Water soluble carbon nanotubes

Multi-walled Carbon nanotube, its role and implications in biological systems are currently under evaluation and became interesting for many researchers primarily working on the interface of chemistry, physics and biology. However, concerns about the potential toxicity of multi-walled carbon nanotubes have been raised. To carry such affords, herein we investigate the effects of carboxylic acid functionalized water soluble carbon nanotube (wsCNT) on the growth of gram Cicer arietinum plant. The growth of gram plants was observed with and without the presence of wsCNT to demonstrate that carboxylated functionalized multi-walled carbon nanotubes showed better growth and under more wsCNT, the growth was enhanced without showing apparent toxicity. Although this is a preliminary study with a small group of plants, our results encourage further confirmation studies with larger groups of plants.


Since the discovery of carbon nanotube (CNT)1, exploitation of its application is sought in all possible arena of life and role of CNT in biological systems and medicine is highly important and these area needs newer approaches to do so. For the biological application the important task to make CNT first fairly water soluble is crucial. We have made a simple approach to achieve that and started using water soluble CNT 2 as probe in different biological aspects. The present study deals with its effect on the growth of gram C. arietinum seed under different concentrations of wsCNT.

There are many reports of ingesting of single wall carbon nanotube in macrophage cells without showing any toxic effect3. Gas and water flow measurement through micro fabricated membranes in which aligned CNTs having diameters less than 2 nm served as pores to show that the gas and water permeability of nanotube based membranes were several orders of magnitude higher than those of commercial polycarbonate membranes4. Molecular dynamic simulation on osmotically driven transport of water molecules through hexagonally packed carbon nanotube membrane were simulated in relevance to CNT semi permeable membrane to separate components of pure water and salt solution5. Molecular dynamics simulation of flows of water inside CNTs was also studied6 . However, experimental findings on such phenomena are lacking. Molecular transport across cellular membranes is essential to many of life’s processes. In the molecular life, water and minerals are essential components for growth and their transport to different cells and organs are critically important for survival of a living entity. In vascular plants, root helps plant in transport of water and solutes7 and involved in pumping of water across the plasma membrane into the cytoplasm of cells8 . Pumping of water is due to the water potential caused by the transpiration. We used dicotyledonous plant of gram – C. arietinum seed as it has a very short life cycle, and its vascular bundles are arranged in ring in comparison to monocotyledonous plant in which the vascular bundles are scattered. The growth of gram C. arietinum seed were observed under different concentrations of wsCNT; and it was found that the plant grown in solution having maximum concentration of wsCNT showed maximum growth.

Materials and Methods

Water soluble multiwalled carbon nanotubes (wsCNT) wsCNT which were synthesized as by the prescribed method with slight modification from the previous method2 like standing the carbon soot in concentrated nitric acid overnight and decanted off the sample to remove excess of acid and the black mass was washed with distilled water several times till it was neutral. At the final stage of washing, decantation resulted loss of materials and so the residual water was removed under boiling water bath. Repeated adding water and evaporation under boiling water bath removed trace amount of volatile nitric acid and the nitrate free final wash has been tested using Griess reagent9 . The black residue was finally vacuum dried (300 mg) and subjected to analysis. The highly cabroxylated CNT (wsCNT) thus formed became readily soluble in water under sonication and remained in solution for months without precipitation.


Seeds

eeds of common gram C. arietinum were kept in a dry place in the dark under room dark under room temperature before use. Sprouted (one day) gram seeds were grown in different concentrations of wsCNT (a stock of wsCNT with its concentration 1.45gm /liter was used after sonication to dissolve).


Germination

Seeds were immersed in a 10% sodium hypochlorite solution for 10 min to ensure surface sterility (USEPA, 1996), then, they were soaked in DI-water for germination for one day. Then, sprouted one day gram seeds were then transferred onto the sample vials, which were grown in different concentrations of wsCNT. After 13 days, growth in different parts of the plants like shoot and roots were observed



For Fluorescence

Stock solution of 0.009 gm wsCNT and 0.001 gm CdSO4, (0.004 mmol) (purchased from Sigma Aldrich) was prepared in 10 ml double distilled water and refluxed for 3.5 hrs followed by stirring for 1 hour. Ammonium sulphide was prepared with 25 ml NH4OH in which H2S was passed for 1 minute. 300 µl stock solution was taken in vial 1ml water, into which 1-2 drops of ammonium sulphide was added, to the transverse section (T.S.) and lateral section (L.S) of root. Slides were then prepared and watched under fluorescence microscopy. Ammonium sulphide addition is a necessary step as it converts the CdSO4 into CdS which in turn fluorescence the channel made by wsCNT. After two hours of this exposure, the solution mixture was removed and the root part of the sprouted seed was washed with running distilled water to free it from external CdSO4. The washed sprouted seed root was now dipped into 2ml of distilled water pre-saturated with H2S gas. After 30 minutes, the entire sprouted seed was washed with running distilled water and slides were then prepared from the T.S section of the root. Florescence microscopic images of CdS incorporated into wsCNT showed very distinct tubular structures due to the fluorescence of CdS inside the wsCNT. The excitation wavelength used was 371 nm.





In this study, we report the comparative growth of sprouted (one day) gram seed in the presence of different concentrations of wsCNT in comparison with controlled one, which were imaged by Scanning electron microscope (SEM) equipped with an energy-dispersive X-ray analysis and were recorded with FEI Quanta 200 Hv and “Tecnai 20 G2” 200 kV STWIN used for Transmission electron microscopic (TEM) analysis (Figure 1).








Figure 1 -(A) Scanning electron microscopy image having the scale bar of 5µm; (B) its EDAX analysis showing the presence of carbon and oxygen only; (C) Transmission electron microscopy scale bar 100 nm; (D) High Resolution transmission electron microscopy (inner diameter approx 12 nm) having the scale bar of 5 nm.


To compare the growth in different parts of the plants like shoot and roots, three different sets of five vials were used. In the first set, seeds were grown under controlled condition in the second set 100µl wsCNT solution is added in 5ml double distilled water ; in the third set of vials the concentration of the wsCNT is 200µl wsCNT in 5 ml double distilled water . And for comparison the water level; shoot length, root numbers and root length were observed for 13 days (Figure 2).





showing the comparative growth of gram plants in controlled, 100µl and 200µl wsCNT solution . Comparing the size of wsCNT (10-30 nm) shown in (Figure 1) and xylem (few microns), it can be assumed that the CNT capillary structure may get introduced inside the lumen of treachery elements since the size difference between these two, drifts wsCNT to be incorporated within the xylem according to the concept of the formation of a “large capillary”. This is formed inside the treachery elements of the xylem by head to tail arrangement of one carbon nanotube to the second and thus it provides channelling through which water is conducted. Carbon nanotube thus providing channels through which water can be conducted (Figure 3).




Here in, effects were observed that wsCNT which were initially in the form of cluster aggregates like spaghetti; get aligned in the vascular bundle due to endo-osmotic root pressure caused by xylem10. These vascular bundles run all through the plant and consist of xylem and phloem. Alignment of carbon nanotubes within the treachery elements of xylem has been established by optical microscopy (Figure 4) from the wsCNT treated sprouted gram seed Florescence microscopic images of CdS incorporated into wsCNT showed very distinct tubular structures due to the fluorescence of CdS inside the wsCNT. The excitation wavelength used was 371 nm. The presence of wsCNT in the plant root (especially in the xylem) can be detected by the images obtained from optical microscope shown





(Figure 4) in the absence and in the presence of wsCNT.



