We prepared samples by electron beam physical vapor deposition EB-PVD followed by ion bombardment. The samples were than characterized by photoluminescence (PL), x-ray photoelectron spectroscopy (XPS). PL was used to characterize the available energy states. XPS was used to determine the binding energies. The ML’s are comprised of 100 alternating layers of SiO2/SiO2+Cu.

High energy ion beams are used to modify co-deposited nanolayer films of alternated materials (e.g. insulator and metal, two different semiconductors, even more complex arrangements) to form nanodots through localized nucleation. The particular application being considered here is for high efficiency thermoelectric conversion systems. The performance of a thermoelectric converter is generally given by the figure of merit, ZT, which is a function of the Seebeck coefficient, electrical conductivity, and thermal conductivity. A high performance device would have a maximized electrical conductivity and a minimized thermal conductivity (maximum electron transport, minimal phonon transport). The current models of electron and phonon transportation through 1D, 2D, 3D quantum regimented structures assume an infinitely repetitive perfect structural “cell”, with complicated algorithms requiring intensive computing power. The main focus for this modeling effort is to reduce the three-dimensional problem to a single dimensional approximation without sacrificing the quality of the result. The nanostructure being investigated has Si and Ge quantum dots arranged with perfect periodicity in all three Cartesian directions, with the heat and electricity flow monitored in the z-direction (cross-plane as initially layered). Non-Equilibrium Green’s Functions Formalism (NEGF) is the mode for calculating the theoretical electrical properties assuming a one-dimensional quantum well arrangement in the z-direction (with finite boundaries in the x and y directions) with tight binding (nearest neighbor approximation). The results are to be compared with experimental measurements on such structures.

The performance of the thermoelectric devices and materials 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. We have prepared 100 alternating nanolayered films of SiO2/SiO2+CoSb3 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 at the three different fluences to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. We have characterized 100 alternating nanolayered films of SiO2/SiO2+CoSb3 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 three different fluences.

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. We have prepared 100 alternating multi-nano layer of SiO2/SiO2+Cu superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ions bombardments have been performed at the different fluences using the AAMU Pelletron ion beam accelerator 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. To characterize the thermoelectric thin films before and after Si ion bombardments we have measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences.

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

We have prepared 100 periodic nano-layers of SiO2/AgSiO2 with Au layer deposited on both sides as metal contacts. The deposited multi-layer films have a periodic structure consisting of alternating layers where each layer is 3.3 nm thick. The purpose of this research is to tailor the figure of merit of the thermoelectric materials generated from the nanolayers of nanocrystals of Ag with SiO2 as host and as buffer layer using a combination of co-deposition and MeV ions bombardment taking advantage of energy deposited in the MeV ion track to nucleate nanoclusters. The electrical and thermal properties of the nanolayered structures were studied before and after 5 MeV Si ions bombardment at various fluences to form nanocrystals. In addition to thermoelectric properties, some optical properties of the SiO2/SiO2+Ag multi-layer superlattice films have been studied.

The efficiency of the thermoelectric devices is limited by the properties of n- and p-type semiconductors. 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. In this study we prepared the thermoelectric generator device of SiO2/SiO2+Au multi-layer super-lattice films using the ion beam assisted deposition (IBAD). In order to determine the stoichiometry of the elements of SiO2 and Au in the grown multilayer films and the thickness of the grown multi-layer films Rutherford Backscattering Spectrometry (RBS) and RUMP simulation software package was used. The 5 MeV Si ion bombardments was performed to make quantum clusters in the multi-layer super-lattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardments we measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences.

Thermoelectric materials are being important due to their application in both thermoelectric power generation and microelectronic cooling. The thermoelectric power generations convert the heat change to electricity. The waste of heat could be useful if the thermoelectric power generation is applied. Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. A high thermal conductivity causes too much heat leakage through heat conduction. 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. In this study, we prepared thermoelectric generator devices of SiGe at the thickness of 112 nm using the ion beam assisted deposition (IBAD) system. Rutherford Backscattering Spectrometry (RBS) analysis was used for the elemental analysis. The 5 MeV Si ion bombardment was performed using the AAMU Pelletron ion beam accelerator to make quantum clusters in the film to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardment we measured the cross plane Seebeck coefficient, electrical conductivity by Van der Pauw method, and thermal conductivity by 3w method for different fluences.

We have deposited 50 nano-layers of 710 nm of SiO2/SiO2+ZrNiSn with a periodic structure consisting of alternating layers where each layer is about 14 nm thick. The purpose of this research is to generate nanolayers of nanostructures of ZrNiSn with SiO2 as host and as buffer layer using a combination of co-deposition and MeV ion bombardment taking advantage of the energy deposited in the MeV ions track to nucleate nanostructures. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/ĸ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and ĸ is the thermal conductivity. ZT can be increased by increasing S, increasing σ, or decreasing ĸ. The electrical and thermal properties of the layered structures were studied before and after bombardment by 5 MeV Si ions at seven different fluences ranging from 1014 to 1015 ions/cm2 in order to form nanostructures in layers of SiO2 containing few percent of ZrNiSn. Rutherford Backscattering Spectrometry (RBS) was used to monitor elemental analysis of the film.

