Synthesis, Structure and Application of Intramolecularly-Coordinated Gallium Chalcogenides: Suitable Single-Source precursors for GaxSey Materials

Article abstract of DOI:10.1002/chem.201802688

Studies have been focused on the synthesis of N→Ga-coordinated organogallium selenides and tellurides [L¹Ga(μ-Se)]₂ (1), [L²Ga(μ-Se)]₂ (2) and [L¹Ga(μ-Te)]₂ (3), respectively, containing either N,C,N- or C,N-chelating ligands L^{1, 2} (L¹ is {2,6-(Me₂NCH₂)₂C₆H₃}^? and L² is {2-(Et₂NCH₂)-4,6-tBu₂-C₆H₂}^?) having Ga/E (E=Se or Te) atoms in 1/1 ratio. To change the Ga/E ratio, an unusual N→Ga-coordinated organogallium tetraselenide L¹Ga(κ²-Se₄) (4) was prepared. An unprecedented complex (L¹Ga)₂(μ-Te₂)(μ-Te) (5), as the result of the non-stability of 3, was also isolated. Compound 2 is a suitable single-source precursor for the preparation of amorphous GaSe thin films by the spin coating. Moreover, simple heating of an octadecylamine solution of 2 provided, after work up, monoclinic Ga₂Se₃ crystals with different crystallinity according to conditions used. Therefore, compound 2 may be also used as a source of Ga₂Se₃ in the low-temperature doping process of Bi₂Se₃.

Full text of DOI:10.1002/chem.201802688

A Journal of
Accepted Article
Title: Synthesis, structure and application of intramolecularly
coordinated gallium chalcogenides: Suitable single source
precursors for GaxSey materials
Authors: Tomas Ricica, Libor Dostal, Zdenka Ruzickova, Ludvik
Benes, Petr Nemec, Marek Bouska, Jan Macak, Petr Knotek,
Pavlina Ruleova, and Roman Jambor
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To be cited as: Chem. Eur. J. 10.1002/chem.201802688
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FULL PAPER
DOI: 10.1002/chem.200((will be filled in by the editorial staff))
Synthesis, structure and application of intramolecularly coordinated gallium
chalcogenides: Suitable single source precursors for Ga Se materials
x
y
[
a]
[a]
[a]
[a]
[b]
Tomáš Řičica, Libor Dostál, Zdenka Růžičková, Ludvík Beneš, Petr Němec, Marek
[b]
[c]
[a]
[a]
[a]
Bouška, * Jan M. Macak, Petr Knotek, Pavlína Ruleová and Roman Jambor *
1

Abstract: Our studies have been focused on
the synthesis of N→Ga coordinated
organogallium selenides and tellurides
organogallium tetraselenide L Ga( -Se
4
)
with different crystallinity according to
conditions used. Therefore, compound 2
(4) was prepared. An unprecedented
1
complex (L Ga)
2
(-Te
2
)(-Te) (5) as the
may be also used as source of Ga
temperature doping process of Bi
2
Se
3
in low
1
2
[
[
L Ga(-Se)]
L Ga(-Te)]
2
(1), [L Ga(-Se)]
(3), respectively, containing
2
(2) and
result of the non-stability of 3 was also
isolated. Compound 2 is suitable single
source precursor for the preparation of
amorphous GaSe thin films by the spin
coating. Moreover, simple heating of
octadecylamine solution of 2 provided, after
2
Se .
3
1
2
1
,2
either N,C,N- or C,N-chelating ligands L
Keywords: 13 group element • thin
layer • Ga Se material • doping •
spin coating
1
-
2
(
(
(
L is {2,6-(Me
2
NCH
2
)
2
C
6
H
3
} and L is {2-
X
Y
-
Et NCH )-4,6-tBu
2
2
2
-C
6
H
2
} ) having Ga/E
E = Se or Te) atoms in 1/1 ratio. To change
the Ga/E ratio, unusual N→Ga coordinated
2 3
work up, the monoclinic Ga Se crystals
only few SSPs for CVD of GaE materials. The deposition of GaE
from [RGa(μ -E)] (R = tBu, CEtMe , CEt Me) with cubane
structure was firstly reported by Barron and co-workers
Thereafter, cubic Ga Se thin films have been deposited from
When {Ga(μ-Te)[N(iPr PTe) ]} was used
as SSP, the deposition of a mixture of cubic Ga Te , monoclinic
The resulting
material contained phosphorus content at 15−20% according to
3
4
2
2
Introduction
[
10]
2
11]
3
Amorphous thin films based on chalcogenides form an important
field for today’s research and development. These materials show
wide potential in the area of photonics, infrared optics, sensors,
medicine, computer memories, or military applications.[1] The
applications of amorphous III-VI materials are based on broad IR
[
[
Me
2
Ga(SePiPr
2
)
2
N].
2
2
3
2
12]
3
[
GaTe, and hexagonal Te has been obtained.
[
12]
energy-dispersive X-ray spectroscopy (EDX). In 2013, Reid and
coworkers prepared telluroether and selenoether complexes of
[
2]
transparency, photovoltaic devices, or can be used as layers for
[
3]
III−V devices passivation. Amorphous chalcogenide thin films are
GaCl
Ga
3
and used them as SSPs for low pressure CVD of single phase
.[13] In contrast, the deposition of amorphous GaSe layers was
typically fabricated by the physical vapour deposition (PVD)
methods. For GaE (E = Se, Te) materials, this method was used
2
E
3
[
4]
[
14]
reported infrequently.
GaSe thin films were deposited at room
[
5]
for synthesis of the hexagonal GaSe thin films, the production of
temperature onto glass substrate and carbon stub by thermal
[
6]
[7]
[9]
2
D GaSe crystals, monolayers, nanoribbons[8] or nanosheets.
[
14b]
evaporation technique,
by PVD
while GaSe nanosheets were deposited
Chemical vapour deposition (CVD) for GaE (E = Se, Te) synthesis
is also possible, but CVD method is strongly influenced by the
character of the single source precursors (SSP). However, there are
[
14c]
and similarly, amorphous Ga Se films were deposited
2
3
[
15]
onto glass substrate by PVD. Those are the reasons for the single
source precursors’ application to develop good quality amorphous
GaSe thin films presented in this work. Moreover, we have showed
the possible preparation of amorphous GaS material by spin coating
method using organometallic N→Ga coordinated organogallium
[
a]
T. Řičica, L. Dostál, Z. Růžičkova, L. Beneš, R. Jambor, P. Knotek,P.
Ruleová, Department of General and Inorganic Chemistry, University of
Pardubice, 532 10 Pardubice, Czech Republic E-mail:
roman.jambor@upce.cz,
[16]
sulphides as suitable SSPs, recently. To expand our studies on the
synthesis of remaining amorphous III-VI materials by the spin
coating method, here we focus on the synthesis of N→Ga
1
coordinated organogallium selenides and tellurides [L Ga(-Se)]
2
[
b]
c]
M. Bouška, P. Němec, Department of Graphic Art and Photophysics,
University of Pardubice, 532 10 Pardubice, Czech Republic, E-mail:
marek.bouska@upce.cz
2
1
(1), [L Ga(-Se)]
2
(2) and [L Ga(-Te)]
2
(3), respectively,
containing either N,C,N- or C,N-chelating ligands L (L is {2,6-
1,2
1
-
2
-
(
Me
2
NCH
2
)
2
C
6
H
3
}
and
L
2 2 2 6 2
is {2-(Et NCH )-4,6-tBu -C H } ).
[
J. M. Macak, Center of Materials and Nanotechnologies, Faculty of
Chemical Technology, University of Pardubice, 530 02 Pardubice, Czech
Republic
Compounds 1 – 3 contain Ga/E atoms in 1/1 ratio. An unusual
1

N→Ga coordinated organogallium complexes L Ga( -Se
4
) (4) and
1
(
L Ga)
2
(-Te )(-Te) (5) were also prepared. Compounds 1 - 5
2
Supporting information for this article is available on the WWW under
http://www.chemeurj.org/ or from the author.
were further tested as potential single source precursors for the
preparation of either amorphous GaSe or GaTe thin films by spin
1
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Chemistry - A European Journal
10.1002/chem.201802688
coating method or for the preparation of polycrystalline Ga
materials.
2
Se
3
of the Ga–Se distance is 2.3624(5) - 2.4097(6) Å) are just within the
currently known range (2.37 - 2.54 Å) for organogallium Ga-Se
[
10-12,17,18]
species.
sulfide [L Ga(-S)]
It should be also noted, that analogous gallium
3 3
was found to be trimer with six member Ga S ,
1
3
Results and Discussion
2
[16]
2
while similar dimeric structure was found for [L Ga(-S)] .
Synthesis and characterization of compounds 1 - 5
The treatment of L1,2GaCl
with one eq. of Li
E or Li
Se
4
(E
7 8 7 8
Table 1:. Selected bond lengths (Å) and angles (deg) for 1, 2·2(C H ), 4 and 5·C H .
2
2
2
=
Se, Te generated in situ, see Scheme 1) yielded the N→Ga
1
coordinated dimeric organogallium chalcogenides [L Ga(-Se)]
2
(1),
1
2·2(C
7
H
8
)
4
7 8
5·C H
2
1
[
L Ga(-Se)]
2
(2), [L Ga(-Te)]
2
(3) and organogallium
) (4). In addition, complex 3 is sensitive at
(E = Se)
(E = Se)
(E = Se)
(E = Te)
1

tetraselenide L Ga( -Se
light and decomposes to unprecedented complex (L Ga)
4
1
2
(-Te
2
)(-
Ga(1)–C(1)
Ga(1)–N(1)
1.969(4)
2.130(3)
4.383(4)
2.3680(5)
2.3711(5)
-
1.986(4)
2.130(3)
-
1.952(7)
2.445(5)
2.371(5)
2.3996(9)
2.4101(9)
-
1.973(5)
2.222(4)
3.008(5)
Te) (5).
Te
1,2
THF
1,2
compound 3
1
1
L
GaCl2
+ 2 Li[HBEt3]
+
E
[L Ga(-E)]2
L Ga
GaL
-
2 LiCl
light sensitive
Ga(1)–N(2)
1
Te Te
5
1
2
3
: L , E = Se
2
Ga(1)–E(1)
2.2624(5)
2.4097(6)
-
2.5424(6)
2.5872(6)
2.5597(2)
2.5970(6)
: L , E = Se
NMe2
NEt2
1
: L , E = Te
Ga(1)–E(2)
1
THF
1
L GaCl2
+ 2 Li[HBEt3]
+
4 Se
L Ga(-Se)4
Ga(2)–Te(1)
Ga(2)–Te(3)
N(1)–Ga(1)–E(1)
C(1)–Ga(1)–E(1)
C(1)–Ga(1)–N(1)
-
2 LiCl
NMe2
4
1
2
L
L
-
-
-
108.48(8)
10á.48(8)
85.36(13)
111.66(9)
136.13(13)
85.35(16)
94.09(15)
129.89(19)
78.12(2)
105.25(11)
123.47(6)
81.98(19)
Scheme 1. Synthesis of N→Ga coordinated organogallium chalcogenides 1 - 5
Single crystals suitable for X-ray diffraction analysis (XRD) of
, 2·2(C ), 4 and 5·C were obtained from saturated
1
7
H
8
7 8
H
toluene/hexane solutions of the parent complexes at room
temperature or at 4°C for 4. The molecular structures are shown in
Figures 1 and 2, respectively; selected bond lengths and angles are
given in Table 1. Crystallographic data are summarized in Table S1
in the Supplementary material.
1

In the case of molecular structure L Ga( -Se
4
) (4), monomeric
4
arrangement with five membered GaSe ring was observed.
1
Figure 1. PovRay presentation of molecular structures of [L Ga(-Se)]
2
(1) and
2
1

[
L Ga(-Se)]
2
(2). Hydrogen and solvate molecules are omitted.
Figure 2. PovRay presentation of molecular structures of L Ga( -Se
L1Ga)
(-Te )(-Te) (5). Hydrogen and solvate molecules are omitted.
4
) (4) and
(
2
2
The molecular structures of 1 and 2 revealed dimeric nature of
The Ga1 atom is five-coordinated by carbon and both nitrogens
of the ligand L and by two Se atoms of ( -Se ) fragment. The C1,
4
Se1 and Se2 atoms form an equatorial plane, while both nitrogens
are in axial positions (N1-Ga1-N2 155.2(2)°) of the distorted
trigonal-bipyramidal arrangement of the Ga1 atom. The presence of
N→Ga coordination is demonstrated by bond distances Ga1–N1/N2
1
,2
[
L Ga(-Se)]
2
with central four member Ga
2
Se
2
core without any
1

substantial effect of the ligand. The Ga atoms in 1 and 2 are four-
coordinated by carbon and one nitrogen (the Ga1–N1 distances are
1
,2
2
.130(3) Å for 1 and 2) atom of the L ligands and by two selenide
atoms. In both cases, the coordination arrangement of the Ga atoms
can be defined as distorted tetrahedron. Found values for C1–Ga1–
N1 bond angles (85.36(13) for 1 and 85.35(16)° for 2) thus represent
the largest deviation from an ideal shape. The Ga1–N2 bond
distances (4.383(3) Å) also suggests no coordination of second
=
2.445(5)/ 2.371(5) Å, respectively. Compound 3 represents the
first structurally characterized organogallium complex containing
GaSe
4
fragment, with Se−Se bond lengths ranging from 2.3252(10)
1
to 2.3463(10). It seems that the presence of the ligand L is crucial
for the isolation of this fragment since similar ( -S
also isolated in related L Ga( -S ).
4
1
nitrogen atom of L ligand in 1. Dimeric structures of 1 and 2 are

4
) fragment was
analogous to gallium selenides [RGa(µ
2
-Se)]
2
(R is
, (Mes =
core are
1

[16]
{
2
(Me
,4,6-Me
3
Si)
2
C(Ph)C(Me
3
Si)N}) and [(Mes)C
6
H
7
NGa(µ
2
-Se)]
2
[
17]
3
-C
6
2
H )
but tetrameric cubanes with Ga
18]
4
Se
4
[
more pronounced. The Ga-Se bond lengths in 1 and 2 (the range
2
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Chemistry - A European Journal
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Isolation of 4 is rare evidence of the stabilization of tetraselenide
Figure 3. a) SEM image, b) AFM image of the surface of 1500 rpm spin-coated
2
chain by 13 group elements, and inorganic indium polyselenides
GaSe thin films fabricated using [L Ga(μ-Se)]
2
SSP.

4-

2-
[
In
2
( Se
4
)
4
(-Se
5
)] or [In( Se
4
)(-Se)]
2
are probably the
[
19]
closest analogues of 3.
Neutral organometallic tetraselenide
Elemental and SEM EDX analysis of the GaSe thin layer
revealed content of carbon and nitrogen at levels bellow 10 and 1
analogues of the main group elements are known, however. Tokitho

et al., reported synthesis of tetraselenagermolanes Tbt(Tip)Ge( -
atomic %, respectively (see Table S2 and S3 in SI), similarly to

[18a]
Se
tris[bis(trimethylsilyl)methyl]phenyl
mterphenyl, Tip = 2,4,6-triisopropylphenyl).
4
)
and stanolanes Tbt(Ditp)Sn( -Se
4
)
=
(Tbt
2,2''-diisopropyl-
=
2,4,6-
2 3 3 4
Ga Se material obtained by LPCVD from [Cp*Ga(μ -Se)] .
,
Ditp
Energy dispersive X-ray (EDX) spectroscopy revealed that the
composition of the resulting semiconducting thin film is Ga54.9Se45.1
for 1500 rpm and Ga54.2Se45.8 for 2000 rpm respectively, suggesting
minimal dependence of the chemical composition of the deposited
material on the spinning speed (see Table 2). The ratio of Ga/Se
atoms in 2 is therefore retained in the prepared GaSe thin film.
[
20]
While dimeric organogallium selenides 1 - 2 are stable, this is
not the case for the parent telluride 3. This complex is sensitive on
1
light and it rearranges to unprecedented complex (L Ga)
2
(-Te )(-
2
2-
2 3
Te) (5), where the five membered Ga Te ring contains telluride Te
2
-
and ditelluride (Te
2
)
fragment. Both Ga atoms in 5 are four-
1
coordinated by nitrogen and carbon atom of the L ligand and by
Optical functions of prepared GaSe layers as well as their
thicknesses were obtained from the analysis of variable angle
spectroscopic ellipsometry (VASE) data measured using an
ellipsometer with automatic rotating analyzer within samples grown
on silicon substrates. The thickness of the as-dried GaSe thin film is
dependent on the spinning speed and ranges from 23.7±0.9 to
50.1±0.5 nm (see Table 2).
two telluride atoms (the range of Ga–Te distances is 2.5423(6) -
2
.5872(6) Å). Complex
characterized compound with M
group elements. There is one similar silicon-tellurium-
heterocycle reported by Jutzi et al., who reported the reaction of
decamethylsilicocen (Cp*) Si with Bu PTe, that provided the
,2,4,3,5-tritelluradisilol (Cp*Si) (-Te )(-Te) (Cp*
pentamethylcyclopentadienyl). The Te–Te bond length in the
later complex is 2.681(1), somewhat shorter than in 5 (2.7366(6) Å).
5
represents the first structurally
2
3
Te fragment in the chemistry of
1
3
2
3
1
2
2
=
[
21]
Table 2. Characteristics of spin coated GaSe films deposited at 1000, 1500 and
2000 rpm: chemical composition (±1 at. %), film thickness, refractive index (at λ = 1.5
μm), optical band gap (Eopt) and root-mean-square (RMS) roughness values.
1
13
1
All compounds were also characterized by H and C{ H}
NMR spectroscopy and data are consistent with the structures. The 3
1
→
5 rearrangement can be monitored by the H spectroscopy, where
2
the singlet of CH groups at δ 3.63 ppm of 3 is slowly changing to
AB spin system at δ 3.40 ppm of 5 (Figures S29 and 30 in SI).
Spinning speed (rpm)
Property
000(a)
(b)
2000(b)
1
1500
Ga (at. %), determined via EDX
51.5
48.5
54.9
45.1
54.2
45.8
Se (at. %), determined via EDX
film thickness (nm), determined
via VASE
refractive index, determined via
VASE
Deposition of GaSe thin films by spin coating using 2 as SSP
2
11.6 ±1.5
.96±0.01
23.7±0.9
50.1±0.5
Due to the non-stability of 3, stable complexes 1, 2 and 4 were
studied as potential SSPs for gallium selenide deposition having
Ga/Se atoms in 1/1 or 1/4 ratio. The thermogravimetric analyses
showed the multistep decomposition of 1 and 4, while compound 2
starts decomposing at 250ºC and continues till 320ºC as one step
decomposition (see Figures S1-3 in SI). For 2, comparison of
observed (62%) mass losses with total expected (65%) indicate
smooth formation of GaSe. Previously, we have reported on the
deposition of amorphous GaS material from N→Ga coordinated
organogallium sulfides by spin-coating method, where the complex
1
2.23±0.01
2.26±0.01
E
opt [eV], determined by VASE
2.27±0.05
12.87±0.01
2.42±0.1
8.09±0.01
2.41±0.1
6.39±0.01
RMS (nm), determined via AFM
2 2
(a) prepared from propylamine/CH Cl solution of 2, (b) prepared from
propylamine solution of 2,
The refractive index found for amorphous GaSe thin films
range from n = 2.23 to 2.26 at λ = 1.5 μm (see Table 2, and Figure
4
GaSe thin films produced by vacuum evaporation (n ≈ 2.41 at λ =
1.6
). Importantly, this value is close to those found for amorphous
[
22]
1
1
[16]
μm).
Moreover,
when
more
concentrated
[
L Ga(-S)]
3
with different ligand L was the most suitable.
was dissolved in
-
1
propylamine/CH
2
2
Cl solution of 2 (c = 0.09 mol.l ) was used for the
Similarly to this process, compound
2
-
1
preparation of the amorphous GaSe thin film, thickness of this as-
dried film was 211.5±1.5 nm (Table 2). To conclude, the thickness
and optical band gap energy (Eopt) of the as-dried GaSe thin films
were dependent on the spinning speeds (1000-2000 rpm) and range
from 23.7±0.9 to 211.6±1.46 nm and Eopt = 2.27±0.05 to 2.42±0.1
eV, respectively (see Table 2). To compare, GaSe thin films
produced by vacuum evaporation presented band gap corresponding
to the amorphous phase (Tauc’s procedure) of ~1.93 eV and the
propylamine (c = 0.06 mol.l ) and used as SSP for the preparation
of GaSe thin films by spin coating (for experimental details see SI).
All prepared GaSe thin films were amorphous, as detected by XRD
(Figure S4 in SI). The scanning electron microscopy (SEM) (Fig. 3a,
for different magnifications see Figure S31) and atomic force
microscopy (AFM) (Fig. 3b) images showed relatively smooth
surface of thin films with root mean square roughness lower than ~
1
3 nm.
[
22]
direct bandgap value of ~2.15eV.
3
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Chemistry - A European Journal
10.1002/chem.201802688
Figure 4. Typical dispersion of the refractive index of spin-coated GaSe thin film
(1500 rpm)
The refractive index for all prepared amorphous GaSe thin films
n ≈ 1.96-2.26 at λ = 1.5 μm, Table 2, Figure 4) is comparable to
(
those found for vacuum evaporated GaSe films (n ≈ 2.41 at λ = 1.6
μm) noting that the chemical composition of the latter was probably
9
richer in selenium content due to the fact that GaSe starting
material was used.
Figure 5. SEM images of Ga
2
Se
3
material obtained from octadecylamine solution (a)
[
22]
and octadecylamine/PVP solution (b) of 2.
Application of 2 for doping of Bi
2 3
Se
The needles have an average length of 550 ± 150 nm. Moreover,
the addition of PVP into the octadecylamine solution of 2 provided
the crystalline monoclinic Ga Se in the form of agglomerated
2 3
particles. By analyses of sets of SEM images, it was revealed that
the agglomerated particles have an average diameter of 600 ± 150
Since the thermogravimetric analyses suggested low temperature of
the decomposition of 2, the attempts to prepare GaSe material by the
heating of the solution of SSP 2 were carried out. Heating of
octadecylamine solution of 2 at 350°C provided, after work up, the
nm (Figure 5b). Thus, during the reaction yielding Ga
influences the structure of the resulting material,
2
Se3, PVP
but has no
influence on the crystallinity of the resulting material (as apparent
from XRD shown in Figure S10 in SI). The monoclinic Ga Se
material was also obtained from selenoether complexes of GaCl by
crystalline monoclinic Ga
S5, S6 in SI). Similar results were also obtained by Barron, who
prepared Ga Se material after the annealing at higher temperatures
starting from [Cp*Ga(-Se)]
2 3
Se , identified by XRD and EDX (Figures
[
28]
2
3
2
3
[18a]
4
.
Optical diffuse reflectance
3
UV/Vis/NIR spectroscopy was performed for the Ga34.7Se65.3 to
estimate the optical band gap energy Eopt = 2.56±0.05 eV (Figure S7
[
13]
LPCVD method,
while cubic phase of Ga
2
Se
3
was obtained by
[
13]
[11]
CVD deposition from [Cp*Ga(-Se)]
4
or [Me Ga(SePiPr ) N].
2 2 2
[
23]
in SI).
This value is higher than value for macroscopic cubic
Their peak broadening translated to crystalline domains of
approximately 68 and 24 Å for Ga Se , respectively.
[
24]
single crystal (~2.07 eV) but corresponds well to the band gap
values of zigzag-line vacancy-ordered crystal Ga
2
3
[25]
2 3
Se (~2.56 eV).
Raman spectrum (Figure S8 in SI) is formed by the sharp intensive
band peaking at ~150 cm corresponding to the localized breathing
motion of Se atoms around Ga vacancies in the vacancy ordered
Since the heating of solution of 2 can smoothly provide
monoclinic Ga Se material, we wondered if SSP 2 can be used as
organometallic way of doping of semiconductors. For a preliminary
check of this idea, we performed the doping study on Bi Se . This
material, used widely as a component of thermoelectric (TE)
-
1
2
3
1
[26a]
monoclinic Ga
~
the crystalline Ga
2
Se
3
crystalline phase (A 1g mode).
The bands at
2
3
250 and ~290 cm- represent longitudinal and transverse mode of
1
[
26b]
2
Se
3
and corresponds to a group of at least
[
29]
materials,
elements (5N purity, Sigma-Aldrich) at 720°C for 1 hour in quartz
ampoules. The synthetized Bi Se material was air-quenched to
room temperature and powdered in agate mortar. The bulk of Bi Se
was added to the octadecylamine solution of 2 that has been used as
a source of Ga Se for the doping of Bi Se (for experimental details
was synthetized by heating stoichiometric mixture of
three vibrational modes with various symmetry representations (A
, B ) that have been assigned to localized vibrational modes of
vacancy-disordered Ga
1
,
B
1
2
2
3
[
26c,d]
2
Se3.
Due to the lack of the signal at 115
2
3
-
1
cm responsible to the Ga-O bond, we can deduce low degree of
[
27]
oxidation, if any. The histogram of the hydrodynamic diameter
of the re-dispersed powder has bimodal character with the higher
population at the 500 – 600 nm (60% of the cumulative intensity)
Figure S9 in SI). The SEM analysis indicates that the Ga Se
3
2
3
2
3
D
H
see SI). The suspension was heated to 350°C for 60 minutes and an
isolated material was compacted in a graphite die using hot-pressing
technique (T=480°C and p=75 MPa) which provides rectangular
(
2
material is formed as an interesting needle-like structure, as shown
in Fig. 5a.
3
samples of dimensions 3.5 x 1.7 x 15 mm . The samples were
characterized by measurement of electrical conductivity , Hall
H
coefficient R , and Seebeck coefficient S. The results are shortly
summarized in Figure 6 and Table 3 (for detailed measurements see
SI, Figures S11 – 17).
4
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Chemistry - A European Journal
10.1002/chem.201802688
nature of the ligand and compound 2 has been found as suitable SSP
for GaSe deposition only. The thin films of GaSe materials obtained
after thermal annealing are amorphous. The chemical composition,
film thickness, refractive index, Eopt and roughness values were
determined from EDX, VASE and AFM measurements within spin
coated GaSe films deposited at 1500, 2000, and 2500 rpm. The
obtained values fall into the regions reported for the GaSe materials
prepared by other techniques. Since the similar procedure was also
previously applied for the preparation of amorphous GaS material, it
seem that this method can be useful for synthesis of amorphous
semiconducting thin layers using the organometallic compounds as
SSPs. In addition, TG analysis also suggested the possible suitability
-
1
5
3
1
7
6
5
2
S (V.K )
5 -1 -1
-
60
90

