R-3 Repository :: Browsing by Author "Yang, Jian"

Browsing by Author "Yang, Jian"

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Applications of Nanophotonic Photothermal Effects and Their Theoretical Modeling
(2019-11-15) Yang, Jian; Nordlander, Peter
Many of the fascinating applications of nanophotonics utilize the photothermal effects in which nanophotonic resonances enhance optical absorption and generate heat. The resulting high temperature in nanostructures has been applied in water purification, medical treatment and chemical reactions. However, theoretical modeling of nanophotonic thermal effects is often challenging because of the involved multi-physical processes. Here, we demonstrate three novel applications of nanophotonic photothermal effects with a particular emphasis on theoretical modeling: plasmon-accelerated photothermal curing of epoxy, optical-force-dominated directional reshaping of photothermally softened nanoparticles, and photothermoelectric effect in a semiconductor device. Our models successfully explained the experimental findings and gave us deeper understanding of the nanoscale photothermal systems.
Comparison study of ring current simulations with and without bubble injections
(Wiley, 2016) Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.
For many years, stand-alone ring current models have been successfully producing storm time ring current enhancements without specifying explicit localized transient injections along their outer boundaries. However, both observations and simulations have suggested that the frequent burst flows or bubble injections can contribute substantially to the storm time ring current energy. In this paper, we investigate the difference in the spatial and temporal development of the ring current distribution with and without bubble injections using the Rice Convection Model-Equilibrium. The comparison study indicates that the simulation with bubble effects smoothed out along geosynchronous orbit can predict approximately the same large-scale ring current pressure distribution and electric potential pattern as the simulation with bubble effects included. Our results suggest that the increase of the hot plasma population along geosynchronous orbit can be envisaged as an integrated effect of bubble injections from the near-Earth plasma sheet. However, the observed fluctuations in the plasma population and electric field can only be captured when the mesoscale injections are included in the simulation. We also confirmed again that adiabatic convection of fully populated flux tubes cannot inject the ring current from the middle plasma sheet. The paper provides a justification for using stand-alone ring current models in the inner magnetosphere to simulate magnetic storms, without explicit consideration of bubbles and magnetic buoyancy effects inside geosynchronous orbit.
Current Sheet Thinning in the Wake of a Bubble Injection
(Wiley, 2022) Wang, Wenrui; Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.; Nakamura, Rumi; Cui, Jun
A crucial property of the substorm growth phase is the current sheet thinning, which is often attributed to adiabatic convection. Injecting low-entropy bubbles reduce pressure-balance inconsistencies and restore current sheet thickness to its initial value. Recent observations from Cluster and MMS showed additional thinning of the current sheet in the wake of a transitory bubble injection compared with the configuration before the injection. We employ the Rice Convection Model-MHD coupled code to investigate how the transport of bubbles causes the fast thinning. The simulation results reconstructed the observations' most prominent characteristics. We find more earthward transport of the magnetic flux in the bubble than its wake, therefore depleting magnetic flux and stretching the magnetic field lines there. Interestingly, additional R0-sense field-aligned currents close the enhanced dawn-to-dusk current behind the bubble.
Giant photothermoelectric effect in silicon nanoribbon photodetectors
(Springer Nature, 2020) Dai, Wei; Liu, Weikang; Yang, Jian; Xu, Chao; Alabastri, Alessandro; Liu, Chang; Nordlander, Peter; Guan, Zhiqiang; Xu, Hongxing; Laboratory for Nanophotonics
The photothermoelectric (PTE) effect enables efficient harvesting of the energy of photogenerated hot carriers and is a promising choice for high-efficiency photoelectric energy conversion and photodetection. Recently, the PTE effect was reported in low-dimensional nanomaterials, suggesting the possibility of optimizing their energy conversion efficiency. Unfortunately, the PTE effect becomes extremely inefficient in low-dimensional nanomaterials, owing to intrinsic disadvantages, such as low optical absorption and immature fabrication methods. In this study, a giant PTE effect was observed in lightly doped p-type silicon nanoribbons caused by photogenerated hot carriers. The open-circuit photovoltage responsivity of the device was 3-4 orders of magnitude higher than those of previously reported PTE devices. The measured photovoltage responses fit very well with the proposed photothermoelectric multiphysics models. This research proposes an application of the PTE effect and a possible method for utilizing hot carriers in semiconductors to significantly improve their photoelectric conversion efficiency.
