Strategy of solution process precursors for phase change memory

Article abstract of DOI:10.1016/j.poly.2019.114289

In this study, the relationship between the steric hindrance of the alpha carbon substituent group of aminoalkoxy ligand and formation of germanium telluride (GeTe) and antimony telluride (Sb₂Te₃) was elucidated. A series of germaniu

Full text of DOI:10.1016/j.poly.2019.114289

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Strategy of Solution Process Precursors for Phase Change Memory
Jeong Min Hwang, Ji Hun Lee, Hyo-Suk Kim, Chan Woo Park, Dagyum Yoo,
Bo Keun Park, Chang Gyoun Kim, Taek-Mo Chung
PII:
S0277-5387(19)30734-X
https://doi.org/10.1016/j.poly.2019.114289
POLY 114289
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Reference:
Polyhedron
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21 November 2019
Please cite this article as: J.M. Hwang, J.H. Lee, H-S. Kim, C.W. Park, D. Yoo, B.K. Park, C.G. Kim, T-M. Chung,
Strategy of Solution Process Precursors for Phase Change Memory, Polyhedron (2019), doi: https://doi.org/10.1016/
j.poly.2019.114289
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Synthetic Strategy of Solution Process Precursors for Phase Change Memory
Jeong Min Hwang+a, Ji Hun Lee+a, Hyo-Suk Kim+a, Chan Woo Parka,b, Dagyum Yooa,c, Bo Keun
Parka,c, Chang Gyoun Kima, and Taek-Mo Chung*a,c
aThin Film Materials Research Center, Korea Research Institute of Chemical Technology
141 Gajeongro, Yuseong, Daejeon 34114, Republic of Korea
bDepartment of Chemistry, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic
of Korea
cDepartment of Advanced Materials and Chemical Engineering, University of Science and
Technology (UST), 217 Gajeong-ro
+ These authors contributed equally
Tel: +82-042-860-7359
E-mail: tmchung@krict.re.kr
ABSTRACT. In this study, the relationship between the steric hindrance of the alpha carbon
substituent group of aminoalkoxy ligand and formation of germanium telluride (GeTe) and
1

antimony telluride (Sb2Te3) was elucidated. A series of germanium and antimony precursors was
prepared using aminoalkoxide-type bidentate ligands of different sizes such as dmampH, dmapH
and dmaeH. These precursor materials were further treated with bis(trimethylsilyl)tellurium in
hexadecane through thermal reaction and studied with powder X-ray diffraction (pXRD) to
compare the formation of germanium telluride (GeTe) and antimony telluride (Sb2Te3) alloys
which are potential precursor materials for phase change random access memory devices. While
the pXRD patterns of the thermal reaction materials of compounds 2 and 3 at 190 °C revealed a
rhombohedral phase of GeTe and tellurium, compounds 5 and 6 at 190 °C showed a
rhombohedral phase of Sb2Te3 and tellurium at this temperature. These results suggested that
the formation of chalcogenide alloys was more favorable when relatively less bulk ligand was
used.
Keywords: Aminoalkoxy Ligand; Antimony Telluride; Germanium Telluride; Phase Change
Random Access Memory; Precursor Chemistry
1. INTRODUCTION
Materials that exist in two distinct states, either amorphous or crystalline phases, and are
capable of switching between them are known as phase change materials. Previous research has
revealed that the crystalline and amorphous phases of such materials can be switched repeatedly
at a desired operating temperature. Owing to the different electrical properties of the material in
its different phases, the materials are able to store information. This feature reflects the
2

tremendous potential of phase change materials for application in the field of information
technology. These materials are have gained widespread recognition owing to their application in
rewritable optical phase change storage system such as CDs and DVDs, and current aspiration for
these materials include developing phase change random access memory (PCRAM) devices as a
next generation data storage technology. Novel phase change materials must demonstrate non-
volatile memory and also compete with flash memory drives in terms of high read and write
speeds in dynamic random access memory (DRAM) [1-3].
For example, chalcogenides, non-metallic group 16 elements, are known to be suitable for
PCRAM devices as they exhibit numerous glass transition and melting temperatures, which gives
them different electrical resistivities. This property allows chalcogenides to exist in two different
phases, i.e., amorphous and crystalline. Typically, when applied as a binary state device, the
amorphous phase can represent the ‘OFF’ state logic of ‘0’ by having high resistance while the
crystalline phase represents the ‘ON’ state logic of ‘1’ by having a lower resistance [4-6].
Switching of the resistance state from high to low can be achieved by applying voltage that is
higher than the threshold voltage. On the other hand, it can be reversed by applying current
through the memory device while the material is being heated above its melting point to return to
its amorphous status.
Among the various materials reported to date, the alloy of Ge and Sb, Ge2Sb2Te5 (GST225), is
a widely known general phase change material for PCRAM devices. It is a pseudo binary
compound, GeTe−Sb2Te3, made up of Ge material that has good data stability and Sb material
with fast switching speeds [7-14].
Recently, the synthesis of nanostructured metal chalcogenide materials by solution processing
3

has been reported. Previous research has mainly focused on the synthesis of crystalline metal
chalcogenide nanomaterials by thermal decomposition of single metal precursors [15-17].
However, it is difficult to control the atomic ratio of the desired materials using single source
materials. Therefore, studies on dual source materials, i.e., using separate metal and chalcogen
sources, have been performed [17-21]. While various organometallic precursors have been
studied to obtain these materials, aminoalkoxide-based complexes are garnered interest owing to
their good reactivity with the chalcogen source in a solution reaction. These complexes have also
been used as precursors for atomic layer deposition and chemical vapor deposition for metal
oxide thin film growth [22-25].
In recent years, extensive studies have been conducted on the synthesis of metal chalcogenides
by solution processing using aminoalkoxide precursors and its mechanism [26,27]. Schulz et al.
reported the synthesis and mechanism of antimony and germanium telluride materials from the
reaction of aminoalkoxide complexes of antimony and germanium with Te(SiEt3)2.
Aminoalkoxide-containing precursors were reacted with Te(SiEt3)2 to generate antimony
telluride or germanium telluride with silyl ether, Et3SiOC2H4Me2, as a byproduct in
diisopropylbenzene (DIPB) under inert conditions and studied using temperature dependent in
situ 1H NMR.
Our group recently attempted the synthesis of GeTe using a Ge precursor with an
aminoalkoxide ligand, i.e., Ge(dmamp)2, (dmampH = 1-(dimethylamino)-2-methylpropan-2-ol).
Interestingly, the reaction of this precursor with bis(trimethylsilyl)tellurium was unsuccessful and
GeTe was not formed. This was probably attributable to the sterically bulky α-carbon substituents
of the aminoalkoxy ligand that prevented bond formation between silicon and oxygen, as shown
4

in Fig. 1.
Fig 1. Synthetic mechanism of GeTe
To elucidate the phenomena described above, we compared aminoalkoxide-based precursors
with different substituents. Since the solution process is a convenient and well-established
method, the reactivity of various aminoalkoxide-based precursors with dialkylsilyl tellurium was
investigated to compare the electronic and steric effects of the ligands and identify the best
organic ligands for alternative precursors. Herein, we report the preparation of germanium
precursors, Ge(dmamp)2 (1), Ge(dmap)2 (2), and Ge(dmae)2 (3), and antimony precursors,
Sb(dmamp)3 (4), Sb(dmap)3 (5), and Sb(dmae)3 (6). These precursors were used for thermal
reactions with bis(trimethylsilyl)tellurium in hexadecane to form chalcogenide alloys for
PCRAM devices by varying the sizes of the aminoalkoxide ligands (dmapH = 1-
(dimethylamino)propan-2-ol, dmaeH = 2-(dimethylamino)ethan-1-ol). All of the synthesized
materials were characterized by powder X-ray diffraction (pXRD) studies to track the
relationship between the steric effect and hindrance to the formation of GeTe and Sb2Te3. Results
from pXRD revealed that the reason for the failure of formation GeTe from Ge(dmamp)2 was
due to the hindrance effect of methyl groups when compared with the successful formation of
germanium telluride (GeTe) and antimony telluride (Sb2Te3) using relatively smaller ligands
5

used during the thermal reaction.
Chart 1. Aminoalkoxide type ligands used in this study
2. Experimental
All manipulations were performed under a dry, oxygen-free nitrogen or argon atmosphere
using standard Schleck techniques or in a glove box. All solvents were purified by the Innovative
Technology PS-MD-4 solvent purification system. All reagents were purchased from Sigma
Aldrich
and/or
Acros.
Functionalized
bidentate
amino
alcohols,
dmampH,
(CH3)2NCH2C(CH3)2OH, and Na(dmamp) were prepared according to a literature procedure [24].
Na(dmap) and Na(dmae) were prepared following a similar procedure as for Na(dmamp).
Ge(dmamp)2 was synthesized by modifying a previously reported method[28]. Although
Ge(dmae)2 and Sb(dmae)3 compounds are known, they were synthesized following the same
method as for Ge(dmamp) [29,30]. Ge(dmap)2 and Ge(dmae)2 were prepared by a similar
procedure as for Ge(dmamp)2. Sb(dmamp)3 was obtained by modifying reported methods [31,32].
1
13
Sb(dmap)3 and Sb(dmae)3 were prepared in a similar manner as Sb(dmamp)3. H NMR and C
NMR spectra were recorded on Bruker DPX 500 MHz FT-NMR spectrometer. All samples for
NMR measurements were contained in sealed NMR tubes and referenced using benzene-d6 as the
standard. Powder X-ray diffraction (pXRD) patterns of the materials obtained by thermal reaction
of the complexes were measured using a Rigaku D/Max-2200 V X-ray diffractometer operating
at 40 kV and 40 nA using Cu Kα as the target.
6

2.1. Preparation of starting materials
Na(dmamp). dmampH (5.1 g, 43.5 mmol) was slowly added to a suspension of sodium (1.0 g,
43.5 mmol) in hexane (50 mL) at 0 °C, and the mixture was allowed to reflux overnight. After
cooling to room temperature, the solvent was removed to obtain Na(dmamp) as a white powder
1
(5.3 g, 87%). H NMR (C6D6, 500 MHz): δ 1.23 (s, 6H, OC(CH3)2), 2.24 (s, 8H, N(CH3)2 and
CH2).
Na(dmap). dmapH (8.9 g, 87 mmol) was slowly added to a suspension of sodium (2.0 g, 87
mmol) in hexane (100 mL) at 0 °C, and the mixture was allowed to reflux overnight. After
cooling to room temperature, the solvent was removed to obtain Na(dmap) as a white powder
1
(8.9 g, 82%). H NMR (C6D6, 500 MHz): δ 1.25 (d, 3H, OCCH3), 2.03 (d, 1H, NCH2), 2.20 (t,
1H, NCH2), 2.25 (s, 6H, N(CH3)2), 4.28 (m, 1H, OCH).
Na(dmae). dmaeH (7.7 g, 87 mmol) was slowly added to a suspension of sodium (2.0 g, 87
mmol) in hexane (100 mL) at 0 °C, and the mixture was allowed to reflux overnight. After
cooling to room temperature, the solvent was removed to obtain Na(dmae) as a white powder
1
(7.7 g. 80%). H NMR (C6D6, 500 MHz): δ 2.30 (s, 6H, N(CH3)2), 2.50 (t, 2H, NCH2), 4.15 (t,
2H, OCH2).
2.2. Preparation of germanium complexes 1−3)
Ge(dmamp)2 (1). GeCl2·dioxane (0.80 g, 3.50 mmol) was slowly added to a solution of
Na(dmamp) (1.0 g, 7.30 mmol) in hexane. The reaction mixture was allowed to stir overnight at
room temperature. After filtering the mixture to remove the salts, the filtrate was concentrated in
7

vacuo to afford the desired product. Pure product was obtained as a colorless liquid by
1
distillation under vacuum (80 °C/0.5 Torr). Yield: 0.9 g (81%); H NMR (C6D6, 500 MHz): δ
1.37 (s, 6H, OC(CH3)2), 2.25 (s, 6H, N(CH3)2), 2.31 (s, 2H, CH2N).
Ge(dmap)2 (2). GeCl2·dioxane (1.0 g, 4.30 mmol) was slowly added to a solution of Na(dmap)
(1.1 g, 8.8 mmol) in hexane. The reaction mixture was allowed to stir overnight at room
temperature. After filtering the resultant solution, the filtrate was concentrated in vacuo to afford
the product. Pure product was obtained as a colorless liquid by distillation under vacuum
(80 °C/0.5 Torr). Yield: 0.77 g (65%); 1H NMR (C6D6, 500 MHz): δ 1.09 (d, 3H, OCCH3), 1.76
(d, 1H, NCH2), 1.92 (s, 6H, N(CH3)2), 2.00 (t, 1H, NCH2), 3.66 (m, 1H, OCH). 13C NMR (C6D6,
125 MHz): δ 23.4 (N(CH3)2), 43.7 (NCH2), 66.2 (OCH), 68.1 (CHCH3). IR (KBr, cm−1): 830,
945, 1026, 1145, 1346, 1457, 2568, 2638, 2776, 2818, 2850, 2640. Anal. Calcd. for
C10H24N2O2Ge: C, 43.4; H, 8.73; N, 10.11%. Found: C, 42.5; H, 8.14; N, 9.12%.
Ge(dmae)2 (3). GeCl2·dioxane (1.0 g, 4.30 mmol) was slowly added to a solution of Na(dmae)
(1.0 g, 8.90 mmol) in hexane. The reaction mixture was allowed to stir overnight at room
temperature. The mixture was subsequently filtered to remove the salts and the filtrate was
1
concentrated in vacuo to afford the product as white solid. Yield: 0.99 g (93%); H NMR (C6D6,
13
500 MHz): δ 2.23 (s, 6H, N(CH3)2), 2.43 (t, 2H, NCH2), 3.92 (t, 2H, OCH2). C NMR (C6D6,
125 MHz): δ 45.9 (N(CH3)2), 61.8 (NCH2), 66.9 (OCH2). IR (KBr, cm−1): 776, 876, 945, 1035,
1123, 1276, 1370, 1455, 1616, 2517, 2600, 2663, 2773, 2942. Anal. Calcd. for C8H20N2O2Ge: C,
38.6; H, 8.10; N, 11.3%. Found: C, 39.2; H, 9.03; N, 11.7%.
2.3. Preparation of Ge(dmatfp)2
8

Ge(dmatfp)2 was synthesized by modifying the synthetic method of Ge(dmamp)2. GeCl2·dioxane
(3.2 g, 14 mmol) was slowly added to a solution of Na(dmatfp) (5.0 g, 28 mmol) in
tetrahydrofuran (THF). The reaction mixture was allowed to stir overnight at room temperature.
Subsequently, the mixture was filtered to remove salts, and the filtrate was concentrated in vacuo
to afford the desired product. Pure product was obtained as a white solid by sublimation under
vacuum (90 °C/0.5 Torr). Yield: 4.0 g (75%); 1H NMR (C6D6, 500 MHz): δ 1.86 (s, 7H, N(CH3)2,
CH2N), 2.83 (t, 1H, CH2N), 4.19 (br, 1H, OCH(CF3)). 13C NMR (C6D6, 125 MHz): δ 56.8
(N(CH3)2), 72.7 (NCH2), 73.1 (OCH), 124.8 (CHCF3).
2.4. Preparation of antimony complexes 4−6
Sb(dmamp)3 (4). SbCl3 (1.0 g, 4.40 mmol) was slowly added to a solution of Na(dmamp) (2.0 g,
14.60 mmol) in hexane. The reaction mixture was allowed to stir overnight at room temperature
and then filtered to remove salts. The filtrate was concentrated in vacuo to afford the desired
product. The pure product was obtained as a colorless liquid by distillation under vacuum
1
condition (120 °C/0.5 Torr). Yield: 1.57 g (76%); H NMR (C6D6, 500 MHz): δ 1.50 (s, 6H,
C(CH3)2), 2.25 (s, 6H, N(CH3)2), 2.45 (s, 2H, CH2N).
Sb(dmap)3 (5). SbCl3 (1.2 g, 5.30 mmol) was slowly added to a solution of Na(dmap) (2.0 g,
16.00 mmol) in hexane. The reaction mixture was allowed to stir overnight at room temperature.
After filtering the resulting solution, the filtrate was concentrated in vacuo to afford the product
1
as a white solid. Yield: 2.07 g (91%); H NMR (C6D6, 500 MHz): δ 1.24 (d, 3H, OCCH3), 1.96
(d, 1H, NCH2), 2.19 (s, 6H, N(CH3)2), 2.27 (t, 1H, NCH2), 4.12 (br, 1H, OCH). 13C NMR (C6D6,
125 MHz): δ 23.4 (N(CH3)2), 43.7 (NCH2), 66.2 (OCH), 68.1 (CHCH3). Melting point : 71 °C.
IR (KBr, cm−1): 499, 578, 612, 698, 773, 945, 983, 1037, 1144, 1176, 1206, 1311, 1456, 2780,
9

2821, 2845, 2946. Anal. Calcd. for C15H36N3O3Sb: C, 32.0; H, 8.47; N, 9.81%. Found: C, 33.5;
H, 7.26; N, 9.11%.
Sb(dmae)3 (6). SbCl3 (1.3 g, 5.70 mmol) was slowly added to a solution of Na(dmae) (2.0 g,
18.00 mmol) in hexane. The reaction mixture was allowed to stir overnight at room temperature.
After removing the salts by filtration, the filtrate was concentrated in vacuo to afford the desired
1
product as a white solid. Yield: 1.23 g (56%); H NMR (C6D6, 500 MHz): δ 2.30 (s, 6H,
N(CH3)2), 2.47 (br, 2H, NCH2), 4.07 (br, 2H, OCH2). 13C NMR (C6D6, 125 MHz): δ 45.7
(N(CH3)2), 61.5 (NCH2), 66.3 (OCH2). IR (KBr, cm−1): 574, 776, 876, 946, 1035, 1121, 1277,
1370, 1456, 1614, 2664, 2730, 2774, 2817, 2849, 2944, 2974. Anal. Calcd. for C12H30N3O3Sb: C,
37.5; H, 7.83; N, 10.9%. Found: C, 37.5; H, 8.14; N, 9.73%.
2.4. Thermal reaction of prepared compounds
The thermal reaction was conducted according to a literature procedure [26]. Germanium
complexes (3.5 mmol) and bis(trimethylsilyl)tellurium (1 mL, 3.5 mmol) were added to
hexadecane (19 mL, 64.6 mmol) at room temperature. The solution was heated overnight at
150 °C or 190 °C under a nitrogen atmosphere. Subsequently, the reaction mixture was cooled to
room temperature and centrifuged at 10,000 rpm for 7 min. The obtained black precipitates were
washed three times with toluene.
Ge(dmatfp)2 (3.5 mmol) and bis(trimethylsilyl)tellurium (1 mL, 3.5 mmol) were mixed in
hexadecane (19 mL, 64.6 mmol) at room temperature. The solution was heated overnight at
150 °C or 190 °C under nitrogen. The reaction mixture was subsequently cooled to room
10

temperature and centrifuged at 10,000 rpm for 7 min. The obtained black precipitates were
washed thrice with toluene.
Antimony complexes (2.4 mmol) and bis(trimethylsilyl)tellurium (1 mL, 3.5 mmol) were
added to hexadecane (19 mL, 64.6 mmol) at room temperature. The solution was heated
overnight at 190 °C under nitrogen atmosphere. Subsequently, the reaction mixture was cooled to
room temperature and centrifuged at 10,000 rpm for 7 min. The obtained black precipitates were
washed with toluene three times.
All synthesized materials were characterized by powder X-ray diffraction (pXRD) to study the
relationship between the steric effect and formation of GeTe and Sb2Te3 from the thermal
reaction.
3. RESULTS AND DISCUSSION
Scheme 1. Synthesis of germanium complexes (1-3) and antimony complexes (4-6)
Scheme 1 summarizes the synthesis of Ge and Sb-containing compounds prepared in this
study. Reaction of GeCl2·dioxane with 2 equivalents of Na(dmamp) afforded a colorless liquid,
11

