bluuebunny/crossref_metadata_2025 huggingface dataset:
Oriented Graphitic Carbon Film Grown by Mass-Selected Ion Beam Deposition at Elevated Temperatures
Authors: Kulik J. , Lempert G. , Grossman E. , Lifshitz Y.
Published: April 2011

Mass-selected ion-beam deposition using 120 eV C+ ions has been used to grow a carbon film on a Si substrate held at 200° C. The structure of the film has been characterized by transmission electron microscopy and electron energy loss spectroscopy. The film is graphitic and highly oriented with the c-axis lying parallel to the substrate. Moreover, the film is under significant biaxial stress such that the graphitic layer spacing is reduced by 4% from that of ambient pressure graphite. This oriented structure evolves due to the mobility of the carbon atoms at 200 °C. The material is sufficiently crystalline on the nanometer scale so as to produce Bragg diffraction discs in a convergent beam electron diffraction pattern using a 2.5 nm probe.
Computing Thin Film Mechanical Properties With the Oliver and Pharr Method
Authors: Wolff P.J. , Lucas B.N. , Herbert E.G.
Published: April 2011

A commonly used technique to compute mechanical properties from indentation tests is the Oliver and Pharr method. Using dimensional analysis and finite element modeling, this paper investigates errors when the Oliver and Pharr method is used to compute thin film properties.
Structural and Mechanical Properties of Diamond-Like Carbon Films Prepared by Pulsed Laser Deposition With Varying Laser Intensity
Authors: Bonelli M. , Ferrari A. C. , Fioravanti A. P. , Miotello A. , Ossi P. M.
Published: April 2011

Diamond-like carbon (DLC) films have been prepared by pulsed laser deposition (PLD) (wavelength 248 nm), ablating highly oriented pyrolytic graphite (HOPG) at room temperature in a vacuum of 10−2Pa, at fluences between 0.5 and 35 Jcm−2. Films have been deposited on Si(100) with and without a SiC interlayer. Structural analysis, such as visible and UV Raman, Infrared and Electron Energy Loss (EEL) spectroscopies show that the films are hydrogen-free and undergo a transition, from mainly disordered graphitic to up to 80% tetrahedral amorphous carbon (ta-C), above a laser threshold fluence of 5 J cm−2. The measured residual stresses of as deposited ta-C films do not exceed 2 GPa. Scratch tests show excellent adhesion properties. Low friction coefficients (0.05-0.1) have been measured in ambient humidity. Nanoindentation indicates that film hardness is as high as 70 GPa
Interaction of Oxygen with Nanophase Carbons Investigated by Electron Spin Resonance Spectroscopy
Authors: Manivannan A. , Punnoose A. , Seehra M.S.
Published: April 2011

Interaction of oxygen with three commercial activated carbons (GX203, P1400 and MEED50 supplied by PICA USA Inc., with BET surface areas of 1000, 1150 and 2000 m2/g respectively) is investigated using 9 GHz electron spin resonance (ESR) spectroscopy. All three carbons give a single ESR line with g = 2.0028(3), but the linewidth ΔH and the spin concentration Ns, are strongly affected by exposure to oxygen. The ESR parameters (g, ΔH, Ns) are measured for different partial pressures of oxygen. For the highly evacuated samples, δH ≃ 1.2 Oe and Ns≃ 1019/gm and these results are interpreted in terms of uncompensated surface dangling bonds. Oxygen exposure broadens the line and reduces Ns, in direct relation to the surface areas of the carbons and the effect is reversible. Possible effects of the paramagnetic oxygen on dangling bonds are discussed.
Tribochemistry of ZDOL Decomposition on Carbon Overcoats in Ultra-High Vacuum (UHV)
Authors: Bhatia C.S. , Chen C.-Y. , Fong W. , Bogy D.B.
Published: April 2011

Tribochemical studies of the effect of lubricant bonding on the tribology of the head/disk interface (HDI) were conducted using hydrogenated (CHx) carbon disk samples coated with perfluoropolyether ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated A1203-TiC sliders and also thermal desorption experiments in an ultra-high vacuum (UHV) tribochamber. We observed that a larger mobile lubricant portion significantly enhances the wear durability of the (head/disk interface) HDI by providing a reservoir to constantly replenish the lubricant displaced in the wear track during drag tests. In the thermal desorption tests we observed two distinct temperatures of desorption. The mobile ZDOL layer is desorbed at the lower thermal desorption temperature and the residual bonded ZDOL layer is desorbed at the higher thermal desorption temperature. We also observed that the hydrogen evolution from CHx overcoats initiates lubricant catalytic decomposition with uncoated A1203/TiC sliders, forming CF3 (69) and C2F5(119). The generation of Hydroflouric acid (HF) during thermal desorption experiments provides the formation mechanism of Lewis acid, which is the necessary component for catalytic reaction causing Z-DOL lube degradation
Electrical and Electrochemical Properties of a-C:N:H Films
Authors: Pleskov Yu.V. , Krotova M.D. , Polyakov V.I. , Khomich A.V. , Rukovishnikov A.I. , Druz B.L. , Zaritskiy I.
Published: April 2011

