N. Vouroutzis

LDPE/plasticized starch blends containing PE-g-MA copolymer as compatibilizer

In the present study a series of polyethylene/plasticized starch blends were prepared using a poly(ethylene-g-maleic anhydride) copolymer as a reactive compatibilizer. Uncompatibilized blends were also prepared for comparison purposes. The prepared blends were studied using mechanical properties measurements and SEM microscopy to determine their morphology. The blends were also exposed to activated sludge to determine their biodegradability.

Structural and spectroscopic magneto-optic studies of Pt–Ni multilayers

Ptm–Nin multilayers were grown by e-beam evaporation under ultrahigh vacuum; m and n will depict the number of atomic planes of the corresponding constituents in one modulation period and, in this work, they were varied between 1 and 14. X-ray diffraction and conventional electron microscopy experiments revealed a fcc polycrystalline structure with excellent modulation. Magneto-optic properties, studied at room temperature between 1.5 and 5.2 eV, were found to depend strongly on both m and n. Perpendicular anisotropy was exhibited for samples with thin Ni layers and, unexpectedly, for thicker Ni layers when Pt layers became considerably thin (m∼2). Comparison of the magneto-optic features of two similar samples grown on glass and polyimide revealed that the choice between glass and polyimide does not affect magneto-optic properties.

Phase transformation of hydrogen free amorphous carbon films under ion beam bombardment

Abstract The features of hydrogen free tetrahedral amorphous carbon films (ta-C) prepared by radio frequency (RF) magnetron sputtering at room temperature, with a high portion of sp 3 bonds, were examined by transmission electron microscopy. As grown specimens, presenting characteristic amorphous rings, were easily transformed to microcrystalline by low energy Ar ion beam bombardment. Characteristic polycrystalline rings on electron diffraction patterns, identified with a very good accuracy to the diamond reflections, revealed the phase transformation that takes place without any heating treatment under room temperature conditions. The crystallite grains size found to be up to 40 nm together with SiC crystallites were detected in several specimens treated under similar bombardment conditions.

Control of morphological transitions during heteroepitaxial island growth by reflection high-energy electron diffraction

Abstract In this work we studied the formation of well-faceted features during the growth of Ge and SiC islands on (001)Si representing a lattice mismatch of 4 and 20%, or a Stranski–Krastanov and Vollmer–Weber growth mode, respectively. A method to recognize morphological transitions in situ by reflection high-energy electron diffraction is presented. The analysis of the pattern is based on the appearance of 2D and 3D diffraction features as well as on the shift of the position of transmission spots due to refraction effects on tilted planes. The latter effect will be demonstrated for the formation of Ge-hut clusters on Si with its typical {105} facets as well for the formation of Si pyramids with {11 n } facets ( n ≈5–9) during nucleation of SiC islands.

Morphological features related to micropipe closing in 4H-SiC

The closing of micropipes during sublimation epitaxy has been studied. Shallow trenches are formed along the direction of the step-flow growth in the vicinity of closed micropipes. The trenches are related to a serious disturbance of the flowing steps and the formation of stacking faults in the (0001) basal plane as well as in the (11¯00) plane. A micropipe closes when the speed of the growth steps is higher than the spiral growth around the micropipe. This mechanism is related to a bending of the micropipe along the trench and the progressive emission of elementary screw dislocations along the trench. The morphology of the disturbed steps at the trenches and the related defects have been studied by transmission electron microscopy and atomic force microscopy. Supporting evidences are presented with optical micrographs from etched epilayers. Image forces, which are developed by the growth steps, stabilize the bending of the micropipes. The limitation of the bending is also discussed.

