Self-templating growth of copper nanopearl-chain arrays in electrodeposition.

We report here a unique in-plane self-templating electrochemical growth of arrays of copper nanopearl chains from an ultrathin layer of CuSO4 electrolyte. Scanning electron microscopy indicates that the electrodeposit filaments form equally spaced bundles, which consist of long, straight, pearl-chain-like copper filaments with corrugated periodic structure. The bundle separation can be tuned by changing the applied electric current in electrodeposition. Experiments show that the periodic morphology on the nanopearl chain corresponds to the periodic distribution of copper and cuprous oxide. The mechanism for the bundle formation is discussed.

Acoustic surface evanescent wave and its dominant contribution to extraordinary acoustic transmission and collimation of sound.

We demonstrate both theoretically and experimentally the physical mechanism that underlies extraordinary acoustic transmission and collimation of sound through a one-dimensional decorated plate. A microscopic theory considers the total field as the sum of the scattered waves by every periodically aligned groove on the plate, which divides the total field into far-field radiative cylindrical waves and acoustic surface evanescent waves (ASEWs). Different from the well-known acoustic surface waves like Rayleigh waves and Lamb waves, ASEW is closely analogous to a surface plasmon polariton in the optical case. By mapping the total field, the experiments well confirm the theoretical calculations with ASEWs excited. The establishment of the concept of ASEW provides a new route for the integration of subwavelength acoustic devices with a structured solid surface.

Interplay between external strain and oxygen vacancies on a rutile TiO2(110) Surface.

Comprehensive first-principle calculations on strained rutile TiO2(110) indicate that the formation energy of different types of oxygen vacancies depends on the external strain. For the unstrained state, the energetically favorable oxygen vacancy (EFOV) appears on the bridging site of the first layer; when 3% tensile strain along [11[over ]0] is applied, EFOV moves to the in-plane site, while 2% compressive strain along either [001] or [11[over ]0] shifts EFOV to the subbridging site. We therefore suggest that the distribution of oxygen vacancies can be engineered by external strain, which may help to improve the applications of a TiO2 surface where oxygen vacancy plays an important role.

Role of interference between localized and propagating surface waves on the extraordinary optical transmission through a subwavelength-aperture array.

We report in this Letter that when radiation is incident on a metal surface perforated with an array of ring-shaped subwavelength apertures, the phase difference between the propagating surface Bloch wave and the localized surface wave can be tailored by the geometrical parameters of the array so as to affect the shape of the transmission spectrum. Above the resonant frequency of the aperture, interference between the two kinds of surface waves leads to a minimum in the transmission spectrum, whereas below it, the interference leads to a maximum. We suggest that this feature provides flexibility in engineering surface-wave-based all-optical devices.

Extraordinary acoustic transmission through a 1D grating with very narrow apertures.

Recently, there has been an increased interest in studying extraordinary optical transmission (EOT) through subwavelength aperture arrays perforated in a metallic film. In this Letter, we report that the transmission of an incident acoustic wave through a one-dimensional acoustic grating can also be drastically enhanced. This extraordinary acoustic transmission (EAT) has been investigated both theoretically and experimentally, showing that the coupling between the diffractive wave and the wave-guide mode plays an important role in EAT. This phenomenon can have potential applications in acoustics and also might provide a better understanding of EOT in optical subwavelength systems.

Long-range ordering effect in electrodeposition of zinc and zinc oxide.

In this paper, we report the long-range ordering effect observed in the electro-crystallization of Zn and ZnO from an ultrathin aqueous electrolyte layer of ZnSO4 . The deposition branches are regularly angled, covered with random-looking, scalelike crystalline platelets of ZnO. Although the orientation of each crystalline platelet of ZnO appears random, transmission electron microscopy shows that they essentially possess the same crystallographic orientation as the single-crystalline zinc electrodeposit underneath. Based on the experimental observations, we suggest that this unique long-range ordering effect results from an epitaxial nucleation effect in electrocrystallization.

Negative birefraction of acoustic waves in a sonic crystal.

