Fig. 1

Sections of an example mass spectrum illustrate the presence of a H⁺, \({\text{H}}_{2}^{ + }\), \({\text{H}}_{3}^{ + }\), and O⁺ peaks; b Cu²⁺, \({\text{O}}_{2}^{1 + }\), Ga²⁺, and CuO²⁺ peaks; c Cu⁺, \({\text{CuH}}_{ 2}^{ 1+ }\), Ga⁺, and CuO¹⁺ peaks; and d Cu₃O²⁺ peaks. The laser pulse energy is 40 pJ, the laser pulse frequency is 100 kHz, and the specimen tip base temperature is 20 K