bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated microfluidic chip for rapid DNA digestion and time-resolved capillary electrophoresis analysis
Authors: Lin Che-Hsin , Wang Yao-Nan , Fu Lung-Ming
Published: March 2012

An integrated microfluidic chip is proposed for rapid DNA digestion and time-resolved capillary electrophoresis (CE) analysis. The chip comprises two gel-filled chambers for DNA enrichment and purification, respectively, a T-form micromixer for DNA/restriction enzyme mixing, a serpentine channel for DNA digestion reaction, and a CE channel for on-line capillary electrophoresis analysis. The DNA and restriction enzyme are mixed electroomostically using a pinched-switching DC field. The experimental and numerical results show that a mixing performance of 97% is achieved within a distance of 1 mm from the T-junction when a driving voltage of 90 V/cm and a switching frequency of 4 Hz are applied. Successive mixing digestion and capillary electrophoresis operation clearly present the changes on digesting φx-174 DNA in different CE runs. The time-resolved electropherograms show that the proposed device enables a φx-174 DNA sample comprising 11 fragments to be concentrated and analyzed within 24 min. Overall, the results presented in this study show that the proposed microfluidic chip provides a rapid and effective tool for DNA digestion and CE analysis applications.
Dilute sulfuric acid hydrolysis of tropical region biomass
Authors: Hernández I. P. , Pérez-Pimienta José A. , Messina Sarah , Saldaña Durán Claudia E.
Published: March 2012

Although ethanol can be produced from a wide range of biomass materials, biomass, from the tropical region, like mango (skin or bagasse) is a crop residue readily available today as a non-conventional crop for the saccharification process that has had little attention. It has the benefits to be found in large quantities and in an industrial level is completely separated into its components with a free access for acid or enzymatic hydrolysis. These agro-industrial waste as well as other materials like sugarcane bagasse and pine wood are abundant enough, and in virtue of their high carbohydrate content hold tremendous potential for large-scale bioethanol production. The objective of this work is to develop a comparative analysis using dilute acid hydrolysis process between mango (skin and bagasse), sugarcane bagasse, and pine wood. The biomass was subjected to pretreatments like alkaline hydrolysis using calcium sulfate and sodium hydroxide, water immersion, and water autoclaved at 121 °C. Experimental results showed that the maximum percentages of sugar recovery were for sugarcane bagasse—56.62%, pine wood—82.36%, mango skin—97.37%, and mango bagasse—202.91%. From the tested biomass materials, only mango bagasse has a considerable fraction of already digestible sugar that does not undergo a pretreatment + hydrolysis process.
Studying enzymatic bioreactions in a millisecond microfluidic flow mixer
Authors: Buchegger Wolfgang , Haller Anna , van den Driesche Sander , Kraft Martin , Lendl Bernhard , Vellekoop Michael
Published: March 2012

In this study, the pre-steady state development of enzymatic bioreactions using a microfluidic mixer is presented. To follow such reactions fast mixing of reagents (enzyme and substrate) is crucial. By using a highly efficient passive micromixer based on multilaminar flow, mixing times in the low millisecond range are reached. Four lamination layers in a shallow channel reduce the diffusion lengths to a few micrometers only, enabling very fast mixing. This was proven by confocal fluorescence measurements in the channel’s cross sectional area. Adjusting the overall flow rate in the 200 μm wide and 900 μm long mixing and observation channel makes it possible to investigate enzyme reactions over several seconds. Further, the device enables changing the enzyme/substrate ratio from 1:1 up to 3:1, while still providing high mixing efficiency, as shown for the enzymatic hydrolysis using β-galactosidase. This way, the early kinetics of the enzyme reaction at multiple enzyme/substrate concentrations can be collected in a very short time (minutes). The fast and easy handling of the mixing device makes it a very powerful and convenient instrument for millisecond temporal analysis of bioreactions.
Direction dependence of displacement time for two-fluid electroosmotic flow
Authors: Lim Chun Yee , Lam Yee Cheong
Published: March 2012

Electroosmotic flow that involves one fluid displacing another fluid is commonly encountered in various microfludic applications and experiments, for example, current monitoring technique to determine zeta potential of microchannel. There is experimentally observed anomaly in such flow, namely, the displacement time is flow direction dependent, i.e., it depends if it is a high concentration fluid displacing a low concentration fluid, or vice versa. Thus, this investigation focuses on the displacement flow of two fluids with various concentration differences. The displacement time was determined experimentally with current monitoring method. It is concluded that the time required for a high concentration solution to displace a low concentration solution is smaller than the time required for a low concentration solution to displace a high concentration solution. The percentage displacement time difference increases with increasing concentration difference and independent of the length or width of the channel and the voltage applied. Hitherto, no theoretical analysis or numerical simulation has been conducted to explain this phenomenon. A numerical model based on finite element method was developed to explain the experimental observations. Simulations showed that the velocity profile and ion distribution deviate significantly from a single fluid electroosmotic flow. The distortion of ion distribution near the electrical double layer is responsible for the displacement time difference for the two different flow directions. The trends obtained from simulations agree with the experimental findings.
Numerical study of dc-biased ac-electrokinetic flow over symmetrical electrodes
Authors: Yang Ng Wee , Ramos Antonio , Cheong Lam Yee , Rodriguez Isabel
Published: March 2012

