706 research outputs found
Usability engineering practices in software development organizations: The Greek and the Italian case study
This paper reports the results of a study of software development organizations’ approach towards usability, conducted on software development organizations in Greece, extending a survey conducted in Southern Italy in 2011. The results show that the organization performing usability evaluation is nearly the same in both countries as well as the key advantages and the problems in performing usability evaluation emphasized by Italian and Greek respondents. A difference in the understanding of usability evaluation concept between the two studies emerged
Transmission through a biased graphene bilayer barrier
We study the electronic transmission through a graphene bilayer in the
presence of an applied bias between layers. We consider different geometries
involving interfaces between both a monolayer and a bilayer and between two
bilayers. The applied bias opens a sizable gap in the spectrum inside the
bilayer barrier region, thus leading to large changes in the transmission
probability and electronic conductance that are controlled by the applied bias.Comment: 10 pages, 8 figures, extended versio
A Fully Tunable Single-Walled Carbon Nanotube Diode
We demonstrate a fully tunable diode structure utilizing a fully suspended
single-walled carbon nanotube (SWNT). The diode's turn-on voltage under forward
bias can be continuously tuned up to 4.3 V by controlling gate voltages, which
is ~6 times the nanotube bandgap energy. Furthermore, the same device design
can be configured into a backward diode by tuning the band-to-band tunneling
current with gate voltages. A nanotube backward diode is demonstrated for the
first time with nonlinearity exceeding the ideal diode. These results suggest
that a tunable nanotube diode can be a unique building block for developing
next generation programmable nanoelectronic logic and integrated circuits.Comment: 14 pages, 4 figure
Atomic Scale Memory at a Silicon Surface
The limits of pushing storage density to the atomic scale are explored with a
memory that stores a bit by the presence or absence of one silicon atom. These
atoms are positioned at lattice sites along self-assembled tracks with a pitch
of 5 atom rows. The writing process involves removal of Si atoms with the tip
of a scanning tunneling microscope. The memory can be reformatted by controlled
deposition of silicon. The constraints on speed and reliability are compared
with data storage in magnetic hard disks and DNA.Comment: 13 pages, 5 figures, accepted by Nanotechnolog
Extraordinary sensitivity of the electronic structure and properties of single-walled carbon nanotubes to molecular charge-transfer
Interaction of single-walled carbon nanotubes with electron donor and
acceptor molecules causes significant changes in the electronic and Raman
spectra, the relative proportion of the metallic species increasing on electron
donation through molecular charge transfer, as also verified by electrical
resistivity measurements.Comment: 15 pages, 5 figurre
Conductance of Distorted Carbon Nanotubes
We have calculated the effects of structural distortions of armchair carbon
nanotubes on their electrical transport properties. We found that the bending
of the nanotubes decreases their transmission function in certain energy ranges
and leads to an increased electrical resistance. Electronic structure
calculations show that these energy ranges contain localized states with
significant - hybridization resulting from the increased curvature
produced by bending. Our calculations of the contact resistance show that the
large contact resistances observed for SWNTs are likely due to the weak
coupling of the NT to the metal in side bonded NT-metal configurations.Comment: 5 pages RevTeX including 4 figures, submitted to PR
Negative Thermal Expansion Coefficient of Graphene Measured by Raman Spectroscopy
The thermal expansion coefficient (TEC) of single-layer graphene is estimated
with temperature-dependent Raman spectroscopy in the temperature range between
200 and 400 K. It is found to be strongly dependent on temperature but remains
negative in the whole temperature range, with a room temperature value of
-8.0x10^{-6} K^{-1}. The strain caused by the TEC mismatch between graphene and
the substrate plays a crucial role in determining the physical properties of
graphene, and hence its effect must be accounted for in the interpretation of
experimental data taken at cryogenic or elevated temperatures.Comment: 17 pagese, 3 figures, and supporting information (4 pages, 3
figures); Nano Letters, 201
Application of Graphene within Optoelectronic Devices and Transistors
Scientists are always yearning for new and exciting ways to unlock graphene's
true potential. However, recent reports suggest this two-dimensional material
may harbor some unique properties, making it a viable candidate for use in
optoelectronic and semiconducting devices. Whereas on one hand, graphene is
highly transparent due to its atomic thickness, the material does exhibit a
strong interaction with photons. This has clear advantages over existing
materials used in photonic devices such as Indium-based compounds. Moreover,
the material can be used to 'trap' light and alter the incident wavelength,
forming the basis of the plasmonic devices. We also highlight upon graphene's
nonlinear optical response to an applied electric field, and the phenomenon of
saturable absorption. Within the context of logical devices, graphene has no
discernible band-gap. Therefore, generating one will be of utmost importance.
Amongst many others, some existing methods to open this band-gap include
chemical doping, deformation of the honeycomb structure, or the use of carbon
nanotubes (CNTs). We shall also discuss various designs of transistors,
including those which incorporate CNTs, and others which exploit the idea of
quantum tunneling. A key advantage of the CNT transistor is that ballistic
transport occurs throughout the CNT channel, with short channel effects being
minimized. We shall also discuss recent developments of the graphene tunneling
transistor, with emphasis being placed upon its operational mechanism. Finally,
we provide perspective for incorporating graphene within high frequency
devices, which do not require a pre-defined band-gap.Comment: Due to be published in "Current Topics in Applied Spectroscopy and
the Science of Nanomaterials" - Springer (Fall 2014). (17 pages, 19 figures
Nanoscopic Tunneling Contacts on Mesoscopic Multiprobe Conductors
We derive Bardeen-like expressions for the transmission probabilities between
two multi-probe mesoscopic conductors coupled by a weak tunneling contact. We
emphasize especially the dual role of a weak coupling contact as a current
source and sink and analyze the magnetic field symmetry. In the limit of a
point-like tunneling contact the transmission probability becomes a product of
local, partial density of states of the two mesoscopic conductors. We present
expressions for the partial density of states in terms of functional
derivatives of the scattering matrix with respect to the local potential and in
terms of wave functions. We discuss voltage measurements and resistance
measurements in the transport state of conductors. We illustrate the theory for
the simple case of a scatterer in an otherwise perfect wire. In particular, we
investigate the development of the Hall-resistance as measured with weak
coupling probes.Comment: 10 pages, 5 figures, revte
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