Iron oxide nanoparticles, including magnetite, maghemite and hematite, are promising electrode active materials for lithium ion batteries due to their low cost, high capacity and environmental friendliness. Though the electrochemical properties of each kind of iron oxide nanoparticles have been intensively studied, systematic comparison of the three kinds of iron oxides is hardly reported. This paper reports the study and comparison of the electrochemical properties of magnetite, maghemite and hematite nanoparticles with the same shape and size. In this work, hematite and maghemite nanoparticles were obtained from commercial magnetite nanoparticles by thermal treatments at different conditions. Their crystalline structures were characterized by X-ray diffraction (XRD), their magnetic properties were measured by a vibration sample magnetometer (VSM), and their particle morphologies were analyzed by scanning electron microscopy (SEM). Composite electrodes were made from iron oxide nanoparticles with carbon black as the conducting material and PVDF as the binding material (iron oxide : carbon black : PVDF = 70 : 15 : 15). Prototype lithium ion batteries (CR2032 button cells) were assembled with iron oxide composite electrodes as cathodes, metal lithium as anodes, and Celgard 2400 porous membrane as separators. The impedance and discharge-charge behaviors were characterized by a Solartron electrochemical workstation and an Arbin battery tester, respectively. It was found that at the same shape and size, hematite nanoparticles has higher specific discharge and charge capacities than magnetite and maghemite nanoparticles.
This paper reports the synthesis of three types of iron oxide nanotubes, including hematite (α-Fe2O3), maghemite (γ-Fe2O3) and magnetite (Fe3O4), and their applications in neuroscience and drug delivery. Two methods, template-assisted thermal decomposition method and hydrothermal method, were used for synthesizing hematite nanotubes, and maghemite nanotubes were obtained from hematite nanotubes by thermal treatment. Template-assisted filtering method was used for synthesizing magnetite nanotubes from ferrofluid. The crystalline, morphology and magnetic properties of the synthesized iron oxide nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. The biocompatibility of the synthesized hematite nanotubes was confirmed by the survival and differentiation of PC12 cells in the presence of the hematite nanotubes coupled to nerve growth factor (NGF). The capacity of hematite nanotubes for coupling and leasing NGF was confirmed by cultivating PC12 cells in the presence of NGF-loaded hematite nanotubes. The drug loading and release capabilities of hematite nanotubes were tested by using ibuprofen sodium salt (ISS) as a drug model. Based on the experimental results presented in this paper, it can be concluded that iron oxide nanotubes have good biocompatibility with neurons, could be used in guding neurite growth, and are promising candidates for drug delivery.
This report discusses our work on synthesis of hematite and maghemite nanotubes, analysis of their biocompatibility
with pheochromocytoma cells (PC12 cells), and study of their applications in the culture of dorsal root ganglion (DRG)
neurons and the delivery of ibuprofen sodium salt (ISS) drug model. Two methods, template-assisted thermal
decomposition method and hydrothermal method, were used for synthesizing hematite nanotubes, and maghemite
nanotubes were obtained from the synthesized hematite nanotubes by thermal treatment. The crystalline, morphology
and magnetic properties of the hematite and maghemite nanotubes were characterized by X-ray diffraction (XRD),
scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. The biocompatibility of
the synthesized hematite nanotubes was confirmed by the survival and differentiation of PC12 cells in the presence of
the hematite nanotubes coupled to nerve growth factor (NGF). To study the combined effects of the presence of
magnetic nanotubes and external magnetic fields on neurite growth, laminin was coupled to hematite and maghemite
nanotubes, and DRG neurons were cultured in the presence of the treated nanotubes with the application of external
magnetic fields. It was found that neurons can better tolerate external magnetic fields when magnetic nanotubes were
present. Close contacts between nanotubes and filopodia that were observed under SEM showed that the nanotubes and
the growing neurites interacted readily. The drug loading and release capabilities of hematite nanotubes synthesized by
hydrothermal method were tested by using ibuprofen sodium salt (ISS) as a drug model. Our experimental results
indicate that hematite and maghemite nanotubes have good biocompatibility with neurons, could be used in regulating
neurite growth, and are promising vehicles for drug delivery.
