Nanometric Chemical Analysis of Beam-Sensitive Materials: A Case Study of STEM-EDX on Perovskite Solar Cells.

Quantitative chemical analysis on the nanoscale provides valuable information on materials and devices which can be used to guide further improvements to their performance. In particular, emerging families of technologically relevant composite materials such as organic-inorganic hybrid halide perovskites and metal-organic frameworks stand to benefit greatly from such characterization. However, these nanocomposites are also vulnerable to damage induced by analytical probes such as electron, X-ray, or neutron beams. Here the effect of electrons on a model hybrid halide perovskite is investigated, focusing on the acquisition parameters appropriate for energy-dispersive X-ray spectroscopy in a scanning transmission electron microscope (STEM-EDX). The acquisition parameters are systematically varied to examine the relationship between electron dose, data quality, and beam damage. Five metrics are outlined to assess the quality of STEM-EDX data and severity of beam damage, further validated by dark field STEM imaging. Loss of iodine through vacancy creation is found to be the primary manifestation of electron beam damage in the perovskite specimen, and iodine content is seen to decrease exponentially with electron dose. This work demonstrates data acquisition and analysis strategies that can be used for studying electron beam damage and for achieving reliable quantification for a broad range of beam-sensitive materials

Twin plane re-entrant mechanism for catalytic nanowire growth.

A twin-plane based nanowire growth mechanism is established using Au catalyzed Ge nanowire growth as a model system. Video-rate lattice-resolved environmental transmission electron microscopy shows a convex, V-shaped liquid catalyst-nanowire growth interface for a ⟨112⟩ growth direction that is composed of two Ge {111} planes that meet at a twin boundary. Unlike bulk crystals, the nanowire geometry allows steady-state growth with a single twin boundary at the nanowire center. We suggest that the nucleation barrier at the twin-plane re-entrant groove is effectively reduced by the line energy, and hence the twin acts as a preferential nucleation site that dictates the lateral step flow cycle which constitutes nanowire growth.S. H. acknowledges funding from ERC grant InsituNANO (project number 279342). A. D. G. acknowledges funding from the Marshall Aid Commemoration Commission and the National Science Foundation. C. D. acknowledge funding from the Royal Society. P.V. acknowledges the support of ONR grant N00014-12-1-0198. We gratefully acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University.This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/nl404244u. (AD Gamalski, PW Voorhees, C Ducati, R Sharma, S Hofmann, Nano Letters 2014, 14, 1288–1292

Compressed sensing electron tomography of needle-shaped biological specimens--Potential for improved reconstruction fidelity with reduced dose.

Electron tomography is an invaluable method for 3D cellular imaging. The technique is, however, limited by the specimen geometry, with a loss of resolution due to a restricted tilt range, an increase in specimen thickness with tilt, and a resultant need for subjective and time-consuming manual segmentation. Here we show that 3D reconstructions of needle-shaped biological samples exhibit isotropic resolution, facilitating improved automated segmentation and feature detection. By using scanning transmission electron tomography, with small probe convergence angles, high spatial resolution is maintained over large depths of field and across the tilt range. Moreover, the application of compressed sensing methods to the needle data demonstrates how high fidelity reconstructions may be achieved with far fewer images (and thus greatly reduced dose) than needed by conventional methods. These findings open the door to high fidelity electron tomography over critically relevant length-scales, filling an important gap between existing 3D cellular imaging techniques.The research leading to these results has received funding from the European Union Seventh Framework Programme under Grant Agreement 312483 - ESTEEM2 (Integrated Infrastructure Initiative–I3), as well as from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC grant agreement 291522 - 3DIMAGE. B.W. and E.S. acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG) within the framework of the SPP 1570 as well as through the Cluster of Excellence “Engineering of Advanced Materials” at the Friedrich-Alexander-Universität ErlangenNürnberg. G.D. and C.D. acknowledge funding from the ERC under grant number 259619 PHOTO EM. B.W. acknowledges the Research Training Group “Disperse Systems for Electronic Applications” (DFG GEPRIS GRK 1161). R.L. acknowledges a Junior Research Fellowship from Clare College.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.ultramic.2015.10.02

Continuous flow chemical vapour deposition of carbon nanotube sea urchins.

Hybrid structures consisting of functional materials enhanced by carbon nanotubes (CNTs) have potential for a variety of high impact applications, as shown by the impressive progress in sensing and mechanical applications enabled by CNT-enhanced materials. The hierarchical organisation of CNTs with other materials is key to the design of macroscale devices benefiting from the unique properties of individual CNTs, provided CNT density, morphology and binding with other materials are optimized. In this paper, we provide an analysis of a continuous aerosol process to create a hybrid hierarchical sea urchin structure with CNTs organized around a functional metal oxide core. We propose a new mechanism for the growth of these carbon nanotube sea urchins (CNTSU) and give new insight into their chemical composition. To corroborate the new mechanism, we examine the influence of CNT growth conditions on CNTSU morphology and demonstrate a new in-line characterisation technique to continuously monitor aerosol CNT growth during synthesis, which enables industrial-scale production optimization. Based upon the new formation mechanism we describe the first substrate-based chemical vapour deposition growth of CNTSUs which increases CNT length and improves G to D ratio, which also allows for the formation of CNTSU carpets with unique structures.Jean de La Verpilliere is supported by the EPSRC Cambridge NanoDTC, EP/G037221/1, the Cambridge Home EU Scholarship Scheme (CHESS) and the Schiff Foundation Studentships. Michael De Volder is supported by an ERC starting grant (HIENA - 337739)

Solid Electrolyte Interphase Growth and Capacity Loss in Silicon Electrodes.

The solid electrolyte interphase (SEI) of the high capacity anode material Si is monitored over multiple electrochemical cycles by (7)Li, (19)F, and (13)C solid-state nuclear magnetic resonance spectroscopies, with the organics dominating the SEI. Homonuclear correlation experiments are used to identify the organic fragments -OCH2CH2O-, -OCH2CH2-, -OCH2CH3, and -CH2CH3 contained in both oligomeric species and lithium semicarbonates ROCO2Li, RCO2Li. The SEI growth is correlated with increasing electrode tortuosity by using focused ion beam and scanning electron microscopy. A two-stage model for lithiation capacity loss is developed: initially, the lithiation capacity steadily decreases, Li(+) is irreversibly consumed at a steady rate, and pronounced SEI growth is seen. Later, below 50% of the initial lithiation capacity, less Si is (de)lithiated resulting in less volume expansion and contraction; the rate of Li(+) being irreversibly consumed declines, and the Si SEI thickness stabilizes. The decreasing lithiation capacity is primarily attributed to kinetics, the increased electrode tortuousity severely limiting Li(+) ion diffusion through the bulk of the electrode. The resulting changes in the lithiation processes seen in the electrochemical capacity curves are ascribed to non-uniform lithiation, the reaction commencing near the separator/on the surface of the particles.This work was partially supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, under the Batteries for Advanced Transportation Technologies (BATT) Program subcontract #7057154 and the European Commission (EC), through the project EuroLion. G.D. and C.D. acknowledge funding from the ERC under Grants 259619 PHOTO EM and 312483 ESTEEM2. A.L.M. is an awardee of a Schiff Foundation Studentship and a nanoDTC Associate. M.L. is an awardee of the Weizmann Institute of Science - National Postdoctoral Award for Advancing Women in Science and thanks the EU Marie Curie intra-European fellowship for funding.This is the author accepted manuscript. The final version is available from the American Chemical Society via http://dx.doi.org/10.1021/jacs.6b0288

Interface and Composition Analysis on Perovskite Solar Cells.

Organometal halide (hybrid) perovskite solar cells have been fabricated following four different deposition procedures and investigated in order to find correlations between the solar cell characteristics/performance and their structure and composition as determined by combining depth-resolved imaging with time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and analytical scanning transmission electron microscopy (STEM). The interface quality is found to be strongly affected by the perovskite deposition procedure, and in particular from the environment where the conversion of the starting precursors into the final perovskite is performed (air, nitrogen, or vacuum). The conversion efficiency of the precursors into the hybrid perovskite layer is compared between the different solar cells by looking at the ToF-SIMS intensities of the characteristic molecular fragments from the perovskite and the precursor materials. Energy dispersive X-ray spectroscopy in the STEM confirms the macroscopic ToF-SIMS findings and allows elemental mapping with nanometer resolution. Clear evidence for iodine diffusion has been observed and related to the fabrication procedure.We acknowledge Lucio Cinà, Simone Casaluci, Stefano Razza and Narges Yaghoobi Nia for the technical support, “Polo Solare Organico” Regione Lazio, the “DSSCX” MIUR-PRIN2010 and FP7 ITN “Destiny” for funds. G.D., S.C. and C.D. acknowledge funding from ERC under grant number 259619 PHOTO EM. C.D. acknowledges financial support from the EU under grant number 312483 ESTEEM2.This is the final version of the article. It was first available from ACS via http://dx.doi.org/10.1021/acsami.5b0803

Multicomponent signal unmixing from nanoheterostructures: overcoming the traditional challenges of nanoscale X-ray analysis via machine learning.

