Taehwan Moon  Hyun Jae Lee  Seung Dam Hyun  Baek Su Kim  Ho Hyun Kim  Cheol Seong Hwang 《Advanced Electronic Materials》2020,6(6)

A transistor is fabricated with a 2D electron gas (2DEG) channel at the Al₂O₃ (AO)/SrTiO₃ (STO) interface. The threshold voltage (V_th) shift of the 2DEG channel in the Pt/AO/2DEG/STO stack induced by negative bias stress is investigated. Two‐terminal current–voltage and capacitance–voltage characterization through the gate and the source reveals that the metallic 2DEG channel turns into a semiconducting channel when the negative bias stress is applied. Transfer curve measurement with various stress conditions on the 2DEG field‐effect transistor is performed to evaluate the effect of the negative bias stress. The V_th becomes positive, and the channel conductance decreases after the application of negative bias stress. These variations are promoted by large stress bias and temperature. Electron energy loss spectroscopy analysis via scanning transmission electron microscopy reveals that the chemical state of the interface changes from oxygen‐deficient to stoichiometric. Therefore, the change in the channel state from metallic to semiconducting originates from the decrease of oxygen vacancy concentration at the interface.  相似文献   

    

David J. Walwark  Thomas P. Martin  John K. Grey 《Advanced Electronic Materials》2020,6(6)

Photoinduced oxidation (doping) of conjugated polymers by complexation with oxygen can have a significant impact on electronic properties and performance in device environments. Nanofiber model forms of poly(3‐hexylthiophene) (P3HT) are investigated using single molecule spectroscopy that possess similar morphological qualities as their bulk thin film counterparts yet, heterogeneity is confined to the spatial dimensions of these particles. Specifically, P3HT nanofibers assembled in anisole solutions contain both aggregated and nonaggregated (amorphous) chains with distinct electronic properties. Excitation intensity dependent photoluminescence (PL) emission imaging is then used to expose differences in oxygen affinity and reactivity upon photoexcitation. Nanofiber regions with low PL yields tend to show faster PL intensity saturation that also degrade much faster following periods of high excitation intensity soaking. Conversely, other regions show gains in PL intensity and virtually no saturation. These PL “gainer” and “loser” behaviors are assigned as originating from amorphous and aggregated P3HT chains, respectively. The apparent propensity of aggregated chains to undergo latent oxygen doping indicates a greater affinity probably due to a larger extent of electronic delocalization in these structures. The results shed new light on degradation factors studied frequently at the bulk material level, which often lacks sufficient sensitivity to specific structural forms.  相似文献   

    

Atul Rangadurai  Honglue Shi  Prof. Hashim M. Al-Hashimi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(28):11358-11362

Biomolecules undergo motions on the micro-to-millisecond timescale to adopt low-populated transient states that play important roles in folding, recognition, and catalysis. NMR techniques, such as Carr–Purcell–Meiboom–Gill (CPMG), chemical exchange saturation transfer (CEST), and R_1ρ are the most commonly used methods for characterizing such transitions at atomic resolution under solution conditions. CPMG and CEST are most effective at characterizing motions on the millisecond timescale. While some implementations of the R_1ρ experiment are more broadly sensitive to motions on the micro-to-millisecond timescale, they entail the use of selective irradiation schemes and inefficient 1D data acquisition methods. Herein, we show that high-power radio-frequency fields can be used in CEST experiments to extend the sensitivity to faster motions on the micro-to-millisecond timescale. Given the ease of implementing high-power fields in CEST, this should make it easier to characterize micro-to-millisecond dynamics in biomolecules.  相似文献   

    

A. I. Korolkov  Sergei A. Nazarov  A. V. Shanin 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2016,96(10):1245-1260

A problem of scattering by a resonator connecting two 2D waveguides is studied. The incident wave is one of the waveguide modes taken at the spectral parameter close to a threshold of the continuous spectrum. It is shown that in the general case the reflection coefficient for such a mode is close to ‐1 (this case corresponds to an almost perfect reflection). Also it is shown that in some special cases the reflection coefficient is close to 0, and an almost perfect transmission is observed. The behavior of scattering at near‐threshold frequencies is determined by solutions corresponding to the threshold spectral parameter and crucially depends on whether stabilizing solutions do exist or not. Anomalous transmission is observed when there exist only solutions growing at infinity.  相似文献   

    

Chinh Tam Le  Daniel J. Clark  Farman Ullah  Velusamy Senthilkumar  Joon I. Jang  Yumin Sim  Maeng‐Je Seong  Koo‐Hyun Chung  Hyoyeol Park  Yong Soo Kim 《Annalen der Physik》2016,528(7-8):551-559

