Spatially constrained coordinated navigation for a multi-robot system

In this paper we present a method for navigating a multi-robot system through an environment while additionally maintaining a predefined set of constraints. Examples for constraints are the requirement to maintain a direct line-of-sight between robots or to ensure that the multi-robot system maintains communication. Our approach is based on graph structures that model movements and constraints separately, in order to cover different kind of robots and a large class of possible constraints. Additionally, the separation of movement and constraint graph allows us to use known graph algorithms like Steiner tree heuristics or the multi-point relay algorithm to solve the problem of finding a target configuration for the robots. To connect the movements of the robots with the given constraints, we introduce separated connection graphs which allow assembling valid navigation plans fast. This paper presents some theoretical insight into the problem of coordinated navigation for multi-robot systems with spatial constraints as well as a practical solution. Experiments in simulation and with real robots show the feasibility of the approach.     

Modular Functionalization of Electrodes by Cross‐Coupling Reactions at Their Surfaces

Due to the increasing importance of modified electrodes for many applications in nanotechnology, including molecular electronics, bioelectronics, and sensors, there is a need to find ways to chemically attach suitable molecular films onto the electrodes. Combining the electroreduction of aryl diazonium salts with the Sonogashira cross‐coupling reaction, a new modular technique to modify electrodes is presented. The new technique allows a wide range of functional groups to be introduced onto electrode surfaces with high surface coverage by the functional subunit. Various organic subunits, including redox chromophores, are successfully attached to platinum electrodes. The corresponding films are characterized using cyclic voltammetry, X‐ray photoelectron spectroscopy, atomic force microscopy, and contact‐angle measurements. The electroreduction of diazonium salts is successfully achieved on a broad variety of conducting and semiconducting surfaces, which shows that the technique is applicable to a broad variety of substrates.     

Composite Nanostructures of TiO2 and ZnO for Water Splitting Application: Atomic Layer Deposition Growth and Density Functional Theory Investigation

The commercialization of solar fuel devices requires the development of novel engineered photoelectrodes for water splitting applications which are based on redundant, cheap, and environmentally friendly materials. In the current study, a combination of titanium dioxide (TiO₂) and zinc oxide (ZnO) onto nanotextured silicon is utilized for a composite electrode with the aim to overcome the individual shortcomings of the respective materials. The properties of conformal coverage of TiO₂ and ZnO layers are designed on the atomic scale by the atomic layer deposition technique. The resulting photoanode shows not only promising stability but also nine times higher photocurrents than an equivalent photoanode with a pure TiO₂ encapsulation onto the nanostructured silicon. Density functional theory calculations indicate that segregation of TiO₂ at the ZnO surfaces is favorable and leads to the stabilization of the ZnO layers in water environments. In conclusion, the novel designed composite material constitutes a promising base for a stable and effective photoanode for the water oxidation reaction.     

Consideration of temperature and current stress testing on flip chip solder interconnects

This work discusses the experimental set-up and data interpretation for high temperature and current stress tests of flip chip solder joints using the four-point Kelvin measurement technique. The single solder joint resistance responses are measured at four different four-point Kelvin structure locations in a flip chip package. Various temperatures (i.e., 125–165 °C) and electric current (i.e., 0.6–1.0 A) test conditions are applied to investigate the solder joint resistance degradation behavior and its failure processes. Failure criterion of 20% and 50% joint resistance increases, corresponding to solder and interfacial voiding, are employed to evaluate the solder joint electromigration reliability. The absolute resistance value is substantially affected by the geometrical layout of the metal lines in the four-point Kelvin structure, and this is confirmed by finite element simulation.Different current flow directions and strengths yielded different joint resistance responses. The anode joint, where electrons flow from the die to the substrate, usually measured an earlier resistance increase than the cathode joint, where electrons flow in the opposite direction. The change in measured joint resistances can be related to solder and interfacial voiding in the solder joint except for ±1 A current load, where resistance drop mainly attributed to the broken substrate Cu metallization as a result of “hot-spot” phenomenon. The solder joint temperature increases above the oven ambient temperature by ～25 °C, ～40 °C and ～65 °C for 0.6 A, 0.8 A and 1.0 A stress current, respectively. It is found that two-parameter log-normal distribution gives a better lifetime data fitting than the two-parameter Weibull distribution. Regardless of failure criterion used, the anode joint test cells usually calculated a shorter solder joint mean life with a lower standard variation of 0.3–0.6, as compared to the cathode joint test cells with a higher standard variation of 0.8–1.2. For a typical flip chip solder joint construction, electromigration reliability is mainly determined by the under bump metallization consumption and dissolution, with intermetallic compound formation near the die side of an anode joint.     

