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Articles de revues sur le sujet "Electronic Properties - Semiconductor Nanocrystals (NCs)"
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Qiao, Fen. « Semiconductor Nanocrystals for Photovoltaic Devices ». Materials Science Forum 852 (avril 2016) : 935–38. http://dx.doi.org/10.4028/www.scientific.net/msf.852.935.
Texte intégralRésumé :
Recently, photovoltaic devices based on colloidal semiconductor nanocrystals (NCs) have attracted a great interest due to their flexible synthesis with tunable band gaps and shape-dependent optical and electronic properties. However, the surface of NCs typically presents long chain with electrically insulating organic ligands, which hinder the device applications for NCs. So the major challenge of NCs for photovoltaic devices application is to decrease the inter NC space and the height of the tunnel barriers among NCs, therefore increase the transport properties of NCs. In this article, recent development of colloidal semiconductor NCs and possible routes for improving transport properties of colloidal NCs were reviewed. Among those methods, the thermal annealing approach provides a simple and cost-effective way to fabricate superlattice and to decrease the inter-space among NCs, which may be used for the preparation of other nanocrystalline superstructure and functional devices.
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Kovalenko, Maksym V., Loredana Protesescu et Maryna I. Bodnarchuk. « Properties and potential optoelectronic applications of lead halide perovskite nanocrystals ». Science 358, no 6364 (9 novembre 2017) : 745–50. http://dx.doi.org/10.1126/science.aam7093.
Texte intégralRésumé :
Semiconducting lead halide perovskites (LHPs) have not only become prominent thin-film absorber materials in photovoltaics but have also proven to be disruptive in the field of colloidal semiconductor nanocrystals (NCs). The most important feature of LHP NCs is their so-called defect-tolerance—the apparently benign nature of structural defects, highly abundant in these compounds, with respect to optical and electronic properties. Here, we review the important differences that exist in the chemistry and physics of LHP NCs as compared with more conventional, tetrahedrally bonded, elemental, and binary semiconductor NCs (such as silicon, germanium, cadmium selenide, gallium arsenide, and indium phosphide). We survey the prospects of LHP NCs for optoelectronic applications such as in television displays, light-emitting devices, and solar cells, emphasizing the practical hurdles that remain to be overcome.
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Harfenist, S. A., Z. L. Wang, T. G. Schaaff et R. L. Whettent. « A BCC Superlattice of Passivated Gold Nanocrystals ». Microscopy and Microanalysis 4, S2 (juillet 1998) : 716–17. http://dx.doi.org/10.1017/s1431927600023709.
Texte intégralRésumé :
A recent development in the study of nanocrystalline materials has been the self-assembly of passivated nanometer scale building blocks into larger, well ordered structures reaching the micron scale. Nanocrystal supercrystals (NCS) have been observed in metallic, semiconductor, and magnetic materials. In most cases the nanocrystals (NXs) are encapsulated in some inert medium that effectively protects the nanocrystal core and its unique electronic and optical properties. Here we describe the self-assembly of gold nanocrystals (∼4.5 nm core diameter), passivated with hexanethiol self-assembled-monolayers into ordered regions exhibiting a body-centered-cubic (bcc) superstructure. Transmission Electron Microscopy (TEM) imaging and Electron Diffraction (ED) experiments were used to characterize the NCSs and their resulting superstructures.A large agglomeration of NCSs can be seen in figure 1. One can clearly see regions of periodicity within the nanocrystal aggregation.
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Sayevich, Vladimir, Chris Guhrenz et Nikolai Gaponik. « All-Inorganic and Hybrid Capping of Nanocrystals as Key to Their Application-Relevant Processing ». MRS Advances 3, no 47-48 (2018) : 2923–30. http://dx.doi.org/10.1557/adv.2018.445.
Texte intégralRésumé :
AbstractThe design of the surface chemistry of colloidal semiconductor nanocrystals (NCs) presents a powerful synthetic approach that allows to tune the optical and electronic properties of the particles in independent and precisely desired manner, to provide chemical and colloidal stability in diverse media, and, finally, to control their targeted applicability ranging from catalysis, medicine to advanced electronic devices. In this article, we summarize the successful functionalization of colloidal NCs with specifically chosen ligands using a novel ligand-exchange strategy. To transform diverse colloidal NCs into a competitive class of solution-processed semiconductors for electronic applications, we replaced the pristine, insulating ligands with tiny inorganic and hybrid inorganic/organic species. The surface modification with inorganic ions modulates the charge carrier density in NC units and guarantees enhanced interparticle interactions. The subsequent functionalization of the all-inorganic-capped NCs with organic molecules leads to the formation of hybrid inorganic/organic-capped NCs. For example, the introduction of short amine molecules enables to preserve the optical and electronic characteristics of their all-inorganic counterparts, while extending the solubility range and improving the ability to form long-range ordered 2D and 3D superstructures. Moreover, these short amines can be further used as convenient axillary co-ligands facilitating the surface functionalization of all-inorganic NCs with other biocompatible molecules, such as polyethylene glycol (PEG). This opens further perspectives for NCs not only in optoelectronic but also in biological and medical applications.
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Casanova-Cháfer, Juan, Rocío García-Aboal, Pedro Atienzar et Eduard Llobet. « Gas Sensing Properties of Perovskite Decorated Graphene at Room Temperature ». Sensors 19, no 20 (20 octobre 2019) : 4563. http://dx.doi.org/10.3390/s19204563.
Texte intégralRésumé :
This paper explores the gas sensing properties of graphene nanolayers decorated with lead halide perovskite (CH3NH3PbBr3) nanocrystals to detect toxic gases such as ammonia (NH3) and nitrogen dioxide (NO2). A chemical-sensitive semiconductor film based on graphene has been achieved, being decorated with CH3NH3PbBr3 perovskite (MAPbBr3) nanocrystals (NCs) synthesized, and characterized by several techniques, such as field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Reversible responses were obtained towards NO2 and NH3 at room temperature, demonstrating an enhanced sensitivity when the graphene is decorated by MAPbBr3 NCs. Furthermore, the effect of ambient moisture was extensively studied, showing that the use of perovskite NCs in gas sensors can become a promising alternative to other gas sensitive materials, due to the protective character of graphene, resulting from its high hydrophobicity. Besides, a gas sensing mechanism is proposed to understand the effects of MAPbBr3 sensing properties.
