Xianghui Hou

Low‐Threshold Electrically Pumped Random Lasers

Electrically pumped random lasers are realized in ZnO nanocrystallite films in a simple metal-oxide-semiconductor structure. By introducing an i-ZnO layer, a threshold current of 6.5 mA is obtained. The reported results provide a simple route to electrically pumped random lasing (see figure) with relatively low threshold, a significant step towards the future applications of this kind of laser.

Tribological performance of Graphene/Carbon nanotube hybrid reinforced Al2O3 composites.

Tribological performance of the hot-pressed pure Al2O3 and its composites containing various hybrid contents of graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs) were investigated under different loading conditions using the ball-on-disc method. Benchmarked against the pure Al2O3, the composite reinforced with a 0.5 wt% GNP exhibited a 23% reduction in the friction coefficient along with a promising 70% wear rate reduction, and a hybrid reinforcement consisting of 0.3 wt.% GNPs + 1 wt.% CNTs resulted in even better performance, with a 86% reduction in the wear rate. The extent of damage to the reinforcement phases caused during wear was studied using Raman spectroscopy. The wear mechanisms for the composites were analysed based on the mechanical properties, brittleness index and microstructural characterizations. The excellent coordination between GNPs and CNTs contributed to the excellent wear resistance property in the hybrid GNT-reinforced composites. GNPs played the important role in the formation of a tribofilm on the worn surface by exfoliation; whereas CNTs contributed to the improvement in fracture toughness and prevented the grains from being pulled out during the tribological test.

Charge transport in flexible solar cells based on conjugated polymer and ZnO nanoparticulate thin films

ZnO nanoparticulate thin films were fabricated on flexible indium tin oxide (ITO) covered polyethylene terephthalate (PET) substrates by spin coating technology and were used in flexible solar cells with a hybrid polymer, due to the benefit of low temperature processes. The flexible solar cells with a structure of PET/ITO/ZnO/regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/Ag have shown a photovoltaic performance with open circuit voltage of 0.56 V, short-circuit current density of 12.55 mA cm−2, fill factor of 0.36 and power conversion efficiency of 2.51%. The opposite J–V curves of the devices with ZnO and without ZnO were attributed to the opposite charge transport directions, which suggested the electron transport and hole blocking role of ZnO. The photoluminescence intensity of P3HT was totally quenched in the P3HT:PCBM thin film while there was no photoluminescence quench in the ZnO/P3HT double layer thin film, which clearly indicates that the exciton dissociation occurs at the interface between P3HT:PCBM instead of that between ZnO and P3HT. Therefore, it is reasonable to infer that the electrons transported to ZnO are from the lowest unoccupied molecular orbital (LUMO) of PCBM instead of the LUMO of P3HT according to the quenching experiment results combined with the J–V curve and energy level diagram. The identification of the charge transport directions and the exciton–dissociation interface will benefit the further improvement of photovoltaic performance by optimization of material selection, device design and process technology.

Modification of multi-walled carbon nanotubes with cobalt phthalocyanine: effects of the templates on the assemblies

Cobalt phthalocyanine (CoPc) assemblies are prepared using several kinds of multiwalled carbon nanotube (MWCNT) templates by in situ solid synthesis in a muffle furnace. The products are characterized by infrared spectroscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and differential thermal analysis-thermogravimetry. The electrocatalytic activity of the obtained MWCNT-templated CoPc assemblies is measured by cyclic voltammograms in an oxygen-saturated 0.5 M H2SO4. The results show that the CoPc assemblies have several different structures: CoPc nanothreads supported by MWCNTs, nanocrystals mixed with MWCNTs and CoPc/MWCNT coaxial nanotubes. The size and the structure of CoPc assemblies are controlled by the interfacial interaction, including π–π interaction, hydrogen bond and coordinate bond, between CoPc and the MWCNTs, which strongly depend on the microstructure of the MWCNTs. Thermal analysis shows CoPc/MWCNT coaxial nanotubes exhibit higher thermal stability than the assemblies with the structure of CoPc nanothreads supported by MWCNTs and nanocrystals linked to MWCNTs. In addition, the cyclic voltammogram measurements show they display different electrochemical characteristics depending on their structures. CoPc/MWCNT assemblies with coaxial nanotube structure have better electrocatalytic activity to oxygen reduction than the others.

