bluuebunny/crossref_metadata_2025 huggingface dataset:
Power Generation from Piezoelectric Lead Zirconate Titanate Fiber Composites
Authors: Mohammadi Farhad , Khan Ajmal , Cass Richard B.
Published: April 2011

Power generation from lead zirconate titanate (PZT) piezoelectric fibers in the form of 1–3 composites under application of an external force was investigated. Green fibers consisting of PZT powder dispersed in a cellulose binder were made by the Viscous Suspension Spinning Process (VSSP). The composites were made by firing sheets of parallel green PZT fibers at 1270 °C, and then laminating the sintered sheets in epoxy. Composites of several PZT fiber diameters (15, 45, 120, and 250 μm), with the fiber volume fraction fixed at ∼0.4, were investigated. Transducers comprised of electrode and poled plates of the composites, in which the plate thickness direction was in the fiber axis direction, were made. Power generation experiments were conducted by dropping a 33 g stainless steel ball onto the electroded face of each transducer from a height of 10 cm and recording the output voltage on an oscilloscope. A peak voltage of 350 V corresponding to 120 mW of peak power was obtained. The output voltage and power was the highest for the transducers made with the smallest diameter fibers (15μm) and increased with increasing of transducer thickness. The average piezoelectric coefficient, d33, of the transducers was about 300 pC/N and decreased with decreasing transducer thickness. In this paper, the power generation capability and dielectric properties of the laminated 1–3 fiber composites are discussed.
Current-voltage Characteristics of Single CdSe Colloidal Nanodots Measured by Conductive-tip Atomic Force Microscopy
Authors: Tanaka Ichiro , Kawasaki Eri , Ohtsuki O. , Uno K. , Hara M. , Asami H. , Murase T. , Kamiya I.
Published: April 2011

We have investigated current-voltage characteristics of individual CdSe colloidal nanodots by conductive-tip atomic force microscopy (AFM). The colloidal nanodots were spun-coat and scattered on a self-assembled monolayer of thiophene molecules formed on Au (111) surfaces for single dot measurements. A thin SiO2 layer was deposited on the sample surface in order to prevent the dots being moved by the tip during measurement. We imaged the topography of isolated single dots by AFM operated in contact mode, and measured current-voltage characteristics with the conductive tip positioned on single dots; large conductivity changes which suggest resonant tunneling through a quantized energy level in the dot was observed even at room temperature.
Optical Properties of Semimagnetic Quantum Dots
Authors: Mackowski S. , Nguyen T. A. , Jackson H. E. , Smith L. M. , Kossut J. , Karczewski G. , Heiss W.
Published: April 2011

Measurements of optical properties of epitaxially grown CdMnTe quantum dots are presented. Magnetic ions are incorporated into the structure by passivating the substrate surface with Mn prior the quantum dot deposition. As expected, the intensity of intra-Mn transition increases with the time of manganese passivation. The formation of magnetic quantum dots is evidenced by presence of single emission lines in the micro-photoluminescence spectrum. The width of single dot emission lines is much broader than observed for non-magnetic quantum dots. The broadening is caused by thermal fluctuations of magnetization in quantum dots. Resonant spectroscopy results indicate that the exciton-optical phonon scattering is the main energy relaxation mechanism in these structures. The measurements suggest that post-growth thermal processing offers the possibility of tuning the magnetic properties of these structures.
Quantitative Charge Imaging of Silicon Nanocrystals by Atomic Force Microscopy
Authors: Feng Tao , Atwater Harry A.
Published: April 2011

Quantitative understanding of charging and discharging of Si nanocrystals in SiO2 films on Si substrate is essential to their application in floating gate nonvolatile memory devices. Charge imaging by atomic force microscopy (AFM) or electrostatic force microscopy (EFM) can provide qualitative information on such system, while a further step is needed. We have developed a generalized method of images, which can solve Poisson equation for multiple dielectric layers, to simulate the charge imaging of Si nanocrystals by non-contact mode AFM under different sample geometries. Simulated images can be compared with experimental images thoroughly to estimate the total amount and distributions of trapped charges, which is also useful in the study of time evolution of charges or dissipation problems.
Equilibrium Analysis of Lattice-Mismatched Nanowire Heterostructures
Authors: Ertekin E. , Greaney P.A. , Sands T. D. , Chrzan D. C.
Published: April 2011

The quality of lattice-mismatched semiconductor heterojunctions is often limited by the presence of misfit dislocations. Nanowire geometries offer the promise of creating highly mismatched, yet dislocation free heterojunctions. A simple model, based upon the critical thickness model of Matthews and Blakeslee for misfit dislocation formation in planar heterostructures, illustrates that there exists a critical nanowire radius for which a coherent heterostructured nanowire system is unstable with respect to the formation of misfit dislocations. The model indicates that within the nanowire geometry, it should be possible to create perfect heterojunctions with large lattice-mismatch.
New Nanocrystalline si Floating Gate Structue for Nonvolatile Memory Application
Authors: Wu L.C. , Shi J.J. , Chen K.J. , Xu J. , Li W. , Ma Z.Y. , Dai M. , Wu D. , Li A.D. , Huang X.F.
Published: April 2011

