Luis F Fonseca | University of Puerto Rico Rio Piedras (original) (raw)

Papers by Luis F Fonseca

MRS Proceedings, 1998

The luminescent properties of porous silicon (PSi) films in the visible region were used to impro... more The luminescent properties of porous silicon (PSi) films in the visible region were used to improve the photoresponse of PSi/Si-wafer and PSi/Si p-n junctions UV detector prototypes in the region below 500nm. A luminescent PSi overlayer was formed on top of the Si wafers and p-n junctions by electrochemical anodization. These overlayers have emission spectra peaking close to 690nm. In the case of the PSi/Si wafer, the PSi film was produced with a high optical transparency above 600nm and highly absorbent below this value. With such characteristics, the incident UV radiation is partially absorbed and converted into visible radiation that can be highly transmitted through the PSi film and efficiently absorbed by the wafer or the junction. The UV measurements show enhancement of the photoresponse at 366nm as compared with control prototypes without PSi. Details about the enhancement process are discussed.

MRS Proceedings, 2000

We have studied the microstructure, the transport and the phototransport properties of the Si cry... more We have studied the microstructure, the transport and the phototransport properties of the Si crystallites network in Si-SiO2 composites. We have found that in our co-sputtered samples the average crystallite diameter, d, decreases from 40 to 5 nm as the content of the silicon, x, decreases from 80 to 40 volume%, and that the percolation of the network sets is at x ≈ 40 vol%. A simultaneous study of the photoluminescence (PL) shows the, quantum confinement, expected red shift of its peak with increasing d. On the other hand the very strong observed decrease of the PL intensity with x is interpreted here as due to a deconfinement effect that is dominated by the increase in the cluster size of connected Si crystallites. The results suggest that a closed random packing of the Si crystallites will be the preferred network for high intensity electroluminescence.

Bulletin of the American Physical Society, 2016

Submitted for the MAR16 Meeting of The American Physical Society Ferromagnetic properties of mang... more Submitted for the MAR16 Meeting of The American Physical Society Ferromagnetic properties of manganese doped iron silicide. ANGEL RUIZ-REYES, LUIS F. FONSECA, University of Puerto Rico, RENAT SABIRIANOV, University of Nebraska at Omaha-We report the synthesis of high quality Iron silicide (FeSi) nanowires via Chemical Vapor Deposition (CVD). The materials exhibits excellent magnetic response at room temperature, especially when doped with manganese showing values of 2.0 X 10-04 emu for the FexMnySi nanowires. SEM and TEM characterization indicates that the synthesized nanowires have a diameter of approximately 80nm. MFM measurements present a clear description of the magnetic domains when the nanowires are doped with manganese. Electron Diffraction and XRD measurements confirms that the nanowires are single crystal forming a simple cubic structure with space group P213. First-principle calculations were performed on (111) FeSi surface using the Vienna ab initio simulation package (VASP). The exchange correlations were treated under the Ceperley-Alder (CA) local density approximation (LDA). The Brillouin Zone was sampled with 8x8x1 k-point grid. A total magnetic moment of about 10 µB was obtained for three different surface configuration in which the Iron atom nearest to the surface present the higher magnetization. To study the effect of Mn doping, Fe atom was replaced for a Mn. Stronger magnetization is presented when the Mn atom is close to the surface. The exchange coupling constant have been evaluated calculating the energy difference between the ferromagnetic and anti-ferromagnetic configurations.

Nanoscale, 2019

The advanced PdCo NW sensors developed for the detection of hydrogen at a wide temperature range ... more The advanced PdCo NW sensors developed for the detection of hydrogen at a wide temperature range showed excellent low-temperature stability.

