Detonation nanodiamonds (NDs) were deposited on the surface of aligned carbon nanotubes (CNTs) by immersing a CNT array in an aqueous suspension of NDs in dimethylsulfoxide (DMSO). The structure and electronic state of the obtained CNT–ND hybrid material were studied using optical and electron microscopy and Infrared, Raman, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. A non-covalent interaction between NDs and CNT and preservation of vertical orientation of CNTs in the hybrid were revealed. We showed that current-voltage characteristics of the CNT–ND cathode are changed depending on the applied field; below ~3 V/µm they are similar to those of the initial CNT array and at the higher field they are close to the ND behavior. Involvement of the NDs in field emission process resulted in blue luminescence of the hybrid surface at an electric field higher than 3.5 V/µm. Photoluminescence measurements showed that the NDs emit blue-green light, while blue luminescence prevails in the CNT–ND hybrid. The quenching of green luminescence was attributed to a partial removal of oxygen-containing groups from the ND surface as the result of the hybrid synthesis.
Some instances of electron field emitters are characterized by frequency-dependent hysteresis in their current-voltage characteristics. We argue that such emitters can be classified as memristive systems and introduce a general framework to describe their response. As a specific example of our approach, we consider field emission from a carbon nanotube array. Our experimental results demonstrate a low-field hysteresis, which is likely caused by an electrostatic alignment of some of the nanotubes in the applied field. We formulate a memristive model of such phenomenon whose results are in agreement with the experimental results.
Diamond is an important material for electrical and electronic devices. Because the diamond is in contact with the metal in these applications, it becomes necessary to study the metal–diamond interaction and the structure of the interface, in particular, at elevated temperatures. In this work, we study the interaction of the (100) and (111) surfaces of a synthetic diamond single crystal with spattered titanium and molybdenum films. Atomic force microscopy reveals a uniform coating of titanium and the formation of flattened molybdenum nanoparticles. A thin titanium film is completely oxidized upon contact with air and passes from the oxidized state to the carbide state upon annealing in an ultrahigh vacuum at 800 °C. Molybdenum interacts with the (111) diamond surface already at 500 °C, which leads to the carbidization of its nanoparticles and catalytic graphitization of the diamond surface. This process is much slower on the (100) diamond surface; sp2-hybridized carbon is formed on the diamond and the top of molybdenum carbide nanoparticles, only when the annealing temperature is raised to 800 °C. The conductivity of the resulting sample is improved when compared to the Ti-coated diamond substrates and the Mo-coated (111) substrate annealed at 800 °C. The presented results could be useful for the development of graphene-on-diamond electronics.
We propose an original technique for the grating metasurfaces fabrication by low-power ultraviolet (UV) laser treatment of fluorinated graphene (FG) films with the focus on terahertz applications. The laser treatment reduces dielectric FG to its conductive counterparts, increasing DC conductivity to 170 S·m-1 for treated areas. The electromagnetic (EM) response of the grating metasurfaces studied by THz time-domain spectroscopy in the 100 GHz – 1 THz frequency range demonstrates enhanced resonant transmittance through metasurfaces. The intensity and position of transmittance peak could be tuned by changing the metasurface geometry, i.e. the period of the structure and width of the reduced and unreduced areas. In particular, the decrease of the reduced FG area width from 400 µm to 170 µm leads to the shift of the resonance peak from 0.45 THz to the higher frequencies, 0.85 THz. Theoretical description based on the multipole theory supported by finite element numerical calculations confirms the excitation of the dark state in the metasurface unit cells comprising reduced and unreduced FG areas at resonance frequency determined by the structure geometrical features. Fabricated metasurfaces have been proved to be efficient narrowband polarizers being rotated by 50◦ about the incident THz field vector.
Arrays of aligned carbon nanotubes (CNTs) are anisotropic nanomaterials possessing a high length-to-diameter aspect ratio, channels passing through the array, and mechanical strength along with flexibility. The arrays are produced in one step using aerosol-assisted catalytic chemical vapor deposition (CCVD), where a mixture of carbon and metal sources is fed into the hot zone of the reactor. Metal nanoparticles catalyze the growth of CNTs and, during synthesis, are partially captured into the internal cavity of CNTs. In this work, we considered various stages of multi-walled CNT (MWCNT) growth on silicon substrates from a ferrocene–toluene mixture and estimated the amount of iron in the array. The study showed that although the mixture of precursors supplies evenly to the reactor, the iron content in the upper part of the array is lower and increases toward the substrate. The size of carbon-encapsulated iron-based nanoparticles is 20–30 nm, and, according to X-ray diffraction data, most of them are iron carbide Fe3C. The reasons for the gradient distribution of iron nanoparticles in MWCNT arrays were considered, and the possibilities of controlling their distribution were evaluated.
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