Doubling the mobility of InAs/InGaAs selective area grown nanowires

Selective area growth (SAG) of nanowires and networks promise a route toward scalable electronics, photonics, and quantum devices based on III-V semiconductor materials. The potential of high-mobility SAG nanowires however is not yet fully realised, since interfacial roughness, misfit dislocations at the nanowire/substrate interface and nonuniform composition due to material intermixing all scatter electrons. Here, we explore SAG of highly lattice-mismatched InAs nanowires on insulating GaAs(001) substrates and address these key challenges. Atomically smooth nanowire/substrate interfaces are achieved with the use of atomic hydrogen (a-H) as an alternative to conventional thermal annealing for the native oxide removal. The problem of high lattice mismatch is addressed through an InxGa1-xAs buffer layer introduced between the InAs transport channel and the GaAs substrate. The Ga-In material intermixing observed in both the buffer layer and the channel is inhibited via careful tuning of the growth temperature. Performing scanning transmission electron microscopy and x-ray diffraction analysis along with low-temperature transport measurements we show that optimized In-rich buffer layers promote high-quality InAs transport channels with the field-effect electron mobility over 10 000 cm2 V-1 s-1. This is twice as high as for nonoptimized samples and among the highest reported for InAs selective area grown nanostructures.The project was supported by Microsoft Quantum, the European Research Council (ERC) under Grant No. 716655 (HEMs-DAM), and the European Union Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant No. 722176. The authors acknowledge Dr. Keita Ohtani for technical support and fruitful discussions. D.V.B. is grateful to Dr. Juan-Carlos Estrada Saldaña for careful reading of the manuscript. The authors thank Francesco Montalenti, Marco Albani and Leo Miglio for scientific discussions. ICN2 acknowledges funding from Generalitat de Catalunya 2017 SGR 327. ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work has been performed in the framework of Universitat Autònoma de Barcelona Materials Science Ph.D. program. The HAADF-STEM microscopy was conducted in the Laboratorio de Microscopias Avanzadas at Instituto de Nanociencia de Aragon-Universidad de Zaragoza. M.C.S. has received funding from the European Unionâs Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No. 754510 (PROBIST). The funding agency is Consejo Superior de Investigaciones Científicas (CSIC) and the project reference is “Research Platform on Quantum Technologies PTI-001”

Systematic Collaborative Reanalysis of Genomic Data Improves Diagnostic Yield in Neurologic Rare Diseases

Altres ajuts: Generalitat de Catalunya, Departament de Salut; Generalitat de Catalunya, Departament d'Empresa i Coneixement i CERCA Program; Ministerio de Ciencia e Innovación; Instituto Nacional de Bioinformática; ELIXIR Implementation Studies (CNAG-CRG); Centro de Investigaciones Biomédicas en Red de Enfermedades Raras; Centro de Excelencia Severo Ochoa; European Regional Development Fund (FEDER).Many patients experiencing a rare disease remain undiagnosed even after genomic testing. Reanalysis of existing genomic data has shown to increase diagnostic yield, although there are few systematic and comprehensive reanalysis efforts that enable collaborative interpretation and future reinterpretation. The Undiagnosed Rare Disease Program of Catalonia project collated previously inconclusive good quality genomic data (panels, exomes, and genomes) and standardized phenotypic profiles from 323 families (543 individuals) with a neurologic rare disease. The data were reanalyzed systematically to identify relatedness, runs of homozygosity, consanguinity, single-nucleotide variants, insertions and deletions, and copy number variants. Data were shared and collaboratively interpreted within the consortium through a customized Genome-Phenome Analysis Platform, which also enables future data reinterpretation. Reanalysis of existing genomic data provided a diagnosis for 20.7% of the patients, including 1.8% diagnosed after the generation of additional genomic data to identify a second pathogenic heterozygous variant. Diagnostic rate was significantly higher for family-based exome/genome reanalysis compared with singleton panels. Most new diagnoses were attributable to recent gene-disease associations (50.8%), additional or improved bioinformatic analysis (19.7%), and standardized phenotyping data integrated within the Undiagnosed Rare Disease Program of Catalonia Genome-Phenome Analysis Platform functionalities (18%)

