Supporting Information
A Versatile Precursor System for Supercritical Fluid
Electrodeposition of Main-Group Materials
Philip N. Bartlett,*[a] Jennifer Burt,[a] David A. Cook,[a] Charles Y. Cummings,[a]
Michael W. George,[b, c] Andrew L. Hector,[a] Mahboba M. Hasan,[a] Jie Ke,[b] William Levason,[a]
David Pugh,[a] Gillian Reid,[a] Peter W. Richardson,[a] David C. Smith,[d] Joe Spencer,[d]
Norhidayah Suleiman,[b] and Wenjian Zhang[a]
chem_201503301_sm_miscellaneous_information.pdf
PREPARATION OF CHLOROMETALLATE SALTS
All preparations were carried out under a dry dinitrogen atmosphere using standard Schlenk
and glove-box techniques. [NnBu4]Cl, GeCl4, H3PO2, SnCl2, GaCl3, InCl3, SbCl3, BiCl3, and
SeCl4 were obtained from Sigma and used as received. TeCl4 was obtained from Strem.
EtOH was distilled from Mg/I2 and CH2Cl2 was dried by distillation from CaH2.
Infrared spectra were recorded as Nujol mulls between CsI plates using a Perkin-Elmer
Spectrum 100 spectrometer over the range 4000200 cm-1. 1H and
13
C{1H} NMR spectra
were recorded in CD2Cl2 solution at 295 K using a Bruker DPX-400 spectrometer and are
referenced to the residual solvent resonance.
119
Sn and
71
Ga spectra were run in CH2Cl2 at
295 K on a Bruker DPX-400 spectrometer and referenced to Me4Sn, with [Cr(acac)3] added
as a relaxation agent, and [Ga(H2O)6]3+ at pH =1 in H2O, respectively. Microanalyses were
undertaken by London Metropolitan University.
[NnBu4][GeCl3]. Prepared according to the literature procedure.[1] Crystals were obtained by
recrystallisation from hot EtOH (Figure S1).
[NnBu4][SnCl3]. SnCl2 (0.19 g, 1.0 mmol) was dissolved in EtOH (6 ml) and a solution of
[NnBu4]Cl (0.28 g, 1.0 mmol) in EtOH (6 mL) was added. The resulting colourless solution
was stirred for 17 h, then the solvent was concentrated in vacuo to yield a white solid which
was collected by filtration and dried in vacuo. A second crop was obtained by removing the
solvent from the filtrate. Spectroscopic data confirmed this was the same product. Combined
yield: 0.33 g, 70%. In subsequent preparations the solvent was removed completely in vacuo
to yield the spectroscopically and analytically pure product. Anal. calc. for C16H36Cl3NSn
(467.53): C, 41.1; H, 7.8; N, 3.0. Found: C, 40.9; H, 7.9; N, 2.9%.
119
Sn NMR
(CH2Cl2/CD2Cl2, 295 K): δ = –40.8 (s) ppm, and is unchanged in the presence of a 10-fold
excess of [NnBu4]Cl. IR (Nujol): ν = 297 (s), 260 (vs) (Sn–Cl) cm−1. Raman: ν = 295 (vs),
258 (s), 128 (s), 115 (s) (SnCl) cm1.
[NnBu4][GaCl4]. Prepared in an analogous manner to [NEt4][GaCl4] in accordance with the
literature procedure.[2] 71Ga NMR (CH2Cl2, 295 K): δ = +251 (s) ppm, unchanged in the
presence of a 10-fold excess of [NnBu4]Cl.
[NnBu4][InCl4], [NnBu4][SbCl4], [NnBu4][BiCl4], [NnBu4]2[SeCl6] and [NnBu4]2[TeCl6].
Prepared in accordance with the literature procedure.[3] [NnBu4][InCl4]: 115In NMR (CH2Cl2,
295 K): δ = +447 (s) ppm, unchanged in the presence of a 10-fold excess of [NnBu4][BF4].
1
[NnBu4][InCl4]: 115In NMR (CH2Cl2, 295 K): δ = +447 (s) ppm, unchanged in the presence of
a 10-fold excess of [NnBu4][BF4].
