Structure of nanocrystalline and amorphous materials from electron diffraction in the TEM

Electron diffraction from thin films can be recorded in the TEM with either convergent beam (CBED) or parallel beam (SAED, NBD) illumination. Although CBED carries a wealth of information from single crystalline regions, parallel illumination is preferred for the structure examination of either nanocrystalline (nc) or amorphous thin films. Both the sharp rings in the former case and the diffuse rings in the latter case can be quantitatively analysed with the ProcessDiffraction program, which is distributed free of charge [1]. Both the volume fractions and the possible preferred orientation of the nc phases can be quantified with this program [2-4]. The short range order for either nc or amorphous materials can be determined with that program [5-7 volt meg egy cikk ahol hasznaltam amorfra]. When Bragg reflections are analysed it gives the global structure, while the pair distribution function (PDF) provides the local structure. Differences between local and global structures are exemplified e.g. in [8]. Recently, a possibility was implemented in ProcessDiffraction to apply a “Mask”, i.e. to disregard pre-selected parts of the pattern from processing. In addition to eliminating the possible distortion in the ring-averages caused by the presence of “Beam-stop”, the Mask also facilitates separation of incoherently superposed components, like the sc?-spots originated from traces of the not-completely removed substrate when the ring pattern from the layer is to be analysed. The example in Fig. 1 shows the effect of masking, while Fig. 2 demonstrates the change in lattice parameter due to mutual solution of the two phase-components (AlN and TiN) in each other. Refinement of such lattice parameter changes is also included in the program. The talk will also include examples from determination of local structure through PDF-analysis. Special problems of calibration, scattered radiation when using selected area aperture and possible distortions of lenses as a function of lens settings are also discussed. These problems are more serious in PDF-analysis than in evaluation of Bragg-reflections

Lead isotope composition and host phases in airborne particulate matter from Budapest, Hungary

Lead is a frequent potentially toxic pollutant of the urban environment. Its risk assessment in the airborne particulate matter requires data both on its speciation and potential sources. In this paper we present results on detailed mineralogical (XRD and TEM) and geochemical (selective chemical extractions and lead isotope ratio analyses) study of total suspended particulate (TSP) matter samples from Budapest, Hungary to fulfil this requirements. Total lead concentrations showed significant enrichment in the studied TSP samples as compared to its geochemical background value. It could be associated to several host phases. The potentially mobile fraction of lead, which could be also harmful to human, can be as high as 16% of the total lead. This is represented by Pb sorbed on the surface of clay minerals and in form of carbonates (and sulphates). Contrarily, between 20 and 30% of total lead of TSP materials is hosted by magnetite, a highly resistant mineral. However, its fast oxidation during combustion processes to hematite and/or weathering in the acidifying urban environment to ferrihydrite may result in the enhanced mobilization of lead. Lead isotope composition of the TSP samples suggests the mixing of several sources for this metal with slight variation among the sampling sites. Despite the phasing out of leaded gasoline, its contribution to the Pb content of the TSP was observed. Our data also supported that the presence of lead of gasoline origin decreases in the airborne TSP in the last decade in Budapest. Another important source for lead is found to be the coal combustion due to domestic and industrial heating. Lead isotope ratio data suggest additional source(s) for this metal at least in certain localities, but further investigations are necessary to specify them

Transformations in CrFeCoNiCu High Entropy Alloy Thin Films during In-Situ Annealing in TEM

In-situ TEM-heating study of the microstructural evolution of CrFeCoNiCu high entropy alloy (HEA) thin films was carried out and morphological and phase changes were recorded. Post annealing investigation of the samples was carried out by high resolution electron microscopy and EDS measurements. The film is structurally and morphologically stable single phase FCC HEA up to 400 °C. At 450 °C the formation of a BCC phase was observed, however, the morphology of the film remained unchanged. This type of transformation is attributed to diffusionless processes (martensitic or massive). From 550 °C fast morphological and structural changes occur, controlled by volume diffusion processes. Fast growing of a new intermetallic phase is observed which contains mainly Cr and has large unit cell due to chemical ordering of components in <100> direction. The surface of the films gets covered with a CrO-type layer, possibly contributing to corrosion resistance of these

SESONAL AND VERTICAL VARIATION OF MINERALOGY AND PARTICLE SIZE DISTRIBUTION OF SETTLED DUST ALONG A HIGH BUILDING

Settled dust may affect air quality due to its mineralogical and particle size composition. We studied the mineralogical and particle size composition of settled dust collected seasonally at four heights and both sides of a high building next to a busy road in Budapest, Hungary. Particle size distribution of samples shows two maxima (at 12 and 37 m). The ratio of fine particles and also the maximum particle size is higher at the windward side of the building. No characteristic vertical distribution pattern was observed. However, summer samples exhibit higher ratio of coarse particles. Major mineral dust components are characteristic of surrounding geology. Clay minerals and amorphous materials enrich in the fine particle fraction (<20 m). Gypsum from constructing materials also appears there. Despite that dolomite is originated from dolomite hill behind the building its amount is higher at the front side due to special air flow conditions. In summer, carbonates and clay minerals show significant increase probably due to the re-suspension of local materials during the dry-surface periods. Vertical variation of dust mineralogy is the most conspicuous for clay minerals demonstrating the dual source of these phases as local and remote sources exert antagonistic effect on their deposition