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1Latest Papers from Table of Contents or Articles in PressG. Zhang ; C. Li ; Q. Li ; B. Li ; D. M. Larkin ; C. Lee ; J. F. Storz ; A. Antunes ; M. J. Greenwold ; R. W. Meredith ; A. Odeen ; J. Cui ; Q. Zhou ; L. Xu ; H. Pan ; Z. Wang ; L. Jin ; P. Zhang ; H. Hu ; W. Yang ; J. Hu ; J. Xiao ; Z. Yang ; Y. Liu ; Q. Xie ; H. Yu ; J. Lian ; P. Wen ; F. Zhang ; H. Li ; Y. Zeng ; Z. Xiong ; S. Liu ; L. Zhou ; Z. Huang ; N. An ; J. Wang ; Q. Zheng ; Y. Xiong ; G. Wang ; B. Wang ; Y. Fan ; R. R. da Fonseca ; A. Alfaro-Nunez ; M. Schubert ; L. Orlando ; T. Mourier ; J. T. Howard ; G. Ganapathy ; A. Pfenning ; O. Whitney ; M. V. Rivas ; E. Hara ; J. Smith ; M. Farre ; J. Narayan ; G. Slavov ; M. N. Romanov ; R. Borges ; J. P. Machado ; I. Khan ; M. S. Springer ; J. Gatesy ; F. G. Hoffmann ; J. C. Opazo ; O. Hastad ; R. H. Sawyer ; H. Kim ; K. W. Kim ; H. J. Kim ; S. Cho ; N. Li ; Y. Huang ; M. W. Bruford ; X. Zhan ; A. Dixon ; M. F. Bertelsen ; E. Derryberry ; W. Warren ; R. K. Wilson ; S. Li ; D. A. Ray ; R. E. Green ; S. J. O'Brien ; D. Griffin ; W. E. Johnson ; D. Haussler ; O. A. Ryder ; E. Willerslev ; G. R. Graves ; P. Alstrom ; J. Fjeldsa ; D. P. Mindell ; S. V. Edwards ; E. L. Braun ; C. Rahbek ; D. W. Burt ; P. Houde ; Y. Zhang ; H. Yang ; E. D. Jarvis ; M. T. Gilbert
American Association for the Advancement of Science (AAAS)
Published 2014Staff ViewPublication Date: 2014-12-17Publisher: American Association for the Advancement of Science (AAAS)Print ISSN: 0036-8075Electronic ISSN: 1095-9203Topics: BiologyChemistry and PharmacologyComputer ScienceMedicineNatural Sciences in GeneralPhysicsKeywords: Adaptation, Physiological ; Animals ; Biodiversity ; *Biological Evolution ; Birds/classification/*genetics/physiology ; Conserved Sequence ; Diet ; *Evolution, Molecular ; Female ; Flight, Animal ; Genes ; Genetic Variation ; *Genome ; Genomics ; Male ; Molecular Sequence Annotation ; Phylogeny ; Reproduction/genetics ; Selection, Genetic ; Sequence Analysis, DNA ; Synteny ; Vision, Ocular/genetics ; Vocalization, AnimalPublished by: -
2Latest Papers from Table of Contents or Articles in PressM. A. Groenen ; A. L. Archibald ; H. Uenishi ; C. K. Tuggle ; Y. Takeuchi ; M. F. Rothschild ; C. Rogel-Gaillard ; C. Park ; D. Milan ; H. J. Megens ; S. Li ; D. M. Larkin ; H. Kim ; L. A. Frantz ; M. Caccamo ; H. Ahn ; B. L. Aken ; A. Anselmo ; C. Anthon ; L. Auvil ; B. Badaoui ; C. W. Beattie ; C. Bendixen ; D. Berman ; F. Blecha ; J. Blomberg ; L. Bolund ; M. Bosse ; S. Botti ; Z. Bujie ; M. Bystrom ; B. Capitanu ; D. Carvalho-Silva ; P. Chardon ; C. Chen ; R. Cheng ; S. H. Choi ; W. Chow ; R. C. Clark ; C. Clee ; R. P. Crooijmans ; H. D. Dawson ; P. Dehais ; F. De Sapio ; B. Dibbits ; N. Drou ; Z. Q. Du ; K. Eversole ; J. Fadista ; S. Fairley ; T. Faraut ; G. J. Faulkner ; K. E. Fowler ; M. Fredholm ; E. Fritz ; J. G. Gilbert ; E. Giuffra ; J. Gorodkin ; D. K. Griffin ; J. L. Harrow ; A. Hayward ; K. Howe ; Z. L. Hu ; S. J. Humphray ; T. Hunt ; H. Hornshoj ; J. T. Jeon ; P. Jern ; M. Jones ; J. Jurka ; H. Kanamori ; R. Kapetanovic ; J. Kim ; J. H. Kim ; K. W. Kim ; T. H. Kim ; G. Larson ; K. Lee ; K. T. Lee ; R. Leggett ; H. A. Lewin ; Y. Li ; W. Liu ; J. E. Loveland ; Y. Lu ; J. K. Lunney ; J. Ma ; O. Madsen ; K. Mann ; L. Matthews ; S. McLaren ; T. Morozumi ; M. P. Murtaugh ; J. Narayan ; D. T. Nguyen ; P. Ni ; S. J. Oh ; S. Onteru ; F. Panitz ; E. W. Park ; H. S. Park ; G. Pascal ; Y. Paudel ; M. Perez-Enciso ; R. Ramirez-Gonzalez ; J. M. Reecy ; S. Rodriguez-Zas ; G. A. Rohrer ; L. Rund ; Y. Sang ; K. Schachtschneider ; J. G. Schraiber ; J. Schwartz ; L. Scobie ; C. Scott ; S. Searle ; B. Servin ; B. R. Southey ; G. Sperber ; P. Stadler ; J. V. Sweedler ; H. Tafer ; B. Thomsen ; R. Wali ; J. Wang ; S. White ; X. Xu ; M. Yerle ; G. Zhang ; J. Zhang ; S. Zhao ; J. Rogers ; C. Churcher ; L. B. Schook
Nature Publishing Group (NPG)
Published 2012Staff ViewPublication Date: 2012-11-16Publisher: Nature Publishing Group (NPG)Print ISSN: 0028-0836Electronic ISSN: 1476-4687Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsKeywords: Animals ; Demography ; Genome/*genetics ; Models, Animal ; Molecular Sequence Data ; *Phylogeny ; Population Dynamics ; Sus scrofa/*classification/*geneticsPublished by: -
3Articles: DFG German National LicensesStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: In situ processing of YBa2Cu3O7−x (YBCO) superconducting thin films by pulsed laser evaporation is a technique critically dependent on the processing conditions (substrate temperature, oxygen partial pressure, etc.), and on the deposition setup, including the oxygen nozzle geometry required for incorporation of oxygen. It has been found necessary to have the oxygen nozzle directed toward the substrate during deposition for growth of high-quality superconducting thin films without further annealing [R. Singh et al., Appl. Phys. Lett. 55, 2351 (1989)]. We have taken optical emission spectra of YBCO plasma during the following deposition conditions: (1) In vacuum, (2) in 200 mTorr oxygen ambient with the oxygen nozzle directed toward the substrate, (3) in 200 mTorr oxygen ambient with oxygen nozzle directed toward the target, and (4) with the +300 V biasing ring interposing the target and the substrate. Our results show that enhanced formation of YO and CuO might lead to the growth of thin film at a lower substrate temperature under the biasing condition. A strong dependence of the Cu i (324.75 nm) neutral peak intensity and of the appearance of the molecular peaks such as YO on different deposition geometry is seen. These results provide important insight into the characteristics of plasma transport and deposition by the pulsed laser evaporation technique.Type of Medium: Electronic ResourceURL: -
4Articles: DFG German National LicensesNarayan, J. ; Godbole, V. P. ; Matera, G. ; Singh, R. K.
