G. Schmerber - Profile on Academia.edu (original) (raw)
Papers by G. Schmerber
Physica B: Condensed Matter
Low temperature specific heat, AC magnetic susceptibility and magnetization measurements were per... more Low temperature specific heat, AC magnetic susceptibility and magnetization measurements were performed on the Ce7X 3 compounds (X = Ni, Ru, Rh, Pd, Ir and Pt). They exhibit coexistence of magnetic order (MO), heavy fermion (HF) and intermediate valence (IV) behaviour and the results are interpreted in terms of the three Ce sublattices (1Ce~, 3Ce H and 3Cenl) present in the ThTFe3-type structure. From entropic considerations it is found that sublattice Ce m presents an IV behaviour in all these compounds and Celt show MO or have a HF behaviour depending on the Ce-ligand electronic structure. The Ce~ atoms (more than 6 ,~ distant from each other) exhibit MO only when the Ce H sublattice provides a high density of electronic states.
Physical Review B
We performed the resonant inverse photoemission ͑RIPE͒ study on CePd 3 at the prethreshold region... more We performed the resonant inverse photoemission ͑RIPE͒ study on CePd 3 at the prethreshold region of the Ce-N 4,5 absorption edge. The surface effects on RIPE spectra are discussed through the investigation of the resonance behaviors. Comparison between the RIPE spectra and the calculated resonant-excitation probability of the intermediate states indicates the existence of specific excitation energy range, where a strong resonant enhancement occurs for the bulk or the surface 4 f spectrum.
Structural, optical and electrical properties of Ag doped PbS thin films: role of Ag concentration
Journal of Materials Science: Materials in Electronics
Inverse magnetoresistance in Fe/Si ion beam sputtered sandwiches
Journal of Applied Physics
ABSTRACT
Photoluminescence of Nd-doped SnO2 thin films
Ferromagnétisme à température ambiante et effet de l'irradiation dans des semi-conducteurs magnetiques de type ZnCoO
Absence of ferromagnetism in Al-doped Zn0.9Co0.10O diluted magnetic semiconductors
Structural, optical, and electrical properties of Yb-doped ZnO thin films prepared by spray pyrolysis method
Journal of Applied Physics, 2011
Yb-doped ZnO thin films were prepared on glass substrates by spray pyrolysis technique in order t... more Yb-doped ZnO thin films were prepared on glass substrates by spray pyrolysis technique in order to investigate the insertion of Yb ions in the ZnO matrix and the related optical properties of the films. The molar ratio of Yb in the spray solution was varied in the range of 0-5 at. %. X-ray diffraction patterns showed that the undoped and
Structural and photoluminescence properties of ZnO thin films prepared by sol-gel process
Journal of Applied Physics
The present study focuses on the structural and optical properties of ZnO thin films fabricated b... more The present study focuses on the structural and optical properties of ZnO thin films fabricated by sol-gel process and spin coated onto Si (100) and quartz substrates. The ZnO films have a hexagonal wurtzite structure with a grain size of about 50 nm. The x-ray photoelectron spectroscopy measurements reveal the presence of Zn 2+ and of zinc hydroxyl groups at the film. Optical properties were studied by photoluminescence (PL) and absorption spectroscopy at low and room temperatures. The absorption spectrum is dominated by a sharp excitonic peak at room and low temperatures. At room temperature, PL observations show two transitions: one near the absorption edge in the ultraviolet (UV) region and the second centered at 640 nm, characteristic of the deep electronic levels in the bandgap. The spectrum at 6 K is dominated by donor bound exciton lines and donor-acceptor pair transitions. LO-phonon replica and two-electron satellite transitions are also observed. These optical characterist...
International Journal of Modern Physics B, 2008
Sr 2 CoMoO 6 and Sr 2 CoMoO 6-δ ceramics have been obtained by solid state reaction in air and in... more Sr 2 CoMoO 6 and Sr 2 CoMoO 6-δ ceramics have been obtained by solid state reaction in air and in a H 2/ N 2 gas mixture. At room temperature, as shown by X-ray diffraction, both compounds have a tetragonal perovskite-like structure with doublet unit-cell parameters, space group I4/m, with a = 5.5575, c = 7.9342 in Sr 2 CoMoO 6 and a = 5.5683 and c = 7.9395 in Sr 2 CoMoO 0.95. The latter contains small traces of Co and SrCoO 2.61, with an almost expansion. The magnetic susceptibility indicates that Sr 2 CoMoO 6 is an antiferromagnet with TN = 37 K. The magnetization was found to be the same in both samples, while the electric properties, originating from the oxygen content, are drastically affected.
