F. Negreiros | UFABC - Federal University of ABC (original) (raw)

Papers by F. Negreiros

Physical Review B, 2010

Heteroepitaxy has been widely studied by many different theoretical and experimental techniques. ... more Heteroepitaxy has been widely studied by many different theoretical and experimental techniques. Each technique focuses on some features of the growth process, and only by combining the information each provides a full characterization can be given. In this work, the growth of Pd on Ni͑111͒, Pd on Cu͑111͒, Cu on Pd͑111͒, and Ni on Pd͑111͒ is studied with a purely energetic approach which consists of determining a unit cell with a size that depends on the relation between the lateral misfit of the deposited film and the substrate. The energetic is evaluated using a semiempirical coupled with a genetic algorithm global search method to determine with accuracy the relaxation magnitudes of the system. With this approach, features such as interlayer spacings, variation in the film's lattice parameter with coverage, and diffusion influence in the growth process are studied qualitative and quantitatively. The results obtained are directly compared with experimental findings from literature and also presented in this work. The theory-experiment comparison shows that the methodology used is successful in describing qualitatively most features of all four systems. However, for the Pd on Cu͑111͒ case, poor agreement is found, and the analysis of the influence of diffusion and temperature suggests that a somewhat complex alloy formation in the interface is expected for this particular system.

Physical Review B, 2013

ABSTRACT Electronic excited states at a bcc(110) lithium surface, both bare and covered by ionic ... more ABSTRACT Electronic excited states at a bcc(110) lithium surface, both bare and covered by ionic ultrathin (1–2 monolayers) LiF epitaxial films, are investigated via many-body perturbation theory calculations achieving an atomistic level of detail. The full self-consistent solution of the GW equations is used to account for correlation effects and to properly describe the screened potential in the vacuum. In addition to the correct prediction of image-potential states, we find that the mixing between resonances and image states and the charge compression due to the dielectric ultrathin overlayer give rise to excitations with a hybrid localized but low-lying character whose accurate description cannot intrinsically be achieved via simple models or low-level calculations, but which are expected to play a crucial role in determining the electronic response and transport properties of these systems.

ACS Catalysis, 2012

ABSTRACT The activity of AgxAu3?x/MgO(100) clusters in CO oxidation is investigated computational... more ABSTRACT The activity of AgxAu3?x/MgO(100) clusters in CO oxidation is investigated computationally via systematic sampling techniques. It is found that these subnanometer species transform after ligand adsorption into reaction complexes which catalyze CO oxidation through a variety of different mechanisms, occurring via both Langmuir?Hinshelwood and Eley?Rideal paths and in some cases directly involving the oxide support. The alloyed Ag2Au1 cluster is proposed as the best catalyst in terms of efficiency and robustness.

The Journal of Physical Chemistry C, 2011

The Journal of Physical Chemistry C, 2012

In this work, a systematic study of the influence of growth conditions on the anomalous formation... more In this work, a systematic study of the influence of growth conditions on the anomalous formation of ternary In x Ga 1-x As nanowires is presented. Free-standing nanowires, of nominal InAs composition, were grown by molecular beam epitaxy on GaAs (111)B substrates at different temperatures and As 4 beam equivalent pressures. The morphology, chemical composition, and crystal structure of the nanowires were investigated by scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffraction techniques. It was found that a strong incorporation of Ga occurs during the growth creating a homogeneous ternary In x Ga 1-x As alloy in the nanowires with very low residual strain. The GaAs molar fraction was found to increase with the growth temperature and to decrease with the As 4 beam equivalent pressure. A nanowire growth model, taking into account the creation and diffusion of Ga adatoms from the substrate surface toward the nanowires, was used to explain the incorporation of Ga atoms and the formation of the ternary alloy. This model predicts that the GaAs/InAs composition ratio in the nanowires follows an Arrhenius law as a function of the growth temperature with an inverse square root dependency of the As 4 beam equivalent pressure as a pre-exponential factor. The theory was found to fit well the experimental data with an activation energy of 1 eV. It is also shown that the activation energy corresponds to the energy necessary to create Ga adatoms on the surface of the GaAs (111)B substrate. Both experimental and theoretical results show that in this range of growth conditions the limiting factor for the formation of the In x Ga 1-x As alloy in the nanowires is not the diffusion length of the Ga and In adatoms on the substrate surface and nanowires side walls but the density of available Ga adatoms on the substrate surface.

