Mildred S. Dresselhaus

Bio: Mildred S. Dresselhaus is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Carbon nanotube & Raman spectroscopy. The author has an hindex of 136, co-authored 762 publications receiving 112525 citations. Previous affiliations of Mildred S. Dresselhaus include University of California, Los Angeles & Universidade Federal de Minas Gerais.

Defect‐Enhanced Dispersion of Carbon Nanotubes in DNA Solutions

Abstract: Since DNA, a well-known biopolymer, has proven to be effective for dispersing and sorting carbon nanotubes, intensive studies have been carried out in order to obtain both theoretical and experimental understanding of the DNA–nanotube interaction. The ultrasonication process has been applied to dispersing a strongly bundled aggregate of carbon nanotubes in a nanotube suspension containing DNA in order to overcome the attractive van der Waals forces between adjacent tubes. The strong hydrodynamic shear forces generated by the ultrasonication process create a space within the bundled nanotubes, which allows the DNA molecules to impinge and become adsorbed on the outer surface of the nanotubes through a hydrophobic interaction, thereby leading to a stable nanotube emulsion through the formation of DNA– nanotube hybrid structures. Until now, single-stranded DNA has proven to be more effective for dispersing nanotubes than double-stranded DNA, and the combination of the short complementary oligonucleotides d(GT)3 and d(AC)3 exhibit an even superior dispersing ability. Moreover, theoretical studies have assumed that the shape of carbon nanotubes constitutes a perfect cylinder. However, the catalytic growth of carbon nanotubes in the reaction chamber inevitably involves the formation of defects (e.g. vacancies, nonhexagonal rings, and foreign atoms), which modify the electronic structure and surface properties of the tubes 14] and are expected to ultimately alter the interaction between nanotubes and DNA. In order to be able to reproducibly assemble nanotube–DNA hybrid structures as bio-medical devices, it is essential to consider the effects of defects within carbon nanotubes. Herein, the role of defects generated on the sidewall of carbon nanotubes is studied by directly comparing the dispersibility of defective and crystalline thin (small outer diameter) multi-walled carbon nanotubes (MWNTs) in aqueous DNA solutions. The dispersibility of nanotubes depend strongly on the density of the defects on the sidewall. More specifically, crystalline tubes thermally treated at 2300 8C exhibit a dispersibility twice as low as that of the as-grown tubes in aqueous DNA solutions. Theoretical calculations shown herein support the conclusion that defect sites exhibit high reactivity toward the adsorption of DNA. There are three reasons for selecting thin MWNTs rather than single-walled carbon nanotubes (SWNTs) for this study: 1) Thin MWNTs exhibit a strongly bundled structure like SWNTs because of their small diameter below 10 nm, 2) they are structurally stable up to 2800 8C, while SWNTs and DWNTs are easily transformed into graphitic material at these high temperatures, 17] and 3) their diameter is too large (above 2 nm) for the manifestation of detailed quantum effects associated with 1D dispersion relations. As a general metric for comparing the structural integrity of SWNTs or DWNTs, the intensity of the Dband, which is explained by double-resonance theory, 19] is suitable for evaluating the quality of SWNTs containing only a small number of defects. However, due to the breakdown of the van Hove singularities, this approach is not applicable to SWNTs or MWNTs containing many defects. As a tool for controlling the defect density in as-grown defective thin MWNTs, we choose high-temperature thermal treatment 21] instead of the commonly used chemical treatment. Oxidative chemical treatment can introduce both chemical moieties and defects on the sidewall of the tubes, which might affect the tube–tube interactions as well as their dispersibility. In other words, it is difficult to separate the role of defects within tubes from the effects of chemical treatment in evaluating the dispersibility of tubes in DNA solutions. The effects of high-temperature annealing on the defect density of carbon nanotubes are clearly observed as consecutive changes in the Raman spectra (Figure 1 a). Although there are no distinct changes in the G-band located at 1582 cm 1 (E2g2 graphite mode), the intensities of the D-band (a defect-induced mode) at 1350 cm 1 decrease with increasing thermal treatment temperatures, and saturate for samples prepared at 2300 8C in argon. This temperature range is consistent with the region in conventional carbon materials where the mobility of carbon atoms increases abruptly. Therefore, a drastic decrease in the R value (the intensity of the D-band divided by the intensity of the G-band) from 0.42 to 0.1 (see inset in Figure 1 a) indicates the effective removal (or annealing) of defects within carbon nanotubes by the high-temperature thermal treatment. In order to visualize the improvement of the structural integrity, we carried out detailed SEM and TEM studies on pristine tubes (Figures 1 b, c) and tubes thermally treated at 2300 8C (FigACHTUNGTRENNUNGures 1 d, e). Pristine tubes consisting of undulated fringes and amorphous carbon layers (Figure 1 c) were transformed into crystalline tubes (Figure 1 e) featuring straight linear fringes lengthwise along the tube. Fortunately, there were no appa[a] J. H. Kim, Prof. M. Kataoka, Dr. D. Shimamoto, Prof. H. Muramatsu, Dr. Y. C. Jung, T. Tojo, Prof. T. Hayashi, Prof. Y. A. Kim, Prof. M. Endo Faculty of Engineering Shinshu University, 4-17-1 Wakasato, Nagano-shi 380-8553 (Japan) Fax: (+ 81) 26-269-5208 E-mail : yak@endomoribu.shinshu-u.ac.jp [b] Prof. M. Terrones Advanced Materials Department IPICYT, San Luis Potosi 78210 (M xico) [c] Prof. M. S. Dresselhaus Massachusetts Institute of Technology Cambridge, Massachusetts 02139-4307 (USA)

