bluuebunny/crossref_metadata_2025 huggingface dataset:
RF SOP (System On Package) Using Passive Embedded Substrate
Authors: Kang NamKee , Kim Junchul , Kim Dongsu , Yoo ChanSei , Ryu JongIn , Cho Hyunmin
Published: April 2011

The convergence paradigm of today, which can be characterized as multi function and high effectiveness, strongly requires an integration of RF/analog function and high-speed digital function into a single IC or package. System on Package (SOP) is a promising technology for system integration in order to meet these current trends and requirements. A passive embedded substrate is one of the most critical issues to achieve small-size and high-functional devices and modules with high integration density and deign flexibility for wireless communications.

This paper will describe integration approach for passive embedded substrate for RF applications. With the several examples such as multi-band front end module and passive/active integrated modules, the advantages of the integration using passive embedded substrates will be described with some design considerations.
Piezoelectric Materials for Advanced Integrated RF Components
Authors: Al Ahmad Mahmoud , Coccetti Fabio , Plana Robert
Published: April 2011

This paper will first address the piezoelectric material characterization using a capacitance measurement technique. An original simple and efficient technique for the determination of the d33 piezoelectric coefficient of lead zirconate titanate thin films is described. Classical capacitor plate theory and piezoelectric material analysis are used to calculate the capacitance variation in lead zirconate titanate film, enabling piezo-electric coefficient to be determined. The technique outlined here avoids the use of mechanical/optical apparatus that may require heavy preparation of sample substrate geometry. Then, this work also treats design and fabrication issues associated with innovative tunable front-end components which combine two different ceramic technologies, namely multilayer ceramic circuit boards (low temperature cofired ceramics or LTCC) and piezoelectric actuator technology within a single device.
Low-Power Liquid Lens Having Si Cylinder Chamber for Capsule Endoscope
Authors: Seo Sangwon , Han Seungoh , Seo Jun-Ho , Kim Young-Mok , Kang Moon-Sik , Min Nam-Gi , Choi Woo-Bum , Sung Man-Young
Published: April 2011

The liquid lens based on MEMS technology can be an appropriate solution to improve the imaging capability of a capsule endoscope because it can be realized small enough and also consume negligible power. In this paper, a cylinder-type liquid lens was designed to minimize the dead area and then fabricated with MEMS technology combining the silicon thin-film process and the wafer bonding process where the multiple dielectric layer of Teflon, silicon nitride and thermal oxide was formed on the cylinder wall. The focal length of the lens module including the fabricated liquid lens was changed reproducibly as a function of the applied voltage. With the change of 30V in the applied bias, the focal length of the constructed lens module could be tuned in the range of about 42cm. The fabricated liquid lens was also proven to be small enough to be adopted in the capsule endoscope, which means the liquid lens can be utilized for the imaging capability improvement of the capsule endoscope.
Structural and photoconducting properties of MBE and MOCVD grown III-nitride double-heterostructures
Authors: Hauguth-Frank Sindy , Lebedev Vadim , Tonisch Katja , Romanus Henry , Kups Thomas , Büchner Hans-Joachim , Jäger Gerd , Ambacher Oliver , Schober Andreas
Published: April 2011

Investigations on standing wave (SW) interferometry come in focus of interest in the course of ongoing miniaturization of high precision length measurement systems. A key problem within these efforts is the development of a transparent ultra-thin photodetector for sampling the intensity profile of the generated SW. Group III-materials are promising candidates to ensure a good photodetector performance combined with the required optical transparency. In this work, we report on the interrelation of strain and dislocation density along with the influence of the structural properties on the sensitivity of double-heterostructure III-nitride photodetectors grown by molecular beam and metal organic vapour phase epitaxy.
A Buried Silicon Nanocrystals Based High Gain Coefficient SiO2/SiOX/SiO2 Strip-Loaded Waveguide Amplifier on Quartz Substrate
Authors: Lian Cheng-Wei , Lin Gong-Ru
Published: April 2011

Si-rich SiOX strip-loaded waveguide with silicon (Si) nanocrystals contributed amplified spontaneous emission at 750-850 nm with associated spectral linewidth of 140 nm is characterized. By using variable stripe length (VSL) method we demonstrate the optical gain and loss coefficients of 65 and 5 cm−1, respectively, for such a waveguide amplifier. The optical gain and loss coefficients are observed by fitting the one dimensional amplifier equation. The small-signal power gain of 18.4 dB at wavelength of 805 nm under He-Cd laser pumping of 40 mW at 325 nm is obtained from the SiO2/SiOX/SiO2 waveguide amplifier with length of 1 cm.
Advanced Laser Diode Cooling Concepts
Authors: Feeler Ryan , Junghans Jeremy , Stephens Edward , Kemner Greg , Barlow Fred , Wood Jared , Elshabini Aicha
Published: April 2011

A new, patent-pending method of cooling high-power laser diode arrays has been developed which leverages advances in several areas of materials science and manufacturing. This method utilizes multi-layer ceramic microchannel coolers with small (100's of microns) integral water channels to cool the laser diode bar. This approach is similar to the current state-of-the-art method of cooling laser diode bars with copper microchannel coolers. However, the multi-layer ceramic coolers offer many advantages over the copper coolers, including reliability and manufacturing flexibility. The ceramic coolers do not require the use of deionized water as is mandatory of high-thermal-performance copper coolers.

