X-ray Reflectivity Patterns Research Articles

Structural order and magnetic anisotropy transition in Co/Fe multilayers

Co/Fe multilayers were electron-beam evaporated in ultrahigh vacuum onto quartz substrates keeping the Co layer thickness (10 nm) constant and changing that of Fe (10–30 nm). For Fe layer thicknesses up to 24 nm, the magnetization substantially lies in the film plane and shows a uniaxial magnetic anisotropy. The coercive field measured along the easy axis is ∼10 Oe, and the x-ray reflectivity patterns show a superlattice behavior. For a Fe layer thickness equal to 30 nm, the in-plane texture strongly decreases, the coercive field increases up to ∼100 Oe, the magnetization direction forms an out-of-plane angle of ∼36° and a stripe magnetic domain structure takes place. The observed in-plane anisotropy and the changing in the magnetic order as a function of the iron layer thickness is discussed and justified, assuming that the growth of the first Co layer occurs by the nucleation of ordered zones, influencing the subsequent layer order via exchange interaction.

The fabrication of stable platinum–silicon oxide multilayers for X-ray mirrors

An investigation has been carried out to determine the conditions required for the fabrication of stable SiO 2–Pt multilayers using DC-magnetron sputtering for the Pt and RF-magnetron sputtering for the SiO 2. As a preliminary investigation, single layers of Pt on SiO 2 were analysed by X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS) to develop a model of the Pt–SiO 2 interface layer. The results indicated that a distinct interface layer develops as a Pt silicate approximately 6 Å thick. SiO 2–Pt multilayers fabricated with a period d>65 Å using pure argon as the sputtering gas, display X-ray reflectivity patterns which can be accurately characterised by a repeating bilayer model. When d<65 Å the multilayer becomes unstable upon exposure to air. Additional peaks develop in the XRR pattern which increase in magnitude with time. These peaks arise from the expansion of the SiO 2 layers in the multilayer starting from the top bilayer and gradually working through the multilayer. In the as-prepared specimens the SiO 2 layers are incompletely oxidised and have a composition SiO x ( x<2) and, on exposure to air, oxygen diffuses through the multilayer surface converting the SiO x to SiO 2. By introducing a small partial pressure of oxygen into the sputtering gas during deposition, multilayers with d<65 Å remained stable on exposure to air. Under these conditions the density of the platinum layers determined from XRR measurements was reduced by approximately 25%. XPS showed that the platinum layer contained bonded oxygen in the form of platinum oxide PtO x ( x<1). SiO 2/PtO x multilayers have been fabricated with periods down to 13 Å, but the intensity of the first order peak drops off dramatically once the thickness of the PtO x layer is less that 10–12 Å.

X-ray reflectivity and glancing-incidence diffraction from thin metallic Cr layers

Abstract The annealing effects on thin Cr layers deposited by rf sputtering are investigated by X-ray reflectivity and glancing-incidence diffraction. It is shown that annealing induces a phase segregation which dramatically changes the features of the X-ray reflectivity pattern. This study allows us to present and discuss the main features of X-ray reflectivity, which make it a powerful tool for the non-destructive analysis of thin single layers or multilayers and interfaces.

Temperature- and time-dependent investigations of cadmium stearate and uranyl stearate multilayers by means of neutron reflectivity measurements

Langmuir-Blodgett (LB) multilayers of cadmium and uranyl stearate salts, prepared by sequential transfer of deuterated and non-deuterated bilayers on a silicon support, have been investigated by neutron reflectivity measurements at the TAS8 beam line at Risø. Freshly prepared LB multilayers already show an intermixing of the bilayers which can be attributed to incomplete transfer of the monolayer from the water surface to the substrate. This becomes visible via the reduced intensity of that superlattice peak which probes the contrast in scattering length density between the deuterated and the non-deuterated monolayers. Further experiments reveal that the intermixing increases as a function of temperature. The kinetics of this process have been investigated by combined temperature- and time-dependent X-ray and neutron reflectivity measurements. For annealing temperatures below 55 °C cadmium stearate films show a dramatic decrease in intensities of the superstructure peaks, indicating an increase of intermixing. Taking into account the fact that the X-ray reflectivity patterns remain nearly unchanged, this intermixing is interpreted as discrete hopping of the fatty acid salt molecules between various bilayer sites. Its time constant decreases as a function of temperature and vanishes close to the melting point of the stearic acid phase at about 75 °C. The Arrhenius-like activation energy for the hopping process was estimated to be about 1.9 eV. For uranyl stearate samples we already observed complete intermixing at about 40 °C, which is interpreted in terms of the reduced lateral interaction among the hydrocarbon chains induced by the bigger counterions.

Structural Parameters of Multilayers as Deduced from X-ray Specular Reflectivity: Effect of Statistical Thickness Fluctuations

An analysis is given of the way in which thickness fluctuations in a multilayer can affect the grazing incidence X-ray reflectivity pattern. It is shown that peak shifts, broadening and height variations can result. They alter in a predictable way the parameter values derived from a fit with an ideal lattice. A principle for designed Bragg reflectors is also proposed.

