F. Carcenac

Using polydimethylsiloxane as a thermocurable resist for a soft imprint lithography process

Nanoimprint lithography has been investigated using polydimethylsiloxane as a thermocurable resist. This novel process allowed us to reduce both pressure (<10 bars) and temperature (80 °C) when compared to a conventional imprinting process with a thermoplastic polymer resist such as polymethylmethacrylate. Using a new formulation of the elastomeric material, we have demonstrated high quality imprinting of both micronic and nanometric structures with no evidence of any viscous flow problems. The excellent etching resistance of the polydimethylsiloxane structures to a reactive ion etching silicon process and the compatibility with a lift-off procedure for pattern transfer are also presented.

Fabrication and characterization of microlens arrays using a cantilever-based spotter

We present a quantitative study on the fabrication of microlenses using a low-cost polymer dispending technique. Our method is based on the use of a silicon micro-cantilever robotized spotter system. We first give a detailed description of the technique. In a second part, the fabricated microlenses are fully characterized by means of SEM (Scanning Electron Microscope), AFM (Atomic Force Microscopy) non contact optical profilometry and Mach-Zehnder interferometry. Diameters in the range [25-130mum] are obtained with an average surface roughness of 2.02nm. Curvature radii, focal lengths as well as aberrations are also measured for the first time: the fabricated microlenses present focal lengths in the range [55-181mum] and exhibit high optical quality only limited by diffraction behaviour with RMS aberration lower than lambda/14.

Fabrication of multiple nano-electrodes for molecular addressing using high-resolution electron beam lithography and their replication using soft imprint lithography

Abstract We investigate the ability for High Resolution Electron Beam Lithography (HREBL) to fabricate multiple nano-electrodes with the smallest gap in the smallest area. By using both standard PolyMethylMethAcrylate (PMMA) as resist and standard MIBK/IPA development, we show that up to 10 nano-electrodes can be realized in an area as small as 65 nm. The obtained structures have been used either for the realization of embedded electrodes in SiO 2 by wet etching followed by lift-off, or for the fabrication of molds for Nano-Imprint Lithography using PMMA as a mask for Reactive Ion Etching of silicon. Preliminary results on the replication of these molds using a soft nano-imprint process are also presented.

Probing the electronic properties of individual carbon nanotube in 35 T pulsed magnetic field

After optimization of the alignment and the nano-contact processes of isolated single wall and double-walls carbon nanotube, we investigate the high magnetic field effects on the electronic transport properties of an individual metallic CNT. We develop pioneer multi-probes magneto-transport experiments under a 35 T pulsed field which reveal an unexpected oscillatory behavior of RðHÞ inconsistent with existing theories.

Interdigitated nanoelectrodes for nanoparticle detection

Experimental results on the electrical detection of metal nanoparticles adsorbed on interdigitated nanoelectrode based devices are presented. By adjusting the gap between these electrodes to the diameter of the nanoparticles, we demonstrate that efficient bridging of the electrodes can take place. This phenomenon leads to a strong modification of the conductance of the device. The capability of the nanoelectrodes to detect single adsorption events electrically is demonstrated and reveals that the sensitivity reaches the individual nanoparticle level. This result is proven by current–voltage measurements at room temperature performed in solution during the adsorption of the nanoparticles and after the deposition process and surface drying. The capability of the devices to perform quantitative measurements is also addressed. Even if individual adsorption events could be detected one by one in solution, current–voltage measurements performed after the deposition and drying show that a correlation between the number of particles immobilized on the sensing area of the devices and the electrical characteristic remains difficult. The current flow is dominated by tunnel transport through the junctions formed between the nanoparticles and the nanoelectrodes and the dispersion of the electrical characteristics of the junctions is a limitation for quantifying the number of nanoparticles involved in the electrical response.

Alignment and nano-connections of isolated carbon nanotubes

We report a new approach for the alignment and the electrical nano-connection of isolated carbon nanotubes (CNTs). Through a novel combination of proven technics, we have been able to align isolated carbon nanotubes and selectively contact those CNTs by high resolution electron beam lithography (HREBL). Resistance versus temperature (R(T)) experiments have been carried out to determine the reliability of the metal-CNTs interface and to probe the electronic conductance of the CNT.

Imprint lithography using thermo-polymerisation of MMA

We investigate a new approach for imprint lithography which consists in using a thermo-polymerisation reaction under the mold rather than the softening of a polymerised thermoplastic resist. We use as a demonstrator, methylmethacrylate (MMA) monomers. We show that the major problem of this technique is to keep a reasonable amount of the solution containing the monomer species in between the sample and the mold; this is due to its extreme fluidity and high evaporation rate. However, we demonstrate that the use of various silane molecular layers deposited on both the sample and the mold enables the achievement of the imprinting process. We found that under appropriate conditions, no residual layer of polymer is left under the imprinted features, due to the concept of a minimum activation volume allowing the polymerisation reaction to occur. This result opened the possibility to directly perform a transfer procedure like lift-off, without any need for a dry etching process.

Joule heated metallic microwire devices for sub-microsecond T-jump experiments

We report a study of the transient heating response of submicrometric gold wires on oxidized Si substrates, highlighting their potential as versatile platforms for creating fast temperature variations (T-jumps). To characterize electrically the transient heating response, we developed an original differential resistance setup that excites single wires with current pulses and provides a signal proportional to the ΔT induced. A reproducible sub-microsecond transient heating response (for ΔT?80?C) was observed for the heaters, regardless the substrate temperature or the presence of a thermal load (polymer film) on the surface. We also developed a simplified mathematical model that reproduced the main experimental observations and provided valuable insights into the dynamics and stability of the heating process. As a proof of concept, our electrical setup was also coupled to a time-resolved optical microscopy setup to detect the transient thermal response of a well-known luminescent thermometer molecule (Rhodamine B).