This paper presents a numerical study of DC-biased AC-electrokinetic (DC-biased ACEK) flow over a pair of symmetrical electrodes. The flow mechanism is based on a transverse conductivity gradient created through incipient Faradaic reactions occurring at the electrodes when a DC-bias is applied. The DC biased AC electric field acting on this gradient generates a fluid flow in the form of vortexes. To understand more in depth the DC-biased ACEK flow mechanism, a phenomenological model is developed to study the effects of voltage, conductivity ratio, channel width, depth, and aspect ratio on the induced flow characteristics. It was found that flow velocity on the order of mm/s can be produced at higher voltage and conductivity ratio. Such rapid flow velocity is one of the highest reported in microsystems technology using electrokinetics.
Investigation on CO2 laser irradiation inducing glass strip peeling for microchannel formation
Authors: Wang Z. K. , Zheng H. Y.
Published: March 2012

The study investigates the use of CO2 laser to induce glass strip peeling off to form microchannels on soda lime gass substrate. The strip peeling exhibits a strong dependence on the energy deposition rate on the glass surface. In spite of the vast difference in the combination of laser power and scanning speed, when the ratio of the two makes the energy deposition rate in the range 3.0-6.0 J/(cm2 s), the temperature rising inside glass will be above the strain point and reach the softening region of the glass. As a result, glass strip peeling is able to occur and form microchannels with dimensions of 20-40 μm in depth and 200-280 μm in width on the glass surface. Beyond this range, higher energy depsotion rate would lead to surface melting associated with solidification cracks and lower energy deposition rate causes the generation of fragment cracks.
Cell separation and transportation between two miscible fluid streams using ultrasound
Authors: Liu Yang , Hartono Deny , Lim Kian-Meng
Published: March 2012

This paper presents a two-stream microfluidic system for transporting cells or micro-sized particles from one fluid stream to another by acoustophoresis. The two fluid streams, one being the original suspension and the other being the destination fluid, flow parallel to each other in a microchannel. Using a half-wave acoustic standing wave across the channel width, cells or particles with positive acoustic contrast factors are moved to the destination fluid where the pressure nodal line lies. By controlling the relative flow rate of the two fluid streams, the pressure nodal line can be maintained at a specific offset from the fluid interface within the destination fluid. Using this transportation method, particles or cells of different sizes and mechanical properties can be separated. The cells experiencing a larger acoustic radiation force are separated and transported from the original suspension to the destination fluid stream. The other particles or cells experiencing a smaller acoustic radiation force continue flowing in the original solution. Experiments were conducted to demonstrate the effective separation of polystyrene microbeads of different sizes (3 μm and 10 μm) and waterborne parasites (Giardia lamblia and Cryptosporidium parvum). Diffusion occurs between the two miscible fluids, but it was found to have little effects on the transport and separation process, even when the two fluids have different density and speed of sound.
Rapid and cost-effective fabrication of selectively permeable calcium-alginate microfluidic device using “modified” embedded template method
Authors: Asthana Amit , Ho Lee Kwang , Kim Kyeong-Ohn , Kim Dong-Myung , Kim Dong-Pyo
Published: March 2012

In this paper, we have presented a non-lithographic embedded template method for rapid and cost-effective fabrication of a selectively permeable calcium-alginate (Ca-alginate) based microfluidic device with long serpentine delay channel. To demonstrate the versatility of the presented method, we have demonstrated two different strategies to fabricate serpentine long delay channels without using any sophisticated microfabrication techniques, in formal lab atmosphere. The procedure presented here, also, enables the preparation of a multilayered microfluidic device with channels of varying dimensions, in a single device without using any sophisticated micromachining instrumentation. In addition, we have also qualitatively studied the diffusion of small and large molecules from a Ca-alginate based microfluidic device and proposed a method to effectively control the out-flow of macro biomolecules from the crosslinked Ca-alginate matrix to create a selectively permeable matrix required for various biological and biomimetic applications, as mentioned in the Introduction section of this work.
Electrowetting on dielectric driven droplet resonance and mixing enhancement in parallel-plate configuration
Authors: Lee Chiun-Peng , Chen Hsin-Chien , Lai Mei-Feng
Published: March 2012

This study experimentally verifies that the mixing process in a droplet can be enhanced by driving the droplet at resonant frequencies and at alternating driving frequencies using a parallel-plate electrowetting on dielectric device. The mixing time, which is defined as the time required for reaching the well-mixed state, in a resonant droplet is found to be significantly shorter than that in a non-resonant droplet. Besides, it is also found that a higher driving potential leads to a better mixing effect, especially at resonant frequencies. Furthermore, when a droplet is driven by alternating two driving frequencies, especially two resonant frequencies, the mixing efficiency is found to be significantly enhanced for a specific alternating duration of these two frequencies.
Focused ion beam milling of microchannels in lithium niobate
Authors: Sridhar Manoj , Maurya Devendra K. , Friend James R. , Yeo Leslie Y.
Published: March 2012

