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Титов, В. В., А. А. Лисаченко, И. Х. Акопян, М. Э. Лабзовская i Б. В. Новиков. "Долгоживущие центры фотокатализа, создаваемые в ZnO резонансным возбуждением экситона". Физика твердого тела 61, nr 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 i Mohammad Reza Vaezi. "Synthesis of ZnO Nanoparticles via Sol-Gel Process Using Triethanolamine as a Novel Surfactant". Defect and Diffusion Forum 273-276 (luty 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 i Z. HASSAN. "STRUCTURAL AND OPTICAL PROPERTIES OF LARGE-SCALE ZnO NANOWIRES AND NANOSHEETS PREPARED BY DRY THERMAL OXIDATION". Surface Review and Letters 16, nr 06 (grudzień 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 i Thi Kim Hang Pham. "Effects of Growth Temperature on Morphological and Structural Properties of ZnO Films". Journal of Technical Education Science, nr 72A (28.10.2022): 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., i M. Rusop. "Synthesis of ZnO Complex Structures at Different Molar Ratio of Zn (NO3)2 and KOH by Precipitation Method". Advanced Materials Research 576 (październik 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, nr 2 (1.04.2020): 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 i Yunfei Sun. "Progress in ZnO Nanosensors". Sensors 21, nr 16 (16.08.2021): 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 i in. "Synthesis of ZnO/Au Nanorods for Self Cleaning Applications". Journal of Nanoscience and Nanotechnology 21, nr 4 (1.04.2021): 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 i Dong Jun Park. "Effect of Buffer Thickness on the Formation of ZnO Nanorods Grown by MOCVD". Solid State Phenomena 124-126 (czerwiec 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 i K. Kali. "Impact of Thickness and Substrate on Optical Properties of Zno Thin Films". Bangladesh Journal of Physics 27, nr 1 (13.10.2020): 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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Zolfaghari, Mahmoud, i Mahshid Chireh. "Effect of Mn Dopant on Lattice Parameters and Band Gap Energy of Semiconductor ZnO Nanoparticles". Advanced Materials Research 829 (listopad 2013): 784–89. http://dx.doi.org/10.4028/www.scientific.net/amr.829.784.
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ZnO belongs to the II-VI semiconductor group with a direct band-gap of 3.2-3.37 eV in 300K and a high exciton binding energy of 60 meV. It has good transparency, high electron mobility, wide, and strong room-temperature luminescence. These properties have many applications in a wide area of emerging applications. Doping ZnO with the transition metals gives it magnetic property at room temperature hence making it multifunctional material, i.e. coexistence of magnetic, semiconducting and optical properties. The samples can be synthesized in the bulk, thin film, and nanoforms which show a wide range of ferromagnetism properties. Ferromagnetic semiconductors are important materials for spintronic and nonvolatile memory storage applications. Doping of transition metal elements into ZnO offers a feasible means of tailoring the band gap to use it as light emitters and UV detector. As there are controversial on the energy gap value due to change of lattice parameters we have synthesized Mn-doped ZnO nanoparticles by co-precipitation method with different concentrations to study the effect of lattice parameters changes on gap energy. The doped samples were studied by XRD, SEM, FT-IR., and UV-Vis. The XRD patterns confirm doping of Mn into ZnO structure. As Mn concentrations increases the peak due to of Mn impurity in FT-IR spectra becomes more pronounces hence confirming concentrations variation. We find from UV-Vis spectra that the gap energy due to doping concentration increases due to the Goldschmidt-Pauling rule this increase depends on dopant concentrations and increases as impurity amount increases.
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Zhang, Lei, Liang Heng Wang, Ming Kai Li, Xun Zhong Shang i Yun Bin He. "Structural and Optical Properties of ZnO1-xSx Thin Films Grown by Pulse Laser Deposition on Glass Substrates". Materials Science Forum 787 (kwiecień 2014): 18–22. http://dx.doi.org/10.4028/www.scientific.net/msf.787.18.
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With a wide band gap of 3.4 eV and a large exciton binding energy of 60 meV at room temperature, ZnO is attractive for blue and ultra-violet optoelectronic devices, and transparent conducting oxide films for photovoltaic applications. For a semiconductor to be useful, particularly in reference to optoelectronic devices, band gap engineering is of great importance in device development. Alloying of MgO and CdO with ZnO has been studied extensively in comparison to other ZnO alloys incorporating equivalent anions like ZnO1-xSx (ZnOS). In this work, high-quality ZnOS thin films were grown on glass substrates by pulsed laser deposition using a ZnS ceramic target with varying O2 partial pressures between 0 and 6 Pa. ZnOS alloys with a wurtzite structure were achieved and no evident phase separation was observed in the whole composition range as determined by X-ray diffraction. The optical transmission measurements show that the average transmittance in the visible range of the films is about 80%. The absorption edges of the films first shift towards low-energy side with increasing the oxygen partial pressure and then blueshift when the oxygen partial pressure is over 2 Pa. The bandgap energies of the ZnOS films were calculated to change from 3.06 to 3.72 eV, showing a nonlinear variation with a bowing behavior that was previously reported.
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Singh, Nagendra Pratap, S. A. Shivashankar i Rudra Pratap. "Defect Driven Emission from ZnO Nano Rods Synthesized by Fast Microwave Irradiation Method for Optoelectronic Applications". MRS Proceedings 1633 (2014): 75–80. http://dx.doi.org/10.1557/opl.2014.254.
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ABSTRACTBecause of its large direct band gap of 3.37 eV and high exciton binding energy (∼60 meV), which can lead to efficient excitonic emission at room temperature and above, ZnO nanostructures in the würtzite polymorph are an ideal choice for electronic and optoelectronic applications. Some of the important parameters in this regard are free carrier concentration, doping compensation, minority carrier lifetime, and luminescence efficiency, which are directly or indirectly related to the defects that, in turn, depend on the method of synthesis. We report the synthesis of undoped ZnO nanorods through microwave irradiation of an aqueous solution of zinc acetate dehydrate [Zn(CH3COO)2. 2H2O] and KOH, with zinc acetate dihydrate acting as both the precursor to ZnO and as a self-capping agent. Upon exposure of the solution to microwaves in a domestic oven, ZnO nanorods 1.5 µm -3 µm and 80 nm in diameter are formed in minutes. The ZnO structures have been characterised in detail by X-ray diffraction (XRD), selective area electron diffraction (SAED) and high-resolution scanning and transmission microscopy, which reveal that each nanorod is single-crystalline. Optical characteristics of the nanorods were investigated through photoluminescence (PL) and cathodoluminescence (CL). These measurements reveal that defect state-induced emission is prominent, with a broad greenish yellow emission. CL measurements made on a number of individual nanorods at different accelerating voltages for the electrons show CL intensity increases with increasing accelerating voltage. A red shift is observed in the CL spectra as the accelerating voltage is raised, implying that emission due to oxygen vacancies dominates under these conditions and that interstitial sites can be controlled with the accelerating voltage of the electron beam. Time-resolved fluorescence (TRFL) measurements yield a life time (τ) of 9.9 picoseconds, indicating that ZnO nanorods synthesized by the present process are excellent candidates for optoelectronic devices.
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Mahendra, Robert, Mariesta Arianti, Dyah Sawitri i Doty Dewi Risanti. "Synthesis of Various ZnO Nanotree Morphologies through PEG-Assisted Co-Precipitation Method". Advanced Materials Research 1112 (lipiec 2015): 66–70. http://dx.doi.org/10.4028/www.scientific.net/amr.1112.66.
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ZnO, with direct wide band gap of 3.37 eV and high excitonic binding energy of 60 meV has been attracting much attention due to its wide range of applications, for transparent electronics, solar cells, and other optoelectronics device. We present a simple, single step process to produce ZnO nanotrees using co-precipitation method. As a precursor, zinc nitrate dehydrate was stabilized by hexamethylene tetraamine (HMTA) and 3-9 mM polyethylene glycol (PEG) was added at 180°C for 3-6 hours followed by residual polymer removal. Scanning Electron Microscopy revealed the typical rod-like branched nanostructures were achieved. For longer annealing time the PEG-assisted growth process indeed exhibited a distinctive c-direction inhibition responsible for the lateral growth and subsequent branching of ZnO, in which the branch growth in sample with PEG amount of 0.05 g is the slowest. Some amounts of PEG up to 0.03 g are sensitive to affect several parameters, such as, lattice stress, unit cell volume, density of film and dislocation density.
