Diffraction before destruction using X-ray free-electron lasers (XFELs) has the potential to dete... more Diffraction before destruction using X-ray free-electron lasers (XFELs) has the potential to determine radiation-damage-free structures without the need for crystallization. This article presents the three-dimensional reconstruction of the Melbournevirus from single-particle X-ray diffraction patterns collected at the LINAC Coherent Light Source (LCLS) as well as reconstructions from simulated data exploring the consequences of different kinds of experimental sources of noise. The reconstruction from experimental data suffers from a strong artifact in the center of the particle. This could be reproduced with simulated data by adding experimental background to the diffraction patterns. In those simulations, the relative density of the artifact increases linearly with background strength. This suggests that the artifact originates from the Fourier transform of the relatively flat background, concentrating all power in a central feature of limited extent. We support these findings by s...
Ž ny. A comparative study of stabilities is presented for a variety of C polyanions. Formation en... more Ž ny. A comparative study of stabilities is presented for a variety of C polyanions. Formation enthalpies of dimers and 60 p monomers were determined from those of AM1 optimized R C ny monomers using thermochemical considerations. In m 60 contrast to cycloadduct polymers, singly bonded polymers become more stable with increasing charge and a crossover occurs at around n s 3. Geometries were analyzed in terms of bond and charge distributions. The polyanion geometries of Na RbC and Na C salts are in agreement with X-ray results. q 1998 Elsevier Science B.V.
We used infrared and Raman spectroscopy to investigate single crystals of the compound C60(C~H,2)... more We used infrared and Raman spectroscopy to investigate single crystals of the compound C60(C~H,2)0.88(C7H8)0.05 We observed the signatures of the individual components Csa and pentane in the infrared spectrum with minimal changes when compared to solvent-free solid or solution spectra. The corresponding Raman spectrum shows that while the molecular Cso frequencies remain unchanged, there are some additional lines, probably due to symmetry effects of the solid state. We conclude that the material is a true clathrate with no electronic interaction between the constituents. Unlike the infrared spectrum pentane lines are not observed in Raman spectra.
Pergamon Solid State Communications, Vol. 105, No. 11, pp. 685-687, 1998 1998 Elsevier Science Lt... more Pergamon Solid State Communications, Vol. 105, No. 11, pp. 685-687, 1998 1998 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038-1098/98 $19.00+.00 PH: 50038-1098(97)102149 STANDING WAVES AND KOSSEL LINE PATTERNS IN STRUCTURE DETERMINATION S. Marchesini,M. Belakhovsky,a AQR Baron, b G. Faigel,` M. Tegze` and P. Kamp" epartement de Recherche Fondamentale sur la Matiere Condense (SP2M/IRS), CEA, Grenoble 38054 Cedex 9 France bESRF, BP 220 38043 Grenoble Cedex, France ` ...
Among the future x-ray sources linac based x-ray free electron lasers are close to realization. T... more Among the future x-ray sources linac based x-ray free electron lasers are close to realization. They will produce extremely short (<100fsec) and intense hard x-ray pulses (~10 12 ph/pulse). The unique features of this beam will allow the study of the atomic structure and the different physical and chemical processes in solids at a level not accessible today. However, to understand the experimental results one has to have a detailed picture of what happens during the burst in the sample. In several suggested applications small samples containing only 10 3-10 6 atoms are the possible candidates. In order to have a feeling about the atomic motions, we performed model calculations on the dynamics of particles of a cluster in an intense hard x-ray pulse. The movement of the particles was followed by non-relativistic classical dynamics. The main processes: photoabsorption, Auger process, inelastic and elastic scattering of electrons were taken in to account by their respective cross sections. Here we report our findings on clusters containing various elements. The results show that the clusters disintegrate via Coulomb explosion, similarly to small clusters in intense laser beam. However, the dynamics of the explosion is significantly different. We map the parameters of the explosion as a function of cluster size, pulse length, and first neighbor distance. We discuss the consequences of our results to single molecule imaging by the free electron laser pulses, recently proposed by Neutze et al [1]. The critical evaluation of these results gives guidelines and sets important limits on experimental conditions of future experiments aiming single molecule structure solution.
