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56 items found (0 items not approved), displaying 51 to 56.[First/Prev] 1, 2, 3, 4, 5, 6 [Next/Last]

Instruments / Technical Area	Publication Details	Published
	Electron Ptychographic Diffractive Imaging of Boron Atoms in LaB6 Crystals Peng Wang , Fucai Zhang , Si Gao , Mian Zhang , Angus I. Kirkland Scientific Reports 7 DOI: 10.1038/s41598-017-02778-x Open Access Show Abstract ▼ Abstract: Ptychographic diffractive imaging has the potential for structural determination of materials without the constraints of relatively small, isolated samples required for conventional coherent diffractive imaging. The increased illumination diversity introduced using multiple measurements (overlapped probe positions) also provides higher sensitivity to phase changes in weakly scattering samples. The resolution of a ptychographic reconstruction is ultimately determined by the diffraction limit for the wavelength of the radiation used. However, in practical experiments using electrons either the maximum collection angle of the detector used to record the data or the partial coherence of the source impose lower resolution limits. Nonetheless for medium energy electrons this suggests a potential sub 0.1 nm spatial resolution limit, comparable to that obtained using aberration corrected instruments. However, simultaneous visualization of light and heavier atoms in specimens using ptychography at sub 0.1 nm resolution presents a significant challenge. Here, we demonstrate a ptychographic reconstruction of a LaB6 crystal in which light B atoms were clearly resolved together with the heavy La atoms in the reconstructed phase. The technique used is general and can also be applied to non-crystalline and extended crystalline samples. As such it offers an alternative future basis for imaging the atomic structure of materials, particularly those containing low atomic number elements.	Jun 2017
E02-JEM ARM 300CF	Atomic structure and formation mechanism of sub-nanometer pores in 2D monolayer MoS 2 Shanshan Wang , Huashan Li , Hidetaka Sawada , Christopher S. Allen , Angus I. Kirkland , Jeffrey C. Grossman , Jamie Warner Nanoscale 6 DOI: 10.1039/C7NR01127J Show Abstract ▼ Abstract: AbstractWe use electron-beam nanofabrication to create sub-nanometer (sub-nm) pores in 2D monolayer MoS2 with fine control over the pore size down to 0.6 nm, corresponding to the loss of a single Mo atom and surrounding S atoms. The sub-nm pores are created in situ with 1 nm spatial precision in the MoS2 lattice by control of the angstrom sized probe in an aberration corrected scanning transmission electron microscope with real time tracking of the pore creation. Dynamics of the sub-nm pore creation are captured at the atomic scale and reveal the mechanism of nanopore formation at accelerating voltages of 60 and 80 kV to be due to displacing a Mo atom from the lattice site onto the surface of the MoS2. This process is enabled by the destabilization of the Mo bonding from localized electron beam induced S atom loss. DFT calculations confirm the energetic advantage of having the ejected Mo atom attach on the sheet surface rather than being expelled into vacuum, and indicate sensitivity of the nanopore potential as a function of the adsorption position of the ejected Mo atom. These results provide detailed atomic level insights into the initial process of single Mo loss that underpins the nucleation of a nanopore and explains the formation mechanism of sub-nm pores in MoS2.	May 2017
I13-2-Diamond Manchester Imaging	Synchrotron X-ray tomographic quantification of microstructural evolution in ice cream – a multi-phase soft solid Enyu Guo , Guang Zeng , Daniil Kazantsev , Peter Rockett , Julian Bent , Mark Kirkland , Gerard Van Dalen , David S. Eastwood , David Stjohn , Peter D. Lee Rsc Adv. 7, 15561 - 15573 DOI: 10.1039/C7RA00642J Diamond Proposal Number(s): [12194, 12195] Open Access Show Abstract ▼ Abstract: Microstructural evolution in soft matter directly influences not only the material's mechanical and functional properties, but also our perception of that material's taste. Using synchrotron X-ray tomography and cryo-SEM we investigated the time–temperature evolution of ice cream's microstructure. This was enabled via three advances in synchrotron tomography: a bespoke tomography cold stage; improvements in pink beam in line phase contrast; and a novel image processing strategy for reconstructing and denoising in line phase contrast tomographic images. Using these three advances, we qualitatively and quantitatively investigated the effect of thermal changes on the ice cream's microstructure after 0, 7 and 14 thermal cycles between −15 and −5 °C. The results demonstrate the effect of thermal cycling on the coarsening of both the air cells and ice crystals in ice cream. The growth of ice crystals almost ceases after 7 thermal cycles when they approach the size of the walls between air cells, while air cells continue to coarsen, forming interconnected channels. We demonstrate that the tomographic volumes provide a statistically more representative sample than cryo-SEM, and elucidate the three dimensional morphology and connectivity of phases. This resulted in new insights including the role of air cells in limiting ice crystal coarsening.	Mar 2017
