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ABSTRACT: We report on grazing-incidence small-angle x-ray scattering (GISAXS) study of 3D nanoparticle arrays prepared by two different methods from colloidal solutions-layer-by-layer Langmuir-Schaefer deposition and spontaneous self-assembling during the solvent evaporation. GISAXS results are evaluated within the distorted wave Born approximation (DWBA) considering the multiple scattering effects and employing a simplified multilayer model to reduce the computing time. In the model, particular layers are represented by nanoparticle chains where the positions of individual nanoparticles are generated following a model of cumulative disorder. The nanoparticle size dispersion is considered as well. Three model cases are distinguished-no shift between the neighboring chains (AA stacking), a shift equal to half of the mean interparticle distance (AB stacking) and random shift between the chains. The first two cases correspond to vertically correlated nanoparticle positions across different chains. A comparison of the experimental GISAXS patterns with the model cases enabled us to distinguish important differences between the 3D arrays prepared by the two methods. In particular, laterally ordered layers without vertical correlation of the nanoparticle positions were found in the nanoparticle multilayers prepared by the Langmuir-Schaefer method. On the other hand, the solvent evaporation under particular conditions produced highly ordered 3D nanoparticle assemblies where both laterally and vertically correlated nanoparticle positions were found.
Nanotechnology 02/2012; 23(4):045704. · 3.98 Impact Factor
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ABSTRACT: We have developed a scanning magneto-optical Kerr microscope dedicated to localization and measurement of the in-plane magnetization of ultra-thin layered magnetic nanostructures with high sensitivity and signal-to-noise ratio. The novel light detection scheme is based on a differential photodetector with automatic common mode noise rejection system with a high noise suppression up to 50 dB. The sensitivity of the developed detection scheme was tested by measurement of a single Co layer and a giant magnetoresistance (GMR) multilayer stack. The spatial resolution of the Kerr microscope was demonstrated by mapping an isolated 5×5 μm spin-valve pillar.
The Review of scientific instruments 08/2011; 82(8):083706. · 1.52 Impact Factor
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P Siffalovic,
L Chitu,
K Vegso,
E Majkova,
M Jergel,
M Weis, S Luby,
I Capek,
J Keckes,
G A Maier,
A Satka,
J Perlich,
S V Roth
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ABSTRACT: An in situ small-angle x-ray scattering study of the nanoparticle displacement in a self-assembled monolayer as a function of a supporting membrane strain is presented. The average nanoparticle spacing is 6.7 nm in the unstrained state and increases in the applied force direction, following linearly the membrane strain which reaches the maximum value of 11%. The experimental results suggest a continuous mutual shift of the nanoparticles and their gradual separation with the growing stress rather than nanoparticle islands formation. No measurable shift of the nanoparticles was observed in the direction perpendicular to the applied stress.
Nanotechnology 09/2010; 21(38):385702. · 3.98 Impact Factor
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ABSTRACT: The spontaneous self-assembly process of superparamagnetic nanoparticles in a fast-drying colloidal drop is observed in real time. The grazing-incidence small-angle X-ray scattering (GISAXS) technique is employed for an in situ tracking of the reciprocal space, with a 3 ms delay time between subsequent frames delivered by a new generation of X-ray cameras. A focused synchrotron beam and sophisticated sample oscillations make it possible to relate the dynamic reciprocal to direct space features and to localize the self-assembly. In particular, no nanoparticle ordering is found inside the evaporating drop and near-surface region down to a drop thickness of 90 microm. Scanning through the shrinking drop-contact line indicates the start of self-assembly near the drop three-phase interface, in accord with theoretical predictions. The results obtained have direct implications for establishing the self-assembly process as a routine technological step in the preparation of new nanostructures.
Small 12/2008; 4(12):2222-8. · 8.35 Impact Factor
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ABSTRACT: A thorough study of x-ray diffuse scattering from the spin valve structures suitable for current induced magnetization switching is presented. We used complete reciprocal space maps of diffusely scattered x rays to show the effect of bottom Au electrode on the morphology of buried spin valve interfaces. The thickness and roughness of each layer, as well as vertical and lateral roughness correlation lengths, were obtained. The impact of interfaces morphology on the magnetic properties, especially on the increase of spin valve coercivity, was measured and simulated within the frame of Néel magnetostatic coupling model based on the parameters from the x-ray diffuse scattering data. Measurement of x-ray diffuse scattering presents a rapid and nondestructive technique for in-depth and self-contained analysis of spin valve layers and interfaces.