The behavior of small samples in very short and intense hard x-ray pulses is studied by molecular... more The behavior of small samples in very short and intense hard x-ray pulses is studied by molecular dynamics type calculations. The main emphasis is put on the effect of various tamper layers about the sample. This is discussed from the point of view of structural imaging of single particles, including not only the distortion of the structure but also the background conditions. A detailed picture is given about the Coulomb explosion, with explanation of the tampering mechanism. It is shown that a thin water layer is efficient in slowing down the distortion of the atomic structure, but it gives a significant contribution to the background.
1 Research Institute for Solid State Physics, РОВ 49, H-1525 Budapest, Hungary 2 Department of So... more 1 Research Institute for Solid State Physics, РОВ 49, H-1525 Budapest, Hungary 2 Department of Solid State Physics, Eötvös Lóránd University, Múzeum krt. 6-8, H-1088 Budapest, Hungary 3 Department of Physics, State University of New York, Stony Brook, ...
Acta Crystallographica Section A Foundations and Advances
In this work, the results obtained by single X-ray diffraction (XRD); even if for larger R-factor... more In this work, the results obtained by single X-ray diffraction (XRD); even if for larger R-factor, are confirmed by another independent technique, one can study the vibrational spectroscopy with symmetry and group theory character tables. This method can be applied on the whole molecule or a part of it, mainly we search for function groups such as H2O, an ionic part such as NH 4+ or metal halide such as (MnBrx). The fine XRD data results five possible solutions for the same molecule with the same chemical formula, although the R-factor values are so close, this method can distinguish between these possible solutions upon the crystal structure. The study of C5H10(NH3)2(MnCl4Br2) results one solution of XRD is confirmed by IR and Raman spectroscopy. The space group of the molecule Ima2 with R= 3.33, The (MnCl4Br2) belongs to D4h of 5 Raman peaks and different 5 IR peaks. The Mn2(MnCl4Br2) is C2, C2h or Cs according To the location of Mn atoms to the octahedral, the suitable solution is C2h which expects 12 IR and another 9 Raman peaks with good agreement with IR and Raman results.
Az atomi felbontasu rontgen holografia elmeleti alapjait 1991-ben dolgoztuk ki es nehany evel kes... more Az atomi felbontasu rontgen holografia elmeleti alapjait 1991-ben dolgoztuk ki es nehany evel kesőbb vegeztuk el az első sikeres kiserletet. Jelen palyazat fő celja az atomi felbontasu rontgen holografia es egy uj, a holografiaval rokon meresi modszer, a szogatlagolt rugalmas szoras tovabbfejlesztese es alkalmazasa volt. Holografia meresek segitsegevel kimutattuk, hogy a La0.7Sr0.3MnO3 kristaly fazisatalakulasanal nem lep fel statikus Jahn-Teller torzulas, ahogy korabban felteteleztek. Kiserleti adatokbol megmutattuk, hogy a szogatlagolt szoras eredmenyekent kapott kep ugyanazt az informaciot hordozza, mint a hagyomanyos egykristaly diffrakcio soran egyenkent osszegyűjtott intenzitas adatok. Megvalositottunk egy ujfajta elektron holografia merest egy erre a celra atepitett pasztazo elektron mikroszkop segitsegevel. Eredmenyeket ertunk el a holografikus es diffrakcios kiertekelesi modszerek tovabbfejlesztese teren. Kidolgoztunk egy eljarast a kis intenzitasu szoraskepek osztalyozasar...
