Applying grazing incidence X-ray reflectometry (XRR) to characterising nanofilms on mica

Molecularly smooth mica has hitherto not been widely used as a substrate for the X-ray reflectometry (XRR) technique. That is largely due to the difficulty of achieving flatness over a sufficiently large area of mica. Here we show that this difficulty can be overcome by slightly bending the mica substrate over an underlying cylinder; the enhanced rigidity of the bent mica sheet along the axis of the cylinder provides sufficient flatness along this axis for XRR measurements. To test this method, we have employed it to characterise three types of nanofilms on mica in air: (A) Cr-Au thin films; (B) a surface-grown zwitterionic polymer brush; and (C) a Langmuir-Blodgett (LB) phospholipid monolayer, using a table-top X-ray reflectometer. Fitting the obtained reflectivity curves with the standard Parratt algorithm allows us to extract the structural information of the nanofilms (both thickness and apparent roughness). Our simple method points to how XRR may be exploited as a useful characterisation tool for nanofilms on mica.     

X-ray induced fluorescence spectrometry at grazing incidence for quantitative surface and layer analysis

Summary Single layers and layer systems on diverse substrates were measured by Total Reflection X-Ray Fluorescence (TXRF) spectrometry. The angular dependence of the fluorescence intensities at grazing incidence allows the elemental composition, density and thickness of the layers to be evaluated using model calculations.     

Total reflection X-ray fluorescence and grazing incidence X-ray spectrometry — Tools for micro- and surface analysis. A review

A review of Total Reflection X-ray Spectrometry and related methods covering literature of four decades is presented. History, theory, instrumentation, sample preparation, and applications are summarized and some examples are given. New developments and trends are discussed with respect to emerging nano-technologies in all fields of sciences.     

Depth-profiling of vertical sidewall nanolayers on structured wafers by grazing incidence X-ray flourescence

The Physikalisch-Technische Bundesanstalt (PTB), Germany's national metrology institute, developed an alignment strategy to specify elemental depth profiling in vertical sidewall layers on structured wafers. For this purpose, PTB's irradiation chamber for 200 mm and 300 mm silicon wafers was used to combine total-reflection X-ray fluorescence (TXRF) and grazing incidence XRF (GIXRF) techniques by employing monochromatized undulator radiation of the BESSY II electron storage ring. 3-D test structures were fabricated to develop an optimal alignment strategy allowing for depth profiling in such nanolayers. The test structures consisted of silicon bars with widths/spacings either in the μm or in the nm range. In order to be able to differentiate the sidewalls more easily from the remainder of the structures, they were provided with an additional silicon nitride layer. Four structure types of different bar width and density parameters on two 200 mm silicon wafers were investigated. The alignment procedure developed in the present work consists of three main steps and allows for distinct excitation of multiple sidewalls of one kind. Information about depth-dependent sidewall contamination, layer thickness and composition can be obtained by this approach. First results obtained on these test structures demonstrate the application potential of this new technique. In principle, depth-dependent chemical speciation should also be possible using GIXRF in combination with near edge absorption X-ray fine structure (NEXAFS).     

Applicability of a cut-off reflector for grazing incidence X-ray fluorescence analysis

The applicability of a cut-off reflector, instead of the commonly used multilayer reflector, for grazing incidence X-ray fluorescence (GI-XRF) analysis is demonstrated. Owing to the precise angular adjustment possible in the total reflection X-ray fluorescence (TXRF) spectrometer developed in house, it is possible to adjust the cut-off reflector so as to pass all X-ray energies up to Cu-K_α, eliminating Cu-K_β and higher X-ray energies emitted from a Cu target X-ray generator. The advantage of this technique is that one gets a higher flux of Cu-K_α radiation (>98%) compared to 80–90% from a good quality multilayer optics. Moreover, the same cut-off reflector, used at different grazing angles, serves the purpose for different primary beam energies. The suitability of such an arrangement for GI-XRF analysis for surface characterization has been demonstrated by analyzing a 50 ng aqueous residue of Fe on top of a float glass substrate. The GI-XRF results thus obtained are compared with those obtained using a multilayer monochromator in the primary beam as well as with theoretical calculations.     

Observation of zinc phthalocyanine aggregates on a water surface using grazing incidence X-ray scattering

Reported here are the structural properties of a zinc 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine Langmuir monolayer on a water surface under progressive lateral compression investigated by grazing incidence X-ray scattering. Grazing incidence diffuse X-ray scattering out of the specular plane (GIXOS) is exploited to determine specular reflectivity-like information where the phase change of flat-lying molecules on the surface to edge-standing molecules perpendicular to the surface is directly observed. Furthermore, grazing incident X-ray diffraction (GIXD) is used to investigate the in-plane ordering of the system where it has been found that in the high-density state (approximately 0.35 nm2 per molecule) the system can be considered to be a monolayer consisting of arrays of side-by-side lying cofacially aggregated cylindrical rodlike entities.     

