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1 / Nanoworld : the keys for understanding

 It was on December 29, 1959, at the annual meeting of the American Physical Society, that Richard Feynman gave his lecture entitled “There's plenty of room at the bottom.” With this rather peculiar title, the American physicist urged the scientific community to undertake an exploration of the universe of the infinitesimally small. But it wasn't until the 1980s and the inventions of the Scanning Tunneling Microscope (STM, see illustration) and the Atomic Force Microscope (AFM), that the nanoworld (i.e., length-scales between 1 and 100 nanometers) really opened up for researchers.1 Scientists were finally able to look at molecules, DNA, and the atomic structure of matter. “To be able to work at this scale, the most important prerequisite is to see what you're doing,” shares Christian Joachim, chemist at CNRS' Center for Material Elaboration and Structural Studies (CEMES).2 By the end of the 1980s, through the extreme precision of their tools (especially by using STM or AFM tips), scientists were able to manipulate atoms one by one. This process kick-started the field of nanosciences, the study of the fundamental physical-chemical properties of nanometer-sized objects. With progressively more efficient tools, the design, fabrication, and manipulation of objects, materials, and even machines of nanometric dimensions could finally begin.

 

scanning tunneling microscope

 

The Scanning Tunneling Microscope (STM) is used to study the surfaces of conducting materials. It makes it possible to visualize the atoms and obtain images at an atomic scale. The principle is simple: an extremely fine metallic tip–a nanotip–ending in a few atoms, even a single atom, hovers over the surface of the material a few nanometers away. An electric voltage is applied between the tip and the surface. Electrons can then tunnel through this distance and produce an electric current. By scanning the tip over the surface, a relief map is created and the atoms can thereby be located and their relative position measured with a precision of the order of 0.1 nm. With this tip, atoms can also be manipulated and moved one by one.

 

 

But why strive to see so deep into the heart of matter? “Because of the new properties that matter exhibits at this scale and which are not found in larger objects,” states Jean-Yves Marzin, physicist and director of CNRS' Photonics and Nanostructures Laboratory (LPN) in Marcoussis. Similarly, Gérard Benassayag, physicist at CEMES, sees in the nanosciences a path to discovering “in small dimensions the effects that are hidden in large ones.” Stated differently, many different properties of materials–optical, catalytic, mechanical, magnetic, thermal, electrical–depend in large part on their size. At the nanometer scale, certain properties appear, others disappear, some are vastly improved while others are disrupted and no longer follow the laws of classical physics. At this scale, physicists apply the laws of quantum mechanics: For example, electrons no longer move around as part of an uninterrupted current  but travel separately, one by one.

 

We can already understand the scientific stakes of nanoscience: Understanding how matter is structured at small scales, and one day being able to control these properties to design new devices, circuits, and even systems. And these scientific stakes meet those of industry. Starting in the 1950s, the advent of silicon integrated circuits has set off one of history's most important technological revolutions: microelectronics. To this day, the electronics industry continues to develop in accordance with Moore's laws, which state that: (i) the size of a transistor (semiconductor device) is reduced by half every 18 months, making it possible to increase the density of integration and the performance of electronic circuits, and (ii) that the cost of a manufacturing facility doubles every 36 months. Inevitably, the miniaturization and growing density of transistors (currently 130 nm for the Pentium 4, approaching the realm of nanoscience) lead to problems with manufacturing and reliability. Researchers are now imagining ways to bypass these problems by exploring the nanoworld and proposing alternative architectures for the circuits of tomorrow.

 

 

1ere image nanos

© L. Médard/CNRS Photothèque

Tool for studying and displaying nano-objects. On the left of the screen, carbon nanotubes deposited on a silicon substrate, visualized through an Atomic Force Microscope (AFM), seen in the background.


But nanoscience and nanotechnology are not only having an impact on microelectronics but also affecting almost every scientific discipline (medicine, biotechnologies, chemistry, environmental sciences, etc.) and also the whole field of materials (metals, polymers, and ceramics). “Thanks to nanotechnologies, our laboratories create and study artificial atoms, or nano-objects, with specific behaviors and properties,” states Michel Lannoo, Director of the MIPPU department at CNRS.3 And in addition to the fundamental aspect of this research, laboratories are already turning out a multitude of promising applications: nanocomposites for improving the performance of polymers or ceramics; carbon nanotubes and silicon nanowires for electronics; drugs programmed to act directly on their target; nanoparticles for trapping pollutants in water, and many more. Yes, nanotechnology is expanding, as an increasing number of laboratories in France and around the world are focusing their attention and pouring resources into this field. A lively competition was sparked in the last four years between the US, Japan, and Europe to master this technology. The US government spends an annual $1 billion on nanoscience and nanotechnology research, Japan close to $850 million, while the national governments of the EU countries spend a collective €700 million on their national research institutions in this field. This enthusiasm is justified by the prospect of impressive economic returns. According to the US National Science Foundation, goods and services linked to nanotechnology will generate a trillion dollar market over the next 10 years.

