Bibliographies thématiques / High Exciton Binding Energy (60 meV)

Littérature scientifique sur le sujet « High Exciton Binding Energy (60 meV) »

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Publié le 7 septembre 2023

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Articles de revues sur le sujet "High Exciton Binding Energy (60 meV)"

Титов, В. В., А. А. Лисаченко, И. Х. Акопян, М. Э. Лабзовская et Б. В. Новиков. « Долгоживущие центры фотокатализа, создаваемые в ZnO резонансным возбуждением экситона ». Физика твердого тела 61, n^o 11 (2019) : 2158. http://dx.doi.org/10.21883/ftt.2019.11.48422.537.

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Along with TiO_2, ZnO is the main photocatalyst for a wide class of redox reactions used to convert light energy into chemical and for environmental cleanup. It has been shown that the creation in ZnO of surface intrinsic defects in ZnO i.e. vacancies in the anionic and cationic sublattices (F-type and V-type centers) - makes it possible to create long-lived (up to 10^3 s) photocatalysis centers and thus fundamentally (tens of times) to increase the quantum yield of reactions. Slow surface states — photocatalysis centers — are created by the diffusion of electrons and holes generated during interband transitions in the volume of the photoactivated sample. However, the transfer efficiency is sharply reduced due to carrier recombination and losses when overcoming the Schottky surface barrier. In this work, In order to reduce these losses during energy transfer to the surface, we used in this work neutral energy carriers — excitons. The high (60 meV) exciton binding energy in ZnO allows it to move at room temperature without decay. The radiation loss of the exciton energy in our experiments is effectively reduced by the formation of a surface 2D structure. The results obtained confirm the high efficiency of the exciton channel for the formation of surface long-lived F and V centers of photocatalysis in the processes of oxygen photoadsorption and photodesorption, imitating the full cycle of the redox photocatalytic reaction.

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Shokuhfar, Ali, Javad Samei, A. Esmaielzadeh Kandjani et Mohammad Reza Vaezi. « Synthesis of ZnO Nanoparticles via Sol-Gel Process Using Triethanolamine as a Novel Surfactant ». Defect and Diffusion Forum 273-276 (février 2008) : 626–31. http://dx.doi.org/10.4028/www.scientific.net/ddf.273-276.626.

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Current researches show a growing interest in Zinc Oxide (ZnO) nanoparticles. ZnO is a semiconductor with a wide direct band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature. Several methods have been developed in order to synthesize ZnO nanoparticles. Chemical methods, among them sol-gel process, are more convenient. Sol-gel is common for producing metal oxide nanoparticles because of its simplicity, cheapness and high quality products. In this research ZnO nanoparticles were prepared via the sol-gel process. ZnAc2.2H2O as precursor and TEA (Triethanolamine) as a novel surfactant were used in a methanolic solution. MEA (Monoethanolamine) and DEA (Diethanolamine) have been highly used before. In this research, solutions with different weight ratios of ZnAc to TEA (1:2, 1:1 and 2:1) were obtained. After drying, all samples were calcinated at 500 °C for 1 hr. Obtained nanoparticles were characterized with the hope of achieving better properties.

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TNEH, S. S., H. ABU HASSAN, K. G. SAW, F. K. YAM et Z. HASSAN. « STRUCTURAL AND OPTICAL PROPERTIES OF LARGE-SCALE ZnO NANOWIRES AND NANOSHEETS PREPARED BY DRY THERMAL OXIDATION ». Surface Review and Letters 16, n^o 06 (décembre 2009) : 901–4. http://dx.doi.org/10.1142/s0218625x09013451.

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In this work, we report the morphology and optical properties of zinc oxide ( ZnO ) layers prepared by dry thermal oxidation at different annealing conditions. Morphology studies using scanning electron microscope (SEM) show that the amount of nanowires and nanosheets increases with the introduction of a flow of O2 gas. High-resolution X-ray diffraction (HR-XRD) data show that typical polycrystalline ZnO nanostructure layers have been deposited. Near-perfect stoichiometry of Zn and O atom vacancies has been observed from energy dispersion spectroscopy (EDS) spectrum. Photoluminescence (PL) spectra show strong peaks at UV and green regions. An increase in the stoichiometry of ZnO has been achieved with the oxygen gas flow during annealing indicating that deep-level defects represented by interstitial oxygen and antisite oxygen are gas pressure dependent. A single exciton peak with binding energy 60 meV has been observed at room temperature.

