bluuebunny/crossref_metadata_2025 huggingface dataset:
Grain boundary structure in B2 Fe-Al ordered alloys: an atomic-scale simulation
Authors: Besson R. , Becquart C. S. , Legris A. , Morillo J.
Published: April 2011

We calculated the atomic structure of the (310)[001] symmetric tilt grain boundary (GB) in B2 ordered Fe-Al, using empirical and ab initio potentials. Including a proper treatment of the influence of small departures from bulk B2 stoichiometry on chemical potentials through a thermodynamic point-defect model, we obtain low energy GB variants geometrically close to the usual ones deduced from the coincidence site lattice (CSL) theory. In Al-rich alloys, both methods predict GB Al segregation whereas in Fe-rich alloys, the empirical (resp. ab initio) approach leads to Fe (resp. Fe or no) segregation. With both methods, strong GB chemical effects triggered by the bulk composition appear, showing that in B2 Fe-Al, GB properties may be strongly influenced by small bulk composition changes.
Fluctuation-Induced Nucleation of PLC Bands
Authors: Sapalidis P. , Dodou D. , Hähner P. , Zaiser M. , Aifan tis E.C.
Published: April 2011

The inuence of mesoscopic strain-rate uctuations on the n ucleation of localized deformation bands (PLC bands) in dynamically strain ageing materials is discussed. It is shown that uctuations ma y lead to a macroscopic localization of plastic ow even if linear stability analysis (LSA) of the macroscopic constitutiv e equations predicts stable deformation beha vior. The resulting quantitative corrections to linear stability analysis are evaluated, and implications for the reliabilit y of LSA results are discussed.
Influence of Antimony Doping on Nanoscale Arsenic Clusters and Dislocation Loops in Low-Temperature Grown Gallium Arsenide Films
Authors: Chaldyshev V.V. , Bert N.A. , Romanov A.E. , Suvorova A.A. , Kolesnikova A.L. , Preobrazhenskii V.V. , Putyato M.A. , Semyagin B.R. , Werner P.
Published: April 2011

Transmission electron microscopy was employed to study the microstructure of GaAs films grown by molecular-beam epitaxy at low temperature and delta-doped with Sb. Thus obtained material contained 0.5 at.% of excess arsenic that precipitates upon post-growth anneals. The Sb doping was found to strongly affect the microstructure of arsenic clusters and their ripening rate upon annealing. Segregation of Sb impurities in the As clusters was revealed. In contrast to the well known pure As clusters, the As-Sb clusters induced strong local deformations in the surrounding GaAs matrix. Relaxation of these deformations resulted in formation of dislocation loops, which was studied both experimentally and theoretically.
Influence of Oxidation On Boron Sgregation to Grain Boundaries of In-Situ Fractured Ni3Al Alloys
Authors: Koch S. A. , Agterveld D. T. L van , Palasantzas G. , Hosson J. Th. M. De
Published: April 2011

Scanning electron and scanning Auger microscopy studies were performed on in-situ fractured B-doped hypostoichiometric Ni3Al alloys. The Auger measurements on the fracture surface showed a very small amount or the total absence of B. Further, B segregated to the grain boundaries during subsequent exposure to the ambient system ultra-high vacuum environment at room temperature. The B segregation appeared to be driven by a mechanism of electronic nature related to Ni enrichment and O supplied from the environment. Ni-oxidation at room temperature is in accordance with model predictions for small beam sizes (≤10 µm) based on the premise that the electron beam creates additional nucleation sites around of which oxide growth occurs. With increasing the size of the e-beam the oxidation process becomes slower and chemisorption of oxygen plays a significant role. As a result the Ni-oxide depth decreases drastically with increasing spot size and offers an alternative route for monitoring the thickness of NiO in a nanometer range.
Segregation of Fission Products to Surfaces of UO2
Authors: Stanek C.R. , Grimes Robin W. , Bradford Mark R.
Published: April 2011

In order to predict the release rates of fission products from UO2 nuclear fuel, it is necessary to determine the energetics associated with their segregation from the bulk to surfaces. Here segregation is determined by calculating the total energy of a simulation repeat unit which includes a fission product, as a function of the distance of the fission product from the surface. We have investigated the possibility that specific fission products segregate preferentially to certain surfaces. In particular, Ce4+ and Zr4+ segregate to the (100) surface, while Ba2+ and Sr2+ segregate to the (111) surface. Two issues make these calculations more complex. First, charged defects need to be compensated by oxygen vacancies. For example, divalent Ba2+ and Sr2+ substituting on uranium sites are compensated by a single oxygen vacancy. Second, certain surfaces, such as the (100), are inherently unstable, but can be stabilized by oxygen vacancies. Arrangements of these surface defects lead to complex surface structures that affect segregation energetics.
Microscopic Structure and Energetics of the Pd/SrTio3 (001) Interface
Authors: Ochs Thorsten , Köstlmeier Sibylle , Elsässer Christian
Published: April 2011

The microscopic structure and energetics of a SrTio3 (001) surface covered with thin layers of pd were investigated by means of ab-initio electronic-structure calculations. A mixed-basis pseudopotential technique based on the local density functional theory was employed. Supercells containing srTio3 sunstrates, with either SrO or Tio2 surface terminations, and pd films of varying thicknedd were used to model the (001) surfaces and the (001) heterophase interfaces. The Tio2 terminated subtrate is energetically favoured for the adhesion of Pd films, with the Pd atoms bonded on top of the O atoms. The film adhesion is strongest for one (001) layer of fcc Pd and becomes weaker with increasing film thickness.
Activation of an Al-Zn-Mg-Li alloy by the Presence of Precipitates to be used as Sacrificial Anode
Authors: Valdez S. , Talavera M. A. , Genesca J. , Juarez-Islas J. A.
Published: April 2011

