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Surface enhanced Raman spectroscopy of fullerene C 60 drop-deposited on the silvered porous silicon

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Surface enhanced Raman spectroscopy (SERS) of fullerene C60 drop-deposited from the 1.410⁻⁴ M aqueous solutions on the silvered porous silicon (Ag/PS) is reported for the first time. The used concentration is found to be not detected by the ordinary Raman spectroscopy. It is shown that SERS-spectrum of the fullerene deposited from the air-aged solution are characterized by less intensity than that of the fullerene solution kept out of the air. This indicates degradation of the fullerene solution due to oxidation. The results are prospective for the fast qualitative and quantitative analysis of the fullerene-based materials.
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Surface enhanced Raman spectroscopy of fullerene C60 drop-deposited
on the silvered porous silicon
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Surface enhanced Raman spectroscopy of fullerene C60
drop-deposited on the silvered porous silicon
N Khinevich1, K Girel1, H Bandarenka1, V Salo2, A Mosunov2
1Belarusian State University of Informatics and Radioelectronics, Minsk, 220013,
Republic of Belarus
2Sevastopol State University, Sevastopol, 299053, Russian Federation
Abstract. Surface enhanced Raman spectroscopy (SERS) of fullerene C60 drop-deposited
f-4 M aqueous solutions on the silvered porous silicon (Ag/PS) is reported for
the first time. The used concentration is found to be not detected by the ordinary Raman
spectroscopy. It is shown that SERS-spectrum of the fullerene deposited from the air-aged
solution are characterized by less intensity than that of the fullerene solution kept out of the
air. This indicates degradation of the fullerene solution due to oxidation. The results are
prospective for the fast qualitative and quantitative analysis of the fullerene-based
materials.
Introduction
60707684 molecules are called fullerenes. In
these molecules, atoms of carbon are located at the vertices of regular hexagons or pentagons that
cover the surface of sphere or spheroid. C60 occupies special position among all the fullerenes. This
molecule demonstrates the highest symmetry and, as a consequence, the greatest stability.
Fullerenes are characterized by a number of unique properties including high sorption capacity,
photoconductivity, mechanical strength, low surface energy, biocompatibility, etc. Thorough study
              
storage, catalytic systems, micro- and nanoelectronics and biomedicine [1]. Accurate qualitative
and quantitative analysis of the fullerenes is an urgent task to realize their successful application.
Considering biomedicine, this problem has to be overcome at very low concentrations to control
fullerene transfer through biological membranes, accumulation in proteins or cells and interaction
with other submicron bioorganic objects. Scanning tunneling microscopy, nuclear magnetic
resonance spectroscopy, different methods of vibrational spectroscopy have been used to study the
fullerenes [2]. Since the beginning of fullerene discovery its Raman frequencies have been
calculated [3] and measured [2]. Theoretical analysis [4] showed that 46 fundamental modes can be
       60 molecular vibrations. Two of these modes are
characterized by Ag symmetry, one Au, three 1g, four 1u, five 2u, six Gg, six Gu, eight
g and seven u  1u symmetry are active during registration of the
gg symmetries are active in Raman spectroscopy, while
the other t           
Raman spectroscopy comparing to other techniques is in possibility to realize SERS effect. This
means enormous enhancement of the Raman intensity by study of analyte adsorbed on the
nanostructured metallic surfaces that are usually called SERS substrates. SERS spectroscopy
allows to detect and investigate trace amounts of substances and thus is very attractive for the study
of fullerenes. Several approaches of registration of C60 SERS spectrum in nonaqueous Ag and Au
colloidal systems have been already developed [5, 6]. These methods provide good sensitivity,
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however, the solvent media contributes to the resulting Raman spectrum. That is why it requires to
make additional manipulations to see only the Raman spectra of fullerenes. In this work, we
propose to solve such a problem by using SERS substrate based on porous silicon (PS). PS covered
with metallic nanostructures can be used as an effective SERS substrate [7]. In this work, we were
able to register intensified Raman scattering of the C60 fullerene thanks to the SERS substrate
composed of silver nanoparticles on PS (Ag/PS). According to our knowledge, such results have
not been previously published.
Experimental
Fabrication of SERS substrates based on PS consists of two major steps: formation of porous
template and deposition of metallic nanostructures on its surface. PS was fabricated by an
electrochemical anodization of n+-type silicon wafer in electrolyte of HF, deionized H2O and
C3H7OH mixed in the volume ratio 1:3:1. Prior to anodization process silicon wafer was cleaned in
a solution NH4OH, H2O2 and H2O mixed in a volume ratio of 1:1:4. To remove native oxide from
silic                  
average pore diameter is 60 nm. Silver nanostructures were formed on PS by a chemical deposition
from aqueous solution of AgNO3. Deposition process was carry out at room temperature. Before
applying of analyte SERS-substrates were rinsed in HCl aqueous solution to remove contaminants
which adsorbed on the surface of the substrates from environment. Fullerenes C60 were drop-
deposited on the Ag/PS substrate from the air-age    
          -4 M. SERS-spectra of
fullerene were recorded with the 3D scanning confocal microscope Confotec NR500 using 633 nm
laser and signal accumulation time 1 s. The laser spot varied in the 500 nm range while power of
laser beam coming from the microscope objective was about 0.68 mW.
Results and discussion
Combinations of PS morphologies and regimes of metal deposition give rise to create the metallic
nanostructures with fascinating SERS characteristics. In this work we used regimes of Ag/PS
samples formation favourable for the most effective SERS according to [7]. SERS substrates
presented silver nanostructures on the external surface of PS with an average size of silver
nanoparticles in the range varying from 50 to 300 nm. Figure 1 shows SEM images of the virgin
Ag/PS samples and those after drop deposition of the fullerene C60 at different magnifications. It is
well-seen that the analyte is non-uniformly distributed on the Ag/PS surface (Fig. 1, b). Figure 1, f
presents enlarged top view of the fullerene-coated Ag/PS. Following this image fullerene molecules
formed the fullerite crystals with dimensions of 150 360 nm that are coalesced in aggregates of

