Lauge Gammelgaard

Microfabricated photoplastic cantilever with integrated photoplastic/carbon based piezoresistive strain sensor

We present an SU-8 micrometer sized cantilever strain sensor with an integrated piezoresistor made of a conductive composite of SU-8 polymer and carbon black particles. The composite has been developed using ultrasonic mixing. Cleanroom processing of the polymer composite has been investigated and it has been shown that it is possible to pattern the composite by standard UV photolithography. The composite material has been integrated into an SU-8 microcantilever and the polymer composite has been demonstrated to be piezoresistive with gauge factors around 15–20. Since SU-8 is much softer than silicon and the gauge factor of the composite material is relatively high, this polymer based strain sensor is more sensitive than a similar silicon based cantilever sensor.

Actuation of microfabricated tools using multiple GPC-based counterpropagating-beam traps.

We explore the functionalities of a generalized phase contrast (GPC) -based multiple-beam trapping system for the actuation of various microfabricated SiO2 structures in liquid suspension. The arrays of optical traps are formed using two counterpropagating light fields, each of which is spatially reconfigurable in both cross-sectional geometry and intensity distribution, either in a user-interactive manner or under computer supervision. Design of microtools includes multiple appendages with rounded endings by which optical traps hold and three-dimensionally actuate individual tools. Proof-of-principle demonstrations show the collective and user-coordinated utility of multiple beams for driving microstructured objects. The potential to integrate these optically powered microtools may lead to more complex miniaturized machineries - a closely achievable goal with the real-time reconfigurable optical traps employed in this work.

Direct measurement of electrical conductance through a self-assembled molecular layer.

The self-assembly of organic molecules on surfaces is a promising approach for the development of nanoelectronic devices. Although a variety of strategies have been used to establish stable links between molecules, little is known about the electrical conductance of these links. Extended electronic states, a prerequisite for good conductance, have been observed for molecules adsorbed on metal surfaces. However, direct conductance measurements through a single layer of molecules are only possible if the molecules are adsorbed on a poorly conducting substrate. Here we use a nanoscale four-point probe to measure the conductivity of a self-assembled layer of cobalt phthalocyanine on a silver-terminated silicon surface as a function of thickness. For low thicknesses, the cobalt phthalocyanine molecules lie flat on the substrate, and their main effect is to reduce the conductivity of the substrate. At higher thicknesses, the cobalt phthalocyanine molecules stand up to form stacks and begin to conduct. These results connect the electronic structure and orientation of molecular monolayer and few-layer systems to their transport properties, and should aid in the rational design of future devices.

A complementary metal-oxide-semiconductor compatible monocantilever 12-point probe for conductivity measurements on the nanoscale

We present a complementary metal-oxide-semiconductor compatible, nanoscale 12-point-probe based on TiW electrodes placed on a SiO2 monocantilever. Probes are mass fabricated on Si wafers by a combination of electron beam and UV lithography, realizing TiW electrode tips with a width down to 250nm and a probe pitch of 500nm. In-air four-point measurements have been performed on indium tin oxide, ruthenium, and titanium-tungsten, showing good agreement with values obtained by other four-point probes. In-vacuum four-point resistance measurements have been performed on clean Bi(111) using different probe spacings. The results show the expected behavior for bulk Bi, indicating that the contribution of electronic surface states to the transport properties is very small.

The conductivity of Bi(111) investigated with nanoscale four point probes

The room temperature conductance of Bi(111) was measured using microscopic four point probes with a contact spacing down to 500 nm. The conductance is remarkably similar to that of the bulk, indicating that surface scattering is not a major mechanism for restricting the mobility at this length scale. Also, the high density of electronic surface states on Bi(111) does not appear to have a major influence on the measured conductance. The lower limit for the resistivity due to electronic surface states is found to be around 5 Ω. With such a value for the surface resistivity, surface conduction should not be a significant factor to inhibit the observation of the predicted semiconductor to semimetal transition for thin films of Bi.

Suppression of the Ag/Si surface conductivity transition temperature by organic adsorbates

We present temperature dependent nanoscale four-contact conductance measurements performed on a submonolayer coverage of cobalt phthalocyanine on Si(111)–(3×3)Ag. The presence of the organic adsorbates suppresses the reversible Ag/Si surface phase transition temperature and reduces the magnitude of the accompanying switching of the surface conductance. The absence of an observable Kondo effect is also discussed in terms of the reported electron transfer between the Ag/Si surface and the Co2+ ion.

Wafer scale integration of catalyst dots into nonplanar microsystems

In order to successfully integrate bottom-up fabricated nano- structures such as carbon nanotubes or silicon, germanium, or III-V nanowires into microelectromechanical systems on a wafer scale, reli- able ways of integrating catalyst dots are needed. Here, four methods for integrating sub-100-nm diameter nickel catalyst dots on a wafer scale are presented and compared. Three of the methods are based on a p-Si layer utilized as an in situ mask, an encapsulating layer, and a sacrificial window mask, respectively. All methods enable precise positioning of nickel catalyst dots at the end of a microcantilever, while avoiding con- tamination of the used cleanroom process equipment. The methods are suitable for fabrication of scanning probe tips and nanoelectrodes for advanced characterization probes.

Optically driven microtools fabricated by UV lithography and RIE

We demonstrate the use of multiple optical traps for driving various microfabricated silica structures in liquid host medium. Multiple counterpropagating-beam traps are formed using a generalized phase contrast (GPC) -based optical trapping system. A combination of UV-lithography and reactive-ion etching (RIE) is employed to fabricate the microtools whose design includes having multiple appendages with rounded endings by which optical traps hold and actuate them. Experiments show the collective and user-coordinated utility of multiple beams for driving microstructured objects whose future integration may lead to optically controlled micromachineries.