262 research outputs found
Low temperature epitaxial silicon growth using electron cyclotron resonance plasma deposition
The development of a process for the low temperature (\u3c600° C) growth of epitaxial silicon is an important technological issue. Conventional growth processes involve temperatures in excess of 1000° C. At these temperatures autodoping and impurity redistribution limit the feature size achievable in VLSI fabrication. As the typical feature sizes move into the submicron region, new processes for epitaxial silicon deposition will be needed. Another application for a low temperature growth process is the fabrication of solar cells on inexpensive metallurgical grade silicon wafers. Impurity diffusion from the wafer during conventional epitaxial silicon growth limits the quality of the solar cells if expensive high purity wafers are not used. We have used electron cyclotron resonance (ECR) plasma deposition to grow high quality epitaxial silicon films on silicon wafers. This growth technique relies on the deposition of silicon from a highly energetic hydrogen and silane plasma. The presence of the hydrogen in the plasma provides reactive etching of the silicon surface during growth. This reduces the oxygen and carbon contamination in the film as well as increasing the number of available growth sites on the surface by displacing the adsorbed hydrogen. By optimizing the growth pressure, substrate temperature, microwave power, substrate bias and silane to hydrogen ratio we have developed a process which provides enhanced growth rates and good uniformity at temperatures (425-575° C) significantly below those used in conventional processes. The structural and electrical properties of the films have been characterized using SEM, TEM, Raman spectroscopy, UV reflectance, spreading resistance profiles, Hall mobility measurements, and both four-point probe and van der Pauw resistivity measurements
Systems and Methods for Inducing Effects in a Signal
A system for inducing an effect in a raw audio signal comprises a computing device for receiving a first audio signal and a second audio signal from a signal source, and the second audio signal comprises the first audio signal induced with an effect. The system further comprises logic that parameterizes the effect in the second audio signal into an artificial neural network (ANN)
In-Situ Diagnostics of Carbon Nanotube Production by Laser Ablation
This presentation involves emission and laser induced fluorescence (LIP) data obtained during carbon nanotube production by double pulse laser oven method. Recent LIP data of nickel indicate longer decay (of the order of few milliseconds) of nickel atomic vapor. This contrasts with less than a millisecond decays of C2 and C3 observed in the plume. The possible role of nickel in the kinetics of carbon nanotube formation will be discussed. Evolution of the laser ablated plume is recorded as plume images which are correlated with the transient emission and LIP dat
At Home/Chez Soi Winnipeg Site: Later Implementation Evaluation Report
Research report. iv, 20 pp., digital file.This report is the second documenting the implementation of the Mental Health Commission of
Canada’s At Home/Chez Soi project in Winnipeg, covering the late 2010 to late 2011 period. It reports
on the changes in program fidelity over this time, and reflects on continued and emerging strengths and
challenges in the implementation of the project. The results demonstrate that, while there are
challenges, there have been many positive results for participants.Mental Health Commission of Canad
The Impact of Beam Variations on Power Spectrum Estimation for 21 cm Cosmology II: Mitigation of Foreground Systematics for HERA
One key challenge in detecting 21 cm cosmological signal at z > 6 is to
separate the cosmological signal from foreground emission. This can be studied
in a power spectrum space where the foreground is confined to low delay modes
whereas the cosmological signal can spread out to high delay modes. When there
is a calibration error, however, chromaticity of gain errors propagates to the
power spectrum estimate and contaminates the modes for cosmological detection.
The Hydrogen Epoch of Reionization Array (HERA) employs a high-precision
calibration scheme using redundancy in measurements. In this study, we focus on
the gain errors induced by nonredundancies arising from feed offset relative to
the HERA's 14 meter parabolic dish element, and investigate how to mitigate the
chromatic gain errors using three different methods: restricting baseline
lengths for calibration, smoothing the antenna gains, and applying a temporal
filter prior to calibration. With 2 cm/2 degree perturbations for
translation/tilting motions, a level achievable under normal HERA operating
conditions, the combination of the baseline cut and temporal filtering
indicates that the spurious gain feature due to nonredundancies is
significantly reduced, and the power spectrum recovers the clean
foreground-free region. We found that the mitigation technique works even for
large feed motions but in order to keep a stable calibration process, the feed
positions need to be constrained to 2 cm for translation motions and 2 degree
for tilting offset relative to the dish's vertex.Comment: Accepted for publication in Ap
Low temperature epitaxial silicon film growth using high vacuum electron-cyclotron-resonance plasma deposition
We report on the growth technique and electrical properties of epitaxial Si films grown at low temperatures using an electron‐cyclotron‐resonance plasma deposition technique. We have used standard high vacuum apparatus to grow high quality films at 450–525 °C. A critical step in achieving high quality films is an in situ hydrogen plasma cleaning of the wafer before growth. We have systematically studied the influence of ion bombardment during growth by biasing the substrate, and find that the films are crystalline for substrate bias voltages less negative than about −15 V, but become polycrystalline as the magnitude of the negative bias is increased. The crystallinity of the film was measured using Raman spectroscopy. The undoped films are n type with carrier concentrations in the 1016–1017 cm−3 range. The Hall mobilities measured for the films are comparable to values obtained in bulk Si crystals. We can achieve abrupt profiles in carrier concentrations between the heavy doped substrate and the epilayer, with no evidence of diffusion.Peer reviewedElectrical and Computer Engineerin
Circadian regulation of mouse suprachiasmatic nuclei neuronal states shapes responses to orexin.
