Jeffrey W. Kysar

Bio: Jeffrey W. Kysar is an academic researcher from Columbia University. The author has contributed to research in topics: Deformation (engineering) & Electron backscatter diffraction. The author has an hindex of 35, co-authored 139 publications receiving 21356 citations. Previous affiliations of Jeffrey W. Kysar include Columbia University Medical Center & Harvard University.

CHAPTER 5:Microfabrication of Nanoporous Gold

Abstract: Fabrication of microstructures comprising NPG requires precise control over selective corrosion of the precursor alloy. In many designs, the precursor alloy is constrained to a substrate, and complex surface reconstruction during dealloying potentially leads to a high overall stress in the newly formed NPG. Hence, constrained NPG thin films or suspended NPG structures often develop cracks in fabrication. Similarly, nanovoids in thin-film precursor alloys or low Au content in the precursor alloys may lead to fractures in the NPG thin films, which compromise the integrity and functionality of the resulting architecture. Recently developed scalable electrochemical methods for which the rate of removal of the less noble elements in the precursor alloy can be precisely controlled produce crack-free blanket films constrained to a substrate. In this chapter, conventional as well as newly developed NPG fabrication techniques are assessed from a microscale fabrication perspective, with regard to the NPG product quality, means of tailoring the final porous structure, and their compatibility with the standard microdevice fabrication techniques.

Brittle to Ductile Transition in Intermetallic Alloys

Abstract: Two distinct approaches are commonly invoked to explain the brittle to ductile transition of a material in the presence of a crack. In one approach, dislocation mobility plays the key role. In the other approach, the competition between crack tip dislocation nucleation and cleavage failure plays the key role. The two approaches are reconciled in the present study.

Crack-opening Interferometry at Interfaces of Transparent Materials and Metals

Abstract: Crack-opening interferometry is a technique whereby one can directly measure the normal opening displacement of a crack that exists in a transparent material. Here, wer extend the techique to situations in which the crack lies along the interface between a stransparent material and a highly reflective metal. We discuss how the intensity distribution and the placement of the fringes vary with reflectivity of the metal. However, because the fringe spacing is not affected, the fringes can still be interpreted in terms of normal crack-opening displacement profile. The paper reports experimental measurements of crack-opening displacement profile of an interface crack in a copper-sapphire bircystal. The results show the crack-opening displacement profile to be that of a constant opening angle.

Experimental Characterization and Simulation of Three Dimensional Plastic Deformation Induced by Microscale Laser Shock Peening

Abstract: Different experimental techniques and 3D FEM simulations are employed to characterize and analyze the three dimensional plastic deformation and residual strain/stress distribution for single crystal Aluminum under microscale laser shock peening assuming finite geometry. Single pulse shock peening at individual locations was studied. X-ray micro-diffraction techniques based on a synchrotron light source affords micron scale spatial resolution and is used to measure the residual stress spatial distribution along different crystalline directions on the shocked surface. Crystal lattice rotation due to plastic deformation is also measured with electron backscatter diffraction (EBSD). The result is experimentally quantified and compared with the simulation result obtained from FEM analysis. The influence of the finite size effect, crystalline orientation are investigated using single crystal plasticity in FEM analysis. The result of the 3D simulations of a single shock peened indentation are compared with the FEM results for a shocked line under 2D plain strain deformation assumption. The prediction of overall character of the deformation and lattice rotation fields in three dimensions will lay the ground work for practical application of μLSP.Copyright © 2004 by ASME

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.

Atomically thin MoS2: a new direct-gap semiconductor

Abstract: The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N=1,2,…,6 S-Mo-S monolayers have been investigated by optical spectroscopy Through characterization by absorption, photoluminescence, and photoconductivity spectroscopy, we trace the effect of quantum confinement on the material's electronic structure With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by more than 06 eV This leads to a crossover to a direct-gap material in the limit of the single monolayer Unlike the bulk material, the MoS₂ monolayer emits light strongly The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 10⁴ compared with the bulk material

Graphene: Status and Prospects

Abstract: Graphene is a wonder material with many superlatives to its name. It is the thinnest known material in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic mobility, have zero effective mass, and can travel for micrometers without scattering at room temperature. Graphene can sustain current densities six orders of magnitude higher than that of copper, shows record thermal conductivity and stiffness, is impermeable to gases, and reconciles such conflicting qualities as brittleness and ductility. Electron transport in graphene is described by a Dirac-like equation, which allows the investigation of relativistic quantum phenomena in a benchtop experiment. This review analyzes recent trends in graphene research and applications, and attempts to identify future directions in which the field is likely to develop.

Large-scale pattern growth of graphene films for stretchable transparent electrodes

Abstract: Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.

Graphene and Graphene Oxide: Synthesis, Properties, and Applications

Abstract: There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.