Xiaoguang Li

Bio: Xiaoguang Li is an academic researcher from University of Science and Technology of China. The author has contributed to research in topics: Magnetization & Ferroelectricity. The author has an hindex of 38, co-authored 273 publications receiving 5180 citations. Previous affiliations of Xiaoguang Li include Anhui University & Academia Sinica.

Isotope effect in spin response of pi-conjugated polymer films and devices.

Abstract: The origin of the effect that a magnetic field has on various electronic properties of organic semiconductors is still controversial. It is now shown that substituting hydrogen for deuterium in conducting polymers changes the response to a magnetic field substantially, proving the essential part played by hyperfine interaction in this effect.

Thermoelectric properties of individual electrodeposited bismuth telluride nanowires

Abstract: For an electrodeposited bismuth telluride (BixTe1−x) nanowire from one batch with x found to be about 0.46, the Seebeck coefficient (S) was measured to be 15%–60% larger than the bulk values at temperature 300K. For four other nanowires from a different batch with x≈0.54, S was much smaller than the bulk values. The electrical conductivity of the nanowires showed unusually weak temperature dependence and the values at 300K were close to the bulk values. Below 300K, phonon-boundary scattering dominated phonon-phonon Umklapp scattering in the nanowires, reducing the lattice thermal conductivity.

Thermoelectric and structural characterizations of individual electrodeposited bismuth telluride nanowires

Abstract: The thermoelectric properties and crystal structure of individual electrodeposited bismuth telluride nanowires (NWs) were characterized using a microfabricated measurement device and transmission electron microscopy. Annealing in hydrogen was used to obtain electrical contact between the NW and the supporting Pt electrodes. By fitting the measured Seebeck coefficient with a two-band model, the NW samples were determined to be highly n-type doped. Higher thermal conductivity and electrical conductivity were observed in a 52 nm diameter monocrystalline NW than a 55 nm diameter polycrystalline NW. The electron mobility of the monocrystalline NW was found to be about 19% lower than that of bulk crystal at a similar carrier concentration and about 2.5 times higher than that of the polycrystalline NW. The specularity parameter for electron scattering by the NW surface was determined to be about 0.7 and partially specular and partially diffuse, leading to a reduction in the electron mean-free path from 61 nm in ...

Competition between ferromagnetic metallic and paramagnetic insulating phases in manganites

Abstract: La0.67Ca0.33Mn1−xCuxO3 (x=0 and 0.15) epitaxial thin films were grown on the (100) LaAlO3 substrates, and the temperature dependence of their resistivity was measured in magnetic fields up to 12 T by a four-probe technique. We found that the competition between the ferromagnetic metallic (FM) and paramagnetic insulating (PI) phases plays an important role in the observed colossal magnetoresistance (CMR) effect. Based on a scenario that the doped manganites approximately consist of phase-separated FM and PI regions, a simple phenomenological model was proposed to describe the CMR effect. Using this model, we calculated the resistivity as functions of temperature and magnetic field. The model not only qualitatively accounts for some main features related to the CMR effect, but also quantitatively agrees with the experimental observations.

Spin response in organic spin valves based on La 2 ∕ 3 Sr 1 ∕ 3 Mn O 3 electrodes

Abstract: We fabricated spin-valve devices made of organic semiconductor thin films sandwiched between ferromagnetic half-metal ${\mathrm{La}}_{2∕3}{\mathrm{Sr}}_{1∕3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSMO) and cobalt electrodes, using three different organic molecules. Subsequently, we studied the spin injection and transport properties by measuring the device magnetoresistance (MR) response at various biasing voltages $V$ and temperatures $T$. We found that the spin-valve MR response in all devices monotonically decreases with $V$ and is asymmetric with respect to the voltage polarity. We also found a steep MR decrease with $T$, where it vanishes at $T\ensuremath{\sim}220\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, similar to other MR responses in inorganic tunneling junction devices based on LSMO and Co ferromagnetic electrodes. In contrast, the spin-$\frac{1}{2}$ photoluminescence detected magnetic resonance of the organic interlayer, which directly depends on the spin-lattice relaxation rate of polarons in the organic semiconductor, was found to be temperature independent. We thus conclude that the steep MR dependence on $T$ is due to the temperature dependence of the interfacial spin polarization of the LSMO electrode, which also drastically decreases up to $T\ensuremath{\sim}220\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We thus conclude that (i) the spin-lattice relaxation time in organic semiconductors should not be the limiting factor in fabricating room temperature organic spin valves, and (ii) in order to achieve room temperature spin-valve operation with substantial MR value, spin-injection electrodes other than LSMO need to be involved, having large and less temperature dependent spin polarization.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Nanostructured metal chalcogenides: synthesis, modification, and applications in energy conversion and storage devices

Abstract: Advanced energy conversion and storage (ECS) devices (including fuel cells, photoelectrochemical water splitting cells, solar cells, Li-ion batteries and supercapacitors) are expected to play a major role in the development of sustainable technologies that alleviate the energy and environmental challenges we are currently facing. The successful utilization of ECS devices depends critically on synthesizing new nanomaterials with merits of low cost, high efficiency, and outstanding properties. Recent progress has demonstrated that nanostructured metal chalcogenides (MCs) are very promising candidates for efficient ECS systems based on their unique physical and chemical properties, such as conductivity, mechanical and thermal stability and cyclability. In this review, we aim to provide a summary on the liquid-phase synthesis, modifications, and energy-related applications of nanostructured metal chalcogenide (MC) materials. The liquid-phase syntheses of various MC nanomaterials are primarily categorized with the preparation method (mainly 15 kinds of methods). To obtain optimized, enhanced or even new properties, the nanostructured MC materials can be modified by other functional nanomaterials such as carbon-based materials, noble metals, metal oxides, or MCs themselves. Thus, this review will then be focused on the recent strategies used to realize the modifications of MC nanomaterials. After that, the ECS applications of the MC/modified-MC nanomaterials have been systematically summarized based on a great number of successful cases. Moreover, remarks on the challenges and perspectives for future MC research are proposed (403 references).

Nanoscale thermal transport. II. 2003–2012

Abstract: A diverse spectrum of technology drivers such as improved thermal barriers, higher efficiency thermoelectric energy conversion, phase-change memory, heat-assisted magnetic recording, thermal management of nanoscale electronics, and nanoparticles for thermal medical therapies are motivating studies of the applied physics of thermal transport at the nanoscale. This review emphasizes developments in experiment, theory, and computation in the past ten years and summarizes the present status of the field. Interfaces become increasingly important on small length scales. Research during the past decade has extended studies of interfaces between simple metals and inorganic crystals to interfaces with molecular materials and liquids with systematic control of interface chemistry and physics. At separations on the order of ∼1 nm, the science of radiative transport through nanoscale gaps overlaps with thermal conduction by the coupling of electronic and vibrational excitations across weakly bonded or rough interface...

Semiconductor nanowires for energy conversion.

Abstract: Semiconductor nanowires represent an important class of nanostructure building block for photovoltaics as well as direct solar-to-fuel application because of their high surface area, tunable bandgap and efficient charge transport and collection. In this talk, I will highlight several recent examples in this lab using semiconductor nanowires and their heterostructures for the purpose of solar energy harvesting. In addition, we have also discovered that the thermoconductivity of the silicon nanowires can be significantly reduced due to phonon scattering, pointing to a very promising approach to design better thermoelectrical materials. It is important to note that the engines that generate most of the world's power typically operate at only 30–40 per cent efficiency, releasing roughly 15 terawatts of heat to the environment. If this “wasted heat” could be recycled, the impact globally would be enormous. Our silicon nanowire thermoelectric technology could have a significant impact in alternative energy generation.