Magnetic nanomaterials, especially nanoparticles and nanotubes, are among the most widely used nanomaterials for
biomedical applications, and they are also the most promising nanomaterials for clinical treatments. This paper starts
with the fundamentals for nanomedicine and magnetic nanomedicine. After discussing the basic requirements for the
biomedical applications, the properties and the biomedical applications of magnetic nanoparticles and nanotubes are
discussed. Our results indicate that, with suitable functionalization, iron oxide nanomaterials are non-toxic to biological
systems, and they are ideal drug carriers which can be remotely controlled by external magnetic fields. At the final part
of this paper, the challenges and our approach for targeted drug delivery with controlled release are discussed.
Tubular nanomaterials possess hollow structures as well as high aspect ratios. In addition to their unique physical and
chemical properties induced by their nanoscale dimensions, their inner voids and outer surfaces make them ideal
candidates for a number of biomedical applications. In this work, three types of tubular nanomaterials including carbon
nanotubes, hematite nanotubes, and maghemite nanotubes, were synthesized by different chemical techniques. Their
structural and crystalline properties were characterized. For potential bioapplications of tubular nanomaterials,
experimental investigations were carried out to demonstrate the feasibility of using carbon nanotubes, hematite
nanotubes, and maghemite nanotubes in glucose sensing, neuronal growth, and drug delivery, respectively. Preliminary
results show the promise of tubular nanomaterials in future biomedical applications.
The emerging field of nanotechnology offers the development of new materials and methods for crucial neuroscience
applications namely (a) promoting survival and growth of the neurons, and (b) monitoring physiological signals
generated in the nervous system such as excitation, synaptic transmission, release of neurotransmitter molecules and
cell-to-cell communication. Such bio-devices will have several novel applications in basic science, laboratory
analysis and therapeutic treatments. Our goals in this field of research include (a) development of new biocompatible
substrates to guide and promote neuronal growth along specific pathways; (b) designing a neuron-friendly,
bio-molecule delivery system for neuroprotection; (c) monitoring of electrical activity from neuron and also from
neuronal networks; (d) determining the diffusion and intracellular localization of nanomaterial interacting with
neurons at high resolution; and (e) detection of release of neurotransmitter molecules by means of newly designed
nanosensors. Here we describe the fabrication and use of magnetic nanotubes and nanowire electrode arrays in studies
using a cell culture model of neuronally differentiating rat pheochromocytoma (PC 12) cells. The magnetic nanotubes
were fabricated by a template method yielding hematite (α-Fe2O3) nanotubes. These nanotubes were coupled with
nerve growth factor (NGF). Vertically aligned nanowires were fabricated on glass substrates using the
lithography-assisted template bonding (LATB) method. Rat pheochromocytoma (PC12) cells were cultured on these
nanotubes and polylysine coated nanowire electrodes. Our results showed that magnetic nanotube bound NGF was
available to PC12 cells as they showed significant differentiation into neurons. PC12 cells growing on nanowires in
the presence of NGF differentiated into neurons capable of synthesis and release of dopamine upon stimulation. The
neurons grew healthy neurites appearing to form synapses with other neurons in the dish. These results show that the
magnetic nanotubes were capable of delivering neurotrophic molecules and the nanowire electrodes are
neuron-friendly, promote cell to cell communication and can be used as bio-sensors in the nervous system.
The paper describes the synthesis of vertically aligned CNTs and the development of magnetic nanotube
substrates for biological applications. The vertical alignment of the CNTs on a silicon substrate for the use in biological
sensor systems has been explored. The preliminary experiments to determine the binding and growth of biological
samples with CNTs have been described. The potential to use the CNTs as electrode for elctrical stimulation is explored.
The growth of magnetic nanotubes and the possibility of utilizing them as scaffold for cellular growth is demonstrated.
The paper also described the sythesis and development of the magnetic carbon nanotubes, combining the salient features
of the CNTs and MNTs. All the nanotubes are optically charaterizd using SEM and TEM techniques. The magentization
of the nanotubes are evaluated using the VSM. Cellular binding is determined using SEM and flourescent microscopy
images.
It is known that multi walled carbon nanotubes (MWCNTs) is an excellent materials for biosensing applications and
with the introduction of Pt nanoparticles (Pt-MWCNTs) of about 3nm in diameter in MWCNTs greatly increases the
current sensitivity and also the signal to noise ratio. We fabricated the CNT- based glucose sensor by immobilization the
bio enzyme, glucose oxidase (GoX), on the Pt-MWCNT and electrode were prepared. The sensor has been tested
effectively for both the abnormal blood glucose levels- greater than 6.9 mM and less than 3.5 mM which are the
prediabetic and diabetic glucose levels, respectively. The current signal obtained from the Pt-MWCNT was much higher
compared to the MWCNT based sensors.
This report discusses the effects of magnetic nanotubes on the differentiation and growth of neurons. The magnetic
nanotubes used in this study are hematite nanotubes synthesized using template method, and their structural and
magnetic properties have been characterized by scanning electron microscopy (SEM), transmission electron microscopy
(TEM) and vibrating sample magnetometer (VSM). PC-12 cells are differentiated into neurons in the presence of
magnetic nanotubes to confirm the biocompatibility and cytotoxic effects of magnetic nanotubes during the processes of
neuron differentiation and neuronal growth. The morphological changes and synapse formation of neurons are
investigated, and the contact effects of magnetic nanotubes on neurite (axon and dendrites) outgrowth are explored. This
research allows us to understand the interaction between magnetic nanomaterials and neurons, and pave the way towards
developing potential treatments using the magnetic nano tubes for neurodegenerative disorders and injuries to the
nervous system in the future.
In this paper, we present how the photonic properties of zinc oxide (ZnO) nanowires can be used to potentially
advance the effectiveness of Photodynamic therapy (PDT), one of the most recent and promising approaches among
cancer therapies. Presently, PDT employs laser light to activate intravenously or topically administered photosensitizers
to give rise to highly reactive singlet oxygen which has a very short lifetime and is capable of biochemical damage to
cell membranes of the tumor. A probe that can monitor in real time the penetration depth of the laser in the tumor and
also the evolution of the singlet oxygen, which is critical for tumor eradication, is capable of improving the efficacy of
PDT quite significantly. Such a probe, by providing real time feedback, can help us determine whether to increase or
decrease the light exposure dose and also if further local administration of photosensitizers is required or not. ZnO
nanowires are known to be photoconductive and recent research also demonstrated the temperature dependence of the
photocurrent in the nanowires. They are also sensitive to blue and other near UV spectra which is same range of
activation wavelengths of most photosensitizers, and hence making them a good candidate for a potential PDT
monitoring probe. ZnO nanowires were fabricated on silicon substrates by vapor phase deposition using e-beam
evaporated gold as a catalyst. Control of the dimensions of the nanowires could be achieved by varying the dimensions
of the catalyst by means of e-beam evaporation process. Photoluminescence properties of ZnO nanowires were
investigated at UV and near UV wavelengths. Further, ZnO is also known for its antimicrobial properties, thereby ruling
out any possibility of bacterial infection because of the implanted probe. This study was done to compliment the
existing expertise of our research group in the design and fabrication of several nanowire based probes and
microsensors specifically for neuroelectronic and nanomedicine applications.
