Supercritical CO2 extraction of porogen phase: An alternative route to nanoporous dielectrics

DOI: 10.1557/JMR.2004.0413We present a supercritical CO2 (SCCO2) process for the preparation of nanoporous organosilicate thin films for ultralow dielectric constant materials. The porous structure was generated by SCCO2 extraction of a sacrificial poly(propylene glycol) (PPG) from a nanohybrid film, where the nanoscopic domains of PPG porogen are entrapped within the crosslinked poly(methylsilsesquioxane) (PMSSQ) matrix. As a comparison, porous structures generated by both the usual thermal decomposition (at approximately 450 °C) and by a SCCO2 process for 25 and 55 wt% porogen loadings were evaluated. It is found that the SCCO2 process is effective in removing the porogen phase at relatively low temperatures (<200 °C) through diffusion of the supercritical fluid into the phase-separated nanohybrids and selective extraction of the porogen phase. Pore morphologies generated from the two methods are compared from representative three-dimensional (3D) images built from small-angle x-ray scattering (SAXS) data.Professor Gangopadhyay and Professor Simon acknowledge the financial support of this work from the Semiconductor Research Corporation and from the National Science Foundation Grant No. CMS-0210230. The authors would also like to acknowledge initial support provided by the State of Texas Advanced Technology Program (ATP Grant No. 003644-0229-1999). The SAXS experiments were performed at the Advanced Photon Source at Argonne National Laboratory, which is supported by the United States Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38. Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, a national user facility operated by Stanford University on behalf of the United States Department of Energy, Office of Basic Energy Sciences

Single-molecule Detection in Nanogap-embedded Plasmonic Gratings

We introduce nanogap-embedded silver plasmonic gratings for single-molecule (SM) visualization using an epifluorescence microscope. This silver plasmonic platform was fabricated by a cost-effective nano-imprint lithography technique, using an HD DVD template. DNA/RNA duplex molecules tagged with Cy3/Cy5 fluorophores were immobilized on SiO2-capped silver gratings. Light was coupled to the gratings at particular wavelengths and incident angles to form surface plasmons. The SM fluorescence intensity of the fluorophores at the nanogaps showed approximately a 100-fold mean enhancement with respect to the fluorophores observed on quartz slides using an epifluorescence microscope. This high level of enhancement was due to the concentration of surface plasmons at the nanogaps. When nanogaps imaged with epifluorescence mode were compared to quartz imaged using total internal reflection fluorescence (TIRF) microscopy, more than a 30-fold mean enhancement was obtained. Due to the SM fluorescence enhancement of plasmonic gratings and the correspondingly high emission intensity, the required laser power can be reduced, resulting in a prolonged detection time prior to photobleaching. This simple platform was able to perform SM studies with a low-cost epifluorescence apparatus, instead of the more expensive TIRF or confocal microscopes, which would enable SM analysis to take place in most scientific laboratories

Electric field and temperature-induced removal of moisture in nanoporous organosilicate films

doi:10.1063/1.1757019The effects of bias-temperature-stress (BTS) or simply temperature-stress (TS) on nanoporous low-k methylsilsesquioxane films are studied. Initially, the as-given and O2 ashed/etched films exhibit physical adsorption of moisture as revealed from the electrical behavior of the samples after 15 days. The temperature stressing at 170 °C volatilized the adsorbed water but is unable to remove chemisorb and hydrophillic Si-OH groups. As a result, the TS films remain susceptible to moisture. BTS at 170 °C also removes adsorbed water. More important, the surfaces under the metal-insulator structure were dehydroxylated by breaking the chemisorb Si-OH group facilitating the formation of siloxane bonds that prevents adsorption of moisture even after 60 days.The authors would like to acknowledge Dorel Toma of TEL for providing the samples, and SRC and NSF for funding this research

