ABSTRACT Low-energy electron diffraction, x-ray diffraction, and x-ray absorption techniques are ... more ABSTRACT Low-energy electron diffraction, x-ray diffraction, and x-ray absorption techniques are used to investigate the atomic structure of ternary silicides (MSi2, M = Co, Fe). 100 Å thick Co1−xFexSi2 films (with 0 ≤ × ≤ 1) were grown by codeposition onto a Si(111) substrate held at room temperature. The as-deposited films are metallic and adopt an ordered cubic structure of CsCl-type with essentially random vacancies, very similar to that of room-temperature grown FeSi2 and CoSi2 silicides. Upon annealing at 650°C, Fe-rich (x ≥ 0.85) films invariably convert into a semiconducting phase with a structure similar to the orthorhombic β-FeSi2 one. Yet, most interestingly, an almost cubic structure is preserved for x ≤ 0.85. Nevertheless, x-ray diffraction reveals a demixion into a Co rich CaF2-type silicide and a Fe-rich phase with a nearly cubic α-FeSi2 type structure. Extended x-ray absorption fine structure measurements indicate a local environment of Fe atoms similar to that in CsCl-type or α-FeSi2-type structure over the whole 0 < x < 0.85 composition range, showing that Fe does not merely substitute for Co atoms in a perfect CaF2-type CoSi2 structure, even for very low Fe content. In contrast, the local environment of Co atoms is similar to that in CoSi2 for Co-rich ternary compounds. Substantial modifications around Co sites are although observed in Fe richer silicides, suggesting that for x < 0.5, an appreciable amount of Co is incorporated in the α-FeSi2-type silicide phase.
Physical review. B, Condensed matter, Jan 15, 1996
Electronic and structural properties of epitaxial CoSi x layers have been investigated by means o... more Electronic and structural properties of epitaxial CoSi x layers have been investigated by means of core-level and valence-band photoemission, x-ray photoelectron diffraction, and extended x-ray-absorption fine-structure (EXAFS) experiments. CoSi x layers of various x ...
Physical review. B, Condensed matter, Jan 15, 1995
Pseudomorphic iron-silicide phases grown on Si(111) have been studied by means of low-energy elec... more Pseudomorphic iron-silicide phases grown on Si(111) have been studied by means of low-energy electron-diffraction, x-ray photoelectron-diffraction, and surface extended x-ray-absorption fine-structure experiments at the Fe K edge (7110 eV). These silicides have been epitaxially grown by codeposition of Fe and Si onto a room-temperature Si(111) substrate with silicide stoichiometry ranging from FeSi to FeSix (x~2). In all cases, they were
Physical review. B, Condensed matter, Jan 15, 1994
Auger-electron diffraction (AED) and surface-extended x-ray-absorption fine structure (SEXAFS) ha... more Auger-electron diffraction (AED) and surface-extended x-ray-absorption fine structure (SEXAFS) have been used to obtain a complete description of the atomic structure of a two-dimensional epitaxial Er silicide layer on Si(111). AED reveals that a monolayer of Er is located underneath a buckled Si double layer. The relevant Er-Si interlayer spacings are determined by means of single scattering cluster simulations and
ABSTRACT ErSi2−x silicides, bulk and epitaxially grown on Si(111), are investigated by X-ray abso... more ABSTRACT ErSi2−x silicides, bulk and epitaxially grown on Si(111), are investigated by X-ray absorption spectroscopy at Er L edges in order to determine the effects of the relaxation due to the silicon vacancies on the local environment of erbium in those materials. The value of the shortest Er-Si bond length derived from the L1 edge data is found to be 2.95 ± 0.03 Å, in agreement with previous neutron diffraction data giving an orthorhombic-hexagonal deformation of the AlB2 structure where the Si vacancies are ordered. The same bond length is deduced from L3 edge data recorded from epitaxial film. This result is consistent with a simple model for the relaxation due to the vacancies in these epitaxial films, where the hexagonal symmetry is preserved. The effect of the strain due to the mismatch to the Si substrate is also evidenced from EXAFS. Preliminary results on a two-dimensional erbium silicide layer are given, showing the strong anisotropy of Er environment for one monolayer Er coverage.
Metastable cubic Fe silicide layers epitaxially grown by MBE and SPE on Si (1 1 1) have been inve... more Metastable cubic Fe silicide layers epitaxially grown by MBE and SPE on Si (1 1 1) have been investigated by SEXAFS. These thin films exhibit 1 x 1 or 2 x 2 LEED pattern, depending on the thermal treatments. Fe atoms are surrounded by Si NN at 2.35 ~ and Fe NNN at 2.70/~. The results are consistent with CsCl-type or a-FeSi2 derived structures.
