Grazing-incidence Small-angle X-ray Scattering Measurements Research Articles

Mechanistic insights into the colloidal assembly of mesoporous silica using in-operando cross-scale X-ray scattering and spectroscopic measurements

Advancing a mechanistic understanding of the colloidal to solid-phase transformations of silica allows us to tune these meso-scale structures. In this study, we probe the structural transformations associated with the formation of mesoporous silica particles, SBA-15 using in-operando Small Angle X-ray Scattering (SAXS) and Grazing Incidence-Small Angle X-ray Scattering (GI-SAXS). The chemical transformations associated with the hydrolysis and condensation of silica particles is investigated using Attenuated Total Reflection – Fourier Transform Infrared Spectroscopy (ATR-FTIR) measurements. Fast polymerization of Si-O-Si species to form mesoporous silica is noted when SBA-15 is synthesized in the presence of nitrate salts, due to the “salting-in” effect or enhanced solubility of polymers. However, aging the silica particles resulted in plate-like morphologies in the absence of the nitrate salt and spherical morphologies in the presence of nitrate salt. Early onset of nucleation of silica particles in the presence of nitrate salts was captured using GI-SAXS measurements. These studies show that the rational basis for developing new synthesis routes for accelerated kinetics or specific meso-scale structures can be informed by detailed characterization of the evolution in chemistry and meso-scale structure of these materials.

Probing Surface Morphology using X-ray Grating Interferometry

X-ray reflectometry (XRR), a surface-sensitive technique widely used for characterizing surfaces, buried interfaces, thin films, and multilayers, enables determination of the electron density distribution perpendicular to a well-defined surface specularly reflecting X-rays. However, the electron density distribution parallel to the surface cannot be determined from an X-ray reflectivity curve. The electron density correlation in the lateral direction is usually probed by measuring the grazing-incidence small-angle X-ray scattering (GISAXS). GISAXS measurement, however, typically requires using a collimated X-ray point beam to distinguish the GISAXS from the specularly reflected X-rays, and so the sample must be scanned in the lateral direction with the point beam to investigate variations in the surface and interface morphology for a region larger than the size of the beam. In this paper, we report a new approach based on X-ray grating interferometry: an X-ray sheet beam is used instead of an X-ray point beam. A method using this approach can simultaneously provide one-dimensional real-space images of X-ray reflectivity, surface curvature, and ‘dark-field’ contrast with a field-of-view of more than a few millimetres. As a demonstration, a sample having a 400 nm line and space SiO2 pattern with a depth of 10 nm on its surface was used, and the dark-field contrast due to the unresolved line and space structure, creating GISAXS in the lateral direction, was successfully observed. Quantitative analysis of these contrasts provided the real-space distribution of the structural parameters for a simple model of the grating structure. Our study paves the way to a new approach to structure analysis, providing a quantitative way to investigate real-space variations in surface and interface morphology through wavefront analysis.

Distortion analysis of crystalline and locally quasicrystalline 2D photonic structures with grazing-incidence small-angle X-ray scattering

In this study, grazing-incidence small-angle X-ray scattering (GISAXS) is used to collect statistical information on dimensional parameters in an area of 20 × 15 mm on photonic structures produced by nanoimprint lithography. The photonic structures are composed of crystalline and locally quasicrystalline two-dimensional patterns with structure sizes between about 100 nm and 10 µm to enable broadband visible light absorption for use in solar-energy harvesting. These first GISAXS measurements on locally quasicrystalline samples demonstrate that GISAXS is capable of showing the locally quasicrystalline nature of the samples while at the same time revealing the long-range periodicity introduced by the lattice design. The scattering is described qualitatively in the framework of the distorted-wave Born approximation using a hierarchical model mirroring the sample design, which consists of a rectangular and locally quasicrystalline supercell that is repeated periodically to fill the whole surface. The nanoimprinted samples are compared with a sample manufactured using electron-beam lithography and the distortions of the periodic and locally quasiperiodic samples are quantified statistically. Owing to the high sensitivity of GISAXS to deviations from the perfect lattice, the misalignment of the crystallographic axes was measured with a resolution of 0.015°, showing distortions of up to ±0.15° in the investigated samples.

