Anonymous says:

A worst-case scenario regarding nanotechnology is "grey goo" - what is "grey goo" and how serious do you think this risk is?

posted on Fri, 01/19/2007 - 9:16am
P. Alex Greaney's picture
P. Alex Greaney says:

The term "grey-goo" was coined by the famous nanotechnology proponent
Eric Drexler to describe a possible catastrophic end point of creating
nano-scale self-replicating robots. The idea explained by Drexler is
that if these robots get out of control they would carry on performing
their basic tasks, that is, replicating, and would eventually consume
all living things on earth, turning it into a seething mass of
nano-robots---or grey-goo. It is a particularly vivid and alarming
image; however, thankfully, it is at the moment the stuff of science
fiction. Eric Drexler himself said "I wish I had never used the term
'grey goo'", (Nature 10 June 2004).

Making nano-robots is not the ultimate aim of nanotechnology. Rather
it is to exploit the special properties of materials that occur when
the materials are tens of nanometers in size. That said the
cautionary message of the grey-goo scenario is still pertinent. We
must be careful in the development and adoption of nanotechnology
because, as with all human endeavors, we cannot fully foresee all the
implications of our actions. We must ensure that the benefits
outweigh the potential dangers whilst being mindful that the
people enjoying the benefits may not be the same people hazarding the

posted on Mon, 01/29/2007 - 11:01am
Anonymous's picture
Anonymous says:

How did you get into this field of study?

posted on Fri, 01/19/2007 - 9:20am
P. Alex Greaney's picture
P. Alex Greaney says:

I grew up in the UK and while in high school I enjoyed both
Chemistry and Physics. Not being able to chose between them I studied
Materials Science at university. This is the study of stuff, that is
materials, which are a part of everyone's daily life, from the ceramics
used to make toilets to the polymers used in bullet proof vests, and
from the metal used to make airplanes to the semiconductors used for
computer chips.

My undergraduate studies taught me a lot about what we understand in
the world, but my graduate studies taught me about how much we still
don't fully understand. One example is the field of nanoscience. Why
is it that many things behave differently when the become very small?
The basic laws of physics governing how materials work is not changing but something about their extremely small size affects their properties.
For theorists, trying to unravel these mysteries makes
nanoscience an exciting field to work in.

posted on Mon, 01/29/2007 - 11:01am
Anonymous's picture
Anonymous says:

What exactly is nanotechnology? Is there nanotechnology in the iPod Nano?

posted on Fri, 01/19/2007 - 9:20am
P. Alex Greaney's picture
P. Alex Greaney says:

Nanotechnology is the deliberate engineering of materials at scales of
less than 100 nanometers to achieve size-dependent properties. This
means that nanotechnologqy is about making things very, very small---on
purpose---and then making use of the special way that these very small
things behave.

Whether any of the technology inside Apple's iPod Nano satisfies this
description I do not know. I am afraid that you will have to ask Apple
that question.

posted on Mon, 01/29/2007 - 11:01am
chris opland's picture
chris opland says:

I have heard that nanotubes will allow us to have an elevator to space. How long until that happens?

posted on Sat, 01/20/2007 - 4:00pm
P. Alex Greaney's picture
P. Alex Greaney says:

The space elevator is an ingenious idea that would allow cargo to be
carried cheaply into space. The fundamental concept is to use the
earth's rotation to maintain a tethered counterweight out in
space---like a gigantic teatherball. As the cable connecting the
counterweight to earth would be taught it would be possible for some
sort of machine to climb up and down it ferrying things into space.

As the counterweight is tethered it must rotate at the same rate as the earth, and so in order to work the counterweight needs to be far enough away from the earth that the centrifugal force wanting to fling it into space is larger than the force from the earth's gravitational attraction. This occurs if the weight is more than 35,800 km above the earth's equator (about one tenth the of the distance to the moon). So, at least in terms of distance, the space elevator is a long way off!