Electrochemical impedance in H2SO4solutions and kinetics of redox reactions in the Fe(CN)63-/4-system were studied on amorphous nitrogenated diamond-like carbon (a-C:N:H) thin-film electrodes. Parameters of point defects (trapping centers) were also measured by the Deep Level Transient Spectroscopy techniques. The films have been fabricated onp- andi-type silicon and quartz substrates, using direct ion beam deposition from an RF inductively coupled N2+ CH4plasma source. The increase in N2/CH4ratio in the gas mixture lead to a decrease in the electrical resistivity and optical bandgap of the films from 3×1010to 5×106Ω cm and from 1.3 to 0.6 eV, respectively. Simultaneously, the concentration of electrically active point defects increased significantly and the charge transfer at the a-C:N:H film/redox electrolyte interface was facilitated
Non-Electrical Poling in Novel Ferroelectric Polymers
Authors: Tasaka S. , Furutani O. , Inagaki N.
Published: April 2011

Non-electrical poling was proposed in novel ferroelectric polymers including such as polythioureas, polycyanophenylenesulfides, and polyvinyfluorides. This poling method utilizing the cooperativity of molecular dipoles can be called “surface energy poling” and takes agvantage of the energy difference inthe top and bottom surface of apolar aggregate (dipole glass) to form a remanent polarization. A ferroelectric polymer film sandwiched between a metal with higher surface energy and PTFE film with lower surface energy were heated to Tp=Tc (glass tramsition temperature or ferroelectric transition) × 1.2 and cooled slowly to room temperature. In the thin films less than 10μm, we observed the remanent polarization which gives a large pyroand piezo-electric constant as well as that obtained by electrical poling. This poling is effective for homogenious structures such as amophous ferroelectric polymers.
Challenges to the Transition to the Practical Application of IPMC as Artificial-Muscle Actuators
Authors: Bar-Cohen Y. , Leary S. , Yavrouian A. , Oguro K. , Tadokoro S. , Harrison J. , Smith J. , Su J.
Published: April 2011

In recent years, electroactive polymers (EAP) materials have gained recognition as potential actuators with unique capabilities having the closest performance resemblance to biological muscles. Ion-exchange membrane metallic composites (IPMC) are one of the EAP materials with such a potential. The strong bending that is induced by IPMC offers attractive actuation for the construction of various mechanisms. Examples of applications that were conceived and investigated for planetary tasks include a gripper and wiper. The development of the wiper for dust removal from the window of a miniature rover, planned for launch to an asteroid, is the subject of this reported study. The application of EAP in space conditions is posing great challenge due to the harsh operating conditions that are involved and the critical need for robustness and durability. The various issues that can affect the application of IPMC were examined including operation in vacuum, low temperatures, and the effect of the electromechanical and ionic characteristics of IPMC on its actuation capability. The authors introduced highly efficient IPMC materials, mechanical modeling, unique elements and protective coatings in an effort to enhance the applicability of IPMC as an actuator of a planetary dust-wiper. Results showed that the IPMC technology is not ready yet for practical implementation due to residual deformation that is introduced under DC activation and the difficulty to protect the material ionic content over the needed 3-years durability. Further studies are under way to overcome these obstacles and other EAP materials are also being considered as alternative bending actuators.
Conduction Behavior of Doped Polyaniline Under High Current Density and the Performance of an all Polymer Electromechanical System
Authors: Xu Haisheng , Bharti V. , Cheng Z.-Y. , Zhang Q. M.
Published: April 2011

In many device applications, such as electro-acoustic transducers and actuators based on high strain electroactive polymers, there are many advantages to utilize conductive polymers as electrodes. However, in these applications, a high electric power usually is required which translates to high voltage and high current in the system. Hence, the maximum current density which a conducting polymer can carry is of great interest and importance. In this paper, the conduction behavior at high current density of doped polyaniline(PANI) is reported. It was found that the current density deviates strongly from the ohmic relation with the electric field in high current density region and a saturation of the current density was observed. The maximum current density Jm observed is proportional to the conductivity of the samples and for PANI doped with HCSA, Jm can reach as high as 1200 A/cm2. Making use of the conducting polymer as the electrodes for the electrostrictive P(VDF-TrFE) copolymer, an all-polymer electromechanical system was fabricated. The all-polymer films exhibit similar or larger electric field induced strain responses than those from films with gold electrodes, presumably due to reduced mechanical clamping from the electrodes. In addition, the all-polymer system also exhibits comparable dielectric and polarization properties to those of gold-electroded P(VDF-TrFE) films in a wide temperature (from −50°C to 120°C) and frequency range (from 1Hz to 1MHz). These results demonstrate that polyaniline can be used for many electro-acoustic devices and provide improved performance.
Effect of the Pore Formation on the Solution Flow through Acrylamide Gel
Authors: Tamagawa H. , Popovic S. , Taya M.
Published: April 2011

A simple synthesis method of porous acrylamide gel is proposed. Pore formation in gel body is dominated by the amount of polymerization initiator, accelerator and gelation temperature. We investigated the influence of these factors on the number and the size of pores. Gelation temperature control is the easiest and the most effective way to create a number of large pores in a gel body. We also investigated the pore volume fraction dependence of solution flow through the gels. Solution flow rate was found to be promoted with the increase of pore volume fraction.
Computer Controlled Pulsed Pecvd Reactor for Laboratory Scale Deposition of Plasma Polymerized Thin Films
Authors: Pedrow P. D. , Shepsis L. V. , Mahalingam R. , Osman M. A.
Published: April 2011

A pulsed PECVD reactor has been successfully constructed for laboratory scale studies of plasma polymerized thin films. A computer control system based on National Instrument's LABVIEW software controls power supply sequence, feed injection, and introduction of RF energy. An optical fiber and a photo diode allow the user to monitor the emitted light for each pulse. A fast ionization gauge is used to characterize the pressure evolution over time, subsequent to acetylene gas injection. Substrates with diameter as large as 10 cm can be accommodated within the reactor. Both aniline liquid and acetylene gas have been used as reactor feed. The deposited plasma-polymerized films were characterized using AFM and SEM. Electrical conductivity of plasma polymerized acetylene film was also measured
Role of Vacancies and Solute Atoms on Grain Boundary Sliding
Authors: Vetrano J.S. , Henager C.H. , Simonen E.P.
Published: April 2011

It is necessary for grain boundary dislocations to slide and climb during the grain boundary sliding process that dominates fine-grained superplastic deformation. The process of climb requires either an influx of vacancies to the grain boundary plane or a local generation of vacancies. Transmission electron microscopy (TEM) observations of grain boundaries in superplastically deformed Al-Mg-Mn alloys quenched under load from the deformation temperature have revealed the presence of nano-scale cavities resulting from a localized supersaturation of vacancies at the grain boundary. Compositional measurements along interfaces have also shown an effect of solute atoms on the local structure. This is shown to result from a coupling of vacancy and solute atom flows during deformation and quenching. Calculations of the localized vacancy concentration indicate that the supersaturation along the grain boundary can be as much as a factor often. The effects of the local supersaturation and solute atom movement on deformation rates and cavity nucleation and growth will be discussed.
On the Relationship Between Grain Boundary Sliding and Intragranular Slip During Superplastic Deformation
Authors: Sheikh-Ali A. D. , Szpunar J. A. , Garmestani H.
Published: April 2011

This paper examines grain boundary sliding under the conditions of plastic strain incompatibility that is the most frequent case in polycrystalline materials. Two components of grain boundary sliding: dependent and independent on intragranular slip are distinguished. Theoretical estimate of a ratio between slip induced sliding and intragranular slip is obtained. It is concluded that slip and sliding are rather independent than interrelated processes.
High-Strain Rate Superplasticity in Three Contrasting Fine Grained Aluminum Alloys
Authors: Todd R.I. , Kim J.S. , Zahid G.H. , Prangnell P.B.
Published: April 2011

The superplastic properties and microstructures of three contrasting fine grained aluminium alloys were investigated. These included (i) a powder metallurgy MMC, (ii) a severely deformed spray cast alloy, and (iii) the Zn-22%Al eutectoid alloy. The results showed some differences in the details of behaviour between the alloys. One of these was the presence of true work hardening, associated with dislocation activity, in the MMC, and its absence in the microduplex Zn-Al eutectoid alloy. In addition, the powder route MMC had the high threshold stress (up to 10MPa) commonly encountered in such materials, whereas this was not the case with the cast and severely deformed alloy, indicating that the threshold stress was associated with the presence of ceramic particles in the MMC (oxide + reinforcement). In all the alloys, however, the m value tended to increase with temperature, and this led to a corresponding increase in elongation with temperature until the microstructure became destabilised. In the two predominantly single phase alloys studied this destabilisation corresponded to the solvus temperature. The constantly changing m value indicates that there is no unique value of this parameter. The same was found to be true of the grain size exponent, p. The direct interpretation of apparent activation energies in terms of simple physical processes should be made with care in the light of the present results, as (i) the microstructures of two of the alloys were found to change continuously and significantly with small changes in temperature, and (ii) the fact that m is a function of temperature necessarily implies that the apparent activation energy is a function of stress.
Routes to Develop Fine-Grained Magnesium Alloys and Composites for High-Strain Rate Superplasticity
Authors: Mukai Toshiji , Watanabe Hiroyuki , Nieh T. G. , Higashi Kenji
Published: April 2011

Superplastic properties of magnesium alloys and their composites were reviewed with a special emphasis on the achievement of high strain rate superplastic forming. The role of grain size on superplastic deformation mechanisms was particularly addressed. Commercial Mg-Al-Zn alloys and a ZK60-based composite are used as model materials to illustrate the underlining principles leading to the observation of high strain rate superplasticity. In this paper, experimental results from several processing routes, including thermomechanical processing, severe plastic deformation, and extrusion of machined chips and rapidly solidified powders, are presented. High strain rate superplasticity (HSRS) is demonstrated in ZK60-based composites.
SPD Processing and Superplasticity in Ultrafine-Grained Alloys
Authors: Valiev R.Z. , Islamgaliev R.K.
Published: April 2011

Severe plastic deformation (SPD), for example by intense plastic straining under high pressure, is an innovative technique for producing ultrafine-grained (UFG) metals and alloys. The SPD fabricated UFG structures can lead to enhanced superplasticity, which, however, depends strongly on processing parameters. The present paper focuses on examples of attaining enhanced superplasticity in several alloys, subjected to SPD and considers the relationship between processing – UFG structures – superplastic properties in SPD produced materials.
“Monolithic Shape Memory Alloy Actuators”: A New Concept for Developing Smart Micro-Devices
Authors: Bellouard Y. , Lehnert T. , Sidler T. , Gotrhardt R. , Clavel R.
Published: April 2011

