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1

Nitrogen doping of single crystal ZnO  

NASA Astrophysics Data System (ADS)

Zinc oxide (ZnO) is a wide band gap semiconductor with a range of potential optical, electronic, and mechanical applications. The lack of control over defects, in particular reliable p-type doping, is a problem that needs to be overcome. Nitrogen is a promising acceptor dopant. We incorporated nitrogen-hydrogen (N-H) complexes in ZnO during chemical vapor transport (CVT) growth, using ammonia as an ambient. Using commercial ZnO as a seed, we obtained bulk single-crystal growth. The N-H bond-stretching mode gives rise to an infrared (IR) absorption peak at 3150.6 cm-1 at liquid helium temperatures. Isotopic substitutions result in the expected frequency shifts, providing an unambiguous identification of these complexes. The N-H complexes are stable up to ˜700 C. Annealing in oxygen appears to enhance the dissociation of the N-H bond, an observation that could prove useful in achieving reliable p-type conductivity.

McCluskey, M. D.; Jokela, S. J.; Tarun, M. C.

2010-03-01

2

Sensitization of ZnO single crystal electrodes with CdSe quantum dots.  

PubMed

CdSe quantum dots (QDs) were attached to single crystal ZnO(0001) and ZnO(1100) substrates using capping groups, 4-mercaptobenzoic acid, 2-mercaptoacetic acid, 3-mercaptopropionic acid, 8-mercaptooctanoic acid, and 11-mercaptoundecanoic acid, as bifunctional linker molecules. The spectral response and photosensitization yields of the adsorbed QDs were studied with photocurrent spectroscopy. Atomic force microscopy (AFM) was used to verify the surface structure of the ZnO crystals and to examine the coverage and arrangement of the QDs on the single crystal surface. The inner-sphere aqueous redox couple Sx(2-)/S(2-), often used as a regenerator for chalcogenide-based QDs, as well as outer-sphere redox couples such as ferrocene, were able to regenerate the photoexcited CdSe QDs and suppress their photocorrosion. Differences in the binding of the QDs to different ZnO crystal faces are also reported. PMID:25274289

Liang, Yongqi; Thorne, James E; Kern, Meghan E; Parkinson, B A

2014-10-28

3

Characterization of bulk ZnO single crystal grown by a CVT method  

NASA Astrophysics Data System (ADS)

Hall effect, photoluminescence spectroscopy (PL), mass spectroscopy and X-ray diffraction have been used to study bulk ZnO single crystal grown by a closed seeded chemical vapor transport method. Enhancement of n-type electrical conduction and increase of nitrogen concentration are observed of the ZnO samples after high temperature annealing. The results suggest that vacancy is dominant native defect in the ZnO material. These phenomena are explained by a generation of shallow donor defect and suppression of deep level defects in ZnO after the annealing.

Wei, Xuecheng; Zhao, Youwen; Dong, Zhiyuan; Li, Jinmin

2008-03-01

4

Encapsulation of nanoparticles into single-crystal ZnO nanorods and microrods  

PubMed Central

Summary One-dimensional single crystal incorporating functional nanoparticles of other materials could be an interesting platform for various applications. We studied the encapsulation of nanoparticles into single-crystal ZnO nanorods by exploiting the crystal growth of ZnO in aqueous solution. Two types of nanodiamonds with mean diameters of 10 nm and 40 nm, respectively, and polymer nanobeads with size of 200 nm have been used to study the encapsulation process. It was found that by regrowing these ZnO nanorods with nanoparticles attached to their surfaces, a full encapsulation of nanoparticles into nanorods can be achieved. We demonstrate that our low-temperature aqueous solution growth of ZnO nanorods do not affect or cause degradation of the nanoparticles of either inorganic or organic materials. This new growth method opens the way to a plethora of applications combining the properties of single crystal host and encapsulated nanoparticles. We perform micro-photoluminescence measurement on a single ZnO nanorod containing luminescent nanodiamonds and the spectrum has a different shape from that of naked nanodiamonds, revealing the cavity effect of ZnO nanorod. PMID:24778975

Notarianni, Marco; Rintoul, Llew; Motta, Nunzio

2014-01-01

5

X-ray Characterisation of Zinc Oxide (ZnO) Single Crystal Substrates  

SciTech Connect

Single crystal substrates of low defect density are paramount for fully realizing the numerous applications of zinc oxide (ZnO) wide bandgap semiconductors. While ZnO substrates are commercially available from various vendors, very little information is available on the structural properties of these substrates. Therefore, an extensive evaluation of available substrates would serve as a basis for the development of ZnO based devices and technologies. In this study, bulk ZnO single crystal substrates grown by different growth techniques have been characterised using synchrotron white beam X-ray topography and high resolution X-ray diffraction. The substrates exhibit a wide range of dislocation densities from as high as 10{sup 6} cm{sup -2} down to less than 1000 cm{sup -2} depending on the growth technique employed. The authors evaluation reveals that ZnO crystals grown by the hydrothermal technique possess the best structural quality with dislocation densities of 800-1000 cm{sup -2} and rocking curves with a full width half maximum of less than 12 arc seconds.

Dhanaraj, G.; Raghothamachar, B; Dudley, M

2010-01-01

6

Native deep level defects in ZnO single crystal grown by CVT method  

NASA Astrophysics Data System (ADS)

Hall effect, photoluminescence (PL), infrared absorption, deep level transient spectroscopy (DLTS), and Raman scattering have been used to study property and defects of ZnO single crystal grown by a chemical vapor transport method (CVT). As-grown ZnO is N type with free electron density of 10 16-10 17cm -3. It has a slight increase after 900°C annealing in oxygen ambient. The DLTS measurement revealed four deep level defects with energy at 0.30eV, 0.50eV, 0.68eV and 0.90eV in the as-grown ZnO sample, respectively. After the high temperature annealing, only the 0.5eV defect survive and has a concentration increase. PL results of the as-grown and annealed ZnO indicate that the well-known green emission disappear after the annealing. The result suggests a correlation between the 0.68eV defect and the green PL peak. Results of P-doped ZnO were also compared with the undoped ZnO sample. The nature of the defects and their influence on the material property have been discussed.

Zhao, Youwen; Zhang, Fan; Zhang, Rui; Dong, Zhiyuan; Wei, Xuecheng; Zeng, Yiping; Li, Jinmin

2008-03-01

7

Structure and stability of NH complexes in single-crystal ZnO S. J. Jokela and M. D. McCluskeya  

E-print Network

into single-crystal ZnO, using seeded chemical vapor transport in an ammonia ambient. An infrared IR reversed. In the present experiments, a seed crystal was placed at the deposition end. Seed crystals wereStructure and stability of N­H complexes in single-crystal ZnO S. J. Jokela and M. D. Mc

McCluskey, Matthew

8

Improved photocatalytic activity of single crystal ZnO nanorod derived from highly effective P/N heterojunction  

SciTech Connect

Graphical abstract: Schematic showing on photocatalytic degradation 2,4-DCP of ZnO NRs/BDD heterojunction. - Highlights: • Single-crystal ZnO nanorods based P/N heterojunction has been synthesized. • Vertical growth ZnO NRs on BDD can effectively photocatalytic decompose 2,4-DCP. • The rate constant of photocatalysis can be enhanced due to P/N heterojunction. - Abstract: Highly effective single-crystal ZnO nanorods based P/N heterojunction has been synthesized by a controllable crystal seed-induced hydrothermal vertical growth method, which facilitates the separation of the photogenerated electrons and holes due to its endogenous space charge region and suitable band structure. Therefore, photocatalytic activity for degradation of the toxic pollutants is markedly enhanced.

Yan, Xiaoyan, E-mail: yanxiaoyan0312@163.com [School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024 (China); Gong, Changwei, E-mail: cw_gong2008@yahoo.com.cn [School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024 (China); Wang, Jian; Liang, Liping [School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024 (China); Zhao, Li [School of Mechanical Engineering, Hubei University of Technology, Hubei 430068 (China); Zhang, Mingang; Chai, Yuesheng [School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024 (China)

2013-10-15

9

Growth of high-quality ZnO single crystals by seeded CVT using the newly designed ampoule  

NASA Astrophysics Data System (ADS)

The high-quality ZnO single crystals were grown by seeded chemical vapor transport (CVT) in a newly designed ampoule using carbon as a transport agent. The well-faceted crystal of about 5×5×5 mm 3 can be grown reproducibly. Secondary ion mass spectroscopy (SIMS) analysis, X-ray rocking curve (XRC) and photoluminescence (PL) measurements demonstrate that the grown single crystal is of high purity and high crystallinity.

Hong, Sang-Hwui; Mikami, Makoto; Mimura, Kouji; Uchikoshi, Masahito; Yasuo, Akihiko; Abe, Seishi; Masumoto, Katashi; Isshiki, Minoru

2009-07-01

10

Optical signatures of photoinduced Zn vacancies in ZnO single crystal  

SciTech Connect

193-nm excimer laser interaction with ZnO single-crystal at 0.05–500?KW/cm{sup 2} intensities is investigated under ultra high vacuum conditions by time resolved photoluminescence (PL) spectroscopy. A dominant 3.18?eV PL emission band at 295?K is observed. This band shows unusually long 0.52?±?0.01??s lifetime, indicating a defect mediated emission mechanism. The demonstrated negative thermal quenching for this band confirms its free electron to acceptor type transition. The involved acceptor is attributed to zinc vacancy with ?100?meV shallow acceptor state. This study finds that 193-nm interactions produce Zn vacancies in transient states at 0.05–50?KW/cm{sup 2} excitation intensities and in stable state at 500 KW/cm{sup 2} or above intensities. The transient zinc vacancy production at such low intensities further validates the Frenkel pair creation as mechanism for creating these defects in ZnO single-crystal.

Khan, Enamul H., E-mail: enamul-khan@wsu.edu [Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814 (United States)

2014-01-07

11

Thermal annealing effect on spin coherence in ZnO single crystals Z. Yang,1,a),b)  

E-print Network

by atomic force microscopy. Temperature-dependent Hall-effect studies indicate that decreased mobilityThermal annealing effect on spin coherence in ZnO single crystals Z. Yang,1,a),b) Y. Li,2 D. C after annealing at 500 C, as indicated by time-resolved Kerr-rotation pump-probe magneto

Yang, Zheng

12

Comparative study of deep defects in ZnO microwires, thin films and bulk single crystals  

NASA Astrophysics Data System (ADS)

Electrical properties of a ZnO microwire grown by carbo-thermal evaporation, a ZnO thin film grown by pulsed-laser deposition and a hydrothermally grown ZnO bulk crystal are compared. Deep defects were investigated by means of deep-level transient spectroscopy. The defect level E3 was observed in all samples investigated. Additionally, a defect labelled T2 that preferentially forms under Zn-rich condition was detected in the microwire, the thin film and the bulk sample. Our results indicate that VZn is likely involved in this defect.

Schmidt, F.; Müller, S.; von Wenckstern, H.; Dietrich, C. P.; Heinhold, R.; Kim, H.-S.; Allen, M. W.; Grundmann, M.

2013-08-01

13

Luminescence evolution of ZnO single crystal under low-energy electron beam irradiation  

NASA Astrophysics Data System (ADS)

The effects of electron beam irradiation on the luminescence of ZnO single crystals were investigated by cathodoluminescence. We have found that the evolution of the intensity during the e-beam irradiation depends on the surface polarity. For O-face, the ultraviolet (UV) emission decreases exponentially and approaches an asymptotic value. For Zn-face, it first increases and then decreases. The decrease components are similar in both faces. If we halt the e-beam irradiation, the UV intensity recovers partially. These results suggest that the decrease in the UV evolution is related to metastable bulk defect reactions at the subsurface region while the increase is related to surface reaction such as electron-stimulated desorption.

Dierre, B.; Yuan, X. L.; Sekiguchi, T.

2008-08-01

14

Glycine adsorption and photo-reaction over ZnO(000?) single crystal  

NASA Astrophysics Data System (ADS)

The adsorption and reaction of the amino acid glycine (NH2CH2COOH) are studied experimentally on the polar single crystal surface of zinc oxide, ZnO(000?), by X-ray photoelectron spectroscopy (XPS) under UV light in presence and absence of molecular O2. Deposition at 350 K mainly resulted in a largely deprotonated monolayer (NH2CH2COO-(a) + OH(s); where O is surface oxygen, (a) is for adsorbed and (s) is for surface species) identified by its XPS C1s binding energy at 289.3 eV (COO), 286.7 eV (CH2) and XPS O1s at 531.8 eV (COO). A decrease in the signals of all functional groups of the adsorbed glycine (monitored by their C1s, O1s, and N1s lines) is seen upon UV excitation in the absence and presence of O2 pressures up to 5 × 10- 6 mbar. The photoreaction cross sections extracted from the decrease in the C1s peaks were found to be = 2.6 × 10- 18 (COO(a)) and 1.4 × 10- 18(CH2) cm2. The photoactivity of the ZnO(000?) surface under UHV-conditions is found to be comparable to that seen in direct photolysis of amino acids in solution.

Gao, Y. K.; Traeger, F.; Wöll, C.; Idriss, H.

2014-06-01

15

Low energy oxygen implantation induced improved crystallinity and optical properties of surface modified ZnO single crystals  

NASA Astrophysics Data System (ADS)

We report on the low energy oxygen implantation induced improvement in crystallinity and optical properties of surface modified ZnO single crystals. Undoped ZnO (0 0 0 1) single crystal wafers are implanted with 100 keV oxygen ions at a dose of 5 × 10 13 and 5 × 10 14 cm -2 and subsequently annealed at 500 and 600 °C in oxygen ambient. The as-implanted and annealed ZnO wafers are studied by Rutherford back scattering spectrometry (RBS), channeling, Raman, photoluminescence (PL), and Fourier transform infrared spectroscopy (FTIR). Channeling studies show a relatively high ?min (>20%) in the virgin ZnO wafer. After implantation and two-step annealing, RBS studies show improved crystallinity. Raman line width analysis for the E2high mode indicates reduction in strain in the annealed samples as compared to the virgin ZnO wafer. As-implanted samples show drastic quenching of the near band-edge (NBE) PL band due to defects created by the implantation. However, after two-step annealing, the low-dose implanted sample show a five-fold increase in intensity ratio of NBE band (376 nm) to defect related broad band (˜530 nm) at room temperature. Implantation induced changes in the composition and improved crystallinity in the near surface region is accounted for the major improvement in the PL emission.

Giri, P. K.; Kumari, Satchi; Goswami, D. K.

2009-10-01

16

Photonic crystal heterostructures fabricated by TiO2 and ZnO inverse opals using colloidal crystal template with single kind of microspheres  

NASA Astrophysics Data System (ADS)

The fabrication of photonic crystal heterostructures is important for the applications in the fields of integrated photonic crystal chips, multi-frequency optical Bragg filters or mirrors. However, multiple steps of self-assembly process of microspheres are always employed in the fabrication of photonic crystal heterostructures, which may produce lattice mismatches of colloidal crystals. Therefore, photonic crystal heterostructures fabricated by using colloidal crystal template with single kind of microspheres were investigated in this paper. A colloidal crystal template with uniform periodicity was firstly formed by monodispersed polystyrene microsphere. Then ZnO was electrodeposited into the interstices of the template. The thickness of ZnO was controlled to be less than the thickness of the template by varying the deposition time. After the TiO2 precursor was filled into the top voids in the template, the polystyrene colloidal crystal template was removed and photonic crystal heterostructures fabricated by ZnO and TiO2 were formed. Both the dielectric constant and the periodicity of the two parts of the heterostructures are different due to the shrinkage of the sol-gel process. The ZnO/TiO2 heterostructures have a broad photonic stop band which is the superposition of photonic stop bands of ZnO inverse opals and TiO2 inverse opals.

Zhang, Yongna; Fu, Ming; Wang, Jigang; He, Dawei; Wang, Yongsheng

2012-09-01

17

Analysis of strained surface layers of ZnO single crystals after irradiation with intense femtosecond laser pulses  

SciTech Connect

Structural modifications of ZnO single crystals that were created by the irradiation with femtosecond laser pulses at fluences far above the ablation threshold were investigated with micro-Raman spectroscopy. After light-matter interaction on the femtosecond time scale, rapid cooling and the pronounced thermal expansion anisotropy of ZnO are likely to cause residual strains of up to 1.8% and also result in the formation of surface cracks. This process relaxes the strain only partially and a strained surface layer remains. Our findings demonstrate the significant role of thermoelastic effects for the irradiation of solids with intense femtosecond laser pulses.

Schneider, Andreas; Sebald, Kathrin; Voss, Tobias [Semiconductor Optics, Institute of Solid State Physics, University of Bremen, D-28359 Bremen (Germany)] [Semiconductor Optics, Institute of Solid State Physics, University of Bremen, D-28359 Bremen (Germany); Wolverson, Daniel [Nanoscience Group, Department of Physics, University of Bath, BA2 7AY Bath (United Kingdom)] [Nanoscience Group, Department of Physics, University of Bath, BA2 7AY Bath (United Kingdom); Hodges, Chris; Kuball, Martin [Center for Device Thermography and Reliability (CDTR), H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom)] [Center for Device Thermography and Reliability (CDTR), H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom)

2013-05-27

18

Formation of a ZnO{sub 2} layer on the surface of single crystal ZnO substrates with oxygen atoms by hydrogen peroxide treatment  

SciTech Connect

Formation of a ZnO{sub 2} layer by H{sub 2}O{sub 2} treatment for single crystal ZnO (0001) substrates was studied. X-ray diffraction (XRD) peaks of ZnO{sub 2} with a pyrite structure were observed in XRD 2{theta}-{omega} scan patterns of the O-face of single crystal ZnO (0001) substrates with H{sub 2}O{sub 2} treatment, but these peaks were not observed in patterns of the Zn-face of ZnO (0001) substrates with H{sub 2}O{sub 2} treatment. XRD {omega} scan patterns of the ZnO (0002) plane of the O-face of single crystal ZnO (0001) substrates were broadened at the tail of the pattern by H{sub 2}O{sub 2} treatment, but such broadening was not observed in that plane of the Zn-face. Grain structure of ZnO{sub 2} layers was clearly observed in atomic force microscopy (AFM) images for the O-face of ZnO (0001) substrates with H{sub 2}O{sub 2} treatment. Spectra of X-ray photoelectron spectroscopy (XPS) of the O-face of ZnO (0001) substrates with H{sub 2}O{sub 2} treatment showed a definite peak shift of the O 1s peak. It is thought that a pyrite structure of ZnO{sub 2} is easily formed around an O atom of the O-face of ZnO (0001) substrates. Results of XRD measurements, the AFM image, and XPS measurement of the H{sub 2}O{sub 2}-treated single crystal ZnO (1010) substrate that has oxygen atoms on the surface appeared to be the same as those of the O-face of ZnO (0001) substrates.

Kashiwaba, Y. [Department of Electronic Engineering, Sendai National College of Technology, 4-16-1 Ayashi-chuo, Sendai 989-3128 (Japan); Abe, T.; Nakagawa, A.; Niikura, I.; Kashiwaba, Y.; Daibo, M.; Fujiwara, T.; Osada, H. [Iwate University, 4-3-5 Ueda, Morioka 020-8551 (Japan)

2013-03-21

19

Rutherford backscattering and nuclear reaction analyses of hydrogen ion-implanted ZnO bulk single crystals  

NASA Astrophysics Data System (ADS)

The origins of low resistivity in H ion-implanted ZnO bulk single crystals are studied by Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) photoluminescence (PL), and Van der Pauw methods. The H-ion implantation (peak concentration: 1.45 × 1020 cm-3) into ZnO is performed using a 500 keV implanter. The resistivity decreases from 2.5 × 103 ? cm for unimplanted ZnO to 6.5 ? cm for as-implanted one. RBS measurements show that Zn interstitial as a shallow donor is not recognized in as-implanted samples. From photoluminescence measurements, the broad green band emission is observed in as-implanted samples. NRA measurements for as-implanted ZnO suggest the existence of the oxygen interstitial. The origins of the low resistivity in the as-implanted sample are attributed to both the H interstitial as a shallow donor and complex donor between H and disordered O. The activation energy of H related donors estimated from the temperature dependence of carrier concentration is 29 meV.

Kaida, T.; Kamioka, K.; Ida, T.; Kuriyama, K.; Kushida, K.; Kinomura, A.

2014-08-01

20

Hydrogen released from bulk ZnO single crystals investigated by time-of-flight electron-stimulated desorption  

NASA Astrophysics Data System (ADS)

Electron beam (e-beam) irradiation effects on ZnO single crystals have been investigated by using time-of-flight electron-stimulated desorption (TOF-ESD). The samples were irradiated by using a continuous 0.5 or 1.5 keV e-beam, while the TOF-ESD spectra were taken by using a pulsed 0.5 keV e-beam. For both the O-terminated and Zn-terminated surfaces, the major desorption is H+ desorption. The main trend of H+ desorption intensity and evolution as a function of irradiation time is similar for both faces. The H+ peak is much higher after 1.5 keV irradiation than after 0.5 keV irradiation. The intensity of the H+ peak decreases exponentially as a function of irradiation time and partially recovers after the irradiation is stopped. These observations suggest that the main contribution of the H+ desorption is hydrogen released from the dissociation of H-related defects and complexes in the bulk region of the ZnO by e-beam irradiation. This finding can be used to explain the reported ultraviolet degradation of ZnO single crystals under electron irradiation observed by cathodoluminescence. The surfaces play a lesser role for the H+ desorption, as there are differences of the decreasing rate between the two faces and additionally the intensity of the H+ peak for both the unclean O-face and Zn-facesis smaller than that for clean faces. While the H+ desorption is mainly dominated by the bulk region, O+ desorption is more influenced by the surfaces. There are two kinds of O+ desorbed from ZnO having 13.0 ?s TOF and 14.2 ?s TOF. The O+ desorption depends on the surface polarity, the surface conditions and the energy used for irradiation.

Dierre, Benjamin; Yuan, Xiaoli; Ueda, Kazuyuki; Sekiguchi, Takashi

2010-11-01

21

Nitrogen and hydrogen in bulk single-crystal ZnO S.J. Jokela, M.C. Tarun, M.D. McCluskey  

E-print Network

O as a seed, we obtained bulk single-crystal growth. The N­H bond-stretching mode gives rise to an IR is carefully removed. If a seed crystal is to be used, it must be attached and in good thermal contact.elsevier.com/locate/physb Physica B Fig. 1. Schematic diagram of the CVT growth system. Single-crystal ZnO is grown on a seed

McCluskey, Matthew

22

Growth of ZnO single crystal thin films on c-plane (0 0 0 1) sapphire by plasma enhanced molecular beam epitaxy  

Microsoft Academic Search

ZnO single crystal thin films were grown by plasma enhanced molecular beam epitaxy on (0 0 0 1) sapphire. The growth modes of ZnO epilayers were investigated by reflection high-energy electron diffraction. A transition from two-dimensional nucleation to three-dimensional nucleation is found at the initial growth stage. Optical properties of the films, studied by photoluminescence spectroscopy, exhibit a dominant bound

Yefan Chen; D. M. Bagnall; Ziqiang Zhu; Takashi Sekiuchi; Ki-tae Park; Kenji Hiraga; Takafumi Yao; S. Koyama; M. Y. Shen; T. Goto

1997-01-01

23

(55)Mn pulsed ENDOR spectroscopy of Mn(2+) ions in ZnO thin films and single crystal.  

PubMed

(55)Mn pulsed electron nuclear double resonance (ENDOR) experiments were performed at X-band on high spin S=5/2 Mn(2+) ions incorporated at zinc lattice sites in heteroepitaxial ZnO thin films. The films have been prepared by pulsed laser deposition and the manganese ions were doped during the growth process. We examine how the c/a lattice axes ratio of the ZnO films influences the (55)Mn hyperfine (hf) and nuclear quadrupole (nq) coupling parameters of the Mn(2+) probe ions. The results are compared with those obtained for Mn(2+) ions present as impurities in ZnO single crystals and revealed that the (55)Mn nq coupling monitors sensitively the structural distortions in the bonding environment of the Mn(2+) ions. The experiments provided the full axially symmetric (55)Mn hf and nq interaction tensors. The latter is found to be very sensitive to small axial distortions of the MnO4 tetrahedrons. In particular, the (55)Mn pulsed ENDOR spectra of the ZnO:Mn thin films are strongly subjected to strain effects in the nq coupling parameter indicating a variation of the local structural parameters for the heteroepitaxial films. In the analysis of the (55)Mn pulsed ENDOR spectra the axial and cubic zero field splitting of the Mn(2+) ions was taken into account and intensity effects in the ENDOR spectra due to the zero field splitting effects were discussed. PMID:24993844

Böttcher, Rolf; Pöppl, Andreas; Lorenz, Michael; Friedländer, Stefan; Spemann, Daniel; Grundmann, Marius

2014-08-01

24

Hydrogen released from bulk ZnO single crystals investigated by time-of-flight electron-stimulated desorption  

SciTech Connect

Electron beam (e-beam) irradiation effects on ZnO single crystals have been investigated by using time-of-flight electron-stimulated desorption (TOF-ESD). The samples were irradiated by using a continuous 0.5 or 1.5 keV e-beam, while the TOF-ESD spectra were taken by using a pulsed 0.5 keV e-beam. For both the O-terminated and Zn-terminated surfaces, the major desorption is H{sup +} desorption. The main trend of H{sup +} desorption intensity and evolution as a function of irradiation time is similar for both faces. The H{sup +} peak is much higher after 1.5 keV irradiation than after 0.5 keV irradiation. The intensity of the H{sup +} peak decreases exponentially as a function of irradiation time and partially recovers after the irradiation is stopped. These observations suggest that the main contribution of the H{sup +} desorption is hydrogen released from the dissociation of H-related defects and complexes in the bulk region of the ZnO by e-beam irradiation. This finding can be used to explain the reported ultraviolet degradation of ZnO single crystals under electron irradiation observed by cathodoluminescence. The surfaces play a lesser role for the H{sup +} desorption, as there are differences of the decreasing rate between the two faces and additionally the intensity of the H{sup +} peak for both the unclean O-face and Zn-facesis smaller than that for clean faces. While the H{sup +} desorption is mainly dominated by the bulk region, O{sup +} desorption is more influenced by the surfaces. There are two kinds of O{sup +} desorbed from ZnO having 13.0 {mu}s TOF and 14.2 {mu}s TOF. The O{sup +} desorption depends on the surface polarity, the surface conditions and the energy used for irradiation.

Dierre, Benjamin; Sekiguchi, Takashi [Advanced Electronic Materials Center, National Institute for Materials Science (NIMS), Tsukuba 305-0044 (Japan); Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-0003 (Japan); Yuan, Xiaoli [Advanced Electronic Materials Center, National Institute for Materials Science (NIMS), Tsukuba 305-0044 (Japan); Ueda, Kazuyuki [Nano High-Tech Research Center, Graduate School of Engineering, Toyota Technological Institute, Nagoya 468-8511 (Japan)

2010-11-15

25

Formation of isolated Zn vacancies in ZnO single crystals by absorption of ultraviolet radiation: a combined study using positron annihilation, photoluminescence, and mass spectroscopy.  

PubMed

Positron annihilation spectra reveal isolated zinc vacancy (V(Zn)) creation in single-crystal ZnO exposed to 193-nm radiation at 100 mJ/cm(2) fluence. The appearance of a photoluminescence excitation peak at 3.18 eV in irradiated ZnO is attributed to an electronic transition from the V(Zn) acceptor level at ~100 meV to the conduction band. The observed V(Zn) density profile and hyperthermal Zn(+) ion emission support zinc vacancy-interstitial Frenkel pair creation by exciting a wide 6.34 eV Zn-O antibonding state at 193-nm photon-a novel photoelectronic process for controlled V(Zn) creation in ZnO. PMID:23863026

Khan, Enamul H; Weber, Marc H; McCluskey, Matthew D

2013-07-01

26

Nature of red luminescence band in research-grade ZnO single crystals: A "self-activated" configurational transition  

NASA Astrophysics Data System (ADS)

By implanting Zn+ ions into research-grade intentionally undoped ZnO single crystal for facilitating Zn interstitials (Zni) and O vacancies (VO) which is revealed by precise X-Ray diffraction rocking curves, we observe an apparent broad red luminescence band with a nearly perfect Gaussian lineshape. This red luminescence band has the zero phonon line at ˜2.4 eV and shows distinctive lattice temperature dependence which is well interpreted with the configurational coordinate model. It also shows a low "kick out" thermal energy and small thermal quenching energy. A "self-activated" optical transition between a shallow donor and the defect center of Zni-VO complex or VZnVO di-vacancies is proposed to be responsible for the red luminescence band. Accompanied with the optical transition, large lattice relaxation simultaneously occurs around the center, as indicated by the generation of multiphonons.

Chen, Y. N.; Xu, S. J.; Zheng, C. C.; Ning, J. Q.; Ling, F. C. C.; Anwand, W.; Brauer, G.; Skorupa, W.

2014-07-01

27

Origins of low resistivity and Ge donor level in Ge ion-implanted ZnO bulk single crystals  

SciTech Connect

The energy level of Ge in Ge-ion implanted ZnO single crystals is studied by Hall-effect and photoluminescence (PL) methods. The variations in resistivity from ?10{sup 3} ?cm for un-implanted samples to ?10{sup ?2} ?cm for as-implanted ones are observed. The resistivity is further decreased to ?10{sup ?3} ?cm by annealing. The origins of the low resistivity are attributed to both the zinc interstitial (Zn{sub i}) related defects and the electrical activated Ge donor. An activation energy of Ge donors estimated from the temperature dependence of carrier concentration is 102 meV. In PL studies, the new peak at 372 nm (3.33 eV) related to the Ge donor is observed in 1000 °C annealed samples.

Kamioka, K.; Oga, T.; Izawa, Y.; Kuriyama, K. [College of Engineering and Research Center of Ion Beam Technology, Hosei University Koganei, Tokyo 184-8584 (Japan); Kushida, K. [Departments of Arts and Sciences, Osaka Kyoiku University Kashiwara, Osaka 582-8582 (Japan)

2013-12-04

28

Thiol dosing of ZnO single crystals and nanorods: Surface chemistry and photoluminescence  

NASA Astrophysics Data System (ADS)

Adsorption of thiols on ZnO(0001) and ZnO nanorods has been investigated using X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). Ultrahigh vacuum (UHV) dosing of sputter-cleaned ZnO(0001) with methanethiol (MT), 1-dodecanethiol (DDT), and 3-mercaptopropyltrimethoxysilane (MPTMS) leads to S2p peaks with a binding energy of 163.3 eV. Similar results for MPTMS are obtained for sputter-cleaned ZnO(0001) that is pre-dosed with water to form hydroxyl groups. In all cases, the absence of a free thiol S2p peak at 164.2 eV indicates that bonding to the surface occurs via the thiol end of the molecule. A DDT-dosed ZnO(0001) sample stored for 10 days in UHV and heated to temperatures as high as 150 °C exhibits minimal changes in its S/Zn atomic ratio, confirming chemisorption and the presence of a strong bond to the surface. UPS shows that MT adsorption on sputtered ZnO(0001) leads to a 0.7 eV increase in work function and perturbation of the MT molecular orbitals, again consistent with chemisorption. Dry ZnO nanorods have been exposed to MT while monitoring their photoluminescence. XPS and Raman spectroscopy confirm thiol adsorption. Relative to dry ZnO, adsorption causes a decrease in intensity of the visible emission peak, but the UV peak remains unchanged. These results indicate that Znsbnd S bond formation quenches radiative decay to the valence band from defect states, possibly by methanethiolate adsorption filling oxygen vacancies.

Singh, Jagdeep; Im, Jisun; Watters, Evan J.; Whitten, James E.; Soares, Jason W.; Steeves, Diane M.

2013-03-01

29

ZnO dense nanowire array on a film structure in a single crystal domain texture for optical and photoelectrochemical applications  

NASA Astrophysics Data System (ADS)

A single crystal domain texture quality (a unique in-plane and out-of-plane crystalline orientation over a large area) ZnO nanostructure of a dense nanowire array on a thick film has been homogeneously synthesized on a-plane sapphire substrates over large areas through a one-step chemical vapor deposition (CVD) process. The growth mechanism is clarified: a single crystal [0\\bar {2}1] oriented ZnAl2O4 buffer layer was formed at the ZnO film and the a-plane sapphire substrate interface via a diffusion reaction process during the CVD process, providing improved epitaxial conditions that enable the synthesis of the high crystalline quality ZnO nanowire array on a film structure. The high optoelectronic quality of the ZnO nanowire array on a film sample is evidenced by the free exitonic emissions in the low-temperature photoluminescence spectroscopy. A carrier density of ˜1017 cm-3 with an n-type conductivity of the ZnO nanowire array on a film sample is obtained by electrochemical impedance analysis. Finally, the ZnO nanowire array on a film sample is demonstrated to be an ideal template for a further synthesis of a single crystal quality ZnO-ZnGa2O4 core-shell nanowire array on a film structure. The fabricated ZnO-ZnGa2O4 sample revealed an enhanced anticorrosive ability and photoelectrochemical performance when used as a photoanode in a photoelectrochemical water splitting application.

Zhong, Miao; Sato, Yukio; Kurniawan, Mario; Apostoluk, Aleksandra; Masenelli, Bruno; Maeda, Etsuo; Ikuhara, Yuichi; Delaunay, Jean-Jacques

2012-12-01

30

Nitrogen and hydrogen in bulk single-crystal ZnO  

NASA Astrophysics Data System (ADS)

Zinc oxide (ZnO) is a wide band gap II-VI semiconductor with optical, electronic, and mechanical applications. Nitrogen is a promising acceptor dopant. Nitrogen-hydrogen (N-H) complexes were introduced into ZnO during chemical vapor transport (CVT) growth, using ammonia as a doping source. The N-H bond-stretching mode gives rise to an infrared (IR) absorption peak at 3151 cm -1 at liquid-helium temperatures. Along with passivating acceptors, hydrogen also acts as a shallow donor. In the previous work, we observed an IR peak at 3326 cm -1 that corresponds to a hydrogen donor. It is possible that this donor is actually a Ca-OH complex.

Jokela, S. J.; Tarun, M. C.; McCluskey, M. D.

2009-12-01

31

Deep level transient spectroscopy studies of n-type ZnO single crystals grown by different techniques.  

PubMed

In the present study single-crystalline ZnO samples grown from the vapor phase, the melt, and a high-temperature aqueous solution (hydrothermal growth) are investigated before and after hydrogen plasma treatments, by means of deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS. Dominant DLTS peaks are found to appear in the range of 120-350 K for all materials. The DLTS spectra depend on the procedure of growth of the ZnO. The thermal stabilities of the defects in an oxygen atmosphere and in an oxygen-lean atmosphere are analyzed. The origin of the DLTS peaks is discussed. PMID:21813951

Scheffler, L; Kolkovsky, Vl; Lavrov, E V; Weber, J

2011-08-24

32

Electron-hole recombination on ZnO(0001) single-crystal surface studied by time-resolved soft X-ray photoelectron spectroscopy  

NASA Astrophysics Data System (ADS)

Time-resolved soft X-ray photoelectron spectroscopy (PES) experiments were performed with time scales from picoseconds to nanoseconds to trace relaxation of surface photovoltage on the ZnO(0001) single crystal surface in real time. The band diagram of the surface has been obtained numerically using PES data, showing a depletion layer which extends to 1 ?m. Temporal evolution of the photovoltage effect is well explained by a recombination process of a thermionic model, giving the photoexcited carrier lifetime of about 1 ps at the surface under the flat band condition. This lifetime agrees with a temporal range reported by the previous time-resolved optical experiments.

Yukawa, R.; Yamamoto, S.; Ozawa, K.; Emori, M.; Ogawa, M.; Yamamoto, Sh.; Fujikawa, K.; Hobara, R.; Kitagawa, S.; Daimon, H.; Sakama, H.; Matsuda, I.

2014-10-01

33

Characterization of Mn and Fe diffusion into ZnO Films and single crystals for diluted magnetic semiconductor applications  

Microsoft Academic Search

There is growing interesting in the use of transition metal (TM) doped ZnO films as a diluted magnetic semiconductor for room temperature spintronics applications. Various methods of doping have been investigated including ion implantation and co-deposition during the growth process. In essentially all approaches, doping either accompanies, or is followed by, an annealing step intended to achieve a uniform distribution

R. Gateau; D. H. Hill; R. A. Bartynski; P. Wu; Y. Lu

2006-01-01

34

Epitaxial Growth and Properties of Cobalt-doped ZnO on ?-Al?O? Single-Crystal Substrates  

SciTech Connect

Co-doped ZnO (CoxZn?-xO) is of potential interest for spintronics due to the prediction of room-temperature ferromagnetism. We have grown epitaxial CoxZn?-xO films on Al?O?(012) substrates by metalorganic chemical vapor deposition using a liquid precursor delivery system. High concentrations of Co (x < 0.35) can be uniformly incorporated into the film without phase segregation. Co is found to be in the ?² oxidation state, independent of x. This material can be grown n type by the deliberate incorporation of oxygen vacancies, but not by inclusion of ~1 at. % Al. Semiconducting films remain ferromagnetic up to 350 K. In contrast films without oxygen vacancies are insulating and nonmagnetic, suggesting that exchange interaction is mediated by itinerant carriers. The saturation and remanent magnetization on a per Co basis was very small (< 0.1 ?B/Co), even in the best films. The dependence of saturation magnetization, as measured by optical magnetic circular dichroism, on magnetic field and temperature, agrees with the theoretical Brillouin function, demonstrating that the majority of the Co(II) ions behave as magnetically isolated S = 3/2 spins.

Tuan, Allan C.; Bryan, John D.; Pakhomov, Alexandre; Shutthanandan, V.; Thevuthasan, Suntharampillai; McCready, David E.; Gaspar, Dan J.; Engelhard, Mark H.; Rogers, J. W.; Krishnan, Kannan M.; Gamelin, Daniel R.; Chambers, Scott A.

2004-08-30

35

Crystal growth of ZnO bulk by CVT method using PVA  

NASA Astrophysics Data System (ADS)

Seeded crystal growth of Zinc oxide (ZnO) by the closed ampoule chemical vapor transport (CVT) is carried out using polyvinyl alcohol (PVA) as a transport agent. Under the conditions of TS=1100 °C, ? T=10 K and the amount of PVA=0.13-0.91 mg/cm 3, single-crystalline ZnO was grown continuously on the ZnO seed-crystal, of which the surface was (0 0 0 1) Zn-face. The grown crystals had well-marked growth facets belonged to {1 0 1¯0} and {1 0 1¯ 1} faces. The color of the crystals was changed from pale yellow to dark orange-red depending on the amount of PVA. Typical electron density and the Hall mobility of the crystals were 1×10 17 cm -3 and 2×10 2 cm 2/V s at 300 K, respectively.

Udono, H.; Sumi, Y.; Yamada, S.; Kikuma, I.

2008-04-01

36

Evolution of ZnO nano-crystals grown on a profiled sapphire(0001) substrate with Au nano-crystals  

Microsoft Academic Search

This paper reports the structural evolution of ZnO nano-crystals deposited on profiled Au\\/sapphire(0001) substrates by radio frequency sputtering. In contrast to the typical catalytic growth of ZnO nano-crystals with Au seeds, ZnO was initially formed as nano-discs on top of the Au nano-crystals, and their eventual shape became a replica of the cuboctahedral Au nano-crystals. The ZnO nano-discs transformed into

S. H. Seo; Hyon Chol Kang

37

Deformation-Free Single-Crystal Nanohelixes of Polar Nanowires  

E-print Network

Deformation-Free Single-Crystal Nanohelixes of Polar Nanowires Rusen Yang, Yong Ding, and Zhong Lin, deformation-free, single-crystal nanohelixes/nanosprings of piezoelectric ZnO are reported. The nanohelixes observed for carbon nanotubes,1 SiC2 and amorphous silicon carbide.3 The carbon coils are created due

Wang, Zhong L.

38

Mechanism of photonic crystal and waveguide effects in ZnO nanorods  

NASA Astrophysics Data System (ADS)

Two different shaped ZnO nanorods were grown on ZnO buffered Al2O3 substrate by laser interference lithography and hydrothermal method. The light waveguide within ZnO nano rod and photonic crystal effects in arrayed ZnO nanorods was calculated by 3D-finite dimension time domain(3D-FDTD) programs. The ZnO photonic crystal effect and number of modes of ZnO nanorod was governed by arrangement and shape of ZnO nanorod, respectively.

Kim, Tae Un; Kim, Seon Hoon; Ki, Hyun Chul; Kim, Doo Gun; Gang, Myeng Gil; Kim, Hwe Jong; Kim, Jin Hyeok

2013-03-01

39

Refractive index of a single ZnO microwire at high temperatures  

NASA Astrophysics Data System (ADS)

We report a study of refractive index of a wurtzite ZnO single crystal microwire at a temperature range from room temperature to about 400 K using optical cavity modes. The photoluminescence (PL) spectra of the ZnO microwire at different temperatures were performed using a confocal micro-photoluminescence setup. The whispering gallery modes observed in the PL spectra show a redshift both in the ultraviolet and the visible range as the temperature rises. The redshift is used to extract the refractive index of the ZnO microwire. The dispersion relations are deduced at different temperatures, and the results show that the refractive index increases with raising temperature for both transverse electric and transverse magnetic modes. The refractive index increases faster at a shorter wavelength, which is due to the fact that the shorter wavelength is closer to the resonance frequencies of ZnO microwire according to the Lorentz oscillator model.

Qiu, Kangsheng; Zhao, Yanhui; Gao, Yunan; Liu, Xiangbo; Ji, Xiaofan; Cao, Shuo; Tang, Jing; Sun, Yue; Zhang, Dongxiang; Feng, Baohua; Xu, Xiulai

2014-02-01

40

Chemically assisted vapour transport for bulk ZnO crystal growth  

NASA Astrophysics Data System (ADS)

A chemically assisted vapour phase transport (CVT) method is proposed for the growth of bulk ZnO crystals. Thermodynamic computations have confirmed the possibility of using CO as a sublimation activator for enhancing the sublimation rate of the feed material in a large range of pressures (10 -3 to 1 atm) and temperatures (800-1200 °C). Growth runs in a specific and patented design yielded single ZnO crystals up to 46 mm in diameter and 8 mm in thickness, with growth rates up to 400 ?m/h. These values are compatible with an industrial production rate. N type ZnO crystals ( ?=182 cm 2/(V s) and n=7 10 15 cm -3) obtained by this CVT method (Chemical Vapour Transport) present a high level of purity (10-30 times better than hydrothermal ZnO crystals), which may be an advantage for obtaining p-type doped layers ([Li] and [Al] <10 +15 cm -3). Structural (HR-XRD), defect density (EPD), electrical (Hall measurements) and optical (photoluminescence) properties are presented.

Santailler, Jean-Louis; Audoin, Claire; Chichignoud, Guy; Obrecht, Rémy; Kaouache, Belkhiri; Marotel, Pascal; Pelenc, Denis; Brochen, Stéphane; Merlin, Jérémy; Bisotto, Isabelle; Granier, Carole; Feuillet, Guy; Levy, François

2010-11-01

41

Shallow carrier traps in hydrothermal ZnO crystals  

NASA Astrophysics Data System (ADS)

Native and hydrogen-plasma induced shallow traps in hydrothermally grown ZnO crystals have been investigated by charge-based deep level transient spectroscopy, photoluminescence and cathodoluminescence microanalysis. The as-grown ZnO exhibits a trap state at 23 meV, while H-doped ZnO produced by plasma doping shows two levels at 22 meV and 11 meV below the conduction band. As-grown ZnO displays the expected thermal decay of bound excitons with increasing temperature from 7 K, while we observed an anomalous behaviour of the excitonic emission in H-doped ZnO, in which its intensity increases with increasing temperature in the range 140-300 K. Based on a multitude of optical results, a qualitative model is developed which explains the Y line structural defects, which act as an electron trap with an activation energy of 11 meV, being responsible for the anomalous temperature-dependent cathodoluminescence of H-doped ZnO.

Ton-That, C.; Lem, L. L. C.; Phillips, M. R.; Reisdorffer, F.; Mevellec, J.; Nguyen, T.-P.; Nenstiel, C.; Hoffmann, A.

2014-08-01

42

Single Crystal Membranes  

NASA Technical Reports Server (NTRS)

Single crystal a- and c-axis tubes and ribbons of sodium beta-alumina and sodium magnesium beta-alumina were grown from sodium oxide rich melts. Additional experiments grew ribbon crystals containing sodium magnesium beta, beta double prime, beta triple prime, and beta quadruple prime. A high pressure crystal growth chamber, sodium oxide rich melts, and iridium for all surfaces in contact with the melt were combined with the edge-defined, film-fed growth technique to grow the single crystal beta-alumina tubes and ribbons. The crystals were characterized using metallographic and X-ray diffraction techniques, and wet chemical analysis was used to determine the sodium, magnesium, and aluminum content of the grown crystals.

Stormont, R. W.; Morrison, A.

1974-01-01

43

SINGLE CRYSTAL NEUTRON DIFFRACTION.  

SciTech Connect

Single-crystal neutron diffraction measures the elastic Bragg reflection intensities from crystals of a material, the structure of which is the subject of investigation. A single crystal is placed in a beam of neutrons produced at a nuclear reactor or at a proton accelerator-based spallation source. Single-crystal diffraction measurements are commonly made at thermal neutron beam energies, which correspond to neutron wavelengths in the neighborhood of 1 Angstrom. For high-resolution studies requiring shorter wavelengths (ca. 0.3-0.8 Angstroms), a pulsed spallation source or a high-temperature moderator (a ''hot source'') at a reactor may be used. When complex structures with large unit-cell repeats are under investigation, as is the case in structural biology, a cryogenic-temperature moderator (a ''cold source'') may be employed to obtain longer neutron wavelengths (ca. 4-10 Angstroms). A single-crystal neutron diffraction analysis will determine the crystal structure of the material, typically including its unit cell and space group, the positions of the atomic nuclei and their mean-square displacements, and relevant site occupancies. Because the neutron possesses a magnetic moment, the magnetic structure of the material can be determined as well, from the magnetic contribution to the Bragg intensities. This latter aspect falls beyond the scope of the present unit; for information on magnetic scattering of neutrons see Unit 14.3. Instruments for single-crystal diffraction (single-crystal diffractometers or SCDs) are generally available at the major neutron scattering center facilities. Beam time on many of these instruments is available through a proposal mechanism. A listing of neutron SCD instruments and their corresponding facility contacts is included in an appendix accompanying this unit.

KOETZLE,T.F.

2001-03-13

44

Hydrothermal synthesis, characterizations and photoluminescence study of single crystalline hexagonal ZnO nanorods with three dimensional flowerlike microstructures  

NASA Astrophysics Data System (ADS)

A simple, low-cost, and environmentally benign hydrothermal approach has been successfully developed to synthesize uniform, large-scale well-crystallized ZnO nanorods with different aspect ratios that were united together to form three dimensional (3D) flowerlike structures. The method involved direct growth of ZnO 3D microstructures using aqueous solution of Zn(CH3COO)2 as the precursor and NaOH to adjust the pH of resultant solution. Surfactants or templates were not used during the entire synthetic process. Moreover, the morphology evolution of the ZnO nanorods with reaction time suggests a recrystallization-dissolution-growth mechanism that continuously takes place for prolonged interval of time. The XRD pattern of the as-grown ZnO nanorods and relevant analyses confirm the well crystallized hexagonal structure of the ZnO microstructures and no evidence of any other impurity phases. SEM observations reveal that the ZnO product grew in the form of nanorods that were united together to form 3D flowerlike morphology. The high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) shows that the ZnO nanorods were single crystalline and grew along the c-axis of the crystal plane. PL measurements of the as-synthesized nanorods exhibit excellent excitation features and strong band-edge UV luminescence even at room temperature. The uniform single crystalline, defect free, and high aspect ratio nanorods may find promising applications in optoelectronics and photo-catalysts. The growth habit of ZnO crystal is also illustrated. This method is suitable for large-scale production of ZnO microstructures and could be extended for syntheses of other metal oxides.

Kale, Rohidas B.; Hsu, Yung-Jung; Lin, Yi-Feng; Lu, Shih-Yuan

2014-05-01

45

Single photon emission from ZnO nanoparticles  

SciTech Connect

Room temperature single photon emitters are very important resources for photonics and emerging quantum technologies. In this work, we study single photon emission from defect centers in 20?nm zinc oxide (ZnO) nanoparticles. The emitters exhibit bright broadband fluorescence in the red spectral range centered at 640?nm with polarized excitation and emission. The studied emitters showed continuous blinking; however, bleaching can be suppressed using a polymethyl methacrylate coating. Furthermore, hydrogen termination increased the density of single photon emitters. Our results will contribute to the identification of quantum systems in ZnO.

Choi, Sumin; Ton-That, Cuong; Phillips, Matthew R.; Aharonovich, Igor, E-mail: igor.aharonovich@uts.edu.au [School of Physics and Advanced Materials, University of Technology Sydney, Ultimo, New South Wales 2007 (Australia); Johnson, Brett C. [Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Parkville, Victoria 3010 (Australia); Castelletto, Stefania [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Melbourne, Victoria 3000 (Australia)

2014-06-30

46

Growth of Zinc Oxide Single Crystals by Vapor Phase Reaction  

Microsoft Academic Search

ZnO single crystals are grown by vapor phase reaction with ZnI2 source. When the growth region is maintained between 1150°C and 1200°C, crystals grow by oxidation, and between 970°C and 1020°C, by hydrolysis. Crystals are mainly needles 15 mm in length or plates 8 mm2 in area. Patterns suggesting their growth mechanisms are observed in their microphotographs. The present experiments

Masami Hirose

1971-01-01

47

Arnold Schwarzenegger SINGLE CRYSTAL SILICON  

E-print Network

Arnold Schwarzenegger Governor SINGLE CRYSTAL SILICON SHEET GROWTH Prepared For: California Energy CRYSTAL SILICON SHEET GROWTH EISG AWARDEE ENERGY MATERIALS RESEARCH 132 Chalmers Drive Rochester Hills, MI

48

Fabrication of inverted opal ZnO photonic crystals by atomic layer deposition  

E-print Network

Fabrication of inverted opal ZnO photonic crystals by atomic layer deposition M. Scharrer, X. Wu, A fabricated three-dimensional optically active ZnO photonic crystals by infiltrating polystyrene opal method to fabricate so-called "inverted opal" structures which have the long-range order, high filling

Cao, Hui

49

Paramagnetism and antiferromagnetic interactions in single-phase Fe-implanted ZnO  

E-print Network

As the intrinsic origin of the high temperature ferromagnetism often observed in wide-gap dilute magnetic semiconductors becomes increasingly debated, there is a growing need for comprehensive studies on the single-phase region of the phase diagram of these materials. Here we report on the magnetic and structural properties of Fe-doped ZnO prepared by ion implantation of ZnO single crystals. A detailed structural characterization shows that the Fe impurities substitute for Zn in ZnO in a wurtzite Zn1?xFexO phase which is coherent with the ZnO host. In addition, the density of beam-induced defects is progressively decreased by thermal annealing up to 900 ?C, from highly disordered after implantation to highly crystalline upon subsequent annealing. Based on a detailed analysis of the magnetometry data, we demonstrate that isolated Fe impurities occupying Zn substitutional sites behave as localized paramagnetic moments down to 2 K, irrespective of the Fe concentration and the density of beam-induced defects....

Pereira, Lino Miguel da Costa; Correia, João Guilherme; Van Bael, M J; Temst, Kristiaan; Vantomme, André; Araújo, João Pedro

2013-01-01

50

Paramagnetism and antiferromagnetic interactions in single-phase Fe-implanted ZnO  

NASA Astrophysics Data System (ADS)

As the intrinsic origin of the high-temperature ferromagnetism often observed in wide-gap dilute magnetic semiconductors becomes increasingly debated, there is a growing need for comprehensive studies on the single-phase region of the phase diagram of these materials. Here we report on the magnetic and structural properties of Fe-doped ZnO prepared by ion implantation of ZnO single crystals. A detailed structural characterization shows that the Fe impurities substitute for Zn in ZnO in a wurtzite Zn1-xFexO phase which is coherent with the ZnO host. In addition, the density of beam-induced defects is progressively decreased by thermal annealing up to 900?° C, from highly disordered after implantation to highly crystalline upon subsequent annealing. Based on a detailed analysis of the magnetometry data, we demonstrate that isolated Fe impurities occupying Zn-substitutional sites behave as localized paramagnetic moments down to 2 K, irrespective of the Fe concentration and the density of beam-induced defects. With increasing local concentration of Zn-substitutional Fe, strong nearest-cation-neighbor antiferromagnetic interactions favor the antiparallel alignment of the Fe moments.

