Alice Galdi

Università degli Studi di Salerno | UNISA · Department of Industrial Engineering (DIIn)

Negative Electron Affinity (NEA) activated GaAs photocathodes are the most popular option for generating a high current ([Formula: see text]1 mA) spin-polarized electron beam. Despite its popularity, a short operational lifetime is the main drawback of this material. Recent works have shown that the lifetime can be improved by using a robust Cs–Sb–...

We use resonant inelastic x-ray scattering to probe the propagation of plasmons in the electron-doped cuprate superconductor Sr_{0.9}La_{0.1}CuO_{2}. We detect a plasmon gap of ∼120 meV at the two-dimensional Brillouin zone center, indicating that low-energy plasmons in Sr_{0.9}La_{0.1}CuO_{2} are not strictly acoustic. The plasmon dispersion, incl...

We use resonant inelastic x-ray scattering (RIXS) to probe the propagation of plasmons in the electron-doped cuprate superconductor Sr$_{0.9}$La$_{0.1}$CuO$_2$ (SLCO). We detect a plasmon gap of $\sim$~120 meV at the two-dimensional Brillouin zone center, indicating that low-energy plasmons in SLCO are not strictly acoustic. The plasmon dispersion,...

Ultrafast-optical-pump -- structural-probe measurements, including ultrafast electron and x-ray scattering, provide direct experimental access to the fundamental timescales of atomic motion, and are thus foundational techniques for studying matter out of equilibrium. High-performance detectors are needed in scattering experiments to obtain maximum...

Mono- and bi-alkali antimonides, X$_2$YSb (X and Y from Group I), are promising for next-generation electron emitters due to their capability of producing high-quality electron beams. However, these materials are not yet well understood, in part due to the technical challenges in growing pure, ordered alkali antimonides. For example, in the current...

Negative Electron Affinity (NEA) activated GaAs photocathodes are the most popular option for generating a high current (> 1 mA) spin-polarized electron beam. Despite its popularity, a short operational lifetime is the main drawback of this material. Recent works have shown that the lifetime can be improved by using a robust Cs-Sb-O NEA layer with...

Transport properties of electron-doped cuprate Sr1−xLaxCuO2 thin films have been investigated as a function of doping. In particular, optimal- and over-doped samples were obtained by tuning the Sr:La stoichiometric ratio. Optimal-doped samples show a non-Fermi liquid behavior characterized by linear dependence of the resistivity from room temperatu...

We grew Sr1-xLaxCuO2 thin films and SrCuO2/Sr0.9La0.1CuO2/SrCuO2 trilayers by reflection high-energy diffraction-calibrated layer-by-layer molecular beam epitaxy, to study their electrical transport properties as a function of the doping and thickness of the central Sr0.9La0.1CuO2 layer. For the trilayer samples, as already observed in underdoped S...

The properties of photoemission electron sources determine the ultimate performance of a wide class of electron accelerators and photon detectors. To date, all high-efficiency visible-light photocathode materials are either polycrystalline or exhibit intrinsic surface disorder, both of which limit emitted electron beam brightness. In this Letter, w...

We report the design and performance of a time-resolved electron diffraction apparatus capable of producing intense bunches with simultaneously single digit micrometer probe size, long coherence length, and 200 fs rms time resolution. We measure the 5d (peak) beam brightness at the sample location in micro-diffraction mode to be 7 × 10 13 A / m 2...

The properties of photoemission electron sources determine the ultimate performance of a wide class of electron accelerators and photon detectors. To date, all high-efficiency visible-light photocathode materials are either polycrystalline or exhibit intrinsic surface disorder, both of which limit emitted electron beam brightness. In this letter we...

We report the design and performance of a time-resolved electron diffraction apparatus capable of producing intense bunches with <200 fs rms duration, single digit micron probe sizes, and simultaneously long coherence length. To generate high brightness electron bunches, the system employs high efficiency, low emittance semiconductor photocathodes...

The discovery of substrate materials has been dominated by trial and error, opening the opportunity for a systematic search. We generate bonding networks for materials from the Materials Project and systematically break up to three bonds in the networks for three-dimensional crystals. Successful cleavage reduces the bonding network to two periodic...

Electrostatically defined perovskite oxide heterostructures, in which carriers are confined by the modulation of the A-site ion charge, offer new possibilities of tuning the magnetic properties of manganite oxides. We investigate the preferential orientation of ferromagnetic and antiferromagnetic moments in ultrathin La0.7Sr0.3MnO3 layers embedded...

Alkali antimonide photocathodes are capable of generating high brightness electron beams given their high quantum efficiency and low mean transverse energy (MTE). Increasing the brightness of the photoemitted electron beams beyond the current state of the art requires surface control of the photocathode at the atomic scale, since the beam brightnes...

