Chemical synthesis and modification of target phases of chalcogenide nanomaterials

Open Access
Author:
Sines, Ian Thomas
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 25, 2012
Committee Members:
  • Raymond Edward Schaak, Dissertation Advisor
  • Christine Dolan Keating, Committee Member
  • Sridhar Komarneni, Committee Member
  • Benjamin James Lear, Committee Member
Keywords:
  • Nanoparticles
  • Conversion chemistry
  • Chalcogenides
  • Non-equilibrium phases
  • Superconductors
  • Single crystals
Abstract:
Inorganic nanoparticles have been at the forefront of materials research in recent years due to their utility in modern technological processes. Chalcogenide nanomaterials are of particular interest because of their wide range of desirable properties for semiconductors, magnetic devices, and energy industries. Primary factors that dictate the properties of the material are the elemental composition, crystal structure, stoichiometry, crystallite size, and particle morphology. One of the most common approaches to synthesize these materials is through solution mediated routes. This approach offers unique advantages in controlling the morphology and particle size that other methods lack. This dissertation describes our recent work on exploiting solution chemical routes to control the crystal structure and composition of chalcogenide nanomaterials. We will start by discussing solution chemistry routes to synthesize non-equilibrium phases of chaclogenide nanomaterials. By using low-temperature bottom-up techniques it is possible to trap kinetically stable phases that cannot be accessed using traditional high-temperature techniques. We used solution chemistry to synthesize and characterize, for the first time, wurtzite-type MnSe. Wurtzite-type MnSe is the end-member of the highly investigated ZnxMn1-xSe solid solution, a classic magnetic semiconductor system. We will then discuss PbO-type FeS, another non-equilibrium phase that is isostructural with the superconducting phase of FeSe. We synthesized phase-pure PbO-type FeS using a low-temperature solvothermal route. We will then discuss the post-synthetic modification of chalcogenides nanomaterials. By exploiting the solubility of Se and S in tri-n-octylphosphine we can selectively extract the chalcogen from preformed chalcogenide nanomaterials. This gives chemists a technique for purification and phase-targeting of particular chalcogenide phases. This method can be modified to facilitate anion exchange. When Te is dissolved in tri-n-octylphosphine prior to chalcogen extraction, the Te replaces the S or Se in the material. We show how this can be utilized to synthesize porous SnTe nanosheets. Both the chalcogen extraction and anion exchange pathways give scientists new tools for the modification of chalcogenide nanomaterials. Before concluding we will briefly discuss a new low-temperature solution-mediated crystal growth technique. This method combines concepts of solution chemistry and metal flux synthesis to generate bulk-scale single crystals of transition-metal stannides. This method has generated micron-scale single crystals of CoSn3, Ni3Sn4, PtSn4, and PdSn4. The low-temperature regime that this synthesis is conducted in may possibly lead to the synthesis of bulk single crystals of non-equilibrium phases.