RSC Advances
PAPER

Cite this: RSC Adv., 2015, 5, 102904

Proton-assisted low-temperature sintering of Cu
ﬁne particles stabilized by a proton-initiating
degradable polymer†
Masaki Matsubara,‡a Tetsu Yonezawa,*a Takato Minoshima,a Hiroki Tsukamoto,aYingqiong Yong,a Yohei Ishida,a Mai Thanh Nguyen,a Hiroki Tanaka,bKazuki Okamotob and Takuya Osakab
Metallic copper ﬁne particles were prepared by chemical reduction of CuO in the presence of thermallydegradable poly-1,4-butanediol-divinylether (BDVE). Because a BDVE thin layer formed on the particle
surfaces, the obtained copper particles were stable and did not undergo obvious oxidation underambient conditions. The ether groups of BDVE were hydrolyzed with protons, and this generated small
fragment molecules. The BDVE-stabilized copper ﬁne particles and their pastes can be therefore sinteredat 150  C in the presence of protons. Electro-conductive ﬁlms with a relatively low resistivity of 8.5 

Received 15th October 2015
Accepted 23rd November 2015105 U cm were obtained on a alumina substrate in the presence of formic acid, and hot pressed
conductive pellets with a resistivity of 2.9  105 U cm were also obtained without any pre-oxidative
annealing in the presence of proton generator molecules at very low temperatures. The hot pressed

DOI: 10.1039/c5ra21402e
www.rsc.org/advancespellets show a high anti-oxidative ability and their corrosion tests revealed their good anti-corrosion
property.

Introduction
Metal nanoparticles and ne particles have attracted extensive
attention in nanotechnology1–5 as well as in electronics.6–8 In
particular, conductive inks and pastes containing a highconcentration of metal nanoparticles and ne particles areimportant candidates for production of printed electronics9–12
that are currently in demand. This is because of their potential
applications in low cost wet processes, especially for producing
exible devices, including organic devices. So far, gold13–15 andsilver16–19 pastes and inks have been frequently applied for
producing electro-conductive lms and patterns owing to theirhigh stability and low resistivity. However, the cost of precious
metals inhibits their economical use and electromigration ofsilver has been a major issue impeding their application.
Copper is a preferable alternative to gold and silver from theviewpoint of cost and electromigration issues. Copper isaDivision of Materials Science and Engineering, Faculty of Engineering, Hokkaido
University, Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan. E-mail:tetsu@eng.hokudai.ac.jpbCorporate Research Center, Daicel Corporation, 1239, Shinzaike, Aboshi-ku, Himeji,
Hyogo 671-1283, Japan† Electronic Supplementary Information (ESI) available: Schematic illustration of
the electro-conductivity measurement. TGA cart of Cu ne particles. SEM image of
the Cu pellets obtained by hot-pressing. See DOI: 10.1039/c5ra21402e‡ Present address: Department of Materials and Environmental Engineering,
National Institute of Technology, Sendai College, 48 Nodayama,
Medeshima-Shiote, Natori 981-1239, Japan.

102904 | RSC Adv., 2015, 5, 102904–102910

a common element, and it has a high electroconductivity.
Moreover, it is not magnetic. Many eﬀorts on the use of inks andpastes of copper particles20–34 and copper organo-complexes35–39
have been made to develop low-temperature sintering processes
including photo and laser irradiation sintering.40–42 However,copper ne particles get oxidized easily even under ambientconditions and this problem limits their application.
In order to overcome this oxidation issue, protection ofcopper particle surfaces against oxidation is of immediate
importance.20–34 Polymers,20–27 surfactants,28–31 including alkylamines,31 and metal,32 and metal oxide33 shells have been used
as an anti-oxidation layer on the particle surfaces. In most cases,
however, the introduction of an anti-oxidation layer on copper
particles means the formation of a non-conductive layer, suchas an organic layer and a metal oxide layer, on the surface ofparticles. The only exception is the formation of a metallic layercomposed of noble metal elements on copper particle surfaces.
However, such noble-metal layers are costly. Further, metaloxides cannot be eliminated from the obtained layers by
thermal sintering. In contrast, polymers are good candidates forprotecting the surface of copper particles against oxidation,20–27
and may be decomposed during sintering. For use in electrocircuits, direct metal–metal contacts in the particle layers
must be obtained during sintering processes to realize better
electro-conductivity. However, organic polymers usually do notevaporate even at high temperatures but directly begin todecompose at 400  C, and polymer-stabilized metal particles
need to be subjected to high-temperature sintering8 or laserThis journal is © The Royal Society of Chemistry 2015