Surface Science, 2010

In this work we report on a very accurate low-energy electron diffraction (LEED) and a DFT study ... more In this work we report on a very accurate low-energy electron diffraction (LEED) and a DFT study of Au(1 1 0)-(1  2) in order to determine its surface geometry. The LEED results indicate a surface missing row reconstruction with a large contraction of ðÀ0:29 AE 0:02Þ Å, a pairing in the second layer ð0:06 AE 0:05Þ Å and in the fourth layer ð0:07 AE 0:04Þ Å, and a buckling in the third layer of 0.30 Å and in the fifth layer of 0.01 Å. These LEED results are in very good agreement with those found by the DFT calculations.

Physical Review Letters, 2013

A sodium chloride monolayer on a Cu(110) surface gives rise to a highly corrugated periodic nanos... more A sodium chloride monolayer on a Cu(110) surface gives rise to a highly corrugated periodic nanostripe pattern of the (100) lattice as observed by scanning tunneling microscopy and low-energy electron diffraction. As revealed by density-functional calculations, this pattern is a consequence of the frustration of the overlayer-substrate chemical bonding produced by epitaxial mismatch. The coexistence of regions of strong Cu-Cl covalent and weak nonbonding interactions leads to a chemically induced topographic modulation here realized in a two-dimensional dielectric. The carpetlike growth of the NaCl layer across Cu step edges induces a distinct contrast inversion in the stripe pattern as a result of the change in epitaxial relationship due to the stacking sequence of the (110) Cu layers. It is demonstrated that the competition between local substrate-overlayer and intraoverlayer interactions can support a well-defined heteroepitaxial relationship of a ionic dielectric film and a metal surface, with important consequences for the nanoscale morphology and related properties.

Nanoscale, 2013

In this study we report a direct, atomic-resolution imaging of calcined Au 24 Pd 1 clusters suppo... more In this study we report a direct, atomic-resolution imaging of calcined Au 24 Pd 1 clusters supported on multiwall carbon nanotubes by employing aberration-corrected scanning transmission electron microscopy. Using gold atoms as mass standards, we confirm the cluster size to be 25 AE 2, in agreement with the Au 24 Pd 1 (SR) 18 precursor used in the synthesis. Concurrently, a Density-Functional/Basin-Hopping computational algorithm is employed to locate the low-energy configurations of free Au 24 Pd 1 cluster. Cage structures surrounding a single core atom are found to be favored, with a slight preference for Pd to occupy the core site. The cluster shows a tendency toward elongated arrangements, consistent with experimental data. The degree of electron transfer from the Pd dopant to Au is quantified through a Löwdin charge analysis, suggesting that Pd may act as an electron promoter to the surrounding Au atoms when they are involved in catalytic reactions.

The Journal of Chemical Physics, 2012

The energetics and kinetic energy barriers of vacancy/atom exchange in a 37-atom truncated octahe... more The energetics and kinetic energy barriers of vacancy/atom exchange in a 37-atom truncated octahedron Ag-Pt binary cluster in the Ag-rich range of compositions are investigated via a firstprinciples atomistic approach. The energy of the local minima obtained considering various distributions of a single vacancy and a few Pt atoms within the cluster and the energy barriers connecting them are evaluated using accurate density-functional calculations. The effects of the simultaneous presence of a vacancy and Pt atoms are found to be simply additive when their distances are larger than first-neighbors, whereas when they can be stabilizing at low Pt content due to the release of strain by the Pt/vacancy interaction or destabilizing close to a perfect Pt(core)/Ag(shell) arrangement. It is found that alloying with Pt appreciably increases the barriers for homotops transformations, thus rationalizing the issues encountered at the experimental level in producing Ag-Pt equilibrated nanoparticles and bulk phase diagram.

Details of the growth and of the surface structure of 1, 2, and 3 monolayers of Au on Pd(100) hav... more Details of the growth and of the surface structure of 1, 2, and 3 monolayers of Au on Pd(100) have been investigated by reflection high-energy electron diffraction (RHEED), quantitative low-energy electron diffraction (LEED)-I(V) analysis and density-functional theory calculations (DFT). Despite the 4.7% misfit between Auand Pd-lattice parameters, no change on the lateral lattice parameter was observed up to a thickness of 10 ML by RHEED, evidencing pseudomorphous growth. Up to 3 ML a (1 × 1) LEED pattern is observed, while at higher coverages a (7 × 1) superstructure is formed. The interlayer distances of the last atomic layers of n-ML-Au/Pd(100) (n = 1, 2, 3) as determined by quantitative LEED and DFT calculations are compared and show only a reasonable agreement. However, DFT results indicate that surface alloying is energetically favorable, and a better match with the experimentally determined interlayer distances is obtained with surface alloy formation.