This is the final version of the article. Available from Wiley via the DOI in this record.Our knowledge of how circadian and homeostatic brain circuits interact to temporally organize physiology and behavior is limited. Progress has been made with the determination that lateral hypothalamic orexin (OXA) neurons control arousal and appetitive states, while suprachiasmatic nuclei (SCN) neurons function as the master circadian clock. During the day, SCN neurons exhibit heterogeneity in spontaneous resting membrane potential (RMP), with some neurons becoming severely depolarized (hyperexcited) and ceasing to fire action potentials (APs), while other neurons rest at moderate RMP and fire APs. Intriguingly, the day phase is when the SCN clock is most readily influenced by arousal, but it is unclear if and how heterogeneity in the excitability state of SCN neurons shapes their response to arousal signals, such as OXA. In whole-cell recordings we show that during the day OXA recruits GABA-GABAAreceptor signaling to suppress the RMP of hyperexcited silent as well as moderately hyperpolarized AP-firing SCN neurons. In the AP-firing neurons, OXA hyperpolarized and silenced these SCN cells, while in the hyperexcited silent neurons OXA suppressed the RMP of these cells and evoked either AP-firing, depolarized low-amplitude membrane oscillations, or continued silence at a reduced RMP. These results demonstrate how the resting state of SCN neurons determines their response to OXA, and illustrate that the inhibitory action of this neurochemical correlate of arousal can trigger paradoxical AP firing.We thank the BBSRC (BB/L007665/1) and the Wellcome Trust
(WT092319MA) for project grant funding to H.D.P and M.D.C.B
Herschel-ATLAS: VISTA VIKING near-IR counterparts in the Phase 1 GAMA 9h data
We identify near-infrared Ks band counterparts to Herschel-ATLAS sub-mm
sources, using a preliminary object catalogue from the VISTA VIKING survey. The
sub-mm sources are selected from the H-ATLAS Phase 1 catalogue of the GAMA 9h
field, which includes all objects detected at 250, 350 or 500 um with the SPIRE
instrument. We apply and discuss a likelihood ratio (LR) method for VIKING
candidates within a search radius of 10" of the 22,000 SPIRE sources with a 5
sigma detection at 250 um. We find that 11,294(51%) of the SPIRE sources have a
best VIKING counterpart with a reliability , and the false
identification rate of these is estimated to be 4.2%. We expect to miss ~5% of
true VIKING counterparts. There is evidence from Z-J and J-Ks colours that the
reliable counterparts to SPIRE galaxies are marginally redder than the field
population. We obtain photometric redshifts for ~68% of all (non-stellar)
VIKING candidates with a median redshift of 0.405. Comparing to the results of
the optical identifications supplied with the Phase I catalogue, we find that
the use of medium-deep near-infrared data improves the identification rate of
reliable counterparts from 36% to 51%.Comment: 20 pages, 20 figures, 3 tables, accepted by MNRA
Precise Measurements of Self-absorbed Rising Reverse Shock Emission from Gamma-ray Burst 221009A
The deaths of massive stars are sometimes accompanied by the launch of highly
relativistic and collimated jets. If the jet is pointed towards Earth, we
observe a "prompt" gamma-ray burst due to internal shocks or magnetic
reconnection events within the jet, followed by a long-lived broadband
synchrotron afterglow as the jet interacts with the circum-burst material.
While there is solid observational evidence that emission from multiple shocks
contributes to the afterglow signature, detailed studies of the reverse shock,
which travels back into the explosion ejecta, are hampered by a lack of
early-time observations, particularly in the radio band. We present rapid
follow-up radio observations of the exceptionally bright gamma-ray burst GRB
221009A which reveal an optically thick rising component from the reverse shock
in unprecedented detail both temporally and in frequency space. From this, we
are able to constrain the size, Lorentz factor, and internal energy of the
outflow while providing accurate predictions for the location of the peak
frequency of the reverse shock in the first few hours after the burst.Comment: 11 figures, 4 table
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