The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Thomas E Murphy - One of the best experts on this subject based on the ideXlab platform.
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strong anisotropic thermal conductivity of Nanoporous Silicon
Journal of Applied Physics, 2015Co-Authors: Kyowon Kim, Thomas E MurphyAbstract:Nanoporous Silicon is known to have a thermal conductivity that is orders of magnitude smaller than the bulk crystalline Silicon from which it is formed. Even though the strong columnar microscopic structure of porous Silicon indicates the possibility of highly anisotropic thermal properties, there have been no measurements. We report here an experimental investigation of this anisotropy. An analytical heat spreading model with 3ω thermal conductivity measurement method was used to derive both in-plane and cross-plane conductivities. Additionally, we describe a finite element analysis that supports the experimental measurements. Our measurements reveal that because of the nanoscale columnar nature of the material, the in-plane thermal conductivity of Nanoporous Silicon is 1–2 orders of magnitude smaller than the cross-plane thermal conductivity and 2–3 orders of magnitude smaller than that of crystalline Silicon, making it comparable to the best thermal insulators available.
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laser written Nanoporous Silicon ridge waveguide for highly sensitive optical sensors
Optics Letters, 2012Co-Authors: Jinan Xia, A Rossi, Thomas E MurphyAbstract:We report that low-loss ridge waveguides are directly written on Nanoporous Silicon layers by using an argon-ion laser at 514 nm up to 100 mW. Optical characterization of the waveguides indicates light propagation loss lower than 0.5 dB/cm at 1550 nm after oxidation. A Mach–Zehnder interferometer sensor is experimentally demonstrated using the waveguide in its sensing branch, and analytical results indicate that very high sensitivity can be achieved. With large internal surface area, versatile surface chemistry, and adjustable index of refraction of porous Silicon, the ridge waveguides can be used to configure Mach–Zehnder interferometers, Young’s interferometers, and other photonic devices for highly sensitive optical biosensors and chemical sensors as well as other applications.
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terahertz surface plasmon propagation in Nanoporous Silicon layers
Applied Physics Letters, 2010Co-Authors: Thomas E MurphyAbstract:We describe the fabrication and measurement of a terahertz surface plasmon waveguide in which the optical mode is localized within a Nanoporous Silicon slab. We compare the propagation characteristics among waveguides with different porous layer thickness, and present an analytical model that accurately describes the dispersion and loss in the waveguides.
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Nanoporous Silicon multilayers for terahertz filtering
Optics Letters, 2009Co-Authors: Thomas E MurphyAbstract:We describe the fabrication, simulation, and measurement of a terahertz (THz) filter composed of Nanoporous Silicon multilayers. Using electrochemical etching, we fabricated a structure composed of alternating high- and low-index layers that achieves 93% power reflectivity at the target wavelength of 1.17 THz, with a stopband of 0.26 THz. The measured reflection and transmission spectra of the multilayer filter show excellent agreement with calculations based on the refractive indices determined separately from single-layer measurements. This technique could provide a convenient, flexible, and economical way to produce THz filters, which are essential in a variety of future applications.
Yongho Choa - One of the best experts on this subject based on the ideXlab platform.
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Silicon solar cell with Nanoporous structure formed on a textured surface
Journal of the American Ceramic Society, 2009Co-Authors: Bum Sung Kim, Don Hee Lee, Sun Hee Kim, Kunjae Lee, Nosang V Myung, Yongho ChoaAbstract:A Nanoporous Silicon (Si) surface was formed on monocrystalline Silicon solar cells by electrochemical etching. The galvanostatic mode was applied to conventional n–p–p+ solar cells, which were fabricated by pyramidal texturing, phosphorous diffusion, screen-printing, rapid thermal firing, and laser isolation (effective area of 144.7 cm2). Without an additional antireflection layer such as SiNx, the anodic reaction of the Si wafer could provide uniform porous layers on a pyramidal surface (111) with relatively low reflectance, and it would improve the photovoltaic performance.
James L Mcgrath - One of the best experts on this subject based on the ideXlab platform.