Experimental and modeled data is presented that demonstrates thermal performance equal to or better than copper microchannel coolers that are commercially available. Results of long-term, high-flow tests are also presented to demonstrate the resistance of the ceramic coolers to erosion. The materials selected for these coolers allow for the laser diode bars to be mounted using eutectic AuSn solder. This approach allows for maximum solder bond integrity over the life of the part.
Non-selective optical wavelength-division multiplexing devices based on a-SiC:H multilayer heterostuctures
Authors: Vieira Manuela , Fernandes Miguel , Louro Paula , Vieira Manuel Augusto , Barata Manuel , Fantoni Alessandro
Published: April 2011

In this paper we present results on the optimization of multilayered a-SiC:H heterostructures for wavelength-division (de) multiplexing applications. The non selective WDM device is a double heterostructure in a glass/ITO/a-SiC:H (p-i-n) /a-SiC:H(-p) /a-Si:H(-i')/a-SiC:H (-n')/ITO configuration. The single or the multiple modulated wavelength channels are passed through the device, and absorbed accordingly to its wavelength, giving rise to a time dependent wavelength electrical field modulation across it. The effect of single or multiple input signals is converted to an electrical signal to regain the information (wavelength, intensity and frequency) of the incoming carriers. Here, the (de) multiplexing channels is accomplished electronically, not optically. This approach has advantages in terms of cost since several channels share the same optical components; and the electrical components are typically less expensive than optical ones. An electrical model gives insight into the device operation
Tailoring Quantum Dot Saturable Absorber Mirrors for Ultra-Short Pulse Generation
Authors: Lumb Matthew , Clarke Edmund , Farrell Dominic , Damzen Michael , Murray Ray
Published: April 2011

We have designed and grown a series of quantum dot semiconductor saturable absorber mirrors (QD-SESAMs) for a range of operating wavelengths, incorporating innovative design and processing features to optimise the device performance. Using a range of reflectivity studies, ellipsometric measurements and both time-integrated and time-resolved spectroscopic studies, we have conducted detailed investigations of device performance. Extensive modelling work of dielectric multilayers has been undertaken which supports our experimental findings and allows us to understand and design novel structures in order to improve and tailor device characteristics, including dielectric capping and non-normal incidence. We demonstrate samples designed for operation with the higher excited-states of the QDs which produced a self-starting train of mode-locked pulses with a temporal duration of 200 ps at a repetition rate of 78 MHz in a Nd:YVO4 solid-state laser. We also present SESAMs incorporating electronically coupled QD bilayers, allowing long wavelength operation.
Effect of Ag and Au doping on the photocatalytic activity of TiO2 supported on textile fibres
Authors: Uddin Mohammed Jasim , Cesano Federico , Scarano Domenica , Bordiga Silvia , Zecchina Adriano
Published: April 2011

A simple method to develop TiO2, Ag or Au-doped TiO2 thin films on cotton textiles for advanced applications, is reported. The homogeneous TiO2 thin films have been deposited on cotton textiles by using sol-gel method at low temperature (100° C), whereas Ag and Au nanoparticles were then deposited on the pre-existent TiO2 films by photoreduction. The Ag/TiO2 covered cotton fibres show multichromic behaviour (grey colour under visible light and brown colour upon ultraviolet light exposure) as well as photoactivity. The Au-TiO2 film coated the cotton textile produces a purple colour with excellent self cleaning properties. The original and treated fibres have been characterized by several techniques (SEM, HRTEM, FTIR, Raman, UV–vis spectroscopy and XRD).
Printing of Patterned Copper on Pliable, Microtextured PDMS/Ceramic Composites
Authors: Apaydin Elif , Zhou Yijun , Hansford Derek , Koulouridis Stavros , Volakis John
Published: April 2011

In this work, we present a novel printing technique that enables the usage of PDMS and ceramic powder mixed PDMS composites (we refer as “PDMS-ceramic composites” in this context), as a substrate for printing of copper conduction layers. This technique is based on microtransfer molding (μTM) and lift-off for pattern formation [4]. Another key feature is the usage of microtextured PDMS and PDMS-ceramic composites before any copper film deposition. Our microtextured surface is composed of pyramid shaped wells (100 μm depth and 150 μm sides on PDMS surface). The poor adhesion between PDMS and copper is overcome by oxygen plasma application and titanium deposition before copper layer.

In order to demonstrate the convenience of this technique in RF applications, copper conduction lines (5 mm wide, different lengths) were printed on microtextured PDMS substrates. These transmission lines successfully maintained a low resistance during large strain. The printed lines have the DC resistance of 0.5 Ω and conductivity of 1.3e6 S/m, and the transmission analysis of these lines show good results especially in the MHz range when compared to copper tape measurements.

Apart from the conduction lines, the substrates can have ranging dielectric constants from 3 (no powder) to 23 (50% D270 powder, provided by TransTech) by volume mixing rule. Dielectric constant is important for RF applications, especially antenna designs. Therefore, provided with a range of dielectric constants, these composite substrates are a great promise in RF field for pliable antenna fabrication [5]. For experiment purposes, some of the transmission lines are printed on these composite substrates as well as pure PDMS.

