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As hydrogen gas increasingly becomes critical as a carbon-free energy carrier, the demand for robust hydrogen sensors for leak detection and concentration monitor will continue to rise. However, to...

The magneto-chiroptical properties of Ag/Co composite chiral nanohole arrays (CCNAs) are investigated. The intrinsic circular dichroism of CCNA samples was induced by in-plane symmetry breaking by ...

The optical and magnetoplasmonic properties of Ag/Co and Ag/Co/Ag multilayer nanohole arrays have been investigated. By including a top- and bottom-Ag plasmonic layer onto a Co ferromagnetic perfor...

A simple and versatile touchspinning method is demonstrated for the fabrication of core-sheath nanofibrous piezoelectric yarns with a single filament electroconductive core. The polyvinylidene fluo...

The thickness dependent magneto-optical Faraday rotation in Co ferromagnetic thin films and perforated periodic Co nano-hole arrays were investigated. It was observed that the optical response and Faraday rotation of Co nano-hole arrays were strongly dependent on the thickness of the film, and the Faraday rotation reached the maximum amplitude at an optimal thickness value of 30–50 nm, which contrasted with the Co thin films where the Faraday rotation increased with the film thickness. In addition, the Faraday rotation spectra of Co nano-hole arrays showed a weak resonantly enhanced peak at the anti-resonance modes (or Wood’s anomalies) on the transmission spectra, which correspond to the enhanced local electric field at the film and surrounding medium interfaces. All experimental results were confirmed by the finite-difference time domain calculations.

The use of hydrogen as a clean and renewable alternative to fossil fuels requires a suite of flammability mitigating technologies, particularly robust sensors for hydrogen leak detection and concentration monitoring. To this end, we have developed a class of lightweight optical hydrogen sensors based on a metasurface of Pd nano-patchy particle arrays, which fulfills the increasing requirements of a safe hydrogen fuel sensing system with no risk of sparking. The structure of the optical sensor is readily nano-engineered to yield extraordinarily rapid response to hydrogen gas (, Detecting hydrogen is important for development of renewable energy sources. Here, the authors present lightweight optical hydrogen sensors based on a metasurface of PdCo nano-patchy particle arrays, which achieve sensitive hydrogen detection in less than 1 s, and without risk of sparking.

The concept of nanogenerators (NGs) based on textiles was introduced to impart functional attributes to textiles for developing smart textiles and integrating wearable electronics of various functionalities. The human body can generate sufficient mechanical energy that can be harvested by the piezoelectric NGs (PENGs) and used to power up low power consuming wearable electronics. Two simple and easy approaches for coating a highly conductive weave-able metal electrode with polyvinylidene fluoride (PVDF) piezoelectric polymer to construct two different types of coaxial yarn-based PENGs (Y-PENGs) are presented in this paper. The proposed techniques result in the in-situ formation of the β phase of the PVDF. The Y-PENGs are based on facile solution coating and touchspun nanofibers (TSNFs) coating of the inner electrode. The solution-coated Y-PENG (SC-YPENG) showed 5.12 V of peak open-circuit voltage (V oc) and 41.25 nA of peak short circuit current (I sc). Whereas the TSNFs coated Y-PENG (NFC-YPENG) showed 5.08 V of peak V oc and 29.1 nA of peak I sc. In a series connection, the average peak V oc were synergized by ∼2.53 and ∼2.4 factor respectively for the SC-YPENG and the NFC-YPENG. The Y-PENGs were able to charge capacitors and run LEDs. Additionally, our coated inner electrode shows great flexibility, thereby it could be knitted or woven into smart textiles to run wearable electronics sustainably.

