Synthesis of ultra-thin copper nanowires using tris...
Transcript of Synthesis of ultra-thin copper nanowires using tris...
1
Supporting Information for:
Synthesis of ultra-thin copper nanowires using
tris(trimethylsilyl)silane for high-performance and low-haze
transparent conductors
Fan Cui, 1,2,3 Yi Yu,1,3 Letian Dou, 1,2,3 Jianwei Sun, 1,3 Qin Yang, 1 Christian
Schildknecht,2 Kerstin Schierle-Arndt2 and Peidong Yang1,2,3,4,5 *
1Department of Chemistry, University of California, Berkeley, CA 94720, USA. 2California
Research Alliance (CARA), BASF Corporation, Berkeley, CA 94720, USA. 3Materials Sciences
Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. 4Kavli Energy
NanoSciences Institute at the University of California, Berkeley and the Lawrence Berkeley
National Laboratory, Berkeley, California 94720, USA. 5Department of Materials Science and
Engineering, University of California at Berkeley, Berkeley, California 94720, USA.
*Correspondence and requests for materials should be addressed to P. Yang (email:
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Materials and Methods
Regents:
Tris(trimethylsilyl)silane (TTMSS, 97%), copper (II) chloride dihydrate (CuCl2·2H2O,
99.999%), oleylamine (70%), oleic acid (90%), and nitrocellulose filter membranes (25
mm diameter, 220 nm pore size), were purchased from Sigma-Aldrich and used as
received. Unless otherwise stated, all of other chemicals were purchased from Sigma-
Aldrich and used as received.
Experimental details:
Synthesis of copper nanowires:
In a typical reaction, 85 mg of CuCl2·2H2O (0.5 mmol) and 5 g of oleylamine were
mixed in a reaction vessel and then sonicated at room temperature to fully dissolve
copper precursor. 0.5 g of tris(trimethylsily)silane (2 mmol) was added in to the solution
as reducing regent. The resulting clear blue mixture was heated up to 120 °C until the
solution turned into light yellow. Afterwards, the reaction temperature was slowly turned
up to and kept at 165 for 10 h while stirring. The color of the solution turned reddish
brown, indicating formation of copper nanowires. The product was harvested by
centrifugation at 6000 rmp for 5 mins. Then, the nanowires were washed repeatedly with
toluene using centrifugation-redispersion cycles to remove excess oleylamine. Finally,
the product was dispersed in toluene for further characterization and film fabrication.
Synthesis of silver nanowires1
Silver nanowires were synthesized following reported method in literature1. 0.34 g of
PVP (poly vinylpyrrolidone) was dissolved in 20 ml ethylene glycol in a reaction tube.
The solution was heated up and kept at 170 °C. Then, 0.025 g of AgCl was added to the
mixture upon vigorous stirring. After three minutes, 0.1 g of AgNO3 dissolved in
ethylene glycol was added drop wise to the mixture. The reaction was allowed to carry
out for another 30min when it was cooled down. Ag nanowires was centrifuged down
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and washed with methanol 3 times. Finally, the nanowires were redispersed in methanol
for further characterization and film fabrication.
Fabrication of copper nanowire transparent conductor
To make a conductive thin film, copper nanowires were diluted using toluene and
sonicated for 15 min to form a homogenous suspension. The thin film was constructed by
filtering down the nanowires from the dispersion onto a nitrocellose porous membrane
(pore size 220 nm) via vacuum filtration. The nanowire network was transferred to a
transparent substrate (glass or PET) by applying pressure to the back side of the
membrane and forcing an intimate contact with the substrate. The copper nanowire thin
film was then annealed under forming gas (10% H2 and 90% Ar) at 200 for 30 min to
improve junction contact.
Fabrication of silver nanowire transparent conductor
Ag nanowires were diluted using methanol and sonicated for 15min to form a
homogenous suspension. The thin film was constructed by filtering down the nanowires
from the dispersion onto a polytetrafluorethylene (PTFE) membrane filter (purchased
from Sartorius, pore size 450nm). The nanowire network was transferred on to a
transparent substrate (glass) by applying pressure to the back side of the membrane.
Characterizations:
The morphologies of the as-grown copper nanowires were examined using a transmission
electron microscope (TEM, Hitachi H7650) and scanning electron microscope (SEM,
JOEL JSM - 6340F). The structure of copper nanowires was analyzed using high
resolution transmission electron microscopy (HRTEM, FEI Tecnai G20), selected area
electron diffraction (SAED) and X-ray diffraction pattern analysis (Bruker D8 Advance).
Exit-wave reconstruction was performed using MacTempas software. Sheet resistance of
nanowire thin film was measured using a four-point probe method (CDE-RESMAP-270).
