An Electron Diffraction Study on Mixed PdCl2 / SnCl2 Catalysts for Electroless Plating

Abstract

The activated or catalyzed surface conditions for initiating electroless metal deposition were studied by means of transmission electron microscopy and electron diffraction analysis. Four mixed PdC1JSnC12 catalysts, including two commercial samples, and five accelerators (NaOH, HC1, H2SO4, NH4OH, and NI-I4BF4) were used in this study. The acceleration with NaOH gave the finest remaining particles which were almost bare active nuclei, while the acceleration with ammonate group (NH4OH and NI-I4BF4) coagulated small particles to produce high density particles. The electron diffraction patterns after activation, for the catalysts prepared in our laboratory, showed amorphous broad diffraction rings which were explained as fcc structure, while for the commercial catalysts, they showed relatively sharp and netlike profiles which could be attributed to orthorhombic structure. The electron diffraction patterns after acceleration with NaOH became the sharper profiles of fcc structure, however in the case of ammonate group, they showed the complicated profiles of non-fcc structure. Finally the catalytically active sites or nuclei are discussed.There have been two groups of investigations of the PdC12/SnC12 catalyst solution initiating electroless plating onto nonmetallic substrates, namely, to focus on whether the catalytic activity is due to Pd-Sn solute complexes or to the presence of colloidal particles in the catalyst solution. Matijevid et al. (1) concluded that colloidal particles in solution exhibit catalytic activity on the basis of colloid science measurements. The present authors (2) also showed the colloidal states to be active by photospectroscopy (u.v. and vl) and electron microscopy. The final active sites initiating metal deposition have been discussed with some results of electron diffraction (3, 4), MSssbauer (5), and Rutherford scattering spectroscopies (6). By electron diffraction analysis Feldstein et al.(3) showed the fcc diffraction patterns which were due to Pd3Sn. Cohen et al. (5) using MSssbauer spectroscopy constructed a model in which the colloidal particles consist of Pd-Sn alloy core with a stabilizing layer of adsorbed Sn(II) ions. Meek (6) indicated from Rutherford scattering measurement that the Pd/Sn ratio becomes(~ <) 1 after activation and ___3 after acceleration and finally ~6 at the initial stage of copper plating. The present authors (2) derived the conclusion from x-ray photoelectron spectroscopy that the Pd/Sn ratio after acceleration depends on the catalyst activity and that it is less than unity. In this communication, we will discuss the surface conditions of Pd-Sn particles on the substrate revealed by electron diffraction study and also investigate the acceleration effect on surface conditions. ExperimentalThree samples of PdC1JSnCI~ catalysts which were employed in the previous study (2) and the commercial sample "F" were used and the detailed preparations and compositions were previously shown in Ref.(2). The sample "A" (low catalytic activity) and "D" (high catalytic activity)...

Microstructure evolution during electroless copper deposition

“…These diffused diffraction rings cause difficulty in determining an exact lattice constant, but it is estimated as =0.4 nm on average. This agrees in general with those obtained by Osaka et al, [8], The particle size effect, the variation of Pd/Sn concentration ratios in the particles, and possible strain effects may contribute to the diffuseness of the electron diffraction rings.…”

“…The sensitization and activation process by double immersion in SnClj and PdClj solutions has been studied [1][2][3] and one-step activation in PdClj-SnClj colloid solution followed by acceleration (HCl or NH4HF2 and others) was also investigated [4][5][6][7][8]. In contrast to the detailed chemical analyses presented in these researches [1][2][3][4][5][6][7][8], we studied the activation process through microstructure analysis by scanning transmission electron microscopy (STEM). This method provides information on sizes and distributions as well as chemical composition of the catalytic particles.…”

Characterization of PdSn catalysts for electroless metal deposition

“…The Cu on the accelerated samples, as on the unacceleratcd sample, is distributed as larger clumps and small nuclei. Such a distribution was also observed by Osaka et al [20]. After acceleration, the Cu tends to be more distributed as clumps; the extent of the increased clumping depends on the accelerator used.…”

“…Additionally, Matijevic et al [14] point out that the absence of light scattering from a solution does not prove the absence of a colloid. Osaka et al [20] and Horkans et al [21] have used electron microscopy to investigate the effect of different accelerators on the PdSn catalyst layer. Horkans et al [21] prepared thin epoxy samples for direct transmission electron microscopy on substrates chemically simEar to epoxy boards.…”

Acceleration of Electrocatalytic Activity on Pt–Sn Nanoparticles

“…Consequently, chemical baths are commonly used for this purpose and thereby accelerate the "take" of UPD Cu onto the Pd nanoparticle surfaces. 26 26,28,32 The effect of accelerators on surface colloidal distribution, particle size, and surface Sn concentration has been investigated with respect to electroless UPD of Cu on Pd. NaOH is the best chemical agent for the removal of Sn from Pd nanoparticles, removing nearly all of the Sn, causing little catalyst agglomeration, and maintaining the original Pd crystal structure.…”