Kossel lines are formed when radiation from point x-ray sources inside a single crystal are diffr... more Kossel lines are formed when radiation from point x-ray sources inside a single crystal are diffracted by the crystal itself. In principle, Kossel line patterns contain full information on the crystalline structure: phase and magnitude of the structure factors. The phase is coded into the profile of the lines. Although this was known for a long time, experimental realization has not been presented. In this work we demonstrate experimentally that phases can be directly determined from the profile of the Kossel lines. These measurements are interesting not only theoretically, but they would facilitate structure solution of samples within extreme conditions, such as high pressure, high and low temperatures, high magnetic fields and extremely short times. The parallel measurement of many diffraction lines on a stationary sample will allow a more efficient use of the new generation of x-ray sources the X-ray free electron lasers (XFELs). Traditionally, the atomic order in crystalline substances is determined by x-ray diffraction. Measuring diffraction peaks, we obtain the magnitude of the scattered waves, but the phase information is lost. However, for direct structure determination both the magnitude and the phase of the structure factors should be known. In practice, the loss of phase information is compensated by additional knowledge, such as atomicity, positivity of electron density, known part of the structure, composition, etc. Clever algorithms, like direct 1 , Patterson 2 , dual space 3 methods, have been developed to incorporate and use our extra knowledge to solve the structure. Nevertheless, from time to time scientists tried to work out methods that allow experimental determination of the phase. The reason of this "quest" is that the knowledge of phase would greatly facilitate structure solution, especially in the case of non-centrosymmetric crystals. The best known approach is the controlled variation of the structure factor by various methods 4-7. However, in this case special sample must be prepared, which limits applicability. Another approach is the three-beam diffraction, where three reflections are simultaneously excited 8,9. Although it was shown that this method works, the practical application is not widespread, due to experimental difficulties. Another possibility is atomic resolution holography using inside sources or detectors 10-12. This method can give the local atomic arrangement in orientationally ordered samples by a direct transformation of the holographic pattern which contains the phase. However, the measurement of x-ray holograms are technically complicated, time consuming and only relatively simple structures (10-100 atoms) can be determined. Hutton, Trammell and Hannon 13 and in an independent work Stephan et al. 14 suggested the use of Kossel line patterns as source of phase information of diffraction peaks produced by inside x-ray sources. Hutton and co-workers based their method on the analysis of the fine structure of individual Kossel lines. They gave a theoretical prediction for the angular dependence of the Kossel line profile. They showed that in the Bragg case and in special conditions 13 the line shape strongly depends on the phase of the structure factor (see Supplementary Movie 1). Although they described the necessary experimental conditions in detail, there has been no experimental work measuring a Kossel pattern (i.e. many Kossel lines in parallel) and determine the fine structure of all lines, so far. There has been a pioneering experiment 15 , in which the fine structure of a single Kossel line was measured, and its phase was determined, within very special conditions. The reason, why these type of measurements are scarce is the technical difficulties (see Supplementary Information, "Design Considerations of the Experimental Setup" and Ref. 16). In this paper we present experimental evidence for the direct determination of the phase of structure factors from the fine structure of measured Kossel lines. Further, we show that the special conditions given in Refs 13,15 can be relaxed, leading to wider applicability. We also discuss the unique possibilities given by the Kossel technique, i.e. obtaining structural data on a steady sample at extreme conditions such as
Solid state amorphization of vacuum evaporated multilayers (ML) were examined on samples with an ... more Solid state amorphization of vacuum evaporated multilayers (ML) were examined on samples with an overalI composition Fe45B55 and Fe layer thickness ranging from 1.5 to 10 nm. The samples were examined by parallel beam X-ray diffraction and by Mossbauer spectroscopy (MS). A 3 nm thick amorphous interface is observed in the as-received samples independently from the thickness of the bee-Fe layer. MS results indicate a broad concentration distribution in this amorphous interface. The thickness of the amorphous layer can be increased by heat treatments below 600 K at least up to 6 nm. INTRODUCTION Although solid state amorphization in the Fe-B system by mechanical alloying was reported by several groups [1,2,3,4] the diffusion amorphization of ML samples seemed to be unsuccessful according to the very few published results [5,6]. In order to investigate the details of the diffusion process and the propelties of the interface between the layers we prepared a series of samples with different Fe layer thicknesses starting from 1.5 run. The Fe-B system is a very well known model system of studies on amorphous alloys and amorphous phase formation by rapid quenching from the liquid as well as crystallization properties are