Hα Absorption in Transiting Exoplanet Atmospheres

AbstractRecent observations by Jensen et al. of Hα absorption by the upper atmosphere of HD189733b have motivated the need for a theoretical understanding of the distribution of n=2 hydrogen within hot Jupiter atmospheres. With this in mind, we model the n=2 state of atomic hydrogen in a hydrostatic atmosphere in thermal and photoionization equilibrium. Both collisional and radiative transitions are included in the calculation of the n = 2 state level population. In our model, the Hα absorption is dominated by a τ ~ 1 shell composed of metastable 2s hydrogen located within the neutral atomic layer, with the contribution coming roughly uniformly throughout the layer instead of from a specific impact parameter. An ionization rate an order of magnitude over the expected value can reproduce the observed transit depth.

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Observational manifestations of ‘cosmological dinosaurs’ at redshifts z ∼ 20

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab689 ◽

2021 ◽

Vol 503 (2) ◽

pp. 3081-3088

Author(s):

V K Dubrovich ◽

Yu N Eroshenko ◽

S I Grachev

Keyword(s):

Black Hole ◽

Atomic Hydrogen ◽

Radiation Transfer ◽

Ring Width ◽

High Mass ◽

Primordial Black Hole ◽

Array Type ◽

Local Sources ◽

Order Of Magnitude ◽

Very High

ABSTRACT We consider a primordial black hole of very high mass, $10^9\!-\!10^{10}\, \mathrm{M}_\odot$, surrounded by the dark matter and bayonic halo at redshifts z ∼ 20 without any local sources of energy release. Such heavy and concentrated objects in the early Universe were previously called ‘cosmological dinosaurs’. Spectral distribution and spatial variation of the brightness in the 21-cm line of atomic hydrogen are calculated with the theory of radiation transfer. It is shown that a narrow and deep absorption arises in the form of the spherical shell around the primordial black hole at the certain radius. The parameters of this shell depend almost exclusively on the mass of the black hole. The angular diameter 18 arcsec of the absorption ring at z ∼ 20 is well within the current technical possibilities of the Square Kilometre Array type telescopes. But the observation of the ring width itself requires an order of magnitude better resolution.

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Impurity and Stoichiometry Control in Atomic Layer Epitaxy

MRS Proceedings ◽

10.1557/proc-262-143 ◽

1992 ◽

Vol 262 ◽

Author(s):

H. Yokoyama ◽

K. Ikuta ◽

N. Inoue

Keyword(s):

Point Defects ◽

Resonant Tunneling ◽

Room Temperature ◽

Defect Density ◽

Atomic Layer ◽

Negative Resistance ◽

Atomic Layer Epitaxy ◽

Tunneling Diode ◽

Order Of Magnitude ◽

Stoichiometry Control

ABSTRACTWe investigate the intrinsic point defects in epilayers grown by atomic layer epitaxy (ALE). Ga vacancies and antisite As atoms in the epilayers are detected by photoluminescence spectroscopy. This shows that the ALE epilayer was grown under As-rich conditions. We propose increasing the TMG flux to reduce the number of point defects. With this method, the number of point defects in ALE epilayers can be decreased to less than that in conventionally grown epilayers. Moreover, it is'found that these point defects are formed by the incomplete Ga coverage, not by the steric hindrance as previously suggested. The carbon concentration is decreased by one order of magnitude by using nitrogen instead of hydrogen as the carrier gas. As an application of this low defect density, we fabricated a GaAs/AlAs resonant tunneling diode and observed the negative resistance at room temperature.

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Enhanced Electrical Properties of Atomic Layer Deposited LaxAlyO Thin Films with Stress Relieved Preoxide Pretreatment

Materials ◽

10.3390/ma11091601 ◽

2018 ◽

Vol 11 (9) ◽

pp. 1601

Author(s):

Xing Wang ◽

Hongxia Liu ◽

Lu Zhao ◽

Yongte Wang

Keyword(s):

Electrical Properties ◽

Atomic Layer ◽

Breakdown Field ◽

Gate Leakage Current ◽

Interface Engineering ◽

Order Of Magnitude ◽

Mis Capacitor ◽

The Impact ◽

Breakdown Field Strength ◽

Gate Leakage Current Density

The impact of stress relieved preoxide (SRPO) interface engineering on the physical and electrical properties of LaxAlyO films was investigated. It was proved that the SRPO pretreatment has little influence on the surface morphology of LaxAlyO films and the chemical bond composition of LaxAlyO/Si interface. However, the SRPO pretreated MIS capacitor displayed obvious improvement in decreasing the amount of trapped oxide charges and interfacial traps. As a result, a reduction of more than one order of magnitude in the gate leakage current density was obtained. The breakdown field strength and TDDB reliability of the LaxAlyO film treated with SRPO were also enhanced.

