InAs nanowire transistors with multiple, independent wrap-gate segments

We report a method for making horizontal wrap-gate nanowire transistors with up to four independently controllable wrap-gated segments. While the step up to two independent wrap-gates requires a major change in fabrication methodology, a key advantage to this new approach, and the horizontal orientation more generally, is that achieving more than two wrap-gate segments then requires no extra fabrication steps. This is in contrast to the vertical orientation, where a significant subset of the fabrication steps needs to be repeated for each additional gate. We show that cross-talk between adjacent wrap-gate segments is negligible despite separations less than 200 nm. We also demonstrate the ability to make multiple wrap-gate transistors on a single nanowire using the exact same process. The excellent scalability potential of horizontal wrap-gate nanowire transistors makes them highly favourable for the development of advanced nanowire devices and possible integration with vertical wrap-gate nanowire transistors in 3D nanowire network architectures.Comment: 18 pages, 5 figures, In press for Nano Letters (DOI below

Convolutional nets for reconstructing neural circuits from brain images acquired by serial section electron microscopy

Neural circuits can be reconstructed from brain images acquired by serial section electron microscopy. Image analysis has been performed by manual labor for half a century, and efforts at automation date back almost as far. Convolutional nets were first applied to neuronal boundary detection a dozen years ago, and have now achieved impressive accuracy on clean images. Robust handling of image defects is a major outstanding challenge. Convolutional nets are also being employed for other tasks in neural circuit reconstruction: finding synapses and identifying synaptic partners, extending or pruning neuronal reconstructions, and aligning serial section images to create a 3D image stack. Computational systems are being engineered to handle petavoxel images of cubic millimeter brain volumes

Self assembled materials for solar cell application

In der vorliegenden Arbeit wurden Materialien und Aufbauten für Hybrid Solarzellen entwickelt und erforscht. rnDer Vergleich zweier bekannter Lochleitermaterialien für Solarzellen in einfachen Blend-Systemen brachte sowohl Einsicht zur unterschiedlichen Eignung der Materialien für optoelektronische Bauelemente als auch neue Erkenntnisse in Bereichen der Langzeitstabilität und Luftempfindlichkeit beider Materialien.rnWeiterhin wurde eine Methode entwickelt, um Hybrid Solarzelle auf möglichst unkomplizierte Weise aus kostengünstigen Materialien darzustellen. Die „Eintopf“-Synthese ermöglicht die unkomplizierte Darstellung eines funktionalen Hybridmaterials für die optoelektronische Anwendung. Mithilfe eines neu entwickelten amphiphilen Blockcopolymers, das als funktionelles Templat eingesetzt wurde, konnten mit einem TiO2-Precursor in einem Sol-Gel Ansatz verschiedene selbstorganisierte Morphologien des Hybridmaterials erhalten werden. Verschiedene Morphologien wurden auf ihre Eignung in Hybrid Solarzellen untersucht. Ob und warum die Morphologie des Hybridsystems die Effizienz der Solarzelle beeinflusst, konnte verdeutlicht werden. Mit der Weiterentwicklung der „Eintopf“-Synthese, durch den Austausch des TiO2-Precursors, konnte die Solarzelleneffizienz von 0.15 auf 0.4 % gesteigert werden. Weiterhin konnte die Übertragbarkeit des Systems durch den erfolgreichen Austausch des Halbleiters TiO¬2 mit ZnO bewiesen werden.rnNew materials and assemblies were designed and tested for hybrid solar cell application. A simple blending approach was used to prepare hybrid solar cells in a convenient, cheap and fast method. Nano crystalline TiO2 rods were blended with different hole conducting materials and tested in solar cell devices. Comparing their performance in photovoltaic devices, while experimental conditions are kept identical, showed that the choice of solvent and photovoltaic characterization conducted in inert atmosphere is of different influence for different hole conducting materials. External influences as long term stability were investigated.rnIn comparison to the blend approach a new one-pot approach was invented to prepare a nanostructured, multi-functional material with orthogonal properties. It consists of TiO2 as a functional metal oxide and a new amphiphilic block-copolymer poly(ethyleneoxide)-b-poly(triphenylamine) (PEO-b-PTPA) that was synthesized. The hybrid material was obtained within a single step via self assembly in solution. Therefore a method had to be found to obtain crystalline TiO2 under mild conditions. Within the materials synthesis the block-copolymer not only acts as a templating agent but also adds an electronic functionality to the resulting hybrid material. During the synthesis a variety of self assembled morphologies ranging from spheres to wires were created in a controlled fashion. The obtained morphology depends on the weight fraction of the polymer, solvent, TiO2 precursor and acid. Studying films on silicon wafers with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) a ternary phase diagram could be mapped whereas the crystallinity of TiO2 could be proved by high resolution-TEM. Different morphologies of this self assembled hybrid material were tested for solar cell application. Even for devices with layer thicknesses of the active material below 10 nm power conversion efficiencies up to 0.15 % at 1 sun and 1.5 AM were observed. The solar cell efficiency was increased with further development of the one-pot approach by changing the precursor. A polyethyleneglycole modified titanate was used as precursor in combination with the functional block copolymer PEO-b-PTPA. Again self-assembled network morphologies were obtained and tested in solar cell devices. While the formation of percolating networks is of general importance the solar cell performance was found to depend on the morphological design of the hybrid material. With the aid of conductive scanning force microscopy, it was proven to preserve a percolating network despite an increase of the active layer thickness. In combination with a special functionalized Ti-precursor hybrid bulk heterojunction solar cells having a maximum power conversion efficiency of 0.4 % at 1 sun and 1.5 AM were obtained.r

Design and Development of an Autonomous Car using Object Detection with YOLOv4

Future cars are anticipated to be driverless point-to-point transportation services capable of avoiding fatalities To achieve this goal auto-manufacturers have been investing to realize the potential autonomous driving In this regard we present a self-driving model car capable of autonomous driving using object-detection as a primary means of steering on a track made of colored cones This paper goes through the process of fabricating a model vehicle from its embedded hardware platform to the end-to-end ML pipeline necessary for automated data acquisition and model-training thereby allowing a Deep Learning model to derive input from the hardware platform to control the car s movements This guides the car autonomously and adapts well to real-time tracks without manual feature-extraction This paper presents a Computer Vision model that learns from video data and involves Image Processing Augmentation Behavioral Cloning and a Convolutional Neural Network model The Darknet architecture is used to detect objects through a video segment and convert it into a 3D navigable path Finally the paper touches upon the conclusion results and scope of future improvement in the technique use

Chemical Synthesis at Surfaces with Atomic Precision: Taming Complexity and Perfection

Scanning probe microscopy (SPM) is a powerful tool to study the structure and dynamics of molecules at surfaces and interfaces as well as to precisely manipulate atoms and molecules by applying an external force, by inelastic electron tunneling, or by means of an electric field. The rapid development of these SPM manipulation modes made it possible to achieve fine‐control over fundamental processes in the physics of interfaces as well as chemical reactivity, such as adsorption, diffusion, bond formation, and bond dissociation with precision at the single atom/molecule level. Their controlled use for the fabrication of atomic‐scale structures and synthesis of new, perhaps uncommon, molecules with programmed properties are reviewed. Opportunities and challenges towards the development of complex chemical systems are discussed, by analyzing potential future impacts in nanoscience and nanotechnology.journal articlereview2019 Dec 192019 11 28importe

A Stochastic Approach to Shortcut Bridging in Programmable Matter

In a self-organizing particle system, an abstraction of programmable matter, simple computational elements called particles with limited memory and communication self-organize to solve system-wide problems of movement, coordination, and configuration. In this paper, we consider a stochastic, distributed, local, asynchronous algorithm for "shortcut bridging", in which particles self-assemble bridges over gaps that simultaneously balance minimizing the length and cost of the bridge. Army ants of the genus Eciton have been observed exhibiting a similar behavior in their foraging trails, dynamically adjusting their bridges to satisfy an efficiency trade-off using local interactions. Using techniques from Markov chain analysis, we rigorously analyze our algorithm, show it achieves a near-optimal balance between the competing factors of path length and bridge cost, and prove that it exhibits a dependence on the angle of the gap being "shortcut" similar to that of the ant bridges. We also present simulation results that qualitatively compare our algorithm with the army ant bridging behavior. Our work gives a plausible explanation of how convergence to globally optimal configurations can be achieved via local interactions by simple organisms (e.g., ants) with some limited computational power and access to random bits. The proposed algorithm also demonstrates the robustness of the stochastic approach to algorithms for programmable matter, as it is a surprisingly simple extension of our previous stochastic algorithm for compression.Comment: Published in Proc. of DNA23: DNA Computing and Molecular Programming - 23rd International Conference, 2017. An updated journal version will appear in the DNA23 Special Issue of Natural Computin

Layer-by-layer nanoparticles for glaucoma therapy

Glaucoma, a sever neurodegenerative ocular disease, is one of the leading causes of blindness worldwide. An increased intraocular pressure (IOP) is regarded as its main risk factor. The IOP is generated in the anterior eye due to a resistance to the outflow of the aqueous humor through the trabecular outflow pathway. Recently, connective tissue growth factor (CTGF) was identified to increase the resistance to aqueous humor outflow by enhancing the extracellular matrix deposition and contractility of cells in the trabecular meshwork (TM). Post transcriptional gene silencing using small interfering RNA (siRNA) is an elegant strategy to reduce elevated levels of CTGF and consequently IOP. Nevertheless, delivering nucleic acids of this type remains a challenge. This work describes the development of hyaluronic acid functionalized layer-by-layer nanoparticles for the delivery of siRNA to the TM

Harnessing the physicochemical properties of DNA as a multifunctional biomaterial for biomedical and other applications

The biological purpose of DNA is to store, replicate, and convey genetic information in cells. Progress in molecular genetics have led to its widespread applications in gene editing, gene therapy, and forensic science. However, in addition to its role as a genetic material, DNA has also emerged as a nongenetic, generic material for diverse biomedical applications. DNA is essentially a natural biopolymer that can be precisely programed by simple chemical modifications to construct materials with desired mechanical, biological, and structural properties. This review critically deciphers the chemical tools and strategies that are currently being employed to harness the nongenetic functions of DNA. Here, the primary product of interest has been crosslinked, hydrated polymers, or hydrogels. State-of-the-art applications of macroscopic, DNA-based hydrogels in the fields of environment, electrochemistry, biologics delivery, and regenerative therapy have been extensively reviewed. Additionally, the review encompasses the status of DNA as a clinically and commercially viable material and provides insight into future possibilities