Showing papers by "Xiang Zhang published in 2003"
TL;DR: In this article, the authors investigate the coupling between pairs of elliptical metal particles by simulations and experiments and demonstrate that the resonant wavelength peak of two interacting particles is red-shifted from that of a single particle because of near-field coupling.
Abstract: The collaborative oscillation of conductive electrons in metal nanoparticles results in a surface plasmon resonance that makes them useful for various applications including biolabeling. We investigate the coupling between pairs of elliptical metal particles by simulations and experiments. The results demonstrate that the resonant wavelength peak of two interacting particles is red-shifted from that of a single particle because of near-field coupling. It is also found that the shift decays approximately exponentially with increasing particle spacing and become negligible when the gap between the two particles exceeds about 2.5 times the particle short-axis length.
1,492 citations
TL;DR: In this article, the subwavelength imaging quality of a metamaterial superlens is studied numerically in the wave vector domain and examples of image compression and magnification are given and resolution limits are discussed.
Abstract: The subwavelength imaging quality of a metamaterial superlens is studied numerically in the wave vector domain. Examples of image compression and magnification are given and resolution limits are discussed. A minimal resolution of λ/6 is obtained using a 36 nm silver film at 364 nm wavelength. Simulation also reveals that the power flux is no longer a good measure to determine the focal plane of superlens due to the elevated field strength at exit side of the metamaterial slab.
304 citations
TL;DR: In this study, chitosan was coated on the surface of polyethyleneterephthalate granules through a dip and phase inversion process and was examined for humic acid removal in a series of batch adsorption experiments, suggesting the formation of organic complex between the protonated amino groups and humic Acid.
221 citations
TL;DR: In this article, a two-dimensional cubic lattice consisting of thin metal wires, having wire diameter of 30 μm, lattice constant of 120 μm and wire length of 1 mm, was constructed using microstereolithography.
Abstract: Metamaterials, which contain engineered subwavelength microstructures, can be designed to have positive or negative e and μ at desired frequencies. In this letter, we demonstrate a metamaterial which has a “plasmonic” response to electromagnetic waves in the terahertz (THz) range. The sharp change of reflection and transmission at this plasma frequency makes the structure a high pass filter. The reflection response is characterized by Fourier transform infrared spectroscopy, and a plasma frequency at 0.7 THz is observed, which agrees with the theoretical calculation. The metamaterial is a two-dimensional cubic lattice consisting of thin metal wires, having wire diameter of 30 μm, lattice constant of 120 μm, and wire length of 1 mm. The microstereolithography technique is employed to fabricate the high-aspect-ratio lattice.
204 citations
TL;DR: In this article, the authors showed that the transmission of evanescent waves rapidly grows with the film thickness up to about 50 nm, after which it decays as loss becomes significant.
Abstract: Recent theoretical work suggested the possibility of constructing a super-resolution diffraction-free lens by using a negative refractive index medium (NRIM). The key proposition is that evanescent waves can be greatly enhanced by increasing the thickness of the NRIM. We report here experimental evidence that confirms that the transmission of evanescent waves rapidly grows with the film thickness up to about 50 nm, after which it decays as loss becomes significant. These findings represent the first step toward the understanding and realization of a diffraction-free lens.
177 citations
TL;DR: In this article, a bipolar micro direct methanol fuel cell (μDMFC) with high power density and simple device structure was presented, where a proton exchange membrane-electrode assembly was integrated in a Si-based μDMFC with micro channels 750 μm wide and 400 μm deep, fabricated using silicon micromachining.
Abstract: We present a bipolar micro direct methanol fuel cell (μDMFC) with high-power density and simple device structure. A proton exchange membrane-electrode assembly was integrated in a Si-based μDMFC with micro channels 750 μm wide and 400 μm deep, fabricated using silicon micromachining. The μDMFC has been characterized at near room temperature, showing a maximum power density of 47.2 mW/cm2 when 1 M methanol was fed at 60 °C. The cell voltage dependence on the current density agrees well with the modified Tafel model, in which regimes of kinetic polarization and ohmic polarization are observed without significant presence of the concentration polarization.
167 citations
TL;DR: The Shidao complex at the eastern extremity of the Sulu ultrahigh pressure (UHP) terrane is composed of oldest pyroxene syenites, quartz syenite and youngest granite intrusives of the K-rich shoshonitic series as discussed by the authors.