The chemical composition of core-shell nanoparticle clusters have been determined through principal component analysis (PCA) and independent component analysis (ICA) of an energy-dispersive X-ray (EDX) spectrum image (SI) acquired in a scanning transmission electron microscope (STEM). The method blindly decomposes the SI into three components, which are found to accurately represent the isolated and unmixed X-ray signals originating from the supporting carbon film, the shell, and the bimetallic core. The composition of the latter is verified by and is in excellent agreement with the separate quantification of bare bimetallic seed nanoparticles.D.R. acknowledges support from the Royal Society’s Newton International Fellowship scheme. B.R.K. thanks the U.K. EPSRC for financial support (EP/J500380/1). F.d.l.P. and C.D. acknowledge funding from the ERC under grant no. 259619 PHOTO EM. P.A.M and P.B. acknowledges financial support from the European Research Council under the European Union’s Seventh Framework Programme (FP7/ 2007-2013)/ERC grant agreement 291522-3DIMAGE. P.A.M. also acknowledges financial support from the European Union’s Seventh Framework Programme of the European Commission: ESTEEM2, contract number 312483.This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b00449

Binder free three-dimensional sulphur/few-layer graphene foam cathode with enhanced high-rate capability for rechargeable lithium sulphur batteries.

A novel ultra-lightweight three-dimensional (3-D) cathode system for lithium sulphur (Li-S) batteries has been synthesised by loading sulphur on to an interconnected 3-D network of few-layered graphene (FLG) via a sulphur solution infiltration method. A free-standing FLG monolithic network foam was formed as a negative of a Ni metallic foam template by CVD followed by etching away of Ni. The FLG foam offers excellent electrical conductivity, an appropriate hierarchical pore structure for containing the electro-active sulphur and facilitates rapid electron/ion transport. This cathode system does not require any additional binding agents, conductive additives or a separate metallic current collector thus decreasing the weight of the cathode by typically ∼20-30 wt%. A Li-S battery with the sulphur-FLG foam cathode shows good electrochemical stability and high rate discharge capacity retention for up to 400 discharge/charge cycles at a high current density of 3200 mA g(-1). Even after 400 cycles the capacity decay is only ∼0.064% per cycle relative to the early (e.g. the 5th cycle) discharge capacity, while yielding an average columbic efficiency of ∼96.2%. Our results indicate the potential suitability of graphene foam for efficient, ultra-light and high-performance batteries.Kai Xi thanks the Cambridge Overseas Trust. P.R.K. acknowledges funding from the Cambridge Commonwealth Trust. S.H. acknowledges funding from ERC grant InsituNANO (no. 279342), EPSRC under grant GRAPHTED (project reference EP/K016636/1) and Grant EP/H047565/1. This research was partially supported by the EU FP7 Work Programme under grant GRAFOL (project reference 285275). XP and CD acknowledge funding from the ERC under grant number 259619 PHOTO EM.This is the accepted manuscript. The final version is available from RSC at http://pubs.rsc.org/en/Content/ArticleLanding/2014/NR/C4NR00326H#!divAbstract

Fully inkjet-printed two-dimensional material field-effect heterojunctions for wearable and textile electronics.

Fully printed wearable electronics based on two-dimensional (2D) material heterojunction structures also known as heterostructures, such as field-effect transistors, require robust and reproducible printed multi-layer stacks consisting of active channel, dielectric and conductive contact layers. Solution processing of graphite and other layered materials provides low-cost inks enabling printed electronic devices, for example by inkjet printing. However, the limited quality of the 2D-material inks, the complexity of the layered arrangement, and the lack of a dielectric 2D-material ink able to operate at room temperature, under strain and after several washing cycles has impeded the fabrication of electronic devices on textile with fully printed 2D heterostructures. Here we demonstrate fully inkjet-printed 2D-material active heterostructures with graphene and hexagonal-boron nitride (h-BN) inks, and use them to fabricate all inkjet-printed flexible and washable field-effect transistors on textile, reaching a field-effect mobility of ~91 cm2 V-1 s-1, at low voltage (<5 V). This enables fully inkjet-printed electronic circuits, such as reprogrammable volatile memory cells, complementary inverters and OR logic gates