Paper

RSC Advances

irradiation42 to remove polymers. We have demonstrated thatoxidative sintering can form copper oxide dots on the particle
surface and these dots change to metallic necking under
reductive sintering.26,27,31 However, this two-step sintering
process involves quite a long sintering time of 8 hours. From
this point of view, decomposition of the stabilizing polymer
molecules at a moderate temperature into small fragments thatcan be evaporated or eliminated is favourable for lowtemperature sintering with a shorter time. Some polymers
used in biomedical applications can be decomposed intomonomer species or small fragments in the presence of protons
at biocompatible temperature.43–45 These polymers can be used
to stabilize copper ne particles in electro-conductive pastes
and joining materials for low-temperature sintering. As joining
materials, these degradable polymer-stabilized Cu particles also
have a good potential because lead-free solder alloy46 hasa higher melting point, limiting its use in manufacturing ofelectro-circuits.
In this paper, for the rst time, we present a novel strategy of
low-temperature sintering of novel proton-assisted degradable
polymer-stabilized copper ne particles in which the polymer
can undergo proton-assisted degradation. Protons facilitatedthe hydrolysis of ether bonds in the main chain of polymers,
resulting in small fragments. Cu conductive pellets were obtained by hot-pressing in the presence of a thermal proton
generator, and the Cu conductive lms were obtained byannealing in a reductive atmosphere with formic acid asa proton donor. The polymer decomposition by protons is the
key factor to achieve good electro-conductivity. The diﬀerence
between favourable proton generators of pellets and lms will
also be discussed.

solution. 1.25 cm3 of hydrazine monohydrate (N2H4$H2O) was
added into the mixture at 50  C, and the mixed dispersion was
stirred for 2 h. Aer reduction, the brown precipitates werecollected by decantation, and then washed 4 times with ethanol
by centrifugation, and then drying at room temperature underN2. Finally, 3.1 g of Cu ne particle powder was obtained.
Larger-scale production of BDVE-stabilized Cu ne particles
was also performed. For the purpose of scale up, we choseethanol as the solvent instead of THF due to its low cost, and set
the reaction temperature to 78  C. 1.32 g of BDVE was dissolved
into 200 cm3 of ethanol in a round bottom ask with a reux
condenser. 16 g of CuO microparticles was dispersed into thissolution. Then, this solution was reuxed at 78  C with stirring
at 800 rpm. For the complete reduction of the large amount of
CuO, an excess amount of hydrazine monohydrate (50 cm3) was
introduced into this mixture. An explosive boiling of the reaction mixture occurred once soon aer addition of hydrazine.
Aer stirring for 2 h, Cu ne particles were collected bydecantation, and then washed 4 times with ethanol by centrifugation. 13.0 g of BDVE-stabilized Cu ne particle powder was
obtained in the large-scale synthesis.
Preparation of conductive Cu pellets at high pressure
Preparation of Cu conductive pellets at high pressure is asfollows: well-mixed 1.0 g of Cu particle powder prepared as
described above and 10 mg of BPMS as the proton generator
were introduced into a stainless vessel with diameter of 13 mm
and then compacted for 30 min by a hot press machine (Ah2003, AS ONE Corp.) at 100 MPa at various temperatures (25,80, and 100  C) under air.
Preparation of Cu ink and conductive Cu lm

