Patterning of silicon surfaces with noncontact atomic force microscopy: Field-induced formation of nanometer-size water bridges

6 pages, 9 figures.Nanometer-size water bridges have been used to confine the oxidation of silicon surfaces with a noncontact atomic force microscope. The formation of a water bridge between two surfaces separated by a gap of a few nanometers is driven by the application of an electrical field. Once a liquid bridge is formed, its length and neck diameter can be modified by changing the tip-sample separation. The liquid bridge provides the ionic species and the spatial confinement to pattern Si(100) surfaces in noncontact force microscopy. The method is applied to write arrays of several thousands dots with a periodicity of 40 nm and an average width of 10 nm.The work was supported by the Commission of the European Communities (Project 22955, LASMEDS), Comunidad Autónoma de Madrid and the DGICYT of Spain (PB-94-0016).Peer reviewe

Sistema y procedimiento de inspección de superficies de estructuras micro y nanomecánicas

Sistema de inspección de superficies dispuesto para detectar características de desplazamiento relativo y/o de vibración de diversos puntos de una pluralidad de elementos (51) que forman parte de una estructura mecánica (5), comprendiendo dicho sistema: una fuente de luz (1) dispuesta para generar, al menos, un haz de luz (11); un detector sensible a la posición (2) dispuesto para recibir el haz de luz cuando es reflejado fuera de la estructura mecánica (5) y para generar, al menos, una señal de salida en respuesta a la recepción de dicho haz de luz; un sistema de control electrónico (3); un medio de exploración (4) para el desplazamiento relativo de dicho haz de luz con relación a la estructura mecánica (5) con el fin de explorar dicha estructura mecánica con el haz de luz, siguiendo las instrucciones del sistema de control electrónico (3); caracterizado porque dicho sistema de control electrónico (3) está dispuesto para controlar el medio de exploración (4) con el fin de desplazar el haz de luz por la estructura mecánica a lo largo de una primera trayectoria (A) con objeto de detectar una pluralidad de posiciones de referencia subsiguientes (C), cada una en un elemento, a lo largo de dicha primera trayectoria (A), en el que dicho sistema de control electrónico (3) está asociado operativamente con dicho detector sensible a la posición (2) para determinar dichas posiciones de referencia (C) como resultado de un análisis de, al menos, una señal de salida de dicho detector sensible a la posición (2); en el que dicho sistema de control electrónico (3) está dispuesto además para controlar el medio de exploración (4) para desplazar el haz de luz por la estructura mecánica a lo largo de una pluralidad de segundas trayectorias (B), estando asociada cada una de dichas segundas trayectorias (B) con una de dichas posiciones de referencia (C); dicho sistema de control electrónico está dispuesto además para obtener, durante el desplazamiento del haz de luz a lo largo de cada una de dichas segundas trayectorias (B), una pluralidad de salidas de señales de posición de dicho detector sensible a la posición (2).Peer reviewedConsejo Superior de Investigaciones Científicas (España)T3 Traducción de patente europe

Coherent optical transduction of suspended microcapillary resonators for multi-parameter sensing applications

Characterization of micro and nanoparticle mass has become increasingly relevant in a wide range of fields, from materials science to drug development. The real-time analysis of complex mixtures in liquids demands very high mass sensitivity and high throughput. One of the most promising approaches for real-time measurements in liquid, with an excellent mass sensitivity, is the use of suspended microchannel resonators, where a carrier liquid containing the analytes flows through a nanomechanical resonator while tracking its resonance frequency shift. To this end, an extremely sensitive mechanical displacement technique is necessary. Here, we have developed an optomechanical transduction technique to enhance the mechanical displacement sensitivity of optically transparent hollow nanomechanical resonators. The capillaries have been fabricated by using a thermal stretching technique, which allows to accurately control the final dimensions of the device. We have experimentally demonstrated the light coupling into the fused silica capillary walls and how the evanescent light coming out from the silica interferes with the surrounding electromagnetic field distribution, a standing wave sustained by the incident laser and the reflected power from the substrate, modulating the reflectivity. The enhancement of the displacement sensitivity due to this interferometric modulation (two orders of magnitude better than compared with previous accomplishments) has been theoretically predicted and experimentally demonstrated

Integrated optical readout for miniaturization of cantilever-based sensor system

We present the fabrication and characterisation of an integrated optical read-out scheme based on single-mode waveguides for cantilever-based sensors. The cantilever bending is read out by monitoring changes in the optical intensity of light transmitted through the cantilever that also acts as a waveguide. The complete system is fabricated in the photo-sensitive polymer SU-8. We show theoretical calculations on the expected sensitivity both when operated in air and liquid and compare these with experimental characterisation of the system in air where the cantilever is deflected mechanically. The experimental results compare well with the results obtained from the theoretical calculations.Peer reviewe

Effect of the adsorbate stiffness on the resonance response of microcantilever sensors

