Evaluation of Key Factors for Preparing High Brightness Surfaces of Aluminum Films Electrodeposited from AlCl3-1-Ethyl-3-Methylimidazolium Chloride-Organic Additive Baths

• Published in: Electrochimica acta Vol. 215; pp. 556 - 565
• Main Authors: Uehara, Kazuma, Yamazaki, Keitaro, Gunji, Takao, Kaneko, Shingo, Tanabe, Toyokazu, Ohsaka, Takeo, Matsumoto, Futoshi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2016
• Subjects: 4-Pyridinecarboxylic Acid Hydrazide; Additive; Aluminum; Electrodeposition; Ionic Liquid; Ionic Liquid; 4-Pyridinecarboxylic Acid Hydrazide; Electrodeposition; Additive; Aluminum
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2016.08.125

[Display omitted] •The bath composition was optimized to achieve a deposited Al films with the highest brightness.•The use of 4-pyridinecarboxylic acid hydrazide (4-PCAH) as an additive resulted in the highest brightness.•The reflectivity of the Al films prepared with 4-PCAH as an additives was 84% at 450nm.•The relationship between the brightness of the Al films and the structure of the additives was evaluated. The effects of additives, such as 4-pyridinecarboxylic acid hydrazide (4-PCAH) and its analogs, and organic solvents, such as toluene, benzene and xylene, on the brightness of aluminum (Al) prepared using constant-current deposition from an ionic liquid of ethyl-3-methylimidazolium chloride (EMIC)-aluminum chloride (AlCl3) were investigated by light spectroscopy, scanning electron microscopy (SEM), reflectivity tests, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy. In order for the deposited Al films to exhibit high brightness, a combined use of 4-PCAH and toluene is effective. Moreover, the relationship between the brightness (i.e., reflectance) of the prepared Al films and the molecular structure of a variety of additives was clarified. Both a pyridine ring and an acetyl hydrazine group are necessary for constituting an effective additive. The structural isomers of a given additive bring about different surface brightness, e.g., for PCAHs the reflectance at 450nm is in the order of para-isomer>meta-isomer>ortho-isomer. It was considered that in 4-PCAH electron-withdrawing acetyl hydrazine group is bounded to the pyridine ring, and consequently the electron density around the nitrogen atom in the pyridine ring is decreased, which is conducive to the adsorption of 4-PCAH on the cathode of deposited Al films. In addition, the reflectance was found to increase with decreasing the crystalline domain size of Al deposits and with increasing the reaction resistance for Al electrodeposition. The reaction mechanism of Al electrodeposition from the present ionic liquid media containing various additives is also discussed briefly.