Nevin Naguib

In situ chemical experiments in carbon nanotubes

Abstract Understanding the interaction of water-based liquids with carbon at the nanoscale is very important for exploring the potential of carbon nanotubes in nanofluidic chips, probes, and capsules for drug delivery. By using hydrothermal synthesis, we produced closed hydrophilic multiwall carbon nanotubes filled with aqueous fluid. They allow for the first time high-resolution in situ studies of an interface between fluid and carbon in TEM. Strong interaction between the liquid and walls, intercalation of nanotubes with O–H species and dissolution of walls upon heating have been demonstrated. Thermodynamics simulation was used to explain the interaction of nanotubes with fluid.

Structure and Properties of Carbon Nanotube Reinforced Nanocomposites

Carbon nanotubes (CNT) possess many unique characteristics that promise to revolutionize the world of structural materials resulting in significant impact on our capability to build lighter, smaller and higher performance structures for aerospace and many other industrial applications. When the CNT are aligned, micromechanical studies showed the potential of an order of magnitude increase in mechanical properties comparing to the state of the art carbon fiber reinforced composites. The coelectrospinning process is introduced as a pathway to realize this potential by aligning and carrying the CNT in the form of nanocomposite fibrils; thus forming the precursor for linear, planar and 3D fiber assemblies for macrocomposites. In this study, SWNT were purified and dispersed in polyacrylonitrile solution for co-electrospinning into nanocomposite fibrils. The structure, composition and physical properties of these composite fibrils were characterized by Raman spectroscopy, TEM, AFM, and TGA.

Dielectrophoretic assembly of carbon nanofiber nanoelectromechanical devices

We report a technique for the assembly of bottom-up nanomechanical devices. This technique employs the dielectrophoretic manipulation of nanostructures within a multiple layer lithography process. Mechanical resonators were specifically produced by assembling and clamping tubular carbon fibers onto prefabricated pads. Our preliminary results showed that an assembled cantilevered fiber with length L=5 /spl mu/m and width of W=180 nm possessed a resonant frequency of f=1.17 MHz. A shorter L=3-/spl mu/m-long singly clamped resonator of similar width showed a resonance of f=3.12 MHz. This frequency range is in agreement with the low gigapascal bending moduli previously reported for carbon structures showing extensive volume defects. This technology would allow the integration of bottom-up nanostructures with other more established fabrication processes, thus allowing the deployment of engineered nanodevices in integrated systems.

Low-scatter bare aluminum optics via chemical mechanical polishing

Traditionally, aluminum optics have been produced via a combination of machining, lapping, and diamond turning techniques. The surface roughness and diffraction grating effects resultant from diamond turning have largely limited the use of these optics to IR applications. Work arounds for this problem have included nickel coatings which are subsequently polished to a required finish for use in visible and/or ultraviolet spectra. Unfortunately, this introduces additional costs as well as bimetallic effects that can limit the application of such components. We have developed chemical mechanical polishing (CMP) techniques that allow high quality optical surfaces to be produced on bare aluminum alloy such as 6061-T6. Alloy properties such as grain size, inclusions, and voids can impact all types of finishing processes. The CMP method, however, has been very robust in polishing performance over a range of alloy types and properties. Surface roughness <20 Å rms is readily attainable with this process, and values below 10 Å have been produced with proper process conditions and alloy properties. The monolithic mirrors produced via CMP techniques have been compared against other current alternatives such as diamond turned aluminum, nickel coated aluminum, and aluminized glass. Data indicate the aluminum mirrors produced via CMP can provide performance improvements versus the alternatives based on measurements comparing parameters such as surface roughness, surface quality, reflectivity, and bidirectional reflectance distribution function.

The Preparation of World-Class Single Crystal Silicon Carbide Wafers Using High Rate Chemical Mechanical Planarization Slurries

The influence of the chemical mechanical planarization process on the 4o off-axis 4HN SiC removal rate for silicon carbide slurry produced by Cabot Microelectronics Corporation (CMC) has been studied. A detailed kinetic analysis was applied and the linearity of an Arrhenius-like activation energy plot suggests that the primary removal occurs from particles adhered to the pad surface.

High Rate Silicon Carbide Polishing to Ultra-smooth Surfaces

Silicon Carbide has a unique combination of properties that include a nearly diamond-like hardness, intrinsic electrical semiconductivity and a high thermal conductivity. This combination of properties has led to its use in a number of applications including substrates for Light Emitting Diodes (LEDs), power, RF (radio frequency) and other electronic devices in addition to mirror substrates and optical devices as well as stop layers in integrated circuit chip manufacture. In addition, the chemical inertness and high hardness of SiC has historically resulted in low removal rates during chemical mechanical Planarization (CMP). Recent efforts in our labs have led to being able to polish single crystal silicon carbide at removal rates up to 400 nm/hr yielding a root mean squared roughness on the order of a nanometer as determined by AFM and interferometry. The high rates and smoothness obtained are expected to translate to other types of silicon carbide. Fundamental studies by FTIR, streaming potential and ESCA have been done to elucidate the mechanism of silicon carbide polishing.

Performance of CMP-Processed Monolithic Aluminum Mirrors

CMP processing of bare aluminum alloys has been shown to yield low surface roughness. The translation of roughness into mirror performance is compared through BRDF and veiling glare measurements for various aluminum processing techniques.