One step electrodeposited CZTS thin films: Preparation and characterization
2014 International Renewable and Sustainable Energy Conference (IRSEC), 2014
Solid State Communications, 1994
Magnetic (X), thermal (Ce), and transport (p) measurements on Ce~4Xst (X = An, Ag and Cu) are pre... more Magnetic (X), thermal (Ce), and transport (p) measurements on Ce~4Xst (X = An, Ag and Cu) are presented. All these compounds show antiferromagnetic type order at low temperatures, with TN = 0.9 K (Au), 1.1 K (Ag)and 3.2 K (Cu). Within the Gd14Agsx-type structure the Ce atoms sit in different sublattices denoted by I (2 atoms), II (6 atoms) and III (6 atoms), therefore the results can be interpreted in terms of three different behaviors of Ce depending on its local environment. From the entropy involved in the magnetically ordered (MO) phase it can be established that the Cett and Cem atoms order in Cel4Ausl and Ce14Agsl, while the Cet order in Cel4Cus1. There is a large linear contribution to Cp at T > TN, 7HT = 0.81 (Au), 1.24 (Ag) and 3.1 (Cu) J/mol K 2, which indicates the coexistence of MO and heavy fermions. In the case of Cex4Cus1, the magnetic contribution to Ct, from sublattice Cel around TN, resembles that of a modulated system and the characteristic temperatures for Cell and Cetll atoms are estimated from p(T) as: TK=16 K and >120 K respectively.
Journal of Physics: Conference Series, 2014
Structural, magnetic (M) and thermal (Cm) studies on Ce2(Ni1−yPdy)2Sn alloys are presented within... more Structural, magnetic (M) and thermal (Cm) studies on Ce2(Ni1−yPdy)2Sn alloys are presented within the 0 ≤ y ≤ 0.55 range of concentration, showing evidences for itinerant to local electronic transformation. At variance with RKKY type interactions between localized moments µ ef f , the substitution of Ni by isoelectronic Pd leads the antiferromagnetic transition to decrease from TN 3.8 K to 1.2 K between y = 0 and 0.48, while M (H) measured at H = 5 T and 1.8 K rises from 0.12 up to 0.75µB/Ce-at. Furthermore, the Cm(TN) jump increases with concentration whereas |θP | decreases. The magnetic entropy Sm(T) grows moderately with temperature for y = 0 due to a significant contribution of excited levels at low energy, while at y = 0.5 it shows a incipient plateau around Sm = Rln2. All these features reflect the progressive ground state transformation of from itinerant to a local character. Another peculiarity of this system is the nearly constant value of Cm(TN) that ends in an entropy bottleneck as TN decreases. Consequently, the system shows a critical point at ycr ≈ 0.48 with signs of ferromagnetic behavior above Hcr ≈ 0.3T. A splitting of the Cm(TN) maximum, tuned by field and concentration, indicates a competition between two magnetic phases, with respective peaks at TN ≈ 1.2 K and TI ≈ 1.45 K.
In this work, we use rf magnetron sputtering to deposit at room temperature a ZnO thin film on to... more In this work, we use rf magnetron sputtering to deposit at room temperature a ZnO thin film on top of a photoactive material based on P3HT:PCBM blend for organic photovoltaic devices. We investigate the influence of the sputtering conditions on the ZnO crystallinity, on the substrate layer nanoscale morphology and on the photovoltaic device performances. We show that, under appropriate sputtering conditions, the modification of the P3HT:PCBM film causes no functional damage of the photoactive layer, and leads to an improved performance of the photovoltaic devices.
