Detection of Interstellar Ortho-D2H+ with SOFIA

We report on the detection of the ground-state rotational line of ortho-D2H+ at 1.477 THz (203 mu m) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) on. board the Stratospheric Observatory For Infrared Astronomy (SOFIA). The line is seen in absorption against. far-infrared continuum from the protostellar binary IRAS 16293-2422 in Ophiuchus. The para-D2H+ line at 691.7 GHz was not detected with the APEX telescope toward this position. These D2H+ observations complement our previous detections of para-H2D+ and ortho-H2D+ using SOFIA and APEX. By modeling chemistry and radiative transfer in the dense core surrounding the protostars, we find that the ortho-D2H+ and para-H2D+ absorption features mainly originate in the cool (T <18 K) outer envelope of the core. In contrast, the ortho-H2D+ emission from the core is significantly absorbed by the ambient molecular cloud. Analyses of the combined D2H+ and H2D+ data result in an age estimate of similar to 5. x. 10(5) yr for the core, with an uncertainty of similar to 2. x. 10(5) yr. The core material has probably been pre-processed for another 5. x. 10(5) years in conditions corresponding to those in the ambient molecular cloud. The inferred timescale is more than 10 times the age of the embedded protobinary. The D2H+ and H2D+ ions have large and nearly equal total (ortho+ para) fractional abundances of similar to 10(-9) in the outer envelope. This confirms the central role of H-3 + in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also D-3(+) should be abundant in these conditions.Peer reviewe

Annihilation of structural defects in chalcogenide absorber films for high-efficiency solar cells

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In polycrystalline semiconductor absorbers for thin-film solar cells, structural defects may enhance electron-hole recombination and hence lower the resulting energy conversion efficiency. To be able to efficiently design and optimize fabrication processes that result in high-quality materials, knowledge of the nature of structural defects as well as their formation and annihilation during film growth is essential. Here we show that in co-evaporated Cu(In,Ga)Se-2 absorber films the density of defects is strongly influenced by the reaction path and substrate temperature during film growth. A combination of high-resolution electron microscopy, atomic force microscopy, scanning tunneling microscopy, and X-ray diffraction shows that Cu(In,Ga)Se-2 absorber films deposited at low temperature without a Cu-rich stage suffer from a high density of - partially electronically active - planar defects in the {112} planes. Real-time X-ray diffraction reveals that these faults are nearly completely annihilated during an intermediate Cu-rich process stage with [Cu]/([In] + [Ga]) > 1. Moreover, correlations between real-time diffraction and fluorescence analysis during Cu-Se deposition reveal that rapid defect annihilation starts shortly before the start of segregation of excess Cu-Se at the surface of the Cu(In,Ga)Se-2 film. The presented results hence provide direct insights into the dynamics of the film-quality-improving mechanism

Metall sulfide assisted crystallyzation of strongly (001) textured tungstendisulfide thin films

