Browsing all articles in Projects
Dec
28

Nanopatterning with dendrimers

Author Rémi Longtin    Category Nanopatterning     Tags , ,

Presentation

The following section is a short introduction to my most recent research (2007 to 2009) at the University of Geneva in the laboratory for colloids and surface chemistry.

G10 PAMAM dendrimer on silicaThe adsorption of macromolecules at the solid-liquid interface is a very common yet complicated phenomenon. One has simply to think of what happens when a drop of blood falls on a surface. Blood is a complex colloidal system. The fluid contains several macromolecules (proteins, biopolymers) as well as ions (Fe, K, Cl, Na etc.) and other cells all interacting with each other and with the surface. Preventing or promoting the adsorption of blood (or its specific constituents) to a surface may be critical in some biomedical applications. This example illustrates how macromolecular adsorption is ubiquitous, yet can be of great importance for both industry and fundamental science.

In terms of nano-technological applications, charged macromolecules from solutions can be used to pattern mineral surfaces. Typically, an interface will acquire a charge when immersed in a solution, water in this case. Similarly, the macromolecule’s ionizable functional groups can take or release protons, thus have a pH-dependent charge. When the charges of both molecule and surface have opposite signs and are of sufficient magnitude, adsorption via electrostatic interactions occurs.
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May
16

ZnO nanostructures

Introduction

ZnO nanostructureNanotechnology and nanoscience have certainly been one of the most popular fields of research in the last decade. Manufacturing processes are now able to carry out the deterministic synthesis of nanostructures with properties radically different from their macroscopic forms, enabling the realization of previously unthinkable devices. Despite these advances, few nanofabrication techniques feature the required characteristics for the commercial manufacturing of these new products in an effective fashion since they are either too slow, or too expensive and complex.

This page is a summary of my doctoral thesis project, accomplished at the Laboratory for multiscale mechanics at the École Polytechnique de Montréal (LM2, mechanical engineering). The main objective of this project was to develop a new manufacturing technique allowing the local synthesis of nanostructures on a surface for their eventual integration into nanodevices. The desired process has to be selective, reproducible, versatile, simple, fast and inexpensive for potential industrial utilization. Moreover, the manufacturing process must have a minimal environmental impact for sustainable development.

To implement the required specifications, a laser process combining the characteristics of laser-induced chemical liquid deposition (LCLD) and of sol-gel synthesis was proposed. The technique is very simple and consists of three steps. A precursor solution is first prepared. Next, a droplet of a controlled volume is transferred on a substrate by means of a micropipette. The droplet is then irradiated using a laser emitting in the infrared to induce the fast synthesis of nanostructures.

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Nov
20

Laser fabrication

Introduction

Freeform fabrication is a type of manufacturing process that allows the fabrication of 3D objects with a large variety of shapes, structure and composition. Laser-assisted chemical vapor deposition (LCVD) is a freeform fabrication technique that allows the deposition of micro-scale structures at a high growth rate with the flexibility of conventional CVD.

The LCVD process

During chemical vapour deposition (CVD), energy is given to a gas (the precursor gas) which contains the atom that we want to deposit. This energy dissociated the gaseous molecules by a series of chemical reactions in order to obtain a solid product (the deposit) on a surface where we want the deposition to occur (the substrate). This can be conceptualized by the following equation which describes the deposition of the gaseous species ABu :
ABu →  A(↓) + u B(↑)

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Mar
31

Nanotube production

Author Frédéric Larouche    Category Nanotubes     Tags

What are carbon nanotubes?

Structure of carbon nanotubes

Figure 1: Geometric structure of nanotubes

The discovery of carbon nanotubes in 1991, by the japanese researcher Sumio Iijima, during the study of fullerenes (C60) synthesis reveals a new cristalline form of carbon. These cylindric structures of carbon consist of a graphitic plane rolled into a tube having a nanometric diameter (10-9 meter = 1 nanometer) and can be divided in two groups: single wall carbon nanotubes (C-SWNT) and multi-walls carbon nanotubes (C-MWNT).

Figure 2: Schematic of C-SWNT and C-MWNT

Figure 2: Schematic of C-SWNT and C-MWNT

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Jul
16

Hydrogen storage

Introduction

The automobile fleet is contributing significantly to air quality degradation in large cities. The use of hydrogen as a fuel is interesting since combustion delivers a lot of energy without polluting. However, some obstacles, like the efficient storage of this gas, remain before it can be implemented in the transportation industry.

Figure 1: Hydrogen powered car built by BMW

Figure 1: Hydrogen powered car built by BMW

Hydrogen storage solutions

The United States Department of energy (DOE) has fixed two targets for hydrogen storage solutions applied to automotive transportation. The first target requires a ratio of hydrogen weight / tank weight that is superior to 0,065 (6,5% weight). This target limits the weight of the tank. The second target requires a hydrogen volumetric density higher than 62 kg/m in order to limit the volume of the tank.

Four main solutions were proposed to solve this problem:

  • Compression or liquefaction of hydrogen
  • Metal hydrides
  • Chemical tanks
  • Adsorbent materials

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Feb
15

Hydrogen storage – literature

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Contact me by email to get the password.

Reference books

R. Saito, G. Dresselhaus and M. S. Dresselhaus, Physical Properties of carbon nanotubes, Imperial College Press, Londres, 1998

G. Gao, T. Cagin and W. A. Goddard III, Energetics, Structure, Mechanical and Vibrational Properties of Single Walled Carbon Nanotubes (SWNT), Foresight Institute, 1997 (pdf©)

D. Frenkel and B. Smit, Understanding molecular simulation: from algorithms to applications, Academic Press, San Diego, 1996

C. Ngô and H. Ngô, Physique statistique, Masson, Paris, 1995

R. A. Oriani, The physical and metallurgical aspects of hydrogen in metals, Fourth International Conference on Cold Fusion, 1993 (pdf)

Nanotube fabrication methods

S. Iijima, Helical microtubules of graphitic carbon, Nature 354 (1991), 56-58 (pdf©)

S. Iijima and T. Ichihashi, Single-shell carbon nanotubes of 1-nm diameter, Nature 363 (1993), 603-605 (pdf©)

A. Thess, R. Lee, P. Nikolaev, H. Dai, P. Petit, J. Robert, C. Xu, Y. H. Lee, S. G. Kim, A. G. Rinzler, D. T. Colbert, G. E. Scuseria, D. Tománek, J. E. Fischer and R. E. Smalley, Crystalline Ropes of Metallic Carbon Nanotubes, Science 273 (1996), 483-487 (pdf©)
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