Panning for Gold: Spectroscopy of Heavy Elements for Neutron Star Mergers

The astrophysical origin of heavy Z elements remains an open question. Spectroscopy of neutron star merger ejecta provides a new opportunity to directly probe regions where heavy elements may be forming, specifically as a result of active r-process nucleosynthesis. However, the comparable laboratory and/or theoretical atomic data are not available for even low charge states of these elements for comparison. In this work, we present experimental and theoretical investigations on the electronic structure of Au I, Au II, and Au III. Using the Compact Toroidal Hybrid plasma apparatus at Auburn University, we ablate and excite neutral Au and report line lists for Au I, Au II, and Au III. Future work includes comparable spectroscopy on the near-by heavy elements Re, Os, Ir, and Pt at both the Compact Toroidal Hybrid and the Clemson University Electron Beam Ion Trap

Perspectives on Astrophysics Based on Atomic, Molecular, and Optical (AMO) Techniques

About two generations ago, a large part of AMO science was dominated by experimental high energy collision studies and perturbative theoretical methods. Since then, AMO science has undergone a transition and is now dominated by quantum, ultracold, and ultrafast studies. But in the process, the field has passed over the complexity that lies between these two extremes. Most of the Universe resides in this intermediate region. We put forward that the next frontier for AMO science is to explore the AMO complexity that describes most of the Cosmos.Comment: White paper submission to the Decadal Assessment and Outlook Report on Atomic, Molecular, and Optical (AMO) Science (AMO 2020

Perspectives on Astrophysics Based on Atomic, Molecular, and Optical (AMO) Techniques

About two generations ago, a large part of AMO science was dominated by experimental high energy collision studies and perturbative theoretical methods. Since then, AMO science has undergone a transition and is now dominated by quantum, ultracold, and ultrafast studies. But in the process, the field has passed over the complexity that lies between these two extremes. Most of the Universe resides in this intermediate region. We put forward that the next frontier for AMO science is to explore the AMO complexity that describes most of the Cosmos

Characterization of GaSb/Sb Heterostructures By Scanning Tunneling Microscopy

Program year: 1994/1995Digitized from print original stored in HDRGaSb/Sb heterostructures hold the promise of being very interesting materials. Properties introduced by the growth of the semiconductor and semi-metal together may prove to be very useful in various electronic devices. Various configurations of were grown at the University of Houston for STM characterization. The equipment necessary for the characterization of the heterostructures was already in place in the laboratory. Using this equipment, samples were placed in an ultra-high vacuum(UHV) system by means of a linear motion device. They were cleaved in UHV to expose a clean surface and then transported by means of a second linear motion device to the STM. There a characterization using of their electronic and spatial structure was made. Specifically, band gap values and offsets were determined, as well as Fermi levels. Also, with the imaging capabilities of the STM, the surface structure was investigated. Special tips were fabricated for this work

Ion transport through macrocapillaries – Oscillations due to charge patch formation

We present results on ion transport through large bore capillaries (macrocapillaries) that probe both the geometric and ion-guided aspects of this ion delivery mechanism. We have demonstrated that guiding in macrocapillaries exhibits position- and angle-dependent transmission properties which are directly related to the capillary material (either metal or insulator) and geometry. Specifically, we have passed 1 keV Rb+ ions through glass and metal macrocapillaries, and have observed oscillations for the transmitted ion current passing through the insulating capillaries. Straightforward calculations show that these oscillations can be attributed to beam deflections from charge patches that form on the interior walls of the capillary. The absence of these oscillations in the metal capillary data serve as further confirmation of the role of charge patch formation

Charge Exchange Cross Sections for Noble Gas Ions and N2 between 0.2 and 5.0 keV

Charge transfer of an electron from a neutral atom to an ion is a fundamental interaction that plays a dominant role in the energy balance of atmospheric and astrophysical plasmas. The present investigation measured the charge exchange cross sections of noble gas ions (He + , Ne + , Ar + , Kr + ) with N 2 in the intermediate energy range 0.2–5.0 keV. The systems were chosen because there remains a lack of consensus amongst previous measurements and regions where there were no previous measurements. A description of the mechanical design for an electrically floated gas cell is described herein