 

In Europe, nanotechnology has become a major objective of the European Commission's sixth Framework Program for Research and Technological Development (FP6) and will absorb some 10% of the program's budget. In France, the Ministry of Research and more recently the National Agency for Research launched a program entitled “Nanosciences and Nanotechnologies” as a priority sector (see box, p. 22). According to science historian Bernadette Bensaude-Vincent,4 “industrialists are in a mindset of maximum reduction of the use of raw materials,” hence both cutting manufacturing costs and gaining independence from producers. This “dematerialization” translates into a reduced consumption of steel, aluminum and plastic, and a switch to products that are lighter and more powerful. “The advent of nanotechnology is a part of this trend,” concludes Bensaude-Vincent.

While governments, conscious of the strategic importance of exploring the nanoworld, are financing public research, industrial involvement is still rather timid. The reason is that there are still few applications that are commercially viable today. Noteworthy, though, are the introduction of nanocomposites in the running boards of General Motors pickup trucks and the existence of nanoparticle-based cosmetic products.

And there is yet another obstacle: the potential dangers of nanoparticles. Robert Plana, a researcher at the Laboratory of Systems Analysis and Architecture (LAAS)5 fears possible social rejection of these technologies by society. For Lannoo, in order to work with full knowledge of the facts, and address any public concerns, it is important “to rigorously study the impact of nanotechnology on health and the environment. But we should also be careful not to ban certain types of research too prematurely.” A number of high-level French teams already have significant know-how in characterization, modeling, handling, and fabrication of nano-objects.

 

 

NANO-OBJECTS, NANOMACHINES AND NANOMATERIALS

 

modeling

© J.-L. Barrat / L. Mattioni / J. Wittmer

Modeling, another means of “penetrating” and understanding the nanoworld. Here, a model of a melt of polymers reinforced by nano-objects.


At CEMES, for example, physicists and chemists know how to prepare nanometer-sized objects–nanoparticles or nano-clusters, two-dimensional thin films, crystals for optics, carbon materials (nanotubes, nanowires, and fullerenes) and synthetic molecules–through various chemical and physical methods. Researchers can observe the atomic structure of the surface of materials through scanning electronic microscopes (STMs and AFMs) and within the bulk through X-ray diffraction. They are also able to modify matter by manipulating atoms, using a combination of imaging tools and focused ion beams. “We can analyze the resulting properties of these nano-objects and, if they prove interesting, try to take advantage of them.” says Benassayag. So how exactly are these new objects fabricated? There are two distinct methods. The top-down approach developed through microelectronics, consists of reducing the dimensions of an object to nanometric sizes, within the limits of the fabrication tools and the operation of the object in question. The bottom-up approach, developed in research laboratories, consists of starting with atoms and molecules and assembling them in a controlled manner to form new objects, structures and machines.

 

The top-down approach suffers from miniaturization problems that can affect reliability  when reaching very small scales. One example is optical lithography, currently the most commonly used technique in the microprocessor industry, that makes it possible to write and reproduce patterns on a thin resin film and subsequently to etch them on a semiconductor. This method is also used for fabricating nano-structured substrates, by patterning their surface with nanometer-scale relief on which physicists and chemists can place nanoparticles, to create new materials (see box). However, the further the descent into nanometer dimensions, the harder it becomes to adapt this method to mass production. CNRS researchers are exploring alternative methods to improve on the top-down option. Nano-imprinting, for example, consists of duplicating nanostructures initially fabricated on a polymer mold by very high resolution lithography (Laas); Electronic nanolithography and nanowriting use focused ion beams, in which a scanning beam acts as a stylus for drawing nanostructures on surfaces (Laboratory of Photonics and Nanostructures (LPN) in Marcoussis).

 

femme nanos

© L. Médard/CNRS Photothèque

A “chemical” method for synthesizing nano-objects (nanotubes and chemical vapor deposition). In the reactor pictured here, carbon nanotubes are being made.


 

The bottom-up approach based on chemical principles makes it possible to create artificial objects (synthetic molecules, clusters)–which do not exist naturally–by using atoms and molecules. Here too, numerous processes exist but still remain confined to laboratories. According to Christian Joachim of CEMES, a single atom or molecule must be studied for itself and for its functions. “That's why we design, synthesize and study unimolecular nanomachines capable of calculating, acting mechanically and communicating,” he explains. “We are developing all the synthetic chemistry, the modern techniques for nanocommunication and nanomanipulation, to be able to control a single molecule and exchange information with it.” The goal is to make a machine with the fewest atoms possible. One of the spectacular results obtained in such a way is the molecular wheelbarrow, made up of two wheels, two arms, and two legs. When it encounters an atom, this nanomachine is capable of hooking it under itself and depositing it further. Today's nanomachines still have no motor and need to be pushed with a nano-tip to move, but they can help us understand the future capabilities of nanorobots. Another priority for the team is to develop a binary calculation unit, less than 1 nm in size, with a single molecule. Atomic nanowires will then need to be connected to this molecule for data input and output. “In brief,” concludes Joachim, “we are developing the technological basis for the ultimate miniaturization of future computers.”