In micro-robotics and for micro-systems, one cannot simply scale down conventional actuators. Specific difficulties like friction forces between parts and the assembly have to be considered carefully and need a special design strategy adapted to this “micro-world”. Shape Memory Alloys (SMA) have strong potential in micro actuators. So far, most of SMA devices used the SMA material as a part of a mechanical system, which raised several problems when scaling down. In this paper, a concept of monolithic SMA micro-devices, which consists in considering the SMA as a mechanical system by itself, is presented. Several applications are shown to illustrate this concept.
Hypersonic and Dielectric Studies of Relaxor Ferroelectric Single Crystal
Authors: Tu Chi-Shun , Schmiidt V.H. , Yeh C.-H. , Chen L.-F. , Tsai C.-L.
Published: April 2011

Both the longitudinal (LA) Brillouin back-scattering spectra and dielectric permittivity along the [001] direction have been measured as a function of temperature for a relaxor ferroelectric single crystal (PbMg1/3Nb2/3O3)0.68(PbTiO3)0.32 (PMN-32%PT). A sharp ferroelectric phase transition (which is associated with a Landau-Khalatnikov-like phonon damping maximum) was observed near 445 K. As temperature increases, a diffuse phase transition was detected near 280 K. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 280 and 445 K for heating procedure) are diffuse first-order and first-order, It respectively. The dielectric data prove the existence of an electric dipolar relaxation process below 300 K.
On Magnetostrictive Transducer Applications
Authors: Flatau Alison B. , Dapino Marcelo J. , Calkins Frederick T.
Published: April 2011

This paper provides an overview of magnetostrictive transducer technology. The bi-directional coupling between the magnetic and mechanical states of a magnetostrictive material provides a transduction mechanism that can be used both for actuation and sensing. The current interest in design of adaptive smart structures, coupled with the advent of materials that exhibit high sensor figures of merit, such as Metglas and giant magnetostrictive materials such as Terfenol-D has lead to a renewed interest in the engineering of optimized magnetostrictive transducer designs. A survey of recent applications for giant magnetostrictive materials as both sensors and actuators and their use in smart structure applications will be presented along with a brief discussion of some pertinent device design issues. Examples of magnetostrictive actuation used to produce displacements, force and acoustic waves are summarized. Magnetostrictive sensor configurations that measure motion, stress or force, torque, magnetic fields and target characteristics are discussed. A very brief look at transducer modeling and experimental results is included and schematics of a number of actuator and sensor configurations are presented.
Loss Mechanisms in Piezoelectrics
Authors: Uchino K. , Zheng J. , Chen Y.H. , Du X. , Hirose S. , Takahashi S.
Published: April 2011

Losses in piezoelectrics are considered in general to have three different mechanisms; dielectric, mechanical and piezoelectric losses. This paper deals with the phenomenology of losses, first, then how to measure these losses separately in experiments.
Modeling and Experiments for Deformation Under Load in Ni-Mn-Ga Ferromagnetic Shape Memory Alloy
Authors: Murray S. J. , Allen S. M. , O'Handley R. C.
Published: April 2011

A simple model is proposed to relate strain, stress, field and anisotropy in a ferromagnetic shape memory alloy (FSMA) and experiments were performed to test the validity of the model. The model is presented as applied to the case of orthogonal field and load in a NiMn-Ga FSMA. The model predicts threshold-type strain behavior as field changes at constant load or as load changes with constant field. The measured behavior of strain with stress at constant field approximated the predictions of the model. Field-induced strain remained constant at about 6% with the addition of stress until such a stress was applied that the mechanical energy overcame the anisotropy of the sample and the strain was reduced to 0. The model's predictions of critical strain behavior with applied field at constant stress were qualitatively accurate at some stress levels, but under-predicted the field necessary to produce strain.
Microstructural Effects on Piezoelectric Cracking
Authors: Fulton C.C. , Gao H.
Published: April 2011

The successful development of smart structures using piezoelectric sensors and actuators depends on a thorough characterization of the mechanical limits of these materials. However, fundamental discrepancies between theoretical predictions and empirical observations of their cracking behavior hinder attempts to provide appropriate design guidelines. The complex microstructure of a piezoelectric ceramic leads to severe nonlinear effects at the crack tip, motivating a physics-based investigation of the fracture mechanics. Specifically, the switching and saturation that occur at the level of individual polar domains require a multiscale viewpoint in order to evaluate the conditions which control crack advance. We introduce a model for domain switching based on discrete electric dipoles superimposed on a homogeneous medium with the macroscopic material properties. Each dipole then represents the deviation of a given domain's polarization vector from the linear constitutive law. Within this framework, we develop a relationship between the apparent loads applied to a cracked sample and the local energetic forces driving the crack. Shrinking the length scale down to the crack tip reveals a “singularity conversion”, from the apparent combination of stress and electrical intensity factors to purely mechanical effective opening forces. Using the energy release rate derived from these local stress singularities to predict the dependence of failure load on applied electric field, we are able to reproduce the trends observed in the laboratory.
High-Temperature Properties of Langasite
Authors: Fritze H. , Tuller H. L. , Borchardt G. , Fukuda T.
Published: April 2011

Materials such as langasite (La3Ga5SiO14) and related compounds are promising candidates for piezoelectric applications at high temperatures. In particular, langasite does not exhibit phase transformations up to the melting point of 1470 °C. Langasite was investigated with respect to potential applications in high temperature resonator devices. In contrast to current resonator materials, we have observed bulk oscillations at temperatures of up to 750 °C in langasite devices. At 700 °C the mass load response for 0.78 mm thick resonators is approximately 0.10 µg/Hz.