[S.l.] : American Institute of Physics (AIP)
Published 1992Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We report here enhancement of nucleation and adhesion of diamond films on nondiamond substrates such as copper, stainless steel, and silicon substrates. The enhancement of nucleation is accomplished by pulsed laser irradiation which converts some of the amorphous carbon on the surface into the diamond phase or forms a reaction product that facilitates nucleation of diamond phase. The laser can also be used to evaporate carbon preferentially, leaving behind diamond particles unaffected. By pulsed laser irradiation it is possible to melt the substrate and embed the diamond particles into it, thus improving the adhesion of the diamond film.Type of Medium: Electronic ResourceURL: -
5Articles: DFG German National LicensesStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We have investigated the formation of MgO and yttria-stabilized ZrO2(YSZ) thin films on Si(100) substrates using laser (wavelength 248 nm pulse duration 40 ns, and repetition rate 5 Hz) physical vapor deposition method. The films were deposited from solid targets of MgO and polycrystalline YSZ in appropriate ambient with the substrate temperature optimized at 650 °C. The absorption coefficient in the MgO target was enhanced by Ni doping. The films were characterized using scanning and transmission electron microscopy (plan and cross section), x-ray diffraction, and Rutherford-backscattering spectrometry. The films were found to be polycrystalline with a texture. The thin films of MgO exhibited 〈111〉 texture, while the YSZ films contained both 〈111〉 and 〈200〉 textures.Type of Medium: Electronic ResourceURL: -
6Articles: DFG German National LicensesSingh, R. K. ; Holland, O. W. ; Narayan, J.
[S.l.] : American Institute of Physics (AIP)
Published 1990Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We have theoretically and experimentally analyzed the laser-induced evaporation process for deposition of superconducting thin films from bulk targets. The spatial thickness variations have been found to be significantly different from a conventional thermal deposition process. Unlike a cos θ thickness variation expected from a thermal evaporation process, the laser evaporation process is characterized by a forward-directed deposit with a sharp variation in its thickness as a function of distance from the center of the deposit. We have studied in detail the interactions of nanosecond excimer laser pulses with bulk YBa2Cu3O7 targets leading to evaporation, plasma formation, and subsequent deposition of thin films. A theoretical model for simulating the pulsed laser evaporation (PLE) process has been developed. This model considers an anisotropic three-dimensional expansion of the laser-generated plasma, initially at high temperature and pressure. The forward-directed nature of laser deposition has been found to result from anisotropic expansion velocities of the plasma edges arising due to the density gradients in the gaseous plasma.The physical process of the laser ablation technique for deposition of thin films can be classified into three separate interaction regimes: (i) interaction of the laser beam with the bulk target, (ii) plasma formation and initial isothermal expansion, and (iii) adiabatic expansion leading to deposition of thin films. The first two regimes occur during the time interval of the laser pulse, while the last regime initiates after the laser pulse terminates. Under PLE conditions, the evaporation of the target is assumed to be thermal in nature, while the plasma expansion dynamics is nonthermal as a result of interaction of the laser beam with the evaporated material. The expansion velocities of the plasma edges are related to the initial dimensions and temperature of the plasma, and the atomic weight of the respective species present in it. Preliminary calculations have been carried out on spatial thickness variations as a function of various parameters in PLE deposited thin films. The effects of the various beam and substrate parameters including energy density and substrate-target distance affecting the nature of deposition of superconducting thin films have been theoretically examined. Experimental results have been obtained from thin films deposited on silicon substrates by XeCl pulsed excimer laser (λ=308 nm, τ=45×10−9 s) irradiation. The spatial thickness and compositional variations in thin films have been determined using Rutherford backscattering technique and the results compared with the theoretical calculations.Type of Medium: Electronic ResourceURL: -
7Articles: DFG German National LicensesKumar, Ashok ; Ganapathi, L. ; Kanetkar, S. M. ; Narayan, J.
[S.l.] : American Institute of Physics (AIP)
Published 1991Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: Single-chamber in situ laser processing of high-Tc YBa2Cu3O7−δ film on stainless steel (302) substrates with yttria-stabilized zirconia (YSZ) buffer layers, has been carried out using a multitarget deposition system. YSZ and YBa2Cu3O7−δ films were deposited sequentially by KrF excimer laser (λ=248 nm) at substrate temperature of 650 °C. The films were characterized by x-ray diffraction, four point probe ac electrical resistivity, scanning electron microscopy and Auger electron spectroscopy (AES) techniques. Due to the matching of the thermal expansion coefficient of YSZ with stainless steel and its diffusion barrier characteristics, good quality high-Tc films have been grown on stainless steel substrates with superconducting transition temperature, Tc (onset), of 92 K and Tco (zero resistivity temperature) of 84 K. AES depth profiling indicated little interdiffusion of Fe across the interface of YSZ and stainless steel. A laser evaporation method was used for patterning the YBa2Cu3O7−δ films and critical current density, Jc, was measured to be ∼5×104 Acm−2 at 40 K. It was observed that the zero resistivity temperature significantly changed with the variation of buffer layer thickness, buffer layer processing temperature, and ambient oxygen partial pressure during the deposition of YBa2Cu3O7−δ.Type of Medium: Electronic ResourceURL: -
8Articles: DFG German National LicensesSingh, R. ; Sinha, S. ; Hsu, N. J. ; Ng, J. T. C. ; Chou, P. ; Thakur, R. P. S. ; Narayan, J.
