Terahertz near-field microscopy

We report on apertureless terahertz (THz) microscopy and its application for serniconductor characterization. Extreme subwavelength resolutions down to 150nm are achieved with few-cycle THz pulses having a bandwidth of 3THz. The imaging mechanism is characterize by time-resolved THz techniques. We find that apertureless THz microscopy can be well described by the electronic resonance of the scanning-tip interacting with the sample's surface. The capacitance between tip and surface is a key parameter, which provides insight into the local high frequency permittivity of the semiconductor structure. Applying electromodulation techniques allows for imaging electronic charge distributions in microstructured semiconductors. The sensitivity of THz microscopy suffices to detect as few as about 5000 electrons.