This work reports the influence of microstructure on the electrochemical efficiency of Al- alloys to be used as sacrificial anodes. The microstructure of as-cast Al-ingots was characterized by X-ray diffractometry and scanning electron microscope (equipped with WDS microanalysis facilities). The electrochemical behavior was investigated in 3% NaCl solution simulating sea water at room temperature. Regarding microstructure, X-ray diffractometry detected the presence of the α-Al phase, and the τ-Al2Mg3Zn3, Mg7Zn3 and δ-AlLi precipitates. SEM observations confirmed the presence of α-Al dendrites with τ-Al2Mg3Zn3 and Mg7Zn3 particles in matrix. In interdendritic regions, it was observed the presence of the eutectic α-Al + τ-Al2Mg3Zn3 plus some primary Mg7Zn3 particles. δ-AlLi particles were identified at this step only by X-ray diffractometry. Finally, it was detected that an uniform distribution of precipitates in the α-Al dendrites together with an uniform distribution of a fine eutectic gave as a result in as-cast ingots an electrochemical efficiency up to 61.4 %.
Atomistic Simulation and Density Functional Analysis of Ni(111)-ZrO2(100)(Cubic) and NiO(111)-Ni(111)-ZrO2(100)(Cubic) Interfaces
Authors: Guo Chang-Xin , Ellis Donald E. , Dravid Vinayak P. , Brewer Luke
Published: April 2011

The atomic arrangement and electronic structure in the vicinity of Ni(111)- ZrO2(100)(Cubic) and NiO(111)-Ni(111)-ZrO2(100)(Cubic) interfaces have been studied by atomistic simulation and by first-principles Density Functional theory. “Depth Profiling” is carred out in both methodologies, to determine modifications of cohesive energy and electron distribution of atomic layers from the interface plane. The energy profiling results show the interface consists of only a few atomic layers. Simulation results and electron density analyses are in good agreement with High Resolution Spatially Resolved Electron Microscopy data.
Non-Equilibrium Wetting at Aluminium-Sapphire Interfaces
Authors: Levi George , Kaplan Wayne D.
Published: April 2011

Under most experimental conditions, the wetting of Al2O3 by liquid Al is a non-equilibrium phenomenon characterised by the continuous oxidation of Al. While the effect of oxygen at the liquid Al-vapour interface appears to be well understood, less is known about the influence of oxygen at the liquid Al-sapphire interface, due to a lack of microstructural evidence. Sessile drop experiments of liquid Al on sapphire (α-Al2O3) were conducted under a low pressure (10-3Torr) controlled Ar atmosphere as a function of oxygen partial pressure, temperature and/or time. Microstructural investigations of the samples from the wetting experiments indicated that two different dominant processes occur at the liquid Al-sapphire interface: epitaxial growth of new α-Al2O3 layers on the sapphire substrate at temperatures below ≍1100°C and dissolution of the sapphire substrate at temperatures above ≍1100°C.

The microstructural evidence indicates possible mechanisms by which oxygen is involved in the non-equilibrium wetting and adhesion of liquid Al on sapphire. The non-wetting to wetting transition in this system may be explained by the formation of an oxygen-rich interphase at the liquid Al-sapphire interface.
Sol-Gel Derived Pyroelectric Barium Strontium Titanate Thin films for Infrared Detector Applications
Authors: Cheng Jian-Gong , Tang Jun , Guo Shao-Ling , Chu Jun-Hao
Published: April 2011

Ba0.8Sr0.2TiO3 thin films that are suitable for infrared detector applications have been prepared with a sol-gel process using a highly diluted precursor solution. Columnar structure with grain size close to 200 nm was obtained with layer-by-layer homoepitaxy due to a very small thickness of individual layer. The measured pyroelecrtic coefficient is larger than 3.1×10划4 C/m2K at the temperatures ranging from 10 to 26 °C and reaches the maximum value of 4.1×10划4 C/m2K at 16.8 °C. The infrared detectivity of 4.6×107 cmHz1/2W划1 has been obtained at 19 °C and 10 Hz in the Ba0.8Sr0.2TiO3 films deposited on thick (500 μm) platinum coated silicon substrates. The better infrared response can be expected by the improvement in the thermal isolation of pyroelectric element and the electrode materials.
A Modified SBN System for Pyroelectric Sensors
Authors: Amorín H. , Guerrero F. , Portelles J. , Venet M. , Fundora A. , Siqueiros J. M.
Published: April 2011

The Thermally Stimulated Depolarization Current (TSDC) and pyroelectric properties of the modified SBN ferroelectric ceramic system were studied for different lanthanum and titanium doping concentrations. The TSDC measurements show the pyroelectric peak for all compositions while a second smaller peak at higher temperature, possibly associated to induced vacancy-impurity dipoles, is also observed in all cases. The second peak contribution was experimentally and mathematically eliminated to determine the remanent polarization and pyroelectric coefficient, both associated only to permanent ferroelectric dipoles. The figures of merit for sensor devices are determined for all compositions and compared with those of other pyroelectric systems. The La0.03Sr0.255Ba0.7 Nb1.95Ti0.05O5.975 sample, in particular, has excellent pyroelectric response, making this material very suitable for pyroelectricity-derived applications.
Piezoresponse Measurement and Imaging of Electromechanical PZT and PZN-BT thin Films
Authors: Morros C. , Corbett M.H. , Catalan G. , Gregg J.M. , Bowman R.M.
Published: April 2011