We report a direct experiment evidence for holes and electrons charging in a new nanocrystalline Si (nc-Si) floating gate structure (SiO2/nc-Si/SiO2/c-Si) fabricated in-situ by plasma oxidation and layer by layer deposition technique in a plasma enhanced chemical vapor deposition (PECVD) system. In this nc-Si floating gate structures, the thickness of tunneling SiO2 layer is about 2 nm and the mean grain size of nc-Si is 6 nm obtained from Raman scattering and AFM measurements. The discrete quantum level and Coulomb charging energy for a single electron have been observed in large ensemble of nc-Si dots by frequency dependent capacitance spectroscopy, which demonstrates that the Coulomb blockade for electron in nc-Si dots is larger than size fluctuation effects on the quantum confinement for our nc-Si floating gate structure. Quantitatively, the experiment results of capacitance spectroscopy are in good agreement with the theoretical calculations. By contrasted with silicon single electron transistor memory made by using ultra fancy nanotechnology, nc-Si based memory can be fabricated with a minimum perturbation of conventional silicon technology and may be closest to industrial application.
Formation and Cathodoluminescence of Silicon Nanoclusters in Silica
Authors: Zamoryanskaya Maria V. , Sokolov Vladimir I.
Published: April 2011

The process of formation of silicon nanoclusters in a silicate matrix by the focused electron beam of high power and their cathodoluminescent properties were studied in this paper. The size of the silicon clusters and their concentration depend on the electron beam power and on the properties of the silicate matrix (density, porosity, composition). In this paper we studied the evolution of cathodoluminescent properties in bulk silicon oxide, porous silicon oxide glass, silicagel (n·SiO2·m·H2O) and opal. The result of the modification of silica is the appearance of the CL bands at 2.3eV in green region, and the bands at 1.4 and 1.1eV. The CL intensity of these bands increases during the interaction with electron beam. The volt-ampere characteristics of the modified areas of the silica are non-linear and depend on the time of the interaction and the power of the electron beam. We relate the appearance of these new CL bands with formation of oxygen-deficit defects and silicon clusters.
Characterization of nanographite and carbon nanotubes by polarization dependent optical spectroscopy
Authors: Grüneis Alexander , Saito Riichiro , Samsonidze Georgii G. , Pimenta Marcos A. , Jorio Ado , Souza Filho Antonio G. , Dresselhaus Gene , Dresselhaus Mildred S.
Published: April 2011

The optical absorption for ? electrons as a function of the electron wavevector k is investigated by first order perturbation theory in graphite and single wall carbon nanotubes (SWNTs). The matrix element connecting two states in the valence and conduction bands is found to be significantly anisotropic in k-space and polarization dependent. In the case of graphite, the absorption shows a node around the equi-energy contour, and in the case of SWNTs we obtain selection rules that allow only transitions between certain pairs of subbands. The strength of the optical absorption is not only diameter dependent but also chirality dependent. The implications of the optical absorption matrix element on the resonant conditions are discussed.
Quantitative V-L-S Growth Model and Experiments of Fe Catalyzed Si Nanowire Formation
Authors: Zhou Guangwen , Yang Judith C. , Xu Fengting , Barnard John A. , Zhang Z.
Published: April 2011

We report the formation of Si nanowires (SiNWs) by vapor-liquid-solid (V-L-S) mechanism where Si atoms are pumped from Si wafer. This happens when a material has the large difference of activity in its pure (Si) and alloy state (Si-Fe). We developed a kinetic model to quantitatively describe the growth of the nanowires. The model predicts that the length of the nanowires increases linearly with the growth time.
Field Emission Properties of BN/C and BN@C Hybrid Nanotubes
Authors: Meunier Vincent , Buongiorno Nardelli Marco , Shelton William , Roland Christopher , Bernholc Jerry , Zacharia Thomas
Published: April 2011

Our simulations predict that boron-nitride (BN) doping in carbon nanotubes can greatly improve the field emission properties of these systems. The intrinsic electric field associated with the polarity of the B-N bond enhances the emitted current density through a reduction of the work function at the tip. Using a combination of real-space and plane-wave ab initio methods, we show that this effect is present in both coaxial (BN@C) and linear (BN/C) nanotubular assemblies. While in the coaxial geometry the improvement amounts to a factor of five, the current density is predicted to increase by up to two orders of magnitude in BN/C superlattices.
Synthesis, Self-assembly and Magnetic Properties of FePtCu Nanoparticle Arrays
Authors: Sun Xiangcheng , Kang S. S. , Harrell J. W. , Nikles David E. , Dai Z. R. , Li J. , Wang Z. L.
Published: April 2011

FePtCu nanoparticles with varying composition were synthesized by chemical solution-phase reduction of platinum and copper reagents and thermal decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers. As prepared the particles had fcc structure with an average diameter of 3.5 nm and were superparamagnetic. The particles were well dispersed in hydrocarbon solvents and could be self-assembled into two or three dimensions particles arrays with a variety of close-packing arrangements. Heat-treatment of the self-assembled films at temperatures above 550°C transformed the particles from the fcc to the L10 phase, giving in-plane coercivities as high as 9000 Oe. X-ray diffraction revealed that the Cu remained in the annealed FePtCu films and the presence of an extra peak, indicated a second phase was present. Consistent with one or more phases, the magnetic hysteresis curves could be decomposed into a hard component (Hc > 5,000 Oe) and a soft component (Hc < 2,000 Oe). Unlike our earlier results for Ag in FePt, adding Cu to FePt did not lower the temperature required for phase transformation from the fcc to the fct L10 phase.
Molecular-Dynamics Study of the Mechanical Properties of Metallic Nanowires
Authors: Nakajima T. , Shintani K.
Published: April 2011

