Nanotechnology Questions

Recently we have received several questions here from people interested in learning more about nanotechnology and career prospects, or about general nanotech progress in broad fields such as computers or medicine.

We'd like to be able to respond, but as stated in our message about mechanical engineering, our area of specialty is molecular manufacturing and the policy issues raised by that transformative near-future capability.

Almost all of the research and development occurring today in nanotechnology -- whether related to mechanical engineering, chemistry, pharmaceuticals, materials science, computing, medicine, or other areas -- is not directly connected to CRN's main focus. Therefore, we can't comment authoritatively on most of that work, nor on career opportunities.

For general information about today's nanotech, you may want to begin your research at Nanotechnology Now; for employment opportunities, try tinytechjobs.

Comments

[mahajan rahul]

Respected sir

i am doing work in NIPER ( R & D ) on Nanotecnology . sir need information regarding the,

1. how does affect the following the things on preparation of nanoparticles-
polymer (polycaprolactone)
solvent (org ethyl acetate/acetone/methanol)
surfactant ( PVA)
CHITOSAN
drug (such as cyclosporine)

[MAHAJAN RAHUL]

sir ,

how to solve the resuspension problem .

[mohit]

how far do use see the scope of nanotechnology as a fuel as well as a energy source?

[Martin Coppa, CRN]

mohit,

Molecular Nanotechnology (MNT) and Molecular Manufacturing (MM) will not be fuel sources in and of themselves. Rather, the technology will enable the production of incredibly sophisticated products. As a fuel source, MM will allow the production of extremely inexpensive solar cells as well as efficient long-lasting batteries (maybe hydrogen fuel cells?). I personally feel that with the advent of a MM capability, the vast amounts of energy generated by the sun will cause other large-scale means of energy generation (hydroelectric dams, wind power) to become secondary. For instance, CRN has pointed out that the US has many square miles of roads all over the country; if we had the technology to produce diamond encased, networked solar cells on every square centimeter of that roadway:

1) Maintenance would be virtually unnecessary due to the extreme strength properties of diamond,

2) The area covered could potentially generate the energy currently consumed by the US and require no more area than is currently being utilized,

3) Power circuits could be integrated into the roadway, effectively eliminating the need for power lines along the side of these roads.

Without a need for power lines along every stretch of road, we've GAINED useable land, in addition to land currently used by power plants and the like which would become obsolete.

[John B]

Martin -

If such a thing as a diamond-covered solar cell roadway were to become available, I'd expect you'd see a strong lobby from current power generators' organizations against it (with the possible exception of the oil and/or coal lobbies, if the initial diamondoid materials are based off of petroleum- or coal-derived carbon, and if these companies didn't see the writing on the wall.)

Additionally, being diamond is not a perfect fix to structural issues - there're still the planar weaknesses crystalline structures exhibit. (Look at how traditional diamond facetting is done, for instance - with a medium-strength rap)

I'd wonder how well diamondoid solar cells would work under snow, sand, oil, and other materials you could expect to build up over roadways. Would it get slippery in the rain? Would it potentially short out over swamplands or in the rain?

However it might not necessarily need assembler-style tech, altho' that might be the most efficient way to make such devices. Simple 'tiles' of diamondoid with buckytube conductors could be plant-fabricated and sent to construction sites.

-John

[Martin Coppa, CRN]

John,

I don't deny that MM "could severely disrupt the present economic structure, greatly reducing the value of many material and human resources, including much of our current infrastructure. Despite utopian post-capitalist hopes, it is unclear whether a workable replacement system could appear in time to prevent the human consequences of massive job displacement." as presented at http://crnano.org/dangers.htm I'm feel corporations will likely be reluctant to accept a technology which will eliminate any need for their products.

I also agree that diamond is not a perfect fix to structural issues. I'm saying that a diamond coating of roadways will not hinder the structural integrity of the road while enabling solar cells to operate without utilizing any extra land. Currently, vast arrays of cells can be networked for electrical power, like at a school down the block from me, or they can be fastened to rooftops, like they are on my roof. The difference being: The school down the block has to use valuable space to generate their power, while my roof can be used both as a roof and a power source.