In this study, we utilized picosecond pulses from an Nd:YAG laser to investigate the nonlinear optical characteristics of monolayer MoSe₂. Two‐step growth involving the selenization of pulsed‐laser‐deposited MoO₃ film was employed to yield the MoSe₂ monolayer on a SiO₂/Si substrate. Raman scattering, photoluminescence (PL) spectroscopy, and atomic force microscopy verified the high optical quality of the monolayer. The second‐order susceptibility χ⁽²⁾ was calculated to be ～50 pm V^?1 at the second harmonic wavelength ～810 nm, which is near the optical gap of the monolayer. Interestingly, our wavelength‐dependent second harmonic scan can identify the bound excitonic states including negatively charged excitons much more efficiently, compared with the PL method at room temperature. Additionally, the MoSe₂ monolayer exhibits a strong laser‐induced damage threshold ～16 GW cm^?2 under picosecond‐pulse excitation_. Our findings suggest that monolayer MoSe₂ can be considered as a promising candidate for high‐power, thin‐film‐based nonlinear optical devices and applications.  相似文献   

    

《Optics and Lasers in Engineering》2016

In this paper we report a simple method to fabricate a novel subwavelength structure surface on fused silica substrate using one-step reactive ion etching with two-dimensional polystyrene colloidal crystals as masks. The etching process and the morphologies of the obtained structure are controlled. We show that the period of the obtained fused silica pillar-like arrays were determined by the initial polystyrene nanoparticle size. The height of pillar arrays can be adjusted by controlling the etching duration, which is proved to be of importance in tailoring the antireflection properties of subwavelength structures surface. The novel subwavelength structures surface exhibit excellent broadband antireflection properties, but the size of the pillar affects the antireflective properties in short wavelength region. We anticipate this method would offer a convenient and scalable way for inexpensive and high-efficiency high power laser field designs.  相似文献   

    

Huicong Li;Tian Xiang; 《Studies in Applied Mathematics》2024,153(1):e12683

We study global existence, boundedness, and convergence of nonnegative classical solutions to a Neumann initial-boundary value problem for the following possibly cross-diffusive SIS (susceptible–infected–susceptible) epidemic model with power-like infection mechanism generalizing the standard mass action incidence:  相似文献   

    

Yaojing Zhang  Keyi Zhong  Hon Ki Tsang 《Laser u0026amp; Photonics Reviews》2021,15(2):2000336

Integrated Raman lasers have been well explored using silica and silicon platforms for decades. A well-known equation with negligible nonlinear losses is employed for predictions of Raman lasing threshold powers in critically coupled cavities. However, nonlinear losses are known to be highly detrimental to silicon devices. Herein, for the first time, including the effects of linear loss, nonlinear losses, and cavity design, a new general equation that predicts the onset of Raman lasing in a cavity is derived and validated experimentally. Generally, a cavity with a small effective area, a short length, and high quality factors (Qs) at both pump and Stokes wavelengths can lase at relatively low pump power. This theory is verified by the experimental results with sub-milliwatt threshold powers in 2.8 mm long multimode cavities with different Qs at different pump wavelengths. The derived Raman gain coefficients from the measurements follow the scaling rules of Raman gain. This work advances the understanding of Raman lasing in high-Q multimode cavities. It also shows that Raman lasing at O/S-band is possible in racetrack resonators without needing any reverse bias and the broad operation wavelength is promising for single-chip silicon devices operating at all communication bands.  相似文献   

    

Ghulam Dastgeer  Haider Abbas  Duk Young Kim  Jonghwa Eom  Changhwan Choi 《固体物理学:研究快报》2021,15(1)

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Bo Yang  Wenwei Liu  Duk-Yong Choi  Zhancheng Li  Hua Cheng  Jianguo Tian  Shuqi Chen 《Advanced Optical Materials》2021,9(21):2100895

Despite structural colors based on metasurfaces drawing enormous attentions due to the high resolutions and superior durability, few researches focus on transmission colors in RGB model with high saturation because high-monochromaticity transmission peak is hard to be realized. Herein, a strategy of high-performance transmission structural colors in RGB model with high saturation, full hue, high efficiency, easy manufacturability, and polarization independence by means of Al-Si₃N₄ nanoblocks deposited on glass substrate is proposed. The coupling between Wood's anomaly and Mie lattice resonance is capable of introducing magnetic-dipole and electric-quadrupole resonances, creating enhanced resonant peak with full width of half maximum (FWHM) of 50 nm and efficiency of over 70% in transmission mode. High-saturation transmission colors occupying 150% standard RGB (sRGB) space can be obtained for the first time by tailoring the geometric parameters. Besides, it is also demonstrated that the hybrid nanostructures can realize full-hue colors with constant resolutions, which is significant for imaging applications. The designed method has potential for further extending the applications of transmission colors.  相似文献