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.

Ion Implantation in Diamond, Graphite and Related Materials

Abstract: 1. Introduction.- 2. Carbon Materials: Graphite, Diamond and Others.- 2.1 Structure and Materials.- 2.1.1 Graphite.- 2.1.2 Graphite-Related Materials.- 2.1.3 Carbon Fibers.- 2.1.4 Glassy Carbon.- 2.1.5 Graphite Intercalation Compounds.- 2.1.6 Diamond.- 2.1.7 CVD Diamond Films.- 2.1.8 Diamond-Like Carbon Films.- 2.2 Properties of Graphite.- 2.2.1 Lattice Properties.- 2.2.2 Electronic and Transport Properties.- 2.2.3 Optical Properties.- 2.2.4 Thermal Properties.- 2.2.5 Mechanical Properties.- 2.3 Properties of Diamond.- 2.3.1 Lattice Properties.- 2.3.2 Electronic and Transport Properties.- 2.3.3 Optical Properties.- 2.3.4 Thermal Properties.- 2.3.5 Mechanical Properties.- 2.3.6 Chemical Properties.- 3. Ion Implantation.- 3.1 Energy Loss Mechanisms.- 3.2 Parameters of Implantation.- 3.2.1 Energy of Implantation.- 3.2.2 Implantation Range.- 3.2.3 Implantation Fluence (Dose) and Beam Current (Dose Rate).- 3.3 Radiation Damage.- 3.4 Energy Loss Simulations.- 4. Ion Beam Analysis Techniques.- 4.1 Rutherford Backscattering Spectroscopy.- 4.2 Nuclear Reaction Analysis.- 4.3 Particle Induced X-Ray Emission (PIXE).- 4.4 Channeling.- 4.5 Elastic Recoil Detection (ERD).- 4.6 Secondary Ion Mass Spectroscopy (SIMS).- 4.7 Channeling Studies in Graphite-Based Materials.- 4.8 Stoichiometric Characterization of GICs by RBS.- 4.9 Ion Channeling in GICs.- 5. Other Characterization Techniques.- 5.1 Raman Spectroscopy.- 5.2 Other Optical and Magneto-Optical Techniques.- 5.3 Electron Microscopies and Spectroscopies.- 5.4 X-Ray-Related Characterization Techniques.- 5.5 Electronic Transport Measurements.- 5.6 Electron Spin Resonance (ESR).- 5.7 Hyperfine Interactions.- 5.7.1 Mossbauer Spectroscopy.- 5.7.2 Perturbed Angular Correlations (PAC).- 5.8 Mechanical Properties.- 6. Implantation-Induced Modifications to Graphite.- 6.1 Lattice Damage.- 6.2 Regrowth of Ion-Implanted Graphite.- 6.3 Structural Modification.- 6.4 Modification of the Electronic Structure and Transport Properties.- 6.5 Modification of Mechanical Properties.- 6.6 Implantation with Ferromagnetic Ions.- 6.7 Implantation-Enhanced Intercalation.- 6.8 Implantation with Hydrogen and Deuterium.- 7. Implantation-Induced Modifications to Graphite-Related Materials.- 7.1 Glassy Carbon.- 7.2 Carbon Fibers.- 7.3 Disordered Graphite.- 7.4 Carbon-Based Polymers.- 8. Implantation-Induced Modifications to Diamond.- 8.1 Structural Modifications and Damage-Related Electrical Conductivity.- 8.2 Volume Expansion.- 8.3 Lattice Damage.- 8.4 Damage Annealing and Implantations at Elevated Temperatures.- 8.5 Electrical Doping.- 8.6 Impurity State Identification.- 8.7 Electronic Device Realization.- 8.8 New Materials Synthesis.- 8.9 Improving Mechanical Properties.- 9. Implantation-Induced Modifications to Diamond-Related Materials.- 9.1 Diamond-Like Carbon (a-C:H) Films.- 9.1.1 DC Conductivity.- 9.1.2 Optical Characterization.- 9.1.3 Structural Modifications and Hydrogen Loss.- 9.1.4 Attempts to Dope a-C:H by Ion-Implantation.- 9.1.5 Discussion of Implantation-Induced Effects in DLC.- 9.2 Diamond Films.- 10. Concluding Remarks.- References.

Tuning Electronic Structure of Single Layer MoS2 through Defect and Interface Engineering

Abstract: Transition-metal dichalcogenides (TMDs) have emerged in recent years as a special group of two-dimensional materials and have attracted tremendous attention. Among these TMD materials, molybdenum disulfide (MoS2) has shown promising applications in electronics, photonics, energy, and electrochemistry. In particular, the defects in MoS2 play an essential role in altering the electronic, magnetic, optical, and catalytic properties of MoS2, presenting a useful way to engineer the performance of MoS2. The mechanisms by which lattice defects affect the MoS2 properties are unsettled. In this work, we reveal systematically how lattice defects and substrate interface affect MoS2 electronic structure. We fabricated single-layer MoS2 by chemical vapor deposition and then transferred onto Au, single-layer graphene, hexagonal boron nitride, and CeO2 as substrates and created defects in MoS2 by ion irradiation. We assessed how these defects and substrates affect the electronic structure of MoS2 by performing X-ray pho...

Low-Frequency Interlayer Raman Modes to Probe Interface of Twisted Bilayer MoS2

Abstract: van der Waals homo- and heterostructures assembled by stamping monolayers together present optoelectronic properties suitable for diverse applications. Understanding the details of the interlayer stacking and resulting coupling is crucial for tuning these properties. We investigated the low-frequency interlayer shear and breathing Raman modes (<50 cm–1) in twisted bilayer MoS2 by Raman spectroscopy and first-principles modeling. Twisting significantly alters the interlayer stacking and coupling, leading to notable frequency and intensity changes of low-frequency modes. The frequency variation can be up to 8 cm–1 and the intensity can vary by a factor of ∼5 for twisting angles near 0° and 60°, where the stacking is a mixture of high-symmetry stacking patterns and is thus sensitive to twisting. For twisting angles between 20° and 40°, the interlayer coupling is nearly constant because the stacking results in mismatched lattices over the entire sample. It follows that the Raman signature is relatively unifor...

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.