To accelerate the reduction in tuberculosis (TB) incidence, it is necessary to optimize the use of innovative tools and approaches available within a local context. This study evaluated the use of an existing network of community health workers (CHW) for active case finding, in combination with mobile chest X-ray (CXR) screening events and the expansion of Xpert MTB/RIF testing eligibility, in order to reach people with TB who had been missed by the current system. A controlled intervention study was conducted from January 2018 to March 2019 in five intervention and four control districts of two low to medium TB burden cities in Viet Nam. CHWs screened and referred eligible persons for CXR to TB care facilities or mobile screening events in the community. The initial diagnostic test was Xpert MTB/RIF for persons with parenchymal abnormalities suggestive of TB on CXR or otherwise on smear microscopy. We analyzed the TB care cascade by calculating the yield and number needed to screen (NNS), estimated the impact on TB notifications and conducted a pre-/postintervention comparison of TB notification rates using controlled, interrupted time series (ITS) analyses. We screened 30,336 individuals in both cities to detect and treat 243 individuals with TB, 88.9% of whom completed treatment successfully. All forms of TB notifications rose by +18.3% (95% CI: +15.8%, +20.8%). The ITS detected a significant postintervention step-increase in the intervention area for all-form TB notification rates (IRR(β6) = 1.221 (95% CI: 1.011, 1.475); p = 0.038). The combined use of CHWs for active case findings and mobile CXR screening expanded the access to and uptake of Xpert MTB/RIF testing and resulted in a significant increase in TB notifications. This model could serve as a blueprint for expansion throughout Vietnam. Moreover, the results demonstrate the need to optimize the use of the best available tools and approaches in order to end TB.

We studied spin dynamics of charge carriers in the superlattice-like Ruddlesden-Popper hybrid lead iodide perovskite semiconductors, 2D (BA)2(MA)Pb2I7 (with MA = CH3NH3, and BA = CH3(CH2)3NH3), and 3D MAPbI3 using the magnetic field effect (MFE) on conductivity and electroluminescence in their light emitting diodes (LEDs) at cryogenic temperatures. The semiconductors with distinct structural/bulk inversion symmetry breaking, when combined with colossal intrinsic spin–orbit coupling (SOC), theoretically give rise to giant Rashba-type SOC. We found that the magneto-conductance (MC) magnitude increases monotonically with the emission intensity and saturates at ≈0.05% and 0.11% for the MAPbI3 and (BA)2(MA)Pb2I7, respectively. The magneto-electroluminescence (MEL) response with similar line shapes as the MC response has a significantly larger magnitude, and essentially stays constant at ≈0.22% and ≈0.20% for MAPbI3 and (BA)2(MA)Pb2I7, respectively. The sign and magnitude of the MC and MEL responses can be quantitatively explained in the framework of the Δg-based excitonic model using rate equations. Remarkably, the width of the MEL response in those materials linearly increases with increasing the applied electric field, where the Rashba coefficient in (BA)2(MA)Pb2I7 is estimated to be about 7 times larger than that in MAPbI3. Our studies might have significant impact on future development of electrically-controlled spin logic devices via Rashba-like effects.

Magnetic anisotropy plays an important role in determining the magnetic functionality of thin film based electronic devices. We present here, the first systematic study of the correlation between magnetoresistance (MR) response in organic spin valves (OSVs) and magnetic anisotropy of the bottom ferromagnetic electrode over a wide temperature range (10 K–350 K). The magnetic anisotropy of a La0.67Sr0.33MnO3 (LSMO) film epitaxially grown on a SrTiO3 (STO) substrate was manipulated by reducing film thickness from 200 nm to 20 nm. Substrate-induced compressive strain was shown to drastically increase the bulk in-plane magnetic anisotropy when the LSMO became thinner. In contrast, the MR response of LSMO/OSC/Co OSVs for many organic semiconductors (OSCs) does not depend on either the in-plane magnetic anisotropy of the LSMO electrodes or their bulk magnetization. All the studied OSV devices show a similar temperature dependence of MR, indicating a similar temperature-dependent spinterface effect irrespective of LSMO thickness, resulting from the orbital hybridization of carriers at the OSC/LSMO interface.

The optical properties in visible – near infrared range of Pd nano-hole arrays (PNA) and Pd thin films under hydrogen absorption – desorption processes have been investigated. The PNA samples show plasmonic resonances with about three times more transmission than that of the Pd thin film samples with a similar thickness. Remarkably, due to the plasmonic effect the PNA samples exhibit two times larger transmission change, normalized to the Pd cover area, under the hydrogen absorption/desorption processes at the Wood’s anomaly positions. The PNA sample can be used as a hydrogen sensor that has a better signal-to-noise ratio than the one based on the corresponding Pd thin film. The experimental results are confirmed by the finite-difference time domain (FDTD) calculations.

