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a-LAO/STO interface sheet conductance, Gs , as a function of thebackground gas pressure, p, for O2 (blue dots) and Ar (red diamonds). The dash-dot lines are guide for the eye. The dotted line corresponds to the detection limit of the instrument.
2D images (left column) and corresponding 1D spectra (right column) of the LAO plume emission in (a) oxygen and (b) argon background gases, acquired at a delay τ = 3.3 μs after the laser pulse, for three different oxygen pressures: 10−3 mbar (lower panels), 10−2 mbar (central panels), and 10−1 mbar (upper panels). The plume propagation direction is along the z-axis, and z = 0 marks the position of the target surface, while the x-axis is parallel to the target surface. To facilitate the comparison among images and spectra, the intensity is multiplied by an appropriate factor (shown in parenthesis in each panel). The labels in each upper right spectrum show the assignment of the most intense emission features.
Maximum kinetic energy of the Al atoms, KEmax , as a function of the background gas pressure, p, for Ar (top panel, hexagons) and O2 (bottom panel, triangles). In each panel, the dependence of sheet conductance, Gs , on p for the a-LAO/STO heterostructures deposited in Ar (top panel, rhombi) and O2 (bottom panel, dots) is also reported. Note that the lower limits for the sheet conductance and the maximum kinetic energy are set to 10−9 Ω−1 (i.e., the detection limit for the transport measurements) and 1/40 eV (i.e., the thermal energy available at room temperature), respectively.
Schematic representation of the diffusion of oxygen from the STO substrate to the oxygen deficient a-LAO film activated by the arrival of chemically active species (e.g., Al in the case of the LAO plume) during the film growth. A kinetic energy of these reactive species larger than an activation energy threshold of ≈1 eV is needed to ensure a conducting interface as a result of forming oxygen vacancies (VO) in SrTiO3.
Variation of the [LaO*]/[La*] emission intensity ratio with pressure, p, at a distance of ≈40 mm from the target surface. The data at 10−4 mbar in oxygen is taken as reference and its value is put equal to 1.0. The intensity ratio at 10−1 mbar is evaluated at the plume stopping distance of ≈20 mm from the target surface.
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