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modification of Nanoporous Silicon nitride with stable and functional organic monolayers
Chemistry of Materials, 2017Co-Authors: Dean G Johnson, James L Mcgrath, Henry H Chung, Jirachai Getpreecharsawas, Alexander A ShestopalovAbstract:This study describes the formation of functional organic monolayers on thin, Nanoporous Silicon nitride membranes. We demonstrate that the vapor-phase carbene insertion into the surface C–H bonds can be used to form sub-5 nm molecular coatings on Nanoporous materials, which can be further modified with monolayers of polyethylene glycol (PEG) molecules. We investigate composition, thickness, and stability of the functionalized monolayers and the changes in the membrane permeability and pore size distribution. We show that, due to the low coating thickness (∼7 nm), the functionalized membrane retains 80% of the original gas permeance and 40% of the original hydraulic permeability. We also show that the carbene/PEG functionalization is hydrolytically stable for up to 48 h of exposure to water and that it can suppress nonspecific adsorption of the proteins BSA and IgG. Our results suggest that the vapor-phase carbenylation can be used as a complementary technology to the traditional self-assembly and polymer ...
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ultrathin membrane fouling mechanism transitions in dead end filtration of protein
ASME 2016 14th International Conference on Nanochannels Microchannels and Minichannels collocated with the ASME 2016 Heat Transfer Summer Conference a, 2016Co-Authors: Karl J P Smith, Joshua D Winans, James L McgrathAbstract:Ultrathin membranes will likely see great utility in future membrane-based separations, but key aspects of the performance of these membranes, especially when they are used to filter protein, remain poorly understood. In this work we perform protein filtrations using new Nanoporous Silicon nitride (NPN) membranes. Several concentrations of protein are filtered using dead end filtration in a benchtop centrifuge, and we track fouling based on the amount of filtrate passed over time. A modification of the classic fouling model that includes the effects of using a centrifuge and allow for the visualization of a transition between pore constriction and cake filtration demonstrate that for a range of protein concentrations, cake filtration supersedes pore constriction after ∼30 seconds at 690 g.Copyright © 2016 by ASME
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Nanoporous Silicon nitride membranes fabricated from porous nanocrystalline Silicon templates
Nanoscale, 2014Co-Authors: Jonpaul S Desormeaux, Joshua D Winans, Sarah E Wayson, Thomas R Gaborski, Tejas S Khire, Christopher C Striemer, James L McgrathAbstract:The extraordinary permeability and manufacturability of ultrathin Silicon-based membranes are enabling devices with improved performance and smaller sizes in such important areas as molecular filtration and sensing, cell culture, electroosmotic pumping, and hemodialysis. Because of the robust chemical and mechanical properties of Silicon nitride (SiN), several laboratories have developed techniques for patterning nanopores in SiN using reactive ion etching (RIE) through a template structure. These methods however, have failed to produce pores small enough for ultrafiltration (<100 nm) in SiN and involve templates that are prone to microporous defects. Here we present a facile, wafer-scale method to produce Nanoporous Silicon nitride (NPN) membranes using porous nanocrystalline Silicon (pnc-Si) as a self-assembling, defect free, RIE masking layer. By modifying the mask layer morphology and the RIE etch conditions, the pore sizes of NPN can be adjusted between 40 nm and 80 nm with porosities reaching 40%. The resulting NPN membranes exhibit higher burst pressures than pnc-Si membranes while having 5× greater permeability. NPN membranes also demonstrate the capacity for high resolution separations (<10 nm) seen previously with pnc-Si membranes. We further demonstrate that human endothelial cells can be grown on NPN membranes, verifying the biocompatibility of NPN and demonstrating the potential of this material for cell culture applications.
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a structure permeability relationship of ultrathin Nanoporous Silicon membrane a comparison with the nuclear envelope
Journal of the American Chemical Society, 2008Co-Authors: Eunkyoung Kim, James L Mcgrath, Christopher C Striemer, Hui Xiong, David Z Fang, P M Fauchet, Shigeru AmemiyaAbstract:We report on a simple, quantitative relationship between structure and permeability of a novel ultrathin Nanoporous membrane based on nanocrystalline Silicon. Large permeability of the free-standing nanomembrane to Ru(NH3)63+, O2, or 1,1‘-ferrocenedimethanol, which was able to be measured for the first time by employing scanning electrochemical microscopy, is proportional to the density (67 μm-2) and average radius (5.6 nm) of nanopores. As solution electrolyte concentration decreases down to 0.01 M, the nanopores are selectively “closed” against Fe(CN)64- because of electrostatic repulsion against negative charges at the pore wall. Permeability of the Silicon nanomembrane was compared to permeability of the nuclear envelope to find that the channel diameter of the nuclear pore complex that perforates the nuclear envelope is much larger than the average diameter of the Silicon nanopores and concomitantly a hypothetical diameter of 10 nm.