Experimental
Materials
CuO microparticles (0.9 mm) used as the metal source were
supplied by Nisshin Chemco (Japan). Hydrazine monohydrate
as a reducing reagent, tetrahydrofuran (THF), and ethanol werepurchased from Junsei (Japan). Formic acid was obtained from
Kanto (Japan). Poly-1,4-butanediol divinyl ether (BDVE, MW ¼
ca. 9000) was synthesized by Daicel. Benzyl 4-hydroxyphenyl
methyl sulfonium hexauoroantimonate (BPMS) was used as
the thermal proton generator (Scheme 1).
Preparation of polymer-stabilized Cu ne particles
The synthetic procedure of BDVE-stabilized Cu ne particles issimilar to the previously reported24,26 and as follows: 0.33 g of
BDVE was dissolved in 20 cm3 of THF in a round-bottom ask,
and then 4.0 g of CuO microparticles were dispersed into thisIn order to prepare the ink with dispersing Cu ne particles, theobtained Cu-particle powder was rst ground by using an
automatic mortar for 30 min and then pulverized by using
a blender. Then, the mixture was dispersed in ethanol and aterpineol using a mixer and an emulsier. Ethanol was removed
from the mixture by evaporation under vacuum and the copper
content of the obtained ink was controlled as 50 wt%. Into thisink, 10 wt% of formic acid as the proton generator was added.
The obtained Cu ink was then immediately deposited on a glass
and an aluminum oxide (Al2O3) substrate by the doctor blade
method to obtain a lm with a thickness of 40 mm and a widthof 20 mm. Aer drying under N2 for 1 h at 40  C, the substrates
were cut into 20 mm  20 mm pieces and annealed at 150  C in
3% H2 in N2 gas ow (2 dm3 min1) for 2 h. The Cu ink
including 1 wt% of BPMS was also prepared and sintered in thesame way.
Characterization

Scheme 1

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Scanning electron microscope (SEM) observations of the particles were performed by using a JEOL JSM-6701F eld emission
SEM with an acceleration voltage of 15 kV. X-ray diﬀraction(XRD) patterns were obtained with a Rigaku Mini Flex II (CuKa). The thermal properties of BDVE and Cu ne particles were
measured by thermogravimetric analysis (TGA) and diﬀerential

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thermal analysis (DTA) with a Shimadzu DTG-60H. TGA-DTA
curves were obtained under air with a heating rate of 1 or
5  C min1. The pellet sample was pulverized into powder
before TGA-DTA measurement. The sheet resistance of thecopper lms and pellets were obtained using a four-point probe
method. In order to obtain reproducible data, six points forlms and four points for pellets were measured with a four
point probe, as shown in Fig. S1,† and the average values are
displayed. Corrosion tests of the conductive Cu pellets werecarried out in the condition of 85  C and 85% relative humidity
for 8 days using an ESPEC (Japan) SH-240 temperature andhumidity testing chamber.

Results and discussion
Preparation and characterization of the BDVE-stabilized Cu
ne particles
BDVE-stabilized Cu ne particles with a nearly spherical shapewere prepared by chemical reduction of CuO micro-particles in
the presence of BDVE. The average particle size was 110  45
nm, as shown in Fig. 1a. We could also obtain the Cu particles ofthe same quality even if they were produced on a large scale with
diﬀerent solvents and reaction temperature. In the case of thelarge-scale production, the average particle size and distribution was 110  38 nm, as shown in Fig. 1b. The XRD
measurement results shown in Fig. 1c indicate that our Cu neparticles were not oxidized under ambient conditions for at

Paperleast 2 weeks and that our Cu ne particles produced on a large
scale also were not oxidized under the same ambient conditionat least 3 weeks. Thus, BDVE layers on the surface of Cu neparticles can prevent particle surface oxidation. As observed in
the SEM image, the particle size is not quite uniform, unfortunately. In our previous study, when gelatin was used as thestabilizing polymer for Cu ne particles for similar-size, whichwere also prepared by hydrazine reduction of CuO microparticles, the particles were almost spherical and the size
distribution was more uniform.24,26 This can be probably
attributed to amino, carboxylic acid and thiol groups that cancoordinate to copper atoms on the particle surface. Such strong
coordination between polymer molecules and particle surface
enable good control of the particle sizes and structure. In
contrast, BDVE has no such coordinative groups in the polymer
chain.
In order to estimate the amount of BDVE attached on thesurface of Cu ne particles, TGA-DTA measurement was carriedout in air (Fig. 2). The mass in the thermogram began to slightly
increase at ca. 87  C (see Fig. S2†), indicating that Cu began to
be gradually oxidized to change into Cu2O. The DTA curve
indicates that above ca. 177  C, Cu2O began to be oxidized to
CuO. At the end of the measurement, Cu was completely
oxidized to CuO. The value of 124.3 wt% also includes theweight loss of decomposed BDVE. The initial Cu ratio of assynthesized Cu particles can be calculated as 1.243/1.252 ¼
0.993 with use of the ratio of MW(CuO)/MW(Cu) ¼ 79.545/
63.546 ¼ 1.252. From this calculation, we can estimate thatthe actual amount of BDVE on the surface of Cu particles is 0.7
wt%.
Pyrolysis behaviors of BDVE with and without acids
Fig. 3 shows the pyrolysis behaviors of BDVE with and without
acids. TGA measurements were carried out under air ow (200
cm3 min1) at the heating rate of 1  C min1. Thermal
decomposition of BDVE began at ca. 180  C in the absence ofacids. In the presence of acids, it is expected that BDVE may
decompose to lighter fragments that will be vaporized easily(a) SEM image of as-synthesized BDVE (poly-1,4-butanedioldivinylether)-stabilized Cu ﬁne particles. (b) SEM image of theparticles produced on the large scale. (c) XRD patterns of BDVEstabilized Cu ﬁne particles. Measurements were performed with theparticles as prepared and stored in air for 1 and 2 weeks.