The method of molecular-dynamics is employed to simulate and investigate the deformation of metallic nanowires under tensile strain. The interactions between metallic atoms are calculated by using the embedded-atom method potential. A model nanowire is preliminarily equilibrated at a specified temperature. Then, the uniform uniaxial extension of the nanowire is performed. The thinning process of a metallic nanowire is observed in the sequential snapshots of its morphological change.
3-D Nanoengineering of Metal Oxides and Oxyhydroxides by Aqueous Chemical Growth
Authors: Vayssieres Lionel , Manthiram Arumugam
Published: April 2011

Advanced nanoparticulate thin films of transition metal oxides consisting of nanorods with different orientations onto various substrates have been successfully grown by aqueous chemical growth without template, surfactant, or applied electric/magnetic field. The synthesis involves the aqueous condensation of metal ions from solutions of metal salts or metal complexes. Such low-cost fabrication of nanoengineered 3-D arrays consisting of 1-D nanorods of iron oxide (hematite), zinc oxide (zincite), and manganese oxyhydroxide (manganite) with parallel and perpendicular orientations onto various substrates are presented.
Luminescence and EPR Study of Lithium-Diffused ZnO Crystals
Authors: Garces N. Y. , Wang Lijun , Chirila M. M. , Halliburton L. E. , Giles N. C.
Published: April 2011

Zinc oxide (ZnO) crystals grown by the seeded chemical vapor transport method have been studied using photoluminescence (PL), thermoluminescence (TL), and electron paramagnetic resonance (EPR) techniques. Lithium acceptors were diffused into the crystals during anneals in LiF powder at temperatures in the 750 to 850°C range. After a lithium diffusion, EPR was used to monitor neutral lithium acceptors and neutral shallow donors, as well as Ni3+, Fe3+, and Cu2+ impurities unintentionally present. Excitonic and deep-level PL emissions were also monitored before and after these diffusions. Two broad overlapping TL emission bands were observed at 117 and 145 K when a Li-diffused crystal was illuminated at 77 K with 325-nm light and then rapidly warmed to room temperature. The two TL bands have the same spectral dependence (the peak in wavelength is 540 nm when the intensity of the light reaches a maximum). These “glow” peaks occur when electrons are thermally released from Ni2+ and Fe2+ ions and recombine with holes at neutral lithium acceptors.
Pulsed Laser Deposition of Stable Cubic ZnO/MgO Multilayers
Authors: Bhattacharya P. , Das Rasmi R. , Katiyar Ram S.
Published: April 2011

Wide bandgap (∼6 eV) ZnO/MgO multilayer thin films have been fabricated using pulsed laser deposition technique from their respective targets on c-plane Al2O3 substrates. The thickness of single ZnO sublayer thickness was varied in the range of 0.75–2.5 nm with a fixed MgO sublayer thickness of 1 nm in order to achieve a total film thickness of ∼300 nm. The structural transition from hexagonal to cubic phase was observed with the decrease in the thickness of single ZnO layer from 2.5 to 0.75 nm that resulted in the increase in bandgap from 3.5 to 6.2 eV. Mg contents of the films were increased from 40 % to 60 % for hexagonal and cubic phases, respectively. The surface roughness and grain structure were not influenced much with the increase of Mg concentration. Resistivity of the films was increased six orders of magnitude with the increase in Mg incorporation. The post annealing at 750° C did not show any significant change in the crystal structure and the optical properties.
Optical Absorption of Large Band-Gap SbxBi1-xI3 Alloys
Authors: Persson C. , Ahuja R. , Souza de Almeida J. , Johansson B. , An C. Y. , Ferreira F.A. , Souza Dantas N. , Pepe I. , Ferreira da Silva A.
Published: April 2011

The optical properties of SbBiI3 alloys have been investigated experimentally by absorption measurements and theoretically by a full-potential augmented plane wave (FPLAPW) method within the generalized gradient approximation. The fundamental band-gap energy of these alloys changes from BiI3- to SbI3-like with increasing percentage of Sb content. The calculated band-gap energies as well as the optical absorption were found to be in a very good qualitatively agreement with the experimental results. We present calculated density-of-states as well as the dielectric functions for evaluation of future experiments.
Carrier recombination in InAs/GaAs Quantum Dot and GaInNAs/GaAs Quantum Well LEDs emitting near 1300 nm.
Authors: Bennett A J , Lofgren L , Stavrinou P N , Roberts C , Murray R , Parry G , Roberts J S
Published: April 2011

We have studied the emission from LEDs based on GaInNAs Quantum Wells (QWs) and InAs Quantum Dots (QDs) as a function of temperature and current. It is found that the carrier loss in GaInNAs QWs is dominated by non-radiative monomolecular and Auger processes resulting in an external quantum efficiency of only 0.08 % at 10 °C and 1000 A cm-2. In contrast, the InAs QDs have a higher external quantum efficiency, peaking at 0.8 % at 10 °C and 5 A cm-2, but this value rapidly decreases as the excited states of the QDs are filled and Auger-like processes become dominant. These results highlight the issues that must be addressed if these materials are to find commercial application: namely, the areal density of QDs must be increased and the material quality of the GaInNAs QWs must be improved.
Changes in Structural and Optical Properties of CdS Thin Films During the Process of Chemical Bath Deposition
Authors: Wei Li , Liang-huan Feng , Ya-ping Cai , Jing-quan Zhang , Jia-gui Zheng , Wei Cai , Li-li Wu , Bing Li , Ye Shao , Dao-lin Cai , Wen-jian Len
Published: April 2011

