Angular correlation of annihilation radiation (ACAR) from silica-powder pellets and silica aerogel has been measured in order to investigate the slowing down of free positronium (Ps) atoms by collisions with silica grains and gas molecules. The data for the pellets and the aerogel in vacuum show that the slowing down of parapositronium (p-Ps) in the free space between the silica grains depends on the number of collisions and hence on the mean distance between the grains. The momentum distribution of orthopositronium (o-Ps) shows further slowing down because of its long lifetime. From the ACAR data obtained from specimens of aerogel 611ed with gases (He, Ne, Ar, Kr, Xe, H2, CH4, CO2, and iso-C4Hqo), the momentum-transfer cross sections between Ps and the gas molecules are estimated. It is concluded that the Ps kinetic energy is transferred only to the translational motion of the gas molecules, i.e. , the excitations of vibration and rotation of the molecules are negligible. PACS number(s): 36.10.Dr, 34.50. -s, 78.70.Bj I. INTR. ODU CTIONIt was observed in the mid 1960s that the angular correlation of annihilation radiation (ACAR) and positron lifetime spectra in metal oxide and metal Huoride powders [1,2] showed formation of positronium (Ps). In 1968, Paulin and Ambrosino [3] reported that the Ps component in the positron lifetime spectra for silica powders depends on the grain diameter. It was postulated that the Ps atoms form inside the grains and then disuse out of them [4]. Paulin and Ambrosino also observed the eA'ect of air on the o-Ps annihilation. Following this, silica powders were used for investigating the interactions between Ps and paramagnetic gases [5 -8].

The high energy density of room temperature (RT) sodium–sulfur batteries (Na‐S) usually rely on the efficient conversion of polysulfide to sodium sulfide during discharging and sulfur recovery during charging, which is the rate‐determining step in the electrochemical reaction process of Na‐S batteries. In this work, a 3D network (Ni‐NCFs) host composed by nitrogen‐doped carbon fibers (NCFs) and Ni hollow spheres is synthesized by electrospinning. In this novel design, each Ni hollow unit not only can buffer the volume fluctuation of S during cycling, but also can improve the conductivity of the cathode along the carbon fibers. Meanwhile, the result reveals that a small amount of Ni is polarized during the sulfur‐loading process forming a polar NiS bond. Furthermore, combining with the nitrogen‐doped carbon fibers, the Ni‐NCFs composite can effectively adsorb soluble polysulfide intermediate, which further facilitates the catalysis of the Ni unit for the redox of sodium polysulfide. In addition, the in situ Raman is employed to supervise the variation of polysulfide during the charging and discharging process. As expected, the freestanding S@Ni‐NCFs cathode exhibits outstanding rate capability and excellent cycle performance.

The carbon nanotube (CNT) and graphene hybrid is an attractive candidate for field emission (FE) because of its unique properties, such as high conductivity, large aspect ratio of CNT, and numerous sharp edges of graphene. We report here a vapor-solid growth of few-layer graphene (FLG, less than 10 layers) on CNTs (FLG/CNT) and Si wafers using a radio frequency sputtering deposition system. Based on SEM, TEM, and Raman spectrum analyses, a defect nucleation mechanism of the FLG growth was proposed. The FE measurements indicate that the FLG/CNT hybrids have low turn-on (0.956 V/μm) and threshold fields (1.497 V/μm), large field enhancement factor (∼4398), and good stability. Excellent FE properties of the FLG/CNT hybrids make them attractive candidates as high-performance field emitters.

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Singlet fission is usually the only reaction channel for excited states in rubrene-based organic light-emitting diodes (OLEDs) at ambient temperature. Intriguingly, we discover that triplet fusion (TF) and intersystem crossing (ISC) within rubrene-based devices begin at moderate and high current densities (j), respectively. Both processes enhance with decreasing temperature. This behavior is discovered by analyzing the magneto-electroluminescence curves of the devices. The j-dependent magneto-conductance, measured at ambient temperature indicates that spin mixing within polaron pairs that are generated by triplet-charge annihilation (TQA) causes the occurrence of ISC, while the high concentrations of triplets are responsible for generating TF. Additionally, the reduction in exciton formation and the elevated TQA with decreasing temperature may contribute to the enhanced ISC at low temperatures. This work provides considerable insight into the different mechanisms that occur when a high density of excited states exist in rubrene and reasonable reasons for the absence of EL efficiency roll-off in rubrene-based OLEDs.

In contrast to the large number of suitable electrode materials, thorough comprehension of the electrolyte remains lacking. Meanwhile, safety issues and side reactions in sodium-ion batteries caused by traditional organic liquid electrolytes are more severe than those in lithium-ion batteries due to the higher chemical reactivity of sodium than that of lithium which will result in a more drastic reaction with liquid electrolyte. Therefore, the discovery of an effective electrolyte remains a major challenge, which hinders the further application of SIBs. Solid-state sodiumion batteries (SSIBs) based on solid-state electrolytes (SSEs) have emerged as an attractive choice to solve these problems, avoiding safety concerns, and severe side reactions with the electrodes. [7] However, the insufficient ionic conductivity of SSEs is the main challenge for the further development of SSIBs. During the past years, many kinds of SSEs had been reported including ceramic-based, sulfide-based, and polymer electrolytes. [8][9][10][11] Although ceramic-based solid-state electrolyte have attracted much attention due to their high ionic conductivity at room temperature, harsh synthetic conditions (for instance, more than 1000 °C and 24 h) and poor contact capability with the electrodes are the main obstacles. Sulfide-based SSEs, featuring softness and superior ionic conductivity, are other promising alternatives with the merits of low-temperature process capability and good contact with the electrodes. Nevertheless, the chemical instability of the sulfide-based SSEs in ambient atmosphere is the biggest obstacle to make easily fabricated and low-cost solid-state sodium-ion batteries.Compared to the SSEs mentioned above, polymer-based SSEs demonstrate remarkable advantages such as excellent flexibility and excellent contact with electrodes. When employing polymer-based SSEs in large-scale industrial applications, the following parameters should be considered: 1) Effective ionic conductivity at room temperature or even at low temperature could guarantee the normal function of SSIBs in a wide temperature range and ensure a durable cycle life; 2) Excellent thermal stability could inhibit the incident caused by thermal runaway; 3) A large electrochemical window can ensure the compatibility between polymer-based SSEs and a high voltage cathode, thus increasing the energy density of the SSIBs but without electrochemical

In this study, a novel hollow carbon matrix was designed and prepared using a facile NaCl crystal template for the effective encapsulation of Se.

N+-bombarded multi-walled carbon nanotubes (N+-bombarded MWCNTs), with different nitrogen atomic percentages, were achieved by different N ion beam currents using ion beam-assisted deposition (IBAD) on MWCNTs synthesized by chemical vapor deposition (CVD). Characterizations of N+-bombarded MWCNTs were evaluated by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and contact angle. For comparison, the in vitro cytocompatibility of the N+-bombarded MWCNTs with different N atomic percentages was assessed by cellular adhesion investigation using human endothelial cells (EAHY926) and mouse fibroblast cells (L929), respectively. The results showed that the presence of nitrogen in MWCNTs accelerated cell growth and proliferation of cell culture. The higher nitrogen content of N+-bombarded MWCNTs, the better cytocompatibility. In addition, N+-bombarded MWCNTs with higher N atomic percentage displayed lower platelet adhesion rate. No hemolysis can be observed on the surfaces. These results proved that higher N atomic percentage led N+-bombarded MWCNTs to better hemocompatibility.