다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Current research into semiconductor clusters is focused on the properties of quantum dots-fragments of semiconductor consisting of hundreds to many thousands of atoms-with the bulk bonding geometry and with surface states eliminated by enclosure in a material that has a larger band gap. Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery.

Semiconductor Clusters, Nanocrystals, and Quantum Dots

New materials hold the key to fundamental advances in energy conversion and storage, both of which are vital in order to meet the challenge of global warming and the finite nature of fossil fuels. Nanomaterials in particular offer unique properties or combinations of properties as electrodes and electrolytes in a range of energy devices. This review describes some recent developments in the discovery of nanoelectrolytes and nanoelectrodes for lithium batteries, fuel cells and supercapacitors. The advantages and disadvantages of the nanoscale in materials design for such devices are highlighted.

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Nanostructured materials for advanced energy conversion and storage devices

Mobility — the transport of people and goods — is a socioeconomic reality that will surely increase in the coming years. It should be safe, economic and reasonably clean. Little energy needs to be expended to overcome potential energy changes, but a great deal is lost through friction (for cars about 10 kWh per 100 km) and low-efficiency energy conversion. Vehicles can be run either by connecting them to a continuous supply of energy or by storing energy on board. Hydrogen would be ideal as a synthetic fuel because it is lightweight, highly abundant and its oxidation product (water) is environmentally benign, but storage remains a problem. Here we present recent developments in the search for innovative materials with high hydrogen-storage capacity.

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Hydrogen-storage materials for mobile applications

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Pores of molecular dimensions can adsorb large quantities of gases owing to the enhanced density of the adsorbed material inside the pores1, a consequence of the attractive potential of the pore walls. Pederson and Broughton have suggested2 that carbon nanotubes, which have diameters of typically a few nanometres, should be able to draw up liquids by capillarity, and this effect has been seen for low-surface-tension liquids in large-diameter, multi-walled nanotubes3. Here we show that a gas can condense to high density inside narrow, single-walled nanotubes (SWNTs). Temperature-programmed desorption spectrosocopy shows that hydrogen will condense inside SWNTs under conditions that do not induce adsorption within a standard mesoporous activated carbon. The very high hydrogen uptake in these materials suggests that they might be effective as a hydrogen-storage material for fuel-cell electric vehicles.

Storage of hydrogen in single-walled carbon nanotubes

1354 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1999 0935-9648/99/1611-1354 $ 17.50+.50/0 Adv. Mater. 1999, 11, No. 16 [6] J. Kido, H. Hayase, K. Hongawa, K. Nagai, K. Okuyama, Appl. Phys. Lett. 1994, 65, 2124. [7] J. Kido, W. Ikeda, M. Kimura, K. Nagai, Jpn. J. Appl. Phys. 1996, 35, L394. [8] T. Sano, M. Fujita, T. Fujii, Y. Hamada, K. Shibata, K. Kuroki, Jpn. J. Appl. Phys. 1995, 34, 1883. [9] L. Liu, W. Li, Z. Hong, J. Peng, X. Liu, C. Liang, Z. Liu, J. Yu, D. Zhao, Synth. Met. 1997, 91, 267. [10] N. Takada, T. Tsutsui, S. Saito, Jpn. J. Appl. Phys. 1994, 33, L863. [11] W. R. Dawson, J. L. Kropp, M. W. Windsor, J. Chem. Phys. 1966, 45, 2410. [12] G. A. Crosby, R. E. Whan, R. M. Alire, J. Chem. Phys. 1961, 34, 743. [13] G. A. Crosby, Mol. Cryst. 1966, 1, 37. [14] T. Forster, Discuss. Faraday Soc. 1959, 27, 7. [15] A. Dogariu, R. Gupta, A. J. Heeger, H. Wang, Synth. Met. 1999, 100, 95. [16] Y. Yang, Q. Pei, A. J. Heeger, J. Appl. Phys. 1996, 79, 934. [17] M. Uekawa, Y. Miyamoto, H. Ikeda, K. Kaifu, T. Nakaya, Synth. Met. 1997, 91, 259. [18] M. Uekawa, Y. Miyamoto, H. Ikeda, K. Kaifu, T. Nakaya, Bull. Chem. Soc. Jpn. 1998, 71, 2253. [19] C. Wu, J. C. Sturm, R. A. Register, J. Tian, E. P. Dana, M. E. Thompson, IEEE Trans. Electron Devices 1997, 44, 1269. [20] M. R. Andersson, G. Yu, A. J. Heeger, Synth. Met. 1997, 85, 1275. [21] M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson, S. R. Forrest, Nature 1998, 395, 151. [22] V. Cleave, G. Yahioglu, P. Le Barny, R. H. Friend, N. Tessler, Adv. Mater. 1999, 11, 285. [23] Z. Bao, Y. Feng, A. Dodabalapur, V. R. Raju, A. J. Lovinger, Chem. Mater. 1997, 9, 1299. [24] F. Pschenitzha, J. C. Sturm, Appl. Phys. Lett. 1999, 74, 1913. [25] J. A. Rogers, Z. Bao, V. R. Raju, Appl. Phys. Lett. 1998, 72, 2716. [26] S. Chang, J. Bharathan, Y. Yang, R. Helgeson, F. Wudl, M. B. Ramey, J. R. Reynolds, Appl. Phys. Lett. 1998, 73, 2561. [27] G. Parthasarathy, P. E. Burrows, V. Khalfin, V. G. Kozlov, S. R. Forrest, Appl. Phys. Lett. 1998, 72, 2138. [28] J. D. Joannopoulos, P. R. Villeneuve, S. Fan, Nature 1997, 386, 143. [29] A. Dodabalapur, E. A. Chandross, M. Berggren, R. E. Slusher, Science 1997, 277, 1787. [30] K. Ohta, A. Ishii, H. Muroki, I. Yamamoto, K. Matsuzaki, Mol. Cryst. Liq. Cryst. 1985, 116, 299. [31] J. C. de Mello, H. F. Wittmann, R. H. Friend, Adv. Mater. 1997, 9, 230. [32] N. C. Greenham, I. D. W. Samuel, G. R. Hayes, R. T. Phillips, Y. A. R. R. Kessener, S. C. Moratti, A. B. Holmes, R. H. Friend, Chem. Phys. Lett. 1995, 241, 89.

A Simple and Complete Purification of Single‐Walled Carbon Nanotube Materials

Electrochromic (EC) materials change their optical properties (darken/lighten) in the presence of a small electric potential difference, and are suitable for application in energy-efficient windows, antiglare automobile rear-view mirrors, sunroofs, displays, and hydrogen sensors. [1–4] The operation of conventional EC devices depends on the reversible electrochemical double injection of positive ions (H + ,L i + ,N a + ) and electrons into the host lattice of multivalent transition metal oxide materials, [5–10] with positive-ion insertion required to satisfy charge neutrality. However, diffusion of positive ions into the oxide layer is often slow, taking minutes to complete. Since the chemical diffusion coefficient of protons (DH+ )i s an order of magnitude larger than that of lithium ions (DLi+), EC systems based on proton electrolytes (e.g., aqueous H2SO4) are mandatory for display applications and preferred for other applications. Unfortunately, proton insertion currently results in rapid degradation of EC films. There are two important criteria for selecting an EC material. The first is the time constant of the ion-intercalation reaction, which is limited both by the diffusion coefficient and by the length of the diffusion path. While the former depends on the chemical structure and crystal structure of the metal oxide, the latter is determined by the material’s microstructure. [11] In the case of a nanoparticle, the smallest dimension is represented by the diffusion path length. Thus, designing a nanostructure with a small radius, while maintaining the proper crystal structure, is key to obtaining a material with fast insertion kinetics, enhanced durability, and superior performance. The second important criterion is coloration efficiency (CE), the change in optical density (OD) per unit inserted charge (Q), that is, CE= D(OD)/DQ. [12] A high CE provides

Crystalline WO3 nanoparticles for highly improved electrochromic applications

A photovoltaic conversion efficiency of 40.8% at 326 suns concentration is demonstrated in a monolithically grown, triple-junction III–V solar cell structure in which each active junction is composed of an alloy with a different lattice constant chosen to maximize the theoretical efficiency. The semiconductor structure was grown by organometallic vapor phase epitaxy in an inverted configuration with a 1.83 eV Ga.51In.49P top junction lattice-matched to the GaAs substrate, a metamorphic 1.34 eV In.04Ga.96As middle junction, and a metamorphic 0.89 eV In.37Ga.63As bottom junction. The two metamorphic junctions contained approximately 1×105 cm−2 and 2–3×106 cm−2 threading dislocations, respectively.

Kim M. Jones

Papers

Storage of hydrogen in single-walled carbon nanotubes

A Simple and Complete Purification of Single‐Walled Carbon Nanotube Materials

Crystalline WO3 nanoparticles for highly improved electrochromic applications

40.8% efficient inverted triple-junction solar cell with two independently metamorphic junctions

Synthesis and characterization of inp quantum dots