Harmonic light-generating metasurface
(2022-11-15) Semmlinger, Michael; Tseng, Ming-lun; Yang, Jian; Zhang, Ming; Tsai, Din Ping; Dong, Liangliang; Ahmadivand, Arash; Nordlander, Peter; Halas, Naomi Jean; Rice University; William Marsh Rice University; Academia Sinica; United States Patent and Trademark Office
A harmonic light-generating metasurface includes a base substrate and a plurality of structures, that include nonlinear material, that are disposed in a pattern on a surface of the base substrate. Each structure of the plurality of structures individually supports a magnetic dipole mode. An electromagnetic field enhancement of the magnetic dipole mode induces generation of a harmonic signal by the plurality of structures. Alternatively, a harmonic light-generating metasurface, includes a base substrate, a supporting substrate that includes a nonlinear material, and a plurality of paired structures disposed in a pattern on a surface of the supporting substrate. Each paired structure, of the plurality of paired structures, collectively supports a toroidal dipole mode. An electromagnetic field enhancement of the toroidal dipole mode penetrates the supporting substrate to induce generation of a harmonic signal by the supporting substrate.
Inner magnetospheric modeling during geomagnetic active times
(2010) Yang, Jian; Toffoletto, Frank R.
In this thesis we show that the entropy parameter PV5/3 , where P is the pressure and V is the volume of a flux tube with unit magnetic flux, plays a central role in the earthward plasma convection from the near- and middle-Earth plasma sheet to the inner magnetosphere. This work presents a series of numerical simulations, investigating the relationship between the value of PV5/3 and the different features of plasma earthward transport that occur during different types of events in geomagnetic active times. The simulations are conducted using the Rice-Convection-Model (RCM) and the Rice-Convection-Model-Equilibrium (RCM-E) that have carefully designed boundary conditions to simulate the effect of various values of PV 5/3. In Chapter 3 we present results of an RCM simulation of a sawtooth event where it is found that a dramatic reduction of PV5/3 on the boundary along a wide range of local times produces interchange convection in the inner magnetosphere and drives spatially quasi-periodic Birkeland currents that suggest an explanation for the finger-like aurora usually observed during this type of event. In Chapter 4 we present results of an RCM-E simulation of an isolated substorm, which is done by imposing depleted PV5/3 (a bubble) in the expansion phase. The results of this simulation reproduce typical features of a substorm and agree fairly well with multipoint observations. Chapter 6 presents a detailed analysis of the RCM-E expansion phase simulation which indicates that the reconfigurations of PV5/3, plasma pressure and magnetic field in an idealized bubble injection event can be quite complicated. Chapter 7 presents results of a superposed epoch study using Geotail data showing that the time variations of PV 5/3 are different in isolated substorms, pseudo-breakups and convection bay events, suggesting that bubbles have different characteristics in different modes of earthward transport. We follow this up with three corresponding RCM-E simulations by representing a sustained bubble, a transient bubble and sustained low PV5/3 plasma along the boundary. The simulations are roughly consistent with theoretical suggestions, superposed epoch results and some other observations. These simulations provide a systematic description of inner magnetospheric configuration during various active events, suggesting the temporal and spatial characteristics of PV5/3 in the plasma sheet as a key in the magnetospheric convection.
Nanophotonic Resonances Accelerate Epoxy Glue Curing and Enhance Deep UV Second Harmonic Generation
(2018-04-13) Yang, Jian; Nordlander, Peter
Nanophotonics, the science of controlling light at the nanoscale, has many important applications in energy harvesting, sensing, display technologies and even in the medical field. Metallic and dielectric nanoparticles support plasmonic and dielectric resonances respectively, and both enhance light-matter interaction at the nanoscale. Here, one application for each type is presented. The first part demonstrates plasmon-accelerated curing of epoxy glue, a popular industrial bonding material. Curing within a relatively short time scale was realized when gold nanoparticles whose plasmonic resonance coincides with the illumination wavelength were embedded. A theoretical model was built and the influence of relevant parameters was investigated. In the second part, I demonstrate dielectric resonance enhanced second harmonic generation (SHG) in the deep ultra violet (DUV). A zinc oxide (ZnO) nanostructure was designed to have a magnetic dipole resonance at 394nm. It enhances the SHG and produces a DUV signal around 197nm. In addition, I propose a novel nonlinear simulation method capable of calculating absolute SHG intensity and study the effect of symmetry breaking. To the best of my knowledge, this is the bluest wavelength achieved with SHG in a dielectric nanostructure.