Impact of sputtered ZnO interfacial layer on the S-curve in conjugated polymer/fullerene based-inverted organic solar cells
Thin Solid Films, 2015
ABSTRACT The impact of crystalline structure changes of sputtered ZnO interfacial layer on perfor... more ABSTRACT The impact of crystalline structure changes of sputtered ZnO interfacial layer on performances of inverted organic solar cells (OSCs) has been investigated. We find that the structural modification of the ZnO cathode interfacial layer, obtained by thermal annealing, plays a crucial role in the origin and solving of the S-curve in conjugated polymer/fullerene photovoltaics. Our results show that the crystallization (i.e. crystallites size) of poly(3- hexylthiophene) (P3HT) evolves as a function of that of ZnO according to the annealing temperature. This evolution can directly impact the interfacial orientation and organization of the chains of P3HT at the ZnO buried interface. Such an ordered profile favors the vertical phase segregation and raises the carrier mobility, which explains the disappearance of the S-shape observed in current density-voltage device characteristics for annealing temperatures above 200 °C. These results adequately address recent research and provide an important insight into the interfacial layers of inverted OSCs.
Observation of the surface 4f state of CePd 7 sby means of the resonant-inverse-photoemission study at the Ce 4d absorption edge
Physical Review B, 1997
The resonant inverse photoemission study (RIPES) of CePd7 , has been carried out at the Ce 4d--&g... more The resonant inverse photoemission study (RIPES) of CePd7 , has been carried out at the Ce 4d-->4f absorption edge. The strong resonant enhancement of the 4f cross section enables us to distinguish two 4f components in the empty electronic state near the Fermi level. The incidence-angle dependence of the RIPES indicates a clear difference between ground-state configurations at the bulk and surface. It is found that the former shows a strongly hybridized 4f state, while the latter shows a localized 4f character. The angle dependence of the RIPES of alpha-Ce metal has been also carried out and similar results as those of CePd7 were obtained. The RIPES at the Ce 4d-->4f edge is found to be a powerful method to investigate the surface 4f state.
Comparative study of thermal and magnetic properties of CeTyX4-y ferromagnets
Physical Review B, 1997
ABSTRACT
Effects of high-temperature annealing on magnetic properties of V-doped GaN thin films grown by MOCVD
ABSTRACT Metal organic chemical vapor deposition (MOCVD) has been used to grow vanadium-doped GaN... more ABSTRACT Metal organic chemical vapor deposition (MOCVD) has been used to grow vanadium-doped GaN (GaN:V) on c-sapphire substrate using VCl4 as the V source. The as-grown GaN:V exhibited a saturated magnetic moment (Ms) of 0.28 emu/cm3 at room temperature. Upon high-temperature annealing treatment at 1100 °C for 7 min under N2 ambient, the Ms of the GaN:V increased by 39.28% to 0.39 emu/cm3. We found that rapid thermal annealing leads to a remarkable increase in surface roughness of the V-doped GaN as well as the electron concentration. The annealing also leads to a significant increase in the Curie temperature (TC), we have identified Curie temperatures about 350 K concluded from the difference between the field-cooled and zero-field-cooled magnetizations. Structure characterization by x-ray diffraction indicated that the ferromagnetic properties are not a result of secondary magnetic phases.
Co doped CdTe powder samples were prepared by solid-state reaction method. In the present work ef... more Co doped CdTe powder samples were prepared by solid-state reaction method. In the present work effect of Co doping on structural, optical, and magnetic properties has been studied. X-ray diffraction studies confirm zinc blend structure for all the samples. The lattice parameter showed linear increase with the increase in Co content. The elemental constituents were characterized by EDAX. Optical studies showed the increase in band gap with increase in Co level. The samples were diluted magnetic semiconductors and exhibited clear hysteresis loop showing room temperature ferromagnetism as confirmed by vibrating sample magnetometer.
Materials Chemistry and Physics, 2008
In this report, several materials such as M/glass (M = Cu, Ru, Ag and Pt) and Pt/Si were investig... more In this report, several materials such as M/glass (M = Cu, Ru, Ag and Pt) and Pt/Si were investigated to test their suitability for studying the early nucleation stage and growth of cobalt clusters. It was found that most of these materials stand as good substrates to be used in the study of the nucleation and growth of electrodeposited cobalt from aqueous solution containing CoSO 4 , CoCl 2 , Na 2 SO 4 and H 3 BO 3. Among theses substrates, Ag shows a transition from instantaneous to progressive nucleation. In the other hand the cobalt electrodeposited on Cu, Ru and Pt substrates followed progressive nucleation. Pt/Si substrates gave short transient time at maximum transient current and instantaneous cobalt nucleation on it surface.
