5 research outputs found
The stability of graphene band structures against an external periodic perturbation; Na on Graphene
We report that the band of graphene sensitively changes as a function
of an external potential induced by Na especially when the potential becomes
periodic at low temperature. We have measured the band structures from the
graphene layers formed on the 6H-SiC(0001) substrate using angle-resolved
photoemission spectroscopy with synchrotron photons. With increasing Na dose,
the band appears to be quickly diffused into background at 85 K whereas
it becomes significantly enhanced its spectral intensity at room temperature
(RT). A new parabolic band centered at 1.15 \AA also forms near
Fermi energy with Na at 85 K while no such a band observed at RT. Such changes
in the band structure are found to be reversible with temperature. Analysis
based on our first principles calculations suggests that the changes of the
band of graphene be mainly driven by the Na-induced potential especially
at low temperature where the potential becomes periodic due to the crystallized
Na overlayer. The new parabolic band turns to be the band of the
underlying buffer layer partially filled by the charge transfer from Na
adatoms. The five orders of magnitude increased hopping rate of Na adatoms at
RT preventing such a charge transfer explains the absence of the new band at
RT.Comment: 6 pages and 6 figure
5GHz Wideband Channel Model in Apartment Building
This paper reports the empirical 5GHz
wideband channel model in apartment building.
The channel measurement system is based on
the pseudo-noise (PN) correlation method. In
measurements, transmitter is fixed at two
different positions in a house while receiver
moves from the rooms of the house to those of
nearby houses in each transmitter position.
From measurement results, propagation loss
and wideband channel characteristics are
analyzed. As a result, we found that the signal
reflected to neighboring buildings proffered
other clusters. Especially, in cases of the
receiver positions where with a big window
and large away from the transmitter, this
phenomenon is emphasized. And transmitter
located at the biased position, could cause the
imbalance of received signal level in a single
house and the interference to neighboring
houses
Understanding the Role of Electronic Effects in CO on the Pt-Sn Alloy Surface via Band Structure Measurements
Using angle-resolved photoemission spectroscopy, we show direct evidence for charge transfer between adsorbed molecules and metal substrates, i.e., chemisorption of CO on Pt(111) and Pt-Sn/Pt(111) 2 x 2 surfaces. The observed band structures show a unique signature of charge transfer as CO atoms are adsorbed, revealing the roles of specific orbital characters participating in the chemisorption process. As the coverage of CO increases, the degree of charge transfer between CO and Pt shows a clear difference to that of Pt-Sn. With comparison to density functional theory calculation results, the observed distinct features in the band structure are interpreted as back-donation bonding states formed between the Pt molecular orbital and the 2 pi orbital of CO. Furthermore, the change in the surface charge concentration, measured from the Fermi surface area, shows that the Pt surface has a larger charge concentration change than the Pt-Sn surface upon CO adsorption. The differences between Pt and Pt-Sn surfaces are due to the effect of Pt-Sn intermetallic bonding on the interaction of CO with the surface
Understanding the Role of Electronic Effects in CO on the Pt-Sn Alloy Surface via Band Structure Measurements
Using angle-resolved photoemission spectroscopy, we show direct evidence for charge transfer between adsorbed molecules and metal substrates, i.e., chemisorption of CO on Pt(111) and Pt-Sn/Pt(111) 2 x 2 surfaces. The observed band structures show a unique signature of charge transfer as CO atoms are adsorbed, revealing the roles of specific orbital characters participating in the chemisorption process. As the coverage of CO increases, the degree of charge transfer between CO and Pt shows a clear difference to that of Pt-Sn. With comparison to density functional theory calculation results, the observed distinct features in the band structure are interpreted as back-donation bonding states formed between the Pt molecular orbital and the 2 pi orbital of CO. Furthermore, the change in the surface charge concentration, measured from the Fermi surface area, shows that the Pt surface has a larger charge concentration change than the Pt-Sn surface upon CO adsorption. The differences between Pt and Pt-Sn surfaces are due to the effect of Pt-Sn intermetallic bonding on the interaction of CO with the surface.11Nsciescopu