On the contribution of plasma sheet bubbles to the storm time ring current
(Wiley, 2015) Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.; Sazykin, Stanislav
Particle injections occur frequently inside 10 Re during geomagnetic storms. They are commonly associated with bursty bulk flows or plasma sheet bubbles transported from the tail to the inner magnetosphere. Although observations and theoretical arguments have suggested that they may have an important role in storm time dynamics, this assertion has not been addressed quantitatively. In this paper, we investigate which process is dominant for the storm time ring current buildup: large-scale enhanced convection or localized bubble injections. We use the Rice Convection Model-Equilibrium (RCM-E) to model a series of idealized storm main phases. The boundary conditions at 14–15 Re on the nightside are adjusted to randomly inject bubbles to a degree roughly consistent with observed statistical properties. A test particle tracing technique is then used to identify the source of the ring current plasma. We find that the contribution of plasma sheet bubbles to the ring current energy increases from ~20% for weak storms to ~50% for moderate storms and levels off at ~61% for intense storms, while the contribution of trapped particles decreases from ~60% for weak storms to ~30% for moderate and ~21% for intense storms. The contribution of nonbubble plasma sheet flux tubes remains ~20% on average regardless of the storm intensity. Consistent with previous RCM and RCM-E simulations, our results show that the mechanisms for plasma sheet bubbles enhancing the ring current energy are (1) the deep penetration of bubbles and (2) the bulk plasma pushed ahead of bubbles. Both the bubbles and the plasma pushed ahead typically contain larger distribution functions than those in the inner magnetosphere at quiet times. An integrated effect of those individual bubble injections is the gradual enhancement of the storm time ring current. We also make two predictions testable against observations. First, fluctuations over a time scale of 5–20 min in the plasma distributions and electric field can be seen in the central ring current region for the storm main phase. We find that the plasma pressure and the electric field EY there vary over about 10%–30% and 50%–300% of the background values, respectively. Second, the maximum plasma pressure and magnetic field depression in the central ring current region during the main phase are well correlated with the Dst index.
Plasmonic nanoparticle-based epoxy photocuring: A deeper look
(Elsevier, 2019) Roberts, Adam T.; Yang, Jian; Reish, Matthew E.; Alabastri, Alessandro; Halas, Naomi J.; Nordlander, Peter; Everitt, Henry O.
Many epoxyﾠadhesivesﾠrequire high temperatures to bondﾠcomposite materials. However, oven heating severely restricts what may be attached or enclosed within composite material-based structures and greatly limits the possibilities for repair. Inspired by initial reports of photothermal epoxy curing usingﾠplasmonicnanoparticles, we examine how laser-illuminated Au nanoparticles embedded within high-temperature epoxy films convert the conventional thermal curing process into a photothermally driven one. Our theoretical investigations reveal that plasmonic nanoparticle-based epoxy photocuring proceeds through a four-stage process: a rapid, plasmon-induced temperature increase, a slow localizedﾠinitializationﾠof the curing chemistry that increases theﾠoptical absorptionﾠof the epoxy film, a subsequent temperature increase as the epoxy absorbs theﾠlaser radiationﾠdirectly, and a final stage that completes theﾠchemical transformationﾠof the epoxy film to its cured state. Our experimental studies validate this model, and also reveal that highly local photocuring can create a stronger bond between composite materials than thermal curing without nanoparticles, at times even stronger than the composite material itself, substantially reducing the time needed for the curing process. Our findings support key advances in our understanding of this approach to the rapid, highly efficient bonding and repair of composite materials.
RCM modeling of bubble injections into the inner magnetosphere: geosynchronous orbit and the ionospheric responses
(Frontiers Media S.A., 2023) Sadeghzadeh, Sina; Yang, Jian; Toffoletto, Frank; Wolf, Richard; Mousavi, Ameneh; Wang, Chih-Ping
Introduction: Accurate characterization of the plasma sheet source population in the ring current region and its outer boundary at geosynchronous orbit is crucial for understanding the dynamics of the Earth’s magnetosphere. The interaction between the ring current and plasma populations from the ionosphere is a focus of extensive research.Methods: We used the Rice Convection Model (RCM) to simulate the transient meso-scale injections of fast flows or plasma sheet bubbles from the outer boundary into the inner magnetosphere and the associated impacts on the ionosphere. We compared our simulation results of the average properties of bulk plasma access to geosynchronous orbit to a number of empirical models. We also examined the role of plasma sheet bubbles in forming field-aligned currents (FACs).Results: Our modeling results show that impulsive plasma sheet injections dramatically alter the average distribution of FACs in the ionosphere. We found both quantitative and qualitative agreements and disagreements when comparing our simulation results to empirical models. Furthermore, we demonstrated that several discrete auroral structures can be identified in the nightside ionosphere in accordance with theupward FACs.Discussion: The significance of plasma sheet bubbles in modifying the averageplasma properties at geosynchronous orbit and FACs in the ionosphere is highlighted by oursimulation findings, offering novel understandings into the dynamics of Earth's magnetosphere,and emphasizing the necessity for further research in this field.