MRS Proceedings, 2002

ABSTRACTWe have synthesized highly photoluminescent monoliths by incorporating nanocrystalline Si... more ABSTRACTWe have synthesized highly photoluminescent monoliths by incorporating nanocrystalline Silicon (nc-Si) from Porous Silicon (PSi) into a Sol Gel Silica matrix. The optically transparent samples are the result of mixing an acid catalyzed solution of Sol-Gel and nc-Si that forms a solution of Si-nanoclusters (Si-n) that eventually after condensation for three days produces the final luminescent material. Photoluminescence (PL) basic studies show a very high orange emission band with a maximum peak that ranges between 600 nm and 750 nm. The PL emission intensity was increased up to ten times the luminescence of the native nano material PSi, the mechanical and thermal stability properties were also greatly improved. The PL corresponds to different concentrations or preparations of Sol-Gel with Si-n (Sol-Si) with a broad size distribution that produces orange and blue emissions, and for this reason we take as our future work to tailor samples with very high Si-n densities for semi...

Journal of Physics D: Applied Physics, 2008

Page 1. Growth and field emission properties of one-dimensional carbon composite structure consis... more Page 1. Growth and field emission properties of one-dimensional carbon composite structure consisting of vertically aligned carbon nanotubes and nanocones This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2009 J. Phys. ...

Electrochimica Acta, 2010

A dual stage technique employing hot filament chemical vapor deposition (HFCVD) and radio frequen... more A dual stage technique employing hot filament chemical vapor deposition (HFCVD) and radio frequency sputtering was used to synthesize SiN/BCNTs (bamboo like carbon nanotubes) on copper substrates. The films were characterized by scanning electron microscopy (SEM), ...

Applied Physics Letters, 2009

Page 1. Probing the structural, crystalline, and electrical properties of carbon nanotubes grown ... more Page 1. Probing the structural, crystalline, and electrical properties of carbon nanotubes grown on nickel filled carbon nanofibers Hongxin Zhang,1 Peter X. Feng,1,a) Peng Jin,2,3 Vladimir I. Makarov,2 Luis Fonseca,1 Gerardo ...

Scientific reports, Jan 10, 2018

Tin selenide (SnSe) has been the subject of great attention in the last years due to its highly e... more Tin selenide (SnSe) has been the subject of great attention in the last years due to its highly efficient thermoelectricity and its possibilities as a green material, free of Pb and Te. Here, we report for the first time a thermoelectricity and transport study of individual SnSe micro- and nano-wires with diameters in the range between 130 nm and 1.15 μm. X-ray diffraction and transmission electron microscopy analyses confirm an orthorhombic SnSe structure with Pnma (62) symmetry group and 1:1 Sn:Se atomic ratio. Electrical and thermal conductivity and the Seebeck coefficient were measured in each individual nanowire using a specialized suspended microdevice in the 150-370 K temperature range, yielding a thermal conductivity of 0.55 Wm K at room temperature and ZT ~ 0.156 at 370 K for the 130 nm diameter nanowire. The measured properties were correlated with electronic information obtained by model simulations and with phonon scattering analysis. The results confirm these structures...

Nanotechnology, Jan 7, 2018

Highly crystalline indium tin oxide (ITO) nanowires were grown via a vapor-liquid-solid method, w... more Highly crystalline indium tin oxide (ITO) nanowires were grown via a vapor-liquid-solid method, with thermal tolerance up to ∼1300 °C. We report the electric and thermoelectric properties of the ITO nanowires before and after heat treatments and draw conclusions about their applicability as thermoelectric building blocks in nanodevices that can operate in high temperature conditions. The Seebeck coefficient and the thermal and electrical conductivities were measured in each individual nanowire by means of specialized micro-bridge thermometry devices. Measured data was analyzed and explained in terms of changes in charge carrier density, impurities and vacancies due to the thermal treatments.