The idea behind the having 'solar roads' is that there is such a large area generating power that shadows from cars, trees, buildings, environmental conditions, etc. limit the total power generated per day to a point still well above the power consumed per day. If the roads in one part of the country are all covered by snow, in another part they are covered by sand, somewhere it's raining, somewhere birds fly over the road, animals cross the road, and all over the country roads are spotted with oil (which would be phased out if electricity were as plentiful as this idea implies), and anything else that is happening over the road, the total power generated by the entire country is still greater than the total power that is consumed. The problem of rain is nonexistent: we have solar cells that are perfectly capable of operating (much less in danger of shorting out) in all weather conditions.

In his paper “Design of a Primitive Nanofactory” on page 49, Chris points out that ,“a square mile of desert land receives more than 500 MW of solar power [I assume he means ‘per day’] (including night and seasons)”. I don’t know exactly how many square miles of road are available or how much energy is used by the US each day, but the idea is a good one.

MM would definitely make production less expensive and it could be programmed to automatically repave roads with this material, but you’re right, your idea of plant fabricating ‘tiles’ would be remarkably useful in countering peak oil (again, assuming we switch to electrically powered transportation) if it were not for the industries you have previously mentioned; unless “they” were to own the patents, factories, and tiles, any such proposal would be met by intense opposition.

- Martin

[Brett Bellmore]

While straight diamond crystal can indeed be cleaved, that's not really a problem. There are two basic approaches that could be taken, or even combined:

1. Tempering. Glass, you may have noticed, is also subject to fracture, in fact it's quite brittle. But if you make a glass object such that it's interior is in tension, and surface is in compression, then cracks originating on the surface are forced shut by the compression, and cannot propagate into the interior. The same can be done with diamond, though building stressed structures could be tricky.

2. Crack stopping microstructure. There are a number of classes of intermediate structures which tend to stop cracks from propagating through a brittle solid, by providing voids which terminate the growing crack. So long as the feature size is small compared to light, they'd have little effect on optical properties.

Now, friction... Rather than trying to make diamond have a high coeficient of friction, and keep the roadbed clean to enhance light transmission, it would be simpler to just roof over all the roads, and do the solar power on the roof. It would certainly have advantages in areas with bad weather...

[Martin Coppa, CRN]

Brett,

I was assuming that the problem of cleaving the diamondoid was limited to crashes/accidents in which an object became airborne and slammed into the road. In that sense, a crack through the surface and circuitry would be a problem. Such an instance would necessarily require some sort of repair, especially if the circuitry was damaged.

Points 1 and 2 would seem likely candidates to strengthen the cells, though I'm sure other properties could and probably would be implemented.

As far as the simplicity of constructing roofs for all roads everywhere versus the simplicity of a high coefficient of friction, I'm unconvinced.

Keeping with the tile idea and assuming the ability to automate the nanofactory’s locomotion along a predetermined route, satisfactory tile placement, ability to observe and compute road curvature and camber, etc., I would think that programming an onboard computer with a few basic properties would be less expensive and require less effort than designing appropriate-height supported shelters for roads. Basic properties of nanofactories producing roadway solar cells might include:

1) The nanofactories are solar powered.

2) Each nanofactory has enough solar cells to recharge its battery in 8 hours and a battery unit capable of storing 36 hours of operating power (for use at night and in case of inclement weather).

3) Nanofactories, their solar cells, and their batteries (utilizing any stored energy of course) can be produced and cannibalized on site depending on the width of the road.

4) Each roadway cell is composed entirely of carbon taken from the surrounding environment.

5) Each roadway solar cell has a similar shape with the solar cell tile in which it is embedded (for my purposes I'll assume this to be only parallelograms and trapezoids).

6) Each cell is oriented with one positive and one negative electrode on each side, which can be connected to adjacent cells or to circuits running along the edge of the tiles.

7) Infrastructure access can be pre-programmed (power monitoring stations, power line junctions, etc.)

8) Each cell is networked within the tile and can be networked with any other adjacent tile, regardless of it’s shape, provided that the common side is aligned and of equal length (for simplicity).

