Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum

In many transition metal oxides (TMOs), oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects, even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well

Growth Control of Oxygen Stoichiometry in Homoepitaxial SrTiO\u3csub\u3e3\u3c/sub\u3e Films by Pulsed Laser Epitaxy in High Vacuum

In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well

Autonomous synthesis of thin film materials with pulsed laser deposition enabled by in situ spectroscopy and automation

Synthesis of thin films has traditionally relied upon slow, sequential processes carried out with substantial human intervention, frequently utilizing a mix of experience and serendipity to optimize material structure and properties. With recent advances in autonomous systems which combine synthesis, characterization, and decision making with artificial intelligence (AI), large parameter spaces can be explored autonomously at rates beyond what is possible by human experimentalists, greatly accelerating discovery, optimization, and understanding in materials synthesis which directly address the grand challenges in synthesis science. Here, we demonstrate autonomous synthesis of a contemporary 2D material by combining the highly versatile pulsed laser deposition (PLD) technique with automation and machine learning (ML). We incorporated in situ and real-time spectroscopy, a high-throughput methodology, and cloud connectivity to enable autonomous synthesis workflows with PLD. Ultrathin WSe2 films were grown using co-ablation of two targets and showed a 10x increase in throughput over traditional PLD workflows. Gaussian process regression and Bayesian optimization were used with in situ Raman spectroscopy to autonomously discover two distinct growth windows and the process-property relationship after sampling only 0.25% of a large 4D parameter space. Any material that can be grown with PLD could be autonomously synthesized with our platform and workflows, enabling accelerated discovery and optimization of a vast number of materials

Unusual Electrical Conductivity Driven by Localized Stoichiometry Modification at Vertical Epitaxial Interfaces

Precise control of lattice mismatch accommodation and cation interdiffusion across the interface is critical to modulate correlated functionalities in epitaxial heterostructures, particularly when the interface composition is positioned near a compositional phase transition boundary. Here we select La1-xSrxMnO3 (LSMO) as a prototypical phase transition material and establish vertical epitaxial interfaces with NiO to explore the strong interplay between strain accommodation, stoichiometry modification, and localized electron transport across the interface. It is found that localized stoichiometry modification overcomes the plaguing dead layer problem in LSMO and leads to strongly directional conductivity, as manifested by more than three orders of magnitude difference between out-of-plane to in-plane conductivity. Comprehensive structural characterization and transport measurements reveal that this emerging behavior is related to a compositional change produced by directional cation diffusion that pushes the LSMO phase transition from insulating into metallic within an ultrathin interface region. This study explores the nature of unusual electric conductivity at vertical epitaxial interfaces and establishes an effective route for engineering nanoscale electron transport for oxide electronics

Coronary bypass surgery with or without surgical ventricular reconstruction

Coronary bypass surgery with or without surgical ventricular reconstruction. Jones RH, Velazquez EJ, Michler RE, Sopko G, Oh JK, O'Connor CM, Hill JA, Menicanti L, Sadowski Z, Desvigne-Nickens P, Rouleau JL, Lee KL; STICH Hypothesis 2 Investigators. Collaborators (379)Bochenek A, Krejca M, Trusz-Gluza M, Wita K, Zembala M, Przybylski R, Kukulski T, Cherniavsky A, Marchenko A, Romanov A, Wos S, Deja M, Golba K, Kot J, Rao V, Iwanochko M, Renton J, Hemeon S, Rogowski J, Rynkiewicz A, Betlejewski P, Sun B, Crestanello J, Binkley P, Chang J, Ferrazzi P, Gavazzi A, Senni M, Sadowski J, Kapelak B, Sobczyk D, Wrobel K, Pirk J, Jandova R, Velazquez E, Smith P, Milano C, Adams P, Menicanti L, Di Donato M, Castelvecchio S, Dagenais F, Dussault G, Dupree C, Sheridan B, Schuler C, Yii M, Prior D, Mack J, Racine N, Bouchard D, Ducharme A, Lavoignat J, Maurer G, Grimm M, Lang I, Adlbrecht C, Religa Z, Biederman A, Szwed H, Sadowski Z, Rajda M, Ali I, Howlett J, MacFarlane M, Siepe M, Beyersdorf F, Cuerten C, Wiechowski S, Mokrzycki K, Hill J, Beaver T, Olitsky D, Bernstein V, Janusz M, O'Neill V, Grayburn P, Hebeler R, Hamman B, Aston S, Gradinac S, Vukovic M, Djokovic L, Benetis R, Jankauskiene L, Friedrich I, Buerke M, Paraforos A, Quaini E, Cirillo M, Chua L, Lim C, Kwok B, Kong S, Stefanelli G, Labia C, Bergh C, Gustafsson C, Daly R, Rodeheffer R, Nelson S, Maitland A, Isaac D, Holland M, Di Benedetto G, Attisano T, Sievers H, Schunkert H, Stierle U, Haddad H, Hendry P, Donaldson J, Birjiniuk V, Harrington M, Nawarawong W, Woragidpunpol S, Kuanprasert S, Mekara W, Konda S, Neva C, Hathaway W, Groh M, Blakely J, Lamy A, Demers C, Rizzo T, Drazner M, DiMaio J, Joy J, Benedik J, Marketa K, Beghi C, De Blasi M, Helou J, Dallaire S, Kron I, Kern J, Bergin J, Phillips J, Aldea G, Verrier E, Harrison L, Piegas L, Paulista P, Farsky P, Veiga-Kantorowitz C, Philippides G, Shemin R, Thompson J, White H, Alison P, Stewart R, Clapham T, Rich J, Herre J, Pine L, Kalil R, Nesralla I, Santos M, Pereira de Moraes M, Michler R, Swayze R, Arnold M, McKenzie N, Smith J, Nicolau J, Oliveira S, Stolf N, Ferraz M, Filgueira J, Batlle C, Rocha A, Gurgel Camara A, Huynh T, Cecere R, Finkenbine S, St-Jacques B, Ilton M, Wittstein I, Conte J, Breton E, Panza J, Boyce S, McNulty M, Starnes V, Lopez B, Biederman R, Magovern J, Dean D, Grant S, Hammon J, Wells G, De Pasquale C, Knight J, Healy H, Maia L, Souza A, McRae R, Pierson M, Gullestad L, Sorensen G, Murphy E, Ravichandran P, Avalos K, Horowitz J, Owen E, Ascheim D, Naka Y, Yushak M, Gerometta P, Arena V, Borghini E, Johnsson P, Ekmehag B, Engels K, Rosenblum W, Swayze R, Amanullah A, Krzeminska-Pakula M, Drozdz J, Larbalestier R, Wang X, Busmann C, Horkay F, Szekely L, Keltai M, Hetzer R, Knosalla C, Nienkarken T, Chiariello L, Nardi P, Arom K, Ruengsakulrach P, Hayward C, Jansz P, Stuart S, Oto O, Sariomanoglu O, Dignan R, French J, Gonzalez M, Edes I, Szathmarine V, Yakub M, Sarip S, Alotti N, Lupkovics G, Smedira N, Pryce J, Cokkinos D, Palatianos G, Kremastinos D, Stewart R, Rinkes L, Esrig B, Baptiste M, Booth D, Ramaiah C, Ferraris V, Menon S, Martin L, Couper G, Rosborough D, Vanhaecke J, Strijckmans A, Carson P, Dupree C, Miller A, Pina I, Selzman C, Wertheimer J, Goldstein S, Cohn F, Hlatky M, Kennedy K, Rankin S, Robbins R, Zaret B, Rouleau J, Desvigne-Nickens P, Jones R, Lee K, Michler R, O'Connor C, Oh J, Rankin G, Velazquez E, Hill J, Beyersdorf F, Bonow R, Desvigne-Nickens P, Jones R, Lee K, Oh J, Panza J, Rouleau J, Sadowski Z, Velazquez E, White H, Jones R, Velazquez E, O'Connor C, Rankin G, Sellers M, Sparrow-Parker B, McCormick A, Albright J, Dandridge R, Rittenhouse L, Wagstaff D, Wakeley N, Burns S, Williams M, Bailey D, Parrish L, Daniels H, Grissom G, Medlin K, Lee K, She L, McDaniel A, Lokhnygina Y, Greene D, Moore V, Pohost G, Agarwal S, Apte P, Bahukha P, Chow M, Chu X, Doyle M, Forder J, Ocon M, Reddy V, Santos N, Tripathi R, Varadarajan P, Oh J, Blahnik F, Bruce C, Lin G, Manahan B, Miller D, Miller F, Pellikka P, Springer R, Welper J, Wiste H, Mark D, Anstrom K, Baloch K, Burnette A, Clapp-Channing N, Cowper P, Davidson-Ray N, Drew L, Harding T, Hunt V, Knight D, Patterson A, Redick T, Sanderford B, Feldman A, Bristow M, Chan T, Diamond M, Maisel A, Mann D, McNamara D, Bonow R, Berman D, Helmer D, Holly T, Leonard S, Woods M, Panza J, McNulty M, Grayburn P, Aston S. SourceDuke Clinical Research Institute, Duke University Medical Center, Durham, NC 27710, USA. [email protected] Abstract BACKGROUND: Surgical ventricular reconstruction is a specific procedure designed to reduce left ventricular volume in patients with heart failure caused by coronary artery disease. We conducted a trial to address the question of whether surgical ventricular reconstruction added to coronary-artery bypass grafting (CABG) would decrease the rate of death or hospitalization for cardiac causes, as compared with CABG alone. METHODS: Between September 2002 and January 2006, a total of 1000 patients with an ejection fraction of 35% or less, coronary artery disease that was amenable to CABG, and dominant anterior left ventricular dysfunction that was amenable to surgical ventricular reconstruction were randomly assigned to undergo either CABG alone (499 patients) or CABG with surgical ventricular reconstruction (501 patients). The primary outcome was a composite of death from any cause and hospitalization for cardiac causes. The median follow-up was 48 months. RESULTS: Surgical ventricular reconstruction reduced the end-systolic volume index by 19%, as compared with a reduction of 6% with CABG alone. Cardiac symptoms and exercise tolerance improved from baseline to a similar degree in the two study groups. However, no significant difference was observed in the primary outcome, which occurred in 292 patients (59%) who were assigned to undergo CABG alone and in 289 patients (58%) who were assigned to undergo CABG with surgical ventricular reconstruction (hazard ratio for the combined approach, 0.99; 95% confidence interval, 0.84 to 1.17; P=0.90). CONCLUSIONS: Adding surgical ventricular reconstruction to CABG reduced the left ventricular volume, as compared with CABG alone. However, this anatomical change was not associated with a greater improvement in symptoms or exercise tolerance or with a reduction in the rate of death or hospitalization for cardiac causes. (ClinicalTrials.gov number, NCT00023595.

