International audienceThe increasingly demand on secondary batteries with higher specific energy densities requires the replace- ment of the actual electrode materials. With a very high theoretical capacity (4200 mAh g−1 ) at low voltage, silicon is presented as a very interesting potential candidate as negative electrode for lithium-ion micro- batteries. For the first time, the electrochemical lithium alloying/de-alloying process is proven to occur, respectively, at 0.15 V/0.45 V vs. Li+ /Li with Si nanowires (SiNWs, 200-300 nm in diameter) synthesized by chemical vapour deposition. This new three-dimensional architecture material is well suited to accom- modate the expected large volume expansion due to the reversible formation of Li-Si alloys. At present, stable capacity over ten to twenty cycles is demonstrated. The storage capacity is shown to increase with the growth temperature by a factor 3 as the temperature varies from 525 to 575 ◦ C. These results, showing an attractive working potential and large storage capacities, open up a new promising field of research

Porous alumina templates have been fabricated by applying an exponential voltage decrease at the end of the anodization process. The time constant η of the exponential voltage function has been used to control the average thickness and the thickness distribution of the barrier layer at the bottom of the pores of the alumina structure. Depending on the η value, the thickness distribution of the barrier layer can be made very uniform or highly scattered, which allows us to subsequently fine tune the electrodeposition yield of nickel nanoparticles/nanowires at low voltage. As an illustration, the pore filling percentage with Ni has been varied, in a totally reproducible manner, between ∼3 and 100%. Combined with the ability to vary the pore diameter and repetition step over ∼2 orders of magnitude (by varying the anodization voltage and electrolyte type), the control of the pore filling percentage with metal particles/nanowires could bring novel approaches for the organization of nano-objects.

Confined lateral alumina templates are fabricated with different pore sizes by changing the acid electrolyte and the anodization voltage. The control of the number of pore rows down to one dimension is also achieved, by controlling the thickness of the starting aluminum film as well as the anodization voltage. We observe that the mechanism of pore formation in the lateral regime is very similar to that in the classical vertical situation.

The effects of an atomic hydrogen (H at ) pretreatment of the catalyst layer on the low temperature growth of single-walled carbon nanotubes (SWCNTs) have been investigated using a modified catalytic chemical vapor deposition system. Well-defined and isolated individual Fe nanoparticles as a catalyst are successfully formed on the defects with high trapping energy which are created on the Al 2 O 3 surface by H at pretreatment, yielding highly dense SWCNTs. The pretreatment mechanism of H at , compared to H 2 , is also discussed. It was also found that the quality of SWCNTs can be enhanced when H at is flowed with CH 4 during nanotubes growth at low temperature. In this case, the undesired carbon products and defects on catalyst seeds and nanotube walls can be selectively removed by H at . Therefore it is essential to use H at in the pretreatment stage for increasing catalytic activity and to keep the size of nanoparticles in the nm range. H at can also be employed in growth stage for enhancing SWCNTs quality and density at low temperature.

International audienceThe formation of gold islands on a transparent conductive oxide by annealing a thin evaporated layer is studied by SEM. The droplets of metal formed this way may catalyze the growth of nanowires or nanotubes to be used in optoelectronic devices. The effect of the initial thickness (between 1 nm and 4 nm) and the annealing temperature (between 70 °C and 650 °C) is investigated. A qualitative description of the evolution is given and quantitative data are obtained by automated image analysis. Number density, area and effective diameter of the aggregates depend heavily on the initial thickness but very slightly on the annealing temperature. Three phenomena are considered to explain the evolution: interfacial stress due to mismatch in the linear expansion coefficient, Ostwald ripening and kinetic aggregation. By comparing the experimental size distributions to the theoretical ones, the relevance of the last two is discussed. As an application, the gold catalyzed CVD growth of silicon nanowires on zinc oxide is demonstrated

— Carbon nanotubes and semiconductor nanowires are a new class of materials currently being studied within the context of molecular electronics. Because of their excellent characteristics, transistors based on carbon nanotubes and semiconductor nanowires could become the workhorse of the post‐CMOS era. Since carbon nanotubes as well as Si or Ge nanowires can be grown at low temperature, using similar CVD‐type processes and on non‐crystalline and non‐refractory substrates, they could (and will) certainly be used in the near future for the fabrication of thin‐film transistors and active‐matrix backplanes. However, the development of these nanomaterials is hampered by the general problems posed by their manipulation, placement, and in‐plane organization. The possible use of CNT random networks (that do not need to be organised) for the fabrication of thin‐film transistors will be reviewed. Then a new way of organizing semiconductor NWs in a thin‐film transistor, based on the use of lateral porous anodic alumina templates, will be presented.