Methods and systems that include a nanotube used as an emitter in the testing and fabrication of integrated circuits. The nanotube emits a signal to a substrate. Based on the signal or the electrical properties, e.g., current induced in the substrate by the signal, the region of the substrate is characterized. The characterization includes topology of the region of the substrate such as determining whether a recess in the substrate has a proper depth or other dimensions or characteristics of the substrate.