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Order of magnitude enhancement of inherently selective atomic layer deposition of zirconia on silicon without deposition on copper: The role of precursor

Vacuum ◽

10.1016/j.vacuum.2021.110686 ◽

2021 ◽

pp. 110686

Author(s):

Soumya Saha ◽

Gregory Jursich ◽

Abhijit H. Phakatkar ◽

Tolou Shokuhfar ◽

Christos G. Takoudis

Keyword(s):

Atomic Layer Deposition ◽

Atomic Layer ◽

Layer Deposition ◽

Order Of Magnitude

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Hydrogen escape from Mars is driven by seasonal and dust storm transport of water

Science ◽

10.1126/science.aba5229 ◽

2020 ◽

Vol 370 (6518) ◽

pp. 824-831

Author(s):

Shane W. Stone ◽

Roger V. Yelle ◽

Mehdi Benna ◽

Daniel Y. Lo ◽

Meredith K. Elrod ◽

...

Keyword(s):

Dust Storm ◽

Atomic Hydrogen ◽

Molecular Hydrogen ◽

Dust Storms ◽

Upper Atmosphere ◽

Lower Atmosphere ◽

Mars Atmosphere ◽

Water Abundance ◽

Neutral Gas ◽

Standard Models

Mars has lost most of its once-abundant water to space, leaving the planet cold and dry. In standard models, molecular hydrogen produced from water in the lower atmosphere diffuses into the upper atmosphere where it is dissociated, producing atomic hydrogen, which is lost. Using observations from the Neutral Gas and Ion Mass Spectrometer on the Mars Atmosphere and Volatile Evolution spacecraft, we demonstrate that water is instead transported directly to the upper atmosphere, then dissociated by ions to produce atomic hydrogen. The water abundance in the upper atmosphere varied seasonally, peaking in southern summer, and surged during dust storms, including the 2018 global dust storm. We calculate that this transport of water dominates the present-day loss of atomic hydrogen to space and influenced the evolution of Mars’ climate.

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Mariner 6: Ultraviolet spectrum of Mars upper atmosphere

Symposium - International Astronomical Union ◽

10.1017/s0074180900102852 ◽

1971 ◽

Vol 40 ◽

pp. 253-256 ◽

Cited By ~ 1

Author(s):

C. A. Barth ◽

W. G. Fastie ◽

C. W. Hord ◽

J. B. Pearce ◽

K. K. Kelly ◽

...

Keyword(s):

Carbon Dioxide ◽

Carbon Monoxide ◽

Spectral Region ◽

Atomic Hydrogen ◽

Atomic Oxygen ◽

Ultraviolet Spectrum ◽

Upper Atmosphere

Emission features from ionized carbon dioxide and carbon monoxide were measured in the 1900- to 4300-Å spectral region. The Lyman-α 1216-Å line of atomic hydrogen and the 1304-, 1356-, and 2972-Å lines of atomic oxygen were observed.

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Development of High-Quality Gate Oxide on 4H-SiC Using Atomic Layer Deposition

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1004.547 ◽

2020 ◽

Vol 1004 ◽

pp. 547-553

Author(s):

A.B. Renz ◽

Oliver J. Vavasour ◽

Peter M. Gammon ◽

Fan Li ◽

Tian Dai ◽

...

Keyword(s):