9) Each tile design has a surface ‘fingerprint’ designed for the shape of the tile so that any curvature in the surface of the road will necessitate a grooved surface at the mm to cm scale designed to increase friction of centrifugal forces and provide the greatest traction in order to maximize a vehicle’s centripetal force. For instance, a trapezoidal shape for curves would have its smaller side towards the inside corner regardless of the direction of the curve; no matter which direction you turn, the surface would always be designed to have greatest friction moving from its smaller side (inside of the curve) toward its larger side (outside of the curve). Square and rectangular tiles might have designs similar to what you see on tire treads today.

With this simple outline, it seems possible that each tile would have a surface explicitly designed to aid traction in the expected direction of motion. Also, this method is analogous to repainting the roads rather than building a long and tall covering that accomplishes the same objective.

Some drawbacks of this may be that:

1) Hauling around batteries and extra solar cells may be prohibitively inefficient.

2) Cannibalization and production of factories may occur far too often… maybe they aren’t cannibalized, but instead creep along with the rest of them until they come upon a fork in the road.

3) Carbon is omnipresent, but it may not be easily accessible to a nanofactory without some kind of processing system, which would add to the bulk and inefficiencies.

4) I’m no electrician, so I may not be truly grasping the scope of electricity these panels will produce. What size wiring will be required for such a load and will it be possible to network the entire country, not to mention the resistance within the wiring and the heat generated by that resistance.

5) What would need to be programmed for infrastructure? I have no idea how you could pre-program where to build external electrodes and the like.

[Martin Coppa, CRN]

In defense of your roof suggestion I would like to examine a few basic properties of nanofactories producing a road covering with solar panels built into it. Again, assuming the ability to automate the nanofactory’s locomotion along a predetermined route, satisfactory tile placement, ability to observe and compute road curvature and camber, etc..

1) The nanofactories are solar powered.

2) Each nanofactory has enough solar cells to recharge its battery in 8 hours and a battery unit capable of storing 36 hours of operating power (for use at night and in case of inclement weather).

3) The roof structure is composed entirely of carbon taken from the surrounding environment.

4) The roof structure is supported by pillars/columns/beams that are somehow anchored to the ground (driven into the ground maybe?).

5) The roof structure is never less than 20’ above the surface of any part of the road. (trucks)

6) The structure is capable of withstanding the elements.

7) The nanofactories can orient themselves with regard to magnetic (or true, which might be slightly more difficult) North.

8) Solar panels are not built into any roofing that faces north. Solar panels are built into any roof that faces East, South, and/or West.

9) All solar panels are networked and enable infrastructure access.

Some advantages of this method are that the cells are less susceptible to dirt and sand hindering their performance; though wind can blow these materials to that height it is highly doubtful that this would be a serious problem. Building a roof structure in which the panels are much closer to directly facing the sun than would be the case for a road, would cause the panels to be immensely more efficient. Instead of having an A framed structure (which could potentially protect drivers from water and snow) you could get much more bang for your buck if, for East-West roads, you had a kind of lean-to where the top only faced due south and was highest on it’s northern side. I’m sure other designs could take advantage of other orientations.

Some drawbacks of this may be that:

1) Hauling around batteries and extra solar cells may be prohibitively inefficient.

2) Carbon is omnipresent, but it may not be easily accessible to a nanofactory without some kind of processing system, which would add to the bulk and inefficiencies.

3) I’m no electrician, so I may not be truly grasping the scope of electricity these panels will produce. What size wiring will be required for such a load and will it be possible to network the entire country, not to mention the resistance within the wiring and the heat generated by that resistance.

4) What would need to be programmed for infrastructure? I have no idea how you could pre-program where to build external electrodes and the like.

5) How is the whole thing anchored to the ground?

6) How much weight would need to be supported? How strong would it have to be to support it’s own weight? How strong would it need to be to consistently and repeatedly resist the elements? More importantly, how much human engineering would be required for different road widths?

7) What would need to be programmed with regard to effective use of area facing south when the roadway can weave in any direction?

[Martin Coppa, CRN]

In conclusion I’d like to look at the pro’s and cons of each and leave the rest up for debate.