ACS Applied Materials & Interfaces, 2014

We report for the first time the fabrication of single-crystal metastable manganese sulfide nanow... more We report for the first time the fabrication of single-crystal metastable manganese sulfide nanowires (γ-MnS NWs) conformally coated with graphitic carbon via chemical vapor deposition technique using a single-step route. Advanced spectroscopy and electron microscopy techniques were applied to elucidate the composition and structure of these NWs at the nanoscale, including Raman, XRD, SEM, HRTEM, EELS, EDS, and SAED. No evidence of α-MnS and β-MnS allotropes was found. The γ-MnS/C NWs have hexagonal cross-section and high aspect ratio (∼1000) on a large scale. The mechanical properties of individual γ-MnS/C NWs were examined via in situ uniaxial compression tests in a TEM-AFM. The results show that γ-MnS/C NWs are brittle with a Young's modulus of 65 GPa. The growth mechanism proposed suggests that the bottom-up fabrication of γ-MnS/C NWs is governed by vapor-liquid-solid mechanism catalyzed by bimetallic Au-Ni nanoparticles. The electrochemical performance of γ-MnS/C NWs as an anode material in lithium-ion batteries indicates that they outperform the cycling stability of stable micro-sized α-MnS, with an initial capacity of 1036 mAh g(-1) and a reversible capacity exceeding 503 mAh g(-1) after 25 cycles. This research advances the integration of carbon materials and metal sulfide nanostructures, bringing forth new avenues for potential miniaturization strategies to fabricate 1D core/shell heterostructures with intriguing bifunctional properties that can be used as building blocks in nanodevices.

MRS Proceedings

We prepared porous silicon (PSi) structures by standard electrochemical processes using aqueous s... more We prepared porous silicon (PSi) structures by standard electrochemical processes using aqueous sodium fluoride (NaF) solutions. We report the dependence of the porous structure on the variation of pH and salt concentration of the etching solution, and the applied current density. The PSi structures were characterized by Scanning Electron Microscopy (SEM) and Secondary Ion Mass Spectroscopy (SIMS) to determine the pore size and distribution and the surface chemical composition. Results obtained from SEM show that the PSi grown has two different structures depending on the current density. Low current densities produce a uniform, high-density arrangement of pores while high current densities yield a sponge-like structural network. SIMS results indicate that the porous framework is covered with a silicon oxide layer.

Journal of Applied Physics

We report the synthesis of high Curie temperature (T C > 800 K) Mn-doped CoSi nanowires. CoSi and... more We report the synthesis of high Curie temperature (T C > 800 K) Mn-doped CoSi nanowires. CoSi and Co 1-x Mn x Si nanowires were synthesized by chemical vapor deposition. Transmission electron microscopy was used to identify a crystalline B20 cubical structure. Zero-field cooling and field cooling measurements confirm spin disorder behaviour at low temperatures. The magnetic properties of doped samples were explained by means of the Ruderman-Kittel-Kasuya-Yosida interaction where the localized Mn atoms interact with the conduction electrons in CoSi providing a net ferromagnetic moment and explaining spin disorder at low temperatures. An individual CoSi nanowire was experimentally analyzed by performing off-axis electron holography, providing information about its local magnetization. Density functional theory calculations were performed to understand the effects of Mn doping, Si-vacancies, and surface atoms in the magnetic properties at the surface of the nanowire. An estimation of the Curie temperature was made using the mean field approximation.

Nanotechnology, Jan 2, 2018

Semiconductors with magnetic response at room temperature are sought for spintronics in solid-sta... more Semiconductors with magnetic response at room temperature are sought for spintronics in solid-state devices. Among possible materials for this applications, the magnetic response of FeSi and doped FeSi have produced contradictory results at the nanoscale and more precise measurements and deeper studies are needed to clarify its potential capabilities. For that reason, in this work, single nanowire measurements of ferromagnetic semiconducting FeSi and Mn-doped Fesi nanostructures have been performed using magnetic force microscopy and electron holography. Results obtained confirm the presence of magnetic domains at room temperature with a magnetic moment per Fe atom of 0.69μ_B. Spin polarized density functional calculations confirm a net magnetic moment between 0.4μ_B-1.3μ_B in Fe surface atoms with an estimated Curie temperature of 417K by means of the molecular field approximation. The nanowires present a crystalline...

MRS Proceedings

Luminescent porous silicon films were created by electrochemical anodization of n-type substrate ... more Luminescent porous silicon films were created by electrochemical anodization of n-type substrate under light illumination. Semi-transparent conducting polypyrrole films were deposited by electrochemical polymerization at a low current density. The SEM micrographs showed that the polymer film impregnates into the wide vertical pores of 1–5 µm and grows sideways suggesting strong current distribution on the walls. The AFM images of polymer surface reveal nanometer size polymer aggregates on the porous layer. The impregnation of the polymer film due to sideways growth provides a useful mean to fabricate stable contact for light emitting diodes from porous silicon.

