Multiple wavelength InGaAs quantum dot lasers using selective area epitaxy

The authors demonstrate multiple wavelength lasers fabricated from InGaAsquantum dots. Selective area epitaxy is used to grow the active region, consisting of five layer stack of InGaAsquantum dots with different band gapenergies in selected regions of the substrate, for fabrication of the lasers. The mechanism responsible for engineering of the band gap of quantum dots is discussed. The performance of the selectively grown lasers is compared to the lasers fabricated from structures grown in a standard, nonselective area growth process.The Australian Research Council is gratefully acknowledged for financial support

Nanophotonic light trapping in solar cells

Nanophotonic light trapping for solar cells is an exciting field that has seen exponential growth in the last few years. There has been a growing appreciation for solar energy as a major solution to the world’s energy problems, and the need to reduce materials costs by the use of thinner solar cells. At the same time, we have the newly developed ability to fabricate controlled structures on the nanoscale quickly and cheaply, and the computational power to optimize the structures and extract physical insights. In this paper, we review the theory of nanophotonic light trapping, with experimental examples given where possible. We focus particularly on periodic structures, since this is where physical understanding is most developed, and where theory and experiment can be most directly compared. We also provide a discussion on the parasitic losses and electrical effects that need to be considered when designing nanophotonic solar cells.This work has been supported by the Australian Research Council and the Australian Solar Institute

Comparing nanowire, multijunction, and single junction solar cells in the presence of light trapping

In this paper we quantify the constraints and opportunities for radial junctionnanowiresolar cells, compared to single junction and multijunction solar cells, when light trapping is included. Both nanowire and multijunction designs are reliant on a very low level of traps in the junction region, and without this, single junction designs are optimal. If low trap density at the junction can be achieved, multijunction cells lead to higher efficiencies than nanowire cells for a given diffusion length, except in the case of submicron diffusion lengths. Thus the radial junctionstructure is not in itself an advantage in general, though if nanowires allow faster deposition or better light trapping than other structures they could still prove advantageous.This work was supported by the Australian Research Council

Asymmetry in photocurrent enhancement by plasmonic nanoparticle arrays located on the front or on the rear of solar cells

We show experimentally that there is asymmetry in photocurrent enhancement by Agnanoparticle arrays located on the front or on the rear of solar cells. The scattering cross-section calculated for front- and rear-located nanoparticles can differ by up to a factor of 3.7, but the coupling efficiency remains the same. We attribute this to differences in the electric field strength and show that the normalized scattering cross-section of a front-located nanoparticle varies from two to eight depending on the intensity of the driving field. In addition, the scattering cross-section of rear-located particles can be increased fourfold using ultrathin spacer layers.This work is financially supported by the Australian Research Council and the Foundation for Fundamental Research on Matter FOM which is supported by NWO, as part of the Joint Solar Program

Designing periodic arrays of metal nanoparticles for light-trapping applications in solar cells

We present criteria for optimizing the light-trapping efficiency of periodic arrays of metal nanoparticles for Si solar cell applications. The scattering cross section of the nanoparticles and the diffraction efficiency of the grating should be maximized in the long wavelength range. The grating pitch should be chosen to allow higher order diffraction modes for long wavelengths while maintaining the highest possible fill factor. These conditions place strong constraints on the optimal parameters (particle size of ∼200 nm and pitch of ∼400 nm) for periodic arrays of metal nanoparticles, in contrast to dielectric gratings, where a relatively wide range of periods and feature sizes can be used for efficient light trapping.The authors acknowledge the A. R. C. and NOW for research conducted at the FOM as a part of the Joint Solar Programme for financial support

Objective structured practical examination as a formative assessment tool for IInd MBBS microbiology students

Background: Assessment drives learning. It is well known that conventional or Traditional Practical Examination (TPE) has several limitations, especially in terms of subjectivity. In OSPE the procedures are standardized, so objectivity is ensured and also reliability maximized. Objectives of the study were to compare TPE & OSPE examination in formative assessment for IInd MBBS microbiology students on the topic culture media and to obtain feedback from students attending OSPE, and faculty.Methods: 76 students were taught about culture media and simultaneously were sensitized about OSPE and TPE, which followed the next week. Informed consent was taken. All students were randomly divided into 2 batches (TPE and OSPE) based on roll call. 71 students were tested, 33 for OSPE and 38 for TPE. Eight OSPE stations were set up with 8 culture media, plus a rest station after station 4. TPE students went for viva-voce to one examiner for same eight culture media. Both OSPE and TPE students were evaluated for a score of 20. OSPE students and the faculty were given a pre-validated questionnaire for feedback.Results: Mean scores, standard deviation (SD) and “p” values were calculated using the T-test from the scores obtained. The mean scores for OSPE and TPE were found to be statistically significant- p-value <0.01. Feedback from OSPE students & faculty was also evaluated.Conclusions: OSPE is more structured and eliminates examiner bias better, and should be practiced in formative assessments and also be introduced in summative assessments

