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Alfredo Pasquarello

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Related publications (226)

First-principles theory of infrared absorption spectra at surfaces and interfaces: Application to the Si(100): H2O surface

We calculate the transverse and the longitudinal infrared absorption spectra of the hydrated silicon surface using a first-principles approach. The absorption spectra are computed for two different configurations of water molecules dissociatively chemisorb ...

2008

Band alignments and defect levels in Si-HfO2 gate stacks: Oxygen vacancy and Fermi-level pinning

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

The determination of band alignments and defect levels is demonstrated for the technologically relevant Si-SiO2-HfO2 gate stack. The proposed scheme, which combines first-principles molecular dynamics for model generation and hybrid density functionals for ...

AIP American Institute of Physics2008

Charge state of the O-2 molecule during silicon oxidation through hybrid functional calculations

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

We study the charge state of the diffusing O-2 molecule during silicon oxidation through hybrid functional calculations. We calculate charge-transition levels of O-2 in bulk SiO2 and use theoretical band offsets to align these levels with respect to the Si ...

2008

Short and intermediate range order in amorphous GeSe2

Alfredo Pasquarello

By using first-principle molecular dynamics within density functional theory, we study the structural properties of amorphous GeSe2 at a temperature T of 300 K. For each property, a statistical average is obtained from six independent partial averages take ...

2008

Band offsets at the Si/SiO2 interface from many-body perturbation theory

Alfredo Pasquarello

We use many-body perturbation theory, the state-of-the-art method for band-gap calculations, to compute the band offsets at the Si/SiO2 interface. We examine the adequacy of the usual approximations in this context. We show that (i) the separate treatment ...

2008

Band offsets at semiconductor-oxide interfaces from hybrid density-functional calculations

Alfredo Pasquarello, Fabien Devynck, Peter Broqvist, Audrius Alkauskas

Band offsets at semiconductor-oxide interfaces are determined through a scheme based on hybrid density functionals, which incorporate a fraction alpha of Hartree-Fock exchange. For each bulk component, the fraction alpha is tuned to reproduce the experimen ...

2008

Carbon diffusion in CVD growth of carbon nanotubes on metal nanoparticles

Alfredo Pasquarello, Oleg Yazyev

Diffusion of carbon is the crucial step in chemical vapor deposition (CVD) growth of carbon nanotubes (CNTs) On metal nanoparticles. Using first principles techniques we model the binding and diffusion of carbon atoms and dimers on late transition (Ni, Pd, ...

2008

Band gap opening at the 6H-SiC(0001) surface passivated by an epitaxial silicon oxynitride layer: A first-principles investigation

Alfredo Pasquarello, Fabien Devynck

Using hybrid density functionals, we investigate the origin of the large band gap experimentally observed at the 6H-SiC(0001) surface when passivated by an epitaxial silicon oxynitride layer. In order to distinguish the effects resulting from the interfaci ...

2008

Defect energy levels in density functional calculations: Alignment and band gap problem

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

For materials of varying band gap, we compare energy levels of atomically localized defects calculated within a semilocal and a hybrid density-functional scheme. Since the latter scheme partially relieves the band gap problem, our study describes how calcu ...

2008

Defect levels of dangling bonds in silicon and germanium through hybrid functionals

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

Defect levels of dangling bonds in silicon and germanium are determined within their respective band gaps through the use of hybrid density functionals. To validate our approach, we first considered the dangling bond in silicon finding two well-separated d ...

2008

Charge transition levels of the Ge dangling bond defect at Ge/insulator interfaces

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

We calculate defect levels of dangling bonds in germanium using hybrid density functionals. To validate our approach, we first consider the dangling bond in silicon finding two well-separated defect levels, in excellent correspondence with their experiment ...

2008

Core-level photoelectron spectroscopy probing local strain at silicon surfaces and interfaces

Alfredo Pasquarello, Oleg Yazyev

Using a first-principles approach, we investigate the origin of the fine structure in Si 2p photoelectron spectra at the Si(100)2x1 surface and at the Si(100)-SiO2 interface. Calculated and measured shifts show very good agreement for both systems. By usin ...

2007

Modeling of atomic-scale processes during silicon oxidation: charge state of the O2 molecule

Alfredo Pasquarello, Audrius Alkauskas

We discuss the ab initio modeling of several processes occurring during silicon oxidation with a particular emphasis on the charge state of the diffusing oxygen molecule. For values of the electron chemical potential falling in the range of the silicon ban ...

2007

Structural and electronic properties of oxygen vacancies in monoclinic HfO2

Alfredo Pasquarello, Peter Broqvist

We study structural and electronic properties of the oxygen vacancy in monoclinic HfO 2 for five different charge states. We use a hybrid density functional to accurately reproduce the experimental band gap. To compare with measured defect levels, we deter ...

2007

Electronic properties of an epitaxial silicon oxynitride layer on a 6H-SiC(0001) surface: A first-principles investigation

Alfredo Pasquarello, Zeljko Sljivancanin, Fabien Devynck

Using a density functional scheme, the authors investigate the electronic properties of an epitaxial silicon oxynitride layer on a 6H-SiC(0001) surface, as recently realized experimentally. Simulated scanning-tunneling-microscopy images of filled and empty ...

AIP American Institute of Physics2007

Vibrational spectra of vitreous SiO2 and vitreous GeO2 from first principles

Alfredo Pasquarello, Luigi Giacomazzi

Using a density-functional approach, we calculate the principal vibrational spectra of vitreous SiO2 and vitreous GeO2 and discuss their analogies and differences. For both glasses, we generate model structures consisting of a random network of corner-shar ...

2007

Band gaps and dielectric constants of amorphous hafnium silicates: A first-principles investigation

Alfredo Pasquarello, Peter Broqvist

Electronic band gaps and dielectric constants are obtained for amorphous hafnium silicates using first-principles methods. Models of amorphous (HfO2)(x)(SiO2)(1-x) for varying x are generated by ab initio molecular dynamics. The calculations show that the ...

AIP American Institute of Physics2007

Atomistic model of the 4H(0001)SiC-SiO2 interface: structural and electronic properties

Alfredo Pasquarello, Feliciano Giustino, Fabien Devynck

Through the sequential use of classical molecular dynamics and first-principles relaxation methods, we generate an abrupt model interface for the 4H(0001)SiC-SiO2 interface showing regular structural parameters without any coordination defect. The valence ...

2007

Protons at the Si-SiO2 interface: a first principle investigation

Alfredo Pasquarello

We studied protons attached to bridging O atoms in the vicinity of the Si(100)-SiO2 interface through density-functional calculations for realistic interface models. These protons do not disrupt the bonding network except in the case of strained SiO bonds ...

2007

Amorphous hafnium silicates: structural, electronic and dielectric properties

Alfredo Pasquarello, Peter Broqvist

Models of amorphous (HfO2)x(SiO2)(1), for varying hafnium, content x are generated by ab initio molecular dynamics. The structural properties are analyzed in terms of pair distribution functions from which typical bond lengths and coordination numbers are ...

2007

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