We present experimental and simulation results for focused ion beam (FIB) milling of microchannels in lithium niobate in this paper. We investigate two different cuts of lithium niobate, Y- and Z-cuts, and observe that the experimental material removal rate in the FIB for both Y-cut and Z-cut samples was 0.3 μm3/nC, roughly two times greater than the material removal rate previously reported in the literature but in good agreement with the value we obtain from stopping and range of ions in matter (SRIM) simulations. Further, we investigate the FIB milling rate and resultant cross-sectional profile of microchannels at various ion beam currents and find that the milling rate decreases as a function of ion dose and correspondingly, the cross-sectional profiles change from rectangular to V-shaped. This indicates that material redeposition plays an important role at high ion dose or equivalently, high aspect ratio. We find that the experimental material removal rate decreases as a function of aspect ratio of the milled structures, in good agreement with our simulation results at low aspect ratio and in good agreement with the material removal rates previously reported in the literature at high aspect ratios. Our results show that it is indeed easier than previously assumed to fabricate nanochannels with low aspect ratio directly on lithium niobate using the FIB milling technique.
Characteristic analysis and comparison of axial flux machines according to magnetization pattern for 500 W-class wind power generator application
Authors: Park Yu-Seop , Jang Seok-Myeong , Ko Kyoung-Jin , Choi Jang-Young , Sung So-Young
Published: March 2012

This paper presents the electromagnetic characteristic analysis of axial flux machines applied to 500(W) class wind power generators. For the dramatic analysis time reduction, analytical method is applied, and comparative analysis is performed according to magnetization patterns of permanent magnets. Due to their structural features, quasi 3-dimensional analysis is employed, and correction function is introduced to consider the flux leakage of the machines. The analysis results are compared with the results by finite element method and experiment to validate the suggested method performed in this paper showing high reliability.
AC-dielectrophoretic characterization and separation of submicron and micron particles using sidewall AgPDMS electrodes
Authors: Lewpiriyawong Nuttawut , Yang Chun
Published: March 2012

The recent development of microfluidic “lab on a chip” devices requires the need to continuously separate submicron particles. Here, we present a PDMS microfluidic device with sidewall conducting PDMS (AgPDMS) composite electrodes capable of separating submicron particles in hydrodynamic flow. In particular, the device can service dual functions. First, the AgPDMS composite electrodes embedded in a sidewall of the device channel allow for performing AC-dielectrophoretic (DEP) characterization through direct microscopic observation of particle behavior. Characterization experiments are carried out for numerous parameters including particle size, medium conductivity, and AC field frequency to reveal important dielectrophoresis DEP information in terms of the crossover frequency and positive/negative DEP behavior under specific frequencies. Second, the device offers an advantage that sidewall AgPDMS composite electrodes can produce strong DEP effects throughout the entire channel height, and thus the robustness of the on-chip particle separation is demonstrated for continuous separation in a flowing mixture of 0.5 and 5 μm particles with 100% separation efficiency.
Impact of high temperature annealing on La diffusion and flatband voltage (Vfb) modulation in TiN/LaOx/HfSiON/SiON/Si gate stacks
Authors: Boujamaa R. , Baudot S. , Rochat N. , Pantel R. , Martinez E. , Renault O. , Detlefs B. , Zegenhagen J. , Loup V. , Martin F. , Gros-Jean M. , Bertin F. , Dubourdieu C.
Published: March 2012

We present a detailed analysis of the impact of high temperature annealing on the chemical and electronic properties of TiN/HfSixOyNz/SiOxNy/Si gate stacks, where an ultra-thin LaOx capping layer (0.4–1 nm) is inserted between the TiN metal gate and the HfSixOyNz dielectric. From our experimental results, we demonstrate that La atoms diffuse through the entire nitrided hafnium silicate and reach the SiOxNy interfacial layer to form a La-silicate. In addition, hard x-ray photoelectron spectroscopy analysis highlights the band alignments’ shift of the gate stacks, which is well related to Vfb shifts based on an interfacial dipole and/or fixed charges model. Finally, this study reveals that the Vfb roll-off phenomenon is amplified with an increasing amount of La atoms near the substrate interface. A correlation between LaOx thickness and interface trap density (Dit) is observed, and a mechanism explaining the roll-off behavior is proposed.
Manipulating liquid plugs in microchannel with controllable air vents
Authors: Liu Hao-Bing , Ting Eng Kiat , Gong Hai-Qing
Published: March 2012

An air venting element on microchannel, which can be controlled externally and automatically, was demonstrated for manipulating liquid plugs in microfluidic systems. The element’s open and closed statuses correspond to the positioning and movement of a liquid plug in the microchannel. Positioning of multiple liquid plugs at an air venting element enabled the merging and mixing of the plugs. Besides these basic functions, other modes of liquid plug manipulations including plug partitioning, multiple plug mixing, and spacing adjustment between liquid plugs, were realized using combination of multiple elements. The structure, operation, and some functions of the element were demonstrated with a microfluidic chip application. The performances of the element including its failure modes, threshold flow rate, and structural optimization were also discussed.
Electromagnetic characteristics of surface modified iron nanowires at x-band frequencies
Authors: Liang W. F. , Yang R. B. , Lin W. S. , Jian Z. J. , Tsay C. Y. , Wu S. H. , Lin H. M. , Choi S. T. , Lin C. K.
Published: March 2012

