bluuebunny/crossref_metadata_2025_split huggingface dataset:
Titanium Dioxide Nanotubes Decorated with Nanoparticles for Dye Sensitized Solar Cells
Authors: Pan Xuan , Zhao Yong , Chen Changhong , Fan Zhaoyang 
Published: April 2011

ABSTRACTThe titanium dioxide (TiO2) nanoparticle (NP) structure has higher surface area and dye loading value to increase photon absorption while the nanotube (NT) can suppress the random walk phenomena to enhance carrier collection. In this work, hydrothermal method was utilized to infiltrate the TiO2 nanotube array by TiO2 nanoparticles with the aim of combining the advantages of both nanostructures to improve dye sensitized solar cells (DSSCs) efficiency. Structure morphology, device performance, and electrochemical properties were investigated. SEM observation confirmed that around 10 nm TiO2 nanoparticles uniformly covered the NT wall. TiO2 NT samples at three different lengths: 8 μm, 13 μm and 20 μm, decorated with different amount of nanoparticles were studied to optimize the structure for light absorption and electron transport to achieve high solar conversion efficiency. Electrochemical impedance spectroscopy (EIS) was also employed to investigate the cells’ parameters: electron lifetime (τ), diffusion length (Ln) et al, to gain insight on the device performance. The incident photon conversion efficiency (IPCE) was also reported.
Noise Mitigation Techniques for Carbon Nanotube-Based Piezoresistive Sensor Systems
Authors: Cullinan Michael A. , Culpepper Martin L. 
Published: April 2011

ABSTRACTCarbon nanotube (CNT)-based piezoresistive strain sensors have the potential to outperform traditional silicon-based piezoresistors in MEMS devices due to their high strain sensitivity. However, the resolution of CNT-based piezoresistive sensors is currently limited by excessive 1/f or flicker noise. In this paper we will demonstrate several noise mitigation techniques that can be used to decrease noise in the CNT-based sensor system without reducing the sensor’s strain sensitivity. First, the CNTs were placed in a parallel resistor network to increase the total number of charge carriers in the sensor system. By carefully selecting the types of CNTs used in the sensor system and by correctly designing the system it is possible to reduce the noise in the sensor system without reducing sensitivity. The CNTs were also coated with aluminum oxide to help protect the CNTs from environmental variations. Finally, the CNTs were annealed to improve contact resistance and to remove adsorbates from the CNT sidewall. Overall, using these noise mitigation techniques it is possible to reduce the total noise in the sensor system by almost two orders of magnitude and increase the dynamic range of the sensors by 29 dB.
Nanorods of Dy Modified BiFeO3 for Multifunctional Device Applications
Authors: Mandal M. , Duttagupta S. P. , Palkar V. R. 
Published: April 2011

ABSTRACTWe have developed material (Bi0.7Dy0.3FeO3)(BDFO) which exhibits the multiferroic behavior at room temperature with significant coupling in bulk as well as thin films. If these properties could be fashioned in nano rods, implementation in devices could be certainly more prominent and straight forward. We have therefore used vertically aligned arrays of silicon rods (~5 μm in length and ~ 500 nm in diameter) as base material to direct the growth of BDFO in rod form. BDFO is deposited on the surface of Si rods by using pulsed laser deposition technique. These BDFO/Si rods are then separated from the support, dispersed into propanol and transferred onto SiO2/Si substrates for testing. X-ray diffraction (XRD) results indicate presence of phase pure BDFO layer on Si rods. Saturation observed at room temperature in magnetic and ferroelectric hysteresis loops confirm the coexistence of ferromagnetic and ferroelectric properties. Change in ferroelectric polarization measured on single rod in the presence of applied magnetic field suggests the coupling behavior between two order parameters. Moreover, change in magnetic domain pattern of BDFO rods associated with applied electric field further supports the presence of coupling behavior in both ways. The vertical and lateral displacement occurring in BDFO/Si rods with applied electric field helps to confirm their piezoresponce behavior. BDFO/Si nanorods with multifunctional properties could find variety of novel device applications with flexibility and simplicity in operation. It might include single rod power generation by means of applied stress or magnetic field.
Three-Dimensional Patterning of Micro/Nanoparticle Assembly with a Single Droplet of Suspension
Authors: Choi Sun , Pisano Albert P. , Zohdi Tarek I. 
Published: April 2011

