bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Antimony on the Thermoelectric Properties of the Cubic Pb9.6SbyTe10−xSexMaterials
Authors: Poudeu Pierre Ferdinand Poudeu , D'Angelo Jonathan , Downey Adam , Pcionek Robert , Sootsman Joseph , Zhou Zhenhua , Palchik Oleg , Hogan Timothy P. , Uher Ctirad , Kanatzidis Mercouri G.
Published: April 2011

The thermoelectric properties of Pb9.6SbyTe10−xSexwere investigated in the intermediate temperature range of 300 – 700 K. The effect of the variation of Sb content (y) on the electronic properties of the materials is remarkable. Samples with compositions Pb9.6Sb0.2Te10−xSex(y = 0.2) show the best combination of low thermal conductivity with moderate electrical conductivity and thermopower. For Pb9.6Sb0.2Te8Se2(x = 2) a maximum figure of merit of ZT ∼ 1.1 was obtained around 700 K. This value is nearly 1.4 times higher than that of PbTe at 700 K. This enhancement of the figure of merit of Pb9.6Sb0.2Te8Se2derives from its extremely low thermal conductivity (∼0.7 at W/m.K at 700 K). High resolution transmission electron microscopy of Pb9.6Sb0.2Te10−xSexsamples shows broadly distributed Sb-rich nanocrystals, which may be the key feature responsible for the suppression of the thermal conductivity.
Fabrication of Grain-Aligned Bulks and Thick Films of Misfit Layered Cobalt Oxides by a Magneto-Scientific Process
Authors: Horii Shigeru , Okamoto Taichi , Kumagai Toshiaki , Uchikoshi Tetsuo , Suzuki Tohru S. , Sakka Yoshio , Shimoyama Jun-ichi , Kishio Kohji
Published: April 2011

We report the preparation of grain-aligned [Ca2CoO3−δ]0.62CoO2 (Ca349) thick films and the conversion of the easy axis of magnetization from the a-axis to the c-axis. The thick films were fabricated by a simultaneous usage of electrophoretic deposition and magnetic alignment methods (MEPD) at high deposition rate with the order of 10 mm/min. Moreover, a multi-layered thick film of Al2O3/Ca349/Al2O3/Ca0.9La0.1MnO3/Al2O3 was also fabricated by the MEPD method by the optimization of condition of each suspension. The conversion of the easy axis was performed crystallochemically for a [Bi2Sr2O4]0.55CoO2 (BiSr222) compound with the easy axis parallel to the a-axis in order to fabricate c-axis grain-oriented bulks by the magnetic alignment method. The substitution of Ca for Sr in the [(Bi0.5Pb0.5)2Sr2O4] block layer induced the change of the easy axis into the c-axis direction, and the magnetic anisotropy was increased by the partial substitution of rare earth elements of Pr, Nd, Tb and Dy for Ca. Using a compound of [(Bi0.5Pb0.5)2(Ca0.8Pr0.2)2O4]0.55CoO2, we have successfully prepared the c-axis grain-aligned bulk by the magneto-scientific method. Our present results indicate that the magneto-scientific method is one of the useful and realistic processes for production of thermoelectric modules.
Thermal Conductivity and Thermoelectric Properties of Novel Rare Earth Boron-Rich Cluster Compounds; Discovery of first undoped n-type B12 icosahedral compound
Authors: Mori Takao
Published: April 2011

Novel rare earth boron icosahedral compounds are investigated as potential high temperature thermoelectric materials. REB50-type compounds and a homologous series of RE-B-C(N) compounds were synthesized and the thermal conductivity and thermoelectric properties measured. Seebeck coefficients in excess of 200 μV/K are observed at temperatures above 1000 K for the REB50-type compounds. Strikingly, n-type behavior was observed for REB22C2N and REB17CN. Up to now, non-doped B12 icosahedral compounds like boron carbide have all been p-type. The discovery of an n-type compound is extremely important in terms of the potential development of this class of compounds as viable thermoelectric materials. Low thermal conductivities of κ < 0.03 W/cm/K at room temperature was observed for these rare earth boron cluster compounds. In comparison among the homologous series in which there are rare earth and B6 octahedra layers separated by an increasing number of B12 icosahedra layers, we observe that the thermal conductivity actually increases as the number of boron cluster layers increases. We find that the rare earth B12 icosahedral cluster compounds in which RE atoms occupy voids among the clusters generally appear to have lower thermal conductivity than boron cluster compounds which do not contain RE atoms.
Selective laser melting of high aspect ratio 3D nickel – titanium structures for MEMS applications
Authors: Chalker Paul , Clare Adam , Davies Sean , Sutcliffe Christopher J. , Tsopanos Sozon
Published: April 2011

Selective laser melting has been used to build high aspect ratio, three-dimensional NiTi components for the first time. The influence of laser dwell time and raster pitch on the density of NiTi shape memory alloy parts and their resolvable feature sizes are reported. The properties of shape memory springs produced by this method are reported and the application of selective laser melted NiTi components in microelectromechanical devices is discussed.
Low-temperature Preparation of Crystallized Zirconia Films by ECR Plasma MOCVD
Authors: Masumoto Hiroshi , Goto Takashi
Published: April 2011

It is known that zirconia has excellent thermal and chemical stability, and oxide ion conduction. Therefore, YSZ is expected to be used as oxide ion conducting materials, optical mirror materials, catalytic materials and heat-resistant materials. Zirconia films have been fabricated by PVD (ex. sputtering and laser-ablation), chemical vapor deposition (CVD) and sol-gel methods. CVD is capable to prepare high quality zirconia films with excellent conformal coverage; however, deposition temperature of conventional CVD was usually high than PVD. On the other hand, an electron cyclotron resonance (ECR) plasma is high-activity plasma and high quality crystalline films can be obtained at low temperature by using ECR plasma. In the present study, zirconia thin films were prepared at low temperatures on quartz, polycarbonate and polyimide substrates by ECR plasma MOCVD.