 

At the Laboratory for Condensed Matter and Nanostructure Physics (LPMCN)6 in Lyon, the bottom-up approach is used to construct the building blocks for nanomaterials. In this laboratory, specialized in the fabrication of clusters–small packets of about a hundred atoms, also called nanoparticles–by gas-phase physical processes, “novel assemblies of atoms are created, and their properties, stability and effectiveness are investigated,” says Alain Perez, Director of LPMCN. The results obtained are interesting: semiconducting silicon cage-type (fullerene) clusters, magnetic nanostructures based on metals (iron, cobalt, nickel) and alloys, and systems for optical applications based on strongly fluorescent clusters and noble metals, like gold and silver.

 

lattic zoom

© C. Deranlot/CNRS Photothèque

Image of a two-dimensional lattice of gold clusters deposited on a graphite substrate, nanostructured using the focused ion beam technique. The defects (nanocraters) created on the substrate, with a 300 nm spacing, trap the clusters.


“Based on these nanoparticles which are delicately placed on suitable substrates, we prepare functional nanostructures and conduct fundamental physical studies according to the purpose of the system obtained. Once the nanostructure has been well studied and the system's properties adapted to implementing a component, we move on to a technology transfer phase with our industrial partners,” concludes Perez, who states that the two approaches, bottom-up and top-down, “are more complementary than opposed. In our case, for example, we use substrates patterned by ionic nano-etching (top-down), on which we deposit our clusters (bottom-up) to make two-dimensional lattices which herald future components with very high integration density.”

Of all the nano-objects, the carbon nanotube is certainly the most fashionable. Accidentally discovered in 1991, this small tube is composed of one or more sheets of carbon, ordered in hexagonal structures, rolled around themselves with a diameter that ranges between 1.4 and 100 nm and a length of about 1 mm. “On paper, the potential is incredible,” explains Catherine Journet, assistant professor and researcher at LPMCN. It can behave like a metal, but it can also be a good semiconductor. Furthermore, it has very interesting optical, chemical, and mechanical properties: It is both light and very resistant to rupture and deformation, it is also very flexible, can bend to very small angles, and be deformed and twisted. This little gem offers truly interesting perspectives both as an electronic component (as connector, optoelectronic component, laser, etc.) and as mechanical reinforcement (in composites), but also for storing energy (in batteries). “In fact, all its properties depend on the number of sheets of graphite and the manner in which they are rolled up,” specifies Journet. And to be able to measure several intrinsic properties of each type of nanotube rapidly, efficiently, and simultaneously, the team of Stephen Purcell, senior researcher at LPMCN, developed an original method based on field effect electron emission.

 

A few applications are already emerging. In the area of mechanics, the Physical Metallurgy and Physics of Materials Study Group in Villeurbanne7 studies particular nanocomposites with a polymer matrix strengthened by nanotubes. In the field of energy, some early trials of storing hydrogen by adsorption have been conducted at the Institute for Science and Engineering of Materials for Processes (IMP) of Odeillo.8 Additionally, flat screen displays based on carbon nanotubes are being developed  at the Laboratory for Electronics and Information Technology (Leti)9 in Grenoble.

But there are other nano-objects valuable for their new properties at a nanometric scale, particularly gold nanoparticles. “In 1982, when a Japanese researcher showed that at sizes of 2 or 3 nm, gold particles became catalytic and were capable of eliminating carbon monoxide, it was thought to be a hoax,” says Olivier Pluchery, physicist and assistant professor at the Paris Institute of Nanosciences.10 “Indeed, gold is the most inert metal that exists in nature.” Physicists have also shown that gold, at nanometric scale, acquires very good optical sensitivity.

Nanosciences and nanotechnologies “represent a priority for today's research,” indicates Plana. To ensure strategic monitoring of these fields, CNRS and the CEA created an Observatory of Micro- and Nanotechnologies (OMNT), whose mission is to spot technological breakthroughs and provide reliable information to French researchers and industrialists in this field.

 

Fabrice Impériali

 

 

 

 

 

 

nanomaterial

© E. Perin / CNRS Photothèque

Nanotechnologies are bolstering electronics, a field that has so far developed in accordance with Moore's Laws. This press makes “nano-imprinted” electronic chips.