[S.l.] : American Institute of Physics (AIP)
Published 1991Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: Metalorganic chemical vapor deposition (MOCVD) has the potential of emerging as a viable technique to fabricate ribbons, tapes, coated wires, and the deposition of films of high-temperature superconductors, and related materials. As a reduced thermal budget processing technique, rapid isothermal processing (RIP) based on incoherent radiation as the source of energy can be usefully coupled to conventional MOCVD. In this paper we report on the deposition and characterization of high quality superconducting thin films of Y-Ba-Cu-O (YBCO) on yttrium stabilized zirconia substrates by RIP assisted MOCVD. Using O2 gas as the source of oxygen, YBCO films deposited initially at 600 °C for 1 min and at 745 °C for 25 min followed by deposition at 780 °C for 45 s are primarily c-axis oriented and zero resistance is observed at 89–90 K. The zero magnetic field current density at 53 and 77 K are 1.2×106 and 3×105 A/cm2, respectively. By using a mixture of N2O and O2 as the oxygen source substrate temperature was further reduced in the deposition of YBCO films. The films deposited initially at 600 °C for 1 min and than at 720 °C for 30 min are c-axis oriented and with zero resistance being observed at 91 K. The zero magnetic field current densities at 53 and 77 K are 3.4×106 and 1.2×106 A/cm2, respectively. To the best of our knowledge this is the highest value of critical current density, Jc for films deposited by MOCVD at a substrate temperature as low as 720 °C. It is envisioned that high energy photons from the incoherent light source and the use of a mixture of N2O and O2 as the oxygen source, assist chemical reactions and lower overall thermal budget for processing of these films.Type of Medium: Electronic ResourceURL: -
9Articles: DFG German National LicensesStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We have investigated the characteristics of diamond nucleation on silicon substrates alloyed with iron during hot-filament chemical vapor deposition of diamond film. It is shown that the presence of FeSi2 phase enhances nucleation of diamond crystals by more than an order of magnitude compared to bare silicon substrates. The FeSi2 was formed by laser deposition of iron on silicon substrates, followed by thermal annealing at 700 °C. The deposition characteristics of diamond and reaction of iron with silicon substrates were investigated as a function of annealing treatments using Rutherford backscattering, x-ray diffraction, Raman and Auger electron spectroscopy, and transmission electron microscopy. Implications of controlling and enhancing the diamond nucleation in the formation of continuous diamond film are discussed.Type of Medium: Electronic ResourceURL: -
10Articles: DFG German National LicensesEffect of the chemical nature of transition-metal substrates on chemical-vapor deposition of diamondStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: Chemical-vapor deposition of diamond on transition-metal substrates of Cu, Ni, Fe, and their alloys NiAl, Ni3Al, FeSi2, and FeSi has been investigated. It is shown that diamond grows easily on Cu with a very small amount of graphite, while on Ni and Fe there is rapid growth of the graphite layer before diamond deposition. The formation of graphite is attributed to the decomposition of carbon-containing precursors due to the strong catalytic reactivity of Ni and Fe substrates with carbon. The deactivation of these substrates by forming NiAl and FeSi2 results in the suppression of graphite and formation of high-quality diamond. However, for Ni3Al and FeSi substrates which are not completely deactivated, deposition of graphite still takes place. A mechanism based on the electronic structure of substrate atoms, particularly on the 3d shell structure of Cu, Ni, and Fe is proposed to understand the above behavior. Requirements for the stabilization of sp3 bonding of carbon on different substrates are discussed.Type of Medium: Electronic ResourceURL: -
11Articles: DFG German National LicensesSingh, Jogender ; Vellaikal, M. ; Narayan, J.