In-situ spectroscopic ellipsometry for monitoring the Ti-Si multilayers during growth and annealing

Abstract The TiSix formation and properties depend strongly on the deposition and annealing process. We employ spectroscopic ellipsometry (SE) to monitor both processes as well as transmission electron microscopy (XTEM) to verify the above results. The Ti and Si layers were deposited by magnetron sputtering on (100)Si. The multilayer thickness is about 930 A and the Si Ti ratio ≈ 2.2 , while the thickness of each TiSi bilayer ≈ 120 A . After deposition of each Ti or Si layer and during annealing of TiSi multilayers up to 680 °C we obtain the SE spectra in the energy region 1.5–5.5 eV. Their analysis and XTEM observations show that during deposition an intermixing of 20 A width at each TiSi interface occurred. By using SE we found that during annealing below 150 °C there is no drastic intermixing or reaction between Ti and Si. A fast interdiffusion of Ti and a-Si and their reaction is observed between 200 and 580 °C. A phase transition occurs at 580 °C from the amorphous Ti5Si3 compound to the C49 TiSi2 structure and above this temperature XTEM depicts that only structural modification within the interdiffused layers of TiSi is observed.

Compositionally gradient PVD CrAlSiN films: structural examination and oxidation resistance

The thermal stability and the resistance against oxidation of quaternary compositionally gradient CrAlSiN coatings deposited on steel substrate are investigated by examining their structural, morphological and chemical features before and after oxidation tests, as well as by quantitative thermal analysis. The as-deposited samples exhibit a columnar structure, with each column consisting of nanocrystals as fine as 20 nm. The as-deposited coating is mainly composed of CrxAl1−xN solid solution nanocrystals, which are embedded in an amorphous SiNx matrix. When exposed to high-temperature dry air environment the coated samples exhibit remarkable stability as they remained intact up to 800°C. Over 800°C, elements from the substrate outdiffused and modified the chemical content of the film, but still remain oxidation-resistant up to 900°C.

Transmission electron microscopy investigation of the structural characteristics of amorphous tetrahedral carbon films

The structural features of a-C films prepared by RF magnetron sputtering, in sequential thin layers, under positive and negative bias voltage onto Si substrate, were examined by transmission electron (TEM) microscopy. The microstructure of the films was investigated by cross section TEM. The amorphous character of the films was obvious from bright field images that also revealed the changes of the surface roughness as a function of the deposition steps and bias conditions. Dark field imaging, with the objective aperture on 〈111〉 diamond reflection position, revealed that the films were rich in sp3 C–C bonds throughout the whole film. Similar images with the objective aperture on 〈002〉 graphite reflection showed the distribution of sp2 C–C bonding in the films.

Microstructure modifications induced by bonded hydrogen in N‐rich SiNx:H films

The effect of bonded hydrogen in the atomic microstructure of nitrogen‐rich SiNx:H films is investigated using extended x‐ray‐absorption fine‐structure spectroscopy (EXAFS). The hydrogen concentration in the examined films, as measured by elastic recoil detection analysis, takes values in the range 25–33 at. %. It is shown that hydrogen, which is mostly bonded to N, alters the film microstructure, as that is determined by the nearest‐neighbor distances and coordination numbers. The measured N–Si nearest‐neighbor distance is modified by the presence of N—H bonds and it is shorter than that corresponding to Si3N4 by 3%. This bond length reduction is attributed to the higher electronegativity of hydrogen than that of the replaced Si atoms. In addition, the coordination number N in the nearest‐neighbor shell, consisting of Si atoms, is reduced to 2 from the expected coordination of 3 in Si3N4. Furthermore, EXAFS detects the presence of partially reacted Si (a‐Si:N) phase, embedded in the SiN matrix, the conce...

Study of the Structural and Mechanical Properties of Nanocrystalline TiAlSiN Gradient Coatings

A study of the structural and mechanical properties of nanocrystalline TiAlSiN gradient coatings deposited by cathodic arc deposition techniques at 500 °C and post-annealed at 525 °C is presented. Analysis of the coatings, chemical composition and microstructure revealed that the coatings have a structure based on (Ti, Al)N nanocrystals with an average size of 10 nm embedded in an amorphous Si3N4 phase. The study of the mechanical properties showed that post-annealing causes improvement and increase of the coatings hardness. A maximum hardness of 48 GPa and elastic modulus of 560 GPa were measured. Also, excellent adhesion to the WC-Co substrate was observed in the post-annealed coatings.