In this study, strain sensors consisting of a pentacene-carbon nanotubes (CNTs) composite layer are fabricated on
flexible substrates, Kapton polyimide films, employing Wheatstone bridge configuration. The sensors were characterized
with bending at 45° with respect to the bridge bias direction for two different bending radii of 50, and 40mm that
corresponds to strains of 1, and 1.25 %, respectively. It was noted that the output signal of the sensors is substantially
enhanced with the addition of CNTs, resulting from the improvement in conductivity of the sensing active layer. This
strain sensor using CNTs-organic semiconductor matrix composite as the active layer fabricated on flexible substrates is
expected to possess better reliability as compared with conventional metallic foils and inorganic semiconductor strain
sensors because of their low Young's modulus (~5GPa). For instance, the high Young's modulus of micro crystalline
silicon (~200GPa) limits its applications for sensors when fabricated on polymeric substrates due to the large modulus
mismatch between them.
This paper presents our study on the synthesis and properties of magnetic nanotubes and their potential in neuroscience
applications. Magnetic nanotubes were prepared by solution filtration through a template followed by thermal annealing
and reduction. SEM and TEM were performed to characterize the as-prepared materials. To explore the potential use of
magnetic nanotubes in neuroscience applications, we cultured neurons on iron oxide nanotube mats, and tested the
effects of magnetic nanotubes on the growth of neurons. Based on our preliminary result, three original approaches for
investigating and modulating neuron activities using magnetic nanotubes are proposed. The progress in this area of
investigation could help to find better treatment for diseases in nervous systems in the future.
Carbon nanotubes exhibit excellent properties which make them a good candidate as the electrode material for bioapplications. In this paper, various carbon nanotube based electrodes were prepared by thick film technique. After enzyme immobilization, they can be used as biosensors for glucose detection. We present our fabrication steps, electrochemical measurement of functional nanotube based biosensors. Also, influences of Ph value and interferences were tested. Preliminary results show purified carbon nanotubes electrodes exhibit better electrochemical performance for glucose detection, compared with other nanotube based electrodes.
It is already established that functional electrical stimulation is an effective way to restore many functions of the brain in disabled individuals. The electrical stimulation can be done by using an array of electrodes. Neural probes stimulate or sense the biopotentials mainly through the exposed metal sites. These sites should be smaller relative to the spatial potential distribution so that any potential averaging in the sensing area can be avoided. At the same time, the decrease in size of these sensing sites is limited due to the increase in impedance levels and the thermal noise while decreasing its size. It is known that current density in a planar electrode is not uniform and a higher current density can be observer around the perimeter of the electrodes. Electrical measurements conducted on many nanotubes and nanowires have already proved that it could be possible to use for current density applications and the drawbacks of the present design in neural probes can be overcome by incorporating many nanotechnology solutions. In this paper we present the design and development of nanowire arrays for the neural probe for the multisite contact which has the ability to collect and analyze isolated single unit activity. An array of vertically grown nanowires is used as contact site and many of such arrays can be used for stimulating as well as recording sites. The nanolevel interaction and wireless communication solution can extend to applications involving the treatment of many neurological disorders including Parkinson’s disease, Alzheimer’s disease, spinal injuries and the treatment of blindness and paralyzed patients with minimal or no invasive surgical procedures.
Aligned polyaniline nanotubules were prepared by electropolymerization/template method. Scanning electron microscopy micrographs reveal their alignment, uniform dimension as well as open-ended properties. Nickel was successfully encapsulated inside the polyaniline nanotubules by chemical treatment followed by electroplating process. Energy dispersive spectroscopy confirms the presence of nickel inside the polyaniline nanotubules.
Organic thin film transistors using pentacene as the active material elaborated on flexible substrates are presented in this paper. Organosilane octadecyltrichlorosilane (OTS) is used to treat the gate oxide surface prior to pentacene deposition. This OTS treatment is expected to improve the device performance in terms of field-effect mobility, subthreshold slope, on/off current ratio, and threshold voltage. To pattern the organic active layer, polymer polyvinyl alcohol (PVA) that is a water-soluble polymer is used as photoresist. By using the PVA, the pentacene film can avoid exposure to harmful organic solvents or developers during patterning. The simulated results of a typical thin film resistors with gate length and width of 20μm and 200 μm, respectively, shows a field-effect mobility of 0.98cm2/Vs in the saturation region for VDS=30V, and an on/off current ratio larger than 106.