(Figure 5) clearly showed the channels fluoresces through the passage of Cd+2 ion subsequently exposed with sulfide to precipitate fluorescing material CdS. To understand the mechanism, inducing growth of the plants, it might be possible that wsCNTs after attaching with the root surface or inner portion of root (such as vascular bundles, cortical region etc.) enhances the capillary action of water absorption as shown by simulated work5,10. Our present work suggested that water is not only occupies these channels but also molecular transport takes place faster inside the plant via xylem where wsCNT acts as membrane that offers both high selectivity and high flux. This consequences almost frictionless and very rapid flow, and the transport is predicted by molecular dynamics, which correlates this enhancement of flux to atomic smoothness of the nanotube surface and to molecular ordering phenomena that may occur on confined length scales in the 1-2 nm range 6 . In atomically smooth pores, the nature of water–wall collision can change from purely diffuse to a combination of Specular and diffused collisions leading to the observed fast transport. This faster transport of water leads to high absorption of water by the roots containing nanotube in the xylem resulting increased length of root, shoot, and root hairs which ultimately increase the productivity. It might be possible that after being adsorbed within the root surface (mainly root hair region) carbon nanotubes retard the salt uptake by making xylem tracheids less porous. As a result of less porosity, it permits the uptake of only small molecules by xylem tracheids where as large molecules became unable to pass through CNTs.
The rate of the survival of the plants (under laboratory condition) grown in CNT solution is more than the plants grown in distilled water only. In the first table it is shown that out of five plants only two plants survived, plants grown with 100 micro liter CNT solution three plants

survived and the plants grown with 200 micro liter CNT solution out of five plants four plants survived, by the end of experiment. The water absorption rate by the plants in the vials containing wsCNT was more than the plants grown in distilled water only. Plants grown in distilled water showed least water absorption, while plants grown with CNT were found to absorb more water and the depletion in water level is more in these vials. The root system of the plants grown with CNT was found to be more branched. The root length (the longest branch of the root) is longest of the plants grown in CNT

MECHANICAL PROPERTIES OF CARBON NANOTUBES

Carbon nanotubes are cylindrical all-carbon molecules composed of concentric graphitic shells with extremely strong covalent bonding of atoms within the shells but very weak van der Waals type interaction between them. Due to the unique atomic structure nanotubes have exceptional electronic and mechanical properties which imply a broad range of possible applications as constituents of nanometer-scale devices and novel composite materials.

In this work we are using computational methods to study the atomistic structure of twist grain boundaries of different rotation angles. We are interested in knowing if the interface of all grain boundaries is comprised of a thin amorphous layer, or if there are certain angles for which the interface is crystalline. We are also interested in the grain boundary energy, since it can be compared to experimental results.

The properties of a carbon nanotube depend on the local atomic configuration and defects. For composite and device development it is essential to understand how structural changes affect the properties and our work strives after shedding some more light on the occurring phenomena. Current projects concentrate on evaluating irradiation and irradiation induced defects as a means to improve carbon nanotube strength, load transfer and inter-shell friction. The tools employed are both classical molecular dynamics and dynamical tight binding methods. Fig. 1 shows an example of a defect typical to irradiation and how such defects can link tubes which efficiently prevents tube-tube slippage

Figure 1. A defect typical to irradiation, a vacancy.

Figure 2.Example of a nanotube bundle in which the nanotubes are linked together by the presence of vacancies

It is becoming clear from recent experiments3-9 that carbon nanotubes (CNTs) are

fulfilling their promise to be the ultimate high strength fibres for use in materials applications.

There are many outstanding problems to be overcome before composite materials, which

reflect the exceptional mechanical properties of the individual nanotubes, can be fabricated.

Arc-discharge methods are unlikely to produce sufficient quantities of nanotubes for such

applications. Therefore, catalytically grown tubes are preferred, but these generally contain

more disorder in the graphene walls and consequently they have lower moduli than the arc-

grown ones. Catalytic nanotubes, however, have the advantage that the amount of disorder

(and therefore their material properties) can be controlled through the catalysis conditions, as

mentioned before. As well as optimizing the material properties of the individual tubes for

any given application, the tubes must be bonded to a surrounding matrix in an efficient way to

enable load transfer from the matrix to the tubes. In addition, efficient load bearing within the

tubes themselves needs to be accomplished, since, for multi-walled nanotubes (MWNTs),

experiments have indicated that only the outer graphitic shell can support stress when the

tubes are dispersed in an epoxy matrix10, and for single wall nanotube (SWNT) bundles (also

known as ropes), it has been demonstrated that shearing effects due to the weak intertube

cohesion gives significantly reduced moduli compared to individual SWNTs6. The reduced

bending modulus of these SWNT bundles is a function of their diameter. An individual tube

has an elastic modulus of about 1 TPa, but this falls to around 100 GPa for bundles 15 to 20

nm in diameter. In summary, there are two main challenges to address: to enable strong

bonding between the CNTs and the surrounding matrix; to create crosslinks between the

shells of MWNTs and also between the individual SWNTs in SWNT bundles, so that loads

can be homogeneously distributed throughout the CNTs. Ideally, both these goals should be

achieved without compromising the mechanical properties of the CNTs too drastically. Efforts

within this group have begun to address these problems using post production modification of

CNTs via chemical means and controlled irradiation.

High resolution transmission electron microscopy (HRTEM) can be used to give

invaluable information about the structure of CNTs, in particular, the amount of

order/disorder within the walls of MWNTs. Atomic force microscopy (AFM) can be used to

measure the mechanical properties of individual CNTs4-7. Use of both techniques has allowed

us to make a correlation between the strength of MWNTs, grown in different ways, with the

amount of disorder within the graphene walls (see below).

The AFM technique developed in our laboratories has already enabled characterisation

of the moduli of SWNT bundles6 and MWNTs, both arc-grown and catalytically grown7. The

method has been described in detail previously6,7. Briefly, it involves depositing CNTs from a

suspension in liquid onto well-polished alumina ultrafiltration membranes with a pore size of

about 200 nm (Whatman anodisc). By chance, CNTs occasionally span the pores and these

can be subjected to mechanical testing on the nanometer length scale. Contact mode AFM

(M5 Park Scientific Instruments) under ambient conditions is used to collect images of the

suspended CNTs at various loading forces. Fig. 4 shows an AFM image of a SWNT bundle

suspended across a pore and a schematic representation of the mechanical test. The maximum

deflection of the CNT into the pore as a function of the loading force can be used to ascertain

whether the behavior is elastic. If the expected linear behavior is observed, the YoungÕs

modulus can be extracted using a continuum mechanics model for a clamped beam

configuration6,7. The suspended length of the CNT, its deflection as a function of load and its

diameter can all be determined from the images, enabling the modulus to be deduced. The

diameter is taken as the height of the tube above the membrane surface at the clamped ends.

Although tip convolution can be a problem in measuring lateral dimensions using AFM, the

height is a reliable measure because the CNTs are essentially incompressible at these loads

(nominal loading forces are in the range 1 to 5 nN). The suspended length can be determined

from line profiles taken either side of the tube. A minimum suspended length is measured

because of the convolution of the tip with the edge of the pore. This means that all the

determined moduli quoted here are minimum values.

The powerful advantage of the AFM technique employed in our laboratory is its

simplicity. There is no need for complex lithographic techniques for suspending and clamping

tubes. The surface forces between the CNTs and the alumina membrane are sufficiently high

to maintain the clamped beam condition in the majority of cases. In addition, the nanotubes

are never exposed to electron radiation during measurement, which is the case for TEM

studies. Radiation will induce defects, if the energy of the electrons is high enough, and

thereby alter the material properties. This is one effect that we are currently utilising in a

positive way in an effort to modulate CNTsÕ mechanical properties. The relative ease of

sample preparation in our AFM method enables a high measurement throughput allowing us

to measure a variety of CNTs synthesized in different ways and to compare the results.