Pereira, L. M. C.; Wahl, U.; Correia, J. G.; Van Bael, M. J.; Temst, K.; Vantomme, A.; Araújo, J. P.

2013-10-01

51

Paramagnetism and antiferromagnetic interactions in single-phase Fe-implanted ZnO.  

PubMed

As the intrinsic origin of the high-temperature ferromagnetism often observed in wide-gap dilute magnetic semiconductors becomes increasingly debated, there is a growing need for comprehensive studies on the single-phase region of the phase diagram of these materials. Here we report on the magnetic and structural properties of Fe-doped ZnO prepared by ion implantation of ZnO single crystals. A detailed structural characterization shows that the Fe impurities substitute for Zn in ZnO in a wurtzite Zn(1-x)Fe(x)O phase which is coherent with the ZnO host. In addition, the density of beam-induced defects is progressively decreased by thermal annealing up to 900 ° C, from highly disordered after implantation to highly crystalline upon subsequent annealing. Based on a detailed analysis of the magnetometry data, we demonstrate that isolated Fe impurities occupying Zn-substitutional sites behave as localized paramagnetic moments down to 2 K, irrespective of the Fe concentration and the density of beam-induced defects. With increasing local concentration of Zn-substitutional Fe, strong nearest-cation-neighbor antiferromagnetic interactions favor the antiparallel alignment of the Fe moments. PMID:24025311

Pereira, L M C; Wahl, U; Correia, J G; Van Bael, M J; Temst, K; Vantomme, A; Araújo, J P

2013-10-16

52

A single-molecule approach to ZnO defect studies: single photons and single defects  

E-print Network

Investigations that probe defects one at a time offer a unique opportunity to observe properties and dynamics that are washed out of ensemble measurements. Here we present confocal fluorescence measurements of individual defects in Al-doped ZnO nanoparticles and undoped ZnO sputtered films that are excited with sub-bandgap energy light. Photon correlation measurements yield both antibunching and bunching, indicative of single-photon emission from isolated defects that possess a metastable shelving state. The single-photon emission is in the range 560 - 720 nm and typically exhibits two broad spectral peaks separated by approximately 150 meV. The excited state lifetimes range from 1 - 13 ns, consistent with the finite-size and surface effects of nanoparticles and small grains. We also observe discrete jumps in the fluorescence intensity between a bright state and a dark state. The dwell times in each state are exponentially distributed and the average dwell time in the bright (dark) state does (may) depend on the power of the exciting laser. Taken together, our measurements demonstrate the utility of a single-molecule approach to semiconductor defect studies and highlight ZnO as a potential host material for single-defect based applications.

N. R. Jungwirth; Y. Y. Pai; H. S. Chang; E. R. MacQuarrie; G. D. Fuchs

2014-02-07

53

Deep-level emission in ZnO nanowires and bulk crystals: Excitation-intensity dependence versus crystalline quality  

SciTech Connect

The excitation-intensity dependence of the excitonic near-band-edge emission (NBE) and deep-level related emission (DLE) bands in ZnO nanowires and bulk crystals is studied, which show distinctly different power laws. The behavior can be well explained with a rate-equation model taking into account deep donor and acceptor levels with certain capture cross sections for electrons from the conduction band and different radiative lifetimes. In addition, a further crucial ingredient of this model is the background n-type doping concentration inherent in almost all ZnO single crystals. The interplay of the deep defects and the background free-electron concentration in the conduction band at room temperature reproduces the experimental results well over a wide range of excitation intensities (almost five orders of magnitude). The results demonstrate that for many ZnO bulk samples and nanostructures, the relative intensity R?=?I{sub NBE}/I{sub DLE} can be adjusted over a wide range by varying the excitation intensity, thus, showing that R should not be taken as an indicator for the crystalline quality of ZnO samples unless absolute photoluminescence intensities under calibrated excitation conditions are compared. On the other hand, the results establish an all-optical technique to determine the relative doping levels in different ZnO samples by measuring the excitation-intensity dependence of the UV and visible luminescence bands.

Hou, Dongchao; Voss, Tobias [Institute of Solid State Physics, University of Bremen, Bremen (Germany); Ronning, Carsten [Institute of Solid State Physics, University of Jena, Jena (Germany); Menzel, Andreas; Zacharias, Margit [Institute of Microsystems Engineering, IMTEK, University of Freiburg, Freiburg (Germany)

2014-06-21

54

Defect spectroscopy of single ZnO microwires  

NASA Astrophysics Data System (ADS)

The point defects of single ZnO microwires grown by carbothermal reduction were studied by microphotoluminescence, photoresistance excitation spectra, and resistance as a function of the temperature. We found the deep level defect density profile along the microwire showing that the concentration of defects decreases from the base to the tip of the microwires and this effect correlates with a band gap narrowing. The results show a characteristic deep defect levels inside the gap at 0.88 eV from the top of the VB. The resistance as a function of the temperature shows defect levels next to the bottom of the CB at 110 meV and a mean defect concentration of 4 × 1018 cm-3. This combination of techniques allows us to study the band gap values and defects states inside the gap in single ZnO microwires and opens the possibility to be used as a defect spectroscopy method.

Villafuerte, M.; Ferreyra, J. M.; Zapata, C.; Barzola-Quiquia, J.; Iikawa, F.; Esquinazi, P.; Heluani, S. P.; de Lima, M. M.; Cantarero, A.

2014-04-01

55

Ultraviolet lasing in high-order bands of three-dimensional ZnO photonic crystals  

E-print Network

. The photonic crystals are inverse opals with high refractive index contrast that simultaneously confine light the fabrication of ZnO inverse opals.13 ZnO has a wide, direct electronic band gap 3.3 eV and a high exciton to a variety of materials.16,17 Polystyrene opal templates are deposited by self-assembly onto glass substrates

Yamilov, Alexey

56

Multimode Resistive Switching in Single ZnO Nanoisland System  

PubMed Central

Resistive memory has attracted a great deal of attention as an alternative to contemporary flash memory. Here we demonstrate an interesting phenomenon that multimode resistive switching, i.e. threshold-like, self-rectifying and ordinary bipolar switching, can be observed in one self-assembled single-crystalline ZnO nanoisland with base diameter and height ranging around 30 and 40?nm on Si at different levels of current compliance. Current-voltage characteristics, conductive atomic force microscopy (C-AFM), and piezoresponse force microscopy results show that the threshold-like and self-rectifying types of switching are controlled by the movement of oxygen vacancies in ZnO nanoisland between the C-AFM tip and Si substrate while ordinary bipolar switching is controlled by formation and rupture of conducting nano-filaments. Threshold-like switching leads to a very small switching power density of 1 × 103?W/cm2. PMID:23934276

Qi, Jing; Olmedo, Mario; Zheng, Jian-Guo; Liu, Jianlin

2013-01-01

57

Multimode resistive switching in single ZnO nanoisland system.  

PubMed

Resistive memory has attracted a great deal of attention as an alternative to contemporary flash memory. Here we demonstrate an interesting phenomenon that multimode resistive switching, i.e. threshold-like, self-rectifying and ordinary bipolar switching, can be observed in one self-assembled single-crystalline ZnO nanoisland with base diameter and height ranging around 30 and 40 nm on Si at different levels of current compliance. Current-voltage characteristics, conductive atomic force microscopy (C-AFM), and piezoresponse force microscopy results show that the threshold-like and self-rectifying types of switching are controlled by the movement of oxygen vacancies in ZnO nanoisland between the C-AFM tip and Si substrate while ordinary bipolar switching is controlled by formation and rupture of conducting nano-filaments. Threshold-like switching leads to a very small switching power density of 1 × 10(3) W/cm(2). PMID:23934276

Qi, Jing; Olmedo, Mario; Zheng, Jian-Guo; Liu, Jianlin

2013-01-01

58

Nondestructive In Situ Identification of Crystal Orientation of Anisotropic ZnO  

E-print Network

Nondestructive In Situ Identification of Crystal Orientation of Anisotropic ZnO Nanostructures, a fast, unambiguous, and nondestructive technique for identification of the crystalline orientation nondestructive tool to probe the chemical composition, physical state, phonon confinement, and lattice dynamics

Wang, Zhong L.

59

Thermal Degradation of Single Crystal Zinc Oxide and the Growth of Nanostructures  

SciTech Connect

Heat treatment of (0001) single crystal zinc oxide (ZnO) seems to degrade the surface morphology at high temperature. The degradation, however, does not suppress the growth of ZnO nanostructures on selective regions of the single crystal ZnO that have been sputtered with metallic zinc (Zn) and annealed at 800 degree sign C. On the uncoated regions, no growth occurs but the presence of pits suggests material loss from the surface. The formation of ZnO nanostructures on the selective regions could be aided by the preferential loss of oxygen as well as zinc suboxides from the uncoated regions. Indirect evidence of the role of oxygen and zinc suboxides can be inferred from the formation of nickel zinc oxide Ni{sub 0.9}Zn{sub 0.1}O and nickel oxide NiO{sub 2} when Zn is replaced by Ni and annealed under similar conditions.

Saw, K. G.; Tan, G. L. [Physics Section, School of Distance Education, Universiti Sains Malaysia, 11800 Penang (Malaysia); Hassan, Z.; Yam, F. K.; Ng, S. S. [Schools of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia)

2010-07-07

60

Formation of quasi-single crystalline porous ZnO nanostructures with a single large cavity  

NASA Astrophysics Data System (ADS)

We report a method for synthesizing quasi-single crystalline porous ZnO nanostructures containing a single large cavity. The microwave-assisted route consists of a short (about 2 min) temperature ramping stage (from room temperature to 120 °C) and a stage in which the temperature is maintained at 120 °C for 2 h. The structures produced by this route were 200-480 nm in diameter. The morphological yields of this method were very high. The temperature- and time-dependent evolution of the synthesized powders and the effects of an additive, vitamin C, were studied. Spherical amorphous/polycrystalline structures (70-170 nm in diameter), which appeared transitorily, may play a key role in the formation of the single crystalline porous hollow ZnO nanostructures. Studies and characterization of the nanostructures suggested a possible mechanism for formation of the quasi-single crystalline porous ZnO nanostructures with an interior space.We report a method for synthesizing quasi-single crystalline porous ZnO nanostructures containing a single large cavity. The microwave-assisted route consists of a short (about 2 min) temperature ramping stage (from room temperature to 120 °C) and a stage in which the temperature is maintained at 120 °C for 2 h. The structures produced by this route were 200-480 nm in diameter. The morphological yields of this method were very high. The temperature- and time-dependent evolution of the synthesized powders and the effects of an additive, vitamin C, were studied. Spherical amorphous/polycrystalline structures (70-170 nm in diameter), which appeared transitorily, may play a key role in the formation of the single crystalline porous hollow ZnO nanostructures. Studies and characterization of the nanostructures suggested a possible mechanism for formation of the quasi-single crystalline porous ZnO nanostructures with an interior space. Electronic supplementary information (ESI) available: TEM images and the corresponding SAED image of a ZnO nanostructure synthesized from the reaction without l(+)-ascorbic acid at the 85 °C time point (Fig. S1). See DOI: 10.1039/c1nr10609k

Cho, Seungho; Kim, Semi; Jung, Dae-Won; Lee, Kun-Hong

2011-09-01

61

Single Crystal Silicon Instrument Mirrors  

NASA Technical Reports Server (NTRS)

The goals for the fabrication of single crystal silicon instrument mirrors include the following: 1) Develop a process for fabricating lightweight mirrors from single crystal silicon (SCS); 2) Modest lightweighting: 3X to 4X less than equivalent solid mirror; 3) High surface quality, better than lambda/40 RMS @ 633nm; 4) Significantly less expensive than current technology; and 5) Negligible distortion when cooled to cryogenic temperatures.

Bly, Vince

2007-01-01

62

A multistep single-crystal-to-single-crystal bromodiacetylene dimerization  

NASA Astrophysics Data System (ADS)

Packing constraints and precise placement of functional groups are the reason that organic molecules in the crystalline state often display unusual physical or chemical properties not observed in solution. Here we report a single-crystal-to-single-crystal dimerization of a bromodiacetylene that involves unusually large atom displacements as well as the cleavage and formation of several bonds. Density functional theory computations support a mechanism in which the dimerization is initiated by a [2 + 1] photocycloaddition favoured by the nature of carbon-carbon short contacts in the crystal structure. The reaction proceeded up to the theoretical degree of conversion without loss of crystallinity, and it was also performed on a preparative scale with good yield. Moreover, it represents the first synthetic pathway to (E)-1,2-dibromo-1,2-diethynylethenes, which could serve as synthetic intermediates for the preparation of molecular carbon scaffolds. Our findings both extend the scope of single-crystal-to-single-crystal reactions and highlight their potential as a synthetic tool for complex transformations.

Hoheisel, Tobias N.; Schrettl, Stephen; Marty, Roman; Todorova, Tanya K.; Corminboeuf, Clémence; Sienkiewicz, Andrzej; Scopelliti, Rosario; Schweizer, W. Bernd; Frauenrath, Holger

2013-04-01

63

A multistep single-crystal-to-single-crystal bromodiacetylene dimerization.  

PubMed

Packing constraints and precise placement of functional groups are the reason that organic molecules in the crystalline state often display unusual physical or chemical properties not observed in solution. Here we report a single-crystal-to-single-crystal dimerization of a bromodiacetylene that involves unusually large atom displacements as well as the cleavage and formation of several bonds. Density functional theory computations support a mechanism in which the dimerization is initiated by a [2 + 1] photocycloaddition favoured by the nature of carbon-carbon short contacts in the crystal structure. The reaction proceeded up to the theoretical degree of conversion without loss of crystallinity, and it was also performed on a preparative scale with good yield. Moreover, it represents the first synthetic pathway to (E)-1,2-dibromo-1,2-diethynylethenes, which could serve as synthetic intermediates for the preparation of molecular carbon scaffolds. Our findings both extend the scope of single-crystal-to-single-crystal reactions and highlight their potential as a synthetic tool for complex transformations. PMID:23511422

Hoheisel, Tobias N; Schrettl, Stephen; Marty, Roman; Todorova, Tanya K; Corminboeuf, Clémence; Sienkiewicz, Andrzej; Scopelliti, Rosario; Schweizer, W Bernd; Frauenrath, Holger

2013-04-01

64

High brightness light emitting diode based on single ZnO microwire  

NASA Astrophysics Data System (ADS)

The ZnO microwires were synthesized repetitively via chemical vapor deposition method. The high power light emitting diode based on the single ZnO microwire/p-GaN heterojunction was realized. A strong ultraviolet emission accompanied by a relatively weak defects-related emission was observed at room temperature photoluminescence spectra of single ZnO microwire. The I-V curve of the heterojunction diode showed obvious rectifying characteristics with a turn-on voltage of about 7 V. Under the forward injection current of 1.1 mA, the ultraviolet electroluminescence centered at 389 nm wavelength could be obtained based on the single ZnO microwire/p-GaN heterojunction diode.

Ding, Meng; Zhao, Dongxu; Yao, Bin; Zhao, Bin; Xu, Xijin

2013-07-01

65

Space-selective precipitation of ZnO crystals in glass by using high repetition rate femtosecond laser irradiation.  

PubMed

We report on three-dimensional (3D) precipitation of ZnO crystals inside a silicate glass by a 500 kHz femtosecond pulse laser. The precipitation and distribution of ZnO crystals in glass are confirmed and analyzed by Raman spectra and Raman mapping. Mirco- luminescence is observed in the laser modified region when excited by femtosecond pulse laser or Xenon lamp. The effect of laser average power on the precipitation of the ZnO crystals has also been investigated. The possibility of 3D optical data storage using the observed phenomena is demonstrated. PMID:25089411

Du, Xi; Zhang, Hang; Cheng, Chen; Zhou, Shifeng; Zhang, Fangteng; Yu, Yongze; Dong, Guoping; Qiu, Jianrong

2014-07-28

66

Optical injection probing of single ZnO tetrapod lasers  

SciTech Connect

The properties of zinc oxide (ZnO) nanotetrapod lasers are characterized by a novel ultrafast two-color pump/stimulated emission probe technique. Single legs of tetrapod species are isolated by a microscope objective, pumped by 267 nm pulses, and subjected to a time-delayed 400 nm optical injection pulse, which permits investigation of the ultrafast carrier dynamics in the nanosize materials. With the optical injection pulse included, a large increase in the stimulated emission at 400 nm occurs, which partially depletes the carriers at this wavelength and competes with the normal 390 nm lasing. At the 390 nm lasing wavelengths, the optical injection causes a decrease in the stimulated emission due to the energetic redistribution of the excited carrier depletion, which occurs considerably within the time scale of the subpicosecond duration of the injection pulse. The effects of the optical injection on the spectral gain are employed to probe the lasing dynamics, which shows that the full width at half maximum of the lasing time is 3 ps.

Szarko, Jodi M.; Song, Jae Kyu; Blackledge, Charles Wesley; Swart, Ingmar; Leone, Stephen R.; Li, Shihong; Zhao, Yiping

2004-11-23

67

A general single-pot heating method for morphology, size and luminescence-controllable synthesis of colloidal ZnO nanocrystals.  

PubMed

Here we demonstrate a single-pot heating approach for controllable synthesis of colloidal zinc oxide nanocrystals from zinc acetylacetonate. Such single-pot heating approaches are inherently amenable to large scale production. We have systematically studied the crystallization process, investigating the growth of nanocrystals and the influence of ligands on the morphology and luminescence of ZnO nanoparticles. We show that the morphology can be tuned to produce dendritic structures, nano-needles, nano-pinecones, nanoclusters, hexagonal pyramid nanoparticles and irregularly-shaped nanoparticles by varying the surfactants and co-surfactants used in synthesis. Moreover, we investigated the effect of ligands on the defect-related photoluminescence of ZnO NPs and demonstrated blue, green, white, yellow, and orange emission. This study opens up new possibilities for the practical use of ZnO nanomaterials for optoelectronic devices and bio-imaging. PMID:23873224

Liu, Xin; Swihart, Mark T

2013-09-01

68

Homoepitaxial ZnO Film Growth  

NASA Technical Reports Server (NTRS)

ZnO films have high potential for many applications, such as surface acoustic wave filters, UV detectors, and light emitting devices due to its structural, electrical, and optical properties. High quality epitaxial films are required for these applications. The Al2O3 substrate is commonly used for ZnO heteroepitaxial growth. Recently, high quality ZnO single crystals are available for grow homoepitaxial films. Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films were also deposited on (0001) Al2O3 substrates. It was found that the two polar ZnO surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which strongly influence the epitaxial film growth. The morphology and structure of homoepitaxial films grown on the ZnO substrates were different from heteroepitaxial films grown on the Al2O3. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

Zhu, Shen; Su, C-H; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; McCarty, P.; George, M. A.; Rose, M. Franklin (Technical Monitor)

2000-01-01

69

Materialization of single multicomposite nanowire: entrapment of ZnO nanoparticles in polyaniline nanowire  

PubMed Central

We present materialization of single multicomposite nanowire (SMNW)-entrapped ZnO nanoparticles (NPs) via an electrochemical growth method, which is a newly developed fabrication method to grow a single nanowire between a pair of pre-patterned electrodes. Entrapment of ZnO NPs was controlled via different conditions of SMNW fabrication such as an applied potential and mixture ratio of NPs and aniline solution. The controlled concentration of ZnO NP results in changes in the physical properties of the SMNWs, as shown in transmission electron microscopy images. Furthermore, the electrical conductivity and elasticity of SMNWs show improvement over those of pure polyaniline nanowire. The new nano-multicomposite material showed synergistic effects on mechanical and electrical properties, with logarithmical change and saturation increasing ZnO NP concentration. PMID:21711928

2011-01-01

70

A general single-pot heating method for morphology, size and luminescence-controllable synthesis of colloidal ZnO nanocrystals  

NASA Astrophysics Data System (ADS)

Here we demonstrate a single-pot heating approach for controllable synthesis of colloidal zinc oxide nanocrystals from zinc acetylacetonate. Such single-pot heating approaches are inherently amenable to large scale production. We have systematically studied the crystallization process, investigating the growth of nanocrystals and the influence of ligands on the morphology and luminescence of ZnO nanoparticles. We show that the morphology can be tuned to produce dendritic structures, nano-needles, nano-pinecones, nanoclusters, hexagonal pyramid nanoparticles and irregularly-shaped nanoparticles by varying the surfactants and co-surfactants used in synthesis. Moreover, we investigated the effect of ligands on the defect-related photoluminescence of ZnO NPs and demonstrated blue, green, white, yellow, and orange emission. This study opens up new possibilities for the practical use of ZnO nanomaterials for optoelectronic devices and bio-imaging.Here we demonstrate a single-pot heating approach for controllable synthesis of colloidal zinc oxide nanocrystals from zinc acetylacetonate. Such single-pot heating approaches are inherently amenable to large scale production. We have systematically studied the crystallization process, investigating the growth of nanocrystals and the influence of ligands on the morphology and luminescence of ZnO nanoparticles. We show that the morphology can be tuned to produce dendritic structures, nano-needles, nano-pinecones, nanoclusters, hexagonal pyramid nanoparticles and irregularly-shaped nanoparticles by varying the surfactants and co-surfactants used in synthesis. Moreover, we investigated the effect of ligands on the defect-related photoluminescence of ZnO NPs and demonstrated blue, green, white, yellow, and orange emission. This study opens up new possibilities for the practical use of ZnO nanomaterials for optoelectronic devices and bio-imaging. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02571c

Liu, Xin; Swihart, Mark T.

2013-08-01

71

Imaging and characterization of piezoelectric potential in a single bent ZnO microwire  

NASA Astrophysics Data System (ADS)

We achieved direct visualization of the piezoelectric potentials in a single bent ZnO microwire (MW) using focused synchrotron radiation (soft x-ray) scanning photoelectron spectro-microscopy. Using radial-line scan across the bent section of ZnO MW, the characteristic core-level shifts were directly related to the spatial distribution of piezoelectric potentials perpendicular to the ZnO polar direction. Using piezoelectric modeling in ZnO, we delineated the band structure distortion and carrier concentration change from tensile to compressed sides by combining the spatial resolved cathodoluminescence characteristics in an individual microwire. This spectro-microscopic technique allows imaging and identification of the electric-mechanical couplings in piezoelectric micro-/nano-wire systems.

Wang, Chiang-Lun; Tsai, Shu-Ju; Chen, Jhih-Wei; Shiu, Hong-Wei; Chang, Lo-Yueh; Lin, Kai-Hsiang; Hsu, Hsu-Cheng; Chen, Yi-Chun; Chen, Chia-Hao; Wu, Chung-Lin

2014-09-01

72

Single-crystalline twinned ZnO nanoleaf structure via a facile hydrothermal process.  

PubMed

A single-crystalline twinned ZnO nanostructure with a 2-dimensional leaf-like morphology (nanoleaves) was synthesized using a facile hydrothermal strategy. The ZnO nanoleaves had 2-fold symmetric branches, which were identified by the existence of an inversion domain boundary (IDB) along the [2110] growth direction of the ribbon-like stems with both side surfaces of the stems terminated with a chemically active Zn-(0001) plane. A proposed growth mechanism suggested that the formation of IDB and the leaf-like shape are related to the dissolution of seed particles on the substrate surfaces and an OH- shielding effect in solution, respectively. Optical measurements revealed visible emission, suggesting the possession of defects in the as-grown and annealed ZnO nanoleaves. In addition, various ZnO nanostructures were synthesized by simply controlling the fabrication conditions. PMID:21449366

Qiu, Jijun; Lil, Xiaomin; Gao, Xiangdong; Gan, Xiaoyan; He, Weizhen; Kim, Hyung-Kook; Hwang, Yoon-Hwae

2011-03-01

73

Nanostructured Calcite Single Crystals with Gyroid Morphologies  

E-print Network

Nanostructured Calcite Single Crystals with Gyroid Morphologies By Alexander S. Finnemore, Maik R of which has a complex, sponge-like structure, and yet is a single crystal of calcite.[2] In contrast calcite crystals. Biologically controlled mineralization depends on the interplay between a number

Steiner, Ullrich

74

Enhancement of Photoluminescence and Electrical Properties of Ga-Doped ZnO Thin Film Grown on alpha-Al2O3(0001) Single-Crystal Substrate by rf Magnetron Sputtering through Rapid Thermal Annealing  

Microsoft Academic Search

Ga2O3 (1 wt%)-doped ZnO (GZO) thin films were deposited on alpha-Al2O3(0001) by rf magnetron sputtering at 550^\\\\circC and a polycrystalline structure was obtained. As-grown GZO thin films show poor electrical properties and photoluminescence (PL). For the improvement of these properties, GZO thin films were annealed at 800-900^\\\\circC in N2 atmosphere for 3 min. After rapid thermal annealing, deep-defect-level emission disappears

Jung Cho; Jongbum Nah; Min-Seok Oh; Jae-Hoon Song; Ki-Hyun Yoon; Hyung-Jin Jung; Won-Kook Choi

2001-01-01

75

Interdigitated single crystal piezoelectric actuator  

NASA Astrophysics Data System (ADS)

Piezoelectric actuators are used as critical units or elements of various electromechanical systems. In this paper, we propose a novel piezoelectric actuator cantilever with double interdigitated electrode patterns. We investigate the possibility of both flexural and longitudinal actuation capabilities of the double interdigitated electrode patterns applied on a piezoelectric cantilever structure. This monomorph structure has the interdigitated electrode patterns top and bottom. The structure also uses single-crystal relaxor ferroelectric material. We separately pattern interdigitated electrodes on the top and bottom surfaces of a PMN-PT single crystal cantilever beam. The interdigitated electrode design on a surface of the cantilever beam results in an electric field gradient. This results in a flapping actuation. Previously, we showed that the vertical field component induced by the interdigitated electrode is dominant over the horizontal component under input bias voltage, and generates subsequent contraction of the surface along the axial direction after poling. In this paper, we show that a contraction on the top surface and an elongation on the bottom leads to upward bending motion because of the differential contraction along the thickness induced by the interdigitated electrode pattern. Similarly, an equivalent elongation on the top and bottom surfaces is shown to lead to longitudinal motion in the double interdigitated electrode sample.

Hong, Yong K.; Moon, Kee S.

2005-12-01

76

Titania single crystals with a curved surface  

NASA Astrophysics Data System (ADS)

Owing to its scientific and technological importance, crystallization as a ubiquitous phenomenon has been widely studied over centuries. Well-developed single crystals are generally enclosed by regular flat facets spontaneously to form polyhedral morphologies because of the well-known self-confinement principle for crystal growth. However, in nature, complex single crystalline calcitic skeleton of biological organisms generally has a curved external surface formed by specific interactions between organic moieties and biocompatible minerals. Here we show a new class of crystal surface of TiO2, which is enclosed by quasi continuous high-index microfacets and thus has a unique truncated biconic morphology. Such single crystals may open a new direction for crystal growth study since, in principle, crystal growth rates of all facets between two normal {101} and {011} crystal surfaces are almost identical. In other words, the facet with continuous Miller index can exist because of the continuous curvature on the crystal surface.

Yang, Shuang; Yang, Bing Xing; Wu, Long; Li, Yu Hang; Liu, Porun; Zhao, Huijun; Yu, Yan Yan; Gong, Xue Qing; Yang, Hua Gui

2014-11-01

77

Growth of ZnSe single crystals  

Microsoft Academic Search

The growth conditions of ZnSe single crystals were investigated by chemical vapor transport (CVT) and physical vapor transport (PVT) methods. The growth temperatures were about 850°C (CVT) and 1100°C (PVT). Single crystals of 18–20mm diameter, 30mm long and orange colored were grown. The homogeneity of crystals was measured. The etch pit density of good crystals is in the range of

C. S Fang; Q. T Gu; J. Q Wei; Q. W Pan; W Shi; J. Y Wang

2000-01-01

78

Improvement in microstructure and crystal alignment of ZnO films grown by metalorganic chemical vapor deposition using a seed layer  

Microsoft Academic Search

An epitaxially aligned ZnO nano-seed layer was used to improve the microstructure and crystal alignment in metalorganic chemical vapor deposited ZnO films on Al2O3 (0 0 0 1) substrates. Comparative investigations were performed on the properties of the ZnO films grown with and without the seed layer. The ZnO film grown directly on the substrate without applying the seed layer

Jae Young Park; Dong Ju Lee; Byung-Teak Lee; Jong Ha Moon; Sang Sub Kim

2005-01-01

79

Improvement in microstructure and crystal alignment of ZnO films grown by metalorganic chemical vapor deposition using a seed layer  

Microsoft Academic Search

An epitaxially aligned ZnO nano-seed layer was used to improve the microstructure and crystal alignment in metalorganic chemical vapor deposited ZnO films on Al2O3 (0001) substrates. Comparative investigations were performed on the properties of the ZnO films grown with and without the seed layer. The ZnO film grown directly on the substrate without applying the seed layer shows an irregular,

Jae Young Park; Dong Ju Lee; Byung-Teak Lee; Jong Ha Moon; Sang Sub Kim

2005-01-01

80

Resistive switching in single epitaxial ZnO nanoislands.  

PubMed

Resistive memory is one of the most promising candidates for next-generation nonvolatile memory technology due to its variety of advantages, such as simple structure and low-power consumption. Bipolar resistive switching behavior was observed in epitaxial ZnO nanoislands with base diameters and heights ranging around 30 and 40 nm, respectively. All four different states (initial, electroformed, ON, and OFF) of the nanoscale resistive memories were measured by conductive atomic force microscopy immediately after the voltage sweeping was performed. Auger electron spectroscopy and other experiments were also carried out to investigate the switching mechanism. The formation and rupture of conducting filaments induced by oxygen vacancy migration are responsible for the resistive switching behaviors of ZnO resistive memories at the nanoscale. PMID:22257020

Qi, Jing; Olmedo, Mario; Ren, Jingjian; Zhan, Ning; Zhao, Jianze; Zheng, Jian-Guo; Liu, Jianlin

2012-02-28

81

Optical studies of anthracene single crystals  

Microsoft Academic Search

Recently the polyacene crystals such as pentacene, tetracene and anthracene have attracted great interest both in research and applications. These ultra-pure molecular crystals are very promising materials for FETs, organic photovoltaic diodes, LEDs and lasing. High purity anthracene crystal have been grown by physical vapor transport. High photo luminecense (PL) quantum efficiency(over 20%) was observed in these pure anthracene single

Yuhong Jiang; Matthew Delong; Z. Valy Vardeny

2001-01-01

82

Domain Engineered Relaxor Ferroelectric Single Crystals  

NASA Astrophysics Data System (ADS)

Single crystal relaxor ferroelectric materials exhibit extraordinary electromechanical properties. They are being applied in high performance sensors, actuators, and transducers. Field induced polarization switching and phase transitions of these crystals lead to complex nonlinear behavior. In recent years experimental investigations have been conducted to characterize the polarization switching and phase transition behavior as a function of crystallographic orientation, temperature, electric field, and stress. The results give insight into the mechanism underlying the observed large field hysteretic behavior. This review article describes the observed behavior and presents results of multiscale modeling that predicts the macroscopic behavior from the single domain single crystal behavior and evolution of crystal variants at the microscale.

Liu, T.; Lynch, C. S.

2006-08-01

83

Inkjet printing of single-crystal films  

Microsoft Academic Search

The use of single crystals has been fundamental to the development of semiconductor microelectronics and solid-state science. Whether based on inorganic or organic materials, the devices that show the highest performance rely on single-crystal interfaces, with their nearly perfect translational symmetry and exceptionally high chemical purity. Attention has recently been focused on developing simple ways of producing electronic devices by

Hiromi Minemawari; Toshikazu Yamada; Hiroyuki Matsui; Jun'ya Tsutsumi; Simon Haas; Ryosuke Chiba; Reiji Kumai; Tatsuo Hasegawa

2011-01-01

84

Method of making single crystal fibers  

NASA Technical Reports Server (NTRS)

Single crystal fibers are made from miniature extruded ceramic feed rods. A decomposable binder is mixed with powders to inform a slurry which is extruded into a small rod which may be sintered, either in air or in vacuum, or it may be used in the extruded and dried condition. A pair of laser beams focuses onto the tip of the rod to melt it thereby forming a liquid portion. A single crystal seed fiber of the same material as the feed rod contacts this liquid portion to establish a zone of liquid material between the feed rod and the single crystal seed fiber. The feed rod and the single crystal feed fiber are moved at a predetermined speed to solidify the molten zone onto the seed fiber while simultaneously melting additional feed rod. In this manner a single crystal fiber is formed from the liquid portion.

Westfall, Leonard J. (inventor)

1990-01-01

85

Organic single-crystal complementary inverter  

NASA Astrophysics Data System (ADS)

The authors demonstrate the operation of an organic single-crystal complementary circuit in the form of a simple inverter. The device is constructed from a high mobility p-type organic single-crystal transistor of tetramethylpentacene (TMPC) and a n-type single-crystal transistor of N ,N'-di[2,4-difluorophenyl]-3,4,9,10-perylenetetracarboxylic diimide (PTCDI). Field-effect mobilities of up to 1.0cm2/Vs are reported for TMPC devices, while a mobility of 0.006cm2/Vs is reported for a n-type PTCDI single-crystal device. Considering that organic single-crystal inverters have not yet been explored, they are representative of potential candidates for use in high-performance complementary circuits.

Briseno, Alejandro L.; Tseng, Ricky J.; Li, Sheng-Han; Chu, Chih-Wei; Yang, Yang; Falcao, Eduardo H. L.; Wudl, Fred; Ling, Mang-Mang; Chen, Hong Zheng; Bao, Zhenan; Meng, Hong; Kloc, Christian

2006-11-01

86

Exciton recombination dynamics in single ZnO tetrapods  

SciTech Connect

We present the optical properties of individual ZnO tetrapods as a function of excitation power and temperature by time-integrated and time-resolved spectroscopy. At 10K, we identify the different excitonic transitions by both their characteristic energy and their excitation power dependence. When we increase the tetrapod temperature we observe that the emission intensity decrease and occur a red shift of the emission energies. Our time-resolved studies confirm the predominance of the radiative recombination at low temperatures (< 45 K). Increasing the temperature opens up the non-radiative channels, which are evidenced by a much faster decay time.

Fernandes-Silva, Lígia C. [Departamento de Física de Materiales, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Martín, Maria D.; Meulen, Herko P. van der; Calleja, José M.; Viña, Luis [Departamento de Física de Materiales, Universidad Autónoma de Madrid, E-28049 Madrid, Spain and Instituto de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Klopotowski, Lukasz [Polish Academy of Sciences, Institute of Physics, 02-668 Warsaw (Poland)

2013-12-04

87

Homojunction p-n photodiodes based on As-doped single ZnO nanowire  

SciTech Connect

Photovoltaic device was successfully grown solely based on the single ZnO p-n homojunction nanowire. The ZnO nanowire p-n diode consists of an as-grown n-type segment and an in-situ arsenic doped p-type segment. This p-n homojunction acts as a good photovoltaic cell, producing a photocurrent almost 45 times larger than the dark current under reverse-biased condition. Our results demonstrate that present ZnO p-n homojunction nanowire can be used as a self-powered ultraviolet photodetector as well as a photovoltaic cell, which can also be used as an ultralow electrical power source for nano-scale electronic, optoelectronic, and medical devices.

Cho, H. D.; Zakirov, A. S.; Yuldashev, Sh. U.; Kang, T. W. [Quantum-Functional Semiconductor Research Center, Dongguk Univ.-Seoul, Seoul 100-715 (Korea, Republic of); Ahn, C. W. [Nano-materials Lab. National Nanofab Center at KAIST, 335 Gwahangno, Daejeon 305-806 (Korea, Republic of); Yeo, Y. K. [Department of Engineering Physics, Air Force Institute of Technology,Wright-Patterson AFB, OH 45433 (United States)

2013-12-04

88

White upconversion of rare-earth doped ZnO nanocrystals and its dependence on size of crystal particles and content of Yb3+ and Tm3+  

NASA Astrophysics Data System (ADS)

Rare earth (RE) doped ZnO nanocrystals were synthesized by chemical combustion method. Bright white upconversion (UC) luminescence with the CIE coordinates close to (0.33, 0.33) was obtained in Er+Tm+Yb tridoped ZnO nanocrystals under the excitation of a cost-effective 980 nm single-wavelength laser diode. The overall and relative UC luminescence intensities of RE doped ZnO nanocrystals were found to be depended highly on the diameter of crystal particles and the concentration of Yb3+ and Tm3+, for which the involved mechanisms were demonstrated. The investigation based on UC spectra, simplified energy level diagram, and excitation power dependence indicated that the remarkable enhancement of the green emission of the RE tridoped sample was due to a dual sensitization of Er3+ by Yb3+ and Tm3+ ions. The RE tridoped ZnO nanocrystals with the CIE coordinates close to (0.33, 0.33) are potentially suitable for the widely realistic application as the multicolor fluorescent labels, due to a fact that they could be cheaply and easily obtained and excited cost effectively.

Liu, Yunxin; Xu, Changfu; Yang, Qibin

2009-04-01

89

Research Advances: Mass Spectrometric Monitoring of Animal Feed for BSE Spread; Ancient Oceans Had Less Oxygen; A Model for the Formation of Piezoelectric Single-Crystal Nanorings and Nanobows  

NASA Astrophysics Data System (ADS)

Recent work by Zhong L. Wang and William Hughes at Georgia Tech demonstrates that ZnO nanorods and nanobows formed by bending single crystal, PSD ZnO nanobelts exclusively supports the electrostatic polar charge model as the dominant bending mechanism.

King, Angela G.

2004-09-01

90

Characterizations of Ohmic and Schottky-behaving contacts of a single ZnO nanowire.  

PubMed

Current-voltage and Kelvin probe force microscopy (KPFM) measurements were performed on single ZnO nanowires. Measurements are shown to be strongly correlated with the contact behavior, either Ohmic or diode-like. The ZnO nanowires were obtained by metallo-organic chemical vapor deposition (MOCVD) and contacted using electronic-beam lithography. Depending on the contact geometry, good quality Ohmic contacts (linear I-V behavior) or non-linear (diode-like) contacts were obtained. Current-voltage and KPFM measurements on both types of contacted ZnO nanowires were performed in order to investigate their behavior. A clear correlation could be established between the I-V curve, the electrical potential profile along the device and the nanowire geometry. Some arguments supporting this behavior are given based on technological issues and on depletion region extension. This work will help to better understand the electrical behavior of Ohmic contacts on single ZnO nanowires, for future applications in nanoscale field-effect transistors and nano-photodetectors. PMID:24060613

Bercu, Bogdan; Geng, Wei; Simonetti, Olivier; Kostcheev, Sergei; Sartel, Corinne; Sallet, Vincent; Lérondel, Gilles; Molinari, Michaël; Giraudet, Louis; Couteau, Christophe

2013-10-18

91

Characterizations of Ohmic and Schottky-behaving contacts of a single ZnO nanowire  

NASA Astrophysics Data System (ADS)

Current-voltage and Kelvin probe force microscopy (KPFM) measurements were performed on single ZnO nanowires. Measurements are shown to be strongly correlated with the contact behavior, either Ohmic or diode-like. The ZnO nanowires were obtained by metallo-organic chemical vapor deposition (MOCVD) and contacted using electronic-beam lithography. Depending on the contact geometry, good quality Ohmic contacts (linear I-V behavior) or non-linear (diode-like) contacts were obtained. Current-voltage and KPFM measurements on both types of contacted ZnO nanowires were performed in order to investigate their behavior. A clear correlation could be established between the I-V curve, the electrical potential profile along the device and the nanowire geometry. Some arguments supporting this behavior are given based on technological issues and on depletion region extension. This work will help to better understand the electrical behavior of Ohmic contacts on single ZnO nanowires, for future applications in nanoscale field-effect transistors and nano-photodetectors.

Bercu, Bogdan; Geng, Wei; Simonetti, Olivier; Kostcheev, Sergei; Sartel, Corinne; Sallet, Vincent; Lérondel, Gilles; Molinari, Michaël; Giraudet, Louis; Couteau, Christophe

2013-10-01

92

Direct writing of 150 nm gratings and squares on ZnO crystal in water by using 800 nm femtosecond laser.  

PubMed

We present a controllable fabrication of nanogratings and nanosquares on the surface of ZnO crystal in water based on femtosecond laser-induced periodic surface structures (LIPSS). The formation of nanogrooves depends on both laser fluence and writing speed. A single groove with width less than 40 nm and double grooves with distance of 150 nm have been produced by manipulating 800 nm femtosecond laser fluence. Nanogratings with period of 150 nm, 300 nm and 1000 nm, and nanosquares with dimensions of 150 × 150 nm2 were fabricated by using this direct femtosecond laser writing technique. PMID:25607200

Liu, Jukun; Jia, Tianqing; Zhou, Kan; Feng, Donghai; Zhang, Shian; Zhang, Hongxin; Jia, Xin; Sun, Zhenrong; Qiu, Jianrong

2014-12-29

93

NEXAFS and XMCD studies of single-phase Co doped ZnO thin films.  

PubMed

A study of the electronic structure and magnetic properties of Co doped ZnO thin films synthesized by ion implantation followed by swift heavy ion irradiation is presented using near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) measurements. The spectral features of NEXAFS at the Co L(3,2)-edge show entirely different features than that of metallic Co clusters and other Co oxide phases. The atomic multiplet calculations are performed to determine the valence state, symmetry and the crystal field splitting, which show that in the present system Co is in the 2+ state and substituted at the Zn site in tetrahedral symmetry with 10Dq = -0.6 eV. The ferromagnetic character of these materials is confirmed through XMCD spectra. To rule out the possibilities of defect induced magnetism, the results are compared with Ar annealed and Ar-ion implanted pure ZnO thin films. The presented results confirm the substitution of Co at the Zn site in the ZnO matrix, which is responsible for room temperature ferromagnetism. PMID:21825451

Singh, Abhinav Pratap; Kumar, Ravi; Thakur, P; Brookes, N B; Chae, K H; Choi, W K

2009-05-01

94

Characterization of zinc selenide single crystals  

NASA Technical Reports Server (NTRS)

ZnSe single crystals of high quality and low impurity levels are desired for use as substrates in optoelectronic devices. This is especially true when the device requires the formation of homoepitaxial layers. While ZnSe is commercially available, it is at present extremely expensive due to the difficulty of growing single crystal boules with low impurity content and the resultant low yields. Many researchers have found it necessary to heat treat the crystals in liquid Zn in order to remove the impurities, lower the resistivity and activate the photoluminescence at room temperature. The physical vapor transport method (PVT) has been successfully used at MSFC to grow many single crystals of II-VI semiconducting materials including ZnSe. The main goal at NASA has been to try to establish the effect of gravity on the growth parameters. To this effect, crystals have been grown vertically upwards or horizontally. Both (111) and (110) oriented ZnSe crystals have been obtained via unseeded PVT growth. Preliminary characterization of the horizontally grown crystals has revealed that Cu is a major impurity and that the low temperature photoluminescence spectra is dominated by the copper peak. The ratio of the copper peak to the free exciton peak is being used to determine variations in composition throughout the crystal. It was the intent of this project to map the copper composition of various crystals via photoluminescence first, then measure their electrical resistivity and capacitance as a function of frequency before proceeding with a heat treatment designed to remove the copper impurities. However, equipment difficulties with the photoluminescence set up, having to establish a procedure for measuring the electrical properties of the as-grown crystals and time limitations made us re-evaluate the project goals. Vertically grown samples designated as ZnSe-25 were chosen to be measured electrically since they were not expected to show as much variation in their composition through their cross-section as the horizontally grown samples.

Gerhardt, Rosario A.

1996-01-01

95

The interaction of 193-nm excimer laser irradiation with single-crystal zinc oxide: Neutral atomic zinc and oxygen emission  

SciTech Connect

We report mass-resolved time-of-flight measurements of neutral particles from the surface of single-crystal ZnO during pulsed 193-nm irradiation at laser fluences below the threshold for avalanche breakdown. The major species emitted are atomic Zn and O. We examine the emissions of atomic Zn as a function of laser fluence and laser exposure. Defects at the ZnO surface appear necessary for the detection of these emissions. Our results suggest that the production of defects is necessary to explain intense sustained emissions at higher fluence. Rapid, clean surface etching and high atomic zinc kinetic energies seen at higher laser fluences are also discussed.

Kahn, E. H. [Washington State University; Langford, S. C. [Washington State University; Dickinson, J. T. [Washington State University; Boatner, Lynn A [ORNL

2013-01-01

96

Broadband single-polarization photonic crystal fiber  

Microsoft Academic Search

We demonstrate a single-mode photonic crystal fiber that supports only one polarization state in a 220-nm-broad spectral region centered at 727 nm. The fiber has a mode-field diameter of 15.5 mum and background losses of <15 dB\\/km in the single-polarization region. To our knowledge, these are the broadest bandwidth and the largest mode size yet reported for a single-polarization fiber.

J. R. Folkenberg; M. D. Nielsen; C. Jakobsen

2005-01-01

97

Oxygen Incorporation in Rubrene Single Crystals  

PubMed Central

Single crystal rubrene is a model organic electronic material showing high carrier mobility and long exciton lifetime. These properties are detrimentally affected when rubrene is exposed to intense light under ambient conditions for prolonged periods of time, possibly due to oxygen up-take. Using photoelectron, scanning probe and ion-based methods, combined with an isotopic oxygen exposure, we present direct evidence of the light-induced reaction of molecular oxygen with single crystal rubrene. Without a significant exposure to light, there is no reaction of oxygen with rubrene for periods of greater than a year; the crystal's surface (and bulk) morphology and chemical composition remain essentially oxygen-free. Grand canonical Monte Carlo computations show no sorbtion of gases into the bulk of rubrene crystal. A mechanism for photo-induced oxygen inclusion is proposed. PMID:24786311

Mastrogiovanni, Daniel D. T.; Mayer, Jeff; Wan, Alan S.; Vishnyakov, Aleksey; Neimark, Alexander V.; Podzorov, Vitaly; Feldman, Leonard C.; Garfunkel, Eric

2014-01-01

98

Neutron detection with single crystal organic scintillators  

SciTech Connect

Detection of high-energy neutrons in the presence of gamma radiation background utilizes pulse-shape discrimination (PSD) phenomena in organics studied previously only with limited number of materials, mostly liquid scintillators and single crystal stilbene. The current paper presents the results obtained with broader varieties of luminescent organic single crystals. The studies involve experimental tools of crystal growth and material characterization in combination with the advanced computer modeling, with the final goal of better understanding the relevance between the nature of the organic materials and their PSD properties. Special consideration is given to the factors that may diminish or even completely obscure the PSD properties in scintillating crystals. Among such factors are molecular and crystallographic structures that determine exchange coupling and exciton mobility in organic materials and the impurity effect discussed on the examples of trans-stilbene, bibenzyl, 9,10-diphenylanthracene and diphenylacetylene.

Zaitseva, N; Newby, J; Hamel, S; Carman, L; Faust, M; Lordi, V; Cherepy, N; Stoeffl, W; Payne, S

2009-07-15

99

Neutron detection with single crystal organic scintillators  

NASA Astrophysics Data System (ADS)

Detection of high-energy neutrons in the presence of gamma radiation background utilizes pulse-shape discrimination (PSD) phenomena in organics studied previously only with limited number of materials, mostly liquid scintillators and single crystal stilbene. The current paper presents the results obtained with broader varieties of luminescent organic single crystals. The studies involve experimental tools of crystal growth and material characterization in combination with the advanced computer modeling, with the final goal of better understanding the relevance between the nature of the organic materials and their PSD properties. Special consideration is given to the factors that may diminish or even completely obscure the PSD properties in scintillating crystals. Among such factors are molecular and crystallographic structures that determine exchange coupling and exciton mobility in organic materials and the impurity effect discussed on the examples of trans-stilbene, bibenzyl, 9,10- diphenylanthracene and diphenylacetylene.

Zaitseva, Natalia P.; Newby, Jason; Hamel, Sebastien; Carman, Leslie; Faust, Michelle; Lordi, Vincenzo; Cherepy, Nerine J.; Stoeffl, Wolfgang; Payne, Stephen A.

2009-08-01

100

Single crystals of metal solid solutions  

NASA Technical Reports Server (NTRS)

The following definitions were sought in the research on single crystals of metal solid solutions: (1) the influence of convection and/or gravity present during crystallization on the substructure of a metal solid solution; (2) the influence of a magnetic field applied during crystallization on the substructure of a metal solid solution; and (3) requirements for a space flight experiment to verify the results. Growth conditions for the selected silver-zinc alloy system are described, along with pertinent technical and experimental details of the project.

Miller, J. F.; Austin, A. E.; Richard, N.; Griesenauer, N. M.; Moak, D. P.; Mehrabian, M. R.; Gelles, S. H.

1974-01-01

101

First Single-Crystal Mullite Fibers  

NASA Technical Reports Server (NTRS)

Ceramic-matrix composites strengthened by suitable fiber additions are being developed for high-temperature use, particularly for aerospace applications. New oxide-based fibers, such as mullite, are particularly desirable because of their resistance to high-temperature oxidative environments. Mullite is a candidate material in both fiber and matrix form. The primary objective of this work was to determine the growth characteristics of single-crystal mullite fibers produced by the laser-heated floating zone method. Directionally solidified fibers with nominal mullite compositions of 3Al2O3 2SiO2 were grown by the laser-heated floating zone method at the NASA Lewis Research Center. SEM analysis revealed that the single-crystal fibers grown in this study were strongly faceted and that the facets act as critical flaws, limiting fiber strength. The average fiber tensile strength is 1.15 GPa at room temperature. The mullite fibers exhibit superior strength retention (80 percent of their room temperature tensile strength at 1450 C). Examined by transmission electron microscopy, these mullite single crystals are free of dislocations, low-angle boundaries, and voids. In addition, they show a high degree of oxygen vacancy ordering. High-resolution digital images from an optical microscope furnish evidence of the formation of a liquid-liquid miscibility gap during crystal growth. These images represent the first experimental evidence of liquid immiscibility for these compositions and temperatures. Continuing investigation with controlled seeding of mullite single crystals is planned.

1997-01-01

102

Diluted magnetism in Mn-doped SrZnO2 single crystals  

NASA Astrophysics Data System (ADS)

We have investigated the magnetic properties of Mn- and Cu-substituted SrZnO2 single crystals (SrZn1-xMnxO2 and SrZn1-xCuxO2). We observed signatures of weak ferromagnetism as a sharp increase of magnetic susceptibility below 5 K even in the low-percentage (x = 0.01) of Mn-substituted single crystals. Magnetic susceptibility data measured parallel or perpendicular to the ab-plane yield anisotropic behavior with Curie-Weiss temperature of about -320 K and -410 K, respectively, suggesting the presence of strong antiferromagnetic couplings among Mn at high temperatures, similar to the Mn-doped ZnO and Fe-doped BaTiO3. In contrast, the SrZn0.99Cu0.01O2 crystal shows paramagnetic behavior down to 2 K.

Rahman, M. R.; Koteswararao, B.; Huang, S. H.; Hoon Kim, Kee; Chou, F. C.

2013-09-01

103

Inkjet printing of single-crystal films  

NASA Astrophysics Data System (ADS)

The use of single crystals has been fundamental to the development of semiconductor microelectronics and solid-state science. Whether based on inorganic or organic materials, the devices that show the highest performance rely on single-crystal interfaces, with their nearly perfect translational symmetry and exceptionally high chemical purity. Attention has recently been focused on developing simple ways of producing electronic devices by means of printing technologies. `Printed electronics' is being explored for the manufacture of large-area and flexible electronic devices by the patterned application of functional inks containing soluble or dispersed semiconducting materials. However, because of the strong self-organizing tendency of the deposited materials, the production of semiconducting thin films of high crystallinity (indispensable for realizing high carrier mobility) may be incompatible with conventional printing processes. Here we develop a method that combines the technique of antisolvent crystallization with inkjet printing to produce organic semiconducting thin films of high crystallinity. Specifically, we show that mixing fine droplets of an antisolvent and a solution of an active semiconducting component within a confined area on an amorphous substrate can trigger the controlled formation of exceptionally uniform single-crystal or polycrystalline thin films that grow at the liquid-air interfaces. Using this approach, we have printed single crystals of the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) (ref. 15), yielding thin-film transistors with average carrier mobilities as high as 16.4cm2V-1s-1. This printing technique constitutes a major step towards the use of high-performance single-crystal semiconductor devices for large-area and flexible electronics applications.

