Claudia Cancellieri - Academia.edu (original) (raw)

Papers by Claudia Cancellieri

During the growth of anodic Al oxide layers water incorporates in the film and therefore influenc... more During the growth of anodic Al oxide layers water incorporates in the film and therefore influences the intrinsic properties of the oxide formed. In this study, we propose a new approach, based on the use of high-resolution neutron imaging, to visualize and quantify the water content in porous Al oxides as a function of anodizing conditions. Water in these porous films is either incorporated directly in the oxide structure (structural) and/or fills the pores (morphological). This preliminary study demonstrates that the differences in water content of porous anodic Al oxide layers are strongly related to the oxide growth parameters but interestingly cannot be directly correlated to a specific change in the amorphous oxide structure or in the pore morphology. Due to the high sensitivity of high-resolution neutron imaging to small changes in the water content, we furthermore show that the morphological water content in Al oxides formed in sulfuric acid as well as in phosphoric acid is ...

Bulletin of the American Physical Society, 2011

Physical Review Letters, 2011

We present a direct comparison between experimental data and ab-initio calculations for the elect... more We present a direct comparison between experimental data and ab-initio calculations for the electrostrictive effect in the polar LaAlO3 layer grown on SrTiO3 substrates. From the structural data, a complete screening of the LaAlO3 dipole field is observed for film thicknesses between 6 and 20 uc. For thinner films, an expansion of the c axis of 2% matching the theoretical predictions for an electrostrictive effect is observed experimentally.

Bulletin of the American Physical Society, 2012

ABSTRACT The conducting interface between the two band insulators LaAlO3 and SrTiO3 [1], with its... more ABSTRACT The conducting interface between the two band insulators LaAlO3 and SrTiO3 [1], with its unique electronic properties, stands as a prominent example of an oxide heterostructure for the realization of multifunctional devices. Using the electric field effect the ground state of this system can be tuned from insulating to superconducting [2]. Recently we demonstrated also the possibility to tune the carriers mobility by changing the deposition conditions of the LaAlO3 film (3) and measured Shubnikov-de Haas oscillations, whose analyses demonstrate the 2D nature of the electronic states at the interface [3,4]. We are currently focusing on the realization of devices where the 2D quantum nature of the electronic states can be fully exploited. We show the feasibility of structures with lateral dimensions down to few hundreds nanometers, using an electron beam lithography based process. The lateral confinement of the electron gas in these devices is demonstrated by a phase coherent transport regime, which can be tuned by electric field.[4pt] [1] A.Ohtomo et al., Nature 427, 423 (2004)[0pt] [2] A.D.Caviglia et al., Nature 456, 624 (2008); C.Bell et al., PRL 103, 226802 (2009)[0pt] [3] A.D.Caviglia et al., PRL 105, 236802 (2010)[0pt] [4] M.Ben Shalom et al., PRL 105,206401 (2010)

Spectroscopy is an extremely important experimental tool providing information on the electronic ... more Spectroscopy is an extremely important experimental tool providing information on the electronic structure of the probed system that has to be seen as a stringent benchmark for the success of any electron structure theory. Photoemission spectroscopy (PES) or its inversethe Bremsstrahlen isochromat spectroscopy (BIS)in their angle-integrated form should reflect the density of states (DOS) rather directly, in particular in the high photon energy regime (XPS). For that reason it is quite common to check the abinitio calculations by comparing the calculated DOS directly to PES spectra. However, this approach ignores the influence of the specific PES matrix elements that in general will introduce an element-and energydependent weight to the partial DOS.

High saturation magnetization, hysteresis-less long linear response range, and resistance to devi... more High saturation magnetization, hysteresis-less long linear response range, and resistance to devicefabrication conditions are figures of merit for magnetic materials in science and technology.Despite advances in materials research, many high-saturating micro- and nanomagnetic materialsare hysteresis-prone, have short linear ranges, and are sensitive to oxidation, resulting in deviceinefficiencies in high-frequency electronics and unpredictable responses in magnetic sensing applications.Holmium oxide is a promising material because of its high magnetic susceptibility,but synthetic options are limited, with low-temperature magnetism incompletely characterized.Here, we present physical vapor deposition synthesis and material characterization of polycrystallineholmium oxide thin films. The product has saturation magnetization exceeding 2 Tesla,linear range (μ₀H) also exceeding 2 Tesla, zero magnetic remanence and coercivity, and resistanceto harsh processing condi...

