150 research outputs found
Enhanced surface diffusion through termination conversion during epitaxial SrRuO3 growth
During the initial growth of the ferromagnetic oxide SrRuO3 on TiO2-terminated SrTiO3, we observe a self-organized conversion of the terminating atomic layer from RuO2 to SrO. This conversion induces an abrupt change in growth mode from layer by layer to growth by step advancement, indicating a large enhancement of the surface diffusivity. This growth mode enables the growth of single-crystalline and single-domain thin films. Both conversion and the resulting growth mode enable the control of the interface properties in heteroepitaxial multilayer structures on an atomic level
On the persistence of polar domains in ultrathin ferroelectric capacitors
The instability of ferroelectric ordering in ultra-thin films is one of the
most important fundamental issues pertaining realization of a number of
electronic devices with enhanced functionality, such as ferroelectric and
multiferroic tunnel junctions or ferroelectric field effect transistors. In
this paper, we investigate the polarization state of archetypal ultrathin
(several nanometres) ferroelectric heterostructures: epitaxial
single-crystalline BaTiO films sandwiched between the most habitual
perovskite electrodes, SrRuO, on top of the most used perovskite substrate,
SrTiO. We use a combination of piezoresponse force microscopy, dielectric
measurements and structural characterization to provide conclusive evidence for
the ferroelectric nature of the relaxed polarization state in ultrathin
BaTiO capacitors. We show that even the high screening efficiency of
SrRuO electrodes is still insufficient to stabilize polarization in
SrRuO/BaTiO/SrRuO heterostructures at room temperature. We identify
the key role of domain wall motion in determining the macroscopic electrical
properties of ultrathin capacitors and discuss their dielectric response in the
light of the recent interest in negative capacitance behaviour.Comment: 13 pages, 4 figure
Surface acoustic wave generation and detection in quantum paraelectric regime of SrTiO-based heterostructure
Strontium titanate (STO), apart from being a ubiquitous substrate for
complex-oxide heterostructures, possesses a multitude of strongly-coupled
electronic and mechanical properties. Surface acoustic wave (SAW) generation
and detection offers insight into electromechanical couplings that are
sensitive to quantum paraelectricity and other structural phase transitions.
Propagating SAWs can interact with STO-based electronic nanostructures, in
particular LaAlO/SrTiO (LAO/STO). Here we report generation and
detection of SAW within LAO/STO heterointerfaces at cryogenic temperatures
(~2 K) using superconducting interdigitated transducers (IDTs). The
temperature dependence shows an increase in the SAWs quality factor that
saturates at K. The effect of backgate tuning on the SAW
resonance frequency shows the possible acoustic coupling with the ferroelastic
domain wall evolution. This method of generating SAWs provides a pathway
towards dynamic tuning of ferroelastic domain structures, which are expected to
influence electronic properties of complex-oxide nanostructures. Devices which
incorporate SAWs may in turn help to elucidate the role of ferroelastic domain
structures in mediating electronic behavior
Gate-tunable optical extinction of graphene nanoribbon nanoclusters
We investigate the optical response of graphene nanoribbons (GNRs) using the broadband nonlinear generation and detection capabilities of nanoscale junctions created at the LaAlO3/SrTiO3 interface. GNR nanoclusters measured to be as small as 1–2 GNRs in size are deposited on the LaAlO3 surface with an atomic force microscope tip. Time-resolved nonlinear optical probes of GNR nanoclusters reveal a strong, gate-tunable second and third harmonic response, as well as strong extinction of visible to near-infrared light at distinct wavelengths, similar to previous reports with graphene
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