Structure- and composition-dependent electron field emission from nitrogenated carbon nanotips

The electron field emission (EFE) properties of nitrogenated carbon nanotips (NCNTPs) were studied under high-vacuum conditions. The NCNTPs were prepared in a plasma-assisted hot filament chemical vapor deposition system using CH4 and N2 as the carbon and nitrogen sources, respectively. The work functions of NCNTPs were measured using x-ray photoelectron spectroscopy. The morphological and structural properties of NCNTPs were studied by field emission scanning electron microscopy, micro-Raman spectroscopy, and x-ray photoelectron spectroscopy. The field enhancement factors of NCNTPs were calculated using relevant EFE models based on the Fowler-Nordheim approximation. Analytical characterization and modeling results were used to establish the relations between the EFE properties of NCNTPs and their morphology, structure, and composition. It is shown that the EFE properties of NCNTPs can be enhanced by the reduction of oxygen termination on the surface as well as by increasing the ratio of the NCNTP height to the radius of curvature at its top. These results also suggest that a significant amount of electrons is emitted from other surface areas besides the NCNTP tops, contrary to the common belief. The outcomes of this study advance our knowledge on the electron emission properties of carbonnanomaterials and contribute to the development of the next-generation of advanced applications in the fields of micro- and opto-electronics.

Composition-dependent structural and electronic properties of α-(Si1−xCx)3N4

The highly unusual structural and electronic properties of the α-phase of (Si1-xCx)3N4 are determined by density functional theory (DFT) calculations using the Generalized Gradient Approximation (GGA). The electronic properties of α-(Si 1-xCx)3N4 are found to be very close to those of α-C3N4. The bandgap of α-(Si 1-xCx)3N4 significantly decreases as C atoms are substituted by Si atoms (in most cases, smaller than that of either α-Si3N4 or α-C3N4) and attains a minimum when the ratio of C to Si is close to 2. On the other hand, the bulk modulus of α-(Si1-xCx)3N 4 is found to be closer to that of α-Si3N 4 than of α-C3N4. Plasma-assisted synthesis experiments of CNx and SiCN films are performed to verify the accuracy of the DFT calculations. TEM measurements confirm the calculated lattice constants, and FT-IR/XPS analysis confirms the formation and lengths of C-N and Si-N bonds. The results of DFT calculations are also in a remarkable agreement with the experiments of other authors.

Temperature-dependent properties of nc-Si thin films synthesized in low-pressure, thermally nonequilibrium, high-density inductively coupled plasmas

Silicon thin films were synthesized simultaneously on single-crystal silicon and glass substrates by lowpressure, thermally nonequilibrium, high-density inductively coupled plasma-assisted chemical vapor deposition from the silane precursor gas without any additional hydrogen dilution in a broad range of substrate temperatures from 100 to 500 °C. The effect of the substrate temperature on the morphological, structural and optical properties of the synthesized silicon thin films is systematically studied by X-ray diffractometry, Raman spectroscopy, UV-vis spectroscopy, and scanning electron microscopy. It is shown that the formation of nanocrystalline silicon (nc-Si) occurs when the substrate temperature is higher than 200 °C and that all the deposited nc-Si films have a preferential growth along the (111) direction. However, the mean grain size of the (111) orientation slightly and gradually decreases while the mean grain size of the (220) orientation shows a monotonous increase with the increased substrate temperature from 200 to 500 °C. It is also found that the crystal volume fraction of the synthesized nc-Si thin films has a maximum value of ∼69.1% at a substrate temperature of 300 rather than 500 °C. This rather unexpected result is interpreted through the interplay of thermokinetic surface diffusion and hydrogen termination effects. Furthermore, we have also shown that with the increased substrate temperature from 100 to 500 °C, the optical bandgap is reduced while the growth rates tend to increase. The maximum rates of change of the optical bandgap and the growth rates occur when the substrate temperature is increased from 400 to 500 °C. These results are highly relevant to the development of photovoltaic thin-film solar cells, thin-film transistors, and flat-panel displays.

