Structural Characteristics of the Si Whiskers Grown by Ni-Metal-Induced-Lateral-Crystallization

Si whiskers grown by Ni-Metal-Induced-Lateral-Crystallization (Ni-MILC) were grown at 413 °C, intentionally below the threshold for Solid State Crystallization, which is 420 °C. These whiskers have significant common characteristics with whiskers grown by the Vapor Liquid Solid (VLS) method. The crystalline quality of the whiskers in both methods is the same. However, in VLS, a crystalline substrate is required, in contrast to the amorphous one in Ni-MILC for the growth of single crystalline whiskers. Moreover, whiskers grown by VLS have a polygonal cross-section with their diameter determined by the diameter of the hemispherical metallic catalysts. On the other hand, in the Ni-MILC, the cross-section of the whiskers depends on the size of the NiSi2 grain from which they are emanated. This was confirmed by observing the crossing whiskers and the rotational Moiré patterns in the crossing area. The structure of disturbed short and thin nonlinear branches on the side-walls of the whiskers was studied. In the whiskers grown by the VLS method, significant contamination occurs by the metallic catalyst degrading the electrical characteristics of the whisker. Such Si whiskers are not compatible with the current CMOS process. Whiskers grown by Ni-MILC at 413 °C are also contaminated by Ni. However, the excess Ni is in the form of tetrahedral NiSi2 inclusions which are coherent with the Si matrix due to the very low misfit of 0.4% between them. These whiskers are compatible with current CMOS process and Thin Film Transistors (TFTs)

STUDY OF THE PHASES OF AIB5IIIX8VI COMPOUNDS

THE COMPOUNDS CUIN5TE8 AND AGIN5SE8 HAVE BEEN STUDIED BY MEANS OF COMBINED ELECTRON MICROSCOPY TECHNIQUES. IT HAS BEEN FOUND THAT THE FIRST COMPOUND HAS A TETRAGONAL STRUCTURE AT ROOM TEMPERATURE WITH C/A=2 AND THE SECOND ONE HAS THREE DIFFERENT TETRAGONAL STRUCTURES WITH C/A=2,4 AND 1 RESPECTIVELY. ALL THE STRUCTURES ARE SUPERSTRUCTURES OF A SPHALERITE-LIKE STRUCTURE. AT HIGHER TEMPERATURES,BOTH COMPOUNDS APPEAR WITH A CUBIC SPHALERITE-LIKE STRUCTURE, BECAUSE OF DISORDERING OF THE CATIONS. THE NUMBER AND THE TYPE OF THE ORIENTATION AND TRANSLATION VARIANTS OF THE STRUCTURES HAVE ALSO BEEN STUDIED. FINALLY, THE TRANSITION STATE, BETWEEN THE LONG AND SHORT RANGE ORDER HAS BEEN STUDIED AND ANALYSED.ΜΕΛΕΤΟΥΝΤΑΙ ΟΙ ΕΝΩΣΕΙΣ CUIN5TE8 KAI AGIN5SE8, ΜΕ ΣΥΝΔΥΑΣΜΟ ΤΕΧΝΙΚΩΝ ΗΛΕΚΤΡΟΝΙΚΗΣ ΜΙΚΡΟΣΚΟΠΙΑΣ. Η ΠΡΩΤΗ ΕΝΩΣΗ ΕΜΦΑΝΙΖΕΤΑΙ ΣΤΗ ΘΕΡΜΟΚΡΑΣΙΑ ΠΕΡΙΒΑΛΛΟΝΤΟΣ ΜΕ ΤΕΤΡΑΓΩΝΙΚΗ ΔΟΜΗ, ΠΟΥ ΕΧΕΙ ΛΟΓΟ C/A=2, ΕΝΩ Η ΔΕΥΤΕΡΗ ΕΜΦΑΝΙΖΕΤΑΙ ΜΕ ΤΡΕΙΣ ΔΙΑΦΟΡΕΤΙΚΕΣ ΤΕΤΡΑΓΩΝΙΚΕΣ ΔΟΜΕΣ ΜΕ ΛΟΓΟΥΣ C/A=2,4 ΚΑΙ 1. ΟΛΕΣ ΟΙ ΔΟΜΕΣ ΕΙΝΑΙ ΥΠΕΡΔΟΜΕΣ ΤΗΣ ΔΟΜΗΣ ΤΥΠΟΥ ΣΦΑΛΕΡΙΤΗ. ΣΕ ΥΨΗΛΟΤΕΡΕΣ ΘΕΡΜΟΚΡΑΣΙΕΣ ΠΑΡΑΤΗΡΗΘΗΚΕ ΚΑΤΑΣΤΡΟΦΗ ΤΗΣ ΤΑΞΕΩΣ ΤΩΝ ΚΑΤΙΟΝΤΩΝ ΚΑΙ ΕΜΦΑΝΙΣΗ ΤΩΝ ΕΝΩΣΕΩΝ ΜΕ ΚΥΒΙΚΗ ΔΟΜΗ ΤΥΠΟΥ ΣΦΑΛΕΡΙΤΗ.ΜΕΛΕΤΟΥΝΤΑΙ ΕΠΙΣΗΣ Ο ΑΡΙΘΜΟΣ ΚΑΙ Ο ΤΥΠΟΣ ΤΩΝ ΠΑΡΑΛΛΑΓΩΝ ΠΡΟΣΑΝΑΤΟΛΙΣΜΟΥ ΚΑΙ ΜΕΤΑΤΟΠΙΣΕΩΣ ΤΩΝ ΔΟΜΩΝ. ΤΕΛΟΣ ΜΕΛΕΤΑΤΑΙ ΚΑΙ ΑΝΑΛΥΕΤΑΙ Η ΜΕΤΑΒΑΤΙΚΗ ΚΑΤΑΣΤΑΣΗ ΜΕΤΑΞΥ ΤΩΝ ΚΑΤΑΣΤΑΣΕΩΝ ΤΑΞΕΩΣ ΕΥΡΕΙΑΣ ΚΑΙ ΠΕΡΙΟΡΙΣΜΕΝΗΣ ΕΚΤΑΣΕΩΣ

Analysis and Implications of Structural Complexity in Low Lattice Thermal Conductivity High Thermoelectric Performance PbTe–PbSnS₂ Composites

The high-performance PbTe–SnTe–PbS thermoelectric system forms a completely new composite PbTe–PbSnS₂ with high n-type figure of merit. Electron diffraction and high-resolution electron microscopy characterization of the thermoelectric composite PbTe + 25% PbSnS₂ reveals that the system is nanostructured, with PbSnS₂nanocrystals in the range of 80 to 500 nm in size. In most of the cases, they are endotaxially grown within the PbTe matrix. Three independent crystal superstructures were observed for the PbSnS₂ inclusions, originating from the same parent SnS-type structure. The presence of the parent structure is not excluded. Modified structural models for two of the superstructures observed in the PbSnS₂ precipitates are proposed. Often, more than one of the structural phases are observed in the same nanocrystal, providing one extra phonon scattering factor in the system. Evidence was also found for the growth process of the nanocrystals, starting from PbS and followed by gradual dissolving of SnS. Our findings suggest that this nanostructured thermoelectric composite exhibits unique structural complexity, which contributes to the low lattice thermal conductivity reported for these nanocomposite materials