The magnetoplasmonic properties of Ag-Co composite nanohole arrays are investigated. It is observed that both plasmonic and magnetic properties of the Ag-Co composite nanohole arrays strongly depend on the composition ratio of Ag and Co. The enhanced optical transmission due to plasmonic resonance decreases with the increase of the Co component while the Faraday rotation effect increases monotonically. The magnetization dynamics of a composite thin film is also modified by the composition as well as the introduction of hole arrays. The Ag-Co composite nanohole arrays with the Co content of 30% show high plasmonic--magneto-optics performances compared with that of Ti-Co composite nanohole array, and annealing of the Ag-Co composites in vacuum can further improve this property. All experimental results are confirmed by the finite-difference time-domain calculations. Such a magnetoplasmonic composite material can act as a class of materials for magnetoplasmonic devices or metamaterial applications.

Magnetic nanoparticles (MNPs) exhibiting superparamagnetic properties might generate large magnetic dipole–dipole interaction with electron spins in organic semiconductors (OSECs). This concept could be considered analogous to the effect of hyperfine interaction (HFI). In order to investigate this hypothesis, Fe3O4 MNPs are used as a dopant for generating random hyperfine-like magnetic fields in a HFI-dominant π-conjugated polymer host, poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MeH-PPV). The magnetoconductance (MC) response in organic light emitting diodes (OLEDs) made by MeH-PPV/MNP blends is used to estimate the effective hyperfine field in the blends. Firstly, we find that the shape of the MC response essentially remains the same regardless of the MNP concentration, which is attributed to the similar functionality between the nuclear spins and magnetic moments of the MNPs. Secondly, the width of the MC response increases with increasing MNP concentration. Magneto-optical Kerr effect (MOKE) experiments and micromagnetic simulation indicate that the additional increase of the MC width is associated with the magnetization of the blend. Finally, the MC broadening has the same temperature dependent trend as the magnetization of the MNPs where the unique effect of the MNPs in their superparamagnetic and ferromagnetic regimes on the MC response is observed. Magneto-photoinduced absorption (MPA) spectroscopy confirms that the MC broadening is not due to defects introduced by the MNPs but a result of their unique superparamagnetic behavior. Our study yields a new pathway for tuning OSECs’ magnetic functionality, which is essential for organic optoelectronic devices and magnetic sensor applications.

Interfacing an organic semiconductor C60 with a non-magnetic metallic thin film (Cu or Pt) has created a novel heterostructure that is ferromagnetic at ambient temperature, while its interface with a magnetic metal (Fe or Co) can tune the anisotropic magnetic surface property of the material. Here, we demonstrate that sandwiching C60 in between a magnetic insulator (Y3Fe5O12: YIG) and a non-magnetic, strong spin-orbit metal (Pt) promotes highly efficient spin current transport via the thermally driven spin Seebeck effect (SSE). Experiments and first principles calculations consistently show that the presence of C60 reduces significantly the conductivity mismatch between YIG and Pt and the surface perpendicular magnetic anisotropy of YIG, giving rise to enhanced spin mixing conductance across YIG/C60/Pt interfaces. As a result, a 600% increase in the SSE voltage (VLSSE) has been realized in YIG/C60/Pt relative to YIG/Pt. Temperature-dependent SSE voltage measurements on YIG/C60/Pt with varying C60 layer thicknesses also show an exponential increase in VLSSE at low temperatures below 200 K, resembling the temperature evolution of spin diffusion length of C60. Our study emphasizes the important roles of the magnetic anisotropy and the spin diffusion length of the intermediate layer in the SSE in YIG/C60/Pt structures, providing a new pathway for developing novel spin-caloric materials.