We describe measurements of the mean transverse energy (MTE) of Cs–Te photocathodes near the photoemission threshold. The MTE displays an unexpected non-monotonic behavior as the drive laser's wavelength is tuned to threshold and changes significantly as the photocathode is cooled to cryogenic temperatures. We show that a simple analytical model of...

The electronic properties of hole- and electron-doped manganites were probed by a combination of x-ray absorption and photoemission spectroscopies. Hole-doped La0.7Ba0.3MnO3 and electron-doped La0.7Ce0.3MnO3 thin films were epitaxially grown on SrTiO3 substrates by means of pulsed laser deposition. Ex-situ x-ray diffraction demonstrated the substra...

High-performance photocathodes for many prominent particle accelerator applications, such as x-ray free-electron lasers, cannot be grown in situ. These highly reactive materials must be grown and then transported to the electron gun in an ultrahigh-vacuum (UHV) suitcase, during which time monolayer-level oxidation is unavoidable. Thin film Cs3Sb ph...

Fundamental understanding of interface mechanisms that generate unexpected physical properties in the cuprate/manganite heterostructures is essential for possible applications as spintronic devices. Here, CaCuO2/La1−xSrxMnO3 (CCO/LSMO) superlattices are investigated, where the infinite‐layer cuprate CCO does not have apical oxygen for Cu in the Ca‐...

Negative Electron Affinity (NEA) activated surfaces are required to extract highly spin-polarized electron beams from GaAs-based photocathodes, but they suffer extreme sensitivity to poor vacuum conditions that results in rapid degradation of quantum efficiency. We report on a series of unconventional NEA activations on surfaces of bulk GaAs with C...

Using room temperature sputtering, we have deposited Gd0.1Ce0·9O1.95 buffer layers at the cathode/electrolyte interface of 10 cm² circular Solid Oxide Fuel Cells. By suitably selecting the in air annealing step, we show the possibility to control the granular properties of the Gd0.1Ce0·9O1.95 buffer layers in order to optimize the Solid Oxide Fuel...

GaAs-based photocathodes are the state-of-the-art in the production of highly spin-polarized electron beams for accelerator and microscopy applications. While various novel structures of GaAs have been shown to increase the degree of polarization and quantum efficiency, all GaAs-based photocathodes require activation to negative electron affinity (...

Crystal cleavage provides a process to create atomically smooth materials surfaces. To identify possible cleavage planes in periodic materials, we generate bonding networks for crystals from MaterialsProject with five or fewer atoms in the primitive unit cell. For three-dimensional crystals, we systematically break up to three bonds in the bonding...

Negative Electron Affinity (NEA) activated surfaces are required to extract highly spin polarized electron beams from GaAs-based photocathodes, but they suffer extreme sensitivity to poor vacuum conditions that results in rapid degradation of quantum efficiency. We report on series of unconventional NEA activations on surfaces of bulk GaAs with Cs,...

Surface science measurement techniques such as x-ray photoemission spectroscopy (XPS) and scanning tunnel mi-croscopy (STM) can provide quantitative information about the composition and the morphology of thin film samples. We successfully transferred Cs-Sb samples from the growth chamber to a surface science XPS/STM system by use of an UHV suitcas...

We have studied the low temperature electrical transport properties of LaxSr1-xCuO2 thin films grown by oxide molecular beam epitaxy on (110) GdScO3 and TbScO3 substrates. The Transmission Electron Microscopy measurements and the X-ray Diffraction analysis confirmed the epitaxy of the obtained films and the study of their normal state transport pro...

Recent research on photocathodes for photoinjectors has focused on the understanding of the photoemission process at low energy (i.e. at photon energy close to the material’s work function) as well as on the study of ordered and innovative photocathode materials, with the aim of minimizing the emittance at the cathode. We here present a preliminary...

Recent research on photocathodes for photoinjectors has fo-cused on the understanding of the photoemission process at low energy (i.e. at photon energy close to the material's work function) as well as on the study of ordered and innovative photocathode materials, with the aim of minimizing the emittance at the cathode. We here present a preliminar...

SrCuO2/Sr0.9La0.1CuO2/SrCuO2 trilayers were grown by oxide-molecular beam epitaxy. The thicknesses of the top and bottom SrCuO2 layers were fixed, while the thickness of the infinite-layer electron-doped cuprate Sr0.9La0.1CuO2 central layer was systematically changed. Transmission electron microscopy, x-ray reflectivity and x-ray diffraction measur...

The use of a doped Ceria buffer layer and Physical Vapour Deposition (PVD) techniques for Solid Oxide Fuel Cells (SOFC) fabrication can limit the former, the formation of electrical insulating lanthanum, and strontium zirconates at the cathode/electrolyte interface, whereas the latter allows a better control of the materials interfaces. These effec...

