Nanoszerkezet kutatás neutronszórással

A csoport munkatársai


A csoport legfrissebb eredményei (angolul)

( 2016)

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

Study of desiccation-tolerant desert cyanobacterium, Leptolyngbya ohadii by means of small-angle neutron scattering. — Cyanobacteria (or blue-green algae), the first photosynthetic organisms capable of producing oxygen, the ancestors of chloroplasts of vascular plants, appeared about 3 billion years ago and contributed significantly to the transformation of our globe to a habitable planet. These organisms can be found in the most diverse terrestrial and aquatic habitats – from hot springs to the Antarctic climate and from the oceans and fresh water lakes to only temporarily moistened rocks and desert soils. In order to acclimate to these different habitats and to adapt to rapidly changing environmental conditions (temperature, illumination intensity, availability of nutrients and water), different cyanobacteria evolved different, multilevel regulatory mechanisms, the details of which are not well understood.

A desiccation-tolerant desert cyanobacterium, Lepto­lyngbya ohadii, a keystone species in desert sand crusts was studied. L. ohadii spends most of the daytime in the desiccated state in strong sunshine, surviving extremely harmful conditions. Recovery of photosynthesis can occur immediately upon the addition of water (in nature, e.g. predawn dew deposition). Desiccation and rehydration in photosynthetic organisms are complex processes; it is important to reveal their structural background. As revealed by small-angle neutron scattering, in the hydrated state, the multilamellar thylakoid membrane system (responsible for the conversion of light energy to chemical energy in the cell) displayed three peaks in the SANS profile: one peak at q=0.072 nm-1 and two additional, higher harmonic features at 0.139 and 0.221 nm-1. These values can be interpreted as the repeat distance (RD) ≈87 nm of thylakoid membranes. In the desiccated state, these peaks were completely lost. The scattering intensity decreased dramatically due to the loss of water and no Bragg peak could be discerned between 0.05 and 0.1 nm-1; instead, a broad shoulder emerged between 0.10 and 0.15 nm-1, which can be assigned to a 20-30 nm shrinkage in the RD (Fig. 1).

Figure 1. Hydrated and dry state of the multilamellar thylakoid membrane system.

Neutron spin echo (NSE) spectrometry using very cold neutrons (VCN). — The concept of spin echo spectrometer on very cold neutrons (wavelengths  λ ~ 10-30 nm) to provide extra high resolution in energy transfer (ΔE ~ 10-13 eV) has been proposed. Measurements of spin echo signals at different wavelengths were realized using broadband spin flippers in combination with Fourier-analysis of λ-spectrum. The application of very cold neutrons should extend the spin echo time diapason radically, t ~ 10-12 -10-3 s. This promises to open a set of novel scientific areas including the spectroscopy of chemical reactions and catalytic processes, conformational transitions in polymers and biological molecules, dynamic modes in carbon structures (fullerenes, nanotubes, graphenes) at scales from few nanometers to microns.

Spin echo spectrometry based on very cold neutrons promises excellent opportunities in studies of molecular, polymeric, biological objects and systems in extra wide range of times from picoseconds to milliseconds at which their complicated dynamics is revealed. New scientific fields for research open up in comprehensive analysis of chemical reactions and catalysis phenomena, subtle features of conformational and structural transformations in biological molecules and their living structures by using very high energy resolution ~ 10-13 eV in neutron inelastic scattering experiments based on the proposed principles of wide-band spin-echo technique. The creation of such advanced NSE-instrument (Fig. 2) is considered in connection with the development of intense source of ultra and very cold neutrons on WWR-M reactor at the Petersburg Nuclear Physics Institute using the principles of deep cooling of neutrons in superfluid helium.

Figure 2. NSE-VCN-spectrometer: neutron beam (n), polarizer (P), radiofrequency flipper (RF), ±π/2-flippers forming the borders of precession fields (B), sample (S), analyzer(A), detector (D).

 

Stabilization of detonation nanodiamonds (DND) hydrosol in physiological media with poly(vinylpyrrolidone) (PVP). — A simple method of stabilization of detonation nanodiamonds with negative Ϛ-potential in isotonic aqueous-saline media was realized by means of complex formation with poly(vinylpyrrolidone). The stability conditions of the complexes were defined and their structure was determined by neutron scattering. The obtained hydrosols of nanodiamond particles stable in physiological medium may be used in biological researches and in medicine as drug carriers.