Relativistic Atomic Structure of Au IV and the Os Isoelectronic Sequence: Opacity Data for Kilonova Ejecta

Direct detection of gravitational waves (GWs) on 17 August 2017, propagating from a binary neutron star merger, or a “kilonova”, opened the era of multimessenger astronomy. The ejected material from neutron star mergers, or “kilonova”, is a good candidate for optical and near infrared follow-up observations after the detection of GWs. The kilonova from the ejecta of GW1780817 provided the first evidence for the astrophysical site of the synthesis of heavy nuclei through the rapid neutron capture process or r-process. Since properties of the emission are largely affected by opacities of the ejected material, enhancements in the available r-process data is important for neutron star merger modeling. However, given the complexity of the electronic structure of these heavy elements, considerable efforts are still needed to converge to a reliable set of atomic structure data. The aim of this work is to alleviate this situation for low charge state elements in the Os-like isoelectronic sequence. In this regard, the general-purpose relativistic atomic structure packages (GRASP0 and GRASP2K) were used to obtain energy levels and transition probabilities (E1 and M1). We provide line lists and expansion opacities for a range of r-process elements. We focus here on the Os isoelectronic sequence (Os I, Ir II, Pt III, Au IV, Hg V). The results are benchmarked against existing experimental data and prior calculations, and predictions of emission spectra relevant to kilonovae are provided. Fine-structure (M1) lines in the infrared potentially observable by the James Webb Space Telescope are highlighted

Encapsulating Ion-Solid Interactions in Metal-Oxide-Semiconductor (MOS) Devices

We report on a measurement of low energy ion irradiation effects on as-grown films of SiO2 on a Si substrate. Beams of normally incident Na+ ions with kinetic energies of 2 keV to 5 keV were focused onto ~ 1900 Å SiO2 films. Aluminum top metal contacts were subsequently deposited onto these targets such that irradiated regions and unexposed (pristine) regions of the target could be compared using capacitance-voltage (C-V) measurements of individual metal-oxide-semiconductor (MOS) devices. The C-V data reveal an energy-dependent shift in the flatband voltage ( VFB) that can be returned to its near-pristine value by a low temperature anneal. An increase in the density of interface states ( Dit) inferred from the C-V curves is found to have a superlinear dependence on the incident kinetic energy. These data are consistent with previously observed UV radiation effects on MOS oxides, where transferred energy leads to electron-hole pair production and the diffusion and trapping of holes throughout the oxide. Our measured trapped hole densities are compared with calculated densities, which are based on the incident ion dose and the predicted ion implantation range, to arrive at a fractional yield for hole survival and measurement within an encapsulated MOS device

Relativistic Atomic Structure of Au IV and the Os Isoelectronic Sequence: Opacity Data for Kilonova Ejecta

Direct detection of gravitational waves (GWs) on 17 August 2017, propagating from a binary neutron star merger, or a “kilonova”, opened the era of multimessenger astronomy. The ejected material from neutron star mergers, or “kilonova”, is a good candidate for optical and near infrared follow-up observations after the detection of GWs. The kilonova from the ejecta of GW1780817 provided the first evidence for the astrophysical site of the synthesis of heavy nuclei through the rapid neutron capture process or r-process. Since properties of the emission are largely affected by opacities of the ejected material, enhancements in the available r-process data is important for neutron star merger modeling. However, given the complexity of the electronic structure of these heavy elements, considerable efforts are still needed to converge to a reliable set of atomic structure data. The aim of this work is to alleviate this situation for low charge state elements in the Os-like isoelectronic sequence. In this regard, the general-purpose relativistic atomic structure packages (GRASP0 and GRASP2K) were used to obtain energy levels and transition probabilities (E1 and M1). We provide line lists and expansion opacities for a range of r-process elements. We focus here on the Os isoelectronic sequence (Os I, Ir II, Pt III, Au IV, Hg V). The results are benchmarked against existing experimental data and prior calculations, and predictions of emission spectra relevant to kilonovae are provided. Fine-structure (M1) lines in the infrared potentially observable by the James Webb Space Telescope are highlighted