Synthesize of metal-semiconductor segmented nanowire by electrodeposition

Abstract

Recently, thermoelectric (TE) is ignited by enhancement of nano-science and engineering that uncovers the possibility of increasing of figure of merit (ZT). As a candidate for thermoelectric materials, metal could not be considered because of their high thermal conductivity. However, according to other research, it is feasible to decrease thermal conductivity of also metal without much degradation of the electrical conductivity, which strongly implies that nanoscale metal can be utilized to improve thermoelectric properties of devices, especially power factor. Semiconductor-semiconductor superlattice nanowire structure has been studied as one of the best candidates for thermoelectric devices, because of their photon scattering characteristics at the interfaces. In this research, instead of semiconductor-semiconductor superlattice structure, metal-semiconductor superlattice structure was synthesized, and its microstructure and electrical properties are investigated. With this structure, improvement of electrical conductivity as well as degradation of thermal conductivity with phonon scattering would be anticipated. Metal-semiconductor superlattice nanowires were acquired with electrochemical displacement method, which can exchange the material which has low reduction potential with more noble materials in aqueous electrolyte. To achieve this, Ni-Ag superlattice structure was firstly prepared as metal-metal superlattice structure. The electrolyte for the electrodeposition of Ni-Ag segmented nanowries was consisted of 0.3 mol/L C6H5Na3O7, 0.7mol/L NiSO4 and AgNO3. Electrodeposition was performed galvanostatically in two electrode cell configuration with anodized aluminum oxide(AAO) template. Cu layer was deposited at the one side of AAO template as a working electrode, platinum coated titanium stripe as counter electrode. The composition of electrodeposits could be controlled by applied potential which is directly related the applied current density. Ni-rich phase could be obtained when the applied current density was over 10mA/cm2 and Ag-rich phase at 0.5mA/cm2. After acquiring Ni-Ag segmented nanowire structure, we synthesized the metal-semiconductor segemented nanowries (Ag-BiTe segmented nanowire) by using galvanic-displacement method. Because standard reduction potential energy of nickel is more negative (-0.25V) than that of BiTe in Bi ion and Te ion contained bath, it is possible to make displacement of Ni with BiTe using galvanic displacement. The morphology was investigated by SEM and composition profile was observed by EDS. In conclusion, nanoscale metal-semiconductor segmented nanowires were synthesized by electrodeposition and electrochemical displacement method. Their structural characteristics and electrical properties were investigated to understand the possibility of this segmented nanowires as a thermelectrical materials.