X-RAY CRYSTALLOGRAPHY
Crystals were obtained as described above. Details of the crystallographic data collection and
refinement are in Table S1. Diffractometer: Rigaku AFC12 goniometer equipped with an
enhanced sensitivity (HG) Saturn724+ detector mounted at the window of an FR-E+
SuperBright molybdenum rotating anode generator (λ1 = 0.71073 Å) with VHF Varimax
optics (100 µm focus). Cell determination, data collection, data reduction, cell refinement and
absorption correction: CrystalClear-SM Expert 2.0 r7.[4] Structure solution and refinement
were routine using WinGX
[5]
and software packages within. enCIFer was used to prepare
material for publication.[6] CCDC 1051033 contains the supplementary crystallographic data
for this paper. This material is available free of charge via the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Figure S1. ORTEP diagram of [NnBu4][GeCl3] showing one of two symmetry-independent
formula units within the asymmetric unit. Ellipsoids are shown at 50% probability and
hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (): GeCl =
2.2801(15)2.3059(17), ClGeCl = 94.77(6)97.48(6).
2
Table S1. Crystal data and structure refinement for [NnBu4][GeCl3]
Empirical formula
C16H36Cl3GeN
Formula weight
421.40
Temperature
100(2) K
Wavelength
0.71073 Å
Crystal system
Monoclinic
Space group
Pc
Unit cell dimensions
a = 9.608(2) Å
= 90°.
b = 12.831(3) Å
= 105.049(4)°
c = 18.330(4) Å
 = 90°.
Å3
Volume
2182.1(8)
Z
4
Density (calculated)
1.283 Mg/m3
Absorption coefficient
1.767 mm-1
F(000)
888
Reflections collected
15134
Independent reflections
6881 [R(int) = 0.0418]
Data / restraints / parameters
6881 / 2 / 388
Goodness-of-fit on
F2
Final R indicesa [I>2sigma(I)]
a
1.005
R1 = 0.039, wR2 = 0.086
R indices (all data)
R1 = 0.051, wR2 = 0.091
Absolute structure parameter
0.507(12)
Extinction coefficient
n/a
Largest diff. peak and hole
0.684 and -0.332 e.Å-3
a
R1 = Σ||Fσ| – |Fc|| / Σ|Fo|; wR2 = [Σw(Fo2 – Fc2)2 / ΣwFo2]1/2.
3
Electrical Conductivity Measurements.
The electrical conductivity of [NnBu4]Cl in scCH2F2 was measured using a newly purposebuilt, high-pressure apparatus.
The conductivity vessel is a three-piece, stainless steel
construction, consisting of a main body, a hollow screw and an electrode holder. Two pieces
of platinum foil (0.5 cm2 each) are mounted to the inner surface of a glass tube that is
attached to the electrode holder. The electrode holder is sealed to the main body with a PTFE
gasket. The metal connection wires for the platinum electrodes are embedded in the PEEK
(polyetheretherketone) tubing and epoxy resins, and fed through the electrode holder and the
hollow screw. The conductivity vessel is immersed in an oil bath and connected to the fluid
delivery unit using PEEK tubing to avoid possible current leakage to the ground. The
maximum working temperature and pressure of the conductivity apparatus is 393 K and 27
MPa, respectively.
The conductivity measurements were made with a JENWAY 4510 conductivity meter. The
cell constant was calibrated using the conductivity solutions of KCl after platinisation of the
platinum electrodes using the standard procedures.[7] At the start of the measurements, a
known amount of [NnBu4]Cl was placed at the bottom of the conductivity vessel. The vessel
was then sealed and heated to a pre-set temperature (e.g. 363 K). The pressure of the system
was increased stepwise by pumping CH2F2 to the vessel. At each pressure step the contents
of the vessel were agitated for more than 5 min before the conductivity was recorded. The
molar concentration of [NnBu4]Cl was kept constant because no [NnBu4]Cl had been
withdrawn from the vessel during the measurements.
Figure 2 shows the electrical conductivity of 0.060 mol dm−3 of [NnBu4]Cl in CH2F2 at 363 K,
together with the conductivity measured previously from a solution with 0.031 mol dm−3 of
[NnBu4][B{3,5-C6H3(CF3)2}4] [8] which has been successfully used to electrodeposit a variety
of materials in SCFs.[9] Although the molar conductivity of [NnBu4]Cl is lower than that of
[NnBu4][B{3,5-C6H3(CF3)2}4], it is possible to achieve the conductivity at a similar level to
that of [NnBu4][B{3,5-C6H3(CF3)2}4] because the high solubility of [NnBu4]Cl allows a
concentrated supercritical fluid solution to be used. Furthermore, unlike [NnBu4][B{3,5C6H3(CF3)2}4], the conductivity of [NnBu4]Cl increases with pressure when the pressure is
above 20 MPa, suggesting that carrying out electrodeposition above 20 MPa is also a method
to improve the conductivity when using [NnBu4]Cl as a supporting electrolyte.