ABSTRACTWe develop a novel patterning technique to create 3D patterns of micro, nanoparticle assembly via evaporative self-assembly based on confinement/release of micro/nano particles assembly based on the coffee-ring effect of evaporating suspension. Based on the presented technique, we demonstrate that the patterns of 3D assembly of various sizes of microparticles (Silica), metal oxide nanoparticles (TiO2, ZnO) and metallic nanoparticles (Ag) can be successfully generated by low-concentrated particle suspension (1.25 wt % ~ 5 wt %) without additional sintering steps and we also show the geometries of the patterns can be finely controlled by adjusting the parameters of the process.
A DFT and HRTEM Study on MoS2/Co: Locating Promoters in Catalytic Nanostructures
Authors: Ramos Manuel , Berhault Gilles , Farias Jose Rurik , Elizalde Jose Trinidad , Ferrer Domingo , Torres Brenda , Chianelli R. R. 
Published: April 2011

ABSTRACTLocating cobalt promoters on catalytically MoS2 structures is a challenging task to achieve; this is due to the size on those MoS2 nanostructures. Previous reports in the literature indicate that specific locations for Co in MoS2 slabs are (1010)-plane creating either a sulfur-Co or Molybdenum-Co termination edge, due to lower energy required for the permutation Mo, S and Co to occur. We present results obtained from Density Functional Theory study done on the interface between MoS2 and Co9S8 crystal structures; the interface show an interesting thiocubane cluster and it is suspected to be the responsible for Mo-S-Co bonding to exist, along with HDS reaction. In order to understand electronic properties on thiocubane Density of States and Mulliken Population Analysis calculations were implemented using Cambridge Serial Total Energy Package (CASTEP). Results indicate a strong electron donation from Co to Mo through intermediate sulfur atom bonded to both metals while an enhanced metallic character is also found.
Nylon 6 reinforced with acrylic polymer nanoparticles. Thermal properties and nano structure
Authors: Huitron-Rattinger Estefania , Alvarado-Tenorio Bonifacio , Romo-Uribe Angel 
Published: April 2011

ABSTRACTThe correlation of thermal properties and nanostructure of nylon 6 (denoted PA6) reinforced with polymer nanoparticles (denoted PNP, size~8 nm) has been investigated. PNPs are highly crosslinked acrylic-based polymers synthesized by the Rohm and Haas Co. PNPs and those grafted with maleic anhydride (denoted PNP-g-MA) were each one dispersed into a commercial PA 6 matrix by melt extrusion, at a concentration of 3 wt%. Thermal analysis showed that the PNPs increased the thermal stability of PA6 and reduced the melting and crystallization temperatures as well as the enthalpy. Small-angle light scattering showed that the PNPs crystallize into a spherulitic morphology, typical of PA6. Isothermal crystallization studies showed that the PNPs act as nucleating agents, accelerating the rate of crystallization. Wide-angle X-ray scattering showed that the composites crystallize in the α-form, and the PNPs reduced the degree of crystallinity, in agreement with thermal analysis results. The smaller degree of crystallinity was also reflected in the long range spacing, it was also reduced by the presence of the PNPs as measured directly by small-angle X-ray scattering.
Formation of Irregular Al Islands by Room-Temperature Deposition on NiAl(110)
Authors: Jing Dapeng , Han Yong , Ünal Bariş , Evans J. W. , Thiel P. A. 
Published: April 2011

ABSTRACTSTM studies reveal that irregular non-equilibrium two-dimensional Al islands form during deposition of Al on NiAl(110) at 300 K. These structures reflect the multiple adsorption sites and diffusion paths available for Al adatoms on the binary alloy surface, as well as the details of inhibited edge diffusion and detachment-attachment kinetics of Al adatoms for numerous distinct step edge configurations. We attempt to capture these features by multi-site lattice-gas modeling incorporating DFT energetics for adatoms both at adsorption sites and transition states. This formulation enables description and elucidation of the observed island growth shapes.
Superconducting Parent Compound Pr2CuO4 Achieved by Special Post-Reduction
Authors: Yamamoto Hideki , Matsumoto Osamu , Yamagami Keitaro , Naito Michio , Krockenberger Yoshiharu 
Published: April 2011

