29 research outputs found
Interface reconstruction in superconducting CaCuO2/SrTiO3 superlattices: A hard x-ray photoelectron spectroscopy study
Here we report about the interface reconstruction in the recently discovered
superconducting artificial superlattices based on insulating CaCuO2 and SrTiO3
blocks. Hard x-ray photoelectron spectroscopy shows that the valence bands
alignment prevents any electronic reconstruction by direct charge transfer
between the two blocks. We demonstrate that the electrostatic built-in
potential is suppressed by oxygen redistribution in the alkaline earth
interface planes. By using highly oxidizing growth conditions, the oxygen
coordination in the reconstructed interfaces may be increased, resulting in the
hole doping of the cuprate block and thus in the appearance of
superconductivity.Comment: 9 pages, 6 figure
Persistent photoconductivity in 2-dimensional electron gases at different oxide interfaces
We report on the transport characterization in dark and under light
irradiation of three different interfaces: LaAlO3/SrTiO3, LaGaO3/SrTiO3, and
the novel NdGaO3/SrTiO3 heterostructure. All of them share a perovskite
structure, an insulating nature of the single building blocks, a polar/non-
polar character and a critical thickness of four unit cells for the onset of
conductivity. The interface structure and charge confinement in NdGaO3/SrTiO3
are probed by atomic-scale- resolved electron energy loss spectroscopy showing
that, similarly to LaAlO3/SrTiO3, extra electronic charge confined in a sheet
of about 1.5 nm in thickness is present at the NdGaO3/SrTiO3 interface.
Electric transport measurements performed in dark and under radiation show
remarkable similarities and provide evidence that the persistent perturbation
induced by light is an intrinsic peculiar property of the three investigated
oxide-based polar/non-polar interfaces. Our work sets a framework for
understanding the previous contrasting results found in literature about
photoconductivity in LaAlO3/SrTiO3 and highlights the connection between the
origin of persistent photoconductivity and the origin of conductivity itself.
An improved understanding of the photo- induced metastable electron-hole pairs
might allow to shed a direct light on the complex physics of this system and on
the recently proposed perspectives of oxide interfaces for solar energy
conversion.Comment: 11 pages, 7 figure
Spatial defects nanoengineering for bipolar conductivity in MoS2
Understanding the atomistic origin of defects in two-dimensional transition metal dichalcogenides, their impact on the electronic properties, and how to control them is critical for future electronics and optoelectronics. Here, we demonstrate the integration of thermochemical scanning probe lithography (tc-SPL) with a flow-through reactive gas cell to achieve nanoscale control of defects in monolayer MoS2. The tc-SPL produced defects can present either p- or n-type doping on demand, depending on the used gasses, allowing the realization of field effect transistors, and p-n junctions with precise sub-ÎĽm spatial control, and a rectification ratio of over 104. Doping and defects formation are elucidated by means of X-Ray photoelectron spectroscopy, scanning transmission electron microscopy, and density functional theory. We find that p-type doping in HCl/H2O atmosphere is related to the rearrangement of sulfur atoms, and the formation of protruding covalent S-S bonds on the surface. Alternatively, local heating MoS2 in N2 produces n-character
Magnetic Behavior of Ni Nanoparticle Films Produced by Two Laser Irradiations in Vacuum
Ni Nanoparticle assembled thin films were prepared using an unconventional approach based on the use of a secondary nanosecond (ns) ultraviolet (UV) laser irradiation interacting with the plume of ablated nanoparticles (NPs) during the femtosecond pulsed laser deposition (fs-PLD). The secondary laser beam determines the reduction of the NPs size and their dispersion by partial vaporization of the NPs during their flight from the target to the substrate. The proper selection of the time delay between fs and ns laser pulses allows the latter to interact selectively with different parts of the NPs plume, controlling, to a certain degree, the reduction of the NPs size and dispersion. Another original effect of the UV laser irradiation is the change in the deposited films topology, due to a reduction of the NP-aggregates density and size, fostering non-uniform dense assemblies of NPs with concentration well above the percolation threshold, with the consequent reduction of the influence of the exchange interactions on the macroscopic magnetic properties. The magnetic behavior of the films prepared using two laser beams with respect to that obtained in the case of fs-PLD only is characterized by higher H-c values (up to approximate to 70%) and a good compromise between the hysteresis loops squareness and moderate exchange interactions, strongly correlated with the NPs topology
Direct measurement of sheet resistance R-square in cuprate systems: Evidence of a fermionic scenario in a metal-insulator transition
The metal-insulator transition (MIT) has been studied in Ba0:9Nd0:1CuO2x=CaCuO2 ultrathin cuprate
structures. Such structures allow for the direct measurement of the 2D sheet resistance R, eliminating
ambiguity in the definition of the effective thickness of the conducting layer in high temperature
superconductors. The MIT occurs at room temperature for experimental values of R close to the
25:8 kuniversal quantum resistance. All data confirm the assumption that each CaCuO2 layer forms a
2D superconducting sheet within the superconducting block, which can be described as weak-coupled
equivalent sheets in parallel