Der Schichtgitterhalbleiter Wolframdisulfid (WS$_\textrm{2}$) ist ein vielversprechender Kandidat als Absorberschicht in Dünnschichtsolarzellen. Es hat eine direkte Bandlücke von 1.8~eV und einen hohen Absorptionskoeffizienten von 10$^{\rm{5}}$~cm$^{\rm{-1}}$. Die van-der-Waals-Oberfläche eines Schichtgitters zeichnet sich durch eine geringe Konzentration an Oberflächenzuständen aus. Daher ist es vorteilhaft, Wolframdisulfid-Schichten mit den van-der-Waals-Ebenen parallel zur Substratoberflache zu wachsen ((001)-Textur), um elektronisch hochwertige pn-Heteroübergänge zu realisieren.\\ In dieser Arbeit wurden für die Präparation von polykristallinen Wolframdisulfid-Schichten, die metallsulfid-unterstützte Kristallisation aus amorphen WS$_\textrm{x}$-Schichten und die metallsulfid-unterstützte Sulfidation von Wolframschichten eingesetzt. Als Promotor der Kristallisation dient dabei Metallsulfid (Metall = Ni, Co, Pd). Mit Metallsulfid-Unterstützung kristallisieren die WS$_\textrm{2}$-Schichten in einer starken (001)-Textur mit lateral großen Kristalliten (bis 10~\upmum).\\ Die Sulfidations- und Kristallisationsprozesse wurde in-situ mittels energiedispersiver R"ontgenbeugung im HASYLAB am DESY in Hamburg verfolgt. Weitere Untersuchungsmethoden waren winkeldispersive Röntgenbeugung, Raster- und Transmissionselektronenmikroskopie sowie elektrische Hall-Messungen. Die Temperatur muss für die Kristallisation zu stark (001)-texturierten Schichten die eutektische Temperatur des Metall-Schwefel-Phasensystems überschreiten. Bei Temperaturen knapp unterhalb dieser Temperatur entstehen Schichten, die ebenfalls kristallisiert sind, aber um mehrere Größenordnungen höhere Leitfähigkeiten aufweisen und in temperaturabhängigen Leitfähigkeitsmessungen metallisches Verhalten zeigen. \\ Optische und elektrische Untersuchungen von durch Kristallisation aus den amorphen WS$_\textrm{x}$-Schichten hergestellten Schichten ergeben thermisch aktivierte Ladungsträgerbeweglichkeiten und Absorptionsspektren, die denen von Wolframdisulfid-Einkristallen nahekommen. Die durch Sulfidation hergestellten Wolframdisulfid-Schichten erreichen ebenfalls hohe Ladungsträgerbeweglichkeiten, weisen aber Transmissionsspektren mit hohen Absorptionen im Energiebereich der Bandlücke auf.\\ Aus den Ergebnissen wird ein modifiziertes Modell der metallsulfid-unterstützten Kristallisation von stark (001)-texturierten Wolframdisulfid-Schichten entwickelt. Dabei unterstützt das sich am Anfang homogen in der Schicht verteilende Metallsulfid ein Kristallwachstum. Nach Überschreiten der eutektischen Temperatur der Metall-Schwefel-Phasensystems bilden sich flüssige Metallsulfidtröpfchen, welche Wolframsulfid lösen, übersättigen und lateral große WS$_\textrm{2}-Kristallite ausscheiden.\\ Trotz der hervorragenden strukturellen, elektrischen und optischen Eigenschaften der kristallisierten Wolframdisulfid-Schichten war es nicht möglich, pn-Übergange und Solarzellen zu präparieren. Als Grund dafür werden Kurzschlüsse über Wolframdisulfid-Korngrenzen zum Rückkontakt gesehen. Das Verhalten der Korngrenzen muss weiter, u.a. mit Leitfähigkeits-Rasterkraftmikroskopie, untersucht werden, um in Zukunft Dünnschichtsolarzellen mit Wolframdisulfid zu realisieren.The layer-type semiconductor tungsten disulfide (WS$_\textrm{2}) is a promising candidate as absorber layer in thin film solar cells. It exhibits a band gap of 1.8 eV and a high absorption coefficient of 10^{\rm{5}}$~cm$^{\rm{-1}}$. Due to the low concentration of surface states at the van der Waals surface of layer-typed semiconductors the films have to be grown with the van der Waals planes parallel to the substrate surface ((001)-texture) to realize electronically good pn-heterojunctions. For the preparation of polycrystalline WS$_\textrm{2}$films the metal-sulfide assisted crystallization from amorphous WS$_\textrm{x}$films and the metal-sulfide assisted sulfidation of metallic tungsten films were used. Metal-sulfide (metal = Ni, Co, Pd) act as promoter for the crystallization and the sulfidation. For this purpose a Ni (Co, Pd) film was deposited on the substrate or on top of the tungsten or tungsten disulfide film. Without this additional metal layer no crystallization or sulfidation occurs. WS$_\textrm{2}$films prepared in this way crystallize in a strong (001) texture with laterally large (upto 10~$\upmu$m) crystallites if the annealing temperature exceeds the eutectic temperature of the metal-sulfur phase system. Annealing temperatures below the eutectic temperature also lead to an enhanced sulfidation or crystallization, respectively, if a thin film of Ni, Pd or Co is involved. However, these films show laterally small crystallites and very high conductivities and no semiconducting behavior. The crystallization and sulfidation processes were observed by in situ energy dispersive X-ray diffraction (EDXRD) at the HASYLAB at DESY in Hamburg. Further investigation were done by angle-dispersive X-ray diffraction, scanning and transmission electron microscopy temperature dependent Hall-measurements. The results lead to new model of the metal-sulfide crystallization process. In a first step Ni (Co, Pd) distributes homogenously in the amorphous tungsten sulfide film. Then the Ni (Co, Pd) assists the crystallization of small and disordered tungsten disulfide crystallites. Liquid nickel sulfide droplets form and dissolve tungsten sulfide once the eutectic temperature of the Ni-S phase system is reached. The droplets act as seeds of the growth of laterally large tungstendisulfide crystallites parallel to the substrate surface. This crystallization process is comparable with the well known vapor liquid solid (VLS) mechanism for the growth of single crystalline nanorods. The structural, optical and electrical properties of such tungsten disulfide films should be adequate for its use as solar-cell absorber. Possible short circuits at the grain boundaries have to be further investigated in the future to realize solar cell devices based on tungsten disulfide thin films