ABSTRACTIt is commonly believed that the parent compounds of high-Tc cupratres are, universally, charge transfer insulators and triggered by Mott physics. In our experiments using metal-organic decomposition (MOD), however, accumulating evidences show that the parent compounds of “electron-doped” superconductors, RE2-xCexCuO4 [RE = rare earth ion] with x = 0, are not Mott insulators but superconductors [1-5]. They have a Tc of 30 K and crystallize in the Nd2CuO4 (T’) structure. Most likely, the sharp contradiction between our results and commonly achieved data originates from the complicated oxygen chemistry in these materials. The as-synthesized specimens contain a fair amount of impurity interstitial oxygen. Throughout the reduction process it is required to remove exclusively impurity oxygen while preserving regular oxygen site occupied in order to obtain superconductivity. With decreasing x the constraints of the reduction process are getting more tight. In this study, we systematically investigated the post-annealing process using MBE-grown T’-Pr2CuO4 films. The MBE films were reduced ex-situ in a tubular furnace following a specially designed 2-step process, as in the case of MOD films. The films were annealed at Ta = 700 - 850°C in a reducing atmosphere (PO2 = 2 x 10−5 − 2 x 10−3 atm) and finally reduced at a lower temperature Tred = 450 – 700°C under vacuum (< 10−4 Torr). The film properties systematically changed with Ta, PO2, and Tred. The optimized Tred varies from 475°C to 650°C mainly depending on Ta, since the microstructure and grain size of the films are determined by Ta. Optimal superconducting properties are Tc of 26 K, while ρ(300 K) = 250 μΩcm, and RRR ~ 10. We believe the combination of thin-film synthesis and specially designed post-reduction process enabled us to obtain nearly intact CuO2 planes. Samples prepared by above-mentioned method unveiled the intrinsic properties of the parent compounds, which are not triggered by Mott physics. This result also agrees with the recent calculation result indicating the parent compounds with T’ structure are not charge transfer insulators [6-8].
Dynamics of hydrogen in Pr2Fe17H4 and Pr2Fe17H5
Authors: Mamontov Eugene , Udovic Terrence J , Rush John J , Isnard Olivier 
Published: April 2011

ABSTRACTWe describe a study of the dynamics of hydrogen in Pr2Fe17H4, where isolated hexagons formed by the interstitial tetrahedral (t) sites of the metal lattice are populated by mobile hydrogen atoms. An activation energy of 0.10 eV has been determined for a localized jump process involving the hopping of these hydrogen atoms among adjacent vertices of each hexagon, slightly lower than that for hydrogen hopping in Pr2Fe17H5, where each hexagon is occupied by two hydrogen atoms.
Charge transfer of n-type GaN photoelectrolysis in HCl solution for H2 gas generation at a counterelectrode
Authors: Fujii Katsushi , Ono Masato , Ito Takashi , Ohkawa Kazuhiro 
Published: April 2011

ABSTRACTIn order to clarify the charge transfer characteristics for H2 generation, photoelectrochemical properties of n-type GaN in HCl solution were investigated. The flatband potential under illumination and the onset voltages of photocurrent located approximately the same position. From the result, we concluded that the positively charged surface by hole capture is the main reason of the extra voltage requirement for H2 generation. The carrier concentration in n-type GaN also affects the photocurrent.
Thermoelectric Study on Polycrystalline La1−xSrxRuO3
Authors: He Jian , Thompson Daniel , Edwards Brad , Tritt Terry M. 
Published: April 2011

ABSTRACTThe otherorhombic distorted perovskite La1−xSrxRuO3 (0.1<x<0.9) polycrystalline samples have been prepared using conventional solid state chemistry reaction. The phase constituent, compositional homogeneity and micro-morphology were checked by X-ray powder diffraction, Energy Disperse X-ray spectroscopy and scanning electron microscopy before characterized by means of the electrical resistivity, thermal conductivity and thermal power measurements. Particularly, the compositional dependence of Seebeck coefficient of present compound was studied in light of the comparison with the strongly correlated system NaxCoO4 and the relevant model proposed by W. Koshibae. Finally, the potential of using La1−xSrxRuO3 as a practical thermoelectric material has been also discussed.
Transient Harman Measurement of the Cross-plane ZT of InGaAs/InGaAlAs Superlattices with Embedded ErAs Nanoparticles
Authors: Singh Rajeev , Bian Zhixi , Zeng Gehong , Zide Joshua , Christofferson James , Chou Hsu-Feng , Gossard Art , Bowers John , Shakouri Ali 
Published: April 2011

