Xiannian Yao

Bio: Xiannian Yao is an academic researcher from Chinese Ministry of Education. The author has contributed to research in topics: Spintronics & Magnetoresistance. The author has an hindex of 4, co-authored 5 publications receiving 258 citations.

Properties and Applications of the β Phase Poly(vinylidene fluoride).

Abstract: Poly(vinylidene fluoride), PVDF, as one of important polymeric materials with extensively scientific interests and technological applications, shows five crystalline polymorphs with α, β, γ, δ and e phases obtained by different processing methods. Among them, β phase PVDF presents outstanding electrical characteristics including piezo-, pyro-and ferroelectric properties. These electroactive properties are increasingly important in applications such as energy storage, spin valve devices, biomedicine, sensors and smart scaffolds. This article discusses the basic knowledge and character methods for PVDF fabrication and provides an overview of recent advances on the phase modification and recent applications of the β phase PVDF are reported. This study may provide an insight for the development and utilization for β phase PVDF nanofilms in future electronics.

Magnetoresistance Effect and the Applications for Organic Spin Valves Using Molecular Spacers

Abstract: Organic spin devices utilizing the properties of both spin and charge inherent in electrons have attracted extensive research interest in the field of future electronic device development. In the last decade, magnetoresistance effects, including giant magetoresistance and tunneling magnetoresistance, have been observed in organic spintronics. Significant progress has been made in understanding spin-dependent transport phenomena, such as spin injection or tunneling, manipulation, and detection in organic spintronics. However, to date, materials that are effective for preparing organic spin devices for commercial applications are still lacking. In this report, we introduce basic knowledge of the fabrication and evaluation of organic spin devices, and review some remarkable applications for organic spin valves using molecular spacers. The current bottlenecks that hinder further enhancement for the performance of organic spin devices is also discussed. This report presents some research ideas for designing organic spin devices operated at room temperature.

Defect states dependence of spin transport in iron phthalocyanine spin valves

Abstract: We fabricated spin-valve devices with a Co/iron phthalocyanine (FePc)/Co stacking structure. The spin-transport properties were systemically studied by varying the measurement temperature and magnetoresistance was confirmed. The estimated value of the spin-diffusion length for the FePc layer is around 30 nm. The existence of defect states was demonstrated based on the analysis of current-voltage curves. Carrier mobilities in the devices were calculated following a trap-filled space charge limited current model, showing the mobility could be up to $2.95\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}/\mathrm{Vs}$ at 290 K. The molecular orientation growth of FePc on Co and the interfacial interaction for FePc/Co are also discussed. This work deepens the understanding of spin transport in organic spin devices.

Unexpected magnetic coupling oscillations for L 1 0 -MnGa /Co (Fe ) films induced by quantum wells

Abstract: Exchange magnetic coupling interactions between $L{1}_{0}\text{-MnGa}$ and ultrathin Co (Fe) films were studied by first-principles calculations. An unexpected oscillation of magnetic coupling was observed by varying the thickness of Co or Fe layer. Moreover, the coupling types are different for Co and Fe with $L{1}_{0}\text{-MnGa}$. The magnetic coupling maintains the ferromagnetic interaction for $L{1}_{0}\text{-MnGa}$/Fe, even if the thickness of Fe layer varies. Interestingly, a change from ferromagnetic to antiferromagnetic couplings appears alternately for $L{1}_{0}\text{-MnGa}$/Co till Co thickness is up to 11 atomic layers. The coupling oscillations were attributed to the quantum well states formed in the Co (Fe) films. The orbital characters of the quantum well states were analyzed. Our results are useful to further understand the magnetic coupling interactions and design new magnetic nanostructures.

Interface hybridization and spin filter effect in metal-free phthalocyanine spin valves

Abstract: Spin-orbit coupling (SOC) has long been regarded as the core interaction to determine the efficiency of spin conserved transport in semiconductor spintronics. In this report, a spin-valve device with a Co/metal-free phthalocyanine (H2Pc)/Co stacking structure is fabricated. The magnetoresistance effect was successfully obtained in the device. It is also found that the magnetoresistance response is relatively smaller than that of metallic phthalocyanines, clearly implying that SOC is not the key factor to affect the magnetoresistance in phthalocyanine spin-valves. The dominant mechanism that determines the spin transport efficiency in the present H2Pc devices was systemically explored by combining both experimental measurements and first-principles calculation analysis. It was noticed that both the crystalline structure and molecular orientation of the H2Pc layer could be modified by the contact under-layer materials, which changes the magnetization intensity of the ferromagnetic metallic electrode due to the strong interface hybridization of Co/H2Pc. Meanwhile, the theoretical calculations clearly demonstrated that the spin filter effect from the second H2Pc layer should be responsible for the decrease of the magnetoresistance response in the present spin-valves compared to those using metallic phthalocyanine layers. This investigation may trigger new insights into the role of SOC strength and interface hybridization in organic spintronics.

An Introduction To Electrospinning And Nanofibers

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New developments in composites, copolymer technologies and processing techniques for flexible fluoropolymer piezoelectric generators for efficient energy harvesting

Abstract: Flexible piezoelectric generators (PEGs) have recently attracted significant interest, as they are able to harvest mechanical energy and convert it to electricity, decreasing reliance on conventional energy sources. These devices enable innovative applications including smart clothing, wearable electronics, on-skin and implantable sensors, as well as harvesting energy from the movement of vehicles, water and wind. Poly(vinylidene fluoride) and related fluoropolymers are the most common flexible piezoelectric materials, widely utilized for their high electromechanical conversion efficiencies, optimal mechanical flexibility, processability and biocompatibility. This critical review covers the processing of fluoropolymers towards the maximization of piezoelectric conversion parameters. Particular emphasis is placed on the correlation between synthetic routes, inclusion of further co-monomers, addition of additives and nanomaterials, as well as processing techniques and the optimized electricity generation in the resultant PEGs, providing an important analysis to complement existing literature. The importance of novel polymer deposition techniques, which reduce reliance on the conventional, highly energetic post-processing steps, is highlighted. Recent advances in fluoropolymer-based flexible PEGs open an array of exciting applications, which rapidly progress towards commercialization. This review provides a timely analysis of this increasingly important field to the cross-disciplinary community of polymer chemists, materials scientists, nanotechnologists, engineers, and industry practitioners.