Epitaxy and interfaces in hybrid nanowires for Majorana-based topological quantum computing

Póster presentado a la 3rd Nanowire Week, celebrada en Pisa (Italia) del 23 al 27 de septiembre de 2019

Strain relaxation mechanisms in ZnSe@ZnTe core-shell nanowires grown horizontally from a guided growth approach

Resumen del trabajo presentado al VIII International Congress on Analytical Nanoscience and Nanotechnology, celebrado en Barcelona (España) del 3 al 5 de julio de 2017.The organization of nanowires on surfaces remains a major obstacle towards their large scale integration into functional devices. In order to overcome these issues, aligned arrays of heterostructured horizontal planar core-shell ZnSe@ZnTe nanowires were grown exploiting the epitaxial relations with the substrate in a guided growth approach to form well organized assemblies. We exploit the directional control of the guided growth for the parallel production of multiple radial p-n heterojunctions. The formed arrays exhibit great optoelectronic properties, with dark currents below the detection limit and upon illumination a rectifying behavior with photovoltaic characteristics. By the use of atomic resolution (S)TEM together with Geometric Phase Analysis (GPA), a deep understanding of the strain fields on the different nanostructures can be obtained. In that framework, we perform a study of the relaxation mechanisms taking place in the structure and how are they affected by the core morphology and substrate orientation with the aim of being able to exploit the strain on them to optimize the electronic behavior of the nanostructures.Peer reviewe

Hybrid nanowire based quantum networks at atomic scale: from growth mechanisms to properties

Resumen del trabajo presentado al MRS Spring Meeting, celebrado en Phoenix, Arizona (USA) del 22 al 26 de abril de 2019

Morphology driven electronic band modulation in semiconductor core-shell nanowires

Resumen del trabajo presentado al Microscopy at the Frontiers of Science Congress Series (MFS), celebrado en el Parque de las Ciencias de Granada (España) del 11 al 13 de septiembre de 2019

Comparative characterization of selective-area growth and vapourliquid- solid III-V semiconductor-superconductor nanowire networks for topological quantum computing

Resumen del póster presentado al Microscopy at the Frontiers of Science Congress Series (MFS), celebrado en el Parque de las Ciencias de Granada (España) del 11 al 13 de septiembre de 2019.The fabrication of reproducible and defect-free nanowire networks with a semiconductor-superconductor heterojunction is a crucial step that needs to be achieved to generate stable enough Majorana states for topological quantum computing. Current approaches involve direct vertical growth of the nanowires by vapour-liquidsolid (VLS), which are arranged in networks due to the growth on tilted surfaces and their coincidence during the growth process, forming only a limited number of interconnections. However, this process has obvious limitations in terms of planar integration and manipulation of the individual nanowires. On the other hand, in order to overcome the practical limitations of this method, alternative horizontal (on-plane) growth processes have arisen in the last few years, being guided growth (GG) and selective-area growth (SAG) the most promising ones. On this basis, SAG by means of molecular beam epitaxy (MBE) is being widely studied for the growth of III-V semiconductors, mainly InAs and InSb, in perfect epitaxy with the superconducting metallic layer that is typically formed by aluminium. Therefore, a detailed characterization of the interface between InSb and Al in SAG nanowire networks, as well as VLS ones, is presented and compared, in order to shine light on the strain mechanisms involved in their growth mechanisms and their origin in terms of growth methods.Peer reviewe

Study of epitaxy in proximity coupled semiconductor - ferromagnetic insulator - superconductor heterostructures for majorana-based topological quantum computing