Zr-hexafluoroacetylacetonato solution was used as a precursor. The source, which was placed in a glass bubbler, was carried into a reactor by Ar gas. A microwave (2.45 GHz, 500 W) was introduced into the ion chamber through a rectangular wave guide. A magnetic field (875 Gauss) was applied to the ion chamber to satisfy the ECR condition. A mirror-type magnetic field (450 Gauss at the substrate stage) was applied in order to raise a plasma density, which results in an increase of the deposition rates of films. Substrate temperature (Ts) was from 30 to 700 C by water-cooling holder and infrared lamp heater. Microwave power was changed from 0 to 900 W. The deposition time was from 30 to 120 minutes.

Cubic, monoclinic and tetragonal zirconia films were obtained over Ts=400 C, and cubic and monoclinic zirconia films were obtained below Ts= C. Cubic and monoclinic zirconia films were also obtained at no heating. The deposition rate increased from 10 to 20 nm/min with increasing Ts from no heating to 600 C. Crystallized zirconia films were obtained on polycarbonate and polyimide substrates at no heating. The ECR plasma was significantly effective to prepare crystallized zirconia films at low temperatures.
High aspect ratio etching of GaSb/AlGaAsSb for photonic crystals
Authors: Nilsen Tron Arne , Martinez Anthony , Bugge Renato , Moscho Aaron , Lester Luke F , Fimland Bjørn-Ove
Published: April 2011

Photonic crystal structures defined by interferometric lithography were etched into GaSb and AlGaAsSb with 90% Al content using Inductively Coupled Plasma (ICP) Reactive Ion Etching (RIE) with BCl3 and BCl3/Ar gas mixture. Effects of DC bias, hole diameter, etch time and gas composition, on the etch rate of GaSb were investigated. Hardened photoresist (PR) was used as an etch mask for the experiments.
Structural Defects in InSb Quantum Wells Grown on GaAs (001) Substrates via Al0.09In0.91Sb/GaSb-AlSb Strained Layer Superlattice/AlSb/GaSb Buffer Layers
Authors: Mishima Tetsuya D. , Edirisooriya Madhavie , Santos Michael B.
Published: April 2011

Structural defects in InSb quantum well (QW) samples have been investigated by transmission electron microscopy (TEM). Using molecular beam epitaxy, an InSb QW with remotely-doped Al0.09In0.91Sb barriers was grown on a GaAs (001) substrate with buffer layers consisting of, in order from the substrate: 1 μm of GaSb, 1 μm of AlSb, 50 nm of GaSb-AlSb strained layer superlattice (SLS), and 3 μm of Al0.09In0.91Sb. Cross-sectional TEM analysis indicates that high densities of threading dislocations (TDs) are created at the two highly lattice-mismatched interfaces, the Al0.09In0.91Sb/GaSb-AlSb SLS and the GaSb/GaAs interfaces. Pairs of stereo images taken from plan-view TEM (PV-TEM) specimens show that TDs propagate through the InSb QW layer. The densities of TDs and micro-twin (MT) defects measured by PV-TEM are 9×108/cm2 and 4×103/cm, respectively. These values are worse than those in an InSb QW layer grown with a different buffer layer by a factor of ∼4. The different buffer layer contains an InSb interlayer that effectively filters out both TDs and MTs. Adopting an interlayer structure and reducing the GaSb and AlSb layer thickness may make it possible to fabricate a lower-defect-density yet thinner InSb QW sample with the type of buffer layer examined in this study.
Epitaxial growth and characterization of BP on Si(100) substrate for use in c-GaN study
Authors: Takeuchi Tomohiko , Nishimura Suzuka , Sakuma Tomoyuki , Matumoto Satoru , Terashima Kazutaka
Published: April 2011

Boronmonophosphide(BP) is one of the suitable materials for a buffer layer between the c-GaN(100) and Si(100) substrates. The growth of BP layer was carried out by MOCVD on Si(100) substrate of 2 inch in diameter. The growth rate was over 2 μm/h without any troubles such as the bowing or cracking. In addition, the thickness of BP epitaxial layer was uniform over a wide area. A careful analysis of x-ray diffraction suggested that the growth of BP epitaxial layer inherited the crystal orientation from Si(100) substrate. Cross-sectional TEM images showed some defects like dislocations near the interface between BP layer and Si substrate. The Hall effect measurements indicated that the conduction type of BP films grown on the both n-Si and p-Si substrates was n-type without impurity doping, and that the mobility and carrier concentrations were typically 357cm2/Vs and 1.5×1020cm−3(on n-Si) and 63cm2/Vs and 1.9×1019cm−3(on p-Si), respectively. In addition, c-GaN was grown on the substrate of BP/Si(100) by RF-MBE.
Stabilization of mixed valencies in Cu, Zn-based oxides
Authors: Nestour Anne Le , Gaudon Manuel , Tréguer-Delapierre Mona , Andriessen Ronn , Demourgues Alain
Published: April 2011