At elevated temperatures, the bulk resistivity of the resonator devices cannot be neglected due to attenuation of the resonance signal. Therefore, the temperature dependence of the electrical properties of langasite resonator devices, including bulk resistivity, capacity and resonance frequency were measured and are presented. The electrical conductivity is characterized by an activation energy of 105 kJ/mol. In order to confirm langasites stability with respect to oxidation-reduction reactions, we examined the oxygen diffusivity by measuring 18O tracer profiles by SIMS. The diffusivity along the Y-axis is given by D = 5-10−5 exp(-140 kJ/mol / RT) cm2/s in the temperature range from 500 to 800 °C. Langasite shows low oxygen diffusion coefficients with respect to other materials which might be investigated using a langasite microbalance. This would, for example, enable oxygen diffusion kinetics to be examined in YBa2Cu3O6 at 600 °C by means of 18O/16O exchange.
Friction Measurement in MEMS Using a New Test Structure
Authors: Crozier B.T. , de Boer M.P. , Redmond J.M. , Bahr D.F. , Michalske T.A.
Published: April 2011

A MEMS test structure capable of measuring friction between polysilicon surfaces under a variety of test conditions has been refined from previous designs. The device is applied here to measuring friction coefficients of polysilicon surfaces under different environmental, loading, and surface conditions. Two methods for qualitatively comparing friction coefficients (µ) using the device are presented. Samples that have been coated with a self-assembled monolayer of the lubricating film perfluorinated-decyltrichlorosilane (PFTS) have a coefficient of friction that is approximately one-half that of samples dried using super-critical CO2 (SCCO2) drying. Qualitative results indicate that µ is independent of normal pressure. Wear is shown to increase µ for both supercritically dried samples and PFTS coated samples, though the mechanisms appear to be different. Super critically dried surfaces appear to degrade continuously with increased wear cycles, while PFTS coated samples reach a steady state friction value after about 105 cycles.
Microinstrument for the Characterization of Submicron Silicon Fibers at High Strain
Authors: Chen J. M. , Reed B. W. , Chen J. M. , Reed B. W. , MacDonald N. C.
Published: April 2011

We present a MEMS microinstrument to interface submicron-scale structures and study their properties. Using this microinstrument integrated with a 150nm diameter silicon fiber that has high fracture strength and a high force micro-actuator, the non-linearity of n-type silicon's piezoresistive effect is measured up to the third order, using data from the high strain range of 0-1% for the first time.
Packaging MEM Sensor Arrays
Authors: Marinis T. F. , Fulginiti D. A. , Clausen H. G.
Published: April 2011

Many applications of MEM sensors require hermetic or high vacuum packaging of sensor clusters. For example, multiple gyroscopes or accelerometers are fabricated on a single chip to improve alignment and stability of input axes or increase the dynamic range of instruments. Chemical sensors are fabricated as large arrays to both improve selectivity and increase the number of species that can be detected. Still larger arrays of sensors must be packaged for hydrophone and bolometer imaging devices. All of these applications place a demanding combination of requirements on the sensor package. The electrical outputs of the sensor array must be well isolated from each other as well as power and excitation signals, while parasitic capacitance is minimized. The package must also be capable of being evacuated and sealed to achieve a pressure of 5 millitorr with a leakage rate below 10−11 [Std cc sec−l]. Finally, the package must be compact and low cost to realize these same attributes of the MEM sensor. This paper describes a packaging approach that is based on low temperature cofired ceramic materials. This technology meets the packaging requirements of sensor arrays and is well suited to the research environment in which the sensor design is continually evolving.
Fatigue Properties for Micro-Sized Ni-P Amorphous Alloy Specimens
Authors: Maekawa S. , Takashima K. , Shimojo M. , Higo Y , Swain M. V
Published: April 2011

Fatigue crack propagation tests at different stress ratios of 0.1 and 0.5 have been performed on microsized Ni-P amorphous alloy specimens to investigate the influence of stress ratio in the crack growth properties of microsized materials. The specimens tested were cantileverbeam-type with dimensions of 10 × 12 × 50 νm3 prepared by focused ion beam machining. Notches with a depth of 3 [m were introduced in all specimens. The entire set of fatigue tests as performed using a newly developed fatigue testing machine in air at room temperature. Fine stripes deduced to be striations were observed on the fatigue fracture surface. Careful measurements of the striation spacings were made. Fatigue crack propagation rate, that is striation spacing, is plotted as a function stress intensity factor range. Fatigue crack propagation rate at stress-ratios of 0.1 and 0.5 in microsized Ni-P amorphous alloy specimens are given by da/dN ∼ 1.3 × 10−8 ΔK;1.16 and da/dN ∼ 3.7 × 10−8 ΔK0.5, respectively. At a given ΔK, crack propagation rate at a stress ratio of 0.5 was higher than that at 0.1. It is considered that a decrease in crack propagation rate at stress ratio of 0.1 is due to adecrease in effective stress intensity factor range ΔKeff, by the effect of crack closure.
Test Channels for Flow Characterization of Processed Plastic Microchannels
Authors: Chen Yandong , Chen Zhongping , Zhao Yonghua , Nelson J. Stuart , Bachman Mark , Chiang Yuh-Min , Chu Charles , Li G. P.
Published: April 2011

Characterization of the flow properties in microfluidic channels is important for designing and building biomedical microdevices, many of which depend on precise fluid flow for their operation. Similarly, in complex fluidic systems, it is important to identify flaws in processing which will potentially restrict, or short circuit the flow of the device. We explore the characterization of flow in plastic microfluidic systems through various test devices..
Inlayed “Atom-like Three-Dimensional Photonic Crystal Structures Created with Femtosecond Laser Microfabrication
Authors: Sun Hong-Bo , Xu Ying , Sun Kai , Juodkazis Saulius , Watanabe Mitsuru , Matsuo Shigeki , Misawa Hiroaki , Nishii Junji
Published: April 2011

Ultrashort laser pulses are utilized for fabrication of three-dimensional (3D) photonic crystals based on a multiphoton absorption process. The basic idea is, when a femtosecond laser pulse is tightly focused into some transparent media, a submicrometer hole will be generated due to microexplosion. By arraying these holes the same way as atoms in general solid crystals, 3D photonic lattices are achieved. Pronounced photonic bandgap effect shows that this technique is promising for tailoring arbitrary-lattice photonic crystals.
Methylamine Growth of SiCN Films Using ECR-CVD
Authors: Wen C.-Y. , Wu J.-J. , Lo H.J. , Chen L.C. , Chen K.H. , Lin S.T. , Yu Y.-C. , Wang C.-W. , Lin E.-K.
Published: April 2011

Continuous polycrystalline SiCN films with high nucleation density have been successfully deposited by using CH3NH2, as carbon source gas in an ECR-CVD reactor. Fom the kinetic point of view, using CH3NH2, as carbon source could provide more abundant active carbon species in the gas phase to enhance the carbon incorporation in the SiCN films. The compositions of the SiCN films analyzed from Rutherford Backscattering Spectroscopy showed that higher [CH3NH2,]/[SiH4] ratio led to higher carbon content in the films. Moreover, a lower carbon content was measured when the film was deposited at higher substrate temperature. The direct band gap of the aforementioned SiCN films determined using PzR is around 4.4 eV, indicating a wide band gap material for blue-UV optoelectronics.
Effect of Precursor Sol Ageing on Sol-Gel Derived Ruthenium Oxide Thin Films
Authors: Bhaskar S. , Majumder S. B. , Dobal P. S. , Katiyar R. S. , Cruz A. L. M. , Fachini E. R.
Published: April 2011

In the present work we have optimized the process parameters to yield homogeneous, smooth ruthenium oxide (RuO2) thin films on silicon substrates by a solution deposition technique using RuCl3.×.H2O as the precursor material. Films were annealed in a temperature range of 300°C to 700°C, and it was found that RuO2 crystallizes at a temperature as low as 400°C. The crystallinity of the films improves with increased annealing temperature and the resistivity decreases from 4.86µΩ-m (films annealed at 400°C) to 2.94pµΩ (films annealed at 700°C). Ageing of the precursor solution has a pronounced effect on the measured resistivities of RuO2 thin films. It was found that the measured room temperature resistivities increases from 2.94µΩ-m to 45.7µΩ-m when the precursor sol is aged for aged 60 days. AFM analysis on the aged films shows that the grain size and the surface roughness of the annealed films increase with the ageing of the precursor solution. From XPS analysis we have detected the presence of non-transformed RuCl3 in case of films prepared from aged solution. We propose, that solution ageing inhibits the transformation of RuCl3 to RuO2 during the annealing of the films. The deterioration of the conductivity with solution ageing is thought to be related with the chloride contamination in the annealed films.
Analysis of a TEOS/Oxygen Plasma: Influence of Energy and Particle Flux on the Deposition Parameters
Authors: Silva M. L. Pereira da , Silva A. N. Rodrigues da , Santiago-Aviles J. J.
Published: April 2011

In this work we looked at deposition parameters such as rate and film microstructure during the plasma enhanced CVD processing of TEOS {Si (OCH2 CH3)4) + O2. This is a multi-component oxide due to the inevitable accidental inclusion of carbonatious contaminants. We decided to characterize the plasma parameters, namely the electron energy (from 50 to 600 eV), and the flux of the reactive species. The deposition chamber was modified by the introduction of a stainless steel tubular ring between the electrodes, such that when a positive bias is applied it is possible to inject electrons into the plasma. A dual role for the tubular ring is the transport of oxygen to different locations in the plasma, and to monitor the influence of the oxygen flux on deposition.
Mid-Infrared Photodetector Using Self-Assembled InAs Quantum Dots Embedded in Modulation-Doped GaAs Quantum Wells
Authors: Lee Seung-Woong , Hirakawa Kazuhiko , Shimada Yozo
Published: April 2011

We have designed and fabricated a quantum dot infrared photodetector which utilizes lateral transport of photoexcited carriers in the modulation-doped A1GaAs/GaAs two-dimensional (2D) channels. A broad photocurrent signal has been observed in the photon energy range of 100–300 meV due to bound-to-continuum intersubband absorption of normal incidence radiation in the self-assembled InAs quantum dots. A peak responsivity was as high as 2.3 A/W. The high responsivity is realized mainly by a high mobility and a long lifetime of photoexcited carriers in the modulation-doped 2D channels. Furthermore, we found that this device has high operation temperature and very high photoconductive gain.
IV-VI Compound Semiconductor Mid-Infrared Vertical Cavity Surface Emitting Lasers Grown by MBE
Authors: Shi Z. , Xu G. , McCann P.J. , Fang X. M. , Dai N. , Bewley W. W. , Felix C. L. , Vurgaftman I. , Meyer J. R
Published: April 2011

