V. Ng

Observation of memory effect in germanium nanocrystals embedded in an amorphous silicon oxide matrix of a metal–insulator– semiconductor structure

The memory effect of a trilayer structure (rapid thermal oxide/Ge nanocrystals in SiO2/sputtered SiO2) was investigated via capacitance versus voltage (C–V) measurements. The Ge nanocrystals were synthesized by rapid thermal annealing of the cosputtered Ge+SiO2 films. The memory effect was manifested by the hysteresis in the C–V curve. Transmission electron microscope and C–V results indicated that the hysteresis was due to Ge nanocrystals in the middle layer of the trilayer structure.

Raman characterization of germanium nanocrystals in amorphous silicon oxide films synthesized by rapid thermal annealing

Raman characterization of germanium (Ge) nanocrystals embedded in amorphous silicon oxide (a-SiO2) films synthesized by rapid thermal annealing (RTA) has been carried out. The samples were prepared by cosputtering Ge and SiO2 targets using a rf magnetron sputtering machine. Ge nanocrystals can only be obtained from samples sputtered with six pieces of Ge attached to the SiO2 target. For samples annealed at different RTA temperatures, the Raman spectra indicated a transition from amorphous to nanocrystalline Ge when annealed between 600 and 750 °C. The spectra were analyzed in terms of phonon confinement model and the estimated nanocrystal size was between 20 and 66 A. A minimum annealing time of 160 s at 750 °C was necessary for Ge nanocrystal formation. Strong visible broadband photoluminescence was observed from the nanocrystals and the photoluminescence showed a blueshift with decrease in the nanocrystal size. The effect of compressive stress on nanocrystal growth was examined by varying the rampup and...

Properties and applications of cobalt-based material produced by electron-beam-induced deposition

The deposition of cobalt-containing material from dicobalt octacarbonyl using a focused electron beam is reported. The material contains between 30% and 50% (atomic) cobalt, with the balance being carbon and oxygen, and comprises nanocrystalline metallic grains embedded in a carbonaceous matrix. Arches bridging two electrodes were fabricated to allow current–voltage (I–V) measurements to be conducted. The material resistivity decreases strongly with the deposition beam current, with values as low as 45 μΩ cm being attainable. Material growth by indirect irradiation is found to give rise to material of high resistivity and can result in highly resistive arches. At low temperatures, three distinctive conduction regimes are observed, with the I–V characteristics flattening out at the origin. At 20 K step-like features suggestive of Coulomb- blockade effects were observed. Magnetic force microscope (MFM) images of the material indicates that it is ferromagnetic in nature. The application of the technique and ...

Self perceived work related stress and the relation with salivary IgA and lysozyme among emergency department nurses

Aims: To assess and compare the self perceived work related stress among emergency department (ED) and general ward (GW) nurses, and to investigate its relation with salivary IgA and lysozyme. Methods: One hundred and thirty two of 208 (63.5%) registered female ED and GW nurses participated in the study. A modified mental health professional stress scale (PSS) was used to measure self perceived stress. ELISA methods were used to determine the salivary IgA and lysozyme levels. Results: On PSS, ED nurses had higher scores (mean 1.51) than GW nurses (1.30). The scores of PSS subscales such as organisational structure and processes (OS), lack of resources (RES), and conflict with other professionals (COF) were higher in ED than in GW nurses. ED nurses had lower secretion rates of IgA (geometric mean (GM) 49.1 μg/min) and lysozyme (GM 20.0 μg/min) than GW nurses (68.2 μg/min, 30.5 μg/min). Significant correlations were observed between PSS and log IgA and lysozyme secretion rates. OS, RES, and COF were correlated with log IgA and lysozyme levels. Conclusion: ED nurses, who reported a higher level of professional stress, showed significantly lower secretion rates of salivary IgA and lysozyme compared to GW nurses. Salivary IgA and lysozyme were inversely correlated with self perceived work related stress. As these salivary biomarkers are reflective of the mucosal immunity, results support the inverse relation between stress and mucosal immunity.

Fabrication and characterization of bit-patterned media beyond 1.5?Tbit/in2

We fabricated bit-patterned media (BPM) at densities as high as 3.3 Tbit/in(2) using a process consisting of high-resolution electron-beam lithography followed directly by magnetic film deposition. By avoiding pattern transfer processes such as etching and liftoff that inherently reduce pattern fidelity, the resolution of the final pattern was kept close to that of the lithographic step. Magnetic force microscopy (MFM) showed magnetic isolation of the patterned bits at 1.9 Tbit/in(2), which was close to the resolution limit of the MFM. The method presented will enable studies on magnetic bits packed at ultra-high densities, and can be combined with other scalable patterning methods such as templated self-assembly and nanoimprint lithography for high-volume manufacturing.

Microstructural and photoluminescence studies of germanium nanocrystals in amorphous silicon oxide films

Ge nanocrystal growth in amorphous silicon oxide film was studied using the transmission electron microscopy and x-ray photoelectron spectroscopy techniques. The as-sputtered sample contained mainly GeO2 and Ge suboxides. GeO2 and/or suboxides dissociate when rapid thermal annealed and provide Ge for nanocrystal formation. Nanocrystals of similar size (∼60 A in diameter) were obtained when annealed at 800 °C. Nanocrystals with diameters of 200–280 A consisting of multiple twin structures near the Si–SiO2 interface were observed when annealed at 1000 °C. The twin structure was attributed to the enhanced diffusion of Ge at 1000 °C and the short annealing time. Our photoluminescence (PL) results show that the best PL response was obtained with samples that exhibit uniform nanocrystal size.Ge nanocrystal growth in amorphous silicon oxide film was studied using the transmission electron microscopy and x-ray photoelectron spectroscopy techniques. The as-sputtered sample contained mainly GeO2 and Ge suboxides. GeO2 and/or suboxides dissociate when rapid thermal annealed and provide Ge for nanocrystal formation. Nanocrystals of similar size (∼60 A in diameter) were obtained when annealed at 800 °C. Nanocrystals with diameters of 200–280 A consisting of multiple twin structures near the Si–SiO2 interface were observed when annealed at 1000 °C. The twin structure was attributed to the enhanced diffusion of Ge at 1000 °C and the short annealing time. Our photoluminescence (PL) results show that the best PL response was obtained with samples that exhibit uniform nanocrystal size.

Are salivary immunoglobulin A and lysozyme biomarkers of stress among nurses

Salivary immunoglobulin A (IgA) and lysozyme have been studied as possible biomarkers of stress. This study examined the stress levels among female nurses in various units and the relationship between these stress levels and salivary IgA and lysozyme secretion. One hundred ninety-five (43%) of 457 eligible female nurses from surgical wards/operating theaters (SURG), medical wards (MED), and outpatient clinics/day-surgery theaters (OPD) completed a self-administered questionnaire. From this group of 195 nurses, 124 provided a salivary sample accumulated over 5 minutes. Stress levels were assessed with a ten-point Stress Assessment Score (SAS) for Asians and a direct question on perceived life stress. Enzyme-linked immunosorbent assay and lyso-plate methods were used to determine salivary IgA and lysozyme levels. Forty-five percent of SURG, 35% of MED, and 17% of OPD nurses scored at least four points on the SAS. SURG nurses had the lowest IgA secretion (geometric mean; 95% confidence interval [CI]) rates (43 micrograms/min; 36 to 51 micrograms/min). The other groups had significantly higher salivary IgA secretion rates: MED (96 micrograms/min; 80 to 116 micrograms/min) and OPD (77 micrograms/min; 60 to 98 micrograms/min) Findings for salivary lysozyme (microgram/min) were similar; SURG (9 micrograms/min; 6 to 13 micrograms/min) MED (19 micrograms/min; 12 to 28 micrograms/min) and OPD (16 micrograms/min; 9 to 28 micrograms/min). The salivary IgA (Spearmans r = -0.22, P = 0.01) but not the lysozyme (Spearmans r = -0.01, P = 0.9) secretion rate correlated negatively with SAS. Nurses working in various units under different conditions experienced dissimilar levels of stress. Salivary IgA, but not lysozyme, correlated inversely with self-reported levels of stress. It may thus be a potential biomarker in future studies on stress.

Germanium diffusion and nanocrystal formation in silicon oxide on silicon substrate under rapid thermal annealing

The effect of rapid thermal annealing temperature on the diffusion of silicon (Si) and germanium (Ge) and the formation of Ge nanocrystals in a silicon oxide matrix was investigated. The formation of Ge nanocrystals was attributed mainly to the reduction of Ge suboxides by Si diffused from the Si substrate. For samples annealed at 800°C, the nanocrystals were uniform in size and distributed evenly in the bulk of the oxide but became denser nearer to the silicon–silicon oxide (Si–SiO2) interface. When the sample was annealed at 900°C, two regions with different nanocrystal densities and size distributions separated by a region void of nanocrystals were observed. The region of denser nanocrystals was located near the Si–SiO2 interface. For annealing at 1000°C, nanocrystals were only observed at the Si–SiO2 interface and these have significant size variation, with the rest of the oxide being void of nanocrystals. The nanocrystals formed at 900 and 1000°C were generally found to be defective.

EXAMINATION STRESS, SALIVARY CORTISOL, AND ACADEMIC PERFORMANCE

Immediately before and after participation in a written final examination, 11 graduate students rated their self-perceived stress and provided saliva samples for cortisol assay. Students rated stress higher before the examination, and these ratings were associated with increased salivary cortisol. Students who reported higher stress and had higher cortisol levels before the examination tended to have significantly lower examination scores.

Can salivary lead be used for biological monitoring of lead exposed individuals

Background: Measurement of blood lead (BPb) is the usual method for biomonitoring of persons exposed to inorganic lead. Aim: To explore the use of salivary lead (SPb) as an alternative. Methods: BPb and SPb levels were measured in a group of 82 lead exposed adults. Results: The mean BPb of the workers was 26.6 μg/dl (SD 8.6, range 10–48) and the mean SPb level 0.77 μg/dl, or 3% of the BPb level. As the SPb distribution was skewed, logarithmic transformation was performed to normalise the distribution. A bivariate scattergram of BPb and logSPb (r = 0.41, p = 0.00) had a line of best fit expressed as BPb = 29.7 + 8.95logSPb. The relation of logSPb and BPb was stronger among non-smokers (r = 0.42) compared to smokers (r = 0.3); and among those without a medical condition (r = 0.44). Multiple linear regression analysis (fitting smoking and medical condition into the model) yielded an R of 0.54, and an adjusted R2 of 0.26. Conclusion: The study findings do not support the use of SPb for biomonitoring at BPb levels ranging from 10 to 50 μg/dl.