Thermoelectric power generation is a promising technology for increasing the efficiency of electrical and optical electrical devices. We prepared samples by Electron Beam evaporating Zn4Sb3 and CeFe2Co2Sb12 thin films on silicon dioxide (silica) substrates. The materials were co-evaporated and then were prepared for gold over-coating. Following electron deposition we performed post ion bombardment at a constant energy of 5 MeV while varying fluence from 1×1012, 1×1013, 1×1014, 1×1015 ions/cm2, respectfully. The production of nano-clusters generated from the MeV Si ions bombardment modifies the electrical and phonon interactions in the materials. Also, we will report on the fluence dependence of the figure of merit, Seebeck Coefficient, thermal conductivity and electrical conductivity. In addition, Rutherford backscattering spectrometry (RBS) was used to analyze the elemental composition and the thickness of the deposited material.

We prepared 8 periodic nano-layers of SiO2/SiO2+Zn4Sb3. The deposited multi-layer films have a periodic structure consisting of alternating layers where each layer is between 1-10 nm thick. The purpose of this research is to generate nanolayers of nanostructures of Zn4Sb3 with SiO2 as host and as buffer layer using a combination of co-deposition and MeV ion bombardment taking advantage of the electronics energy deposited in the MeV ion track due to ionization in order to nucleate nanostructures. The electrical and thermal properties of the layered structures were studied before and after bombardment by 5 MeV Si ions at various fluences to form nanostructures in layers of SiO2 containing Zn4Sb3. Rutherford Backscattering Spectrometry (RBS) was used to monitor the stoichiometry before and after MeV bombardments.

We prepared 50 periodic nano-layers of SiO2/AgxSiO2(1-x). The deposited multi-layer films have a periodic structure consisting of alternating layers where each layer is between 1-10 nm thick. The purpose of this research is to generate nanolayers of nanocrystals of Ag with SiO2 as host and as buffer layer using a combination of co-deposition and MeV ion bombardment taking advantage of the electronics energy deposited in the MeV ion track due to ionization in order to nucleate nanoclusters. Our previous work showed that these nanoclusters have crystallinity similar to the bulk material. Nanocrystals of Ag in silica produce an optical absorption band at about 420 nm. Due to the interaction of nanocrystals between sequential nanolayers there is widening of the absorption band. The electrical and thermal properties of the layered structures were studied before and after 5 MeV Si ions bombardment at various fluences to form nanocrystals in layers of SiO2 containing few percent of Ag. Rutherford Backscattering Spectrometry (RBS) was used to monitor the stoichiometry before and after MeV bombardments.

This work is focused on nanoscale gold particle formation by low-energy ion irradiation in glow-discharge plasma and studying particle growth by increasing time of exposure.

SiO2+Au films on SiO2 substrates produced by ion beam assisted deposition (IBAD) were exposed to ion irradiation at 1.2 keV energy for 1-2 hours. Plasmon resonance appearance caused by nanoparticle formation was observed by Optical Absorption Spectrometry (OAS).

In order to keep the stoichemistry of Bi2Te3 and Sb2Te3 so as to keep the electrical and thermal conductivity advantage of the layered structure of bulk Bi2Te3 and Sb2Te3 in each period of the superlattice, magnetron sputtering, which is operated at relatively low temperature, was used to deposit multiplayer Bi2Te3/Sb2Te3 thermoelectric superlattice device. The two guns in our magnetron sputtering device is oriented at a certain angle to get off-axis plasma plume, which will form lattice with preferential orientation for electrical conductivity in each layer. The super lattice was then bombarded by MeV Si ions with different fluence in order to form nanoscale cluster quantum dot-like structures. In addition to the effect of quantum well confinement of the phonon transmission, the nanoscale clusters produced by the bombardment of ion beam further adversely affect the thermal conductivity. The defect and disorder in the lattice caused by bombardment and the grain boundary of these nanoscale clusters increase the scattering of phonon and increase the chance of the inelastic interaction of phonon and the annihilation of phonon, this limits phonon mean free path. Phonons are chiefly absorbed and dissipated along the lattice, therefore reduces the cross plane thermal conductivity, The increases of the electron density of state in the miniband of nanoscale cluster quantum dot-like structure formed by bombardment also increases Seebeck coefficient, and the electrical conductivity. Eventually, the thermo-electric figure of merit of superlattice films increases.

In this work, Ultra High Molecular Weight Poly Ethylene (UHMWPE) samples were implanted with W + C ion by using Metal-Vapour Vacuum Arc (MEVVA) ion implantation technique. Samples were implanted with W and C atoms with a fluence of 1017ion/cm2 and extraction voltage of 30 kV. Mechanism underlies this modification characterized with ATR-FTIR, UV-VIS-NIR Spectrum and Rutherford Backscattering Spectrometry (RBS). Surface morphology of implanted and unimplanted samples were examined in nanoscale with AFM.

