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Two segments of horizontally grown crystalline ZnO nanorods (NRs) connected with
an amorphous layer have been successfully and reproducibly synthesized using
one-step hydrothermal technique by controlling the growth rate. The confocal
photoluminescence (PL) imaging and spectroscopy of twin ZnO NRs at different
temperatures shows intense red emission with comparably week UV emission. The
strong red emission from the twin NRs is a consequence of structural
imperfections. Both UV and red bands showed signatures of strong temperature
dependent exciton-phonon scattering. Using the intensity ratio of the UV and red
emissions, we show that the individual ZnO NRs can be used as highly sensitive
cryogenic temperature sensors below ∼175 K.
It is unclear whether the concepts and findings of the underlying neurobiology of adult psychopathy apply to youths as well. If so, a life span approach to treatment should be taken. Because youths’ brains are still developing, interventions at an early age may be far more effective in the long run. The aim of this systematic review is to examine whether the neurocognitive and neurobiological factors that underlie juvenile psychopathy, and specifically callous–unemotional (CU) traits, are similar to those underlying adult psychopathy. The results show that youths with CU traits show lower levels of prosocial reasoning, lower emotional responsivity, and decreased harm avoidance. Brain imaging studies in youths with CU traits are still rare. Available studies suggest specific neural correlates, such as a reduced response of the amygdala and a weaker functional connectivity between the amygdala and the ventromedial prefrontal cortex. These findings are largely in line with existing theories of adult psychopathy, such as the dual-hormone serotonergic hypothesis and the integrated emotions systems theory. We recommend that future studies investigate the role of oxytocin, invest in the study of neural mechanisms, and study the precursors, risk factors, and correlates of CU traits in early infancy and in longitudinal designs.
Recently, proportional mean residual life model has received a lot of attention after the importance of the model was discussed by Zahedi . In this paper, we define dynamic proportional mean residual life model and study its properties for different aging classes. The closure of this model under different stochastic orders is also discussed. Many examples are presented to illustrate different properties of the model.
Attention-deficit hyperactivity disorder (ADHD) is linked to increased risk for substance use disorders and nicotine dependence.
To examine the effects of stimulant treatment on subsequent risk for substance use disorder and nicotine dependence in a prospective longitudinal ADHD case–control study.
At baseline we assessed ADHD, conduct disorder and oppositional defiant disorder. Substance use disorders, nicotine dependence and stimulant treatment were assessed retrospectively after a mean follow-up of 4.4 years, at a mean age of 16.4 years.
Stimulant treatment of ADHD was linked to a reduced risk for substance use disorders compared with no stimulant treatment, even after controlling for conduct disorder and oppositional defiant disorder (hazard ratio (HR) = 1.91, 95% Cl 1.10−3.36), but not to nicotine dependence (HR = 1.12, 95% Cl 0.45−2.96). Within the stimulant-treated group, a protective effect of age at first stimulant use on substance use disorder development was found, which diminished with age, and seemed to reverse around the age of 18.
Stimulant treatment appears to lower the risk of developing substance use disorders and does not have an impact on the development of nicotine dependence in adolescents with ADHD.
The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an unprecedented opportunity to investigate the transient sky at radio wavelengths. In this paper we present VAST, an ASKAP survey for Variables and Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP to enable the discovery and investigation of variable and transient phenomena from the local to the cosmological, including flare stars, intermittent pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar scintillation, radio supernovae, and orphan afterglows of gamma-ray bursts. In addition, it will allow us to probe unexplored regions of parameter space where new classes of transient sources may be detected. In this paper we review the known radio transient and variable populations and the current results from blind radio surveys. We outline a comprehensive program based on a multi-tiered survey strategy to characterise the radio transient sky through detection and monitoring of transient and variable sources on the ASKAP imaging timescales of 5 s and greater. We also present an analysis of the expected source populations that we will be able to detect with VAST.
Post-conflict mental health studies in low-income countries have lacked
pre-conflict data to evaluate changes in psychiatric morbidity resulting
from political violence.
This prospective study compares mental health before and after exposure
to direct political violence during the People's War in Nepal.
An adult cohort completed the Beck Depression Inventory and Beck Anxiety
Inventory in 2000 prior to conflict violence in their community and in
2007 after the war.
Of the original 316 participants, 298 (94%) participated in the
post-conflict assessment. Depression increased from 30.9 to 40.6%.
Anxiety increased from 26.2 to 47.7%. Post-conflict post-traumatic stress
disorder (PTSD) was 14.1%. Controlling for ageing, the depression
increase was not significant. The anxiety increase showed a dose–response
association with conflict exposure when controlling for ageing and daily
stressors. No demographic group displayed unique vulnerability or
resilience to the effects of conflict exposure.
