Extrinsic States Research Articles

Tailoring directional chiral emission from molecules coupled to extrinsic chiral quasi-bound states in the continuum

Tailoring directional chiral emission from molecules coupled to extrinsic chiral quasi-bound states in the continuum

Investigation on Fluorescence Origin and Spectral Heterogeneity in Carbon Dots: A Dynamic Perspective

AbstractHeterogeneity in the fluorescence of carbon dots (CDs) has been hard to figure out so far. This could potentially be related to structural factors, size or intermediate fluorophores, especially when employing the bottom‐up synthesis. Herein, we unveil the origin of fluorescence and spectral heterogeneity of CDs using a simple dynamic method. This work reports the room light‐excited green fluorescence and dual‐emissive N‐doped CDs synthesized using a hydrothermal method. Studies were carried out considering the factors of fluorescence phenomena, such as excitation‐independent emission, fluorescent impurities, aggregation and solvation dynamics. The new steady‐state, Excitation‐resolved area‐normalized emission spectroscopy (ERANES) and ensemble measurements, including time‐resolved studies reveal that a heterogeneous environment exists in the ground state. Eventually, the results show the existence of core, edge and surface states in the CDs. Additionally, the fluorescence characteristics depend on the structural functionalization that occurs in both the intrinsic and extrinsic states of the CDs and it is proven that this does not violate the Kasha‐Vavilov rule. Although a highly purified material could still exhibit heterogeneity due to the ensemble emissive states and structural variations. Our results provide insights into the enduring debates about fluorescence and a deeper understanding of the structure‐ property relationship of CDs.

Investigating the Mechanism by Which Intragap States Tailor Light Emission: Case of Copper Deficient and Zn Doped Cu−In−Se Quantum Dots**

AbstractThe large structural tolerance of I–III–VI group quantum dots (QDs) to off‐stoichiometry allows their photoluminescence properties to be adjusted via doping, thereby enabling application in different fields. However, the photophysical processes underlying their photoluminescence mechanism remain significantly unknown. In particular, the transition channels of CuInSe2 QDs, which are altered by intrinsic and extrinsic intragap states, remain poorly reported. Herein, we investigated the photophysical processes associated with intragap states via electrochemical and optical techniques by using copper deficient Cu−In−Se QDs as well as Zn doped Cu−In−Se QDs. When the Cu/In molar ratios of Cu−In−Se QDs increased from 0.3 : 1 to 0.9 : 1, the photoluminescence spectra displayed a red‐shift from 700 nm to 1050 nm. Although there was a blue‐shift after the introduction of Zn2+ dopants in Cu−In−Se QDs, a significant red‐shift occurred (from 660 nm to 760 nm) when the Zn/Cu molar ratios decreased from 0.7 : 0.3 to 0.3 : 0.7. The Gaussian deconvolution results of the photoluminescence spectra and the band gap derived from absorption spectra by fitting supported the fact that the optical transition channels are dependent on the Cu/In and Zn/Cu molar ratios. After the introduction of the Zn2+ ions, the alloyed‐resultant blue‐shift of the emission spectra was observed, primarily due to the enlarged band gap; however, the radiative recombination of prominent intrinsic intragap states is still observed; and only a small proportion of the band‐edge exciton undergoes recombination for the sample with low Zn content. Cyclic voltammetry measurements revealed well‐defined extrinsic ZnCu intragap states (Zn substitution on Cu sites) and intrinsic Cux (x= 1+/2+) states in the band gap. The results presented here provide a better understanding of the varying effects of dopant on photoluminescence in terms of I–III–VI group QDs.

Subacute changes in brain functional network connectivity after nocturnal sodium oxybate intake are associated with anterior cingulate GABA.