4
5
 / (mS cm -1)
4
3
2
1
10
15
20
25
30
p / MPa
Figure S2. Electrical conductivity of 0.060 mol dm−3 of [NnBu4]Cl () and 0.031 mol dm−3 of [NnBu4]
[B{3,5-C6H3(CF3)2}4] (8) () in CH2F2 at 363 K.
EDX DATA
EDX analysis of the electrodeposited samples was performed with a Jeol JSM 6500F field
emission gun scanning electron microscope (FEG-SEM) equipped with an Oxford
Instruments EDX detector, with accelerating voltage = 20 keV. The EDX spectra of the films
are presented in Figure S2. In each case the target element was observed as the dominant
peaks, with peaks from the Au substrate also evident in some cases. Due to the lower melting
point of elemental Ga (MPt = 303 K) compared to the deposition temperature (358 K), the
EDX analysis for this sample was performed on material collected as tiny beads from the
electrode surface. These were rinsed from the surface with acetone, collected by
centrifugation, washed with acetone and ethanol before drying. The EDX spectrum (Figure
S3 (a)) shows that in addition to Ga the material contained several contaminant species that
are attributed to elements previously studied in the same plating cell. The observation of trace
amounts of contaminant species is likely related to the tendency of liquid gallium to readily
form alloys with many other metals. Of the seven other samples, the only contamination
observed was chloride in the films of In and Ge. This chloride is likely to originate from
5
trapped electrolyte species. It is expected that upon optimisation of the washing procedure
these contaminants will be removed.
(a) Ga
(b) In
(c) Ge
(d) Sn
(e) Sb
(f) Bi
(g) Se
(h) Te
Figure S3. EDX spectra of electrodeposited (a) Ga, (b) In, (c) Ge, (d) Sn, (e) Sb, (f) Bi, (g) Se and
(h) Te. The spectra of the elements (b) – (h) were collected from thin films deposited onto evaporated
gold slide electrodes. The spectrum of (a) Ga was obtained on the material collected from the bottom
of the cell, as described in the main body of the text. The deposition potentials and times were 2.0 V
and 5500 s for Ga (a), 1.50 V and 6800 s for In (b), 1.80 V and 5500 s for Ge (c), 1.25 V and
1000 s for Sn (d), 0.75 V and 8000 s for Sb (e), 0.90 V and 1000 s for Bi (f), 1.25 V and 3600 s
for Se (g) and 0.80 V and 3500 s for Te (h). Accelerating voltage = 20 keV.
6
ELECTRODEPOSITION
Electrodeposition of In Films from 2 x 10-3 mol dm-3 [NnBu4][InCl4] Containing 50  10-3
mol dm-3 [NnBu4][BF4] as the Supporting Electrolyte in scCH2F2. Electrodeposition of In
films with [NnBu4]Cl as the supporting electrolyte was hindered by the low solubility of the
[NnBu4][InCl4] precursor in this system. However, it was possible to prepare much thicker In
films from the scCH2F2 solvent by using [NnBu4][BF4] as the supporting electrolyte. The
greater solubility of the [NnBu4][InCl4] precursor in the system with [NnBu4][BF4] is
attributed to the absence of any chloride species, which prevents the formation of the
insoluble [InCl6]3 anion.
Figure S4 presents cyclic voltammetry of 2103 mol dm-3 [NnBu4][InCl4] in scCH2F2 at a 0.5
mm diameter Au electrode with 50103 mol dm-3 [NnBu4][BF4] as the supporting electrolyte.
The deposition onset occurs at approximately 1.30 V and the stripping peak potential is at
0.12 V vs. Pt. The magnitude of the cathodic limiting current density is about 5x greater
than the corresponding system with [NnBu4]Cl as the electrolyte. SEM imaging of an In film
deposited onto an evaporated gold slide electrode in Figure S5a, shows that the film has a
non-uniform morphology. EDX analysis of this film (Figure S5b) shows peaks corresponding
to In and to the Au substrate.