Materials Science and Engineering: B

Abstract For Al alloys (e.g. Al-Si series) surface treatment like anodizing is a necessary step f... more Abstract For Al alloys (e.g. Al-Si series) surface treatment like anodizing is a necessary step for applications in aggressive environments. Si-surface enrichment caused by processing can alter importantly the anodizing process. Model alloys with Si supersaturated in Al layer grown by PVD have been used to investigate the effect of the Si content on the anodizing process. Different Si concentrations of 0, 4, 7, 10 at.% are considered and compared. The morphology and in-depth microstructure of the oxides are derived for the different Si contents and anodizing potentials. Si was found to have a dramatic effect on the void and defect formation during barrier Al oxides growth even for Si concentrations as low as 4 at.%. Importantly, the anodizing oxide layer appears to be heterogeneous in the cross section, with Si accumulation close to the metal oxide interface while pure Al oxide is first formed as a barrier on the top surface.

Acta Materialia, 2016

Abstract The thermal stability of Cu/W nano-multilayers in the temperature range of 400 °C– 800 °... more Abstract The thermal stability of Cu/W nano-multilayers in the temperature range of 400 °C– 800 °C has been investigated by high-resolution scanning electron microcopy, X-ray photoelectron spectroscopy and X-ray diffraction. A repetition of 100 alternating nanolayers of Cu and W with individual thicknesses of 5 nm were prepared by magnetron sputter deposition on an α-Al2O3 substrate. In the as-deposited state, the nano-multilayers exhibit pronounced Cu and W textures with a Cu{111} 1 ¯ >||W{110} 1 ¯ > orientation relationship. Annealing at T ≥ 500 °C results in the appearance of a high number of line-shaped protrusions on the outer surface, which are composed of facetted Cu particles. Annealing at T ≥ 700 °C leads to a gradual degradation of the initial layered structure towards a spheroidized nanocomposite consisting of globular W particles embedded in a Cu matrix (after annealing at 800 °C). An average activation energy of 257 ± 21 kJ/mol (2.66 ± 0.22 eV) related to this degradation process is determined by in-situ high-temperature X-ray diffraction. The experimentally obtained activation energy indicates that the morphological transformation is governed by the diffusion of W along internal interfaces such as Cu/W interphase boundaries and W/W grain boundaries.

Physical Review Materials

Heterostructures of transition metal oxides (TMO) perovskites represent an ideal platform to expl... more Heterostructures of transition metal oxides (TMO) perovskites represent an ideal platform to explore exotic phenomena involving the complex interplay between the spin, charge, orbital and lattice degrees of freedom available in these compounds. At the interface between such materials, this interplay can lead to phenomena that are present in none of the original constituents such as the formation of the interfacial 2D electron system (2DES) discovered at the LAO 3 /STO 3 (LAO/STO) interface. In samples prepared by growing a LAO layer onto a STO substrate, the 2DES is confined in a band bending potential well, whose width is set by the interface charge density and the STO dielectric properties, and determines the electronic band structure. Growing LAO (2 nm) /STO (x nm)/LAO (2 nm) heterostructures on STO substrates allows us to control the extension of the confining potential of the top 2DES via the thickness of the STO layer. In such samples, we explore the dependence of the electronic structure on the width of the confining potential using soft X-ray ARPES combined with ab-initio calculations. The results indicate that varying the thickness of the STO film modifies the quantization of the 3d t 2g bands and, interestingly, redistributes the charge between the d xy and d xz /d yz bands. Advances in thin-film deposition techniques have led to the discovery of a variety of phenomena in artificial heterostructures ranging from the quantum Hall effect to topological

Nature Communications, 2016

Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures resul... more Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally lim...