The transmittance and haze measurement was carried out on an ultraviolet-visible near-
infrared spectrophotometer with an integrating sphere (Shimadzu UV-2550). AFM
images of the copper nanowires and their junction were taken using an Asylum MFP 3D
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in tapping mode. The as-made Cu nanowire film on glass without heat treatment and the
one with 30 minutes forming gas annealing were used for the measurements.
Haze measurement
The haze measurement is carried out by D1003-13 standard2. Shimadzu UV-2550
ultraviolet-visible near-infrared spectrophotometer with an integrating sphere was used
for haze measurement. Four transmittance scans of a sample with different configurations
were acquired for its haze calculations: T1, incident light; T2, total light transmitted by the
specimen; T3, light scattered by the instrument and T4, light scattered by the instrument
and specimen. The haze factor of one specimen can be calculated by the equation:
Haze, % = [(T4/T2) - (T3/T1)].
Unless specified, all haze factors in discussion is the value measured at 550 nm of
wavelength. The contribution of glass substrate is already excluded.
References:
1. Hu, L., Kim, H. S., Lee, J., Peumans, P.; Cui, Y. ACS Nano 2010, 4, 2955–2963.
2. ASTM D1003-13, 2013. Standard Test Method for Haze and Luminous
Transmittance of Transparent Plastics, The American Society for Testing and
Materials, West Conshohocken, PA.
Figur
nanow
amou
dispe
in b)
netwo
Figur
after
re S1. The e
wires synthe
unt of oleic a
ersion. Copp
show severe
ork.
re S2. Nano
exposed in a
effect of olei
esize (a) with
acid in the re
er nanowire
e aggregation
wire surface
air for (a), 2
c acid as a s
h oleic acid (
eaction syste
synthesized
n which is n
e oxides. HR
hours and (b
5
econdary lig
(0.1 g), and
em can greatl
d with oleyla
not suitable f
RTEM image
b), 5 days. A
gand. TEM i
(b), without
ly improve c
amine as the
for the forma
es of the surf
A thin layer o
images of co
t oleic acid. S
copper nano
sole ligands
ation of loos
face of the C
of native oxi
opper
Small
wires’
s (as shown
e nanowire
Cu nanowire
ides is
obser
thickn
furthe
the in
Figur
coppe
cubic
rved on the a
ness is aroun
er growth of
nitial native o
re S3. Single
er product b
c copper nan
as grown cop
nd 2 to 3 nan
f oxide layer
oxide layer w
e crystalline
efore the app
noparticle
pper nanowi
nometer and
r was seen af
would stop f
e cubic coppe
pearance of
6
ires after was
d is consist of
fter 5 days ex
further oxida
er particle. (
five twinned
shing proced
f a mixture o
xposure in a
ation of the c
a) TEM ima
d particles. (
dure. The ox
of Cu2O and
ambient air. T
copper nano
age of the ma
(b) HRTEM
xide layer
d CuO. No
This implies
wire.
ajority of
M image of th
s
he
Figur
coppe
to (f)
With
metal
effect
conce
tende
oleyl
In the
are m
depos
later
the r
chara
chara
detail
re S4. The
er products w
), 0 g, 0.5 g,
presence o
l particles i
tive reducin
entration, th
ency of aniso
amine.
e absence of
mainly attribu
sition on pr
explanation
reaction prod
acterized by
acteristic inte
led high-res
role of oley
with differen
, 1 g, 2 g, 3
of non-coord
is also poss
ng regent in
he shape of
otropic grow
f “catalyzed
uted to two
referentially
is more pla
ducts were
TEM. We
ermediate of
solution TEM
ylamine in c
nt amount of
g, and 5 g
dinate solven
sible which
n this system
f copper pro
wth can also
growth”, on
possible rou
protected f
ausible for th
extracted fr
did not obse
f an oriented
M study on
7
copper nano
f oleylamine
of oleylamin
nt only, the
proves tha
m. With th
oducts beco
be seen corr
ne dimension
utes: oriente
facets. Acco
he following
from the rea
erve any ch
d attachment
n the as gro
owire shape
e within the r
ne were in p
e reduction
at tristrimeth
he increasing
omes better
related with
nal nanomat
d attachmen
ording to ou
g reasons. F
action and t
hain-like inte
t directed syn
wn nanowir
control. TE
reaction syst
presence of
of copper i
hylsiylsilane
g amount o
defined. A
the increasi
terial growth
nt and select
ur experimen
Firstly, differ
their morph
ermediates w
nthesis. Seco
re and it sh
EM images o
tem. From (a
the reactant
on to coppe
e acts as th
of oleylamin
An increasin
ing amount o
h mechanism
tive monome
ntal data, th
rent stages o
hologies wer
which are th
ondly, we di
hows that th
of
a)
ts.