Abstract: The Shidao complex at the eastern extremity of the Sulu ultrahigh pressure (UHP) terrane is composed of oldest pyroxene syenite, quartz syenite and youngest granite intrusives of the K-rich shoshonitic series. U-Pb zircon dating yields nearly concordant ages of 225 ± 2, 211 ± 3 and 205 ± 5 Ma for pyroxene syenite, quartz syenite and granite, respectively. The ages closely postdate the 240 to 220 Ma UHP metamorphism and correspond to the rapid cooling and exhumation of UHP rocks. A close genetic relation may exist between the formation of the Shidao intrusives and the continental collision and UHP metamorphism. However, the K-rich Shidao intrusive rocks are different from common syn-collisional granites in association of K-rich and granitic magmatism. A breakoff model is postulated to explain the formation of the complex. The breakoff of the subducting slab caused the rapid exhumation of the UHP terrane. Mantle upwelling resulted in basaltic magmatism and formation of the K-rich complex. Formation of the Shidao complex marked the cessation of the UHP metamorphism and the oldest ages of 225 ± 2 Ma of the complex is the minimum timing for the UHP metamorphism.
166 citations
TL;DR: It was shown that combinations of three bases within the splice donor consensus sequence were more effective than consensus values in distinguishing real from pseudo splicing sites; two-way base combinations were optimal for distinguishing 3' splice sites.
Abstract: Vertebrate pre-mRNA transcripts contain many sequences that resemble splice sites on the basis of agreement to the consensus,yet these more numerous false splice sites are usually completely ignored by the cellular splicing machinery. Even at the level of exon definition,pseudo exons defined by such false splices sites outnumber real exons by an order of magnitude. We used a support vector machine to discover sequence information that could be used to distinguish real exons from pseudo exons. This machine learning tool led to the definition of potential branch points,an extended polypyrimidine tract,and C-rich and TG-rich motifs in a region limited to 50 nt upstream of constitutively spliced exons. C-rich sequences were also found in a region extending to 80 nt downstream of exons,along with G-triplet motifs. In addition,it was shown that combinations of three bases within the splice donor consensus sequence were more effective than consensus values in distinguishing real from pseudo splice sites; two-way base combinations were optimal for distinguishing 3′ splice sites. These data also suggest that interactions between two or more of these elements may contribute to exon recognition,and provide candidate sequences for assessment as intronic splicing enhancers.
142 citations
TL;DR: This study identifies a means to access deep subwavelength features by use of a metamaterial superlens, a precursor of superlensing, by regenerating evanescent waves by excitation of a surface plasmon.
Abstract: We investigated a precursor of superlensing: regenerating evanescent waves by excitation of a surface plasmon. Because the permittivity of a silver slab approaches -1, we experimentally observed a broadening of surface-plasmon bandwidth. Our study identifies a means to access deep subwavelength features by use of a metamaterial superlens.
121 citations
TL;DR: In this paper, a detailed numerical study of the mode I interlaminar fracture of carbon/epoxy composite laminates with z-fibre reinforcement was performed using a double cantilever beam configuration.
111 citations
TL;DR: In this article, a paper-like template was prepared in a poly(tetrafluoroethylene)-lined autoclave (Parr bomb 4749, 23 mL capacity) and heated at 180±220 C for 1±2 days.
Abstract: Synthesis: Fibrous V 3 O 7 ´H 2 O template crystals were prepared hydrother-mally according to Yamamoto and co-workers [30]: an aqueous solution of VOSO 4 (0.15 M) was sealed in a poly(tetrafluoroethylene)-lined autoclave (Parr bomb 4749, 23 mL capacity) and heated at 180±220 C for 1±2 days. The resulting suspension was filtered, washed several times with water and dried overnight under vacuum (~ 10 ±3 mbar). Coating of the as-prepared green, paper like template as well as the subsequent core removal were performed in one pot. The fibrous solid (35 mg) was dispersed in a 250 mL glass flask containing an isopropanol/ammonia/water solution (respective volumes [mL]: 200:8.3:7.5) by means of an ultrasonic bath set at 40 C (Bandelin Sonorex DK 255 P apparatus, 35 kHz, 320 W). After addition of 0.1 mL TEOS, the ultra-sound intensity was maintained at ~ 200 W during the whole coating reaction (75 min). Then, 1 mL H 2 O 2 was added directly into the dispersion, which was further stirred for about 45 min. The solid was collected by filtration, washed extensively with isopropanol, and afterwards with water. To achieve complete core dissolution as well as elemental purity, the product was redispersed in a diluted H 2 O 2 aqueous solution (0.3 M; 30 mL), stirred for 48 h, washed several times with water, and dried under vacuum. Characterization: Samples were investigated in glass capillaries with a STOE STADI P X-ray powder diffractometer equipped with a curved Ge monochro-mator, a linear position sensitive detector, and using Cu Ka radiation. Scanning electron microscopy (SEM) was performed on a LEO 1530 Gemini apparatus, which was operated at low acceleration voltage (V acc = 1 kV) to minimize charging of the as-synthesized samples. For transmission electron microscopy (TEM), the samples were deposited on a holey carbon foil supported on a copper grid. TEM images were recorded on a CM30 microscope (Philips, Eindhoven, V acc = 300 kV, LaB 6 cathode). Elemental maps of vanadium were obtained at the L ionization edge applying the three-window method [33] on a Tecnai 30F apparatus (Philips, Eindhoven, V acc = 300 kV, field emission gun) equipped with a GIF (Gatan imaging filter). Laser elemental analysis was carried out on a pressed sample pellet using a Perkin Elmer/Sciex Elan 6100 DRC LA-ICP-MS machine. A defining trend in sensing and diagnostics is miniaturiza-tion, the reduction in the size of devices and components …
TL;DR: In this paper, the formation of near-field scanning optical microscopy probe tips from optical fiber by chemical etching was investigated, and it was found that the taper profiles were determined by the nonlinear dynamic evolution of the meniscus of the etchant near the fiber.