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Ong, Si Ci, Usman Ilyas i Rajdeep Singh Rawat. "Nanofabrication using home-made RF plasma coupled chemical vapour deposition system". International Journal of Modern Physics: Conference Series 32 (styczeń 2014): 1460342. http://dx.doi.org/10.1142/s2010194514603421.
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Zinc oxide, ZnO , a popular semiconductor material with a wide band gap (3.37 eV) and high binding energy of the exciton (60 meV), has numerous applications such as in optoelectronics, chemical/biological sensors, and drug delivery. This project aims to (i) optimize the operating conditions for growth of ZnO nanostructures using the chemical vapor deposition (CVD) method, and (ii) investigate the effects of coupling radiofrequency (RF) plasma to the CVD method on the quality of ZnO nanostructures. First, ZnO nanowires were synthesized using a home-made reaction setup on gold-coated and non-coated Si (100) substrates at 950 °C. XRD, SEM, EDX, and PL measurements were used for characterizations and it was found that a deposition duration of 10 minutes produced the most well-defined ZnO nanowires. SEM analysis revealed that the nanowires had diameters ranging from 30-100 mm and lengths ranging from 1-4 µm. In addition, PL analysis showed strong UV emission at 380 nm, making it suitable for UV lasing. Next, RF plasma was introduced for 30 minutes. Both remote and in situ RF plasma produced less satisfactory ZnO nanostructures with poorer crystalline structure, surface morphology, and optical properties due to etching effect of energetic ions produced from plasma. However, a reduction in plasma discharge duration to 10 minutes produced thicker and shorter ZnO nanostructures. Based on experimentation conducted, it is insufficient to conclude that RF plasma cannot aid in producing well-defined ZnO nanostructures. It can be deduced that the etching effect of energetic ions outweighed the increased oxygen radical production in RF plasma nanofabrication.
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Abdullahi, Sabiu Said, Garba Shehu Musa Galadanci, Norlaily Mohd Saiden i Josephine Ying Chyi Liew. "Assessment of Magnetic Properties between Fe and Ni Doped ZnO Nanoparticles Synthesized by Microwave Assisted Synthesis Method". Solid State Phenomena 317 (maj 2021): 119–24. http://dx.doi.org/10.4028/www.scientific.net/ssp.317.119.
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The emergence of Dilute Magnetic Semiconductors (DMS) with a potentials for spintronic application have attracted much researches attention, special consideration has been given to ZnO semiconductor material due to its wide band gap of 3.37 eV, large exciting binding energy of 60 meV, moreover, its ferromagnetic behavior at room temperature when doped with transition metals. MxZn1-xO (M = Fe or Ni) nanoparticles were synthesized by microwave assisted synthesis method calcined at 600°C. The structural, morphological and magnetic properties of these nanoparticles were studied using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Vibrating Sample Magnetometer (VSM) respectively. Single phase Wurtzite hexagonal crystal structure was observed for the undoped and Fe doped ZnO nanoparticles with no any impurity, whereas Ni doped ZnO nanoparticles shows the formation of NiO impurities. The magnetic measurement reveals a diamagnetic behavior for the undoped ZnO meanwhile a clear room temperature ferromagnetism was observed for both Fe and Ni doped ZnO. Fe doped ZnO present a high saturation magnetization compared to Ni doped ZnO. However, Ni doped ZnO present high coercivity. The research was confirmed that Fe doped ZnO material will be good material combination for spintronic applications.
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Verma, K. C., Navdeep Goyal i R. K. Kotnala. "Lattice defect-formulated ferromagnetism and UV photo-response in pure and Nd, Sm substituted ZnO thin films". Physical Chemistry Chemical Physics 21, nr 23 (2019): 12540–54. http://dx.doi.org/10.1039/c9cp02285f.
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The induction of charge and spin in diluted magnetic semiconductor ZnO is explored for spintronic devices and its wide direct band gap (3.37 eV) and large exciton binding energy (60 meV) exhibit potential in UV photodetectors.
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Агекян, В. Ф., А. Ю. Серов i Н. Г. Философов. "Оптические спектры кристаллов GaSe и GaS различной толщины". Физика твердого тела 60, nr 6 (2018): 1211. http://dx.doi.org/10.21883/ftt.2018.06.46002.348.
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AbstractThe transmission spectra of GaSe and GaS crystals of different thicknesses prepared by mechanical stratification of bulk crystals have been investigated. The quantum-size shifts of exciton resonances in thin GaSe samples are as high as 12 meV, which is close to the exciton binding energy. The high-energy interband transitions in GaSe and GaS are observed near 3.4 and 3.7 eV, respectively.
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Tsybeskov, Leonid. "Nanocrystalline Silicon for Optoelectronic Applications". MRS Bulletin 23, nr 4 (kwiecień 1998): 33–38. http://dx.doi.org/10.1557/s0883769400030244.
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Light emission in silicon has been intensively investigated since the 1950s when crystalline silicon (c-Si) was recognized as the dominant material in microelectronics. Silicon is an indirect-bandgap semiconductor and momentum conservation requires phonon assistance in radiative electron-hole recombination (Figure 1a, top left). Because phonons carry a momentum and an energy, the typical signature of phonon-assisted recombination is several peaks in the photoluminescence (PL) spectra at low temperature. These PL peaks are called “phonon replicas.” High-purity c-Si PL is caused by free-exciton self-annihilation with the exciton binding energy of ~11 meV. The TO-phonon contribution in conservation processes is most significant, and the main PL peak (~1.1 eV) is shifted from the bandgap value (~1.17 eV) by ~70 meV—that is, the exciton binding energy plus TO-phonon energy (Figure 1a).
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Li, Teng, Hong Liang Pan i Shi Liang Yang. "Simulation of Optical Properties of Ni-Doped ZnO Based on Density Functional Theory". Advanced Materials Research 846-847 (listopad 2013): 1931–34. http://dx.doi.org/10.4028/www.scientific.net/amr.846-847.1931.
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The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60 meV).Based on first-principles spin-density functional calculations, the electronic structures and reflectivity of pure ZnO have been calculated. We find that theory calculated peaks basal consistent with the experiment results. The absorbing properties of Ni doped ZnO have also been calculated and the relationships between electronic structures and absorbing properties are investigated. The results show that the absorbing properties of Co doped ZnO improved significantly compared to pure ZnO system. Absorption frequency peak moves to low frequency and one absorption band appear at 1236.9nm.The theoretical results have offered a direction for the designing and application of ZnO which could lead to lasing action based on exciton recombination even above room temperature.
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Qaid, Saif M. H., Hamid M. Ghaithan, Huda S. Bawazir i Abdullah S. Aldwayyan. "Surface Passivation for Promotes Bi-Excitonic Amplified Spontaneous Emission in CsPb(Br/Cl)3 Perovskite at Room Temperature". Polymers 15, nr 9 (22.04.2023): 1978. http://dx.doi.org/10.3390/polym15091978.
