bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and ferroelectric behavior of nano-domains in ultra-thin BaTiO3 films
Authors: Drezner Y. , Berger S.
Published: April 2011

Microstructure studies of ultra-thin BaTiO3 thin films (2–10nm thick) show nano-domains having a width as small as one unit cell. Only 180° nano-domains and 90° domain-boundaries are formed in multi-domains structures. The domain-boundaries are formed at {111} twin boundaries. Most of the domains are oriented in parallel to the film plane but out-of-plane domains are also observed. The films exhibit ferroelectric behavior characterized by a polarization hysteresis loop. A remanent polarization of 3nC/cm2, coercive field of 0.7MV/cm were measured in vertical to the film plane. Temperature-dependent polarization measurements show two peaks of the dielectric constant at about 70°C and 110° C. These peaks are attributed to two Curie temperatures associated with the out-of plane and in-plane domain's orientation, respectively. The switching response of the nano-domains is relatively fast in the range of few nano seconds. The switching time decreases with increasing the applied electric field according to a power law dependence.
Property Improvement of Mocvd-Pzt Films Deposited Below 400 °C
Authors: Funakubo Hiroshi , Asano Gouji , Nagai Atsushi , Morioka Hitoshi , Yokoyama Shintaro , Shibutami Tetsuo , Oshima Noriaki , Akiyama Kensuke
Published: April 2011

RuO2/(200-nm thick PZT)/RuO2 capacitors were prepared by MOCVD. RuO2 and PZT films were prepared at 350, and 395 and 445 °C from DER - O2 and Pb(C11H19O2)2 - Zr(O·t-C4H9)4 - Ti(O·i -C3H7)4 - O2 systems, respectively. Clear hysteresis loops originated to ferroelectricity was observed for the PZT films deposited at 445 °C but was not at 395 °C. However, by the addition of 10-nm thick Pt layer prepared on the RuO2 bottom electrode by e-beam evaporation, ferroelectricity above 30 μC/cm2 in remanent polarization (Pr) was obtained for the PZT films deposited at 395 °C. This shows that the existence of Pt layer improved the crystallinity of PZT phase. This capacitor shows hardly fatigue up to 1 × 1010 switching cycles, suggesting the fatigue free characteristics.
Measuring Residual Stress Effects of Acceptor Doping In Tunable Microwave Dielectric Thin Films
Authors: Nothwang W. D. , Cole M. W. , Hubbard C. , Ngo E.
Published: April 2011

There has been a recent shift towards a tunable phase shifter for microwave antenna design. Barium strontium titanate [BaxSr(1-x)TiO3] thin films are the principal materials of interest in these applications, primarily because of their low loss, high dielectric constant and large tunability. Both magnesium doped and undoped films were made, and they were deposited on MgO or Pt-Si substrates using metal organic solution deposition and pulsed laser deposition. Residual stress within these materials is known to have a drastic effect on the material, electrical, and dielectric properties. This becomes of particular importance in thin film materials, where the residual stress can be several orders of magnitude higher than in bulk materials. The residual stress in the films was measured in three ways. A Tencor stress analysis system was employed to measure the change in the substrate curvature due to the film stress, and a nano-indentation method was used to calculate the residual stress in a system by measuring the maximum penetration, the force at maximum penetration, and the slope of the initial unloading curve. These methods were validated using XRD lattice calculations. Stresses as high as 2 GPa were observed under certain conditions. The results also show that the surface region of the films is not stress free at these thicknesses (∼200 nm) as was mathematically suggested.
Low Temperature Deposition of Ba0.96Ca0.04Ti0.84Zr0.16O3 Thin Films on Pt Electrodes by RF Magnetron Sputtering
Authors: Cramer N. , Philofsky Elliot , Kammerdiner Lee , Kalkur T. S.
Published: April 2011

Ba0.96Ca0.04Ti0.84Zr0.16O3 (BCTZ) films acceptor-doped with 0.8 at. % Sc were deposited on Pt/TiO2/SiO2/Si substrates using rf magnetron sputtering. Substrate temperatures throughout the fabrication process remained at or below 450°C, which allows this process to be compatible with many materials commonly used in IC manufacturing. In addition, this process made no use of oxygen in the sputter gas or in annealing atmospheres and thus it remains compatible with easily oxidized materials. A relative dielectric constant of 166 was achieved along with a loss tangent of 0.006 to 0.17 at 10 kHz. The tunability of the dielectric constant was greater than 50 %. Leakage current densities of 1.6×10-8 A/cm2 were observed at 300K with 300 kV/cm of applied electric field. In comparison, Ba1-xSrxTiO3 (BST) films prepared under similar conditions show much greater leakage.
Conduction and Microwave Loss Mechanisms in Ba0.25Sr0.75TiO3 Films
Authors: Vorobiev Andrei , Rundqvist Par , Khamchane Khaled , Gevorgian Spartak
Published: April 2011

Silicon integrated parallel-plate Ba0.25Sr0.75TiO3 (BST) thin film varactors with Au bottom electrode have been prepared and characterized at dc and microwave frequencies. In the frequency range 0.045–45 GHz the varactors reveal extremely low loss tangent values (less than 0.025). However, this is still several times higher than loss in single crystal indicating occurrence of the extrinsic loss mechanisms. The analysis of BST film loss tangent and permittivity, depending on frequency and applied dc field, allow to attribute the dielectric loss to the charged defects. The dc current through varactor is found to be controlled by Poole-Frenkel mechanism associated with field enhanced thermal excitation of charge carriers from internal traps. It is assumed that charged defects and internal traps are the same type of BST film microstructure imperfection and possibly ascribed to be oxygen vacancies. The knowledge of the extrinsic loss mechanism and corresponding microstructure defects allows to optimize the deposition and/or anneal process and further improve the varactor performance.
Investigation of Retention Properties for YMnO3 Based Metal/Ferroelectric/Insulator/Semiconductor Capacitors
Authors: Yoshimura T. , Ito D. , Sakata H. , Shigemitsu N. , Haratake K. , Ashida A. , Fujimura N.
Published: April 2011

The memory retention properties of Pt/YMnO3/Y2O3/Si capacitors were investigated for the application of ferroelectric gate transistors. The epitaxially grown Pt/YMnO3/Y2O3/Si capacitors showed ferroelectric type hysteresis loop on the capacitance-voltage properties. Although the retention time of the as-deposited capacitors was ∼103 s, it was prolonged up to 104 s when the leakage current density was reduced from 4×10-8 A/cm2 to 2×10-9 A/cm2 by the annealing under N2 ambience. To reveal the relationship between the retention time and leakage current, the leakage current mechanism was investigated comparing several conduction mechanisms. It was found that the dominant leakage mechanisms at high and low electric fields were Poole-Frenkel emission from the Y2O3 layer and ohmic conduction, respectively. This result indicates that the leakage current was limited by the Y2O3 layer at high electric field and was mainly dominated by the amount of defects in the YMnO3 layer at low electric field. From the pseudo isothermal capacitance transient spectroscopy (ICTS), it was determined that the trap density was in an order of 1015 cm-3. Since the variation of the leakage current by annealing was observed only in the low electric field region, it is suggested that the retention properties of the Pt/YMnO3/Y2O3/Si capacitors was influenced by the amount of defects in the YMnO3 layer.
Enhanced Piezoelectric Properties of Piezoelectric Single Crystals by Domain Engineering
Authors: Wada Satoshi , Yako Koichi , Kakemoto Hirofumi , Tsurumi Takaaki
Published: April 2011

For tetragonal barium titanate (BaTiO3) single crystals, an electric field (E-field) applied along [111]c direction can induce an engineered domain configuration. In this study, the engineered domain structures with different domain sizes were induced into BaTiO3 single crystals, and their piezoelectric properties were investigated as a function of a domain size. Prior to this study, the dependence of domain configuration on the temperature and the E-field was investigated using a polarizing microscope in order to understand the optimum condition for fine and coarse domain structures. As a result, above Curie temperature (Tc) of 132.2 °C, when the E-field over 6 kV/cm was applied along [111]c direction, the engineered domain configuration with fine domain structure appeared. Moreover, it was also found that this fine domain structure was still stable at room temperature without E-field. On the other hand, the coarse domain structure was obtained by poling at just below Tc. Finally, the piezoelectric properties were measured using the 31 resonators with different kinds of domain sizes. As the result, it was found that the piezoelectric properties such as d31 and k31 increased significantly with decreasing domain sizes.
Novel High Power Piezoelectrics for Transformers and Actuators
Authors: Priya Shashank , Uchino Kenji
Published: April 2011

This letter reports a Pb(Zr0.5Ti0.5)O3 (PZT) based composition, which provides high dielectric, piezoelectric and electromechanical properties. The composition corresponding to 0.2 PZN – 0.8 PZT + 0.5 wt% MnO2 provides the radial mode coupling factor (kp) of 0.58, longitudinal mode piezoelectric constant (d33) of 277 pC/N, dielectric constant (ε33/εo) of 946 and mechanical quality factor (Qm) of 1402. X-ray diffraction, dielectric and polarization-electric field measurements were done to investigate the origin for this high performance. It was found that high soft properties are obtained due to the shifting of PZT composition towards morphotropic phase boundary (MPB) and high hard properties are obtained due to the generation of dipolar defects which pin the polarization. The properties of the composition corresponding to 0.9 PZT – 0.1PMnN (Zr/Ti = 0.51/0.49) modified with 6 mol% Sr were found to be: kp = 0.53, Qm = 800, d33 = 274, ε33/εo = 1290 and tanδ = 1.1 %, with a TCF of -8 ppm/oC (-20 to 80°C). High piezoelectric properties with low TCF shows the suitability of this composition for ultrasonic devices used under fluctuating thermal environment.
Characteristics of Dopant Activation by Sequential Lateral Solidification (SLS)
Authors: Kim Yong-Hae , Sohn Choong-Yong , Chung Choong-Heui , Ko Young-Wook , Lee Jin Ho
Published: April 2011

The characteristics of dopant activation by sequential lateral solidification in poly-Si films is investigated using sheet resistance measurement and Raman measurement. Sheet resistance of n+ and p+ doped poly-Si films decreases exponentially as the laser energy increases. The minimum sheet resistance of n+ doped poly-Si films is 150 Ω/□ which is near to that of rapid thermal annealing (RTA) while the minimum sheet resistance of p+ doped poly-Si films is 180 Ω/□ which is less than a half to that of RTA. The sheet resistance of n+ and p+ doped poly-Si increases as the laser energy increases when the laser energy is above 573 mJ/cm2 at which the nucleation occurs. Raman signal of n+ doped poly-Si films shows single peak at 515 cm-1 with all laser energy and has maximum intensity at 566 mJ/cm2 laser energy. Raman signal of p+ doped poly-Si films shows single peak below 413 mJ/cm2 laser energy and double peak above 444 mJ/cm2 laser energy where the fully melting of p+ doped poly-Si film occurs.
Star-like Aromatic Conjugated Polymers and Dendrimers for OLEDs
Authors: Khotina Irina A. , Baranova Diana Yu. , Burenkova Natalia S. , Gurskaja Anastasia A. , Valetsky Peter M. , Bronstein Lyudmila M.
Published: April 2011

Highly branched photoluminescent polyphenylenes (PP) containing 1,3,5-triphenylbenzene (TPB) fragments were prepared via combination of cyclocondensation of acetylaromatic compounds and Ni0-catalyzed dehalogenation. Defect free PP with star-like fragments were synthesized using Ni0-catalyzed polymerization of aromatic bromides obtained by modification of 1,3,5-tri(p-bromophenyl)benzene. The molecular weights of the polymers were 6700, 8600, and 15300 Da. The maximum photoluminescence in solution (quantum yield of 96%) was obtained for the highly branched polymer with star-like TPB fragments, bearing no Br or acetyl groups. The PP of this kind show also very bright fluorescence in a solid state under UV irradiation at 360 nm so they can be considered as promising materials for OLED applications.
Bioinspired approach of the composite materials: towards the active health monitoring concept
Authors: Gobin P. F. , Salvia M. , Monnier T. , Godin N. , Guy P. , Jayet Y.
Published: April 2011

The classical NDE techniques of periodical maintenance are just now evolving towards the continuous health monitoring of materials and structures. Taking account of the relation of this approach with the bioinspired notion of smart materials, it seems useful to extend this passive concept to a more active one, especially in the case of materials systems as composite materials. Effectively, if sensors and actuators are embedded in a composite structure before curing in order to monitor and improve the processing parameters, they are able, remaining in the structure, to assume the health monitoring and some optimization of the usage in the next stages of the life. Moreover, in slightly damaged systems, it becomes reasonable to use the results collected by the sensors for improvements of safety of materials and structures. Finally in the last stage of the life, when the material is deeply damaged, it is sometimes possible to slow down, and more rarely, to heal the damage.
Tailoring strains through microstructural design
Authors: Vandeperre L.J. , Clegg W.J.
Published: April 2011

Composite structures are presented that allow a wide design space for strains in response to an applied stimulus to be accessed. The basic principle of operation is described and examples of how it can be used to obtain a range of behaviours are given. Experiments were conducted to assess the basic behaviour of building blocks for such composites and it is shown that the results agree reasonable with simple predictions made by considering bending and stretching of the beams in the structures.
Magnetization Process Associated with Rearrangement of Martensite Variants in Iron-Based Ferromagnetic Shape Memory Alloys
Authors: Fukuda Takashi , Sakamoto Tatsuaki , Terai Tomoyuki , Kakeshita Tomoyuki , Kishio Kohji
Published: April 2011

Magnetization processes of Fe-31.2Pd(at.%) and Fe3Pt (S ≈ 0.8) single crystals in martensite state have been examined in order to confirm the propriety of the condition for the rearrangement of variants under magnetic field: τmag>τreq, where τmag is the magnetic shear stress and τreq is the shear stress required for the rearrangement. When the magnetic field is applied along the [001] direction of each specimen, the magnetization curve shows a large hysteresis due to the rearrangement of variants. Its area, i.e., energy dissipation, is nearly the same as that obtained by stress-strain curves, suggesting the path of the rearrangement of variants by magnetic field is essentially the same as that by external stress. From the magnetization curve, the uniaxial magnetocrystalline anisotropy constant Ku is estimated: it is about 350 kJ/m3 for Fe-31.2Pd at 77 K, and is about 500 kJ/m3 for Fe3Pt at 4.2 K. The maximum of τmag, being evaluated from Ku and twinning shear, is about 2.8 MPa for Fe-31.2Pd at 77K and is about 4.3 MPa for Fe3Pt at 4.2K. For Fe-31.2Pd, the value of τreq is obtained by tensile tests at 80 K to be 0.5–2.5MPa, and the above condition is satisfied. The above condition is also confirmed to be adequate by examining the influence of field direction on the magnetic filed-induced strain.
Metal-containing diamond-like carbon-silicon nanocomposite films as temperature sensors
Authors: Takeno T. , Takagi T. , Bozhko A. , Shupegin M. , Sato T.
Published: April 2011

Metal-carbon nanocomposites are characterized by a number of unique properties, perspective for the various-type applications. The presented experimental data on the conductivity of amorphous tungsten- and niobium-containing carbon-silicon nanocomposite films show the possibility of the design of advanced wide-range temperature sensors, which are expected to possess the chemical stability, biocompatibility, mechanical, and other properties typical for this class of materials. The films were deposited onto polycrystalline substrates using combination of PECVD(Plasma Enhanced Chemical Vapor Deposition) of siloxane vapors and magnetron co-sputtering of metal target. The conductivity σ of the films, measured using standard 4-probe technique in the temperature range 80–400K, is characterized by the gradual decrease with temperature. The experimental σ(T) dependences are well fitted by the universal power expression, σ(T)= σ0+aTn, where σ0, a, and n are the fitting parameters dependent on the value of metal concentration. The conductivity mechanisms in the investigated amorphous metal-containing carbon-silicon nanocomposite films are discussed in the framework of the model of inelastic tunneling in amorphous insulators in the presence of the structural transformation in carbon-silicon matrix.
Organically Hybridized SnO2 Sensors for Selective Detection of Gas Molecules
Authors: Matsubara Ichiro , Hosono Kouta , Murayama Norimitsu , Shin Woosuck , Izu Noriya
Published: April 2011

