Characterisation and optimisation of PECVD SiNx as an antireflection coating and passivation layer for silicon solar cells

In this work, we investigate how the film properties of silicon nitride (SiNx) depend on its deposition conditions when formed by plasma enhanced chemical vapour deposition (PECVD). The examination is conducted with a Roth & Rau AK400 PECVD reactor, where the varied parameters are deposition temperature, pressure, gas flow ratio, total gas flow, microwave plasma power and radio-frequency bias voltage. The films are evaluated by Fourier transform infrared spectroscopy to determine structural properties, by spectrophotometry to determine optical properties, and by capacitance–voltage and photoconductance measurements to determine electronic properties. After reporting on the dependence of SiNx properties on deposition parameters, we determine the optimized deposition conditions that attain low absorption and low recombination. On the basis of SiNx growth models proposed in the literature and of our experimental results, we discuss how each process parameter affects the deposition rate and chemical bond density. We then focus on the effective surface recombination velocity S eff, which is of primary importance to solar cells. We find that for the SiNx prepared in this work, 1) S eff does not correlate universally with the bulk structural and optical properties such as chemical bond densities and refractive index, and 2) S eff depends primarily on the defect density at the SiNx-Si interface rather than the insulator charge. Finally, employing the optimized deposition condition, we achieve a relatively constant and low S eff,UL on low-resistivity (≤1.1 Ωcm) p- and n-type c-Si substrates over a broad range of n = 1.85–4.07. The results of this study demonstrate that the trade-off between optical transmission and surface passivation can be circumvented. Although we focus on photovoltaic applications, this study may be useful for any device for which it is desirable to maximize light transmission and surface passivation.This work was supported by an Australian Research Council Linkage between The Australian National University and Braggone Oy under Grant LP0989593

Invited commentary on Stewart and Davis " 'Big data' in mental health research-current status and emerging possibilities"

No abstract available

Form and function of the craniomandibular complex in subterranean rodents

Rodents are the most speciose mammalian order and are represented in arboreal, semiaquatic, subterranean and terrestrial niches. To flourish in such environments, rodents must exhibit morphological traits that can reflect functions that are needed to survive. This thesis focuses on the functional morphology of digging subterranean rodents and in particular, African mole-rats (Bathyergidae). Species dependent, subterranean rodents dig using a number of different methods. This thesis concentrates on the morphological differences in the craniomandibular complex in scratch digging and chisel-tooth digging subterranean rodents. Scratch digging rodents use only their claws to remove softer soil whilst their chisel-tooth digging counterparts use their incisors in concert with their powerful masticatory muscles to remove harder soils.Chapter two looks at morphological traits associated with bite force and gape in African mole-rats (Bathyergidae). The study shows that chisel-tooth digging rodents have morphological traits that are associated with a larger bite force at wider gapes, which is probably achieved by having a temporalis with a greater mechanical advantage.Chapter three examines a selection of chisel-tooth digging, scratch digging and terrestrial rodents. It shows that the upper incisors of chisel-tooth digging rodents have a larger radius of curvature. Also, it shows that chisel-tooth digging rodent cranial shape converges in morphospace and covaries with the upper incisors, although these results were not significant when phylogeny was accounted for.Chapter four shows that, using finite element analysis, the cranium of a chisel-tooth digging mole-rat can create larger bite forces at wider gapes, compared to a scratch digging mole-rat. Using a novel method of combining geometric morphometrics with finite element analysis, this study also shows that the cranium of the chisel-tooth digging rodent deforms less, making it more efficient at performing chisel-tooth digging tasks.Overall, this thesis shows that the craniomandibular form of subterranean rodents can be strongly influenced by function. The digging method used by a subterranean rodent is therefore important to how they have evolved.[Thesis also includes article published in:Biological journal of the Linnean Societyhttp://onlinelibrary.wiley.com/doi/10.1111/bij.12691/fullDOI: 10.1111/bij.12691

Doctor of Philosophy

dissertationCyanobactins are N-to-C macrocyclic peptides that contain diverse modifications such as heterocyclization of Cys, Ser, or Thr, and isoprenylation of Ser, Thr, and Tyr. Although the above can be inferred to occur based on the final products, none of the enzymatic steps en route to cyanobactin biosynthesis had been characterized prior to this work. Indeed, until very recently, nothing at all was known about cyanobactin biosynthesis. Only after cloning and sequencing of the genetic elements required for cyanobactin biosynthesis was their biosynthetic origin deduced. Surprisingly, these complex natural products are biosynthesized by extensive posttranslational modification of ribosomally synthesized precursor peptides. As noted, these precursors are initially synthesized on the ribosome. Following ribosomal synthesis, various modifying enzymes carry out posttranslational modification of the aforementioned amino acids, as well as proteolysis of the precursor peptide to liberate 6-12 amino acid peptidyl groups, which are then macrocyclized. However, the manner in which the disparate genetic components required for cyanobactin biosynthesis functioned enzymatically to create these highly diverse and medicinally interesting compounds was unknown prior to this work. Herein the results of several studies that elucidate the steps en route to cyanobactin biosynthesis are described. The characterized steps include: N- and C-terminal proteolysis, macrocyclization, heterocyclization of Cys, Ser, and Thr, and prenylation of Ser, Thr and Tyr

Skills and Liquidity Barriers to Youth Employment: Medium-term Evidence from a Cash Benchmarking Experiment in Rwanda

We present results of an experiment benchmarking a workforce training program against cash transfers for underemployed young adults in Rwanda. 3.5 years after treatment, the training program enhances productive time use and asset investment, while the cash transfers drive productive assets, livestock values, savings, and subjective well-being. Both interventions have powerful effects on entrepreneurship. But while labor, sales, and profits all go up, the implied wage rate in these businesses is low. Our results suggest that credit is a major barrier to self-employment, but deeper reforms may be required to enable entrepreneurship to provide a transformative pathway out of poverty

Using Household Grants to Benchmark the Cost Effectiveness of a USAID Workforce Readiness Program

We use a randomized experiment to compare a workforce training program to cash transfers in Rwanda. Conducted in a sample of poor and underemployed youth, this study measures the impact of the training program not only relative to a control group but relative to the counterfactual of simply disbursing the cost of the program directly to beneficiaries. While the training program was successful in improving a number of core outcomes (productive hours, assets, savings, and subjective well-being), cost-equivalent cash transfers move all these outcomes as well as consumption, income, and wealth. In the head-to-head costing comparison cash proves superior across a number of economic outcomes, while training outperforms cash only in the production of business knowledge. We find little evidence of complementarity between human and physical capital interventions, and no signs of heterogeneity or spillover effects

Can tournaments induce rational play in the centipede game? Exploring dominance vs. strategic uncertainty

We compare behavior in a one-shot Centipede game across several payoff structures including nonlinear payoff tournaments. Assuming Nash to be optimal, results suggest nonlinear tournament payoffs based on overall relative rewards are not sufficient to increase Nash results in the one-shot Centipede style setting. Evidence suggests that reducing strategic uncertainty is more important than increasing dominance in promoting Nash play.Centipede game, payoff tournaments, experiment, strategic uncertainty, dominance