Journal of Physics D: Applied Physics

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ISSN / EISSN : 0022-3727 / 1361-6463
Published by: IOP Publishing (10.1088)
Total articles ≅ 30,897
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Katharine I Hunter, Himashi P Andaraarachchi,
Journal of Physics D: Applied Physics; https://doi.org/10.1088/1361-6463/ac2695

Abstract:
Enhanced optical properties of silicon quantum dots are pertinent for the light emitting applications including luminiscent solar cell concetrators. Surface passivation plays a crucial role in improving photoluminiscent quantum yield and effective carrier lifetimes of silicon nanocrystals and is often achieved by surface grafting of organic ligands. However, organically passivated silicon quantum dots often suffer from a deterioration of the optical properties when exposed to the environment In this work, we explore the effect of an inorganic amorphous silicon nitride shell (SiNx) on silicon quantum dots and their optical properties. Utilizing a dual plasma appraoch with dual injection ports, we synthesized Si/SiNx core-shell nanoparticles using SiH4, NH3, H2, and Ar. The core-shell nanocrystals were characterized using optical and structural methods, which revealed higher nitridation plasma powers could lead to Si precipiation altering the composition of silicon nitride shell. While as-synthesized Si/SiNx core-shell nanocrystals did not exhibit photoluminiscence, oxidized Si/SiNx core-shell nanocrystals show significantly higher quantum yield (35%) and longer carrier lifetime compared to bare oxidized Si analogues even after enviromental exposure for six months.
Yue Bai, Limin Gu, Xiaole Wang, Zhenyu Huang
Journal of Physics D: Applied Physics; https://doi.org/10.1088/1361-6463/ac2692

Abstract:
Effective control of the sound source directly is the fundamental solution to the noise problem. Herein, we propose a passive, non-closed, and remote scheme for omnidirectional reduction of the sound power radiated from vibrating sources. The physical mechanism of this scheme is to design an acoustic superscatterer based upon the idea of transformation media so that the virtual boundary of the acoustic superscatterer can overlap with the radiation boundary of the sound source to construct drastic multiple scattering effects. Through theoretical analyses and numerical simulations, we confirm the effectiveness of adopting the acoustic superscatterer to significantly suppress the sound radiation power generated by some typical dipolar sources in the air. Our study shows that by arranging no more than two acoustic superscatterers at the designed positions away from a dipolar thin rod, about 90% of the sound radiation power, i.e., 10 dB, can be suppressed in all directions of the dipole axis. This preliminary work would enlighten the research of using passive methods to achieve non-contact omnidirectional noise control of vibrating sources.
, Francesco Piva, Carlo de Santi, Matteo Buffolo, Camille Haller, Jean-Francois Carlin, Nicolas Grandjean, , Enrico Zanoni, Matteo Meneghini
Journal of Physics D: Applied Physics; https://doi.org/10.1088/1361-6463/ac2693

Abstract:
We investigate the density of defects and the degradation rate in InGaN light-emitting diodes having identical dislocation density and epitaxial structure, but different indium content in the quantum well (QW, 12 %, 16 %, 20 %). Our results, based on combined steady-state photocapacitance, light-capacitance voltage, and degradation measurements indicate that: (i) the density of defects in the superlattice underlayer is identical for the three wafers, indicating good and reproducible growth conditions; (ii) the density of defects within the active region of the devices shows a monotonic dependence on the indium content in the quantum wells. These results, consistent with previous studies on the topic, prove unequivocally the important role of indium in favouring the incorporation of point defects, further clarifying the possible mechanisms of defect formation, and give a quantitative assessment of the related effect; (iii) in step-stress experiments, the degradation rate was found to be much stronger for devices having high indium content in the QW. This result can be explained by considering a decrease in injection efficiency due to the generation or transport of defects, or an increment in defect-assisted Auger recombination terms due to the propagation of defects.
, Pegah Eslami, Ghazal Afrasiabpour, Hossein Mirmiranpoor,
Journal of Physics D: Applied Physics; https://doi.org/10.1088/1361-6463/ac2530

Abstract:
Various electrical stimulation applications have been investigated in scientific literature of medicine, such as relieving pain, stimulating blood flow, and promoting wound healing. This study aims at observing the effects of a pulsed electric field (PEF) on advanced glycation end products (AGEs), oxidative stress, and inflammation in diabetes via in vitro and in vivo assays. An in vitro study was carried out to measure the impacts of PEF with an intensity of 7 KV on the function and structure of glycated superoxide dismutase (SOD) through enzymatic activity assay, and circular dichroism (CD), and fluorescence spectroscopy, respectively. For the in vivo experiment, diabetic mice were affected by PEF, and several indices relating to diabetes, including blood glucose level, advanced glycation end products (AGEs), antioxidant activity, oxidative stress biomarkers, and inflammation factors were studied. The result of in vitro assay demonstrated that PEF could modify glycated SOD structure, which this modification could be due to the rearrangement of dipole moments of glycated protein constituents. This modification leads to an 83 % and 31 % increase in enzymatic activity of in vitro and in vivo assays, respectively. The in vivo assessment results show a decrease in oxidative stress biomarkers indices, AGEs content, and inflammatory cytokines concentrations. The study's result unveiled that PEF would be effective in diabetes therapy and could be employed as a complementary method.
, Neha Gupta, Vinay Kumar, Ajay Kumar
Journal of Physics D: Applied Physics; https://doi.org/10.1088/1361-6463/ac24cb