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Truong, Vo Doan Thanh, Thi Thanh Truc Nguyen, Thanh Lan Vo, Hoang Trung Huynh et Thi Kim Hang Pham. « Effects of Growth Temperature on Morphological and Structural Properties of ZnO Films ». Journal of Technical Education Science, n^o 72A (28 octobre 2022) : 39–44. http://dx.doi.org/10.54644/jte.72a.2022.1238.

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Zinc oxide (ZnO) is one of the most promising oxide possibilities for use in a number of industries due to its unique properties. Because of its broad direct bandgap (3.37 eV) and strong exciton binding energy (60 meV) at ambient temperature, ZnO not only conducts electricity well but also transmits visible light and emits UV light. Here, we investigated the effect of growth temperature on ZnO thin films by changing the growth temperatures from 400 oC to 450 oC. Radio-frequency (RF) magnetron sputtering was used to create ZnO thin films on Si(100) substrates. The atomic force microscopy (AFM) results show that the root-mean-square (RMS) roughness decreases from 6.1 ± 1.0 nm to 4.8 ± 0.6 nm as the growth temperatures increase. XRD patterns display the enhancement of ZnO’s structure when increasing the growth temperature. Our findings indicate that controlling growth temperature is the critical factor in producing high quality ZnO thin films.

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Zayana, N. Y., et M. Rusop. « Synthesis of ZnO Complex Structures at Different Molar Ratio of Zn (NO₃)₂ and KOH by Precipitation Method ». Advanced Materials Research 576 (octobre 2012) : 330–33. http://dx.doi.org/10.4028/www.scientific.net/amr.576.330.

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ZnO as a semiconductor with wide direct band gap (3.37 eV) and high exciton binding energy of 60 meV. It has attracted in several applications such as solar cells, field emission, sensor, etc. In this study, different ZnO complex structures were prepared by precipitation method at different molar ratio. Zinc nitrate as zinc source, potassium hydroxide as precipitating agent and sodium dodecly sulphate as surfactant were used to synthesis the ZnO. The effect of different molar ratio on the morphology and size of final product have been investigated. The final products were characterized by X-ray diffraction (XRD) with Cu Kα radiation, field emission scanning electron microscopy (FESEM) with an attached energy dispersive x-ray spectroscopy (EDS) and photoluminescence spectrofluorophotometer (PL). From XRD patterns, all synthesized ZnO shows good crystallinity. Different morphologies of synthesized ZnO were obtained from FESEM including flower composed flakes, flower composed radial rods and single straight rods while the EDS result demonstrates elements Zn and O obtained in the product. A very strong UV emission at ~390 nm observed in PL spectra indicated that the ZnO are of high crystal quality.

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Vyas, Sumit. « A Short Review on Properties and Applications of Zinc Oxide Based Thin Films and Devices : ZnO as a promising material for applications in electronics, optoelectronics, biomedical and sensors ». Johnson Matthey Technology Review 64, n^o 2 (1 avril 2020) : 202–18. http://dx.doi.org/10.1595/205651320x15694993568524.

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Zinc oxide has emerged as an attractive material for various applications in electronics, optoelectronics, biomedical and sensing. The large excitonic binding energy of 60 meV at room temperature as compared to 25 meV of gallium nitride, an III-V compound makes ZnO an efficient light emitter in the ultraviolet (UV) spectral region and hence favourable for optoelectronic applications. The high conductivity and transparency of ZnO makes it important for applications like transparent conducting oxides (TCO) and thin-film transistors (TFT). In this paper, the optoelectronic, electronic and other properties that make ZnO attractive for a variety of applications are discussed. Various applications of ZnO thin film and its devices such as light-emitting diodes (LED), UV sensors, biosensors, photodetectors and TFT that have been described by various research groups are presented.

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Que, Miaoling, Chong Lin, Jiawei Sun, Lixiang Chen, Xiaohong Sun et Yunfei Sun. « Progress in ZnO Nanosensors ». Sensors 21, n^o 16 (16 août 2021) : 5502. http://dx.doi.org/10.3390/s21165502.

