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.

Thermoelectric transport properties of single bismuth nanowires

Abstract: We present a novel technique for measuring the power factor (Seebeck coefficient and resistivity) of a single isolated Bi nanowire. Electron beam lithography is used to pattern electrodes on top of a 40 nm diameter Bi nanowire along with a microscopic heater and thermocouples. Running current through the heater generates a temperature gradient of 0.5 K over a distance of 10 /spl mu/m across the nanowire. Measurement of the Seebeck voltage of the nanowires was not possible due to the highly resistive and non-ohmic contacts. The non-linearity in the i(V) characteristics of the electrical contacts are understood by detailed modeling of the tunneling mechanism made through the electrical contacts. The prospect of using the poor contacts to perform tunneling spectroscopy of the electronic density of states of the nanowires is evaluated using this model.

Controlled growth of one-dimensional clusters of molybdenum atoms using double-walled carbon nanotube templating

Abstract: We report the controlled growth of one-dimensional clusters of molybdenum atoms inside the inner cores of double-walled carbon nanotubes. A combined characterization including high resolution transmission electron microscopy, nitrogen adsorption measurement at 77 K, x-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis reveals that the growth of one-dimensional Mo clusters can be controlled by varying the reaction conditions. The products have specific surface areas of 360‐480 m 2 g 1 , and their characteristic properties are attributed to the presence of Mo cluster, which affect the electronic structure and can be exploited for the development of nanotube electronic devices. © 2009 American Institute of Physics. DOI: 10.1063/1.3089576 The discovery and identification of carbon nanotubes have stimulated scientific and industrial interest due to their outstanding mechanical and electronic properties and potential applications. Recently a unique class of hybrid materials in the form of assembled atomic or cluster chains inside carbon nanotubes suggested to have electronic and mechanical properties that differ from those of empty carbon nanotubes, thus there is a strong interest in developing an efficient fabrication technique so that these filled nanotubes could be used in nanoelectronic and nano-optoelectronic devices. 1

Magneto-optical studies of graphite intercalation compounds

Abstract: High field magnetoreflection measurements are reported on the first observation of interband Landau level transitions in residue and lamellar compounds of graphite intercalated with the halogens Br 2 , IBr and ICl. These magnetoreflection spectra are interpreted to yield a model for the magnetic energy level structure of these intercalation compounds in the dilute limit corresponding to stage ≳5. In this dilute limit, the insensitivity of the magnetoreflection resonances to intercalate concentration shows that near the Fermi level for pure graphite the electronic structure of the intercalation compounds is essentially independent of intercalate concentration. This conclusion results from analysis of both infrared and far-infrared magnetoreflection spectra for Landau level transitions within ±0.1 eV of the graphite Fermi level. The model for the electronic structure deduced from the magnetoreflection spectra is supported by Raman scattering results presented for the in-plane lattice modes of carbon atoms in the graphitic layer planes.

Vacancy clustering and diffusion in heavily P doped Si

Abstract: A kinetic Monte Carlo (KMC) algorithm with a vacancy source and sink has been developed to determine the equilibrium vacancy concentration (CVe) in Si1−xPx alloys. KMC results for CVe exhibit good agreement with the Lomer formula with added entropic terms to account for high P concentrations. They also highlight the role of CVe and clustering on self and impurity diffusion during thermal aging.

Arrays of nanowires on silicon wafers

Abstract: Nanowires made of thermoelectric-relevant materials were grown in the pores of alumina templates fabricated on silicon wafers. This architecture combines the nanometer-scale, self-assembly nature of the anodic alumina with the micro-scale, versatile nature of integrated circuits processing. The nanowires can be made by the pressure injection technique, and even more conveniently by electrochemical deposition. The geometry is adequate for 2-point transport measurements on the nanowire arrays, and for fabrication of nanowire-based devices made of several materials and several components. In this context, a fabrication scheme for a thermoelectric device, containing both n-type and p-type legs, is suggested.

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.