Recently, it has been put forward that bubbles of nanometer scale (nanobubbles) can exist on solid surfaces immersed in aqueous solution, especially on hydrophobic substrates. This interfacial phenomenon has invited extensive interests in both scientific and commercial fields. Experimental evidence including the study of atomic force microscopy (AFM) has been provided to support the existence of nanobubbles. But, there are still many debates in this field. In this paper, a degassing process is combined with direct AFM imaging to prove that the features in the AFM images are nanobubbles. It is found that the morphology of nanobubbles on the highly oriented pyrolytic graphite (HOPG) surface was noticeably deformed during contact mode imaging and their size is extremely sensitive to the imaging force of AFM. By observing nanobubbles in ethanol solution of different concentrations, we found that ethanol solution more concentrated than 20% (V/V) may have a destructive effect on nanobubbles.

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