Mireille Gaillard

Electrical and thermal characterization of carbon nanotube films

The remarkable electrical and thermal properties of carbon nanotubes (CNTs) make them attractive for microelectronics applications and, in particular, for interconnects. A multilayer device was designed in order to measure electrical and thermal properties of CNT films. This device is composed of an iron catalyst thin film deposited by pulsed laser ablation upon which a dense multi-walled carbon nanotube (MWCNT) film was grown by radio frequency plasma enhanced chemical vapor deposition. Finally a thin metallic layer was deposited over all by physical vapor deposition. Scanning electron microscopy images were intensively used to check the length (several tens of micrometers) and diameter (10 to 30 nm) of the nanotubes and to adjust the different steps of the process to get the desired film morphology (dense and vertically aligned). The CNT structure was investigated by high-resolution transmission electron microscopy and Raman spectrometry. The MWCNT carpet showed an ohmic behavior during current-voltage ...

Thermal conductivity measurement of porous silicon by the pulsed-photothermal method

Thermal properties of two types of porous silicon are studied using the pulsed-photothermal method (PPT). This method is based on a pulsed-laser source in the nanosecond regime. A 1D analytical model is coupled with the PPT technique in order to determine thermal properties of the studied samples (thermal conductivity and volumetric heat capacity).At first, a bulk single crystal silicon sample and a titanium thin film deposited on a single crystal silicon substrate are studied in order to validate the PPT method. Porous silicon samples are elaborated with two different techniques, the sintering technique for macroporous silicon and the electrochemical etching method for mesoporous silicon. Metallic thin films are deposited on these two substrates by magnetron sputtering. Finally, the thermal properties of macroporous (30% of porosity and pores diameter between 100 and 1000 nm) and mesoporous silicon (30% and 15% of porosity and pores diameter between 5 and 10 nm) are determined in this work and it is found that thermal conductivity of macroporous (73 W m−1 K−1) and mesoporous (between 80 and 50 W m−1 K−1) silicon is two times lower than the single crystal silicon (140 W m−1 K−1).

Improvement of the identification of multiwall carbon nanotubes carpet thermal conductivity by pulsed photothermal method

Thermal properties in multiwall carbon nanotubes carpets and micro-devices are investigated using a nanosecond photothermal method. Gradually, the identification model and experimental protocol are performed to increase the method accuracy for the thermal conductivity determination. In the experimental protocol, a nanosecond UV monopulse laser beam is used to heat the surface of a multilayer (600 nm of Ti/20 μm of carbon nanotube carpet) sample. In the 1D identification model with two layers and a thermal contact resistance, the effect of the laser excitation temporal shape is taken into account. In this study, this first approach allows to improve the accuracy of apparent thermal conductivity measurements of multiwall carbon nanotubes carpet. The carbon nanotubes carpet apparent thermal conductivity value went from being to 180 ± 5 W×m−1×K−1. In the second approach, two laser beams are coupled in order to increase the interaction time duration from 27 ns to 60 ns. It becomes possible to probe different d...

Laser for carbon nanotubes: From the PLD deposition of the catalytic layer to the thermal characterization by nanosecond pulsed laser

Carbon nanotubes (CNTs) are grown with a three steps process during which the sample is kept under vacuum combining pulsed laser deposition and radio frequency plasma enhanced chemical vapor deposition techniques. As results, the obtained CNTs are densely grown and vertically aligned, multi-walled, 5 to 20 nm in outer diameter. TEM analyses show the well graphitized parallel walls. Catalyst nanoparticles are trapped within or along the body of the CNTs. To characterize their thermal properties by pulsed photothermal method, it is necessary to deposit on the top a metallic thin layer (Ti, about 200 nm) acting as a photothermal transducer. The thermal conductivity and volumetric heat capacity of the CNTs film are identified. They are found to be respectively 210Wm−1K−1 and 5×104JK−1m−3.