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Perovskite-type lead halides exhibit promising performances in optoelectronic applications, for which lasers are one of the most promising applications. Although the bulk structure has some advantages, perovskite has additional advantages at the nanoscale owing to its high crystallinity given by a lower trap density. Although the nanoscale can produce efficient light emission, its comparatively poor chemical and colloidal stability limits further development of devices based on this material. Nevertheless, bulk perovskites are promising as optical amplifiers. There has been some developmental progress in the study of optical response and amplified spontaneous emission (ASE) as a benchmark for perovskite bulk phase laser applications. Therefore, to achieve high photoluminescence quantum yields (PLQYs) and large optical gains, material development is essential. One of the aspects in which these goals can be achieved is the incorporation of a bulk structure of high-quality crystallization films based on inorganic perovskite, such as cesium lead halide (CsPb(Br/Cl)3), in polymethyl methacrylate (PMMA) polymer and encapsulation with the optimal thickness of the polymer to achieve complete surface coverage, prevent degradation, surface states, and surface defects, and suppress emission at depth. Sequential evaporation of the perovskite precursors using a single-source thermal evaporation technique (TET) effectively deposited two layers. The PL and ASEs of the bare and modified films with a thickness of 400 nm PMMA were demonstrated. The encapsulation layer maintained the quantum yield of the perovskite layer in the air for more than two years while providing added optical gain compared to the bare film. Under a picosecond pulse laser, the PL wavelength of single excitons and ASE wavelength associated with the stimulated decay of bi-excitons were achieved. The two ASE bands were highly correlated and competed with each other; they were classified as exciton and bi-exciton recombination, respectively. According to the ASE results, bi-exciton emission could be observed in an ultrastable CsPb(Br/Cl)3 film modified by PMMA with a very low excitation energy density of 110 µJ/cm2. Compared with the bare film, the ASE threshold was lowered by approximately 5%. A bi-exciton has a binding energy (26.78 meV) smaller than the binding energy of the exciton (70.20 meV).
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Skromme, B. J., i G. L. Martinez. "Optical Activation Behavior of Ion Implanted Acceptor Species in GaN". MRS Internet Journal of Nitride Semiconductor Research 5, S1 (2000): 507–13. http://dx.doi.org/10.1557/s1092578300004701.
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Ion implantation is used to investigate the spectroscopic properties of Mg, Be, and C acceptors in GaN. Activation of these species is studied using low temperature photoluminescence (PL). Low dose implants into high quality undoped hydride vapor phase epitaxial (HVPE) material are used in conjunction with high temperature (1300 °C) rapid thermal anneals to obtain high quality spectra. Dramatic, dose-dependent evidence of Mg acceptor activation is observed without any co-implants, including a strong, sharp neutral Mg acceptor-bound exciton and strong donor-acceptor pair peaks. Variable temperature measurements reveal a band-to-acceptor transition, whose energy yields an optical binding energy of 224 meV. Be and C implants yield only slight evidence of shallow acceptor-related features and produce dose-correlated 2.2 eV PL, attributed to residual implantation damage. Their poor optical activation is tentatively attributed to insufficient vacancy production by these lighter ions. Clear evidence is obtained for donor-Zn acceptor pair and acceptor-bound exciton peaks in Zn-doped HVPE material.
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Kutrowska-Girzycka, J., E. Zieba-Ostój, D. Biegańska, M. Florian, A. Steinhoff, E. Rogowicz, P. Mrowiński i in. "Exploring the effect of dielectric screening on neutral and charged-exciton properties in monolayer and bilayer MoTe2". Applied Physics Reviews 9, nr 4 (grudzień 2022): 041410. http://dx.doi.org/10.1063/5.0089192.
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Dielectric engineering of heterostructures made from two-dimensional van der Waals semiconductors is a unique and powerful tool to tailor the electric and optical band gaps solely via the dielectric environment and the crystal thickness modulation. Here, we utilize high quality MoTe2 monolayer and bilayer crystals as a candidate for near-infrared photonic applications. The crystals are exfoliated on various technologically relevant carrier substrates: silicon/silicon dioxide, poly(methyl methacrylate), hexagonal boron nitride, silicon carbide, and silicon nitride. These substrates provide a large range of high frequency dielectric constants from 2.1 to 7.0 for MoTe2-containing heterostructures. We assess the relationship between the environmental dielectric function and Coulomb screening by combining detailed spectroscopic measurements, utilizing low-temperature and high-spatially resolved photoluminescence and contrast reflectivity, with microscopic many-body modeling, to explore the potential of this less-recognized material platform for applications in optoelectronics at photon wavelengths above 1 μm. We observe a redshift of the optical gap emission energy from the monolayer to bilayer regime on the order of 30 meV. Furthermore, the thickness controlled shift is slightly larger than the one induced by the local dielectric environment, which ranges on the order of 20 meV for the MoTe2 monolayers and on the order of 8 meV for the MoTe2 bilayers. We also show that the local dielectric screening barely affects the trion binding energy, which is captured by our microscopic model, accounting for the screened Coulomb potential for the heterostructures.
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HIRAI, T., K. EDAMATSU, T. ITOH, Y. HARADA i S. HASHIMOTO. "EXCITONS IN COLLOIDAL CuI PARTICLES DISPERSED IN A KI CRYSTAL". International Journal of Modern Physics B 15, nr 28n30 (10.12.2001): 3789–92. http://dx.doi.org/10.1142/s0217979201008676.
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We have investigated the luminescence spectra of colloidal CuI particles dispersed in a KI crystal under low- and high-density excitations of the CuI particles at low temperatures. Under the low-density excitation, we have observed the luminescence of both confined and bulk-like exciton transitions in the CuI particles with zincblende and two kinds of hexagonal structures. In the bulk-like particles with the zincblende structure, the emission line of bound excitons with small binding energy of ~5 meV has been recognized. The biexciton luminescence has been observed under the high-density excitation. We discuss the origins of the various excitonic states observed in the CuI particles dispersed in the KI crystal.
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Sun, Bosong, Wenjin Zhao, Tauno Palomaki, Zaiyao Fei, Elliott Runburg, Paul Malinowski, Xiong Huang i in. "Evidence for equilibrium exciton condensation in monolayer WTe2". Nature Physics 18, nr 1 (23.12.2021): 94–99. http://dx.doi.org/10.1038/s41567-021-01427-5.
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AbstractWe present evidence that the two-dimensional bulk of monolayer WTe2 contains electrons and holes bound by Coulomb attraction—excitons—that spontaneously form in thermal equilibrium. On cooling from room temperature to 100 K, the conductivity develops a V-shaped dependence on electrostatic doping, while the chemical potential develops a step at the neutral point. These features are much sharper than is possible in an independent-electron picture, but they can be accounted for if electrons and holes interact strongly and are paired in equilibrium. Our calculations from first principles show that the exciton binding energy is larger than 100 meV and the radius as small as 4 nm, explaining their formation at high temperature and doping levels. Below 100 K, more strongly insulating behaviour is seen, suggesting that a charge-ordered state forms. The observed absence of charge density waves in this state is surprising within an excitonic insulator picture, but we show that it can be explained by the symmetries of the exciton wavefunction. Therefore, in addition to being a topological insulator, monolayer WTe2 exhibits strong correlations over a wide temperature range.
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He, Fuli, Jia Li, Linyang Li, Xiujuan Mao, Ze Liu, Sukai Teng, Jiaxi Wang i Yafan Wang. "Quasiparticle band structures and optical properties of twisted bilayer MoS2". Europhysics Letters 136, nr 1 (1.10.2021): 17001. http://dx.doi.org/10.1209/0295-5075/ac35b9.
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Abstract A twist angle between two adjacent layers is a key approach to adjust the electronic characteristics of the van der Waals bilayer. The main goal of this study is to accurately predict the quasiparticle band structures and optical properties of bilayer MoS2 with different twist angles , 13.17°, 21.79°, 32.10°, and 60°) by using many-body perturbation G 0 W 0 theory and by solving the Bethe-Salpeter equation including excitonic effects on top of the partially G 0 W 0 calculation when spin-orbit coupling is included. Results of band structures and optical absorption spectrum show that the band gap and optical gap are sensitive to twist angle. Moreover, the twist angles and spin-orbit coupling can manipulate exciton binding energy. Our results also show that spin-orbit coupling and interlayer coupling (predominantly) induced spin splitting as large as 270 meV at the valence band of K point. This argument implies that twisted bilayer MoS2 is a powerful system for tuning the photoluminescence emission.