Optical birefringence and dichroism are classical and important effects originating from two independent polarizations of optical waves in anisotropic crystals. Furthermore, the distinct dispersion relations of transverse electric and transverse magnetic polarized electromagnetic waves in photonic crystals can lead to birefringence more easily. However, it is impossible for acoustic waves in the fluid to show such a birefringence because only the longitudinal mode exists. The emergence of an artificial sonic crystal (SC) has significantly broadened the range of acoustic materials in nature that can give rise to acoustic bandgaps and be used to control the propagation of acoustic waves. Recently, negative refraction has attracted a lot of attention and has been demonstrated in both left-handed materials and photonic crystals. Similar to left-handed materials and photonic crystals, negative refractions have also been found in SCs. Here we report, for the first time, the acoustic negative-birefraction phenomenon in a two-dimensional SC, even with the same frequency and the same 'polarization' state. By means of this feature, double focusing images of a point source have been realized. This birefraction concept may be extended to other periodic systems corresponding to other forms of waves, showing great impacts on both fundamental physics and device applications.

Noise-reduced electroless deposition of arrays of copper filaments.

We report here a self-organized electroless deposition of copper in an ultrathin layer CuSO4 of electrolyte. Microscopically the branching rate of the copper deposits is significantly decreased, forming an array of smooth polycrystalline filaments. Compared with a conventional electrodeposition system, no macroscopic electric field is involved and the thickness of the electrolyte layer is greatly decreased. Therefore the electroless deposition takes place in a nearly ideal, two-dimensional diffusion-limited environment. We suggest that restriction of the thickness of the electrolyte film is responsible for the generation of smoother branches of the electrodeposits. Our data also show that even in a diffusion-limited scenario the aggregate morphology is not necessarily very ramified and fractal-like.

Acoustic backward-wave negative refractions in the second band of a sonic crystal.

Acoustic negative refractions with backward-wave (BW) effects were both theoretically and experimentally established in the second band of a two-dimensional (2D) triangular sonic crystal (SC). Intense Bragg scatterings result in the extreme deformation of the second band equifrequency surface (EFS) into two classes: one around the K point and the other around the point of the reduced Brillouin zone. The two classes can lead to BW negative refractions (BWNRs) but with reverse negative refraction dependences on frequencies and incident angles. Not only BWNR but BW positive refraction can be present at EFSs around the K point, so it is possible to enhance the resolution of acoustic waves with a subdiffraction limit regardless of refractions, which is no analogy in both left-handed material and SCs' first band. These abundant characters make refractions in the second band distinguished.

Consecutive rotation of crystallographic orientation in lateral growth.

A consecutive rotation of crystallographic orientation has been observed in lateral crystallization of NH4Cl on a glass substrate, which induces a periodic distribution of faceted and roughened regions on the surface of a crystallite aggregate. Experimental observation indicates that this phenomenon derives from the asymmetric surface energies at the growth front, which deform the nascent nucleus and tilt the crystallographic orientation in the nucleation-mediated layered growth. We suggest that this effect is significant for a class of lateral growth where nucleation plays a dominate role.

Update and projection on HIV/AIDS in Taiwan.

The HIV/AIDS epidemic in Taiwan started in 1986, with 5,221 cases of HIV infections, 1,596 cases of AIDS, and 911 deaths reported through 2003. National surveillance data indicate that men who have sex with men accounted for 48.2% of HIV infections, followed by heterosexual men (33.8%) and heterosexual women (6.1%). Only 353 (6.8%) of all HIV cases are females. The average age of HIV-infected persons, AIDS cases, and deaths was 31.2, 36.2, and 39.0 years, respectively. The incidence of HIV infection has increased by approximately 15% every year since 1997. The continuing epidemic will likely burden the national health care system and may result in an estimated socioeconomic loss of U.S. dollars 1.6 billion in 2010, as 15,125 HIV infections and 1,420 deaths from AIDS are projected. To respond to the HIV/AIDS epidemic in Taiwan, the government has been working with nongovernmental organizations to promote HIV testing, conduct various education programs, and reach out to high-risk groups. HIV/AIDS patients are linked to medical care and provided with free highly active antiretroviral treatment. The main challenge is to reduce HIV-related stigma. Prevention focused on preventing further transmission of HIV by seropositive persons to others is urgently needed in fighting the HIV/AIDS epidemic.

