106 research outputs found
The latent potential of YouTube - Will it become the 21st Century lecturer's film archive?
YouTube (http://www.youtube.com) is an online, public-access video-sharing
site that allows users to post short streaming-video submissions for open
viewing. Along with Google, MySpace, Facebook, etc. it is one of the great
success stories of the Internet, and is widely used by many of today's
undergraduate students. The higher education sector has recently realised the
potential of YouTube for presenting teaching resources/material to students,
and publicising research. This article considers another potential use for
online video archiving websites such as YouTube and GoogleVideo in higher
education - as an online video archive providing thousands of hours of video
footage for use in lectures. In this article I will discuss why this might be
useful, present some examples that demonstrate the potential for YouTube as a
teaching resource, and highlight some of the copyright and legal issues that
currently impact on the effective use of new online video websites, such as
YouTube, for use as a teaching resource.Comment: To be published in October 2008 issue of CAL-laborate
(http://science.uniserve.edu.au/pubs/callab/index.html
Tracking the energies of one-dimensional subband edges in quantum point contacts using dc conductance measurements
The semiconductor quantum point contact has long been a focal point for
studies of one-dimensional electron transport. Their electrical properties are
typically studied using ac conductance methods, but recent work has shown that
the dc conductance can be used to obtain additional information, with a
density-dependent Land\'{e} effective g-factor recently reported [T.-M. Chen et
al, Phys. Rev. B 79, 081301 (2009)]. We discuss previous dc conductance
measurements of quantum point contacts, demonstrating how valuable additional
information can be extracted from the data. We provide a comprehensive and
general framework for dc conductance measurements that provides a path to
improving the accuracy of existing data and obtaining useful additional data. A
key aspect is that dc conductance measurements can be used to map the energy of
the 1D subband edges directly, giving new insight into the physics that takes
place as the spin-split 1D subbands populate. Through a re-analysis of the data
obtained by Chen et al, we obtain two findings. The first is that the 2-down
subband edge closely tracks the source chemical potential when it first begins
populating before dropping more rapidly in energy. The second is that the 2-up
subband populates more rapidly as the subband edge approaches the drain
potential. This second finding suggests that the spin-gap may stop opening, or
even begin to close again, as the 2-up subband continues populating, consistent
with recent theoretical calculations and experimental studies.Comment: Published version available at
http://iopscience.iop.org/0953-8984/23/36/362201 15 pages, 3 figure
What lurks below the last plateau: Experimental studies of the 0.7 x 2e^2/h conductance anomaly in one-dimensional systems
The integer quantized conductance of one-dimensional electron systems is a
well understood effect of quantum confinement. A number of fractionally
quantized plateaus are also commonly observed. They are attributed to many-body
effects, but their precise origin is still a matter of debate, having attracted
considerable interest over the past 15 years. This review reports on
experimental studies of fractionally quantized plateaus in semiconductor
quantum point contacts and quantum wires, focusing on the 0.7 x 2e^2/h
conductance anomaly, its analogs at higher conductances, and the zero bias peak
observed in the d.c. source-drain bias for conductances less than 2e^2/h.Comment: Topical Review for J. Phys.: Condens. Matter, published version
available at http://iopscience.iop.org/0953-8984/23/44/443201/ Document is
131 pages, 43 figure
Near-thermal limit gating in heavily-doped III-V semiconductor nanowires using polymer electrolytes
Doping is a common route to reducing nanowire transistor on-resistance but
has limits. High doping level gives significant loss in gate performance and
ultimately complete gate failure. We show that electrolyte gating remains
effective even when the Be doping in our GaAs nanowires is so high that
traditional metal-oxide gates fail. In this regime we obtain a combination of
sub-threshold swing and contact resistance that surpasses the best existing
p-type nanowire MOSFETs. Our sub-threshold swing of 75 mV/dec is within 25% of
the room-temperature thermal limit and comparable with n-InP and n-GaAs
nanowire MOSFETs. Our results open a new path to extending the performance and
application of nanowire transistors, and motivate further work on improved
solid electrolytes for nanoscale device applications.Comment: 6 pages, 2 figures, supplementary available at journa
A study of transport suppression in an undoped AlGaAs/GaAs quantum dot single-electron transistor
