R. B. Johnson

Superlattice Multinanolayered Thin Films of SiO2/SiO2 + Ge for Thermoelectric Device Applications

Thermoelectric generators convert heat to electricity. Effective thermoelectric materials and devices have a low thermal conductivity and a high electrical conductivity. The performance of thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and K is the thermal conductivity. We have prepared 100 alternating layers of SiO2/SiO2+ Ge superlattice thin films using ion beam–assisted deposition for the thermoelectric generator device application. The 5 MeV Si ion bombardments were performed using the Center for Irradiation Materials’ Pelletron ion beam accelerator to form quantum dots and/or quantum clusters in the multinanolayer superlattice thin films to decrease the cross-plane thermal conductivity and increase the cross-plane Seebeck coefficient and cross-plane electrical conductivity. The thermoelectric and transport properties have been characterized for SiO2/SiO2+ Ge superlattice thin films.

Thermoelectric properties of SiO2/SiO2+CoSb multi-nanolayered thin films modified by MeV Si ions

We have fabricated the thermoelectric generator devices from 100 alternating layers of SiO2/SiO2+CoSb superlattice thin films using the ion beam–assisted deposition. Rutherford backscattering spectrometry was used for quantitative elemental analysis of Si, Co, and Sb in the multilayer films. The thin films were then modified by 5-MeV Si ion bombardments using the Alabama A&M University Pelletron ion beam accelerator. Quantum dots and/or clusters were produced in the nanolayered superlattice films to decrease the cross-plane thermal conductivity, increase the cross-plane Seebeck coefficient, and the cross-plane electrical conductivity. We have characterized the thermoelectric generator devices before and after Si ion bombardments using the thermoelectric, optical, and surface characterization techniques. The optical absorption amplitude decreased when the first fluence of 1 × 1012 ions/cm2 was introduced from the value of 2.8 to about 1.9 at 200 nm. The figure of merit reached the maximum value of about 0.005 at the fluence of 1 × 1013 ions/cm2.

MeV Si Ions Bombardment Effects on the Thermoelectric Properties of Si/Si+Ge Multi-Layer Superlttice Nanolayered Films

Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ or decreasing K. MeV ion bombardment caused defects and disorder in the film and the grain boundaries of these nano-scale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We have prepared 100 alternating layers of Si/Si+Ge nanolayered superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ions bombardments have been performed using the AAMU Pelletron ion beam accelerator to make quantum clusters in the nanolayered superlattice films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. We have characterized the thermoelectric thin films before and after Si ion bombardments as we measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences