Appl Phys A (2011) 103: 421–426
DOI 10.1007/s00339-011-6356-6
Two-photon laser fabrication of three-dimensional silver
microstructures with submicron scale linewidth
Naoto Tsutsumi · Kazuya Nagata · Wataru Sakai
Received: 6 October 2010 / Accepted: 22 January 2011 / Published online: 19 March 2011
© Springer-Verlag 2011
Abstract We show three-dimensional silver microstruc-
tures with a submicron scale linewidth fabricated via two-
photon photoreduction of silver ions in a poly(N-vinylpyr-
rolidone) (PVP) matrix. Femtosecond laser at 508 nm
directly excites the carbonyl group of PVP via two-photon
excitation to reduce silver ions. Lone pair electrons in
PVP stabilized silver ions and lower molecular weight of
PVP prevented silver clusters growing larger. The effect of
molecular weight of PVP on linewidth of silver nanowire is
investigated.
1 Introduction
During the last decade, two-photon and multi-photon in-
duced microfabrication in a solution and in solid materials
have been widely studied [1–8]. Glezer et al. investigated
two-photon writing of bits in transparent glass materials and
presented the possibility of three-dimensional optical data
storage [1]. Using photopolymerization by two-photon ex-
citation, Kawata et al. succeeded microfabrication of self-
standing bull-shaped miniature with a micron scale [2].
Katayama et al. induced voids with a micron scale in poly-
meric materials using two-photon excitation and demon-
strated their use for gratings [3]. They also demonstrated
femtosecond laser pulse induced crystallization in an amor-
phous inorganic (In
2
O
3
+ 1wt%TiO
2
)film[4]. Kaneko et
al. fabricated gold nanoparticle gratings using two-photon
N. Tsutsumi (
) · K. Nagata · W. Sakai
Department of Macromolecular Science and Engineering,
Graduate School of Science and Technology, Kyoto Institute of
Technology, Matsugasaki, Sakyo, Kyoto 606-8585, Japan
e-mail: tsutsumi@kit.ac.jp
Fax: +81-75-724-7805
laser photoreduction of gold ions in a poly (vinyl alcohol)
matrix [5]. Baldacchini et al. demonstrated two-dimensional
silver structures in poly(N-vinylpyrrolidone) (PVP) films
by a multi-photon laser direct writing method [6]. Tanaka
et al. also fabricated three-dimensional electrically conduc-
tive silver microstructures using two-photon laser photore-
duction of silver ions in an aqueous solution [7]. Ishikawa
et al. fabricated the magnetic metamaterial composed of
two-dimensional silver rod pairs with a micron scale us-
ing two-photon photoreduction [8]. Kawata et al. reported
recently the morphology and the size dependence of silver
microstructures in a fatty salts-assisted multi-photon pho-
toreduction process and highest resolution of silver line with
285 nm upon laser irradiation of 800 nm [9].
In this article, we show three-dimensional silver mi-
crostructures with submicron scale linewidth fabricated via
two-photon photoreduction of silver ions in PVP matrix.
The effect of molecular weight of PVP on linewidth of silver
nanowire is investigated.
2 Experimental
Femtosecond laser at 508 nm directly excites the carbonyl
group of PVP via two-photon excitation to reduce silver
ions. Lone pair electrons in PVP stabilized silver ions and
lower molecular weight of PVP prevented to grow sil-
ver clusters larger. Femtosecond laser at 508 nm was de-
rived from the sum frequency mixing of pumping beam
of Ti:sapphire and the signal beam from optical parametric
amplification (OPA). Compared with former studies a near
infrared beam around 780 to 800 nm to excite sensitizer
via a two-photon process to reduce silver ions, a shorter
wavelength is preferred to enhance the lateral spatial reso-
lution (LSR) of fabricated silver nanowire, i.e., to deduce
the linewidth of nanowire.