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Lakshmi, R. Radha, D. Sruthi, K. Prithiv, S. Harippriya i K. R. Aranganayagam. "Synthesis of ZnO and Ag/ZnO Nanorods: Characterization and Synergistic In Vitro Biocidal Studies". Advanced Science Letters 24, nr 8 (1.08.2018): 5490–95. http://dx.doi.org/10.1166/asl.2018.12135.
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The ZnO semiconductor has gained substantial interest in the research community in part because of its large exciton binding energy (60 meV) and direct wide band gap (3.72 eV). ZnO and Ag doped ZnO (Agx Zn1−xO (where x = 0.01, 0.02 and 0.03)) were synthesized by using soft chemical route. The synthesized materials were characterized by using XRD, HRSEM, EDS and HRTEM. The powder XRD pattern indicates that the ZnO and Agx Zn1−xO (where x = 0.01, 0.02 and 0.03) samples exhibits hexagonal wurtzite structure and also the Ag doping decreases the grain size of ZnO nano particles. The micro structural characterizations (HRSEM and HRTEM) reveal the incorporation of Ag into the ZnO lattice and also the formation of nano rods. At the length, the antimicrobial response was also brought against human pathogenic Gram +ve (S. aureus), Gram −ve (E. coli) bacteria and Fungi (C. albicans). Thus the above work brings out the presence of antimicrobial response against the microbes from these nano composites.
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Al-Ani, Ibrahim A. M., Khalil As’Ham, Lujun Huang, Andrey E. Miroshnichenko i Haroldo T. Hattori. "Enhanced strong coupling of WSe2 monolayer by Bound State in the continuum". Journal of Physics: Conference Series 2172, nr 1 (1.02.2022): 012009. http://dx.doi.org/10.1088/1742-6596/2172/1/012009.
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Abstract Due to the large binding energy and direct bandgap, transition-metal dichalcogenides (TMDCs) monolayers have been considered a perfect platform for realising strong coupling at room temperature. It is well established that the quality factor (Q-factor) plays a crucial role in enhancing strong coupling. In this work, we demonstrate the improved strong coupling between the exciton of the WSe2 monolayer and the high Q cavity resonance based on symmetry protected magnetic dipole (MD) bound state in the continuum (BIC). We have found that the Rabi-splitting of the strongly coupled system could be largely enhanced by adjusting the location of the TMDC monolayer, increasing the Q-factor, and reducing the grating thickness. After carefully adjusting the three critical parameters, a Rabi-splitting as high as 38 meV was achieved limited by the oscillator strength of the WSe2 monolayer. Our system could be considered an excellent platform to realise ultra-thin polaritonic devices.
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Ren, Yinjuan, Zhigao Huang i Yue Wang. "Dynamic and giant bandgap renormalization dictates the transient optical response in perovskite quantum dots". Applied Physics Letters 121, nr 25 (19.12.2022): 251103. http://dx.doi.org/10.1063/5.0131286.
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Transient optical response in perovskite quantum dots (QDs) has remained elusive until now, which hinders their full utilization in optoelectronics. Herein, we reveal that the bandgap renormalization (BGR) dictates the main spectral and dynamical features of transient response in CsPbBr3 QDs. By monitoring the absorption spectral evolution of the monodispersed QDs, the representative BGR is explicitly observed, giving rise to the photoinduced absorption at the higher energy side of the lowest exciton peak in transient absorption spectroscopy. The BGR gradually increases upon photoexcitation as a result of the carrier distribution dependent screening effect. We further demonstrate that the BGR arises from both Coulomb screening and phonon heating under high pump intensities in CsPbBr3 QDs. The synergistic effect leads to the giant BGR energy (Δ E > 60 meV) and the unconventional relationship of Δ E [Formula: see text] n1/2, where n is the carrier density. These findings are important for the fundamental understanding and potential applications of the emerging halide perovskite semiconductors.
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Du, Aochen, Wenxiao Zhao, Yu Peng, Xinzhi Qin, Zexi Lin, Yun Ye, Enguo Chen, Sheng Xu i Tailiang Guo. "Cs(Pb,Mn)Br3 Quantum Dots Glasses with Superior Thermal Stability for Contactless Electroluminescence Green−Emitting LEDs". Nanomaterials 13, nr 1 (20.12.2022): 17. http://dx.doi.org/10.3390/nano13010017.
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CsPbX3 (X = Cl, Br or I) perovskite quantum dots (PQDs) have gained increasing interest due to their superior performance in photoelectric applications. In our work, a series of Mn2+ doped CsPbBr3 PQDs were successfully prepared in glasses by melt quenching and in situ crystallization technique. Due to the 4T1 (4G)→6A1 (6S) transition of Mn2+, a slight red shift from 510 nm to 516 nm was found, with the FWHM expansion from 18 nm to 26 nm. The PQDs@glasses showed excellent thermal stability, and the exciton binding energy reached a high level of 412 meV. The changes of the electronic structure after Mn doping CsPbBr3 can be demonstrated by first principles. Finally, a contactless electroluminescence device with the PQDs@glasses was designed based on the principle of electromagnetic induction, which is a potential application for detecting distance in sterile and dust−free environments.
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Su, Rui, Jun Wang, Jiaxin Zhao, Jun Xing, Weijie Zhao, Carole Diederichs, Timothy C. H. Liew i Qihua Xiong. "Room temperature long-range coherent exciton polariton condensate flow in lead halide perovskites". Science Advances 4, nr 10 (październik 2018): eaau0244. http://dx.doi.org/10.1126/sciadv.aau0244.
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Novel technological applications significantly favor alternatives to electrons toward constructing low power–consuming, high-speed all-optical integrated optoelectronic devices. Polariton condensates, exhibiting high-speed coherent propagation and spin-based behavior, attract considerable interest for implementing the basic elements of integrated optoelectronic devices: switching, transport, and logic. However, the implementation of this coherent polariton condensate flow is typically limited to cryogenic temperatures, constrained by small exciton binding energy in most semiconductor microcavities. Here, we demonstrate the capability of long-range nonresonantly excited polariton condensate flow at room temperature in a one-dimensional all-inorganic cesium lead bromide (CsPbBr3) perovskite microwire microcavity. The polariton condensate exhibits high-speed propagation over macroscopic distances of 60 μm while still preserving the long-range off-diagonal order. Our findings pave the way for using coherent polariton condensate flow for all-optical integrated logic circuits and polaritonic devices operating at room temperature.
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Yang, Feng, Kui Ying Li, Jing Zhi Sun, Mang Wang, Gang Wu i Yong Zhao. "Direct Measurement and Identification of Nonradiative Processes in ZnO Nanocrystallines by Combining Photoacoustic Spectroscopy with Surface Photovoltage Spectroscopy". Advanced Materials Research 361-363 (październik 2011): 831–39. http://dx.doi.org/10.4028/www.scientific.net/amr.361-363.831.
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Nonradiative transitions (NRTs) are relaxation processes competing with radiative process. In light emitting diodes and room temperature laser devices, NRTs lower the emission efficiency. In order to prohibit these processes, better understanding is practically needed. But nowadays knowledge of NRTs comes from the analyses of the steady-state and time-resolved photoluminescence spectra, which are indirect evidences because of their radiative nature. Here we report a direct detection of nonradiative processes of ZnO nanocrystallines by combination of photoacoustic spectroscopy (PAS) with field-induced photovoltaic spectroscopy (FISPS) methods. In photoacoustic spectrum of ZnO nanocrystals, a main feature centered at 374 nm and a shoulder feature at 441 nm have been recorded. The surface photovoltage spectrum (SPS) displays a main peak at about 364 nm, which is assigned to band-gap transition. And the FISPS spectrum shows a main feature at 380 nm and a pronounced shoulder at 450 nm. The relative energy of the PAS main feature locates at about 0.1 eV lower than that of band-gap, and the relative energy of the PAS main and shoulder features locates at 60 meV higher than that of FISPS main and shoulder features. These energy spaces are in good consistent with the exciton binding energy reported for ZnO nanostructures. Thus we tentatively ascribe the NRTs to the trapping of the photogenerated excitons to the surface states of ZnO nanocrystallines.