Laboratory spectroscopy techniques to enable observations of interstellar ion chemistry

Molecular ions have long been considered key intermediates in the evolution of molecular complexity in the interstellar medium. However, owing to their reactivity and transient nature, ions have historically proved challenging to study in terrestrial laboratory experiments. In turn, their detection and characterization in space is often contingent upon advances in the laboratory spectroscopic techniques used to measure their spectra. In this Review, we discuss the advances over the past 50 years in laboratory methodologies for producing molecular ions and probing their rotational, vibrational and electronic spectra. We largely focus this discussion around the widespread H(3)(+)cation and the ionic products originating from its reaction with carbon atoms. Finally, we discuss the current frontiers in this research and the technical advances required to address the spectroscopic challenges that they represent. Despite comprising only about 15% of the known molecular inventory of the interstellar medium, molecular ions have an outsized role in driving chemical evolution. This Review examines the advances - and challenges - in laboratory spectroscopy that have enabled the study of ions in space

MILLIMETER WAVE SPECTROSCOPY OF TITANIUM MONOXIDE AND TITANIUM DIOXIDE

K. Namiki et al., JMS 191, 176-182 (1998)S. Brunken et al., ApJ, in press (2008)Author Institution: I. PHYSIKALISCHES INSTITUT, UNIVERSITAT ZU KOLN, Zulpicher Strasse 77, 50937 Koln, Germany; Harvard Smithsonian Center for Astrophysics, School of Engineering and Applied Sciences; Harvard University, 29 Oxford Street Cambridge, MA 02138 USATitanium monoxide, TiO, is a well known astronomical molecule that exhibits prominent electronic absorption lines in the spectra of M and S stars. We present here improved rotational transition frequencies for an astronomical search in the radio band }. The recent laboratory detection of TiO$_2$ in the cm-wave region and its tentative detection in the oxygen-rich supergiant VY~CMa } prompted us to record its rotational spectrum in the mm-wave region. The measurements on TiO and TiO$_2$ were carried out in the frequency range 248-345~GHz using a BWO spectrometer combined with a laser ablation supersonic jet apparatus. Both species were produced by focusing a Nd:YAG laser onto a rod of either pure titanium or titanium dioxide and adding small amounts of oxygen to the He buffer gas. For TiO$_2$, fifty $b$-type rotational transitions of the main isotopomer $^{48}$TiO$_2$ and six transitions of $^{46}$TiO$_2$ have been measured up to $J=22$ and $K_a=8$. For TiO 14 transitions of each of the $^{46}$Ti, $^{48}$Ti, and $^{50}$Ti isotopomers were recorded. The new transitions have been analysed together with previously reported spectral data and improved rotational and centrifugal distortion constants were obtained, providing accurate transition frequencies for future astronomical searches