[S.l.] : American Institute of Physics (AIP)
Published 1993Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We report synthesis of diamond films by pulsed laser irradiation on copper substrate immersed into liquid benzene. It is envisaged that carbon released from benzene at the liquid–solid interface is converted into diamond as a result of rapid quenching from a high temperature. The diamond crystallites were characterized using high resolution transmission electron microscopy imaging and electron diffraction techniques. Growth of thicker diamond films by subsequent chemical vapor deposition has been investigated by transmission and scanning electron microscopy techniques. Thin diamond film deposited during liquid phase provided seed for diamond growth during subsequent chemical vapor deposition.Type of Medium: Electronic ResourceURL: -
12Articles: DFG German National LicensesStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We report here selective deposition and fine-scale patterning of hot filament deposited diamond films by the use of pulsed laser irradiation on silicon and copper substrates. The substrates were abraded with diamond and alumina powders before hot-filament chemical vapor deposition. A drastic enhancement in diamond nucleation (using hot-filament chemical vapor deposition) was observed on specimens treated with diamond powder, whereas enhancement on specimens pretreated with alumina powder was relatively insignificant. We have found that the seeding of diamond crystals was substantially reduced by pulsed laser annealing/melting which removes the plastic damage as well as the seed crystals introduced by diamond powder pretreatment. The selective deposition or fine-scale patterning of diamond films was achieved either by a shadow masking or by scanning a focused laser beam to generate desired patterns. The nucleation can also be enhanced by laser deposition of thin films, such as diamond-like carbon and tungsten carbide (WC), and selective deposition and patterning achieved by controlled removal or deposition of the above films.Type of Medium: Electronic ResourceURL: -
13Articles: DFG German National LicensesNarayan, J. ; White, C. W. ; Aziz, M. J. ; Stritzker, B. ; Walthuis, A.
[S.l.] : American Institute of Physics (AIP)
Published 1985Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We have investigated depth of melting as a function of pulse energy density in amorphous and crystalline silicon layers. The melting threshold for KrF laser pulses (λ=0.249 μm, τ=24×10−9 s) in amorphous (7660-A(ring)-thick) and crystalline silicon layers were determined to be 0.16±0.02 and 0.75±0.05 J cm−2, respectively. The formation of fine- and large-polycrystalline regions was clearly identified in the amorphous silicon layers for energy densities below that needed for complete annealing. The role of explosive recrystallization in the formation of the fine polycrystalline region is discussed.Type of Medium: Electronic ResourceURL: -
14Articles: DFG German National LicensesJames, R. B. ; Narayan, J. ; Wood, R. F. ; Ottesen, D. K. ; Siegfriedt, K. F.
[S.l.] : American Institute of Physics (AIP)
Published 1985Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: The time-resolved optical reflectivity (at 633-nm wavelength) of ion-implanted silicon is measured during and immediately after CO2 laser irradiation [λ=10.6 μm, pulse duration (FWHM)=70 ns] as a function of the energy density of the laser. For a heavily doped sample and incident energy densities greater than 2.9 J/cm2, the reflectivity of the probe beam is found to rapidly jump to 70%, which is consistent with the reflectivity of liquid silicon. The high-reflectivity phase lasts for up to 1 μs, indicating a relatively deep molten layer as compared to similar annealing experiments with a visible or ultraviolet laser. The transmittance and reflectance (at 10.6-μm wavelength) of ion-implanted silicon are also reported as a function of the energy density of the CO2 laser. For energy densities slightly exceeding a threshold value, the transmittance (reflectance) of the tailing edge of the pulse is found to greatly decrease (increase). The interpretation of the optical measurements is based on a thermal model in which surface melting occurs for incident energy densities exceeding a threshold value.Type of Medium: Electronic ResourceURL: -
15Articles: DFG German National LicensesAboelfotoh, M. O. ; Borek, M. A. ; Narayan, J.
