31 research outputs found
Graphene nanoribbons with zigzag and armchair edges prepared by scanning tunneling microscope lithography on gold substrates
The properties of graphene nanoribbons are dependent on both the nanoribbon width and the crystallographic orientation of the edges. Scanning tunneling microscope lithography is a method which is able to create graphene nanoribbons with well defined edge orientation, having a width of a few nanometers. However, it has only been demonstrated on the top layer of graphite. In order to allow practical applications of this powerful lithography technique, it needs to be implemented on single layer graphene. We demonstrate the preparation of graphene nanoribbons with well defined crystallographic orientation on top of gold substrates. Our transfer and lithography approach brings one step closer the preparation of well defined graphene nanoribbons on arbitrary substrates for nanoelectronic applications
Lambda^0 polarization as a probe for production of deconfined matter in ultra-relativistic heavy-ion collisions
We study the polarization change of Lambda^0's produced in ultra-relativistic
heavy-ion collisions with respect to the polarization observed in proton-proton
collisions as a signal for the formation of a Quark-Gluon Plasma (QGP).
Assuming that, when the density of participants in the collision is larger than
the critical density for QGP formation, the Lambda^0 production mechanism
changes from recombination type processes to the coalescence of free valence
quarks, we find that the Lambda^0 polarization depends on the relative
contribution of each process to the total number of Lambda^0's produced in the
collision. To describe the polarization of Lambda^0's in nuclear collisions for
densities below the critical density for the QGP formation, we use the
DeGrand-Miettinen model corrected for the effects introduced by multiple
scattering of the produced Lambda^0 within the nuclear environment.Comment: 9 pages, 6 figures, uses ReVTeX and epsfig.st
Anomalies in thickness measurements of graphene and few layer graphite crystals by tapping mode atomic force microscopy
Atomic Force Microscopy (AFM) in the tapping (intermittent contact) mode is a
commonly used tool to measure the thickness of graphene and few layer graphene
(FLG) flakes on silicon oxide surfaces. It is a convenient tool to quickly
determine the thickness of individual FLG films. However, reports from
literature show a large variation of the measured thickness of graphene layers.
This paper is focused on the imaging mechanism of tapping mode AFM (TAFM) when
measuring graphene and FLG thickness and we show that at certain measurement
parameters significant deviations can be introduced in the measured thickness
of FLG flakes. An increase of as much as 1 nm can be observed in the measured
height of FLG crystallites, when using an improperly chosen range of free
amplitude values of the tapping cantilever. We present comparative Raman
spectroscopy and TAFM measurements on selected single and multilayer graphene
films, based on which we suggest ways to correctly measure graphene and FLG
thickness using TAFM
Strange particle production at RHIC in a single-freeze-out model
Strange particle ratios and pT-spectra are calculated in a thermal model with
single freeze-out, previously used successfully to describe non-strange
particle production at RHIC. The model and the recently released data for phi,
Lambda, anti-Lambda, and K*(892) are in very satisfactory agreement, showing
that the thermal approach can be used to describe the strangeness production at
RHIC.Comment: We have added the comparison of the model predictions to the newly
released Lambda and K*(892) pT-spectra from STA
Effective String Rope Model for the initial stages of Ultra-Relativistic Heavy Ion Collisions
Different approaches to describe initial stages of relativistic heavy ion
collisions are discussed qualitatively and quantitatively. An Effective String
Rope Model is presented for heavy ion collisions at RHIC energies. Our model
takes into account baryon recoil for both target and projectile, arising from
the acceleration of partons in an effective field, produced in the collision.
The typical field strength (string tension) for RHIC energies is about 5-12
GeV/fm, what allows us to talk about ``string ropes''. The results show that a
QGP forms a tilted disk, such that the direction of the largest pressure
gradient stays in the reaction plane, but deviates from both the beam and the
usual transverse flow directions. The produced initial state can be used as an
initial condition for further hydrodynamical calculations. Such initial
conditions lead to the creation of third flow component.Comment: 47 pages, 14 figures. Minor changes were made, style was changed to
"elsart". Paper is accepted to Nucl. Phys.
Theoretical STM signatures and transport properties of native defects in carbon nanotubes
Article on theoretical STM signatures and transport properties of native defects in carbon nanotubes