15 research outputs found
Evolution of the charge density wave state in CuxTiSe2
We present scanning tunneling microscopy and spectroscopy measurements of the charge-density wave state in 1T-TiSe2, Cu0.05TiSe2, and Cu0.06TiSe2 single crystals. Topography images at 4.2 K reveal that the charge density waves are present in all samples studied, although the amplitude of the charge modulation decreases with the Cu doping. Moreover, the chiral phase of the charge density wave is preserved also in Cu-doped samples. Tunneling spectroscopy shows that there is only a partial gap in the pure compound, with bands crossing the Fermi surface. In the Cu-doped samples, the system becomes more metallic due to the increase of the chemical potential
Nature of the metal-insulator transition in few-unit-cell-thick LaNiO<sub>3</sub> films.
Nature of the Metal-Insulator Transition in Few-Unit-Cell-Thick LaNiO\u3csub\u3e3\u3c/sub\u3e Films
The nature of the metal-insulator transition in thin films and superlattices of LaNiO3 only a few unit cells in thickness remains elusive despite tremendous effort. Quantum confinement and epitaxial strain have been evoked as the mechanisms, although other factors such as growth-induced disorder, cation non-stoichiometry, oxygen vacancies, and substrate–film interface quality may also affect the observable properties of ultrathin films. Here we report results obtained for near-ideal LaNiO3 films with different thicknesses and terminations grown by atomic layer-by-layer laser molecular beam epitaxy on LaAlO3 substrates. We find that the room-temperature metallic behavior persists until the film thickness is reduced to an unprecedentedly small 1.5 unit cells (NiO2 termination). Electronic structure measurements using X-ray absorption spectroscopy and first-principles calculation suggest that oxygen vacancies existing in the films also contribute to the metal-insulator transition
Narrow growth window for stoichiometric, layer-by-layer growth of LaAlO3 thin films using pulsed laser deposition
Joint Meeting of the MassDOT Board of Directors and the Fiscal and Management Control Board: Meeting Minutes (2017-05-08)
The nature of the metal-insulator transition in thin films and superlattices of LaNiO3 only a few unit cells in thickness remains elusive despite tremendous effort. Quantum confinement and epitaxial strain have been evoked as the mechanisms, although other factors such as growth-induced disorder, cation non-stoichiometry, oxygen vacancies, and substrate-film interface quality may also affect the observable properties of ultrathin films. Here we report results obtained for near-ideal LaNiO3 films with different thicknesses and terminations grown by atomic layer-by-layer laser molecular beam epitaxy on LaAlO3 substrates. We find that the room-temperature metallic behavior persists until the film thickness is reduced to an unprecedentedly small 1.5 unit cells (NiO2 termination). Electronic structure measurements using X-ray absorption spectroscopy and first-principles calculation suggest that oxygen vacancies existing in the films also contribute to the metal-insulator transition
Strain-Engineered Oxygen Vacancies in CaMnO₃ Thin Films
We demonstrate a novel pathway to control and stabilize oxygen vacancies in complex transition-metal oxide thin films. Using atomic layer-by-layer pulsed laser deposition (PLD) from two separate targets, we synthesize high-quality single-crystalline CaMnO3 films with systematically varying oxygen vacancy defect formation energies as controlled by coherent tensile strain. The systematic increase of the oxygen vacancy content in CaMnO3 as a function of applied in-plane strain is observed and confirmed experimentally using high-resolution soft X-ray absorption spectroscopy (XAS) in conjunction with bulk-sensitive hard X-ray photoemission spectroscopy (HAXPES). The relevant defect states in the densities of states are identified and the vacancy content in the films quantified using the combination of first-principles theory and core–hole multiplet calculations with holistic fitting. Our findings open up a promising avenue for designing and controlling new ionically active properties and functionalities of com..
Strain-Engineered Oxygen Vacancies in CaMnO<sub>3</sub> Thin Films
We
demonstrate a novel pathway to control and stabilize oxygen vacancies
in complex transition-metal oxide thin films. Using atomic layer-by-layer
pulsed laser deposition (PLD) from two separate targets, we synthesize
high-quality single-crystalline CaMnO<sub>3</sub> films with systematically
varying oxygen vacancy defect formation energies as controlled by
coherent tensile strain. The systematic increase of the oxygen vacancy
content in CaMnO<sub>3</sub> as a function of applied in-plane strain
is observed and confirmed experimentally using high-resolution soft
X-ray absorption spectroscopy (XAS) in conjunction with bulk-sensitive
hard X-ray photoemission spectroscopy (HAXPES). The relevant defect
states in the densities of states are identified and the vacancy content
in the films quantified using the combination of first-principles
theory and core–hole multiplet calculations with holistic fitting.
Our findings open up a promising avenue for designing and controlling
new ionically active properties and functionalities of complex transition-metal
oxides via strain-induced oxygen-vacancy formation and ordering