Semiconducting â-Zn4Sb3 and ZrNiSn-based half-heusler compound thin films were prepared by co-evaporation for the application of thermoelectric (TE) materials. High-purity solid zinc and antimony were evaporated by electron beam to grow the â-Zn4Sb3 thin film while high-purity zirconium powder and nickel tin powders were evaporated by electron beam to grow the ZrNiSn-based half-heusler compound thin film. Rutherford backscattering spectrometry (RBS) was used to analyze the composition of the thin films. The grown thin films were subjected to 5 MeV Si ions bombardments for generation of nanostructures in the films. We measured the thermal conductivity, Seebeck coefficient, and electrical conductivity of these two systems before and after 5 MeV Si ions beam bombardments. The two material systems have been identified as promising TE materials for the application of thermal-to-electrical energy conversion, but the efficiency still limits their applications. The electronic energy deposited due to ionization in the track of MeV ion beam can cause localized crystallization. The nanostructures produced by MeV ion beam can cause significant change in both the electrical and the thermal conductivity of thin films, thereby improving the efficiency. We used the 3ù-method measurement system to measure the cross-plane thermal conductivity ,the Van der Pauw measurement system to measure the cross-plane electrical conductivity, and the Seebeck-coefficient measurement system to measure the cross-plane Seebeck coefficient. The thermoelectric figures of merit of the two material systems were then derived by calculations using the measurement results. The MeV ion-beam bombardment was found to decrease the thermal conductivity of thin films and increase the efficiency of thermal-to-electrical energy conversion.

We made 50 and 100 periodic nano-layers of electro-cooling system consisting of SiO2/AuxSiO2(1−x) super lattice with Au layer deposited on both side as metal contact using Ion Beam Assisted Deposition (IBAD) system. The deposited multi-layer films have a periodic structure consisting of alternating layers where each layer is between 1-10 nm thick. The ultimate objective of this research is to tailor the figure of merit of layered structures used as thermoelectric generators. The super lattices were then bombarded by 5 MeV Si ion at different four fluences to form nano-cluster structure. The film thickness and stoichiometry were monitored by Rutherford Backscattering Spectrometry (RBS) before and after MeV bombardments. We measured the thermoelectric efficiency of the fabricated device before and after MeV bombardments. To accomplish this we measured the cross plane thermal conductivity by 3rd harmonic method, measured cross plane Seebeck coefficient, and measured electric conductivity using Van Der Pauw method before and after 5 MeV Si Bombardments. As predicted the electronic energy deposited due to ionization by MeV Si beam in its track produces nano-scale structures which disrupt and confine phonon transmission therefore reducing thermal conductivity, increasing electron density of state so as to increase Seebeck coefficient, and electric conductivity, thus increasing figure of merit. We will present our findings during the meeting.

* Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and by the AAMURI Center for Advanced Propulsion Materials under the contract number NAG8-1933 from NASA, and by National Science Foundation under Grant No. EPS-0447675.

We made p-type nanoscale super lattice thermoelectric cooling devices which consist of multiple periodic layers of Si1−x Gex / Si, The thickness of each layer ranges between 10 and 50 nm. The super lattice was bombarded by 5 MeV Si ion with different fluencies aiming to form nano-cluster quantum dot structures. We estimated the thermo-electric efficiency of the so fabricated devices, measuring the thin film cross plane thermal conductivity by the 3rd harmonic method, measuring the cross plane Seebeck coefficient, and finally measuring the cross plane electric conductivity before and after ion bombardment. As predicted, the thermo-electric Figure of Merit of the films increases with increasing Si ion fluencies. In addition to the effect of quantum well confinement of the phonon transmission, the nano-scale crystal quantum dots produced by the incident Si beam further adversely affects the thermal conductivity by absorbing and dissipating phonon along the lattice, and therefore further reduces the cross plane thermal conductivity, This process increases the electron density of state therefore increasing Seebeck coefficient, and the electric conductivity.

We studied the effects of the low energy ions to induce nucleation of nanoscale crystals on and near surface of silica nano-layer containing low concentrations of Au. Suprasil substrates were coated with thin layer of gold followed by low-energy ion irradiation in a glow discharge plasma. The formation of nanoscale crystals due to low energy ion irradiation were then studied using RBS and optical absorption spectrometry.

We prepared multilayers of semiconducting half-heusler β-Zn4Sb3 and skutterudites CeFe(4-x)CoxSb12 compound thin films by ion beam assisted deposition (IBAD) system for the application of thermoelectric (TE) materials. Rutherford backscattering spectrometry (RBS) was used to analyze the composition of thin films. The thin films were then bombarded by 5 MeV Si ions for generation of nanodots in the films. We measured the cross-plane thermal conductivity by a house developed 3ω-method system, cross-plane Seebeck coefficient by a (MMR) Seebeck system, and cross plane electrical conductivity of these nanolayered systems by a (MMR) Hall system before and after bombardment. Both β-Zn4Sb3 and CeFe(4-x)CoxSb12 systems have been identified as promising thermoelectric materials for the application of thermal-to-electrical energy conversion. The nanodots produced by MeV ion beam can cause significant change in both electrical and thermal conductivity of thin films, thus improving the efficiency. The MeV ion-beam bombardment resulted in decrease in the thermal conductivity of thin films and increase in the efficiency of thermal-to-electrical energy conversion.