Rolled-Up Nanotech: Illumination-Controlled Hydrofluoric Acid Etching of AlAs Sacrificial Layers

<p>Abstract</p> <p>The effect of illumination on the hydrofluoric acid etching of AlAs sacrificial layers with systematically varied thicknesses in order to release and roll up InGaAs/GaAs bilayers was studied. For thicknesses of AlAs below 10 nm, there were two etching regimes for the area under illumination: one at low illumination intensities, in which the etching and releasing proceeds as expected and one at higher intensities in which the etching and any releasing are completely suppressed. The &#8220;etch suppression&#8221; area is well defined by the illumination spot, a feature that can be used to create heterogeneously etched regions with a high degree of control, shown here on patterned samples. Together with the studied self-limitation effect, the technique offers a way to determine the position of rolled-up micro- and nanotubes independently from the predefined lithographic pattern.</p

Quantum Dimensional Zeeman Effect in the Magneto-optical Absorption Spectrum for Quantum Dot - Impurity Center Systems

Magneto-optical properties of the quantum dot - impurity center (QD-IC) systems synthesized in a transparent dielectric matrix are considered. For the QD one-electron state description the parabolic model of the confinement potential is used. Within the framework of zero-range potential model and the effective mass approach, the light impurity absorption coefficient for the case of transversal polarization with respect to the applied magnetic field direction, with consideration of the QD size dispersion, has been analytically calculated. It is shown that for the case of transversal polarization the light impurity absorption spectrum is characterized by the quantum dimensional Zeeman effect.Comment: 18 pages, 1 figure, PDF fil

Euclid preparation: XXIX. Water ice in spacecraft Part I: The physics of ice formation and contamination

Material outgassing in a vacuum leads to molecular contamination, a well-known problem in spaceflight. Water is the most common contaminant in cryogenic spacecraft, altering numerous properties of optical systems. Too much ice means that Euclid’s calibration requirements cannot be met anymore. Euclid must then be thermally decontaminated, which is a month-long risky operation. We need to understand how ice affects our data to build adequate calibration and survey plans. A comprehensive analysis in the context of an astrophysical space survey has not been done before. In this paper we look at other spacecraft with well-documented outgassing records. We then review the formation of thin ice films, and find that for Euclid a mix of amorphous and crystalline ices is expected. Their surface topography – and thus optical properties – depend on the competing energetic needs of the substrate-water and the water-water interfaces, and they are hard to predict with current theories. We illustrate that with scanning-tunnelling and atomic-force microscope images of thin ice films. Sophisticated tools exist to compute contamination rates, and we must understand their underlying physical principles and uncertainties. We find considerable knowledge errors on the diffusion and sublimation coefficients, limiting the accuracy of outgassing estimates. We developed a water transport model to compute contamination rates in Euclid, and find agreement with industry estimates within the uncertainties. Tests of the Euclid flight hardware in space simulators did not pick up significant contamination signals, but they were also not geared towards this purpose; our in-flight calibration observations will be much more sensitive. To derive a calibration and decontamination strategy, we need to understand the link between the amount of ice in the optics and its effect on the data. There is little research about this, possibly because other spacecraft can decontaminate more easily, quenching the need for a deeper understanding. In our second paper, we quantify the impact of iced optics on Euclid’s data

Molecular hydrogen production from amorphous solid water during low energy electron irradiation.

This work investigates the production of molecular hydrogen isotopologues (H2, HD, and D2) during low energy electron irradiation of layered and isotopically labelled thin films of amorphous solid water (ASW) in ultrahigh vacuum. Experimentally, the production of these molecules with both irradiation time and incident electron energy in the range 400 to 500 eV is reported as a function of the depth of a buried D2O layer in an H2O film. H2 is produced consistently in all measurements, reflecting the H2O component of the film, though it does exhibit a modest reduction in intensity at the time corresponding to product escape from the buried D2O layer. In contrast, HD and D2 production exhibit peaks at times corresponding to product escape from the buried D2O layer in the composite film. These features broaden the deeper the HD or D2 is formed due to diffusion. A simple random-walk model is presented that can qualitatively explain the appearance profile of these peaks as a function of the incident electron penetration

