Sergio Zannella - Academia.edu (original) (raw)

Papers by Sergio Zannella

Technical and economical assessments for future power applications of High superconductivity requ... more Technical and economical assessments for future power applications of High superconductivity require the evaluation and comparison of AC losses in first and second generation high tapes. An electrical and a thermometric method were developed and used to measure transport AC loss in OPIT Bi-2223/Ag tapes, Y-123 coated conductors and in new -based superconductors, simulating the AC conditions typical of power devices. The results were compared with analyt- ical models for AC losses calculation. The effect of the magnetic substrates used in coated conductors was also investigated and a simple calculation model was proposed.

International Journal of Modern Physics B, 2003

For power applications of HTS it is crucial to predict their AC losses in the typical operating c... more For power applications of HTS it is crucial to predict their AC losses in the typical operating conditions. We report measurements of energy losses in Bi-2223 multifilamentary tapes carrying AC currents and exposed to AC magnetic fields oriented perpendicular or parallel to their wide surface. Losses have been evaluated at liquid nitrogen temperature by transport and magnetisation measurements. The results have been compared to the experimental values obtained by calorimetric method the values estimated by a numerical model specifically developed of evaluation of AC losses in HTS tapes.

Superconductor Science and Technology, 2004

Abstract: Anomalous voltage peaks have been observed below the critical current in dc transport m... more Abstract: Anomalous voltage peaks have been observed below the critical current in dc transport measurements of superconducting YBCO coated conductors for specific contact arrangements. Using a simple concentrated constant-equivalent circuit, it is predicted that current redistributions due to non-homogeneities in the sample may explain the observed effect.

Superconductor Science and Technology, 2004

We report on the in situ preparation of Y Ba2Cu3O7-dgr films uniformly deposited over large areas... more We report on the in situ preparation of Y Ba2Cu3O7-dgr films uniformly deposited over large areas,>20 × 20 cm2, at 690 °C by thermal co-evaporation onto Ni-5 at.% W biaxially textured tapes buffered with e-beam evaporated CeO2. Typically, the thickness of the YBCO and CeO2 layers was 0.9 and 0.1 µm, respectively. Deposition rates were 0.2 and 2.5 nm s-1,

Physica C: Superconductivity, 1998

AC losses were measured by 4-probe transport method and by external magnetization method in three... more AC losses were measured by 4-probe transport method and by external magnetization method in three samples of Bi-2223rAg tape: a multifilamentary tape with separated filaments, another multifilamentary tape with 'bridges' between filaments, and a two-shell tape. The transport losses agreed with those calculated using I from DC experiment. c Magnetization experiments gave indications about the various paths of induced currents. For the tape with well separated filaments the main part of screening current closes inside individual filaments. Additional screening of the whole filamentary zone involves the normal metal matrix, leading to frequency dependent losses. In the case of tape with 'bridged' filaments, Ž. supercurrents interconnect the filaments into bundles whose screening and loss is frequency-independent. Matching the experimental data indicates that a typical bundle was composed of 8 filaments. Magnetic losses of the two-shell tape were explained by a model for magnetization of superconducting wire with elliptical cross-section.

Physica C: Superconductivity and its Applications, 2007

A novel process for the coated conductors (CC) deposition, characterized by a single CeO 2 buffer... more A novel process for the coated conductors (CC) deposition, characterized by a single CeO 2 buffer layer architecture, and a new oxygenation device for the YBCO layer has been developed. In CC technology, usually the ceria layer thickness must be less than 100 nm to avoid the formation of cracks; in order to ensure an efficient barrier effect, complex and costly multi-buffer layers architectures must be grown. In this work, we describe the way to increase the thickness of crack-free single buffer layer. Single CeO 2 buffer layer is grown on biaxially textured Ni-5 at.%W substrates (RABiTS) by e-beam evaporation technique, introducing different doping elements at various percentages in pure Ceria targets. Since the crack formation in cerium oxide layers mainly depends on the stresses introduced by the lattice mismatch with Ni alloy substrate and on the arrangement of the oxygen vacancies in the lattice, it is possible to reduce these stresses by optimizing the doping in the Ceria layer, thus obtaining very thick and crack-free CeO 2 buffer layers. The texture quality of our samples is tested by XRD, giving a strong in-plane and out-of-plane orientation (FWHM values of about 5°). Optical and electron microscopy shows dense and crack-free thick layers (up to 450 nm) and confirms excellent insulating properties. A novel technique has been developed to enhance the oxygen pressure on the YBCO film during the deposition as the oxygen content is known to be critical for the growth of YBCO films with high T c. A supersonic oxygen nozzle (SNEO) incorporated into the vacuum chamber enables a •10 3 increasing of the local oxygen pressure close to the YBCO layer keeping a 10 À4 mbar background pressure. The work demonstrates that the single thick doped-Ceria buffer layer could be a viable way to reduce CC complexity and production costs and that SNEO apparatus can be used to make the oxygenation process of the YBCO films easier and more reliable.