Pulsed laser deposition (PLD) was used to growth thin films of lead zirconium titanate (PZT) and lead zinc niobate-barium titanate (PZN-BT). The PZT films were prepared from commercial PZT-5H ceramic target and the PZN-BT made from target made using a modified Columbite method. The PZT films had dielectric constants of 300 and loss of 0.03 at 10kHz, whilst for the PZN-BT films they were 350 and 0.03 respectively at 300K. Hysteresis measurements confirmed their switching properties

A piezoresponse microscope based on a modified atomic force microscope was developed to determine electromechanical response at a sub-micrometer resolution. The PZT films yielded d33 ∼100pm/V. Mapping measurements on the PZT demonstrated local switching of individual grains. First measurements of piezoresponse of PZN-BT yielded values in the region 150-200 pm/V.
Ferroelectric and Fatigue Properties of Alkoxy-Derived CaBi2Ta2O9 Thin Films
Authors: Kato Kazumi , Suzuki Kazuyuki , Nishizawa Kaori , Miki Takeshi
Published: April 2011

CaBi2Ta2O9 (CBT) thin films were successfully prepared on Pt-passivated quartz glass substrates using a triple-alkoxide solution. The thin film crystallized to a single phase of perovskite at 750°C via a mixture of fluorite and perovskite phases. The 750°C-annealed thin film showed random orientation and consisted of fine grains with a diameter of about 80 nm. The dielectric constant and loss factor were 124 and 0.04, respectively, and were constant in the frequency range of 10 kHz to 1 MHz. The thin film exhibited P-E hysteresis loops at relatively high voltages. The remanent polarization and coercive electric field were 6.9 μC/cm2 and 170 kV/cm at 13 V, respectivey. The fatigue behaviors against various electric pulse sequences were examined. The polarization did not change when the pulse width was short such as 10-6 s, however, it increased gradually with number of switching cycles when the pulse width was relatively long such as 10-3 s.
Preparation and Characterization of (Bi,La)4Ti3O12 Films by the Sol-Gel Technique
Authors: Tokumitsu Eisuke , Isobe Takeaki , Kijima Takeshi , Ishiwara Hiroshi
Published: April 2011

(BiLa)4Ti3O12 (BLT) films have been fabricated by the sol-gel technique and characterized. It is shown that the partially replacing Bi with La can promote the crystallization, hence can reduce the crystallization temperature of the film. It is also demonstrated that crystalline orientations of sol-gel derived ferroelectric BLT films can be controlled by the growth conditions.
Degradation of Ferroelectric Capacitors during Metal Etching and Ashing Processes
Authors: Park Chanro , Kwon O Sung , Seol Yeo Song , Kim Jin Woong , Yoon Hee Koo
Published: April 2011

Polarization degradation due to metal etch and/or photoresist(PR) strip processes has been investigated for Pt/SrBi2Ta2O9(SBT)/Pt ferroelectric capacitors. Interconnect metal line consisting of TiN/Al/Ti/TiN/Ti layers has been patterned by normal photolithography and plasma etch processes. We used two different sources for metal etcher, helicon or electron cyclotron resonance(ECR) source, and stripped the PR with either microwave or helicon source stripper. Polarization degradation was evaluated by measuring switching and non-switching polarization of the ferroelectric capacitors.

Neither etch machine nor etch parameters played an important role for determining polarization of the ferroelectric capacitors. Photoresist strip process, however, significantly affected the polarization of the ferroelectric capacitors. Factors affecting polarization of the ferroelectric capacitors were presence of hydrogen and plasma density during the strip process. Hydrogen atoms and protons produced by H2O or NH3 plasma penetrated through the dielectric layer and caused hydrogen induced damage. Thus the hydrogen damage was dependent on strip temperature and time. Photoresist strip with high density plasma results in charging damage to ferroelectric capacitors. It is believed that charges from the plasma are trapped at domain boundaries and interfaces, leading to polarization degradation. Damage free metal etching process for the ferroelectric capacitor was applied for the fabrication of the fully working ferroelectric random access memory.
Preparation and Characterization of MFM and MFIS Structures Using Sr2(Ta1划x, Nbx)2O7 Thin Film by Pulsed Laser Deposition
Authors: Okuyama Masanori , Nakaiso Toshiyuki , Noda Minoru
Published: April 2011

Sr2(Ta1划x, Nbx)2O7(STN) ferroelectric thin films have been prepared on SiO2/Si(100) substrates by the pulsed laser deposition (PLD) method. Preferential (110) and (151)-oriented STN thin films are deposited at a low temperature of 600°C in N2O ambient gas at 0.08 Torr. A counterclockwise C-V hysteresis was observed in the metal-ferroelectric-insulator-semiconductor (MFIS) structure using Sr2(Ta0.7, Nb0.3)2O7 on SiO2/Si deposited at 600°C. Memory window in the C-V curve spreads symmetrically towards both positive and negative directions when applied voltage increases and the window does not change in sweep rates ranging from 0.1 to 4.0×103 V/s. The C-V curve of the MFIS structure does not degrade after 1010 cycles of polarization reversal. The gate retention time is about 3.0×103 sec when the voltages and time of write pulse are ±15V and 1.0 sec, respectively, and hold bias was -0.5 V.
Ferroelectric Properties of La-doped Bi4Ti3O12 Thin Films deposited directly on Si by pulse-injection MOCVD
Authors: Kim Joon Hyeong , Kim Jin Young , Kim Hyeong Joon
Published: April 2011