Pro’s of solar-road idea:

Increased traction on paved surfaces due to control of surface properties.
Small number of designs utilized.
Basic idea, nothing more than a new surface with special features.
Extended road life.

Pro’s of solar-roof idea:

Possible emergency shelter.
Immensely more efficient than solar-road cells.
Marginally to markedly more power generated due to less shadows and less solid materials piling on top of the solar cells.
Possible exploitation of ability to aim the cells at the sun.

Con’s of solar-road idea:

Questionable efficiency regarding nanofactory power source
Factory size and cannibalization/production unclear, as well as what happens to the factories when production is complete.
May require processing system to utilize carbon from environment.
Unclear how infrastructure could utilize the resource.
The designs of each tile shape and composition must be programmed in advance.

Con’s of solar-roof idea:

Questionable efficiency regarding nanofactory power source
May require processing system to utilize carbon from environment.
Unclear how infrastructure could utilize the resource.
The designs of each road width must be programmed in advance with specifications regarding strength of support beams and orientation with respect to due south.
Unclear how the structure would be anchored to the ground.

- Martin

[Mike Treder, CRN]

Martin, Brett, and John B -- This is a great discussion, but if we leave it here, it will get lost in the blog fog. Instead, start a new article at Wise-Nano incorporating everyone's ideas.

[Martin Coppa, CRN]

I have posted our comments in full at http://wise-nano.org/w/Solar_cells:_roads_versus_roofs

this will require editing, but it's now at the wise-nano site.

I look forward to comments and constructive criticisms of the ideas I have presented. When I have more time I may add a few more pros and cons.

[Richard Jones]

Can I ask how you propose to make a solar cell with any kind of respectable efficiency entirely out of diamond? Diamond is a wide band-gap semiconductor (the band-gap's about 5.5 eV if I remember right) so its absorption coefficient for visible light is very small. To put that more obviously, you can see through the stuff! Not that I disagree with you that coating unused land with very cheap photovoltaics manufactured in massive areas isn't a good idea; it's just that much better materials are likely to become available from ordinary incremental nanotechnology long before diamondoid MNT arrives (if it ever does). See here for more discussion of this.

[Brett Bellmore]

Actually, Richard, I tend to agree with you about that; Even if we had working Drexlerian nanotechnology, it probably wouldn't make sense to use it to build ALL products. And while carbon is a nice element, and there are several approaches to almost pure carbon based solar power, if you were going to make photovoltaics, you'd want to involve other elements.

Not the least because, after all, carbon IS a relatively rare element, for all that it's important to us carbon based life forms.

[Chris Phoenix, CRN]

There has been talk (in the mainstream science press) of using buckytubes as rectennas for visible frequencies. They're not diamond, but they are carbon, and no one has suggested that a diamond-based mechanosynthesis system would be unable to build them.

Semiconductor buckytubes have been used as LEDs (I don't know what frequency). So carbon can likely be used for building photoelectric elements, though I don't think anyone has yet studied the efficiency.

CVD diamond has been used to build thermionic solar cells with 50% efficiency.

Carbon isn't all that rare--and at the moment we have too much of it in our atmosphere. Extracting it for use in massive public-works projects like solar cell road surfaces or awnings sounds like a great idea to me. (It's worth noting that the amount of carbon required to build such a thing would be a tiny fraction of the carbon used in the road's asphalt.)

Chris

[Richard Jones]

A diamond thermionic cell? That is interesting; because it's not a photovoltaic the band-gap doesn't matter. But the word thermionic gives us a clue - it needs to be hot to work. 1000 C, in fact, which is going to cause us trouble if we try to use it as a road surface. What's worse is the power loss we'll get from radiation. Shoving the numbers into the Stefan-Boltzmann equation (radiated power/unit area = emissivity * Stefan's constant * (temperature)^4) I find radiated power = 150 kW, which is going to cause us trouble as even on a good day you don't get more than about 1 kW per square meter from the sun. It's only going to work in conjunction with a very large-area solar concentration system. I guess you could engineer that, but somehow I don't think Professor Graetzel is going to be losing any sleep.