Gas sensors based on organically hybridized SnO2 films are demonstrated. Upon exposure to CO gas, the electrical resistance of the hybrid sensor with amino groups in the organic components increases (R-increasing response), whereas other reducing gases such as H2 and CH4 gases cause the decreasing in the sensor resistance. For the n-type semiconductors like SnO2, the R-increasing response cannot be explained by the ordinary combustion mechanism. The appearance of the anomalous R-increasing response to CO gas can be controlled by the functional groups of the organic component. The hybrid sensor with hydroxy groups also exhibits the R-increasing response to CO gas, whereas it is not observed for the sensor with alkyl groups. The hybridization can improve gas selectivity of the SnO2 semiconducting gas sensors.
Piezoelectric Transformers for Space Applications
Authors: Carazo Alfredo Vázquez
Published: April 2011

There is a considerable excitement in the space community about the possibility of performing useful missions in space using vehicles that are much smaller in size than current spacecrafts. Lower cost and new type of missions made of this small satellite very attractive for future missions. Spacecraft in the mass range of 1 to 10 kilograms are often referred to as “nanosatellites”. However, the suite of useful missions for nanosatellite is limited by the dearth of space components of suitable scale. Present day nanosatellites are often drifting, uncontrolled packages of instrumentation of very limited capability. The vital subsystem functions of propulsion, power conversion and storage, attitude control, attitude sensing, data storage, command and data handling, and telemetry, tracking and control, are not well supported by these components availability of a number of small, low-cost nanosatellite components in these subsystem areas. This paper introduces the advances on applications based on piezoelectric transformers for nanosatellites.
Influence of Nitrogen Bonds on electrical properties of HfAlOx(N) films fabricated through LL-D&A process using NH3
Authors: Iwamaoto Kunihiko , Nishimura Tomoaki , Tominaga Koji , Yasuda Tetsuji , Kimoto Koji , Nabatame Toshihide , Toriumi Akira
Published: April 2011

We have investigated the influence of nitrogen incorporation into the HfAlOx film prepared by LL-D&A process with NH3 annealing step on structural change and electrical properties. Also, we have evaluated the effects of PDA treatment on electrical properties. Nitrogen concentration in HfAlOx(N) film was enhanced with increasing the NH3 annealing temperature. The shift of Hf 4f average binding energy towards lower side was observed in proportion to nitrogen concentration in HfAlOx(N) film. This result indicates the partial change of the local coordination from O-Hf-O to O-Hf-N. The increase of O-Hf-N component drastically degraded the gate leakage current in HfAlOx(N) film. Nitrogen atoms still maintained in HfAlOx(N) film even after PDA at 850°C in O2 ambient. PDA treatment at higher temperature after D&A(NH3) process improved the flat-band voltage shift and the electron mobility.
Nitrided Hafnium Silicate Film Formation by Sequential Process Using a Hot Wall Batch System and Its Application to MOS Transistor
Authors: Aoyama Tomonori , Torii Kazuyoshi , Mitsuhashi Riichirou , Maeda Takeshi , Kamiyama Satoshi , Horiuchi Atsushi , Kitajima Hiroshi , Arikado Tsunetoshi
Published: April 2011

High quality HfSiON/SiO2 gate dielectrics were successfully formed using a hot wall batch system, which is suitable for mass production. The carbon contamination at HfSiON/SiO2 interface was reduced by a sequential process of the interfacial layer (IL) formation and HfSiOx metal organic chemical vapor deposition (MOCVD). The O3 treatment was found effective to reduce the residual carbon and hydrogen, while the NH3 treatment made the HfSiOx to be HfSiON, which was effective to prevent the phase separation and crystallization during the activation annealing. The NH3 treatment temperature above 700°C is necessary to suppress the boron penetration during the activation annealing at 1050°C for 1 sec in p-channel field effect transistor (p-FET). Equivalent oxide thickness (EOT) of 1.37 nm was achieved for HfSiON· (3nm)/SiO2(0.5nm) gate stack using poly-Si electrode. High effective mobility of 271/62 cm2/Vs (n/p at 0.8 MV/cm) was obtained.
AlON thin films formed by ECR plasma oxidation for high-k gate insulator application
Authors: Yamanaka Go , Uchikawa Takafumi , Ohmi Shun-ichiro , Sakai Tetsushi
Published: April 2011

AlON thin films formed by the electron cyclotron resonance (ECR) plasma oxidation of the AlN thin films deposited on p/p+−Si(100) by the ECR sputtering method were investigated for high-k gate insulator application. The leakage current density was found to be decreased with the ECR plasma oxidation of the AlN thin films. Furthermore, the equivalent oxide thickness (EOT) of 1.5 nm with the leakage current density of 5.1×10−4 A/cm2 (@Vfb−1 V) was obtained after the 1000°C rapid thermal annealing (RTA) because of the high quality interfacial layer formation.
Structural and Electrical Properties of HfO2 Films Grown by Atomic Layer Deposition on Si, Ge, GaAs and GaN
Authors: Fanciulli Marco , Spiga Sabina , Scarel Giovanna , Tallarida Grazia , Wiemer Claudia , Seguini Gabriele
Published: April 2011

HfO2 thin films were grown by atomic layer deposition on Si, Ge, GaAs and GaN substrates, using Hf(OtBu)2 (mmp)2 and HfCl4. The results show that this combination of precursors promotes a conformal and smooth growth of HfO2 films on all substrates. As grown films in the thickness range of 10–20 nm have the same electronic density and smooth surfaces. Films 20 nm thick are polycrystalline with the monoclinic structure, whereas the crystallized fraction in the 10 nm thick layers is much lower. The HfO2 /Ge interface is remarkably sharp. The dielectric constant of the HfO2 films is 15. Low density of interface states and oxide fixed charges are obtained for the films grown on Si. The optimization of the HfO2 interface with the other substrates requires more effort.
Growth of Perovskites with Crystalline Interfaces on Si(100)
Authors: Norga G. J. , Guiller A. , Marchiori C. , Locquet J. P. , Siegwart H. , Halley D. , Rossel C. , Caimi D. , Seo J. W. , Fompeyrine J.
Published: April 2011

The main challenges involved in the growth of an epitaxial oxide film with a crystalline interface to silicon are reviewed: (1) structural matching of the oxide and semiconductor lattices; (2) thermodynamic energy stabilization at the semiconductor–oxide interface, and (3) kinetic control over oxygen motion throughout the deposition process. We report on how this approach can be used to grow epitaxial perovskites of high structural quality from the (Ba, Sr)(Zr,Ti)O3 family with crystalline interfaces on Si (100) by molecular-beam epitaxy.
Passivation of Oxide Layers on 4H-SiC Using Sequential Anneals in Nitric Oxide and Hydrogen
Authors: Williams J. R. , Isaacs-Smith T. , Wang S. , Ahyi C. , Lawless R. M. , Tin C.C. , Dhar S. , Franceschetti A. , Pantelides S.T. , Feldman L.C. , Chung G. , Chisholm M.
Published: April 2011

The interface passivation process based on post-oxidation, high temperature anneals in nitric oxide (NO) is well established for SiO2 on (0001) 4H-SiC. The NO process results in an order of magnitude or more reduction in the interface state density near the 4H conduction band edge. However, trap densities are still high compared to those measured for Si / SiO2 passivated with post-oxidation anneals in hydrogen. Herein, we report the results of studies for 4H-SiC / SiO2 undertaken to determine the effects of additional passivation anneals in hydrogen when these anneals are carried out following a standard NO anneal. After NO passivation and Pt deposition to form gate contacts, post-metallization anneals in hydrogen further reduced the trap density from approximately 1.5 × 1012 cm−2eV−1 to about 6 × 1011 cm−2eV−1 at a trap energy of 0.1 eV below the band edge for dry thermal oxides on both (0001) and (11–20) 4H-SiC.
The Oxide/Nitride Interface: a study for gate dielectrics and field passivation
Authors: Gila B.P. , Luo B. , Kim J. , Mehandru R. , LaRoche J.R. , Onstine A.H. , Lambers E. , Siebein K. , Abernathy C.R. , Ren F. , Pearton S.J.
Published: April 2011

The study of the effects of substrate surface preparation of GaN, both in-situ and ex-situ and the subsequent deposition of dielectric materials is necessary to create a viable GaN FET technology. Surface preparation techniques have been explored using RHEED, AES, SIMS and C-V measurements to produce films of low interface trap density, 1–2E11 eV−1cm−2. A similar study of the as-fabricated HEMT surface was carried out to create a cleaning procedure prior to dielectric passivation. Dielectric films of Sc2O3 and MgO were deposited via gas-source MBE. Post-deposition materials characterization included AES, TEM, XRR and XPS, as well as gate pulse and isolation current measurements for the passivated HEMT devices. From this study, the relationship between the interface structure and chemistry and the quality of the oxide/nitride electrical interface has been determined. The resulting process has led to the near elimination of the current collapse phenomenon. In addition, the resulting oxide/nitride interface quality has allowed for the first demonstration of inversion in GaN.
Investigation of Retention Properties for YMnO3 Based Metal/Ferroelectric/Insulator/Semiconductor Capacitors
Authors: Yoshimura T. , Ito D. , Sakata H. , Shigemitsu N. , Haratake K. , Ashida A. , Fujimura N.
Published: April 2011

The memory retention properties of Pt/YMnO3/Y2O3/Si capacitors were investigated for the application of ferroelectric gate transistors. The epitaxially grown Pt/YMnO3/Y2O3/Si capacitors showed ferroelectric type hysteresis loop on the capacitance-voltage properties. Although the retention time of the as-deposited capacitors was ∼103 s, it was prolonged up to 104 s when the leakage current density was reduced from 4×10−8 A/cm2 to 2×10−9 A/cm2 by the annealing under N2 ambience. To reveal the relationship between the retention time and leakage current, the leakage current mechanism was investigated comparing several conduction mechanisms. It was found that the dominant leakage mechanisms at high and low electric fields were Poole-Frenkel emission from the Y2O3 layer and ohmic conduction, respectively. This result indicates that the leakage current was limited by the Y2O3 layer at high electric field and was mainly dominated by the amount of defects in the YMnO3 layer at low electric field. From the pseudo isothermal capacitance transient spectroscopy (ICTS), it was determined that the trap density was in an order of 1015 cm−3. Since the variation of the leakage current by annealing was observed only in the low electric field region, it is suggested that the retention properties of the Pt/YMnO3/Y2O3/Si capacitors was influenced by the amount of defects in the YMnO3 layer.
The Synthesis and Catalytic Application of a New Class of Imprinted Silica
Authors: Bass John D. , Anderson Sandra L. , Katz Alexander
Published: April 2011

The effect of chemical environment surrounding a synthetic heterogeneous catalyst active site is investigated using the hydrophilic imprinting of silica. Two model reaction systems have been used for this study: (i) Knoevenagel condensation of 3-nitrobenzaldehyde and malononitrile and (ii) Suzuki coupling of bromobenzene and phenylboronic acid. Using a catalyst in which isolated imprinted amines are surrounded by an acidic silanol-rich environment led to rate accelerations of over 120-fold relative to catalysts in which the amines are surrounded by a hydrophobic environment consisting of trimethylsilyl functional groups for system (i). This result parallels our previous study on the effect of the outer sphere composition on rate acceleration of Knoevenagel reactions using isophthalaldehyde as the aldehyde reactant. We also extended our method for the hydrophilic imprinting of bulk silica to organometallic systems, by successfully synthesizing a tethered palladium complex within the imprinted pocket. This material was used as an active catalyst for (ii). Our results show that a hydrophobic framework environment results in higher initial turnover frequencies than an acidic silanol-rich framework for the Suzuki coupling reaction of bromobenzene and phenylboronic acid, albeit with a lower overall effect than observed in the Knoevenagel system (i). Altogether, these results demonstrate the control of chemical reactivity via the rational design of the outer sphere using an imprinting approach.
Steady-State Fluorescence Anisotropy Studies of Molecularly Imprinted Polymer Sensors
Authors: Chen Yin-Chu , Wang Zheming , Yan Mingdi , Prahl Scott A.
Published: April 2011

Molecularly imprinted polymers (MIPs) are used as recognition elements in biochemical sensors. In a fluorescence-based MIP sensor system, it can be difficult to distinguish the analyte fluorescence from the fluorescence of the polymer itself. We studied steady-state fluorescence anisotropy of anthracene imprinted in a polymer (polyurethane) matrix. Vertically polarized excitation light was incident on MIP films coated on silicon wafers; vertically and horizontally polarized emission was measured. We compared the fluorescence anisotropy of MIPs with imprinted molecules, MIPs with the imprinted molecules extracted, MIPs with rebound molecules, and non-imprinted control polymers. It is shown that differences in fluorescence anisotropy between the polymers and imprinted fluorescent molecules may provide a means to discriminate the fluorescence of analyte from that of the background polymer.
Molecular Imprinting of 3-Hydroxybenzoic Acid: Special and General Binding Sites
Authors: Hu Yue , Orwoll Robert A.
Published: April 2011

A resin, imprinted with 3-hydroxybenzoic acid (3HBA), was synthesized from acrylamide (AA, the functional monomer) and ethylene glycol dimethacrylate (EGDMA, the crosslinking agent). Batch analyses showed that the imprinted polymer has a special affinity for the meta-substituted 3HBA, but not for its para-substituted isomer (4HBA) nor for benzoic acid (BA). These results are consistent with the principle that an imprinted resin's ability to recognize is dependent on the target's size, shape, and functionality. Another resin, prepared from AA and EGDMA but in the absence of a template, had similar affinities for 3HBA, 4HBA, and BA; and thus it could not differentiate among the three. The results can be interpreted with a simple two-binding-site model with one site special for 3HBA and the other being more general with similar affinities for 3HBA, 4HBA and BA. The binding of 3HBA to the imprinted resin is characterized by an association constant and the density of each kind of site using a two-site Scatchard equation. The binding sites common to both the imprinted resin and the non-imprinted reference resin were found to have greater affinity but are less numerous than the sites unique to the imprinted resin.
Structural and optical properties of CdSe, CdTe and CdSeTe nanoparticles dispersed in SiO2 films
Authors: Babu Dayal P. , Rama Rao N. V. , Mehta B. R. , Shivaprasad S. M. , Paulson P. D.
Published: April 2011

CdSexTe1-x nanoparticles (with different stoichiometry ratio x) dispersed in silicon dioxide films have been grown by magnetron sputtering technique followed by thermal annealing. Effect of thermal annealing conditions on the structural, compositional, optical and electronic properties of nanoparticles has been studied using GAXRD, XPS, TEM, and spectroscopic ellipsometry techniques. A structural transformation in the nanoparticle core mediated purely by surface layer effects in the case of CdTe and a spontaneous self-organization of nanoparticles into nanorods in the case of CdSe via fractal growth has been observed. Preliminary observations from the ellipsometry measurements carried out on some of these nanoparticle films shows a blue shift of absorption edge.
Optical Properties of CdSe Nanoparticle Assemblies
Authors: Rafael Leon F. , Zaitseva Natalia , Gerion Daniele , Huser Thomas , Krol Denise
Published: April 2011

We report on three-dimensional fluorescence imaging of micron-size faceted crystals precipitated from solutions of CdSe nanocrystals. Such crystals have previously been suggested to be superlattices of CdSe quantum dots [1,2]. Possible applications for these materials include their use in optical and optoelectronic devices. The micron-size crystals were grown by slow evaporation from toluene solutions of CdSe nanocrystals in the range of 3–6 nm, produced by traditional wet-chemistry techniques. By using a confocal microscope with laser illumination, three-dimensional raster-scanning and synchronized hyper-spectral detection, we have generated spatial profiles of the fluorescence emission intensity and spectrum. The fluorescence data of the micro-crystals were compared with spectra of individual nanocrystals obtained from the same solution. The results do not support the assertion that these microcrystals consist of CdSe superlattices.
Optical Interactions and Photoluminescence Properties of Wide-Bandgap Nanocrystallites
Authors: Bergman Leah , Chen Xiang-Bai , Huso Jesse , Walker Althea , Morrison John L. , Hoeck Heather , Penner Margaret K. , Purdy Andrew P.
Published: April 2011

The UV-photoluminescence (PL) properties of GaN and ZnO nanocrystallites and nanocrystallite ensembles were studied utilizing micro-photoluminescence. We address the origin of the light emissions of the nanocrystallite as to whether it is due a bandgap or excitonic recombination process. The other topic presented here focuses on the interaction of the laser with a collective of crystallites; we address the phenomena of intensity saturation at a high density of laser excitations as well as the impact of the vacuum state on the PL characteristics. Our analysis indicates that the PL of both GaN and ZnO nanocrysallites is excitonic-like and very similar to the behavior of the free exciton in bulk materials. Additionally, we attribute the intensity saturation of GaN and ZnO to the laser heating and heat trapping which takes place in the enclosure of the nanocrystallite ensemble. In vacuum the PL energy was found to exhibit a strong PL energy redshift relative to the PL in air. We attribute the observed shift to a thermal effect and analyze it in terms of the conditions enabling a convective cooling in the ensemble: the mean free path of air in atmospheric pressure and in vacuum relative to the interparticle separation inside the ensemble.
Superparamagnetic Iron Oxide Nanoarticles for Biomedical Applications: a focus on PVA as a coating
Authors: Chastellain M. , Petri A. , Hofmann H.
Published: April 2011

Nanoscaled particles showing a superparamagnetic behavior have been intensively studied these past years for biomedical applications and water-based ferrofluids turned out to be promising candidates for various in vivo as well as in vitro applications. Nevertheless, the lack of well-defined particles remains an important problem. One of the major challenges is still the large-scale synthesis of particles with a narrow size distribution. In this work iron oxide nanoparticles are obtained by classical co-precipitation in a water-based medium and are subsequently coated with polyvinyl alcohol. The thus obtained ferrofluids are studied and a focus is made on their colloidal stability.
Controlled Structure of Gallium Oxide and Indium Oxide Nanowires
Authors: Chun Hye Jin , Bae Seung Yong , Park Jeunghee
Published: April 2011

Gallium oxide (Ga2O3) and indium oxide (In2O3) nanostructures were synthesized by chemical vapor deposition (CVD). Ga2O3 nanowires were synthesized using Ga/Ga2O3 mixture and O2. The diameter of the nanowires is 30–80 nm with an average value of 50 nm. They are consisted of single-crystalline monoclinic crystal. While the nanowires grown without catalyst exhibit a significant planar defect, the nanowires grown with nickel catalytic nanoparticles are almost defect-free. The growth direction of the nanowires grown without the catalyst is uniformly [010]. In contrast, the nanowires grown with the catalyst have random growth direction. X-ray diffraction, Raman spectroscopy, and photoluminescence are well correlated with the structural characteristics of the nanowires. The result provides an evidence for the catalyst effect in controlling the structure of nanowires. In2O3 nanostructures were also synthesized in a controlled manner by selecting the catalyst. The reactants were In and In/In2O3 mixture. The nanowires were produced using catalytic Au nanoparticles and Ga. But the unique bifurcated-structure nanobelts were instead grown without Ga. The nanowires have uniform [100] growth direction with rectangular cross-section. We converted the In2O3 nanowires to In2O3-Ga2O3 nanostructures.
Diffusion-Limited Recombination in Dye-Sensitized TiO2 Solar Cells
Authors: Kopidakis Nikos , Benkstein Kurt D. , Lagemaat Jao van de , Frank Arthur J.
Published: April 2011

The effect of doping on the electron transport dynamics and recombination kinetics in dye-sensitized solar cells was investigated. A simple electrochemical method was developed to dope TiO2 nanoparticle films with Li. Increasing the doping levels is found to slow electron diffusion. The electron diffusion time exhibits a light intensity dependence at all doping levels consistent with a multiple electron-trapping model involving native and doping-induced traps. Importantly, the diffusion time and recombination lifetime of photocarriers are observed to increase in unison with increased doping. This is the first observation that electron diffusion limits recombination with the redox electrolyte under normal working conditions of the dye cell. A model is presented that accounts for the observation. The implications of this mechanism on cell performance are also discussed.
The Magnetic Behavior of Triangular Shaped Permalloy Nanomagnet Arrays
Authors: Shiu J. Y. , Tai M. F. , Yao Y. D. , Kuo C. W. , Chen P.
Published: April 2011

During the past few decades, the density of magnetic storage has been improved considerably. To increase the storage capacity, it is necessary to reduce the size of magnetic grains. However, as the domain size decreases, their thermal stability will also decrease, which results in the loss of magnetization. To overcome the limit imposed by such superparamagnetic behavior, lots of recent research attentions have been focused on the patterned magnetic media. To maximize the storage density, it is preferable to create periodical magnetic patterns, in which single-domain magnetic dots are well separated from each other. In this experiment, we have utilized nanosphere lithography to create large-area well-ordered two dimension arrays of permalloy (Ni80Fe20) nanoparticles. Nanosphere lithography is an inexpensive, simple, parallel, and high throughput fabrication technique. We have employed monodisperse polystyrene beads with diameter of 650, 560, 440, 350, 280 nm to fabricate triangle-shaped permalloy (Ni80Fe20) nano-arrays with lateral dimension in the region of 170∼90 nm, and thickness in the region of 10∼50 nm. The magnetic behavior of these triangle-shaped nanomagnet arrays have been investigated by longitudinal magnetic optic Kerr effect (LMOKE) and magnetic force microscopy (MFM). It was found that the coercivity of the permalloy nanoparticle arrays increases with decreasing the thickness of the nanoparticle. This can be attributed to the interface effect between the arrays and the substrate.
Lasing from CdSe/ZnS Quantum Rods in a Cylindrical Microcavity
Authors: Kazes Miri , Lewis David Y. , Ebenstein Yuval , Mokari Taleb , Banin Uri
Published: April 2011

Lasing from CdSe/ZnS quantum rods and quantum dots both in solution and in a film is studied by utilizing a high Q cylindrical microcavity, showing Whispering Gallery Mode (WGM) lasing. CdSe/ZnS quantum rods, in comparison to quantum dots, exhibited remarkably reduced lasing thresholds. In addition, polarization measurements revealed that quantum rods have a linear polarized lasing, in contrast to quantum dots that show no preferable lasing polarization. Furthermore, an efficient and reproducible method is employed for preparation of nanocrystal films inside capillaries by laser irradiation for achieving robust lasing. Further irradiation of the film resulted in a room temperature stable lasing over hundreds of pump pulses, lasing thresholds as low as 0.02mJ and lasing intensities that are three orders of magnitude larger than the saturated fluorescence intensity. This was successfully applied to CdSe/ZnS quantum rod samples of varied dimensions and was also demonstrated for quantum dot samples.
Quantum Conductivity of Spatially Inhomogeneous Systems
Authors: Pozhar Liudmila A.
Published: April 2011

A fundamental quantum theory of conductivity of spatially inhomogeneous systems in weak electro-magnetic fields has been derived using a two-time Green function (TTGF)-based technique that generalizes the original method due to Zubarev and Tserkovnikov (ZT). Quantum current and charge density evolution equations are derived in a linear approximation with regard to the field potentials. Explicit expressions for the longitudinal and transverse conductivity, and dielectric and magnetic susceptibilities have been derived in terms of charge density - charge density and microcurrent - microcurrent TTGFs. The obtained theoretical description and formulae are applicable to any inhomogeneous system, such as artificial molecules, atomic and molecular clusters, thin films, interfacial systems, etc. In particular, the theory is designed to predict charge transport properties of small semiconductor quantum dots (QDs) and wells (QWs), and is a significant step toward realization of a concept of virtual (i.e., theory-based, computational) synthesis of electronic nanomaterials of prescribed electronic properties.
The Effect of Gate Geometry on the Charging Characteristics of Metal Nanocrystal Memories
Authors: Gorur-Seetharam Anirudh , Lee Chungho , Kan Edwin C.
Published: April 2011

This study presents the effect of gate geometry on the charging characteristics of metal nanocrystal memories. The effect is studied by varying the perimeter to area ratio, number of convex corners and concave corners of the gate of a metal-oxide-semiconductor (MOS) capacitor with embedded gold nanocrystals. It can be observed that the nanocrystal charging rate increases for a smaller perimeter to area ratio. The presence of concave and convex corners increases the nanocrystal charging rate. Based on this study it is expected that gate geometries with low perimeter to area ratio and with selected convex and concave corners would increase the nanocrystal charging rate.
Synthesis of boron nitride nanolayers encapsulating iron fine particles and boron nitride nanotubes
Authors: Tokoro Hisato , Fujii Shigeo , Oku Takeo , Muto Shunsuke
Published: April 2011

Boron nitride (BN) nanolayers encapsulating iron (Fe) fine particles have been synthesized by annealing mixtures of hematite (α-Fe2O3) and boron powders at 1373 K for 2 hours in nitrogen atmosphere. The Fe particles had an average diameter of ∼300 nm with BN nanolayers coating of ∼10 nm. The α-Fe2O3 was transformed into Fe and then Fe-B on a process of annealing. The Fe-B was decomposed into Fe and BN, and consequently Fe particles coated with BN nanolayers were synthesized. They showed soft magnetic properties with coercivity of 1.5 kA/m. The BN nanolayers encapsulation was effective on improving oxidation resistance. BN nanotubes with diameter of ∼100 nm were also synthesized as a resultant product by this method.
Aqueous Ferrofluid of Citric Acid Coated Magnetite Particles
Authors: Goodarzi A. , Sahoo Y. , Swihart M. T. , Prasad P. N.
Published: April 2011

Magnetic nanoparticles have found application in medical diagnostics such as magnetic resonance imaging and therapies such as cancer treatment. In these applications, it is imperative to have a biocompatible solvent such as water at optimum pH for possible bio-ingestion. In the present work, a synthetic methodology has been developed to get a well-dispersed and homogeneous aqueous suspension of Fe3O4 nanoparticles in the size range of 8–10 nm. The surface functionalization of the particles is provided by citric acid. The particles have been characterized using transmission electron microscopy, magnetization measurements with a superconducting quantum interference device, FTIR spectroscopy (for surfactant binding sites), thermogravimetric studies (for strength of surfactant binding), and x-ray photoelectron spectroscopy and x-ray diffraction (for composition and phase information). The carboxylate functionality on the surface provides an avenue for further surface modification with fluorescent dyes, hormone linkers etc for possible cell-binding, bioimaging, tracking, and targeting.
Atomic Organization In Magnetic Bimetallic Nanoparticles: An Experimental And Theoretical Approach
Authors: Fromen Marie-Claire , Dennler Samuel , Casanove Marie-José , Lecante Pierre , Morillo Joseph , Bayle–Guillemaud Pascale
Published: April 2011

Ultrafine bimetallic CoRh nanoparticles synthesized by a soft chemical route with compositions ranging from pure cobalt to pure rhodium are investigated using high-resolution and energy filtering transmission electron microscopy techniques as well as wide angle x-ray scattering. In parallel, they are simulated with the use of an n-body semi-empirical interaction model: quenched molecular dynamics and Monte-Carlo Metropolis simulated annealing are performed on these nanoparticles in order to find their most stable isomers as a function of composition and size. A progressive evolution from an original polytetrahedral structure to the face-centered cubic structure with increasing Rh content is observed in these particles. Strong tendency to Co surface segregation is both experimentally evidenced and confirmed by the simulations.