Fig. 1102906 | RSC Adv., 2015, 5, 102904–102910

TGA (blue)-DTA (red) curves of BDVE-stabilized Cu ﬁne particles (dashed line) and Cu pellet pressed at 100  C (solid line). The pellet
was pulverized into powder before the measurement.
Fig. 2This journal is © The Royal Society of Chemistry 2015

Paper

RSC AdvancesFig. 3 TGA charts of BDVE with and without acids. TG measurements
were carried out under air ﬂow (200 cm3 min1) at the heating rate of
1  C min1. (black line) BDVE without acids. (red line) BDVE with 10 wt%
of formic acid. (green line) BDVE with 1 wt% of BPMS. (Inset) Magniﬁed
curve of BDVE with 10 wt% of formic acid.

because acids promote the hydrolysis of ether bonds in the
structure of BDVE. The decomposition when 10 wt% of formic
acids was added can be divided into two stages. Firstly, 12 wt%
of decrease in mass between 30 to 140  C could be attributed toa large amount of evaporated formic acid (b.p. ¼ 100.8  C),
which was supposed to be 10 wt%, as well as a small amount of
decomposed BDVE fragments. Next, weight decrease, indicating
degradation of BVDE, started at 159  C (shown in inset of Fig. 3).
BDVE underwent partial hydrolysis and changed into theevaporable pieces by formic acids during gradual evaporation of
formic acid.
In the eld of controlled polymerization, heat-sensitive andphotosensitive proton generators are oen used for initiating
polymerization. BPMS is one of such heat-sensitive proton
generators. BPMS can be degraded at 100  C to release protons.
In this study, BPMS was used not as the polymerization initiator
but as the BDVE degradation initiator. As can be observedin Fig. 3, evaporation of fragment products began at around100  C.

Preparation of Cu conductive pellets via hot-pressing
BDVE-stabilized Cu particles were pressed in air at 100 MPa for
30 min at various temperatures (25, 80, and 100  C). The Cupellets were 13 mm in diameter and 1 mm in thickness irrespective of the hot-pressing temperature. The obtained resistivities of the hot-pressed Cu pellets are summarized in Fig. 4a.
The Cu pellet pressed at 25  C showed the resistivity of 4.1 
104 U cm. This indicates that some inter-particle contacts weregenerated by high-pressure pressing. Polymer molecules may be
suﬃciently exible to move on the particle surface. The resistivity of the pellet compacted at 80  C decreased to 1.4  104 U
cm, suggesting that heating promotes more rapid movement of
BDVE molecules. Resistivity of the pellet prepared at 100  Cremained 1.4  104 U cm, unfortunately, since the decomposition of BDVE does not proceed under the current temperature.

This journal is © The Royal Society of Chemistry 2015

Fig. 4 (a) Resistivities of hot-pressed Cu pellets with (circles: C) andwithout (triangles: :) BPMS as the thermal acid generator. The resistivity of bulk copper is 1.7  106 U cm and is displayed as the dashedline. (b) XRD patterns of hot-pressed Cu pellets with BPMS. The (111)plane of Cu2O is marked as closed circle (C).

