A methodology for the fabrication by FIB of needle-shape specimens around sub-surface features at the nanometre scale

A novel methodology for the preparation by focused ion beam (FIB) of needle-shape specimens in specific sites underneath the sample surface for their study by electron tomography (ET) is proposed. In particular, we demonstrate this methodology for the fabrication of needles containing InAs/InP quantum dots (QDs). The main challenge of this methodology is the location of specific QDs in the FIB equipment, as they are not visible with the secondary electrons detector. In order to overcome this difficulty, a series of marks visible both in conventional transmission electron microscopy and in the FIB are introduced before the preparation of the needles. The conditions for the fabrication by FIB of needles with optimized characteristics for their study by ET are also detailed.     

A scheme for interpolation by Hankel translates of a basis function

This work discusses interpolation of complex-valued functions defined on the positive real axis $I$ by certain special subspaces, in a variational setting that follows the approach of Light and Wayne [W. Light, H. Wayne, Spaces of distributions, interpolation by translates of a basis function and error estimates, Numer. Math. 81 (1999) 415–450]. The set of interpolation points will be a subset $\{a_1,\dots ,a_n\}$ of $I$ and the interpolants will take the form $u\left(x\right)=\sum _{i=1}^n{\alpha }_i\left({\tau }_{a_i}?\right)\left(x\right)+\sum _{j=0}^{m?1}{\beta }_j{p}_{\mu ,j}\left(x\right)(x\in I)\text{,}$ where $\mu \ge ?1/2,?$ is a complex function defined on $I$ (the so-called basis function), $p_{\mu ,j}\left(x\right)=x^{2j+\mu +1/2}(j\in {\mathbb{Z}}_{+},0\le j\le m?1)$ is a Müntz monomial, ${\tau }_z(z\in I)$ denotes the Hankel translation operator of order $\mu$, and ${\alpha }_i,{\beta }_j(i,j\in {\mathbb{Z}}_{+},1\le i\le n,0\le j\le m?1)$ are complex coefficients. An estimate for the pointwise error of these interpolants is given. Some numerical examples are included.     

<Emphasis Type="Italic">In vitro</Emphasis> bioactivity of 70 wt.% SiO<Subscript>2</Subscript> — 30 wt.% CaO sol-gel glass,doped with 1, 3 and 5 wt.% NbF<Subscript>5</Subscript>

The 70SiO₂-30CaO (wt.%) sol-gel glasses doped with 1, 3 and 5 NbF₅ (wt.%) were prepared via polystep sol-gel route. The synthesized glasses were characterized by XRD, FTIR and SEM. Changes in 1.5 SBF solutions were measured by ICP-AES. XRD of the glasses stabilized at 700°C for 6 hours proved the presence of niocalite. FTIR was consistent with XRD data. The in vitro bioactivity study of all glasses prepared were carried out by soaking in 1.5 simulated body fluid (1.5 SBF) at 37°C for 6 and 12 days in static conditions. The FTIR reveals the formation of A-type and B-type carbonate containing hydroxyapatite (CO₃HA) layer. Changes in 1.5 SBF solutions, after 6 days of soaking, show that the Ca concentration increased significantly, compared to the initial Ca content in the 1.5 SBF solution before in vitro test. After 12 days of immersion, the Ca concentration decreased, i.e., the formation of HA phase consumed Ca from 1.5 SBF solution. For all soaking times, the concentration of P is much lower than that the used 1.5 SBF. Based on these results we suggest that Ca and P play an active role in the future of the glasses. SEM depicts that the different morphology of hydroxyapatite can be formed as a function of soaking time.     

Simultaneous Determination of Mefenamic and Tolfenamic Acids in Real Samples by Terbium-Sensitized Luminescence

A simple luminescent methodology for the simultaneous determination of mefenamic and tolfenamic acids in pharmaceutical preparations and human urine is proposed. Since the native fluorescence of both analytes is not intense, the method takes advantage of the lanthanide-sensitized luminescence, which provides a higher sensitivity. Due to the strong overlapping between the luminescence spectra of both terbium complexes, the use of luminescence decay curves to resolve mixtures of the analytes is proposed, since these curves are more selective. A factorial design with three levels per factor coupled to a central composite design was selected to obtain a calibration matrix of thirteen standards plus eight blank samples that was processed using a partial least-squares (PLS) analysis. In order to assess the goodness of the proposed method, a prediction set of synthetic samples was analyzed, obtaining recovery percentages between 90 and 104?%. Limits of detection, calculated by means of a new criterion, were 14.85?μg L^?1 and 15.89?μg L^?1 for tolfenamic and mefenamic acids, respectively. The method was tested in a pharmaceutical preparation containing mefenamic acid, obtaining recovery percentages close to 100?%. Finally, the simultaneous determination of both fenamates in human urine samples was successfully carried out by means of a correction of the above-explained model. No extraction method neither prior separation of the analytes were needed.     

