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.

The promise of low-dimensional thermoelectric materials

Abstract: The study of thermoelectric materials has recently been revived as an active research field, in part due to the recent demonstration of enhancement in the thermoelectric figure of merit of a two-dimensional (2D) PbTe quantum well system, relative to its three-dimensional (3D) bulk counterpart. Calculations suggest that the thermoelectric performance of any 3D material should show an enhanced thermoelectric figure of merit, when prepared as a 2D multi-quantum well superlattice, utilizing the enhanced density of states at the onset of each electronic subband, and the increased scattering of vibrational waves at the boundary between the quantum well and the adjacent barrier of the superlattice. In principle, low dimensionality also allows certain materials such as bismuth, which are poor thermoelectrics in 3D, to become good thermoelectrics. Thus, the successful fabrication of 1D bismuth nanowires offers new possibilities for the study of 1D systems for possible thermoelectric applications.

Impact of Chlorine Functionalization on High-Mobility Chemical Vapor Deposition Grown Graphene

Abstract: We systematically investigated plasma-based chlorination of graphene and compared its properties before and after such treatment. X-ray photoelectron spectroscopy revealed that a high Cl coverage of 45.3% (close to C2Cl), together with a high mobility of 1535 cm2/(V s), was achieved. The C:Cl ratio n (CnCl) can be effectively tuned by controlling the dc bias and treatment time in the plasma chamber. Chlorinated graphene field-effect transistors were fabricated, and subsequent Hall-effect measurements showed that the hole carrier concentration in the chlorinated graphene can be increased roughly by a factor of 3. Raman spectra indicated that the bonding type between Cl and graphene depends sensitively on the dc bias applied in the plasma chamber during chlorination and can therefore be engineered into different reaction regimes, such as ionic bonding, covalent bonding, and defect creation. Micro-Raman mapping showed that the plasma-based chlorination process is a uniform process on the micrometer scale.

Topographic and Spectroscopic Characterization of Electronic Edge States in CVD Grown Graphene Nanoribbons

Abstract: We used scanning tunneling microscopy and spectroscopy (STM/S) techniques to analyze the relationships between the edge shapes and the electronic structures in as-grown chemical vapor deposition (CVD) graphene nanoribbons (GNRs). A rich variety of single-layered graphene nanoribbons exhibiting a width of several to 100 nm and up to 1 μm long were studied. High-resolution STM images highlight highly crystalline nanoribbon structures with well-defined and clean edges. Theoretical calculations indicate clear spin-split edge states induced by electron–electron Coulomb repulsion. The edge defects can significantly modify these edge states, and different edge structures for both sides of a single ribbon produce asymmetric electronic edge states, which reflect the more realistic features of CVD grown GNRs. Three structural models are proposed and analyzed to explain the observations. By comparing the models with an atomic resolution image at the edge, a pristine (2,1) structure was ruled out in favor of a recons...

Smallest Freestanding Single-Walled Carbon Nanotube

Abstract: Here, we report the successful direct observation of the smallest free-standing single-walled carbon nanotube, which has a diameter of about 043 nm Our single-walled carbon nanotubes were produced by the improved floating reactant method, which combines the conventional substrate and floating catalyst methods using zeolite particles as a floating catalyst support This finding is also important because small-diameter nanotubes were proved to be able to grow without any confinement that limits the tube diameter such as in the tube growth in a template or in the central core of a multiwalled nanotube, as reported in previous studies by other groups The success of obtaining very small single-walled carbon nanotubes opens the door to unprecedented applications of this fascinating material as a true 1D material

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.