A. Heeren

Influence of temperature on HSQ electron-beam lithography

The authors present a study of the influence of temperature on hydrogen silsesquioxane (HSQ) e-beam lithography during drying, developing, and postdevelopment baking. In accordance with the observation that tempering at relatively low temperatures can already lead to noticeable cross-linking, comparable to the effect of e-beam exposure, the authors find that decreasing the prebake temperature below 90°C and drying the HSQ resist at room temperature in vacuum yields better resolution compared with resist that was dried in a furnace or on a hotplate at 90°C or above. Developing the exposed resist not at room temperature (23°C) but at 60°C results in significant contrast enhancement. Further solidification of the developed resist is obtained by baking the material above 300°C. Correlations between these findings and IR data are presented.

Three-dimensional optical antennas: Nanocones in an apertureless scanning near-field microscope

A sharp-tipped gold nanocone and the vertically aligned metallic tip of a near-field optical microscope together form a three-dimensional optical antenna with a highly controllable gap. Confocal measurements with different laser modes show the efficient axial excitation of the cones with a longitudinally polarized field. In the antenna configuration, extremely strong field enhancement up to a factor of 100 is obtained by tuning the gap between the two sharp tips down to few nanometers.

Contactless capturing of particles in liquid using pulsed alternating dielectrophoresis

Dielectrophoresis is an effective method for manipulation of particles in a medium, which can be achieved by applying electrical potentials to appropriately arranged electrodes. In the case of positive dielectrophoresis, the particles will move to regions of strong electric field and be captured at the edge or the surface of the electrodes, usually. The drawback thereby is that the particles may attach to the electrodes, leading to unwanted side effects. Negative dielectrophoresis moves them away from high field regions. In this article, the authors present a new method for contactless capturing of particles by using pulsed alternating dielectrophoresis. A signal sequence consisting of two pulsed ac voltages of different frequencies is applied to the electrodes. Each of them generates either positive or negative dielectrophoresis, respectively. With appropriate settings of dwell times and amplitudes, the particles are attracted toward the electrodes without attaching to them. Furthermore, the average dist...

Catalyst patterning for carbon nanotube growth on elevating posts by self-aligned double-layer electron beam lithography

For gas-flow aligned growth of carbon nanotubes (CNTs), it is important to minimize interaction of the growing CNTs with the substrate. The authors present a method to fabricate thin catalyst films on top of protruding hydrogen silsesquioxane (HSQ) patterns. Self-alignment of the catalyst film with the HSQ pattern is achieved by exposing two layers of resist, polymethyl methacrylate (PMMA) on top of HSQ, simultaneously. By selecting appropriate development parameters for PMMA and HSQ, a common exposure dose can be applied. After a standard lift-off process HSQ is developed and CNTs are grown on the protruding HSQ patterns resulting in gas-flow aligned CNTs that can be further processed, e.g., for the fabrication of CNT based transistors.