Periodic order and defects in Ni-based inverse opal-like crystals on the mesoscopic and atomic scale

The structure of inverse opal crystals based on nickel was probed on the mesoscopic and atomic levels by a set of complementary techniques such as scanning electron microscopy and synchrotron microradian and wide-angle diffraction. The microradian diffraction revealed the mesoscopic-scale face-centered-cubic (fcc) ordering of spherical voids in the inverse opal-like structure with unit cell dimension of $750\pm 10\mathrm{nm}$. The diffuse scattering data were used to map defects in the fcc structure as a function of the number of layers in the Ni inverse opal-like structure. The average lateral size of mesoscopic domains is found to be independent of the number of layers. 3D reconstruction of the reciprocal space for the inverse opal crystals with different thickness provided an indirect study of original opal templates in a depth-resolved way. The microstructure and thermal response of the framework of the porous inverse opal crystal was examined using wide-angle powder x-ray diffraction. This artificial porous structure is built from nickel crystallites possessing stacking faults and dislocations peculiar for the nickel thin films.

Figure 1

The typical top view SEM image of IOLC based on Ni. The inset shows the typical cross section SEM image.

Figure 2

Schematic drawing of the microradian x-ray diffraction experiment with the use of synchrotron radiation.

Figure 3

(a)–(c) Microradian x-ray diffraction patterns of ${\mathrm{Ni}}_{26}$. The patterns are measured at $\omega =0^{\circ }$ (a), $-{35}^{\circ }$ (b), ${55}^{\circ }$ (c). The sketches (d)–(f) illustrate reciprocal lattices for an ideal fcc crystal with the orientations corresponding to patterns (a)–(c).

Figure 4

A sketch illustrating the Bragg rods orthogonal to the sample surface. (a) The top view of the reciprocal space (corresponding to the geometry of the sample surface being perpendicular to the x-ray beam, XY plane). Numbers 1 and 2 denote the projections of two representative Bragg rods. Dark circles shows the projections of staking-dependent reflections. (b) The side view (XZ plane). The thick solid line is the Bragg rod 1; the dashed thick line is the Bragg rod 2. The latter is not in the $Q_y=0$ plane; that is why it is dashed. The inclined solid line shows the intersection of the Ewald sphere with reciprocal lattice points at a certain angle $\omega$.

Figure 5

The profiles of the normalized intensity distribution along Bragg rods 1 (see Fig. 4 for the definition).

Figure 6

Dependencies of IOLC main structural parameters according to microradian x-ray diffraction data. (a) The probability of fcc motif formation $\alpha$, (b) the mosaicity $\delta \varphi$, (c) the average size of structural domain along $\left[20\overline{2}\right]$ direction $L_{\mathrm{trans}}$, and (d) the average size of structural domain along $\left[111\right]$ direction $L_{\mathrm{long}}$.

Figure 7

The 3D visualization of reciprocal space of inverse opal-like crystals (a) ${\mathrm{Ni}}_{3.5}$, (b) ${\mathrm{Ni}}_8$, (c) ${\mathrm{Ni}}_{17}$, and (d) ${\mathrm{Ni}}_{26}$. The numbers 1 and 2 relate to Bragg rods 1 and 2 introduced in Fig. 4.

Figure 8

An example of the typical experimental x-ray powder diffraction pattern with the profile obtained as a result of WPPM refinement and relative difference curve with reference to sample ${\mathrm{Ni}}_{17}$. The peaks are from Ni and Au; the latter are marked with asterisks.

Figure 9

The typical temperature dependence of the lattice parameter with reference to sample ${\mathrm{Ni}}_{17}$.