Srinivas Subramaniam

Development of novel single-wall carbon nanotube?epoxy composite ply actuators

This paper describes a carbon nanotube epoxy ply material that has electrochemical actuation properties. The material was formed by dispersing single-wall carbon nanotubes in a solvent and then solution casting a thin paper using a mold and vacuum oven. In order to take advantage of the high elastic modulus of carbon nanotubes for actuation, epoxy as a chemically inert polymer is considered. An epoxy layer was cast on the surface of the nanotube paper to make a two-layer ply. A wet electrochemical actuator was formed by placing the nanotube epoxy ply in a 2 M NaCl electrolyte solution. Electrochemical impedance spectroscopy and cyclic voltammetry were carried out to characterize the electrochemical properties of the actuator. The voltage–current relationship and power to drive the actuator material were also determined. Compared to previous single-wall carbon nanotube buckypaper tape actuators, which had poor adhesion between the nanotubes and tape, and other nanotube–thermal plastic polymer actuators, which could not provide high strength, the epoxy based actuator has a higher elastic modulus and strength, which will be useful for future structural applications. This demonstrates that a polymer layer can reinforce nanotube paper, which is an important step in building a new structural material that actuates. Further work is under way to develop a solid electrolyte to allow dry actuation. Finally, these actuator plies will be laminated to build a carbon nanocomposite material. This smart structural material will have potential applications that range from use in robotic surgical tools to use as structures that change shape.

Multifunctional carbon nanofiber/nanotube smart materials

This paper discusses the development of new multifunctional smart materials based on Carbon Nanofibers (CNF) and Multi-Wall Carbon Nanotubes (MWCNT). The material properties of CNF/MWCNT are a little lower than the properties of Single Wall Carbon Nanotubes (SWCNT). However, the CNF/MWCNT have the potential for more practical applications since their cost is lower. This paper discusses the development of four CNF/MWCNT-based sensors and actuators. These are: (i) an Electrochemical Wet Actuator for use in a liquid electrolyte, (ii) an Electrochemical Dry Actuator for use in a dry environment, (iii) a Bioelectronic sensor; and (iv) a MWCNT neuron for structural health monitoring. These materials are exciting because of their unique properties and many applications.

In situ Synthesis of Polyaniline in Poly(dimethylsiloxane) Networks Using an Inverse Emulsion Route

Polyaniline (PANI) was successfully prepared in end‐linked poly(dimethylsiloxane) (PDMS) networks using an inverse emulsion method. Its generation as dispersed particles was confirmed by UV/Vis spectrophotometry, Fourier transform infrared spectrometry, scanning electron microscopy and energy dispersive X‐ray analysis. The content, particle sizes and degrees of dispersion of the PANI particles were studied with regard to the pore dimensions of the PDMS networks, which had known cross‐link densities. Variables such as the nature of oxidants, solvent contents, solubility parameters, miscibility properties, and chemical interactions, etc. were also investigated, and a possible reaction mechanism was proposed.

Acquired Progressive Kinking of the Hair

A 15-year-old Caucasian girl was brought to the Cincinnati Children’s Hospital Dermatology Clinic by her mother for an evaluation of abnormal scalp hair. She had a 9-month history of progressive hair loss around the frontal hair line and the vertex. More recently, her hair in those areas had become curly and lighter in color. She noticed that when combed, she lost almost three times more hair than usual in these areas. She had no recent febrile illness or cosmetic hair procedures. There was no family history of hair disorders. Her medications included hydroxychloroquine for arthritis of her fingers, omeprazole for gastroesophageal reflux disorder, and multivitamins. However, she had stopped the hydroxychloroquine 5 weeks prior to being seen to evaluate whether it had caused her hair changes. She did not notice any improvement. Physical examination revealed a pleasant, well-developed adolescent. Her hair was extremely curly, dull, reddishbrown, and coarse along the frontal region (Fig. 1), but the rest of the hair on the scalp was smooth, shiny, dark brown, and straight (Fig. 2). On the vertex, there were fine hairs twisted in a tortuous and irregular way. The scalp showed no alopecia, erythema, or scaliness. She had no apparent abnormalities of her eyelashes, eyebrows, teeth, or nails. Only an occasional hair could be epilated by forceful manual traction. The following laboratory investigations (which were performed elsewhere) were within normal limits: complete blood count, total and free testosterone, thyroid-stimulating hormone, and erythrocyte sedimentation rate. Her progesterone and estradiol levels were consistent with luteal phase. Her dehydroepiandrosterone sulfate (DHEAS) was slightly elevated at 239 μ g /dl (normal 10–237 μ g /dl). An evaluation of the affected hair by scanning electron microscopy revealed partial longitudinal twisting of the hair (Fig. 3) and pili canaliculi (longitudinal grooves in the hair shaft) at irregular intervals (Fig. 4). There was also periodic reduction in hair shaft diameter.