RCM-E and AMIE studies of the Harang reversal formation during a steady magnetospheric convection event
(Wiley, 2014) Yang, Jian; Toffoletto, Frank; Lu, Gang; Wiltberger, Michael
This paper presents the results of a modeling study on the formation of the Harang reversal (HR) during a steady magnetospheric convection event. The Harang reversal is identified as the boundary of the northward and southward electric field in the nightside auroral zone using the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure. We simulate the event with the Rice Convection Model-Equilibrium (RCM-E) by adjusting its boundary conditions to approximately match Time History of Events and Macroscale Interactions during Substorms (THEMIS) and GOES observations in the nightside magnetosphere. Our results show that the HR is collocated with an upward region 1 field-aligned current, where converging ionospheric currents cause a southward/northward electric field on the poleward/equatorward side of the HR. Our results also indicate that the electric field reversal is slightly poleward of the ionospheric east–west current reversal and is to the northeast of the ground magnetic reversal, which is consistent with previous observations. We also test the sensitivity of the HR formation to a variety of parameters in the RCM-E simulations. We find that (1) the reduction of the flux tube entropy parameter PV5/3 near the midnight sector plays a major role in the formation of the HR; (2) a run carried out assuming uniform conductance produced the same major features as the run with more realistic precipitation-enhanced conductance; and (3) the detailed pattern of the polar cap potential distribution plays a minor role, but its dawn-dusk asymmetry significantly controls the location of the HR with respect to midnight. The RCM-E simulations also predict PV5/3 and flow distributions associated with the magnetospheric source of the HR in the plasma sheet, which can be further tested against observations.
RCM-E simulation of a thin arc preceded by a north-south-aligned auroral streamer
(Wiley, 2014) Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.
The Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imager data have recently revealed a repeatable sequence that occurs during many auroral substorms, in which a newly formed thin arc is preceded by an equatorward propagating streamer. The paper aims at modeling this sequence using the Rice Convection Model–Equilibrium. The simulation shows a thin arc arising when a plasma sheet bubble with its PV5/3 reduced to the transition region value arrives at the magnetic transition region. The modeled thin arc consists of two parts: the one east of the streamer is the result of the bubble pushing high PV5/3 flux tubes ahead of it, strengthening the upward region 2 current, and the one west of the streamer is associated with westward drifting bubble particles, sliding along the transition region. The model predicts that (1) the westward and eastward leading edges of the thin arc propagate azimuthally at a speed of ~0.5–2.7 km/s and (2) the streamer-induced thin arc is accompanied by classic signatures of bubble injections.
RCM-E simulation of bimodal transport in the plasma sheet
(American Geophysical Union, 2014) Yang, Jian; Wolf, Richard A.; Toffoletto, Frank R.; Sazykin, Stanislav; Wang, Chih-Ping
Plasma sheet transport is bimodal, consisting of both large-scale adiabatic convection and intermittent bursty flows in both earthward and tailward directions. We present two comparison simulations with the Rice Convection Model-Equilibrium (RCM-E) to investigate how those high-speed flows affect the average configuration of the magnetosphere and its coupling to the ionosphere. One simulation represents pure large-scale slow-flow convection with time-independent boundary conditions; in addition to the background convection, the other simulation randomly imposes bubbles and blobs through the tailward boundary to a degree consistent with observed statistical properties of flows. Our results show that the bursty flows can significantly alter the magnetic and entropy profiles in the plasma sheet as well as the field-aligned current distributions in the ionosphere, bringing them into much better agreement with average observations.
RCM-E simulation of substorm growth phase arc associated with large-scale adiabatic convection
(Wiley, 2013) Yang, Jian; Wolf, Richard A.; Toffoletto, Frank R.; Sazykin, Stanislav
[1] Substorm auroral breakup often occurs on a longitudinally elongated arc at the end of a growth phase. We present an idealized high-resolution simulation with the Rice Convection Model-Equilibrium (RCM-E) to investigate how large-scale adiabatic convection under equilibrium conditions can give rise to an auroral arc. We find that a thin arc that maps to the magnetic transition region at r ~ 8 RE emerges in the late growth phase. The simulation implies that the arc in the premidnight sector is associated with a sheet of additional region 1 sense field-aligned current (FAC) just poleward of the main region 2 FAC, while the arc in the postmidnight sector is associated with the poleward portion of the main upward region 2 FAC. Explanations for the location and the thickness of the arc are proposed, based on the simulation.

Browsing by Author "Yang, Jian"

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