Physica C: Superconductivity, 2005

We report on the in situ route for the continuous fabrication of YBCO coated conductors (CC) by t... more We report on the in situ route for the continuous fabrication of YBCO coated conductors (CC) by thermal co-evaporation. CC architecture consists of YBCO film grown on biaxially textured Ni-alloys tapes buffered with a single layer of CeO2. The buffer layer deposition has been optimized by either e-beam or thermal evaporation using respectively ceria or metallic cerium. Best results have been obtained on CeO2 film, with a thickness less or equal than 100nm, grown in a reducing atmosphere at 690°C with a growth rate of 2.4Å/s. The optimal samples exhibit a highly biaxial texture, as indicated by FWHM values in the range of 5–8° and 4–6° for respectively in- and out-of-plane orientations. The layers are characterized by an uniform and crack-free surface with an average roughness lower than 10nm. SIMS analysis confirms the effectiveness of CeO2 buffer layer against Ni interdiffusion. This template allows to obtain YBCO films strong textured, with good superconductive properties. YBCO texture data are equivalent the CeO2 ones. Midpoint critical temperature, Tc, falls reproducibly in 87–88K range, with transition widths ΔTc<2−3K. Critical current density, Jc, up to 2MA/cm2 at 77K in self-field, have been achieved in a meter long CC corresponding to Ic/width value of 130A/cm-width. Uniformity and reproducibility of long CC properties are under optimization.

Journal of Physics: Conference Series, 2008

The challenge for the commercialization of YBCO Coated Conductors (CC) is the development of a lo... more The challenge for the commercialization of YBCO Coated Conductors (CC) is the development of a low cost manufacturing process to allow for a cheap, fast and continuous deposition of superconducting coatings with high electrical performance. We are currently investigating 2 ways to reduce the CC production costs: i) reducing the complexity of the CC architecture, by growing a single buffer layer based on doped CeO 2 , and ii) utilizing a new reel-to-reel apparatus for long length CC processing, equipped with a cheap and reliable deposition system (PED, Pulsed Electron Deposition). In this work we report on the successful continuous deposition of very thick (up to 700 nm) doped-CeO 2 single buffer layers on biaxially textured Ni-5at%W substrates by PED. XRD patterns display complete orientation and very good texture quality of our samples (FWHM out-of-plane values of ≈ 6°), over 20 cm length. Optical and electron microscopy show a dense and crack-free film surface and dielectric strength measurement confirms excellent insulating properties. Preliminary results indicate that the simplified single buffer layer structure could be a reliable solution for the reduction of HTS CC production costs.

Journal of Physics: Conference Series, 2006

We recently reported on a simple thermal co-evaporation route based on a reel-toreel system, that... more We recently reported on a simple thermal co-evaporation route based on a reel-toreel system, that enables the production of 2 m-long superconducting tapes with I c values up to 120 A/cm-width (J c = 2 MA/cm 2) and T c = 88 K. This work describes the development of a new multi-chamber system designed for the continuous production of these tapes suitable for an industrial process. The system consists in three distinct vacuum chambers connected one with another by two specially designed 50 cm long slits. The length and cross-section of these slits have been calibrated in order to achieve a pressure difference up to 5 orders on magnitude across adjacent chamber. The system is originally conceived for the continuous production of CeO 2 buffered RABiTS Ni-based tapes that require a pre-treatment of the bare metallic tapes in forming gas, followed by CeO 2 deposition and a post-treatment in oxygen. To improve the robustness of the whole tape production process, we have designed and built a novel device based on a supersonic oxygen gas expansion for the continuous in situ oxygenation of YBCO during deposition. Here, we present preliminary results demonstrating the effectiveness of this device. Specifically, thanks to the enhancement of the number of collisions of the O 2 molecules with the substrate due to the focused supersonic beam, we find that the oxygen pressure in the vicinity of the substrate can be up to 3 orders of magnitude higher than the background pressure in the chamber. The main advantage of this supersonic device is the insensitivity of the effective pressure to the substrate-nozzle distance, in the 2-5 mm range, which can be easily controlled during a continuous production process.