Described below are new data on catalytic MWNTs, and arc-grown SWNT bundles that have

been hydrogenated and exposed to a low-level of radiation. Catalytic MWNTs were produced

through decomposition of acetylene over a cobalt/silica catalyst. The previously measured

catalytic MWNTs were produced at a temperature of 900oC 11, whereas the new data

presented here were obtained on MWNTs fabricated at 720oC. The microstructure of the

catalytic MWNTs has a strong dependence on the synthesis temperature which can be readily

seen via HRTEM.

Figure 4. (a) 3D rendering of an AFM image of a SWNT bundle adhered to the alumina ultrafiltration membrane, leading to a clamped beam configuration for mechanical testing. (b) Schematic representation of the measurement technique. The AFM applies a load, F, to the portion of nanotube with a suspended length of L and the maximum deflection d at the center of the beam is directly measured from the topographic image, along with L and the diameter of the tube (measured as the height of the tube above the membrane).

To produce crosslinks between the shells of MWNTs and between the SWNTs of

SWNT bundles, the sp2 carbon bonding must be disrupted to sp3 bonding so that dangling

bonds are available for crosslinking. Since the sp2 bonding is the essence of the CNTs

strength, this must not be disrupted to such a degree that the properties of the individual shells

in MWNTs or individual SWNTs in bundles are degraded. Hydrogenating CNTs is a first step

towards producing them with internal crosslinking. The MWNTs and SWNT bundles were

hydrogenated using a modified Birch reduction using Lithium and methanol in liquid

ammonia12. The SWNT bundles were subsequently exposed to 2.5 MeV electrons with a total

radiation dose of 11 C/cm2. A theoretical estimation of the number of displacements that this

dose produces suggests that it will create about 1 defect per 360 carbon atoms13.

AFM measurements on the hydrogenated, irradiated SWNT bundles are shown in Fig.

5, along with the previous measurements of untreated SWNT bundles6. As before, the bundles

were dispersed in ethanol using an ultrasonic probe and deposited on the alumina membranes

for measurement by AFM in air. Within the errors of our measurement technique a

strengthening of the bundles was not observed: the YoungÕs modulus still decreases in a

similar trend to the as-grown bundles. However, the treatment does not appear to have

compromised the strength of the individual SWNTs either, since the lower diameter bundles

have comparable moduli. In addition, it was noticed that the treated bundles were more

difficult to disperse in ethanol and the morphology of the sample in the AFM showed that the

bundles exhibited a higher degree of aggregation. Taken together these data suggest that the

radiation treatment produced bonding between the tubes but was not sufficient to produce

enough crosslinks within the bundles to reduce shearing effects and produce bundles with

higher YoungÕs moduli. Future efforts will concentrate on optimising the chemistry and

irradiation doses to improve their mechanical properties.

ELECTRONIC PROPERTIES OF CARBON NANOTUBES

Interest in carbon nanotubes has grown at a very rapid rate because of their many

exceptional properties, which span the spectrum from mechanical and chemical robustness to

novel electronic transport properties. Their physics, chemistry and perspectives for

applications are very challenging. Below we highlight the main results of the Lausanne group

and their collaborators on transport, electron spin resonance, elastic and field emission

properties of single wall (SWNT) and multi-wall (MWNT) carbon nanotubes.

SAMPLES

We use MWNTs produced by arc discharge or by thermal decomposition of

hydrocarbons, and SWNTs either prepared by the arc discharge method in the presence of

catalysts or commercially available (Carbolex, Rice University, MER, DEL). The first step in

the study of CNTs is technological: their purification. This is especially true for SWNTs,

which are severely contaminated with magnetic catalyst particles. The purity of the arc-

discharge fabricated MWNTs is much better, since magnetic materials are not used in their

production. Nevertheless they have to be separated from graphitic flakes, polyhedral particles

and amorphous carbon present in the raw soot. For MWNTs, we have developed a soft

purification method, which uses the properties of colloidal suspensions1. We started the

purification with a suspension prepared from 500 ml of distilled water, 2.5 g of SDS (sodium

dodecyl sulfate; a common surfactant) and 50 mg of MWNT arc powder sonicated for 15

minutes. Sedimentation and centrifugation (at 5000 rpm for 10 minutes) removed all graphitic

particles larger than 500 nm from the solution, as confirmed by low magnification SEM

observations (upper part of Fig. 1). We then added surfactant to the solution to reach 12 CMC

(critical micelle concentration). At these surfactant concentrations, micelles form and induce

flocculation, i.e. the formation of aggregates. These aggregates mostly contain large objects,

while smaller objects remain dispersed, and sediment after a certain time, typically a few

days. After decanting the suspension one week later, we repeat the procedure once or twice.

Fig. 1 (lower part) shows scanning electron microscopy images of a MWNT deposit after the

separation procedure. The untreated material contains a large proportion of nanoparticles

(typically 70 % in number and 40 % in weight). After the purification, the material remaining

in suspension consisted nearly exclusively of nanoparticles, while the sediment contained

nanotubes with a content of over 80 % in weight.

Figure 1. Scanning electron (SEM) micrographs of a MWNT deposit (top) and MWNTs after purification and as a Òside-productÊÓ, nanoparticles of carbon.

For SWNTs, the purification of the raw soot has been carried out by oxidative

dissolution of the carbon encapsulated metal particles with concentrated acid, which ensures

maximum efficacy of the process of metal elimination. A weighed amount of the raw soot

was sonicated in an ultrasonic bath at 25 ûC with concentrated nitric acid for a few minutes

and subsequently refluxed for 4-6 h. Thick brown fumes containing oxides of nitrogen were

seen, indicating the rapid oxidation of carbon to carbon dioxide. After cooling, water was

added so as to leave the samples in 6M HNO3 for the next 8-12h, after which, it was

centrifuged several times and the supernatant rejected until the pH of the solution was around

6.5. High resolution transmission electron microscopy of the material from this solution

showed the presence of long ropes of bundled nanotubes accompanied by small amounts of

carbon-coated metal particles. Parallel examination of the unpurified soot indicated that more

than 80% of the metal had been dissolved. The SWNTs in suspension were stabilized by

using a surfactant such as SDS and left undisturbed for 3-5 days until the slow aggregation of

the nanotubes allowed their separation from the nanoparticles in solution. The nanotube

suspension was filtered through a polycarbonate membrane (1 µm pore size) in order to

eliminate most of the particles. On drying, the sediment on the filter paper peeled away to

form a self supporting sheet of carbon nanotubes. Scanning electron micrographs of such a

sediment, like the one in Fig. 2 shows a network of SWNTs.

Figure 2. Scanning electron (SEM) micrographs of (a) a SWNT deposit and (b) a mat of SWNTs after purification. A few nanoparticles and embedded catalyst particles are still present.

MWNTs are also prepared by catalytic decomposition of acetylene (or other carbon-

containing materials) over supported transition metal catalysts in a temperature range of 700800oC.

This reaction can be carried out under relatively mild conditions in a fixed bed flow

reactor at atmospheric pressure. After optimization, the catalytic method can be suitable for

the production of either single and multiwall or spiral carbon nanotubes.

Figure 3. Scanning electron (SEM) micrographs of MWNTs prepared by catalytic decomposition of acetylene

A further advantage of this method is that it enables the deposition of carbon

nanotubes on pre-designed lithographic structures2, producing ordered arrays which can be

used in applications such as thin-screen technology, electron guns etc. The feasibility of the

deposition of carbon nanotubes on a ceramic membrane and its field emission properties was

demonstrated.

Carbon Nanotubes and Graphene for Electronics Applications

Carbon Nanotubes (CNTs) and graphene exhibit extraordinary electrical properties for organic materials, and have a huge potential in electrical and electronic applications such as sensors, semiconductor devices, displays, conductors and energy conversion devices (e.g., fuel cells, harvesters and batteries). This report brings all of this together, covering the latest work from 78 organizations around the World to details of the latest progress applying the technologies. Challenges and opportunities with material production and application are given.

Applications of Carbon Nanotubes and Graphene for electronics applications



Depending on their chemical structure, carbon nanotubes (CNTs) can be used as an alternative to organic or inorganic semiconductors as well as conductors, but the cost is currently the greatest restraint. However, that has the ability to rapidly fall as new, cheaper mass production processes are established, which we cover in this report. In electronics, other than electromagnetic shielding, one of the first large applications for CNTs will be conductors. In addition to their high conductance, they can be transparent, flexible and even stretchable. Here, applications are for displays, replacing ITO; touch screens, photovoltaics and display bus bars and beyond.




In addition, interest is high as CNTs have demonstrated mobilities which are magnitudes higher than silicon, meaning that fast switching transistors can be fabricated. In addition, CNTs can be solution processed, i.e. printed. In other words, CNTs will be able to provide high performing devices which can ultimately be made in low cost manufacturing processes such as printing, over large areas. They have application to supercapacitors, which bridge the gap between batteries and capacitors, leveraging the energy density of batteries with the power density of capacitors and transistors. Challenges are material purity, device fabrication, and the need for other device materials such as suitable dielectrics. However, the opportunity is large, given the high performance, flexibility, transparency and printability. Companies that IDTechEx surveyed report growth rates as high as 300% over the next five years.

Graphene, a cheap organic material, is being enhanced by companies that are increasing its conductivity, to be used in some applications as a significantly cheaper printed conductor compared to silver ink. All this work is covered in this new report from IDTechEx.
Activity from 78 organizations profiled
IDTechEx has researched 78 companies and academic institutions working on carbon nanotubes and graphene, all profiled in the report. While manufacturers in North America focus more on single wall CNTs (SWCNTs); Asia and Europe, with Japan on top and China second, are leading the production of multi wall CNTS (MWCNTs) with Showa Denko, Mitsui and Hodogaya Chemical being among the largest suppliers. The split of number of organizations working on the topic by territory is shown below.


Split of organizations working on carbon nanotubes and graphene for electronics applications by territory

Source IDTechEx



Opportunities for Carbon Nanotube material supply


A number of companies are already selling CNTs with metallic and semiconducting properties grown by several techniques in a commercial scale but mostly as raw material and in limited quantities. However, the selective and uniform production of CNTs with specific diameter, length and electrical properties is yet to be achieved in commercial scale. A significant limitation for the use of CNTs in electronic applications is the coexistence of semiconducting and metallic CNTs after synthesis in the same batch. Several separation methods have been discovered over the last few years which are covered in the report, as is the need for purification.

Opportunities for Carbon Nanotube device manufacture


There are still some hurdles to overcome when using printing for the fabrication of thin carbon nanotube films. There is relatively poor quality of the nanotube starting material, which mostly shows a low crystallinity, low purity and high bundling. Subsequently, purifying the raw material without significantly degrading the quality is difficult. Furthermore there is also the issue to achieve good dispersions in solution and to remove the deployed surfactants from the deposited films. The latest work by company is featured in the report.


Key benefits:


This concise and unique report from IDTechEx gives an in-depth review to the applications, technologies, emerging solutions and players. It addresses specific topics such as:


* Activities of 78 global organizations which are active in the development of materials or devices using carbon nanotubes or graphene.
* Application to conductors, displays, transistors, super capacitors, photovoltaics and much more
* Types of carbon nanotubes and graphene and their properties and impact on electronics
* Current challenges in production and use and opportunities
* Forecasts for the entire printed electronics market which carbon nanotubes and printed electronics could impact


For those involved in making or using carbon nanotubes, or those developing displays, photovoltaics, transistors, energy storage devices and conductors and want to learn about how they can benefit from this technology, this is a must-read report.

Top Ten Nanotech Products

The overwhelming majority of commercially-available nanotech products on the market today are in sports. Last year, we featured Nanogate/Holmenkol's Cerax Nanotech Ski Wax, Babolat Tennis Racquets using nanotubes and longer-lasting nanoparticle tennis balls from Inmat/Wilson. In 2004, sports led the way for nanotechnology commercialization yet again. From golf balls to footwarmers, athlete skin care to new tennis racquets, consumer demand for better exercise equipment and materials is still driving nanotech revenues

Safe Utilization of Advanced Nanotechnology

Many words have been written about the dangers of advanced nanotechnology. Most of the threatening scenarios involve tiny manufacturing systems that run amok, or are used to create destructive products. A manufacturing infrastructure built around a centrally controlled, relatively large, self-contained manufacturing system would avoid these problems. A controlled nanofactory would pose no inherent danger, and it could be deployed and used widely. Cheap, clean, convenient, on-site manufacturing would be possible without the risks associated with uncontrolled nanotech fabrication or excessive regulation. Control of the products could be administered by a central authority; intellectual property rights could be respected. In addition, restricted design software could allow unrestricted innovation while limiting the capabilities of the final products. The proposed solution appears to preserve the benefits of advanced nanotechnology while minimizing the most serious risks.

Advanced Nanotechnology And Its Risks

As early as 1959, Richard Feynman proposed building devices with each atom precisely placed1. In 1986, Eric Drexler published an influential book, Engines of Creation2, in which he described some of the benefits and risks of such a capability. If molecules and devices can be manufactured by joining individual atoms under computer control, it will be possible to build structures out of diamond, 100 times as strong as steel; to build computers smaller than a bacterium; and to build assemblers and mini-factories of various sizes, capable of making complex products and even of duplicating themselves.

Drexler's subsequent book, Nanosystems3, substantiated these remarkable claims, and added still more. A self-contained tabletop factory could produce its duplicate in one hour. Devices with moving parts could be incredibly efficient. Molecular manufacturing operations could be carried out with failure rates less than one in a quadrillion. A computer would require a miniscule fraction of a watt and one trillion of them could fit into a cubic centimeter. Nanotechnology-built fractal plumbing would be able to cool the resulting 10,000 watts of waste heat. It seems clear that if advanced nanotechnology is ever developed, its products will be incredibly powerful.

As soon as molecular manufacturing was proposed, risks associated with it began to be identified. Engines of Creation2 described one hazard now considered unlikely, but still possible: grey goo. A small nanomachine capable of replication could in theory copy itself too many times4. If it were capable of surviving outdoors, and of using biomass as raw material, it could severely damage the environment5. Others have analyzed the likelihood of an unstable arms race6, and many have suggested economic upheaval resulting from the widespread use of free manufacturing7. Some have even suggested that the entire basis of the economy would change, and money would become obsolete8.

Sufficiently powerful products would allow malevolent people, either hostile governments or angry individuals, to wreak havoc. Destructive nanomachines could do immense damage to unprotected people and objects. If the wrong people gained the ability to manufacture any desired product, they could rule the world, or cause massive destruction in the attempt9. Certain products, such as vast surveillance networks, powerful aerospace weapons, and microscopic antipersonnel devices, provide special cause for concern. Grey goo is relevant here as well: an effective means of sabotage would be to release a hard-to-detect robot that continued to manufacture copies of itself by destroying its surroundings.

