9 research outputs found
Structural and Electronic Properties of the Interface between the High-k oxide LaAlO3 and Si(001)
The structural and electronic properties of the LaAlO3/Si(001) interface are
determined using state-of-the-art electronic structure calculations. The atomic
structure differs from previous proposals, but is reminiscent of La adsorption
structures on silicon. A phase diagram of the interface stability is calculated
as a function of oxygen and Al chemical potentials. We find that an
electronically saturated interface is obtained only if dopant atoms segregate
to the interface. These findings raise serious doubts whether LaAlO3 can be
used as an epitaxial gate dielectric.Comment: 4 pages, 5 figure
Thermochemical and Mechanical Stabilities of the Oxide Scale of ZrB\u3csub\u3e2\u3c/sub\u3e+SiC and Oxygen Transport Mecha
Refractory diboride with silicon carbide additive has a unique oxide scale microstructure with two condensed oxide phases (solid+liquid), and demonstrates oxidation resistance superior to either monolithic diboride or silicon carbide. We rationalize that this is because the silica-rich liquid phase can retreat outward to remove the high SiO gas volatility region, while still holding onto the zirconia skeleton mechanically by capillary forces, to form a solid pillars, liquid roof scale architecture and maintain barrier function. Basic assessment of the oxygen carriers in the borosilicate liquid in oxygen-rich condition is performed using first-principles calculations. It is estimated from entropy and mobility arguments that above a critical temperature Tc~1500°C, the dominant oxygen carriers should be network defects, such as peroxyl linkage or oxygen-deficient centers, instead of molecular O2* as in the Deal–Grove model. These network defects will lead to sublinear dependence of the oxidation rate with external oxygen partial pressure. The present work suggests that there could be significant room in improving the high-temperature oxidation resistance by refining the oxide scale microstructure as well as controlling the glass chemistry
The chemistry of La on the Si(001) surface
This paper reports state-of-the-art electronic structure calculations of La
adsorption on the Si(001) surface. We predict La chains in the low coverage
limit, which condense in a stable phase at a coverage of 1/5 monolayer. At 1/3
monolayer we predict a chemically rather inert, stable phase. La changes its
oxidation state from La(3+) at lower coverages to La(2+) at coverages beyond
1/3 monolayer. In the latter oxidation state, one electron resides in a state
with a considerable contribution from La-d and f states.Comment: 10 pages, 13 figures, 3 table
Point defect concentrations in metastable Fe-C alloys
Point defect species and concentrations in metastable Fe-C alloys are
determined using density functional theory and a constrained free-energy
functional. Carbon interstitials dominate unless iron vacancies are in
significant excess, whereas excess carbon causes greatly enhances vacancy
concentration. Our predictions are amenable to experimental verification; they
provide a baseline for rationalizing complex microstructures known in hardened
and tempered steels, and by extension other technological materials created by
or subjected to extreme environments
The interface between silicon and a high-k oxide
The ability to follow Moore's Law has been the basis of the tremendous
success of the semiconductor industry in the past decades. To date, the
greatest challenge for device scaling is the required replacement of silicon
dioxide-based gate oxides by high-k oxides in transistors. Around 2010 high-k
oxides are required to have an atomically defined interface with silicon
without any interfacial SiO2 layer. The first clean interface between silicon
and a high-K oxide has been demonstrated by McKee et al. Nevertheless, the
interfacial structure is still under debate. Here we report on first-principles
calculations of the formation of the interface between silicon and SrTiO3 and
its atomic structure. Based on insights into how the chemical environment
affects the interface, a way to engineer seemingly intangible electrical
properties to meet technological requirements is outlined. The interface
structure and its chemistry provide guidance for the selection process of other
high-k gate oxides and for controlling their growth. Our study also shows that
atomic control of the interfacial structure can dramatically improve the
electronic properties of the interface. The interface presented here serves as
a model for a variety of other interfaces between high-k oxides and silicon.Comment: 10 pages, 2 figures (one color