Following the Morphology Formation In Situ in Printed Active Layers for Organic Solar Cells

The device performance of organic polymer:fullerene bulk heterojunction solar cells strongly depends on the interpenetrating network of the involved donor and acceptor materials in the active layer. Since morphology formation depends on the conditions of film preparation, the final morphology varies for different deposition methods. In order to understand and optimize industrial coating processes and, therefore, the performance of the solar cells produced, a deeper understanding of structure formation is important. In situ measurements of slot‐die printed polymer:fullerene active layers are presented that reveal insights into the evolution of the structure. Polymer crystallization and ordering is monitored by in situ grazing incidence wide angle X‐ray scattering (GIWAXS), and in situ grazing incidence small‐angle X‐ray scattering (GISAXS). The development of the morphology exhibits five stages independent of the drying conditions. Two growth rates are observed, an initial slow formation of poly(3‐hexylthiophene‐2,5‐diyl) crystallites in well‐aligned edge‐on orientation followed by a rapid crystal growth. By combining the GIWAXS and GISAXS measurements, a five‐stage growth and assembly process is found and described in detail along with a proposed model of the structural evolution. The findings are an important step in tailoring the assembly process.

In Situ Study of ALD Processes Using Synchrotron-based X-ray Fluorescence and Scattering Techniques

In this paper, we present an x-ray based approach for in situ characterization during ALD processes. In a first case study the growth of HfO2 on H-terminated and oxidized Si and Ge surfaces is studied. X-ray fluorescence (XRF) is used to monitor the amount of deposited Hf atoms, while grazing incidence small angle x-ray scattering (GISAXS) provides information on the evolution of surface roughness. A second case study concerns the growth of TiO2 in a porous titania film containing ink-bottle mesopores. XRF and GISAXS measurements are used to monitor the Ti uptake and the density of the porous film, respectively.

Note: Comparison of grazing incidence small angle x-ray scattering of a titania sponge structure at the beamlines BW4 (DORIS III) and P03 (PETRA III)

Grazing incidence small angle x-ray scattering (GISAXS) is a powerful technique for morphology investigation of nanostructured thin films. GISAXS measurements at the newly installed P03 beamline at the storage ring PETRA III in Hamburg, Germany, are compared to the GISAXS data from the beamline BW4 at the storage ring DORIS III, which had been used extensively for GISAXS investigations in the past. As an example, a titania thin film sponge structure is investigated. Compared to BW4, at beamline P03 the resolution of larger structures is slightly improved and a higher incident flux leads to a factor of 750 in scattered intensity. Therefore, the acquisition time in GISAXS geometry is reduced significantly at beamline P03.

Preparation of High Refractive index Materials using ZrO<sub>2</sub> Nanoparticles and Glyceryl-<i>N</i>-(2-methacryloyloxyethyl)urethane and Its Properties

We established the metal-oxide nanoparticles dispersion technology using Glyceryl-N-(2-methacryloyloxyethyl) urethane (GLYMOU®) with high affinity for the inorganic materials, such as zirconia (ZrO2, titania (TiO2, and silica (SiO2. The high refractive index optical films were prepared by using ZrO2nanoparticles (grain size: 3 nm) and GLYMOU®. The films were colorless and transparent. As a ZrO2 concentration increased up to 80 wt%, refractive index showed 1.70 at wavelength of 589 nm. Solid-state NMR and first density functional theory (DFT) study confirmed that GLYMOU® was strongly coordinated to the ZrO2 surfaces with hydroxyl groups and urethane bond. The dispersion state of nanoparticles in the hybrid films was investigated by combination of grazing incidence small angle X-ray scattering (GISAXS) and transmission electron microscope (TEM). GISAXS measurements and TEM observations, ZrO2 nanoparticles were finely dispersed in the poly-GLYMOU® matrices. [DOI: 10.1380/ejssnt.2012.85]

Debye–Scherrer rings from block copolymer films with powder-like order

The powder-like orientation of lamellar domains in thin films of the diblock copolymer polystyrene-block-poly(methyl methacrylate) is investigated using grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence small-angle neutron scattering (GISANS). Conventional monochromatic GISANS and GISAXS measurements are compared with neutron time-of-flight GISANS. For angles of incidence and exit larger than the critical angle of total external reflection of the polymer, Debye–Scherrer rings are observed. The position of the Debye–Scherrer rings is described quantitatively based on a reduced version of the distorted-wave Born approximation. A strong distortion of the ring shape is caused by refraction and reflections from the film interfaces. Close to the critical angle, the ring shape collapses into a banana shape.