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Qiao, Fen, Qian Wang, Zixia He, Qing Liu et Aimin Liu. « Self-Assembly of Colloidal Nanorods Arrays ». International Journal of Nanoscience 14, no 01n02 (février 2015) : 1460029. http://dx.doi.org/10.1142/s0219581x14600291.
Texte intégralRésumé :
Recently, self-assembly of colloidal semiconductor nanocrystals (NCs) have attracted a great interest due to their flexible synthesis with tunable band gaps and shape-dependent optical and electronic properties. In particular, nanorods (NRs) superlattice is receiving considerable attention. Typically, the NRs superlattice is prepared by guiding the process of self-assembly through external forces. In this article, recent development of self-assembly approaches at work in fabricating NRs superlattices was reviewed. Despite those effective self-assembly techniques through external controls to obtain NCs assemblies during deposition were widespread used. But these techniques are time consuming, and cannot get rid of the organic capping insulated molecules surrounding the NCs. So there is still a challenge to guarantee the electron/hole dissociation as well as the charge transport of NCs. Here, thermal annealing method that applies selectivity even in the presence of organic molecules will be adopted to obtain colloidal NRs superlattices, and the self-assembly mechanism of NRs were briefly addressed.
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Dzhagan, Volodymyr, Olga Kapush, Nazar Mazur, Yevhenii Havryliuk, Mykola I. Danylenko, Serhiy Budzulyak, Volodymyr Yukhymchuk, Mykhailo Valakh, Alexander P. Litvinchuk et Dietrich R. T. Zahn. « Colloidal Cu-Zn-Sn-Te Nanocrystals : Aqueous Synthesis and Raman Spectroscopy Study ». Nanomaterials 11, no 11 (31 octobre 2021) : 2923. http://dx.doi.org/10.3390/nano11112923.
Texte intégralRésumé :
Cu-Zn-Sn-Te (CZTTe) is an inexpensive quaternary semiconductor that has not been investigated so far, unlike its intensively studied CZTS and CZTSe counterparts, although it may potentially have desirable properties for solar energy conversion, thermoelectric, and other applications. Here, we report on the synthesis of CZTTe nanocrystals (NCs) via an original low-cost, low-temperature colloidal synthesis in water, using a small-molecule stabilizer, thioglycolic acid. The absorption edge at about 0.8–0.9 eV agrees well with the value expected for Cu2ZnSnTe4, thus suggesting CZTTe to be an affordable alternative for IR photodetectors and solar cells. As the main method of structural characterization multi-wavelength resonant Raman spectroscopy was used complemented by TEM, XRD, XPS as well as UV-vis and IR absorption spectroscopy. The experimental study is supported by first principles density functional calculations of the electronic structure and phonon spectra. Even though the composition of NCs exhibits a noticeable deviation from the Cu2ZnSnTe4 stoichiometry, a common feature of multinary NCs synthesized in water, the Raman spectra reveal very small widths of the main phonon peak and also multi-phonon scattering processes up to the fourth order. These factors imply a very good crystallinity of the NCs, which is further confirmed by high-resolution TEM.
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Anni, Marco. « Polymer-II-VI Nanocrystals Blends : Basic Physics and Device Applications to Lasers and LEDs ». Nanomaterials 9, no 7 (19 juillet 2019) : 1036. http://dx.doi.org/10.3390/nano9071036.
Texte intégralRésumé :
Hybrid thin films that combine organic conjugated molecules and semiconductors nanocrystals (NCs) have been deeply investigated in the previous years, due to their capability to provide an extremely broad tuning of their electronic and optical properties. In this paper we review the main aspects of the basic physics of the organic–inorganic interaction and the actual state of the art of lasers and light emitting diodes based on hybrid active materials.
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Camellini, Andrea, Haiguang Zhao, Sergio Brovelli, Ranjani Viswanatha, Alberto Vomiero et Margherita Zavelani-Rossi. « (Invited) Ultrafast Spectroscopy in Semiconductor Nanocrystals : Revealing the Origin of Single Vs Double Emission, of Optical Gain and the Role of Dopants ». ECS Meeting Abstracts MA2022-01, no 20 (7 juillet 2022) : 1104. http://dx.doi.org/10.1149/ma2022-01201104mtgabs.