Atomic Layer Deposition ◽

Photoelectron Spectroscopy ◽

Elevated Temperatures ◽

Dielectric Breakdown ◽

Atomic Layer ◽

Oxide Semiconductor ◽

Gas Treatment ◽

Time Dependent Dielectric Breakdown ◽

Layer Deposition ◽

Order Of Magnitude

A systematic post-deposition annealing study on Silicon Carbide (SiC) metal-oxide-semiconductor capacitors (MOSCAPs) using atomic layer deposition (ALD)-deposited silicon dioxide (SiO2) layers was carried out. Anneals were done in oxidising (N2O), inert (Ar) and reducing (H2:N2) ambients at elevated temperatures from 900°C to 1300°C for 1 hour. Electrical characterisation results show that the forming gas treatment at 1100°C reduces the flatband voltage to 0.23 V from 10 V for as-deposited SiO2 layers. The density of interface traps (DIT) was also reduced by one order of magnitude to 2×1011 cm-2 eV-1 at EC-ET = 0.2 eV. As an indicator of the improvement, characterisation by x-ray photoelectron spectroscopy (XPS) showed that silicon enrichment present in as-deposited layers was largely reduced by the forming gas anneal, improving the stoichiometry. Time-dependent dielectric breakdown (TDDB) results showed that the majority of forming gas annealed samples broke down at breakdown fields of 12.5 MV × cm-1, which is about 2.5 MV × cm-1 higher than for thermally oxidised samples.

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Interaction between atomic hydrogen and YBa2Cu3O7

Journal of Materials Research ◽

10.1557/jmr.1992.2908 ◽

1992 ◽

Vol 7 (11) ◽

pp. 2908-2915 ◽

Cited By ~ 1

Author(s):

Angel L.G. Ponce ◽

Jose J. Fripiat

Keyword(s):

Induction Period ◽

Atomic Hydrogen ◽

Dissociative Chemisorption ◽

Experimental Conditions ◽

Reaction Proceeds ◽

Order Of Magnitude ◽

O Vacancy ◽

The Creation ◽

Approximate Limit

Atomic hydrogen obtained from dissociative chemisorption of molecular H2 on Pt particles deposited on the surface of YBa2Cu3O7 reacts with the oxide in producing O vacancies and intercalating H at 82 °C under a H2 pressure of about 400 Torr. An induction period which extends over 1 h is observed as long as the concentration in O vacancies is below 0.1. Above this approximate limit the reaction proceeds quickly until about 1 mol H2 has been consumed. It then slows down progressively, but it is not completed even after 27 h of reaction and ∼1.4 H2 consumed, under these experimental conditions. The enthalpy for the creation of the O vacancy is 143 kcal/g mol O, while the H intercalation enthalpy is −57.5 kcal/g mol H. It appears that the reaction of molecular H2 over YBa2Cu3O7 not coated with Pt proceeds similarly, but the rate is nearly one order of magnitude slower, under identical conditions. The stoichiometry of the reaction agrees with the earlier suggestion that O1 is a labile oxygen which can be replaced by intercalated H. This site and the interstitial vacant sites in the copper chains square plane would be the first ones to be occupied by intercalated H.

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Dissociation, recombination and attachment processes in the upper atmosphere—I

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1937.0243 ◽

1937 ◽

Vol 163 (915) ◽

pp. 542-553 ◽

Cited By ~ 28

Keyword(s):

Reaction Rates ◽

Upper Atmosphere ◽

Radio Waves ◽

Ionization Density ◽

Pressure Discharge ◽

Mechanical Methods ◽

Order Of Magnitude ◽

Quantitative Manner ◽

The Individual ◽

Atmospheric Ionization

The study of the properties of the earth’s upper atmosphere has now progressed so far as to provide what should be a sufficient basis for the development of a detailed theory. Since the state of the upper atmosphere approximates closely to that of the gas in a low-pressure discharge tube (except for the absence of solid boundaries), it is clear that such a theory must deal with the individual collision processes which can occur in such a system. Until the last few years no satisfactory theory of these phenomena was available, but it is now possible to apply quantum mechanical methods with reasonable expectation of results accurate at least as regards order of magnitude. We therefore propose to make use of these methods to obtain a deeper understanding of the physics of the ionosphere. In this paper we confine ourselves particularly to the qualitative study of certain problems associated with the two upper ionized layers (the E and F regions), making use of information already available concerning the probabilities of the various collision reactions which are important. The detailed evaluation of these reaction rates is being carried out, and in later papers it is hoped to deal with the various problems in a more nearly quantitative manner. The two main strata of atmospheric ionization are the E region extending roughly from 120 to 160 km. and the F region from 180 to 300 km., at night. During the day each splits into two distinct strata forming the E 1 and E 2 and the F 1 and F 2 regions. The ionization density in each region, as determined from experiments with radio waves, exhibits characteristic annual and diurnal variations besides irregular variations of considerable magnitude. The first problem which arises is the reason for the existence of the stratification. This being understood it is then necessary to account for the observed variations of density, the daytime splitting of the layers, and so on.

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