Determination of CoSi2 self-aligned nanostructures with grazing incidence X-ray absorption spectroscopy

Self-aligned nanostructures (SAN) made by reacting Co nanoparticles with crystalline Si substrates at high temperatures were studied with grazing incidence X-ray absorption spectroscopy (GI-XAS). The results from extended X-ray absorption fine structure (EXAFS) analysis and X-ray absorption near-edge spectroscopy (XANES) were used to identify SAN as crystalline CoSi2. Theoretical calculations of EXAFS and XANES spectra of several crystalline cobalt silicides were performed with the FEFF8 package. On the basis of these studies, the SAN samples were determined to contain nearly pure CoSi2.     

A study of cadmium sulfide nanocrystalline films by grazing incidence X-ray diffraction

Thin cadmium sulfide films were prepared on a monocrystalline-crystal silicon substrate by chemical deposition from aqueous solutions. Grazing incidence X-ray diffraction revealed that the cadmium sulfide films are comprised of nanocrystal particles, with 80% of the particles having a size of 5 ± 1 nm. Some nanocrystals have a wurtzite structure, while others, a sphalerite one. The presence of cubic phase in the films is indicative of a nonequilibrium state of the nanocrystalline films. Thirty minutes after the onset of the formation of cadmium sulfide, the size and crystal structure of the constituent particles of the film become independent of the deposition time—only the film thickness increases. In addition, the initial stage of the formation of the cadmium sulfide film is accompanied by the deposition of cadmium hydroxide Cd(OH)₂.     

Phase transition of alkylsilane monolayers studied by temperature-dependent grazing incidence X-ray diffraction

The phase transition of organosilane monolayers on Si-wafer substrate surfaces prepared from octadecyltrichlorosilane (OTS) or docosyltrichlorosilane (DOTS) was investigated on the basis of grazing incidence X-ray diffraction (GIXD) at various temperatures. The OTS monolayer was prepared by a chemisorption method. The DOTS monolayer was prepared by a water-cast method (DOTS). The GIXD measurement clarified that the OTS monolayer also changed from hexagonal phase to amorphous state above a melting point of otadecyl groups. The GIXD measurements also clarified that the molecular aggregation state of the DOTS monolayer changes from an anisotropic phase to an isotropic phase with an increase in temperature. An estimated linear thermal expansion coefficient of the lattice lengths of a and b of the DOTS monolayer in the rectangular crystalline state assigned a similar value to those of bulk polyethylene with an orthorhombic crystalline lattice. The setting angle of the ab plane of the rectangular DOTS monolayer also showed similar behavior to that of the ab plane of bulk polyethylene.     

Analysis of crystalline phases in airborne particulates by grazing incidence X-ray diffractometry

Amounts of crystalline phases of airborne particulates collected on a silicon wafer (10 x 10 mm) using a high-volume air sampler were analyzed by grazing incidence X-ray diffractometry (GIXD). Airborne particulates were classified into five size ranges (1.09-10.5 microm) with a cascade impactor attached on the sampling ports of the high-volume air sampler. GIXD was used throughout this analysis to obtain better sensitivity for small amounts of airborne particulates on the silicon wafer. Calibration standards on the silicon wafer for the diffractometric determination were prepared by the suspension droplet method of the crystalline standards dispersed in cyclohexane. Analytical lines were (020) for gypsum, (101) for quartz, (104) for calcite, (200) for halite, and (110) for sal ammoniac. The sample and the calibrating standards were heated at 350 degrees C for 2 h to avoid mutual interference with gypsum (041 and 221) when calcite and halite were determined. The GIXD method enables us to determine 0.23-13.2 microg of gypsum, quartz, calcite, halite and sal ammoniac in 0.110-0.233 mg of airborne particulates on the silicon wafer.     

Analysis methods in neutron and X-ray reflectometry

Reflectivity analysis has focused on two key areas; overcoming the phase problem and achieving reliable scattering length density profiles using modelling methods. Significant recent advances are the application of Bayes' theorem, the use of a genetic algorithm and the exploitation of magnetic reference layers and anomalous reflection.     

Study of metallic components of historical organ pipes using synchrotron radiation X-ray microfluorescence imaging and grazing incidence X-ray diffraction

A comparative study of the composition and microstructure of two different brass alloys from reed pipes, one from a Spanish baroque organ and the other from a modern one, was carried out. This study allowed us to determine the procedure followed to produce the brass used to make ancient reed pipes. Moreover the distribution and correlation of lead and other trace elements present into the main component of the brass, the copper and zinc phases, of the historical tongues and shallots were established. This chemical composition was compared with that of a tongue from a twentieth-century organ. The whole study was accomplished using a combination of laboratory and synchrotron radiation techniques. X-ray fluorescence was the technique used to obtain elemental and chemical imaging of the main phases and the trace elements at a sub-micrometer scale.     

