FireDrone: multi-environment thermally agnostic aerial robot

Deploying robots in extreme environments reduces risks to human lives. However, robot operating conditions are often limited by environmental factors such as extreme temperatures encountered in fire disasters or polar regions. Especially drones face challenges in carrying thermal management systems protecting vital components, due to limited payload capacity compared to ground robots. Herein, a thermally agnostic aerial robot comprising structural thermally insulating material and a phase change material cooling system, inspired by natural thermal regulation principles, is designed, modelled and experimentally validated. Building on the robot development paradigm of physical artificial intelligence, the concurrent development of materials and design enables the creation of novel physiologically adaptive systems. Polyimide aerogel is applied as one of the main structural materials in the drone's design to adapt the robot's structure and properties to extreme temperatures. Glass fiber reinforcement with silica aerogel particles reduces high-temperature shrinkage and pore structure degradation after exposure to high temperatures and most of the composite aerogel features are preserved. A high technology-readiness-level drone prototype, allowing for operation in a broad range of ambient temperatures, is demonstrated. The proposed technology for thermally agnostic drones may unleash the great potential of aerial robotics in multiple industrial and research applications

Structurally Tunable pH-responsive Phosphine Oxide Based Gels by Facile Synthesis Strategy

Design and synthesis of nanostructured responsive gels have attracted increasing attention, particularly in the biomedical domain. Polymer chain configurations and nanodomain sizes within the network can be used to steer their functions as drug carriers. Here, a catalyst-free facile one-step synthesis strategy is reported for the design of pH-responsive gels and controlled structures in nanoscale. Transparent and impurity free gels were directly synthesized from trivinylphosphine oxide (TVPO) and cyclic secondary diamine monomers via Michael addition polymerization under mild conditions. NMR analysis confirmed the consumption of all TVPO and the absence of side products, thereby eliminating post purification steps. The small-angle X-ray scattering (SAXS) elucidates the nanoscale structural features in gels, that is, it demonstrates the presence of collapsed nanodomains within gel networks and it was possible to tune the size of these domains by varying the amine monomers and the nature of the solvent. The fabricated gels demonstrate structure tunability via solvent–polymer interactions and pH specific drug release behavior. Three different anionic dyes (acid blue 80, acid blue 90, and fluorescein) of varying size and chemistry were incorporated into the hydrogel as model drugs and their release behavior was studied. Compared to acidic pH, a higher and faster release of acid blue 80 and fluorescein was observed at pH 10, possibly because of their increased solubility in alkaline pH. In addition, their release in phosphate buffered saline (PBS) and simulated body fluid (SBF) matrix was positively influenced by the ionic interaction with positively charged metal ions. In the case of hydrogel containing acid blue 90 a very low drug release (<1%) was observed, which is due to the reaction of its accessible free amino group with the vinyl groups of the TVPO. In vitro evaluation of the prepared hydrogel using human dermal fibroblasts indicates no cytotoxic effects, warranting further research for biomedical applications. Our strategy of such gel synthesis lays the basis for the design of other gel-based functional materials

Quantitative Determination of Nanoscale Electronic Properties of Semiconductor Surfaces by Scanning Tunnelling Spectroscopy

Simulation of tunnelling spectra obtained from semiconductor surfaces permits quantitative evaluation of nanoscale electronic properties of the surface. Band offsets associated with quantum wells or quantum dots can thus be evaluated, as can be electronic properties associated with particular point defects within the material. An overview of the methods employed for the analysis is given, emphasizing the critical requirements of both the experiment and theory that must be fulfilled for a realistic determination of electronic properties.</p

Low-temperature tunneling spectroscopy of Ge(111)c(2×8) surfaces

Scanning tunneling spectroscopy is used to study p-type Ge(111)c(2×8) surfaces over the temperature range 7 to 61 K. Surface states arising from adatoms and rest atoms are observed. With consideration of tip-induced band bending, a surface band gap of 0.5±0.1 eV separating the bulk valence band from the surface adatom band is deduced. Peak positions of adatom states are located at energies of 0.09±0.02 eV and 0.24±0.03 eV above this gap. A spectral feature arising from the inversion of the adatom state occupation is also identified. A solution of Poisson’s equation for the tip-semiconductor system yields a value for the interband current in agreement with the observations, for an assumed tip radius of 100 nm. The rest-atom spectral peak, observed at ≈1.0 eV below the valence band maximum, is observed to shift as a function of tunnel current. It is argued that nonequilibrium occupation of disorder-induced surface states produces this shift.</p

Structure and electronic sprectroscopy of steps on GaAs(110) surfaces

Steps on GaAs(110) surfaces, with step-normal vectors parallel to [001], are studied by scanning tunneling microscopy and spectroscopy. Two possible orientations of the steps occur, with outward normal vectors of [001] or [00 - 1], which in simple bulk-terminated form have Ga (cations) or As (anions) on their edges, respectively. The latter type of step in n-type or undoped material is found to retain its bulk-terminated form. A band of states is observed extending out from the valence band, associated with the dangling bonds of the terminating As atoms. It is argued that compensation of the dangling bonds on the step edges is the driving force for the step structure, producing reconstruction of the step edges in certain cases. (C) 2011 Elsevier B.V. All rights reserved

Electronic States of InAs/GaAs Quantum Dots by Scanning Tunneling Spectroscopy

InAs/GaAs quantum-dot heterostructures grown by molecular-beam epitaxy are studied using cross-sectional scanning tunneling microscopy and spectroscopy. Individual InAs quantum dots (QDs) are resolved in the images. Tunneling spectra acquired 3-4 nm from the QDs show a peak located in the upper part of the GaAs bandgap originating from the lowest electron confined state, together with a tail extending out from the valence band from hole confined states. A line-shape analysis is used to deduce the binding energies of the electron and hole QD states.</p

Size, shape, composition, and electronic properties of InAs/GaAs quantum dots by scanning tunneling microscopy and spectroscopy

InAs/GaAs quantum dot (QD) heterostructures grown by molecular beam epitaxy are studied using cross-sectional scanning tunneling microscopy and spectroscopy. The images reveal individual InAs QDs having a lens shape with maximum base diameter of 10.5 nm and height of 2.9 nm. Analysis of strain relaxation of the QDs reveals an indium composition varying from 65% at the base of the QD, to 95% at its center, and back to 65% at its apex. Room-temperature tunneling spectra acquired 3–4 nm from the center of a dot show a peak located in the upper part of the GaAs band gap originating from the lowest electron confined state of the QD, along with a tail in the conductance extending out from the valence band and originating from QD hole states. A computational method is developed for simulating the tunneling spectra using effective-mass bands treated in an envelope function approximation. By comparison of the computations to low-current spectra, the energy of the lowest electron, and highest hole QD states are determined. These energies are found to be in reasonably good agreement both with optical measurements and prior theoretical predictions of Wang et al. [Phys. Rev. B 59, 5678 (1999)]</p