This paper reports a new highly simplified machining process for three dimensional (3D)-fractal nanofabrication based on oxide-only corner lithography. It consists of a repeated sequence of wet etching (silicon), thermal oxidation and wet etching (silicon oxide). The previously reported 3D-fractal fabrication process needed additional low pressure chemical vapor deposition (LPCVD) steps of silicon nitride, as well as local oxidation of silicon (LOCOS). Employing this new procedure, a three generation folded silicon oxide fractal sheet with approx. a 10 µm footprint has been fabricated.

No abstract

No abstract

We report here first results obtained on a novel, in situ renewable mercury microelectrode integrated into an atomic force microscopy (AFM) cantilever. Our approach is based on a fountain pen probe with appropriate dimensions enabling reversible filling with (nonwetting) mercury under changing the applied pressure at a connected mercury supply in a dedicated experimental setup. The fountain pen probe utilizes a special design with vertical pillars inside the channel to minimize mechanical perturbation. In proof of principle experiments, dropping and hanging mercury drop were observed as a function of the applied pressure at the external mercury supply. Electrical conductivity occurred only through the mercury after filling, and the empty fountain pen probe showed excellent electrical insulation. This was demonstrated by chronoamperometric measurements in the electrolyte and by mechanical and electrical contacting of an ITO substrate with a mercury-filled and empty probe in air. Finally, cyclic voltammetry and square wave voltammetry were done in a static mercury electrode fountain pen configuration, demonstrating the principle usability of the mercury probe for electrochemical studies. Our findings are of fundamental importance as they enable further integration of a renewable mercury electrode probe into an AFM setup, which is the subject of ongoing work.

A technique for contactless liquid deposition on the nanoscale assisted by an electric field is presented. By the application of a voltage between the liquid inside a (FluidFM) nanofountain pen AFM probe and a substrate, accurate contactless deposition is achieved. This technique allows for the deposition of polar liquids on non-wetting substrates. Sodium sulfate dried deposits indicate that the spot size and height increases with t0.33±0.04 and t0.35±0.10, respectively. The minimum observed diameter was 70 nm. By measuring the probe deflection and the electric deposition current, we confirm that deposition is truly non-contact. We propose a simple model based on a constant stream of liquid to the substrate, which explains our observations qualitatively.

In this paper a micromachining method for batch fabrication of in-plane atomic force microscope (AFM) probes that consist of a sharp silicon nitride tip on a monocrystalline silicon cantilever is presented. The tips are realized by conformal deposition of silicon nitride inside an anisotropically etched cavity inside a silicon wafer. The best measured radius of the sharp tips was 8 nm. Our fabrication method is fully compatible with silicon-on-insulator (SOI) micromachining, allowing a straightforward monolithic integration of the AFM probes with high-aspect-ratio monocrystalline silicon MEMS. The fabrication method allows for lateral cantilevers, which oscillate in the plane of the fabrication wafer. This allows for simple integration of micromechanical transducers, opening the way towards dedicated probes for high speed AFMs. To demonstrate the innovation potential of this method, three different probe designs were fabricated: a plane passive AFM probe, a probe with integrated electrostatic actuator, and a probe which allows scanning on vertical sidewalls. The passive probes were successfully tested in a commercial AFM set-up. Correct operation of the probes with integrated actuator was demonstrated by actuation under a laser vibrometer.

Electrospray deposition utilizes a high electric field to extract liquid droplets from a capillary nozzle. In this contribution we demonstrate non-contact droplet deposition by electrospray from atomic force microscopy (AFM) probes with a fully integrated microfluidic system, so called FluidFM probes. Electrospray experiments were performed using probes with a pyramidal tip with a sub-micron size aperture in a dedicated setup. The onset voltage as function of the gap between the probe tip and the substrate was measured and compared with a numerical model. Onset voltages in the range 360-410 V were found at 8.5 µm gap height. We observed a reduction in onset voltage with an increase in external pressure. Wetting of the outside of the tip could be reduced by applying a fluorocarbon coating.

The imaging of objects by standard bright field microscopy is limited by the wavelength of light. An advanced high resolution microscopy technique, based on a relatively simple principle, is atomic force microscopy (AFM). In this technique the topography of a surface is mapped by measuring the force acting on an extremely sharp tip when it is scanned over a surface of interest. Nanoscale resolution can be obtained with AFM, which makes it an indispensable tool for nanotechnology. Next to imaging, even more exciting possibilities become available by the integration of additional functions into the probe. In this thesis, this functionalization of AFM probes is explored.Regarding actuation, the integration of an electrostatic microactuator in the probe was investigated, to obtain a mechanically active AFM probe. The motivation for this work comes from the drive towards high-speed (video-rate) AFM, which requires tips that are sharp and made of a durable material (such as silicon nitride). One of the limiting factors in high-speed AFM is the bulk piezo, which suffers from hysteresis and creep and has limited displacement at higher frequencies. By replacing the piezoelectric actuator by an integrated capacitive micro electro mechanical system (MEMS) actuator, higher scan rates can be obtained. To make the actuator integration more straightforward, a silicon-on-insulator (SOI) compatible fabrication process for the fabrication of in-plane tips (tips directed in the plane of the fabrication wafer) was developed and tested. With this process, sharp silicon nitride tips (best measured radius 8 nm) can be batch fabricated on monocrystalline silicon cantilevers. The in-plane aspect of the fabrication allows for arbitrarily shaped cantilevers.Electrochemical sensing functionality in AFM was obtained by filling a nanofountain pen probe with mercury, resulting in an in-situ renewable mercury microelectrode. Both dropping mercury electrode and hanging mercury droplet configurations were obtained by the control of the pressure on the mercury. In the static droplet configuration, chronoamperometric measurements and cyclic and square-wave voltammograms were obtained with the potential of microscale spatial resolution.Liquid deposition in AFM was studied by using fountain pen probes with various tip geometries. Spotting experiments in contact mode showed a t 0.21±0.01 dependence of the spotsize on the contact time. A significant increase in droplet deposition speed was obtained by writing lines, which subsequently break up into droplets. Regular arrays of mono and bimodal dispersed droplets were obtained by varying the tip-substrate speed. By using electrohydrodynamic deposition, scaled down to micrometer sized gaps, contactless deposition of solids dissolved in liquid was achieved. This technique allows for the deposition of polar liquids on nonwetting surfaces, which is challenging for contact mode techniques. Furthermore, the precise z-control in the AFM setup allows for significantly smaller deposits than can be achieved by, fo...