Surface modified iron nanowire nanoparticles were prepared via reduction of iron salts (FeCl3·6H2O) under an applied magnetic field. To minimize the surface oxidation, dextran (0.05 and 0.25 wt. %) was added during the process and formed a thin passive layer over iron nanowires with alcohol and acetone used to wash iron nanowires. The complex permittivity (ɛ′-jɛ′′) and permeability (μ′-jμ″) of absorbers are measured by a cavity perturbation method from 7 to 14 GHz. In the present study, the iron nanowire prepared with 0.25 wt. % dextran and washed by acetone (D25AC) exhibited the best microwave absorption performance. Depending on the test frequency, D25AC possessed the largest permittivity loss ranged from 0.14 to 0.17 and relatively small permeability loss (<0.05). Its high permittivity dissipation is responsible for the excellent microwave absorption performance where the reflection loss was-7.7 dB at a matching frequency of 9.0 GHz.
Room temperature magnetoresistance in CoFeB/SrTiO3/CoFeB magnetic tunnel junctions deposited by ion beam sputtering
Authors: Hassen E. M. J. , Viala B. , Cyrille M. C. , Cartier M. , Redon O. , Lima P. , Belhadji B. , Yang H. X. , Velev J. , Chshiev M.
Published: March 2012

Room temperature transport properties are reported in polycrystalline SrTiO3-based magnetic tunnel junctions deposited by ion beam sputtering. The junctions comprise CoFeB electrodes and the SrTiO3 barrier with thickness varied between 0.9 and 1.9 nm. Resistance area product values between 3 Ω.μm2 and 22 kΩ.μm2 have been measured with a tunnel magnetoresistance ratio ranging from 3.1 to 13% at room temperature. At low barrier thickness (1.2 nm), ferromagnetic coupling between electrodes is observed, indicating the presence of defects in the structure. A post-oxidation step was found to improve transport properties at lower barrier thickness.
Effects of heat treatment and contact resistance on the thermal conductivity of individual multiwalled carbon nanotubes using a Wollaston wire thermal probe
Authors: Bifano Michael F. P. , Park Jungkyu , Kaul Pankaj B. , Roy Ajit K. , Prakash Vikas
Published: March 2012

Thermal conductivity measurements in commercially available, chemical vapor deposition–grown, heat-treated and non-heat-treated multiwalled carbon nanotubes (MWCNTs) are reported. The thermal conductivity of individual samples is measured using a suspended platinum wire as a thermal resistance probe in a “T-type” configuration. Changes in third harmonic voltage are measured across the heated suspended platinum wire as a specimen is attached to the platinum wire’s midpoint. An analytic model is used to correlate the reduction in the average temperature of the probe wire to the thermal resistance (and thermal conductivity) of the attached sample. Experiments are implemented inside a scanning electron microscope equipped with nanomanipulators for sample selection, and a gas injection system for platinum based electron beam-induced deposition to improve thermal contact resistances. The results indicate a nearly 5-fold increase in the average thermal conductivity of MWCNT samples annealed with a 20-h 3000 °C annealing heat treatment compared to the as-grown samples. However, specimen-specific morphological defects, such as kinking, Y-branches, etc., are found to negate, to a large degree, the advantage of the heat treatment process. The thermal contact resistance between the MWCNT and the electron beam–induced deposition contacts is estimated using an anisotropic diffusive mismatch model that includes the effect of fin resistance. Adjusting the thermal conductivity to include the effect of thermal contact resistance is found to increase the thermal conductivity by approximately 5%. Once adjusted for thermal contact resistance, the average thermal conductivity of the heat-treated MWCNT specimens is 228 W/m-K, with the highest measured thermal conductivity being 765 ± 150 W/m-K. The results highlight the importance of MWCNT quality in thermal management applications.
Solar adsorption cooling system: An overview
Authors: Mahesh A. , Kaushik S. C.
Published: March 2012

In this paper, a review of the performance and development of various solar powered adsorption refrigeration systems is presented here. The review covers the current state of theoretical study, choice of adsorbent-adsorbate, experimental performance study, and further scope of research in adsorption cooling system. Finally, detailed summary and suggestions are outlined for proper utilization of thermally operated adsorption refrigeration technologies.
Studies of spectral modification and limitations of the modified paraxial equation in laser wakefield simulations
Authors: Zhu W. , Palastro J. P. , Antonsen T. M.
Published: March 2012