Cu and Zn-based oxides have been developed for the last decades because of their remarkable electronic properties and their relevant UV-Visible-NIR absorption properties. Cu in oxides can adopt various oxidation states (+I, +II, +III) stabilized in various environments (h, Td, D4h, C4v, D2h, Oh). Divalent copper cations can occupy Td or Oh sites in zinc aluminate spinel network. Solid state routes lead to homogeneous phases with Zn1−xCuxAl2O4 compositions. Depending on the inversion rate in the spinel matrix, various absorption bands have been identified in the UV-Visible-CNIR spectrum. The synthesis of the zinc-aluminate spinel solid solution Zn1−xCuxAl2O4 by an esterification route led to monocrystalline nanosized oxides. Two intense absorption bands at 300 and 500 nm can be attributed to charge transfer phenomena between oxygen and Cu2+ cations in tetrahedral and octahedral coordinations. Two other less intense absorption bands centred at 800 nm and 1500 nm are also appearing when the copper rate in the spinel increases but their relative intensity are not in good agreement with those observed in the case of the solid-state synthesis. In the case of the esterification route, the absorption band at 800 nm is much more intense than in the case of the solid-state synthesis. It can only be explained either by a deviation to the centrosymmetric character of octahedral sites or by the occurence of a non negligible amount of monovalent copper cations which give electronic transitions in this energy range. A magnetic study correlated to EPR measurements confirms the occurence of a mixed valence state for copper cations in the solid solution Zn1−xCuxAl2O4. EPR spectra at T=4K show for the small concentration of Cu2+ (x<0.10) a strong anisotropic signal due to the presence of Cu2+ ions in a distorted octahedral symmetry (gx=2.07, gy= 2.15 gz=2.23). Moreover the hyperfine structure, identified on EPR spectra tend to disappear as the compounds are annealed under air because the content of paramagnetic centers Cu2+ (3d9) as well as their interactions become significant. Furthermore, the color changes drastically with the Cu+ (3d10) content. Finally the structural features and UV-Visible-NIR absorption properties of copper-zinc aluminates will be discussed and compared to Cu-doped ZnO.
Characterization of a Dominant Electron Trap in GaNAs Using Deep-Level Transient Spectroscopy
Authors: Johnston Steven W. , Kurtz Sarah R. , Crandall Richard S.
Published: April 2011

Dilute-nitrogen GaNAs epitaxial layers grown by metal-organic chemical vapor deposition were characterized by deep-level transient spectroscopy (DLTS). For all samples, the dominant DLTS signal corresponds to an electron trap having an activation energy of about 0.25 to 0.35 eV. The minority-carrier trap density in the p-type material is quantified based on computer simulation of the devices. The simulations show that only about 2% of the traps in the depleted layer are filled during the transient. The fraction of the traps that are filled depends strongly on the depth of the trap, but only weakly on the doping of the layers and on the conduction-band offset. The simulations provide a pathway to obtain semi-quantitative data for analysis of minority-carrier traps by DLTS.
Towards a Novel Broadband Spectrally Dynamic Solid State Light Source
Authors: Nicol David , Gupta Shalini , Li Nola , Asghar Ali , Graugnard Elton , Summers Christopher , Ferguson Ian
Published: April 2011

The developments of two major components of a three terminal dual wavelength LED for excitation of multiple phosphors are described. Such a configuration will be novel Broadband Spectrally Dynamic Light Emitting Diode (BSDLED). First, work towards a functional tunnel junction in the GaN system is discussed. The developments of p+ and n+ GaN layers are specifically discussed in relation to their use in a buried current spreading contact layer. Second, the analysis of several phosphors and their application in a spectrally dynamic source is explored. The response to multiple wavelengths of the phosphors is analyzed to create a light source that can be tuned in “real time” to a wide range of correlated color temperatures.
Cu Induced Optical Transitions in MOCVD Grown Cu Doped GaN
Authors: Senawiratne Jayantha , Strassburg Martin , Payne Adam , Asghar Ali , Fenwick William , Li Nola , Ferguson Ian , Dietz Nikolaus
Published: April 2011

Optical and structural properties of in situ Cu doped GaN thin films grown on sapphire substrates were optically investigated by means of Raman, photoluminescence (PL), and absorption spectroscopy. Different Cu concentrations in the films were analyzed by secondary ion mass spectroscopy (SIMS) and found to vary from 2×1016cm-3to 5×1017cm-3. Raman studies confirmed high crystalline quality of GaN:Cu with no major structural damages due to Cu incorporation. PL investigation revealed that the origin of the emission around 2.4 eV is most likely due to Cu incorporation. The electrical conductivity of the samples was analyzed by Hall measurements and the found semi-insulating behavior was assigned to the compensation of intrinsic donors by the deep Cu acceptor states.
Preparation of Recycled Polycarbonate/Acrylonitrile-Butadiene-Styrene Composites
Authors: Jung Woo-Hyuk , Tortorella Nathan , Beatty Charles L. , McCarthy Stephen P.
Published: April 2011

The front cover of Motorola cellular phone housings were ground to the same size as original particles prior to use by a knife mill. The mixtures contained 15.2 wt% metals, 1.9 wt% foams, 1.4 wt% rubbers and 81.4 wt% thermoplastics where the major component was a polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blend. The separation of the thermoplastic scraps was performed using the sink-float process in water and salt solution. The impact modification of all housing containing six thermoplastic parts was carried out by the addition of a polyolefin elastomer called as the functionalized polyethylene (PE). Unprinted glass fiber reinforced epoxy circuit boards were size reduced and pulverized using the knife mill and hammer mill. The ground epoxy circuit boards were then classified with a set of testing sieves using Gyro sifter, and their mean diameters were calculated by means of particle size distribution analysis. Izod impact strengths at two temperatures, tensile tests, scanning electron microscopy (SEM) on the fracture surfaces, and dynamic mechanical spectroscopy were performed to characterize the alloys and mixtures compounded by a batch mixer and a twin screw extruder.
The Ultrastructure of Brachiopod Shells - A Mechanically Optimized Material with Hierarchical Architecture
Authors: Griesshaber Erika , Kelm Klemens , Sehrbrock Angelika , Job Reinhart , Schmahl Wolfgang W. , Mader Werner
Published: April 2011