Sodium oxybate (γ-hydroxybutyrate, GHB) is an endogenous GHB/GABAB receptor agonist, clinically used to promote slow-wave sleep and reduce next-day sleepiness in disorders such as narcolepsy and fibromyalgia. The neurobiological signature of these unique therapeutic effects remains elusive. Promising current neuropsychopharmacological approaches to understand the neural underpinnings of specific drug effects address cerebral resting-state functional connectivity (rsFC) patterns and neurometabolic alterations. Hence, we performed a placebo-controlled, double-blind, randomized, cross-over pharmacological magnetic resonance imaging study with a nocturnal administration of GHB, combined with magnetic resonance spectroscopy of GABA and glutamate in the anterior cingulate cortex (ACC). In sum, 16 healthy male volunteers received 50mg/kg GHB p.o. or placebo at 02:30a.m. to maximize deep sleep enhancement and multi-modal brain imaging was performed at 09:00a.m. of the following morning. Independent component analysis of whole-brain rsFC revealed a significant increase of rsFC between the salience network (SN) and the right central executive network (rCEN) after GHB intake compared with placebo. This SN-rCEN coupling was significantly associated with changes in GABA levels in the ACC (pall < 0.05). The observed neural pattern is compatible with a functional switch to a more extrinsic brain state, which may serve as a neurobiological signature of the wake-promoting effects of GHB.

Broadband ultrafast photogenerated carrier dynamics induced by intrinsic defects in &lt;inline-formula&gt;&lt;tex-math id="Z-20231102113631"&gt;\begin{document}$\boldsymbol\beta$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20231173_Z-20231102113631.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20231173_Z-20231102113631.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

The ultra-wide bandgap semiconductor gallium oxide &lt;i&gt;β&lt;/i&gt;-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; with enhanced resistance to the irradiation and temperature is favorable for high-power and high-temperature optoelectronic devices. &lt;i&gt;β&lt;/i&gt;-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; also exhibits great potential applications in the field of integrated photonics because of its compatibility with the CMOS technique. However, a variety of intrinsic and extrinsic defects and trap states coexist in &lt;i&gt;β&lt;/i&gt;-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;, including vacancies, interstitials, and impurity atoms. The defect-related carrier dynamics in &lt;i&gt;β&lt;/i&gt;-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; not only adversely affect the optical and electrical properties, but also directly limit the performance of &lt;i&gt;β&lt;/i&gt;-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; based devices. Therefore, a comprehensive understanding of the carrier transportation and relaxation dynamics induced by intrinsic defects is very important. Supercontinuum-probe spectroscopy can provide a fruitful information about the carrier relaxation processes in different recombination mechanisms, and thus becomes an effective way to study the defect dynamics. In this work, we study the dynamics of carrier trapping and recombination induced by intrinsic defects in pristine &lt;i&gt;β&lt;/i&gt;-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; crystal by using wavelength-tunable ultrafast transient absorption spectroscopy. The broadband absorption spectra induced by the intrinsic defects are strongly dependent on the polarization of pump pulse and probe pulse. Particularly, two absorption peaks induced by the two defect states can be extracted from the transient absorption spectra by subtracting the absorption transients under two probe polarizations. The observed defect-induced absorption features are attributed to the optical transitions from the valence band to the different charge states of the intrinsic defects (such as gallium vacancy). The data are well explained by a proposed carrier capture model based on multi-level energies. Moreover, the hole capture rate is found to be much greater than that of the electron, and the absorption cross-section of the defect state is at least 10 times larger than that of free carrier. Our findings not only clarify the relationship between intrinsic defects and photogenerated carrier dynamics, but also show the importance in the application of &lt;i&gt;β&lt;/i&gt;-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; crystals in ultrafast and broadband photonics.

Adsorption dynamics of O2 on Cu(111): a supersonic molecular beam study.

We have studied the adsorption of O2 on Cu(111) using supersonic molecular beam techniques. For incident energies ranging between 100 and 400 meV, we have determined the sticking probability as a function of angle of incidence, surface temperature, and coverage. Initial sticking probabilities range from near 0 to 0.85 with an onset near 100 meV, making Cu(111) considerably less reactive than Cu(110) and Cu(100). Normal energy scaling applies and reactivity increases appreciably over the entire range of surface temperatures from 90 to 670 K. A strictly linearly decreasing coverage dependence on sticking precludes adsorption and dissociation via an extrinsic or long-lived mobile precursor state. We cannot exclude that sticking also occurs molecularly at the lowest surface temperatures. However, all tell tales from our experiments suggest that sticking is predominantly direct and dissociative. Comparison to earlier data shows implications for the relative reactivity of Cu(111) vs. Cu/Ru(0001) overlayers.