Conflict exposure should be considered in the context of other types of
psychiatric risk factors. Conflict exposure predicted increases in
anxiety whereas socioeconomic factors and non-conflict stressful life
events were the major predictors of depression. Research and
interventions in postconflict settings therefore should consider
differential trajectories for depression v. anxiety and
the importance of addressing chronic social problems ranging from poverty
to gender and ethnic/caste discrimination.
We report white light emission from ZnO nanostructures in powder form, prepared by microwave irradiation-assisted chemical synthesis, in the presence of a structure directing agent. Determination of their crystallinity, actual shape, and orientation was made using X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and optical properties have been studied through photoluminescence (PL), measured using He-Cd laser (325 nm) as the excitation source. There is a noticeable variation in the luminescence correlated with variation of process parameters, such as microwave power, duration of irradiation, and the type/concentration of surfactants. The CIE (Commission Internationale l’Eclairage) diagram shows that the luminescence lies in yellow region of the color space. As the luminescence from the powder of ZnO lies in the yellow region, it is possible to produce white light from the powder of ZnO by using a blue laser as the excitation source.
We describe a method for predicting detection limits of minority
elements in electron energy loss spectroscopy (EELS), and its
implementation as a software package that gives quantitative
predictions for user-specified materials and experimental
conditions. The method is based on modeling entire energy loss
spectra, including shot noise as well as instrumental noise,
and taking into account all the relevant experimental parameters.
We describe the steps involved in modeling the entire spectrum,
from the zero loss up to inner shell edges, and pay particular
attention to the contributions to the pre-edge background. The
predicted spectra are used to evaluate the signal-to-noise ratios
(SNRs) for inner shell edges from user-specified minority elements.
The software also predicts the minimum detectable mass (MDM)
and minimum mass fraction (MMF). It can be used to ascertain
whether an element present at a particular concentration should
be detectable for given experimental conditions, and also to
quickly and quantitatively explore ways of optimizing the
experimental conditions for a particular EELS analytical task.
We demonstrate the usefulness of the software by confirming
the recent empirical observation of single atom detection using
EELS of phosphorus in thin carbon films, and show the effect
on the SNR of varying the acquisition parameters. The case of
delta-doped semiconductors is also considered as an important
example from materials science where low detection limits and
high spatial resolution are essential, and the feasibility of
such characterization using EELS is assessed.
Conjugated polymers are intensively pursued as candidate materials for emission and detection devices with the optical range of interest determined by the chemical structure. On the other hand the optical range for emission and detection can also be tuned by size selection in semiconductor nanoclusters. The mechanisms for charge generation and separation upon optical excitation, and light emission are different for these systems. Hybrid systems based on these different class of materials reveal interesting electronic and optical properties and add further insight into the individual characteristics of the different components. Multilayer structures and blends of these materials on different substrates were prepared for absorption, photocurrent (Iph), photoluminescence (PL) and electroluminscence (EL) studies. Polymers chosen were derivatives of polythiophene (PT) and polyparaphenylenevinylene (PPV) along with nanoclusters of cadmium sulphide of average size 4.4 nm (CdS-44). The photocurrent spectral response in these systems followed the absorption response around the band edges for each of the components and revealed additional features, which depended on bias voltage, thickness of the layers and interfacial effects. The current-voltage curves showed multi-component features with emission varying for different regimes of voltage. The emission spectral response revealed additive features and is discussed in terms of excitonic mechanisms.
In this article we define the s-order equilibrium distribution of a life distribution and establish some interesting properties regarding moments for s-order equilibrium distributions. Results are expected to be useful in reliability and renewal processes.
Recently new partial orderings s-SFR, s-FR, s-ST, s-CV and s-CX have been defined in the literature. These are more general in the sense that most of the earlier known partial orderings reduce to particular cases of these orderings. Moreover, these orderings have helped in defining a new and useful ageing criterion. In this paper, we discuss preservation properties of these orderings under mixtures. Results are expected to be useful in engineering and reliability, where mixtures of distributions arise naturally in numerous situations. Moreover, existing results, specifically for LR, FR and ST orderings under the operation of mixtures, reduce to special cases.
Under a joint development contract with Applied Materials (AMAT) and Texas Instruments (TI), SEMATECH undertook a project (Joint Development Project J100) with a goal of delivering a cost effective, technically advanced Rapid Thermal Processor (RTP). The RTP tool was specified to meet the present and future manufacturing needs of SEMATECH's member companies. The J100 results contained here will focus on the temperature and control performance of the AMAT RTP tool. The J100 results on the temperature measurement and control performance of AMAT's RTP tool using bare backside monitor wafers were presented in part I. In actual manufacturing environments the backside conditions of wafers are not consistent which causes temperature variations during rapid thermal processing. In this experiment, boron monitor wafers with varying backside conditions were used to test the uniformity, repeatability, and stability of the tool. The wafer backside films were fabricated using predictions from emissivity models and were subsequently verified by experimental techniques. In addition, perturbation experiments utilizing boron and arsenic implanted wafers demonstrated a high degree of localized temperature control across the wafers. A 3-sigma temperature variation ranging from 3.0 °C (for wafers with similar backside films) to 6.0 °C (for wafers with varying backside films) was found for all wafers processed during this evaluation. The perturbation experiments, which included a forced temperature offset of two degrees at one of the wafer temperature sensors, resulted in a noticeable change in sheet resistance across the wafer.
