Chemical tuning of the electronic properties in a periodic surfactant-templated nanostructured semiconductor.

In this work, we report the synthesis and characterization of a series of hexagonal nanostructured platinum/tin/tellurium inorganic/surfactant composites. The composites are formed through solution-phase self-assembly of SnTe4(4-) Zintl clusters, which are cross-linked with platinum salts in the presence of a cetyltriethylammonium cationic structure directing agent. The cross-linking utilizes various combinations of Pt(II) and Pt(IV) salts. Low-angle X-ray diffraction indicates that all composites form hexagonal honeycomb (p6mm) structures. A combination of elemental analysis and XANES is used to describe the composition and oxidation states within the composites. We find that the extent of tin telluride self-oligomerization and the platinum:tin telluride ratio both vary, indicating that the composite compensates for different platinum oxidation states by tuning the inorganic composition. Near-IR/visible reflectance spectroscopy and UPS can be used to measure both band gaps and absolute band energies. The results show that while moving from all Pt(II) to all Pt(IV) increases the band gap from 0.6 to 0.8 eV, it increases the absolute valence and conduction band energies by almost a full electronvolt. AC impedance spectroscopy further reveals that the conductivities of the materials can be tuned from 0.009 to 0.003 Omega(-1).cm(-1). Additionally, a capacitance arising from the periodic nanoscale organic domains was observed. The conductivity and band gap were used to estimate carrier mobilities in these composites. Chemical tuning of the electronic properties within related nanostructured composites is a useful tool for designing applications that exploit the properties of nanostructured semiconductors.