Zixu Sun

Efficient light trapping in low aspect-ratio honeycomb nanobowl surface texturing for crystalline silicon solar cell applications

We report a significant reflection reduction over a broadband light spectrum in crystalline silicon via introduction of low aspect-ratio honeycomb nanobowl front surface textures. A restructuration technique is developed to shape nanopores into nanobowls, enabling excellent impedance matching and efficient mode coupling. As a result, an overall reflection down to 2% in the spectrum range of 400–1 100 nm wavelength is achieved. In comparison to nanopores-structured light-trapping configurations, the nanobowls-textures have much smaller parasitic surface area, which mitigates the surface recombination losses. The texturing technique offers a promising approach to high efficiency c-Si thin-film solar cells.

Ultrasmall Sn nanodots embedded inside N-doped carbon microcages as high-performance lithium and sodium ion battery anodes

Sn based materials are promising anodes both in Li-ion batteries and Na-ion batteries due to their high theoretical capacities (994 mA h g−1 for LIBs and 847 mA h g−1 for SIBs, respectively). In order to improve the cycle performance, Sn/N-doped carbon microcage composites (Sn/NMCs) with Sn nanodots uniformly embedded inside the N-doped carbon microcages are synthesized through a simple spray drying process, followed by thermal treatment. When used as electrodes, Sn/NMCs exhibit an initial reversible capacity of 780 mA h g−1 at 200 mA g−1, and maintain 472 mA h g−1 after 500 cycles in LIBs. For Na-ion batteries, Sn/NMCs deliver an initial reversible capacity of 439 mA h g−1 at 50 mA g−1 and maintain 332 mA h g−1 after 300 cycles. The remarkable electrochemical performance is mainly owing to the advanced structure of Sn/NMCs, which could be attributed to the pore-formation using NaCl, and the grain size inhibition of Sn using N-doped carbon. Moreover, this preparation method is accessible to scale up and can be extended to fabricate other electrode materials.

Recombination property of nitrogen-acceptor-bound states in ZnO

The recombination property of nitrogen (N)-related acceptor-bound states in ZnO has been investigated by photoluminescence (PL), time-resolved PL, and selective PL. Several possible recombination processes were discussed by analyzing the relaxation and recombination properties under large Coulomb interaction. It is strongly suggested that bound exciton emission dominates the recombination process related to the N acceptor. The recombination lifetime is 750 ps and the binding energy is 67 meV for N-acceptor-bound exciton at low temperature. (c) 2006 American Institute of Physics.

A scalable formation of nano-SnO2 anode derived from tin metal-organic frameworks for lithium-ion battery

In this work, for the first time, we synthesize a SnO2 nanomaterial through the calcination of tin metal–organic framework (MOF) precursors. X-ray diffraction, field emission scanning electron microscope, transmission electron microscopy, and the Brunauer–Emmett–Teller specific surface area are used to characterize the phases and to observe surface morphologies. This anode material exhibits good electrochemical performance in LIBs with high reversible capacity and cycling stability. The good electrochemical properties could be ascribed to the short transport/diffusion path of electrons and lithium ions and the high contact area between the electrode and electrolyte that results from the nanostructured SnO2. This is low-cost, facile and scalable for mass production of SnO2 nanocomposites as a potential anode material for the next-generation LIBs.

Facile synthesis of Fe-MOF/RGO and its application as a high performance anode in lithium-ion batteries

The use of metal organic frameworks (MOFs) as new promising electrode materials in lithium-ion batteries (LIBs) has attracted significant attention. However, the low electrical conductivity of MOFs has resulted in the poor cycle performance of LIBs. Here, we report a facile synthesis route of Fe-MOF/reduced graphene oxide (RGO) composites using a solvothermal method. When used as anode materials for LIBs, the synthesized Fe-MOF/RGO (5%) composite shows superior Li storage with a reversible capacity of 1010.3 mA h g−1 after 200 cycles and an excellent rate performance. The improved electrochemical performance may be attributed to the synergistic effect of MOFs with high theoretical capacities and RGO with high electrical conductivity.