Minemawari, Hiromi; Yamada, Toshikazu; Matsui, Hiroyuki; Tsutsumi, Jun'ya; Haas, Simon; Chiba, Ryosuke; Kumai, Reiji; Hasegawa, Tatsuo

2011-07-01

104

Physical model construction for electrical anisotropy of single crystal zinc oxide micro/nanobelt using finite element method  

SciTech Connect

Based on conductivity characterization of single crystal zinc oxide (ZnO) micro/nanobelt (MB/NB), we further investigate the physical mechanism of nonlinear intrinsic resistance-length characteristic using finite element method. By taking the same parameters used in experiment, a model of nonlinear anisotropic resistance change with single crystal MB/NB has been deduced, which matched the experiment characterization well. The nonlinear resistance-length comes from the different electron moving speed in various crystal planes. As the direct outcome, crystallography of the anisotropic semiconducting MB/NB has been identified, which could serve as a simple but effective method to identify crystal growth direction of single crystal semiconducting or conductive nanomaterial.

Yu, Guangbin [The Higher Educational Key Laboratory for Measuring and Control Technology and Instrumentations of Heilongjiang Province, Harbin University of Science and Technology, Harbin 150080 (China); Tang, Chaolong [Department of Metallurgical and Materials Engineering, Center for Materials for Information Technology (MINT), University of Alabama, Tuscaloosa, Alabama 35487 (United States); Song, Jinhui, E-mail: jhsong@eng.ua.edu, E-mail: wqlu@cigit.ac.cn [The Higher Educational Key Laboratory for Measuring and Control Technology and Instrumentations of Heilongjiang Province, Harbin University of Science and Technology, Harbin 150080 (China); Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714 (China); Department of Metallurgical and Materials Engineering, Center for Materials for Information Technology (MINT), University of Alabama, Tuscaloosa, Alabama 35487 (United States); Lu, Wenqiang, E-mail: jhsong@eng.ua.edu, E-mail: wqlu@cigit.ac.cn [Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714 (China)

2014-04-14

105

Surface flatness of polished metal single crystals  

SciTech Connect

The Fizeau interference has been utilized to measure the flatness of a metal single crystal after grinding and polishing by standard techniques. It is postulated that deviations from flatness are due to distortions of flexible abrasive substrates during the grinding step. {copyright} {ital 1996 American Vacuum Society}

Tripa, C.E.; Yates, J.T. Jr. [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)

1996-07-01

106

MAGNETIC PROPERTIES OF DYSPROSIUM SINGLE CRYSTALS  

Microsoft Academic Search

Single crystals of metallic dysprosium have been grown by the Bridgman ; method and their magnetic properties have been determined in different ; crystallographic directions of the hexagonal close-packed structure. Below the ; Neel point of 178.5 deg K the individual magnetic moments are aligned ; perpendicular to the c\\/sub o\\/ axis. The moments are aligned in an ; antiferromagnetic

D. R. Behrendt; S. Legvold; F. H. Speddin

1958-01-01

107

Single-crystal ruby fiber temperature sensor  

Microsoft Academic Search

Single-crystal ruby fibers with nominal diameters in the range from 80 to 500?m and lengths up to 170mm have been produced using the laser heated miniature pedestal growth technique. These fibers were tested for use as the basis of fiber optic temperature sensors. Characterization of the fiber fluorescence properties and comparison to bulk samples together with their high melting point

H. C Seat; J. H Sharp; Z. Y Zhang; K. T. V. Grattan

2002-01-01

108

Neutron Scattering Study of Single Crystal PZT  

NASA Astrophysics Data System (ADS)

Single crystal specimens of the technologically important ferroelectric material Pb(Zr1-xTix)O3, or PZT, have only recently been grown for the first time at Simon Fraser University. We have characterized the transition temperatures, thermal expansion, and crystal structure of a PZT single crystal between 10 K and 670 K using neutron scattering methods. This crystal, which has a composition (x˜0.46) that lies close to the morphotropic phase boundary (MPB), exhibits a surprisingly large thermal expansion (˜ 10-3 1/K) that changes sign near 545 K, and a rhombohedral crystal structure at 30 K. In addition we observe an enormous relief of extinction beginning around 650 K, which was observed through the temperature dependence of the (200) Bragg peak. Neutron inelastic measurements are planned as are measurements under an applied electric field. This work was supported by the U. S. Office of Naval Research (Grant No. N00014-1-06-0166). All neutron measurements were performed at the NIST Center for Neutron Research.

Phelan, Daniel; Gehring, Peter; Ye, Zuo-Guang; Long, Xifa

2010-03-01

109

Lightweight optical mirrors formed in single crystal substrate  

NASA Technical Reports Server (NTRS)

This invention is directed to a process for manufacturing a lightweight mirror from a single crystal material, such as single crystal silicon. As a near perfect single crystal material, single crystal silicon has much lower internal stress than a conventional material. This means much less distortion of the optical surface during the light weighting process. After being ground and polished, a single crystal silicon mirror is light weighted by removing material from the back side using ultrasonic machining. After the light weighting process, the single crystal silicon mirror may be used as-is or further figured by conventional polishing or ion milling, depending on the application and the operating wavelength.

Bly, Vincent T. (Inventor)

2006-01-01

110

Substrate Preparations in Epitaxial ZnO Film Growth  

NASA Technical Reports Server (NTRS)

Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. Annealing-temperature dependence of ZnO substrates was studied. ZnO films grown on sapphire substrates have also been investigated for comparison purposes and the annealing temperature of A1203 substrates is 1000 C. Substrates and films were characterized using photoluminescence (PL) spectrum, x-ray diffraction, atomic force microscope, energy dispersive spectrum, and electric transport measurements. It has been found that the ZnO film properties were different when films were grown on the two polarity surfaces of ZnO substrates and the A1203 substrates. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of homoepitaxial ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; George, M. A.

2000-01-01

111

Shock Hugoniot of Single Crystal Copper  

SciTech Connect

The shock Hugoniot of single crystal copper is reported for stresses below 66 GPa. Symmetric impact experiments were used to measure the Hugoniots of three different crystal orientations of copper, [100], [110], [111]. The photonic doppler velocimetry (PDV) diagnostic was adapted into a very high precision time of arrival detector for these experiments. The measured Hugoniots along all three crystal directions were nearly identical to the experimental Hugoniot for polycrystalline Cu. The predicted orientation dependence of the Hugoniot from MD calculations was not observed. At the lowest stresses, the sound speed in Cu was extracted from the PDV data. The measured sound speeds are in agreement with values calculated from the elastic constants for Cu.

Chau, R; Stolken, J; Asoka-Kumar, P; Kumar, M; Holmes, N C

2009-08-28

112

SSME single crystal turbine blade dynamics  

NASA Technical Reports Server (NTRS)

A study was performed to determine the dynamic characteristics of the Space Shuttle main engine high pressure fuel turbopump (HPFTP) blades made of single crystal (SC) material. The first and second stage drive turbine blades of HPFTP were examined. The nonrotating natural frequencies were determined experimentally and analytically. The experimental results of the SC second stage blade were used to verify the analytical procedures. The analytical study examined the SC first stage blade natural frequencies with respect to crystal orientation at typical operating conditions. The SC blade dynamic response was predicted to be less than the directionally solidified blade. Crystal axis orientation optimization indicated the third mode interference will exist in any SC orientation.

Moss, Larry A.; Smith, Todd E.

1987-01-01

113

SSME single-crystal turbine blade dynamics  

NASA Technical Reports Server (NTRS)

A study was performrd to determine the dynamic characteristics of the Space Shuttle Main Engine high pressure fuel turbopump (HPFTP) blades made of single crystal (SC) material. The first and second stage drive turbine blades of HPFTP were examined. The nonrotating natural frequencies were determined experimentally and analytically. The experimental results of the SC second stage blade were used to verify the analytical procedures. The study examined the SC first stage blade natural frequencies with respect to crystal orientation at typical operating conditions. The SC blade dynamic response was predicted to be less than the directionally solidified base. Crystal axis orientation optimization indicated that the third mode interference will exist in any SC orientation.

Moss, Larry A.

1988-01-01

114

Growth of Solid Solution Single Crystals  

NASA Technical Reports Server (NTRS)

The objective of the study is to establish the effects of processing semiconducting, solid solution, single crystals in a microgravity environment on the metallurgical, compositional, electrical, and optical characteristics of the crystals. The alloy system being investigated is the solid solution semiconductor Hg(1-x)Cd(x)Te, with x-values appropriate for infrared detector applications in the 8 to 14 mm wavelength region. Both melt and Te-solvent growth are being performed. The study consists of an extensive ground-based experimental and theoretical research effort followed by flight experimentation where appropriate. The ground-based portion of the investigation also includes the evaluation of the relative effectiveness of stabilizing techniques, such as applied magnetic fields, for suppressing convective flow during the melt growth of the crystals.

Lehoczky, Sandor L.; Szofran, Frank R.; Gillies, Donald C.; Watring, Dale A.

1999-01-01

115

Pyroelectroluminescence of barium beta borate single crystals  

Microsoft Academic Search

Investigations were made of the pyroluminescence properties of barium beta borate single crystals. The measurements were made\\u000a at air pressures of 1–10 Pa and temperatures of 80–400 K. Luminescence was observed as isolated flashes over the entire range\\u000a of experimental conditions. It was observed that the light flashes coincided with the pyrocurrent oscillations.

V. T. Adamiv; Ya. V. Burak; M. R. Panasyuk; I. M. Teslyuk

1998-01-01

116

Single crystal silicon micro-actuators  

Microsoft Academic Search

A novel process suitable for fabricating single-crystal silicon microactuators is described. The process utilizes boron-diffused silicon etch stop to define the silicon microstructure thickness and a dry etch process to form narrow and deep trenches, followed by a silicon-to-glass bonding step and subsequent unmasked wafer dissolution. For rotational microactuators, polysilicon trench filling and sacrificial layer patterning are added to define

K. Suzuki

1990-01-01

117

Ionic diffusion in single crystals of vermiculite  

SciTech Connect

Novel guest-host compounds, based on single crystal vermiculite, were synthesized by diffusive techniques through a new hydrogen vermiculite. Single crystals were chosen because of the ease of characterization. An investigation of the ion transport properties of these single crystals was done to determine the mechanism of conductivity including the predominant charge carrier. Measurements of the ionic conductivity using impedance spectroscopy and X-ray lattice parameters of the ion-exchanged samples strongly suggest that the native cations and not protons are the major current carriers. Single crystals of hydrogen vermiculite were synthesized at room temperature by ion exchange from sodium-vermiculite using 1 molar acetic acid for a one week. Subsequent ion exchange with other cations was found to be much enhanced. Thus transition metals were exchanged in about a week in contrast to the need of several months using previous methods. The ionic conductivity of hydrogen vermiculite was measured and shown to be much lower than that of many other monovalent cations in the same host lattice. Its enthalpy of motion is also much lower. These marked differences suggest that protonic species do not play a significant role in charge transport in these layered materials. These materials were characterized by x-ray powder diffraction, thermogravimetric analysis and acid-base titration. Hydrogen-vermiculite was found to react with organic bases, like methylamine, ethylamine, n-butylamine, n-hexylamine, n-octylamine, n-decylamine, aniline, acrylamide, methacrylaminde, urea, 1,10phenanthroline, and 1,1phenanthroline ferrous sulfate complex, to undergo ion exchange with metal cations like sodium, zinc, copper(II) ions and polymerization reactions could be performed in the galleries of the structure like pyrrole and aniline. Its behavior was compared with that of powdered montmorillonite.

Maraqah, H.R.

1993-01-01

118

Crack Growth in Single-Crystal Silicon  

NASA Technical Reports Server (NTRS)

Report describes experiments on crack growth in single-crystal silicon at room temperature in air. Crack growth in (111) cleavage plane of wafers, 50 by 100 by 0.76 mm in dimension, cut from Czochralski singlecrystal silicon studied by double-torsion load-relaxation method and by acoustic-emission measurements. Scanning electron microscopy and X-ray topography also employed. Results aid in design and fabrication of silicon photovoltaic and microelectronic devices.

Chen, C. P.; Leipold, M. H.

1986-01-01

119

Characterization of Defects in PTerphenyl Single Crystals  

Microsoft Academic Search

White Beam Synchrotron X-ray Topography has been used to characterize defects in solution-grown p-terphenyl single crystals. Defects observed include growth dislocations, mechanically introduced dislocations, macroscopic twins, twin lamellae, and dislocations emitted from twin boundaries. Line direction and Burgers Vector analysis of the growth and mechanically introduced dislocations, using projective geometry calculations and g. b analysis, respectively, are presented, along with

Michael Dudley; Rosemarie Disalvo; Shang-Yun Hou; Bruce M. Foxman; William Jones

1992-01-01

120

Flexible single-crystal silicon nanomembrane photonic crystal cavity.  

PubMed

Flexible inorganic electronic devices promise numerous applications, especially in fields that could not be covered satisfactorily by conventional rigid devices. Benefits on a similar scale are also foreseeable for silicon photonic components. However, the difficulty in transferring intricate silicon photonic devices has deterred widespread development. In this paper, we demonstrate a flexible single-crystal silicon nanomembrane photonic crystal microcavity through a bonding and substrate removal approach. The transferred cavity shows a quality factor of 2.2 × 10(4) and could be bent to a curvature of 5 mm radius without deteriorating the performance compared to its counterparts on rigid substrates. A thorough characterization of the device reveals that the resonant wavelength is a linear function of the bending-induced strain. The device also shows a curvature-independent sensitivity to the ambient index variation. PMID:25409282

Xu, Xiaochuan; Subbaraman, Harish; Chakravarty, Swapnajit; Hosseini, Amir; Covey, John; Yu, Yalin; Kwong, David; Zhang, Yang; Lai, Wei-Cheng; Zou, Yi; Lu, Nanshu; Chen, Ray T

2014-12-23

121

A Spontaneous Single-Crystal-to-Single-Crystal Polymorphic Transition Involving Major Packing Changes.  

PubMed

4,6-O-Benzylidene-?-d-galactosyl azide crystallizes into two morphologically distinct polymorphs depending on the solvent. While the ? form appeared as thick rods and crystallized in P21 space group (monoclinic) with a single molecule in the asymmetric unit, the ? form appeared as thin fibers and crystallized in P1 space group (triclinic) with six molecules in the asymmetric unit. Both the polymorphs appeared to melt at the same temperature. Differential scanning calorimetry analysis revealed that polymorph ? irreversibly undergoes endothermic transition to polymorph ? much before its melting point, which accounts for their apparently same melting points. Variable temperature powder X-ray diffraction (PXRD) experiments provided additional proof for the polymorphic transition. Single-crystal XRD analyses revealed that ? to ? transition occurs in a single-crystal-to-single-crystal (SCSC) fashion not only under thermal activation but also spontaneously at room temperature. The SCSC nature of this transition is surprising in light of the large structural differences between these polymorphs. Polarized light microscopy experiments not only proved the SCSC nature of the transition but also suggested nucleation and growth mechanism for the transition. PMID:25585170

Krishnan, Baiju P; Sureshan, Kana M

2015-02-01

122

Guest exchange through single crystal-single crystal transformations in a flexible hydrogen-bonded framework.  

PubMed

A molecular framework based on guanidinium cations and 1,2,4,5-tetra(4-sulfonatophenyl)benzene (TSPB), an aromatic tetrasulfonate with nominal 2-fold and mirror symmetry, exhibits three crystallographically unique one-dimensional channels as a consequence of molecular symmetry and complementary hydrogen bonding between the guanidinium (G) ions and the sulfonate (S) groups of TSPB. Unlike previous GS frameworks, this new topology is sufficiently flexible to permit reversible release and adsorption of guest molecules in large single crystals through a cyclic shrinkage and expansion of the channels with retention of single crystallinity, as verified by single crystal X-ray diffraction. Moreover, the G4TSPB framework permits guest exchange between various guest molecules through SCSCTs as well as exchange discrimination based on the size and character of the three different channels. The exchange of guest molecules during single crystal-single crystal transformations (SCSCT), a rare occurrence for hydrogen-bonded frameworks, is rather fast, with diffusivities of approximately 10(-6) cm(2) s(-1). Rapid diffusion in the two channels having cross sections sufficient to accommodate two guest molecules can be explained by two-way or ring diffusion, most likely vacancy assisted. Surprisingly, rapid guest exchange also is observed in a smaller channel having a cross-section that accommodates only one guest molecule, which can only be explained by guest-assisted single-file unidirectional diffusion. Several single crystals of inclusion compounds can be realized only through guest exchange in the intact framework, suggesting an approach to the synthesis of single crystalline inclusion compounds that otherwise cannot be attained through direct crystallization methods. PMID:25248132

Xiao, Wenchang; Hu, Chunhua; Ward, Michael D

2014-10-01

123

Enhancement effects on excitonic photoluminescence intensity originating from misaligned crystal blocks and polycrystalline grains in a ZnO wafer  

NASA Astrophysics Data System (ADS)

We have systematically investigated a relation between excitonic photoluminescence intensity and crystal quality in a (0001)-oriented ZnO wafer. We visualize the crystal quality of a whole wafer using a circular polariscopic measurement and a reflection-type X-ray topograph measurement. The reflection-type X-ray topograph exhibits regions of grain-like patterns that result from internal strains. The circular polariscopic map shows that the internal strains induce local stresses. The ?-2 ? X-ray diffraction pattern indicates the presence of misaligned crystal blocks and polycrystalline grains. We have measured photoluminescence spectra and found that the presence of misaligned crystal blocks and polycrystalline grains leads to enhancement of the excitonic photoluminescence intensity. The present phenomenon is attributed to the suppression of exciton diffusion caused by the grain and domain boundaries that connect with the grain-like patterns in the X-ray topograph.

Takeuchi, Hideo

2013-02-01

124

Materials Science and Engineering B 138 (2007) 224227 Synthesis of single crystalline europium-doped ZnO nanowires  

E-print Network

Materials Science and Engineering B 138 (2007) 224­227 Synthesis of single crystalline europium; ZnO; Europium doping; XPS 1. Introduction Synthesizing one-dimensional (1D) nanostructures in semi and studies of the luminescent properties of europium (Eu)-doped semicon- ductors in various morphologies

Kim, Bongsoo

125

Oriented single-crystal-to-single-crystal phase transition with dramatic changes in the dimensions of crystals.  

PubMed

We report here a new polymorph of cocrystal CuQ2-TCNQ that shows an oriented single-crystal-to-single-crystal phase transition along its a-axis at ambient conditions. Upon mechanical stimulation, it converts into another polymorph accompanied by almost doubling its length and halving its thickness. Our crystallographic studies indicate the dramatic changes in crystal dimensions resulted from the prominent changes of molecular stacking patterns. A reasonable mechanism for the phenomenon was proposed on the basis of the structural, microscopic, and thermal analysis. PMID:24372005

Liu, Guangfeng; Liu, Jie; Liu, Yang; Tao, Xutang

2014-01-15

126

Crystal Structure of A-amylose: a Revisit from Synchrotron Microdiffraction Analysis of Single Crystals  

E-print Network

1 Crystal Structure of A-amylose: a Revisit from Synchrotron Microdiffraction Analysis of Single;2 Abstract The three-dimensional structure of A-amylose crystals, as a model of the crystal domains of A-sized single crystals. The resulting datasets allowed a determination of the structure with conventional X

Paris-Sud XI, Université de

127

Chemical vapor deposition of graphene single crystals.  

PubMed

As a two-dimensional (2D) sp(2)-bonded carbon allotrope, graphene has attracted enormous interest over the past decade due to its unique properties, such as ultrahigh electron mobility, uniform broadband optical absorption and high tensile strength. In the initial research, graphene was isolated from natural graphite, and limited to small sizes and low yields. Recently developed chemical vapor deposition (CVD) techniques have emerged as an important method for the scalable production of large-size and high-quality graphene for various applications. However, CVD-derived graphene is polycrystalline and demonstrates degraded properties induced by grain boundaries. Thus, the next critical step of graphene growth relies on the synthesis of large graphene single crystals. In this Account, we first discuss graphene grain boundaries and their influence on graphene's properties. Mechanical and electrical behaviors of CVD-derived polycrystalline graphene are greatly reduced when compared to that of exfoliated graphene. We then review four representative pathways of pretreating Cu substrates to make millimeter-sized monolayer graphene grains: electrochemical polishing and high-pressure annealing of Cu substrate, adding of additional Cu enclosures, melting and resolidfying Cu substrates, and oxygen-rich Cu substrates. Due to these pretreatments, the nucleation site density on Cu substrates is greatly reduced, resulting in hexagonal-shaped graphene grains that show increased grain domain size and comparable electrical properties as to exfoliated graphene. Also, the properties of graphene can be engineered by its shape, thickness and spatial structure. Thus, we further discuss recently developed methods of making graphene grains with special spatial structures, including snowflakes, six-lobed flowers, pyramids and hexagonal graphene onion rings. The fundamental growth mechanism and practical applications of these well-shaped graphene structures should be interesting topics and deserves more attention in the near future. Following that, recent efforts in fabricating large single-crystal monolayer graphene on other metal substrates, including Ni, Pt, and Ru, are also described. The differences in growth conditions reveal different growth mechanisms on these metals. Another key challenge for graphene growth is to make graphene single crystals on insulating substrates, such as h-BN, SiO2, and ceramic. The recently developed plasma-enhanced CVD method can be used to directly synthesize graphene single crystals on h-BN substrates and is described in this Account as well. To summarize, recent research in synthesizing millimeter-sized monolayer graphene grains with different pretreatments, graphene grain shapes, metal catalysts, and substrates is reviewed. Although great advancements have been achieved in CVD synthesis of graphene single crystals, potential challenges still exist, such as the growth of wafer-sized graphene single crystals to further facilitate the fabrication of graphene-based devices, as well as a deeper understanding of graphene growth mechanisms and growth dynamics in order to make graphene grains with precisely controlled thicknesses and spatial structures. PMID:24527957

Yan, Zheng; Peng, Zhiwei; Tour, James M

2014-04-15

128

Phase transition in sarcosine phosphite single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of sarcosine phosphite (SarcH3PO3) have been grown. The amino acid sarcosine is an isomer of the protein amino acid alanine. Both amino acids are described by the same chemical formula but have different structures; or, more specifically, in contrast to the alanine molecule, the sarcosine molecule has a symmetric structure. It has been found that the sarcosine phosphite compound undergoes a structural phase transition at a temperature of approximately 200 K. This result has demonstrated that compounds of achiral amino acids are more susceptible to structural phase transitions.

Lemanov, V. V.; Popov, S. N.; Pankova, G. A.

2011-06-01

129

Triplet exciton dynamics in rubrene single crystals  

NASA Astrophysics Data System (ADS)

The decay of the photoluminescence excited in rubrene single crystals by picosecond pulses is measured over 7 orders of magnitude and more than 4 time decades. We identify the typical decay dynamics due to triplet-triplet interaction. We show that singlet exciton fission and triplet fusion quantum yields in rubrene are both very large, and we directly determine a triplet exciton lifetime of 100±20 ?s, which explains the delayed buildup of a large photocurrent that has been reported earlier for low excitation densities.

Ryasnyanskiy, Aleksandr; Biaggio, Ivan

2011-11-01

130

Conduction mechanism of single-crystal alumina  

NASA Technical Reports Server (NTRS)

The fully guarded three-terminal technique was used to perform conductivity measurements on single-crystal alumina at temperatures of 400-1300 C. The conductivity was also determined as a function of time at various temperatures and applied fields. Further, the fractions of the current carried by Al and O ions (ionic transference numbers) were determined from long-term transference experiments in the temperature range 1100-1300 C. A mathematical model of the conduction mechanism is proposed, and model predictions are compared with experimental results.

Will, Fritz G.; Delorenzi, Horst G.; Janora, Kevin H.

1992-01-01

131

Properties of salt-grown uranium single crystals  

Microsoft Academic Search

Recently single crystals of -uranium were grown from a liquid salt bath. The electrical, magnetic and thermal properties of these crystals have been surveyed. The ratio of the room temperature resistivity of these crystals to the saturation value at low temperature is three times larger than any previously reported demonstrating that the crystals are of higher purity and quality than

J. C. Cooley; R. J. Hanrahan; W. L. Hults; J. C. Lashley; M. E. Manley; C. H. Mielke; J. L. Smith; D. J. Thoma; R. G. Clark; A. R. Hamilton; J. L. OBrien; E. C. Gay; N. E. Lumpkin; C. C. McPheeters; J. Willit; G. M. Schmiedeshoff; S. Touton; B. F. Woodfield; B. E. Lang; Juliana Boerio-Goates

2001-01-01

132

Fabrication of crystals from single metal atoms  

PubMed Central

Metal nanocrystals offer new concepts for the design of nanodevices with a range of potential applications. Currently the formation of metal nanocrystals cannot be controlled at the level of individual atoms. Here we describe a new general method for the fabrication of multi-heteroatom-doped graphitic matrices decorated with very small, ångström-sized, three-dimensional (3D)-metal crystals of defined size. We irradiate boron-rich precious-metal-encapsulated self-spreading polymer micelles with electrons and produce, in real time, a doped graphitic support on which individual osmium atoms hop and migrate to form 3D-nanocrystals, as small as 15?Å in diameter, within 1?h. Crystal growth can be observed, quantified and controlled in real time. We also synthesize the first examples of mixed ruthenium–osmium 3D-nanocrystals. This technology not only allows the production of ångström-sized homo- and hetero-crystals, but also provides new experimental insight into the dynamics of nanocrystals and pathways for their assembly from single atoms. PMID:24861089

Barry, Nicolas P. E.; Pitto-Barry, Anaïs; Sanchez, Ana M.; Dove, Andrew P.; Procter, Richard J.; Soldevila-Barreda, Joan J.; Kirby, Nigel; Hands-Portman, Ian; Smith, Corinne J.; O’Reilly, Rachel K.; Beanland, Richard; Sadler, Peter J.

2014-01-01

133

Single-crystal fiber optics: a review  

NASA Astrophysics Data System (ADS)

Single-crystal (SC) fiber optics have been grown for many years for use as passive fibers for the delivery of IR laser radiation and as active fibers useful as minirod lasers. Most of the early work on SC fiber optics involved the growth of unclad sapphire fibers for the transmission of Er:YAG laser radiation at 2.94 ?m. More recently there has been a renewed interest in rare-earth (RE) doped oxide crystal fibers for use as high power fiber lasers. By analogy with RE doped-bulk laser crystals it is expected that pure YAG and other crystalline SC fibers should be capable of transmitting extremely high laser energies. SC oxide fibers have some distinct advantages over conventional glass fibers including higher thermal conductivity and low stimulated Brillouin scattering (SBS) gain coefficients. The latter can limit the ultimate power output of glass fiber lasers. To date most of the investigators have used the technique of Laser Heated Pedestal Growth (LHPG) to grow unclad SC fibers with diameters ranging from 30 to 350 ?m and in lengths as long as 5 m. The loss for SC sapphire fibers at 2.94 ?m has been measured as low as 0.3 dB/m. In this review we discuss the technique of LHPG, the various SC fiber optics that have been grown for both active and passive applications, and methods that may be used to clad the fibers.

Harrington, James A.

2014-02-01

134

Fabrication of crystals from single metal atoms  

NASA Astrophysics Data System (ADS)

Metal nanocrystals offer new concepts for the design of nanodevices with a range of potential applications. Currently the formation of metal nanocrystals cannot be controlled at the level of individual atoms. Here we describe a new general method for the fabrication of multi-heteroatom-doped graphitic matrices decorated with very small, ångström-sized, three-dimensional (3D)-metal crystals of defined size. We irradiate boron-rich precious-metal-encapsulated self-spreading polymer micelles with electrons and produce, in real time, a doped graphitic support on which individual osmium atoms hop and migrate to form 3D-nanocrystals, as small as 15?Å in diameter, within 1?h. Crystal growth can be observed, quantified and controlled in real time. We also synthesize the first examples of mixed ruthenium-osmium 3D-nanocrystals. This technology not only allows the production of ångström-sized homo- and hetero-crystals, but also provides new experimental insight into the dynamics of nanocrystals and pathways for their assembly from single atoms.

Barry, Nicolas P. E.; Pitto-Barry, Anaïs; Sanchez, Ana M.; Dove, Andrew P.; Procter, Richard J.; Soldevila-Barreda, Joan J.; Kirby, Nigel; Hands-Portman, Ian; Smith, Corinne J.; O'Reilly, Rachel K.; Beanland, Richard; Sadler, Peter J.

2014-05-01

135

Ultrahigh-quality silicon carbide single crystals.  

PubMed

Silicon carbide (SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for next-generation electronic devices. Careful consideration of the thermal conditions in which SiC [0001] is grown has resulted in improvements in crystal diameter and quality: the quantity of macroscopic defects such as hollow core dislocations (micropipes), inclusions, small-angle boundaries and long-range lattice warp has been reduced. But some macroscopic defects (about 1-10 cm(-2)) and a large density of elementary dislocations (approximately 10(4) cm(-2)), such as edge, basal plane and screw dislocations, remain within the crystal, and have so far prevented the realization of high-efficiency, reliable electronic devices in SiC (refs 12-16). Here we report a method, inspired by the dislocation structure of SiC grown perpendicular to the c-axis (a-face growth), to reduce the number of dislocations in SiC single crystals by two to three orders of magnitude, rendering them virtually dislocation-free. These substrates will promote the development of high-power SiC devices and reduce energy losses of the resulting electrical systems. PMID:15329716

Nakamura, Daisuke; Gunjishima, Itaru; Yamaguchi, Satoshi; Ito, Tadashi; Okamoto, Atsuto; Kondo, Hiroyuki; Onda, Shoichi; Takatori, Kazumasa

2004-08-26

136

Synthesis and characterization of superconducting single-crystal Sn nanowires  

E-print Network

June 2003 Single-crystal superconducting tin nanowires with diameters of 40­160 nm have been prepared was attributed by the authors to be related to the ``poor crystal structure;'' that is, a lacking of electronSynthesis and characterization of superconducting single-crystal Sn nanowires Mingliang Tian

137

Piezoelectric single crystals for ultrasonic transducers in biomedical applications.  

PubMed

Piezoelectric single crystals, which have excellent piezoelectric properties, have extensively been employed for various sensors and actuators applications. In this paper, the state-of-art in piezoelectric single crystals for ultrasonic transducer applications is reviewed. Firstly, the basic principles and design considerations of piezoelectric ultrasonic transducers will be addressed. Then, the popular piezoelectric single crystals used for ultrasonic transducer applications, including LiNbO3 (LN), PMN-PT and PIN-PMN-PT, will be introduced. After describing the preparation and performance of the single crystals, the recent development of both the single-element and array transducers fabricated using the single crystals will be presented. Finally, various biomedical applications including eye imaging, intravascular imaging, blood flow measurement, photoacoustic imaging, and microbeam applications of the single crystal transducers will be discussed. PMID:25386032

Zhou, Qifa; Lam, Kwok Ho; Zheng, Hairong; Qiu, Weibao; Shung, K Kirk

2014-10-01

138

Deep level defects in ZnO  

NASA Astrophysics Data System (ADS)

The current understanding on intrinsic and extrinsic defects in ZnO is briefly reviewed. Special attention is given to defects defining the doping asymmetry as well as to approaches and theoretical predictions to control the conductivity of zinc oxide. Silver doping is considered a promising way to achieve hole conductivity in bulk ZnO. Results of defect spectroscopic studies on hydrothermally grown single ZnO crystals with an electron concentration of ?1017 cm-3 and ?1014 cm-3 are presented. Besides several other deep level centers in higher doped materials the Zni related level at Ec- (341±2) meV was found to be the dominating donor level in low doped ZnO. Further thermal post-treatments under inert and oxygen ambient conditions result in electrical intrinsic properties. First experiments on ZnO:Ag gave no hints for a detectable electrical activity of silver.

Bollmann, J.; Simon, D. K.

2014-04-01

139

Solar cell structure incorporating a novel single crystal silicon material  

DOEpatents

A novel hydrogen rich single crystal silicon material having a band gap energy greater than 1.1 eV can be fabricated by forming an amorphous region of graded crystallinity in a body of single crystalline silicon and thereafter contacting the region with atomic hydrogen followed by pulsed laser annealing at a sufficient power and for a sufficient duration to recrystallize the region into single crystal silicon without out-gassing the hydrogen. The new material can be used to fabricate semiconductor devices such as single crystal silicon solar cells with surface window regions having a greater band gap energy than that of single crystal silicon without hydrogen.

Pankove, Jacques I. (Princeton, NJ); Wu, Chung P. (Trenton, NJ)

1983-01-01

140

Effect of Thermal Annealing on the Characteristics of Phosphorus-Implanted ZnO Crystals  

NASA Astrophysics Data System (ADS)

A P-doped ZnO surface layer on undoped ZnO wafers was prepared by phosphorus (P) ion implantation. Hall effect measurement revealed p-type conduction in such layers annealed at 800°C. This indicates that acceptor levels are present in P-doped ZnO, even though the ZnO is still n-type. Micro-Raman scattering in - z( xy) z geometry was conducted on P-implanted ZnO. The E {2/high} mode shift observed toward the high-energy region was related to compressive stress as a result of P-ion implantation. This compressive stress led to the appearance of an A 1(LO) peak, which is an inactive mode. This A 1(LO) peak relaxed during thermal annealing in ambient oxygen at temperatures higher than 700°C. The P2p3/2 peak observed at 135.6 eV by x-ray photoelectron spectroscopy is associated with chemical bond formation leading to 2(P2O5) molecules. This indicates that implanted P ions substituted Zn sites in the ZnO layer. In photoluminescence spectroscopy, the P-related peaks observed at energies ranging between 3.1 and 3.5 eV originated from (A0, X) emission, because of PZn-2VZn complexes acting as shallow acceptors. The acceptor level was observed to be 126.9 meV above the valence band edge. Observation of this P-related emission indicates that ion implantation results in acceptor levels in the P-doped ZnO layer. This suggests that the P2O5 bonds are responsible for the p-type activity of P-implanted ZnO.

Jeong, T. S.; Yu, J. H.; Mo, H. S.; Kim, T. S.; Lim, K. Y.; Youn, C. J.; Hong, K. J.; Kim, H. S.

2014-07-01

141

Growth and characterization of biadmixtured TGS single crystals  

Microsoft Academic Search

Single crystals of triglycine sulfate (TGS) with l-glutamine and l-methionine were grown in aqueous solutions by a slow cooling method. The grown crystals were subjected to single crystal and powder X-ray diffraction studies to identify the morphology and the structure. FTIR and UV–visible spectra reveal the functional group identification and optical property of the grown crystals. The dielectric studies were

T. Bharthasarathi; V. Siva Shankar; R. Jayavel; P. Murugakoothan

2009-01-01

142

Electrical, optical, and analytical characterization of bulk hydrothermal ZnO crystals doped with indium  

NASA Astrophysics Data System (ADS)

Bulk In-doped ZnO crystals have been grown hydrothermally by adding In 2O 3 to the normal nutrient. The major growth occurs along the [1 0 -1 0] direction rather than the usual [0 0 0 1] and [0 0 0 -1] directions; thus, a c-plane crystal has a plate-like shape. Secondary-ion mass spectroscopy (SIMS) measurements reveal an In concentration of about 1.6×10 19 cm -3 in the bulk, with lesser amounts of Al (2.5×10 18), Ga (1.8×10 17), Fe (6.5×10 18), and Li (1.1×10 18). Low-temperature photoluminescence (PL) from the Zn face (0 0 0 1) shows strong, relatively sharp donor-bound exciton (D°X) lines at 3.3609 and 3.3624 eV, attributed to Al and H, respectively, along with much weaker lines at 3.29, 3.22 eV, and 2.35 eV, tentatively assigned, respectively, to a 1-LO-phonon replica of the D°X transitions, a donor-acceptor-pair transition, and the usual green band of unknown origin. The D°X-related PL from the O face (0 0 0 -1) is much broader because of significantly higher In, Li, and Fe concentrations; however, it also includes a weak, sharp In°X line evidently emanating from the bulk region. The Hall-effect measurements in the range 15-320 K reveal an unusual temperature variation of carrier concentration n, mobility ?, and resistivity ?, namely the existence of two flat regions: (1) from 15 to 50 K ( n=7.8×10 18 cm -3, ?=48 cm 2/V s, and ?=0.017 ? cm) and (2) from 250 to 320 K ( n=7.3×10 18 cm -3, ?=83 cm 2/V s, and ?=0.010 ? cm). A mobility analysis based on degenerate electrons gives donor ND and acceptor NA concentrations of about 1.5×10 19 and 7.5×10 18 cm -3, respectively. Remarkably, within error, ND?[In]+[Al]+[Ga] and NA?[Fe]+[Li].

Wang, Buguo; Callahan, Michael J.; Bouthillette, Lionel O.; Bliss, David F.; Look, David C.

2011-03-01

143

Growing single crystals in silica gel  

NASA Technical Reports Server (NTRS)

Two types of chemical reactions for crystal growing are discussed. The first is a metathetical reaction to produce calcium tartrate tetrahydrate crystals, the second is a decomplexation reaction to produce cuprous chloride crystals.

Rubin, B.

1970-01-01

144

Ion Crystal Transducer for Strong Coupling between Single Ions and Single Photons  

E-print Network

A new approach for the realization of a quantum interface between single photons and single ions in an ion crystal is proposed and analyzed. In our approach the coupling between a single photon and a single ion is enhanced ...

Lamata, L.

145

Experimental dynamic metamorphism of mineral single crystals  

NASA Astrophysics Data System (ADS)

This paper is a review of some of the rich and varied interactions between non-hydrostatic stress and phase transformations or mineral reactions, drawn mainly from results of experiments done on mineral single crystals in our laboratory or our co-authors. The state of stress and inelastic deformation can enter explicitly into the equilibrium phase relations and kinetics of mineral reactions. Alternatively, phase transformations can have prominent effects on theology and on the nature of inelastic deformation. Our examples represent five types of structural phase changes, each of which is distinguished by particular mechanical effects. In increasing structural complexity, these include: (1) displacive phase transformations involving no bond-breaking, which may produce anomalous brittle behavior. A primary example is the a- ? quartz transition which shows anomalously low fracture strength and tertiary creep behavior near the transition temperature; (2) martensitic-like transformations involving transformation strains dominated by shear deformation. Examples include the orthoenstatite ? clinoenstatite and w ürtzite ? sphalerite transformations; (3) coherent exsolution or precipitation of a mineral solute from a supersaturated solid-solution, with anisotropy of precipitation and creep rates produced under nonhydrostatic stress. Examples include exsolution of corundum from MgO · nAl 2O 3 spinels and Ca-clinopyroxene from orthopyroxene; (4) order-disorder transformations that are believed to cause anomalous plastic yield strengthening, such as MgO - nAl2O3 spinels; and (5) near-surface devolatilization of hydrous silicate single-crystals that produces a fundamental brittleness thought to be connected with dehydration at microcracks at temperatures well below nominal macroscopic dehydration temperatures. As none of these interactions between single-crystal phase transformations and non-hydrostatic stress is understood in detail, this paper serves as a challenge to field structural geologists to test whether interactions of these types occur in nature, and to theoreticians to reach a deeper understanding of the complex relations between phase transformations, the local state of stress and associated deformation and deformation rates.

Kirby, Stephen H.; Stern, Laura A.

1993-09-01

146

Dynamic characteristics of single crystal SSME blades  

NASA Technical Reports Server (NTRS)

The Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump (HPFTP) blades are currently manufactured using a directionally solidified (DS) material, MAR-M-246+Hf. However, a necessity to reduce the occurrence of fatigue cracking within the DS blades has lead to an interest in the use of a single crystal (SC) material, PWA-1480. A study was initiated to determine the dynamic characteristics of the HPFTP blades made of SC material and find possible critical engine order excitations. This study examined both the first and second stage drive turbine blades of the HPFTP. The dynamic characterization was done analytically as well as experimentally. The analytical study examined the SC first stage HPFTP blade dynamic characteristics under typical operating conditions. The blades were analyzed using MSC/NASTRAN and a finite element model. Two operating conditions, 27500 RPM and 35000 RPM, were investigated.

Moss, L. A.; Smith, T. E.

1987-01-01

147

Constitutive modeling for single crystal superalloys  

NASA Technical Reports Server (NTRS)

A crystallographic approach to constitutive modeling of single crystal superalloys is discussed. The approach is based on identifying the active slip planes and slip directions. The shear stresses are computed on each of the slip planes from applied stress components. The slip rate is then computed on each slip system and the microscopic inelastic strain rates are the sum of the slip in the individual slip systems. The constitutive model was implemented in a finite element code using twenty noted isoparametric solid elements. Constants were determined for octahedral and cube slip systems. These constants were then used to predict tension-compression asymmetry and fatigue loops. Other data was used to model the tensile and creep response.

Stouffer, Donald C.; Dame, L. Thomas; Jayaraman, N.

1985-01-01

148

Magnetoplasticity and diffusion in silicon single crystals  

SciTech Connect

The effect of static magnetic fields on the dynamics of surface dislocation segments, as well as the diffusion mobility of a dopant in silicon single crystals, has been analyzed. It has been experimentally found that the preliminary treatment of p-type silicon plates (the dopant is boron with a concentration of 10{sup 16} cm{sup -3}) in the static magnetic field (B = 1 T, a treatment time of 30 min) leads to an increase in the mobility of surface dislocation segments. The characteristic times of observed changes (about 80 h) and the threshold dopant concentration (10{sub 15} cm{sup -3}) below which the magneto-optical effect in silicon is not fixed have been determined. It has been found that diffusion processes in dislocation-free silicon are magnetically sensitive: the phosphorus diffusion depth in p-type silicon that is preliminarily aged in the static magnetic field increases (by approximately 20%) compared to the reference samples.

Skvortsov, A. A., E-mail: SkvortsovAA2009@yandex.ru; Karizin, A. V. [Moscow State Technical University 'MAMI' (Russian Federation)

2012-01-15

149

Vibration-assisted machining of single crystal  

NASA Astrophysics Data System (ADS)

Vibration-assisted machining offers a solution to expanding needs for improved machining, especially where accuracy and precision are of importance, such as in micromachining of single crystals of metals and alloys. Crystallographic anisotropy plays a crucial role in determining on overall response to machining. In this study, we intend to address the matter of ultra-precision machining of material at the micron scale using computational modelling. A hybrid modelling approach is implemented that combines two discrete schemes: smoothed particle hydrodynamics and continuum finite elements. The model is implemented in a commercial software ABAQUS/Explicit employing a user-defined subroutine (VUMAT) and used to elucidate the effect of crystallographic anisotropy on a response of face centred cubic (f.c.c.) metals to machining.

Zahedi, S. A.; Roy, A.; Silberschmidt, V. V.

2013-07-01

150

Electrical switching in cadmium boracite single crystals  

NASA Technical Reports Server (NTRS)

Cadmium boracite single crystals at high temperatures ( 300 C) were found to exhibit a reversible electric field-induced transition between a highly insulative and a conductive state. The switching threshold is smaller than a few volts for an electrode spacing of a few tenth of a millimeter corresponding to an electric field of 100 to 1000 V/cm. This is much smaller than the dielectric break-down field for an insulator such as boracite. The insulative state reappears after voltage removal. A pulse technique revealed two different types of switching. Unstable switching occurs when the pulse voltage slightly exceeds the switching threshold and is characterized by a pre-switching delay and also a residual current after voltage pulse removal. A stable type of switching occurs when the voltage becomes sufficiently high. Possible device applications of this switching phenomenon are discussed.

Takahashi, T.; Yamada, O.

1981-01-01

151

Rainbow Radiating Single-Crystal Ag Nanowire Nanoantenna Taejoon Kang,  

E-print Network

Rainbow Radiating Single-Crystal Ag Nanowire Nanoantenna Taejoon Kang, Wonjun Choi, Ilsun Yoon rainbow antenna radiation in the Fresnel region. Detailed antenna radiation properties, such as radiating

Kim, Bongsoo

152

Ultraviolet Photoresponse Properties of Single-Walled Carbon Nanotubes Decorated with Thickness-Controlled ZnO Layer by Pulsed Laser Deposition  

NASA Astrophysics Data System (ADS)

We fabricated single-walled carbon nanotubes (SWNTs) covered with a thickness-controlled ZnO layer (ZnO-SWNTs) by pulsed laser deposition (PLD) and investigated their UV photoresponse, induced by the photodesorption of oxygen molecules from the ZnO surface. The magnitude of the negative photocurrent and the recovery time were strongly dependent on the thickness and morphology of the ZnO layer, and were highest when the ZnO layer was 3-4 nm thick. The observed recovery curves of the negative photocurrent were fitted with double-exponential-function curves, which indicate the coexistence of two types of adsorption sites for oxygen molecules on the ZnO surface. The light intensity dependence of the negative photocurrent was also measured.

Itabashi, Kenta; Tabata, Hiroshi; Wongwiriyapan, Winadda; Minami, Shinji; Matsushita, Kazutoshi; Shimazaki, Ryotaro; Ueda, Tsuyoshi; Ito, Tatsuya; Katayama, Mitsuhiro

2012-05-01

153

Crystallization of single phase (K, Na)clinoptilolite  

Microsoft Academic Search

A single phase (K, Na)-clinoptilolite was hydrothermally crystallized without seed crystals from a reactant mixture of (K, Na)-aluminosilicate gel slurry through homogeneous mixing at 150 °C for 144 h. Compositions of the reactant mixtures and reaction temperatures to obtain the clinoptilolite were restricted within narrow limits in the case of syntheses without seed crystals, while the compositions and temperatures were

Shigeo Satokawa; Keiji Itabashi

1997-01-01

154

Investigation on Growth and Surface Analysis of DAST Single Crystals  

SciTech Connect

We have explored the growth of bulk size N, N-dimethylamino-N'-methylstilbazolium p-toluenesulphonate (DAST) using slope nucleation method. The grown crystal was characterized by single crystal X-ray diffraction (XRD), and CHN analyses. The surface morphology of the crystal was analyzed using Scanning electron microscopy (SEM).

Thomas, Tina; Vijay, R. Jerald; Gunaseelan, R.; Sagayaraj, P. [Department of Physics, Loyola College, Chennai - 600 034 (India)

2011-07-15

155

Engineering the crystal growth behavior: “On substrate” MOD formation of ZnO hollow spheres  

NASA Astrophysics Data System (ADS)

In this paper is described an easy, one-pot synthesis of ZnO hollow spheres with sizes ranging from 300 nm to 500 nm, by spin-coating deposition on aluminum substrate. Simplified models explaining the shape formation based on film-substrate interaction are discussed. The characteristic size and shape of the nanostructures obtained by the described method and the properties of ZnO as a low-cost biocompatible material make this methodology of synthesis interesting for a wide range of applications including optoelectronics, catalysis and (bio)sensors.

Tafulo, Paula A. R.; Ferro, Marta; Guerreiro, Ariel; González-Aguilar, Gerardo

2010-03-01

156

UV irradiations enhance anisotropy of ZnO nanorods in crystal growth and ferromagnetism  

NASA Astrophysics Data System (ADS)

The crystalline growth of the preferred orientation in the ZnO nanorods will be profoundly enhanced as we irradiate a specific wave length of ultra-violate (UV) during the sample fabrication. The specific UV photon energy is equivalent to the ZnO band gap. Both samples, with and without UV irradiated undoped nanorods, exhibit the anisotropic ferromagnetism. The electric polarization yields the ferromagnetic anisotropy along the c-axis, which suppresses the ferromagnetism in the same polarized direction and creates a similar multiferroic characteristic. Besides, the specific UV irradiation significantly enhances the ferromagnetic anisotropy.

Yu, Chang-Feng; Sun, Shih-Jye; Hsu, Hua-Shu

2015-01-01

157

Chemistry and Kinetics of ZnO Growth from Alkaline Hydrothermal Solutions  

Microsoft Academic Search

Special features (polar growth and nonstoichiometry) of ZnO single crystals grown on seed plates of various crystallographic orientations in the ZnO–KOH–H2O and ZnO–KOH–LiOH–H2O hydrothermal systems are analyzed. The growth proceeds via the interaction of ZnO2-2 anions with crystal surfaces, and its rate depends on the atomic structure and electric charge of the surface. The mechanism underlying the influence of Li+

L. N. Dem'yanets; D. V. Kostomarov; I. P. Kuz'mina

2002-01-01

158

Crucibleless crystal growth and Radioluminescence study of calcium tungstate single crystal fiber  

NASA Astrophysics Data System (ADS)

In this article, single phase and high optical quality scheelite calcium tungstate single crystal fibers were grown by using the crucibleless laser heated pedestal growth technique. The as-synthesized calcium tungstate powders used for shaping seed and feed rods were investigated by X-ray diffraction technique. As-grown crystals were studied by Raman spectroscopy and Radioluminescence measurements. The results indicate that in both two cases, calcined powder and single crystal fiber, only the expected scheelite CaWO4 phase was observed. It was verified large homogeneity in the crystal composition, without the presence of secondary phases. The Radioluminescence spectra of the as-grown single crystal fibers are in agreement with that present in Literature for bulk single crystals, presented a single emission band centered at 420 nm when irradiated with ?-rays.

Silva, M. S.; Jesus, L. M.; Barbosa, L. B.; Ardila, D. R.; Andreeta, J. P.; Silva, R. S.

2014-11-01

159

Anisotropy of transient photoconductivity in functionalized pentacene single crystals  

E-print Network

to their potential applications in thin film transis- tors, organic light-emitting diodes, solar cells, etc.1 Thin single crystal platelets and polycrystalline thin films are par- ticularly interesting for applicationsAnisotropy of transient photoconductivity in functionalized pentacene single crystals O

Ostroverkhova, Oksana

160

Precipitation of Copper Silicide in Voids in Silicon Single Crystals  

E-print Network

Precipitation of Copper Silicide in Voids in Silicon Single Crystals A thesis presented by Cheng Spaepen Cheng-Yen Wen Precipitation of Copper Silicide in Voids in Silicon Single Crystals Abstract precipitates have filled the open volume. For implementation of this method, precipitation of the Cu silicide

161

The growth technology for 300 mm single crystal silicon  

Microsoft Academic Search

The fabrication technique for 300 mm silicon single crystals and wafers is the central topic of silicon material research recently. The study on the growth technique of 300 mm silicon ingots has been developed in our institute since 1997. The research mainly focuses on the following aspects: (1) process conditions for fabrication of the dislocation-free silicon single crystal; (2) oxygen

H Tu; Q Zhou; G Zhang; J Wang; Q Chang; F Qin; F Fang; Z Wu; G Wan

2001-01-01

162

Single crystal silicon rotary microactuator for hard disk drive  

Microsoft Academic Search

A single crystal silicon rotary microactuator for hard disk drives (HDD) is described in this paper. The microactuator is mounted between the slider and suspension and drives the slider on which a magnetic head element is attached. The microactuator has electrically isolated microstructures with an aspect ratio 20:1 directly processed from a single crystal silicon substrate. It consists of a

J. Q. Mou; Y. Lu; J. P. Yang; Q. H. Li

2003-01-01

163

Semiconductor single crystal external ring resonator cavity laser and gyroscope  

SciTech Connect

A ring laser is described comprising: a semiconductor single crystal external ring resonator cavity having a plurality of reflecting surfaces defined by the planes of the crystal and establishing a closed optical path; and a discrete laser medium disposed in said semiconductor single crystal external ring resonator cavity for generating coherent light in said cavity, wherein said resonator cavity is decoupled from the laser medium.

Spitzer, M.P.

1993-08-31

164

Strain effects in a single ZnO microwire with wavy configurations  

NASA Astrophysics Data System (ADS)

We investigate strain-induced optical modulation in a ZnO microwire with wavy geometries induced by mechanical strains. Curved sections of the wavy ZnO microwire show red-/blue-shifts of near-band-edge emission and broadening of full width at half maximum in cathodoluminescence spectra along the length of the wavy ZnO microwire, compared with straight sections. The observed variations indicate that local strains in the wavy ZnO microwire lead to strain-dependent local changes of its energy band structure. The local bending curvature calculations using a geometric model also provide correlation between the shift of the near-band-edge emission peaks and the bending strain.

Park, Jong Bae; Hong, Woong-Ki; Bae, Tae Sung; Inn Sohn, Jung; Cha, SeungNam; Kim, Jong Min; Yoon, Jongwon; Lee, Takhee

2013-11-01

165

Strain effects in a single ZnO microwire with wavy configurations.  

