Spectroscopy of novel light emitting silicon-based diodes

In this thesis, a working novel silicon light emitting diode is demonstrated. Light emission in silicon has been intensively studied since the 1950s when crystalline silicon was recognized as the dominant material in microelectronics. Although room-temperature emission in silicon has been achieved recently, integration for advanced ultra large scale integration is problematic due to poor external quantum efficiency and manufacturing complexity. With the aim of improving the light emission in silicon, rare-earth deposited silicon and impurity-implanted silicon were studied in this work. Rare-earth erbium has been deposited on crystalline silicon by the laser ablation technique. Sharp, intense room-temperature photoluminescence at 1.54 #mu#m was observed for all annealed samples. The thermal quenching factor measured between 80 K to room temperature is less than 2 which is unseen in the past for crystalline based silicon. However, electroluminescence is only obtainable below 160 K for devices fabricated using the similar concepts. Results from photo luminescence excitation spectroscopy proved that excitation from the silicon band-edge recombination is responsible for the erbium emission. Photoluminescence frequency resolved spectroscopy showed that all the samples exhibited a rather long, temperature independent, luminescence lifetime of 90 #+-# 10 #mu#s. Another approach is carried out to study the light emission in silicon by ion implantation. Samples were produced by low energy boron implantation with various doses up to 2 x 10"1"5 cm"-"2 followed by rapid thermal annealing at around 950 deg. C. Strong intrinsic silicon band-edge photoluminescence at #approx#1.15 #mu#m was observed. Light-emitting diode was made using similar implant and annealing conditions. At room temperature, sharp intense intrinsic silicon electroluminescence is observed with an efficiency of > 2 x 10"-"6, measured under a forward biased current of 30 mA. This anomalous luminescence increases with temperature by a factor of #approx#3 from 80 K to room temperature. TEM shows numerous dislocation loops of interstitial or vacancy type which are related to this silicon band-edge emission. The silicon band-edge emission is also achieved for arsenic-implanted light-emitting diodes during this research period. (author)Available from British Library Document Supply Centre-DSC:DXN035987 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Gait velocity and joint power generation after stroke: Contribution of strength and balance

Objective The aim of the study was to assess the degree to which isometric strength of multiple lower limb muscle groups and balance is associated with gait velocity and joint power generation during gait after stroke. Design Sixty-three participants in a multisite, multinational, cross-sectional, observational study underwent assessment of gait velocity (10-m walk test), standing balance (computerized posturography), and isometric strength (hand-held dynamometry). Twenty-seven participants had joint power generation assessed (three-dimensional gait analysis). Bivariate associations were examined using Spearman’s correlations. Regression models with partial F tests were used to compare the contribution to gait between measures. Results Although all muscle groups demonstrated significant associations with gait velocity (ρ = 0.40–0.72), partial F tests identified that ankle plantar flexor and hip flexor strength made the largest contribution to gait velocity. Ankle plantar flexor strength also had strong associations with habitual and fast-paced ankle power generation (ρ = 0.65 and 0.75). Balance had significant associations with habitual and fast gait velocity (ρ = −0.57 and −0.53), with partial F tests showing that the contribution was independent of strength. Conclusions Ankle plantar flexor and hip flexor strength had the largest contribution to gait velocity. Future research may wish to refocus strength assessment and treatment to target the ankle plantar flexors and hip flexors

Spontaneous miscarriage in first trimester pregnancy is associated with altered urinary metabolite profile

Threatened miscarriage is the most common gynecological emergency, occurring in about 20% of pregnant women. Approximately one in four of these patients go on to have spontaneous miscarriage and the etiology of miscarriage still remains elusive. In a bid to identify possible biomarkers and novel treatment targets, many studies have been undertaken to elucidate the pathways that lead to a miscarriage. Luteal phase deficiency has been shown to contribute to miscarriages, and the measurement of serum progesterone as a prognostic marker and the prescription of progesterone supplementation has been proposed as possible diagnostic and treatment methods. However, luteal phase deficiency only accounts for 35% of miscarriages. In order to understand the other causes of spontaneous miscarriage and possible novel urine biomarkers for miscarriage, we looked at the changes in urinary metabolites in women with threatened miscarriage. To this end, we performed a case-control study of eighty patients who presented with threatened miscarriage between 6 and 10 weeks gestation. Urine metabolomics analyses of forty patients with spontaneous miscarriages and forty patients with ongoing pregnancies at 16 weeks gestation point to an impaired placental mitochondrial β-oxidation of fatty acids as the possible cause of spontaneous miscarriage. This study also highlighted the potential of urine metabolites as a non-invasive screening tool for the risk stratification of women presenting with threatened miscarriage.MOH (Min. of Health, S’pore)Published versio

Quorum Quenching Revisited—From Signal Decays to Signalling Confusion

In a polymicrobial community, while some bacteria are communicating with neighboring cells (quorum sensing), others are interrupting the communication (quorum quenching), thus creating a constant arms race between intercellular communication. In the past decade, numerous quorum quenching enzymes have been found and initially thought to inactivate the signalling molecules. Though this is widely accepted, the actual roles of these quorum quenching enzymes are now being uncovered. Recent evidence extends the role of quorum quenching to detoxification or metabolism of signalling molecules as food and energy source; this includes “signalling confusion”, a term coined in this paper to refer to the phenomenon of non-destructive modification of signalling molecules. While quorum quenching has been explored as a novel anti-infective therapy targeting, quorum sensing evidence begins to show the development of resistance against quorum quenching