Lower Limits of Detection for Single Biological Particles Using Impedance Spectroscopy

Single-cell impedance spectroscopy integrated with lab-on-a-chip systems provides a direct and minimally invasive approach for monitoring and characterizing properties of individual cells in real-time. Here we investigate the theoretical potential and limitations of this technique for analyzing single membrane-bound particles as small as 100 nm in diameter. Our theoretical model suggests a lower limit of detection for single cells on the order of a few microns.

Flipping Carbon Nanotubes to Continuously Produce Strong, Transparent, Multifunctional Sheets

We demonstrate carbon nanotube assembly by cooperatively rotating carbon nanotubes in vertically-oriented nanotube arrays (forests) and make 5-centimeter-wide, meter-long transparent sheets. These self-supporting nanotube sheets are initially formed as a highly anisotropic electronically conducting aerogel that can be densified into strong sheets that are as thin as 50 nanometers. The measured gravimetric strength of orthogonally oriented sheet arrays exceeds that of high strength steel sheet.

Surface-Plasmons-Assisted Nanoscale Photolithography

Photolithography has remained a useful micro-fabrication technology because of its high throughput, low cost, simplicity, and reproducibility over the past several decades. However its resolution is limited at a sub-wavelength scale due to optical diffraction. Among all different approaches to overcoming this problem, such as electron-beam lithography, imprint lithography and scanning probe lithography, near-field optical lithography inherits many merits of the traditional photolithography method. Major drawbacks of this approach include low contrast, low transmission and low density.

Preliminary Results Related to the Design of Virtual Probes for Use in a Nano-Manipulation Test-Bed

This paper discusses the design of virtual probe tip models for use in a nano-manipulation research test-bed (NMRT). The proposed NMRT would help study the feasibility of a given manipulation technique in a virtual environment before physical experiments. For example, NMRT would be able to help users determine if a specific kind of probe tip can be used to pull out a nano-particle from a given substrate. A virtual probe tip model (for instance) would consider the given geometry and material of probe tip and simulate its behavior in a manipulation application in a physics based virtual reality environment. Such a virtual analysis and overall approach would result in considerable saving in time and financial resources with substantial application potential in medical and biotechnology fields where nanoparticle manipulation is useful. Expandability of the NMRT is made possible by designing an ‘information oriented’ or ‘information intensive’ model for a target set of nano-manipulation activities, which maps in detail various attributes related to a target nano-manipulation process [1]. In this approach, information models based on “engineering Enterprise Modeling Language” (eEML) are used. For example, consider an existing information model for interaction of a probe tip with a spherical particle; a user can use an existing information model, or modify it quickly to study the impact of two approaches (eg. manipulation strategy-A versus strategy-B, which may apply a different probe-tip for gripping). For a target nano-manipulation process (for example, the assembly of nano particles using an Atomic Force Microscope probe as a gripper), an information model can represent the core attributes influencing the target process; influencing criteria including constraints, information inputs, and physical inputs can be modeled explicitly and used to drive a target analysis or simulation activity.

Molecular Scale Imaging With a Mutlilayer Superlens

Recent theory [1] suggested a thin negative index film should function as a “superlens”, providing image detail with resolution beyond the diffraction limit—a limitation to which all positive index optics are subject. The superlens allows the recovery of evanescent waves in the image via the excitation of surface plasmons. It has been demonstrated experimentally [2] that a silver superlens allows to resolve features well below the working wavelength. Resolution as high as 60 nanometer (λ/6) half-pitch has been achieved. This unique class of superlens will enable 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. In this paper, we explore the possibility of further refining the image resolution using a multilayer superlens [3]. Using a stable transfer matrix scheme, our numerical calculations show an ultimate imaging resolution of λ/24. This is made possible using alternating stacks of alumina (Al2O3) and silver (Ag) layers to enhance a broad spectrum of evanescent waves via surface plasmon modes. Furthermore, we present the effect of alterations in number of layers and thickness to the image transfer function. With optimized design of multilayer superlens (working wavelength of 387.5nm), our study indicates the feasibility of resolving features of 16nm and below. Moreover, our tolerance analysis indicates that a 380 nm commercial light source would degrade slightly the imaging resolution to about 20nm. Preliminary experiments are ongoing to demonstrate the molecular scale imaging resolution. The development of potential low-loss and high resolution superlens opens the door to exciting applications in nanoscale optical metrology and nanomanufacturing.