Ge(dmamp)2 (1), which was purified by vacuum distillation (90 °C/0.5 Torr), in 81% yield [28].
Ge(dmap)2 (2) and Ge(dmae)2 (3) were synthesized following a similar procedure as for 1. For
these complexes, Na(dmap) and Na(dmae) were used instead of Na(dmamp). Complexes 2 and 3
were obtained as a colorless liquid and white solid in 65% and 93% yields, respectively (Scheme
1). Reaction of SbCl3 with 3 equivalents of Na(dmamp) afforded a colorless liquid, Sb(dmamp)3
(4), which was purified by vacuum distillation (120 °C/0.5 Torr), in 76% yield [31]. Sb(dmap)3
(5) and Sb(dmae)3 (6) were prepared by following a similar procedure as for 4. Complexes 5 and
1
6 were obtained as white solids in 91% and 56% yields, respectively (Scheme 1). The H NMR
spectrum of complex 1 recorded in benzene-d6 showed three singlets at 1.37 ppm (OC(CH3)2),
2.25 ppm (N(CH3)2), and 2.31 ppm (CH2), which were shifted downfield with respect to
Na(dmamp) (δH = 1.23 ppm (OC(CH3)2), 2.24 ppm (N(CH3)2, CH2)). In the case of complex 2,
the signals for the OCCH3, NCH2, N(CH3)2, and OCH groups of the dmap ligand appeared as a
doublet at 1.09 ppm, doublet at 1.76 ppm and triplet at 2.00 ppm, singlet at 1.92 ppm, and a
multiplet at 3.66 ppm, respectively. These peaks were shifted upfield as compared to those of
Na(dmap) (δH = 1.25 ppm (OCCH3), 2.03 ppm (NCH2), 2.20 ppm (NCH2), 2.25 ppm(N(CH3)2,
and 4.28 ppm (OCH)). Further, complex 3 was characterized by a singlet at 2.23 ppm (N(CH3)2)
and two triplets at 2.43 ppm (NCH2) and 3.92 ppm (OCH2), which were upfield with respect to
1
Na(dmae) (δH = 2.30 ppm (N(CH3)2), 2.50 ppm (NCH2), 4.15 (OCH2)). The H NMR spectrum
of complex 4 showed three singlets at 1.50, 2.25, and 2.45 ppm, which corresponded to
OC(CH3)2, N(CH3)2, and CH2 groups, respectively, and downfield with respect to Na(dmamp).
For complex 5, the OCCH3 and N(CH3)2 peaks of the dmap ligand appeared as a doublet at 1.24
ppm and singlet at 2.19 ppm, respectively. The NCH2 protons appeared as two distinctive peaks,
12

one at 1.96 ppm as a doublet and another at 2.27 ppm as a triplet. The OCH proton appeared as a
broad peak at 4.12 ppm. These NMR signals were shifted upfield in comparison to Na(dmap).
The 1H NMR spectrum of complex 6 showed a singlet at 2.30 ppm, and two broad peaks at 2.47
ppm and 4.07 ppm, which corresponded to N(CH3)2, NCH2, and OCH2 groups, respectively.
These signals were upfield with respect to the proton peaks of Na(dmae).
3.1. Thermal decomposition reaction of preparing germanium telluride complexes (GeTe)
Scheme 2. Synthesis of germanium telluride and antimony telluride using complexes (1-3) and
antimony complexes (4-6).
The preparation of germanium telluride (GeTe) using the germanium complexes 1−3 and bis(tr
imethylsilyl)tellurium were investigated in hexadecane at 150 °C and 190 °C (Scheme 2). The p
XRD patterns of the materials by thermal reaction of complexes 1−3 in the presence of bis(trimet
hylsilyl)tellurium are shown in Fig. 2. The pXRD patterns of the thermal reaction products betwe
en complexes 1−3 with bis(trimethylsilyl)tellurium at 150 °C were confirmed to be only telluriu
m (JCPDS Card No: 97-004-0041) (Fig. S9). The pXRD pattern of the reaction products of comp
lex 1 at 190 °C displayed only the hexagonal phase of tellurium (JCPDS Card No: 97-004-0041).
13

