Marcel Lucas

Improved structure and properties of single-wall carbon nanotube spun fibers

This letter describes a method to improve the alignment of single-wall carbon nanotubes in macroscopic fibers produced by a simple spinning process. By contrast to classical composite fibers, where the nanotubes are embedded in a polymeric matrix, they consist of an interconnected network of polymers and nanotubes. This network can be swollen and stretched when the fibers are immersed in an appropriate solvent. The nanotubes alignment, studied by x-ray scattering, is significantly improved by the treatment. The fiber Young’s modulus can also be increased by a factor of 4.

Invited Review Article: Combining scanning probe microscopy with optical spectroscopy for applications in biology and materials science

This is a comprehensive review of the combination of scanning probe microscopy (SPM) with various optical spectroscopies, with a particular focus on Raman spectroscopy. Efforts to combine SPM with optical spectroscopy will be described, and the technical difficulties encountered will be examined. These efforts have so far focused mainly on the development of tip-enhanced Raman spectroscopy, a powerful technique to detect and image chemical signatures with single molecule sensitivity, which will be reviewed. Beyond tip-enhanced Raman spectroscopy and/or topography measurements, combinations of SPM with optical spectroscopy have a great potential in the characterization of structure and quantitative measurements of physical properties, such as mechanical, optical, or electrical properties, in delicate biological samples and nanomaterials. The different approaches to improve the spatial resolution, the chemical sensitivity, and the accuracy of physical properties measurements will be discussed. Applications of such combinations for the characterization of structure, defects, and physical properties in biology and materials science will be reviewed. Due to the versatility of SPM probes for the manipulation and characterization of small and/or delicate samples, this review will mainly focus on the apertureless techniques based on SPM probes.

Combined polarized Raman and atomic force microscopy: In situ study of point defects and mechanical properties in individual ZnO nanobelts

We present a method, polarized Raman (PR) spectroscopy combined with atomic force microscopy (AFM), to characterize in situ and nondestructively the structure and the physical properties of individual nanostructures. PR-AFM applied to individual ZnO nanobelts reveals the interplay between growth direction, point defects, morphology, and mechanical properties of these nanostructures. In particular, we find that the presence of point defects can decrease the elastic modulus of the nanobelts by one order of magnitude. More generally, PR-AFM can be extended to different types of nanostructures, which can be in as-fabricated devices.

Local wettability modification by thermochemical nanolithography with write-read-overwrite capability

The wettability of a thin polymer film was modified twice by thermochemical nanolithography. By means of a first local chemical modification induced by an atomic force microscope tip heated to 110±20°C, hydrophilic patterns are written over an originally hydrophobic polymer surface. By further heating to 190±20°C, a second chemical modification reverses the local wettability change introduced by the first chemical modification. This write-read-overwrite capability can be particularly useful in the design of complex nanofluidic devices.

Tip size effects on atomic force microscopy nanoindentation of a gold single crystal

The effect of tip radius on atomic force microscopy (AFM) nanoindentation is investigated through indentation on the (111) face of a gold single crystal. The hardness is derived using two different methods: by measuring directly the projected area of the residual indent with AFM images and by measuring the cross-sectional area of the indenter before and after each nanoindentation test. The hardness values obtained from the cross-sectional area of the indenter are comparable with those obtained from images of the residual indent scanned with a sharp tip. Two AFM tips of average radii of 70±12 and 112±26 nm are used to indent the sample to various depths ranging from 4 to 50 nm. For depths above 30 nm, hardness values remain constant around 500 MPa for both indenters. For depths below 30 nm, the hardness increases as the indent depth decreases for the sharp and blunt indenters, and the indent depth dependence is observed over a wider depth range for the sharp indenter. For depths below 30 nm, the hardness v...

Size dependence of the mechanical properties of ZnO nanobelts

The Youngs modulus of ZnO nanobelts was measured using an atomic force microscope following the modulated nanoindentation method. The nanobelts have a rectangular cross-section, with width-to-thickness ratios ranging 1–10 and lengths up to a few millimetres. The Youngs modulus of two nanobelts with width-to-thickness ratio of 2.2 and 1.3 was measured at 55 and 108 GPa, respectively, indicating a size dependence of the elastic properties of the nanobelts.

