Synthesis and thermal stability of nanocrystalline chromium disilicide

MnSi ̃1.73 grown on silicon with mass-analyzed low energy dual ion beam epitaxy technique

We report a complete study of the lattice dynamics, dielectric, elastic and piezoelectric properties of hexagonal semiconducting chromium disilicide (CrSi2). From a combined experimental and theoretical study, we have revisited the phonon mode assignments at the zone-center, so that the contradictions met in previous experimental studies between 250 and 300 cm−1 are now explained and understood. We found that the temperature dependence of the Raman frequencies is mainly due to an implicit volume contribution and related to the large Gruneisen parameter. This explains why CrSi2 has a moderate thermal conductivity although its Debye temperature is quite large. Optic and static dielectric constants have also been analyzed and discussed. The elastic constants of CrSi2 are large, but this compound is quite brittle. In addition, the relatively low Poisson coefficient associated to the large negative Cauchy pressure of CrSi2 indicate the angular nature of its bonding. The calculation of its piezoelectric coefficient shows a sizable value with a magnitude similar to that reported for α-quartz. This prediction requires, however, experimental confirmation.

Revisited phonon assignment and electro- mechanical properties of chromium disilicide

Preparation and physical properties of nanosized semiconducting CrSi2 powders

Optical transmission and reflection as well as ellipsometric studies are performed for the semiconducting phases CrSi 2 , MnSi x . and Ir 3 Si3 in the energy region from 0.2 to 5.0 eV. Onsets of strong interband transitions are found around 0.5 eV for the former two compounds and 1.2 eV for the latter one. Optical data analysis for the former two compounds suggests them to be indirect semiconductors whereas for the latter to be a direct one. Main interband features for CrSi 2 and MnSi 1.73 3 appear between 1 and 2 eV and for Ir 3 Si 5 at 3 eV. An explanation of these findings is given in terms of existing band structure and density of states considerations.

Optical interband properties of some semiconducting silicides

CrSi2 thin films are grown by dc magnetron sputtering of Cr single layers on Si and Cr/Si multi-layer configurations on SiO2 and subsequent external annealing. In the optical spectra around the band edge the phonon emission and the absorption branches of the indirect transition at 0.5 eV and the direct transition around 1 eV can be discerned. Spectral features in the reflectivity spectrum at higher energies are discussed on the basis of published density of states calculations. The reflectivity spectrum in the IR region exhibits pronounced structures which can be fitted by a six-oscillator model yielding the TO frequencies, oscillator strengths, and damping constants of the lattice modes. The Raman spectrum shows bands in the 310 to 410 cm−1 wave number region.



Es wurden CrSi2-Schichten durch Gleichstrom-Magnetron-Sputtern von Cr-Einzelschichten auf Si und Cr/Si-Schichten auf SiO2 und nachfolgender externer Temperung hergestellt. In den optischen Spektren im Bereich der Bandkante wurden die Phonon-Emissions- und Absorptions-Zweige des indirekten Ubergangs bei 0,5 eV sowie der direkte Ubergang bei 1 eV erhalten. Die spektrale Abhangigkeit des Reflexionsvermogens bei hoherer Energie wird auf der Grundlage existierender Zustandsdichte-Berechnungen diskutiert. Das Reflexionsspektrum im IR-Bereich weist ausgepragte Strukturen auf, die mit Hilfe eines Modells bestehend aus sechs Oszillatoren angepast werden konnten, woraus die TO-Frequenzen, Oszillatorstarken und Dampfungskonstanten der Gitterschwingungen ermittelt wurden. Das Raman-Spektrum weist Banden im Wellenzahlbereich von 310 bis 410 cm−1 auf.

I. Sieber

Papers

Growth and Optical Characterization of CrSi2 Thin Films