2015 Beckman Symposium   

Phuong Ta

Presentation Date:

Phuong Ta

Synthesis and Characterization of ([SnSe]1.16)m(NbSe2)3 Ferecrystalline Compounds

University of Oregon

Chemistry and Biochemistry

Nanotechnology and nanoscience have developed and grown extensively in the last decade due to the advancement of both synthesis and characterization techniques to make and understand nanomaterials. These compounds can have significantly different physical and chemical properties than their counterpart bulk materials with the same atomic composition. Nanomaterials are characterized by having individual building blocks in the subnanometer (1 nm = 1_10-9 m) scale. While individual nanostructures include materials such as nanotubes, clusters, and quantum dots, collections of nanostructures consist of larger assemblies and superlattices of individual nanostructures. There exists a large undiscovered composites based on these 2D materials, mapping new potentials to create innovative standards at the nanoscale. A number of 3D comprehensive inorganic compounds composed of 2D interwoven constituents with distinctive structures and properties are shaping the face of the new era of materials research. Misfit-layered compounds (MLCs) and ferecrystals (FCs) are examples of aforementioned composites. In the David Johnson lab, we take advantage of the technique called Modulated Elemental Reactant (MER) to optimize the synthesis of these ferecrystals. Previously, compounds that belong to the ([PbSe]1.14)m(NbSe2)1 families were synthesized and thoroughly studied by Alemayehu et al, who introduced the Parallel Resistor Model (PRM) to explain the resistivity of a single NbSe2 layer. The PRM treats the NbSe2 layer as the conducting constituent and the PbSe as the insulating constituent. Based on the assumption that there is no interlayer interaction between the subunits, the model predicts the resistivity of the single conducting layer, NbSe2. Recently, a series of compounds in the ([SnSe]1.16)m(NbSe2)1' and ([SnSe]1.16)m(NbSe2)2' families were prepared. The Parallel Resistor Model was then applied to ([SnSe]1.16)m(NbSe2)1' compounds, but similarly to the analogous ([PbSe]1.14)m(NbSe2)1 compounds, interlayer interaction between the insulating layer and the conducting layer was observed. Similar observations as with the single NbSe2 were made in the ([SnSe]1.16)m(NbSe2)2' compounds, where there are two NbSe2 layers interfacing with SnSe. The electrical properties of both ([SnSe]1.16)m(NbSe2)1 and ([SnSe]1.16)m(NbSe2)2' compounds deviate from the PRM, indicating the presence of interlayer interaction between the subunits. Therefore, if we increase the number of NbSe2 layer to three as in the ([SnSe]1.16)m(NbSe2)3 compounds where 1 < m < 6 families, these series of compounds will obey the PRM, since one layer of NbSe2 will be 'sandwiched' in between two other NbSe2 layers and will not have any interaction with the insulating constituent (SnSe).

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