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Dive into the research topics where David N. Seidman is active.

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Featured researches published by David N. Seidman.


Nature | 2012

High-performance bulk thermoelectrics with all-scale hierarchical architectures

Kanishka Biswas; Jiaqing He; Ivan D. Blum; Chun I. Wu; Timothy P. Hogan; David N. Seidman; Vinayak P. Dravid; Mercouri G. Kanatzidis

With about two-thirds of all used energy being lost as waste heat, there is a compelling need for high-performance thermoelectric materials that can directly and reversibly convert heat to electrical energy. However, the practical realization of thermoelectric materials is limited by their hitherto low figure of merit, ZT, which governs the Carnot efficiency according to the second law of thermodynamics. The recent successful strategy of nanostructuring to reduce thermal conductivity has achieved record-high ZT values in the range 1.5–1.8 at 750–900 kelvin, but still falls short of the generally desired threshold value of 2. Nanostructures in bulk thermoelectrics allow effective phonon scattering of a significant portion of the phonon spectrum, but phonons with long mean free paths remain largely unaffected. Here we show that heat-carrying phonons with long mean free paths can be scattered by controlling and fine-tuning the mesoscale architecture of nanostructured thermoelectric materials. Thus, by considering sources of scattering on all relevant length scales in a hierarchical fashion—from atomic-scale lattice disorder and nanoscale endotaxial precipitates to mesoscale grain boundaries—we achieve the maximum reduction in lattice thermal conductivity and a large enhancement in the thermoelectric performance of PbTe. By taking such a panoscopic approach to the scattering of heat-carrying phonons across integrated length scales, we go beyond nanostructuring and demonstrate a ZT value of ∼2.2 at 915 kelvin in p-type PbTe endotaxially nanostructured with SrTe at a concentration of 4 mole per cent and mesostructured with powder processing and spark plasma sintering. This increase in ZT beyond the threshold of 2 highlights the role of, and need for, multiscale hierarchical architecture in controlling phonon scattering in bulk thermoelectrics, and offers a realistic prospect of the recovery of a significant portion of waste heat.


Acta Materialia | 2002

Precipitation strengthening at ambient and elevated temperatures of heat-treatable Al(Sc) alloys

David N. Seidman; Emmanuelle A. Marquis; David C. Dunand

Yield strength at ambient temperature and creep resistance between 225 and 300°C were investigated in dilute Al(Sc) alloys containing coherent Al3Sc precipitates, which were grown by heat-treatments to radii in the range 1.4–9.6 nm. The dependence of the ambient-temperature yield stress on precipitate size is explained using classical precipitation strengthening theory, which predicts a transition from precipitate shearing to Orowan dislocation looping mechanisms at a precipitate radius of 2.1 nm, in good agreement with experimental data. At 300°C creep threshold stresses are observed and found to be much lower than the yield stresses, indicative of a climb-controlled bypass mechanism. The threshold stress increases with increasing precipitate radius, in qualitative agreement with a climb model taking into account stiffness and lattice mismatches between matrix and precipitates [1].  2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.


Acta Materialia | 2001

Nanoscale structural evolution of Al3Sc precipitates in Al(Sc) alloys

Emmanuelle A. Marquis; David N. Seidman

Precipitation of the Al3Sc (L12) phase in aluminum alloys, containing 0.1, 0.2 or 0.3 wt% Sc, is studied with conventional transmission and high-resolution (HREM) electron microscopies. The exact morphologies of the Al3Sc precipitates were determined for the first time by HREM, in Al-0.1 wt% Sc and Al-0.3 wt% Sc alloys. The experimentally determined equilibrium shape of the Al3Sc precipitates, at 300°C and 0.3 wt% Sc, has 26 facets, which are the 6 {100} (cube), 12 {110} (rhombic dodecahedron), and 8 {111} (octahedron) planes, a Great Rhombicuboctahedron. This equilibrium morphology had been predicted by first principles calculations of the pertinent interfacial energies. The coarsening kinetics obey the (time) 1/3 kinetic law of Lifshitz-Slyozov-Wagner theory and they yield an activation energy for diffusion, 164±9 kJ/mol, that is in agreement with the values obtained from tracer diffusion measurements of Sc in Al and first principles calculations, which implies diffusion-controlled coarsening.  2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.