Structures of regenerated cellulose films revealed by grazing incidence small-angle x-ray scattering

The characteristic in-plane length scales of ultrathin films of regenerated cellulose are measured using noncontact atomic force microscopy (NC-AFM) and grazing incidence small-angle x-ray scattering (GISAXS) in ambient atmosphere and under various humidity conditions. The aim is to elucidate the structural basis for the excellent compatibility of cellulose supports to planar lipid membranes. Films are deposited on silicon wafers by Langmuir-Blodgett (LB) transfer and spin coating. NC-AFM height profiles and the resulting calculated power spectral density functions indicate that both kinds of cellulose films have almost identical root-mean-square roughness values (0.7-0.8 nm) and very similar characteristic length scales (32 nm), respectively. GISAXS measurements, both above and below the critical angle of total external reflection, show that the dominant length scales in the bulk and near the surface of the films are comparable ( approximately 50 nm). The origin of these length scales can be attributed to the bundle of rodlike molecules of cellulose that result during the regeneration process (i.e., as a consequence of the cleavage of the silyl side chains of trimethylsilylcellulose). Exposure of the cellulose samples to various humidities shows that above a relative humidity of 97% a significant swelling of the films occurs, which is consistent with our previous findings. The swelling of films with more than 30 LB monolayers of cellulose induces a remarkable out-of-plane rearrangement of the cellulose bundles, due to a reduced influence of the solid substrate compared to thinner films with only eight to ten LB monolayers.

Performance of X-ray Reflectivity and Grazing-Incidence Small-Angle X-ray Scattering Measurement at Beamline BL15 of the Saga Light Source

An x-ray reflectivity measurement system has been installed in the bending-magnet beamline, named BL15, at the Saga Light Source. This beamline provides synchrotron radiation in the energy range from 2.1 to 23 keV for the performance of x-ray diffraction experiments, x-ray reflectivity measurements, etc. To test the performance of this reflectivity measurement system, we have analyzed the interface of thin films with nanometer-scale thickness on semiconductor substrates. The reflectivity of the order of 10-7 has been observed for a 50-nm thick film of thermal SiO2 on a Si wafer. We have fitted the calculated reflectivity profile with a single layer model to the data, and have obtained the value of thickness. In addition, we have performed grazing-incidence small-angle x-ray scattering (GISAXS) experiments on a MnPt thin film.

Formation of Ge islands from a Ge layer on Si substrate during post-growth annealing

We have deposited a 12 nm thick Ge layer on Si(1 0 0) held at 200 °C by thermal evaporation under high vacuum conditions. Upon subsequent thermal annealing in vacuum, self-assembled growth of nanostructural Ge islands on the Ge layer occurred. Atomic force microscopy (AFM) and grazing incidence small-angle X-ray scattering (GISAXS) were used to characterize such layers. GISAXS measurements evidenced the formation of cylinder shaped structures upon annealing at 700 °C, which was confirmed by AFM measurements with a very sharp tip. A Ge mass transport from the layer to the islands was inferred by X-ray reflectivity and an activation energy of 0.40 ± 0.10 eV for such a process was calculated.

Growth mode, strain state and shape of Ge islands during their growth at different temperatures: a combined in situ GISAXS and GIXD study

The growth mode, strain state and shape of Ge islands were analyzed in situ, during their growth on Si(001), by combining Grazing Incidence Small Angle X-ray Scattering (GISAXS) and Grazing Incidence X-ray Diffraction (GIXD) measurements. GISAXS measurements provide the detailed evolution of the shape of the grown quantum dots (QDs). GIXD allows the monitoring of the island nucleation and the strain state of the QDs. The shape, size, strain and interdiffusion are found to strongly depend on the growth temperature between 773 K and 923 K. At low T, the 3D islands are small, nearly fully relaxed and do not strain the substrate. At higher T, larger islands with significant Si content are grown, and induce deformation in the silicon substrate.

Structural Investigations on Self-Organized Si/SiGe Islands by Grazing Incidence Small Angle X-Ray Scattering

We present a novel technique, based on grazing incidence small angle X-ray scattering (GISAXS), with which information on the shape and the lateral correlation of buried islands can be obtained. The GISAXS measurements were performed on Ge-rich islands grown by molecular beam epitaxy on (001) vicinal substrates with a miscut 2° along the [100] direction. By varying the angle of incidence, GISAXS data sets were obtained for different information depths. These data were analysed quantitatively using a model based on the distorted wave Born approximation. In order to demonstrate the capabilities offered by this technique a 20 period Si/SiGe island multilayer sample was investigated before and after an annealing step at about 750 °C for 80 min. The GISAXS data show that the islands change their shape after annealing. For the top island layer a comparison of the GISAXS data with atomic force microscopy topographs was made.