Brachiopod shells consist of low-magnesium calcite and belong to one of the most intriguing species for studies of marine paleoenvironments, variations in oceanographic conditions and ocean chemistry [6, 7, 11 – 13]. We have investigated the ultrastructure together with nano- and microhardness properties of modern brachiopod shells with transmission electron microscopy (TEM), scanning electron microscopy (SEM), nanoindentation and Vickers microhardness analyses. Brachiopod shells are structured into several layers, a thin, outer, hard, protective primary layer composed of randomly oriented nanocrystalline calcite, which is followed inward towards the soft tissue of the animal by a much softer shell segment (secondary layer) built of long calcite fibres, stacked parallely into blocks. The hardness distribution pattern within the shells is non-uniform and varies on scales as small as a few tens of microns. Our results show that the hardness of this biomaterial is controlled by two predominant features: (1.) The morphological orientation of the calcite fibres (not by the crystallographic orientation of the fibres), and (2.) the amount and distribution pattern of organic material between and within the calcite crystals.
Assembly Design Concepts and Methods of Tailoring of CNT Orientation and Dispertion for Damping/Dynamic Properties of Nanoparticle-Reinforced Multifunctional Materials
Authors: Kireitseu Maksim , Tomlinson G.R. , Williams R.A.
Published: April 2011

In this paper, the concepts of nanotechnology-based fan blade have been introduced and CNT-reinforced hollow micro-balloon-based syntactic foams/composites and damping coatings have been applied so as to develop the next generation aerospace components. The focus in this paper is directed toward the development of the next generation of vibration damping systems, providing a road map to manufacturing technology and design solutions.
Complexes of conjugated polymer and carbon nanotubes: does blending with nanotubes influence the ordering of semi-crystalline polymers?
Authors: Goh Roland , Waclawik Eric Rolfe , Motta Nunzio , Bell John Marcus
Published: April 2011

A detailed study of poly(alkylthiophene) self-assembly and organization on single-walled carbon nanotubes is presented. We show that ordered polymer domains are formed when a conjugated polymer is blended with small amounts of carbon nanotubes. By correlating the lowest energy feature in the absorption spectra of the polymer with ordering, we demonstrate that the degree of ordering in the polymer is enhanced when it is blended with carbon nanotubes. Furthermore, we elucidated the conformation of the polymer chain when it is absorbed onto the nanotube surface and imaged the high degree of ordering in the polymer/carbon nanotube complex by microscopy.
Static Microindentation and Displacement-Sensitive Indentation Tests on Undoped GaAs
Authors: Wang Shanling , Zhang Ming , Bradby Jodie , Pirouz Pirouz
Published: April 2011

Static microindentation as well as dynamic displacement-sensitive indentation (DSI) tests have been performed between RT and 450°C on the (001) surface of undoped GaAs. In the static tests, the 4-fold symmetry reduces to 2-fold symmetry in some studied range of temperatures. The temperature dependence of the indentation diagonal and the crack length has been measured and, from disappearance of indentation cracks, the indentation brittle-to-ductile transition (IBDT) temperature TIBDT has been estimated. It is found that the temperature at which a transition in the energy density in DSI tests occurs nearly coincides with TIBDT as measured by static indentation tests; for undoped GaAs, both these temperatures are in the range of 200-225°C. This is about 100°C lower than the true brittle-to-ductile temperature TBDT, as measured by 4-point bending tests. The difference between TIBDT and TBDT is explained in terms of the superimposed hydrostatic stress component in the indentation experiments, and the crack asymmetry around the indentations is interpreted in terms of the different mobilities of α and β dislocations in GaAs.
Structural and optical properties of delafossite-type CuAlO2 thin films prepared by RF reactive sputtering
Authors: Yang B. , Lu Y. M. , Neumann C. , Polity A. , Wang C. Z. , Meyer B. K.
Published: April 2011

Delafossite-type CuAlO2 thin films have been deposited by radio frequency (RF) reactive sputtering on sapphire using a CuAlO2 ceramic target. A study of structural and optical properties was performed on films of varying deposition parameters such as substrate temperature and oxygen partial pressure and also post annealing. The crystalline phase in the films was identified to be the delafossite structure by x-ray diffraction. The optical properties, such as the wavelength dependence of the transmittance and the band gap, were determined. The average transmittance is 80% in the wavelength range of 400-1500 nm and the band gap is 3.81 eV.
Sol-gel synthesis of neodymium-barium manganites utilizing microwave irradiation
Authors: Chekanova Anastasiya Evgenievna , Vanetsev Alexander Sergeevitch , Eremina Elena Alimovna , Tretyakov Yurii Dmitrievitch
Published: April 2011

Combination of sol-gel technique and microwave treatment is effectively used for the synthesis of neodymium-barium manganite phase with improved microstructure and good magnetic properties.
In-situ TEM studies of magnetization reversal processes in magnetic nanostructures
Authors: Petford-Long Amanda K , Bromwich Thomas , Kohn Amit , Jackson Victoria , Kasama Takeshi , Dunin-Borkowski Rafal , Ross Caroline A
Published: April 2011

One of the most widely studied types of magnetic nanostructure is that used in devices based on the giant magnetoresistance (GMR) or tunnel magnetoresistance (TMR) phenomena. In order to understand the behaviour of these materials it is important to be able to follow their magnetisation reversal mechanism, and one of the techniques enabling micromagnetic studies at the sub-micron scale is transmission electron microscopy. Two techniques can be used: Lorentz transmission electron microscopy and off-axis electron holography, both of which allow the magnetic domain structure of a ferromagnetic material to be investigated dynamically in real-time with a resolution of a few nanometres. These techniques have been used in combination with in situ magnetizing experiments, to carry out qualitative and quantitative studies of magnetization reversal in a range of materials including spin-tunnel junctions, patterned thin film elements and magnetic antidot arrays. Quantitative analysis of the Lorentz TEM data has been carried out using the transport of intensity equation (TIE) approach.
In Situ TEM Investigation of Abnormal Grain Growth in Nanocrystalline Nickel
Authors: Follstaedt David M. , Hattar Khalid , Knapp James A. , Robertson Ian M.
Published: April 2011

In situ transmission electron microscopy was used to show that nanocrystalline nickel produced by pulsed-laser deposition undergoes abnormal grain growth at moderate temperatures (225-400°C). The growth rate was found to increase with thickness for the three film thicknesses examined, 50, 80 and 150 nm. The abnormal growth proceeded in an irregular manner: initiation sites and growth direction were unpredictable, and the grains exhibited no preferred orientation. Some abnormal grains show internal boundaries such as twins, while others exhibited lattice misalignments across the grain body. The grains contain many defects, including dislocations, stacking faults and surprisingly, stacking fault tetrahedra. The stacking fault tetrahedra are not a result of quenching nor of electron irradiation-induced lattice displacements; they instead are thought to form from vacancies trapped in the growing grain as it incorporates lower-density material at the high-angle grain boundaries in the nanocrystalline matrix.
Crystallographic Orientation Control of NanoCrystals Formed by FIB under a Bending Strain
Authors: Kubota Masaki , Halford Timothy Paul , Higo Yakichi
Published: April 2011

The application of nanocrystalline material for data-storage applications requires control over the in-plane and out –of-plane NanoCrystal (NC) orientation. In order to attempt to control the out-of-plane orientation of NCs introduced by the irradiation of Ni-P material with Ga+ ions, this processing has been completed upon material under tensile and compressive strains. The orientations of NCs nucleated have been compared to those introduced into the same material without the application of an external strain. Samples introduced under no external strain have previously been shown to be oriented with <111> parallel to the irradiated plane normal and <110> parallel to the irradiation direction. In this work, NCs nucleated under tensile strains in excess of ≈2 × 10-3 have been oriented with <112> parallel to the irradiated plane normal and <111> parallel to the applied stress direction, although <110> is still parallel to the irradiation direction. NCs formed under tensile strains lower than this critical value, as well as those formed under the compressive strain values tested, have been formed in the same orientation as those formed without the application of an external strain.
Reaction Mechanism for Deposition of Silicon Nitride by Hot-Wire CVD with Ultra High Deposition Rate(>7 nm/s)
Authors: Verlaan Vasco , Houweling Zomer Silvester , Werf Karine van der , Goldbach Hanno D , Schropp Ruud
Published: April 2011

The deposition process of silicon nitride (SiNx) by hot-wire chemical vapor deposition (HW CVD) is investigated by exploring the effects of process pressure and gas-flow ratio on the composition of the deposited SiNx films. Furthermore, experiments with D2 and deuterated silane were performed to gain further insight in the deposition reactions taking place. It appeared that the N/Si ratio in the layers determines the structural properties of the deposited films and since the volume concentration of Si-atoms in the deposited films is constant with N/Si ratio, the structure of the films are largely determined by the quantity of incorporated nitrogen. Because the decomposition rate of the ammonia source gas is much smaller than that of silane, the properties of the SiNx layers are largely determined by the ability to decompose the ammonia and to incorporate nitrogen into the growing material. It appeared that the process pressure greatly enhances the efficiency of the ammonia decomposition, presumably caused by the higher partial pressure of atomic hydrogen. With this knowledge we increased the deposition rate to a very high value of 7 nm/s for dense transparent SiNx films, much faster than conventional deposition techniques for SiNx can offer. Despite this high deposition rate good control over the composition is achieved by varying the flow ratio of the source gasses. Depositions performed with deuterated silane as a source gas reveal that almost all hydrogen in N-rich films originates from ammonia, probably caused by SiNx matrix formation by cross linking reactions
Dual-Chamber Plasma Co-Deposition of Nanoparticles in Amorphous Silicon Thin Films
Authors: Anderson C. , Blackwell C. , Deneen J. , Carter C. B. , Kakalios James , Kortshagen U.
Published: April 2011

The production of hydrogenated amorphous silicon films containing silicon nanocrystal-line inclusions (a/nc-Si:H) is demonstrated using a new deposition process. Crystalline Si nanoparticles around 5 nm in diameter are generated in a flow-through plasma reactor, and are introduced into a downstream capacitively-coupled plasma enhanced chemical vapor deposition reactor where the particles are “co-deposited” with the amorphous phase of the film. Transmis-sion electron microscopy confirms the presence of crystalline inclusions in these films, as well as providing confirmation that the crystalline particles are indeed produced in the flow-through re-actor and not in the capacitive plasma. Electrical measurements indicate an improvement in the dark conductivity of the intrinsic a/nc-Si:H films as the particle concentration is increased, sug-gesting that the particles have a doping effect on the films charge transport properties.
Orientation-Dependent Dewetting of Patterned Thin Si Film on SiO2
Authors: Dornel Erwan , Barbé J-C. , Eymery J. , Crécy F. de
Published: April 2011