A New Intelligent Material Based on Long Carbon Nanotube Arrays

Highly aligned multi-walled carbon nanotube (MWCNT) arrays were synthesized on Si wafers. Water vapor was used to enhance the catalyst performance, which enabled continuous growth of MWCNT arrays for up to 3 hours. Various types of Fe patterning on a Si substrate with a multilayered structure were tested. MWCNT arrays up to 4 mm long were grown by Chemical Vapor Deposition (CVD). Environmental scanning electron microscopy was used to characterize the MWCNT morphology and showed that the nanotubes typically reveal a 20 nm outer diameter and 8 nm inner diameter. To investigate applications, a nanotube tower 1 mm × 1 mm × 4 mm in size was grown and peeled off the Si wafer. Each tower contains millions of individual nanotubes with 20–30 nm diameters. Electrochemical actuation of one MWCNT tower was demonstrated in a 2M NaCl solution. The MWCNT tower actuator operated up to 10 Hz without significantly decreasing strain. Only 1-2 volts was needed to obtain 0.2% strain. The aligned nanotube morphology of the tower is the reason for the high strain in the axial direction, which is an improvement compared to previously tested entangled buckypaper actuators. Cyclic voltammetry (CV) was performed to analyze the redox behavior of the nanotube tower used as an electrode. The CV response showed a sigmodal shape in a 6 mM K3(CN)6 ferrocyanide solution. This behavior provides ideal characteristics for biosensor development and application. Also, the measured electrical volume resistivity of the material was in the range of 0.1 ohm · cm. The overall improvement in the electrochemical actuation and electrical conductivity was much greater than previous nanocomposites obtained by dispersing powdered nanotubes into polymers. The demonstrated good properties suggest nanotube array towers can be considered a novel intelligent material.

Use of Single Crystal Masks for Improved Mill Characteristics in High Current Xenon Plasma FIB instrumentation

High current focused ion beam tools are well placed to support development, and reduce TPT constraints. While these tools possess significant advantages, considerable efforts are underway to understand and optimize the newer technologies. Additionally, the operational performance of Xenon Plasma FIB tools is limited by their large probe’s characteristics, which include curtaining and degradations of milled regions and mediocre final quality of the cross section surface. We have, in our earlier work, looked at understanding the intrinsic design and operational aspects of Xenon Plasma FIBs with the aim of improving performance. This paper will look at an external performance improvement approach [1,2]. We have developed a novel single crystal mask process to optimize the tool for applications in semiconductor failure analysis, which significantly improves performance and matches results from conventional Gabased ion beam systems while retaining the inherent high current TPT benefits of the Xenon Plasma FIB.

Control and Optimization of Parameters in the ESEM at High Temperatures

High temperature processes play a decisive role in microstructure and property development of engineering materials. A fundamental understanding of the behavior of materials at elevated temperatures must precede control and optimization of these processes in advanced applications. Research in the form of ex-situ studies and theoretical modeling has been unsuccessful in developing a complete understanding of high temperature materials phenomenon. In-situ techniques have been plagued by experimental complexity, lack of resolution and thermal degradation effects. Further, insitu studies are typically performed in sterile environments questioning their ability to simulate real world environments and their interaction with the material. Environmental scanning electron microscopy combines the depth-of-field and high resolution advantages of conventional electron microscopy with novel gas based detection mechanisms, permitting observation of materials in a variety of gaseous atmospheres, at pressures as high as 20 Torr. Environmental scanning electron microscopy could provide researchers with a unique tool in dynamic high temperature investigations of materials and processes.

Building smart materials based on carbon nanotubes

The paper discusses the development of polymer composite materials based on carbon nanotubes. Carbon Nanotubes can be used to form polymer hybrid materials that have good elastic properties, piezoresistive sensing, and electrochemical actuation. Of particular interest are smart nanocomposite materials that are strong and self-sensing for structural health monitoring, or self-actuating to improve the performance and efficiency of structures and devices. Since nanoscale research is broad, challenging, and interdepartmental, undergraduate through Ph.D. level students and faculty have combined efforts to attack the special problems related to building nanoscale smart materials. This paper gives an overview of the work being performed to manufacture polymer nanocomposite materials starting from nanotube synthesis through to device fabrication and testing. Synthesis is performed using an EasyTube Nanofurnace, functionalization is done using plasma coating, dispersion using rotary mixing and ultrasonication, and processing using vacuum and pressure casting. Reinforced polymers, a carbon nanotube solid polymer electrolyte actuator, and piezoresistive sensors are being developed for several potential applications. The materials produced indicate that carbon nanotube hybrid smart materials may become a new class of smart material with unique properties and applications, but much work still needs to be done to realize their full potential.

A Comprehensive Approach Towards Optimizing the Xenon Plasma Focused Ion Beam Instrument for Semiconductor Failure Analysis Applications

The xenon plasma focused ion beam instrument (PFIB), holds significant promise in expanding the applications of focused ion beams in new technology thrust areas. In this paper, we have explored the operational characteristics of a Tescan FERA3 XMH PFIB instrument with the aim of meeting current and future challenges in the semiconductor industry. A two part approach, with the first part aimed at optimizing the ion column and the second optimizing specimen preparation, has been undertaken. Detailed studies characterizing the ion column, optimizing for high-current/high mill rate activities, have been described to support a better understanding of the PFIB. In addition, a novel single-crystal sacrificial mask method has been developed and implemented for use in the PFIB. Using this combined approach, we have achieved high-quality images with minimal artifacts, while retaining the shorter throughput times of the PFIB. Although the work presented in this paper has been performed on a specific instrument, the authors hope that these studies will provide general insight to direct further improvement of PFIB design and applications.

A Comparison of Current and Emerging Ion and Laser Beam Techniques for High Throughput Material Removal

Advances in technology have been instrumental in providing materials engineers and scientists with a broad array of techniques and capabilities to support research and applications driving technology. Beam based techniques have unique advantages in these areas providing the means to use a focused probe to inspect and image regions of interest in an as-is manner as well as progressively by sputtering/ablating the sample to expose new surfaces [1, 2]. This provides the analyst with the freedom to choose the best technique suited to his/her application. This paper will provide a comparison of some current and emerging techniques and discuss them comparing their advantages and limitations with the aim of understanding the best ways of using these technologies to maximum benefit.