er
he
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ng
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ms
er
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of
re
he
id
he
nanow
five (
follow
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Third
we o
nanow
distri
by (1
Figur
nanop
coppe
weigh
produ
wire adopts
(111) facets
w the oriente
with one an
dly, there are
observed dur
wire growth
ibution, their
11) facets at
re S5. TEM
particles wit
er nanomate
ht. Nanowire
ucts.
a five-fold t
and it looks
ed attachmen
nother to for
e compelling
ring the ear
h. Besides t
r five-fold n
t the tip) are
image of na
th the dimen
erials (all mo
es take up ar
twinned stru
s like a five-
nt mechanism
rm a continu
g evidences
rly stage of
the fact that
ature and ex
all strongly
anoparticle b
sion ranging
orphology in
round 90% (
8
ucture. The t
fold pyramid
m, two segm
uous wire w
suggesting
f the reactio
t they have
xposed facets
correlated.
byproducts.
g from 30-10
cluded) of a
(by count) am
tips of the n
d. If the gro
ments would
which is not
that the five
on should se
strong corr
s (the nanop
The majorit
00 nm in dia
a typical synt
mong all mo
anowires are
owing mecha
d need to atta
t energetical
e-fold twin
erve as the
relation in
particles are
ty of byprodu
ameter. The y
thesis is arou
orphologies o
e bounded b
anism were t
ach pyramida
lly favorable
nanoparticle
seeds of th
tense of siz
also bounde
ucts are
yield of
und 50% by
of all copper
by
to
al
e.
es
he
ze
ed
r
Figur
imag
(b), 0
above
more
re S6. Tunin
es (Scale bar
0.5 g; and (c)
e three react
nuclei it wi
ng of nanowi
100nm) of c
), 0.25 g. (d)
tion conditio
ll generate, t
ire diameter
copper nanow
), diameter d
ons. During t
the smaller t
9
by changing
wire when th
distribution s
the nucleatio
the seeds.
g reducing a
he TTMSS a
statistics of c
on, the more
agent quantit
adding amou
copper nanow
reducing reg
ty. TEM
unt is (a), 1g;
wire in the
gent, the
;
10
Table S1. The effect of TTMSS quantity, copper precursor concentration and reaction
temperature on copper nanowire synthesis. The red highlighted condition is the optimized
reaction condition used for copper film fabrication.
CuCl2
(mmol)
TTMSS
(mmol)
Temperature
( ) Results
0.5 0 165 No Copper product
0.5 0.05 165 Copper cubes only
0.5 1 165 Nanowires with D ~ 22.5 ± 3.9 nm
0.5 2 165 Nanowires with D ~ 17.5 ± 3.0 nm
0.5 4 165 Nanowires with D ~ 15.5 ± 2.7 nm
0.25 1 165 Nanowires with D ~ 32.3 ± 11.0 nm
1 4 165 Nanowires with D ~ 18.5 ± 4.7 nm
0.5 2 135 No copper product
When no TTMSS in the reaction system, copper chloride cannot be reduced to copper
metal. When small amount of TTMSS (10 % of CuCl2) is added, copper cubic
nanoparticles are observed in the product. However, the yield of Cu (0) is very low.
These imply that TTMSS does act as the effective reducing reagent of copper precursor,
and insufficient loading of silane cannot fully reduce CuCl2. The nanowire diameter can
be tuned by controlling the molar ratio of TTMSS/CuCl2. With set amount of CuCl2, the
nanowire diameter decreases as TTMSS increases. The size of the nanowire is also
sensitive about reactant concentration. Smaller concentration results in thicker nanowires.
The red highlighted condition is chosen as the optimized condition for typical nanowire
growth in this work for the reason that it gives less particle byproducts.
Figur
annea
16.98
summ
nanow
15.00
which
partia
re S7. AFM
aling. Before
8 nm. The m
mation of tw
wire film, th
0 nm which a
h is 5 nm sh
ally wield na
images of c
e annealing,
measured junc
o individual
he measured
add up to 29
ort of the su
anowire toge
copper nanow
the two mea
ction height
nanowire di
diameters o
9.50nm. The
ummation. Th
ether which c
11
wire film (a)
asure nanow
is 33.74 nm
iameters (33
f the two ind
annealed ju
his shows th
can enhance
), before ann
wires have di
m which is alm
3.64 nm). In
dividual wire
unction has th
hat the therm
e the junction
nealing and (
ameter of 16
most the sam
the case ann
es are 14.50
he height of
mal annealing
n contact.
