Colloidal Synthesis of an Exotic Phase of Silicon: the BC8 Structure
Shreyashi Ganguly, Nasrin Kazem, Danielle Carter and Susan M. Kauzlarich
Department of Chemistry, One Shields Avenue, University of California, Davis, CA-95616
Supporting Information
Chemicals:
Silicon tetraiodide (SiI4, 99 % metal basis) was obtained from Alfa Aesar, , 1, 2-hexadecanediol
(1, 2-HDD, 90 % technical grade), 1-dioctylether (DOE, 99 %), 1-octadecene (90 % technical
grade) and n-butyllithium (n-BuLi, 1.6 M in hexane) were obtained from Sigma Aldrich. 1octanol was obtained from Fisher Scientific. 100 mL of DOE was heated to 110 °C under
vacuum and stored in a glove box prior to usage. 1-octanol obtained from Alfa Aesar was purged
with argon for 1 h before using in the reaction. All reactions were carried out using standard
Schlenk line techniques and under argon atmosphere.
Preparation of 1-octanol capped silicon nanoparticles (Si NPs):
For a typical synthesis (1 mmol, 0.536 g) of SiI4 was dissolved in 15 mL of DOE and was
heated to 170 °C. A yellow transparent solution was obtained at this temperature. After stirring
the reaction mixture for 10 min, (3.75 mmol, 2.5 mL) n-BuLi was rapidly injected into the
yellow solution. Within 10 min of stirring, 2 mL (0.012 mmol) of 1-octanol was injected into the
solution. The temperature of the reaction mixture was gradually increased to 280 °C and was left
stirring at that temperature for 72 h; at this temperature the color of the solution changed to dark
brown. The reaction was brought to room temperature by removal of the heating mantle. Once
the reaction mixture was at room temperature, the NPs were precipitated by addition of 3 mL of
hexane and 30 mL of methanol in the glove box. The resulting precipitate was dark brown in
color.
S1
Preparation of 1, 2-hexadecanediol (HDD) capped silicon nanoparticles (Si NPs):
Discrete Si NPs were prepared by combining (1 mmol, 0.536 g) of SiI4 and (0.4 mmol,
0.103 g) of HDD with 15 mL of DOE. The mixture was heated to 170 °C. A yellow color
solution was obtained at this temperature. After stirring the reaction mixture for 10 min, (3.75
mmol, and 2.5 mL) n-BuLi was rapidly injected into the yellow solution. The temperature of the
reaction mixture was further increased to 200 °C and was left stirring at that temperature for 30
min; at this temperature the color of the solution changed to orange. The reaction was brought to
room temperature by removal of the heating mantle. Once the reaction mixture was at room
temperature, the NPs were precipitated by addition of 3 mL of hexane and 30 mL of methanol.
Table S1: Table showing d spacing from calculated lattice fringes of octanol capped Si NPs
matched with PDF #17-0901 from Jade
Area in
image
Calculated
d spacing
(Å)
Closest Si
d spacing
from PDF
#17-0901
Correspon
ding lattice
plane
(A)
1.403
1.409
[332]
(B)
1.534
1.558
[411]
(C)
2.280
2.331
[220]
(A)
(B)
(C)
database
20 nm
S2
Table S2: showing the different planes from PXRD #17-0901 and SAED of the as made Si
octanol capped samples
Rings
1
2
d (Å)*
2.69
2.33
d (Å)
experimental
(SAED)
2.60
2.36
hkl
211
220
*From Jade PXRD database PDF # 17-0901
Figure S1: (a) TEM (b) EDS and (c) SAED of HDD capped Si NPs
S3
Table S3. Selected crystallographic data and refined parameters from Powder XRD experiment
of Si(cI16). Profile Matching is performed using JANA 2006. A Pseudo-Voigt function is used
for profile simulation and a Chebyshev polynomial is used for modelling the background.
Compound
Space group (No.)
Lattice parameters from Profile Matching
Si(cI16)
Ia-3 (206)
6.615(2)
Unit cell volume /A˚3
289.42(7)
Z
16
-3
Calculated density /g ·cm
Diffractometer, wave length λ / A°
2.5774(6)
1.54051
Diffraction set-up
Perpendicular setting
Number of reflections
12
2θ range; step width /degree
Residuals Rp; Rwp; GOF
20-80; 0.0194
1.06; 1.38; 1.13
_ _ _ a s m a de S i
100
o
80
60
In te n s ity (a rb . u n its )
_ _ _ a fte r he a ting to 6 5 0 C
40
20
0
20
30
40
50
60
70
80
2 θ (D eg rees )
Figure S2: Powder X-ray Diffraction (PXRD) of the precipitate of HDD capped Si NPs at room
temperature (black) and after annealing (blue). The calculated PXRD corresponds to Si cubic
structure, BC8, PDF #17-0901.
S4
Si NPs after annealing
Intensity (arb. units)
Si NPs before annealing
BC8
20
30
Si PDF #17-0901
Cubic Diamond
Si PDF #27-1402
50
70
40
60
80
2 θ (Degrees)
Figure S3: Powder X-ray Diffraction (PXRD) of the precipitate of octanol capped Si NPs at
room temperature and after annealing. The calculated PXRD corresponds to Si cubic structure,
BC8, PDF #17-0901 and for cubic diamond PDF #27-1402 was added for reference
100
% Transmittance
90
80
70
-C-CH2-C-CH3-
-C-CH3-
-C-CH2-
60
50
-C-CH2-
40
4000
-Si-OCH33500
3000
2500
2000
-1
1500
1000
500
Wavenumber (cm )
Figure S4: FTIR spectra for the octanol capped Si NPs
S5
Figure S5: (a) Photoluminescence (PL) spectra of Si NPs at an excitation wavelength of 360 nm
and (b) image of the precipitate dissolved in toluene in a glass vial emitting blue fluorescence
when excited with a commercial hand-held low-intensity UV lamp.
S6