We study (Ga,Mn)As diluted magnetic semiconductors in terms of the Ruderman–Kittel–Kasuya–Yosida quantum spin model in Green’s function approach.Random distributions of the magnetic atoms are treated by using an analytical average of magnetic configurations.Average magnetic moments and spin excitation spectra as functions of temperature can be obtained by solving self-consistent equations,and the Curie temperature TC is given explicitly.TC is proportional to magnetic atomic concentration,and there exists a maximum for TC as a function of carrier concentration.Applied to (Ga,Mn)As,the theoretical results are consistent with experiment and the experimental TC can be obtained with reasonable parameters.This modelling can also be applied to other diluted magnetic semiconductors.
As a type of thin film,two dimensional(2D) reticulate architectures built of freestanding single-walled carbon nanotube(SWCNT) bundles are suitable for scalable integration into devices and nanocomposites for many applications.The superior properties of these films,such as optical transparency,unique electrical properties and mechanical flexibility,result not only from the outstanding properties of individual SWCNTs but also from the collective behavior of the individual tubes,with additional properties arising from the tube-tube interactions.In this review,the synthesis,structure and fundamental properties,such as conductivity,transparency,optical nonlinearity and mechanical performance,of "freestanding SWCNT bundle network" thin films and nanocomposites,as well as their application as supercapacitors are highlighted.Some long-standing problems and topics warranting further investigation in the near future are addressed.
In this paper, we propose an efficient way to synthesize carbon nanotube films using ferrocene and ethanol. The as-grown film is free-standing, semi-transparent, and of macro scale size. The tubes in the film are mostly singleor double-walled. The oxidation behavior of the film is studied via Raman spectroscopy, and the result indicates that the inner wall of the double-walled tube is effectively protected from oxidation by the outer wall.
An easily manipulative approach was presented to fabricate electrodes using free-standing single-walled carbon nanotube (SWCNT) films grown directly by chemical vapor deposition.Electrochemical properties of the electrodes were investigated.In comparison with the post-deposited SWCNT papers,the directly grown SWCNT film electrodes manifested enhanced electrochemical properties and sensitivity of sensors as well as excellent electrocatalytic activities.A transition from macroelectrode to nanoelectrode behaviours was observed with the increase of scan rate.The heat treatment of the SWCNT film electrodes increased the current signals of electrochemical analyser and background current,because the heat-treatment of the SWCNTs in air could create more oxide defects on the walls of the SWCNTs and make the surfaces of SWCNTs more hydrophilic.The excellent electrochemical properties of the directly grown and heat-treated free-standing SWCNT film electrodes show the potentials in biological and electrocatalytic applications.
Zn2SnO4 (ZTO) nanowires with a unique dendritic nanostructure were synthesized via a simple one-step thermal evaporation and condensation process. The morphology and microstructure of the ZTO nanodendrite have been investigated by means of field emission scanning electron microscopy (SEM), x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). SEM observation revealed the formation of branched nanostructures and showed that each branch exhibited a unique periodic structure formed by a row of overlaid rhombohedra of ZTO nanocrystals along the axis of the nanobranch. HRTEM studies displayed that the branches grew homoepitaxially as single-crystalline nanowires from the ZTO nanowire backbone. A possible growth model of the branched ZTO nanowires is discussed. To successfully prepare branched structures would provide an opportunity for both fundamental research and practical applications, such as three-dimensional nanoelectronics, and opto-electronic nanodevices.