In this study, apart from the fabrication of transmission lines, this novel technique will be applied in a GPS antenna design for demonstration purposes. This antenna design is a single-fed circularly-polarized stacked antenna for tri-band GPS (L1, L2 and L5) applications [6]. For the fabrication of the antenna, polymer-ceramic materials of ε1=16 and ε2=30 will be utilized as the substrates [6].
Fracture Mechanisms of SiNx Thin-films on Compliant Substrates
Authors: Kattamis Alex Z , Cherenack Kunigunde H , Cheng I-Chun , Long Ke , Sturm James C , Wagner Sigurd
Published: April 2011

The prospect of large-area electronics on polymers, for flexible applications requires a study of thin film fracture mechanisms. To fabricate thin-film transistor (TFT) backplanes on polymer foils the substrate must first be passivated to protect the polymer substrate from chemicals used during processing and to protect the TFTs from substrate out gassing. Silicon nitride (SiNx) is commonly used for this purpose since it tends to adhere well to polymers and is easily deposited by PE-CVD. When rigid thin films such as SiNx are deposited onto compliant substrates, such as polymer foils, stresses caused by built-in strains and the mismatch in coefficients of thermal expansion can cause fracture. The deposited thin films may fracture, and also the polymer substrate below. Using focused-ion beam milling and scanning electron microscopy we analyzed two distinct thin film fracture morphologies for SiNx films on two different types of polymer substrate. One had a relatively low, the other a relatively high coefficient of thermal expansion. For both SiNx/substrate systems the SiNx was under residual compressive stress and the substrate under tension. In one case the compressive stress in the thin films cause them to debond, buckle, and crack. In the other case the tensile stress in the substrate causes it to tear, followed by the fracture of the SiNx film above.
Selective Oxidation and Resistivity Reduction of Cu-Mn Alloy Films for Self-forming Barrier Process
Authors: Iijima Jun , Fujii Yoshito , Neishi Koji , Koike Junich
Published: April 2011

Optimum conditions of annealing atmosphere and temperature for the reduction of Mn content from the Cu-Mn alloy layer in Cu-Mn self-forming barrier process were investigated. Mn was selectively oxidized at the surface by annealing in Ar gas containing an impurity level of O2 (<0.01ppm). Resistivity of the film was decreased to 2.0 μΩcm after annealing. On the other hand, internal oxidation of Cu-Mn alloy was observed with no external protective surface oxide layer in Ar containing more than 10 ppm of O2. An optimum oxygen concentration is found to be in between 0.01 and 10 ppm in 1atm of Ar gas at 350 °C.
Formation of Mn Oxide with Thermal CVD and its Diffusion Barrier Property Between Cu and SiO2
Authors: Neishi Koji , Aki Shiro , Iijima Jun , Koike Junichi
Published: April 2011

A manganese oxide layer was formed by thermal chemical vapor deposition(CVD) on a tetraethylorthosilicate (TEOS) oxide substrate. The thickness of the Mn oxide layer could be varied 2.6 to 10 nm depending on deposition temperature. Heat-treated samples of PVD Cu / CVD Mn oxide /SiO2 indicated no interdiffusion. The CVD Mn oxide was found to be a good diffusion barrier layer.
Effects of Pulse Duration and Polarity on the Electromigration Behavior of Copper Interconnects under Pulsed Current Stress
Authors: Lim Meng Keong , Gan Chee Lip , Ee Yong Chiang , Ng Chee Mang , Zhang Bei Chao , Tan Juan Boon
Published: April 2011

Direct current (D.C.) is usually employed to characterize the electromigration reliability of interconnects. However, D.C. characterization techniques might not reflect the actual reliability of interconnects that are carrying pulsed D.C. or A.C. (alternating current) signals during operation. This study investigates the effects of unipolar and bipolar pulsed current on the electromigration lifetime of copper (Cu) interconnects. A series of long period pulsed current (i.e. 2, 16, 32 and 48 hours) were applied to Cu interconnects. Lifetime enhancement is observed when the half-period of pulsed current is shorter than the medium-time-to-failure (t50) of D.C. stressed samples. Minor increase in resistance occurring in-between pulses for unipolar pulsed current stressed samples, and occurrence of damage healing in bipolar pulsed current stressed samples are reasons attributed for the observed enhanced lifetime. We obtained longer MTF when the period of the pulsed current is shorter.
Semiconductor Film Bonding Technology and Application in Two-axis Hall Sensor Fabrication
Authors: Koh Keishin , Matushita Takashi , Hohkawa Koji
Published: April 2011

We study basic problems of the semiconductor film bonding technology. We propose a new releasing method for a large number of semiconductor films using the film photoresist to protect the semiconductor films. We investigated the basic process conditions. We successfully released a large number of the GaAs film and bonded them on the Si, LiNbO3 substrates and metal Au surface. We estimated the ctystallinity of semiconductor films by X-ray diffraction and Raman spectral. The results clarified that these process were effective. As an application of the semiconductor film bonding technology, we fabricated a two-axis Hall sensor with planar structure. The two-axis hall sensor can measure axial and radial magnetic filed components (Bx and Bz) with a sensitivity of about 9.2 Ω/G for Bz and 4.5 Ω/G for Bx respectively.
Copper CMP with Composite Polymer Core - Silica Shell Abrasives: A Defectivity Study
Authors: Armini Silvia , Whelan Caroline M. , Moinpour Mansour , Maex Karen
Published: April 2011

