Browsing by Subject "Nanoscale materials"

Now showing 1 - 4 of 4

Open Access
Low-temperature synthesis and growth model of thin Mo2C crystals on indium
(Nature Publishing Group, 2021-04-15) Caylan, Ömer Refet; Cambaz Buke, G.
Chemical vapor deposition is a promising technique to produce Mo2C crystals with large area, controlled thickness, and reduced defect density. Typically, liquid Cu is used as a catalyst substrate; however, its high melting temperature (1085 °C) prompted research groups to search for alternatives. In this study, we report the synthesis of large-area thin Mo2C crystals at lower temperatures using liquid In, which is also advantageous with respect to the transfer process due to its facile etching. SEM, EDS, Raman spectroscopy, XPS, and XRD studies show that hexagonal Mo2C crystals, which are orthorhombic, grow along the [100] direction together with an amorphous carbon thin film on In. The growth mechanism is examined and discussed in detail, and a model is proposed. AFM studies agree well with the proposed model, showing that the vertical thickness of the Mo2C crystals decreases inversely with the thickness of In for a given reaction time.
Embargo
Phase transformation and structural development in mechano-synthesized calcium-copper-titanate electroceramics
(Elsevier Ltd, 2024-11-27) Alizadeh, M.; Ardakani, H.A.; Amini, R.; Ghaffari, Mohammad; Pashangeh, S.; Vincenzini, P.
This research focuses on the mechano-synthesis of synthesizing calcium-copper-titanate (CCTO) powder through mechanical alloying of the respective oxides aiming to optimize the production of nanoscale electroceramics with high dielectric properties. Structural characterization was carried out using X-ray diffraction with Rietveld refinement (phase identification and quantification), while transmission electron microscopy was employed to observe particle size changes including the reduction of particle size to nanometric scales (10–35 nm). The mechano-synthesis process involving CaO, CuO, and $TiO_2$ resulted in the creation of perovskite CCTO, with minimal contamination observed from the milling process. Significant particle size reduction, nanostructure formation, and a high level of amorphization, alongside polymorphic transitions in $TiO_2$ during milling that played a critical role in achieving full amorphization, which was essential for the formation of high-purity CCTO. The study demonstrates that after 256 h of milling, 88 wt% of the powder consisted of crystalline CCTO, highlighting the potential for enhanced performance in dielectric and microelectronic applications. There was no detection of either stoichiometric CCTO or any non-stoichiometric phases prior to the complete amorphization of the powders. Therefore, results revealing significant advancements in particle size reduction, nanostructure formation, and amorphization, which influence enhanced material performance. Nucleating and growing the CCTO phase directly from an amorphous state without the formation of intermediate crystalline phases clears the potential for optimizing CCTO production processes.
Open Access
Probing nanoscale domains of J-Aggregates deposited on a mica surface
(American Chemical Society, 2004) Özçelik, S.; Demir, M. M.; Birkan, B.
J-aggregates of 1,1′,3,3′-tetraethyl-5,5′,6,6′- tetrachlorobenzimidazolocarbocyanine (TTBC) were deposited on a mica surface and probed by atomic force microscopy operated at tapping mode in air. Optical spectra showed that J-aggregates were formed in aqueous solutions. Atomic force microscopy images revealed that J-aggregates deposited on mica surfaces mainly present single domains with a mean height of 2.00 ± 0.25 nm and an average diameter of 100 ± 20 nm. Quantitative analysis of the morphology of images indicated that the single domain of J-aggregates exhibits very uniform height and diameter distributions with polydispersity indices of 1.02 and 1.04, respectively. Based on the results, we propose a two-dimensional nanostructure in which TTBC J-aggregates could be arranged in a monolayer.
Open Access
Surface decoration of Pt nanoparticles via ALD with TiO2 protective layer on polymeric nanofibers as flexible and reusable heterogeneous nanocatalysts
(Nature Publishing Group, 2017) Celebioglu, A.; Ranjith, K. S.; Eren, H.; Bıyıklı, Necmi; Uyar, T.
Coupling the functional nanoheterostructures over the flexible polymeric nanofibrous membranes through electrospinning followed by the atomic layer deposition (ALD), here we presented a high surface area platform as flexible and reusable heterogeneous nanocatalysts. Here, we show the ALD of titanium dioxide (TiO2) protective nanolayer onto the electrospun polyacrylonitrile (PAN) nanofibrous web and then platinum nanoparticles (Pt-NP) decoration was performed by ALD onto TiO2 coated PAN nanofibers. The free-standing and flexible Pt-NP/TiO2-PAN nanofibrous web showed the enhancive reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) within 45 seconds though the hydrogenation process with the degradation rate of 0.1102 s-1. The TiO2 protective layer on the PAN polymeric nanofibers was presented as an effective route to enhance the attachment of Pt-NP and to improve the structure stability of polymeric nanofibrous substrate. Commendable enhancement in the catalytic activity with the catalytic dosage and the durability after the reusing cycles were investigated over the reduction of 4-NP. Even after multiple usage, the Pt-NP/TiO2-PAN nanofibrous webs were stable with the flexible nature with the presence of Pt and TiO2 on its surface.