Leaving aside the practical problems of how you make something this
long and how you get one end of it into space, the tether for a space
elevator must be able to carry its own weight as well as support the
weight of whatever is trying to climb up and down it. Such a tether need not be uniform in width---the end of the tether 35,800 km out in space is supporting the whole weight of the tether; however, at half that distance the supported weight is considerably less and the tether need not be as thick. It turns out that at its thickest point the diameter that is required to support the weight of the rest of the cable depends exponentially on the ratio of tensile strength to density of the material that the cable is made from. So, a space elevator tether made from high tensile steel, that might safely maintain a stress of up to 1 GPa would have to have a thickness of a whopping (and impracticable) 100Km at its thickest section, whilst a
tether made from carbon nanotubes, which are a third as dense and can
sustain 50 times the stress, would need a thickness of roughly 1cm at its widest point to be able to support a itself.

It turns out that the mechanical properties of carbon nanotubes are so
remarkable that they are the only material that come close to making
the idea of the space elevator feasible. However, there are still some
materials-related problems. Carbon nanotubes are tiny; only tens of
nanometers wide and few centimeters long. This has several important
consequences for the space elevator: Firstly it makes measuring how
strong carbon nanotubes are very difficult as measuring their strength
requires measuring their width and so we don't have a good idea of exactly how strong carbon nanotubes really are---reported measurements of strength of can vary by as much as a factor of 10. Secondly, it means that the 35,800km tether of a space elevator must be made of lots and lots of nanotubes joined together in some way. In general, the strength of a material is not governed by the material its self
but the defects that reside in it. Rather like a chain that's strength is limited by its weakest link, the longer a cable is the larger the chance of an egregious defect that will lower its strength and cause it to break.

So the space elevator is not just a long distance off; it is many years from being practically possible. That said progress is being made. There are many research groups developing ways to grow carbon nanotubes reliably and inexpensively, and there are also several research groups that have developed ways to spin long yarns made from nanotubes. So, while it may be a long time before we see a carbon nanotube space elevator, carbon nanotubes are already being used for their mechanical properties in more down to earth applications like skis and tennis racquets. Finally, carbon nanotubes are not usefull just for thier mechanical properties. Their electrical and optical properties are also very interesting.

posted on Mon, 02/05/2007 - 6:59pm
Anonymous's picture
Anonymous says:

How can nanotechnology help us in everyday life?

posted on Sat, 01/27/2007 - 4:16pm
P. Alex Greaney's picture
P. Alex Greaney says:

This is a good question. In general it is hard to forecast how any new technology will impact our daily life. For example, who could have predicted that the invention of a device for talking to some one a long way away (the telephone) would not just allow you to call for help in an emergency, but also let you order a pizza, or call your friend to make sure you don't wear the same outfit to a party. The impact on our lives depends not just on what the new technology does but also on how we embrace it. As individuals and our society as a whole we adapt the way we live to take advantage of all resources available to us. So much so that now our daily lives are dependent on the telephone.

In the same way it is hard to predict how nanotechnology might impact
our daily life. Nanotechnology has the potential to make a huge difference to our lives although its effect is likely to be indirect. There are a number products that you may use every day which already use nanotechnology, from stain resistant trousers to sunscreen. However, leaving aside these bagatelles, the real impact that nanotechnology can have is in how it may help us solve some global problems that afflict the whole of humanity. Problems such as managing climate changes, fighting disease, and providing clean drinking water.

There is enormous potential for efficient and inexpensive solar cells using nanoscale phenomena that could harness the sun to provide clean energy, and so reducing our dependence on fossil fuels. Nanotechnology is already being used in the next generation of high power batteries which could power electric vehicles. In medicine, nano-scale materials can be engineered to interact with specific individual biological molecules on the sub-cellular level. These nano-materials are being developed to provide a way of delivering drug therapies to specific diseased cells in you body with out affecting the rest of your healthy cells. On a more basic human level, nanotechnology based methods for cheaply purifying water are being researched. And more importantly still, scientists are devising inexpensive nano sensors that can warn if water is unsafe to drink.