4
j / mA cm-2
2
0
-2
-4
-6
-8
-2.0
-1.5
-1.0
-0.5
0.0
0.5
E (vs. Pt) / V
Figure S4. Cyclic voltammetry of 2103 mol dm−3 [NnBu4][InCl4] in scCH2F2 (17.2 MPa and 358 K)
containing 50103 mol dm3 [NnBu4][BF4] as the supporting electrolyte, measured at a 0.5 mm gold
working electrode and referenced to a Pt pseudo-reference electrode. The potential scan rate
was 50 mV s−1.
7
Table S3. Deposition parameters for 2×10−3 mol dm−3 [NnBu4][InCl4] and 50×10−3 mol dm−3
[NnBu4][BF4]. Pressure = 17.2 MPa, temperature = 358 K.
Element Deposition potential / V vs. Pt Deposition time / s Charge passed / C
In
-1.75
1462
1.77
(a)
(b)
Figure S5. SEM (a) and EDX (b) of a film of In electrodeposited onto a gold evaporated slide
electrode, using [NnBu4][BF4] as the supporting electrolyte. The deposition potential was 1.75 V and
the deposition time was 1470 s. Accelerating voltage = 20 kV.
Electrochemistry of [NnBu4]2[SeCl6] and [NnBu4]2[TeCl6] at Pt and TiN Electrodes in
scCH2F2. Te was found to alloy with gold and Se was poorly adherent on gold electrodes and
therefore other electrode materials were investigated. Cyclic voltammograms of
[NnBu4]2[SeCl6] and [NnBu4]2[TeCl6] in scCH2F2 at Pt and TiN electrode are presented in
Figure S6. The concentration of the [NnBu4]2[SeCl6] and [NnBu4]2[TeCl6] in each experiment
was 2103 mol dm−3, and 50103 mol dm3 [NnBu4]Cl was used as the supporting
electrolyte. The voltammetry shows that for the Se compound the deposition onset shifts from
-1.0 V on Au, to -0.65 V on Pt and -0.60 V on TiN. Although no Se stripping peak is
8
observed on either substrate material, the onset of chloride oxidation is shifted to more
positive potentials compared to that on Au. For the Te compound, the deposition onset
potential on Pt (0.28 V) is similar to that on Au (0.25 V), whereas it is shifted to a more
negative potential on the TiN (0.55 V). Te stripping peaks are observed at 0.27 V on Pt and
0.55 V on TiN. Similar to the Se sample, the onset of chloride oxidation is also shifted to
j / mA cm-2
more positive potentials.
10
(a) Se
0
-10
-1.5
j / mA cm-2
20
-1.0
-0.5
0.0
0.5
(b) Te
10
0
-10
-1.0
-0.5
0.0
0.5
E (vs. Pt) / V
Figure S6. Cyclic voltammetry of (a) [NnBu4]2[SeCl6] and (b) [NnBu4]2[TeCl6] in scCH2F2 (17.2 MPa
and 358 K), measured at a 0.5 mm diameter Pt disk working electrode and referenced to a Pt pseudo9
reference electrode. The concentration of the [NnBu4]x[MCly] redox species in each case was 2103
mol dm−3, and 50103 mol dm3 [NnBu4]Cl was used as the supporting electrolyte. The potential scan
rate was 50 mV s−1.
0.5
i / mA
(a) Se
0.0
-0.5
-1.0
-3
1.0
i / mA
0.5
-2
-1
0
1
2
(b) Te
0.0
-0.5
-1.0
-1.5 -1.0 -0.5
0.0
0.5
1.0
E (vs. Pt) / V
Figure S7. Cyclic voltammetry of (a) [NnBu4]2[SeCl6] and (b) [NnBu4]2[TeCl6] in scCH2F2 (17.2 MPa
and 358 K), measured at a TiN working electrode (surface area approx. 0.25 cm2) and referenced to a
Pt pseudo-reference electrode. The concentration of the [NnBu4]x[MCly] redox species in each case
was 2103 mol dm−3, and 50103 mol dm3 [NnBu4]Cl was used as the supporting electrolyte. The
potential scan rate was 50 mV s−1.