WHAT IS A NANOMATERIAL?

 

A nanomaterial is a controlled arrangement of nano-objects. Using nano-objects, researchers try to improve the properties of materials (resistance to erosion, catalysis, etc.) or create new ones (adherence, aesthetics, optics, electronics, etc.). Several approaches are possible:

– Surface structuring of the materials with nano-objects: the smaller the objects, the larger the surface area for exchange and the greater the reactivity between the material and its environment.

Strengthening of the materials by incorporating nano-objects. An example: composites reinforced by metallic particles to make plastic conductors.

Designing bulk materials with nano-objects. In this case, it is difficult to obtain a large quantity of material. Nano-objects are either integrated in the bulk, or are deposited on the surfaces.

F. I

 

 

 

NANOSCIENCE IN FRANCE

 

In 2001, the Ministry of Research, in partnership with CNRS and the CEA, launched a national program to fund basic research in nanoscience, industry-oriented research in nanotechnology, and to support infrastructures. This program is now being continued by the newly established National Agency for Research (www.gip-anr.fr/appels/2005/pnano.htm).

French basic research in nanoscience involves 210 laboratories, (180 of which are associated with CNRS) and 2000 full-time researchers and academics. As for government spending, France, with its €180 million annual expenditure in nanoscience, is among the top three European countries behind Germany (€250 million), and the United Kingdom (€200 million), but still far behind the US ($1 billion) and Japan ($850 million).

To meet the international competition, the Ministry of Research commissioned CNRS to organize a European network via the Eranet instrument of the European Commission whose purpose is to coordinate scientific policies, programs, and funding of national research organizations. This consortium, called Nanoscience in the European Research Area (NanoSci-ERA), brings together 17 organizations from 12 ERA countries. Its objective is to coordinate the national policies on basic research in nanoscience and support transnational collaborations among the researchers. The first NanoSci-ERA call for proposals was launched in March 2006 (http://www.nanosci-era.org/).

F. I.

> Contact:

Izo Abram, Izo.abram@cnrs-dir.fr

 

 

 

GLOSSARY

 

>> Atomic Force Microscope

This microscope makes it possible to observe the surface of insulating materials such as polymers, ceramics and biological materials with atomic resolution. Its key element is a sharp tip, fixed on a flexible lever arm, which follows the relief of the material to be observed. The deformation of the lever is monitored by a laser beam, measured by a photodetector and recorded on a computer.

 

>> Semiconductor

Materials that are normally non-conducting, but can be made to conduct electricity by “doping,” that is by the introduction of atoms that act as electron donors or acceptors.

 

>> Nano-objects

Zero-dimensional objects: nanoparticles (clusters, colloids, nanocrystals and fullerenes) composed of several tens to a few thousand atoms grouped in packets or assembled in the form of a cage. All three of their dimensions are nanometric.

One-dimensional objects: Carbon nanotubes and nanowires; cylinder-like objects with one long dimension (several micrometers) but nanometric in the two transverse directions.

Two-dimensional objects: nano films or thin films a few nanometers thick deposited on bulk material. Only one dimension (the thickness) is nanometric, while the two other dimensions are usually macroscopic.

 

>> Field effect electron emission

A nanotube, anchored on a substrate, is subjected to a voltage (i.e., an electric field). Electrons are emitted, pass through the surface barrier by tunneling and reach an electroluminescent screen, thus producing an enlarged image of the nanotube.

Notes :

1. Nanometer = 10-9 meter, one billionth of a meter. One atom measures between 0.1 and 0.4 nm. Actually, the first image of an atom was obtained by ionic microscopy in 1953.
2. CEMES: Centre d'Elaboration de Matériaux et d'Etudes Structurales (CNRS lab). View web site
3. Mathematics, computer science, physics , earth sciences and astronomy.
4. Professor at the Université Paris-X and member of Comets (CNRS Ethics Committee).
5. LAAS: Laboratoire d'Analyse et d'Architecture des Systèmes (CNRS lab). View web site
6. CNRS / University Claude Bernard Lyon-I joint lab.
7. CNRS / Insa joint lab. View web site
8. CNRS lab. View web site
9. CEA lab. View web site
10. CNRS / Paris-VI and VII Universities joint lab. View web site

Contacts :

> Christian Joachim
joachim@cemes.fr

> Gérard Benassayag
benassayag@cemes.fr

> Éric Gaffet
eric.gaffet@utbm.fr

> Alain Perez
alain.perez@lpmcn.univ-lyon1.fr

> Catherine Journet
catherine.journet@lpmcn.univ-lyon1.fr

> Stephen Purcell
stephen.purcell@lpmcn.univ-lyon1.fr

> Olivier Pluchery
olivier.pluchery@insp.jussieu.fr


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