Combination of Cold Atmospheric Plasma and Vitamin C Effectively Disrupts Bacterial Biofilms

Cold atmospheric plasma (CAP) is increasingly used in medical applications for eradication of bacterial and tumorcells. CAP treatment devices, known as plasma jet pens, produce reactive oxygen and nitrogen species atatmospheric pressure and room temperature. The produced reactive species are concentrated in a small andprecisely defined area, allowing for high precision medical treatments. CAP has been demonstrated as very effectiveagainst planktonic bacterial cells. Unfortunately, bacterial cells in biofilms are typically aggregated and protected bydense exopolymeric matrix, synthesized and secreted by the bacterial community. The main limitation in using CAPagainst bacterial biofilms is the thick protective matrix of extracellular polymers that shields bacterial cells within thiscomplex architecture. CAP has also been shown to effectively eradicate tumor cells, but the main current limitation isthe susceptibility of the surrounding healthy tissues to higher doses. We have recently demonstrated that vitamin C,a natural food supplement, can be used to destabilize bacterial biofilms and render them more susceptible to theCAP killing treatment. Here we discuss the possible impact that a pre-treatment with vitamin C could have on CAPapplications in medicine. Specifically, we argue that vitamin C could enhance the effectiveness of CAP treatmentsagainst both the bacterial biofilms and some selected tumors

Controlling the properties of InGaAs quantum dots by selective-area epitaxy

Selective growth of InGaAsquantum dots on GaAs is reported. It is demonstrated that selective-area epitaxy can be used for in-plane bandgap energy control of quantum dots.Atomic force microscopy and cathodoluminescence are used for characterization of the selectively growndots. Our results show that the composition, size, and uniformity of dots are determined by the dimensions of the mask used for patterning the substrate. Properties of dots can be selectively tuned by varying the mask dimensions. A single-step growth of a thin InGaAsquantum well and InGaAsquantum dots on the same wafer is demonstrated. By using a single-step growth,dots luminescing at different wavelengths, in the range 1150–1230nm, in different parts of the same wafer are achieved.The Australian Research Council is gratefully acknowledged for the financial support

Graphene based nanosensor for aqueous phase detection of nitroaromatics

A graphene-based nanosensor was fabricated to selectively detect nitrotriazolone (NTO) molecules with a molecularly imprinted film via simple electrical measurements. Molecularly imprinted polymer comprising chitosan was used as sensitive layer. Gold electrodes for electrical measurements were lithographically fabricated on Si/SiO2 substrate, followed by monolayer graphene transfer and polymeric film coating. Monolayer graphene and molecularly imprinted polymer were characterized by ATR-FTIR, UV-Vis, SEM and Raman spectroscopy. Transfer-length measurements (TLM) indicate that the sensor selectively and linearly responds against aqueous NTO solutions within a wide range of concentration of 0.01-0.1 mg mL(-1) that covers the lowest toxic level of NTO determined by USEPA. This nanosensor with embedded electrodes is re-usable and suitable for field applications, offering real-time electrical measurements unlike current techniques where complex analytics are required

Evolutionary Analysis of the Bacillus subtilis Genome Reveals New Genes Involved in Sporulation

Bacilli can form dormant, highly resistant, and metabolically inactive spores to cope with extreme environmental challenges. In this study, we examined the evolutionary age of Bacillus subtilis sporulation genes using the approach known as genomic phylostratigraphy. We found that B. subtilis sporulation genes cluster in several groups that emerged at distant evolutionary time-points, suggesting that the sporulation process underwent several stages of expansion. Next, we asked whether such evolutionary stratification of the genome could be used to predict involvement in sporulation of presently uncharacterized genes (y-genes). We individually inactivated a representative sample of uncharacterized genes that arose during the same evolutionary periods as the known sporulation genes and tested the resulting strains for sporulation phenotypes. Sporulation was significantly affected in 16 out of 37 (43%) tested strains. In addition to expanding the knowledge base on B. subtilis sporulation, our findings suggest that evolutionary age could be used to help with genome mining