Optical Materials, Mar 1, 2010

Nd-and Er-doped silicon rich oxide (SRO) thin films were prepared by rf-sputtering. Different fil... more Nd-and Er-doped silicon rich oxide (SRO) thin films were prepared by rf-sputtering. Different films were obtained by changing target configurations. Al and Al 2 O 3 targets were used to obtain along with silicon rich silicon oxide (SRSO) films, Al-modified SRSO films and silicon rich aluminosilicate (SRAS) films. Differences in spectral shape and emission intensity, in excitation wavelength dependence and excitation photon flux dependence of rare earth ion emissions were observed. Some were related to the added Al. The dependence of the 980 nm peak intensity on the 1530 nm peak intensity of the Er ion emissions for some films was studied and some effect related to the Al co-doping was found. Incorporation of Al into rare earth (RE)-doped silicon rich oxide (SRO) films can then be modified to obtain specific RE ion emission characteristics in such thin films.

Physical Review B Condensed Matter, Jun 1, 1997

Chemical Physics Letters, 2016

AIP Conference Proceedings, 1999

Optical quality, free standing and highly photoluminescent PSi was prepared from both, p- and n-t... more Optical quality, free standing and highly photoluminescent PSi was prepared from both, p- and n-type Si wafers using electrochemical anodization of c-Si. The porosity and the final structural and optical properties of the samples were found to be altered drastically by changing the acid concentration, current density, anodization time as well as the characteristics of the Si-wafer. In optical measurement,

Ferroelectrics, 1984

... Following the procedures used by F. Karal and J. Keller'&amp... more ... Following the procedures used by F. Karal and J. Keller'' a plane wave solution is then assumed for the macroscopic field in the equation resulting from the FSA and the effective dielectric constant corrected for multiple scattering effect is then obtained. ...

MRS Proceedings, 1998

The luminescent properties of porous silicon (PSi) films in the visible region were used to impro... more The luminescent properties of porous silicon (PSi) films in the visible region were used to improve the photoresponse of PSi/Si-wafer and PSi/Si p-n junctions UV detector prototypes in the region below 500nm. A luminescent PSi overlayer was formed on top of the Si wafers and p-n junctions by electrochemical anodization. These overlayers have emission spectra peaking close to 690nm. In the case of the PSi/Si wafer, the PSi film was produced with a high optical transparency above 600nm and highly absorbent below this value. With such characteristics, the incident UV radiation is partially absorbed and converted into visible radiation that can be highly transmitted through the PSi film and efficiently absorbed by the wafer or the junction. The UV measurements show enhancement of the photoresponse at 366nm as compared with control prototypes without PSi. Details about the enhancement process are discussed.

MRS Proceedings, 2000

We have studied the microstructure, the transport and the phototransport properties of the Si cry... more We have studied the microstructure, the transport and the phototransport properties of the Si crystallites network in Si-SiO2 composites. We have found that in our co-sputtered samples the average crystallite diameter, d, decreases from 40 to 5 nm as the content of the silicon, x, decreases from 80 to 40 volume%, and that the percolation of the network sets is at x ≈ 40 vol%. A simultaneous study of the photoluminescence (PL) shows the, quantum confinement, expected red shift of its peak with increasing d. On the other hand the very strong observed decrease of the PL intensity with x is interpreted here as due to a deconfinement effect that is dominated by the increase in the cluster size of connected Si crystallites. The results suggest that a closed random packing of the Si crystallites will be the preferred network for high intensity electroluminescence.

