Sylvain Desilets

Gas-phase synthesis of SWNT by an atmospheric pressure plasma jet

We present here a new method for producing single wall carbon nanotubes (SWNT) based on the atomization of a gaseous mixture (composed of argon, ferrocene and ethylene) in an atmospheric plasma jet. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy were performed to study the samples obtained. They contain SWNT with diameters and structure comparable to those produced by laser ablation and arc discharge techniques. Since this method is continuous and easily scalable, we feel it has potential for large-scale commercial production of SWNT.

Growth of carbon nanotubes on Ohmically heated carbon paper

Abstract Multi-walled carbon nanotubes (MWCNTs) have been grown from ethylene on the fibers of carbon paper by Ohmically heating Co–Ni or Fe catalytic sites supported on the carbon fibers. MWCNTs are mainly tip-grown and have diameters ranging from 10 to 30 nm, depending on the catalyst used. The MWCNTs adhere firmly to the carbon paper with which they are in electrical contact. Cyclic voltammetry of the electrode thus formed indicates that MWCNTs behave like a graphitic material.

Influence of Ni Catalyst Layer and TiN Diffusion Barrier on Carbon Nanotube Growth Rate

Dense, vertically aligned multiwall carbon nanotubes were synthesized on TiN electrode layers for infrared sensing applications. Microwave plasma-enhanced chemical vapor deposition and Ni catalyst were used for the nanotubes synthesis. The resultant nanotubes were characterized by SEM, AFM, and TEM. Since the length of the nanotubes influences sensor characteristics, we study in details the effects of changing Ni and TiN thickness on the physical properties of the nanotubes. In this paper, we report the observation of a threshold Ni thickness of about 4 nm, when the average CNT growth rate switches from an increasing to a decreasing function of increasing Ni thickness, for a process temperature of 700°C. This behavior is likely related to a transition in the growth mode from a predominantly “base growth” to that of a “tip growth.” For Ni layer greater than 9 nm the growth rate, as well as the CNT diameter, variations become insignificant. We have also observed that a TiN barrier layer appears to favor the growth of thinner CNTs compared to a SiO2 layer.

Spectral artifacts from non-uniform samples analyzed by terahertz time-domain spectroscopy.

We report the impact of the spatial coherence distortion on the measured absorption spectra and the identification of materials analyzed by terahertz time-domain spectroscopy. It is shown that the deformation of the terahertz beam wave front can result into the overestimation of the electromagnetic absorption, the generation of artificial absorption peaks and even to the disappearance of characteristic absorption peaks. Obtaining clear absorption spectra without artifacts is crucial for applications based on terahertz imaging and spectroscopy.

Standoff detection of explosives: a challenging approach for optical technologies

Standoff detection of explosives residues on surfaces at few meters was made using optical technologies based on Raman scattering, Laser-Induced Breakdown Spectroscopy (LIBS) and passive standoff FTIR radiometry. By comparison, detection and analysis of nanogram samples of different explosives was made with a microscope system where Raman scattering from a micron-size single point illuminated crystal of explosive was observed. Results from standoff detection experiments using a telescope were compared to experiments using a microscope to find out important parameters leading to the detection. While detection and spectral identification of the micron-size explosive particles was possible with a microscope, standoff detection of these particles was very challenging due to undesired light reflected and produced by the background surface or light coming from other contaminants. Results illustrated the challenging approach of detecting at a standoff distance the presence of low amount of micron or submicron explosive particles.

Use of a spectroscopic lidar for standoff explosives detection through Raman spectra

This paper assesses the potential of detecting explosives (RDX, TNT, PETN, HMX, HMTD, Urea Nitrate) from a distance with a spectroscopic lidar system. For the study, the temporal and spectral resolutions of laser induced fluorescence lidar prototypes were enhanced. The integrated breadboards used easily available Nd:YAG laser wavelengths (266 nm, 355 nm, and 532 nm) to remotely detect the Raman signatures induced in traces of explosives deposited on surfaces. The spectroscopic lidar setup allows for time resolved measurements with high temporal resolution. Raman spectra are observable, even in the presence of fluorescence. Experiments with low average laser power (tens of mWs) have shown the unambiguous capability to detect and identify explosives at distances ranging up to 20 m. Thanks to the combination of UV wavelength for higher Raman cross-sections and efficient gated detection the 355 nm prototype yielded the best compromise. Excitation at 266 nm was expected to yield a better Raman response and was investigated. Less than optimal laser parameters, detection efficiency and strong fluorescence reduced the signal to noise ratio of the 266 nm signals with respect to those at 355 nm and 532 nm showing the importance of optimizing system parameters for high sensitivity detection. Besides the description of the prototypes and an early assessment of their performances, recommendations are also proposed to improve the instrument, leading to an efficient remote sensor for explosives.

Trace explosives detection for finding land mines

Trace Explosive Detectors (TED) technologies have been investigated as a means of confirming the presence of a landmine at a given location. A field trial was performed with a landmine detector prototype based on Ion Mobility Spectrometry. The system was based on the detection of the explosives in soil and had a detection limit of 0.4 ppb w/w for TNT and 7.4 ppb w/w for RDX. The minefield was composed of 51 sites on which the detector performance was evaluated. For most freshly buried sites it was found that the level of explosive was below the detection limit of the prototype. In addition, a quantitative analysis of the residual explosive transfer to the soil by hands was performed. Results showed that the level transferred by hands was in most cases below 0.1 ppb for TNT and at 0.8 ppb w/w or below for RDX. However, it was found that the explosive level contained in the soil increased with time to a level around 2 - 8 ppb w/w for TNT, ten month after the landmine burial. These rough tests have yielded some preliminary results concerning the level of explosives detectable after the burial of landmines and the dynamics of the explosive level build up in the soil with time.

Standoff detection results with the infrared hyperspectral MoDDIFS sensor

The passive standoff monitoring of vapor precursors emanating from a location under surveillance can provide relevant information on the nature of products fabrication. Defence Research & Development Canada Valcartier recently completed the development and field-validation of a novel R&D prototype, MoDDIFS (Multi-option Differential Detection and Imaging Fourier Spectrometer), to address this remote sensing application. The proposed methodology combines the clutter suppression efficiency of the differential detection approach with the high spatial resolution provided by the hyperspectral imaging approach. This consists of integrating a differential CATSI-type (Compact ATmospheric Sounding Interferometer) sensor with the imaging capability of the Hyper-Cam infrared imager. The MoDDIFS sensor includes two configuration options, one for remote gas detection, and the other for polarization sensing of surface contaminants. This paper focuses on the infrared spectral detection of gases. A series of measurements done with MoDDIFS on selected laboratory solvents in vapor form are analyzed and discussed.