Physica B: Condensed Matter
Low temperature specific heat, AC magnetic susceptibility and magnetization measurements were per... more Low temperature specific heat, AC magnetic susceptibility and magnetization measurements were performed on the Ce7X 3 compounds (X = Ni, Ru, Rh, Pd, Ir and Pt). They exhibit coexistence of magnetic order (MO), heavy fermion (HF) and intermediate valence (IV) behaviour and the results are interpreted in terms of the three Ce sublattices (1Ce~, 3Ce H and 3Cenl) present in the ThTFe3-type structure. From entropic considerations it is found that sublattice Ce m presents an IV behaviour in all these compounds and Celt show MO or have a HF behaviour depending on the Ce-ligand electronic structure. The Ce~ atoms (more than 6 ,~ distant from each other) exhibit MO only when the Ce H sublattice provides a high density of electronic states.
Physical Review B
We performed the resonant inverse photoemission ͑RIPE͒ study on CePd 3 at the prethreshold region... more We performed the resonant inverse photoemission ͑RIPE͒ study on CePd 3 at the prethreshold region of the Ce-N 4,5 absorption edge. The surface effects on RIPE spectra are discussed through the investigation of the resonance behaviors. Comparison between the RIPE spectra and the calculated resonant-excitation probability of the intermediate states indicates the existence of specific excitation energy range, where a strong resonant enhancement occurs for the bulk or the surface 4 f spectrum.
Structural, optical and electrical properties of Ag doped PbS thin films: role of Ag concentration
Journal of Materials Science: Materials in Electronics
Inverse magnetoresistance in Fe/Si ion beam sputtered sandwiches
Journal of Applied Physics
ABSTRACT
Photoluminescence of Nd-doped SnO2 thin films
Ferromagnétisme à température ambiante et effet de l'irradiation dans des semi-conducteurs magnetiques de type ZnCoO
Absence of ferromagnetism in Al-doped Zn0.9Co0.10O diluted magnetic semiconductors
Structural, optical, and electrical properties of Yb-doped ZnO thin films prepared by spray pyrolysis method
Journal of Applied Physics, 2011
Yb-doped ZnO thin films were prepared on glass substrates by spray pyrolysis technique in order t... more Yb-doped ZnO thin films were prepared on glass substrates by spray pyrolysis technique in order to investigate the insertion of Yb ions in the ZnO matrix and the related optical properties of the films. The molar ratio of Yb in the spray solution was varied in the range of 0-5 at. %. X-ray diffraction patterns showed that the undoped and
Structural and photoluminescence properties of ZnO thin films prepared by sol-gel process
Journal of Applied Physics
The present study focuses on the structural and optical properties of ZnO thin films fabricated b... more The present study focuses on the structural and optical properties of ZnO thin films fabricated by sol-gel process and spin coated onto Si (100) and quartz substrates. The ZnO films have a hexagonal wurtzite structure with a grain size of about 50 nm. The x-ray photoelectron spectroscopy measurements reveal the presence of Zn 2+ and of zinc hydroxyl groups at the film. Optical properties were studied by photoluminescence (PL) and absorption spectroscopy at low and room temperatures. The absorption spectrum is dominated by a sharp excitonic peak at room and low temperatures. At room temperature, PL observations show two transitions: one near the absorption edge in the ultraviolet (UV) region and the second centered at 640 nm, characteristic of the deep electronic levels in the bandgap. The spectrum at 6 K is dominated by donor bound exciton lines and donor-acceptor pair transitions. LO-phonon replica and two-electron satellite transitions are also observed. These optical characterist...
International Journal of Modern Physics B, 2008
Sr 2 CoMoO 6 and Sr 2 CoMoO 6-δ ceramics have been obtained by solid state reaction in air and in... more Sr 2 CoMoO 6 and Sr 2 CoMoO 6-δ ceramics have been obtained by solid state reaction in air and in a H 2/ N 2 gas mixture. At room temperature, as shown by X-ray diffraction, both compounds have a tetragonal perovskite-like structure with doublet unit-cell parameters, space group I4/m, with a = 5.5575, c = 7.9342 in Sr 2 CoMoO 6 and a = 5.5683 and c = 7.9395 in Sr 2 CoMoO 0.95. The latter contains small traces of Co and SrCoO 2.61, with an almost expansion. The magnetic susceptibility indicates that Sr 2 CoMoO 6 is an antiferromagnet with TN = 37 K. The magnetization was found to be the same in both samples, while the electric properties, originating from the oxygen content, are drastically affected.