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Developing various nanosensors with superior performance for accurate and sensitive detection of some physical signals is essential for advances in electronic systems. Zinc oxide (ZnO) is a unique semiconductor material with wide bandgap (3.37 eV) and high exciton binding energy (60 meV) at room temperature. ZnO nanostructures have been investigated extensively for possible use as high-performance sensors, due to their excellent optical, piezoelectric and electrochemical properties, as well as the large surface area. In this review, we primarily introduce the morphology and major synthetic methods of ZnO nanomaterials, with a brief discussion of the advantages and weaknesses of each method. Then, we mainly focus on the recent progress in ZnO nanosensors according to the functional classification, including pressure sensor, gas sensor, photoelectric sensor, biosensor and temperature sensor. We provide a comprehensive analysis of the research status and constraints for the development of ZnO nanosensor in each category. Finally, the challenges and future research directions of nanosensors based on ZnO are prospected and summarized. It is of profound significance to research ZnO nanosensors in depth, which will promote the development of artificial intelligence, medical and health, as well as industrial, production.

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Tran, Thi Ha, Thi Huyen Trang Nguyen, Manh Hong Nguyen, Nguyen Hai Pham, An Bang Ngac, Hanh Hong Mai, Van Thanh Pham et al. « Synthesis of ZnO/Au Nanorods for Self Cleaning Applications ». Journal of Nanoscience and Nanotechnology 21, n^o 4 (1 avril 2021) : 2621–25. http://dx.doi.org/10.1166/jnn.2021.19110.

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Zinc oxide (ZnO) is a well-known semiconductor with valuable characteristics: wide direct band gap of ˜3.3 eV, large exciton binding energy of 60 meV at room temperature, high efficient photocatalyst, etc. which have been applied in many fields such as optical devices (LEDs, laser), solar cells and sensors. Besides, various low dimensional structures of ZnO in terms of nanoparticles, nanorods, nanoneedles, nanotetrapods find applications in technology and life. This material is also appealing due to the diversity of available processing methods including both chemical and physical approaches such as: hydrothermal, sol–gel, chemical vapor deposition and sputtering. In this report, ZnO nanorods are prepared by hydrothermal method assisted with galvanic-cell effect. The effect of counter electrode materials on the morphology and structure of obtained product was studied. Scanning electron microscopy (SEM) images of the product showed that counter electrodes made of aluminum offers nanorods of higher quality than other materials in terms of uniform size, high density and good preferred orientation. The as-prepared nanorods were then sputtered with gold (Au). ZnO/Au nanostructures show excellent photocatalyst activities which were demonstrated by complete photodegradation of methylene blue (Mb) under UV irradiation and high decomposition rate k of 0.011 min-1.

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Kim, Dong Chan, Bo Hyun Kong, Young Yi Kim, Hyung Koun Cho, Jeong Yong Lee et Dong Jun Park. « Effect of Buffer Thickness on the Formation of ZnO Nanorods Grown by MOCVD ». Solid State Phenomena 124-126 (juin 2007) : 101–4. http://dx.doi.org/10.4028/www.scientific.net/ssp.124-126.101.

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ZnO semiconductor has a wide band gap of 3.37 eV and a large exciton binding energy of 60 meV, and displays excellent sensing and optical properties. In particular, ZnO based 1D nanowires and nanorods have received intensive attention because of their potential applications in various fields. We grew ZnO buffer layers prior to the growth of ZnO nanorods for the fabrication of the vertically well-aligned ZnO nanorods without any catalysts. The ZnO nanorods were grown on Si (111) substrates by vertical MOCVD. The ZnO buffer layers were grown with various thicknesses at 400 °C and their effect on the formation of ZnO nanorods at 300 °C was evaluated by FESEM, XRD, and PL. The synthesized ZnO nanorods on the ZnO film show a high quality, a large-scale uniformity, and a vertical alignment along the [0001]ZnO compared to those on the Si substrates showing the randomly inclined ZnO nanorods. For sample using ZnO buffer layer, 1D ZnO nanorods with diameters of 150-200 nm were successively fabricated at very low growth temperature, while for sample without ZnO buffer the ZnO films with rough surface were grown.

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Das, S., S. Sultana, I. Akter, SC Mazumdar, MA Rahman et K. Kali. « Impact of Thickness and Substrate on Optical Properties of Zno Thin Films ». Bangladesh Journal of Physics 27, n^o 1 (13 octobre 2020) : 59–68. http://dx.doi.org/10.3329/bjphy.v27i1.49726.

