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de Heer, Walter A.

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In situ imaging of field emission from individual carbon nanotubes and their structural damage

2002-02-04 , Wang, Z. L. (Zhong Lin) , Gao, Rui Ping , de Heer, Walter A. , Poncharal, P.

Field emission of individual carbon nanotubes was observed by in situ transmission electron microscopy. A fluctuation in emission current was due to a variation in distance between the nanotube tip and the counter electrode owing to a "head-shaking" effect of the nanotube during field emission. Strong field-induced structural damage of a nanotube occurs in two ways: a piece-by-piece and segment-by-segment pilling process of the graphitic layers, and a concentrical layer-by-layer stripping process. The former is believed owing to a strong electrostatic force, and the latter is likely due to heating produced by emission current that flowed through the most outer graphitic layers.

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Nanomeasurements of individual carbon nanotubes by in situ TEM

2000 , Wang, Z. L. (Zhong Lin) , Poncharal, P. , de Heer, Walter A.

Property characterization of nanomaterials is challenged by the small size of the structure because of the difficulties in manipulation. Here we demonstrate a novel approach that allows a direct measurement of the mechanical and electrical properties of individual nanotube-like structures by in situ transmission electron microscopy (TEM). The techniqueis powerful in a way that it can be directly correlated to the atomic-scale microstructure of the carbon nanotube with its physical properties, thus providing a complete characterization of the nanotube. Applications of the technique will be demonstrated in measurements of the mechanical properties, the electron field emission, and the ballistic quantum conductance of individual carbon nanotubes. A nanobalance technique is demonstrated that can be applied to measure the mass of a single tiny particle as light as 22 fg (1 f = 10⁻¹⁵).

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A New Approach Towards Property Nanomeasurements Using In Situ TEM

2001 , Wang, Z. L. (Zhong Lin) , Poncharal, P. , de Heer, Walter A. , Gao, Rui Ping

Property characterization of nanomaterials is challenged by the small size of the structure because of the difficulties in manipulation. Here we demonstrate a novel approach that allows a direct measurement of the mechanical and electrical properties of individual nanotube-like structures by in-situ transmission electron microscopy (TEM). The technique is powerful in a way that it can directly correlate the atomic-scale microstructure of the carbon nanotube with its physical properties, providing a one-to-one correspondence in structure-property characterization. Applications of the technique will be demonstrated on mechanical properties, the electron field emission and the ballistic quantum conductance in individual nanotubes. A nanobalance technique is demonstrated that can be applied to measure the mass of a single tiny particle as light as 22 fg (1 f= 10-').

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Conductance quantization in multiwalled carbon nanotubes

1999 , Poncharal, P. , Frank, S. , Wang, Z. L. (Zhong Lin) , de Heer, Walter A.

We present results of carbon nanotube conductance measurements. The experiments were performed using an scanning probe microscope (SPM) system where a carbon nanotube fiber is connected to the SPM tip and then lowered into a liquid mercury contact. Experiments were also performed using a modified transmission electron microscope (TEM) specimen holder supplied with piezo and micrometer positioning system. Thus the contacting process of the nanotubes with the mercury could be monitored while simultaneously recording the conductance. These measurements and observations confirm previously reported conductance quantization (Frank et al.: Science 280, 1744 (1998)) of the nanotubes while providing additional details concerning the mercury nanotube contacts.We also report conductance versus voltage characteristics of carbon nanotubes

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Nanomeasurements in Transmission Electron Microscopy

2000-05 , Wang, Z. L. (Zhong Lin) , Poncharal, P. , de Heer, Walter A.

Nanomaterials have attracted a great deal of research interest recently. The small size of nanostructures constrains the application of well-established testing and measurement techniques, thus new methods and approaches must be developed for quantitative measurement of the properties of individual nanostructures. This article reports our progress in using in situ transmission electron microscopy to measure the electrical, mechanical, and field-emission properties of individual carbon nanotubes whose microstructure is well-characterized. The bending modulus of a single carbon nanotube has been measured by an electric field induced resonance effect. A nanabalance techniques is demonstranted that can be applied to measure the mass of a tiny particle as light as 22fg (1 fg = 10⁻¹⁵g), the smallest balance in the world. Quantum conductance was observed in defect-free nanotubes, which led to the transport of a superhigh current density at room temperature without heat dissipation. Finally, the field-emission properties of a single carbon nanotube are observed, and the field-induced structural damage is reported.