We report a study of transport blockade features in a quantum dot
single-electron transistor, based on an undoped AlGaAs/GaAs heterostructure. We
observe suppression of transport through the ground state of the dot, as well
as negative differential conductance at finite source-drain bias. The
temperature and magnetic field dependence of these features indicate the
couplings between the leads and the quantum dot states are suppressed. We
attribute this to two possible mechanisms: spin effects which determine whether
a particular charge transition is allowed based on the change in total spin,
and the interference effects that arise from coherent tunneling of electrons in
the dot
Piezoelectric rotator for studying quantum effects in semiconductor nanostructures at high magnetic fields and low temperatures
We report the design and development of a piezoelectric sample rotation
system, and its integration into an Oxford Instruments Kelvinox 100 dilution
refrigerator, for orientation-dependent studies of quantum transport in
semiconductor nanodevices at millikelvin temperatures in magnetic fields up to
10T. Our apparatus allows for continuous in situ rotation of a device through
>100deg in two possible configurations. The first enables rotation of the field
within the plane of the device, and the second allows the field to be rotated
from in-plane to perpendicular to the device plane. An integrated angle sensor
coupled with a closed-loop feedback system allows the device orientation to be
known to within +/-0.03deg whilst maintaining the sample temperature below
100mK.Comment: 8 pages, 5 figure
Electrometry using the quantum Hall effect in a bilayer 2D electron system
We discuss the development of a sensitive electrometer that utilizes a
two-dimensional electron gas (2DEG) in the quantum Hall regime. As a
demonstration, we measure the evolution of the Landau levels in a second,
nearby 2DEG as the applied perpendicular magnetic field is changed, and extract
an effective mass for electrons in GaAs that agrees within experimental error
with previous measurements.Comment: 3.5 pages, 3 figures, submitted to APL
The influence of atmosphere on the performance of pure-phase WZ and ZB InAs nanowire transistors
We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs
nanowire transistors in several atmospheres: air, dry pure N and O, and
N bubbled through liquid HO and alcohols to identify whether
phase-related structural/surface differences affect their response. Both WZ and
ZB give poor gate characteristics in dry state. Adsorption of polar species
reduces off-current by 2-3 orders of magnitude, increases on-off ratio and
significantly reduces sub-threshold slope. The key difference is the greater
sensitivity of WZ to low adsorbate level. We attribute this to facet structure
and its influence on the separation between conduction electrons and surface
adsorption sites. We highlight the important role adsorbed species play in
nanowire device characterisation. WZ is commonly thought superior to ZB in InAs
nanowire transistors. We show this is an artefact of the moderate humidity
found in ambient laboratory conditions: WZ and ZB perform equally poorly in the
dry gas limit yet equally well in the wet gas limit. We also highlight the
vital role density-lowering disorder has in improving gate characteristics, be
it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase
nanowires.Comment: Accepted for publication in Nanotechnolog
Comment on "Drip Paintings and Fractal Analysis", arXiv:0710.4917v2, by K. Jones-Smith, H. Mathur and L.M. Krauss
In a recent manuscript (arXiv:0710.4917v2), Jones-Smith et al. attempt to use
the well-established box-counting technique for fractal analysis to
"demonstrate conclusively that fractal criteria are not useful for
authentication". Here, in response to what we view to be an extremely
simplistic misrepresentation of our earlier work by Jones-Smith et al., we
reiterate our position regarding the potential of fractal analysis for artwork
authentication. We also point out some of the flaws in the analysis presented
in by Jones-Smith et al.Comment: Comment on arXiv:0710.4917v2 [cond-mat.stat-mech
Origin of the hysteresis in bilayer 2D systems in the quantum Hall regime
The hysteresis observed in the magnetoresistance of bilayer 2D systems in the
quantum Hall regime is generally attributed to the long time constant for
charge transfer between the 2D systems due to the very low conductivity of the
quantum Hall bulk states. We report electrometry measurements of a bilayer 2D
system that demonstrate that the hysteresis is instead due to non-equilibrium
induced current. This finding is consistent with magnetometry and electrometry
measurements of single 2D systems, and has important ramifications for
understanding hysteresis in bilayer 2D systems.Comment: 4 pages, 3 figs. Accepted for publication in PR
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