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de Heer,
Walter A.
de Heer,
Walter A.
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ItemStructured Graphene: from Ballistic Transport to Electronics(Georgia Institute of Technology, 2013-12-02) de Heer, Walter A.The original concept of graphene electronics focused on carbon nanotube properties. Carbon nanotubes were known to be high mobility ballistic, phase coherent conductors and quantum confinement effects produced significant bandgaps. However, it turns out to be very difficult to develop nanotube electronics platform for a variety of reasons including fundamental physical constraints related to the quantum mechanical properties of the metal-to-nanotube contacts. Graphene electronics can in principle overcome the major problems because graphene structures can be patterned using conventional lithography and dissipation at contacts can be controlled. However, these developments rely on the premise that narrow, ballistic graphene ribbons can be produced. Experiments on conventionally patterned graphene structures produced from graphene that is deposited on insulating substrates have been discouraging. The graphene ribbon mobilities are so low due to edge roughness effects, to render this direction to be impracticable. On the other hand, graphene produced on silicon carbide turns has been found to be more immune to edge scattering problems. Moreover, recent developments of template grown graphene structures on silicon carbide are promising. Very narrow ballistic graphene ribbons that demonstrate ballistic transport properties, have been produced with these methods which again brings the original concept of graphene based nanoelectronics back into play.
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ItemCorrelated electron effects in small clusters in low temperatures molecular beams(Georgia Institute of Technology, 2010-11-29) de Heer, Walter A.
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ItemEarly Development of Graphene Electronics(Georgia Institute of Technology, 2009) de Heer, Walter A.Graphene has recently emerged as a material likely to complement or eventually succeed silicon in electronics. From 2001 to 2004, groundbreaking research was pursued behind the scenes at Georgia Tech; various directions were explored, including exfoliation techniques and CVD growth, but epitaxial graphene on silicon carbide emerged as the most viable route. This document provides archival information that may otherwise be difficult to obtain, including two proposals on file with the NSF, submitted in 2001 and 2003, and the first graphene patent, filed in 2003. The 2001 document proposes much of the graphene research carried out during this decade, and the 2003 proposal includes the data that was eventually published in J. Phys. Chem. B in Dec. 2004.
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ItemIn situ imaging of field emission from individual carbon nanotubes and their structural damage(Georgia Institute of Technology, 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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ItemPatterned Graphene Nanoelectronics(Georgia Institute of Technology, 2001-12-19) de Heer, Walter A.This work documents the birth of graphene electronics. Its purpose is to provide a contemporaneous historical account of the existent knowledge of graphene in 2001, the fundamental concepts of graphene nano electronics, and the status quo of experiments at that time. It describes the exfoliated graphene field effect transistor, patterned epitaxial graphene on silicon carbide, chemical vapor deposited graphene as well as potential uses of boron nitride.
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ItemA New Approach Towards Property Nanomeasurements Using In Situ TEM(Georgia Institute of Technology, 2001) Wang, Z. L. (Zhong Lin) ; Poncharal, P. ; de Heer, Walter A. ; Gao, Rui PingProperty 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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ItemNanomechanics of individual carbon nanotubes from pyrolytically grown arrays(Georgia Institute of Technology, 2000-07-17) Gao, Rui Ping ; Wang, Z. L. (Zhong Lin) ; Bai, Zhigang ; de Heer, Walter A. ; Dai, Liming ; Gao, MeiThe bending modulus of individual carbon nanotubes from aligned arrays grown by pyrolysis was measured by in situ electromechanical resonance in transmission electron microscopy (TEM). The bending modulus of nanotubes with point defects was ~30 GPa and that of nanotubes with volume defect was 2–3 GPa. The time-decay constant of nanotube resonance in a vacuum of 1024 Torr was 85 ms. A femtogram nanobalance was demonstrated based on nanotube resonance; it has the potential for measuring the mass of chain-structured large molecules. The in situ TEM provides a powerful approach towards nanomechanics of fiberlike nanomaterials with well-characterized defect structures.
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ItemNanomeasurements in Transmission Electron Microscopy(Georgia Institute of Technology, 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.
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ItemNanomeasurements of individual carbon nanotubes by in situ TEM(Georgia Institute of Technology, 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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ItemConductance quantization in multiwalled carbon nanotubes(Georgia Institute of Technology, 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