Advanced Energy Materials

Journal of Physics: Condensed Matter

Journal of Applied Physics

Spectroscopy of Complex Oxide Interfaces

Soft-X-ray ARPES (SX-ARPES) with its enhanced probing depth and chemical specificity allows acces... more Soft-X-ray ARPES (SX-ARPES) with its enhanced probing depth and chemical specificity allows access to fundamental electronic structure characteristics-momentum-resolved spectral function, band structure, Fermi surface-of systems difficult and even impossible for the conventional ARPES such as three-dimensional materials, buried interfaces and impurities. After a recap of the spectroscopic abilities of SX-ARPES, we review its applications to oxide interfaces, focusing on the paradigm LaAlO 3 /SrTiO 3 interface. Resonant SX-ARPES at the Ti Ledge accentuates photoemission response of the mobile interface electrons and exposes their d xy-, d yz-and d xz-derived subbands forming the Fermi surface in the interface quantum well. After a recap of the electron-phonon interaction physics, we demonstrate that peak-dip-hump structure of the experimental spectral function manifests the Holstein-type large polaron nature of the interface charge carriers, explaining their fundamentally reduced mobility. Coupling of the charge carriers to polar soft phonon modes defines dramatic drop of mobility with temperature. Oxygen deficiency adds another dimension to the rich physics of LaAlO 3 /SrTiO 3 resulting from coexistence of mobile and localized electrons introduced by oxygen vacancies. Oxygen deficiency allows tuning of the polaronic coupling and thus mobility of the charge carriers, as well as of interfacial ferromagnetism connected with various atomic configurations of the vacancies. Finally, we discuss spectroscopic evidence of phase separation at the LaAlO 3 /SrTiO 3 interface. Concluding, we put prospects of SX-ARPES for complex heterostructures, spin-resolving experiments opening the totally unexplored field of interfacial spin structure, and inoperando field-effect experiments paving the way towards device applications of the reach physics of oxide interfaces.

Spectroscopy of Complex Oxide Interfaces

During the growth of anodic Al oxide layers water incorporates in the film and therefore influenc... more During the growth of anodic Al oxide layers water incorporates in the film and therefore influences the intrinsic properties of the oxide formed. In this study, we propose a new approach, based on the use of high-resolution neutron imaging, to visualize and quantify the water content in porous Al oxides as a function of anodizing conditions. Water in these porous films is either incorporated directly in the oxide structure (structural) and/or fills the pores (morphological). This preliminary study demonstrates that the differences in water content of porous anodic Al oxide layers are strongly related to the oxide growth parameters but interestingly cannot be directly correlated to a specific change in the amorphous oxide structure or in the pore morphology. Due to the high sensitivity of high-resolution neutron imaging to small changes in the water content, we furthermore show that the morphological water content in Al oxides formed in sulfuric acid as well as in phosphoric acid is ...

Bulletin of the American Physical Society, 2011

Physical Review Letters, 2011

We present a direct comparison between experimental data and ab-initio calculations for the elect... more We present a direct comparison between experimental data and ab-initio calculations for the electrostrictive effect in the polar LaAlO3 layer grown on SrTiO3 substrates. From the structural data, a complete screening of the LaAlO3 dipole field is observed for film thicknesses between 6 and 20 uc. For thinner films, an expansion of the c axis of 2% matching the theoretical predictions for an electrostrictive effect is observed experimentally.