Under a joint development contract with Applied Materials (AMAT) and Texas Instruments (TI), SEMATECH undertook a project (Joint Development Project J100) with a goal of delivering a cost effective, technically advanced Rapid Thermal Processor (RTP). The RTP tool was specified to meet the present and future manufacturing needs of SEMATECH's member companies. The J100 results contained here will focus on the temperature and control performance of the AMAT RTP tool. The evaluation methodology included passive data collection (PDC) to check the tool stability, screening experiments to isolate the variable interaction and to define the process window, broad range and narrow range sensitivity studies to determine the sheet resistance dependence on thermal budget for small increments in temperature set point, perturbation experiments to determine localized control, and stability experiments to check for drift and process repeatability. The impact of wafer emissivity on source/drain rapidthermal annealing was evaluated by processing wafers with varying backside films. The PDC experiments demonstrated the tool to be stable. Screening experiments revealed the strong effect of temperature, followed by time, and time-temperature interaction on sheet resistance. Boron implanted (p+/n) wafers were found to be sensitive at a temperature of 1025 °C or less for a 10 second anneal whereas arsenic implanted wafers (n+/p) showed greater sensitivity at temperatures ranging from 1025 °C to 1100 °C for a 10 second anneal.
The nucleation and growth characteristics of CVD-W on Ti/TiN barrier layers with SiH4 and H2 reduction chemistries are presented. In particular, the reaction between WF6 (precursor used for depositing W) and the underlying Ti of the barrier stack was studied to better understand the chemistry of ‘volcano’ formation - a phenomena that causes severe defects in the deposited W film. Ti/TiN processing parameters and stack thicknesses were varied, along with the CVD-W deposition chemistry (gas flows, pressures, temperatures and times), to evaluate film properties and characteristics after SiH4 passivation, nucleation and full W plug deposition. The analysis was augmented with cross-sectional Scanning Electron Microscopy (SEM) on short-loop testers and films were characterized using Rutherford Backscattering Spectroscopy (RBS), Secondary Ion Mass Spectroscopy (SIMS), X-ray Diffraction (XRD) and Auger Electron Spectroscopy (AES) techniques. Several processing conditions are recommended for ‘volcano-free’ and ‘defect-free’ CVD-W films.
Sputtered deposited titanium films on silicon substrates were used to study the effects of first rapid thermal anneal temperature, duration of anneal time and thickness of the titanium films for TiSi2 formation. A central composite, coupled with a cross design was used to analyze response surface. Empirical models were developed and contour plots were generated to describe the outcome of the first anneal. A window of operation to control the process of titanium silicide formation was recommended. Response surface analysis of data revealed an operating window of ±10° C for RTA1 for stable TiSi2 formation. Within this window of operation, the within wafer uniformity was found to be at its minimum. Anneal time was found to have minimum effect on the variability although sheet resistance decreases monotonically with increasing anneal time. Thickness of titanium films were found to be very critical in determining final TiSi2 thickness as determined by RBS and/or XRF techniques.
The crystallization of LPCVD a-Si by Rapid Thermal Anneal was investigated. RTA polysilicon films can find application in the fabrication of TFTs for AMLCDs, due to the lower thermal budget associated with fast crystallization at high temperatures. It was found that the grain size of the crystallized films decreases with the temperature, in the range of 700°C to 1100°C, while for higher temperatures the opposite trend is observed. The latter observation was attributed to the high thermal vibration of subcritical clusters, that was assumed responsible for the decline in the nuclei population at high annealing temperatures, combined with the faster crystalline growth rate at high temperatures. RTA silicon films were found to have lower intra-grain defect density, that may result in the improvement of the electrical characteristics of the polysilicon films.
Self aligned refractory metal silicides such as titanium disilicide have been used extensively in VLSI and ULSI structures. Unlike earlier work which has relied on undoped substrates and a single implant species, in the present study TiSi2 formation on phosphorous doped poly-Si in the presence of multiple dopants has been investigated. TEM micrographs are discussed which show the difference in silicide formation for the case of the BF2 and arsenic implanted samples. We have found that the presence of fluorine in the BF2 implant retards the silicide formation for phosphorous doped poly-Si substrates. Additionally, the effect of substrate grain size on TiSi2 formation has been investigated using undoped α-Si and poly-Si substrates.
This work describes process development of various kinds of compound sidewall spacer in submicron CMOS technology to improve gate oxide (GOX) leakage characteristics. This is attained by minimizing the impact of gate-level defects (GLDs) caused by in-process particle incorporation. Transistor characteristics did not suffer from this new sidewall spacer process.