Deposi ion o MoSe
2
flakes using cyclic selenides†
Ja osla Cha o ,
a
Raul Zazpe,
bc
Richa d K umpolec,
d
Jhona an Rod iguez-
Pe ei a,
bc
Da id Pa liˇ
n´
ak,
d
Daniel Poko n´
y,
a
Milan Klika ,
a
Ve onika Jel´
ınko ´
a,
e
Jan M. Macak
bc
and Filip Bu eˇ
s*
ae
The cu en ly limi ed po olio o ola ile o ganoselenium compounds used o a omic laye deposi ion
(ALD) has been ex ended by designing and p epa ing a se ies o ou -, fi e- and six-membe ed cyclic
silylselenides. Thei undamen al p ope ies we e ailo ed by al e na ing he ing size, he numbe o
embedded Se a oms and he used pe iphe al alkyl chains. In con as o o me p epa a ions based on
o ma ion o sodium o li hium selenides, he newly de eloped syn he ic me hod u ilizes a di ec and
easy eac ion o elemen al selenium wi h chlo osilanes. No el 2,2,4,4- e aisop opyl-1,3,2,4-
diselenadisile ane, which ea u es good ade-offbe ween chemical/ he mal s abili y and eac i i y, has
been success ully used o gas- o-solid phase eac ion wi h MoCl
5
affo ding MoSe
2
. A ho ough
cha ac e iza ion o he as-deposi ed 2D MoSe
2
flakes e ealed i s ou -o -plane o ien a ion and high
pu i y. Hence, he de eloped ou -membe ed cyclic silylselenide u ned ou o be well-sui ed Se-
p ecu so o ALD o MoSe
2
.
In oduc ion
Despi e ha ing been de eloped mo e han 50 yea s ago, A omic
Laye Deposi ion (ALD), a hin-lm manu ac u ing echnology,
1
s ill a ac s g owing a en ion wo ldwide.
2
This is due o ALD's
unique ad an ages including high uni o mi y o p epa ed
nanolaye s,
3
p ecise hickness con ol
4
o possibili y o co e
non-plana subs a es like nano ubes.
5
A eac ion be ween
a gaseous p ecu so and ee unc ional g oups o he selec ed
subs a e ensu es accu a e deposi ion o a omic monolaye wi h
minimum o de ec s. On he con a y, exclusi e gas- o-solid
phase eac ion is also one o he bigges ALD limi a ion. Fo
such eac ion, a p ecu so o sufficien ola ili y and he mal
s abili y wi h pe sis ing high eac i i y is essen ial. Finding
a comp omise be ween he a o emen ioned p ope ies is
usually no a simple ask.
T ansi ion me al dichalcogenides (TMDC) o m laye ed
c ys al s uc u es ea u ing chalcogen–me al–chalcogen uni s
bound ia co alen bonds. S oichiome ic MX
2
monolaye s
in e ac s ia weak an de Waals o ces dependen on he
selec ed me al (M), chalcogen (X) and hei sup amolecula
a angemen .
6
TMDC a e oen semiconduc o s wi h a na ow
band gap –an in e es ing abili y exploi able in elec onics,
elec oca alysis o pho oca alysis, especially in wa e spli ing o
hyd ogen e olu ion eac ions (HER). In addi ion o widely
explo ed pe o mance o MoS
2
in he HER,
7,8
MoSe
2
,
9
GaSe
( e . 10) o WSe
2
( e . 11) showed also p omising esul s. Bis-
( ialkylsilyl)selenides
12
a e cu en ly he mos a ou i e ALD
selenium p ecu so s used o deposi ion o he la e selenides.
Recen ly, selenium dime hyldi hioca bama e was success ully
used o deposi ion o Sb
2
Se
3
as p esen ed by Sa ka .
13
Ou
esea ch g oup in oduced bis( ialkyls anyl)selenides
14
and
cyclic silylselenides
15
as Se-p ecu so s wi h dec eased sensi i i y
owa ds ai and mois u e. Six-membe ed selenide con aining
wo selenium a oms u ned ou o be he bes p ecu so so a .
This p omp ed us o explo e he amily o cyclic silylselenides
bea ing mo e selenium a oms u he .
Resul s and discussion
Syn hesis
The gene al eac ion pa hway owa ds cyclic silylselenides is
ou lined in Scheme 1. The syn hesis and he mal p ope ies o 1
( e . 16) 2( e . 17) and 3( e . 17) we e epo ed ea lie , see also
ou ecen communica ion o comp ehensi e cha ac e iza-
ion.
