Factors that Contribute to the Growth of Ag@TiO₂ Nanofibers by Plasma Deposition

Abstract

A model experiment on the plasma deposition of TiO2 on silver is described which can help to identify the factors that control the formation of supported Ag@TiO2 nanofibers during plasma deposition of TiO2 at T > 130 °C. The plasma oxidation of silver and the plasma deposition of TiO2 on dispersed metal particles have also been studied and correlated with film topography. The species in the plasma have been analysed and fiber growth has been followed as a function of deposition time. The experimental evidence indicates that factors controlling fiber formation include silver mobility, stress relaxation of oxidized silver surfaces, chemical reduction of silver oxide, and inhomogeneities of the plasma sheath.

Plasma Deposition of Superhydrophobic Ag@TiO2 Core@shell Nanorods on Processable Substrates

“…The asprepared silver layers (Figure 2a and d), consisted of a continuous and smooth film of agglomerated silver particles. In good agreement with previous studies, [27,28] after plasma oxidation the treated silver was no longer smooth neither continuous as shown in Figure 2 (b) and (e), where it is apparent that the oxidized substrates become highly rough and presented bare silicon areas not covered by silver. On these substrates plasma deposition of TiO 2 rendered a large number of core@shell NRs with a length of 550 nm and a thickness comprised between 80 and 250 nm depending on the deposition time (cf., Figure 2c and f).…”

“…The bright field TEM micrograph of a single Ag@TiO 2 NR in Figure 3(a) shows a high contrast between an inner core attributed to silver (30 nm thick) and an external shell of titanium dioxide. Contrary to the single crystalline character of the silver threads formed in the Ag@TiO 2 NFs developed on bulk silver substrates, [26,27] for the Ag@TiO 2 NRs on processable supports the silver appears in the form of agglomerated particles mostly distributed in the core of the 1D heterostructure although isolated silver clusters can also be observed in the surface of the TiO 2 shell (Figure 3a). This latter fact further supports the key role of the mobility of the silver clusters upon plasma and temperature activation.…”

“…[19][20][21][22][23] When used for this purpose, carbon species from a hydrocarbon plasma bind under the action of metal catalyst particles ending up with the formation of the 1D nanostructures. [37,38] Our original results concerning the formation of Ag@TiO 2 NFs on bulk silver substrates [26][27][28] were accounted for by a ''volcano'' mechanism with no intervention of catalytic effects and where the high mobility of the silver oxide formed during the silver pretreatment with an oxygen plasma was the key process. Although the formation of NRs grown on processable substrates reported here is in part congruent with this model, two additional specific features should be taken into account: (i) the possibility to form vertical and tilted nanostructures and (ii) the formation of quite homogeneous NRs arrays despite the inhomogeneity of the pre-oxidized silver substrates.…”

“…[24,25] The aforementioned Ag@TiO 2 core@shell NFs were also prepared by this technique at T > 403 K by depositing TiO 2 on a plasma oxidized silver foil. [9,[26][27][28] A special feature of those supported Ag@TiO 2 core@shell NFs was that the inner silver core was formed by a 20 nm thick single crystalline thread of this metal.…”

Application of Nanometals Fabricated Using Green Synthesis in Cancer Diagnosis and Therapy

“…[4] In materials science, ENMs are currently being used for the development of solar cells, light-emitting diodes (LEDs), information recording systems and non-linear optical devices. [5] Although ENMs represent numerous advantages in their applications, a number of significant challenges still remain in order to ensure the implementation of synthetic pathways that allow for controlled production of all nanomaterials with desired size, uniform size distribution, morphology, crystallinity, chemical composition, and microstructure, which altogether result in desired physical properties. [6] Another important consideration for the practical application of these materials is the high cost associated to their large scale production, coupled with the tremendous difficulties in separation, recovery, and recycling in industrial applications.…”