of fullerene C60 drop-deposited on the SERS substrates. Measurements of the ordinary Raman
spectra of fullerene deposited on the glass plate, samples of the silicon wafer and Ag-free PS were
impossible due to low concentration of the carbon nanostructures. Both spectra in Figure 2 have
three prominent bands of fullerene C60 such as Hg(1), Ag(1) and Ag(2) [8]. The last one has the
highest intensity and 
mode is caused by the symmetry breaking of the fullerene molecule. For instance, this can be
observed at the molecule polymerization. Linear polymerization is accompanied by the Ag(2) shift
1 1 is usually connected with formation of
C60 dimer or C60O2 [10]. The Ag(2) band of the kept of air fullerene is most intensive near the 1466
cm1 while the maximum of the same band of the air-aged sample is shifted to the 1464 cm1
position indicating the stronger oxidation of the last one. Both samples have a left shoulder in the
Ag(2) band extending to 14591460 cm1 which shows a presence of a small amount of the
polymerized fullerene molecules. This occurs due to C60 photopolymerization at the natural light.
The bands Hg(1) and Ag(1) of the air-aged sample are slightly red-shifted. The kept out of the air
sample is also characterized by weak bands Hg(2) Hg(8) typical for fullerene C60 [8]. The marked
bands in the SERS spectra correspond to ten vibrational modes of fullerene C60 (Ag, Hg ) which are
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Raman-active [4]. SERS intensity of the air-aged sample is about four orders of magnitude lower
than that of the other sample. These results are caused by the changes in the fullerene structure due
to oxidation of the air-aged sample and its destruction.
Figure 1. SEM images of the Ag/PS substrates (a, c, e) before and (b, d, f) after C60 deposition.
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Figure 2. SERS-spectra of fullerene C60 deposited on Ag/PS from (a) kept out of air and (b) air-
aged solutions.
Conclusion
We showed that Ag/PS can be used as effective SERS substrates for the detection and study of the
structure of the submolar concentration of the fullerene C60 aqueous solutions. Structural changes
of the air-aged fullerenes in comparison with the kept out of the air samples were revealed. The
both fullerene samples were photopolymerized. At the same time, the air-aged sample was much
more oxidized in comparison with the kept of the air fullerene solution. The obtained results open
new opportunities for the precise control of the fullerene properties in different materials.
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... The other commercial product (BelSERS substrates [https://science.bsuir.by/en/microelectronics-and-nanotech nology/sers-active-substrates-for-increasing-sensitivity-of-raman-spec troscopy] that is based on the silvered meso-or macro-PS have demonstrated its applicability for detection of peptides [143] and proteins [134], meldonium [171], DNA [148], phospholipids [142], fullerenes [172] and other organic molecules [36,103,105]. ...
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A transfer of fullerene C(60) to water was achieved by sonication of a two-phase system of water and C(60) in organic solvents, namely, benzene and toluene. Resulting aqueous dispersions were analyzed electrochemically, spectroscopically, by MALDI-MS and AFM methods. Samples prepared from benzene yield the formal redox potential very close to a value expected from the correlation of redox potentials and solvent donor numbers. However, these samples are not stable and C(60) precipitates out of the aqueous dispersion. Sonication of the toluene/water system produces stable system, in which the measured formal redox potential of C(60) is less negative. Stabilization of C(60) clusters in water is achieved by the presence of an organic amphiphile and spectroscopic methods indicate the presence of benzoate formed during sonication of a toluene/water mixture.
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Surface enhanced Raman scattering (SERS) spectra of C60 (C70) were obtained in nonaqueous colloidal systems with newly developed methods. The enhancement factor was estimated to be over 10(5). This paper aims at the investigation of a fine influence mechanism for SERS in the nonliquid phase, which may help bring forth the perfect SERS mechanism. The detailed investigation is based on abundant comparative experiments where we found that the SERS effect is sensitive not only to the character of colloidal particles, dielectric constants, and polarizability, but also to the substrates, the solvent intermediate, and even the coating techniques. These detailed comparisons enrich the proofs of the SERS mechanism and provide a new way to optimize SERS systems.