Direct Measurement of Slip Velocities Using Three-Dimensional Total Internal Reflection Velocimetry

The possible existence of slip of liquids in close proximity to a smooth surface is studied experimentally via the dynamics of small particles suspended in a shear flow. Sub-micron fluorescent particles suspended in water are imaged and analyzed using Total Internal Reflection Velocimetry (TIRV). For water flowing over a hydrophilic surface, the measurements are in agreement with previous experiments and indicate that slip, if present, is minimal at low shear rates, but increases slightly as the shear rate increases. Furthermore, surface hydrophobicity can be attributed for additional shear-rate dependent boundary slip. Issues associated with the experimental technique and the interpretation of results are also discussed.

The Local Instabilities of Nanostructures

In this paper we discuss an atomic-scale instability condition for detecting the local elastic limit in nanoscale systems. Without resorting to the continuum stability theory, we formulate an “atomic acoustic tensor” and use the singularity condition as an indicator to inspect local instabilities of the nanoscale structure. The derivation does not depend on the pristine lattice, thus, the indicator suits for not only perfect crystals but also defective media. To validate the applicability of this new quantity, we have performed local instability analysis on carbon nanotubes under axial tension. It is found that the criterion can characterize bond-breaking related instability in both perfect and defective nanotubes.

Effective Thermal Conductivity and Viscosity of Nanofluids

This paper presents a model to determine the effective thermal conductivity (ETC) of nanofluids. The model was developed by considering the geometrical structure of dispersed nanoparticles in base fluids. For the experimental investigation, nanofluids were prepared by suspending aluminum oxide (Φ80 nm) and titanium oxide (Φ15 nm and Φ10×40 nm) nanoparticles in deionized (DI) water and taken through longtime (8–10 hours) sonication for proper mixture of nanoparticles. Cetyltrimethylammoniumbromide (CTAB) surfactant was used to ensure better stability and dispersion of nanoparticles in the base fluids. The thermal conductivity and viscosity of the nanofluids were measured and compared with the predictions by various models. The present model gives better prediction of the effective thermal conductivity of nanofluids compared to existing models.

Fabrication of First-Level Carbon Nanotube Interconnect Via Structures by Thermal Chemical Vapor Deposition

As devices continue to scale down to the 50 nm technology node, current Cu/low k interconnect technology will face a number of challenges including reduced current carrying capabilities, decreased thermal conductivity, and reliability problems due to electromigration at large current densities. Carbon nanotubes (CNTs) with their unique structural, thermal and electrical transport properties have been suggested as a promising candidate as interconnect structures for future microelectronics. In this study we have demonstrated the growth of vertically aligned, highly dense CNT arrays by thermal chemical vapor deposition (CVD). It was found that a thin layer of tantalum (Ta), which was originally used as the barrier layer in copper interconnects, may enhance a uniform growth and better vertical alignments of CNT arrays. We have also developed a nanofabrication process of the first-level CNT via structures.

Programmable Self-Assembly Across the Micro and Nano Scales

Massively parallel self-assembling systems present a promising alternative to conventional manufacturing. Recently, various successful instances of self-assembly have been demonstrated, including applications for commercial products such as RFID tags; however, the full impact of this approach will only be realized once these systems can be programmed or reconfigured on demand (i.e., essentially in software, and without significant hardware changes). In this presentation, we review several projects that lead towards such programmable self-assembling systems. A key concept to achieve this goal is the “programmable surface”, i.e., an engineered surface whose properties (surface forces, hydrophobicity, friction, etc.) can be controlled with high spatial and temporal resolution. We present several projects covering a broad range of issues from realtime control of surface properties, to designs that optimize binding forces between self-assembling components, to computational and algorithmic issues in the modeling of self-assembling systems.