ABSTRACTThe transient Harman technique is used to characterize the cross-plane ZT of InGaAs/InGaAlAs superlattice structures with embedded ErAs nanoparticles in the well layers. ErAs nanoparticles have proven to substantially reduce the thermal conductivity while slightly increasing the electrical conductivity of bulk InGaAs. The InGaAs/InGaAlAs superlattice structure was designed to have a barrier height of approximately 200meV. Although ErAs nanoparticles provide free carriers inside the semiconductor matrix, additional doping with Si increased the Fermi energy to just below the barrier height. The bipolar transient Harman technique was used to measure device ZT of samples with different superlattice thicknesses in order to extract the intrinsic cross-plane ZT of the superlattice by eliminating the effects of device Joule heating and parasitics. High-speed packaging is used to reduce signal ringing due to electrical impedance mismatch and achieve a short time resolution of roughly 100ns in transient Seebeck voltage measurement. The measured intrinsic cross-plane ZT of the superlattice structure is 0.13 at room temperature. This value agrees with calculations based on the Boltzmann transport equation and direct measurements of specific film properties. Theoretical calculations predict cross-plane ZT of the superlattice to be greater than 1 at temperatures greater than 700K.
A Band Structure Phase Diagram Calculation of 2D BiSb Films
Authors: Tang Ming Y. , Dresselhaus Mildred S. 
Published: April 2011

ABSTRACTEver since the birth of thermoelectrics, it has been well known that semiconductors (materials with a relative small bandgap) give the best thermoelectric performance. From quantum mechanics, it is also well known that low dimension quantum confinement leads to changes in the band alignment of a material. Thus, a semimetallic material can be made semiconducting by using low dimensionality quantum confinement effects. BiSb alloys have been of particular interest for thermoelectric application in the temperature range of 70K to 100K. In bulk form, BiSb alloys can either be semimetal or semiconductor, depending on the alloy composition. Moreover, semimetallic BiSb alloys can be made semiconducting by using the low dimensionality quantum confinement concept. With these two previous concepts in mind, it is valuable to further explore the dependence of the band alignment for different alloy concentrations and different confinement conditions for BiSb alloys.Following the study of the effect of the Sb concentration and of the wire diameter on the semimetallic or semiconducting phase of BiSb alloy nanowires, we now examine the corresponding effect of the Sb concentration and the film thickness on the properties of BiSb alloy films. A band structure phase diagram is calculated, giving the details on the dependence of the relative band edge position on the film thickness and the Sb concentration. This phase diagram gives a first hand guideline for choosing the film thickness and the Sb concentration to better improve the thermoelectric performance of BiSb alloy films.
Bi2Te3: Structural Modulations in Epitaxially Grown Superlattices and Bulk Materials
Authors: Peranio Nicola , Eibl Oliver , Nurnus Joachim 
Published: April 2011

ABSTRACTMultiquantum well structures of Bi2Te3 are predicted to show an enhancement of the thermoelectric figure of merit ZT. Electron-conducting Bi2Te3 thin films and superlattices (SL) with a period of 12 nm were epitaxially grown on BaF2 substrates by molecular beam epitaxy. The microstructure was investigated by transmission electron microscopy. The SL could be imaged with strong contrast yielding a period of 12.0±0.5 nm. The SL is slightly bent with an amplitude of 30 nm and a wave length of 400 nm. Threading dislocations were found with a density of 2·109 cm−2. The SL interfaces are strongly bent close to threading dislocations, undisturbed regions have a maximum lateral size of 500 nm. A structural modulation (nns) with a wave length of 10 nm was found in Bi2Te3 thin films, superlattices and bulk materials. The structural modulation is found to be of general character for Bi2Te3 materials and is superimposed to the average structure. It was analysed in detail by stereomicroscopy in bulk material yielding a pure structural modulation with a displacement vector parallel to [5,-5,1] and a wave vector parallel to (1,0,10). The investigations showed the presence of none, one or two (nns). The number of (nns) and thereby the thermoelectric properties might be controlled by the growth parameters. Phonons should be scattered on the sinusoidal strain field of the (nns) yielding (i) a significantly decreased thermal conductivity, (ii) a reduced dimensionality and (iii) anisotropic transport coefficients in the basal plane.
Phase Segregation and Thermoelectric Properties of AgPbmSbTem+2m=2,4,6, and 8
Authors: Sootsman Joseph , Pcionek Robert , Kong Huijun , Uher Ctirad , Kanatzidis Mercouri G 
Published: April 2011

