This paper reports that a large amount of Mn-doped ZnO nanorods have been synthesized through thermal evaporation. The morphologies and properties are studied with x-ray diffraction, a scanning electron microscope, transmission electron microscope and Raman spectroscope. The results indicate that the manganese atoms occupy the zinc vacancies in the wurtzite lattice of ZnO without forming secondary phases. The exact manganese content has been studied by the x-ray fluorescence spectrum. Meanwhile, the magnetic moment versus temperature result proves that the as-prepared Mn-doped ZnO nanorods show ferromagnetic properties at temperatures as high as 400 K. These studies provide a good understanding of the origin of magnetic properties in diluted magnetic semiconductors.
We demonstrate an effective method to prepare a new condensed form of single-walled carbon nanotubes(crystal of SWNTs) using a series of diamond wire drawing dies.X-ray diffraction indicates that the SWNTs form a two-dimensional triangular lattice with a lattice constant of 19.62 ?.An intertube spacing of 3.39 ? of between adjacent SWNTs results in a sharp(002) reflection in the X-ray diffraction pattern.Meanwhile,we developed an approach based on the Coulomb explosion to separate SWNTs from their bundle.The separated SWNTs have a typical length of several microns and form a nanotree at one end of the original bundle.The separation is convenient and involves no surfactant.In studying devices comprising SWNTs,we find that a four-probe technique can be employed to study the filling of and flow within the inner channel of an individual SWNT.Current/voltage can drive water molecules to have directional flow along an SWNT,and the flowing of water inside an SWNT can induce a voltage gradient force(an induced electromotive force) along the SWNT.This energy conversion is realized by the mutual coupling of water dipoles and charge carriers present in SWNTs.The results suggest that SWNTs can be exploited as molecular channels for water and may find potential application in nanoscale energy conversion.Moreover,a surface-energy generator comprising SWNTs was demonstrated to harvest the surface energy of ethanol.The performance(the induction rate for Voc,the value of Voc and the output power) can be significantly enhanced by the Marangoni effect.
In this work we report that when ferromagnetic metals (Fe,Co and Ni) are thermally evaporated onto n-layer graphenes and graphite,a metal nanowire and adjacent nanogaps can be found along the edges regardless of its zigzag or armchair structure.Similar features can also be observed for paramagnetic metals,such as Mn,Al and Pd.Meanwhile,metal nanowires and adjacent nanogaps cannot be found for diamagnetic metals (Au and Ag).An external magnetic field during the evaporation of metals can make these unique features disappear for ferromagnetic and paramagnetic metal;and the morphologies of diamagnetic metal do not change after the application of an external magnetic field.We discuss the possible reasons for these novel and interesting results,which include possible one-dimensional ferromagnets along the edge and edge-related binding energy.
In this work,different effects of substrates on the morphologies of single-walled carbon nanotubes(SWNTs)are studied.SWNTs were produced by floating catalytic chemical vapor deposition using CH4as carbon source gas and Ar as carrier gas.Then the SWNTs were deposited on lithography-patterned different substrates.The as-grown SWNTs at the boundaries between SiO2and metal were characterized by scanning electron microscopy,atomic force spectroscopy and Raman spectroscopy.It is found that SWNTs deposited on low-conductivity substrates trend to have curved morphologies and some of them form rings,while SWNTs deposited on metal substrates remain straight and orientated.The mechanism of these effects was also discussed,which is closely related to the thermal conductivities and the principle of energy dissipation.
We report the assisted role of water vapor in crystallographic cutting of graphene via iron catalysts in reduced atmosphere. Without water, graphene can be tailored with smooth trenches composed of straight lines with angles of 60℃ or 120℃ between two adjacent trenches. After the addition of water, new chacteristics are found: such as almost no iron particles can be detected along the trenches; each trench becomes longer and lots of graphene nanoribbons can be generated. The underlying mechanism is proposed and discussed, which is attributed to stimulating and lengthening of the catalytic activity of iron particles by water vapor.
In this work,the thermal properties of a single-walled carbon nanotube (SWCNT) crystal are studied.The thermal conductivity of the SWCNT crystal is found to have a linear dependence on temperature in the temperature range from 1.9 K to 100.0 K.In addition,a peak (658 W/mK) is found at a temperature of about 100.0 K.The thermal conductivity decreases gradually to a value of 480 W/mK and keeps almost a constant in the temperature range from 100.0 K to 300.0 K.Meanwhile,the specific heat shows an obvious linear relationship with temperature in the temperature range from 1.9 K to 300.0 K.We discuss the possible mechanisms for these unique thermal properties of the single-walled carbon nanotube crystal.
In this paper,we report that an electromotive force (EMF) can be induced in a rope of aligned single-walled carbon nanotubes (SWNTs) when water droplets fall on this rope.The magnitude of this EMF depends sensitively on the slant angle of the SWNTs.Most interestingly,both the magnitude and the direction of the induced EFM can be modulated by applying a current to the SWNTs.The concepts of electrical slip and no-slip are proposed and can be quantitatively described by "electrical slip resistance".This kind of generator does not need any magnet,rotor,etc and shows quite a different operating mechanism and design compared with a conventional large scale hydroelectric power generator.