(Bi,La)4Ti3O12(BLT) thin films were prepared on Si(100) substrates by the pulse injection metalorganic chemical vapor deposition (MOCVD) process, in which Ti and La precursors were injected with periodic pauses while Bi precursor was supplied continuously. In case of the pulse injection method, the film composition was relatively uniform and the Bi content at the interface was relatively uniform and the Bi content at the interface was increased. The BLT films, which were deposited by the pulse injection MOCVD, showed better crystallinity and thinner ionterfacial amorphous layer than the continuous BLT films. The continuous BLT films, although measured at 1 MHz showed similar C-V characteristics to those measured at low frequency region, and their flatband voltages also shifted severely to the negative voltage direction. On the other hand, the pulse BLT films exhibited clockwise ferroelectric hysteresis in the C-V curves. The memory window and the leakage current density were about 2V and 1.46×10−7 A/cm2 at 9V (180 kV/cm), respectively.
Suppression of Oxidation of an Epitaxial (100)ZrN Film on Si During the Deposition of Ir Film
Authors: Horii Sadayoshi , Horita Susumu
Published: April 2011

The epitaxial (100)ZrN film on the (100)Si substrate is oxidized during Ir film sputtering deposition on (100)ZrN/(100)Si structure. Although the oxidation could be suppressed somewhat by increasing the deposition rate of the Ir film, it was not enough. In order to suppress the oxidation completely, 10 pieces of 10 × 10 mm2 Zr metallic plates were circularly placed on the non-erosion area of the Ir disc target. Using this target, the oxidation of the ZrN film was suppressed perfectly. Also, by adjusting of the diameter of the placed Zr circle, the contamination caused by Zr to the Ir film is avoided.
MOCVD Kinetics of Precursors for Ferroeletric SBT film
Authors: Baeri A. , Condorelli G.G. , Fragalà I.L.
Published: April 2011

The metal organic chemical vapour deposition kinetics of Sr(hfa)2(tet) (H-hfa =1,1,1,5,5,5-hexafluoroacetylacetone and tet= tetraglyme) and Bi(C6H5)3 single precursors have been studied upon varying operational deposition parameters, namely temperature and precursor partial pressure. These precursors are of interest for the MOCVD of SBT ferroeletric thin films. Depending upon experimental conditions, deposition processes occur either in the reaction rate limited regime or in the mass transport regime. Kinetics controlled by reaction rates (T deposition< 673 K) gives insights on the process mechanisms. The activation energies of the Sr and Bi deposition processes have been determined from the Arrhenius plots.

SrBi2Ta2O9 films were grown on industrial Pt/Ti/SiO2/Si substrates and perovskite phase films were obtained after annealing in O2 environment at 1073K.
Manufacturability Study for Etching High-Density BST/Pt Capacitors
Authors: Hwang Jay
Published: April 2011

Profile control, process repeatability and productivity concerns in etching Pt electrodes are reviewed specifically for application in fabricating high-density BST/Pt capacitors. The approach of using a high temperature cathode in a high-density reactive plasma chamber has produced a repeatable >85° Pt profile, stable etch rate and low particle results over a 500-wafer marathon test. A “corrosion-like” BST defect can be prevented by adding a post etch treatment to remove any corrosive residue from the wafer surface. A feasible manufacturing solution for etching BST/Pt capacitors for future high-density DRAM application is demonstrated.
Imaging Mechanism and Quantification of Scanning Probe Microscopies on Ferroelectric Surfaces
Authors: Kalinin Sergei V. , Bonnell Dawn A.
Published: April 2011

In the last few years a wide spectrum of non-contact, intermittent contact and contact scanning probe microscopies have been applied to imaging ferroelectric surfaces. The imaging mechanism in non-contact SPM is ultimately related to the total charge distribution on the ferroelectric surface, including both polarization and screening charges. Contact voltage modulation (piezoresponse) force microscopy (PFM) is sensitive to both local polarization via electromechanical coupling and surface charge via capacitive interactions. In the present research we analyze the electrostatic and electromechanical contrast in PFM using analytical solutions for the electrostatic sphere-dielectric plane problem and for the piezoelectric indentation problem. The contribution of electrostatic forces to the image is estimated. Variable-temperature PRI imaging of domain structures in BaTiO3 is performed and the temperature dependence of the piezoresponse is compared with the Ginzburg - Devonshire theory.
Self-polarization Mechanism in Textured Pyroelectric Pb(Ti1-xZrx)O3 films
Authors: Suchaneck G. , Gerlach G. , Poplavko Yu. , Kosarev A. I. , Andronov A. N.
Published: April 2011

Self-polarization of Pb(Ti1−xZrx)O3 (PZT) thin films is explained on the basis of the formation of a TiO2−x-enriched interlayer close to the bottom electrode. Electrons provided by oxygen vacancies generate a n-type interface layer in the PZT at the electrode. A graded ferroelectric layer is then formed by electron injection from the bottom electrode and electron trapping on Ti4+ ions. A “built-in” difference in free energy forms which acts to pole the ferroelectric. Band bending was observed by contact potential difference measurements at a distance of 70 to 90 nm from the bottom electrode.
Near field Optical second Harmonic Imaging of the Polydomain Structure of Epitaxial PbZrxTi1−xO3 thin films
Authors: Liang H.Y. , Smolyaninov I.I. , Lee C.H. , Davis C.C. , Nagarajan V. , Ramesh R.
Published: April 2011

Near field optical second harmonic microscopy has been applied to imaging of the c/a/c/a polydomain structure of epitaxial PbZrxTi1−xO3 thin films in the 0<x<0.4 range. An uncoated adiabatically tapered fiber tip was employed in our microscope which, according to our previous research [5] could yeild a resolution of up to 80 nm. Experimentally measured nearfield second harmonic images have been compared with the results of theoretical calculations. Good agreement between theory and experiment has been demonstrated. Thus, novel optical technique for nanometer scale ferroelectric domain imaging has been developed.
Magnetic Losses in Thick Barium-Hexaferrite Films on MgO (111)
Authors: Yoon S.D. , Oliver S.A. , Shi P. , Zuo X. , Vittoria C.
Published: April 2011