Carbon nanotubes with certain shapes and 2D or 3D structures have versatile potential applications. Aligned and coiled carbon nanotubes were synthesized by microwave chemical vapor deposition. Due to its faster heating and cooling processes, microwave chemical vapor deposition can be an economic method for various carbon material fabrications. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were performed to observe the micro- and nano-structure of these materials. Their properties and potential applications were also discussed.
This paper presents the design and development of a gas sensor based on phase monitoring of reflected waves at radio frequencies for various dichloromethane vapors. Composite thin film with functionalized carbon nanotubes (f-CNT) and polymethylmethacrylate (PMMA) was employed as a sensing material on a coplanar waveguide and its impedance was monitored for various concentrations. Conductivity change of the composite due to absorption of dichloromethane vapors was clearly observed by resistance measurements. When the f-CNTs/PMMA composite is exposed to dichloromethane with low vapor concentration, phase monitoring of reflected waves from resistive load exhibited higher sensitivity than resistance measurements. With high sensitivity at radio frequency, a wireless gas sensing network integrated with power divider and antenna is introduced.
Nanosized tin oxide particles have shown excellent performance when used as anode material in lithium ion batteries. To further improve their electrochemical properties, functionalized carbon nanotubes were introduced during the homogenous precipitation synthesis. Various material characterization techniques such as XRD, SEM, TEM, TGA and BET were performed to check their crystalline, micro- and nano-structure, thermal stability and surface area. Compared with blank tin oxide nanoparticles, much finer tin oxide nanoparticles with higher surface area were observed with the presence of functional carbon nanotubes. It is proposed that functional carbon nanotubes play an important role for nanoparticles' nucleation, growth, coagulation processes. The potential application of this composite in lithium ion batteries is discussed.
Microfabrication techniques such as bulk micromachining and surface micromachining currently employed to conceive MEMS are largely derived from the standard IC and microelectronics technology. Even though many MEMS devices with integrated electronics have been achieved by using the traditional micromachining techniques, some limitations have nevertheless to be underlined: 1) these techniques are very expensive and need specific installations as well as a cleanroom environment, 2) the materials that can be used up to now are restricted to silicon and metals, 3) the manufacture of 3D parts having curved surfaces or an important number of layers is not possible. Moreover, for some biological applications, the materials used for sensors must be compatible with human body and the actuators need to have high strain and displacement which the current silicon based MEMS do not provide. It is thus natural for the researchers to 'look' for alternative methods such as Microstereolithography (MSL) to make 3D sensors and actuators using polymeric based materials. For MSL techniques to be successful as their silicon counterparts, one has to come up with multifunctional polymers with electrical properties comparable to silicon. These multifunctional polymers should not only have a high sensing capability but also a high strain and actuation performance. A novel UV-curable polymer uniformly bonded with functionalized nanotubes was synthesized via a modified three-step in-situ polymerization. Purified multi-walled nanotubes, gained from the microwave chemical vapor deposition method, were functionalized by oxidation. The UV curable polymer was prepared from toluene diisocyanate (TDI), functionalized nanotubes, and 2-hydroxyethyl methacrylate (HEMA). The chemical bonds between -NCO groups of TDI and -OH, -COOH groups of functionalized nanotubes help for conceiving polymeric based MEMS devices. A cost effective fabrication techniques was presented using Micro Stereo Lithography and an example of a micropump was also described. The wireless concept of the device has many applications including implanted medical delivery systems, chemical and biological instruments, fluid delivery in engines, pump coolants and refrigerants for local cooling of electronic components.
