Showing papers by "Nicholas X. Fang published in 2009"
TL;DR: In this paper, the first experimental demonstration of focusing ultrasound waves through a flat acoustic metamaterial lens composed of a planar network of subwavelength Helmholtz resonators is presented.
Abstract: We present the first experimental demonstration of focusing ultrasound waves through a flat acoustic metamaterial lens composed of a planar network of subwavelength Helmholtz resonators. We observed a tight focus of half-wavelength in width at 60.5 kHz by imaging a point source. This result is in excellent agreement with the numerical simulation by transmission line model in which we derived the effective mass density and compressibility. This metamaterial lens also displays variable focal length at different frequencies. Our experiment shows the promise of designing compact and lightweight ultrasound imaging elements.
471 citations
Posted Content•
TL;DR: The first experimental demonstration of focusing ultrasound waves through a flat acoustic metamaterial lens composed of a planar network of subwavelength Helmholtz resonators is presented, showing the promise of designing compact and lightweight ultrasound imaging elements.
Abstract: We present the first experimental demonstration of focusing ultrasound waves through a flat acoustic metamaterial lens composed of a planar network of subwavelength Helmholtz resonators. We observed a tight focus of half-wavelength in width at 60.5 KHz by imaging a point source. This result is in excellent agreement with the numerical simulation by transmission line model in which we derived the effective mass density and compressibility. This metamaterial lens also displays variable focal length at different frequencies. Our experiment shows the promise of designing compact and light-weight ultrasound imaging elements.
434 citations
TL;DR: The presence of the thin layer of Ge changes the growth kinetics of the electron-beam-evaporated Ag, leading to Ag films with smooth surface morphology and high electrical conductivity, which are very promising for large-scale applications as molecular anchors, optical metamaterials, plasmonic devices, and several areas of nanophotonics.
Abstract: We demonstrate an effective method for depositing smooth silver (Ag) films on SiO2/Si(100) substrates using a thin seed layer of evaporated germanium (Ge). The deposited Ag films exhibit smaller root-mean-square surface roughness, narrower peak-to-valley surface topological height distribution, smaller grain-size distribution, and smaller sheet resistance in comparison to those of Ag films directly deposited on SiO2/Si(100) substrates. Optically thin (∼10−20 nm) Ag films deposited with ∼1−2 nm Ge nucleation layers show more than an order of magnitude improvement in the surface roughness. The presence of the thin layer of Ge changes the growth kinetics (nucleation and evolution) of the electron-beam-evaporated Ag, leading to Ag films with smooth surface morphology and high electrical conductivity. The demonstrated Ag thin films are very promising for large-scale applications as molecular anchors, optical metamaterials, plasmonic devices, and several areas of nanophotonics.
309 citations
TL;DR: In this article, a vectorial description of induced field is given, which complements the information obtained from experiments, and the results of radiative emission under electron excitation show an excellent agreement with experiments.
Abstract: Cathodoluminescence spectroscopy has been performed on silver nanoparticles in a scanning electron microscopy setup. Peaks appearing in the visible range for particles fabricated on silicon substrate are shown to arrive from excitation of out-of-plane eigenmodes by the electron beam. Monochromatic emission maps have been shown to resolve spatial field variation of resonant plasmon mode on length scale smaller than 25 nm. Finite-difference time-domain numerical simulations are performed for both the cases of light excitation and electron excitation. The results of radiative emission under electron excitation show an excellent agreement with experiments. A complete vectorial description of induced field is given, which complements the information obtained from experiments.
130 citations
Posted Content•
TL;DR: The results of radiative emission under electron excitation show an excellent agreement with experiments, and a complete vectorial description of induced field is given, which complements the information obtained from experiments.
Abstract: Cathodoluminescence spectroscopy has been performed on silver nanoparticles in a scanning electron microscopy setup. Peaks appearing in the visible range for particles fabricated on silicon substrate are shown to arrive from excitation of out of plane eigenmodes by the electron beam. Monochromatic emission maps have been shown to resolve spatial field variation of resonant plasmon mode on length scale smaller than 25nm. Finite-difference time-domain numerical simulations are performed for both the cases of light excitation and electron excitation. The results of radiative emission under electron excitation show an excellent agreement with experiments. A complete vectorial description of induced field is given, which complements the information obtained from experiments.
