Artykuły w czasopismach: „Nanocrystals - Surface Defects”

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Korbutyak, D. V. "SURFACE LUMINESCENCE OF A2B6 SEMICONDUCTOR QUANTUM DOTS (REVIEW)". Optoelektronìka ta napìvprovìdnikova tehnìka 56 (7.12.2021): 27–38. http://dx.doi.org/10.15407/iopt.2021.56.027.

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Semiconductor zero-dimensional nanocrystals – quantum dots (QDs) – have been increasingly used in various fields of opto- and nanoelectronics in recent decades. This is because of the exciton nature of their luminescence, which can be controlled via the well known quantum-dimensional effect. At the same time, at small nanocrystall sizes, the influence of the surface on the optical and structural properties of nanocrystals increases significantly. The presence of broken bonds of surface atoms and point defects – vacancies and interstial atoms – can both weaken the exciton luminescence and create new effective channels of radiant luminescence. In some cases, these surface luminescence becomes dominant, leading to optical spectra broadening up to the quasi-white light. The nature of such localized states often remains unestablished due to the large number of the possible sorts of defects in both of QD and its surrounding. In contrast to exciton luminescence, which can be properly described within effective-mass approximations, the optical properties of defects relay on chemical nature of both defect itsself and its surrounding, what cannot be provided by “hydrogen-type coulomb defect” approximation. Moreover, charge state and related to this lattice relaxation must be taken into account, what requires an application of atomistic approach, such as Density functioal theory (DFT). Therefore, this review is devoted to the study of surface (defect) states and related luminescence, as well as the analysis of possible defects in nanocrystals of semiconductor compounds A2B6 (CdS, CdZnS, ZnS), responsible for luminescence processes, within ab initio approach. The review presents the results of the authors' and literature sources devoted to the study of the luminescent characteristics of ultra-small (<2 nm) QDs.

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Natrayan, L., P. V. Arul Kumar, S. Kaliappan, S. Sekar, Pravin P. Patil, R. Jayashri i E. S. Esakki Raj. "Analysis of Incorporation of Ion-Bombarded Nickel Ions with Silicon Nanocrystals for Microphotonic Devices". Journal of Nanomaterials 2022 (16.08.2022): 1–7. http://dx.doi.org/10.1155/2022/5438084.

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Nanotechnology is playing a greater role in biomedical engineering. Microphotonic technology is on another side, having faster growth with more requirements. The nanocrystals are a part of nanotechnology which uses silicon for manufacturing. These silicon nanocrystals have the optical property mostly used in microphotonic devices. Silicon nanocrystals are of biocompatibility with less toxicity. Therefore, the advancement in the silicon nanocrystal helps develop more microphotonic devices for biological purposes. One critical factor of silicon nanocrystal is the surface defects or surface imperfections. Surface passivation is the method employed for rectifying this disadvantage of silicon nanocrystal. Another major thing is that silicon nanocrystals are size dependent. So proper variation on the surface is required for yielding high performance of the nanocrystal. After characterizing the surface of the silicon nanocrystal, ion bombardment can occur. Nickel is a lustrous white chemical element which is less reactive when it is of a smaller size. So ion bombardment of nickel ion on the surface of the silicon nanocrystal can be done to improvise the performance of the microphotonic devices. Nearly there is an excess of 20 a.u. of photoluminescence intensity yielded. The relative fluorescence is also increased by 150 a.u. This research work enhanced the silicon nanocrystal using ion bombardment of nickel ion, which increased energy traps resulting in more intensities.

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Li, Xinke, Fangtian You, Hongshang Peng i Shihua Huang. "Synthesis and Near-Infrared Luminescent Properties of NaGdF4:Nd3+@NaGdF4 Core/Shell Nanocrystals with Different Shell Thickness". Journal of Nanoscience and Nanotechnology 16, nr 4 (1.04.2016): 3940–44. http://dx.doi.org/10.1166/jnn.2016.11818.

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The near-infrared to near-infrared (NIR-to-NIR) photoluminescence of nanocrystals has outstanding advantages in biological imaging. NaGdF4:Nd3+ core nanocrystals and NaGdF4:Nd3+@NaGdF4 core/shell nanocrystals with different shell thicknesses were synthesized by a simple solvothermal method. The obtained nanocrystals were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The phase of all nanocrystals is hexagonal. NaGdF4:Nd3+ core nanocrystals have an average size of 6 nm. By controlling core–shell ratio for 1:2 and 1:3, we obtained NaGdF4:Nd3+@NaGdF4 core/shell nanocrystals with average sizes of 10 nm and 11 nm, respectively. When excited at 808 nm, strong NIR emission was observed. The emission peaks at ∼860 nm, ∼1060 nm and ∼1330 nm correspond to the transitions from the 4F3/2 statetothe 4I9/2, 4I11/2 and 4I13/2 state of Nd3+ ions, respectively. The emission intensity of NaGdF4:Nd3+@NaGdF4 core/shell nanocrystals is stronger than that of the core. The intensity increases with the increase of shell thickness. The shell improves the luminous efficiency by reducing surface defects. The decay time of Nd3+ emission in NaGdF4:Nd3+@NaGdF4 core/shell nanocrystal is longer than that in NaGdF4:Nd3+ core, indicating that the shell isolates effectively the emitting ions (Nd3+)from the quenching defects. With the increase of shell thickness, the decay time becomes longer. Within a certain range of shell thickness, thicker shell can protect the emitting Nd3+ ions on the surface of core nanocrystals more effectively.

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Erdem, Emre. "Defect induced p-type conductivity in zinc oxide at high temperature: electron paramagnetic resonance spectroscopy". Nanoscale 9, nr 31 (2017): 10983–86. http://dx.doi.org/10.1039/c7nr03988c.

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It has been observed that the defect centers on the surface play a crucial role in the conductivity behavior of ZnO. Above 300 °C only surface defects can be visible in EPR spectra for ZnO nanocrystals which indicate p-type conductivity.

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Xu, Lili, Man Wang, Qing Chen, Jiajia Yang, Wubin Zheng, Guanglei Lv, Zewei Quan i Chunxia Li. "Rare Earth Hydroxide as a Precursor for Controlled Fabrication of Uniform β-NaYF4 Nanoparticles: A Novel, Low Cost, and Facile Method". Molecules 24, nr 2 (19.01.2019): 357. http://dx.doi.org/10.3390/molecules24020357.

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In recent years, rare earth doped upconversion nanocrystals have been widely used in different fields owing to their unique merits. Although rare earth chlorides and trifluoroacetates are commonly used precursors for the synthesis of nanocrystals, they have certain disadvantages. For example, rare earth chlorides are expensive and rare earth trifluoroacetates produce toxic gases during the reaction. To overcome these drawbacks, we use the less expensive rare earth hydroxide as a precursor to synthesize β-NaYF4 nanoparticles with multiform shapes and sizes. Small-sized nanocrystals (15 nm) can be obtained by precisely controlling the synthesis conditions. Compared with the previous methods, the current method is more facile and has lower cost. In addition, the defects of the nanocrystal surface are reduced through constructing core–shell structures, resulting in enhanced upconversion luminescence intensity.

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Matsui, Yutaka, Teppei Kazama i Atsushi Yamashita. "Influence of surface modification by organic molecules on optical properties of Eu³⁺-doped ZnO nanocrystals". Japanese Journal of Applied Physics 62, nr 3 (1.03.2023): 035001. http://dx.doi.org/10.35848/1347-4065/acbbb4.

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Abstract We have fabricated Eu3+-doped ZnO (ZnO:Eu) nanocrystals (NCs) surface-modified with organic molecules such as dodecylamine (DDA) and tri-n-octylphosphine oxide (TOPO) and have studied their optical properties. In the ZnO:Eu NCs without surface modification, strong broad photoluminescence (PL) band due to surface defects is observed, so the Eu3+ PL peaks are not observed because they are covered by the strong surface-defect PL band. In the DDA-capped ZnO:Eu NCs, the Eu3+ PL and the exciton PL are observed because of suppression of the surface-defect PL caused by the inactivation of the surface defects. Contrary to expectations, the surface modification with TOPO suppressed not only the surface-defect PL but also the exciton PL. As a result, the ZnO:Eu NCs with red PL due to the Eu3+ ions have been successfully prepared. We discuss the influence of surface modification by DDA and TOPO on optical properties.

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Kukushkin S. A., Osipov A. V., Redkov A. V., Stozharov V. M., Ubiyvovk E. V. i Sharofidinov Sh. Sh. "Peculiarities of nucleation and growth of InGaN nanowires on SiC/Si substrates by HVPE". Technical Physics Letters 48, nr 2 (2022): 66. http://dx.doi.org/10.21883/tpl.2022.02.53584.19056.

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The growth of InGaN layers on hybrid SiC/Si substrates with orientations (100), (110), and (111) by the HVPE method was studied at temperatures that wittingly exceed the temperature of InN decomposition onto nitrogen atoms and metallic In (1000oC). On substrates with orientations (110) and (111), the formation of InGaN whisker nanocrystals was observed. The shape and growth mechanisms of nanocrystals were investigated. It is shown that nanocrystals nucleate on the (111) surface only inside V-defects formed at the points where screw dislocations exit onto the surface. On the (110) surface, nanocrystals are formed only on pedestals that arise during the film growth. An explanation is given for the difference in the growth mechanisms of nanocrystals on substrates of different orientations. Keywords: InGaN, heterostructures, SiC on Si, silicon, whisker nanocrystals, nanostructures, atomic substitution method

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Xue, Xiaogang, Hualin Chi, Xiuyun Zhang, Juan Xu, Jian Xiong i Jinsheng Zheng. "Oriented assembly of CdS nanocrystals via dynamic surface modification-tailored particle interaction". Physical Chemistry Chemical Physics 21, nr 35 (2019): 19548–53. http://dx.doi.org/10.1039/c9cp03403j.

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Кукушкин, С. А., А. В. Осипов, А. В. Редьков, В. М. Стожаров, Е. В. Убыйвовк i Ш. Ш. Шарофидинов. "Особенности зарождения и роста нитевидных нанокристаллов InGaN на подложках SiC/Si методом хлорид-гидридной эпитаксии". Письма в журнал технической физики 48, nr 4 (2022): 24. http://dx.doi.org/10.21883/pjtf.2022.04.52080.19056.

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The growth of InGaN layers on hybrid SiC/Si substrates with orientations (100), (110), and (111) by the HVPE method was studied at temperatures that wittingly exceed the temperature of InN decomposition onto nitrogen atoms and metallic In (1000C). On substrates with orientations (110) and (111), the formation of InGaN nanocrystals was observed. The shape and growth mechanisms of nanocrystals were investigated. It is shown that nanocrystals nucleate on the (111) surface only inside V-defects formed at the points where screw dislocations exit onto the surface. On the (110) surface, nanocrystals are formed only on pedestals that arise during the film growth. An explanation is given for the difference in the growth mechanisms of nanocrystals on substrates of different orientations.

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Forde, Aaron, Erik Hobbie i Dmitri Kilin. "Role of Pb2+ Adsorbents on the Opto-Electronic Properties of a CsPbBr3 Nanocrystal: A DFT Study". MRS Advances 4, nr 36 (2019): 1981–88. http://dx.doi.org/10.1557/adv.2019.268.

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ABSTRACTFully inorganic lead halide perovskite nanocrystals (NCs) are of interest for photovoltaic and light emitting devices due to optoelectronic properties. Understanding the surface chemistry of these materials is of importance as surface defects can introduce trap-states which reduce their functionality. Here we use Density Functional Theory (DFT) to model surface defects introduced by Pb2+ on a CsPbBr3 NC atomistic model. Two types of defects are studied: (i) an under-coordinated Pb2+ surface atom and (ii) Pb2+ atomic or molecular adsorbents to the NC surface. From the DFT calculations we compute the density of states (DOS) and absorption spectra of the defect models to the pristine fully-passivated NC model. We observe that for the low surface defect regime explored here that neither (i) or (ii) produce trap-states inside of the bandgap and exhibit bright optical absorption for the lowest energy transition. From the models studied, it was found that the Pb2+ atomic absorbent provides broadening of the conduction band edge, which implies chemisorption of Pb2+ to the NC surface. At higher defect densities it would be expected that Pb2+ atomic absorbents would introduce trap-states and degrade the opto-electronic properties of these materials.

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Liu, Hu, Yongsheng Yu, Weiwei Yang, Wenjuan Lei, Manyi Gao i Shaojun Guo. "High-density defects on PdAg nanowire networks as catalytic hot spots for efficient dehydrogenation of formic acid and reduction of nitrate". Nanoscale 9, nr 27 (2017): 9305–9. http://dx.doi.org/10.1039/c7nr03734a.

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LAYEK, ARUNASISH, i ARINDAM CHOWDHURY. "ZnO-NANOCRYSTALS IN STRONG CONFINEMENT REGIMES: INSIGHT ON RELAXATION DYNAMICS OF DEFECT STATES RESPONSIBLE FOR THE VISIBLE LUMINESCENCE". International Journal of Nanoscience 10, nr 04n05 (sierpień 2011): 681–85. http://dx.doi.org/10.1142/s0219581x11008940.

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The broad visible photoluminescence (PL) observed in ZnO nanocrystals (NCs) is widely attributed to multiple low lying surface-defects. We have performed steady state and time-resolved PL measurements on size-selected ZnO NCs in the strong confinement regimes. Our results show that radiative relaxation rates and coupling between excitons and surface defect states vary dramatically for sizes between 2 nm and 3 nm. Energy dependent PL lifetimes reveal that relaxation dynamics of these defect states in the blue- and red-edge of the emission are very different from each other.

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Xiong, Yu, Pingyu Xin, Wenxing Chen, Yu Wang, Shaolong Zhang, Hanlin Ren, Hongpan Rong i in. "PtAl truncated octahedron nanocrystals for improved formic acid electrooxidation". Chemical Communications 54, nr 32 (2018): 3951–54. http://dx.doi.org/10.1039/c8cc00970h.

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Peng, Ling Ling, Bi Tao Liu i Tao Han. "Fluorescence Enhancement of ZnS Nanocrystals via Ultraviolet Irradiation". Applied Mechanics and Materials 556-562 (maj 2014): 27–31. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.27.

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ZnS nanocrystals were prepared via chemical precipitation method and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) and photoluminescence (PL) spectra. The results indicated that the ZnS nanocrystals have cubic zinc blende structure and diameter is 3.68 nm as demonstrated by XRD. The morphology of nanocrystals is spherical measured by TEM which shows the similar particle size. The photoluminescence spectrum peaking at about 424 nm was due mostly to the trap-state emission, and a satellite peak at 480nm ascribed to the dangling bond of S in the surface of ZnS nanocrystals. The emission intensity of ZnS was enhanced after ultraviolet irradiation, the enhancement of the Photoluminescence intensity was due to the elimination of the surface defects after ultraviolet irradiation, for the growth of the coated shell on ZnS nonacrystals, the Photoluminescence intensity was increased as ultraviolet irradiation time growth, finally tends to be stable for the surface state of nanocrystals steady.

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Lee, Hyun Joo, i Soo Il Lee. "Surface Passivation of CdS/Zn2 SiO4b Nanocomposites Prepared by a Wet Chemical Route". Journal of Nanoscience and Nanotechnology 6, nr 11 (1.11.2006): 3369–72. http://dx.doi.org/10.1166/jnn.2006.012.

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Highly luminescent CdS/Zn2SiO4 nanocrystals were prepared by a wet chemical method. The effect of surface passivation was observed in photoluminescence measurements of CdS nanocrystals embedded in colloidal nanocrystallite or amorphous Zn2SiO4 matrix. The resultant luminescent emission of as-prepared CdS/Zn2SiO4 nanocomposite thin films displays two distinct components. One is attributed to the band-edge emission and the other is due to the surface defects. The effect of aging on CdS/Zn2SiO4 nanocomposite thin films has been investigated, showing the active role of Zn2SiO4 matrixin modifying the surface states.

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Chen, Lan, Pete Fleming, Virginia Morris, Justin D. Holmes i Michael A. Morris. "Size-Related Lattice Parameter Changes and Surface Defects in Ceria Nanocrystals". Journal of Physical Chemistry C 114, nr 30 (12.07.2010): 12909–19. http://dx.doi.org/10.1021/jp1031465.

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Mudedla, Sathish Kumar, Maisa Vuorte, Elias Veijola, Kaisa Marjamaa, Anu Koivula, Markus B. Linder, Suvi Arola i Maria Sammalkorpi. "Effect of oxidation on cellulose and water structure: a molecular dynamics simulation study". Cellulose 28, nr 7 (3.03.2021): 3917–33. http://dx.doi.org/10.1007/s10570-021-03751-8.

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AbstractEnzymatic cleavage of glycocidic bonds is an important, green and biocompatible means to refine lignocellulosic biomass. Here, the effect of the resulting oxidation point defects on the structural and water interactions of crystalline cellulose {100} surface are explored using classical molecular dynamics simulations. We show that even single oxidations reduce the connections within cellulose crystal significantly, mostly via local interactions between the chains along the surface plane but also via the oxidation defects changing the structure of the crystal in direction perpendicular to the surface. Hydrogen bonding on the surface plane of cellulose is analyzed to identify onset of desorption of glucose chains, and the desorption probed. To assess the actual soluble product profile and their fractions resulting from lytic polysaccharide monooxygenase (LPMO) enzyme oxidation on real cellulose crystal samples, we employ High-Performance Anion-Exchange Chromatography with Pulsed Amperometric-Detection (HPAEC-PAD) technique. The findings demonstrate the LPMO oxidation results in soluble glucose fragments ranging from 2 to 8 glucose units in length. Additionally, significantly more oxidized oligosaccharides were released in LPMO treatment of AaltoCell than Avicel, the two studied microcrystalline cellulose species. This is likely to result from the large reactive surface area preserved in AaltoCell due to manufacturing process. Furthermore, as can be expected, the oxidation defects at the surfaces lead to the surfaces binding a larger amount of water both via direct influence by the defect but also the defect induced protrusions and fluctuations of the glucose chain. We quantify the enhancement of water interactions of cellulose crystals due to the oxidation defects, even when no desorption takes place. The molecular simulations indicate that the effect is most pronounced for the C1-acid oxidation (carboxylic acid formation) but present also for the other defects resulting from oxidation. The findings bear significance in understanding the effects of enzymatic oxidation on cellulose nanocrystals, the difference between cellulose species, and cleavage of soluble products from the cellulosic material.

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Jia, Tiekun, Chenxi Sun, Nianfeng Shi, Dongsheng Yu, Fei Long, Ji Hu, Jilin Wang i in. "Efficient Oxygen Vacancy Defect Engineering for Enhancing Visible-Light Photocatalytic Performance over SnO2−x Ultrafine Nanocrystals". Nanomaterials 12, nr 19 (25.09.2022): 3342. http://dx.doi.org/10.3390/nano12193342.

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Regardless of its good electron-transfer ability and chemical stability, pure Zn2SnO4 (ZSO) still has intrinsic deficiencies of a narrow spectral response region, poor absorption ability, and high photo-activated carrier recombination rate. Aiming to overcome the deficiencies above-mentioned, we designed a facile hydrothermal route for etching ZSO nanoparticles in a dilute acetic acid solution, through which efficient oxygen vacancy defect engineering was accomplished and SnO2−x nanocrystals were obtained with an ultrafine particle size. In comparison with the untreated ZSO nanoparticles, the specific surface area of SnO2−x nanocrystals was substantially enlarged, subsequently leading to the notable augmentation of active sites for the photo-degradation reaction. Aside from the above, it is worth noting that SnO2−x nanocrystals were endowed with a broad spectral response, enhancing light absorption capacity and the photo-activated carrier transfer rate with the aid of oxygen vacancy defect engineering. Accordingly, SnO2−x nanocrystals exhibited significantly enhanced photoactivity toward the degradation of the organic dye rhodamine B (RhB), which could be imputed to the synergistic effect of increasing active sites, intensified visible-light harvesting, and the separation rate of the photo-activated charge carrier caused by the oxygen vacancy defect engineering. In addition, these findings will inspire us to open up a novel pathway to design and prepare oxide compound photocatalysts modified by oxygen vacancy defects in pursuing excellent visible-light photoactivity.

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Li, Yingwei, Wuding Ling, Qifeng Han, Tae Whan Kim i Wangzhou Shi. "Localized surface plasmon resonances and its related defects in orthorhombic Cu3SnS4 nanocrystals". Journal of Alloys and Compounds 633 (czerwiec 2015): 347–52. http://dx.doi.org/10.1016/j.jallcom.2015.02.042.

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Toma, Maria, Oleksandr Selyshchev, Yevhenii Havryliuk, Aurel Pop i Dietrich R. T. Zahn. "Optical and Structural Characteristics of Rare Earth-Doped ZnO Nanocrystals Prepared in Colloidal Solution". Photochem 2, nr 3 (2.07.2022): 515–27. http://dx.doi.org/10.3390/photochem2030036.

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ZnO nanocrystals doped with Nd, Gd, and Er were synthesized using a soft chemical process in ambient atmosphere. Pseudospherical and hexagonal nanocrystals (NC) of the wurtzite phase with a mean size of (7.4 ± 1.7) nm were obtained. The presence of rare earth (RE) dopants was confirmed by X-ray fluorescence (XRF) spectroscopy. The ZnO nanocrystals exhibited simultaneously narrow excitonic- and broad trap/surface-related photoluminescence (PL), both of which were affected by doping with RE atoms. Doping reduced the total PL intensity, suppressing the excitonic emission by a greater extent than the broad band PL. Also, doping resulted in a blue shift of the trap/surface-related emission, while the energy of the excitonic peak remained unchanged. Resonant Raman spectra additionally confirmed the wurtzite phase of ZnO NCs and revealed a shift of the A1-LO mode towards lower frequency upon doping that could be caused by the mass effect of RE atoms, point defects, and increases in charge carrier concentration. Fitting of the spectra with Voigt profiles showed better results with two surface optical (SO) phonon modes that were previously theoretically predicted for the wurtzite ZnO phase. The influence of RE doping on PL and Raman spectra can be explained by the incorporation of RE ions into the ZnO nanostructures, where the dopants act as non-radiative defects.

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Lisovskyy, I. P., M. V. Voitovych, V. V. Voitovych i I. M. Khacevich. "Influence of Radiation on the Luminescence of Silicon Nanocrystals Embedded into SiO2Film". Journal of Nanomaterials 2016 (2016): 1–7. http://dx.doi.org/10.1155/2016/9674741.

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Influence ofγ-irradiation on light emission properties of silicon nanocrystals imbedded into SiO2film is investigated. It was shown that small doses ofγ-irradiation (103–105 rad) lead to enhancement of photoluminescence intensity in the nc-Si/SiO2samples. This effect was explained by radiation induced passivation of recombination active centers on the nanocrystals surface. High doses of irradiation (~107 rad) lead to the photoluminescence intensity decrease up to 2 times. Radiation treatment of silicon oxide films with embedded amorphous silicon inclusions resulted only in the decrease of the photoluminescence intensity within the whole range of doses (103–5 × 107 rad). Radiation defects resulting in partial quenching of photoluminescence are characterized with the distributed activation energy of annealing with the peak position at ~0.96 eV and the frequency factor 107 s−1. The nature of such defects and the mechanisms of their creation are discussed.

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Ye, Chen, i Yu Huan. "Studies on Electron Escape Condition in Semiconductor Nanomaterials via Photodeposition Reaction". Materials 15, nr 6 (13.03.2022): 2116. http://dx.doi.org/10.3390/ma15062116.

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In semiconductor material-driven photocatalysis systems, the generation and migration of charge carriers are core research contents. Among these, the separation of electron-hole pairs and the transfer of electrons to a material’s surface played a crucial role. In this work, photodeposition, a photocatalysis reaction, was used as a “tool” to point out the electron escaping sites on a material’s surface. This “tool” could be used to visually indicate the active particles in photocatalyst materials. Photoproduced electrons need to be transferred to the surface, and they will only participate in reactions at the surface. By reacting with escaped electrons, metal ions could be reduced to nanoparticles immediately and deposited at electron come-out sites. Based on this, the electron escaping conditions of photocatalyst materials have been investigated and surveyed through the photodeposition of platinum. Our results indicate that, first, in monodispersed nanocrystal materials, platinum nanoparticles deposited randomly on a particle’s surface. This can be attributed to the abundant surface defects, which provide driving forces for electron escaping. Second, platinum nanoparticles were found to be deposited, preferentially, on one side in heterostructured nanocrystals. This is considered to be a combination result of work function difference and existence of heterojunction structure.

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Schaper, Andreas K., Fritz Phillipp i Haoqing Hou. "Melting Behavior of Copper Nanocrystals Encapsulated in Onion-like Carbon Cages". Journal of Materials Research 20, nr 7 (1.07.2005): 1844–50. http://dx.doi.org/10.1557/jmr.2005.0230.

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Nanoparticulate materials are promising objects for studying the processes that triggermelting of solids. On a pyrolytic route, we successfully encapsulated 20–60 nm diameter Cu nanocrystals within multilayer graphitic carbon spheres. In situ electron microscope observations of the melting and displacement of the encapsulated Cu nanocrystals at temperatures up to 1175 K have provided clear evidence of the process of surface melting and its dependence on the quality of the metal/carbon interface. Detection of crystal defects inside the Cu particles during melting and vaporization has proved that the metal phase maintains its solid crystalline state in the particle center. Indications of the influence of surface anisotropy on the melting behavior were obtained. The carbon cages as a whole remained unchanged during the observations.

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Chung, Sung-Yoon, Si-Young Choi, Tae-Hwan Kim i Seongsu Lee. "Surface-Orientation-Dependent Distribution of Subsurface Cation-Exchange Defects in Olivine-Phosphate Nanocrystals". ACS Nano 9, nr 1 (13.01.2015): 850–59. http://dx.doi.org/10.1021/nn506495x.

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Ma, Xiaoqing, Zongkai Wu, Emily J. Roberts, Ruirui Han, Guodong Rao, Zeqiong Zhao, Maximilian Lamoth, Xiaoli Cui, R. David Britt i Frank E. Osterloh. "Surface Photovoltage Spectroscopy Observes Sub-Band-Gap Defects in Hydrothermally Synthesized SrTiO3 Nanocrystals". Journal of Physical Chemistry C 123, nr 41 (6.09.2019): 25081–90. http://dx.doi.org/10.1021/acs.jpcc.9b06727.

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Villa, Irene, Anna Vedda, Mauro Fasoli, Roberto Lorenzi, Niklaus Kränzlin, Felix Rechberger, Gabriele Ilari i in. "Size-Dependent Luminescence in HfO2 Nanocrystals: Toward White Emission from Intrinsic Surface Defects". Chemistry of Materials 28, nr 10 (3.05.2016): 3245–53. http://dx.doi.org/10.1021/acs.chemmater.5b03811.

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Yu, Xiaomei, Boseong Kim i Yu Kwon Kim. "Highly Enhanced Photoactivity of Anatase TiO2 Nanocrystals by Controlled Hydrogenation-Induced Surface Defects". ACS Catalysis 3, nr 11 (7.10.2013): 2479–86. http://dx.doi.org/10.1021/cs4005776.

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Harrigan, William L., Samuel E. Michaud, Keith A. Lehuta i Kevin R. Kittilstved. "Tunable Electronic Structure and Surface Defects in Chromium-Doped Colloidal SrTiO3−δ Nanocrystals". Chemistry of Materials 28, nr 2 (8.01.2016): 430–33. http://dx.doi.org/10.1021/acs.chemmater.6b00049.

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Moreira, Ibério de P. R., Jacek C. Wojdeł, Francesc Illas, Mario Chiesa i Elio Giamello. "Evidence of magnetic ordering of paramagnetic surface defects on partially hydroxylated MgO nanocrystals". Chemical Physics Letters 462, nr 1-3 (wrzesień 2008): 78–83. http://dx.doi.org/10.1016/j.cplett.2008.07.060.

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Babak, Jaleh, Ashrafi Ghazaleh, Gholami Nasim, Azizian Saeid, Golbedaghi Reza, Habibi Safdar i Parsian Hosein. "Study of Heating Effect on Specific Surface Area, and Changing Optical Properties of ZnO Nanocrystals". Advanced Materials Research 403-408 (listopad 2011): 1205–10. http://dx.doi.org/10.4028/www.scientific.net/amr.403-408.1205.

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In this work ZnO nanocrystal powders have been synthesized by using Zinc acetate dehydrate as a precursor and sol-gel method. Then the products have been annealed at temperature of 200-1050°C, for 2 hours. The powders were characterized using X-ray diffraction (XRD), UV-vis absorption and photoluminescence (PL) spectroscopy. The morphology of refrence ZnO nanoparticles have been studied using Transmission Electron Microscope (TEM). During the annealing process, increase in nanocrystal size, defects and energy gap quantitative, and decrease in specific surface area have been observed.

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DESAI, RUCHA, SANJEEV K. GUPTA, SHREE MISHRA, P. K. JHA i A. PRATAP. "THE SYNTHESIS OF TiO2 NANOPARTICLES BY WET-CHEMICAL METHOD AND THEIR PHOTOLUMINESCENCE, THERMAL AND VIBRATIONAL CHARACTERIZATIONS: EFFECT OF GROWTH CONDITION". International Journal of Nanoscience 10, nr 06 (grudzień 2011): 1249–56. http://dx.doi.org/10.1142/s0219581x11008381.

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Low temperature calcination methods have been developed to obtain anatase TiO2 nanocrystals using three different synthesis routes. The DSC thermograms have been used to set the annealing temperature. Various size of TiO2 nanocrystals ranging from 8 nm to 16.5 nm have been used to synthesize by setting up the annealing temperature and time. The X-ray diffraction (XRD) and Raman spectrum have been used to identify and confirm the anatase crystal structure having long range ordering. The photoluminescence (PL) spectra have been recorded as a function of particle size and excitation power, which is attributed to the defects inside the grain that can migrate into the grain surface region during annealing. In a typical TiO2 nanocrystals (sample TN12), luminescence efficiency increases with the decrease in size due to e -/ h + recombination process.

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Xu, Heng, i Benjamin Wiley. "Single-Crystal Electrochemistry Uncovers the Role of Citrate in the Anisotropic Growth of Ag Nanostructures". ECS Meeting Abstracts MA2022-01, nr 23 (7.07.2022): 1182. http://dx.doi.org/10.1149/ma2022-01231182mtgabs.

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Shape-controlled synthesis of metal nanocrystals is usually achieved by the addition of capping agents and serves an important approach to endowing metal nanomaterials with desired properties.1 A widely accepted hypothesis in the role of capping agents is they suppress the atomic deposition on the facets they selectively adsorb to, which leads to anisotropic growth.2 However, the roles of capping agents are often qualitatively deduced from the shape of metal nanocrystals formed, making it difficult to rationally design a synthetic condition for a certain shape or aspect ratio. Single-crystal electrochemical measurements have been used to uncover the facet-selective roles of a wide range of capping agents, such as chloride in the synthesis of Cu nanowires, bromide in the synthesis of Au nanorods, and iodide in the synthesis of Cu microplates.3-6 However, the anisotropic growth revealed by the growth of these nanocrystals is 10 times higher than that predicted by the single-crystal electrochemical measurements, indicating planar defects, such as twin planes and stacking faults, can also cause anisotropic growth. To elucidate the effects surface capping and defects in the anisotropic growth of metal nanocrystals, the work presented here combines synthetic methods and electrochemical measurements to reveal the roles of citrate in the growth of seeds with different structures.7 The single-crystal Ag seeds (Figure 1A) grow into cuboctahedra in the absence of citrate (Figure 1B) and octahedra in the presence of citrate (Figure 1C), which closely matches the shape prediction from the electrochemical measurements. Linear sweep voltammetry (LSV) measurements under the synthetic conditions demonstrate the anisotropic growth with citrate is a result of citrate selectively suppressing the oxidation of a reducing agent, ascorbic acid, and citrate does not affect silver ion reduction. The Ag nanoplate seeds with planar defects (Figure 1D) undergo isotropic growth in the absence of citrate (Figure 1E), but exhibit 30~100 times more anisotropic growth in the presence of citrate than the single-crystal seeds and electrochemical prediction (Figure 1F). Further investigation suggests planar defects can catalyze silver atom deposition to the nanoplate side planes and citrate suppresses surface diffusion to the nanoplate basal planes. (1) Yang, T.-H.; Shi, Y.; Janssen, A.; Xia, Y., Surface Capping Agents and Their Roles in Shape-Controlled Synthesis of Colloidal Metal Nanocrystals. Angew. Chem., Int. Ed. 2020, 59, 15378-15401. (2) Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E., Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics? Angew. Chem., Int. Ed. 2009, 48, 60-103. (3) Kim, M. J.; Brown, M.; Wiley, B. J., Electrochemical investigations of metal nanostructure growth with single crystals. Nanoscale 2019, 11, 21709-21723. (4) Kim, M. J.; Alvarez, S.; Chen, Z.; Fichthorn, K. A.; Wiley, B. J., Single-Crystal Electrochemistry Reveals Why Metal Nanowires Grow. J. Am. Chem. Soc. 2018, 140, 14740-14746. (5) Brown, M.; Wiley, B. J., Bromide Causes Facet-Selective Atomic Addition in Gold Nanorod Syntheses. Chem. Mater. 2020, 32, 6410-6415. (6) Kim, M. J.; Cruz, M. A.; Chen, Z.; Xu, H.; Brown, M.; Fichthorn, K. A.; Wiley, B. J., Isotropic Iodide Adsorption Causes Anisotropic Growth of Copper Microplates. Chem. Mater. 2021, 33, 881-891. (7) Xu, H.; Wiley, B. J., The Roles of Citrate and Defects in the Anisotropic Growth of Ag Nanostructures. Chem. Mater. 2021, 33, 8301-8311. Figure 1

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Narra, Sudhakar, Po-Sen Liao, Sumit S. Bhosale i Eric Wei-Guang Diau. "Effect of Acidic Strength of Surface Ligands on the Carrier Relaxation Dynamics of Hybrid Perovskite Nanocrystals". Nanomaterials 13, nr 11 (24.05.2023): 1718. http://dx.doi.org/10.3390/nano13111718.

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Perovskite nanocrystals (PeNCs) are known for their use in numerous optoelectronic applications. Surface ligands are critical for passivating surface defects to enhance the charge transport and photoluminescence quantum yields of the PeNCs. Herein, we investigated the dual functional abilities of bulky cyclic organic ammonium cations as surface-passivating agents and charge scavengers to overcome the lability and insulating nature of conventional long-chain type oleyl amine and oleic acid ligands. Here, red-emitting hybrid PeNCs of the composition CsxFA(1−x)PbBryI(3−y) are chosen as the standard (Std) sample, where cyclohexylammonium (CHA), phenylethylammonium (PEA) and (trifuluoromethyl)benzylamonium (TFB) cations were chosen as the bifunctional surface-passivating ligands. Photoluminescence decay dynamics showed that the chosen cyclic ligands could successfully eliminate the shallow defect-mediated decay process. Further, femtosecond transient absorption spectral (TAS) studies uncovered the rapidly decaying non-radiative pathways; i.e., charge extraction (trapping) by the surface ligands. The charge extraction rates of the bulky cyclic organic ammonium cations were shown to depend on their acid dissociation constant (pKa) values and actinic excitation energies. Excitation wavelength-dependent TAS studies indicate that the exciton trapping rate is slower than the carrier trapping rate of these surface ligands.

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Dai, Qilin, Hongwei Song, Guohui Pan, Xue Bai, Hui Zhang, Ruifei Qin, Lanying Hu, Haifeng Zhao, Shaozhe Lu i Xinguang Ren. "Surface defects and their influence on structural and photoluminescence properties of CdWO4:Eu3+ nanocrystals". Journal of Applied Physics 102, nr 5 (wrzesień 2007): 054311. http://dx.doi.org/10.1063/1.2773639.

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Reifsnyder Hickey, Danielle. "(Invited) In Situ TEM Studies of Colloidal Inorganic Nanocrystals for Energy Applications". ECS Meeting Abstracts MA2022-02, nr 20 (9.10.2022): 917. http://dx.doi.org/10.1149/ma2022-0220917mtgabs.

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Sustainable technologies will be essential for meeting future energy demands. Therefore, it is critical to be exploring the fundamental science of materials for photovoltaics and catalysis. For these applications, nanomaterials hold great promise due to their unique, size-dependent properties, tunability, and solution processability. Additionally, nanomaterials offer an effective testbed to understand structural transformations in bulk materials, and to take advantage of effects related to having a high surface area to volume ratio. Transmission electron microscopy (TEM) allows a unique window into the atomic structures of nanomaterials by enabling high-resolution imaging, electron diffraction, and compositional analysis. Specifically, this work explores local structural and compositional transformations by examining how colloidal nanocrystals transform under in situ conditions during imaging. Focusing on halide perovskite nanocrystals for photovoltaic applications and metal nanocrystals for catalytic applications, the roles of size, shape, and composition will be explored, as well as the impact of atomic defects. The degradation of halide perovskites is a major issue facing the field and can be mitigated by an in-depth understanding of the structural changes that occur during degradation processes. For instance, the relative stability of different compositions and dissimilar geometries can provide insights into which factors could improve the longevity of photovoltaic devices. Similarly, metallic nanocrystals for heterogeneous catalysis rely on reactive surfaces, which can be identified, examined, and transformed during in situ TEM experiments. This presentation will describe progress toward understanding transformation mechanisms in these two classes of nanocrystals, and it will provide comparative insights across the systems.

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Bornacelli, Jhovani, Jorge Alejandro Reyes Esqueda, Luis Rodríguez Fernández i Alicia Oliver. "Improving Passivation Process of Si Nanocrystals Embedded in SiO2Using Metal Ion Implantation". Journal of Nanotechnology 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/736478.

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We studied the photoluminescence (PL) of Si nanocrystals (Si-NCs) embedded in SiO2obtained by ion implantation at MeV energy. The Si-NCs are formed at high depth (1-2 μm) inside the SiO2achieving a robust and better protected system. After metal ion implantation (Ag or Au), and a subsequent thermal annealing at 600°C under hydrogen-containing atmosphere, the PL signal exhibits a noticeable increase. The ion metal implantation was done at energies such that its distribution inside the silica does not overlap with the previously implanted Si ion . Under proper annealing Ag or Au nanoparticles (NPs) could be nucleated, and the PL signal from Si-NCs could increase due to plasmonic interactions. However, the ion-metal-implantation-induced damage can enhance the amount of hydrogen, or nitrogen, that diffuses into the SiO2matrix. As a result, the surface defects on Si-NCs can be better passivated, and consequently, the PL of the system is intensified. We have selected different atmospheres (air, H2/N2and Ar) to study the relevance of these annealing gases on the final PL from Si-NCs after metal ion implantation. Studies of PL and time-resolved PL indicate that passivation process of surface defects on Si-NCs is more effective when it is assisted by ion metal implantation.

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Neshchimenko, Vitaly V., Chun Dong Li, Mikhail M. Mikhailov i Andrei Dudin. "Effect of the Surface Morphology of Zinc Oxide Particles on their Radiation Stability". Defect and Diffusion Forum 386 (wrzesień 2018): 338–42. http://dx.doi.org/10.4028/www.scientific.net/ddf.386.338.

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The effect of protons exposure on the diffuse reflectance spectra of the zinc oxide with different shape particles has been investigated. Particles were micro-, nanocrystals, star and flower shape particles. The synthesis of the particles was carried out by the hydrothermal method using zinc acetate chemicals. The surface morphology, surface area and crystal structure of the particles have been investigated. Evaluating the changes in spectral reflectance it was found that the radiation stability of the micro particles is higher than the radiation stability of the other nanostructured particles. The high stability of the micro particles optical properties is due to the effect of low accumulation of radiation-induced defects.

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Zha, Yanfang, Yun Wang, Yuhang Sheng, Xiaowei Zhang, Xinyue Shen, Fangjian Xing, Cihui Liu, Yunsong Di, Yingchun Cheng i Zhixing Gan. "Stable and broadband photodetectors based on 3D/2D perovskite heterostructures with surface passivation". Applied Physics Letters 121, nr 19 (7.11.2022): 191904. http://dx.doi.org/10.1063/5.0122091.

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Despite increasing research interest in two-dimensional (2D) perovskites, the stability and spectral response range of the photodetectors based on 2D perovskites are yet far from satisfactory. In this work, a semiconductor heterojunction is constructed based on dimethyl itaconate (DI) treated (BA)2PbI4 microplates and CsPb(Brx/I1−x)3 nanocrystals. The DI treatment not only passivates the defects but also blocks the moisture, resulting in improved stability and suppressed defect trapping. Meanwhile, the type-II heterojunctions facilitate the separation of electron–hole pairs. As a result, the photodetector based on the DI-(BA)2PbI4/CsPb(Brx/I1−x)3 exhibits a responsivity up to 209 nA/mW and a detectivity up to 5.9 × 108 Jones with a broad spectral response range of 400–600 nm. Furthermore, after storage in the ambient environment for 10 days, the responsivity retains about 70%, which is significantly ameliorated compared to the photodetector based on bare (BA)2PbI4 (drops more than 90%). Therefore, this work demonstrates that surface passivation and 2D/three-dimensional heterojunctions are promising strategies to improve responsivity, broaden spectral response range, and enhance stability of photodetectors based on 2D perovskites.

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Ji, Shu Hua, Xiao Zhou Li, Da Sen Wang, Hua Dong Yu i Chun Yang Wang. "Material Removal Property in Low Energy Ion Beam Etching". Advanced Materials Research 706-708 (czerwiec 2013): 142–47. http://dx.doi.org/10.4028/www.scientific.net/amr.706-708.142.

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Ion beam etching can achieve nanometer size easily, processing in nanometer size, then put forward higher requirements on the workpiece surface. Ion beam etching is based on the Sigmund sputtering principle to remove the material, and the defects such as vacancies and interstitials in substrate material atomic lattice will be produced in this process. When these defects are enough, they lead to material damage. This paper is based on this effect to explore the effect of the processing parameters like Ar ion incident energy and incident angle of plasma beam on the implantation depth and the lattice change, through the SRIM software simulation which Ar ions used to the silica etching, moreover, forecast and put forward the suitable parameters for ion beam etching of nanocrystals on the workpiece, to produce the smaller nanowires damage.

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Diaz Cano, Aaron I., i Brahim El Filali. "Photoluminescence Study of ZnO Nanosheets with embedded Cu Nanocrystals." MRS Proceedings 1617 (2013): 101–6. http://dx.doi.org/10.1557/opl.2013.1171.

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ABSTRACTIn this work a simple method to produce the ZnO nanosheets (NSs) with inclusions of Cu nanocrystals by means of electrochemical etching without the necessity of any surfactant has been presented. The Raman spectroscopy demonstrates that the amorphous samples of ZnO-Cu present appreciable changes in its vibrational behavior after the thermal treatment at 400°C in ambient atmosphere. The study of Photoluminescence (PL) shows monotonous increasing the bands centered in 3.07, 2.41, 2.03 and 1.57 eV versus etching time in freshly prepared samples. The intensity variation of the PL bands, the changes in vibrational behavior, as well as the impact of the copper content and preparation conditions allow identifying emission inside the visible spectral range related to the surface defects that is interesting for the future possible application this ZnO system in room temperature “white” light-emitting diodes.

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Yun, Rui, Li Luo, Jingqi He, Jiaxi Wang, Xiaofen Li, Weiren Zhao, Zhaogang Nie i Zhiping Lin. "Mixed-Solvent Polarity-Assisted Phase Transition of Cesium Lead Halide Perovskite Nanocrystals with Improved Stability at Room Temperature". Nanomaterials 9, nr 11 (30.10.2019): 1537. http://dx.doi.org/10.3390/nano9111537.

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Cesium lead halide perovskite nanocrystals (NCs) have attracted enormous interest in light-emitting diode, photodetector and low-threshold lasing application in terms of their unique optical and electrical performance. However, little attention has been paid to other structures associated with CsPbBr3, such as CsPb2Br5. Herein, we realize a facile method to prepare dual-phase NCs with improved stability against polar solvents by replacing conventional oleylamine with cetyltrimethyl ammonium bromide (CTAB) in the reprecipitation process. The growth of NCs can be regulated with different ratios of toluene and ethanol depending on solvent polarity, which not only obtains NCs with different sizes and morphologies, but also controls phase transition between orthorhombic CsPbBr3 and tetragonal CsPb2Br5. The photoluminescence (PL) and defect density calculated exhibit considerable solvent polarity dependence, which is ascribed to solvent polarity affecting the ability of CTAB to passivate surface defects and improve stoichiometry in the system. This new synthetic method of perovskite material will be helpful for further studies in the field of lighting and detectors.

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Chen, Sijie, Jianwu Wei i Qi Pang. "Enhancing Photoluminescence and Stability of CsPbI3 Perovskite Quantum Dots via Cysteine Post-Processing". Crystals 13, nr 1 (27.12.2022): 45. http://dx.doi.org/10.3390/cryst13010045.

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Red-emitting cesium lead iodide (CsPbI3) perovskite quantum dots (CQDs) are extremely unstable due to their structural composition and the weak binding force of ligands on the surface of nanocrystals. Herein, we report an effective method to enhance the photoluminescence and stability of CQDs by simple post-processing with cysteine (Cys). Compared to the pristine CQDs with a photoluminescence quantum yield (PLQY) of 38.61%, the Cys-processed one has fewer surface defects, obtaining a PLQY of 70.77%, nearly twice as much as the pristine samples, and, simultaneously, the Cys-processed CQDs retained more than 86% of the initial PL intensity after 20 days of storage in the atmosphere. This research provides a new idea for the preparation of high-performance and red-emitting quantum dots.

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LIU, Zhiming, Guoliang LIU i Xinlin HONG. "Influence of Surface Defects and Palladium Deposition on the Activity of CdS Nanocrystals for Photocatalytic Hydrogen Production". Acta Physico-Chimica Sinica 35, nr 2 (2019): 215–22. http://dx.doi.org/10.3866/pku.whxb201803061.

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WU, Kai. "Influence of Surface Defects and Pd Modification on the Activity of CdS Nanocrystals for Photocatalytic Hydrogen Production". Acta Physico-Chimica Sinica 35, nr 2 (2019): 135–36. http://dx.doi.org/10.3866/pku.whxb201806111.

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Belyakov, V. A., V. A. Burdov i K. V. Sidorenko. "Effect of surface defects on radiative interband recombination in silicon nanocrystals highly doped with hydrogen-like impurities". Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques 4, nr 6 (listopad 2010): 987–93. http://dx.doi.org/10.1134/s1027451010060182.

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Bryan, J. Daniel, Steven A. Santangelo, Sean C. Keveren i Daniel R. Gamelin. "Activation of High-TCFerromagnetism in Co2+:TiO2and Cr3+:TiO2Nanorods and Nanocrystals by Grain Boundary Defects". Journal of the American Chemical Society 127, nr 44 (listopad 2005): 15568–74. http://dx.doi.org/10.1021/ja0543447.

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Kadim, Akeel M. "White Light Generation from Emissive Hybrid Nanocrystals CdSe/CdTe/CdS Core/Shell/Shell System". Nano Hybrids and Composites 27 (listopad 2019): 1–10. http://dx.doi.org/10.4028/www.scientific.net/nhc.27.1.

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New nanocrystals (NCs) were engineered with a core/shell/shell system consisting of CdSe core/ CdTe shell/ CdS shell. The white light generation mechanism was described depending on mixing colors from the illuminated CdSe/CdTe/CdS core/shell/shell nanocrystals. The color mixed in CdSe/CdTe/CdS core/shell/shell NCs system were used to generate extreme white light when illuminated by InGaN/GaN UV LED (λ=360 nm) the core/shell/shell NCs system tuned the chromaticity coordinates to (0.332, 0.340) and increased the intensity of the emitted white light. The synthesis of the CdSe/CdTe/CdS core/shell/shell NCs were confirmed by SEM, AFM, XRD and photoluminescence (PL) experiments due to create of surface states defects information. This enhancement was recognized to the overlap of emission with the photoluminescence (PL) spectrum of CdSe/CdTe/CdS core/shell/shell NCs which indications to a cold white light generation. Current-voltage (I–V) characteristics indicate that the output current is good compared to the few voltages (6 V) used which give acceptable results to get a generation of white light.

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Sánchez-Godoy, Humberto Emmanuel, i Andrés Fabián Gualdrón-Reyes. "Recent Insights to Prepare High-Quality Perovskite Nanocrystals via “Green” and Ecofriendly Solvents and Capping Agents". Applied Sciences 13, nr 10 (19.05.2023): 6227. http://dx.doi.org/10.3390/app13106227.

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The synthesis of halide perovskite nanocrystals (PNCs) with mesmerizing photophysical properties has allowed for the fast development of efficient optoelectronic and photovoltaic devices, as well as making them ideal photocatalysts for solar-driven chemical reactions. However, the use of traditional oleic acid/oleylamine with low binding energy and the introduction of some phosphine- and sulfur-based ligands generate the emergence of highly defective PNCs with poor stability, fast quenching of their PL features, and increase in the toxicity of the final perovskite product. In this review, we will show the use of prominent “green” and ecofriendly solvents and capping ligands with the capability to enhance the quality of the PNCs by suppressing structural defects. By introducing promising ecofriendly agents such as biogenic species and ligands extracted from natural sources, it is possible to favor the radiative recombination dynamics into the perovskite, being beneficial to enhance the device performance. Novel passivation alternatives or synthetic routes are highlighted in this contribution, giving a deeper understanding of the control of surface chemistry in PNCs through ligand engineering to prolong the stability of the nanocrystals.

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Xiong, Shangmin, Seung-Yub Lee i Ismail Cevdet Noyan. "Average and local strain fields in nanocrystals". Journal of Applied Crystallography 52, nr 2 (26.02.2019): 262–73. http://dx.doi.org/10.1107/s1600576719000372.

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This article presents a rigorous and self-consistent comparison of lattice distortion and deformation fields existing in energy-optimized pseudo-spherical gold nanoparticles obtained from real-space and powder diffraction strain analysis techniques. The changes in atomic positions resulting from energy optimization (relaxation) of ideally perfect gold nanoparticles were obtained using molecular dynamics modeling. The relaxed atomic coordinates were then used to compute the displacement, rotation and strain components in all unit cells within the energy-optimized (relaxed) particles. It was seen that all of these terms were distributed heterogeneously along the radial and tangential directions within the nanospheroids. The heterogeneity was largest in the first few atomic shells adjacent to the nanoparticle surface, where the continuity of crystal lattice vectors originating from the interior layers was broken because of local lattice rotations. These layers also exhibited maximum shear and normal strains. These (real-space) strain values were then compared with the average lattice strains obtained by refining the computed diffraction patterns of such particles. The results show that (i) relying solely on full-pattern refinement techniques for lattice strain analysis might lead to erroneous conclusions about the dimensionality and symmetry of deformation within relaxed nanoparticles; (ii) the lattice strains within such relaxed particles should be considered `eigenstrains' (`inherent strains') as defined by Mura [Micromechanics of Defects in Solids, (1991), 2nd ed., Springer]; and (iii) the stress/strain state within relaxed nanoparticles cannot be analyzed rigorously using the constitutive equations of linear elasticity.

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Chen, Kaiwang, Dengliang Zhang, Qing Du, Wei Hong, Yue Liang, Xingxing Duan, Shangwei Feng i in. "Synergistic Halide- and Ligand-Exchanges of All-Inorganic Perovskite Nanocrystals for Near-Unity and Spectrally Stable Red Emission". Nanomaterials 13, nr 16 (14.08.2023): 2337. http://dx.doi.org/10.3390/nano13162337.

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All-inorganic perovskite nanocrystals (NCs) of CsPbX3 (X = Cl, Br, I) are promising for displays due to wide color gamut, narrow emission bandwidth, and high photoluminescence quantum yield (PLQY). However, pure red perovskite NCs prepared by mixing halide ions often result in defects and spectral instabilities. We demonstrate a method to prepare stable pure red emission and high-PLQY-mixed-halide perovskite NCs through simultaneous halide-exchange and ligand-exchange. CsPbBr3 NCs with surface organic ligands are first synthesized using the ligand-assisted reprecipitation (LARP) method, and then ZnI2 is introduced for anion exchange to transform CsPbBr3 to CsPbBrxI3−x NCs. ZnI2 not only provides iodine ions but also acts as an inorganic ligand to passivate surface defects and prevent ion migration, suppressing non-radiative losses and halide segregation. The luminescence properties of CsPbBrxI3−x NCs depend on the ZnI2 content. By regulating the ZnI2 exchange process, red CsPbBrxI3−x NCs with organic/inorganic hybrid ligands achieve near-unity PLQY with a stable emission peak at 640 nm. The CsPbBrxI3−x NCs can be combined with green CsPbBr3 NCs to construct white light-emitting diodes with high-color gamut. Our work presents a facile ion exchange strategy for preparing spectrally stable mixed-halide perovskite NCs with high PLQY, approaching the efficiency limit for display or lighting applications.

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