Geometric Properties of Time-Optimal Controls With State Constraints Using Strong Observability

This article considers minimum time optimal control problems with linear dynamics subject to state equality constraints and control inequality constraints. In the absence of state constraints, there are well-known sufficient conditions to guarantee that optimal controls are at the boundary or extreme points of the control set. With strong observability as the key tool, analogous conditions are derived for problems subject to both extrinsic and intrinsic state constraints. Understanding these geometric properties enables exact convex relaxations. The relaxation technique is used to convert a nonconvex quadratic program to a second-order cone program and a mixed integer linear program to a linear program. The relaxations accelerate numerical solution times by factors of 18 000 and 150, respectively. As such, the theorems and relaxations are seen as important tools for real-time optimization-based control.

Deterministic Excitation of Polarization-Sensitive Extrinsic Anapole State in Si Nanodisk Clusters.

Nanoparticle clusters provide new degrees of freedom for light control due to their mutual interaction compared with an individual one. Here, the authors demonstrate theoretically and experimentally a type of optical anapole (a nonradiating state) termed as extrinsic anapole, with mode field spreading across Si nanodisk dimers unlike the intrinsic one that is confined within individual nanodisks. The extrinsic anapole is sensitive to the polarized excitation. When the electric vector E of excitation is perpendicular to the dimer axis, the coupled toroidal dipole (TD) mode is largely enhanced and broadened to be spectrally overlapped with the electric dipole (ED) mode. The destructive interference of these two modes results in the generation of the extrinsic anapole. However, it vanishes when E is parallel to the dimer axis. Such polarization dependence can be relieved with the participation of the third nanodisk. Scattering spectra of Si nanodisk trimers stay almost unchanged under different polarized excitations, although the near-field distributions are quite different. Finally, enhanced white-light emission is observed in Si nanodisk clusters, which can be attributed to the near-infrared absorption enhancement induced by extrinsic anapole states. The findings manifest that high-index all-dielectric nanodisk clusters are promising for light manipulation based on mode interference.

High-responsivity self-powered UV photodetector performance of pristine and V-doped ZnO nano-flowers

Wurtzite ZnO nanostructures are suitable for high-performance, self-powered photodetectors (PDs) because of their attractive optoelectronic properties. In this study, highly sensitive ultra-violet self-powered PDs with high responsivity/detectivity and large external quantum efficiency was developed by V-doped ZnO nanoflower samples onto an ITO glass substrate. Highly faceted pristine and V-doped ZnO nanoflowers were produced using a simple, low-cost co-precipitation method. The presence of Na+ ions in the precursor solution appeared to control the morphology of the nanomaterial. Various physicochemical characterizations showed that the variation of the Na+ ion concentration inhibits the reaction at selected regions, causing the branching of nanostructures to form ZnO nanoflowers. Room- and low-temperature photoluminescence studies showed that V-doping increases the extrinsic carrier density and produces many intrinsic and extrinsic defect states, which reduce the e−–h+ recombination rate significantly and produce a large photocurrent under UV illumination. The V-ZnO-based self-powered UV PD device showed a 156 % increase in photocurrent compared to pristine ZnO-based PDs, with very short response/recovery times of 0.22/0.23 s under 382 nm UV illumination of 1.14 mW/cm2, and excellent responsivity (5.1 × 103 mA/W), very high external quantum efficiency (5.5 × 104 %), and large detectivity (4.0 × 1013 Jones). Therefore, the current work presents a simple way to obtain high-performance self-powered UV PDs that can open up a new horizon to fabricate new-generation optoelectronic devices for diverse applications.

Structural and optical investigations in undoped and rare-earth doped zinc oxide nanoparticles for photon upconversion based applications

The present work reports comprehensive investigations of the physical properties of undoped and rare-earth (RE3+) doped ZnO based upconversion nanoparticles. X-ray diffraction analysis of these nanoparticles reveals the hexagonal wurtzite structure. The induced-strain value of the RE3+ doped ZnO nanoparticles increased by almost one order of magnitude, and their mean particle size reduced from 36 nm to 17 nm. The scanning electron microscopic images showed that the particles retained the spherical shape in the undoped and doped conditions. The elemental maps confirmed the uniform distribution of the RE3+ dopants. The recorded absorbance spectrum for the doped nanoparticles showed significant absorption in ultraviolet and near infra-red regions owing to the band-band transitions and the deep defect level transitions that are induced due to intrinsic and extrinsic defect states. A detailed analysis of the defect states of these samples is described based on the Urbach energy studies. An intense peak observed at 980 nm suggests the possibility of photon upconversion in the doped nanoparticles. A simplified energy diagram (as depicted below) has demonstrated the multi-photon absorption and possible upconversion mechanisms. The optical absorption spectrum of RE3+ doped ZnO nanocrystals encourages the promising application of these materials in diverse fields, particularly in biomedical and photovoltaic applications.