IEEE Transactions on Appiled Superconductivity, 2005

Technical and economical assessments for future power applications of High Tc superconductivity r... more Technical and economical assessments for future power applications of High Tc superconductivity require the evaluation and comparison of AC losses in first and second generation high Tc tapes. An electrical and a thermometric method were developed and used to measure transport AC loss in OPIT Bi-2223/Ag tapes, Y-123 coated conductors and in new MgB2-based superconductors, simulating the AC conditions typical

IEEE Transactions on Appiled Superconductivity, 2003

A market penetration of HTS-based applications requires the development of a low-cost continuous ... more A market penetration of HTS-based applications requires the development of a low-cost continuous production system for long HTS conductors. We report on deposition and characterization of YBa 2 Cu 3 O 7 CeO 2 structures on metallic substrates prepared by a thermal co-evaporation technique. X-ray diffraction analysis reveals good biaxial orientation of both layers with in-and out-of-plane FWHM = 8 and 9 respectively on biaxially textured Ni-Fe or Ni-W and on polycrystalline Hastelloy C276 substrates. YBCO films are metallic and superconducting with onset 88 K. Work is in progress to scale up the process for long tapes.

IEEE Transactions on Applied Superconductivity, 2006

Modeling and design of superconducting power devices (e.g. fault current limiters), based on seco... more Modeling and design of superconducting power devices (e.g. fault current limiters), based on second generation HTS tapes, requires accurate evaluation and prediction of AC losses. Transport AC losses measurements have been performed on samples of YBCO coated conductors at 77 K, as a function of current. The results have been compared with the classical analytical model for self field AC losses calculation, taking into account the role of the magnetic substrate.

Cryogenics, 1994

Long Bi-2223/Ag tapes were successfully fabricated by means of hot extrusion and repeated cold-ro... more Long Bi-2223/Ag tapes were successfully fabricated by means of hot extrusion and repeated cold-rolling and sintering processes. On short pressed tapes, after the third thermomechanical cycle, critical current densities Je as high as 36 kA/cm 2 at 77 K and 64 kA/cm 2 at 65 K, 0 T were achieved. On 5 m long tapes Je values higher than 10 kA/cm 2 at 77 K, 0 T were obtained. The Ic uniformity of long tapes was found to be within 10% for all the investigated regions.

Advances in Science and Technology, 2006

We report on recent progress towards the continuous deposition of YBCO Coated Conductors (CC) by ... more We report on recent progress towards the continuous deposition of YBCO Coated Conductors (CC) by thermal co-evaporation. This is an attractive vacuum technique thanks to the simplicity, low cost and intrinsic uniformity over large areas. Recently, we published the in situ preparation route of 1 μm thick superconducting YBCO films deposited onto CeO2 buffered Ni biaxially textured tapes using a reel-to-reel system; end-to-end critical current densities Jc's at 77 K and self-field, measured by transport measurements are in the 1-2 MA/cm2 range for 1 m. long samples, with zero-resistance Tc= 87 K and transition widths DTc<3 K. In spite of the very good CC’s performances reported by a number of laboratories all over the world, several steps must be optimized in order to limit the CC production costs, in particular concerning the complexity of the CC architecture and the choice and optimization of the YBCO deposition technique. We specifically address the following critical points...

Applied Physics Letters, 1987

We have fabricated thin films of YBa2Cu3Ox by dc triode sputtering from two metallic targets. Pos... more We have fabricated thin films of YBa2Cu3Ox by dc triode sputtering from two metallic targets. Post-annealing in pure O2 after sputtering resulted in superconducting films with a Tc onset as high as 89 K and a midpoint Tc of 75 K. We report preliminary results of films deposited on sapphire, MgO and sol-gel coatings of ZrO2 on sapphire, with and without buffer layers of Ag. The chemical and physical structures of these films were analyzed by using several x-ray diffraction techniques and Rutherford backscattering spectroscopy.