One step electrodeposited CZTS thin films: Preparation and characterization
2014 International Renewable and Sustainable Energy Conference (IRSEC), 2014
Solid State Communications, 1994
Magnetic (X), thermal (Ce), and transport (p) measurements on Ce~4Xst (X = An, Ag and Cu) are pre... more Magnetic (X), thermal (Ce), and transport (p) measurements on Ce~4Xst (X = An, Ag and Cu) are presented. All these compounds show antiferromagnetic type order at low temperatures, with TN = 0.9 K (Au), 1.1 K (Ag)and 3.2 K (Cu). Within the Gd14Agsx-type structure the Ce atoms sit in different sublattices denoted by I (2 atoms), II (6 atoms) and III (6 atoms), therefore the results can be interpreted in terms of three different behaviors of Ce depending on its local environment. From the entropy involved in the magnetically ordered (MO) phase it can be established that the Cett and Cem atoms order in Cel4Ausl and Ce14Agsl, while the Cet order in Cel4Cus1. There is a large linear contribution to Cp at T > TN, 7HT = 0.81 (Au), 1.24 (Ag) and 3.1 (Cu) J/mol K 2, which indicates the coexistence of MO and heavy fermions. In the case of Cex4Cus1, the magnetic contribution to Ct, from sublattice Cel around TN, resembles that of a modulated system and the characteristic temperatures for Cell and Cetll atoms are estimated from p(T) as: TK=16 K and >120 K respectively.
Journal of Physics: Conference Series, 2014
Structural, magnetic (M) and thermal (Cm) studies on Ce2(Ni1−yPdy)2Sn alloys are presented within... more Structural, magnetic (M) and thermal (Cm) studies on Ce2(Ni1−yPdy)2Sn alloys are presented within the 0 ≤ y ≤ 0.55 range of concentration, showing evidences for itinerant to local electronic transformation. At variance with RKKY type interactions between localized moments µ ef f , the substitution of Ni by isoelectronic Pd leads the antiferromagnetic transition to decrease from TN 3.8 K to 1.2 K between y = 0 and 0.48, while M (H) measured at H = 5 T and 1.8 K rises from 0.12 up to 0.75µB/Ce-at. Furthermore, the Cm(TN) jump increases with concentration whereas |θP | decreases. The magnetic entropy Sm(T) grows moderately with temperature for y = 0 due to a significant contribution of excited levels at low energy, while at y = 0.5 it shows a incipient plateau around Sm = Rln2. All these features reflect the progressive ground state transformation of from itinerant to a local character. Another peculiarity of this system is the nearly constant value of Cm(TN) that ends in an entropy bottleneck as TN decreases. Consequently, the system shows a critical point at ycr ≈ 0.48 with signs of ferromagnetic behavior above Hcr ≈ 0.3T. A splitting of the Cm(TN) maximum, tuned by field and concentration, indicates a competition between two magnetic phases, with respective peaks at TN ≈ 1.2 K and TI ≈ 1.45 K.
In this work, we use rf magnetron sputtering to deposit at room temperature a ZnO thin film on to... more In this work, we use rf magnetron sputtering to deposit at room temperature a ZnO thin film on top of a photoactive material based on P3HT:PCBM blend for organic photovoltaic devices. We investigate the influence of the sputtering conditions on the ZnO crystallinity, on the substrate layer nanoscale morphology and on the photovoltaic device performances. We show that, under appropriate sputtering conditions, the modification of the P3HT:PCBM film causes no functional damage of the photoactive layer, and leads to an improved performance of the photovoltaic devices.
