Carmen Kar Man Fung

Dielectrophoretic batch fabrication of bundled carbon nanotube thermal sensors

We present a feasible technology for batch assembly of carbon nanotube (CNT) devices by utilizing ac electrophoretic technique to manipulate multiwalled bundles on an Si/SiO/sub 2/ substrate. Based on this technique, CNTs were successfully and repeatably manipulated between microfabricated electrodes. By using this parallel assembly process, we have investigated the possibility of batch fabricating functional CNT devices when an ac electrical field is applied to an array of microelectrodes that are electrically connected together. Preliminary experimental results showed that over 70% of CNT functional devices can be assembled successfully using our technique, which is considered to be a good yield for nanodevices manufacturing. Besides, the devices were demonstrated to potentially serve as novel thermal sensors with low power consumption (/spl sim/microwatts) with electronic circuit response of approximately 100 kHz in constant current mode operation. In this paper, we will present the fabrication process of this feasible batch manufacturable method for functional CNT-based thermal sensors, which will dramatically reduce production costs and production time of nanosensing devices and potentially enable fully automated assembly of CNT-based devices. Experimental results from the thermal sensors fabricated by this batch process will also be discussed.

Rapid assembly of carbon nanotubes for nanosensing by dielectrophoretic force

The carbon nanotube (CNT) has been widely studied for its electrical, mechanical, and chemical properties since its discovery. However, to manipulate these nanosize tubes, atomic force microscopy (AFM) is typically used to manipulate them one-by-one. This is time-consuming and unrealistic for batch fabrication. In this paper, we will present the manipulation of carbon nanotubes using dielectrophoretic manipulation to rapidly build practical nanosensors. Thus far, we have demonstrated thermal sensors for temperature and fluid-flow measurements. We have also shown that this electrokinetic based manipulation technique is compatible with MEMS fabrication processes, and hence, MEMS structures embedded with carbon nanotube sensing elements can be built in the future with new functionalities.

A PMMA-based micro pressure sensor chip using carbon nanotubes as sensing elements

A polymer-based MEMS pressure sensor was fabricated using bulk multi-walled carbon nanotube (MWNT) as piezoresistive sensing elements. The development of the pressure sensor includes fabrication of 300/spl mu/m thick polymethylmethacrylate (PMMA) diaphragms using SU8 molding/hot-embossing technique and AC electrophoretic manipulation of MWNT bundles on the diaphragms. We have measured the pressure-resistance dependency of these MWNT-based micro sensors and preliminary results indicated that the MWNT sensors were capable of sensing input pressure variations. Moreover, the I-V measurements of the resulting devices revealed that the nominal resistance of the sensing elements can be adjusted by annealing the MWNTs through electrical current heating, which offers a potential method for resistance-off set calibration. Based on these experimental evidences, we propose that carbon nanotubes (CNTs) is a novel material for fabricating micro pressure sensors on polymer substrates - which may serve as alternative sensors for silicon based pressure sensors when bio-compatibility and low-cost applications are required.

Development of Infrared Detectors Using Single Carbon-Nanotube-Based Field-Effect Transistors

Carbon nanotube is a promising material to fabricate high-performance nanoscale-optoelectronic devices owing to its unique 1-D structure. In particular, different types of carbon-nanotube-infrared detectors have been developed. However, most previous reported carbon-nanotube-IR detectors showed poor device characteristics due to limited understanding of their working principles. In this paper, three types of IR detectors were fabricated using carbon-nanotube field effect transistors (CNTFETs) to investigate their performance: 1) symmetric Au-CNT-Au CNTFET IR detector; 2) symmetric Ag-CNT-Ag CNTFET IR detector; and 3) asymmetric Ag-CNT-Au CNTFET IR detector. The theoretical analyses and experimental results have shown that the IR detector using an individual single-wall carbon nanotube (SWCNT), with asymmetric Ag-CNT-Au CNTFET structure, can suppress dark current and increase photocurrent by electrostatic doping. As a result, an open-circuit voltage of 0.45 V under IR illumination was generated, which is the highest value reported to date for an individual SWCNT-based photodetector. The results reported in this paper have demonstrated that the CNTFET can be used to develop high-performance IR sensors.

Investigation of human keratinocyte cell adhesion using atomic force microscopy

UNLABELLED Desmosomal junctions are specialized structures critical to cellular adhesion within epithelial tissues. Disassembly of these junctions is seen consequent to the development of autoantibodies directed at specific desmosomal proteins in blistering skin diseases such as pemphigus. However, many details regarding cell junction activity under normal physiological and disease conditions remain to be elucidated. Because of their complex structure, desmosomal junctions are not well suited to existing techniques for high-resolution three-dimensional structure-function analyses. Here, atomic force microscopy (AFM) is used for detailed characterization and visualization of the cell junctions of human epithelial cells. We demonstrate the ability to image the detailed three-dimensional structure of the cell junction at high magnification. In addition, the effect of specific antibody binding to desmosomal components of the cell junction is studied in longitudinal analyses before and after antibody treatment. We show that antibodies directed against desmoglein 3 (a major component of the desmosomal structural unit, and the major target of autoantibodies in patients with pemphigus vulgaris) are associated with changes at the cell surface of the human keratinocytes and alterations within keratinocyte intercellular adhesion structures, supporting the assertion that cell structures and junctions are modified by antibody binding. The present study indicates that the molecular structure of gap junctions can be more completely analyzed and characterized by AFM, offering a new technological approach to facilitate a better understanding of disease mechanisms and potentially monitor therapeutic strategies in blistering skin diseases. FROM THE CLINICAL EDITOR Disassembly of desmosomal junctions is seen in blistering skin diseases such as Pemphigus. This present study demonstrates that the molecular structure of gap junctions can be more completely analyzed and characterized by atomic force microscopy.

