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Journal of Materials Chemistry 01/2012; 22(34):17625-17629. · 5.97 Impact Factor
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ABSTRACT: In this work, we report the results of our study on the magnetization-reversal properties in a bilayered magnetic antidot lattice (BMAL) system consisting of upper perforated thick Co layer of 40 nm and lower continuous thin Ni layer of 5 nm, probed by using a superconducting-quantum-interference-device (SQUID) magnetometer and by magnetic-force microscopy (MFM). Such a BMAL structure was fabricated by using photolithography and controlled wet-etching processes. A systematic study on the in-plane anisotropy, and the switching-field properties was carried out. The atomic-force-microscopy (AFM) image clearly indicated that the anti-dot array structures are well defined, and the local element composition was confirmed by using the energy dispersive spectra (EDS). The room-temperature hysteresis curves, taken along different directions of the applied magnetic-field, were proved to be useful to understand the magnetic anisotropy in the sample. A kind of uniaxial anisotropy with easy axis along 0° and hard axis along 90° of applied field direction was observed. To get a comprehensive knowledge about the domain configuration, we performed the MFM imaging along the easy and hard axis of the lattice. The MFM images revealed well-defined periodic domain networks which can be ascribed to the anisotropies such as magnetic uniaxial anisotropy, configurational anisotropy, etc. The observed changes in the magnetic properties are closely related to the patterning that pins the domains as well as to the magneto-anisotropic BMAL structure.
IEEE Transactions on Magnetics 11/2011; · 1.36 Impact Factor
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ABSTRACT: The Tactical Ground Reporting (TIGR) system provides a unique multimedia patrol preparation and debriefing tool tailored to the needs of the patrol leader, and is used by all U.S. Army brigades in Iraq and Afghanistan. The distribution of data from geographically dispersed patrols requires network awareness and policy flexibility. The TIGR system utilizes an application overlay on to the tactical network that is tailored to the distribution of rich media. This architecture results in the theater-wide replication of compressed reports and meta-data, while the storage of full-quality media is distributed to the node closest to where the media was created. Thumbnail and other compressed media representations are replicated according to policy to meet soldier needs. Full-quality media can be accessed on demand from any location in the network. Network utilization is controlled by a policy-based content subscription system, a priority queuing mechanism, and the discrete scheduling of network traffic. In this paper, we focus on the requirements for media rich tactical applications, detail a system that meets those requirements, and discuss experiences using TIGR in theater.
Military Communications Conference, 2009. MILCOM 2009. IEEE; 11/2009
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ABSTRACT: Cable theory is used to model fibers (neural or muscular) subjected to an extracellular stimulus or activating function along the fiber (longitudinal stimulation). There are cases however, in which activation from fields across a fiber (transverse stimulation) is dominant and the activating function is insufficient to predict the relative stimulus thresholds for cells in a bundle. This work proposes a general method of quantifying transverse extracellular stimulation using ideal cases of long fibers oriented perpendicular to a uniform field (circular cells in a 2-D extracellular domain). Several methods are compared against a fully coupled model to compute electrical potentials around each cell of a bundle and predict the magnitude of applied plate potential (Phi p ) needed to activate a given cell (Phi<sub>pact</sub>). The results show that with transverse stimulation, the effect of cell presence on the external field must be considered to accurately compute Phi<sub>pact</sub>. They also show that approximating cells as holes can accurately predict firing order and Phi<sub>pact</sub> of cells in bundles. Potential profiles from this hole model can also be applied to single cell models to account for time-dependent transmembrane voltage responses and more accurately predict Phi<sub>pact</sub>. The approaches used herein apply to other examples of transverse cell stimulation where cable theory is inapplicable and coupled model simulation is too costly to compute.
IEEE Transactions on Neural Systems and Rehabilitation Engineering 11/2009; · 3.44 Impact Factor
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ABSTRACT: A novel synthesis and growth method achieving vertically aligned zinc oxide (ZnO) nanowires on a silicon dioxide (SiO(2)) coated silicon (Si) substrate is demonstrated. The growth direction of the ZnO nanowires is determined by the crystal structure of the ZnO seed layer, which is formed by the oxidation of a DC-sputtered Zn film. The [002] crystal direction of the seed layer is dominant under optimized thickness of the Zn film and thermal treatment. Vertically aligned ZnO nanowires on SiO(2) coated Si substrate are realized from the appropriately thick oxidized Zn seed layer by a vapor-solid growth mechanism by catalyst-free thermal chemical vapor deposition (CVD). These experimental results raise the possibility of using the nanowires as functional blocks for high-density integration systems and/or photonic applications.
