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

Real-Time Observation of Temperature-Induced Surface Nanofaceting in M-Plane α-Al2O3.

The spontaneous crystal surface reconstruction of M-plane α-Al2O3 is employed for nanopatterning and nanofabrication in various fields of research including, among others, magnetism, superconductivity, and optoelectronics. In this reconstruction process the crystalline surface transforms from a planar morphology to one with a nanoscale ripple patterning. However, the high sample temperature required to induce surface reconstruction made in situ studies of the process seem unfeasible. The kinetics of ripple pattern formation therefore remained uncertain, and thus production of templates for nanofabrication could not advance beyond a trial-and-error stage. We present an approach combining in situ real-time grazing incidence small-angle X-ray scattering experiments (GISAXS) with model-based analysis and with ex situ atomic force microscopy (AFM) to observe this morphological transition in great detail. Our approach provides time-resolved information about all relevant morphological parameters required to trace the surface topography on the nanometer scale during reconstruction, i.e., the time dependence of the pattern wavelength, the ripple length, width, and height, and thus their facet angles. It offers a comprehensive picture of this process exemplified by a M-plane α-Al2O3 surface annealed at 1325 °C for 930 min. Fitting the model parameters to the experimental GISAXS data revealed a Johnson–Mehl–Avrami–Kolmogorov type of behavior for the pattern wavelength and a predominantly linear time dependence of the other parameters. In this case the reconstruction resulted in a crystalline surface fully patterned with asymmetric ripple-shaped nanostructures of 75 nm periodicity, 15 nm in height, and 630 nm in length. By elucidating the time dependence of these morphological parameters, this study shows a powerful way to significantly advance the predictability of annealing outcome and thus to efficiently customize nanopatterned α-Al2O3 templates for improved nanofabrication routines.

SGTools: a suite of tools for processing and analyzing large data sets from in situ X-ray scattering experiments

In situ synchrotron small-angle X-ray scattering (SAXS) is a powerful tool for studying dynamic processes during material preparation and application. The processing and analysis of large data sets generated from in situ X-ray scattering experiments are often tedious and time consuming. However, data processing software for in situ experiments is relatively rare, especially for grazing-incidence small-angle X-ray scattering (GISAXS). This article presents an open-source software suite (SGTools) to perform data processing and analysis for SAXS and GISAXS experiments. The processing modules in this software include (i) raw data calibration and background correction; (ii) data reduction by multiple methods; (iii) animation generation and intensity mapping for in situ X-ray scattering experiments; and (iv) further data analysis for the sample with an order degree and interface correlation. This article provides the main features and framework of SGTools. The workflow of the software is also elucidated to allow users to develop new features. Three examples are demonstrated to illustrate the use of SGTools for dealing with SAXS and GISAXS data. Finally, the limitations and future features of the software are also discussed.

On the assessment by grazing-incidence small-angle X-ray scattering of replica quality in polymer gratings fabricated by nanoimprint lithography

Grazing-incidence small-angle X-ray scattering (GISAXS) can be used to characterize the replica quality of polymer gratings prepared by thermal nanoimprint lithography (NIL). Here it is shown using GISAXS experiments that a series of NIL polymer gratings with different line quality present characteristic features that can be associated with the level of defects per line. Both stamps and NIL polymer gratings exhibit characteristic semicircle-like GISAXS patterns. However NIL polymer gratings with defective lines exhibit GISAXS patterns with an excess of diffuse scattering as compared to those of the corresponding stamps. In a first approach, this effect is attributed to a reduction of the effective length of the lines diffracting coherently as the number of defects per line increases.