Optical measurements and Burstein Moss effect in optical properties of Nb-doped BaSnO3 perovskite

The research for novel transparent electrodes has gained popularity due to the low abundance and the high cost of Indium. In this paper, we used first-principles calculations employing density functional theory with the exchange-correlation energy functional approximation Generalized Gradient Approximation to analyze the optical, structural, and electronic properties of Niobium doped Barium tin oxide with 12.5%, 6.25%, and 3.125% of doping. The electronic structure calculations show an indirect bandgap of Barium tin oxide. Niobium induces extrinsic donor energy states around the bottom of the conduction band giving rise to an improvement in the electrical conductivity in the system. The Fermi level shifts upward to the conduction band, a typical characteristic of an n-type semiconductor. Burstein Moss effect was found in the optical measurements for the dope systems, leading to an increase in the apparent bandgap. A diminution in the absorption coefficient in the UV–visible range of the light was presented. These characteristics suggest that Nb-doped BaSnO3 is a promising transparent conducting oxide and can be useful for optoelectronic applications.

Free-Standing ZnO:Mo Nanorods Exposed to Hydrogen or Oxygen Plasma: Influence on the Intrinsic and Extrinsic Defect States.

Cationic doping of ZnO nanorods has gained increased interest as it can lead to the production of materials with improved luminescent properties, electrical conductivity and stability. We report on various Mo-doped ZnO powders of nanorods synthesized by the hydrothermal growth method. Further annealing or/and cold hydrogen or oxygen plasma modification was applied. The atomic structure of the as-grown and plasma-modified rods was characterized by X-ray diffraction. To identify any possible changes in morphology, scanning electron microscopy was used. Paramagnetic point defects were investigated by electron paramagnetic resonance. In particular, two new types of defects were initiated by the plasma treatment. Their appearance was explained, and corresponding mechanisms were proposed. The changes in the luminescence and scintillation properties were characterized by photo- and radioluminescence, respectively. Charge trapping phenomena were studied by thermally stimulated luminescence. Cold plasma treatment influenced the luminescence properties of ZnO:Mo structures. The contact with hydrogen lead to an approximately threefold increase in intensity of the ultraviolet exciton-related band peaking at ~3.24 eV, whereas the red band attributed to zinc vacancies (~1.97 eV) was suppressed compared to the as-grown samples. The exciton- and defect-related emission subsided after the treatment in oxygen plasma.

Tuning Exciton Recombination Pathways in Inorganic Bismuth-Based Perovskite for Broadband Emission

Single-component emitters with broadband emission are attractive but challenging for illumination and display applications. The two-dimensional organic-inorganic hybrid perovskites have exhibited outstanding broad emission property due to low electronic dimensionality and strong exciton-phonon coupling. However, few layered all-inorganic lead-free perovskites with broadband emission have been explored, and the explicit mechanism of exciton recombination in them also needs in-depth understanding. Herein, the inorganic bismuth-based perovskite Cs 3 Bi 2 Br 9 achieves the stable broadband emission under ambient temperature and pressure by tuning the exciton recombination pathways via antimony (Sb) doping, and the photoluminescence quantum yield (PLQY) realizes an enhancement from 2.9% to 15.9%. The photoluminescence excitation (PLE) spectra indicate that the doped Sb introduces newly extrinsic self-trapped states. The incorporation of Sb promotes the transfer of free excitons (FEs) to extrinsic self-trapped excitons (STEs) observed from Sb content-dependent steady-state PL spectra and, meanwhile, reduces the nonradiative recombination of the generated extrinsic STEs, which are primarily responsible for the remarkably enhanced broad emission. Furthermore, femtosecond transient absorption results elucidate a clear exciton dynamics, in which the transition from FEs to STEs might arise through the gradient energy levels, and finally extrinsic STEs at various energy states contribute to the broadband emission.

