bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Wireless MEMS Inertial System for Health Monitoring of Structures
Authors: Kok Ronald , Furlong Cosme , Pryputniewicz Ryszard J.
Published: April 2011

Advancements in microelectromechanical technologies have lead to progressive design of small footprint, low dynamic mass and actuation power, and high-resolution MEMS inertial sensors. In this paper, development of instrumentation and methodologies for wireless health monitoring of structures using MEMS inertial sensors is presented. A dedicated experimental setup is developed to characterize specific MEMS inertial sensors and structures. Studies presented in this paper include development and characterization of a prototype wireless data acquisition system to transmit analog and digital signals. Results show that the frequency response of the prototype wireless data acquisition system is compatible with the frequency response of the MEMS inertial sensors utilized. The prototype wireless MEMS inertial system is applied to perform tilt and rotation measurements. It is shown that with the wireless MEMS system it is possible to achieve an angular resolution of 1.8 mrad.
Piezoelectric Actuators for Synthetic Jet Applications
Authors: Mossi Karla , Bryant Robert
Published: April 2011

Synthetic jets have been identified and utilized widely in airflow control applications. These jets of air are usually created by the use of compressed air, or an electromechanically driven vibrating platform. All of these approaches produce desired results in airflow-control such as enhanced lift and increased maneuverability. Despite the results however, system weight, size, response time and force limit their use in aircraft applications where space is a premium. The objective of this study is to characterize the relevant properties for the design of a synthetic jet utilizing three types of piezoelectric actuators as mechanical diaphragms. The limiting parameters of the actuators for this application are shape and volumetric space. Thus, the actuators were circular with a diameter of 6.35 cm, and overall device cavity volume no larger than 147.5 cm3 on a 7 cm x 7 cm areal coverage. The actuators tested were pre-stressed curved metallic unimorphs, bimorphs, and radial field diaphragms. These piezoelectric elements were chosen because of their geometry, quasi-isostatic topography and overall free-displacement. Each actuator was affixed about its perimeter in a cavity, and relevant parameters such as clamped displacement, and jet velocity though a pre-determined dimensional slot, were measured.
Cyclic magnetic-field -induced deformation and magneto-mechanical fatigue of Ni-Mn-Ga ferromagnetic martensites
Authors: Müllner P. , Chernenko V. A. , Mukherji D. , Kostorz G.
Published: April 2011

Four Ni-Mn-Ga single crystals exhibiting modulated 10M and 14M martensites were exposed to rotating magnetic fields of 1 and 2 T. Large periodic magnetic-field-induced strains were obtained for crystals that had been subjected to a mechanical stress while the martensite formed on cooling and to deformation in a magnetic field prior to the experiments with rotating field. A reduction of the magnetic-field-induced strain and fracture occurred when the field-induced strain was close to the transformation strain whereas a constant magneto-mechanical response was detected over more than 10 million field cycles when the field-induced strain was small. The cyclic magneto-mechanical response is related to the interaction of groups of twinning dislocations and twin boundaries. If the dislocations move in large groups, they nucleate cracks at twin boundaries. If the dislocations move in small groups, no cracks are formed resulting in a long lifetime.
Development of Texture-Controlled Bulky Actuator/Sensor Materials by Combining Rapid-Solidified Fiber/Ribbon Elements and Spark Plasma Sintering/Joining(SPSJ)
Authors: Furuya Y. , Yokoyama M. , Saito C. , Okazaki T. , Omori M.
Published: April 2011

The authors have showed that rapid-solidified (RS) melt-spun fiber/ribbon/foil type samples have very often strongly textured fine columnar grains, and those can have very high performance of the metallic actuator/sensor properties. However, as for the applications of these sample materials in smart material systems, the developed rapid-solidified samples are thought to be inevitably too small force to move the machines and structures in the engineering field. In this paper, we propose one novel material processing technique that can produce the bulk type solid-state actuator/sensor materials by combing the rapid-solidified fiber/ribbon and short time spark plasma sintering/joining (SPS) method. The produced samples, both 1) the disk-type sample from stacked layers of RS-ribbons and 2)the sintered compact from ball-milled RS-fibers of shape memory Ti50Ni40Cu10 (NITINOL) alloy, showed clear thermoelastic phase transformation by DSC evaluation as well as shape recovery. The same approach was also tried for making bulky magnetostrictive FeGa(Galfenol) alloy systems from stacked FeGa ribbons. Laminated FeGa ribbons maintained large magnetostriction of about 100–200ppm under increasing stressed condition as much as in the case of the strongly textured ribbon sample.
The Development of Active and Sensitive Structural Material Systems
Authors: Asanuma Hiroshi
Published: April 2011

This paper describes new concepts the author has proposed and demonstrated to realize metal and polymer based sensitive and/or active structural material systems suitable for smart structures. Most of the developments have been done by simple and innovative methods without using sophisticated and expensive sensors and actuators. The following topics are mainly examined: (1) forming optical interference and loss type strain sensors in epoxy matrix simply by embedding and breaking notched optical fiber in it; (2) forming a multifunctional sensor in aluminum matrix for temperature and strain monitorings by embedding an oxidized nickel fiber; (3) fabricating multifunctional composites by using conventional structural materials -an active laminate of CFRP/aluminum of which unidirectional actuation is realized by electrical resistance heating of carbon fiber in the CFRP layer and its curvature change can be monitored using optical fiber multiply fractured in the CFRP layer; (4) fabricating active fiber-reinforced metals such as SiC/Al and SiC/Ni systems by laminating a reinforced layer with a unreinforced layer to cause thermal deformation. In the case of SiC/Al composite, actuation was performed only in the fiber direction and is useful for making a light-weight active panel. In the case of SiC/Ni composite, actuation took place up to above 1200K and is useful for making a high temperature actuator.
Fundamental Investigation of Ferromagnetic Shape Memory Alloys: A New Perspective
Authors: Sullivan Matthew R. , Ateya Daniel A. , Pirotta Steven , Shah Ashish A. , Wu G. H. , Chopra Harsh Deep
Published: April 2011

In the present study, the evolution of micromagnetic structure and microstructure is studied in-situ both as a function of temperature and applied magnetic field, using single crystal Fe-Pd and Ni-Mn-Ga Heusler alloys. Through the development of a novel technique called ‘Magnetic Transition Spectrum’ to study temperature dependent domain dynamics, the relative sequence of micromagnetic reconfiguration with respect to the martensitic transformation has been determined for the first time. Results show that the FSMAs may be viewed as magnetic mosaics, a new perspective, which is also more amenable to modeling the physical properties of these alloys. Finally, the concept of magnetic mosaics has been used to synthesize a novel class of materials with engineered magnetic anisotropies, and is briefly discussed.
Phase Transformations of Ferromagnetic Fe-Pd-Pt-Based Shape Memory Alloys
Authors: Yang Gwon-seung , Jonasson Reid , Baek Seung-nam , Murata Kinzo , Inoue Shozo , Koterazawa Keiji , Jeong Soon-jong , Mizuuchi Kiyoshi , Inoue Kanryu
Published: April 2011

Several ternary Fe-Pt-Pd alloys with the compositions of Fe-(25-x) at% Pt-x at% Pd and Fe-y at% Pt-(30-y) at% Pd were investigated to study their phase transformations in order to develop ductile ferromagnetic shape memory alloys appearing around room temperature. Alloys were prepared by vacuum floating induction melting, followed by hot rolling at 1000°C and homogenization at 900° C. Homogenized alloys were heat treated at 650°C for various periods of time in vacuum for atomic ordering in encapsulated quartz tubes, and quenched into iced water. It was found that in general the transformation temperatures changes with heat treatment time. In the case of Fe-23at.%Pt-2at.%Pd, Ms temperature increased and the difference between Ms and Mf increased with increasing heat treatment time, which was different from Fe3Pt where a degree of order becomes one. As heat treatment time increased, there was a tendency in that a strong first-order transformation in the disordered state was replaced by a weak first-order transformation. The Curie temperature of the alloys rose drastically with the addition of Pd, along with the transformation temperatures. Fe-23at.%Pt-2at.%Pd showed good shape memory effect after 8 hours of heat treatment at 650°C. This alloy showed much better shape recovery than any other binary Fe-Pt and Fe-Pd shape memory alloys.
Elasticity Study in Ferromagnetic Shape Memory Alloys
Authors: Dai Liyang , Cullen James , Cui Jun , Wuttig Manfred
Published: April 2011

The temperature dependences of the elastic constants of Ni0.50Mn0.284Ga0.216 and Fe3Pd were studied. Measurements were conducted by the ultrasonic continuous wave method. Anomalous behavior of the elastic constants temperature dependence in austenitic NiMnGa was observed, especially an abrupt 15% softening of C11 at the Curie temperature. The latter anomaly was found to be strongly influenced by the presence and orientation of applied magnetic fields. In martensitic NiMnGa, the temperature dependences of the velocities of all eleven elastic wave modes had abrupt changes at 220K, which indicate a structural phase change from the tetragonal to a second phase at lower temperature. The temperature and magnetic field effects in Fe3Pd were also studied by the elastic constants measurements.
Nanoscale investigation of polar structure of (1-x)PbMg1/3Nb2/3O3-xPbTiO3 single crystals
Authors: Shvartsman V. V. , Wojtas M. , Vakhrushev S. , Kholkin A. L.
Published: April 2011

ABSTRACT (1-x)PbMg1/3Nb2/3O3-xPbTiO3 (PMN-PT) single crystals of different compositions were studied via piezoresponse force microscopy (PFM). Piezoelectric contrast has been observed in 0.9PMN-0.1PT above the temperature of structural transition indicating spatial distribution of polarization and was attributed to the existence of polar clusters. The domain patterns were found to change drastically with increasing Ti content. In particular, the piezoresponse images of 0.8PMN-0.2PT combine both relaxor and ferroelectric features and in 0.65PMN-0.35PT crystals only micron-sized ferroelectric domains were observed. The evolution of the polar structures with increasing temperature and under external electric field was also investigated. The nature of the observed phenomena is discussed based on the current understanding of the relaxor state in ferroelectrics and possible influence of PFM instrumentation
Structural and dielectric properties of Ca1-x MgxCu3Ti4O12 thin films
Authors: Bermúdez L. A. , Guzman R. P. , Tomar M.S. , Melgarejo R.E.
Published: April 2011

Ca1-xMgxCu3Ti4O12 material has been synthesized by chemical route for different compositions and thin films have been deposited by spin coating. X-ray diffraction and Raman spectroscopy were used for detailed characterization of this material for both powder and thin films. X-ray diffraction shows single phase film material for different compositions x < 0.80. The initial measurements on dielectric response indicates high dielectric constant > 10, 000 for the composition x = 0.1.
Fabrication and Characterization of TiNi/AL Smart Composites
Authors: Lee Gyu Chang , Lee Jun Hee. , Park Young Chul
Published: April 2011

An attempt was made to fabricate composite material of an Al alloy matrix reinforced by TiNi shape memory fiber using a hot-press method and to investigate its microstructures and mechanical properties. The analysis of SEM and EDS showed that the composite material had good interface bonding. The stress-strain behavior of the composite material was evaluated at room temperature and 363 K as a function of pre-strain, and it showed that the yield stress at 363 K is higher than that at room temperature. It is also found that the yield stress of the composite material increased with increasing the amount of pre-strain and depended on the volume fraction of the fiber and heat treatment. The smartness of the composite could be given due to the shape memory effect of the TiNi fiber, which generated compressive residual stress in the matrix material when heated after being pre-strained. Microstructural observation revealed that interfacial reactions occurred between the matrix and fiber, creating two intermetallic layers.
Characterization of NiTiNOL for Smart Structural Systems using ACES Methodology
Authors: Mizar Shivananda P. , Pryputniewicz Ryszard J.
Published: April 2011

SMAs are engineering alloys that recover extensive amounts of deformation when subjected to a temperature change. The recovery of deformation is as result of a phase transformation from martensite to austenite. For example, for NiTiNOL, a very popular SMA, this transformation occurs at 60°C. Actuation is a type of shape memory process that utilizes deformation recovery that is used in smart structural systems. These systems are designed to detect and control structural deformations due to external time varying loads encountered during functional operation. In this paper, the actuating properties of NiTiNOL are characterized using an analytical, computational, and experimental solution (ACES) methodology. Analytical models are utilized to calculate the deformation under dynamic loads. Finite element method (FEM) is used for computational investigations. Optoelectronic holography (OEH) is the experimental method utilized to obtain temperature dependent behavior of NiTiNOL. As a result of the phase transformation, NiTiNOL undergoes a stiffness change indicated by a change in the modulus of elasticity from 33 GPa to 75 GPa. Deformations of NiTiNOL samples subjected to static loads at different temperatures were measured indicating recovery of 85% due to the phase transformation. In addition, amplitudes of vibration were measured as a function of excitation frequency and temperature to determine the effects of phase transformation. The results show effectiveness of NiTiNOL in development of smart structural systems
Fabrication and characterization of freestanding NiMnGa films
Authors: Rumpf Holger , Craciunescu Corneliu , Feydt Jürgen , Gilles Achim , Wuttig Manfred , Quandt Eckhard
Published: April 2011

Freestanding Ni50Mn30Ga20 films of 13 μm thickness were fabricated by DC magnetron sputtering and analyzed. Magnetic measurements revealed the influence of the post deposition rapid thermal annealing process on the ferromagnetic hysteresis. Ferromagnetic properties evolved after annealing at 400°C. Thermal annealing of at least 600°C led to polycrystalline films that transformed reversibly and martensitically as shown by structural analysis and differential scanning calorimetry. Transformation temperatures and enthalpies of transformation of the martensitic transformation were strongly influenced by the temperature of the rapid annealing process. It is proposed that the annealing data reflect the evolution of the crystalline state.
Thermo-Mechanical Characteristics of Ti-Ni-Cu Shape Memory Alloy Fabricated by Pulse-Current Pressure Sintering Method
Authors: Kyogoku Hideki , Kadomura Takeshi , Komatsu Shinichiro , Yoshida Fusahito , Sakuma Toshio
Published: April 2011

The Ti-Ni-Cu shape memory alloy by elemental powders was fabricated by means of a pulse-current pressure sintering method that can produce high-density sintered compacts in a very short sintering time. The fabrication conditions of Ti-Ni-Cu alloy and the influence of Cu content in Ti-Ni-Cu alloy on the tensile properties and thermo-mechanical characteristics were investigated. The relative density of the as-sintered compacts was around 97% at any Cu content. The microstructure, tensile properties and thermo-mechanical characteristics of the as-sintered compacts were improved greatly by performing a solid solution heat-treatment. The yielding behavior due to the stress-induced martensite in stress-strain curves of the alloy took place after elastic deformation at any Cu content. The deformation resistance of the alloys changed with Cu content, and it was lowest around 9at% in Cu content. The tensile strength and elongation of the alloy with Cu content around 9at% were more than 400 MPa and 6%, respectively. It was found that the thermo-mechanical behavior of the alloy becomes stable by performing cyclic deformation.
Temperature-Responsive Polymers for Biological Applications
Authors: Rackaitis M. , Manias E.
Published: April 2011

Water soluble polymers with tunable lower critical solution temperature (LCST) are of increasing interest for biological applications such as cell patterning, smart drug release, DNA sequencing etc. The present study addresses control of the polymer temperature response in water by varying chemical composition of the monomer. In order to achieve this a series of polymers were designed and synthesized based on an ethyleneoxide/ethylene monomer (EO/EE). Polymers were synthesized using polycondensation reactions of difunctional m-EO and n-EE oligomers. The cloud point follows linearly the balance of hydrophobic/hydrophilic interaction and can be tailored in the range of 7 – 70°C by varying the m/n composition and polymer type. Polymer grafting onto the silicon surface exhibits similar solubility behaviour. Adhesion energy measurements show that grafted polymers have solubility cloud points at the temperatures that are close to the ones of the bulk polymer solutions.
Exploration of an Electroactive Polymer as an Actuator for Microrobotics
Authors: Bielmeier C. , Walter W.
Published: April 2011

The development of lightweight low power consumption actuators is critical to the development of micro-robotics. Electroactive Polymers (EAP), i.e. Nafion N-117, meet these requirements. In the actuation of an EAP, the current does not remain constant over time. The development of a circuit model of current draw over time to best predict a current dynamic has been explored. While the material mimics a parallel plate capacitor, it has been found that capacitance plays no role in achieving steady state current levels. This development is critical to understanding and developing the material as an actuator.
Synthesis and VOC gas sensing properties of Polypyrrole / MoO3 Nanohybrids
Authors: Hosono Kouta , Matsubara Ichiro , Murayama Norimitsu , Woosuck Shin , Izu Noriya
Published: April 2011

We have prepared polypyrrole (PPy) / MoO3 nanohybrid thin films and evaluated their volatile organic compound (VOC) gas sensing properties. The (PPy)xMoO3 thin films have been prepared by intercalation reactions of highly oriented MoO3 thin films. Intercalation of hydrated sodium ions successfully proceeded without loosing the crystallographic orientation. The (PPy)xMoO3 thin films was obtained by replacing the hydrated sodium ions with PPy. The (PPy)xMoO3 thin films can detect formaldehyde gas by increasing in their electrical resistance, whereas they showed no response to toluene.
Point defects in thin HfAlOx films probed by monoenergetic positron beams
Authors: Uedono Akira , Mitsuhashi Riichiro , Horiuchi Atsushi , Torii Kazuyoshi , Yamabe Kikuo , Yamada Keisaku , Suzuki Ryouichi , Ohdaira Toshiyuki , Mikado Tomohisa
Published: April 2011

Thin HfAlOx films grown on SiON(0.9 nm)/Si by atomic layer deposition technique were characterized by using monoenergetic positron beams. The lifetimes of positrons in the HfAlOx film after post-deposition annealing (PDA) ranged between 412–403 ps. Since these lifetimes were longer than the lifetime of positrons trapped by point defects in metal oxides, such as LaCoO3, PbTiO3, and BaTiO3, the positrons in HfAlOx films were considered to annihilate from the trapped state by open spaces which exist intrinsically in their amorphous structure. The line-shape parameter S of the Doppler broadening spectrum corresponding to the annihilation of positrons in HfAlOx films decreased by PDA, and the S value decreased with increasing an O2-content in an atmosphere during PDA (0.004–1%). The observed behavior of the S value was attributed to the shrinkage of the open spaces due to the change in the matrix structure of HfAlOx. After P+- and B+-implantation into poly-Si films grown on the HfAlOx films, the diffusion of positrons in the Si substrates toward the HfAlOx film was suppressed. This fact was attributed to positive charges introduced near the HfAlOx films.
Properties of Ultra-Thin Thermal Silicon Nitride
Authors: Buchheit Katherine M. , Takeuchi Hideki , King Tsu-Jae
Published: April 2011

Growth behavior and film properties of ultra-thin Si3N4 layers formed by RTN (rapid thermal nitridation) were characterized. The self-limiting growth characteristics of the RTN process are appealing for precise thickness control in the range of 0.5–2.5nm. From SCA (surface charge analysis), the existence of negative fixed charge and electron traps in nitrides was found, in contrast to positive fixed charge and hole traps in oxides, and improvements in interface properties were seen after high temperature annealing. From annealing ambient dependences, the physical origin of the electron traps is likely N-H bonds in the nitride films. AFM (atomic force microscopy) analysis revealed that an atomically flat nitride surface is obtained by post-nitridation spike annealing, but a longer anneal leads to a rougher surface. Effectiveness of ultra-thin nitride barriers against boron penetration from a p+ poly-Si gate was also confirmed by SRA (spreading resistance analysis).
Study of HfAlOx Films Deposited by Layer-by-Layer Growth for CMOS High-k Gate Dielectrics
Authors: Toriumi Akira , Nabatame Toshihide , Horikawa Tsuyoshi
Published: April 2011

We have investigated ternary metal oxide films for high-k gate dielectrics by using a layer-by-layer deposition & annealing method so as to keep the dielectric constant of the film high with no crystallization. HfAlOx films have been prepared by alternating deposition of HfO2 and Al2O3 layers, where it is a key for the improvement of the film quality to understand the intermixing process between two layers by thermal treatments. So, we first discuss the atomic diffusion and structural change of the HfO2/Al2O3 “superlattice” film as a function of the annealing temperature by changing the Hf/Al ratio. In a typical case of the film with HfOx/AlOx=3Å/9Å cycle, a clear superlattice peak is observed below 750 °C by XRD. Above 850 °C, a different type of crystalline structure with no superlattice peaks is observed. These results indicate that the intermixing in HfO2/Al2O3 (3Å/9Å) films occurs between 750 and 850 °C. The intermixing onset temperature increases with increasing Al content in Hf/Al ratio.

To further increase the crystallization temperature, nitrogen incorporation into the film is considered, and effects of the nitrogen incorporation into HfAlOx films are studied from the structural and electrical viewpoints. The results indicate that there is a tradeoff between crystallization restriction and leakage current degradation for the nitrogen incorporation into HfAlOx films.
Low-temperature growth of HfO2 dielectric layers by Plasma-Enhanced CVD
Authors: Losurdo M. , Giangregorio M.M. , Luchena M. , Capezzuto P. , Bruno G. , Barreca D. , Gasparotto A. , Tondello E.
Published: April 2011

HfO2 dielectric layers have been grown on p -type Si(100) by plasma enhanced chemical vapor deposition (PE-CVD), using Ar-O2 plasmas and hafnium(IV) tetra-t -butoxide as precursors. In-situ control of the plasma phase is carried out by optical emission spectroscopy (OES) and quadrupolar mass spectrometry (QMS).

Structural and optical properties of the HfO2 layers and of the HfO2/Si interface are investigated by spectroscopic ellipsometry (SE) in the photon energy range 1.5–6.0 eV‥ SE data are corroborated by results obtained from glancing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).

The effect of the substrate temperature (RT-250°C) and precursor flow on the thickness of interfacial SiO2 layer and on the HfO2 microstructure is investigated. The growth dynamics of HfO2 film and SiO2 interface layer is also discussed.
Oxide-Semiconductor Interface Characterization Using Kelvin Probe-AFM In Combination With Corona-Charge Deposition
Authors: Lägel Bert , Ayala Maria D. , Oborina Elena , Schlaf Rudy
Published: April 2011

Corona charge deposition methods in combination with spatially resolved surface potential measurements have become a standard tool for Si oxide quality monitoring. Based on this technique oxide-semiconductor interface parameters such as surface barrier height, oxide thickness and oxide charge density can now be monitored in-line with commercially available devices. The ongoing downscaling of integrated circuits into the sub-100 nm regime makes the development of high resolution oxide screening methods increasingly important.

However, currently available commercial devices are limited in their spatial resolution since they employ the traditional vibrating Kelvin probe technique, restricting their lateral resolution to several μm. In order to increase the lateral resolution of this measurement method we have combined the corona-charge deposition technique with Kelvin Probe AFM. We present initial results of this novel measurement technique and demonstrate its feasibility by measurements on lithographically prepared oxide patterns on Si wafers with different oxide thicknesses.
Field-induced reactions of water molecules at Si-dielectric interfaces
Authors: Tsetseris L. , Zhou X. , Fleetwood D. M. , Schrimpf R. D. , Pantelides S. T.
Published: April 2011

Water molecules and water-related species are present to a varying degree in SiO2 and other dielectrics and at Si-dielectric interfaces. Their presence, even in small concentrations, constitutes a critical reliability problem for present day ultrathin dielectrics. Here we present first-principles density functional calculations that probe the reactivity of water molecules at the Si-dielectric interface. We report results on different possible reaction pathways for water at the interface, including dissociation of water that can lead to the release of H+ ions. The released protons can migrate along the interface and depassivate dangling bonds. Results are also presented for the reaction of water with a hydrogen atom migrating laterally along the interface that lead to the creation of hydronium species. These atomic-scale mechanisms may account for at least some of the creation of interface traps and oxide trapped charge, the two features that give rise to negative bias temperature instability (NBTI), a well known reliability phenomenon that occurs in MOSFETs under normal operating and stress conditions.
Ultra Shallow Incorporation of Nitrogen into Gate Dielectrics by Pulse Time Modulated Plasma
Authors: Fukuda Seiichi , Suzuki Yoshimune , Hirano Tomoyuki , Kato Takayoshi , Kashiwagi Akihide , Saito Masaki , Kadomura Shingo , Minemura Youichi , Samukawa Seiji
Published: April 2011

In order to obtain a controllability in the nitrogen depth profile in the oxy-nitride gate dielectrics which has been known to have a strong effect on MOS reliability, micro second ordered pulse was used for the inductive coupled plasma source in our pulse time modulated plasma. The radio frequency (RF) of source plasma and pulse frequency were 12.56 MHz and 10 kHz (100 micro second), respectively. Pulse duty ratio was varied from 20 to 100 %. 1.7nm thick thermal silicon dioxide films were subjected to the pulse time modulated plasma and analyzed by SIMS to see the depth profile of nitrogen. A new finding is that both the concentration and the peak position of nitrogen atoms in silicon dioxide films depend on the pulse duty ratio and plasma radiation time. NBTI lifetime was improved with decreased interface state density. We also used this technique to high-k material and investigated process characteristics of nitridation
Silicate interface formation during the deposition of Y2O3 on Si
Authors: Durand C. , Vallée C. , Dubourdieu C. , Bonvalot M. , Gautier E. , Joubert O.
Published: April 2011

The interface behaviour during PE-MOCVD deposition of Y2O3 thin films on Si/SiO2 (8 Å) substrates has been investigated by XPS, TEM and OES analysis. The deposition process involves the sequential injection of MO precursors into the CVD chamber and is assisted by an O2 plasma. The injection frequency greatly influences the interface behaviour in terms of thickness and composition. The O2 plasma and the solvent also greatly affect substrate oxidation, and subsequently interface formation during deposition. Several mechanisms are discussed to account for substrate oxidation in view of a careful control of interface formation.
Microstructure and Electrical Properties of Zinc Oxide Thin Film Varistors Prepared by RF Sputtering
Authors: Chang Keng-Ming , Liu Chuan-Pu , Tsai Chon-Ming
Published: April 2011

The thin film varistors of ZnO-Bi2O3 multilayer junctions were fabricated by RF sputtering. The nonlinear I-V characteristics and nonlinear coefficient, α, under reverse bias were found to be effected by the composition and structure of the varistor multilayers. The threshold voltage is predominantly determined by the microstructure and thickness of the Bi2O3 layer in thin film varistors, while that can be tuned by altering the donor density in ZnO, which was achieved by varying Al doping concentration or sputtering conditions. The higher leakage current and lower nonlinear coefficient associated with the ZnO layer doped with Al (ZnO:Al) can be improved by inserting another ZnO layer doped with selective transition metal impurities between ZnO:Al and Bi2O3 layers. The microstructure and defects of the multilayers were investigated in detail and related to the performance of the electrical properties.
Growth of Scandium Magnesium Oxide on GaN
Authors: Onstine A H , Herrero A , Gila B P , Kim J , Mehandru R , Abernathy C R , Ren F , Pearton S J
Published: April 2011

Sc2O3 and MgO have been previously shown to be promising gate dielectrics for III-nitride devices. However, even though the films are initially epitaxial, they possess large numbers of defects due to the large mismatch with GaN. Thus further improvements in interface electrical characteristics will require a reduction in the interfacial mismatch between the oxides and the GaN. This paper discusses the feasibility of reducing the Sc2O3 lattice constant via the introduction of Mg and in particular investigates the relationship between growth parameters and microstructure for the resulting ScMgO alloy. Increasing the magnesium cell temperature was found to increase the growth rate but have little effect on surface roughness. Higher Mg cell temperatures also produced evidence in x-ray diffraction (XRD) of a second phase of MgScO which has the rock salt crystal structure and contains ∼2%Sc. Increasing the substrate temperature from 100°C to 300°C was found to have little effect on the growth rate and dramatically increased surface roughness. However higher substrate temperature combined with a lower Mg cell temperature produced a more uniform oxygen profile as determined by depth profiling Auger Electron Spectroscopy (AES). From AES and XRD, the solid solubility limit for ScxMg1−xO with the Bixbyite structure was reached at about XMg =0.28
Characterization of Metal-Ferroelectric-Metal-Insulator-Semiconductor (MFMIS) FETs Using (Sr,Sm)0.8Bi2.2Ta2O9 (SSBT) Thin Films
Authors: Saiki Hirokazu , Tokumitsu Eisuke
Published: April 2011

We have fabricated and characterized Pt (60nm) / (Sr,Sm)0.8Bi2.2Ta2O9 (SSBT, 130nm) / Pt (60nm) / Ti (10nm) / SiO2 (10nm) / p-Si (MFMIS:metal-ferroelectric-metal-insulator-semiconductor) structure FETs. The area ratio, the ratio of SSBT capacitor area to SiO2 capacitor, is varied from 1 to 15 in the MFMIS-FETs. It is demonstrated that MFMIS-FETs with area ratio of 6 have memory window of 0.5V with supply voltage of 5 V. Dependence of memory window on the area ratio is discussed.
A Thermogravimetric Study of Alakanethiolate Monolayer-Capped Gold Nanoparticle Catalysts
Authors: Maye Mathew M. , Chen Sandy , Chan Wai-Ben , Wang Lingyan , Njoki Peter , Lim I-Im-. S. , Mitchell Jennifer , Han Li , Luo Jin , Zhong Chuan-Jian
Published: April 2011

The application of molecularly-capped gold nanoparticles (1–5 nm) in catalysis (e.g., electrocatalytic oxidation of CO and methanol) requires a thorough understanding of the surface composition and structural properties. Gold nanoparticles consisting of metallic or alloy cores and organic encapsulating shells serve as an intriguing model system. One of the challenges for the catalytic application is the ability to manipulate the core and the shell properties in controllable ways. There is a need to understand the relative core-shell composition and the ability to remove the shell component under thermal treatment conditions. In this paper, we report results of a thermogravimetric analysis of the alkanethiolate monolayer-capped gold nanoparticles. This investigation is aimed at enhancing our understanding of the relative core-shell composition and thermal profiles.
Formation and Properties of Silicon/Silicide/Oxide Nanochains
Authors: Kohno Hideo , Ohno Yutaka , Ichikawa Satoshi , Akita Tomoki , Tanaka Koji , Takeda Seiji
Published: April 2011

Silicon/silicide/oxide nanochains, which have an alternate arrangement of silicon/copper silicide composite nanoparticles and oxide nanowires, were fabricated using silicon/oxide nanochains as templates. Photoluminescence was observed at room temperature and considered to be due to recombination of excitons in oxide. Electrostatic potential in the material was also investigated by electron holography. No visible potential bending at the silicon/silicide interface was detected.
Exciton photoluminescence and energy transfer in nanocrystalline Si/ Si dioxide superlattice structures
Authors: Timoshenko V. Yu. , Shalygina O. A. , Lisachenko M. G. , Kashkarov P. K. , Kovalev D. , Heitmann J. , Zacharias M. , Kamenev B. V. , Tsybeskov L.
Published: April 2011

Photoluminescence (PL) of nanocrystalline Si (nc-Si) assemblies formed by thermal crystallization of amorphous Si/SiO2 and SiO/SiO2 superlattices (SLs) has been investigated at different temperatures and excitation conditions. The low temperature resonant PL spectroscopy reveals phonon-assisted excitonic recombination. At room temperature the samples formed from a-SiO/SiO2 SLs possess relatively high PL quantum yield (∼ 1%). The PL transients have non-exponential decay, which indicates the exciton energy transfer in nc-Si ensembles. The excitonic energy of Er-doped nc-Si SL structures can be almost completely transferred to Er ions incorporated in SiO2 matrix that results in a strong emission line at 0.81 eV.
GaP Nanostructures: Nanowires, Nanobelts, Nanocables, and Nanocapsules
Authors: Seo Hee Won , Bae Seung Yong , Park Jeunghee
Published: April 2011

Various GaP nanostructures such as nanowires, nanobelts, nanocables, and nanocapsules were synthesized by sublimation of ball-milled powders. They have a single-crystalline zinc blende structure with [111] growth direction. The morphology and structure were controlled by reactant gas, growth time, flow rate, and growth temperature. The size, morphology and properties of the nanostructures were examined by scanning electron microscopy, transmission electron microscopy, electron energy-loss spectroscopy (EELS), electron diffraction, energy dispersive x-ray spectroscopy, powder x-ray diffraction, and Raman spectroscopy using a 514.5 nm argon ion laser. The photoluminescence was carried out using the 458 nm line of an argon ion laser as the excitation source. The GaP nanowires are straight, cylindrical, and smooth in surface, with mean diameter of 40 nm and length up to 300 mm. The nitrogen-doped nanobelts and nanowires were synthesized by ammonia ambient gas. EELS data reveals that the nitrogen doping occurs mainly in the surface region. The PL spectrum shows the typical isoelectronic bound exciton peaks in the range of 2.11∼2.25 e V, suggesting a concentration of (1018 cm-3 nitrogen atoms. We also synthesized two types of GaP nanocables; GaP nanowire sheathed with the amorphous silicon oxide layers and with the graphite layers. The core-shell diameter is under 30 nm and the outerlayer can be removed by acid treatment to produce the 10 nm diameter GaP nanowires. The GaP encapsulated with BCN nanotubes were synthesized under the ammonia flow using the ball-milled carbon-containing boron oxide powders. The number of BCN layers is typically 10∼20.
Low Temperature Gas Phase Synthesis of Germanium Nanowires
Authors: Mathur Sanjay , Shen Hao , Werner Ulf
Published: April 2011

Single crystal Ge nanowires (NWs) were obtained in high yield by gas phase decomposition of germanium di-cyclopentadienylide ([Ge(C5H5)2]), at 325 °C on iron substrates. Highresolution electron microscopy (SEM/TEM) showed Ge NWs to be uniform in terms of diameter (20 nm) and length (> 25 μm). The wire growth is selective and appears to be governed by a Ge-Fe alloy epilayer formed by the reaction between Ge clusters and iron substrate, during the initial stages of the CVD process. The supersaturation of Ge-Fe solid-solution with respect to Ge content induces the spontaneous formation of single crystal germanium nuclei that act as templates for the nanowire growth. X-ray and electron diffraction revealed the NWs to be single crystals of cubic germanium with a preferred growth direction[11–2]. The proposed base-growth model on Fe substrate is supported by TEM, EDX and XPS studies.
Energy exchange between optically excited Silicon Nanocrystals and Molecular Oxygen
Authors: Gross E. , Kovalev D. , Künzner N. , Diener J. , Koch F. , Timoshenko V. Yu. , Fujii Minoru
Published: April 2011

We report on the photosensitizing properties of optically excited Silicon (Si) nanocrystal assemblies that are employed for an efficient generation of singlet oxygen. Spin triplet state excitons confined in Si nanocrystals transfer their energy to molecular oxygen (MO) adsorbed on the nanocrystal surface. This process results in a strong suppression of the photoluminescence (PL) from the Si nanocrystal assembly and in the excitation of MO from the triplet ground state to singlet excited states. The high efficiency of the energy transfer if favored by a broad energy spectrum of photoexcited excitons, a long triplet exciton lifetime and a highly developed surface area of the nanocrystal assembly. Due to the specifics of the coupled system Si nanocrystal – oxygen molecule all relevant physical parameters describing the photosensitization process are accessible experimentally. This includes the role of resonant and phonon-assisted energy transfer, the dynamics of energy transfer, and its mechanism.
Diffuse x-ray scattering from InGaAs/GaAs quantum dots
Authors: Köhler Rolf , Grigoriev Daniil , Hanke Michael , Schmidbauer Martin , Schäfer Peter , Besedin Stanislav , Pohl Udo W. , Sellin Roman L. , Bimberg Dieter , Zakharov Nikolai D. , Werner Peter
Published: April 2011

Multi-fold stacks of In0.6Ga0.4As quantum dots embedded into a GaAs matrix were investigated by means of x-ray diffuse scattering. The measurements were done with synchrotron radiation using different diffraction geometries. Data evaluation was based on comparison with simulated distributions of x-ray diffuse scattering. For the samples under consideration ((001) surface) there is no difference in dot extension along [110] and [-110] and no directional ordering. The measurements easily allow the determination of the average indium amount in the wetting layers. Data evaluation by simulation of x-ray diffuse scattering gives an increase of Incontent from the dot bottom to the dot top.
Dark exciton signatures in time-resolved photoluminescence of single quantum dots
Authors: Smith Jason M. , Dalgarno Paul A. , Warburton Richard J. , Gerardot Brian D. , Petroff Pierre M.
Published: April 2011

Time-resolved photoluminescence of single charge tuneable quantum dots allows us to probe the differences in recombination dynamics between neutral and negatively charged excitons. We find that the luminescence decay from a neutral exciton contains a second lifetime component of several nanoseconds that is not present in the luminescence from singly or doubly charged excitons. We attribute the slowly decaying component to excitation cycles in which the initial exciton formed in the dot is dark, with angular momentum M = 2, and which subsequently scatters into the bright state with M = 1.

