Selective metal deposition in hydrophobic porous cavities of self-organized honeycomb-patterned polymer films by all-wet electroless plating

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Abstract

We report selective metal deposition of self-organized honeycomb-patterned polymer (hp) films possessing hydrophobic surfaces by all-wet electroless plating. Nickel/phosphorus (Ni/P) coated hp films were fabricated as follows. A catalytic nucleus of electroless plating was adsorbed on hp films by immersion in a saturated ethanol solution of palladium(II) chloride (PdCl2). Homogeneous metal deposition on the hydrophobic surface of the hp film was easily carried out by all-wet process. In addition an ultrahydrophobic surface of pincushion-structured polymer (ps) films having periodic pillars which was obtained by peeling off a top layer of the hp film was metal-coated by the same all-wet process. It was found that immersion in the saturated ethanol solution of PdCl2 is suitable for catalyzation on hydrophobic surfaces for metal deposition by all-wet electroless plating. To use differences of wettability of honeycomb structures between inner and outer surfaces of porous cavities, site-selective Ni/P deposition in porous cavities was carried out by immersion in a palladium chloride acid aqueous solution after ethanol treatment.

Introduction

Ordered metallic structure ranging from submicron to micron scale is one of the significant matters in electronics and photonics. Ordered metallic materials have been fabricated by template synthesis method using organic ordered structures such as lithographed polymer films [1], imprinted polymer films [2], and so on. Recently we have reported that honeycomb-patterned polymer (hp) films were prepared by casting the solution of polystyrene and amphiphilic copolymer 1 (see Fig. 1) by using condensed water droplet arrays as templates [3]. In addition, pincushion-structured polymer (ps) films were fabricated by simple peeling off a top layer of the hp film with adhesive tapes [4].

Ordered metallic layers were prepared by electroless plating of the hp film and the ps film coated by a sputtered platinum/palladium (Pt/Pd) layer [5]. The metallic layer completely reflected the periodic structure of the template films acts as catalytic nuclei carrier of electroless plating. However, the sputtering method gave some disadvantages such as expensive equipment, high running costs, limit of sample size and heating damage of the polymer templates. All-wet metal deposition was used to solve these problems. All-wet metal deposition requires only wet processes including catalyzation, activation, sensitization, metal deposition, and rinse. Commonly used catalyzation process is immersion in a catalytic aqueous solution containing palladium salts. Therefore the template materials must have suitable surfaces for catalyst adsorption such as hydrophilic surfaces [6], chemical-modified surface [7], and physical-modified surfaces [8].

In this report, we demonstrate metallization of the hydrophobic hp and ps films possessing periodic structure by all-wet process (see Fig. 2). All-wet deposition enables us to give wide surface metal deposition easily. In addition, ordered metallic structures were fabricated by site-selective metal deposition of porous cavities of the hp film to use differences of wettability between inner and outer surfaces of the honeycomb structure by all-wet electroless plating.

Section snippets

Preparation of honeycomb-patterned films and pincushion-structured films

The amphiphilic copolymer 1 used in this study was synthesized and characterized according to some previous reports [9]. Honeycomb-patterned polymer (hp) films were prepared by casting a chloroform solution of polystyrene (Mw = 280 000 g mol−1, Aldrich, USA) and the amphiphilic copolymer 1 (10:1 mixture) on a glass substrate with condensed water droplet arrays as templates [9]. Pincushion-structured polymer (ps) films were fabricated by peeling off a top layer of the hp films with adhesive tape [4].

Ni/P coating of the hp films

Fig. 3a indicates an SEM image of the hp film having regular pores of 7.0 μm in a diameter. The pore edge accumulates the amphiphilic compound 1 [10] and layer thickness of the edge is estimated to be less than 0.50 μm by a magnified SEM image of the pore edge as shown in Fig. 3b. Ni/P electroless plating of the hp film was carried out by immersion in a PdCl2 catalytic solution and then in a Ni/P electroless plating bath. Fig. 3c and d show SEM images of Ni/P coated hp films prepared by using the

Conclusion

In this report we demonstrated metal coating on hydrophobic surfaces of the polymer film having ordered structures by all-wet deposition process. Wettability of a catalytic solution on the substrate surface is very important for all-wet electroless plating. The saturated ethanol solution of PdCl2 is best suited to catalytic solution of polymer films having hydrophobic surfaces by all-wet electroless plating. In addition, site-selective metal deposition of porous cavities of the hp film was

References (10)

  • W.J. Dressick et al.

    Chem. Mater.

    (1993)
  • P.C. Hidber et al.

    Langmuir

    (1996)
  • O. Karthaus et al.

    Langmuir

    (2000)
    O. Karthaus et al.

    Mater. Sci. Eng.

    (1999)
  • H. Yabu et al.

    Langmuir

    (2005)
  • H. Yabu et al.

    Langmuir

    (2006)
There are more references available in the full text version of this article.

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