MeV Si Ions Bombardment Research Articles

Fabrication and Characterization of Thermoelectric Generators From SiO2/SiO2+Au Nano-layered Superlattices

AbstractThe 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.

Thickness and MeV Si ions bombardment effects on the thermoelectric properties of Ce3Sb10 thin films

The three single layer Ce3Sb10 thin films were grown on silicon dioxide and quartz (suprasil) substrates with thicknesses of 297, 269 and 70nm using ion beam assisted deposition (IBAD) technique. The high-energy cross plane Si ion bombardments with constant energy of 5MeV have been performed with varying fluence from 1×1012, 1×1013, 1×1014, 1×1015ions/cm2. The Si ions bombardment modified the thermoelectric properties of films as expected. The fluence and temperature dependence of cross plane thermoelectric parameters that are Seebeck coefficient, electrical and thermal conductivities were determined to evaluate the dimensionless figure of merit, ZT. Rutherford backscattering spectrometry (RBS) enabled us to determine the elemental composition of the deposited materials and layer thickness of each film.

Fabrication And Characterization of Thermoelectric Generators From SiGe Thin Films

AbstractThermoelectric 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.

MeV Si Ions Bombardment Effects on the Properties of Nano-Layers of SiO2/SiO2+Ag

ABSTRACTWe have grown 100 periodic SiO2/SiO2+Ag multi-nano-layered systems where the SiO2+Ag layers were 7.26 nm and SiO2 buffer layer were 4 nm, total thickness is 563 nm. Using interferometer as well as in-situ thickness monitoring, we measured the thickness of the layers; using Rutherford Backscattering Spectrometry (RBS) measured the concentration and distribution of Ag in SiO2. The electrical conductivity, thermal conductivity and the Seebeck coefficient of the layered structure were measured at room temperature before and after bombardment by 5 MeV Si ions. The energy of the Si ions were chosen such that the ions are stopped in the silicon substrate and only electronic energy due to ionization is deposited in the layered structure. The electrical conductivity measured using Van der Pauw method. Thermal conductivity of the thin films was measured using an in-house built 3ω thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity we calculated the figure of merit (ZT). We will report our findings of change in the figure of merit as a function of the bombardment fluence.

Improvement on thermoelectric properties of multilayered Si 1−xGe x/Si by ion beam bombardment

We made n-type nano-scale thin film thermoelectric (TE) devices that consist of multiple periodic layers of Si 1− x Ge x /Si. The period is about 10 nm. The structure was modified by 5 MeV Si ion bombardment that formed a nano-scale cluster structure. In addition to the effect of confinement of the phonon transmission, formation of nanoclusters by the ionization energy of incident MeV Si ions further increases the scattering of phonons, increasing the chance of inelastic interaction of phonons, resulting in more annihilation of phonons. This limits phonon mean free path. Phonons are absorbed and dissipated along the layers rather than in the direction perpendicular to the layer interfaces, therefore cross plane thermal conductivity is reduced. The increase of the density of electronic states due to the formation of nanocluster minibands increases the cross plane Seebeck coefficient and increases the cross plane electric conductivity of the film. Eventually, the thermoelectric figure of merit of the TE film increases.

MeV Si ions bombardment effects on thermoelectric properties of sequentially deposited SiO2/AuxSiO2(1−x) nano-layers

We prepared 50 periodic nano-layers of electro-cooling system consisting of SiO2/AuxSiO2(1−x) super lattice with Au layer deposited on both sides as metal contacts. The deposited multilayer films have a periodic structure consisting of alternating layers where each layer is 10nm thick. The purpose of this research is to tailor the figure of merit of layered structures used as thermoelectric generators. The super lattices were then bombarded by 5MeV Si ions at three different fluences to form nano-cluster structure. Rutherford backscattering spectrometry (RBS) was used to monitor the film thickness and stoichiometry before and after MeV bombardment. We measured the thermoelectric efficiency of the fabricated device before and after 5MeV bombardment measuring the cross plane thermal conductivity by third harmonic method, measuring cross plane Seebeck coefficient, and measuring electric conductivity using Van der Pauw method. 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.