Journal of Applied Physics 02/2007; 101(3):033538-033538-5. · 2.17 Impact Factor
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ABSTRACT: Magnetic films were prepared by pulsed laser ablation of amorphous magnetic ribbons (composition Co67Cr7Fe4Si8B14, Fe73.5Nb3Cu1Si13.5B9, and Fe40Ni40B20) and permalloy foils (composition FexNi1-x with x=22,50). Depositions were performed in a vacuum of (2–4)10-5Pa by KrF excimer laser pulses at fluences of between 2 and 7Jcm2. Films were deposited on oxidized silicon wafers, placed 60–80mm apart from the target. Films were analyzed by SEM, XRD, RBS, and EDS. Ferromagnetic resonance (FMR) spectra were studied at GHz frequencies. From RBS and EDS measurements it follows that the stoichiometry of the targets is preserved in the films to a large extent. The films deposited from amorphous targets remain amorphous. From FMR studies it follows that Fe and Fe-Ni rich films exhibit properties close to those of bulk alloys, having very low magnetization motion damping parameter () of 7.0–7.8107rad/s, which are appropriate for fast magnetic sensors.
Applied Physics A 08/2004; 79(4):1251-1254. · 1.63 Impact Factor
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Advanced Semiconductor Devices and Microsystems, 2004. ASDAM 2004. The Fifth International Conference on; 02/2004
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Advanced Semiconductor Devices and Microsystems, 2004. ASDAM 2004. The Fifth International Conference on; 02/2004
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Y. Chushkin,
M. Ulmeanu, S. Luby,
E. Majkova,
I. Kostic,
P. Klang,
V. Holý,
Z. Bochníček,
M. Giersig,
M. Hilgendorff,
T. H. Metzger
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ABSTRACT: We studied the ordering of colloidal Co nanoparticles on various types of substrates by grazing-incidence small-angle x-ray scattering, transmission electron microscopy, and scanning electron microscopy. Particles of 5–6 nm radius were deposited by spin coating in order to obtain uniform distribution of the particles over a large surface area. Only by the grazing-incidence small angle x-ray scattering technique could the distribution of particles on a large surface area be analyzed in detail. For quantitative analysis of the spectra the distorted-wave Born approximation approach was applied. From simulations of the spectra the particle radius, the spherical shape, the mean spacing between the particles, and the type of ordering were determined. The distribution of the particles on the surface can be described by a hexagonal close-packed structure with local order. This corresponds to the transmission electron microscopy data obtained for the same type of substrate. The parameters that affect the ordering of Co nanoparticles are discussed. © 2003 American Institute of Physics.
Journal of Applied Physics 12/2003; 94(12):7743-7748. · 2.17 Impact Factor
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ABSTRACT: The sub-picosecond laser microstructuring of multilayer gratings is presented in this paper. A micromachining system operating
with a 0.5ps KrF laser at 248nm was used to etch grating structures with a groove width of 1–2μm in Mo/Si and Si/Mo multilayers.
Atomic force microscopy, scanning electron microscopy and X-ray reflectivity were used to characterize the microetched patterns.
The ω-scans around the 1st Bragg maximum show symmetric satellites up to 3rd order, with positions corresponding to the grating
period. The use of sub-picosecond laser pulses minimizes the thermally affected zone and enhances the quality of the etched
features. Short pulse laser processing is advantageous for the fabrication of high spatial resolution microstructures required
in X-ray optics.
Applied Physics A 01/2003; 76(5):763-766. · 1.63 Impact Factor
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ABSTRACT: The signal response in layered giant magnetoresistance (GMR) structures is studied in an external ac magnetic field at 50 Hz with an increasing amplitude swing. Co-Ag multilayers (MLs) were evaporated onto Si substrates. The thickness of Co and Ag layers was 1.2 nm and 5.5 nm, respectively. MLs with only N=2, 3, 4 periods were fabricated to expose the relative higher influence of top and bottom ferromagnetic Co layers of ML having a higher density of magnetic flux than the central layers. Experimental results are explained in terms of simulations of inhomogeneous magnetic field distribution in ML. Simulations were performed by an appropriate software tool. The results are of some relevance for the design and applications of smart magnetic GMR sensors.