 

The reliable evidences for the formation of stable DND-PVP complexes in hydrosol were obtained with particle sizes 30-35 nm when the ratio of weight concentrations of the component reached r = CPVP/CDND ~ 0.5. In the range of r = 0.3÷0.5, complexes with sizes 30-35 nm are formed, stable in isotonic NaCl solution. At lower r, the amount of PVP is not sufficient to form such complexes, and at larger r, PVP forms a more dense shell around DND particles, resulting an increase of their stability in aqueous-saline media. With the use of PVP, the cluster chain structure formed by the DND particles was observed. It was possible to achieve the stability of such structures of DND particles in isotonic solutions for a long period of time (several months) by varying the amount of PVP in the system. The studied systems are promising for use in medicine due to their high stability in isotonic media. The use of PVP will allow to introduce the drugs to DND-PVP complexes, which will be stable drug carriers.

Cultural heritage-related studies with the aid of neutrons. — Firing conditions in old-fired clay bricks were studied by means of small-angle neutron scattering. Masonry and chimney brick samples (Úpice, 1876, Telé, 1950) from Czech Republic, were compared to samples of raw clay from the sites of the original quarries. Bricks produced with different raw materials could be distinguished on the basis of the fractal exponent of the scattering surface of pores.

Firing temperature of archaeological pottery wares was determined by means of neutron scattering. A series of control samples with known firing conditions revealed linear correlation between firing temperature and p-exponent of the Porod-approximation of SANS intensity versus momentum transfer curves. Based on this correlation, the firing temperatures of 17 archaeological ceramic samples from the Early Medieval site of Keszthely have been determined in a non-invasive manner.

Scientific analysis of the ceramic artefacts (20 pcs) of the 6th century AD cemetery of Szólád (Hungary) was carried out. During the pottery analysis thin-section petrography (resulting in mineralogical data), Prompt-Gamma Activation Analysis and Neutron Activation Analysis (resulting in major and trace elemental composition) was made. These methods allowed to apply two different statistical models where both types of data (qualitative mineralogical and quantitative chemical) were incorporated into the analysis (“mixed-mode”): multidimensional scaling (MDS) and multifactorial analysis (MFA). They were studied separately, together or weighted. The aim of the analyses was to distinguish different material groups based on their mineralogical and chemical composition which refer either to local or import pottery production. The analyses resulted in two separate material groups, both of local origin, and four individual vessels, which could be defined as import production.

Optimization of new borosilicate glasses for conditioning High-Level-Waste (HLW) materials. The immobilization process of HLW materials in borosilicate glasses is generally accepted in the literature. Stable and compact structure, multi-component matrix glasses with a compact structure, namely borosilicate-based glasses doped with 30wt% CeO2, Nd2O3 and Eu2O3 lanthanides were investigated. They were used for chemical modelling of the actinides, with the aim to clear up the correlation between structural characteristics and to find answer for a possible incorporation of Ce, Nd and Eu elements. Based on neutron and X-ray diffraction measurements combined with Reverse Monte Carlo simulation, a comprehensive structural study of the glasses was done. The special interest of this system lies in the different glass forming mechanisms of SiO2 and B2O3. The shortest second-neighbour distances obtained for the (Si,B)-Ce, (Si,B)-Nd and (Si,B)-Eu pair correlation functions suggest that lanthanide ions take part partially as network former in the structure. These pronounced correlations show that Ce, Nd and Eu atoms can be incorporated in the matrix glass structure.

Hybrid silica materials with ordered pore structure. — Hybrid silica materials have been synthesized and studied by a variety of experimental methods including scattering techniques. The materials were prepared using organically modified precursors with methyl and aminopropyl functional groups, as well as using templating surfactant molecules with different alkyl tail lengths. These additives influence the pore structure, ordering and the chemical nature of pore surface such as hydrophobicity, which allow to control and tailor the properties of the materials for various applications. The methyl-modified materials were tested for their drug-uptake and -release properties, and a strong correlation between the methyl content and the in vitro dissolution rate of ketoprofen has been achieved, demonstrating the potential applicability of such co-condensation type of synthesis for practical applications.

The microstructure of ODS steels processed by friction steel welding (FSW), friction steel welding, has been investigated by methods of small-angle neutron scattering with magnetic contrast variation, and electron microscopy. The particle size distribution of the nano-sized yttrium oxide and its derivatives (Fig. 3) shows a strong change with the parameters of the welding process. The relative number of particles in the range of 2-80 nm decreases, partially dissolves in the stir zone with respect to the base material, and this effect is stronger in the case of higher tool rotation speed, i.e., higher heat input during the welding.

Figure 3. Representative TEM images and the statistically correct size distribution of the ceramic precipitates.

Eredmények 2016-ban

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.