Resumen del póster presentado al Microscopy at the Frontiers of Science Congress Series (MFS), celebrado en el Parque de las Ciencias de Granada (España) del 11 al 13 de septiembre de 2019.One of the current endeavors in quantum technology consists of the development of topological quantum computers, which stand out as promising candidates because, contrary to the quantum states of ordinary individually trapped particles such as electrons, the topological properties of the quantum system ensure a higher stability when subjected to small perturbations. Among the different classes of topological states, the so-called Majorana bound states are of great interest, as signatures of their appearance have been observed recently in hybrid III-V semiconductor superconductor nanowires. A way to induce the topological properties, without the need of external magnetic fields that could modify the band structure of the nanowire, is given by the coupling to ferromagnetic insulators. Composite tri-crystals of semiconductor-ferromagnetic insulator-superconductor materials, such as InAs-EuS-Al, have been proposed to overcome the challenge of building adequate topological systems, where the absence of crystal defects and impurities, particularly at the interfaces between materials, is of extreme importance. Therefore, our work is centered around the study of the crystal quality of the nanostructures, especially focusing on the epitaxial relationship between the composing materials. Mainly by the means of High-angle annular dark-field (HAADF) imaging in Scanning Transmission Electron Microscopy (HAADF-STEM), where we analyze the crystal phases and interfaces at atomic scale and check the coupling of different materials atom by atom (column), combined with Electron Energy Loss Spectroscopy (EELS) in order to gain data on the chemical composition distribution, we study nanostructures grown by different techniques, in varying geometrical layouts and growth conditions. Namely, we have analyzed vertically grown nanowires of InAs by the Vapor-Liquid-Solid (VLS) method, with selective covering of the several facets with EuS and Al to observe possible favored crystal orientations depending on the faceting, planar samples of EuS layers grown on InAs by Molecular Beam Epitaxy (MBE), which is the preferred synthesis method due to its ultra-pure environment, and also the growth of InAs on GaAs substrate in the form of nanowires forming networks created by the method of Selective Area Growth (SAG)7-10, since the development of said networks is one of the final goals for the construction of the logic gates used for the calculations in a topological quantum computer. By applying Geometric Phase Analysis (GPA) to HAADF-STEM micrographs with atomic resolution, we are able to detect structural defects and deformations, such as twin boundaries, misfit dislocations, rotation and compression/dilatation within the crystal phases of these nanostructures

Electrochemical Stability of Rhodium–Platinum Core–Shell Nanoparticles: An Identical Location Scanning Transmission Electron Microscopy Study [Video 7]

Animated movie with segmented low-resolution tomographic reconstruction of Rh@Pt/C NPs at 10 000 potential cycles.Rhodium–platinum core–shell nanoparticles on a carbon support (Rh@Pt/C NPs) are promising candidates as anode catalysts for polymer electrolyte membrane fuel cells. However, their electrochemical stability needs to be further explored for successful application in commercial fuel cells. Here we employ identical location scanning transmission electron microscopy to track the morphological and compositional changes of Rh@Pt/C NPs during potential cycling (10 000 cycles, 0.06–0.8 VRHE, 0.5 H2SO4) down to the atomic level, which are then used for understanding the current evolution occurring during the potential cycles. Our results reveal a high stability of the Rh@Pt/C system and point toward particle detachment from the carbon support as the main degradation mechanism.Peer reviewe

Electrochemical Stability of Rhodium–Platinum Core–Shell Nanoparticles: An Identical Location Scanning Transmission Electron Microscopy Study [Video 6]

Animated movie with segmented low-resolution tomographic reconstruction of Rh@Pt/C NPs at 4000 potential cycles.Rhodium–platinum core–shell nanoparticles on a carbon support (Rh@Pt/C NPs) are promising candidates as anode catalysts for polymer electrolyte membrane fuel cells. However, their electrochemical stability needs to be further explored for successful application in commercial fuel cells. Here we employ identical location scanning transmission electron microscopy to track the morphological and compositional changes of Rh@Pt/C NPs during potential cycling (10 000 cycles, 0.06–0.8 VRHE, 0.5 H2SO4) down to the atomic level, which are then used for understanding the current evolution occurring during the potential cycles. Our results reveal a high stability of the Rh@Pt/C system and point toward particle detachment from the carbon support as the main degradation mechanism.Peer reviewe