Laser pulses propagating through plasma undergo spectral broadening through local energy exchange with driven plasma waves. For propagation distances on the order of the energy depletion length, spectral shifts can be comparable to the laser central frequency and wavenumber, a result of approximate action conservation. Here, we examine the local spectral shift, energy depletion, and action conservation of nonlinear laser pulses using the modified paraxial simulation code WAKE. Breakdown of the modified paraxial equation (MPE), which is based on the assumption of slow temporal variation of the pulse envelope, is monitored via consideration of the wave action. Although action is theoretically conserved for the continuous MPE, we observe that for large red shifts, action decays for the discrete implementation. Numerical analysis of the propagation algorithm verified the observed behavior. Increasing resolution improves action conservation up to a time, which is identified to be the validity limit for the MPE. Increased resolution also leads to increased simulation times and eliminates the strength of the MPE solver–efficiency.
Structural, electrical, and terahertz transmission properties of VO2 thin films grown on c-, r-, and m-plane sapphire substrates
Authors: Zhao Yong , Hwan Lee Joon , Zhu Yanhan , Nazari M. , Chen Changhong , Wang Haiyan , Bernussi Ayrton , Holtz Mark , Fan Zhaoyang
Published: March 2012

The structure, metal-insulator transition (MIT), and related Terahertz (THz) transmission characteristics of VO2 thin films obtained by sputtering deposition on c-, r-, and m-plane sapphire substrates were investigated by different techniques. On c-sapphire, monoclinic VO2 films were characterized to be epitaxial films with triple domain structure caused by β-angle mismatch. Monoclinic VO2 β angle of 122.2° and the two angles of V4+–V4+ chain deviating from the am axis of 4.4° and 4.3° are determined. On r-sapphire, tetragonal VO2 was determined to be epitaxially deposited with VO2 (011)T perpendicular to the growth direction, while the structural phase transformation into lower symmetric monoclinic phase results in (2¯11) and (200) orientations forming a twinned structure. VO2 on m-sapphire has several growth orientations, related with the uneven substrate surface and possible inter-diffusion between film and substrate. Measurements of the electrical properties show that the sample on r-sapphire has MIT property superior to the other two samples, with a resistivity change as large as 9 × 104 times and a transition window as narrow as 3.9 K, and it has the highest resistivity with the lowest free carrier density in the insulating phase. THz transmission measurements on VO2 films grown on r-plane sapphire substrates revealed intensity modulation depth as large as 98% over a broadband THz region, suggesting that VO2 films are ideal material candidates for THz modulation applications.
A quantum dipole–modified work function for a simplified electron emission barrier
Authors: Jensen Kevin L.
Published: March 2012

Changes in electron density near the surface of a metal gives rise to the largest part of its work function, but a small contribution arises from the penetration of electrons into the classically forbidden region and the dipole component which results. An analytic model of the dipole term is difficult for the image charge potential, but it is shown, first, that a slab plus triangular barrier (STB) potential has a straightforward solution and, second, that it fits well with a general “shape factor” method to find the transmission probability (and, from it, the current density). The shape factors for rectangular, triangular, quadratic, STB, and image charge potentials are compared: it is shown that, just as the STB potential is intermediate between the rectangular and triangular potentials, the image charge potential is intermediate between the triangular and quadratic potentials. The evaluation of parameters needed for a general thermal-field-photoemission equation is demonstrated. Finally, the STB model enables a shifted electron density representation that is useful to estimate the increasing dipole component to the work function and the corresponding decrease in current density for high fields. Modifications to treat semiconductors are briefly described.
Impact of plasma noise on a direct thrust measurement system
Authors: Pottinger S. J. , Lamprou D. , Knoll A. K. , Lappas V. J.
Published: March 2012

In order to evaluate the accuracy and sensitivity of a pendulum-type thrust measurement system, a linear variable differential transformer (LVDT) and a laser optical displacement sensor have been used simultaneously to determine the displacement resulting from an applied thrust. The LVDT sensor uses an analog interface, whereas the laser sensor uses a digital interface to communicate the displacement readings to the data acquisition equipment. The data collected by both sensors show good agreement for static mass calibrations and validation with a cold gas thruster. However, the data obtained using the LVDT deviate significantly from that of the laser sensor when operating two varieties of plasma thrusters: a radio frequency (RF) driven plasma thruster, and a DC powered plasma thruster. Results establish that even with appropriate shielding and signal filtering the LVDT sensor is subject to plasma noise and radio frequency interactions which result in anomalous thrust readings. Experimental data show that the thrust determined using the LVDT system in a direct current plasma environment and a RF discharge is approximately a factor of three higher than the thrust values obtained using a laser sensor system for the operating conditions investigated. These findings are of significance to the electric propulsion community as LVDT sensors are often utilized in thrust measurement systems and accurate thrust measurement and the reproducibility of thrust data is key to analyzing thruster performance. Methods are proposed to evaluate system susceptibility to plasma noise and an effective filtering scheme presented for DC discharges.
Synchronization of parallel-connected spin-transfer oscillators via magnetic feedback
Authors: Xu Jian-qing , Jin Guojun
Published: March 2012

We propose an array of spin-transfer oscillators (STOs) to be parallel-connected and synchronized via magnetic feedback. Based on numerically solving the Landau-Lifshitz-Gilbert-Slonczewski equation and theoretically analyzing the Kuramoto model, the cooperative dynamics of these STOs is studied in detail and the optimal orientation of magnetic feedback is determined. It is found that a large locked bandwidth can be obtained by simply increasing the number of coupled STOs and modulating the total phase shift of feedback signals. Specifically, for ten parallel-connected STOs, the locked bandwidth can be 12 times larger than that obtained from the serially connected STOs.
Europium location in the AlN: Eu green phosphor prepared by a gas-reduction-nitridation route
Authors: Yin Liang-Jun , Zhu Qiang-Qiang , Yu Wei , Hao Lu-Yuan , Xu Xin , Hu Feng-Chun , Lee Ming-Hsien
Published: March 2012

