The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. Herein we show that metallic interfaces can be realized in SrTiO 3 -based heterostructures with various insulating overlayers of amorphous LaAlO 3 , SrTiO 3 and yttria-stabilized zirconia films. On the other hand, samples of amorphous La 7/8 Sr 1/8 MnO 3 films on SrTiO 3 substrates remain insulating. The interfacial conductivity results from the formation of oxygen vacancies near the interface, suggesting that the redox reactions on the surface of SrTiO 3 substrates play an important role.

ICP-MS is becoming a competitive technique for the measurement of plutonium isotopes. However, the abundance sensitivity (tailing of 238 U to m/z=239 and 240), isobaric and polyatomic ions interferences (e.g. U H +) are the most critical challenges for determination of low-level plutonium in high uranium samples. This work presents a new method to solve this problem using ICP-MS with two tandem quadrupole separators and dynamic collision/reaction cell combined with chemical separation. The interference of uranium hydrides (238 U 1 H + and 238 U 1 H2 +) was effectively eliminated using CO2 as reaction gas by converting hydrides to oxides of uranium ions (UO + /UO2 +), but still keep the intensity of Pu + signal. The tailing interference of 238 U + (abundance sensitivity) was intensively eliminated by significantly suppressing the 238 U + signal using CO2 as reaction gas and using two tandem quadrupole mass separators in the ICP-MS/MS. With these approaches, the overall interference of uranium was reduced to <110-8 , which is 3 orders of magnitude better than the conventional ICP-MS. Combined with chemical separation with a decontamination factor of 10 5 for uranium, an overall factor of 10 12 for elimination of uranium interference was achieved. The developed method was demonstrated to enable accurate determination of <10-15 g/g level plutonium isotopes in environmental samples even in uranium debris sample with a U/Pu atomic ratio up to 10 12. The developed method was validated by the analysis of spiked solution and certified reference materials of soil.

Following the recent success of monolithically integrated Perovskite/Si tandem solar cells, great interest has been raised in searching for alternative wide bandgap top-cell materials with prospects of a fully earthabundant, stable and efficient tandem solar cell. Thin film chalcogenides (TFCs) such as the Cu 2 ZnSnS 4 (CZTS) could be suitable top-cell materials. However, TFCs have the disadvantage that generally at least one high temperature step (> 500 • C) is needed during the synthesis, which could contaminate the Si bottom cell. Here, we systematically investigate the monolithic integration of CZTS on a Si bottom solar cell. A thermally resilient double-sided Tunnel Oxide Passivated Contact (TOPCon) structure is used as bottom cell. A thin (< 25 nm) TiN layer between the top and bottom cells, doubles as diffusion barrier and recombination layer. We show that TiN successfully mitigates in-diffusion of CZTS elements into the c-Si bulk during the high temperature sulfurization process, and find no evidence of electrically active deep Si bulk defects in samples protected by just 10 nm TiN. Post-process minority carrier lifetime in Si exceeded 1.5 ms, i.e., a promising implied open-circuit voltage (i-V oc) of 715 mV after the high temperature sulfurization. Based on these results, we demonstrate a first proof-of-concept two-terminal CZTS/Si tandem device with an efficiency of 1.1% and a V oc of 900 mV. A general implication of this study is that the growth of complex semiconductors on Si using high temperature steps is technically feasible, and can potentially lead to efficient monolithically integrated two-terminal tandem solar cells.

High-temperature CO2 electrolyzers offer exceptionally efficient storage of renewable electricity in the form of CO and other chemical fuels, but conventional electrodes catalyze destructive carbon deposition. Ceria catalysts are known carbon inhibitors for fuel cell (oxidation) reactions, however for the more severe electrolysis (reduction) conditions, catalyst design strategies remain unclear. Here we establish the inhibition mechanism on ceria and show selective CO2 to CO conversion well beyond the thermodynamic carbon deposition threshold. Operando X-ray photoelectron spectroscopy during CO2 electrolysis -using thin-film model electrodes consisting of samarium-doped ceria, nickel, and/or yttria-stabilized zirconia -together with density functional theory modeling reveal the crucial role of oxidized carbon intermediates in preventing carbon buildup. Using these insights, we demonstrate stable electrochemical CO2 reduction with a scaledup 16 cm 2 ceria-based solid oxide cell under conditions that rapidly destroy a nickel-based cell, leading to substantially improved device lifetime.Main Text: CO2 utilization is expected to play a key role in achieving a carbon-neutral sustainable energy economy. Electrochemical CO2 reduction, in particular, is a promising way to store intermittent electricity derived from solar and wind in the form of chemicals, such as synthetic hydrocarbons compatible with the existing energy infrastructure, and is therefore an essential technology in decarbonization strategies [1][2][3][4] . Currently, the most efficient CO2 electrolysis technology is the elevated-temperature solid oxide electrochemical cell (SOC), which utilizes O 2as the mobile ion. SOCs produce CO and O2 at the thermoneutral voltage of ~1.46 V with current densities exceeding 1 A/cm 2 -similar to steam electrolysis, which can be carried out simultaneously in the same cell to produce syngas or methane 1,2,5,6 . The same SOC can be operated in reverse as a fuel cell to re-oxidize the fuel products, thereby enabling operation as a flow battery 6,7 . Another important application is O2 (and CO) production from the CO2-rich atmosphere of Mars for rocket propulsion and life support, which will be demonstrated on the NASA Mars 2020 rover 8 .

We report on the fabrication of a 5.2% efficiency Cu 2 ZnSnS 4 (CZTS) solar cell made by pulsed laser deposition (PLD) featuring an ultra-thin absorber layer (less than 450 nm). Solutions to the issues of reproducibility and micro-particulate ejection often encountered with PLD are proposed. At the optimal laser fluence, amorphous CZTS precursors with optimal stoichiometry for solar cells are deposited from a single target. Such precursors do not result in detectable segregation of secondary phases after the subsequent annealing step. In the analysis of the solar cell device, we focus on the effects of the finite thickness of the absorber layer. Depletion region width, carrier diffusion length, and optical losses due to incomplete light absorption and back contact reflection are quantified. We conclude that material-and junction quality is comparable to that of thicker state-of-the-art CZTS devices, even though the efficiency is lower due to optical losses.

A new method for evaluating negative ion and electron parameters from the current–voltage characteristics of electric probes is presented. A theoretical model and its related numerical procedures are established and errors included are estimated. Temperatures and densities of negative ions and electrons in a magnetic multipolar-confined plasma of Ar and Ar/SF6 mixtures are determined with allowable errors for various density ratios of the negative ion to the electron.

The monolithic tandem integration of third-generation solar energy materials on silicon holds great promise for photoelectrochemistry and photovoltaics. However, this can be challenging when it involves high-temperature reactive processes, which would risk damaging the Si bottom cell. One such case is the high-temperature sulfurization/selenization in thin film chalcogenide solar cells, of which the kesterite Cu2ZnSnS4 (CZTS) is an example. Here, by using very thin (<10 nm) TiN-based diffusion barriers at the interface, with different composition and properties, we demonstrate on a device level that the protection of the Si bottom cell is largely dependent on the barrier layer engineering. Several monolithic CZTS/Si tandem solar cells with open-circuit voltages (Voc) up to 1.06 V and efficiencies up to 3.9% are achieved, indicating a performance comparable to conventional interfacial layers based on transparent conductive oxides, and pointing to a promising alternative design in solar energy conversion devices.

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