Nanotechnology 06/2008; 19(23):235601. · 3.98 Impact Factor
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ABSTRACT: Exptl. results for microwave transmission losses of individual multi-walled C nanotubes (MWNTs) are presented. Samples with MWNTs, as well as samples without MWNTs, were fabricated with 2 types of electrode materials (Nb vs. Cr/Au) and configurations to compare a.c. transmissions loss as passive devices at room temp. In the MWNT-Nb samples, the transmitted current is higher and attenuation is lower than the MWNT-Cr/Au samples. However, the transmission loss increases much faster in the Nb samples than Cr/Au samples with increasing frequency. Overall, their S-parameter measurements from 0.5 GHz to 110 GHz support frequency-dependent microwave dissipation of the MWNTs and the metal-electrode contact. [on SciFinder (R)]
Physica Status Solidi A: Applications and Materials Science. 01/2008; 205:261-265.
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ABSTRACT: Electrothermal tuning mechanisms for nanoelectromech. resonators are demonstrated. Voltages induced by oscillation of Al/SiC nanoresonators around 10 MHz in a moderate magnetic field are measured using a room-temp. tabletop setup in moderate vacuum. The dynamic range as well as the resonance frequency of the resonator can be reversibly controlled by electrothermal tuning using DC voltage. This paper presents exptl. results that demonstrates the effect of the resonance frequency, Q factor and dynamic range during the electrothermal tuning process. As the input DC power increases, Q factor decreases due to the decrease in the resonance frequency, and SNR decreases due to the reduced amplitude and increased noise. This can be explained by thermal relaxation of the resonator structure during the tuning process, and Johnson noise and eddy current effects assocd. with the magnetomotive transduction. [on SciFinder (R)]
Solid-State Electronics. 01/2008; 52:1388-1393.
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Applied Physics Letters 01/2008; 93(11). · 3.84 Impact Factor
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ABSTRACT: Effects of electrothermal tuning mechanisms for nanoelectromechnical resonators are demonstrated. Voltages induced by oscillation of Al/SiC nanoresonators in a moderate magnetic filed are measured using a room-temperature tabletop setup in moderate vacuum. The dynamic range as well as the resonance frequency of the resonator can be reversibly controlled by electrothermal tuning using DC voltage. This paper presents experimental results on the resonance frequency, Q factor and dynamic range during the electrothermal tuning. As the input DC power increases, Q factor decreases due to the decrease in the resonance frequency, and SNR decreases due to the reduced amplitude or increased noise.
37th European Solid State Device Research Conference, 2007. ESSDERC; 10/2007
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ABSTRACT: Vertically aligned ZnO nanorods were grown on the substrate by sonication. Transmission electron microscopy, photoluminescence, and X-ray diffraction were performed for nanorods synthesized by sonication, which leads to formation of ZnO crystals. For field emission measurements, ZnO nanorods were used as cathode and a green phosphor coated ITO glass was used as anode, where cathode and anode plates were separated by a spacer of 270 mum. Therefore, due to the easy fabrication process and good field emission characteristics, these sonochemically synthesized ZnO nanorods can be regarded as one of key potential field emitters.
Vacuum Nanoelectronics Conference, 2007. IVNC. IEEE 20th International; 08/2007
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ABSTRACT: Carbon nanotubes (CNTs) are considered as promising candidates for transmission lines as well as microcircuit interconnects in future nanoscale electronic systems. Owing to the growing interest in the use of microwave signals, understanding the transmission properties at high frequencies is essential to assess the applicability of multi-walled carbon nanotubes (MWNTs). In this work, we measured two-port properties of individual MWNTs using a network analyser from a frequency of 0.5 to 50 GHz. The radio-frequency transmission parameters were obtained from the measured S-parameter data. Our results show the frequency dependence of the equivalent resistance of MWNTs, which decreases with increasing frequency. This confirms that metallic CNTs will be useful for transmitting GHz signals in nanoelectric devices.
Nanotechnology 05/2007; 18(25):255701. · 3.98 Impact Factor
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ABSTRACT: Metallic carbon nanotubes (CNTs) are promising as transmission lines or interconnects in radio-frequency nanoelec. circuits. This paper presents passive network properties of individual multi-walled carbon nanotubes (MWNTs) up to 110 GHz measured at room temp. From the S-parameter data, frequency-dependent elec. properties of the MWNT were extd. using an equiv. R-L-C circuit model. The ac impedance of the MWNT decreases significantly with increasing frequency, as predicted by earlier theor. work. In particular, the equiv. resistance decreases a few hundred times. Our findings show that MWNTs can carry high-frequency currents much better than dc. [on SciFinder (R)]
New Journal of Physics. 01/2007; 9:265-275.
