pH-dependent surface properties of the gallium nitride – Solution interface mapped by surfactant adsorption

Jianan Wang, X. Zhang, Constance Wang, Hua Li, Haoran Li, Stacia Keller, Umesh K. Mishra, Brett D. Nener, Giacinta Parish, Rob Atkin

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


Hypothesis: The surface charge of gallium nitride (GaN) in contact with solution is controlled by pH via surface protonation and deprotonation, similar to silica. Ionic surfactants adsorb on surfaces via electrostatic and hydrophobic interactions and can be utilized to reflect the surface charge of GaN. Experiments: The surface charge properties of Ga-polar GaN in solution were probed as a function of pH using atomic force microscopy (AFM). AFM soft-contact images and force curves were used to study the pH-dependent adsorption of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecylsulfate (SDS) on GaN surfaces. To further confirm the AFM results, GaN/AlGaN/GaN heterostructure-based ion sensing devices were used to measure the surfactant adsorption over the same pH range. Findings: SDS aggregates adsorb on GaN below pH 2.75 while CTAB aggregates adsorb above pH 10. This shows that the GaN surface carries substantial net positive charge at low pH, and negative charge at high pH. There is no clear SDS or CTAB adsorption on the GaN surface between pH 3 and 9.75, which indicates the surface is weakly charged. GaN/AlGaN/GaN heterostructure-based devices confirm these results, and demonstrate the utility of these devices for measuring surfactant adsorption.

Original languageEnglish
Pages (from-to)680-688
Number of pages9
JournalJournal of Colloid and Interface Science
Publication statusPublished - 15 Nov 2019


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