Synchronizing gas injections and time-resolved data acquisition for perturbation-enhanced APXPS experiments

An experimental approach is described in which well-defined perturbations of the gas feed into an Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) cell are fully synchronized with the time-resolved x-ray photoelectron spectroscopy data acquisition. These experiments unlock new possibilities for investigating the properties of materials and chemical reactions mediated by their surfaces, such as those in heterogeneous catalysis, surface science, and coating/deposition applications. Implementation of this approach, which is termed perturbation-enhanced APXPS, at the SPECIES beamline of MAX IV Laboratory is discussed along with several experimental examples including individual pulses of N-2 gas over a Au foil, a multi-pulse titration of oxygen vacancies in a pre-reduced TiO2 single crystal with O-2 gas, and a sequence of alternating precursor pulses for atomic layer deposition of TiO2 on a silicon wafer substrate.Peer reviewe

Atomic layer deposition of cobalt(II) oxide thin films from Co(BTSA)(2)(THF) and H2O

In this work, we have studied the applicability of Co(BTSA)(2)(THF) [BTSA = bis(trimethylsilyl)amido] (THF = tetrahydrofuran) in atomic layer deposition (ALD) of cobalt oxide thin films. When adducted with THF, the resulting Co(BTSA)(2)(THF) showed good volatility and could be evaporated at 55 degrees C, which enabled film deposition in the temperature range of 75-250 degrees C. Water was used as the coreactant, which led to the formation of Co(II) oxide films. The saturative growth mode characteristic to ALD was confirmed with respect to both precursors at deposition temperatures of 100 and 200 degrees C. According to grazing incidence x-ray diffraction measurements, the films contain both cubic rock salt and hexagonal wurtzite phases of CoO. X-ray photoelectron spectroscopy measurements confirmed that the primary oxidation state of cobalt in the films is +2. The film composition was analyzed using time-of-flight elastic recoil detection analysis, which revealed the main impurities in the films to be H and Si. The Si impurities originate from the BTSA ligand and increased with increasing deposition temperature, which indicates that Co(BTSA)(2)(THF) is best suited for low-temperature deposition. To gain insight into the surface chemistry of the deposition process, an in situ reaction mechanism study was conducted using quadrupole mass spectroscopy and quartz crystal microbalance techniques. Based on the in situ experiments, it can be concluded that film growth occurs via a ligand exchange mechanism. Published by the AVS.Peer reviewe

Atomic Layer Deposition of Photoconductive Cu2O Thin Films

Herein, we report an atomic layer deposition (ALD) process for Cu2O thin films using copper(II) acetate [Cu(OAc)(2)] and water vapor as precursors. This precursor combination enables the deposition of phase-pure, polycrystalline, and impurity-free Cu2O thin films at temperatures of 180-220 degrees C. The deposition of Cu(I) oxide films from a Cu(II) precursor without the use of a reducing agent is explained by the thermally induced reduction of Cu(OAc)(2) to the volatile copper(I) acetate, CuOAc. In addition to the optimization of ALD process parameters and characterization of film properties, we studied the Cu2O films in the fabrication of photoconductor devices. Our proof-of-concept devices show that approx- imately 20 nm thick Cu2O films can be used for photodetection in the visible wavelength range and that the thin film photoconductors exhibit improved device characteristics in comparison to bulk Cu2O crystals.Peer reviewe

AD Leonis: Radial Velocity Signal of Stellar Rotation or Spin–Orbit Resonance?

AD Leonis is a nearby magnetically active M dwarf. We find Doppler variability with a period of 2.23 days, as well as photometric signals: (1) a short-period signal, which is similar to the radial velocity signal, albeit with considerable variability; and (2) a long-term activity cycle of 4070 ± 120 days. We examine the short-term photometric signal in the available All-Sky Automated Survey and Microvariability and Oscillations of STars (MOST) photometry and find that the signal is not consistently present and varies considerably as a function of time. This signal undergoes a phase change of roughly 0.8 rad when considering the first and second halves of the MOST data set, which are separated in median time by 3.38 days. In contrast, the Doppler signal is stable in the combined High-Accuracy Radial velocity Planet Searcher and High Resolution Echelle Spectrometer radial velocities for over 4700 days and does not appear to vary in time in amplitude, phase, period, or as a function of extracted wavelength. We consider a variety of starspot scenarios and find it challenging to simultaneously explain the rapidly varying photometric signal and the stable radial velocity signal as being caused by starspots corotating on the stellar surface. This suggests that the origin of the Doppler periodicity might be the gravitational tug of a planet orbiting the star in spin–orbit resonance. For such a scenario and no spin–orbit misalignment, the measured v sin i indicates an inclination angle of 15°̣5 ± 2°̣5 and a planetary companion mass of 0.237 ± 0.047 M Jup