Barium hexaferrite films having thickness from 3 to 30 μm were deposited onto 0.5 mm Magnesium Oxide (111) substrates, and were examined by vibrating sample magnetometry, torque magnetometry, x-ray diffraction, and scanning electron microscope measurements. Ferrimagnetic resonance measurements were taken with the magnetic field applied perpendicular to the film plane. The FMR linewidth values for as-produced 3 - 30 μm films was 0.45 - 0.70 kOe, and was reduced to 0.06 - 0.45 kOe after annealing at 1000 °C for 2 hours. Further annealing increased the linewidth. The FMR linewidth for the 30 μm thick film was also found to decrease upon mechanically removing 55 ∼ 77 % of the substrate thickness. A 6-fold in-plane anistropy symmetry in the anisotropy energy was observed in torque magnetometry measurements for films thicker than 30 μm. These results can be interpreted as due to film inhomogeneity, stress, and the growth of small regions of non c-axis textured material.
Elastic and Inelastic Properties of Electroplated Nickel Used in LIGA Techniques
Authors: Skandar Basrour , Patrick Delobelle
Published: April 2011

The aim of this paper is a wide investigation at the micro scale of the elastic and inelastic properties of electroplated Nickel, which is extensively used in the LIGA techniques. Using a nano-indentation set-up, we have obtained the Berkovitch's hardness HB and the Young's modulus E. These mechanical properties are affected by the current densities used during the electroplating as well as the nature of the substrates. The roughness Ra was obtained thanks to confocal microscopy and a linear behavior of HB versus 1/ Ra corresponds to a Hall and Petch relation. The yield stress Y0 and the ultimate strength Q have been deduced from the experimental measurements using a Finite Element Method (FEM).Q has been found sensitive to the deposition conditions. Moreover (Y0+Q) has shown a linear dependence versus the hardness HB. Finally, Nickel microbeams fabricated by LIGA technique have been characterized with a bending test. The data deduced from this method, i.e. E and Y0+Q, are in good agreement with the results obtained by nano-indentation.
Dielectric and Pulsed Spectroscopy of Shear Mode PZT Microactuator
Authors: Brünahl Jürgen , Grishin Alex , Khartsev Sergey
Published: April 2011

Ferroelectric lead zirconate titanate (PZT) is the main industrial product in piezoelectric ceramic materials used for sensor and actuator applications. High precision in manufacturing of microelectromechanical systems is essential to get demanded performance accuracy. An adequate and preferably non-destructive measurement technique is desired to characterize the materials properties at various stages of device fabrication as well as to find correlation between the processing parameters, microstructure and functional properties. We report on a new pulsed technique, which has been employed to characterize all relevant properties of special machined array of PZT channels quickly, reliably and reproducibly: dielectric constant, loss factor tan σ, electromechanical coupling coefficient, resonance frequency and mechanical quality factor Q as well as temperature dependencies of these parameters.
Multilayer Materials for Electrostatic Switches
Authors: Phillips Mark A , Peterson Brennan L , Esber Christine M , Hwang Jesse , Clemens Bruce M
Published: April 2011

Metal multilayers are a unique way to manufacture reliable conductive members for MEMS devices. These members are particularly suited for electrostatic switches. Unlike elemental Al, which experiences curvature problems during processing, the residual stress in these beams can be controlled and calibrated during stress measurements to have repeatable shapes and stresses upon release. In this study, curvature experiments were performed to determine the optimal deposition parameters (pressure, thickness) to produce metal multilayer beams with zero average stress and zero bending moment, which can be obtained by alternating tensile and compressive layers within. Resistivity measurements were made to determine the effect of interfaces on resistivity.
Effect of La on the Growth of Cu6Sn5 Intermetallic Compound for Improved Sn-Pb Solder Joints
Authors: Ma Xin , Fang Hongyuan , Qian Yiyu , Yoshida Fusahito
Published: April 2011

Small amount of rare earth element La were added into the traditional Sn60-Pb40 solder alloy in order to improve the reliability of solder joints. The results of aging tests of solder joints showed that, the growth of interface Cu6Sn5 intermetallic compound was depressed by La addition. Furthermore, the thermal fatigue life of solder joints was improved by 3 times. Thermodynamic analysis indicated that La had higher affinity with Sn in the Sn-Pb-La system, and then the driving force for Cu6Sn5formation was reduced since the activity of Sn was lowered.
Measurements of Residual Stress in the Layers of Thin Film Micro-Gas Sensors
Authors: Kim Youngman , Choo Sung-Ho
Published: April 2011

The mechanical properties of thin film materials are known to be different from those of bulk materials, which are generally overlooked in practice. The difference in mechanical properties can be misleading in the estimation of residual stress states in micro-gas sensors with multi-layer structures during manufacturing and in service.

In this study the residual stress of each film layer in a micro-gas sensor was measured according to the five difference sets of film stacking structure used for the sensor. The Pt thin film layer was found to have the highest tensile residual stress, which may affect the reliability of the micro-gas sensor. For the Pt layer the changes in residual stress were measured as a function of processing variables and thermal cycling.
Control of Stress with Growth Conditions and Mechanical Parameters Determination of 3C-SiC Heteroepitaxial Thin Films
Authors: Gourbeyre C. , Chassagne T. , Berre M. Le , Ferro G. , Malhaire C. , Monteil Y. , Barbier D.
Published: April 2011

We report here on the influence of the epitaxial growth conditions on the residual stress of heteroepitaxial 3C-SiC grown on silicon using atmospheric-pressure chemical vapour deposition (APCVD) and on the determination of its mechanical properties. 3C-SiC films were grown on (100) Si substrates in a vertical reactor by APCVD. SiH4 and C3H8 are used as precursor gases and H2 as carrier gas. The growth procedure involves the formation of a carburization buffer layer at 1150°C under a mixture of H 2 and C3H8. The epitaxial growth occurs then at 1350°C by adding SiH 4.

