In Situ Surface Enhanced Raman Spectroscopy Analysis of the Electrochemical Deposition Processes Using Plasmon Antenna Sensors

Electrochemical deposition processes such as electrolytic and electroless deposition have been widely applied to form thin films and devices featuring their controllability and capability to deposit uniform layers.  We have applied these processes to fabricate various functional micro/nano structures such as ultra-high density data storage devices etc.[1].  While these processes could potentially achieve the atomic level control, they are quite complicated since numbers of species play various roles during the deposition.  Furthermore, they take place at solid-liquid interface where the way of analysis is quite limited, although molecular/atomic level understanding of the processes is significant in order to achieve further precise control.  For this, we have employed ab initio molecular orbital (MO) and density functional theory (DFT) calculations to theoretically investigate the deposition processes, and have proposed the models of the reaction of reductants for electroless-deposition, as well as the effect of additives [2].  While they could provide insights to mechanistic understanding of the reactions, it would further strengthen these models if experimental or “direct” evidence could be obtained.

In order to achieve this, we focused upon surface enhanced Raman spectroscopy (SERS), and proposed so-called plasmon antenna sensors which have nanofabricated surface designed to obtain extremely high enhancement effect, i.e., the sensitivity, and applied them to analyze various processes taking place at solid/liquid interfaces [3,4]. 

The plasmon antenna is classified into following two types; the “reflection” type antenna consists of plasmon-active metals such as Ag and Au with centrifuged-grooves-like nanostructure, the pitch of which was designed according to the wave length of the incident laser to optimize the enhancement effect.  For the analysis of electrochemical process, this antenna can be directly used as working electrode.  We also developed “transmission” type antenna which can be applied to analyze various processes and materials.  We employed electrodeposition and electroless deposition to fabricate these antenna devices. 

One of the features of these methods is extremely high sensitivity in vertical direction up to sub nm level, which is quite advantageous for atomic scale analysis of the reactions at the electrode surface; for example, we analyzed the behavior of hydrazine and hypophosphate ion for electroless deposition process, as well as the effect of additives such as thiourea, and investigated their interaction from molecular-level aspects.  Based upon this approach, we also developed a system to analyze the behavior of additives in the pores of TSV (through silicon via). A model-pore is fabricated using a Si substrate with electroless-deposited nanoparticles of Au at the surface, which was covered with a trench-shaped structure consisting of poly(dimethylsiloxane)(PDMS).  The incident laser was focused at the substrate surface covered with Au nanoparticle through the PDMS, and it was confirmed that the signal of additives could be detected in situ in high sensitivity, without interference of the signals originated from PDMS, and their behavior was investigated in detail.

This work was financially supported in part by "Development of Systems and Technology for Advanced Measurement and Analysis," Japan Science and Technology Agency, and Grant-in-Aid for Scientific Research, MEXT, Japan.

[1] T. Ouchi, Y. Arikawa, Y. Konishi, T. Homma, Electrochim. Acta, 55, 8081 (2010).

[2] M. Kunimoto, K. Endo, H. Nakai, T. Homma, Electrochim. Acta. 100, 311 (2013).

[3] B. Jiang, T. Ouchi, N. Shimano, A. Otomo, M. Kunimoto, M. Yanagisawa, T. Homma, Electrochim. Acta, 100, 317 (2013).

[4] B. Jiang, M. Kunimoto, M. Yanagisawa, T. Homma, J. Electrochem. Soc., 160, D366 (2013).