Supported particle track etched polyimide membranes: a grazing incidence small-angle X-ray scattering study

Particle track etched polyimide membranes on silicon substrates covered with a native oxide layer are investigated. Preparation steps similar to the common classical particle track etched membrane production, giving rise to free-standing membranes, are successfully applied to the supported membranes. Polyimide films are used as a starting material for a template preparation based on high energy ion irradiation. The film/membrane structure is probed at different length scales by grazing incidence small-angle X-ray scattering at each individual preparation step. In addition, characterization with atomic force microscopy, variable-angle spectroscopic ellipsometry, Fourier transform infrared transmission, and attenuated total reflection spectroscopy is performed. An amount of 6 +/- 1 vol % pores inside the polyimide film is detected. The pores are oriented perpendicular to the substrate surface and have a conical shape, yielding a slightly reduced pore size at the substrate/film interface.     

Study of surface oxidation of iron foils by grazing incidence electron-induced X-ray emission spectroscopy

Surface oxidation of metallic iron was studied by grazing incidence electron-induced X-ray emission spectroscopy. We have shown the feasibility of the quantitative chemical-state analysis in the nanometer depth range on the basis of the results by Monte Carlo simulations in the grazing incidence setup. It is also found that the self-absorption effect is not negligible in the nanometer depth range.     

Direct observation of liquid crystal phases under nanoconfinement: A grazing incidence X-ray diffraction study

We have controlled the molecular orientation of nematic and smectic A liquid crystal (LC) phases in a porous anodic aluminium oxide (AAO) film, in which the pore diameter was varied from 20 nm to 100 nm. Surface anchoring to induce planar and homeotropic molecular arrangement was controlled by chemical modification of the AAO inner surface. Direct observation of the molecular orientation of LC phases was performed using grazing incidence X-ray diffraction technique, showing in-plane and out-of-plane molecular orientation, and the corresponding layer orientation. The systematic investigation of LC phases under nanoconfinement will be useful to design various kinds of physicochemical environments to control the orientation of other soft matters.     

X-ray Cherenkov radiation under conditions of grazing incidence of relativistic electrons onto a target surface

X-ray Cherenkov radiation in the vicinity of the photoabsorption edge of a target is considered in this work. A possibility of substantial increase in the yield of emitted photons under conditions of grazing incidence of emitted electrons onto the target surface is shown. We discuss peculiarities in the process of X-ray Cherenkov radiation from a multilayer nanostructure as well as possibilities of focusing emitted X-rays with the use of grazing-angle optics.     

Combining imaging ellipsometry and grazing incidence small angle X-ray scattering for in situ characterization of polymer nanostructures

A combination of microbeam grazing incidence small angle X-ray scattering (μGISAXS) and imaging ellipsometry is introduced as a new versatile tool for the characterization of nanostructures. μGISAXS provides a local lateral and depth-sensitive structural characterization, and imaging ellipsometry adds the position-sensitive determination of the three-dimensional morphology in terms of thickness, roughness, refractive index, and extinction coefficient. Together μGISAXS and imaging ellipsometry enable a complete characterization of structure and morphology. On the basis of an example of buildup of nanostructures from monodisperse colloidal polystyrene nanospheres on a rough solid support, the scope of this new combination is demonstrated. Roughness is introduced by a dewetting structure of a diblock copolymer film with one block being compatible with the colloidal nanoparticles and one block being incompatible. To demonstrate the potential for kinetic investigations, μGISAXS and imaging ellipsometry are applied to probe the drying process of an aqueous dispersion of nanospheres on such a type of rough substrate.     

X-ray and neutron reflectometry for the investigation of polymer diffusion

Summary X-ray and neutron reflectometry are novel tools for the investigation of polymer interfaces. For this method we demonstrate the high resolution on the vertical length scale which is normally better than 1 nm and the ideal applicability for the analysis of polymer diffusion by showing both simulations and measurements. The limits and difficulties are discussed. We look at the broadening of the interface between two polystyrene films during interdiffusion slightly above the glass transition temperature. For short times we prove two distinct time regimes for polymer diffusion. This is achieved with a double layer system consisting of a deuterated and a protonated polystyrene film. The roughness of the individual films is well below 1 nm.     

X-ray and neutron reflectometry study of glow-discharge plasma polymer films

Radio-frequency glow-discharge plasma polymer thin films of allylamine (AA) and hexamethyldisiloxane (HMDSO) were prepared on silicon wafers and analyzed by a combination of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray reflectometry (XRR), and neutron reflectometry (NR). AFM and XRR measurements revealed uniform, smooth, defect-free films of 20-30 nm thickness. XPS measurements gave compositional data on all elements in the films with the exception of hydrogen. In combination with XRR and NR, the film composition and mass densities (1.46 and 1.09 g cm(-)(3) for AA and HMDSO, respectively) were estimated. Further NR measurements were conducted with the AA and HMDSO films in contact with water at neutral pH. Three different H(2)O/D(2)O mixtures were used to vary the contrast between the aqueous phase and the polymer. The amount of water penetrating the film, as well as the number of labile protons present, was determined. The AA film in contact with water was found to swell by approximately 5%, contain approximately 3% water, and have approximately 24% labile protons. The HDMSO polymer was found to have approximately 6% labile protons, no thickness increase when in contact with water, and essentially no solvent penetration into the film. The difference in the degree of proton exchange within the films was attributed to the substantially different surface and bulk chemistries of the two films.