The agglomeration of a Silicon On Insulator (001) film during a thermal annealing at 900°C and 950°C under hydrogenated atmosphere has been characterized by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). At this temperature, the Si faceting along {110}, {111} and {113} planes is interpreted by a surface energy anisotropy. The anisotropy of the diffusion coefficient is also revealed by the formation of Si line along the <510>, <110> and <100> directions. A mechanism of the pearling instability of the <510> lines is proposed.
Photocarrier Radiometric Lifetime Measurements of Intrinsic Amorphous-Crystalline Silicon Heterostructure
Authors: Leong Keith R , Mandelis Andreas , Kherani Nazir P , Zukotynski Stefan
Published: April 2011

Intrinsic hydrogenated amorphous silicon films were deposited by the DC saddle field system on crystalline silicon wafers. The substrate temperature of the amorphous film, crystalline silicon surface cleaning schemes, and the native oxide etchant were varied. The transport parameters of the amorphous-crystalline silicon heterostructures were evaluated by Photocarrier Radiometric (PCR) lifetime measurements. PCR bulk lifetime estimates were obtained using the quinhydrone in methanol solution to passivate the crystalline silicon surface. We present the effectiveness of the PCR system in evaluating different surface passivation schemes.
Combination of Metal Nano-Imprint and Excimer Laser Annealing for Location Control of Si Thin-Film Grain
Authors: Nakagawa Gou , Asano Tanemasa
Published: April 2011

A novel method of locating Si thin-film grains by combining metal nano-imprint and excimer laser annealing (ELA) is demonstrated. Metal nano-imprint at the a-Si film surface is used for the purpose of creating Si crystal nuclei which act as the seed for the subsequent crystallization by using ELA. The annealing to form nuclei at imprinted sites was carried out at temperatures below 450oC. ELA using XeCl laser of the sample with capping SiOx film resulted in the formation of over 2.0 μm-sized Si crystal grains at controlled position. Electron back-scattering pattern (EBSP) analysis showed that about 75% of the boundaries inside the location-controlled grains were the coincidence site lattice boundaries.
Correlation Between Annealing Temperature and Crystallinity of Si Films Prepared by Thermal Plasma Jet Crystallization Technique
Authors: Kaku Hirotaka , Higashi Seiichiro , Okada Tatsuya , Murakami Hideki , Miyazaki Seiichi
Published: April 2011

Transient reflectivity of amorphous Si (a-Si) films during thermal plasma jet (TPJ) irradiation has been measured to characterize the phase transformation in millisecond time domain. The a-Si films first transform to crystalline by solid phase crystallization (SPC) followed by melting of the film, and then solidifies to the final crystalline state. By increasing the SPC temperature from about 1100 K to 1300 K, the duration of phase transformation decreases from about 1 ms to 100 μs. The crystallinity of the SPC films is improved not only by annealing the films at a high temperature but also annealing them with longer duration.
Bias Stress Stability of Asymmetric Source-Drain a-Si:H Thin Film Transistors
Authors: Shin Kwang-Sub , Lee Jae-Hoon , Lee Won-kyu , Park Sang-Geun , Han Min-Koo
Published: April 2011

The threshold voltage (VT) degradation of asymmetric source-drain a-Si:H TFTs due to the electrical stress has been investigated. In the absence of a drain bias (VG=15V, VD=0V), the threshold voltage (VT) shifts of asymmetric TFTs were similar to that of symmetric TFT. However, in the presence of drain bias (VG=15V, VD=20V), the VT shifts of asymmetric TFTs were less than symmetric TFT. The VT shifts of ‘L’ and ‘J’ shaped TFT were 0.29V, 0.24V respectively, while the VT shift of ‘I’ shaped TFT was 0.42V.

The less VT degradation of the asymmetric source-drain a-Si:H TFT compared with the symmetric TFT may be explained by the defect creation model. Since the actual drain width of asymmetric TFT is longer than symmetric TFT at the same W/L ratio, the charge depletion due to the drain bias is larger than that of the asymmetric TFT. Due to the less carrier concentration in the channel, the asymmetric a-Si:H TFT shows the less VT degradation compared with the symmetric TFT.
Nanocrystalline Silicon Films Deposited by RF PECVD for Bottom-gate Thin-film Transistors
Authors: Esmaeili Rad Mohammad Reza , Lee Czang-Ho , Sazonov Andrei , Nathan Arokia
Published: April 2011

Thin-film transistors (TFTs) in active-matrix organic light emitting diode (AMOLED) displays are required to supply high and stable driving current to OLEDs. Top-gate TFTs with nanocrystalline silicon (nc-Si) active layer have shown promise to render high mobility and stable driving current. However, to be compatible with current production facilities, bottom-gate TFTs are demanded. Currently, bottom-gate nc-Si TFTs show insufficient field effect mobility and exhibit driving current instability due to presence of amorphous incubation layer at the interface with gate dielectric. Our research is motivated by the need to eliminate the incubation layer. In order to do so, we studied nc-Si deposition process to find the RF PECVD deposition regimes which lead to minimum incubation layer.

We have deposited a set of undoped nc-Si films by 13.56 MHz PECVD at 250°C by varying RF power, reactor pressure, silane and hydrogen flow rates. Raman spectroscopy, constant-photocurrent method (CPM) and optical absorption have been used to measure film crystallinity, defect density and optical bandgap, respectively. Carrier transport in the films has been studied using dark conductivity, photoconductivity and conductivity activation energy measurements.

