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53 items found (0 items not approved), displaying 51 to 53.[First/Prev] 1, 2, 3, 4, 5, 6 [Next/Last]

Instruments / Technical Area	Publication Details	Published
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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