extensi vely studied [7]. The amorphous phase can be prepared in a wide concentration range (from 12 to 90 at% B) by vacuum coevaporation or sputtering. There are only a few crystalline phases (FeB, Fe2B and Fe3B) which cannot support appreciable off-stochiometry. The MS parameters -isomer shift (IS), quadrupole splitting (QS) and hyperfine field (HF)strongly depend on the B concentration of the amorphous phase [8,9] and this way they make possible a consistent estimation of the unknown composition. All these properties make it an ideal system to study the validity of free energy considerations in predicting the concentration range of amorphous phase formation by solid state diffusion. This was calculated to be 32-47 at % B for the Fe-B system [10]. EXPERIMENTAL Multilayered samples with an overall composition Fe45B55 were evapntated either to aluminium foil or Si single crystal substrate in a vacuum of 10-7 Pa with an evaporation rate approx. 0.1 nm/s. The sample holder was cooled by liquid nitrogen during evaporation. The substrate was first covered with 30 nm boron to prevent contamination from the substrate and the topmost layer was boron, as well, of 5 11m width. Samples with 1.5, 2.5, 3.5 and 10 nm Fe layer thickness were prepared with appropriate B layer thickness to get an Fe45B55 overall composition. The layer thickness was controlled by a quartz oscillator. Due to the geometry of the evaporation chamber there is a O. I nm variation of the layer thickness within the sample. The total thickness of the samples was about 200 nm. Heat treatments were also made in the high vacuum evaporation chamber. Parallel beam X-ray diffraction was carried out at the Brookhaven National Synchrotron Light Source X3B I beam line. The 0.11467 nm wavelength was selected by a Si (lll) channel cut monochromator. The sample was mounted on a two circle goniometer. The diffracted beam was detected by a scintillation counter after a Ge single crystal analyzer. This arrangement allowed measurements from 0.8 degree with a 0.002 degree resolution. Fe57 Mossbauer spectroscopy (MS) was made on a standard constant acceleration spectrometer. Samples on the Al substrate were folded up and were measured in transmission geometry whereas samples evaporated on Si single crystal were measured by conversion electron Mossbauer spectroscopy (CEMS). The 776 Mechanically Alloyed and Nanocrystalline Materials helium temperature measurements were made on the Al substrate samples in a Janis cryostat equipped with a superconducting magnet. RESULTS and DISCUSSION The quality of the evaporated multilayers was checked on a few selected samples by X-ray diffraction at small angles corresponding to the layer periodicity. Fig. 1 shows that the multilayer periodicities Fig. 2. Samples on Al substrate had broader diffraction peaks than those on Si substrate. The coherence length calculated from the width of the diffraction peaks ranged from 40 to 75 nm in case of the samples on Al substrates. Side peaks originating from the total thickness of the samples appeared only in case of the samples evaporated on the Si substrate and the separation of these peaks agrees with the 200 nm total thickness.
Diffraction before destruction using X-ray free-electron lasers (XFELs) has the potential to dete... more Diffraction before destruction using X-ray free-electron lasers (XFELs) has the potential to determine radiation-damage-free structures without the need for crystallization. This article presents the three-dimensional reconstruction of the Melbournevirus from single-particle X-ray diffraction patterns collected at the LINAC Coherent Light Source (LCLS) as well as reconstructions from simulated data exploring the consequences of different kinds of experimental sources of noise. The reconstruction from experimental data suffers from a strong artifact in the center of the particle. This could be reproduced with simulated data by adding experimental background to the diffraction patterns. In those simulations, the relative density of the artifact increases linearly with background strength. This suggests that the artifact originates from the Fourier transform of the relatively flat background, concentrating all power in a central feature of limited extent. We support these findings by s...
Ž ny. A comparative study of stabilities is presented for a variety of C polyanions. Formation en... more Ž ny. A comparative study of stabilities is presented for a variety of C polyanions. Formation enthalpies of dimers and 60 p monomers were determined from those of AM1 optimized R C ny monomers using thermochemical considerations. In m 60 contrast to cycloadduct polymers, singly bonded polymers become more stable with increasing charge and a crossover occurs at around n s 3. Geometries were analyzed in terms of bond and charge distributions. The polyanion geometries of Na RbC and Na C salts are in agreement with X-ray results. q 1998 Elsevier Science B.V.
We used infrared and Raman spectroscopy to investigate single crystals of the compound C60(C~H,2)... more We used infrared and Raman spectroscopy to investigate single crystals of the compound C60(C~H,2)0.88(C7H8)0.05 We observed the signatures of the individual components Csa and pentane in the infrared spectrum with minimal changes when compared to solvent-free solid or solution spectra. The corresponding Raman spectrum shows that while the molecular Cso frequencies remain unchanged, there are some additional lines, probably due to symmetry effects of the solid state. We conclude that the material is a true clathrate with no electronic interaction between the constituents. Unlike the infrared spectrum pentane lines are not observed in Raman spectra.