Spintronics (also known as spin-based electronics) is an emerging technology that exploits the intrinsic spin transport of electrons other than their fundamental electronic charge. Organic semiconductors (OSCs) are composed of light elements that have weak spin-orbit interaction; consequently, they have long spin relaxation times, which makes them viable candidates for spin-transport materials in spintronics devices. Two types of organic spintronics devices have been extensively studied in the past few years: organic spin valves (OSVs) and organic light-emitting diodes (OLEDs), in which both conductivity and electroluminescence (EL) have been strongly modulated by an external magnetic field. In addition, optically detected magnetic resonance (ODMR) is an excellent complementary tool for investigating the electron-spin dynamics in OSCs. In this chapter, we describe the role of hyperfine interaction (HFI) in the spin response of films and devices based on conjugated polymers (CPs) made of protonated, H-hydrogen, deuterated, D-hydrogen, and 13C-rich chains. We experimentally prove that the HFI indeed plays a crucial role in all three spin responses. First, OLEDs based on the D-polymer show substantial narrower magneto-conductance (MC) and magneto-electroluminescence (MEL) responses. And the ultra-small MC and MEL responses at magnetic fields of few Gauss are also strongly isotope-dependent. Second, due to the longer obtained spin diffusion, OSV devices based on D-polymer show substantially larger magneto-resistance (MR) than devices based on H-polymers or C13-rich polymers. Films based on the D-polymer show considerably narrower polaron spin-half resonance than for H-polymers and C13-rich polymers. We also describe the time-resolved magneto-photoinduced absorption in π-conjugated copolymers in the time domain of picosecond to millisecond. Finally, our theoretical model describes these time-resolved magneto-photoinduced absorption results.

In the preceding review paper, Paper I [Journal of Science: Advanced Materials and Devices 1 (2016) 128–140], we showed the major experimental and theoretical studies on the first organic spintronic subject, namely organic magnetoresistance (OMAR) in organic light emitting diodes (OLEDs). The topic has recently been of renewed interest as a result of a demonstration of the magneto-conductance (MC) that exceeds 1000% at room temperature using a certain type of organic compounds and device operating condition. In this report, we will review two additional organic spintronic devices, namely organic spin valves (OSVs) where only spin polarized holes exist to cause magnetoresistance (MR), and spin organic light emitting diodes (spin-OLEDs) where both spin polarized holes and electrons are injected into the organic emissive layer to form a magneto-electroluminescence (MEL) hysteretic loop. First, we outline the major advances in OSV studies for understanding the underlying physics of the spin transport mechanism in organic semiconductors (OSCs) and the spin injection/detection at the organic/ferromagnet interface (spinterface). We also highlight some of outstanding challenges in this promising research field. Second, the first successful demonstration of spin-OLEDs is reviewed. We also discuss challenges to achieve the high performance devices. Finally, we suggest an outlook on the future of organic spintronics by using organic single crystals and aligned polymers for the spin transport layer, and a self-assembled monolayer to achieve more controllability for the spinterface.

Organic spintronics is an emerging and potential platform for future electronic devices. Significant progress has been made in understanding the spin injection, manipulation, and detection in organic spin valves in the past decade plus since its discovery. Studies have also been advanced to a range of materials combination of organic semiconductors and ferromagnetic electrodes for improving their performance especially at high temperatures. In addition, there are several remarkable studies on development of the spin valves as a multifunctional device. However, the research in this field is still in its infancy and there is a need to resolve many issues which keep this field far away from applications. In this report, we review major advances in organic spin valves such as understanding the underlying physics in spin injection and transport, high temperature operations, and functionality. We also highlight some of the outstanding challenges in this promising research field. Finally, we suggest an outlook on the future of organic spintronics.

Charge transport in amorphous organic semiconductors is governed by carriers hopping between localized states with small spin diffusion length. Furthermore, the interfacial resistance of organic spin valves (OSVs) is poorly controlled resulting in controversial reports of the magnetoresistance (MR) response. Here, surface-initiated Kumada transfer polycondensation is used to covalently graft π-conjugated poly(3-methylthiophene) brushes from the La0.67Sr0.33MnO3 (LSMO) bottom electrode. The covalent attachment along with the brush morphology allows control over the LSMO/brush interfacial resistance and large spacer mobility. Remarkably, with 15 nm brush spacer layer, an optimum MR effect of 70% at cryogenic temperatures and a MR of 2.7% at 280 K are observed. The temperature dependence of the MR is nearly an order of magnitude weaker than that found in control OSVs made from spin-coated poly(3-hexylthiophene). Using a variety of different brush layer thicknesses, the thickness-dependent MR at 20 K is investigated. A spin diffusion length of 17 nm at −5 mV junction voltage rapidly increased to 48.4 nm at −260 mV.

