Force-gradient-induced mechanical dissipation of quartz tuning fork force sensors used in atomic force microscopy

We have studied the dynamics of quartz tuning fork resonators used in atomic force microscopy taking into account mechanical energy dissipation through the attachment of the tuning fork base. We find that the tuning fork resonator quality factor changes even for the case of a purely elastic sensor-sample interaction. This is due to the effective mechanical imbalance of the tuning fork prongs induced by the sensor-sample force gradient which in turn has an impact on the dissipation through the attachment of the resonator base. This effect may yield a measured dissipation signal that can be different to the one exclusively related to the dissipation between the sensor and the sample. We also find that there is a second order term in addition to the linear relationship between the sensor-sample force gradient and the resonance frequency shift of the tuning fork that is significant even for force gradients usually present in atomic force microscopy which are in the range of tens of N/m.Comment: 9 pages, 3 figures and supplemental informatio

Peces marinos de los ordenes Gadiformes, Ophidiiformes y Lophiiformes en aguas colombianas del Pacífico oriental tropical

This document compiles information and records from different reference museum holdings, from around the world, of species of Gadiforms, Ophidiiforms and Lophiiforms from Colombian waters of the Pacific. Also included are records of species of these groups from adjacent waters. The latter records could indicate biogeographic connectivity – i.e. that the same species also occur in Colombian waters, but due to inadequate sampling efforts, they have not yet been collected.En el presente documento se recopila información y registros de colecciones de referencia de diferentes museos del mundo de las especies de Ophidiiformes, Gadiformes, and Lophiiformes de aguas colombianas del Pacífico. También se incluyen registros de colección de especies de estos grupos en aguas adyacentes. Estos últimos podrían indicar conectividad biogeográfica – i.e., que la misma especie ocurra también en aguas colombianas, pero que debido a un insuficiente esfuerzo de muestreo no ha sido colectada a la fecha

Dynamics of quartz tuning fork force sensors used in scanning probe microscopy

We have performed an experimental characterization of the dynamics of oscillating quartz tuning forks which are being increasingly used in scanning probe microscopy as force sensors. We show that tuning forks can be described as a system of coupled oscillators. Nevertheless, this description requires the knowledge of the elastic coupling constant between the prongs of the tuning fork, which has not yet been measured. Therefore tuning forks have been usually described within the single oscillator or the weakly coupled oscillators approximation that neglects the coupling between the prongs. We propose three different procedures to measure the elastic coupling constant: an opto-mechanical method, a variation of the Cleveland method and a thermal noise based method. We find that the coupling between the quartz tuning fork prongs has a strong influence on the dynamics and the measured motion is in remarkable agreement with a simple model of coupled harmonic oscillators. The precise determination of the elastic coupling between the prongs of a tuning fork allows to obtain a quantitative relation between the resonance frequency shift and the force gradient acting at the free end of a tuning fork prong.Comment: 16 pages, 6 figures, 2 Table

Carbon-fiber tips for scanning probe microscopes and molecular electronics experiments

We fabricate and characterize carbon-fiber tips for their use in combined scanning tunneling and force microscopy based on piezoelectric quartz tuning fork force sensors. An electrochemical fabrication procedure to etch the tips is used to yield reproducible sub-100-nm apex. We also study electron transport through single-molecule junctions formed by a single octanethiol molecule bonded by the thiol anchoring group to a gold electrode and linked to a carbon tip by the methyl group. We observe the presence of conductance plateaus during the stretching of the molecular bridge, which is the signature of the formation of a molecular junction.Comment: Conference Proceeding (Trends in NanoTechnology 2011, Tenerife SPAIN); Nanoscale Research Letters, (2012) 7:25

Carbon fibre tips for scanning probe microscopy based on quartz tuning fork force sensors

We report the fabrication and the characterization of carbon fibre tips for their use in combined scanning tunnelling and force microscopy based on piezoelectric quartz tuning fork force sensors. We find that the use of carbon fibre tips results in a minimum impact on the dynamics of quartz tuning fork force sensors yielding a high quality factor and consequently a high force gradient sensitivity. This high force sensitivity in combination with high electrical conductivity and oxidation resistance of carbon fibre tips make them very convenient for combined and simultaneous scanning tunnelling microscopy and atomic force microscopy measurements. Interestingly, these tips are quite robust against occasionally occurring tip crashes. An electrochemical fabrication procedure to etch the tips is presented that produces a sub-100 nm apex radius in a reproducible way which can yield high resolution images.Comment: 14 pages, 10 figure

On Limitations of the Ultrasonic Characterization of Pieces Manufactured with Highly Attenuating Materials

Some technical aspects of two Spanish cooperation projects, funded by DPI and Innpacto Programs of the R&D National Plan, are discussed. The objective is to analyze the common belief about than the ultrasonic testing in MHz range is not a tool utilizable to detect internal flaws in highly attenuating pieces made of coarse-grained steel. In fact high-strength steels, used in some safe industrial infrastructures of energy & transport sectors, are difficult to be inspected using the conventional “state of the art” in ultrasonic technology, due to their internal microstructures are very attenuating and coarse-grained. It is studied if this inspection difficulty could be overcome by finding intense interrogating pulses and advanced signal processing of the acquired echoes. A possible solution would depend on drastically improving signal-to-noise-ratios, by applying new advances on: ultrasonic transduction, HV electronics for intense pulsed driving of the testing probes, and an “ad-hoc” digital processing or focusing of the received noisy signals, in function of each material to be inspected. To attain this challenging aim on robust steel pieces would open the possibility of obtaining improvements in inspecting critical industrial components made of highly attenuating & dispersive materials, as new composites in aeronautic and motorway bridges, or new metallic alloys in nuclear area, where additional testing limitations often appear.The Spanish I+D National Plan (MINECO), by funding the Projects: Fundamental Research / DPI2011 – 22438, and INNPACTO Program / IMAAD - IPT-020000-2010-0004

Peces marinos de los órdenes Stomiiformes, Aulopiformes y Myctophiformes en aguas colombianas del Pacífico oriental tropical

These expeditions have explored portions of the ocean below 200 m, making knowledge accessible about deepsea life that has not been recorded by any national agency until date. Only a few studies of Colombian ichthyologists have reported on species belonging to these orders (Sterling 1976, Rubio 1987, Beltrán-León & Rubio 1994). Rubio (1987), for example, compiled information about the distribution of many of the deep-sea fish species of the Colombian Pacific, many of them without a collection register in Colombian waters. Beltrán-León & Rios (2000) documented the early stages of many groups of deep-sea fishes in the Pacific, including several of the three orders examined in this paper.Estas expediciones han explorado porciones del océano por debajo de los 200 m, haciendo accesible el conocimiento de la vida en estas zonas que no ha sido obtenido por ninguna agencia nacional hasta la fecha. Solo algunos estudios a cargo de ictiólogos nacionales han reportado ocasionalmente especies pertenecientes a estos ordenes (Sterling 1976, Rubio1987, Beltrán-León & Rubio 1994). Por ejemplo, Rubio (1987) recopiló información sobre la distribución de muchas especies de peces de profundidad del Pacífico colombiano, muchas de ellas sin un registro de colección en aguas colombianas. Beltrán-León & Ríos (2000) documentaron los estadios larvales de una gran cantidad de grupos de zonas profundas, incluyendo muchas de las especies examinadas en el presente documento