Texte intégralRésumé :
A wide variety of materials with nanometre dimensions are increasingly explored for photonic applications. Among them, semiconductor nanocrystals (NCs) are very promising for a variety of uses, including light emission devices (LEDs), lasers, detectors, photovoltaic cells, biological labelling and sensing [1]. Key advantage of NCs is the possibility to tailor their optical response by controlling the electronic structure (“wave function engineering”) through the choice of composition, size and shape. Significant and interesting results have been obtained with heterostructured and doped NCs. Beyond single wavelength tuneable band-edge emission, other regimes have been demonstrated such as intragap emission, simultaneous emission on two different wavelengths, amplified spontaneous emission and laser emission. The luminescent properties are governed by exciton decay, which can proceed through radiative or nonradiative pathways, following different routes. The study of exciton dynamics can allow elucidating the processes connected to single or dual emission and to optical gain. This, in turn, can lead to the identification of the functional and structural characteristics that are responsible for these behaviors. Exciton relaxation occurs on picosecond timescales, so ultrafast optical techniques are required to perform these studies. In this talk, we present studies carried out by ultrafast pump-probe spectroscopy technique, with 100-fs time resolution, on CdSe/CdS and PbS/CdS heterostructured NCs, with different geometries (core/shell, dot-in-rod, dot-in-bulk, with sharp or graded interface) [2-6] and CdSeS and CdZnSe doped NCs [7,8]. These NCs are optically active in the visible and near-infrared spectral region, show single and dual colour photoluminescence emission, optical gain, laser emission and intragap emission [2-9]. The analysis of the experimental data allowed us to unravel the decay processes: the initials take place in a few ps, leading to the ultimate emitting state whose lifetime can extend to hundreds of ps to few ns, allowing for efficient luminescence and optical gain. Our data on heterostructures allowed us to clarify the role of the volume and of the shape of the outer component and the effect of the interface [2-4]. We found that dual emission is possible for both thick and thin quantum-confined shells, and for different interfaces. We studied the decoupling of excitons lying in the two different component of the NC (core exciton and shell exciton) and we revealed the evolution of the exciton barrier known as dynamic hole-blockade effect. We showed that these phenomena are strictly connected to dual emission and optical gain and we identified the condition for their maximum efficiency, in term of band alignment and band transitions. Our results provide a comprehensive understanding of the physical phenomena governing dual-emission mechanisms, suppression of Auger recombination, optical gain and laser emission in heterostructured NCs. Experiments on CdZnSe NCs doped with Mn and on CdSeS NCs engineered with sulfur vacancies, enabled us to disclose donor and acceptor localized states in the band gap. We observed the carrier dynamics responsible for intragap emission which is associated to the emergence of a transient Mn3+ state [7], in the first case, and to a donor state below the conduction band introduced by sulfur vacancies [8], in the latter case. In conclusion, the study of the exciton dynamics in different NCs allowed us to elucidate the relation between structural-morphological characteristics (shape, volume, and interface) and unconventional emission capabilities (dual emission and optical gain) in heterostructures and the photophysics of electronic states introduced by doping. This knowledge is very important to control NC functionalities toward new multilevel electronic or photonic schemes and in applications such as lasers [9], photoelectrochemical (PEC) cell [10], white light emission [11], ratiometric sensing [12]. [1] P. V. Kamat and G. D. Scholes, J. Phys. Chem. Lett. 7, 584 (2016) [2] G. Sirigu et al., Phys. Rev. B 96, 155303 (2017) [3] V. Pinchetti et al., ACS Nano 10, 6877-6887 (2016) [4] H. Zhao et al., Nanoscale 8, 4217-4226 (2016) [5] M. Zavelani-Rossi et al., Nano Lett. 10, 3142-3150 (2010) [6] R. Krahne et al., Appl. Phys. Lett. 98, 063105 (2011) [7] K. Gahlot et al., ACS Energy Lett. 4, 729−735 (2019) [8] F. Carulli et al., Nano Lett. 21, 6211−6219 (2021) [9] M. Zavelani-Rossi et al., Laser & Photonics Reviews 6, 678-683 (2012) [10] L. Jin et al., Nano Energy 30, 531-541 (2016) [11] S. Sapra et al., Adv. Mater. 19, 569 (2007) [12] J. Liu et al., ACS Photonics, 2479 (2019)
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Deng, Yuan, Yicheng Zeng, Wanying Gu, Pan Huang, Geyu Jin, Fangze Liu, Jing Wei et Hongbo Li. « Colloidal Synthesis and Ultraviolet Luminescence of Rb2AgI3 Nanocrystals ». Crystals 13, no 7 (16 juillet 2023) : 1110. http://dx.doi.org/10.3390/cryst13071110.
Texte intégralRésumé :
Semiconductor nanocrystals (NCs) hold immense potential as luminescent materials for various optoelectronic applications. While significant progress has been made in developing NCs with outstanding optical properties in the visible range, their counterparts emitting in the ultraviolet (UV) spectrum are less developed. Rb2AgI3 is a promising UV-emitting material due to its large band gap and high stability. However, the optical properties of low-dimensional Rb2AgI3 NCs are yet to be thoroughly explored. Here, we synthesized Rb2AgI3 NCs via a hot injection method and investigated their properties. Remarkably, these NCs exhibit UV luminescence at 302 nm owing to self-trapped excitons. The wide-bandgap nature of Rb2AgI3 NCs, combined with their intrinsic UV luminescence, offers considerable potential for applications in UV photonic nanodevices. Our findings contribute to the understanding of Rb2AgI3 NCs and pave the way for exploiting their unique properties in advanced optoelectronic systems.
Thèses sur le sujet "Electronic Properties - Semiconductor Nanocrystals (NCs)"
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Zbydniewska, Ewa. « Electronic properties of coupled semiconductor nanocrystals and carbon nanotubes ». Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10010/document.
Texte intégralRésumé :
Ce travail de thèse décrit les propriétés électroniques de nanodispositifs couplés entre transistors à nanotubes de carbone (CNTFETs) et nanocristaux semiconducteurs colloïdaux CdSe/ZnS individuels en régime de détection de charge unique à température ambiante. Les transferts de charges élémentaires entre nanotubes et nanocristaux sont mis en évidence par les fluctuations temporelles du courant des transistors à tension de grille fixée, et font apparaître un signal à deux niveaux (bruit télégraphique ou RTS), observé sur des échelles de temps entre 1s et 0.1 ms. Les temps d’occupation τ des niveaux de courant suivent une loi de puissance P(τ)~τ-α où l’exposant α varie entre 1.5 et 4 (typiquement proche de 2.8). Cette observation suggère que les fluctuations de charges observées sont à la base des phénomènes de "clignotement optique" des nanocristaux colloïdaux étudiés. L’analyse spectroscopique des dispositifs permet d’attribuer ce clignotement à des pièges dans la bande interdite des nanocristaux, avec une énergie de chargement Ec de l’ordre de 200 meV. L’approche présentée dans ce travail peut être étendue à des mesures électro-optiques, et donc permettre une meilleure compréhension des phénomènes physiques contrôlant les propriétés optoélectroniques de nanodispositifs à base de nanocristaux semiconducteursWe study the electronic properties of coupled semiconductor nanocrystals and carbon nanotubes. We report measurements of single electron transfers between single CdSe colloidal nanocrystal coupled to a carbon nanotube field effect transistor at room temperature in ambient conditions. The measurements consist of nanotube current level monitoring as a function of time for fixed gate voltage. We observe a sequence of high - low currents (random telegraph signal) on time scales up to several seconds with ms sampling time. We attribute the two level current fluctuations to the transfer of single electron onto the nanocrystal. The probability of the occupation time τ at the high or low current state follows a power law of the form P(τ)~τ-α where exponent α lies between 1.5 and 4 (typically close to 2.8). The observation suggests that the two-level current switching is similar to the fluorescence intermittency (optical blinking) observed in individual quantum dots. The spectroscopic analysis of the devices based on coupled semiconductor nanocrystals and carbon nanotubes is consistent with the charging of nanocrystal defect states with a charging energy of Ec ~ 200 meV. The approach developed here enables to probe the trap state dynamics in quantum dots in ambient air and room temperature from a purely electrical approach, and therefore to better understand the physics at hand in (opto)electronic devices based on quantum dots
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Shcheglov, Kirill V. Atwater Harry Albert. « Synthesis, optical and electronic properties of group IV semiconductor nanocrystals / ». Diss., Pasadena, Calif. : California Institute of Technology, 1997. http://resolver.caltech.edu/CaltechETD:etd-01172008-081522.