Bayesian search for low-mass planets around nearby M dwarfs. Estimates for occurrence rate based on global detectability statistics

Mikko Tuomi, 'Bayesian search for low-mass planets around nearby M dwarfs - estimates for occurrence rate based on global detectability statistics', Monthly Notices of the Royal Astronomical Society, Vol. 441 (2): 1545-1569, first published online 8 May 2014. The version of record is available online at doi: 10.1093/mnras/stu358 © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.Due to their higher planet-star mass ratios, M dwarfs are the easiest targets for detection of low-mass planets orbiting nearby stars using Doppler spectroscopy. Furthermore, because of their low masses and luminosities, Doppler measurements enable the detection of lowmass planets in their habitable zones that correspond to closer orbits than for solar-type stars. We re-analyse literature Ultraviolet and Visual Echelle Spectrograph (UVES) radial velocities of 41 nearby Mdwarfs in a combination with new velocities obtained from publicly available spectra from the HARPS-ESO spectrograph of these stars in an attempt to constrain any low-amplitude Keplerian signals. We apply Bayesian signal detection criteria, together with posterior sampling techniques, in combination with noise models that take into account correlations in the data and obtain estimates for the number of planet candidates in the sample. More generally, we use the estimated detection probability function to calculate the occurrence rate of low-mass planets around nearby M dwarfs. We report eight new planet candidates in the sample (orbiting GJ 27.1, GJ 160.2, GJ 180, GJ 229, GJ 422, and GJ 682), including two new multiplanet systems, and confirm two previously known candidates in the GJ 433 system based on detections of Keplerian signals in the combined UVES and High Accuracy Radial velocity Planet Searcher (HARPS) radial velocity data that cannot be explained by periodic and/or quasi-periodic phenomena related to stellar activities. Finally, we use the estimated detection probability function to calculate the occurrence rate of low-mass planets around nearby M dwarfs. According to our results, M dwarfs are hosts to an abundance of low-mass planets and the occurrence rate of planets less massive than 10M? is of the order of one planet per star, possibly even greater. Our results also indicate that planets with masses between 3 and 10 M⊕ are common in the stellar habitable zones of M dwarfs with an estimated occurrence rate of 0.21+0.03 -0.05 planets per star.Peer reviewe

In situ reaction mechanism study on atomic layer deposition of intermetallic Co3Sn2 thin films

In this work, a growth mechanism of an intermetallic Co3Sn2 thin film is studied in situ with a quartz crystal microbalance (QCM) and quadrupole mass spectrometer (QMS). The film is deposited by atomic layer deposition (ALD) from CoCl2 (TMEDA) and Bu3SnH precursors (TMEDA = N,N,N' ,N' - tetramethylethylenediamine). Balanced reaction equations are resolved by fitting the QMS and QCM data, and a step-by-step growth mechanism is determined for the process. During the CoCl2 (TMEDA) pulse, only 1-chlorobutane is formed as a byproduct. However, during the Bu3SnH pulse, two byproducts, BuCl and Bu3SnCl, were clearly detected, indicating that two competing reaction pathways exist during that pulse. Preliminary studies on another intermetallic ALD process, Ni3Sn2, revealed that the reactions occur similarly as in the Co3Sn2 process.Peer reviewe