As for fullerenes, yes, they are potentially good candidates as components in photovoltaics, but they usually need to be blended with a semiconducting polymer as the hole transporter. The resulting blend is indeed almost all carbon and hydrogen, but as it isn't covalently bonded it seems a better candidate for using self-assembly to get the desired nanostructure rather than MNT.

[Tom Craver]

Richard:
Something seems odd in your number of 150kW. Was that calculated with an assumption of 1 square meter as the "unit area"? As long as you can concentrate sunlight > 150:1, why should the size of the collector matter?

Of course, that approach is only suitable for direct sunlight (no cloudy days, unless some sort of wave-guide approach can be used to concentrate diffuse light) and you'd want to do something to adapt to the shifting angle to the sun - maybe an array of tiny mechanical sun-tracking lenses in/under a transparent road surface.

Also - why assume that diamond or even carbon is the only thing MM could work with? Once you have nanomanipulators capable of mechano-chemistry, why would one not be able to use those with a wide range of chemical tips? At a minimum, implanting precisely patterned impurities into a diamond structure during construction sounds easy.

I've read (though not well understanding how it works) about "artificial matter". Could one build a structure of diamond and dopant atoms - or even just cleverly shaped and isolated bits of diamond - to create a "simulated silicon" photocell?

[Brett Bellmore]

I think the simplest answer is that, once we have assmeblers functioning with some minimally complete toolbox of mechanosynthetic reactions, expanding the toolbox to include other reactions and elements will proceed quite rapidly.

And, yes, on Earth you can always extract carbon from the atmosphere, but in space you might find it a bit scarce.

[Martin Coppa, CRN]

Richard,

Your point, “Can I ask how you propose to make a solar cell with any kind of respectable efficiency entirely out of diamond? Diamond is a wide band-gap semiconductor (the band-gap's about 5.5 eV if I remember right) so its absorption coefficient for visible light is very small. To put that more obviously, you can see through the stuff!”, was answered by Chris (thanks Chris) before I had a chance to answer you.

I clearly stated that, “Each roadway cell [and roof structure] is composed entirely of carbon taken from the surrounding environment.” I did not state that every carbon atom would be used to produce diamond. Chris perceptively noticed this and mentioned exactly what I was implying - buckytubes. The benefit of having a transparent diamond housing for a photovoltaic cell is quite obvious.

Self-assembly is a good idea, maybe there could be another separate system in addition to the system required to extract carbon from the atmosphere (which should then be expanded to produce more carbon per second to use in the formation of nanotubes); if this were the case, and it isn’t too difficult to get the nanotubes into the factory, this would increase production.

Richard and Brett,

While it may not be the most efficient or productive material to use in photovoltaic cells, carbon is readily available from our atmosphere. Within our atmosphere, other elements currently used in solar cells such as Tellurium, Arsenide, and Indium are found in relatively miniscule concentrations. In this sense (as opposed to Brett’s comment regarding the lack of carbon in space – to which I would reply that the most efficient and effective materials available could be chosen and transported for use in space, even though he is talking about relative concentrations within the universe while I’m talking about concentrations on the surface of Earth), it seems that a nanofactory with supply lines transporting relatively rare elements across vast distances - from source to factory, wherever the two may be located - would be far less useful than a system which could extract materials from its immediate environment and convert those materials into useful products on the spot.

Tom,

Your idea, “adapt to the shifting angle to the sun - maybe an array of tiny mechanical sun-tracking lenses in/under a transparent road surface”, is worthy of consideration. My original intent was to formulate a bare-bones analysis in order to compare two different ideas for such a project. Impurities could be easily incorporated into designs but I reiterate that my objective was not to analyze the best possible solar cells, only to analyze purely carbon based construction. As Brett's last post states, the toolbox can be expected to grow quite rapidly after the assembler breakthrough, but for the sake of simplicity with regard to supplying materials, I have omitted any reagents beyond easily accessible carbon.

As for determining the best possible materials for such a project, I defer that honor to you fine gentlemen.

- Martin

[Richard Jones]

Tom, yes, sorry, unit area is a square meter. And indeed, as I said, you could get round this problem by concentrating sunlight from a wide area. The difficulty with this is, besides the added engineering complexity, the scope for additional energy loss further reducing the efficiency.