Bulletin of the American Physical Society, 2012

ABSTRACT The conducting interface between the two band insulators LaAlO3 and SrTiO3 [1], with its... more ABSTRACT The conducting interface between the two band insulators LaAlO3 and SrTiO3 [1], with its unique electronic properties, stands as a prominent example of an oxide heterostructure for the realization of multifunctional devices. Using the electric field effect the ground state of this system can be tuned from insulating to superconducting [2]. Recently we demonstrated also the possibility to tune the carriers mobility by changing the deposition conditions of the LaAlO3 film (3) and measured Shubnikov-de Haas oscillations, whose analyses demonstrate the 2D nature of the electronic states at the interface [3,4]. We are currently focusing on the realization of devices where the 2D quantum nature of the electronic states can be fully exploited. We show the feasibility of structures with lateral dimensions down to few hundreds nanometers, using an electron beam lithography based process. The lateral confinement of the electron gas in these devices is demonstrated by a phase coherent transport regime, which can be tuned by electric field.[4pt] [1] A.Ohtomo et al., Nature 427, 423 (2004)[0pt] [2] A.D.Caviglia et al., Nature 456, 624 (2008); C.Bell et al., PRL 103, 226802 (2009)[0pt] [3] A.D.Caviglia et al., PRL 105, 236802 (2010)[0pt] [4] M.Ben Shalom et al., PRL 105,206401 (2010)

Spectroscopy is an extremely important experimental tool providing information on the electronic ... more Spectroscopy is an extremely important experimental tool providing information on the electronic structure of the probed system that has to be seen as a stringent benchmark for the success of any electron structure theory. Photoemission spectroscopy (PES) or its inversethe Bremsstrahlen isochromat spectroscopy (BIS)in their angle-integrated form should reflect the density of states (DOS) rather directly, in particular in the high photon energy regime (XPS). For that reason it is quite common to check the abinitio calculations by comparing the calculated DOS directly to PES spectra. However, this approach ignores the influence of the specific PES matrix elements that in general will introduce an element-and energydependent weight to the partial DOS.

High saturation magnetization, hysteresis-less long linear response range, and resistance to devi... more High saturation magnetization, hysteresis-less long linear response range, and resistance to devicefabrication conditions are figures of merit for magnetic materials in science and technology.Despite advances in materials research, many high-saturating micro- and nanomagnetic materialsare hysteresis-prone, have short linear ranges, and are sensitive to oxidation, resulting in deviceinefficiencies in high-frequency electronics and unpredictable responses in magnetic sensing applications.Holmium oxide is a promising material because of its high magnetic susceptibility,but synthetic options are limited, with low-temperature magnetism incompletely characterized.Here, we present physical vapor deposition synthesis and material characterization of polycrystallineholmium oxide thin films. The product has saturation magnetization exceeding 2 Tesla,linear range (μ₀H) also exceeding 2 Tesla, zero magnetic remanence and coercivity, and resistanceto harsh processing condi...

Materials Science and Engineering: B

Abstract For Al alloys (e.g. Al-Si series) surface treatment like anodizing is a necessary step f... more Abstract For Al alloys (e.g. Al-Si series) surface treatment like anodizing is a necessary step for applications in aggressive environments. Si-surface enrichment caused by processing can alter importantly the anodizing process. Model alloys with Si supersaturated in Al layer grown by PVD have been used to investigate the effect of the Si content on the anodizing process. Different Si concentrations of 0, 4, 7, 10 at.% are considered and compared. The morphology and in-depth microstructure of the oxides are derived for the different Si contents and anodizing potentials. Si was found to have a dramatic effect on the void and defect formation during barrier Al oxides growth even for Si concentrations as low as 4 at.%. Importantly, the anodizing oxide layer appears to be heterogeneous in the cross section, with Si accumulation close to the metal oxide interface while pure Al oxide is first formed as a barrier on the top surface.

Acta Materialia, 2016

Abstract The thermal stability of Cu/W nano-multilayers in the temperature range of 400 °C– 800 °... more Abstract The thermal stability of Cu/W nano-multilayers in the temperature range of 400 °C– 800 °C has been investigated by high-resolution scanning electron microcopy, X-ray photoelectron spectroscopy and X-ray diffraction. A repetition of 100 alternating nanolayers of Cu and W with individual thicknesses of 5 nm were prepared by magnetron sputter deposition on an α-Al2O3 substrate. In the as-deposited state, the nano-multilayers exhibit pronounced Cu and W textures with a Cu{111} 1 ¯ >||W{110} 1 ¯ > orientation relationship. Annealing at T ≥ 500 °C results in the appearance of a high number of line-shaped protrusions on the outer surface, which are composed of facetted Cu particles. Annealing at T ≥ 700 °C leads to a gradual degradation of the initial layered structure towards a spheroidized nanocomposite consisting of globular W particles embedded in a Cu matrix (after annealing at 800 °C). An average activation energy of 257 ± 21 kJ/mol (2.66 ± 0.22 eV) related to this degradation process is determined by in-situ high-temperature X-ray diffraction. The experimentally obtained activation energy indicates that the morphological transformation is governed by the diffusion of W along internal interfaces such as Cu/W interphase boundaries and W/W grain boundaries.

