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Observation and Control of Interfacial Defects in ZnO/ZnSe Coaxial Nanowires

100%

Bhutto W., Wu Z., Cao Y., Wang W., Kang J.

vol. 125

issue 4

994-996

ZnO/ZnSe coaxial nanowires with different ZnO core diameters were synthesized by using a two-step chemical vapor deposition. The scanning electron microscopy images demonstrated that the coaxial nanowires with small ZnO core diameter had the smoother surface than that with large ZnO core diameter. A coherent ZnSe layer with wurtzite structure was observed in the nanowire interface between the ZnO core and the ZnSe shell by high resolution transmission electron microscopy. This coherent layer is beneficial to reduce the defect density and improve the crystal quality by suppressing the phase transition. It was found that the coherent thickness was significantly related to the ZnO core diameter. For the nanowire with large ZnO core, a thin critical thickness of 2 - 3 nm was obtained. As a result, a layer of zinc blende ZnSe appeared outside the nanowire, and a lot of defects existed in the interface between the ZnSe layers with different phase structures. For the nanowire with small ZnO core, however, the critical thickness increased and a coherent coaxial structure was observed with the same lattice spacing in the ZnO core and the ZnSe shell. To obtain defect-free coaxial nanowire, an optimal structure was also proposed by theoretical calculation.

Rheological and Thermal Transport Characteristics of a Transformer Oil Based Ferrofluid

73%

Paulovičová K., Tóthová J., Rajňák M., Wu Z., Sundén B., Wadsö L., Tobiáš T., Kopčanský P., Timko M., Lisý V.

Acta Physica Polonica A

2018

vol. 133

issue 3

564-566

Ferrofluids based on insulating liquids are intensively studied as a potential substitute of liquid dielectric in high voltage technologies. In this work we focus on the experimental investigation of flow and thermal transport characteristics of a ferrofluid based on transformer oil (Mogul) and iron oxide nanoparticles. The magneto-rheological behavior of the ferrofluid was studied by a rotational rheometer in the shear rate range from 1 to 1000 s¯¹ and magnetic field up to 1 T. By means of a thermal constants analyzer and a transient plane source method we obtained the thermal conductivity, specific heat and thermal diffusivity values for the studied oil and the ferrofluid. It is shown that the Newtonian character of the ferrofluid changes to a non-Newtonian with application of the magnetic field. The notable magneto-viscous effect has been observed especially at low shear rates. We found that the doping of the transformer oil by 3 wt% of the nanoparticles results in a thermal conductivity enhancement by about 3.2%.

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2 Acta Physica Polonica A

1 2018

1 2014

2 Wu Z.

1 Bhutto W.

1 Cao Y.

1 Kang J.

1 Kopčanský P.

1 Lisý V.

1 Paulovičová K.

1 Rajňák M.

1 Sundén B.

1 Timko M.

1 Tobiáš T.

1 Tóthová J.

1 Wadsö L.

1 Wang W.

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Observation and Control of Interfacial Defects in ZnO/ZnSe Coaxial Nanowires

Rheological and Thermal Transport Characteristics of a Transformer Oil Based Ferrofluid