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J. H. Lee,
S. H. Lee,
W. S. Kim,
H. J. Lee,
J. N. Heo,
T. W. Jeong,
C. W. Baik,
S. H. Park,
SeGi Yu,
J. B. Park,
Y. W. Jin, J. M. Kim,
J. W. Moon,
M. A. Yoo,
J. W. Nam,
S. H. Cho,
J. S. Ha,
T. I. Yoon,
J. H. Park,
D. H. Choe
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ABSTRACT: Electron emission current degradation is often observed from printed single wall carbon nanotube emitters during field emission process. After a highly imposed emission, structural deformation of emitters from thin crystalline nanotube bundle to thick amorphous-type carbon fiber was observed. This deformation seems to relate to the current degradation, deteriorating the efficiency of field emission either by increasing the resistance of emitters or by decreasing the field enhancement factor of emitter tips. Two possible mechanisms of structural deformation are internal structural transformation by Joule heating under excessively imposed emission current and continuous adsorption of carbon particles on actively working emitters.
Applied Physics Letters 12/2006; 89(25):253115-253115-3. · 3.84 Impact Factor
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ABSTRACT: Nanoelectromechanical (NEM) devices were developed for memory. The concept of a switch unit employing carbon nanotubes (CNT) was extended to random access memory (RAM). The unique vertical structure of these nanotubes allows a high integration density for devices. The easy fabrication process can give a high yield and reliability to device
Custom Integrated Circuits Conference, 2006. CICC '06. IEEE; 10/2006
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Taewon Jeong,
Jungna Heo,
Jeonghee Lee,
Sanghyun Park,
Yongwan Jin, J. M. Kim,
Taesik Oh,
Chongwyun Park,
Ji-Beom Yoo,
Byoungyun Gong,
Naesung Lee,
SeGi Yu
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ABSTRACT: Multiwalled carbon nanotube (MWNT) emitters fabricated by the metal intermediation process were studied. This was intended to allow strong adhesion and high electrical contact between the cathode electrode and MWNT emitters. The process was performed by hot-pressed bonding of a metal layer to a MWNT film surface, where the metal layer was deposited on a main substrate. Through this process, MWNTs have open and sharp ends, and the metal layer and the MWNTs have strong electrical contact. Together with unchanged crystallinity of MWNTs as before the process, these effects improve the field emission properties, resulting in 64% reduction of turn on field and two to three orders of magnitude increase of current density.
Journal of Applied Physics 10/2006; · 2.17 Impact Factor
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ABSTRACT: Recently, fully-implantable middle ear hearing devices (F-IMEHD) to enhance the hearing ability of auditory impaired persons have been developed in several countries. The implantable hearing device requires an external controller and a non-invasive power transmitter for recharging an internal battery of the device. This study shows the implementation of an inductively coupled control unit to be able to recharge the battery and transmit a control signal to the implanted device by designing the structure of coupled antennas and the data protocol using an on-off keying modulation. The implemented control unit has the advantages that it makes the implanted device reduce the power consumption and increase a recharging interval by externally supplying the power of a control signal receiver instead of using an internal battery. Through the experimental results, it has been verified that the implemented control unit has the performance of transmitting power and control signal to a F-IMEHD
Engineering in Medicine and Biology Society, 2005. IEEE-EMBS 2005. 27th Annual International Conference of the; 02/2006
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ABSTRACT: Various nano-devices based on vertical nanotubes were developed. Carbon nanotubes (CNTs) were employed as a functional part or a nano structure of a nanoelectromechanical (NEM) switch, nano-capacitor, and NEM-dynamic random access memory (DRAM). The unique vertical structure of nanotubes allows high integration density for devices.
Emerging Technologies - Nanoelectronics, 2006 IEEE Conference on; 02/2006
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ABSTRACT: A nanoelectromechanical (NEM) device developed for dynamic random access memory (DRAM) is reported. A vertical nanotube structure is employed to form the electromechanical switch and capacitor structure. The mechanical movement of the nanotube defines 'ON' and 'OFF' states and the electrical signals which result lead to charge storage in a vertical capacitor structure as in a traditional DRAM. The vertical structure contributes greatly to a decrease in cell dimension. The main concept of the NEM switch and capacitor can be applied to other memory devices as well
Electron Devices Meeting, 2005. IEDM Technical Digest. IEEE International; 01/2006
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Applied Physics Letters 01/2006; 89(26). · 3.84 Impact Factor
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ABSTRACT: We report the fabrication process and the electrical characteristics of a nanocapacitor structure using metal-insulator-carbon nanotube-metal layers. The structure shows high capacitance and the possibility of ultrahigh integration density due to the unique nanotube structure. Nanoscale and high-aspect-ratio patterns are achieved by electron beam lithography for the fabrication of these vertical nanostructures. This structure can be substituted for capacitors based on the silicon pillar structure in dynamic random access memory or as a nanoscale capacitor for various nanoelectronic devices.
Applied Physics Letters 12/2005; 87(26):263103-263103-3. · 3.84 Impact Factor
