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Image of the Month
Posted Date: June 1, 2013
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STM image (0.7 V/2 pA) showing two CoPc islands with kinks in different directions of the CoPc lattice. (b) Possible model to explain the kinks, where the shifted row jumps to the neighboring equivalent site. Image acquired at 50K.

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150 × 150 nm2 STM image (100 pA/0.16 V) of graphene on the Ir(111) surface before CoPc deposition. (inset) Atomically resolved STM image of the moiré (1 nA/0.1 V). The hexagonal pattern is the moiré caused by the lattice mismatch between graphene and Ir.

Reference:

The Journal of Physical Chemistry C – dx.doi.org/10.1021/jp306439h | J. Phys. Chem. C 2012, 116, 20433−20437

Credits:

Sampsa K. Hamalaïnen, Mariia Stepanova, Robert Drost, Peter Liljeroth, Jouko Lahtinen, and Jani Sainio – Department of Applied Physics, Aalto University School of Science in Otakaari, Finland.

Microscope:

RHK Technology VT UHV 7500 Scanning Tunneling Microscope (STM)

Control System:

RHK Technology SPM 1000 Control System

Abstract:

We have studied the adsorption and self assembly of cobalt phthalocyanine (CoPc) on epitaxial graphene grown on iridium (111) by scanning tunneling microscopy (STM), Auger electron spectroscopy, and low energy electron diffraction (LEED). CoPc deposited on graphene/Ir(111) at room-temperature self-assembles into large, well-ordered domains with a nearly square unit cell. On the basis of the observed LEED pattern and STM images, a detailed structure for the overlayer is proposed. Despite the corrugation of the moiré pattern of graphene on Ir(111), its hexagonal symmetry is not translated to the CoPc layer. This is in contrast to systems with stronger graphene−metal interaction that makes graphene on Ir(111) a convenient, clean, and well defined model system for studying molecular doping of graphene.

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Image of the Month
Posted Date: May 1, 2013
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Initial test of Nazin Group RHK PanScan-STM with Closed Cycle Cryostat provides atomic resolution with HOPG at 14 K.

RHK is proud to highlight the first atomic resolution image acquired on our PanScan SPM connected to a running Closed-Cycle Helium Cryostat.  This unique STM was developed in collaboration with Dr. George Nazin in the Chemistry Department at the University of Oregon, whose group acquired this image.

In addition to being an extremely stable SPM, this microscope includes an integrated parabolic mirror with three-axis manipulator to allow highly efficient light collection from the tunnel junction.   This first atomically resolved image acquired at 14K demonstrates a high-level of isolation from the vibration of the Closed-Cycle Cryostat.  The goal of a helium-free STM has been an elusive dream for the many researchers unable to secure a steady supply of affordable liquid helium.

RHK’s new helium-free PanScan STM enables every researcher to run their SPM at cryogenic temperatures endlessly without the trouble and expense of liquid helium.

Credits:

Dr. George Nazin, Assistant Professor, Physical Chemistry, University of Oregon

Microscope:

RHK LT PanScan-STM customized for light collection

Control System:

RHK R9-STM and PMC100

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Image of the Month
Posted Date: April 1, 2013
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Left Image – STM images of (a, b) the buffer layer and (d) QFMLG. Panel (a) shows the long-range periodicity imposed on the buffer layer by the substrate. The solid and dashed diamond designates the (6 x 6). Images in panel (a) were taken with a sample bias of +1.7 V. Under optimal tunneling conditions (main image in panel a) as opposed to earlier stages (inset in (a)) the atomic lattice superimposed on the (6 · 6) periodicity is revealed. Panels (b, d) are zoomed-in images of the buffer layer and QFMLG imaged with a sample bias of -0.223 V and +0.103 V, respectively. The upper insets in (b, d) present the structural models of the buffer layer and QFMLG, respectively. The lower insets in panels (b) and (d) are zoomed in 2D Fast Fourier Transforms (2DFFT) of one of the (1 · 1) spots of the graphene lattice with the quasi-(6 · 6) satellite spots visible only on the buffer layer. Scale bar 0.58 nm-1. Panel (c) shows atomically resolved STM images taken on the buffer layer and QFMLG and the corresponding line profiles along the graphene periodicity. The STM images in panel (c) have been filtered to remove noise. All measurements were taken in constant-current mode with the current set to 0.3 nA.