(10  .m )
19 -3
N (10 cm )
2
-1 -1
ln  (cm V s )
H
-
1
0
-
120
2 3
of 2 for the thermal synthesis of the crystalline Ga Se material. The
0
2
4
6
8
10
heating of ODA of 2 provided a needle-like structure with an
average length of 550 ± 150 nm. Moreover, the complex 2 has been
x (% Ga Se )
2
3
2
also used as the doping agent for Bi Se3. The results indicate that
this way of doping is well comparable with direct melt doping.
More importantly, this way of doping opens the possibility to
Figure 6. Seebeck coefficient S, electrical conductivity , concentration of free
carriers N and Hall electron mobility of free carriers ln  as a function of content
Ga Se in Bi Se at 400 K.
H
2 3
introduce nanoinclusions of foreign phases (GaSe, Ga Se ,
2
3
2
3
[
32]
2 4
Ga BiSe ), which can enhance TE properties markedly.
We observed a moderate increase of the electron concentration.
This increase could be ascribed to formation of gallium interstitials
It should be noted that despite the presence of different ligands
L1,2 both organogallium selenides [L Ga(μ-Se)]
1,2
are dimers with
2
[
30]
within Bi
high
2
Se
permittivity matrix
The electron concentration seems to saturate for
3
structure.
Namely, the
become ionised in
2 2
four membered Ga Se ring, where the gallium atoms are four
coordinated due to one N→Ga coordination. On the other hand, the
the
according to
equation
.
evidence for multi-step decomposition of 1 suggests, that the
higher concentrations of Ga. The electrical conductivity peaks for
the lowest concentration of Ga and then decreases as a result of
competing increase of electron concentration and decreasing Hall
electron mobility µ =R . Accordingly, the Seebeck coefficient
H H
decreases with increasing Ga concentration. The Hall mobility
1
presence of the second CH
2
NMe
2
group in ligand L makes the
2 2
cleavage more difficult and the existence of the second CH NMe
group starts additional eliminations in the SSP. The mechanism is
however still unknown. On the other hand, it is also evident, that the
1
presence of L ligand is crucial for the stabilization of five
decreases monotonically with concentration of Ga due to increasing
membered GaSe
4
ring with five coordinated central atom. As the
number of defects
(for SEM images see Figure S32) that is in
result of two N→Ga coordination in 3, this SSP does not decompose
accordance with results obtained on Ga-doped single crystals.[30] The
formation of Ga interstitials is clearly in accordance with saturation
of electron concentration as evidenced by transport measurements.
1
,2
in one step, similarly to 1. Ligands L were not able to stabilize
parent organogallium tellurides. Therefore, we are currently
developing sterically demanding C,N-chelating ligands.
It is worth mentioning that when 87 mg of 2 (contain 30 mg of
Experimental Section
GaSe) has been used for doping of 1g of Bi
2 3
Se , the formation of
Supporting Information. Experimental details, NMR spectra for prepared complexes,
new phase Ga BiSe has been observed according to XRD
2
4
crystallographic parameters, XRD data of the Ga
X Y
Se materials (CCDC nos. 1823353-
examinations (Figure S18 in SI). This suggests that the above
developed method may be also suitable for the preparation of
uncommon phases, since this phase was not observed in the
1
823356 for 1, 2·2(C ), 4 and 5·C , respectively), Raman spectra, XRF spectra,
7
H
8
7 8
H
Variable Angle Spectroscopic Ellipsometry (VASE).
previous studies, where Ga
2
Bi
4 7 4 4 9
Se , Ga Bi Se phases were observed
[
31]
Acknowledgements
only.
Generally, no foreign phases within the doping process are
observed. Here, the doping process consists mostly in diffusion of
Ga to interstitial positions since the doping is performed well below
melting temperature.
We are grateful to the Czech Science Foundation (project no. 18-03823S) for supporting
this work. This work was also supported by the Ministry of Education, Youth and
Sports of the Czech Republic.(project LM2015082). We would like to thank K. Ruzicka
for TG analysis and Mrs. L. Hromadko for SEM analyses, respectively.
Conclusion
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Table 3. Results of XRD analysis of samples after hot pressing: content Ga, lattice parameters a, c, V, impurities, the relative density (it is defined as a ratio experimental/theoretical
densities); and transport parameters: Seebeck coefficient S, electrical conductivity , Hall coefficient R , mobility ln  and concentration of free charge carriers N at 400K.
H
H
w %
Ga Se
at x %
Ga Se
3
V [Å3]
foreign
phase
3
-1
N [1019cm-3]
-1
-1 -1
2
-1 -1
a [Å]
c [Å]
/
t
S [VK ]
-111.7
-59.7
[ m ]
R
H
[cm C ] ln 
H
(cm V s )
2
3
2
0
1
3
5
0
4.13894
4.13962
4.13849
4.13976
28.6365
28.63383
28.63683
28.63169
424.844
424.944
424.756
424.940
96%
98%
94%
91%
114026
209477
82720
80444
-0.516
-0.173
-0.239
-0.191
6.378
1.2
3.6
2.6
3.3
1.8
5.2
8.7
5.895
3.4%
-69.1
5.289
Ga
2
BiSe
4
-80.6
5.034
6
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Chemistry - A European Journal
10.1002/chem.201802688
Entry for the Table of Contents
Single Source Precursor
a
a
Tomáš Řičica , Libor Dostál ,
a
Zdenka Růžičková , Ludvík
Beneš , Petr Němec , Marek
Bouška , Jan M. Macak , Petr
Knotek , Pavlína Ruleová and
a
b
b
c
a
a
a
Roman Jambor *
Synthesis, structure and application
of intramolecularly coordinated
gallium chalcogenides: Suitable
Synthesis of gallium chalcogenides
with Ga Se , GaSe or Ga Te rings
is shown. Dimeric specie has been
successfully applied for amorphous
GaSe thin film preparation as well as
2
2
4
2
3
for doping of Bi
temperature doping
2
Se
3
. New low
process
single source precursors for Ga
materials
x y
Se
provided evidence of new phase
Ga BiSe
2
4
.
7
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