Eu doped aluminum nitride phosphors were successfully synthesized by a novel gas-reduction-nitridation route with a reaction temperature of 1400 °C and a soaking time of 3 h. The obtained AlN:Eu phosphors were analyzed to elucidate the location of the Eu luminescent center. High-resolution transmission electron microscopy and transmission electron microscopy-energy dispersive spectra proved that Eu was located in the crystal lattice of AlN, then EXAFS revealed that Eu occupied a highly distorted Al site coordinated by four nitrogen at about 2.30–2.40 Å, and the second nearest neighbors of Eu were 12 Al. This could be confirmed by the first-principles calculations based on the obtained local structure around the Eu luminescence center, where the theoretical absorption spectrum was similar to the experimental excitation spectrum. X-ray appearance near edge structure showed that Eu existed in terms of both Eu3+ and Eu2+ ions, which could be related to the limited location space of Eu. High temperature treatment could significantly increase the amount of Eu2+ by the expansion of the crystal lattice, leading to an increased green luminescence of the obtained AlN:Eu phosphors.
Contacts shielding in nanowire field effect transistors
Authors: Pitanti Alessandro , Roddaro Stefano , Vitiello Miriam S. , Tredicucci Alessandro
Published: March 2012

Conductive metallic contacts can significantly affect the operation of field effect transistors fabricated starting from semiconductor nanowires deposited on a dielectric substrate. Screening effects can also lead to systematic errors in the estimates of transport parameters obtained on the basis of simple uniform capacitive models. We study the role of contacts in both back- and lateral-gate transistor geometries and provide rules of thumbs to predict screening effects in real devices. Additionally, we show how the contacts influence charge density profiles within the wire, focusing in particular on their evolution when transistors nonlinear properties are addressed.
Radiation interaction with tilt grain boundaries in β-SiC
Authors: Swaminathan Narasimhan , Wojdyr Marcin , Morgan Dane D. , Szlufarska Izabela
Published: March 2012

Interaction between grain boundaries and radiation is studied in 3C-SiC by conducting molecular dynamics cascade simulations on bicrystal samples with different misorientation angles. The damage in the in-grain regions was found to be unaffected by the grain boundary type and is comparable to damage in single crystal SiC. Radiation-induced chemical disorder in the grain boundary regions is quantified using the homonuclear to heteronuclear bond ratio (χ). We found that χ increases nearly monotonically with the misorientation angle, which behavior has been attributed to the decreasing distance between the grain boundary dislocation cores with an increasing misorientation angle. The change in the chemical disorder due to irradiation was found to be independent of the type of the grain boundary.
Threading dislocation-governed degradation in crystal quality of heteroepitaxial materials: The case of InAlN nearly lattice-matched to GaN
Authors: Chen Z. T. , Fujita K. , Ichikawa J. , Egawa T.
Published: March 2012

The crystal qualities of InAlN nearly lattice-matched (LM) to GaN with different thicknesses have been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the crystal quality of InAlN starts to degrade when the InAlN thickness exceeds several hundred nanometers, forming a structure consisting of two sub-layers with one sub-layer coherent to GaN and the other being degraded. Moreover, the degradation was found to be governed by the threading dislocations (TDs) propagation from the underlying GaN layer, rather than by the misfit strain between InAlN and GaN. Based on TEM observations, the growth evolution of the two-sub-layer structure is proposed, which is different from those conventional mechanisms of crystal-quality degradation in heteroepitaxial material. The results of InAlN nearly LM to GaN are suggested to be helpful in understanding the growths of lattice-mismatched systems of other In-contained III-nitrides, including InGaN/GaN.
Shell models of two-dimensional Coulomb crystals: Assessment and comparison with the three-dimensional case
Authors: Cioslowski Jerzy , Albin Joanna
Published: March 2012

Three shell models, differing in accuracy and computational cost, are formulated for two-dimensional Coulomb crystals. Offering a new means of predicting and analyzing properties of these species, the new models also provide new insights into their previously derived three-dimensional counterparts. In particular, analysis of the individual components of the energy error points out to the neglect of the positional relaxation as the main source of the differences between the approximate and exact energies. Within the realm of shell models, the two-dimensional case turns out to be somewhat more challenging than the three-dimensional one. Due to the lack of exact closed-form expressions for the optimal shell radii, it is computationally more expensive and the energy predictions at the same level of approximation are less accurate (as indicated by the maximum relative energy error of 0.15% vs. that of 0.03% found for spherical Coulomb crystals).
An ac electroosmosis device for the detection of bioparticles with piezoresistive microcantilever sensors
Authors: Arefin Md Shamsul , Porter Timothy L.
Published: March 2012

