Cydale Smith

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.

Surface-enhanced Raman spectroscopy scattering from gold-coated ceramic nanopore substrates: effect of nanopore size

Abstract. The dependence of magnitude of the electric near-field on the separation between metal nanoparticles for surface-enhanced Raman spectroscopy (SERS) substrates was experimentally verified. Diameters of gold-coated nanopores in a ceramic alumina substrate were varied to study the charge buildup near interparticle junctions and its effect on the enhancement factor due to SERS. The substrates were characterized by sensing a Rhodamine dye and calculating the associated Raman enhancement factors. Decreasing Au interparticle distance increases the electric near-field and shifts the plasmon resonance peak accordingly.

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.

Characterization of gold nanodots arrangements in SiO2/SiO2+Au nanostructured metamaterials

Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. For this study, we have prepared a thermoelectric generator device of SiO2/SiO2+Au multi-nano-layered thin film systems using ion beam-assisted deposition followed by 5 MeV Si ion bombardment. The ion bombardment causes the Au atoms to nucleate into metallic nanoclusters. However, as the kinetic energy of the Si ions decreases with the depth of the sample, so does the electronic stopping power responsible for the Au nucleation. This produces variations in the size and spacing of the nanoclusters. Here, we are investigating the effects of the size and arrangement variations within the device on the electrical and thermal transports within the system. We characterized the thin film system, using I–V characterization, conductance measurement, quasi-static capacitance, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy.

Optical actuators based on photorefractive materials controlled by holographic gratings

All-optical actuators based on static or moving holographic gratings could have an advantage over current actuators because of their smaller size, less power and less RF interference. Instead of an ultrasonic wave produced by an electrically driven piezoelectric actuator as in ultrasonic motors, the wave resulted from mechanical deformation of the crystal caused by photo-generated electric charge distribution due to the converse piezoelectric effect. The charge distribution was periodical since it was produced by a holographic grating generated by two interfering coherent laser beams. Surface gratings associated with holographic volume gratings in photorefractive crystals of iron-doped lithium niobate have been studied using diffraction of a reflected probe beam and high-resolution phase-shifted interferometric profilometry. Both techniques show that the surface gratings do in fact exist in the form of periodical corrugations of the same period as that of the volume grating. The maximum amplitude of the surface grating measured by both techniques was close to 6.5 nm. We also demonstrated that the periodical electric forces on the surface were capable of assembling polystyrene microspheres along the fringes of the grating.

Nonlinear optical waveguides based on metal nanocluster composites produced by ion beam implantation

We present the results of analysis of microstructural and optical properties of composite nonlinear optical waveguides made by ion implantation of LiNbO3 with MeV ions of silver. Light guiding properties were studied by the prism coupling method, and nonlinear optical susceptibility was characterized using the Z-scan method. Special attention was paid to the influence of a host material and heat treatment on light guiding, optical absorption, and third order susceptibility.

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

Thermoelectric Generators of Sequentially Deposited Si/Si+Ge Nano-layered Superlattices

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 = S2sσ/ KTC, σ is the electrical conductivity T/KTC, where S is the Seebeck coefficient, T is the absolute temperature and KTC is the thermal conductivity. In this study we have prepared the thermoelectric generator device of Si/Si+Ge multi-layer superlattice films using the ion beam assisted deposition (IBAD). To determine the stoichiometry of the elements of Si and Ge in the grown multilayer films and the thickness of the grown multi-layer films Rutherford Backscattering Spectrometry (RBS) and RUMP simulation software package were used. The 5 MeV Si ion bombardments were performed to make quantum clusters in the multi-layer superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. Keywords: Ion bombardment, thermoelectric properties, multi-nanolayers, Figure of merit.

Mechanisms of formation of nonlinear optical light guide structures in metal cluster composites produced by ion beam implantation

Ion implantation has been shown to produce a high density of metal colloids in glasses and crystalline materials. The high-precipitate volume fraction and small size of metal nanoclusters formed leads to values for the third-order susceptibility much greater than those for metal doped solids. This has stimulated interest in use of ion implantation to make nonlinear optical materials. On the other side, LiNbO{sub 3} has proved to be a good material for optical waveguides produced by MeV ion implantation. Light confinement in these waveguides is produced by refractive index step difference between the implanted region and the bulk material. Implantation of LiNbO{sub 3} with MeV metal ions can therefore result into nonlinear optical waveguide structures with great potential in a variety of device applications. The authors describe linear and nonlinear optical properties of a waveguide structure in LiNbO{sub 3}-based composite material produced by silver ion implantation in connection with mechanisms of its formation.