15
The gene al me hodology u ilizes Li
2
Se, p epa ed om
elemen al Se and i s eac ion wi h Li o LiBHE
3
and subsequen
a
Ins i u e o O ganic Chemis y and Technology, Facul y o Chemical Technology,
Uni e si y o Pa dubice, S uden sk´
a 573, Pa dubice, 53210, Czech Republic. E-mail:
[email p o ec ed]
b
Cen e o Ma e ials and Nano echnologies, Facul y o Chemical Technology,
Uni e si y o Pa dubice, N´
am.
ˇ
Cs. Legi´
ı565, Pa dubice, 53002, Czech Republic
c
Cen al Eu opean Ins i u e o Technology, B no Uni e si y o Technology, Pu kyˇ
no a
123, B no, 61200, Czech Republic
d
Depa men o Physical Elec onics, CEPLANT—R&D Cen e o Plasma and
Nano echnology Su ace Modica ions, Facul y o Science, Masa yk Uni e si y,
Ko l´
aˇ
sk´
a 267/2, 61137 B no, Czech Republic
e
The Ins i u e o Technology and Business in
ˇ
Cesk´
e Budˇ
ejo ice, Ok uˇ
zn´
ı517/10, 370
01,
ˇ
Cesk´
e Budˇ
ejo ice, Czech Republic
†Elec onic supplemen a y in o ma ion (ESI) a ailable: Fu he syn he ic de ails,
NMR spec a, GC/MS eco ds, DSC/TGA cu es, SEM pic u es, Raman spec a and
XPS spec a. See DOI: 10.1039/d0 a10239c
Ci e his: RSC Ad .,2021,11, 22140
Recei ed 4 h Decembe 2020
Accep ed 17 h June 2021
DOI: 10.1039/d0 a10239c
sc.li/ sc-ad ances
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eac ion wi h app op ia e dichlo osilane (Me hod A). Compa ed
o o me ly p epa ed 3, he syn hesis o asymme ic compound
4s a s om inexpensi e silanes and affo ds highe yield along
wi h mo e ola ile selenide. No el ou -membe ed cycle 6con-
aining wo selenium a oms was p epa ed in he same way in
almos quan i a i e yield, which signican ly acili a ed i s
isola ion.
Using bulkie Bu
2
SiCl
2
ga e no eac ion al hough he eac-
ion empe a u e was ele a ed o BF
3
$OE
2
was added. On he
con a y, he eac ion wi h Me
2
SiCl
2
ga e e ame hyl-
subs i u ed ou -membe ed cycle simila ly o 6(as moni o ed
by GC/MS). Howe e , i s e y eac i e na u e made i s isola ion
e y difficul e en when a s ic ine a mosphe e was main-
ained. Te ae hyl de i a i e 5showed signican ly imp o ed
s abili y and acile isola ion bu i s NMR showed a mix u e o
wo p oduc s gi ing almos he same signals wi h only small
diffe ence in chemical shis (see he ESI†). On he con a y, no
o he p oduc was de ec ed by GC/MS. The o me p epa a ion
o 5employing Na
2
Se ins ead o Li
2
Se epo ed also o ma ion
o six-membe ed cycle con aining h ee Se a oms in 40% yield.
18
Hence, we p epa ed Na
2
Se, by eac ing Se wi h NaBHE
3
, which
was subsequen ly ea ed wi h E
2
SiCl
2
o iP
2
SiCl
2
(Me hod B)
o affo d simila mix u e o 5and exclusi ely 6. Compounds 5
and 6o he same quali y we e p epa ed ega dless using Na
2
Se
o Li
2
Se and none six-membe ed cycle was de ec ed in bo h
cases. All o ou a emp s o isola e and iden i y he unknown
compound p epa ed along wi h 5 ailed. Since ou main goal is
o design simple selenium p ecu so o ALD wi h easy
syn hesis and isola ion, we ha e excluded 5 om u he
s udies. When compa ing bo h eac ions using Na
2
Se o Li
2
Se
(Me hods B o A), he la e showed be e yields. Employing
Me hod A, e aisop opyl cyclic selenide 6can be p epa ed and
isola ed almos quan i a i ely.
Selenium can be educed o silylselenoles o bis( ialkyl)
selenides using ialkylsilanes. This was  s ly epo ed o
E
3
Si–SeH ( e . 19) and cHex
3
Si–SeH ( e . 20) and la e also o
o he silanes as demons a ed in ou ecen wo k.
21
Based on
hese obse a ions, we de eloped a new syn he ic me hod
owa ds ou -membe ed cycles 6and 7, which u ilizes a di ec
eac ion o elemen al selenium wi h dialkylchlo osilanes in he
p esence o amine (Me hod C). Compa ed o syn hesis o o me
silylselenoles ca ied ou a 250 C wi hin 48 h, he newly
de eloped me hod equi es only sligh ly aised eac ion
empe a u e (120 C) and sho eac ion ime (3 h). Mo eo e , i
u ilizes eadily a ailable and inexpensi e s a ing ma e ials,
a oids eac i e li hium species and e en excludes sol en s.
Scheme 1 Reac ion pa hway owa ds cyclic silylselenides.
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Pu ica ion o p oduc s 6and 7is simple and in ol es only
l a ion and c ys alliza ion a 78 C. De i a i e 6is s able and
can wi hs and ambien condi ions o se e al hou s o e en
days in case o 7. I s o ed unde an ine a mosphe e a 5C,
no deg ada ion was obse ed ae se e al mon hs. These
p ope ies make 6and 7 e y p omising Se-p ecu so s o ALD.
A low-yielding (11%) pho ochemical p epa a ion o 7including
i s X- ay s uc u e has been o me ly epo ed by Saak e al.
22
De i a i e 6was p epa ed o he  s ime. A simila eac ion
wi h Me
2
SiHCl p o ided a a ie y o p oduc s, which amoun s
depend on he used empe a u e and canno be easily isola ed.
A small amoun o he a o emen ioned six-membe ed cycle was
de ec ed i he eac ion was ca ied ou unde ele a ed
empe a u e o 250 C (see he ESI† o mo e de ails). S uc u e
and pu i y o he p epa ed silylselenides ha e been con med
by
1
H/
13
C/
29
Si/
77
Se NMR and GC/MS analysis (see he ESI† o
de ails).
The mal p ope ies
Besides easy syn hesis and acile isola ion, he mal s abili y and
ola ili y a e c ucial p ope ies o ALD p ecu so s. The mal
p ope ies o selenides 4–7we e s udied by DSC and TG analysis
a a mosphe ic p essu e; o he mal p ope ies o 1–3see ou
p e ious communica ion.
15
DSC he mog ams a e shown in
Fig. 1 and Table 1 ( o comple e eco ds including bo h cooling/
hea ing p og ams see Fig. S22–S25 in he ESI†). Liquid 4was
 s ly cooled o 100 C, while he sample solidied amo -
phously a a ound 90 C. I s e e se hea ing e ealed cold
c ys alliza ion a 62 C ollowed by b oad mel ing p ocess
appea ing a 21 C. The sample began o e apo a e a a ound
+150 C and was comple ely e apo a ed a +210 C. The DSC o
liquid 5showed wo peaks o c ys alliza ion a 0 and 64 C
unde cooling as well as wo mel ing p ocesses (b oad a +2 and
sha p a 63 C) unde hea ing p og am. This is mos p obably
due o a o emen ioned mix u e. Ne e heless, he sample was
comple ely e apo a ed a +265 C. Selenide 6unde wen c ys-
alliza ion ollowed by mel ing ha appea ed a +3 and +32 C. I
was e apo a ed be ween 220 and 285 C. Analogical he mal
beha io was eco ded o 7, which ea u es highe he mal
obus ness (T
m
¼170 C, T
c
¼157 C) and comple e e apo a ion
a 315 C. The TGA shown in Fig. 1 co obo a es he DSC
measu emen s and con med he good ola ili y o a ge
o ganoselenides (see also Fig. S26–S29 in he ESI†). The highes /
lowes ola ili y was obse ed o de i a i e 4/7subs i u ed wi h
me hyl/ bu yl alkyl chains, which implies ha he mal p ope -
ies o 1–7a e easily unable by p ope alkyl subs i u ion.
Mo eo e , ze o esidues we e de ec ed ae TGA indica ing
sufficien he mal s abili y du ing hea ing.
P epa a ion o MoSe
2
akes by ALD
In ou ecen wo k on MoSe
2
deposi ion by ALD,
15
we ha e
iden ied ha six-membe ed silylselenides bea ing wo sele-
nium a oms pe o med be e han  e-membe ed analogues.
Especially compound 3showed ou s anding pe o mance in
MoSe
2
deposi ion. Hence, we ha e selec ed selenide 6as
a model compound o su ace eac ion wi h MoCl
5
and depo-
si ion o MoSe
2
. I ea u es ou -membe ed s uc u e bea ing
wo selenium a oms and acile p epa a ion, easy isola ion, good
ola ili y and he highes a ained yields using Me hods A–C.
The deposi ion o MoSe
2
has been ca ied ou in a cus om
he mal ALD sys em (see Expe imen al pa o ALD p ocess
de ails). Glass, annealed i anium oil (wi h TiO
2
su ace in he
ana ase phase) and silicon wa e (wi h SiO
2
su ace) we e used
as subs a es. The ALD cycle was comp ised o ou s eps
desc ibed as ollows: Se p ecu so (800 ms)–N
2
pu ge (5 s)–Mo
p ecu so (800 ms)–N
2
pu ge (5 s). The numbe o cycles applied
we e 800 and he deposi ion empe a u e was 300 C (de ailed
desc ip ion in Expe imen al sec ion). The mo phology and
s uc u e o he as-deposi ed MoSe
2
on he diffe en subs a es
was cha ac e ized by means o scanning elec on mic oscope
(SEM) as displayed in Fig. 2. The ein, one can obse e he MoSe
2
g ew as 2D aky nanoshee s, mainly o ien ed ou -o -plane.
ALD p ocesses applying same numbe o cycles bu diffe en
Se dose, namely 400 and 1200 ms (while keeping Mo dose
800 ms), we e conduc ed in o de o e i y he sel -limi ing
Fig. 1 TGA ( op) and DSC (bo om) eco ds o 4(g een), 5(black), 6
( ed) and 7(blue).
Table 1 Fundamen al he mal p ope ies o s udied cyclic selenides
4–7
Comp. T
ca
[C] T
mb
[C] T
Ec
[C]
462 21 +150 o +210
564/0 63/+2 +160 o +265
6+3 +32 +220 o +285
7+157 +170 +250 o +315
a
Tempe a u e o c ys alliza ion.
b
Tempe a u e o mel ing.
c
Range o
e apo a ion.
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na u e o he p ocess. Co esponding SEM op iew images om
annealed Ti oils and Si wa e , oge he wi h he SEM c oss-
sec ion o he Si wa e , a e shown in he Fig. S30.†The ein,
he MoSe
2
deposi ed applying a Se dose o 800 and 1200 ms
showed simila ea u es, i.e. he densi y and size o MoSe
2
akes, indica ing a sa u a ion egime and con ming he sel -
limi ing na u e o he p ocess.
Addi ionally, he deposi ion empe a u e dependence was
s udied conduc ing ALD p ocesses (800 cycles) a diffe en
empe a u es, 250 and 200 C (in addi ion o 300 C). In con as
o 2D aky c ys alli es ob ained a 250 C, he as-deposi ed
MoSe
2
a 200 C exhibi ed g anula mo phology (see Fig. S31†
o he co esponding SEM images). These esul s e ealed
a he mal dependence o as-deposi ed MoSe
2
mo phology.
G azing Inciden X-Ray Diff ac ome y (GI-XRD) cha ac e -
iza ion o as-deposi ed MoSe
2
a 300 C p o ided he co e-
sponding GI-XRD pa e ns on he diffe en subs a es shown in
he Fig. 3. The pa e ns clea ly exhibi ed diff ac ion peaks a 2q
13.5, which ma ched well wi h he (002) plane o hexagonal
(2H) MoSe
2
, and con med he p esence o MoSe
2
wi h ou -o -
plane o ien a ion in line wi h he SEM images.
The as-deposi ed MoSe
2
s uc u e was u he cha ac e ized
by means o Raman spec oscopy, a pa amoun echnique o
he assessmen o laye ed ma e ials. The co esponding Raman
spec a and ob ained om as-deposi ed MoSe
2
a 300 C (see
Fig. 4) and 200 and 250 C (see Fig. S32†) exhibi ed cha ac e -
is ic 2H-MoSe
2
peaks, namely, A
1g
(ou -o -plane) and E
1
2g
(in-
plane) modes a 238 and 285 cm
1
, espec i ely.
23
The ew-laye ed na u e o he deposi ed 2D MoSe
2
was
con med by he ed shio he A
1g
peak as compa ed o he
peak posi ion o MoSe
2
powde (242 cm
1
), while he obse ed
diffe ence in he ela i e in ensi ies be ween he A
1g
and
E
1
2g
modes indica ed he p e ailing ou -o -plane o ien a ion, as
obse ed in he SEM images and XRD esul s.
24
Fig. 2 SEM op images a wo diffe en magnifica ions o he as-
deposi ed ALD MoSe
2
a 300 C upon 800 cycles (800 ms Se dose) on
diffe en subs a es. The as-deposi ed MoSe
2
shows 2D flaky nano-
shee s mo phology mainly ou -o -plane o ien ed.
Fig. 3 XRD pa e ns o he as-deposi ed ALD MoSe
2
on diffe en
subs a es upon 800 ALD cycles (800 ms Se dose). The plane (002)
e ealed he ou -o -plane o ien a ion o he as-deposi ed ALD MoSe
2
a 300 C onTianium oil ( op), silicon wa e (middle) and glass (down).
Fig. 4 Raman spec a ob ained om ( op) MoSe
2
powde and as-
deposi ed ALD MoSe
2
on i anium oil (middle) and glass (down) a
300 C upon 800 ALD cycles (800 ms Se dose).
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X- ay Pho oelec on Spec oscopy (XPS) analysis was con-
duc ed o assess he su ace chemical composi ion o he as-
deposi ed MoSe
2
. He e, i is impo an o no e ha he use o
ad en i ious ca bon (284.8 eV) as a e e ence o adjus he
binding ene gy scale was no eliable, basically due o he s ong
o e lapping o C 1s signal wi h Se LMM. Ins ead, he binding
ene gy o Mo 3d a 228.3 eV co esponding o MoSe
2
was used
o his pu pose.
25,26
Fig. S33†shows he XPS su ey spec a o
MoSe
2
deposi ed a 300 C on glass, annealed Ti oils and Si
wa e , whe eas Fig. S34†exhibi s he XPS su ey spec a ob-
ained o MoSe
2
deposi ed a 200 and 250 C on Si wa e . The
lecolumn in Fig. 5, shows he decon olu ion o he XPS high
esolu ion spec a o Mo 3d ob ained om as-deposi ed ALD
MoSe
2
a 300 C on he diffe en subs a es. The mos in ense
double s (o ange) cen e ed a 228.3 and 231.4 eV co esponds o
Mo(IV)–Se, co obo a ing he g ow h o MoSe
2
. The peaks a
229.9 and 233.0 eV (g een) we e a ibu ed o Mo–Se–O. Ac ually,
he p esence o Mo–Se–O bonds e idences bo h he chemical
eac ion o he Se p ecu so wi h he hyd oxyl g oups om he
subs a es su ace, and he pos e io eac ion o he esul ing
chemiso bed coun e pa wi h he Mo p ecu so . The las
double a 232.5 and 235.7 eV (blue) was associa ed wi h
Mo(VI)–O, o igina ed upon he eac ion o MoCl
5
wi h he
hyd oxyl g oups om he subs a e su ace du ing he ea ly
s age o he deposi ion p ocess. Rega ding he decon olu ion o
he XPS high esolu ion spec a o Se 3d ( igh column o Fig. 5),
i exhibi ed ou componen s asc ibed o wo Se 3d
5/2
and Se
3d
3/2
spin–o bi spli ing. The  s and mos in ense double
loca ed a 53.8 and 54.7 eV, co esponding o Mo–Se bonds,
which unambiguously co obo a ed he g ow h o MoSe
2
. And
he second double wi h he peaks cen e ed a 55.2 and 56.1 eV,
a ibu ed o Mo–Se–O, con ming he p esence o his species
in Mo 3d. Rega ding he MoSe
2
deposi ed a 250 C (see
Fig. S35†) he decon olu ed XPS high esolu ion spec a o Mo
3d and Se 3d exhibi ed he same ea u es han hose desc ibed
o MoSe
2
deposi ed a 300 C. In con as , he MoSe
2
deposi ed
a 200 C (Fig. S35†) displayed a double a 54.7 and 55.6 eV in
he Se 3d decon olu ed XPS high esolu ion spec a asc ibed o
Se–Se o Se
0
. This would sugges ha he chemical eac ion
be ween he Mo and Se p ecu so s could be he mally limi ed a
a deposi ion empe a u e o 200 C.
As compa ed o he XPS esul s ob ained in ou p e ious
wo k om he MoSe
2
deposi ed using selenides 1and 3,
15
one
mus no ice ele an diffe ences: (i) he absence o chlo ine
esidues (mainly p esen by Mo–Cl species) and (ii) he well-
dened Se 3d double . Those diffe ences sugges ed he
absence o impu i ies (o he chemical species) and comple e
ligand exchange eac ion be ween selenide 6and MoCl
5
esul ing in a high pu i y as-deposi ed ALD MoSe
2
.