Defect controls by silicon doping in non-polar a-plane AlGaN epi-layers

Deposition of high-quality Si-doped crystalline AlGaN layers, especially non-polar-grown AlGaN layers, is critical and remains difficult in preparing AlGaN-based light-emitting diodes (LEDs), as the Si-doping-induced variations of crystalline structures are still under exploration. In this work, structural characterizations of Si-doped AlxGa1−xN layers were carried out by associating with examination of their carrier recombination behaviors in photoluminescence (PL) processes, to clarify the physical mechanism on how Si doping controls the formation of structural defects in AlGaN alloy. The obtained results showed that Si doping induced extrinsic shallow donor states and increased the densities of point defects like cation vacancies. On the contrary, Si doping suppressed formation of line defects like dislocations and planar defects like stacking faults with suitable doping concentration. These results may guide further improvement of UV-LEDs based on AlGaN alloy.

Extrinsic and Intrinsic Anomalous Metallic States in Transition Metal Dichalcogenide Ising Superconductors.

The metallic ground state in two-dimensional (2D) superconductors has attracted much attention but is still under intense scrutiny. Especially, the measurements in the ultralow temperature region are challenging for 2D superconductors due to the sensitivity to external perturbations. In this work, the resistance saturation induced by external noise, named as the "extrinsic anomalous metallic state", is observed in 2D transition metal dichalcogenide (TMD) superconductor 4Ha-TaSe2 nanodevices. However, with further decreasing temperature, credible evidence of the intrinsic anomalous metallic state is obtained by adequately filtering external radiation. Our work indicates that, at ultralow temperatures, the anomalous metallic state can be experimentally revealed as the quantum ground state in 2D crystalline TMD superconductors. Besides, Ising superconductivity revealed by ultrahigh in-plane critical field (Bc2∥) going beyond the Pauli paramagnetic limit (Bp) is detected in 4Ha-TaSe2, from the one-unit-cell device to the bulk situation, which might be due to the weak coupling between the TaSe2 submonolayers.

Interfacial Electron-Phonon Coupling Constants Extracted from Intrinsic Replica Bands in Monolayer FeSe/SrTiO_{3}.

The observation of replica bands by angle-resolved photoemission spectroscopy has ignited interest in the study of electron-phonon coupling at low carrier densities, particularly in monolayer FeSe/SrTiO_{3}, where the appearance of replica bands has motivated theoretical work suggesting that the interfacial coupling of electrons in the FeSe layer to optical phonons in the SrTiO_{3} substrate might contribute to the enhanced superconducting pairing temperature. Alternatively, it has also been recently proposed that such replica bands might instead originate from extrinsic final state losses associated with the photoemission process. Here, we perform a quantitative examination of replica bands in monolayer FeSe/SrTiO_{3}, where we are able to conclusively demonstrate that the replica bands are indeed signatures of intrinsic electron-boson coupling, and not associated with final state effects. A detailed analysis of the energy splittings and relative peak intensities between the higher-order replicas, as well as other self-energy effects, allows us to determine that the interfacial electron-phonon coupling in the system corresponds to a value of λ=0.19±0.02, providing valuable insights into the enhancement of superconductivity in monolayer FeSe/SrTiO_{3}. The methodology employed here can also serve as a new and general approach for making more rigorous and quantitative comparisons to theoretical calculations of electron-phonon interactions and coupling constants.

(Invited) Schottky Barrier Height Control at Metal/Ge Interface by Insertion of Nitrogen Contained Amorphous Layer