Effects of MeV Si ions bombardments on thermoelectric properties of sequentially deposited BixTe3/Sb2Te3 nano-layers

We made 50 periodic nano-layers of BixTe3/Sb2Te3 superlattice films with Au layers deposited on both sides as metal contacts. Each alternating layer is 5nm thick. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT. The purpose of this study is to tailor the figure of merit of layered structures used as thermoelectric generators. The superlattices were bombarded by 5MeV Si ions at seven different fluences to form nano-cluster structures. Rutherford backscattering spectrometry (RBS) was used to determine the film thickness and stoichiometry. To get the figure of merit before and after MeV bombardments, we measured the cross plane thermal conductivity by 3rd harmonic method, cross plane Seebeck coefficient and electrical conductivity using Van der Pauw method. The electronic energy deposited due to ionization by the MeV Si beam in its track produces nano-scale structures. This disrupts and confines phonon transmission thereby reducing thermal conductivity and increasing electron density, which in turn increases the Seebeck coefficient and the electrical conductivity. These combine to then increase the figure of merit for these superlattice films.

Properties of Nano-layers of Nanoclusters of Ag in SiO2 Host produced by MeV Si ion bombardment

AbstractWe 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.

Effects of MeV Si ion bombardments on the Properties of Nano-layers of SiO2/SiO2+Zn4Sb3

AbstractWe 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.

Fluence Dependence of Thermoelectric Properties Induced By Ion Bombardment of Zn4Sb3 and CeFe2Co2Sb12 thin films

AbstractThermoelectric 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.

MeV Ion-Beam Bombardment Effects on The Thermoelectric Figures of Merit of Zn4Sb3 and ZrNiSn-Based half-heusler compounds

AbstractSemiconducting â-Zn4Sb3and 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-Zn4Sb3thin 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.

Effect of MeV Si Ion Bombardment on Thermoelectric Characteristics of Sequentially Deposited SiO2/AuxSiO2(1-x) Nanolayers

ABSTRACTWe 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.

MeV Si ion bombardments of thermoelectric BixTe3/Sb2Te3 multilayer thin films for reducing thermal conductivity

BixTe3/Sb2Te3 multilayer thin films were grown as thermoelectric (TE) materials using electron-beam evaporation. Solid antimony (III) telluride and bismuth (III) telluride were used for the growth of BixTe3 and Sb2Te3 layers. Rutherford backscattering spectroscopy (RBS) analysis shows that the grown antimony telluride film has the stoichiometry of Sb2Te3 and the bismuth telluride film is Bi1.1Te3. The grown multilayer films have a periodic structure consisting of alternating Bi1.1Te3 and Sb2Te3 layers. The Bi1.1Te3/Sb2Te3 multilayer thin films with five or seven layers were analyzed by RBS. The grown Bi1.1Te3 and Sb2Te3 monolayer thin films and Bi1.1Te3/Sb2Te3 multilayer thin films were bombarded by 5MeV Si ions. The thermal conductivity of the grown films was measured by a 3ω-method thermal conductivity measurement system. The multilayer structure and MeV Si ion bombardment made the films to have a lower thermal conductivity.

Secondary neutral and ionized particle measurements under MeV-energy ion bombardment

We have measured both secondary neutral and ionized particles from an InSb target under 3.0MeV Si ion bombardment. Measurements of both ions and neutrals have not been carried out so far in the MeV-energy range. The mass spectra and axial emission energy distributions of secondary particles were investigated. Secondary ions were measured with a linear- and a reflective-type time-of-flight technique, whereas secondary neutral particles were photo-ionized by a UV pulsed laser (ArF: 193nm) and measured with a reflective-type time-of-flight technique. Different results were obtained for neutral particles in comparison with ionized particles. The mean energy of neutral Sb atoms was much lower than that of neutral In atoms, whereas the mean energies of secondary In and Sb ions were nearly equal.