Alignment of Carbon Nanotubes in Macroscopic Fibers

A simple spinning process has been recently developed to assemble carbon nanotubes into long macroscopic fibers. Due to the high aspect ratio of the nanotubes, the fiber’s physical properties are expected to depend significantly on the nanotube orientation. The alignment of the nanotubes is studied by X‐ray scattering. It is characterized by the Full Width at Half Maximum (FWHM) of the azimuthal intensity distribution. Our first studies gave FWHM≈75°. Treatments developed to improve nanotube alignment, such as solvent‐wetting or drawing of the fibers, are reported here. Results obtained from nanotubes synthesized by the arc‐discharge method and by the HiPCO process are discussed. Stretched fibers processed with HiPCO single‐wall nanotubes exhibit FWHMs as low as 32°. Moreover, the above‐mentioned treatments induce a substantial increase (by a factor 4) of their Young’s modulus. An example of electromechanical actuation is reported.

Shock compression of pyrolytic graphite to 18 GPa: Role of orientational order

Shock wave response of highly-oriented pyrolytic graphite (HOPG) compressed to stresses above the phase transformation onset (∼20 GPa) depends strongly on the HOPG orientational order [Erskine and Nellis, Nature 349, 317 (1991)]. To gain insight into this finding, which is not understood, and because corresponding results do not exist at stresses below the transition stress, the shock compression responses of three grades of pyrolytic graphite, differing in their orientational order, were examined at peak stresses below ∼20 GPa. Measured wave profiles and the corresponding end states reveal significant differences in the shock wave response of highly oriented ZYB-grade HOPG, less oriented ZYH-grade HOPG, and as-deposited pyrolytic graphite (PG). For peak stresses above 9 GPa, ZYB-grade HOPG exhibits a two-wave structure (elastic-inelastic response); the large elastic wave amplitudes for ZYB-grade increase linearly with peak stress, reaching 16 GPa for a peak stress of 18 GPa. In contrast, ZYH-grade HOPG a...

Nanomechanics: Fundamentals and Application in NEMS Technology

A nano-electromechanical system (NEMS) combines nanometer-sized actuators, sensors and electronic devices into a complex circuit. An intense effort has been made to develop versatile NEMS for the miniaturization of the existing devices and to design the new ones, with a wide range of applications in the field of electronics, chemistry and biology. All applications require a good understanding of the mechanical properties at the nanoscale and their influence on the other physical/chemical properties. In this chapter, the size dependence of the mechanical properties of nanostructures is discussed in detail and the influence of surface effects, defects and phase transitions is reviewed. The most commonly used techniques for studying the mechanical properties at the nanoscale are described and the potential applications of NEMS in biological/chemical sensing, data storage, telecommunications and electrical power generation are also presented.

Deformation Behavior of the Raman Radial Breathing Modes of Single-Wall Carbon Nanotubes in Composites

Raman spectroscopy is a technique widely used to study the vibrational modes of carbon nanotubes. The low-frequency Radial Breathing Modes (RBMs) are frequently used to characterize carbon nanotube samples. We report a Raman spectroscopic study on the strain-induced intensity variations of the RBMs of Single-Wall Carbon Nanotubes (SWNTs) in epoxy/SWNT composites. The RBM intensities have been found to vary significantly over a range of strain between -0.3% and 0.7%. The trend (increase or decrease) as well as the magnitudes of the intensity variation depends on the nanotube diameter and its chirality. Using tight-binding calculations, we have shown that these intensity variations can be explained entirely by resonance theory. Electronic density of states calculations confirm that the energy separation between the Van Hove singularities shifts with strain. The nanotubes are thus moved closer or further away from resonance, causing the intensity variations. It is demonstrated that through the use of resonance theory, a tentative chirality can be assigned to each type of SWNT from knowledge of its RBM position and the effect of strain upon the RBM intensity, thus determining its entire structure.