Szálszerű nanoszerkezetek vizsgálata mikroszkópos és diffrakciós módszerekkel = Investigation of filament-like nanostructures by microscopic and diffraction methods

Különböző szénhidrogének és bennük oldott metallocének porlasztásos pirolízisével előállított szén nanocsövek vizsgálatával megállapítottuk, hogy xilol szénforrás, illetve ferrocén/nikkelocén keverék esetén állíthatóak elő a legjobb minőségű nanocsövek. Nitrogéntartalmú, bambuszos jellegű szén nanocsöveket állítottunk elő különböző összetételű benzol-piridin keverékek, illetve benzilamin és bennük oldott ferrocén pirolízisével. A csövek pásztázó alagútspektroszkópos görbéje a beépült nitrogén hatására aszimmetrikus, a 0.2 ? 0.8 eV tartományban többletállapotok vannak jelen. A cső mentén haladva a görbe változik, bár a jellege hasonló marad. Kis molekulasúlyú alkoholok és bennük oldott ferrocén alkalmazásával porlasztásos pirolízissel egyfalú szén nanocsöveket sikerült növesztenünk. Mennyiségük a molekulasúly növekedésével csökken, vagyis metanol esetén maximális. Megállapítottuk, hogy víz alatti váltóáramú elektromos ívben történő szén nanocső növesztéskor az elektródák 90°-os szöge esetén lesz a nanocsövek mennyisége a legnagyobb. Különböző rendezetlen szén nanocső hálózatok gáz (gőz)-érzékelési tulajdonságainak összehasonlító vizsgálatával az előállítási módszertől és a funkcionalizálás módjától függő, jelentősen eltérő érzékenységeket tapasztaltunk a különböző, alkalmazott gőzökre. A minták átlagos érzékenysége jellemzően a funkciós csoportok mennyiségével volt arányos. Ionbesugárzás hatására a minták érzékenysége nagyrészt csökkent a korábbi állapothoz képest. | Carbon nanotubes were produced by the spray pyrolysis of different hydrocarbon/metallocene solutions. Best quality tubes can be obtained in case of xylene as carbon source and ferrocene/nickelocene mixture. Nitrogen containing, bamboo shaped carbon nanotubes were produced by the pyrolysis of ferrocene solution in benzene-pyridine mixtures and benzylamine. Scanning tunneling spectroscopy of the tubes showed asymmetric curves with extra states in the 0.2 ? 0.8 eV range as an effect of nitrogen incorporation. Differences could be observed along the tubes but the character of the curves was similar. Single wall carbon nanotubes were grown by the pyrolysis of ferrocene solution in low molecular weight alcohols. The amount of the tubes was the highest in case of methanol and decreased as the molecular weight increased. The amount of carbon nanotubes was found to be the highest when the angle of the graphite electrodes was 90° in case of nanotube growth in underwater AC electric arc. Comparative study of gas sensing properties of random carbon nanotube networks showed significantly varying sensitivities to the applied vapors, depending on the nanotube production method and the way of functionalization. The average sensitivity was typically proportional with the number of functional groups. Ion irradiation of the samples caused in most cases the decrease of the sensitivity

Dynamic strain in gold nanoparticle supported graphene induced by focused laser irradiation

Graphene on noble-metal nanostructures constitutes an attractive nanocomposite with possible applications in sensors or energy conversion. In this work we study the properties of hybrid graphene/gold nanoparticle structures by Raman spectroscopy and Scanning Probe Methods. The nanoparticles (NPs) were prepared by local annealing of gold thin films using focused laser beam. The method resulted in a patterned surface, with NPs formed at arbitrarily chosen microscale areas. Graphene grown by chemical vapour deposition was transferred onto the prepared, closely spaced gold NPs. While we found that successive higher intensity (6 mW) laser irradiation increased gradually the doping and the defect concentration in SiO2 supported graphene, the same irradiation procedure did not induce such irreversible effects in the graphene supported by gold NPs. Moreover, the laser irradiation induced dynamic hydrostatic strain in the graphene on Au NPs, which turned out to be completely reversible. These results can have implications in the development of graphene/plasmonic nanoparticle based high temperature sensors operating in dynamic regimes

Determination of the STM tip-graphene repulsive forces by comparative STM and AFM measurements on suspended graphene

