book of abstracts - IM2NP

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A B S T R A C T S FRIDAY, JULY 2 N A N O S E A 2 0 1 0 11H20-11H40 Ordered growth of multi-walled nanotubes on Ge nanocrystals. A. Capasso1, E. Waclawik1, J. M. Bell1, S. Ruffell2, A. Sgarlata3, M. Scarselli3, M. De Crescenzi3 and N. Motta1 (1Queensland University of Technology, Brisbane, Australia; 2Australian National University, Canberra, Australia; 3 University of Rome “Tor Vergata”, Rome, Italy). 1 – Introduction Role of catalyst in carbon nanotubes (CNTs) synthesis is still under debate. In the past, transition metals have been regarded as essential for carbon diffusion and subsequent nucleation of a graphitic tube-like structure. Recent studies however show that particles of many other materials (metallic and semiconducting) could fulfill this task, provided their size falls in the nanometer range. Semiconductor nanoparticles can decompose the carbon gas source and thus result very active as catalyst in the nanotube synthesis. Ge nanocrystals in particular have a much lower melting point compared to bulk: carbon can then diffuse inside the crystal and allow the nucleation of a nanotube once the super-saturation regime is reached. 2 – Experimental details In the present paper, we report a synthesis of CNTs on Si surfaces by using Ge as catalyst. The Si substrates have been pre-patterned by nanoindentation, creating a grid of micro indents. Ge evaporation in ultra-high vacuum leads to the formation of small Ge nanoparticles, which result ordered on the patterns. CNTs are then grown by low-pressure chemical vapor deposition of acetylene. Multi walled nanotubes arise from Ge nanoparticles in small bundles all over the surface, whereas on patterned areas a more limited yet quite ordered growth occurs nearby the indents. The samples are imaged by Field Emission-SEM and AFM. EDX elemental analysis and Raman spectroscopy provide further evidence of the metal-free nature of this synthesis. 3 – Conclusion Our results confirm that it is possible to grow CNTs without the use of any metal catalyst. By means of surface nanoindentation, Ge nanocrystals can be assembled in controlled position and then employed as seeds for the tube nucleation. This approach could be viable for integrating pure CNTs in specific sites on a semiconductor, opening a way for the conception of enhanced electronic devices. 11H40-12H00 Boron Nanotubes and its properties: semiempirical investigations. Zaporotskova I.V., Perevalova E.V., Zaporotskova N.P (Volgograd State University, Volgograd, 400062, Universitetskii prospect, 100, Russia). The problem of formation possibility nanotubular structures is actively discussed now. We considered the fragments of single-wall boron nanotubes (n,n) (n=4,5,6,9,11,12). Calculations were carried out by IB-CCC method [1]. The analysis of band-gap showed that all of them are semiconductors. Energy of deformation decreases with increase of the diameter of B-tubes (n, n). We considered the B-nanotubes (n,0) (n=4,5,6,8,12). In this case deformation energy is increases with increase of the diameter of tubes (n,0). Calculations of boron tube (6, 6) which contained various defects of structure were obtained by the semiempirical MNDO scheme. We research substitution imperfection of B atom by atom C, ions С+ , С-. 137
A B S T R A C T S FRIDAY, JULY 2 N A N O S E A 2 0 1 0 We found out substitution energy of defects and its energy level. We studied the B-tube with hole and determined the energy of defect activation and the relative portion of vacancies. At the moment active search of new surface structures capable of effective adsorption of different gases is being carried out. We have investigated an binding opportunity between the H, F, O, Cl atoms and the outer surface of B-nanotube (6,6) and have studied the mechanism of this process. The calculations are carried out with the use of quantum chemical MNDO scheme. Regular hydrogenation of boron nanotubes was investigated. We can confirm that generation of gas-phase hydrogen composite materials based on boron nanotube is possible. [1] Litinsky A.O., Lebedev N.G., Zaporotskova I.V. Jurnal phyzicheskoi himii. 69. № 1, 189 (1995). 12H00-12H20 Epitaxial growth and magnetic properties of Mn5Ge3 compound on Ge(111) A. Spiesser1, A. Watanabe2, S.F. Olive-Mendez, M.-T. Dau1, L.A. Michez1, S. Nozaki2, A. Glachant1, V. Le Thanh1 ( 1 Centre Interdisciplinaire de Nanoscience de Marseille (CINaM-CNRS), Aix-Marseille Université, Campus de Luminy, case 913, 13288 Marseille, France 2 Department of Electronic Engineering, the University of Electro-Communications, 1-5-1 Chofugaoka, Chofu-shi, Tokyo 182-8585, Japan) 1 – Introduction The emerging field of spintronics, which is regarded as next-generation electronics, would be dramatically boosted if room-temperature ferromagnetism could be added to semiconductor devices and integrated circuits that are compatible with silicon CMOS technology. Among numerous approaches such as growth of Ge1-xMnx diluted magnetic semiconductors or using spin injection from a transition metal across a thin oxide barrier layer, the synthesis of Mn5Ge3/Ge heterostructures is of particular interest since Mn5Ge3 is intermetallic and ferromagnetic up to room temperature. Achieving a high-quality epitaxial Mn5Ge3 film on Ge not only allows a direct and high efficient injection of spin by tunnel effect through the Schottky barrier but also offers a direct route to be integrated into group-IV semiconductors. 2 – Abstract Epitaxial growth of Mn5Ge3/Ge(111) have been investigated by combining structural characterizations via reflection high-energy electron diffraction (RHEED), transmission electronic microscopy (TEM) and magnetic characterizations using vibrating sample magnetometer (VSM), superconducting quantum interference device (SQUID) magnetometers. It is shown that despite a misfit as high as 3.7% between Mn5Ge3 and Ge(111), high quality Mn5Ge3 films with an atomically smooth interface can be obtained. However, no pseudomorphic growth was observed as in covalent heteroepitaxial systems, Mn5Ge3 films were found to be fully strain relieved even after the deposition of a monolayer thick film. We have also investigated the effect of the film thickness on the structural and magnetic properties of Mn5Ge3 films. For films whose thickness is smaller than 50 nm, the easy axis of magnetization lies in the layers and the hard axis is perpendicular to the sample surface. When the film thickness increases, the coercive field becomes progressively smaller and the easy axis of magnetization is found to get out of the hexagonal basal (001) plan 138
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