Our results reveal that silane and hydrogen flow rates are the most contributing factors to film characteristics. The results also indicate that the reactor pressure does not have a significant effect on the film crystallinity. However, CPM data confirm that to obtain lower defect density, medium or high deposition pressures are preferred. We obtained films with dark conductivity and Raman crystallinity in the order of 10-6-10-7S/cm and 60-80 %, respectively. Furthermore, we have deposited nc-Si films as thin as 20nm with 60% crystallinity, which is crucial for bottom-gate TFTs. Finally, four different sets of bottom-gate TFTs have been fabricated by changing gate dielectric compositions and changing [SiH4]/([SiH4] + [H2]) gas flow ratio. The device performance, relationship to the film structure and deposition process, and future improvements will be discussed in details.
Channel Cracking Technique For Toughness Measurement Of Sioch Low-K Films
Authors: Brillet-Rouxel Helene , Dupeux Michel , Braccini Muriel , Orain Stéphane
Published: April 2011

The technique of channel cracking is used to study the crack growth in SiOCH low-k films. Various film thicknesses are produced using consecutive PECVD deposits on silicon substrates in up to the critical thickness for which spontaneous cracks appear. After determining mechanical properties and residual stresses of these films, samples are cleaved, and subjected to four-point bending tests. During the loading in ambient environment, cracks propagate from defects due to cleavage. Propagation of these cracks is observed in situ in order to correlate crack growth velocities to film thickness and total stress in the film. These results allow plotting crack growth rate versus stress intensity factor for crack velocity varying from 10-9 to 10-4 m/s for a stress intensity factor about 0.1 MPa√m. Moreover, in this range of velocities a model is proposed for this material to determine the film stress required to produce channel cracking, for a given film thickness.
Aqueous Based Single Wafer Cleaning Process Development and Integration into 65nm Process Flow using Metal Hard Mask
Authors: Lin Miao-Chun , Wang Mei-Qi , Weng Cheng-Ming , Chou Chopin , Liao JH , Tang Jianshe , Weng Willey , Lu Wei , Chen Han-Wen , Lee John TC
Published: April 2011

As the industry develops processes for the 65 and 45 nm technology nodes, post etch/ash cleaning faces new challenges with far more stringent requirements on surface cleanliness and materials loss. The introduction and integration of new materials, such as metal hard mask, creates additional requirements for wafer cleaning due to the occurrence of new defect modes related to metal hard mask. These include organometallic residue and metal fluorite compounds precipitating with time. We have developed a novel aqueous solution (AQ) based single wafer cleaning process to address these new defect modes. Physical characterization results and process integration electrical data and reliability data (TEM cross section review of the vias) are presented in this paper.

The main conclusions can be summarized as follows: (1) In the dual damascene Cu/low-k process flow with hard mask, there are three typical residues after etch/ash: generic polymer residue, organometallic residue strongly bonded to metal maks, and time-dependent metal fluoride residue. (2) Generic polymer residue is very well characterized [1,2] and is usually easy to remove with solvent or aqueous solution [2,3]. (3)We developed an oxidizing chemistry based process to undercut the hard mask for the organometallic residue removal, which proved highly effective. (4)The time-dependent metal fluoride reside makes queue time control after etch/ash very critical (<1 hour). We developed a process with a fluorine based aqueous chemistry to address the metal fluoride residue, which proved highly effective. With this new process, queue time control is not required. (5) The post etch/ash cleaning for the Cu/low-k structure with metal hard mask typically employs the solvent/dry plasma ash multi-step procedure [4]. The new process developed in this research reduced the multi-step process to one wet clean step with two different aqueous chemistries in sequence. (6) The integration electrical data shows that the new single step aqueous cleaning process performance is comparable to, or even better than that from the solvent/dry plasma ash multi cleaning process. (7) Blanket Cu loss with the new process is about 23A/min, however TEM analysis of the vias after full integration shows Cu loss, we are working to improve the integration related Cu loss.
Epitaxial GaN Layer Growth Using Nitrogen Enriched TiN Buffer Layers
Authors: Ito Kazuhiro , Uchida Yu , Lee Sang-jin , Tsukimoto Susumu , Ikemoto Yuhei , Hirata Koji , Shibata Naoki , Murakami Masanori
Published: April 2011

About 20 years ago, the discovery of an AlN buffer layer lead to the breakthrough in epitaxial growth of GaN layers with mirror-like surface, using a metal organic chemical vapor deposition (MOCVD) technique on sapphire substrates. Since then, extensive efforts have been continued to develop a conductive buffer layer/substrate for MOCVD-grown GaN layers to improve light emission of GaN light-emitting diodes. In the present study, we produced MOCVD-grown, continuous, flat epitaxial GaN layers on nitrogen enriched TiN buffer layers with the upper limit of the nitrogen content of TiN deposited at room temperature (RT) on sapphire substrates. It was concluded that the nitrogen enrichment would reduce significantly the TiN/GaN interfacial energy. The RT deposition of the TiN buffer layers suppresses their grain growth during the nitrogen enrichment and the grain size refining must increase nucleation site of GaN. In addition, threading dislocation density in the GaN layers grown on TiN was much lower than that in the GaN layers grown on AlN.
Investigation of NBTI Recovery During Measurement
Authors: Entner Robert , Grasser Tibor , Enichlmair Hubert , Minixhofer Rainer
Published: April 2011