Iron silicide thin films (200Å Fe(Si1−xFex) with 0⩽x⩽1 and local cubic CsCl structure) have been ... more Iron silicide thin films (200Å Fe(Si1−xFex) with 0⩽x⩽1 and local cubic CsCl structure) have been grown by coevaporation at room temperature (RT) on Si(111). X-ray magnetic circular dichroism (XMCD) and magneto-optic Kerr effect (MOKE) measurements indicate that the films are ferromagnetic at RT for x ranging from 1 (pure Fe) to 0.15 (Fe1.35Si). The magnetization is parallel to the film
ABSTRACT The epitaxial growth of a cubic Fe silicide phase on Si(111) has been confirmed by means... more ABSTRACT The epitaxial growth of a cubic Fe silicide phase on Si(111) has been confirmed by means of X-ray photoelectron diffraction (XPD) and surface-extended X-ray absorption fine-structure (SEXAFS) experiments. XPD experiments show that a 5-monolayer Fe film deposited on Si(111) and subsequently annealed at ~ 500 °C has a cubic structure. SEXAFS measured at the Fe K edge (7110 eV) reveals that Fe atoms are coordinated with eight Si atoms with bond length of (2.38 ± 0.04) Å and with six Fe atoms with bond length of (2.71 ± 0.04) Å. All measurements lead to the conclusion that this cubic silicide has a CsCl-type structure.
Si2p core level photoemission as well as X-ray polarization dependent surface extended absorption... more Si2p core level photoemission as well as X-ray polarization dependent surface extended absorption fine structure (SEXAFS) have been used to characterize the interface of a twodimensional erbium silicide with Si(l1 l). This silicide, which consists of a hexagonal erbium monolayer located underneath a buckled Si top layer, was grown by deposition of one monolayer of erbium on clean Si(1 l l ) and annealing in the 400-6W°C temperature range. Photoemission experiments reveal a Schottky barrier height 6 as low as 0.13 rt 0.05 eV while for thicker erbium silicide layers Idg is found to be = 0.3 eV. SEXAFS measured at the Er L3 edge shows the location of erbium atoms in the eclipsed threefold hollow sites of the Si substrate.The average distance of erbium to the silicon of the substrate is found to be 3.10 * 0.04 A, whereas the distance of erbium atoms to their three first neighbors in the Si top layer is found to be 2.94 k 0.04 A.
ABSTRACT Low-energy electron diffraction, x-ray diffraction, and x-ray absorption techniques are ... more ABSTRACT Low-energy electron diffraction, x-ray diffraction, and x-ray absorption techniques are used to investigate the atomic structure of ternary silicides (MSi2, M = Co, Fe). 100 Å thick Co1−xFexSi2 films (with 0 ≤ × ≤ 1) were grown by codeposition onto a Si(111) substrate held at room temperature. The as-deposited films are metallic and adopt an ordered cubic structure of CsCl-type with essentially random vacancies, very similar to that of room-temperature grown FeSi2 and CoSi2 silicides. Upon annealing at 650°C, Fe-rich (x ≥ 0.85) films invariably convert into a semiconducting phase with a structure similar to the orthorhombic β-FeSi2 one. Yet, most interestingly, an almost cubic structure is preserved for x ≤ 0.85. Nevertheless, x-ray diffraction reveals a demixion into a Co rich CaF2-type silicide and a Fe-rich phase with a nearly cubic α-FeSi2 type structure. Extended x-ray absorption fine structure measurements indicate a local environment of Fe atoms similar to that in CsCl-type or α-FeSi2-type structure over the whole 0 < x < 0.85 composition range, showing that Fe does not merely substitute for Co atoms in a perfect CaF2-type CoSi2 structure, even for very low Fe content. In contrast, the local environment of Co atoms is similar to that in CoSi2 for Co-rich ternary compounds. Substantial modifications around Co sites are although observed in Fe richer silicides, suggesting that for x < 0.5, an appreciable amount of Co is incorporated in the α-FeSi2-type silicide phase.
Physical review. B, Condensed matter, Jan 15, 1996
Electronic and structural properties of epitaxial CoSi x layers have been investigated by means o... more Electronic and structural properties of epitaxial CoSi x layers have been investigated by means of core-level and valence-band photoemission, x-ray photoelectron diffraction, and extended x-ray-absorption fine-structure (EXAFS) experiments. CoSi x layers of various x ...