The evolution of the morphology of Ni-oxide nanostructures on Ag(100) as a function of temperatur... more The evolution of the morphology of Ni-oxide nanostructures on Ag(100) as a function of temperature has been followed experimentally by scanning tunneling microscopy (STM) and theoretically by density-functional theory (DFT) calculations. After reactive deposition at room temperature and annealing at 450 K, the NiO(2 × 1) phase embedded into the Ag substrate is formed due to kinetic stabilization during growth.

Physical Review B, 2007

Atomistic modeling of the formation process of Au-Ag nanoparticles is performed using the Bozzolo... more Atomistic modeling of the formation process of Au-Ag nanoparticles is performed using the Bozzolo-Ferrante-Smith method for alloys for the energetic. Silver segregation to the surface, surface structure and orientation, and weak Au-Ag interactions are identified as the main features driving the formation process.

Physical Review B, 2007

The energy of metallic ͑Ni, Cu, Pd, Ag, Pt, and Au͒ nanoparticles up to 5000 atoms are studied by... more The energy of metallic ͑Ni, Cu, Pd, Ag, Pt, and Au͒ nanoparticles up to 5000 atoms are studied by equivalent crystal theory ͑ECT͒, a quantum approximate method ͑QAM͒ that describes the ground state structure and the surface properties of metals and semiconductors at zero temperature. ECT relies on the universal binding energy relation to predict with precision and speed the energy of a crystal in a specific configuration. For each pure metallic nanoparticle of each chosen motif ͑icosahedron, octahedron, and decahedron͒, the energy variation with the number of atoms N at is studied. Crossover and minimum energy values are calculated and/or estimated and compared with the results obtained by molecular dynamics ͑MD͒. Our results confirm the qualitative behavior ͑i.e., icosahedron shapes are less energetic for small sizes, decahedron for medium sizes, and octahedron for bigger sizes͒ predicted by MD, but the calculated crossover and minimum energy values are, in general, larger for all metals and geometries examined. Also, we studied the trends in relaxation between layers and the behavior of the average radius R av of each relaxed nanoparticle as N at was increased. For each motif, the most stable structures ͑i.e., with the best truncation͒ follow a simple law of R av in terms of N at . This simple law is unchanged for the four different motifs and can be extended for all six metals after a simple parametrization is performed.

The Journal of Chemical Physics, 2013

The energy landscape and kinetics of medium-sized Ag-Au and Ag-Ni nanoalloy particles are explore... more The energy landscape and kinetics of medium-sized Ag-Au and Ag-Ni nanoalloy particles are explored via a discrete path sampling approach, focusing on rearrangements connecting regions differing in chemical order. The highly miscible Ag 27 Au 28 supports a large number of nearly degenerate icosahedral homotops. The transformation from reverse core-shell to core-shell involves large displacements away from the icosahedron through elementary steps corresponding to surface diffusion and vacancy formation. The immiscible Ag 42 Ni 13 naturally forms an asymmetric core-shell structure, and about 10 eV is required to extrude the nickel core to the surface. The corresponding transformation occurs via a long and smooth sequence of surface displacements. For both systems the rearrangement kinetics exhibit Arrhenius behavior. These results are discussed in the light of experimental observations.

ACS Nano, 2014

Metal tungstates (with general formula MWO4) are functional materials with a high potential for a... more Metal tungstates (with general formula MWO4) are functional materials with a high potential for a diverse set of applications ranging from low-dimensional magnetism to chemical sensing and photoelectrocatalytic water oxidation. For high level applications, nanoscale control of film growth is necessary, as well as a deeper understanding and characterization of materials properties at reduced dimensionality. We succeeded in fabricating and characterizing a two-dimensional (2-D) copper tungstate (CuWO4). For the first time, the atomic structure of an ultrathin ternary oxide is fully unveiled. It corresponds to a CuWO4 monolayer arranged in three sublayers with stacking O-W-O/Cu from the interface. The resulting bidimensional structure forms a robust framework with localized regions of anisotropic flexibility. Electronically it displays a reduced band gap and increased density of states close to the Fermi level with respect to the bulk compound. These unique features open a way for new applications in the field of photo- and electrocatalysis, while the proposed synthesis method represents a radically new and general approach toward the fabrication of 2-D ternary oxides.