Technical and economical assessments for future power applications of High superconductivity requ... more Technical and economical assessments for future power applications of High superconductivity require the evaluation and comparison of AC losses in first and second generation high tapes. An electrical and a thermometric method were developed and used to measure transport AC loss in OPIT Bi-2223/Ag tapes, Y-123 coated conductors and in new -based superconductors, simulating the AC conditions typical of power devices. The results were compared with analyt- ical models for AC losses calculation. The effect of the magnetic substrates used in coated conductors was also investigated and a simple calculation model was proposed.

International Journal of Modern Physics B, 2003

For power applications of HTS it is crucial to predict their AC losses in the typical operating c... more For power applications of HTS it is crucial to predict their AC losses in the typical operating conditions. We report measurements of energy losses in Bi-2223 multifilamentary tapes carrying AC currents and exposed to AC magnetic fields oriented perpendicular or parallel to their wide surface. Losses have been evaluated at liquid nitrogen temperature by transport and magnetisation measurements. The results have been compared to the experimental values obtained by calorimetric method the values estimated by a numerical model specifically developed of evaluation of AC losses in HTS tapes.

Superconductor Science and Technology, 2004

Abstract: Anomalous voltage peaks have been observed below the critical current in dc transport m... more Abstract: Anomalous voltage peaks have been observed below the critical current in dc transport measurements of superconducting YBCO coated conductors for specific contact arrangements. Using a simple concentrated constant-equivalent circuit, it is predicted that current redistributions due to non-homogeneities in the sample may explain the observed effect.

Superconductor Science and Technology, 2004

We report on the in situ preparation of Y Ba2Cu3O7-dgr films uniformly deposited over large areas... more We report on the in situ preparation of Y Ba2Cu3O7-dgr films uniformly deposited over large areas,&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;20 × 20 cm2, at 690 °C by thermal co-evaporation onto Ni-5 at.% W biaxially textured tapes buffered with e-beam evaporated CeO2. Typically, the thickness of the YBCO and CeO2 layers was 0.9 and 0.1 µm, respectively. Deposition rates were 0.2 and 2.5 nm s-1,

Physica C: Superconductivity, 1998

AC losses were measured by 4-probe transport method and by external magnetization method in three... more AC losses were measured by 4-probe transport method and by external magnetization method in three samples of Bi-2223rAg tape: a multifilamentary tape with separated filaments, another multifilamentary tape with 'bridges' between filaments, and a two-shell tape. The transport losses agreed with those calculated using I from DC experiment. c Magnetization experiments gave indications about the various paths of induced currents. For the tape with well separated filaments the main part of screening current closes inside individual filaments. Additional screening of the whole filamentary zone involves the normal metal matrix, leading to frequency dependent losses. In the case of tape with 'bridged' filaments, Ž. supercurrents interconnect the filaments into bundles whose screening and loss is frequency-independent. Matching the experimental data indicates that a typical bundle was composed of 8 filaments. Magnetic losses of the two-shell tape were explained by a model for magnetization of superconducting wire with elliptical cross-section.

Physica C: Superconductivity and its Applications, 2007

A novel process for the coated conductors (CC) deposition, characterized by a single CeO 2 buffer... more A novel process for the coated conductors (CC) deposition, characterized by a single CeO 2 buffer layer architecture, and a new oxygenation device for the YBCO layer has been developed. In CC technology, usually the ceria layer thickness must be less than 100 nm to avoid the formation of cracks; in order to ensure an efficient barrier effect, complex and costly multi-buffer layers architectures must be grown. In this work, we describe the way to increase the thickness of crack-free single buffer layer. Single CeO 2 buffer layer is grown on biaxially textured Ni-5 at.%W substrates (RABiTS) by e-beam evaporation technique, introducing different doping elements at various percentages in pure Ceria targets. Since the crack formation in cerium oxide layers mainly depends on the stresses introduced by the lattice mismatch with Ni alloy substrate and on the arrangement of the oxygen vacancies in the lattice, it is possible to reduce these stresses by optimizing the doping in the Ceria layer, thus obtaining very thick and crack-free CeO 2 buffer layers. The texture quality of our samples is tested by XRD, giving a strong in-plane and out-of-plane orientation (FWHM values of about 5°). Optical and electron microscopy shows dense and crack-free thick layers (up to 450 nm) and confirms excellent insulating properties. A novel technique has been developed to enhance the oxygen pressure on the YBCO film during the deposition as the oxygen content is known to be critical for the growth of YBCO films with high T c. A supersonic oxygen nozzle (SNEO) incorporated into the vacuum chamber enables a •10 3 increasing of the local oxygen pressure close to the YBCO layer keeping a 10 À4 mbar background pressure. The work demonstrates that the single thick doped-Ceria buffer layer could be a viable way to reduce CC complexity and production costs and that SNEO apparatus can be used to make the oxygenation process of the YBCO films easier and more reliable.

Physica C: Superconductivity, 2005

We report on the in situ route for the continuous fabrication of YBCO coated conductors (CC) by t... more We report on the in situ route for the continuous fabrication of YBCO coated conductors (CC) by thermal co-evaporation. CC architecture consists of YBCO film grown on biaxially textured Ni-alloys tapes buffered with a single layer of CeO2. The buffer layer deposition has been optimized by either e-beam or thermal evaporation using respectively ceria or metallic cerium. Best results have been obtained on CeO2 film, with a thickness less or equal than 100nm, grown in a reducing atmosphere at 690°C with a growth rate of 2.4Å/s. The optimal samples exhibit a highly biaxial texture, as indicated by FWHM values in the range of 5–8° and 4–6° for respectively in- and out-of-plane orientations. The layers are characterized by an uniform and crack-free surface with an average roughness lower than 10nm. SIMS analysis confirms the effectiveness of CeO2 buffer layer against Ni interdiffusion. This template allows to obtain YBCO films strong textured, with good superconductive properties. YBCO texture data are equivalent the CeO2 ones. Midpoint critical temperature, Tc, falls reproducibly in 87–88K range, with transition widths ΔTc<2−3K. Critical current density, Jc, up to 2MA/cm2 at 77K in self-field, have been achieved in a meter long CC corresponding to Ic/width value of 130A/cm-width. Uniformity and reproducibility of long CC properties are under optimization.

Journal of Physics: Conference Series, 2008

The challenge for the commercialization of YBCO Coated Conductors (CC) is the development of a lo... more The challenge for the commercialization of YBCO Coated Conductors (CC) is the development of a low cost manufacturing process to allow for a cheap, fast and continuous deposition of superconducting coatings with high electrical performance. We are currently investigating 2 ways to reduce the CC production costs: i) reducing the complexity of the CC architecture, by growing a single buffer layer based on doped CeO 2 , and ii) utilizing a new reel-to-reel apparatus for long length CC processing, equipped with a cheap and reliable deposition system (PED, Pulsed Electron Deposition). In this work we report on the successful continuous deposition of very thick (up to 700 nm) doped-CeO 2 single buffer layers on biaxially textured Ni-5at%W substrates by PED. XRD patterns display complete orientation and very good texture quality of our samples (FWHM out-of-plane values of ≈ 6°), over 20 cm length. Optical and electron microscopy show a dense and crack-free film surface and dielectric strength measurement confirms excellent insulating properties. Preliminary results indicate that the simplified single buffer layer structure could be a reliable solution for the reduction of HTS CC production costs.

Journal of Physics: Conference Series, 2006

We recently reported on a simple thermal co-evaporation route based on a reel-toreel system, that... more We recently reported on a simple thermal co-evaporation route based on a reel-toreel system, that enables the production of 2 m-long superconducting tapes with I c values up to 120 A/cm-width (J c = 2 MA/cm 2) and T c = 88 K. This work describes the development of a new multi-chamber system designed for the continuous production of these tapes suitable for an industrial process. The system consists in three distinct vacuum chambers connected one with another by two specially designed 50 cm long slits. The length and cross-section of these slits have been calibrated in order to achieve a pressure difference up to 5 orders on magnitude across adjacent chamber. The system is originally conceived for the continuous production of CeO 2 buffered RABiTS Ni-based tapes that require a pre-treatment of the bare metallic tapes in forming gas, followed by CeO 2 deposition and a post-treatment in oxygen. To improve the robustness of the whole tape production process, we have designed and built a novel device based on a supersonic oxygen gas expansion for the continuous in situ oxygenation of YBCO during deposition. Here, we present preliminary results demonstrating the effectiveness of this device. Specifically, thanks to the enhancement of the number of collisions of the O 2 molecules with the substrate due to the focused supersonic beam, we find that the oxygen pressure in the vicinity of the substrate can be up to 3 orders of magnitude higher than the background pressure in the chamber. The main advantage of this supersonic device is the insensitivity of the effective pressure to the substrate-nozzle distance, in the 2-5 mm range, which can be easily controlled during a continuous production process.

IEEE Transactions on Appiled Superconductivity, 2005

Technical and economical assessments for future power applications of High Tc superconductivity r... more Technical and economical assessments for future power applications of High Tc superconductivity require the evaluation and comparison of AC losses in first and second generation high Tc tapes. An electrical and a thermometric method were developed and used to measure transport AC loss in OPIT Bi-2223/Ag tapes, Y-123 coated conductors and in new MgB2-based superconductors, simulating the AC conditions typical

IEEE Transactions on Appiled Superconductivity, 2003

A market penetration of HTS-based applications requires the development of a low-cost continuous ... more A market penetration of HTS-based applications requires the development of a low-cost continuous production system for long HTS conductors. We report on deposition and characterization of YBa 2 Cu 3 O 7 CeO 2 structures on metallic substrates prepared by a thermal co-evaporation technique. X-ray diffraction analysis reveals good biaxial orientation of both layers with in-and out-of-plane FWHM = 8 and 9 respectively on biaxially textured Ni-Fe or Ni-W and on polycrystalline Hastelloy C276 substrates. YBCO films are metallic and superconducting with onset 88 K. Work is in progress to scale up the process for long tapes.

IEEE Transactions on Applied Superconductivity, 2006

Modeling and design of superconducting power devices (e.g. fault current limiters), based on seco... more Modeling and design of superconducting power devices (e.g. fault current limiters), based on second generation HTS tapes, requires accurate evaluation and prediction of AC losses. Transport AC losses measurements have been performed on samples of YBCO coated conductors at 77 K, as a function of current. The results have been compared with the classical analytical model for self field AC losses calculation, taking into account the role of the magnetic substrate.

Cryogenics, 1994

Long Bi-2223/Ag tapes were successfully fabricated by means of hot extrusion and repeated cold-ro... more Long Bi-2223/Ag tapes were successfully fabricated by means of hot extrusion and repeated cold-rolling and sintering processes. On short pressed tapes, after the third thermomechanical cycle, critical current densities Je as high as 36 kA/cm 2 at 77 K and 64 kA/cm 2 at 65 K, 0 T were achieved. On 5 m long tapes Je values higher than 10 kA/cm 2 at 77 K, 0 T were obtained. The Ic uniformity of long tapes was found to be within 10% for all the investigated regions.

Advances in Science and Technology, 2006

We report on recent progress towards the continuous deposition of YBCO Coated Conductors (CC) by ... more We report on recent progress towards the continuous deposition of YBCO Coated Conductors (CC) by thermal co-evaporation. This is an attractive vacuum technique thanks to the simplicity, low cost and intrinsic uniformity over large areas. Recently, we published the in situ preparation route of 1 μm thick superconducting YBCO films deposited onto CeO2 buffered Ni biaxially textured tapes using a reel-to-reel system; end-to-end critical current densities Jc's at 77 K and self-field, measured by transport measurements are in the 1-2 MA/cm2 range for 1 m. long samples, with zero-resistance Tc= 87 K and transition widths DTc<3 K. In spite of the very good CC’s performances reported by a number of laboratories all over the world, several steps must be optimized in order to limit the CC production costs, in particular concerning the complexity of the CC architecture and the choice and optimization of the YBCO deposition technique. We specifically address the following critical points...

Applied Physics Letters, 1987

We have fabricated thin films of YBa2Cu3Ox by dc triode sputtering from two metallic targets. Pos... more We have fabricated thin films of YBa2Cu3Ox by dc triode sputtering from two metallic targets. Post-annealing in pure O2 after sputtering resulted in superconducting films with a Tc onset as high as 89 K and a midpoint Tc of 75 K. We report preliminary results of films deposited on sapphire, MgO and sol-gel coatings of ZrO2 on sapphire, with and without buffer layers of Ag. The chemical and physical structures of these films were analyzed by using several x-ray diffraction techniques and Rutherford backscattering spectroscopy.