Current ultraviolet (UV) curable polymer techniques for MEMS fabrication pose certain challenges due to the electrical and mechanical properties of the polymer. A novel UV-curable polymer uniformly bonded with functionalized nanotubes was synthesized via a modified three-step in-situ polymerization. Purified multi-walled nanotubes, gained from the microwave chemical vapor deposition method, were functionalized by oxidation. X-ray photoelectron spectroscopy (XPS) was used to identify the -OH and -COOH groups attached to nanotube surface. The UV curable polymer was prepared from toluene diisocyanate (TDI), functionalized nanotubes, and 2-hydroxyethyl methacrylate (HEMA). The chemical bonds between -NCO groups of TDI and -OH, -COOH groups of functionalized nanotubes were confirmed by Fourier transform infrared (FTIR) spectra. This new UV-curable polymer is expected to be a cost-effective solution with a variety of applications in UV coating, phase shifters for telecommunications and global positioning systems, and polymer and BioMEMS devices.
Carbon nanotubes (CNTs) are an interesting class of nanostructures which can be thought of as arising from the folding of a layer of graphite (a graphene sheet ) to form a hollow cylinder composed of carbon hexagons. However, practical applications are still limited by the intricate process of synthesis and the inability of present day methods for large scale production of carbon nanotubes. Morevoer high quality nanotubes with functionalization capability with polymers are desired for polymer MEMS, Nanodevices and BioMEMS. In this paper, an innovative CVD approach using microwave energy was developed for large scale production of single wall and multiwall carbon nanotubes (MWNTs). Straight and helical carbon nanotubes were obtained when acetylene decomposed over the cobalt catalyst at 700°C created by microwave field. The scanning electron microscopy (SEM) of microwave driven MWNTs revealed their homogenous nature. The high resolution electron microscopy (HRTEM) showed typical MWNT has 26 layers. The average diameter of the tubes was observed 20-30 nm. Electron microscope observations showed higher yield of nanotubes obtained from microwave CVD than thermal filament CVD method.
Coiled carbon nanotubes exhibit excellent mechanical and electrical properties because of the combination of coil morphology and properties of nanotubes. They could have potential novel applications in nano-composite, nano-electronic devices as well as nano-electromechanical system (NEMS). In this work, synthesis of regularly coiled carbon nanotubes is presented. It involves pyrolysis of hydrocarbon gas over metal/support catalyst by conventional thermal filament CCVD and microwave CCVD methods. The growth mechanism and structural and electrical properties of coiled carbon nanotubes are also discussed.
Microfabrication techniques such as bulk micromachining and surface micromachining currently employed to conceive MEMS are largely derived from the standard IC and microelectronics technology. Even though many MEMS devices with integrated electronics have been achieved by using the traditional micromachining techniques, some limitations have nevertheless to be underlined: 1) these techniques are very expensive and need specific installations as well as a cleanroom environment, 2) the materials that can be used up to now are restricted to silicon and metals, 3) the manufacture of 3D parts having curved surfaces or an important number of layers is not possible. Moreover, for some biological applications, the materials used for sensors must be compatible with human body and the actuators need to have high strain and displacement which the current silicon based MEMS do not provide. It is thus natural for the researchers to look for alternative methods such as Microstereolithography (MSL) to make 3D sensors and actuators using polymeric based materials. For MSL techniques to be successful as their silicon counterparts, one has to come up with multifunctional polymers with electrical properties comparable to silicon. These multifunctional polymers should not only have a high sensing capability but also a high strain and actuation performance. A novel UV-curable polymer uniformly bonded with functionalised nanotubes was synthesized via a modified three-step in-situ polymerization. Purified multi-walled nanotubes, gained from the microwave chemical vapor deposition method, were functionalised by oxidation. The UV curable polymer was prepared from toluene diisocyantae (TDI), functionalised nanotubes, and 2-hydroxyethyl methacrylate (HEMA). The chemical bonds between -NCO groups of TDI and -OH, -COOH groups of functionalised nanotubes help for conceiving polymeric based MEMS devices. A cost effective fabrication techniques was presented using Micro Stereo Lithography and an example of a micropump was also described. The wireless concept of the device has many applications including implanted medical delivery systems, chemical and biological instruments, fluid delivery in engines, pump coolants and refrigerants for local cooling of electronic components.
