Electronic Supplementary Material
Journal of Nanoparticle Research
The isolated flat silicon nanocrystals (2D structures) stabilized
with perfluorophenyl ligands
Andrey S. Orekhov1, Sergei V. Savilov2, Valery N. Zakharov2, Alexandr V. Yatsenko2, Leonid
A. Aslanov2*
1
Institute of Crystallography, Russian Academy of Sciences, Leninskii prospect, 59,
119333, Russia
Moscow,
2
Department of Chemistry, M.V. Lomonosov Moscow State University, Leninskie Gory,
Moscow, 119991, Russia
Experimental Section
For synthesis of Si nanoparticles, the following reagents were used: bromopentafluorobenzene
(99.98% purity) from SIA”S&M-Invest”; 1,2-dimethoxyethane ( 99%), potassium (99.5%),
tetrabromosilane (99.99%) from Sigma Aldrich; mercury, redistilled (99.9%), lithium, granular (99%)
from Alfa Aesar.
Nanocrystalline silicon with the perfluorophenyl ligands on the surface (FPh-nc-Si) was
synthesized in several steps by the following method. Dispersion of nc-Si with the bromide ligands was
synthesized in a Schlenk reactor in dry Ar atmosphere. The dried 1,2-dimethoxyethane (50 ml) and
potassium (2.62g, 68 mmol) were heated to 85ºC with stirring. Potassium was thus dispersed to particles
1-3 mm in diameter. Then SiBr4 (5.43g, 15 mmol) solution in 1,2-dimethoxyethane (10 ml) was added
to the reaction mixture. Yellowish-brown dispersion was formed after stirring for an hour, the total
reaction time being ~ 2h.
Concentration of the bromide ligands on nc-Si surface was determined by titration of the obtained
dispersion (1 ml) with 0.04M KOH and appeared to be 0.2 mol/liter. In order to obtain perfluorophenyl
lithium, the alkylating reagent, bromopentafluorobenzene C6F5Br (20% excess to concentration of the
bromide ligands on nc-Si surface) and lithium amalgam (10% excess to C6F5Br) were used.
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Lithium amalgam was synthesized in a Schlenk reactor in dry Ar atmosphere. Mercury (31.13g, 155
mmol) and lithium (0.092g, 13 mmol) were heated to 200ºC on oil bath and mixed to homogeneity, after that
the amalgam was cooled to room temperature.
Perfluorophenyllithium was synthesized at -17 ºC in the same Schlenk reactor where lithium amalgam
had been prepared: 1,2-dimethoxyethane (5 ml) and C6F5Br (0.74 ml, 1.65 mmol) were added, and the
reaction mixture was stirred for 50 min.
The bromide ligands on nc-Si surface were replaced by perfluorophenyl groups at -17 ºC in a Schlenk
reactor with perfluorophenyllithium. Dispersion of nc-Si with the bromide ligands on the surface (25
ml) obtained in the first step of synthesis was added to a Schlenk reactor, the reaction mixture was
stirred for 1h. The final color of dispersion was intensive dark-yellow.
The resulting dispersion of nc-Si coated with the perfluorophenyl ligands was treated with dry HCl
for 1 min in order to remove excess of C6F5Li. Yellow nc-Si dispersion with the perfluorophenyl ligands
on nc-Si surface was formed over the mercury layer.
IR spectra were recorded using a Tensor 27 FTIR spectrometer (Bruker) with 1 cm-1 resolution and
signal averaging via 32 scans. Solid samples were formed by evaporation of nc-Si dispesion, films were
deposited on ZnSe crystal (ATR-FTIR) and KBr plate and dried in vacuum at 80ºC in order to remove
the solvent.
TEM images were obtained using a TITAN 80-300 high-resolution electron microscope (FEI, USA)
with correction of spherical aberration in light- and dark-field modes at accelerating voltage 300 kV and
a JEOL JEM 2100F/Cs electron microscope (JEOL Co. Ltd) with field emission generator (FEG)
equipped with a spherical aberration corrector (CEOS GmbH, Germany), Tridiem energy filter and
electron energy loss spectrum analyzer (Gaton Inc., USA) at accelerating voltage 200 kV. The data were
processed and interpreted using Digital Micrograph (Gatan), TIA (FEI) and JEMS (Switzerland)
packages.
The XPS patterns were obtained using a Kratos Axis Ultra DLD spectrometer, AlKa radiation with a
neutralizer, calibrated for C1s of hydrocarbons (284.8 эV). Transmission energy 160 eV (general
spectrum) and 20 эV (separate lines).
For TEM studies, samples were prepared by deposition of suspension on the standard copper electron
microscope grids with solid ultrathin carbon film (~3 nm) or precoated with polyvinylformale.
The morphology of nc-Si particles was also studied using a Nanoprix 2000 atomic force-field
microscope in a semi-contact mode. Dispersion of nc-Si was deposited as a thin layer on a
monocrystalline silicon support and dried. For most solvents, the particle aggregates were obtained as a
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result of this procedure, but using C6F5Br as a dispersion medium and dispersing the small-sized silicon
lamellae, we avoided formation of aggregates.
The photoluminescence spectra of solid samples were studied using a Perkin-Elmer LS-55
luminescence spectrometer.
Reproducibility of our results was tested by multiple syntheses under the varied experimental conditions;
dimensions, composition and structure of nanoparticles were monitored by TEM.
Supplementary Figures:
240000
C1s
O1s
200000
Intensity, c/s
160000
120000
OKLL
F1s
CKLL
FKLL
80000
Hg4d
Cl2s
40000
Si2s
Cl2p
Si2p
0
1200
1000
800
600
Binding energy, eV
Fig. S1 General XPS pattern of the sample.
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400
200
0
2400
2000
Intensity, c/s
1600
Si2p
102.4
1200
800
Hg4f5/2
400
112
108
Si2p
103.3
104
Hg4f7/2
100
96
Binding energy, eV
Fig. S2 XPS pattern of Si2p and Hg4f lines of the sample. Mercury lines and silicon line superimpose:
The excitation section of mercury lines is large, that is why they yield a noticeable signal even at low
concentration of mercury.
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Fig. S3 BF TEM image (a) and size distribution plot (b) of spherical silicon nanoparticles.
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Fig. S4 STEM image (HAADF, Z-contrast) of spherical Si nanoparticles.
Inset: diffraction pattern from amorphous silicon nanoparticles.
It should be noted that contrast observed in the particle image (BF TEM mode) is rather weak, and
particles have been destroyed under 300 kV electron beam illumination during 2-3 sec (diffraction
pattern fully disappeared).
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a)
b)
c)
Fig. S5 Analysis of nc-Si lamellae by AFM:
a) nanoprofilometry data on the morphology of the nc-Si surface; b)cross-section line of nc-Si
lamellae; c) profile measurement of nc-Si lamellae along the cross-section line (b).
S7
Fig. S6 PL spectrum of nanosilicon stabilized with the perfluorophenyl ligands
(___ ex = 350 nm, --- ex = 375 nm, … ex = 400 nm).
S8