Chemical bath deposition (CBD) techniques for the growth of CdS polycrystalline thin films are now well developed. However, there usually appear different structures, grain sizes and energy gaps in CdS polycrystalline films by CBD, which implies that the influence of growth process on the structures and properties of CBD CdS thin films must be considered. In this paper, the optical, compositional and structural properties of CBD CdS thin films in the reaction process have been studied by XRD, AFM, XPS and optical transmission spectra measurements. The results can be explained using atomic mechanism and lattice transition in the CdS thin films.
Development of An On-Chip Semiconducting Readout For Subsurface Optical Data
Authors: Loghry William K. , Ianno N. J. , Dillon R. O.
Published: April 2011

A preliminary device was investigated as a first step in making an on-chip electrical readout based on the semiconductor CdS for a novel 3-D optical data storage method. The optical data is stored in glass as subsurface nanometer size defects called voxels. These voxels display secondary harmonic generation (SHG) to 800 nm input light. The device begins with an indium tin oxide film on a glass substrate coated with a film of Al2O3. In this preliminary device the Al2O3 was patterned via optical lithography with a periodic array of 10 micron holes that were filled with electrodeposited CdS. X-ray diffraction, and energy dispersive X-ray analysis were used to characterize the CdS. The device operation depends on the ability of the CdS with a bandgap of 2.4 eV to detect the 3.1 eV SHG light from the voxels while remaining unresponsive to 1.6 eV input light. The electrodeposited CdS was found to absorb 400 nm light at least a factor of 10 times greater than 800 nm light. Light to dark photocurrent ratios of 15 to 63 were observed from the CdS pillars using a 150 W xenon broadband light source. A light to dark ratio of about one was found when a long pass optical filter allowed only wavelengths above 750 nm. Thus the 10 micron CdS pillars have detected 400 nm light while rejecting the 800 nm input light.
Comparison of the Strain and Stress in Bonded and Epitaxial Gallium Arsenide on Silicon by Photoreflectance Spectroscopy Measurements
Authors: Gallis Spyros , Deligeorgis George , Georgakilas Alexandros , Alexe Marin
Published: April 2011

The presence of an internal strain arising from the GaAs/spin-on-glass (SOG)/Si bonding procedure was investigated. In addition, the magnitude of any residual stress at room temperature and the mechanisms that may impose a stress, leading to elastic or plastic deformation of the bonded GaAs films, were identified.

A comparative study of biaxial strain and stress, as a function of temperature in the range of 80- 300 K, in a bonded 2 μm-thick GaAs/SOG/Si sample and in an epitaxial 2 μm-thick GaAs/Si sample, grown by molecular beam epitaxy (MBE), will be presented. The type and magnitude of strain were determined by photoreflectance spectroscopy. In the case of GaAs/SOG/Si, the strain in the GaAs layer was found to be negligible, with compressive character, at room temperature and tensile in all other measured temperatures, whereas for the epitaxial GaAs/Si, the strain was taking significant tensile values in all temperatures. Furthermore, the strain for both samples was increasing with temperature reduction, as it is expected for a thermal strain induced by the different thermal expansion coefficients of GaAs and Si.

The comparative study indicated clearly that the bonded GaAs/SOG/Si films are essentially strain-free at room temperature. This is a very important result for the good reliability of laser diodes that can be processed from such bonded GaAs material, which also has a crystal quality similar to that of the available GaAs substrates.
Interdiffusion, Crystallinity and Exchange Bias in MnxPt1-x/Co Bilayers
Authors: Morales Erie H. , Wang Yikuan , Lederman D.
Published: April 2011

The structure of the antiferromagnet (AF) in the Ta/ MnxPt1-x/Co /Ta system must have the face-centered tetragonal CuAu structure in order to obtain a measurable exchange bias (HE). The formation of this structure has an onset temperature of approximately 240 °C. Increasing the annealing temperature increases the amount of CuAu ordering, which increases HE, and also increases the MnPt/Co interdiffusion, which decreases HE. These two competing processes result in an optimum annealing temperature that maximizes HE.
Crystal-field Effect on Magnetic Moment and Exchange-Coupling for Fe/W(100) and Fe/W(110)
Authors: Qian X. , Hübner W.
Published: April 2011

The Full-potential Linearized Augmented Plane-wave (FP-LAPW) method was employed to investigate the magnetic properties of 1 monolayer (ML) Fe on W(100) and W(110) substrates. Magnetic moments of the Fe overlayer are found to be very different with ∼2.0 μB for Fe on W(100) and ∼2.56 μB for Fe on W(110). The exchange coupling between Fe film and W substrate are also found to be orientation-dependent. The electronic coupling in Fe/W(100) thin film is found to be more long-range, compared to the one in Fe/W(110). These differences could be explained by the differences of local atomic bonding and crystal-field splitting in these two orientations.
Correlation between Magnetic Property and Cation Distribution in Z-type Hexagonal Barium-Ferrite (Ba3Co2-xFe24+xO41) by Neutron Diffraction
Authors: Takada Yukio , Tachibana Takeshi , Nakagawa Takashi , Yamamoto Takao A. , Shimada Takeshi , Kawano Shinji
Published: April 2011