In this work we present a rigorous investigation of the negative bias temperature instability (NBTI) recovery process during measurement intervals in comparison to the numerical solution of an extended reaction-diffusion (RD) model. In contrast to previous work, the RD model has been implemented in a multi-dimensional device simulator and is solved self-consistently together with the semiconductor device equations. This allows us to directly use many commonly approximated quantities such as the oxide electric field and the interface hole concentration in a self-consistent manner. In addition, the influence of the trapped charges can be more accurately considered by using a distributed Shockley-Read-Hall interface trap-charge model which has been coupled to the RD model. Thus, due to the self-consistent solution procedure, also the feedback of these charged interface-states on the Poisson equation is considered which influences the observed threshold voltage shift. Experimental data confirm the model which has been calibrated to a wide range of temperatures using a single set of parameters.
Enhanced Phonon-Energy Coupling: Dramatic Reduction of Leakage Current of Silicon Oxide
Authors: Chen Zhi , Guo Jun , Samantaray Chandan B
Published: April 2011

We study in detail a newly discovered effect, phonon-energy-coupling enhancement (PECE) effect, produced by rapid thermal processing (RTP). It includes two aspects: (1) Strengthening Si-D bonds and Si-O bonds and (2) Change of energy band structure and effective mass due to thermal shock. It is shown that not only Si-D bonds but also Si-O bonds have been strengthened dramatically, leading to enhancement of robustness of the oxide structure and the oxide/Si interface. For thick oxides (>3 nm), the gate leakage current has been reduced by two orders of magnitude and the breakdown voltage has been improved by ~30% due to phonon-energy coupling. For ultrathin oxides (2.2 nm), the direct tunneling current has been reduced by five-orders of magnitude, equivalent to that of HfO2, probably due to the increased effective mass and barrier height.
Atomistic Analysis of Crystal Plasticity in Copper Nanowire
Authors: McEntire R. S. , Shen Y.-L.
Published: April 2011

Plastic deformation in a model copper wire under tensile loading is modeled using three dimensional atomistic simulations. The primary objective is to gain fundamental insight into the nano-scale deformation features. An initial defect is utilized in the model to trigger plastic deformation in a controlled manner. A parametric study is performed by varying the atomic interaction range used in the model. When the interaction distance is small, dislocation slip is observed to be the dominant deformation mechanism. A slight increase in the interaction range results in phase transition from the FCC structure to a BCC structure. Re-orientation of the BCC lattice also occurs at later stages of the deformation. The phase transition mechanism is further enhanced if the nanowire is attached to a flat substrate.
Investigation of the Influence of Grain Size, Texture and Orientation on the Mechanical behavior of Freestanding Polycrystalline Gold Films
Authors: Wang Liwei , Prorok Bart
Published: April 2011

Polycrystalline gold thin films with thickness of 250nm, 500nm and 1000nm were deposited on Si substrates by means of both E-Beam evaporation and sputtering techniques. High-resolution SEM, including electron-backscattered diffraction (EBSD), was employed to provide a crystallographic analysis including grain orientation maps of the studied films. The Membrane Deflection Experiment (MDE) was employed to perform the microscale tensile testing. The Young's modulus of gold films deposited by E-Beam evaporation was measured consistently in the range of 55-62 GPa while it increased to 68-72 GPa for sputtered films. Plastic yielding of the e-beam and sputtered films was contrasted due to varying microstructure of each deposition technique, which appears to assert a measure of control on the deformation mechanics.
Directly Measuring the Adhesive and Elastic Properties of Bacteria using a Surface Force Apparatus: Effect of Desiccation
Authors: Heo Cheol Ho , Maier Raina M , Curry Joan E
Published: April 2011

Bacterial adhesion is the first step in biofilm formation which impacts numerous environmental, industrial and medical processes. Examples of undesirable consequences of biofilm formation include metal rust, sewage sludge and bacteria-related diseases. Desirable consequences are biofiltration and bioremediation. Bacteria are resilient and can survive in harsh environments. A severe stress is desiccation since dehydration can damage DNA and change the properties of proteins. Some bacteria protect against dehydration by accumulating sugars such as sucrose and trehalose while others undergo a transformation from an active to a dormant state. Evaporative deposition of bacteria on a surface shows that some bacteria aggregate to form two dimensional patterns which may be important for nutrient sharing and survival in dry conditions. Since bacteria are increasingly being employed as components in biosensors and biofilm reactors, it is important to understand the material properties of bacteria in dry conditions for these applications. For a decade, Atomic Force Microscopy (AFM) has been the primary tool used to study the adhesion and elastic properties of individual bacteria. In this work we show it is possible to use a Surface Forces Apparatus (SFA) to measure elastic and adhesive properties of small collections of surface bound bacteria. The measurements are conducted with incomplete, patterned bacterial films and we have developed a protocol to image the contact area with AFM after the experiment. Using the SFA, we measured the force profile between aPseudomonas aeruginosaPAO1 film and a bare mica surface.P. aeruginosaPAO1 is a ubiquitous gram-negative soil bacterium and is also an opportunistic pathogen. We repeated the measurement in the same contact position for six days to determine the effect of desiccation on the film material properties.
Processing of Dense Nanocrystalline Zirconia Thin Films by Sol-Gel
Authors: Peters Christoph , Bockmeyer Matthias , Krüger Reinhard , Weber André , Ivers-Tiffée Ellen
Published: April 2011

Via metal organic deposition (MOD) sapphire substrates were multiple dip-coated with a molecular dispersive 8 mol% Y2O3 doped ZrO2 (8YSZ) sol to prepare dense, crack-free thin films. The thin films were consecutively exposed to a tempering program with several rapid thermal annealing (RTA) steps and a final dwell temperature between 500 °C and 1400 °C for 24 h. Grain growth, phase, stoichiometry and macroscopic density of the thin films were analyzed by XRD and SEM. Grain sizes ranged between a few nanometers in diameter at 500 °C and several hundreds of nanometers at 1400 °C.