The Relationship Between Brightness of Aluminum Films Fabricated Using an AlCl3-1-Ethyl-3-Methylimidazolium Chloride-Toluene Bath and Molecular Structure of Additives

Abstract

In our previous study, we showed that the addition of 4-pyridinecarboxylic acid hydrazide (4-PCAH) to an EMIC/AlCl3/toluene mixture improved the brightness of the deposited Al film [1]. The prepared Al films clearly reflect the characters on the surface so that the characters can be read. The reflectivity of the Al surface prepared with EMIC/AlCl3/toluene/4-PCAH was 84% at 450 nm; to the best of our knowledge, this is the highest value achieved. In this study, to elucidate why the addition of 4-PCAH to the EMIC/AlCl3/toluene bath effectively improves the brightness of the electrodeposited Al surfaces, a systematic series of molecules as additives were studied, and the results obtained for each molecule were compared carefully to determine the relationship between the brightness of the prepared Al surface and the molecular structure of the additive. The effect of additives, such as 4-PCAH and its analogs, on the surface brightness, electrodeposition efficiency and chemical composition of prepared Al films was examined using SEM, visible light reflectance measurements and XPS. The decrease in the surface roughness of the Al films causes the high surface brightness. The strong relationship (Fig. 1) between the high brightness and molecular structure of the additives included in the bath was elucidated via a systematic study of various additives. 4-PCAH achieved the highest surface brightness of the electrodeposited Al films prepared with various additives used in this study. [1] X. Fang, K. Uehara, S. Kaneko, S. Sato, T. Tanabe, T. Gunji, F. Matsumoto, Electrochemistry 84 (2016) 17-24. Figure 1. (A)Micrographs of the Al film surfaces obtained by the electrodeposition of Al from EMIC/AlCl3/toluene/4-PCAH baths, (B) Summary of the relationship between the reflectance of the prepared Al films at a wavelength of 450 nm and the molecular structure of the additive. Preparation conditions of the Al film: deposition time 2 h, constant current density 8 mAcm-2; bath composition: EMIC:AlCl3= 33.3 : 66.7 (mol%), toluene concentration: 9.25 M, additive concentration: 1.8 mM. Figure 1