10
Electrodeposition of Se and Te at TiN Electrodes in scCH2F2. Thin films of Se and Te
were electrodeposited potentiostatically from scCH2F2 onto TiN electrodes. The deposition
potentials and times were specifically selected for each element in order to obtain films of
sufficient thickness for EDX and XRD analyses. Te was deposited at 1.5 V, and Se was
deposited at 2.0 V. After depressurisation, the deposited film electrodes were removed from
the cell inside a nitrogen-purged glovebox and then washed by dipping into CH2Cl2 solution
to dissolve away residual electrolyte salts. The deposited films were analysed by SEM, EDX
and XRD.
SEM images of the Se (Figure S8a) and Te (Figure S9a) samples show that both deposited
elements have quite uniform morphologies across the electrode surface. For both samples, the
crystalline facets are clearly visible. The EDX spectra of the Se (Figure 8b) and Te (Figure
9b) films show that the target element was observed as the dominant peaks in both spectra.
Table S4. Deposition parameters for [NnBu4]2[TeCl6] and [NnBu4]2[SeCl6] onto TiN and Pt electrodes.
The concentration of the precursor compounds was 2×10−3 mol dm−3 with 50×10−3 mol dm−3
[NnBu4]Cl used as the supporting electrolyte. Pressure = 17.2 MPa, temperature = 358 K.
Element Deposition potential / V vs. Pt Deposition time / s Charge passed / C
Te
-1.50
1114
0.94
Se
-2.00
3600
1.55
11
(a)
(b)
Figure S8. SEM (a) and EDX (b) of a film of Se electrodeposited onto a TiN electrode. The
deposition potential was -2.0 V and the deposition time was 3600 s. Accelerating voltage = 20 kV.
12
(a)
(b)
Figure S9. SEM (a) and EDX (b) of a film of Te electrodeposited onto a TiN electrode. The
deposition potential was 1.5 V and the deposition time was 1100 s. Accelerating voltage = 20 kV.
13
XRD DATA FOR ELECTRODEPOSITED FILMS
Gallium. Deposits as a liquid – no XRD data.
Indium. The indium XRD data were collected on a film deposited from [InCl4]- in
[NnBu4][BF4] as those from the chloride electrolyte were very thin. No orientation was
observed in the grazing incidence scan (Figure S9) and this was confirmed from a symmetric
scan (small amount of AuIn2 alloy was observed in this geometry due to the greater
penetrating depth).
In-CC-06102014


In ICSD
Sn-PR-03071404
Counts
Sn ICSD
Bi 11081406
Bi ICSD


Te-09071405


Te ICSD
Au ICSD
20
30
40
50
/ degrees
60
70
80
Figure S10. Grazing incidence diffraction patterns (1° incidence angle) for In, Sn, Bi and Te
deposited on gold, with labels showing the sample numbers used. * marks the positions of peaks due
to Au0.3Te0.7 alloy, and ● marks the positions of AuIn2 peaks.
Germanium. The as-deposited germanium on gold contained only very broad reflections due
to germanium with short range order (close to amorphous) (Figure S11) Annealing at 700 °C
for 1 h under argon resulted in crystallisation of Ge with the standard diamond structure
(Figure S12).
14
Au, (1 1 1)
8.0e+003
Au, (2 2 0)
Ge, (3 3 1)
Ge, (4 0 0)
Ge, (3 1 1)
2.0e+003
Au, (3 1 1)
Au, (2 0 0)
Ge, (2 2 0)
4.0e+003
Ge, (1 1 1)
Intensity (counts)
6.0e+003
0.0e+000
20
30
40
50
60
70
80
2-theta (deg)
Figure S11. Grazing incidence XRD pattern of Ge on gold.
Figure S12. Grazing incidence XRD pattern of Ge on gold after annealing in argon at 700 °C. Note
the gold has partially delaminated, resulting in splitting of some reflections.
Tin. Good quality films by XRD were obtained on gold (Figure S13 and Table 2). The
grazing incidence scan showed some evidence of alignment through elongation of the 200
reflection. This is also observed in the symmetric scan (Figure S13), but only shows a small
15
amount of <100> preferred orientation. The symmetric scan also shows the presence of
AuSn4 and Au5Sn alloys, presumably at the gold/tin interface since these were not seen in the
grazing incidence data.
Au
Counts
Sn-0307201404Au

 

Au
200
101
211
Sn (ICSD)
220
20
30
40
301
50
60
70
80
2 / degrees
Figure S13. Symmetric XRD scan of tin deposited on gold. * marks the positions of reflections due
to AuSn4 and Au5Sn
Antimony. Grazing incidence pattern on gold contained mainly aurostibite AuSb2 but also
some antimony (Figure S14). Growth on TiN produced nice Sb films (Figure S15 and Table
2) and there was no evidence of preferred orientation in the grazing incidence or symmetric
scans.