The results of copper Chemical Mechanical Planarization (CMP) experiments with a model slurry chemistry based on the combination of Glycine-water-Benzotriazole (Gly-H2O2-BTA), and different types of composite A (silane coupling agents between the polymer core and the silica shell) and B (electrostatic attraction between the polymer core and the silica shell) abrasives, are presented. While the presence of BTA allows a ten-fold reduction in the static etch rate from 95 nm/min. to 10 nm/min., combining oxidizer and complexing agent leads to removal rates higher than 400 nm/min. Different surface morphology and RMS roughness are observed after polishing with composite abrasives and different peroxide concentrations. Oxidizer concentrations as low as 0.1 vol.% lead to high non-uniformity and defectivity values. In particular, composite B performs better than pure colloidal/fumed silica during copper CMP using the IC-1000 pad, giving comparable Material Removal Rate (MRR), but a better surface finish due to the contribution of the elasticity of the polymer in gently transferring the applied load to the wafer surface. Cu CMP with pure polymer particles is a promising alternative to the hard inorganic material especially if combined with suitable surfactants that act from both particle stabilization and friction reduction / lubrication improvement perspectives.

The use of the medium/high-hardness pad IC-1000 is compared to the use of a soft Politex pad. In the former case, differences in terms of MRR, MRS roughness, and total defects are observed between the composite abrasives A and B; in the latter case, the behaviour of the two composites is similar. In the case of a soft pad in combination with composite abrasives, there is a remarkable improvement in the defectivity without any loss in MRR.

As revealed by SEM inspection of the composite particles collected in the slurry drain after CMP, for all the composites, the silica shell coverage is not disrupted by the shear forces and chemistry during the 1 min. polishing. Consequently, the stability and agglomeration properties of the particles in the complex Cu CMP chemistry can be helpful in explaining the experimental results in terms of MRR and surface finishing.
Persistent Photocurrent in InP Nanowires Heteroepitaxially Bridged Between Single Crystal Si Surfaces
Authors: Sarkar Ataur , Islam M. Saif , Yi Sungsoo , Talin A. Alec
Published: April 2011

Room temperature photoelectrical characterization with 325-nm ultraviolet and 633-nm visible laser excitations is performed on lateral p-type InP nanowires bridged between vertically oriented heavily p-doped single crystal silicon electrodes. Experimental results under 5 V bias demonstrate persistent photoconductivity through a slow decay of excess photocurrent with relaxation times ∼110 s and ∼50 s for the UV and visible laser illuminations, respectively. Persistent photocurrent originates from the long recombination time due to carrier trapping in vacancies, defect centers, and surface states in the InP nanowires. The study opens a new understanding of trap physics of nanowire heterostructures, a critical investigation for applications of these materials in photonic devices.
GaN and InGaN Nanowires on Si Substrates by Ga-Droplet Molecular Beam Epitaxy
Authors: Goodman Kevin , Wang Kejia , Luo Xiangning , Simon John , Kosel Tom , Jena Debdeep
Published: April 2011

Molecular beam epitaxy growth of GaN and InGaN nanowires is accomplished on Si (111) substrates using Ga-droplet nucleation. Typical diameters range from 25-80 nm and lengths can be varied by increasing the growth time; the growth rate is ∼0.25 microns/hour. The nanowires have been characterized structurally and optically. Photoluminescence spectra show band-edge emission of GaN nanowires centered at 362 nm at 290 K. Transmission electron microscopy images unveil that the nanowires are highly crystalline, and grow along the 0001 polar direction. Indium has also been successfully incorporated into GaN nanowires by modifying the growth conditions; the InGaN nanowires emit at ∼520 nm, which provides a possible route to solving strain related problems of high In-composition InGaN based efficient green emitters.
WO3-x Nanorod Arrays Based Sensors with High Sensitivity and Quick Response for Detecting Pollutants
Authors: Wang Xinpeng , Lou Jie , Wang Zhenbo , Feng Peter Xianping
Published: April 2011

Tungsten oxide nanorod arrays deposited on the cylindrical substrate have been used for fabrication of a two-dimensional (2D) sensor. The sensibility and capacity towards methane and acetone at different temperatures have been examined. Experimental data have indicated that the newly designed sensor is highly sensitive to methane with low cross sensitivity towards possible mixed organic gas acetone, relying on the operating temperature. At room temperature (20°C), a quick response time and recovery time of the sensor, less than 10 ms, have been obtained.
Noise properties of a single ZnO nanowire device
Authors: Soo Han Choi , Kim Dong Wook , Jang Do Young , Ji Hyun Jin , Kim Sang Woo , Park So Jung , Moon Seung Eon , Kim Gyu Tae
Published: April 2011

The low frequency noise of individual ZnO nanowire (NW) field effect transistors (FETs) exposed to air is systematically characterized. The measured noise power spectrum shows a classical 1/f type. The noise amplitude is independent of source-drain current and inversely proportional to gate voltage. The extracted Hooge's constant of ZnO NW is found to be 6.52×10−3. In addition, the low frequency noise of ZnO NW according to NW resistance and contact property are investigated. The noise amplitude is proportional to the square of ZnO NW resistance. If a sample shows a nonlinear current-voltage (I-V) characteristic due to a poor electrical contact, the noise power spectrum is proportional to the third power of current instead of the square of current.
Direct Growth of Single Walled Carbon Nanotubes for the Characterization of Structural and Electronic Properties
Authors: Wu Jianfeng , Walenza-Slabe Joel , Gutu Timothy , Jiao Jun
Published: April 2011

Fabricating horizontally aligned single wall carbon nanotubes (CNTs) with controlled properties has been one of the significant challenges for field-effect transistor (FET) applications. This report demonstrates a novel procedure for the fabrication of horizontally aligned single walled CNTs using the focused ion beam (FIB) and chemical vapor deposition (CVD). This method allows the morphologies, internal structures, and elemental compositions of CNTs to be directly analyzed in the scanning electron microscope (SEM) and transmission electron microscope (TEM) and avoids any sample preparation procedures that might alter the structure of the CNTs. The techniques of electron beam and ion beam induced deposition (EBID and IBID) of Pt electrodes to the CNT ends were compared and both were found to produce metal contamination around the target area. The fabrication of large area electrodes to assist in testing the CNT's electronic properties, including contact resistance and I-V characteristics was investigated. Using this fabrication technique we were able to perform an I-V sweep on a CNT circuit as well as detect the metal contamination on the CNTs which occurred as a result of electrode deposition.
Large scale synthesis of vertical aligned CNT array on irregular quartz particles
Authors: Zhang Qiang , Huang Jiaqi , Zhao Mengqiang , Qian Weizhong , Wang Yao , Wei Fei
Published: April 2011

Vertically aligned carbon nanotube (VACNT) arrays grown on quartz particles were produced in large amount via a floating catalysis process. Initially fast synchronous growth of VACNT arrays was observed, which is independently of the irregular shape and rough surface of the quartz particles. However, long VACNT arrays cracked and scattered anisotropically, depending on the irregular particles. The VACNTs have inner diameter of about 8.0 nm and relatively wide outer diameter distribution with a mean value of 36 nm. The outer diameter of CNTs, however, can be further decreased to 19 nm by tuning carbon source and concentration of catalyst precursor. The VACNTs have a high purity up to 97%. This work presents a simple way for controllable continuous production of VACNT array in large scale.
Entanglement and the Nonlinear Elastic Behavior of Forests of Coiled Carbon Nanotubes
Authors: Coluci Vitor R. , Fonseca Alexandre F. , Galvao Douglas S. , Daraio Chiara
Published: April 2011

A model for the elastic response of a foamlike forest of coiled carbon nanotubes under mechanical impact is proposed according to recent experiments reported in the literature. A force vs. displacement relation is derived for different geometries of the impacting object (sphere, cube and circular cone). In the model, entanglement among neighboring coils in the superior part of the forest is explicitly taken into account and we show that it allows the full description of the strongly nonlinear elastic behavior of the forest.
Field Emission Properties of Large Area Carbon Nanotube Cathodes in DC and Pulse Modes
Authors: Liao Qingliang , Zhang Yue , Xia Liansheng , Qi Junjie , Huang Yunhua , Qin Zi , Yang Ya , Gao Zhanjun
Published: April 2011

A large area carbon nanotube cathode was fabricated by use of a screen printing method. The emission properties of the cathode were investigated in both direct current and pulse mode experiments. In the direct current mode, the cathode has high field enhancement factor and high emission current density. In the double-pulse mode, the emission current density can approach 267 A/cm2 at an applied electric field of 15.4 V/um. Steady intense electron beams were obtained from the cathode. The results proved that the emission mechanism of CNTs at pulse electric field is plasma-induced field emission. The carbon nanotube cathode is suitable for not only field emission display applications but also high-power microwave device applications.
Molecular Dynamics Simulations of Ionic Liquids: Influence of Polarization on IL Structure and Ion Transport
Authors: Borodin Oleg
Published: April 2011

Many-body polarizable force field has been developed and validated for a wide class of ionic liquids. Classical molecular dynamics (MD) simulations have been performed on 29 ionic liquids. This presentation will focus on ability of developed force fields to predict condensed phase properties and on understanding the influence of many-body polarizable interactions on the ionic liquid structure and transport.
Ionic Liquids Interactions with Materials Surfaces Applications in Tribology and Nanotechnology
Authors: Bermúdez Maria-Dolores , Carrión Francisco-José , Iglesias Patricia , Jiménez Ana-Eva , Martínez-Nicolás Ginés , Sanes José
Published: April 2011

The extraordinary combination of high thermal stability, low volatility and the possibility of tailoring the physical and chemical properties of ionic liquids (ILs) by modifying their molecular features such as the length and nature of the cation lateral chains and the anion size and composition, has open the field of application of these green ordered fluids.

ILs have shown their ability to provide effective lubrication with very low friction coefficients and wear rates under conditions for which the currently used lubricating fluids fail. These conditions cover strategic technologies such as aerospace, microelectronics and nanotechnology applications.

At the present moment, there exist no liquid lubricants for high temperature, high vacuum and cryogenic conditions. We have determined the lubricating ability of ILs under extreme temperature conditions.