E02-JEM ARM 300CF	Atomic Structure and Dynamics of Single Platinum Atom Interactions with Monolayer MoS 2 Huashan Li , Shanshan Wang , Hidetake Sawada , Grace G. D. Han , Thomas Samuels , Christopher S. Allen , Angus I. Kirkland , Jeffrey C. Grossman , Jamie H. Warner Acs Nano DOI: 10.1021/acsnano.7b00796 Diamond Proposal Number(s): [16854] Show Abstract ▼ Abstract: We have studied atomic level interactions between single Pt atoms and the surface of monolayer MoS2 using aberration-corrected annular dark field scanning transmission electron microscopy at an accelerating voltage of 60 kV. Strong contrast from single Pt atoms on the atomically resolved monolayer MoS2 lattice enables their exact position to be determined with respect to the MoS2 lattice, revealing stable binding sites. In regions of MoS2 free from surface contamination, the Pt atoms are localized in S vacancy sites and exhibit dynamic hopping to nearby vacancy sites driven by the energy supplied by the electron beam. However, in areas of MoS2 contaminated with carbon surface layers, the Pt atoms appear at various positions with respect to the underlying MoS2 lattice, including on top of Mo and in off-axis positions. These variations are due to the Pt bonding with the surrounding amorphous carbon layer, which disrupts the intrinsic Pt–MoS2 interactions, leading to more varied positions. Density functional theory (DFT) calculations reveal that Pt atoms on the surface of MoS2 have a small barrier for migration and are stabilized when bound to either a single or double sulfur vacancies. DFT calculations have been used to understand how the catalytic activity of the MoS2 basal plane for hydrogen evolution reaction is influenced by Pt dopants by variation of the hydrogen adsorption free energy. This strong dependence of catalytic effect on interfacial configurations is shown to be common for a series of dopants, which may provide a means to create and optimize reaction centers.	Mar 2017
E02-JEM ARM 300CF	Atomic Structure and Spectroscopy of Single Metal (Cr, V) Substitutional Dopants in Monolayer MoS 2 Alex W. Robertson , Yung-chang Lin , Shanshan Wang , Hidetaka Sawada , Christopher S. Allen , Qu Chen , Sungwoo Lee , Gun-do Lee , Joohee Lee , Seungwu Han , Euijoon Yoon , Angus I. Kirkland , Heeyeon Kim , Kazu Suenaga , Jamie H. Warner Acs Nano 10, 10227 - 10236 DOI: 10.1021/acsnano.6b05674 Show Abstract ▼ Abstract: Dopants in two-dimensional dichalcogenides have a significant role in affecting electronic, mechanical, and interfacial properties. Controllable doping is desired for the intentional modification of such properties to enhance performance; however, unwanted defects and impurity dopants also have a detrimental impact, as often found for chemical vapor deposition (CVD) grown films. The reliable identification, and subsequent characterization, of dopants is therefore of significant importance. Here, we show that Cr and V impurity atoms are found in CVD grown MoS2 monolayer 2D crystals as single atom substitutional dopants in place of Mo. We attribute these impurities to trace elements present in the MoO3 CVD precursor. Simultaneous annular dark field scanning transmission electron microscopy (ADF-STEM) and electron energy loss spectroscopy (EELS) is used to map the location of metal atom substitutions of Cr and V in MoS2 monolayers with single atom precision. The Cr and V are stable under electron irradiation at 60 to 80 kV, when incorporated into line defects, and when heated to elevated temperatures. The combined ADF-STEM and EELS differentiates these Cr and V dopants from other similar contrast defect structures, such as 2S self-interstitials at the Mo site, preventing misidentification. Density functional theory calculations reveal that the presence of Cr or V causes changes to the density of states, indicating doping of the MoS2 material. These transferred impurities could help explain the presence of trapped charges in CVD prepared MoS2.	Nov 2016
B23-Circular Dichroism	Photo-induced optical activity in phase-change memory materials Konstantin B. Borisenko , Janaki Shanmugam , Benjamin A. O. Williams , Paul Ewart , Behrad Gholipour , Daniel W. Hewak , Rohanah Hussain , Tamas Javorfi , Giuliano Siligardi , Angus Kirkland Scientific Reports 5, 26 DOI: 10.1038/srep08770 PMID: 25740351 Diamond Proposal Number(s): [7201, 8000, 8674, 9375] Open Access Show Abstract ▼ Abstract: We demonstrate that optical activity in amorphous isotropic thin films of pure Ge2Sb2Te5 and N-doped Ge2Sb2Te5N phase-change memory materials can be induced using rapid photo crystallisation with circularly polarised laser light. The new anisotropic phase transition has been confirmed by circular dichroism measurements. This opens up the possibility of controlled induction of optical activity at the nanosecond time scale for exploitation in a new generation of high-density optical memory, fast chiroptical switches and chiral metamaterials.	Mar 2015

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