Standardless Quantitative Analysis by X-Ray Spectrometry

Errors in standardless analysis arise from inaccuracies in atomic data, detection efficiency of the detector, the normalization and the sensitivity to the errors of the spectrum processing, and ZAF correction (which converts the ratio of the measured intensities into concentration). Other sources of error encountered in fully quantitative analysis (using standards) also remain in the standardless version. Calculation of the Lα standard intensities also requires incorporation of non-radiative transitions. Both the experimentally found dependence of the net Lα intensities on the atomic number and the corresponding peak-to-background ratios (P/B) indicate that an empirical increase in the calculated non-radiative transitions is necessary. Either the subshell ionization cross-sections are higher for the L1 and L2 subshells than they are for the L3 subshell or the Coster-Kronig transition rates are larger than reported in the literature. Independent experimental data would be needed especially for the ionization cross-sections of the individual L subshells. Experimental data pertinent to the conventional energy dispersive (ED) detectors with a Be window are discussed in this paper. The average error of the standardless analysis is 3-10% which should be compared with the average error of the fully quantitative ED analysis, which is 2-6%, depending on the ZAF procedure used. An extensive comparative assessment of the standardless procedures is urged

Determining Projections of Grain Boundaries from Diffraction Data in Transmission Electron Microscope

AbstractGrain boundaries (GB) are characterized by disorientation of the neighboring grains and the direction of the boundary plane between them. A new approach presented here determines the projection of GB that can be used to determine the latter one. The novelty is that an additional parameter of GB is quantified in addition to the ones provided by the orientation maps, namely the width of the projection of the GB is measured from the same set of diffraction patterns that were recorded for the orientation map, without the need to take any additional images. The diffraction patterns are collected in nanobeam diffraction mode in a transmission electron microscope, pixel-by-pixel, from an area containing two neighboring grains and the boundary between them. In our case, the diffraction patterns were recorded using the beam scanning function of a commercially available system (ASTAR). Our method is based on non-negative matrix factorization applied to the mentioned set of diffraction patterns. The method is encoded in a MATLAB environment, making the results easy to interpret and visualize. The measured GB-projection width is used to determine the orientation of the GB-plane, as given in the study by Kiss et al.</jats:p

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

TEM analysis of Si thin films prepared by diode laser induced solid phase epitaxy at high temperatures

The solid phase crystallization of amorphous silicon thin films deposited on 〈111〉-oriented wafers at high temperatures was investigated. The films were heated up by diode laser irradiation for some milliseconds to seconds. Time resolved reflectivity measurements together with numerical temperature calculations showed that temperatures above 1000 C were reached before significant crystallization took place. By comparing two different laser intensities it is shown that random nucleation and growth dominate solid phase epitaxy if high temperatures are reached faster. The interface between epitaxially grown and randomly crystallized material is very rough which can be attributed to contaminations found at the substrate-film interface. © 2014 Elsevier B.V

HYBRID ALUMINUM MATRIX COMPOSITES PREPARED BY SPARK PLASMA SINTERING (SPS)

Aluminum Matrix composites have been intensively investigated over a long time due to their unique combination of beneficial properties including low density, high strength to weight ratio, increased hardness, advantageous tribology, corrosion resistance, etc. In the present work we studied the combined effect of various reinforcing phases including Al2O3, SiC, Si3N4 and graphene on the aluminum matrix. The composites were fabricated by powder metallurgical method, in which the powder blend was rapidly sintered by spark plasma sintering. The main conclusion was that hybrid composite can perform better only if the development of porosity is eliminated by improving the wettability of the reinforcing particles

Phase formation sequence in the Ti/InP system during thin film solid-state reactions

The metallurgical properties of the Ti/InP system meet a great interest for its use as a contact in the scope of various applications such as the Si Photonics. The investigations conducted on this system highlight the initiation of a reaction between the Ti and the InP substrate during the deposition process conducted at 100 °C. The simultaneous formation of two binary phases, namely, Ti2In5 and TiP, is attributed to the compositional gradient induced in the InP by the wet surface preparation and enhanced by the subsequent in situ Ar+ preclean. Once formed, the TiP layer acts as a diffusion barrier inhibiting further reaction up to 450 °C in spite of the presence of an important Ti reservoir. At higher temperature, however, i.e., from 550 °C, the reaction is enabled either by the enhancement of the species diffusion through the TiP layer or by its agglomeration. This reaction gives rise to the total consumption of the Ti2In5 and Ti while the TiP and In phases are promoted. © 2017 Author(s)