Using gate-modulated Raman scattering and electron-phonon interactions to probe single-layer graphene: A different approach to assign phonon combination modes

Abstract: D. L. Mafra,1,2 J. Kong,2 K. Sato,3 R. Saito,3 M. S. Dresselhaus,2,4 and P. T. Araujo2,* 1Departamento de Fisica, Universidade Federal de Minas Gerais, 30123-970 Belo Horizonte, Brazil 2Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 3Department of Physics, Tohoku University, Sendai 980-8578, Japan 4Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA (Received 18 October 2012; published 30 November 2012; corrected 4 December 2012)

Carbon nanotube network-silicon oxide non-volatile switches

Abstract: The integration of carbon nanotubes with silicon is important for their incorporation into next-generation nano-electronics. Here, the authors demonstrate a non-volatile switch that utilizes carbon nanotube networks to electrically contact a conductive nano-crystal silicon filament in silica.

Interband Transitions for Metals in a Magnetic Field

Abstract: A quantum-mechanical derivation of the frequency and magnetic field dependence of the optical reflection and transmission in metals is given. Both interband and intraband direct transitions are considered and explicit results are obtained for a model of two simple parabolic bands having energy extrema at k=0. Spin splitting is neglected. The calculated line shape is in good agreement with the magnetoreflection experiment of Brown et al. in bismuth. The results for the limiting cases of zero interband coupling or of zero magnetic field are in agreement with previous work. The study of the interband transitions in a magnetic field is shown to yield valuable information on the band structure of metals. The advantage of this method over magnetoplasma and zero-field interband studies is discussed.

Electric Field Effect in Atomically Thin Carbon Films

Abstract: We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10 13 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by applying gate voltage.

Helical microtubules of graphitic carbon

Abstract: THE synthesis of molecular carbon structures in the form of C60 and other fullerenes1 has stimulated intense interest in the structures accessible to graphitic carbon sheets. Here I report the preparation of a new type of finite carbon structure consisting of needle-like tubes. Produced using an arc-discharge evaporation method similar to that used for fullerene synthesis, the needles grow at the negative end of the electrode used for the arc discharge. Electron microscopy reveals that each needle comprises coaxial tubes of graphitic sheets, ranging in number from 2 up to about 50. On each tube the carbon-atom hexagons are arranged in a helical fashion about the needle axis. The helical pitch varies from needle to needle and from tube to tube within a single needle. It appears that this helical structure may aid the growth process. The formation of these needles, ranging from a few to a few tens of nanometres in diameter, suggests that engineering of carbon structures should be possible on scales considerably greater than those relevant to the fullerenes. On 7 November 1991, Sumio Iijima announced in Nature the preparation of nanometre-size, needle-like tubes of carbon — now familiar as 'nanotubes'. Used in microelectronic circuitry and microscopy, and as a tool to test quantum mechanics and model biological systems, nanotubes seem to have unlimited potential.

The rise of graphene

Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The electronic properties of graphene

Abstract: This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.