Physical Review B, 2010

Heteroepitaxy has been widely studied by many different theoretical and experimental techniques. ... more Heteroepitaxy has been widely studied by many different theoretical and experimental techniques. Each technique focuses on some features of the growth process, and only by combining the information each provides a full characterization can be given. In this work, the growth of Pd on Ni͑111͒, Pd on Cu͑111͒, Cu on Pd͑111͒, and Ni on Pd͑111͒ is studied with a purely energetic approach which consists of determining a unit cell with a size that depends on the relation between the lateral misfit of the deposited film and the substrate. The energetic is evaluated using a semiempirical coupled with a genetic algorithm global search method to determine with accuracy the relaxation magnitudes of the system. With this approach, features such as interlayer spacings, variation in the film's lattice parameter with coverage, and diffusion influence in the growth process are studied qualitative and quantitatively. The results obtained are directly compared with experimental findings from literature and also presented in this work. The theory-experiment comparison shows that the methodology used is successful in describing qualitatively most features of all four systems. However, for the Pd on Cu͑111͒ case, poor agreement is found, and the analysis of the influence of diffusion and temperature suggests that a somewhat complex alloy formation in the interface is expected for this particular system.

Physical Review B, 2013

ABSTRACT Electronic excited states at a bcc(110) lithium surface, both bare and covered by ionic ... more ABSTRACT Electronic excited states at a bcc(110) lithium surface, both bare and covered by ionic ultrathin (1–2 monolayers) LiF epitaxial films, are investigated via many-body perturbation theory calculations achieving an atomistic level of detail. The full self-consistent solution of the GW equations is used to account for correlation effects and to properly describe the screened potential in the vacuum. In addition to the correct prediction of image-potential states, we find that the mixing between resonances and image states and the charge compression due to the dielectric ultrathin overlayer give rise to excitations with a hybrid localized but low-lying character whose accurate description cannot intrinsically be achieved via simple models or low-level calculations, but which are expected to play a crucial role in determining the electronic response and transport properties of these systems.

ACS Catalysis, 2012

ABSTRACT The activity of AgxAu3?x/MgO(100) clusters in CO oxidation is investigated computational... more ABSTRACT The activity of AgxAu3?x/MgO(100) clusters in CO oxidation is investigated computationally via systematic sampling techniques. It is found that these subnanometer species transform after ligand adsorption into reaction complexes which catalyze CO oxidation through a variety of different mechanisms, occurring via both Langmuir?Hinshelwood and Eley?Rideal paths and in some cases directly involving the oxide support. The alloyed Ag2Au1 cluster is proposed as the best catalyst in terms of efficiency and robustness.

The Journal of Physical Chemistry C, 2011

The Journal of Physical Chemistry C, 2012

In this work, a systematic study of the influence of growth conditions on the anomalous formation... more In this work, a systematic study of the influence of growth conditions on the anomalous formation of ternary In x Ga 1-x As nanowires is presented. Free-standing nanowires, of nominal InAs composition, were grown by molecular beam epitaxy on GaAs (111)B substrates at different temperatures and As 4 beam equivalent pressures. The morphology, chemical composition, and crystal structure of the nanowires were investigated by scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffraction techniques. It was found that a strong incorporation of Ga occurs during the growth creating a homogeneous ternary In x Ga 1-x As alloy in the nanowires with very low residual strain. The GaAs molar fraction was found to increase with the growth temperature and to decrease with the As 4 beam equivalent pressure. A nanowire growth model, taking into account the creation and diffusion of Ga adatoms from the substrate surface toward the nanowires, was used to explain the incorporation of Ga atoms and the formation of the ternary alloy. This model predicts that the GaAs/InAs composition ratio in the nanowires follows an Arrhenius law as a function of the growth temperature with an inverse square root dependency of the As 4 beam equivalent pressure as a pre-exponential factor. The theory was found to fit well the experimental data with an activation energy of 1 eV. It is also shown that the activation energy corresponds to the energy necessary to create Ga adatoms on the surface of the GaAs (111)B substrate. Both experimental and theoretical results show that in this range of growth conditions the limiting factor for the formation of the In x Ga 1-x As alloy in the nanowires is not the diffusion length of the Ga and In adatoms on the substrate surface and nanowires side walls but the density of available Ga adatoms on the substrate surface.