For millions of people in the developing world being able to take safe
drinking water for granted will make an enormous difference to their
daily life. On the other hand providing an effective clean renewable
energy source will, for many of us, not change our day to day lives, but will allow us to continue the standard of living that we are accustomed to without the ruinous consequences of environmental destruction and global climate change.

posted on Mon, 02/05/2007 - 7:03pm
Anonymous's picture
Anonymous says:

how did they come up with the name nano?

posted on Sat, 02/03/2007 - 2:44pm
P. Alex Greaney's picture
P. Alex Greaney says:

The term "nano" used in nanotechnology comes from the "Le Systeme International d'Unites" or SI units. This is the internationally agreed upon set of units of measure that includes meters, kilograms, and seconds and is based on the French metric system that was introduced around the time of the French revolution.

As well as defining a fundamental set of units such as the length of a meter and the duration of a second, the SI system includes an set of prefixes that denote powers of 1000 of something. These prefixes provide a concise way of referring to large and small quantities. For example, instead of having to say one-hundred-thousand volts we can use the prefix "kilo" meaning 1000 and say 100 kilovolts or we can even use the prefix "mega" (meaning one million or (1000)x(1000)) and say 0.1 megavolts.

As science has progressed to study larger and smaller things more prefixes have been invented so that we now have a prefix for every power of 1000 from "yotta", which is one septillion (or 1 followed by 24 zeros), down to "yocto", which is one septillionth (one divided by one septillion). The prefix nano was invented in 1960 to mean one billionth, so a nanometer---the length-scale with which nanotechnology is concerned---is 0.000000001 of a meter.

The etymology of the prefix is the ancient Greek word "nanos" meaning dwarf or little old man. Why the International Committee for Weights and Measures chose the Greek word for dwarf rather than the Latin word "pumilius" or the Danish word "dvaerg" I do not know. They have used both of these languages for the roots of other prefixes. Similarly, the choice of "dwarf" over "midget", "pygmy", "lilliputian", or even the more mundane "tiny" is equally perplexing.

posted on Tue, 03/20/2007 - 3:35pm
Anonymous's picture
Anonymous says:

Could nanotechnology be dangerous?

posted on Sun, 02/11/2007 - 2:36pm
P. Alex Greaney's picture
P. Alex Greaney says:

Yes. Everything unknown has the potential to be dangerous. Only by studying things do we learn what the risks or benefits are. We should not let the potential for risk thwart intellectual discovery but we should, and do, proceed circumspectly.

Even if fully understand it most human technology has the potential to be harmful, either by misuse or by malicious intent. However, by using our understanding of the technology, and the science underpinning it, we are able to manage the risks and ensure that the they are out weighed by benefits the technology offers. A good example is an x-ray machine. X-rays are damaging to the human body and can cause cancer. However if you have broken your arm the minor risk from the exposure to x-rays is far out weighed by benefits of a doctor being able to identify the break and correctly set the bone.

We know that nanotechnology has enormous potential to help human-kind as it provides a direct way of engineering properties of materials by changing their size. However we are still in the early stages. At the moment we know relatively little about the long term toxicology of nano-stuff, nor do we know about how easily the could get in the environment and what the long term effects of this would be. Only by studying these issues will we find out.

posted on Tue, 03/20/2007 - 3:38pm
Alexandra the greatness's picture
Alexandra the greatness says:

why is it called nanotechnology?

posted on Wed, 02/14/2007 - 12:20pm
P. Alex Greaney's picture
P. Alex Greaney says:

The word "nanotechnology" is umbrella term that covers all researchers working on making technological advances by controlling the structure of materials on the nanometer size scale. This is not confined to any particular field of study but includes engineers, biologists, physicists, and chemists. Many things---across many fields of study---start to behave differently then the get down to the nanometer size scale. There are many reasons for this different behavior and the science behind size dependent behavior in biochemistry is very different from small size effects in materials science. However, in all cases this give us a new and direct way to engineer the properties of things towards out technological goals by controlling the size.

posted on Tue, 03/20/2007 - 3:39pm
Anonymous's picture
Anonymous says:

Can you explain what personal nanofactories are and how they would work?

posted on Sat, 02/17/2007 - 12:49pm
P. Alex Greaney's picture
P. Alex Greaney says:

Nanofactories are a more elaborate extension of the idea of nano-robot assemblers. They are a more complicated hierarchical system which aim would overcome some of the issues of scale and time that prohibit nano-robot assemblers from being practically useful. The idea is that one would supply your nanofactory with some basic chemicals. Millions of nanoscale machines break these chemicals into their individual atoms and then millions more machines would assemble these into small building blocks such as simple pairs of atoms. These small building blocks are then taken by other machines and assembled into larger blocks---which are in turn assembled into still larger blocks. After 30 or so iterations of this assembly process: hey presto! you have a new television.

The ability to build something large and complicated like a television or computer chip in one go is very appealing. It would free us from many of the constraints that limit modern manufacturing. There are some amazing animated movies on the internet illustrating the concept beautifully (for example and it is easy to think that these devices will soon be revolutionizing or lives; however, if we think a little more carefully about the problem we see that human engineered nanofactories will remain a dream of futurists.

One of the often quoted arguments against the practicality of nano-robot assemblers is that even if you had millions of them it would take tens or hundreds of years to build anything big enough for us to be able to see it with the naked eye. The problem has to do with scale. Any object weighing a few grams is composed of approximately one-hundred-billion-trillion (1 followed by 23 zeros) individual atoms. So that if we had a million nano-assemblers each assembling a million atoms per second, it would take them around 3 thousand years to build an object weighing a few grams. The nano-factory idea overcomes this problem to some extent with its hierarchical design; however, a similar problem exists with the size of the blue print for whatever the nanofactory is making. If the end product contains one-hundred-billion-trillion atoms then we need some way of telling the factory the position of all of those atoms, and that requires a lot of data to be stored, processed and transmitted. For most devices that we use, such as a television, we do not need to know the positions of all the atoms in it; however there are a few cases where this is no longer the case. We are now approaching the realm where the individual transistors within a computer ship are on the nanoscale and are countable numbers of atoms in size. For these very specialized applications even an extremely slow and expensive nanofactory is very desirable.

The most fundamental problem is that chemistry dose not work in the same way as we would assume from the intuition we acquire from our daily surroundings. In our everyday world things are deterministic, we can make cogs and leavers and we know how they will move when we use them. On the atomic scale every process is stochastic---meaning random. The net motion of atoms is a result in an imbalance in random backwards and forwards motion. Similarly we cannot pick up and atom and then just as easily let go of it again because the things that we are using to pick up the atom are other atoms.

Although human engineered nanofactories are unlikely, personal nanofactories do exist, and they are very personal indeed. Every cell in our bodies can be considered a personal nanofactory as it acts in just the way I descried above. There are enzymes that act as templates to build proteins with atomic precision. These proteins are assembles into larger building blocks which are used to make the skeletal structure of the cell. There are even motors that drive up and down this structure transporting these building blocks to the places in the cell where they are required.

posted on Mon, 04/02/2007 - 11:51am
Anonymous's picture
Anonymous says:

What are the risks of making nanotubes that mimic nature? What are the positives and negatives of this type of use for nanotechnology?

posted on Sat, 02/17/2007 - 12:53pm
P. Alex Greaney's picture
P. Alex Greaney says:

Carbon nanotubes, like diamond and graphite, are naturally occurring structures of carbon. They form when carbon is vaporised and cooled very quickly, as can occur in an electric arc. They can also form under more easily controlled conditions with the help metal catalyst particles. The catalyst seeds the growth of the tube and the tube grows off the end of the metal particle. Although carbon nanotubes occur naturally, the conditions under which they form are unusual and so their existence was only discovered in 1991. Since then scientists have come to realize the phenomenal properties of carbon nanotubes and some researchers are trying to make use of them in applications that mimic nature.