Pergamon Solid State Communications, Vol. 105, No. 11, pp. 685-687, 1998 1998 Elsevier Science Lt... more Pergamon Solid State Communications, Vol. 105, No. 11, pp. 685-687, 1998 1998 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038-1098/98 $19.00+.00 PH: 50038-1098(97)102149 STANDING WAVES AND KOSSEL LINE PATTERNS IN STRUCTURE DETERMINATION S. Marchesini,M. Belakhovsky,a AQR Baron, b G. Faigel,` M. Tegze` and P. Kamp&amp;amp;quot; epartement de Recherche Fondamentale sur la Matiere Condense (SP2M/IRS), CEA, Grenoble 38054 Cedex 9 France bESRF, BP 220 38043 Grenoble Cedex, France ` ...
Among the future x-ray sources linac based x-ray free electron lasers are close to realization. T... more Among the future x-ray sources linac based x-ray free electron lasers are close to realization. They will produce extremely short (<100fsec) and intense hard x-ray pulses (~10 12 ph/pulse). The unique features of this beam will allow the study of the atomic structure and the different physical and chemical processes in solids at a level not accessible today. However, to understand the experimental results one has to have a detailed picture of what happens during the burst in the sample. In several suggested applications small samples containing only 10 3-10 6 atoms are the possible candidates. In order to have a feeling about the atomic motions, we performed model calculations on the dynamics of particles of a cluster in an intense hard x-ray pulse. The movement of the particles was followed by non-relativistic classical dynamics. The main processes: photoabsorption, Auger process, inelastic and elastic scattering of electrons were taken in to account by their respective cross sections. Here we report our findings on clusters containing various elements. The results show that the clusters disintegrate via Coulomb explosion, similarly to small clusters in intense laser beam. However, the dynamics of the explosion is significantly different. We map the parameters of the explosion as a function of cluster size, pulse length, and first neighbor distance. We discuss the consequences of our results to single molecule imaging by the free electron laser pulses, recently proposed by Neutze et al [1]. The critical evaluation of these results gives guidelines and sets important limits on experimental conditions of future experiments aiming single molecule structure solution.
The behavior of small samples in very short and intense hard x-ray pulses is studied by molecular... more The behavior of small samples in very short and intense hard x-ray pulses is studied by molecular dynamics type calculations. The main emphasis is put on the effect of various tamper layers about the sample. This is discussed from the point of view of structural imaging of single particles, including not only the distortion of the structure but also the background conditions. A detailed picture is given about the Coulomb explosion, with explanation of the tampering mechanism. It is shown that a thin water layer is efficient in slowing down the distortion of the atomic structure, but it gives a significant contribution to the background.
1 Research Institute for Solid State Physics, РОВ 49, H-1525 Budapest, Hungary 2 Department of So... more 1 Research Institute for Solid State Physics, РОВ 49, H-1525 Budapest, Hungary 2 Department of Solid State Physics, Eötvös Lóránd University, Múzeum krt. 6-8, H-1088 Budapest, Hungary 3 Department of Physics, State University of New York, Stony Brook, ...
Acta Crystallographica Section A Foundations and Advances
In this work, the results obtained by single X-ray diffraction (XRD); even if for larger R-factor... more In this work, the results obtained by single X-ray diffraction (XRD); even if for larger R-factor, are confirmed by another independent technique, one can study the vibrational spectroscopy with symmetry and group theory character tables. This method can be applied on the whole molecule or a part of it, mainly we search for function groups such as H2O, an ionic part such as NH 4+ or metal halide such as (MnBrx). The fine XRD data results five possible solutions for the same molecule with the same chemical formula, although the R-factor values are so close, this method can distinguish between these possible solutions upon the crystal structure. The study of C5H10(NH3)2(MnCl4Br2) results one solution of XRD is confirmed by IR and Raman spectroscopy. The space group of the molecule Ima2 with R= 3.33, The (MnCl4Br2) belongs to D4h of 5 Raman peaks and different 5 IR peaks. The Mn2(MnCl4Br2) is C2, C2h or Cs according To the location of Mn atoms to the octahedral, the suitable solution is C2h which expects 12 IR and another 9 Raman peaks with good agreement with IR and Raman results.
Az atomi felbontasu rontgen holografia elmeleti alapjait 1991-ben dolgoztuk ki es nehany evel kes... more Az atomi felbontasu rontgen holografia elmeleti alapjait 1991-ben dolgoztuk ki es nehany evel kesőbb vegeztuk el az első sikeres kiserletet. Jelen palyazat fő celja az atomi felbontasu rontgen holografia es egy uj, a holografiaval rokon meresi modszer, a szogatlagolt rugalmas szoras tovabbfejlesztese es alkalmazasa volt. Holografia meresek segitsegevel kimutattuk, hogy a La0.7Sr0.3MnO3 kristaly fazisatalakulasanal nem lep fel statikus Jahn-Teller torzulas, ahogy korabban felteteleztek. Kiserleti adatokbol megmutattuk, hogy a szogatlagolt szoras eredmenyekent kapott kep ugyanazt az informaciot hordozza, mint a hagyomanyos egykristaly diffrakcio soran egyenkent osszegyűjtott intenzitas adatok. Megvalositottunk egy ujfajta elektron holografia merest egy erre a celra atepitett pasztazo elektron mikroszkop segitsegevel. Eredmenyeket ertunk el a holografikus es diffrakcios kiertekelesi modszerek tovabbfejlesztese teren. Kidolgoztunk egy eljarast a kis intenzitasu szoraskepek osztalyozasar...
Kossel lines are formed when radiation from point x-ray sources inside a single crystal are diffr... more Kossel lines are formed when radiation from point x-ray sources inside a single crystal are diffracted by the crystal itself. In principle, Kossel line patterns contain full information on the crystalline structure: phase and magnitude of the structure factors. The phase is coded into the profile of the lines. Although this was known for a long time, experimental realization has not been presented. In this work we demonstrate experimentally that phases can be directly determined from the profile of the Kossel lines. These measurements are interesting not only theoretically, but they would facilitate structure solution of samples within extreme conditions, such as high pressure, high and low temperatures, high magnetic fields and extremely short times. The parallel measurement of many diffraction lines on a stationary sample will allow a more efficient use of the new generation of x-ray sources the X-ray free electron lasers (XFELs). Traditionally, the atomic order in crystalline substances is determined by x-ray diffraction. Measuring diffraction peaks, we obtain the magnitude of the scattered waves, but the phase information is lost. However, for direct structure determination both the magnitude and the phase of the structure factors should be known. In practice, the loss of phase information is compensated by additional knowledge, such as atomicity, positivity of electron density, known part of the structure, composition, etc. Clever algorithms, like direct 1 , Patterson 2 , dual space 3 methods, have been developed to incorporate and use our extra knowledge to solve the structure. Nevertheless, from time to time scientists tried to work out methods that allow experimental determination of the phase. The reason of this "quest" is that the knowledge of phase would greatly facilitate structure solution, especially in the case of non-centrosymmetric crystals. The best known approach is the controlled variation of the structure factor by various methods 4-7. However, in this case special sample must be prepared, which limits applicability. Another approach is the three-beam diffraction, where three reflections are simultaneously excited 8,9. Although it was shown that this method works, the practical application is not widespread, due to experimental difficulties. Another possibility is atomic resolution holography using inside sources or detectors 10-12. This method can give the local atomic arrangement in orientationally ordered samples by a direct transformation of the holographic pattern which contains the phase. However, the measurement of x-ray holograms are technically complicated, time consuming and only relatively simple structures (10-100 atoms) can be determined. Hutton, Trammell and Hannon 13 and in an independent work Stephan et al. 14 suggested the use of Kossel line patterns as source of phase information of diffraction peaks produced by inside x-ray sources. Hutton and co-workers based their method on the analysis of the fine structure of individual Kossel lines. They gave a theoretical prediction for the angular dependence of the Kossel line profile. They showed that in the Bragg case and in special conditions 13 the line shape strongly depends on the phase of the structure factor (see Supplementary Movie 1). Although they described the necessary experimental conditions in detail, there has been no experimental work measuring a Kossel pattern (i.e. many Kossel lines in parallel) and determine the fine structure of all lines, so far. There has been a pioneering experiment 15 , in which the fine structure of a single Kossel line was measured, and its phase was determined, within very special conditions. The reason, why these type of measurements are scarce is the technical difficulties (see Supplementary Information, "Design Considerations of the Experimental Setup" and Ref. 16). In this paper we present experimental evidence for the direct determination of the phase of structure factors from the fine structure of measured Kossel lines. Further, we show that the special conditions given in Refs 13,15 can be relaxed, leading to wider applicability. We also discuss the unique possibilities given by the Kossel technique, i.e. obtaining structural data on a steady sample at extreme conditions such as