This work reports on the behavior of piezoresistive microcantilever sensors under optimizing conditions of ac electroosmotic enhancement. Piezoresistive microcantilevers are used as sensor elements for detection of concentrated bio-particles. Without preconcentrating the samples, using ac electroosmosis, these bio-particles have been manipulated onto the piezoresistive microcantilever. A piezoresistive microcantilever senses the dimensional changes upon particle exposure as a resistance change. This paper represents the integration of ac electroosmosis with a piezoresistive micro-cantilever sensor for the detection of bio-particles. A working prototype is presented here, and the experiments are conducted on Herpes Simplex type-1 virus (HSV-1) and Escherichia Coli (E. coli) bacteria.
An analysis of Mn-Zn ferrite microstructure by impedance spectroscopy, scanning transmission electron microscopy and energy dispersion spectrometry characterizations
Authors: Loyau V. , Wang G.-Y. , Bue M. Lo , Mazaleyrat F.
Published: March 2012

AC (alternative current) resistivity measurement results on Mn-Zn sintered ferrite were analyzed in the 0.1–500 MHz range. From electrical point of view, the material could be represented by an equivalent circuit of parallel resistance-capacitance cells connected in series corresponding to the contributions from bulk grains in one hand, and grain boundary layers in the other hand. The experimental resistivity curves were fitted with the model. The as obtained parameters give information on dielectric properties and conductivity of both bulk grains and boundary layers. For the studied material, it appears that the resistivity at low frequencies is increased 27 times due to the boundary layers effects. Scanning transmission electron microscopy and energy dispersion spectrometry characterization where performed in order to detect impurities at a grain boundary layer which can explain those wide differences between bulk grains and boundary layers electrical properties. It appears that the two components have close chemical compositions, but some calcium impurities segregate at the boundary which increases dramatically the resistivity of these layers. Furthermore, the bulk grains show relative permittivity around 350 at low frequency which is much smaller than the one measured for the whole material which is in the 50,000–100,000 range. This giant-dielectric behavior can be explained by an internal barrier layer at the grain boundaries. At last, the components of classical eddy current losses including losses due to ohmic effects and (true) dielectric losses on both bulk grain and boundary layers are distinguished.
SixSb2Te materials with stable phase for phase change random access memory applications
Authors: Gu Yifeng , Song Sannian , Song Zhitang , Cheng Yan , Du Xiaofeng , Liu Bo , Feng Songlin
Published: March 2012

The physical and electrical properties of SixSb2Te system materials with various Si contents have been systemically studied with the aim of finding the most suitable composition for the phase change random access memory (PCRAM) applications. SixSb2Te shows better thermal stability than Ge2Sb2Te5 due to no Te separation under high annealing temperatures. The increase of Si content can enhance the data retention ability of SixSb2Te materials. When the value of x is larger than 0.44, the 10-year data retention temperature for SixSb2Te will exceed 110 °C, which meets the long-term data retention requirement. Furthermore, Si-rich SixSb2Te materials exhibit the improvement on thickness change after annealing compared with Ge2Sb2Te5. In addition, the PCRAM devices based on SixSb2Te (x = 0.31, 0.44) were fabricated and the electrical operations were carried out. Both of them show the outstanding performances with long-term operations.
Component analysis of a mixed beam generated by vacuum electrospray of an ionic liquid
Authors: Fujiwara Yukio , Saito Naoaki , Nonaka Hidehiko , Ichimura Shingo
Published: March 2012

Vacuum electrospray of a quaternary ammonium ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl) amide (DEME-TFSA), was investigated to develop a primary ion source for secondary ion mass spectrometry (SIMS). Since the ionic liquid contains many methyl and ethyl groups as well as protons, its beam is expected to efficiently produce protonated molecules for SIMS analysis of organic materials. Experimental results showed that the beam consisted of charged particles of m/z about 1000 and charged droplets of m/z > 105. The current components of both the charged particles and droplets changed with the applied voltage and the flow rate of the ionic liquid. With decreasing flow rate, the current component of the charged droplets increased, whereas that of the charged particles decreased. The m/z values of the charged droplets diminished with decreasing flow rate and increasing capillary voltage. In addition to masses and charge numbers, the numbers of the charged droplets and the charged particles were estimated.
Depairing current density in superconducting film with shear deformation
Authors: Yong Huadong , Zhou Youhe
Published: March 2012

In this work, the influence of the shear deformation on the depairing current density in superconducting film is analyzed theoretically. The modified effective free energy is proposed by relating the dependence of the order parameter on the shear deformation. Based on the elastic theory, it is assumed that the coupling energy is the sum of volume change energy and shear strain energy. We obtain the complex deformation dependence of the depairing current density. The results reveal that the shear deformation plays an important role in degrading the current density.
The dispersive behavior of collective excitations in fluids: An experimental test for the generalized collective modes theory
Authors: Bencivenga F. , Cunsolo A.
Published: March 2012

The predictions of the generalized collective modes (GCM) theory on the non-hydrodynamic dispersion of collective excitations of liquids and supercritical fluids have been tested against previous inelastic x-ray scattering measurements on samples of increasing complexity. We observed a good agreement between experimental results and theoretical predictions within the hypothesis that sound propagation is adiabatic. Overall, the performed comparison provides an experimental validation of GCM predictions and shows that, even in the transition region between the hydrodynamic and the mesoscopic regimes, thermal fluctuations have a minor influence on the dispersion, whose non-hydrodynamic effects are mostly driven by viscoelastic phenomena.
Note: Particle transport through deformable pore geometries
Authors: Ghosh Pulak K. , Marchesoni Fabio
Published: March 2012

