Nanostructure research by neutron scattering

Project staff

Latest results:

The research group has been involved in several research projects and various user measurements performed on the neutron scattering instruments operated by the members of the Group: Small-Angle Neutron Scattering (SANS) instrument, Time-of-Flight spectrometer, Three-axis spectrometer, Reflectometer and PSD Diffractometer. Some of the results are specified below.

Estimation of out-of-plane correlation length in periodic Ni(Mo)-Ti multilayers. — Interface roughness strongly influences the reflectivity of neutron supermirrors (SM). The out-of-plane correlation of the interface roughness was studied using X-ray off-specular reflectometry in DC-sputtered periodic Ni(Mo)-Ti multilayers. Long-range roughness replication is manifested in sharp off-specular resonant diffuse scattering peaks. The finite out-of-plane correlation length leads to peak broadening. Using kinematical approach, a lower estimate of 1000, 3200 and 2800 Å out-of-plane correlation lengths was found for samples of Ni and Ti layer thickness (69, 57) Å, (96, 67) Å and (118, 85) Å, respectively. This work was made in collaboration with the Functional Nanostructures group and the Research Centre for Natural Sciences.

Figure 1. Specular and off-specular X-ray Dq-D2q scans (at l = 1.54 Å) for the periodic multilayer using different offsets. The inset shows the w-scan for detector angles 1.2˚ and 1.4° with the applied offset angles in the main figure.

SANS features of thylakoid membranes of vccn1-1 (Cl- channel) mutant Arabidopsis. — The behaviour of thylakoid membranes of vccn1-1 (Cl- channel) mutant Arabidopsis plant, along with its wild types was studied by SANS. The thylakoid membranes of their leaves retained their periodic organizations: they exhibited SANS profiles with a Bragg peak at around 0.026–0.028 Å-1. The Bragg peak of detached, infiltrated leaves from dark-adapted vccn1-1 mutant showed a shift to higher q values as compared to the wild type. This proved to be true for the isolated thylakoid membrane from vccn1-1 mutant: the small difference between the vccn1-1 mutant and wild type persisted despite the shifts in the q values. These SANS measurements while showed the preservation of the regular, periodic organization of grana thylakoid membrane, revealed smaller lamellar repeat distances in vccn1-1 mutants, indicating a somewhat tighter stacking and/or narrower lumen compared to the wild type – evidently due to changes in the electrostatic conditions. We also studied the differences between vccn1-1 and wild type upon KCl and KNO3 treatment. KCl and KNO3 caused minor shifts in the position of Bragg peak to higher q values both in the wild type and vccn1-1.

Vitrification-development of glass matrices for high-level radioactive wastes. — New glassy samples suitable to retain the radionuclides, and to block access to the biosphere were successfully prepared. The atomic structure of the glasses was studied by neutron and X-ray diffraction measurements. It was established that the basic network structure consisted of tetrahedral SiO4 units and of mixed trigonal BO3 and tetrahedral BO4 units which formed mixed [4]Si-O-[3]B, [4]Si-O-[4]B bond-linkages. The shortest second-neighbour distances were obtained for the Si-U and B-U pair correlation functions, indicating that U atoms could be incorporated in the matrix glass structure even when they were present with high concentration. It was shown that the stable amorphous system could incorporate maximum 40 w% high-level waste.

SANS measurements on archaeological ceramic samples from the Late Roman / Early Medieval archaeological settlement of Keszthely (Hungary) have been performed at the Yellow Submarine and FSANS instruments. A correlation between the firing temperature and the SANS curves was set up, showing that the method – as complementary to others – was suitable for analysing the high-temperature nanostructural behaviour of ceramics. No linear dependence between sizes of pores, cracks, voids and firing temperature, and no significant difference between the small-angle scattering of tempered and not tempered samples was found; however, linear dependence of exponent p (obtained from the curve fitting) on temperature was observed allowing to determine the firing temperature of the archaeological samples from Keszthely.

Polystyrene (PS) membranes modified by fullerenes and star-shaped polymers with fullerene centers (6-polystyrene-arms stars with a single C60-center and double centered C60 fullerenes having 12 arms) were studied by SANS. The samples were saturated with D-toluene that lead to the filling of the free volume in polymers, and caused a formation of chain-like channels grouped into submicron structures. The size of a polymer segment consisting of 8 monomer units (0.3 nm) and the correlation radius of the fullerene stars (1 nm) were measured. The measurement revealed that the fullerene complex is composed of 26 segments that agrees with the functionality (f ~ 6) of the star/stars when its arm is composed of 4-5 segments. Data analysis using the formalism of correlation functions (Fig. 2) has revealed three structural levels, therefore the segmental size, correlation radius and the average distance between the neighboring stars were calculated. These results enabled to perform similar measurements on membranes and films modified by fullerenes and star-shaped polymers. These PS membranes are used – among others - as gas separating membranes. The filling degree was maximal for the linear polymer, and it decreased for PS with free fullerene C60. In the case of a matrix composed of 6-arm polymer, the formation of fine channels having a lower total free volume was observed. Using the 12-arm stars in the matrix, the permeability became higher due to the appearance of molecular order. The simple embedding of free fullerene into PS-matrix became more homogeneous via linking the chains (van der Waals interactions). The star addition regulated the structure and migration of channels via formation of gradient regions and more pronounced short range order in the case of 12-arm stars.

Figure 2. The normalized coherent cross section σN(q) (a) and the coherent correlation function G(R)  (b). Fitting curves (a,b) and partial correlation functions (b) are shown.

Time-of-flight neutron diffraction (TOF-ND) analysis of archaeological objects in the framework of Cultural heritage related projects – 1. Late Bronze Age defensive and offensive armors and other objects excavated from the same tomb ('Lendület' project) showed extremely homogeneous intergranular elemental distribution; the missing of texture and stress indicated that the armors were heated to high temperature together, probably during a burial rite. 2. Fragments of copper and bronze cauldrons from the Hunnic period recovered in Hungary  ('Iperion') were found to be as-cast high-purity copper (with few exceptions), free from any plastic deformation. Low-bronze objects could be related to a different culture.  3. Damascus blades from the Wallace Collection ('Iperion') showed oriental distributions of the cementite grains, besides the texture and stress analyses of the ferrite phase. It was shown that high-carbon oriental blades can be divided into two groups by the methods of forging. In one type the cementite inclusions were randomly oriented while in the other the c-axis of Fe3C crystallites were perpendicular to the plane of the blade. 4. Silver dishes related to the Seuso treasure of extremely great value can be investigated by non-destructive methods only. At first, two silver plates found in the bed of the Sava river before 1908 were studied. An earlier non-destructive elemental analysis has shown relatively strong macroscopic distribution of copper. The high-precision TOF-ND and PGAA analyses have shown that copper is homogeneously distributed in the bulk. Phase and texture analyses have been performed as well.