We have determined the conditions for the formation of tribocorrosion reaction products at metal-metal and metal-polymer interfaces. In the case of fluorine or phosphorus-containing imidazolium ionic liquids, formation of metallic fluorides and phosphates at the contact surfaces is the determining wear mechanism step.

The surface interactions of imidazolium room temperature ILs have been studied in a variety of materials in sliding contact under variable conditions, both as neat lubricants and as additives of conventional basestocks.

The ability of ILs molecules to interact with surfaces has also been explored in nanotechnology applications. It is well known that the use of ILs as solvents in the synthetic route, allows the control of size and shape of a variety of nanoparticles. We have developed new polymer/IL/nanoparticle nanocomposites where the size, morphology and distribution of the nanoparticles are controlled by surface interactions with IL molecules.
In-situ Investigation of the Mechanical and Electrical Properties of Nanosized Silicon Powders
Authors: Pluemel Ingo , Wiggers Hartmut
Published: April 2011

The use of nanosized Silicon powders in nanoelectronics and photovoltaics enables new technologies and promises to reduce the production costs of devices like solar cells and printable electronics significantly. However, to understand their electrical behavior and mechanical properties, such systems must be examined carefully. In porous systems like powders, the macroscopic electrical properties result from transport mechanisms such as hopping and tunneling between particles as well as from structural properties such as the amount and shape of particle contacts. Theoretical approaches like the strongest stresses network or the brick layer model can only describe this complex relation in a simplyfied way and need to be accompanied by suitable experiments. Nanosized pure and doped Silicon powders, synthesized in a microwave supported plasma reactor, were characterized by determining in-situ the conductance, impedance, and the change of porosity while applying a uniaxial mechanical pressure ranging from 7.5 to 750MPa. The porosity change of the powder during electrical measurements was characterized by means of a laser interferometer to determine the mechanical properties of the powder more accurately. Conductance measurements as a function of the applied pressure show an exponential dependence for nanosized particles and a power law for microsized particles. Simple scaling considerations in respect of the particle size cannot explain this fundamentally different behavior. Therefore a more sophisticated model is needed. A time dependent change in conductance together with a decrease in porosity was observed while applying a constant pressure, suggesting friction limited compaction of the powder. For a constant external force, the comparison of different samples leads to a clear power law dependence between the conductance of pressed samples and their mean particle diameter. This size effect spans seven orders of magnitude of the conductance while the particle size changes by only a factor of ten, and it clearly exceeds any influence of the doping concentration and the variation of the sample mass. To separate the contributions of the particle cores, particle-particle, and particle-electrode contacts to the complex conductance and capacitance, impedance spectroscopy was performed. In agreement with the observed compaction of the powder, the spectra show a strong increase of the sample capacitance and conductance as a function of the applied pressure.
Energy Dissipation in the Mechanical-Diode Jump of a Nanoscale Contact
Authors: Martínez Juan J. , Cuberes M. Teresa
Published: April 2011

In Ultrasonic Force Microscopy, the mechanical diode response refers to the quasistatic cantilever deflexion in the presence of surface out-of-plane ultrasonic vibration of sufficiently high amplitude. The effect has been described by introducing ultrasonic-amplitude-dependent tip-sample force-distance curves [Phys. Rev. 61 (2000) 13997]. Here, we demonstrate that the ultrasonic hysteresis phenomenon is qualitatively explained taking into account that for certain ultrasonic amplitudes, the modified tip-sample forces lead to two stable quasi-static equilibrium states, separated by an energy barrier. Experimental UFM data obtained on mica at ambient conditions are discussed in terms of ultrasonic-induced quasi-static equilibrium states, taking into account the role of the surface water layer.
Size effects on the Mechanical Behavior of Nanometric W/Cu Multilayers
Authors: Girault Baptiste , Geandier Guillaume , Eyidi Dominique , Renault Pierre-Olivier , Le Bourhis Eric , Goudeau Philippe
Published: April 2011

The mechanical behavior of nanostructured stratified W/Cu composites prepared by ion beam sputtering has been investigated using a method combining X-ray diffraction and tensile testing. Tests were performed on a synchrotron light source to analyze the elastic response of the tungsten phase. Three different microstructures have been analyzed: the specimen composed of the thinner tungsten layers reveals an elastic behavior different from the one expected assuming bulk elastic constants. However, Transmission Electron Microscopy (TEM) and Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) measurements reveal discontinuities in the copper layers. As the strain in the related copper clusters as well grains boundary contributions are not experimentally accessible, atomistic calculation are of utmost importance. Polycrystalline materials have already been constructed through the Voronoï method and thanks to TEM observations. Atomistic simulation and calculation are underway to validation.
An Improvement of the Doerner-Nix Function for Substrate Effects in Ultrathin Films
Authors: Zhou BO , Prorok Barton C
Published: April 2011