We report studies of magnetoresistance (MR) in double-layer organic spin valves (DOSV) using tris (8-hydroxyquinolinato) aluminum (Alq3) spacers. The device exhibits three distinct resistance levels depending on the relative magnetizations of the ferromagnetic electrodes. We observed a much weaker bias voltage dependence of MR in the device compared to that in the conventional organic spin valve (OSV). The MR magnitude reduces by the factor of two at 0.7 V bias voltage in the DOSV compared to 0.02 V in the conventional OSV. Remarkably, the MR magnitude reaches 0.3% at 6 V bias in the DOSVs, the largest MR response ever reported in OSVs at this bias. Our finding may have a significant impact on achieving high efficient bipolar OSVs strictly performed at high voltages.

Gas sensors are critical for facilitating the safety and integrity of systems used in the hydrogen energy and storage systems. It is challenging for any sensing technology to meet all the performance requirements for emerging applications, such as dynamic measuring range, response time, and sensitivity. Here, we propose an optical hydrogen gas sensor platform based on Pd bilayer plasmonic nano-lattices (BPNL), which is comprised of two parallel, subwavelength-separated hexagonal arrays of Pd nano-patchy particles and nano-holes. Optical transmission studies of the BPNL structure and its isolated sub-structures of nano-patches (NPs) and nano-hole arrays (NHs) upon hydrogen sorption show distinct optical isotherms with different spectral changes and response times in the visible-to-near-infrared region. Experiments and finite-difference time-domain (FDTD) calculations show that the strong electromagnetic coupling between localized and propagating plasmonic modes of the NPs and NHs, respectively, leads to the unique optical properties of the BPNL and their subsequent change upon hydrogen sorption. Notably, the BPNL structure possesses an extended optical response range and enhanced sensitivity for hydrogen detection. Additionally, the optical response time of the BPNL structure is an order of magnitude faster than that of the isolated array sensors in the low hydrogen pressure range. Finally, we demonstrate that the sensing characteristics of such a BPNL platform can be further improved by tuning its structural parameters.

Toroidal dipoles, unlike electric and magnetic dipoles, are formed due to currents flowing on the surface of a torus along it’s meridians. We investigate the toroidal dipole response in a graphene based infinite 2D array of terahertz (THz) metamaterial (MM) and report the active tuning of the toroidal resonances. Each metamolecule in our proposed MM configuration consists of two joint split ring resonators (SRRs) made up of graphene material with two gaps in each resonator. We examine actively tunable response of the toroidal excitations with respect to a change in the Fermi energy of graphene material. The toroidal effect is elaborated using surface current and magnetic field profiles at the resonance frequency of the metamolecule structure. The modulation of the metamaterial’s toroidal response and effect on Q factor is further examined by changing the relaxation time of graphene. The excitation of toroidal resonances at terahertz frequencies and their dynamic control could be significant in designing efficient tunable modulators, filters and sensors.

Hyperfine interaction (HFI), originating from the coupling between spins of charge carriers and nuclei, has been demonstrated to strongly influence the spin dynamics of localized charges in organic semiconductors. Nevertheless, the role of charge localization on the HFI strength in organic thin films has not yet been experimentally investigated. In this study, the statistical relation hypothesis that the effective HFI of holes in regioregular poly(3-hexylthiophene) (P3HT) is proportional to $1/{N}^{0.5}$ has been examined, where $N$ is the number of the random nuclear spins within the envelope of the hole wave function. First, by studying magnetoconductance in hole-only devices made by isotope-labeled P3HT we verify that HFI is indeed the dominant spin interaction in P3HT. Second, assuming that holes delocalize fully over the P3HT polycrystalline domain, the strength of HFI is experimentally demonstrated to be proportional to $1/{N}^{0.52}$ in excellent agreement with the statistical relation. Third, the HFI of electrons in P3HT is about 3 times stronger than that of holes due to the stronger localization of the electrons. Finally, the effective HFI in organic light emitting diodes is found to be a superposition of effective electron and hole HFI. Such a statistical relation may be generally applied to other semiconducting polymers. This Letter may provide great benefits for organic optoelectronics, chemical reaction kinetics, and magnetoreception in biology.

We review the fi rst 10 years of research on organic spin-valve devices in the fi eld of organic spintronics. The device fi gure of merit, magnetoresistance, is governed by the hyperfi ne interaction of the organic interlayer and the ability of the ferromagnetic electrodes to inject spin-polarized carriers. By choosing a deuterated π -conjugated polymer with a relatively long spin diffusion length as the organic interlayer and using a thin LiF buffer layer to raise the Fermi level of the cathode, a bipolar spin-valve device could be obtained in which the electroluminescence emission intensity is controlled by an external magnetic fi eld. We show that the underlying physics of this spin-organic light-emitting diode is very different from that of a unipolar organic spin valve because of the magnetic properties of the spin-polarized bipolar space charge limited current in the device.