PubMed

We investigate strain-induced optical modulation in a ZnO microwire with wavy geometries induced by mechanical strains. Curved sections of the wavy ZnO microwire show red-/blue-shifts of near-band-edge emission and broadening of full width at half maximum in cathodoluminescence spectra along the length of the wavy ZnO microwire, compared with straight sections. The observed variations indicate that local strains in the wavy ZnO microwire lead to strain-dependent local changes of its energy band structure. The local bending curvature calculations using a geometric model also provide correlation between the shift of the near-band-edge emission peaks and the bending strain. PMID:24140605

Park, Jong Bae; Hong, Woong-Ki; Bae, Tae Sung; Sohn, Jung Inn; Cha, SeungNam; Kim, Jong Min; Yoon, Jongwon; Lee, Takhee

2013-11-15

166

Microscale Laser Peen Forming of Single Crystal  

SciTech Connect

As the result of quickly increased requirement in many industrial products resulting from microtechnology, laser thermal microforming and microsurface treatment [microscale laser shock peening (?LSP)] have been well studied. By combining the beneficial effects of these two processes with a controlled bending deformation, microscale laser peen forming (?LPF) attracts more attention recently since it not only improves the fatigue life of the material but also shapes microscale metallic parts at the same time. In the present study, ?LSP of single crystal aluminum was presented to study anisotropic material response. Local plastic deformation was characterized by lattice rotation measured through electron backscatter diffraction. Residual stress distributions of both sides of a peened sample, characterized by x-ray microdiffraction, were compared with the results obtained from finite element method simulation. ?LPF anisotropic behavior was investigated in three effective slip systems via both the anisotropic slip line theory and numerical method. Also, the work hardening effect resulted from self-hardening, and latent hardening was analyzed through comparing the results with and without considering hardening.

Wang,Y.; Fan, Y.; Kysar, J.; Vukelic, S.; Yao, Y.

2008-01-01

167

Advanced single crystal for SSME turbopumps  

NASA Technical Reports Server (NTRS)

The objective of this program was to evaluate the influence of high thermal gradient casting, hot isostatic pressing (HIP) and alternate heat treatments on the microstructure and mechanical properties of a single crystal nickel base superalloy. The alloy chosen for the study was PWA 1480, a well characterized, commercial alloy which had previously been chosen as a candidate for the Space Shuttle Main Engine high pressure turbopump turbine blades. Microstructural characterization evaluated the influence of casting thermal gradient on dendrite arm spacing, casting porosity distribution and alloy homogeneity. Hot isostatic pressing was evaluated as a means of eliminating porosity as a preferred fatigue crack initiation site. The alternate heat treatment was chosen to improve hydrogen environment embrittlement resistance and for potential fatigue life improvement. Mechanical property evaluation was aimed primarily at determining improvements in low cycle and high cycle fatigue life due to the advanced processing methods. Statistically significant numbers of tests were conducted to quantitatively demonstrate life differences. High thermal gradient casting improves as-cast homogeneity, which facilitates solution heat treatment of PWA 1480 and provides a decrease in internal pore size, leading to increases in low cycle and high cycle fatigue lives.

Fritzemeier, L. G.

1989-01-01

168

ZnO thin film deposition using colliding plasma plumes and single plasma plume: Structural and optical properties  

NASA Astrophysics Data System (ADS)

We report the comparative study on synthesis of thin films of ZnO on glass substrates using IR laser ablated colliding plasma plumes and conventional pulsed laser deposition using 355 nm in oxygen ambient. The optical properties of deposited films are characterized using optical transmission in the UV-visible range of spectrum and photoluminescence measurements. X-ray diffraction and atomic force microscopy are used to investigate the surface morphology of synthesized ZnO films. The films synthesized using colliding plumes created with 1064 nm are non-polar a-plane ZnO with transmission in UV-visible (300-800 nm) region ˜60% compared to polycrystalline thin film deposited using single plume which has chunk deposition and poor optical response. However, deposition with 355 nm single plume shows polar c-axis oriented thin film with average roughness (˜thickness) of ˜86 nm (˜850 nm) compared to ˜2 nm (˜3 ?m) for 1064 nm colliding plumes. These observed differences in the quality and properties of thin films are attributed to the flux of mono-energetic plasma species with almost uniform kinetic energy and higher thermal velocity reaching the substrate from interaction/stagnation zone of colliding plasma plumes.

Gupta, Shyam L.; Thareja, Raj K.

2013-12-01

169

Ultraviolet/blue light-emitting diodes based on single horizontal ZnO microrod/GaN heterojunction  

PubMed Central

We report electroluminescence (EL) from single horizontal ZnO microrod (MR) and p-GaN heterojunction light-emitting diodes under forward and reverse bias. EL spectra were composed of two blue emissions centered at 431 and 490 nm under forward biases, but were dominated by a ultraviolet (UV) emission located at 380 nm from n-ZnO MR under high reverse biases. Light-output-current characteristic of the UV emission reveals that the rate of radiative recombination is faster than that of the nonradiative recombination. Highly efficient ZnO excitonic recombination at reverse bias is caused by electrons tunneling from deep-level states near the n-ZnO/p-GaN interface to the conduction band in n-ZnO. PMID:25232299

2014-01-01

170

Single crystal to single crystal transformation and hydrogen-atom transfer upon oxidation of a cerium coordination compound.  

PubMed

Trivalent and tetravalent cerium compounds of the octamethyltetraazaannulene (H2omtaa) ligand have been synthesized. Electrochemical analysis shows a strong thermodynamic preference for the formal cerium(IV) oxidation state. Oxidation of the cerium(III) congener Ce(Homtaa)(omtaa) occurs by hydrogen-atom transfer that includes a single crystal to single crystal transformation upon exposure to an ambient atmosphere. PMID:23534677

Williams, Ursula J; Mahoney, Brian D; Lewis, Andrew J; DeGregorio, Patrick T; Carroll, Patrick J; Schelter, Eric J

2013-04-15

171

Study of single crystals of metal solid solutions  

NASA Technical Reports Server (NTRS)

The growth of single crystals of relatively high melting point metals such as silver, copper, gold, and their alloys was investigated. The purpose was to develop background information necessary to support a space flight experiment and to generate ground based data for comparison. The ground based data, when compared to the data from space grown crystals, are intended to identify any effects which zero-gravity might have on the basic process of single crystal growth of these metals. The ultimate purposes of the complete investigation are to: (1) determine specific metals and alloys to be investigated; (2) grow single metal crystals in a terrestrial laboratory; (3) determine crystal characteristics, properties, and growth parameters that will be effected by zero-gravity; (4) evaluate terrestrially grown crystals; (5) grow single metal crystals in a space laboratory such as Skylab; (6) evaluate the space grown crystals; (7) compare for zero-gravity effects of crystal characteristics, properties, and parameters; and (8) make a recommendation as to production of these crystals as a routine space manufacturing proceses.

Doty, J. P.; Reising, J. A.

1973-01-01

172

High cycle fatigue crack initiation in single crystals and polycrystals  

NASA Astrophysics Data System (ADS)

The objective of this research is to analyze the high-cycle fatigue crack initiation in both monocrystalline and polycrystalline ductile metals. Persistent slip bands have been observed in both single crystals and polycrystals in numerous high-cycle fatigue tests. Extrusions and intrusions at the free surface of fatigued specimens are the favorable sites for fatigue crack initiation. In the present study, the micromechanic theory of high-cycle fatigue crack initiation, proposed by Lin and Ito, is extended to include the crystal anisotropic effect on the growth of extrusions in polycrystals and to study the high-cycle fatigue deformation in single crystals. Previous studies based on Lin and Ito model mainly concerned the fatigue crack initiation in aluminum and its alloys. The elastic anisotropy of individual crystals is insignificant and was accordingly neglected. However, the anisotropy of the elastic constants of some other metallic crystals, such as titanium and some intermetallic compounds, is not negligible. In this study, the effect of crystal anisotropy is considered by using Eshelby's equivalent inclusion method. The polycrystal of Nisb3Al intermetallic compound is analyzed for studying the effect on fatigue crack initiation. The model of fatigue crack initiation of polycrystals is applied to analyze the fatigue deformation in single crystals. The residual stress field in a single crystal is calculated by using a superposition method. The fatigue deformation of single crystals under the constant plastic strain amplitude control is investigated.

Teng, Ningjun

173

Grooving wear of single-crystal tungsten carbide  

Microsoft Academic Search

The anisotropic nature of tungsten carbide (WC) single crystals has been evaluated in single-tip scratch testing and in multiple-tip abrasion. The single-tip grooves were made with a Vickers diamond indenter and the abrasion tests were performed with diamond and silica grits. All tests were performed on both the prism and basal planes of the WC crystals. A polycrystalline binderless carbide

H Engqvist; S Ederyd; N Axén; S Hogmark

1999-01-01

174

Ion crystal transducer for strong coupling between single ions and single photons  

E-print Network

A new approach for realization of a quantum interface between single photons and single ions in an ion crystal is proposed and analyzed. In our approach the coupling between a single photon and a single ion is enhanced via the collective degrees of freedom of the ion crystal. Applications including single-photon generation, a memory for a quantum repeater, and a deterministic photon-photon, photon-phonon, or photon-ion entangler are discussed.

L. Lamata; D. R. Leibrandt; I. L. Chuang; J. I. Cirac; M. D. Lukin; V. Vuletic; S. F. Yelin

2011-02-21

175

Single-crystal gallium nitride nanotubes  

Microsoft Academic Search

Since the discovery of carbon nanotubes in 1991 (ref. 1), there have been significant research efforts to synthesize nanometre-scale tubular forms of various solids. The formation of tubular nanostructure generally requires a layered or anisotropic crystal structure. There are reports of nanotubes made from silica, alumina, silicon and metals that do not have a layered crystal structure; they are synthesized

Joshua Goldberger; Rongrui He; Yanfeng Zhang; Sangkwon Lee; Haoquan Yan; Heon-Jin Choi; Peidong Yang

2003-01-01

176

Constricted hysteresis loops in Fe and Ni single crystals  

NASA Astrophysics Data System (ADS)

Magnetic hysteresis loops reflect the variety of magnetic domain structures and have been considered to have normal rectangular or leaf-like shapes in standard ferromagnets such as Fe and Ni metals. We report on observations of constricted hysteresis loops in Fe and Ni single crystals with very low defect densities. The constricted loops were observed below T=150 K and in a medium temperature range from 150 to 430 K in Fe and Ni single crystals, respectively. These constricted loops disappear by weak plastic deformation for both single crystals. The origin of constricted hysteresis loops was explained by eddy current effects under less domain wall pinning due to dislocations.

Takahashi, Seiki; Kobayashi, Satoru; Shishido, Toetsu

2010-11-01

177

A study of crystal growth by solution technique. [triglycine sulfate single crystals  

NASA Technical Reports Server (NTRS)

The advantages and mechanisms of crystal growth from solution are discussed as well as the effects of impurity adsorption on the kinetics of crystal growth. Uncertainities regarding crystal growth in a low gravity environment are examined. Single crystals of triglycine sulfate were grown using a low temperature solution technique. Small components were assembled and fabricated for future space flights. A space processing experiment proposal accepted by NASA for the Spacelab-3 mission is included.

Lal, R. B.

1979-01-01

178

Hole mobility in organic single crystals measured by a ``flip-crystal'' field-effect technique  

Microsoft Academic Search

We report on single crystal high mobility organic field-effect transistors prepared on prefabricated substrates using a ``flip-crystal'' approach. This method minimizes crystal handling and avoids direct processing of the crystal that may degrade the field-effect transistors' electrical characteristics. A chemical treatment process for the substrate ensures a reproducible device quality. With limited purification of the starting materials, hole mobilities of

C. Goldmann; S. Haas; C. Krellner; K. P. Pernstich; D. J. Gundlach; B. Batlogg

2004-01-01

179

Stability of Detached Grown Germanium Single Crystals  

NASA Technical Reports Server (NTRS)

Detachment of the melt meniscus from the crucible during semiconductor Bridgman growth experiments has been observed in recent years, especially under microgravity experiments. Under earth conditions, the hydrostatic pressure counteracts the mechanism, whereby it is more difficult to achieve detached Bridgman growth. Attempts to get stable detached growth under terrestrial conditions have been discussed in the literature and have been the subject of recent experiments in our own group. The advantage of crystals grown without wall contact is obvious: In general, they possess a higher crystal quality than conventional Bridgman grown crystals with wall contact. However, due to the interaction of different parameters such as the wetting behavior of the melt with the crucible, and the dependence of the growth angle with the shape of the melt meniscus, the mechanism leading to detachment is very complicated and not completely understood. We have grown several doped and undoped Germanium crystals with the detached Bridgman and the normal Bridgman growth technique. Pyrolytic boron nitride containers were used for all growth experiments. In the detached grown crystals the typical gap thickness between the pBN crucible and the crystal is in the range of 10 to 100 micrometers, which was determined by performing profilometer measurements. Etch pit density measurements were also performed and a comparison between detached and attached grown crystals will be given. An interesting feature was detected on the surface of a detached grown crystal. Strong surface striations with an average axial distance of 0.5 mm were observed around the whole circumference. The maximum fluctuation of the gap thickness is in the range of 5-10 micrometers. These variations of the detached gap along the crystal axis can be explained by a kind of stiction of the melt/crucible interface and thus by a variation of the meniscus shape. This phenomenon leading to the fluctuation of the gap thickness will be discussed in detail.

Schweizer, M.; Volz, M. P.; Cobb, S. D.; Vujisic, L.; Szofran, F. R.; Rose, M. Franklin (Technical Monitor)

2001-01-01

180

Stability of Detached Grown Germanium Single Crystals  

NASA Technical Reports Server (NTRS)

Detachment of the melt meniscus from the crucible during semiconductor Bridgman growth experiments has been observed in recent years especially, under microgravity experiments. Under earth conditions, the hydrostatic pressure counteracts the mechanism, whereby it is more difficult to achieve detached Bridgman growth. Attempts to get stable detached growth under terrestrial conditions have been discussed in the literature and have been the subject of recent experiments in our own group. The advantage of crystals grown without wall contact is obvious: In general, they possess a higher crystal quality than conventional Bridgman grown crystals with wall contact. However, due to the interaction of different parameters such as the wetting behavior of the melt with the crucible, and the dependence of the growth angle with the shape of the melt meniscus, the mechanism leading to detachment is very complicated and not completely understood. We have grown several doped and undoped Germanium crystals with the detached Bridgman and the normal Bridgman growth technique. Pyrolytic boron nitride containers were used for all growth experiments. In the detached grown crystals the typical gap thickness between the pBN crucible and the crystal is in the range of 10 to 100 microns, which was determined by performing profilometer measurements. Etch pit density measurements were also performed and a comparison between detached and attached grown crystals will be given. An interesting feature was detected on the surface of a detached grown crystal. Strong surface striations with an average axial distance of 0.5mm were observed around the whole circumference. The maximum fluctuation of the gap thickness is in the range of 5-10 microns. These variations of the detached gap along the crystal axis can be explained by a kind of stiction of the melt/crucible interface and thus by a variation of the meniscus shape. This phenomenon leading to the fluctuation of the gap thickness will be discussed in detail.

Schweizer, M.; Volz, M. P.; Cobb, S. D.; Motakef, S.; Szofran, F. R.; Curreri, Peter A. (Technical Monitor)

2002-01-01

181

Hydrogen Donors in ZnO M.D. McCluskey, S.J. Jokela, and W.M. Hlaing Oo  

E-print Network

donors in ZnO. To address these issues, we performed vibrational spectroscopy on bulk, single-crystal ZnO is wurtzite. 4H, 6H, and 2H denote the hexagonal polytypes of SiC. GaN SiC ZnO Diamond Cubic 3.27 (379 in the blue-to-ultraviolet (UV) region of the spectrum [1,3]. GaN, silicon carbide (SiC), and diamond have

McCluskey, Matthew

182

Growth and characterization of ammonium acid phthalate single crystals  

NASA Astrophysics Data System (ADS)

Ammonium acid phthalate (AAP) has been synthesized and single crystals were grown by slow evaporation solution growth technique. The unit cell parameters were confirmed by single crystal X-ray diffraction analysis and it belongs to orthorhombic system with the space group of Pcab. The high resolution X-ray diffraction studies revealed the crystalline perfection of the grown crystal. The various functional groups of AAP were identified by FT-IR and Raman spectral analyses. Thermal stability of the grown crystals was studied by TGA/DTA. The optical properties of the grown crystals were analyzed by UV-Vis-NIR and photoluminescence spectral studies. The mechanical property of the grown crystal was studied by Vickers microhardness measurement. The growth features of AAP were analyzed by chemical etching.

Arunkumar, A.; Ramasamy, P.

2013-04-01

183

Growth and characterization of organic material 4-dimethylaminobenzaldehyde single crystal.  

PubMed

The organic material 4-dimethylaminobenzaldehyde single crystals were grown by slow evaporation technique. The grown crystal was confirmed by the single crystal and powder X-ray diffraction analyses. The functional groups of the crystal have been identified from the Fourier Transform Infrared (FTIR) and FT-Raman studies. The optical property of the grown crystal was analyzed by UV-Vis-NIR and photoluminescence (PL) spectral measurements. The thermal behavior of the grown crystal was analyzed by thermogravimetric (TG) and differential thermal analyses (DTA). Dielectric measurements were carried out with different frequencies by using parallel plate capacitor method. The third order nonlinear optical properties of 4-dimethylaminobenzaldehyde was measured by the Z-scan technique using 532 nm diode pumped continuous wave (CW) Nd:YAG laser. PMID:25168233

Jebin, R P; Suthan, T; Rajesh, N P; Vinitha, G; Madhusoodhanan, U

2015-01-25

184

Growth and characterization of organic material 4-dimethylaminobenzaldehyde single crystal  

NASA Astrophysics Data System (ADS)

The organic material 4-dimethylaminobenzaldehyde single crystals were grown by slow evaporation technique. The grown crystal was confirmed by the single crystal and powder X-ray diffraction analyses. The functional groups of the crystal have been identified from the Fourier Transform Infrared (FTIR) and FT-Raman studies. The optical property of the grown crystal was analyzed by UV-Vis-NIR and photoluminescence (PL) spectral measurements. The thermal behavior of the grown crystal was analyzed by thermogravimetric (TG) and differential thermal analyses (DTA). Dielectric measurements were carried out with different frequencies by using parallel plate capacitor method. The third order nonlinear optical properties of 4-dimethylaminobenzaldehyde was measured by the Z-scan technique using 532 nm diode pumped continuous wave (CW) Nd:YAG laser.

Jebin, R. P.; Suthan, T.; Rajesh, N. P.; Vinitha, G.; Madhusoodhanan, U.

2015-01-01

185

Growing intermetallic single crystals using in situ decanting  

SciTech Connect

High temperature metallic solution growth is one of the most successful and versatile methods for single crystal growth, and is particularly suited for exploratory synthesis. The method commonly utilizes a centrifuge at room temperature and is very successful for the synthesis of single crystal phases that can be decanted from the liquid below the melting point of the silica ampoule. In this paper, we demonstrate the extension of this method that enables single crystal growth and flux decanting inside the furnace at temperatures above 1200°C. This not only extends the number of available metallic solvents that can be used in exploratory crystal growth but also can be particularly well suited for crystals that have a rather narrow exposed solidification surface in the equilibrium alloy phase diagram.

Petrovic, Cedomir; Canfield, Paul; Mellen, Jonathan

2012-05-16

186

The Growth of Large Single Crystals.  

ERIC Educational Resources Information Center

Presented is an experiment which demonstrates principles of experimental design, solubility, and crystal growth and structure. Materials, procedures and results are discussed. Suggestions for adapting this activity to the high school laboratory are provided. (CW)

Baer, Carl D.

1990-01-01

187

Designed three-dimensional freestanding single-crystal carbon architectures.  

PubMed

Single-crystal carbon nanomaterials have led to great advances in nanotechnology. The first single-crystal carbon nanomaterial, fullerene, was fabricated in a zero-dimensional form. One-dimensional carbon nanotubes and two-dimensional graphene have since followed and continue to provide further impetus to this field. In this study, we fabricated designed three-dimensional (3D) single-crystal carbon architectures by using silicon carbide templates. For this method, a designed 3D SiC structure was transformed into a 3D freestanding single-crystal carbon structure that retained the original SiC structure by performing a simple single-step thermal process. The SiC structure inside the 3D carbon structure is self-etched, which results in a 3D freestanding carbon structure. The 3D carbon structure is a single crystal with the same hexagonal close-packed structure as graphene. The size of the carbon structures can be controlled from the nanoscale to the microscale, and arrays of these structures can be scaled up to the wafer scale. The 3D freestanding carbon structures were found to be mechanically stable even after repeated loading. The relationship between the reversible mechanical deformation of a carbon structure and its electrical conductance was also investigated. Our method of fabricating designed 3D freestanding single-crystal graphene architectures opens up prospects in the field of single-crystal carbon nanomaterials and paves the way for the development of 3D single-crystal carbon devices. PMID:25329767

Park, Ji-Hoon; Cho, Dae-Hyun; Moon, Youngkwon; Shin, Ha-Chul; Ahn, Sung-Joon; Kwak, Sang Kyu; Shin, Hyeon-Jin; Lee, Changgu; Ahn, Joung Real

2014-11-25

188

Research on TGS single crystal growth with modulated structure  

NASA Astrophysics Data System (ADS)

The experimental results of TGS crystal growth with modulated structure (periodic laminar of ferroelectric domains) is briefly discussed in this paper. The method used here is to add some DL-alanine additive in the solution of TGS and to apply the electric field during crystal growth, the direction of which is periodically varied. By using this method, TGS single crystals containing a nearly regular and flat periodic laminar structure of ferroelectric domains have been fabricated.

Wang, Wenshan; Qi, Ming

1986-12-01

189

Characterization of phosphoric acid doped TGS single crystals  

Microsoft Academic Search

Single crystals of phosphoric acid (H3PO4) doped triglycine sulfate (TGSP) are grown from aqueous solution containing 10–50mol% of H3PO4. Large sized crystals of dimension (70mm×40mm×25mm) suitable for IR detector applications are obtained with 20mol% of H3PO4. They exhibit elongated domains, and the domain density is higher than in undoped TGS crystals. FT-IR analysis indicates the presence of both zwitter and

Aparna Saxena; Vinay Gupta; K. Sreenivas

2004-01-01

190

X-ray topographic examination of large paraffin single crystals  

Microsoft Academic Search

The internal microstructure of large melt-grown paraffin (n-eicosane, C20H42) single crystals was examined by the Lang x-ray diffraction projection topographic technique. Crystal selection was facilitated by use of an electro-optical system which permitted instantaneous display of Laue transmission x-ray diffraction patterns on a television monitor. The crystals were oriented and topographic diffraction planes were selected by the use of a

Robert E. Green; Edward N. Farabaugh; John M. Crissman

1975-01-01

191

Growth and polytypism of single crystals of cadmium bromide  

NASA Astrophysics Data System (ADS)

Single crystals of cadmium bromide have been grown by Bridgman-Stockbarger technique and their polytypism studied by X-ray diffraction. Oscillation photographs obtained from several different regions of the crystals have revealed the occurrence of only the small-period polytype 6R in the crystals. The results have been compared with those reported earlier for the isostructural compounds CdI 2 and PbI 2.

Chaudhary, S. K.; Trigunayat, G. C.

1985-12-01

192

Single-drop optimization of protein crystallization  

PubMed Central

A completely new crystal-growth device has been developed that permits charting a course across the phase diagram to produce crystalline samples optimized for diffraction experiments. The utility of the device is demonstrated for the production of crystals for the traditional X-ray diffraction data-collection experiment, of microcrystals optimal for data-collection experiments at a modern microbeam insertion-device synchrotron beamline and of nanocrystals required for data collection on an X-ray laser beamline. PMID:22869140

Meyer, Arne; Dierks, Karsten; Hilterhaus, Dierk; Klupsch, Thomas; Mühlig, Peter; Kleesiek, Jens; Schöpflin, Robert; Einspahr, Howard; Hilgenfeld, Rolf; Betzel, Christian

2012-01-01

193

Single-drop optimization of protein crystallization.  

PubMed

A completely new crystal-growth device has been developed that permits charting a course across the phase diagram to produce crystalline samples optimized for diffraction experiments. The utility of the device is demonstrated for the production of crystals for the traditional X-ray diffraction data-collection experiment, of microcrystals optimal for data-collection experiments at a modern microbeam insertion-device synchrotron beamline and of nanocrystals required for data collection on an X-ray laser beamline. PMID:22869140

Meyer, Arne; Dierks, Karsten; Hilterhaus, Dierk; Klupsch, Thomas; Mühlig, Peter; Kleesiek, Jens; Schöpflin, Robert; Einspahr, Howard; Hilgenfeld, Rolf; Betzel, Christian

2012-08-01

194

Identification of a donor-related recombination channel in ZnO thin films Matthias Brandt,* Holger von Wenckstern, Gabriele Benndorf, Martin Lange, Christof P. Dietrich, Christian Kranert,  

E-print Network

O or heavily aluminum- doped ZnO buffer layer. The properties of the recombination mechanism were probed oxide with very promising properties for applications in optoelectronics, among them its direct band gap. From these studies, numerous reports emerged on the luminescence properties of ZnO single crystals

Nabben, Reinhard

195

Study of single crystals of metal solid solutions  

NASA Technical Reports Server (NTRS)

The parameters and requirements for growing single crystals of relatively high melting point metals in a zero gravity environment are studied. The crystal growth of metals such as silver, copper, gold, and alloys with a melting point between 900-1100 C is examined.

Doty, J. P.; Reising, J. A.

1973-01-01

196

Growth of large single crystals of the orthorhombic paracetamol  

NASA Astrophysics Data System (ADS)

A new procedure for the growth of large (cm-range) single crystals of the metastable orthorhombic (s.g. Pcab) polymorph of paracetamol is described. The crystals were grown by very slow cooling of hot water solutions under the conditions, when the multiple nucleation was prevented. The samples were characterized by DSC and X-ray diffraction.

Mikhailenko, M. A.

2004-05-01

197

Hertzian Fracture in Single Crystals with the Diamond Structure  

Microsoft Academic Search

Extension of an earlier theory of Hertzian fracture in brittle isotropic materials is here made to include the case of brittle single crystals, with particular reference to crystals having the diamond structure. A detailed description is first given of the inhomogeneous stress field in a flat, elastic specimen loaded normally with a hard sphere. The geometry of cracks growing in

B. R. Lawn

1968-01-01

198

Brittlestar-Inspired Microlens Arrays Made of Calcite Single Crystals.  

PubMed

Unique concave microlens arrays (MLAs) made of calcite single crystals with tunable crystal orientations can be readily fabricated by template-assisted epitaxial growth in solution without additives under ambient conditions. While the non-birefringent calcite (001) MLA showed excellent imaging performance like brittlestar's microlens arrays, the birefringent calcite (104) MLA exhibited remarkable polarization-dependent optical properties. PMID:25366272

Ye, Xiaozhou; Zhang, Fei; Ma, Yurong; Qi, Limin

2014-11-01

199

Single crystal orientation effects in shock initiation of PETN explosive  

SciTech Connect

Over the past nine years in Los Alamos we have studied shock initiation of detonation in single crystals of PETN explosive. We have demonstrated the effects of point defects and crystal orientation on shock sensitivity. Here we report recent work on orientation effects and anomalous detonation in <110> orientation at 4 GPa. 5 refs.

Dick, J.J.

1988-01-01

200

Constitutive modeling of creep of single crystal superalloys  

E-print Network

In this work, a constitutive theory is developed, within the context of continuum mechanics, to describe the creep deformation of single crystal superalloys. The con- stitutive model that is developed here is based on the fact that as bodies deform...

Prasad, Sharat Chand

2006-10-30

201

On the deformation mechanisms in single crystal Hadfield manganese steels  

SciTech Connect

Austenitic manganese steel, so called Hadfield manganese steel, is frequently used in mining and railroad frog applications requiring excessive deformation and wear resistance. Its work hardening ability is still not completely understood. Previous studies attributed the work-hardening characteristics of this material to dynamic strain aging or an imperfect deformation twin, a so-called pseudotwin. Unfortunately, these previous studies have all focused on polycrystalline Hadfield steels. To properly study the mechanisms of deformation in the absence of grain boundary or texture effects, single crystal specimens are required. The purpose of this work is the following: (1) observe the inelastic stress-strain behavior of Hadfield single crystals in orientations where twinning and slip are individually dominating or when they are competing deformation mechanisms; and (2) determine the microyield points of Hadfield single crystals and use micro-mechanical modeling to predict the stress-strain response of a single crystal undergoing micro-twinning.

Karaman, I.; Sehitoglu, H.; Gall, K. [Univ. of Illinois, Urbana, IL (United States). Dept. of Mechanical and Industrial Engineering] [Univ. of Illinois, Urbana, IL (United States). Dept. of Mechanical and Industrial Engineering; Chumlyakov, Y.I. [Siberian Physical and Technical Inst., Tomsk (Russian Federation). Physics of Plasticity and Strength of Materials Lab.] [Siberian Physical and Technical Inst., Tomsk (Russian Federation). Physics of Plasticity and Strength of Materials Lab.

1998-02-13

202

Growth and properties of shaped single crystals of lithium fluoride  

NASA Astrophysics Data System (ADS)

Shaped single crystals of lithium fluoride have been produced by the Stepanov method using shapers which are wetted and unwetted by the melt. Dislocation structure, porosity, optical properties, ion conductivity, and distribution of magnesium impurities have been studied.

Antonov, P. I.; Krymov, V. M.; Hartmann, E.

1990-07-01

203

Magnetic properties of Gd doped Y and Sc single crystals  

Microsoft Academic Search

Magnetization measurements on 5 and 15% ScGd single crystals show typical spin glass like behaviour for fields parallel and perpendicular to the c axis of the hexagonal structure. In contrast for1, 2 and 3% Gd doped in Y single crystals there is a cusp in the susceptibility but no irreversibility below the temperature of the cusp. Spin-flop like transitions in

R. Wendler; P. Pureur; A. Fert; K. Baberschke

1984-01-01

204

Melt growth of high purity cadmium bromide single crystals  

NASA Astrophysics Data System (ADS)

The earlier attempts to grow pure single crystals of cadmium bromide by zone-melting have proved difficult due to the very high vapour pressure of the compound. The problem has been successfully overcome now by suitably employing the method of vertical zone-refining, which has helped to reduce the loss of material by evaporation to just 3%. Highly pure single crystals have been grown and results of their preliminary X-ray diffraction analysis have been briefly reported.

Singh, Kulvinder; Trigunayat, G. C.

1989-10-01

205

Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals  

DOEpatents

A method of fabricating bulk YBa{sub 2}Cu{sub 3}O{sub x} where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa{sub 2}Cu{sub 3}O{sub x} are heated in the presence of a Nd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub y} seed crystal to a temperature sufficient to form a liquid phase in the YBa{sub 2}Cu{sub 3}O{sub x} while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa{sub 2}Cu{sub 3}O{sub x} material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material. 7 figs.

Todt, V.; Miller, D.J.; Shi, D.; Sengupta, S.

1998-07-07

206

Growth of single crystals by vapor transport  

NASA Technical Reports Server (NTRS)

The primary objectives of the program were to establish basic vapor transport and crystal growth properties and to determine thermodynamic, kinetic and structural parameters relevant to chemical vapor transport systems for different classes of materials. An important aspect of these studies was the observation of the effects of gravity-caused convection on the mass transport rate and crystal morphology. These objectives were accomplished through extensive vapor transport, thermochemical and structural studies on selected Mn-chalcogenides, II-VI and IV-VI compounds.

Wiedemeier, H.

1978-01-01

207

Measurement of single crystal surface parameters  

NASA Technical Reports Server (NTRS)

The sticking coefficient and thermal desorption spectra of Cs from the (110) plane of W was investigated. A sticking coefficient of unity for the monolayer region was measured for T 250 K. Several distinct binding states were observed in the thermal desorption spectrum. Work function and electron reflection measurements were made on the (110) and (100) crystal faces of Mo. Both LEED and Auger were used to determine the orientation and cleanliness of the crystal surfaces. The work function values obtained for the (110) and (100) planes of Mo were 4.92 and 4.18 eV respectively.

Swanson, L. W.; Bell, A. E.; Strayer, R. W.

1972-01-01

208

Catalyzed growth of doped TGS single crystals for infrared applications  

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with Pr3+ Sm3+, Pd2+, Co2+, Pt4+ and PO43- with L-alanin were grown from aqueous solutions by means of the slow cooling method. Surface morphology, domain structure and P-E hysteresis loops have been investigated. The model of catalyzed growth of {001}and{101}crystal pyramids on the basis of metal-glycine complexes has been suggested. We have found on the basis of experimental results that TGS single crystals doped with Pt4+ and L-alanin are excellent materials for construction of infrared detectors.

Novotny, Jan; Zelinka, J.; Podvalova, Z.

2002-03-01

209

Hydroxyethylammonium maleate (HEAM) single crystal for optical limiting applications  

NASA Astrophysics Data System (ADS)

A novel hydroxyethylammonium maleate single crystal was grown by slow evaporation solution method for the first time. The structure of the title compound is determined by single crystal X-ray diffraction. The linear optical properties were studied using ultraviolet-visible and photoluminescence spectroscopy. The third-order nonlinear optical property of title compound was studied by Z-scan technique to determine its nonlinear absorption and nonlinear refraction. Thermal property was studied by thermogravimetry, differential thermal analysis and differential scanning calorimetric analyses. The mechanical stability of the material was studied by Vickers microhardness tester. Further, etching study was done to examine the defects in the crystal.

Sudharsana, N.; Hamad, S.; Venugopal Rao, S.; Krishnakumar, V.; Nagalakshmi, R.

2015-02-01

210

Investigation of localized deformation in NiAl single crystals  

SciTech Connect

Deformation of NiAl single crystals was studied using finite element analysis to investigate the modes of localized deformation. Constitutive parameters and hardening characteristics of the active slip systems were estimated by comparing numerical simulation results with experimental results. Deformation of tensile specimens of NiAl single crystal was simulated when loaded along different crystal orientations to understand the deformation mechanism that results in various localized modes of deformation. In particular, the formation of shear bands and kink bands was studied and the material and geometric characteristics that influence the formation of such localization were investigated.

Kumar, A.V.; Yang, Culho; Seelam, V.B.R. [Univ. of Florida, Gainesville, FL (United States). Dept. of Mechanical Engineering

1998-07-01

211

Fatigue Failure Criteria for Single Crystal Nickel Superalloys  

NASA Technical Reports Server (NTRS)

High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine and rocket engine turbopump blades is a pervasive problem. Single crystal turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry and NASA because of their superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys. Single-crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the pan geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades is complicated to predict due to the material orthotropy and variations in crystal orientations. A fatigue failure criteria based on the maximum shear stress amplitude [delta t max] on the 30 slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criteria reduces the scatter in uniaxial LCF test data, for four different specimen orientations, for PWA 1484 at 1200 F in air, quite well. A power law curve fit of the failure parameter, delta t max, vs. cycles to failure is presented.

Arakere, Nagaraj K.

1999-01-01

212

Elastic Moduli, Pressure Derivatives, and Temperature Derivatives of Single-Crystal Olivine and Single-Crystal Forsterite  

Microsoft Academic Search

Ultrasonic wave velocities in single-crystal forsteritc (F) and single-crystal olivine (0) have been measured as a function of pressure and of temperature near ambient conditions. Shear and longitudinal velocities were measured in eighteen independent modes, so that each of the nine elastic constants could be calculated by at least two independent equations. The adiabatic stiffness constants c{j (in Mb), their

Mineo Kumazawa; Orson L. Anderson

1969-01-01

213

Crystal structure, spectral, thermal and dielectric studies of a new zinc benzoate single crystal  

NASA Astrophysics Data System (ADS)

Single crystals of zinc benzoate with a novel structure were grown in gel media. Sodium metasilicate of gel density 1.04 g/cc at pH 6 was employed to yield transparent single crystals. The crystal structure of the compound was ascertained by single crystal X-ray diffractometry. It was noted that the crystal belongs to monoclinic system with space group P21/c with unit cell parameters a = 10.669(1) Å, b = 12.995(5) Å, c = 19.119(3) Å, and ? = 94.926(3)°. The crystal was seen to possess a linear polymeric structure along b-axis; with no presence of coordinated or lattice water. CHN analysis established the stoichiometric composition of the crystal. The existence of functional groups present in the single crystal system was confirmed by FT-IR studies. The thermal characteristic of the sample was analysed by TGA-DTA techniques, and the sample was found to be thermally stable up to 280 °C. The kinetic and thermodynamic parameters were also determined. UV-Vis spectroscopy corroborated the transparency of the crystal and revealed the optical band gap to be 4 eV. Dielectric studies showed decrease in the dielectric constant of the sample with increase in frequency.

Bijini, B. R.; Prasanna, S.; Deepa, M.; Nair, C. M. K.; Rajendra Babu, K.

2012-11-01

214

Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys  

NASA Technical Reports Server (NTRS)

High cycle fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Single crystal nickel turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493, PWA 1484, RENE' N-5 and CMSX-4. These alloys play an important role in commercial, military and space propulsion systems. Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades are complicated to predict due to the material orthotropy and variations in crystal orientations. Fatigue life estimation of single crystal turbine blades represents an important aspect of durability assessment. It is therefore of practical interest to develop effective fatigue failure criteria for single crystal nickel alloys and to investigate the effects of variation of primary and secondary crystal orientation on fatigue life. A fatigue failure criterion based on the maximum shear stress amplitude /Delta(sub tau)(sub max))] on the 24 octahedral and 6 cube slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criterion reduces the scatter in uniaxial LCF test data considerably for PWA 1493 at 1200 F in air. Additionally, single crystal turbine blades used in the alternate advanced high-pressure fuel turbopump (AHPFTP/AT) are modeled using a large-scale three-dimensional finite element model. This finite element model is capable of accounting for material orthotrophy and variation in primary and secondary crystal orientation. Effects of variation in crystal orientation on blade stress response are studied based on 297 finite element model runs. Fatigue lives at critical points in the blade are computed using finite element stress results and the failure criterion developed. Stress analysis results in the blade attachment region are also presented. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to significantly increase a component S resistance to fatigue crack growth with- out adding additional weight or cost. [DOI: 10.1115/1.1413767

Arakere, N. K.; Swanson, G.

2002-01-01

215

Raman spectra of deuteriated taurine single crystals  

NASA Astrophysics Data System (ADS)

The polarized Raman spectra of partially deuteriated taurine [(ND 3+) 0.65(NH 3+) 0.35(CH 2) 2SO 3-] crystals from x( zz) x and x( zy) x scattering geometries of the A g and B g irreducible representations of the factor group C 2h are reported. The temperature-dependent Raman spectra of partially deuteriated taurine do not reveal any evidence of the structural phase transition undergone by normal taurine at about 250 K, but an anomaly observed in the 180 cm -1 band at ˜120 K implies a different dynamic for this band (which is involved in a pressure-induced phase transition) in the deuteriated crystal.

Souza, J. M. de; Lima, R. J. C.; Freire, P. T. C.; Sasaki, J. M.; Melo, F. E. A.; Filho, J. Mendes; Jones, Derry W.

2005-05-01

216

Shock Driven Twinning in Tantalum Single Crystals  

SciTech Connect

Recovery based observations of high pressure material behavior generated under high explosively driven flyer based loading conditions are reported. Two shock pressures, 25, and 55 GPa and four orientations {l_brace}(100), (110), (111), (123){r_brace} were considered. Recovered material was characterized using electron backscatter diffraction along with a limited amount of transmission electron microscopy to assess the occurrence of twinning under each test condition. Material recovered from 25 GPa had a very small fraction of twinning for the (100), (110), and (111) oriented crystals while a more noticeable fraction of the (123) oriented crystal was twinned. Material recovered from 55 GPa showed little twinning for (100) orientation slightly more for the (111) orientation and a large area fraction for the (123) orientation. The EBSD and TEM observations of the underlying deformation substructure are rationalized by comparing with previous static and dynamic results.

McNaney, J M; HSUING, L M; Barton, N R; Kumar, M

2009-07-20

217

Scintillation Properties of Praseodymium Activated Single Crystals  

Microsoft Academic Search

Scintillation properties of LuAG:Pr grown by Furukawa Co. Ltd., Japan, have been studied. The best crystals display light outputs up to 19000 ph\\/MeV and an energy resolution of 4.6% at 662 keV. The scintillation yield is found to be a function of size and temperature of the sample; it can be enhanced by 40% upon heating to 450 K. Radioluminescence

Winicjusz Drozdowski; Pieter Dorenbos; J. T. M. de Haas; R. Drozdowska; A. Owens; K. Kamada; K. Tsutsumi; Y. Usuki; T. Yanagida; A. Yoshikawa

2008-01-01

218

Polychromatic Microbeam Diffraction Characterization of Individual ZnO Nanostructures  

SciTech Connect

We have used the focused, polychromatic beam available at sector 34 of the APS to characterize the local lattice structure and perfection of several different forms of ZnO meso- and nano-structures. Using Kirkpatrick-Baez mirrors for white-beam focusing, we have developed scanning x-ray techniques capable of mapping the spatially-resolved lattice structure, strain and composition. Off-axis undulator radiation is routinely focused to ~0.5 mm and beams as small as 90 nm have been demonstrated. Laue diffraction patterns are collected using a CCD area detector, and computer analysis provides spatial maps of the crystal phase, grain orientations (texture), and the local strain tensor. We have demonstrated the ability to map the structure of individual meso- and nano-structures using ZnO fabricated in several different shapes: rods, belts and tapered styluses. TEM samples serve as ideal x-ray microdiffraction samples due to the low background signal. Even when mounted on a relatively-thick crystal substrate, full diffraction patterns can be measured from ZnO rods as narrow as 200 nm diameter. We find that all of the ZnO structures have a facetted, hexagonal crystal structure, with the c-axis often along the rod axis. Larger diameter rods are essentially perfect single crystals, wheras thinner rods show a high degree of flexibility and hence large local mosaic spread along the rod axis. For stylus samples, the tapered region where the diameter decreases remains a single crystal.

Budai, John D [ORNL; Yang, Wenge [Carnegie Institution of Washington; Liu, W. [Argonne National Laboratory (ANL); Tischler, Jonathan Zachary [ORNL; Pan, Zhengwei [ORNL; Heo, YW [University of Florida, Gainesville; Norton, David P. [University of Florida; Larson, Ben C [ORNL; Ice, Gene E [ORNL

2006-01-01

219

Method of making macrocrystalline or single crystal semiconductor material  

NASA Technical Reports Server (NTRS)

A macrocrystalline or single crystal semiconductive material is formed from a primary substrate including a single crystal or several very large crystals of a relatively low melting material. This primary substrate is deposited on a base such as steel or ceramic, and it may be formed from such metals as zinc, cadmium, germanium, aluminum, tin, lead, copper, brass, magnesium silicide, or magnesium stannide. These materials generally have a melting point below about 1000 C and form on the base crystals the size of fingernails or greater. The primary substrate has an epitaxial relationship with a subsequently applied layer of material, and because of this epitaxial relationship, the material deposited on the primary substrate will have essentially the same crystal size as the crystals in the primary substrate. If required, successive layers are formed, each of a material which has an epitaxial relationship with the previously deposited layer, until a layer is formed which has an epitaxial relationship with the semiconductive material. This layer is referred to as the epitaxial substrate, and its crystals serve as sites for the growth of large crystals of semiconductive material. The primary substrate is passivated to remove or otherwise convert it into a stable or nonreactive state prior to deposition of the seconductive material.

Shlichta, P. J. (inventor); Holliday, R. J. (inventor)

1986-01-01

220

''6-Degrees of Freedom'' Single Crystal Plasticity Experiments  

SciTech Connect

A deformation experiment has been developed specifically for the purpose of validation of dislocation dynamics simulations of plastic flow up to strains on the order of 1% [1]. The experiment has been designed so that a compressive uniaxial stress field is essentially super imposed on the test sample, and the crystal is free to deform with 3 orthogonal translation directions, and 3 rotation/tilt axes of freedom and has been given the name ''6-degrees of freedom'' (6DOF) experiment. The rotation, tilt and translation of the crystal are monitored by 5 laser displacement gages and 3 extensometers. Experiments are being performed on high purity Mo single crystals orientated for ''single slip''. All of the experiments are performed in pairs, with one test sample having highly polished surfaces for optical light and AFM slip-trace analyses, and the other having 4 strain gage rosettes mounted on the sides for measurement of the bi-axial surface strains during testing. All of the experimental data is used together to determine the slip activity of the orientated single crystal during deformation. Experimental results on high-purity Mo single crystals are presented. The results of these experiments show that slip behavior is in substantial deviation from the expected ''Schmid'' behavior. These experimental results bring into question some of the fundamental assumptions used in both the construction of crystal plasticity constitutive relationships and rules for dislocation mobility use in 3-D dislocation dynamics simulations.

Lassila, D H; Florando, J N; LeBlanc, M M; Arsenlis, T; Rhee, M

2003-05-21

221

Crystal Structure, Physical Properties, and Electrochemistry of Copper Substituted LiFePO4 Single Crystals  

E-print Network

indicate that the dark brown color originates from interionic d-d transitions. A part of the lithium ions phosphate, with the olivine structure, has been synthesized hydrothermally as dark-brown single crystals

Ceder, Gerbrand

222

Contact properties and surface reaction kinetics of single ZnO nanowire devices fabricated by dielectrophoresis  

NASA Astrophysics Data System (ADS)

This work describes the development of ZnO nanowire (NW) devices for ultraviolet detection and cost-effective gas sensing. A dielectrophoresis (DEP) flow cell fabricated for the integration of NWs on different substrates is presented. The system includes the possibility to set characteristic parameters such as alternating current (AC) frequency, amplitude or flow speed in order to control NW trapping on specific sites defined by micro-gapped electrodes. The electrical characteristics of the rectifying metal/NW contact fabricated by DEP are investigated in darkness and under direct illumination of the metal-NW interface through the ZnO NW. A significant downshift of the turn-on voltage is observed in the current-voltage characteristics during the illumination with photon energies higher than the ZnO bandgap. The reduction is attributed to a barrier height lowering induced by interface charge emission. The effects of AC bias on the thermal drift of the DC average current in NW devices are also discussed. Finally, the reaction kinetics of ethanol and water vapors on the NW surface are compared through the analysis of the DC current under direct exposure to gas flows. Device responses to more complex compound mixtures such as coffee or mint are also monitored over time, showing different performance in both cases.

Pau, J. L.; García Núñez, C.; García Marín, A.; Guerrero, C.; Rodríguez, P.; Borromeo, S.; Piqueras, J.

2014-03-01

223

Low-cost single-crystal turbine blades, volume 2  

NASA Technical Reports Server (NTRS)

The overall objectives of Project 3 were to develop the exothermic casting process to produce uncooled single-crystal (SC) HP turbine blades in MAR-M 247 and higher strength derivative alloys and to validate the materials process and components through extensive mechanical property testing, rig testing, and 200 hours of endurance engine testing. These Program objectives were achieved. The exothermic casting process was successfully developed into a low-cost nonproperietary method for producing single-crystal castings. Single-crystal MAR-M 247 and two derivatives DS alloys developed during this project, NASAIR 100 and SC Alloy 3, were fully characterized through mechanical property testing. SC MAR-M 247 shows no significant improvement in strength over directionally solidified (DS) MAR-M 247, but the derivative alloys, NASAIR 100 and Alloy 3, show significant tensile and fatigue improvements. Firtree testing, holography, and strain-gauge rig testing were used to determine the effects of the anisotropic characteristics of single-crystal materials. No undesirable characteristics were found. In general, the single-crystal material behaved similarly to DS MAR-M 247. Two complete engine sets of SC HP turbine blades were cast using the exothermic casting process and fully machined. These blades were successfully engine-tested.

Strangman, T. E.; Dennis, R. E.; Heath, B. R.

1984-01-01

224

Long single ZnO nanowire for logic and memory circuits: NOT, NAND, NOR gate, and SRAM.  

PubMed

We demonstrate logic and static random access memory (SRAM) circuits using a 100 ?m long and 100 nm thin single ZnO nanowire (NW), which acts as a channel of field-effect transistors (FETs) with Al2O3 dielectrics. NW FETs are thus arrayed in one dimension to consist of NOT, NAND, and NOR gate logic, and SRAM circuits. Two respective top-gate NW FETs with Au and indium-tin-oxide (ITO) were connected to form an inverter, the basic NOT gate component, since the former gate leads to an enhanced mode FET while the latter to depletion mode due to their work function difference. Our inverters showed a high voltage gain of 22 under a 5 V operational voltage, resulting in successful operation of all other devices. We thus conclude that our long single NW approach is quite promising to extend the field of nano-electronics. PMID:23584636

Lee, Young Tack; Ali Raza, Syed Raza; Jeon, Pyo Jin; Ha, Ryong; Choi, Heon-Jin; Im, Seongil

2013-05-21

225

Method for harvesting rare earth barium copper oxide single crystals  

DOEpatents

A method of preparing high temperature superconductor single crystals is disclosed. The method of preparation involves preparing precursor materials of a particular composition, heating the precursor material to achieve a peritectic mixture of peritectic liquid and crystals of the high temperature superconductor, cooling the peritectic mixture to quench directly the mixture on a porous, wettable inert substrate to wick off the peritectic liquid, leaving single crystals of the high temperature superconductor on the porous substrate. Alternatively, the peritectic mixture can be cooled to a solid mass and reheated on a porous, inert substrate to melt the matrix of peritectic fluid while leaving the crystals melted, allowing the wicking away of the peritectic liquid. 2 figs.

Todt, V.R.; Sengupta, S.; Shi, D.

1996-04-02

226

Long single ZnO nanowire for logic and memory circuits: NOT, NAND, NOR gate, and SRAM  

NASA Astrophysics Data System (ADS)

We demonstrate logic and static random access memory (SRAM) circuits using a 100 ?m long and 100 nm thin single ZnO nanowire (NW), which acts as a channel of field-effect transistors (FETs) with Al2O3 dielectrics. NW FETs are thus arrayed in one dimension to consist of NOT, NAND, and NOR gate logic, and SRAM circuits. Two respective top-gate NW FETs with Au and indium-tin-oxide (ITO) were connected to form an inverter, the basic NOT gate component, since the former gate leads to an enhanced mode FET while the latter to depletion mode due to their work function difference. Our inverters showed a high voltage gain of 22 under a 5 V operational voltage, resulting in successful operation of all other devices. We thus conclude that our long single NW approach is quite promising to extend the field of nano-electronics.We demonstrate logic and static random access memory (SRAM) circuits using a 100 ?m long and 100 nm thin single ZnO nanowire (NW), which acts as a channel of field-effect transistors (FETs) with Al2O3 dielectrics. NW FETs are thus arrayed in one dimension to consist of NOT, NAND, and NOR gate logic, and SRAM circuits. Two respective top-gate NW FETs with Au and indium-tin-oxide (ITO) were connected to form an inverter, the basic NOT gate component, since the former gate leads to an enhanced mode FET while the latter to depletion mode due to their work function difference. Our inverters showed a high voltage gain of 22 under a 5 V operational voltage, resulting in successful operation of all other devices. We thus conclude that our long single NW approach is quite promising to extend the field of nano-electronics. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr01015e

Lee, Young Tack; Ali Raza, Syed Raza; Jeon, Pyo Jin; Ha, Ryong; Choi, Heon-Jin; Im, Seongil

2013-05-01

227

Isotropic behavior of an anisotropic material: single crystal silicon  

NASA Astrophysics Data System (ADS)

Zero defect single crystal silicon (Single-Crystal Si), with its diamond cubic crystal structure, is completely isotropic in most properties important for advanced aerospace systems. This paper will identify behavior of the three most dominant planes of the Single-Crystal Si cube (110), (100) and (111). For example, thermal and optical properties are completely isotropic for any given plane. The elastic and mechanical properties however are direction dependent. But we show through finite element analysis that in spite of this, near-isotropic behavior can be achieved with component designs that utilize the optimum elastic modulus in directions with the highest loads. Using glass frit bonding to assemble these planes is the only bonding agent that doesn't degrade the performance of Single-Crystal Si. The most significant anisotropic property of Single-Crystal Si is the Young's modulus of elasticity. Literature values vary substantially around a value of 145 GPa. The truth is that while the maximum modulus is 185 GPa, the most useful <110< crystallographic direction has a high 169 GPa, still higher than that of many materials such as aluminum and invar. And since Poisson's ratio in this direction is an extremely low 0.064, distortion in the plane normal to the load is insignificant. While the minimum modulus is 130 GPa, a calculated average value is close to the optimum at approximately 160 GPa. The minimum modulus is therefore almost irrelevant. The (111) plane, referred to as the natural cleave plane survives impact that would overload the (110) and/or (100) plane due to its superior density. While mechanical properties vary from plane to plane each plane is uniform and response is predictable. Understanding the Single-Crystal Si diamond cube provides a design and manufacture path for building lightweight Single-Crystal Si systems with near-isotropic response to loads. It is clear then that near-isotropic elastic behavior is achievable in Single-Crystal Si components and will provide subsecond thermal equilibrium and sub-micron creep.