Relaxation of Electronically Excited Hydrogen Peroxide in Liquid Water Insights from Auger Electron Emission

Autoionization electron spectroscopy is applied to study non radiative relaxation processes of hydrogen peroxide aqueous solution irradiated by soft X rays. The high kinetic energy part of the oxygen 1s H2O2 aq Auger electron spectrum reveals di cationic final states with considerably lower energy than for neat liquid water. Assisted by quantum chemical calculations, it is argued that such lower energy states arise from two fundamentally different relaxation processes. One is local Auger decay, yielding H2O22 aq species, and here the low final state energy arises from charge delocalization across the molecular O O bond. Alternatively, non local di cationic states can form, corresponding to a charge separated complex comprising H2O2 and a neighboring water molecule. Different charge separation mechanisms, depending on whether or not proton dynamics of the core level excited or ionized H2O2 molecule is involved, are discussed. We also present for the first time the partial electron yield X ray absorption spectrum of liquid water, which is useful in interpreting the respective spectra from H2O2 in water, especially when identifying solute specific excitation

Accurate vertical ionization energy and work function determinations of liquid water and aqueous solutions

The absolute scale electronic energetics of liquid water and aqueous solutions, both in the bulk and at associated interfaces, are the central determiners of water based chemistry. However, such information is generally experimentally inaccessible. Here we demonstrate that a refined implementation of the liquid microjet photoelectron spectroscopy PES technique can be adopted to address this. Implementing concepts from condensed matter physics, we establish novel all liquid phase vacuum and equilibrated solution metal electrode Fermi level referencing procedures. This enables the precise and accurate determination of previously elusive water solvent and solute vertical ionization energies, VIEs. Notably, this includes quantification of solute induced perturbations of water s electronic energetics and VIE definition on an absolute and universal chemical potential scale. Defining and applying these procedures over a broad range of ionization energies, we accurately and respectively determine the VIE and oxidative stability of liquid water as 11.33 0.03 eV and 6.60 0.08 eV with respect to its liquid vacuum interface potential and Fermi level. Combining our referencing schemes, we accurately determine the work function of liquid water as 4.73 0.09 eV. Further, applying our novel approach to a pair of exemplary aqueous solutions, we extract absolute VIEs of aqueous iodide anions, reaffirm the robustness of liquid water s electronic structure to high bulk salt concentrations 2 M sodium iodide , and quantify reference level dependent reductions of water s VIE and a 0.48 0.13 eV contraction of the solution s work function upon partial hydration of a known surfactant 25 mM tetrabutylammonium iodide . Our combined experimental accomplishments mark a major advance in our ability to quantify electronic structure interactions and chemical reactivity in liquid water, which now explicitly extends to the measurement of absolute scale bulk and interfacial solution energetics, including those of relevance to aqueous electrochemical processe

Status quo in physiological proteomics of the uncultured Riftia pachyptila endosymbiont

Riftia pachyptila, the giant deep-sea tube worm, inhabits hydrothermal vents in the Eastern Pacific ocean. The worms are nourished by a dense population of chemoautotrophic bacterial endosymbionts. Using the energy derived from sulfide oxidation, the symbionts fix CO(2) and produce organic carbon, which provides the nutrition of the host. Although the endosymbionts have never been cultured, cultivation-independent techniques based on density gradient centrifugation and the sequencing of their (meta-) genome enabled a detailed physiological examination on the proteomic level. In this study, the Riftia symbionts' soluble proteome map was extended to a total of 493 identified proteins, which allowed for an explicit description of vital metabolic processes such as the energy-generating sulfide oxidation pathway or the Calvin cycle, which seems to involve a reversible pyrophosphate-dependent phosphofructokinase. Furthermore, the proteomic view supports the hypothesis that the symbiont uses nitrate as an alternative electron acceptor. Finally, the membrane-associated proteome of the Riftia symbiont was selectively enriched and analyzed. As a result, 275 additional proteins were identified, most of which have putative functions in electron transfer, transport processes, secretion, signal transduction and other cell surface-related functions. Integrating this information into complex pathway models a comprehensive survey of the symbiotic physiology was established