Mid-infrared vertical cavity surface emitting lasers (VCSELs) using PbSe as the active material and broadband high reflectivity Pb1−xSrxSe/BaF 2 distributed Bragg reflectors (DBR) as bottom and top mirrors were grown by molecular beam epitaxy. By pulsed optical pumping, this first IV-VI semiconductor VCSEL operated up to 290K at a wavelength of 4.5 µm. Further optimization of such VCSELs could lead to room temperature continuos wave operation.
InNxSb1−x Light Emitting Diodes Grown by MBE
Authors: Johnson A. D. , Bennett R. H. , Newey J. , Pryce G J , Williams G M , Burke T. M. , Jones J. C. , Keir A. M.
Published: April 2011

We present the first reported MBE growth of light emitting diodes (LED's) with active regions made up of InSb/ InNxSbl−x (O<x<0.02) superlattices, grown onto InSb(100) substrates. Such dilute alloys of nitrogen in other III-V materials have been shown to exhibit very large bandgap bowing parameters due to differences in atomic size and the electro-negativity of nitrogen. Novel growth techniques have been developed to enable epitaxy of high quality InNxSbl−x, using an electron cyclotron resonance (ECR) plasma source. Material characterisation was performed by double crystal x-ray diffraction (DXRD) and transmission electron microscopy (TEM), and nitrogen composition has been determined using DXRD and secondary ion mass spectrometry (SIMS). To determine the effect of nitrogen on bandgap, the structures have been fabricated into LED's with InSb/InNxSbl−x superlattice active regions with period ∼1100A. For a nitrogen content of ∼0.3%, the peak emission of the diodes shifts from ∼6pm to >71µm at room temperature.
Defects in CdTe-Based Photodetectors
Authors: Valdna V.
Published: April 2011

The photoluminescence spectra, defect composition and optoelectronic properties of chlorine doped CdTe monocrystals, thick layers and thin films are investigated. It is supposed that the complex defect (VCd-2ClTe) is a neutral defect that causes high resistivity of Cl doped CdTe. This complex can dissociate into two charged defects (VCd-ClTe) and ClTe at 300 K. Acentre (VCd-ClTe) is a stable defect that is responsible for p-type conductivity of Cl doped CdTe. Depending on the C1 concentration high resistivity, high photoconductivity or high p-type conductivity can be formed in CdTe that is only chlorine doped.
Electrical Characterization of InAs/(GaIn)Sb Infrared Superlattice Photodiodes for the 8 to 12νm Range
Authors: Bürkle L. , Fuchs F. , Kiefer R. , Pletschen W. , Sah R. E. , Schmitz J.
Published: April 2011

InAs/(GaIn)Sb superlattice photodiodes with a cutoff wavelength of 8.711μm show adynamic impedance of R0A= 1.5 kωcm2at 77 K and a responsivity of 2 A/W, corresponding to a detectivity of D*= 1 x 1012 cmv√Hz/W. Diffusion limited performance is observed above 100 K. At lower temperatures the diodesare limited by generation-recombination currents. An analysis of the influence of different diode sidewall passivations on the surface contribution to the diode leakage current is presented. The out-of-plane electron mobility as well as the relative contributions of the electron and hole diffusion currents to the diode current were determined by a measurement of the magnetic field dependence of the reverse saturation current density of the diodes
UPS of a-Si:H: What is the energy of the Er 4f states?
Authors: Tessler Leandro R. , Piamonteze Cínthia , Iniguez Ana Carola , Siervo Abner de , Landers Richard , Morais Jonder
Published: April 2011

One very important problem concerning erbium-doped silicon is the electronic structure of the Er3+ impurities. In particular, it is still not clear if the 4f levels can be treated as frozen core levels or their overlap with s and p states of their neighbors must be considered explicitly. For crystalline Si, the 4f levels have been supposed to be anywhere between 20 eV below the valence band and within the energy gap. In this paper we report on the first ultraviolet photoemission spectroscopy (UPS) measurements on Er-doped a-Si:H. Samples of a-Si:H with different Er contents (up to 1 at. % Er) were prepared by co-sputtering from a Si target partially covered with metallic Er platelets. In order to enhance the Er states relative to the Si and H states, the excitation energy was tuned between 40 and 140 eV with a synchrotron light source. At 140 eV excitation energy the cross-section of the Er 4f and 5p states is more than an order of magnitude higher than the cross section of the Si 3s or 3p states. As the Er concentration increases, a shoulder and then a peak appears at 10.0±0.5 eV binding energy. The intensity and width of this peak is well correlated with the Er concentration, and with the Er 5p and 5p½ levels at 26 and 32 eV binding energy, respectively. We attribute the peak at 10.0±0.5 eV binding energy to the Er 4f level. These are the only occupied states that can be related to the presence of Er, indicating that these levels are not valence states and consequently can be treated as frozen core levels.
The Emergence of an Amorphous-Silicon Based Photonic Technology; Optical Memories to 3-D Photonic Crystals
Authors: Hata N. , Fortmann C. M.
Published: April 2011