It is well known that Te(SiMe3)2 is thermally unstable and decomposes in solution at high temper
atures with subsequent formation of tellurium. Te(SiMe3)2 did not react with Ge precursors and si
mply decomposed to tellurium [33,34]. In contrast, the pXRD patterns of the materials formed in
the thermal reaction of 2 and 3 at 190 °C were confirmed to be the rhombohedral phase of GeTe (
JCPDS Card No: 01-071-4854) and tellurium. Additionally, the EDS results of the materials obta
ined by the thermal reaction at 190 °C displayed GeTe (Ge:Te = 28:43) in complex 2 and GeTe (
Ge:Te = 25:47) in complex 3. GeTe was formed at a temperature at which Te(SiMe3)2 could react
with the Ge precursors without pyrolysis.
Fig 2. pXRD pattern of thermal reaction products of germanium complexes (1-3) at 190 ºC.
Additional experiments were conducted to clearly define the substituent structural steric hindran
ce effect of the α-carbon of the aminoalkoxy ligand on the resulting GeTe. For this purpose, germ
anium compounds containing −CF3 as the substituent, Ge(dmatfp)2, was synthesized using amino
alkoxide ligands with same skeleton as dmapH (dmatfpH = 3-(dimethylamino)-1,1,1-trifluoropro
pan-2-ol) [35,36]. The thermal generation of GeTe was investigated to identify whether the result
14

ing compounds were affected by the electronic effects through the thermal reaction of the Ge(dm
atfp)2 with bis(trimethylsilyl)tellurium in the same way as in the previous experiment. The pXRD
pattern of the materials synthesized by the thermal reaction of Ge(dmatfp)2 and bis(trimethylsilyl)
tellurium at 190 °C was confirmed to be the rhombohedral phase of GeTe (JCPDS Card No: 01-0
71-4854) and tellurium (JCPDS Card No: 97-004-0041) (Fig. S10). EDS analysis of the material
s formed by the thermal reaction of Ge(dmatfp)2 and bis(trimethylsilyl)tellurium at 190 °C showe
d GeTe where Ge:Te was 17:31. Therefore, we concluded that the steric hindrance on the α-carbo
n of the aminoalkoxy ligand was a more important factor than the electronic effects in the therma
l synthesis of GeTe.
3.2. Thermal decomposition reaction of preparing antimony telluride complexes (Sb2Te3)
Antimony telluride (Sb2Te3) was synthesized by reacting the antimony complexes 4−6 with
bis(trimethylsilyl)tellurium via thermal treatment in hexadecane at 190 °C (Fig. 3). The pXRD
pattern of the product in the case of complex 4 confirmed it as tellurium (JCPDS Card No: 01-
086-2268). Similarly, Te(SiMe3)2 did not react with Sb(dmamp)3 and simply decomposed to
tellurium. In contrast, the pXRD patterns of the materials formed in the thermal reaction of 5 and
6 were confirmed as coexisting rhombohedral phase of Sb2Te3 (JCPDS Card No: 01-071-0393)
and hexagonal phase of tellurium. Moreover, EDS of the obtained materials confirmed the
formation of Sb2Te3 (Sb:Te = 12:27) and Sb2Te3 (Sb:Te = 21:36) from complexes 5 and 6,
respectively.
15

Fig 3. pXRD pattern of thermal reaction products of antimony complexes (4-6) at 190 ºC.
4. CONCLUSIONS
Germanium and antimony complexes containing aminoalkoxide ligands were synthesized and
used for the preparation of germanium telluride (GeTe) and antimony telluride (Sb2Te3) by
thermal reaction in the presence of bis(trimethylsilyl)tellurium in solution. The pXRD patterns of
the thermal reaction products of germanium and antimony compounds at 190 °C revealed a
mixture of rhombohedral GeTe and Sb2Te3, which had good yields with complexes having the
least substituted ligands on the alkoxy carbon of aminoalkoxides. These results showed that the
steric hindrance on the alkoxy carbon should be removed while designing organic ligands to
obtain better properties of germanium and antimony precursors for PCRAM devices
■ ASSOCIATED CONTENT
Supporting information
16

1H and 13C NMR spectra of complexes 1-6, pXRD patterns of resultants of 1-3 at 150 °C, pXRD
patterns of resultants of Ge(dmatfp)2 are provided in the supporting information.
■ AUTHOR INFORMATION
Corresponding Authors
*E-mail: tmchung@krict.re.kr
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENT
This research was supported by a Grant from the Development of smart chemical materials for
IoT devices Project through the Korea Research Institute of Chemical Technology (KRICT) of
Republic of Korea (SI1921-20).
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20

Series of germanium and antimony precursors with varying α−carbon substituent group were
synthesized. Prepared substances were further converted into GeTe or Sb2Te3 by thermal reaction
to elucidate the size and electronic effects of α−carbon substituent suggesting that less bulky
group leads to better conversion of desired complexes.
21