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Schill, Alexander Wilhem. « Interesting Electronic and Dynamic Properties of Quantum Dot Quantum Wells and other Semiconductor Nanocrystal Heterostructures ». Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11514.
Texte intégralRésumé :
Some interesting electronic and dynamic properties of semiconductor nanocrystal heterostructures have been investigated using various spectroscopic methods. Semiconductor nanocrystal heterostructures were prepared using colloidal synthesis techniques. Ultrafast transient absorption spectroscopy was used to monitor the relaxation of hot electrons in CdS/HgS/CdS quantum dot quantum wells. Careful analysis of the hot electron relaxation in CdS/HgS/CdS quantum dot quantum wells reveals an energy dependent relaxation mechanism involving electronic states of varying CdS and HgS composition. The composition of the electronic states, combined with the layered structure of the nanocrystal permits the assignment of CdS localized and HgS localized excited states. The dynamic effect of surface passivation is then shown to have the strongest influence on excited states that are localized in the HgS layer.
New quantum dot quantum well heterostructures of different sizes and compositions were also prepared and studied. The dynamic properties of CdS/CdSe/CdS colloidal quantum wells suggest simultaneous relaxation of excited electrons within the CdS core and CdSe shell on the sub-picosecond time scale. Despite the very different electronic structure of CdS/CdSe/CdS compared to CdS/HgS/CdS, the time scales of the relaxation and electron localization were very similar.
Enhancement of trap luminescence was observed when CdS quantum dots were coated with silver. The mechanism of the enhancement was investigated using time-resolved spectroscopic techniques.
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Shcheglov, Kirill Vadim. « Synthesis, optical and electronic properties of group IV semiconductor nanocrystals ». Thesis, 1997. https://thesis.library.caltech.edu/211/1/Shcheglov_kv_1997.pdf.
Texte intégralRésumé :
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Every operating control system must deal with constraints. On the one hand, the range and rate of change of the input or manipulated variable is limited by the physical nature of the actuator (saturation limits). On the other hand, process state variables or outputs (pressures, temperatures, voltages) may not be allowed to exceed certain bounds arising from equipment limitation, safety considerations, or environmental regulations.
A rich theory exists for designing controllers - both linear ([...],LQG, LTR, pole-placement) and nonlinear (nonlinear [...], control, feedback linearization, sliding mode control, gain scheduling). However, none of these popular and fashionable controller design techniques account for the presence of input or output constraints. Although occasionally these constraints may be neglected, in general, they lead to design and operating problems unless they are accounted for properly.
In traditional control practice, overrides or mode selection schemes are used to deal with output constraints: they switch between a "bank" of controllers, each of which is designed to achieve a specific objective. In both cases (saturation limit and mode selection), a control input nonlinearity is introduced into the operating system.
Despite its significance, the study of the constrained control problem has received far less attention than the traditional unconstrained (linear and nonlinear) control theory. With few exceptions, most of the controller design techniques for constrained systems are by-and-large ad-hoc, with very little guarantees of stability, performance and robustness to plant model uncertainty.
The objective of this thesis is to take a broad approach towards the constrained control problem. One part of the thesis is devoted to the development of a systematic and unifying theory for studying the so-called Anti-Windup Bumpless Transfer (AWBT) problem. The other part aims towards the development of a general novel approach for the synthesis of a robust model predictive control (MPC) algorithm.
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Group IV semiconductor (Si, Ge and Sn) nanocrystals were synthesized in dielectric matrixes by ion implantation of the respective species into the matrix to form a supersaturated solid solution and subsequent precipitation by thermal annealing. The resulting structure was characterized by Transmission Electron Microscopy and Raman spectroscopy. It was found that nanocrystals of these materials can be effectively synthesized with diameters in the nanometer range. Ge nanocrystals in SiO[...] were extensively characterized, particle size distributions were counted from TEM results and were used to compare experimental photoluminescence spectra with theoretical predictions. Unusual nanostructures were formed in samples co-implanted with Ge and Sn and annealed at 600°C. Raman spectroscopy indicated a possibility of significant alloying of Ge and Sn in these nanostructures. Optical properties of Si nanocrystals in silicon dioxide were investigated by photoluminescence spectroscopy as well. It was found that while Ge nanocrystal system luminescence is mostly due to defects in the matrix produced by ion implantation, Si nanocrystal sample luminescence is due to the Si nanocrystals themselves. The luminescence is above the bulk Si bandgap and supports the quantum confined excitonic luminescence theory. Light emitting devices were fabricated using both systems. Electroluminescence was observed for both Si and Ge, albeit with rather low efficiency, in the 10[...] - 10[...] range. Electroluminescence from Si nanocrystal containing devices was spectrally similar to photoluminescence from that system, with a band about 800 nm, consistent with electronic excitation of radiative transitions in Si nanocrystals. Cubic nonlinearities were measured for both Ge and Si nanocrystals and found to be 10[...] - 10[...] esu range. Finally, an interesting interferometric arrangement which has a potential to be useful for investigating nanoscale structures was theoretically described.
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Arora, Vikas. « Design and synthesis of semiconductor nanocrystals to modify their optical and electronic properties ». Thesis, 2018. http://localhost:8080/iit/handle/2074/7563.
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Viswanatha, Ranjani. « Growth Kinetics And Electronic Properties Of Semiconducting Nanocrystals In The Quantum Confined Regime ». Thesis, 2006. https://etd.iisc.ac.in/handle/2005/403.