Over the last decade, alkali-antimonides have been in- vestigated as high QE cathodes in green light and more recently as ultra-low intrinsic emittance cathodes in near- threshold red wavelengths at cryogenic temperatures [1]. Nano-meter scale surface non-uniformities (physical rough- ness and chemical roughness or work function variations) are tho...

The majority of photocathode materials in use in acceler- ator applications have been discovered empirically through trial and error with little guidance from material science cal- culations. Alternatively, one can envision a process which is heavily guided by computational search using latest ad- vances in density functional theory (DFT). In this...

Single crystalline photocathodes with small electron ef- fective mass are supposed to enable ultra-low emittance beams, by taking advantage of the conservation of trans- verse (crystal) momentum. We present a preliminary study on photoemission from epitaxial films of La-doped BaSnO3 with (100) orientation. We demonstrate here the possibility of gen...

Single crystalline photocathodes with small electron effective mass are supposed to enable ultra-low emittance beams, by taking advantage of the conservation of transverse (crystal) momentum. We present a preliminary study on photoemission from epitaxial films of La-doped BaSnO 3 with (100) orientation. We demonstrate here the possibility of genera...

The superconducting properties of Sr1–xLaxCuO2 thin films are strongly affected by sample preparation procedures, including the annealing step, which are not always well controlled. We have studied the evolution of Cu L2,3 and O K edge x-ray absorption spectra (XAS) of Sr1–xLaxCuO2 thin films as a function of reducing annealing, both qualitatively...

The asymmetry between electron and hole doping in high critical-temperature superconducting (HTS) cuprates is key information for the understanding of Cooper pair formation mechanisms. Despite intensive studies on different cuprates, a comprehensive description of related magnetic and charge excitations is still fragmentary. In the present work, ar...

We report on epitaxialgrowth of Bi2Se3 topological insulator thin films by Pulsed Laser Deposition(PLD).X-ray diffraction investigation confirms that Bi2Se3 with a single (001)-orientation can be obtained on several substrates in a narrow (i.e., 20 °C) range of deposition temperatures and at high deposition pressure (i.e., 0.1 mbar). However, only...

Charge ordering has emerged as a likely candidate for a universal ordering parameter in both hole- and electron-doped cuprates. In the electron-doped cuprates, however, charge order has only been detected in the R2−xCexCuO4 (R=La,Nd) family. With its simple structure lacking both structural distortions and magnetic ions, the infinite-layer cuprate...

(SrMnO3)x/(La0.7Sr0.3MnO3)y/(SrMnO3)z (x,y,z=number of unit cells) trilayers have been grown using a Reflection High Energy Electron Diffraction calibrated layer by layer molecular beam epitaxy technique. X-Ray Reflectivity and X-Ray Diffraction measurements confirm the structural quality and the abruptness of the interfaces. Electrical transport p...

The interplay between quantum interference effects and superconductivity has been investigated in infinite layer Sr1-xLaxCuO 2δ thin films by using a combination of standard dc electric transport measurements and noise characterization. A marked resistivity upturn at a temperature of 110 K has been observed in underdoped samples, which also showed...

The normal-state resistivity of thin films of the infinite-layer electron-doped cuprate Sr 1−x La x CuO 2±δ has been investigated. Under-doped samples, which clearly show a metal-to-insulator transition (MIT) at low temperatures, have allowed the determination of the fundamental physical mechanism behind the upturn of the resistivity, namely the qu...

The interplay between quantum interference effects (QIEs) and superconductivity has been investigated in infinite layer Sr1-xLaxCuO2±y (SLCO) thin films, by using a combination of standard dc electric transport measurements and noise characterization. The films were grown using a shuttered layer-by-layer process in a dual chamber Molecular Beam Epi...

Two-dimensional materials, such as graphene, topological insulators, and two-dimensional electron gases, represent a technological playground to develop coherent electronics. In these systems, quantum interference effects, and in particular weak localization, are likely to occur. These coherence effects are usually characterized by well-defined fea...

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Lanthanum manganites with a massive concentration of La defects can be stabilized in the form of thin films, by exploiting the structural stress produced by a substrate such as SrTiO3. They undergo an insulator-to-metal transition (IMT) like those doped by divalent ions, which is here studied by measuring the optical conductivity of LaxMnO films wi...

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We report on the progress towards an all epitaxial oxide layer technology on silicon substrates for epitaxial piezoelectric microelectromechanical systems. (101)-oriented epitaxial tetragonal BaTiO3 (BTO) thin films were deposited at two different oxygen pressures, 5.10�2 mbar and 5.10�3 mbar, on SrRuO3/Yttria-stabilized zirconia (YSZ) buffered sil...