Microfabrication techniques such as bulk micromachining and surface micromachining currently employed to conceive MEMS are largely derived from the standard IC and microelectronics technology. Even though many MEMS devices with integrated electronics have been achieved by using the traditional micromachining techniques, some limitations have nevertheless to be underlined: 1) these techniques are very expensive and need specific installations as well as a cleanroom environment, 2) the materials that can be used up to now are restricted to silicon and metals, 3) the manufacture of 3D parts having curved surfaces or an important number of layers is not possible. Moreover, for some biological applications, the materials used for sensors must be compatible with human body and the actuators need to have high strain and displacement which the current silicon based MEMS do not provide. It is thus natural for the researchers to look for alternative methods such as Microstereolithography (MSL) to make 3D sensors and actuators using polymeric based materials. For MSL techniques to be successful as their silicon counterparts, one has to come up with multifunctional polymers with electrical properties comparable to silicon. These multifunctional polymers should not only have a high sensing capability but also a high strain and actuation performance. A novel UV-curable polymer uniformly bonded with functionalized nanotubes was synthesized via a modified three-step in-situ polymerization. Purified multi-walled nanotubes, gained from the microwave chemical vapor deposition method, were functionalized by oxidation. The UV curable polymer was prepared from toluene diisocyanate (TDI), functionalized nanotubes, and 2 hydroxyethyl methacrylate (HEMA). The chemical bonds between NCO groups of TDI and OH, COOH groups of functionalized nanotubes help for conceiving polymeric based MEMS devices. A cost effective fabrication techniques was presented using Micro Stereo Lithography and an example of a micropump was also described. The wireless concept of the device has many applications including implanted medical delivery systems, chemical and biological instruments, fluid delivery in engines, pump coolants and refrigerants for local cooling of electronic components.
Current ultraviolet (UV) curable polymer techniques for MEMS fabrication pose certain challenges due to the electrical and mechanical properties of the polymer. A novel UV-curable polymer uniformly bonded with functionalized nanotubes was synthesized via a modified threestep in-situ polymerization. Purified multi-walled nanotubes, gained from the microwave chemical vapor deposition method, were functionalized by oxidation. X-ray photoelectron spectroscopy (XPS) was used to identify the —OH and —COOH groups attached to nanotube surface. The UV curable polymer was prepared from toluene diisocyanate (TDI), functionalized nanotubes, and 2-hydroxyethyl methacrylate (HEMA). The chemical bonds between —NCO groups of TDI and —OH, -COOH groups of functionalized nanotubes were confirmed by Fourier transform infrared (FTIR) spectra. This new UV-curable polymer is expected to be a costeffective solution with a variety of applications in UV coating, phase shifters for telecommunications and global positioning systems, and polymer and BioMEMS devices.
Carbon nanotubes (CNTs) are an interesting class of nanostructures which can be thought of as arising from the folding layer of graphite (a graphene sheet) to form a hollow cylinder composed of carbon hexagons. However, practical applications are still limited by the intricate process of synthesis and the inability of present day methods for large scale production of carbon nanotubes. Moreover high quality nanotubes with functionalization capability with polymers are desired for polymer MEMS, Nanodevices and BioMEMS. In this paper, an innovative CVD approacah using microwave energy was developed for large scale production of single wall and multiwall carbon nanotubes (MWNTs). Straight and helical carbon nanotubes were obtained when acetylene decomposed over the cobalt catalyst at 700°C created by microwave field. The scanning electron microscopy (SEM) of microwave driven MWNTs revealed their homogeneous nature. The high resolution electron microscopy (HRTEM) showed typical MWNT has 26 layers. The average diameter of the tubes was observed 20-30 nm. Electronc microscope observations showed higher yield of nanotubes obtained from microwave CVD than thermal filament CVD method.
