nanomat.fr

Search       
Members access   
 
Home > Introduction Français  Français  

Nano-objects and nanostructures
prepared by bottom-up approach :
stakes and perspectives.




 

Nanoscience, in the same way as biology, is without a doubt one of the most promising fields of scientific and technological development in the 21st century.
Over the last decade, the rapid development of researches on integrated functional materials – of which the dimensional characteristics are only a few nanometers – has caused the fields of fundamental and applied chemistry and physics to reassess. Already, pertinent lengths such as the photon wavelengths in optics or the correlation length in magnetic systems, represent the critical dimensions beyond which the properties are profoundly modified. The collaboration between chemists and physicists, as well as designers and users is essential to successfully explore and develop different fields. France possesses undeniable assets. The fundamental interest and associated technological stakes, such as spintronics, information storage, magnetoresistive sensors and biosensors, catalysis, etc., justify the regrouping of forces at a national level, and a proactive collaboration between the various contributors.

Within the framework of the National Program on Nanosciences, significant resources are already dedicated to the miniaturization of microelectronic components through the support of micro and nano technologies clusters.
The "top-down" type preparation methods rely upon physical techniques, such as sputtering, MBE (molecular beam epitaxy), laser ablation, OMVPE (organometallic vapor phase epitaxy), or lithography techniques that enable a wide range of nanostructures to be elaborated. These complex methods do not always enable the dimensional and structural characteristics to be adequately monitored.  Moreover, the processing of material as it is elaborated may cause reactions to the various interfaces (because it primarily concerns multilayers), precipitation phenomena, or phase transformations.
An additional way to the nano-fabrication and nano-manipulation procedures used in physics, is to start from the ultimate limit – or in other words from the atomic scale – to design and prepare totally new materials from “soft” chemical reactions, thus opening the route to scales unexplored until now. The building of objects in a “step-by-step” manner, by capturing the relationship between structure/properties in view of optical applications (sensors, displayers, guides, photonic crystals, etc.), magnetism, catalysis and photocatalysis, phase separations (nanomembranes), or even vectorization (specific encapsulation), seemed to be out of reach 15 years ago. However, the development of new tools and synthesis protocols has introduced new and interesting perspectives in this field.
It would appear at this time, that it is crucial to support at the national level a “bottom-up” approach for the design of individual objects or even systems – showing a self-organization of these objects – that exhibit remarkable physical properties. This is important, even if the applications' perspectives sometimes appear at a later time. The recent developments in nanophysics demonstrate the stakes in this field.
The nanostructures and nanomaterials obtained through chemical processes may be divided into two large classes. The first class contains nanometric-sized objects (molecules, clusters, aggregates, wires, etc.) that are isolated or organised into networks; the second contains nano or mesoporous cristallised materials, which exhibit a network of tunnels or cavities obtained by molecular templating.
In the first class, those most often studied are molecular clusters, metals and metallic oxides, chalcogenides and III-V and II-VI semiconductors, fullerenes, as well as carbon nanotubes.
Because of their small size (confinement effect), and their large surface/volume ratio, these materials offer properties (electronic, magnetic, optical, chemical, etc.) that differ from volume properties, and which offer numerous application capabilities.
The second category groups together the nano or microporous solids that have a tridimensional framework, with cavities varying between one and approximately ten nanometres. The aluminosilicates from alkaline metals or alkaline earth metals (zeolites) and metallophosphates, are the cause for numerous undertakings on the role of structuring agents (organic or inorganic species) in harnessing the size and shape of pores. These studies have been extended to porous solids with hybrid frameworks, involving strong binding between organic and inorganic species, that can also be synthesised by using molecular templates.

The organisation of nano-objects on surfaces or in porous structures remains in the exploratory stage, despite the fundamental and applied applications for such systems. One of the favoured approach is the design of molecular precursor nano-structures that are associated with hybrid structures (objects on/in a semi-conductor, inorganic, etc., substrate), as well as the study of the parameters that govern the magnetic, optical or transport properties in relation to system design.
Today, we can confirm that within this field there are strong competencies, but since this field is in essence multidisciplinary and requires the support of heavy equipment, it has become crucial to consolidate our forces
.

          
 
 
 
This network is funded by the French programme on nanosciences,
involving the French Ministry of Research, CNRS and CEA


Maintained by the Institut de Physique et Chimie des Matériaux de Strasbourg.
Mail to :
webmaster@ipcms.u-strasbg.fr
 
Conception et réalisation : Heptades, solutions multimédia - Ligne graphique : Atelier C