Fire performance and design of load bearing light gauge steel frame wall systems exposed to realistic design fires

This paper presents the fire performance results of light gauge steel frame (LSF) walls lined with single and double plasterboards, and externally insulated with rock fibre insulation as obtained using a finite element analysis based parametric study. A validated numerical model was used to study the influence of various fire curves developed for a range of compartment characteristics. Data from the parametric study was utilized to develop a simplified method to predict the fire resistance ratings of LSF walls exposed to realistic design fire curves. Further, this paper also presents the details of suitable fire design rules based on current cold-formed steel standards and the modifications proposed by previous researchers. Of these the recently developed design rules by Gunalan and Mahendran [1] were investigated to determine their applicability to predict the axial compression strengths and fire resistance ratings (FRR) of LSF walls exposed to realistic design fires. Finally, the stud failure times obtained from fire design rules and finite element studies were compared for LSF walls lined with single and double plasterboards, and externally insulated with rock fibres under realistic design fire curves.

Fire resistance rating of light gauge steel frame walls exposed to realistic design fires : a review and development of time equivalent approach

This paper presents the details of research undertaken on the development of an energy based time equivalent approach for light gauge steel frame (LSF) walls. This research utilized an energy based time equivalent approach to obtain the fire resistance ratings (FRR) of LSF walls exposed to realistic design fires with respect to standard fire exposure [1]. It is based on the equal area concept of fire severity and relates to the amount of energy transferred to the member. The proposed method was used to predict the fire resistance of single and double plasterboard lined and externally insulated LSF walls. The predicted fire resistance ratings were compared with the results from finite element analyses and fire design rules for three different wall configurations. This paper presents the review of the available time equivalent approaches and the development of energy based time equivalent approach for the prediction of fire resistance ratings of LSF walls exposed to realistic design fires.

Asymptotic minimax robust and misspecified Lorden quickest change detection for dependent stochastic processes

The quick detection of an abrupt unknown change in the conditional distribution of a dependent stochastic process has numerous applications. In this paper, we pose a minimax robust quickest change detection problem for cases where there is uncertainty about the post-change conditional distribution. Our minimax robust formulation is based on the popular Lorden criteria of optimal quickest change detection. Under a condition on the set of possible post-change distributions, we show that the widely known cumulative sum (CUSUM) rule is asymptotically minimax robust under our Lorden minimax robust formulation as a false alarm constraint becomes more strict. We also establish general asymptotic bounds on the detection delay of misspecified CUSUM rules (i.e. CUSUM rules that are designed with post- change distributions that differ from those of the observed sequence). We exploit these bounds to compare the delay performance of asymptotically minimax robust, asymptotically optimal, and other misspecified CUSUM rules. In simulation examples, we illustrate that asymptotically minimax robust CUSUM rules can provide better detection delay performance at greatly reduced computation effort compared to competing generalised likelihood ratio procedures.

Determination of strain-rate-dependent mechanical behavior of living and fixed osteocytes and chondrocytes using atomic force microscopy and inverse finite element analysis

The aim of this paper is to determine the strain-rate-dependent mechanical behavior of living and fixed osteocytes and chondrocytes, in vitro. Firstly, Atomic Force Microscopy (AFM) was used to obtain the force-indentation curves of these single cells at four different strain-rates. These results were then employed in inverse finite element analysis (FEA) using Modified Standard neo-Hookean Solid (MSnHS) idealization of these cells to determine their mechanical properties. In addition, a FEA model with a newly developed spring element was employed to accurately simulate AFM evaluation in this study. We report that both cytoskeleton (CSK) and intracellular fluid govern the strain-rate-dependent mechanical property of living cells whereas intracellular fluid plays a predominant role on fixed cells’ behavior. In addition, through the comparisons, it can be concluded that osteocytes are stiffer than chondrocytes at all strain-rates tested indicating that the cells could be the biomarker of their tissue origin. Finally, we report that MSnHS is able to capture the strain-rate-dependent mechanical behavior of osteocyte and chondrocyte for both living and fixed cells. Therefore, we concluded that the MSnHS is a good model for exploration of mechanical deformation responses of single osteocytes and chondrocytes. This study could open a new avenue for analysis of mechanical behavior of osteocytes and chondrocytes as well as other similar types of cells.

Controlled electroluminescence of n-ZnMgO/p-GaN light-emitting diodes

Effective control of room-temperature electroluminescence of n-ZnMgO/p-GaN light-emitting diodes (LEDs) over both emission intensity and wavelength is demonstrated. With varied Mg concentration, the intensity of LEDs in the near-ultraviolet region is increased due to the effective radiative recombination in the ZnMgO layer. Furthermore, the emission wavelength is shifted to the green/yellow spectral region by employing an indium-tin-oxide thin film as the dopant source, where thermally activated indium diffusion creates extra deep defect levels for carrier recombination. These results clearly demonstrate the effectiveness of controlled metal incorporation in achieving high energy efficiency and spectral tunability of the n-ZnMgO/p-GaN LED devices.

Raman-active wurtzite CdO nanophase and phonon signatures in CdO/ZnO heterostructures fabricated by nonequilibrium laser plasma ablation and stress control

A combination of laser plasma ablation and strain control in CdO/ZnO heterostructures is used to produce and stabilize a metastable wurtzite CdO nanophase. According to the Raman selection rules, this nanophase is Raman-active whereas the thermodynamically preferred rocksalt phase is inactive. The wurtzite-specific and thickness/strain-dependent Raman fingerprints and phonon modes are identified and can be used for reliable and inexpensive nanophase detection. The wurtzite nanophase formation is also confirmed by x-ray diffractometry. The demonstrated ability of the metastable phase and phonon mode control in CdO/ZnO heterostructures is promising for the development of next-generation light emitting sources and exciton-based laser diodes.

Control of cell cycle progression by phosphorylation of cyclin-dependent kinase (CDK) substrates

The eukaryotic cell cycle is a fundamental evolutionarily conserved process that regulates cell division from simple unicellular organisms, such as yeast, through to higher multicellular organisms, such as humans. The cell cycle comprises several phases, including the S-phase (DNA synthesis phase) and M-phase (mitotic phase). During S-phase, the genetic material is replicated, and is then segregated into two identical daughter cells following mitotic M-phase and cytokinesis. The S- and M-phases are separated by two gap phases (G1 and G2) that govern the readiness of cells to enter S- or M-phase. Genetic and biochemical studies demonstrate that cell division in eukaryotes is mediated by CDKs (cyclin-dependent kinases). Active CDKs comprise a protein kinase subunit whose catalytic activity is dependent on association with a regulatory cyclin subunit. Cell-cycle-stage-dependent accumulation and proteolytic degradation of different cyclin subunits regulates their association with CDKs to control different stages of cell division. CDKs promote cell cycle progression by phosphorylating critical downstream substrates to alter their activity. Here, we will review some of the well-characterized CDK substrates to provide mechanistic insights into how these kinases control different stages of cell division.

Visible-light-induced selective photocatalytic oxidation of benzylamine into imine over supported Ag/AgI photocatalysts

Titanate nanotubes (TNT) supported AgI nanoparticles were prepared by a two-step method: the deposition of Ag2O on titanate nanotubes from AgNO3 solution and the subsequent I-adsorption process from NaI solution. It is found that the supported AgI samples exhibited excellent photoactivity for the selective oxidation of benzylamine to the corresponding imine under visible light illumination and the photocatalyst can be used for many times without apparent activity loss. X-ray diffraction studies, transmission electron microscopy, diffuse reflectance UV-Vis spectroscopy and nitrogen adsorption measurements were used for the characterization of the as-prepared and recycled AgI samples. It is found that under visible light irradiation, AgI partially decomposed to produce Ag/AgI nanostructure and thus stabilized. The photoactivity of supported Ag/AgI for the selective oxidation of benzylamine was studied in terms of the light intensity, wavelength, temperature and substituent. It is proposed that the formation of plasmonic Ag nanoparticles should be responsible for the high activity and selectivity.

