Light emission from a scanning tunneling microscope: Fully retarded calculation

The light emission rate from a scanning tunneling microscope (STM) scanning a noble metal surface is calculated taking retardation effects into account. As in our previous, non-retarded theory [Johansson, Monreal, and Apell, Phys. Rev. B 42, 9210 (1990)], the STM tip is modeled by a sphere, and the dielectric properties of tip and sample are described by experimentally measured dielectric functions. The calculations are based on exact diffraction theory through the vector equivalent of the Kirchoff integral. The present results are qualitatively similar to those of the non-retarded calculations. The light emission spectra have pronounced resonance peaks due to the formation of a tip-induced plasmon mode localized to the cavity between the tip and the sample. At a quantitative level, the effects of retardation are rather small as long as the sample material is Au or Cu, and the tip consists of W or Ir. However, for Ag samples, in which the resistive losses are smaller, the inclusion of retardation effects in the calculation leads to larger changes: the resonance energy decreases by 0.2-0.3 eV, and the resonance broadens. These changes improve the agreement with experiment. For a Ag sample and an Ir tip, the quantum efficiency is $\approx$ 10$^{-4}$ emitted photons in the visible frequency range per tunneling electron. A study of the energy dissipation into the tip and sample shows that in total about 1 % of the electrons undergo inelastic processes while tunneling.Comment: 16 pages, 10 figures (1 ps, 9 tex, automatically included); To appear in Phys. Rev. B (15 October 1998

The Pristine survey -- XXIII. Data Release 1 and an all-sky metallicity catalogue based on Gaia DR3 BP/RP spectro-photometry

We use the spectro-photometric information of ~219 million stars from Gaia's DR3 to calculate synthetic, narrow-band, metallicity-sensitive CaHK magnitudes that mimic the observations of the Pristine survey, a survey of photometric metallicities of Milky Way stars that has been mapping more than 6,500 deg^2 of the northern sky with the CFHT since 2015. These synthetic magnitudes are used for an absolute re-calibration of the deeper Pristine photometry and, combined with broadband Gaia information, synthetic and Pristine CaHK magnitudes are used to estimate photometric metallicities over the whole sky. The resulting metallicity catalogue is accurate down to [Fe/H]~-3.5 and is particularly suited for the exploration of the metal-poor Milky Way ([Fe/H]<-1.0). We make available here the catalogue of synthetic CaHK_syn magnitudes for all stars with BP/RP information in Gaia DR3, as well as an associated catalogue of more than ~30 million photometric metallicities for high S/N FGK stars. This paper further provides the first public DR of the Pristine catalogue in the form of higher quality recalibrated Pristine CaHK magnitudes and photometric metallicities for all stars in common with the BP/RP information in Gaia DR3. We demonstrate that, when available, the much deeper Pristine data greatly enhances the quality of the derived metallicities, in particular at the faint end of the catalogue (G_BP>16). Combined, both catalogues include more than 2 million metal-poor star candidates as well as more than 200,000 and ~8,000 very and extremely metal-poor candidates. Finally, we show that these metallicity catalogues can be used efficiently, among other applications, for Galactic archaeology, to hunt for the most metal-poor stars, and to study how the structure of the Milky Way varies with metallicity, from the flat distribution of disk stars to the spheroid-shaped metal-poor halo. (Shortened)Comment: 30 pages, 24 figures, submitted to A&A. First two authors are co-first author. The CaHK photometry catalogue and the two photometric metallicity catalogues are available, before acceptance, as large compressed csv files at: https://seafile.unistra.fr/d/ee0c0f05719d4368bcbb

Dynamics of a high-eccentricity planet in a large planetesimal disc

Clustering of orbital characteristics for distant Solar System objects has been proposed to indicate the presence of a ninth planet. Simulations show that the planets orbit would have to have a mass of 5–10 Solar masses, a semi-major axis of 400–800 AU, an eccentricity of 0.2–0.5 and an inclination of 15–25°. Simulations of a planet scattering off a giant planet into a highly eccentric orbit, show that the scattered planet can circularise its orbit by dynamical friction with a planetesimal disc, providing a hypothesis of the origins of Planet Nine. The simulations show an increase in the planets inclination not explained by dynamical friction. In this thesis a further examination of the increasing inclination is presented. Some of the theory of the Kozai–Lidov resonance, phase space, dynamical friction and the Miyamoto–Nagai potential is presented. The results show that a highly eccentric planet travelling through a planetesimal disc is reliably circularised and achieves high inclination at some point of its evolution. The phase space for the Kozai–Lidov resonance for this setup is explored. Additional fixed points at 0 and 180 degrees, which are not present in the regular Kozai cycle, are found to play a major role in the dynamics as the planet is circularised. An attempt was made to model the planetesimal disc with the Miyamoto–Nagai potential. Simulations were performed for different values of the disc parameters. The resulting phase portraits lacked the additional fixed points produced by the planetesimal disc.Ända sedan 1781, när William Herschel upptäckte Uranus, så har astronomer letat efter planeter som ligger ännu längre ut. Solsystemet är ett stort ställe, så om man vill hitta någonting så krävs lite vägledning till var man ska leta. 2016 publicerade astronomerna Konstantin Batygin och Mike Brown en studie om små objekt utanför Neptunus, där de hade upptäckt att många av de här himlakropparnas banor delar vissa egenskaper. De föreslog att det här orsakas av en oupptäckt planet, kallad Planet Nio, på en utdragen omloppsbana långt ifrån de planeterna vi redan känner till. Ett problem med den här hypotesen är att vi inte vet hur Planet Nio skulle ha hamnat så långt bort. Om den bildades där ute så förklarar det inte hur den omloppsbana blev så utdragen. I andra teorier föreslås det att den bildades någon annanstans. Solen hade kunnat ta planeten från en annan stjärna som passerat för nära, eller så kunde Planet Nio ha bildats med de andra planeterna och blivit utslungad av något nära möte. Om den senare teorin stämmer så skulle det förklara varför banan är så utdragen, det är vanligt för objekt som har slungats ut bortom de andra planeterna. Men det finns ett problem med teorin, den har svårt att förklara varför den förslagna banan lutar så mycket jämfört med de andra planeterna. 2018 föreslog Linn Eriksson vid Lunds Universitet en ny ide för hur planetens bana hade kunnat utvecklas, från att den slungats ut, tills att den är på den bana som forskarna tror at den har. I hennes modell så interagerar planeten med ett asteroidbälte som inte har upptäckts än. Projektet var mest fokuserat på hur excentrisk banan skulle bli, men mot förmodan så fick planetens bana en lutning som matchar förutsägelserna som gjorts. Det här kandidatarbetets fokus har legat på att förstå varför banan fick lutningen och hur planeten och bältet interagerar. Det här arbetet kan vara användbart för astronomer i flera områden. Med en förbättrad förståelse för hur Planet Nio bildats så ökar våra chanser att en dag hitta den. Om teorin stämmer så skulle den kunna stödja olika teorier om planetbildning. Även om vi inte hittar Planet Nio så skulle arbetet kunna användas för att bättre förstå hur planeter runt andra stjärnor beter sig, eftersom många av dem har banor som likar banan som föreslagits för Planet Nio

Axonal outgrowth on nano-imprinted patterns

Nanotechnology has provided methods to fabricate surface patterns with features down to a few rim. If cells or cell processes exhibit contact guidance in response to such small patterns is an interesting question and could be pertinent for many applications. In the present study we investigated if axonal outgrowth was affected by nano-printed patterns in polymethylmethacrylate (PMMA)-covered silicon chips. To this end adult mouse sympathetic and sensory ganglia were mounted in Matrigel (R) on the chips close to the nano-patterns. The patterns consisted of parallel grooves with depths of 300 nm and varying widths of 100-400 nm. The distance between two adjacent grooves was 100-1600 nm. The chips were cultured in medium containing 25 ng/ml of nerve growth factor to stimulate axonal outgrowth. After 1 week of incubation. axonal outgrowth was investigated by immunocytochemistry or scanning electron microscopy. Axons displayed contact guidance on all patterns. Furthermore, we found that the nerve cell processes preferred to grow on ridge edges and elevations in the patterns rather than in grooves, a seemingly claustrophobic behavior. We conclude that axons of peripheral neurons might be guided by nanopatterns on PMMA when the lateral features are 100 nm or larger. The present results can be utilized for nerve regenerating scaffolds or the construction of a stable, high-resolution electronic interface to neurons, which is required for future brain machine interfaces. (c) 2005 Elsevier Ltd. All rights reserved

Axonal guidance on patterned free-standing nanowire surfaces

We demonstrate high-fidelity guidance of axons using rows of nanowires. The axons are prevented from crossing the rows, making it possible to guide and sort a large number of axons as opposed to when chemical patterns are used. Focal adhesion forms at the nanowires establishing a possible site of information transfer between the surface and the cells. Rows of gallium phosphide (GaP) nanowires were epitaxially grown on GaP(111) substrates in patterns defined by electron beam lithography

Rectifying and Sorting of Regenerating Axons by Free Standing Nanowire Patterns: A highway for nerve fibers

We present an EBL-defined nanowire pattern that can sort axons coming from different directions on a substrate. The pattern defines tracks for left-bound traffic and right-bound traffic, which opens up new possibilities for designing neural networks on a chip

Gallium phosphide nanowire arrays and their possible application in cellular force investigations

The authors report the fabrication of gallium phosphide nanowire arrays that can be used for cellular force measurements. The nanowire positions are defined using electron beam lithography and the nanowires are grown using metal organic vapor phase epitaxy. By varying the nanowire diameter, length, and spacing from substrate to substrate, they can expect to probe cell forces over several orders of magnitude, depending on the chosen substrate. The small diameter of the nanowires allows them to densely pack the array and to achieve unprecedented spatial resolution for future cell force-array applications