A self-optimizing electrodeposition process for fabrication of calcium phosphate coatings

A self-optimizing electrochemical deposition method, named cathode rotation electrodeposition process, is put forward in this work for the fabrication of calcium phosphate coatings. Because the metallic substrate rotates with high speed, the centrifugal and friction forces could clear away hydrogen bubbles and poor-adhesion deposition particles produced on the substrate in due course. The process possesses a self-optimizing character, and only deposition particles with enough bonding strength can be selected as coating units. Compared with conventional electrodeposition process, this novel process could provide us with more compact and homogeneous calcium phosphate coatings on the substrate.

Internal friction behavior of carbon–carbon composites

Abstract The fundamental internal friction behavior of carbon–carbon composites is studied. Two internal friction mechanisms are proposed according to the special internal friction characteristics in carbon–carbon composites. A thermoelastic mechanism, which is independent of amplitude, mainly leads to the internal friction increase with increasing frequency. The other is a static hysteresis mechanism that internal friction depends on the amplitude but is independent of frequency. Moreover, it is very interesting that some abnormal internal friction phenomena can be observed. The variation characteristics of internal friction and dynamic modulus versus temperature in carbon–carbon composites are quite different from other materials. This special behavior may be a result of interfacial CTE effects, as well as the coordination effects of the individual response of the fibers, matrix and interface of carbon–carbon composites. Finally, the validity of internal friction analysis methods for densification process monitoring and non-destructive inspection of carbon–carbon composites is discussed for the first time. The results indicate that internal friction testing methods have great potential for monitoring process and inspecting components of carbon–carbon composites non-destructively.

Synthesis of hybrid graphene carbon-coated nanocatalysts

A hybrid of many few-layer graphene carbon-coated Fe nano particles was produced by pyrolysis of iron tetrapyridinoporphyrazine. It shows high electrochemical activity for oxygen reduction, and exhibits high saturation magnetization and a negligible magnetic hysteresis, suitable for magnetic catalysts and catalyst-support particles.

Modeling of chemical vapor infiltration process for fabrication of carbon–carbon composites by finite difference methods

Abstract A finite difference (FD)-based method is proposed to describe the chemical vapor infiltration (CVI) processes for fabrication of carbon–carbon composites. The continuous, unsteady-state CVI processing can be divided into many discrete steady-state depositions by this model. Long cylindroid unidirectional carbon–carbon composites are prepared using the isothermal CVI technique to verify the accuracy of the FD methods. Experimental research shows that the modeling values are in good agreement with experimental data. The deviation of infiltration threshold and final bulk density are both minor with error less than 10%. Moreover, computational porosity at different cross-sections of preforms is also consistent with experimental values. The effect of deposition temperature, fiber volume fraction, and size of composites, on densification is analyzed using the FD model, which results in some useful information. Bulk density, infiltration threshold, uniformity, are described quantitatively by regression equations.

Densification of unidirectional carbon–carbon composites by isothermal chemical vapor infiltration

Abstract The aim of this research was to investigate the densification of cylindrical unidirectional C–C composites by isothermal chemical vapor infiltration. Several different preforms with different fiber volume fractions were prepared, and it was found that the preforms with the lower fiber volume fraction have a more rapid rate of densification and the final density is higher. The problem of infiltrating uniformly, as well as the effects of large penetrating holes in the preform on densification was also discussed.

Epitaxial hetero-structure of CdSe/TiO2 nanotube arrays with PEDOT as a hole transfer layer for photoelectrochemical hydrogen evolution

The photocatalytic decomposition of water is believed to be able to help mitigate the crisis of fossil fuel depletion. However, the photocatalytic hydrogen production remains challenge to obtain high and stable photoconversion efficiency. Here we report an epitaxial hetero-structure of CdSe/TiO2 nanotube arrays as efficient photo-anodes via simple room-temperature, low-cost electrochemical deposition. With the help of the similar d spacing with TiO2, CdSe sensitization layer is epitaxially grown on the tube wall of the TiO2 nanotubes, resulting in an ideal coherent grain boundary and single crystal growth. The resultant photo-anode produces 30% more photocurrent than those samples without coherent grain boundary. Notably, the especial epitaxial hetero-structure is beneficial to decrease the recombination site and accelerate the separation of photogenerated electron-hole pairs. Furthermore, an ultrathin PEDOT surface layer was developed on the epitaxial hetero-structure of CdSe/TiO2 nano-tube arrays in which it functions as both a physical passivation barrier and a hole transfer layer. As a result, significantly enhanced photocurrent density and substantially better stability have been achieved. This methodology may be providing a new pathway of epitaxial growth for preparing the heterogeneous junction materials which have similar d spacing.