N. Frangis

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.

Continuous series of one-dimensional structures in the compounds Bi2+xSe3, Bi2+xTe3, Sb2+xTe3, (Bi2Te3)nGeTeand (Sb2Te3)nGeTe

Abstract Electron microscopy techniques were used to characterise the commensurate and incommensurate superstructures formed after the addition of cations to the isostructural compounds Bi2Se3, Bi2Te3 and Sb2Te3. The observed electron diffraction patterns were analysed, using a method closely related to the “cut and projection” method, hereby assuming the building blocks of the superstructures to be 5-layer and 7-layer lamellae. This assumption was confirmed by high resolution electron microscopy images.

Continuous series of one-dimensional structures in compounds based onM2X3 (M =Sb, Bi; X =Se, Te)

Abstract For compounds of the type M 2 X 3 (Bi 2 Te 3 , Bi 2 Se 3 , Sb 2 Te 3 ), doping with Ge (Sn or Pb), as well as addition of excess cations, leads to the formation of continuous series of 1 D superstructures which can now be characterized by means of electron microscopy. The systems Ge δ Bi 2 Te 3 and Bi 2+δ are discussed as model systems. Analysis of the electron diffraction patterns with the fractional shift method suggests the superstructures are built up of sequences of five- and seven-layer lamellae. This interpretation is confirmed by direct (high resolution) images. From a comparison between experimental high resolution images and computed images, a model for the five- and seven-layer lamellae is presented. A modified “cut and projection” method is described and applied to derive the sequences of “5” and “7” bands from the (approximate) q -values of the (quasi)commensurate diffraction patterns.

Amorphization and defect recombination in ion implanted silicon carbide

The damage produced in silicon carbide single crystals by ion implantation was investigated by Rutherford backscattering channeling and transmission electron microscopy techniques. Implantations were performed at liquid nitrogen and at room temperatures with several ions to examine the effect of the ion mass and of the substrate temperature on the damaging process. The damage accumulation is approximately linear with fluence until amorphization occurs when the elastic energy density deposited by the ions overcomes a critical value. The critical energy density for amorphization depends on the substrate temperature and is greatest at 300 K indicating that defects recombination occurs already at room temperature. Formation of extended defects never occurred and point defects and uncollapsed clusters of point defects were found before amorphization even in the case of light ion implantation. The atomic displacement energy has been estimated to be ∼12 eV/atom from the analysis of the damage process in dilute c...

Electron microscopy characterization of TiN films on Si, grown by d.c. reactive magnetron sputtering

The structural characteristics of titanium nitride films deposited by d.c. reactive magnetron sputtering on (001) silicon wafers were studied by cross-section transmission electron microscopy and in-situ spectroscopic ellipsometry (SE). The growth habit of the films, the shape and the size of the crystallites were investigated versus deposition temperature, bias voltage and nitrogen flow rate. The surface micro-roughness was also studied by atomic force microscopy. The films exhibit a columnar growth showing preferred orientation along (111) direction. High-resolution transmission electron microscopy (TEM) observations reveal that the Si substrate does not affect the mode of growth. The SE measurements and TEM observations strongly suggest that TiN rich in nitrogen is formed at nitrogen flow rates in the range 1.9–3 sccm. At a nitrogen flow rate FN = 1.7 sccm the stoichiometric compound Ti2N is formed which exhibits a completely different mode of growth. The ability of the in-situ SE to monitor small structural changes induced by small changes of the growth conditions was tested by the deposition of sequential layers. In this respect SE is a powerful method to control TiN deposition.

The role of surface vibrations and quantum confinement effect to the optical properties of very thin nanocrystalline silicon films

We report on a spectroscopic study of very thin nanocrystalline silicon films varying between 5 and 30nm. The role of quantum confinement effect and surface passivation of nanograins in optical properties are examined in detail. The coupling between surface vibrations and fundamental gap Eg as well as the increase of interaction between them at the strong confinement regime (⩽2nm) are proposed for the observable pinning of Eg in luminescence measurements.

Effect of exciton migration on the light emission properties in silicon nanocrystal ensembles

Different silicon nanocrystal (Si NC) systems in which Si NCs were either entirely isolated or loosely interconnected were studied by photoluminescence (PL) and time-resolved PL decay measurements in the range between 70 and 290 K, in order to investigate the role of exciton migration in the PL properties. We examined three kinds of samples: (a) two light emitting mesoporous Si (PSi) films with different porosities, grown on p-type Si, (b) a heavily oxidized light emitting anisotropic macroporous Si film, and (c) a film consisted of a Si NC superlattice with six Si NC/SiO2 bilayers, grown by low pressure chemical vapor deposition of amorphous Si (α-Si), followed by high temperature thermal oxidation. In the two mesoporous Si films of the first case, the Si NCs show a degree of interconnection that depends on the porosity, whereas in the two other cases the NCs were isolated by SiO2, the degree of electrical isolation depending on the thickness of the SiO2 interlayer between them. Temperature dependent PL ...

Influence of grain size on ultrafast carrier dynamics in thin nanocrystalline silicon films

The ultrafast carrier dynamics in thin nanocrystalline silicon films (10 and 20nm thick) on quartz over a broad spectral range using optical pumping at a moderate fluence of 2.5mJ∕cm2 were studied. The films were composed of randomly oriented silicon nanocrystals of various sizes and shapes. The authors probed a fast and a slow relaxation mechanism. The slow decay (∼300ps) was attributed to bulk nanocrystal states similar to those of bulk silicon, while the faster one (∼3ps) was attributed to surface states at grain boundaries, more dominant in the smaller nanocrystals due to their larger surface/volume ratio.

Electrical and structural properties of Ga0.51In0.49P/GaAs heterojunctions grown by metalorganic vapor‐phase epitaxy

Undoped and Se‐doped Ga0.51In0.49P/GaAs single heterojunctions grown by metalorganic vapor‐phase epitaxy (MOVPE) are characterized with deep‐level transient spectroscopy and transmission electron microscopy (TEM). The undoped MOVPE material, grown at 710 °C, is characterized by a deep electron trap with an activation energy that takes values in the range 700–900 meV. Se doping suppresses the formation of this trap when the doping level is higher than 5×1017 cm−3. Furthermore, Se doping suppresses the persistent photoconductivity that is observed in the undoped samples. Finally, analysis with cross‐section TEM reveals that the samples undergo partial spinodal decomposition in a direction nearly vertical to the interface.

Structural and optical characterization of two-dimensional arrays of Si nanocrystals embedded in SiO2 for photovoltaic applications

We report on the structural and optical characterization of two-dimensional arrays of silicon nanocrystals (SiNCs) suitable for photovoltaic applications. Single and multiple SiNC layers were grown on quartz by low pressure chemical vapor deposition of Si and subsequent thermal oxidation steps. The single SiNC layers consisted of one SiNC layer embedded in two silicon dioxide (SiO2) layers, whereas the multi-layered structure consisted of five SiNC layers of equal thickness separated by SiO2 layers. SiNC layers with thicknesses ranging from 2 to 25 nm were investigated. A thorough structural characterization of the films was carried out by combining grazing incidence x-ray diffraction, x-ray reflectivity, and transmission electron microscopy (TEM). Both XRD and TEM measurements revealed that the SiNC layers were polycrystalline in nature and composed of SiNCs, separated by grain boundaries, with their vertical size equal to the SiNC layer and their lateral size characterized by a narrow size distribution....