The authors present a theoretical model to predict the resonance frequency shift due to molecule adsorption on micro- and nanocantilevers. They calculate the frequency shift experienced by cantilevers made of either silicon or the polymer SU-8, when two adsorbates, myosin protein and an alkanethiol, are attached to the cantilever surface. They demonstrate that the effect of the adsorbate stiffness can be comparable or even larger than the mass effect, producing positive frequency shifts. The results provide methods for decoupling both opposite effects and routes for the design of resonators with high sensitivity to molecule adsorption based on either stiffness or mass effects.Peer reviewe

Procedimiento de bioanálisis de moléculas de ácido nucleico en una muestra y biosensor para su implementación

Peer reviewedConsejo Superior de investigaciones CientíficasT3 Traducción de patente europe

Origin of the response of nanomechanical resonators to bacteria adsorption

Resonant microcantilevers are being actively investigated as sensitive mass sensors for biological detection. By performing experiments of adsorption of the bacteria Escherichia coli on singly clamped microcantilevers, we demonstrate that the effect of the added mass is not the only and may not be the main origin of the response of these sensors. The experiments show that the magnitude and sign of resonance frequency shift both depend critically on the distribution of the adsorbed bacterial cells on the cantilever. We relate this behavior to the added mass that shifts the resonance to lower frequencies and the higher effective flexural rigidity of the cantilever due to the bacteria stiffness that shifts the resonance to higher frequencies. Both effects can be uncoupled by positioning the cells where each effect dominates, near the free cantilever end for measuring the added mass or near the clamping for measuring the increase of flexural rigidity.One of the authors (D.R.) acknowledges the fellowship funded by the Autonomic Community of Madrid. This work was supported by the Spanish National Research Council (CSIC), Project No. 200550M056.Peer reviewe

Fabrication of gold nanowires on insulating substrates by field-induced mass transport

A method for the fabrication of nanometer size gold wires on insulating surfaces is presented. An oscillating gold-coated atomic force microscope tip is brought into close proximity of a silicon dioxide surface. The application of a negative sample voltage produces the transport of gold atoms from the tip to the surface. The voltage is applied when there is a tip–surface separation of ∼3 nm. The finite tip–surface separation enhances the tip lifetime. It also allows the application of sequences of multiple voltage pulses. Those sequences allow the fabrication of continuous nanowires. The atomic force microscope gold deposition is performed at room temperature and in ambient conditions which makes the method fully compatible with standard lithographic techniques. Electron transport measurements of the wires show a clear metallic behavior. Electrical resistivities of ∼ 3×10−7 Ω m and current densities of up to 5×1011 A m−2 are reported.This work was supported by the Dirección General de Enseñanza Superior e Investigación (PB98-0471) and the European Commission (MONA-LISA, GRD1-2000-25592). One of the authors (M.C.) acknowledges financial support from the Comunidad de Madrid.Peer reviewe

Physics of nanomechanical spectrometry of viruses

There is an emerging need of nanotools able to quantify the mechanical properties of single biological entities. A promising approach is the measurement of the shifts of the resonant frequencies of ultrathin cantilevers induced by the adsorption of the studied biological systems. Here, we present a detailed theoretical analysis to calculate the resonance frequency shift induced by the mechanical stiffness of viral nanotubes. The model accounts for the high surface-to-volume ratio featured by single biological entities, the shape anisotropy and the interfacial adhesion. The model is applied to the case in which tobacco mosaic virus is randomly delivered to a silicon nitride cantilever. The theoretical framework opens the door to a novel paradigm for biological spectrometry as well as for measuring the Young's modulus of biological systems with minimal strains.We acknowledge financial support from the Spanish Science Ministry (MINECO) through projects MAT2012-36197 and from European Research Council through Starting Grant NANOFORCELLS (ERC-StG-2011-278860).Peer Reviewe

Spatially Multiplexed Micro-Spectrophotometry in Bright Field Mode for Thin Film Characterization

Thickness characterization of thin films is of primary importance in a variety of nanotechnology applications, either in the semiconductor industry, quality control in nanofabrication processes or engineering of nanoelectromechanical systems (NEMS) because small thickness variability can strongly compromise the device performance. Here, we present an alternative optical method in bright field mode called Spatially Multiplexed Micro-Spectrophotometry that allows rapid and non-destructive characterization of thin films over areas of mm2 and with 1 μm of lateral resolution. We demonstrate an accuracy of 0.1% in the thickness characterization through measurements performed on four microcantilevers that expand an area of 1.8 mm2 in one minute of analysis time. The measured thickness variation in the range of few tens of nm translates into a mechanical variability that produces an error of up to 2% in the response of the studied devices when they are used to measure surface stress variations.The authors acknowledge the financial support by European Research Council through Starting Grant NANOFORCELLS (ERC-StG-2011-278860). P. M. Kosaka acknowledges funding from the Fundación General CSIC ComFuturo program. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI