bluuebunny/crossref_metadata_2025_split huggingface dataset:
Approaches Toward Chemically Prepared Multiple Quantum Well Structures
Authors: Cronin S. B. , Koga T. , Sun X. , Ding Z. , Huang S.-C. , Kaner R. B. , Dresselhaus M. S. 
Published: April 2011

AbstractAn enhanced thermoelectric figure of merit, ZT, has been predicted for Bi2Te3 in the form of 2-dimensional quantum wells. A new approach to making multiple quantum well (MQW) structures for thermoelectric applications utilizing a chemical intercalation technique is proposed and investigated. It is proposed that by starting from Li intercalated Bi2Te3 and Bi2Se3, the layers of these materials can be separated by chemical means. The layers of Bi2Te3 or Bi2 Se3 can then be restacked, by self-assembly, forming a non-periodic array of quantum wells. These chemically prepared MQWs are characterized by X-ray diffraction, SEM (scanning electron microscopy) and TEM (transmission electron microscopy) at various stages in the sample preparation to assess the degree to which the actual samples match the proposal. Experimental measurements of the Seebeck coefficient (S) and the electrical conductivity (σ) were performed over a range of temperatures for the initial bulk materials. It is found that some of the steps in the proposed fabrication have been achieved but still much improvement is needed before any practical thermoelectric 2D-system can be provided.
Thermoelectric Properties of the Half-Heusler Compound (Zr,Hf)(Ni,Pd)Sn
Authors: Browning V. M. , Poon S. J. , Tritt T. M. , Pope A. L , Bhattacharya S. , Volkov P. , Song J. G. , Ponnambalam V. , Ehrlicha A. C. 
Published: April 2011

AbstractRecent measurements of the thermoelectric transport properties of a series of the half- Heusler compound ZrNiSn are presented. These materials are known to be bandgap intermetallic compounds with relatively large Seebeck coefficients and semimetallic to semiconducting transport properties. This makes them attractive for study as potential candidates for thermoelectric applications. In this study, trends in the thermoelectric power, electrical conductivity and thermal conductivity are examined as a function of chemical substitution on the various fcc sub-lattices that comprise the half-Heusler crystal structure. These results suggest that the lattice contribution to the thermal conductivity may be reduced by increasing the phonon scattering via chemical substitution. The effects of these substitutions on the overall power factor and figure-of-merit will also be discussed.
LnPdSb and Ln3Au3Sb4: New Thermoelectric Materials
Authors: Mastronardi K. , Young D. , Wang C.-C. , Ramirez A. P. , Khalifah P. , Cava R. J. 
Published: April 2011

AbstractThe thermoelectric properties near ambient temperature of half-Heusler alloys based on HoPdSb, DyPdSb, and ErPdSb are reported. The Seebeck coefficients are between 60 and 250 μV/K. The resistivities range between 0.6 and 20 mΩcm, and the majority carriers are p-type. Thermal conductivities are smallest in intentionally disordered materials. The highest ambient temperature ZT obtained is 0.06. Band structure calculations are presented, and are compared to those for ZrNiSn. It is suggested that half-Heusler alloys with 18 electrons per formula unit may represent a large class of thermoelectric materials. The thermoelectric properties of another family of cubic symmetry antimonides, based on Ho3Au3Sb4 and Sm3Au3Sb4, are also reported.
Diamond and Polycrystalline Diamond for MEMS Applications: Simulations and Experiments
Authors: Çağin Tahir , Che Jianwei , Gardos Michael N. , Goddard William A. 
Published: April 2011

AbstractTo date most of the MEMS devices are been based on Silicon. This is due to the technological know-how accumulated on manipulating, machining, manufacturing of Silicon. However, only very few devices involve moving parts. This is because of the rapid wear arising from high friction in these Silicon based systems. Recent tribometric experiments carried out by Gardos on Silicon and polycrystalline diamond show that this rapid wear is caused by a variety of factors, related both to surface chemistry and cohesive energy density of these likely MEMS bearing materials. Therefore, theoretical and tribological characterization of Si and PCD surfaces is essential prior to device fabrication to assure reliable MEMS operation unded various atmospheric environments, especially at elevated temperatures.In this paper, we summarize tribological experiments and theoretical studies of friction and wear processes on diamond surfaces. We studied the atomic friction of diamond (100)-surface employing an extended bond-order-dependent potential for hydrocarbon systems in MD simulations.
Micro-Tensile and Fatigue Testing of Copper Thin Films on Substrates
Authors: Hommel M. , Kraft O. , Baker S. P. , Arzt E. 
Published: April 2011

AbstractA special micro-tensile tester was used to carry out tensile tests of thin copper films on substrates. The elastic strain in the film was measured in-situ using x-ray diffraction and the total strain with an external strain gage. From the elastic strains the stresses in the films were calculated and stress-strain curves were obtained. It was observed that the flow stress increases with decreasing film thickness. The method was also applied to investigate the mechanical behavior of films under cyclic loading.
Surface Dipoles Influence the Wettability of Terminally Fluorinated Organic Films
Authors: Colorado Ramon , Graupe Michael , Takenaga Mitsuru , Koini Thomas , Lee T. Randall 
Published: April 2011

AbstractThe correlation of differences in the wettabilities of partially fluorinated self-assembled monolayers (SAMs) to changes in the chemical structure and composition of the films was explored by contact angle goniometry and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). SAMs of simple alkanethiols (CH3(CH2)nSH with n = 9-15) and their CF3-terminated analogs (CF3(CH2)nSH with n = 9-15) were prepared by adsorption from solution onto evaporated gold. Advancing contact angles of hexadecane were measured on both the terminally fluorinated surfaces and the hydrocarbon surfaces. These data were compared to those obtained using a series of polar aprotic contacting liquids. As expected, the contact angles of hexadecane were higher on the CF3-terminated SAMs than on the CH3-terminated SAMs. The contact angles of the polar aprotic solvents, however, were measurably lower on the CF3- terminated SAMs than on the CH3-terminated SAMs. These observations were rationalized on the basis that the introduction of the CF3 terminal groups yields oriented surface dipoles that interact with the dipoles of the polar contacting liquids. Further support for this model was provided by the observation of an inverse parity (“odd-even”) effect in the wettabilities of the polar aprotic solvents on the CF3-terminated surfaces. Analysis by PM-IRRAS revealed that both types of films consist of predominately trans-extended alkyl chains with relatively few gauche defects in a densely packed arrangement. The high degree of order is consistent with the detection of the parity effect, where small changes in the orientation of the tail groups can be sensed by contact angle measurements only in highly ordered organic thin films. The significance of the dipole-oriented dipole interaction in describing interfacial wettabilities is discussed.
Determining the High-temperature Properties of Thin Films Using Bilayered Cantilevers
Authors: Tada H. , Nieva P. , Zavracky P. , Miaoulis I.N. , Wong P.Y. 
Published: April 2011

AbstractHigh-temperature applications of microelectromechanical systems (MEMS), especially in new temperature sensor designs, require an accurate knowledge of the temperature-dependent thermophysical properties of the materials. Although the measurement of the mechanical properties of materials at room temperature has been widely conducted, the same techniques often cannot be used for high-temperature property measurements. In this study, a new technique was developed to find the thermal expansion coefficient of thin films at high temperatures. Bilayered cantilever beams undergo thermally induced deflection at high temperatures, which can be measured and correlated to material properties. An imaging system was developed for the experimental measurement of the beam curvature for temperatures up to 1000°C. To find the high-temperature property of thin films, a bilayered beam, consisting of polycrystalline silicon and silicon dioxide, was designed such that the change in the property of SiO2 had little effect on the curvature of the beam. Furthermore, numerical analysis showed that the Young's modulus of Si also had negligible effect on the curvature. Therefore, the analytical model for beam curvature was simplified to be only a function of the thermal expansion coefficient of Si layer. Using this model, the thermal expansion coefficient of polycrystalline Si film was determined for temperature range between room temperature and 1000°C. The method can be easily modified to find the Young's modulus of Si, as well as properties of SiO2.
Thin Film Stress Measurement with a Tunneling Sensor
Authors: Zhang P. , Vinci R. P. , Bravman J. C. , Kenny T. W. 
Published: April 2011

AbstractA new technique of measuring thin film stress with a tunneling sensor is presented. Basic measurement concepts, preliminary results on thin film stress measurement, and fabrication processes for the tunneling stress measurement sensor are described. The feasibility of implementing this technique for in-situ stress monitoring during thin film deposition demonstrated.
Etch Selectivity of Novel Epitaxial Layers for Bulk Micromachining
Authors: Borenstein J. T. , Gerrish N. D. , Currie M. T. , Fitzgerald E. A. 
Published: April 2011

AbstractThe present work demonstrates very high etch selectivity for a novel epitaxial layer in several standard bulk micromachining etchants. High selectivities have previously been achieved using high-concentration boron diffusions, resulting in a wide array of high performance micromechanical sensors. However, doping gradients, precipitates and dislocation arrays generated from the high boron concentrations can have deleterious effects on device performance. In this work, we report on the performance of a novel epitaxial structure composed of a silicon-germanium alloy device layer over a graded buffer layer. Chemical and microstructural analysis of the epitaxial layers reveal high purity and minimal defect densities. The selectivities of this layer and of boron-diffused layers are determined for a variety of etching conditions. High selectivity against low-doped silicon substrates is demonstrated in both ethylenediamine pyrocatechol and potassium hydroxide. Micromachined structures built using the SiGe epitaxial layer show smooth surfaces and precise build dimensions.
Silicon Electromachining Processes in Aqueous Solutions
Authors: Kovler M. , Starosvetsky D. , Nemirovsky Y. , Yahalom J. 
Published: April 2011

AbstractHigh rate of etching of silicon was obtained by non conventional cathodic polarization in alkaline solutions. When the process was carried out at potentials more negative than −10 V it caused electropolishing of the etched surface. Shifting the potential in the cathodic direction increases the etch-rate parabolically and enhances the effect of polishing. The etch-rate increased by more than two orders of magnitude over the potential range from −10 to −40 V, and reached the value of about 250 micron/hour at 60 °C. Additionally, the etch-rate of n-Si was found to be markedly enhanced by illumination.
Microfabricated Silicon Carbide Microengine Structures
Authors: Lohner Kevin A. , Chen Kuo-Shen , Ayon Arturo A. , Spearing S. Mark 
Published: April 2011

AbstractA research and development program is underway to develop technology for a MEMS-based microgas turbine engine. The thermodynamic requirements of power-generating turbomachinery drive the design towards high rotational speeds and high temperatures. To achieve the specified performance requires materials with high specific strength and creep resistance at elevated temperatures. The thermal and mechanical properties of silicon carbide make it an attractive candidate for such an application. Silicon carbide as well as silicon-silicon carbide hybrid structures are being designed and fabricated utilizing chemical vapor deposition of relatively thick silicon carbide layers (10–100 μm) over time multiplexed deep etched silicon molds. The silicon can be selectively dissolved away to yield high aspect ratio silicon carbide structures with features that are hundreds of microns tall.Research has been performed to characterize the capabilities of this process. Specimens obtained to date show very good conformality and step coverage with a fine (≈0.1 μm dia.) columnar microstructure. Surface roughness (Rq) of the films is on the order of 100 nm, becoming rougher with thicker deposition. Residual stress limits the achievable thickness, as the strain energy contained within the compressive film increases its susceptibility to cracking. Room temperature biaxial mechanical testing of CVD silicon carbide exhibits a reference strength of 724 MPa with a Weibull modulus, m =16.0.
Investigation of Temperature and Composition Dependence of Relaxor Ferroelectric (1-x)PZN :xPT Using Micro-Raman Spectroscopy
Authors: Gupta S. , Katiyar R.S. , Bhalla A. S. 
Published: April 2011

AbstractMicro-Raman spectra of relaxor ferroelectric (RFE) in the (1-x)Pb(Zn1/3Nb2/3)O3 :xTiO3 solid solution series have been measured as a function of temperature (70-580K) and composition (x = 0.02, 0.085, and 0.11). Micro-Raman spectra have been recorded in frequency range of 30-1000cm-1 and have been analyzed for all the Raman modes observed in terms of integrated intensity, phonon width and phonon frequency position. No soft mode like behavior is observed in the measured frequency range. We do observe two multiple phase transitions at 67°C (340K) and 147°C (420K) for the composition ≤ 0.91PZN:09PT, but both the transitions are slightly diffused in nature.
Lithium-Iodine Intercalation in The Ferroelectric Layered Compound Bi4Ti3O12-x
Authors: Kijima T. , Kimura S. , Kawahara Y. , Ohe K. , Yada M. , Machida M. 
Published: April 2011

AbstractThe reaction of Bi4Ti3O12-x with lithium iodide under an atmosphere of iodine at 400°C was found to afford a novel intercalation compound Lil3Bi4Ti3O11. The brownish red bismuth titanate is monoclinic with the lattice parameters of a=5.7417(2), b=5.4016(2), c=36.787(1) Å and ß=88.93(1) deg. The pathway to the new intercalation compound is proposed on the basis of X-ray, XPS, SEM and compositional observations.
An Tiferro Magnetic-Ferromagnetic Cu-O-Cu Coupljng Change in Copper Oxides: Se1-xTexCuO3 Perovskites
Authors: Subramanian M. A. , Ramirez A. P. 
Published: April 2011

AbstractSe1-xTeCuO3 (O≤x<1) phases crystallizing in perovskite structure with divalent copper at the octahedral sites have been characterized by x-ray diffraction, magnetization measurements and specific heat. The perovskites are unusual for possessing an extremely small A-site cation (Se4+, Te4+) with Cu-O-Cu bond angles in the range 120-130°. A continuous evolution in both structural and bulk properties is observed between the ferromagnetic (FM) ground state for x = 0 and an antiferromagnetic (AF) state for x = 1. The correlation of structural and magnetic properties allows the first determination of the Cu-O-Cu bond angle where the superexchange interaction sign changes, providing a quantitative realization of the Anderson-Goodenough-Kanemori rules for copper-oxide compounds.
Vapour Phase Growth of Layered MoO3: A New Kinetic Approach for Volatile Metal Oxides
Authors: Zeng H.C. 
Published: April 2011

AbstractA simple yet versatile growth kinetic method (and device) has been developed in conjunction with present vapour phase preparation of layered MoO3 (orthorhombic). Using purified air at atmospheric pressure a sufficient amount of oxygen is warranted to ensure stoichiometry of grown metal oxide. The empirical vapour condensation rate of MoO3 is RE = 1.20×10-3ΔP2.07 over 642 to 660°C, where ΔP is the partial pressure difference of MoO3 between the source and condensed crystals. Based on observed crystal morphology and XRD result, a more precise MoO3 condensation kinetic model has been developed to explain the layer-by-layer growth of the layered structure. The driving force of the condensation growth is investigated with respect to the experimental set-up. On the basis of this work, it is suggested that the new kinetic approach is suitable for other volatile metal oxides or inorganic crystalline materials when an appropriate preparative atmosphere is selected.
Structural Studies and Order-Disorder Phenomenon in a Series of New Quaternary Tellurates of the Type A2+M4+Te6+O6
Authors: Woodward P.M. , Sleight A.W. , Duw L.-S. , Grey C.P. 
Published: April 2011

AbstractFive new compounds in the AxMTeO6 family were prepared and structurally characterized: Li2GeTeO6, Na2TiTeO6, Na2SnTeO6, and two forms of Na2GeTeO6. All compounds are layered structures based on various stacking arrangements of MTeO62- layers. Structural characterizations were carried out using a variety of tools, including Rietveld refinements of x-ray and neutron powder diffraction data, solid state MAS NMR and Raman spectroscopy. With the exception of Na2TiTeO6, the MTeO62-layers show a high degree of M4+/Te6+ order, but various degrees of disorder are present in the stacking of these layers. Disorder in the layer stacking favors the ilmenite structure, where both M4+ and Te6+ centered octahedra share faces with the AO6 octahedra. Coherent layer stacking favors an ordered variation of the α-TlSbO3 structure, where the AO6 octahedra preferentially share faces with either the MO6 or the TeO6 octahedra.
Influence of The Preparation Conditions on the Structure of Hydrotalcite Layered Double Hydroxides
Authors: Lukashin A.V. , Kalinin S.V. , Nikiforov M.P , Zhirov A.I , Kheifets L.I. , Privalov V.I , Vertegel A.A. 
Published: April 2011

AbstractInfluence of the precipitation conditions on the structure of Mg – Al layered double hydroxides (LDH) was investigated. XRD measurements demonstrate that species with hydrotalcite structure forms at high pH of reaction mixture (pH = 9 - 11), while at lower pH values (pH = 7 - 8) species with meixnerite structure arise. At the same time 27Al NMR studies of samples obtained at pH > 10 reveal the presence of tetrahedrally coordinated aluminum. XRD, NMR and IR data suggest that partial substitution of CO32- for Al(OH)4- in the interlayer space with subsequent formation of oxoaluminate bridges takes place at high pH. The optimal conditions for the preparation of intercalation-active materials were proposed.
In-Situ Neutron Diffraction Studies of Mixed Conducting Sr-Fe-Co-O Materials
Authors: Mitchell B.J. , Richardson J.W. , Ma B. , Hodges J.P. 
Published: April 2011

AbstractSrFeCo0.5Oy has been identified as a potential dense ceramic membrane material used for gas separation at elevated temperatures. Neutrons play an important role in the study of such materials, particularly due to the favorable scattering lengths of Fe, Co and O. In-situ neutron diffraction experiments allow these materials to be studied under a wide range of temperatures and oxygen partial pressures. Results indicate very complex behavior of individual phases during synthesis and under operational membrane conditions.
Preparation and Magnetoresistance of Lanthanum Manganites and Silver Chalcogenide Thin Films
Authors: Dahmen Klaus-H. , Chuprakov Ilya S. , Gillman Ed S. , Li M. Ming 
Published: April 2011

AbstractThe effect of texture and orientation on the resistance (0T and 6T) and magnetoresistance (MR) of Lal-xCaxMnO3 (LCMO) and Ag2Te thin films on various substrates has been investigated. Similar features were found in the MR dependence of thin films of these compounds despite the fact that they belong to different types of MR materials. Epitaxial or strongly oriented films exhibit a peaked MR behavior while for polycrystalline films this curve does not have sharp features. Sign reversal effect of MR was found also in thin films of Ag2Te. MR changes from positive at transverse field-,current orientation to negative at parallel orientation.
Nitrogen/Oxygen Substitution within PO4 Tetrahedra: A Right Answer to the Poor Chemical Durability of Phosphate Glasses
Authors: Le Sauze A. , Montagne L. , Palavit G. , Marchand R. 
Published: April 2011

AbstractBy using both alumina addition and nitrogen/oxygen substitution within PO4 tetrahedra, it is possible to prepare durable phosphate glasses without affecting their specific properties such as low melting temperatures and high thermal expansion coefficients. In particular, “LiKMgAlPON” nitrogen-rich glass compositions have a chemical durability on the same order as soda lime window glass, associated with a glass processing temperature as low as 800°C.
Synthesis of Aluminum Nitride Whiskers Via a Vapor-Liquid-Solid Process
Authors: Dai Ying , Nan Ce-Wen 
Published: April 2011

AbstractAluminum nitride whiskers were synthesized by nitridation of commercial aluminum powder at 1623K in a nitrogen atmosphere. The starting materials consisted of aluminum and carbon black. The carbon acted as a barrier between aluminum powders during nitridation and was removed by heating in air at 923K. The whiskers were about 0.5-1μm in diameter and 10-20μm in length. The droplets at the whisker tips showed that the whiskers grew via a vapor-liquid-solid mechanism. The morphologies of the whiskers were studied by means of SEM and TEM. The formation of the whiskers depended on the processing conditions.
New Quaternary Selenoantimonates AHgSbSe3 (A = Rb, Cs): Synthesis, Structures and Optical Properties
Authors: Chen Zhen , Wang Ru-Ji , Li Jing 
Published: April 2011

AbstractSolvothermal reactions in ethylenediamine have resulted in two quaternary mercury containing selenoantimonates: RbHgSbSe3 (I) and CsHgSbSe3 (II). Compound I crystallizes in monoclinic system, space group P2l/c (no. 14) with a = 7.758(2)Å, b = 11.234(2)Å, c = 8.849(2) Å, β = 106.60(3)°, V = 739.1(3)Å3, Z = 4. Compound II crystallizes in orthorhombic system, space group Cmcm (no. 63) with a = 4.444(1)Å, b = 15.514(6)Å, c = 11.261(7) Å, V = 776.4(6) Å3, Z = 4. Both compounds are layered materials and their crystal structures are closely related. Both contain layers of 2[HgSbSe3-] separated by alkali-metal cations A+ (Rb, Cs). Diffuse reflectance experiments show that both compounds are semiconductors with estimated band gaps of 1.7 eV for I and 1.6 eV for II, respectively.
Rationalization of Electrical Properties of The NiS2-xSex System
Authors: Honig J.M. 
Published: April 2011

AbstractThe electrical and optical properties of the NiS2-xSex system are interpreted in terms of a band structure diagram that places a Mott-Hubbard, correlation-split Ni 3deg and the S 3pσ* band in the vicinity of the Fermi level. A variety of seemingly problematic experimental findings are resolved by adoption of this hypothesis.
Synthesis of (Si2Ge)Cx and Related Ge1-xCx Phases in The Si-Ge-C System
Authors: Nesting David , McMurran Jeff , Kouvetakis John 
Published: April 2011

AbstractThe synthesis and characterization of binary and ternary semiconductor alloys and ordered phases based on C, Si and Ge are described. Thin films of these materials were synthesized using molecular precursors such as (SiH3)4C and (GeH3)4C in which the Si4C and Ge4C tetrahedra are incorporated as building blocks during deposition. Materials systems prepared include a new ordered structure (Si2Ge)1-xCx (x=5%), and Ge1-xCx hybrids of Ge and C-diamond. The (Si2Ge)Cx phase has a P 3ml structure formed by ordering of the [111] lattice planes in a Ge-Si-Si sequence. The Ge-C materials display unusual morphologies ranging from coherent heterostructures to carbide nanorods and quantum dots which are formed by CVD reactions utilizing a new family of (GeH3)4-xCHx (x=0-2) precursors. The morphology and microstructure in the samples is dependent upon the molecular design of the precursor and the carbon concentration.