Добірка наукової літератури з теми "Heterostructure NCs"

A broadband photodetector response in the ultraviolet (UV)-to-green range (up to 530 nm) based on perovskite CsPbBr3 nanocrystals (NCs)/ZnO-microwires (MWs) heterostructures was realized via a convenient spin-coating method. Under UV light (365 nm) illumination, compared with a bare-ZnO-MW-based photodetector, the CsPbBr3-NCs/ZnO-MWs-heterostructure-based photodetector exhibited a faster photoresponse (<0.1 s) and higher current responsivity (93.50 AW−1), external quantum efficiency (3399%), and detectivity (4.4 × 1010). In addition, the photodetector based on CsPbBr3-NCs/ZnO-MWs heterostructures also exhibited a very fast photoresponse to green light (530 nm). These can be ascribed to the strong light-trapping ability of CsPbBr3 NCs and high charge-transfer efficiency at the CsPbBr3-NCs/ZnO-MWs-heterojunction interface due to the built-in field, which facilitates the spatial separation of the photogenerated carriers. Therefore, this work will develop perovskite/ZnO nanomaterials as promising building blocks for broadband photodetectors and wider optoelectronic applications.

Iron oxide (Fe2O3)–titanium dioxide (TiO2) heterostructure nanocomposite has been used for contaminant decomposition and antibacterial application. However, both the photogenerated electrons and holes of TiO2 may transfer to Fe2O3 due to straddling band alignment in type-I heterostructure, which is not helpful to more efficiently inhibit the electron–hole recombination. In this paper graphene-Fe2O3–TiO2 (GFT) heterostructure nanocomposites (NCs) were fabricated to facilitate the separation of photo-induced electrons and holes according to their staggered energy level, further improve dye degradation efficiency and antibacterial activity. GFT NCs were fabricated through a simple hydrothermal method. X-ray diffraction patterns and transmission electron microscopy images indicated that Fe2O3 and TiO2 were successfully loaded on graphene. UV-Vis spectra showed that GFT NCs had higher absorption against sunlight. Under simulated sunlight irradiation, GFT NCs could effectively degraded dyes and inhibit bacterial growth.

Practical applications of CsPbX3 nanocrystals (NCs) are limited by their poor stability. The formation of a heterojunction between CsPbX3 NCs and oxides is an effective means to protect perovskite from polar solvents and other external factors. Significantly improving the stability and photocatalytic properties of the core/shell perovskite is very important for its application in photoelectric and photocatalytic technology. Here, we report the synthesis of asymmetrical CsPbBr3/TiO2 core–shell heterostructure NCs at the single-particle level by hot-injection liquid-phase synthesis and sol–gel method, where each CsPbBr3 NCs is partially covered by titanium dioxide. We tested not only the optical properties of the material but also the electrochemical impedance and photocurrent density of the material in sodium sulfate solution. It is shown that the type II arrangement is generated at the heterogeneous interface, which greatly facilitates the separation of electron–hole pairs and increases the carrier transport efficiency. Compared with CsPbBr3 NCs, CsPbBr3/TiO2 has higher photocatalytic efficiency. More crucially, due to the protection of the titanium dioxide shell, the product has higher long-term stability in humid air compared with bare CsPbBr3 NCs. The asymmetrical core–shell heterostructure prepared in this study not only improves the stability of CsPbX3 NCs but also provides some ideas for optoelectronic device applications and TiO2-based photocatalysts.

Core/shell hetero-nanostructures are promising materials for fabricating optoelectronic devices, photodetectors, bioimaging, and biosensing. The CdSe/CdS core/shell nanocrystals (NCs) were synthesized in a wet chemical reaction. The shell thickness was modified by varying reaction times. The structure and optical properties as a function of the CdS shell thickness were investigated. A systematic redshift of the first exciton absorption peaks and photoluminescent (PL) spectra occurred after coating with CdS confirmed the shell growth over the CdSe core. The PL's intensity increased compared with that of bare NCs. The formation of high-quality NCs with uniform size distribution was shown in the transmission electron microscopy (TEM) image and confirmed by the narrow PL band and small FWHM.

Cerium oxide and tin oxide nanocomposites (CeO2-SnO2 NCs) were successfully synthesized via a simple co-precipitation method. The structure and properties of the synthesized materials were characterized using several X-ray and electron-based techniques including XRD, FE-SEM, TEM, EDS and BET to unravel the structure, morphology, element composition and specific surface area. The XRD and BET results showed that the NCs have the characteristic crystalline structures of SnO2 and CeO2-SnO2 NCs, and high specific surface area (66.45 and 86.29 m2/g), respectively. Amorphous phase of CeO2 and SnO2 were not found in XRD patterns. EDS analysis confirms the absence of all element composition and the FE-SEM and TEM analysis observed as particles having the clear spherical morphologies with the average particle size of of SnO2 and CeO2-SnO2 NCs was about 13 and 10 nm, respectively.

Colloidal semiconductor nanocrystals (NCs) attract significant interest in recent years due to their narrow and tunable emission wavelength in the visible range, as well as high photoluminescence quantum yield (PLQY), which are highly desired in display technologies. The high-quality NCs have been recognized as vital luminescent materials in realizing next-generation display devices. With further development, NCs with near-unity PLQY have been successfully synthesized through engineering of the core/shell heterostructure. However, as the external quantum efficiency (EQE) of the nanocrystal light-emitting diodes (LEDs) approaches the theoretical limit of about 20%, the low out-coupling factor proposes a challenge of enhancing the performance of a device when using the spherical QDs. Hence, the anisotropic NCs like nanoplatelets (NPLs) are proposed as promising solutions to improve the performance of nanocrystal LEDs. In this review, we will summarize the synthetic strategies of two-dimensional (2D) NPLs at first. Then, we will introduce fundamental concepts of LEDs, the main approaches to realize LEDs based on nanoplatelets, and the recent progress. Finally, the challenges and opportunities of LEDs based on anisotropic NCs are also presented.

Introduction: Finding a novel photocatalyst for photocatalytic degradation operating in the wavelength range from UV to visible light has been considered a great potential for environmental remediation. Herein, TiO2 nanocubics (NCs) decorated Ag nanoparticles (NPs) with various concentrations were developed. Methods: The crystal structure, morphological and chemical characteristics of prepared photocatalysts were thoroughly analyzed by a series of main analyses (X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), and UVVis spectra). Results: The results revealed that a significantly promoting visible-light photocatalytic behavior of TiO2NCs@Ag photocatalyst was observed. The photocatalytic methyl orange (MO) degradation of the as-synthesized Ag anchored TiO2NCs photocatalyst (85% and 62% under UV light and visible light, respectively) exhibited outstanding photocatalytic efficacy compared with pristine TiO2 NCs. The achieved results could be assigned to the synergistic effects between TiO2NCs and Ag- NPs, leading to enhanced charge carrier separation and improved absorption ability in visible-light response. Conclusion: This work facilitates designing and developing high-efficiency heterostructure photocatalysts for practical works related to environmental deterioration.

There has been a lot of interest in the manufacture of stable, high-efficiency photocatalysts. In this study, initially Cr doped ZnFe2O4 nanoparticles (NPs) were made via surfactant-assisted hydrothermal technique. Then Cr-ZnFe2O4 NPs were modified by incorporating S-g-C3N4 to enhance their photocatalytic efficiency. The morphological, structural, and bonding aspects were analyzed by XRD, FTIR, and SEM techniques. The photocatalytic efficiency of the functional Cr-ZnFe2O4/S-g-C3N4 (ZFG) heterostructure photocatalysts was examined against MB under sunlight. The produced ZFG-50 composite has the best photocatalytic performance, which is 2.4 and 3.5 times better than that of ZnFe2O4 and S-g-C3N4, respectively. Experiments revealed that the enhanced photocatalytic activity of the ZFG nanocomposite was caused by a more effective transfer and separation of photo-induced charges. The ZFG photocatalyst can use sunlight for treating polluted water, and the proposed modification of ZnFe2O4 using Cr and S-g-C3N4 is efficient, affordable, and environmentally benign. Under visible light, Gram-positive and Gram-negative bacteria were employed to ZFG-50 NCs’ antimicrobial activity. These ZFG-50 NCs also exhibit excellent antibacterial potential.

In this work we report the results of the synthesis, structural and optical characterization of SiO2/Ge/SiO2heterostructures by reactive RF sputtering. The SiO2films were grown by reactive sputtering employing a plasma mixture of oxygen and argon. The Ge layer was grown employing an Ar atmosphere. The samples were prepared on p-type Si (1 1 1) substrates by reactive sputtering. The effect of the partial pressure of oxygen on the electronic properties of the heterostructure is reported[1]. Structural characterization was carried out by grazing angle X-ray difraction. Surface roughness was quantified by atomic force microscopy. The presence of Ge nanocrystals (Ge-NCs) was evidenced by X-ray diffraction. The vibrational properties were studied by Raman spectroscopy. The Raman spectra showed modes associated to germanium indicating the formation of low dimensionality germanium particles embedded within a SiO2matrix. Photoluminescence emission is observed around ~1.7 eV and it is associated to the quantum confinement of carriers in Ge-NCs. Ohmic contacts were deposited using a van der Pauw geometry employing an a AuSb alloy for the contacts. Temperature dependent Hall (T-Hall) measurements were done between 35 K and 150 K, using the van der Pauw method. The results indicated low resistivity values that could be explained due to some variable range hopping conduction mechanism.

Orientador: Fernando Iikawa
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-08-21T01:34:49Z (GMT). No. of bitstreams: 1 Girardi_TiagoIllipronti_M.pdf: 2091533 bytes, checksum: 1e5e58f3f5149c97c47c1bf44b7aa186 (MD5) Previous issue date: 2012
Resumo: Neste trabalho, estudamos o efeito de diferentes condições de interface de InP/GaAs nas propriedades ópticas de pontos quânticos auto-organizados, crescidos por epitaxia de feixe químico, no modo Stranskii-Krastanov. Espera-se que os pontos quânticos de InP/GaAs apresentem alinhamento de bandas do tipo II, e somente os elétrons ficam confinados, enquanto os buracos ficam localizados nas camadas de GaAs em volta do ponto quântico, atraídos pelo elétron. No entanto, devido ao efeito de mistura de átomos nas interfaces o perfil de potencial nas interfaces pode ser alterado significativamente, afetando, com isso, as propriedades ópticas dos pontos quânticos. Foram estudadas amostras com as seguintes condições de interface entre a camada de InP e as camadas de GaAs: inclusão ou não de uma camada de InGaP em uma ou nas duas interfaces. O InGaP gera uma barreira para ambos os tipos de portadores de carga em uma junção tanto com o GaAs como InP e evita a difusa de As das camadas de GaAs para a de InP. Através de medidas de fotoluminescência resolvida no tempo, observamos a variação do tempo de decaimento da emissão óptica associada aos pontos quânticos de acordo com as diferentes condições de interface. Foi observado um tempo curto de decaimento em amostras sem a inclusão de InGaP e com a inclusão apenas na interface superior, enquanto foi observado um tempo longo quando incluímos camadas de InGaP em ambas as interfaces. O tempo de decaimento curto é incompatível com o alinhamento de bandas do tipo II, que deveria separar espacialmente o elétron do buraco. A partir desses resultados e estudos anteriores a esse trabalho, pudemos concluir que o tempo curto se deve à mistura de átomos nas regiões de ambas as interfaces, gerando ligas que localizam os portadores próximos um ao outro. O tempo longo na amostra contendo InGaP nas duas interfaces é atribuído à separação espacial do elétron e do buraco. O efeito de mistura de átomos nas interfaces, neste caso, não forma uma liga na interface que localize os dois tipos de portadores próximos um ao outro. Isso pode ser uma alternativa de preparação de pontos quânticos de InP/GaAs onde se mantém separados espacialmente o elétron e o buraco
Abstract: We studied the effect of different interface conditions on the optical properties of InP/GaAs self-assembled quantum dots grown by chemical beam epitaxy in the Stranskii-Krastanov mode. InP/GaAs quantum dots is expected to present type II band alignment, and only electrons are confined, whereas the holes are localized in the GaAs layers around the quantum dot, attracted by the electron. However, due to the atomic intermixing effect in the interface the potential profile can be strongly changed, affecting the optical properties of the quantum dots. We studied samples with the following conditions at the interfaces between the InP layer and GaAs layers: the inclusion, or the lack of, a InGaP layer at one of or both interfaces. InGaP generates a barrier for both types of carriers in a junction with GaAs and InP, and avoid the diffusion of As from the GaAs layers to the InP one. Using time-resolved photo-luminescence, we observed a change of the optical emission decay times associated to the quantum dots as the interface condition is changed. We observed a short decay lifetime in samples without InGaP layers and with the inclusion in the top interface only, whereas we observed a long decay time when we included InGaP layers in both interfaces. The short decay lifetime is incompatible with the type II band alignment, where the electron and the hole should be spatially separated. Using these and other previous results, we concluded that the short decay lifetime is due to the atomic intermixing in both interfaces regions, forming alloys that localize the carriers near each other. The long lifetime observed for sample containing InGaP in both interfaces is attributed to the large electron-hole spatial separation. In this case intermixing effects at the interfaces do not form a potential well to localize the carries near each other
Mestrado
Física
Mestre em Física

Submitted by JÚLIO HEBER SILVA (julioheber@yahoo.com.br) on 2017-05-03T20:30:01Z No. of bitstreams: 2 Dissertação - Douglas Carlos de Sousa Silva - 2017.pdf: 3036182 bytes, checksum: c02aa9da97c239bf3b1954923b5ee8a0 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-05-04T11:06:57Z (GMT) No. of bitstreams: 2 Dissertação - Douglas Carlos de Sousa Silva - 2017.pdf: 3036182 bytes, checksum: c02aa9da97c239bf3b1954923b5ee8a0 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Made available in DSpace on 2017-05-04T11:06:57Z (GMT). No. of bitstreams: 2 Dissertação - Douglas Carlos de Sousa Silva - 2017.pdf: 3036182 bytes, checksum: c02aa9da97c239bf3b1954923b5ee8a0 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-04-07
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Nanostructured materials, such as: Ag2MoO4 and ZnO are of great importance because they have unique characteristics and properties, and can be applied in sensors, catalysis, photoluminescence, among other applications. In this work, the Ag2MoO4 and ZnO powders were synthesized separately and in the form of heterostructures, by two different routes, coprecipitation (CP), at room temperature and coprecipitation with subsequent microwave assisted hydrothermal treatment (CPMAHT), at 130 ° C for 30 min, with a heating rate of 10 ° C / min. The heterostructures composed of both materials, Ag2MoO4 and ZnO present in molar proportions ranging from 0.25-2.00%, were synthesized by coprecipitation with subsequent sonochemical processing (CPSP). The Ag2MoO4 samples were obtained with pure cubic phase of spinel type with crystallite size of 143 nm for the sample obtained by CP and 90 nm for the sample obtained by CPTHAM. For the ZnO the hexagonal phase of the wurtzite type, with crystallite sizes of 19 and 49 nm, was obtained for the samples obtained by CP and CPTHAM, respectively. The phases of both Ag2MoO4 and ZnO were observed for the heterostructures obtained by CPSP. The structural and morphological characterization of the obtained materials was performed using X-ray diffraction (XRD) techniques and scanning electron microscopy (SEM). The diffusion reflectance UV-Vis spectroscopy (DRS) was performed to determine the band gap values of the materials. The photoluminescent property was investigated by means of the photoluminescence spectroscopy (PHS) technique, with an improvement in the photoluminescent property of broadband for all the obtained heterostructures. It was also observed that the synergism of the Ag2MoO4 and ZnO materials in the heterostructures resulted in an improvement in the photocatalytic property, leading to a 90% discoloration of the rhodamine B dye in 90 min for the photocatalysis using the Ag2MoO4: 2 ZnO heterostructure.
Materiais nanoestruturados, tais como: o Ag2MoO4 e o ZnO são de grande importância por apresentarem características e propriedades únicas, podendo ser aplicados em sensores, catálise, fotoluminescência, dentre outras aplicações. Neste trabalho, os pós de Ag2MoO4 e ZnO foram sintetizados na sua forma pura por duas rotas diferentes, coprecipitação (CP) a temperatura ambiente e coprecipitação com posterior tratamento hidrotérmico assistido por microondas (CPTHAM), a 130 °C durante 30 min, com taxa de aquecimento de 10 °C/min. Heteroestruturas compostas por ambos os materiais, Ag2MoO4 e ZnO foram obtidas com proporções de 0,25; 0,50; 1 e 2 mols de ZnO para 1 mol de Ag2MoO4. Estas heteroestruturas foram sintetizadas por coprecipitação com posterior processamento sonoquímico (CPPS). As amostras de Ag2MoO4 foram obtidas com fase cúbica pura do tipo espinélio com tamanho de cristalito de 143 nm para a amostra obtida por CP e 90 nm para a amostra obtida por CPTHAM. Para o ZnO foi obtida a fase hexagonal do tipo wurtzita, com tamanhos de cristalito de 19 e 49 nm, para as amostras obtidas por CP e CPTHAM, respectivamente. Foram observadas ambas as fases, tanto do Ag2MoO4 quanto do ZnO para as heteroestruturas obtidas por CPPS. A caracterização estrutural e morfológica dos materiais obtidos foi realizada utilizando das técnicas de difração de raios X (DRX) e microscopia eletrônica de varredura (MEV). A espectroscopia de UV-Vis por reflectância difusa (ERD) foi realizada para determinação dos valores de “band gap” dos materiais. A propriedade fotoluminescente foi investigada por meio da técnica de espectroscopia de fotoluminescência (EFL), sendo observado uma melhora na propriedade fotoluminescente de banda larga para todas as heteroestruturas obtidas. Foi observado também que a sinergia dos materiais Ag2MoO4 e ZnO nas heteroestruturas resultou em uma melhora na propriedade fotocatalítica, levando a uma descoloração do corante rodamina B de 90 % em 90 min para a fotocatálise usando a heteroestrutura Ag2MoO4: 2 ZnO.