1. IntroductionGe is attracted great attention as a candidate of channel material for future CMOS devices and near-infrared optical devices, owing to its high intrinsic carrier mobility and narrow bandgap. One of the difficulties to realize Ge-based devices is to control of Schottky barrier height (SBH) at metal/Ge interface. It is widely known any metal/Ge contact shows high electron barrier height (ΦBN > 0.5 eV) due to Fermi level pinning at metal/Ge interface. Our group found a method to alleviate the FLP, by which sputter-deposited TiN/Ge and ZrN/Ge contacts showed low ΦBN (< 0.10 eV) and high hole barrier height (ΦBP > 0.56 eV) [1]. From detailed structural analyses, it was clarified that the FLP alleviation was induced by a nitrogen-contained amorphous interlayer (a-IL) formed during TiN(ZrN) sputter-deposition. If we can change the kind of metal on a-IL, we may extend the control range of SBH. In this paper, we demonstrate the wide range SBH control for metal/a-IL/Ge contacts.2. Experimental, Results, and DiscussionsFigure 1 shows the fabrication procedure of the metal/a-IL/Ge structure. An a-IL was formed by the ZrN film sputter deposition and subsequent etching by dilute HF solution. Ag, Al, and Cu, were respectively deposited using thermal evaporation and patterned by the removal of photoresist. In figure 1, a dark field-STEM image of an Ag/a-IL/Ge contact is shown. An a-IL with dark contrast was clearly observed between the Ag and the Ge, implying that the ZrN film can be removed by a dilute HF solution while the a-IL can be retained on the Ge substrate.Figures 2 shows J–V characteristics at 200 K for Cu/a-IL/n-Ge contacts, respectively. Here, higher rf power during the ZrN deposition makes thicker a-IL. It was found that the insertion of the a-IL significantly modulated the J–V characteristics. The rectifying feature on n-Ge becomes weak with an increase in rf power. Other metals also show a similar tendency (data are not shown).Figure 3 represents the ΦBN versus work function of the metal (ΦM) plot. In this figure, slope factor (S) and effective charge neutrally level (ΦCNL,eff) are also indicated for each rf power. The weaker rf power leads to the larger S value. Interestingly, a S for contacts with a rf power of 50 W was around 0.26, which is close to S (0.27) of Si [2], suggesting that it is possible to widely control the SBH by forming contacts with N-contained a-IL.It is well known that the ΦCNL of metal/Ge interface is located near the E V edge, as shown in Fig. 4(a) [3]. To explain the dependences of S andΦCNL,eff in this study, two effects should be considered, which are the decrease in the intrinsic states and the creation of additional extrinsic states. We consider the decrease in the intrinsic states is dominated by the passivation of surface dangling bonds by a-IL. On the other hand, the creation of additional localized extrinsic states are associated with the interface dipoles related Ge-N bond [4], i.e., the extrinsic states cause a shift of ΦCNL to compensate the positively charged dipoles at the Ge side of the interface, causing the decrease in ΦCNL,eff. When the rf power was as low as 50 W (thin a-IL), the density of extrinsic states was low, as shown in Fig. 4(b). Therefore, the Fermi level can be modulated depending on the ΦM, as shown in Fig. 3 (50 W, blue line). In the case of a thick a-IL (rf power of 200 W), high-density extrinsic states could be generated. As a result, the modulation of ΦM became impossible, as shown in Fig. 4 (200 W, black line).3. ConclusionIn conclusion, we succeeded in wide controlling SBH of metal/Ge contacts with N-contained a-ILs. The SBH swing and CNL position were strongly depend on the rf power during ZrN sputter deposition, i.e., the thickness of a-IL. Under the low power condition, a S-value of 0.26 was achieved, which is comparable to that of Si. The dependences of S and ΦCNL on the rf power were explained by an extrinsic states model associated with N-related interfacial dipoles.

Oxygen Sensing of Pt/PEO-TiO2 in Humid Atmospheres at Moderate Temperatures

Here, we show that the presence of adsorbed water improves the oxygen-sensing properties of Pt/TiO at moderate temperatures. The studied interface is based on porous plasma electrolytic oxidized titanium (PEO-TiO) covered with platinum clusters. The electrical resistance across Pt/PEO-TiO is explained by an electronic depletion layer. Oxygen adsorbates further increase the depletion by inducing extrinsic interface states, which are occupied by TiO conduction band electrons. The high oxygen partial pressure in ambient air substantially limits the electron transport across the interface. Our DC measurements at defined levels of humidity at 30 C show that adsorbed water counteracts this shortcoming, allowing oxygen sensing at room conditions. In addition, response and recovery times from temporal oxygen exposure decrease with humidity. We attribute the effects to competing adsorption processes and reactions of water with adsorbed oxygen species and/or lattice oxygen, which involve electron re-injection to the TiO conduction band. Elevated temperatures up to 170 attenuate the effects, presumably due to the lower binding strength to the surface of molecular water compared with oxygen adsorbates.