Impact of sputtered ZnO interfacial layer on the S-curve in conjugated polymer/fullerene based-inverted organic solar cells
Thin Solid Films, 2015
ABSTRACT The impact of crystalline structure changes of sputtered ZnO interfacial layer on perfor... more ABSTRACT The impact of crystalline structure changes of sputtered ZnO interfacial layer on performances of inverted organic solar cells (OSCs) has been investigated. We find that the structural modification of the ZnO cathode interfacial layer, obtained by thermal annealing, plays a crucial role in the origin and solving of the S-curve in conjugated polymer/fullerene photovoltaics. Our results show that the crystallization (i.e. crystallites size) of poly(3- hexylthiophene) (P3HT) evolves as a function of that of ZnO according to the annealing temperature. This evolution can directly impact the interfacial orientation and organization of the chains of P3HT at the ZnO buried interface. Such an ordered profile favors the vertical phase segregation and raises the carrier mobility, which explains the disappearance of the S-shape observed in current density-voltage device characteristics for annealing temperatures above 200 °C. These results adequately address recent research and provide an important insight into the interfacial layers of inverted OSCs.
Observation of the surface 4f state of CePd 7 sby means of the resonant-inverse-photoemission study at the Ce 4d absorption edge
Physical Review B, 1997
The resonant inverse photoemission study (RIPES) of CePd7 , has been carried out at the Ce 4d--&g... more The resonant inverse photoemission study (RIPES) of CePd7 , has been carried out at the Ce 4d-->4f absorption edge. The strong resonant enhancement of the 4f cross section enables us to distinguish two 4f components in the empty electronic state near the Fermi level. The incidence-angle dependence of the RIPES indicates a clear difference between ground-state configurations at the bulk and surface. It is found that the former shows a strongly hybridized 4f state, while the latter shows a localized 4f character. The angle dependence of the RIPES of alpha-Ce metal has been also carried out and similar results as those of CePd7 were obtained. The RIPES at the Ce 4d-->4f edge is found to be a powerful method to investigate the surface 4f state.
Comparative study of thermal and magnetic properties of CeTyX4-y ferromagnets
Physical Review B, 1997
ABSTRACT
Effects of high-temperature annealing on magnetic properties of V-doped GaN thin films grown by MOCVD
ABSTRACT Metal organic chemical vapor deposition (MOCVD) has been used to grow vanadium-doped GaN... more ABSTRACT Metal organic chemical vapor deposition (MOCVD) has been used to grow vanadium-doped GaN (GaN:V) on c-sapphire substrate using VCl4 as the V source. The as-grown GaN:V exhibited a saturated magnetic moment (Ms) of 0.28 emu/cm3 at room temperature. Upon high-temperature annealing treatment at 1100 °C for 7 min under N2 ambient, the Ms of the GaN:V increased by 39.28% to 0.39 emu/cm3. We found that rapid thermal annealing leads to a remarkable increase in surface roughness of the V-doped GaN as well as the electron concentration. The annealing also leads to a significant increase in the Curie temperature (TC), we have identified Curie temperatures about 350 K concluded from the difference between the field-cooled and zero-field-cooled magnetizations. Structure characterization by x-ray diffraction indicated that the ferromagnetic properties are not a result of secondary magnetic phases.
Co doped CdTe powder samples were prepared by solid-state reaction method. In the present work ef... more Co doped CdTe powder samples were prepared by solid-state reaction method. In the present work effect of Co doping on structural, optical, and magnetic properties has been studied. X-ray diffraction studies confirm zinc blend structure for all the samples. The lattice parameter showed linear increase with the increase in Co content. The elemental constituents were characterized by EDAX. Optical studies showed the increase in band gap with increase in Co level. The samples were diluted magnetic semiconductors and exhibited clear hysteresis loop showing room temperature ferromagnetism as confirmed by vibrating sample magnetometer.
Materials Chemistry and Physics, 2008
In this report, several materials such as M/glass (M = Cu, Ru, Ag and Pt) and Pt/Si were investig... more In this report, several materials such as M/glass (M = Cu, Ru, Ag and Pt) and Pt/Si were investigated to test their suitability for studying the early nucleation stage and growth of cobalt clusters. It was found that most of these materials stand as good substrates to be used in the study of the nucleation and growth of electrodeposited cobalt from aqueous solution containing CoSO 4 , CoCl 2 , Na 2 SO 4 and H 3 BO 3. Among theses substrates, Ag shows a transition from instantaneous to progressive nucleation. In the other hand the cobalt electrodeposited on Cu, Ru and Pt substrates followed progressive nucleation. Pt/Si substrates gave short transient time at maximum transient current and instantaneous cobalt nucleation on it surface.