Abstract:
Multi-layer ceramic capacitors with high recoverable energy storage density and large energy efficiency play a crucial in modern electronic devices. Various ferroelectric ceramic materials with relaxor characteristics and large dielectric constant are the most favorable candidates for achieving superior energy storage performance. Herein, a novel lead-free (1-x)Ba0.80Ca0.20TiO3-x(Bi0.80Mg0.20)(Ti0.65Mg0.30)O3 (BCT-BMT) ceramic materials were prepared by two-stage mechano-chemical activation technique. BMT substitution in Ca modified BaTiO3 has resulted in substantial improvement in microstructural characteristics and subsequently an improvement in energy storage performance in comparison to pure BCT. The introduction of BMT in BCT has resulted in transformation into relaxor ceramics, which is vital for obtaining high recoverable energy storage density and large energy efficiency. In the present investigation, the composition with 0.65BCT-0.35BMT shows a typical relaxor characteristic along with large breakdown strength and substantially large dielectric constant. As a result of improvement in electrical properties, the composition 0.65BCT-0.35BMT possesses an ultra-high recoverable energy density of 3.09 J/cm3 along with a moderately high energy efficiency of ~80.15%. The obtained results indicate the effectiveness of BMT substitution on the energy storage properties and excellent compatibility between BCT and BMT phases.
Sayan Prodhan, Kamlesh Kumar Chauhan, Manobina Karmakar, Anima Ghosh, Sayan Bhattacharyya,
Journal of Physics D: Applied Physics; https://doi.org/10.1088/1361-6463/ac24c7

Abstract:
Organic-inorganic halide perovskite has emerged as the front-runner of absorber materials for highly efficient solar cells in the recent years. Incorporation of metallic (Au, Ag) nano-particles (NP) within the perovskite contributes towards effective tuning of their opto-electronic properties via enhancing the channels of solar energy transfer and promotion of carrier transport. Placing dielectric shell over metal nanoparticle further enhances the carrier mobility and reduces the carrier recombination in semiconductor material. Here, we have extensively investigated the effect of [email protected] core-shell nanocrystal (NC) on hot carrier cooling dynamics and excited carrier recombination dynamics in bulk MAPbI3-XClX perovskite using femtosecond transient absorption spectroscopy with temporal and spectral resolution of 120 fs and 0.8 nm respectively. Hot carrier (HC) cooling dynamics indicates the formation of longitudinal optical (LO) phonon within first 0.6ps and a delayed conversion of LO phonon to longitudinal acoustic (LA) phonon from 8 ps to 15.87 ps due to incorporation of [email protected] core-shell nanocrystal (NC) in bulk perovskite. Delayed conversion of LO-LA phonon confirms the presence of enhanced "hot phonon bottleneck" effect in modified bulk perovskite. Further, the investigation of carrier recombination dynamics shows that at a fixed pump fluence of 3.19 μJ/cm2, - the rate constants decrease nearly one order of magnitude for (i) Auger recombination (from 1.2x10-32 cm6s-1 to 1.7x10-34 cm6s-1), (ii) band to band recombination (from 8 x 10-14 cm3s-1 to 8 x 10-15 cm3s-1) and (iii) trap state recombination (from 5.5x108 μs-1 to 5x107μs-1) after the modification of bulk perovskite by [email protected] core-shell nanocrystal (NC). Our study reveals the presence of enhanced hot phonon bottleneck effect and reduced recombination rate constants in [email protected] core-shell NC modified perovskite that paves the way for the development of highly efficient perovskite based solar cell.
, Jennifer Selvidge, Eamonn T Hughes, Justin Norman, Chen Shang, Robert W Herrick, John E Bowers
Journal of Physics D: Applied Physics; https://doi.org/10.1088/1361-6463/ac24c9

Abstract:
Misfit dislocations classically form at interfaces when an epitaxially strained film exceeds a critical thickness. We show that metastable misfit dislocations also form between layers nominally below critical thickness with respect to each other when externally driven threading dislocations have significant dissimilarities in dislocation mobility in these layers controlled by glide kinetics. The InAs quantum dot laser on silicon presents a technologically important case for this phenomenon where threading dislocations are pinned by indium-containing regions but glide in GaAs or AlGaAs cladding regions driven by thermal expansion mismatch strain with silicon during sample cool down following growth. This generates long misfit dislocations adjacent to the active region that is responsible for gradual degradation in performance. We calculate the driving force for misfit dislocation formation and its dynamics in model structures, building up to full lasers, and describe the design of intentionally introduced indium-containing trapping layers that displace the misfit dislocations away from the active region, which is key to long laser lifetime. We show that factors controlling dislocation glide kinetics: doping, indium alloying, and dislocation core character have a strong influence on the final structure of defects. Yet, the introduction of indium must be done with care, illustrated using two cases where indium is not useful to overall device defect engineering.
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