109 citations
TL;DR: The implementation of an innovative three dimensional microfabrication technology coupled with numerical simulation to enhance the mass transport in 3D cell culture and the regulation of metabolism and the growth of yeast cells by controlling the density of micro-capillaries is presented.
Abstract: We present in this paper the implementation of an innovative three dimensional (3D) microfabrication technology coupled with numerical simulation to enhance the mass transport in 3D cell culture. The core of this microfabrication technology is a high-resolution projection micro stereolithography (PμSL) using a spatial light modulator as a dynamic mask which enables a parallel fabrication of highly complex 3D microstructures. In this work, a set of poly (ethylene glycol) microfabricated bioreactors are demonstrated with PμSL technology. We observed both experimentally and numerically the regulation of metabolism and the growth of yeast cells by controlling the density of micro-capillaries. Further development of these 3D microfabricated bioreactors is expected to provide artificially constructed tissues for clinical applications.
46 citations
TL;DR: In this paper, a partially crosslinked polymer is used as a sacrificial support to fabricate fully 3D microstructures and moving parts using a projection microstereolithography (PµSL) system.
Abstract: We present in this paper a novel method to fabricate fully three-dimensional (3D) microstructures and moving parts using a partially crosslinked polymer as sacrificial supports. This is realized on a projection microstereolithography (PµSL) which produces both the microstructure and the sacrificial part simultaneously using digital grayscale images. To establish the selectivity of the etchant to the partially crosslinked sacrificial parts, we measured the etching rate as a function of photo-crosslinking light intensity and the light exposure time. This technology may enable more complex scaffolds in tissue engineering and smart hydrogel devices.
22 citations
TL;DR: In this article, an alternative approach for the fabrication of ultradense gold (Au) nanostructures using hydrogen silsesquioxane (HSQ) resists was proposed.
Abstract: Metal nanostructures have been routinely fabricated by lift-off process using electron-beam lithography. However, for ultradense structures, this method has been limited by metal film thickness with resulting poor pattern quality. The authors report an alternative approach for the fabrication of ultradense gold (Au) nanostructures using hydrogen silsesquioxane (HSQ). Due to the high resolution and excellent etch durability of HSQ resists, ultradense Au gratings with high quality were fabricated. As a promising application, they demonstrate that these structures can be applied to surface-enhanced Raman scattering (SERS) for bioanalysis. Ultradense Au structures fabricated using HSQ resists have proven to be a robust and effective SERS-active substrate.
12 citations
TL;DR: In this paper, the authors demonstrate the possibility of using the solid ionic conductor Ag2S for the fabrication of sub-100nnm features in a Cu film and evaluate the physical properties of the Cu-Ag2S interface through an electroimpedance spectroscopy study.
Abstract: In this letter we demonstrate the possibility of using the solid ionic conductor Ag2S for the fabrication of sub-100 nnm features in a Cu film. We also evaluate the physical properties of the Cu–Ag2S interface through an electroimpedance spectroscopy study. Cu meander lines of 60 nm in width were obtained and the screening length and the surface adatom concentration of Cu on the interface were also evaluated to be 20 nm and 1012/cm2 respectively.
5 citations
TL;DR: In this article, the authors used a micro-forming-like embossing process to engrave nano-scale features onto a solid electrolyte tool surface using an e-beam fabricated Si mold.