Conclusions
In summa y, we ha e in es iga ed a se ies o ou -,  e- and six-
membe ed cyclic silylselenides as po en ial Se-p ecu so s o
ALD. They we e p epa ed in a s aigh o wa d manne
employing elemen al selenium and chlo osilanes. The sol en -
ee Me hod C, which s a s om Se and comme cially a ail-
able and inexpensi e chlo osilanes, is in pa icula ope a ion-
ally e y simple, a oids gene a ion o li hium o sodium
selenides and affo ds ou -membe ed de i a i es 6and 7in
good yields o 77 and 61%, espec i ely. The pe o med DSC and
TG analysis e ealed ha ola ili y can be ailo ed by choosing
p ope pe iphe al alkyl subs i uen s. Especially no el silylsele-
nide 6bea ing isop opyl g oups showed e y good ade-off
be ween i s chemical s abili y and sufficien ola ili y. I s ALD
eac ion wi h MoCl
5
success ully p o ided 2D MoSe
2
nano-
shee s ha we e cha ac e ized by SEM, GI-XRD, Raman spec-
oscopy and XPS. Compa ed o p e ious silylselenides,
p ecu so 6showed comple e ligand exchange eac ion and i s
ALD affo ded MoSe
2
o high pu i y.
Expe imen al
The NMR and GC/MS spec a we e eco ded wi h a B uke
AVANCE 400 ins umen and a GC/EI-MS congu a ion
Fig. 5 XPS high- esolu ion spec a o Mo 3d (le ) and Se 3d ( igh )
co esponding o as-deposi ed ALD MoSe
2
upon 800 ALD cycles a
300 C (800 ms Se dose).
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including gas ch oma og aphy Agilen Technologies 6890N
(HP-5MS, 30 m column, I.D. 0.25 mm, lm 0.25 mm) equipped
wi h a mass de ec o Ne wo k MS de ec o 5973 (EI 70 eV, ange
33–550 Da). Me
4
Si and Me
2
Se we e used as in e nal s anda ds
o
1
H/
13
C/
29
Si and
77
Se NMR measu emen s (d¼0 ppm).
The mal p ope ies o a ge molecules we e measu ed by
diffe en ial scanning calo ime y (DSC) wi h a Me le -Toledo
STARe Sys em DSC 2/700 equipped wi h FRS 6 ce amic senso
and cooling sys em HUBER TC100-MT RC 23 o by he mog a-
ime ic analysis (TGA) wi h a Me le -Toledo STARe Sys em
TGA 2 equipped wi h a ho izon al u nace LF (400 W, 1100 C),
balance XP5 ( esolu ion 1 mg) and cooling sys em HUBER
Minichille 600. DSC he mog ams o he a ge compounds
we e measu ed in aluminous c ucibles wi h a small hole in he
lid unde N
2
ine a mosphe e. DSC cu es we e de e mined
wi h a scan a e o 5 C min
1
wi hin he ange 100 C o
+400 C.
The syn hesis and wo kup we e pe o med unde A a mo-
sphe e o in a ni ogen-lled glo ebox. All used sol en s we e
p ope ly d ied be o e use. The used glasswa e was pou ed in o
sodium hypochlo i e ba h o des oy emaining o ganic sele-
nides be o e cleaning.
Gene al me hod A
D y THF (40 ml) and ne selenium powde (1.0 g, 12.6 mmol)
we e placed o a 100 ml Schlenk ask. The suspension was
cooled o 0 C and LiBHE
3
(25.2 ml, 25.2 mmol, 1 M solu ion in
THF) was added slowly. The mix u e was s i ed a 25 C o 2 h
o ming whi e suspension o Li
2
Se. The co esponding dia-
lkyldichlo osilane (1 o 0.5 eq. o 5/6o 4) dissol ed in THF (10
ml) was added d opwise and he eac ion mix u e was s i ed a
25 C o 15 h. The sol en was e apo a ed in acuo, d y hexane
(30 ml) was added and he solu ion was l e ed ia a cannula.
The hexane solu ions o 4o 5we e e apo a ed in acuo and he
emaining yellowish oil was pu ied by acuum dis illa ion. The
hexane solu ion o 6was cooled o 78 C oaffo d colou less
solid, while he supe na an was emo ed ia a sy inge. The
nal p oduc was d ied in acuo.
Gene al me hod B
D y THF (40 ml) and ne selenium powde (1.0 g, 12.6 mmol)
we e placed o a 100 ml Schlenk ask. The suspension was
cooled o 0 C and NaBHE
3
(25.2 ml, 25.2 mmol, 1 M solu ion
in THF) was added slowly. The mix u e was s i ed a 25 C o
2 h o ming da k iole suspension o Na
2
Se. The emaining
p ocedu e is simila o Me hod A.