Kvantitatív elektronmikroszkópia = Quantitative transmission electron microscopy

A projekt keretében kvantitatív transzmissziós elektronmikroszkópos módszereket fejlesztettünk, majd e módszerek használhatóságát anyagtudományi problémák megoldása során demonstráltuk. "Imaging plate (IP)" segítségével végzett nagy pontosságú (egy millió szürkeségi fokozatot megkülönböztető) méréseinket használtuk mind a valós térbeli (HRTEM) képi információ, mind pedig a reciprok térbeli diffrakciós információ kisérleti rögzítésére. Új módszert dolgoztunk ki az elektron diffrakciós (ED) ábrák, valamint HRTEM képek kvantitatív feldolgozására nanokristályos vékonyrétegek kvalitatív és kvantitatív fázisanalízise, valamint egyes kristály szemcsék indexelése céljából. A méréseket szerkezeti modellekből számolt mennyiségekkel (HRTEM szimuláció, kinematikus diffrakció) hasonlítottuk össze. Inhomogén, összetett szerkezeti modellek megalkotását (atomi koordináták számítását) is saját fejlesztésű programunk segíti. Módszereinket a következő problémák megoldásánál használtuk: grafén sík-darabokat tartalmazó CNx-szerkezetek kialakulása; félvezetők (Ge, Si) és fémek reakcióinak kezdeti szakaszai; légköri eredetű koromszemcsék és vulkanikus szilikátok felépítése; beágyazottan izolált Co-szemcsék előállítása és fázisszelekciója; SiC poláros tulajdonságainak hatása a növekedésre; Cu/Mg multirétegekben az intermetallikus nukleációjának aszimmetriája. Eredményeinket nemzetközi konferenciákon és iskolákon mutattuk be és 11 referált folyóiratcikkben közöltük (kumulatív impakt faktor 27,24). | We developed quantitative transmission electron microscopy methods within the framework of the project and demonstrated the utility of them in solving problems from materials science. With the help of imaging plates, experimental images from real space (HRTEM) and from reciprocal space (diffraction patterns) were recorded with high accuracy (with one million gray levels). We developed a new method to process both the electron diffraction (ED) patterns and the HRTEM images quantitatively to result in both qualitative and quantitative phase analysis and to index patterns from individual crystal grains. The measured quantities were compared to similar ones (simulated HRTEM images and calculated kinematic diffraction), calculated from structural models. Construction of a structural model for inhomogeneous, complex structures is helped by a computer program also developed in this project. These methods helped us in solving the following problems: development of CNx structures from curved gaphene-sheets; initial stages of reaction between semiconductors (Ge, Si) and metals; structure of airborne soot particles and of volcanic silicates; formation of embedded, isolated Co nanoparticles and the phase selection during their formation; effect of the polarity of SiC on the growth; asymmetry in the nucleation of the intermetallic in Cu/Mg multilayer systems. Or results were presented at international conferences and schools and published in 11 papers in referenced journals (with cumulative impact factor of 27.24)

High glass forming ability correlated with microstructure and hydrogen storage properties of a Mg-Cu-Ag-Y glass

Thermal characterization of an as-cast Mg54Cu28Ag7Y11 bulk metallic glass revealed that this alloy exhibits excellent glass forming ability. High-resolution X-ray diffraction study and transmission electron microscopy show that heating and isothermal annealing treatment results in the nucleation of nanocrystals of several phases. The average size of these nanocrystals (~15-20 nm) only slightly varies with prolonged annealing, only their volume fraction increases. High-pressure calorimetry experiments indicate that the as-cast fully amorphous alloy exhibits the largest enthalpy of hydrogen desorption, compared to partially and fully crystallized states. Since the fully crystallized alloy does not desorb hydrogen, it is assumed that hydrogen storage capacity correlates only with the crystalline volume fraction of the partially crystallized Mg54Cu28Ag7Y11 BMG and additional parameters (crystalline phase selection, crystallite size, average matrix concentration) do not play a significant role