Effect of grain size and pores on the dielectric constant of nanocrystalline diamond films

The nanocrystalline diamond films with different morphologies and roughness were synthesized by a bias-assisted hot filament chemical vapor deposition method. It was found that the nanocrystalline diamond film exhibited low-k dielectric properties with the increase of CH4 concentration during diamond deposition. The low-k nanocrystalline diamond film with grain size of around 40nm and dielectric constant of 2.4 was obtained at the CH4 concentration of 16% and the bias of −140V. The low dielectric constant can be mainly attributed to the decrease of diamond grain sizes and the formation of more nanopores in as-grown nanocrystalline diamond film, both of which were discussed in details based on the grain size determined band gap expansion effect and the two-phase dielectric mixing model, respectively.

Facial Synthesis of Three-Dimensional Cross-Linked Cage for High-Performance Lithium Storage.

Silicon/C composite is a promising anode material for high-energy Li-ion batteries. However, synthesizing high-performance Si-based materials at large scale and low cost remains a huge challenge. Here, we for the first time report the preparation of an interconnected three-dimensional (3D) porous Si-hybrid architecture by using a spray drying method. In this unique structure, the highly robust C-CNT-RGO cages not only can improve the conductivity of the electrode and buffer the volume expansion but also suppress the Si nanoparticles aggregation. As a result, the 3D Si@po-C/CNT/RGO electrode achieves long-life cycling stability at high rates (a reversible capacity of 854.9 mA h g(-1) at 2 A g(-1) after 500 cycles and capacity decay less than 0.013% per cycle) and good rate capability (1454.7, 1198.8, 949.2, 597.8, and 150 mA h g(-1) at current densities of 1, 2, 4, 10, and 20 A g(-1), respectively). Moreover, this novel electrode could deliver high reversible capacities and long-life stabilities even with high mass loading density (764.9 mA h g(-1) at 1.0 mg cm(-2) after 500 cycles and 472.2 mA h g(-1) at 1.5 mg cm(-2) after 400 cycles, respectively). This cheap and scalable strategy can be extended to fabricate other materials with large volume expansion (Sn, Ge, transition-metal oxides) and 3D porous carbon for other potential applications.

Nonradiative recombination effect on photoluminescence decay dynamics in GaInNAs∕GaAs quantum wells

The influence of nonradiative recombination on the photoluminescence (PL) decay dynamics in GaInNAs∕GaAs quantum wells is studied by time-resolved photoluminescence under various excitation intensities. It is found that the PL decay process strongly depends on the excitation intensity. In particular, under the moderate excitation levels the PL decay curves exhibit unusual nonexponential behavior and show a convex shape. By introducing a new parameter of the effective concentration of nonradiative recombination centers into a rate equation, the observed results are well simulated. The cw PL data further demonstrate the nonradiative recombination effect on the optical properties of GaInNAs∕GaAs quantum wells.

The exchange biaslike effect in tetrahedral spinels Cu1−xZnxCr2O4(x=0.1,0.3)

Exchange biaslike phenomenon is observed in the Zn doped spinel polycrystalline CuCr2O4. The magnetic hysteresis loop shifts in both horizontal and vertical directions at 5 K after the samples are cooled down to 5 K in a magnetic field. The nature of this magnetic anisotropy arises from the freezing properties of the local anisotropy in the cluster glass system. The magnetic shifts along both directions can be observed directly under the principle that the spins of a cluster are frozen in random orientations upon zero field, and aligned to the field direction upon field cooling.

A composite with SiOx nanoparticles confined in carbon framework as an anode material for lithium ion battery

A composite with ultrafine SiOx (x = 1.57, around 2 nm) nanoparticles confined in a carbon framework is synthesized by a simple thermopolymerization process and subsequent heat treatment. In the composite, the carbon framework can provide a consecutive network to improve the electrical conductivity of the composite and cushion the volume expansion to prevent the active material peeling from the current collector. The ultrafine SiOx nanoparticles can alleviate mechanical strain and shorten the diffusion/transport distance of lithium ions and electrons. In consequence, the as-synthesized composite delivers a high reversible capacity of 540 mA h g−1 at a current density of 500 mA g−1 after 200 cycles. The composite delivers good electrochemical performance, making it a promising candidate for the next-generation high-energy LIBs.