BDNF SNPs are implicated in comorbid alcohol dependence in schizophrenia but not in alcohol-dependent patients without schizophrenia

Aims The functional BDNF single nucleotide polymorphism (SNP) rs6265 has been associated with many disorders including schizophrenia and alcohol dependence. However, studies have been inconsistent, reporting both positive and negative associations. Comorbid alcohol dependence has a high prevalence in schizophrenia so we investigated the role of rs6265 in alcohol dependence in Australian populations of schizophrenia and alcohol dependent patients. Methods Two BDNF SNPs rs6265 and a nearby SNP rs7103411 were genotyped in a total of 848 individuals. These included a schizophrenia group (n = 157) and a second schizophrenia replication group (n = 235), an alcohol dependent group (n = 231) that had no schizophrenia diagnosis and a group of healthy controls (n = 225). Results Allelic association between rs7103411 and comorbid alcohol dependence was identified (P = 0.044) in the primary schizophrenia sample. In the replication study, we were able to detect allelic associations between both BDNF SNPs and comorbid alcohol dependence (rs6265, P = 0.006; rs7103411, P = 0.014). Moreover, we detected association between both SNPs and risk-taking behaviour after drinking (rs6265, P = 0.005; rs7103411, P = 0.009) and we detected strong association between both SNPs and alcohol dependence in males (rs6265, P = 0.009; rs7103411, P = 0.013) while females showed association with multiple behavioural measures reflecting repetitive alcohol consumption. Haplotype analysis revealed the rs6265-rs7103411 A/C haplotype is associated with comorbid alcohol dependence (P = 0.002). When these SNPs were tested in the non-schizophrenia alcohol dependent group we were unable to detect association. Conclusion We conclude that these BDNF SNPs play a role in development of comorbid alcohol dependence in schizophrenia while our data does not indicate that they play a role in alcohol dependent patients who do not have schizophrenia.

Nanomorphology influence on the light conversion mechanisms in highly efficient diketopyrrolopyrrole based organic solar cells

In this work, diketopyrrolopyrrole-based polymer bulk heterojunction solar cells with inverted and regular architecture have been investigated. The influence of the polymer:fullerene ratio on the photoactive film nanomorphology has been studied in detail. Transmission Electron Microscopy and Atomic Force Microscopy reveal that the resulting film morphology strongly depends on the fullerene ratio. This fact determines the photocurrent generation and governs the transport of free charge carriers. Slight variations on the PCBM ratio respect to the polymer show great differences on the electrical behavior of the solar cell. Once the polymer:fullerene ratio is accurately adjusted, power conversion efficiencies of 4.7% and 4.9% are obtained for inverted and regular architectures respectively. Furthermore, by correlating the optical and morphological characterization of the polymer:fullerene films and the electrical behavior of solar cells, an ad hoc interpretation is proposed to explain the photovoltaic performance as a function of this polymer:blend composition.

Cubic silsesquioxanes for use in solution processable organic light emitting diodes (OLED)

Commercial products using organic light emitting diode (OLED) display technology have begun to appear in cell phones, mp3 players and even televisions. One key area that has allowed and will allow for this technology to continue its ascension into the flat panel display and lighting markets is materials R and D. From this perspective, recent progress in cubic silsesquioxane (SSQ) based materials may provide some new advantageous properties well suited for OLEDs. In this feature article we provide an overview of recent progress in the synthesis, characterization and implementation of SSQ-based materials with properties well suited for application in solution processable organic/polymer electronics, specifically OLEDs.

Photophysical characterization of light-emitting poly(indenofluorene)s

Time-resolved photoluminescence spectroscopy experiments of three poly(2,8-indenofluorene) derivatives bearing different pendant groups are presented. A comparison of the photophysical properties of dilute solutions and thin films provides information on the chemical purity of the materials. The photophysical properties of poly(2,8-indenofluorene)s are correlated with the morphological characteristics of their corresponding films. Wide-angle X-ray scattering experiments reveal the order in these materials at the molecular level. The spectroscopic results confirm the positive impact of a new synthetic approach on the spectral purity of the poly(indenofluorene)s. It is concluded that complete side-chain substitution of the bridgehead carbon atoms C-6 and C-12 in the indenofluorene unit, prior to indenofluorene ring formation, reduces the probability of keto formation. Due to the intrinsic chemical purity of the arylated derivative, identification of a long-delayed spectral feature, other than the known keto band, is possible in the case of thin films. Controlled doping experiments on the arylated derivative with trace amounts of an indenofluorene-monoketone provide quantitative information on the rates of two major photophysical processes, namely, singlet photoluminescence emission and singlet photoluminescence quenching. These results allow the determination of the minimum keto concentration that can affect the intrinsic photophysical properties of this polymer. The data suggest that photoluminescence quenching operates in the doped films according to the Stern-Volmer formalism.