Automated Valet Parking as Part of an Integrated Travel Assistance

The integration of automated valet parking (automated search of a parking space and execution of the parking maneuver) in a comprehensive travel assistance approach promises great benefits for a traveler. In particular, it aims at increasing comfort, optimizing travel time and improving energy efficiency for changing means of transport (where one of them is a car) within a whole multimodal travel chain. In this paper an automated valet parking system as part of a travel assistant is presented. Besides giving an overview of the overall system, the main components (namely the environment perception and automation modules of the fully automated vehicle, a mobile phone application as human machine interface and a parking space occupancy detection camera as part of the parking area infrastructure) are described. The system was successfully tested on three different parking areas, where one of these areas was located at Braunschweig main station

Vibrational Excitation Hindering an Ion-Molecule Reaction: The c-C3H2+ - H-2 Collision Complex

Experiments within a cryogenic 22-pole ion trap have revealed an interesting reaction dynamic phenomenon, where rovibrational excitation of an ionic molecule slows down a reaction with a neutral partner. This is demonstrated for the low-temperature hydrogen abstraction reaction c-C3H2+ + H-2, where excitation of the ion into the v(7) antisynunetric C-H stretching mode decreased the reaction rate coefficient toward the products c-C3H3+ + H. Supported by high-level quantum-chemical calculations, this observation is explained by the reaction proceeding through a C-C3H2+ - H2 collision complex in the entrance channel, in which the hydrogen molecule is loosely bound to the hydrogen atom of the c-C3H2+ ion. This discovery enables high-resolution vibrational action spectroscopy for c-C3H2+ and other molecular ions with similar reaction pathways. Moreover, a detailed kinetic model relating the extent of the observed product depletion signal to the rate coefficients of inelastic collisions reveals that rotational relaxation of the vibrationally excited ions is significantly faster than the rovibrational relaxation, allowing for a large fraction of the ions to be vibrationally excited. This result provides fundamental insight into the mechanism for an important class of chemical reactions, and is capable of probing the inelastic collisional dynamics of molecular ions

Unidirectional Double- and Triple-Hydrogen Rearrangement Reactions Probed by Infrared Ion Spectroscopy

Zeh D, Bast M, Martens J, et al. Unidirectional Double- and Triple-Hydrogen Rearrangement Reactions Probed by Infrared Ion Spectroscopy. Journal of the American Society for Mass Spectrometry. 2022.Unidirectional double-hydrogen (2H) and triple-hydrogen (3H) rearrangement reactions occur upon electron-ionization-induced fragmentation of trans-2-(4-N,N-dimethylaminobenzyl)-1-indanol (1), trans-2-(4-methoxybenzyl)-1-indanol (2), 4-(4-N,N-dimethylaminophenyl)-2-butanol (3), and related compounds, as reported some 35 years ago (Kuck, D.; Filges, U. Org. Mass Spectrom. 1988, 23, 643-653). These unusual intramolecular redox processes were found to dominate the mass spectra of long-lived, metastable ions. The present report provides independent evidence for the structures of the product ions formed by the 2H and 3H rearrangement in an ion trap instrument. The radical cations 1+ and 3+ as well as ionized 1-(4-N,N-dimethylaminophenyl)-5-(4-methoxyphenyl)-3-pentanol, 5+, were generated by electrospray ionization from anhydrous acetonitrile solutions. The 2H and 3H fragment ions were obtained by collision-induced dissociation and characterized by IR ion spectroscopy and density functional theory calculations. Comparison of the experimental and calculated infrared ion spectra enabled the identification of the 2H rearrangement product ion, C9H14N+ (m/z 136), as an N,N-dimethyl-para-toluidinium ion bearing the extra proton ortho to the amino group, a tautomer which was calculated to be 31 kJ/mol less stable than the corresponding N-protonated form. The 3H rearrangement product ion, C8H13N+ (m/z 123), formerly assumed to be a distonic ammonium ion bearing a cyclohexadienyl radical, was now identified as a conventional radical cation, ionized N,N-dimethyl-2,3-dihydro-para-toluidine. Thus, the 3H rearrangement represents an intramolecular transfer hydrogenation between a secondary alcohol and an ionized aromatic ring. Based on these structural assignments, more detailed mechanisms for the unidirectional 2H and 3H rearrangement reactions are proposed