The nature of the scattering mechanism is revealed by the dependence of the lifetime on the electrical bias applied across the charge-tuneable device. That the lifetime changes by an order of magnitude within a short bias range implies that the dark-to-bright transmutation does not occur through a simple spin flip. Rather it appears to come about by the dot briefly entering a higher energy charging state which allows exchange of the existing electron with another from the n-type contact region. We model the lifetimes and relative intensities of the two decay components using a simple rate equation analysis.
Measurement Techniques for Thermoelectric Materials and Modules
Authors: Hogan Tim , Loo Sim , Guo Fu , Short Jarrod
Published: April 2011

Thermoelectrics is a multidiscipline area of study, rich in condensed matter physics, chemistry, engineering, and material science. The figure of merit used for evaluating individual materials consists of three interdependent material properties. The measurement of these properties should be taken on the same sample for all three measurements, preferably simultaneously. Each of these measurements requires close attention to potential sources of losses for accurate analysis of the materials and testing of theoretical models. For example, relatively simple scanning measurement techniques can be used to gain insight into accurate geometry measurements and influences of contact dimensions. In addition, the field of thermoelectrics spans a wide temperature range, from cryogenic temperatures to > 1000 °C. This requires systems capable of large temperature variations, and/or multiple measurement systems for various ranges of interest. Additional measurements, such as Hall effect, help to gain further insight into the material properties and their optimization. The number and importance of measurements is further extended as the development of devices from these new materials is initiated, where studies of contact resistance and overall device performance must be evaluated. For mechanical robustness of fabricated modules, properties such as the coefficient of thermal expansion, and grain size for the new materials are of interest. Models for device behavior are useful in evaluating the measured results and further extracting material and device properties. In this paper, we review measurements used in evaluating bulk thermoelectric materials some of the information that can be extracted from these measurements, along with a model that can be used in conjunction with these measurements for module design.
Using the Compatibility Factor to Design High Efficiency Segmented Thermoelectric Generators
Authors: Jeffrey Snyder G. , Caillat T.
Published: April 2011

Using thermoelectric compatibility, efficient thermoelectric generators are rationally designed. With examples, compatible and incompatible systems are explained and materials proposed for targeted development. The compatibility factor explains why segmentation of TAGS with SnTe or PbTe produces little extra power, while filled skutterudite increases the efficiency from 10.5% to 13.6%. High efficiency generators are designed with compatible n-type La2Te3, and similar p-type material, while incompatible SiGe alloys actually reduce the efficiency. A refractory metal with high p-type thermopower (> 100 μV/K) is required for development. The Chevrel compound Cu4Mo6Se8is a compatible p-type metal that provides a modest increase in efficiency. A fully segmented generator using Bi2Te3-type, PbTe, TAGS, Zn4Sb3, skutterudite, La2Te3, and Chevrel compounds between 25° C and 1000° C will achieve 18.1% conversion efficiency.
Influence of Doping Concentration and Ambient Temperature on the Cross-Plane Seebeck Coefficient of InGaAs/InAlAs superlattices
Authors: Zhang Yan , Vashaee Daryoosh , Singh Rajeev , Shakouri Ali , Zeng Gehong , Chiu Yi-Jen
Published: April 2011

We have developed thin film heaters/sensors that can be integrated on top of superlattice microcoolers to measure the Seebeck coefficient perpendicular to the layer. In this paper, we discuss the Seebeck coefficients of InGaAs/InAlAs superlattices grown with Molecular Beam Epitaxy (MBE) that have different doping concentrations, varying between 2e18, 4e18, and 8e18 to 3e19 cm−3. It was interesting to find out that – contrary to the behavior in bulk material – the Seebeck coefficient did not decrease monotonically with doping concentration. A preliminary theory of thermoelectric transport in superlattices in the regime of miniband formation has been developed to fit the experimental results. The miniband formation could enhance the thermoelectric power factor (Seebeck coefficient square times electrical conductivity) and thereby improve the Figure of merit, ZT. With this improvement, InGaAs/InAlAs superlattice microcooler become a promising candidate for on-chip temperature control.
Thermoelectric Properties of Bi-substituted Ca3Co4O9 Single Crystal
Authors: Mikami M. , Chong K. , Funahashi R.
Published: April 2011

We have grown single crystals of Bi-substituted Ca3Co4O9 by a solution method. The cationic ratio (Ca, Bi)/Co of the grown crystals measured by an energy dispersive X-ray spectrometer tended to exceed that of the starting ratio (Ca, Bi)/Co=3/4. For instance, the average cationic composition of the grown crystals was Ca:Bi:Co=3.3:0.3:4, while that of the starting material was Ca:Bi:Co=2.7:0.3:4. So, the crystallographic structure of the obtained crystals may correspond to the Ca2Co2O5 phase rather than the Ca3Co4O9 phase. Thermoelectric properties in the direction of ab-axis were measured at various temperatures. Seebeck coefficient (S) of Ca3.3Bi0.3Co4O9+δ is positive and increases with increasing temperature from 130 to 200 μV/K in a temperature region of 300–973 K. The electrical resistivity (ρ) of the sample is about 1.5 mΩcm at whole temperature region of 300–973 K. This value is lower than that of non-substituted Ca3Co4O9. The thermoelectric power factor (S2/ρ) is improved by the Bi-substitution, resulting from the reduction of resistivity.
Phonons and Thermal Conductivity in Skutterudite Thermoelectrics
Authors: Kendziora C. A. , Nolas G. S.
Published: April 2011

We study Raman phonon vibrations and relate them to thermal conductivity for empty and filled skutterudites designed for thermoelectric applications, where low thermal conduction is critical. Polarized Raman scattering spectra of crystallite and polycrystalline samples are compared with theoretical predictions and analyzed in comparison to the thermal conduction properties. Our emphasis is on the CoSb3 skutterudite and its filled derivatives, including materials with Ge, Sn, and La in the cages. We observe a strong correlation between aspects of the Raman spectrum and low thermal conductivity. This presents Raman spectroscopy as a characteristic screening tool for potential thermoelectrics and is a crucial step toward predicting lattice thermal conductivities.