Hot pressing was also carried out in the presence of BPMS. In
the presence of BPMS as the proton generator, the pellets
pressed at 25 and 80  C showed similar resistivities as thepellets obtained without BPMS (6.0  104 and 1.5  104 U
cm, respectively). However, the resistivity was dramaticallydecreased to 2.9  105 U cm in the case of the pressing
temperature of 100  C. This result indicates that the BDVE
surrounding Cu particles was decomposed at 100  C by the acidderived from BPMS, as shown in Fig. 3, resulting in the densely
packed Cu particles in the pellet with metal–metal directcontacts (see the SEM image in Fig. S3†).
Fig. 4b shows the XRD patterns of the pellets pressed with
BPMS. It is shown that the surface of the Cu particles waspartially oxidized to Cu2O, aer being heated and pressed in air
at 80  C and 100  C for 30 min. The Cu pellet prepared at 100  C
contained 4 wt% of Cu2O, as per calculation using the reference
intensity ratio (RIR) method.47 This partial oxidation can be
explained by the two reasons. TGA-DTA measurement of BDVEstabilized Cu ne particles (dashed line of Fig. 2 and S2†)
indicates that they began to be oxidized at ca. 87  C. The other isdecomposition of BDVE by BPMS at high temperatures. Despite
the oxidation, Cu pellets showed a low resistivity of 2.9  105 U

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RSC Advances

cm at pressing temperature of 100  C in the presence of BPMS,
which is in accordance with the low-temperature decomposition of BDVE. This resistivity value is extremely low even though
the most particles shall be remained covered by BDVE that is
not degraded, only 17 times higher than bulk copper.
Aer pressing at 100  C, the pellet was pulverized into
powder and its TGA-DTA measurement was performed (solidlines of Fig. 2 and S2†). Comparing with the curves of the asprepared BDVE-stabilized Cu ne particles, the pellet shows
better anti-oxidation ability. The Cu particles in the pellet began
to be oxidized at 120  C, that is, 33  C higher than the asprepared Cu ne particles BDVE can be decomposed at ca.
100  C in the presence of BPMS. However, all decomposedcomponents were not evaporated during pressing. As indicatedin Fig. 5, Cu ne particles in the pellet prepared at 100  C werecovered by BDVE polymer residues. This image indicates thatthe polymer residues aer pressing densely covered the surfaceof particles and necking parts. This phenomenon strongly
prevents oxidation of copper in the pellet as observed in the
TGA-DTA curves in Fig. 2 and S2.†
Corrosion tests of these hot-pressed conductive Cu pellets
revealed that the resistivities of pellets could last for 8 days in
the oppressive condition of 85  C and 85% relative humidity as
shown in Fig. 6. This good anti-corrosion stability can be
attributed to the polymer layer on Cu particles and neckings asshown in Fig. 5. This low-temperature proton-aided hotpressing is a quite useful process to obtain highly conductive
copper pellets.

Paper

Corrosion tests of the hot-pressed conductive Cu pellets with
BPMS. The condition of the test was 85  C and 85% relative humidity.
The resistivities were increased after 1 day in the condition. However,
the resistivities lasted for other 7 days without any obvious increase.
Fig. 6

formic acid as the proton generator was introduced into the ink
just before application on substrates. Then, the ink was printed
onto a glass and an Al2O3 substrates by using the doctor blade
method. Aer printing, the Cu lm was dried at 40  C under N2
ow. The obtained Cu lm was annealed at 150  C in 3% H2 in
N2 gas for 2 h. Fig. 7a shows the XRD patterns of Cu lm on theglass before and aer annealing. The Cu lm was not oxidized
during annealing. The surface of the Cu lm was observed by
SEM (Fig. 7b). In this image, both the necking structures

Preparation of the Cu ne-particle ink and conductive lms
via acid-assisted sintering
Printing electronics using metal-particle inks or pastes has been
attracted much attention so far as an ecological method torealize highly conductive electronic circuits. Therefore, we tried
to prepare an ink containing above the obtained BDVEstabilized Cu ne particles.
BDVE-stabilized Cu ne particles were re-dispersed into 50
wt% of a-terpineol to form an electro-conductive ink. 10 wt% of

SEM image of the fracture surface of a Cu ﬁne particle pellet
pressed at 100  C. Cu ﬁne particles are covered by BDVE polymer
residues.

Fig. 5102908 | RSC Adv., 2015, 5, 102904–102910

Fig. 7 (a) XRD patterns of Cu ﬁlms on a glass before and after sintering.

