Hans-Joachim Münzer

Local field enhancement effects for nanostructuring of surfaces

We report on a method that allows the nanostructuring of surfaces with intense laser pulses. For this purpose isolated polystyrene spheres with diameters in the order of the laser wavelength were deposited on a silicon or glass surface. Illumination with short and ultrashort laser pulses produced holes underneath these particles. Calculations of the field near the particles make clear that geometrical optics, that is, focusing by a spherical lens, as well as near‐field effects, contribute to the size and shape of these holes. This technique can be utilized for the parallel structuring of large surface areas with a single laser shot.

OPTICAL RESONANCE AND NEAR-FIELD EFFECTS IN DRY LASER CLEANING

Optical problems, related to the particle on the surface, i.e. optical resonance and near-field effects in laser cleaning are discussed. It is shown that the small transparent particle with size by the order of the wavelength may work as a lens in the near-field region. This permits to focus laser radiation into the area with the sizes, smaller than the radiation wavelength. It leads to 3D effects in surface heating and thermal deformation, which influences the mechanisms of the particle removal.

A circuit for measuring the gap voltage of a scanning tunneling microscope on a nanosecond time scale

We demonstrate a new circuit design for fast measurements of the voltage drop across the gap of a scanning tunneling microscope (STM) based on the simultaneous operation of two different amplifiers. The first is a fast instrumentation amplifier, sensing directly the voltage drop across the tunneling barrier, the second is a medium speed current amplifier with an overall gain of 108 V/A, suitable for normal STM operation. We obtained a time resolution of 10 ns measuring the plasma ignition under a STM tip during illumination with an intense 10 ns laser pulse. Possible applications include the study of STM point contacts.

An approach to spectroscopy and phase measurements in scanning plasmon near-field microscopy

A new optical setup for plasmon near-field optical microscopes is introduced which allows to improve the signal/background ratio independently of the wavelength used and therefore makes the spectroscopy feasible. Calculated and experimental examples demonstrate this improvement obtained by addition of ellipsometric components. Furthermore, a first measurement in combination with a scanning tunnelling microscope shows that it is possible to extrude phase information from this setup as well.