Acta Materialia | 2003

Mechanical properties of Al(Sc,Zr) alloys at ambient and elevated temperatures

Christian B. Fuller; David N. Seidman; David C. Dunand

This study investigates the mechanical properties of ternary Al(Sc,Zr) alloys containing 0.27–0.77 vol.% of Al 3(Sc,Zr) precipitates with an average radius r = 224 nm. Microhardness values at ambient temperature follow predictions of the Orowan dislocation bypass mechanism, with a transition to the precipitate shearing mechanism predicted for r larger than 2 nm. Addition of Zr to binary Al(Sc) alloys delays the onset and kinetics of over-aging at 350 and 375 °C, but has little influence on the magnitude of the peak microhardness. Creep deformation at 300 °C is characterized by a threshold stress, which increases with r in the range 2–9 nm, in agreement with prior results for binary Al(Sc) alloys and a recently developed general climb model considering elastic interactions between dislocations and coherent, misfitting precipitates. At constant r and precipitate volume fraction, Zr additions do not significantly improve the creep resistance of Al(Sc) alloys.  2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Journal of Applied Physics | 1984

Early stages of oxygen segregation and precipitation in silicon

A. Bourret; J. Thibault‐Desseaux; David N. Seidman

The early stages of oxygen segregation at dislocation and precipitation in the bulk have been investigated by high‐resolution electron microscopy in Czochralski grown silicon. Two kinds of precipitates are observed: a crystalline silica phase, coesite, and an amorphous phase. Both forms coexist after 650 °C heat treatment: the so‐called rodlike defects are in fact long 〈011〉 ribbons of coesite associated with interstitial dipoles. This crystalline form is favored by a high oxygen supersaturation and a low carbon content. Above 870 °C amorphous platelets of silica are formed on the {100} planes, whereas coesite is no longer observed but interstitial dislocation loops are always present. The strain produced by such precipitates is partially relaxed by Si interstitial emission, which explains the internal formation of dislocations. It is suggested that both forms are nucleated on two different species of nuclei. At 〈011〉 dislocation cores it is shown that the coesite phase is stabilized over a wide range of ...


Ultramicroscopy | 2003

Efficient sampling for three-dimensional atom probe microscopy data.

Olof C. Hellman; John Blatz du Rivage; David N. Seidman

The best calculation of concentration profiles, isoconcentration surfaces or Gibbsian interfacial excesses from three-dimensional atom-probe microscopy data requires a compromise between spatial positioning error and statistical sampling error. For example, sampling from larger spatial regions decreases the statistical error, but increases the error in spatial positioning. Finding the appropriate balance for a particular calculation can be tricky, especially when the three-dimensional nature of the data presents an infinite number of degrees of freedom in defining surfaces, and when the statistical error is changing from one region of a sample to another due to differences in collection efficiency or atomic density. We present some strategies for approaching these problems, focusing on efficient algorithms for generating different spatial samplings. We present a unique double-splat algorithm, in which an initial, fine-grained sampling is taken to convert the data to a regular grid, followed by a second, variable width splat, to spread the effective sampling distance to any value desired. The first sampling is time consuming for a large dataset, but needs only be performed once. The second splat is done on a regular grid, so it is efficient, and can be repeated as many times as necessary to find the correct balance of statistical and positioning error. The net effect is equivalent to a Gaussian spreading of each data point, without the necessity of calculating Gaussian coefficients for millions of data points. We show examples of isoconcentration surfaces calculated under different circumstances from the same dataset.


Journal of the American Chemical Society | 2014

High ZT in p-Type (PbTe)1–2x(PbSe)x(PbS)x Thermoelectric Materials

Rachel J. Korkosz; Thomas C. Chasapis; Shih Han Lo; Jeff W. Doak; Yoon Jun Kim; Chun I. Wu; Euripidis Hatzikraniotis; Timothy P. Hogan; David N. Seidman; C. Wolverton; Vinayak P. Dravid; Mercouri G. Kanatzidis

Lead chalcogenide thermoelectric systems have been shown to reach record high figure of merit values via modification of the band structure to increase the power factor or via nanostructuring to reduce the thermal conductivity. Recently, (PbTe)1-x(PbSe)x was reported to reach high power factors via a delayed onset of interband crossing. Conversely, the (PbTe)1-x(PbS)x was reported to achieve low thermal conductivities arising from extensive nanostructuring. Here we report the thermoelectric properties of the pseudoternary 2% Na-doped (PbTe)1-2x(PbSe)x(PbS)x system. The (PbTe)1-2x(PbSe)x(PbS)x system is an excellent platform to study phase competition between entropically driven atomic mixing (solid solution behavior) and enthalpy-driven phase separation. We observe that the thermoelectric properties of the PbTe-PbSe-PbS 2% Na doped are superior to those of 2% Na-doped PbTe-PbSe and PbTe-PbS, respectively, achieving a ZT ≈2.0 at 800 K. The material exhibits an increased the power factor by virtue of valence band modification combined with a very reduced lattice thermal conductivity deriving from alloy scattering and point defects. The presence of sulfide ions in the rock-salt structure alters the band structure and creates a plateau in the electrical conductivity and thermopower from 600 to 800 K giving a power factor of 27 μW/cmK(2). The very low total thermal conductivity values of 1.1 W/m·K of the x = 0.07 composition is accounted for essentially by phonon scattering from solid solution defects rather than the assistance of endotaxial nanostructures.