Substrate effects continue to be the key issue in interrogating thin films by nanoindentation. In this study, we studies amorphous thin films of several different materials deposited onto a silicon wafer. These materials span from being considerable softer than the substrate to films significantly harder than the substrate. The thin film Young's modulusEfwas measured with a MTS Nanoindenter XP system using the continuous stiffness measurement (CSM). The so-called “flat region” was observed in the early stage of nearly every CSM modulus-displacement curve for all materials studied. The depth of this region (hcr) was found to vary with the material. Based on the experimental data, we were able to modify the Doerner & Nix model for thin film indentation on a substrate, particularly their parameter alpha (α). The modified relation was found to be adept at closely matching all experimental data collected, which spanned both soft films on hard substrates and hard films on soft substrates.
Coupled Nanoscratch and 4-Point Bending Evaluations of Adhesion in SiCN/Cu/Ta/TaN/SiO2/Si Stacked Layers
Authors: Yoneda Kouji , Shimizu Satoshi , Kojima Nobuo , Sato Chikai , Ye Jiping
Published: April 2011

Nanoscratch test used for small area measurements and four-point bending test applied for quantitative measurements were coupled to evaluate the adhesive strengths of SiCN/Cu/Ta,/TaN/SiO2/Si stacked layers. The similarities and differences of the two methods concerning adhesion, position of the delamination interface, and plastic deformation of the delaminated film were estimated. It was found that the nanoscratch test gave similar adhesion properties when the delamination interface was the same as that formed by the four-point bending test. The four-point bending test displayed clearer results compared to the nanoscratch test because energy for delamination was not used in plastic deformation and the crack could propagate further. These results suggest that coupling the nanoscratch and four-point bending tests is powerful way to estimate and understand adhesion of thin film materials.
Simulations of Nonlinear Strongly Anisotropic, Misfitting Crystals and Thin Films
Authors: Torabi Solmaz , Wise Steven , Li Shuwang , Voigt Axel , Lowengrub John , Zhou Peng
Published: April 2011

We present a new approach for modeling strongly anisotropic crystal and epitaxial growth using regularized, anisotropic Cahn-Hilliard-type equations as a model for the growth and coarsening of thin films. When the surface anisotropy is sufficiently strong, sharp corners form and unregularized anisotropic Cahn-Hilliard equations become ill-posed. Our models contain a high order Willmore regularization to remove the ill posedness at the corners. A key feature of our approach is the development of a new formulation in which the interface thickness is independent of crystallographic orientation. In our previous work, we have provided matched asymptotic analysis to show the convergence of our diffuse interface model to the analytical sharp interface model. In previous models there was no such convergence to sharp interface model when the Willmore energy was considered. We present 2D numerical results using an adaptive, nonlinear multigrid finite-difference method. In particular, we find excellent agreement between the computed shapes using the Cahn-Hilliard approach, with a finite but small Willmore regularization, with dynamical numerical simulations of a sharp interface model. The equilibrium shapes from our diffuse model are compared with an analytical sharp-interface theory recently developed by Spencer [1] at the corners, and there is excellent match. Away from the corners there is an excellent agreement between the diffuse model and the classical Wulff shape. Finally, in order to model the misfit and displacement strains, we add the elastic energy and corresponding forces to our diffuse model. We analyze numerically the effect of elastic stress on the corner regularization in terms of two parameters: one parameter that describes the relative strength of the elastic energy to surface energy and the second that characteristics the strength of the surface energy anisotropy. Adding elastic energy modifies the equilibrium shape and in particular affects the shape of the corners. We can predict different Qdot shapes, such as pyramids and domes, based on the strength of the elastic interactions.
Dislocation Nucleation and Growth in MOCVD GaN/AlN Films on Stepped and Step-free 4H-SiC Mesa Substrates
Authors: Twigg Mark E. , Picard Yoosuf N. , Bassim Nabil D. , Caldwell Joshua D. , Mastro Michael A. , Eddy Charles R. , Henry Richard L. , Holm Ronald T. , Neudeck Philip G. , Trunek Andrew J. , Powell J. Anthony
Published: April 2011

Using transmission electron microscopy, we have analyzed dislocations in AlN nucleation layers and GaN films grown by metallorganic chemical vapor deposition (MOCVD) on the (0001) surface of epitaxially-grown 4H-SiC mesas with and without steps. For 4H-SiC substrates free of SiC surface steps, half-loop nucleation and glide parallel to the AlN/SiC interfacial plane play the dominant role in strain relief, with no mechanism for generating threading dislocations. In contrast, 4H-SiC mesa surfaces with steps give rise to regions of high stress at the heteroepitaxial interface, thereby providing an environment conducive to the nucleation and growth of threading dislocations, which act to accommodate misfit strain by the tilting of threading edge dislocations.
Nacre: A Unique Biomaterial Patterned by Liquid Crystals
Authors: Checa Antonio Gerardo , Cartwright Julyan H.E. , Escribano Bruno , Sáinz-Díaz Ignacio
Published: April 2011

The sequence of formation of the organic and inorganic components of nacre in bivalves and gastropods is re-studied. We reach the conclusion that interlamellar membranes are formed well in advance of the other elements. In this way, we support and refine the compartment theory for the formation of nacre. We explain the arrangement of chitin crystallites within a single interlamellar membrane and the layering of interlamellar membranes as a process of formation of a liquid crystal.
Biologically Engineered Quantum Dots for Biomedical Applications
Authors: Chornokur Ganna , Ostapenko Sergei , Emirov Yusuf , Korsunska Nadezhda , Wolcott Abraham , Zhang Jin , Phelan Catherine , Nagaram Abhilasha , Sellers Thomas
Published: April 2011