Solid state amorphization of vacuum evaporated multilayers (ML) were examined on samples with an ... more Solid state amorphization of vacuum evaporated multilayers (ML) were examined on samples with an overalI composition Fe45B55 and Fe layer thickness ranging from 1.5 to 10 nm. The samples were examined by parallel beam X-ray diffraction and by Mossbauer spectroscopy (MS). A 3 nm thick amorphous interface is observed in the as-received samples independently from the thickness of the bee-Fe layer. MS results indicate a broad concentration distribution in this amorphous interface. The thickness of the amorphous layer can be increased by heat treatments below 600 K at least up to 6 nm. INTRODUCTION Although solid state amorphization in the Fe-B system by mechanical alloying was reported by several groups [1,2,3,4] the diffusion amorphization of ML samples seemed to be unsuccessful according to the very few published results [5,6]. In order to investigate the details of the diffusion process and the propelties of the interface between the layers we prepared a series of samples with different Fe layer thicknesses starting from 1.5 run. The Fe-B system is a very well known model system of studies on amorphous alloys and amorphous phase formation by rapid quenching from the liquid as well as crystallization properties are extensi vely studied [7]. The amorphous phase can be prepared in a wide concentration range (from 12 to 90 at% B) by vacuum coevaporation or sputtering. There are only a few crystalline phases (FeB, Fe2B and Fe3B) which cannot support appreciable off-stochiometry. The MS parameters -isomer shift (IS), quadrupole splitting (QS) and hyperfine field (HF)strongly depend on the B concentration of the amorphous phase [8,9] and this way they make possible a consistent estimation of the unknown composition. All these properties make it an ideal system to study the validity of free energy considerations in predicting the concentration range of amorphous phase formation by solid state diffusion. This was calculated to be 32-47 at % B for the Fe-B system [10]. EXPERIMENTAL Multilayered samples with an overall composition Fe45B55 were evapntated either to aluminium foil or Si single crystal substrate in a vacuum of 10-7 Pa with an evaporation rate approx. 0.1 nm/s. The sample holder was cooled by liquid nitrogen during evaporation. The substrate was first covered with 30 nm boron to prevent contamination from the substrate and the topmost layer was boron, as well, of 5 11m width. Samples with 1.5, 2.5, 3.5 and 10 nm Fe layer thickness were prepared with appropriate B layer thickness to get an Fe45B55 overall composition. The layer thickness was controlled by a quartz oscillator. Due to the geometry of the evaporation chamber there is a O. I nm variation of the layer thickness within the sample. The total thickness of the samples was about 200 nm. Heat treatments were also made in the high vacuum evaporation chamber. Parallel beam X-ray diffraction was carried out at the Brookhaven National Synchrotron Light Source X3B I beam line. The 0.11467 nm wavelength was selected by a Si (lll) channel cut monochromator. The sample was mounted on a two circle goniometer. The diffracted beam was detected by a scintillation counter after a Ge single crystal analyzer. This arrangement allowed measurements from 0.8 degree with a 0.002 degree resolution. Fe57 Mossbauer spectroscopy (MS) was made on a standard constant acceleration spectrometer. Samples on the Al substrate were folded up and were measured in transmission geometry whereas samples evaporated on Si single crystal were measured by conversion electron Mossbauer spectroscopy (CEMS). The 776 Mechanically Alloyed and Nanocrystalline Materials helium temperature measurements were made on the Al substrate samples in a Janis cryostat equipped with a superconducting magnet. RESULTS and DISCUSSION The quality of the evaporated multilayers was checked on a few selected samples by X-ray diffraction at small angles corresponding to the layer periodicity. Fig. 1 shows that the multilayer periodicities Fig. 2. Samples on Al substrate had broader diffraction peaks than those on Si substrate. The coherence length calculated from the width of the diffraction peaks ranged from 40 to 75 nm in case of the samples on Al substrates. Side peaks originating from the total thickness of the samples appeared only in case of the samples evaporated on the Si substrate and the separation of these peaks agrees with the 200 nm total thickness.
Uploads
Papers by Gyula Faigel