Swing-up and positioning control of an inverted wheeled cart pendulum system with chaotic balancing motions

This paper explores the problem of swinging-up an inverted pendulum formed by a rod attached to a wheeled cart with a hanging bob at its opposite end. The system is driven by the wheeled cart platform system, which is formed by a cart, wheels with counterbalance and connecting-rods. The model of the system is initially obtained under the assumption of rolling without slipping of the wheels, which is then verified by computing the reaction forces. The motion of the wheeled cart is initially oscillating, whereas the rod can move freely giving rise to an under-actuated mechanical system. From the harmonic prescribed motion for the wheeled cart, necessary conditions for chaotic rod motion are deduced by means of the Melnikov function. Once the chaotic oscillation has been reached and the rod is close to the upright position, the force over the wheeled cart is commutated to a control law based on the pole-placement plus integrator technique. This procedure allows driving the rod and the wheeled cart system to the upright position and to a prescribed set point respectively. The onset of strange attractors is crucial in the design of the control law, whose performance to obtain rolling without slipping is researched by means of sensitive dependence, power spectral density, Lyapunov exponents and reaction forces. The results of the analytical calculations are verified by full numerical simulations.     

Nanostructured Au/Si substrate for organic molecule SERS detection

Nanoparticles of noble metals, such as gold and silver, exhibit unique and tunable optical properties on account of their surface plasmon resonance. In particular, gold nanoparticles on silicon substrates are attractive for future nanoscale sensors and optical devices due to their resistance to oxidation and due to their electrical and optical properties. In this study, we developed a nanostructured gold/macroporous silicon (Au/PS) substrate capped with 11-mercaptoundecanoic acid (11-MUA) with ultra-sensitive detection properties achieved in characterization, an approach based on surface-enhanced Raman scattering (SERS). Surface-enhanced Raman scattering allows us to detect substances at a low concentration level and to observe structural details of a thiol molecule bonded to small film thicknesses. Raman measurements were carried out at 514 nm and 785 nm. In order to emphasize the effect of the Si microstructuration on the efficiency of this new substrate (Au/PS) proposed for SERS experiments, the same molecule (11-MUA) was adsorbed on it as well as on gold/atomically flat silicon (Au/Si) and on commercial Klarite (Mesophotonics) substrates. Systematic studies realized by Raman spectroscopy, electron microscopy, and X-ray spectroscopy show the influence of silicon substrate texturing and metallic deposition conditions, including time and temperature on the optical phenomena.     

The Effect of Cluster Size on the Intra-Cluster Ionic Polymerization Process

Polyaromatic hydrocarbons (PAHs) are widespread in the interstellar medium (ISM). The abundance and relevance of PAHs call for a clear understanding of their formation mechanisms, which, to date, have not been completely deciphered. Of particular interest is the formation of benzene, the basic building block of PAHs. It has been shown that the ionization of neutral clusters can lead to an intra-cluster ionic polymerization process that results in molecular growth. Ab-initio molecular dynamics (AIMD) studies in clusters consisting of 3–6 units of acetylene modeling ionization events under ISM conditions have shown maximum aggregation of three acetylene molecules forming bonded C₆H₆⁺ species; the larger the number of acetylene molecules, the higher the production of C₆H₆⁺. These results lead to the question of whether clusters larger than those studied thus far promote aggregation beyond three acetylene units and whether larger clusters can result in higher C₆H₆⁺ production. In this study, we report results from AIMD simulations modeling the ionization of 10 and 20 acetylene clusters. The simulations show aggregation of up to four acetylene units producing bonded C₈H₈⁺. Interestingly, C₈H₈⁺ bicyclic species were identified, setting a precedent for their astrochemical identification. Comparable reactivity rates were shown with 10 and 20 acetylene clusters.     

“Breathing” in Adsorbate‐Responsive Metal Tetraphosphonate Hybrid Materials

Breathe easy : Reversible H₂O and NH₃ gas uptake by 2D calcium tetraphosphonates (see figure) is accompanied by framework structural changes similar to those previously reported for some carboxylate‐based hybrids. This breathing mechanism is accompanied by a volume increase of 55 %, while maintaining the topology and crystallinity of the material.

     

Modeling the heating of biological tissue based on the hyperbolic heat transfer equation

In modern surgery, a multitude of minimally intrusive operational techniques are used which are based on the point heating of target zones of human tissue via laser or radiofrequency currents. Traditionally, these processes are modeled by the bioheat equation introduced by Pennes, who considers Fourier’s theory of heat conduction. We present an alternative and more realistic model established using the hyperbolic equation of heat transfer. To demonstrate some features and advantages of our proposed method, we apply the results obtained to different types of tissue heating with high energy fluxes, in particular radiofrequency heating and pulsed laser treatment of the cornea to correct refractive errors. We hope that the results from our approach will help with refining surgical interventions in this novel field of medical treatment.