Nanotechnology: views of Scientists and Engineers
Nanomaterials
a) What would you add to/change about
the working group’s definition of nanotechnology?
The group were generally happy with both definitions.
The following points were made:
Nanoscience:
- It was noted that colloid science covers
a very similar dimension range. Care is needed to
distinguish what is new about nanoscience compared
to much of chemistry
- The upper and lower size limits should
be fuzzy: for example photonic crystals go up to 300nm;
atom manipulation is sub 1 nm nanoscience.
- The definition does not directly acknowledge
sub-atomic or quantum phenomena.
Nanotechnology:
- This should be expanded to include the
word ‘systems’, eg a functional set of
components – a combination of nano (possibly
more than one aspect) and meso technology will be
essential in practice.
- This definition implies that nanotechnology
will always follow on from nanoscience (‘the
application of this knowledge’) whilst in practise
both nanoscience and nanotechnology will take place
simultaneously, and perhaps technology before the
‘science’. This is not unique to nanotechnology:
there are many examples of complicated & well-developed
technologies where the underpinning science is not
well understood.
b) What is the current state of knowledge
in the field of your breakout group, and where is research
going?
i) Definitions by dimensionality
It is convenient to classify nanomaterials in terms
of the dimensionality of the nanostructures involved.
Thus
3-D: (confined in 3 dimensions) e.g. quantum dots, particles,
precipitates, colloids, catalysts, etc.
2-D: (confined in 2-D, extended in 1-D) e.g. nanotubes,
fibres, interconnects/wires, fibrils, etc.
1-D: (confined in 1-D, extended in 2-D) e.g. surface
coatings, thin films, device junctions (diodes etc.),
interfaces etc.
1-D nanosystems are generally well understood and
technologically advanced. Atom scale control is already
possible for devices and coatings by various deposition
techniques.
2-D systems are moderately understood in terms of properties,
but manufacture is much less advanced.
3-D nanosystems provide the greatest challenges in terms
of both properties and controlled manufacture. This
is also where the dramatic increase in surface area,
and hence chemical activity, is most evident.
A general remark – the electrical transport
properties across interfaces remain poorly understood
in terms of science/predictive capability. This affects
all nanomaterials.
ii) Biology related
Considerable synergy exists between biostructures and
nanomaterials. This is an active area of opportunity.
For example much research has been undertaken on using
cells as scaffolding on which to build clusters –
bio- to inorganic templating. Similarly, templated inorganic
surfaces affect cellular function.
c) What applications of this technology
currently exist, and what can be envisaged in the short
and long term?
i) Sunscreens
These typically contain both physical and chemical components.
There is currently a limited understanding of which
the most important wavelengths are that need to be protected
against. Once this understanding increases it is hoped
to develop tuned systems.
Little is known about the fate of sunscreens, including
their metabolism, adsorption through skin, and where
they end up in the environment.
Enhanced DNA repair enzymes are currently being incorporated
into cosmetic formulations.
The driver for the use of nanoparticles in sunscreens
was actually cosmetic: viscous, white pastes were not
popular so the particle size needed to be lowered in
order to overcome this. One obvious side effect was
the dramatic increase in surface area. Free radicals
are thought to damage skin, and are generated by the
surface of the nanoparticle components. Two methods
have been devised to overcome this problem of particle
activity. One involves coating the particles –
however, it is difficult to achieve an even coverage.
More efficient is the use of p-type (rather than n-type)
semiconductor materials. These can be produced by doping
the original materials prior to mixing them with the
other components of the sunscreens.
Free radical damage has been shown with in vitro models,
but it is considerably harder to demonstrate in vivo.
ii) Self-cleaning windows
These involved the use of highly activated titanium
dioxide, engineered to be highly hydrophobic, very anti-bacterial,
utilising n-type doped materials.
iii) Nanocrystalline alloys
One example of how properties can significantly change
on the nanoscale is the strength of materials. For example,
nanocrystalline materials become considerably stronger
as the particle size decreases. Nanocrystalline nickel
is as strong as hardened steel, and nanocrystalline
aluminium alloys can be up to twice as strong as their
conventional equivalents. The nanostructuring can be
made in two main ways: electroplating and consolidation
from powder. Electroplating is preferable to consolidation
as it does not involve the use of any ultrafine particles.
The latter involve processing difficulties and possible
hazards.
iv) Micromachined silicon sensors
There are a number of mass produced, cheap, efficient
micromachined sensors (such as accelerometers) used
in cars, cameras etc. Whilst these do not necessarily
do anything completely new, they are smaller allowing
either more sensors or freeing up space to allow miniaturisation.
They are also easily intergrated with electronics.
v) Field-emission array displays
It was thought that a large electronics company intends
to launch a 28”x70” screen on the market
in 2004 or 2005 that is based on field-emission arrays
rather than quantum dots. They are based on a ‘bucky
paste’ that contains a volatile solvent, and nanotubes/particles.
During annealing the solvent is evaporated and the nanocomponents
self-assemble. The result is a screen with lower power
consumption and heat generation.
vi) Films and coatings
There are a large number of coatings and films that
are 1-d nanomaterials. Examples include:
- Multiwell quantum well lasers
- Smart materials such as self-cleaning
surfaces
- Super hard coatings (some are carbide
based)
- GMR read heads on PC hard drives. Magnetic
nanostructures
- Coatings on fibre optic cables and other
devices
vi) Environmental drivers
New alternative sources of energy are one potential
driver for nanomaterials. Applications include fuel
cells, nanomaterials with better electrical and mechanical
properties, low cost photovoltaics and (perhaps) utilising
carbon nanotubes to store hydrogen. Fraser Armstrong,
(Oxford), has been working on bio-fuel cells.
vii) Biomaterials
Bristol based company Nanomagnetics are currently manufacturing
magnetic nanoparticles via a biological route. Research
has also been undertaken on using yeast to produce similar
materials.
viii) Bioremediation
Another possible application for nanomaterials is bioremediation.