A 2-D PVDF force sensing system for micro-manipulation and micro-assembly

Despite the enormous research efforts in creating new applications with MEMS, the research efforts at the backend such as packaging and assembly are relatively limited. We present our ongoing development of a polyvinylidene fluoride (PVDF) multi-direction micro-force sensing system that can be potentially used for force-reflective manipulation of micro-mechanical devices or micro-organisms over remote distances. Thus far, we have successfully demonstrated 1D and 2D sensing systems that are able to sense force information when a micro-manipulation probe-tip is used to lift a micro mass supported by 2 /spl mu/m/spl times/30 /spl mu/m/spl times/200 /spl mu/m polysilicon beams. Hence, we have shown that force detection in the 50 /spl mu/N range is possible with PVDF sensors integrated with commercial micro-manipulation probe-tips.

Automated Nanomanufacturing System to Assemble Carbon Nanotube Based Devices

In this paper we report the design and implementation of a novel automated manufacturing system for carbon nanotube (CNT)-based nanodevices, which integrates a new dielectrophoretic (DEP) microchamber into a robotic-based deposition workstation. The microchamber has been fabricated to separate and select CNTs with the desired electronic property by using DEP force. Moreover, a series of tools for mass-producing consistent nanodevices has been developed with the CNT deposition workstation, such as computer-controllable micromanipulators and a micro-active nozzle. Detailed experimental studies of the CNT separation and deposition processes have been performed on both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Preliminary results show that CNTs could be manipulated to multiple pairs of microelectrodes repeatedly. Consistent I—V characteristics and CNT formations of the fabricated devices were obtained. The yield of semi-conducting CNTs was also increased by using our system. Therefore, by using the proposed CNT separation and deposition system, CNT-based nanodevices with specific and consistent electronic properties can be manufactured automatically and effectively.

Engineering the band gap of carbon nanotube for infrared sensors

Carbon nanotube (CNT) has been found to be one of the promising semiconducting materials for nanoelectronic sensors due to its unique electrical properties. Our group has developed a spectrum sensor using a single CNT and demonstrated its performance. In this paper, a steady and high-yield CNT band gap engineering will be developed and used to manufacture an appropriate CNT for infrared (IR) detection. The fabrication and experimental result of the CNT-based spectrum sensor will be presented. The results indicate that the CNT-based spectrum sensor is capable to sense near IR and middle-wave IR signals at room temperature.

Investigating dynamic structural and mechanical changes of neuroblastoma cells associated with glutamate-mediated neurodegeneration

Glutamate-mediated neurodegeneration resulting from excessive activation of glutamate receptors is recognized as one of the major causes of various neurological disorders such as Alzheimers and Huntingtons diseases. However, the underlying mechanisms in the neurodegenerative process remain unidentified. Here, we investigate the real-time dynamic structural and mechanical changes associated with the neurodegeneration induced by the activation of N-methyl-D-aspartate (NMDA) receptors (a subtype of glutamate receptors) at the nanoscale. Atomic force microscopy (AFM) is employed to measure the three-dimensional (3-D) topography and mechanical properties of live SH-SY5Y cells under stimulus of NMDA receptors. A significant increase in surface roughness and stiffness of the cell is observed after NMDA treatment, which indicates the time-dependent neuronal cell behavior under NMDA-mediated neurodegeneration. The present AFM based study further advance our understanding of the neurodegenerative process to elucidate the pathways and mechanisms that govern NMDA induced neurodegeneration, so as to facilitate the development of novel therapeutic strategies for neurodegenerative diseases.

Nanoresonant signal boosters for carbon nanotube based infrared detectors

We report the development of a sensitive carbon nanotube (CNT) infrared detector whose signals are boosted by nanoantenna-like features. This assembly is fabricated using nanoassembly of CNTs and a standard photolithographic process, together with nanoantenna-like features that are designed to create a resonance structure necessary to boost the electric field intensity at the CNT sensor. A novel approach is employed to find the near-field effect of the antenna. As a result, these effects are verified and demonstrated experimentally in this paper. The first experimental demonstration of a practical infrared device with nanoantenna-like structures is reported; it shows that the photocurrent is increased by an order of magnitude. The proposed fabrication and design process enables a ready integration of resonance structures into the manufacture of infrared devices, and opens the possibility of developing high fidelity infrared sensors with wide sensing range.