Clearly, the unrestricted availability of advanced nanotechnology poses grave risks, which may well outweigh the benefits of clean, cheap, convenient, self-contained manufacturing. As analyzed in Forward to the Future: Nanotechnology and Regulatory Policy10, some restriction is likely to be necessary. However, as was also pointed out in that study, an excess of restriction will enable the same problems by increasing the incentive for covert development of advanced nanotechnology. That paper considered regulation on a one-dimensional spectrum, from full relinquishment to complete lack of restriction. As will be shown below, a two-dimensional understanding of the problem—taking into account both control of nanotech manufacturing capability and control of its products—allows targeted restrictions to be applied, minimizing the most serious risks while preserving the potential benefits.

Nanotech Manufacturing and Its Products

The technology at the heart of this dilemma is molecular manufacturing. A machine capable of molecular manufacturing—whether nanoscale or macroscale—has two possible functions: to create more manufacturing capacity by duplicating itself, and to manufacture products. Most products created by molecular manufacturing will not possess any capacity for self-duplication, or indeed for manufacturing of any kind; as a result, each product can be evaluated on its own merits, without worrying about special risks. A nanotechnology-based manufacturing system, on the other hand, could build weapons, grey goo, or anything else it was programmed to produce. The solution, then, is to regulate nanofactories; products are far less dangerous. A nanotechnology-built car could no more turn into grey goo than a steel-and-plastic car could.

Some products, however, will be powerful enough to require restriction. Weapons built by nanotechnology would be far more effective than today's versions. Very small products could get lost and cause nano-litter, or be used to spy undetectably on people. And a product that included a general molecular manufacturing capability would be, effectively, an unregulated nanofactory—horrifyingly dangerous in the wrong hands. Any widespread use of nanotechnology manufacturing must include the ability to restrict, somehow, the range of products that can be produced.

If it can be done safely, widespread use of molecular manufacturing looks like a very good idea for the following reasons:
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The ability to produce duplicate manufacturing systems means that manufacturing capacity could be doubled almost for free.
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A single, self-contained, clean-running personal nanofactory could produce a vast range of strong, efficient, carbon-based products as they are needed.
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Emergency and humanitarian aid could be supplied quickly and cheaply.
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Many of the environmental pressures caused by our current technology base could be mitigated or removed entirely.
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The rapid and flexible manufacturing cycle will allow many innovations to be developed rapidly.

Although a complete survey and explanation of the potential benefits of nanotechnology is beyond the scope of this paper, it seems clear that the technology has a lot to offer.

All of these advantages should be delivered as far as is consistent with minimizing risks. Humanitarian imperatives and opportunities for profit both demand extensive use of nanotechnology. In addition, failure to use nanotechnology will create a pent-up demand for its advantages, which will virtually guarantee an uncontrollable black market. Once molecular manufacturing has been developed, a second, independent development project would be both far easier and far more dangerous than the original project. The first nanofactory must be made available for widespread use to reduce the impetus for independent development11.

Development of nanotechnology must be undertaken with care to avoid accidents; once a nanotechnology-based manufacturing technology is created, it must be administered with even more care. Irresponsible use of molecular manufacturing could lead to black markets, unstable arms races ending in immense destruction, and possibly a release of grey goo. Misuse of the technology by inhumane governments, terrorists, criminals, and irresponsible users could produce even worse problems—grey goo is a feeble weapon compared to what could be designed. It seems likely that research leading to advanced nanotechnology will have to be carefully monitored and controlled.

However, the same is not true of product research and development. The developer of nanotechnology-built products does not need technical expertise in nanotechnology. Once a manufacturing system is developed, product designers can use it to build anything from cars to computers, simply by reusing low-level designs that have previously been developed. A designer may safely be allowed to play with pieces 1,000 atoms on a side (one billion atoms in volume). This is several times smaller than a bacterium and 10,000,000 times smaller than a car.

Working with modular “building blocks” of this size would allow almost anything to be designed and built, but the blocks would be too big to do the kind of molecular manipulation that is necessary for nano-manufacturing or to participate in biochemical reactions. A single block could contain a tiny motor or a computer, allowing products to be powered and responsive. As long as no block contained machinery to do mechanochemistry, the designer could not create a new kind of nanofactory.

Once designed and built, a product of molecular manufacturing could be used by consumers just like a steel or plastic product. Of course, some products, such as cars, knives, and nail guns, are dangerous by design, but this kind of danger is one that we already know how to deal with. In the United States, Underwriter's Laboratories (UL), the Food and Drug Administration, and a host of industry and consumer organizations work to ensure that our products are as safe as we expect them to be. Nanotechnology products could be regulated in the same way. And if a personal nanofactory could only make approved products, it could be widely distributed, even for home use, without introducing any special risks.

Nanofactory Technology: Regulating Risk, Preserving Benefit

It is generally assumed, incorrectly, that devices built with nanotechnology must be quite small. This has led to fears that molecular manufacturing systems will be hard to control and easy to steal. In fact, as analyzed by Drexler and others in the field, the products of nanoscale mechanochemical plants can be attached together within the enclosure of a single device. Small building blocks can be joined to make bigger blocks; these blocks can be joined with others, and so on to form a product. This process is called convergent assembly, and it allows the creation of large products from nanoscale parts. In particular, convergent assembly will allow one nanofactory to build another nanofactory. There is no need to use trillions of free-floating assembler robots; instead, the assemblers—now called fabricators—are securely fastened inside the factory device, where they feed the smallest conveyor belts.

A typical personal nanofactory (PN) might be the size of a microwave oven. Since the fabricators are fastened into the factory and dependent on its power grid, they have no need to navigate around the product they are building—this improves efficiency—and they have no chance of functioning independently. In addition, the entire nanofactory can be controlled through a single interface, which allows restrictions to be built into the interface. It can simply refuse to produce any product that has not been approved. (The improved security of tethered nanotechnology factories has been a theme in at least one work of science fiction12.)

If a PN will only build safe products, and will refuse to build any product that has not been approved as safe, then the factory itself can be considered safe. It could even build a duplicate PN on request. With the restrictions built in, the second one would be as safe as the first. As long as the restrictions work as planned, there is no risk of grey goo, no risk of undesirable weapons or unapproved products, and no risk of producing unrestricted nanofactories that could be used to make bad products.

At the same time, products that were approved could be produced in any quantity desired. The products could even be customized, within limits—and the limits could be quite broad, for some kinds of products. If desired, the PNs (and the products) could have tracking devices built in to further deter inappropriate use.

With personal nanofactories that can only produce approved designs, the safety of molecular manufacturing does not depend on restricting the use of the factories. Instead, it depends on choosing correctly which products to approve. The nanofactory itself, as a product, can be approved for unlimited copying. This means that the abundant, cheap, and convenient production capability of advanced nanotechnology can be achieved without the risks associated with uncontrolled molecular manufacturing. A two-dimensional view of the risks of nanotechnology, which separates the means of production from the products, allows the design and implementation of policy that is minimally restrictive, yet still safe.

Using Nanotechnology Safely

A safe personal nanofactory design must build approved products, while refusing to build unapproved products. It must also be extremely tamper-resistant; if anyone found a way to build unapproved products, they could make an unrestricted, unsafe nanofactory, and distribute copies of it. The product approval process must also be carefully designed, to maximize the benefits of the technology while minimizing the risk of misuse. Restricted nanofactories avoid the extreme risk/benefit tradeoff of other nanotechnology administration plans, but they do require competent administration.