Abstract: The probe tip is the key component in scanning probe microscopes and their applications in the nanoscale imaging and nanofabrication. In this work, we have investigated the formation of near-field scanning optical microscopy probe tips from optical fiber by chemical etching. Static and dynamic etchings and their combinations are studied. The etching process is optimized, and tips with short tapers, small apertures (about 50 nm) and large aperture cone angles (40°) are successfully obtained. Multiple-tapered tips are also fabricated by using different dynamic regimes. It is found that the taper profiles are determined by the nonlinear dynamic evolution of the meniscus of the etchant near the fiber.
TL;DR: In this article, the synthesis and photoluminescence properties of nitrogen-doped ZnO films were investigated using X-ray diffraction, and the first-principle total energy calculation showed that nitrogen-induced acceptor energy level is located at 0.4 eV above the valence band maximum.
TL;DR: In this paper, the use of cold expansion process as a life extension technique on aircraft structural joints was investigated and the results indicate that significant life improvements can be obtained through cold expansion applied at all percentages of fatigue life tested in this work with the optimum stage being around 25% of the baseline life.
15 Sep 2003
TL;DR: In this article, a plasmonic mask with subwavelength hole arrays was used to expose a photoresist layer to the atomic force microscope (AFM) for high contrast dot arrays.
Abstract: We have investigated the novel plasmonic nanolithography by exposing a photoresist layer through a plasmonic mask, which is an opaque metal film with subwavelength hole arrays in it. The hole arrays of various diameters are fabricated by using focused ion beam (FIB). Through the lithography, the hole array patterns are transferred to negative photoresists. As a result, high contrast dot arrays with the smallest diameter of 120 nm, equivalent to /spl sim//spl lambda//3, are observed by atomic force microscope (AFM).
TL;DR: In this paper, the capability of four closed-form solutions for calculating cold expansion-induced residual stresses for three aerospace grade aluminium alloys of medium thickness was investigated, and it was shown that good prediction of crack growth life can be obtained if a suitable closed form model is used.
TL;DR: In this article, a simplified heating and pulling method for formation of near-field scanning optical microscopy probing tips from optical fibers was developed, and the as-prepared tips were subsequently bended by pulsed laser heating and metal coating.
Abstract: We have developed a simplified heating and pulling method for formation of near-field scanning optical microscopy probing tips from optical fibers. Laser power and continuous pulling force are two key processing parameters investigated. We found a narrow working range of laser power of 1.85–1.95 W and the pulling force of 0.5–0.9 lb, with the optimum conditions of 1.90 W and 0.74 lb. Tips with short taper (∼300 μm), small apex (∼50 nm), and large aperture cone angles (∼45°) have been achieved. The as-prepared tips are subsequently bended by pulsed laser heating and metal coating. Digitized bending from 10° to 90° can be achieved by linearly adjustment of the laser dose. The fabricated tips have shown good light guiding.
TL;DR: The phenomenon of nonsense-associated altered splicing raises the possibility that the recognition of in-frame nonsense codons is used generally for exon identification during pre-mRNA splicing, but nonsense codon frequencies in pseudo exons and in regions flanking 5' splice sites are no greater than that expected by chance.
Abstract: The phenomenon of nonsense-associated altered splicing raises the possibility that the recognition of in-frame nonsense codons is used generally for exon identification during pre-mRNA splicing However, nonsense codon frequencies in pseudo exons and in regions flanking 5 splice sites are no greater than that expected by chance, arguing against the widespread use of this strategy as a means of rejecting potential splice sites
TL;DR: In this article, a new volumetric heating mechanism originating from SRH (Shockley-Read-Hall) non-radiative recombination and photon recycling is proposed and modeled based on recent experimental findings.
Abstract: Coupled thermal and carrier transports (electron/hole generation, recombination, diffusion and drifting) in laser photoetching of GaAs thin film is investigated. A new volumetric heating mechanism originating from SRH (Shockley–Read–Hall) non-radiative recombination and photon recycling is proposed and modeled based on recent experimental findings. Both volumetric SRH heating and Joule heating are found to be important in the carrier transport, as well as the etching process. SRH heating and Joule heating are primarily confined within the space-charge region, which is about 20 nm from the GaAs surface. The surface temperature rises rapidly as the laser intensity exceeds 105 W/m2. Below a laser intensity of 105 W/m2, the thermal effect is negligible. The etch rate is found to be dependent on the competition between photovoltaic and photothermal effects on surface potential. At high laser intensity, the etch rate is increased by more than 100%, due to SRH and Joule heating.
28 Oct 2003
TL;DR: In this article, a new class of composite nano particles, which is consisted of stacked alternative metal/dielectric layers, called nanoburger, is presented. And the optical properties of these nanaburger particles are studied by using discrete dipole approximation method.
Abstract: Strong Raman signals have been observed in various molecules attached to rough metal film surfaces or nano silver/gold particles. This phenomenon is denoted as surface enhanced Raman scattering (SERS). Recent experiments have shown that the effective cross sections of Raman scattering can reach the same level that of fluorescence of good laser dyes, making SERS a promising single-molecular detection tool. The commonly used substrates for SERS consist of colloidal Ag/Au particle aggregates, where SERS active sites, called “hot spots”, are only found by chance and not controllable. The poor repeatability and controllability of these SERS substrates have prevented SERS from viable industrial applications, therefore it is imperative to design and fabricate optimized "hot spots" with desired plasmon resonance frequency in a controllable fashion. In this paper, we present a new class of composite nano particles, which is consisted of stacked alternative metal/dielectric layers, called nanoburger. We study optical properties of these nanoburger particles by using discrete dipole approximation method. The numerical results show that nanoburger particles possess many advantages over single layered particles, including high brightness or scattering intensity, high local field enhancements, and more freedom of tuning plasmon resonance wavelength. Another important merit of the nanoburger particles is that they can be fabricated with traditional micro/nano lithography techniques, and thus are integrable with techniques such as lab-in-a-chip.
TL;DR: A mass spectrometric depletion spectrum for NO 2 in superfluid (0.37 K) helium nanodroplets is reported in this article, where transitions are broadened and blue-shifted relative to their gas phase counterparts.
01 Jan 2003
TL;DR: In this paper, the excitation-power dependence of hydrostatic pressure coefficients (dE/dP) of InxGa1-xN/InyGa1yN multiple quantum wells is reported.
Abstract: Excitation-power dependence of hydrostatic pressure coefficients (dE/dP) of InxGa1-xN/InyGa1-yN multiple quantum wells is reported. When the excitation power increases from 1.0 to 33 mW, dE/dP increases from 26.9 to 33.8 meV/GPa, which is an increase by 25%. A saturation behavior of dE/dP with the excitation power is observed. The increment of dE/dP with increasing carrier density is explained by an reduction of the internal piezoelectric field due to an efficient screening effect of the free carriers on the field.
03 Nov 2003
TL;DR: In this paper, a near-field multiphoton optical microscopy was demonstrated using 120 fs laser pulses at 790 nm in an apertureless near field optical microscope, which produced the lithographic features with ~ 70 nm resolution.
Abstract: Near-field multiphoton optical lithography is demonstrated by using ~120 fs laser pulses at 790 nm in an apertureless near-field optical microscope, which produce the lithographic features with ~ 70 nm resolution. The technique takes advantage of the field enhancement at the extremity of a metallic probe to induce nanoscale multiphoton absorption and polymerization in a commercial photoresist, SU-8. Even without optimization of the resist or laser pulses, the spatial resolution of this technique is as high as λ/10, nearly a factor of two smaller than the previous multiphoton lithography in the far field.
15 Sep 2003
TL;DR: In this article, an electric bias was applied between the Au substrate and the conductive tip of a scanning probe microscope to stimulate the pattern generation and the line width and apparent height of the pattern was related to the bias voltage and there exists a threshold below which no pattern can be generated.
Abstract: Information storage utilizing the bi-stable state of organic molecules has been a hot topic in molecular electronics, due to the promising future of single molecule devices. We demonstrated in this paper nanometer-scale pattern generation on the self-assembled monolayer of [2]rotaxane. The organic molecules are covalently bonded to the Au(111) surface of the substrate through the di-thiol groups at one end of the molecules. Electric bias was applied between the Au substrate and the conductive tip of a scanning probe microscope to stimulate the pattern generation. The line width and apparent height of the pattern is related to the bias voltage and there exists a threshold, below which no pattern can be generated.
28 Oct 2003
TL;DR: In this paper, the effect of particle sizes with particle plasmon resonant wavelength and the coupling between pair of elliptical metallic disks and ellipsoid particles by simulations and experiments was studied.
Abstract: Nano gold particles interact strongly with visible light to excite the collaborative oscillation of conductive electrons within nano particles resulting in a surface plasmon resonance which makes them useful for various applications including bio-labeling. In this paper, we study the effect of particle sizes with particle plasmon resonant wavelength and the coupling between pair of elliptical metallic disks and ellipsoid particles by simulations and experiments. The red-shift resonant peak wavelength of coupled particles to that of single particle is due to particle plasmons near-field coupling. The shift decays is approximately exponentially with increasing particle spacing, and reaches zero when the gap between the two particles exceeds about 2.5 times the particle short axis length. It is also found that the exponential decay of peak shift with particle gap is size independent but shape dependent.
15 Sep 2003
TL;DR: In this article, the authors present experimental and computer simulation studies on the plasmon resonance of single nano Au particles and nano Au particle pairs in close proximity and show that the resonant wavelength peak of two particle plasmons is red-shifted in comparison to that of a single particle and the shift decays approximately exponentially with particle spacing, and drops to zero when the gap between two particles exceeds about 2.5 times the particle short axis length.
Abstract: Nano metal particles which interact strongly with visible light make themselves useful for molecular detection and biosensing. To facilitate the useful application for these nano particles, it is important to design and fabricate the particles at a desired frequency. In this paper, we present our experimental and computer simulation studies on the plasmon resonance of single nano Au particles and nano Au particle pairs in close proximity. The results show that the resonant wavelength peak of two particle plasmons is red-shifted in comparison to that of a single particle and the shift decays approximately exponentially with particle spacing, and drops to zero when the gap between two particles exceeds about 2.5 times the particle short axis length. It is also found that the decay function of the resonant wavelength shift is size-independent.
03 Nov 2003
TL;DR: In this paper, the authors present experimental evidence on enhanced transmission of evanescent waves via surface plasmon at a thin silver film operating near surface plasma resonant frequency, which represents the first step toward the understanding and realization of a diffraction-free lens by using negative refractive index medium.
Abstract: Recent theoretical works have suggested the possibility of constructing a diffraction-free lens by using a negative refractive index medium (NRIM). The key theoretical proposition is that evanescent waves can be greatly enhanced by increasing the thickness of the NRIM. We present here experimental evidence on enhanced transmission of evanescent waves via surface plasmon at a thin silver film operating near surface plasma resonant frequency. We found the transmission of evanescent waves rapidly grows with the film thickness up to about 50 nm, after which it decays as loss becomes significant. These experiments also demonstrated the broadening of enhanced transmission spectrum as photon energy approaches plasma resonance eAg = -1 condition. These findings represent the first step toward the understanding and realization of a diffraction-free lens by using NRIM.
TL;DR: In this paper, the authors present a first-principles study of wave dynamics in random slabs by solving the Bethe-Salpeter equation including weak localization, and the pulse evolution in space and time shows anomalous nondiffusive behavior.
Abstract: We present a first-principles study of wave dynamics in random slabs by solving the Bethe-Salpeter equation including weak localization. The pulse evolution in space and time shows anomalous nondiffusive behavior. This is in agreement with microwave studies of nonexponential decay of pulsed transmission and explains recent optical pulsed measurements.
20 Oct 2003
TL;DR: In this article, a theoretical model is developed to analyze the deflection and adhesion between thin polymer beams under capillary force, and a sublimation process is successfully developed to release the 3D microstructures without the adhesion.
Abstract: Micro-stereolithography (μSL) is capable of fabrication of highly complex three-dimensional (3D) microstructures by selectively photo-induced polymerization from the monomer resin. However, during the evaporative drying of structures from liquid resin, the 3D microstructures often collapse due to the capillary force. In this work, a theoretical model is developed to analyze the deflection and adhesion between thin polymer beams under capillary force. The
detachment length of the test structures and adhesion energy of a typical μSL polymer (HDDA) are obtained experimentally which are important for MEMS structure design. Finally, we successfully developed a sublimation process to release the 3D microstructures without the adhesion.