16
Figure S14. Grazing incidence XRD of antimony deposited on gold.
Bismuth. Good quality grazing incidence patterns were obtained for Bi on gold (Figure S10
and Table 2). No orientation was observed in grazing incidence or in a symmetric scan.
Si
Sb-CC-TiN-170315-S1
Sb ICSD
Counts
Si
Se-28111408
Se ICSD
Te-18111403
Te ICSD
TiN ICSD
20
30
40
50
60
70
80
2 / degrees
Figure S15. Grazing incidence XRD patterns of Se and Te deposited on TiN.
17
Selenium. Data for Se deposited on Au (Figure S16) show the apparent presence of an alloy
phase that resembled Au87In13 (P63/mmc, a = 2.851(9) and c = 4.80(3) Å) but presumably is a
similar Sb-Au alloy. Growth on TiN produces a good quality selenium pattern (Figure S15)
with one unidentified peak at 38°. Refined XRD parameters are in Table 2. There was no
evidence of preferred orientation from the grazing incidence or from symmetric scans.
Figure S16. Grazing incidence XRD of a deposit of Se on gold.
Tellurium. Good data were obtained for Te electrodeposited on gold (Figure S10 and Table
2) but some alloying was seen even in grazing incidence. Some elongation of the 012
reflection (which overlaps with gold so has significant uncertainty) observed in the grazing
incidence scans. Alloy reflections are not enhanced relative to the Te pattern in the symmetric
XRD (Figure S17) suggesting it is not limited to the Au/Te interface. The symmetric scan
shows clear elongation of the 003 reflection strong <001> preferred orientation.
18
003
Te-Au-09071405
012
112
Counts
101
100
113
111
110 

021
220
022
222
Te from ICSD
20
30
40
50
60
70
80
2 / degrees
Figure S17. Symmetric XRD pattern of tellurium deposited on gold. Note that the 012 reflection
overlaps with the gold 111. * marks positions of Au0.3Te0.7 reflections, the one at 44° is also the
position of the Au 200.
Good quality Te films were grown on TiN (Figure S18 and Table 2). The grazing incidence
scan (Figure S15) shows some elongation of the 101 and 012 reflections and this is replicated
in the symmetric scan (Figure S18) so there is no evidence of any specific orientation.
Te-18111403
Counts


011
Te ICSD
012
110
100
20
22-1
120 224
015
113 222 2-22 303
202
220
300 114
003 201
111 200 005 022
112
30
40
50
60
70
80
90
2 / degrees
Figure S18. Symmetric XRD pattern of tellurium deposited on TiN. * Marks positions of TiN
reflections.
19
RAMAN DATA FOR ELECTRODEPOSITED FILMS
Figure S19. Representative Raman spectra of various electrodeposited elements measured using 702
nm excitation.
Raman spectra were measured in air for electrodeposited samples of Ge, Se, Sb, Te and Bi,
Figure S19. It was not possible to acquire Raman spectra for the electrodeposited Sn, In or Ga
due to screening in these metallic samples. The Raman spectra of the Ge sample, presented in
Figure S19 has a Raman peak at 270 cm-1, indicative of amorphous Ge.[10] The low energy
structuring in this spectrum is luminescence. The electrodeposited Se, presented in Figure
S19 (top right) has a distinct, sharp peak at 233 cm-1, which is similar to Raman peaks
observed in amorphous Se.[11],[12] The elements, Bi and Sb have similar Raman spectra as
seen in Figure S19. Experimentally, in the case of Sb we observe two sharp Raman peaks at
115 cm-1 and 150 cm-1, in good agreement with the expected TO and LO phonon modes
observed for crystalline Sb.[13],[14] In the case of Bi we observe two Raman peaks at 70 and 97
cm-1 corresponding to the Eg and A1g Raman bands observed for crystalline Bi.[15] In addition,
the Raman spectra of Te in Figure S19, has two distinct Raman peaks appearing at 120 and
140 cm-1, with an additional, weaker, peak at 94 cm-1, in good agreement with the ETO, A1 and
20
ETO Raman bands of crystalline Te at 92.2, 120 and 140 cm-1 presented by Pine and
Dresselhaus.[16]
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