For as-deposited films the measurement techniques implemented are substrate curvature measurements, AFM, and nano-indentation. For micromachined self-suspended SiC membranes, load deflection measurements were used. The substrate curvature measurement leads to the determination of the residual stress in the deposited SiC film. We show that we can achieve 3C-SiC layers with a compressive or a tensile state having equivalent crystallinity. Whereas thermal mismatch just accounts for tensile stresses, we demonstrate that 3C-SiC thin films may have compressive stresses by using specific conditions for the formation of the buffer layer. The early stage of growth is indeed of major importance.

Regarding the mechanical properties, the 3C-SiC Young's modulus was determined using nano-indentation. Its mean value reaches 378 GPa comparable to the calculated value of 307 GPa. As test structures, we have processed self-suspended SiC membranes. Load deflection measurements enable the determination of the Young's modulus and the residual stress of the self-suspended films. For self-suspended SiC membranes, the absolute value of the residual stress in the SiC thin films decreases compared to the as-deposited films and takes a mean value of 170 MPa in a tensile state.
Fabrication of MEMS Components Based on Ultrananocrystalline Diamond Thin Films and Characterization of Mechanical Properties
Authors: Sumant A. V. , Auciello O. , Krauss A. R. , Gruen D. M. , Ersoy D. , Tucek J. , Jayatissa A. , Stach E. , Moldovan N. , Mancini D. , Busmann H. G. , Meyer E. M.
Published: April 2011

The mechanical, thermal, chemical, and tribological properties of diamond make it an ideal material for the fabrication of MEMS components. However, conventional CVD diamond deposition methods result in either a coarse-grained pure diamond structure that prevents high- resolution patterning, or in a fine-grained diamond film with a significant amount of intergranular non-diamond carbon. At Argonne National Laboratory, we are able to produce phase-pure ultrananocrystalline diamond (UNCD) films for the fabrication of MEMS components. UNCD is grown by microwave plasma CVD using C60-Ar or CH4-Ar plasmas, resulting in films that have 3-5 nm grain size, are 10-20 times smoother than conventionally grown diamond films, and can have mechanical properties similar to that of single crystal diamond. We used lithographic patterning, lift-off, and etching, in conjunction with the capability for growing UNCD on SiO2 to fabricate 2-D and 3-D UNCD-MEMS structures. We have performed initial characterization of mechanical properties by using nanoindentation and in-situ TEM indentor techniques. The values of Hardness (∼88 GPa) and Young's modulus (∼ 864 GPa) measured are very close to those of single crystal diamond (100 GPa and 1000 GPa respectively). The results show that UNCD is a promising material for future high performance MEMS devices.
Young's Modulus and Fracture Strength of Three Polysilicons
Authors: Sharpe W. N. , Jackson K. , Coles G. , LaVan D. A.
Published: April 2011

Polysilicon specimens from Cronos, Sandia, and Standard MEMS, Inc. were tested in tension. The specimens were nominally 6 or 20 μm wide and 250 or 1000 μm long. The Cronos and the Standard MEMS specimens had thicknesses of 1.5, 2.0, and 3.5 μm; whereas, the Sandia specimens were all 2.5 μm thick.

There was no dramatic difference in Young's modulus for the three materials. A total of 117 tests were run, and the average modulus for all three materials was 157 ± 9 GPa. However, the strengths were quite different: 1.56 ± 0.25 GPa for the Cronos material, 2.85 ± 0.40 GPa for Sandia's, and 2.04 ± 0.30 GPa for the SMI polysilicon.
High-Cycle Fatigue of Polycrystalline Silicon Thin Films in Laboratory Air
Authors: Muhlstein C. L. , Brown S.B. , Ritchie R.O.
Published: April 2011

When subjected to alternating stresses, most materials degrade, e.g., suffer premature failure, due to a phenomenon known as fatigue. It is generally accepted that in brittle materials, such as ceramics, cyclic fatigue can only take place where there is some degree of toughening, implying that premature fatigue failure would not be expected in polycrystalline silicon where such toughening is absent. However, the fatigue failure of polysilicon is reported in the present work, based on tests on thirteen thin-film (2 μm thick) specimens cycled to failure in laboratory air (∼25°C, 30-50% relative humidity), where damage accumulation and failure of the notched cantilever beams were monitored electrically during the test. Specimen lives ranged from about 10 seconds to 34 days (5 × 105 to 1 × 1011 cycles) with the stress amplitude at failure being reduced to ∼50% of the low-cycle strength for lives in excess of 109 cycles.
Challenges in DMD™ Assembly and Test
Authors: Jacobs S. Joshua , Malone Joshua J. , Miller Seth A. , Gonzalez Armando , Robbins Roger , Lopes Vincent C.
Published: April 2011