In the biological world living organisms have had millions of years to adapt and evolve amazing solutions challenging structural problems. One example is the hairs on the feet of a gecko that allow it to adhere to walls and walk on the ceiling. Researchers are trying to use carbon nanotubes (amongst many other things) to mimic the structure of the hairs on geckos' feet. The goal is to make a new kind of adhesive that could stick to walls like the gecko but would also use the superior properties of carbon nanotbes and so, unlike the gecko, could also stick to very hot things.

The danger that we face when we try to mimic natural solutions to design problems is that in nature function often dose not just stem one clever design feature but rather comes from a systems in which every component is subtly interdependent. When we try to imitate nature with other materials we run the risk of missing the subtlety and balance that really makes the biological solution work.

posted on Mon, 04/02/2007 - 11:53am
Markgot1337'd's picture
Markgot1337'd says:

Is it true that someone made a model car outof atoms and the wheels are buckyballs?

posted on Sun, 02/18/2007 - 4:44pm
P. Alex Greaney's picture
P. Alex Greaney says:

Yes! In 2005 researchers at Rice University made a 4 nanometer long car that had organic carbon molecules for axles and bucky balls for wheels (Nano Letters October 2005). In fact, that was all it had, it was simply two pairs of axled wheels like a cart. The car is essentially a single molecule and was made by a series of chemical reactions. The goal in making the nano-car was to learn about manipulating molecules into complicated structures such as this, and the cars themselves have been used to studying friction at the atomic scale by pushed the car across an atomically smooth gold surface.

Since their first bucky ball car the team at Rice have gone on to make several other more complicated nano cars which have different molecules for wheels. They have even made a car has has a small motor that turns in one direction propelling the car when light is shined on it.

posted on Mon, 04/02/2007 - 11:54am
Anonymous's picture
Anonymous says:

Will nano technology help scientists end Global Warming?

posted on Sat, 03/10/2007 - 3:25pm
P. Alex Greaney's picture
P. Alex Greaney says:

No. Science in general can not stop global warming, nor is it the roll of scientists to do so. Science is a way of understanding the observations that we make about the world around us. Science can provide us with understanding about the earth's atmosphere, its ocean currents, and how these, and many other things, play a role in influencing the earths climate. Science can inform us about how the earth's climate is changing and what combination of factors might be causing it. Science can even even help predict how humankind's actions might influence the climate in the future. However, science can not change anything. Action to stop continuing human influence on the climate can only come from our individual willingness to do so, and collectively through political political action. Technology in general (including nanotechnology) may provide us with tools that could make such individual changes easier and collective changes more politically palatable. For example providing devices that make more efficient uses of electrical energy, and providing cost effective alternatives to fossil fuels. However these will only impact global climate change if we make use of them.

posted on Mon, 04/02/2007 - 11:57am
From the Museum Floor's picture

What are nanotubes?

posted on Mon, 03/12/2007 - 1:31pm
P. Alex Greaney's picture
P. Alex Greaney says:

Solid carbon can take may forms, called allatropes, in which the atoms of carbon are are arranged in different repeating patterns. Diamond, one of the hardest materials known on earth, and graphite, the very soft material that is used to make pencil lead are both alatropes of carbon. In diamond each carbon atom bonds to four other carbon atoms whilst in graphite each carbon atom is bonded to three other carbon atoms. Generally speaking carbon atoms likes to put as much space between each of its bonds as is possible so in diamond the atoms are arranged in a uniform tetrahedral pattern while in graphite the atoms are arranged into a sheet which is only one atom thick. All the atoms in the sheet lie in the same plane and the bonds form a honeycomb-like pattern of tesselating hexagons. A single sheet of carbon atoms is called graphene and graphite (the stuff in your pencil) is made up of millions of them all stacked on top of each other like a ream of paper. The atoms within a graphene sheet are strongly bonded together but each sheet is only weakly bonded to the other sheets, which is why the pencil you write with can be so soft and diamond is so incredibly hard whilest both are made from solid carbon.

