Nano

This paper presents a review on the selected highlights of highly-functional devices in two-dimensional photonic crystals slab structure. By introducing artificial defects in the photonic crystals (that is, defect engineering), novel photonic devices of line-defect waveguides and point-defect nanocavity are demonstrated. For more efficient manipulation of photons, the fundamentals of heterostructure photonic crystals are also reviewed. Heterostructures consist of multiple photonic crystals with different lattice-constants and they provide further high-functionalities such as multiple wavelength operation while maintaining optimized performance and the enhancement of photon manipulation efficiency. Because of the importance of high quality (Q) nanocavity for realization of nanophotonic devices, we also review the design rule of high Q nanocavities and present recent experiments on nanocavities with Q factors in excess of one million (~ 1.2 × 10⁶). The progress of defect engineering and heterostructure in two-dimensional photonic crystals slab structure will accelerate development in ultrasmall photonic chips, cavity quantum electrodynamics, optical sensors, etc.

A newly luminescent nanomaterial, monoclinic wolframite-type HgWO₄ nanoshuttles (length: 200–300 nm; diameter: 100–150 nm) is prepared through ultrasonic method. For HgWO₄ nanoshuttles, the fluorescent (FL) emitting peaks at 430 and 330 nm obviously blue shift compared with those of corresponding bulk crystals. Meanwhile, the latter almost disappear after ultrasonic irradiation procedure. A UV-visible blue-shifted (about 130 nm) absorption peak is observed at 280 nm and a new absorption peak is observed at 203 nm. FTIR results show all absorption peaks below 800 cm^-1 shift to a longer wavenumber region, whereas those above 800 cm^-1 remain invariable. All those unique optical performances might result from both quantum size effects and the involvement of the incompact d¹⁰ electrons. Moreover, the possible synthesis mechanism of HgWO₄ nanoshuttles is also investigated.

Though subject to intensive studies, the formation mechanism of buckminsterfullerene C₆₀ and related higher fullerenes has long evaded discovery. To elucidate their atomistic self-assembly mechanism, we have performed high-temperature quantum chemical molecular dynamics simulations on carbon vapor model systems initially consisting of C₂ molecules. Our simulations reveal a coherent mechanism how highly ordered fullerene cages naturally self-assemble under nonequilibrium conditions, following a series of irreversible processes from the polymerization of C₂ molecules to vibrationally excited giant fullerenes, which then shrink by C₂ evaporation down to the smallest spherical, isolated pentagon rule obeying species C₇₀ and C₆₀ as the smallest and kinetically most stable species of the shrinking process. We show that the potential energy surface associated with giant fullerene cage growth, measured by an average cluster curvature, is downhill all the way, and in agreement with high-level energetics from density functional theory. This fullerene formation mechanism is a good example of dynamic self-assembly leading to dissipative structures far from thermodynamic equilibrium, and the "shrinking hot giant" road provides a natural explanation for the observed cage size distributions in a random optimization process consistent with several important experimental observations.

The copper nanoparticle chains have been synthesized through a self-assembly process with sodium polymethacylic acid as the template. The resulted nanoparticle chains were 0.8–1.5 μm long, and the composed nanoparticles were about 30 nm in diameter. The self-assembly formation mechanism has been proposed.

This article has been retracted because it is an English translation of a Chinese paper that was published earlier, with some additional content in the later part. This is inappropriate and violates the scientific rule of anti-plagiarism. We regret that this was not detected before the article was accepted for publication in the journal.

The alignment and dynamic response of carbon nanotubes (CNTs) in nematic liquid crystal (NLC) medium induced by strong electric field have been observed through polarizing optical microscope. Density-functional calculations suggest that LC molecule anchors helically to the CNT wall to enhance π-stacking with a binding energy of nearly -2.0 eV due to a considerable amount of charge transfer from LC molecule to CNT, resulting in the formation of excess charges and permanent dipole moment in CNTs. Under strong electric field, the motion of CNTs distorted the director of adjacent LC molecules. Our detailed analysis of dynamics revealed that the four-lobe textures in vertical cell and two vertical stripes in in-plane switching cell were strongly correlated, i.e., the side view of textures by the vertical motion of CNTs in vertical cell was similar to the textures in in-plane switching cell. Interestingly, the magnitude of textures in microscope was strongly dependent on the size of CNTs and the applied field strength. The statistical size distribution of textures similar to that of CNTs provided information for the degree of dispersion of CNTs.

Finite-size effects in armchair (n,n) carbon nanotubes are studied as a function of the tube length by using the generalized tight-binding calculations. End structures of the tubes considered here are caps formed from hemispherical pieces of I_h fullerenes and hydrogen-free open ends. It has been clarified that the dimensionality in electronic structures of the finite-length nanotubes only depends on an aspect ratio of the tube diameter to the length of the cylindrical region. The aspect ratio where the finite-length tubes exhibit one-dimensional properties is found to be about four. The results corroborate that the nanotubes with their length of 10–100 nm experimentally observed could be regarded as one-dimensional electron systems.

Carbon nanotubes (CNTs) were selectively grown in etched ion tracks in SiO₂ layers on Si. For this sake, Ni-catalyst nanocrystals were initially deposited within the ion tracks by galvanic deposition. The characteristics of plasma-enhanced chemical vapor deposition (PECVD)- and thermal chemical vapor deposition (TCVD)-grown CNTs, such as structural details and length distribution, were investigated. In addition, field emission properties were studied. The analysis revealed that the emerging PECVD-grown CNTs were of cylindrical and/or conical shape and usually had diameters as large as the etched tracks. The exponential length distribution of these CNTs can be well understood by applying a simple defect-growth model. For contrast, many narrow and curled CNTs were found to cluster in spots well separated from each other, after applying TCVD instead of PECVD. The Raman investigations of PECVD-grown CNTs showed that Si–O–C and Si–C phases had formed during the growth of the CNTs. These ion-track-correlated PECVD-grown CNTs open the way for the production of novel 3D nanoelectronic devices based on the TEMPOS concept. These structures are also excellent candidates for experiments on channeling in CNTs. Application as field emitting devices, however, appears unfavorable due to poor mean-field enhancement factors and insufficient stability.