The Digital Micromirror Device™ (DMD™) developed at Texas Instruments is a spatial light modulator composed of 500,000 to 1.3 million movable micromachined aluminum mirrors. The DMD™ serves as the engine for the current generation of computer-driven slide and video projectors, and for next generation devices in digital television and movie projectors. The unique architecture and applications of the device present several packaging and test challenges. This paper provides a description of package humidity modeling and verification testing, as well as an overview of the automated optical testing and test equipment that have been developed to support manufacturing of the DMD™.
MEMS Materials and Fabrication Technology on Large Areas: The Example of an X-ray Imager
Authors: Daniel J.H. , Krusor B. , Lau R. , Lu J.P. , Wang Y. , Mulato M. , Apte R.B. , Street R.A. , Goredema A. , Boils-Boissier D.C. , Silver S.E. , Kazmaier P.M.
Published: April 2011

Micromachining has potential applications for large area image sensors and displays, but conventional MEMS technology, based on crystalline silicon wafers cannot be used. Instead, large area devices use deposited films on glass substrates. This presents many challenges for MEMS, both as regards materials for micro-machined structures and the integration with large area electronic devices. We are exploring the novel thick photoresist SU-8, as well as plating techniques for the fabrication of large area MEMS. As an example of its application, we have applied this MEMS technology to improve the performance of an amorphous silicon based image sensor array. SU-8 is explored as the structural material for the X-ray conversion screen and as a thick interlayer dielectric for the thin film readout electronics of the imager.
Formation of Biaxially Textured MgO Buffer Layers using Ion-Beam Assisted Pulsed Laser Deposition
Authors: Hühne Ruben , Beyer Christoph , Holzapfel Bernhard , Oertel Carl-Georg , Schultz Ludwig , Skrotzki Werner
Published: April 2011

MgO thin films were deposited on amorphous substrates using ion-beam assisted pulsed laser deposition. The texture formation was investigated in-situ with RHEED. The microstructure of the films was observed by AFM. Using an ion beam at an angle of 55° with respect to the substrate normal, strong nucleation textures develop. Above 250°C a cube texture is observed in films thinner than 10 nm. During further growth this nucleation texture changes in a way that the <200> direction becomes parallel to the ion beam. This change can be explained by the anisotropic sputter rate of MgO found in sputter experiments on single crystals. Moreover, MgO films were deposited homoepitaxially on MgO single crystals above 250°C with internal stresses dreasing with increasing deposition temperature. This result gives rise to hope that homoepitaxial growth of MgO on the nucleation layer without ion-beam assistance should be possible in future PLD-experiments keeping the desired cube texture in thicker films.
DTA/TGA Study of Eutectic Melting in the System BaF2-BaO-Y2O3-CuOx−H2O
Authors: Cook Lawrence P. , Wong-Ng Winnie , Suh Julia
Published: April 2011

Differential thermal analysis and thermogravimetric analysis (DTA/TGA) experiments have been completed in the BaF2-BaO-Y2O3-CuOx-H2O system at various oxygen pressures to determine the effect of adding solid BaF2and gaseous H2O (at pH2O = 2.5 kPa) on the eutectic melting in the system BaO-Y2O3-CuOx. We have investigated the eutectic melting temperature over the range of pO2 = 20 Pa to pO2 = 0.1 MPa under the following conditions: 1) without BaF2 or H2O; 2) with H2O only; 3) with BaF2 only; 4) with both BaF2 and H2O. Results indicate that without BaF2 or H2O, eutectic melting is depressed from 917°C at pO2 = 0.1 MPa to 838°C at pO2 = 1 kPa. At oxygen pressures below 1 kPa, down to pO2 = 20 Pa, no further lowering of eutectic melting temperature was observed. The topologies of the temperature vs. log pO2 curves for various combinations of BaF2 and H2O were similar to that for the experiments without BaF2 or H2O, but all curves were shifted to lower temperatures. For the experiments with addition of BaF2 only, H2O only, and BaF2 with H2O, the eutectic melting temperatures as a function of pO2 were lowered by, respectively, 5°C - 15°C, 15°C - 25°C and 20°C - 30°C. Application of results to the “BaF2ex-situ” method of processing Ba2YCu3Ox coated conductors is discussed.
Superfluid Density in Ultrathin YBCO Films
Authors: Delimova Lyuba A. , Grekhov Igor V. , Liniichuk Ivan A. , Veselovsky Ivan A. , Traito Konstantin B. , Lahderanta Erkki
Published: April 2011

We studied the transition of 8 nm-thick YBCO films deposited with and without YBaCuNbO buffer from the superconducting to resistive state due to the temperature or transport current increase. For both film types, the current –voltage characteristics and resistive transition followed the Kosterlitz-Thouless transition model. The superfluid densities were found from the Kosterlitz-Thouless transition temperature TKT to be about 3% and 1.3% of the total carrier density in YBCO with and without buffer, respectively. We believe that the low superfluid densities indicate the presence of weak links in the film.
Nanofiller Modification of Phase Stability in PS/PMMA Blends
Authors: Ji G. , Clement F. , Giannelis E.P.
Published: April 2011

The effect of nanoparticles on the phase stability of an immiscible PS/PMMA blend was studied in thin film samples. Using AFM and selective dissolution we find that nanoparticles affect the domain evolution of the polymer blend. Annealing of the pure PS/PMMA blend at 190 °C leads to PS drops that protrude from the PMMA surface. Films containing the nanoparticles show similar surface features but these features become less regular and tend to get shallower and larger as the amount of nanoparticles increases. The characteristic length of the PS drops in the pure blend film is ∼ 7 microns and they cover 22 % of the surface. The corresponding numbers for the film containing 10% nanoparticles are 15 microns and 65%, respectively.
Investigation into the Thermal and Mechanical Behavior of PMMA/Alumina Nanocomposites
Authors: Ash Benjamin J. , Stone Jason , Rogers Diana F. , Schadler Linda S. , Siegel Richard W. , Benicewicz Brian C. , Apple Thomas
Published: April 2011