Ex Situ In Vacuo and In Situ Studies on Mechanisms of ALD Processes

This master's thesis consists of two parts related to atomic layer deposition (ALD) processes: a literature survey of so-called ex situ in vacuo analysis methods used in investigations of the ALD chemistry and a summary of the work performed by the author using in situ methods. The first part of the thesis is divided into four sections. In the first two sections ALD as a thin film deposition method is introduced, and in situ and ex situ in vacuo publications related to ALD are summarized. The third section is a general overview of ex situ in vacuo analysis methods, and the final section a literature review covering publications where ex situ in vacuo techniques have been employed in studying ALD processes, with a strong emphasis on analysis methods which are based on the use of x-rays. The second part of the thesis consists of in situ quartz crystal microbalance and quadrupole mass spectrometry studies of the V(NEtMe)4/D2O, V(NEtMe)4/O3, Mg(thd)2/TiF4 and Cu2(CH3COO)4/D2O ALD processes. The experimental apparatus and related theory are given a brief overview, followed by a presentation and discussion of the results.Tämä pro gradu –tutkielma koostuu kahdesta osasta: atomikerroskasvatus(ALD)prosessien tutkimisessa käytettyjen niin sanottujen ex situ in vacuo –analyysimenetelmien kirjallisuuskatsauksesta, sekä kirjoittajan itse tekemistä in situ –tutkimuksista. Tutkielman ensimmäinen osa on jaettu neljään osioon. Näistä kahdessa ensimmäisessä esitellään ALD ohutkalvojen kasvatusmenetelmänä ja tiivistetään ALD-prosessien ex situ in vacuo –tutkimukset. Kolmas osio on yleiskatsaus erilaisista ex situ in vacuo –menetelmistä ja viimeinen osio kirjallisuuskatsaus, joka kattaa sellaiset julkaisut, missä ex situ in vacuo –menetelmiä on käytetty ALD-prosessien tutkimisessa. Katsauksessa painotutaan erityisesti röntgensäteitä käyttäviin analyysimenetelmiin. Tutkielman toinen osa koostuu seuraavien ALD prosessien in situ kvartsikidevaaka ja kvadrupolimassaspektrometritutkimuksista: V(NEtMe)4/D2O, V(NEtMe)4/O3, Mg(thd)2/TiF4 ja Cu2(CH3COO)4/D2O. Aluksi annetaan yleiskatsaus käytetystä laitteistosta ja siihen liittyvästä teoriasta, minkä jälkeen esitellään tutkimusten tulokset

Towards space-grade 3D-printed, ALD-coated small satellite propulsion components for fluidics

Abstract Space technology has been an early adopter of additive manufacturing (AM) as a way of quickly producing relatively complex systems and components that would otherwise require expensive and custom design and production. Space as an environment and long-term survivability pose challenges to materials used in AM and these challenges need to be addressed. Atomic layer deposition (ALD) is an effective coating method enabling conformal and precise coating of the complete AM print. This work analyses how an ALD coating of aluminium oxide on acrylonitrile butadiene styrene (ABS) and polyamide PA 2200 plastic AM prints benefits and protects them. This was studied in the context of in-space propulsion fluidics, where propellant flow properties also matter. AM was performed with material extrusion and selective laser sintering methods that are commonly used. Tests were performed with a simple bang-bang controller test setup and a mass spectrometer, and the existence of the coating was confirmed with scanning electron microscope imaging.Peer reviewe

Constructing Spacecraft Components Using Additive Manufacturing and Atomic Layer Deposition : First Steps for Integrated Electric Circuitry

Funding Information: We thank the European Space Agency (ESA), who has supported parts of this research as part of the HighPEEK project (ESA Contract No. 4000127834/19/UK/AB). In particular, Ugo Lafont and Paul Greenway (ESA) have our gratitude. We also deeply appreciate the help given by Daniel Leese (exchange student at Aalto University), Kirsi Kukko, Ashish Mohite and Olli Knuuttila (Aalto University), Lorenz Schmuckli and Pekka Rummukainen (Aalto University, retired), and Katja Väyrynen and Marko Vehkamäki (University of Helsinki). Publisher Copyright: © 2021 American Society of Civil Engineers.Many fields, including the aerospace industry, have shown increased interest in the use of plastics to lower the mass of systems. However, the use of plastics in space can be challenging for a number of reasons. Ultraviolet radiation, atomic oxygen, and other phenomena specifically associated with space cause the degradation of polymers. Here we show a path toward creation of space-grade components by combining additive manufacturing (AM) and atomic layer deposition (ALD). Our method produced ALD Al2O3 coated thermoplastic parts suitable for space applications. The highlight of this work is a significant reduction in outgassing, demonstrated using residual gas analyzer (RGA) sampling. Compared to uncoated parts, the ALD Al2O3 coating decreased the outgassing of polyether ether ketone (PEEK), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), and nanodiamond-doped polylactide (ND-PLA) by 46%, 49%, 58%, and 65%, respectively. The manufacturing method used in this work enables the use of topology optimization already in the early concept creation phase. The method is ideally suited for spacecraft applications, in which the volume and mass of parts is critical, and could also be adapted for in-space manufacturing. (c) 2021 American Society of Civil Engineers.Peer reviewe