The magneto-plasmonic properties of Ag-Co composite nano-triangle arrays are investigated. Both plasmonic and magnetic properties of the samples are found to strongly depend on the composition ratio of Ag and Co. Composite nano-triangle arrays exhibit strong plasmonic properties and low magneto-optics (MO) effect with high composition of Ag, and vice versa. The enhanced magneto-optic effect is also observed to be coincident with the localized surface plasmon resonance (LSPR) properties, i.e. the maximum Faraday effect occurs at the LSPR wavelength, which is due to locally high E-field. The composite triangle arrays with the 60% Co content show high plasmonic-MO performances characterized by magneto-optics-plasmonic correlation factor. All experimental results are confirmed by finite-difference time domain calculations.

Utilizing the magneto-resistance response of organic light emitting diodes (OLEDs) at ultra-small magnetic field we show that both the value and direction of the local earth magnetic field ( B E ) can be accurately obtained. We further demonstrate a ‘compass response’ in the magneto-conductance and magneto-electro-luminescence of OLEDs based on three isotopes of a π-conjugated polymer. We found that both responses are dependent on the direction of a small, fixed magnetic field B 0 (≈50 μT) with respect to B E , and this effect is used to determine B E direction. We conjecture that living creatures may use the same principle for magneto-reception and navigation.

We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant 12C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Jullière equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz2 orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface.

The magnetoconductance (MC) of unipolar and bipolar organic diodes based on active layers made of the π-conjugated polymer DOO-PPV is presented in the range of magnetic field strength, B below about 100 mT, and for various polymer exchange isotopes. The MC( B ) response is composed of two main regions: (i) a “sign-reversal” region for | B | B ) reverses its sign reaching a maximum absolute value |MC| m at B = B m ; and (ii) a monotonic region for | B | > 2 mT, where MC( B ) monotonically increases (decreases) for bipolar (unipolar) devices with an approximate Lorentzian line shape of width, Δ B . Similar behavior has been observed for the magneto-electroluminescence in bipolar devices. We found that MC( B ) in both field regions is strongly isotope dependent; in particular both B m and Δ B are larger for nuclei with larger hyperfine interaction (HFI) constant. The complete MC( B ) response, including the novel sign-reversal component is explained by a model of spin-coupled pairs of either same or opposite charge polarons, in which the HFI is explicitly included in the electronic spin Hamiltonian.

Although the hyperfine interaction (HFI) has been foreseen to play an important role in organic spin response, clear experimental evidence for it has been scarce. We studied and compared spin dynamics in films and organic spin-valve (OSV) devices based on π-conjugated polymers made of protonated, H-, deuterated, D-hydrogen (having a weaker HFI strength, a HFI ), and 13 C-rich chains (having stronger a HFI ). We demonstrate that HFI indeed plays a crucial role in the spin dynamics of all three polymer isotopes. Films based on the D-polymer show substantial narrower optically detected magnetic resonance of spin ½ polarons; whereas due to the longer spin diffusion, OSV devices based on D-polymers show substantially larger magnetoresistance. We also found that the giant magnetoresistance (GMR) steep temperature dependence in OSV devices is isotope independent, showing that is due to the magnetic response of the ferromagnetic electrodes. In addition, we found that the GMR steep voltage dependence is isotope dependent indicating that is due to a spin injection process at the electrodes, rather than spin transport through the organic interlayer. Finally we report GMR response in OSV devices made of C 60 interlayer having very weak HFI. These devices show sharp GMR response, and may therefore be excellent candidates for room temperature operation.