Gene al me hod C
Elemen al selenium (1.0 g, 12.6 mmol) along wi h dialkyl-
chlo osilane (1 eq.) and E NiP
2
(2.2 ml, 1.64 g, 12.6 mmol) we e
in oduced in o a p essu e essel lled wi h a gon and con-
aining a magne ic s i e . The mix u e was s i ed a 120 C o
3 h and hen was cooled o 25 C o solidi y. A second s i e was
added along wi h hexane (15 ml) and he mix u e was igo ously
s i ed and shook un il a yellow solu ion wi h a whi e p ecipi a e
we e o med. The mix u e was l e ed ia cannula and cooled o
78 C oaffo d yellowish c ys als, while he hexane was
emo ed ia a sy inge. The c ys al p oduc was d ied in acuo.
2,2,4,4,5,5-Hexame hyl-1,3,2,4,5-diselena isilolane (4)
The i le compound was p epa ed om Me
4
Si
2
Cl
2
(1.2 ml, 1.2 g,
6.3 mmol) and Me
2
SiCl
2
(0.8 ml, 0.8 g, 6.3 mmol) ollowing he
Me hod A. Yellowish liquid (1.6 g, 75%) wi h bp ¼95–100 C(1
o ).
1
H-NMR (400 MHz, 25 C, C
6
D
6
): d(
1
H) ¼0.45 (s, 12H,
CH
3
), 0.78 (s, 6H, CH
3
) ppm.
13
C-NMR APT (100 MHz, 25 C,
C
6
D
6
): d(
13
C) ¼0.6, 9.9 ppm.
29
Si-NMR (80 MHz, 25 C, C
6
D
6
):
d(
29
Si) ¼13.9, 24.9 ppm.
77
Se-NMR (76 MHz, 25 C, C
6
D
6
):
d(
77
Se) ¼303.5 ppm. EI-MS: m/z¼319 (30), 211 (20), 73 (100).
2,2,4,4-Te ae hyl-1,3,2,4-diselenadisile ane (5)
The i le compound was p epa ed om E
2
SiCl
2
(1.9 ml, 1.99 g,
12.6 mmol) ollowing he Me hod A (1.9 g, 92%) o Me hod B
(0.9 g, 43%). Compound 5was p epa ed as a mix u e wi h
insepa able impu i y. Yellow liquid wi h bp ¼120–140 C(1
o ). EI-MS: m/z¼332 (20, M
+
), 303 (100), 275 (30), 245 (20), 217
(20), 59 (10). Fo he NMR spec a see he ESI.†
2,2,4,4-Te aisop opyl-1,3,2,4-diselenadisile ane (6)
The i le compound was p epa ed om iP
2
SiCl
2
(2.3 ml, 2.3 g,
12.6 mmol) ollowing he Me hod A (2.4 g 99%) o Me hod B
(1.8 g, 72%). I was also p epa ed om iP
2
SiHCl (2.2 ml, 1.9 g,
12.6 mmol) ollowing he Me hod C (1.9 g, 81%). Yellowish
liquid.
1
H-NMR (400 MHz, 25 C, C
6
D
6
): d(
1
H) ¼1.15 (d, J¼
7 Hz, 24H, CH
3
), 1.21–1.30 (m, 4H, CH) ppm.
13
C-NMR APT (100
MHz, 25 C, C
6
D
6
): d(
13
C) ¼17.72, 18.37 ppm.
29
Si-NMR (80
MHz, 25 C, C
6
D
6
): d(
29
Si) ¼18.1 ppm.
77
Se-NMR (76 MHz,
25 C, C
6
D
6
): d(
77
Se) ¼402.33 ppm. EI-MS: m/z¼388 (10, M
+
),
345 (100), 303 (20), 275 (20), 231 (20), 59 (10).
2,2,4,4-Te a- e -bu yl-1,3,2,4-diselenadisile ane (7)
The i le compound was p epa ed om Bu
2
SiHCl (2.6 ml, 2.3 g,
12.6 mmol) ollowing he Me hod C (1.7 g, 61%). O ange c ys-
als.
1
H-NMR (400 MHz, 25 C, C
6
D
6
): d(
1
H) ¼1.23 (s, 36H,
CH
3
) ppm.
13
C-NMR APT (100 MHz, 25 C, C
6
D
6
): d(
13
C) ¼25.12,
29.19 ppm.
29
Si-NMR (80 MHz, 25 C, C
6
D
6
): d(
29
Si) ¼19 ppm.
77
Se-NMR (76 MHz, 25 C, C
6
D
6
): d(
77
Se) ¼321.9 ppm. EI-MS:
m/z¼387 (100), 345 (80), 246 (20), 57 (20).