[S.l.] : American Institute of Physics (AIP)
Published 2000Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We have studied the reaction between Cu and ε1-Cu3Ge thin films and Si1−xGex (x=0.5) alloy layers epitaxially grown on Si(100) in the temperature range of 250–400 °C. In this temperature range, Cu reacts with the alloy to form a Cu3Si1−xGex ternary phase with an ordered body-centered-cubic crystal structure, and no Ge segregation occurs during the reaction. Unlike ε1-Cu3Ge, the Cu3Si1−xGex films exhibit a high-room-temperature resistivity of ∼150 μΩ cm. However, the Cu3Si1−xGex phase is not observed when Ge is added to Cu to form ε1-Cu3Ge. In contrast to the results reported for films of ε1-Cu3Ge formed on Si(100) substrates, the outdiffusion of Si into the ε1-Cu3Ge films is found to be suppressed when the films are formed on Si0.5Ge0.5 layers at temperatures up to 500 °C, and their resistivity remains low (typically less than 10 μΩ cm at room temperature), indicating the increased stability of ε1-Cu3Ge on Si1−xGex alloys. Furthermore, the ε1-Cu3Ge films form a sharp interface with the Si0.5Ge0.5 layers. These results indicate that ε1-Cu3Ge is an attractive candidate for contacts to SiGe-based devices. © 2000 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
16Articles: DFG German National LicensesStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: A comparative study of ablation plasma plumes originated from single crystal graphite (SCG) and amorphous carbon (a-C) targets during the preparation of diamond-like carbon (DLC) films by KrF excimer pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum, the emission lines of carbon neutral C and ions of C+, C2+, and C3+ can be observed from both the SCG and a-C plasma plumes. The emission intensity from C atoms increases with laser energy density (EL) increase for both cases. The C2 emission intensity from the SCG plasma plume changes drastically with EL, while that from the a-C plasma plume is almost constant. The C2/C emission intensity ratio for the a-C case decreases with EL increase. As for the SCG case, the C2/C ratio decreases with EL increase up to 3.0 J/cm2, and increases slightly with further EL increase. Nanohardness of the deposited films decreases with the increase of the C2/C emission intensity ratio. It is suggested that for both the SCG and a-C target cases, the C2 molecule in the ablated plasma plume may not play an important role in producing high quality DLC films. It is further proposed that the threshold of laser fluence for the formation of diamond-like character film using KrF excimer PLD is 2.1 J/cm2(0.84×108 W/cm2) for the a-C target and 3.0 J/cm2(1.2×108 W/cm2) for the SCG target. The C2 vibrational temperature of the SCG and the a-C plasma plumes show different features on both the laser energy density and nitrogen pressure dependencies. Through optical emission spectroscopy and Langmuir probe measurements in vacuum and nitrogen background, it is concluded that there are many particles with higher mass in the SCG plasma plume, especially at relatively lower laser energy density below 3.0 J/cm2. © 2000 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
17Articles: DFG German National LicensesKalyanaraman, R. ; Oktyabrsky, S. ; Narayan, J.
[S.l.] : American Institute of Physics (AIP)
Published 1999Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We have studied systematically the role of silver in improving microstructure and properties of Y1Ba2Cu3O7−δ (YBCO) thin films. We have more than doubled the grain size to nearly 1.8 μm and reduced processing temperatures by incorporating Ag in the YBCO films, which is accomplished by using a composite target containing 15% by weight of Ag. These films show approximately four times higher Jc than the best films obtained on MgO(001) substrates deposited from stoichiometric Y1Ba2Cu3O7−δ targets. Study of the silver content in the film as a function of the deposition temperature shows clearly a decreasing concentration with increasing temperature and a segregation of the Ag to the surface. The increased oxygen content in the films is also observed at lower processing temperatures, providing strong support for the efficient oxygenation of YBCO via the presence of silver. A qualitative model suggests that the formation of silver oxide, rapid surface diffusion of Ag on MgO surfaces, and the nonreactivity of Ag with YBCO are the key aspects to the improvement in microstructure. The possibility of extending these ideas to the growth of oxides is also discussed, along with the fabrication of in-situ superconducting-metal junctions with 3D geometries. © 1999 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
18Articles: DFG German National LicensesVispute, R. D. ; Narayan, J. ; Dovidenko, K. ; Jagannadham, K. ; Parikh, N. ; Suvkhanov, A. ; Budai, J. D.