Shailesh N Sharma - One of the best experts on this subject based on the ideXlab platform.
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role of surface texturization on the gas sensing properties of nanostructured porous Silicon films
Physica E-low-dimensional Systems & Nanostructures, 2007Co-Authors: Shailesh N Sharma, G Bhagavannarayana, Umesh Kumar, R Debnath, Chandra S MohanAbstract:Abstract In this work, by means of high-resolution X-ray diffraction, excitation λ-dependent photoluminescence (PL) and Fourier transform infrared studies, it has been demonstrated that hydrogen-passivated porous Silicon (PS) films with high PL and stability can be obtained on p-type Si(1 0 0) substrate by simple texturization process rather than by resorting to any anodic, chemical or thermal oxidation of PS [T. Karacali, B. Cakmak, H. Efeoglu, Opt. Express 11 (2003) 1237]. PS formed on textured substrates is superior to PS formed on polished Silicon substrates at the same current density and time of anodization. The application of PS films formed on textured substrate as a gas sensor has been demonstrated and it shows higher sensitivity values upon exposure to ethanol as compared with polished PS specimens of similar porosity. The improved properties are attributed to the formation of highly porous vertical layers separating macroscopic domains of Nanoporous Silicon.
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role of surface texturization in the formation of highly luminescent stable and thick porous Silicon films
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2006Co-Authors: Shailesh N Sharma, G Bhagavannarayana, R K Sharma, S T LakshmikumarAbstract:Abstract Porous Silicon (PS) films were prepared by anodization on polished and textured substrates of (1 0 0) Si at different current densities for a fixed anodization time of 30 min. Using scanning electron microscopy (SEM), high-resolution X-ray diffractometry (HRXRD) and photoluminescence (PL) decay measurements, we have demonstrated that the texturization of Silicon surface is a simple and effective method for the formation of mechanically stable thick porous Silicon films. The PS formed on textured substrates exhibits higher porosity, negligible PL decay, better adherence to the substrate and non-fractured surface morphology compared to that formed on polished Silicon substrates under the same preparation conditions. The morphology of the PS film as observed by SEM indicates the formation of highly porous vertical layers separating macroscopic domains of Nanoporous Silicon. The lattice mismatch or strain measurements from HRXRD revealed that a variety of good quality PS films having different strain values (by varying the current density) corresponding to wide range of band gaps suitable for sensor applications can be formed on textured substrate.
Zuzanna S Siwy - One of the best experts on this subject based on the ideXlab platform.
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versatile ultrathin Nanoporous Silicon nitride membranes
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Ivan Vlassiouk, Pavel Yu Apel, Sergey N Dmitriev, Ken Healy, Zuzanna S SiwyAbstract:Single- and multiple-nanopore membranes are both highly interesting for biosensing and separation processes, as well as their ability to mimic biological membranes. The density of pores, their shape, and their surface chemistry are the key factors that determine membrane transport and separation capabilities. Here, we report Silicon nitride (SiN) membranes with fully controlled porosity, pore geometry, and pore surface chemistry. An ultrathin freestanding SiN platform is described with conical or double-conical nanopores of diameters as small as several nanometers, prepared by the track-etching technique. This technique allows the membrane porosity to be tuned from one to billions of pores per square centimeter. We demonstrate the separation capabilities of these membranes by discrimination of dye and protein molecules based on their charge and size. This separation process is based on an electrostatic mechanism and operates in physiological electrolyte conditions. As we have also shown, the separation capabilities can be tuned by chemically modifying the pore walls. Compared with typical membranes with cylindrical pores, the conical and double-conical pores reported here allow for higher fluxes, a critical advantage in separation applications. In addition, the conical pore shape results in a shorter effective length, which gives advantages for single biomolecule detection applications such as nanopore-based DNA analysis.