Z-type hexagonal ferrite samples in which cobalt is partially substituted with iron, Ba3Co2-xFe24+xO41(x= 0, 0.2, 0.4, 0.6), were prepared by the ceramic process under a sintering oxygen partial pressure,PO2= 21.3 or 101.3 kPa, at 1573 K. The influence of the substitution ratio and oxygen partial pressure on the complex permeability was investigated by examining the cobalt distribution over various cation sites in the Z-type structure with the neutron powder diffraction analysis performed at 294 K (neutron wave length was 1.006Å). The neutron diffraction pattern was studied with the Rietveld method. A significant difference in the preferential occupation of cobalt on various kind of cation sites was observed between the samples obtained underPO2= 21.3 and 101.3 kPa. Almost all cobalt atoms are on the 12koctahedral site at the boundary between S- and R-blocks in the sample ofx= 0,PO2= 21.3 kPa. On the other hand, in the sample ofx= 0,PO2= 101.3 kPa, cobalt atoms are as well on other sites, the 12koctahedral site at the boundary between S- and T-blocks, the 4etetrahedral site in S-block, the 2aoctahedral site in T-block and the 2dfive fold (trigonal bypiramid) site in T-block.
Magnetoresistance and Hall Effect Characterisation on Magnetic Thin Films Multilayers
Authors: Neamtu Jenica , Volmer Marius
Published: April 2011

We have performed both Hall effect, and magnetoresistance measurements on thin films of Permalloy (Py 10 nm) and Py(tPy)/Cu(tCu)/Py(tPy) multilayers deposited on thermally oxidized Si substrates, where tPy=4 and 10 nm and tCu=4 and 8 nm. The measurements were made at room temperature in a setup that allows us to perform both Hall effect and magnetoresi stance measurements. The Hall effect measurements were performed varying the angle, Δθ, between the magnetic field direction and the normal to the film plane from 0 to 90 degrees. The measured voltages present hysteresis loops at low magnetic field even for Δθ=0°. From these measurements we can obtain some information regarding the magnetic properties of our samples.
Progress in Epitaxial Oxides on Semiconductors
Authors: Yu Z. , Liang Y. , Li H. , Curless J. , Overgaard C. , Droopad R. , Wei Y. , Hu X. , Craigo B. , Finder J. , Eisenbeiser K. , Talin A. , Smith S. , Voight S. , Wang J. , Marshall D. , Jordan D. , Edwards J. , Moore K.
Published: April 2011

In this paper, we review the recent progress in the area of epitaxial oxides on semiconductors at Motorola Labs. Critical issues such as surface preparation, initial nucleation and growth behaviors of SrTiO3 (STO) thin film epitaxy on Si(001) are addressed. Using a systematic approach, high-quality epitaxial STO films are successfully grown on semiconductor substrates such as Si, silicon-on-insulator (SOI) and Ge. Amorphous interfacial layer between the epitaxial STO and the semiconductor can be eliminated or tailored by controlling oxide growth process and parameters. STO-based metal-oxide-semiconductor (MOS) capacitors and transistors are fabricated and tested, in order to explore the potential of STO as high-k gate dielectrics for future generation CMOS transistor technology. In addition, high-quality STO epitaxial films are utilized as thin buffer layers for fabricating integrated oxide heterostructures on semiconductors. Various perovskite oxide films such as SrZrO3, LaAlO3 and Pb(Zr,Ti)O3 are deposited epitaxially on STO-buffered Si(001) for potential high-k gate dielectrics and surface-acoustic-wave (SAW) device applications.
The Influence of Defects on Compatibility and Yield of the HfO2-PolySilicon Gate Stack for CMOS Integration
Authors: Kaushik V. S. , DeGendt S. , Carter R. , Claes M. , Rohr E. , Pantisano L. , Kluth J. , Kerber A. , Cosnier V. , Cartier E. , Tsai W. , Young E. , Green M. , Chen J. , Jang S-A. , Lin S. , Delabie A. , Elshocht S. V. , Manabe Y. , Richard O. , Zhao C. , Bender H. , Caymax M. , Heyns M.
Published: April 2011

Hafnium-based dielectrics are under wide consideration for high-K gate dielectric applications. Since the gate electrode typically used in CMOS integration consists of polysilicon with n- or p-type dopants, compatibility of the HfO2layer with the polySi deposition and dopant activation steps is critical. Capacitors were fabricated with HfO2films deposited by ALD and MOCVD, and using polysilicon gate electrodes deposited by CVD processes. These devices showed leakage failures with yields that were observed to depend on the area, dielectric thickness and annealing conditions during the process. Investigation of the root cause of these leakage failures suggested that the leakage failures may be caused by a defect-related mechanism. The implication of this is that the leakage occurs at localized ‘defect’ sites rather than broadly through the HfO2layer. Emission microscopy analysis and physical characterization of the HfO2film were used to corroborate the proposed model. Defect density was observed to be strongly dependent on the processing of the dielectric film. In order to make Hf-based dielectric stacks compatible with polysilicon for conventional CMOS transistor integration with acceptable yield, further postdeposition treatment may be necessary to eliminate or cure the defects.
Recent Development of Al2O3-based Gas-sensing Materials
Authors: Yu P. , Xiao D. Q. , Pan Y. , Li P. , Yang Z. H. , Zhu J. G.
Published: April 2011

γ-Al2O3-based gas sensing materials were invented, and three kinds of gas sensors, i.e. hydrogen, methane, and alcohol gas sensors, made from these materials were fabricated in our group years ago. Recently, the ether, ethane and gasoline gas sensors have also been made respectively from the nano-powders of γ-Al2O3-based gas sensing materials with different additives. In this paper the sensitivities and selectivites of the three new kinds of the gas sensors are reported, and the effect of the particle size of the nano-powder of the material on the performance of the methane sensors is also studied.
Intermediate Annealing Behavior And Grain Growth Of Al-Cu-Fe Quasicrystalline Coatings
Authors: Daniels M. J. , King D. , Zabinski J. S. , Bilello J. C.
Published: April 2011

