Thomas J. Scheidemantel

Microstructured optical fibers as high-pressure microfluidic reactors

Deposition of semiconductors and metals from chemical precursors onto planar substrates is a well-developed science and technology for microelectronics. Optical fibers are an established platform for both communications technology and fundamental research in photonics. Here, we describe a hybrid technology that integrates key aspects of both engineering disciplines, demonstrating the fabrication of tubes, solid nanowires, coaxial heterojunctions, and longitudinally patterned structures composed of metals, single-crystal semiconductors, and polycrystalline elemental or compound semiconductors within microstructured silica optical fibers. Because the optical fibers are constructed and the functional materials are chemically deposited in distinct and independent steps, the full design flexibilities of both platforms can now be exploited simultaneously for fiber-integrated optoelectronic materials and devices.

Improved thermoelectric devices using bismuth alloys

We present first-principles transport calculations for bismuth utilizing the linearized-augmented plane-wave method. From the calculated transport distribution, we compute transport coefficients and our results agree well with experiment. Furthermore, we derive the power factor and find two pronounced maxima excelling even the power factor of Bi2Te3. These maxima can be related to the points of steepest slope in the transport distribution. This insight provides a very valuable guideline for the search of improved thermoelectric materials. The maximum in the power factor leads to a thermoelectric figure of merit of 1.44, which is considerably larger than the one for Bi2Te3.

Electronic structure of β-As2Te3

Abstract We present calculations of the electronic structure of Bi2Te3-structure type ( R 3 m ) β-As2Te3 using the state-of-the-art full potential linearized augmented plane wave method implemented in the WIEN2K code. Bi2Te3–structure type arsenic telluride, which forms when monoclinic arsenic telluride is quenched from high temperatures or compressed, is found to be a direct gap semiconductor with e g =0.12 eV. We also calculated the electronic structure of Bi2Te3 using the same method for comparison. In contrast to earlier calculations, we optimized the lattice parameters within density functional theory. The lowest conduction band and highest valence band of β-As2Te3 are similar to those of Bi2Te3 over much of the Brillouin zone, but exhibit a modest difference at the Γ point. β-As2Te3 will likely have a large thermoelectric power in view of its similarity to Bi2Te3, including the presence of six-fold degenerate band edges.

FLAPW investigation of the stability and equation of state of rectangulated carbon

The rectangulated carbon structure can be formed by buckling the graphene layers of graphite and linking them together with four-membered cyclobutane-like rings. Baughman et al. proposed rectangulated carbon as a candidate for the structure of the transparent phase of carbon that forms upon room temperature compression of graphite. Here we present a full-potential linear augmented plane wave (FLAPW) investigation of the stability and equation of state of rectangulated carbon. The total energy and equation of state of graphite and diamond are also calculated for comparison with rectangulated carbon. The local spin-density approximation (LSDA) and the generalized gradient approximation (GGA) give similar results for diamond and rectangulated carbon, but different results for graphite. The pressure estimated for the transition from graphite to rectangulated carbon using the LSDA is slightly higher than is observed for single crystal graphite. The energy differences between diamond and rectangulated carbon are in accord with earlier calculations. The agreement at 25 GPa between the calculated diffraction pattern for rectangulated carbon and the observed diffraction pattern for transparent carbon is not as good as the agreement at 0.1 MPa.

Integrated optoelectronics in an optical fiber

Integration of semiconductor and metal structures into optical fibers to enable fusion of semiconductor optoelectronic function with glass optical fibers is discussed. A chemical vapor deposition (CVD)-like process, adapted for high pressure flow within microstructured optical fibers allows for flexible fabrication of such structures. Integration of semiconductor optoelectronic devices such as lasers, detectors, and modulators into fibers may now become possible.

Toward a First-Principles Determination of Transport Coefficients

The efficiency of a thermoelectric device depends on its geometrical design and on the transport coefficients of the material that constitutes the active thermoelements. The figure of merit of the material

High pressure CVD inside microstructured optical fibres

Z = \frac{{\sigma S^2 }} {\kappa }

Fabrication of extreme aspect ratio wires within photonic crystal fibers

(1) is an expression involving the electrical conductivity a, the thermopower or Seebeck coefficient Sand the thermal conductivity κ. This quantity that has units of inverse temperature is the key to determine if a particular material has potential for thermoelectric applications.