Compact shock wave generating device for drug delivery

Genetic Engineering and Biotechnology News reported that "the burgeoning markets that surround biopharmaceuticals, RNA interference screening, and stem cell research are limited by the lack of a silver bullet for successful gene transfer. Because stable transfection is hard to achieve in primary cell lines, this application continues to be an important untapped niche in the transfection market." Inventors developed a microdevice creating shock waves from the reaction of nanoenergetic materials of fuel and oxidizer in nanoscale. The shock waves then permeabilize target cells allowing delivery of genetic material into the cells. The characteristics of the shock wave that can be controlled include pulse intensity, and pulse duration. The tunability of the shock waves allows the device to be adapted for use in a wide range of applications. DNA and nanoparticle delivery have been demonstrated. As compared to existing cell transfection products, this device achieves a significantly greater transfection success rate, significantly greater cell survival rate, and should cost less than most, if not all other methods. The invention was compared with commercially available chemical-based transfections (SiPort NeoFx, SiPort Amine, Lipofectamine 2000, Lipofectamine LTX, Transit LT1), and electroporation. The prototype of the invention produced transfection and survivability rates in excess of 99% while none of the existing transfection methods resulted in a rate greater than 10%, and the survivability of those transfected cells ranged from 0% to 80%. This device has the potential to revolutionize cell transfection, as the shock waves are particularly good at making the cell membranes porous, while at the same time the shock waves are gentle and do not cause catastrophic damage during the transfection, so cells survive. Potential Areas of Applications: * Cell Transfection * Shockwave drug delivery for killing cancer cells * Precision drug delivery of imaging particles * Fragmentation of kidney stones * Destruction of plaques Patent Status: Prototype tested and patent application 12/253,706 published Inventor(s): Dr. Shubhra Gangopadhyay, Ph.D.; Dr. Steven Apperson, Ph.D.; Dr. Luis Polo-Parada, Ph.D.; Dr. Keshab Gangopadhyay, Ph.D.; Dr. Andrey Bezmelnitsyn, Ph.D. Contact Info: Dr. Wayne McDaniel, Ph.D. ; [email protected] ; 573-884-330

Design and development of nanoenergetic materials with tunable combustion characteristics [abstract]

In recent years, nanoengineered thermites with tunable and tailored characteristics have attracted a great deal of attention owing to their enormous potential as excellent reactive materials, green primers, and structural energetic materials etc. Nanothermites are typically composed of metal oxide (oxidizer) and metal (fuel) nanoparticles. A variety of nanostructured oxidizers such as Fe2O3, CuO, Bi2O3 and MoO3 etc have been prepared in our laboratory. Various morphologies of oxidizers include nanorods, nanoparticles, and mesoporous structures exhibiting high surface area. Surfactant templating method has been developed for the synthesis of ammonium nitrate (NH4NO3) nanoparticles with a size distribution of 10-100nm. The physical and the chemical properties such as morphology, surface area, purity, composition, crystal structure of these metal oxide nanostructures have been determined by a host of characterization tools. Among the nanothermites, CuO nanorods/Al nanoparticles exhibit the best combustion performance measured in terms of combustion wave speed of 2600 100 m/s and reactivity of 11 1 MPa/msec. Nanothermites based on CuO nanorods/Al nanoparticles were then modified by mixing with polymers such as nitrocellulose (NC) and/or explosives such as (NH4NO3) nanoparticles, RDX (micron and nano size) and CL20 and the reaction rates of these nanocomposites were determined. Among the polymers, nitrocellulose coating of nanothermites is very interesting. Both the NC and the Teflon coated CuO/Al based nanothermite systems exhibit the ability to generate shock waves during their fast combustion. The NC coating has shown tremendous potential to reduce the high sensitivity of nanothermites to electrostatic discharge (ESD), friction and impact. Experimentally measured combustion characteristics are found to correlate very well with the physical and chemical characteristics of metal oxide nanostructures. The developed technology in our lab demonstrates the potential to tune and tailor the combustion characteristics of nanothermites to the desired level by proper choice and combination of fuel and oxidizer materials, their dimensions, and the process of self-assembly with reduced sensitivity. Potential Areas of Applications: * Microthrusters; * Propellants; * Propellant Initiators; * Suitable Replacements for Lead and Sulfur based Primers; * Shockwave drug delivery system

Entropy driven spontaneous formation of highly porous films from polymer-nanoparticle composites

doi: 10.1088/0957-4484/20/42/425602Nanoporous materials have become indispensable in many fields ranging from photonics, catalysis and semiconductor processing to biosensor infrastructure. Rapid and energy efficient process fabrication of these materials is, however, nontrivial. In this communication, we describe a simple method for the rapid fabrication of these materials from colloidal dispersions of Polymethyl Silsesquioxane nanoparticles. Nanoparticle-polymer composites above the decomposition temperature of the polymer are examined and the entropic gain experienced by the nanoparticles in this rubric is harnessed to fabricate novel highly porous films composed of nanoparticles. Optically smooth, hydrophobic films with low refractive indices (as low as 1.048) and high surface areas (as high as 1325 m2 g−1) have been achieved with this approach. In this communication we address the behavior of such systems that are both temperature and substrate surface energy dependent. The method is applicable, in principle, to a variety of nanoparticle-polymer systems to fabricate custom nanoporous materials.We gratefully acknowledge the financial support from National Institute of Health (Award number 2-U42RR014821) and the US army

Charge storage characteristics of ultra-small Pt nanoparticle embedded GaAs based non-volatile memory

Charge storage characteristics of ultra-small Pt nanoparticle embedded devices were characterized by capacitance-voltage measurements. A unique tilt target sputtering configuration was employed to produce highly homogenous nanoparticle arrays. Pt nanoparticle devices with sizes ranging from ∼0.7 to 1.34 nm and particle densities of ∼3.3–5.9 × 1012 cm−2 were embedded between atomic layer deposited and e-beam evaporated tunneling and blocking Al2O3 layers. These GaAs-based non-volatile memory devices demonstrate maximum memory windows equivalent to 6.5 V. Retention characteristics show that over 80% charged electrons were retained after 105 s, which is promising for device applications

Self-Aligned Microchip Device for Automated Measurement of Quantal Exocytosis [abstract]

Biomedical Tissue Engineering, Biomaterials, & Medical Devices Poster SessionNeurons and endocrine cells secrete neurotransmitters and hormones as a method for cell-to-cell communication through the process of exocytosis. Disruption of exocytosis underlie neurological disorders such as Parkinson's disease and the accounts for the toxicity of clostridial neurotoxins. In order to study the regulation of exocytosis it is important to carry out studies at the level of single-cells and resolve single-vesicle release events. Carbon-fiber microelectrodes are commonly used to perform single-cell measurements but are slow and labor-intensive to use. Therefore we are developing microchip devices with arrays of electrochemical electrodes for high-throughput measurement of single-vesicle release events. One challenge in the development of these devices is automatically targeting individual cells to each recording electrode. Here we describe a microchip device that uses a self-aligning surface chemistry approach to target individual cells to each electrochemical microelectrode in an array. The microelectrodes are small and “cytophilic” in order to promote adhesion of a single cell whereas all other areas of the chip are covered with a thin “cytophobic” film to block cell attachement and facilitate movement of cells to electrodes. This cytophobic film also insulates unused areas of the conductive film. Amperometric spikes resulting from single-granule fusion events were recorded on the device and had amplitudes and kinetics similar to those measured using carbon-fiber microelectrodes. Use of this device will increase the pace of basic neuroscience research and may also find applications in assaying neurotoxins and development of pharmaceuticals

Ultra-Broadband Infrared Absorption by Tapered Hyperbolic Multilayer Waveguides

Ultra-broadband strong absorption over 92% covering the infrared wavelength range of 1 ~ 6μm is demonstrated by using the tapered hyperbolic Au-SiO2 multilayer waveguides on glass substrates. Such broadband absorption is formed by the stop-light modes at various wavelengths located at different waveguide widths. A planar hyperbolic waveguide model is built to determine the stop-light modes by considering both forward and backward guided modes. The stop-light modes located inside the Au-SiO2 multilayer waveguide are simulated at the absorption peaks by reducing the Au loss. Tapered multilayer waveguides with varying top widths are further simulated, fabricated and measured, indicating the almost linear relation between the waveguide width and the stop-light wavelength. Moreover, the broadband absorption of tapered waveguide is proved to be angle-insensitive and polarization-independent, and the heat generation and temperature increase are also discussed

Sub-2 nm Size-Tunable High-Density Pt Nanoparticle Embedded Nonvolatile Memory

DOI: 10.1109/LED.2009.2033618The charge-storage characteristics of a metal-oxide-semiconductor (MOS) structure containing size-tunable sub-2 nm Pt nanoparticles (NPs) between Al2O3 tunneling and capping oxide layers were studied. Significantly different amounts of memory window were obtained with the different sizes of Pt NP embedded MOS structures and reached a maximum of 4.3 V using a 1.14 nm Pt NP, which has the strongest charging capability caused by optimum size and the largest particle density obtained in our deposition method. Satisfactory long-term nonvolatility was attained in a low electric field due to the Coulomb blockade and quantum confinement effects in ~ 1 nm Pt NP. These properties are very promising in view of device application