Which leads us to the question of what the efficiency actually is. This turns out to be a case study of the dangers of following science through press releases. The press release says the efficiency can be 50%, compared to 15% for silicon solar cells, and this is the figure that propagated through all the media reports of the work. But when I looked the original paper up in Applied Physics Letters the only 50% mentioned is the possibility that you could achieve up to 50% of the Carnot efficiency. For 1000 C, the Carnot efficiency is 77%, which gives as a theoretical upper limit on efficiency of 38%. But this is before you've taken any account of the radiation losses, losses in the collecter and absorber and so on. Even with the very simple engineering of a silicon photovoltaic you go from a cell efficiency of 24% to a module efficiency of 10-15% just with the losses associated with packaging it.

Finally, Tom asks; "Could one build a structure of diamond and dopant atoms - or even just cleverly shaped and isolated bits of diamond - to create a "simulated silicon" photocell?" Maybe one could; an analogy is the whole story of getting porous nanostructured silicon to do optoelectronic tricks that ordinary silicon can't do. My point, though, is to question why one would go to all these lengths to persuade a material to do something it isn't really suited to do when cheap alternatives are likely to be available long before this engineering becomes feasible.

[John B]

Richard states, "My point, though, is to question why one would go to all these lengths to persuade a material to do something it isn't really suited to do when cheap alternatives are likely to be available long before this engineering becomes feasible."

Are you certain that this would be the case? If so, how?

If there's a chance that such a situation does not come to pass, might it behoove us to look into alternate ways to increase capabilities? If something better comes along, so be it - but until such is proven, isn't it better to have multiple irons in the fire until we know which one's the 'winner'?

Additionally, if we presuppose carbon nanoassembly by some method, the formation of 'cleverly shaped and isolated bits of diamond' would be quite easy - leading to a capability for such a technology to extend beyond the mechanical level you seem to limit it to.

-John

[Brett Bellmore]

I happen to suspect that a lot of products in a world with nanotechnology, even working nanofactories, would not be made of diamonoid specified to atomic precision. The energy cost of making something with a general purpose nanofactory is likely to be quite high, after all, and if a product doesn't require atomic precision, and is going to be mass produced in huge quantities, that can be a telling factor. Especially for something like solar cells, where you have to worry about time to payback the original energy investment.

What's likely to be made with the nanofactory, is the solar cell manufacturing equipment, not the solar cells themselves.

[Richard Jones]

John, I'm not certain of anything that concerns the future. But non-conventional photovoltaics based on incremental nanotechnology, with the potential to be mass-produced in large areas, are beginning to move out of the lab into commercial development. I gave a brief overview here.

[Chris Phoenix, CRN]

Brett, it remains to be seen whether the material and quantum advantages of atomically precise manufacture will win over the energy advantages of bulk processing. I suspect they will; my very primitive nanofactory architecture projects an energy cost of 200 kWh/kg, while aluminum requires 15 kWh/kg just for smelting. As a structural material, a kg of nanostructured diamond goes a lot farther than 13 kg of aluminum... (But I'm certainly not ruling out the utility of MM-built factories.)

Richard, non-MM photovoltaics (and direct solar hydrogen) may make a significant dent in our fossil fuel usage. But there's still the problem of ramping up all the manufacturing plants. And that depends on industrial-scale testing, which can take years. MM should speed up large-scale prototyping, move manufacturing closer to the end user, reduce cost, and produce more integrated (flexible) products. I expect that most innovative products will end up being built this way. And I expect more and more products to be innovative as innovation becomes less risky. Organizations with too much inertia will be outcompeted; this may include various nations.

Chris

[John B]

Richard -

The two nations mentioned in your article (US & UK) are approaching a terawatt annual usage by your figures, and the factory you mention generated 30 megawatts capacity per year. Assuming a 5% production output gain per year, it'll take over 58 years to reach a terawatt of total production. This leaves open a big long window for nanotech to reach some degree of capability.

Note also that I rather doubt human power consumption will stay constant over the next 50+ years, and that world electrical consumption is currently somewhere in excess of 13 terawatts according to http://www.eia.doe.gov/oiaf/ieo/electricity.html

-John