Abstract: The recent growth in optoelectronics, nanoelectronics, nanooptics, and chemical and biological sensing has been fueled by the ability to fabricate nanostructures with ever smaller features. However, several significant constraints still remain in terms of cost, limited pattern size, processing conditions, pattern flexibility, and so on. Fabrication of features as small as 50 nm at ambient conditions with high pattern flexibility and low cost remains a serious challenge. Here we report a new solid-state electrochemical imprinting process that is carried out at ambient conditions, requires nominal pressure and very low electric potential, eliminates any liquid electrolytes, shows very high reproducibility, and promises the capability to scale up for large area patterning while retaining a significant cost advantage. Through combination of the best merits of nanoimprint lithography, micro forming, and the solid-state electrochemical imprinting technique, S4, (recently introduced by Hsu et al., Nano Lett., 2007, 7, 446; and Schultz et al., J. Vac. Sci. Techol. B, 2007, 25, 2419), we show a very high pattern flexibility to create nano-scale metallic features. As a first step, we use a micro-forming-like embossing process to engrave nano-scale features onto a solid electrolyte tool surface using an e-beam fabricated Si mold. Silver sulfide, Ag2S, is used as a solid electrolyte because of its favorable mechanical properties for micro forming and its excellent electrochemical properties. This ionic compound is ductile and has a relatively low yield stress at 80MPa. Followed by embossing, the patterned solid electrolyte surface is then used to carry out the S4 process, creating a negative image on a metallic substrate. This process eliminates the costly Focused Ion Beam milling used by Hsu et al. to create features on the electrolyte tool. It is also highly favorable for large-area patterning as well as mass-production of metallic substrates restricted only by the capability to fabricate the mold at first step. The embossed solid-electrolyte tool surface can be easily trimmed off with a microtome; the tool can then be re-used for embossing and patterning metallic substrates. Using this process we demonstrate the ability to fabricate silver nanostructures with features 30 sq. mm. Such large scale fabrication is highly desired for applications like biomimetics and patterning for superhydrophobic surfaces.
3 citations
14 Oct 2009
TL;DR: In this paper, the relation between near-field enhancement and far-field extinction spectra of three-fold rotationally symmetric nanopatterns consisting of metal nano-triangles was studied.
Abstract: We study the relation between near-field enhancement and far-field extinction spectra of three-fold rotationally symmetric nanopatterns consisting of metal nano-triangles. Our symmetry analysis benefits the understanding of the plasmon resonance phenomena in these nanopatterns.
Posted Content•
TL;DR: In this article, the authors numerically studied the Fizeau Doppler shift of surface modes in a moving plasmonic metamaterial and found an abrupt transition in the sign of phase shift when silver film reaches a critical thickness.
Abstract: In this work, we numerically study the Fizeau-Doppler shift of surface modes in a moving plasmonic metamaterial. At proper surface plasmon resonance conditions, a slow group velocity is resulted in the metamaterials, and our simulation indicates a phase shift up to 4 orders of magnitude larger than the normal mode. In addition, both appreciable positive and negative photon drag could be observed. We also found an abrupt transition in the sign of phase shift when silver film reaches a critical thickness. This opens new opportunities in applications such as compact optical gyroscopes and accelerometers.
Posted Content•
TL;DR: In this article, a smooth and low loss silver (Ag) optical superlens capable of resolving features at 1/12th of the illumination wavelength with high fidelity was demonstrated. But this was made possible by utilizing state-of-the-art nanoimprint technology and intermediate wetting layer of germanium (Ge) for the growth of flat silver films with surface roughness at sub-nanometer scales.
Abstract: We demonstrate a smooth and low loss silver (Ag) optical superlens capable of resolving features at 1/12th of the illumination wavelength with high fidelity. This is made possible by utilizing state-of-the-art nanoimprint technology and intermediate wetting layer of germanium (Ge) for the growth of flat silver films with surface roughness at sub-nanometer scales. Our measurement of the resolved lines of 30nm half-pitch shows a full-width at half-maximum better than 37nm, in excellent agreement with theoretical predictions. The development of this unique optical superlens lead promise to parallel imaging and nanofabrication in a single snapshot, a feat that are not yet available with other nanoscale imaging techniques such as atomic force microscope or scanning electron microscope.
TL;DR: The authors measured the phase delay of the squeezed light emerging from individual plasmonic holes on thin metal film by confocal microscope and observed a large phase shift, beyond prediction from earlier theoretical models.
Abstract: We measured the phase delay of the squeezed light emerging from individual plasmonic holes on thin metal film by confocal microscope. A large phase shift has been observed, beyond prediction from earlier theoretical models.