Physical review. B, Condensed matter, Jan 15, 1995
Pseudomorphic iron-silicide phases grown on Si(111) have been studied by means of low-energy elec... more Pseudomorphic iron-silicide phases grown on Si(111) have been studied by means of low-energy electron-diffraction, x-ray photoelectron-diffraction, and surface extended x-ray-absorption fine-structure experiments at the Fe K edge (7110 eV). These silicides have been epitaxially grown by codeposition of Fe and Si onto a room-temperature Si(111) substrate with silicide stoichiometry ranging from FeSi to FeSix (x~2). In all cases, they were
Physical review. B, Condensed matter, Jan 15, 1994
Auger-electron diffraction (AED) and surface-extended x-ray-absorption fine structure (SEXAFS) ha... more Auger-electron diffraction (AED) and surface-extended x-ray-absorption fine structure (SEXAFS) have been used to obtain a complete description of the atomic structure of a two-dimensional epitaxial Er silicide layer on Si(111). AED reveals that a monolayer of Er is located underneath a buckled Si double layer. The relevant Er-Si interlayer spacings are determined by means of single scattering cluster simulations and
ABSTRACT ErSi2−x silicides, bulk and epitaxially grown on Si(111), are investigated by X-ray abso... more ABSTRACT ErSi2−x silicides, bulk and epitaxially grown on Si(111), are investigated by X-ray absorption spectroscopy at Er L edges in order to determine the effects of the relaxation due to the silicon vacancies on the local environment of erbium in those materials. The value of the shortest Er-Si bond length derived from the L1 edge data is found to be 2.95 ± 0.03 Å, in agreement with previous neutron diffraction data giving an orthorhombic-hexagonal deformation of the AlB2 structure where the Si vacancies are ordered. The same bond length is deduced from L3 edge data recorded from epitaxial film. This result is consistent with a simple model for the relaxation due to the vacancies in these epitaxial films, where the hexagonal symmetry is preserved. The effect of the strain due to the mismatch to the Si substrate is also evidenced from EXAFS. Preliminary results on a two-dimensional erbium silicide layer are given, showing the strong anisotropy of Er environment for one monolayer Er coverage.
Metastable cubic Fe silicide layers epitaxially grown by MBE and SPE on Si (1 1 1) have been inve... more Metastable cubic Fe silicide layers epitaxially grown by MBE and SPE on Si (1 1 1) have been investigated by SEXAFS. These thin films exhibit 1 x 1 or 2 x 2 LEED pattern, depending on the thermal treatments. Fe atoms are surrounded by Si NN at 2.35 ~ and Fe NNN at 2.70/~. The results are consistent with CsCl-type or a-FeSi2 derived structures.
Iron silicide thin films (200Å Fe(Si1−xFex) with 0⩽x⩽1 and local cubic CsCl structure) have been ... more Iron silicide thin films (200Å Fe(Si1−xFex) with 0⩽x⩽1 and local cubic CsCl structure) have been grown by coevaporation at room temperature (RT) on Si(111). X-ray magnetic circular dichroism (XMCD) and magneto-optic Kerr effect (MOKE) measurements indicate that the films are ferromagnetic at RT for x ranging from 1 (pure Fe) to 0.15 (Fe1.35Si). The magnetization is parallel to the film
ABSTRACT The epitaxial growth of a cubic Fe silicide phase on Si(111) has been confirmed by means... more ABSTRACT The epitaxial growth of a cubic Fe silicide phase on Si(111) has been confirmed by means of X-ray photoelectron diffraction (XPD) and surface-extended X-ray absorption fine-structure (SEXAFS) experiments. XPD experiments show that a 5-monolayer Fe film deposited on Si(111) and subsequently annealed at ~ 500 °C has a cubic structure. SEXAFS measured at the Fe K edge (7110 eV) reveals that Fe atoms are coordinated with eight Si atoms with bond length of (2.38 ± 0.04) Å and with six Fe atoms with bond length of (2.71 ± 0.04) Å. All measurements lead to the conclusion that this cubic silicide has a CsCl-type structure.
Si2p core level photoemission as well as X-ray polarization dependent surface extended absorption... more Si2p core level photoemission as well as X-ray polarization dependent surface extended absorption fine structure (SEXAFS) have been used to characterize the interface of a twodimensional erbium silicide with Si(l1 l). This silicide, which consists of a hexagonal erbium monolayer located underneath a buckled Si top layer, was grown by deposition of one monolayer of erbium on clean Si(1 l l ) and annealing in the 400-6W°C temperature range. Photoemission experiments reveal a Schottky barrier height 6 as low as 0.13 rt 0.05 eV while for thicker erbium silicide layers Idg is found to be = 0.3 eV. SEXAFS measured at the Er L3 edge shows the location of erbium atoms in the eclipsed threefold hollow sites of the Si substrate.The average distance of erbium to the silicon of the substrate is found to be 3.10 * 0.04 A, whereas the distance of erbium atoms to their three first neighbors in the Si top layer is found to be 2.94 k 0.04 A.
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