Jeremy M. Higgins
University of Wisconsin-Madison
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Jeremy M. Higgins.
Journal of Materials Chemistry | 2011
Jeannine R. Szczech; Jeremy M. Higgins; Song Jin
Thermoelectric materials can be used for solid state power generation and heating/cooling applications. The figure of merit of thermoelectric materials, ZT, which determines their efficiency in a thermoelectric device, remains low for most conventional bulk materials. Nanoscale and nanostructured thermoelectric materials are promising for increasing ZT relative to the bulk. This review introduces the theory behind thermoelectric materials and details the predicted and demonstrated enhancements of ZT in nanoscale and nanostructured thermoelectric materials. We discuss thin films and superlattices, nanowires and nanotubes, and nanocomposites, providing a ZT comparison among various families of nanocomposite materials. We provide some perspectives regarding the origin of enhanced ZT in nanoscale and nanostructured materials and suggest some promising and fruitful research directions for achieving high ZT materials for practical applications.
Journal of Materials Chemistry | 2010
Andrew L. Schmitt; Jeremy M. Higgins; Jeannine R. Szczech; Song Jin
Transition metal silicides represent an extremely broad set of refractory materials that are currently employed for many applications including CMOS devices, thin film coatings, bulk structural components, electrical heating elements, photovoltaics, and thermoelectrics. Many of these applications may be improved by making 1-dimensional nanomaterials. Chemical synthesis of silicide nanowires is more complicated compared to other classes of nanomaterials due to the complex phase behaviour between metals and silicon and the complex stoichiometries and structures of their resulting compounds. Recently, several synthetic strategies have been developed to overcome this challenge resulting in increasing reports of silicide nanowires in the literature. These strategies are highlighted in this feature article, along with future synthetic challenges and a review of the applications emerging from current silicide nanowires.
Journal of the American Chemical Society | 2008
Jeremy M. Higgins; Andrew L. Schmitt; Ilia A. Guzei; Song Jin
We report the synthesis, structural identification, and electrical properties of the first one-dimensional (1-D) nanomaterials of a semiconducting higher manganese silicide (MnSi(2-x)) with widths down to 10 nm via chemical vapor deposition of the single-source precursor Mn(CO)(5)SiCl(3). The complex Nowotny chimney ladder structure of these homologous higher manganese silicides, also referred to as Mn(n)Si(2n-m), MnSi(1.75), or MnSi(1.8), contributes to the excellent thermoelectric performance of the bulk materials, which would be enhanced by phonon scattering due to 1-D nanoscale geometry. The morphology, structure, and composition of MnSi(2-x) nanowires and nanoribbons are examined using electron microscopy and X-ray spectroscopy. Elaborate select area electron diffraction analysis on single-crystal nanowires reveals the phase to be Mn(19)Si(33), one of a series of crystallographically distinct higher manganese silicides that have a Nowotny chimney ladder structure. Electrical transport study of single nanowires shows that they are degenerately doped with a low resistivity (17 mohms x cm) similar to the bulk.
Nano Letters | 2008
Andrew L. Schmitt; Jeremy M. Higgins; Song Jin
We report single-crystal nanowires of magnetic semiconducting Fe1-xCoxSi alloys synthesized using a two-component single source precursor approach. Extending our previous syntheses of FeSi and CoSi nanowires from Fe(SiCl3)2(CO)4 and Co(SiCl3)(CO)4 precursors, we found that a homogeneous solution formed upon mixing these two precursors due to melting point suppression. This liquid constitutes the single-source precursor suitable for delivery through chemical vapor deposition, which enables the chemical synthesis of Fe1-xCoxSi alloy nanowires on silicon substrates covered with a thin (1-2 nm) SiO2 layer. Using scanning and transmission electron microscopy and energy dispersive X-ray spectroscopy and mapping, we demonstrate two homogenously mixed alloy nanowire samples with very different Co substitution concentrations (x): 6+/-5%, the ferromagnetic semiconductor regime, and 44+/-5%, the helical magnetic regime. The magnetotransport properties of these alloy nanowires are pronouncedly different from that of the host structures FeSi and CoSi, as well as from one another, and consistent with the physical properties as expected for their corresponding compositions. These novel magnetic semiconducting silicide nanowires will be important building blocks for silicon-based spintronic nanodevices.