Amorphous silicon is an ideal system for optical engineering since its optical properties can drastically be changed through its ability to absorb such impurities as hydrogen whose contents range from zero to beyond twenty percent. In this work we report light-induced changes in its optical properties which may add potential in active optical engineering. Considerable changes in the phases in reflected polarized lights from transparent-substrate side of amorphous silicon films are observed both after prolonged illumination of intense light at the light-soaking temperature range from 40 to 250 °C. Most of the changes are localized to amorphous silicon region near substrate-film interfaces. Illumination time dependencies and annealing characteristics are examined, and physics behind these observed changes are discussed.
Recombination and Resistive Losses in Amorphous Silicon / Crystalline Silicon Heterojunction Solar Cells
Authors: Jensen Nils , Rau Uwe , Werner Jürgen H.
Published: April 2011

This contribution investigates the electronic properties of a-Si:H/c-Si solar cells and explains their electrical output parameters open circuit voltage, short circuit current, and fill factor. Our device analysis is based on measurements of the internal quantum efficiency, of current/voltage and capacitance/voltage curves. We find carrier recombination within the crystalline silicon absorber material to be responsible for the limitation of the open circuit voltage. The short circuit current is restricted by collection losses in the absorber material and by absorption in the electrically inactive a-Si:H emitter. Resistive losses affecting the fill factor originate from the transport of minority carriers across the interface. The I/V curves measured at low temperatures reveal a characteristic S-shaped behavior. This effect increases with decrasing temperature and stems from the minority carrier transport, which is hindered by the band offset between a-Si:H and c-Si. We propose a new analytical model to describe this anomalous behavior.
Spin-Dependent Processes In Thin-Film Silicon Solar Cells
Authors: Lips K. , Müller R. , Kanschat P. , Finger F. , Fuhs W.
Published: April 2011

We report on electrically detected magnetic resonance (EDMR) studies in three different types of thin-film silicon solar cells: (i) c-Si absorbers with epitaxially grown silicon thin-film emitters (ii) c-Si absorbers with hydrogenated amorphous silicon (a-Si:H) emitters, and (iii) microcrystalline silicon (µc-Si:H) pin diodes. Although cells of type (i) and (ii) are of a similar structure their EDMR spectra are completely different. We identify surface recombination via Pb0 centers in cells with c-Si emitters but hopping transport through conduction bandtail states in the 30 nm thin a-Si:H emitter layer. No signals related to interface recombination are detected in either cell. The EDMR signals of cell (iii) are identified as hopping among tail states of the conduction band with a subsequent nonradiative tunneling transition to neutral dangling bonds. At elevated temperature recombination is suggested to be dominated by direct capture. The EDMR signal of the dark current can be described with a simple diode model only involving diffusion and recombination currents.
Selective Area Cell Adhesion on Amorphous Silicon Using Patterned Self-Assembled Monolayers
Authors: Smith Laura L. , Wang Kai , Parsons Gregory N. , Hernandez Raquel , Brown Dennis T.
Published: April 2011

The compatibility of inorganic materials with living tissues and biological compounds is crucial in many areas, including medical diagnostics, biosensors, drug delivery, etc. In this work, we are interested in the interaction of living mammalian cells with semiconductor surfaces for novel thin-film biosensor devices. Amorphous silicon may give advantages over crystalline silicon for some devices because of its large-area, low-temperature compatibility, and its large optical absorption coefficient in the visible spectrum. Amorphous silicon thin films (500Å) deposited on quartz glass were cleaned using ambient UV/O3 treatment, leaving the surface largely OH-terminated and hydrophilic. The hydrophilic surface was then exposed to a vapor of octyltrichlorosilane (CH3(CH2)7SiCl3, OTS). The resulting surface was strongly hydrophobic, with advancing contact angles with water <106°. This organic surface was masked to reserve areas of uncoated hydrophilic substrate, and placed in a cell culture (BHK-21 cells) to observe cell adhesion and proliferation. A high degree of cell attachment was observed on the UV/O3-treated surfaces (~400 cells/mm2) compared to ~450 cells/mm2 on the culture dish control surface, indicating cell proliferation and growth. Little cell adhesion occurred on the hydrophobic organiccoated surface (~40 cells/mm2), and the cells remained round and only minimally attached. On masked surfaces, the organic-free areas showed dense, well-adhered cell growth while the coated areas showed much fewer and rounded cells. On all samples as well as control surfaces, cell death was <1%. These results suggest a means for selectively controlling cell adhesion to thin film electronic device surfaces, through the patterning of hydrophobic surface coatings.
Multi-Band Electron Paramagnetic Resonance Study of Microcrystalline and Cluster Silicon Embedded in SiO2
Authors: Ehara Takashi , Ikoma Tadaaki , Tero-Kubota Shozo
Published: April 2011

Dangling bond defects (DB) in silicon microcrystallines and clusters embedded in SiO2 have been studied by X- and Q-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra due to the DB were remarkably depending on the grain size, which was controlled by annealing temperature. The microcrystalline containing film shows a broad and unsymmetrical EPR signal at g = 2.006 with the line width of 13 G in X-band spectra. The signal can be simulated by using the anisotropic g-values of Pb center. The Si cluster samples obtained from the annealing at less than 800°C give an asymmetric EPR spectra at about g = 2.004 with the line width of about 9 G in X-band. The EPR signal due to the E' center was also observed.