Deposi ion o MoSe
2
The deposi ion o MoSe
2
was ca ied ou in a cus om-made
he mal ALD sys em applying a deposi ion empe a u e o
300 C a a chambe p essu e o 2 mba . The Mo p ecu so ,
MoCl
5
(S em, anhyd ous 99.6%), and syn hesized 6we e
hea ed up o ge sufficien ly high apou p essu e a 120 and
155 C, espec i ely. The p ecu so s-en iched ca ie gas was
deli e ed h ough sepa a e hea ed s ainless s eel lines (sepa a e
o each p ecu so ) di ec ly in o he cylind ical deposi ion
chambe o diame e 50 mm and leng h 300 mm. The
subs a es we e placed on he s ainless s eel holde o dimen-
sions 35 80 mm placed in he cen e o he p ecisely
empe a u e-con olled chambe . The MoSe
2
ALD p ocess
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s a ed immedia ely ae 5 pulses o ul apu e wa e , applied o
inc ease he numbe o hyd oxyl ac i e si es on he subs a es
su ace. The ALD cycle was comp ised o ou s eps desc ibed as
ollows: Se p ecu so (800 ms)–N
2
pu ge (5 s)–Mo p ecu so
(800 ms)–N
2
pu ge (5 s). The numbe o cycles applied was 800.
In pa allel, ALD p ocesses applying he same numbe o cycles
bu diffe en Se dose, namely 400 and 1200 ms ( o a xed Mo
dose o 800 ms) we e conduc ed in o de o e i y he sel -
limi ing na u e o p ocess. As o he deposi ion empe a u e
dependence, i was e alua ed by ALD p ocesses conduc ed a
200 and 250 C (in addi ion o 300 C). N
2
(99.999%) was used as
a ca ie gas. The p ecu so s we e boos ed om he hea ed
s anda d s ainless s eel bubble s (S em, ca alog no. 98-0276) a
aow a e o 40 s anda d cubic cen ime e pe minu e (sccm) in
all p ocesses.
MoSe
2
cha ac e iza ion
The s uc u e and mo phology o he as-deposi ed MoSe
2
we e
assessed by eld emission scanning elec on mic oscope (FE-
SEM JEOL JSM 7500F).
X- ay diff ac ion (XRD) analysis was ca ied ou using Pan-
aly ical Empy ean wi h Cu ube and Pixcel3D de ec o . G azing
incidence XRD was pe o med applying an inciden angle o 1
deg ee. The pa e ns we e eco ded in ange o 5
–65, s ep size
was 0.026 deg ee.
Raman mic o-spec ome e HORIBA LabRAM HR E olu ion
sys em coupled by wi h a con ocal mic oscope was o conduc
Raman measu emen s aken by 532 nm (g een) lase exci a ion
sou ce in he ange 100–500 cm
1
. All spec a we e ca e ully
co ec ed by baseline co ec ion and noise educ ion. Spikes
we e elimina ed by spec a accumula ion o manually in he
LabSpec 6 sowa e.
The su ace chemical composi ion o MoSe
2
was moni o ed
by X- ay pho oelec on spec oscopy (XPS) (ESCA2SR, Scien a-
Omic on) using a monoch oma ic Al Ka(1486.7 eV) X- ay
sou ce. Due o he s ong o e lapping o C 1s signal wi h Se
LMM, he binding ene gy scale was e e enced o he binding
ene gy o Mo 3d a 228.3 eV co esponding o MoSe
2
.
25,26
The
decon olu ion o he Mo 3d spec a included he use o eigh
componen s since Mo 3d has a s ong o e lapping wi h he Se
3s signal. F om hose, six componen s co esponded o he
h ee spin–o bi spli ing o Mo 3d, Mo 3d
5/2
and Mo 3d
3/2
,i.e.
h ee chemical species and he emaining wo co espond o Se
3s signals.
Conflic s o in e es
The e a e no conic s o decla e.
Au ho con ibu ions
Funding acquisi ion: FB, JMM; in es iga ion: JC, RZ, RK, JR-P,
DP, DP, MK, VJ; me hodology: JC, RZ; p ojec adminis a ion:
FB, JMM; w i ing –o iginal d a: JC, RZ; w i ing – e iew &
edi ing: FB.
Acknowledgemen s
This esea ch was suppo ed by he Czech Science Founda ion
(18-03881S) and he Minis y o Educa ion, You h and Spo s o
he Czech Republic (MEYS CR, p ojec s LM2018097, LQ1601,
LM2018103). We hank M L. H omadko o SEM
measu emen s.
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