Nature | 2013

Colossal injection of catalyst atoms into silicon nanowires

Oussama Moutanabbir; Dieter Isheim; Horst Blumtritt; Stephan Senz; Eckhard Pippel; David N. Seidman

The incorporation of impurities during the growth of nanowires from the vapour phase alters their basic properties substantially, and this process is critical in an extended range of emerging nanometre-scale technologies. In particular, achieving precise control of the behaviour of group III and group V dopants has been a crucial step in the development of silicon (Si) nanowire-based devices. Recently it has been demonstrated that the use of aluminium (Al) as a growth catalyst, instead of the usual gold, also yields an effective p-type doping, thereby enabling a novel and efficient route to functionalizing Si nanowires. Besides the technological implications, this self-doping implies the detachment of Al from the catalyst and its injection into the growing nanowire, involving atomic-scale processes that are crucial for the fundamental understanding of the catalytic assembly of nanowires. Here we present an atomic-level, quantitative study of this phenomenon of catalyst dissolution by three-dimensional atom-by-atom mapping of individual Al-catalysed Si nanowires using highly focused ultraviolet-laser-assisted atom-probe tomography. Although the observed incorporation of the catalyst atoms into nanowires exceeds by orders of magnitude the equilibrium solid solubility and solid-solution concentrations in known non-equilibrium processes, the Al impurities are found to be homogeneously distributed in the nanowire and do not form precipitates or clusters. As well as the anticipated effect on the electrical properties, this kinetics-driven colossal injection also has direct implications for nanowire morphology. We discuss the observed strong deviation from equilibrium using a model of solute trapping at step edges, and identify the key growth parameters behind this phenomenon on the basis of a kinetic model of step-flow growth of nanowires. The control of this phenomenon provides opportunities to create a new class of nanoscale devices by precisely tailoring the shape and composition of metal-catalysed nanowires.


Acta Materialia | 2003

Effect of Mg addition on the creep and yield behavior of an Al–Sc alloy

Emmanuelle A. Marquis; David N. Seidman; David C. Dunand

The relationships between microstructure and strength were studied at room temperature and 300 °C in an Al–2 wt% Mg–0.2 wt% Sc alloy, containing Mg in solid-solution and Al3Sc (L12 structure) as nanosize precipitates. At room temperature, the yield strength is controlled by the superposition of solid-solution and precipitation strengthening. At 300 °C and at large applied stresses, the creep strength, which is characterized by a stress exponent of ~5, is significantly improved compared to binary Al–Sc alloys, and is independent of the size of the Al 3Sc precipitates. At small applied stress, a threshold stress exists, increasing from 9% to 70% of the Orowan stress with increasing Al 3Sc precipitate radius from 2 to 25 nm. An existing model based on a climb-controlled bypass mechanism is in semiquantitative agreement with the precipitate radius dependence of the threshold stress. The model is, however, only valid for coherent precipitates, and the Al 3Sc precipitates lose coherency for radii larger than 11 nm. For semi-coherent precipitates with radii greater than 15 nm, the threshold stress remains high, most likely because of the presence of interfacial misfit dislocations.


Materials Science and Engineering A-structural Materials Properties Microstructure and Processing | 2002

Microstructure and mechanical properties of a 5754 aluminum alloy modified by Sc and Zr additions

Christian B. Fuller; Albert Krause; David C. Dunand; David N. Seidman

The effects of various heat treatments upon the microstructure and mechanical properties of a rolled 5754 aluminum alloy modified with 0.23 wt.% Sc and 0.22 wt.% Zr were investigated. Grain size, as well as precipitate size, type, and morphology were observed by optical and transmission electron microscopies. Two populations of the Al3Sc1� x Zrx phase were present: (i) large incoherent precipitates formed during solidification and hot-rolling; and (ii) fine coherent precipitates formed from secondary precipitation, which improved alloy strength, as shown by hardness, tensile, and fatigue measurements. Aging, however, also produced two types of grain-boundary precipitates, Al6Mn and b-Al3Mg2, which contributed to poorer fatigue behavior and reduced ductility. # 2002 Elsevier Science B.V. All rights reserved.

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Zugang Mao

Northwestern University

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