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Chi, Le Ha, Pham Duy Long, Hoang Vu Chung, Do Thi Phuong, Do Xuan Mai, Nguyen Thi Tu Oanh, Thach Thi Dao Lien i Le Van Trung. "Galvanic-Cell-Based Synthesis and Photovoltaic Performance of ZnO-CdS Core-Shell Nanorod Arrays for Quantum Dots Sensitized Solar Cells". Applied Mechanics and Materials 618 (sierpień 2014): 64–68. http://dx.doi.org/10.4028/www.scientific.net/amm.618.64.
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Zinc oxide (ZnO) is recognized as one of the most attractive metal oxides because of its direct wide band gap (3.37 eV) and large exciton binding energy (60 meV), which make it promising for various applications in solar cells, gas sensors, photocatalysis and so on. Here, we report a facile synthesis to grow well-aligned ZnO nanorod arrays on SnO2: F (FTO) glass substrates without the ZnO seed layer using a Galvanic-cell-based method at low temperature (<100°C). CdS quantum dot thin films were then deposited on the nanorod arrays in turn by an effective successive ionic layer adsorption and reaction (SILAR) process to form a ZnO/CdS core-shell structure electrode. Structural, morphological and optical properties of the ZnO/CdS nanorod heterojunctions were investigated. The results indicate that CdS quantum dot thin films were uniformly deposited on the ZnO nanorods and the thickness of the CdS shell can be controlled by varying the number of the adsorption and reaction cycles. The number of quantum dots layers affects on photovoltaic performance of the ZnO/CdS core-shell nanorod arrays has been investigated as photoanodes in quantum dots sensitized solar cells.
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Badran, Rashad I., Yas Al-Hadeethi, Ahmad Umar, Saleh H. Al-Heniti, Bahaaudin M. Raffah, M. Shahnawaze Ansari i Asim Jilani. "Temperature-dependent heterojunction device characteristics of n-ZnO nanorods/p-Si assembly". Materials Express 10, nr 1 (1.01.2020): 29–36. http://dx.doi.org/10.1166/mex.2020.1595.
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Heterojunction diode based on n-ZnO nanorods/p-Silicon (Si) assembly was fabricated, examined and reported here. Horizontal quartz tube thermal evaporation technique was used for the growth of ZnO nanorods on Si substrate. The nanorods were characterized by several techniques to examine the structural, morphological, scattering and electrical properties. Wurtzite hexagonal phase of the grown aligned nanorods was observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The appearance of a sharp Raman peak at 438 cm–1 was observed and it is related to the E2(high) mode of the wurtzite hexagonal phase of ZnO. The electrical properties of the fabricated heterojunction assembly were examined at different temperatures (298∼398 K) in both reverse and forward biased conditions, and a good stability was observed over the entire temperature range. A reduction in the turn-on and breakdown voltage was observed with increasing temperature. By increasing the temperature, the effective potential barrier height was increased, while quality factor was decreased. The observed activation energy was found to be ∼93.4 meV, higher than the exciton binding energy of ZnO.
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Sharma, Rakesh Kumar, Sandeep Patel i Kamlesh Chandra Pargaien. "Mn-Doped ZnO Micro and Nanocrytals: Synthesis, Characterization and Properties". Advanced Materials Research 665 (luty 2013): 182–88. http://dx.doi.org/10.4028/www.scientific.net/amr.665.182.
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The development of highly sensitive, selective, reliable, low power and compact sensing devices to detect gas is of major importance for terrestrial and space applications. The gas response to different gases and chemicals is related to a great extent to the surface state and morphology of the materials. Zinc oxide (ZnO) is a direct wide band gap semiconductor with an energy gap of ~3.37 eV and a large exciton binding energy of ~60 meV at room temperature (RT) is a promising candidate for functional component for devices and materials in chemical and gas sensors and so on. ZnO nanostructures with various interesting structures and properties have been synthesized, such as nanoparticles, nanorods, nanobelts, nanocombs, nanowires, tetrapod nanostructures. Mn-doped hexagonal (ZnO) semiconductor micro and nanostructures have been synthesized by a simple one-step aqueous solution method at relatively low temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and photoluminescence spectroscopy (PL) have been used to characterize the samples in detail. The XRD studies revealed that Mn doped ZnO micro and nanostructures had wurtzite structure (hexagonal). The as-synthesized ZnO micro and nanostructures consist of very uniform and no secondary phase is observed. X-ray diffraction and EDX results provide the evidence that Mn is incorporated into the ZnO crystals. A strong and wide ultraviolet emission has been observed for the Mn doped ZnO micro and nanocrystals as evidenced by the photoluminescence spectra at room temperature.PL spectra reveals that as synthesized samples are highly pure and crystalline. Magnetism in these samples was also studied by using vibrating sample magnetometer.
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Kim, Yun Hae, Jin Woo Lee, Riichi Murakami, Dong Myung Lee, Jin Cheol Ha i Pang Pang Wang. "Effect of Atmosphere Temperature on Physical Properties of ZnO/Ag/ZnO on PET Films". Advanced Materials Research 988 (lipiec 2014): 125–29. http://dx.doi.org/10.4028/www.scientific.net/amr.988.125.
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Transparent conductive layers on flexible substrates are important components of today’s optoelectronic technology. They are used in filters for plasma displays, low-e windows, solar cells, etc. At present, in-doped indium oxide (ITO) layers on PET substrate is the predominant transparent conducting oxide film in diverse practical applications. However, ITO is a relatively expensive material because indium is not abundant, but aluminum-doped zinc oxide (AZO) film is emerging as an alternative potential candidate to ITO thin film due to its abundance as a raw material, nontoxic nature, cost-effectiveness, easy fabrication, and good stability in plasma. They have, however, several drawbacks: they exhibit relatively high electrical resistance (sheet resistance, 20-200Ω), considerable emissivity, and significant absorption in the spectral region 1-2μm, in which transition from high transmittance to high reflectance takes place. Furthermore, these films do not block solar thermal radiation (0.7-3μm), which may cause overheating problems to devices such as electro-chromic and photovoltaic devices. On the other hand, ITO/Ag/ITO multilayer films are used to achieve high transparent conducting properties. A thin silver layer of about 10nm thickness is embedded between two ITO layers. The ITO/Ag/ITO film has very low sheet resistance, high optical transparency in the visible range, relatively lower thickness than single-layered ITO film, and better durability than single-layered silver film. In terms of ZnO, which is a wide direct band-gap semiconductor, ZnO has a band-gap energy of 3.37 eV with a binding energy as high as 60 meV at room temperature. ZnO has been applied to various domains for excellent physical and chemical properties, such as piezoelectric sensors, rheostats , gas sensors, semiconductor lasers, and transparent conductive films.
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Sun, Ya Juan, i Wan Xing Wang. "Optical and Electrical Properties of P-Type N-Doped ZnO Film". Key Engineering Materials 609-610 (kwiecień 2014): 113–17. http://dx.doi.org/10.4028/www.scientific.net/kem.609-610.113.
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Since ZnO is a wide band gap (3.37 eV) semiconductor with a large exitonic binding energy (60 meV), it has been considered as a candidate for various applications, such as ultraviolet (UV) light emitting diodes and laser diodes. For the applications of ZnO-based optoelectronic devices, it is necessary to produce n and p type ZnO films with the high quality. Since ZnO is naturally n-type semiconductor material due to intrinsic defects, such as oxygen vacancies, zinc interstitials, etc., it is easy to produce n-type ZnO with high quality. However, it is difficult to produce low-resistive and stable p-type ZnO due to its asymmetric doping limitations and the self-compensation effects of the intrinsic defects. According to the theoretical studies, p-type ZnO can be realized using group-V dopants substituting for O, such as N, P and As. Among them, N has been suggested to be an effective acceptor dopant candidate to achieve p-type ZnO, because that nitrogen has a much smaller ionic size than P and As and the energy level of substitutional NOis lower than that of substitutional POand AsO.Transparent p-type ZnO: N thin films have been fabricated using the pulsed laser deposition method at deposition temperatures 800 °C under the O2and N2mixing pressure 6Pa. N-doped ZnO films were deposited on sapphire substrate using metallic zinc (99.999%) as target. The structural, optical and electrical properties of the films were examined by XRD, UV-visit spectra and Hall effect measurement. We found that thin film contain the hexagonal ZnO structure. The Hall effect measurement revealed that the carrier concentration is 5.84×10181/ cm3, and Hall mobility is 0.26 cm2/Vs, electrical resistivity is 4.12ohm-cm. Film thickness is 180nm. Besides, Visible light transmittance is more than 80%, and calculative band-gap is 3.1 eV, which is lower than ZnO.
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Rabiee, Navid, Mojtaba Bagherzadeh, Amir Mohammad Ghadiri, Mahsa Kiani, Abdullah Aldhaher, Seeram Ramakrishna, Mohammadreza Tahriri, Lobat Tayebi i Thomas J. Webster. "Green Synthesis of ZnO NPs via Salvia hispanica: Evaluation of Potential Antioxidant, Antibacterial, Mammalian Cell Viability, H1N1 Influenza Virus Inhibition and Photocatalytic Activities". Journal of Biomedical Nanotechnology 16, nr 4 (1.04.2020): 456–66. http://dx.doi.org/10.1166/jbn.2020.2916.
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Among different forms of metallic nanoparticles (NPs), zinc oxide (ZnO) NPs with a very special bandgap of 3.37 eV and considerable binding energy of excitation (60 meV at room temperature), have been classified as high-tech nanoparticles. This study aimed to synthesize ZnO NPs using the extract from Salvia hispanica leaves. The synthesized nanoparticles were fully characterized and the photocatalytic activity was evaluated through the degradation of methylene blue. Additionally, the potential in vitro biological activities of such ZnO NPs in terms of their antibacterial activity were determined, as well as their antioxidant (30 minutes), antiviral (48 hours) and mammalian cell viability properties (48 and 72 hours). This study is the first investigation into the synthesis of such green ZnO NPs mediated by this plant extract, in which both photocatalytic and biomedical properties were found to be promising. The IC50 values for the antibacterial activities were found to be around 17.4 μg mL–1 and 28.5 μg mL–1 for S. aureus and E. coli, respectively, and the antioxidant activity was comparable with the standard BHT. However, the H1N1 inhibition rate using the present green ZnO NPs was lower than oseltamivir (up to about 40% for ZnO NPs and above 90% for oseltamivir) which was expected since it is a drug, but was higher than many synthetic nanoparticles reported in the literature. In addition, the mammalian cell viability assay showed a higher than 80% cellular viability in the presence of 5, 10 and 20 μg mL–1 nanoparticles, and showed a higher than 50% cellular viability in the presence of 50 and 75 μg mL–1 nanoparticles. In this manner, this study showed that these green ZnO NPs should be studied for a wide range of medical applications.
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Dawka, Sahil, Pengjun Duan, Raju Sapkota i Chris Papadopoulos. "Thin Film Photodetectors Based on Zinc Oxide Nanoinks". ECS Meeting Abstracts MA2022-01, nr 31 (7.07.2022): 1329. http://dx.doi.org/10.1149/ma2022-01311329mtgabs.
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Zinc oxide (ZnO) has many useful properties for electronics and optoelectronics including wide band gap, large exciton binding energy, low-cost, ease of processing and availability [1]. This has led to increased interest and development of thin film electronics, transparent conductors, solar cells, light-emitting diodes, lasers, photodetectors and various sensors based on ZnO materials [2, 3]. The high surface areas and tunable properties of ZnO nanostructures make them particularly suitable for applications such as sensing and photonic devices [4, 5]. In this work, we present results on nanostructured ZnO thin film photodetectors fabricated using nanoparticle inks (nanoinks) obtained via planetary ball milling (PBM) of bulk powders. PBM [6] is an emerging solution-based nanofabrication approach that can quickly produce nanoink suspensions at low-cost by nanoscale grinding, without complex processing and suitable for thin film coating of various materials on different substrates [7]. The thin film photodetector devices were fabricated by depositing PBM ZnO nanoink onto flat insulating glass substrates followed by contact formation as shown schematically in Fig. 1a: PBM was performed using ZnO powder in ethylene glycol (EG) or deionized (DI) water solvent (a.k.a. colloidal grinding) with zirconia grinding beads. The grinding speed and time were varied between 200 and 1000 rpm and 10 min. and 60 min., respectively. A few μL of the resulting ZnO nanoink was used to coat the substrate surface and dried at ~ 100 °C. Lastly, two electrical contacts to the resulting films were made using silver paint and copper tape. Analysis of ZnO films after deposition showed they consist of nanostructured particles with sizes reaching below 100 nm, as displayed in the scanning electron microscopy (SEM) and atomic force microscopy (AFM) images in Fig. 1b, depending on grinding conditions (speed, time). The optical properties of the ZnO thin films were evaluated via photoluminescence measurements (Fig. 1c), which, in addition to interband transitions in the UV, displayed longer wavelength emission peaks due to surface and bulk defect states. Such deep level states are dependent on grinding parameters and thus allow the accessible spectrum for the nanostructured ZnO films to be extended into the visible region in a tunable manner. Two-terminal photoconductance data of the ZnO PBM nanoink thin film devices were obtained using a probe station and precision source-measure unit, with and without illumination, under ambient atmosphere and at room temperature. Fig. 1d shows current vs. voltage curves obtained for a typical photodetector device, which display current increasing proportional to incident light intensity. This behavior can be explained by electron-hole pair creation and desorption of surface oxygen species (leading to vacancies that act as donors) upon photon absorption, which leads to an increase in conductance. This is consistent with previous studies where ZnO thin films have been used for photoconductive sensor applications, validating PBM nanoink as a suitable synthesis technique for the active material in photodetectors. Compared to standard ZnO thin films, the PBM nanoink method allows both particle dimensions and surface states to be tailored and optimized for different photodetector applications in a straightforward manner by adjusting grinding conditions. In particular, both UV and visible light detection can be tuned via the solution-based ZnO nanoink approach presented without additional material/chemical processing. Such PBM nanoinks thus offer the potential of realizing low-cost photodetectors and multifunctional thin film coatings for applications in optoelectronics, imaging, environmental monitoring and communications. References [1] C. Klingshirn, Phys. Status Solidi B, 244, 3027 (2007). [2] R. Chen and L. Lan, Nanotechnology, 30, 312001 (2019). [3] J. Huang, A. Yin and Q. Zheng, Energy Environ. Sci., 4, 3861 (2011). [4] Y. Tu et al., ACS Sens., 5, 3568 (2020). [5] W. Tian et al., Adv. Mater., 25, 4625 (2013). [6] C. F. Burmeister and A. Kwade, Chem Soc. Rev., 42, 7660 (2013). [7] R. Sapkota, J. Zou, S. Dawka, J. E. Bobak and C. Papadopoulos, Appl. Nanosci., 8, 1437 (2018). Figure 1
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Wei, M., D. Zhi i J. L. MacManus-Driscoll. "Self Seeded ZnO Nanowire Growth by Ultrasonic Spray Assisted Chemical Vapour Deposition". MRS Proceedings 879 (2005). http://dx.doi.org/10.1557/proc-879-z10.2.
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AbstractZnO, which exhibits a direct bandgap of 3.37 eV at room temperature with a large exciton binding energy of 60 meV,is of considerable technological importance because of its potential use in short-wavelength devices, such as ultraviolet (UV) light-emitting diodes and laser diodes. The fabrication and application of 1-D ZnO nanostructures has attracted considerable interest in recent years. In this work, we produced single crystal nanowires of zinc oxide using a novel self-seeded growth using ultrasonic spray assisted chemical vapour deposition, in which a nanocrystalline seed layer was first deposited onto a glass substrate and the nanowires subsequently grown using a different precursor concentration and substrate temperature. The diameter of the nanowires is in the range of 20-80 nm and the length of the wires is as long as 10 μm. The single crystal nature of the nanowires was revealed by high resolution transmission electron microscopy. The formation of liquid droplets due to the reducing atmosphere and the higher temperature during the nanowire growth was found to be the key step of the ZnO nanowire formation.
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Tagliente, Maria Antonella, Marcello Massaro, Giovanni Mattei, Paolo Mazzoldi, Giovanni Pellegrini, Valentina Bello i Daniela Carbone. "On the Structural and Optical Properties of ZnO Nanoparticles Formed in Silica by Ion Implantation". MRS Proceedings 942 (2006). http://dx.doi.org/10.1557/proc-0942-w08-36.
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ABSTRACTZinc Oxide (ZnO) is a II-VI semiconductor material with a wide direct band-gap of 3.37 eV at room temperature (RT). In the past decades, the material has been used for a variety of applications such as gas sensors, surface acoustic wave devices, or transparent contacts. Recently, ZnO has gained a new substantial interest primarily because to its potentialities for optoelectronic and spintronic applications. The renewed interest has been fueled by the availability of high-quality bulk substrates, reports of p-type conduction and theoretical predictions of its ferromagnetic behavior at room temperature when doped with transition metals. In the domain of optoelectronics, its main applications include devices emitting in the blue and UV regions by exploiting its wide band-gap such as light-emitting and laser diodes. With respect to several wide band-gap semiconductor materials, ZnO has the advantage of a larger exciton binding energy (about 60 meV) which paves the way for an intense near-band-edge excitonic emission at room and higher temperatures. On the other hand, a band gap engineering can be also achieved by the incorporation of Cadmium and Magnesium atoms into the ZnO lattice.Many techniques have been used to prepare ZnO in various forms, such as single crystals, powders and films. In the past few years, the great attention toward materials with nanometric size have motivated a number of studies on the synthesis of ZnO nanocrystals. Ion implantation is one of the most effective and versatile technique to obtain nanoparticles. ZnO particles embedded in silica matrix have been successfully prepared by ion implantation followed by thermal oxidation.In this work, we report on a detailed structural and optical characterization of the ZnO-silica nanocomposites by using several complementary techniques; in particular, Glancing Incidence X-ray Diffraction (GIXRD), Rutherford Backscattering Spectrometry (RBS), linear Optical Absorption (OA) in the UV-near IR spectrum and Photo-Luminescence (PL). The ZnO nanoparticles embedded in SiO2 matrix were prepared by implanting the substrates with 130 keV Zn+ ions at doses of 1, 1.5 and 2´1017 ions/cm2. Subsequently, the implanted samples were annealed for 1h in a furnace at a temperature between 500 and 800°C under flowing O2 gas. X-ray diffraction results indicate the formation of Zn and ZnO nanoparticles in the as-implanted and annealed samples, respectively. Moreover, the ZnO nanocrystals embedded in the SiO2 matrix have a (002) preferred orientation. After the oxidation, the optical absorption spectra show an absorption edge at about 374 nm by confirming the presence of the ZnO particles. A relatively strong exciton photoluminescence peak was observed at room temperature under pulsed N2 laser excitation at l=337nm. The results obtained, peculiarly related to the implantation doses and annealing temperature, are discussed.
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Rebane, Y. T., Y. G. Shreter i M. Albrecht. "Excitons Bound to Stacking Faults in Wurtzite GaN". MRS Proceedings 468 (1997). http://dx.doi.org/10.1557/proc-468-179.
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ABSTRACTA model of the exciton bound to stacking faults (SF) in GaN is suggested. It is shown that SFs are potential wells (depth ∼ 120 meV) for electrons and potential barriers (∼ 60 meV) for holes. The binding energy of the exciton at stacking faults is estimated as 30 − 60 meV. The 364 nm line in GaN photoluminescence is attributed to excitons at stacking faults.
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Wang, Jian, Daniel Moses, Alan J. Heeger, N. Kirova i S. Brazovski. "Electric Field Induced Ionization of the Exciton in Poly(Phenylene Vinylene)". MRS Proceedings 660 (2000). http://dx.doi.org/10.1557/proc-660-jj2.10.
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ABSTRACTThe exciton binding energy (Eb) and the band gap energy (Eg) of poly(phenylene vinylene), PPV, have been determined by photoconductivity excitation profile spectroscopy as a function of light polarization, applied electric field, and temperature. The spectral signature of the exciton is a narrow peak (100 meV full width at half maximum) that emerges just below the band edge upon increasing the external field, the temperature or the defect density. The exciton peak is observed only for light polarized parallel to the chain axis. The exciton binding energy is obtained from the energy of the exciton peak with respect to the band edge and, independently from analysis of the field dependence of the exciton dissociation. It is Eb ≈ 60 meV.
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Panda, Nihar Ranjan, i Dojalisa Sahu. "Exhibition of novel photocatalytic activity and photoluminescence properties with high inhibition towards bacterial growth by hydrothermally grown ZnO nanorods". Current Nanoscience 16 (28.07.2020). http://dx.doi.org/10.2174/1573413716999200728175722.
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Background: Metal oxide nanomaterial such as; ZnO shows novel structural, optical, electrical and antibacterial properties due to wide band gap (3.37 eV) and high excitonic binding energy (60 meV). Probing these inherent properties of nanosized ZnO with different morphology has generated new interest among researchers Objective: To investigate the size dependent functional attributes, ZnO nanorods were prepared by hydrothermal method and the photocatalytic (PC) efficiency was studied. The photoluminescence (PL) property of ZnO nanorods was also studied by recording the emission spectrum under photo-excitation. These nanorods (NRs) were coated on cotton fabric to study the effectiveness of these NRs in defending and inhibiting the growth of different bacteria Methods: The crystallographic structure and morphology of the ZnO samples were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopic (FESEM) measurements. PL measurement at room temperature was undertaken by exciting the sample with light of wavelength 350 nm. The PC property of ZnO NRs was studied in degrading organic dyes like methylene blue. Bacteria like Staphylococcus aureus, Escherichia coli and Bacillus subtilis were cultured and the inhibition of growth of these bacteria was studied by the application of ZnO. To enhance the microbe defence mechanism of fabric, we coated these NRs on fabric test samples and investigated the bacterial growth on it. Results: XRD and FESEM studies reveal the dimension of the synthesized products in nano range. These nanorods are of high density and surface roughness as per the FESEM study. PL measurement shows the presence of strong UV emission at 382 nm with defect emissions in the blue-green region opening up the path for ZnO to be used in fabrication of optoelectronic devices. PC study reveals that 89% degradation of methylene blue (MB) dye is achievable in 180 min using these ZnO catalysts. The anti-bacterial study shows that the minimum inhibitory concentration (MIC) of ZnO nanorods coated on the fabric against S. aureus is found to be 3.5 mg/ml which is the minimum as compared to E. coli (7.5 mg/ml) and B. subtilis (5.5 mg/ml). The study further enunciates that fabric coated with ZnO samples exhibited considerably high inhibition activity toward S. aureus. Conclusion: The study shows that ZnO NRs can be effectively used for fabrication of UV-LASER/LED. Photocatalytic efficiency of ZnO will be useful for degradation of organic dyes controlling environment pollution. It further enunciates that fabric coated with ZnO samples exhibited considerably high inhibition activity toward S. aureus (skin bacteria) which will be helpful in defending microbes if used in surgical cotton bandages
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Jung, Eilho, Jin Cheol Park, Yu-Seong Seo, Ji-Hee Kim, Jungseek Hwang i Young Hee Lee. "Unusually large exciton binding energy in multilayered 2H-MoTe2". Scientific Reports 12, nr 1 (16.03.2022). http://dx.doi.org/10.1038/s41598-022-08692-1.
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AbstractAlthough large exciton binding energies of typically 0.6–1.0 eV are observed for monolayer transition metal dichalcogenides (TMDs) owing to strong Coulomb interaction, multilayered TMDs yield relatively low exciton binding energies owing to increased dielectric screening. Recently, the ideal carrier-multiplication threshold energy of twice the bandgap has been realized in multilayered semiconducting 2H-MoTe2 with a conversion efficiency of 99%, which suggests strong Coulomb interaction. However, the origin of strong Coulomb interaction in multilayered 2H-MoTe2, including the exciton binding energy, has not been elucidated to date. In this study, unusually large exciton binding energy is observed through optical spectroscopy conducted on CVD-grown 2H-MoTe2. To extract exciton binding energy, the optical conductivity is fitted using the Lorentz model to describe the exciton peaks and the Tauc–Lorentz model to describe the indirect and direct bandgaps. The exciton binding energy of 4 nm thick multilayered 2H-MoTe2 is approximately 300 meV, which is unusually large by one order of magnitude when compared with other multilayered TMD semiconductors such as 2H-MoS2 or 2H-MoSe2. This finding is interpreted in terms of small exciton radius based on the 2D Rydberg model. The exciton radius of multilayered 2H-MoTe2 resembles that of monolayer 2H-MoTe2, whereas those of multilayered 2H-MoS2 and 2H-MoSe2 are large when compared with monolayer 2H-MoS2 and 2H-MoSe2. From the large exciton binding energy in multilayered 2H-MoTe2, it is expected to realize the future applications such as room-temperature and high-temperature polariton lasing.
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Wang, Jue, Christina Manolatou, Yusong Bai, James Hone, Farhan Rana i Xiaoyang Zhu. "Disorder of Excitons and Trions in Monolayer MoSe2". Journal of Chemical Physics, 19.09.2022. http://dx.doi.org/10.1063/5.0108001.
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The optical spectra of transition metal dichalcogenide (TMDC) monolayers are dominated by excitons and trions. Here we establish the dependences of these optical transitions on disorder from hyperspectral imaging of h-BN encapsulated monolayer MoSe2. While both exciton and trion energies vary spatially, these two quantities are almost perfectly correlated, with spatial variation in the trion binding energy of only ~0.18 meV. In contrast, variation in the energy splitting between the two lowest energy exciton states is one order of magnitude larger at ~1.7 meV. Statistical analysis and theoretical modeling reveal that disorder results from dielectric and bandgap fluctuations, not electrostatic fluctuations. Our results shed light on disorder in high quality TMDC monolayers, its impact on optical transitions, and the many-body nature of excitons and trions.
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Skromme, B. J., J. Jayapalan, D. Wang i O. F. Sankey. "Magnetoluminescence and Resonant Electronic Raman Scattering Investigation of Donors and Excitons in Hydride Vpe and Mocvd GaN". MRS Proceedings 482 (1997). http://dx.doi.org/10.1557/proc-482-537.
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AbstractThe donor and exciton states in ultra high-quality heteroepitaxial GaN grown by hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD) on sapphire substrates are investigated using low temperature photoluminescence (PL), reflectance, magnetospectroscopy in fields up to 12 T, and resonant electronic Raman scattering (RERS). The A free exciton is confirmed to have a binding energy of about 26.4 meV, independent of strain in the material. Bound n=2 exciton peaks are distinguished in the PL spectrum by their thermalization and sample dependence. The Si donor is shown to have a binding energy of about 21 meV using Si-doped HVPE samples grown at Epitronics. Up to five additional residual donor species are observed when comparing various HVPE and MOCVD samples. Pronounced temperaturedependence of the two-electron satellites is observed, suggesting the existence of unresolved excited rotator states of the neutral donor-bound exciton. Highly resolved magnetic splitting patterns are observed in the two-electron satellites. A nonperturbative theory of these donor splittings is developed, including anisotropy. Resonant electronic Raman scattering from residual donors is reported, and yields improved linewidths compared to PL.
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Skromme, B. J. "Photoluminescence, Magnetospectroscopy, and Resonant Electronic Raman Studies of Heteroepitaxial Gallium Nitride". MRS Internet Journal of Nitride Semiconductor Research 4, nr 1 (1999). http://dx.doi.org/10.1557/s1092578300000715.
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Optical spectroscopy, including low and room temperature photoluminescence (PL), reflectance, PL measurements in high magnetic fields up to 12 T, and resonantly-enhanced electronic Raman scattering (RERS) in zero and high magnetic field, has been used to investigate exciton and impurity states and surface recombination in high quality heteroepitaxial GaN grown on sapphire and SiC. Theoretical finite-difference calculations of the donor states as a function of magnetic field have been carried out for comparison, including the effects of anisotropy in the effective mass and dielectric constant. Up to six residual donor species are observed in material grown by hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD) from their n=2 and n=3 two-electron satellites observed in PL and by RERS. The donor-related nature of the relevant transitions is confirmed from their magnetic field dependence, and the spectral resolution is improved at high fields. The Si donor level is determined to have a binding energy of about 21 meV from observation of its two-electron satellite in lightly Si-doped HVPE material. The free exciton binding energy is shown to be about 26.4 meV, independent of strain, based on observations of the n=2 free exciton. The room temperature band-edge PL peak is confirmed to be free excitonic in nature, based on its linewidth and on comparison with simple reflectance measurements. Reflectance from the edge of a thick HVPE layer shows clear evidence of A, B, and C excitons obeying the relevant selection rules at both low and room temperature. Surface chemical treatments are shown to have substantial effects on room temperature PL efficiency. Passivation with ammonium or sodium sulfide solutions, in particular, yields increases in PL efficiency by a factor of five to seven over air-exposed surfaces. The passivation effect is stable in air, lasting at least one month.
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Wang, Fanjie, Chong Wang, Andrey Chaves, Chaoyu Song, Guowei Zhang, Shenyang Huang, Yuchen Lei i in. "Prediction of hyperbolic exciton-polaritons in monolayer black phosphorus". Nature Communications 12, nr 1 (24.09.2021). http://dx.doi.org/10.1038/s41467-021-25941-5.
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AbstractHyperbolic polaritons exhibit large photonic density of states and can be collimated in certain propagation directions. The majority of hyperbolic polaritons are sustained in man-made metamaterials. However, natural-occurring hyperbolic materials also exist. Particularly, natural in-plane hyperbolic polaritons in layered materials have been demonstrated in MoO3 and WTe2, which are based on phonon and plasmon resonances respectively. Here, by determining the anisotropic optical conductivity (dielectric function) through optical spectroscopy, we predict that monolayer black phosphorus naturally hosts hyperbolic exciton-polaritons due to the pronounced in-plane anisotropy and strong exciton resonances. We simultaneously observe a strong and sharp ground state exciton peak and weaker excited states in high quality monolayer samples in the reflection spectrum, which enables us to determine the exciton binding energy of ~452 meV. Our work provides another appealing platform for the in-plane natural hyperbolic polaritons, which is based on excitons rather than phonons or plasmons.
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Chu, Zihao, Huanqing Chen, Xinrui Mao, Yanping Li, Wanjin Xu i Guang Zhao Ran. "Anisotropic Exciton-Polaritons in 2D Single-Crystalline PEA2PbBr4 Perovskites at Room Temperature". Journal of Physics D: Applied Physics, 31.01.2023. http://dx.doi.org/10.1088/1361-6463/acb783.
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Abstract Two-dimensional (2D) single-crystalline perovskites are a suitable material for investigating the strong exciton-photon interaction due to the large exciton binding energy. Here, we in-situ grow high-quality 2D single-crystalline PEA2PbBr4 thin film in-between a pair of distributed Bragg reflectors (DBRs) and construct an anisotropic exciton-polariton microcavity. The clear evidence for strong exciton-photon coupling is observed and represented by a large coupling strength of 211.8 meV. The observed TE-TM splitting at the point where in-plane wave vector is zero indicates the crystal birefringence. The effective refractive indices for these two orthogonal polarization directions are derived to have a large difference, corresponding to a material index difference of 0.28 and then the in-plane refractive index ellipse is built for the material. This work shows that the 2D anisotropic perovskite microcavity can not only behave as a platform for characterizing the anisotropic properties of a material but also as a promising room-temperature polaritonic device.