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Image of the Month
Posted Date: September 1, 2016
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Figure 1:  The sample is graphene grown on SiC by Joshua Robinson’s group at Penn State. The image is a large scale (50nm) high resolution (2048px) simultaneously collected dI/dV and topo image. Taken at 200mV and 0.1nA. dI/dV setting is 10mV excitation at 1kHz. The Moire pattern is clear in the main image, while the zoom shows atomic resolution.

Graphene grown on SiC is one of the most promising routes for producing large-scale graphene devices and heterostructures. Here we studied topography and variations in local density of states of graphene grown on SiC by Joshua Robinson’s group at Penn State.  This characterization of the base graphene growth is in preparation for developing work that aims to understand the local electronic states across graphene heterostructures. The figure shows a large scale image (50nm) taken at a high resolution (2048px) and a simultaneously collected dI/dV map (at 200mV and 0.1nA) from Shawna Hollen’s group at University of New Hampshire. The large scale image shows a superposition of a Moire pattern and electronic variations, while the zoom shows details down to atomic resolution.

Shruti Subramanian in Joshua Robinson’s group at Penn State grew the graphene on SiC samples. Jake Riffle in Shawna Hollen’s group at University of New Hampshire took the STM/STS data.

Credits:
Jake Riffle2, Shruti Subramanian1, Joshua Robinson1 and Shawna Hollen2

Department of Materials Science and Engineering and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

University of New Hampshire, Department of Physics, 9 Library Way, Durham, NH 03824

Images and data graciously provided by Professor Shawna Hollen, University of New Hampshire, Durham, New Hampshire.

Microscope:
RHK PanScan Freedom STM/AFM

Control System:
RHK R9 Control System

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Panscan Freedom SPM,  VT Beetle
Events
Event Date: August 23, 2016

8/23-8/25
2A Hall, 1F Exhibition Center, BEXCO, Busan, Korea
http://ivc20.com/index.php

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PRIcon
Image of the Month
Posted Date: August 1, 2016
institution

Figure 1:  STM images of atomic level oxidation at two sequential exposure times, t = 3 min and t = 4 min. Circles indicate areas of change, e.g., a bright site converting to dark after additional SMB−O2 exposure, and an area where a single bright site changed into a pair of adjacent bright sites. Images were taken at 2 V and 230 pA.. (DOI: 10.1021/acs.jpcc.6b01360   J. Phys. Chem. C 2016, 120, 8191−8197)

The site-specific locations of molecular oxygen reactivity on Si(111)-(7 Å~  7) surfaces were examined using kinetic energy selected supersonic molecular beams in conjunction with in situ  scanning tunneling microscopy. We herein present a detailed visualization of the surface as it reacts in real-time and real-space when exposed to molecular oxygen with translational energy Ei  = 0.37 eV. Atomically resolved images reveal two channels for oxidation leading to the formation of dark and bright reaction sites. The darks sites dominate the reaction throughout the range of exposures sampled and exhibit almost no preference for occurrence at the corner or inner adatom sites of the reconstructed (7 Å~  7) unit cell. The bright sites show a small preference for corner vs. inner site reactivity on the reconstructed (7 Å~  7) unit cell. The bright site corner preference seen here at elevated kinetic energies and with selected incident kinematics is smaller than that typically observed for more conventional thermal (background dosed) oxidation processing. These observations suggest that two adsorption pathways, trapping-mediated chemisorption and direct chemisorption, occur simultaneously when using energetic molecular oxygen but with modified relative probability as compared with thermal dosing. These results demonstrate the efficacy of using angle- and energy-selected supersonic molecular beams to gain a topographical diagram of the accessible reactive potential surface energy and precise control of semiconductor oxidation, a process that is of growing importance as we seek to create high-quality and precisely defined oxides having atomic dimensions.

Credits:
Bryan Wiggins, L. Gaby Avila-Bront, Ross Edel, and S. J. Sibener*

The James Franck Institute and Department of Chemistry, The University of Chicago 929 East 57th Street, Chicago, Illinois 60637, United States

Images and data graciously provided by Steve Sibener, University of Chicago, Chicago, Illinois.

Microscope:
RHK Custom PanScan STM/AFM

Control System:
RHK R9 Control System

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Panscan Freedom SPM,  VT Beetle
Events
Event Date: July 25, 2016

7/25-7/29
East Midlands Conference Centre at the University of Nottingham, UK
RHK represented by Windsor Scientific
http://ncafm2016.iopconfs.org/home

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