The driver would be to design systems capable of fixing
heavy metals, PCBs, cyanide and other environmentally
damaging materials.
ix) Improving understanding existing technologies
Nanoscience and nanotechnology have provided improved
analytical tools that can be used to increase our understanding
of existing technologies. For example, it is now possible
to study biomolecules by trapping them in nanostructures
making x-ray crystallography possible. The probe microscopies
(esp. AFM) provide rapid, easy surface characterisation
for thin film manufacture.
d) What are the potential hold-ups
in turning research into products? What is needed (time,
money etc) to enable this process to happen?
i) Hazards
There are three stages during which the hazards of any
material need to be assessed:
- In production
- In use
- In disposal
There are a number of hazard-related issues associated
with the production of nanomaterials:
- Very fine powders can be pyrophoric,
so good housekeeping is required. Electrodeposition
or melt spinning can be used to avoid these problems.
- Fluid based systems have many advantages,
not least that they avoid free fine-scale particles.
However, they generate the problem of how to deal
with the disposal of the manufacturing process feedstocks.
This problem is not unique to nanomaterials, but is
still a serious issue.
- Lessons might be learnt from microbiological
aerosol production where there are many well-established
practices to deal with fine particles.
ii) Quantum dots
There is currently no reliable method of producing quantum
dots of the same size reproducibly, either by lithography
or the colloidal route. This is a significant limitation
for their wider application. In contrast quantum lasers
are a possibility as they require fewer dots to function.
iii) Electron transport across material junctions
The long standing problem of the Schottky barrier /
Ohmmic barrier, and understanding exactly how electrons
transfer at material junctions, causes difficulties
for nano- as for conventional materials. Alloy-based
nanomaterials will often be made in a trial and error
approach to obtain the required electrical properties.
A related issue is a lack of understanding of how charges
get into and out of cells, which has huge importance
to bio-nanomaterials.
iv) Protein misfolding
It is not known how nanoparticles will interact with
proteins. There is the possibility of causing protein
misfolding, which is known to sometimes have damaging
effects.
v) Empirical understanding of complex many
particle systems
Much of our current understanding of multiphase systems
is empirical at best. This knowledge has been built
up over many years of chemical engineering and physical
chemistry studying ‘real’ systems such as
food. Surfactant and colloid science has only started
to fully utilise DLVO theory on the attractive and repulsive
forces between particles in the past 10-15 years although
the theory’s key papers were published by Derjaguin
and Landau in 1941 and Vervey and Overbeek in 1948.
It was noted that ‘real’ systems are significantly
more complicated than model ones, where our understanding
is better. Impurities will influence surface properties,
even at very low levels. There is clearly a need for
nanoscience study of particle surfaces and interfaces.
vi) Toxicity issues
Experience from other materials (e.g. asbestos) shows
that it is not necessary to have a complete understanding
of precisely how a new material might affect people
in order to determine regulation. Rather, it is essential
to know what the dose response is. It is not sufficient
to assess the properties of the individual chemical
components that make up nanomaterials, as the toxicity
will depend on the particle size, particle concentration
and surface area.
A huge number of fine particles are produced from a
wide range of other existing processes (car exhausts,
masonry etc) that will/may have an impact on human health.
Nanoparticles are not new! The bio-interactions of fine
particles are not well-known, for example whether the
particles can pass through skin or go into cells. It
is also not known how the toxicity will vary from either
the bulk or molecularly dispersed material. It can be
postulated that nanoparticles might have a greater toxicity
than a molecularly dispersed form of the same material
due to either the combination of particle shape and
size (cf silicosis).
Peter Dobson, University of Oxford, is involved in organising
an EU workshop during summer 2004 on the direct absorption
of fine particles through the skin.
It is also important to find out where nanoparticles
go once they enter the body via different routes, and
ultimately where they go inside cells. This might be
achieved by studying luminescent tagged systems.
vii) Lessons from asbestos
Whilst there is not a full understanding of the mechanisms
that make asbestos toxic, there is sufficient understanding
to prevent significant harm to people. It is known that
the size and shape of the particles is important, although
the influence of exact shape, durability, solubility
and surface chemistry, are not well understood.
e) What are the science 'fictions'
in this field?
i) Public perceptions
There is a perception that things that are too small
to be seen are somehow in the realm of science fiction.
It is important for scientists to engage with the public
about nanoscience and nanotechnology to inform them
about the opportunities and risks
For example, the use of clean rooms in the fabrication
of nanomaterials can be a cause of disquiet amongst
the public. Clean rooms are often associated (e.g. in
movies) with highly infectious diseases and radiation,
and not the life improving technologies such as integrated
circuit manufacture, where they are mostly actually
used.
Smart materials and self-replicating materials are
often confused. This distinction is important and needs
to be made clear. ‘Self-replicating’ may
cause alarm, with erroneous visions of intelligent nano-machines.
ii) Exaggerated proposals from scientists
Scientists making exaggerated claims about their research
and in research proposals can do considerable damage.
These claims fuel public perceptions that nanotechnology
is either ‘science fiction,’ or dramatic
and radical, and therefore risky.
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