Structural ordering in InGaAs/GaAs superlattices

Various x-ray techniques have been applied to a study of semiconductor superlattices consisting of 100-period of InxGa1−xAs (15 Å)/GaAs (100 Å) grown on GaAs(100) substrates by molecular beam epitaxy. Structural parameters pertaining to the morphology of interfaces and thickness variations were obtained. The interfaces in these superlattices are found to be highly correlated, and the layers all show a high degree of crystallinity. Splittings in the x-ray reflectivity and diffraction patterns in one of the samples provide clear evidence for pronounced thickness modulation, and direct comparison of the diffraction satellite peaks with results of high resolution transmission electron microscopy indicates that there exists a lateral structural ordering in the [110] direction during epitaxial growth.

Structural Parameters of Multilayers from X-ray Reflectivity: an Easy-to-Handle Approach

An analytical approximation was derived for the calculation of the grazing-incidence X-ray reflectivity pattern in a defect-free multilayer. The approximation is valid in the low-reflectivity θ ranges. For k = (4πsin θ)/λ > 0.28 Å−1 (θ > 2° with Cu Kα radiation), the formula deviates by at most 1% from the rigorous matricial approach in the case of most metallic multilayers. The main advantage of the approximation is that it allows the identification of features in the reflectance pattern, from which desired structural parameters (average layer thicknesses, external and internal roughness) can be estimated easily. This approach yields average structural parameters, best approximating those of a real multilayer but ignoring possible defects.

Synthesis and X-ray reflection pattern of?-eucryptite

Synthesis and X-ray reflection pattern of?-eucryptite

Bentonite deposits at Hattari, Hokkaido (II)

The Hattari bentonite deposits which are situated at the southwestern end of the Shakotan Peninsula occur in the Miocene green tuff formation. This formation in the neighborhood of the deposits is divided into the following three zones from the lower side by kinds of zeolites in the tuff: (1) Analcime zone in the northeastern part of this mining area. (2) Non-zeolite zone in the middle part. (3) Clinoptilolite zone in the southwestern part. These zones do not always correspond with the subdivision of the strata. The bentonite deposits are found in the clinoptilolite zone and the ore bodies form irregularly lenticular beds. The original rock of the bentonite is rhyolitic vitric tuff. The main mineral compositions of the ore are montmorillonite, zeolite, α-cristobalite, opal, quartz, plagioclase and biotite. Microscopically, montmorillonite fills up the interspaces of glass fragments, and is also formed in these marginal zones. Most of zeolite, α-cristobalite and opal are probably included in glass fragments. X-ray investigation shows that bentonite in water is mechanically divided into montmorillonite group and zeolite one which is identified as clinoptilolite. The differential thermal analysis curve of the material shows no remarkable thermal peak up to 1, 000°C. X-ray powder reflections after heating at 100°C, ......, 800°C, 850°C, 900°C and 1, 000°C and effects of the treatments with HCl against the material do not completely agree with the already known data of clinoptilolite. The rate of swelling of the bentonite is related to the shape of 15_??_; peak of X-ray reflection pattern, and it decreases by repetition of swelling and drying. The cation-exchange capacity of the bentonite is 96 me/100gr. It is considered that the existence of the hydrothermal sulfides ore deposits in this mining area, the relation with the division of the strata and the zonal arrangement of zeolities, the mode of occurrence of the bentonite, and the silicification and adulariazation of the country rocks show that the Hattari bentonite deposits might be formed by a diagenesis and a hydrothermal alteration of vitric tuff.

Bentonite deposits at Hattari, Hokkaido (I)

The Hattari bentonite deposits which are situated at the southwestern end of the Shakotan Peninsula occur in the Miocene green tuff formation. This formation in the neighborhood of the deposits is divided into the following three zones from the lower side by kinds of zeolites in the tuff: (1) Analcime zone in the northeastern part of this mining area. (2) Non-zeolite zone in the middle part. (3) Clinoptilolite zone in the southwestern part. These zones do not always correspond with the subdivision of the strata. The bentonite deposits are found in the clinoptilolite zone and the ore bodies form irregularly lenticular beds. The original rock of the bentonite is rhyolitic vitric tuff. The main mineral compositions of the ore are montmorillonite, zeolite, α-cristobalite, opal, quartz, plagioclase and biotite. Microscopically, montmorillonite fills up the interspaces of glass fragments, and is also formed in these marginal zones. Most of zeolite, α-cristobalite and opal are probably included in glass fragments. X-ray investigation shows that bentonite in water is mechanically divided into montmorillonite group and zeolite one which is identified as clinoptilolite. The differential thermal analysis curve of the material shows no remarkable thermal peak up to 1, 000°C. X-ray powder reflections after heating at 100°C, ......, 800°C, 850°C, 900°C and 1, 000°C and effects of the treatments with HCl against the material do not completely agree with the already known data of clinoptilolite. The rate of swelling of the bentonite is related to the shape of 15_??_; peak of X-ray reflection pattern, and it decreases by repetition of swelling and drying. The cation-exchange capacity of the bentonite is 96 me/100gr. It is considered that the existence of the hydrothermal sulfides ore deposits in this mining area, the relation with the division of the strata and the zonal arrangement of zeolities, the mode of occurrence of the bentonite, and the silicification and adulariazation of the country rocks show that the Hattari bentonite deposits might be formed by a diagenesis and a hydrothermal alteration of vitric tuff.