Surface Science, 2010

In this work we report on a very accurate low-energy electron diffraction (LEED) and a DFT study ... more In this work we report on a very accurate low-energy electron diffraction (LEED) and a DFT study of Au(1 1 0)-(1  2) in order to determine its surface geometry. The LEED results indicate a surface missing row reconstruction with a large contraction of ðÀ0:29 AE 0:02Þ Å, a pairing in the second layer ð0:06 AE 0:05Þ Å and in the fourth layer ð0:07 AE 0:04Þ Å, and a buckling in the third layer of 0.30 Å and in the fifth layer of 0.01 Å. These LEED results are in very good agreement with those found by the DFT calculations.

Physical Review Letters, 2013

A sodium chloride monolayer on a Cu(110) surface gives rise to a highly corrugated periodic nanos... more A sodium chloride monolayer on a Cu(110) surface gives rise to a highly corrugated periodic nanostripe pattern of the (100) lattice as observed by scanning tunneling microscopy and low-energy electron diffraction. As revealed by density-functional calculations, this pattern is a consequence of the frustration of the overlayer-substrate chemical bonding produced by epitaxial mismatch. The coexistence of regions of strong Cu-Cl covalent and weak nonbonding interactions leads to a chemically induced topographic modulation here realized in a two-dimensional dielectric. The carpetlike growth of the NaCl layer across Cu step edges induces a distinct contrast inversion in the stripe pattern as a result of the change in epitaxial relationship due to the stacking sequence of the (110) Cu layers. It is demonstrated that the competition between local substrate-overlayer and intraoverlayer interactions can support a well-defined heteroepitaxial relationship of a ionic dielectric film and a metal surface, with important consequences for the nanoscale morphology and related properties.

Nanoscale, 2013

In this study we report a direct, atomic-resolution imaging of calcined Au 24 Pd 1 clusters suppo... more In this study we report a direct, atomic-resolution imaging of calcined Au 24 Pd 1 clusters supported on multiwall carbon nanotubes by employing aberration-corrected scanning transmission electron microscopy. Using gold atoms as mass standards, we confirm the cluster size to be 25 AE 2, in agreement with the Au 24 Pd 1 (SR) 18 precursor used in the synthesis. Concurrently, a Density-Functional/Basin-Hopping computational algorithm is employed to locate the low-energy configurations of free Au 24 Pd 1 cluster. Cage structures surrounding a single core atom are found to be favored, with a slight preference for Pd to occupy the core site. The cluster shows a tendency toward elongated arrangements, consistent with experimental data. The degree of electron transfer from the Pd dopant to Au is quantified through a Löwdin charge analysis, suggesting that Pd may act as an electron promoter to the surrounding Au atoms when they are involved in catalytic reactions.

The Journal of Chemical Physics, 2012

The energetics and kinetic energy barriers of vacancy/atom exchange in a 37-atom truncated octahe... more The energetics and kinetic energy barriers of vacancy/atom exchange in a 37-atom truncated octahedron Ag-Pt binary cluster in the Ag-rich range of compositions are investigated via a firstprinciples atomistic approach. The energy of the local minima obtained considering various distributions of a single vacancy and a few Pt atoms within the cluster and the energy barriers connecting them are evaluated using accurate density-functional calculations. The effects of the simultaneous presence of a vacancy and Pt atoms are found to be simply additive when their distances are larger than first-neighbors, whereas when they can be stabilizing at low Pt content due to the release of strain by the Pt/vacancy interaction or destabilizing close to a perfect Pt(core)/Ag(shell) arrangement. It is found that alloying with Pt appreciably increases the barriers for homotops transformations, thus rationalizing the issues encountered at the experimental level in producing Ag-Pt equilibrated nanoparticles and bulk phase diagram.

Details of the growth and of the surface structure of 1, 2, and 3 monolayers of Au on Pd(100) hav... more Details of the growth and of the surface structure of 1, 2, and 3 monolayers of Au on Pd(100) have been investigated by reflection high-energy electron diffraction (RHEED), quantitative low-energy electron diffraction (LEED)-I(V) analysis and density-functional theory calculations (DFT). Despite the 4.7% misfit between Auand Pd-lattice parameters, no change on the lateral lattice parameter was observed up to a thickness of 10 ML by RHEED, evidencing pseudomorphous growth. Up to 3 ML a (1 × 1) LEED pattern is observed, while at higher coverages a (7 × 1) superstructure is formed. The interlayer distances of the last atomic layers of n-ML-Au/Pd(100) (n = 1, 2, 3) as determined by quantitative LEED and DFT calculations are compared and show only a reasonable agreement. However, DFT results indicate that surface alloying is energetically favorable, and a better match with the experimentally determined interlayer distances is obtained with surface alloy formation.