DOE Hydrogen Sorption Center of Excellence: Synthesis and Processing of Single-Walled Carbon Nanohorns for Hydrogen Storage and Catalyst Supports

The objective of the project was to exploit the unique morphology, tunable porosity and excellent metal supportability of single-walled carbon nanohorns (SWNHs) to optimize hydrogen uptake and binding energy through an understanding of metal-carbon interactions and nanoscale confinement. SWNHs provided a unique material to understand these effects because they are carbon nanomaterials which are synthesized from the 'bottom-up' with well-defined, sub-nm pores and consist of single-layer graphene, rolled up into closed, conical, horn-shaped units which form ball-shaped aggregates of {approx}100-nm diameter. SWNHs were synthesized without metal catalysts by the high-temperature vaporization of solid carbon, so they can be used to explore metal-free hydrogen storage. However, SWNHs can also be decorated with metal nanoparticles or coatings in post-processing treatments to understand how metals augment hydrogen storage. The project first explored how the synthesis and processing of SWNHs could be modified to tailor pore sizes to optimal size ranges. Nanohorns were rapidly synthesized at 20g/hr rates by high-power laser vaporization enabling studies such as neutron scattering with gram quantities. Diagnostics of the synthesis process including high-speed videography, fast pyrometry of the graphite target, and differential mobility analysis monitoring of particle size distributions were applied in this project to provide in situ process control of SWNH morphology, and to understand the conditions for different pore sizes. We conclude that the high-temperature carbon-vaporization process to synthesize SWNHs is scalable, and can be performed by electric arc or other similar techniques as economically as carbon can be vaporized. However, the laser vaporization approach was utilized in this project to permit the precise tuning of the synthesis process through adjustment of the laser pulse width and repetition rate. A result of this processing control in the project was to eliminate the large (2-3 nm) internal pores of typical SWNHs which were found not to store hydrogen effectively. Post processing treatments of the as-synthesized SWNHs focused on pore size, surface area, and metal decoration in order to understand the effects of each on measured hydrogen uptake. Wet chemistry and gas-phase oxidation treatments were developed throughout the life of the project to adjust the interstitial and slit pore sizes of the as-produced SWNHs, and increase the surface area to a maximum value of 2200 m2/g. In addition, wet chemistry approaches were used to develop methods to decorate the nanohorns with small Pt and Pd nanoparticles for metal-assisted hydrogen storage. Finally, oxygen-free decoration of SWNHs with alkaline earth metals (Ca) was developed using pulsed laser deposition and vacuum evaporation in order to produce surface coatings with high static electric fields sufficient to polarize and bind dihydrogen. Decoration of SWNHs with Pt and Pd nanoparticles resulted in enhanced binding energy (NREL, 36 kJ/mol), as well as enhancement in the room temperature uptake of 0.6 wt.% (for undecorated, oxidized, pure-C SWNHs at 20 bar), to 1.6 wt% for Pt- and Pd-decorated SWNHs at 100 bar, comparable to MOF-177 materials. NIST neutron scattering on gram quantity Pt- and Pd-decorated SWNHs showed clear evidence for 'spillover' type losses of molecular hydrogen and determined the onset temperature for this effect to be between 150K < T < 298K.High (2142 m2/g) surface area SWNH materials with variable pore sizes and metal-decorated SWNHs were demonstrated with metals (Pt, Pd) resulting in increased excess storage (3.5 wt. % at 77K). Compression results in bulk SWNH samples with density 1.03 g/cm3, and 30 g/L volumetric capacity. In summary, SWNHs were found to be unique carbon nanomaterials which can be produced continuously at high rates from vaporization of pure carbon. Their inherent pore structure exhibits significant room temperature hydrogen storage in sub-nm pores, and their morphology serves as an excellent metal catalyst support for small (2-3 nm nanoparticles). Pt- and Pd-nanoparticle-decorated SWNHs exhibit clear evidence for metal-assisted hydrogen storage which is activated at T>150 K, permitting additional room-temperature storage up to 1.8 wt.% at 100 bar. One of the key results of the project were theoretical predictions for doped, decorated, and filled nanostructures with distributed charge to maintain high static electric fields sufficient to polarize and bind hydrogen. This concept indicates a promising new direction for hydrogen storage materials