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During the last decades, ZnO has emerged as the most promising material in optoelectronic and optical applications in the visible region as well as in the infrared and UV region. It is because of the broad direct band gap of 3.37 eV at ambient temperature and high exciton binding energy of 60 meV allowing it to utilize the ultraviolet region. In this investigation, the optical characteristics of ZnO thin film of various thicknesses (300 nm, 600 nm, 900 nm) deposited on Quartz, Fused silica and Sapphire have been studied as a function of wavelength and photon energy. To obtain this, the equations for thin film have been derived, simulated and visualized by Matlab coding language. It is observed that with the increase in the photon energy, the refractive index and extinction coefficient show an increasing tendency. The results represent that among three substrates Fused silica has the lowest refractive index, reflectance and absorbance. In the visible region, the transmission spectra show that the average transmittance of all films is 85%-95%, which is superior for solar continuums. The performance of Fused silica as transparent conducting material is better than other substrates. The present investigation might provide an environment friendly and low cost material for optoelectronic and solar cell devices. Bangladesh Journal of Physics, 27(1), 59-68, June 2020

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Actes de conférences sur le sujet "High Exciton Binding Energy (60 meV)"

Onga, Masaru, Yijin Zhang, Toshiya Ideue et Yoshihiro Iwasa. « Exciton Hall effect and transport of valley exciton in monolayer MoS2 ». Dans JSAP-OSA Joint Symposia. Washington, D.C. : Optica Publishing Group, 2017. http://dx.doi.org/10.1364/jsap.2017.7a_a404_2.

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Transition metal dichalcogenides (TMDs) have attracted vast interest as layered semiconductors with high electrical and optical properties. Among them, monolayer MoS2 is a direct gap semiconductor with its gap energy in the visible range (Fig. 1(a)). Interestingly, excitonic states in monolayer MoS2 are stabilized owing to the intrinsic two-dimensional nature, and the binding energy reaches several hundred meV.

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Wegener, M., I. Bar-Joseph, G. Sucha, M. N. Islam, N. Sauer, T. Y. Chang et D. S. Chemla. « Femtosecond dynamics of excitonic absorption in the infrared InGaAs quantum wells ». Dans Quantum Wells for Optics and Opto-Electronics. Washington, D.C. : Optica Publishing Group, 1989. http://dx.doi.org/10.1364/qwoe.1989.mb4.

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Excitons in III-V quantum wells (QW) are strongly coupled to polar longitudinal optical (LO) phonons. The binding energies of the quasi 2D excitons (Eb ≈ 1-10 meV) are smaller than the energies of the LO-phonons (ℏΩLO=30-40meV). Excitons are thus unstable against LO-phonon collisions which can ionize them and release a free electron hole pair with substantial excess energy. It is clear that this process is temperature dependent. At high temperature the collision rate increases and the excitonic life time can be reduced significantly. An experimental investigations of the dynamics of excitonic nonlinearities in GaAs QWs using femtosecond spectroscopic techniques, was able to time resolve the room temperature exciton ionization . An unexpected finding of these experiments was that a population of excitons is more efficient than electron-hole (e-h) plasma in reducing the strength of the exciton resonances. The experimental findings in GaAs QWs were qualitatively explained by a theory2 that accounts only for the effects of the Fermi statistic and completely neglects the long range screening. An extension of this theory was recently presented by Zimmermann3 which uses an elegant technique to performe exact infinite summations over all excitonic states (bound and unbound).

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Miller, D. A. B. « Physics and applications of room temperature excitonic electroabsorption in quantum wells ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1985. http://dx.doi.org/10.1364/oam.1985.ws1.

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Quantum well systems, where electrons and holes are confined in thin (e.g., 100-Å) layers of a narrow band gap semiconductor (e.g., GaAs) by the adjacent wider band gap semiconductor layers (e.g., GaAIAs), show several interesting optical effects. In addition to making exciton absorption resonance resolvable at room temperature, the confinement results in the quantum-confined Stark effect (QCSE)1; with electric fields perpendicular to the layers of the material, the excitonic absorption shifts by large amounts (e.g., 40 meV). This effect enables high-speed modulators of micron thickness to be made.2 It can be explained as a Stark shift of the exciton energy in which the confinement inhibits the field ionization (which normally would destroy the resonance). Shifts as large as four times the binding energy can be seen at fields corresponding to 200 times the classical ionization field. The structures can also simultaneously operate as photodetectors with photocurrent proportional to absorbed power. Since absorbed power depends on voltage (field) through the QCSE, a simple electronic circuit (e.g., a resistor and bias supply) gives optoelectronic feedback which is the principle of the self-electrooptic effect device (SEED).3 Positive feedback gives optical bistability, while with negative feedback, linearized modulation and optical level shifting are possible. These devices are compatible with diode lasers and semiconductor electronics in wavelengths, power levels, voltages, materials, and fabrication, and offer very low energy operation (e.g., –10 fJ/ square micron).

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