Bulletin of the American Physical Society, 2016

Submitted for the MAR16 Meeting of The American Physical Society Ferromagnetic properties of mang... more Submitted for the MAR16 Meeting of The American Physical Society Ferromagnetic properties of manganese doped iron silicide. ANGEL RUIZ-REYES, LUIS F. FONSECA, University of Puerto Rico, RENAT SABIRIANOV, University of Nebraska at Omaha-We report the synthesis of high quality Iron silicide (FeSi) nanowires via Chemical Vapor Deposition (CVD). The materials exhibits excellent magnetic response at room temperature, especially when doped with manganese showing values of 2.0 X 10-04 emu for the FexMnySi nanowires. SEM and TEM characterization indicates that the synthesized nanowires have a diameter of approximately 80nm. MFM measurements present a clear description of the magnetic domains when the nanowires are doped with manganese. Electron Diffraction and XRD measurements confirms that the nanowires are single crystal forming a simple cubic structure with space group P213. First-principle calculations were performed on (111) FeSi surface using the Vienna ab initio simulation package (VASP). The exchange correlations were treated under the Ceperley-Alder (CA) local density approximation (LDA). The Brillouin Zone was sampled with 8x8x1 k-point grid. A total magnetic moment of about 10 µB was obtained for three different surface configuration in which the Iron atom nearest to the surface present the higher magnetization. To study the effect of Mn doping, Fe atom was replaced for a Mn. Stronger magnetization is presented when the Mn atom is close to the surface. The exchange coupling constant have been evaluated calculating the energy difference between the ferromagnetic and anti-ferromagnetic configurations.

Nanoscale, 2019

The advanced PdCo NW sensors developed for the detection of hydrogen at a wide temperature range ... more The advanced PdCo NW sensors developed for the detection of hydrogen at a wide temperature range showed excellent low-temperature stability.

MRS Proceedings, 2002

ABSTRACTWe have synthesized highly photoluminescent monoliths by incorporating nanocrystalline Si... more ABSTRACTWe have synthesized highly photoluminescent monoliths by incorporating nanocrystalline Silicon (nc-Si) from Porous Silicon (PSi) into a Sol Gel Silica matrix. The optically transparent samples are the result of mixing an acid catalyzed solution of Sol-Gel and nc-Si that forms a solution of Si-nanoclusters (Si-n) that eventually after condensation for three days produces the final luminescent material. Photoluminescence (PL) basic studies show a very high orange emission band with a maximum peak that ranges between 600 nm and 750 nm. The PL emission intensity was increased up to ten times the luminescence of the native nano material PSi, the mechanical and thermal stability properties were also greatly improved. The PL corresponds to different concentrations or preparations of Sol-Gel with Si-n (Sol-Si) with a broad size distribution that produces orange and blue emissions, and for this reason we take as our future work to tailor samples with very high Si-n densities for semi...

Journal of Physics D: Applied Physics, 2008

Page 1. Growth and field emission properties of one-dimensional carbon composite structure consis... more Page 1. Growth and field emission properties of one-dimensional carbon composite structure consisting of vertically aligned carbon nanotubes and nanocones This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2009 J. Phys. ...

Electrochimica Acta, 2010

A dual stage technique employing hot filament chemical vapor deposition (HFCVD) and radio frequen... more A dual stage technique employing hot filament chemical vapor deposition (HFCVD) and radio frequency sputtering was used to synthesize SiN/BCNTs (bamboo like carbon nanotubes) on copper substrates. The films were characterized by scanning electron microscopy (SEM), ...

Applied Physics Letters, 2009

Page 1. Probing the structural, crystalline, and electrical properties of carbon nanotubes grown ... more Page 1. Probing the structural, crystalline, and electrical properties of carbon nanotubes grown on nickel filled carbon nanofibers Hongxin Zhang,1 Peter X. Feng,1,a) Peng Jin,2,3 Vladimir I. Makarov,2 Luis Fonseca,1 Gerardo ...