In 1991 researchers in Japan observed another allatrope of carbon that they called nanotubes. In carbon nanotubes each atom is also joined to three other carbon atoms and form a sheet as in graphene; however, in a nanotubes, as the name suggests, the sheet is rolled up and joins back onto its self, forming a seamless tube. These nanotubes are very narrow---only tens or hundreds of atoms in circumference (in the range of one to tens of nanometers)---but very long by comparison---up to centimeters in length (a million nanometers). This means that in two directions the carbon nanotube looks like a molecule and in the third direction, that is, along its axis, it looks like a macroscopic material. This combination of the sheet-like structure of carbon, the unusual tube geometry, the quasi-one-dimensional structure and convergence of nanometer and macroscopic length-scales gives carbon nanotubes a incredibly diverse range of unusual and extreme properties. For example, nanotubes can be either conducting (like a metal) or semiconducting (like silicon) depending on how they are rolled up. Their ecetrical properties may lead to faster computer chips and their optical properties could lead to low-power televisions and displays. Carbon nanotubes are also amazingly stiff (hard to deform elastically), very strong (takes lots of force to break), and tough (requires lots of energy to break), and their strength to density ratio is unparalleled. They have a very high thermal conductivity which can have unusual length dependent properties. Carbon nanotubes can be single walled or double walled or multiwalled. Nested tubes can slide over each other with very low friction and have an unusual spring-like behavior. The insides of nanotubes can be filled with things to make nano-pipes and nano-test-tubes. The outside of nanotubes can be coated with things to allow them to interact with a wide range of different materials. And finally the nanotubes can be bundled together and spun into fibers. Moreover, it is not just carbon that is of interest. Since the discovery of carbon nanotubes scientists have discovered that the nanotube structure is not unique to carbon and that some other materials, such as boron nitride, can also form nanotubes. All of these phenomena and their potential applications makes research into nanotubes very interesting, exiting and fast moving field of study at the moment.

posted on Mon, 04/02/2007 - 12:00pm
Ashley H's picture
Ashley H says:

Nanobots are pretty scary things. Do you think that they could actually take over our earth if released into the population?

posted on Thu, 03/15/2007 - 10:26am
Anonymous's picture
Anonymous says:

Have nanotubes been assembled in various dimensions so that
they might be telescoped?

posted on Mon, 04/02/2007 - 5:40pm
P. Alex Greaney's picture
P. Alex Greaney says:

Yes they have, and moreover they do not have to be assembled, they can occur this way naturally. Depending on how they are grown carbon nanotubes can form concentrically nested bundles of nanotubes (like
the layers in a leek). These are called multiwalled carbon nanotubes. Generally when nanotubes are grown the ends of the tube are closed, and so in multiwalled tubes the inter tubes are completely encapsulated by the outer ones. Researchers at Berkeley first discovered a way of breaking open the ends of the outer tubes and pulling out the inner tubes like a trombone. So far researchers have only seen trombone like behavior in which an inner section slides past an outer section rather than telescoping behavior in which there are many sliding sections.

The sliding tubes are very interesting. They behave like tiny springs---once an extended tube is released it springs back to the retracted configuration by itsself. Unlike conventional spring which pull with more tension the further you extend them the nanotube springs always pull with the same tension.

There are many potential applications for tromboning nanotubes. One that is particularly appealing is the ability to make tunable resonators. As carbon nanotubes are so long and thin they can be used as string like resonators---like a guitar string---but as carbon nanotubes are so small and light the frequencies are very high. Just as with a guitar string the longer the nanotube the lower its frequency. The tromboning properties of multiwalled tubes alows their length to be changed with out changing the tension in the tube and so alows one to tube the resonant frequency of the tube. Scientists at NASA have developed new kinds of robots that walk in a new way using tetescoping sections. There are some great movies on the internet at There is some hope that tromboning nanotubes may make this new type of locomotion possible on the nanoscale.

posted on Thu, 04/05/2007 - 11:16pm
Sara I's picture
Sara I says:

The Buzz intro said that some animals (like frogs) use nano scale sensors. Do humans have the ability to detect anything at a nano scale?

posted on Mon, 04/16/2007 - 1:12pm