KEYWORDS: Ferromagnetics, Fermium, Frequency modulation, System on a chip, Medium wave, Diffusion, Condensed matter, Spintronics, Semiconductors, Microwave radiation
Spin-orbit coupling (SOC) and the spin diffusion length in condensed matter are crucial parameters for spintronics applications. In order to study these, we have succeeded in employing a pulsed spin-pumping method based on ferromagnetic resonance (FMR) to generate pure spin currents from ferromagnetic (FM) substrates into non-FM semiconductor layers1 which can then be detected through the inverse spin-Hall effect (ISHE). When the FM is in FMR with a pulsed microwave (MW) excitation, a pure spin-current is generated in the non-FM layer which can circumvent potential impedance mismatches between the FM and the non-FM layer and, therefore generate a strong pulsed ISHE signal. Due to the low duty cycle of the pulsed excitation, MW excitation powers can be used that are strong enough to generate pronounced ISHE signals even in materials with weak SOC such as carbon-based materials. This sensitivity allows for the study of the quantitative nature of the ISHE and thus, to apply scrutiny to a number of questions about the ISHE effect in general, including how strongly FMR-driving field inhomogeneities affect a measured ISHE current, the relationship of ISHE voltages to the ISHE current in devices consisting of layers with different conductivities, as well the experimental conditions which have to be monitored during an ISHE experiment in order to ensure reproducibility.
This work was supported by the National Science Foundation (DMR-1404634 – Sample preparation and Experiments) and the NSF-Material Science & Engineering Center (DMR-1121252- Polymer Synthesis and Facilities) at the University of Utah.
1. D. Sun et al., Nature Materials 15, 863–869 (2016). doi:10.1038/nmat4618
In hybrid halide perovskite, the effectiveness of charge transport in relation to film microstructure and processing has remained elusive. In this study we succeeded in tuning grain size and grain boundary chemistry through solvent vapor annealing, which resulted in an increase in charge-carrier mobility by one order of magnitude. To understand the mechanism responsible for the enhanced charge transport, we performed a series of complementary measurements. Atomic force microscopy revealed an increase in grain size and uniformity, and optical microscopy showed a macroscopic reorganization of the film structure. X-ray diffraction measurements of the MAPbI3-xClx films confirmed the removal of preferential orientation after 20 min of solvent annealing at room temperature, in N,N-dimethylformamide. The presence of additional peaks was assigned to the formation of the solvent complex MAI:DMF:PbI2 and the PbI2:DMF ligand, and the content of these phases was monitored as a function of annealing time. Charge-carrier mobility was evaluated from field-effect transistor measurements in devices with gold top contacts and SiO2 bottom-gate dielectric. We obtained ambipolar transport, with both hole and electron mobility exceeding 10cm2/Vs at room temperature. We propose that this remarkable enhancement in electrical properties resulted from an increase in the grain size and passivation of grain boundaries via formation of intermediate solvent complexes formed from unreacted material. This work has allowed us to gain unprecedented insight into the impact of film morphology on charge transport in perovskite materials, an important milestone towards achieving high-performance optoelectronic devices such as transistors, photovoltaics, light emitting diodes, and photodetectors.
We have fabricated a spin photovoltaic device composed of a vertical spin-valve based on hybrid organic–inorganic perovskite as a spacer layer, of which resistance may be tuned by external light illumination. The magnetoconductivity of this device may be tuned from zero to reach exceptionally high values of 100 k% by controlling the illumination intensity close to the open circuit voltage. In addition, the device photocurrent can be also turned by sweeping the external magnetic field when the effects of the light intensity and applied bias voltage are judicially balanced.
Organometallic hybrid perovskites have attracted intense attentions recently, as a new family of solution processable semiconductors for photoenergy conversion and light emission purposes. Specifically, CH3NH3PbBr3 is one type of emissive perovskites, but its quantum efficiency largely depends on the preparation procedure. Here, we use the fluorescence lifetime imaging (FLIM) technique to investigate the relation between microscopic structures and photoluminescence (PL) in CH3NH3PbBr3 polycrystalline films. By dripping poor solvents (chlorobenzene or chloroform) to accelerate the crystallization during the film preparation, we could decrease the crystal domain size from 10 μm down to 500 nm, and the corresponding PL intensity increases significantly. From the FLIM characterization of these films, we find that the PL emission is mostly from the edge of crystal domains. The PL dynamics indicates that the radiative decay of edge state is much more efficient than that of the bulk state, and the bulk state of photoexcitation undergoes an energy transfer to the edge state. This finding explains the origin of enhanced PL from CH3NH3PbBr3 films when treated with poor solvents and provides useful information for further improvement on the PL efficiency of hybrid perovskite materials.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.