Microfabrication techniques such as bulk micromachining and surface micromachining currently employed to conceive MEMS are largely derived from the standard IC and microelectronics technology. Even though many MEMS devices with integrated electronics have been achieved by using the traditional micromachining techniques, some limitations have nevertheless to be underlined: 1) these techniques are very expensive and need specific installations as well as a cleanroom environment, 2) the materials that can be used up to now are restricted to silicon and metals, 3) the manufacture of 3D parts having curved surfaces or an important numberof layers is not possible. Moreover, for some biological applications, the materials used for sensors must be compatible with human body and the actuators need to have high strain and displacement which the current silicon based MEMS do not provide. It is thus natural for the researchers to 'look' for alternative methods such as Microstereolithography (MSL) to make 3D sensors and actuators using polymeric based materials. For MSL techniques to be successful as their silicon counterparts, one has to come up with multifunctional polyers with electrical properties comparable to silicon. These multifunctional polymers should not only have a high sensing capability but also a high strain and actuation performance. A novel UV-curable polymer uniformly bonded with functionalized nanotubes was synthesized via a modified three-step in-sity polumerization. Purified multi-walled nanotubes, gained from the microwave chemical vapor deposition method, were functionalized by oxidation. The UV curable polymer was prepared from toluene diisocyanate (TDI), functionalized nanotubes, and 2-hydroxyethyl methacrylate (HEMA). The chemical bonds between -NCO groups of TDI and -OH, -COOH groups of functionalized nanotubes help for conceiving polymeric based MEMS devices. A cost effective fabrication techniques was presented using Micro Stereo Lithography and an example of a micropump was also described. The wireless concept of the device has many applications including implanted medical delivery systems, chemical and biological instruments, fluid delivery engines, pump coolants and refrigerants for local cooling of electronic components.
Microfabrication techniques such as bulk micromachining and surface micromachining currently employed to conceive MEMS are largely derived from the standard IC and microelectronics technology. Even though many MEMS devices with integrated electronics have been achieved by using the traditional micromachining techniques, some limitations have nevertheless to be underlined: 1) these techniques are very expensive and need specific installations as well as a clean room environment, 2) the materials that can be used up to now are restricted to silicon and metals, 3) the manufacture of 3D parts having curved surfaces or an important number of layers is not possible. Moreover, for some biological applications, the materials used for sensors must be compatible with human body and the actuators need to have high strain and displacement which the current silicon based MEMS do not provide.
KEYWORDS: Carbon, Microwave radiation, Chemical vapor deposition, Ceramics, Nickel, Titanium, Microelectromechanical systems, Toxic industrial chemicals, Scanning electron microscopy, Chemical species
In this paper, synthesis of carbon and ceramic microcoils by microwave chemical vapor deposition method is presented. Carbon microcoils were synthesized over nickel catalyst using acetylene as carbon source by microwave technique. Titanium carbide microcoils were gained by direct titanization to carbon microcoils .A comparison is given between conventional thermal filament CVD and microwave CVD methods. Particular attention is given to the potential applications of carbon and ceramic microcoils for MEMS.
Carbon Nano Tubes (CNT) with their unique structure, have already proven to be valuable in their application as tips for scanning probe microscopy, field emission devices, nanoelectronics, H2- storage, electromagnetic absorbers, ESD, EMI films and coatings and structural composites. For many of these applications, highly purified and functionalized CNT which are compatible with many host polymers are needed. A novel microwave CVD processing technique to meet these requirements has been developed at Penn State Center for the Engineering and Acoustic Materials and Devices (CEEAMD). This method enables the production of highly purified carbon nano tubes with variable size (from 5-40 nm) at lost cost (per gram) and high yield. Whereas, carbon nano tubes synthesized using the laser ablation or arc discharge evaporation method always include impurity due to catalyst or catalyst support. The Penn State research is based on the use of zeolites over other metal/metal oxides in the microwave field for a high production and uniformity of the product. An extended conventional purification method has been employed to purify our products in order to remove left over impurity. A novel composite structure can be tailored by functionalizing carbon nano tubes and chemically bonding them with the polymer matrix e.g. block or graft copolymer, or even cross-linked copolymer, to impart exceptional structural, electronic and surface properties. Bio- and Mechanical-MEMS devices derived from this hybrid composite are presented.
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