(b), after
6.66 nm and
me with the
nealed
nm and
f 24.46nm
g can
d
Figur
is the
melt
resist
nanow
nanow
nanow
condu
Figur
most
and (
re S8. Depen
e optimized a
the nanowir
tance is obse
wire film is
wire. The tem
wire and dam
uctivity
re S9. SEM
nanowires a
c) 260 , w
ndency betw
annealing tem
e to form int
erved. When
almost insol
mperature ca
mage the nan
images of n
are intact; (b
when most of
ween film she
mperature. I
timate conta
n the annealin
lated due to t
annot be too
nowire perco
nanowire con
b) 230 , wh
f the nanowir
12
eet resistanc
If the temper
act at the wir
ng temperatu
the presence
o high either.
olation, whic
nducting film
hen some of
res are defor
ce and annea
rature is low
re-wire junct
ure is lower
e of oxides o
. Overheatin
ch will resul
m when anne
the nanowir
rmed.
aling tempera
wer, it cannot
tion. An incr
than 150
on the surfac
ng will sever
lt in degradin
ealed at (a) 2
res are visibl
ature. 200
t effectively
rease in shee
, the
ce of the
rely melt
ng in film
200 when
ly melted;
et
Figur
mech
polye
(MEL
of 80
angle
is app
when
extra
cycle
re S10. Con
hanical bendi
ethylene tere
LINEX® ST
0~90 ohms/sq
e is around 9
plied with m
n the sheet w
ordinary flex
es of bending
ductivity per
ing. Inset, fl
ephthalate (P
T506) were p
q) on PET (1
90 degree. IT
mechanical be
was bended 5
xibility. The
g.
rformance o
exible coppe
PET). Transp
purchased fro
175 micron)
TO on PET s
ending. The
00 cycles. In
e sheet resista
13
of ITO and C
er nanowire
parent PET (
om TEKRA
was purcha
hows severe
sheet resista
n compariso
ance shows
Cu nanowire
conducting
(175 micron)
A. ITO (sheet
ased from Sig
e degradation
ance increase
on, copper na
almost no ch
conductor u
film fabrica
) substrates
t resistance a
gma-Aldrich
n in conduct
ed almost 10
anowire film
hange even a
upon
ated on
at the range
h. Bending
tivity when i
00 times
m exhibit
after 1000
it
Figur
transp
Trans
suppo
The b
bendi
of ou
condu
were
proce
re S11. Shee
parent films
sparent PET
orting substr
bending angl
ing angle is
ur as made fi
uctivity rem
made from
ess. The four
et resistance
after applied
(175 micron
rate. Four be
le is 180 deg
90 degree of
lm. The film
ains its origi
the same bat
r films tests h
(normalized
d with multi
n) substrates
ending radii
gree for tests
f the test wit
ms show grea
inal value du
tch of coppe
have the she
14
d for clear co
iple bending
s (MELINEX
were tested
s with bendin
th bending ra
at resistance
uring the wh
er nanowires
eet resistance
omparison) p
g cycles with
X® ST506) w
: 8.2mm, 4.3
ng radius sm
adius of 8.2
towards me
hole experim
s and underw
e of 33 ± 3
performance
h various ben
were used a
3mm, 3.2mm
maller than 5
mm due to t
echanical ben
ment. All the
went the sam
ohms/sq.
e of flexible
nding radius.
s the
m and 2.0mm
mm. The
the small siz
nding and th
films tested
me fabrication
.
m.
ze
he
n
Figur
sized
Vacu
Figur
repre
keep
the co
re S12. SEM
d nitrocellulo
uum filtration
re S13. Stab
sents a diffe
the high con
onductivity o
M images of
ose membran
n can effecti
bility test of c
erent loading
nductivity pe
of the coppe
(a) copper n
nes and (b) c
vely remove
copper nano
g amount. It i
ermanently.
er film degra
15
nanowires wh
copper nanow
e most of the
owire transpa
is also worth
After severa
ades significa
hich were fil
wires drop c
e nanoparticl
arent conduc
h to note tha
al months’ ex
antly.
ltered by 22
asted on sili
le byproduct
ctors. Each c
at the Cu NW
xposure in a
0 nm pore-
con wafer.
ts.
color
W film canno
ambient air,
ot
Figur
Figur
transp
total
re S14. Cop
re S15. Visu
parent condu
transmittanc
per film is fu
ual comparis
uctor and an
ce.
fully oxidized
son between
ultra-thin co
90
16
d after 3 mo
a silver nan
opper nanow
days in air
nths storage
nowire (with
wire conduct
e in air
mean diame
ting film wit
eter of 50nm
th the same
m)