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Long-term aging of Ag/a-C:H:O nanocomposite coatings in air and in aqueous environment

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ABSTRACT

Nanocomposite coatings of silver particles embedded in a plasma polymer matrix possess interesting properties depending on their microstructure. The film microstructure is affected among others also by the RF power supplied during the deposition, as shown by transmission electron microscopy. The optical properties are characterized by UV–vis–NIR spectroscopy. An anomalous optical absorption peak from the Ag nanoparticles is observed and related to the microstructure of the nanocomposite films. Furthermore, a long-term aging of the coatings is studied in-depth in ambient air and in aqueous environments. It is shown that the studied films are not entirely stable. The deposition conditions and the microstructure of the films affect the processes taking place during their aging in both environments.

No MeSH data available.


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UV–vis–NIR absorbance spectra of Ag/a-C:H:O nanocomposite films deposited at different RF powers as measured right after their deposition. The optical spectrum of the glass substrate is displayed for comparison. Each of the films is listed with its corresponding thickness.
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Figure 7: UV–vis–NIR absorbance spectra of Ag/a-C:H:O nanocomposite films deposited at different RF powers as measured right after their deposition. The optical spectrum of the glass substrate is displayed for comparison. Each of the films is listed with its corresponding thickness.

Mentions: The optical properties of the as-deposited Ag/a-C:H:O nanocomposites were characterized within the UV–vis–NIR spectral ranges on samples prepared in the same deposition process as the corresponding films for the characterization of the microstructure by TEM. The absorbance spectra of the nanocomposite films deposited at different RF powers as measured right after their deposition are displayed in figure 7. As can be seen, the spectra of the Ag/a-C:H:O films deposited at powers lower than 60 W reveal a strong anomalous absorption roughly around 500 nm with a long tail of gradually decreasing absorbance towards the NIR spectral range. This absorbance peak is typical for composite nanomaterials containing metallic nanoparticles. It appears due to the well-known phenomenon of surface plasmon resonance (SPR) as a result of collective oscillations of conduction electrons after an interaction between the nanoparticle and the electromagnetic field of the light [56]. As can be seen in the spectra presented in figure 7, three characteristics of the absorbance peaks change with the different powers during the deposition: the intensity of the absorbance, the position of the absorbance maximum and also the full width at half maximum (FWHM) of the absorbance peak. Particularly, the intensity of the absorbance increases from 0.43 for the film deposited at 30 W up to 0.87 for the film deposited at 55 W, the position of the SPR gradually shifts to the longer wavelengths, from 447 nm for the film deposited at 30 W up to 557 nm for the film deposited at 55 W, and finally the FWHM increases from 133 nm for the narrowest absorption peak of the film deposited at 30 W up to 353 nm for the film deposited at 55 W. These three absorbance peak parameters are closely connected to the microstructure of the coatings as will be discussed in the following section in detail. In short, the increasing intensity of the absorption is caused mainly by the increased size of nanoparticles, while the red-shift of the peak originates in the decreasing shape factor [1, 56]. Also, the absorption peaks are much broader with the increasing deposition power due to the increasing inhomogeneity of the sizes of the silver nanoparticles (broader distributions) which gives rise to different plasmon modes [57]. Further, it can be seen that the spectrum of the nanocomposite film deposited at the power of 60 W differs from the others. The exact position of the SPR peak is difficult to locate due to the broadness of the peak and the film has rather high absorbance of about 0.8–0.9 within the whole NIR spectral range. This phenomenon can be ascribed to the absorption of light by the free electrons (inter- and intraband electron excitations) due to the percolated structure of this nanocomposite. The absorbance spectrum resembles that of a continuous silver thin film rather than the spectra of discontinuous nanocomposites with separated nanoparticles or with island-like structures revealing SPR.


Long-term aging of Ag/a-C:H:O nanocomposite coatings in air and in aqueous environment
UV–vis–NIR absorbance spectra of Ag/a-C:H:O nanocomposite films deposited at different RF powers as measured right after their deposition. The optical spectrum of the glass substrate is displayed for comparison. Each of the films is listed with its corresponding thickness.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036476&req=5

Figure 7: UV–vis–NIR absorbance spectra of Ag/a-C:H:O nanocomposite films deposited at different RF powers as measured right after their deposition. The optical spectrum of the glass substrate is displayed for comparison. Each of the films is listed with its corresponding thickness.
Mentions: The optical properties of the as-deposited Ag/a-C:H:O nanocomposites were characterized within the UV–vis–NIR spectral ranges on samples prepared in the same deposition process as the corresponding films for the characterization of the microstructure by TEM. The absorbance spectra of the nanocomposite films deposited at different RF powers as measured right after their deposition are displayed in figure 7. As can be seen, the spectra of the Ag/a-C:H:O films deposited at powers lower than 60 W reveal a strong anomalous absorption roughly around 500 nm with a long tail of gradually decreasing absorbance towards the NIR spectral range. This absorbance peak is typical for composite nanomaterials containing metallic nanoparticles. It appears due to the well-known phenomenon of surface plasmon resonance (SPR) as a result of collective oscillations of conduction electrons after an interaction between the nanoparticle and the electromagnetic field of the light [56]. As can be seen in the spectra presented in figure 7, three characteristics of the absorbance peaks change with the different powers during the deposition: the intensity of the absorbance, the position of the absorbance maximum and also the full width at half maximum (FWHM) of the absorbance peak. Particularly, the intensity of the absorbance increases from 0.43 for the film deposited at 30 W up to 0.87 for the film deposited at 55 W, the position of the SPR gradually shifts to the longer wavelengths, from 447 nm for the film deposited at 30 W up to 557 nm for the film deposited at 55 W, and finally the FWHM increases from 133 nm for the narrowest absorption peak of the film deposited at 30 W up to 353 nm for the film deposited at 55 W. These three absorbance peak parameters are closely connected to the microstructure of the coatings as will be discussed in the following section in detail. In short, the increasing intensity of the absorption is caused mainly by the increased size of nanoparticles, while the red-shift of the peak originates in the decreasing shape factor [1, 56]. Also, the absorption peaks are much broader with the increasing deposition power due to the increasing inhomogeneity of the sizes of the silver nanoparticles (broader distributions) which gives rise to different plasmon modes [57]. Further, it can be seen that the spectrum of the nanocomposite film deposited at the power of 60 W differs from the others. The exact position of the SPR peak is difficult to locate due to the broadness of the peak and the film has rather high absorbance of about 0.8–0.9 within the whole NIR spectral range. This phenomenon can be ascribed to the absorption of light by the free electrons (inter- and intraband electron excitations) due to the percolated structure of this nanocomposite. The absorbance spectrum resembles that of a continuous silver thin film rather than the spectra of discontinuous nanocomposites with separated nanoparticles or with island-like structures revealing SPR.

View Article: PubMed Central - PubMed

ABSTRACT

Nanocomposite coatings of silver particles embedded in a plasma polymer matrix possess interesting properties depending on their microstructure. The film microstructure is affected among others also by the RF power supplied during the deposition, as shown by transmission electron microscopy. The optical properties are characterized by UV–vis–NIR spectroscopy. An anomalous optical absorption peak from the Ag nanoparticles is observed and related to the microstructure of the nanocomposite films. Furthermore, a long-term aging of the coatings is studied in-depth in ambient air and in aqueous environments. It is shown that the studied films are not entirely stable. The deposition conditions and the microstructure of the films affect the processes taking place during their aging in both environments.

No MeSH data available.


Related in: MedlinePlus