McCarter, Douglas R.; Paquin, Roger A.

2013-09-01

228

Hydrogen-induced degradation in strontium titanate single crystals  

NASA Astrophysics Data System (ADS)

Hydrogen-induced degradation in strontium titanate single crystals was studied through an electrochemical hydrogen charging process, in which the silver electrodes of the crystals were made a cathode in 0.01 M NaOH solution to evolve hydrogen by electrolysis of water. After the process, the resistance of the crystals was decreased by more than one order of magnitude, the dielectric loss was obviously increased, and the capacitance became more dependent on frequency. It is proposed that atomic hydrogen generated by electrolysis of water diffuses into the crystals and exists as a charged interstitial impurity donating electrons to the conduction band of the crystals. Attention should be paid to this hydrogen-induced degradation when the reliability of perovskite-type ferroelectric devices and components is studied.

Chen, W. P.; Dai, J. Y.; Wang, Y.; Lai-Wah Chan, H.

2005-08-01

229

TGS single crystals doped by Pd(II) ions  

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with Pd(II) were grown from aqueous solutions by means of the slow cooling method. Concentration of the doping compound PdSO 4 in the growth solutions varied from 0.3 to 5 mol%. Morphology, domain structure and P- E hysteresis loops have been investigated. The effect of the dopant on the crystal growth velocity is explained on the basis of the notion of an activated Pd(II)-glycine complex.

Novotný, J.; Prokopová, L.; Mi?ka, Z.

2001-06-01

230

Pyroelectric properties of phosphoric acid-doped TGS single crystals  

Microsoft Academic Search

Pyroelectric properties of phosphoric acid (H3PO4)-doped triglycine sulfate (TGSP) single crystals grown from solutions containing 0.1-0.5 mol of H3PO4 have been studied. Incorporation of H3PO4 into the crystal lattice is found to induce an internal bias field (Eb) and is observed through the presence of a sustained polarization and pyroelectricity beyond the transition temperature. The internal bias field has been

Aparna Saxena; M. Fahim; Vinay Gupta; K. Sreenivas

2003-01-01

231

Low temperature pyroelectric properties of modified TGS single crystals  

Microsoft Academic Search

Pyroelectric and dielectric properties of three different single crystals in the triglycine sulphate (TGS) family have been studied in the temperature range from 20K to room temperature. These crystals are: (1) unmodified TGS; (2) TGS with L-alanine doping and partial substitution of (PO4) for (SO4), abbreviated as ATGSP; (3) TGS with L-alanine doping and partial substitution of (AsO4) for (SO4)

Zhang Peilin; Zhong Weilie; Fang Changshui; Zhao Huansui; Li Cuiping

1990-01-01

232

Growth and characterization of lithium yttrium borate single crystals  

SciTech Connect

Single crystals of 0.1% Ce doped Li{sub 6}Y(BO{sub 3}){sub 3} have been grown using the Czochralski technique. The photoluminescence study of these crystals shows a broad emission at ? 420 nm corresponding to Ce{sub 3+} emission from 5d?4f energy levels. The decay profile of this emission shows a fast response of ? 28 ns which is highly desirable for detector applications.

Singh, A. K.; Singh, S. G.; Tyagi, M.; Desai, D. G.; Sen, Shashwati [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai- 400085 (India)

2014-04-24

233

Orientation effects in nanoindentation of single crystal copper  

Microsoft Academic Search

Numerical simulations and experimental results of nanoindentation on single crystal copper in three crystallographic orientations [(100), (011) and (111)] using a spherical indenter (3.4?m radius) were reported. The simulations were conducted using a commercial finite element code (ABAQUS) with a user-defined subroutine (VUMAT) that incorporates large deformation crystal plasticity constitutive model. This model can take full account of the crystallographic

Y. Liu; S. Varghese; J. Ma; M. Yoshino; H. Lu; R. Komanduri

2008-01-01

234

Growth Defect Studies in SiC Single Crystals  

Microsoft Academic Search

Growth defects in vapor grown 6H-SiC single crystals have been studied using a combination of techniques, including: synchrotron white beam x-ray topography (SWBXT), conventional optical microscopy, fluorescence microscopy, and epi-fluorescence laser scanning confocal microscopy (LSCM). These studies of crystal sections cut both parallel and perpendicular to the [0001] growth axis focused on growth dislocations of screw character running approximately parallel

Michael Dudley; William M. Vetter

1996-01-01

235

Nucleation kinetics, growth and studies of ?-alanine single crystals  

NASA Astrophysics Data System (ADS)

Solubility and metastable zone width for the re-crystallized salt of ?-alanine was determined. Induction period measurement for the selected supersaturation ratios at room temperature (31 °C) was carried out for supersaturated aqueous solutions of ?-alanine and it is noticed that induction period decreases with increase of supersaturation ratio. The nucleation parameters such as Gibbs free energy change, radius and number of molecules of the critical nucleus, interfacial tension and the nucleation rate have been evaluated by classical nucleation theory. Single crystals of ?-alanine were grown using the optimized nucleation parameters by solution method and grown crystals have been subjected to various studies like XRD studies, FTIR, optical, thermal and SHG studies.

Shanthi, D.; Selvarajan, P.; HemaDurga, K. K.; Lincy Mary Ponmani, S.

2013-06-01

236

Lithium niobate single-crystal and photo-functional device  

DOEpatents

Provided are lithium niobate single-crystal that requires a low voltage of not larger than 10 kV/nm for its ferroelectric polarization inversion and of which the polarization can be periodically inverted with accuracy even at such a low voltage, and a photo-functional device comprising the crystal. The crystal has a molar fraction of Li.sub.2 O/(Nb.sub.2 O.sub.5 +Li.sub.2 O) of falling between 0.49 and 0.52. The photo-functional device can convert a laser ray being incident thereon.

Gopalan, Venkatraman (State College, PA); Mitchell, Terrence E. (Los Alamos, NM); Kitamura, Kenji (Tsukuba, JP); Furukawa, Yasunori (Tsukuba, JP)

2001-01-01

237

Polymer single crystal meets nanoparticle, toward ordered hybrid materials  

NASA Astrophysics Data System (ADS)

Judiciously selected polymer single crystal (PSC) systems can interplay with 1-D and 0-D nanoparticles, forming ordered hybrid structures. In this presentation, I will first focus on patterning PSCs on individual carbon nanotubes (CNT). Using both controlled solution crystallization, thin film crystallization and physical vapor deposition methods, CNTs were periodically decorated with PSCs, resulting in nano hybrid shish-kebab (NHSK) structures. Because the polymer kebabs can be easily removed, these unique NHSKs can serve as templates to fabricate a variety of CNTs-containing hybrid materials with controlled pattering on the CNT surface. Sub-20 nanometer alternating patterning was achieved by using crystalline block copolymers. The mechanism was attributed to the crystallization induced block copolymer phase separation. This pattern was successfully used to template nanoparticles (NP) pattering on CNTs. In the second part of the talk, I will discuss fabricating Janus NPs and patterning these NPs using PSCs. Single crystals of thiol-terminated polyethylene oxide (PEO) were incubated in a gold sol. Au-S bonds were formed between the AuNPs and the PEO single crystal surfaces. The inter-particle spacing was controlled by PEO molecular weights, the incubation time, and the annealing temperatures after incubation. The planar geometry of the PSCs led to Janus NP formation. A series of NP dimers, trimers and tetramers were synthesized. NP nanowires were also fabricated. We anticipate that this observation could lead to controlled synthesis of artificial molecules and NP chains for a variety of optical, electronic, and biomedical applications.

Li, Christopher

2009-03-01

238

The Load Capability of Piezoelectric Single Crystal Actuators  

NASA Technical Reports Server (NTRS)

Piezoelectric lead magnesium niobate-lead titanate (PMN-PT) single crystal is one of the most promising materials for electromechanical device applications due to its high electrical field induced strain and high electromechanical coupling factor. PMN-PT single crystal-based multilayer stack actuators and multilayer stack-based flextensional actuators have exhibited high stroke and high displacement-voltage ratios. The actuation capabilities of these two actuators were evaluated using a newly developed method based upon a laser vibrometer system under various loading conditions. The measured displacements as a function of mechanical loads at different driving voltages indicate that the displacement response of the actuators is approximately constant under broad ranges of mechanical load. The load capabilities of these PMN-PT single crystal-based actuators and the advantages of the capability for applications will be discussed.

Xu, Tian-Bing; Su, Ji; Jiang, Xiaoning; Rehrig, Paul W.; Hackenberger, Wesley S.

2006-01-01

239

The Load Capability of Piezoelectric Single Crystal Actuators  

NASA Technical Reports Server (NTRS)

Piezoelectric lead magnesium niobate-lead titanate (PMN-PT) single crystal is one of the most promising materials for electromechanical device applications due to its high electrical field induced strain and high electromechanical coupling factor. PMN-PT single crystal-based multilayer stack actuators and multilayer stack-based flextensional actuators have exhibited high stroke and high displacement-voltage ratios. The actuation capabilities of these two actuators were evaluated using a newly developed method based upon a laser vibrometer system under various loading conditions. The measured displacements as a function of mechanical loads at different driving voltages indicate that the displacement response of the actuators is approximately constant under broad ranges of mechanical load. The load capabilities of these PMN-PT single crystal-based actuators and the advantages of the capability for applications will be discussed.

Xu, Tian-Bing; Su, Ji; Jiang, Xiaoning; Rehrig, Paul W.; Hackenberger, Wesley S.

2007-01-01

240

Single Crystal Synthesis and STM Studies of High Temperature Superconductors  

NASA Technical Reports Server (NTRS)

This is a final report for the work initiated in September of 1994 under the grant NAG8-1085 - NASA/OMU, on the fabrication of bulk and single crystal synthesis, specific heat measuring and STM studies of high temperature superconductors. Efforts were made to fabricate bulk and single crystals of mercury based superconducting material. A systematic thermal analysis on the precursors for the corresponding oxides and carbonates were carried out to synthesized bulk samples. Bulk material was used as seed in an attempt to grow single crystals by a two-step self flux process. On the other hand bulk samples were characterized by x-ray diffraction, electrical resistivity and magnetic susceptibility, We studied the specific heat behavior in the range from 80 to 300 K. Some preliminary attempts were made to study the atomic morphology of our samples. As part of our efforts we built an ac susceptibility apparatus for measuring the transition temperature of our sintered samples.

Barrientos, Alfonso

1997-01-01

241

Constitutive modelling of single crystal and directionally solidified superalloys  

NASA Technical Reports Server (NTRS)

The trend towards improved engine efficiency and durability places increasing demands on materials that operate in the hot section of the gas turbine engine. These demands are being met by new coatings and materials such as single crystal and directionally solidified nickel-base superalloys which have greater creep/fatigue resistance at elevated temperatures and reduced susceptibility to grain boundary creep, corrosion and oxidation than conventionally cast alloys. Work carried out as part of a research program aimed at the development of constitutive equations to describe the elevated temperature stress-strain-time behavior of single crystal and directionally solidified turbine blade superalloys is discussed. The program involves both development of suitable constitutive models and their verification through elevated temperature tension-torsion testing of single crystals of PWA 1480.

Jordan, E. H.; Walker, K. P.

1986-01-01

242

Mechanical properties of hydroxyapatite single crystals from nanoindentation data  

PubMed Central

In this paper we compute elasto-plastic properties of hydroxyapatite single crystals from nanindentation data using a two-step algorithm. In the first step the yield stress is obtained using hardness and Young’s modulus data, followed by the computation of the flow parameters. The computational approach is first validated with data from existing literature. It is observed that hydroxyapatite single crystals exhibit anisotropic mechanical response with a lower yield stress along the [1010] crystallographic direction compared to the [0001] direction. Both work hardening rate and work hardening exponent are found to be higher for indentation along the [0001] crystallographic direction. The stress-strain curves extracted here could be used for developing constitutive models for hydroxyapatite single crystals. PMID:21262492

Zamiri, A.; De, S.

2011-01-01

243

Photoinduced p-Type Conductivity in n-Type ZnO  

NASA Astrophysics Data System (ADS)

Ag/[BaTiO3/?-Fe2O3]/ZnO composite films were grown on an n-type silicon (100) single-crystal substrate by magnetron sputtering, and annealed at various temperatures. Capacitance-voltage (C-V) curves show that the capacitance gradually increases with increasing annealed temperature. In addition, ZnO exhibits n-type conductivity in the dark but p-type conductivity under incandescent lamp illumination. The photoinduced p-type conductivity in n-type ZnO should be related to a special n-type ZnO layer originating from high-temperature annealing. The current-voltage (I-V) curves of the [BaTiO3/?-Fe2O3]/ZnO thin films display a strong photoconductivity effect.

Zhao, W. X.; Sun, B.; Shen, Z.; Liu, Y. H.; Chen, P.

2015-01-01

244

DOI: 10.1002/ejic.200701306 Facile Gram-Scale Growth of Single-Crystalline Nanotetrapod-Assembled ZnO  

E-print Network

FULL PAPER DOI: 10.1002/ejic.200701306 Facile Gram-Scale Growth of Single-Crystalline Nanotetrapod on a gram-scale for the first time. The gram-scale bulk nano-ZnO is synthesized from ZnO powder with great

Liu, Jie

245

Single-crystal neutron diffraction investigation on crystals belonging to the langasite family: a comparative study.  

PubMed

Crystals of the langasite family are of interest as they are piezoelectric in different devices. The properties of these classes of crystals can be modified within certain limits by isomorphous substitution. Single-crystal neutron diffraction studies were carried out for LGT (La(3)Ga(5.5)Ta(0.5)O(14)), LGST (La(3)Ga(5.25)Ta(0.25)Si(0.5)O(14)) and LGZrT (La(3)Ga(5.25)Ta(0.25)Zr(0.5)O(14)) as the neutron study gives a better average picture of the crystal properties over a macroscopic region of the grown crystal. The effect of small substitutions at various sites on the piezoelectric properties of the crystal was studied. PMID:20841917

Chitra, R; Choudhury, R R

2010-10-01

246

Low-temperature solution growth of ZnO nanocone/highly oriented nanorod arrays on copper.  

PubMed

Solution-phase approaches to one-dimensional (1D) ZnO nanostructure arrays are appealing because of their good potential for scale-up. Allowing for a wide variety of substrate material compatibility and saving energy, it is very essential to further research the low-temperature growth process of 1D ZnO nanostructure arrays and its detailed growth mechanism. In this study, large-scale misaligned hexagonal ZnO nancone arrays were synthesized on bare copper foil, while large-scale well-aligned, and highly oriented ZnO nanorod arrays were grown on seeded copper foil through a facile solution processing method at normal atmospheric pressure at 35 °C. X-ray diffraction analysis verified the crystalline nature of the ZnO nanocone/nanorods, and transmission electron microscopy further confirmed the single-crystal nature and the preferential growth direction of the ZnO nanocone/nanorods. The room-temperature photoluminescence measurement qualitatively identified the intrinsic point defects in the ZnO nanocones/nanorods. Besides, the detailed growth behavior of ZnO was discussed with and without a ZnO seed layer, which provides useful information to propose the growth mechanism of the nanocone/nanorods in the low-temperature solution. The method developed here can be easily scaled up to fabricate ZnO nanostructures for many important applications in field emission display, gas sensors, and superhydrophobic surfaces. PMID:25254950

Xia, Yongmei; Zhang, Youfa; Yu, Xinquan; Chen, Feng

2014-10-16

247

Lead pyrovanadate single crystal as a new SRS material  

SciTech Connect

Lead pyrovanadate Pb{sub 2}V{sub 2}O{sub 7} single crystals of optical quality suitable for laser experiments are obtained. Vibrational modes are identified based on the analysis of the polarised Raman spectra of the single crystals. The main parameters (width at half maximum, peak and integral intensities) of the spectral lines most promising for SRS conversion in this material are estimated. These parameters are compared with the corresponding parameters of the most frequently used lines of known Raman materials: yttrium and gadolinium vanadates, potassium and lead tungstates, and lead molybdate. (active media)

Basiev, Tasoltan T; Voronko, Yu K; Maslov, Vladislav A; Sobol, A A; Shukshin, V E [A M Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2011-02-28

248

Two-photon-induced singlet fission in rubrene single crystal.  

PubMed

The two-photon-induced singlet fission was observed in rubrene single crystal and studied by use of femtosecond pump-probe spectroscopy. The location of two-photon excited states was obtained from the nondegenerate two-photon absorption (TPA) spectrum. Time evolution of the two-photon-induced transient absorption spectra reveals the direct singlet fission from the two-photon excited states. The TPA absorption coefficient of rubrene single crystal is 52 cm?GW at 740 nm, as obtained from Z-scan measurements. Quantum chemical calculations based on time-dependent density functional theory support our experimental data. PMID:23676057

Ma, Lin; Galstyan, Gegham; Zhang, Keke; Kloc, Christian; Sun, Handong; Soci, Cesare; Michel-Beyerle, Maria E; Gurzadyan, Gagik G

2013-05-14

249

Two-photon-induced singlet fission in rubrene single crystal  

NASA Astrophysics Data System (ADS)

The two-photon-induced singlet fission was observed in rubrene single crystal and studied by use of femtosecond pump-probe spectroscopy. The location of two-photon excited states was obtained from the nondegenerate two-photon absorption (TPA) spectrum. Time evolution of the two-photon-induced transient absorption spectra reveals the direct singlet fission from the two-photon excited states. The TPA absorption coefficient of rubrene single crystal is 52 cm/GW at 740 nm, as obtained from Z-scan measurements. Quantum chemical calculations based on time-dependent density functional theory support our experimental data.

Ma, Lin; Galstyan, Gegham; Zhang, Keke; Kloc, Christian; Sun, Handong; Soci, Cesare; Michel-Beyerle, Maria E.; Gurzadyan, Gagik G.

2013-05-01

250

Apparatus And Method For Producing Single Crystal Metallic Objects  

DOEpatents

A mold is provided for enabling casting of single crystal metallic articles including a part-defining cavity, a sorter passage positioned vertically beneath and in fluid communication with the part-defining cavity, and a seed cavity positioned vertically beneath and in fluid communication with the sorter passage. The sorter passage includes a shape suitable for encouraging a single crystal structure in solidifying molten metal. Additionally, a portion of the mold between the sorter passage and the part-defining cavity includes a notch for facilitating breakage of a cast article proximate the notch during thermal stress build-up, so as to prevent mold breakage or the inclusion of part defects.

Huang, Shyh-Chin (Latham, NY); Gigliotti, Jr., Michael Francis X. (Scotia, NY); Rutkowski, Stephen Francis (Duanesburg, NY); Petterson, Roger John (Fultonville, NY); Svec, Paul Steven (Scotia, NY)

2006-03-14

251

Growth of single-crystal diamonds in microwave plasma  

NASA Astrophysics Data System (ADS)

A microwave plasma (2.45 GHz) was used for depositing single crystal diamond layers at the deposition rate up to 40 ?m/h in hydrogen-methane mixtures on the substrates from natural and synthetic diamond with the (100) deposition surface and with the size up to 5 × 5 mm. The structure and the defect-impurity composition of the fabricated single crystals with the thickness up to 600 ?m have been investigated using Raman spectroscopy, photoluminescence spectroscopy, cathode luminescence spectroscopy, and electron and optical microscopy. A high quality and purity of the diamond layers deposited from a plasma was confirmed.

Bolshakov, A. P.; Ralchenko, V. G.; Polskiy, A. V.; Konov, V. I.; Ashkinazi, E. E.; Khomich, A. A.; Sharonov, G. V.; Khmelnitsky, R. A.; Zavedeev, E. V.; Khomich, A. V.; Sovyk, D. N.

2012-12-01

252

Synthesis of Large Single Crystals of LaMnPO  

NASA Astrophysics Data System (ADS)

The compound LaMnPO is isostructural with LaFeAsO, a recently discovered high-temperature superconductor, but optical spectroscopy and transport measurements of this compound have been heretofore limited by small crystal size. Accordingly, crystal syntheses from Sn, Pb and molten salt fluxes (including NaCl/KCl, LiCl/NaCl, KCl, CaCl2, BaCl2/CaCl2 and KCl/CaCl2) were investigated. Fluorine doping was explored; concentrations less than 30 at.% (nominal) had no effect on crystal size; concentrations greater than 40 at.% (nominal) did not yield crystals. Once growth parameters were optimized, the crystals grew in a flat rectangular shape with black luster; their composition was verified with powder and single crystal x-ray diffraction. Successful growths yielded crystals with dimensions up to 3.2 mm by 1 mm by 10 ?m, a significant improvement upon previously reported growths in the literature. These large crystals enabled our group to perform a wide range of experiments that were previously restricted to polycrystalline materials. It may be feasible to extend these methods to the synthesis of similar compounds.

Smith, Greg; Simonson, Jack; Marques, Carlos; Leyva, Victor; Aronson, Meigan

2011-03-01

253

Low-temperature solution growth of ZnO nanotube arrays  

PubMed Central

Summary Single crystal ZnO nanotube arrays were synthesized at low temperature in an aqueous solution containing zinc nitrate and hexamethylenetetramine. It was found that the pH value of the reaction solution played an important role in mediating the growth of ZnO nanostructures. A change in the growth temperature might change the pH value of the solution and bring about the structure conversion of ZnO from nanorods to nanotubes. It was proposed that the ZnO nanorods were initially formed while the reaction solution was at a relatively high temperature (~90 °C) and therefore enriched with colloidal Zn(OH)2, which allowed a fast growth of ZnO nanocrystals along the [001] orientation to form nanorods. A decrease in the reaction temperature yielded a supersaturated solution, resulting in an increase in the concentration of OH? ions as well as the pH value of the solution. Colloidal Zn(OH)2 in the supersaturated solution trended to precipitate. However, because of a slow diffusion process in view of the low temperature and low concentration of the colloidal Zn(OH)2, the growth of the (001) plane of ZnO nanorods was limited and only occurred at the edge of the nanorods, eventually leading to the formation of a nanotube shape. In addition, it was demonstrated that the pH might impact the surface energy difference between the polar and non-polar faces of the ZnO crystal. Such a surface energy difference became small at high pH and hereby the prioritized growth of ZnO crystal along the [001] orientation was suppressed, facilitating the formation of nanotubes. This paper demonstrates a new strategy for the fabrication of ZnO nanotubes on a large scale and presents a more comprehensive understanding of the growth of tube-shaped ZnO in aqueous solution at low temperature. PMID:21977402

Chae, Ki-Woong; Zhang, Qifeng; Kim, Jeong Seog; Jeong, Yoon-Ha

2010-01-01

254

Growth of Solid Solution Single Crystals  

NASA Technical Reports Server (NTRS)

The solidification of a solid solution semiconductor, having a wide separation between liquidus and serious has been extensively studied in ground based, high magnetic field and Spacelab experiments. Two alloys of mercury cadmium telluride have been studied; mercury cadmium telluride with 80.0 mole percent of HgTe and 84.8 mole percent respectively. These alloys are extremely difficult to grow by directional solidification on earth due to high solutal and thermal density differences that give rise to fluid flow and consequent loss of interface shape and composition. Diffusion controlled growth is therefore impossible to achieve in conventional directional solidification. The ground based experiments consisted of growing crystals in several different configurations of heat pipe furnaces, NASA's Advanced Automated Directional Solidification Furnace (AADSF), and a similar furnace incorporated in a superconducting magnet capable of operating at up to 5T. The first microgravity experiment took place during the flight of STS-62 in March 1994, with the AADSF installed on the second United States Microgravity Payload (USMP-2). The alloy was solidified at 3/4 inch per day over a 9 day period, and for the first time a detailed evaluation was performed of residual acceleration effects. The second flight experiment took place in the fourth United States Microgravity Payload Mission (USMP-4) in November 1997. Due to contamination of the furnace system by a previously processed sample, the sample was not received until May 1998, and the preliminary analysis shows that the conditions prevailing during the experiment were quite different from the requirements requested prior to the mission. Early results are indicating that the sample may not accomplish the desired objectives. As with the USMP-2 mission, the results of the ground based experiments were compared with the crystal grown in orbit under microgravity conditions. On the earth, it has been demonstrated that the application of the magnetic field leads to a significant reduction in fluid flow, with improved homogeneity of composition. The field strength required to suppress flow increases with diameter of the material. The 8 mm diameter sample used here was less than the upper diameter limit for a ST magnet. The configuration for USMP-4 was changed so that the material was seeded and other processing techniques were also modified. It was decided to examine the effects of a strong magnetic field under the modified configuration and parameters. A further change from USMP-2 was that a different composition of material was grown, namely with 0.152 mole fraction of cadmium telluride rather than the 0.200 of the USMP-2 experiment. The objective was to grow highly homogeneous, low defect density material of a composition at which the conduction band and the valence band of the material impinge against each other. As indicated, the furnace was contaminated during the mission. As a result of solid debris remaining in the furnace bore, the cartridge in this experiment, denoted as SL1-417, was significantly bent during the insertion phase. During translation the cartridge scraped against the plate which isolates the hot and cold zones of the furnace. Thermocouples indicated that a thermal assymetry resulted. The scraping in the slow translation or crystal growth part of the processing was not smooth and it is probable that the jitter was sufficient to give rise to convection in the melt. Early measurements of composition from the surface of the sample have shown that the composition varies in an oscillatory manner.

Lehoczky, Sandor L.; Szofran, F. R.; Gillies, Donald C.; Watring, D. A.

1999-01-01

255

Angle-dependent photodegradation over ZnO nanowire arrays on flexible paper substrates  

PubMed Central

In this study, we grew zinc oxide (ZnO) nanowire arrays on paper substrates using a two-step growth strategy. In the first step, we formed single-crystalline ZnO nanoparticles of uniform size distribution (ca. 4 nm) as seeds for the hydrothermal growth of the ZnO nanowire arrays. After spin-coating of these seeds onto paper, we grew ZnO nanowire arrays conformally on these substrates. The crystal structure of a ZnO nanowire revealed that the nanowires were single-crystalline and had grown along the c axis. Further visualization through annular bright field scanning transmission electron microscopy revealed that the hydrothermally grown ZnO nanowires possessed Zn polarity. From photocatalytic activity measurements of the ZnO nanowire (NW) arrays on paper substrate, we extracted rate constants of 0.415, 0.244, 0.195, and 0.08 s-1 for the degradation of methylene blue at incident angles of 0°, 30°, 60°, and 75°, respectively; that is, the photocatalytic activity of these ZnO nanowire arrays was related to the cosine of the incident angle of the UV light. Accordingly, these materials have promising applications in the design of sterilization systems and light-harvesting devices. PMID:25593556

2014-01-01

256

Relaxor-PT single crystals: observations and developments.  

PubMed

Relaxor-PT based ferroelectric single crystals Pb(Zn?/?)Nb(?/?)O?-PbTiO? (PZNT) and Pb(Mg?/?)Nb(?/?)O?-PbTiO? (PMNT) offer high performance with ultra-high electromechanical coupling factors k?? > 0.9 and piezoelectric coefficients d??s > 1500 pC/N. However, the usage temperature range of these perovskite single crystals is limited by T(RT)-the rhombohedral to tetragonal phase transition temperature, which occurs at significantly lower temperatures than the Curie temperature T(C), a consequence of curved morphotropic phase boundaries (MPBs). Furthermore, these <001>-oriented crystals exhibit low mechanical quality Q and coercive fields, restricting their usage in high-power applications. In this survey, recent developments on binary and ternary perovskite relaxor-PT crystal systems are reviewed with respect to their temperature usage range. General trends of dielectric and piezoelectric properties of relaxor-PT crystal systems are discussed in relation to their respective T(C)/T(RT). In addition, two approaches have been implemented to improve mechanical Q, including acceptor dopants, analogous to hard polycrystalline ceramics, and anisotropic domain engineering, enabling low-loss crystals with high coupling for high-power applications. PMID:20889397

Zhang, Shujun; Shrout, Thomas

2010-10-01

257

Growth of Solid Solution Single Crystals  

NASA Technical Reports Server (NTRS)

The solidification of a solid solution semiconductor, having a wide separation between liquidus and solidus has been extensively studied in ground based, high magnetic field and Spacelab experiments. Two alloys of mercury cadmium telluride have been studied; with 80.0 mole percent of HgTe and 84.8 mole percent of HgTe respectively, the remainder being cadmium telluride. Such alloys are extremely difficult to grow by directional solidification on earth due to high solutal and thermal density differences that give rise to fluid flow and consequent loss of interface shape and composition. Diffusion controlled growth is therefore impossible to achieve in conventional directional solidification. The ground based experiments consisted of growing crystals in several different configurations of heat pipe furnaces, NASA's Advanced Automated Directional Solidification Furnace (AADSF), and a similar furnace incorporated in a superconducting magnet capable of operating at up to 5T. The first microgravity experiment took place during the flight of STS-62 in March 1994, with the AADSF installed on the second United States Microgravity Payload (USMP-2). The alloy was solidified at 3/4 inch per day over a 9 day period, and for the first time a detailed evaluation was performed correlating composition variations to measured residual acceleration. The second flight experiment took place in the fourth United States Microgravity Payload Mission (USMP-4) in November 1997. Due to contamination of the furnace system, analysis shows that the conditions prevailing during the experiment were quite different from the requirements requested prior to the mission. The results indicate that the sample did accomplish the desired objectives.

Lehoczky, Sandor L.; Szofran, F. R.; Gillies, Donald C.

2001-01-01

258

A single crystal multiple-wavelength electro-optic modulator  

Microsoft Academic Search

A new multi-wavelength low voltage electro-optic modulator has been constructed using the r41coefficient in a single crystal of ADP. It is intended for use in multi-color laser display and recording systems employing a single source such as a krypton-ion laser. The modulator accepts a coaxial mixed wavelength beam and separates the colors using a set of direct view spectroscopic prisms.

J. Schlafer; V. J. Fowler

1971-01-01

259

Engineering chromium related single photon emitters in single crystal diamond  

E-print Network

Color centers in diamond as single photon emitters, are leading candidates for future quantum devices due to their room temperature operation and photostability. The recently discovered chromium related centers are particularly attractive since they possess narrow bandwidth emission and a very short lifetime. In this paper we investigate the fabrication methodologies to engineer these centers in monolithic diamond. We show that the emitters can be successfully fabricated by ion implantation of chromium in conjunction with oxygen or sulfur. Furthermore, our results indicate that the background nitrogen concentration is an important parameter, which governs the probability of success to generate these centers.

I Aharonovich; S Castelletto; B C Johnson; J C McCallum; S Prawer

2010-09-29

260

Engineering chromium related single photon emitters in single crystal diamond  

E-print Network

Color centers in diamond as single photon emitters, are leading candidates for future quantum devices due to their room temperature operation and photostability. The recently discovered chromium related centers are particularly attractive since they possess narrow bandwidth emission and a very short lifetime. In this paper we investigate the fabrication methodologies to engineer these centers in monolithic diamond. We show that the emitters can be successfully fabricated by ion implantation of chromium in conjunction with oxygen or sulfur. Furthermore, our results indicate that the background nitrogen concentration is an important parameter, which governs the probability of success to generate these centers.

Aharonovich, I; Johnson, B C; McCallum, J C; Prawer, S

2010-01-01

261

pH-triggered conduction of amine-functionalized single ZnO wire integrated on a customized nanogap electronic platform  

NASA Astrophysics Data System (ADS)

The electrical conductance response of single ZnO microwire functionalized with amine-groups was tested upon an acid pH variation of a solution environment after integration on a customized gold electrode array chip. ZnO microwires were easily synthesized by hydrothermal route and chemically functionalized with aminopropyl groups. Single wires were deposited from the solution and then oriented through dielectrophoresis across eight nanogap gold electrodes on a platform single chip. Therefore, eight functionalized ZnO microwire-gold junctions were formed at the same time, and being integrated on an ad hoc electronic platform, they were ready for testing without any further treatment. Experimental and simulation studies confirmed the high pH-responsive behavior of the amine-modified ZnO-gold junctions, obtaining in a simple and reproducible way a ready-to-use device for pH detection in the acidic range. We also compared this performance to bare ZnO wires on the same electronic platform, showing the superiority in pH response of the amine-functionalized material.

Cauda, Valentina; Motto, Paolo; Perrone, Denis; Piccinini, Gianluca; Demarchi, Danilo

2014-01-01

262

pH-triggered conduction of amine-functionalized single ZnO wire integrated on a customized nanogap electronic platform.  

PubMed

The electrical conductance response of single ZnO microwire functionalized with amine-groups was tested upon an acid pH variation of a solution environment after integration on a customized gold electrode array chip. ZnO microwires were easily synthesized by hydrothermal route and chemically functionalized with aminopropyl groups. Single wires were deposited from the solution and then oriented through dielectrophoresis across eight nanogap gold electrodes on a platform single chip. Therefore, eight functionalized ZnO microwire-gold junctions were formed at the same time, and being integrated on an ad hoc electronic platform, they were ready for testing without any further treatment. Experimental and simulation studies confirmed the high pH-responsive behavior of the amine-modified ZnO-gold junctions, obtaining in a simple and reproducible way a ready-to-use device for pH detection in the acidic range. We also compared this performance to bare ZnO wires on the same electronic platform, showing the superiority in pH response of the amine-functionalized material. PMID:24484615

Cauda, Valentina; Motto, Paolo; Perrone, Denis; Piccinini, Gianluca; Demarchi, Danilo

2014-01-01

263

Polymer single crystal membrane from liquid/liquid interface  

NASA Astrophysics Data System (ADS)

Vesicles, mimicking the structure of cell membrane at the molecular scale, are small membrane-enclosed sacks that can store or transport substances. The weak mechanical properties and the nature of environment-sensitivity of the current available vesicles: liposomes, polymersomes, colloidsomes limit their applications as an excellent candidate for targeting delivery of drugs/genes in biomedical engineering and treatment. Recently, we developed an emulsion-based method to grow curved polymer single crystals. Varying the polymer concentration and/or the emulsification conditions (such as surfactant concentration, water-oil volume ratio), curved crystals with different sizes and different openness could be obtained. This growing process was attributed to polymer crystal growth along the liquid/liquid interface. In addition, the liquid/liquid interfacial crystal growth is promising for synthesis of enclosed hollow sphere.

Wang, Wenda; Li, Christopher

2013-03-01

264

Synthesis of high surface area ZnO powder by continuous precipitation  

SciTech Connect

Graphical abstract: High surface area ZnO powders are synthesized by a low temperature continuous precipitation under ultrasonication. Urea is used as precipitating agent so that no contamination of ZnO powder emanating from precipitating agent, such as, alkalis, is observed. pH and type of precursor greatly affects the surface area and other properties. In this manuscript, we report a very simple and effective continuous precipitation to synthesize high surface area ZnO powder. Highlights: Black-Right-Pointing-Pointer The synthesis of high surface area ZnO powder was achieved at 90 Degree-Sign C in a continuous precipitation unit. Black-Right-Pointing-Pointer Continuous precipitation unit was ultrasonicated to improve final product homogeneity. Black-Right-Pointing-Pointer Precipitation intermediate, hydrozincite, was led to high surface area ZnO powder. Black-Right-Pointing-Pointer The synthesized ZnO nanoparticles had a rather uniform mesoporous structure. -- Abstract: Synthesis of high surface area ZnO powder was achieved by continuous precipitation using zinc ions and urea at low temperature of 90 Degree-Sign C. The powder precipitated resulted in high-purity single-phase ZnO powder when calcined at 280 Degree-Sign C for 3 h in air. The solution pH and the precipitation duration strongly affected the surface area of the calcined ZnO powder. Detailed structural characterizations demonstrated that the synthesized ZnO powder were single crystalline with wurtzite hexagonal phase. The powdered samples precipitated by homogeneous precipitation crystallized directly to hydrozincite without any intermediate phase formation. The phase structures, morphologies and properties of the final ZnO powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering particle size analysis (DLS), and nitrogen physisorption in order to determine the specific surface area (BET) and the pore size distribution (BJH).

Boz, Ismail, E-mail: ismailb@istanbul.edu.tr [Istanbul University, Faculty of Engineering, Department of Chemical Engineering, Avcilar, Istanbul 34320 (Turkey)] [Istanbul University, Faculty of Engineering, Department of Chemical Engineering, Avcilar, Istanbul 34320 (Turkey); Kaluza, Stefan [Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitaetsstr. 150, Bochum 44780 (Germany)] [Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitaetsstr. 150, Bochum 44780 (Germany); Boroglu, Mehtap Safak [Istanbul University, Faculty of Engineering, Department of Chemical Engineering, Avcilar, Istanbul 34320 (Turkey)] [Istanbul University, Faculty of Engineering, Department of Chemical Engineering, Avcilar, Istanbul 34320 (Turkey); Muhler, Martin [Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitaetsstr. 150, Bochum 44780 (Germany)] [Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitaetsstr. 150, Bochum 44780 (Germany)

2012-05-15

265

The viscoplastic behavior of Hastelloy-X single crystal  

NASA Technical Reports Server (NTRS)

A viscoplastic constitutive model for simulating the behavior of Hastelloy-X single crystal material was derived based on crystallographic slip theory. To determine the appropriate constitutive model constants and to test the predictions of the model, tests on Hastelloy-X crystals were carried out, including the rate sensitivity, cyclic hardening, nonproportional hardening, relaxation, and strain rate dip tests. It was found necessary to include cube slip in the model in order to correlate the uniaxial behavior of the single crystal, to incorporate the interaction effects in both the hardening and the dynamic recovery evolution equations for the drag stress, and to successfully capture correct strain rate sensitivity under biaxial tension-torsion loading conditions.

Jordan, Eric H.; Shi, Shixiang; Walker, Kevin P.

1993-01-01

266

Ultrasonic characterization of single crystal langatate  

NASA Astrophysics Data System (ADS)

Langatate (LGT), a synthetic piezoelectric crystal with chemical composition La3Ga5.5Ta0.5O14, has recently received significant interest in the sensor and frequency control communities as a possible alternative to quartz owing to its higher piezoelectric coupling, structural stability up to 1400°C and presence of temperature compensated acoustic wave (AW) orientations. With these exciting properties, LGT is expected to find applications in AW sensor, timing, and frequency control. This thesis focuses on the characterization of the acoustic wave material properties of LGT up to 120°C. Such a characterization is critical for the design and fabrication of LGT acoustic wave devices. The elastic and piezoelectric constants were determined through measurements of bulk acoustic wave phase velocities by two independent methods, the pulse echo overlap technique and a combined resonance technique. The extracted constants and temperature coefficients enabled the identification of a range of particularly interesting LGT surface acoustic wave (SAW) orientations with Euler angles (90°, 23°, 118-124°) that exhibits predicted electromechanical coupling up to 0.7% and reduced or zero temperature coefficient of delay (TCD). The consistency of the determined constants and temperature coefficients was established using SAW measurements of seven crystallographic orientations at temperatures ranging up to 120°C. Measured SAW phase velocities and TCDs were found to be in agreement with predictions based on the determined constants. Two of the seven SAW orientations exhibited temperature compensation within 40°C of room temperature, agreeing with predictions. Deposition of SiAlON films on top of LGT SAW devices for surface protection in chemically and mechanically harsh environments was also investigated. SiAlON films deposited by reactive RF magnetron co-sputtering of Al and Si targets were controlled to within a few percent for film thickness and composition. SiAlON thin film clastic constants were extracted using differential SAW delay line methods and were found to be: C11,s = 160 +/- 30 GPa and C44,s = 55 +/- 5 GPa. SiAlON films up to 800 nm in thickness were shown to have no measurable effect on the TCD of LGT SAW delay lines.

Sturtevant, Blake T.

267

A Study of Single Crystal Fatigue Failure Criteria  

NASA Technical Reports Server (NTRS)

This paper presents the results of a study whose objective was to study the applicability of different failure equations in modeling low cycle fatigue (LCF) test data for single crystal test specimens. A total of four failure criteria were considered in this study. One of the failure equations was developed by Pratt & Whitney and is based on normal and shear strains on the primary crystallographic slip planes of the single crystal material. Other failure equations considered are based on isotropic criteria. Because these failure equations were originally developed for isotropic materials such as structural steel, they were modified to be applicable to the single crystal slip systems of the LCF specimen material. By observing how closely the various equations were able to reduce the scatter in the LCF test data, the applicability of those equations in modeling the LCF test data was assessed. It is desired to subsequently use the failure equation with the highest correlation in the development of a new single crystal failure criterion for the Alternative Turbopump Development (ATD) for the space shuttle main engine (SSME) High Pressure Fuel Turbopump (HPFTP).

Sayyah, Tarek; Swanson, Gregory R.; Schonberg, William P.

2000-01-01

268

Unified constitutive model for single crystal deformation behavior with applications  

NASA Technical Reports Server (NTRS)

Single crystal materials are being used in gas turbine airfoils and are candidates for other hot section components because of their increased temperature capabilities and resistance to thermal fatigue. Development of a constitutive model which assesses the inelastic behavior of these materials has been studied in 2 NASA programs: Life Prediction and Constitutive Models for Engine Hot Section Anisotropic Materials and Biaxial Constitutive Equation Development for Single Crystals. The model has been fit to a large body of constitutive data for single crystal PWA 1480 material. The model uses a unified approach for computing total inelastic strains (creep plus plasticity) on crystallographic slip systems reproducing observed directional and strain rate effects as a natural consequence of the summed slip system quantities. The model includes several of the effects that have been reported to influence deformation in single crystal materials, such as shear stress, latent hardening, and cross slip. The model is operational in a commercial Finite Element code and is being installed in a Boundary Element Method code.

Walker, K. P.; Meyer, T. G.; Jordan, E. H.

1988-01-01

269

Reliability analysis of single crystal NiAl turbine blades  

NASA Technical Reports Server (NTRS)

As part of a co-operative agreement with General Electric Aircraft Engines (GEAE), NASA LeRC is modifying and validating the Ceramic Analysis and Reliability Evaluation of Structures algorithm for use in design of components made of high strength NiAl based intermetallic materials. NiAl single crystal alloys are being actively investigated by GEAE as a replacement for Ni-based single crystal superalloys for use in high pressure turbine blades and vanes. The driving force for this research lies in the numerous property advantages offered by NiAl alloys over their superalloy counterparts. These include a reduction of density by as much as a third without significantly sacrificing strength, higher melting point, greater thermal conductivity, better oxidation resistance, and a better response to thermal barrier coatings. The current drawback to high strength NiAl single crystals is their limited ductility. Consequently, significant efforts including the work agreement with GEAE are underway to develop testing and design methodologies for these materials. The approach to validation and component analysis involves the following steps: determination of the statistical nature and source of fracture in a high strength, NiAl single crystal turbine blade material; measurement of the failure strength envelope of the material; coding of statistically based reliability models; verification of the code and model; and modeling of turbine blades and vanes for rig testing.

Salem, Jonathan; Noebe, Ronald; Wheeler, Donald R.; Holland, Fred; Palko, Joseph; Duffy, Stephen; Wright, P. Kennard

1995-01-01

270

Intrinsic electron and hole defects in stabilized zirconia single crystals  

Microsoft Academic Search

Intrinsic defects have been produced in yttria- and calcia-stabilized zirconia (YSZ or CaSZ) single crystals either by x irradiation at 300 and 77 K or by thermochemical reduction at 1370, 1670, and 1870 K. The spectroscopic properties of the defects have been studied by electron paramagnetic resonance (EPR), optical absorption, and photoemission techniques. Their thermal stability and bleaching characteristics have

V. M. Orera; R. I. Merino; Y. Chen; R. Cases; P. J. Alonso

1990-01-01

271

Pyroelectric properties of the modified triglycine sulphate (TGS) single crystals  

Microsoft Academic Search

Several doping substitutions (Li, Mn, D, P, As) in the TGS structure have been studied and the pyroelectric and dielectric properties measured. In the case of TGS single crystals modified by partial substitution of (P04 and (As04) groups for the (S04). higher pyroelectric coefficients and an enhancement of the pyroelectric material figure of merit (p\\/K) > 2 x TGS have

A. S. Bhalla; C. S. Fang; L. E. Cross; Yao Xi

1984-01-01

272

Growth of single crystals of bismuth sulpho iodide in gel  

Microsoft Academic Search

Single crystals of bismuth sulpho iodide have been grown in sodium silicate gel at room temperature by diffusing suitable reactants. In the first batch of experiments 3 to 7 g solution of BiCl3 was diffused into the gel containing 10 to 15% KI. Platelets of dimensions upto 5 mm were obtained in a period of 30 days. When thiourea of

R. Roop Kumar; G. Raman; F. D. Gnanam

1989-01-01

273

High definition TV projection via single crystal faceplate technology  

NASA Astrophysics Data System (ADS)

Single crystal phosphor faceplates are epitaxial phosphors grown on crystalline substrates with the advantages of high light output, resolution, and extended operational life. Single crystal phosphor faceplate industrial technology in the United States is capable of providing a faceplate appropriate to the projection industry of up to four (4) inches in diameter. Projection systems incorporating cathode ray tubes utilizing single crystal phosphor faceplates will produce 1500 lumens of white light with 1000 lines of resolution, non-interlaced. This 1500 lumen projection system will meet all of the currently specified luminance and resolution requirements of Visual Display systems for flight simulators. Significant logistic advantages accrue from the introduction of single crystal phosphor faceplate CRT's. Specifically, the full performance life of a CRT is expected to increase by a factor of five (5); ie, from 2000 to 10,000 hours of operation. There will be attendant reductions in maintenance time, spare CRT requirements, system down time, etc. The increased brightness of the projection system will allow use of lower gain, lower cost simulator screen material. Further, picture performance characteristics will be more balanced across the full simulator.

Kindl, H. J.; St. John, Thomas

1993-03-01

274

Temperature Dependence of Plastic Deformation in White Tin Single Crystals  

Microsoft Academic Search

Tensile experiments have been carried out over a wide range of temperatures on single crystals of high-purity white tin with low dislocation density. From the observations of slip lines it is found that different slip systems are activated for different temperature regions and for different orientations of specimens. By deformation with the (100)[010] slip system the cell structure is formed

Muneo Nagasaka

1989-01-01

275

Studies on Slip in Fe2%V Alloy Single Crystals  

Microsoft Academic Search

In an attempt to measure the critical resolved shear stress for slip of bcc metals, Fe-2%V single crystals were compressed along [110] direction, constraining the side faces, (001) and (00\\\\bar{1}), with a pair of fixed walls. Under these conditions, all slips are geometrically expected to be suppressed, and consequently [100] or [010] slip will be activated. Electron microscope study on

Shin Takeuchi

1969-01-01

276

Low temperature magnetic transitions of single crystal HoBi  

SciTech Connect

We present resistivity, specific heat and magnetization measurements in high quality single crystals of HoBi, with a residual resistivity ratio of 126. We find, from the temperature and field dependence of the magnetization, an antiferromagnetic transition at 5.7 K, which evolves, under magnetic fields, into a series of up to five metamagnetic phases.

Fente, A. [Universidad Autonoma de Madrid; Suderow, H. [Universidad Autonoma de Madrid; Vieira, S. [Universidad Autonoma de Madrid; Nemes, N. M. [Instituto de Ciencia de Materiales de Madrid; Garcia-Hernandez, M. [Instituto de Ciencia de Materiales de Madrid; Budko, Sergei L. [Ames Laboratory; Canfield, Paul C. [Ames Laboratory

2013-09-04

277

Optical waveguides of single-crystal garnet films  

NASA Astrophysics Data System (ADS)

We report light-wave propagation experiments in single-crystal epitaxially grown garnet films. The discussion includes refractive index and lattice constant considerations for various garnets, and also the use of iron garnet films on gallium garnet substrates as magneto-optical waveguides useful in integrated optics.

Tien, P. K.; Martin, R. J.; Blank, S. L.; Wemple, S. H.; Varnerin, L. J.

1972-09-01

278

Numerical aperture of single-mode photonic crystal fibers  

Microsoft Academic Search

We consider the problem of radiation into free space from the end-facet of a single-mode photonic crystal fiber (PCF). We calculate the numerical aperture NA = sin ? from the half-divergence angle ? ? tan-1 (?\\/??) with ??2 being the effective area of the mode in the PCF. For the fiber first presented by Knight et al. (1996), we find

Niels Asger Mortensen; Jacob Riis Folken; Peter M. W. Skovgaard; Jes Broeng

2002-01-01

279

Low-cost single-crystal turbine blades, volume 1  

NASA Technical Reports Server (NTRS)

The exothermic casting process was successfully developed into a low cost nonproprietary method for producing single crystal (SC) castings. Casting yields were lower than expected, on the order of 20 percent, but it is felt that the casting yield could be significantly improved with minor modifications to the process. Single crystal Mar-M 247 and two derivative SC alloys were developed. NASAIR 100 and SC Alloy 3 were fully characterized through mechanical property testing. SC Mar-M 247 shows no significant improvement in strength over directionally solidified (DS) Mar-M 247, but the derivative alloys, NASAIR 100 and Alloy 3, show significant tensile and fatigue improvements. The 1000 hr/238 MPa (20 ksi) stress rupture capability compared to DS Mar-M 247 was improved over 28 C. Firtree testing, holography, and strain gauge rig testing were used to evaluate the effects of the anisotropic characteristics of single crystal materials. In general, the single crystal material behaved similarly to DS Mar-M 247. Two complete engine sets of SC HP turbine blades were cast using the exothermic casting process and fully machined.

Strangman, T. E.; Heath, B.; Fujii, M.

1983-01-01

280

A model for Large Electrostrictive Actuation in Ferroelectric Single Crystals  

E-print Network

1 A model for Large Electrostrictive Actuation in Ferroelectric Single Crystals D. Shilo1 , E will allow larger strains at lower mechanical loads. Keywords: Ferroelectrics; Actuation; Electromechanical Institute of Technology, Pasadena, CA 91125, USA A new mode of large electrostrictive actuation, based on 90

Bhattacharya, Kaushik

281

Some Debye temperatures from single-crystal elastic constant data  

USGS Publications Warehouse

The mean velocity of sound has been calculated for 14 crystalline solids by using the best recent values of their single-crystal elastic stiffness constants. These mean sound velocities have been used to obtain the elastic Debye temperatures ??De for these materials. Models of the three wave velocity surfaces for calcite are illustrated. ?? 1966 The American Institute of Physics.

Robie, R.A.; Edwards, J.L.

1966-01-01

282

Green “planting” nanostructured single crystal silver  

PubMed Central

Design and fabrication of noble metal nanocrystals have attracted much attention due to their wide applications in catalysis, optical detection and biomedicine. However, it still remains a challenge to scale-up the production in a high-quality, low-cost and eco-friendly way. Here we show that single crystalline silver nanobelts grow abundantly on the surface of biomass-derived monolithic activated carbon (MAC), using [Ag(NH3)2]NO3 aqueous solution only. By varying the [Ag(NH3)2]NO3 concentration, silver nanoplates or nanoflowers can also be selectively obtained. The silver growth was illustrated using a galvanic-cell mechanism. The lowering of cell potential via using [Ag(NH3)2]+ precursor, together with the AgCl crystalline seed initiation, and the releasing of OH? in the reaction process, create a stable environment for the self-compensatory growth of silver nanocrystals. Our work revealed the great versatility of a new type of template-directed galvanic-cell reaction for the controlled growth of noble metal nanocrystals. PMID:23515002

Zhao, Hong; Wang, Fei; Ning, Yuesheng; Zhao, Binyuan; Yin, Fujun; Lai, Yijian; Zheng, Junwei; Hu, Xiaobin; Fan, Tongxiang; Tang, Jianguo; Zhang, Di; Hu, Keao

2013-01-01

283

X-ray crystal spectroscopy with stationary-state single-crystal utilizing Laue diffraction  

Microsoft Academic Search

A new type of x-ray crystal spectrometry has been designed to characterize a hard x-ray spectrum of each pulse emission from a laser-induced plasma x-ray source. Utilizing the Laue diffraction and a two-dimensional detector, it makes possible the measurement of diffracted monochromatic x rays without any time difference using a single crystal in a stationary state. Thus, a hard x-ray

Kazumasa Honda; Tadayuki Ohchi; Isao Kojima; Shigeki Hayashi

2001-01-01

284

Microwave Induced Direct Bonding of Single Crystal Silicon Wafers  

NASA Technical Reports Server (NTRS)

We have heated polished doped single-crystal silicon wafers in a single mode microwave cavity to temperatures where surface to surface bonding occurred. The absorption of microwaves and heating of the wafers is attributed to the inclusion of n-type or p-type impurities into these substrates. A cylindrical cavity TM (sub 010) standing wave mode was used to irradiate samples of various geometry's at positions of high magnetic field. This process was conducted in vacuum to exclude plasma effects. This initial study suggests that the inclusion of impurities in single crystal silicon significantly improved its microwave absorption (loss factor) to a point where heating silicon wafers directly can be accomplished in minimal time. Bonding of these substrates, however, occurs only at points of intimate surface to surface contact. The inclusion of a thin metallic layer on the surfaces enhances the bonding process.

Budraa, N. K.; Jackson, H. W.; Barmatz, M.

1999-01-01

285

Ultralarge negative dispersion single-polarization photonic crystal fiber  

NASA Astrophysics Data System (ADS)

The concept of employing a central air hole in the core is exploited to obtain an ultralarge negative dispersion photonic crystal fiber (PCF) over the wavelength range of 1350 to 1650 nm. The results show that the fiber may exhibit an average dispersion well over -500 ps/nm-km with a flattened dispersion profile. It is also found that the fiber shows a high birefringence in the order of 10-2 over the entire wavelength bands of interest. The endlessly single-mode behavior of PCFs is utilized to ensure the single modedness of the proposed fiber. Also, the technique of liquid crystal infiltration is exploited to suppress one of the two orthogonal modes of the fundamental mode. Along with the single-polarization behavior, the fiber shows an even more negative dispersion profile with less dispersion variation.

Islam, Md. Asiful; Alam, M. Shah

2014-09-01

286

Shock wave-induced phase transition in RDX single crystals.  

PubMed

The real-time, molecular-level response of oriented single crystals of hexahydro-1,3,5-trinitro-s-triazine (RDX) to shock compression was examined using Raman spectroscopy. Single crystals of [111], [210], or [100] orientation were shocked under stepwise loading to peak stresses from 3.0 to 5.5 GPa. Two types of measurements were performed: (i) high-resolution Raman spectroscopy to probe the material at peak stress and (ii) time-resolved Raman spectroscopy to monitor the evolution of molecular changes as the shock wave reverberated through the material. The frequency shift of the CH stretching modes under shock loading appeared to be similar for all three crystal orientations below 3.5 GPa. Significant spectral changes were observed in crystals shocked above 4.5 GPa. These changes were similar to those observed in static pressure measurements, indicating the occurrence of the alpha-gamma phase transition in shocked RDX crystals. No apparent orientation dependence in the molecular response of RDX to shock compression up to 5.5 GPa was observed. The phase transition had an incubation time of approximately 100 ns when RDX was shocked to 5.5 GPa peak stress. The observation of the alpha-gamma phase transition under shock wave loading is briefly discussed in connection with the onset of chemical decomposition in shocked RDX. PMID:17718475

Patterson, James E; Dreger, Zbigniew A; Gupta, Yogendra M

2007-09-20

287

Is the methanation reaction over Ru single crystals structure dependent?  

PubMed

The influence of monoatomic steps and defects on the methanation reaction over ruthenium has been investigated. The experiments are performed on a Ru(0 1 54) ruthenium single crystal, which contains one monoatomic step atom for each 27 terrace atoms. The methanation activity is measured at one bar of hydrogen and CO in a high pressure cell, which enables simultaneous measurements of the local reactivity of the well defined single crystal surface and the global reactivity of the entire crystal and its auxiliary support. By adding sulfur we observe that the measured activity from the well defined stepped front-side of the crystal is poisoned faster than the entire crystal containing more defects. We also observe that additional sputtering of the well-defined front-side increases the reactivity measured on the surface. Based on this, we conclude that the methanation reaction takes place on undercoordinated sites, such as steps and kinks, and that the methanation reaction is extremely structure dependent. Simulations of the flow, temperature, and product distributions in the high pressure cell are furthermore presented as supplementary information. PMID:21258708

Vendelbo, Søren B; Johansson, Martin; Nielsen, Jane H; Chorkendorff, Ib

2011-03-14

288

Growth and characterization of terbium fumarate heptahydrate single crystals  

NASA Astrophysics Data System (ADS)

The growth of terbium fumarate heptahydrate single crystals was achieved by single gel diffusion technique using silica gel as a medium of growth. The effect of various growth parameters on the nucleation rate of these crystals was studied. The crystals were characterized by different physico-chemical techniques of characterization. Powder X-ray diffraction pattern showed that terbium fumarate is a crystalline compound. Fourier transform infrared spectroscopy was performed for the identification of water and other functional groups present in the compound. UV-vis and photoluminescence spectrophotometric experiments were carried out to study the optical properties of the grown crystals. Elemental analysis suggested the chemical formula of the crystals to be Tb2(C4H2O4)3·7H2O. The presence of seven molecules of water was also supported by the thermogravimetric analysis. The hydrated compound was found to be thermally stable upto a temperature of about 110 °C and its anhydrous form up to the temperature of 410 °C. The thermal decomposition of the compound in the nitrogen atmosphere leads to the formation of terbium oxide as the final product. An attempt was made to relate the experimental results with the classical nucleation theory.

Want, B.; Shah, M. D.

2014-03-01

289

EPR observations of trivalent titanium in orthophosphate single crystals  

SciTech Connect

The ground state spectroscopic properties of the 3d/sup 1/ electronic configuration ion Ti/sup 3 +/ have been investigated using EPR spectroscopy. Trivalent titanium was incorporated as a dilute impurity in single crystals of the tetragonal, zircon-structure hosts ScPO/sub 4/, YPO/sub 4/, and LuPO/sub 4/. The EPR spectrum of Ti/sup 3 +/ was observed in the as-grown orthophosphate crystals, and low temperature irradiations were not required to produce the trivalent state. The EPR results show that Ti/sup 3 +/ occupies a substitutional cation site in the host orthophosphate single crystals. Axial spin-Hamiltonian parameters were determined at 77 K, and these results are compared to those obtained previously for the 4d/sup 1/ and 5d/sup 1/ configuration ions Zr/sup 3 +/ and Hf /sup 3 +/ in the same host crystals. Titanium-doped orthophosphate crystals containing isotopically enriched /sup 47/Ti or /sup 49/Ti were also grown and employed in determinations of the hyperfine parameters. The g-values observed here for Ti/sup 3 +/, and determined previously for Zr/sup 3 +/ and Hf /sup 3 +/ are not accounted for by the published second-order expressions indicating that additional coupling mechanisms are operative.

Abraham, M.M.; Boatner, L.A.; Aronson, M.A.

1986-07-01

290

Single crystal to single crystal transition in (10, 3)-d framework with pyrazine-2-carboxylate ligand: Synthesis, structures and magnetism  

SciTech Connect

Assembling of pyrazine-2-carboxylate (Pzc) acid with nickel chlorine under solvothermal condition with MeOH as solvent gave a porous complex 1 {l_brace}[Ni(Pzc)ClH{sub 2}O]{center_dot}MeOH{r_brace}{sub n} with 1D channels. In 1 the ligands and metal ions are connected by three of each other and a rare (10,3)-d topology net is gained. The MeOH molecules filled in the 1D channels as guests. It is interesting that 1 undergoes a single-crystal-to-single-crystal transformation to another complex 2 when the guest MeOH molecules in the channels are exchanged by water molecules. Magnetic study indicates anti-ferromagnetic couplings exist in the two complexes and the guest exchange in the complex has little influence on the magnetism. - Graphical abstract: A porous complex 1 with rare (10,3)-d net was gained, and 1 underwent a single-crystal-to-single-crystal transformation to another phase 2. Highlights: Black-Right-Pointing-Pointer New (10,3)-d net was obtained with pyrazine-2-carboxylate ligands as a triangular node. Black-Right-Pointing-Pointer The complex 1 has a 1D channel filled with methanol molecules as guests. Black-Right-Pointing-Pointer 1 could undergo SCSC structural transition to 2 after guests exchanged. Black-Right-Pointing-Pointer Antiferromagnetic interactions were found in 1 and 2.

Yang, Qian [School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China) [School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China); Department of Chemistry, Tianjin Key Lab on Metal and Molecule-based Material Chemistry, Nankai University, Tianjin 300071 (China); Zhao, Jiong-Peng, E-mail: horryzhao@yahoo.com [School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China)] [School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China); Liu, Zhong-Yi [College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Tianjin Normal University, Tianjin 300387 (China)] [College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Tianjin Normal University, Tianjin 300387 (China)

2012-12-15

291

Single crystal growth, crystal structure and characterization of a novel crystal: L-arginine 4-nitrophenolate 4-nitrophenol dehydrate (LAPP)  

NASA Astrophysics Data System (ADS)

A novel organic crystal, L-arginine 4-nitrophenolate 4-nitrophenol dehydrate (LAPP), synthesized and grown from aqueous solution, is presented. X-ray single diffraction shows that LAPP belongs to the monoclinic crystallographic system with space group P2 1. FT-IR and UV/vis/NIR transmission spectra have been employed to characterize the crystal. The computational calculation based on the density functional theory at the B3LYP/6-31G (d, p) level has been used to compute the first-order hyperpolarizability of LAPP relating to different molecular models. The morphology, nonlinear characteristic and thermal stability of the crystal have also been investigated.

Wang, L. N.; Wang, X. Q.; Zhang, G. H.; Liu, X. T.; Sun, Z. H.; Sun, G. H.; Wang, L.; Yu, W. T.; Xu, D.

2011-07-01

292

Single crystal growth and anisotropic crystal-fluid interfacial free energy in soft colloidal systems.  

PubMed

We measure the anisotropy of the crystal-fluid interfacial free energy in soft colloidal systems. A temperature gradient is used to direct crystal nucleation and control the growth of large single crystals in order to achieve well-equilibrated crystal-fluid interfaces. Confocal microscopy is used to follow both the growth process and the equilibrium crystal-fluid interface at the particle scale: heterogeneous crystal nucleation, the advancing interface, and the stationary equilibrium interface. We use the measured growth velocity to determine the chemical potential difference between crystal and fluid phases. Well-equilibrated, large crystal-fluid interfaces are then used to determine the interfacial free energy and its anisotropy directly from thermally excited interface fluctuations. We find that while the measured average interfacial free energy is in good agreement with values found in simulations, the anisotropy is significantly larger than simulation values. Finally, we investigate the effect of impurities on the advancing interface. We determine the critical force needed to overcome impurity particles from the local interface curvature. PMID:21867183

Nguyen, Van Duc; Hu, Zhibing; Schall, Peter

2011-07-01

293

Growth and electrical properties of mercury indium telluride single crystals  

SciTech Connect

A novel photoelectronic single crystal, mercury indium telluride (MIT), has been successfully grown by using vertical Bridgman method (VB). The crystallinity, thermal and electrical properties of the MIT crystal were investigated. The results of X-ray rocking curve show that the as-grown MIT crystal has good crystal quality with the FWHM on (3 1 1) face of about 173 in. DSC measurement reveals that the Hg element is easy to solely evaporate from the compound when the temperature is higher than 387.9 deg. C in the open system. Hall measurements at room temperature show that the resistivity, carrier density and mobility of the MIT crystal were 4.79 x 10{sup 2} {omega} cm, 2.83 x 10{sup 13} cm{sup -3} and 4.60 x 10{sup 2} cm{sup 2} V{sup -1} s{sup -1}, respectively. The reduction of carrier mobility and the increase of the resistivity are related to the adding of In{sub 2}Te{sub 3} into HgTe, which changes the energy band structure of the crystal.

Wang Linghang [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072 (China)], E-mail: uswlh@yahoo.com.cn; Dong Yangchun; Jie Wanqi [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072 (China)

2007-11-06

294

Single-crystal CsBr infrared fibers  

NASA Astrophysics Data System (ADS)

A study of the crystal growth, optical losses, and mechanical behavior of single-crystal CsBr infrared fibers is presented. The fibers were grown with a modified pull down technique and showed total losses in the range 2-5 dB/m at 10.6 microns, as well as excess scattering loss from surface imperfections such as growth striations, subgrain boundaries, and flaws. The main absorption loss at the CO2 wavelength is attributed to SO4(2-) ions contained in the raw materials. Because of their yield strength in addition to their flexibility, the (001)-oriented fibers are considered the best mechanically.

Mimura, Y.; Okamura, Y.; Ota, C.

1982-08-01

295

Spatial Coherence Preservation By Synthetic Single Diamond Crystals  

SciTech Connect

The degree of spatial coherence after x-ray diffraction by synthetic single diamond crystals was investigated. The coherence preservation was measured by means of the Talbot effect for x-rays at the optics beamline BM5 at the ESRF. The (111)- and (100)- oriented specimens of type Ib and IIa were grown by De Beers. To establish a correlation between the coherence degradation and the surface quality, 3D surface topography was measured with an optical interferometric profiler and an AFM. Likewise, to pinpoint the relationship with crystalline quality, the samples were characterized by means of double crystal x-ray diffractometry with microscopic resolution.

Hoszowska, J.; Freund, A. K.; Guigay, J.-P.; Rommeveaux, A. [European Synchrotron Radiation Facility, 6 Jules Horowitz, F-38043 Grenoble (France)

2004-05-12

296

Heavy ion passive dosimetry with silver halide single crystals  

NASA Technical Reports Server (NTRS)

A method of detecting radiation damage tracks due to heavy particles in large single crystals of the silver halides is described. The tracks, when made visible with a simple electrical apparatus, appear similar to tracks in emulsions. The properties of the crystals, the technique of printing out the tracks, and evidence concerning the threshold energy for registering particles indicates that this method may find application in heavy ion dosimetry. The method has been found to be sensitive to stopping He nuclei and relativistic M group cosmic rays. Some impurities strongly influence the printout of the tracks, and the effects of these impurities are discussed.

Childs, C. B.; Parnell, T. A.

1972-01-01

297

Electron Paramagnetic Resonance of Yb3+ in Scheelite Single Crystals  

Microsoft Academic Search

The electron paramagnetic resonance spectra of the ground state of trivalent ytterbium have been observed in eight single crystals with scheelite structure at 4.2°K and X band frequencies. The crystals used were CdMoO4, CaWO4, CaMoO4, SrWO4, SrMoO4, PbWO4, PbMoO4, and BaWO4. The tetragonal spectra for Yb171, Yb173, and the even isotopes of ytterbium were best fitted with an axial spin

J. P. Sattler; J. Nemarich

1970-01-01

298

Submicrometer Single Crystal Diffractometry for Highly Accurate Structure Determination  

NASA Astrophysics Data System (ADS)

Submicrometer single crystal diffractometry for highly accurate structure determination was developed using the extremely stable and highly brilliant synchrotron radiation from SPring-8. This was achieved using a microbeam focusing system and the submicrometer precision low-eccentric goniometer system. We demonstrated the structure analyses with 2×2×2 ?m3 cytidine, 600×600×300 nm3 BaTiO3, and 1×1×1 ?m3 silicon. The observed structure factors of the silicon crystal were in agreement with the structure factors determined by the Pendellösung method and do not require absorption and extinction corrections.

Yasuda, Nobuhiro; Fukuyama, Yoshimitsu; Toriumi, Koshiro; Kimura, Shigeru; Takata, Masaki

2010-06-01

299

Submicrometer Single Crystal Diffractometry for Highly Accurate Structure Determination  

SciTech Connect

Submicrometer single crystal diffractometry for highly accurate structure determination was developed using the extremely stable and highly brilliant synchrotron radiation from SPring-8. This was achieved using a microbeam focusing system and the submicrometer precision low-eccentric goniometer system. We demonstrated the structure analyses with 2x2x2 {mu}m{sup 3} cytidine, 600x600x300 nm{sup 3} BaTiO{sub 3}, and 1x1x1 {mu}m{sup 3} silicon. The observed structure factors of the silicon crystal were in agreement with the structure factors determined by the Pendelloesung method and do not require absorption and extinction corrections.

Yasuda, Nobuhiro; Fukuyama, Yoshimitsu; Kimura, Shigeru [Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198 (Japan); Japan Science and Technology Agency, CREST, 5, Sanbancho, Chiyoda, Tokyo 102-0075 (Japan); Toriumi, Koshiro [Japan Science and Technology Agency, CREST, 5, Sanbancho, Chiyoda, Tokyo 102-0075 (Japan); University of Hyogo, 3-2-1 Kouto, Kamigori, Ako, Hyogo 678-1297 (Japan); Takata, Masaki [Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198 (Japan); Japan Science and Technology Agency, CREST, 5, Sanbancho, Chiyoda, Tokyo 102-0075 (Japan); RIKEN SPring-8 Center, Harima Institute, 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5148 (Japan)

2010-06-23

300

Copper doping of ZnO crystals by transmutation of 64Zn to 65Cu: An electron paramagnetic resonance and gamma spectroscopy study  

NASA Astrophysics Data System (ADS)

Transmutation of 64Zn to 65Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5 keV gamma ray from the 65Zn decay and the positron annihilation peak at 511 keV. Their presence confirmed the successful transmutation of 64Zn nuclei to 65Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu2+ ions (where 63Cu and 65Cu hyperfine lines are easily resolved). A spectrum from isolated Cu2+ (3d9) ions acquired after the neutron irradiation showed only hyperfine lines from 65Cu nuclei. The absence of 63Cu lines in this Cu2+ spectrum left no doubt that the observed 65Cu signals were due to transmuted 65Cu nuclei created as a result of the neutron irradiation. Small concentrations of copper, in the form of Cu+-H complexes, were inadvertently present in our as-grown ZnO crystal. These Cu+-H complexes are not affected by the neutron irradiation, but they dissociate when a crystal is heated to 900 °C. This behavior allowed EPR to distinguish between the copper initially in the crystal and the copper subsequently produced by the neutron irradiation. In addition to transmutation, a second major effect of the neutron irradiation was the formation of zinc and oxygen vacancies by displacement. These vacancies were observed with EPR.

Recker, M. C.; McClory, J. W.; Holston, M. S.; Golden, E. M.; Giles, N. C.; Halliburton, L. E.

2014-06-01

301

Copper doping of ZnO crystals by transmutation of {sup 64}Zn to {sup 65}Cu: An electron paramagnetic resonance and gamma spectroscopy study  

SciTech Connect

Transmutation of {sup 64}Zn to {sup 65}Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5?keV gamma ray from the {sup 65}Zn decay and the positron annihilation peak at 511?keV. Their presence confirmed the successful transmutation of {sup 64}Zn nuclei to {sup 65}Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu{sup 2+} ions (where {sup 63}Cu and {sup 65}Cu hyperfine lines are easily resolved). A spectrum from isolated Cu{sup 2+} (3d{sup 9}) ions acquired after the neutron irradiation showed only hyperfine lines from {sup 65}Cu nuclei. The absence of {sup 63}Cu lines in this Cu{sup 2+} spectrum left no doubt that the observed {sup 65}Cu signals were due to transmuted {sup 65}Cu nuclei created as a result of the neutron irradiation. Small concentrations of copper, in the form of Cu{sup +}-H complexes, were inadvertently present in our as-grown ZnO crystal. These Cu{sup +}-H complexes are not affected by the neutron irradiation, but they dissociate when a crystal is heated to 900?°C. This behavior allowed EPR to distinguish between the copper initially in the crystal and the copper subsequently produced by the neutron irradiation. In addition to transmutation, a second major effect of the neutron irradiation was the formation of zinc and oxygen vacancies by displacement. These vacancies were observed with EPR.

Recker, M. C.; McClory, J. W., E-mail: John.McClory@afit.edu; Holston, M. S.; Golden, E. M.; Giles, N. C. [Department of Engineering Physics, Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio 45433 (United States); Halliburton, L. E. [Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506 (United States)

2014-06-28

302

The interaction of 193 nm excimer laser radiation with single-crystal zinc oxide: generation of long lived highly excited particles with evidence of Zn Rydberg formation  

SciTech Connect

We observe intense Zn ion and atom emissions when single-crystal ZnO is exposed to 193-nm excimer laser radiation at fluences below the threshold for optical breakdown. Zn+ and ground state Zn are readily identified by mass-selected, time-of-flight techniques using a quadrupole mass spectrometer. Particles are also detected with Channeltron electron multipliers that cannot be mass selected. We provide evidence that these particles correspond to high lying Rydberg states of atomic Zn produced by a resonance excitation involving two laser photons.

Kahn, E. H. [Washington State University, Pullman; Langford, S. C. [Washington State University, Pullman; Dickinson, J. T. [Washington State University, Pullman; Boatner, Lynn A [ORNL

2014-01-01

303

Synthesis of ZnO nanowires and their applications as an ultraviolet photodetector.  

PubMed

High purity ZnO nanowire arrays were synthesized uniformly on a 1.5 cm x 2 cm tin-doped indium oxide (ITO) glass substrate. The ZnO nanowire arrays were formed with a uniform diameter distribution of 30-50 nm and a length of about 5 microm, synthesized via thermal decomposition of zinc acetate at 300 degrees C in air. Analysis by X-ray diffraction and transmission electron microscopy showed that the ZnO nanowires are of single crystal structure with a preferred growth orientation of [001]. A study of the growth mechanism showed that it is a vapor-solid (VS) growth process. The synthesis of these nanowires begins with the processes of dehydration, vaporization, decomposition, and oxidation of the zinc acetate. Next, the ZnO clusters are deposited to form seeds that give rise to selective epitaxial growth of the ZnO nanowires. Optical analysis of ZnO nanowires was performed by UV-visible and fluorescence spectrophotometry, investigating both the photocurrent characteristics and UV photoresponse of the ZnO nanowire photodetectors. A study of optical properties showed that the as-produced ZnO nanowires have great potential as UV photodetectors/sensors. PMID:19452935

Lin, Chih-Cheng; Lin, Wang-Hua; Li, Yuan-Yao

2009-05-01

304

Epitaxial growth of ZnO thin films exhibiting room-temperature ultraviolet emission by atmospheric pressure chemical vapor deposition  

Microsoft Academic Search

ZnO films have been grown on sapphire(0001) substrates by means of the atmospheric pressure halide vapor phase epitaxy technique using ZnI2 and O2 as starting materials. The ZnO films showed a full width at half maximum of the (0002) X-ray peak of 20.2 min and a reflection high-energy electron diffraction pattern similar to that of a single crystal. A band-edge

Kazuhiko Kaiya; Kouji Omichi; Naoyuki Takahashi; Takato Nakamura; Shinji Okamoto; Hajime Yamamoto

2002-01-01

305

Substrate Atomic-Termination-Induced Anisotropic Growth of ZnO Nanowires/Nanorods by the VLS Process  

E-print Network

), a rotary pump system, and a gas controlling system. Commercial (Alfa Aesor) ZnO and SnO2 powders/nanorods. In this paper, using a model system of the Sn-catalyzed growth of ZnO nanostructures on a single-crystal Zn the structural point of view, Zn and oxygen atoms are arranged alternatively layer-by-layer along the c axis so

Wang, Zhong L.

306

Nucleation kinetics, growth and studies of ?-alanine single crystals.  

PubMed

Solubility and metastable zone width for the re-crystallized salt of ?-alanine was determined. Induction period measurement for the selected supersaturation ratios at room temperature (31 °C) was carried out for supersaturated aqueous solutions of ?-alanine and it is noticed that induction period decreases with increase of supersaturation ratio. The nucleation parameters such as Gibbs free energy change, radius and number of molecules of the critical nucleus, interfacial tension and the nucleation rate have been evaluated by classical nucleation theory. Single crystals of ?-alanine were grown using the optimized nucleation parameters by solution method and grown crystals have been subjected to various studies like XRD studies, FTIR, optical, thermal and SHG studies. PMID:23548638

Shanthi, D; Selvarajan, P; HemaDurga, K K; Lincy Mary Ponmani, S

2013-06-01

307

Photoluminescence of ZnO infiltrated into a three-dimensional photonic crystal  

SciTech Connect

The effect of the photonic band gap (stopband) of the photonic crystal, the synthesized SiO{sub 2} opal with embedded zinc oxide, on its luminescence in the violet spectral region is studied. It is shown that the position of the photonic band gap in the luminescence and reflectance spectra of the infiltrated opal depends on the diameter of the constituent nanoglobules, the volume fraction of zinc oxide, and on the signal's acceptance angle. It is found that, for the ZnO-opal nanocomposites, the emission intensity is decreased and the luminescence decay time is increased in the spatial directions, in which the photonic band gap coincides in spectral position with the luminescence peak of zinc oxide. The change in the decay time can be attributed to the change in the local density of photonic states in the photonic band gap.

Gruzintsev, A. N. [Russian Academy of Sciences, Institute of Microelectronic Technology and Ultra-High-Purity Materials (Russian Federation)], E-mail: gran@iptm.ru; Emelchenko, G. A.; Masalov, V. M. [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation)

2009-08-15

308

Effect of metallic dopants on potassium acid phthalate (KAP) single crystals  

Microsoft Academic Search

Optically transparent single crystals of Cu2+ and Zn2+ doped potassium acid phthalate (KAP) were grown in aqueous solution by slow evaporation technique at room temperature. Single crystal X-ray diffraction analysis confirmed the changes in the lattice parameters of the doped crystals. The presence of functional groups in the crystal lattice has been determined qualitatively by Fourier transform infrared (FTIR) analysis.

V. Chithambaram; S. Jerome Das; R. Arivudai Nambi; K. Srinivasan; S. Krishnan

2010-01-01

309

Determining thermodynamic properties of molecular interactions from single crystal studies.  

PubMed

The concept of single crystals of macromolecules as thermodynamic systems is not a common one. However, it should be possible to derive thermodynamic properties from single crystal structures, if the process of crystallization follows thermodynamic rules. We review here an example of how the stabilizing potentials of molecular interactions can be measured from studying the properties of DNA crystals. In this example, we describe an assay based on the four-stranded DNA junction to determine the stabilizing potentials of halogen bonds, a class of electrostatic interactions, analogous to hydrogen bonds, that are becoming increasing recognized as important for conferring specificity in protein-ligand complexes. The system demonstrates how crystallographic studies, when coupled with calorimetric methods, allow the geometries at the atomic level to be directly correlated with the stabilizing energies of molecular interactions. The approach can be generally applied to study the effects of DNA sequence and modifications of the thermodynamic stability of the Holliday junction and, by inference, on recombination and recombination dependent processes. PMID:23933330

Vander Zanden, Crystal M; Carter, Megan; Ho, Pui Shing

2013-11-01

310

Ultrafast dynamics of excitons in tetracene single crystals  

SciTech Connect

Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states S{sub n} on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S{sub 1} on a 40 ps timescale. The high energy Davydov component of the S{sub 1} exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale.

Birech, Zephania; Schwoerer, Heinrich, E-mail: heso@sun.ac.za [Laser Research Institute, Stellenbosch University, Stellenbosch 7600 (South Africa)] [Laser Research Institute, Stellenbosch University, Stellenbosch 7600 (South Africa); Schwoerer, Markus [Department of Physics, University of Bayreuth, Bayreuth (Germany)] [Department of Physics, University of Bayreuth, Bayreuth (Germany); Schmeiler, Teresa; Pflaum, Jens [Experimental Physics VI, University of Würzburg and Bavarian Center for Applied Energy Research, Würzburg (Germany)] [Experimental Physics VI, University of Würzburg and Bavarian Center for Applied Energy Research, Würzburg (Germany)

2014-03-21

311

Constitutive modeling of superalloy single crystals with verification testing  

NASA Technical Reports Server (NTRS)

The goal is the development of constitutive equations to describe the elevated temperature stress-strain behavior of single crystal turbine blade alloys. The program includes both the development of a suitable model and verification of the model through elevated temperature-torsion testing. A constitutive model is derived from postulated constitutive behavior on individual crystallographic slip systems. The behavior of the entire single crystal is then arrived at by summing up the slip on all the operative crystallographic slip systems. This type of formulation has a number of important advantages, including the prediction orientation dependence and the ability to directly represent the constitutive behavior in terms which metallurgists use in describing the micromechanisms. Here, the model is briefly described, followed by the experimental set-up and some experimental findings to date.

Jordan, Eric; Walker, Kevin P.

1985-01-01

312

Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures  

NASA Technical Reports Server (NTRS)

This report describes the results of a comprehensive study of plastic deformation of aluminum single crystals over a wide range of temperatures. The results of constant-stress creep tests have been reported for the temperature range from 400 degrees to 900 degrees F. For these tests, a new capacitance-type extensometer was designed. This unit has a range of 0.30 inch over which the sensitivity is very nearly linear and can be varied from as low a sensitivity as is desired to a maximum of 20 microinches per millivolt with good stability. Experiments were carried out to investigate the effect of small amounts of prestraining, by two different methods, on the creep and tensile properties of these aluminum single crystals. From observations it has been concluded that plastic deformation takes place predominantly by slip which is accompanied by the mechanisms of kinking and polygonization.

Johnson, R D; Young, A P; Schwope, A D

1956-01-01

313

Synthesis and characterization of single-crystal strontium hexaboride nanowires.  

PubMed

Catalyst-assisted growth of single-crystal strontium hexaboride (SrB6) nanowires was achieved by pyrolysis of diborane (B2H6) over SrO powders at 760-800 degrees C and 400 mTorr in a quartz tube furnace. Raman spectra demonstrate that the nanowires are SrB6, and transmission electron microscopy along with selected area diffraction indicate that the nanowires consist of single crystals with a preferred [001] growth direction. Electron energy loss data combined with the TEM images indicate that the nanowires consist of crystalline SrB 6 cores with a thin (1 to 2 nm) amorphous oxide shell. The nanowires have diameters of 10-50 nm and lengths of 1-10 microm. PMID:18950235

Jash, Panchatapa; Nicholls, Alan W; Ruoff, Rodney S; Trenary, Michael

2008-11-01

314

Flextensional Single Crystal Piezoelectric Actuators for Membrane Deformable Mirrors  

NASA Technical Reports Server (NTRS)

Large aperture and light weight space telescopes requires adaptive optics with deformable mirrors capable of large amplitude aberration corrections at a broad temperature range for space applications including NASA missions such as SAFIR, TPF, Con-X, etc. The single crystal piezoelectric actuators produced at TRS offer large stroke, low hysteresis, and an excellent cryogenic strain response. Specifically, the recently developed low profile, low voltage flextensional single crystal piezoelectric actuators with dimensions of 18 x 5 x 1 mm showed stroke larger than 95 microns under 300 V. Furthermore, flextensional actuator retained approx. 40-50% of its room temperature strain at liquid Nitrogen environment. In this paper, ATILA FEM design of flextensional actuators, actuator fabrication, and characterization results will be presented for the future work on membrane deformable mirror.

Jiang, Xiaoning; Sahul, Raffi; Hackenberger, Wesley S.

2006-01-01

315

A piezoelectric single-crystal ultrasonic microactuator for driving optics.  

PubMed

At the millimeter scale, the motions or force out puts generated by conventional piezoelectric, magnetostrictive, photostrictive, or electromagnetic actuators are very limited. Here, we report a piezoelectric ultrasonic microactuator (size: 1.5 × 1.5 × 5 mm, weight: 0.1 g) made of PIN-PMN-PT single crystal. The actuator converts its high-frequency microscopic displacements (nanometer to micrometer scale) into a macro scopic, centimeter-scale linear movement of a slider via frictional force, resulting in a speed up to 50 mm/s and a very high unit volume direct driving force of 26 mN/mm(3) (which is ~100 times higher than a voice coil motor and ~4 times higher than a piezoceramic ultrasonic motor). This work shows the feasibility of using piezoelectric single-crystal-based ultrasonic microactuator for miniature drive of optics in next-generation mobiles and cameras. PMID:23443709

Guo, Mingsen; Dong, Shuxiang; Ren, Bo; Luo, Haosu

2011-12-01

316

Ultrafast dynamics of excitons in tetracene single crystals.  

PubMed

Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states S(n) on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S1 on a 40 ps timescale. The high energy Davydov component of the S1 exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale. PMID:24655187

Birech, Zephania; Schwoerer, Markus; Schmeiler, Teresa; Pflaum, Jens; Schwoerer, Heinrich

2014-03-21

317

Ultrafast dynamics of excitons in tetracene single crystals  

NASA Astrophysics Data System (ADS)

Ultrafast exciton dynamics in free standing 200 nm thin tetracene single crystals were studied at room temperature by femtosecond transient absorption spectroscopy in the visible spectral range. The complex spectrally overlapping transient absorption traces of single crystals were systematically deconvoluted. From this, the ultrafast dynamics of the ground, excited, and transition states were identified including singlet exciton fission into two triplet excitons. Fission is generated through both, direct fission of higher singlet states Sn on a sub-picosecond timescale, and thermally activated fission of the singlet exciton S1 on a 40 ps timescale. The high energy Davydov component of the S1 exciton is proposed to undergo fission on a sub-picoseconds timescale. At high density of triplet excitons their mutual annihilation (triplet-triplet annihilation) occurs on a <10 ps timescale.

Birech, Zephania; Schwoerer, Markus; Schmeiler, Teresa; Pflaum, Jens; Schwoerer, Heinrich

2014-03-01

318

Thermal fatigue of NiAl single crystals  

SciTech Connect

Single crystals of [001]-oriented NiAl single crystals were subjected to thermal fatigue by a method which employs induction heating of disk-shaped specimens heated in an argon atmosphere. Several time-temperature heating and cooling profiles were used to produce different thermal strain histories in specimens cycled between 973 K and 1,473 K. After thermal cycling, pronounced shape changes in the form of diametrical elongations along {l{underscore}angle}100{r{underscore}angle} directions with accompanying increases in thickness at and near the {l{underscore}angle}100{r{underscore}angle} specimen axes were observed. The deformations were analyzed in terms of operative slip systems in tension and compression, ratchetting (cyclic strain accumulation), and the elastic properties of NiAl. The experimental results correlate best with thermal stresses associated with the large elastic anisotropy of NiAl.

Kush, M.T.; Holmes, J.W.; Gibala, R.

1999-07-01

319

Aging and memory effect in magnetoelectric gallium ferrite single crystals  

NASA Astrophysics Data System (ADS)

Here, we present a time and temperature dependent magnetization study to understand the spin dynamics in flux grown single crystals of gallium ferrite (GaFeO3), a known magnetoelectric, ferroelectric and ferrimagnet. Results of the magnetic measurements conducted in the field-cooled (FC) and zero-field-cooled (ZFC) protocols in the heating and cooling cycles were reminiscent of a "memory" effect. Subsequent time dependent magnetic relaxation measurements carried out in ZFC mode at 30 K with an intermittent cooling to 20 K in the presence of a small field show that the magnetization in the final wait period tends to follow its initial state which was present before the cooling break taken at 20 K. These observations provide an unambiguous evidence of single crystal gallium ferrite having a spin glass like phase.

Singh, Vijay; Mukherjee, Somdutta; Mitra, Chiranjib; Garg, Ashish; Gupta, Rajeev

2015-02-01

320

Engineering domain configurations for enhanced piezoelectricity in barium titanate single crystals  

E-print Network

Engineering domain configurations for enhanced piezoelectricity in barium titanate single crystals piezoelectric responses of barium titanate single crystals under different crystallographic orientations, and use it to explain the ultrahigh piezoelectric response recently observed in a 270 cut barium titanate

Li, Jiangyu

321

Ultrafast carrier dynamics in pentacene, functionalized pentacene, tetracene, and rubrene single crystals  

E-print Network

photoconduc- tivity in organic single crystals and polycrystalline thin films over picosecond time scales,7 the transient photoconductivity in pentacene, functionalized pentacene, tetracene, and rubrene single crystals charge photogeneration and a peak photoconductive response that increases as the temperature decreases

Ostroverkhova, Oksana

322

Crystal growth, structure analysis and characterisation of 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid single crystal  

SciTech Connect

Single crystal of dielectric material 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid has been grown by slow evaporation solution growth method. The grown crystal was harvested in 25 days. The crystal structure was analyzed by Single crystal X - ray diffraction. UV-vis-NIR analysis was performed to examine the optical property of the grown crystal. The thermal property of the grown crystal was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The dielectric measurements were carried out and the dielectric constant was calculated and plotted at all frequencies.

Sankari, R. Siva, E-mail: sivasankari.sh@act.edu.in [Department of Physics, Agni College of Technology, Thalambur, Chennai-603103 (India); Perumal, Rajesh Narayana [Department of Physics, SSN College of Engineering, Kalavakkam, Chennai-603110 (India)

2014-04-24

323

Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys  

NASA Technical Reports Server (NTRS)

High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine engines is a pervasive problem affecting a wide range of components and materials. HCF is currently the primary cause of component failures in gas turbine aircraft engines. Turbine blades in high performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys. Single-crystal Nickel-base superalloys were developed to provide superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys previously used in the production of turbine blades and vanes. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. PWA1493, identical to PWA1480, but with tighter chemical constituent control, is used in the NASA SSME (Space Shuttle Main Engine) alternate turbopump, a liquid hydrogen fueled rocket engine. Objectives for this paper are motivated by the need for developing failure criteria and fatigue life evaluation procedures for high temperature single crystal components, using available fatigue data and finite element modeling of turbine blades. Using the FE (finite element) stress analysis results and the fatigue life relations developed, the effect of variation of primary and secondary crystal orientations on life is determined, at critical blade locations. The most advantageous crystal orientation for a given blade design is determined. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to optimize blade design by increasing its resistance to fatigue crack growth without adding additional weight or cost.

Arakere, Nagaraj K.; Swanson, Gregory R.

2000-01-01

324

Frictional properties of single crystals HMX, RDX and PETN explosives.  

PubMed

The frictional properties of single crystals of cyclotetramethylene tetranitramine (HMX), cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN) secondary explosives are examined using a sensitive friction machine. The explosive crystals used for the measurements are at least 3.5 mm wide. The friction coefficients between crystals of the same explosive (i.e., HMX on HMX, etc.), crystals of different explosives (i.e., HMX on RDX, etc.), and each explosive and a well-polished gauge steel surface are determined. The frictional surfaces are also studied under an environmental scanning electron microscope (ESEM) to analyze surface microstructural changes under increasing loading forces. The friction coefficients vary considerably with increasing normal loading forces and are particularly sensitive to slider shapes, crystal roughness and the mechanical properties of both the slider and the sample. With increasing loading forces, most friction experiments show surface damage, consisting of grooves, debris, and nano-particles, on both the slider and sample. In some cases, a strong evidence of a localized molten state is found in the central region of the friction track. Possible mechanisms that affect the friction coefficient are discussed based on microscopic observations. PMID:20688432

Wu, Y Q; Huang, F L

2010-11-15

325

Properties of salt-grown uranium single crystals.  

SciTech Connect

Recently single crystals of {alpha}-uranium were grown from a liquid salt bath. The electrical, magnetic and thermal properties of these crystals have been surveyed. The ratio of the room temperature resistivity of these crystals to the saturation value at low temperature is three times larger than any previously reported demonstrating that the crystals are of higher purity and quality than those in past work. The resistive signatures of the CDW transitions at 43, 37 and 22 K are obvious to the naked eye. The transition at 22 K exhibits temperature hysteresis that increases with magnetic field. In addition the superconducting transition temperature from resistivity is 820 mK and the critical field is 80 mT. Contrary to earlier work where the Debye temperature ranged from 186 to 218 K, the Debye temperature extracted from the heat capacity is 254 K in good agreement with the predicted value of 250 K. Magnetoresistance, Hall effect and magnetic susceptibility measurements are underway. In time, measurements made on these crystals may help us to understand the origin of superconductivity and its relation to the CDW transitions in pure uranium.

Cooley, J. C. (Jason C.); Hanrahan, R. J. (Robert J.); Hults, W. L. (William L.); Lashley, J. C. (Jason C.); Manley, M. E. (Michael E.); Mielke, C. H. (Charles H.); Smith, J. L. (James L.); Thoma, D. J. (Dan J.); Clark, R. G. (Robert G.); Hamilton, A. R.; O'Brien, J. L. (Jeremy L.); Gay, E. C. (Eddie C.); Lumpkin, N. E.; McPheeters, C. C. (Charles C.); Willit, J.; Schmiedeshoff, G. M. (George M.); Touton, S. (Sharon); Woodfield, B. F. (Brian F.); Lang, B. E. (Brian E.); Boerio-Goates, Juliana

2001-01-01

326

Elastic and Piezoelectric Coefficients of Single-Crystal Barium Titanate  

Microsoft Academic Search

Mechanical resonance and antiresonance frequencies were measured on barium titanate single-crystal elements maintained under electric dc bias from -50°C to +150°C. A complete set of elastic, piezoelectric, and dielectric constants of the tetragonal modification at 25°C is obtained. The elastic compliances show substantial deviation from cubic symmetry. Measurements in the orthorhombic state show longitudinal compliance four times higher than in

Don Berlincourt; Hans Jaffe

1958-01-01

327

Growth of Semiconductor Single Crystals from Vapor Phase  

NASA Astrophysics Data System (ADS)

Growth of single crystals from the vapor phase is considered to be an important method to obtain stoichiometric crystalline materials from inexpensive and readily available raw materials. Elements or compounds which are relatively volatile can be grown from vapor phase. Most II-VI, I-III-VI2, and III-N compounds are high-melting-point materials which may be grown as single crystals by careful use of vapor phase. The chemical vapor transport (CVT) method has been widely used as an advantageous method to grow single crystals of different compounds at temperatures lower than their melting points. This method is quite useful for the growth of II-VI and I-III-VI2 compounds, which generally have high melting point and large dissociation pressure at the melting point. In addition, they undergo solid-state phase transition during cooling or heating processes, which makes the growth of these compounds by some other methods, such as from the melt, difficult. In addition, the low growth temperature involved reduces defects produced by thermal strain, pollution from the crucible, and the cost of the growth equipment. II-VI compound semiconductors cover a very broad range of electronic and optical properties due to the large range of their energy gaps. These materials in the form of bulk single crystals or thin films are used in light emitters, detectors, linear and nonlinear optical devices, semiconductor electronics, and other devices. The development of growth technology for II-VI compound semiconductors from the vapor phase with the necessary theoretical background is important. I-III-VI2 chalcopyrite compounds are of technological interest since they show promise for application in areas of visible and infrared light-emitting diodes, infrared detectors, optical parametric oscillators, upconverters, far-infrared generation, and solar energy conversion.

Dhanasekaran, Ramasamy

328

Single crystal silicon as a low-temperature structural material  

NASA Astrophysics Data System (ADS)

In neutron scattering applications, it is frequently desirable to construct a sample container from a material that is strong but has very little neutron absorption of scattering. Single crystal silicon is very good by these criteria but it is difficult to work with because of its brittleness. A technique for gluing silicon was developed that yields high strength joints at low temperatures and allows very compact designs for sample containers.

Roach, P. R.

1984-07-01

329

Low temperature properties of calcia-stabilized zirconia single crystal  

Microsoft Academic Search

We investigated the internal friction, thermal conductivity and heat release for the single crystal of calciastabilized cubic\\u000a zirconia. From the experimental data we determined the values of distribution parameterSNOW coupling constant ? and the temperature\\u000a of the thermal activation of the tunneling systems and compared the results with the theory of the tunneling model and the\\u000a soft potential model. All

S. Abens; K. Topp; S. Sahling; R. O. Pohl

1996-01-01

330

Electrons trapped in single crystals of sucrose: Induced spin densities  

SciTech Connect

Electrons are trapped at intermolecular sites in single crystals of sucrose {ital X} irradiated at 4.2 K. The coupling tensors for the hyperfine couplings between the electron and surrounding protons have been deduced from electron-nuclear double resonance (ENDOR) data. Electron spin densities at nearby hydroxy protons are positive, whereas spin densities at the more remote protons of carbon-bound hydrogen atoms are negative. The origin of these negative spin densities is discussed.

Box, H.C.; Budzinski, E.E.; Freund, H.G. (Biophysics Department, Roswell Park Memorial Institute, Buffalo, New York 14263 (USA))

1990-07-01

331

Numerical aperture of single-mode photonic crystal fibers  

Microsoft Academic Search

We consider the problem of radiation into free space from the end-facet of a single-mode photonic crystal fiber (PCF). We calculate the numerical aperture NA=sin theta from the half-divergence angle theta ~ tan^{-1}(lambda\\/pi w) with pi w^2 being the effective area of the mode in the PCF. For the fiber first presented by Knight et al. we find a numerical

N. A. Mortensen; J. R. Folken; P. M. W. Skovgaard; J. Broeng

2002-01-01

332

Occurrence and stability of trivalent zirconium in orthophosphate single crystals  

SciTech Connect

EPR spectroscopy has been used in investigations of the unusual 3+ valence state of zirconium. The EPR spectrum of Zr/sup 3 +/, which was initially observed as a parasitic signal in Fe-doped single crystals of ScPO/sub 4/, was definitively identified by preparing single crystals of ScPO/sub 4/ doped with isotopically enriched (94.6%)/sup 91/Zr. Single crystals of LuPO/sub 4/ and YPO/sub 4/ doped with both naturally abundant and isotopically enriched Zr were also grown and investigated. The EPR spectrum of Zr/sup 3 +/ could be observed at room temperature in the ''as-grown'' single crystals of both ScPO/sub 4/ and LuPO/sub 4/; and, accordingly, the 3+ state is stable at room temperature in these hosts. The spectrum of Zr/sup 3 +/ in the YPO/sub 4/ host could only be observed following a ..gamma.. irradiation at 77 K, and this spectrum decayed rapidly with increasing temperature. Axial spin-Hamiltonian parameters were determined for Zr/sup 3 +/ in all three hosts at a sample temperature of 77 K and at room temperature for the ScPO/sub 4/ and LuPO/sub 4/ hosts. In the case of the latter two hosts, the spin-Hamiltonian parameters were found to exhibit a small temperature dependence. The observed g values were not accounted for by previously published second-order expressions indicating that additional coupling mechanisms are operative.

Abraham, M.M.; Boatner, L.A.; Ramey, J.O.; Rappaz, M.

1984-12-15

333

Sapphire matrix composites reinforced with single crystal YAG phases  

Microsoft Academic Search

An investigation of fabrication technology on eutectic composites consisting of Al2O3 phases and YAG (Y3Al5O12) phases was carried out by applying the unidirectional solidification process. Unidirectionally solidified eutectic composites consisting of sapphire phases and single crystal YAG phases could be fabricated successfully by lowering a Mo crucible at a speed of 5 mm h-1 under a pressure of 10-5 mmHg

Y. Waku; H. Ohtsubo; N. Nakagawa; Y. Kohtoku

1996-01-01

334

Excitonic photoconductivity of 4BCMU polydiacetylene single crystals  

Microsoft Academic Search

Thermal annealing of 4BCMU single crystals increases the transition energy of excitons from 2.0 to 2.3eV and a similar increase is observed for the free carrier gap resolved by electroabsorption spectra. This modification leads to a significant change of the photocurrent threshold which after the transformation shifts to the excitonic absorption edge. Since the exciton binding energy of 0.5eV is

S Möller; G Weiser; C Lapersonne-Meyer

2001-01-01

335

Low-temperature growth and characterization of single crystalline ZnO nanorod arrays using a catalyst-free inductively coupled plasma-metal organic chemical vapor deposition.  

PubMed

Vertically aligned ZnO nanorod arrays have been synthesized on c-plane sapphires at a low temperature of 400 degrees C using catalyst-free inductively coupled plasma (ICP) metal organic chemical vapor deposition (MOCVD) technique by varying the ICP powers. Diameters of the ZnO nanorods changed from 200 nm to 400 nm as the ICP power increased from 200 to 400 Watt. TEM and XRD investigations indicated that the ZnO nanorod arrays grown at ICP powers above 200 Watt had a homogeneous in-plane alignment and single crystalline nature. PL study at room temperature (RT) and 6 K confirmed that the ZnO nanorod arrays in the present study are of high optical quality as well as good crystalline quality, showing only exciton-related emission peaks without any trace of defect-related deep level emissions in visible range. The blueshift of exciton emission peak in RTPL spectra was also found as rod diameter decreased and it is deduced that this shift in emission energy may be due to the surface resonance effect resulted from the increased surface-to-volume ratio, based on the observation and behavior of the surface exciton (SX) emission in the high-resolution 6 K PL spectra. PMID:19198399

Jeong, Sang-Hun; Lee, Chang-Bae; Moon, Won-Jin; Song, Ho-Jun

2008-10-01

336

Diamond turning of Si and Ge single crystals  

SciTech Connect

Single-point diamond turning studies have been completed on Si and Ge crystals. A new process model was developed for diamond turning which is based on a critical depth of cut for plastic flow-to-brittle fracture transitions. This concept, when combined with the actual machining geometry for single-point turning, predicts that {open_quotes}ductile{close_quotes} machining is a combined action of plasticity and fracture. Interrupted cutting experiments also provide a meant to directly measure the critical depth parameter for given machining conditions.

Blake, P.; Scattergood, R.O.

1988-12-01

337

Method for thermal processing alumina-enriched spinel single crystals  

DOEpatents

A process for age-hardening alumina-rich magnesium aluminum spinel to obtain the desired combination of characteristics of hardness, clarity, flexural strength and toughness comprises selection of the time-temperature pair for isothermal heating followed by quenching. The time-temperature pair is selected from the region wherein the precipitate groups have the characteristics sought. The single crystal spinel is isothermally heated and will, if heated long enough pass from its single phase through two pre-precipitates and two metastable precipitates to a stable secondary phase precipitate within the spinel matrix. Quenching is done slowly at first to avoid thermal shock, then rapidly. 12 figs.

Jantzen, C.M.

1995-05-09

338

Method for thermal processing alumina-enriched spinel single crystals  

DOEpatents

A process for age-hardening alumina-rich magnesium aluminum spinel to obtain the desired combination of characteristics of hardness, clarity, flexural strength and toughness comprises selection of the time-temperature pair for isothermal heating followed by quenching. The time-temperature pair is selected from the region wherein the precipitate groups have the characteristics sought. The single crystal spinel is isothermally heated and will, if heated long enough pass from its single phase through two pre-precipitates and two metastable precipitates to a stable secondary phase precipitate within the spinel matrix. Quenching is done slowly at first to avoid thermal shock, then rapidly.

Jantzen, Carol M. (Aiken, SC)

1995-01-01

339

Single particle detection in CMOS compatible photonic crystal nanobeam cavities.  

PubMed

We report the label-free detection of single particles using photonic crystal nanobeam cavities fabricated in silicon-on-insulator platform, and embedded inside microfluidic channels fabricated in poly-dimethylsiloxane (PDMS). Our system operates in the telecommunication wavelength band, thus leveraging the widely available, robust and tunable telecom laser sources. Using this approach, we demonstrated the detection of polystyrene nanoparticles with dimensions down to 12.5nm in radius. Furthermore, binding events of a single streptavidin molecule have been observed. PMID:24514817

Quan, Qimin; Floyd, Daniel L; Burgess, Ian B; Deotare, Parag B; Frank, Ian W; Tang, Sindy K Y; Ilic, Rob; Loncar, Marko

2013-12-30

340

ATMOSPHERIC EFFECTS ON THE PERFORMANCE OF CDZNTE SINGLE CRYSTAL DETECTORS  

SciTech Connect

The production of high-quality ternary single-crystal materials for radiation detectors has progressed over the past 15 years. One of the more common materials being studied is CdZnTe (CZT), which can be grown using several methods to produce detector-grade materials. The work presented herein examines the effects of environmental conditions including temperature and humidity on detector performance [full-width at half-maximum (FWHM)] using the single pixel with guard detector configuration. The effects of electrical probe placement, reproducibility, and aging are also presented.

Washington, A.; Duff, M.; Teague, L.

2010-05-12

341

SINGLE-CRYSTAL SAPPHIRE OPTICAL FIBER SENSOR INSTRUMENTATION  

SciTech Connect

In this research program, several optical instruments for high temperature measurement based on single crystal sapphire material are introduced and tested for real-time, reliable, long-term monitoring of temperatures for coal gasifier. These are sapphire fiber extrinsic Fabry-Perot interferometric (EFPI) sensor; intensity-measurement based polarimetric sapphire sensor and broadband polarimetric differential interferometric (BPDI) sapphire sensor. Based on current evaluation and analysis of the experimental results, the broadband polarimetric differential interferometric (BPDI) sensor system was chosen for further prototype instrumentation development. This approach is based on the self-calibrating measurement of optical path differences (OPD) in a single-crystal sapphire disk, which is a function of both the temperature dependent birefringence and the temperature dependent dimensional changes. The BPDI sensor system extracts absolute temperature information by absolute measurement of phase delays. By encoding temperature information in optical spectrum instead of optical intensity, this sensor guarantees its relative immunity to optical source power fluctuations and fiber losses, thus providing a high degree of long-term measurement stability which is highly desired in industrial applications. The entire prototype for BPDI system including the single crystal sapphire probe, zirconia prism, alumina extension tube, optical components and signal processing hardware and software have shown excellent performance in the laboratory experiments shown in this report.

