Influence of selenium vapor postannealing on the electrical transport properties of PbSe–WSe 2 nanolaminates

  • PDF / 128,934 Bytes
  • 6 Pages / 584.957 x 782.986 pts Page_size
  • 20 Downloads / 257 Views

DOWNLOAD

REPORT


ul Zschack Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, 60439

Matt Beekman and David C. Johnsona) Department of Chemistry, University of Oregon, Eugene, Oregon, 97403-1205 (Received 17 November 2010; accepted 11 March 2011)

The influence of annealing time and annealing temperature under controlled partial pressure of selenium on the in-plane electrical transport properties of specimens of [(PbSe)0.99]1[WSe2]1 turbostratic nanolaminates was studied. The annealing treatments were found to be very effective in reducing carrier concentrations and improving carrier mobility in the annealed films, which is attributed to the reduction of compositional and structural defects. As a result, room temperature Hall mobilities greater than 60 cm2 V 1s 1 are observed in spite of the small in-plane domain sizes (on the order of 10 nm) that are related to the turbostratic disorder. The technique appears promising for decreasing the concentration of kinetically trapped defects in these and related self-assembled nanostructures, a key challenge to evaluating the expected potential for controlling electrical and thermal transport properties via designed nanostructure in these and related materials.

I. INTRODUCTION

The promise of achieving specific functional properties through nanostructure motivates substantial synthetic efforts to prepare new and unconventional materials. Developing an understanding of the exceptional properties of such materials is of key importance. Toward these aims, we have recently developed1–3 a general synthetic approach to the preparation of new families of thin film intergrowth compounds, derived from layered linear intergrowths4 of rock salt-like monochalcogenide (e.g., PbSe, BiSe, etc.) and transition metal dichalcogenide components (e.g., WSe2, NbSe2, etc.), using the method of modulated elemental reactants (MER).5 These novel nanolaminate materials exhibit exceptionally low thermal conductivities, on the order of 0.1 Wm 1K 1 and 0.4–0.5 Wm 1K 1, perpendicular and parallel to the layering, respectively.6,7 These extremely low thermal conductivities can be attributed to the unusual nanostructure that can be described as “turbostratic” disorder,8 a key aspect which also makes them structurally distinct from the bulk misfit-layered compounds from which the nanostructure of these materials is derived.4 The controllable “nano-architecture” in material systems such as these new misfit-layered compounds presents a potential route to tunable physical properties,

a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.77 1866

J. Mater. Res., Vol. 26, No. 15, Aug 14, 2011

http://journals.cambridge.org

Downloaded: 13 Mar 2015

in particular with respect to electrical transport and thermoelectric properties. However, a key challenge that must be overcome is control of the distribution of compositional and structural defects inherently trapped by the low temperature, nonequilibrium nature of the synthetic route.2,9 Consequently, it is of interest