Graphene grown by chemical vapour deposition is transferred on top of flat gold nanoislands and characterized by scanning tunnelling microscopy (STM) and atomic force microscopy (AFM). Graphene bubbles are formed with lateral dimensions determined by the size and shape of nanoislands. These graphene bubbles can be squeezed during STM imaging using bias voltages of less than 250 mV and tunnelling currents of 1 nA. Similarly, the graphene suspended over gold nanovoids is deflected 4-5 nm by the STM tip when imaging at low bias voltages (U = 30 mV). Nanoindentation measurements performed by AFM show that the squeezing of graphene bubbles occurs at repulsive forces of 20-35 nN, and such forces can result in deflections of several nanometres in suspended graphene parts, respectively. Comparing the AFM and STM results, this study reveals that mechanical forces of the order of 10-8 N occur between the STM tip and graphene under ambient imaging conditions and typical tunnelling parameters

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Novel graphene/Sn and graphene/SnOx hybrid nanostructures: Induced superconductivity and band gaps revealed by scanning probe measurements

Abstract The development of functional composite nanomaterials based on graphene and metal nanoparticles (NPs) is currently the subject of intense research interest. In this study we report the preparation of novel type of graphene/Sn and graphene/SnOx (1 ≤ x ≤ 2) hybrid nanostructures and their investigation by scanning probe methods. First, we prepare Sn NPs by evaporating 7–8 nm tin on highly oriented pyrolytic graphite substrates. Graphene/Sn nanostructures are obtained by transferring graphene on top of the tin NPs immediately after evaporation. We show by scanning tunnelling microscopy (STM) and spectroscopy (STS) that tin NPs reduce significantly the environmental p-type doping of graphene. Furthermore, we demonstrate by low-temperature STM and STS measurements that superconductivity is induced in graphene, either directly supported by Sn NPs or suspended between them. Additionally, we prepare SnOx NPs by annealing the evaporated tin at 500 °C. STS measurements performed on hybrid graphene/SnOx nanostructures reveal the electronic band gap of SnOx NPs. The results can open new avenues for the fabrication of novel hybrid superconducting nanomaterials with designed structures and morphologies

Introducing nanoscaled surface morphology and percolation barrier network into mesoporous silica coatings

Mesoporous silica thin films were patterned at the sub-micron scale utilizing the ion hammering effect in order to combine the advantages of mesoporous character and surface morphology, while preserving the interconnected pore system or creating laterally separated porous volumes surrounded by nonpermeable compact zones. Porous silica coatings were prepared by a sol-gel method with an ordered and disordered pore system using micellar templates. A hexagonally ordered Langmuir-Blodgett type monolayer of silica spheres was applied as a mask against Xe+ ion irradiation. The ion energy was chosen according to Monte-Carlo simulations to achieve structures with high lateral contrast between irradiated and unirradiated, i.e., masked areas. The disordered pore system proved to be more resistant against ion bombardment. Although the created surface morphologies were similar, the main character of the pore system could be tailored to be interconnected or separated by controlling the ion fluence. Confocal fluorescence images and ellipsometric porosimetry measurements confirmed that the contribution of transition zone between the intact masked and damaged regions to the porosity is negligible. Furthermore, the majority of the porous volume can be preserved as an interconnected pore system by the application of low ion fluence. By increasing the fluence value, however, separated porous volumes can be created at the expense of the total pore volume

Mapping the nanomechanical properties of graphene suspended on silica nanoparticles

Using nanoparticles to impart extrinsic rippling in graphene is a relatively new method to induce strain and to tailor the properties of graphene. Here we study the structure and elastic properties of graphene grown by chemical vapour deposition and transferred onto a continuous layer of SiO2 nanoparticles with diameters of around 25 nm, prepared by Langmuir-Blodgett technique on Si substrate. We show that the transferred graphene follows only roughly the morphology induced by nanoparticles. The graphene membrane parts bridging the nanoparticles are suspended and their adhesion to the AFM tip is larger compared to that of supported graphene parts. These suspended graphene regions can be deformed with forces of the order of 10 nN. The elastic modulus of graphene was determined from indentation measurements performed on suspended membrane regions with diameters in the 100 nm range.Comment: in Journal of Experimental Nanoscience (2016