Polymethylmethacrylate (PMMA) nanocomposites were synthesized by free radical polymerization in the presence of various weight percentages of alumina (Al2O3) nanoparticles. The resulting nanocomposites show an average increase of 600% in strain-to-failure and the appearance of a well-defined yield point. Concurrently, the glass transition temperature (Tg) of the composites decreased 20°C, while the ultimate strength and the Young's modulus decreased by 20% and 15%, respectively.
Extracting Dispersion from Roughness
Authors: Tricot Claude
Published: April 2011

A mathematical analysis of surfaces may help to understand how the carbon black is dispersed into polymer. Rubber samples are broken out, and the rupture interface is scanned with a prolometer. The roughness is detected at the micron scale. Roughness functions are dened, measuring the average oscillations of the surface. The roughness behaviour is “fractal” for small scales until around 10 microns, then become linear. A roughness ratio is defined, depending both on the scale and on the mixing time. There is evidence to suggest that the roughness ratio does not depend on the polymer, but only on the dispersion of the filler. A dispersion factor is derived, and results are shown on three diserent compounds.
Nanofiller-Polymer Interactions At and Above the Glass Transition Temperature
Authors: Zhu Ai-jun , Sternstein Sanford S.
Published: April 2011

Rheological data are reported for a series of fumed silica filled PVAc samples, using fillers of different specific surface areas and surface treatments. Data at the glass transition temperature and 45 C above Tg are presented. The addition of filler systematically increases Tg, and all samples obey time-temperature superposition. However, temperature normalized and frequency normalized plots of loss modulus indicate that there is no change in the dispersion of the glass transition, with the only exception being a surface modified with covalently bonded polymer chains. Thus, contrary to expectations, an increase in filler content or change in surface treatment has no effect on the relative shape of the relaxation time spectrum at the glass transition. At 45 C above Tg, different behavior is observed. The filler concentration has a major effect on the nonlinearity of dynamic moduli vs. strain amplitude, with higher filler content reducing the strain amplitude at which nonlinear behavior is observed. Specific filler surface treatments result in major changes in the shape of the loss factor versus strain amplitude relationship. These results suggest that interfacial interactions strongly modify the far-field polymer behavior with respect to chain entanglement slippage at large strains.
Restricted Dynamics in Polymer-Filler Systems
Authors: Arrighi V. , Gagliardi S. , Higgins Julia S.
Published: April 2011

Composites in which fibres or fillers are incorporated into a polymeric component exhibit improved mechanical strength compared to the polymer matrix. This reinforcement effect strongly depends on the properties of the interphase and the specific interactions between the polymer and the reinforcing additive.

A wide range of experimental methods have been used to assess the effect of active fillers on the mobility of the polymer chains. The experimental results from NMR, dielectric spectroscopy and dynamical thermal analysis reveal that the mobility of chain units adjacent to the adsorbed surface differs considerably from the bulk.

We have used quasielastic neutron scattering to investigate the dynamic properties of poly(dimethyl siloxane) (PDMS) filled with silica particles. This technique which probes the motion of the hydrogen atoms has been extensively used to study the local dynamics of polymeric materials. In this paper we show that QENS provides detailed information on the reduced mobility of chain segments in polymer-filler systems.

QENS measurements were carried out on PDMS filled with hydrophilic Aerosil with different specific surface area (average diameter 7 and 20 nm). Detailed data analysis indicates that the QENS spectra of the polymer-filler composites can be described by the sum of two contributions: (a) a quasielastic component due to chains not affected by the presence of the fillers and (b) an elastic term from those chain segments strongly affected by the presence of fillers. The latter depends on the specific surface area of the particles and their weight fraction in the composite.
Polymer-Clay Nanocomposite Materials: Solution and Bulk Properties
Authors: Schmidt Gudrun , Nakatani Alan I. , Butler Paul D. , Ferreiro Vincent , -Karim Alamgir , Han Charles C.
Published: April 2011

The influence of shear on viscoelastic polymer-clay solutions was investigated by means of small-angle neutron scattering (SANS) under shear. SANS measured the shearinduced orientation of polymer and platelets. With increasing shear rate an anisotropic scattering pattern developed. At higher shear rates, the scattering anisotropy increases due to the increased orientation of the clay platelets in the shear field. Cessation of shear leads to fast recovery demonstrating the system to be highly elastic. As a result of drying, these solutions produce translucent nanocomposite films with a microporous membrane character. Depending on the preparation and degree of polymer-clay film dispersion, it is possible to modify the morphology and elastic properties of nanocomposite materials. Atomic Force Microscopy (AFM) reveals the network character and the development of morphology as a function of polymer concentration. Preliminary SANS experiments on the films will be correlated to morphologies obtained from AFM.
A Preliminary Study on Rice Husk Filled Polypropylene Composite
Authors: Sun Luyi , -Xiao Min , Xiao Peng , Song Jianhua , Wang Weixing , Zhang Yafeng , Gong Kecheng
Published: April 2011

The major inorganic component of the rice husk (RH) is silica (∼20%)[1]. In the past, the utilization of RH mainly concentrated on the ash of the rice husk, such as using rice husk ash (RHA) as filler in plastics, especially in polypropylene (PP). In this work, RH was directly used as filler in PP. Some treatments were applied to the RH. PP composites of different filler loadings were compounded using a laboratory size two-roll mixer at a temperature of 180° C for a period of 5 minutes. The tensile strength of the RH-PP composites increased steadily with increasing filler loading until about 20% loading. The impact strength of the composites decreased with the increasing filler loading. Torques and melt index (MI) of composites with various filler loadings were investigated. The MI of the composite decreased with the increasing filler loading. RH showed more potential than RHA as PP filler.