Nano Letters | 2010
Jeremy M. Higgins; Ruihua Ding; John P. DeGrave; Song Jin
We report the synthesis, structural characterization, and magnetotransport of single-crystalline nanowires of manganese monosilicide, MnSi. Bulk MnSi has unusual magnetic orderings, helimagnetism, and skyrmions at ambient pressure, and high pressure studies have revealed partial magnetic ordering and non-Fermi liquid behavior. MnSi nanowires were synthesized using chemical vapor deposition of MnCl(2) onto silicon substrates. The morphology, structure, and composition of these nanowires were analyzed using electron microscopy and X-ray spectroscopy. The low-temperature magnetoresistance characteristics of MnSi nanowires reveal the first signature of helimagnetism in one-dimensional nanomaterials.
ACS Nano | 2011
Chaoyi Yan; Jeremy M. Higgins; Matthew S. Faber; Pooi See Lee; Song Jin
We report the synthesis, phase transformation, and electrical property measurement of single-crystal NiGe and ε-Ni(5)Ge(3) nanowires (NWs). NiGe NWs were spontaneously synthesized by chemical vapor deposition of GeH(4) onto a porous Ni substrate without the use of intentional catalysts. The as-grown NWs of the orthorhombic NiGe phase were transformed to the hexagonal ε-Ni(5)Ge(3) phase by thermal annealing induced Ni enrichment. This controllable conversion of germanide phases is desirable for phase-dependent property study and applications, and the observation of novel metastable ε-Ni(5)Ge(3) phase suggests the importance of kinetic factors in such nanophase transformations. Electrical studies reveal that NiGe NWs are highly conductive, with an average resistivity of 35 ± 15 μΩ·cm, while the resistivity of ε-Ni(5)Ge(3) NWs is more than 4 times that of the NiGe phase. NWs of nickel germanides, particularly NiGe, would be useful building blocks for germanium-based nanoelectronic devices.
Nano Letters | 2011
John P. DeGrave; Andrew L. Schmitt; Rachel S. Selinsky; Jeremy M. Higgins; D. J. Keavney; Song Jin
We report a general method for determining the spin polarization from nanowire materials using Andreev reflection spectroscopy implemented with a Nb superconducting contact and common electron-beam lithography device fabrication techniques. This method was applied to magnetic semiconducting Fe(1-x)Co(x)Si alloy nanowires with x̅ = 0.23, and the average spin polarization extracted from 6 nanowire devices is 28 ± 7% with a highest observed value of 35%. Local-electrode atom probe tomography (APT) confirms the homogeneous distribution of Co atoms in the FeSi host lattice, and X-ray magnetic circular dichroism (XMCD) establishes that the elemental origin of magnetism in this strongly correlated electron system is due to Co atoms.
ACS Nano | 2011
Jeremy M. Higgins; Penelope Carmichael; Andrew L. Schmitt; Stephen Lee; John P. DeGrave; Song Jin
We present the chemical vapor deposition (CVD) reactions of the single source precursor Fe(SiCl(3))(2)(CO)(4) over Si, Ge, CoSi(2)/Si, and CoSi/Si substrates to explore the growth and doping processes of silicide nanowires (NWs). Careful investigation of the composition and morphology of the NW products and the intruded silicide films from which they nucleate revealed that the group IV elements (Si, Ge) in the NW products originate from both the precursor and the substrate, while the metal elements incorporated into the NWs (Fe, Co) originate from vapor phase precursor delivery. The use of a Ge growth substrate enabled the successful synthesis of Fe(5)Si(2)Ge NWs, the first report of a metal silicide-germanide alloy NW. Further, investigation of the pyrolysis of the CoSiCl(3)(CO)(4) precursor revealed independent delivery of Co and Si species during CVD reactions. This understanding enabled a new, more robust two-precursor synthetic route to Fe(1-x)Co(x)Si alloy NWs using Fe(SiCl(3))(2)(CO)(4) and CoCl(2).
Physical Review B | 2017
Annie Weathers; Jesús Carrete; John P. DeGrave; Jeremy M. Higgins; Arden L. Moore; Jae Hyun Kim; Natalio Mingo; Song Jin; Li Shi
Size effects on vibrational modes in complex crystals remain largely unexplored, despite their importance in a variety of electronic and energy conversion technologies. Enabled by advances in a four-probe thermal transport measurement method, we report the observation of glass-like thermal conductivity in
Archive | 2014
Ankit Pokhrel; John P. DeGrave; Dong Liang; Jeremy M. Higgins; Song Jin
\ensuremath{\sim}20