Ptychographic X‐Ray Imaging of Colloidal Crystals

Abstract

dipolar interactions. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The flexibility of colloidal crystals and their response to external stimuli [16][17][18] along with their unique optical properties such as the strongly pronounced structural color and photonic band gap makes them attractive for many applications. [19][20][21][22][23][24][25] Moreover, defects, which determine the mechanical properties of many engineering materials such as metals, [26] can be studied with "atomic" resolution using colloidal crystals. [27][28][29] The high penetration depth of X-rays makes them an ideal tool to access important statistically averaged spatial information about the colloidal crystal structure and disorder over macroscopic sample volume. [7,30,31] Further access to local structure of colloidal crystals can be gained by using microscopy with Fresnel optics and soft X-rays, [32,33] but unfortunately the use of soft X-rays significantly limits the penetration depth. Alternatively, compound refractive lenses (CRLs) can be used as an objective lens for hard X-rays to study thicker samples. [34][35][36] This technique provides full field of view, however, resolution is limited by the resolving power of the optical elements and contrast is limited by using hard X-rays. [37] Ptychographic coherent X-ray imaging is applied to obtain a projection of the electron density of colloidal crystals, which are promising nanoscale materials for optoelectronic applications and important model systems. Using the incident X-ray wavefield reconstructed by mixed states approach, a high resolution and high contrast image of the colloidal crystal structure is obtained by ptychography. The reconstructed colloidal crystal reveals domain structure with an average domain size of about 2 µm. Comparison of the domains formed by the basic close-packed structures, allows us to conclude on the absence of pure hexagonal close-packed domains and confirms the presence of random hexagonal close-packed layers with predominantly face-centered cubic structure within the analyzed part of the colloidal crystal film. The ptychography reconstruction shows that the final structure is complicated and may contain partial dislocations leading to a variation of the stacking sequence in the lateral direction. As such in this work, X-ray ptychography is extended to high resolution imaging of crystalline samples. Ptychography [+]

In situ characterization of crystallization and melting of soft, thermoresponsive microgels by small-angle X-ray scattering

“…The rhcp structure is typically found for colloidal spheres, as the spheres pack into close packed hexagonal planes while the stacking sequence of the planes is random, leading to alternating fcc and hexagonal close-packed (hcp) crystal structures. 14,[49][50][51][52] The Bragg peaks can be identified as the hexagonal close packed , ,…”

SAXS Investigation of Core–Shell Microgels with High Scattering Contrast Cores: Access to Structure Factor and Volume Fraction

“…For relatively large microgels with sizes in the micron range, optical microscopy techniques have been used for investigating the local organization of microgel systems on a single-particle level. ,, The overlapping of microgels in dense packings however limits the resolution in optical microscopy. In addition, different scattering methods, such as dynamic and static light scattering (DLS and SLS) or small-angle X-ray and neutron scattering (SAXS and SANS), were frequently employed to study the bulk structure and dynamics of microgel systemsmostly focusing on microgels too small to be observed with optical microscopy. − A major advantage of scattering methods over microscopy methods is that much higher particle numbers can be addressed in one measurement giving access to ensemble averages with great statistics. At high volume fractions, in particular, where microgels form colloidal crystals, scattering methods are much more powerful to resolve the long-range 3D order.…”

Colloidal crystal order and structure revealed by tabletop extreme ultraviolet scattering and coherent diffractive imaging

“…Coherent diffractive imaging with hard X-rays from synchrotron sources have recently demonstrated the possibility to image the three-dimensional structure of single colloidal crystal grains [30,31] and enabled two-dimensional microscopy of colloidal crystals with relatively large (418 nm in diameter) nanosphere size [32]. Past work used EUV HHG CDI at a wavelength of 30nm to record scatter patterns from a sparse region of large 2µm core-size silica spheres [33], and achieved a spatial resolution between 250nm and 440nm.…”