The transport properties of manganite thin films characterized by a weak-localization transition have been studied. Detailed voltage noise measurements show a specific 1/f noise spectrum below the transition temperature. A theoretical interpretation in terms of universal conductance fluctuations explains the nature of the unconventional electric no...

In perovskite oxide materials, because of the insertion of multiple valence states ions (e.g., Mn in manganites) at atomic A-site (i.e., at the center of perovskite cubic cell), an enhancement of the ferromagnetic metallic state together with a strong orbital order of Mn-ions is established. Such a feature goes beyond the conventional theoretical f...

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Superconducting Sr1–xLaxCuO2 thin films have been grown on GdScO3 substrates by reflection high-energy electron diffraction calibrated layer-by-layer molecular-beam epitaxy. X-ray diffraction analysis has confirmed the infinite layer structure after an in situ vacuum annealing step. In situ photoemission spectroscopy indicates that the vacuum annea...

We report the growth of epitaxial Pb(Zr0.54Ti0.46)O3 (PZT) thin films on yttria-stabilized zirconia buffered silicon substrates by pulsed laser deposition. We demonstrate a full in plane epitaxy of the buffer layer, showing a RMS roughness of less than 0.3 nm for a 120 nm thick layer. This buffer layer allows the growth of fully (110) textured oxid...

SrRuO(3) is a strong itinerant ferromagnet showing many features of 'bad metals' together with Fermi liquid behavior at very low temperature. The intriguing magnetic and transport properties of SrRuO(3) are tightly related to structure, as commonly observed in transition metal oxides. Here we report on the correlation of structural parameters (latt...

La0.65Sr0.35MnO3-δ (LSMO) films (δ ≈ 0, 0.07, 0.12) were studied by hard x-ray photoelectron spectroscopy. It is found that the Mn 3d valence band states shift to higher binding energies for oxygen-deficient samples, while their overall width decreases as a result of the reduced density of charge carriers. The concurrent disappearance of the well-s...

We here report on the occurrence of strong orbital order driven by off-stoichiometry in oxide manganite films. Multiple-electronic-valence Mn ions are possibly substituted into the perovskite atomic A site (namely, A-site manganites). By combining state-of-the-art synchrotron ultrafine spectroscopies, we did provide evidence of a high ferromagnetic...

Oxygen 1s → 2p (K-edge) x-ray absorption spectra mimic the density of metalliclike states of transitionmetal oxides, thus shedding light on the electronic band structure near Fermi energies of these compounds. We take here advantage of x-ray linear dichroism measurements at the O K edge of different (SrMnO3)n(LaMnO3)2n superlattices, of SrMnO3 and...

We report on the role of oxygen content alone on structural and transport properties of La0.65Sr0.35MnO3�d (LSMO) thin films. Identical films were deposited side-by-side during a single deposition run and subsequently post-annealed separately in vacuum to systematically vary the oxygen content. All films remained coherently strained to the SrTiO3 s...

This thesis work deals with the magnetic, orbital and transport properties of (LaMnO3)2N(SrMnO3)N digital superlattices and of LaxMnO3-d thin films, both deposited by molecular beam epitaxy (MBE) technique on SrTiO3 substrates. The (LaMnO3)2N(SrMnO3)N digital superlattices represent the new kind of heterostructure, actually under intensive study, c...

The magnetization configuration in small La0.7Sr0.3MnO3 elements is investigated as a function of geometry, film thickness, magnetic field, and temperature using x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). The patterned elements were defined by focused ion beam (FIB) lithography, and consist of elements varying...

Magnetic measurements by complementary techniques have shown that the substitution of Mn2+ in the A site strongly influences the electronic and magnetic properties of nonstoichiometric LaxMnO3-delta thin films (x=0.66-->1.07). We have studied a series of samples deposited on SrTiO3 (100) substrates by molecular beam epitaxy. SQUID magnetometer has...

Double-exchange (DE) mechanisms in RE1-xAExMnO3 manganites (where RE is a trivalent rare-earth ion and AE is a divalent alkali-earth ion) relies on the strong exchange interaction between two Mn3+ and Mn4+ ions through interfiling oxygen 2p states. Nevertheless, the role of RE and AE ions has ever been considered ``silent'' with respect to the DE c...

Double-exchange mechanisms in RE$_{1-x}$AE$_{x}$MnO$_{3}$ manganites (where RE is a trivalent rare-earth ion and AE is a divalent alkali-earth ion) relies on the strong exchange interaction between two Mn$^{3+}$ and Mn$^{4+}$ ions through interfiling oxygen 2p states. Nevertheless, the role of RE and AE ions has ever been considered "silent" with r...