One way to secure a personal nanofactory is to build in only a limited number of safe designs. The user could ask it to produce any one of those designs, but with no way to feed in more blueprints, the factory could never build anything else. This simple scheme is fairly reliable, but not very useful. It also poses the risk that someone could take apart the factory and find a way to reprogram its design library.

A more useful and secure scheme would be to connect the PN to a central controller, and require it to ask for permission each time it was asked to manufacture something. This would allow new designs to be added to the design library after the nanofactory was built. In addition, the PN would have to report its status back to the central controller. The system could even be designed to require a continuous connection; a factory disconnected from the network would permanently disable itself.

This would greatly reduce the opportunity to take the factory apart, since it could report the attempt in real time, and failed attempts would result in immediate arrest of the perpetrator. This permanent connection would also allow the factory to be disabled remotely if a security flaw were ever discovered in that model. Finally, a physical connection would allow the location of the factory to be known, and jurisdictional limits to be imposed on its products.

Current cryptographic techniques permit verification and encryption of communication over an unsecured link. These are used in smart cards and digital cellular phones, and will soon be used in digital rights management13. Using such techniques, each personal nanofactory would be able to verify that it was in communication with the central library. Only designs from the library could be manufactured. In addition, each design could come with a set of restrictions. For example, medical tools might only be manufactured at the request of a doctor. Commercial designs could require payment from a user. Designs under development could be manufactured only by the inventor, until they were approved and released. A design that did not come from the central library would not have the proper cryptographic signature, and the factory would simply refuse to build it.

Product Design Parameters

Rapid innovation is a key benefit of nanotechnology. The rapid and flexible manufacturing process allows a design to be built and tested almost immediately. Because designers of nano-built products do not have to do any actual nanotechnology research, a high level of innovation can be accommodated without giving designers any access to dangerous kinds of products. As mentioned above, a design with billion-atom, sub-micron blocks—permitting specification of near-biological levels of complexity—would still pose no risk of illicit self-replication. The minimum building block size in a design could be restricted by the design system. A fully automated evaluation and approval process could also consider the energy and power contained in the design, its mechanical integrity, and the amount of computer power built in. The block-based design system provides a simple interface to the block-based convergent assembly system. A variety of design systems could be implemented using the same nanofactory hardware, and the designer would not have to become an expert on the process of construction to create buildable designs.

With a safe-design personal nanofactory, adults—and even children—could safely play with advanced robotics, inventing and constructing almost anything they could imagine. (Today, adults as well as children find it worthwhile to play with the Lego MindStorms™ system14.) More powerful products would require an engineering certification. This could be given to any responsible adult, since even a malicious product engineer would be unable to bypass the factory's programming and cause it to make illicit fabricators. A product that included chemical or nanomechanical manipulation ability would have to be carefully controlled, even during the design phase, to prevent the designer from building something that could be used for illicit nanomanufacturing.

Risks and dangers associated with products could be assessed on a per-product basis. Many products, produced with simplified design kits, could be approved with only automated analysis of their design. Most others could be approved after a safety and efficacy assessment similar to today's approval processes. Only rarely would a new degree of nanotechnological functionality be required, so each case could be carefully assessed before the functionality was added to appropriately restricted design programs.

Product approval for worldwide availability could depend on any of several factors. First, unless designed with a child-safe design program, it could be evaluated for engineering safety. Second, if the design incorporated intellectual property, the owner of the property could specify licensing terms. Third, local jurisdictional restrictions could be imposed, tagging the file according to where it could and could not be manufactured. Finally, the design would be placed in the global catalog, available for anyone to use.

Nanotechnology offers the ability to build large numbers of products that are incredibly powerful by today's standards. This possibility creates both opportunity and risk. The problem of minimizing the risk is not simple; excessive restriction creates black markets, which in this context implies unrestricted nano fabrication. Selecting the proper level of restriction is likely to pose a difficult challenge.

control of the molecular manufacturing capacity, and control of the products. Such a system has many advantages. A well-controlled manufacturing system can be widely deployed, allowing distributed, cheap, high-volume manufacturing of useful products and even a degree of distributed innovation. The range of possible nanotechnology-built products is almost infinite. Even if allowable products were restricted to a small subset of possible designs, it would still allow an explosion of creativity and functionality.

Preventing a personal nanofactory from building unapproved products can be done using technologies already in use today. It appears that the nanofactory control structure can be made virtually unbreakable. Product approval, by contrast, depends to some extent on human institutions. With a block-based design system, many products can be assessed for degree of danger without the need for human intervention; this reduces subjectivity and delay, and allows people to focus on the few truly risky designs.

In addition to preventing the creation of unrestricted molecular manufacturing devices, further regulation will be necessary to preserve the interests of existing commercial and military institutions. For example, the effects of networked computers on intellectual property rights have created concern in several industries15, and the ability to fabricate anything will surely increase the problem. National security will demand limits on the weapons that can be produced

The Silicon Valley Faire

The tour of the molecular world showed some products of molecular manufacturing, but didn't show how they were made. The technologies you remember from the old days have mostly been replaced—but how did this happen? The Silicon Valley Faire is advertised as "An authentic theme park capturing life, work, and play in the early Breakthrough years." Since "work" must include manufacturing, it seems worth a visit.

A broad dome caps the park — "To fully capture the authentic sights, sounds, and smells of the era," the tourguide politely says. Inside, the clothes and hairstyles, the newspaper headlines, the bumper-to-bumper traffic, all look much as they did before your long nap. A light haze obscures the buildings on the far side of the dome, your eyes burn slightly, and the air smells truly authentic.

The Nanofabricators, Inc., plant offers the main display of early nanotechnology. As you near the building, the tourguide mentions that this is indeed the original manufacturing plant, given landmark status over twenty years ago, then made the centerpiece of the Silicon Valley Faire ten years later, when . . . With a few taps, you reset the pocket tourguide to speak up less often.

Pocket Libraries

As people file into the Nanofabricator plant, there's a moment of hushed quiet, a sense of walking into history. Nanofabricators: home of the SuperChip, the first mass-market product of nanotechnology. It was the huge memory capacity of SuperChips that made possible the first Pocket Library.

This section of the plant now houses a series of displays, including working replicas of early products. Picking up a Pocket Library, you find that it's not only the size of a wallet, but about the same weight. Yet it has enough memory to record every volume in the Library of Congress—something like a million times the capacity of a personal computer from 1990. It opens with a flip, the two-panel screen lights up, and a world of written knowledge is at your fingertips. Impressive.

"Wow, can you believe these things?" says another tourist as he fingers a Pocket Library. "Hardly any video, no 3-D–just words, sound, and flat pictures. And the cost! I wouldn't have bought `em for my kids at that price!"

Your tourguide quietly states the price: about what you remember for a top-of-the-line TV set from 1990. This isn't the cheap manufacturing promised by mature nanotechnology, but it seems like a pretty good price for a library. Hmm . . . how did they work out the copyrights and royalties? There's a lot more to this product than just the technology . . .

Nanofabrication

The next room displays more technology. Here in the workroom where SuperChips were first made, early nanotech manufacturing is spread out on display. The whole setup is surprisingly quiet and ordinary. Back in the 1980s and 1990s, chip plants had carefully controlled clean rooms with gowns and masks on workers and visitors, special workstations, and carefully crafted air flows to keep dust away from products. This room has none of that. It's even a little grubby.

