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.

Modifying materials by intercalation

Abstract: For the past decade, materials research has focused on synthesizing new materials and generating new structural arrangements that exhibit specific desired properties. Some of the greatest advances in this area have come out of work on intercalation compounds, which are formed by the insertion of atomic or molecular layers of a guest chemical species—an intercalant—between layers in a host material. Figure 1 illustrates the basic structure of intercalation compounds. Part a of the figure depicts graphite intercalated with lithium; this structure is described as “commensurate,” because the atoms in each layer of guest material are in registry with those in the neighboring layers of the host material. Part b of the figure shows the incommensurate nature of graphite intercalated with ferric chloride. Although graphite intercalation compounds have been synthesized for over 150 years, it is only very recently that methods have been perfected to the point that one can prepare materials with specific structures a...

X‐Ray Spectroscopic Investigation of Chlorinated Graphene: Surface Structure and Electronic Effects

Abstract: Chemical doping of graphene represents a powerful means of tailoring its electronic properties. Synchrotron-based X-ray spectroscopy offers an effective route to investigate the surface electronic and chemical states of functionalizing dopants. In this work, a suite of X-ray techniques is used, including near edge X-ray absorption fi ne structure spectroscopy, X-ray photoemission spectroscopy, and photoemission threshold measurements, to systematically study plasma-based chlorinated graphene on different substrates, with special focus on its dopant concentration, surface binding energy, bonding confi guration, and work function shift. Detailed spectroscopic evidence of C‐Cl bond formation at the surface of single layer graphene and correlation of the magnitude of p-type doping with the surface coverage of adsorbed chlorine is demonstrated for the fi rst time. It is shown that the chlorination process is a highly nonintrusive doping technology, which can effectively produce strongly p-doped graphene with the 2D nature and long-range periodicity of the electronic structure of graphene intact. The measurements also reveal that the interaction between graphene and chlorine atoms shows strong substrate effects in terms of both surface coverage and work function shift.

Effect of quantized electronic states on the dispersive Raman features in individual single-wall carbon nanotubes

Abstract: This work reports how resonance Raman experiments are used to study details of the electronic structure of individual single-wall carbon nanotubes ~SWNTs! by measuring the phonon spectra and how the quantized electronic structure affects the dispersive Raman features of SWNTs. We focus our analysis on the dispersive D and G8 bands observed in the Raman spectra of isolated semiconducting nanotubes. By using a laser excitation energy of 2.41 eV, we show that both the D-band and G8-band frequencies are dependent on the wave vector kii where the electrons are confined in the one-dimensional subbandi of the electronic structure of SWNTs. By making use of the (n,m) assignment for each tube, we theoretically correlate the observed frequency dependences for the D- and G8-band modes with the electronic structure predicted for each ( n,m) pair and we determine the dependence of v D and v G8 on the diameter and chirality for individual electronic transitions Eii for nanotube bundles. We use the D- and G8-band dependence on electron wave vector k ii to predict the dominant phonon wave vector q selected by the quantum-confined electronic statekii and to explain the anomalous dispersion observed for v D and v G8 in SWNT bundles as a function of laser excitation energy, yielding excellent agreement between experiment and theory.

Angle-tunable transmissive grating

Abstract: A tunable transmissive grating comprises a transmissive dispersive element (1), a reflective element (2) and an angle t formed between the two elements. A first optical path is formed according to the angle t, wherein light dispersing from the dispersive element is directed onto the reflective element and reflects therefrom. At least one element is rotatable about a rotational center (6) to cause a second optical path and thereby tune the wavelength of the light reflecting from the reflective element. Both elements can be rotatable together around a common rotational center point (6) according to certain embodiments, and/or each element can be independently rotated around a rotational axis associated only with that element. According to some embodiments, the relative angle t formed between the elements is held constant; however, in other embodiments t can vary. A control system can be used to operate the device.

The fermi surface of graphite

Abstract: Recent magnetoreflection measurements in pyrolytic graphite have been interpreted using the magnetic energy levels obtained from the McClure-lnoue secular equation and the appropriate selection rules for interband transitions. Combining these results with those of the de Haas - van Alphen effect, the band parameters of the Slonczewski-Weiss model have been evaluated and the Fermi surface determined. The magnetoreflection experiment indicates considerable warping of the Fermi surface, particularly for holes. Further experiments to determine this warping more precisely are 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.