[S.l.] : American Institute of Physics (AIP)
Published 1996Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: High-quality ceramics based heteroepitaxial structures of oxide-nitride-semiconductors, i.e., SrTiO3/TiN/Si(100) have been fabricated by in situ pulsed laser deposition. The dependence of substrate temperature and oxygen partial pressure on the crystalline quality of the SrTiO3 films on Si with epitaxial TiN template has been examined. We found that epitaxial growth occurs on TiN/Si(100) above 500 °C, initially at a reduced O2 pressure (10−6 Torr), and followed by a deposition in the range of 5–10×10−4 Torr. X-ray diffraction (aitch-theta, ω, and Φ scans) and transmission electron microscope (TEM) results revealed an excellent alignment of SrTiO3 and TiN films on Si(100) with a cube-on-cube epitaxy. Rutherford backscattering and ion channeling results show a channeling minimum yield (χmin) of ∼13% for the SrTiO3 films. High-resolution TEM results on the SrTiO3/TiN interface show that the epitaxial SrTiO3 film is separated from the TiN by an uniform 80–90 A(ring) crystalline interposing layer presumably of TiNxO1−x (oxy-nitride). The SrTiO3 film fabricated at 700 °C showed a high relative dielectric constant of 312 at the frequency of 1 MHz. The electrical resistivity and the breakdown field of the SrTiO3 films were more than 5×1012 Ω cm and 6×105 V cm−1, respectively. An estimated leakage current density measured at an electric field of 5×105 V/cm−1 was less than 10−7 A/cm2. © 1996 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
19Articles: DFG German National LicensesDovidenko, K. ; Oktyabrsky, S. ; Narayan, J. ; Razeghi, M.
[S.l.] : American Institute of Physics (AIP)
Published 1996Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: The details of epitaxial growth and microstrictural characteristics of AlN films grown on sapphire (0001), (101¯2) and Si (100), (111) substrates were investigated using plan-view and cross-sectional high-resolution transmission electron microscopy and x-ray diffraction techniques. The films were grown by metalorganic chemical vapor deposition using TMA1+NH3+N2 gas mixtures. Different degrees of epitaxy were observed for the films grown on α-Al2O3 and Si substrates in different orientations. The epitaxial relationship for (0001) sapphire was found to be (0001)AlN(parallel)(0001)sap with in-plane orientation relationship of [011¯0]AlN(parallel)[1¯21¯0]sap. This is equivalent to a 30° rotation in the basal (0001) plane. For (101¯2) sapphire substrates, the epitaxial relationship was determined to be (112¯0)AlN(parallel)(101¯2)sap with the in-plane alignment of [0001]AlN(parallel)[1¯011]sap. The AlN films on (0001) α-Al2O3 were found to contain inverted domain boundaries and a/3〈112¯0〉 threading dislocations with the estimated density of 1010 cm−2. The density of planar defects (stacking faults) found in AlN films was considerably higher in the case of (101¯2) compared to (0001) substrates. Films on Si substrates were found to be highly textured c axis oriented when grown on (111) Si, and c axis textured with random in-plane orientation on (100) Si. The role of thin-film defects and interfaces on device fabrication is discussed. © 1996 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
20Articles: DFG German National LicensesVispute, R. D. ; Narayan, J. ; Wu, Hong ; Jagannadham, K.
[S.l.] : American Institute of Physics (AIP)
Published 1995Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: Aluminum nitride thin films have been grown epitaxially on Si(111) substrates, for the first time, by pulsed laser ablation of sintered AlN target. The influence of process parameters such as laser energy density, substrate temperature, pulse repetition rate, nitrogen partial pressure, etc. on epitaxial growth has been investigated to obtain high quality AlN films. These films were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, x-ray diffraction (aitch-theta and ω scans) technique, high resolution transmission electron microscopy, and scanning electron microscopy. The films deposited at laser energy density in the range of 2–3 J/cm2, substrate temperature of 750 °C, and base pressure of 3×10−7 Torr are single phase and highly oriented along c axis normal to the Si(111) planes. The results of x-ray diffraction and electron microscopy on these films clearly show the epitaxial growth of the AlN films with an orientational relationship of AlN[0001] (parallel) Si[111] and AlN[21¯1¯0] (parallel) Si[011¯]. The AlN/Si interface was found to be quite sharp without any indication of interfacial reaction. Laser physical vapor deposition is shown to produce high quality epitaxial AlN films with smooth surface morphology when deposited under optimized conditions. © 1995 American Institute of Physics.Type of Medium: Electronic ResourceURL: