Scaling the Stiffness, Strength, and Toughness of Ceramic‐Coated Nanotube Foams into the Structural Regime

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108652/1/adfm201400851-sup-0001-S1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/108652/2/adfm201400851.pd

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Controlled synthesis of templated vertical carbon nanotube structures

Single-walled and double-walled carbon nanotubes (SWNTs and DWNTs, respectively) possess excellent electronic and thermal transport properties while offering high strength. As such, they have been identified as excellent electronic candidates for applications including electronics, thermal management, radiation sources, and biological sensors. SWNTs and DWNTs have commercial potential in electron emitters for flat panel displays, gas and biological sensors, metallic electrical interconnects, and semiconducting channels for field effect transistors. While proof of concept experiments and prototypes have verified the performance of SWNTs in these applications, full utilization of their potential has been hindered by the lack of a reliable platform upon which to manufacture devices and a lack of synthesis control. Many prototype devices (such as field effect transistors) rely on dispensing CNTs in solution upon functionalized substrates to bridge one or more CNTs across electrical contacts. Other applications, such as electron emission devices and electrical interconnects, often rely on largely uncontrolled growth of dense CNTs mats. The objective of this research is the development of a controllable method for the production of vertical SWNT and DWNT-based electronic devices utilizing technology that is readily available in the semiconductor industry. The ideal device structure will preferentially yield SWNTs and/or DWNTs and will allow for easy integration of post-synthesis processing techniques, such as contact metallization to individual CNTs, to customize the device for various applications. This thesis details the development of a modified porous anodic alumina template (PAA) containing a thin CNT catalyst layer directly embedded into the pore walls. CNT synthesis using; the template selectively catalyzes SWNTs and DWNTs from the embedded catalyst layer to the top PAA surface, creating a vertical CNT channel within the pores. Subsequent processing allows for easy contact metallization and adaptable functionalization of the CNTs and template for a myriad of applications. Equally important is the optimization of the PECVD synthesis conditions used to grow individual vertical SWNTs, which is described in detail in this dissertation. Finally, a post-processing technique used to create a simple two-terminal CNT device from the template is described in detail, and more complicated device structures based on the structure are proposed

Freestanding vertically oriented single-walled carbon nanotubes synthesized using microwave plasma-enhanced CVD

Freestanding single-walled carbon nanotubes (SWCNTs) have been synthesized in a vertical direction, perpendicular to the growth substrate, using applied DC substrate bias in a microwave plasma-enhanced chemical vapor deposition (PECVD) synthesis process. The degree of alignment and spatial density of SWCNTs demonstrate a strong dependence on the magnitude of applied bias, with increased alignment and decreased density with increased bias. The unique synthesis environment created by the application of a negative substrate bias in PECVD aligns SWCNTs along electric field lines and decreases SWCNT density due to bombardment by positively charged hydrogen ions. Multi-excitation wavelength Raman spectroscopy reveals shifts in dominant RBM peaks with the application of dc bias. Use of this technique to orient SWCNTs in the vertical direction may allow for three-dimensional SWCNT-based device architectures

Dendrimer-assisted low-temperature growth of carbon nanotubes by plasma-enhanced chemical vapor deposition

Using a shielded growth approach and N2-annealed, nearly monodispersed Fe2O3 nanoparticles synthesized by interdendritic stabilization of Fe3+ species within fourth-generation poly(amidoamine) dendrimers, carbon nanotubes and nanofibers were successfully grown at low substrate temperatures (200-400 degreesC) by microwave plasma-enhanced chemical vapor deposition

Parametric study of synthesis conditions in plasma-enhanced CVD of high-quality single-walled carbon nanotubes

High-quality single-walled carbon nanotubes (SWCNTs) have been synthesized from H2–CH4 mixtures on a MgO-supported bimetallic Mo/Co catalyst using microwave plasma-enhanced chemical vapor deposition (PECVD). Reaction parameters including temperature, H2:CH4 ratio, plasma power, and synthesis time have been examined to assess their influence on SWCNT synthesis. Raman spectroscopy and high-resolution field emission scanning electron microscopy reveal that the quality, selectivity, density and predominant diameter of SWCNTs depend on the varied synthesis parameters. Results of this study can be used to optimize SWCNT synthesis conditions and products and to improve understanding of the growth of SWCNTs by PECVD

In-place fabrication of nanowire electrode arrays for vertical nanoelectronics on Si substrates

Vertical arrays of Pd nanowire electrodes with controllable and reproducible diameters and lengths are fabricated using a porous anodic alumin

Spallation of Isolated Aluminum Nanoparticles by Rapid Photothermal Heating

The spallation of isolated aluminum (Al) nanoparticles (NPs) is initiated using rapid photothermal heating. The Al NPs exhibited a nominal diameter of 120 nm, with an average oxide shell thickness of 3.8 nm. Photothermal heating was achieved by coupling a focused laser (446 nm wavelength) to an optical grating substrate and to the plasmonic resonance of the Al NPs themselves. These factors enhanced the absorption cross section by a factor of 8–18 compared to no substrate and generated an Al NP heating rate on the order of 107–108 K/s. Observations indicate that molten Al is ejected from the heated NP, indicating that melting of the Al core is required for spallation. A graphene layer atop the grating substrate encouraged the formation of discrete particles of ejected Al, while irregular elongated filament products were observed without the graphene layer. Numerical simulations indicate that laser-heated Al NPs reach temperatures between approximately 1000 and 1500 K. These observations and experimental conditions are consistent with those anticipated for the melt dispersion mechanism, a thermomechanical reaction mechanism that has not previously been clearly demonstrated. Activating and controlling this mechanism is anticipated to enhance applications ranging from biological phototherapy to energetic materials