G. Villanueva

Metallic Nanowires by Full Wafer Stencil Lithography

Aluminum and gold nanowires were fabricated using 100 mm stencil wafers containing nanoslits fabricated with a focused ion beam. The stencils were aligned and the nanowires deposited on a substrate with predefined electrical pads. The morphology and resistivity of the wires were studied. Nanowires down to 70 nm wide and 5 mum long have been achieved showing a resistivity of 10 microOmegacm for Al and 5 microOmegacm for Au and maximum current density of approximately 10(8) A/cm(2). This proves the capability of stencil lithography for the fabrication of metallic nanowires on a full wafer scale.

Special cantilever geometry for the access of higher oscillation modes in atomic force microscopy

Employing higher oscillation modes of microcantilevers promises higher sensitivity when applied as sensors, for example, for mass detection or in atomic force microscopy. Introducing a special cantilever geometry, we show that the relation between the resonance frequencies of the first and second resonance modes can be modified to separate them further or to bring them closer together. In atomic force microscopy the latter is of special interest as the photodiode of the beam deflection detection limits the accessible frequency range. Using finite element simulations, we optimized the design of the modified cantilever geometry for a maximum reduction of the frequency of the second oscillation mode with respect to the first mode. Cantilevers were fabricated by silicon micromachining and subsequently utilized in an ultrahigh vacuum Kelvin probe force microscope imaging the surface potential of C60 on graphite.

Polymeric MOEMS Variable Optical Attenuator

In this letter, we take advantage of the high coefficient of thermal expansion (CTE) of a chemically amplified, epoxy-based negative polymer (SU-8) to define a low-power consumption polymeric variable optical attenuator that combines the working principles of microoptoelectromechanical systems and photonic lightwave circuits. The SU-8 symmetric structure comprises a seismic mass and four mechanical beams. Three multimode waveguides are defined on this structure: two of them are located on the frame and the third one in the middle of the seismic mass. Aluminum is used as a heater electrode extending over two of the mechanical beams and part of the seismic mass. When a dc voltage is applied, the mechanical beams bend, resulting in a misalignment between the waveguides. Experimental results have shown a power consumption of 12 mW at 20 dB with a working wavelength of 633nm emitted from a light-emitting diode

Fundamentals of Nanomechanical Resonators

This authoritative book introduces and summarizes the latest models and skills required to design and optimize nanomechanical resonators, taking a top-down approach that uses macroscopic formulas to model the devices. The authors cover the electrical and mechanical aspects of nano electromechanical system (NEMS) devices. The introduced mechanical models are also key to the understanding and optimization of nanomechanical resonators used e.g. in optomechanics. Five comprehensive chapters address: The eigenmodes derived for the most common continuum mechanical structures used as nanomechanical resonators; The main sources of energy loss in nanomechanical resonators; The responsiveness of micro and nanomechanical resonators to mass, forces, and temperature; The most common underlying physical transduction mechanisms; The measurement basics, including amplitude and frequency noise. The applied approach found in this book is appropriate for engineering students and researchers working with micro and nanomechanical resonators

3-D modulable PDMS-based microlens system

The design, simulation, fabrication and characterization of 3-D modulable micro-optical system based on poly-dimethilsiloxane (PDMS) are presented in this paper. This system consists on two uncoupled PDMS lenses with different diameter (2 and 10 microm). Under stretching conditions, the dimensions of the small lens are not modified, whereas the geometry of the bigger lens is shifted from spherical to elliptical. A combination of different technologies is used to fabricate this microsystem: silicon, polymer and soft-lithography microfabrication techniques. This combination allows obtaining structures with a simple and mass production technology. Experimental results confirm the predicted numerical simulations, showing that, when the structure is under stretching conditions, the first focus is virtually invariable whereas the second focus becomes a Sturm zone.

Stenciled conducting bismuth nanowiresa)

Stencil lithography is used here for the fabrication of bismuth nanowires using thermal evaporation. This technique provides good electrical contact resistance by having the nanowire structure and the contact pads deposited at the same time. It has also the advantage of modulating nanowires’ height as a function of their width. As the evaporated material deposits on the stencil mask, the apertures shrink in size until they are fully clogged and no more material can pass through. Thus, the authors obtain variable-height (from 27 to 95 nm) nanowires in the same evaporation. Upon their morphological (scanning electron microscopy and atomic force microscopy) and electrical characterizations, the authors obtain their resistivity, which is independent of the nanowire size and is the lowest reported for physical vapor deposition of Bi nanowires (1.2×10−3 Ω cm), only an order of magnitude higher than that of bulk bismuth.

T-shaped microcantilever sensor with reduced deflection offset

The authors have designed and fabricated arrays of microcantilevers with a geometry that shows reduced initial angular offset and angle deviation between the cantilevers of the array. This feature allows to detect the displacement of the cantilevers using the optical beam deflection technique and a single split photodetector. The structure is analytically and numerically simulated to demonstrate its feasibility. In addition, experimental measurements of the angle offset corroborate the offset and the angle deviation reduction. Finally, they illustrate the potential of these micromechanical structures as sensors by measuring a monolayer of single stranded DNA.

Direct Etching of High Aspect Ratio Structures Through a Stencil

This paper reports the feasibility of the fabrication of high aspect ratio structures on substrates via dry etching through a stencil mask placed onto the sample. It demonstrates the possibility to use standard equipment and processes with this novel masking technique, which allows the patterning of fragile and pre-structured surfaces, and avoids the use of resist or additional coating of the sample, reducing costs and processing time. Aspect ratios as high as 13:1 and pattern transfer with a gap of 100 ¿m are demonstrated.

Piezoresistive Microcantilevers for Biomolecular Force Detection

This paper reports the development of piezoresistive microcantilevers for the detection of biomolecules by the measurement of intermolecular binding forces. The detection of the small forces involved in molecular recognition (<100 pN) requires cantilevers with a high force sensitivity and small spring constant. This can be obtained with cantilevers with submicron thickness and width in the micrometer range. We have fabricated polycrystalline silicon cantilevers in a dedicated technology and also in a commercial CMOS process. The cantilevers have been tested by applying a known displacement with an AFM instrument. For the CMOS-integrated cantilevers, which include on-chip amplifying circuits, a force sensitivity of 11 muV/pN and a force resolution of 27 pN have been measured.

Microcollimator for Micrometer-Wide Stripe Irradiation of Cells Using 20–30 keV X Rays

Abstract Pataky, K., Villanueva, G., Liani, A., Zgheib, O., Jenkins, N., Halazonetis, D. J., Halazonetis, T. D. and Brugger, J. Microcollimator for Micrometer-Wide Stripe Irradiation of Cells Using 20–30 keV X Rays. Radiat. Res. 172, 252–259 (2009). The exposure of subnuclear compartments of cells to ionizing radiation is currently not trivial. We describe here a collimator for micrometer-wide stripe irradiation designed to work with conventional high-voltage X-ray tubes and cells cultured on standard glass cover slips. The microcollimator was fabricated by high-precision silicon micromachining and consists of X-ray absorbing chips with grooves of highly controlled depths, between 0.5–10 μm, along their surfaces. These grooves form X-ray collimating slits when the chips are stacked against each other. The use of this device for radiation biology was examined by irradiating human cells with X rays having energies between 20–30 keV. After irradiation, p53 binding protein 1 (53BP1), a nuclear protein that is recruited at sites of DNA double-strand breaks, clustered in lines corresponding to the irradiated stripes.