Spontaneous formation of periodic nanostructured film by electrodeposition: Experimental observations and modeling.

In this paper we report the spontaneous formation of a nanostructured film by electrodeposition from an ultrathin electrolyte layer of CuSO4. The film consists of straight periodic ditches and ridges, which corresponds to the alternating deposition of nanocrystallites of copper and copper plus cuprous oxide, respectively. The periodicity on the film may vary from 100 nm to a few hundred nanometers depending on the experimental conditions. In the formation of the periodically nanostructured film, oscillating voltage/current has been observed across the electrodes, and the frequency depends on the pH of the electrolyte and the applied current/voltage. A model based on the coupling of [Cu2+] and [H+] in the electrodeposition is proposed to describe the oscillatory phenomena in our system. The calculated results are in agreement with the experimental observations.

Quasi-phase-matched generation of tunable blue light in a quasi-periodic structure.

We present what is to our knowledge a new approach to generating tunable blue light by cascaded nonlinear frequency conversion in a single LiTaO3 crystal. Simultaneous quasi-phase matching of an optical parametric generation process and a sum-frequency mixing process is achieved by means of structuring the crystal with a quasi-periodic optical superlattice. The spectral (wavelength tuning and bandwidth) and power characteristics of the blue-light generation are studied with a fixed-wavelength 532-nm picosecond laser and a wavelength-tunable nanosecond optical parametric oscillator (OPO) as the pump sources. By tuning the OPO wavelength, we could tune the blue output over approximately 20 nm. Temperature tuning of the blue output at a fixed pump wavelength of 532 nm was limited to approximately 1.5 nm. A maximum blue power of 15 microW was generated at a pump power of 0.5 mW, corresponding to an efficiency of 3%.

New type of polariton in a piezoelectric superlattice.

We studied the propagation of an electromagnetic (EM) wave in a piezoelectric superlattice. Because of the piezoelectric effect, a transverse polarization can be induced by a longitudinal wave which couples strongly to the EM wave in some particular frequency regions, resulting in the creation of a new type of polariton that does not exist in ionic crystals. The forbidden band associated with the polariton is not due to the Bragg reflection, but rather to the coupling.

A novel conotoxin from Conus betulinus, kappa-BtX, unique in cysteine pattern and in function as a specific BK channel modulator.

A novel conotoxin, kappa-conotoxin (kappa-BtX), has been purified and characterized from the venom of a worm-hunting cone snail, Conus betulinus. The toxin, with four disulfide bonds, shares no sequence homology with any other conotoxins. Based on a partial amino acid sequence, its cDNA was cloned and sequenced. The deduced sequence consists of a 26-residue putative signal peptide, a 31-residue mature toxin, and a 13-residue extra peptide at the C terminus. The extra peptide is cleaved off by proteinase post-processing. All three Glu residues are gamma-carboxylated, one of the two Pro residues is hydroxylated at position 27, and its C-terminal residue is Pro-amidated. The monoisotopic mass of the toxin is 3569.0 Da. Electrophysiological experiments show that: 1) among voltage-gated channels, kappa-BtX is a specific modulator of K(+) channels; 2) among the K channels, kappa-BtX specifically up-modulates the Ca(2+)- and voltage-sensitive BK channels (252 +/- 47%); 3) its EC(50) is 0.7 nm with a single binding site (Hill = 0.88); 4) the time constant of wash-out is 8.3 s; and 5) kappa-BtX has no effect on single channel conductance, but increases the open probability of BK channels. It is concluded that kappa-BtX is a novel specific biotoxin against BK channels.

Formation of nanostructured copper filaments in electrochemical deposition.

In this paper, we report in detail the studies of a different self-organized copper electrodeposition carried out in an ultrathin layer of CuSO4 electrolyte. On a macroscopic scale, the morphology of the electrodeposit is fingerlike. Microscopically, each fingering branch consists of long, straight copper filaments with periodic corrugated nanostructures. Branching rate of the electrodeposit is significantly decreased, compared with the patterns grown in conventional systems. Detailed information of the growth environment in the ultrathin electrodeposition system is provided, the formation mechanism of the periodic nanostructures on the deposit filaments is explored, and the origin of the significant descent of branching rate of the electrodeposit is discussed.