A. Wang; G. Pickrell; R. May

2002-09-10

342

Segregation effects in Fe microalloyed NiAl single crystals  

SciTech Connect

The low density, excellent oxidation resistance and high thermal conductivity of the intermetallic phase NiAl compared to conventional nickel-based superalloys make NiAl based materials suitable for gas turbine applications. The lack of room-temperature ductility has been one of the barriers which hamper the technical use of the new material. Recently, a significant enhancement of room temperature tensile ductility up to 6% of soft <110> oriented NiAl single crystalline samples by microalloying with Fe, Ga or Mo was reported, compared with {approximately} 1 to 2% of binary stoichiometric NiAl. Dopant elements can display a rather inhomogeneous distribution along the crystal due to the redistribution of solute during directional solidification. Furthermore, the solute pile-up ahead of the smooth solidification front may lead to a morphological instability and to a transition from the single crystalline to a cellular/dendritic solidification mode. The scope of this paper is, therefore, to investigate the Fe distribution along the directionally solidified NiAl(Fe) crystals and possible transitions in microstructure, in order to reveal limitations for microalloying and to find out appropriate levels of dopant concentration and process parameters for homogeneously microalloyed NiAl single crystals.

Vaerst, G.; Loeser, W.; Leonhardt, M.; Oswald, S. [Inst. fur Festkoerper- und Werkstofforschung Dresden (Germany)] [Inst. fur Festkoerper- und Werkstofforschung Dresden (Germany)

1995-10-15

343

Growth and characterization of pure and doped bis thiourea zinc acetate: Semiorganic nonlinear optical single crystals  

Microsoft Academic Search

Metal–organic coordination complex single crystals bis thiourea zinc acetate (BTZA) and Cd2+ doped BTZA have been synthesized and grown successfully by slow-cooling technique from their aqueous solutions. Single crystals of pure and Cd2+ doped BTZA with dimensions of 35×4×2mm3 and 10×5×6mm3, respectively were obtained with well defined morphology. The as grown single crystals are characterized by single crystal XRD studies

M. Lydia Caroline; S. Vasudevan

2009-01-01

344

Acquisition of Single Crystal Growth and Characterization Equipment  

SciTech Connect

Final Report for DOE Grant No. DE-FG02-04ER46178 'Acquisition of Single Crystal Growth and Characterization Equipment'. There is growing concern in the condensed matter community that the need for quality crystal growth and materials preparation laboratories is not being met in the United States. It has been suggested that there are too many researchers performing measurements on too few materials. As a result, many user facilities are not being used optimally. The number of proficient crystal growers is too small. In addition, insufficient attention is being paid to the enterprise of finding new and interesting materials, which is the driving force behind much of condensed matter research and, ultimately, technology. While a detailed assessment of this situation is clearly needed, enough evidence of a problem already exists to compel a general consensus that the situation must be addressed promptly. This final report describes the work carried out during the last four years in our group, in which a state-of-the-art single crystal growth and characterization facility was established for the study of novel oxides and intermetallic compounds of rare earth, actinide and transition metal elements. Research emphasis is on the physics of superconducting (SC), magnetic, heavy fermion (HF), non-Fermi liquid (NFL) and other types of strongly correlated electron phenomena in bulk single crystals. Properties of these materials are being studied as a function of concentration of chemical constituents, temperature, pressure, and magnetic field, which provide information about the electronic, lattice, and magnetic excitations at the root of various strongly correlated electron phenomena. Most importantly, the facility makes possible the investigation of material properties that can only be achieved in high quality bulk single crystals, including magnetic and transport phenomena, studies of the effects of disorder, properties in the clean limit, and spectroscopic and scattering studies through efforts with numerous collaborators. These endeavors will assist the effort to explain various outstanding theoretical problems, such as order parameter symmetries and electron-pairing mechanisms in unconventional superconductors, the relationship between superconductivity and magnetic order in certain correlated electron systems, the role of disorder in non-Fermi liquid behavior and unconventional superconductivity, and the nature of interactions between localized and itinerant electrons in these materials. Understanding the mechanisms behind strongly correlated electron behavior has important technological implications.

Maple, M. Brian; Zocco, Diego A.

2008-12-09

345

Large pyramid shaped single crystals of BiFeO{sub 3} by solvothermal synthesis method  

SciTech Connect

Synthesis parameters are optimized in order to grow single crystals of multiferroic BiFeO{sub 3}. 2 to 3 mm size pyramid (tetrahedron) shaped single crystals were successfully obtained by solvothermal method. Scanning electron microscopy with EDAX confirmed the phase formation. Raman scattering spectra of bulk BiFeO3 single crystals have been measured which match well with reported spectra.

Sornadurai, D.; Ravindran, T. R.; Paul, V. Thomas; Sastry, V. Sankara [Condensed Matter Physics Division, Materials Science Group, Physical Metallurgy Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu (India); Condensed Matter Physics Division, Materials Science Group (India)

2012-06-05

346

NUMERICAL SIMULATIONS OF CRACK TIP STRESS-STRAIN FIELDS IN SINGLE CRYSTAL NICKEL-BASE SUPERALLOYS  

E-print Network

NUMERICAL SIMULATIONS OF CRACK TIP STRESS-STRAIN FIELDS IN SINGLE CRYSTAL NICKEL-BASE SUPERALLOYS, FRANCE ABSTRACT This work deals with the finite element analysis of cracks in single crystal Nickel crack in a CT specimen. After a presentation of these crack tip fields in single crystals (Rice [1

Paris-Sud XI, Université de

347

Synthesis of Calcite Single Crystals with Porous Surface by Templating of Polymer Latex Particles  

E-print Network

Synthesis of Calcite Single Crystals with Porous Surface by Templating of Polymer Latex Particles in solution. After template removal, well-defined, calcite single crystals exhibiting a rhombohedral morphology and uniform surface pores are obtained. The surface pore size of the calcite single crystals can

Qi, Limin

348

Tip-Induced Calcite Single Crystal Nanowear Ramakrishna Gunda, and Alex A. Volinsky  

E-print Network

Tip-Induced Calcite Single Crystal Nanowear Ramakrishna Gunda, and Alex A. Volinsky Department Wear behavior of freshly cleaved single crystal calcite (CaCO3) was investigated by continuous scanning of effects. The wear regime is due to abrasive wear. Single crystal calcite hardness of 2.8±0.3 GPa

Volinsky, Alex A.

349

Irradiated Single Crystals for High Temperature Measurements in Space Applications Alex A. Volinsky1  

E-print Network

formation and accumulation in diamond and SiC single crystals, which causes overall lattice expansionIrradiated Single Crystals for High Temperature Measurements in Space Applications Alex A. Volinsky temperature, if the exposure time is known. This paper describes the use of irradiated single crystal high

Volinsky, Alex A.

350

Low-Leakage Superconducting Tunnel Junctions with a Single-Crystal Al2O3 Barrier*  

E-print Network

Low-Leakage Superconducting Tunnel Junctions with a Single-Crystal Al2O3 Barrier* S Oh1,2 , K Cicak Abstract We have developed a two-step growth scheme for single-crystal Al2O3 tunnel barriers. The barriers environment, a morphologically intact single-crystal Al2O3 layer is obtained. Tunnel junctions fabricated from

Martinis, John M.

351

Atomic force microscopy of insulin single crystals: direct visualization of molecules and crystal growth.  

PubMed Central

Atomic force microscopy performed on single crystals of three different polymorphs of bovine insulin revealed molecularly smooth (001) layers separated by steps whose heights reflect the dimensions of a single insulin hexamer. Whereas contact mode imaging caused etching that prevented molecular-scale resolution, tapping mode imaging in solution provided molecular-scale contrast that enabled determination of lattice parameters and polymorph identification while simultaneously enabling real-time examination of growth modes and assessment of crystal quality. Crystallization proceeds layer by layer, a process in which the protein molecules assemble homoepitaxially with nearly perfect orientational and translational commensurism. Tapping mode imaging also revealed insulin aggregates attached to the (001) faces, their incorporation into growing terraces, and their role in defect formation. These observations demonstrate that tapping mode imaging is ideal for real-time in situ investigation of the crystallization of soft protein crystals of relatively small proteins such as insulin, which cannot withstand the lateral shear forces exerted by the scanning probe in conventional imaging modes. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 PMID:8842243

Yip, C M; Ward, M D

1996-01-01

352

Application of electrochemically deposited nanostructured ZnO layers on quartz crystal microbalance for NO2 detection  

NASA Astrophysics Data System (ADS)

The research was fixed on sensing behavior of ZnO nanostructured (NS) films to NO2 concentrations in the environment. The ZnO NS layers are deposited by electrochemical method on quartz resonators with Au electrodes. The sorption properties of ZnO layers were defined by measuring the resonant frequency shift (?f) of the QCM-ZnO structure for different NO2 concentrations. The measurements were based on the correlation between the frequency shift of the QCM and additional mass loading (?m) on the resonator calculated using Sauerbrey equation for the AT-cut quartz plate. Frequency – Time Characteristics (FTCs) of the samples were measured as a function of different NO2 concentrations in order to define the sorption abilities of ZnO layers. The experiments were carried out on a special set up in a dynamical regime. From FTCs the response and the recovery times of the QCM-ZnO structure were measured with varying NO2. Frequency shift changed from 23 Hz to 58Hz when NO2 was varied in the range of 250ppm – 5000ppm. The process of sorption was estimated as reversible and the sorption as physical. The obtained results demonstrated that QCM covered with the electrochemically deposited nanostructured ZnO films can be used as application in NO2 sensors.

Georgieva, B.; Petrov, M.; Lovchinov, K.; Ganchev, M.; Georgieva, V.; Dimova-Malinovska, D.

2014-11-01

353

Synthesis of Au-decorated V2O5@ZnO heteronanostructures and enhanced plasmonic photocatalytic activity.  

PubMed

A ternary plasmonic photocatalyst consisting of Au-decorated V2O5@ZnO heteronanorods was successfully fabricated by an innovative four-step process: thermal evaporation of ZnO powders, CVD of intermediate on ZnO, solution deposition of Au NPs, and final thermal oxidization. SEM, TEM, EDX, XPS, and XRD analyses revealed that the interior cores and exterior shells of the as-prepared heteronanorods were single-crystal wurtzite-type ZnO and polycrystalline orthorhombic V2O5, respectively, with a large quantity of Au NPs inlaid in the V2O5 shell. The optical properties of the ternary photocatalyst were investigated in detail and compared with those of bare ZnO and V2O5@ZnO. UV-vis absorption spectra of ZnO, V2O5@ZnO, and Au-decorated V2O5@ZnO showed gradually enhanced absorption in the visible region. In addition, gradually decreased emission intensity was also observed in the photoluminescence (PL) spectra, revealing enhanced charge separation efficiency. Because of these excellent qualities, the photocatalytic behavior of the ternary photocatalyst was studied in the photodegradation of methylene blue under UV-vis irradiation, which showed an enhanced photodegradation rate nearly 7 times higher than that of bare ZnO and nearly 3 times higher than that of V2O5@ZnO, mainly owing to the enlarged light absorption region, the effective electron-hole separation at the V2O5-ZnO and V2O5-Au interfaces, and strong localization of plasmonic near-field effects. PMID:25140838

Yin, Haihong; Yu, Ke; Song, Changqing; Huang, Rong; Zhu, Ziqiang

2014-09-10

354

Polarity Effects of Substrate Surface in Epitaxial ZnO Film Growth  

NASA Technical Reports Server (NTRS)

Epitaxial ZnO films were grown on the two polar surfaces (0-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films are also deposited on the (000 I) Al203 substrates. It is found that the two polar surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which are strongly inference the epitaxial film growth. The morphology and structure of epitaxial films on the ZnO substrates are different from the film on the Al203 substrates. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite Surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth using reactive sputtering deposition.

Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; George, M. A.; McCarty, P.

1999-01-01

355

Facile synthesis of porous single crystalline ZnO nanoplates and their application in photocatalytic reduction of Cr(VI) in the presence of phenol.  

PubMed

Porous single crystalline ZnO nanoplates were successfully synthesized through a facile and cost-effective hydrothermal process at low temperature condition, followed by annealing of the zinc carbonate hydroxide hydrate precursors. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) measurements. The porous single crystalline ZnO nanoplates are with 12nm thickness and pore ranging from 10nm to several tens of nanometers. The porous structure of the ZnO nanoplates caused large amount of surface defects which worked as photogenerated holes' shallow trappers and largely restrained the recombination of photogenerated electrons and holes, resulting in a significantly high photocatalytic activity and durability toward the photoreduction of Cr(VI) under UV irradiation. Moreover, a synergistic effect, that is, increased photocatalytic reduction of Cr(VI) and degradation of phenol, can be observed. Furthermore, the synergistic photocatalytic mechanism has also been discussed. Those results present an enlightenment to employ porous single crystalline nanomaterials to remove Cr(VI) and organic pollutants simultaneously. PMID:24922098

Jin, Zhen; Zhang, Yong-Xing; Meng, Fan-Li; Jia, Yong; Luo, Tao; Yu, Xin-Yao; Wang, Jin; Liu, Jin-Huai; Huang, Xing-Jiu

2014-07-15

356

Synthesis of ZnO nanorod–nanosheet composite via facile hydrothermal method and their photocatalytic activities under visible-light irradiation  

SciTech Connect

ZnO composite films consisting of ZnO nanorods and nanosheets were prepared by low-temperature hydrothermal processing at 80 °C on seeded glass substrates. The seed layer was coated on glass substrates by sol–gel dip-coating and pre-heated at 300 °C for 10 min prior to hydrothermal growth. The size of the grain formed after pre-heat treatment was ?40 nm. A preferred orientation seed layer at the c-axis was obtained, which promoted vertical growth of the ZnO nanorod arrays and formation of the ZnO nanosheets. X-ray diffraction patterns and high-resolution transmission electron microscope (HR-TEM) images confirmed that the ZnO nanorods and nanosheets consist of single crystalline and polycrystalline structures, respectively. Room temperature photoluminescence spectra of the ZnO nanorod–nanosheet composite films exhibited band-edge ultraviolet (UV) and visible emission (blue and green) indicating the formation of ZnO crystals with good crystallinity and are supported by Raman scattering results. The formation of one-dimensional (1D) ZnO nanorod arrays and two-dimensional (2D) ZnO nanosheet films using seeded substrates in a single low-temperature hydrothermal step would be beneficial for realization of device applications that utilize substrates with limited temperature stability. The ZnO nanorods and nanosheets composite structure demonstrated higher photocatalytic activity during degradation of aqueous methylene blue under visible-light irradiation. -- Graphical abstract: Schematic illustration of ZnO nanorod–nanosheet composite structure formation by hydrothermal at low-temperature of 80 °C against time. Highlights: • Novel simultaneous formation of ZnO nanorods and nanosheets composite structure. • Facile single hydrothermal step formation at low-temperature. • Photoluminescence showed ultraviolet and visible emission. • Feasible application on substrates with low temperature stability. • Improved photocatalytic activity under visible-light irradiation.

Tan, Wai Kian [Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580 (Japan); Abdul Razak, Khairunisak; Lockman, Zainovia [School of Materials and Mineral Resources, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang (Malaysia); Kawamura, Go; Muto, Hiroyuki [Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580 (Japan); Matsuda, Atsunori, E-mail: matsuda@ee.tut.ac.jp [Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580 (Japan)

2014-03-15

357

ZnO nanomaterials synthesized from thermal evaporation of ball-milled ZnO powders  

Microsoft Academic Search

Three different ZnO nanomaterials (nanobelts, nanorods, and nanowires) were synthesized at three different substrate temperatures from the thermal evaporation of ball-milled ZnO powders at 1380°C. Transmission electron microscopy revealed that the ZnO nanobelts are single crystalline with the growth direction perpendicular to the (011?0) lattice planes, and that the ZnO nanorods and nanowires are single crystalline with the growth directions

Jong-Soo Lee; Myung-IL Kang; IL-Woo Park; Soo-Won Kim; Woon Kap Cho; Hyon Soo Han; Sangsig Kim

2003-01-01

358

Pyroelectric properties of phosphoric acid-doped TGS single crystals  

NASA Astrophysics Data System (ADS)

Pyroelectric properties of phosphoric acid (H3PO4)-doped triglycine sulfate (TGSP) single crystals grown from solutions containing 0.1-0.5 mol of H3PO4 have been studied. Incorporation of H3PO4 into the crystal lattice is found to induce an internal bias field (Eb) and is observed through the presence of a sustained polarization and pyroelectricity beyond the transition temperature. The internal bias field has been estimated theoretically by fitting the experimentally measured data on temperature dependence of the pyroelectric coefficient (lgr), dielectric constant (egr') and polarization (P). A high Eb value in the range 9 × 103-15.5 × 104 V m-1 is obtained for crystals grown with 0.1-0.5 mol of H3PO4 in the solution, and a specific concentration of 0.2-0.25 mol of H3PO4 in the solution during crystal growth is found to be optimum for a high figure of merit for detectivity, Fd = 428 µC m-2 K-1.

Saxena, Aparna; Fahim, M.; Gupta, Vinay; Sreenivas, K.

2003-12-01

359

Photorefractive properties of lithium niobate single crystals doped with copper  

NASA Astrophysics Data System (ADS)

Raman scattering with excitation in the ultraviolet, visible, and near infrared and electron paramagnetic resonance are used to study the photorefractive properties of nominally pure, stoichiometric (R = Li/Nb = 1) single crystals of lithium niobate grown from a melt with 58.6 mol% Li2O (LiNbO3stoich), nominally pure crystals with a congruent composition (LiNbO3congr, R = 0.946), and Cu-doped crystals with a congruent composition (LiNbO3:Cu, [Cu] = 0.015 mass%). Optical irradiation is found to cause charge exchange of copper cations, Ca2+ ? Cu, in the LiNbO3:Cu ([Cu] = 0.015 mass%) crystals. Thus, crystalline LiNbO3:Cu ([Cu] = 0.015 mass%) manifests photorefractive properties as a result of charge exchange of copper ions during laser irradiation, in addition to the contribution from intrinsic defects with localized electrons previously observed in LiNbO3stoich and LiNbO3congr.

Sidorov, N. V.; Yanichev, A. A.; Gabain, A. A.; Palatnikov, M. N.; Smirnov, A. N.

2013-05-01

360

Employing a cylindrical single crystal in gas-surface dynamics  

NASA Astrophysics Data System (ADS)

We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based low energy electron diffraction/retarding field Auger electron spectrometer (AES) apparatus identifies surface structures present on the outer surface of the cylinder, while a separate double pass cylindrical mirror analyzer AES verifies surface cleanliness. A supersonic molecular beam, skimmed by a rectangular slot, impinges molecules on a narrow longitudinal strip of the surface. Here, we use the King and Wells technique to demonstrate how surface structure influences the dissociation probability of deuterium at various kinetic energies. Finally, we introduce spatially-resolved temperature programmed desorption from areas exposed to the supersonic molecular beam to show how surface structures influence desorption features.

Hahn, Christine; Shan, Junjun; Liu, Ying; Berg, Otto; Kleijn, Aart W.; Juurlink, Ludo B. F.

2012-03-01

361

Employing a cylindrical single crystal in gas-surface dynamics.  

PubMed

We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based low energy electron diffraction/retarding field Auger electron spectrometer (AES) apparatus identifies surface structures present on the outer surface of the cylinder, while a separate double pass cylindrical mirror analyzer AES verifies surface cleanliness. A supersonic molecular beam, skimmed by a rectangular slot, impinges molecules on a narrow longitudinal strip of the surface. Here, we use the King and Wells technique to demonstrate how surface structure influences the dissociation probability of deuterium at various kinetic energies. Finally, we introduce spatially-resolved temperature programmed desorption from areas exposed to the supersonic molecular beam to show how surface structures influence desorption features. PMID:22443756

Hahn, Christine; Shan, Junjun; Liu, Ying; Berg, Otto; Kleijn, Aart W; Juurlink, Ludo B F

2012-03-21

362

Magnetic field controlled FZ single crystal growth of intermetallic compounds  

NASA Astrophysics Data System (ADS)

Intermetallic rare-earth-transition-metal compounds with their coexistence of magnetic ordering and superconductivity are still of great scientific interest. The crystal growth of bulk single crystals is very often unsuccessful due to an unfavorable solid-liquid interface geometry enclosing concave fringes. The aim of the work is the contactless control of heat and material transport during floating-zone single crystal growth of intermetallic compounds. This control is provided by a tailored design of the electromagnetic field and the resulting electromagnetically driven convection. Numerical simulations for the determination of the electromagnetic field configuration induced by the RF heater coil and the solution of the coupled heat and hydrodynamic equations were done for the model substance Ni with and without additional magnetic field. As a result, an innovative magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt ranging from intensive inwards/outwards flows to flows almost at rest. The selection of parameters necessary for the desired fluid flow is determined from numerical simulation. The basis for the calculations are the process-related fluid flow conditions which are determined by the mode of heating, heat radiation at the free surface and material parameters. This treatment of the problem leads to the customised magnetic field for the special intermetallic compound. The application of the new magnetic system leads to a distinct improvement of the solid-liquid interface validated on experiments with the model substance Nickel.

Hermann, R.; Behr, G.; Gerbeth, G.; Priede, J.; Uhlemann, H.-J.; Fischer, F.; Schultz, L.

2005-02-01

363

Strain incompatibility and residual strains in ferroelectric single crystals  

PubMed Central

Residual strains in ferroelectrics are known to adversely affect the material properties by aggravating crack growth and fatigue degradation. The primary cause for residual strains is strain incompatibility between different microstructural entities. For example, it was shown in polycrystalline ferroelectrics that residual strains are caused due to incompatibility between the electric-field-induced strains in grains with different crystallographic orientations. However, similar characterization of cause-effect in multidomain ferroelectric single crystals is lacking. In this article, we report on the development of plastic residual strains in [111]-oriented domain engineered BaTiO3 single crystals. These internal strains are created due to strain incompatibility across 90° domain walls between the differently oriented domains. The average residual strains over a large crystal volume measured by in situ neutron diffraction is comparable to previous X-ray measurements of localized strains near domain boundaries, but are an order of magnitude lower than electric-field-induced residual strains in polycrystalline ferroelectrics. PMID:23226595

Pramanick, A.; Jones, J. L.; Tutuncu, G.; Ghosh, D.; Stoica, A. D.; An, K.

2012-01-01

364

Electronic properties of graphene-single crystal diamond heterostructures  

SciTech Connect

Single crystal diamond has been used as a substrate to support single layer graphene grown by chemical vapor deposition methods. It is possible to chemically functionalise the diamond surface, and in the present case H-, F-, O-, and N-group have been purposefully added prior to graphene deposition. The electronic properties of the resultant heterostructures vary strongly; a p-type layer with good mobility and a band gap of ?0.7?eV is created when H-terminated diamond layers are used, whilst a layer with more metallic-like character (high carrier density and low carrier mobility) arises when N(O)-terminations are introduced. Since it is relatively easy to pattern these functional groups on the diamond surface, this suggests that this approach may offer an exciting route to 2D device structures on single layer graphene sheets.

Zhao, Fang; Thuong Nguyen, Thuong; Golsharifi, Mohammad; Amakubo, Suguru; Jackman, Richard B., E-mail: r.jackman@ucl.ac.uk [London Centre for Nanotechnology and Department of Electronic and Electrical Engineering, University College London, 17-19 Gordon Street, London WC1H 0AH (United Kingdom); Loh, K. P. [Department of Chemistry, National University of Singapore, 3 Science Drive, Singapore 117543 (Singapore)

2013-08-07

365

Development of a thermal stress analysis system for anisotropic single crystal growth  

NASA Astrophysics Data System (ADS)

We developed a thermal stress analysis system for anisotropic single crystal growth. The analysis system takes account of crystal anisotropy in elastic constants and thermal expansion coefficients and can deal with the thermal stress analyses of five kinds of single crystals, that is, cubic crystal, trigonal crystal, monoclinic crystal, tetragonal crystal and orthorhombic crystal. After calculating thermal stress, we can obtain several stress components for evaluation of macro-cracking and crystal quality such as the maximum principal stress, the Mises equivalent stress and stress components acting on the cleavage plane. This analysis system is combined with a pre- and post-processor code MSC/PATRAN to prepare the input data and to visualize the results. As a numerical example obtained from the present system, the results of thermal stress analyses are shown for a lead molybdate (PMO; PbMoO 4) bulk single crystal that belongs to the tetragonal crystal lattice.

Miyazaki, N.

2002-03-01

366

Defect studies of thin ZnO films prepared by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

Thin ZnO films were grown by pulsed laser deposition on four different substrates: sapphire (0 0 0 1), MgO (1 0 0), fused silica and nanocrystalline synthetic diamond. Defect studies by slow positron implantation spectroscopy (SPIS) revealed significantly higher concentration of defects in the studied films when compared to a bulk ZnO single crystal. The concentration of defects in the films deposited on single crystal sapphire and MgO substrates is higher than in the films deposited on amorphous fused silica substrate and nanocrystalline synthetic diamond. Furthermore, the effect of deposition temperature on film quality was investigated in ZnO films deposited on synthetic diamond substrates. Defect studies performed by SPIS revealed that the concentration of defects firstly decreases with increasing deposition temperature, but at too high deposition temperatures it increases again. The lowest concentration of defects was found in the film deposited at 450° C.

Vl?ek, M.; ?ížek, J.; Procházka, I.; Novotný, M.; Bulí?, J.; Lan?ok, J.; Anwand, W.; Brauer, G.; Mosnier, J.-P.

2014-04-01

367

A simple route to vertical array of quasi-1D ZnO nanofilms on FTO surfaces: 1D-crystal growth of nanoseeds under ammonia-assisted hydrolysis process  

PubMed Central

A simple method for the synthesis of ZnO nanofilms composed of vertical array of quasi-1D ZnO nanostructures (quasi-NRs) on the surface was demonstrated via a 1D crystal growth of the attached nanoseeds under a rapid hydrolysis process of zinc salts in the presence of ammonia at room temperature. In a typical procedure, by simply controlling the concentration of zinc acetate and ammonia in the reaction, a high density of vertically oriented nanorod-like morphology could be successfully obtained in a relatively short growth period (approximately 4 to 5 min) and at a room-temperature process. The average diameter and the length of the nanostructures are approximately 30 and 110 nm, respectively. The as-prepared quasi-NRs products were pure ZnO phase in nature without the presence of any zinc complexes as confirmed by the XRD characterisation. Room-temperature optical absorption spectroscopy exhibits the presence of two separate excitonic characters inferring that the as-prepared ZnO quasi-NRs are high-crystallinity properties in nature. The mechanism of growth for the ZnO quasi-NRs will be proposed. Due to their simplicity, the method should become a potential alternative for a rapid and cost-effective preparation of high-quality ZnO quasi-NRs nanofilms for use in photovoltaic or photocatalytics applications. PACS: 81.07.Bc; 81.16.-c; 81.07.Gf. PMID:22027275

2011-01-01

368

Spontaneous phase transformation and exfoliation of rectangular single-crystal zinc hydroxy dodecylsulfate nanomembranes.  

PubMed

Free-standing two-dimensional (2D) nanostructures, exemplified by graphene and semiconductor nanomembranes, exhibit exotic electrical and mechanical properties and have great potential in electronic applications where devices need to be flexible or conformal to nonplanar surfaces. Based on our previous development of a substrate-free synthesis of large-area, free-standing zinc hydroxy dodecylsulfate (ZHDS) hexagonal nanomembranes, herein, we report a spontaneous phase transformation of ZHDS nanomembranes under extended reaction time. The hexagonal ZHDS sheets transformed into rectangular single crystal nanomembranes with sizes of hundreds of micrometers. They contain long-range-ordered zinc vacancies that can be fitted into an orthorhombic superlattice. A surplus of dodecylsulfate ions and a deficit of Zn(2+) diffusion near the water surface are believed to be the factors that drive the phase transformation. The phase transformation starts with the formation of zinc vacancies at the topmost layer of the hexagonal hillock, and propagates along the spiral growth path of the initial hexagonal sheets, which bears a great resemblance to the classic "periodic slip process". Mechanical property characterization of ZHDS nanomembranes by nanoindentation shows they behave much like structural polymers mechanically due to the incorporation of surfactant molecules. We also developed a one-step exfoliation and dehydration method that converts ZHDS nanomembranes to ZnO nanosheets using n-butylamine. This work provides a further understanding of the growth and stability of ZnO-based nanomembranes, as well as advisory insight for the further development on solution-based synthesis of free-standing, single-crystalline 2D nanostructures. PMID:23730895

Wang, Fei; Jakes, Joseph E; Geng, Dalong; Wang, Xudong

2013-07-23

369

Crystal structures of carbonates up to Mbar pressures determined by single crystal synchrotron radiation diffraction  

NASA Astrophysics Data System (ADS)

The recent improvements at synchrotron beamlines, currently allow single crystal diffraction experiments at extreme pressures and temperatures [1,2] on very small single crystal domains. We successfully applied such technique to determine the crystal structure adopted by carbonates at mantle pressures. The knowledge of carbon-bearing phases is in fact fundamental for any quantitative modelling of global carbon cycle. The major technical difficulty arises after first order transitions or decomposition reactions, since original crystal (apx. 10x10x5 ?m3) is transformed in much smaller crystalline domains often with random orientation. The use of 3D reciprocal space visualization software and the improved resolution of new generation flat panel detectors, however, allow both identification and integration of each single crystal domain, with suitable accuracy for ab-initio structure solution, performed with direct and charge-flipping methods and successive structure refinements. The results obtained on carbonates, indicate two major crystal-chemistry trends established at high pressures. The CO32- units, planar and parallel in ambient pressure calcite and dolomite structures, becomes non parallel in calcite- and dolomite-II and III phases, allowing more flexibility in the structures with possibility to accommodate strain arising from different cation sizes (Ca and Mg in particular). Dolomite-III is therefore also observed to be thermodynamically stable at lower mantle pressures and temperatures, differently from dolomite, which undergoes decomposition into pure end-members in upper mantle. At higher pressure, towards Mbar (lowermost mantle and D'' region) in agreement with theoretical calculations [3,4] and other experimental results [5], carbon coordination transform into 4-fold CO4 units, with different polymerisation in the structure depending on carbonate composition. The second important crystal chemistry feature detected is related to Fe2+ in Fe-bearing magnesite, which spontaneously oxidises at HP/HT, forming Fe3+ carbonates, Fe3+ oxides and reduced carbon (diamonds). Single crystal diffraction approach allowed full structure determination of these phases, yielding to the discovery of few unpredicted structures, such as Mg2Fe2C4O13 and Fe13O19, which can be well reproduced in different experiments. Mg2Fe2C4O13 carbonate present truncated chain C4O13 groups, and Fe13O19 oxide, whose stoichiometry is intermediate between magnetite and hematite, is a one-layer structure, with features encountered in superconducting materials. The results fully support the ideas of unexpected complexities in the mineralogy of the lowermost mantle, and single crystal technique, once properly optimized in ad-hoc synchrotron beamlines, is fundamental for extracting accurate structural information, otherwise rarely accessible with other experimental techniques. References: [1] Merlini M., Hanfland M. (2013). Single crystal diffraction at Mbar conditions by synchrotron radiation. High Pressure Research, in press. [2] Dubrovinsky et al., (2010). High Pressure Research, 30, 620-633. [3] Arapan et al. (1997). Phys. Rev. Lett., 98, 268501. [4] Oganov et al. (2008) EPSL, 273, 38-47. [5] Boulard et al. (2011) PNAS, 108, 5184-5187.

Merlini, M.

2013-12-01

370

Electronic properties study of CePtIn single crystal  

NASA Astrophysics Data System (ADS)

Heavy fermion CePtIn and CePdIn, together with the isoelectronic valence fluctuator CeNiIn, crystallizing in a hexagonal ZrNiAl-type structure, have attracted the attention of researchers for many years. We present magnetization, specific heat and electrical resistivity data measured on a CePtIn single crystal. The measured data show certain anisotropy of electronic properties, which is discussed in terms of a competition of RKKY and Kondo interactions. No clear trace of magnetic phase transition is observed down to 0.4 K. The specific heat and electrical resistivity data indicate a non-Fermi liquid state at low temperatures, which is discussed with respect to the isostructural CeNi0.4Pd0.6In and CeNi0.6Pd0.4In compounds, showing very similar electronic properties and lattice parameters.

Klicpera, M.; Javorský, P.

2014-03-01

371

Phase transitions in potassium ammonium dihydrogen phosphate single crystals  

NASA Astrophysics Data System (ADS)

An apparatus for growing single crystals from aqueous solution by the slow evaporation method was constructed. Mixed crystals of K1-x(NH 4)xH2PO4 (KADP) with (NH4)H 2PO4 (ADP) fractions of 0.021 and 0.12 were successfully grown. Their composition was determined by means of the x-ray powder diffraction method. This analysis also suggests that those crystals are a mixture of two phases even at room temperature. The details of the structure of the additional phase could not be determined. The dielectric constant epsilon of the mixed crystals as well as pure KH2PO4 (KDP) was measured along the polar axis in the temperature range from 20 K to 300 K. The frequency range of the applied electric field was from 100 Hz to 10 MHz. The data were analyzed by means of the standard Landau theory of phase transitions with coupling terms reflecting the interaction between the electric and elastic degrees of freedom. The temperature dependence of epsilon follows a typical Curie-Weiss behavior in the range of approximately 30 K aboveTc for all crystals studied. The value of the critical temperature decreases with increasing ammonium ion content in agreement with previously published results. The analysis of the frequency dependence of the dielectric susceptibility clearly indicates the existence of two dispersion processes: resonant and relaxational. The former is attributed to the piezoelectric activity of all the crystals studied. The latter is the result of the response of the permanent dipole moments present in ferroelectric crystals to the applied electric field. In the case of mixed crystals the relaxational dispersion is characterized by a distribution of relaxation times. Its mean relaxation time as well as its width increases with decreasing T. This is a typical behavior for mixed crystals for which the two end members of the solid solution in their pure form undergo ferroelectric and antiferroelectric phase transitions, respectively. This behavior is a result of competing long range interactions. New results for the temperature dependence of the CE66 and CE11 elastic constants of the crystals were obtained by means of the Brillouin spectroscopy. In addition to that the soft acoustic mode behaviour was also studied by means of the piezoelectric resonance method. Both of them gave qualitatively similar results which also correlate very well with the dielectric measurements. All major differences could be explained by assuming an inhomogeneous distribution of the ammonium ions in the KDP matrix. The Brillouin results were also analyzed by means of the Landau theory. It approximates very well the temperature dependence of the CE66 elastic constant in the paraelectric phase region for all crystals studied. The measured values of CE66 below Tc are in general lower than those predicted by the model. The greater the NH4 content the bigger the discrepancy. Moreover, the analysis of the temperature dependence of the CE66 elastic constant indicates the existence of a new phase in the mixed materials. Its stability region broadens with increasing NH4 concentration. For the crystal with the highest ammonium concentration studied it coincides with the dielectric plateau region between 70 K and 55 K. At temperatures below the plateau region the K0.88(NH4)0.12H 2PO4 sample scattered the laser light very strongly. This is most likely caused by defects and sample inhomogeneities but annealing the sample for two hours at 400 K does not result in any significant change.

Bromberek, Marek

372

Temperature and frequency dependent dielectric behavior of lead potassium niobate single crystal  

E-print Network

of the pyroelectric current The pyroelectric charge as a function of temperature in BaTiOs single crystal Temperature dependence of the pyroelectric current in Colemanite crystal Real permittivity vs temperature of PKN single crystal at 50Hz, 500Hz, 10KHz, 85KHz... for various potential applications, such as laser modulators, pyroelectric and infrared detectors, SAW device substrate material, optoelectronics device material, and other ferroelectric based devices. Single crystals having TB a The Journal of Applied...

Hossain, Akram

2012-06-07

373

Single crystal silicon capacitors with low microwave loss in the single photon regime  

E-print Network

We have fabricated superconducting microwave resonators in a lumped element geometry using single crystal silicon dielectric parallel plate capacitors with C >2 pF. Aluminum devices with resonant frequencies between 4.0 and 6.5 GHz exhibited an average internal quality factor Q_i of 2 x 10^5 in the single photon excitation regime at T = 20 mK. Attributing all the observed loss to the capacitive element, our measurements correspond to a loss tangent of intrinsic silicon of 5 x 10^-6. This level of loss is an order of magnitude lower than is currently observed in structures incorporating amorphous dielectric materials, thus making single crystal silicon capacitors an attractive, robust route for realizing long-lived quantum circuits.

S. Weber; K. W. Murch; D. H. Slichter; R. Vijay; I. Siddiqi

2011-02-14

374

Field emission properties of single crystal chromium disilicide nanowires  

NASA Astrophysics Data System (ADS)

The composition, crystal structure, and field emission properties of high-crystallinity chromium disilicide (CrSi2) nanowires synthesized by a vapor deposition method have been studied. High resolution transmission electron microscopy, energy dispersive spectroscopy, and selected area electron diffraction studies confirm the single-crystalline structure and composition of the CrSi2 nanowires. Field emission measurements show that an emission current density of 0.1 ?A/cm2 was obtained at a turn-on electric field intensity of 2.80 V/?m. The maximum emission current measured was 1.86 mA/cm2 at 3.6 V/?m. The relation between the emission current density and the electric field obtained follows the Fowler-Nordheim equation, with an enhancement coefficient of 1140. The electrical conductivity of single nanowires was measured by using four-point-probe specialized microdevices at different temperatures, and the calculated values are close to those reported in previous studies for highly conductive single crystal bulk CrSi2. The thermal tolerance of the nanowires was studied up to a temperature of 1100 °C. The stability of the field emission current, the I-E values, their thermal tolerance, and high electrical conductivity make CrSi2 nanowires a promising material for field emission applications.

Valentín, L. A.; Carpena-Nuñez, J.; Yang, D.; Fonseca, L. F.

2013-01-01

375

Analysis of synthetic diamond single crystals by X-ray topography and double-crystal diffractometry  

NASA Astrophysics Data System (ADS)

Structural features of diamond single crystals synthesized under high pressure and homoepitaxial films grown by chemical vapor deposition (CVD) have been analyzed by double-crystal X-ray diffractometry and topography. The conditions of a diffraction analysis of diamond crystals using Ge monochromators have been optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) formed during crystal growth have been revealed. The nitrogen concentration in high-pressure/high-temperature (HPHT) diamond substrates is estimated based on X-ray diffraction data. The formation of dislocation bundles at the film-substrate interface in the epitaxial structures has been revealed by plane-wave topography; these dislocations are likely due to the relaxation of elastic macroscopic stresses caused by the lattice mismatch between the substrate and film. The critical thicknesses of plastic relaxation onset in CVD diamond films are calculated. The experimental techniques for studying the real diamond structure in optimizing crystal-growth technology are proven to be highly efficient.

Prokhorov, I. A.; Ralchenko, V. G.; Bolshakov, A. P.; Polskiy, A. V.; Vlasov, A. V.; Subbotin, I. A.; Podurets, K. M.; Pashaev, E. M.; Sozontov, E. A.

2013-12-01

376

Structural and optical properties of MgO doped ZnO  

SciTech Connect

Samples of ZnO, Zn{sub 0.5}Mg{sub 0.5}O and MgO were prepared by co-precipitation method. X-ray diffraction (XRD) pattern infers that the sample of ZnO is in single-phase wurtzite structure (hexagonal phase, space group P6{sub 3}mc), MgO crystallizes in cubic Fd3m space group and Zn{sub 0.5}Mg{sub 0.5}O represents mixed nature of ZnO and MgO lattices. Similar features were observed from Raman spectroscopy. The energy band gaps estimated from UV-Vis spectroscopy are found to be 4.21 and 3.42 eV for ZnO and Zn{sub 0.5}Mg{sub 0.5}O samples respectively.

Verma, Kavita; Shukla, S.; Varshney, Dinesh, E-mail: vdinesh33@rediffmail.com [School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore-452001 (India); Varshney, M. [Department of Physics, M. B. Khalsa College, Raj Mohallah, Indore-452002 (India); Asthana, A. [Department of Chemistry, Govt. B. V. T. PG Autonomous College, Durg- 491001 (India)

2014-04-24

377

Wet Chemical Approaches to Patterned Arrays of Well-Aligned ZnO Nanopillars Assisted by Monolayer Colloidal Crystals  

E-print Network

photolithography,7,11,12 e-beam lithog- raphy,13 laser-interference lithography,14 anodic aluminum oxide tempating properties.6 In particular, the alignment of such 1D ZnO nanostructures into ordered nanoarrays can bring catalysts or oxide seed layer on a substrate surface using various patterning techniques including

Qi, Limin

378

Synthesis, characterization and optical properties of sheet-like ZnO  

SciTech Connect

Highlights: {yields} Sheet-like ZnO with regular hexagon shape was synthesized with a two-step method. {yields} Sheet-like ZnO predecessor was synthesized at low temperature in open system. {yields} The diameter and thickness of ZnO sheet can be controlled conveniently. {yields} This low-cost and environmentally benign approach is controllable and reproducible. {yields} Sheet-like ZnO may have potential application in optical and electrical devices. -- Abstract: Sheet-like ZnO with regular hexagon shape and uniform diameter has been successfully synthesized through a two-step method without any metal catalyst. First, the sheet-like ZnO precursor was synthesized in a weak alkaline carbamide environment with stirring in a constant temperature water-bath by the homogeneous precipitation method, then sheet-like ZnO was obtained by calcining at 600 {sup o}C for 2 h. The structures and optical properties of sheet-like ZnO have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and UV-vis-NIR spectrophotometer. The results reveal that the product is highly crystalline with hexagonal wurtzite phase and has appearance of hexagon at (0 0 0 1) plane. The HRTEM images confirm that the individual sheet-like ZnO is single crystal. The PL spectrum exhibits a narrow ultraviolet emission at 397 nm and a broad visible emission centering at 502 nm. The band gap of sheet-like ZnO is about 3.15 eV.

Liu, Changzhen [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China)] [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China); Meng, Dawei, E-mail: dwmeng@cug.edu.cn [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China) [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China); State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China); Wu, Xiuling [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China) [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China); State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China); Wang, Yongqian; Yu, Xiaohong; Zhang, Zhengjie [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China)] [Faculty of Material Science and Chemistry Engineering, Engineering Research Center of Nano-Geo Materials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China); Liu, Xiaoyang [State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China)] [State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China)

2011-09-15

379

Shock response of He bubbles in single crystal Cu  

NASA Astrophysics Data System (ADS)

With large-scale molecular dynamics simulations, we investigate shock response of He nanobubbles in single crystal Cu. For sufficient bubble size or internal pressure, a prismatic dislocation loop may form around a bubble in unshocked Cu. The internal He pressure helps to stabilize the bubble against plastic deformation. However, the prismatic dislocation loops may partially heal but facilitate nucleation of new shear and prismatic dislocation loops. For strong shocks, the internal pressure also impedes internal jetting, while a bubble assists local melting; a high speed jet breaks a He bubble into pieces dispersed among Cu. Near-surface He bubbles may burst and form high velocity ejecta containing atoms and small fragments, while the ejecta velocities do not follow the three-dimensional Maxwell-Boltzmann distributions expected for thermal equilibrium. The biggest fragment size deceases with increasing shock strength. With a decrease in ligament thickness or an increase in He bubble size, the critical shock strength required for bubble bursting decreases, while the velocity range, space extension and average velocity component along the shock direction, increase. Small bubbles are more efficient in mass ejecting. Compared to voids and perfect single crystal Cu, He bubbles have pronounced effects on shock response including bubble/void collapse, Hugoniot elastic limit (HEL), deformation mechanisms, and surface jetting. HEL is the highest for perfect single crystal Cu with the same orientations, followed by He bubbles without pre-existing prismatic dislocation loops, and then voids. Complete void collapse and shear dislocations occur for embedded voids, as opposed to partial collapse, and shear and possibly prismatic dislocations for He bubbles. He bubbles lower the threshhold shock strength for ejecta formation, and increase ejecta velocity and ejected mass.

Li, B.; Wang, L.; E, J. C.; Ma, H. H.; Luo, S. N.

2014-12-01

380

Aspects of single crystal and thin film high field electroluminescence  

NASA Astrophysics Data System (ADS)

Electro-optical investigations of unimplanted and ion implanted ZnS and ZnSe direct current electroluminescent (DCEL) devices under reverse bias have enabled advances to be made in understanding some of the physical processes which govern the behavior of such devices. The three types of devices studied were ZnS thin films, ZnS single crystal diodes and ZnSe single crystal diodes. For reasons discussed in the text, greatest stability and uniformity in electroluminescence characteristics were achieved using ion implanted ZnSe single crystals and experiments were predominantly based on such devices. A complicated, but effective, fabrication procedure which involved a multilayer contact structure enabled stable current-voltage characteristics and uniform electroluminescence to be obtained from the ion implanted ZnSe diodes. From the current-voltage characteristics it is clear that the dominant mechanism responsible for the observed current in such devices is the tunnelling of electrons through the Schottky barrier. Analysis of the electroluminescence and cathodoluminescence of ZnSe and ZnS single crystal devices in which both manganese ions and erbium ions have been implanted in the same region and to the same concentration allowed relative cross-sections for impact excitation of the Mn(2+) ions and Er(3+) ions to be calculated. From these calculations it was concluded that the exchange scattering mechanism is responsible for the excitation of Mn(2+) ions. From the applied voltage dependence of the spectral emission intensities of Er(3+) ion transitions in an implanted ZnSe:Er device, the electron energy distribution was shown to be of the Druyvesteyn type. Under certain simplifying assumptions, such an energy distribution can be derived theoretically from the Boltzmann transport equation. Combining theory with experiment shows that the scattering centres which are responsible for the production of a Druyvesteyn distribution have very large impact cross-sections. It is thus concluded that complex molecules, probably involving Er(3+) ions and native lattice defects, are present in these devices.

Swift, Michael Joseph Robert

1989-12-01

381

Aspects of Single Crystal and Thin Film High Field Electroluminescence  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Electro-optical investigations of unimplanted and ion implanted ZnS and ZnSe direct current electroluminescent (DCEL) devices under reverse bias have enabled advances to be made in understanding some of the physical processes which govern the behaviour of such devices. The three types of devices studied were ZnS thin films, ZnS single crystal diodes and ZnSe single crystal diodes. For reasons discussed in the text, greatest stability and uniformity in electroluminescence characteristics were achieved using ion implanted ZnSe single crystals and experiments were predominantly based on such devices. A complicated, but effective, fabrication procedure which involved a multilayer contact structure enabled stable current-voltage characteristics and uniform electroluminescence to be obtained from the ion implanted ZnSe diodes. From the current-voltage characteristics it is clear that the dominant mechanism responsible for the observed current in such devices is the tunnelling of electrons through the Schottky barrier. Analysis of the electroluminescence and cathodoluminescence of ZnSe and ZnS single crystal devices in which both manganese ions and erbium ions have been implanted in the same region and to the same concentration allowed relative cross-sections for impact excitation of the Mn^{2+ } ions and Er^{3+} ions to be calculated. From these calculations it was concluded that the exchange scattering mechanism is responsible for the excitation of Mn^ {2+} ions. From the applied voltage dependence of the spectral emission intensities of Er^{3+} ion transitions in an implanted ZnSe:Er device, the electron energy distribution was shown to be of the Druyvesteyn type. Under certain simplifying assumptions, such an energy distribution can be derived theoretically from the Boltzmann transport equation. Combining theory with experiment shows that the scattering centres which are responsible for the production of a Druyvesteyn distribution have very large impact cross-sections (~ 10^{-12}-10 ^{-13} cm^2). It is thus concluded that complex molecules, probably involving Er^{3+} ions and native lattice defects, are present in these devices.

Swift, Michael Joseph Robert

382

Coherent Josephson phase qubit with a single crystal silicon capacitor  

E-print Network

We have incorporated a single crystal silicon shunt capacitor into a Josephson phase qubit. The capacitor is derived from a commercial silicon-on-insulator wafer. Bosch reactive ion etching is used to create a suspended silicon membrane; subsequent metallization on both sides is used to form the capacitor. The superior dielectric loss of the crystalline silicon leads to a significant increase in qubit energy relaxation times. T1 times up to 1.6 micro-second were measured, more than a factor of two greater than those seen in amorphous phase qubits. The design is readily scalable to larger integrated circuits incorporating multiple qubits and resonators.

U. Patel; Y. Gao; D. Hover; G. J. Ribeill; S. Sendelbach; R. McDermott

2012-10-04

383

EPR studies of gamma-irradiated taurine single crystals  

NASA Astrophysics Data System (ADS)

An EPR study of gamma-irradiated taurine [C 2H 7NO 3S] single crystal was carried out at room temperature. The EPR spectra were recorded in the three at mutually perpendicular planes. There are two magnetically distinct sites in monoclinic lattice. The principle values of g and hyperfine constants for both sites were calculated. The results have indicated the presence of 32?O -2 and 33?O -2 radicals. The hyperfine values of 33?O -2 radical were used to obtain O-S-O bond angle for both sites.

Bulut, A.; Karabulut, B.; Tapramaz, R.; Köksal, F.

2000-04-01

384

Single Molecule Studies on Dynamics in Liquid Crystals  

PubMed Central

Single molecule (SM) methods are able to resolve structure related dynamics of guest molecules in liquid crystals (LC). Highly diluted small dye molecules on the one hand explore structure formation and LC dynamics, on the other hand they report about a distortion caused by the guest molecules. The anisotropic structure of LC materials is used to retrieve specific conformation related properties of larger guest molecules like conjugated polymers. This in particular sheds light on organization mechanisms within biological cells, where large molecules are found in nematic LC surroundings. This review gives a short overview related to the application of highly sensitive SM detection schemes in LC. PMID:24077123

Täuber, Daniela; von Borczyskowski, Christian

2013-01-01

385

Epitaxial Liftoff for Fully Single Crystal Ferroelectric Thin Films  

NASA Astrophysics Data System (ADS)

High-frequency signal transmission demands in RF and microwave systems, such as electronic phased-array radar and scanning antennas, call for innovative approaches in materials technology. Outstanding issues in such systems are the fabrication of low-loss, highly tunable capacitive elements made of thin-film ferroelecrics. This program used a new epitaxial liftoff technique developed at Columbia University to reduce high-quality, single-crystal films of ferroelectrics such as strontium titanate (ST), potassium tantalate, KTaO3 and potassium tantalate niobate (KTN) for use in microwave devices.

Osgood, Richard M., Jr.; Levy, Miguel; Bakhru, Hassaram; Cross, Eric

2002-08-01

386

Carrier doping and interlayer coupling in HTSC single crystals  

SciTech Connect

Experimental results of the effect of carrier doping on the irreversibility lines in (La,Sr){sub 2}CuO{sub 4{minus}{delta}} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8 + {delta}} single crystals are summarized. As a function of Sr or oxygen contents, systematic and dramatic widening of the irreversible regions in the B {minus} T phase diagram was observed in both systems. The present study suggests the critical importance of carrier concentration which directly affects the interlayer coupling strength and dimensionality of the flux line lattice in all the layered HTSC compounds as a universal feature.

Kishio, K.; Shimoyama, J.; Kimura, T.; Kotaka, Y.; Kitazawa, K. [Univ. of Tokyo (Japan). Dept. of Applied Chemistry; Yamafuji, K. [Kyushu Univ., Fukuoka (Japan). Dept. of Electronics; Li, Q.; Suenaga, M. [Brookhaven National Lab., Upton, NY (United States). Div. of Materials Science

1994-09-01

387

Luminescence of lead thiogallate single crystals doped with cerium ions  

NASA Astrophysics Data System (ADS)

The luminescence of single crystals of lead thiogallate PbGa2S4: Ce3+ has been studied. The observed nonmonotonic temperature dependence of the integrated luminescence intensity of PbGa2S4: Ce3+ has been explained by the energy transfer from the electronic excitations of the matrix to impurity ions and by the temperature quenching of the Ce3+ ion luminescence. The observed structure of the 4 f 05 d 1-4 f 1 (2 F 7/2) band of the Ce3+ ion luminescence indicates the existence, at least, two types of Ce3+ ion centers in PbGa2S4.

Asatryan, G. R.; Badikov, V. V.; Kulinkin, A. B.; Feofilov, S. P.

2015-01-01

388

A macroscopic model for magnetic shape-memory single crystals  

NASA Astrophysics Data System (ADS)

A rate-independent model for the quasi-static magneto-elastic evolution of a magnetic shape-memory single crystal is presented. In particular, the purely mechanical Souza-Auricchio model for shape-memory alloys is here combined with classical micro-magnetism by suitably associating magnetization and inelastic strain. By balancing the effect of conservative and dissipative actions, a nonlinear evolution PDE system of rate-independent type is obtained. We prove the existence of so-called energetic solutions to this system. Moreover, we discuss several limits for the model corresponding to parameter asymptotics by means of a rigorous ?-convergence argument.