The evolution of the morphology of Ni-oxide nanostructures on Ag(100) as a function of temperatur... more The evolution of the morphology of Ni-oxide nanostructures on Ag(100) as a function of temperature has been followed experimentally by scanning tunneling microscopy (STM) and theoretically by density-functional theory (DFT) calculations. After reactive deposition at room temperature and annealing at 450 K, the NiO(2 × 1) phase embedded into the Ag substrate is formed due to kinetic stabilization during growth.

Physical Review B, 2007

Atomistic modeling of the formation process of Au-Ag nanoparticles is performed using the Bozzolo... more Atomistic modeling of the formation process of Au-Ag nanoparticles is performed using the Bozzolo-Ferrante-Smith method for alloys for the energetic. Silver segregation to the surface, surface structure and orientation, and weak Au-Ag interactions are identified as the main features driving the formation process.

Physical Review B, 2007

The energy of metallic ͑Ni, Cu, Pd, Ag, Pt, and Au͒ nanoparticles up to 5000 atoms are studied by... more The energy of metallic ͑Ni, Cu, Pd, Ag, Pt, and Au͒ nanoparticles up to 5000 atoms are studied by equivalent crystal theory ͑ECT͒, a quantum approximate method ͑QAM͒ that describes the ground state structure and the surface properties of metals and semiconductors at zero temperature. ECT relies on the universal binding energy relation to predict with precision and speed the energy of a crystal in a specific configuration. For each pure metallic nanoparticle of each chosen motif ͑icosahedron, octahedron, and decahedron͒, the energy variation with the number of atoms N at is studied. Crossover and minimum energy values are calculated and/or estimated and compared with the results obtained by molecular dynamics ͑MD͒. Our results confirm the qualitative behavior ͑i.e., icosahedron shapes are less energetic for small sizes, decahedron for medium sizes, and octahedron for bigger sizes͒ predicted by MD, but the calculated crossover and minimum energy values are, in general, larger for all metals and geometries examined. Also, we studied the trends in relaxation between layers and the behavior of the average radius R av of each relaxed nanoparticle as N at was increased. For each motif, the most stable structures ͑i.e., with the best truncation͒ follow a simple law of R av in terms of N at . This simple law is unchanged for the four different motifs and can be extended for all six metals after a simple parametrization is performed.

The Journal of Chemical Physics, 2013

The energy landscape and kinetics of medium-sized Ag-Au and Ag-Ni nanoalloy particles are explore... more The energy landscape and kinetics of medium-sized Ag-Au and Ag-Ni nanoalloy particles are explored via a discrete path sampling approach, focusing on rearrangements connecting regions differing in chemical order. The highly miscible Ag 27 Au 28 supports a large number of nearly degenerate icosahedral homotops. The transformation from reverse core-shell to core-shell involves large displacements away from the icosahedron through elementary steps corresponding to surface diffusion and vacancy formation. The immiscible Ag 42 Ni 13 naturally forms an asymmetric core-shell structure, and about 10 eV is required to extrude the nickel core to the surface. The corresponding transformation occurs via a long and smooth sequence of surface displacements. For both systems the rearrangement kinetics exhibit Arrhenius behavior. These results are discussed in the light of experimental observations.

ACS Nano, 2014

Metal tungstates (with general formula MWO4) are functional materials with a high potential for a... more Metal tungstates (with general formula MWO4) are functional materials with a high potential for a diverse set of applications ranging from low-dimensional magnetism to chemical sensing and photoelectrocatalytic water oxidation. For high level applications, nanoscale control of film growth is necessary, as well as a deeper understanding and characterization of materials properties at reduced dimensionality. We succeeded in fabricating and characterizing a two-dimensional (2-D) copper tungstate (CuWO4). For the first time, the atomic structure of an ultrathin ternary oxide is fully unveiled. It corresponds to a CuWO4 monolayer arranged in three sublayers with stacking O-W-O/Cu from the interface. The resulting bidimensional structure forms a robust framework with localized regions of anisotropic flexibility. Electronically it displays a reduced band gap and increased density of states close to the Fermi level with respect to the bulk compound. These unique features open a way for new applications in the field of photo- and electrocatalysis, while the proposed synthesis method represents a radically new and general approach toward the fabrication of 2-D ternary oxides.