Texte intégralRésumé :
Properties of nanocrystals are extremely sensitive to their sizes when their sizes are smaller or of the order of the excitonic diameter due to the quantum confinement effect. The interest in this field has been concentrated basically in understanding the size-property relations of nanocrystals, for example, the pronounced variation in the bandgap of the material or the fluorescence emission properties, by tuning the sizes of the nanocrystals. Thus, the optical and electronic properties of semiconductor nanocrystals can be tailor-made to suit the needs of the specific application and hence is of immense importance. One of the major aspects necessary for the actual realization of the various applications is the ability to synthesize nanocrystals of the required size with a controlled size distribution. The growing demand to obtain such nanocrystals with the required size and controlled size distribution is met largely by the solution route synthesis of nanocrystals, that constitutes an important class of synthesis methods due to their ease of implementation and the high degree of flexibility. The main difficulty of this method is that the dependence of the average size and the size distribution of the generated particles on parameters of the reaction are not understood in detail and therefore, the optimal reaction conditions are arrived at essentially in an empirical and intuitive manner. From a fundamental point of view, understanding the growth kinetics of various nanocrystals can provide a deeper insight into the phenomena. The study of growth kinetics can be experimentally achieved by measuring the time evolution of diameter using several in-situ techniques like UV-absorption and small angle X-ray scattering. Having understood the mechanism of growth of nanocrystals, it is possible to obtain the required size of the nanocrystal using optimized synthesis conditions. The properties of these high quality nanocrystals can be further tuned by doping with a small percentage of magnetic ions. The optical and magnetic properties of these nanocrystals play an important role in the various technological applications. The first part of the thesis concentrates on the theoretical methods to study the electronic structure of semiconductor nanocrystals. The second part describes the studies performed on growth of various nanocrystal systems, both in the presence and absence of capping agents. The third part of the thesis describes the studies carried out on ZnO and doped ZnO nanocrystals, synthesized using optimal conditions that were obtained in the earlier part of the thesis. The thesis is divided into five chapters which are described below.
Chapter 1 provides a brief overall perspective of various interesting properties of semiconductor nanocrystals, including various concepts relevant for the study of such systems.
Chapter 2 describes experimental and theoretical methods used for the study of nanocrystals reported in this thesis.
In Chapter 3 of this thesis, we report results of theoretical studies carried out on III-V and II-VI semiconductors using the tight-binding (TB) methodology.
Chapter 4 presents the investigations on the growth kinetics of several nanocrystal systems.
Chapter 5 presents experimental investigations carried out on undoped and various transition metal (TM) doped ZnO nanocrystals.
In summary, we have performed electronic structure calculations on various nanocrystal systems, devised a novel method to obtain the size distribution from UV-absorption spectrum and studied the mechanism of growth in the presence and absence of capping agents in various II-VI semiconductors. Using the optimal conditions obtained from the growth studies, we prepare high quality ZnO nanocrystals of required size, both in free-standing and capped states and doped it with small percentages of various transition metals like Mn, Cu and Fe. We have then studied their optical and magnetic properties.
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Viswanatha, Ranjani. « Growth Kinetics And Electronic Properties Of Semiconducting Nanocrystals In The Quantum Confined Regime ». Thesis, 2006. http://hdl.handle.net/2005/403.
Texte intégralRésumé :
Properties of nanocrystals are extremely sensitive to their sizes when their sizes are smaller or of the order of the excitonic diameter due to the quantum confinement effect. The interest in this field has been concentrated basically in understanding the size-property relations of nanocrystals, for example, the pronounced variation in the bandgap of the material or the fluorescence emission properties, by tuning the sizes of the nanocrystals. Thus, the optical and electronic properties of semiconductor nanocrystals can be tailor-made to suit the needs of the specific application and hence is of immense importance. One of the major aspects necessary for the actual realization of the various applications is the ability to synthesize nanocrystals of the required size with a controlled size distribution. The growing demand to obtain such nanocrystals with the required size and controlled size distribution is met largely by the solution route synthesis of nanocrystals, that constitutes an important class of synthesis methods due to their ease of implementation and the high degree of flexibility. The main difficulty of this method is that the dependence of the average size and the size distribution of the generated particles on parameters of the reaction are not understood in detail and therefore, the optimal reaction conditions are arrived at essentially in an empirical and intuitive manner. From a fundamental point of view, understanding the growth kinetics of various nanocrystals can provide a deeper insight into the phenomena. The study of growth kinetics can be experimentally achieved by measuring the time evolution of diameter using several in-situ techniques like UV-absorption and small angle X-ray scattering. Having understood the mechanism of growth of nanocrystals, it is possible to obtain the required size of the nanocrystal using optimized synthesis conditions. The properties of these high quality nanocrystals can be further tuned by doping with a small percentage of magnetic ions. The optical and magnetic properties of these nanocrystals play an important role in the various technological applications. The first part of the thesis concentrates on the theoretical methods to study the electronic structure of semiconductor nanocrystals. The second part describes the studies performed on growth of various nanocrystal systems, both in the presence and absence of capping agents. The third part of the thesis describes the studies carried out on ZnO and doped ZnO nanocrystals, synthesized using optimal conditions that were obtained in the earlier part of the thesis. The thesis is divided into five chapters which are described below.
Chapter 1 provides a brief overall perspective of various interesting properties of semiconductor nanocrystals, including various concepts relevant for the study of such systems.
Chapter 2 describes experimental and theoretical methods used for the study of nanocrystals reported in this thesis.
In Chapter 3 of this thesis, we report results of theoretical studies carried out on III-V and II-VI semiconductors using the tight-binding (TB) methodology.
Chapter 4 presents the investigations on the growth kinetics of several nanocrystal systems.
Chapter 5 presents experimental investigations carried out on undoped and various transition metal (TM) doped ZnO nanocrystals.
In summary, we have performed electronic structure calculations on various nanocrystal systems, devised a novel method to obtain the size distribution from UV-absorption spectrum and studied the mechanism of growth in the presence and absence of capping agents in various II-VI semiconductors. Using the optimal conditions obtained from the growth studies, we prepare high quality ZnO nanocrystals of required size, both in free-standing and capped states and doped it with small percentages of various transition metals like Mn, Cu and Fe. We have then studied their optical and magnetic properties.
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Sanders, Kirsty Gail. « Electronic properties of low dimensional carbon materials ». Thesis, 2016. http://hdl.handle.net/10539/21681.
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A Dissertation submitted to the Faculty of Science, University of the Witwatersrand,
Johannesburg, in ful lment of the requirements for the degree of Master of Science. Johannesburg 2016.Low dimensional carbon systems are of immense interest in condensed matter physics due to their exceptional and often startling electric and magnetic properties. In this dissertation we consider two of these materials - graphene and nanocrystalline diamond. The effect of synthesis parameters on the quality of graphene is examined and it is found that controlling the partial pressure of the synthesis gases plays a critical role in determining the quality of the sample. Superconductivity in Boron doped nanocrystalline diamond (B-NCD) is considered and weak localisation along with a Berezinsky-Kosterlitz-Thouless (BKT) transition is identified in the samples. Furthermore we explore theoretically the problem of electric transport through a double quantum dot system coupled to a nanomechanical resonator. We find resonant tunnelling when the difference between the energy levels of the dots equals an integer multiple of the resonator frequency, and that while initially increasing the electron phonon coupling (g) increases the current through the sample further increase in g inhibits electric transport through the quantum dots.
LG2017
Livres sur le sujet "Electronic Properties - Semiconductor Nanocrystals (NCs)"
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I, Klimov Victor, dir. Semiconductor and metal nanocrystals : Synthesis and electronic and optical properties. New York : Marcel Dekker, Inc., 2004.
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Inelastic light scattering of semiconductor nanostructures : Fundamentals and recent advances. Berlin : Springer, 2006.
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Klimov, Victor I. Semiconductor and Metal Nanocrystals : Synthesis and Electronic and Optical Properties. Taylor & Francis Group, 2003.
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Klimov, Victor I. Semiconductor and Metal Nanocrystals : Synthesis and Electronic and Optical Properties. Taylor & Francis Group, 2003.
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Victor, I. Klimov. Semiconductor and Metal Nanocrystals : Synthesis and Electronic and Optical Properties. Taylor & Francis Group, 2003.
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Klimov, Victor I. Semiconductor and Metal Nanocrystals : Synthesis and Electronic and Optical Properties. Taylor & Francis Group, 2003.
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Klimov, Victor I. Semiconductor and Metal Nanocrystals : Synthesis and Electronic and Optical Properties. Taylor & Francis Group, 2003.
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Klimov, Victor I. Semiconductor and Metal Nanocrystals : Synthesis and Electronic and Optical Properties. Taylor & Francis Group, 2003.
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Klimov, Victor I. Semiconductor and Metal Nanocrystals : Synthesis and Electronic and Optical Properties (Optical Engineering). CRC, 2003.
Trouver le texte intégralChapitres de livres sur le sujet "Electronic Properties - Semiconductor Nanocrystals (NCs)"
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Chen, Tupei. « Electronic and Optical Properties of Si and Ge Nanocrystals ». Dans Semiconductor Nanocrystals and Metal Nanoparticles, 215–54. Taylor & Francis Group, 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742 : CRC Press, 2016. http://dx.doi.org/10.1201/9781315374628-7.
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Brus, Louis E. « Electronic and Optical Properties of Semiconductor Nanocrystals : From Molecules to Bulk Crystals ». Dans Nanophase Materials, 433–48. Dordrecht : Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-1076-1_48.
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C.A. Silva, Anielle, Amanda I.S. Barbosa, Alessandra S. Silva, Elisson A. Batista, Thaís K. de Lima Rezende, Éder V. Guimarães, Ricardo S. Silva et Noelio O. Dantas. « Diluted Magnetic Semiconductors Nanocrystals : Saturation and Modulation ». Dans Nanocrystals [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96679.
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Diluted Magnetic Semiconductor (DMS) nanocrystals are a new class of materials formed by doping the semiconductor with transition metals (TM), which gives interesting magneto-optical properties. These properties are attributed to the exchange interaction between the pure semiconductor’s sp-electrons and the localized TM d-electrons. This book chapter shows exciting results of new DMS developed by the group, both in powder form and embedded in glassy systems. Depending on the concentration of doping ions, saturation of the incorporation of substitutional and interstitial sites in the nanocrystal structure may occur, forming other nanocrystals. In this context, we investigated the doping saturation limit in nanopowders of DMS Zn1-xMnxO NCs and Zn1-xMnxTe, Zn0.99-xMn0.01CoxTe, and Bi2-xCoxS NCs synthesized in glassy matrices. Thus, the sites’ saturation into the crystalline lattice of nanocrystals is a topic little reported in the literature, and we will comment on this work. Therefore, we will show results from the group about the modulation and saturation in diluted magnetic semiconductors nanocrystals in this work.
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C.A. Silva, Anielle, Eliete A. Alvin, Francisco R.A. dos Santos, Samanta L.M. de Matos, Jerusa M. de Oliveira, Alessandra S. Silva, Éder V. Guimarães et al. « Doped Semiconductor Nanocrystals : Development and Applications ». Dans Nanocrystals [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96753.
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This chapter aims to show significant progress that our group has been developing and the applications of several doped semiconductor nanocrystals (NCs), as nanopowders or embedded in glass systems. Depending on the type of dopant incorporated in the nanocrystals, the physical, chemical, and biological properties can be intensified. However, it can also generate undesired toxic effects that can potentially compromise its use. Here we present the potential of zinc oxide NCs doped with silver (Ag), gold (Au), and magnesium (Mg) ions to control bacterial diseases in agriculture. We have also performed biocompatibility analysis of the pure and Ag-doped sodium titanate (Na2Ti3O7) NCs in Drosophila. The doped nanocrystals embedded in glassy systems are chrome (Cr) or copper (Cu) in ZnTe and Bi2Te3 NCs for spintronic development nanodevices. Therefore, we will show several advantages that doped nanocrystals may present in the technological and biotechnological areas.
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Chelikowsky, James R. « Algorithms for Predicting the Physical Properties of Nanocrystals and Large Clusters ». Dans Computational Nanoscience, 1–25. The Royal Society of Chemistry, 2011. http://dx.doi.org/10.1039/bk9781849731331-00001.
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The electronic structure problem for nanoscale systems is a computationally challenging problem. The large number of degrees of freedom, both electronic and nuclear, and requiring a highly precise solution, make the problem impossible to solve without some effective approximations. Here I illustrate some advances in algorithm developments by solving the electronic structure problem within density functional theory in real space using pseudopotentials and density functional theory. The algorithms presented are based on a Chebyshev-filtered subspace iteration, which results in a significant speedup over methods based on standard sparse iterative diagonalization. I illustrate this method for a variety of nanostructures by calculating the electronic and vibrational states for silicon nanocrystals, the electronic properties of doped semiconductor nanocrystals, and the magnetic properties of metallic iron clusters.
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Shimoi, Norihiro. « Nonthermal Crystalline Forming of Ceramic Nanoparticles by Non-Equilibrium Excitation Reaction Field of Electron ». Dans Nanocrystals [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.97037.
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In this work, we have discovered a method of forming ZnO thin films with high mobility, high carrier density and low resistivity on plastic (PET) films using non-equilibrium reaction fields, even when the films are deposited without heating, and we have also found a thin film formation technique using a wet process that is different from conventional deposition techniques. The field emission electron-beam irradiation treatment energetically activates the surface of ZnO particles and decomposes each ZnO particles. The energy transfer between zinc ions and ZnO surface and the oxygen present in the atmosphere around the ZnO particles induce the oxidation of zinc. In addition, the ZnO thin films obtained in this study successfully possess high functional thin films with high electrical properties, including high hole mobility of 208.6 cm2/Vs, despite being on PET film substrates. These results contribute to the discovery of a mechanism to create highly functional oxide thin films using a simple two-dimensional process without any heat treatment on the substrate or during film deposition. In addition, we have elucidated the interfacial phenomena and crosslinking mechanisms that occur during the bonding of metal oxide particles, and understood the interfacial physical properties and their effects on the electronic structure. and surface/interface control, and control of higher-order functional properties in metal/ceramics/semiconductor composites, and contribute to the provision of next-generation nanodevice components in a broad sense.
Actes de conférences sur le sujet "Electronic Properties - Semiconductor Nanocrystals (NCs)"
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Goncharova, Olga V., et Sergey A. Tikhomirov. « Nonlinear Optical Properties of Thin-Film Quasi-Zero-Dimensional Media Depending on the Matrix Materials ». Dans The European Conference on Lasers and Electro-Optics. Washington, D.C. : Optica Publishing Group, 1996. http://dx.doi.org/10.1364/cleo_europe.1996.cfg6.
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Three-dimensional confinement of excitons or electrons motion in nanometer-sized microcrystallites (nanocrystals – NCs) is an important phenomenon in physics, and is expected to bring a significant improvement to ultrafast functional devices. In the past ten years, several types of quasi-zero-dimensional (QZD) media such as dielectric matrices containing dispersed semiconductor or metal NCs have been realized by using various techniques. Recently, we have succeeded in the preparation of thin-film QZD media [1]. Such media are very suitable for investigating the effect of the microstructure (including the average size, the concentration, the arranging types of NCs and the matrix material) on the quantum confinement of the electron-hole motion.
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Klimov, Victor I., et Vladimir A. Karavanskii. « Ultrafast Optical Nonlinearities in CuxS Nanocrystals ». Dans Nonlinear Optics : Materials, Fundamentals and Applications. Washington, D.C. : Optica Publishing Group, 1996. http://dx.doi.org/10.1364/nlo.1996.nthe.17.
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Three-dimensional (3D) carrier confinement in semiconductor nanocrystals (NC's) results in size-dependent photoluminescence and absorption spectra and significantly modifies the nonlinear optical properties and carrier dynamics with respect to those in bulk materials. So far, most experimental and theoretical studies have concentrated on NC's formed by direct-gap II-VI semiconductors such as CdS and CdSe. Recently, we reported the preparation, linear and picosecond nonlinear transmission of NC's of a new type: NC's formed by different copper sulfide phases [1]. Depending on the copper deficiency, the energy band gap in copper sulfide varies from 1.2 (x = 2) to 1.5 eV (x = 1.8) with an accompanying transformation of the semiconductor from indirect-gap to direct-gap one. These interesting properties as well as a small electron mass provide the broad phase/size controlled tuning range and give the opportunity to compare the effects of 3D confinement on nonlinear optical proterties in direct and indirect-gap semiconductors.
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Klimov, Victor I., et Duncan W. McBranch. « Ultrafast Optical Nonlinearities and Carrier Dynamics in Direct- and Indirect-Gap Semiconductor Nanocrystals ». Dans Chemistry and Physics of Small-Scale Structures. Washington, D.C. : Optica Publishing Group, 1997. http://dx.doi.org/10.1364/cps.1997.ctua.3.
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Semiconductor nanocrystals (NCs) exhibit large and fast optical nonlinearities, and efficient photo- and electroluminescence that make them promising materials for applications in optoelectronics and ultrafast optical switching. The nonlinear optical and luminescent properties of NCs are significantly affected by carrier dynamics. Carrier trapping and a nonradiative Auger process are believed to play a major role in the early stages of carrier relaxation, resulting in ultrafast picosecond and subpicosecond dynamics measured in femtosecond pump-probe, photoluminescence (PL) up-conversion, and photoecho experiments.
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Lipovskii, A. A., E. V. Kolobkova et V. D. Petrikov. « Optical Properties of Novel Phosphate with Embedded Semiconductor Nanocrystals ». Dans EQEC'96. 1996 European Quantum Electronic Conference. IEEE, 1996. http://dx.doi.org/10.1109/eqec.1996.561797.
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Banin, U., J. C. Lee, A. A. Guzelian et A. P. Alivisatos. « Size Dependent Electronic Level Structure of Colloidal InAs Nanocrystal Quantum Dots ». Dans Chemistry and Physics of Small-Scale Structures. Washington, D.C. : Optica Publishing Group, 1997. http://dx.doi.org/10.1364/cps.1997.ctua.2.
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Semiconductor nanocrystals serve as model systems for evolution of bulk properties from the solid state to the molecular regime.1 In this work we study a fundamental question related with quantum confinement in semiconductors - the evolution of the electronic level structure with size in InAs nanocrystals.
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Bawendi, Moungi G. « Semiconductor Nanocrystallites : Building Blocks for Quantum Dot Structures ». Dans Chemistry and Physics of Small-Scale Structures. Washington, D.C. : Optica Publishing Group, 1997. http://dx.doi.org/10.1364/cps.1997.ctua.1.
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Bawendi, Moungi G. « II-VI Semiconductor Nanocrystals as Isolated Quantum Dots and in Complex Structures ». Dans Quantum Optoelectronics. Washington, D.C. : Optica Publishing Group, 1995. http://dx.doi.org/10.1364/qo.1995.qfa1.
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Semiconductor crystallites which are 10's of Angstroms show a striking evolution of electronic properties with size.1 These particles (quantum dots) are large enough to exhibit a crystalline core, but small enough that solid state electronic and vibrational band structure is not yet developed. We use a recently developed synthetic method for the fabrication of high quality nanometer size (1-10 nm) II- VI semiconductor crystallites with narrow size distributions (σ<5%), emphasizing CdSe.2 Optical characterization of their electronic structure reveals both molecular and bulk-like characteristics as well as properties which are unique to nanometer size crystallites. We observe a number of discrete electronic transitions, assign them as coming from the creation of delocalized "particle-in-a- sphere" states using the theory of Ref. 3, and study their dependence on crystallite diameter.4
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Kang, Ki Moon, Hyo-Won Kim, Il-Wun Shim et Ho-Young Kwak. « Syntheses of Specialty Nanomaterials at the Multibubble Sonoluminescence Condition ». Dans ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-68320.
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In recent years, a large number of nano-size semiconductors have been investigated for their potential applications in photovoltaic cells, optical sensor devices, and photocatalysts [1, 2, 3]. Nano-size semiconductor particles have many interesting properties due mainly to their size-dependent electronic and optical properties. Appropriately, many speciality of nanomaterials such as CdS and ZnS semiconductor particles, and other metal oxides such as ZnO and lithium-titanate oxide (LTO) have been prepared. However, most of them were prepared with toxic reactants and/or complex multistep reaction processes. Particularly, it is quite difficult to produce LTO nanoparticles, since it typically requires wearisome conditions such as very high temperature over 1000 °C, long producing times, and so on. To overcome such problems, various core/shell type nanocrystals were prepared through different methods such as the hydrothermal synthetic method, microwave, and sonochemistry. Also many coating methods on inorganic oxide nanoparticles were tried for the preparations of various core-shell type nanocrystals. Sonoluminescence (SL) is a light emission phenomenon associated with the catastrophic collapse of a gas bubble oscillating under an ultrasonic field [4]. Light emission of single bubble sonoluminescence (SBSL) is characterized by picosecond flashes of the broad band spectrum extending to the ultraviolet [5, 6]. The bubble wall acceleration has been found to exceed 1011 g at the moment of bubble collapse. Recently observed results of the peak temperature and pressure from the sonoluminescing gas bubble in sulfuric acid solutions [9] were accurately predicted by the hydrodynamic theory for sonoluminescence phenomena [7, 10, 11, 12], which provides a clue for understanding sonochemical reactions inside the bubble and liquid layer adjacent to the bubble wall. Sonochemistry involves an application of sonoluminescence. The intense local heating and high pressure inside the bubbles and liquid adjacent bubble wall from such collapse can give rise to unusual effects in chemical reactions. The estimated temperature and pressure in the liquid zone around the collapsing bubble with equilibrium radius 5 μm, an average radius of bubbles generated in a sonochemical reactor at a driving frequency of 20 kHz with an input power of 179 W, is about 1000 °C and 500 atm, respectively. At the proper condition, a lot of transient bubbles are generated and collapse synchronistically to emit blue light when high power ultrasound is applied to liquid, and it is called multibubble sonoluminescence (MBSL). Figure 1 shows an experimental apparatus for MBSL with a cylindrical quartz cell, into which a 5 mm diameter titanium horn (Misonix XL2020, USA) is inserted [13]. The MBSL facilitates the transient supercritical state [14].in the liquid layer where rapid chemical reactions can take place. In fact, methylene blue (MB), which is one of a number of typical textile dyestuffs, was degraded very fast at the MBSL condition while MB does not degrade under simple ultrasonic irradiation [13]. MBSL has been proven to be a useful technique to make novel materials with unusual properties. In our study, various metal oxides such as ZnO powder [15], used as a primary reinforcing filler for elastomer, homogeneous Li4Ti5O12 nanoparticles [16], used for electrode materials, and core/shell nanoparticles such as CdS coating on TiO2 nanoparticles [17] and ZnS coating on TiO2 nanoparticles [18], which are very likely to be useful for the development of inorganic dye-sensitized solar cells, were synthesized through a one pot reaction under the MBSL condition. Figure 2 shows the XRD pattern of ZnO nanoparticles synthesized from zinc acetate dehydrate (Zn(CH3CO2)2 · 2H2O, 99.999%, Aldrich) in various alcohol solutions with sodium hydroxide (NaOH, 99.99%, Aldrich) at the MBSL condition. The XRD patterns of all powers indicate hexagonal zincite. The XRD pattern for the ZnO nanoparticles synthesized is similar to the ZnO powder produced by a modified sol-gel process and subsequent heat treatment at about 600 °C [19] as shown in Fig.3. The average particle diameter of ZnO powder is about 7 nm. A simple sonochemical method for producing homogeneous LTO nanoparticles, as shown schematically in Fig. 4. First, LiOH and TiO2 nanoparticles were used to prepare LiOH-coated TiO2 nanoparticles as shown in Fig.5. Second, the resulting nanoparticles were thermally treated at 500 °C for 1 hour to prepare LTO nanoparticles. Figure 6 shows a high resolution transmission electron microscope image of LTO nanoparticles having an average grain size of 30–40 nm. All the nanoparticle synthesized are very pure in phase and quite homogeneous in their size and shape. Recently we succeeded in synthesizing a supported nickel catalyst such as Ni/Al2sO3, MgO/Al2O3 and LaAlO3, which turned out to be effective for methane decomposition [20]. Sonochemistry may provide a new way to more rapidly synthesize many specialty nanoparticles with less waste [21]. This clean technology enables the preparation of new materials such as colloids, amorphous particles [22], and various alloys.