A powder composite AlCuFe target was used to produce 10 micron films of a quasicrystalline precursor phase by RF sputtering onto polycrystalline alumina substrates. X-ray studies have determined this precursor to be a nano-quasicrystalline phase, despite previous reports of an amorphous structure. Anneals for various times at temperatures between 450°C and 550°C showed the evolution and grain growth of the quasicrystalline approximant structure as a function of both variables. Synchrotron diffraction studies showed a bimodal grain size distribution of the quasicrystalline approximant structure for anneals at 450 °C for 1 hour, below a previously reported transition temperature of 475 °C. Composition analysis of annealed films by XPS depth profiling showed the surface composition to be nearly stoichiometric Al2O3 and extensive oxygen penetration to 160 nm. X-ray diffraction studies have been correlated with cross section microscopy to characterize the development of quasicrystalline films from their precursors. Anneals for longer times and at higher temperatures showed no evidence of a bimodal distribution or remaining nanoquasicrystalline phases.
A Simple Model for the Formation of Step-Free Surfaces
Authors: Chang Kee-Chul , Blakely Jack M.
Published: April 2011

Arrays of step-free regions on the surface of silicon have been created either by evaporating atoms from craters[1] or by depositing atoms on mesas[2]. In most cases the maximum extent of the step-free regions is limited by the occurrence of circular pits or islands in the crater or mesa structures. We model the process of step clearing and nucleation of these pits and islands by approximating the initial surface by an array of circular steps whose movement is mediated by adatoms. BCF (Burton-Cabrera-Frank) theory[3] is used to incorporate the effects of surface diffusion, evaporation and the deposition of atoms on the surface. We include the effects of step curvature and step interactions. If the step spacing is large enough, we find that the innermost step moves outwards to create a step-free region; otherwise it moves inward and leads to large scale smoothening of the surface. Pit or island nucleation in the center of the craters or mesas is also included in the model by using classical nucleation theory. We investigate the effect of deposition flux and temperature on the formation of step-free surfaces and compare the results to reported experiments on silicon and to some of our recent work on sapphire.
Large-Area Film Structure Consisted by Aggregation of Zinc Oxide Micro-Whiskers
Authors: Tokita Shuji , Ohshi Shigeo , Saitoh Hidetoshi
Published: April 2011

We developed a chemical-vapor deposition (CVD) apparatus with a 0.5×240 mm2 slit-type nozzle that scans at an area of 240×315 mm2 in the atmosphere. This apparatus forms uniform oxide crystals on substrates through the decomposition process of precursors emitted from the nozzle. In this study, ZnO whiskers were synthesized on a single-crystalline 8-inch wafer of (100)-oriented silicon using this apparatus. Morphological and crystallographic properties of the samples were evaluated using scanning electron microscopy and X-ray diffractometry.
Molecular-Dynamics Simulation of the Initial Period of Cluster Deposition
Authors: Shintani K. , Nakajima T. , Taniguchi Y.
Published: April 2011

The initial periods of deposition process of metal clusters in the soft-landing regime are investigated by the molecular-dynamics simulation. The embedded-atom method potential is adopted for calculation of the interaction between metallic atoms. The predictor-corrector method for second-order differential equations is employed for integration of the equations of motion. A simulation begins with equilibration of clusters and a substrate at a specified temperature. The lowest atomic layer in the substrate is fixed and the next few atomic layers are set to be velocity-scaling layers during the deposition process. The periodic boundary conditions are imposed in the horizontal directions. A single cluster with no velocity is deposited on the substrate. The simulations are performed at different temperatures of the clusters and substrate and for different sizes of clusters. How the morphological transition of the deposited nanostructures is affected by these parameters is discussed.
Stress evolution during deposition and during annealing of TixAly-alloy films
Authors: Lackner St. , Abermann R.
Published: April 2011

The main objective of this paper is a series of experiments designed to elucidate the origin of large fluctuations in the growth stress of aluminium rich TixAly-alloy films found in earlier experiments. The internal stress of the various alloy films was measured in situ under UHV-conditions during as well as after deposition, using a cantilever beam technique. In parallel experiments the microstructure of the different films was investigated by TEM.

The experiments were started assuming that the fluctuations in the stress vs. thickness curve of aluminium rich TixAly-alloy films indicate unstable films. In order to test this hypothesis, we have performed annealing experiments with alloy films of which the aluminium content was varied from 50% to 75%. The films were formed by evaporating the alloy components from two separate evaporation sources onto alumina substrate films at 27°C substrate temperature.

The growth stress of the Ti50Al50-alloy film exhibits a large tensile stress, which increases linearly with film thickness and a negligible stress change after deposition. Increasing the aluminium content lowers the tensile stress built up and the average stress in the Ti25Al75-alloy film is compressive but stress changes after deposition are still very small. This experimental evidence is interpreted to indicate that layer by layer growth is the representative growth mode for these films. The origin of the growth stress of these films is assumed to be the grain boundary relaxation mechanism proposed by R.W. Hoffman. The differences in the growth stress in films with varying aluminium content are assumed to originate from changes in the magnitude of the attractive forces in the grain boundaries, defects etc‥

Annealing these films gives rise to irreversible tensile stress changes. These stress changes in the Ti25Al75-alloy film are about four times that measured during annealing of the Ti50Al50-alloy film. A pronounced tensile stress feature in the temperature range between 230°C and 260°C is interpreted to be due to segregation of aluminium in the alloy film and to the alloy film surface. This aluminium segregation is negligible in alloy films with an aluminum content lower than 67%. With the experimental evidence presented in this paper we are able to show that aluminium segregation is the reason for the large fluctuations in the stress vs. thickness curves of aluminium rich alloy films when the two alloy components are evaporated simultaneously from two separate evaporation sources.
Surface Roughness Evolution in Amorphous Tantalum Oxide Films Deposited by Pulsed Reactive Sputtering
Authors: Jain Pushkar , Juneja Jasbir S. , Karabacak Tansel , Rymaszewski Eugene J. , Lu Toh –Ming
Published: April 2011

The growth front roughness of Ta2O5 amorphous films grown by pulsed plasma d.c. reactive sputtering has been investigated using atomic force microscopy. Film deposition during reactive sputter deposition is explained based on dynamic scaling hypothesis in which both time and space scaling are considered simultaneously. The interface width w increases as a power law with deposition time t, w ∼ tβ, with β = 0.45 ± 0.03. The lateral correlation length ξ grows as ξ ∼ t1/z, with 1/z = 0.61 ± 0.07. The roughness exponent extracted from the slope of height-height correlation analysis is α = 0.79 ± 0.04. The results are similar to that obtained by sputtering of elemental materials, and do not fit to any of the presently known growth models. Monte Carlo simulations were carried out based on a recently developed re-emission model, where incident flux distribution, shadowing, sticking coefficient, and surface diffusion mechanisms were accounted for in the deposition process. An important finding is that sticking coefficient must be less than unity to obtain the observed β value (∼0.45).
Segregation of Yttrium Ions as to the Surfaces of t-ZrO2
Authors: Redfern S.E. , Stanek C. R. , Grimes R.W. , Rawlings R.D.
Published: April 2011

Atomistic simulation has been used to predict the segregation of defect clusters containing two substitutional Y3+ ions and one charge compensating oxygen vacancy to the (100) and (101) surfaces of t-ZrO2. The most stable orientation of the defect cluster depends on its distance from the surface. Significantly, segregation energies vary greatly between surfaces. For example, the defect cluster is equally stable up to a depth of 9Å from the (100) surface but only to a depth of 4Å below the (101) surface. In both cases, segregation energies are negligible 12Å beneath the surface.
The Properties of a Na-Doped Twist Boundary in SrTiO3 from First Principles
Authors: Astala Roope K. , Bristowe Paul D.
Published: April 2011

The segregation of Nasr impurities to a Σ = 5 [001] twist boundary in SrTiO3 is studied using DFT-based plane-wave pseudopotential techniques. The formation energies of the impurities are calculated as a function of oxygen chemical potential and electron chemical potential. The results indicate a strong driving force for segregation to the boundary and that the Na impurities exhibit acceptor-like behaviour. The atomic displacements caused by the impurities are small both in the bulk and at the grain boundary. Based on the results a model is suggested in which Nasr segregation is driven by soft relaxation of the electronic structure.
Effect of Thin Y-O and Si-O Films on In-situ Formed CaO Coatings on V-4%Cr-4%Ti in Liquid 2.8 at.% Ca-Li
Authors: Park Jong-Hee , Sawada A. , Kestle B. , Rink D. , Natesan K. , Mattas R. F.
Published: April 2011

We are developing electrically insulated coatings for the liquid-metal/structural-material interface of the breeder blanket for magnetic fusion reactors. Our earlier experimental studies indicated that sintered Y2O3 is compatible with liquid Li. In continuing studies, we have deposited thin (0.2 and 0.8 μm) yttrium films on V-4Cr-4Ti structural material by physical vapor deposition (PVD). Annealing the thin Y-metallic PVD film on O-charged V-4Cr-4Ti at 750°C for 17 h formed an oxide film by the solid-state reaction between O and Y. Both energy dispersive spectroscopy (EDS) and X-ray diffraction indicated that the Y-metallic films converted to either YVO3 or Y8V2O17 after annealing. When these samples were exposed in 2.8 at.% Ca-Li at temperatures of 700°C for 99 h, a uniformly microstructured CaO layer was formed on the top of the Y-V oxides, but localized Y was not detected by cross-sectional EDS analysis. The addition of Si was found to minimize the V incorporation in the in-situ forming film.
Molecular Dynamics Computer Simulations of Calcium-Alumino-Silicate Intergranular Films between the basal and prism planes of α-Al2O3
Authors: Garofalini Stephen H. , Zhang Shenghong
Published: April 2011

Molecular dynamics computer simulations using a robust multibody potential were used to study the structure of the intergranular films (IGFs) formed between two different crystallographic orientations of α-Al2O3crystals. The simulations show a localized ordering of the IGF at the interface of both the basal and prism planes caused by preferential adsorption of specific ions from the IGF onto the crystal planes. However, the results of the adsorption have significantly different effects on crystal growth of the specific orientations. The preferential adsorption of Ca ions from the IGF onto the (0001) surface inhibit growth in the <0001> direction. However, Ca does not affect adsorption of O and Al from the IGF onto the (1120) surface and potential growth of this orientation in the <1120> direction. The results are consistent with experimental data regarding anisotropic grain growth in this system and provide an atomistic view of this behavior.
Interface Conduction between Conductive ReO3 Thin Film and NdBa2Cu3O6 Thin Film
Authors: Ohkubo Manabu , Fukai Kumiko , Matsuo Kohji , Iwata Nobuyuki , Yamamoto Hiroshi
Published: April 2011

The Re oxide films were deposited on quartz glasses by RF reactive sputtering from a Re metal target. The lowest resistivity was observed in the film in-situ annealed at 200?C in Ar atmosphere and showed the order of 10-4 Ωcm of which the value was still about 10 times as large as that of a single crystal ReO3. The temperature dependence of the resistivity revealed a metallic behavior. A superconductivity did not take place in the bilayered film of ReO3 / NdBa2Cu3O6. In the interface region the resistivity minimum probably caused by the Kondo effect was observed in the neighborhood of 120K.
Synthesis and Properties of High-Manganese Iron-Based Bulk Amorphous Metals as Non-Ferromagnetic Amorphous Steel Alloys
Authors: Joseph S. , Shiflet Gary J. , Ponnambalam V. , Keppens Veerle M. , Taylor R. , Petculescu G.
Published: April 2011

High-manganese ferrous-based alloys containing 10–20 at. % Mn have been investigated as prospective iron-based structural amorphous metals with magnetic transition temperatures far below the ambient temperature. Many of these alloys are found to have a high reduced glass transition temperature of 0.6–0.63 and large supercooled liquid region of 40–90 °C. Rod-shaped amorphous samples with diameters reaching 4 mm are obtained by employing simple injection casting. The search for good glass-forming alloys has been guided by an atomistic approach coupled with the realization of low-lying liquidus temperatures via proper alloying. The tensile yield strengths and Vickers hardness of the new amorphous metals far exceed those known in high-strength steel alloys, and the elastic moduli are comparable to those reported for super-austenitic steels. The present high-manganese amorphous Fe-alloys also show promise as very good corrosion-resistant materials.
Magnetostriction and Coercivity of Soft Magnetic Fe-(Al, Ga)-(P, C, B, Si) Bulk Glassy Alloys
Authors: Makino Akihiro , Bitoh Teruo , Inoue Akihisa
Published: April 2011

The relationship between coercivity (Hc) and magnetostriction (λs) of the glassy Fe-(Al, Ga)-(P, C, B, Si) alloys has been discussed. The glassy Fe-(Al, Ga)-(P, C, B, Si) alloys exhibit lower Hc and lower Is compared with the conventional Fe-based amorphous alloys with the same λs and Fe content, respectively. Theoretical analysis on the basis of domain-wall movement suggests that the low Hc results from the long-range homogeneous structure of the glassy alloys, which realizes a low density of pinning centers. The good combination of high glass-forming ability and good soft magnetic properties (especially low Hc) indicates the possibility of future development as new bulk glassy soft magnetic materials.
Crystallization Behavior of Mechanically Alloyed Zr-Cu-Al-Ni Glass Composites Containing Second-Phase ZrC Particles
Authors: Deledda S. , Eckert J. , Schultz L.
Published: April 2011

We report on mechanical alloying of elemental powders with nominal composition Zr55Cu30Al10Ni5 together with up to 30 vol.% of ZrC particles which results in the formation of a metallic glass matrix in which the carbide particles are homogeneously dispersed and, at the same time, reduced to nanometer size. The thermal stability is investigated by isochronal differential scanning calorimetry and is found to be strongly affected by increasing the ZrC volume fraction. Comparison with calorimetric data for single-phase mechanically alloyed Zr-Cu-Al-Ni-C glassy powders suggests that dissolved carbon, originating from non-negligible ZrC-dissolution processes during mechanical alloying, is responsible for the changes in the glass transition and the crystallization behavior. Isothermal calorimetric data are also presented and discussed in the framework of the Johnson-Mehl-Avrami model. The carbon atoms dissolved in the glassy phase are suggested to slow down the kinetics of overall crystallization. On the other hand, for large ZrC volume fractions nucleation of crystalline phases is promoted by the second-phase particles and changes in the Avrami exponent from n = 4 to n = 3 suggest that the nucleation rate approaches zero after the early stages of crystallization.
The Effect of Atomic-Scale Open-Volume on Flow and Fracture Processes in a Zr-Ti-Ni-Cu-Be Bulk Metallic Glass
Authors: Suh Daewoong , Dauskardt Reinhold H.
Published: April 2011

Effects of atomic-scale open-volume regions in metallic glass structure on the flow and fracture behavior of a Zr-Ti-Ni-Cu-Be bulk metallic glass were examined. Studies of relaxation time scales showed that atomic arrangement processes for viscous flow were significantly retarded with annealing. Plane strain fracture toughness was significantly decreased and fatigue crack crack-growth rates were dramatically increased, indicating degradation of resistance to crack extension as a result of annealing. Fracture morphology completely changed from vein patterns to cleavage-like features with little evidence of plasticity with annealing. The positron lifetime and Doppler broadening experiments revealed decreased open-volume regions as a result of annealing. The loss of stress relief ability by retarded crack tip viscous flow as a result of the anneal-out of open-volume regions is believed to contribute to observed annealing embrittlement.
Systematic Trends and Empirical Modeling of Lead Uptake by Cements and Cement Minerals
Authors: Ochs Michael , Talerico Caterina , Lothenbach Barbara , Giffaut Eric
Published: April 2011

Uptake of Pb was investigated for different hydrated fresh and leached Portland and high-alumina cements, different CSH phases including tobermorite, portlandite, as well as for several relevant cement Al-minerals. Except for highly degraded cement, CSH minerals are the most important phases for Pb uptake. A systematic analysis of our data and a comparison with recent literature data for CSH phases [1] shows that Pb uptake is characterized by three trends: 1) between pH 10–13, Pb uptake decreases with increasing pH, 2) Pb uptake increases with increasing Fe content in the clinker, and 3) Pb uptake is dependent on the Pb concentration in the solution. Following these findings, an empirical model was developed based on regression analyses of uptake vs. Pb concentration, pH, and Fe content in the clinker. The resulting relation can predict Kd values for a large range of fresh and leached cements, as well as for individual cement minerals under different experimental conditions. Model application to independent data on cement phases, whole cement, and mortar gave very good agreements.