Physical Review Materials

Heterostructures of transition metal oxides (TMO) perovskites represent an ideal platform to expl... more Heterostructures of transition metal oxides (TMO) perovskites represent an ideal platform to explore exotic phenomena involving the complex interplay between the spin, charge, orbital and lattice degrees of freedom available in these compounds. At the interface between such materials, this interplay can lead to phenomena that are present in none of the original constituents such as the formation of the interfacial 2D electron system (2DES) discovered at the LAO 3 /STO 3 (LAO/STO) interface. In samples prepared by growing a LAO layer onto a STO substrate, the 2DES is confined in a band bending potential well, whose width is set by the interface charge density and the STO dielectric properties, and determines the electronic band structure. Growing LAO (2 nm) /STO (x nm)/LAO (2 nm) heterostructures on STO substrates allows us to control the extension of the confining potential of the top 2DES via the thickness of the STO layer. In such samples, we explore the dependence of the electronic structure on the width of the confining potential using soft X-ray ARPES combined with ab-initio calculations. The results indicate that varying the thickness of the STO film modifies the quantization of the 3d t 2g bands and, interestingly, redistributes the charge between the d xy and d xz /d yz bands. Advances in thin-film deposition techniques have led to the discovery of a variety of phenomena in artificial heterostructures ranging from the quantum Hall effect to topological

Nature Communications, 2016

Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures resul... more Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally lim...

Advanced Energy Materials

Journal of Physics: Condensed Matter

Journal of Applied Physics

Spectroscopy of Complex Oxide Interfaces

Soft-X-ray ARPES (SX-ARPES) with its enhanced probing depth and chemical specificity allows acces... more Soft-X-ray ARPES (SX-ARPES) with its enhanced probing depth and chemical specificity allows access to fundamental electronic structure characteristics-momentum-resolved spectral function, band structure, Fermi surface-of systems difficult and even impossible for the conventional ARPES such as three-dimensional materials, buried interfaces and impurities. After a recap of the spectroscopic abilities of SX-ARPES, we review its applications to oxide interfaces, focusing on the paradigm LaAlO 3 /SrTiO 3 interface. Resonant SX-ARPES at the Ti Ledge accentuates photoemission response of the mobile interface electrons and exposes their d xy-, d yz-and d xz-derived subbands forming the Fermi surface in the interface quantum well. After a recap of the electron-phonon interaction physics, we demonstrate that peak-dip-hump structure of the experimental spectral function manifests the Holstein-type large polaron nature of the interface charge carriers, explaining their fundamentally reduced mobility. Coupling of the charge carriers to polar soft phonon modes defines dramatic drop of mobility with temperature. Oxygen deficiency adds another dimension to the rich physics of LaAlO 3 /SrTiO 3 resulting from coexistence of mobile and localized electrons introduced by oxygen vacancies. Oxygen deficiency allows tuning of the polaronic coupling and thus mobility of the charge carriers, as well as of interfacial ferromagnetism connected with various atomic configurations of the vacancies. Finally, we discuss spectroscopic evidence of phase separation at the LaAlO 3 /SrTiO 3 interface. Concluding, we put prospects of SX-ARPES for complex heterostructures, spin-resolving experiments opening the totally unexplored field of interfacial spin structure, and inoperando field-effect experiments paving the way towards device applications of the reach physics of oxide interfaces.

Spectroscopy of Complex Oxide Interfaces