TEM characterization of Si nanowires grown by CVD on Si pre-structured by nanosphere lithography

Silicon nanowires (SiNWs) were grown on Si(1 0 0) and Si(1 1 1) substrates by chemical vapour deposition (CVD) via the vapour–liquid–solid (VLS) mechanism with small gold particles used as seeds. In order to control the diameter of nanowires, their density on the substrate and their orientation we controlled the size and the distribution of Au seed particles. This was accomplished using nanosphere lithography (NSL) by which regular arrays of Au nanoparticles can be generated. This allowed us to grow single-crystalline SiNWs perpendicular to the surface of Si(1 1 1) substrates. The SiNWs and their Au caps were studied with respect to their morphology and composition using TEM, HREM and EFTEM methods. Clusters of Au are observed along the surface of SiNWs and the existence of a thin Si film on gold particles capping the SiNWs is demonstrated.     

A comparison of noninvasive reconstruction of epicardial versus transmembrane potentials in consideration of the null space

We compare two source formulations for the electrocardiographic forward problem in consideration of their implications for regularizing the ill-posed inverse problem. The established epicardial potential source model is compared with a bidomain-theory-based transmembrane potential source formulation. The epicardial source approach is extended to the whole heart surface including the endocardial surfaces. We introduce the concept of the numerical null and signal space to draw attention to the problems associated with the nonuniqueness of the inverse solution and show that reconstruction of null-space components is an important issue for physiologically meaningful inverse solutions. Both formulations were tested with simulated data generated with an anisotropic heart model and with clinically measured data of two patients. A linear and a recently proposed quasi-linear inverse algorithm were applied for reconstructions of the epicardial and transmembrane potential, respectively. A direct comparison of both formulations was performed in terms of computed activation times. We found the transmembrane potential-based formulation is a more promising source formulation as stronger regularization by incorporation of biophysical a priori information is permitted.     

0.18μm铜金属双重镶嵌工艺中空间成像套刻精度分析

由于空间成像套刻(Overlay)技术的预算随集成电路(IC)设计规范的紧缩而吃紧,因此,Overlay测量技术准确度的重要意义也随之提高。通过对后开发(AfterDevelopDI)阶段和后蚀刻(AfterEtchFI)阶段的Overlay测量结果进行比较,研究了0.18μm设计规范下的铜金属双重镶嵌工艺过程中的Overlay准确度。在确保对同一个晶圆进行后开发(DI)阶段和后蚀刻(FI)阶段测试的条件下,我们对成品晶圆的5个工艺层进行了比较。此外,还利用CD-SEM(线宽-扫描电子显微镜)测量了某个工艺层(PolyGate)上的芯片内Overlay,并与采用分割线方法的光学Overlay测量结果进行了比较。发现对芯片内overlay的校准存在着严重的局限性,即在应用CD-SEM时缺乏合适的结构进行Overlay测量。我们还将继续为大家提供定量的比较结果,同时也会向大家推荐组合的CD-SEM测量结构,使其能够被应用到今后的光刻设计中。     

The role of photon statistics in fluorescence anisotropy imaging.

Anisotropy imaging can be used to image resonance energy transfer between pairs of identical fluorophores and, thus, constitutes a powerful tool for monitoring protein homo-association in living single cells. The requirement for only a single fluorophore significantly simplifies biological preparation and interpretation. We use quantitative methods for the acquisition and image processing of anisotropy data that return the expected error of the anisotropy per pixel based on photon statistics. The analysis methods include calibration procedures and allow for a balance in spatial, anisotropy, and temporal resolution. They are featured here with anisotropy images of fluorescent calibration beads and enhanced green fluorescent protein complexes in live cells.     

Densification of Oxide Nanoparticle Thin Films by Irradiation with Visible Light

A technique is presented that allows for altering of the physical characteristics of films of TiO₂ nanoparticles by exposure to visible light. In this technique, dye‐sensitized oxide nanoparticles are deposited on a substrate by dip‐coating. Photodissociation of the organic ligand layer leads to cross‐linking of the nanoparticles. Consequently, irradiated films have a decreased porosity, an increased index of refraction and an increased hydrophobicity. Films irradiated with green light are compared to films irradiated with UV light. Within experimental error, visible‐ and UV‐illumination induces the same changes in the films. The mechanism of surfactant elimination in dye‐sensitized oxide particles is discussed, patterning is demonstrated, and prospective applications of the technique are considered.