Advanced Semiconductor Devices and Microsystems, 2002. The Fourth International Conference on; 11/2002
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ABSTRACT: Structural characterization of a fully etched amorphous W/Si multilayer grating with a lateral periodicity of 800 nm is performed by x-ray reflectivity in the coplanar and non-coplanar modes using a scintillation detector and a two-dimensional gas-filled detector, respectively. Three-dimensional reciprocal space constructions were used to explain the scattering features recorded in both geometries. Coplanar coherent grating truncation rods were fitted by a dynamical theory for rough gratings. Comparison of the reflectivity from the reference planar multilayer completes the study.
Journal of Physics D Applied Physics 05/2001; 34(10A):A188. · 2.54 Impact Factor
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ABSTRACT: X-ray reflectivity and diffuse scattering measurements at grazing incidence including 2 theta and omega scans were done using Cu K alpha 1 radiation on W/Si multilayers deposited obliquely at different angles and on W1-xSix/Si multilayers of different compositions. The reflectivity and omega scans were simulated by the Fresnel optical computational code and within the distorted-wave Born approximation, taking the vertical roughness correlation into account, respectively. The root-mean-square interface roughness increases by about 15% while lateral correlation length decreases by nearly one order of magnitude on increasing deposition angle of the W/Si multilayers up to 47 degrees . Simultaneously the vertical roughness correlation decreases, which is shown also by 2 theta scans. Thus rougher, less correlated interfaces and an increased tendency for agglomeration appear. No root-mean-square interface roughness change was detected for W1-xSix/Si multilayers with x up to x=0.67 while the lateral correlation length decreased by one order of magnitude, interfaces being more correlated vertically. The interfaces do not exhibit the fractal behaviour in either type of multilayer.
Journal of Physics D Applied Physics 12/1998; 28(4A):A241. · 2.54 Impact Factor
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ABSTRACT: Structural characterization of a fully etched amorphous W/Si multilayer grating with lateral periodicity 800 nm is performed by x-ray reflectivity. Grating truncation rod profiles have been calculated using a matrix modal eigenvalue approach of the dynamical theory of reflectivity by gratings which generalizes the Fresnel transmission and reflection coefficients for lateral diffraction. The interface roughness in rough gratings has been taken into account by a coherent amplitude approach which damps the generalized Fresnel coefficients. Scanning electron microscopy pictures complete the study.
Journal of Physics D Applied Physics 12/1998; 32(10A):A220. · 2.54 Impact Factor
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ABSTRACT: We present a structural study of two amorphous periodic W/Si
multilayer gratings obtained by etching the planar multilayer up to the
multilayer substrate based on scanning-electron and atomic force
microscopy observations and X-ray reflectivity measurements of coherent
grating truncation rods. Two different exposure modes to prepare resist
mask were examined to optimize the resulting grating structure. The real
structural parameters of a more perfect grating were extracted from
fitting the measured grating truncation rods. The simulations are based
on the matrix modal eigenvalue approach of the dynamical theory of
reflectivity by gratings which generalizes the Fresnel transmission and
reflection coefficients for lateral diffraction. The interface
imperfections are taken into account by the coherent amplitude approach
which averages the propagation matrices of the wave field over random
interface displacements
Advanced Semiconductor Devices and Microsystems, 1998. ASDAM '98. Second International Conference on; 11/1998
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ABSTRACT: W1−xSix/Si multilayers (MLs) (x⩽0.66) were deposited onto oxidized Si substrates, heat treated by rapid thermal (RTA) and standard furnace annealing up to 1000 °C for 30 s and 25 min, respectively, and analyzed by various x-ray techniques and Rutherford backscattering spectrometry. W1−xSix/Si MLs are more stable the higher the value of x because the driving force for interdiffusion is suppressed by the doping; the temperature for complete interdiffusion increases from 500 to 850 °C as x increases from 0 to 0.66. The as-deposited MLs were amorphous. Their thermal stability increases with increasing x. The interface roughness is independent of x but increases with increasing RTA temperature. The reflectivity of W1−xSix/Si MLs is lower than that of W/Si because of lower optical contrast. © 1997 American Institute of Physics.
