2-dimensional electron gas 1 AlGaN/GaN heterostructures 1 Aluminum gallium nitride 1 Amino acids 1 Carboxylation 1 Chemical and biological sensing 1 Conductivity measurements 1 Electric conductivity measurement 1 Electron gas 1 Gallium nitride 1 HEMT 1 High electron mobility transistors 1 III-V semiconductors 1 Intermolecular interactions 1 Molecules 1 NEXAFS 1 Phase interfaces 1 Preferential orientation Sensor 1 Sensors 1 Transistor 1 Transistors 1 X ray photoelectron spectroscopy 1 XPS 1 Zwitterion 1