Langmuir, Vol.19, No.15, 6283-6296, 2003
Direct patterning of NiB on glass substrates using microcontact printing and electroless deposition
We investigate a method to direct the electroless deposition (ELD) of NiB on glass by microcontact-printing a reagent from an elastomeric stamp onto a glass substrate. There are three variants of this method depending on the reagent to be printed. ELD of a metal on a glass substrate necessitates the pretreatment of the glass with organic linkers that can bind a catalyst from solution. We use colloidal Pd/Sn as catalyst and immobilize these particles via an amino-functionalized silane such as 3-(2-aminoethylamino)-propyltrimethoxysilane (EDA-Si) grafted to the glass substrate. The first variant includes microcontact-printing EDA-Si onto glass to bind the colloidal Pd/Sn catalyst at well-defined locations on the substrate. Here, the stamp is first hydrophilized with an O-2-based plasma and then inked using different methods that include wet-inking, inking of the silane through the vapor phase, and contact inking. ELD of NiB initiates in those regions of the substrate that were previously microcontact-printed. This approach entails the problem of inking and printing of an excess of silane, which can be washed away from the printed regions and can thereby induce the ELD of NiB grains adjacent to the desired pattern. In the second approach, the entire glass is uniformly derivatized with EDA-Si, and colloidal Pd/Sn particles are inked onto a stamp and microcontact-printed to activate the substrate where desired. These colloids do not diffuse on the substrate during printing and subsequent steps, allowing the formation of NiB patterns having excellent contrast and accuracy even over areas as large as 4" in diameter. Similar to the first method, inking and reusing stamps is inconvenient because the colloids are suspended in a solution of concentrated HCl and the stamp needs to be hydrophilized and covered with a thin layer of a polyelectrolyte to achieve homogeneous inking of the stamp with these colloids. The third and most promising approach is to derivatize the glass substrate homogeneously with both EDA-Si and Pd/Sn colloids and then deactivate the catalyst selectively prior to the ELD step by microcontact-printing eicosanethiol (ECT). In this case, it is possible to employ hydrophobic PDMS stamps, to reuse them, to optimize the inking and printing conditions, and to form high-quality NiB structures with lateral dimensions ranging from several hundred to below 1 Pm. This work suggests that microcontact printing (muCP) and ELD can be combined in a variety of manners to provide interesting alternatives to conventional microfabrication methods that otherwise include the deposition of metals in a vacuum process and patterning methods based on photolithography.