Structural characterization of poly-Si Films crystallized by Ni Metal Induced Lateral Crystallization.

The growth of the poly-Si films was studied by Transmission Electron Microscopy (TEM) after Ni Metal Induced Lateral Crystallization (Ni-MILC) of amorphous Si films at 413 °C. Significant differences in the morphology and the mode of growth of the films were observed, in comparison to films grown at temperatures above 500 °C. It was shown that at 413 °C the Solid Phase Crystallization (SPC), which acts in parallel with the Ni-MILC process at temperatures above 500 °C is suppressed. The suppression of SPC results in substantial change in the mode of growth. The poly-Si film grown at 413 °C consists of whiskers, which can be classified into two categories. Those growing fast along the <111> direction, which were already observed in conventional Ni-MILC above 500 °C and whiskers grown along random crystallographic orientations having significantly slower growth rates. Because of the large difference in growth rates of the whiskers, significant orientation filtering due to growth-velocity competition is observed. The uniform poly-Si films consist of a mixture of fast <111> type whiskers and slow ones, grown in other orientations, resulting in a tweed-like structure.

Thin film and interface properties during ZnO deposition onto high-barrier hybrid/PET flexible substrates.

The combination of transparent conductive oxides with high-barrier films deposited onto flexible polymeric substrates is of considerable importance in order to improve the efficiency, lifetime and stability of flexible electronic devices. In this work, ZnO thin films have been deposited onto high-barrier hybrid/PET flexible substrates by pulsed DC magnetron sputtering, at room temperature and by applying different power values on the target. The employment of in situ and real-time Vis-fUV (1.5-6.5 eV) spectroscopic ellipsometry allowed the investigation of the growth mechanisms of ZnO thin films as well as the modification procedure in the hybrid's surface. Island growth is dominant during the initial stages of deposition concerning low target power regime, whereas layer-by-layer deposition prevails at the high target power regime. The hybrid's modified layer of approximately 10nm was confirmed by the transmission electron microscopy measurements which additionally revealed a columnar structure of the film with a nanocrystalline morphology. The estimated size of the nanocrystals ( approximately 15 nm and above) was compatible with atomic force microscopy (AFM) measurements. Finally, the evolution of the optical parameters (energy gap and absorption peaks) of the ZnO films during the deposition was similar.

Self-assembled hexagonal ordering of Si nanocrystals embedded in SiO(2) nanodots.

Highly dense hexagonally ordered two-dimensional arrays of Si nanocrystals embedded in SiO(2) nanodots were fabricated on a silicon substrate by using a self-assembled porous anodic alumina thin film as a masking layer through which electrochemical oxidation of the Si substrate and ultralow energy Si implantation took place. After removal of the alumina film and high temperature annealing of the samples, hexagonally ordered Si nanocrystals embedded within SiO(2) nanodots were obtained, having sizes in the few tens of nanometer range. The fabricated ordered structures show significant potential for applications either in basic physics experiments or as building blocks for nanoelectronic and nanophotonic devices.

Well-orientated cubic boron nitride nanocrystals as studied by high-resolution transmission electron microscopy.

In a boron nitride thin film, grown on a Si (100) substrate by radio frequency magnetron sputtering, a striking nanostructure is observed by high-resolution transmission electron microscopy. It consists of cubic boron nitride nanocrystals with a rather good triangular shape, pointing always to the substrate. The nanocrystals are usually highly defected and present their own interesting internal structure. Texture formation is observed within a nanocrystal, with all the subgrains observed to have a common <011> axis, which is also approximately parallel to a <011> axis of the Si substrate, i.e. the nanocrystals are very well structurally orientated in relation to the Si substrate (self-organized). Dislocations and stacking faults are also found in the nanocrystals.

Structural models for twin interfaces in Pd thin films.

In a Pd thin film grown on a 6H-SiC (0001) substrate, several twin interfaces have been observed, classified as (1) {111}Sigma = 3 twin interfaces and (2) {221}Sigma = 3 twin interfaces. The first ones are coherent twin interfaces and in some cases exhibit steps of one or more atomic layers in height. The second ones are perpendicular to the first ones. They usually appear with a rigid-body displacement, but in some cases no displacement was observed. Models for the interfaces are proposed.

Nanostructuring, compositional fluctuations, and atomic ordering in the thermoelectric materials AgPb(m)SbTe(2+m). The myth of solid solutions.

The nature of the thermoelectric materials Ag(1-x)Pb(m)SbTe(m+2) or LAST-m materials (LAST for Lead Antimony Silver Tellurium) with different m values at the atomic as well as nanoscale was studied with powder/single-crystal X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy. Powder diffraction patterns of different members (m = 0, 6, 12, 18, infinity) are consistent with pure phases crystallizing in the NaCl-structure-type (Fmm) and the proposition that the LAST family behaved as solid solutions between the PbTe and AgSbTe2 compounds. However, electron diffraction and high resolution transmission electron microscopy studies suggest the LAST phases are inhomogeneous at the nanoscale with at least two coexisting sets of well-defined phases. The minority phase which is richer in Ag and Sb is on the nanosized length scale, and it is endotaxially embedded in the majority phase which is poorer in Ag and Sb. Moreover, within each nanodomain we observe extensive long range ordering of Ag, Pb, and Sb atoms. The long range ordering can be confirmed by single crystal X-ray diffraction studies. Indeed, data collections of five different single crystals were successfully refined in space groups of lower symmetry than Fmm including P4/mmm and Rm. The results reported here provide experimental evidence for a conceptual basis that could be employed when designing high performance thermoelectric materials and dispel the decades long belief that the systems (AgSbTe2)(1-x)(PbTe)x are solid solutions.