Self-Assembled Organic Functional Nanotubes and Nanorods and Their Sensory Properties

Self-assembled, one-dimensional nanostructures of N,N′-bis(2-(trimethylammonium iodide)ethylene)perylene-3,4,9,10-tetracarboxyldiimide (PTCDI-I) with tunable morphologies were successfully prepared by a facile evaporation method. PTCDI-I nanotubes with diameters of approximately 100−300 nm were obtained by the evaporation of the aqueous solution of PTCDI-I, while long nanorods with diameters of approximately 200−300 nm were produced by slow evaporation of the methanolic solution of PTCDI-I. Studies of the nanostructures formed at different stages suggested that the formation of nanotubes and nanorods could be ascribed to different crystallization processes from different solutions. The PTCDI-I nanostructures were redox-active, and four-probe measurements based on a single nanotube or nanorod exhibited resistance decreased by 2 to 3 orders of magnitude after being exposed to reducing agents such as hydrazine or phenylhydrazine. Such high resistance modulations indicate that these nanostructures will be useful as building blocks for electronic nanodevices and sensors

Investigation of <i>n</i>-Layer Graphenes as Substrates for Raman Enhancement of Crystal Violet

In this work, Raman signals from crystal violet (CV) molecules on n-layer graphenes are clearly observed while these signals are invisible on SiO2/Si substrate under the same deposition condition with the same concentration of CV solution. This indicates that n-layer graphenes can be used as substrates for enhancing Raman signals of adsorbed CV molecules. The enhanced efficiency is found to be closely related to the layer number n. These conclusions can be further confirmed by Raman spectra of CV molecules on gold-decorated n-layer graphenes. The Raman enhancement effect of n-layer graphenes is attributed to chemical mechanism (CM) while electromagnetic mechanism (EM) dominates the enhancement effect of gold. Thus, graphene provides a convenient way to study CM exclusively. The morphology and density of gold nanostructures on n-layer graphenes play a significant role in the EM related Raman enhancement effect

Thickness-Dependent Morphologies and Surface-Enhanced Raman Scattering of Ag Deposited on <i>n</i>-Layer Graphenes

After thermal deposition of silver films onto n-layer graphenes, the following results have been obtained. First, the dependence of silver morphologies on the layer number is studied via controlling the sample temperature at 298, 333, and 373 K. This can be attributed to the changes in surface properties and/or surface diffusion coefficient of n-layer graphenes at different temperatures. Second, Raman scattering of n-layer graphenes is greatly enhanced after Ag deposition and the enhancement factors depend on the layer number of n-layer graphenes. Monolayer graphene has the largest enhancement factors, and the enhancement factors decrease with layer number increasing. For graphite, almost no enhancement effect has been detected. Third, the dependences of the enhancement factors on laser wavelength, thickness, and morphologies (nanoparticle size and spacing) of silver film are also studied. The Raman enhancement observed here is mainly attributed to the coupled surface plasmon resonance (SPR) absorption of silver nanoparticles

Architecture of CuS/PbS Heterojunction Semiconductor Nanowire Arrays for Electrical Switches and Diodes

CuS/PbS p–n heterojunction nanowires arrays have been successfully synthesized. Association of template and DC power sources by controllable electrochemistry processes offers a technique platform to efficiently grow a combined heterojunction nanowire arrays driven by a minimization of interfacial energy. The resulting p–n junction materials of CuS/PbS show highly uniform 1D wire architecture. The single CuS/PbS p–n heterojunction nanowire based devices were fabricated, and their electrical behaviors were investigated. The independent nanowires exhibited a very high ON/OFF ratio of 1195, due to the association effect of electrical switches and diodes

Modification on Single-Layer Graphene Induced by Low-Energy Electron-Beam Irradiation

In this work, we present studies of the effects of electron-beam irradiation on the modification of single-layer graphene. Micro-Raman spectra show that the D, D′, and D + G Raman bands, which are invisible for pristine graphene, appear after the graphenes are irradiated by low-energy electron-beam irradiation (10 keV), and the intensities of these peaks increase with increasing irradiation time, indicating disorder in graphene. The characteristics of G and 2D bands of graphene are also studied before and after irradiation. In the meantime, the height of graphene is studied by atomic force microscopy and found to increase for increasing irradiation time due to the contaminant deposition on graphene. The effects introduced by irradiation can be recovered partly by vacuum annealing. These results provide important information about the modification of graphene under electron-beam irradiation

Coulomb Explosion: A Novel Approach to Separate Single-Walled Carbon Nanotubes from Their Bundle

A novel approach based on Coulomb explosion has been developed to separate single-walled carbon nanotubes (SWNTs) from their bundle. With this technique, we can readily separate a bundle of SWNTs into smaller bundles with uniform diameter as well as some individual SWNTs. The separated SWNTs have a typical length of several microns and form a nanotree at one end of the original bundle. More importantly, this separating procedure involves no surfactant and includes only one-step physical process. The separation method offers great conveniences for the subsequent individual SWNT or multiterminal SWNTs device fabrication and their physical properties studies

Lattice Selective Growth of Graphene on Sapphire Substrate

In this work, we report a systematic study of CVD synthesizing graphene on different crystal faces of sapphire (c-Plane, m-Plane, and r-Plane). Nickel films are deposited on sapphire substrates with c-Plane, m-Plane, and r-Plane to catalyzing the growth of graphene by CVD (Chemical Vapor Deposition) method. It is only on c-Plane sapphire substrates that graphene can be found after growth and etching off nickel. In the case of m-Plane and r-Plane sapphire substrates, graphene forms only on the top surface of nickel films, but none at the interface between nickel and sapphire. Oxygen plasma treatment is introduced to certify that graphene on c-Plane sapphire does not originate from the top surface of nickel film. Selective formation of graphene is attributed to lattice structures of sapphire’s different faces. Moreover, influences of nickel’s thickness and growth time are studied by a series of control experiments

Thickness-Dependent Morphologies of Gold on <i>N</i>-Layer Graphenes

Thickness-Dependent Morphologies of Gold on N-Layer Graphene

ZnO Tetrapods Designed as Multiterminal Sensors to Distinguish False Responses and Increase Sensitivity

Individual zinc oxide tetrapods were designed as multiterminal sensors by the e-beam lithography method. Different from double-terminal sensors, these sensors can give multiple responses to a single signal at the same time. The designed tetrapod devices were employed to detect light with different wavelength. The results indicate that they are remarkable optoelectronic devices, sensitive to ultraviolet light, and have advantages on distinguishing noises and increasing sensitivity. This should be helpful for weak signal measurements of nanodevices