Scientific reports, Jan 10, 2018

Tin selenide (SnSe) has been the subject of great attention in the last years due to its highly e... more Tin selenide (SnSe) has been the subject of great attention in the last years due to its highly efficient thermoelectricity and its possibilities as a green material, free of Pb and Te. Here, we report for the first time a thermoelectricity and transport study of individual SnSe micro- and nano-wires with diameters in the range between 130 nm and 1.15 μm. X-ray diffraction and transmission electron microscopy analyses confirm an orthorhombic SnSe structure with Pnma (62) symmetry group and 1:1 Sn:Se atomic ratio. Electrical and thermal conductivity and the Seebeck coefficient were measured in each individual nanowire using a specialized suspended microdevice in the 150-370 K temperature range, yielding a thermal conductivity of 0.55 Wm K at room temperature and ZT ~ 0.156 at 370 K for the 130 nm diameter nanowire. The measured properties were correlated with electronic information obtained by model simulations and with phonon scattering analysis. The results confirm these structures...

Nanotechnology, Jan 7, 2018

Highly crystalline indium tin oxide (ITO) nanowires were grown via a vapor-liquid-solid method, w... more Highly crystalline indium tin oxide (ITO) nanowires were grown via a vapor-liquid-solid method, with thermal tolerance up to ∼1300 °C. We report the electric and thermoelectric properties of the ITO nanowires before and after heat treatments and draw conclusions about their applicability as thermoelectric building blocks in nanodevices that can operate in high temperature conditions. The Seebeck coefficient and the thermal and electrical conductivities were measured in each individual nanowire by means of specialized micro-bridge thermometry devices. Measured data was analyzed and explained in terms of changes in charge carrier density, impurities and vacancies due to the thermal treatments.

ACS Applied Materials & Interfaces, 2014

We report for the first time the fabrication of single-crystal metastable manganese sulfide nanow... more We report for the first time the fabrication of single-crystal metastable manganese sulfide nanowires (γ-MnS NWs) conformally coated with graphitic carbon via chemical vapor deposition technique using a single-step route. Advanced spectroscopy and electron microscopy techniques were applied to elucidate the composition and structure of these NWs at the nanoscale, including Raman, XRD, SEM, HRTEM, EELS, EDS, and SAED. No evidence of α-MnS and β-MnS allotropes was found. The γ-MnS/C NWs have hexagonal cross-section and high aspect ratio (∼1000) on a large scale. The mechanical properties of individual γ-MnS/C NWs were examined via in situ uniaxial compression tests in a TEM-AFM. The results show that γ-MnS/C NWs are brittle with a Young's modulus of 65 GPa. The growth mechanism proposed suggests that the bottom-up fabrication of γ-MnS/C NWs is governed by vapor-liquid-solid mechanism catalyzed by bimetallic Au-Ni nanoparticles. The electrochemical performance of γ-MnS/C NWs as an anode material in lithium-ion batteries indicates that they outperform the cycling stability of stable micro-sized α-MnS, with an initial capacity of 1036 mAh g(-1) and a reversible capacity exceeding 503 mAh g(-1) after 25 cycles. This research advances the integration of carbon materials and metal sulfide nanostructures, bringing forth new avenues for potential miniaturization strategies to fabricate 1D core/shell heterostructures with intriguing bifunctional properties that can be used as building blocks in nanodevices.

MRS Proceedings

We prepared porous silicon (PSi) structures by standard electrochemical processes using aqueous s... more We prepared porous silicon (PSi) structures by standard electrochemical processes using aqueous sodium fluoride (NaF) solutions. We report the dependence of the porous structure on the variation of pH and salt concentration of the etching solution, and the applied current density. The PSi structures were characterized by Scanning Electron Microscopy (SEM) and Secondary Ion Mass Spectroscopy (SIMS) to determine the pore size and distribution and the surface chemical composition. Results obtained from SEM show that the PSi grown has two different structures depending on the current density. Low current densities produce a uniform, high-density arrangement of pores while high current densities yield a sponge-like structural network. SIMS results indicate that the porous framework is covered with a silicon oxide layer.