Journal of Applied Physics 02/1997; 81(5):2229-2235. · 2.17 Impact Factor
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ABSTRACT: Tungsten/silicon multilayers with tungsten layers of a thickness of 1–2 nm were prepared by means of electron beam deposition. Their structure and thermal stability under rapid thermal annealing were investigated by a combination of x-ray diffraction techniques and cross-sectional transmission electron microscopy. The crystallization behavior was found to depend on the interdiffusion and mixing at the tungsten/silicon interfaces during deposition as well as during annealing. The as-deposited tungsten/silicon multilayers were amorphous and remained stable after annealing at 250 °C/40 s. Interdiffusion and crystallization occurred after annealing all samples from 500 °C/40 s up to 1000 °C/20 s. By performing the same heat treatment in the tungsten/silicon multilayers, the formation of body-centered cubic W was observed with a layer thickness ratio δW/δsi = 1, whereas tetragonal WSi2 was detected in tungsten/silicon multilayers with a layer thickness ratio of δw/δsi ∼0.25. This dependence of the crystallization products on the layer thickness ratio δw/δsi originates from the different phenomena of interdiffusion and mixing at the tungsten/silicon interfaces. The possible formation of bcc tungsten as a first stage of crystallization of tungsten-silicon amorphous phase, rich in tungsten, is discussed.
Journal of Materials Research. 09/1993; 8(10):2600 - 2607.
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ABSTRACT: Interdiffusion phenomena, thermal damage and ablation of W/Si and Si/W bilayers and multilayers under XeCl-excimer laser (=308 nm) irradiation at fluences of 0.15, 0.3 and 0.6 J/cm2 were studied. Samples were prepared by UHV e-beam evaporation onto oxidized Si. The thickness of W and Si layers and the total thickness of the structures were 1–20 nm and 40–100 nm, respectively. 1 to 300 laser pulses were directed to the same irradiation site. At 0.6 J/cm2 the samples were damaged even by a single laser pulse. At 0.3 J/cm2 WSi2 silicide formation, surface roughening and ablation were observed. The threshold for significant changes depends on the number of pulses: it was between 3–10 pulses and 10–30 pulses for bilayers with W and Si surfaces, respectively, and more than 100 pulses for multilayers with the same total thickness of tungsten. At 0.15 J/cm2 the periodicity of the multilayers was preserved. Temperature profiles in layered structures were obtained by numerical simulations. The observed differences of the resistance of various bilayers and multilayers against UV irradiation are discussed.
Applied Physics A 04/1993; 56(5):429-436. · 1.63 Impact Factor
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ABSTRACT: We report a study of the formation of tungsten silicide at the W-Si interface, induced by multipulse (up to 300 shots) XeCl excimer-laser irradiation of W(150 nm)/Si and W(500 nm)/Si samples. Laser fluences ranging from 0.6 to 1.8 J/cm2 were used. After laser treatment the samples were examined by different diagnostic techniques: Rutherford backscattering spectrometry, X-ray scattering, resistometry, and surface profilometry. Numerical computations of the evolution and depth profiles of the temperature in the samples as a consequence of a single 30 ns laser pulse were performed as well. The results indicate that it is possible to obtain a tungsten silicide layer at the W-Si interface at quite low fluences. The layer thickness increases with the number of laser pulses. Complete reaction of the 150 nm thick W film with silicon was obtained at the fluence of 1.2 J/cm2 between 30 and 100 laser pulses and at 1.5 J/cm2 after 30 laser pulses. The sheet resistance of these silicides was 5–10 . At the used fluences for the 500 nm thick W film only the onset of silicide synthesis at the W-Si interface was observed.
Applied Physics A 03/1993; 56(4):391-396. · 1.63 Impact Factor
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ABSTRACT: Titanium films 120 nm thick deposited on single-crystalline silicon (c-Si) as well as poly-Si/SiO2/c-Si substrates were subjected to Nd: glass laser irradiation. Laser fluences of 1,1.5, and 2 J/cm2 were used at the pulse duration of 30 ns. From RBS analysis it follows that on c-Si substrate titanium suicide is formed using one pulse of 1.5 J/cm2 energy density. On the substrate with surface overlayers lower fluence (1 J/cm2) was sufficient. Under these conditions the sheet resistance of the samples decreased from the initial value 5 / to 2–3 /. The smaller threshold density of energy for suicide formation in Ti/polySi/SiO2/c-Si structure is shown to be a consequence of the SiO2 underlayer, which is a poorer heat conductor than silicon. The experimental results of the suicide synthesis are in semi-quantitative accordance with the numerical computations of the temperature vs time evolution and depth temperature distribution in our samples.
Applied Physics A 01/1989; 48(6):503-507. · 1.63 Impact Factor