(b) SEM image of the Cu ﬁlm sintered at 150  C in 3% H2 in N2 gas. (c)Cross-sectional SEM image of (b). The thickness of ﬁlm was 4.8 mm
marked as red arrowed line.

This journal is © The Royal Society of Chemistry 2015

Paperbetween copper particles and the inter-particle connections
could be observed. The thickness of annealed Cu lm was 4.8mm, as observed in Fig. 7c. Aer annealing in 3% H2 in N2 gas,
the sheet resistance and resistivity for the resulting lm were0.18 U sq1 and 8.5  105 U cm, respectively. As the decomposed BDVE fragments formed by the addition of formic acid
were evaporated at 150  C, the copper–copper direct contact
area between particles increased. The Cu lm was also annealed
at 100  C in 3% H2 in N2 gas for 2 h, but the obtained copper
layer was unfortunately an insulator. This is because that
decomposed fragments of BDVE were not evaporated at 100  C
as shown in Fig. 3.
As indicated in Fig. 3, BPMS works as a good thermal proton
generator. As indicated above, hot-pressed Cu pellets (at 100  C)
assisted by BPMS showed low resistivity of 2.9  105 U cm. We
have also prepared a Cu ink with 1 wt% of BPMS, and copper
particle layers were prepared by the doctor blade method.
Surprisingly, the layers showed non-conductive property aersintering even at 150  C in 3% H2 in N2 gas for 2 h.
At this moment, we have not obtained clear evidences to
explain the diﬀerence between the favourable proton generatorsin the two cases. BPMS decomposes BDVE at a much lower
temperature than formic acid does. The decomposition of BDVE
to easily evaporated fragments as a result of hot pressing is very
important because the contacts between copper ne particles
can be easily generated by the external pressure when no
organic molecules are found on the surface. In contrast, without
an external pressure, copper ne particles cannot move easily
when the particles lose the outer layer. However, when they arecovered by polymers, at temperatures above the glass transition
temperature of the polymer, copper particles can move slightly
and connect the particle surfaces. Therefore, interparticle
connections could be formed in the case of addition of formic
acid due to a relatively high pyrolysis temperature as shown in
Fig. 3.
In this sintering process, the evaporation of polymer fragments and the formation of interparticle contacts are the mostimportant factors to achieve electro-conductivity. Thus, sintering with formic acid makes the Cu lm electro-conductive.

Conclusions
In summary, we have used a polymer, which undergoes protonassisted degradation, to stabilize copper ne particles for therst time. Proton-assisted single-step sintering of polymerstabilized Cu ne particles was successfully performed ata low temperature to obtain highly conductive Cu pellets andlms. In fact, only 0.7 wt% of polymer layer on the surface ofparticles could provide Cu ne particles with the anti-oxidation
ability. In our system, acids promote the hydrolysis of polymer
and the fragments of decomposed polymer can be evaporated ata low temperature. In the presence of a thermal acid generator,
the Cu conductive pellet was obtained by hot pressing at 100  C.
In spite of oxidation of the surface layer, Cu particles weredensely packed and the resultant pellets showed the low resistivity of 2.9  105 U cm. The hot pressed pellets showed betteranti-oxidative property than the as-prepared Cu ne particles.
This journal is © The Royal Society of Chemistry 2015

RSC Advances

Also, the hot pressed pellets showed good anti-corrosion
stability at 85  C and 85% of relative humidity. Furthermore,
formic acid can decompose the polymer. Aer sintering in thepresence of reductive gas and formic acid, a conductive Cu lmwith the low resistivity of 8.5  105 U cm was successfully
prepared. In this sintering process, the evaporation of polymer
fragments and the formation of dense inter-particle contacts are
the key factors to realize high electro-conductivity. The
decomposable-polymer-protected Cu particles are therefore
promising candidates for obtaining the electro-conductive lms
and pellets via low-temperature sintering. This novel strategy
could enable the application of low-temperature sintering ofrelatively large ne particles for use in printed electronics.

Acknowledgements
This work is partially supported by Hokkaido University (to TY).
MTN acknowledges the nancial support from F3 program of
Hokkaido University. TY also thanks a partial support from
Shinsei Foundation, Murata Foundation and Network Joint
Research Center for Materials and Devices, Japan.

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