The development and popularity of wearable electronics increase demand for wearable energy harvesters that can scavenge energy from environment or human body movements. In this paper, we present a novel yarn as a wearable piezoelectric nanogenerator (PNG) consisting of a layer of electrospun poly(vinylidene fluoride) (PVDF) nanofibers integrated with PVDF film around a silver deposited nylon filament acting as an inner electrode. Electrospun PVDF nanofiber was wrapped around core yarn using a customized electrospinning device followed by coating of PVDF solution. The mesh of PVDF electrospun layer ensured uniform coating of PVDF solution, and the after coated PVDF film improved interfacial properties with inner electrode as well as strengthened the abrasion resistance of the piezoelectric polymer layer. The resultant unique yarn produced an average peak voltage of 0.52 V, peak current of 18.76 nA, and power density of 5.54 μW cm−3 under a cyclic compression of 0.02 MPa at 1.85 Hz, which is significantly higher than the energy output of a yarn with only a PVDF electrospun nanofibrous layer. More importantly, the high-performance was retained after 50 000 cycles of compression. The flexible yarn-based PNG device with good energy output and durability demonstrated its great promise to be used as a wearable energy harvester.

Hyperfine interaction (HFI) has been considered as a dominant spin mixing mechanism in conventional semiconducting polymers causing large magnetoconductance (MC) in organic diodes. However, the relationship between the MC width or HFI strength and the MC magnitude has not been investigated. We studied the correlation between the width and the magnitude of the MC response in organic diodes made by several conventional π-conjugated semiconducting polymers. First, by comparing the MC responses in electron- and hole-only unipolar devices made by the same polymer, we found that the electron-only device with a larger MC width always show a larger MC magnitude than that in the corresponding hole-only device. Second, we intentionally decreased and increased the charge localization or HFI strength in these unipolar devices by controlling their annealing temperature and UV irradiation, respectively. We found that the MC magnitude in these unipolar devices generally increases when the HFI strength increases but with different rates. We conclude that the width of MC or HFI strength is a crucial but not a unique factor that influences the MC magnitude. Finally, although the HFI in bipolar devices is smaller than that in the corresponding electron-only devices, the MC magnitude in bipolar devices is always larger than that in the electron-only devices suggesting that their underlying mechanisms are different.

We report on large enhancement of the longitudinal spin Seebeck effect (LSSE) in the Y3Fe5O12 (YIG)/Pt system at room temperature due to the addition of a thin layer of organic semiconductor (C60) in between the YIG and the Pt. LSSE measurements show that the LSSE voltage increases significantly, from the initial value of 150 nV for the YIG/Pt structure to 240 nV for the YIG/C60(5nm)/Pt structure. Radio-frequency transverse susceptibility experiments reveal a significant decrease in the surface perpendicular magnetic anisotropy (PMA) of the YIG film when C60 is deposited on it. These results suggest that the LSSE enhancement may be attributed to increased spin mixing conductance, the decreased PMA, and the large spin diffusion length of C60.

We perform charge-induced absorption and electroluminescence spectroscopy in a set of organic magnetoresistive devices made from different π-conjugated polymers. These experiments measure the singlet exciton, triplet exciton and polaron densities in live devices under an applied magnetic field. In most devices we find that the singlet exciton, triplet exciton and polaron densities and conductivity all increase with increasing magnetic field. However, in regio-regular polythiophene devices the polaron density decreases with increasing field. Our experiments test the predictions of three different models that were proposed to explain organic magnetoresistance. These models are based on different spin-dependent interactions, namely exciton formation, triplet-exciton polaron quenching and bipolaron formation.

In inorganic semiconductor spintronics the spin-diffusion length is usually limited by spin–orbit coupling. Here we examine the effect of spin–orbit coupling in organic spintronics. We consider singly charged π -conjugated polymer chains. We show that the diagonal matrix elements for spin–orbit coupling are zero. Even the off-diagonal matrix elements are zero or negligibly small unless a twisted, non-planar polymer chain is considered. We calculate these matrix elements as a function of twist angle using tight-binding wavefunctions. We show that time reversal symmetry prevents spin–orbit induced spin-precession and propose a phonon-assisted spin-flip process.

Because of the light elements involved, the spin–orbit coupling in organic materials is small. Therefore, the spin of charged polarons in these materials is expected to be a well conserved quantity. The conviction in the community grows that the main source of spin relaxation is in fact the coupling of the polaron spin to the random hyperfine fields of the hydrogen nuclei. By considering reactions between polarons forming bipolarons or excitons in the presence of these hyperfine fields we explain line shapes of the intrinsic magnetoresistance observed in disordered organic semiconductors. We also show how these hyperfine fields determine the spin-diffusion length in these semiconductors and how this affects the magnetoresistance line shapes of organic spin valves.