Modeling and analyzing temperature-dependent parameters of Ni/β-Ga2O3 Schottky barrier diode deposited by confined magnetic field-based sputtering

In this work, the temperature-dependent parameters of Ni/β-Ga2O3 Schottky barrier diode (SBD) were analyzed and modeled. The simulation is to elucidate the physical phenomenon behind this temperature dependence. At room temperature, the deviation of SBD parameters from the ideal case is due to the Schottky barrier height ( inhomogeneity. A model is developed for this inhomogeneity in which an interfacial defected layer (IDL) is formed. Defects (extrinsic states) are related to plasma and Ar atom bombardment used in the confined magnetic field-based sputtering to realize the Ni Schottky contact diffusion in β-Ga2O3. Ni diffuses, upon annealing, to compensate defects in this IDL. It was found that the Schottky barrier height () and threshold voltage decrease with increasing temperature. This decrease is related to intrinsic and extrinsic states (plasma and Ar bombardment). However, the ideality factor (η) increases which is related to the series resistance (R S) increase. The increase is related to the interfacial layer and nickel resistance increase with increasing temperature.

Using Extrinsic Evidence to Excuse a Liability Insurer's Duty to Defend

Most Americans and American businesses purchase liability insurance to protect against financial loss should they ever be sued. In furnishing this protection, liability insurers contractually promise policyholders that they will defend them against lawsuits seeking covered damages and indemnify them for such damages up to the policy limits. As important as the insurer’s promise of indemnification is to an insured, the insurer’s agreement to defend the insured in litigation is an equally essential aspect of the liability insurance bargain. An insurer must decide whether it has a duty to defend its insured at the outset of a case. There are two approaches to determining an insurer’s duty to defend. First, there is the eight corners rule, under which the factual allegations in the plaintiff’s complaint or petition are compared with the policy, and the insurer owes a defense only if those allegations potentially implicate the insurer’s duty to indemnify the insured. Second, there is the extrinsic evidence approach. Courts employing an extrinsic evidence approach hold that an insurer must look beyond the pleadings and consider any facts brought to its attention or any facts that it reasonably could discover at the time suit was filed in deciding whether it has a duty to defend. Liability insurance policies typically provide that the insurer will pay the cost of the insured’s defense in addition to the policy’s liability limits. This is a potentially significant expense for the insurer because defense costs may, and often do, exceed any settlement or judgment ultimately paid. Given the expense associated with providing a defense, it is not surprising that an insurer may want to disclaim its duty to defend based on extrinsic evidence that establishes that it will have no duty to indemnify the insured. Of course, an insurer generally cannot decline to defend its insured if, in making that determination, it is limited to the facts alleged in the plaintiff’s petition or complaint; after all, even in extrinsic evidence states, it usually is the allegations in that pleading that triggered the insurer’s duty to defend in the first place. Thus, insurers frequently test their ability to rely on extrinsic evidence to disclaim their duty to defend when the plaintiff’s complaint or petition alleges facts that trigger the duty. In other words, if an insurer must, in many states, consider extrinsic evidence in accepting its duty to defend, can it also rely on extrinsic evidence to deny or exit a defense? The answer generally is no; the use of extrinsic evidence is rarely a two-way street. Although the general rule holds that an insurer may not rely on extrinsic evidence to refuse to defend an insured, some courts that adhere to the general rule occasionally recognize exceptions. Plus, there is a contrary minority rule. It is therefore fair to ask whether an insurer should be allowed to rely on extrinsic evidence to disclaim or extinguish its duty to defend when the plaintiff’s complaint or petition alleges facts that implicate coverage, and, if so, under what circumstances? This question is timely first because of two 2020 Texas Supreme Court decisions addressing it and offering different answers based on the facts presented: Richards v. State Farm Lloyds and Loya Insurance Co. v. Avalos. Second, as Richards and Loya demonstrate, insurers’ use of extrinsic evidence to excuse their defense obligations is an ongoing litigation strategy. That is not to say that the strategy is good or bad, but it is to say that the extrinsic evidence issue will continue to surface in key cases in various jurisdictions. Third, while insurers’ use of extrinsic evidence to defeat the duty to defend is hotly contested by policyholders, courts that have considered the issue over the years have rarely discussed it in meaningful fashion in their opinions. The resulting lack of guidance hampers courts either confronting the issue for the first time or entertaining reconsideration of prior holdings. This Article provides that guidance.