Adsorption and deposition of anthraquinone-2-carboxylic acid on alumina studied by inelastic electron tunneling spectroscopy, infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy

The adsorption state of anthraquinone-2-carboxylic acid (AQ-2-COOH) deposited from acetone solutions (0.01-1.00 mg/ml) on native oxide surfaces of Al films was characterized by inelastic electron tunneling spectroscopy, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. The oxide was prepared on evaporated Al films at room temperature in an oxygen-dc glow discharge. The morphology of the deposited AQ-2-COOH on the oxide surfaces was observed and analyzed by atomic force microscopy. These surface analyses showed that AQ-2-COOH is adsorbed predominantly as a uniform nanometer-scale film of carboxylate anions on the oxide surfaces deposited from solutions with concentrations lower than or equal to 0.02 mg/ml. It was found that AQ-2-COOH is adsorbed as both a uniform film of anions and as micron-sized particles of neutral molecules with heights of a few tens of nanometers when AQ-2-COOH is deposited from solutions with concentrations higher than 0.02 mg/ml. A comparison of the results obtained by these surface analytical techniques clearly shows the features and advantages of these analytical techniques.