In the middle of a big square table are a half-dozen steel tanks, about the size and shape of old-fashioned milk cans. Each can has a different label identifying its contents: MEMORY BLOCKS, DATA-TRANSMISSION BLOCKS, INTERFACE BLOCKS. These are the parts needed for building up the chip. Clear plastic tubes, carrying clear and tea-colored liquids, emerge from the mouths of the milk cans and drape across the table. The tubes end in fist-sized boxes mounted above shallow dishes sitting in a ring around the cans. As the different liquids drip into each dish, a beater like a kitchen mixer swirls the liquid. In each dish, nanomachines are building SuperChips.

A Nanofab "engineer," dressed in period clothing complete with name badge, is setting up a dish to begin building a new chip. "This," he says, holding up a blank with a pair of tweezers, "is a silicon chip like the ones made with pre-breakthrough technology. Companies here in this valley made chips like these by melting silicon, freezing it into lumps, sawing the lumps into slices, polishing the slices, and then going through a long series of chemical and photographic steps. When they were done, they had a pattern of lines and blobs of different materials on the surface. Even the smallest of these blobs contained billions of atoms, and it took several blobs working together to store a single bit of information. A chip this size, the size of your fingernail, could store only a fraction of a billion bits. Here at Nanofab, we used bare silicon chips as a base for building up nanomemory. The picture on the wall here shows the surface of a blank chip: no transistors, no memory circuits, just fine wires to connect up with the nanomemory we built on top. The nanomemory, even in the early days, stored thousands of billions of bits. And we made them like this, but a thousand at a time–" He places the chip in the dish, presses a button, and the dish begins to fill with liquid.

"A few years latter," he adds, "we got rid of the silicon chips entirely"—he props up a sign saying THIS CHIP BUILD BEGAN AT: 2:15 P.M., ESTIMATED COMPLETION TIME: 1:00 A.M.—" and we sped up the construction process by a factor of a thousand."

The chips in the dishes all look pretty much the same except for color. The new chip looks like dull metal. The only difference you can see in the older chips, further along in the process, is a smooth rectangular patch covered by a film of darker material. An animated flowchart on the wall shows how layer upon layer of nanomemory building blocks are grabbed from solution and laid down on the surface to make that film. The tourguide explains that the energy for this process, like the energy for molecular machines within cells, comes from dissolved chemicals—from oxygen and fuel molecules. The total amount of energy needed here is trivial, because the amount of product is trivial: at the end of the process, the total thickness of nanomemory structure—the memory store for a Pocket Library—amounts to one-tenth the thickness of a sheet of paper, spread over an area smaller than a postage stamp.

Molecular Assembly

The animated flowchart showed nanomemory building blocks as big things containing about a hundred thousand atoms apiece (it takes a moment to remember that this is still submicroscopic). The build process in the dishes stacked these blocks to make the memory film on the SuperChip, but how were the blocks themselves built? The hard part in this molecular-manufacturing business has got to be at the bottom of the whole process, at the stage where molecules are put together to make large, complex parts.

The Silicon Valley Faire offers simulations of this molecular assembly process, and at no extra charge. From the tourguide, you learn that modern assembly processes are complex; that earlier processes—like those used by Nanofabricators, Inc.—used clever-but-obscure engineering tricks; and that the simplest, earliest concepts were never built. Why not begin at the beginning? A short walk takes you to the Museum of Antique Concepts, the first wing of the Museum of Molecular Manufacturing.

A peek inside the first hall shows several people strolling around wearing loosely fitting jumpsuits with attached goggles and gloves, staring at nothing and playing mime with invisible objects. Oh well, why not join the fools' parade? Stepping through the doorway while wearing the suit is entirely different. The goggles show a normal world outside the door and a molecular world inside. Now you, too, can see and feel the exhibit that fills the hall. It's much like the earlier simulated molecular world: it shares the standard settings for size, strength, and speed. Again, atoms seem 40 million times larger, about the size of your fingertips. This simulation is a bit less thorough than the last was—you can feel simulated objects, but only with your gloved hands. Again, everything seems to be made of quivering masses of fused marbles, each an atom.

"Welcome," says the tourguide, "to a 1990 concept for a molecular-manufacturing plant. These exploratory engineering designs were never intended for actual use, yet they demonstrate the basics of molecular manufacturing: making parts, testing them, and assembling them."

Machinery fills the hall. Overall, the sight is reminiscent of an automated factory of the 1980s or 1990s. It seems clear enough what must be going on: Big machines stand beside a conveyor belt loaded with half-finished-looking blocks of some material (this setup looks much like Figure 2); the machines must do some sort of work on the blocks. Judging by the conveyor belt, the blocks eventually move from one arm to the next until they turn a corner and enter the next hall.

FIGURE 2: ASSEMBLER WITH FACTORY ON CHIP

A factory large enough to make over 10 million nanocomputers per day would fit on the edge one of today's integrated circuits. Inset shows an assembler arm together with workpiece on a conveyor belt.

Since nothing is real, the exhibit can't be damaged, so you walk up to a machine and give it a poke. It seems as solid as the wall of the nanocomputer in the previous tour. Suddenly, you notice something odd: no bombarding air molecules and no droplets of water—in fact, no loose molecules anywhere. Every atom seems to be part of a mechanical system, quivering thermal vibration, but otherwise perfectly controlled. Everything here is like the nanocomputer or like the tough little gear; none of it resembles the loosely coiled protein or the roiling mass of the living cell.

The conveyor belt seems motionless. At regular intervals along the belt are blocks of material under construction: workpieces. The nearest block is about a hundred marble-bumps wide, so it must contain something like 100 x 100 x 100 atoms, a full million. This block looks strangely familiar, with its rods, crank, and the rest. It's a nanocomputer—or rather, a block-like part of a nanocomputer still under construction.

Standing alongside the pieces of nanocomputer on the conveyor belt, dominating the hall, is a row of huge mechanisms. Their trunks rise from the floor, as thick as old oaks. Even though they bend over, they rear overhead. "Each machine," your tourguide says, "is the arm of a general-purpose molecular assembler.

One assembler arm is bent over with its tip pressed to a block on the conveyor belt. Walking closer, you see molecular assembly in action. The arm ends in a fist-sized knob with a few protruding marbles, like knuckles. Right now, two quivering marbles—atoms—are pressed into a small hollow in the block. As you watch, the two spheres shift, snapping into place in the block with a quick twitch of motion: a chemical reaction. The assembler arm just stands there, nearly motionless. The fist has lost two knuckles, and the block of nanocomputer is two atoms larger.

The tourguide holds forth: "This general-purpose assembler concept resembles, in essence, the factory robots of the 1980s. It is a computer-controlled mechanical arm that moves molecular tools according to a series of instructions. Each tool is like a single-shot stapler or rivet gun. It has a handle for the assembler to grab and comes loaded with a little bit of matter—a few atoms—which it attaches to the workpiece by a chemical reaction." This is like the rejoining of the protein chain in the earlier tour.

Molecular Precision

The atoms seemed to jump into place easily enough; can they jump out of place just as easily? By now the assembler arm has crept back from the surface, leaving a small gap, so you can reach in and poke at the newly added atoms. Poking and prying do no good; when you push as hard as you can (with your simulated fingers as strong as steel), the atoms don't budge by a visible amount. Strong molecular bonds hold them in place.

Your pocket tourguide—which has been applying the power of a thousand 1990s supercomputers to the task of deciding when to speak up—remarks, "Molecular bonds hold things together. In strong, stable materials atoms are either bonded, or they aren't, with no possibilities in between. Assemblers work by making and breaking bonds, so each step either succeeds perfectly or fails completely. In pre-breakthrough manufacturing, parts were always made and put together with small inaccuracies. These could add up to wreck product quality. At the molecular scale, these problems vanish. Since each step is perfectly precise, little errors can't add up. The process either works, or it doesn't."