Morphology of epitaxial magnetic alloy nanostructures grown on WSe2(0001) studied by grazing-incidence small-angle X-ray scattering

The morphology of epitaxial alloy nanostructures grown on a van der Waals-type WSe2(0001) surface was studied using grazing-incidence small-angle X-ray scattering (GISAXS). Assemblies of 111-oriented islands of (Co,Cr)Pt3and (Co,Fe)Pt alloys were grown at different deposition temperatures, with nominal thicknesses from 0.1 to 3 nm, resulting in various island densities. Evaluation of the GISAXS patterns indicates that for similar growth conditions CrPt3islands are flatter than CoPt or FePt islands and exhibit larger island volumes. These features are correlated with the better wetting behaviour and more negative formation enthalpy of the CrPt3alloy. For dense arrays of self-assembled CoPt islands, much smaller island volumes are extracted from GISAXS experiments than are observed by scanning tunnelling microscope imaging, which indicates that only the upper parts of the islands contribute to the GISAXS signal. Another aspect that needs to be taken into account for interpreting GISAXS patterns is the sensitivity of GISAXS to facetting and thus its capacity to extract the island shape. The latter is strongly dependent on the island size. For islands with an average volume smaller than ∼20 nm3, the shape cannot be determined unequivocally. Furthermore, for dense island assemblies with some size dispersity, the identification of steep side-wall facets from the GISAXS patterns is not straightforward as observed for truncated tetrahedron-shaped CoPt3islands.

Synthesis and phase-separation behavior of α,ω-difunctionalized diblock copolymers

A series of diblock copolymers of n-pentyl methacrylate and methyl methacrylate (PPMA/PMMA BCP) with one or two terminal functional groups was prepared by sequential anionic polymerization of PMA and MMA using an allyl-functionalized initiator and/or and end-capping with allyl bromide. Allyl functional groups were successfully converted into OH groups by hydroboration. The morphology in bulk was examined by temperature-dependent small-angle X-ray measurements (T-SAXS) and transmission electron microscopy (TEM) showing that functional groups induced a weak change in d-spacings L0 as well as in the thermal expansion behavior. T-SAXS proved that the lamellar morphologies were stable over multiple heating/cooling cycles without order-disorder transition (ODT) until 300 °C. While non-functionalized BCP formed parallel lamellae morphologies, additional OH-termination at the PMMA block forced in very thin films (ratio between film thickness and lamellar d-spacing below 1) the generation of perpendicular lamellae morphology through the whole film thickness, as shown by Grazing-incidence small-angle X-ray scattering experiments (GISAXS) measurements. Functionalized BCP were successfully used in thin films as templates for silica nanoparticles in an in-situ sol–gel process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Strain and composition of ultrasmall Ge quantum dots studied by x-ray scattering and in situ surface x-ray absorption spectroscopy

Investigations of the structural properties of ultrasmall Ge dots, grown through a thin silicon oxide layer on Si(001), have been performed by combining (i) grazing incidence x-ray diffraction, (ii) grazing incidence small angle x-ray scattering (GISAXS), and (iii) surface extended x-ray absorption fine structure (SEXAFS). Grazing incidence x-ray diffraction observations show that the dots are highly strained to the Si(001) substrate. The dot shape and composition, as determined by GISAXS experiments and in situ SEXAFS, strongly depend on the thickness and the composition of the silicon oxide layer covering the surface of the silicon substrate. Ge dots grown through 1.2nm thick SiO2 are round shaped with a Ge content of about 60% whereas dots grown through 0.3nm thick SiOx are facetted and composed of almost pure Ge.

Grazing incidence small-angle X-ray scattering: an advanced scattering technique for the investigation of nanostructured polymer films.

Hamburg workshop on the "application of synchrotron radiation in chemistry"With grazing incidence small-angle X-ray scattering (GISAXS) the limitations of conventional small-angle X-ray scattering with respect to extremely small sample volumes in the thin-film geometry are overcome. GISAXS turned out to be a powerful advanced scattering technique for the investigation of nanostructured polymer films. Similar to atomic force microscopy (AFM), a large interval of length between molecular and mesoscopic scales is detectable with a surface-sensitive scattering method. While with AFM only surface topographies are accessible, with GISAXS the buried structure is also probed. Because a larger surface area is probed, GISAXS also has a much larger statistical significance compared to AFM. Due to the high demand on collimation, GISAXS experiments are based on synchrotron radiation. Nanostructures parallel and perpendicular to the sample surface observable in thin poly(styrene- block-isoprene) diblock copolymer films are presented as an example of the possibilities of GISAXS.