I. M. Iskandarova

Impact of oxygen on the work functions of Mo in vacuum and on ZrO2

The electronic properties of molybdenum surfaces and interfaces with monoclinic zirconia (Mo∕m-ZrO2) of different stoichiometries are investigated through first-principles calculations. We show that oxygen adsorption on the Mo(110) surface strongly increases the Mo vacuum work function, and that a similar trend is observed for the Mo(110) work function on zirconia upon oxygenation of the stoichiometric Mo∕m-ZrO2 interface, albeit to a smaller extent. As expected, Mo∕m-ZrO2 interface reduction/oxidation decreases/increases the Mo effective work function. However, interface overoxidation leading to the formation of a thin MoOx layer between Mo and m-ZrO2 (Mo∕MoOx∕m-ZrO2) causes a work-function decrease with respect to the stoichiometric Mo∕m-ZrO2 interface value. This result is especially surprising because calculations indicate that subsurface oxidation of Mo slabs increases the Mo vacuum work function. Moreover, the calculated vacuum work function of rutile MoO2(110) slab is ∼6.0eV, considerably larger th...

First-principles investigation of the WC∕HfO2 interface properties

The thermodynamic and electronic properties of tungsten carbide surfaces and interfaces with monoclinic hafnia (WC∕m-HfO2) are investigated through first-principles calculations. We show that oxidation of the WC surface and of the WC∕m-HfO2 interface is energetically favorable. An oxygen monolayer on the W-terminated WC(0001) surface gives rise to a larger vacuum work function than that for the C-terminated WC(0001) surface, while the opposite result is obtained for the WC(0001) effective work function on hafnia: a carbon intermediate layer results in larger work function than an oxygen intermediate layer. This result is explained by the atomic structure of the intermediate layers neighboring the interface which differ if the interface is O or C rich.

Roughness simulation for thin films prepared by atomic layer deposition

The kinetic lattice Monte Carlo method for film growth simulation without taking crystallization into account was applied to study the roughness of the HfO2 film grown by atomic layer deposition at 100–500°C from HfCl4 and H2O. The calculations were performed using a simplified kinetic mechanism of the growth of HfO2 films obtained by reducing the detailed kinetic mechanism developed earlier. Ab initio quantum-chemical calculations were performed to determine the kinetic parameters of diffusion processes on the surface of hafnium oxide that could influence film roughness. Because of the special features of atomic layer deposition, the rate of film growth and film roughness were finite even if surface relaxation was ignored. It was found that, irrespective of the temperature, the diffusion of hydrogen and adsorbed HfCl4 complexes did not change the profile of the growing film and only insignificantly increased the mean rate of growth. The results obtained were also qualitatively applicable to zirconium dioxide at fairly low (≤100°C) temperatures in the absence of crystallization.

Segregation trends of the metal alloys Mo-Re and Mo-Pt on HfO2 : A first-principles study

Using first-principles calculations, we compared the segregation trends at the surface of metal alloys with those at an interface with HfO2. The choice of this oxide was motivated by its significance as a potential replacement for SiO2 in advanced transistors. We considered Mo–Re and Mo–Pt alloys as typical examples of disordered and ordered alloys, respectively. The segregation to the surface/interface was analyzed in terms of metal and oxygen adsorption energies. It is shown that chemical bonding at the metal/oxide interface strongly influences segregation both in Mo–Re and Mo–Pt alloys. In particular, bonding with oxygen atoms at the oxide/Mo–Re alloy interface depletes the Re content of the interfacial layer. In the case of Mo–Pt on HfO2 an oxygen-rich interface promotes the formation of one monolayer (but not two monolayers) of Mo separating PtMox from HfO2, while a stoichiometric interface favors an abrupt PtMox∕HfO2 interface. This study also shows that the presence of Mo in the alloy stabilizes Pt...