We report on a short-wavelength, “blue” spectral shift of the photoluminescence (PL) spectrum in CdSeTe/ZnS core/shell quantum dots (QDs) caused by bioconjugation with several monoclonal cancer related antibodies (ABs). Scanning PL spectroscopy was performed on samples dried on solid substrates at various temperatures. The influence of the AB chemical origin on the PL spectral shift was observed. The conjugation QD-AB reaction was confirmed using the agarose gel electrophoresis technique. The spectral shift is strongly increased and the process facilitated when the samples are dried above room temperature. The PL spectroscopic mapping revealed a profile of the PL spectral shift across the dried QD-AB spot. Transmission Electron Microscopy analyses of the samples were performed to reveal the shape and size of individual QDs. A mechanism of the “blue” shift is attributed to changes in the QD electronic energy levels caused by local stress field applied to the bio-conjugated QD.
A Miniaturized Cell Stretching Tool using Ionic Polymer Metal Composites Actuator
Authors: Hitsumoto Shin , Ihara Tadashi , Morishima Keisuke
Published: April 2011

In this paper, we proposed a novel miniaturized cell stretching tool using an Ionic Polymer-Metal Composites (IPMC) actuator. An IPMC is small, light weight and can be fabricated in any shape. And it drives flexibly like a living thing by low voltage. In this study, the PDMS chamber with PDMS membrane of 20 μEm thick for cell culturing had been fabricated on IPMC. And cultured cells were stretched by IPMC. The displacements of PDMS membrane were measured by a laser displacement sensor. And then, cells were cultured on PDMS membrane and stretched them by the motion of IPMC in an incubator. The results show that the PDMS membrane and cells were stretched by IPMC. This is the first fabrication of a cell stretching tool using IPMC. The potentiality of cell stretching tool using IPMC was demonstrated.
New Nanocomposite Biomaterials Controlling Surface and Bulk Properties using Supercritical Carbon Dioxide
Authors: Hoshi Toru , Sawagushi Takashi , Matsuno Ryosuke , Konno Tomohiro , Takai Madoka , Ishihara Kazuhiko
Published: April 2011

The molecular composite composed of polyethylene (PE) and poly(vinyl acetate) (PVAc) prepared using supercritical carbon dioxide (scCO2) and its surface modification for biocompatible surface demonstrated the creation of novel polymer biomaterials. In this study, this modification process was applied to the PE narrow tube (inside diameter: 300μm, outside diameter: 600μm, length: 5m). It was confirmed that PVAc was uniformly generated in PE tube by infrared imaging measurement of cross-section. After the acetyl group on the surface was hydrolyzed, phospholipid polymer was immobilized to the hydroxyl group on the surface of the tube. The phospholipid polymer immobilized surface showed a drastic reduction in protein adsorption. The surface of the minute and slender tube can be effectively modified using the feature of carbon dioxide whose surface tension is near zero. The modification technology by scCO2 is a promising for creation of variously-shaped new biomaterials.
Crystal Chemistry of Hydrogen Storage Materials
Authors: Jones Martin Owen , David William I. F. , Johnson Simon R. , Sommariva Marco , Lowton Rebecca L. , Nickels Elizabeth A. , Edwards Peter P.
Published: April 2011

We review here work on two classes of compounds that have been promoted as potential hydrogen storage materials; alkali metal amides and borohydrides, highlighting how their crystal structure and chemical properties may be used to influence the key hydrogen absorption and desorption parameters in these materials.
Nanogravimetric Evaluation of Hydrogen Uptake in Thin Film Materials by A Quartz Crystal Microbalance
Authors: Xu Tao
Published: April 2011

To study the hydrogen storage materials in their thin film format provides a unique approach to investigate many interfacial phenomena associated with current research on hydrogen storage materials. However, the challenge is to establish a reliable method to measure weight change of at least a few tens of nanograms in pressurized hydrogen gas. We demonstrate the application of a quartz crystal microbalance for direct mass-metric evaluation of hydrogen storage materials in the pressure range of 0˜40 bars. The frequency shift of a quartz crystal coated with hydrogen absorbing materials is affected by the hydrogen mass uptake on the crystal, the pressure and the viscosity of the gases, and the crystal surface roughness, of which the roughness contribution has no direct analytical expression. Through a control experiment on the same crystal in helium, the roughness contribution in hydrogen can be derived and the frequency shift due to the hydrogen mass uptake is obtained.
AC Loss Properties in Bi2223 Multifilamentary Tapes with Enhanced Transverse Resistivity by Introducing Oxide Barriers
Authors: Inada Ryoji , Mitsuno Yoshiki , Soguchi Kazuma , Nakamura Yuichi , Oota Akio , Li Chengshan , Zhang Pingxiang
Published: April 2011

Bi2223 multifilamentary tapes with enhanced transverse resistivity by introducing Ca2CuO3 and SrZrO3 as interfilamentary barriers were prepared and their AC loss properties were examined under AC external magnetic field. To improve the deformation properties of these oxide powders, 20-30wt% Bi2212 powders were mixed with them. The mixed oxide powders were introduced among the twisted Bi2223 filaments by using dip-coating method. AC loss properties under AC parallel or perpendicular field were measured and compared with the results for the tape without barriers. The loss measurements were carried out by changing both the amplitude and the frequency of external field. Based on the experimental results, the effect of barrier introduction on the loss reductions was discussed.