What pore geometries work best: Sharp or smooth? This is a key question in the design of a variety of artificial nanodevices. Numerical simulation indicates that Brownian diffusion along a corrugated channel of assigned cross section is larger for cusp-like pores.
Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering thermometry using a narrowband time-asymmetric probe pulse
Authors: Stauffer Hans U. , Miller Joseph D. , Roy Sukesh , Gord James R. , Meyer Terrence R.
Published: March 2012

A narrowband, time-asymmetric probe pulse is introduced into the hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering (fs/ps RCARS) technique to provide accurate and precise single-shot, high-repetition-rate gas-phase thermometric measurements. This narrowband pulse—generated by inserting a Fabry-Pérot étalon into the probe-pulse beam path—enables frequency-domain detection of pure-rotational transitions. The unique time-asymmetric nature of this pulse, in turn, allows for detection of resonant Raman-active rotational transitions free of signal contamination by nonresonant four-wave-mixing processes while still allowing detection at short probe-pulse delays, where collisional dephasing processes are negligible. We demonstrate that this approach provides excellent single-shot thermometric accuracy (<1% error) and precision (∼2.5%) in gas-phase environments.
Global classical large solutions to a 1D fluid-particle interaction model: The bubbling regime
Authors: Fang Daoyuan , Zi Ruizhao , Zhang Ting
Published: March 2012

This paper is concerned with the 1D fluid-particle interaction model in the so-called bubbling regime which describes the evolution of particles dispersed in a viscous compressible fluid. The model under investigation is described by the conservation of fluid mass, the balance of momentum and the balance of particle density. We obtained the global existence and uniqueness of the classical large solution to this model with the initial fluid density ρ0 admitting vacuum.
Modulation of electromagnic waves by alternating currents through left-handed ferromagnetic microwires
Authors: García-Miquel H. , Carbonell J. , Sánchez-Dehesa J.
Published: March 2012

We present experimental results of electromagnetic wave modulation by the application of AC currents along a ferromagnetic microwire at the frequency range where left-handed transmission is observed. It is demonstrated that transmitted microwave signals through a waveguide mount are modulated by the current applied to the wire. From the measurements, we have extracted information about the magnetic susceptibility behavior of the microwires.
The domain formation in Fe/Ni/Fe nanoscale magnetic antidot arrays
Authors: Cheng Ruihua , Rosenberg A. , McIlroy D. N. , Holman Z. , Zhang D. , Kranov Y.
Published: March 2012

In this paper we report the superconducting quantum interference device (SQUID) and magnetic force microscope (MFM) measurements of magnetic multilayer nanoscale antidot samples. The systems used consist of Fe(60 Å)/Ni(90 Å)/Fe(60 Å) (FeNiFe) multilayer antidots with hexagonal lattice fabricated on nanochannel glass (NCG) substrates with antidot diameters of 260, 362, 530, and 800 nm. The results indicate that the domain structure is commensurate with the holes due to the pinning effect of the antidots. This pinning effect is inversely proportional to the diameter of the antidots. The field dependent MFM data show that the hexagonal antidot lattice induces a weak anisotropy with the magnetic easy axis along the nearest neighbor direction. The unit cell in the antidot arrays could be used for data storage.
Improving the quality factor of cantilevers in viscous fluids by the adaptation of their interface
Authors: Linden J. , Oesterschulze E.
Published: March 2012

The adaptation of the fluid-microresonator interface enables the operation of cantilevers with high quality factor in viscous fluids. Partial wetting was proposed to implement the adapted interface by meniscus formation. An excellent quality factor of 79 was achieved in water applying the concept of partial wetting to thin film silicon nitride cantilevers. Compared to the quality factor calculated from Sader’s theory of the hydrodynamic damping of fully immersed cantilevers, this is an improvement by more than one decade. As a first application the partially wetted cantilevers were employed as mass sensors in water revealing a sensitivity of 2.77 fg/Hz.
Low temperature laser scanning microscopy of a superconducting radio-frequency cavity
Authors: Ciovati G. , Anlage Steven M. , Baldwin C. , Cheng G. , Flood R. , Jordan K. , Kneisel P. , Morrone M. , Nemes G. , Turlington L. , Wang H. , Wilson K. , Zhang S.
Published: March 2012

An apparatus was developed to obtain, for the first time, 2D maps of the surface resistance of the inner surface of an operating superconducting radio-frequency niobium cavity by a low-temperature laser scanning microscopy technique. This allows identifying non-uniformities of the surface resistance with a spatial resolution of about 2.4 mm and surface resistance resolution of ∼1 μΩ at 3.3 GHz. A signal-to-noise ratio of about 10 dB was obtained with 240 mW laser power and 1 Hz modulation frequency. The various components of the apparatus, the experimental procedure and results are discussed in detail in this contribution.