But what about those definite, complete failures? Fired by scientific curiosity, you walk to the next assembler, grab the tip, and shake it. Almost nothing happens. When you shove as hard as you can, the tip moves by about one-tenth of an atomic diameter, then springs back. "Thermal vibrations can cause mistakes by causing parts to come together and form bonds in the wrong place," the tourguide remarks. "Thermal vibrations make floppy objects bend further than stiff ones, and so these assembler arms were designed to be thick and stubby to make them very stiff. Error rates can be kept to one in a trillion, and so small products can be perfectly regular and perfectly identical. Large products can be almost perfect, having just a few atoms out of place." This should mean high reliability. Oddly, most of the things you've been seeing outside have looked pretty ordinary—not slick, shiny, and perfect, but rough and homey. They must have been manufactured that way, or made by hand. Slick, shiny things must not impress anyone anymore.

Molecular Robotics

By now, the assembler arm has moved by several atom-widths. Through the translucent sides of the arm you can see that the arm is full of mechanisms: twirling shafts, gears, and large, slowly turning rings that drive the rotation and extension of joints along the trunk. The whole system is a huge, articulated robot arm. The arm is big because the smallest parts are the size of marbles, and the machinery inside that makes it move and bend has many, many parts. Inside, another mechanism is at work: The arm now ends in a hole, and you can see the old, spent molecular tool being retracted through a tube down the middle.

Patience, patience. Within a few minutes, a new tool is on its way back up the tube. Eventually, it reaches the end. Shafts twirl, gears turn, and clamps lock the tool in position. Other shafts twirl, and the arm slowly leans up against the workpiece again at a new site. Finally, with a twitch of motion, more atoms jump across, and the block is again just a little bit bigger. The cycle begins again. This huge arm seems amazingly slow, but the standard simulation settings have shifted speeds by a factor of over 400 million. A few minutes of simulation time correspond to less than a millionth of a second of real time, so this stiff, sluggish arm is completing about a million operations per second.

Peering down at the very base of the assembler arm, you can get a glimpse of yet more assembler-arm machinery underneath the floor: Electric motors spin, and a nanocomputer chugs away, rods pumping furiously. All these rods and gears move quickly, sliding and turning many times for every cycle of the ponderous arm. This seems inefficient; the mechanical vibrations must generate a lot of heat, so the electric motors must draw a lot of power. Having a computer control each arm is a lot more awkward now than it was in pre-breakthrough years. Back then, a robot arm was big and expensive and a computer was a cheap chip; now the computer is bigger than the arm. There must be a better way—but then, this is the Museum of Antique Concepts.

Building-Blocks into Buildings

Where do the blocks go, once the assemblers have finished with them? Following the conveyor belt past a dozen arms, you stroll to the end of the hall, turn the corner, and find yourself on a balcony overlooking a vaster hall beyond. Here, just off the conveyor belt, a block sits in a complex fixture. Its parts are moving, and an enormous arm looms over it like a construction crane. After a moment, the tourguide speaks up and confirms your suspicion: "After manufacturing, each block is tested. Large arms pick up properly made blocks. In this hall, the larger arms assemble almost a thousand blocks of various kinds to make a complete nanocomputer.

The grand hall has its own conveyor belt, bearing a series of partially completed nanocomputers. Arrayed along this grand belt is a row of grand arms, able to swing to and fro, to reach down to lesser conveyor belts, pluck million-atom blocks from testing stations, and plug them into the grand workpieces, the nanocomputers under construction. The belt runs the length of the hall, and at the end, finished nanocomputers turn a corner—to a yet-grander hall beyond?

After gazing at the final-assembly hall for several minutes, you notice that nothing seems to have moved. Mere patience won't do: at the rate the smaller arms moved in the hall behind you, each block must take months to complete, and the grand block-handling arms are taking full advantage of the leisure this provides. Building a computer, start to finish, might take a terribly long time. Perhaps as long as the blink of an eye.

Molecular assemblers build blocks that go to block assemblers. The block assemblers build computers, which go to system assemblers, which build systems, which–at least one path from molecules to large products seems clear enough. If a car were assembled by normal-sized robots from a thousand pieces, each piece having been assembled by smaller robots from a thousand smaller pieces, and so on, down and down, then only ten levels of assembly process would separate cars from molecules. Perhaps, around a few more corners and down a few more ever-larger halls, you would see a post-breakthrough car in the making, with unrecognizable engine parts and comfortable seating being snapped together in a century-long process in a hall so vast that the Pacific Ocean would be a puddle in the corner . . .

Just ten steps in size; eight, starting with blocks as big as the ones made in the hall behind you. The molecular world seems closer, viewed this way.

Molecular Processing

Stepping back into that hall, you wonder how the process begins. In every cycle of their sluggish motion, each molecular assembler gets a fresh tool through a tube from somewhere beneath the floor, and that somewhere is where the story of molecular precision begins. And so you ask, "Where do the tools come from?", and the tourguide replies, "You might want to take the elevator to your left."

Stepping out of the elevator and into the basement, you see a wide hall full of small conveyor belts and pulleys; a large pipe runs down the middle. A plaque on the wall says, "Mechanochemical processing concept, circa 1990." As usual, all the motions seem rather slow, but in this hall everything that seems designed to move is visibly in motion. The general flow seems to be away from the pipe, through several steps, and then up through the ceiling toward the hall of assemblers above.

After walking over to the pipe, you can see that it is nearly transparent. Inside is a seething chaos of small molecules: the wall of the pipe is the boundary between loose molecules and controlled ones, but the loose molecules are well confined. In this simulation, your fingertips are like small molecules. No matter how hard you push, there's no way to drive your finger through the wall of the pipe. Every few paces along the pipe a fitting juts out, a housing with a mechanically driven rotating thing, exposed to the liquid inside the pipe, but also exposed to a belt running over one of the pulleys, embedded in the housing. It's hard to see exactly what is happening.

The tourguide speaks up, saying, "Pockets on the rotor capture single molecules from the liquid in the pipe. Each rotor pocket has a size and shape that fits just one of the several different kinds of molecule in the liquid, so the process is rather selective. Captured molecules are then pushed into the pockets on the belt that's wrapped over the pulley there, then—"

"Enough," you say. Fine, it singles out molecules and sticks them into this maze of machinery. Presumably, the machines can sort the molecules to make sure the right kinds go to the right places.

The belts loop back and forth carrying big, knobby masses of molecules. Many of the pulleys—rollers?—press two belts together inside a housing with auxiliary rollers. While you are looking at one of these, the tourguide says, "Each knob on a belt is a mechanochemical-processing device. When two knobs on different belts are pressed together in the right way, they are designed to transfer molecular fragments from one to another by means of a mechanically forced chemical reaction. In this way, small molecules are broken down, recombined, and finally joined to molecular tools of the sort used in the assemblers in the hall above. In this device here, the rollers create a pressure equal to the pressure found halfway to the center of the Earth, speeding a reaction that –"

"Fine, fine," you say. Chemists in the old days managed to make amazingly complex molecules just by mixing different chemicals together in solution in the right order under the right conditions. Here, molecules can certainly be brought together in the right order, and the conditions are much better controlled. It stands to reason that this carefully designed maze of pulleys and belts can do a better job of molecule processing than a test tube full of disorganized liquid ever could. From a liquid, through a sorter, into a mill, and out as tools: this seems to be the story of molecule processing. All the belts are loops, so the machinery just goes around and around, carrying and transforming molecular parts.