fabrication-and-optimization-of-type-ii-silicon-clathrate-films

Fabrication and Optimization of Type II Silicon Clathrate Films

Silicon clathrates (SiCL) are a class of cage-structured materials with tuneable optoelectronic properties, offering significant potential for ...

University of Strasbourg

Using the first-principles full potential linearized augmented plane wave method, the electronic structure of Sr(2-x)La(x)Fe(1+y/2)Mo(1-y/2)O6 (SLFMO) double-perovskite systems is investigated for x = 1/2 and 1 and for y = +1 and -1. Substituting Sr atoms by La atoms allows one to tune the electrons added into the minority spin band and enhances the half-metal feature--according to the rigid band shift model--even if the magnetization decreases with increasing La concentration. By taking into account the chemical disorder on the Fe and Mo sites, resulting from the introduction of La as shown experimentally, it is shown (i) that a supplemental magnetization reduction occurs because the magnetic moment on the Fe antisite is opposite to the one on the Fe regular sites and (ii) that the half-metal feature is preserved in SLFMO for x = 1/2 and 1 contrary to the case for SFMO. Finally, because surface or interface Fe deficiency should have a more limited impact on the spin polarization than for SFMO, SLFMO/SrTiO3 multilayers are investigated in order to confirm this prediction by determining the spin polarization at the interface, which is found to remain high.

Ab initio study of the electronic and magnetic properties of Sr(2-x)La(x)Fe(1+y/2)Mo(1-y/2)O6 double perovskites.

The electric polarization in the multiferroic GaFeO(3) system is determined from its electronic structure using first principles methods and the modern theory of polarization. By carefully following the electric polarization on a path connecting the polar and centrosymmetric structures, it is found to be -25 μC cm(-2), which is ten times larger than a previous estimation given in the literature a few years ago and two times smaller than the value obtained in a recent similar study. The switching of this electric polarization through a centrosymmetric structure is discussed in terms of the total energy barrier. It is exhibited that such a switching is particularly difficult to achieve in relation to the tetrahedral environment of half of the Ga atoms. The switching via domain wall motion is also discussed.

First principles study of the electric polarization and of its switching in the multiferroic GaFeO3 system.

Type I and type II silicon clathrates are guest-host structures made of silicon polyhedral cages large enough to contain atoms that can be either inserted or evacuated with only a slight volume change of the structure. This feature is of interest not only for batteries or storage applications but also for tuning the properties of the silicon clathrate films. The thermal decomposition process can be tuned to obtain Na8Si46 and Na2<x<10Si136 silicon clathrate films on intrinsic and p-type c-Si (001) wafer. Here, from a unique synthesized NaxSi136 film, a range of resistivity of minimum four order of magnitude is possible by using post-synthesis treatments, switching from metallic to semiconductor behavior as the Na content is lowered. Extended exposition to sodium vapor allows us to obtain fully occupied Na24Si136 metallic films, and annealing under iodine vapor is a way to reach the guest-free Si136, a semiconducting metastable form of silicon with a 1.9 eV direct bandgap. Electrical measurements and resistance vs temperature measurements of the silicon clathrate films further discriminate the behavior of the various materials as the Na concentration is changing, additionally shouldered by density functional theory calculations for various guest occupations, further motivating the urge of an innovative pathway toward true guest-free type I and type II silicon clathrates.

Article	Year
Ab initio study of the electronic and magnetic properties of Sr(2-x)La(x)Fe(1+y/2)Mo(1-y/2)O6 double perovskites. Journal of physics. Condensed matter : an Institute of Physics journal\| PubMed ID: 22223617	2012
First principles study of the electric polarization and of its switching in the multiferroic GaFeO3 system. Journal of physics. Condensed matter : an Institute of Physics journal\| PubMed ID: 22481484	2012
Tunability of silicon clathrate film properties by controlled guest-occupation of their cages. The Journal of chemical physics\| PubMed ID: 37096857	2023

Daniel Stoeffler

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