ABSTRACTThe preparation and characterization of the AgPbmSbTem+2 family of compounds with m=2, 4, 6, and 8 is reported. Phase segregation was observed in all of these materials. The lattice thermal conductivity of these samples is low (<1.1 W/m-K). Powder x-ray diffraction, thermal analysis, and electron microscope investigations of these systems show that ideal solid solutions are not formed. The transport properties of these composite materials are presented and suggest that they could have promising thermoelectric properties when optimized.
The Dynamics of the Guests in Filled Germanium Clathrates
Authors: Hermann Raphael P. , Grandjean Fernande , Keppens Veerle , Schweika Werner , Nolas George S. , Mandrus David G. , Sales Brian C. , Christen Hans M. , Bonville Pierre , Long Gary J. 
Published: April 2011

ABSTRACTIn the filled gallium-germanium clathrates, R8Ga16Ge30, where R is Ba, Sr, or Eu, the guests are located in two large cages and are weakly bound to the crystalline clathrate framework. The caged guests exhibit a localized “rattling” vibrational mode that provides an efficient mechanism for reducing the thermal conductivity. Inelastic neutron scattering and nuclear inelastic scattering measurements have yielded the phonon density of states in R8Ga16Ge30; the line width of the localized vibrational modes is found to be an important parameter in determining the lattice thermal conductivity. Neutron diffraction studies on R8Ga16Ge30 have shown that the guests in the larger cage are located off-center, and it was proposed that their jumping about the four off-center locations is responsible for the observed glass-like thermal conductivity at temperatures below 10 K. The detection of such slow guest motion is challenging because the typical time and energy scales involved are ca. 4 ns and 1 µeV, respectively. We have studied the slow europium tunneling dynamics in Eu4Sr4Ga16Ge30 by both Mössbauer and microwave absorption spectroscopy.
Splitting of Guest Atom Sites and Lattice Thermal Conductivity in Ba-Ga-Ge Clathrate Compounds
Authors: Okamoto Norihiko L. , Tanaka Katsushi , Inui Haruyuki 
Published: April 2011

ABSTRACTThe crystal structures of some type-I and -III clathrate compounds in the Ba-Ga-Ge system have been investigated by synchrotron X-ray powder diffraction at room temperature, paying special attention to the changes of the cage structure and the splitting behavior at the guest atom site upon alloying with Ga. For both types of the clathrate compounds, the split distance of the Ba(2) sites increases with the increase in the Ga content, corresponding to the change in the size and shape of the encapsulating polyhedral cage. Lattice thermal conductivity at room temperature has a positive correlation with the atomic displacement parameter (ADPsplit) based on the split-site model but has an inverse correlation with the split distance of the Ba(2) sites, indicating that a dominant factor of reducing the lattice thermal conductivity is not thermal vibration at the split sites but thermal jump among the split sites.
Effect of Ga-doping on the Thermoelectric Properties of Ba-Ge Type-III Clathrate Compounds
Authors: Kim Jung-Hwan , Okamoto Norihiko L. , Tanaka Katsushi , Inui Haruyuki 
Published: April 2011

ABSTRACTEffect of Ga addition on the thermoelectric properties of Ba-Ge type-III clathrate has been investigated as a function of Ga content and temperature. The substitution of Ga atom for Ge atom leads to the decrease of carrier (electron) concentration. Electrical conduction is of n-type for all clathrate compounds investigated and the values of electrical resistivity and Seebeck coefficient increase with the increase in the Ga content and in temperature. Both electronic and lattice thermal conductivity decrease with the increase in the Ga content because of the decreased carrier concentration and the increased extent of the rattling motion of Ba atoms encapsulated in open-dodecahedron, respectively. A very high ZT value of 1.25 is obtained at 670 °C for Ba24Ga15Ge85.