Journal of Applied Physics

We report the synthesis of high Curie temperature (T C > 800 K) Mn-doped CoSi nanowires. CoSi and... more We report the synthesis of high Curie temperature (T C > 800 K) Mn-doped CoSi nanowires. CoSi and Co 1-x Mn x Si nanowires were synthesized by chemical vapor deposition. Transmission electron microscopy was used to identify a crystalline B20 cubical structure. Zero-field cooling and field cooling measurements confirm spin disorder behaviour at low temperatures. The magnetic properties of doped samples were explained by means of the Ruderman-Kittel-Kasuya-Yosida interaction where the localized Mn atoms interact with the conduction electrons in CoSi providing a net ferromagnetic moment and explaining spin disorder at low temperatures. An individual CoSi nanowire was experimentally analyzed by performing off-axis electron holography, providing information about its local magnetization. Density functional theory calculations were performed to understand the effects of Mn doping, Si-vacancies, and surface atoms in the magnetic properties at the surface of the nanowire. An estimation of the Curie temperature was made using the mean field approximation.

Nanotechnology, Jan 2, 2018

Semiconductors with magnetic response at room temperature are sought for spintronics in solid-sta... more Semiconductors with magnetic response at room temperature are sought for spintronics in solid-state devices. Among possible materials for this applications, the magnetic response of FeSi and doped FeSi have produced contradictory results at the nanoscale and more precise measurements and deeper studies are needed to clarify its potential capabilities. For that reason, in this work, single nanowire measurements of ferromagnetic semiconducting FeSi and Mn-doped Fesi nanostructures have been performed using magnetic force microscopy and electron holography. Results obtained confirm the presence of magnetic domains at room temperature with a magnetic moment per Fe atom of 0.69μ_B. Spin polarized density functional calculations confirm a net magnetic moment between 0.4μ_B-1.3μ_B in Fe surface atoms with an estimated Curie temperature of 417K by means of the molecular field approximation. The nanowires present a crystalline...

MRS Proceedings

Luminescent porous silicon films were created by electrochemical anodization of n-type substrate ... more Luminescent porous silicon films were created by electrochemical anodization of n-type substrate under light illumination. Semi-transparent conducting polypyrrole films were deposited by electrochemical polymerization at a low current density. The SEM micrographs showed that the polymer film impregnates into the wide vertical pores of 1–5 µm and grows sideways suggesting strong current distribution on the walls. The AFM images of polymer surface reveal nanometer size polymer aggregates on the porous layer. The impregnation of the polymer film due to sideways growth provides a useful mean to fabricate stable contact for light emitting diodes from porous silicon.

Optical Materials, Mar 1, 2010

Nd-and Er-doped silicon rich oxide (SRO) thin films were prepared by rf-sputtering. Different fil... more Nd-and Er-doped silicon rich oxide (SRO) thin films were prepared by rf-sputtering. Different films were obtained by changing target configurations. Al and Al 2 O 3 targets were used to obtain along with silicon rich silicon oxide (SRSO) films, Al-modified SRSO films and silicon rich aluminosilicate (SRAS) films. Differences in spectral shape and emission intensity, in excitation wavelength dependence and excitation photon flux dependence of rare earth ion emissions were observed. Some were related to the added Al. The dependence of the 980 nm peak intensity on the 1530 nm peak intensity of the Er ion emissions for some films was studied and some effect related to the Al co-doping was found. Incorporation of Al into rare earth (RE)-doped silicon rich oxide (SRO) films can then be modified to obtain specific RE ion emission characteristics in such thin films.

Physical Review B Condensed Matter, Jun 1, 1997

Chemical Physics Letters, 2016

AIP Conference Proceedings, 1999

Optical quality, free standing and highly photoluminescent PSi was prepared from both, p- and n-t... more Optical quality, free standing and highly photoluminescent PSi was prepared from both, p- and n-type Si wafers using electrochemical anodization of c-Si. The porosity and the final structural and optical properties of the samples were found to be altered drastically by changing the acid concentration, current density, anodization time as well as the characteristics of the Si-wafer. In optical measurement,

Ferroelectrics, 1984

... Following the procedures used by F. Karal and J. Keller'&amp... more ... Following the procedures used by F. Karal and J. Keller'' a plane wave solution is then assumed for the macroscopic field in the equation resulting from the FSA and the effective dielectric constant corrected for multiple scattering effect is then obtained. ...