Right Image– (a) Current vs. voltage (I–V) curves and (b) differential conductance spectra acquired on the buffer layer (red line) and on QFMLG (blue line). The I–V curves in (a) are an average of multiple curves. The spectrum of the buffer layer reveals a low density of states ranging from around -0.5 V to +0.5 V, whereas hydrogen intercalation restores the semimetallic behavior of QFMLG expected for pristine graphene. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Credits:
Sarah Golera,b, Camilla Colettia,c, Vincenzo Piazzaa, Pasqualantonio Pingueb, Francesco Colangelob, Vittorio Pellegrinib, Konstantin V. Emtsevc, Stiven Fortic, Ulrich Starkec, Fabio Beltrama,b, Stefan Heunb
aCenter for Nanotechnology Innovation @ NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
bNEST, Istituto Nanoscienze – CNR and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
cMax-Planck-Institut fuer Festkoerperforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany

Microscope:
RHK Technology UHV 7000

Control System:
RHK Technology SPM 1000 Control System

Reference :
CARBON 51 (2013) 249–254

Abstract:
On the SiC(0001) surface (the silicon face of SiC), epitaxial graphene is obtained by subli- mation of Si from the substrate. The graphene film is separated from the bulk by a car- bon-rich interface layer (hereafter called the buffer layer) which in part covalently binds to the substrate. Its structural and electronic properties are currently under debate. In the present work we report scanning tunneling microscopy (STM) studies of the buffer layer and of quasi-free-standing monolayer graphene (QFMLG) that is obtained by decou- pling the buffer layer from the SiC(0001) substrate by means of hydrogen intercalation. Atomic resolution STM images of the buffer layer reveal that, within the periodic structural corrugation of this interfacial layer, the arrangement of atoms is topologically identical to that of graphene. After hydrogen intercalation, we show that the resulting QFMLG is relieved from the periodic corrugation and presents no detectable defect sites.

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Image of the Month
Posted Date: March 1, 2013
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Figure 1. (b) dI/dV measured at an applied load of 72 nN on fluorinated graphene and pristine graphene. A band gap of 2.9 eV was measured after fluorination.
Figure 2. 500 × 500 nm2 images of (a) topography and (b) friction measured on the fluorinated graphene using contact mode AFM (applied load = 71 nN). (c) Plot of friction force versus applied load measured on pristine and on fluorinated graphene.

Credits:
Sangku Kwon,†,⊥ Jae-Hyeon Ko,‡,⊥ Ki-Joon Jeon,§ Yong-Hyun Kim,*,‡,∥ and Jeong Young Park*,†,∥
Graduate School of EEWS (WCU), KAIST, Daejeon 305-701, Republic of Korea
Graduate School of Nanoscience and Technology (WCU), KAIST, Daejeon 305-701, Korea §School of Electrical Engineering, University of Ulsan, Ulsan 680-749, Republic of Korea
KAIST Institute for the NanoCentury, KAIST, Daejeon 305-701, Republic of Korea

Microscope:
RHK Technology UHV 7500

Control System:
RHK Technology SPM 1000 Control System

Reference:
Nano Lett. 2012, 12, 6043−6048

Abstract:
Atomically thin graphene is an ideal model system for studying nanoscale friction due to its intrinsic two-dimensional (2D) anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro- and nanomechanical devices. Here, we report unexpectedly enhanced nanoscale friction on chemically modified graphene and a relevant theoretical analysis associated with flexural phonons. Ultrahigh vacuum friction force microscopy measurements show that nanoscale friction on the graphene surface increases by a factor of 6 after fluorination of the surface, while the adhesion force is slightly reduced. Density functional theory calculations show that the out-of-plane bending stiffness of graphene increases up to 4-fold after fluorination. Thus, the less compliant F-graphene exhibits more friction. This indicates that the mechanics of tip-to- graphene nanoscale friction would be characteristically different from that of conventional solid-on-solid contact and would be dominated by the out-of-plane bending stiffness of the chemically modified graphene. We propose that damping via flexural phonons could be a main source for frictional energy dissipation in 2D systems such as graphene.

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