Bessoud, Anne-Laure; Kružík, Martin; Stefanelli, Ulisse

2013-04-01

389

Polarization-dependent exciton dynamics in tetracene single crystals.  

PubMed

We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission (SF) in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors. PMID:25554147

Zhang, Bo; Zhang, Chunfeng; Xu, Yanqing; Wang, Rui; He, Bin; Liu, Yunlong; Zhang, Shimeng; Wang, Xiaoyong; Xiao, Min

2014-12-28

390

Relaxor-based ferroelectric single crystals for electromechanical actuators  

Microsoft Academic Search

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1\\/3Nb2\\/3)O3 - PbTiO3 (PZN-PT) and Pb(Mg1\\/3Nb2\\/3)O3 - PbTiO3 (PMN- PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3 (PZT's), morphotropic phase boundary compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d33's) > 2500 pC\\/N and subsequent strain levels up to > 0.6%

Seung Eek Park; Venkata Vedula; Ming Jen Pan; Wesley S. Hackenberger; Patrick Pertsch; Thomas R. Shrout

1998-01-01

391

Relaxor based ferroelectric single crystals for electro-mechanical actuators  

Microsoft Academic Search

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1\\/3Nb2\\/3)O3?PbTiO3 (PZN-PT) and Pb(Mg1\\/3Nb2\\/3)O3?PbTiO3 (PMN-PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3 (PZTs), morphotropic phase boundary (MPB) compositions were not essential for high piezoelectric strain. Piezoelectric coefficients\\u000a (d33’s ) >2200 pC\\/N and subsequent strain levels up to >0.5% with minimal hysteresis were observed.

S.-E. Park; Thomas R. Shrout

1997-01-01

392

Polarization-dependent exciton dynamics in tetracene single crystals  

NASA Astrophysics Data System (ADS)

We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission (SF) in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors.

Zhang, Bo; Zhang, Chunfeng; Xu, Yanqing; Wang, Rui; He, Bin; Liu, Yunlong; Zhang, Shimeng; Wang, Xiaoyong; Xiao, Min

2014-12-01

393

Nonlinear microwave switching response of BSCCO single crystals  

SciTech Connect

Measurements of the surface impedance in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystal with microwave currents flowing along the {cflx c} axis show clear evidence of a step-like nonlinearity. The surface resistance switches between apparently quantized levels for microwave field strength changes < 1 mG. This nonlinear response can arise from the presence of intrinsic Josephson junctions along the {cflx c} axis of these samples driven by the microwave current.

Jacobs, T.; Sridhar, S. [Northeastern Univ., Boston, MA (United States). Dept. of Physics; Willemsen, B.A. [Northeastern Univ., Boston, MA (United States). Dept. of Physics]|[Rome Lab., Hanscom AFB, MA (United States); Li, Qiang [Brookhaven National Lab., Upton, NY (United States); Gu, G.D.; Koshizuka, N. [Superconductivity Research Lab., Tokyo (Japan)

1996-06-01

394

Magnetic multi-domain resonance in single crystal ferrite platelets  

NASA Astrophysics Data System (ADS)

We have observed ferromagnetic resonance (FMR) on single crystal platelets of Zn and Co substituted M-type hexagonal ferrites. FMR was observed with both swept field and swept frequency measurements. The results were compared, and agreed well, with calculations of resonance frequencies based on periodic arrays of stripes and bubble domains. In addition to the resonance parameters necessary to describe the results in the magnetically saturated regime, our calculations take into account the wall energy, which results in a field dependence of the domain spacing, which in turn strongly affects the resonances near saturating fields.

Rachford, F. J.; Lubitz, P.; Vittoria, C.

1981-03-01

395

Physical properties of stoichiometric CeN single crystals  

NASA Astrophysics Data System (ADS)

The preparation and definition of stoichiometric large (3-5 mm edge length) single crystals of CeN are described. The band structure is discussed and compared with X-ray-photoemission-spectra (XPS), Bremsstrahlen-isochromat-spectroscopy (BIS) and optical reflectivity. CeN is intermediate valent with partially occupied and empty 4f states near EF. The specific heat is measured until 0.3 K and the ? term exhibits a sharp upturn toward the lowest temperatures. The Debye temperature is evaluated. The magnetic susceptibility is a large Pauli term pointing to a high density of states at EF as expected for a fractionally filled 4f1 state.

Wachter, P.; Zhigadlo, N. D.

396

Coherent Josephson phase qubit with a single crystal silicon capacitor  

NASA Astrophysics Data System (ADS)

We have incorporated a single crystal silicon shunt capacitor into a Josephson phase qubit. The capacitor is derived from a commercial silicon-on-insulator wafer. Bosch reactive ion etching is used to create a suspended silicon membrane; subsequent metallization on both sides is used to form the capacitor. The superior dielectric loss of the crystalline silicon leads to a significant increase in qubit energy relaxation times. T1 times up to 1.6 ?s were measured, more than a factor of two greater than those seen in amorphous phase qubits. The design is readily scalable to larger integrated circuits incorporating multiple qubits and resonators.

Patel, U.; Gao, Y.; Hover, D.; Ribeill, G. J.; Sendelbach, S.; McDermott, R.

2013-01-01

397

Experimental study of the irreversible magnetization in a ? single crystal  

NASA Astrophysics Data System (ADS)

Magnetization cycles and relaxation measurements as a function of temperature and field are reported for a very thin 0953-2048/10/4/004/img9 single crystal (thickness 0953-2048/10/4/004/img10). The fishtail effect was observed between 15 and 26 K at about 400 Oe, at which the relaxation rate was also found to increase rapidly. The observed behaviour is attributed to the field-induced two-dimensional to three-dimensional crossover in the vortex lattice in the presence of bulk pinning and surface barriers which dominate in different regions of the B - T phase diagram.

Fiorani, D.; Rybachuk, V. A.; Testa, A. M.; Kalinov, A. V.; Murashov, V. A.

1997-04-01

398

Annealing of deformed olivine single-crystals under 'dry' conditions  

NASA Astrophysics Data System (ADS)

Knowledge of rheological properties of Earth's materials is essential to understand geological processes. Open questions are the water content and crystallographic orientation dependences of dislocation creep rate, because the dominant slip system changes with increasing water content, which suggest different dislocations have different water content dependence. This project focuses on olivine, which is the most abundant mineral of the upper mantle. It is also considered to be the weakest phase and hence should control the rheology of the upper mantle. Several slip systems were reported for olivine, which are [100](010), [001](010), [001](100) and [100](001), each of which appear under different water content and stress conditions [1]. For this purpose we started to obtain data for 'dry' conditions, providing basic knowledge to understand the effect of water. Variation in dislocation creep rate according to change in physical conditions can be estimated by dislocation recovery experiments [2]. In this technique, deformed crystals are annealed, in which the dislocation density is expected to decrease due to coalescence of two dislocations. Dislocation densities are measured before and after the annealing. Dislocation mobility, which should be directly proportional to the dislocation creep rate, is estimated based on the change in dislocation density and duration of annealing. This technique has significant advantages partly because informations of strain rate and deviatoric stress, which are difficult to measure, are unnecessary, and partly because dislocation annealing is conducted under quasi-hydrostatic conditions, which allows wide ranges of P and T conditions. The first step of the experiments is to deform a single crystal of olivine. For this purpose, we developed an assembly, which deforms a single crystal in simple-shear geometry and prevent breakage, sub-grain formation and recrystallization of the crystal. Olivine single-crystals were placed in the high-pressure assembly so that a particular slip system is activated. The assemblies were compressed to 3 GPa. The shear deformation was conducted at 1600 K. EBSD measurements indicate that the recovered crystals are single crystals and sub-grain formation did not occur in most cases. The second step is to anneal the samples under the same P-T conditions as those of the deformation experiments. Annealing experiments are also performed at ambient pressures at 1600 K. Dislocation density was measured by means of the oxidation decoration technique [3]. The samples were firstly polished and then oxidized at 1200 K for 50 min. The dislocations are preferably oxidized, so that presence of dislocation can be observed using SEM. First Results indicate that the dislocation density decreased by annealing by 1/4 with an annealing period of 10 h for dislocations with b = [001]. References [1] H. Jung and S. I. Karato. Water-induced fabric transitions in olivine. Science, 293(5534):1460-1463, 2001. [2] S. I. Karato, D. C. Rubie, and H. Yan. Dislocation recovery in olivine under deep upper mantle conditions: Implications for creep and diffusion. Journal of Geophysical Research, 98(B6):9761-9768, 1993. [3] D. L. Kohlstedt, C. Goetze, W. B. Durham, and J. V. Sande. New technique for decorating dislocations in olivine. Science, 191(4231):1045-1046, March 1976.

Blaha, Stephan; Katsura, Tomoo

2013-04-01

399

Characteristic properties of Raman scattering and photoluminescence on ZnO crystals doped through phosphorous-ion implantation  

NASA Astrophysics Data System (ADS)

P-doped ZnO was fabricated by means of the ion-implantation method. At the Raman measurement, the blue shift of the E2high mode and A1(LO) phonon of the inactive mode were observed after the P-ion implantation. It suggested to be caused by the compressive stress. Thus, Hall effect measurement indicates that the acceptor levels exists in P-doped ZnO while still maintaining n-type ZnO. From the X-ray photoelectron spectroscopy, the chemical bond formation of the P2p3/2 spectrum consisted of 2(P2O5) molecules. Therefore, the implanted P ions were substituted to the Zn site in ZnO. From the photoluminescence (PL) spectra, P-related PL peaks were observed in the energy ranges of 3.1 and 3.5 eV, and its origin was analyzed at PZn-2VZn complexes, acting as a shallow acceptor. With increasing temperatures, the neutral-acceptor bound-exciton emission, (A0, X), shows a tendency to quench the intensity and extend the emission linewidth. From the relations of the intensity and the linewidth as a function of temperature, the broadening of linewidth was believed to the result that the vibration mode of E2high participates in the broadening process of (A0, X) and the change of luminescent intensity was attributed to the partial dissociation of (A0, X). Consequently, these facts indicate that the acceptor levels existed in P-doped ZnO layer by the ion implantation.

Jeong, T. S.; Yu, J. H.; Mo, H. S.; Kim, T. S.; Lim, K. Y.; Youn, C. J.; Hong, K. J.

2014-02-01

400

Characteristic properties of Raman scattering and photoluminescence on ZnO crystals doped through phosphorous-ion implantation  

SciTech Connect

P-doped ZnO was fabricated by means of the ion-implantation method. At the Raman measurement, the blue shift of the E{sub 2}{sup high} mode and A{sub 1}(LO) phonon of the inactive mode were observed after the P-ion implantation. It suggested to be caused by the compressive stress. Thus, Hall effect measurement indicates that the acceptor levels exists in P-doped ZnO while still maintaining n-type ZnO. From the X-ray photoelectron spectroscopy, the chemical bond formation of the P2p{sub 3/2} spectrum consisted of 2(P{sub 2}O{sub 5}) molecules. Therefore, the implanted P ions were substituted to the Zn site in ZnO. From the photoluminescence (PL) spectra, P-related PL peaks were observed in the energy ranges of 3.1 and 3.5?eV, and its origin was analyzed at P{sub Zn}-2V{sub Zn} complexes, acting as a shallow acceptor. With increasing temperatures, the neutral-acceptor bound-exciton emission, (A{sup 0}, X), shows a tendency to quench the intensity and extend the emission linewidth. From the relations of the intensity and the linewidth as a function of temperature, the broadening of linewidth was believed to the result that the vibration mode of E{sub 2}{sup high} participates in the broadening process of (A{sup 0}, X) and the change of luminescent intensity was attributed to the partial dissociation of (A{sup 0}, X). Consequently, these facts indicate that the acceptor levels existed in P-doped ZnO layer by the ion implantation.

Jeong, T. S.; Yu, J. H.; Mo, H. S.; Kim, T. S.; Lim, K. Y.; Youn, C. J., E-mail: cjyoun@chonbuk.ac.kr [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center (SPRC), Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Hong, K. J. [Department of Physics, Chosun University, Gwangju 501-759 (Korea, Republic of)

2014-02-07

401

Structural, optical, mechanical and dielectric studies of pure and doped L-Prolinium Trichloroacetate single crystals  

NASA Astrophysics Data System (ADS)

In the present work, pure and metal substituted L-Prolinium trichloroacetate (LPTCA) single crystals were grown by slow evaporation method. The grown crystals were subjected to single crystal X-ray diffraction (XRD), powder X-ray diffraction, FTIR, UV-Visible-NIR, hardness, photoluminescence and dielectric studies. The dopant concentration in the crystals was measured by inductively coupled plasma (ICP) analysis. Single crystal X-ray diffraction studies of the pure and metal substituted LPTCA revealed that the grown crystals belong to the trigonal system. Ni2+ and Co2+ doping slightly altered the lattice parameters of LPTCA without affecting the basic structure of the crystal. FTIR spectral analysis confirms the presence of various functional groups in the grown crystals. The mechanical behavior of pure and doped crystals was analyzed by Vickers's microhardness test. The optical transmittance, dielectric and photoluminescence properties of the pure and doped crystals were analyzed.

Renuka, N.; Ramesh Babu, R.; Vijayan, N.; Vasanthakumar, Geetha; Krishna, Anuj; Ramamurthi, K.

2015-02-01

402

Crystal ion slicing of single crystal thin films for optical and electrical applications  

NASA Astrophysics Data System (ADS)

Thin film technologies are the most important element in modern integrated electrical and optical circuits development. Heterogeneous thin film structures make it possible to realize multi-functional highly integrated systems. Recently a new technology called Crystal Ion Slicing (CIS), utilizing ion implantation to slice thin films from single crystal substrates, has been developed at Columbia University. This technique allows the use of existing high quality single crystal wafers to form single-crystal thin films. Thus many materials, which are otherwise very difficult to obtain in thin film form, can now be obtained for thin film device integration. In the course of my thesis work, solutions to three issues of ion-slicing have been considered: applicability of ion-slicing to different materials, integration of sliced thin films, and device fabrication on the sliced thin films. To achieve specific functions, particular material properties are often required. Thus, many thin film technologies have been developed for different materials. In this work, CIS has been applied for wide range of materials such as LiNbO3, YIG, BaTiO3 (BTO), KTaO3 (KTO), and SrTiO3 (STO). CIS processing was adjusted for each material to slice high quality thin films faster. LiNbO3 slicing is well developed and large freestanding films, ˜15 x 15mm, are producible. YIG has been sliced by helium implantation and wet etching. BTO can be sliced by hydrogen implantation and heat treatment. KTO can be sliced by hydrogen implantation and wet etching. Single crystal BaTiO3 thin films have been fabricated for the first time through this work. The second issue considered is the size of ion-sliced films. To fabricate large thin films required for actual devices, a support wafer concept was introduced. Before slicing process, support wafers were bonded to implanted target materials to provide mechanical support for fragile films. The bonded implanted wafer was sliced into a large thin film without damage. This method solved the issue of handling a fragile freestanding thin films. More generally, wafer bonding is important for two applications: fabrication of large films and heterogeneous integration of thin films. Integration of magnetooptical devices on semiconductor platforms was demonstrated by bonding a garnet crystal on a semiconductor surface. Two bonding methods were demonstrated for these purposes; direct wafer bonding and anodic bonding. (Abstract shortened by UMI.)

Izuhara, Tomoyuki

403

Enhancing blue luminescence from Ce-doped ZnO nanophosphor by Li doping  

NASA Astrophysics Data System (ADS)

Undoped ZnO, Ce-doped ZnO, and (Li, Ce)-codoped ZnO nanophosphors were prepared by a sol-gel process. The effects of the additional doping with Li ions on the crystal structure, particle morphology, and luminescence properties of Ce-doped ZnO were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and photoluminescence spectroscopy. The results indicate that the obtained samples are single phase, and a nanorod shaped morphology is observed for (Li, Ce)-codoping. Under excitation with 325 nm light, Ce-doped ZnO phosphors show an ultraviolet emission, a green emission, and a blue emission caused by Zn interstitials. The spectrum of the sample codoped with a proper Li concentration features two additional emissions that can be attributed to the Ce3+ ions. With the increase of the Li doping concentration, the Ce3+ blue luminescence of (Li, Ce)-codoped ZnO is obviously enhanced, which results not only from the increase of the Ce3+ ion concentration itself but also from the energy transfer from the ZnO host material to the Ce3+ ions. This enhancement reaches a maximum at a Li content of 0.02, and then decreases sharply due to the concentration quench. These nanophosphors may promise for application to the visible-light-emitting devices.

Shi, Qiang; Wang, Changzheng; Li, Shuhong; Wang, Qingru; Zhang, Bingyuan; Wang, Wenjun; Zhang, Junying; Zhu, Hailing

2014-09-01

404

Enhancing blue luminescence from Ce-doped ZnO nanophosphor by Li doping  

PubMed Central

Undoped ZnO, Ce-doped ZnO, and (Li, Ce)-codoped ZnO nanophosphors were prepared by a sol-gel process. The effects of the additional doping with Li ions on the crystal structure, particle morphology, and luminescence properties of Ce-doped ZnO were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and photoluminescence spectroscopy. The results indicate that the obtained samples are single phase, and a nanorod shaped morphology is observed for (Li, Ce)-codoping. Under excitation with 325 nm light, Ce-doped ZnO phosphors show an ultraviolet emission, a green emission, and a blue emission caused by Zn interstitials. The spectrum of the sample codoped with a proper Li concentration features two additional emissions that can be attributed to the Ce3+ ions. With the increase of the Li doping concentration, the Ce3+ blue luminescence of (Li, Ce)-codoped ZnO is obviously enhanced, which results not only from the increase of the Ce3+ ion concentration itself but also from the energy transfer from the ZnO host material to the Ce3+ ions. This enhancement reaches a maximum at a Li content of 0.02, and then decreases sharply due to the concentration quench. These nanophosphors may promise for application to the visible-light-emitting devices. PACS 78.55.Et; 81.07.Wx; 81.20.Fw PMID:25258604

2014-01-01

405

Relaxor-based ferroelectric single crystals for electromechanical actuators  

NASA Astrophysics Data System (ADS)

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1/3Nb2/3)O3 - PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3 - PbTiO3 (PMN- PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3 (PZT's), morphotropic phase boundary compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d33's) > 2500 pC/N and subsequent strain levels up to > 0.6% with minimal hysteresis were observed. Crystallographically, high strains are achieved for <001> oriented rhombohedral crystals, though <111> is the polar direction. Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics could be achieved, being related to an E-field induced phase transformation. Strain vs. E-field behavior under external stress was also much superior to that of conventional piezoelectric ceramics. High electromechanical coupling (k33) > 90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators.

Park, Seung Eek E.; Vedula, Venkata; Pan, Ming-Jen; Hackenberger, Wesley S.; Pertsch, Patrick; Shrout, Thomas R.

1998-07-01

406

Effective symmetry and physical properties of twinned perovskite ferroelectric single crystals  

E-print Network

Effective symmetry and physical properties of twinned perovskite ferroelectric single crystals Jirí properties of twinned ferroelectric crystals with perovskite structure were analyzed. The twins or twinbands perovskite structure. When a single fer- roelectric crystal is poled along [001] of the cubic coor- dinates

Cao, Wenwu

407

Growth of single crystal PrFeAsO 1-y and its characterization  

NASA Astrophysics Data System (ADS)

We have successfully grown single crystals of oxygen deficient oxypnictide superconductor PrFeAsO 1-y using high pressure synthesis technique. Typical crystal size is about 600 × 800 × 30 ?m 3, with its T c = 44 K. Their resistivity measurements under magnetic field yield the anisotropic factor ? ? 5, consistent with previous results on smaller single crystals.

Ishikado, M.; Shamoto, S.; Kito, H.; Iyo, A.; Eisaki, H.; Ito, T.; Tomioka, Y.

2009-10-01

408

Sm^Nd dating of spatially controlled domains of garnet single crystals: a new method of  

E-print Network

Sm^Nd dating of spatially controlled domains of garnet single crystals: a new method of high of the method using the core and bulk ages of garnet single crystals, according to the Sm^Nd decay system exposure of the Salinian terrane, California. We have micro-sampled the garnet crystals over specific

Ganguly, Jibamitra

409

Slip systems in NiAl single crystals at 300°K and 77°K  

Microsoft Academic Search

Single crystals of NiAl have been examined by transmission electron microscopy after plastic deformation at 300°K and 77°K. In agreement with earlier work, it is found that single crystals generally slip along ?100?. Further, it is shown that crystals oriented so that there is zero applied stress on the dislocations of b = ?100?, deform by the movement of dislocations

M. H. Loretto; R. J. Wasilewski

1971-01-01

410

Crystal chemistry of epitaxial ZnO on (1 1 1) MgAl 2O 4 produced by hydrothermal synthesis  

NASA Astrophysics Data System (ADS)

ZnO powders and epitaxial thin films were synthesized hydrothermally in aqueous solutions of zinc nitrate and ammonia at 150°C. Powder yield and particle size varied with changes in pH from 7 to 10.5. The films grew with a c-axis orientation on (1 1 1) MgAl 2O 4 substrates, with an out-of-plane orientation given by (1 1 1) s||(0 0 0 1) Zn, and an in-plane orientation given by ( overline112) s||(11 2¯0) Zn. Based on etching studies, the polarity of the films was determined to be zinc faced (0 0 0 1). The in-plane orientation relation corresponds to a 30° rotation of the close packed oxygen directions of the two respective structures. This rotation produces periodic, tetrahedrally coordinated Zn sites at the spinel/ZnO interface and facilitates the epitaxy of ZnO with only a small lattice strain. The crystal chemistry of the interfacial atomic layer that lies between the spinel and wurtzite is discussed in relation to cation coordination and charge balance.

Andeen, David; Loeffler, Lars; Padture, Nitin; Lange, F. F.

2003-11-01

411

Bithermal fatigue of a nickel-base superalloy single crystal  

NASA Technical Reports Server (NTRS)

The thermomechanical fatigue behavior of a nickel-base superalloy single crystal was investigated using a bithermal test technique. The bithermal fatigue test was used as a simple alternative to the more complex thermomechanical fatigue test. Both in-phase and out-of-phase bithermal tests were performed on (100)-oriented coated and bare Rene N4 single crystals. In out-of-plane bithermal tests, the tensile and compressive halves of the cycle were applied isothermally at 760 and 982 C, respectively, while for the in-phase bithermal tests the temperature-loading sequence was reversed. The bithermal fatigue lives of bare specimens were shorter than the isothermal fatigue lives at either temperature extreme when compared on an inelastic strain basis. Both in-phase and out-of-phase bithermal fatigue life curves converged in the large strain regime and diverged in the small strain regime, out-of-phase resulting in the shortest lives. The coating had no effect on life for specimens cycled in-phase; however, the coating was detrimental for isothermal fatigue at 760 C and for out-of-phase fatigue under large strains.

Verrilli, Michael J.

1988-01-01

412

Joint Development of a Fourth Generation Single Crystal Superalloy  

NASA Technical Reports Server (NTRS)

A new, fourth generation, single crystal superalloy has been jointly developed by GE Aircraft Engines, Pratt & Whitney, and NASA. The focus of the effort was to develop a turbine airfoil alloy with long-term durability for use in the High Speed Civil Transport. In order to achieve adequate long-time strength improvements at moderate temperatures and retain good microstructural stability, it was necessary to make significant composition changes from 2nd and 3rd generation single crystal superalloys. These included lower chromium levels, higher cobalt and rhenium levels and the inclusion of a new alloying element, ruthenium. It was found that higher Co levels were beneficial to reducing both TCP precipitation and SRZ formation. Ruthenium caused the refractory elements to partition more strongly to the ' phase, which resulted in better overall alloy stability. The final alloy, EPM 102, had significant creep rupture and fatigue improvements over the baseline production alloys and had acceptable microstructural stability. The alloy is currently being engine tested and evaluated for advanced engine applications.

Walston, S.; Cetel, A.; MacKay, R.; OHara, K.; Duhl, D.; Dreshfield, R.

2004-01-01

413

Tribological properties of sintered polycrystalline and single crystal silicon carbide  

NASA Technical Reports Server (NTRS)

Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

Miyoshi, K.; Buckley, D. H.; Srinivasan, M.

1982-01-01

414

Process for Making Single-Domain Magnetite Crystals  

NASA Technical Reports Server (NTRS)

A process for making chemically pure, single-domain magnetite crystals substantially free of structural defects has been invented as a byproduct of research into the origin of globules in a meteorite found in Antarctica and believed to have originated on Mars. The globules in the meteorite comprise layers of mixed (Mg, Fe, and Ca) carbonates, magnetite, and iron sulfides. Since the discovery of the meteorite was announced in August 1996, scientists have debated whether the globules are of biological origin or were formed from inorganic materials by processes that could have taken place on Mars. While the research that led to the present invention has not provided a definitive conclusion concerning the origin of the globules, it has shown that globules of a different but related chemically layered structure can be grown from inorganic ingredients in a multistep precipitation process. As described in more detail below, the present invention comprises the multistep precipitation process plus a subsequent heat treatment. The multistep precipitation process was demonstrated in a laboratory experiment on the growth of submicron ankerite crystals, overgrown by submicron siderite and pyrite crystals, overgrown by submicron magnesite crystals, overgrown by submicron siderite and pyrite. In each step, chloride salts of appropriate cations (Ca, Fe, and Mg) were dissolved in deoxygenated, CO2- saturated water. NaHCO3 was added as a pH buffer while CO2 was passed continuously through the solution. A 15-mL aliquot of the resulting solution was transferred into each of several 20 mL, poly(tetrafluoroethylene)-lined hydrothermal pressure vessels. The vessels were closed in a CO2 atmosphere, then transferred into an oven at a temperature of 150 C. After a predetermined time, the hydrothermal vessels were removed from the oven and quenched in a freezer. Supernatant solutions were decanted, and carbonate precipitates were washed free of soluble salts by repeated decantations with deionized water.

Golden, D. C.; Ming, Douglas W.; Morris, Richard V.; Lofgren, Gary E.; McKay, Gordan A.; Schwandt, Craig S.; Lauer, Howard V., Jr.; Socki, Richard A.

2004-01-01

415

Growth and properties of Lithium Salicylate single crystals  

SciTech Connect

An attractive feature of {sup 6}Li containing fluorescence materials that determines their potential application in radiation detection is the capture reaction with slow ({approx}< 100 keV) neutrons: {sup 6}Li + n = {sup 4}He + {sup 3}H + 4.8MeV. The use of {sup 6}Li-salicylate (LiSal, LiC{sub 6}H{sub 5}O{sub 3}) for thermal neutron detection was previously studied in liquid and polycrystalline scintillators. The studies showed that both liquid and polycrystalline LiSal scintillators could be utilized in pulse shape discrimination (PSD) techniques that enable separation of neutrons from the background gamma radiation. However, it was found that the efficiency of neutron detection using LiSal in liquid solutions was severely limited by its low solubility in commonly used organic solvents like, for example, toluene or xylene. Better results were obtained with neutron detectors containing the compound in its crystalline form, such as pressed pellets, or microscopic-scale (7-14 micron) crystals dispersed in various media. The expectation drown from these studies was that further improvement of pulse height, PSD, and efficiency characteristics could be reached with larger and more transparent LiSal crystals, growth of which has not been reported so far. In this paper, we present the first results on growth and characterization of relatively large, a cm-scale size, single crystals of LiSal with good optical quality. The crystals were grown both from aqueous and anhydrous (methanol) media, mainly for neutron detection studies. However, the results on growth and structural characterization may be interesting for other fields where LiSal, together with other alkali metal salicylates, is used for biological, medical, and chemical (as catalyst) applications.

Zaitseva, N; Newby, J; Hull, G; Saw, C; Carman, L; Cherepy, N; Payne, S

2009-02-13

416

Synthesis, crystal growth, structural, thermal, optical and mechanical properties of solution grown 4-methylpyridinium 4-hydroxybenzoate single crystal  

NASA Astrophysics Data System (ADS)

Organic nonlinear optical material, 4-methylpyridinium 4-hydroxybenzoate (4MPHB) was synthesized and single crystal was grown by slow evaporation solution growth method. Single crystal and powder X-ray diffraction analyses confirm the structure and crystalline perfection of 4MPHB crystal. Infrared, Raman and NMR spectroscopy techniques were used to elucidate the functional groups present in the compound. TG-DTA analysis was carried out in nitrogen atmosphere to study the decomposition stages, endothermic and exothermic reactions. UV-visible and Photoluminescence spectra were recorded for the grown crystal to estimate the transmittance and band gap energy respectively. Linear refractive index, birefringence, and SHG efficiency of the grown crystal were studied. Laser induced surface damage threshold and mechanical properties of grown crystal were studied to assess the suitability of the grown crystals for device applications.

Sudhahar, S.; Krishna Kumar, M.; Sornamurthy, B. M.; Mohan Kumar, R.

2014-01-01

417

Crystal growth and composition-property relationship of Ce3Pd20Si6 single crystals  

NASA Astrophysics Data System (ADS)

To elucidate the discrepancies in low-temperature data reported on the quantum critical heavy fermion compound Ce3Pd20Si6 and reveal the compound’s intrinsic properties, single crystals of varying stoichiometry were grown by various techniques—from the melt and from high-temperature solutions using fluxes of various compositions. The resulting stoichiometry of the crystals as well as their physical properties show sizable dependence on the different growth techniques. The Ce content ?Ce varies by more than 3at.% among all grown single crystals. We have revealed a systematic dependence of the residual resistance ratio, the lattice parameter, the (lower) phase-transition temperature TL , and the maximum in the temperature dependent electrical resistivity Tmax with ?Ce . This clarifies the sizable variation in the values of TL reported in the literature. We discuss the physical origin of the observed composition-property relationship in terms of a Kondo lattice picture. We predict that a modest pressure can suppress TL to zero and thus induce a quantum critical point.

Prokofiev, A.; Custers, J.; Kriegisch, M.; Laumann, S.; Müller, M.; Sassik, H.; Svagera, R.; Waas, M.; Neumaier, K.; Strydom, A. M.; Paschen, S.

2009-12-01

418

Fabrication of Schottky barrier diodes using H2O2-treated non-polar ZnO 1?0?1?¯0 substrates  

NASA Astrophysics Data System (ADS)

Non-polar single crystal ZnO 1 0 1bar 0 substrates with hydrogen peroxide (H2O2) treatment were characterized and applied to Schottky barrier diodes. Formation of a ZnO2 layer with a polycrystalline structure was confirmed by 2? scans of X-ray diffraction (XRD) measurements. Tails of the X-ray rocking curve of ZnO 1 0 1bar 0 planes were broadened with increase in H2O2 treatment time. Grain structures were clearly observed on the surfaces of ZnO 1 0 1 bar0 substrates with H2O2 treatment by an atomic force microscope, and the root mean square roughness of the ZnO2 surface was about 5 nm. The current density-voltage (J-V) characteristics of Pd/ZnO/Al structures using ZnO 1 0 1 bar0 substrates without H2O2 treatment were ohmic. The J-V characteristics of Pd/ZnO2/ZnO/Al structures using ZnO 1 0 1 bar0 substrates with H2O2 treatment time of 5 min showed good rectifying characteristics. The ideality factor n of this diode was 1.7 and the barrier height between Pd films and the ZnO2 layer on the ZnO 1 0 1 bar0 plane was estimated to be 0.92 eV.

Kashiwaba, Yasuhiro; Sakuma, Mio; Abe, Takami; Nakagawa, Akira; Niikura, Ikuo; Kashiwaba, Yasube; Daibo, Masahiro; Osada, Hiroshi

2013-12-01

419

A preliminary review of organic materials single crystal growth by the Czochralski technique  

NASA Technical Reports Server (NTRS)

The growth of single crystals of organic compounds by the Czochralski method is reviewed. From the literature it is found that single crystals of benzil, a nonlinear optical material with a d sub 11 value of 11.2 + or - 1.5 x d sub 11 value of alpha quartz, has fewer dislocations than generally contained in Bridgman crystals. More perfect crystals were grown by repeated Czochralski growth. This consists of etching away the defect-containing portion of a Czochralski grown crystal and using it as a seed for further growth. Other compounds used to grow single crystals are benzophenone, 12-tricosanone (laurone), and salol. The physical properties, growth apparatus, and processing conditions presented in the literature are discussed. Moreover, some of the possible advantages of growing single crystals of organic compounds in microgravity to obtain more perfect crystals than on Earth are reviewed.

Penn, B. G.; Shields, A. W.; Frazier, D. O.

1988-01-01

420

Imatinib (Gleevec@) conformations observed in single crystals, protein-Imatinib co-crystals and molecular dynamics: Implications for drug selectivity  

NASA Astrophysics Data System (ADS)

Structure and dynamics of the Leukemia drug, Imatinib, were examined using X-ray crystallography and molecular dynamics studies. Comparison of conformations observed in single crystals with several reported co-crystals of protein-drug complexes suggests existence of two conserved conformations of Imatinib, extended and compact (or folded), corresponding to two binding modes of interaction with the receptor. Furthermore, these conformations are conserved throughout a dynamics simulation. The present study attempts to draw a parallel on conformations and binding patterns of interactions, obtained from small-molecule single-crystal and macromolecule co-crystal studies, and provides structural insights for understanding the high selectivity of this drug molecule.

Golzarroshan, B.; Siddegowda, M. S.; Li, Hong qi; Yathirajan, H. S.; Narayana, B.; Rathore, R. S.

2012-06-01

421

Improvement of GaN light-emitting diodes with surface-treated Al-doped ZnO transparent Ohmic contacts by holographic photonic crystal  

NASA Astrophysics Data System (ADS)

This letter presents a holographic photonic crystal (H-PhC) Al-doped ZnO (AZO) transparent Ohmic contact layer on p-GaN to increase the light output of GaN-based LEDs without destroying the p-GaN. The operating voltage of the PhC LEDs at 20 mA was almost the same as that of the typical planar AZO LEDs. While the resultant PhC LED devices exhibited significant improvements in light extraction, up to 1.22 times that of planar AZO LEDs without PhC integration. Temperature dependence of the integrated photoluminescence intensity indicates that this improvement can be attributed to the increased extraction efficiency due to the surface modification. These results demonstrate that the surface-treated AZO layer by H-PhCs is suitable for fabricating high-brightness GaN-based LEDs.

Yang, W. F.; Liu, Z. G.; Xie, Y. N.; Cai, J. F.; Liu, S.; Gong, H.; Wu, Z. Y.

2012-06-01

422

Secondary orientation effects in a single crystal superalloy under mechanical and thermal loads  

NASA Technical Reports Server (NTRS)

The nickel-base single crystal superalloy PWA 1480 is a candidate blading material for the advanced turbopump development program of the SSME. In order to improve thermal fatigue resistance of the turbine blades, the single crystal superalloy PWA 1480 is grown along the low modulus zone axes (001) crystal orientation by a directional solidification process. Since cubic single crystal materials such as PWA 1480 exhibit anisotropic elastic behavior, the stresses developed within the single crystal superalloy due to mechanical and thermal loads are likely to be affected by the exact orientation of the secondary crystallographic direction with respect to the geometry of the turbine blade. The effects of secondary crystal orientation on the elastic response of single crystal PWA 1480 superalloy were investigated.

Kalluri, Sreeramesh; Abdul-Aziz, Ali; Mcgaw, Michael A.

1991-01-01

423

Synthesis, Growth, Spectral and Optical Properties of Glycinyl Urea Single Crystal  

SciTech Connect

Single crystals of Glycinyl Urea were grown from aqueous solution by slow evaporation technique at room temperature. The cell parameters of the grown crystals were estimated by Single X-ray diffraction studies. The functional groups present in the grown crystals were ascertained using FTIR spectrum analysis. UV-visible transmittance spectrum was recorded to study the optical transparency of the grown crystal. The non-linear optical property has been tested by Kurtz powder technique.

Shanthi, N. Theresita [Department of Physics, V. V. College of engineering, Thisaiyanvilai-627 657, Tamilnadu (India); Selvarajan, P. [Department of Physics, Aditanar College of Arts and Science, Tiruchendur-628 216, Tamilnadu (India); Rose, A. S. J. Lucia [Department of Physics, St. Mary's College, Thoothukudi-628 001, Tamilnadu (India)

2011-10-20

424

Crystal growth, structural, thermal and mechanical behavior of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of L-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV-Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker's microhardness method.

Mahadevan, M.; Ramachandran, K.; Anandan, P.; Arivanandhan, M.; Bhagavannarayana, G.; Hayakawa, Y.

2014-12-01

425

Studies on synthesis, growth, structural, optical properties of organic 8-hydroxyquinolinium succinate single crystals  

SciTech Connect

8-hydroxyquinolinium succinate (8HQSU), an organic material has been synthesized and single crystals were grown by employing the technique of slow evaporation. The structure of the grown crystal was elucidated by using single crystal X-ray diffraction analysis. 8HQSU crystal belongs to the monoclinic crystallographic system with non-centro symmetric space group of P2{sub 1}. FT-IR spectral investigation has been carried out to identify the various functional groups present in the grown crystal. UV–vis spectral studies reveal that 8HQSU crystals are transparent in the entire visible region and the cut-off wavelength has been found to be 220nm.

Thirumurugan, R., E-mail: singlecrystalxrd@gmail.com; Anitha, K., E-mail: singlecrystalxrd@gmail.com [School of Physics, Madurai Kamaraj University, Madurai-625021 (India)

2014-04-24

426

Large molecular dynamics simulations of collision cascades in single-crystal, bi-crystal, and poly-crystal UO 2  

NASA Astrophysics Data System (ADS)

Classical molecular dynamics simulations have been carried out to study the primary damage due to ?-decay self-irradiations in single-, bi-, and poly-crystal UO 2 matrices. In all the cases no amorphization has been found, only the creation of few point defects is observed. However, in all grain boundary systems numerous point defects are created along the interfaces. Furthermore, cascade morphologies depend strongly on the grain boundary structure. For symmetrical tilt grain boundaries with small misorientation angles (lower than 20°) the structure at the grain boundaries is composed of edge dislocations, whereas for higher misorientation angles is formed by Schottky defects. The grain boundary structure in the poly-crystal is found to be highly disordered. For the last two systems, cascades seem stopped by the interfaces unlike those with edge dislocation grain boundaries. These types of interface act like sink which traps moving atoms.

Van Brutzel, L.; Vincent-Aublant, E.; Delaye, J.-M.

2009-09-01

427

Growth of zinc cadmium thiocyanate single crystal for laser diode frequency-doubling  

NASA Astrophysics Data System (ADS)

Zinc cadmium thiocyanate (ZnCd(SCN) 4, ZCTC) crystal is a promising nonlinear optical material as the source of blue-violet light by laser diode frequency-doubling. A series of experiments on the growth of ZCTC crystal are reported in this paper. A larger single crystal, with size 7×7×13 mm 3, was successfully obtained from the NH 4Cl-NH 4SCN-H 2O mixed solvent by using the solvent-evaporation method. The problems in the growth of ZCTC single crystal are discussed and the key to growing large and transparent single ZCTC crystals is proposed.

Jiang, Xue-Ning; Xu, Dong; Yuan, Duorong; Lu, Mengkai; Guo, Shiyi; Zhang, Guanghui; Wang, Xinqiang; Fang, Qi

2001-02-01

428

Role of surface chemistry in adhesion between ZnO nanowires and carbon fibers in hybrid composites.  

PubMed

Low interface strength is a persistent problem in composite materials and cascades to limit a variety of bulk material properties such as lamina shear strength. Whiskerization has long been pursued as a method to reinforce the interphase and improve both the single fiber interface strength as well as the bulk properties. Recent developments have shown that ZnO nanowire whiskerization can effectively improve the properties of a bulk composite without requiring the high temperatures that previous deposition processes needed. Although the efficacy of a ZnO nanowire interphase has been established, the mechanism for adhesion of the interphase to the fiber has not been identified. Specifically, the addition of the ZnO nanowires to the surface of the fibers requires that the ZnO nanowires have strong chemical adhesion to the fiber surface. This work will create a variety of chemical environments on the surface of the fibers through new and common chemical functionalization procedures and quantify the surface chemistry through X-ray photoelectron spectroscopy. The effect of fiber surface chemistry on the adhesion of the ZnO is assessed through single fiber fragmentation testing. The interface strength is found to strongly correlate with the concentration of ketone groups on the surface of the fibers. Following the experimental observations, liftoff of a ZnO crystal from a graphene surface was simulated with a variety of surface functionalizations. The computational models confirm the preference for ketone groups in promoting adhesion between ZnO and graphite. PMID:23281964

Ehlert, Gregory J; Galan, Ulises; Sodano, Henry A

2013-02-01

429

Crystal growth and spectroscopic properties of Er3+ ions doped CdF2 single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of Er3+:CdF2 with good optical quality were grown by a Bridgman technique after purification of the starting materials. Absorption and emission spectra are recorded at room temperature. The Judd-Ofelt (JO) analysis was applied to obtain the three phenomenological intensity parameters and the transition strengths. These JO parameters are used to calculate the radiative transition probabilities, the radiation lifetimes and the branching ratios. The results obtained are in good agreement with those of other fluoride laser materials. We also carried out luminescence measurements for red and green emission. The studied host may offer infrared and visible laser emissions.

Djellab, S.; Diaf, M.; Labbaci, K.; Guerbous, L.

2014-04-01

430

Twin nucleation and migration in FeCr single crystals  

SciTech Connect

Tension and compression experiments were conducted on body-centered cubic Fe -47.8 at pct. Cr single crystals. The critical resolved shear stress (CRSS) magnitudes for slip nucleation, twin nucleation and twin migration were established. We show that the nucleation of slip occurs at a CRSS of about 88 MPa, while twinning nucleates at a CRSS of about 191 MPa with an associated load drop. Following twin nucleation, twin migration proceeds at a CRSS that is lower than the initiation stress ( Almost-Equal-To 114-153 MPa). The experimental results of the nucleation stresses indicate that the Schmid law holds to a first approximation for the slip and twin nucleation cases, but to a lesser extent for twin migration particularly when considerable slip strains preceded twinning. The CRSSs were determined experimentally using digital image correlation (DIC) in conjunction with electron back scattering diffraction (EBSD). The DIC measurements enabled pinpointing the precise stress on the stress-strain curves where twins or slip were activated. The crystal orientations were obtained using EBSD and used to determine the activated twin and slip systems through trace analysis. - Highlights: Black-Right-Pointing-Pointer Digital image correlation allows to capture slip/twin initiation for bcc FeCr. Black-Right-Pointing-Pointer Crystal orientations from EBSD allow slip/twin system indexing. Black-Right-Pointing-Pointer Nucleation of slip always precedes twinning. Black-Right-Pointing-Pointer Twin growth is sustained with a lower stress than required for nucleation. Black-Right-Pointing-Pointer Twin-slip interactions provide high hardening at the onset of plasticity.

Patriarca, L. [Politecnico di Milano, Department of Mechanical Engineering, Via La Masa 34, I-20156 Milano (Italy)] [Politecnico di Milano, Department of Mechanical Engineering, Via La Masa 34, I-20156 Milano (Italy); Abuzaid, Wael [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801 (United States)] [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801 (United States); Sehitoglu, Huseyin, E-mail: huseyin@illinois.edu [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801 (United States)] [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801 (United States); Maier, Hans J. [Lehrstuhl fuer Werkstoffkunde (Materials Science), University of Paderborn, 33095 Paderborn (Germany)] [Lehrstuhl fuer Werkstoffkunde (Materials Science), University of Paderborn, 33095 Paderborn (Germany); Chumlyakov, Y. [Physics of Plasticity and Strength of Materials Laboratory, Siberian Physical and Technical Institute, 634050 Tomsk (Russian Federation)] [Physics of Plasticity and Strength of Materials Laboratory, Siberian Physical and Technical Institute, 634050 Tomsk (Russian Federation)

2013-01-15

431

High-Temperature Thermoelectric Properties of NaxCoO2-delta Single Crystals  

Microsoft Academic Search

We measure the high-temperature thermoelectric properties of the NaxCoO2-delta single crystal for the first time. The NaxCoO2-delta single crystals are prepared by a flux technique, and the resulting flaky single crystals are very thin on the c-axis. The in-plane electrical resistivity (rho), the thermoelectric power (S) and the in-plane thermal conductivity (kappa) are measured in the range of 300 K

Kenjiro Fujita; Tadashi Mochida; Kazuo Nakamura

2001-01-01

432

Surface and bulk diffusion of HDO on ultrathin single-crystal ice multilayers on Ru(001)  

Microsoft Academic Search

The kinetics of HDO surface and bulk diffusion on ultrathin (25-192 BL; 90-700 Å) single-crystal H216O ice multilayers were studied using a combination of laser-induced thermal desorption (LITD) probing and isothermal desorption depth-profiling. The single-crystal hexagonal ice multilayers were grown epitaxially on a single-crystal Ru(001) metal substrate with the basal (001) facet of ice parallel to the Ru(001) surface. HDO

Frank E. Livingston; Galen C. Whipple; Steven M. George

1998-01-01

433

Surface and bulk diffusion of HDO on ultrathin single-crystal ice multilayers on Ru(001)  

Microsoft Academic Search

The kinetics of HDO surface and bulk diffusion on ultrathin (25–192 BL; 90–700 Å) single-crystal H216O ice multilayers were studied using a combination of laser-induced thermal desorption (LITD) probing and isothermal desorption depth-profiling. The single-crystal hexagonal ice multilayers were grown epitaxially on a single-crystal Ru(001) metal substrate with the basal (001) facet of ice parallel to the Ru(001) surface. HDO

Frank E. Livingston; Galen C. Whipple; Steven M. George

1998-01-01

434

Synthesis and re-investigation of the elastic properties of single-crystal magnesium silicate perovskite  

Microsoft Academic Search

Single crystals of MgSiO3 in the perovskite structure have been grown at a peak pressure of 26 GPa and temperature of approximately 1600 K using a 2000 ton uniaxial split-sphere high-pressure apparatus (USSA-2000). The specimens were subsequently utilized to re-investigate the single-crystal elastic properties of this phase at ambient conditions using laser Brillouin spectroscopy. The nine adiabatic single-crystal elastic stiffness

Amir Yeganeh-Haeri

1994-01-01

435

Analysis of Phase Separation in Czochralski Grown Single Crystal Ilmenite  

NASA Technical Reports Server (NTRS)

Ilmenite (FeTiOs) is a wide bandgap semiconductor with an energy gap of 2.58 eV. Ilmenite has properties suited for radiation tolerant applications, as well as a variety of other electronic applications. Single crystal ilmenite has been grown from the melt using the Czochralski method. Growth conditions have a profound effect on the microstructure of the samples. Here we present data from a variety of analytical techniques which indicate that some grown crystals exhibit distinct phase separation during growth. This phase separation is apparent for both post-growth annealed and unannealed samples. Under optical microscopy, there appear two distinct areas forming a matrix with an array of dots on order of 5 pm diameter. While appearing bright in the optical micrograph, atomic force microscope (AFM) shows the dots to be shallow pits on the surface. Magnetic force microscope (MFM) shows the dots to be magnetic. Phase identification via electron microprobe analysis (EMPA) indicates two major phases in the unannealed samples and four in the annealed samples, where the dots appear to be almost pure iron. This is consistent with micrographs taken with a scanning probe microscope used in the magnetic force mode. Samples that do not exhibit the phase separation have little or no discernible magnetic structure detectable by the MFM.

Wilkins, R.; Powell, Kirk St. A.; Loregnard, Kieron R.; Lin, Sy-Chyi; Muthusami, Jayakumar; Zhou, Feng; Pandey, R. K.; Brown, Geoff; Hawley, M. E.

1998-01-01

436

Thermal conductivity of 4H-SiC single crystals  

NASA Astrophysics Data System (ADS)

Thermal diffusivity and specific heat of 4H-SiC crystals as a function of temperature are measured, respectively, from room temperature to 600 °C. The thermal conductivity normal to c-axis was calculated from the measured data for both N-type and V-doped semi-insulating (SI) 4H-SiC single crystals. The thermal conductivity of N-type sample normal to c axis is proportional to T-1.26. It is approximately 280 W/mK at the room temperature. For V-doped SI sample, the thermal conductivity is proportional to T-1.256 and it is about 347 W/mK at room temperature, bigger than that of N-type sample. For semiconductor materials, total thermal conductivity is the sum of the contributions of lattice and carrier thermal conductivities. Temperature dependent Raman spectrum showed that the life time of phonons for N-type sample is shorter than that for SI sample. Accordingly thermal conductivity contributions from both lattice and carrier components are relatively small for N-type sample.

Wei, Rusheng; Song, Sheng; Yang, Kun; Cui, Yingxin; Peng, Yan; Chen, Xiufang; Hu, Xiaobo; Xu, Xiangang

2013-02-01

437

Redetermination of olivenite from an untwinned single-crystal  

PubMed Central

The crystal structure of olivenite, ideally Cu2(AsO4)(OH) [dicopper(II) arsenate(V) hydroxide], was redetermined from an untwinned and phosphate-containing natural sample, composition Cu2(As0.92P0.08O4), from Majuba Hill (Nevada, USA). Olivenite is structurally analogous with the important rock-forming mineral andalusite, Al2OSiO4. Its structure consists of chains of edge-sharing, distorted [CuO4(OH)2] octa­hedra extending parallel to [001]. These chains are cross-linked by isolated AsO4 tetra­hedra through corner-sharing, forming channels in which dimers of edge-sharing [CuO4(OH)] trigonal bipyramids are located. The structure is stabilized by medium to weak O—H?O hydrogen bonds. In contrast to the previous refinements from powder and single crystal X-ray data, all non-H atoms were refined with anisotropic displacement parameters and the H atom was located. PMID:21201567

Li, Chen; Yang, Hexiong; Downs, Robert T.

2008-01-01

438

Scintillation properties of CsI:In single crystals  

NASA Astrophysics Data System (ADS)

Scintillation properties of CsI:In single crystals have been investigated. Scintillation yield of CsI:In measured with the 24 ?s integration time is around 27,000 ph/MeV, reaching the saturation at 0.005 mol% of the activator. However, luminescence yield of CsI:In is close to CsI:Tl scintillation crystals, which is around 60,000 ph/MeV. This difference is explained by the presence of an ultra-long afterglow in CsI:In scintillation pulse. Thermoluminescence studies revealed a stable trap around 240 K that is supposed to be related to millisecond decay components. The best measured energy resolution of (8.5±0.3)% was achieved at 24 ?s peaking time for a CsI sample doped with 0.01 mol% of In. Temperature stability of CsI:In radioluminescence intensity was found to be remarkably high. Its X-ray luminescence yield remains stable up to 600 K, whereafter thermal quenching occurs. The latter property gives CsI:In a potential to be used in well logging applications.

Gridin, S.; Belsky, A.; Moszynski, M.; Syntfeld-Kazuch, A.; Shiran, N.; Gektin, A.

2014-10-01

439

Laser Raman study of single crystals of deuterated cadmium fluorosilicate  

NASA Astrophysics Data System (ADS)

A laser Raman study of oriented single crystals of CdSiF 6:6D 2O at room temperature as well as at 10 K in all the six polarization geometries has been made. Also a detailed temperature dependent Raman study from room temperature to 10 K in ( yy) polarization in the region of internal vibrations and lattice modes has been made. Abrupt changes have been observed in frequency shift, line-width and intensity of some of the bands at about 235 K. Some doubly degenerate modes show splitting at the same temperature. From these observations a phase change at about 235 K is inferred for this salt. It has been suggested that when the system is cooled, the lattice contracts and the water molecules lose their reorientational freedom to some extent which might result in the distortion of the [Cd(OD 2) 6] 2+ octahedra triggering a phase transition.

Thakur, Ganesh; Verma, A. L.

1989-01-01

440

Growth and characterization of single crystal refractory oxide fibers  

NASA Astrophysics Data System (ADS)

Single-crystal Nd:YAG, sapphire, and LiNbO3 fibers 30-500 microns in diameter have been produced using the pedestal growth method. It is shown that stable growth is possible with typical diameter reduction ratios of 2-4:1; the laser power necessary to produce a stable melt zone varies from over 20 watts for a 1-mm rod of sapphire to several hundred milliwatts for 100-micron fibers of LiNbO3. The major problem with the current growth system is insufficient control over fiber diameter fluctuations. Fibers produced to date have diameters varying by up to 5 percent. A second-generation growth system is described which is expected to produce fibers with precisely controlled diameters.

Fejer, M.; Byer, R. L.; Feigelson, R.; Kway, W.

1982-12-01

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